Photoresist outgassing in high energy and high current ion implantation

Photoresist (PR) outgassing during ion implantation can alter the real-time measurements of implanted dose, limit the maximum allowed dose rate, and introduce unwanted changes to as-implanted depth profiles. Equipment manufacturers assume that the instantaneous gas load resulting from PR outgassing is almost exclusively hydrogen, However, we show that this is not the case during a significant portion of many production implant processes. In particular, we show that high energy implants are typically characterized by constant gas loads in which up to 50% of the evolved gas consists of species other than hydrogen, while in high current implants, the peak pressure excursions often occur during the first few per cent of the implant, when the effluents are largely carbon monoxide (CO) and hydrocarbons (HC). These differences are shown to be quantitatively related to both the instantaneous dose rate, and to the proximity of the dose endpoint to the critical dose. For example, we show how the gas composition from a 150 kV P source/drain implant begins to abruptly change from approximately 40% H₂, 60% (CO+CO₂+HC) at a critical dose of 4.5E14, to saturate at 95% H₂ at a dose of 1E15. We believe this transition to be a consequence of PR amorphization, since the critical dose is in good agreement with the PR outgassing model of T.C. Smith