Study of enhancing carrier mobility using tensilely strained Si films

采用热线槽法在极低衬底温度下生长了外延Si和应变Si_<1-y>C_y薄膜。在该方法中，反应气体被HW有效地分解，并且可以提供大量的原子氢以改善Si膜的结晶性。在衬底温度<sub>为150-250℃，气压为0.015-0.03Torr的条件下，用SiH_4在Si（100）衬底上外延生长了Si薄膜。当温度超过300℃或气压超过0.06Torr时，薄膜的结晶性变为非晶或多晶<sub>。用C_2H_2气体向薄膜中引入碳，用氢稀释法也能在低T_2下外延生长<sub>。在如此低的T_2下，在外延膜中观察到了氢的掺入<sub>.热退火导致氢的解吸。通过红外吸收和拉曼散射光谱检测到退火薄膜中Si网络中C的局域振动模（607 cm ~ 2<-1>）。当C_2H_2/SiH_4为0.01时，取代C的浓度为0.9%。X射线倒易点阵图表明Si<1-y>_C_y合金<1-y>为假晶生长。SiH_2（CH_3）_2掺杂的薄膜中取代碳含量最高，为3.5%。用PH_3进行了原位磷掺杂。Si薄膜在PH_3/SiH_4 = 0.03%时生长，有C和无C时生长的薄膜均为Si薄膜。Si_<1-y>C_y膜的电子浓度低于Si膜。然而，在700℃退火后，该值增加到与Si膜相同的水平，即5 × 10 - <18>4cm-3<-3>。这表明在生长态Si_ C_y薄膜中发生了掺杂中和<1-y>。

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.