Wet silicon etch process for TSV reveal

This paper presents a wet process as a simple and cost-effective alternative to the polish/plasma etch TSV reveal process. By combining silicon thickness measurement, wet etch, and cleaning in a single-wafer process system, this platform provides a low cost-of-ownership solution for TSV reveal. The process uses a wet etch chemistry with a fast etch rate and high selectivity, in a single-wafer process tool. The new selective etch chemistry improves the etch rate by 50% or more over traditional Si etchants currently used in the industry, such as tetramethylammonium hydroxide (TMAH). This new etch chemistry also has high silicon-etch selectivity over the oxide liner and Cu, with etch rate (ER) ratios greater than 10,000 and 1000, respectively. TMAH is not a component in the chosen chemistry because of safety concerns specifically related to TMAH toxicity. Variations in the depth of the Si overburden occur due to non-uniformities in post-grind thickness, via depth, and bonding. To compensate, an algorithm is used to control etch profiles. Integration of wafer thickness measurements before and after etching-within the single-wafer equipment-provides the high-accuracy process control needed for high-volume manufacturing. Improvement in surface roughness and etch uniformity are achieved with this wet process through the combination of chemistry performance and process optimization.