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Author(s)

Ana Paula Mousinho Mansano

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
• Defense date: 2001-02-19

Examining board members

Antonio Carlos Seabra; Luiz Otávio Saraiva Ferreira; Megumi Saito

• Advisor: Antonio Carlos Seabra

Abstract

This work presents a single layer lithographic process developed for MEMS aplications similar to the HARMS process. It is based on the application of optical lithography, silylation and dry development of a 22 ´MICROMETROS´ layer optical resist (AR-P 322 from All Resist GmbH). We studied the silicon incorporation in the novolac AR-P 322 resist when using a chemical silylation solution bath (70% xylene, 25% PGMEA, and 5% HMCTS). The bath temperature was varied from 40 to 80´DEGREE´C and the immersion time from 1 to 4 minutes. The best silylation condition was determined from FTIR, RBS and SEM analysis to be 40´DEGREE´C bath temperature and 2 minutes immersion time. We also investigated the use of e-beam lithography for this process since it is maskless. We concluded that the AR-P 322 optical resist is electron sensitive (working dose of about 150 ´MICROMETROS´C/´cm POT.2´). Nonetheless, we haven\'t succeed in obtaining enough contrast (selectivity) between exposed and non-exposed areas with e-beam lithography. For optical exposure of about 1200 mJ/´cm POT.2´, the silylation contrast is reasonable as confirmed by SEM analysis and the structures obtained. To study the dry development process we used an ´O IND.2´ plasma etching step, with the reactor either in RIE or ICP mode. The maximum etch rate for the RIE mode was 1.2 ´MICROMETRO´/min with greater than 0.8 anisotropy, when the pressure was varied from 30 to 120 mTorr. The RIE mode showed better results than the ICP mode since its etch rate was 5 times greater and the samples had less residues. In order to separate the influence of the silylation step from the dry etching step in the development of the process, we first characterized the dry etching step by using a tri-layer process. The tri-layer process used the same resist and showed a 7:1 aspect ratio as measured for 2.5´ MICROMETROS´ width structures. Combining the developed silylation and etching steps (with minor adjustments), and using optical exposure, it was possible to obtain 10:1 aspect ratio structures as measured on 2µm width - 20 ´MICROMETROS´ deep structures, as initially proposed by this work. (AU)