Negative photoresists for optical lithography

Negative photoresists are materials that become insoluble in developing solutions when exposed to optical radiation. They were the first systems used to pattern semiconductor devices, and still comprise the largest segment of the photoresist industry because they are widely used to define the circuitry in printed wiring boards. However, the current use of negative resists in the semiconductor industry has been limited by past difficulties in achieving high-resolution patterns. Recent advances in the chemistry of negative-resist systems, however, have provided materials with wide processing latitude and high resolution that are used to manufacture IBM's advanced CMOS devices and to achieve high-aspect-ratio patterns for micromachining applications. This paper provides an overview of the history and chemistry of negative-resist systems and their development in IBM.