1. Improve the two-step growth process
At present, the commercial production adopts a two-step growth process, but the number of substrates that can be loaded at one time is limited, the six-chip machine is relatively mature, and the 20-piece machine is still mature, and the number of sheets is large, resulting in insufficient wafer uniformity. The development trend is two directions: one is to develop more substrate wafer growth in the reaction chamber at one time, more suitable for large-scale production technology to reduce costs; the other is highly automated repeatability Monolithic device.
2. Hydride vapor phase wafer (HVPE) technology
This technique allows the rapid growth of thick films with low dislocation density, which can be used as substrates for homogenous wafer growth by other methods. And the GaN thin film separated from the substrate is likely to be a substitute for the bulk single crystal GaN chip. The disadvantage of HVPE is that it is difficult to precisely control the film thickness, the reaction gas is corrosive to the device, and the purity of the GaN material is further improved.
3. Selective wafer growth or lateral wafer growth techniques
This technique can further reduce the dislocation density and improve the crystal quality of the GaN wafer layer. First, a layer of GaN is deposited on a suitable substrate (sapphire or silicon carbide), and a polycrystalline SiO mask layer is deposited thereon, and then a GaN window and a mask layer are formed by photolithography and etching techniques. article. During the subsequent growth process, the wafer GaN is first grown on the GaN window and then grown laterally on the SiO strip.
4. Suspended wafer technology (Pendeo-epitaxy)
By using this method, a large number of lattice defects in the wafer layer due to lattice mismatch and thermal mismatch between the substrate and the wafer layer can be greatly reduced, thereby further improving the crystal quality of the GaN wafer layer. The GaN wafer layer is first grown in a two-step process on a suitable substrate (6H-SiC or Si). The wafer film is then etched selectively to the substrate. This forms the columnar structure of the GaN/buffer layer/substrate and the alternate shape of the grooves. The GaN wafer layer is then grown, and the grown GaN wafer layer is suspended above the trenches, which is a lateral wafer growth on the sidewalls of the original GaN wafer layer. With this method, no mask is required, thus avoiding contact between the GaN and the pickle material.
5. Develop UV LED wafer material with short wavelength
It also produces white light for the development of UV trichromatic phosphor compounds.