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Metal discolor defect was observed by in-line visual inspection after HDP oxide deposition. The defect was easily to be detected on metal lin side-wall which located on isolated or open area. FIB cross-section analysis showed the defect was metal void, as shown in Fig-2..The metal void was about 1/4-1/2 of metal line width which had serious reliability concem (Electron migration). However, CP yield and WAT testing data could not screen out this problem.The study results showed that the metal void defect had a strong correlation with thermal effect of deposition process.Stronger thermal effect on wafer would cause more serious metal void problem.The improvement strategy was to reduce the thermal effect during oxide deposition process. Multi-steps oxide deposition recipe was developed to solve the metal void problem. Investigation results showed that th HDP multi-steps recipe is very effective to eliminate metal void defect