利用超高真空化學分子磊晶系統進行低溫矽與矽鍺磊晶及其於元件之應用

Abstract

在本論文中,我們詳細研究了利用超高真空化學分子磊晶系統進行低溫矽 與矽鍺磊晶的成長機制.矽與矽鍺磊晶的成長利用 Si2H6及GeH4作為其氣 體源,正型及負型之摻雜則使用0.1%B2H6及100 ppm PH3 二種氣體. GeH4 相對於總流量之比例及總氣體流量對矽鍺磊晶層中鍺含量及其成長速率有 極大影響. 此結果可由不同成長條件時氣體流量,晶片表面活化位置之相 關反應速率及氫原子的脫離來解釋. 在Si2H5及GeH4流量維持一定時,我們 發現矽鍺磊晶層中硼摻雜之濃度隨著GeH4流量增加而增加,這是因為GeH4 流量增加時,氫原子脫離速率亦隨之增加而導致晶片表面活化位置增多所 致. 在矽及矽鍺磊晶的磷摻雜方面,當PH3流量相當高時,矽及矽鍺磊晶的 磷摻雜濃度有著不同的表現,前者呈飽和現象而後者呈線性關係. 這是因 為成長磷摻雜之矽及矽鍺磊晶時,磷對於其表面活化位置之遮蔽效應不同 所致. 這個理由亦可用於解釋在高流量之PH3時,矽鍺磊晶之成長速率相對 減少的比例較矽磊晶為少的現象. Pure Si2H6 and GeH4 are used to grow Si and Si1-xGex epilayers at 550C by ultrahigh vacuum-chemical molecular epitaxy (UHV- CME). 0.1% B2H6 and 100 ppm PH3 diluted in H2 are used as the p- type and N-type dopant gases in Si/Si1-xGex epitaxy. The Ge mole fraction x and the growth rate of Si1-xGex epilayers show very strong dependence oon the total source gas flow rate([GeH4]]+ [Si2H6]) and the source gas ratio ([GeH4]]/[GeH4]+[Si2H6]). The results can be explained by the relationships of the source fluxes, relative incorporation efficiency at activated surface sites and hydrogen desorption under different growth conditions. The boron concentration of Si1-xGex increases with increasing GeH4 flow rate by keeping Si2H6 and B2H6 flow rates constant. It may be due to the increase of the increase of the surface sites which is caused by the increase of the hydrogen desorption rate when a higher Ge mole fraction epilayer isgrown. The phosphorus concentrations of Si and Si1-xGex show different behavior with PH3 fluxat higher Ph3 flow rates while one increases linerly and the other becomes saturated, respectively. These results can be explained by a model based on the different levels of the effects of phosphorus blocking of surface-activated sites between Si and Si1-xGex epilayers. This effect can also be used to explain the fact that a smaller decrease in the growth rates of Si1-xGex epilayers occurs at a higher PH3 flow rate.