Semiconductor

25 May 2017

Automated Non-Destructive Imaging and Characterization of Graphene/hBN Moiré Pattern with Non-Contact Mode AFM

Graphene has attracted researchers' attention due to its unique band gap structure, which allows it to be used in high-mobility semiconductor devices. However, realization of such a graphene-based high-performance device has been challenging due to lack of a suitable substrate. This challenge has been recently addressed by the development of epitaxial growth of graphene on hexagonal boron nitride (hBN)[1, 2].hBN is a suitable substrate for graphene due to its highly similar hexagonal patterns. A moiré pattern is the superlattice generated as the result of a ~2% mismatch between graphene and hBN lattices, with periodicity values larger than each of the two materials' lattice constants by two orders of magnitude[3].

28 Dec 2016

Scanning Capacitance Microscopy Characterization of Vacuum-Channel Nanoelectronic Devices

Efforts to harden electronic components and systems using solid-state devices against the effects of radiation and heat for use in space travel has become a major engineering opera-tion for space exploration agencies around the world. Such work has not only been been time-consuming, but expensive as well with the majority of deliverable solutions being costlier and technologically older than what is typically available to consumers for other types of application.

1 Sep 2016

Electrical Characterization of Semiconductor Device Using SCM and SKPM Imaging

  By John Paul Pineda, Gerald Pascual, Byong Kim, and Keibock Lee Technical Marketing, Park Systems Inc., Santa Clara, CA, USA INTRODUCTION Semiconductor devices are the foundation of modern electronics due to their importance in the function of electrical circuitry with components such as transistors, diodes, and integrated circuits. These devices have become ubiquitous in a wide range of applications. The most common of which are the design and manufacture of 1) common analog appliances such as radios and 2) digital circuits for use in computer hardware. [1] Key electrical parameters such as dopant concentration level, carrier type, and defect densities are fundamental factors that influence the performance of semiconductor devices. Thus, a technique that can measure these characteristics and investigate samples with nanoscale features must be utilized in evaluating device reliability. There are several methods for the characterization of semiconductors. Examples include Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Secondary Ion Mass Spectroscopy (SIMS), Electron Beam Induced Current (EBIC) and one-dimensional Capacitance Voltage (C-V), among others [2]. However, some of these methods are destructive, others have laborious sample preparation requirement, and others still do not effectively determine two-dimensional quantities of sub-device scale. The need for next-generation characterization tools was driven by these shortcomings as well as the realization that ever-smaller device geometry and high reliability requirements were beginning to trend within the industry. To satisfy this new degree of difficulty in the metrology of semiconductor device processes, various types of scanning probe microscopy (SPM) have been deployed to meet the challenge. Scanning Capacitance Microscopy (SCM) and Scanning Kelvin Probe Microscopy (SKPM) combined with Atomic Force Microscopy (AFM) are the most powerful methods for characterization of semiconductor devices because of their non-destructive scanning ability, accuracy in measurements of samples with nanoscale features, and the lack of any sample preparation. In addition, the integration of these methods with AFM enables it to acquire both topography and electrical property data simultaneously without changing the sample or tip. To this end, SCM and SKPM were used to investigate an SRAM device and the data shows that these techniques are effective means for the electrical properties characterization of semiconductor devices. EXPERIMENTAL An SRAM sample [3] was investigated using a Park NX20 AFM system [4]. The electrical properties of the sample were characterized under ambient air conditions using two different techniques: SCM and SKPM. A cantilever with a metal-coated tip was utilized in both techniques. In SCM [5], the sample topography is collected using contact mode AFM simultaneously with capacitance imaging all in a single scan. The electrical properties of the sample are measured from the variation in radio frequency (RF) amplitude signal due to changes in capacitance between the tip and the sample. The hardware configuration of this mode consists of several modules including the cavity resonator, frame module, SCM probehand, SCM sample holder, and an SCM cantilever chip with a connected probe wire. The SCM probehand was connected to an RF sensor, comprised of the cavity resonator and frame module, to detect the change in capacitance between the probe tip and the sample during scanning. The frame module generates and amplifies the driving signal which oscillates the resonator during SCM measurements. The cavity resonator transforms the capacitance change between the probe tip and the sample into an RF signal. The resonant frequency of the resonator is proportional to 1/√LC, where L is inductance of the resonator, and C is the capacitance. For this study, a resonance RF curve with a peak of 697.8 MHz was used (see Figure 1). This curve is steepest at an operating resonant frequency of 705.4 MHz. This is the point on the curve where changes in amplitude due to frequency shifts, induced by tip-sample capacitance changes, would be most easily observed. The output signal from the resonator is monitored and coupled with a lock-in technique to acquire the final capacitance map reported here. In this experiment, a lock-in amplifier, embedded internally in the NX electronics, with an AC voltage frequency of 17 kHz was selected after optimizing the scan parameters for acquiring topography data. Parameters for SCM imaging were also optimized by closely monitoring the SCM signal. The AC bias amplitude selected was 1 V, while for AC bias, the phase chosen was a 0° reference phase. A second order filter with a 1 ms time constant was also selected for monitoring the output signals. A sensitivity value of 1 V was set to remove unwanted noise in the signals. In SKPM mode, there are two interaction forces between the AC biased tip and the sample: the electrostatic force and Van der Waals force. The Van der Waals force is harnessed to generate the sample’s surface topography while the electrostatic force between the tip and sample generates data for the sample’s electrical properties. The obtained cantilever deflection signal contains both sets of information; therefore, a method that can completely separate these signals is the key to successful imaging. There have been methods introduced to accomplish this, one of which is two-pass scanning. However, this method is two times slower than typical AFM imaging as two separate scans need to be conducted. In the Park NX20, lock-in amplifiers embedded its electronics are used to separate signals. This allows for the acquisition of both topography and EFM data in a single-pass scan. Two amplifiers are used by the system, named lock-in 1 and lock-in 2. Lock-in 1 obtains the topography information by analyzing the tip motion caused by the Van der Waals interaction, while lock-in 2 obtains electrical property information by analyzing the frequency of the applied AC voltage signal to the tip which, in turn, generates an electrostatic force interaction with the sample. The frequency of the applied AC voltage signal is chosen to be smaller (~17 kHz) than the cantilever oscillation frequency (70-330 kHz), enough so that the two signals do not interfere each other [6]. In this experiment, lock-in 2 with an AC voltage