Real-time, in-situ measurement of film thickness and uniformity during plasma ashing of photoresist

This paper will discuss the performance ofequipment which monitors and so controls photoresist thickness and uniformity during plasma ashing without interfering with the process. Practical monitoring of a subtractive process of this type is significantly more complex than monitoring deposition processes. An initial absolute thickness measurement is needed. In addition, the device must view the layer through a luminous medium, and cannot rely on simple optical interference fringe counting. The equipment is self-calibrating and sensitive to layers dnm thick. An application to partial plasma resist ashing in high uniformity equipment will be described. Application to other films (e.g. oxide) will be discussed.