H2O Vapor Heat Treatment Research Articles

Annihilation of photo induced minority carrier caused by ion implantation and rapid thermal annealing

We report decreases in the minority carrier effective lifetime τeff of 700-µm-thick silicon substrates coated with 43-nm-thick thermally grown SiO2 layers by Ge ion implantation with a dose of cm−2 at 150 keV and rapid thermal annealing (RTA) at 1100 °C for 50 s. Ge ion implantation decreased the crystalline volume ratio in the top 157 nm region because of lattice damage. It also markedly decreased τeff to and s when 635 and 980 nm lights were continuously illuminated to the implanted surface, respectively. Small τeff values resulted from serious damage with a high surface recombination velocity S of cm/s and a short bulk lifetime of s in the 200 µm deep surface region. Although RTA successfully recrystallized the Ge-implanted surface region, it further decreased τeff to and s in the cases of 635 and 980 nm light illuminations to the top surfaces, respectively. RTA caused a high density of recombination sites with a high S value of cm/s on the top and rear surfaces. There was a high density of interface traps of eV−1 cm−2. Pa H2O vapor heat treatment at 260 °C for 3 h markedly increased τeff to and s in the cases of 635 and 980 nm light illuminations. The interface trap density was decreased to eV−1 cm−2. Low temperature post annealing is effective in curing the recombination defect states induced by RTA.

Crystallization of Amorphous Silicon Thin Films by Microwave Heating

ABSTRACTWe report crystallization of amorphous silicon (a-Si) thin films and improvement of thin film transistors (TFTs) characteristics using 2.45 GHz microwave heating assisted with carbon powders. Undoped 50-nm-thick a-Si films were formed on quartz substrates and heated by microwave irradiation for 2, 3, and 4 min. Raman scattering spectra revealed that the crystalline volume ratio increased to 0.42 for the 4-min heated sample. The dark and photo electrical conductivities measured by Air mass 1.5 at 100 mW/cm2 were 2.6x10-6 and 5.2x10-6 S/cm in the case of 4-min microwave heating followed by 1.3x106-Pa-H2O vapor heat treatment at 260°C for 3 h. N channel polycrystalline silicon TFTs characteristics were improved by the combination of microwave heating with high-pressure H2O vapor heat treatment. The threshold voltage decreased from 5.3 to 4.2 V and the effective carrier mobility increased from 18 to 25 cm2/Vs.

Heat treatment of amorphous silicon p-i-n solar cells with high-pressure H2O vapor

We report improvement in characteristics of hydrogenated amorphous silicon (a-Si:H ) p-i-n structured solar cells by high-pressure H2O vapor heat treatment. a-Si:H p-i-n solar cells were formed on glass substrates coated with textured SnO2 layer. P-, i-, and n-type a-Si:H layers were subsequently formed by plasma enhanced chemical vapor deposition. Finally an indium-tin-oxide layer was coated on the n-type a-Si:H surface. Heat treatment at 210°C with 2×105 Pa H2O vapor for 1h was applied to the a-Si:H p-i-n solar cells. Electrical characteristics were measured when samples were kept in dark and illuminated with light of AM 1.5 at 100mW/cm2. The heat treatment with H2O vapor increased fill factor (FF) and the conversion efficiency from 0.54 and 7.7% (initial) to 0.57 and 8.4%, respectively. Marked improvement in solar cell characteristics was also observed in the case of a poor a-Si:H p-i-n solar cell. FF and the conversion efficiency were increased from 0.29 and 3.2% (initial) to 0.56 and 7.7%, respectively.

Surface Passivation of Crystalline Silicon by Combination of Amorphous Silicon Deposition with High-Pressure H2O Vapor Heat Treatment

A high minority carrier effective lifetime τeff of crystalline silicon was achieved by hydrogenated amorphous silicon (a-Si:H) films formed by a combination of plasma-enhanced chemical vapor deposition at 150 °C with high-pressure H2O vapor heat treatment. τeff was 1.6×10-4, 3.0×10-4, and 1.15×10-3 s for n-type silicon substrates coated with 3-, 10-, and 50-nm-thick a-Si:H films treated with 1.0×106 Pa H2O vapor heat treatment between 180 and 300 °C for 1 h. Light-induced passivation enhancement was demonstrated when 620-nm light was illuminated at the 50-nm-thick a-Si:H surface. τeff increased from 8.5×10-4 to 1.15×10-3 s probably caused by field effect passivation induced by hole trapping at the SiOx formed by H2O vapor heat treatment for 1 h. On the other hand, τeff was further increased to 1.2×10-3 s by 1.0×106 Pa H2O vapor heat treatment at 300 °C for 3 h for the sample formed with the 50-nm-thick a-Si:H film. However, no increase in τeff was observed by light illumination at the a-Si:H surface, probably because the SiOx clusters became stable and had no hole trapping property.

