The study on the characteristics of low temperature silicon nitride thin film for gate spacer using remote plasma atomic layer deposition

Abstract

As the device scaling continues under the sub-100nm, short channel effects have emerged and new transistor designs and materials have been introduced to solve them. To fulfill the requirements for increasing device performance, high-k metal gate (HKMG) technology have been introduced as gate stack. Introduction of HKMG have made gate spacers important because gate spacers have to protect gate stack against oxygen ingress and etch processing steps and determine the spacing between the contacts in the transistor. Therefore, the gate spacers require high etch resistance against processing steps and a precise thickness control. Silicon nitride is the most commonly used for gate spacers, due to its superior etch resistance and barrier properties against dopant and oxygen. Silicon nitride for HKMG gate spacers must be deposited at low temperature and high conformality. Conventional LPCVD and PECVD processes can not satisfy these requirements. PEALD has been considered as a deposition method to fulfil needs of gate spacer. Silicon nitride PEALD process development research can be divided into ammonia-based process and nitrogen-based process depending on the reaction gas. The ammonia-based PEALD process has excellent step coverage, but low etch rates continue to be a problem. Because of the low process temperature, the hydrogen content in the film is high and the hydrogen concentration lowers the etching resistance. Nitrogen-based PEALD process has very good etch characteristics, however, it is reported that the step coverage is less than 60%. In this thesis, we developed low temperature silicon nitride (ALD) process of less than 400 ℃ and investigated thin film properties and electrical properties and aimed to improve thin film characteristics. The first experiment was to improve the properties of the ammonia-based ALD process silicon nitride film. The ALD process conditions were established using TSA (Tri-Silyl-Amine) and ammonia plasma, and the ammonia radical was changed to improve the thin film characteristics. The applied plasma power was used as a parameter to increase the NH radical ratio and lower the H radical ratio. As the radicals change, the hydrogen content in the thin film was decreased, and the excellent etching characteristics were obtained even in the low temperature ammonia - based ALD process. In the second experiment, a remote plasma was applied in a nitrogen - based ALD process. The reported low step coverage of nitrogen-based processes is due to the lower step coverage of the side step coverage. In order to improve the applicability of the side step, far - field plasma was applied to make the radical reaction, which is more random than the ion having the linearity, to be the main subject of reaction. In the last experiment, the characteristics of the thin film were observed by the plasma surface treatment during the process in order to lower the hydrogen content. As a control, argon and hydrogen were used as a control, and the change of physical properties of the thin film was observed with a recycle of super-cycle type, and the hydrogen content of the existing silicon nitride thin film was further lowered. As a result, the etching resistance of the low-temperature silicon nitride thin film can be further improved.