Plasma Annealing Process Research Articles

Low-Temperature As-Grown Crystalline β-Ga2O3 Films via Plasma-Enhanced Atomic Layer Deposition.

We report on the low-temperature growth of crystalline Ga2O3 films on Si, sapphire, and glass substrates using plasma-enhanced atomic layer deposition (PEALD) featuring a hollow-cathode plasma source. Films were deposited by using triethylgallium (TEG) and Ar/O2 plasma as metal precursor and oxygen co-reactant, respectively. Growth experiments have been performed within 150-240 °C substrate temperature and 30-300 W radio-frequency (rf) plasma power ranges. Additionally, each unit AB-type ALD cycle was followed by an in situ Ar plasma annealing treatment, which consisted of an extra (50-300 W) Ar plasma exposure for 20 s ending just before the next TEG pulse. The growth per cycle (GPC) of the films without Ar plasma annealing step ranged between 0.69 and 1.31 Å/cycle, and as-grown refractive indices were between 1.67 and 1.75 within the scanned plasma power range. X-ray diffraction (XRD) measurements showed that Ga2O3 films grown without in situ Ar plasma annealing exhibited amorphous character irrespective of substrate temperature and rf power values. With the incorporation of the in situ Ar plasma annealing process, the GPC of Ga2O3 films ranged between 0.76 and 1.03 Å/cycle along with higher refractive index values of 1.75-1.79. The increased refractive index (1.79) and slightly reduced GPC (1.03 Å/cycle) at 250 W plasma annealing indicated possible densification and crystallization of the films. Indeed, X-ray measurements confirmed that in situ plasma annealed films grow in a monoclinic β-Ga2O3 crystal phase. The film crystallinity and density further enhance (from 5.11 to 5.60 g/cm3) by increasing the rf power value used during in situ Ar plasma annealing process. X-ray photoelectron spectroscopy (XPS) measurement of the β-Ga2O3 sample grown under optimal in situ plasma annealing power (250 W) revealed near-ideal film stoichiometry (O/Ga of ∼1.44) with relatively low carbon content (∼5 at. %), whereas 50 W rf power treated film was highly non-stoichiometric (O/Ga of ∼2.31) with considerably elevated carbon content. Our results demonstrate the effectiveness of in situ Ar plasma annealing process to transform amorphous wide bandgap oxide semiconductors into crystalline films without needing high-temperature post-deposition annealing treatment.

Low-temperature plasma annealing of sputtered indium tin oxide for transparent and conductive thin-films on glass and polymer substrates

This paper reports on the development of a low-temperature plasma annealing process for indium tin oxide (ITO) thin-films deposited by magnetron sputtering. The study investigates the influence of the type of plasma (argon (Ar) vs. oxygen (O2)) and its duration on the optical transmission coefficient and electrical resistivity of the films depending on the power and O2 concentration during their deposition. A low sputtering power of 100 W combined with an O2 concentration of 6 vol% followed by a 40-min Ar plasma anneal at 300 W produces ITO films with an average transmission of 94% in the visible spectrum and a resistivity of 2.3×10−3Ω cm. Sputtering without O2 results in a transmission of 89% and a resistivity of 9×10−4Ω cm. The annealing depth is found to be 370 nm. We deposited and annealed conductive, transparent ITO tracks below 50 ∘C on a polyimide substrate and thereby operated integrated light sources on a fully transparent and highly flexible optical probe.

The Effects of Thermal and Atmospheric Pressure Radio Frequency Plasma Annealing in the Crystallization of TiO2 Thin Films

Amorphous TiO2 thin films were respectively annealed by 13.56 MHz radio frequency (RF) atmospheric pressure plasma at discharge powers of 40, 60, 80 W and thermal treatment at its corresponding substrate temperature (Ts). Ts was estimated through three measurement methods (thermocouple, Newton’s law of cooling and OH optical emission spectra simulation) and showed identically close results of 196, 264 and 322 °C, respectively. Comparing with thermal annealing, this RF atmospheric pressure plasma annealing process has obvious effects in improving crystallization of the amorphous films, based on the XRD and Raman analysis of the film. Amorphous TiO2 film can be changed to anatase film at about 264 °C of Ts for 30 min plasma treatment, while it almost remains amorphous after 322 °C thermal treatment for the same time.

