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Selectively Depositing Noble Metals on Thick Copper Layers

IP.com Disclosure Number: IPCOM000030143D
Publication Date: 2004-Jul-29
Document File: 2 page(s) / 19K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that selectively deposits noble metals (such as Ag, Au etc.) on thick copper structures to increase the oxidation resistance of copper and to reduce copper electro-migration with minimum resistance impact.

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Selectively Depositing Noble Metals on Thick Copper Layers

Disclosed is a method that selectively deposits noble metals (such as Ag, Au etc.) on thick copper structures to increase the oxidation resistance of copper and to reduce copper electro-migration with minimum resistance impact.

Background

Thick copper lines are required to redistribute the stress generated by the copper bumps. Redistributing the stress prevents the ILD in the lower layers from cracking. Thick copper lines also help in redistributing bump current, thereby reducing the formation of hot spots. However, the thick copper lines are susceptible to corrosion due to the non-hermetic sealing of the spin-on polymer layer that covers them. The elevated temperatures (>250 °C) that the copper layer is exposed to during curing can also produce copper corrosion. Depositing a noble metal layer on the copper will prevent the oxidation of copper and at the same time act as a barrier for copper diffusion.

General Description

The disclosed method selectively deposits a noble metal on the thick copper lines; resistance to corrosion is enhanced without radically decreasing electrical conductivity. A noble metal layer capping copper also acts as a barrier for copper diffusion (see Figure 1). The following are the steps for the disclosed method:

1.      Activate the copper surface by etching in mildly acidic or basic medium to remove the native oxide prior to depositing the metal.

2.      Immerse the wafers in a electroless bath to d...