Sensitive chlorine‐containing resists for X‐ray lithography

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Abstract
New resists containing chlorine to enhance absorption to PdLα X‐radiation at 4.37 Å have higher sensitivity than currently available high‐speed electron resists when used in a high‐throughput PdLα X‐ray exposure system developed by Maydan and coworkers. Of the three classes of materials examined the poly(chloroalkyl acrylates) have the best properties. The sensitivity and contrast of these negative resists are dependent on the amount of Cl present, the structure of the chloroalkyl side chain, the inclusion of reactive functional groups, and molecular weight. Contrast is found to decrease with increasing sensitivity achieved by either increasing molecular weight or incorporating more reactive glycidyl groups. We suggest that such behavior, which is not predicted by theories of radiationinduced crosslinking, has its origin in competitive formation of intramolecular crosslinks with the desired, intermolecular crosslinks. Poly(2, 3‐dichloro‐1‐propyl acrylate) has been investigated in greatest detail. Samples of this polymer requiring a dose of 7 mJ/cm2 for 50 percent of the initial resist thickness (2 min exposure) have been used successfully to wet etch 1 μm features into SiO2, Al and Cr and 2 μm features into phosphosilicate glass. It has moderate resistance to ion milling and good resistance to plasma etching with Freon‐based plasmas.

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