Passivation of Silicon Surfaces by Formation of Thin Silicon Oxide Films Formed by Combination of Induction-Coupled Remote Oxygen Plasma with High Pressure H2O Vapor Heat Treatment

ABSTRACTWe report formation of thin silicon oxide films on the silicon surfaces by combination of oxygen radical and high pressure H2O vapor heat treatment for passivation of silicon surfaces at a low temperature. Oxygen plasma was generated by 13.56 MHz radio frequency induction-coupled remote plasma with mixed gases of O2 and Ar at 2 sccm, 2x10-2 Pa and at a power of 50 W. Oxygen radical was produced from the plasma via a metal mesh closing plasma in the reactor. The top surfaces of 20 Wcm n-type silicon substrates with the rear surface coated by thermally grown SiO2 layers were exposed by oxygen radical from 1 to 5 min to oxidize the silicon surface. The samples were subsequently annealed with 9.0x105 Pa H2O vapor heat treatment at 260oC for 3 h. The effective minority carrier lifetime estimated using photo-induced carrier microwave absorption system in the case of 635 nm light illumination at 1.5 mW/cm2 to the top surface increased from 1.3x10-4 to 5.1x10-4s as the oxygen radical treatment duration increased from 1 to 5 min. The recombination velocity decreased from 380 to 90 cm/s. 500 kHz capacitance response with bias gate voltages characteristics of metal oxide semiconductor structure resulted in the effective oxide thicknesses (EOT) ranging from 1.3 to 1.7 nm. These results indicate a capability of thin oxide formation and effective passivation of silicon surfaces at a low temperature.

Defect Reduction in Polycrystalline Silicon Thin Films at 150 °C

We report defect reduction in 50-nm-thick laser-crystallized polycrystalline silicon (poly-Si) films by a combination of hydrogen plasma at 100 W for 5 s at room temperature with 4.7×105 Pa H2O vapor heat treatment at 150 °C for 6 h. The present treatment increased the photoconductivity to 1×10-3 S/cm for undoped poly-Si films under the illumination of 532 nm light at 100 mW/cm2. It also increased the electrical conductivity to 30 S/cm for 2×1019 cm-3 phosphorus-doped poly-Si films. Those values were comparable to those for samples treated with 1.3×106 Pa H2O vapor heat treatment for 3 h at 260 °C. Hydrogen concentration increased from 1.6 to 5.4 at. % as hydrogen plasma duration increased from 5 to 120 s. It was decreased by subsequent H2O vapor heat treatment at 150 °C, and ultimately ranged from 1.1 to 4.5 at. %. Hydrogen atoms play a catalytic role in the dissociation of H2O molecules at 150 °C.

Analysis of Microwave Absorption Caused by Free Carriers in Silicon

Microwave absorption caused by free carriers was investigated. A 9.35 GHz microwave interferometer was constructed. The transmissivity of 525-µm-thick silicon substrates decreased from 60.4 to 3.8% as the resistivity decreased from 1000 to 4 Ω cm. This characteristic was explained well by a numerical analysis using the free carriers absorption theory. Microwave free carrier photo absorption caused by light-induced carriers was also investigated for p-type silicon samples coated with 100 nm thermally grown SiO2 layers as well as SiOx layers deposited by the vacuum evaporation method. The effective minority carrier lifetime and recombination velocity were analyzed in the case of the photo induced carrier generation with 532 nm light illumination. The effective minority carrier lifetime was increased from 360 to 540 µs and the recombination velocity was decreased from 78 to 30 cm/s by 1.3 ×106 Pa H2O vapor heat treatment at 260 °C for 3 h for light illumination at 0.315 mW/cm2 in the case of the thermally grown SiO2/Si because of the passivation of SiO2/Si interfaces. They were markedly increased from 30 to 380 µs and from 1300 to 60 cm/s, respectively, by the H2O vapor heat treatment in the case of the vacuum-evaporated SiOx/Si.

