Yoshiyuki Tani

ArF quarter-micron projection lithography with an aspherical lens system

Abstract A 5X aspherical refractive lens with 60% transmittance at 193 nm wavelength was successfully designed by decreasing the thickness of the lens material. An ArF excimer laser lithographic tool was constructed by the same concept as KrF excimer laser stepper except an aspherical lens was used to demonstrate 0.25 μ m resolution. 0.25 μ m line and space patterns could be resolved using 0.5 μ m thick PMMA.

Quarter micron KrF excimer laser lithography

For quarter-micron KrF excimer laser lithography, a chemically amplified positive resist with high stability and process compatibility has been developed. 0.25- mu m line and space patterns and 0.35- mu m contact hole patterns have been obtained using this resist. The multiple interference effect due to reflection from air and substrate is reduced by using an overcoat film or antireflective coating. The overcoat film is made of a water-soluble polyvinylalcohol derivative. The refractive index of this polymer is 1.3, which is suitable for the resist (index

Optimization of Amorphous Carbon-Deposited Antireflective Layer for Advanced Lithography

Critical dimension variation due to the multiple interference effect is the greatest problem for improving the actual resolution limit in optical lithography. To overcome this problem, amorphous carbon-deposited antireflective layer has been developed. This paper reports on the results of optimization for the antireflective layer film and application to advanced lithography. First, we optimized the deposition process of antireflective layer by measuring the reflectivity. Second, we applied the antireflective layer films in i-line (365 nm) and KrF excimer laser (248 nm) lithography. With the antireflective layer films, the reflectivity from the substrate reduces to less than 20%, which leads to a multiple interference effect of less than 1/7. With optimized antireflective layer films, resolution and depth-of-focus are almost same as those of the films without antireflective layer.

Application of Photobleachable Positive Resist and Contrast Enhancement Material to KrF Excimer Laser Lithography

In this paper, we present the application of photobleachable positive deep-UV resist and contrast enhancement material (CEM) to KrF excimer laser lithography. The effects of the photobleaching characteristics of the resist and CEM on the resist pattern angles and profiles were examined and optimization of these materials was performed. High-aspect-ratio 0.5 µm-line-and-space patterns were successfully obtained by optimization of the materials. PROLITH (positive resist optical lithography model) has excellently reproduced actual pattern profiles.

Evaluation of resists using ArF excimer laser projection lithography

In order to study the feasibility of ArF excimer laser lithography, we developed the projection system installing a refractive 5X reduction lens. We investigated a pattern fabrication by using several resists and this ArF excimer exposure system. Quarter-micron patterns have been fabricated by using newly developed ArF excimer laser projection system with refractive-projection lenses of monochromatic-spherical and monochromatic-aspherical type. Speckle-free line and space patterns below 0.25 micron with excellent quality have been obtained by aspherical lens. In conclusion, ArF excimer laser lithography has been confirmed as an effective technology to fabricate quarter micron patterns. Furthermore, ArF excimer laser lithography is feasible using a modified KrF excimer laser lithography system. However, ArF excimer laser lithography needs a suitable resist material. And also, we study about fundamental resist materials for ArF excimer laser lithography.

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).

