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Disclosed is a process for subtracting geometries defined by one lithography mask from another lithography mask, where the two intersect using a modified Image Reversal Process (IRP).
English (United States)
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Technique for Selectively Removing Geometries From a Lithographically
Defined Pattern Using a Modified Image Reversal Process
Disclosed is a process for subtracting geometries defined by one lithography
mask from another lithography mask, where the two intersect using a modified
Image Reversal Process (IRP).
The IRP permits the use of a positive photoresist with a negative mask.
The modified IRP involves doping a positive resist with a material to thermally
degrade the dissolution enhancer. The modified IRP photoresist forms a
substitute after exposure and bake. The substitute acts as a dissolution inhibitor
to become insoluble in developer.
This is the area defined by the first dark field lithography
mask. The photoresist is then exposed using the second dark field
lithography mask, causing previously unexposed regions to become
soluble in developer.
IRP is described in the following steps:
1. Prepare the Image Reversal Photoresist by doping
the positive photoresist.
2. Prepare the wafers to promote adhesion.
3. Coat wafers with primer.
4. Coat wafers with Image Reversal Photoresist.
5. Pre-expose bake.
6. Expose first dark field mask (Fig. 1).
7. Hard bake wafers (Fig. 2).
8. Expose second dark field mask (Fig. 3).
9. Develop wafers. Rinse and dry wafers (Fig. 4).
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