| 摘要: | 本研究中，分析金、銅/金、及鎳/金與磷化銦鎵接觸之蕭特基特性。研究中發現剛蒸鍍好的金、銅/金、及鎳/金與磷化銦鎵接觸之蕭特基位障分別為0.99、 0.99、以及0.93 eV。 針對蕭特基接觸之熱穩定性分析結果發現，銅/金結構較金及鎳/金與磷化銦鎵接觸有較佳的熱穩定性。而從穿透式電子顯微鏡所量測到的橫截面微結構來看，當熱處理溫度為300?C時，金會擴散至磷化銦鎵層並且隨溫度增加，擴散至磷化銦鎵層之元素金會聚集成一塊塊較大的區塊。金屬銅則有較高的熱穩定性，在熱處理溫度達到500?C時，銅會擴散至磷化銦鎵層。此外，由於金屬銅有較好的導熱性及較低的電子遷移電阻，因此我們發現，銅擴散至磷化銦鎵層較為均勻並有明顯的副層(sublayer)形成。 經由原子力顯微鏡(atomic forced microscopy; AFM)、掃描式電子顯微鏡(scanning electron microscopy; SEM)、X光繞射儀(x-ray diffractometry; XRD)、穿透式電子顯微鏡(transmission electron microscopy; TEM)、以及歐傑電子光譜(Auger electron spectroscopy)之縱深分析的量測結果，可以發現，當熱處理溫度達到500?C時，原先明顯的一層金屬銅，已經消失不見，銅元素在此熱處理溫度下相當不穩定，極易與其他元素反應，除了向外擴散與金反應形成Cu3Au2的合金層外，同時也會向下擴散至磷化銦鎵層而形成CuP2合金，進而破壞蕭特基接觸之元件特性。因此，導致銅與磷化銦鎵接觸之蕭特基特性變差的原因，主要是由於銅金屬層擴散至磷化銦鎵層而形成CuP2合金所造成。此外，利用深層能階暫態光譜(deep-level transient spectroscopy; DLTS)分析結果顯示，銅擴散至磷化銦鎵層，在磷化銦鎵材料中形成深層的施體陷阱(donor trap)，其形成之活化能約為0.72eV。 研究中進一步觀測金屬銅隨著熱處理溫度的提高以及熱處理時間的拉長，擴散至磷化銦鎵層的情形。結果顯示，其擴散深度隨著熱處理溫度的上升及熱處理時間的延長，有明顯增加的趨勢。從擴散深度與熱處理時間的關係中，我們可以推算出當熱處理溫度為500?C時，銅與磷化銦鎵間形成CuP2合金的活化能以及擴散常數分別為0.93eV與1.37 ? 103 nm2/s。 最後，研究中利用金屬鎢作為阻擋銅擴散之擴散阻擋層(diffusion barrier layer)，進而提升銅與磷化銦鎵接觸之熱穩定性，從AFM以及TEM的量測結果顯示，利用金屬鎢(厚度為100nm)作為銅與磷化銦鎵接觸間的擴散阻擋層，可以明顯提升銅與磷化銦鎵蕭特基接觸之元件熱穩定性。 We have demonstrated the Schottky diodes performances for Au, Cu/Au, and Ni/Au contact to the InGaP layer. The Schottky barrier heights for the as-deposited samples of Au, Cu/Au, and Ni/Au metallic structures contact to the InGaP layer are 0.99, 0.99, and 0.93eV, respectively. These Schottky diodes were thermal annealed in a RTA system to investigate the thermal stability. The metallic structure of Cu/Au was found to have a superior thermal stability than that of Au and Ni/Au contact to the InGaP layer. Following, the cross-sectional microstructures conducted from TEM observation were used to study the interface evolutions between metals and semiconductor and degradation mechanism for metals contacts to the InGaP. The metallic Au would indiffuse into the InGaP layer at annealed temperature of 300?C and tend to congregated to from huge Au-rich areas with increasing the annealing temperature. However, the metallic Cu was more stable and indiffused into the InGaP layer as the annealing temperature reaching 500?C. The indiffusion of Cu is more uniform than that of Au and a form an obvious sublayer in the original InGaP layer. This was attributed to the superior thermal conductivity and lower electronmigration resistance of the metallic Cu. The measurement results of AFM, SEM, XRD, TEM, and AES depth profile were also used to analyze the degradation mechanisms. We found that Cu layer was unstable and completely released as annealing temperature reached 500oC. The metallic Cu would react with the metallic Au layer to form a Cu3Au2 intermetallic layer and indiffuse into the InGaP layer to create the CuP2 binary alloy. Therefore, we concluded that the thermal degradation mechanism of Cu/InGaP Schottky contacts was due to the release and indiffusion of the element Cu, and the subsequent formation of the CuP2 binary alloy. Furthermore, we also calculated the reaction parameters for Cu indiffusing into the InGaP layer. The indiffusion of Cu into the InGaP layer would form a sublayer and the thickness also increased with increasing annealing temperatures and times. From the relationship between the sublayer thickness and annealing times, we could determine the activation energy of the CuP2 binary alloy was 0.93eV and the diffusion constant was also found to be 1.37 ? 103 nm2/s at annealing temperature of 500?C. Eventually, to improve the thermal stability for the Schottky diodes, the refractory metal of W was employed as a diffusion barrier layer between the Cu and InGaP layer. Combined with AFM and TEM measurement results, a thin W layer deposited between the Cu and InGaP layer could effectively obstruct the indiffusion of Cu into the InGaP layer at annealing temperature of 550oC for 1 min. |
