Bonding Si wafers at uniform separation

We have developed a bonding process for Si wafers which call be used to space wafers uniforuily at distances ≥ 0.lμm over an area as large as 20-40cm². Wafers bonded this way have been used at cryogenic temperatures and have been recycled successfully. The bonding process is one whereby a wafer with all SiO₂ pattern is brought into intimate contact with another wafer by using hydrostatic pressure. Bonding takes place at a temperature of 1150°C and involves a chemical reaction between Si and SiO₂. The resulting structure can be evaluated by using the infrared optical techniques and by filling the space between the wafers with superfluid Helium.