테라헤르츠 시간 영역 분광법을 이용한 실리콘웨이퍼 증착물의 두께 예측에 관한 연구

Abstract

: Recently, the demand for semiconductors has increased due to the growth of industries such as wireless communication, Internet of Things (IoT), artificial intelligence (AI), and auto-driving. The silicon wafers are used as fundamental materials due to their high utilization in semiconductor production. For insulation and etching, materials such as SiO2, SiNx, and photo resistors are deposited on the silicon wafer. PECVD (Plasma Enhanced Chemical Vapor Deposition) process has been used for mass production. However, it was confirmed that the deposition thickness uniformity between silicon wafers and within the silicon wafer occur due to the imbalance of plasma and inlet gas. For this reason, demand for NDE technology to monitor this thickness uniformity has been increased. Since, the deposition thickness measurement method using an ellipsometer takes a long time by measuring the thickness through the polarization characteristic of thin film at ±90°, the thickness measurement method using an ellipsometer is difficult to apply to the semiconductor ln-line process. In addition, the NDE method using X-ray may affect the human health and the performance of the semiconductor chip due to the high energy of the X-ray. In this study, a research was conducted to predict the thickness of a material deposited on a silicon wafer through a non-destructive inspection technique using a terahertz wave (THz wave). The THz wave is suitable for a non-contact non-destructive test because it has straightness in the air and a property of penetrating non-metallic materials. Since the THz wave is an electromagnetic wave in the frequency range (0.1-10 THz) that has low energy, the THz wave is harmless to the human body and does not affect the performance of the semiconductor. Using the transmission mode of the Terahertz Time-Domain Spectroscopy (THz-TDS) system, the THz wave in the 0.1-3.0 THz range was irradiated on the silicon wafer on which SiO2 was deposited, and the behavior of the THz wave in the silicon wafer was analyzed. It was confirmed the change of the complex refractive index according to the thickness of the SiO2 layer. Based on this, an algorithm to predict the thickness of the SiO2 layer was developed, and it was confirmed that it can be predicted with an error within 5%.