利用特殊接觸電極研究橫向擴散元件之自發熱效應與可靠度

Abstract

隨著半導體業的發展，高功率金氧半場效電晶體被廣泛的應用在電力電子元件上，LDMOS(橫向兩次擴散之金氧半場效電晶體)通常在高壓積體電路中做驅動元件、電力切換元件、射頻功率電晶體。在本論文中，主要是利用特殊接觸電極來對LDMOS做可靠度分析。 在此論文中，主要討論在不同的熱載子加壓後，LDMOS的電性退化程度，我們提出一個三區域的電荷幫浦實驗(three-region charge pumping technique)來觀察不同的區域有何不同的損害產生。同時利用特殊的金屬電極來研究LDMOS的低頻雜訊(Flicker Noise)，可以了解到不同的閘極電壓下所量到的低頻雜訊分別代表不同的區域，最後利用二維方向的模擬來解釋實驗上的結果。在實驗上發現，在最大閘極漏電流的加壓條件下，由於在LDMOS的通道部分有介面缺陷及在鳥嘴區有氧化層電荷的產生，所以造成最嚴重的集極電流退化以及低頻雜訊的增加，同時利用電荷幫浦實驗，可萃取介面缺陷以及氧化層電荷產生的速率。 接著，我們利用特殊的金屬接觸電極以及快速的暫態電路來研究LDMOS的自發熱效應(self-heating effect)。自發熱效應與瞬間熱載子加壓後的元件退化關係亦在此論文中研究。研究發現，交流的加壓條件由於LDMOS沒有自發熱效應，所以會比直流的加壓條件有較嚴重的熱載子退化。交流加壓的頻率與退化程度同時也在此論文中研究。

Lateral Double-Diffused MOS (LDMOS) have been widely utilized in power electronics, for example, LCD drivers, power switch, and ratio frequency power transistor in high voltage integrated circuits. In this study, we will characterize the self-heating and hot carrier reliability issues in LDMOS by using an additional metal contact structure. Degradation of electrical characteristics in LDMOS transistors in various hot carrier stress modes is investigated. A novel three-region charge pumping technique is proposed to characterize interface trap (Nit) and bulk oxide charge (Qox) creation in the LDMOS. A special metal contact structure is fabricated to identify the flicker noise in MOS and LDMOS. The correlation of flicker noise degradation and stress induced oxide damage region will be analyzed. A two-dimensional numerical device simulation is performed to explain the measurement result. Our characterization shows that max. Ig stress causes largest drain current degradation and flicker noise degradation because of both interface trap generation in the channel and bulk oxide charge creation in the bird’s beak region. The growth rates of Nit and Qox are extracted from the proposed charge pumping method. Self-heating effect (SHE) in LDMOS is also investigated by using the special metal contact structure and a fast transient circuit. Transient hot carrier degradation in LDMOS is also investigated. Our characterization shows that drain current degradation in AC stress is more serious than in DC stress because of the elimination of self-heating effect. The stress-frequency dependence of device degradation mode due to self-heating effect will be analyzed.