WetEtchRates.WilliamsMuller.00546406

WetEtchRates.WilliamsMuller.00546406 - 256 JOURNAL OF...

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256 JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 5, NO. 4, DECEMBER 1996 Etch Rates for Micromachining Processing Kirt R. Williams, Student Member, IEEE, and Richard S. Muller, Life Fellow, IEEE Abstruct- The etch rates for 317 combinations of 16 ma- terials (single-crystal silicon, doped, and undoped polysilicon, several types of silicon dioxide, stoichiometric and silicon-rich silicon nitride, aluminum, tungsten, titanium, TVW alloy, and two brands of positive photoresist) used in the fabrication of microelectromechanical systems and integrated circuits in 28 wet, plasma, and plasmaless-gas-phase etches (several HP solutions, H3P04, HNO3 + H20 + N-F, KOH, Type A aluminum etchant, HZ 0 + HZ 02 + HF, H2 02, piranha, acetone, HF vapor, XeF2, and various combinations of SF6, CF4, CHF3, C12, 02, N2, and He in plasmas) were measured and are tabulated. Etch preparation, use, and chemical reactions (from the technical literature) are given. Sample preparation and MEMS applications are described for the materials. [193] I. INTRODUCTION HEM DESIGNING a new process to fabricate micro- ma&ined devices, the etch rate of each layer that is to be patterned must be known. While the etch rates of many etchants that target specific materials (e.g., thermally grown silicon dioxide in 5:l buffered hydrofluoric acid) are com- monly known, the etch rates of the masking and underlying films are frequently not quoted in the literature. This paper provides this information for 317 different combinations of 16 materials and 28 etches used in the micromachining of micro- electromechanical systems (MEMS) and in integrated-circuit processing. These etch-rate data, based on tests performed in the U. C. Berkeley Microfabrication Laboratory (Berkeley Microlab), are tabulated in Tables I and 11. The first sections of this paper describe the preparation and use of the wet and dry etches in Tables I and 11, listing chemical reactions and variation of etch rate with such factors as temperature and concentration, based on literature on the subject. Recognizing that there are many sources of etch-rate variation, brief lists of these sources are given at the end of these wet- and dry-etch sections. The succeeding sections describe the sample preparation and MEMS applications for each of the materials, the measurement techniques used, and finally discuss the data in the tables. 11. ?kE WET ETCHES A. Comparison of Wet and Dry Etches The etches in the tables are divided into wet and plasma and plasmaless-gas-phase (“dry”) etches. The advantages and disadvantages of wet and dry etching are well known 111, Manuscript received January 10, 1996; revised July 1, 1996. Subject Editor, K. Najafi. This work was supported by the Berkeley Sensor & Actuator Center. The authors are with the Berkeley Sensor
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WetEtchRates.WilliamsMuller.00546406 - 256 JOURNAL OF...

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