Roughness evolution of high-rate deposited a-SiN x :H films studied by atomic force microscopy and real time spectroscop
- PDF / 675,424 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 7 Downloads / 135 Views
A9.35.1
Roughness evolution of high-rate deposited a-SiNx:H films studied by atomic force microscopy and real time spectroscopic ellipsometry P.J. van den Oever, M.C.M. van de Sanden, and W.M.M. Kessels Dept. of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands ABSTRACT The scaling behavior of the roughness evolution of silicon nitride (a-SiNx:H) films with different mass densities (deposited from SiH4-N2-H2 and SiH4-NH3 based plasmas) has been investigated by atomic force microscopy and real time spectroscopic ellipsometry. The observed roughness exponent α is similar for both films, whereas the growth exponent β is a factor of two smaller for the higher density films. The relation between the lower value of β and the higher mass density is discussed. INTRODUCTION
Relative IQE at 1020 nm
Level of bulk passivation
Plasma deposited amorphous silicon nitride (a-SiNx:H) has a broad range of applications due to the versatile character of the material. The material properties can be tuned by the plasma settings and deposition temperature. Besides the applications, which are already common in industry, emerging applications are the use of a-SiNx:H as encapsulation material for organic LEDs and as functional antireflection coating on (multi-)crystalline silicon solar cells. Besides the reduction of reflection losses, hydrogen from the a-SiNx:H can induce bulk passivation of defects states in the lower quality silicon material that is used to reduce the cost of photovoltaic energy. The use of a-SiNx:H for such an antireflection coating will result in a significant increase of the efficiency of the solar cell (e.g., from 12% to 15% for multi-crystalline Si solar cells). The density of a-SiNx:H seems to play an essential role in the majority of its applications. For example, a correlation between a high level of bulk passivation in solar cells and a high film density has been observed. Also surface 1.2 passivation, caused by band bending and fixed charges in the a-SiNx:H film, might benefit from a dense a-SiNx:H film. Figure 1 shows the relative internal quantum efficiency (IQE) of 1.1 multi-crystalline silicon solar cells (produced from the same silicon material) versus the mass density of the film. Clearly, the IQE, which is a measure for bulk passivation, increases for higher 1.0 mass densities [1]. 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3 A common hypothesis is that there is a Mass density (g/cm ) relation between the density of a material and the Figure 1. The IQE, relative to the IQE roughness of the growing surface: a higher obtained for an antireflection coating surface roughness results generally in lower without bulk passivation, versus the mass density films. To explore a possible relation density of the a-SiNx:H films. The figure is between the density and the roughness evolution taken from Ref. [1]. of the surface, films have been deposited at high
A9.35.2
rates by the expanding thermal plasma from two different gas mixtures (an Ar-NH3-SiH4 plasma and an Ar-N2-H2-Si
Data Loading...
