The present invention provides a method for forming by plasma CVD a silicon nitride film that can be formed over heat-sensitive elements as well as an electroluminescent element and that has favorable barrier characteristics. The radiation devices include a first radiation device and a second radiation device. Then, whether errors exist in the current setting values of the relevant control parameters and flags of all the relevant control units are automatically checked. At least one strengthening bar is provided which has a first portion coupled to the front crossbar and a second portion coupled to the handle cross-member. The distance measuring component is aligned with the machine tool and the workpiece holder.