添加高熔點元素對GeSbSn相變化光碟薄膜之光學性質及微結構的影響

Abstract

開發具有高結晶速率的相變化材料以應用在高倍速相變化光碟片是可複寫相變化光碟的發展目標之ㄧ。本實驗以直流磁控共鍍的方式鍍製(GeSbSn)100-xMx薄膜(M=Ta、Fe、Ru、Ni或Co)於Si基板及玻璃基板上，藉由薄膜熱性質分析結果篩選出(GeSbSn)100-xFex與(GeSbSn)100-xCox薄膜作進一步的研究，探討GeSbSn薄膜添加Fe或Co後光學性質與熱性質的改變，以及其應用在可複寫光記錄媒體的可行性。 熱分析實驗結果發現添加Fe或Co會使薄膜相變化溫度與活化能下降，顯示添加Fe或Co會提高薄膜結晶速率。光譜分析結果顯示，(GeSbSn)100-xFex與(GeSbSn)100-xCox薄膜具有良好之光吸收率，但當x=8.20~16.75 at.%時，(GeSbSn)100-xCox薄膜反射率對比值則隨著Co含量增加而降低。而添加Fe之薄膜則當Fe含量為7.10~9.75 at.%時對比值增加，當Fe含量大於12.91 at.%時對比值反而降低。由XRD結構分析結果顯示，初鍍(GeSbSn)100-xFex薄膜(x=0~22.93)與(GeSbSn)100-xCox薄膜(x=0~16.75)均為非晶質結構。經過250℃，30分鐘熱處理後，薄膜產生結晶，其中(GeSbSn)100-xFex薄膜(x=0~9.75)結晶相主要仍是Sb相，當Fe含量大於16.63 at.%時，薄膜結晶相至少包含Sb、Fe與FeSb相；(GeSbSn)100-xCox薄膜中，當Co含量大於8.20 at.%時，薄膜結晶相包含Sb與CoSb3相。由TEM觀察薄膜微結構，GeSbSn薄膜經過250℃，30分鐘熱處理後之平均晶粒大小約為27.9nm，添加7.10 at.%的Fe後晶粒變小，平均晶粒大小約為17.6nm，而當Fe含量增加為16.63 at.%時，晶粒大小約為30.1nm。另外，添加9.79 at.%的Co後晶粒變小，平均晶粒大小約為16.8nm，但呈現較不規則狀。當Co含量為16.75 at.%時晶粒發生不規則成長，晶粒大小約介於30~200nm，平均晶粒大小約為96nm。

One of the main development in rewritable phase change optical disk is to find out high crystallization speed materials for high-speed phase change optical disk application. In this study, (GeSbSn)100-xMx thin films (M=Ta、Fe、Ru、Ni or Co) are deposited on nature-oxidized Si wafer and glass substrates by DC magnetron co-sputtering. From the thermal analysis, we choose (GeSbSn)100-xFex and (GeSbSn)100-xCox thin films to investigated the effects of Fe or Co on the optical properties and microstructures of these films, and investigate its possibility for rewritable phase change optical media application. Thermal analysis shows that doping Fe or Co into GeSbSn thin film can decrease the activation energy and phase change temperature of the film. This indicates that the crystallization speed of the GeSbSn film will be increased. The optical property analysis shows that (GeSbSn)100-xFex and (GeSbSn)100-xCox films have good absorption. The optical contrast of (GeSbSn)100-xCox film decreases with increasing Co conent as x = 8.20~16.75. The optical contrast of (GeSbSn)100-xFex film increases with Fe content as x in the range of 7.10~9.75 but decreases with Fe content when x=12.91~16.63. The X-ray diffraction analysis shows that the as-deposited (GeSbSn)100-xFex and (GeSbSn)100-xCox films are amorphous structure. After annealing at 250℃ for 30 min, the major crystalline phase of (GeSbSn)100-xFex film (x=0~9.75) is Sb. The Sb、Fe and FeSb crystalline phases are appeared as x>16.63. After same annealing condition, the Sb and SbCo3 crystalline phase are found in the (GeSbSn)100-xCox film (x>8.20). The TEM analysis shows that the average grain size of the GeSbSn film is about 27.9 nm after annealing at 250℃ for 30 min. After doping Fe, average grain size of the GeSbSn film is decreased, it decreases to 17.6 nm as 7.10 at.% Fe is added. However, the grain size is increased to about 30.1 nm when 16.63 at.% Fe is added. On the other hands, as 9.79 at.% Co is doped into the GeSbSn film, average grain size of the film is decreased to about 16.8 nm, and the grain shape is irregular. When 16.75 at.% Co is added, the grain grows irregularly, the grain size is in the range of 30 to 200 nm and the average size is about 96 nm.