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Post crystallization of ECR-CVD deposited uc-Si:H films using RTA, PRTA, MIC, and PRTA combined with MIC
本論文以電子迴旋共振化學氣相沉積(ECR-CVD)系統在固定製程壓力10 mtorr、微波功率1000 W及氫氣稀釋比96 %條件下，改變基底溫度290 ~ 500℃沉積微晶矽薄膜，及以此薄膜沉積在不同金屬(Al、Au)上，在沉積時即利用金屬誘發(MIC)其結晶，再利用快速熱回火(RTA)及脈衝快速熱回火(PRTA)進行後續的回火處理，以觀察其對薄膜結晶度及晶粒大小的影響。微晶矽薄膜的特性利用Raman光譜儀、原子力顯微鏡(AFM)、歐傑(Auger)電子能譜儀、及掃描式電子顯微鏡(SEM)的量測，分析沉積的微晶矽薄膜在回火前後薄膜結晶度、晶粒大小、粗糙度、晶粒均勻平整度、及薄膜縱深元素的分析。
實驗結果顯示，在無金屬誘發情況下，基底溫度為440及355℃時，兩者的結晶度一致，但較基底溫度為290℃試片的結晶度較好，拉曼光譜半高寬由15.0 cm-1減少為13.0 cm-1，結晶度在69 ~ 70%之間有增加的趨勢。經RTA及PRTA回火後，其拉曼特徵峰位置右移接近520cm-1且結晶度增加為72%，基底溫度為440℃經PRTA回火後的晶粒大小(240 nm)較RTA(203 nm)略大，但明顯較回火前(91 nm)大許多。
在Al金屬誘發結晶的情況下，隨著基底溫度的增加，薄膜特徵峰位置由515 cm-1右移至518 cm-1，半高寬由13.1 cm-1縮小為11.5 cm-1，結晶度由64%增至70%，當基底溫度大於355℃時結晶效果更加明顯，且結晶顆粒亦明顯增大為210 nm。經RTA及PRTA的回火處理，其結晶程度較回火前的為佳，拉曼光譜半高寬(FWHM)最小為10.6cm-1，最大結晶度為75%，經PRTA回火後的結晶度優於經RTA回火後的結晶度，亦優於回火前的結晶度。薄膜在基底溫度為440℃經PRTA回火後其結晶顆粒尺寸為272 nm，較經RTA回火(228 nm)及回火前的晶粒大小(210 nm)增大。
在Au金屬誘發結晶中，隨基底溫度的上升薄膜結晶度愈好，在基底溫度為355及500℃下經RTA回火前後拉曼光譜疊圖圖形一致，與基底溫度為290℃時經RTA回火後拉曼光譜圖形有明顯差異。在基底溫度為500℃時經RTA回火後，拉曼光譜半高寬縮短為10.0 cm-1，特徵峰位置為521cm-1，結晶度達84 %，結晶程度良好。薄膜在基底溫度為355℃時的結晶顆粒大小(680 nm)較基底溫度為290及500℃時的大，但晶粒大小分佈不均。薄膜在基底溫度為500℃時經RTA回火後的平均晶粒大小約為530 nm，且薄膜晶粒大小分佈均勻，變異約在6%。
綜合上述，使微晶矽薄膜有效再結晶成多晶矽薄膜的方法包含提高沉積時基底溫度，運用即時金屬誘發(in-situ MIC)及加上後續快速熱回火及脈衝快速熱回火。結合in-situ MIC、RTA及PRTA的處理，能夠明顯有效地增加結晶度及結晶大小。使用與矽共晶溫度較低的金屬(Au)較容易誘發結晶，且隨基底溫度的增加其結晶度及晶粒大小隨之增大，經RTA回火後的結晶顆粒大小較均勻。
In this study, μc-Si:H films were deposited onto glass substrate or onto a thin Al or Au metal films, which were previously coated onto glass substrate, using ECR-CVD system under 10 mtorr process pressure, 1000 W microwave power, and 96 % hydrogen dilution, and 290 to 500℃ substrate temperature. The μc-Si:H films deposited onto thin Al or Au metal films could be in-situ recrystallized by the metal film, this process is called in-situ metal-induced crystallization (MIC). Both films with and without in-situ MIC treatment were also annealed using rapid thermal annealing (RTA) or pulse rapid thermal annealing (PRTA). The recrystallization of these μc-Si:H films before and after RTA and PRTA post heat treatment were investigated. The crystallinity, grain size, film roughness, film uniformity, and the metal atom distribution were measured and analysed using Raman spectrometer, atomic force microscope (AFM), scanning electron microscope and Auger electron spectrometer.
For the μc-Si:H films without in-situ MIC, the crystallinity of the film increases from 69 to 70% as the substrate temperature increases from 290 to 440℃. The crystallinity of the films deposited at 440℃ and 355℃ is almost the same but is higher than that of the film deposited at 290℃. The full width at half maximum (FWHM) of the Raman peak decreases from 15.0 to 13.0 cm-1. The Raman peak shifts approach to 520 cm-1 and the crystallinity increases to 72% for the films after RTA and PRTA post heat treatment. The grain size (240 nm) of the PRTA-treatment film is slightly larger than that (203 nm) of the RTA-treatment film, but is obviously larger than the 91 nm of the film without post heat treatment.
For the μc-Si:H films with Al in-situ MIC, the Raman peak shifts from 515 to 518cm-1, the FWHM decreases from 13.1 to 11.5cm-1, the crystallinity increases from 64% to 70%, and the grain size increases to about 210nm as the substrate temperature increases from 290 to 440℃. The FWHM of the Raman peak decreases to 10.6cm-1 and the crystallinity increases to about 75% for the films after RTA and PRTA post heat treatment. To increase the crystallinity and grain size of the films, the PRTA treatment is better than RTA treatment. For the films deposited at 440℃, the grain size (272nm) of the PRTA-treatment film is higher than that (228nm) of the RTA-treatment film and that (210nm) of the film without post heat treatment.
For the μc-Si:H films with Au in-situ MIC, after RTA treatment, the crystallinity and the grain size of the films deposited at 355 and 500℃ are larger than the film deposited at 290℃. For the film deposited at 500℃ and after RTA treatment, the peak position and FWHM of the Raman peak are 521cm-1 and 10.0cm-1. The crystallinity can be increased to about 84%. The grain size of the film deposited at 355℃ and after RTA treatment is about 680 nm, but the variation of the grain size is about 42%. The grain size of the film deposited at 500℃ and after RTA treatment is about 530 nm, the variation of the grain size is about 6%.
To increase the crystallinity and the grain size of the ECR-CVD depositedμc-Si:H films can be controlled by increasing the substrate temperature, using Al or Au in-situ MIC and by RTA and PRTA post heat treatment. The combination of in-situ MIC and RTA or PRTA post heat treatment can effectively recrystallize the μc-Si:H films to poly-Si films at low temperature and within a very short time period.
The crystallization of μc-Si:H films is much easier using Au metal with low metal-Si eutectic temperature. The grain size and crystallinity of the films can be increased using the high substrate temperature and post RTA and PRTA heat treatment. The variation of grain size is small for the films after post heat treatment.
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