Seitaro Matsuo

Selective etching of Si relative to SiO2 without undercutting by CBrF3 plasma

Etching characteristics with selectivity similar to conventional CF4 plasma etching but without undercutting are realized by plasma‐reactive sputter etching, based on the reactivity of the incident ions combining fluorocarbons with low reactive halogens. In particular, the method with CBrF3 is practically useful for selective etching of Si, poly‐Si, and Mo relative to SiO2 in high‐accuracy pattern transfer.

Ultrathin oxide films deposited using electron cyclotron resonance sputter

Ultrathin oxide films (SiO2,u2009Al2O3,Ta2O5) with a minimum thickness of 2 nm have been deposited at low temperature by electron cyclotron resonance (ECR) sputter utilizing a plasma source coupled with a divided microwave beam. The uniformity of the film thickness was within ±2% over a 150 mm wafer. The surface roughness measured by atomic force microscopy was only 0.48 nm for a 100-nm-thick Al2O3 film. The fixed charge density of the Al/SiO2/Si metal oxide semiconductor capacitors decreased with increasing oxygen flow rate and substrate temperature during SiO2 deposition. A very low fixed charge density of about 5×1010u200acm−2 was obtained without annealing the capacitor. The resistivities of SiO2, Al2O3, and Ta2O5 films with thicknesses from 2 to 40 nm were on the order of 1015u200aΩu200acm. Under low electric fields the leakage current was a hopping current and under high electric fields it was a Poole–Frenkel current. The typical dielectric strength was 10 MV/cm for SiO2 and Al2O3 films. A high dielectric constant ...

Anisotropic Etching of Si and WSiN Using ECR Plasma of SF6–CF4 Gas Mixture

The characteristics of Si etching with electron cyclotron resonance (ECR) plasma of SF6–CF4 are studied in order to improve anisotropy in dry etching using fluoride gases. Si undercutting is decreased by increasing the amount of CF4. Si patterns with vertical sidewalls are obtained with an etch rate of 40 nm/min. Oxygen addition to SF6–CF4 increases Si/SiO2 etching selectivity to more than 10, but does not cause any undercutting. It is concluded that carbon (C) that decomposes from CF4 protects the pattern sidewall from undercutting by fluorine radicals. These results are applied to the anisotropic etching of WSiN as the gate material for GaAs metal-semiconductor field effect transistors (MESFETs). WSiN patterns are more vertical when the chamber inner wall exposed to SF6–CF4 ECR plasma is stainless steel rather than quartz. This is attributed to the reduction of the amount of CO, which possibly forms volatile tungsten-carbonyl [W(CO)6] and, along with fluorine radicals, causes undercutting. It is confirmed that the stainless steel inner wall does not cause serious wafer contamination by metallic elements when WSiN patterns are almost vertically etched.

Optical intensity modulator with three−dimensional waveguide

A LiTaO3 optical waveguide modulator, in which a laser beam is confined in both transverse dimensions, has been fabricated. The three−dimensional waveguiding operation was achieved by using an ion−etched thin core slab and a slit metal cladding. Waveguide porperties for 0.633− and 1.15−μm laser beams and dc and rf modulation performance for a 1.15−μm beam are described.

Tantalum and tantalum nitride films deposited by electron cyclotron resonance sputtering as barriers to copper diffusion

Tantalum (Ta) and tantalum nitride (TaN) films deposited by electron cyclotron resonance (ECR) sputtering have been investigated as barriers to Cu diffusion in very large scale integrated interconnections. An ECR plasma source coupled with divided microwaves was used to deposit Ta and TaN films. The addition of N2 to Ar enabled the ECR TaN film to be easily deposited by using a Ta metal target at low temperature without external substrate heating. To investigate the barrier characteristics, sample with Cu/ECR–Ta/SiO2 and Cu/ECR–TaN/SiO2 structures were heat treated in Ar at 550 and 650u200a°C, respectively, and analyzed by secondary ion mass spectroscopy, which determined the Cu diffusion density. The normalized signal intensity ratio of Cu to Si at the interface between the barrier metal and SiO2 was 0.035 for the ECR TaN film and 0.087 for the ECR Ta film, but 0.26 for the rf-sputtered TaN film. ECR sputter deposited films had excellent characteristics for use as barriers to Cu diffusion.

0.1 μm WSiN-gate fabrication of GaAs metal-semiconductor field effect transistors using electron cyclotron resonance ion stream etching with SF6–CF4–SiF4–O2

We investigate etching characteristics of WSiN gates using electron cyclotron resonance ion stream etching with a SF6–CF4–SiF4–O2 gas mixture, and we fabricate 0.1 μm WSiN gates for ultrahigh speed GaAs metal-semiconductor field effect transistors (MESFETs). A vertical WSiN gate etched pattern is obtained as a result of CF4 addition. Moreover, uniform etching over the entire wafer can be attained with high selectivity between the WSiN and the GaAs and with accurate control of the gate length. A current-gain cutoff frequency (fT) of 131.4 GHz with a 3σ value of 5.0 GHz in whole wafer has been obtained for 0.1 μm gate GaAs MESFETs.

Kinetic‐energy measurement of a neutral stream extracted from Ar electron cyclotron resonance plasma

The kinetic energy of a neutral stream within Ar electron cyclotron resonance plasma was evaluated by means of time‐of‐flight mass spectroscopy. The median energy in the distribution of the neutral stream ranged between 10 and 20 eV for pressure from 1.4 to 2.9×10−4 Torr. This energy is almost equal to that of the ions. The energy of the neutral stream could be controlled by adjusting the gas pressure. A higher pressure broadened the energy distribution of the neutral stream.