SOI wafer and method for producing it
View Patent ↗An SOI wafer is constructed from a carrier wafer and a monocrystalline silicon layer having a thickness of less than 500 nm, an excess of interstitial silicon atoms prevailing in the entire volume of the silicon layer. The SOI wafers may be prepared by Czochralski silicon single crystal growth, the condition v/G<(v/G) crit =1.3×10 −3 cm 2 /(K·min) being fulfilled at the crystallization front over the entire crystal cross section, with the result that an excess of interstitial silicon atoms prevails in the silicon single crystal produced; separation of at least one donor wafer from this silicon single crystal, bonding of the donor wafer to a carrier wafer, and reduction of the thickness of the donor wafer, with the result that a silicon layer having a thickness of less than 500 nm bonded to the carrier wafer remains.
1. A method for producing an SOI wafer comprising a carrier wafer and a monocrystalline silicon layer having a thickness of less than 500 nm, an excess of interstitial silicon atoms prevailing in the entire volume of the silicon layer, comprising:
a) producing a silicon single crystal by Czochralski crucible pulling, the condition v/G<(v/G) crit =1.3×10 −3 cm 2 /(K×min) being fulfilled at the crystallization front over the entire crystal cross section, with the result that an excess of interstitial silicon atoms prevails in the silicon single crystal produced,
b) separating of at least one donor wafer from the silicon single crystal,
e) bonding the donor wafer to a carrier wafer, and
f) reducing of the thickness of the donor wafer to provide a silicon layer having a thickness of less than 500 nm, bonded to the carrier wafer.
2. The method of claim 1 , wherein a separating layer is produced in the donor wafer before it is bonded to the carrier wafer, and wherein at least a portion of the reduction of the thickness of the donor wafer after bonding to the carrier wafer is effected by splitting along the separating layer.
3. The method of claim 2 , wherein the production of the separating layer comprises the implantation of ions.
4. The method of claim 2 , wherein the splitting along the separating layer is achieved by a thermal treatment, the action of mechanical forces, or a combination thereof.
5. The method of claim 2 , wherein the split part of the donor wafer that is not bonded to the carrier wafer is used as a donor wafer again after the surface of the donor wafer has been smoothed.
6. The method of claim 1 , further comprising, following step B),
c) implanting ions into a surface of the donor wafer to form a separation layer,
and wherein reduction of the thickness of the donor wafer in step f) comprises splitting the donor wafer along the separation layer.
7. The method of claim 3 , wherein the ions implanted comprise ions of elements selected from the group consisting of hydrogen, helium, and mixtures thereof.
8. The process of claim 1 , further comprising:
c1) forming a separation layer by implanting at least one of argon ions or silicon ions into a surface of the donor wafer to form a gettering layer, and diffusing hydrogen into the gettering layer to form a separation layer,
and wherein reduction of the thickness of the donor wafer in step f) comprises splitting the donor wafer along the separation layer.
9. The method of claim 1 , further comprising:
d) oxidizing a surface of the donor wafer to form a silicon oxide insulating film,
and wherein the donor wafer is bonded to the carrier wafer in step e) such that said insulating film is located between the carrier wafer and the donor wafer.
10. The method of claim 6 , further comprising:
d) oxidizing a surface of the donor wafer to form a silicon oxide insulating film,
and wherein the donor wafer is bonded to the carrier wafer in step e) such that said insulating film is located between the carrier wafer and the donor wafer.
11. The method of claim 9 , wherein the thickness of the insulating film is between 1 nm to 30 nm, wherein the insulating film has a thickness homogeneity of less than 1% when the thickness is from 3 nm to 30 nm, and a thickness homogeneity of less than 2% when the thickness is from 1 nm to less than 3 nm.
12. The method of claim 1 , wherein the defect density of agglomerated interstitial silicon atoms in the donor wafer is less than 10 4 /cm 3 .
13. The method of claim 1 , wherein the thickness of the silicon layer from the donor wafer after step f) is 100 nm or less, and the surface defect density of agglomerated interstitial silicon atoms is less than 0.1/cm 2 .
14. The method of claim 1 , wherein the oxygen content of the donor wafer is from 3×10 17 /cm 3 to 7×10 17 /cm 3 .
15. The method of claim 1 , wherein the oxygen content of the donor wafer is from 5×10 17 /cm 3 to 7×10 17 /cm 3 .
16. The method of claim 1 , wherein a separating layer is formed below a surface of the donor wafer in a step c), and wherein step f) of reducing the thickness of the donor wafer comprises splitting along the separation layer by thermal treatment, the action of mechanical forces, or a combination thereof, to form an SOI wafer and a donor wafer remnant of lesser thickness than the original donor wafer.
17. The method of claim 16 , wherein the donor wafer remnant is used again as a donor wafer to be bonded to a carrier wafer.
18. The method of claim 1 , wherein the silicon layer is free of oxidation stacking faults.