In the semiconductor industry chain, especially in the third-generation semiconductor (wide bandgap semiconductor) industry chain, there are substrates and epitaxial layers. What is the significance of the epitaxial layer? What is the difference between the epitaxial layer and the substrate?
First of all, let’s popularize a small concept: wafer preparation includes two major links: substrate preparation and epitaxial process. The substrate is a wafer made of semiconductor single crystal material. The substrate can directly enter the wafer manufacturing link to produce semiconductor devices, or it can be processed by epitaxy to produce epitaxial wafers. Epitaxy refers to the process of growing a new single crystal on a single crystal substrate that has been carefully processed by cutting, grinding, and polishing. The new single crystal can be the same material as the substrate, or it can be a different material (homogeneous epitaxy). Epitaxy or heteroepitaxial growth). Since the newly formed single crystal layer grows along the substrate crystal phase, it is called an epitaxial layer (usually a few microns thick. Taking silicon as an example: the meaning of silicon epitaxial growth is to grow a layer of crystal with good lattice structure integrity on a silicon single crystal substrate with a certain crystal orientation and different resistivity and thickness from the substrate), and the substrate with the epitaxial layer is called an epitaxial wafer (epitaxial wafer = epitaxial layer + substrate). Device manufacturing is carried out on the epitaxial layer.
For the traditional silicon semiconductor industry chain, making devices on silicon wafers (especially high-frequency and high-power) cannot achieve the requirements of high breakdown voltage in the collector region, small series resistance, and small saturation voltage drop. The development of epitaxial technology has successfully solved this difficulty. Solution: Grow a layer of high resistance on a silicon substrate with extremely low resistance. The device is made on the epitaxial layer, so that the high resistivity epitaxial layer ensures that the tube has a high breakdown voltage, and the low resistance substrate reduces the resistance of the substrate, thereby reducing the saturation voltage drop, thus solving the contradiction between the two. In addition, the epitaxial technologies such as vapor phase epitaxy and liquid phase epitaxy of III-V, II-VI and other molecular compound semiconductor materials such as GaAs have also been greatly developed and have become indispensable process technologies for the production of most microwave devices, optoelectronic devices, power devices, etc., especially the successful application of molecular beam and metal organic vapor phase epitaxy in thin layers, superlattices, quantum wells, strained superlattices, and atomic-level thin layer epitaxy, which has laid a solid foundation for the development of “band engineering”, a new field of semiconductor research.
Regarding the third generation of semiconductor devices for silicon carbide devices, almost all of these semiconductor devices are made on the epitaxial layer, and the silicon carbide wafer itself is only used as a substrate. Parameters such as the thickness of SiC epitaxial materials and the background carrier concentration 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 the background carrier concentration. Therefore, silicon carbide epitaxial technology plays a decisive role in fully exerting the performance of silicon carbide devices. Almost all SiC power devices are prepared based on high-quality SiC epitaxial wafers, and the production of epitaxial layers is an important part of the wide bandgap semiconductor industry.
What is the significance of homogeneous epitaxy?
Epitaxy is divided into homogeneous epitaxy and heterogeneous epitaxy. Homogeneous epitaxy is the growth of an epitaxial layer of the same material as the substrate on the substrate. What is the significance of homogeneous epitaxy? For example, SiC substrate, epitaxial SiC, is there any difference between this and making it directly on SiC wafers? – Improve product stability and reliability. Although homogeneous epitaxy is the growth of epitaxial layers of the same material as the substrate, although the materials are the same, it can improve the material purity and uniformity of the wafer surface. Compared with the polished wafers processed by mechanical polishing, the substrate processed by epitaxy has high surface flatness, high cleanliness, fewer micro defects, and fewer surface impurities, so the resistivity is more uniform, and it is easier to control surface defects such as surface particles, stacking faults, and dislocations. Epitaxy not only improves the performance of the product, but also ensures the stability and reliability of the product.
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