Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Controlling current distribution within bath
Reexamination Certificate
1999-12-21
2002-06-25
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Controlling current distribution within bath
C205S105000, C205S157000, C205S291000, C204S229500, C204SDIG009, C204S912000
Reexamination Certificate
active
06409903
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electroplating apparatus and method for the electrodeposition of a metal onto a substrate immersed in an electroplating bath and, more particularly, to the electroplating of copper onto semiconductor wafers which copper plating is relatively uniform and minimizes bum-through of a seed layer on the wafer used to initiate the electroplating.
2. Description of Related Art
Industrial chemists have devised many applications for electroplating of metals onto various substrates. They typically adopt a simple, direct-current (DC) power supply which is designed to maintain a constant-current. This is the so-called galvanostatic mode of electroplating, in which the potential across the anode and cathode in the plating cell varies in order to maintain the current level. Such a mode of control is obviously beneficial if the quality of the coating is optimized by the selected current density and, perhaps, if high throughputs are desired. Although more complex waveforms have been devised to apply either a simple DC-pulse (square waveform) or a set of alternating pulses (combination of square waveforms having alternating polarity), these applications have been much more specialized and have been less widely adopted in common industrial applications.
The use of complex potential-and/or current-step waveforms have also been used in academic research. For example, electrochemists have employed potential step and current step methods as analytical tools to characterize the kinetics of redox reactions. In potential step experiments, the potential is adjusted to different levels to probe the different regimes of electroactivity of the species involved. Such methods have proven effective at characterizing redox systems under mass-transport limiting conditions. Current step techniques have been used to study rapid and quasi-reversible electrode reactions. Double-layer capacitance information can also be gained from these methods. Both potential step and current step methods have been especially useful when investigating complex, multicomponent electrode systems.
SUMMARY OF THE INVENTION
The present invention employs certain aspects of such aforementioned current and potential “step” waveforms to overcome serious manufacturing defects encountered in volume production of electroplated substrates covered by a thin film of the appropriate metallic “seed layer”, where such seed layers are typically less than 0.2 microns thick. Such defects, hereafter referred to as “bum through”, represent local thickness inhomogeneities in the thin seed layer that are a result of an attempt to inject electrical current into the thin, metal seed layer using discrete point contacts.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a multistep electroplating process for wafers and other substrates which provides a uniform electroplated substrate and minimizes burn-through of a seed layer on the substrate used to initiate plating.
It is another object of the present invention to provide an apparatus for electroplating which provides a uniform metal plating onto a substrate and which minimizes burn-through of a seed layer on the substrate used to initiate the electroplating.
A further object of the invention is to provide electroplated articles including copper plated semiconductor wafers made using the apparatus and method of the invention.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a multistep electroplating process for electroplating a seed layer containing substrate such as a semiconductor wafer with copper or other metal comprising the steps of:
inserting a substrate having a seed layer to initiate metal plating thereon into an electroplating apparatus comprising a metal plating solution, an anode and multiple cathode electrical perimeter contacts to the seed layer;
exposing the seed layer, anode and the perimeter contacts to the metal plating solution;
plating onto the seed layer and substrate by applying to the anode and perimeter contacts for a first time period a voltage, preferably constant, below a predetermined threshold voltage; and
continuing the plating onto the plated substrate by applying after the first time period a current, preferably constant, to the anode and perimeter contacts for a second time period the current producing a voltage below the predetermined threshold voltage.
In another aspect of the invention a multistep electroplating process for plating a seed layer containing substrate such as a semiconductor wafer with copper or other metal is provided comprising the steps of:
inserting a substrate having a seed layer to initiate metal plating thereon into an electroplating apparatus comprising a metal plating solution, an anode and multiple cathode electrical perimeter contacts to the seed layer;
exposing the seed layer, anode and perimeter contacts to the metal plating solution; and
plating onto the seed layer and substrate by applying to the anode and perimeter contacts a current pre-programmed to ramp up to a current value, preferably constant, from a first current value which current produces during the ramping a voltage below a predetermined threshold voltage.
In another aspect of the invention, an apparatus for electroplating a seed layer containing substrate such as a semiconductor wafer with copper or other metal which is immersed in an electroplating bath comprises:
a tank containing a metal plating solution;
an anode in the metal plating solution;
a cathode substrate positioned in the electrolyte having a seed layer thereon facing the anode, the seed layer having multiple cathode perimeter electrical contacts;
means for supplying a current to the anode and cathode in the apparatus to apply to the anode and perimeter contacts for a first time period a voltage, preferably constant, below a predetermined threshold voltage; and
means for supplying after the first time period a current, preferably constant, to the anode and perimeter contacts for a second time period the current producing a voltage below the predetermined threshold voltage.
In another aspect of the invention, an apparatus for electroplating a seed layer containing substrate such as a semiconductor wafer with copper or other metal comprises:
a tank containing a metal plating solution;
an anode in the metal plating solution;
a cathode substrate positioned in the electrolyte having thereon a seed layer facing the anode, the seed layer having multiple cathode perimeter electrical contacts; and
means for supplying a current to the anode and perimeter contacts which current is preprogrammed to ramp up to a current value, preferably constant, from a first current value which current produces during the ramping a voltage below a predetermined threshold voltage.
In another aspect of the invention electroplated articles including metal (copper) plated semiconductor wafers are provided which are made using the apparatus and method of the invention.
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Lowenheim, “Electroplating”, pp. 143-144, c. (no month available) 1978.
Chung Dean S.
Korejwa Josef W.
Walton Erick G.
DeLio & Peterson LLC
Kotulak Richard M.
Tomaszewski John J.
Wong Edna
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