Method for the simultaneous double-side grinding of a plurality of semiconductor wafers

1. A method for the simultaneous double-side grinding of a plurality of semiconductor wafers during which the wafer thickness is decreased, wherein each semiconductor wafer lies such that it is freely moveable in a cutout of one of a plurality of carriers caused to rotate by means of a rolling apparatus and is thereby moved on a cycloidal trajectory, wherein the semiconductor wafers are machined in material-removing fashion between two rotating working disks, wherein each working disk comprises a working layer containing bonded abrasive, wherein the magnitude of the ratio of the difference in the magnitudes of the theoretical wear (r) of the two working layers to the mean value of the magnitudes of the wear of the two working layers for each radial position r is less than 1/1000, wherein the magnitude of the theoretical wear of each working layer is given by

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r

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e

min

e

max

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2

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2

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2

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i

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(

r

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2

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where α indicates the pitch radius of the circulating movement of the carriers on the working disks about the midpoint of the rolling apparatus; e indicates the distance between the currently considered reference point and the midpoint of the corresponding carrier; l(e) indicates the arc length—running within the area of the semiconductor wafer—of the circle with radius e about the midpoint of the corresponding carrier; r indicates the radial position with respect to the midpoint of the working disks; σ i indicates the angular velocity of the circulation of the carriers about the midpoint of the working disks; ω i indicates the angular angular velocity of the inherent rotation of the carriers about their respective midpoints, e min =max{0; e ecc −R} and e max =e ecc +R where R=radius of the semiconductor wafer denote the lower and upper limits of the integration over e; e ecc indicates the eccentricity of the semiconductor wafer in the carrier and the index i=o for the upper working disk or i=u for the lower working disk indicates whether the angular velocities σ i and ω i relate to the upper or the lower working disk.

2. The method of claim 1 , wherein the change in the thickness homogeneity of each of the working layers on account of wear amounts to less than a hundredth of the magnitude of the thickness decrease of the semiconductor wafers during the simultaneous double-side grinding, wherein the thickness homogeneity of a working layer is defined as the difference between largest and smallest thickness over the entire area of the respective working layer that comes into contact with the semiconductor wafers.

3. The method of claim 1 , wherein the proportion of the total material removal of material removal brought about by abrasive released in the course of the wear of the working layers is always less than the proportion of material removal brought about by abrasive fixedly bonded in the working layer.

4. The method of claim 3 , wherein the thickness decrease of the working layers on account of wear during the simultaneous double-side grinding amounts to less than 10% of the thickness decrease of the semiconductor wafers.

5. The method of claim 3 , wherein the thickness decrease of the working layers on account of wear during the simultaneous double-side grinding amounts to less than 2% of the thickness decrease of the semiconductor wafers.

6. The method of claim 1 , wherein the temperature in a working gas between the two rotating working disks is kept constant during machining.

7. The method of claim 6 , wherein at least 5% of the area of each semiconductor wafer is always in contact with the working layers during the simultaneous double-side grinding.

8. The method of claim 6 , wherein the working layers are connected to the respective working disks in releasable fashion so as to be easily changeable.

9. The method of claim 8 , wherein the working layers are connected to the respective working disks by adhesive bonding, by covering, magnetically, electrostatically, by means of vacuum, or by hook and loop fastener.

10. The method of claim 6 , wherein a dressing block with a dressing grain whose grain size is equal to that of the abrasive grain used in a working layer is used for the dressing or trimming of the working layer.

11. The method of claim 10 , wherein the working layer is dressed or trimmed predominantly by means of loose grain no longer bonded in the dressing block.

12. The method of claim 6 , wherein the temperature in the working gap is kept constant by measuring the temperature in the working gap and varying the flow rate or the temperature or flow rate and temperature of the coolant, which flows through in each case at least one cooling labyrinth in each of the two working disks, according to the measured temperature.

13. The method of claim 6 , wherein the temperature in the working gap is kept constant by measuring the temperature in the working gap and varying the flow rate or the temperature or flow rate and temperature of the cooling lubricant, which is fed to the working gap, according to the measured temperature.

14. The method of claim 1 , wherein per unit time the magnitude of the number of revolutions of the carriers about the midpoint of the rolling apparatus and relative to each of the two working disks is greater than the magnitude of the number of revolutions of the individual carriers about their respective midpoints.

