Remote plasma atomic layer deposition of SiNx gate spacer using BDEAS and N2 plasma

Abstract

As device scaling has decreased to less than 100 nm in recent years, short channel effects have become prominent. In response, new transistor designs and materials have been introduced to solve this problem. To improve device performance, HKMG technology was introduced into the gate stack, which protects the gate stack from oxygen ingress in the gate spacer and etching process steps; furthermore, it plays an important role in determining the spacing between the contacts in the transistor. Therefore, the gate spacer must have high etch resistance, precise thickness control, step coverage for the process steps, and high resistance to oxygen and wetness. Conventional PECVD and thermal ALD do not sufficiently meet these requirements. To solve this issue, silicon nitride was deposited through PEALD at a low temperature range (250-400℃). In this study, a lowtemperature silicon nitride PEALD process (below 400℃) was explored to develop thin film characteristics and step coverage in patterns. We minimized toxic by-products by using Cl-free precursor and BDEAS, and also deposited stoichiometry silicon nitride using hydrogen-free N 2 plasma. The silicon nitride (SiN x) using BDEAS and N2 remote plasma was investigated. The growth rate of SiN x thin films was saturated at 250~400℃, and the growth rate was approximately 0.48Å /cycle. The physical and chemical properties of the SiN x were investigated as a function of plasma power. We were able to obtain the stoichiometric SiN x thin film at 500W, and thin film with better etching resistance could be confirmed by wet etch rate test as the plasma power increased. SiN x films showed a stoichiometry N/Si ration of ~1.3 with impurity level of carbon content under 3%. The density of the SiN x film at 500W (2.87g/cm 3 ), which is a sufficiently high density, was slightly higher than that low plasma power (2.75g/cm 3 ). The Si2p and N1s peaks of X-ray Photoelectron Spectroscopy (XPS) demonstrate deposition using N2 plasma also follows the surface reaction of that plasma power. Electrical properties such as breakdown voltage decreased at higher RF plasma power. Through C-V analysis, SiN x thin film was deposited close to the previously reported dielectric constant of silicon nitride. As a result, the side step coverage decreased from 59% to 36% for the narrow pattern (AR : 7.5) depending on the depth, and the bottom step coverage is 53%. By increasing the plasma power (100W~500W), the wet etch rate was 23.1Å/min, which is much lower than the case of low plasma power (45.0Å/min).