OPTIMIZATION OF NITRIDE DEPOSITION PROCESS USING TAGUCHI METHOD

Abstract

In this work, Taguchi method of optimization is being employed in the deposition process of silicon nitride to obtain the targeted deposition rates of 250 Å/min and refractive index in the range of 1.8 to 2.2. The deposition of the silicon nitride (Si3N4) films is carried out using Plasma Enhanced Chemical Vapor Deposition (PECVD) method to take advantage of lower temperature operation and cost as well as higher surface uniformity and throughput [1]. The statistical ‘Design Expert’ software is being used to identify the factors that significantly affect the performance of the process and to obtain the optimum combination of parameters which will produce the targeted responses. From the results of ANOVA, it is found that the most significant factors that affect the deposition rate are 5% SiH4/Ar gas ratio and pressure, while Nitrogen (N2) flow rate is the most significant factor for the refractive index. The combination of input parameters of RF power of 60 Watt, pressure of 1000 mTorr, 5% SiH4/Ar gas ratio of 80 sccm and Nitrogen (N2) flow rates of 310 sccm is found to be the optimum combinations to produce the targeted responses. In order to validate the solution obtained from the software, confirmation experiment is conducted. A very small percentage of differences which are of between 1.8% to 6.6% are obtained between predicted and actual value for both the deposition rates and refractive index.