Optimized dopant imaging for GaN by a scanning electron microscopy.

We have developed a strongly excited objective lens with a built-in secondary electron detector to provide ultra-high resolution images with high quality at low to medium accelerating voltages. The JSM-6320F is a scanning electron microscope (FE-SEM) equipped with this lens and an incident beam divergence angle control lens (ACL).The objective lens is so strongly excited as to have peak axial Magnetic flux density near the specimen surface (Fig. 1). Since the speciien is located below the objective lens, a large speciien can be accomodated. The working distance (WD) with respect to the accelerating voltage is limited due to the magnetic saturation of the lens (Fig.2). The aberrations of this lens are much smaller than those of a conventional one. The spherical aberration coefficient (Cs) is approximately 1/20 and the chromatic aberration coefficient (Cc) is 1/10. for accelerating voltages below 5kV. At the medium range of accelerating voltages (5∼15kV). Cs is 1/10 and Cc is 1/7. Typical values are Cs-1.lmm. Cc=l. 5mm at WD=2mm. and Cs=3.lmm. Cc=2.9 mm at WD=5mm. This makes the lens ideal for taking ultra-high resolution images at low to medium accelerating voltages.

Doping-dependent contrast in secondary electron images of p/n junctions in silicon obtained in a field-emission scanning electron microscope was observed and characterized. The optimum experimental conditions for observing this ‘‘electronic’’ contrast were established by investigating the effect of microscope and material parameters on the magnitude of the contrast. The contrast between the bright p-type areas and the darker n-type areas was maximized at an accelerating voltage of ∼1 kV, and when a through-the-lens detector configuration was employed. Secondary electron contrast profiles of boron doped p+/n junctions in silicon showed a good correlation with secondary ion mass spectroscopy depth profiles of the atomic concentration down to the 1017 cm−3 level. However, similar results were not obtainable for n+/p junctions. It is demonstrated that this contrast effect may be exploited for obtaining two-dimensional dopant profiles directly from secondary electron images of p+/n junctions provided that the technique is empirically calibrated against a one-dimensional dopant profiling method.

The National Technology Roadmap for Semiconductors (NTRS) has established some stringent requirements on two-dimensional dopant profiling. This work explores the reasons behind these metrology requirements, and also presents the difficulty of achieving these goals from the metrologist’s point of view. The goal of this paper is to present a more complete description of the metrology needs, including such issues as dopant statistics, surface profiling, active versus total concentrations, and physical regions of interest in a transistor in order to establish better metrology targets.

Laparoscope is the essential tool for minimally invasive surgery (MIS) within the abdominal cavity. However, the focal length of a conventional laparoscope is fixed. Therefore, it suffers from the tradeoff between field of view (FOV) and spatial resolution. In order to obtain large optical magnification to see more details, a conventional laparoscope is usually designed with a small working distance, typically less than 50mm. Such a small working distance limits the field of coverage, which causes the situational awareness challenge during the laparoscopic surgery. We developed a multi-resolution foveated laparoscope (MRFL) aiming to address this limitation. The MRFL was designed to support a large working distance range from 80mm to 180mm. It is able to simultaneously provide both wide-angle overview and high-resolution image of the surgical field in real time within a fully integrated system. The high-resolution imaging probe can automatically scan and engage to any subfield of the wide-angle view. During the surgery, MRFL does not need to move; therefore it can reduce the instruments conflicts. The FOV of the wide-angle imaging probe is 80° and that of the high-resolution imaging probe is 26.6°. The maximum resolution is about 45um in the object space at an 80mm working distance, which is about 5 times as good as a conventional laparoscope at a 50mm working distance. The prototype can realize an equivalent 10 million-pixel resolution by using only two HD cameras because of its foveation capability. It saves the bandwidth and improves the frame rate compared to the use of a super resolution camera. It has great potential to aid safety and accuracy of the laparoscopic surgery.

