Mask-to-wafer alignment using x-ray-printed alignment marks in x-ray lithography

摘要

ithography can be used to achieve deep sub-micron design groundrules. With X-ray, as with other lithographic systems, mix and match techniques are often used to achieve timely, cost effective implementation. This can, in some cases, reduce overlay accuracy and complicate mask and wafer layout. In this paper we will present methods which will facilitate the use of X-ray lithography in mix and match environments to simplify layout and improve overlay accuracy. An alignment scheme for 0.35 micron CMOS device fabrication and a method for printing alignment marks for the next X-ray level are described. In this scheme all the critical levels such as oxide isolation, polysilicon gate, contact, and first metallization levels are printed using X-ray lithography with the same X-ray stepper (Karl Suss XRS200/2). All other noncritical levels are printed optically. The initial wafer lot using this scheme has been successfully processed to the first metallization level. The X-ray stepper alignment system can compensate for the first order overlay components such as translation and rotation. This feature is very useful for compensating for certain mask difference and process induced distortion. However, mask magnification difference must be compensated otherwise. A linear regression method has been used to analyze the overlay data and the results are fed back to the stepper for correction. A 3-sigma overlay distribution $PLU@/$MIN 180 nm has been achieved.