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Detailed study of the composition of hydrogenated SiNX layers for high-quality silicon surface passivation

: Mächel, H.; Lüdemann, R.


Journal of applied physics 92 (2002), No.5, pp.2602-2609
ISSN: 0021-8979
ISSN: 1089-7550
Journal Article
Fraunhofer ISE ()
Fourier transform infrared spectroscopy; plasma enhanced chemical vapor deposition; PECVD; bonding concentration; lifetime measurements; high-efficiency solar cells; plasma deposition

We have analyzed the role of the bond densities of a-SiN/sub x/:H films on the passivation properties at the SiN/sub x/:H/Si interface. The films are deposited onto silicon wafers by plasma enhanced chemical vapor deposition using a 13.56 MHz direct plasma system and a SiH/sub 4//N/sub 2//H/sub 2/ gas mixture. Fourier transform infrared spectroscopy measurements are performed in order to obtain the bonding concentration of Si-Si, Si-H, Si-N and N-H. The passivation properties are deduced by lifetime measurements using a microwave-detected photoconductance decay technique. Carrier lifetimes of the SiN/sub x/:H- passivated silicon wafers of up to 1200 mu s correlate to surface recombination velocities, S/sub eff/, as low as 4-6 cm/s. This means that the films provide excellent passivation of silicon surfaces, which is necessary for high-efficiency solar cells. The Si-H bond density and the total bond density are considered as measures of the passivation quality. Models for the formation of K/sup +/ centers and for the passivation pathways during the plasma deposition are proposed. The addition of a further hydrogen source to the plasma gas (H/sub 2/) leads to a better defect passivation of Si dangling bonds during the deposition.