NTT develops semiconductor film stripping process

This technology can manufacture thin GaN-based semiconductor thin film devices with a thickness of 2 μm at low cost, and is expected to expand the application range of GaN-based semiconductor thin film materials, such as solar cells that absorb ultraviolet rays efficiently after visible light transmission, and thin LEDs with a thickness of 200 μm. Wait. Further, by increasing the area of ​​the peelable film element, it is also expected to laminate other materials on a large-area film element to form a film element having a new function.

According to NTT, when a GaN-based semiconductor thin film device is laminated and processed on a sapphire substrate, the thickness of the substrate must be about 0.5 mm. Therefore, the world is studying how to completely peel the film member from the substrate after processing and attach it to other substrates. NTT's Institute of Physical Science Foundation focused on the development of BN (boron nitride) with the same layered crystal structure as graphite, and developed the MeTRe method (Mechanical Transfer using a Release layer). The MeTRe method can maintain the crystal face after peeling intact, so that the process of flattening the surface after peeling which is necessary for the previously proposed transfer method can be omitted. Moreover, the use of the MeTRe method does not require large equipment and chemical agents, and it is expected to significantly reduce manufacturing time and manufacturing costs.

As a high-quality laminated layered BN film which is one of the development points, the MeTRe method laminates a high-quality BN film having a layered crystal structure on a substrate, and laminates a high-quality film element thereon. In such a configuration, the BN film functions as a perforation of the stamp between the substrate for growth and the film member, and can be easily peeled off and attached to other substrates. According to NTT, this time, by finding the best film formation conditions, the lamination of high-quality BN films with uniform crystal orientation was achieved.

Two development points are high-quality stacked GaN thin film components on layered BN thin films. The development technique firstly laminates AlxGa1-xN (aluminum gallium nitride) or AlN (aluminum nitride) with different crystal structures on the layered BN thin film. As a buffer layer, a GaN thin film element is then laminated. When GaN having a wurtzite structure is directly laminated on a layered BN film, it is difficult to have a crystal structure. Al-containing AlxGa1-xN and AlN have good wettability with the substrate, and are widely used for lamination on substrates having different crystal structures. By using such a substance as a buffer layer between the layered BN film and GaN, a high-quality film element can be laminated regardless of the crystal structure.