frequency of 17 kHz was selected after optimizing scan parameters for topography data acquisition. Furthermore, a separate DC bias was applied to the cantilever and controlled for to create a feedback loop that would zero out the electrical oscillation between the tip and the sample caused by the application of an AC bias to the cantilever. The value of this offsetting DC bias that zeroes out the AC bias-induced electrical oscillation is considered to be a measure of surface potential [6, 7]. Figure 1. Resonance RF curve displaying the SCM detector signal (V) versus frequency (MHz). The optimal frequency to oscillate the resonator to achieve the highest detection sensitivity in SCM imaging is 705.4MHz RESULTS & DISCUSSIONS The region of interest in this investigation is in the sample’s NMOS region. The acquired images from each technique were analyzed using XEI software developed by Park Systems which mapped the acquired signals to a color table. The topography data acquired in both techniques clearly show the NMOS region but no significant information related to the type and level of dopant concentration. This is in contrast with the electrical property data acquired in each mode showing not only the NMOS structure, but also the type and level of doping concentrations across the sample. Figure 2, shown below, is the topography and SCM measurement of the SRAM sample with regions of different doping levels from 2x1016 cm-3 to 2x1020 cm-3. The SCM image clearly shows various regions doped with different types of dopants and at varying concentration levels. The various steps in the color gradient are particularly helpful with observing concentration levels as several regions on the device show various shades of bright (p dopant presence) and dark (n dopant presence) color mapping. The intensity of the shading correlates to the degree with which those regions are doped with extremely bright and dark areas having the lowest and highest dopant concentration levels. For example, the device’s p-channel with a doping level of 1x1017 cm-3 is clearly visible in the SCM image. The narrow regions of the p-channel approximately 100 nm wide show the separation of regions with alternating dopant types in the configuration of a typical NPN transistor. Furthermore, the resolution of SCM is high enough to show multiple darker spots present in what device fabricators intended to be a continuously solid bright line of positively doped material on the left side of the device. Characterizing electrical properties with this level of detail can be key in understanding the functionality of a semiconductor device. As with the SCM and topography images, the corresponding line profiles generated after scanning can also yield significant insight into the design of the device. Here we first consider the line profile for the topography data indicated in red on Figure 2. When compared to the SCM image with the device features labeled, one can see that each NPN transistor device is separated from the next by boundaries nearly 1 μm in depth with high levels of positive dopant concentration. The edges of each boundary are bordered by a slightly raised area of about 0.1 μm. If one were to overlay this topography data onto the SCM image, the edges of each boundary can be seen to have lower dopant concentration (darker color) than the n+ contacts making up the NPN transistors. This is further supported by the line profile of the SCM data (green line on figure 2) where the regions immediately before and after the boundaries (which again, feature large decreases in positive dopant concentration) are measured at slightly more negative μV levels -30 μV) than the rest of the negatively doped portions (-10 μV) of the device shown in the SCM image. An additional observation can be made in the central portion of the area of interest where p-channels of an elevated height around 0.1 μm can be detected perpendicular to the p-epi region of the device. These central p-channels have a relatively lower concentration of positive dopant (approaching 80-90 μV) where they are seen bright along the both green line in the SCM image as well as in the image as a whole While SCM provides excellent topography and electrical property data with high spatial resolution, it is a technique that is enabled through the purchase of additional hardware from many microscopy vendors. Furthermore SCM must be performed using contact mode AFM which results in the consumption of probes at an accelerated pace compared to non-contact mode AFM. In situations limited by hardware availability or fiscal considerations, electrical characterization of semiconductor devices can still be performed at a diminished, yet viable manner using SKPM, a surface potential measurement technique. Although not as effectively detailed, SKPM can provide researchers with images and data comparable to that acquired with SCM. Both techniques can characterize the structure of the device and reveal the dopant concentrations in various regions across the area of interest. Areas with negative dopant concentrations are again presented as darker areas and those with positive dopant concentrations are shown to be brighter. The key differences between the two techniques are that of lateral resolution and dopant detection sensitivity. Comparing the SCM image with the SKPM image, one can see the p-channels of the device are much wider when observed in SKPM. One possible explanation of this difference is that SKPM is designed to see potential over an entire sample surface whereas SCM makes direct contact with the sample surface to detect capacitance responses. An alternative explanation would be that SKPM can be influenced by charges in the ambient air around the tip as well as in moisture that has adhered to the sample, both of which are possible sources of alterations in charge distribution. SCM on the other hand has the tip engage the surface of the tip directly, penetrating through any possible moisture layer, creating a point of direct contact which is less likely to be affected by parasitic charges from the scanning enviro nment. Figure 2. Topography (top-left) and SCM (top-right) data acquired from the sample device. Topography line profile (red line, y-axis on left) and SCM line profile (green, y-axis on right): Doping level: p-epi (2x1016 cm-3), n well (2x1017 cm-3), p channel (1x1017 cm-3) , n+ contacts (2x1020 cm-3) SUMMARY The topography and electrical properties of an SRAM sample have been characterized using SCM and SKPM with a Park NX20 AFM system. The data collected in this investigation reveals that both techniques can provide qualitative and quantitative information for electrical characterization of semiconductor devices. The results demonstrate that SCM provides greater lateral resolution and higher contrast mapping of electrical properties, including dopant type and level of concentration, when compared to SKPM. However, SKPM remains an effective source of data that can be used to reach similar conclusions about a sample under investigation as SCM. Overall, the techniques described in this study will successfully provide researchers and device engineers with key electrical parameters information to better evaluate the device reliability and monitor semiconductor device processes at nanoscale level. Figure 3. Topography (left) and SKPM (right) data acquired in SKPM mode. p-epi (2x1016 cm-3), n well (2x1017 cm-3), p-channel (1x1017 cm-3), n+ contacts (2x1020 cm-3). Figure 4. EFM amplitude (top-left), EFM phase (top-right), p-epi (2x1016 cm-3), n well (2x1017 cm-3), p-channel (1x1017 cm-3), n+ contacts (2x1020 cm-3).

4 Aug 2016

Wafer defects can’t hide from Park Systems

Atomic Force Microscopy (AFM) leader Park Systems has simplified 300mm silicon wafer defect review by automating the process of obtaining high-resolution 3D images, making it faster and simpler than ever before.

