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Amorphous indium-gallium-zinc oxide (a-IGZO) attracts much attention for next-generation flat-panel displays due to the large band gap, visible light transparency, printability, thickness-uniformity and low-temperature in film deposition. Using a-IGZO films, thin-film-transistors (TFTs) are realized, which show superior behavior compared with amorphous Si-based TFT. In order to further improve a-IGZO TFT performance via source-drain resistance reduction, plasma treatment, excimer laser annealing and ion implantation methods as the sheet resistance reduction techniques were investigated. Among them, the ion implantation methods have depth control ability through insulator layers and good verticality. In our previous work we elucidated that a-IGZO sheet resistance reduction can be attributed to oxygen vacancy (Vo) generated by noble gas implantation. However, there is still much room for clarifying and improving the implantation method, since it is difficult to measure the gas itself and vacancies profiles in a-IGZO due to small ionization cross sections and small existence ratio. In addition many injectable ion species in a-IGZO are not investigated in detail. In this work, we carried out one of the conventional ion boron (B+) or noble gas neon ion (Ne+) implantations and investigations in 50-nm-thick a-IGZO film on glass. Electron transport properties of B+ or Ne+ implanted a-IGZO films as a function of the a-IGZO depth were investigated by room temperature Hall measurements combined with wet etchings. In case of Ne+ implanted a-IGZO film, we estimated Vo relation density depth profile consistent with the electron concentration depth profile in a-IGZO and implanted Ne density depth profile, since the Ne itself cannot be a donor. In case of B+ implanted a-IGZO film, the Vo concentration profile is not agreement with electron concentration profile only, but also agreement the B profiles at the deep position in the a-IGZO. On the other hand, bonding analyses by X-ray photoelectron spectroscopy (XPS) were carried out. From the XPS results, we find that Vo increases after the Ne+ implantation in a-IGZO and Boron-Oxygen bonding is dominant for the implanted B+ in a-IGZO, which indicates also that boron itself contribute the a-IGZO resistance reduction. Based on the knowledges obtained by the Hall measurements and the XPS results, we carried out a-IGZO TFT processes with gate length L g = 4-10 um and channel width 10 um via the appropriate ion energies and doses of B+ or Ne+ implantation. The TFTs show off current 10-12 A/mm, on/off ratio ~108 in the case of the both ions from relations between gate voltage and drain current. In addition, we investigated the device scalability. The electrical channel length (L eff) is not the same as the L g, and is determined by the carrier profile at the gate edges. L eff = L g - ΔL is obtained by the transmission line method (TLM). From TLM results, we find that the ΔL < 1 um in case of the B+ implantations and ΔL ~ 1 um in case of the Ne+ implantations. In summary, we elucidated that a-IGZO sheet resistance reduction can be attributed to Vo or boron itself. In addition, a-IGZO TFT processes with the ion implantations were carried out, which indicate good on/off ratios and microfabrication possibilities for industrial application. We expect that the B+ or Ne+ implantations in a-IGZO films are useful as resistance control technique for a-IGZO device processing. This work is supported by Beam and Plasma Technology Laboratories Research and Development Division NISSIN ELECTRIC CO., LTD. in the large number of sample preparations and analyses.

We investigated electron transport properties of an argon ion (Ar+) implanted a-IGZO film on glass by Hall measurement combined with wet etching. As a result, we obtained concentration and mobility of electron as a function of depth in the a-IGZO from the surface, and high concentration area in depth distributed deeper compared with one of the argon plasma treated a-IGZO. In addition, we estimated the implanted Ar atom and oxygen vacancy depth-profiles in the a-IGZO. We confirmed Ar stopping powers of a-IGZO and the donor level of 0.05-0.1 eV below bottom of conduction band energy, which can be applied to resistance control technique for a-IGZO device processes.

We report formation of low resistivity n-type doped silicon region at 300°C by the method of two-step ion implantation. Phosphorus ions with a dose of 2×1014 cm−2 at 70 keV followed by hydrogen ions with 1×1016 cm−2 at 8 keV were implanted at RT to the both surfaces of single crystalline silicon substrates. Post heating at 300°C for 90 min decreased the sheet resistivity to 417 Ω/sq. The activation ratio was estimated as 75% under the assumption of electron mobility of 50 cm2/Vs in the doped region. Moreover, the minority carrier effective lifetime (τ eff ) was also increased to 253 μs. This indicates a low density of surface recombination defect states of 6.4×1010 cm−2. In contrast, a high sheet resistivity of 8×104 Ω/sq and a low τ eff of 64 μs resulted from a single phosphorus ion implantation with 2×1014 cm−2 at 70 keV followed by 300°C heating for 90 min. The hydrogen ion implantation probably decreased the silicon bonding energy to easily move phosphorus atoms in the silicon lattice sites at 300°C and passivated the doped region by terminating silicon dangling bonds.

