Study of enhancing carrier mobility using tensilely strained Si films

采用热丝（HW）细胞法在极低的衬底温度下生长外延Si和应变Si_<1-y>C_y薄膜。该方法能有效地分解反应物气体，并能提供大量的原子氢，提高硅薄膜的结晶度。在衬底温度（T_<sub>）为150 ~ 250℃，压力为0.015 ~ 0.03 torr的条件下，仅用SiH_4在Si（100）上生长了外延Si薄膜。在300℃以上的T_<sub>或0.06Torr以上的压力下，薄膜的结晶度变为无定形或多晶。用C_2H_2气体将碳引入薄膜中，用氢稀释也可以在低T_<sub>下实现外延生长。在T_<sub>时，外延膜中出现了氢的掺入现象。热退火引起氢的解吸。利用红外吸收光谱和拉曼散射光谱在退火膜中检测到Si中C的局域振动模式（607cm^<-1>）。当C_2H_2/SiH_4比为0.01时，取代C的浓度为0.9%。x射线倒易点阵映射表明Si_<1-y>C_y合金呈伪晶生长。等离子体cvd也用于生长应变Si_<1-y>C_y薄膜。加入SiH_2 (CH_3)_2后，膜中取代碳含量最高，达到3.5%。采用PH_3进行原位磷掺杂。在PH_3/SiH_4为0.03%的条件下，添加C和不添加C的Si薄膜均生长。Si_<1-y>C_y薄膜的电子浓度低于Si薄膜。而在700℃退火后，该值增加到与Si膜相同的水平，为5x10^<18>cm^<-3>。说明在生长的Si_<1-y>C_y薄膜中发生了掺杂中和。

Hot Wire (HW) Cell method was applied to grow epitaxial Si and strained Si_<1-y>C_y films at very low substrate temperature. In this method, the reactant gas was decomposed efficiently by HW and large amount of atomic hydrogen could be supplied to improve the crystallinity of Si films. The epitaxial Si films were grown on Si (100) at the substrate temperature (T_<sub>) of 150-250℃ and the pressure of 0.015-0.03Torr by using only SiH_4. The crystallinity of the films became amorphous or polycrystalline either at T_<sub> of over 300℃ or the pressure of over 0.06Torr. Carbon was introduced to the films by using C_2H_2 gas and the epitaxial growth at low T_<sub> was also possible by using hydrogen dilution. The hydrogen incorporation was observed in the epitaxial films at such low T_<sub>. The thermal annealing caused to desorb the hydrogen. Local vibration mode of C in Si network (607cm^<-1>) was detected in the annealed films by IR absorption and Raman scattering spectroscopy. The concentration of substitutional C was 0.9% when the ratio C_2H_2/SiH_4 was 0.01. Furthermore, X-ray reciprocal lattice mapping indicated the pseudomorphic growth of Si_<1-y>C_y alloy.Plasma-CVD was also applied to grow strained Si_<1-y>C_y films. The highest substitutional C content of 3.5% was obtained in the films with SiH_2 (CH_3)_2 addition. In-situ phosphorus doping was carried out by using PH_3. The Si films, with and without C addition, were grown at the same PH_3/SiH_4 ratio of 0.03%. The electron concentration of Si_<1-y>C_y film was lower than that of Si film. However, the value was increased up to the same level of the Si film after annealing at 700℃, which was 5x10^<18>cm^<-3>. It means that the dopant neutralization occurred in the as-grown Si_<1-y>C_y films.