Silicon nitride (SiNx:H) layers were deposited using a high deposition rate Hot-Wire CVD technique (up to 5 nm/s) and their application as passivating antireflection coating on multicrystalline silicon solar cells was investigated. An important aspect is the hydrogen release and diffusion during a short annealing treatment at temperatures well above the deposition temperature. Such annealing treatments (firing) are used during contact formation of multicrystalline solar cells.
A series of SiNx:H layers with Si/N ratio in the range of 0.7-1.45 was first characterized using optical R/T measurements, Fourier Transformed Infrared Spectroscopy (FTIR) and Elastic Recoil Detection (ERD) to determine optical constants n and k, Si-H, N-H and Si-N bond densities, Si-H peak position and H content. To get more insight in the passivation process during firing, which takes place at roughly 800 °C, samples with a N/Si ratio of 1.2 were annealed at this temperature for different times (15 s – 10 min). The total bonded H content, measured with FTIR, using conventional proportionality constants as proposed by Lanford and Rand , seems to show an increase within the first 60 s. At longer annealing times, the bonded H content decreases, as expected. The behavior of the H content under annealing measured by FTIR and ERD can be explained by using different matrix elements for calculating the H content from the FTIR data. The matrix element for the N-H stretching mode (3343 cm-1) was determined to be (4.7±0.2)x1020 cm-2 while the Si-H stretching (2193 cm-1) was found to be (0.55±0.04)x1020 cm-2. Such high matrix elements for the N-H stretching mode have not been reported earlier. The value of the Si-H stretching mode matrix element is within the reported values for different back bonding scenarios, but low for a peak position of 2193 cm-1. The ratio between the matrix elements of 8.5 differs strongly from the ratio of 2 observed by Lanford  or Bohne .