CURVATURE CHANGING OR FLATTENING OF ANODICALLY BONDED SILICON AND BOROSILICATE GLASS

A method has been developed to change or to remove stress in anodicall y bonded silicon and glass compounds (Pyrex or Tempax). The technology is based on the structural relaxation of the glass at temperatures at which no viscous flow is to be seen. Due to the structural relaxation , a shrinkage of the glass occurs at sufficiently high temperatures an d leads to a bend change of the bonded wafers. As a result, at room te mperature or at the working temperature stress-free compounds as well as those with lower and even with opposite stress and curvature can be produced. The structural relaxation of the glass has been studied by investigating the shrinkage of glass rods during isothermal annealing. The applicability to the curvature change of anodically bonded silico n and Tempax has been proved. Finally, the influence of the developed method on the decomposition and on the thermal expansion coefficient o f the glass has been studied.