Air bubble formation and dissolution in dispensing nanoimprint lithography

Abstract

We report an experimental and theoretical study of two most critical yet still to-be-answered issues in dispensing-based nanoimprint lithography (D-NIL): air bubble formation and absorption, and discuss their impact on NIL yield and throughput. Using real-time observation via video, we found two different mechanisms for air bubble formation (feature pinning and multi-droplet encircling), and studied the dynamic behaviour of the air absorption and air bubble shrinking under different conditions. Furthermore, we developed theoretical models and simulation programs of the air absorption and bubble shrinking based on molecular diffusion theory and hydrodynamics. We compared these models with experiments, and found excellent agreement. Our study shows that the key factors that affect the air dissolution time (and hence the air bubble shrinking time) are air bubble initial size, imprinting pressure, air solubility, and resist residue layer thickness. One of our key conclusions from the study, which has significant practical importance, is that although the air in a bubble can be completely dissolved in a resist liquid as long as the bubble is smaller than a certain size, the air absorption time might be too long for the dispensing-NIL operating in atmosphere or poor vacuum to have a necessary throughput in mass manufacturing.

Simulation and Mitigation of Pattern and Process Dependencies in Nanoimprint Lithography

“…This challenge may be accentuated when many resist droplets are dispensed per pattern, perhaps in an attempt to tailor droplet volumes and/or positions to pattern density variations across the stamp pattern. Entrapped gas takes a finite time to dissolve into the resist before curing can take place, and dissolution of the gas may limit the throughput with which patterns can be imprinted with a particular defect density [13], [14]. Defects arising from entrapped gas are likely to be largely systematic, since uncured resist is usually dispensed in a determined pattern, although we anticipate that random variation in the placement of resist droplets can give a random component to the occurrence of such defects.…”

Nanomanufacturing : nano-structured materials made layer-by-layer.

“…In so doing we take on the unique aspect of accounting for the fate of the displaced gas in the process not only from fluid displacement but from dissolution (cf. work by Liang et al, 2007). In Chapter 3 we address our meso-scale and machine/wafer scale models of the nanoimprint lithography process with a unique blend of numerical algorithms designed to accommodate the governing physics.…”

“…Flows in complex geometries are typically studied using full three-dimensional simulations in a large-scale, unstructured finite element code, such as GOMA [Schunk et al (2006)]. Yet, problems involving thin fluid layers, such as coating flows with tensioned webs [Feng (1998), Nam and Carvalho (2010)] and imprint lithography [Bailey et al (2001), Liang et al (2007), Sreenivasan (2008), Chauhan et al (2009)], may benefit significantly from the mathematical order reduction provided by lubrication theory using shell-type elements within a larger 3-D code. Shell elements have been used for decades in the solid mechanics community for modeling thin materials [Bathe and Dvorkin (1986), Bischoff and Ramm (1997), NguyenThanh2008], but their use in fluid dynamics has been relatively rare [Heil and Pedley (1995)].…”

“…While there have been considerable work on unconfined or multilayer lubrication flows, modeled by the thin film equations [Oron et al (1997)], there have been no computational treatments of confined multiphase lubricating flows together with a free interface across the thin film. Such flows may arise in nanomanufacturing processes [Liang et al (2007), Chauhan et al (2009)], problems involving capillary rise [Taylor (1712), Hauksbee (1712), Higuera2008], and in air entrainment in coating flows [Kistler and Scriven (1984), Coyle et al (1986)]. In continuum, 3-D fluid calculations, the level-set method is commonly used for tracking fluid-fluid interfaces and incorporating the effect of surface tension [Brackbill et al (1992), Kang et al (2000), Sussman (2003), Sussman et al (2007)].…”

Nanoimprint Lithography

“…One of the key conclusions from the study, which has significant practical importance, is that although the air in a bubble can be completely dissolved in a resist liquid as long as the bubble is smaller than a certain size, the air absorption time might be too long for the dispensing-NIL operating in atmosphere or poor vacuum to have a necessary throughput in mass manufacturing. In addition, when the residual layer thickness is close to zero or a critical thickness, the bubble dissolution process can be significantly slowed down (Liang et al, 2007).…”