11 Jul 2016

Electrical Characterization of Semiconductor Device Using SCM and KPFM Imaging

Semiconductor devices are the foundation of modern electronics due to their importance in the function of electrical circuitry with components such as transistors, diodes, and integrated circuits. These devices have become ubiquitous in a wide range of applications. The most common of which are the design and manufacture of 1) common analog appliances such as radios and 2) digital circuits for use in computer hardware. [1] Key electrical parameters such as dopant concentration level, carrier type, and defect densities are fundamental factors that influence the performance of semiconductor devices. Thus, a technique that can measure these characteristics and investigate samples with nanoscale features must be utilized in evaluating device reliability. There are several methods for the characterization of semiconductors.

7 Jul 2016

Studying Post-etching Silicon Crystal Defects on 300 mm Wafer by Automatic Defect Review AFM

Ardavan Zandiatashbara*, Patrick A. Taylorb, Byong Kima, Young-kook Yooa, Keibock Leea, Ahjin Joc, Ju Suk Leec, Sang-Joon Choc, and Sang-il Parkc a Park Systems Inc., 3040 Olcott St., Santa Clara, CA, USA 95054 b SunEdison Semiconductor, St Peters, MO, USA 63376 c Park Systems Corp., KANC 4F, Iui-Dong 906-10, Suwon, Korea 443-270   ABSTRACT Single crystal silicon wafers are the fundamental elements of semiconductor manufacturing industry. The wafers produced by Czochralski (CZ) process are very high quality single crystalline materials with known defects that are formed during the crystal growth or modified by further processing. While defects can be unfavorable for yield for some manufactured electrical devices, a group of defects like oxide precipitates can have both positive and negative impacts on the final device. The spatial distribution of these defects may be found by scattering techniques. However, due to limitations of scattering (i.e. light wavelength), many crystal defects are either poorly classified or not detected. Therefore a high throughput and accurate characterization of their shape and dimension is essential for reviewing the defects and proper classification. While scanning electron microscopy (SEM) can provide high resolution twodimensional images, atomic force microscopy (AFM) is essential for obtaining three-dimensional information of the defects of interest (DOI) as it is known to provide the highest vertical resolution among all techniques [1]. However AFM's low throughput, limited tip life, and laborious efforts for locating the DOI have been the limitations of this technique for defect review for 300 mm wafers. To address these limitations of AFM, automatic defect review AFM has been introduced recently [2], and is utilized in this work for studying DOI on 300 mm silicon wafer. In this work, we carefully etched a 300 mm silicon wafer with a gaseous acid in a reducing atmosphere at a temperature and for a sufficient duration to decorate and grow the crystal defects to a size capable of being detected as light scattering defects [3]. The etched defects form a shallow structure and their distribution and relative size are inspected by laser light scattering (LLS). However, several groups of defects couldn't be properly sized by the LLS due to the very shallow depth and low light scattering. Likewise, SEM cannot be used effectively for post-inspection defect review and classification of these very shallow types of defects. To verify and obtain accurate shape and three-dimensional information of those defects, automatic defect review AFM (ADR AFM) is utilized for accurate locating and imaging of DOI. In ADR AFM, non-contact mode imaging is used for non-destructive characterization and preserving tip sharpness for data repeatability and reproducibility. Locating DOI and imaging are performed automatically with a throughput of many defects per hour. Topography images of DOI has been collected and compared with SEM images. The ADR AFM has been shown as a non-destructive metrology tool for defect review and obtaining three-dimensional topography information. Keywords: Atomic force microscopy, defect review, defect classification, defect inspection, non-contact mode, failure analysis, automated AFM, metrology.   1. MOTIVATION As integrated devices continue to shrink, incoming bare silicon wafer defectivity requirements become more and more stringent. The inspection of bare silicon wafers for surface defects is predominantly accomplished by measuring the difference in laser light scattering (LLS) between the clean surface and a surface defect, where the intensity of the scattered signal is compared to the LLS of a standard latex sphere. The actual surface defectivity can originate from added particles, topological defects, and crystal imperfections. To be able to reduce the number of defects one must know the source of the defect. LLS inspection can only give defectivity counts and a relative size. Therefore, one must rely on defect review techniques such as SEM and AFM to determine the nature and origin of the defects. In this study we focus on very small crystal imperfections which are not easily observed by LLS without some means to make them larger. We have used a decorative etching technique to highlight crystal imperfections to be studied by LLS, SEM, and AFM. The defect analysis can only be accomplished with accurate and reproducible defect coordinate transfer between analysis tools. Here we show how we have successfully and reliably found and characterized the decorated defects by AFM.   2. ADR AFM PROCEDURE The process in ADR AFM is depicted in figure 1. During this process, the defects of interest are located accurately and imaged non-destructively. Two factors are essential in order to achieve these objectives. First proper linkage between ADR AFM and LLS inspection tool is required to minimize the positioning errors and locate the defects accurately. The linkage for blank wafers is achieved by sample coordinate alignment. Generally there are no alignment markers or fiducials available on blank wafers to be used for alignment. Therefore ADR AFM uses specialized vision to perform the sample alignment properly. Another important factor in AFM defect review is non-contact mode imaging which is required for non-destructive imaging of the samples while preserving AFM tip life such that the tip can last throughout the process for multiple defects. Figure 1. The schematic shows ADR AFM process for this study. After completing coordinate mapping, ADR AFM will automatically perform survey scan, zoom-in scan, processing, analysis, and classification for each defect. 2.1 Coordinate alignment Sample coordinate alignment is needed for proper linkage between the stage coordinates of ADR AFM and LLS inspection tool. In the case of blank wafers, no fiducial or alignment marker exists on the sample to be used for sample alignment. To overcome this challenge, a coarse alignment followed by a fine alignment is performed. In the coarse alignment, three randomly selected peripheral and the notch or an angular reference are selected to correct for translational and rotational errors. This is followed by a fine alignment to eliminate positioning errors due to non-affinity between the stage coordinates of ADR AFM and LLS inspection tool. A few large defects with known inspection coordinates are used for performing fine alignment. Since the defects are hardly visible in a standard AFM optical image, an enhanced vision is used to locate the defects in the optics of the ADR AFM and utilize the defects as aligner markers. Upon the sample alignment, ADR AFM is able to locate additional defects accurately. More details on coordinate alignment can be found in ref [2]. 2.2 Enhanced vision Enhanced vision is utilized during fine coordinate alignment to locate the defects in the optical vision of ADR AFM. The technique is developed based on well-known differential frame averaging of the optical frames collected from the sample surface at two accurately separated locations. The sample can be moved accurately since ADR AFM uses a separated Z and XY scanners configuration. This architecture was initially developed to eliminate the crosstalk between the XY and Z scanners (which has been a common artifact in tube scanner based AFM systems) [2]. In this setup, sample is moved by XY scanner while tip is following the sample topography by Z scanner. In enhanced vision, the optical frames of the sample are collected at two precisely separated locations, and then the final frame is generated from the difference between the collected frames. The resulting frame possesses an enhanced contrast of surface details which are not easily observable in the standard vision of ADR AFM. A comparison between the frames collected by standard vision versus enhanced vision is depicted in figure 2.   