DUV Photoresists Research Articles

Novel Photoacid Generators.

A new class of compounds which are non-ionic and halogen-free photo acid generators applicable for g-line, i-line and DUV photoresists is reported. The compounds exhibit high solubility in PGMEA, thermal stability in a phenolic polymer matrix up to 140°C, storage stability below 40°C more than 1 year, red-shifted absorption profile reaching to 490nm, effective acid generation in terms of quantum yield and high sensitivity in resist formulations with various exposure wavelength. An application example of the new photoacid generator for chemically amplified negative resist is presented.

Evaluation of ma-N 2400 series DUV photoresist for electron beam exposure

Several DUV positive and negative tone resists were developed for the photolithography at wavelengths of 248 nm and shorter. Most of these DUV photoresists are sensitive to electron beam exposure, too. In this paper the results of electron beam exposure of the negative tone ma-N 2400 series DUV photoresist will be presented. This resist has no chemical amplification and no critical process steps. Further, the resist provides a good resistivity to plasma etching processes, so that it can be used successfully for etch and lift-off processes. The necessary exposure doses for the resist layers spincoated with thicknesses between 0.3 and 0.8 @mm on silicon wafers were in the range between 60 and 120 @mC/cm^2. The exposed resist was developed with the metal ion free developer MIF 726. Patterns down to the low submicrometer region were generated. Developing properties, sensitivities and resolution of the electron beam exposed ma-N 2400 series resist tested under various conditions will be presented.

Process optimisation of DUV photoresists for electron beam lithography

This paper describes work carried out to optimise two DUV photoresists for high resolution electron beam lithography using experimental design techniques. Shipley UV5 TM positive tone resist and UVN2 negative tone resist have been studied. Screening experiments were initially carried out to identify significant factors influencing processing. For UV5 a Box-Behnken design was carried out and used to produce response surface plots. In-air delay effects were significant for UVN2. Optimised procedures were used to produce 70 nm lines and spaces in 300 nm thick layers of UV5 and discrete lines of 60 nm in 300 nm thick films of UVN2.

Status and future of DUV photoresists for the semiconductor industry

This paper reviews the development of positive DUV resists at IBM and Shipley. The review begins with APEX-E the prototypical chemically amplified positive DUV resist used throughout the semiconductor industry. The paper then follows the emergence of new resist technology to overcome the weaknesses of first generation DUV resists like APEX-E. These improvements include feature-specific resists for low k 1 processing, improved delay stability, improved PEB sensitivity, better etch resistance, and reduced substrate dependence. A new series of annealing type resists, UV5, UV6, and Titan have demonstrated all of these improvements.

High resolution electron beam lithography studies on Shipley chemically amplified DUV resists

The electron beam exposure characteristics of two new Shipley DUV photoresists, UVIII and UVN have been investigated. UVIII is a positive resist which gives good linewidth control down to 100 nm lines and spaces with 60 nm features being possible at a dose of 40 μC/cm2 and a beam voltage of 50 kV. UVN is a negative resist with a sensitivity of 20 μC/cm2 at 50 kV which gives much poorer dimensional control and has an ultimate resolution of 70 nm isolated lines or 140 nm lines and spaces.

DUV resist etch selectivity improvements using UV stabilization

The transition from i-line to DUV (248 nm) processing requires lithography and plasma engineers to address the issue of pattern transfer. The issue of the etch selectivity of DUV photoresists being lower than novolak based i-line photoresists becomes critical at hole and metal levels. Here the selectivity of resist to the substrate are on the order of two or three to one. The traditional approach of just increasing the resist thickness does not become an option as aspect ratios can increase to more than 3.5 for the resist process. A combination of improving the etch selectivity and implementing a stabilization process with DUV resists allows the use of thinner resists. We demonstrate improvements in etch selectivity at the contact level using UV/Bake™ stabilization of the resist films.

Effects of Airborne Molecular Contamination on DUV Photoresists.

This paper will report post-exposure delay results using Shipley UVIBISTM deep UV resist. The variables of the experiments include: processing delays (expose to post-exposure-bake and coat to exposure), different levels of ammonia, different substrates, and processing conditions. Better delay stability is observed when standing waves are reduced by processing. When standing waves are present, scumming tends to occur at the nodes; acid depletion near the nodal region prevents adequate deprotection for development to occur.The methods for detecting airborne contamination are ion mobility spectrometry for ammonia and thermal desorption gas chromatography for 1-methyl-2-pyrrolidone (NMP). Fourier transfer infrared (FFIR) spectroscopy is used to monitor the deprotection reaction of UVIIHS photoresist films with and without delays.

The Lithographic Performance and Contamination Resistance of a New Family of Chemically Amplified DUV Photoresists.

A new contamination resistant 248nm DUV resist (ESCAP-E) has been developed to alleviate the difficulties encountered with the environmental contamination sensitivity of chemically amplified DUV photoresists. The formulation and processing of ESCAP-I; have been designed to permit thermal annealing of resist films to reduce the free volume and diffusivity of airborne contaminants into the resist film. The resist formulation is robust enough to permit post exposure bake delays of up to four hours without change or reduction of resist lithographic performance. The lithographic performance evaluated on 0.50NA 248nm steppers indicates linearity to 0.25μm, excellent exposure latitude and depth of focus.

Some resists based on chemically-amplified crosslinking of phenolic polymers.

Imageable thin films that contain phenolic polymers, acid activated crosslinking agents, and Bronsted acid generators have been developed into a variety of high resolution, high sensitivity resists suitable for use in semiconductor fabrication. Formulations have been optimized for use as DUV photoresists, electron beam resists and X-ray resists. Resists for g- and i-line exposure require the addition of a photosensitizer. Negative imaging versions of these resists contain radiation activated acid generators. Positive imaging versions contain radiation activated base generators and thermally activated acid generators. In either case the imaged resist is crosslinked and stable to temperatures in excess of 200°C.

The growth of semi-insulating gallium arsenide by the LEC process : B. Lent, M. Bonnet, N. Visentin and J. P. Duchemin. Microelectron. J.13 (1), 5 (1982)

Several DUV positive and negative tone resists were developed for the photolithography at wavelengths of 248 nm and shorter. Most of these DUV photoresists are sensitive to electron beam exposure, too.In this paper the results of electron beam exposure of the negative tone ma-N 2400 series DUV photoresist will be presented. This resist has no chemical amplification and no critical process steps. Further, the resist provides a good resistivity to plasma etching processes, so that it can be used successfully for etch and lift-off processes.The necessary exposure doses for the resist layers spincoated with thicknesses between 0.3 and 0.8 μm on silicon wafers were in the range between 60 and 120 μC/cm2. The exposed resist was developed with the metal ion free developer MIF 726. Patterns down to the low submicrometer region were generated.Developing properties, sensitivities and resolution of the electron beam exposed ma-N 2400 series resist tested under various conditions will be presented.