Keibock Lee

Semiconductor device dimensions have been moving to 1X-nm node and below for years now in order to continually meet market demand for faster and more efficient designs year-to-year. Device fabrication methods have improved all the way from 65 nm in 2006 to reaching the 1X node at 14 nm in 2014. Current projections by the International Technology Roadmap for Semiconductors have the first sub-1X node devices at 7 nm debuting as soon as perhaps 2017 [1]. To continue at this pace, manufacturers must have the capability to meet metrology requirements that simultaneously call for enhancements in resolution, precision, and accuracy. Tools to meet these needs must provide nanoscale imaging for critical dimension measurement and results that can be repeatable and accurate enough to enhance productivity in a mass production environment [2].

The need to measure sample surface features have become increasingly important in many applications such as manufacturing semiconductor devices and monitoring the structural characteristics of biological samples. There are some AFM techniques used in measurement of sample topography. Examples include tapping mode and contact mode. However, these modes require a tip-sample interaction that can lead to sample damage and tip quality degradation. The need for a technique that can measure surface topography without touching the sample surface is very real, especially for samples sensitive to surface deformation.

Magnetization reversal plays a major role in designing the switching mechanisms of magnetic nanostructures in a high density storage device. In this study, magnetization reversal in a magnetic patterned array sample was successfully investigated using an atomic force microscopy (AFM) system via magnetic force microscopy (MFM). The magnetic property and topography data of a sample surface were obtained simultaneously and the data shows that the two signals are well separated by the two-pass scanning method. The MFM images demonstrate that a majority of the circular dot domain structures with 148 nm width on the sample surface experienced a magnetization reversal during the scan with a few domains remaining in their original state.

In order to identify and understand the root cause of a problem then develop an appropriate countermeasure, it is sometimes necessary to characterize a sample in situ. Several cutting edge applications follow this necessity such as: 1) the study of failure mechanisms in battery electrodes, 2) the study of membrane transport of ions between cells, and 3) the study of static and dynamic biomechanics at the cellular level. Common to all these applications is the need to perform in situ measurements of a sample experiencing a phenomenon while in an electrolyte solution. Techniques such as Atomic Force Microscopy (AFM) have been used for inliquid imaging of samples before, but AFM cannot be considered an ideal solution.

Nanoscale frictional measurement, or nanotribology, is an effective approach to identify surface compositional differences for a wide variety of materials, including polymer blends, thin films and semiconductors. Lateral Force Microscopy (LFM), a derivative mode in Atomic Force Microscopy (AFM), is particularly powerful in identification and mapping of the relative difference in frictional characteristics with superior spatial resolution. In this study, two samples with heterogeneous surface compositions, i.e., Sample 1 that consisted of polymer on glass and Sample 2 which contained graphene on Si, were analyzed with LFM, a mode that comes standard in all AFM systems from Park Systems. In Sample 1, homogeneously distributed circular features within the sample were seen from the topography, and the two materials, i.e., polymer and glass, were not easily distinguishable. However, two components with dramatically different frictional properties were clearly observed from the LFM images, which is indispensable to discriminate the two materials. In Sample 2, graphene and Si were differentiated unambiguously from the LFM signal, whereas the difference between the two materials from the topography result is relatively weak. Our results in this report showcased that LFM is ideal to analyze samples which consist of heterogeneous compositions with different frictional coefficients, while the topography is relatively flat.

Collagen is a protein that provides structure in various connective tissues in animals and can be found in ligaments, tendons, and skin. The characterization of collagen's mechanical properties at nanoscale can potentially reveal significant insights into the causes of macroscale phenomena such as the elasticity of skin and its degradation as we age. One tool that has been used to acquire nanoscale data of collagen is the atomic force microscope (AFM).

The Atomic Force Microscopy has provided those in research and industry with high resolution nanoscale measurements and imaging, but has long been limited by its relatively slow imaging speed. For certain applications such as crystal nucleation and growth, materials transportation and protein self-assembly process [1-3], it is important to keep track of the topography changes and particle transportation.

