Author

Mule'Stagno, Luciano.

Title

QUANTITATIVE NON-DESTRUCTIVE STUDY OF SUB-MICRON DEFECTS IN VERY LARGE SCALE INTEGRATED-CIRCUIT SILICON USING TRANSMITTED AND REFLECTED INFRA-RED LASER SCATTERING (VLSI).

Source

Dissertation Abstracts International. Volume: 57-10, Section: B, page: 6326.

Abstract

The limits and capabilities of the Scanning Infra-Red Microscope (SIRM) and the Optical Precipitate Profiler (OPP) to detect oxygen precipitate defects in silicon were investigated. Two sets of specimens were made and studied. One set had wafers containing the same bulk defect density, but had different precipitate growth thermal treatments. These treatments resulted in defects of different mean sizes ranging from 30 to 150 nm. The other set had defects of approximately the same size, but they had different defect densities ranging from about 1 x 10^9 defects/cm^3 to 1 x 10^(11) defects/cm^3. The first set was carefully characterized by transmission electron microscopy (TEM) to obtain an accurate size distribution of the defects in each sample. The defect densities were then measured by the OPP, the SIRM, and the cleave-and-etch technique and compared with the TEM measurements. In the second sample the defect density was measured only by the cleave-and-etch technique and then by the SIRM.

It was found that the scattering by precipitates in the SIRM and OPP varied with equivalent defect radius as r^(6.1+/-0.9) and r^(3.2+/-0.3), respectively. These results are consistent with simple Rayleigh scattering theoretical dependencies of r^6 and r^3, within measurement error. The two instruments also revealed the same bulk microdefect density as found using the TEM and the cleave-and-etch technique. Graphs of scattering versus precipitate dimensions were plotted to establish the dependence of scattering on defect sizes. These graphs can be used as calibration curves for the instruments in future studies. It was found that both instruments were unable to resolve very small precipitates found after short growth thermal cycles at 1000 degrees C. The OPP was able to detect precipitates down to an equivalent radius of about 15 nm, while the SIRM detected precipitates having an equivalent radius of about 30 nm or larger. It was also found that these instruments have a limit on the maximum density of defects which they can detect. For densities higher than a critical density the scattering signal does not increase. This is expected due to the finite volume sampled by the beams that these instruments use. For the SIRM this critical density was found to be about 5 x 10^(10) defects/cm^3, which implied a sampling probe volume of 16 um^3--which is within 20% of that predicted by theory.