Development and improvement of methods for reducing contamination of silicon-kerf from wafer slicing

During wafer slicing, it is shown that carbon contamination can be limited by using organic additive in low concentration. In this way, a reduction of a factor two or three of carbon level in silicon-kerf could be obtained by changing the coolant added to water, with a concentration ten times lower than usual. A second proposed evolution concerns the beam composition, which is usually filled with aluminum-based compounds. New polyester resin beams filled with silicon powder were successfully tested: they did not affect the cutting performance and allows to decrease aluminum concentration in silicon-kerf to a few tens of ppm instead of hundreds. With this evolution of the beams, the main residual contaminant becomes nickel. It was shown that chemical treatment reduced metals in a ratio of three and that after an additional thermal treatment, the carbon level decreased by a factor of six, to reach about zero point two percent. As a conclusion, thanks to cutting liquid and beam composition change, a three-N purity of raw silicon-kerf has been reached at the exit of wafer slicing, without modifying the cutting process. Moreover, additional soft chemical treatment, followed by thermal treatment can reduce carbon concentration and increase silicon-kerf purity to four-N. An improvement of a factor one hundred compared to classical industrial silicon-kerf

Development and improvement of methods for reducing contamination of silicon-kerf from wafer slicing

International audienceThe work, carried out within the framework of the European project ICARUS, concerns the quality improvement of silicon powder resulting from wafer slicing, in photovoltaic industry. Wafering commonly uses diamond-wire sawing and causes the loss of about 35% of silicon which could be valued as raw material. This silicon kerf is contaminated by light elements , in particular oxygen and carbon, and metals in the amounts of several percent for the firsts and hundreds or even thousands of ppm for the seconds, with preponderant elements such as aluminium and nickel. They come from cutting liquid, wire, brick holder and spontaneous oxidation of silicon in water. Therefore, the purity of raw silicon-kerf from wafering is 2N (99%) at best.The aim of the present study is to reach at least 4N (99.99%) silicon-kerf purity with an approach combining a slight adaptation of the cutting process, with an emphasis on industrially acceptable solutions, and light chemical and thermal treatments. Firstly, it is shown that the use of a coolant with low Carbon Oxygen Demand (COD) allows reducing carbon content by half, compared with usual liquid, to approach 1% C by weight. Secondly, alternative beams made of polyester resin filled with silicon powder allow to drastically decrease aluminium content. Then, a hydrochloric acid treatment, followed with a heating step at 500°C under argon flow, allows dividing carbon concentration by six and that of metals by almost three. The final silicon purity effectively reaches 4N, excluding oxygen and carbon. This quality could be further improved by segregation processes to get solar grade silicon

Development and improvement of methods for reducing contamination of silicon-kerf from wafer slicing

International audienceThe work, carried out within the framework of the European project ICARUS, concerns the quality improvement of silicon powder resulting from wafer slicing, in photovoltaic industry. Wafering commonly uses diamond-wire sawing and causes the loss of about 35% of silicon which could be valued as raw material. This silicon kerf is contaminated by light elements , in particular oxygen and carbon, and metals in the amounts of several percent for the firsts and hundreds or even thousands of ppm for the seconds, with preponderant elements such as aluminium and nickel. They come from cutting liquid, wire, brick holder and spontaneous oxidation of silicon in water. Therefore, the purity of raw silicon-kerf from wafering is 2N (99%) at best.The aim of the present study is to reach at least 4N (99.99%) silicon-kerf purity with an approach combining a slight adaptation of the cutting process, with an emphasis on industrially acceptable solutions, and light chemical and thermal treatments. Firstly, it is shown that the use of a coolant with low Carbon Oxygen Demand (COD) allows reducing carbon content by half, compared with usual liquid, to approach 1% C by weight. Secondly, alternative beams made of polyester resin filled with silicon powder allow to drastically decrease aluminium content. Then, a hydrochloric acid treatment, followed with a heating step at 500°C under argon flow, allows dividing carbon concentration by six and that of metals by almost three. The final silicon purity effectively reaches 4N, excluding oxygen and carbon. This quality could be further improved by segregation processes to get solar grade silicon

Diamond wire sawing: State of the art and perspectives

International audienc

Li-Mn-O aerogels

The Li-Mn-O materials described here were obtained by drying liquid gels at low-surface tension conditions, a process which produces high surface area disordered materials in which the microporous structure can be controlled with simple manipulations of the parent gel. The technique of synthesis is simple, inexpensive, and in general may be applied to other intercalation compounds synthesized via sol-gel routes. The aerogels offer a direct way to study the interconnected solid network assembled by sol-gel processes, which would collapse if processed by normal dehydration. Since the interconnected solid network is preserved in the aerogel, the properties such as high specific surface area and high specific energy observed in the aerogel represent inherent properties of the network formed in the liquid gel stage

Comparative analysis of mechanical strength of diamond-sawn silicon wafers depending on saw mark orientation, crystalline nature and thickness

International audienc

Electrochemical and synchrotron XAS studies of lithium intercalation into vanadium pentoxide aerogels and nanocomposites

Vanadium pentoxide aerogels are pillared nanocomposites with exceptional stability, intercalation capacity, and reversibility. X-ray absorption spectroscopy (XAS) measurements on pristine and doped materials have revealed details of the oxidation state and local structure of the host material and of the polyvalent doping species. XANES measurements at the Cu K-edge for Cu0.1 V2O5 show the atomic level reversibility of the structure upon Li+ insertion/release cycling. © 2001 Elsevier Science B.V