15. The method of claim 14 , wherein the lengths of the trajectories which the semiconductor wafers cover relative to the two working disks are approximately identical.

16. The method of claim 15 , wherein the magnitude of the ratio of the difference in the lengths of the trajectories which the semiconductor wafers cover relative to the two working disks and the mean value of the lengths of said trajectories is less

17. A method for the simultaneous double-side grinding of a plurality of semiconductor wafers during which the wafer thickness is decreased, wherein each semiconductor wafer lies such that it is freely moveable in a cutout of one of a plurality of carriers caused to rotate by means of a rolling apparatus and is thereby moved on a cycloidal trajectory, wherein the semiconductor wafers are machined in material-removing fashion between two rotating working disks, wherein each working disk comprises a working layer containing bonded abrasive, wherein for each working layer the magnitude of the theoretical wear (r) for each radial position r deviates by less than 30% from the theoretical wear averaged over the entire working layer, where the magnitude of the theoretical wear of each working layer is given by

ℜ

i

⁡

(

r

)

=



∫

e

min

e

max

⁢

a

2

⁢

σ

i

2

+

e

2

⁢

ω

i

2

+

(

r

2

-

a

2

-

e

2

)

⁢

σ

i

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ω

i

σ

i

-

ω

i

2

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2

⁢

(

a

2

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r

2

+

e

2

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r

2

+

a

2

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e

2

)

-

r

4

-

a

4

-

e

4

(

σ

i

-

ω

i

2

·

a

2

-

e

2

r

⁢

2

+

σ

i

+

ω

i

2

)

·

l

⁡

(

e

)

·

ⅆ

e



.

where α indicates the pitch radius of the circulating movement of the carriers on the working disks about the midpoint of the rolling apparatus; e indicates the distance between the currently considered reference point and the midpoint of the corresponding carrier; l(e) indicates the arc length—running within the area of the semiconductor wafer—of the circle with radius e about the midpoint of the corresponding carrier; r indicates the radial position with respect to the midpoint of the working disks; σ i indicates the angular velocity of the circulation of the carriers about the midpoint of the working disks; ω i indicates the angular velocity of the inherent rotation of the carriers about their respective midpoints, e min =max{0; e ecc −R} and e max =e ecc +R where R=radius of the semiconductor wafer denote the lower and upper limits of the integration over e; e ecc indicates the eccentricity of the semiconductor wafer in the carrier and the index i=o for the upper working disk or i=u for the lower working disk indicates whether the angular velocities σ i and ω i relate to the upper or the lower working disk. than 20% .

18. The method of claim 17 wherein the change in the thickness homogeneity of each of the working layers on account of wear amounts to less than a hundredth of the magnitude of the thickness decrease of the semiconductor wafers during the simultaneous double-side grinding, wherein the thickness homogeneity of a working layer is defined as the difference between largest and smallest thickness over the entire area of the respective working layer that comes into contact with the semiconductor wafers.

19. The method of claim 17 , wherein the temperature in a working gas between the two rotating working disks is kept constant during machining.

20. The method of claim 19 , wherein the temperature in the working gap is kept constant by measuring the temperature in the working gap and varying the flow rate or the temperature or flow rate and temperature of the coolant, which flows through in each case at least one cooling labyrinth in each of the two working disks, according to the measured temperature.

21. The method of claim 19 , wherein the temperature in the working gap is kept constant by measuring the temperature in the working gap and varying the flow rate or the temperature or flow rate and temperature of the cooling lubricant, which is fed to the working gap, according to the measured temperature.

22. The method of claim 17 wherein per unit time the magnitude of the number of revolutions of the carriers about the midpoint of the rolling apparatus and relative to each of the two working disks is greater than the magnitude of the number of revolutions of the individual carriers about their respective midpoints.

23. The method of claim 22 , wherein the lengths of the trajectories which the semiconductor wafers cover relative to the two working disks are approximately identical.

24. The method of claim 23 , wherein the magnitude of the ratio of the difference in the lengths of the trajectories which the semiconductor wafers cover relative to the two working disks and the mean value of the lengths of said trajectories is less than 20%.