The possibility of using chemical methods to etch out the cores of dislocations from mc-Si wafers was explored. The aim was to maximise the aspect ratio of the depth of the etched structure to its diameter. The Secco etch (1:2 0.15MK2Cr2O7; 49%HF) was first investigated as a function of time and temperature. This etch removed material from dislocation cores much faster than grain boundaries or the bulk, and produced tubular holes at dislocations. Aspect ratios of up to 7:1 were achieved for 15μm-deep tubes. The aspect ratio decreased with tube depth and for 40μm-deep tubes was just 2:1, which was not suitable for use in bulk multicrystalline silicon photovoltaics. Also investigated was a range of etches based upon weaker oxidising agents. An etch comprising 1:3 0.01MI2; 49%HF attacked dislocation cores, but its etching behaviour was extremely slow (<0.1μm/h) and the pits produced had a low aspect ratio (<2:1).

Chemical Etching to Dissolve Dislocation Cores in Multicrystalline Silicon. N.J.Gregori, J.D.Murphy, J.M.Sykes, P.R.Wilshaw: Physica B, 2012, 407[15], 2970-3