Provided is an in-situ method of cleaning a vaporizer of an atomic layer deposition apparatus during a dielectric layer deposition process, to prevent nozzle blocking in the vaporizer and an atomic layer deposition apparatus. During the dielectric layer deposition process, the following steps are repeated: supplying a first source gas for dielectric layer deposition into a chamber of an atomic layer deposition apparatus; purging the first source gas; supplying a second source gas into the chamber of the atomic layer deposition apparatus; purging the second source gas, the in-situ method of cleaning the vaporizer is performed after supplying the first source gas for dielectric layer deposition and before supplying the first source gas again.