A study on silicon nodules due to the Si precipitation in wafer fabrication

In this paper, silicon nodules due to Si precipitation were investigated in wafer fabrication. Line inspection found particle contamination on bondpads and large metal 1 lines of some wafers. Cross sectional SEM results showed that some nodules were found in the metal 1 layer. EDX analysis confirmed that they were Si nodules as a high Si peak was detected on the nodules. These nodules had resulted in open failure in some metal lines. Based on the failure analysis results, we concluded that the silicon nodules were due to silicon precipitation. The preventive actions taken were to check the target if the Si value in Al exceeds the normal value, to control the parameter strictly during metal deposition and to reduce the thermal cycles after metal deposition.