Browse Prior Art Database

METHOD FOR ETCHING GOLD IN AN MRIE

IP.com Disclosure Number: IPCOM000007960D
Original Publication Date: 1996-Nov-01
Included in the Prior Art Database: 2002-May-08
Document File: 1 page(s) / 60K

Publishing Venue

Motorola

Related People

Doug Mitchell: AUTHOR [+3]

Abstract

A standard under bump metallurgy (UBM) used in the electroplated gold bump process is TiW/Au. Wet chemistry etches including KII,, KCN or Thio- urea based etch solutions have long been used to remove the Au film. Hot H,O, is then used to remove the TiW layer. Both processes suffer from the typical problems associated with wet etches. Sta- bility of bath chemistry, uniformity of etch as well as chemical usage and waste are some of the issues. With the increasing demand for higher I/OS and smaller die, undercut of the UBM becomes signifi- cant on the smaller fine pitch bumps.

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MmROLA Technical Developments

METHOD FOR ETCHING GOLD IN AN MRIE

by Doug Mitchell, Frank Carney and Harry Geyer

  A standard under bump metallurgy (UBM) used in the electroplated gold bump process is TiW/Au. Wet chemistry etches including KII,, KCN or Thio- urea based etch solutions have long been used to remove the Au film. Hot H,O, is then used to remove the TiW layer. Both processes suffer from the typical problems associated with wet etches. Sta- bility of bath chemistry, uniformity of etch as well as chemical usage and waste are some of the issues. With the increasing demand for higher I/OS and smaller die, undercut of the UBM becomes signifi- cant on the smaller fine pitch bumps.

  In the past gold has been dry etched using an Ion Milling technique which simply bead blasts the film off with Argon ions. This tends to be a dirty process with high levels of particulates from the equipment shielding. Because of sidewalls associated with the non planarized passivation processes, there is always the risk of leaving Au/TiW film on steps as in Figure 1. This leads to either shorts or string-

ers if the adhesion of the metal to the sidewalls fails. Most milling equipment is set up to angle the stage so that this material may be removed but the height of the gold bumps will create shadowing problems affecting the removal of the UBM.

  By moving the etch processes into a Reactive Ion Etcher it is possible to eliminate many of the above issues. It has been shown that it is p...