The H+ or Ar+ precursor implantation at room temperature (RT) was proposed to activate boron atoms subsequently implanted in single crystalline silicon by post heating at a low temperature. The two-step ion implantation of 1.5×1016 cm−2 H+ at 8 keV followed by 1.0×1015 cm−2 B+ at 40 keV for both surfaces of silicon and 1.0×1014 cm−2 Ar+ at 70 keV followed by 1.0×1015 cm−2 B+ at 40 keV resulted in low sheet resistivities of 520 and 890 Ω/sq, respectively by post heating at 300°C for 30 min. Their activation ratios were estimated as 22 and 13%. The optimization of the projected ranges of 79 nm for 6×1013 cm−2 Ar+ at 70 keV and of 46 nm for B+ at 10 keV further decreased the sheet resistivity to 392 Ω/sq and increased the activation ratio to 29.5%. The activation of B+ implanted region at 300°C probably resulted from a decrease in the activation energy induced by a decrease in the silicon bonding energy promoted by the first H+ or Ar+ precursor implantation.

A plasma flood gun (PFG) has been developed for NISSIN Implanter “iG5” [1] and “iG6” for Gen5.5 and 6.0 FPD processing under high vacuum. This PFG contains a multi-cusp type arc chamber with a filament cathode. It generates the ions and electrons using a low feed Xenon (Xe) gas. In this paper, we investigated the neutralization of positive and negative charges on an insulator by the PFG under high vacuum conditions. The potential of the Al sheet on the insulator plate which was raised up to +1 or −1 kV in advance was neutralized to −0.005 kV in the 0.3 and 1.2 seconds by the PFG, respectively. We also reported the neutralization of the positive and negative charge pairs on the front and back surfaces of an insulator by the PFG.

Ion implantation of 1.5xl016-cm−2 H+ at 8 keV or 1.0xl014-cm−2 Ar+ at 70 keV was carried out at room temperature (RT) to crystalline silicon in advance of ion implantation of 1.0×10-15-cm−2B+ at RT. Decrease in the crystalline volume ratio and generation of crystalline defects were promoted by the first H+ or Ar+ implantation. Subsequently post heating at 300°C for 30 min decreased the sheet resistivity to 520 and 890 Ω/sq in the cases of the H+ and Ar+ implantation, respectively. The decreases in the sheet resistivity by 300°C post annealing is interpreted that formation of crystalline defects by the first H+ or Ar+ implantation decreased the activation energy for moving boron atoms from the interstitial to lattice sites and achieved carrier generation at the low temperature.

For the manufacturing process of display for mobile devices using Low Temperature Poly-crystalline Silicon Thin Film Transistor (LTPS-TFT), ion doping processes have been required. Nissin developed ion doping systems which were referred as iG series and they have already been used in production lines of many panel makers. In these systems, the basic concept of ion source and beam line has been unchanged. We use a multi-cusp ion source with hot cathodes to produce source plasma. Ribbon shaped ion beams extracted through a large area plasma electrode system are introduced into an analyzing magnet and only the dopant ions are transported to the target. In our ion source, the ratio of B+ in BF3 plasma can be increased by applying positive potential to a plasma electrode with respect to plasma chamber, whereas that of BF2+, BF+, F+ can be selectively decreased. This allows obtaining higher B+ beam currents from the ion source efficiently. In addition, the position of the filaments inside the plasma chamber is optimized for B+ beam extraction. However, for PHx+ beam extraction, the position was not switched. We developed a new mechanism which could adjust the position of the filaments without breaking high vacuum. The filament position can be changed by using the metal bellows expansion joint attached to the plasma chamber. By this mechanism, the filament position can be optimized for both of B+ and PHx+ beam extraction. For example, in iG6, if we inserted the filaments 30 mm deeper than original filament position into the plasma chamber, we could decrease arc current by 40% to obtain the same PHx+ beam current.

Ion doping tools which have ability to process large size glass substrate with high productivity are briefly described. Such tools might develop new fields that utilize ion implantation technology. So far we tried several applications. In this study, three applications for which large area treatment will be essential to commercial production are reported.

A plasma flood gun (PFG) has been developed for Nissin implanter "iG5 [1]" and "iG6" for Gen. 5.5 and 6.0 flat panel display (FPD) process. The PFG with a filament cathode can supply high electron flux in order to neutralize the surface charge of glass substrate irradiated by the high current ion beam [2]. We investigated the charge-up of the target glass substrates irradiated by the ion beam and the neutralization effect by the PFG using the Single Langmuir probes. The PFG effectively reduced charge-up voltage, and this neutralization effect appeared uniformly at the all part of the glass surface in the large size ribbon beam.

Buried void layer formation in silicon substrates was achieved by hydrogen ion implantation followed by 940-nm infrared laser rapid heating. P-type silicon substrates coated with 100-nm-thick thermally grown SiO2 layers were implanted with hydrogen atoms at 5x10 15 and 3x10 16 cm -2 at 60 keV. Structural investigation with analysis of optical reflectivity spectra revealed that 3x10 16 cm -2 implantation caused a void layer with a void ratio of 0.04 at a depth of 250 nm close to the position of hydrogen peak concentration. Laser irradiation at 4.2x10 4 W/cm 2 increased the void ratio to 0.12. No void layer was observed at ion implantation stage for sample with 5x10 15 cm -2 -hydrogen atoms. Laser irradiation at 4.9x10 4 W/cm 2 formed a void layer with a void ratio of 0.013 at a depth of 255 nm.

