Influence of film thickness, molecular weight, and substrate on the physical properties of photoresist polymer thin films

Lovejeet Singh; Peter J. Ludovice; Clifford L. Henderson

doi:10.1117/12.485134

12 June 2003 Influence of film thickness, molecular weight, and substrate on the physical properties of photoresist polymer thin films

Lovejeet Singh, Peter J. Ludovice, Clifford L. Henderson

Author Affiliations +

Proceedings Volume 5039, Advances in Resist Technology and Processing XX; (2003) https://doi.org/10.1117/12.485134
Event: Microlithography 2003, 2003, Santa Clara, California, United States

Abstract

The influence of film thickness, molecular weight, and substrate on the glass transition temperature and coefficient of thermal expansion for poly(methyl methacrylates) thin films, a traditional electron beam resist material, has been studied in detail. Variable angle spectroscopic ellipsometry was used to measure the change in film thickness and polymer refractive index for polymer film thicknesses ranging from approximately 30 nm to 650 nm. The T_g for the polymer thin films was determined using changes in the rate of film thickness expansion as a function of temperature. It was observed that the film T_g exhibits a strong dependence on both the film thickness, the polymer molecular weight, and the substrate used. The T_g of poly(methyl methacrylates) films on hexamethyldisilazane (HMDS) coated silicon surfaces decreased with decreasing film thickness below a critical film thickness of approximately thirteen times the radius of gyration of the polymer. The T_g of poly(methyl methylacrylate) films on silicon native oxide surfaces increased with decreasing film thickness below a critical film thickness of approximately six times the radius of gyration of the polymer. The coefficient of thermal expansion also exhibited dependence on film thickness, molecular weight, and substrate used. It was found that the T_g of polymer thin films can be modeled using a “master” curve based on reduced variables, where T_g is normalized by the its bulk value and film thickness is normalized by the polymer radius of gyration. Master curves based on this scaling have successfully been generated for the two different polymer-substrate systems used in this work. The possible implications of this phenomena for ultrathin resist film behavior is also discussed.

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Lovejeet Singh, Peter J. Ludovice, and Clifford L. Henderson "Influence of film thickness, molecular weight, and substrate on the physical properties of photoresist polymer thin films", Proc. SPIE 5039, Advances in Resist Technology and Processing XX, (12 June 2003); https://doi.org/10.1117/12.485134

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