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Method for protecting copper surfaces from oxidation and enabling direct wire bonding to Cu bond pads

IP.com Disclosure Number: IPCOM000100637D
Publication Date: 2005-Mar-15
Document File: 3 page(s) / 57K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for protecting copper surfaces from oxidation and enabling direct wire bonding to copper (Cu) bond pads. Benefits include improved functionality, improved performance, improved reliability, improved process simplification, and improved yield.

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Method for protecting copper surfaces from oxidation and enabling direct wire bonding to Cu bond pads

Disclosed is a method for protecting copper surfaces from oxidation and enabling direct wire bonding to copper (Cu) bond pads. Benefits include improved functionality, improved performance, improved reliability, improved process simplification, and improved yield.

Background

      Conventionally, an intervening conductive, noncorrosive metal layer is required as a cap for Cu bond pads for wire bonding. Wire bonds are typically formed from gold wire. They connect the last layer of metal on the integrated circuit (IC) die to the exterior environment. The last layer of metal within a high performance integrated circuit is typically copper. However, copper is not a self-passivating metal and easily corrodes when exposed to the ambient environment. The Cu bond pads must be protected for wire bonding.

      The main barrier to wire bonding gold (Au) wires to Cu bond pads is the corrosion susceptibility of Cu to form oxides on exposure to ambient conditions. Various techniques have been used unsuccessfully to protect the Cu from exposure to the ambient environment.

              Cu bond pads require protective pads or other permanent conductive features over the copper pads to prevent corrosion of the exposed copper. These caps are typically made of a less corrosion susceptible or self-passivating material, such as:

•             Tungsten (W)

•             Titanium (Ti)

•             Tantalum (Ta)

•             Aluminum (Al)

              Al is one of the more common cap materials used. The inclusion of protective pads in the structure is undesirable because of the additional materials, processing steps, and manufacturing complexity which potentially decrease die yield and increases cost.

General description

              The disclosed method protects copper surfaces from oxidation and enables direct wire bonding to copper (Cu) bond pads without using an intervening metallic layer.

The method protects the copper wiring from exposure until just before the wire bond or other electrical connection is formed. As a result, the requirement for additional structures, such as conductive pads, is eliminated.

      The disclosed method includes a chemical cleaning with a mild hydrochloric acid (HCl) to remove any corrosion from the surface of the Cu bond pad. This coating is preferably applied by electroless plating, which enables the film to be selectively electroplated on top of the Cu bond pads. The cleaning is...