We have developed an ultra-high current ion implantation system for high throughput wafer processing. The ion source is designed based on implanters used in the flat panel display industry to produce 80 cm high beams which exceed 80 mA. Multiple wafers are processed at a time with the large-sized beam. The implantation tool exhibited throughput of 107 and 38 wafers per hour for 1E16 and 1E17 ions/cm2, respectively. Successful InP layer transfer with smooth surface was demonstrated using Smart Cut™ technology.

A multi-cusp ion source was designed for Nissin ion doping system "iG5" developed for GEN5.5 processes. It has many points of similarity to iG4 ion source. The extraction area and the internal volume of the plasma chamber are scaled up. And the method to obtain high current B+ beams is same as iG4 ion source. On the other hand, iG5 ion source has an added feature on the extraction system. We use new developed multi-slit extraction system to obtain stable beams with small divergence. The target boron beam current density of 1mA/cm (that is 130mA) was obtained.

We have developed a new implantation tool for the generation 5.5 glass. 150 cm high ion beams, which are bigger than the glass height, are extracted from the ion source. After being bent by the mass separation magnet, the beams reach the glass which is standing upright. The new tool exhibits high throughput in high dose applications because of high beam current capability. To cut down on time and workload of maintenance, dedicated kits were designed. A new cleaning method developed to extend the ion source lifetime showed excellent performance of reduction in the beam glitches.

An accurate dose distribution control system was developed for a Nissin iG4 ion implanter, which is utilized for low temperature polycrystalline silicon thin film transistors (LTPS‐TFT), to improve dose uniformity under a photoresist outgas environment. The system consisted of a scan speed controller for glass substrates and monitors of ion beam flux to the target and pressure. To examine the performance, silicon wafers fixed on a glass sheet covered with photoresist were implanted. The dose uniformity was evaluated by measuring sheet resistance. Good uniformity was demonstrated with the use of the dose control under pressure variations of one order of magnitude.

A multi‐cusp ion source with large area extraction area has a capacity to extract high current ion beams. However it is difficult to obtain high current boron ion beams from boron trifluoride plasma as input power density is low and BF2+ is a main ion species. It was found that fluoride ion currents were selectively decreased by applying positive potential to a plasma electrode with respect to a plasma chamber. Using this method to a multi‐cusp ion source with adequate magnet configuration, high current boron ion beams of 500 μA/cm were obtained.

A mass analyzing ion implantation system (called Ion Doping iG4) was developed for FPD manufacturing. One of most important concept of iG4 is to transport a sheet ion beam maintaining its current density profile from the ion source to the target, which leads good mass resolution and simple control of the beam profile. The system has a bucket type ion source which provides a sheet ion beam whose longer dimension of the cross section is 800 mm the 4th generation FPD glass substrate generally sized 730mm × 920mm. The sheet ion beam is mass‐analyzed with a dipole sector magnet with a long pole gap. In order to enhance through‐put for Source Drain implantation processes, we modified the ion source to increase high beam currents and obtained 300μA/cm for Boron ion beams and 500μA/cm for Phosphorus ion beams. Better uniformity and higher mass resolution were achieved by optimizing shape of the analyzing magnet pole faces.

The Nissin ion doping system ID6700 for TFT LCD fabrication uses a large area ion source generating a uniform line beam which irradiates a large glass substrate. A uniform ion beam can be obtained across a large substrate over 600 mm, which is automatically tuned by individually adjusting the heating currents of the three filaments based on the beam profile data taken by a built-in multiple-slot Faraday array. The fraction of hydrogen ions in the beam has been successfully reduced to less than 10% by preventing the hydrogen ion extraction by applying a magnetically retarding configuration in the source plasma. A unique mass separation structure using permanent magnets has been placed close to the beam extraction system of the bucket type ion source to form a purified large area uniform beam to process the large glass substrate with high throughput.

We developed a multi-cusp ion source for Nissin ion doping system iG5 which is used in low temperature poly-crystalline silicon processes for flat panel display (FPD) manufacturing. In this ion source, BF3 or PH3 diluted H2 plasmas are produced and large area ribbon ion beams are extracted. In general, ion ratio of B(+) in BF3 plasma is much smaller than BF2 (+) in multi-cusp ion sources. We developed a new method to increase B(+) ratio and obtained mass analyzed B(+) target current of 130 mA. We employed newly improved multi-slot type electrodes for the beam extraction system and obtained stable beams with the uniformity of below 3%. In BF3 plasmas, several undesirable metal fluorides are produced in the plasma chamber and deposited on the electrode system, which cause glitches and poor beam uniformity. We introduce several cleaning methods.