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Method for sealed edges of bonded wafers for 3D wafer-stacking applications

IP.com Disclosure Number: IPCOM000012779D
Publication Date: 2003-May-28
Document File: 3 page(s) / 35K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for sealed edges of bonded wafers for 3D wafer-stacking applications. Benefits include improved reliability.

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Method for sealed edges of bonded wafers for 3D wafer-stacking applications

Disclosed is a method for sealed edges of bonded wafers for 3D wafer-stacking applications. Benefits include improved reliability.

Background

        � � � � � Bonded patterned metal wafers are potential candidates for 3-dimensional integrated circuits (ICs). To integrate their subsequent processing, one of the wafers must be ground to a thickness of less than 10 microns. During this process, the wafers typically break or crack at the edges, causing significant loss in yield and adding to the cost. The conventional thinning process has not solved this problem.

General description

        � � � � � The disclosed method seals the edges of bonded patterned metal wafers for protection from corrosion and mechanical support during grinding.

        � � � � � The key elements of the method include:

•        � � � � Bead of underfill material, such as epoxy, at the edge of the wafers

•        � � � � Underfill material that diffuses into the unbonded regions near the edges of the wafers

•        � � � � Curing by exposure to UV light or by heating to moderate temperatures

        � � � � � Because the underfill is only applied at the edges, additional process steps may not be required to clean the whole wafers after this treatment. In some cases, the wafers may need to be heated to moderate temperatures.

Advantages

        � � � � � The disclosed method provides advantages, including:

•        � � � � Improved yield due to preventing edge chipping during wafer thinning

•        � � � � Improved yield due to protecting exposed patterned metal surfaces from ambient atmosphere, minimizing corrosion

Detailed description

        � � � � � The disclosed method can be implemented using the following process steps:

1.        � � Align and bond patterned metal wafers using a commercial tool.

2.        � � Put the bonded wafers in a vacuum chamber and evacuate the chamber. This step pumps out any air between the bonded wafers. The bonded wafers are typically separated by a gap of about 200 nm. The dimensions of the metal patterns are typically between 3-10 microns in width, 0.1 micron in height, and 5 microns in pitch.

3.        � � Heat the chuck holding the bonded wafers to a moderate temperature of approximately 70–100 °C.

4.        � � Preheat the underfill material, such as epoxy-based encapsulant, to moderate temperatures to reduce its viscosity.

5.        � � Apply a thin bead of underfill material to the edge of the bonded wafers. Heating the underfill prior to coating the wafers aids in reducing the viscosity and increasing the penetration distance. Optionally, the underfill material may be unfilled. Filler particles are typically as big or bigger than the 200-nm gap and inhibit penetration of the underfill. Suitable encapsulants could be epoxy based, cyanate-ester based, or benzocyclobutene (BCB) based. Encapsulant requirements include:         � � � � �
        �...