Impact of resist shrinkage on the template release process in nanoimprint lithography

Abstract

Template release in nanoimprint lithography was computationally studied. The impact of resist shrinkage on template release load is described. The resist shrinkage affects the state of the boundary status between resist and template, and is a factor that influences whether the resist adheres to or separates from the template. When the resist fully adheres to the template, the release load increases due to residual stress as the residual layer becomes thinner. This is because compressive stress at the residual layer is induced by resist shrinkage in the pattern cavity. In addition, the release load increases when the resist partially adheres to the template, a consequence of the decrease in interfacial area. This is because the decrement of interface area due to concentration of stress.

Interfacial Interactions during Demolding in Nanoimprint Lithography

“…Simulations are useful investigation tools for revealing the physics behind the lithography technique and optimizing the NIL process parameters [ 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 ]. Computational simulation helps to facilitate a better understanding of the details of the demolding process that may not be easily revealed by experiments (e.g., stress distributions in the resist during demolding), which is essential for optimizing the NIL process.…”

“…Assuming a small linear shrinkage (e.g., 0.5%) upon curing (i.e., resist still fully adheres to the mold), the volume shrinkage of the resist within the pattern cavity pulls down the mold, which induces a compressive stress in the residual layer ( Figure 4 ). This compressive stress decreases as the residual layer thickness increases, and therefore, the increased residual layer thickness is effective in reducing the demolding load [ 54 ].…”

“…The polymerization primarily reveals a vertical densification, which is somewhat decreasing with increasing pattern aspect ratio (i.e., larger features exhibit more contraction), possibly because the lateral shrinkage strain is fixed at the interface between the cured resist and the rigid silicon substrate [ 51 , 62 ]. In contrast, Tochino et al reported that the stress induced near the sidewall of the resist is generally larger than that at the upper wall [ 54 ]. Nevertheless, both vertical and lateral components of the shrinkage displacements require further investigations due to their impacts on the demolding process.…”

“…Nevertheless, both vertical and lateral components of the shrinkage displacements require further investigations due to their impacts on the demolding process. The compressive stress is also large in the residual layer [ 52 , 54 ], which induces squeezing stress toward the pattern sidewalls [ 63 , 64 , 65 , 66 ].…”

“…A major issue in the NIL process is the high defect rate as a result of mechanical pressing, which causes difficult demolding [ 50 , 54 , 108 ], as also briefly discussed in the previous sections. The adhesion and the lateral and friction forces [ 109 ] that originate during imprinting cause the fracture of the mold and/or the resist [ 50 ], as well as strong adhesion between the mold and the resist [ 89 , 90 ].…”