In the basic chip manufacturing process, a glass layer with holes is generally bonded to another glass layer with channels. For more complex devices, multi-stack bonding is required. Micronit has in-house capabilities to bond multiple wafers into a single wafer stack. This is also suitable when a large internal volume is required. Devices can then be stacked in order to increase the internal volume.
Micronit uses a variety of different bonding techniques, depending on the application of the chip and the materials which need to be bonded together.
Direct aligned bonding is done by creating a so-called prebond between two wafers, which is then annealed at high temperature, which makes the bond very strong. Routinely, fluid pressures of 100 bar can be reached, for certain structures the pressure tolerance can go up as high as 300 bar / 2175 psi. Micronit is one of the few companies in microtechnology that offers both direct glass to glass and glass to silicon bonding (without an intermediate layer) with accurate wafer-to-wafer aligning.
Anodic bonding is based on the application of an electrical field across the bond interface, while heating the wafer pair. This method is especially suitable for glass-silicon combinations, when the process temperature must be lower than the annealing temperature during direct bonding (although temperatures during anodic bonding are still in the order of 350-450 degrees C.
Room temperature bonding
In the case of having to join two very dissimilar materials (generally in terms of CTE), room temperature bonding can provide a solution. With a novel laser-assisted bonding process (see figure), Micronit is able to use only very localized heating to bond the two substrates together. This method provides a hermetically sealed bond interface, and also offers the possibility of integrating sensitive layers or components into the bonded wafer stack.