1.Graphite Crystal Boat with CVD-SiC Coating
Graphite is easy to process and can be made into a single-piece crystal boat through multiple procedures from a single block material. As graphite is a porous material, a SiC layer with a thickness of approximately 100μm must be coated on its surface to prevent the partical problem caused by direct exposure of the graphite surface to various semiconductor manufacturing. However, the thickness of the CVD-SiC coating is not easy to control, especially in some deep holes and corners where the coating may be thinner. Due to the mismatch of CTE (coefficient of thermal expansion) between the graphite body and the SiC film (25-1400℃, with an average of 4.4×10e-6/℃ for SIC and 7.1×10e-6/℃ for graphite), the SiC film usually tends to fall off after several temperature rises and falls. When graphite is exposed, corrosive gases or liquids will enter the porous graphite body and be difficult to remove completely, thus leading to the generation of partical in high-temperature processes. This SiC coated graphite boat is the cheapest and has the shortest lifespan, approximately one year.
2.Recrystallized SiC Crystal Boat with CVD-SiC Coating
Recrystallized SiC crystal boats are usually formed by sintering and processing several unit parts first, then bonding each part with Si paste at high temperatures to form a crystal boat, and finally applying a CVD-SiC coating (about 100um). Because recrystallization is porous, partical can also be introduced into semiconductor processes without a SiC coating. In addition, the Si paste in the bonding zone cannot withstand the same high temperature as the SiC material. The manufacturing process of this recrystallized SiC crystal boat with CVD-SiC coating is the longest and the cost is very high. Compared with the graphite crystal boat coated with SiC, the recrystallized SiC crystal boat coated with CVD-SiC has no CTE mismatch problem, but acid washing and collision can also cause the SiC coating to fall off. Its service life is slightly longer, about 2 to 3 years.
3.One-piece SiC Crystal Boat Without CVD Coating
For crystal boats without CVD coating, the surface must be dense. There are two types of dense SiC materials: pressureless sintered SiC (SSiC) and reaction-sintered SiC (RBSiC, also known as silicon-permeated SiC, SiSiC). However, neither of these two types of SiC can be fused into one unit like quartz. It is not easy to form SiC from powder and burn it into an approximate shape of a one-piece single-piece crystal boat. Moreover, SiC is very hard and difficult to process, which leads to an extremely high processing cost for one-piece single-piece SiC crystal boats. Although RBSiC is slightly easier to form an approximate shape than SSiC, it is still very hard. In addition, RBSC contains 10 to 15% free Si, which makes it unable to withstand the same high temperatures as SSiC materials. Generally, it can withstand temperatures below 1400 ° C. Moreover, the free Si is easily etched by HF acid, leading to partical.
4.Kallex SiC Modular Crystal Boat
The unit parts are processed through forming, sintering and grinding using pressureless sintered SiC material with a purity of 99.675%. Then combine them together with SSiC screws, nuts, etc., and fix them with SSiC pins to ensure the load-bearing capacity. Without SiC coating, there is no risk of partical coating damage. Moreover, it can be used for a long time in harsh environments, such as high temperatures (1600℃) and HF acid, with a service life of more than five years.
Post time: Aug-19-2025