Silica glass is a highly pure glass made of pure silicon dioxide (SiO2). For some etching processes, stainless steel may not be resistant enough to be used as material of the vacuum chamber. In these cases, the plasma chamber can also be made of silica glass which resists practically any type of etching attack. As is the case with the vacuum chamber, the windows of the plasma chamber and sometimes also the product carriers are made of silica glass if stainless steel is not resistant enough. Silicon wafers for etching are placed in a silica glass boat.