Apparatus for bonding wafers and an optically-transparent thin film made from the same
A novel apparatus for bonding of two polished substrates includes a plasma source in a ultra-high vacuum (UHV) chamber and a wafer-guiding element to control and guide wafers in the UHV chamber, where after a plasma activation process the wafers are guided and pressed against each other to form a covalent bond between wafer surfaces. The plasma activation process involves deposition of mono-layer or sub-monolayer metallic atom on the surface of substrates. After deposition of metallic layers, a high-force actuation presses the wafers and forms a covalent bond between the wafers. Then, the bonded wafer pair is ion-sliced or thinned to form single crystalline optical thin film. An annealing process oxidizes the deposited metallic layers and produces optically-transparent single crystalline thin film. An optical waveguide may be fabricated by this thin film while utilizing an electro-optic effect to produce optical modulators and other photonic devices.
1. A method for producing an optically-transparent thin-film wafer, the method comprising steps of:
smoothening a surface of a core substrate from a first wafer and a surface of a handle substrate from a second wafer, wherein the core substrate is made of a single crystalline material;
depositing one or more thin metallic layers on at least one of the core substrate and the handle substrate with an optional intermediate layer;
bonding the surface of the core substrate from the first wafer and the surface of the handle substrate from the second wafer to form a bonded pair, which is achieved by a bonding pressure provided by a wafer-bonding apparatus operating in a vacuum chamber to assist atomic diffusion bonding;
crystal ion-slicing or thinning the core substrate bonded to the handle substrate to form a thin film made of the core substrate; and
annealing the thin film at an elevated temperature to allow oxidation or diffusion of the one or more metallic layers into the core substrate or to the handle substrate, which consequently enhances optical transparency of the thin film.
2. The method of claim 1 , wherein the single crystalline material is lithium niobite, lithium tantalate, or another electro-optic crystal.
3. The method of claim 1 , wherein the one or more metallic layers deposited on the core substrate or the handle substrate are at least one of titanium, chromium, tantalum, nickel, niobium, aluminum, or another metallic layer with a thickness of one mono-layer, sub-mono layer, or several mono-layers.
4. The method of claim 1 , wherein the optically-transparent thin-film wafer has a thickness between 50 nm to 5000 nm.
5. The method of claim 1 , wherein the handle substrate is made from silicon or quartz.
6. The method of claim 1 , wherein the intermediate layer is made of silicon dioxide with a thickness between 100 nm to 10 um.
7. The method of claim 1 , wherein the intermediate layer is a distributed Bragg mirror structure.