From the working principle of LED , the wafer material is the core part of LED. In fact, the main photoelectric parameters such as wavelength, brightness and forward voltage of LED are basically dependent on the wafer material. Wafer technology and equipment are the key to wafer fabrication technology. Metal-Organic Chemical Vapor Deposition (MOCVD) technology is used to grow thin-layer single crystals of III-V, II-VI compounds and alloys. The main method. Here are some trends in LED future wafer technology.
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-piece machine is relatively mature, and the 20-piece machine is still mature, and the number of wafers is large, resulting in insufficient wafer uniformity. The development trend is two directions: one is to develop a technology that can load more substrate wafers in the reaction chamber at one time, which is more suitable for large-scale production 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 deposit a layer of GaN on a suitable substrate (sapphire or silicon carbide), deposit a polycrystalline SiO mask layer on it, and then use lithography and etching techniques to form a GaN window and mask layer. 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 selectively etched down 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 lays a solid foundation for the development of UV trichromatic phosphor white LEDs. There are many high-efficiency phosphors that can be excited by UV light, and the luminous efficiency is much higher than that of the currently used YAG:Ce system, which makes it easy to bring white LEDs to a new level.
6. Develop multiple quantum well chip technology
The multi-quantum well type is a quantum well doped with different impurities during the growth process of the light-emitting layer of the chip to directly emit white light by a plurality of photon recombinations emitted by different quantum wells. The method improves the luminous efficiency, can reduce the cost, and reduces the control difficulty of the packaging and the circuit; but the technical difficulty is relatively large.
7. Develop "photon recycling" technology
In January 1999, Sumitomo of Japan developed a white LED of ZnSe material. The technology is to first grow a layer of CdZnSe film on the ZnSe single crystal substrate. After energization, the blue light emitted by the film and the substrate ZnSe act to generate complementary yellow light, thereby forming a white light source. In the same way, the Photonics Research Center of Boston University in the United States stacked a layer of AlInGaP semiconductor composite on a blue GaN-LED, which also produced white light.
LED wafer process
Substrate>>Structural Design>>Buffer Layer Growth>>N-type GaN Layer Growth>>Multi-Quantum Well Light-Emitting Layer Growth>>P-Type GaN Layer Growth>>Annealing>>Detection (Photofluorescence, X-Ray)>> Wafer Wafer>>Design, processing reticle>>lithography>>ion etching>>N-type electrode (coating, annealing, etching)>>P-type electrode (coating, annealing, etching)>>dicing> >Graph sorting and grading (small soup)
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