Glass wafer processing

Ion-Exchange Phenomenon

Silicate glass wafers implemented by Teem Photonics are principally composed of an amorphous network of SiO2 and Na+ alikaline ions impurities. These ions are weakly bonded to the matrix. As a consequence, when a heated glass wafer is immersed in a molten salt bath containing other alkaline ions like K+, Ag+ or Tl+, an ion-exchange process between the glass and the bath can take place at the glass surface. Once alkaline ions from the bath are located into the glass, they can move into the silica matrix through thermal diffusion or electrical conduction processes.

The ion-exchange process leads to the change of the glass composition and properties close to its surface. One affected property is the local refractive index. The refractive index variation can be brought about by both ionic polarisability and radius differences between the implemented alkaline ions. The latter difference can also imply the creation of mecanical stress in the glass matrix. The table below sums up the characterisctics of major exchanged ions couples.

It is straight forward to understand that one can take advantage of this phenomenon to create optical waveguides at the surface of a glass wafer. Since more than 10 years, Teem Photonics has built a photonics integrated circuits platform based on a Ag+/Na+ ion-exchange into a specially developped silicate glass. The waveguide manufacturing process based on this ion-exchange phenomenon is described here.