Numerous researchers have observed the bubble fromation at SiC/SiO2 interface from 1300℃ to 1700℃. 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°C and when Si is present, the bubble is formed at 1770℃. These results are very close to the prior observations, but the calculation can not explain the observation of bubble below 1500℃.