Figure 2. a) Standard vs. b) enhanced vision images of a small defect on the surface of a bare silicon wafer are shown. The insets show a magnified view of the defect. The small defect is easily observable in enhanced vision. The larger image dimensions are 550 μm × 413 μm. 2.3 Non-contact mode imaging Non-contact mode is the standard imaging mode in ADR AFM. It is essential to maintain tip sharpness during the defect review process from the first to the last defect that is located and imaged. In addition to keeping tip costs low, wellmaintained tip sharpness ensures consistent image quality and accuracy between the images of all defects during the process. It therefore enables the automated system to uninterruptedly locate and image the defects with a high throughput. In order to perform non-contact mode imaging, the AFM cantilever is oscillated at its resonance frequency. The oscillating cantilever is brought close enough to the sample that the oscillation amplitude reduces to a pre-defined setpoint due to the van der Waals tip sample interaction. ADR AFM maintains the oscillation amplitude to avoid tip contacting the sample. As the tip scans the sample surface, the oscillation amplitude is maintained by moving the cantilever up and down with the Z scanner to maintain its tip sample interaction in attractive regime. More details on non-contact mode imaging can be found in reference [4]. Although ADR AFM's functionality is based on non-contact mode imaging, it is capable of performing in other dynamic or contact imaging modes if needed. 2.4 Automatic defect search and imaging The significant improvements in throughput of defect review are obtained by ADR AFM due to its fully automated process. Once defect coordinates from LLS inspection tool are entered into ADR AFM, coordinate alignment is performed, the defect is located and imaging starts for the list of selected defects. The process of locating and imaging the defects is fully automated. The automation includes locating the defect, tip-sample engagement, non-contact mode parameter optimization, survey scan, optimizing the scan size, final scan, processing, and defect classification. Defects 4 can be classified into two groups of bumps and pits. Defects are typically located within ±10 μm of their LLS coordinates.   3. SAMPLE PREPARATION (ETCHING PROCESS)  Bare 300mm diameter CZ silicon wafers were treated with a gaseous acid in a reducing atmosphere at a temperature and for a sufficient duration to grow the crystal imperfections [3]. The size and shape of the decorated defects depends on the nature of the original defect as shown in figure 3. Once decorated, the defect size is capable of being detected as LLS event. The LLS inspection tool locates and sizes the LLS events, providing the coordinates to be used by the SEM and AFM. Figure 3. Schematic of the process used to decorate crystal imperfections for defect inspection.   4. RESULTS A wafer containing surface decorated defects was inspected by a LLS tool and 34 defects were selected to be reviewed by ADR AFM. The coordinates of the defects were entered to ADR AFM, coordinate alignment performed, and the defects were located and imaged by ADR AFM. The first 21 defects had been imaged by SEM before being studied by ADR AFM. However, SEM images only provide aerial two-dimensional view of defects without sufficient information on the defects depth and out of plane dimensions. The remaining 13 defects were not found by SEM despite the signal collected by the LLS tool. The summarized results of decorated defect study with ADR AFM and comparison with SEM results are demonstrated in figure 4. ADR AFM was able to find all the 34 defects including those that had not been found by SEM.   Figure 4. The results of defect review with ADR AFM and comparison with SEM are shown. ADR AFM was able to locate and image all the 34 defects. The defects selected to be reviewed by ADR AFM belong to eight types according to their LLS signal. The tentative classification by the LLS tool is based on the defect's light scattering which is dependent on morphology, depth, and presenece of a central defect. As the decorative etching process proceeds, crystal imperfections are exposed and etch at a different rate than the perfect crystal surface. Defects exposed at the initial stages of the etch are deeper and more developed than defects exposed late in the etching proccess. Defects with an inverted pyramid shape are generally deeper and posses higher LLS signal. They are classified as "Facet". Defects with curved shape formed during the late stages of etching are shallower. These defects are classified as "Shallow". Some defects are exposed at an intermediate point in the decorative etch and have some degree of faceted walls with curved bottom. This category is classfied as "Both". Defects which have only started to be decorated have a very weak LLS signal and are classified as "Too shallow". The defects are also categorized whether or not they have the center defect, hence, a total of eight defect types were identified. The defect classification is tabulated in figure 5. As we go from left to right side of the table in figure 5, the LLS signal become weaker. This was attributed to the depth of defects and the sharpness of the defect's edges. AFM images confirmed the depth difference between different classes of defects. Since the AFM images contain Z heights, we were able to use a banded color scale to depict the surface topography of the defects more accurately in 2D view.   Figure 5. Defect classification based on the LLS, SEM and AFM data .   5. DISCUSSION Figure 6 depicts a comparison between the data collected with SEM vs. AFM for the same defect. Primary SEM image provides an aerial 2D view of the defect. However, the shallow depth of the defect reaches the limitations of SEM, hence, poor contrast in the image. As indicated in figure 5, shallower defects were not found by SEM. A secondary electron image helps identify the center defect. Identification of center defect by secondary electron is possible only if the defect was found in primary SEM image. On the other hand, AFM image not only provides an aerial view of the defect, it also contains the height/depth values for each pixel. Therefore, more information can be obtained about the true topology of the defect by using a 3D representation of the AFM image or using a contoured color scale. Contoured color scales can also help understanding the topology of the defect in aerial view as shown in figure 5. As indicated before, AFM has the highest vertical resolution among all imaging techniques [1], hence, better contrast of AFM images in aerial view.   Figure 6. Comparison between the data collected with SEM versus AFM. SEM image provides an aerial 2D view of the defect. Secondary electron image indicates the presence of center defect. AFM image, in addition to aerial 2D view, includes the 3D data. Therefore a line profile, 3D demonstration, and contoured color scale can be utilized to obtain more information. All of the 34 defects were found by ADR AFM including the 13 defects that were not found by SEM. Figure 7 depicts the AFM images a defect that was not found by SEM. The defect depth is below 4 nm and contains a center defect. This example indicates once again the limitation of SEM resolution in out of plane direction.   Figure 7. AFM data for defect #24, which was not found by SEM. It was indicated above that ADR AFM is a non-destructive imaging technique. It utilizes non-contact mode imaging for survey scan and final imaging scan. However, SEM beam can still modify the sample surface. Figure 8 indicates the sample contamination as a result of electron beam "burning" the surface during SEM imaging. These SEM burn-mark sizes are related to the SEM magnification. Figure 8 shows that several SEM magnifications were used in analyzing this defect. Figure 8.  AFM of a Facet defect with several SEM burn-marks.   6. SUMMARY We have demonstrated the power of the ADR AFM to provide quality 3D information for defect review on bare silicon wafers. With the automated ADR AFM this type of analysis is simple and yet powerful.   REFERENCES [1] G. T. Smith, Industrial Metrology: Surfaces and Roundness.: Springer, 2002. [2] Ardavan Zandiatashbar et al., "High-throughput automatic defect review for 300mm blank wafers with atomic force microscope," in Proc. SPIE 9424, Metrology, Inspection, and Process Control for Microlithography XXIX, 2015, p. 94241X. [3] J. Libert and L. Fei, Method to Delineate Crystal Related Defects.: PCT Publication, WO2013055368(A1). [4] Ardavan Zandiatashbar, "Sub-angstrom roughness repeatability with tip-to-tip correlation," NanoScientific, no. Winter, pp. 14-16, 2014. [5] Ajay Kumar and Banqiue Wu, "Extreme Ultraviolet Lithography: A Review," Journal of Vacuum Science & Technology B, pp. 1743 - 1761, 2007. [6] James A. Folta, J. Courtney Davidson , Cindy C. Larson, Christopher C. Walton, and Patrick A. Kearney, "Advances in low-defect multilayers for EUVL mask blanks," in Proceedings of SPIE 4688, Emerging Lithographic Technologies VI, 173, 2002.

