NOVELTY - The method of forming multi-layered silicon nitride thin films having different refractive indexes on a silicon wafer using plasma-enhanced chemical vapor deposition process, comprises changing a plasma frequency to be applied, while not changing a composition ratio of a mixed gas for plasma generation to sequentially form thin films corresponding to a plasma composition of the plasma frequency. External radio frequency generators are included in an apparatus for performing the plasma-enhanced chemical vapor deposition process.    USE - Useful for forming multi-layered silicon nitride thin films having different refractive indexes on a silicon wafer using plasma-enhanced chemical vapor deposition process. The thin films are useful in solar battery module.    ADVANTAGE - The method consumes less time to manufacture the mulit-layered thin film structure with desired refractive indexes by selectively changing the plasma frequency while not changing the component ratio of the mixed gas for plasma generation, reduces the loss of raw material, reduces the manufacturing cost, and improves the uniformity and refractive indexes of the multi-layered silicon nitride thin film structure.    DETAILED DESCRIPTION - The method of forming multi-layered silicon nitride thin films having different refractive indexes on a silicon wafer using plasma-enhanced chemical vapor deposition process, comprises changing a plasma frequency to be applied, while not changing a composition ratio of a mixed gas for plasma generation to sequentially form thin films corresponding to a plasma composition of the plasma frequency. External radio frequency generators are included in an apparatus for performing the plasma-enhanced chemical vapor deposition process, and the plasma frequency is changed by a selective operation of the generators. The plasma composition is decided by changing the plasma frequency application time of the generators by predetermined periods. The silicon wafer is useful for manufacturing semiconductors and solar batteries, and a glass substrate is useful for manufacturing thin film transistors. The silicon nitride thin films are formed by supplying a mixed gas having silicon hydride and ammonia and an atmospheric gas of nitrogen/argon into a reaction chamber (100) of an apparatus for performing the plasma-enhanced chemical vapor deposition process. A 5-50 MHz generator is considered as a high-frequency generator, and a 10-500 KHz generator is considered as a low-frequency generator. The high-frequency generator and the low-frequency generator are sequentially operated to change the plasma composition, and are alternately operated at 1-60 seconds to form silicon nitride thin films having predetermined refractive indexes. An INDEPENDENT CLAIM is included for a solar battery module.    DESCRIPTION OF DRAWING(S) - The diagram shows a shower-head type plate electrode plasma-enhanced chemical vapor deposition apparatus: (100) Reaction chamber; #(200) Chamber cover; #(300) Susceptor; #(400) Substrate; #(500, 600) External radio frequency generators.