Gabi Neubauer

The Role of Indentation Depth on the Measured Hardness of Materials

Ultra micro-indentation tests on Ni and Cu samples showed increasing hardness with decreasing penetration depth over a range from 200 to 2000 nm. The results suggest increased strain hardening with decreased indentation depth. To establish that this is a real material effect, a series of tests were conducted on amorphous materials, for which strain hardening is not expected. The hardness of Metglas ® was found to be independent of depth. A simple model of the dislocation densities produced under the indenter tip describes the data well. The model is based on the fact that the high density of dislocations expected under a shallow indentation would cause an increase in measured hardness. At large depths, the density of geometrically necessary dislocations is sufficiently small to have little effect on hardness, and the measured hardness approaches the intrinsic hardness of the material.

Epitaxial staircase structure for the calibration of electrical characterization techniques

Frequently electrical characterization techniques [such as the spreading resistance probe (SRP)], rely on the availability of a set of well-calibrated, homogeneously doped Si samples to establish the calibration curves (and parameters) necessary for the conversion of resistance measurements into carrier profiles. Although ideally such a calibration should be verified daily, in practice, time considerations limit the daily verification to one (or a few) calibration samples. To remedy this situation a special multilayer Si structure has been grown consisting of a decreasing B-doped staircase containing seven flat 4–5 μm thick calibration layers doped from 1020/cm3 down to 1015/cm3 separated by slightly (factor 2–3) higher doped 1–2 μm thick interface layers. The latter are included to facilitate the SRP calibrations as the SRP correction factor within the calibration layers now becomes very close to one. Since presently, a calibration curve can be generated quickly from a single measurement, daily measureme...

Two‐dimensional scanning capacitance microscopy measurements of cross‐sectioned very large scale integration test structures

Scanning probe technology, with its inherent two‐dimensionality, offers unique capabilities for the measurement of electrical properties on a nanoscale. We have developed a setup which uses scanning capacitancemicroscopy (SCM) to obtain electrical information of cross‐sectioned samples while simultaneously acquiring conventional topographical atomic force microscopy(AFM) data. In an extension of our work on very large scale integration cross sections, we have now obtained one‐dimensional and two‐dimensional SCM data of cross sections of blanket‐implanted, annealed Si wafers as well as special test structures on Si. We find excellent agreement of total implant depth obtained from SCM signals of these cross‐sectioned samples with conventional secondary ion mass spectrometry(SIMS) profiles of the same samples. Although no modeling for a direct correlation between signal output and absolute concentration has yet been attempted, we have inferred quantitative dopant concentrations from correlation to SIMS depth profiles obtained on the same sample. By these means of indirect modeling, we have found that our SCM technique is sensitive to carrier density concentrations varying over several orders of magnitude, i.e., <1×1015 to 1×1020 atoms/cm3, with a lateral resolution of 20–150 nm, depending on tip and dopant level.

Quantitative scanning capacitance microscopy analysis of two-dimensional dopant concentrations at nanoscale dimensions

We have applied the scanning capacitance microscopy (SCM) technique of twodimensional (2-D) semiconductor dopant profiling to implanted silicon cross sections. This has permitted the first direct comparison of SCM profiling scans to secondary ion mass spectroscopy (SIMS) depth profiles. The results compare favorably in depth and several readily identifiable features of the SIMS profiles such as peak concentration and junction depth are apparent in the SCM scans at corresponding depths. The application of dopant profiling to two dimensions is possible by calibrating the SCM levels with the one-dimensional (1-D) SIMS data. Furthermore, we have subsequently simulated the SCM results with an analytic expression readily derivable from 1-D capacitance vs voltage capacitance-voltage theory. This result represents a significant breakthrough in the quantitative measurement of 2-D doping profiles.

Imaging VLSI Cross Sections by Atomic Force Microscopy

Imaging is an integral part of VLSI technology development and quality control in device manufacturing. We report a novel application of Atomic Force Microscopy to image VLSI cross sections of metallographically polished samples. The major advantage of this technique over conventional imaging techniques, such as Scanning or Transmission Electron Microscopy, is the higher resolution achievable in combination with higher throughput and an easy access to quantitative data, such as line widths or re-entrant angles. We observe a very good correlation of AFM VLSI cross section images, acquired in air, with those acquired by SEM and TEM.

Hardness and Modulus Studies on Dielectric Thin Films

We report hardness and Youngs modulus measurements on various dielectric thin films. Hardness and modulus information was derived from indentation experiments with a Berkovich triangular-based diamond indenter in an ultra micro-indentation instrument (UMIS). We studied the effect of moisture content and phosphorous doping on hardness and Youngs modulus of low temperature Chemical Vapor Deposition (CVD) Si-oxides and found that dehydration and densification tend to harden samples, whereas increased P-doping results in a lower hardness. Hardness values of silicon nitride, silicon oxynitride, sputtered oxide, spin-on-glass and APCVD Si-oxides are compared. We also discuss how deposition conditions and chemical compositions correlate to dielectric properties such as stress as well as moisture uptake, thermal expansion coefficients and hardness and modulus values. Using these results, thermal stresses in encapsulated Al lines have been calculated and the calculated stress in Al is higher when encapsulated with dielectric films with higher moduli.