14 Jul 2014

Accurate dopant profiles of semiconductor device structures with QuickStep Scanning Capacitance Microscopy

High Throughput Electrical Measurements with No Sacrifice in Signal Sensitivity   Summary With the implementation of QuickStep Scan, the throughput of the Scanning Capacitance Microscopy (SCM) measurement was dramatically increased, as much as ten times the standard SCM scan speeds, without compromising signal sensitivity, spatial resolution or data accuracy. In QuickStep scan, the XY scanner stops at each pixel point to record the data, and it makes a fast jump between the pixel points.     Introduction Scanning Capacitance Microscopy (SCM) images spatial variations in capacitance. One of the most common applications of SCM is mapping of the carrier concentration on the non-uniformly doped samples. In semiconductor manufacturing, the ability to characterize the dopant profile is important in identifying causes of failure as well as in making design advancements. For device characterization, SCM provides the unique ability to measure quantitative 2D dopant profiles.   Structure of SCM The SCM consists of a conductive metal probe tip and a highly sensitive capacitance sensor in addition to the normal Atomic Force Microscopy (AFM) components. Like Electrostatic Force Microscopy (EFM), SCM applies a voltage between the tip and the sample as in Metal-Oxide-Semiconductor (MOS) structures. Figure 1. The MOS capacitor is formed by the SCM tip and semiconductor sample   The total capacitance is determined by the oxide thickness and the thickness of depletion layer which depends on the carrier concentration in the silicon substrate and the applied DC voltage between the tip and the semiconductor. The applied AC bias voltage produces capacitance variation at fixed DC bias. The SCM detects differential capacitance (dC/dV) at fixed DC and AC bias voltage as the tip moves across different regions in carrier concentration. Figure 2. Positively and negatively trapped charges in the insulator on the semiconductor cause a parallel shift in high-frequency C-V and dC/dV curve along the voltage axis   Conventional SCM vs. QuickStep SCM In order to improve the signal-to-noise ratio, conventional SCM adopts very slow scan speeds as a means of giving the detector enough time to collect data. QuickStep Scan differs from conventional methodology of slow continuous movement. Here, XY scanner stops at each pixel point to record the data and then makes a fast and rapid hop to the next measurement points. This effectively speeds up the scan rate while maintaining the same signal sensitivity of the measurements by conventional SCM at slow scan speeds. Figure 3. In QuickStep scan, the XY scanner stops at each pixel point to record the data. It makes a fast jump between the pixel points.   Conventional SCM starts to lose the signal integrity as the scan rate increases, evidenced by the divergence between forward and backward scan signal. The QuickStep SCM maintains the same signal sensitivity as that of slow moving conventional SCM despite scanning at 5~10 times faster scan rates. Figure 4. High Throughput QuickStep Scan is ten times faster than conventional SCM scan with no compromise of signal sensitivity, spatial resolution, or data accuracy   In addition, Park SCM is optimized for the best signal-to-noise ratio in the industry by selecting the optimal RF frequency that matches the doping range of sample, over a wide RF band from 600MHz to 2000MHz. From the resonance curve acquired one can maximize the resolution and sensitivity of the SCM probe by choosing the operating frequency which is at the maximum slope.  Figure 5. (a) A change in the tip-sample capacitance. (b) Comparison of RF band of operating frequency between Park SCM in red and conventional SCM in blue. Resonance curves of different materials are plotted as a reference.   Even when using a very low AC bias voltages, Park SCM detector suppresses noise level and maintains a high signal-to-noise ratio, enough to tell the doping concentration less than an order of magnitude. This helps the semiconductor and device engineers perform failure analysis (FA) more accurately and efficiently with less effort and time. Figure 6. The n-doped silicon sample has areas of varying dopant concentration, imaged by Park SCM. The doping concentration of less than an order of magnitude is clearly distinguishable.   Conclusion: Results of QuickStep SCM by Park NX AFM Series. In short, QuickStep SCM is several times faster than conventional SCM, without sacrificing any measurement accuracy. It identifies causes of failure analysis, helps innovate the semiconductor design, and detects dopant concentration difference less than an order of magnitude.

