Process for producing semiconductor wafers
Semiconductor wafers are produced by a process wherein a single-crystal ingot of semiconductor material is pulled and at least one wafer is removed from the ingot, wherein the wafer is subjected to a thermal treatment comprising a heat treatment step in which a radial temperature gradient acts on the wafer, wherein an analysis of the wafer of semiconductor material with respect to the formation of defects in the crystal lattice, so-called stress fields, is carried out.
1. A process for producing semiconductor wafers comprising the following steps in the given sequence:
a) pulling a single-crystal rod of a semiconductor material from a melt and optionally cylindrically grinding the rod,
b) separating a plurality of semiconductor wafers from the rod;
c) removing at least one wafer for analysis from the single-crystal rod,
d) performing a first thermal treatment step corresponding to a thermal budget to which the wafer is subjected during fabrication of semiconductor devices on the wafer, and performing a second thermal treatment step with the at least one wafer of semiconductor material, wherein in the second thermal treatment step a radial temperature gradient acts on at least one side of the semiconductor wafer from the inside outward or from the outside inward,
e) analyzing the wafer of semiconductor material treated in step d) with respect to the possible formation and/or the extent of stress fields,
f) distinguishing this wafer and further wafers of the plurality of semiconductor wafers separated from a rod section represented by this wafer into stress-optimized wafers conforming to the thermal budget to which the wafers are subjected during the fabrication of semiconductor devices on the wafer from rejected wafers not conforming to this thermal budget.
2. The process for producing semiconductor wafers of claim 1 , wherein the radial temperature gradient acts on all regions of the wafer excluding an edge region of the wafer with an edge exclusion of 20 mm.
3. The process of claim 1 , wherein the radial temperature gradient acts on all regions of the wafer excluding an edge region of the wafer with an edge exclusion of 10 mm.
4. The process of claim 1 , wherein the heat treatment step for generating a radial temperature gradient is effected by means of a plurality of radially arranged heat sources separately controllable in their radiation intensity.
5. The process for producing semiconductor wafers of claim 1 , wherein the temperature gradient acting on the wafer extends over n adjacent radial zones, wherein n is an integer and is greater than 1.
6. The process for producing semiconductor wafers of claim 5 , wherein the temperature gradient between two adjacent zones is 1 to 50 kelvin.
7. The process for producing semiconductor wafers of claim 1 , wherein the thermal treatment comprises a heating phase, a holding phase and a cooling phase, wherein the holding phase corresponds to the heat treatment step for generating the radial temperature gradient acting on the wafer.
8. The process for producing semiconductor wafers of claim 1 , wherein the thermal treatment step for generating a radial temperature gradient is carried out in a gas atmosphere comprising one or more gases selected from the group consisting of O 2 , H 2 , NH 3 , He and Ar.
9. The process of claim 1 , wherein based on the determination of the stress fields in the at least one wafer, the single-crystal rod from which this at least one wafer was removed is assigned a particular specification with respect to stress fields.
10. The process of claim 1 , wherein a single wafer of the plurality of wafers is analyzed.
11. The process for producing semiconductor wafers of claim 5 , wherein the temperature gradient between two adjacent zones is 5 to 30 kelvin.
12. A process for producing a plurality of stress free or stress optimized semiconductor wafers having a front side, a rear side, and a circumferential edge, comprising the following steps:
a) receiving a thermal budget for fabricating semiconductor devices on a semiconductor wafer;
b) pulling a single-crystal rod of the semiconductor and optionally cylindrically grinding the rod;
c) separating a plurality of semiconductor wafers from the single-crystal rod;
d) identifying a test semiconductor wafer having properties representative of the plurality of semiconductor wafers;
e) performing a first thermal treatment step corresponding to the thermal budget referred to in step a) on the test semiconductor wafer;
f) performing a second thermal treatment on the test semiconductor wafer following step e) to establish a radial temperature gradient in at least one interior zone of the semiconductor wafer, the at least one interior zone positioned at least 10 mm inward from the circumferential edge of the test semiconductor wafer;
g) analyzing the test wafer for stress fields to determine whether the test semiconductor wafer has no stress or a level of stress suitable for fabricating semiconductor devices according to the thermal budget; and
h) classifying the remaining plurality of semiconductor wafers as stress optimized wafers or rejected wafers in accordance with the result of step g).
13. The process of claim 12 , wherein the second thermal treatment establishes n adjacent radial zones, wherein n is an integer greater than 1.
14. The process of claim 12 , wherein the plurality of wafers are wafers sawn from an ingot segment having a length of at least 20 cm and having the same crystal structure along its length.
15. The process of claim 12 , wherein the thermal budget corresponds to a treatment of 3 hours at 780° C. followed by 16 hours at 1000° C.
16. The process of claim 12 , wherein the plurality of stress free or stress optimized semiconductor wafers are stress free semiconductor wafers.
17. The process of claim 1 , wherein during the first thermal treatment step, the wafer has no radial temperature gradient.