The Silicon-Hydrogen System

The diffusion of H in Si is complex due to the presence of several charge states and the fact that hydrogen is often present in different forms it can be atomic, molecular (or larger clusters), or bound to a defect or impurity. The probability of the formation of these different forms depends on the defect and impurity concentration in the material and the hydrogen concentration itself. Thus, the 

The earliest work on the behavior of hydrogen in crystalline silicon (c-Si) found that hydrogen is very mobile in c-Si and that, in the temperature regime between 900 and 1,200°C, the diffusion coefficient could be expressed as 

Experimental and theoretical studies on H diffusion in silicon at lower temperatures, where trapping of hydrogen at defects and impurities and H2-molecule formation are significant, discovered much lower effective diffiisivities. Values for the H-diffiision coefficient in silicon expected from an extrapolation of the diffusion coefficient of (11.1) to lower temperatures are several orders of magnitude higher than experimentally obtained diffiisivities. This is illustrated in Fig. 11.2, which shows (11.1) and (11.2) extrapolated to low temperatures with experimentally determined values from Johnson et al. (1986). 

Detailed information about the evolution of Si-H complexes in H ion-implanted silicon were gained by the infrared vibrational studies of Weldon et al. (1997) and Chabal et al. (1999). Implanted H atoms form complexes of the form VxHy or IxHy, where V denotes a silicon vacancy and / denotes silicon interstitial. Also observed was the so-called H2 complex, a hydrogen molecule formation in which one H atom is located at the bond-centered site and the other at the antibond site, with a silicon lattice atom residing between the H2 bonds. Upon annealing of the H ion-implanted samples, the IR studies uncover a net loss of bound hydrogen 

Detailed information about the evolution of Si-H complexes in H ion-implanted silicon were gained by the infrared vibrational studies of Weldon et al. 

---

In the silicon tetrachloride system, hydrogen chloride has a profound effect in reducing the rate of the last alkoxylation step ° -... 

---