The negative tone photoresist SU-8 permits the creation of micrometer-scale structures by optical lithography. It is also the most used photoresist in soft lithography for the fast-prototyping of microfluidic devices. Despite its importance, the effect of capillary forces on SU-8 multi-layering onto topographical features has not been thoroughly studied. In particular, the profile of the added layer has not been examined in detail. The overlaying process exhibits a set of distinct behaviors, or regimes, depending on the relative thickness of the overlay and the underlying rectangular pattern. We demonstrate how capillary effects control the profile of multi-layer microchannels in a predictable manner. We derive a simple static model to describe the evolution of the overlay as a function of dimensionless geometric parameters. Our study provides a critical understanding of the parameters that govern multi-layer spin coating.

中文翻译：

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SU-8的多层显示出从圆形轮廓到平面轮廓的独特几何过渡。

负性光刻胶SU-8允许通过光刻形成微米级的结构。它也是软光刻中最常用于微流控设备快速原型制作的光刻胶。尽管它很重要，但毛细作用力对SU-8多层地形特征的影响尚未得到充分研究。特别地，未详细检查添加层的轮廓。取决于覆盖层的相对厚度和下面的矩形图案，覆盖过程展示出一组不同的行为或方式。我们演示了毛细管效应如何以可预测的方式控制多层微通道的轮廓。我们推导了一个简单的静态模型来描述覆盖层随无量纲几何参数的变化。