5 June 1998 Surface chemistry of GaAs wafers and reaction with chemically amplified resists during resist processing
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The surface preparation of wafers used with chemically- amplified resist is critical for successful resist processing. GaAs wafers provide an additional complexity because the composition of the surface can be greatly affected by the chemical treatment and subsequent resist processing conditions. In order to get consistent rust with GaAs wafers, we have found that the surface composition of the wafer has to be determined. Secondary ion mass spectrometry (SIMS) and electron spectroscopy for chemical analysis were used to determine the surface composition before and after the treatment with HCl. A non-destructive and simple method of contact angle measurement was used to provide advance warning of difficulties with adhesion between GaAs and Shipley SAL605 negative-tone chemically- amplified resist. An observed correlation between the contact angel of water suggested that, when it was in the range of 60 degrees to 75 degrees, the wafers generally showed good adhesion when using aqueous developer, Shipley MF312. From the work of direct measurement of the wafer surface before and after treatment, we have found conditions that permit patterning linewidths on the order of 0.15 micron in 0.5 micron thick resist. The effects of each of the surface treatments found to influence the adhesion will be described in terms of the chemical changes on the wafer surface and their effect on the resist chemistry.
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Bing Lu, Bing Lu, Olga Vladimirsky, Olga Vladimirsky, James Welch Taylor, James Welch Taylor, Niru V. Dandekar, Niru V. Dandekar, "Surface chemistry of GaAs wafers and reaction with chemically amplified resists during resist processing", Proc. SPIE 3331, Emerging Lithographic Technologies II, (5 June 1998); doi: 10.1117/12.309610; https://doi.org/10.1117/12.309610

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