溝槽式閘極功率金氧半場效電晶體Qgd特性改善研究

Abstract

溝槽式閘極功率金氧半場效電晶體 (Trench Gate Power MOSFET)為高頻低壓的功率元件主流，就其發展藍圖而言，隨著元件密度的提升，閘極-汲極間電荷(Qgd) 會變大，使閘極的充放電速度變慢而影響元件的效能。本論文之研究主要是針對0.4微米之高密度溝槽式閘極功率金氧半場效電晶體Qgd電性參數特性的改善來做探討。我們利用PECVD-TEOS方法在溝槽底部沉積一介電質薄膜來降低高密度功率電晶體Qgd，然而傳統的PECVD的製程溫度大都介於300℃~400℃之間，在此溫度下，介電質薄膜沉積於溝槽底部及側壁的速率幾乎相同，而難以藉由後續製程將介電質薄膜留在溝槽底部。因此我們提高PECVD-TEOS的製程溫度來解決改善此一沉積現象，藉著製程條件最佳化的參數設定，有效地在將介電質薄膜沉積於溝槽式閘極功率金氧半場效電晶體的溝槽底部，成功的降低高密度元件的Qgd，並通過可靠度的測試且可量產之條件。

Trench Gate Power MOSFET is the most popular power device for high frequency and low voltage utilization. The charge from gate to drain (Qgd) will become higher while the device density increasing. This study evaluates the PECVD-TEOS oxide film deposited at trench bottom for 0.4um high density trench gate power MOSFET for device performance improvement. As we know, the deposition temperature for general PECVD-TEOS process is between 300℃ and 400℃.Under this process temperature condition, the oxide deposition rate is almost the same for trench sidewall and trench bottom. It is hard to keep an oxide film at trench bottom during trench sidewall oxide removed process. We propose to increase the PECVD-TEOS process temperature to improve deposition ratio of trench bottom to trench sidewall, and an optimum process flow is applied to form a thicker oxide at trench bottom for high density trench gate power MOSFET. The device demonstrates a significant reduction in Qgd, and this process flow is available for production and the products also pass the reliability test.