Abstract

We describe a novel control approach for form accuracy of microlenses with continuous relief by control of exposure threshold. The approach can be achieved by analysis of the exposure distribution on photoresist and by deriving a relationship between the exposure distributions and the internal photoactive compound concentration (PAC) of the photoresist. The feature of parallel PAC curves for a specific value is determined in this way. We then analyze the development process and discover its critical effect on the approach. Finally we establish the relationship between the PAC distribution and the form accuracy of the relief. Not only is the fabricated relief height significantly increased to as high as 100 µm by use of this method, but we also realized effective fine control of the form accuracy of the continuous relief. With this approach we obtained micro-optic elements with 100-µm relief height and a form error (rms value) of less than 1 µm.

© 2005 Optical Society of America

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References

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    [CrossRef]
  7. C. L. Henderson, S. Pancholi, S. A. Chowdhury, C. G. Wilson, and R. R. Dammel, �??Photoresist characterization for lithography simulation: II. Exposure parameter measurements,�?? in Advances in Resist Technology and Processing XIV, R. G. Tarascon-Auriol, ed., Proc. SPIE 3049, 816�??828 (1997).
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    [CrossRef]

Electrochem. Solid-State Lett.

C. A. Mack and G. Arthur, �??Notch model for photoresist dissolution,�?? Electrochem. Solid-State Lett. 1, 86�??88 (1998).
[CrossRef]

IEEE Trans. Electron Devices

F. H. Dill, W. P. Hornberger, P. S. Hauge, and J. M. Shaw. �??Characterization of positive photoresist,�?? IEEE Trans. Electron Devices 22, 445�??452 (1975).
[CrossRef]

Microelectron. Eng.

Y. Oppliger P. Sixt, J.M. Stauffer, J. M. Mayor, P. Regnault, and G. Voirin, �??One-step 3D shaping using a gray-tone mask for optical and microelectronic applications,�?? Microelectron. Eng. 23, 449�??454 (1994).
[CrossRef]

Opt. Eng.

C. Du, X. Dong, C. Qiu, Q. Deng, and C. Zhou, �??Profile control technology for high performance microlens array,�?? Opt. Eng. 43, 2595�??2602 (2004).
[CrossRef]

Opt. Lett.

Proc. SPIE

C. A. Mack, M. J. Maslow, A. Sekiguchi, and R. A. Carpio, �??New model for the effect of developer temperature on photoresist dissolution,�?? in Advances in Resist Technology and Processing XV, W. Conley, ed., Proc. SPIE 3333, 1218�??1231 (1998).

G. G. Arthur, C. Wallace, and B. Martin, �??Comparison of recent development models in optical lithography simulation,�?? in Metrology, Inspection, and Process Control for Microlithography XII, B. Singh, ed., Proc. SPIE 3332, 538�??549 (1998).

C. L. Henderson, S. Pancholi, S. A. Chowdhury, C. G. Wilson, and R. R. Dammel, �??Photoresist characterization for lithography simulation: II. Exposure parameter measurements,�?? in Advances in Resist Technology and Processing XIV, R. G. Tarascon-Auriol, ed., Proc. SPIE 3049, 816�??828 (1997).

C. L. Henderson, P. C. Tsiartas, S. Pancholi, S. A. Chowdhury, K. D. Dombrowski, C. G. Wilson, and R. R. Dammel, �??Photoresist characterization for lithography simulation: III. Development parameter measurements,�?? in Advances in Resist Technology and Processing XIV, R. G. Tarascon-Auriol, ed., Proc. SPIE 3049, 805�??815 (1997).

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Figures (9)

Fig. 1.
Fig. 1.

PAC versus depth in photoresist for different exposure doses.

Fig. 2.
Fig. 2.

Reciprocal of developing velocity, 1/R, vs. photoresist exposure depth, Z (exposure dose ranging from 500 to 3000 mJ/cm2)

Fig. 3.
Fig. 3.

Photoresist developing depth, Z0, vs. developing time(exposure dose ranging from 500 to 3000 mJ/cm2).

Fig. 4.
Fig. 4.

Flow-chart of the form control technique

Fig. 5.
Fig. 5.

Exposure distribution on photoresist surface with parameters of A=0.2063µm-1,B=0.0214µm-1, C=0.02cm2/mJ,

Fig. 6.
Fig. 6.

Calculated internal PAC distribution by employing the exposure distribution as shown in Fig.5.

Fig. 7.
Fig. 7.

Mask used for the mask-moving technique.

Fig. 8.
Fig. 8.

Measure two-dimensional profile of the concave microlensarray by use of the profilometer, Alpha Step 500.

Fig. 9.
Fig. 9.

Comparison between target profile and measured profile.

Equations (18)

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I ( x , z , t ) z = I ( x , z , t ) [ AM ( x , z , t ) + B ] ,
M ( x , z , t ) t = I ( x , z , t ) M ( x , z , t ) C .
ln [ M ( x , z , t ) ] = 0 t I ( x , z , t ) C dt + k .
Q ( x , z , t ) = 0 t I ( x , z , t ) dt ,
M ( x , z , t ) = k 0 exp [ Q ( x , z , t ) C ] ,
k 0 = exp ( k ) ,
M ( x , z , t ) = exp [ CQ ( x , z , t ) ] .
I ( x , z , t ) z = I ( x , z , t ) { A exp [ CQ ( x , z , t ) ] + B } .
Q ( x , z , t ) z = BQ ( x , z , t ) A 0 t I ( x , z , t ) exp [ CQ ( x , z , t ) ] dt .
Q ( x , z , t = 0 ) = 0 ,
Q ( x , z , t ) z = { B × Q ( x , z , t ) A C exp [ CQ ( x , z , t ) ] } A C .
Q ( x , z , t ) z = A C { exp [ CQ ( x , z , t ) 1 ] } B × Q ( x , z , t ) .
M ( x , z , t ) z = A × M × ( 1 M ) B × M × ln ( M ) ,
M ( x , 0 , t ) = exp [ CQ ( x , 0 , t ) ] .
R ( M ) = R max ( 1 M ) n [ ( a + 1 ) ( 1 M ) n _ notch a + ( 1 M ) n _ notch ] + R min ,
a = ( n _ notch + 1 ) ( n _ notch 1 ) ( 1 M th _ notch ) n _ notch .
T ( Z 0 ) = 0 z 0 Z R ( Z ) dZ ,
f ( x ) = Z M = M P ( x ) ,

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