SummaryWe report the working of a novel detector design based on a Bessel Box (BB) electron energy analyser in a scanning electron microscope (SEM). We demonstrate the application of our detector for elemental identification through Auger electron detection in an SEM environment and its potential as a complementary technique to energy dispersive X‐ray (EDX) spectroscopy. We also demonstrate energy‐filtered secondary electron imaging of a copper‐on‐silicon sample using an electron pass energy of 12 eV.Lay DescriptionAdvancements in the field of the Scanning Electron Microscopy have been one of the major nanotechnology enablers. A Scanning Electron Microscope (SEM) generates a magnified image of the sample by bombarding it with an electron beam and detecting the electrons that scatter off the surface along with the electrons that are generated in the sample. Conventional detectors such as the Everhart‐Thornley detector (ET) or through‐the‐lens (TTL) detectors, either offer little to no energy analysis (ET) or limited energy filtering capability (e.g the low‐pass energy filter in TTL). This information is crucial to interpret the image of the sample under study. What is needed is a smart and compact detector that can detect electrons and furnish energy inside the SEM chamber. Here, we report a novel secondary electron (SE) detector design with energy analysis capability for use in scanning electron microscopes. The detector is based on the design of a Bessel Box (BB) energy analyser. We have designed and experimentally tested it in an SEM environment. The band‐pass filter action of the detector enables the BB to be operated at a selected energy and allows a narrow window of energies to be detected for generating energy‐filtered images.

Quantitative two-dimensional (2D) dopant profiling of a gatelike structure is achieved by scanning capacitance microscopy (SCM) on a cross-sectioned polished silicon wafer. The gatelike structures consist of heavily implanted n+ regions separated by a lighter doped n region underneath a 0.56 μm gate. The SCM is operated in the constant change capacitance mode while scanning with a 37 nm radius tip. The 2D SCM data are converted to dopant density through a physical model of the SCM/silicon interaction. The model parameters are adjusted so that the SCM dopant profile far from the gate edge fits the vertical secondary ion mass spectrometry (SIMS) profile. A 15% error in average accuracy is found between SCM and SIMS profiles evaluated over the dopant range of 1020–1017 cm−3. The same model parameters are used for all points in converting the 2D SCM data, indicating that the accuracy of the full 2D result should be comparable to that of the vertical profile. A direct comparison of the 2D SCM and 2D TSUPREM4 results is made for the first time. The agreement is generally good, but there are some notable differences.

A scanning microscope using only a field emission gun, without auxiliary lenses, has been described elsewhere. It has been shown capable of 100 Å resolution using transmitted electrons with a beam current of 10-10 amps. Detectors have now been installed to test its performance using secondary electrons.Detection of secondary electrons in this microscope differs in some ways from detection in a conventional scanning microscope. First, the operating vacuum of 10-9 to 10-10 Torr places restrictions on detector construction and materials. Second, the high beam current reduces the noise restrictions on detector and amplifier. Third, the large possible working distance (up to ∿ 8 cm for a beam diameter of 200 Å) increases flexibility in the mechanical design.

We demonstrate the surface potential sensitivity of secondary electron (SE) imaging of titania thin film by scanning electron microscopy (SEM), and discuss the image formation mechanism. The 1‐nm titania film on Si substrate was imaged as bright region against the substrate. The SE image of the film varied with SE detector, but did not with primary electron energy. The contrast of the film was reversed by only 1‐nm carbon deposition. This result suggests that a slight change of surface potential altered the efficiency of secondary electron emission. This high sensitivity of secondary electrons to the surface potential is promising for improvement of thin‐film observation by SEM. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The optical deflectometer facilitates the characterization of deformation for the safety assessment of large structures. Actual displacement is determined by multiplying pixel displacement by a constant scaling factor, which potentially introduces errors if a large displacement occurs within a small working distance. In this study, a novel deflection measurement method has been proposed considering variations of the scaling factor to attenuate errors in large deformation measurements. As the structure deflects, the scaling factor is updated according to the changes in the working distance and local pitch angle. We first investigated how the scaling factor affects off-axis deflection measurements using a set of simulated deflection data. An experiment using a monocular camera for measuring close-range large off-axis structural deflection has been conducted to determine the vertical displacement produced by a controllable translation frame. Results, compared to traditional methods, show improved accuracy and efficiency.

