以四階段成長法在低壓化學氣相沉積系統成長立方晶型碳化矽

Growth of 3C-SiC on Si(100) by low pressure chemical vapor deposition using a modified four-step process

陳威佑(Chen, Wei Yu)

指導教授 ： 黃振昌

國立清華大學/工學院/材料科學工程學系/博士(2010年)

https://doi.org/10.6843/NTHU.2010.00279

摘要

A modified four-step method has been developed to grow a void-free 3C-SiC film of high quality on Si(100) in a mixed gas of SiH4-C3H8-H2 using low pressure chemical vapor deposition. A diffusion step was added after the carburization step in the traditional three-step method (clean, carburization, growth), and no cooling between each step was required. X-ray photoelectron C 1s spectra support that the formation of Si-C bonds can be greatly improved in the as-carburized Si(100) surface after diffusion at 1350 °C for 300 s. A thick 3C-SiC film of good crystal quality was grown on the as-diffused SiC layer during the growth step, confirmed by both X-ray diffraction and electron diffraction data. Hall effect measurements were used to characterize the electrical properties of SiC films. All the SiC films are n-type. The Hall mobility and carrier concentration of a SiC film of 1.5 µm thick increase from 320 to 395 cm2/(V s) and from 1.6 × 1017 cm-3 to 2.7 × 1017 cm-3, respectively, when the diffusion step is added.
The atomic arrangement and bonding characteristics of void-free 3C-SiC/Si(100) grown by the modified four-step method are also presented. Without the diffusion step, Si–C bonds are partially formed in the as-carburized layer on Si(100). The ratio of C–C bonds to Si–C bonds is about 7:3, which can be lowered to about 1:9 after the diffusion step at 1350°C for 5 min or at 1300°C for 7 min according to C 1s core level spectra. The residual C–C bonds cannot be removed, which is associated with an irregular atomic arrangement (amorphous) located either at the 3C-SiC/Si(100) interface or at the intersection of twin boundaries in the 3C-SiC buffer layer based on the lattice image taken by transmission electron microscope. The diffusion step helps the formation of Si–C bonds more completely and results in a SiC buffer layer of high quality formed on Si(100) before the growth step. However, twins and stacking faults still appear in the 3C-SiC buffer layer after the diffusion step. The formation mechanism of the 3C-SiC buffer layer is proposed and discussed.
Growth of 3C-SiC films on Si(100) using a modified four-step method in the mixed gas of SiH4 and CH4 was performed in a low pressure chemical vapor deposition. The influences of experimental parameters such as flow ratio of precursors, carburization temperature and time on crystal quality of 3C-SiC were investigated and compared with our previous work in the case of C3H8. The thicker buffer layer with rougher surface and voids were observed using CH4 as precursor that result from the lower pyrolysis efficiency of CH4. X-ray photoelectron C 1s spectra shows that unlike only C-C and C-Si bonds residing in the buffer layer when using C3H8 as precursor, additional C-H bonds accompany with C-C and C-Si bonds in the case of CH4, which may result in the worse crystal quality of 3C-SiC films.

關鍵字

方晶型碳化矽 ； 低壓化學氣相沉積 ； 四階段成長法

並列摘要

本篇論文係利用四階段成長法，在低壓化學氣相沉積系統成長無孔洞立方晶形碳化矽，並探討不同反應氣體(矽甲烷-丙烷-氫氣與矽甲烷-甲烷-氫氣)在矽基板上成長立方晶型碳化矽的差異。四階段成長法省略了傳統三階段成長法中降溫的步驟，並在碳化步驟後新增一擴散改質步驟。在矽甲烷-丙烷-氫氣反應氣體系統中，實驗結果顯示，碳化緩衝層經過30分鐘1350 oC的擴散改質之後，能有效地提升表面的碳矽鍵結生成。經由X光繞射及穿透式電子繞射分析結果指出，在改質後碳化緩衝層上能成長出無孔洞的高品質的立方晶型碳化矽薄膜。在電性方面，藉由霍爾效應量測可知，四階段製程成長的碳化薄膜為n型半導體，在經過擴散改質後，碳化矽薄膜的霍爾遷移率可從320 cm2/(V s) 提升至395 cm2/(V s)，載子濃度也從1.6 × 1017 cm-3提升至2.7 × 1017 cm-3。
擴散改質步驟中的溫度及時間對碳化緩衝層中原子排列及表面鍵結變化的效應也被深入的探討。根據X光光電子能譜儀的分析結果，在未經擴散改質前，緩衝層中只有部分的碳矽鍵結形成，碳碳鍵結和碳矽鍵結的比例約為7:3。經過7分鐘1300oC或是5分鐘1350 oC的擴散改質後，可將碳碳鍵結和碳矽鍵結的比例降低至1:9。表面鍵結比例的變化說明了擴散改質步驟能有效提升緩衝層表面碳矽鍵結並且影響後續成長之碳化矽薄膜的結晶特性。然而藉由高解析穿透式電子顯微鏡的觀察發現，雙晶及疊差等的面缺陷仍然存在於經過改質後的緩衝層中。殘餘的碳碳鍵結訊號(~10%)可能是來自於位於緩衝層與矽基板的介面及雙晶交界處不規則的原子排列。最後並根據分析結果，提出並討論四階段成長法中碳化緩衝層的可能形成機制。
在矽甲烷-甲烷-氫氣反應氣體系統中，我們探討有關四階段成長法中各步驟的實驗參數對碳化矽薄膜結晶特性的影響，並比較矽甲烷-甲烷-氫氣與矽甲烷-丙烷-氫氣兩者結果的差異。實驗結果顯示，當使用甲烷為碳源成長立方晶型碳化矽薄膜時，其結晶特性較差，碳化緩衝層也因為碳化不完全，造成較粗糙的表面形貌並且有介面孔洞的存在。甲烷熱裂解效率較低是導致碳化不完全的主要原因。X光光電子能譜的分析結果顯示出以甲烷為碳源所成長的碳化緩衝層，除了具有和以丙烷為碳源的緩衝層一樣的碳碳鍵結與碳矽鍵結之外，還存在部分的碳氫鍵結。此一碳氫鍵結的存在可能是導致薄膜結晶特性較差的原因。

並列關鍵字

3C-SiC ； low pressure vapor phase deposition ； modified four-step method

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