Wenqing Shi, Cathy Lee, Gerald Pascual, John Paul Pineda, Byong Kim, Keibock Lee Park Systems Inc., Santa Clara, CA USA ABSTRACT Electromechanical couplingin materials is a key property that provides functionality to a variety of applications,including sensors, actuators, IR detectors, energy harvesting and biology. Most materials exhibit electromechanical coupling in nanometer-sized domains. Therefore, to understand the relationships between structure and function of these materials, characterization at nanoscale is required. This electromechanical coupling property can be directly measured in a non-destructive manner using piezoelectric force microscopy (PFM), a mode that comes standard in all Park atomic force microscopes (AFMs). Here in this application note, we developed a novel technique termed as PinPoint™ PFM and demonstrated the application of PinPoint PFM in the characterization of annealed phenanthrenethin film on top of an ITO surface. The phenanthrenematerial has been a challenging sample to get quality topographical and piezoelectric response data from using conventional SPM methods. The main difficulty is due to the rod-shaped nanostructures on the sample surface being very susceptible to displacement by a scanning probe's tip. The invention of Park's latest PinPoint PFM technique gives researchers both a friction-less imaging technology that overcomes this difficulty and the means to achieve publication-ready image quality in much less time than previously possible with older methods. Here we demonstrated, not only can image well-resolved individual rod-shaped phenanthrene structures, but also differences in electrical polarization expressed as differences in PFM contrast (brighter areas showing a positive polarization and darker areas a negative polarization) without image distortions. Introduction Piezoelectric effect, is an intrinsic material property, in which the application of an electric field leads to thickness changes and/or shearing of the material. This unique electromechanical coupling property has been employed in a wide range of applications ranging from medical imaging and energy harvesting, to actuators and sensors.1 Example of piezoelectric materials include crystals (i.e., quartz), biological materials (i.e., DNA, bones and proteins) and man-made materials such as synthetic ceramics (barium titanate and zinc oxide) and some organic thin films.3 Driven by the developing nanotechnology and the increasing demands for miniaturization of electronic devices, characterization of piezoelectric effect at micro- and nanoscale has attracted significant interest. Piezoelectric force microscopy (PFM), also termed as dynamic-contact electrostatic force microscopy (DC-EFM) by Park, is an atomic force microscopy (AFM) based method that allows for high-resolution imaging, quantification and manipulation of piezoelectric materials at micron- and nanometer-length scale. Conventional PFM is usually performed in contact mode, and concurrent topographic imaging and piezoresponse measurements is obtained. In conventional PFM operation, an electrically-biased conductive tip is brought in contact with the surface of a piezoelectric material. Through application of an AC modulation to the conductive tip, the piezoelectric response of the material can then be measured by tracking the deflection of the cantilever as a result of sample’s local expansion or contraction based on the applied electric field. As these surface displacement are often very small with a low signal-to-noise ratio, and, thus, a lock-in amplifier is used for the detection of the amplitude and phase of the piezoelectric response signal. In terms of the AC bias frequency selection, a frequency that’s much lower compared to the cantilever’s resonance frequency is used. In addition, a DC bias can be applied to the sample to switch the domains of the piezoelectric material. Since the atomic force microscopy’s photodiode is position-sensitive, piezoelectric force microscopy can also identify the direction of electrical polarization in piezoelectric or ferroelectric domains. There are two modes of PFM imaging: vertical PFM (VPFM) and lateral PFM (LPFM), which are sensitive to domains polarized out-of-plane and in-plane, respectively.2 (Figure 1) In vertical piezoelectric force microscopy, in the presence of piezoelectric domains that point out-of-plane or perpendicular to the sample surface (Figure 1a-b), the cantilever will deflect vertically with respect to the sample surface in response to the applied electric field. Therefore, the PFM signal will appear bright for domains that point upward and dark for domains that point downward. In lateral piezoelectric force microscopy, in the presence of in-plane piezoelectric domains that’s parallel to the surface, a displacement shearing on the surface will occur. As a result, a torsional displacement of the cantilever will be induced, which in turn will be captured by the position sensitive photo detector as a lateral deflection. (Figure 1c-d) Fig. 1.A schematic representation of (a-b) vertical and (c-d) lateral PFM. The AFM laser shows vertical deflections which correspond with (a) downward or (b) upward out-of-plane electrical polarization. In lateral PFM, the cantilever will exhibit torsion in response to (c-d) lateral in-plane polarization directions. Black arrows indicate the direction of polarization vector in each case assuming that the relationship between polarization and crystal orientation is conserved. In this application note, piezoelectric force microscopy is performed utilizing the newly-developed PinPoint™ mode by Park Systems as opposed to the conventional contact mode. Performance comparison of PinPoint™ PFM and conventional PFM was carried out on annealed phenanthrene film, and improved resolution was observed in both topography and piezoelectric response signal with PinPoint™ PFM. In PinPoint™ PFM mode, the AFM probe monitors its feedback signal, approaches towardsthe sample surface until a predefined force threshold point is reached, measures the Z scanner’s height, then the AFM probe is rapidly retracted away from the surface to a user-defined height. The XY scanner stops during the piezoelectric response acquisition, and the probe-substrate contact time is controlled to allowsufficient time for quality data acquisition (Figure 2). PinPoint PFM allows higher spatial resolution with optimized piezoelectric response measurement over different sample surface.PinPoint PFM was designed to replace the conventional contact PFM and is an enhanced design that eliminates the problems of the tip wearing out during contact mode topography and diminished contact time. The PinPoint™ PFM technology has proven to solve all of the shortcomings of conventional PFM including quick tip wear, degradation of resolution, low signal to noise ratio, and