Low pressure and low temperature hermetic wafer bonding using microwave heating

Abstract

We bonded gold on silicon substrates (Au/Si) for a MEMS application by using microwave radiation in a single-mode cavity. Microwave radiation selectively heats materials; the energy is deposited in the metallic portion of the substrates in this application. This concentration of the energy forms the bonding rather quickly and with minimal heating of the substrate. The short bonding process-time allows for minimal diffusion of the Si into the metallization. Since no pressure is applied to form the bonding, mechanical stresses are minimized. The substrates bonded by our technique formed a hermetically sealed micro-cavity. Preliminary He leak-tests from these bonded samples show leakrates on the order of 3x109atom cc/s.

Polymer bonding by induction heating for microfluidic applications

“…Budraa et al used microwave heating to bond 5mm x 5mm MEMS test pieces [33]. The test pieces were silicon dies with gold frames and every bond was made with two of them.…”

On-Wafer Monolithic Encapsulation by Surface Micromachining With Porous Polysilicon Shell

“…In a hybrid approach (shown in the left column in Fig. 1), a separate substrate is bonded to the MEMS wafer to cap the MEMS components using a wide variety of bonding techniques, either in a form of direct surface bonding or using an intermediate layer [1]- [4]. While wafer bonding has been proven and is being widely used in industry, monolithic thin-film encapsulation has been considered to be potentially more cost effective.…”

Localized back-side heating for low-temperature wafer-level bonding

“…A number of localized heating methods have been reported in the literature using lasers [3,4], microwaves [5], resistive elements and induction [6]. The main drawback for all of these methods is the difficulty in applying them at the wafer level and a limited range of materials that can be used in their application.…”