This invention relates to processing of semiconductor wafers using a multi-chambered wafer processing device to form layers on a silicon wafer. Multi-chambered wafer processing devices do multiple sputtering and etching steps in the same device. One such multi-chambered wafer processing device is the MRC machine produced by Materials Research Corporation in Orangeburg, N.Y. The typical processing steps done on a multi-chambered wafer processing device can include sputter etching, forming titanium layers, forming titanium nitride layers, and forming aluminum layers. A problem noticed in the forming of aluminum layers using multi-chambered wafer processing devices is staining and voids in the aluminum layer. The aluminum layer formed on the silicon wafer can have discolorations or stains which in a later annealing step form voids or holes.
The suggested reasons for the aluminum layer voiding problem included incomplete nucleation of the aluminum layer. The nucleation sites are the points at which the grains in the metal film including the aluminum start to crystallize. It is desired that these nucleation sites be closely packed. It was thought that the voiding may have been caused by the incomplete nucleation of the aluminum layer, and that in later annealing steps, the voids were formed.
Another suggested reason for the voiding was that an aluminum layer formed on the silicon wafer was too thin, and was thus unstable during the annealing step.