1 January 1988 Improvements In Photolithography Performance By Controlled Baking
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Abstract
Experimental tests were conducted on the hot plate of a 4-inch single-wafer baking oven in order to characterize the dynamics of the wafer temperature during baking, and a factorial experiment was carried out to investigate the significance of these thermal effects on photolithography performance. The purpose was to quantify the effect of temperature overshoot on the critical dimensions, the resist photosensitivity value, and the film thickness, which are the three most significant photolithography outputs. The experimental results indicate that the baking ovens commonly exhibit temperature overshoot by exceeding the prescribed processing temperature. Levels of overshoot of 3°C and 4°C at both the soft-bake and post-exposure bake steps are responsible for statistically significant deviations in critical dimensions and in photosensitivity, with respect to a reference population of films processed under controlled temperature overshoots of 1°C or less. A temperature overshoot of 3°C in the soft-bake cause a small, but statistically significant, increase in CD of 0.011 pm, an increase in ET of 7.5 msec, and a thinning. in resist thickness of 78A. Also, an overshoot of 4°C or greater at post-exposure bake causes an increase in CD's of 0.024 pm, and an increase in ET of 17.5 msec. Further, if overshoots of 3°C or greater at both SB and at PEB occur, then the total CD mean shift is 0.035 μm and the ET mean shift is 25 msec. These output deviations produce a loss in process capability quantitatively measured by the reduction of the process capability index Cpk.
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Oscar D. Crisalle, Cynthia L. Bickerstaff, Dale E. Seborg, Duncan A. Mellichamp, "Improvements In Photolithography Performance By Controlled Baking", Proc. SPIE 0921, Integrated Circuit Metrology, Inspection, and Process Control II, (1 January 1988); doi: 10.1117/12.968380; https://doi.org/10.1117/12.968380
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KEYWORDS
Semiconducting wafers

Optical lithography

Critical dimension metrology

Process control

Metrology

Photoresist materials

Inspection

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