26 Dec 2013

AFM Metrology Considerations of Hard Disk Manufacturing

Why Atomic Force Microscope? As the design rule becomes smaller, traditional metrology tools, such as stylus and optical profilers, and CD-SEM are unable to meet the precision metrology requirements from magnetic recording industry.  Virtually all the feature sizes in manufacturing steps are in nanoscale, especially that of defect review and pole-tip-recession. Atomic Force Microscope (AFM) routinely performs sub-nanometer measurements in ambient atmosphere, and consequently has gained attention as a new candidate for nanoscale metrology tool. However, old AFM systems based on a piezoelectric tube scanner cannot meet the metrology requirements in the industrial applications due to the intrinsic background curvature and crosstalk between the XY & Z axes.   AFM Products Utilizing Piezoelectric Tube Scanners Cannot Meet the Industry Requirement Figure 1.Old piezoelectric tube based AFMs are (a) marginally acceptable in relative dimensioning of two objects right next to each other, but completely useless in absolute dimensioning of an object and (b) even worse in the relative dimensioning of the two separated objects.   The limitation of the piezoelectric tube scanner based AFMs are best demonstrated in Figure 1. Old piezoelectric tube scanner based AFMs are marginally acceptable in relative dimensioning of two objects when placed side by side; however, the problem arises when one needs to know the absolute dimensioning of an object as shown in Figure 1 (a). It gets even worse when two objects are separated as shown in Figure 1 (b); even the relative dimensioning of the two separated objects cannot be performed by the tube based AFMs. Figure 2. The Piezoelectric tube scanner used in conventional AFMs is not an orthogonal 3-D actuator. Each axis movement is nonlinear, the XY-Z crosstalk with non-linearity inevitably results in a significant background curvature. Moreover, it has a low resonance frequency (< 1 kHz) and low force.   The problem originated from intrinsic limitations with the piezoelectric tube scanner as shown in Figure 2. The piezoelectric tube is made of ferroelectric ceramics that deform by several nm if a voltage is applied to the electrode on the surface. As the piezoelectric tube itself is not orthogonal in three dimensions, and each axis movement is non-linear, the XY-Z crosstalk with non-linearity inevitably results in a significant background curvature as shown in Figure 3. Note that the XY- scanner of old piezoelectric tube based AFMs have more than 80 nm out-of-plane deviation over only 15 μm scan. These conventional AMFs attempt to flatten the background curvature using the second or third order fitting, and due to this every scan data of their AFMs are the result of the “line-by-line” flattening, which is imbedded in their operating software. As a marketing and sales policy, some AFM company engineers are never allowed to demonstrate the raw data of their AFMs (Park Systems can help customers with turning off the imbedded software correction). It is unfortunate that even some of experienced engineers and scientists are deliberately misled to believe that the processed and flattened data of these old piezoelectric tube based AFMs are the raw data. Figure 3. (a) The background curvature of a piezoelectric tube based AFM in raw data and (b) the line-profile cross section of the background curvature. The XY-scanner of old piezoelectric tube based AFMs have more than 80 nm out-of-plane deviation over only 15 μm scan.   The high order fitting and flattening of the background curvatures in piezoelectric tube based ATMs become fatal issues in magnetic recording industry as the feature sizes of manufacturing process become smaller to nanoscale and the absolute AFM dimensioning of such feature is required.   Park Systems AFM Can Meet the Industry Requirements Introduced by the original innovators and pioneers of AFM technology after 4 years of intensive product development, the Park AFM from Park Systems represents breakthroughs in every aspect of AFM technology (For details, see “The Park AFM: the Technology Behind the True Non-Contact AFM” under XE Mode menu).  Physical separation of the XY-scanner from the Z-scanner completely removes background curvature from the fundamental level, and effectively eliminates the cross-talk and non-linearity problems that are intrinsic to old piezoelectric tube based AFM systems (Figure 4 (a)).3 This uniquely designed AFM systems from Park Systems not only increases the data collecting speed by at least 10 times compared to a conventional piezoelectric tube type scanner, but also improves the error due to the inherent non-linearity of the scanner itself. Figure 4. (a) In Park AFM, the Z-scanner is separated from the XY-scanner; the XY-scanner actuates only the sample and the Z-scanner actuates only the probe. (b) 2D guided XY flexure scanner used in Park AFM. This single module parallel-kinematics stage has low inertia and minimal out-of-plane motion, providing the best orthogonality, high responsiveness, and axis-independent performance.   In the Park AFMM, the XY-scanner is a Body Guided Flexure scanner as shown in Figure 4 (b), which is used to scan a sample in the XY direction only. The flexure hinge structure of the XY-scanner guarantees highly orthogonal 2D movement with minimum out of plane motion. Due to the Parallel Kinematics design, the XY-scanner of the Park AFM also has low inertia and axis-independent performance. Figure 5. Unprocessed raw AFM images of a bare silicon wafer taken with a (a) Park Systems’ AFM, and with a (b) conventional tube based AFM. (c) The line-profile cross sections of these background curvatures.   Figure 5 (a) shows unprocessed raw AFM images of a bare silicon wafer taken with a Park AFM as shown in Figure 5 (a), and with a piezoelectric tube based AFM as shown in Figure 5 (b). Since the bare silicon wafer is atomically flat, the curvatures in the images are due to the artifacts induced by the scanner. Figure 5 (c) compares the line-profile cross sections of background curvatures in Figure 5 (a) and (b). The 2D flexure stage of the Park AFM has only 1-2 nm of out-of-plane motion for the scan range of 50 μm (0.01% background curvature), compared to 80 nm by the tube scanner over the same scan range (0.53% background curvature). In addition, the Park AFM is the first and only AFM in the market that realizes True Non-Contact mode in every specification, not just in principle but in practice. True Non-Contact mode achieves an unprecedented tip-sample distance, combined with superb tip and sample preservation. The advantages of true non-contact mode enable the ultimate resolution of AFM and measurement accuracy which are without peer in the AFM industry. (For details, see “What is the Ultimate Resolution of AFM?” in True Non-Contact AFM under XE Mode menu).   Defect Review Analysis Figure 6. Images of a hard disk surface taken by a (a) Park Systems’ AFM and by a (b) conventional piezoelectric tube based AFM.   The immediate advantage of the zero background curvature in the Park AFM is demonstrated in the defect review analysis of a hard disk surface. Figure 6 shows images of a hard disk surface acquired by a Park Systems’ Park AFM as shown in Figure 6 (a) and a piezoelectric tube based AFM as shown in Figure 6 (b). Both images came from a comparison study in real fab condition by the same hard disk industry client. The images are obtained after deglitching those lines due to door opening & closing in the fab facility as shown in Figure 7. Note the striking difference between the two in Figure 6. The image taken by the piezoelectric tube based AFM is processed by a line-by-line curvature flattening, and one can clearly notice the distortion in the image as a result of the curvature flattening. The two edges look more flat, and the center has more variation. As pointed out earlier, a tube scanner has quite a bit of background curvature, approximately 80 nm over 15 μm scan. Since the current image by the piezoelectric tube based AFM is about 10 μm in scan size, it would have a significant background curvature. Without the curvature flattening, the image would be so curved to the point that one cannot even see the line features on a hard disk. Even with the curvature flattening, the nanoscale features on the hard disk would undoubtedly get distorted due to the high order fitting from the flattening process. Making matters worse, the door deglitching adds to the distortion as it is impossible to fit correctly both the glitches and the background curvature. The RMS roughness from such data is bound to be wrong. Figure 7. The deglitching of a hard disk surface image taken by Park Systems AFM. The glitches are generated when a door is closed or opened in the actual fab facility of a hard disk industry client. Note that the door glitches are removed without affecting the texture of the original raw data.   