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Abstract

In accordance with the present invention, a method for forming solder bumps begins with a wafer that has been patterned with bond pad areas. A plurality of distinct metal layers are then deposited over the wafer. Subsequently, solder is deposited by way of plating through a mask over the metal layers in the bond pad areas. After the removal of the mask, the metal layers outside of the soldered areas are etched using a dilute phosphoric acid solution, which includes phosphoric acid, acetic acid, hydrogen peroxide, and deionized water. By the use of this solution, the metal layers are removed without attacking the soldered areas. Thus, a pattern of solder bumps are formed. The metal layers include distinct layers of aluminum, nickel-vanadium, and copper. Alternatively, the aluminum layer is eliminated. Further, the dilute phosphoric acid solution has approximately 10% phosphoric acid, 84% deionized water, 5% acetic acid, and 1% hydrogen peroxide by volume, which is used for the etching step preferably performed at a temperature of approximately 70.degree. C. for a period between about 60 to 600 seconds. With the present invention, a single etchant, a dilute phosphoric acid solution, is used to remove the deposited metal layers outside of the soldered areas. This increases the efficiency of forming solder bumps of high integrity, which are then suitable for flip chip applications.

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First Claim