Study of dynamical formation and shape of microlenses formed by the reflow method

S. Audran; B. Faure; B. Mortini; C. Aumont; R. Tiron; C. Zinck; Y. Sanchez; C. Fellous; J. Regolini; J. P. Reynard; G. Schlatter; G. Hadziioannou

doi:10.1117/12.656371

29 March 2006 Study of dynamical formation and shape of microlenses formed by the reflow method

S. Audran, B. Faure, B. Mortini, C. Aumont, R. Tiron, C. Zinck, Y. Sanchez, C. Fellous, J. Regolini, J. P. Reynard, G. Schlatter, G. Hadziioannou

Author Affiliations +

Proceedings Volume 6153, Advances in Resist Technology and Processing XXIII; 61534D (2006) https://doi.org/10.1117/12.656371
Event: SPIE 31st International Symposium on Advanced Lithography, 2006, San Jose, California, United States

Abstract

Microlenses arrays are commonly used in CMOS images sensors to focus the incident light onto the photosensitive area of the pixel. These microlenses are fabricated using a thermal reflow method. Currently, due to the fast evolution of CMOS Imager technology, the understanding of the mechanisms involved in microlens formation becomes essential to better control what occurs during the process. We have seen in a previous study that the complexity of the reflow method comes from the competition between two phenomena occurring during the melt bake step: on one hand the surface tension tends to push the resist patterns into a spherical shape, on the other hand the resist crosslinking reaction drastically increases the resist viscosity hindering the microlens formation. In this paper the influence of resist crosslinking, resist volume and resist/substrate interface on the final shape of the microlens has been investigated. It appears that the contact angle between microlens and substrate varies depending on substrate wettability but is the same whatever the resist volume for a given substrate/resist combination. The microlens shape depends also significantly on bake temperature and crosslinking kinetics. In fact the right tuning of process conditions seems to be the key parameter in the control of the final microlens shape because it enables to adjust the kinetics of each mechanism and thus favour the microlens formation with regards to resist crosslinking.

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S. Audran, B. Faure, B. Mortini, C. Aumont, R. Tiron, C. Zinck, Y. Sanchez, C. Fellous, J. Regolini, J. P. Reynard, G. Schlatter, and G. Hadziioannou "Study of dynamical formation and shape of microlenses formed by the reflow method", Proc. SPIE 6153, Advances in Resist Technology and Processing XXIII, 61534D (29 March 2006); https://doi.org/10.1117/12.656371

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