Dear Magali,

This is a common problem for all DC electroplating processes. The problem occurs
due to crowding of current lines near the edges of the plating mould (increased
current density near the edges). In case your plated structures are separated by
large areas where plating does not occur, this phenomenon will be even more
pronounced. A possible solution is strategic placement of dummy structures on
your mask layout. These structures will then act as "current thieves" during
plating, thus resulting in a more even plating of your structures. This can also
be combined with at bulky metal ring around your wafer during plating that - if
properly connected to the power supply - will act as a global "current thief"
resulting in more parallel current lines between anode and cathode (the wafer),
and thus a more even plating.

Another solution is to convert from DC plating to pulse reversal plating. During
pulse reversal material will primarily be dissolved from the regions tending to
overplate, thus causing more even plating of your structures. However, please
note that some electrolytes are not compatible with pulse reversal plating.

Best regards,
Frank
------------------------
Frank Engel Rasmussen
Industrial Ph.D. student, MEMS research group
Mikroelektronik Centret
Oersteds Plads
Building 345 (east), DTU
DK-2800 Kgs. Lyngby
Denmark
www.mic.dtu.dk

        -----Oprindelig meddelelse-----
        Fra: Magali Brunet [mailto:mbrunet@nmrc.ucc.ie]
        Sendt: to 17-10-2002 09:58
        Til: mems-talk@memsnet.org
        Cc:
        Emne: [mems-talk] Edges problem in through-mask NiFe electroplating



        Dear all,

        On a silicon wafer where a Cu seed layer is sputtered, I am depositing
        photoresist (8um thick) to create patterns and then electroplating  NiFe
        through the patterns (5um thick).

        The deposit has an even thickness except at the edges where there is a
        big overplating. (kind of
        "dog hears")

        Does anyone have an idea on how to get rid of this edge problem?

        Thanks a lot in advance,

        Magali
        --
        PEI Technologies,
        NMRC, Lee Maltings, University College,
        Cork, Ireland.

        Tel: +353 21 4 904279
        Fax: +353 21 4 270271
        email: mbrunet@nmrc.ie



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