Self-sacrificial surface-micromachining using Poly(methyl methacrylate)

This thesis describes work performed on a novel form of surface-micromachining, called self-sacrificial surface-micromachining, and an poly(methyl methacrylate) (PMMA) as both the structural and the sacrificial materials. PMMA is a common material in microfabrication processes, as it is an important resist material for many types of radiation. The same properties that make it useful as a resist also make PMMA particularly suited for the unusual form of surface-micromachining described herein. Considerable work on characterizing the exposure and development of PMMA was undertaken to complete this thesis. In general, PMMA is a very well characterized material. Its relatively simple chemistry and huge importance as a resist has led to an extensive literature. However, the radiation source used in this thesis is fairly unusual, deep-UV at 254nm. Consequently, the literature on PMMA irradiated at this wavelength is very thin, necessitating further research to support the development of the surface-micromachining process. The main contribution of this thesis is the introduction of self-sacrificial surface-micromachining. In contrast to traditional surface-micromachining, self-sacrificial processes do not deposit separate structural and sacrificial materials. Instead, a self-sacrificial process deposits a single material, and relies on an in-situ chemical modification to convert it froma structural material to a sacrificial material, or vice versa. Pattern transfer through in-situ chemical change, rather than etching, is the characteristic that separates traditional surface-micromachining from its self-sacrificial variant. Self-sacrificial processes show a number of interesting properties compared to traditional surface-micromachining. The resulting process is capable of fabricating standard surface-micromachining components, although details obviously require changes due to different mechanical and electrical properties. Because of the particular material system used to illustrate self-sacrificial processing, the entire process can be carried out at low temperatures. The process described in this work is, therefore, also notable as a potential approach to integrating surface-micromachining and CMOS. This thesis discusses the concept of self-sacrificial surface-micromachining, as well as discusses the details necessary to implement a self-sacrificial process using a particular material, PMMA.