IN-SITU END-POINT DETECTION DURING DEVELOPMENT OF SUBMICROMETER GRATING STRUCTURES IN PHOTORESIST

We describe a practical method for monitoring the evolution of the dep th of grating structures exposed in photoresist during development of the resist. A diagnostic laser of nonexposing wavelength illuminates, through a quartz window, the grating surface immersed in developer sol ution. The intensity of the diffracted -1 order is monitored. The inte nsities vary with time due to feature growth by dissolution. Using rea listic models for the shape of the grooves created, we predict grating efficiency versus feature geometry for the grating in both air and de veloper solution. This knowledge allows us to make a determination of the stopping point during development that gives us the maximum gratin g efficiency for operation in air. The shape of the efficiency curve v ersus time during development also makes possible the determination of complete dissolution of the grating troughs to the substrate. This re al-time monitoring corrects for exposure and bake variations, for exam ple, and it permits the recycling of developer solution and thus decre ases the waste stream for grating manufacture. It also allows for the determination of the end point for deep (>500 nm) gratings that show m ultiple extrema during development.