Adhesion Promoting Photo-Acid Generator APPAG - A New Class of Lithographic Material
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1002-N05-03
Adhesion Promoting Photo-acid Generator APPAG - A New Class of Lithographic Material Shalini Sharma1, Geeta Sharma1, and Robert Meagley2 1 Molecular Foundry, MSD, Lawrence Berkeley National Lab, Berkeley, CA, 94720 2 Components Research, Intel Corp., Berkeley, CA, 94720 ABSTRACT Photo-acid generator (PAG) is the key component responsible for the increased sensitivity of chemically amplified resists in use today for microelectronics production. Concentration variation of PAG through the thickness of the photoresist film adversely affects materialís performance. To offset reduced acid concentration at the bottom of the resist, we have developed adhesion promoting photo acid generators, called as a class ìAPPAGî that enhance acid concentration at interface between the resist and the substrate. An overview on the preparation and characterization of two siloxane based APPAG materials along with a performance comparison of commercial DUV and EUV resists on APPAG is provided. Longer diffusion length photo-acid generator (APPAG 9) retained square profile of critical dimension (CD) at offfocus values and was found to give nearly a 50% improvement in depth of focus for 250nm node DUV lithography. For EUV lithography, both shorter diffusion length APPAG 6 and APPAG 9 were shown to substantially improve performance envelope for 100nm dense lines and spaces at reduced post exposure bake (PEB). INTRODUCTION Chemical amplification leads to enhanced sensitivity of photo-resists by using acid generated from a photo-acid generator (PAG) during exposure. During a subsequent bake a single acid molecule acts as a catalyst and takes part in up-to 1000 deprotection reactions with the acid labile side-chains of the resist polymer. In this way extremely high sensitivities have been reported [1, 2, 3]. Many factors limit the amount of radiation and consequently the amount of photo-generated acid available at the bottom of the resist which include but are not limited to absorption of light by resist polymer or additives, loss of focus, substrate basicity, and molecular anisotropy [4, 5].This results in the so called ëfootedí bottom profile of the CD in a positive tone resist, as opposed to the desired square profile. To compensate for reduced acid concentration at the bottom of the resist we report synthesis of siloxane based photo acid generator under-layers and their application in DUV and EUV lithography. The adhesion promoting phenomenon results from siloxane moieties which are known to form self assembled monolayers on silicon oxide substrates. EXPERIMENT All the chemicals were purchased either from Aldrich, Fluka or Alfa-Aesar and were used as received without further purification. Silver salts were dried prior to use by heating the salts at 100 ∞C in vacuum for two days. 1H and 13C NMR spectra were recorded on a Bruker 400 MHz spectrometer at University of California, Berkeley and referenced to protio impurities of deuterosolvents. ESI/MS were obtained on in-house Esquire HCT Plus 00042 instrument.
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