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Recently, the journal "Nature" published a new technology for laser thinning of gallium nitride single crystals, and its authors include Nobel laureate Hiroshi Amano.

According to reports, this technology can increase the production capacity of gallium nitride substrates by 3 times, and at the same time can save the substrate polishing process, so it helps to reduce the manufacturing cost of gallium nitride single crystal devices, and this technology is also expected to be applied to silicon carbide single crystal devices. 

According to the literature, a research team composed of Nagoya University and the National Institute of Materials Science of Japan has developed a new GaN substrate thinning technology-laser thinning technology.

Previously, they have demonstrated that GaN single crystals can be cut with a laser, and the cut GaN substrates can be reused after polishing.

This time, they have proved through experiments that this technology is also suitable for GaN-on-GaN HEMT device fabrication, that is, thinning using a laser process after device fabrication, which can significantly reduce the consumption of GaN substrates.

High loss and low yield

Traditional technology has many limitations

As we all know, GaN is a very ideal material for making power devices. However, GaN substrates are expensive, and GaN-based devices fabricated on GaN substrates have not yet been commercialized in a wide range of fields. Therefore, in order to reduce the consumption of expensive GaN substrates as much as possible, the thinner the substrate slices, the higher the yield, which is the goal pursued by the dicing technology.But traditional technology has many limitations.

        Firstly, the loss is large. The traditional technology cannot avoid the notch loss during the slicing process, and the substrate surface cannot be polished and reused, and a device layer can be obtained by requiring more GaN substrates.

        Secondly, the yield rate is low. The general process of traditional technology is to slice first, and then bond the corresponding crystals before subsequent manufacturing. Then a series of issues such as bonding device layers, such as chemical and thermal effects, need to be considered. In the process, the possibility of defective products is increased.

        Most of the traditional technologies are to first cut a GaN substrate from a GaN crystal, and then slice from the substrate for subsequent manufacturing. However, it is unavoidable that the problems of large loss and low yield will be caused.Previously, only one device layer was fabricated per 400-micron-thick GaN substrate.

New technology:

Reduce 300% GaN substrate loss

In order to break through the limitations of the above-mentioned technologies, the research team has developed a new method for thinning GaN substrates based on laser technology, which can minimize the consumption of expensive GaN substrates, and every 100 microns thick GaN substrate can To make a device layer, the loss is reduced by 300% compared to the past.

        This technique has been shown to allow thinning after device fabrication, and no significant fractures were observed in thinned devices during experiments, and no detrimental effects on electrical properties were observed.

        There is also a notable highlight of this technology: thinning after device fabrication, the amount of GaN substrate consumed will be only the thickness of the sliced device layer, which can be removed by polishing for reuse. In other words, the use of this new technology is expected to achieve zero loss of GaN substrates!

In addition, thinning after device fabrication makes it easier to obtain thin GaN layers. The thinner the device, the better the heat dissipation, the better the performance.

        It is mentioned in the literature that this new technology is similar to the traditional Smart Cut™ technology, which uses ion implantation to cut very thin GaN layers with sub-micron thickness. But laser cutting technology is difficult to cut out such thin layers of GaN because GaN is decomposed during the laser cutting process.

        To this end, the team pioneered the backside laser irradiation method to lift off the device layers.

        The experimental results show that the GaN-on-GaN HEMT can still work normally when the GaN-on-GaN HEMT is thinned to a thickness of 50 μm by laser technology, and the electrical characteristics of the device before and after slicing do not change much. This means that the laser thinning process can be applied even after device fabrication. It can also be used as a semiconductor process to fabricate thin devices with a thickness of about 10 μm without polishing the GaN substrate.