金屬(鋁、鎳)誘導非晶矽側向結晶之研究

Abstract

在本論文中，我們將研究結果分成三個部份。第一部份主要係闡述鋁誘發側向結晶的機制。藉由使用光阻相關製程，於一沉積在玻璃基板上厚度為100奈米的非晶矽層上，熱蒸鍍一層厚度為100奈米的島狀鋁膜，使用電壓及電流參數為15伏特/3.5安培與25伏特/5.6安培兩組不同參數。掃描式電子顯微鏡的分析發現島狀鋁膜呈現平滑以及具有結晶性晶粒的形貌。在748及823 K的溫度下進行不同時間的退火製程，在具有結晶性晶粒的試片中很明顯可以觀察到鋁誘發側向結晶的現象，但在平滑的試片中則無此現象。穿透式電子顯微鏡的分析可發現鋁誘發側向結晶的機制是藉由兩層之間的交換所造成，首先，在鋁誘發結晶的過程中，島狀鋁膜會和下方的非晶矽層進行垂直的交換，然後在更進一步的退火過程中，這些產生的鋁顆粒伴隨著鋁誘發結晶會和剩下的非晶矽層進行側向的層交換，進而產生鋁誘發側向結晶的現象。 第二部分的研究係探討壓應力對於非晶矽薄膜的鎳誘發側向結晶的影響。使用鎳片施加3.7 至265.8 MPa壓應力於鍍在玻璃基板上的非晶矽層上並在823 K做一小時的熱處理後，移除鎳片及所施加的應力，然後在823 K的溫度下再做一至四小時的熱處理。實驗結果指出當初始壓應力增加時，金屬誘發側向結晶的程度會降低，而所有的試片在熱處理的過程中呈現相同的側向結晶速率。這部分的研究指出藉由施加適當的壓應力(~4 MPa)，可有效減少在多晶矽中殘留的鎳含量。 第三部分係研究旋轉塗佈製程對於非晶矽層上金屬誘發側向結晶的影響。使用微乳膠合成法製作濃度分別為10-3、5 × 10-3及10-2 M 的含鎳奈米顆粒的溶液，接著分別在500、750及1000 rpm的旋轉速率下旋轉塗佈到沉積在玻璃基板的非晶矽層上。大小約為200到500奈米的鎳奈米顆粒會和非晶矽層反應形成鎳矽化物(NiSi2)，此鎳矽化物和結晶矽間有晶格失配，因此金屬誘發側向結晶可以在823 K的溫度下發生。實驗結果可以發現當鎳的濃度大於48 ppm時會發生金屬誘發側向結晶。當製程參數為500 rpm和5 × 10-3 M時，藉由控制鎳奈米顆粒的量與分佈可產生分佈最均勻的多晶矽層。此外，在退火熱處理後，殘留的鎳含量可減少至於38 ppm，遠低於現有的同類製程。

This dissertation mainly deals with the mechanism and optimization of metal-induced lateral crystallization of amorphous silicon. The first part elucidates the mechanism of aluminum-induced lateral crystallization (AILC), which has remained blurry to date. By means of a photoresist-based process, Al islands (100 nm) were thermally evaporated using parameters of 15 V, 3.5 A, and 25 V, 5.6 A onto a 100nm-thick amorphous silicon (a-Si) layer deposited on a glass substrate. Scanning electron microscopy (SEM) examinations indicated that the Al islands exhibited either smooth or crystalline-grain morphology. Annealing processes were carried out at 748 and 823 K for various periods of time. After annealing, AILC could be clearly observed in samples with crystalline-grain morphology, but not in the one with smooth Al island morphology. Transmission electron microscopy (TEM) analyses revealed that the mechanism of AILC is mainly dominated by two layer exchange processes. The Al islands first exchanged vertically with the underlying a-Si layer during AIC, and then the generation of Al particles accompanying AIC caused a lateral layer exchange with the remaining a-Si layer with further annealing. In the second part, the effect of compressive stress on nickel-induced lateral crystallization (NILC) of amorphous silicon thin films was investigated. Here, we described an alternative method enabling the metal-induced lateral crystallization (MILC) of a-Si films. Glass substrates coated with a-Si films were contacted with ground nickel sheets under compressive stresses ranging from 3.7 to 265.8 MPa at 823 K for 1 h. Subsequently, the nickel sheet and stress were removed and the specimens were annealed at 823 K for 1 to 4 h. The experimental results indicated that the extent of MILC decreased when the preliminary compressive stress was increased, while all specimens exhibited the same rate of lateral crystallization during annealing. The present study indicates that, by applying an appropriate compressive stress (~4 MPa), an effective method to reduce the residual Ni content in polycrystalline silicon (poly-Si) can be obtained. In the third part, we described another method for converting the amorphous silicon film into poly-Si film via MILC. Nickel nanoparticle containing solution prepared by microemulsion synthetic method with concentration of 10-3, 5 × 10-3, and 10-2 M was spin coated on a-Si deposited on glass substrate with spin speed of 500, 750, and 1000 rpm, respectively. The nickel nanoparticles (~200-500 nm) react with a-Si to form nickel silicide (NiSi2), which has very small lattice mismatch with crystalline silicon, thus, can trigger MILC at 823 K. Our results reveal that the MILC will occur if the Ni concentration is larger than 48 ppm. The combination of 500 rpm and 5 × 10-3 M gave rise to the most uniformly distributed poly-Si by controlling the distribution and amount of Ni nanoparticles. Moreover, after the annealing heat treatment, the residual nickel content can be reduced to very low ~38 ppm.