In the wafer preparation process, there are two core links: one is the preparation of the substrate, and the other is the implementation of the epitaxial process. The substrate, a wafer carefully crafted from semiconductor single crystal material, can be directly put into the wafer manufacturing process as a basis to produce semiconductor devices, or it can be further enhanced through epitaxial processes.
So, what is denotation? In short, epitaxy is the growth of a new layer of single crystal on a single crystal substrate that has been finely processed (cutting, grinding, polishing, etc.). This new single crystal layer and the substrate can be made of the same material or different materials, so that homogeneous or heteroepitaxial growth can be achieved as needed. Because the newly grown single crystal layer will expand according to the crystal phase of the substrate, it is called an epitaxial layer. Its thickness is generally only a few microns. Taking silicon as an example, silicon epitaxial growth is to grow a layer of silicon with the same crystal orientation as the substrate, controllable resistivity and thickness, on a silicon single crystal substrate with a specific crystal orientation. A silicon single crystal layer with perfect lattice structure. When the epitaxial layer is grown on the substrate, the whole is called an epitaxial wafer.
For the traditional silicon semiconductor industry, manufacturing high-frequency and high-power devices directly on silicon wafers will encounter some technical difficulties. For example, the requirements of high breakdown voltage, small series resistance and small saturation voltage drop in the collector area are difficult to achieve. The introduction of epitaxy technology cleverly solves these problems. The solution is to grow a high-resistivity epitaxial layer on a low-resistivity silicon substrate, and then fabricate devices on the high-resistivity epitaxial layer. In this way, the high-resistivity epitaxial layer provides a high breakdown voltage for the device, while the low-resistivity substrate reduces the resistance of the substrate, thereby reducing the saturation voltage drop, thereby achieving high breakdown voltage and small Balance between resistance and small voltage drop.
In addition, epitaxy technologies such as vapor phase epitaxy and liquid phase epitaxy of GaAs and other III-V, II-VI and other molecular compound semiconductor materials have also been greatly developed and have become the basis for most microwave devices, optoelectronic devices and power devices. Indispensable process technologies for production, especially the successful application of molecular beam and metal-organic vapor phase epitaxy technology in thin layers, superlattices, quantum wells, strained superlattices, and atomic-level thin-layer epitaxy have become a new field of semiconductor research. The development of “Energy Belt Project” has laid a solid foundation.
As far as the third-generation semiconductor devices are concerned, almost all such semiconductor devices are made on the epitaxial layer, and the silicon carbide wafer itself only serves as the substrate. The thickness of SiC epitaxial material, background carrier concentration and other parameters directly determine the various electrical properties of SiC devices. Silicon carbide devices for high-voltage applications put forward new requirements for parameters such as the thickness of epitaxial materials and background carrier concentration. Therefore, silicon carbide epitaxial technology plays a decisive role in fully utilizing the performance of silicon carbide devices. The preparation of almost all SiC power devices is based on high-quality SiC epitaxial wafers. The production of epitaxial layers is an important part of the wide bandgap semiconductor industry.
Post time: May-06-2024