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Method to Monitor and Control Boil-Over of Hydrogen Peroxide Based Solutions

IP.com Disclosure Number: IPCOM000117089D
Original Publication Date: 1995-Dec-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Cooper, EI: AUTHOR [+4]

Abstract

Solutions based on hydrogen peroxide are used to etch metal films for microelectronics fabrication. In the electrochemical fabrication of C4s, (Controlled Collapse Chip Connection), a solution of hydrogen peroxide (H&sub2.O&sub2.), potassium EDTA and potassium sulfate is used to selectively remove the TiW seed layer. The TiW etching is carried out at above ambient temperature, typically 50 degree C, and in the presence of PbSn C4s and Cu and CrCu Ball Limiting Metallurgies (BLMs). The TiW etch bath, after etching several batches of wafers and storage over an extended period of time at 50 degree C, sometimes exhibits the phenomenon of boil-over or rapid decomposition of the hydrogen peroxide. This is accompanied by excessive gas evolution and an increase in the bath temperature.

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Method to Monitor and Control Boil-Over of Hydrogen Peroxide Based
Solutions

      Solutions based on hydrogen peroxide are used to etch metal
films for microelectronics fabrication.  In the electrochemical
fabrication of C4s, (Controlled Collapse Chip Connection), a solution
of hydrogen peroxide (H&sub2.O&sub2.), potassium EDTA and potassium
sulfate is used to selectively remove the TiW seed layer.  The TiW
etching is carried out at above ambient temperature, typically
50 degree C, and in the presence of PbSn C4s and Cu and CrCu Ball
Limiting Metallurgies (BLMs).  The TiW etch bath, after etching
several batches of wafers and storage over an extended period of time
at 50 degree C, sometimes exhibits the phenomenon of boil-over or
rapid decomposition of the hydrogen peroxide.  This is accompanied by
excessive gas evolution and an increase in the bath temperature.

      The key to controlling boil-over is to control the catalytic
decomposition of H&sub2.O&sub2.  in the etch bath.  EDTA complexes
the metal ions that accumulate in the bath during etching, thus
preventing the catalytic decomposition of H&sub2.O&sub2..  However,
the EDTA in the etchant is attacked by the hydrogen peroxide and its
complexation capabilities decrease with time.

      The vigorous sample bubbling during operator-initiated
boil-over can be used to qualitatively determine the etch bath
stability.  The common EDTA determination methods fail for these
types of solutions, because EDTA gradually degrades into different
compounds which still possess significant complexing capacity.
Thermometric titration, using a metal ion solution as titrant, has
been shown as an effective method to monitor the risk of boil-over.
Fig. 1 shows the derivative of the temperature and illustrates the
effect of metal ion addition and subsequent EDTA quenching of the
solution.  The addition of 0.1 ml of 5000 ppm Cu sup 2+  solution to
50 ml of 5 M H&sub2.O&sub2.  at 50 degree C results in an increase
in the solution temperature and a positive temperature derivative.
The rise in temperature is accompanied...