The global demand for pure Si has recently increased multifold. The primary reason for this boost remains environmental concerns leading to an interest in converting sunlight into electricity by use of a photovoltaic cell. For use in such applications, the silicon must be 99.99 % or greater. In most cases, this purity is achieved by fractional crystallization of metallic grade silicon. Enhanced purification to 99.9999999 % is required to construct the silicon wafer. Such ultra purity is achieved by pulling a seed crystal from a melt.
Assurance of the purity is of paramount concern in the production of silicon. For establishing the quality of silicon, it becomes necessary to consider relatively larger amounts (10 gm) of a sample for digestion as it contains significantly low levels of contamination. Around 50 ml of Hydrofluoric acid and Nitric acid is needed for digestion per sample. In addition, all this acid needs to be added in small increment to suppress the aggressive reaction. Presence of the dust-free environment is essential for this 4-hour long digestion to eliminate contamination from the surrounding.
Currently, digestion is performed using multiple manual additions of reagents in a cleanroom. It is a nightmare for an analyst to conduct these digestions. Bundled in cleanroom attire he has to spend hours in front of fuming samples adding small increments of acids. Apart from the risk of exposure to toxic acids, there is every possibility of inconsistent acid addition affecting the end results. Long digestion time and need for special attention to each sample do not deliver the required throughput by industry.
Automation provides a viable pathway for dealing with the situation. Vulcan, the Automated Block Digestion System equipped with ULPA filter is ideally suited tool to be used in such a situation. Vulcan from Questron Technologies Corp. comes with Teflon syringes for dispensing acids. All the reagent paths made from Teflon or PFA material. The digestion blocks are made from Teflon coated graphite. The system has an enclosure equipped with ULPA filter air. All these features of Vulcan provide the environment necessary for digesting semiconductor grade Silicon efficiently and economically.
Vulcan possesses the capacity to automatically dispense acids providing safety while digestion process. Through software operating Vulcan, it is merely a matter of adjusting a few parameters to set up timely delivery of small reagent amounts and control temperature during digestion. Once automated, Vulcan can digest up to 60 samples meeting the demand for quality control laboratory.
Automating the digestion Silicon using Vulcan from Questron not only provides the required ultrapure environment but also increased the laboratory throughput while providing safety.