J. S. McMurray

Advances in experimental technique for quantitative two-dimensional dopant profiling by scanning capacitance microscopy

Several advances have been made toward the achievement of quantitative two-dimensional dopant and carrier profiling. To improve the dielectric and charge properties of the oxide–silicon interface, a method of low temperature heat treatment has been developed which produces an insulating layer with consistent quality and reproducibility. After a standard polishing procedure is applied to cross-sectional samples, the samples are heated to 300 °C for 30 min under ultraviolet illumination. This additional surface treatment dramatically improves dielectric layer uniformity, scanning capacitance microscopy (SCM) signal to noise ratio, and C–V curve flat band offset. Examples of the improvement in the surface quality and comparisons of converted SCM data with secondary ion mass spectrometry (SIMS) data are shown. A SCM tip study has also been performed that indicates significant tip depletion problems can occur. It is shown that doped silicon tips are often depleted by the applied SCM bias voltage causing errors...

Scanning capacitance microscope methodology for quantitative analysis of p-n junctions

Quantification of dopant profiles in two dimensions (2D) for p-n junctions has proven to be a challenging problem. The scanning capacitance microscope (SCM) capability for p-n junction imaging has only been qualitatively demonstrated. No well-established physical model exists yet for the SCM data interpretation near the p-n junction. In this work, the experimental technique and conversion algorithm developed for nonjunction samples are applied to p-n junction quantification. To understand the SCM response in the active p-n junction region, an electrical model of the junction is proposed. Using one-dimensional secondary ion mass spectrometry (SIMS) data, the carrier distribution in the vertical dimension is calculated. The SIMS profile and carrier distribution is then compared with the SCM data converted using a first-order model. It is shown that for a certain class of profiles, the SCM converted dopant profile fits well to the SIMS data in one dimension. Under this condition, it is possible to identify t...

Direct comparison of two-dimensional dopant profiles by scanning capacitance microscopy with TSUPREM4 process simulation

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 r...

Two dimensional dopant and carrier profiles obtained by scanning capacitance microscopy on an actively biased cross-sectioned metal–oxide–semiconductor field-effect transistor

Scanning capacitance microscopy (SCM) was developed to measure two dimensional (2D) dopant and carrier profiles on passive semiconductor devices. This capability has now been extended for the first time to electrically biased cross-sectional devices. An electrical bias is applied to the source/drain of a device while a SCM image is being acquired. 2D SCM profiles are obtained as a function of applied bias, providing a method for determining the carrier distribution in a functioning device. The acquired SCM data is converted to carrier density using a physical conversion model developed for 2D dopant profiling. The SCM carrier profiles agree qualitatively with the predictions of device simulation. The SCM imaging of actively biased devices provides a means to directly compare electrical device characteristics with electrical device and process models. The measured carrier profiles may eventually be used to improve the accuracy of the 2D dopant profile extracted from the SCM data.

Noise in scanning capacitance microscopy measurements

Scanning capacitance microscopy (SCM) is a powerful tool for two-dimensional (2D) dopant/carrier profiling. Currently noise limits the accuracy of 2D dopant profiles obtained by SCM. In an effort to reduce noise, a systematic analysis of different SCM noise sources is provided. The main noise sources during SCM measurements are capacitance sensor noise and oxide–semiconductor surface induced noise. For adequate tip size, the dominant noise in SCM measurements is caused by variations in the quality of surface. On as-polished surfaces, nonstationary noise is observed. This noise is likely caused by the variations in the density of oxide traps. Tip induced charging of these traps and local variations or fluctuations in discharge time during SCM imaging cause the noise level and noise pattern to be different from image to image. Heat treatment under ultraviolet irradiation or in a hydrogen ambient is found to be an effective way to reduce or even eliminate this type of SCM noise. Stationary surface noise is m...

Spatial mapping of ordered and disordered domains of GaInP by near‐field scanning optical microscopy and scanning capacitance microscopy

Imaging of topography, locally induced photoluminescence and Fermi‐level pinning in adjacent ordered and disordered domains on a cleaved GaInP sample is performed using a near‐field scanning optical microscope and scanning capacitance microscope at room temperature in air. Highly localized photoluminescence spectra obtained by the near‐field scanning optical microscope on these domains show spectral peaks at 680 nm (ordered) and 648 nm (disordered) GaInP. The near‐field scanning optical microscope and scanning capacitance microscope data confirm previously published data, indicating that the electronic surface structure of ordered GaInP is significantly different from that of disordered GaInP. Both approaches indicate that the Fermi‐level at the surface of ordered GaInP is pinned, while the Fermi‐level at the surface of disordered GaInP is not pinned. The size, structure, and position of the ordered and disordered domains observed by the near‐field scanning optical microscope and scanning capacitance micr...

Application of electron holography to analysis of submicron structures

Importance of effects of charging and sample thickness variation across depletion region is discussed using one-dimensional p-n junction in bulk Si and silicon-on-insulator (SOI) structures prepared by mechanical polishing. It is shown that good correlation between results of electron holography and secondary ion mass spectroscopy can be achieved without consideration of “dead layers.” Analysis of laser annealed n-type field-effect transistor (n-FET) devices in SOI structures showed that laser annealing does not cause lateral dopant diffusion of arsenic to resolution of electron holography. It is demonstrated that junction overlap can be achieved with “laser-only” integration scheme. Examples are given on how electron holography can provide insight into integration scheme for development of a p-FET device with embedded SiGe source/drain regions and evaluation of effect of proximity of shallow trench isolation on dopant depletion.

Inverse modeling applied to Scanning Capacitance Microscopy for improved spatial resolution and accuracy

Scanning Capacitance Microscopy (SCM) is capable of providing two-dimensional information about dopant and carrier concentrations in semiconducting devices. This information can be used to calibrate models used in the simulation of these devices prior to manufacturing and to develop and optimize the manufacturing processes. To provide information for future generations of devices, ultra-high spatial accuracy (<10 nm) will be required. One method, which potentially provides a means to obtain these goals, is inverse modeling of SCM data. Current semiconducting devices have large dopant gradients. As a consequence, the capacitance probe signal represents an average over the local dopant gradient. Conversion of the SCM signal to dopant density has previously been accomplished with a physical model which assumes that no dopant gradient exists in the sampling area of the tip. The conversion of data using this model produces results for abrupt profiles which do not have adequate resolution and accuracy. A new in...

Surface and tip characterization for quantitative two dimensional dopant profiling by scanning capacitance microscopy

In the present work, recent improvements in sample preparation and a tip quality evaluation are reported. A new method for cross-sectional surface preparation has been developed. The sample is heated at a temperature of 200–300C while being exposed to ultraviolet irradiation. This additional surface treatment improves dielectric layer uniformity, signal to noise ratio, and C-V curve flat band offset. The performance of three types of tips are also compared. It is shown that heavily doped silicon as well as worn tips are often depleted by the applied bias voltage causing errors in the Scanning Capacitance Microscope (SCM) measured dopant profile. When these effects are tested for and eliminated, SCM quantitative profiling over a 5-decade range of dopant density is demonstrated.