Etching optimization of post aluminum-silicon thermomigration process residues

• Al2O3 is etched by inductively coupled plasma without additional mask.
• BCl3 is proved to be more effective than CHF3/Ar to remove aluminum oxide.
• Acceptable selectivity of Al2O3 over both Si and SiO2 is achieved with BCl3.
• All residues are selectively removed by combinsing both wet and dry etches.

Al–Si thermomigration is an attractive means to produce through-wafer isolation walls for power devices. The unintentional layers of Al2O3 formed due to the necessary oxygen-containing ambient, after the thermomigration process, must be removed from the surfaces of Si wafer. In this regard, both dry and wet etching recipes are investigated in this article. Residues of Al2O3 and Al–Si alloy are eliminated without additional mask by a two-step etching process. BCl3 plasma treatment is proved to be effective to strip off the aluminum oxide layer with acceptable loss of silicon and silicon dioxide. Subsequent wet etching using commercial wet solution enables to remove the rest of Al-containing residues.

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