Hiroyoshi Tanabe

Resolution improvement with annular illumination

In order to improve resolution and Depth Of Focus (DOF) in reduction projection aligner, authors investigated an annular illumination method in which the center portion of light source is screened. This paper describes the improved resist pattern resolution and DOF with annular illumination. The pattern deformation induced by annular illumination was also investigated. Furthermore, an optimization method of light source shape and its results were described. First, basic annular illumination characteristics were analyzed using simulation, and then its effect was confirmed experimentally in i-line exposure

Large assist feature phase-shift mask for sub-quarter-micrometer window pattern formation

To improve the depth of focus of isolated windows, large assist feather technique has been proposed. This large assist method uses the assist features having almost the same size as main patterns, and the quartz substrate was vertically etched at the assist features. These large assist features were not printed on a wafer by mask topography effect; that is, the light intensity at large assist feature was decreased by the scattering effect of the vertical quartz edges. In this large assist feature masks, the phase shift angle of an assist feature has large effect on focus latitude. We chose two phase shift angles: 180 degrees for small sigma illumination and 360 degrees for annular illumination. The performances of two large assist feature masks were evaluated by using a 0.55 NA, valuable sigma, and KrF excimer laser stepper. Moreover, we applied surface insoluble layer to the assist feature method. Large assist features having the same size as main patterns were not printed on resist surface for 0.16 - 0.2 micrometer windows. Wide DOF (0.8 micrometer) of 0.16 micrometer window was obtained by using this method.

Fast optical proximity correction: analytical method

In automating optical proximity correction, calculation speed becomes important. In this paper we present a novel method for calculating proximity corrected features analytically. The calculation will take only several times the amount it takes to calculate intensity of one point on wafer. Therefore, the calculation will become extremely faster than conventional repetitive aerial image calculations. This method is applied to a simple periodic pattern. The simulated results show great improvement on linearity after correction and have proved the effectiveness of this analytical method.

Monolayer Halftone Phase-Shifting Mask for KrF Excimer Laser Lithography

A new monolayer halftone phase-shifting mask has been developed. The phase-shifting film consists of the compounds SiO 2 and Cr 2 O 3 . The transmittance of the film is controlled by changing the mixing ratio of the two materials. Our mask can be easily fabricated because the structure of the mask is very simple and the film is considerably thicker than the Cr layer of the original double-layer halftone phase-shifting mask. Experimental results using a KrF excimer laser stepper confirm the effect of increasing the depth of focus of hole patterns

Photoacid structure effects on environmental stability of 193-nm chemically amplified positive resists

The effects of photoacid structure on environmental stability at post exposure bake (PEB) and during post exposure delay (PED) for 193-nm chemically amplified positive resists were investigated. It was found that the influence of airborne contamination at PEB was less than that during PED. The acidity and size of generated photoacids have a great impact on environmental stability, as well as on lithographic performance; weak acid with moderate size (/spl sim/ 100 /spl Aring//sup 3/) exhibited both high environmental stability and high resist contrast.

Chromium Fluoride Attenuated Phase-Shifting Mask for Argon Fluoride Excimer Laser Lithography

Chromium fluoride (CrF) film was chosen as the phase shifter for attenuated phase-shifting masks because of its high transmittance at 193 nm. The refractive index n and absorption coefficient k was derived by using the reflectance-transmittance (RT) method. Using argon fluoride (ArF) excimer laser exposure equipment and a chemically amplified positive resist, fine hole patterns were resolved. Depth of focus (DOFs) with 0.24 µm were extended to 30%. The resolution limit was 0.20 µm, while it was 0.22 µm with a conventional mask.

Modeling of optical images in resists by vector potentials

A new model is presented to calculate the electromagnetic fields inside a resist according to vector potentials. The model can handle three-dimensional electromagnetic fields with fewer variables than Maxwell’s equation. The perturbation theory is applied to this model to describe the resist bleaching process.

High-transmittance rim-type attenuated phase-shift masks for sub-0.2-μm hole patterns

The lithographic performance of high- and standard- transmittance attenuated phase shift masks (PSMs) was investigated in order to determine the suitability of applying attenuated PSMs to the fabrication of 0.15-micrometers hole patterns. Both PSMs had rim structures to eliminate side lobes, and they have two layers on the quartz substrate: a chromium-fluoride attenuated phase shifter layer and an opaque chromium layer. Both PSMs had similar lithographic performances that were high enough for 0.15 micrometers hole patterns.

Dissolution characteristics of chemically amplified 193 nm resists

The dissolution kinetics of two types of chemically amplified positive 193 nm resists were investigated; a ter-polymer resist consisting of poly(tricyclodecylacrylate-co-tetrahydrodpyranyl-methacrylate-co-methacrylic acid) and triphenylsulfonium triflate as a photoacid generator, and a copolymer resist consisting of poly(carboxytetracyclododecylmethacrylate-co-tetrahydro-pyranyloxy-carbonyl-tetracyclododecylmethacrylate) and triphenylsulfonium triflate as a photoacid generator. The dissolution rate contrast was higher and the slope of dissolution rate curve was steeper for the ter-polymer resist than those for the copolymer resist. However, the Arrhenius plots of the dissolution rates were straight lines for both resists irrespective of the exposure doses. This indicates that only one mechanism determines the dissolution of both resists, and it is believed that the dominant rate-determining step in both resists is the tetramethylammoniumhydroxide penetration into the resist films. The resolution capabilit...

Deblocking reaction of chemically amplified ArF positive resists

Deblocking reaction mechanisms and lithographic performance in chemically amplified positive ArF resists were investigated by analyzing acid concentration and blocking level. The resists consisted of triphenylsulfonium triflate as a acid generator and either the copolymer, poly(carboxy- tetracyclododecyl methacrylate70-co- tetrahydropyranylcarboxy-tetracyclododecyl methacrylate30) or the terpolymer, poly(tricyclodecylacrylate60- co-tetrahydropyranylmethacrylate20-co-methacrylic acid20). The deblocking reaction mechanisms were evaluated from Arrhenius plots of the deblocking reaction rate constant. It was found that the deblocking reaction of both resists is ruled by two rate-determining steps, i.e., reaction-controlled in the low-temperature region and acid- diffusion-controlled in the high-temperature region. Furthermore, the copolymer resist had better post-exposure- delay (PED) stability. To clarify this result, acid loss caused by air-born contamination effect on deblocking reaction was investigated. The change of amount of blocking group by acid loss was small for the copolymer. Therefore the copolymer resist had better PED stability. Furthermore, the post-exposure bake (PEB) sensitivity of linewidth of the copolymer resist was smaller than that of the terpolymer resist. Both deblocking reaction rate constant and reverse reaction rate constant of the copolymer resist increased with PEB temperature. As a result, equilibrium constant of the copolymer was not valuable with temperature. This is the reason why the copolymer resist has low PEB sensitivity. It is concluded that small acid loss effect on deblocking reaction induces better PED stability. A resist with reverse reaction has an advantage for PEB temperature sensitivity.