The Si precipitation problem in aluminium alloy (Al-Si-Cu) metallization

Some lots of wafers were reported with low yield due to ANADC pattern functional failure. SEM, EDX and 155 Wright etch techniques were used to identify the root causes. Cross sectional results found the nodules on substrate at the contact area. EDX analysis confirmed them to be silicon nodules. After 155 Wright etch [100] square silicon crystalline hillocks were found on the substrate at the contact area. It is concluded that silicon nodules on the substrate at the contact area had resulted in an open circuit and low yield. These silicon nodules were due to Si precipitation on the substrate of the contacts.