Depth profile analysis of solar cells by Secondary Neutral Mass Spectrometry using conducting mesh

Abstract

Depth profile analysis of solar cells was performed by Secondary Neutral Mass Spectrometry (SNMS), which is a suitable technique for quantitative analysis of the composition of layered structures. However, in the case of insulating samples or samples prepared on non-conductive substrates (e.g. microslide, oxidized silicon wafer) the charge accumulation on the sample surface due to ion beam bombardment can cause a serious problem by destroying the resolution of depth profile. The high frequency (HF) mode of electron-gas SNMS seems to be a good solution for this problem. Another method to prevent the charge accumulation on a sample surface can be a conducting mesh (e.g. copper, stainless steel) placed on the surface. Using one of the two methods mentioned above can help us to get rid of the charging effect, i.e. to neutralize the surface charge during measurements. But in the case of solar cell analysis these two methods should be applied simultaneously during depth profiling. The experimental results performed on p-i-n:Si (p-type/intrinsic/n-type) diodes have proved that SNMS measurement in HF operation mode combined with a mesh is very efficient in the determination of doping levels of phosphorus and boron with good depth resolution, even in the case of 500–600nm thick samples.