Polycarbonate Heat Molding for Soft Lithography

Abstract

wafers. This type of fabrication requires user expertise to be successful as most of the steps are manual, are associated with high material and equipment costs, demand specialized facilities that may not be available to everyone, and are challenging for mass fabrication. This creates a barrier for the utilization and adaptation of this technology especially for nonexperts and also can cause issues for the commercialization of the products fabricated through this approach. [5] Furthermore, soft lithography has also been challenging because of problems related to the properties of the master molds. The composite nature of Si-Pr master molds results in limited casting lifetime. The differences between the thermal expansion coefficient of the photoresist and the silicon layers result in thermal stress and consequent delamination after a number of heating-cooling cycles. [6] This issue becomes more prominent when thicker photoresist layers with high-aspect-ratio features are present in the master mold. Fabrication of Si-Pr master molds with highaspect-ratio features also poses additional problems such as the repeatability of the uniformity of spin-coating thickness, challenges associated with developing high-aspect ratio indentations (e.g., trenches), and poor adhesion between crosslinked photoresist and silicon wafers. Furthermore, damage can occur in high-aspect ratio features during the manual peeling of the cured PDMS from the mold, which is frequently experienced during the PDMS replica molding process. Such issues render Si-Pr master molds fragile and not particularly robust.To overcome the issues associated with Si-Pr master molds, several other master mold fabrication techniques have been used including mechanical micromilling and 3D printing. Mechanical micromilling allows for fabrication of high-resolution master molds on a diversity of substrates automatically through computer-aided manufacturing (CAM) software and automated stages. [7] However, mechanical micromilling also requires sophisticated tools and expensive equipment, cannot be scaled up for mass production easily, and fabrication parameters are needed to be optimized for each substrate type and geometry. Also, the aspect ratio of the trenches and microwells are limited due to micro end mill failure [8] along with the inability of the milling process to produce sharp inner corners. [7] Another approach is 3D printing in the additive manufacturing domain, which has been improving its ability to create more complex master mold geometries with automation in shorter time periods. [9,10] However, this approach is limited in its feature Soft lithography enables rapid microfabrication of many types of micro systems by replica molding elastomers into master molds. However, master molds can be very costly, hard to fabricate, vulnerable to damage, and have limited casting life. Here, an approach for the multiplication of master molds into monolithic thermoplastic sheets for further soft lithographic fabrication is introduced. The technique is tested with ma...

Benchtop One‐to‐One Nanocontact Replication Across Length Scales from 100 nm to 10 cm via Ambient Polycarbonate Molding

“…Fast and economic replication of masters will enable researchers to scale up fabrication by multiplexing and share their designs, whereas the relative simplicity of our protocol will help promote interdisciplinary work that relies on such masters. In comparison with concurrent exploration of heat molding with PDMS to create PC replicas by Sonmez et al, [ 16 ] our solvent‐assistant replication protocol is even faster, less reliant on specialized apparatus, and has a better resolution.…”

“…[ 14,15 ] It has been recently adapted for making one‐to‐one replicas of lithographically fabricated masters by thermally molding PDMS negatives. [ 16 ] Sub‐nanometer patterns have been also imprinted into polyurethane (PU) by exposing uncured prepolymer to UV light while in conformal contact with a “master.” [ 17,18 ]…”

Polycarbonate Masters for Soft Lithography

“…However, such masters are expensive, require curing equipment, and large-area fabrication may be challenging due to the need for a uniform UV illumination [8]. Further, during the pouring and the degassing steps, the PDMS micro features, especially high aspect ratio ones, can get distorted by the instantaneous drag force exerted on them by the uncured polymer [12]. Moreover, some UV curable resins have low heat deflection temperature that imposes a constraint on the PDMS curing temperature, increasing the curing time and reducing the fabrication throughput [12].…”

“…Further, during the pouring and the degassing steps, the PDMS micro features, especially high aspect ratio ones, can get distorted by the instantaneous drag force exerted on them by the uncured polymer [12]. Moreover, some UV curable resins have low heat deflection temperature that imposes a constraint on the PDMS curing temperature, increasing the curing time and reducing the fabrication throughput [12]. Ultimately, polyurethane solutions cannot be degassed after being poured on the PDMS mold [8].…”

Multi-step proportional miniaturization to sub-micron dimensions using pre-stressed polymer films

“…We applied this new capability to fabricate patterns in a silicon wafer that can be used as a functional substrate for many applications such as diffraction grating based sensors 14,15 or as a master template for so lithography applications. 16,17…”