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A unique set of processing conditions is used to obtain a negative resist image from a positive resist without the use of resist additives.
English (United States)
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Image Reversal of Positive Photoresist Without Additives
A unique set of processing conditions is used to obtain a negative resist
image from a positive resist without the use of resist additives.
Image reversal is obtained by exposing the resist to an image in a warm (70
to 90 degrees Celsius), dry (<1% relative humidity) environment. After image
exposure, the resist is blanket exposed at room temperature in an ambient
having >30% relative humidity and developed in the conventional manner using a
dilute aqueous alkali developer.
The following is a specific process sequence from which good reversal
images are obtained : 1. Apply and dry positive resist on a silicon wafer at 75
degrees Celsius for 5 minutes. 2. While maintaining the temperature at 75
degrees in a dry nitrogen (N2) atmosphere, image expose the resist. 3. Change
the environment of the wafer to room temperature air having relative humidity of
30% or greater and blanket expose the resist. 4. Develop the resist using an
aqueous solution of 15 grams/ liter sodium metasilicate pentahydrate.