Abstract

This paper deals with the development of an etch recipe for the etching of InP by Reactive ion etching (RIE), a vital process step in the fabrication of microstructures. RIE is a dry etching scheme, wherin effective pattern transfer can be achieved due to its inherent anisotropic characteristics for certain process conditions. RIE is preferred to other dry etching schemes since it is simple, robust and is widely used in industry. The main aim of our research is to design micromechanically tunable optical filters for wavelength division multiplexing (WDM) systems. In this system, transmission takes place in the second and third optical communication window, namely in the region of zero material dispersion (1300 nm) and minimum attenuation (1550 nm) respectively. InP based devices are widely used for this application since they are compatible with the above mentioned WDM transmission wavelengths. The key properties investigated in this thesis were the material etch rate, the selectivity of the material with res to the mask, the side wall steepness and the surface morphology. The examined process parameters have been the rf-power, the flow rate, the pressure inside the chamber, the substrate temperature and the various ratios of gas combinations. Improved values of etch rate and selectivity have been achieved with respect to past results by optimizing the process conditions. Etch rates as high as 120 nm/min have been achieved using CH4 / H2 with infinite values of selectivity for certain process parameters. Measurements have also been made on InP samples using the scanning electron microscope and the atomic force microscope for determining the side wall steepness and the roughness of the etched surface. Side wall slopes close to 90° and surface roughnesses below 0.4 nm (rms) have been achieved. The earlier reported problems of polymer deposition on top of the mask was strongly suppressed. In addition measurements have been carried out on various samples to establish process stability, an absolute necessity for realis vel recipe.