溝渠式金氧半場效電晶體的閘極氧化層可靠度之改良研究

Abstract

Power MOSFET元件主要應用在可承載高電流、高電壓之分離式元件。早期主要以平面式結構(Planar MOSFET)設計為主，但隨著元件縮小製作與減少通道缺陷的問題，後來開發出以溝渠式結構(Trench MOSFET)設計的產品。溝渠型(Trench)電源管理IC在低成本與低耗能上有較佳的表現，但其產品應用電壓相對較低，難以符合家電用品市場與自動車的應用需求。本論文研究針對 Trench Power MOSFET的製程,改善閘極崩潰電壓(Gate breakdown Voltage)的承受度，改善 60nm 閘極氧化層崩潰電壓由21V(3.5MV/cm)提升到崩潰電場超過48V (8MV/cm) 而且崩潰電壓達到C模式呈現，已達到材料本身所限制的正常現象。在製程上，本論文以等向性電漿蝕刻與犧牲氧化層修補缺陷的方式改善溝渠底部形狀，並加入後段熱趨入製程的低氧成長的方式，有效地改善溝渠轉角處因應力導致閘極氧化層偏薄的問題，成功的提高元件的閘極氧化層崩潰電壓，並通過可靠度的測試達到量產之條件。

Power MOSFET has been widely used in the carrying high-current, high-voltage discrete components. While the planar power MOSFET was first adopted as the choice of design, trench power MOSFET becomes the mainstream due to device scaling and the need for reducing channel defects. Although trench power MOSFET offers better performance in the cost and low-current, its low applied voltage makes it difficult to meet the demand for appliances market such as automobile and motocycles. The aim of this thesis is to enhance the gate breakdown voltage of the trench power MOSFET to > 45V. Combined changes in the process module and integration flow have improved the trench corner, resulting in enhanced breakdown voltage of thin gate oxide. In the process modules and integration flow, an isotropic plasma etching was introduced to improve the shape of the trench bottom. In addition, trace oxygen was introduced in the thermal drive-in step in order to repair the defect in the sacrificial oxide layer. The 60 nm gate oxide breakdown voltage of 21V (3.5 MV/cm) was enhanced to a breakdown electric field greater than 8MV/cm, which is a C mode, a behavior of the normal material.