poor reproducibility of data. Fig. 2.A schematic representation of PinPoint mode operation. The probe approaches towards the sample surface until a pre-defined force threshold is reached, then the Z scanner height is recorded. The XY scanner stops and the piezoelectric response is measured. Then the probe retracts away from the surface and move to the next pixel. The process repeats to collect the topography map and the piezoelectric response map. Experimental A Park NX10 AFM was used to image the annealed phenanthrene surface, and the topography signal and PFM quad signal were acquired in both conventional PFM imaging and PinPoint™ PFM imaging. In conventional PFM imaging, a NSC36-C (nominal spring constant k = 0.6 N/m and resonance frequency f = 65 kHz) coated with Cr and Au on both the front and back side was used in conventional PFM imaging. The nominal radius of the tip curvature is ~25 nm. Scan size was 20 μm × 20 μm. Scan rate was 0.2 Hz. The AFM tip was biased with AC potential with an amplitude of 4.5 V and a frequency of 17 kHz. No external bias was applied to the sample during imaging. The force set point used in the experiment was 6.84 nN. In PinPoint™ PFM imaging, a conductive NANOSENSORS™ PointProbe® Plus-Electrostatic Force Microscopy (PPP-EFM) cantilever (nominal spring constant k = 2.8 N/m and resonance frequency f = 25 kHz) coated with Ptlr5 on both the front and back sides was used in PinPoint™ PFM imaging. The nominal radius of the tip curvature is ~25 nm. Scan size was 20 μm × 20 μm. Same as the conventional PFM experiment, a AC potential with an amplitude of 4.5 V and a frequency of 17 kHz was applied to the tip, and no DC potential was applied to the sample. The force set point used in the experiment was 196.8 nN. The retract height was 0.3 μm. The retract/approach speed was 20 μm/s. The contact time between the probe and the sample surface was controlled at 1 ms. Results and Discussion In Figure 3, the topography and the piezoelectric response maps of the annealed phenanthrene thin film on ITO surface imaged with both conventional PFM and PinPoint™ PFM are shown. The images obtained via conventional PFM are shown in Figure 3a (topography) and Figure 3b (piezoelectric response), and the images collected by PinPoint PFM are shown in Figure 3c (topography) and Figure 3d (piezoelectric response). From the topography images (Figure 3a and 3c), the annealed phenanthrene polymer was resolved under both imaging modes and observed to be rod-shaped features with pointy ends. The height of polymer rods was measured to be ranging from 50 to 400 nm, while the width of the polymer rods was measured to be between several hundred of nm to a couple of μm. It is noteworthy that the quality of the topography image obtained via PinPoint PFM is significantly improved compared to that taken with conventional PFM mode. In Figure 3c, under PinPoint PFM imaging conditions, the annealed phenanthrene polymer were well-distinguished from the ITO substrate. However, in Figure 3a, under conventional PFM imaging conditions, image artifacts can be seen throughout the entire scan area, indicating that the probe was scratching on the surface repeatedly. Of note, for conventional PFM measurement, our initial attempt was to use PPP-EFM (f = 2.8 N/m) as the probe, which is the same as the one used in the PinPoint PFM measurements. However, the probe was constantly scratching on the surface and the image quality was very poor. A cantilever with smaller force constant, NSC36-C (f = 0.6 N/m) was used instead, in hope to alleviate the scraping on the surface. Albeit the NSC36-C has a smaller force constant compared to that of PPP-EFM, the probe was still dragging on the surface and resulted in imaging artifacts as seen in Figure 3a. In PinPoint PFM, on the other hand, since the probe was retracted away from the surface to a safe height at every pixel prior to approach towards the surface, the scratching between the probe and the underlying substrate was effectively eliminated, leading to significantly improved imaging quality. Figure. 3.a) Topography image taken with conventional PFM mode; b) PFM quad image taken with conventional PFM mode; c) Topography image taken with PinPoint PFM mode; d) PFM quad image taken with PinPoint PFM mode. Scan size: 20 μm × 20 μm. Similar results were observed in the piezoelectric response images (Figure 3b and Figure 3d).By comparing the results of the two techniques, one can easily determine that PinPoint PFM has better performance compared to conventional PFM in the detection of piezoelectric response as the image obtained under PinPoint PFM was much better compared to that taken with conventional PFM mode. Figure. 4. Hysteresis curves for the amplitude (a) and phase (b) signal taken with the phenanthrene polymer film. Figure 4a and 4b are hysteresis curves for the PFM amplitude and PFM phase signals of the phenanthrene film. These hysteresis curves were obtained by measuring the piezoelectric response at a specific location of the sample while applying the sample bias from -1.5 V to +1.5 V. The hysteresis curves provide localized information with respect to the switching properties of piezoelectric material. In Figure 4a, a characteristic “butterfly” shape that is similar to the ideal strain versus bias curve was observed in the amplitude signal. In addition, the coercive voltage, which is a measure of ability to withstand an external electric field without depolarization, is ~0.3 V. In Figure 4b, the phase hysteresis loop is shown, which is the typical response of a ferroelectric material. Conclusions Here in this application note, imaging performance of PinPoint PFM mode and conventional PFM mode was compared on phenanthrene film annealed on ITO surface. The PinPoint PFM mode introduced by Park Systems has proven to offer significantly-improved quality in both topography and piezoelectric response measurement. The advanced PinPoint mechanism eliminates the frictional force between the probe and the substrate, enabling concurrent high-resolution topography and piezoelectric response mapping of the surface. In addition, the response in strain (PFM amplitude) and polarization (phase) as a function of applied voltage was examined to obtain insights regarding material characteristics such as coercive voltage and hysteresis. Taken in total, PinPoint PFM mode is the ideal approach to characterize and quantify localized piezoelectric response at nanoscale, with maximized tip life and sample originality as a result of minimal frictional force between tip and sample. References [1] Ikeda T. Piezoelectricity. Oxford university press; 1990. [2] Soergel E. Piezoresponse force microscopy (PFM). J Phys D Appl Phys. 2011;44(46):464003. [3] Vijaya MS. Piezoelectric Materials and Devices: Applications in Engineering and Medical Sciences. CRC Press; 2012. .

