Tadao Kato

Cold and Low-Energy Ion Etching (COLLIE)

It is shown that a new cold and low-energy ion etching system (COLLIE) is effective as a dry etching technique for fabrication of VLSI devices. In the COLLIE system, plasma instabilities are suppressed by an MHD stable magnetic field consisting of a solenoid coil and multicusp magnets. The ion temperature, which is strongly related to plasma instabilities, is lowered below 2 eV in this system. Etched profiles show a strong anisotropic feature without applying any external electrical bias. As small angular distribution of incident ions to a sample is realized, the microloading effect is greatly improved.

Dielectric breakdown of silicon oxide studied by scanning probe microscopy

The applicability of scanning probe microscopy in the dielectric breakdown characteristics of silicon oxide has been demonstrated. Our study demonstrates that the measurement on the oxide is free from the effect of trapped charge created by Fowler–Nordheim tunneling when a sufficient distance is maintained between the measuring points. In this condition, for a 13-nm-thick oxide, the dielectric breakdown voltages were found to be so uniform as to fluctuate only 1%. We applied this method to oxides on the wafers from two different vendors, and found that the dielectric breakdown strength of the oxide depends on the difference on the Si substrates. We also applied this method to a square oxide pattern surrounded by a field oxide, and the result was that the dielectric breakdown strength of the oxide on the edge is lower than the one in the center.

Characterization of Silicon Implanted with Focused Ion Beam by Raman Microprobe

Damage to silicon implanted with Si++, Au++ and Be++ ions using focused ion beams has been evaluated by a Raman microprobe technique. A quantitative evaluation of damage to ion-implanted silicon was made by comparing the intensities of Raman scattering from implanted and unimplanted areas. The minimum dose at which damage is detectable by Raman measurements is 9×1011 ions/cm2 for Au++, 7.5×1012 ions/cm2 for Si++ and 7.5×1013 ions/cm2 for Be++. From the depth distribution of the damage measured using laser lines of different wavelengths, it is inferred that damage at the near-surface region in Be++ implanted silicon is reduced by self annealing during high-dose-rate implantation and that a channeling effect causes the saturation dose in Be++ implantation to be higher than that in other ion implantations.

Unique resist profiles with Be and Si focused ion beam lithography

The delineation of resist patterns has been investigated for two kinds of ions, Be and Si. Patterns consisting of 0.2 μm lines and spaces were fabricated in 0.7 μm thick resist with good repeatability and accuracy. This shows that the influence of proximity effects can be disregarded. The broadening of patterns was observed for Si exposure because of the more significant influence of recoil atoms. As a special application of focused ion beam lithography, a new process for fabricating a mushroom gate electrode for a GaAs microwave field‐effect transistor (FET) was demonstrated utilizing the particular exposure characteristics of the different ion species.

I–V characteristics of modified silicon surface using scanning probe microscopy

Using scanning probe microscopy, we have modified a silicon surface and measured its current–voltage (I–V) characteristics. In the modified area, both an increase in film thickness and a decrease in current caused by field-induced oxidation (FIO) have been observed. The I–V characteristics of the FIO film shows a good fit to a Fowler–Nordheim (FN) tunneling current model. The barrier height determined by a FN plot shows a good agreement with that of conventional metal–oxide–semiconductor structure with thermal thick silicon oxide.

Two-layer resist structure for electron-beam fabrication of a submicrometer gate length GaAs device

A two-layer resist structure using EBR-9 and PMMA for fabricating a fine metal line with a mushroom-like cross-sectional profile is reported. The structure provides T-shaped resist cavities with undercut profiles using electron-beam exposure. With the optimum developing condition, the bottom opening is as small as 0.1 µm, and the top opening is wide enough not to require an additional exposure in order to obtain a mushroom-like metal lift-off pattern. A Monte Carlo calculation is carried out in order to analyze the profile of the two-layer resist structure, and it is shown that an undercut T-shaped resist profile with a 0.1-µm bottom opening can be obtained using a high-sensitivity resist on a low-sensitivity resist structure. A 0.15-µn mushroom-like lift-off metal profile has been fabricated on a 0.1-µm recessed GaAs substrate by the use of this resist structure.

Stable performance Nb variable thickness microbridge type Josephson junctions: A reproducible fabrication technique

A novel method of fabrication, as described in the following, was developed that ensures a good reproducibility of the junction. Namely, poly‐Si was deposited over a Si substrate whose surface had been previously thermally oxidized. The poly‐Si overlaid surface was then thermally oxidized. The bridge configuration of the junction was microprocessed by means of electron beam lithography. The fabricated configuration served as a mask in depositing the Nb layer on the substrate by means of rf sputtering to conclude the fabrication of a microbridge Josephson junction. The final process of the formation of the variable thickness microbridge configuration was readily carried out by placing another properly shaped mask over the masking bridge or by forming an SiO2 layer over the poly‐Si layer. The SiO2 layer was processed by selective plasma etching so that it would act as a mask over the bridge portion. The stabilization of the characteristics of the junction has been achieved due to the passivation which takes...

Focused ion beam technologies for lithographic applications

Abstract Focused ion beam (FIB) technologies have the advantages of high resolution and maskless fabrication, which play an important role in the lithographic process for the development of advanced semiconductor devices. FIB lithography has the added advantage of obtaining a T-shaped edge profile for the fabrication of a “mushroom gate” of GaAs FETs by the use of different ion species. A GaAs HEMT fabricated by using hybrid exposure of Be2+ and Si2+ shows a minimum noise figure of 0.83 dB with an associated gain of 7.7 dB at 18 GHz. The capability of maskless fabrication has been applied to defect repair of the lithographic photomask. An opaque defect is removed by ion beam sputtering, and a clear defect is repaired by chemical vapor deposition with the assistance of ion beam irradiation. A repair with high positional accuracy can be performed because the ion beam can be precisely positioned Extra ions penetrating the glass substrate reduce the light transmissivity, and change the characteristics of the pattern transfer. This problem is now eliminated by incorporating a post-dry etching process.

Effects of plasma parameters on etching characteristics with ECR plasma

Abstract In order to realize submicron patterns for VLSI devices, it is necessary to form patterns having anisotropic profiles, without damage and contamination. In this paper, we report the results of the study on etching characteristics of poly-Si and parameters of Electron Cyclotron Resonance (ECR) plasma. The relationships between the etching characteristics and the plasma parameters are investigated. It has been found that there is a strong relationship between the etching characteristics and the plasma parameters. Etch rate depends linearly on both ion current and ion energy. These two parameters can be controlled independently by microwave power and gas pressure.

Reactive Ion Beam Etching Using a Selective Gallium Doping Method

A maskless process has been realized by combining reactive ion beam etching (RIBE) with focused ion beam (FIB) technology. Si patterns of 0.3 µm with no undercutting can be obtained using RIBE with electron cyclotron resonance (ECR) plasma. A Ga compound is formed as an in situ etching mask.