An operational two level photoresist technology

Of the many multilevel resist technologies, the two level technique devised by B.J. Lin (1) of IBM is potentially one of the most attractive from a production standpoint, due to its simplicity. This paper will briefly review the technique, and discuss the development of a production-oriented technology based on two level resist (TLR). Like all multilevel resist techniques, the TLR system involves the transfer of a pattern imaged in a thin layer into a thick underlayer (in this case, positive photoresist and PMMA). Here, the transfer is accomplished using a blanket deep UV exposure and subsequent wet development of the PMMA. This paper will discuss the design, construction and use of a deep UV blanket exposure system capable of a throughput in excess of 200 three-inch Wafers per hour. This blanket exposure tool employs a unique cadmium arc lamp source developed specifically for this application. The exposure-development characteristics of PMMA using this cadmium arc lamp exposure system will also be covered. The PMMA development chemistry used provides good resolution, short development times and is compatible with automated equipment. The utility of the technology will be illustrated by examples which demonstrate improved linewidth control over that achieved using only conventional positive resist.