Process for hydrophilically bonding substrates
A process for hydrophilic bonding first and second substrates, comprising: —bringing the first and second substrates into contact to form a bonding interface between main surfaces of the first and second substrates, and—applying a heat treatment to close the bonding interface. The process further comprises, before the step of bringing into contact, depositing, on the main surface of the first and/or second substrate, a bonding layer comprising a non-metallic material that is permeable to dihydrogen and that has, at the temperature of the heat treatment, a yield strength lower than that of at least one of the materials of the first substrate and of the second substrate located at the bonding interface. The layer has a thickness between 1 and 6 nm, and the heat treatment is carried out at a temperature lower than or equal to 900° C., and preferably lower than or equal to 600° C.
1. A process for hydrophilic bonding of a first substrate to a second substrate, comprising:
bringing the first substrate and the second substrate into contact, so as to form a bonding interface between a main surface of the first substrate and a main surface of the second substrate; the second substrate being a silicon substrate covered with a layer of native silicon oxide;
applying a heat treatment suitable for closing the bonding interface, the heat treatment comprising oxidizing a surface segment of the silicon of the second substrate through the layer of native silicon oxide;
wherein the process comprises, before the step of bringing into contact, depositing, on the main surface of at least one the first and the second substrate, a bonding layer comprising a non-metallic material that is permeable to dihydrogen and that has, at a temperature of the heat treatment, a yield strength lower than a yield strength of at least one of a material of the first substrate and a material of the second substrate located at the bonding interface, the bonding layer having a thickness between 1 and 6 nm; and
wherein the temperature of the heat treatment is lower than or equal to 900° C.
2. The process of claim 1 , wherein the first substrate comprises a silicon-oxide surface layer other than a native oxide, and the bonding layer is deposited on the silicon-oxide surface layer.
3. The process of claim 2 , wherein the silicon-oxide surface layer is formed by thermal oxidation of the first substrate.
4. The process of claim 1 , further comprising, after the application of the heat treatment for closing the bonding interface, a step of thinning the first substrate so as to transfer a thin layer of the first substrate to the second substrate.
5. The process of claim 4 , further comprising, between the deposition of the bonding layer and the step of bringing the first substrate and the second substrate into contact, forming a silicon-oxide surface layer on the first substrate and implanting ionic species in the first substrate through the silicon-oxide surface layer so as to form a weakened region delineating a semiconductor layer to be transferred.
6. The process of claim 1 , further comprising, between the deposition of the bonding layer and the step of bringing the first and second substrates into contact, implementing a hydrophilic treatment of the main surface of the substrates that includes applying water to the main surface of the substrates in order to form a film of water on the main surface.
7. The process of claim 1 , further comprising, before the deposition of the bonding layer, a step of cleaning the main surface on which the bonding layer is to be deposited with an oxidizing solution.
8. The process of claim 1 , wherein the non-metallic material of the bonding layer is chosen from amorphous silicon and amorphous germanium.
9. The process of claim 8 , wherein the non-metallic material of the bonding layer is amorphous silicon and the amorphous-silicon layer is formed in an epitaxial reactor at a temperature below 550° C.
10. The process of claim 9 , wherein the amorphous-silicon layer is formed from a precursor chosen from: disilane (Si 2 H 6 ), silane (SiH 4 ) or a liquid precursor of formula Si n H 2n+2 , where n is an integer higher than 2.
11. The process of claim 1 , wherein the temperature of the heat treatment is lower than or equal to 600° C.
12. The process of claim 1 , further comprising, after the application of the heat treatment for closing the bonding interface, a step of thinning the first substrate so as to transfer a thin layer of the first substrate to the second substrate.
13. The process of claim 1 , further comprising, between the deposition of the bonding layer and the step of bringing the first and second substrates into contact, implementing a hydrophilic treatment of the main surface of the substrates that includes applying water to the main surface of the substrates in order to form a film of water on the main surface.
14. The process of claim 1 , further comprising, before the deposition of the bonding layer, a step of cleaning the main surface on which the bonding layer is to be deposited with an oxidizing solution.
15. The process of claim 1 , wherein the non-metallic material of the bonding layer is chosen from amorphous silicon and amorphous germanium.