Iwao Higashikawa

IMPROVEMENT OF THE YOUNG'S MODULUS OF SIC FILM BY LOW-PRESSURE CHEMICAL VAPOR DEPOSITION WITH B2H6 GAS

SiC is one of the potential materials for use as an x‐ray mask substrate. It is preferable for an x‐ray mask substrate to have a large elastic modulus, so as to suppress any distortion of the extremely minute and precise patterns. The improvement of the Young’s modulus of polycrystalline SiC film using low‐pressure chemical vapor deposition with the introduction of B 2H6 in the source gas was investigated. The Young’s modulus increased with the addition of B2H6, and a maximum value of 600 GPa, which was 25% higher than in the case without B2H6, was reached at a source gas ratio B/Si=0.02. Two models which would possibly explain this phenomenon are discussed, and the theory which takes into account the interaction between carrier and ion core is found to provide a more plausible explanation of the results.

Submicron Optical Lithography Using A KrF Excimer Laser Projection Exposure System

The potential of excimer laser lithography was studied by using a newly developed KrF excimer laser exposure system which employed an achromatic lens of 0.37 NA. As a result, a resolution limit of 0.3 μm was achieved by the use of PMGI resist on a tri-level structure. However, for the case of resist exposure on a bare Si wafer, the resist film remailed locally in layers along the nodes of the standing waves, and fine pattern could not be obtained. This phenomenon is called spotted development in this paper. The spotted development, which is due to strong standing waves within the resist film, was successfully solved by the use of new resist process technologies such as a bias exposure method and excimer laser image reversal process.

KrF Excimer Laser Projection Lithography: 0.35 μm Minimum Space VLSI Pattern Fabrication by a Tri-Level Resist Process

An excimer laser exposure system has been newly developed, which adopts a 0.37 NA achromatic projection lens and a 248 nm wavelength KrF excimer laser as a light source. Irregular PMMA development was observed for exposures on a silicon substrate. Theoretical simulation clarified that an initial 0.02 µm thickness variation caused more than 0.16 µm thick resist residues due to intense standing waves. The standing waves could be suppressed by the use of a tri-level resist process so that VLSI patterns of 0.35 µm minimum space could be obtained.

Evaluation of phase and transmittance error on deep-UV halftone phase-shift mask

The effect of phase shift and transmittance fluctuation in a mask plate have been studied. The differences of these optical properties of halftone phase shift masks result in critical dimension(CD) error on a wafer so that these fluctuation in a plate reduce the process window across the exposure field. In considering CD error budget, such factors as phase shift and transmittance has to be taken into account. To estimate this budget, a set of test masks were fabricated, in which phase shift and transmittance are varied, and the exposures using these masks under the same conditions were performed.

Growth rate and deposition process of silicon carbide film by low-pressure chemical vapor deposition

The growth rate and deposition process of polycrystalline silicon carbide by low-pressure chemical vapor deposition with the introduction of hydrogen chloride gas were investigated. Analogous to the case of silicon, the growth rate was well described by a model that included nucleation of particles in the gas phase, a change of the reaction species from hydrides to chlorides, and etching or inhibition of growth by hydrogen chloride. The film stress was considerably influenced by the introduction of hydrogen chloride, which is thought to change the reaction path.

Stress Control and Etching Study of W-Re as X-Ray Mask Absorber.

Stress control and etching of W-Re as X-ray mask absorber was studied. The W-Re film was deposited using an rf magnetron sputtering apparatus with two material targets. The substrates were revolved by themselves and over the W and Re targets to achieve uniform film thickness and stress. When the content ratio of W to Re was 1:1, non-columnar film structure was obtained. The stress repeatability, when the deposited film stress is near zero, was ±5 x 10 8 dyn/cm 2 . To further control the stress, implantation of Ar ions was carried out with an acceleration voltage of 180 kV. The stress change was 1 x 10 9 dyn/cm 2 compressive at the ion dose of about 6 x 10 15 ions/cm 2 . The etching of W-Re was carried out using SF 6 and CHF 3 gas mixture and a Cr etching mask by applying magnetron reactive ion etching. The etching selectivity between W-Re and Cr was over 250 in the CHF 3 content below 60%. We applied two-step etching to remove etch-obstructing films on the W-Re surface, and fabricated 0.1 μm lines and spaces of 0.5-μm-thick W-Re film.