Improvement in SiO2 Film Properties Formed by Sputtering Method at 150 °C

The quantity of hysteresis phenomena in capacitance response for metal–oxide–semiconductor (MOS) capacitors with 100-nm-thick SiO2 films formed by the sputtering method was reduced by remote oxygen plasma treatment followed by high-pressure H2O vapor heat treatment at 150 °C. In order to determine the quantity of hysteresis phenomena in capacitance response, we defined hysteresis charge as the difference in fixed oxide charge density for round bias voltage application. As-fabricated MOS capacitor samples had a high density of hysteresis charges of 1.0×1012 cm-2. The density of hysteresis charge was not decreased by 4.7×105-Pa-H2O-vapor heat treatment at 150 °C for 3 h. On the other hand, it was markedly reduced to 1.0×1011 cm-2 by 13.56-MHz-radio frequency remote oxygen plasma treatment at 300 W and 150 °C followed by 4.7×105-Pa-H2O-vapor heat treatment at 150 °C for 3 h. Hysteresis phenomena are probably caused by a temporal electron charging up of SiO2 films.

Polysilazane Precursor Used for Formation of Oxidized Insulator

ABSTRACTWe report on SiO2 film formation using Polysilazane precursor treated with remote oxygen plasma and high-pressure H2O vapor heating. Polysilazane precursor films with a thickness of 130 nm were formed on silicon substrates by spin coating method. They were annealed at 350°C in remote oxygen plasma at a pressure of 2.0×10−2 Pa and a 13.56×106 Hz radio frequency power of 300 W for 3h followed by 1.3×106-Pa-H2O vapor heating at 260°C for 3 h. Polysilazane precursor films were entirely oxidized by high-pressure H2O vapor heat treatment, and the density of Si-N bonding and Si-H bonding in Polysilazane precursor films were effectively dissociated by the combination of high-pressure H2O vapor heat treatment with remote oxygen plasma treatment. While MOS(Metal-Oxide-semiconductor) capacitors fabricated only by high-pressure H2O vapor heat treatment had a high specific dielectric constant of 6.1, a fixed oxide charge density of 1.3×1012 cm−2 and a density of interface trap of 5.4×1011 cm−2eV−1, the remote oxygen plasma treatment followed by high-pressure H2O vapor heat treatment allowed us to reduce them to 4.1 and 1.6×1011 cm−2, 4.2×1010 cm−2eV−1, respectively.

Defect Reduction in Polycrystalline Silicon Thin Films by Heat Treatment with High-Pressure H2O Vapor

We investigated defect reduction in laser crystallized polycrystalline silicon (poly-Si) films by heat treatment with 1.3×106 Pa H2O vapor. The H2O vapor heat treatment at 260 °C for 6 h reduced the spin density in laser crystallized poly-Si films from 2.0×1018 (initial) to 6.5×1016 cm-3. The activation energy of the reaction for defect reduction was 0.26 eV. Photoconductivity under 532 nm light illumination at 100 mW/cm2 was increased from 2.7×10-6 (initial) to 3.3×10-5 S/cm by heat treatment for 1 h. The oxygen concentration in the silicon films was increased by 1.1×1019 cm-3 by heat treatment, although the hydrogen concentration was decreased by 1.4×1020 cm-3. This suggests that oxygen atoms have an important role in defect state reduction in polycrystalline silicon films.

Defect Reduction Treatment for Plasma–Tetraethylorthosilicate–SiO2 by High-Pressure H2O Vapor Heat Treatment

Improvements in the electrical and structural properties of tetraethylorthosilicate (TEOS) SiO2 films fabricated by plasma-enhanced chemical vapor deposition (PECVD) method were investigated using high-pressure H2O vapor heat treatment. The density of interface trap states was reduced from 3.3×1012 (initial) to 5.1×1010 cm-2 eV-1 by 1.3×106 Pa H2O vapor heat treatment at 260°C for 9 h. The density of fixed charges was also reduced from 6.1×1011 to 1.3×1011 cm-2. The full width at half-maximum (FWHM) of the optical absorption band corresponding to vibration of Si–O–Si bonding was reduced from 82.9 to 78.1 cm-1. Narrowing in FWHM of the Si 2p core level peak measured by X-ray photoelectron spectroscopy (XPS) was also observed. The reduction in the FWHM probably results from improvement of the Si–O bonding network.

Analysis of plasma treatment and vapor heat treatment for thin-film transistors by extracting trap densities at front and back interfaces

Hydrogen (H) plasma treatment, oxygen (O) plasma treatment and water (H2O)-vapor heat treatment for polycrystalline-silicon (poly-Si) thin-film transistors (TFTs) have been analyzed by separately extracting trap density at a front silicon-oxide interface (DF) and trap density at a back interface (DB). It is found that the H plasma treatment is apt to generate DF and DB. The O plasma treatment reduces DF, while the H2O-vapor heat treatment reduces both DF and DB. Improvement of transistor characteristics of poly-Si TFTs depends on understanding these results.