Lanthanum modified lead zirconate titanate thin films by sol-gel and plasma annealing for integrated passive nanophotonic devices

Lanthanum modified lead zirconate titanate (PLZT) thin films were prepared by sol-gel and the plasma annealing process. The PLZT thin films are pure perovskite phase and highly crystalline. The polarization-electric loops confirmed quadratic PLZT thin films. The optical properties were determined by a spectroscopic ellipsometry analyzer, showing an absorption coefficient of near zero and an energy gap of around 3.6 eV. The insertion losses of the optical devices based on PLZT films are less than 5 dB. These films have the potential to be applied in the field of integrated nanophotonic devices.

Nitrogen Plasma Processing of SiO2/4H-SiC Interfaces

A nitrogen plasma annealing process for gate dielectric applications in 4H-SiC metal oxide semiconductor (MOS) technology has been investigated. This process results in substantially greater interfacial N coverage at the SiO2/4H-SiC interface and lower interface trap densities than the state-of-the-art nitric oxide (NO) annealing process. Despite these exciting results, the field-effect mobility of MOS field-effect transistors (MOSFETs) fabricated by use of this process is very similar to that of NO-annealed MOSFETs. These results emphasize the importance of understanding mobility-limiting mechanisms in addition to charge trapping in next-generation 4H-SiC MOSFETs.

Crystallization of amorphous silicon thin film by using a thermal plasma jet

Amorphous silicon (a-Si) films deposited on glass substrates were crystallized using a thermal plasma jet and the treated films are analyzed to find the relationship between plasma characteristics and crystallization process conditions. The crystallization process conditions were found to have different optimal operating regimes depending on the nozzle geometry. Numerical analysis of the thermal plasma jets showed that the different operating regimes for crystallization were caused by modifications of the plasma characteristics by the nozzle geometry. It is revealed that a stepped-divergent nozzle is more efficient for the thermal plasma annealing process than the conventional cylindrical one due to the broadened high-temperature region and the lowered axial velocity in the plasma jet.

Preparation of amorphous carbon films by layer-by-layer hydrogen plasma annealing method and their luminescence properties

A layer-by-layer hydrogen plasma annealing method was used to fabricate hydrogenated amorphous carbon (a-C:H) films in plasma chemical vapor deposition system by using methane and hydrogen as the reactant gases. The influences of hydrogen annealing conditions on the structures and photoluminescence behavior were systematically investigated. It was found that the photoluminescence (PL) properties of a-C:H films were strongly affected by the hydrogen plasma annealing process. The PL characteristics are believed to relate to the film network relaxation rather than the change of the optical band gap. Two intense PL bands, which were located at both the green and blue-violet regions, were observed at room temperature. For some annealed a-C:H films, the resonant features were observed in photoluminescence excitation spectra, which is consistent with the exciton-like recombination model.

Low Temperature RF Plasma Annealing Using A NH3-N2 Gas Mixture

Techniques such as plasma etching, electron-beam lithography, X-ray lithography, ion etching, sputtering and ion implantation are used to Increase the density of Integration of semiconductor devices. All these techniques introduce undesirable radiation damage into the processed device. Annealing techniques are used to reduce or remove completely the radiation induced defects. The conventional postmetallization low temperature (400–450 °C) annealing using Forming gas (10% H2-90% N2) does not anneal all the charge pentres in many device structures. We have employed a novel low temperature (350°C) rf plasma technique using a NH3-N2 gas mixture to anneal bipolar structures. Vertical pnp transistors made with high energy ion implantation and having poor electrical characteristics have been dramatically improved after 30 min annealing with this new technique. The value of the ideality factor of the base current which was about 1.4 before annealing approached the ideal value of 1.0 after 30 min annealing. Optical emission spectroscopy of the NH3-N2 glow discharge shows the presence of NH radicals, atomic hydrogen and nitrogen ion molecules during the plasma annealing. The atomic hydrogen passivates electrically active defects in the oxide and at the Si/SiO2 interface. A nitridation process occurs at the surface of the top BPSG layer, where a thin silicon nitride film is formed and plays the role of a capping layer which inhibits saturation phenomena. Angle-resolved XPS and ellipsometry have been used to analyze the surface of a silicon wafer exposed to this plasma annealing process. A qualitative model is also proposed to explain the mechanisms involved in this novel NH3-N2 rf plasma annealing process.