Numerical analyses of peel demolding for UV embossing of high aspect ratio micro-patterning

Abstract

Ultraviolet (UV) embossing, involving molding against micro-structured molds, is a quick and efficient method to mass produce high aspect ratio micro-features. A crucial challenge to the repeatability and large-scale application of this technique is successful demolding, which escalates in difficulty with increasing aspect ratio, due to increased polymer-mold mechanical interlocking. Some of the key factors affecting UV embossing include the crosslinked polymer shrinkage and material properties, interfacial strength between polymer to mold and the demolding method. This paper presents a new method to simulate the demolding of UV cured polymer from a nickel mold. Hyperelastic material model and rate-independent cohesive zone modeling were employed in the numerical simulation; linear elastic polymer response, although relatively easy to apply, was not adequate. Progressive shrinkage was implemented, leading to delamination of the polymer-mold interface. The subsequent peeling of the cured polymer from the mold was modeled with increasing prescribed displacement. The optimal shrinkage degree was found to increase from 0.92 to 1.9% with increasing mold aspect ratio (aspect ratio is defined as height to width ratio) from 5 to 10.

A Simulation Study on the Effect of Cross-Linking Agent Concentration for Defect Tolerant Demolding in UV Nanoimprint Lithography

“…In the first step following the works of Chan-Park, Yeo, and Shibata, thermal contraction was used to simulate polymerization shrinkage caused by UV curing of the resist. A pseudothermal expansion coefficient was assigned only to the resist and the equivalent shrinkage strain (measured from the experiment) was applied by cooling down the assembly to an appropriate temperature.…”

“…Friction can be ignored, however, if lateral shrinkage of the resist breaks the resist free of the stamp sidewalls eliminating contact during demolding. 53,54 In our study in order to obtain more accurate results, friction was not ignored. To obtain friction coefficients at the resist/stamp interface, friction force microscopy was conducted using a commercial atomic force microscopy (AFM, Agilent 5500).…”

“…Therefore, on the vertical sidewalls friction has to be overcome to advance and complete interfacial debonding. Friction can be ignored, however, if lateral shrinkage of the resist breaks the resist free of the stamp sidewalls eliminating contact during demolding. , …”

Recent progress in fabrication methods for micro structures on optical thin film

“…Amirsadeghi [27] [33] 研究了交联收缩、 固化材料模量、交界破坏强度和韧性以及脱模的加载 方式对脱模应力的影响, 获得了实现最小主应力的最 优收缩量. Yeo等人 [34] 运用超弹性材料模型建立了率 无关内聚力模型, 研究了深宽比为14的微细结构的脱 膜工艺, 优化了脱模过程并获得了最优收缩量.…”

Characterizing mechanical behaviors of a flexible AMOLED during the debonding process

“…Their results showed that interfacial delamination of the organic and inorganic layers is predominant when short cracks form between the layers; at considerable crack lengths, failure results mainly from channel cracking in the inorganic layer. Yeo et al (2009) employed numerical simulations for determining the microstructural stresses exerted during peel demolding in the ultraviolet embossing process. Cohesive zone modeling was used to model the interface between the resin and the mold.…”