Hideo Yoshihara

Silicon nitride single‐layer x‐ray mask

In LP‐CVD process, preparation of silicon nitride film with small tensile stress and low refractive index was investigated as a function of deposition temperature and reactant gas ratio (SiH2Cl2/NH3). The small stress film with low refractive index can be prepared easily by high temperature deposition. Applying the film to an x‐ray mask membrane, a new silicon nitride single‐layer x‐ray mask with a large area window (such as 50 mm in diameter) and high transparency to visible light is realized. Using this mask, a submicron resist pattern (0.5 μm line and space) can be replicated easily by Si–K x‐ray exposure system.

Friction and Wear Behavior of Hard Carbon Films

The friction and wear properties of hard carbon films deposited by a hot cathode glow discharge in ethylene or methane were examined by using a reciprocating tribometer in vacuum and in air. A hard carbon film composed of mixed diamond and graphite crystal shows high friction in vacuum. On the other hand, hard carbon amorphous film containing hydrogen shows an extremely low friction coefficient on the order of 0.01 in vacuum.

SiC synthesis by a plasma deposition process

The preparation of silicon carbide films at substrate temperatures lower than 600 °C and deposition rates greater than 0.2 μm h-1 was studied. A new process (the plasma deposition process) in which all the reactant species were supplied by pure gases was investigated. In this process the gas pressure is of the order of 10-3 Torr and the deposition rate is independent of the substrate temperature and the cathode potential and can be controlled by the gas throughput and the r.f. power. For a high r.f. input power the chemical composition of the SiC films is equal to the mixing ratio of the reactant gases. The films prepared were found to be amorphous and silicon carbide like by reflection high energy electron diffraction and IR transmission spectroscopy analyses. Properties of the films such as transparency, adhesion, hardness and corrosion resistance are improved with both increasing r.f. power and increasing cathode potential. The SiC films are transparent and show high hardnesses, excellent corrosion resistance and excellent adhesion to both silicon substrates and fused quartz substrates. A large compressive film stress ranging from 2 × 108 to 5 × 109 dyn cm-2 was found.

Enhanced ARE apparatus and TiN synthesis

To apply the activated reactive evaporation (ARE) process to coatings for telecommunication components, the deposition rate must be less than 0.1 μm/min. To accomplish this slow rate, an electron emitting electrode was attached to the ARE apparatus. Electrons emitted from the electrode ’’enhanced’’ the ARE process. In the enhanced ARE process, the generation of plasma and evaporation of metal can be controlled independently. Therefore, the deposition rate can be controlled widely, and resistance heating and laser heating can be used for evaporation instead of electron beam heating. The enhanced ARE process was tested by synthesizing titanium nitride. Since N2 gas pressure can be varied widely in the enhanced ARE process, the chemical composition of the Ti–N films is more easily controlled than with the ARE process. Ti2N film synthesized by the enhanced ARE process showed a maximum hardness of Hv:2824 kg/mm2.

A plasma x‐ray source for x‐ray lithography

Employing a gas‐‘‘puff’’ z‐pinch plasma, a high brightness and compact plasma x‐ray source has been constructed by using a high‐repetition‐rate discharge and a new x‐ray extraction method. The high‐repetition‐rate discharge (3 Hz) is attained by using a fast‐acting gas valve, capable of operating stably under gas plenum pressures below 300 Torr. This low gas pressure discharge makes possible high‐conversion efficiency of electrical input to x‐rays, highly reliable plasma pinching, and a drastic reduction of debris resulting from electrode vaporization. An axial x‐ray exposure is required to reduce the blur in pattern replication caused by the penumbral effect. To carry out the axial exposure, the high‐energy particles emitted from the plasma are removed using a plasma reflector plate and magnet. The x rays are efficiently extracted through a window highly transparent to x rays. With this x‐ray source, 9–14 A x rays with 200 J per pulse (600 W average power) are obtained using Ne gas plasma in a 3 Hz opera...

Application of x-ray mask fabrication technologies to high resolution, large diameter Ta Fresnel zone plates

Abstract High-resolution and large diameter condenser Fresnel zone plates were fabricated in a 0.35-μm-thick Ta layer on an SiN membrane. A newly developed conversion algorithm was applied where sub-field length and position are randamized in order to supress the evolution of small figures at pattern divided parts such as subfield boundaries in the conventional conversion algorithm. A single layer resist system was adopted to write large diameter, ultra-fine, dense ring patterns. FZPs with the outer-most linewidth of 50 nm was successfully fabricated by applying the subtractive x-ray mask fabrication process.

Extendibility of synchrotron radiation lithography to the sub‐100 nm region

This article discusses the resolution of synchrotron radiation lithography in the sub‐100 nm region, taking into consideration the mass production of large‐scale integrated circuits, under attainable conditions for the x‐ray mask, proximity gap, and resist processes. Resolution and exposure latitude for line‐and‐space patterns are markedly improved by using a mask with a contrast of only 2.5. Resolutions of 90, 80, 70, and 60 nm can be achieved with proximity gaps of 30, 20, 15, and 10 μm if a high‐contrast resist and a low‐surface tension developer are used. The latitude will be 10% for pattern sizes as small as 70 nm when the proximity gap is narrower than 15 μm. The effects of mask duty [which is defined to be the ratio of the absorber (line) width to the pattern pitch, i.e., duty cycle] on the optimum exposure dose and mask linearity are also evaluated.

Silicon Nitride Single-Layer X-Ray Mask

In the low pressure chemical vapor deposition process, preparation of silicon nitride with low film stress and low refractive index is investigated as a function of deposition temperature and reactant gas ratio SiH2Cl2/NH3. The silicon nitride film with a stress of 15 kg/mm2 and refractive index of 2.3 is formed at the deposition temperature of 850°C and the SiH2Cl2/NH3 ratio of 4/1. Using the film as an X-ray mask, a silicon nitride single-layer X-ray mask is realized, which has a 30 ×30 mm window and has high transparency to visible light.

An X-ray mask using SiC membrane deposited by ECR plasma CVD

Abstract The ECR plasma CVD system has been improved for depositing SiC films for X-ray mask membranes. This system makes it possible to deposit SiC films with small tensile stress, high optical transparency and high strength at temperatures below 800°C. The SiC film is available for an X-ray mask membrane with 0.1- μ m Ta absorber patterns. Besides the thickness uniformity, the stress uniformity of the membrane is necessary in fabricating a highly accurate X-ray mask.

Ta Film Properties for X-Ray Mask Absorbers

The properties of absorber materials for X-ray masks which can be patterned by a subtractive process are investigated. Highly pure film can be deposited using Xe rather than Ar as a working gas of RF sputtering. The stress of the Ta film can be controlled more precisely than either Re or W. Ta film deposited by RF sputtering is highly oriented, and has a high purity and a high density. Furthermore, its stress does not change even after annealing at 400?C.