Michael P. C. Watts

Step and Repeat UV nanoimprint lithography tools and processes

Step and FlashTM Imprint Lithography (S-FILTM) process is a step and repeat nano-replication technique based on UV curable low viscosity liquids. Molecular Imprints, Inc. (MII) develops commercial tools that practice the S-FIL process. The current status of the S-FIL tool and process technology is presented in this paper. The specific topics that are covered include: • Residual layer control • Etch process development • Patterning of lines, contacts and posts • CD control • Defect and process life • Alignment and magnification control

Development of imprint materials for the Step and Flash Imprint Lithography process

The Step and Flash Imprint Lithography (S-FILTM) process is a step and repeat nano-replication technique based on UV curable low viscosity liquids. Molecular Imprints, Inc. (MII) develops commercial tools that practice the S-FIL process. This talk will present the imprint materials that have been developed to specifically address the issue of process life and defects. The S-FIL process involves field-to-field dispensing of low viscosity (<5 cps) UV cross-linkable monomer mixtures. The low viscosity liquid leads to important advantages that include: • Insensitivity to pattern density variations • Improved template life due to a lubricated template-wafer interface avoids “hard contact” between template and wafer • Possibility for lubricated (in-situ) high-resolution alignment corrections prior to UV exposure The materials that are optimal for use in the S-FIL process need to possess optimal wetting characteristics, low evaporation, no phase separation, excellent polymer mechanical properties to avoid cohesive failure in the cured material, low adhesion to the template, and high adhesion to the underlying substrate. Over 300 formulations of acrylate based monomer mixtures were developed and studied. The imprint materials were deemed satisfactory based on the process of surviving imprinting more than 1500 imprints without the imprints developing systematic or repeating defects. For the purpose of these process studies, printing of sub-100 nm pillars and contacts is used since they represent the two extreme cases of patterning challenge: pillars are most likely to lead to cohesive failure in the material; and contacts are most likely to lead to mechanical failure of the template structures.

Design and performance of a step and repeat imprinting machine

Molecular Imprints, Inc. (MII) has developed the ImprioTM 100, which is the first commercial step and repeat imprint lithography system with field-to-field alignment. This system is designed to implement the UV curable nano-replication capability of the Step and FlashTM Imprint Lithography (S-FILTM) process. To-date, the Imprio 100 system has demonstrated: 1) Full 200 mm wafer coverage with lithographically useful patterning; 2) Full wafer residual thickness control to enable practical etching (thickness variation < 50 nm, 3 sigma); 3) Field edge control compatible with 50 um kerf regions. 4) Multi-day CD uniformity measured on an analytical SEM < 2 nm, 3 sigma with no process adjustments; 5) Etch pattern transfer including break-through etch of residual material, followed by a bi-layer etch through thick planarization layers; 6) Initial level-to-level alignment target acquisition with accuracy of better than 100 nm. 7) Low air borne particle counts in tool microenvironment consistent with Class 0.1 while imprinting.

Fabrication of nanometer sized features on non-flat substrates using a nano-imprint lithography process

The Step and Flash Imprint Lithography (S-FILTM) process is a step and repeat nano-imprint lithography (NIL) technique based on UV curable low viscosity liquids. Generally nano-imprint lithography (NIL) is a negative acting process which makes an exact replica of the imprint mold and is subsequently dry developed to reveal the underlying substrate material. The authors have demonstrated a novel imprint process, which reverses the tone of the imprint and enables dry develop on nonflat wafers with good critical dimension control and resist layer thickness. This positive acting NIL process termed SFIL/RTM (reverse tone S-FIL), enables nano-imprinting over intrinsic substrate topology of the type commonly found on single side polished substrates. This paper describes the SFIL/R process and the results of pattern transfer on single side polished silicon wafers.

Fabrication of nano and micro optical elements by step and flash imprint lithography

The Step and Flash Imprint Lithography (S-FILTM) process is a step and repeat nano-imprint lithography (NIL) technique based on UV curable low viscosity liquids.1,2,3Investigation by this group and others has shown that the resolution of replication by imprint lithography is limited only by the size of the structures that can be created on the template (mold). S-FIL uses field-to-field drop dispensing of UV curable liquids for step and repeat patterning. This approach allows for micro and nano-fabrication of devices with widely varying pattern densities and complicated structures. Wire grid polarizers and micro lenses are two examples for optical components that can be formed using SFIL technology. Step and Flash Imprint Lithography Reverse (S-FIL/R) tone has been used to form resist patterns for a number of different device types 1,4,6. The authors have employed S-FIL/R and dry develop techniques to form resist patterns with 100 nm period useful for the fabrication of wire grid polarizers. S-FIL/R has a number of advantages over interference lithography techniques for the fabrication of sub 200 nm period grating structures including but no limited to pattern repeatability, vibration insensitivity, high aspect ratio feature formation, greater extendibility and high resolution. The authors have devised imprint and dry etching processes for resist and substrate patterning to form Al based wire grid polarizers with 100 nm pitch. The fabrication processes and resulting devises will be described. While S-FIL is useful for in the formation of resist patterned wafers, it is also capable of forming devices by functional material patterning. Polymer micro lenses are a good examples of functional material devices useful for a number of applications including CMOS and CCD cameras. The fact that lens geometry is defined by the template and requires no post imprint processing provides a strong advantage over current lens formation approaches. Recent results and the state of current micro lens fabrication by S-FIL is described.

Status of Step and Flash Imprint Lithography tools and processes

The Step and Flash/sup TM/ Imprint Lithography (S-FIL/sup TM/) process is a step and repeat nanoreplication technique based on UV curable low viscosity liquids. This article discusses various process capability of S-FIL including imprint resolution and line edge roughness; field-to-field CD control; imprinted film thickness uniformity; process life and defect data; and overlay alignment accuracy.