Electrical properties of solid-phase crystallized polycrystalline silicon films

Analyses of free-carrier optical absorption and Hall-effect current measurements indicated in high carrier mobilities of 32 cm2/Vs and 30 cm2/Vs, respectively, and low carrier densities of 5.0×1019 cm-3 and 3.8×1019 cm-3, respectively, for 1.1×1020 cm-3-phosphorus-doped solid-phase crystallized polycrystalline silicon films fabricated at 600 °C for 48 h. The silicon films had good crystalline properties of the crystalline grains and a low crystalline volume fraction of 0.43. A XeCl excimer laser anneal at 500 mJ/cm2 effectively increased the carrier density to 1.1×1020 cm-3, and also increased the crystalline volume fraction to 0.93. Moreover, H2O-vapor heat treatment at 1.3×106 Pa for 3 h at 260 °C reduced the density of the defect states from 6.2×1018 cm-3 to 2.6×1018 cm-3.

Oxygen plasma and high pressure H 2 O vapor heat treatments used to fabricate polycrystalline silicon thin film transistors

Oxygen plasma and high pressure H2O vapor heat treatment were applied to fabrication of n-channel polycrystalline silicon thin film transistors (poly-Si TFTs). 13.56 MHz-oxygen-plasma treatment at 250 °C, 100 W for 5 min effectively reduced defect states of 25-nm-thick silicon films crystallized by 30 ns-pulsed XeCl excimer laser irradiation. 1.3×106-Pa-H2O vapor heat treatment at 260 °C for 3 h was carried out in order to improve electrical properties of SiOx gate insulators and SiOx/Si interfaces. A carrier mobility of 470 cm2/V s and a low threshold voltage of 1.8 V were achieved for TFTs fabricated with crystallization at 285 mJ/cm2.

Electrical Properties of Solid Phase Crystallized Silicon Films

ABSTRACTIn this study, the carrier mobility and density for solid phase crystallized (SPC) silicon films fabricated at 600 °C for 48 hours are analyzed by free carrier optical absorption. The carrier mobility is 40 cm2/Vs for SPC films doped with 6×1019-cm−3-phosphorus atoms. This analysis suggests the SPC films have fine crystalline grains closed to single crystalline silicon. In addition, initial carrier density was 3×1019 cm−3, which increased to 6×1019 cm−3by XeCl excimer laser irradiation of 500mJ/cm2. The inactivated regions in SPC films are reduced by laser irradiation. However, the electrical conductivity after laser irradiation for SPC films doped with 6×1018-cm−3-phosphorus atoms decreased from 3.3 to 0.018 S/cm as laser energy density increased to 500mJ/cm2. On the other hand, the electrical conductivity increased from 14.7 to 31.3 S/cm with similar increase of laser energy density after H2O vapor heat treatment at 260°C for 3 hours with 1.3 MPa. Furthermore, the characteristics of n-channel TFTs fabricated with initial SPC films as well as SPC films which was irradiated by laser at 425mJ/cm2 are also researched. The threshold voltage is decreased from 3.8 to 2.0 V by laser irradiation. Threshold voltages of both cases are decreased from 3.8 to 2.4 V for no-laser irradiation and from 2.0 to 0.8 V for laser irradiation, after H2O vapor heat treatment at 310°C for 1 hour with 9.0MPa. Based on the above trial, the defect reduction method combining laser irradiation and H2O vapor heat treatment has proved to be very effective for SPC films and SPC TFTs.

Electrical Properties and Defect States of Laser Crystallized Polycrystalline Silicon Films

ABSTRACTIn this paper, changes in electrical properties of laser crystallized silicon films doped with 8.5×1017-cm−3-phosphorus atoms as a function of laser shot number are investigated. The samples are treated with plasma hydrogenation for 30 sec at 130 Pa at 250 °C and additional H2O vapor heat treatment at 260 °C for 3 hours with 1.3 MPa. The electrical conductivity at room temperature become about 10−6∼10−-5 S/cm as laser shot number increases from 1 to 100. After hydrogenation and additional H2O vapor heat treatment, electrical conductivity remarkably increases to 100∼101S/cm. At laser irradiation of 20 or 50 shots after both treatments, the density of defect at deep level states and tail states are determined 1.15×1017 cm−3 and 5.7×1017cm−3 using an analysis program. Potential barrier height at grain boundary is 0.048 eV. The effective carrier density and carrier mobility are markedly increased up to1017cm−3 and 209 cm2/Vs by hydrogenation and additional H2O vapor heat treatment.