Bruce F. Griffing

Contrast Enhancement - A Route To Submicron Optical Lithography

A new method for the production of submicron photopatterns is described. Good quality images are obtainable even under very low contrast illumination through the use of photobleachable materials in conjunction with standard photoresists. The method consists of applying a thin photobleachable layer to the photoresist surface prior to the conventional exposure step. The bleachable layer (contrast-enhancing layer or CEL) is subsequently removed and the resist developed in the ordinary way. Examples of vertical-walled submicron patterns fabricated using an Optimetrix 10:1 DSW system demonstrate that the CEL process compares well with other advanced photolithographic techniques.

Deep-Ultraviolet (UV) Source For Two-Level Resist Technology

High resolution optical lithography demands a sophisticated photoresist technology. Recent work in this arfa has concentrated on multilevel resists. An example is a two layer resist (TLR) technique which uses a thin top layer of positive resist over a thick layer of PMMA. The pattern formed in the thin top layer serves as a mask for a deep UV blanket exposure of the thick PMMA bottom layer. Previously, no deep UV source existed which was well suited to this application. This paper describes the development of such a UV source and its application to high resolution optical lithography. The TLR technique requires a UV source with output in the 200-230nm range and essentially no output below 200nm or between 230 and 300nm. A specially designed low pressure Cd arc lamp has been constructed for this application. The lamp is unique in the way the output is maximized in the 215-230nm range. The lamp is very efficient, converting 10% of its input into output at these wavelengths. Using the new lamp, resist (PMMA) structures of 0.5μ width having 3:1 vertical:horizontal aspect ratios have been fabricated. Such patterns have been used as etch masks for CC14 plasma etching of 0.5μ patterns in polysilicon. The large aspect ratio of the resist patterns was important in preventing resist degradation (during etching) from affecting the final polysilicon geometry.