SEMICON Japan 2025:New Movements in Manufacturing Process Technologies

SEMICON Japan 2025 was held at Tokyo Big Sight from December 17 to 19. Below are selected highlights picked up through a subjective lens.

KOBELCO Promotes Post-IGZO Sputtering Targets

While not entirely “What's New,” one of the most impactful exhibits was the oxide semiconductor sputtering target for displays “the KOS Series” promoted by Kobelco Research Institute. This original oxide semiconductor target is based on conventional IGZO (InGaZnO) doped with Sn, achieving carrier mobility of 20-30 cm²/V・s, which is 2-3 times higher than that of standard IGZO.

Pic.1 Oxide semiconductor sputtering target for 300 mm wafer

A prototype etch-stopper-type bottom-gate TFT fabricated by the KOBELCO Group demonstrated high performance, with mobility of 29.1 cm²/V・s, Vth = 0.5 V, and S.S factor = 0.17 V/dec. The amorphous film can be deposited at a relatively low temperature of 350 ℃ using conventional DC magnetron sputtering and can be wet-etched with acid.

The targets are available not only in circular and rectangular planar types but also in cylindrical rotary types. In recent years, demand for rotary targets offering a high material utilization rate of around 50% has been increasing.

Incidentally, in the display field, the targets have already been adopted for mass production by TFT-LCD and OLED manufacturers in China and South Korea, and they appear to be steadily eroding the stronghold long held by conventional IGZO targets.

AI-Equipped Systems Improve IJ Printing Stability and Accuracy

In manufacturing equipment, Elephantech showcased its presence by exhibiting the actual unit of its high-precision inkjet printer “ELP04 PILOT,” which was specially developed for the company's proprietary nano Cu ink and paste, along with printed Cu ink/paste samples.

Pic.2 IJ printed sample on glass

The ELP04 PILOT is an inkjet system equipped with a proprietary AI platform called “NeuralJet.” By modeling and compensating in real time for error factors such as positional misalignment, nozzle-to-nozzle variation, printhead assembly errors, and fluctuations in nozzle condition, the system achieves stable ink ejection and high landing accuracy. In practice, it has achieved repeatability of less than 1 μm.

This means that even when printing droplets with a diameter of 20 μm into grooves 40 μm wide, 100% of the droplets land within the grooves. At the booth, samples printed by inkjet on glass and silicon wafers were displayed. Typical printed line-and-space resolution was L&S = 50 μm / 50 μm, demonstrating a 100% yield at this resolution.

Fine Patterns Using Ag Sintered Metal for Glass Substrates

Pic.3 Ag patterning sample using Ag sintered metal electrode

In process technology, Micro Engineering Laboratory, a company specializing in patterning, proposed a wiring formation technology for glass substrates using Ag sintered metal. As one might expect, the key feature is strong adhesion to glass substrates, along with excellent wettability when solder is bonded after Ag wiring formation.

Using a commercially available photosensitive Ag paste from Toray (Raybrid) and following coating, exposure, development, and firing processes, the company achieved fine patterns with a minimum L&S of 15 μm / 15 μm. The resulting resistivity was 3 × 10^-6 Ω・cm. However, because the firing temperature is relatively high 500 - 600℃, the process is limited to substrates such as glass and silicon wafers.

High-Boiling-Point Solvent Reduces Drying Nonuniformity After Resist Coating

In materials-related exhibits, DAICEL introduced a unique high-boiling-point solvent for photoresists called “CELTOL.” With a boiling point of 150 - 200℃, adding 5 - 10 wt% of CELTOL to photoresist allows the film to dry more slowly during the post-coating drying process on the substrate. As a result, coating nonuniformity is less likely to occur compared with photoresists formulated with conventional low-boiling-point solvents.