Microscopy is the art and science of visually observing small objects. Electrons are electrically charged subatomic particles typically responsible for the flow of electrical current. Scanning is a method of observation where the focus of attention is moved in a chosen pattern and desired information is gained by assembling observations in sequence. In a scanning electron microscope (SEM), a beam of electrons is scanned in a regular pattern over a small object, and the image of the object appears on a screen by displaying the image points in synchrony with the movements of the electron beam on the object.A familiar example of image scanning is a television receiver, where a picture is created on a screen by rapidly scanning an electron beam across the phosphor face of the television tube. The beam striking the phosphor produces light, which is seen as a picture. The signal that modulates the electron beam in a television set is created in a television camera, which is scanned in the same way that the television screen is scanned. In a SEM, the signals come from special detectors in the microscope, not from an optical camera. Otherwise, the image display in a SEM is very similar to television. Although it is typical for SEM images to be scanned at a slower rate than are television signals, some SEMs display images at the same speed as television.The most common signal for detection in a SEM is the secondary electron signal. Secondary electrons are low‐speed electrons (having energies less than about 50 eV) that result from the interaction of the primary (i.e. beam) electrons with the sample. The secondary electrons are detected, usually by a scintillator/photomultiplier detector, and the resulting signal modulates the display screen.Secondary electrons are popular because they provide a kind of shading that gives a three‐dimensional appearance to an image, making it easy to visualize the structural relationships of parts of the sample (Figure 1).Other signals provide information of a more analytical nature. The signal produced by backscattered electrons is directly (although not exactly proportionally) related to the atomic number of the material being struck by the primary beam. Diffracted electrons provide information about crystal spacings and orientations in the sample. Induced‐current signals are particularly interesting for studying the response of active electronic components.The resolution of a SEM image depends on the quality of the optical system that forms the electron beam, including the nature of the electron source. Most SEMs can typically resolve objects as small as 10 nm. The resolution of specialized SEMs is better than 1 nm. In contrast, the resolution of light microscopes is limited by the wavelength of light to about 500 nm.The magnification of a SEM is not directly related to the optical system, very unlike a light microscope. The magnifying power of a SEM is related to the ratio between the size of the scan on the object compared to the size of the scan on the image display. In this way a SEM functions like a mechanical pantograph that was used, typically in older days, for copying drawings. If the arms of the pantograph were of equal length, the drawing would be copied the same size. If the arms were adjusted to different lengths, the drawing could be magnified or reduced.The primary advantage of a SEM is that it provides familiar‐looking images of surfaces with higher resolution and greater depth‐of‐field than an optical microscope. Although the images are typically familiar looking, the contrast mechanism in a SEM is not the same as the contrast provided by light, and an observer expecting always to interpret a SEM image the same way as a light image could easily be fooled.As the electron beam consists of electrically charged particles, the sample for SEM observation must either be inherently electrically conducting or must be made electrically conducting to yield good images. Otherwise, electrical charge builds up on the sample, the yield of secondary electrons is changed, and the scanning beam can become erratic. Low‐voltage or low‐vacuum SEMs can be used to reduce the charging problem.

Dopant contrast from secondary electron (SE) imaging is essentially determined by the local electronic band structure at the surface of the solid specimen being analysed in the scanning electron microscope (SEM). To study dopant contrast mechanisms on inhomogeneously doped semiconductors, we have developed a quantitative model by using a numerical method based on a combination of finite-element carrier and potential modelling and Monte Carlo simulation of SE emission and contrast detection. This combined model enables distinction between the effects of specimen internal fields (surface band-bending), microscopic external fields (patch fields) and any macroscopic external fields applied in the SEM.

