Arsenic speciation in gallium arsenide semiconductor wafer processing waste

Torrance, Keith and Keenan, Helen (2010) Arsenic speciation in gallium arsenide semiconductor wafer processing waste. In: SEGH 2010, 2010-06-28 - 2010-07-03. (Unpublished)

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Waste streams from three different gallium arsenide (GaAs) semiconductor wafer processing steps, backside grinding, lapping and polishing, were investigated to determine the form of the arsenic in solution. Total arsenic content was determined using inductively coupled plasma-mass spectrometry (ICP-MS) and found to be in excess of the EU discharge limit of 0.5mgL-1 for all three processes, with arsenic content highest in wafer polishing waste slurry (>2,000mgL-1), followed by wafer lapping (10 – 100 mgL-1) with wafer grinding having the lowest arsenic content (<10mgL-1). To better understand the chemistry of the waste slurries, arsenic speciation was performed on the slurries using IC-ICP-MS and anodic stripping voltammetry (ASV). Results are presented, which show that the highest As (V): As(III) is found in polishing slurry waste, where almost 100% of the arsenic present is in the form of As(V). This is consistent with chemical polishing using a strong oxidising agent at high pH. The As(V) content of the lapping and grinding slurries showed greater variability and changed over time. We interpret this as being due to progressive oxidation of As(III), particularly in the presence of aluminium oxide. It is found that the mechanism of GaAs removal from the wafer during polishing is controlled by the redox chemistry and solubility of the oxide products. Arsenic speciation has important implications for the environmental impact of semiconductor processing waste and recommendations made for the safe handing and disposal of arsenic-rich waste.