Numerous researchers have observed the bubble fromation at SiC/SiO2 interface from 130$0^{circ}C$ to 1$700^{circ}C$. According to thermodynamic calculation, the bubble could be formed from the microscopic impurities which result from the chemical vapor deposition of SiC. When C-impurity is present at the interface, it is calculated that the bubble is formed at 1511$^{circ}C$ and when Si is present, the bubble is formed at 177$0^{circ}C$. These results are very close to the prior observations, but the calculation can not explain the observation of bubble below 150$0^{circ}C$.