Masaru Sasago

Resist interaction in 193-/157-nm immersion lithography

We have investigated the interaction of resists with water and perfluoropolyether (PFPE) as immersion fluids. We found that some unique behaviors occurred in immersion lithography. An acetal protected poly(p-hydroxystyrene) type resist in water immersion showed decreased resist thickness after exposure. The deprotection reaction during exposure appeared to be accelerated by water. A COMA (cycloolefine-mareic anhydride alt-copolymer) type resist in water immersion showed an increased dissolution rate. FT-IR measurements indicated that the hydrolysis of maleic anhydride occurred during exposure and post-exposure baking. A reduction in the dissolution rate was observed in the immersion lithography of most resists. In water immersion, the formation of a surface insoluble layer and swelling was observed. We confirmed that a photochemical acid generator (PAG) or generated acid eluted into the water by TOF-SIMS. In PFPE immersion, we think that PFPE penetrating across the resist film blocks the penetration of the alkaline aqueous developer.

Half-Micron KrF Excimer Laser Stepper Lithography With New Resist And Water-Soluble Contrast Enhanced Materials

Half-micron patterns have been fabricated using a newly developed high-speed KrF excimer laser stepper system with new resist, NOEL (Novolak based resist for Excimer Laser), and water-soluble contrast enhanced material, WSP-EX.

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

Improved Bilayer Resist System Using Contrast-Enhanced Lithography With Water-Soluble Photopolymer

A new water-soluble contract enhanced material, WSP (Water-soluble Photopolymer), has been developed. The WSP is composed of a mainpolymer and a photobleachable reagents. The mainpolymer is a water-soluble polymer mixed with pullulan (refined through biotechnological process) and polyvinyl-pyrolidone (PVP). The photo-bleachable reagent is of a diazonium compound gorup. The introduction of the mainpolymer and photobleach-able reagent mixture has improved filmity, gas transparency, photobleaching characteristics and solubility in alkaline which are essential to the device fabrication. Submicron photoresist patterns are successfully fabricated by a simple sequence of photolithography process. The WSP layer has been applied to the bilayer resist system--deep-UV portable conformable masking (PCM)--that is not affected by VLSIs topography, and is able to fabricate highly accurate pattern. The aqueous developable layer, PMGI, with high organic solvent resistance is used in the bottom layer. Therefore, no interfacial mixing with conventional positive resist top layer is observed. Furthermore, deep-UV exposure method has been used for the KrF excimer laser optical system in order to increase high throughput. From the experiments, it has been confirmed that good resist transfer profile can be realized by the use of WSP, and that the submicron resist patterns with high aspect-ratio can be developed on the nonplaner wafer with steps of up to 41m by the combination of the WSP with the PCM system. By this technology, has been improved the weak point: variation in the line width due to the thickness of contrast-enhanced layer when the CEL technology is applied, and dependency of both the finished resist profile and the line-width accuracy on the thickness of the top layer resist when the PCM system is adopted.

New 157-nm resist platform based on etching model for fluoropolymers

We designed platforms for a 157-nm resist polymer that have both high transparency and high etch resistance. We measured the etching rate of various fluoropolymers under the conditions of poly etch and oxide etch processes. Most of the fluoropolymers showed good correlation with an etching rate ratio and a value of (NC-NO-NF) / NT (NT, NC, NO, and NF was the number of total atoms, carbon, oxygen, and fluorine atom in a monomer unit, respectively). This index, (NC-NO-NF) / NT was named IERF (index for etch resistance of fluoropolymers). It became easy to design a fluoropolymer that has high etch resistance using this index. Moreover, the acrylic polymer that has a particular kind of fluorinated alicyclic compound in its side chain was not in the above-mentioned correlation, however, it was found to have higher etch resistance. Base upon these results, two platforms were built, one of the copolymer type with polyacrylate (PA) and polystyrene (PS), the other of the copolymer type with PA and polycycloolefin (PC). Resists belonging to the two platforms were made and a high resolution of 85 nm or less was obtained by using the Microstepper (NA0.6, (sigma) 0.3, alternating phase shift mask). These resists showed a slightly higher etch resistance as compared with a COMA (cycloolefin-maleic anhydride) type resist with comparatively high etch resistance even during the ArF resist.

Improved outline phase-shifting mask (OL-PSM) for reduction of the mask error enhancement factor

We propose a new resolution enhancement technology (RET) for enhancing the resolution of contact hole patterns. The technology uses an attenuated mask with phase shifting aperture. The phase shifter is laid out based on the OL-PSM and CL-PSM algorithm. These RETs are called “Mask Enhancer”. Aerial images of random hole patterns are strongly enhanced by using the Mask Enhancer. We used the Mask Enhancer in 100-nm hole pattern fabrication in ArF lithography. The process window is strongly improved and the MEEF is drastically reduced compared to att-PSM.

Impact of water and top-coats on lithographic performance in 193-nm immersion lithography

We have investigated the impact of water and top-coats on the resist in water immersion lithography by analyzing the dissolution behavior and the film constitution. We used a resist development analyzer (RDA) and a quartz crystal microbalance (QCM) to study the dissolution behavior. The film constitution was studied through the gradient shaving preparation (GSP) method in combination with TOF-SIMS. The GSP/TOF-SIMS method reveals the constitution of a top-coat/resist film. We found that, in a resist, the photo acid generator (PAG) anion at a depth of about 30 nm from the surface leached into water and a surface insoluble layer formed during immersion. The estimated amount of leaching was about 5% of the original content. The formation of an intermixing layer with a low dissolution rate was observed for some top-coat and resist combinations. The thickness of the intermixing layer and the formation behavior were made clear. We believe the intermixing layer was caused by the top-coat solvent eluting resist components. In a top-coat, a PAG existed within the top-coat and the PAG anion leached into the water. Top-coats blocked gaseous decomposed products from the resist film during PEB. These results are useful for estimating patterning characteristics and the defectivity due to materials for actual immersion exposure.

Nonhomogeneous Pattern Formation in the Dissolution Processes of Novolak-Diazonaphthoquinone Resists

The development mechanisms of irradiated novolak-diazonaphthoquinone resists have been studied on the basis of the atomic force microscopy (AFM) data of resist surface images. The characteristic surfaces with large holes or island structures, that is, nonhomogeneous surfaces, have been observed at the exposure doses near the beginning of the film thickness reduction. The changes in the size of holes and island structures roughly correspond to the changes of cluster size estimated by percolation theory. From the dissolution pattern changes which depend on exposure dose, it is considered that an adequate exposure dose is indispensable for high-precision patterns and such an exposure dose determines the sensitivity of positive-type resists.

CD control using latent image for lithography

As a design rule of LSI device gets smaller, critical dimension (CD) control becomes increasingly difficult. This creates a new technology to CD control accurately. The technology utilizes intensity of light diffracted from latent image consisting of periodic patterns in undeveloped photoresist, and its possibility has been reported for several years. We have developed a new method of the CD control by monitoring profile of the latent image using atomic force microscope (AFM). The reduction of CD variation using this method is achieved by controlling development time from the relationship between the profile of the latent image and CD after development. We have tried to apply this method to a resist process in KrF excimer laser lithography and found usefulness of the method for 0.25 micrometers lithography.