Room-temperature direct bonding of electroplated Au patterns flattened by a thermal imprint process

• Rough surfaces of electroplated Au patterns were flattened by thermal imprinting.
• Almost the entire area of a 100-μm-wide pattern was flattened.
• Large bonding strength was obtained by using a flattening process.
• Narrow multi-wall line patterns were designed for the bonding strength and hermeticity.
• Bonding strength was further improved by flattening and a multi-wall narrow pattern.

This paper reports on the flattening of a rough surface of an electroplated Au pattern on a Si wafer by the thermal imprint process and its application to surface-activated room-temperature bonding. An ultra-flat sapphire wafer was pressed onto the rough surface of an electroplated Au pattern on a Si wafer for 10 min at 200 °C with an applied pressure of 150 MPa. As a result, almost entire area of the 100-μm-wide pattern was flattened. Flattened Au patterns on Si wafer were bonded to a Au thin film on a Si wafer by surface-activated room-temperature bonding. A large bonding strength above 200 MPa was obtained. Narrow multi-wall line patterns were designed in order to ensure the bonding strength and hermeticity. The bonding strength was further improved by a combination of flattening and the multi-wall narrow pattern.

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