Electroplating and wet etching

The electroplating area has 2 components: Anisotropic wet etching, and electrolytic metal growth.

Anisotropic wet etching

The anisotropic chemical etching is to etch Silicon chemically on depths of a few microns to several hundred microns with an alkaline chemical solution. The redox reaction that occurs between silicon and the solution lead the dissolution of the preferential directions. The realization of a prior nitride or Silicon oxide mask can locate this etching and achieve grounds (membrane, cavities, and trenches).

Electroplating

This technique is to turn the metal ions in a solution in metal deposits. The deposit can be full substrate or localized in thicknesses ranging from a few µm to several hundred µm.  The silicon substrate is immersed in a solution containing metal ions to be deposited. A current is imposed between the substrate is counter electrode. This current will allow the transformation of the ions in metal atoms. The composition of the bath, the density of the current, and the agitation influences the characteristics of the deposit.

Know how

  • Anisotropic wet etching

    • KOH: the rate for  the <100> plans rangs from 0.5 to 2.5 µm/min for concentrations of 20 to 50% by weight and temperatures of 50 to 90 °. This solution of attack requires a mask in Silicon nitride

    •  TMAH : the rate for the <100> plans rangs from 0.2 to 1 µm/min for concentrations of 20 to 50% by weight and temperatures of 50 to 90 °. This solution does not etch oxide and therefore allows membranes.

 KOH etching
  • IPA influence on TMAH etching












    TMAH 20% - 2 min

    TMAH 20% + 17 % IPA - 2 min


  • Electroplating

    • Gold :Continuous current full plate or in a resist mould  for thicknesses up to 10 µm. Can be deposited on 4 or 6 inches substrates. This deposit is with low mechanical stress< 10 MPa and homogeneous (inhomogeneity &LT; 5%)

  • MEMS - RF



    • Copper : Continuous or pulsed current,  full plate or in a resist mould for depths up to 100 µm


    Energy convertor

    • Co-Ni-Fe: Continuous current,  full plate or in a resist mould for depths up to a few tenth of µm


    Micro converter for power device

    • Platinum : Continuous current,  in a resist or alumina mould for depths up to a few µm


      Nanowires


    • SAC : Continuous current,  in a resist mould for depths up to 100 of µm


       SAC bumps before et after reflow

    • Gold : By immersion for the protection of deposited copper.


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