Paper PS1-TuA1
Process Performance of CO₂ In Situ Photoresist Ashing Processes and Their Influence on ULK Materials Modifications

Tuesday, October 16, 2007, 1:40 pm, Room 606

An in situ ashing process for removing photoresist (PR) layers is desired by industry as an alternative to remote plasma ashing processes since it could be more easily integrated with plasma etching processes. In this work, we examined the feasibility of CO₂ as source gas for in situ PR ashing processes compatible with ULK materials, and performed characterization of 193 nm PR ashing along with ULK (JSR LKD 5109, and several other candidate materials) damage evaluation. Reducing CO₂ pressure from 100 to 10 mTorr increased the ion density and led to a higher PR ashing rate (substrate at 10 °C, line of sight interaction), while suppressing ULK damage (non-line-of-sight interaction). Low pressure operation using CO₂ enabled a high ashing efficiency (AE) which is defined as the amount of PR removed over the amount of ULK material damaged (for a given time). The CO₂ AE at 10 mTorr is ~5 times improved relative to O₂ and comparable to the best values we have measured for typical H₂ based remote plasma ashing processes. For the CO₂ in situ ashing processes, we examined sidewall damage introduced in ULK trench structures employing scanning electron microscopy (SEM). We also used a gap structure to simulate exposure of ULK materials in actual trench sidewalls. This allowed characterization of ULK surface modifications induced by the indirect plasma exposure using ellipsometry, X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). These results will be presented, along with a discussion of issues derived from real pattern transfer processes such as etching/ashing interaction and the influence of slight ion bombardment to ULK sidewall during in situ ashing.