In-situ monitoring of submicron polysilicon linewidths using diffraction gratings

The measurement of pattern integrity is performed as a part of process control in all wafer manufacturing environments. Typically this measurement is performed off-line on pilot material using a top down scanning electron microscope (SEM). With the advent of sub- micron geometries and small lot wafer fabrication centers, it has become important to monitor the processes on a wafer by wafer basis. An in situ technique using diffraction grating test patterns has been used to monitor the pre-etch and post-etch linewidths on a polysilicon etch chamber. The technique is capable of linewidth measurements to 0.25 microns with pitches as small as 0.7 microns. A comparison of the in situ polysilicon linewidth measurements with off-line SEM measurements shows measurement differences of less than 10% indicating a measurement accuracy on that order. The repeatability of the diffraction technique is shown to be approximately 0.01 micron in comparison to the typical SEM repeatability of 0.025 micron.