Abstract

A method is described for quick alignment of photolithographic masks over silicon substrates. Moiré reflection patterns are observed from grids etched on the silicon wafer and grids located on the photolithographic masks. A restricted class of moiré patterns provides information on both the direction and degree of misalignment during all phases of alignment. Alignment accuracy of 0.2 μm has been achieved even when there were separations of 30 μm between the mask and wafer. The moiré patterns can be observed visually through standard mask-alignment facilities. The etched grids are found to retain their diffraction properties during the operations of reoxidation and epitaxial growth.

© 1972 Optical Society of America

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References

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  1. F. L. Howland, K. M. Poole, Bell Syst. Tech. J. 49, 1997 (1970).
  2. V. Ronchi, Z. Phys. 37, 732 (1926).
    [Crossref]
  3. G. Oster, M. Wasserman, C. Zwerling, J. Opt. Soc. Am. 54, 169 (1964).
    [Crossref]
  4. M. Stecher, J. Phys. 32, 247 (1964).
  5. P. S. Theocaris, Moiré Fringes in Strain Analysis (Pergamon Press, New York1969).
  6. R. M. Springer, D. H. Harris, Human Factors 11, 189 (1969).
  7. J. Guild, The Interference Systems of Crossed Diffraction Gratings (Oxford U. P., London, 1956).

1970 (1)

F. L. Howland, K. M. Poole, Bell Syst. Tech. J. 49, 1997 (1970).

1969 (1)

R. M. Springer, D. H. Harris, Human Factors 11, 189 (1969).

1964 (2)

1926 (1)

V. Ronchi, Z. Phys. 37, 732 (1926).
[Crossref]

Guild, J.

J. Guild, The Interference Systems of Crossed Diffraction Gratings (Oxford U. P., London, 1956).

Harris, D. H.

R. M. Springer, D. H. Harris, Human Factors 11, 189 (1969).

Howland, F. L.

F. L. Howland, K. M. Poole, Bell Syst. Tech. J. 49, 1997 (1970).

Oster, G.

Poole, K. M.

F. L. Howland, K. M. Poole, Bell Syst. Tech. J. 49, 1997 (1970).

Ronchi, V.

V. Ronchi, Z. Phys. 37, 732 (1926).
[Crossref]

Springer, R. M.

R. M. Springer, D. H. Harris, Human Factors 11, 189 (1969).

Stecher, M.

M. Stecher, J. Phys. 32, 247 (1964).

Theocaris, P. S.

P. S. Theocaris, Moiré Fringes in Strain Analysis (Pergamon Press, New York1969).

Wasserman, M.

Zwerling, C.

Bell Syst. Tech. J. (1)

F. L. Howland, K. M. Poole, Bell Syst. Tech. J. 49, 1997 (1970).

Human Factors (1)

R. M. Springer, D. H. Harris, Human Factors 11, 189 (1969).

J. Opt. Soc. Am. (1)

J. Phys. (1)

M. Stecher, J. Phys. 32, 247 (1964).

Z. Phys. (1)

V. Ronchi, Z. Phys. 37, 732 (1926).
[Crossref]

Other (2)

P. S. Theocaris, Moiré Fringes in Strain Analysis (Pergamon Press, New York1969).

J. Guild, The Interference Systems of Crossed Diffraction Gratings (Oxford U. P., London, 1956).

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Figures (4)

Fig. 1
Fig. 1

Conventional alignment technique.

Fig. 2
Fig. 2

Moiré alignment technique.

Fig. 3
Fig. 3

Experimental results showing moiré pattern as viewed through an alignment microscope resulting from 4-μ pitch grid etched and reoxidized on silicon and 3.8-μ pitch grid on mask.

Fig. 4
Fig. 4

Tracing of diffracted light passing through two grids.

Equations (12)

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( X - S ) 2 + Y 2 = n 2 a 2 , ( X + S ) 2 + Y 2 = k 2 a 2 ,
P = n ± k ,
[ X 2 / ( P 2 / 4 ) ] ± { Y 2 / [ P 2 / ( 4 - S ) ] } = 1 ,
X 2 + Y 2 = [ ( P + 1 2 ) a b / ( a - b ) ] 2 ,
b = Z a ,
R = 1 2 ( a Z / Z - 1 ) .
R = n a ,
Accuracy = ± [ ( a / 2 ) / n ] .
Accuracy = ± ( a / 2 ) ( Z - 1 / Z ) .
Z min = ( L min + A min ) / L min ;
Accuracy = ± [ L min A min / ( L min + A min ) ] ,
Accuracy ± A min .

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