| 摘要: | 本研究旨在利用直流脈衝磁控濺鍍法於矽基板磊晶單晶鍺薄膜。鍺的能隙為0.66eV，作為吸收紅外光波長一直有很好的表現，並在光偵測器、太陽能電池均有很好的成果，但鍺的成本比同為半導體的矽高上許多，也因此若能使用矽基鍺薄膜取代鍺基板能減少許多成本支出。
物理氣相沉積法(PVD)有著無毒和無易爆氣體的安全製程環境，加上製程成本相對CVD低廉許多，但物理上矽和鍺的晶格不匹配造成結晶品質難以提升，差排缺陷亦容易造成暗電流、載子複合區域等問題。
直流脈衝(Pulsed DC)作為直流磁控濺鍍(DC Magnetron Sputtering, DCMS)的延伸，透過在極短時間切換為供應20V左右的電壓使得電荷確實排除，避免電荷累積，相比傳統DC能提供更高的濺鍍效率。
原先高功率脈衝磁控濺鍍(High-power Impulse Magnetron Sputtering, HiPIMS)亦被當作DCMS的分支，但其瞬間的高功率使得靶材離子解離產生的自濺鍍因而被視為新的技術，並且在鍍製上因為其極小的占空比不容易導致靶材過熱，在應用面上比Pulsed DC更廣。
本實驗透過改變濺鍍功率、氫氣流量、偏壓以及改變脈衝時間(on/off time)和頻率來觀察對於鍺薄膜的影響，結果來看，品質最好的鍺薄膜未加入退火的試片XRD半高寬已經到1990 arcsec，且只有些許的拉伸應力，而在受到拉伸應力時，鍺薄膜可以吸收較長波長，是對於應用上也有較好的結果。
;In this research, DC pulsed magnetron sputtering method has been applied to grow a single crystal germanium film on the silicon substrate. The energy bandgap of germanium is 0.66eV which is good for absorbing infrared light wavelength and becomes a popular material for photodetectors and solar cells. However, the cost of germanium is higher than silicon. One of the methods to reduce the cost is applied a germanium thin film on the silicon substrate to replace the germanium substrate.
Physical vapor deposition (PVD), the process without toxic and explosive gases, is safer than chemical vapor deposition (CVD). However, the physical lattice mismatch between silicon and germanium makes it difficult to improve the crystal quality and eliminate defects. The defects resulted in the dark current and the carrier recombination, pulsed DC is extended from the DC magnetron sputtering, DCMS, by providing 20V in few microseconds to eliminate the charge accumulation on target. In other word, it can improve the sputtering efficiency during process.
In this research, the high-power impulse magnetron sputtering (HiPIMS) is also applied to a DCMS system. To compare DCMS with HiPIMS, we can find that HiPIMS can ramp up power up to one or two order of magnitudes than DCMS, which can dissociate target material during sputtering. Moreover, a shorter on-time in the impulse means the lower temperature on the target.
In this experiment, the influences on the germanium films by adjusting the sputtering power, hydrogen flow rate, bias voltage, and changing the pulse time (on/off-time) and frequency have been analyzed. As a result, the good quality germanium film has been fabricated with the XRD FWHM 1990 arcsec, and also with only a little tensile stress successfully. |
