Abstract

To satisfy the increasing demand for extremely tight overlay accuracy in semiconductor manufacturing processes, all the measurement error factors in alignment systems and overlay measurement tools need be identified and eliminated. The principle of most alignment systems is based on image processing of target marks on the wafer under bright-field illumination. Although the phenomenon that the sensitivity to the alignment error varies with the step height (SH) of the mark has been known and used for evaluating the performance of the alignment optics, no investigation has been made into the origin and the physical mechanism of the phenomenon. We propose a simplified optical model that can account for the origin of the asymmetric image and clarify its relation to the SHs. The model is validated with simulation and experimental results. The improved performance of an alignment system using marks with optimally designed SHs is demonstrated.

© 2007 Optical Society of America

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References

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  1. See http://public.itrs.net/.
  2. D. J. Coleman, P. J. Larson, A. D. Lapata, W. A. Muth, and A. Starikov, "On the accuracy of overlay measurements: tool and mark asymmetry effects," Proc. SPIE 1261, 139-161 (1990).
  3. T. Kanda, K. Mishima, E. Murakami, and H. Ina, "Alignment sensor corrections for tool induced shift (TIS)," Proc. SPIE 3051, 846-855 (1997).
  4. H. Ina, K. Sentoku, T. Matsumoto, H. Sumitani, and M. Suita, "Alignment mark optimization to reduce tool- and wafer-induced shift for XPA-1000," Jpn. J. Appl. Phys. 38, 7065-7070 (1999).
    [CrossRef]

1999

H. Ina, K. Sentoku, T. Matsumoto, H. Sumitani, and M. Suita, "Alignment mark optimization to reduce tool- and wafer-induced shift for XPA-1000," Jpn. J. Appl. Phys. 38, 7065-7070 (1999).
[CrossRef]

1997

T. Kanda, K. Mishima, E. Murakami, and H. Ina, "Alignment sensor corrections for tool induced shift (TIS)," Proc. SPIE 3051, 846-855 (1997).

1990

D. J. Coleman, P. J. Larson, A. D. Lapata, W. A. Muth, and A. Starikov, "On the accuracy of overlay measurements: tool and mark asymmetry effects," Proc. SPIE 1261, 139-161 (1990).

Coleman, D. J.

D. J. Coleman, P. J. Larson, A. D. Lapata, W. A. Muth, and A. Starikov, "On the accuracy of overlay measurements: tool and mark asymmetry effects," Proc. SPIE 1261, 139-161 (1990).

Ina, H.

H. Ina, K. Sentoku, T. Matsumoto, H. Sumitani, and M. Suita, "Alignment mark optimization to reduce tool- and wafer-induced shift for XPA-1000," Jpn. J. Appl. Phys. 38, 7065-7070 (1999).
[CrossRef]

T. Kanda, K. Mishima, E. Murakami, and H. Ina, "Alignment sensor corrections for tool induced shift (TIS)," Proc. SPIE 3051, 846-855 (1997).

Kanda, T.

T. Kanda, K. Mishima, E. Murakami, and H. Ina, "Alignment sensor corrections for tool induced shift (TIS)," Proc. SPIE 3051, 846-855 (1997).

Lapata, A. D.

D. J. Coleman, P. J. Larson, A. D. Lapata, W. A. Muth, and A. Starikov, "On the accuracy of overlay measurements: tool and mark asymmetry effects," Proc. SPIE 1261, 139-161 (1990).

Larson, P. J.

D. J. Coleman, P. J. Larson, A. D. Lapata, W. A. Muth, and A. Starikov, "On the accuracy of overlay measurements: tool and mark asymmetry effects," Proc. SPIE 1261, 139-161 (1990).

Matsumoto, T.

H. Ina, K. Sentoku, T. Matsumoto, H. Sumitani, and M. Suita, "Alignment mark optimization to reduce tool- and wafer-induced shift for XPA-1000," Jpn. J. Appl. Phys. 38, 7065-7070 (1999).
[CrossRef]

Mishima, K.

T. Kanda, K. Mishima, E. Murakami, and H. Ina, "Alignment sensor corrections for tool induced shift (TIS)," Proc. SPIE 3051, 846-855 (1997).

Murakami, E.

T. Kanda, K. Mishima, E. Murakami, and H. Ina, "Alignment sensor corrections for tool induced shift (TIS)," Proc. SPIE 3051, 846-855 (1997).

Muth, W. A.

D. J. Coleman, P. J. Larson, A. D. Lapata, W. A. Muth, and A. Starikov, "On the accuracy of overlay measurements: tool and mark asymmetry effects," Proc. SPIE 1261, 139-161 (1990).

Sentoku, K.

H. Ina, K. Sentoku, T. Matsumoto, H. Sumitani, and M. Suita, "Alignment mark optimization to reduce tool- and wafer-induced shift for XPA-1000," Jpn. J. Appl. Phys. 38, 7065-7070 (1999).
[CrossRef]

Starikov, A.

D. J. Coleman, P. J. Larson, A. D. Lapata, W. A. Muth, and A. Starikov, "On the accuracy of overlay measurements: tool and mark asymmetry effects," Proc. SPIE 1261, 139-161 (1990).

Suita, M.

H. Ina, K. Sentoku, T. Matsumoto, H. Sumitani, and M. Suita, "Alignment mark optimization to reduce tool- and wafer-induced shift for XPA-1000," Jpn. J. Appl. Phys. 38, 7065-7070 (1999).
[CrossRef]

Sumitani, H.

