Silicon micromachining with applications in microoptics

Abstract: The microsystems technology (MST) is strongly evolving, constantly finding new application areas. Here, the area of microoptics is presented with examples of different solutions that MST has made possible within optical sensors, actuators, and optoelectronic systems. The most commonly used processes for microfabrication are presented together with a description of single crystalline silicon as a material.In this thesis, bulk silicon micromachining techniques have been used to make optical mirrors and assembly systems for low cost assembly of optical devices. The optical mirrors were formed by revealing crystallographic planes by wet anisotropic etching of silicon. The assembly systems consist of thin flexible holding structures which press optical fibres and quadratic chips into well-defined grooves and pits in a silicon carrier. These systems were produced in one etch step by using a photovoltaic etch stop technique.Further, a fibre-optic pressure sensor for measurements in the coronary arteries of the heart is presented. It is a light intensity modulating pressure sensor which is integrated with the guide wire used during balloon dilatation of constricted coronary arteries. The sensor element was made by wet anisotropic etching of silicon. The improved fabrication process is described in detail.The last part of the thesis treats fundamental etch studies on single crystalline silicon. First, a method for investigation of the angular dependence during dry etching (RIE) is presented. Differently oriented surfaces, formed in silicon by wet anisotropic etching, were covered by a material for subsequent dry etching and examination.Finally, an investigation on the influence from bond interfaces on subsequent wet anisotropic etching of silicon is presented. This investigation was made on hydrophobically and hydrophilically bonded silicon wafers etched in KOH and tetramethyl ammonium hydroxide (TMAH).