鍺基可寫一次光碟記錄薄膜之微結構及光學性質研究

Abstract

近年來使用於短波長之可寫一次光碟的記錄媒體材料中，由於有機染料在短波長碟片旋轉塗布中所產生的不均勻性及製造過程的污染問題不易解決，無機可寫一次記錄材料被視為取代有機染料層的方式之一，因此本實驗研究以金屬誘發結晶理論，鍍製半導體-金屬二元合金以及半導體/（金屬元素、相變化材料）bilayer兩種方式作為無機可寫一次光碟片之記錄層材料。由熱分析實驗結果顯示Ge100-XCuX、Ge/Al、Ge/Au以及Ge/InSbTe薄膜之反射率的變化溫度分別在310 ℃~320 ℃、275 ℃~285 ℃、190 ℃~200 ℃以及130 ℃~140 ℃之間。由X-ray繞射分析顯示Ge100-XCuX薄膜初鍍時，薄膜會形成過飽和之ε- Cu3Ge單相結構的介穩態，而經過400 ℃、30分鐘熱處理後，則會變成Ge和ε- Cu3Ge雙相結構的穩定狀態；Ge/Al薄膜初鍍時，薄膜由於厚度較薄，並無明顯結晶峰出現，而經過280 ℃、30分鐘熱處理後，則會出現Ge3Al5 (004)。由TEM微結構觀察Ge100-XCuX初鍍薄膜，為過飽和之ε-Cu3Ge相，經過400 ℃、30分鐘熱處理後，在EDX分析中發現Ge晶粒的析出，會形成ε-Cu3Ge與Ge兩相共存的結構；Ge/Al初鍍薄膜之TEM電子繞射分析顯示具有Ge3Al5(200)的結晶相，經過280 ℃、30分鐘熱處理後，會形成Ge、Al(111)以及 Ge3Al5三個結晶相共存的結構；TEM電子繞射分析顯示初鍍Ge/Au薄膜之具有Ge2Au3以及Au之結晶相，經過220℃、320℃之30分鐘熱處理後，在220 ℃會在Ge層形成具有Ge2Au3 (3 2 1)優選方位，晶面間距3.20 Å之介穩態，經過320 ℃熱處理之後， 則有Ge(1 1 1)，晶面間距3.26 Å之晶相析出，形成Au、Ge與Ge2Au3共存的結構。Ge/InSbTe bilayer經過熱處理之後，在130 ℃~140 ℃產生反射率變化，主要是來自於InSbTe層的相變化，經過熱處理溫度的增加，在接近Ge之結晶溫度時，除了Ge層本身開始結晶之外，InSbTe層與Ge交互擴散，Ge亦會與InSbTe形成Ge1Sb2Te4 (009)或四元合金的結晶相。動態測試的結果顯示，Ge/Al在12倍速FVD測試下jitter值為6.3%，符合使用於FVD之記錄媒體；Ge/Au在藍光下的對比值較佳，HD DVD碟片測試中PRSNR值為21.3 dB、SbER 值為3*10-8、Modulation值為0.76，均符合HD DVD規格。Ge/InSbTe記錄薄膜在DVD 4X寫入速度時，最佳jitter值7.7%，在DVD 8X寫入速度時， jitter值為7.9%。Ge/InSbTe bilayer在DOW實驗中，第二次寫入之後，其Jitter上升至13.5%，並隨著寫擦次數的增加，在DOW次數為3時達到18%。

At present, write-once optical disc is made of organic dye. However, uniformity and environmental pollution issues are difficult to be reduced for the high density recording disc. Hence, ionrganic recording materials were proposed to replace the organic materials. In this study, metal induced crystallization (MIC) mechanism for alloy and bilayer structure of inorganic recording thin films were investigated. Four kinds of recording media, Ge100-XCuX, Ge/Al, Ge/Au and Ge/PCM thin film were studied. Thermal analysis shows that the phase-transition temperatures of the Ge100-XCuX, Ge/Al, Ge/Au film is 310~320 ℃, 275℃~285 ℃, 190 ℃~200 ℃and 130 ℃~140 ℃, respectively. The X-ray diffraction analysis reveals that the as-deposited Ge100-XCuX film is a supersaturated ε-Cu3Ge single phase structure. It becomes Ge and ε-Cu3Ge two phases structure after post-annealed at 400 ℃ for 30min. The as-deposited Ge/Al bilayer film is amorphous structure. It becomes Ge3Al5 (004) phase structure after post-annealed at 280 ℃ for 30min, The TEM analysis shows that after annealing at 400 ℃ for 30min, the Ge grain segregate in the Ge100-XCuX matrix, and the film was transformed to ε-Cu3Ge and Ge phases, Ge3Al5 was found in as-deposited Ge/Al films, after 280 ℃, 30mins annealing, it will transform to Ge(111), Al(111), and Ge3Al5. As-deposited Ge/Au bilayer had by Ge2Au3 and Au crystal phase. Ge2Au3 interface was founed by cross-sectional TEM image, after 220 ℃, 30 min annealing. Inter-diffusion of Au atoms into Ge layer formed a Ge2Au3 (3 2 1) metastable phase with d-spacing 3.20 Å, when the annealing temperature was further increased to 320 ℃, closed packed plane of Ge (1 1 1) with d-spacing 3.26 Å would segregate out of the meatastable Ge2Au3 phase. The Ge/PCM bilayer was amorphous at as-deposited state. After continuous annealing from room temperature, it has 2 phase change temperature at 130~140 ℃ and 500~520 ℃, respectively. The phase change temperature at 130~140 ℃ was owing to the phase change of InSbTe layer and few amount of Ge Crystallites. As the annealing temperature is further increased to 520 ℃, which is closed to the crystallization temperature of pure Ge, the InSbTe layer and Ge layer start to inter-diffusion to each other. In this step, it will form Ge1Sb2Te4 (009) or 4 elements alloy compound, which is different from the MIC mechanism of Ge/Metal bilayer structure. The dynamic tests show that jitter value of Ge/Al was 6.3% under 12X FVD formation; PRSNR, SbER and modulation of Ge/Au bilayer under 1~2X HD DVD formation are 21.3 dB, 3*10-8 and 0.76, respectively. On the other hand, the jitter value of Ge/PCM was 7.9% under 8X DVD formation, and the DOW experiment indicated that the jitter value of Ge/InSbTe was 13.5% and 18% after second and third direct over write.