Abstract: The silicon nitride coating,a gate insulation material for fabrication of thin film transistor liquid crystal display,was synthesized by plasma-enhanced chemical vapor deposition(PECVD) on large glass substrate(2500 mm×2200 mm),one workpiece at a time,in industrial production.The influence of the accumulated number of deposition-cycle on the chamber-wall cleanliness and properties of the SiN_x coatings,including but not limited to the thickness,deposition-rate,porosity,uniformity,compactness and density,was investigated.The results show that the multiple deposition cycles had a major impact.For instance,as the number of deposition-cycle increased in the newly-cleaned vacuum chamber,the conductivity of chamber wall decreased;the deposition-rate and average thickness of SiN_x-coatings increased,accompanied by improved uniformity and deteriorated compactness,porosity and density.