Nam-Goo Cha

Evaluation of Vacuum Venting for Micro-injection Molding

Abstract While the effect of vacuum venting has been reported for injection molding of micro and nanoscale features, the limited research has produced conflicting results. To clarify the positive effect of vacuum venting on replication of microscale features, this work focused on the interactions between vacuum venting and (1) feature size, (2) material type in terms of melt viscosity and wettability, and (3) injection velocity and mold temperature. A metal-polymer hybrid tooling with a range of positive microscale features was employed to mold polystyrene and polymethylmethacrylate parts. Overall, vacuum venting always effective in feature definition (sharpness of edges) enhancement, but provided increases in depth ratio that depended on material (melt viscosity and wettability) and processing conditions (i.e., injection velocity, and mold temperature).

Enhancement of surface replication by gas assisted microinjection moulding

Abstract Achieving perfect replication of micro- and nanostructured surfaces without creating sink marks in the parts is challenging. Therefore, gas assisted injection moulding (GAIM) was investigated as a method to enhance moulding quality in polypropylene, polymethylmethacrylate (PMMA) and thermoplastic polyurethane (TPU) parts. For all three polymers, the GAIM did not improve replication (depth ratios) of low aspect ratio microfeatures moulded using tooling with positive features, but did significantly enhance replication of higher aspect ratio trenches and tapered holes. The enhanced replication was attributed to better filling, and with the semicrystalline polymer, significantly less shrinkage. GAIM sometimes enhanced the edge definition of the features, and as expected, reduced sink marks in the polypropylene surfaces.

Development of the Large-area Au/Pd Transfer-printing Process Applying Both the Anti-Adhesion and Adhesion Layers

This paper describes an improved strategy for controlling the adhesion force using both the antiadhesion and adhesion layers for a successful large-area transfer process. An MPTMS (3-mercaptopropyltrimethoxysilane) monolayer as an adhesion layer for Au/Pd thin films was deposited on Si substrates by vapor self assembly monolayer (VSAM) method. Contact angle, surface energy, film thickness, friction force, and roughness were considered for finding the optimized conditions. The sputtered Au/Pd (17 nm) layer on the PDMS stamp without the anti-adhesion layer showed poor transfer results due to the high adhesion between sputtered Au/Pd and PDMS. In order to reduce the adhesion between Au/Pd and PDMS, an anti-adhesion monolayer was coated on the PDMS stamp using FOTS (perfluorooctyltrichlorosilane) after plasma treatment. The transfer process with the anti-adhesion layer gave good transfer results over a large area (20 mm 20 mm) without pattern loss or distortion. To investigate the applied pressure effect, the PDMS stamp was sandwiched after 90 rotation on the MPTMS-coated patterned Si substrate with 1- depth. The sputtered Au/Pd was transferred onto the contact area, making square metal patterns on the top of the patterned Si structures. Applying low pressure helped to remove voids and to make conformal contact; however, high pressure yielded irregular transfer results due to PDMS stamp deformation. One of key parameters to success of this transfer process is the controllability of the adhesion force between the stamp and the target substrate. This technique offers high reliability during the transfer process, which suggests a potential building method for future functional structures.

Deposition and Characterization of Antistiction Layer for Nanoimprint Lithography by VSAM (Vapor Self Assembly Monolayer)

Nanoimprint lithography (NIL) is a new lithographic method that offers a sub-10nm feature size, high throughput, and low cost. One of the most serious problems of NIL is the stiction between mold and resist. The antistiction layer coating is very effective to prevent this stiction and ensure the successful NIL results. In this paper, an antistiction layer was deposited by VSAM (vapor self assembly monolayer) method on silicon samples with FOTS (perfluoroctyltrichlorosilane) as a precursor for making an antistiction layer. A specially designed LPCVD (low pressure chemical vapor deposition) was used for this experiment. All experiments were achieved after removing the humidity. First, the evaporation test of FOTS was performed for checking the evaporation temperature at low pressure. FOTS was evaporated at 5 Tow and . In order to evaluate the temperature effect on antistiction layer, chamber temperature was changed from 50 to with 0.1ml of FOTS for 1 minute. Good hydrophobicity of all samples was shown at about of contact angle and under of hysteresis. The surface energies of all samples calculated by Lewis acid/base theory was shown to be about 15mN/m. The deposited thicknesses of all samples measured by ellipsometry were almost 1nm that was similar value of the calculated molecular length. The surface roughness of all samples was not changed after deposition but the friction force showed relatively high values and deviations deposited at under . Also the white circles were founded in LFM images under . High friction forces were guessed based on this irregular deposition. The optimized VSAM process for FOTS was achieved at , 5 Torr for 1 hour. The hot embossing process with 4 inch Si mold was successfully achieved after VSAM deposition.

Fabrication and Characterization of an Antistiction Layer by PECVD (plasma enhanced chemical vapor deposition) for Metal Stamps

【Nanoimprint lithography (NIL) is a novel method of fabricating nanometer scale patterns. It is a simple process with low cost, high throughput and resolution. NIL creates patterns by mechanical deformation of an imprint resist and physical contact process. The imprint resist is typically a monomer or polymer formulation that is cured by heat or UV light during the imprinting process. Stiction between the resist and the stamp is resulted from this physical contact process. Stiction issue is more important in the stamps including narrow pattern size and wide area. Therefore, the antistiction layer coating is very effective to prevent this problem and ensure successful NIL. In this paper, an antistiction layer was deposited and characterized by PECVD (plasma enhanced chemical vapor deposition) method for metal stamps. Deposition rates of an antistiction layer on Si and Ni substrates were in proportion to deposited time and 3.4 nm/min and 2.5 nm/min, respectively. A 50 nm thick antistiction layer showed 90% relative transmittance at 365 nm wavelength. Contact angle result showed good hydrophobicity over 105 degree.

Effect of processing parameters, antistiction coatings, and polymer type when injection molding microfeatures

CF_2

Methods for forming metal-polymer hybrid tooling for forming parts having micro features

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Fabrication of nano- and micro-scale UV imprint stamp using diamond-like carbon coating technology.

CF_3

Chemical and Nanomechanical Characteristics of Fluorocarbon Thin Films Deposited by Using Plasma Enhanced Chemical Vapor Deposition

peaks were founded in ATR-FTIR analysis. The thicknesses and the contact angle of a 50 nm thick antistiction film were slightly changed during chemical resistance test using acetone and sulfuric acid. To evaluate the deposited antistiction layer, a 50 nm thick film was coated on a stainless steel stamp made by wet etching process. A PMMA substrate was successfully imprinting without pattern degradations by the stainless steel stamp with an antistiction layer. The test result shows that antistiction layer coating is very effective for NIL.】