Carbon nanotubes (CNTs) are a popular sample for various nanotechnology studies. However, they are very difficult to synthesize en masse. As a result, researchers have started looking at alternatives with similar properties. One of the candidates to replace CNTs in some nanocomposite materials is cellulose nanowhiskers (CNWs), structures that can be readily produced from plant sources.

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).

Nanotechnology has received increased attention within the scientific community due to its application in a number of fields ranging from electronics to biomedical technologies [1]. Progress in many of these applications depends mainly on the capability to fabricate nanostructured materials that include polymers and semiconductors, among others [2, 3]. Several methods have been introduced for the fabrication of nanostructures; the more common ones are electron beam lithography and focused ion beam lithography. However, these methods are not straightforward and are expensive to operate. One powerful method designed to overcome these problems is atomic force microscopy (AFM) nanolithography [1-3]. This technique is simple and less expensive [2]. AFM nanolithography is divided into two general groups based on their mechanistic and operational principles, bias-assisted and force-assisted AFM lithography [2]. In bias-assisted method, a bias voltage is applied to the tip to generate an oxide pattern on metallic or semiconductor substrate [4, 5]. Whereas, force-assisted method applies a large force to the tip to produce fine grooves on the surface of polymer like samples by mechanically scratching, pushing or pulling the surface atoms and molecules with a sharp tip; the interaction between the tip and the sample is mainly mechanical [2, 3].

Conductive AFM (C-AFM) is uniquely suited to perform electrical measurements such as current distribution with nanoscale precision and can be performed in contact mode, tapping mode, or PinPoint™ mode. Here we perform C-AFM on ZnO nanorods, which have been widely studied due to their remarkable performance in electronics, optics, photonics, and photocatalysis.