5.2 Multiple-Bath Methods
139
thickness ratio of the subsequent layers, while the thickness of each layer is determined by the residence time above the particular solution and the current applied
at that position. Another means of the thickness regulation is the application of an
off-time period at either of the plating positions, and the alternating operation of the
current sources is also possible.
Since the electrode is in contact with some of the solution during the entire process
(apart from the short periods when it passes above the separator of the cell chambers),
the inertness of the atmosphere can be ensured more easily than with the subsequent
immersion method. Nevertheless, the wiping blades between the cell chambers exert
a mechanical force onto the deposit that can lead to an unwanted wear load.
The typical rotation rate of the rotating electrode system presented in Fig. 5.2 was
10–30 rpmin. It could be used successfully to plate Ni/Cu and Ni/NiP x multilayers,
but its application for Co/Cu multilayers failed. The reason obviously lies in the high
inclination of the relatively aggressive copper electrolyte to displace cobalt deposited
in the previous rotation phase of the cathode.
A rotating cylinder-type multichamber deposition apparatus was also reported
[32]. Here, the cathode is a cylinder with vertical axis, and the sections aligned along
the surface of the cylinder in the direction of rotation include polishing chambers
after both deposition steps. The operation principles reported were the same as for
the rotating disc system (simultaneous or alternating on-time periods for the two
deposition chambers, variation in each current density), and even the typical rotation
rate was in the same range. The advantage of the inclusion of the grinding chambers
was that the roughening of the deposits with the increase in the thickness could
be efficiently counteracted, and shiny deposits up to a millimetre thickness could
be achieved for Ni/Cu multilayers. Polishing during the preparation of the deposit
improved the layer structure significantly, even though the process was optimized
for about 100 nm minimum layer thicknesses.
5.2.4 Bath Change by Using Flow Cells With Multiple
Solution Inlets
It is often desired to retain the independence of the baths used for depositing each
layers and providing well-controlled electrode surface conditions at the same time.
All these conditions can be fulfilled by applying a setup presented earlier in Fig. 4.1
(including the permanent potential control with appropriate potential steps when
solutions are exchanged, exclusion of the mixing of the baths, absence of oxygen
etc.). Although the electrolyte pumping apparatus shows a large commonality, the
systems used to plate layers thicker than a monolayer also have different features.
When the layer to be produced is plated in a process which is not surface limited,
the concentration of the electrolyte solution is normally much larger than in the case
when monolayers are produced. This also means that the solution exchange in the
flow cell leads to a significant loss of electrolyte solution, even if the pumping is
139
thickness ratio of the subsequent layers, while the thickness of each layer is determined by the residence time above the particular solution and the current applied
at that position. Another means of the thickness regulation is the application of an
off-time period at either of the plating positions, and the alternating operation of the
current sources is also possible.
Since the electrode is in contact with some of the solution during the entire process
(apart from the short periods when it passes above the separator of the cell chambers),
the inertness of the atmosphere can be ensured more easily than with the subsequent
immersion method. Nevertheless, the wiping blades between the cell chambers exert
a mechanical force onto the deposit that can lead to an unwanted wear load.
The typical rotation rate of the rotating electrode system presented in Fig. 5.2 was
10–30 rpmin. It could be used successfully to plate Ni/Cu and Ni/NiP x multilayers,
but its application for Co/Cu multilayers failed. The reason obviously lies in the high
inclination of the relatively aggressive copper electrolyte to displace cobalt deposited
in the previous rotation phase of the cathode.
A rotating cylinder-type multichamber deposition apparatus was also reported
[32]. Here, the cathode is a cylinder with vertical axis, and the sections aligned along
the surface of the cylinder in the direction of rotation include polishing chambers
after both deposition steps. The operation principles reported were the same as for
the rotating disc system (simultaneous or alternating on-time periods for the two
deposition chambers, variation in each current density), and even the typical rotation
rate was in the same range. The advantage of the inclusion of the grinding chambers
was that the roughening of the deposits with the increase in the thickness could
be efficiently counteracted, and shiny deposits up to a millimetre thickness could
be achieved for Ni/Cu multilayers. Polishing during the preparation of the deposit
improved the layer structure significantly, even though the process was optimized
for about 100 nm minimum layer thicknesses.
5.2.4 Bath Change by Using Flow Cells With Multiple
Solution Inlets
It is often desired to retain the independence of the baths used for depositing each
layers and providing well-controlled electrode surface conditions at the same time.
All these conditions can be fulfilled by applying a setup presented earlier in Fig. 4.1
(including the permanent potential control with appropriate potential steps when
solutions are exchanged, exclusion of the mixing of the baths, absence of oxygen
etc.). Although the electrolyte pumping apparatus shows a large commonality, the
systems used to plate layers thicker than a monolayer also have different features.
When the layer to be produced is plated in a process which is not surface limited,
the concentration of the electrolyte solution is normally much larger than in the case
when monolayers are produced. This also means that the solution exchange in the
flow cell leads to a significant loss of electrolyte solution, even if the pumping is