Takeshi Matsumoto’s scientific contributions

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.

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.

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.

Ion beam instabilities on a wide ribbon beam which cross-section is 150 cm × 10 cm are discussed. At low energy conditions, we detected two kinds of instabilities on the ion beam extracted from BF3 plasmas. One kind of the instabilities is that onset of the instability is dependent on the extraction current from the ion source. This instability occurred when the extraction current exceeded 300 - 350 mA at the energy of 15keV. Another is that the onset is dependent on the BF2+ beam current. The BF2+ beam current became unstable when it exceeded about 20 μA/cm2 at 15keV. Energy dependence of these instabilities is also discussed.

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.

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.

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.

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.

Ion beam irradiation was employed to produce alignment layers for liquid crystal (LC) displays. The alignment characteristics were compared with those by the conventional rubbing method. Ion incident angle to the films played an important role in LC sample optical qualities. A new ion irradiation method to realize a multi-domain structure for a wide viewing angle was demonstrated.