Optimisation and characterisation of LPCVD silicon nitride thin film growth

Abstract

In this master thesis project a Low Pressure Chemical Vapor Deposition (LPCVD) furnace was used to deposit thin (100-200 nm) silicon nitride films onto silicon wafers. Twelve different runs were performed, each with a specific set of values for different deposition parameters. The parameters in question were dichlorosilane (DCS) to ammonia (NH3) ratio, total flow, pressure, and temperature. Analysis of the properties of these films where then made by the use of ellipsometry, atomic force microscopy (AFM), and stylus profilometry. From the obtained results, conclusions could be made of how different deposition parameters affect film properties such as deposition rate, refractive index, thickness uniformity over a wafer, roughness, and stress. The most desired properties were low stress and low roughness. The analysis revealed that it was difficult to achieve this goal, and suggests the following combination of parameters for a result as close as possible to the desired: T = 770 °C, P = 150 mTorr, DCS:NH3 ratio = 3:1, total flow = 200 sccm. Prior to the laboratory work, an initial literature study of papers regarding similar subjects was conducted. This provided clues to the range of interest to use for the deposition parameters in this project.