Shin Yokoyama

Atomic layer controlled deposition of silicon nitride with self‐limiting mechanism

Thin (2–10 nm) silicon nitride films have been grown by repetitive plasma nitridation of Si using a NH3 remote plasma and deposition of Si by a SiH2Cl2 thermal reaction. The deposition rate is self‐limited at nearly half‐molecular layer (ML) per one deposition cycle. The process window for the half‐ML/cycle of growth has been investigated with respect to the NH3 plasma power, SiH2Cl2 exposure time, and substrate temperature. The thickness fluctuation of the film over a 2 in. wafer is within measurement accuracy of the ellipsometer (± 1.9%) for the atomic layer controlled film while it is ± 8.5% for all the remote‐plasma chemical vapor deposition film.

NH3-annealed atomic-layer-deposited silicon nitride as a high-k gate dielectric with high reliability

Extremely thin (equivalent oxide thickness, Teq=1.2 nm) silicon-nitride high-k (er=7.2) gate dielectrics have been formed at low temperatures (⩽550 °C) by an atomic-layer-deposition (ALD) technique with subsequent NH3 annealing at 550 °C. A remarkable reduction in leakage current, especially in the low dielectric voltage region, which will be the operating voltage for future technologies, has made it a highly potential gate dielectric for future ultralarge-scale integrated devices. Suppressed soft breakdown events are observed in ramped voltage stressing. This suppression is thought to be due to a strengthened structure of Si–N bonds and the smoothness and uniformity at the poly-Si/ALD-silicon-nitride interface.

Atomic layer controlled deposition of silicon nitride and in situ growth observation by infrared reflection absorption spectroscopy

Abstract We have previously reported that silicon nitride films can be grown by repetitive plasma nitridation of Si using a NH3 remote-plasma and deposition of Si by a SiH2Cl2 thermal reaction. For this process, the deposition rate is self-limited at nearly half-molecular-layer (ML) per one deposition cycle. In this paper, the growth mechanism of the atomic layer deposition (ALD) of silicon nitride has been investigated by in situ Fourier transform infrared reflection absorption spectroscopy (FTIR-RAS). The AFM observation showed that the surface microroughness of the ALD grown silicon nitride film on the thermal CVD Si3N4 is very large, which suggests the islands growth. On the other hand, the roughness is almost maintained after the growth on the hydrogen terminated Si and SiO2 substrates. These results are explained taking account the surface hydrogen atoms. Furthermore, in order to reduce the ion energy of the NH3 plasma, the effect of the magnetic field is investigated.

Low-temperature formation of silicon nitride gate dielectrics by atomic-layer deposition

Thin (equivalent oxide thickness Teq of 2.4 nm) silicon nitride layers were deposited on Si substrates by an atomic-layer-deposition (ALD) technique at low temperatures (<550 °C). The interface state density at the ALD silicon nitride/Si-substrate interface was almost the same as that of the gate SiO2. No hysteresis was observed in the gate capacitance–gate voltage characteristics. The gate leakage current was the level comparable with that through SiO2 of the same Teq. The conduction mechanism of the leakage current was investigated and was found to be the direct tunneling. The ALD technique allows us to fabricate an extremely thin, very uniform silicon nitride layer with atomic-scale control for the near-future gate dielectrics.

Atomic-layer-deposited silicon-nitride/SiO2 stacked gate dielectrics for highly reliable p-metal–oxide–semiconductor field-effect transistors

An extremely thin (∼0.4 nm) silicon-nitride layer has been deposited on thermally grown SiO2 by an atomic-layer-deposition (ALD) technique. The boron penetration through the stacked gate dielectrics has dramatically been suppressed, and the reliability has been significantly improved, as confirmed by capacitance–voltage, gate-current–gate-voltage, and time-dependent dielectricbreakdown characteristics. The ALD technique allows us to fabricate an extremely thin, very uniform silicon-nitride layer with atomic-scale control.

