電漿輔助化學氣相沈積碳氮化矽薄膜 之應力研究

Abstract

碳氮化矽薄膜在目前的微機電系統應用中，常被用來作為懸臂或是感應器的材料。 在微機電系統中使用的材料需要可以耐高溫，且在高溫環境裝不易氧化，且對於不同的腐蝕性化學環境中可以維持運作功能，碳氮化矽薄膜除了可以耐高溫、耐腐蝕外，其機械性質比其他陶瓷材料良好，且其物理性質可隨成分調動，使其可以靈活運用於各個領域之中。本研究使用矽碳比(C:N:Si=3:1:1)的單一前驅物1,3,5-trimethyl-1,3,5-trivinylcyclo- trisilazane (VSZ)、利用電漿輔助化學氣相沉積法製備碳氮化矽薄膜，並且與其他兩種單一前驅物所沉積之碳氮化矽薄膜作比較。本研究、控制不同的沉積溫度、加入氮氣或是甲烷共同沉積碳氮化矽薄膜、另外對上述碳氮化矽薄膜行使紫外光輔助退火及一般熱退火處理改進其機械性質。本研究目的:(1)暸解不同條件下所沉積碳氮化矽薄膜及後處理後之殘留應力,(2)進而探討碳氮化矽薄膜結構與殘留應力的關係，以及(3)建立改變應力的機制及關鍵原素。 我們藉由傅立葉轉換紅外光譜儀得到之光譜分析材料結構，我們觀察到，沉積後之薄膜應力主要被Si-N-Si的鍵角所影響，若對應矽氮(Si-N)的波峰有藍位移現象，代表生成鍵角較大之Si-N-Si結構，因薄膜產生向內回復鍵角的力，使得材料應力傾向拉應力；反之，若對應矽氮(Si-N)的波峰有紅位移現象，代表生成鍵角較小之Si-N-Si結構，薄膜內部將產生向外回復鍵角的力，使得材料應力傾向壓應力。另一方面，我們討論氮氫(N-H)和矽氫(Si-H) 鍵結含量，因這些鍵結會影響主結構的彈性，進一步影響熱膨脹係數。在與氮氣共同沉積的實驗中，氮氫(N-H)鍵結以及矽氫(Si-H)鍵結增加的情況將使得材料整體彈性較高，熱膨脹係數減少，最後在表現應力上會增強張應力的趨勢；反之，加入甲烷共同沉積下，減少氮氫(N-H)及矽氫(Si-H)的鍵結含量，會使得材料整體結構彈性較低，熱膨脹係數相對較大，應力表現則會增強壓應力的趨勢，在此研究中，對於氮氫(N-H)及矽氫(Si-H)同時消長的情況中，我們甚至可以藉由矽氫(Si-H)面積估算應力大小。此外，在後處理的實驗中可以觀察到矽氮(Si-N)及矽碳(Si-Ｃ)的交聯過程將使得薄膜收縮，而此收縮將會導致材料在受後處理後趨向張應力。

Silicon carbonitride film (SiCxNy) have found applications as a material for fabricating cantilevers and sensor in the microelectromechanical systems (MEMS) due to its excellent resistant to oxidation, thermal stability, and mechanical properties under high temperature or corrosive environment. Yet, the thermal stress of SiCxNy films and their tenability are critical for the performance of MEMS. In this study, we characterized the stress behavior of plasma-enhanced-chemical-vapor-deposition (PECVD) SiCxNy films using a single precursor, 1,3,5-trimethyl-1,3,5-trivinylcyclo- trisilazane (VSZ) with a C/Si ratio of 3 (C:N:Si=3:1:1) and 3 vinyl groups, and two other precursors. In specific, SiCxNy films were deposited at various substrate temperatures from 100 to 300 ᵒC under 1 torr. Co-deposition with methane (CH4) or nitrogen (N2) was used to modulate the stress of SiCxNy films. Since thermal post-treatment is commonly used in the MEMS and CMOS fabrication, we also explored the stress behavior of SiCxNy films post-treated by thermal annealing and UV-assisted annealing at 400 oC. The aims of this thesis are (1) to characterize the stress of SiCN films deposited and post- treated in various conditions, (2) to explore the relationship between the stress behavior and the structure of SiCxNy films, and (3) to establish the mechanisms affecting the stress of SiCxNy films. FT-IR spectroscopy is used to analyze the peak position and intensity of the chemical bonds and structures of SiCxNy films deposited at various temperatures using VSZ alone or co-deposition with N2 or CH4. The bond angle of Si-N-Si matrix structure is attributed to be the dominant factor controlling the film stress of SiCxNy films. A larger Si-N-Si bond angle, which correlated with its peak position in infrared spectra, yields higher tensile stress. The other controlling factor is the concentration of the terminal Si-H and N-H bonds in the thin films. An increase of such terminal bonds yields tensile stress in SiCxNy co-deposited by VSZ and N¬2 due to an increase of the thermal expansion coefficient. On the other hand, a reduction of such terminal bonds leads to more compressive stress for SiCxNy films co-deposited by VSZ and CH4. Moreover, the film stress can be estimated based on the Si-H peak area if N-H and Si-H terminal groups both increases. The post-annealing treatment of the SiCxNy thin film induces Si-N and Si-C crosslinking reaction, which produces an inward force leading to film shrink. A larger film shrinkage shall yield a larger tensile film stress upon post-annealing.