功率電晶體的溝槽式閘極氧化層之最佳化研究

Abstract

功率電晶體具有低導通阻抗及高崩潰電壓的特性，因此功率電晶體在結構上擁有數微米的磊晶矽耐壓區及垂直式的元件結構。傳統的垂直式雙擴散金氧半功率電晶體由於平面通道的影響，元件密度及導通阻抗值具有其特性極限，而未達到高元件密度與低導通阻抗的要求，所以將閘極溝槽化及為必然的驅勢。隨著積體電路製程技術的進步，溝槽式閘極的結構已能逐漸克服其製程上的困難，本論文乃探討溝槽式功率電晶體之製程最佳化。 溝槽式功率電晶體特性的優劣與垂直閘極氧化層的特性有很大的關係，不同於平面氧化層的成長，垂直氧化層在溝槽邊角上承受極為嚴酷的考驗。溝槽邊角的圓形化可使垂直氧化層的品質獲得改善。本論文主要探討兩種改善溝槽邊角的方法: 犧牲氧化層法以及氫氣快速回火法。此外，本倫文探討閘極氧化層的各種成長條件。

Power MOSFET is characterized by a low on-resistance and high blocking voltage characteristics. The basic structure of power MOSFET consists of an epitaxial layer for voltage blocking and a drain electrode at the substrate contact. In the conventional vertical double diffused MOSFET, the on-resistance and packing density are limited by the horizontal channel of the device. The trench gate MOSFET, has a much improved on-resistance and packing density because of its vertical channel, however, it has a much complicated fabrication process. This thesis investigates the process optimization of the trench gate power MOSFET. The characteristics of the trench gate power MOSFET are closely related to the quality of gate oxide grown on the side wall of the trench. In particular, the quality of gate oxide at trench corners is of critical importance to the performance of the device. Rounding of the trench corners indicates the improvement of the device characteristics. In this thesis, two schemes are investigated with regarded to the rounding of the trench corner, namely, sacrificial oxidation prior to the gate oxidation and rapid thermal annealing (RTA) in hydrogen ambient prior to the gate oxidation. Moreover, oxidation conditions are investigated with respect to the improvement of gate oxide quality.