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.