Enhancing the development rate model in optical lithography simulation of ultrathick resist films for applications such as MEMS and LIGA

Abstract

A development rate model for lithography simulation of extremely thick resist films is presented. Methods used in the extraction of lithographic modelling parameters for simulation packages such as PROLI1'H/2' are examined. The results account for hitherto liule-considered aspects of the development process which, when implemented in the simulations, give good agreement with practical results. Effects examined include the variation in photoresist dissolution properties as a function of depth into the resist film and diffusion of the developer/resist in the spaces surrounding features. These refinements, which are particularly useful for micro-electromechanical systems (MEMS) and lithographie, galvanoformung und abformung (LIGA) applications, can also be applied to conventional lithography in situations where the development models of commercially available software are unable to provide accurate results. The technique also provides a method for quantifying the effectiveness of mechaical, megasonic or ultrasonic agitation during development.Such improvements to the simulation tools should lead to a better understanding of the practical problems encountered and thus to better engineered resist materials.

A three-dimensional microstructuring technique exploiting the positive photoresist property

“…In addition, the measured dissolution rate of the thinlayer thickness might be insufficient if the thick-photoresist dissolution property is considered as the multi-layer thinphotoresist property, because variation of the photoresist properties in the thickness direction (e.g. the influence of solvent gradients or variation of the photoresist properties) becomes non-negligible [44,55,69,70], while the Poor Man's DRM approach is sufficient for the measurement of thick-photoresist dissolution property, because the photoresist development curve is simply measured using a profile meter or a confocal microscope. This development curve takes into account not only the effect of the resultant photochemical reaction on the dissolution rate but also other thicknessdependent effects on the dissolution property, such as UV light refraction in the photoresist layer and reflection at the substrate surface.…”

“…These reports include the characterization of the DNQ photoresist property [33][34][35][36][37], photolithography simulation models [38][39][40][41][42][43][44][45][46][47][48], and so on. In the past few years, a growing number of research groups reported the DNQ photoresist as a thick photoresist for MEMS applications [49][50][51][52][53][54][55][56][57][58][59]. However, compared to the previously reported studies of the DNQ photoresist with thickness of less than 25 μm, the number of publications on 3D thick-photoresist microstructures using more than 25 μm thickness and its detail experimental study is very limited [20,60].…”

Moving mask UV lithography for three-dimensional structuring

“…Over the past few years, several studies have been conducted on lithography process simulation [12] and simulation software for the thin photoresist lithography, such as PROLITH [13] and SOLID [14], which have already been commercialized. However, thick photoresist with micron scale features differs in development characteristics from thin photoresist [15]. Also, difficulty is encountered in simulating sequential development profiles of a 3D resist microstructure having a thickness of several tens of microns, due to the lack of a proper exposure and development model.…”