H. Ina, K. Sentoku, T. Matsumoto, H. Sumitani, and M. Suita, "Alignment mark optimization to reduce tool- and wafer-induced shift for XPA-1000," Jpn. J. Appl. Phys. 38, 7065-7070 (1999).
[CrossRef]

Jpn. J. Appl. Phys.

H. Ina, K. Sentoku, T. Matsumoto, H. Sumitani, and M. Suita, "Alignment mark optimization to reduce tool- and wafer-induced shift for XPA-1000," Jpn. J. Appl. Phys. 38, 7065-7070 (1999).
[CrossRef]

Other

See http://public.itrs.net/.

D. J. Coleman, P. J. Larson, A. D. Lapata, W. A. Muth, and A. Starikov, "On the accuracy of overlay measurements: tool and mark asymmetry effects," Proc. SPIE 1261, 139-161 (1990).

T. Kanda, K. Mishima, E. Murakami, and H. Ina, "Alignment sensor corrections for tool induced shift (TIS)," Proc. SPIE 3051, 846-855 (1997).

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Figures (18)

Fig. 1
Fig. 1

TIS, WIS, and their interaction on a mark signal.

Fig. 2
Fig. 2

Results of TIS-compensation measurements with two different overlay measurement tools.

Fig. 3
Fig. 3

(Color online) Optical system for the alignment.

Fig. 4
Fig. 4

(a) Alignment pattern and (b) its sectional image intensity profile for SOI calculation.

Fig. 5
Fig. 5

Image intensity profile of alignment mark for SHs varied from λ / 16 to 8 λ / 16 for coma λ / 4 .

Fig. 6
Fig. 6

Variation of the SOI with a SH for two different values of coma.

Fig. 7
Fig. 7

Variation of the SOI with a SH for two different illumination conditions realized by rotation of the bundle fiber.

Fig. 8
Fig. 8

Optical model used for simulation by Code V. FFT, fast Fourier transform.

Fig. 9
Fig. 9

Results of simulation for coma 0.071 λ .

Fig. 10
Fig. 10

Variation of the SOI with the SH of alignment mark for different amounts of comas.

Fig. 11
Fig. 11

(Color online) Ideally aligned illumination beam (left) and decentered illumination beam (right) on pupil surface, and deviation from telecentricity.

Fig. 12
Fig. 12

(Color online) Variation of intensity profile with the SH of the alignment mark, for the case of decentered illumination.

Fig. 13
Fig. 13

Variation of the SOI with the SH of the alignment mark, for different amounts of decentering in the illumination beam.

Fig. 14
Fig. 14

Simplified optical model based on six scattered rays.

Fig. 15
Fig. 15

Graphical explanation for the new criteria TIS2.

Fig. 16
Fig. 16

TIS2 versus comatic aberration.

Fig. 17
Fig. 17

TIS2 versus telecentricity.

Fig. 18
Fig. 18

Alignment performance with and∕or without TIS2-based tuning.

Tables (1)

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Table 1 Parameters Used for Simulation

Equations (90)

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65   nm
632 .8   nm
100 ×
4   μm × 30   μm
SOI = 100 ( a b ) / c ,
λ / 16
± 10   nm
λ / 16
2 λ / 16
3 λ / 16
4 λ / 16
5 λ / 16
6 λ / 16
7 λ / 16
8 λ / 16
4 λ / 16
λ / 4
λ / 20
λ / 100
λ / 4
λ / 20
λ / 2
λ / 2
39.6   nm
79 .2   nm
512 × 512
λ / 16
0.07 λ
± 0.06 λ
± 0.07 λ
± 0.08 λ
( γ = 0 )
20   mrad
± 10
± 15
± 20
λ / 2
± α
ϕ C M
ϕ C M
ϕ S H
ϕ S H k ( 1 + cos α ) h 2 k h
k = 2 π / λ
A = exp ( j ω t ) + exp [ j ( ω t + ϕ C M ) ] + exp [ j ( ω t + ϕ C M + ϕ S H ) ] ,
B = exp [ j ( ω t + ϕ S H ) ] + exp ( j ω t ) + exp [ j ( ω t + ϕ C M ) ] .
a = | A | 2 = 3 + 2 cos ( ϕ C M ) + 2 cos ( ϕ S H ) + 2 cos ( ϕ S H + ϕ C M ) ,
b = | B | 2 = 3 + 2 cos ( ϕ C M ) + 2 cos ( ϕ S H ) + 2 cos ( ϕ S H ϕ C M ) .
SOI ( a b ) sin ( ϕ C M ) sin ( ϕ S H ) = sin ( ϕ C M ) sin ( 2 k h ) .
λ / 2
sin ( ϕ C M )
λ / 8
λ / 8
λ / 8
3 λ / 8
λ / 8
3 λ / 8
λ / 8
3 λ / 8
λ / 8
3 λ / 8
λ / 8
3 λ / 8
L S
D 1
D 2
λ / 8
3 λ / 8
L 0 = L S + D 1 + D 2
D 1 + D 2
L 180 = L S D 1 D 2
D 1 + D 2
TIS2 ( L 0 L 180 ) / 2 = D 1 + D 2 .
λ / 8
λ / 8
3 λ / 8
3 λ / 8
2   nm
1 .4   mrad
80   nm
49   nm
± 20   nm
40   nm
λ / 8
λ / 8
3 λ / 8
± 20   nm
λ / 16
8 λ / 16
λ / 4
0.071 λ

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