Characterization of physical-chemical drivers of Hg1−xGdxTe etch rate using time of flight—Secondary ion mass spectrometry and optical interferometry

Time of flight-secondary ion mass spectrometry (TOF-SIMS) is a Hg1−xCdxTe surface diagnostic tool with unprecedented analysis capabilities, including analyzing a 0.5-µm diameter spot, high mass resolution, elemental and molecular composition scrutiny, applicability to insulators, and surface film sensitivity in the part per million range. The present investigation demonstrates the power of TOF-SIMS when coupled with optical interferometry in understanding process reproducibility and uniformity critical to the fabrication of Hg1−xCdxTe detector arrays at RVS. Previous published works and unpublished studies at RVS have shown that geometry and fluid dynamics influence the lateral uniformity of surface chemistry, topography, and etch rates. By combining a set of photolithographically delineated features having various relative areas of photoresist-coated and uncoated regions in varying proximity to each other with various wet etching chemistries, we have exploited TOF-SIMS interrogation along with optical interferometry to investigate physical-chemical drivers of etch rate variation with window geometry orientation with respect to vertical gravity etchant fluid draining direction and proximity to other structures. This study has given us the ability to deconvolve two important etch rate drivers (depletion of etchant species and cross-contamination of etched windows) and elucidate their roles in enhancing and diminishing etch rates for features having far and close proximities to neighboring structures, respectively. This information allows a more judicious optimization of processing technology.