Characteristics of ALD Silicon Nitride Grown with HCDS

Abstract

Silicon nitride (Si3N4) layer has been broadly used in the industry of manufacturing semiconductor for many years. Silicon nitride (Si3N4) has remarkably better characteristics than any other materials that are used for an insulator or barrier materials. Stoichiometric silicon nitride (Si3N4) film has not only very lower wet etch rate, but also other superior characteristics comparing to silicon dioxide (SiO2). Unfortunately, making a stoichiometric silicon nitride (Si3N4) is not an easy process to achieve. It has been possible to grow stoichiometric silicon nitride (Si3N4) layer with Chemical Vapor Deposition (CVD) at high temperature (700C – 800C), but very difficult to get stoichiometric silicon nitride (Si3N4) layer by Atomic Layer Deposition (ALD) method at lower temperature. In this study, Plasma Enhanced Atomic Layer Deposition (PEALD) method is used to deposit silicon nitride (Si3N4) films using Hexachlorodisilane (HCDS) as a silicon precursor and varied reactant gases to see how they can affect silicon nitride (Si3N4) characteristics such as Refractive Index (RI) and wet etch rate. Unfortunately, this study has not been able to measure the compositions for all sample wafers tested because some samples get almost no deposition on the substrate so that silicon to nitride ratio comparison for each condition cannot be performed. Also, none of result has shown Refractive Index (RI) greater than 2.0 We should also take into account how to reduce chlorine (Cl) impurity when using chlorine based precursors since silicon nitride (Si3N4) deposited with HCDS (Si2Cl6) is chlorine (Cl) rich, and it can degrade device performance by causing leakage issue as an example. Also, precursor condensation and reaction byproducts occurred on the reaction chamber wall with Low temperature silicon nitride (Si3N4) process should be considered and dealt with carefully because this will be the source of defective particulates on the device substrates and cause yield problems as well. Or we need to develop new silicon precursor that will give higher growth rate, stoichiometric silicon to nitrogen ratio in the grown film and less chlorine for silicon nitride (Si3N4) deposition.