PROCESSING CONTROL FOR 0.25 MU-M X-RAY-EXPOSURES OF COMMERCIALLY AVAILABLE RESISTS - THE POTENTIAL FOR ADAPTIVE-CONTROL

The processing of chemically amplified resists to yield 0.25 mu m stru ctures requires control of a number of key parameters. Some of these m ay be at the limits of the control range or at the limits of achievabl e uniformity. Where it may not be possible to improve the control or t he uniformity, it may be possible to use adaptive control to compensat e. The focus of this article is to explore what is needed for adaptive control with two commercial x-ray resists, Shipley SAL 505 (negative tone) and Hoechst AZ PF-514 (positive tone) and to explore the feasibi lity of adaptive control with the SAL 605 resist. Statistical optimiza tion has been used previously to provide robust process latitude by fo cusing on the preexposure bake temperature and time, the x-ray dose, a nd the postexposure bake temperature and time. To determine the requir ed control and the slope of the linewidth change with the change in ea ch variable, a statistical model of the response surface was construct ed. The statistical results and new work with developer normality poin t out the major contributions from the wafer baking conditions using a track vacuum hot plate. The different slopes of the variations with l inewidth suggest that whole wafer compensation may be possible for cer tain parameters, and that field-to-field variation arising from hot pl ate uniformity might be compensated for the SAL 605 resist with anothe r Preliminary results with Fourier transform infrared spectroscopy wil l be presented that support these approaches and suggest that further efforts to provide in-line measurements might be justified by correlat ing the infrared cross-linking signal with the processing parameter th at yields the correct linewidth. (C) 1995 American Vacuum Society.