Ion-induced interface defects in a-Si:H/c-Si heterojunction: possible roles and kinetics of hot mobile hydrogens

Abstract

Interface defects in state-of-the-art semiconductors have a strong impact on device performance. These defects are often generated during device fabrication, in which a variety of plasma processing is used for deposition, etching and implantation. Here, we present the ion-induced defects in hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si) heterojunction. The experiments of argon ion (Ar+) irradiation over an a-Si:H/c-Si stack are systematically performed. The results suggest that the defects are generated not only by the impact of Ar+ (i.e. well-known effects), but also by another unique effect associated with “hot” mobile hydrogens (H). The mobile H atoms generated near the a-Si:H surface by the impact of Ar+ diffuse deeper, and they generate the a-Si:H/c-Si interface defects such as dangling bonds. The diffusion length of mobile H is determined to be 2.7 ± 0.3 nm, which indicates efficient reactions of mobile H with weak bonds in an a-Si:H network structure.

Ion bombardment-induced defect reduction at a-Si:H/c-Si interfaces: possible microstructural changes and mobile hydrogen roles

“…30) The simulation results and diffusion kinetics are described in the supplementary material in reference. 38) The diffusion should be enhanced for the low-density porous material, which is a case for the low-T s grown defect-rich a-Si:H, described above in Sect. 4.1.…”

“…The deformation of the network structure results in the dissociation of Si-H x bonds, generating mobile H atoms near the surface. [32][33][34][35][36][37][38] The mobile H atoms generated via this process diffuse inside an a-Si:H layer, where the diffusion is considered to depend on the mobile H kinetic energy and the material microstructure. The mobile H kinetic energy is known to be several eV from the transport of ions in matter simulations, 58,59) which is larger than a diffusion barrier of ≈0.5 eV.…”

“…7(c)], the interface DB defects can be terminated with mobile H atoms, as described above. However, the interface defects are also generated via the reactions between the interface bonds and mobile H atoms, 38) schematically shown in Fig. 7(d).…”

“…30,31) The mobile H atoms diffuse easily in an a-Si:H network structure, and they react with Si-Si, Si-H x bonds, and/or DB defects. [32][33][34][35][36][37][38] In this type of heterostructure, the c-Si surface defects, i.e. the a-Si:H/c-Si interface defects of DBs, are highly deteriorative, [16][17][18] because they are located on the c-Si absorber surface and they induce the recombination of photocarriers generated in c-Si.…”

Defect generation and recovery in high-k HfO2/SiO2/Si stack fabrication

“…With this number, the density of deep-level defects is estimated to be the order of 10 10 cm −2 or less at the thermal oxide/Si interface, from an equation in Ref. 31. For comparison, the lifetime is measured for an as-received Si wafer with ≈2.4 nm thick native oxide, which shows τ = 2.4 μs, as shown in the lower left.…”