Growth and electrical properties of atomic-layer deposited ZrO2 /Si-nitride stack gate dielectrics

We deposited ZrO2 thin films by atomic-layer deposition (ALD) using zirconium tertiary–butoxide [Zr(t-OC4H9)4, (ZTB)] and H2O source gases on Si substrates at low temperatures. We grew ZrO2 films layer by layer in a temperature range of 175–250 °C to minimize surface roughness. The deposited ZrO2 film thickness had self-limiting properties with the exposure time of ZTB and vapor pressures of ZTB and H2O. The deposition rate per cycle was independent of the vapor pressure of ZTB from 0.01 kPa to 0.04 kPa. Transmission electron microscopy revealed that the formation of an SiOx interfacial layer could be suppressed by using an ALD ZrO2/ALD Si-nitride (∼0.5 nm) stack structure. We found the fixed charge, interface trap density, and leakage current density in the ALD ZrO2/ALD Si-nitride stack dielectrics to be less than those in ALD ZrO2 dielectrics. In spite of the same equivalent oxide thickness of 1.6 nm, the relative dielectric constant er (11.5) of the ALD ZrO2/ALD Si-nitride stack capacitor was higher th...

Electron Spin Resonance in Discharge-Produced Silicon Nitride

ESR signal from the defects in plasma-deposited silicon nitride has been observed, for the first time. The g-value (2.0055) is identical with that of silicon dangling bonds in amorphous Si:H, and the linewidth (14.5 G) is two times as large as that of amorphous Si:H for spin densities below 1018 cm-3, above which narrowing of the linewidth takes place as in the case of amorphous Si:H. It is suggested that most of dangling bonds of nitrogen atoms in the silicon nitride are passivated by bonded-hydrogen and silicon dangling bonds are mainly responsible for the ESR signal. A correlation between the spin density and leakage current through the film is also discussed.

Characterization of photochemical processing

Thermally grown SiO2 and crystalline GaAs surfaces exposed to an etching gas under an ArF excimer laser irradiation have been studied by in situ x‐ray photoelectron spectroscopy (XPS). Reaction kinetics of photochemical etching and resulting products on the solid surfaces have been revealed from the chemical shifts of adsorbates and substrate atoms. Etching products in SiO2/(NF3+H2) system are confirmed to be SiF4, N2O, and NO2. For the etching of GaAs in HCl, GaCl3 and AsCl3 are found to be the most probable products in the gas phase.

Characterization of plasma‐deposited silicon nitride films

Structural and electrical properties of plasma‐deposited silicon nitride (SiN) have been investigated. The compositional ratio of Si to N estimated by Auger analysis is found to be uniform in the direction of the film thickness. The numbers of Si‐H and N‐H bonds of the order of ∼1021/cm3 have been obtained by calculating the vibrational spectra. The two types of trapping states which are responsible for the Poole‐Frenkel conduction are found in SiN from the current DLTS measurement. The barrier height at the SiN/Si interface determined by the internal photoemission ranges from 1.7 to 2.5 eV, being dependent on the film thickness. From these results, current transport mechanisms through SiN films are quantitatively discussed, and it is demonstrated that the carrier transport is dominated by the Fowler‐Nordheim tunneling at low temperatures and by the Poole‐Frenkel conduction at high temperatures.

Atomic-layer selective deposition of silicon nitride on hydrogen-terminated Si surfaces

Atomic layer selective deposition of silicon nitride films on the hydrogen-terminated Si surface has been investigated. The film is deposited by alternate supply of SiH2Cl2, and NH3 dissociated by thermal catalytic reaction on a tungsten filament. Thin (<4 nm) silicon nitride films can be selectively grown on a hydrogen-terminated Si surface. However, no film growth takes place on thermal chemically-vapor-deposited (CVD) silicon nitride in the initial ∼30 deposition cycles. The mechanism of the selective deposition is studied by means of Fourier transform infrared attenuated total reflection (FT-IR-ATR) spectroscopy. It is shown that the film growth takes place only on the surface with Si–Hx (x=1∼3) bonds, because the first nitridation by NH3 exposure occurs only at the surface with Si–Hx bonds. Once the surface N–Hy (y=1 or 2) bonds are formed, the SiH2Cl2 molecules react with the N–Hy bonds and the film growth starts to take place. On the other hand, no film growth takes place on the thermal CVD silicon nitride since there are no Si–Hx and N–Hy bonds on the surface. By using the thermal catalytic method, the film quality is improved in comparison with films deposited by using NH3 plasma.