電漿輔助化學氣相沉積碳氮化矽薄膜之應力與熱膨脹係數研究

Intrinsic stress and thermal expansion coefficient of PECVD silicon carbonitride films using silazane precursors

孫韻茹(Yun-Ru Sun)

指導教授 ： 呂志鵬

國立交通大學/工學院/材料科學與工程系所/碩士(2018年)

摘要

電漿輔助化學氣相沉積之碳氮化矽薄膜因為其所需的製程溫度低以及可隨成分變動的機械性質，在目前的微機電系統應用中，常被用來作為懸臂或是薄膜的材料。舉例而言，此類薄膜可用作具有應力的額外層，附加沉積在懸臂的結構當中以用來消除或最小化元件中的殘留應力。 因此，碳氮化矽薄膜的應力（包括本質應力和熱應力）對於微機電系統元件的性能至關重要。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，並且與另一種單一前驅物所沉積之碳氮化矽薄膜作比較，以探討薄膜的本質應力及熱膨脹係數。具體而言，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，另外對上述不同沉積溫度的碳氮化矽薄膜進行紫外光輔助退火以調變其機械性質。本研究目的:(1)暸解不同處理條件下所製備的碳氮化矽薄膜之本質應力與熱膨脹係數,(2)進而探討碳氮化矽薄膜結構與本質應力及熱膨脹係數的關係，以及(3)建立改變應力的機制及關鍵因素。
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受主結構當中的Si-N比例多寡所影響，若主結構當中的Si-N比例增加，即表示薄膜結構傾向於接近純氮化矽膜的結構，使得材料應力傾向拉應力；反之，若主結構當中的Si-N比例減少，即表示薄膜結構傾向於接近純碳化矽膜的結構，使得材料應力傾向表現壓應力。另一方面，薄膜結構當中未交聯的部份-包括來自於前驅物的殘留環狀結構，以及終端基像是氮氫(N-H)和矽氫(Si-H) 鍵結亦會影響薄膜的應力，此類結構的增加會使碳氮化矽薄膜的應力傾向於拉伸應力，這是由於此類結構在薄膜中扮演著微空隙的角色，而這些空隙提供了釋放壓縮應力的空間。 反之，若是此類結構減少將導致碳氮化矽薄膜的壓縮應力增加。

關鍵字

電漿輔助化學氣相沉積 ； 矽碳氮膜 ； 應力 ； 熱膨脹係數

並列摘要

Plasma-enhanced-chemical-vapor-deposition (PECVD) silicon carbonitride film (SiCxNy) have been applied as a material for fabricating cantilevers or membrane in the microelectromechanical systems (MEMS) due to its low deposition temperature and tunable mechanical properties. For instance, PECVD SiCxNy films can be used as an extra layer with stress deposited in the cantilevers to eliminate or minimize the residual stress in device. In consequence, the stress of SiCxNy films, which include the intrinsic stress and thermal stress, are critical for the performance of MEMS. In this study, we characterized the intrinsic stress and thermal expansion coefficient 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 another precursor. 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 applied 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 UV-assisted annealing at 400 oC. In addition, in order to explore the thermal expansion coefficient of SiCxNy films, the thermal stress of films deposited at 100 oC and 300 oC were analysized. The aims of this thesis are (1) to characterize the intrinsic stress and thermal expansion coefficient of SiCxNy films deposited in various conditions, (2) to explore the relationship between the stress behavior as well as thermal expansion coefficient 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 as well as the UV-annealing post-treatment. The Si-N ratio in matrix structure is attributed to be the dominant factor controlling the film stress of SiCxNy films. A higher Si-N ratio in matrix structure, which indicates a more siliconnitride-like structure, yields higher tensile stress. The other controlling factor is the un-crosslink parts including the retained cyclic structures of precursor and the concentration of terminal Si-H and N-H bonds in the thin films. An increase of such structures yields tensile stress in SiCxNy films due to an increase of micro-voids that offer space to release compress stress. On the other hand, a reduction of such structures leads to more compressive stress for SiCxNy films.

並列關鍵字

PECVD ； SiCN ； stress ； thermal expansion coefficient

參考文獻

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