Operation of any semiconductor device can be presented by unique configuration of the electrical field (potential) and charge (doping) distribution within the device. More specifically, the status of operation is described by the quasi-Fermi energy (QFE) profile across the device. Visualization of the dynamic operation of the device and quantitative measurements of the QFE profile is provided by differential voltage contrast (DVC), which is a modification of the secondary electron imaging in a scanning electron microscope (SEM). The DVC consists of storing two images of a tested semiconductor device. Exposed to the electron beam is a cross section, for example, of a field effect transistor (FET). The first image, covering the entire inside of the FET from source to drain, is taken when the device is not biased. The second image of the same area is taken when the transistor is biased. The secondary electron signal is enhanced or retarded by actual distribution of a potential across the tested device. Subtraction pixel by pixel of the two carefully aligned images removes morphologic contrast from the screen, takes away surface features and contamination of the sample, and reveals the contribution of the electrical field to the changes of contrast. The calibration procedure allows measurement of the potential distribution with a precision of 0.05 V. The first derivative of a potential profile provides for distribution of the electrical field and the second derivative gives the doping profile across the tested device. A variety of semiconductor devices such as p-n junctions, Zener diodes, MOSFET's, MESFET's, solar cells and optical detectors, quantum well lasers, etc., were tested. Videotaping of the tested devices allows us to observe the changes in the electrical field and charge distribution as the device operates in a wide range of electrical or optical signals.

Study on time resolution of single event TOF-RBS measurement

Transmission electron microscope (TEM) specimen preparation by focused ion beam (FIB) milling requires delicate polishing of a thin window of material during the final stages of the procedure. Over or underpolishing is common and requires extra microscope resources to correct. Despite some methods for lamella thickness measurement being available, the majority of users judge the final polishing step subjectively from scanning electron microscope (SEM) images acquired between milling steps. Here we demonstrate successful thickness determination of thin silicon lamellae using calibrated secondary electron detectors in a FIB-SEM dual-beam chamber. Unlike previous thickness measurement methods it does not require long acquisition times, the use of in-chamber scanning transmission electron microscope (STEM) or energy dispersive x-ray spectroscopy detectors. The calibration aligns a SEM image to an electron energy loss spectroscopy (EELS) map of lamella thickness acquired in a TEM. This calibration reveals the greyscale-thickness dependence of two secondary electron SEM detectors: the through-lens detector (TLD) and the in-chamber electron detector (ICE). It was found that lamella thickness estimation for TLD images is accurate for areas thinner than 0.4 t/λ, whilst ICE images are most accurate for areas thicker than 0.5 t/λ up to 1.1 t/λ. The procedure presented here allows objective lamella thickness determination during the final stages of FIB specimen preparation using conventional imaging modes for common secondary electron detectors. LAY DESCRIPTION: Successful analysis of a material in a transmission electron microscope requires very thin windows of the material to be fabricated. Despite the quality of this analysis relying heavily on the thickness of the window, measuring thickness during window fabrication is not common practice. The authors show that it is possible to measure the thickness of the window directly in a focused-ion-beam chamber with a scanning electron microscope without altering the fabrication procedure, and using electron detectors common to most microscopes.

Quantitative two-dimensional (2D) dopant profiling for 0.25 micron CMOS technology was demonstrated using secondary ion mass-spectrometry (SIMS) and scanning capacitance spectroscopy (SCS). P-well and N-well dopant profiles measured by 2D SIMS are in agreement with TSUPREM4 (TS4) simulations. TS4 was pre-calibrated to the specific technology using 1D SIMS and electrical data. 2D SIMS, TS4 and SCS show agreement on the well boundary location. SCS is an advanced form of scanning capacitance microscopy (SCM) devised for pn-junction delineation. 2D SIMS dopant profiling with lateral resolution of 10 nm (limited by the lithography pixel size) and sensitivity of 1/spl times/10/sup 17/ cm/sup -3/ was realized on commercial equipment.