| Popis: |
Trends in optical lithography lead to 0.35 micrometers resolution as being the next critical linewidth for semiconductor production. The 64 Mb DRAM technologies will require this. Current i-line lithography techniques lack sufficient production tolerance for 0.35 micrometers . To achieve greater depth of focus and exposure latitude, a number of new techniques are being explored. These include phase shifting masks, multiple focal plane exposures, surface imaging, DUV lithography as well as off-axis illumination. This paper examines the contribution of off-axis illumination towards the improvement of process latitude. Experimental data using 0.54 and 0.48 NA lenses are presented showing the relative advantages and disadvantages of this technique. This data is evaluated for its potential production use for 0.35 micrometers lithography. The effect of off-axis illumination is evaluated for isolated lines, dense lines, sagittal/tangential lines, and contact features. To examine thin film effects, a number of commercially available photoresist processes are used for these tests. In addition, novel solutions to limitations encountered with off-axis illumination are modeled and experimentally verified. |
