The leakage current mechanism of the chemical vapor deposition film has been investigated. In the case of an as‐deposited amorphous film, the presence of impurities such as carbon and hydrogen remaining in the film leads to the Poole‐Frenkel type leakage current. The oxidation of these impurities results in a reduction in leakage current. plasma is especially effective for oxidizing impurities, leading to a drastic reduction of the leakage current. However, plasma cannot reduce the leakage current of the film crystallized at 700°C. This leakage current is not due to C and H, but rather to Si penetraed into the film from the underlying poly‐Si electrode. Therefore, the amorphous film treated by plasma is most suitable for DRAM use.