Re-entrant cavity heat sinks formed by anisotropic etching and silicon direct wafer bonding

Abstract

A silicon re-entrant cavity heat sink for enhanced liquid cooling of silicon multichip packages can be fabricated using a two-step anisotropic etching process, followed by silicon direct wafer bonding. The authors report a novel method of formation of such re-entrant cavities using silicon integrated circuit processing. Cavity mouth openings ranging from 500 to 7.5 mu m have been batch fabricated with the two-step process. The re-entrant cavities suppress the temperature overshoot normally associated with the transition between the free convection and nucleate boiling regimes of liquid immersion cooling. It was observed that boiling occurs at heat fluxes below 2 W/cm/sup 2/.<>