Sub-0.15 μm pattern replication using a low-contrast X-ray mask

Mask contrast optimization is essential for replicating sub-0.15-µ m patterns with relatively large mask-to-wafer gaps, e.g., larger than 20 µ m, which is strongly desired for industrial production. We have confirmed that decreasing the mask contrast to around 4 is very effective for increasing the exposure latitude for the grating patterns with pitch around 0.24 µ m, without deteriorating the exposure quality of larger patterns. The obtained exposure latitude for 0.12 µ m lines and spaces at the gap of 20 µ m was ±8.7% for ±10% replicated line-width change. How the mask pattern bias affects the replicated pattern was checked using the 0.24-µ m-pitch grating patterns. It was revealed that the dependence of the absorber width bias on the replicated pattern width is weaker than the linear correlation, as is suggested from the calculation of the Fresnel diffraction feature. It seems that when applying the larger mask-to-wafer gap to resolve a given pitch of grating patterns, the replicated pattern width becomes less sensitive to the line/space ratio on the mask.

Management of pattern generation system based on i-line stepper

A Device mask of 180nm generation was fabricated by Photomask Repeater system and the performance of it proved to be high by the results of fabricated mask. Great margins between the results of the fabricated mask and specifications suggest that lower graded masks can be used as master masks. From this point of view, error budgets were estimated about CD uniformity and pattern placement. The required specifications for master mask were estimated for 180nm and 130nm lithography. In CD uniformity the specification is 50nm(3?) for 180nm and 30nm(3?) for 130nm lithography. In pattern placement the specification is 75nm(3?) for 180nm and 50nm(3?) for 130nm lithography. In defect size the specification is lOOOnm for 180nm and 900nm for 130nm lithography. The requirements of master mask are rather rough even for 130nm lithography and enough realistic.

Effects of mask line-and-space ratio in replicating near-0.1-μm patterns in X-ray lithography

In replicating line-and-space ( L/S ) patterns by X-ray proximity printing, optimizing the mask duty together with mask contrast is crucial to obtain high resolution in the 0.1 µ m region. We have successfully replicated L/S down to the pitch of 0.18 µ m, and evaluated the effects of mask L/S ratio. It was confirmed that the mask L/S ratio is transferred to the replicated pattern more faithfully as the proximity gap becomes narrower, and the ratio should be about 1:1 to achieve large exposure latitude together with wide dose margin. The results of our calculation agreed well with the experimental results upon introducing novel criteria to estimate replicated pattern width. Exposure latitude for 0.1±0.01 µ m L/S replication using the gaps of 10 and 15 µ m was within ±12% with feasible pattern profiles, although the specification of measured mask L/S differed from the ideal one. Even for the gap of 20 µ m the exposure latitude remained within ±6%.

New pattern generation system based on i-line stepper: photomask repeater

New pattern generation system, Photomask Repeater, based on i-line stepper has been developed. This system can transfer device patterns from master masks onto a photomask plate with 22mm field size. To print a chip larger than the 22mm field, stitching technology has been developed. Critical dimension error in the region where shots are stitched is the key issue of this technology. Quantification of critical dimension deviation induced by shot misplacement was carried out by calculation. Introducing exposure dose gradation, it was reduced less than 1.5nm. Form measurements of real exposed mask this technique proved to be able to stitch shots seamlessly. Major two specifications, pattern placement accuracy and critical dimension uniformity, were evaluated. Both specifications required for 150nm photomask were fully satisfied. Availability of the photomask repeater to memory device and system on chip is discussed.