Abstract

An optical inspection system has been developed that detects parameter fluctuations in an optical disk pregroove structure (groove pitch, depth, and width). This optical system was devised using a laser diffraction phenomenon. Groove parameters are measured and calculated from diffracted-light intensity ratios; the groove width is calculated from the second-order diffracted-light intensity ratio to that for the first order. The groove depth is given from the first-order ratio to the zeroth-order light intensity. In addition to this groove parameter inspection, this system is capable of groove defect detection using a spatial filter whose passband is designed to be between the zeroth- and the first-order diffracted-light areas.

© 1984 Optical Society of America

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References

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  1. K. Bulthuls et al. “Ten Billion Bits on a Disk,” IEEE Spectrum 8, 26 (1979).
  2. A. Iwamoto, H. Sekizawa, “Rotation-, Shift-, and Magnification-Insensitive Periodic-Pattern-Defects Optical Detection System,” Appl. Opt. 19, 1196 (1980).
    [CrossRef] [PubMed]
  3. A. Papoulis, Systems and Transforms with Application in Optics (McGraw-Hill, New York, 1968).

1980 (1)

1979 (1)

K. Bulthuls et al. “Ten Billion Bits on a Disk,” IEEE Spectrum 8, 26 (1979).

Appl. Opt. (1)

IEEE Spectrum (1)

K. Bulthuls et al. “Ten Billion Bits on a Disk,” IEEE Spectrum 8, 26 (1979).

Other (1)

A. Papoulis, Systems and Transforms with Application in Optics (McGraw-Hill, New York, 1968).

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Figures (11)

Fig. 1
Fig. 1

Diffracted light from a hypothetical optical disk surface. The reflected light fr(x) can be decomposed into two components, fPW(x) and fW(x).

Fig. 2
Fig. 2

Relationship between the groove width normalized by the pitch and the diffracted-light intensity ratio (I2n/In) When (W/P) is situated between 0.25 and 0.5, which is a typical parameter range, the optimum n is found to be 1.

Fig. 3
Fig. 3

Diffracted-light intensity ratio (In/I0) dependent on the groove depth. The most sensitive depth measurement is made by using (I1/I0).

Fig. 4
Fig. 4

Defect detection bandpass filter: C denotes the passband frequency range, and ξ0 shows the passband center frequency.

Fig. 5
Fig. 5

Optical disk inspection system. The pregroove parameter measuring section and defect pick-up optical system are compactly mounted with data processing equipment.

Fig. 6
Fig. 6

Optical inspection system, external view. Parameter measurement section is shown on the right. On the left the defect detecting section is displayed.

Fig. 7
Fig. 7

(a) Detected pregroove defect map; (b) the parameter fluctuations along the radius.

Fig. 8
Fig. 8

Measured data calibrated with SEM data.

Fig. 9
Fig. 9

Bandpass filter output vs irregular groove pitch fluctuation. The larger (ξ0/P) makes the higher measuring sensitivity; however, the single-value zone becomes limited.

Fig. 10
Fig. 10

Defect detection sensitivity vs bandpass filter center frequency (ξ0). The optimum condition for defect detection is given at around (ξ0/P) = 0.5.

Fig. 11
Fig. 11

Bandpass filter output vs groove defect size. The defect detection sensitivity becomes higher when measurement is made at smaller (ξ0/P).

Equations (17)

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f r ( x ) = f P - W ( x ) m = - N N δ ( x - m P ) + f W ( x ) m = - N N δ ( x - m P - P 2 ) ,
f P - W ( x ) = { 0 x > ( P - W ) / 2 , 1 x ( P - W ) / 2 , f W ( x ) = { 0 exp ( j 4 π D λ )             x > W / 2 , x W / 2 ,
F r ( ξ ) = { ( P - W ) sinc [ ( P - W ) ξ ] + W sinc ( W ξ ) exp [ - j π ( 4 D λ + P ξ ) ] · sin [ 2 π ( N + 1 2 ) P ξ ] sin ( π P ξ ) ,
I 0 = 1 - 2 W P ( 1 - W P ) [ 1 - cos ( 4 D λ π ) ] ,
I n = 2 W 2 P 2 sinc 2 ( n W P ) [ 1 - cos ( 4 D λ π ) ] .
P = λ / sin θ .
W = P n π cos - 1 ( I 2 n I n ) ,
D = λ 4 π cos - 1 { 1 - P 2 2 W [ ( I 0 I n ) W sinc 2 ( n W P ) + P - W ] } .
P = λ cos θ 0 sin θ ,
D = λ 4 π · cos ( θ 0 ) · cos - 1 { 1 - P 2 2 W [ ( I 0 I n ) W sinc 2 ( n W P ) + P - W ] } .
f T ( x ) = f r ( x ) + g ( x ) .
F T ( ξ ) = F r ( ξ ) + G ( ξ ) ,
I ~ C G ( ξ 0 ) 2 ,
I τ = 8 C τ 2 sinc 2 ( τ ξ 0 ) sin 2 ( π W ξ 0 ) [ 1 - cos ( 4 D λ π ) ] ,
g ( x ) = f L ( x ) δ ( x - W 2 ) + f R ( x ) δ ( x + W 2 ) ,
f L ( x ) = { 0 x > τ 2 , - 1 + exp ( j 4 D π / λ ) x τ 2 , f R ( x ) = { 0 x > τ 2 , 1 - exp ( j 4 D π / λ ) x τ 2 .
I D ~ C d 4 π exp ( - d 2 π 2 ξ 0 2 ) ,

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