The image acquired using a Park Systems AFM correctly reflects the texture of the original sample. As the background curvature remains absolute minimum, the removal of door glitches is the only correction to be made, and it can be easily implemented without using high order fitting and changing the original raw image data as shown in Figure 7.   Pole-Tip-Recession (PTR) 1 : True Non-Contact AFM vs. Tapping AFM The density of information on a hard disc drive depends on the distance between the read-and-write head of a hard-disk drive. Usually the head is floating on an air cushion that builds up between the rotating hard-disk plate and the read-and-write head that “flies” at a distance to the hard disk of several nanometers. The active parts for read-and-write action are two ferritic poles that guide and focus the magnetic field close to the disk as shown in Figure 8. The pole-tip recession (PTR) is the difference in height between the pole tip material and the air-bearing surface (ABS). As one way of increasing the storage density in rigid disk drives, many efforts were taken to minimize the head-media gap, and consequently resulted in signal loss;4,5 the pole tip had to be recessed as little as possible, only to the point of preventing damage by contact with the disk. For this reason, the nano-metrology of PTR is a critical task6 with significant economic impact. Figure 8. The pole-tip-recession (PTR) of a hard disk drive is the difference in height between the pole tip material and the air-bearing surface (ABS). The image is a cross section of a typical thin film head showing the pole tips, undercoat/overcoat, gap, and the air bearing surface (ABS).   Since the reference plane (ABS) is far from the pole tip, the small height of PTR is easily buried in the background curvature of the piezoelectric tube scanner, which is more than ten times larger than the PTR height.9, 10 It gets even worse when the images taken with piezo tube based AFMs are line-by-line flattened with high order polynomial fitting. The background curvature poses a significant bottleneck in the PTR metrology. As the pole tip region has a typical height of a few nanometers and a width of 50 mm, the resulting background curvature these AFMs would be a few hundred nanometers over the scan range of 50 mm. Figure 9 shows a flattened image taken by a piezoelectric tube based AFM using tapping mode. First, note the residual background curvature even after line-by-line flattening. Since there are air-bearing surfaces at the sides, the average is flat, but the inside, recessed region, looks curved upward. That’s the major problem with image processing, since you do not know if the curvature is coming from the original surface, from a scanner artifact, or from the sly image processing. Figure 9. Image of the pole-tip region taken by a piezoelectric tube scanner based AFM in tapping mode. The background curvature is similar to the height change in the pole tip area.   There is an even more pressing issue of tapping force changing the PTR morphology in conventional piezoelectric tube based AFMs. Note that the pole-tip (the half moon shaped area with two vertical stripes on its left) in the PTR image by the piezoelectric tube based AFM is located lower than its surroundings, contrary to the design as shown in Figure 8. Here, we have found that the tapping mode AFM can cause serious artifacts due to the tapping force because the pole-tip is made of softer materials and the tapping force depresses the pole tip more than its surroundings and generate incorrect PTR values. In tapping mode, as stated in the original paper, the tip is made to strike the surface on each oscillation with sufficient oscillation amplitude and energy to overcome the stickiness of the surface.11 In other words, the tip depresses the sample surface by striking on it at each oscillation cycle. If the sample is homogeneous, the overall depression would not change the topography. However, if the sample is composed of various materials, the tapping force will depress the soft areas more than the harder areas. This phenomenon will not be obvious if the thickness of different materials is small, or if the sample surface is not smooth. However, in the case of PTR, this effect is prominent since the sample surface is very flat, and each material has large thickness. In order to verify this, we performed Force Modulation Microscopy (FMM). As shown in Figure 10, the pole tip area appears much darker than its surrounding, which means the pole tip is much softer than its surrounding. This is in accordance with the material properties of the pole tip, made of permalloy, and its surrounding, made of alumina. Figure 10. Force Modulation Microscopy (FMM) image showing local variations in surface stiffness.   Figure 11 shows an unprocessed raw data of the same sample taken with Park Systems’ Park AFM in True Non-Contact AFM mode. As shown in the line profile of Figure 11, the recessed region is completely flat with raised Air Bearing Surfaces (ABS) at both sides. Moreover, the pole tip area is located higher than its alumina coated region, as was designed to be. This conclusively demonstrates the superiority of the Park AFM performance especially in its zero background curvature and True Non-Contact AFM. Figure 11. PTR region imaged with Park Systems’ Park AFM in True Non-Contact AFM mode. The image shows no background curvature.   Pole-Tip-Recession (PTR) 2: Two Height Peaks in ABS Area. As shown in Figure 8, the ABS area is used as a reference plane for the subsequent measurements of the PTR. Therefore, the accurate reference height of the ABS area is critical in performing more rigorously and reliably characterizing the PTR. In Figure 12, the histogram of the ABS area image taken by Park Systems’ Park AFM clearly shows two peaks. The peaks are separated by about 1.65 nm. This simply reflects what we see optically in the ABS area, i.e., dark and bright regions. Two regions have obviously different heights. Please note that the distinction of the two height peaks in the ABS area is an important measure of an AFM performance in itself. Conventional piezoelectric tube based AFMs cannot distinguish the two height peaks since such nano-metrological differentiation is impossible due to the intrinsic background curvature and subsequent flattening. Figure 12. The histograms of two ABS and one PTR areas whose images are taken by Park Systems’ AFM. In other words, the mean value of heights in ABS area will change depending on the size and location of selected areas. However, the median values of the two peaks will remain the same regardless of the size and location of selected ABS areas.   The averaged value of heights in a given ABS area will change by the distribution of dark and bright regions in the area. In other words, the mean value of heights in ABS area will change depending on the size and location of selected areas. However, the median values of the two peaks will remain the same regardless of the size and location of selected ABS areas. If one can distinguish two height peaks in a given ABS area, median values of the ABS area represent more accurate, more reliable, and more consistent reference height for PTR characterization.   Conclusion It is apparent that old AFMs based on piezoelectric tube scanners are not suitable in hard disk metrology due to their scanner’s artifacts. We also noticed that the tapping mode can not only cause a serious amount of damage to the PTR, but also change the relative height measurements between regions of different materials. Moreover, there is always the undeniable fact that tapping causes faster tip damage compared to True Non-Contact. Whether in defect review or in PTR metrology, the zero background curvature and True Non-Contact mode of the Park AFM are found to be critical in the accurate and reliable metrology of the hard disk industry.   References 1. V. Ashok et al., IEEE Trans. Mag. 36, 2736 (2000). 2. Martin Smallen, and Jerry J. K. Lee, Trans. ASME 115, 382 (1993). 3. J. Kwon et al., Rev. Sci. Instrum. 74, 4378 (2003). 4. W. Scott et al, J. Appl. Phys. 87, 6182 (2000). 5. W. Scott, and B. Bharat, J. Appl. Phys. 91, 8328 (2002). 6. C. Nadimpalli, F.E. Talke, Tran. ASME 117, 580 (1995). 7. D. Zipperian, Datatech (1996) pp. 163-168. 8. D. Zipperian, and Dallas Meyer, IDEMA insight (Jan./Feb. 1999) pp. 8-11. 9. K. Babcock, and P. Hopkins, Datatech (1996) pp. 155-160. 10. K. Babcock, and P. Hopkins, IDEMA insight (Jan./Feb. 1997) pp. 7-8. 11. Q. Zhong, D. Inniss, K. Kjoller, and V. B. Elings, Surf. Sci. Lett. 290, L688 (1993).

