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Reduce SRAF printing with non-acidic top coat in immersion lithography

IP.com Disclosure Number: IPCOM000198359D
Publication Date: 2010-Aug-05
Document File: 2 page(s) / 28K

Publishing Venue

The IP.com Prior Art Database

Abstract

This invention demonstrates the solution of using non acidic top coats to minimize sub-resolution assist features (SRAF) printing in immersion lithography.

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Reduce SRAF printing with non-acidic top coat in immersion lithography

For advanced photolithography, it is necessary to include sub-resolution assist features (SRAFs) to ensure the robustness of the lithography process. At 32 nm node and beyond, contact holes printed at first exposure in a double exposure process (CA), contact holes printed at second exposure in a double exposure process (CB) and vias at x level ( Vx) are the most critical processes due to the rapid decrease of depth of focus (DOF). Therefore, the use of SRAFs becomes imperative to keep DOF at a sufficient level through pitch in addition to the benefits of improving image contrast and circularity of the contact holes.

Traditionally, lithographers use extensive computation tools to optimize the source for regular RET and/or phase shift mask. Recently, the computational lithography has been extended to the source mask optimization (SMO) approach to obtain the best image contrast in the state of the art immersion 193nm exposure tools. SMO mask typically incorporates large amounts of many different kinds of complex SRAF shapes. SRAFs are not supposed to be printed.

Due to the aggressive use of these SRAFs, they have been observed in many printed images beyond the prediction of current simulation models. To solve this problem, engineers must find a way to minimize SRAFs printing. The problem is summarized as follows:

Due to:

• All the manufacture products are using acidic top coat in immersion lith...