Polymer deformation and filling modes during microembossing

Abstract

This work investigates the initial stages of polymer deformation during hot embossing micro-manufacturing at processing temperatures near the glass transition temperature (Tg) of polymer films having sufficient thickness such that polymer flow is not supply limited. Several stages of polymer flow can be observed by employing stamp geometries of various widths and varying imprint conditions of time and temperature to modulate polymer viscosity. Experiments investigate conditions affecting cavity filling phenomena, including apparent polymer viscosity. Stamps with periodic ridges of height and width 4 µm and periodicity 30, 50 and 100 µm emboss trenches into polymethyl methacrylate films at Tg − 10 °C < Temboss < Tg + 20 °C. Imprint parameters of time, temperature and load are correlated with replicated polymer shape, height and imprinted area. Polymer replicates are measured by atomic force microscopy and inspected by scanning electron microscopy. Cavity size and the temperature dependence of polymer viscosity significantly influence the nature of polymer deformation in hot embossing micro-manufacturing and must be accounted for in rational process design.

Confinement and flow dynamics in thin polymer films for nanoimprint lithography

“…[10][11][12][13][14] On the other hand, confinement will also directly impact the flow pattern. This parameter is prominent in a number of numerical studies of embossing 15,16 but there is still a good deal of confusion over this issue. On the one hand, some studies of NIL reflow 17,18 completely neglect the direct impact of confinement on flow rate.…”

Impact of polymer film thickness and cavity size on polymer flow during embossing : towards process design rules for nanoimprint lithography.

“…Elastic solid simulations modeled the polymer with the nonlinear stressstrain behavior of a Moony-Rivlin material. The studies showed both single and dual peak flow confined near the master sidewall as described above [6,7], and noted the effect of film thickness to retard deformation. The authors concluded that polymer in NIL shows rubber-like elastic dynamics above T g with volume compression under high loads in thick polymer films, suggesting that the elastic component of polymers plays a large role in deformation even at temperatures well above T g .…”

“…These simulations showed the buckling region was the result of capillary forces acting over the large cavity width, where the polymer preferentially wetted the master surface. When surface tension effects were removed from the simulations, smooth single or dual peaks were observed dependent on cavity width, as observed in viscous flow experiments [6]. Other simulations and experiments [10,11] investigated purely nanometer scale geometries and film thicknesses.…”

“…This system resulted in polymer flow with shear deformation at the mold surface and extensional stretching at the cavity center. Experiments at the micrometer scale [6] studied microembossing with indenter width 2 µm, cavity height 4 µm, and cavity widths 30 µm, 50 µm, and 100 µm and 15 -20 µm thick PMMA films over a temperature range from T g -10 °C to T g + 20 °C. A region of localized high strain occurred near the cavity sidewall, resulting in a deforming polymer peak that spread laterally and vertically to fill the cavity.…”

Development of a multi-layer microelectrofluidic platform

“…Figure 4 showed some typical hot embossing results. The filling mechanism of the cavity was a single-peak mode rather than the dual-peak mode reported in some studies (Heyderman et al 2000;Rowland and King 2004). In the dual-peak mode, the phenomenon was seen under a two-dimensional surface profilometric scan, as two peaks climbing up the cavity walls.…”