Contrast Enhancement Material Research Articles

Applications of contrast enhancement material to photobleachable deep ultraviolet resist

The applications of a contrast enhancement material, which is composed of 5‐diazo‐meldrum’s acid as a photobleachable reagent, poly(styrene‐co‐maleic acid half‐isopropylate) as a matrix resin, and diethylene glycol dimethyl ether as a solvent, to a photobleachable deep UV resist are presented. The contrast enhancement material with high‐contrast capability was very effective on such a resist, and high‐aspect‐ratio patterns of the resist were successfully obtained. The material characterizations of the contrast enhancement material have been also demonstrated using positive resist optical lithography model (PROLITH).

Characterization of diazonaphthoquinone–novolac resin-type positive photoresist for g-line and i-line exposure using water-soluble contrast enhancement materials

We describe the characterization of conventional diazonaphthoguinone–novolac resin‐type positive photoresist for g‐line (436‐nm) and i‐line (365‐nm) exposure using water‐soluble contrast enhancement materials. In the experiments, the Rayleigh’s theoretical resolution and contrast enhancement capability of the water‐soluble contrast enhancement materials were set to be equal between the each wavelength exposure. As a result, the pattern profiles of the resist were better, however, the latitude of depth of focus was worse for g‐line exposure than for i‐line exposure. Mask linearity had no difference between them. It was found that the improvement of the pattern profiles for i‐line exposure was achieved by using a higher photobleachable photoresist at i‐line.

New Water‐Soluble Contrast Enhancing Material for I‐Line Lithography

A new water‐soluble contrast enhancing material (CEM) has been developed for use with i‐line (365 nm) lithography. The CEM is composed of poly (p‐styrene sulfonic acid), p‐morpholinobenzene diazonium chloride zinc chloride salt and deionized water. The poly (p‐styrene sulfonic acid) effectively prevents degradation of the diazonium salt in water and therefore stabilizes the formulation. Resolutions of 0.5 μm are demonstrated Using conventional photoresist with the water‐soluble CEM. The method is easy to use compared to earlier contrast enhancing materials, in that no barrier coating or special stripping of the CEM is required.

Very large scale integrated pattern registration improvement by photoablation of resist-covered alignment targets

A principal limitation for densely packed, submicrometer very large scale integrated circuits is reproducible registration accuracy. The resist covering the alignment targets is a major contributor to poor and nonreproducible alignment signals. Further, the availability of new imaging materials (contrast enhancing materials and multilayer resists systems) allows for submicrometer production resolution, but with the limitation that the alignment signal may be further degraded. This study presents data on registration improvement resulting from the removal of patterning material covering alignment targets. The patterning materials were removed by photoablation using an excimer laser system operating at 193 nm. The removal involves the illumination of the target area with 10–12 laser pulses of ∼17‐ns duration. During the illumination the contrast enhancing material and resist disintegrate into largely molecular fragments that are scavenged by an air‐bearing nozzle. Electrical probe measurements of polysilicon wafers processed with this technique displayed three‐sigma registration variation of better than 850 Å.

The optimum contrast enhancement layer in microlithography

We have used a microlithographic modeling program to investigate the optimization of a contrast enhancement material (CEM). The CEM parameters were varied over a wide range and for each case the exposure intensity was adjusted to produce a resist profile with the prescribed dimension. The slope of the resist profile constitutes a measure of the contrast and should be as high as possible. We demonstrate the trade-off between maximizing this quantity and keeping the exposure penalty as low as possible. The latitude to exposure variations will also be discussed.

Characterization of a Newly Developed Contrast Enhancement Material for G-line Exposure

The bleaching characteristics for a contrast enhancement layer (CEL) material were succesfully described by parameters A, B and C; these were used for the modeling of a positive photoresist exposure. As a result, it was clarified that both the A and C values should be large, but the B value must be as small as possible. According to the obtained information, a new CEL material was proposed, which consists of the diazonium compound and the alkyl modified phenol resin. Using the composed CEL material, a submicron resist pattern with a steep profile was obtained. Furthermore, it was found that the development latitude increases, but that the exposure latitude does not change upon using the CEL.

Study of half-micron photolithography by means of contrast enhanced lithography process

A simple, but efficient, analysis method has been developed to evaluate material properties, process conditions, and effectiveness of contrast enhanced lithography (CEL). The method, realized as a result of the systematic calculation and concept, is based on the evaluation of the energy transmittance of the contrast enhancing material (CEM). In practical applications of the new method to the design and evaluation of both CEM characteristics and half‐micron contrast enhanced photolithography, the method has been proved to be useful in the precise design as it shows good agreement with experimental results. The study has brought us pieces of important information on such design as the optimum exposure conditions, the ideal CEM characteristics, etc. Based on the information, we have developed a new CEM, water soluble photopolymer (WSP) for i and g lines. Through the simulation, it has been confirmed that the ultimate resolution can be improved by 20% to 30%.

Unidirectional deposition of aluminum using nozzle jet beam technique

We have observed completely nonconformal Al step coverage using nozzle jet expansion deposition technique. In this technique, pure Al was evaporated in a graphite crucible at a temperature up to 1600 °C. The vapor was then ejected through a small nozzle into a vacuum region of 10−6 Torr. The ejected beam was subsequently ionized by electron bombardment and a potential up to several kilovolts was applied to the beam. The SEM micrographs showed no evidence of sidewall coating for vias (1 μm feature size) with almost vertical steps. Liftoff structures were formed using a combination of contrast enhancing material (CEM) and AZ1470. No Al was observed on the photoresist sidewall all across the 3 in. wafer; after liftoff, 0.4 μm clean isolated openings were observed in the Al layer. Metallized contacts 0.3 μm apart and 1 μm in width devoid of ‘‘flags’’ were also obtained. Our computer simulation study indicated that the angular extent of the jet beam source is smaller than a typical electron-beam evaporation source.

Simple algebraic description of photoresist exposure and contrast enhancement

Equations are given that allow the facile calculation of transmittance and concentration profiles for solid photosensitive systems of arbitrary optical absorbance, including absorbing photoproducts and medium. The results are applied to the measurement of resist exposure parameters, the determination of light intensity for a wafer stepper (dosimetry), and the analysis of contrast enhancement materials and other photobleaching image modification techniques.

Simulated performance of a contrast-enhancement material

SAMPLE simulations of the performance of the contrast-enhancement material CEM-388 from General Electric were made using measured material parameters. Addition of an enhancement layer to a single-layer resist process significantly reduces the linewidth variations due to the standing-wave effect. Addition of an enhancement layer to a bilevel resist process containing dye in the bottom layer marginally improves defocus performance.