B2H6 Gas Research Articles

Effective p+-Doping of a-Si:H and a-Sic:H Layers by Plasma Assisted Boron Diffusion

ABSTRACTDoping of a-Si:H and a-SiC:H has been performed by plasma enhanced boron migration from thin (5–30 nm) Si0.2B0.8 layers on top of the substrate into the growing i-film. Transport coefficients for this plasma assisted diffusion (PAD) evaluated from SIMS profiles (D* = 10−15 … 10 cm2/s for a-Si:H, 10−15 cm2/s for a:SiC:H) by far exceed those for thermal diffusion after film deposition (10−21 cm2/s). Boron profiles are strongly governed by deposition parameters like substrate temperature, types and energies of radicals growing the film. Boron migration can be modelled assuming particle extraction from the network to the surface by bombardment of ions and atoms and high surface mobility of BHx radicals as a result from interaction with the plasma. Temperature dependent dark conductivity measurements show doping efficiencies comparable to B2H6 gas phase doping, but leaving plasma parameters optimized for i-film Leposition unchanged. Thin a-SiC:H layers are effectively p+-doped without affecting transmission, as no layer is optically detectable after PAD.

Auger investigation of boron‐doped SiO2/Si

B‐doped SiO2 grown on Si(100) wafers using standard B2H6 gas source processing for times varying between 5 and 90 min has been investigated with Auger electron spectroscopy. The resulting film consists of ∠100‐Å B2O3 layer on a B‐doped SiO2 region separated from B‐doped Si by a Si–B phase. The growth rate of B‐doped oxide is considerably faster than dry‐O2‐grown SiO2. A simple model of oxide growth gives a 6–10‐fold increase in solubility and at least a 5–7‐fold increase in the effective diffusion coefficient of O in SiO2 in the presence of B. The Si–B phase forms already at short deposition times, reaching a maximum B concentration of (4±2) × 1022 cm−3. The width of the phase increases and grows into a lamellar structure, with the number and amplitude of lamellae depending on deposition time.