Method of bonding two substrates
The invention relates to a method of forming a structure comprising a thin layer of semiconductor material transferred from a donor substrate onto a second substrate, wherein two different atomic species are co-implanted under certain conditions into the donor substrate so as to create a weakened zone delimiting the thin layer to be transferred. The two different atomic species are implanted so that their peaks have an offset of less than 200 Å in the donor substrate, and the substrates are bonded together after roughening at least one of the bonding surfaces.
1. A method for reducing edge voids and blisters when forming a structure comprising a thin layer of semiconductor material transferred from a donor substrate onto a second substrate, which method comprises:
co-implanting two different atomic species into the donor substrate so as to create a weakened zone delimiting the thin layer to be transferred, each of the species having a maximum concentration at a so-called “peak” depth, with the two different atomic species implanted so that their peaks are aligned at substantially identical depths; and
molecularly bonding the donor and second substrates together by:
cleaning the surface of one or both of the substrates by means including a chemical bath under conditions selected so that the surface is etched by less than 10 Å to avoid blister formation during subsequent bonding wave propagation;
heating at least one or both of the substrates to a temperature in the range of 45° C. to 70° C. then contacting the substrates;
propagating a bonding wave between the substrates while retaining the substrate temperature in the range of 45° C. to 70° C. to reduce or eliminate edge voids during bonding wave propagation; and
transferring part of the donor substrate to the second substrate so as to form the thin layer on the second substrate.
2. The method of claim 1 , wherein the peaks of the two atomic species have an offset of less than 200 Å in the donor substrate.
3. The method of claim 1 , wherein the two different atomic species are hydrogen and helium.
4. The method of claim 3 , wherein the donor substrate comprises a silicon substrate covered with a silicon oxide layer having a thickness of about 1450 Å, the hydrogen has an implantation energy of about 32 keV so that the hydrogen implantation peak lies at a depth of about 2450 Å in the donor substrate, and the helium has an implantation energy of between about 47 and 50 keV.
5. The method of claim 1 , wherein the cleaning includes applying a bath that contains NH 4 OH, H 2 O 2 and H 2 O at a temperature of 40° C. and 55° C., the bath having a NH 4 OH/H 2 O weight ratio of between about 1/2 and 3/4.
6. The method of claim 5 , wherein the cleaning further includes applying a bath that includes HCl, H 2 O 2 and H 2 O.
7. The method of claim 6 , wherein the cleaning includes sequentially applying a bath of ozone, followed by the NH 4 OH, H 2 O 2 , and H 2 O bath, and then by the HCl, H 2 O 2 , and H 2 O bath.
8. The method of claim 6 , wherein cleaning includes sequentially applying a bath of sulfuric acid and oxygenated water, followed by the NH 4 OH, H 2 O 2 and H 2 O bath, and then by the HCl, H 2 O 2 , and H 2 O bath.
9. The method of claim 6 , wherein cleaning includes applying a dry ozone bath, followed by the NH 4 OH, H 2 O 2 and H 2 O bath, and then by the HCl, H 2 O 2 , and H 2 O bath.
10. The method of claim 6 , wherein the NH 4 OH, H 2 O 2 , and H 2 O bath has a temperature of about 40° C., and is applied for about three minutes, wherein the HCl, H 2 O 2 , and H 2 O bath has an HCl content of about 0.3% to 2% by weight, an H 2 O 2 content of about 0.3% to 2% by weight, a temperature of about 30° C., and is applied for about three minutes.
11. The method of claim 1 , which further comprises treating at least one substrate with a plasma activation treatment prior to placing the substrates in surface to surface contact.
12. The method of claim 10 , wherein plasma activation includes applying an O 2 -based plasma, N 2 -based plasma, or O 2 and N 2 -based plasma and is conducted in a manner to reduce surface roughness of one or both substrates.
13. The method of claim 1 , wherein the heating includes thermal conduction or radiation and is applied locally at a peripheral zone of at least one of the substrates.
14. The method of claim 1 , wherein the heating includes thermal conduction or radiation and is applied uniformly over the entire surface of at least one of the substrates to be bonded.
15. The method of claim 1 , wherein the first and second substrates are made of semiconductor materials.