Characterization of Oxidation Induced Substrate Loss

Post implant resist strip for sub-65 nm highdose implant (HDI) poses challenges with regard to Si substrate loss due to oxidation. In order to ensure the desired device characteristics, this loss must be kept to a minimum, typically less than 4A loss per strip/wet clean cycle. Conventional metrology techniques such as Ellipsometry, XPS and EOT (effective oxide thickness measurements using capacitance) have difficulty in measuring substrate loss as they make a measurement of native oxide thickness rather than substrate loss. Additionally quantitative measurements such as spectrophotometry and ICPMS measure dissolved silicon and are limited to wet clean process steps only. This paper reports on wafer mass loss as a direct linear measurement technique to quantify substrate loss. Mass loss measurement displays the ability to differentiate with a high degree of resolution mass loss in the sequential ash / clean / anneal process.