In order to investigate etching of silica crucibles by silicon melts d
uring silicon crystal growth, an in situ observation was made on forma
tion of white dots with brown edges, called ''brownish rings'', at the
silica-silicon melt interface. The formation of brownish rings was fo
und to be influenced by melt temperature, OH concentration in silica g
lasses and oxygen concentration in silicon melts. The growth of browni
sh rings shows a linear dependence on dipping time and the growth mech
anism is essentially the same as that for the devitrification of silic
a glasses. These results suggest that in order to control the etching
of silica crucibles during silicon crystal growth, it is important to
control both properties of silica glass and oxygen concentration in si
licon melts.