低溫碳化矽薄膜之特性探討及電性分析

Abstract

在本論文中，我們有系統地探討了以電子迴旋共振化學氣相沉積法(ECR- CVD)製備碳化矽薄膜時各項實驗參數所扮演的角色，並將其最佳化，亦探 討了不同退火方式對碳化矽薄膜在結構上及電性上的影響;在磷摻雜的碳 化矽薄膜方面，藉由霍爾效應量測，詳實地分析其內載子膿度及移動率的 變化情形。在成長碳化矽薄膜方面，我們主要探討了微波能量、反應氣體 流量比、反應室壓力、以及基板溫度對鍍膜特性的影響 。我們發現，低 的微波能量會使得甲烷氣體的離解率太低，且電漿中的物質不夠高，只能 成長出多晶矽，在較高微波能量下，鍍膜中才會有碳化矽的成份出現;而 隨著能量的增加，碳化矽的結晶性亦會變好。反應氣體流量比則有一個最 佳質存在，若矽烷比例高於此質，鍍膜會有變成多晶矽的傾向，反之，則 會有變成非晶碳化矽的傾向;反應室壓力及基板溫度的效應則不若微波能 量及反應氣體流量比那樣明顯。我們首度嘗試將成長基板的溫度降至室溫 範圍，並成功地在矽晶板上成長出具有1500埃晶粒大小的碳化矽薄膜;我 們先前利用甲烷產生的電漿對基板表面作一處理，再以此表面已形成六成 碳化矽鍵結的矽晶片作為成長碳化矽薄膜的基板，有效地遏止了低溫下缺 陷的產生。不同的退火方式被應用於不同的微波能量製備的碳化矽薄膜， 以期改善其結晶特性，同時也應用在磷摻雜的碳化矽薄膜以提高其內在的 雜質活化率。傳統的爐管退火對提升碳化矽晶體大小的效果有限，即使經 過1000C，8小時的處理，晶粒仍無明顯變化;快速退火相較上有較佳的結 果，但這兩種固相再結晶的處理方式在增大碳化矽晶粒大小的效果上都不 如連續脈波CO2雷射來的顯著，對非晶碳化矽膜而言，在20瓦的功率亦無 法使其發生溶融狀態，因此所引起的晶粒改善度亦是有限。 在最後一章 中，我們在成長碳化矽薄膜的同時通入磷化氫氣體以達成摻入雜質的目地 ，經由電子顯微鏡的觀察，我們發現磷原子具有增進結晶碳化矽的效能。 為了進行霍爾效應量測( Hall effect measurement )我們研究了鋁、鎳 、及鈷等金屬與N型碳化矽間的電性行為，並以TLM( Transmission Line model )方法決定出其各別之接觸阻質，在經過退火之N型碳化矽薄膜方面 ，經過高瓦數雷射退火的試片具有最大晶粒，且在霍爾效應量測中發現， 其活化雜質效果最好，可達5.3 X 10 e16 cm-3，且載子移動率( Carrier mobility )可達到24.96 cm2/V.s以上，再其次為快速退火，統爐管則幾 乎不起任何作用。 In this dissertation, we systematically study the roles of each experimental parameter played during the deposition of SiC by electron cyclotron resonance chemical vapor deposition (ECR- CVD). The film structures and electrical properties of doped/ undoped SiC films underwent different annealing treatments are studied mainly by transmssion electron microscopy (TEM) and Hall effect measurement. In depositing SiC thin films, we investigate the effects of microwave power, reaction gas ratio, chamber pressure, andsubstrate temperature on the films. These results show that there is an optimum value of the reaction gas ratio. On the Si-rich side, films will prone to be polycrystalline (poly-) Si. While on the methane-rich side, it will change into amorphous (a-) SiC. A low microwave power will result in poly-Si films even under the proper gas ratio. SiC bonding appears at higher microwave powers and the film crystallinity increase with it. Chamber pressure and substrate temperature have minor effects on the SiC films.The 1500 A gain size SiC film is successfully demonstrated at room-temperature for the first time. A CH4 plasma treatment is conducted on the Si substrate prior to SiC film growth to generate a 64 % SiC bonding covered surface. This pre-treated substrate can effectively suppress the damages induced by H-plasma etching.Different annealing techniques were applied to the SiC films prepared at various microwave powers for crystallinity improvement. Traditional furnace annealing (FA) has limited influences on the high melting-point material. Rapid thermal annealing (RTA) can achieve a better results. The continuous-wave (CW) CO2 laser annealing (LA) can induce liquid-phase recrystallization in a- SiC. For poly-SiC, because of the elevation of melting-point, the energy density of a 20 W CO2 laser can not induce molten status.In the last chapter, the deposition of in-situ doped N- SiC films are investigated. To perform the Hall effect measurement, the a-Si/Ni/, Mo/Co/, and Al/N-SiC systems are studied by transmission line model (TLM). The annealing techniques mentioned above are also applied to the N-SiC films. CW CO2 laser again stands for the most effective annealing tool. Carrier concentration of 5.3 x 10e16 cm-3 and mobility of 24.96 cm2/Vs are obtained at 20 W laser power. RTA can activate some dopants while Fa has hardlyany influence.