Abstract
Defects known as “craters” because of their resemblance to actual craters (Fig. 1) can cause scrap events, lower die yields, and increased cycle time due to the necessary process reworks to remove the defect source. Affected wafers exhibit a delaminated metal seed layer along the defect site, resulting in inconsistent gold plating atop the seed layer (Fig. 2). Without a uniform plated-gold layer, wafers must either be scrapped or reworked due to increased risk of copper migration through the collector layer [1].
Crater defect formation has been revealed with the help of cross-sectional SEM (Scanning Electron Microscope) using FIB (Focused Ion Beam). A pinhole is created through the seed layer being deposited atop a particle. The pinhole enables NH4OH to galvanically corrode the underlying metal within the multi-metallic seed layer during the pre-plating clean. This galvanic corrosion of the seed layer then causes nonuniform gold plating. Leveraging this finding, it is explored how modifying this pre-clean step can significantly reduce crater defect prevalence, as with the seed layer more intact, gold plating remains uniform.
Through this multi-faceted approach, both the prevalence and impact of crater defects is reduced through halting the frequency of initial pinhole formation and mitigating the impact of the subsequent galvanic corrosion.
F. Narcia
Skyworks Solutions, Inc.
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12.14 – Root-Cause Analysis and Reduction of Crater Defect Formation for GaAs Wafers During Backside Processing
R. Newman, Skyworks Solutions, Inc.T. Hossain, Skyworks Solutions, Inc.F. Narcia, Skyworks Solutions, Inc.T. Ma, Skyworks Solutions, Inc.M. Arif Zeeshan, Skyworks Solutions Inc.