Brian G. Rennex

Carrier concentration dependence of the scanning capacitance microscopy signal in the vicinity of p–n junctions

Scanning capacitance microscopy (SCM) was used to image (1) boron dopant gradients in p-type silicon and (2) identical boron dopant gradients in n-type silicon. The bias voltage dependence of the apparent p–n junction location in the (SCM) images was measured. The theoretical bias voltage dependence of the apparent p–n junction location of the same structures was determined using a two-dimensional, numerical Poisson equation solver. The simulations confirm that, for symmetric step p–n junctions, the apparent junction coincides with the electrical junction when the bias voltage is midway between the voltage that produces the peak SCM response on the p-type side and the voltage that produces the peak response on the n-type side. This rule is only approximately true for asymmetrically doped junctions. We also specify the extent of the region on the junction high and low sides from which valid carrier profiles may be extracted with a simple model.

A capacitance–voltage model for polysilicon-gated MOS devices including substrate quantization effects based on modification of the total semiconductor charge☆

Abstract We present a model for simulating the capacitance–voltage ( C – V ) characteristics of polysilicon-gated MOS devices with thin oxides. The model includes substrate quantization effects through a modification of the total semiconductor charge. Therefore, solutions for C – V can be quickly obtained without the computational burden of solving over a physical grid. The model includes polysilicon depletion by self-consistently solving the charge balance equation. We conclude with comparisons of the C – V characteristics obtained with this model and those obtained by self-consistent solutions to the Schrodinger and Poisson equations. Good agreement was observed over a wide range of oxide thickness (2.0–15.0 nm) and substrate doping (10 15 –10 18 cm −3 ).

Comparison of experimental and theoretical scanning capacitance microscope signals and their impact on the accuracy of determined two-dimensional carrier profiles

The accuracy with which two-dimensional carrier profiles can be extracted from scanning capacitance microscopy (SCM) images of doped structures in silicon depends on the model used to interpret the SCM differential capacitance data. This work validates models of the SCM by comparing the calculated SCM signal to the measured signal for a variety of sample parameters, measurement conditions, and capacitance sensors from different manufacturers. The magnitude of the capacitance sensor high-frequency voltage is measured and its effect on ΔC–V curves and extracted carrier profiles is quantified. Two nonidealities commonly observed in SCM signals, U-shaped C–V curves and double zero crossing in the SCM signal at the p–n junctions, are related to the measurement parameters and explained.

Error Analysis for the National Bureau of Standards 1016 mm Guarded Hot Plate

An error analysis is given for the 1-meter Guarded Hot Plate at the National Bureau of Standards. This apparatus is used to measure the thermal resistance of insulation materials. The individual contributions to uncertainty in thermal resistance are discussed in detail. The total uncertainty is estimated to be less than 0.5 percent at sample thicknesses up to 150 mm (6 inches) and less than 1 percent at a thickness of 300 mm (12 inches).

Towards reproducible scanning capacitance microscope image interpretation

Scanning capacitance microscope (SCM) images, and the two-dimensional (2D) dopant profiles extracted from them, show poor reproducibility from laboratory to laboratory. Major factors contributing to SCM image variability include: poor sample surface and oxide quality, excess carrier generation from stray light, reduced sensor dynamic range from stray capacitance, and use of nonoptimal SCM operating voltages. This article discusses the sources of SCM image variability, how they affect the measured SCM images, and possible approaches for mitigating their effects. Recommended procedures for extracting quantitative 2D are discussed. Finally, a set of informal research materials is introduced consisting of a complementary metal-oxide-semiconductor transistor pair, an identical pair without metallization, and a pair of transistor-like structures with the conductivity type of the source/drains reversed. These structures are intended for use with the FASTC2D software to help improve laboratory-to-laboratory dopan...

FASTC2D: Software for extracting 2D carrier profiles from scanning capacitance microscopy images

FASTC2D is a Windows based computer program for conversion of two-dimensional (2D) scanning capacitance microscope (SCM) images of doped silicon into 2D carrier profiles. It utilizes interactive, user-friendly software to allow a user to enter electrical and measurement parameters, to model the tip, and to navigate among the various choices for calculation and analysis. It achieves fast carrier profile extraction using interpolation on a rigorous database of theoretical SCM response calculated off-line.

Dopant characterization round-robin study performed on two-dimensional test structures fabricated at Texas Instruments

The lack of a two-dimensional (2D) dopant standard and hence a priori knowledge of dopant distribution makes it impossible to unambiguously judge accuracy of any experimental or theoretical effort to characterize silicon doping in two-dimensions. Recently a strong progress has been made in quantitative scanning capacitance microscopy (SCM), scanning spreading resistance microscopy (SSRM), secondary electron (SE) and transmission electron microscopy (TEM) doping profiling. Several research groups have claimed an ability of quantitative 2D dopant characterization. A round-robin study involving various analytical techniques and comprehensive numerical simulations should help to evaluate an accuracy of available quantitative techniques and set some helpful standard for further development. We report on a world-wide round-robin study performed on CMOS 2D test structures fabricated at Texas Instruments (TI). Seven research groups, which represent an advanced SCM, SSRM and TEM dopant profiling, participated in t...

Comparison of measured and modeled scanning capacitance microscopy images across p-n junctions

Scanning capacitance microscope (SCM) image contrast measured on ion implanted P+/P and P+/N junction structures with identical dopant profiles, as a function of SCM operating conditions, is compared to a theoretical model of the SCM based on a two-dimensional finite-element solution of Poisson’s equation. Measured ΔC/ΔV versus bias voltage curves were found to agree with the theoretical model. For the P+/P structure, the lateral dopant profile is extracted using the model and compared to a Monte-Carlo simulation of the implanted profile. The image contrast of the P+/N junction structure and the dependence of the apparent junction location on SCM bias voltage is compared to model predictions calculated using the known dopant profile. The SCM quiescent operating point where the apparent junction location in an SCM image and the actual metallurgical p-n junction coincide is defined.

Scanning Capacitance Microscopy for measuring device carrier profiles beyond the 100 nm generation

Scanning Capacitance Microscopy (SCM) is a leading candidate for a metrology capable of measuring the two-dimensional (2-D) carrier profiles of cross-sectioned silicon transistors. Since 1992, there has been a program at the National Institute of Standards and Technology in the United States to develop the measurement techniques and theoretical modeling necessary to make SCM a practical metrology for quantitative measurement of 2-D carrier profiles. The SCM carrier profiling technique will be described in detail from sample preparation, to SCM image measurement, and to extraction of the final 2-D carrier profile.