Identification of defects in silicon wafers using copper deposition technique
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Date
2016-06
Authors
Muhammad Azim Zulkifli
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Abstract
Single crystal silicon can be made by Czochralski (CZ) process. During the process, several crystal-grown-in defects like crystal-originated particles (COPs, also known as D-defects), dislocation loops, oxygen precipitates and stacking faults are formed. Particularly, COPs present in single-crystal silicon ingots are vacancy agglomerate voids. Copper deposition technique is used as an alternative method to determine and locate the defects in oxide thin films. Copper deposition technique is implemented on the basis of electrolysis process.In this study, Si wafers were oxidized at 1100 oC for 4 hours. The defects became weak spotsof oxide layer and degraded oxide layer differently. During copper deposition process, electric field was build up between copper plate (anode) and SiO2 layer (cathode). The weak spots of oxide layer would electrically breakdown inelectric field. The localized breakdown of SiO2 layer provided conducting paths for current to pass through. Therefore, the copper ions dissolved from copper plate (anode) would deposit on the breakdown spots of the oxide surface as copper dots. Thedefects integrated in the oxide layer degraded the oxide layer differently. This phenomenon was observed when a higher defect density of copper dots was obtained with increasing of applied field and time of decoration process. When higher electric field was applied to the oxide layer, those weak spots that did not breakdown initially wouldnot be able to withstand the stress field. Besides, long deposition duration increased the formation copper dots as a result of copper ions build up which increased the conductivity of methanol. A higher oxide stress field would stress the oxide layer, causing more localized breakdown of SiO2 layer. Consequently, more copper dots with larger size weregrown on the wafer surface. The copper dots were surrounded by grey ring. The data analysis from Energy Dispersive X-Ray Spectroscopy (EDX) shows that elements of Mg, Cu, Si, O, Ca and C were found in the formation of the copper dots and the surroundings.