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

We describe a practical method for monitoring the evolution of the depth 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 solution. The intensity of the diffracted -1 order is monitored. The intensities vary with time due to feature growth by dissolution. Using realistic models for the shape of the grooves created, we predict grating efficiency versus feature geometry for the grating in both air and developer solution. This knowledge allows us to make a determination of the stopping point during development that gives us the maximum grating efficiency for operation in air. The shape of the efficiency curve versus time during development also makes possible the determination of complete dissolution of the grating troughs to the substrate. This real-time monitoring corrects for exposure and bake variations, for example, and it permits the recycling of developer solution and thus decreases the waste stream for grating manufacture. It also allows for the determination of the end point for deep (>500 nm) gratings that show multiple extrema during development.