Proceedings PaperPlasma Resist Image Stabilization Technique (PRIST) Update
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The plasma resist image stabilization technique (PRIST) can effectively stabilize the developed resist image in the production of integrated circuits6 This fluorocarbon plasma treatment allows the resist to be baked in excess of 210 C without measurable change in dimensions. The typical PRIST treatment is exercised in a CF4 plasma at a low RF power (25 W) for a short time (30 sec). This low power and short time combination could cause problems at times, especially when the PRIST is exercised in an inductively coupled barrel reactor. These problems are attributed to the plasma instability due to the system design. Most plasma systems are not designed for such low power and short time operation. We can minimize these problems and improve the process reliability by operating the reactor at a power level for which the system was designed. This paper reports the results of the PRIST experiments using a mixture of CF4 diluted in nitrogen, argon, or helium. The results indicate that one can reduce the concentration of CF4 to less than 1% and still obtain excellent resist pattern after the post-baking. This reduction in CF4 concentration permits increasing both RF power and treatment duration without increasing the nitride etch rate. In addition to improving the process reliability, this increase in time and power allows one to select a series of power and time combinations to achieve the desired results.