Beyond contrast curve approach: a grayscale model applied to sub-5µm patterns

Pierre Chevalier; Patrick Quéméré; Charlotte Beylier; Sébastien Bérard-Bergery; Nacima Allouti; Marion Paris; Vincent Farys; Jérôme Vaillant

doi:10.1117/12.2514234

26 March 2019 Beyond contrast curve approach: a grayscale model applied to sub-5μm patterns

Pierre Chevalier, Patrick Quéméré, Charlotte Beylier, Sébastien Bérard-Bergery, Nacima Allouti, Marion Paris, Vincent Farys, Jérôme Vaillant

Author Affiliations +

Proceedings Volume 10958, Novel Patterning Technologies for Semiconductors, MEMS/NEMS, and MOEMS 2019; 109581E (2019) https://doi.org/10.1117/12.2514234
Event: SPIE Advanced Lithography, 2019, San Jose, California, United States

Abstract

CMOS imaging has experienced significant developement in the last decades. At the center of this progress lies the pixel, composed of a light sensitive area (photodiode) coupled to a network of transistors. As the pixels sizes shrink, the light sensitive area gets smaller and requires light focusing assistance. To address this issue, microlenses are added to the top of the pixels stack. The microlenses are made of polymer resist transparent to the wavelength of interest. Creating such structures is not straightforward and requires complex process steps, especially when arrays of multiple shapes and sizes are needed. The grayscale approach appears as a promising alternative since this unconventional lithography method can produce variable shapes and sizes in a single lithography step. Mask data preparation is the most critical step for grayscale lithography. A widespread strategy is to experimentally establish the relationship between a given dose (corresponding to a specific chromium density on the mask) and the remaining resist thickness after development. The relationship, also known as contrast curve, is used as a transfer function to compute a suitable mask for the given resist. Our approach is to create a simplified grayscale model able to predict the resist response under any given mask and illumination condition. Using the classic contrast curve approach we have designed a mask composed of sub 5μm patterns and evaluated the resist profile prediction of the contrast curve approach compared to our grayscale model on various patterns including microlenses, pyramids and bowl shapes. Reults show that the contrast curve approach is no longer appropriate when the dimensions reduce below 5μm.

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Pierre Chevalier, Patrick Quéméré, Charlotte Beylier, Sébastien Bérard-Bergery, Nacima Allouti, Marion Paris, Vincent Farys, and Jérôme Vaillant "Beyond contrast curve approach: a grayscale model applied to sub-5μm patterns", Proc. SPIE 10958, Novel Patterning Technologies for Semiconductors, MEMS/NEMS, and MOEMS 2019, 109581E (26 March 2019); https://doi.org/10.1117/12.2514234

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