A New Positive Resist for KrF Excimer Laser Lithography

Photolithography using KrF excimer laser (248 nm) is the most exciting technology which has the capability of resolution below 0.5 pm. However good profiles of resist patterns are not obtained by the KrF excimer laser lithography because of strong absorption of conventional deep UV resist such as naphtoquinonediazide-novolac resin type. In order to resolve this problem, a new positive resist (STAR-P) for KrF excimer laser lithography has been developed. This resist is composed of 2-diazo-1,3-dicarbonyl compounds for a sensitizer, which is an alkaline dissolution inhibitor for base polymer, poly (stylene-co-maleic acid half ester) as a base polymer, and diethylene glycol dimethyl ester as a coating solvent. 2-diazo-1,3-dicarbonyl compounds have a strong absorption peak at around 248nm, and are effectively bleached by KrF excimer laser exposure. Moreover, the transmittance of base polymer at 1.0pm thickness is 70% at 248nm. In this study, the photobleachability, thermal stability and inhibition of these sensitizers were evaluated on several 2-diazo-1,3-dicarbonyl compounds which had different substuents. The resolution of these resists were evaluated by a KrF excimer laser stepper system (NA:0.36). The new resist with 1,7-bis(3-chlorosulfony1-4-methyl phenyl)-4-diazo-3,5-heptanedione as sensitizer (STAR-P2) shows the best results. Strong photobleaching occurred at around. 248 nm by KrF excimer laser exposure. The loss of resist thickness at unexposed regions after developing was hardly observed. It was found that chlorosulfonyl groups have a superior capacity for alkaline inhibition. Gamma (γ) value was 2.71, and it was much higher than that of conventional positive resist of naphtoquinonediazide-novolac resin type (1.05). High aspect ratio sub-micron patterns were obtained in spite of the 1.Oμm resist thickness. In conclusion, a new positive resist for KrF excimer laser lithography has been developed. As STAR-P2 has excellent photobleachability for the KrF excimer laser exposure, high aspect ratio patterns can be attained at 1pm thickness. A new single-layer-resist system for KrF excimer laser lithography is realized by using this new resist (STAR-P2).

Evaluation of resist materials for KrF excimer laser lithography

Good resist patterns are not obtained for KrF excimer laser lithography using conventional naphtoquinonediazide novalac resin deep UV resist because of the strong photoabsorption of the resist at 248nm wavelength. In this paper we report the development of new high transparency positive resists, STAR-P and MASTER, using poly(styrene-co-maleic acid half ester) base polymer and sensitizers. These resists have excellent transmittance as high as 70% and photobleaching characteristics resulting in resolution of 0.45 micron with excellent pattern profiles with greater than 80 degree wall angle. These resists also have excellent dry etch resistance comparable to conventional novolac resist during silicon dioxide etch. These resists are good candidates for development and manufacturing of sub-half micron VLSI devices.

Application of photoacid generating chemistry to photobleachable deep‐ultraviolet resist

The high optical density of the conventional positive resist in the deep UV region (190 nm to 300 nm) prevents its use in the fabrication of high contrast patterns. The photobleachable deep UV resist composed of a 1,3‐dicarbonyl‐2‐diazo compound as the alkaline dissolution inhibitor and an alkaline‐soluble styrene polymer as the resin matrix, which we developed, is one promising approach to resolve these problems. Using this resist, high contrast 0.5 μm patterns were obtained with a KrF excimer laser stepper. In this paper, we have applied photoacid generators to such photobleachable resists. The photoacid generator used was triphenylsulfonium hexafluoroarsenate, and it greatly enhanced the sensitivity and contrast of the resist. The decomposition of diazo compound in the resist was significantly enhanced (and the dissolution characteristics improved) in the presence of the onium salt. This novel positive resist utilizing chemical amplification more than meets the requirements for KrF excimer laser lithog...

New Pattern Transfer Technology For G-line Lithography

New pattern transfer technology for G-line lithography has been developed. G-line lithography using steppers have become the main tool in the production of submicron design rule VLSI. To adapt G-line lithography for half-micron design rule VLSI production, we have developed new and simple pattern transfer technology. High contrast patterns and resolution were obtained in this technology. This was achieved by using a soak process to treat the resist surface before exposure in the conventional resist process. The surface treatment was done by dipping the wafer in a solution of tetramethyl ammonium hydroxide(TMAH) rather than a chlorobenzene solution. And also, we combined with new pattern transfer technology with CEL (contrast enhanced lithography) to control the aerial image. The resists were imaged by using G-line steppers with NA value of 0.54 and 0.45. The positive photoresists used were S1400(Shipley), TSMR-Vl(Tokyo Ohka) and TSMR-CRB2(Tokyo Ohka dyed resist). A conventional developer for positive photoresist was used for the surface treatment by TMAH alkaline solution. In this process, we have evaluated the baking step either before or after the image exposure in the conventional process in order to compare pattern profiles.