IN-SITU ULTRASONIC MONITORING OF PHOTORESIST DEVELOPMENT

We have developed an in situ method to measure the change in thickness of photoresist during development. The phase of a high frequency ultr asound signal is monitored as it is reflected from the silicon/photore sist interface during resist development. The method was tested using a 1.5 mu m film of Shipley 1811 resist. The total phase change during development of 19 degrees was consistent with theoretical calculations at 280 MHz, and this change was used to obtain the resist thickness d uring development. The method was used to find the development rate of this positive-tone resist as a function of exposure dose in the 20-68 mJ/cm(2) range. As expected, there was an increase in development rat e as the exposure time increased; this continued up to about 40 s of e xposure, beyond which the rates were essentially unchanged. Measuremen ts on a wafer with microelectronic devices ranging in topography from 0.10 to 1.0 mu m show that the method is applicable to wafers with typ ical circuit topography. (C) 1998 American Institute of Physics. [S000 3-6951(98)03341-5].