氮化鋁磊晶薄膜於不同基板上殘餘應力機制之研究

以迴旋濺鍍(helicon sputtering)系統，低溫500˚C沉積1um厚度的氮化鋁(AlN)薄膜於c軸取向之藍寶石(Sapphire)、氮化鎵(4um-GaN/Sapphire)以及(111)-面取向之氧化鎂(MgO)等三種不同的基板之上。透過拉曼光譜量測觀察E2(high)聲子頻率之位移以及X光繞射量測分析薄膜晶格應變，並與文獻中無受應力之AlN的E2(high)聲子頻率相比，呈藍位移(blue shift)的現象，這意味著濺鍍於GaN(0002)、Sapphire(0006)以及MgO(111)基板上之AlN薄膜受一殘餘的壓縮應變(residual compressive strain)影響，分析結果顯示，薄膜與基板彼此間熱膨脹係數之差異主導著最後薄膜的殘餘應變。藉由拉曼聲子峰值位置的偏移以及晶格常數的變化我們獲得一線性的關係，其雙軸應力係數為 -2.71 ± 0.3 cm-1/GPa。而進一步地觀察於MgO(111)基板上不同厚度的AlN薄膜與殘餘應變之間的關係發現，可以使用控制薄膜的厚度的方法，加以消除殘餘應力對薄膜的物理性質甚或是光電元件的表現造成影響。本實驗中除了X光繞射量測，亦建立了拉曼光譜量測為另一簡單且有效率的監測方式，用以量測AlN薄膜中的雙軸應力。

關鍵字

低溫濺鍍、氮化鋁、拉曼光譜、熱膨脹係數、殘餘應力

並列摘要

Epitaxial films of wurtzite AlN were grown on c-plane sapphire, GaN(0002) and MgO(111) by helicon sputtering system. The lattice strain of the films was analyzed by high-resolution X-ray diffraction and E2 (high)-phonon frequency was observed by Raman scattering. The compressive strain was induced by the thermal expansion coefficient mismatch between film and substrates during the cooling process from elevated growth temperatures, which pushed the phonon peak position of AlN toward longer wavelength. The analysis showed that the thermal mismatch between the epilayers and the sub-strates played a major role in determining the residual stress in the films. A lin-ear coefficient of -2.71 ± 0.3 cm-1/GPa characterizing the relationship between the Raman-shift and the biaxial stress of the AlN films was obtained. Furthermore, the results were clearly revealed by Raman spectra, in which the phonon peak position of AlN film decreased with the film thickness increased on MgO(111) substrates. The work here established Raman spectra as another simple and effective method for monitoring the biaxial stress in AlN epilayers.

並列關鍵字

low-temperature sputtering, AlN, Raman spectra, thermal expan-sion coefficient, residual stress

參考文獻

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[3] F C Wang, C L Cheng, Y F Chen, C F Huang and C C Yang, “Residual thermal strain in thick GaN epifilms revealed by cross-sectional Raman scatter-ing and cathodoluminescence spectra”, Semicond. Sci. Technol. 22 (2007) 896–899

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氮化鋁磊晶薄膜於不同基板上殘餘應力機制之研究

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