26 Dec 2013

Programmable Data Density (PDD) for High Throughput Feature Measurement

Park Systems, the Nanotechnology Solutions Partner for HDD Industry Park Systems serves the hard disk drive (HDD) industry with automated nanotechnology measurement solutions including atomic force microscopes, software, and global service and support. Partnering with world leaders in HDD industry, Park Systems has been successfully delivering optimized solutions for the most challenging imaging and measurement needs in the industry.  The company’s HDD-Optimize program is a state-of the-art nanotechnology solutions service for the hard disk drive industry. Under the systematic approach of the program, Park Systems ensures rapid alignment and performance of the Park AFM nanotechnology measurement platform with the specific requirement of its customers.   Limitations in Current Method of Slider Metrology Need to take a separate image to compensate for background curvature Tact time: ~5min Not enough pixel resolutions for small region of interest, i.e. writer pole Tact time: ~5min Manual search and find of small region of interest for high resolution imaging Tact time: ~30min Low Measurement Throughput : One Writer Pole Image takes ~40 minutes - Labor intensive manual process - High labor cost     Going Beyond Conventional PTR Measurements The overall mechanical characterization of sliders now involves - A variety of metrology systems and  - A variety of resolution requirements In order to improve yield and reliability of slider manufacturing, one has to go beyond conventional PTR measurements Answer: Programmable Data Density   XE-PTR: For In-line Pole Tip Recession Metrology of Hard Disk Sliders Continuing the company’s impressive track record of developing optimized solutions, Park Systems introduces XE-PTR, an automatic AFM which revolutionizes the way sliders in HDD are imaged and analyzed. The new XE-PTR significantly increases accuracy and throughput for the slider’s pole tip recession imaging process with the innovative Programmable Data Density (PDD) capability. Inline Automation  Automatic Data Acquisition and Analysis of Sliders  Allowable Sample Types: Rowbars, Sliders  Artifact Free Metrology by Crosstalk Elimination  Longer Tip Life by True Non-Contact Mode  High Throughput Feature Measurement by PDD  Automatic Tip Exchange (Optional)  HGA Sample Fixture (Optional)   Current Limitations of Conventional AFM  Piezo tube is not an orthogonal 3-D actuator (scanner bowing)  Non-Contact Mode not possible due to slow z-servo response  Measurement throughput is prohibitively limiting What should we do?  New AFM platform to eliminate intrinsic hysteresis and non-linearity of piezotube  New AFM platform to improve Z-servo bandwidth to enable non-contact mode  New AFM platform to enable smart algorithm to scan sample features of interest   The Programmable Data Density (PDD) Overcomes the Challenges    2-D PDD (more pixels for both X and Y-axis) is realized!  Imaging of variable pixel density for the region of interest  Automatically detects the region of interest   2-Zone PDD for Writer Pole : Enables High Resolution Imaging of Small Region in One Scan.   Single 2-Zone PDD PTR Measurement : Park AFM vs. Conventional AFM  The Ultimate Improvement in throughput (more than 400%)!!   Obtains PTR,writer pole, and other features in All-in-One image scan   Summary: Key Benefits of Programmable Data Density  High Throughput Feature Measurement by Programmable Data Density (PDD)  Imaging of variable pixel density for the region of interest  Automatically detects the small region of interest  Obtains PTR, writer pole, and other features, All-in-One Scan (7 min), For conventional AFM, it takes ~40 min or longer

24 Dec 2013

Etched Silicon Structures

Metrology – Non-Contact Mode With the increasing shrinkage of device sizes, the characterization of thin films and their structures becomes critical to optimizing the resulting device at the end of line.  For example, CD etch variation is directly related to the angle of the resist profile.  In the images below, the strength of the Park AFM instruments to measure wall angles is demonstrated. The etch angle between Silicon  (111) and (100) is 54.7 degrees.  The measured etch angle of the silicon structure is approximately 54.6 degrees. The measured angle of the etched silicon holes shows a consistent angle on all sides.  Very low angle measurements, such as these, can be measured with confidence using the high flatness scanner of the Park AFM.   Sample:   -  Top:  Etched Si (111) with etch angle 54.7 degrees  -  Bottom:  Etched Si Structure Image Conditions:   -  True Non-Contact Mode System Requirement:  -  Closed-loop AFM System  -  Decoupled XY and Z scanners  -  High Flatness XY scanner The Benefits The key factors effecting angle measurement are:  -  the orthogonality of the      scanners used to image      the sample  -  half cone angle of      cantilever tip  -  system drift The decoupled XY and Z scanner design minimizes artifacts resulting in enhanced wall angle measurement repeatability.