Movable Anode Chamber for Uniform Wafer Electroplating
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Solution Overview
Problem
The challenge in copper damascene processing for integrated circuits is the non-uniform plating thickness distribution due to the 'terminal effect' caused by high Ohmic resistance drop from the edge to the center of large wafers, especially as the industry transitions from 300 mm to 450 mm wafers, leading to uneven metal deposition.
Innovation Solution
A plating apparatus with a movable anode chamber or shield is used to mitigate the terminal effect by varying the distance between the anode and an ionically resistive ionically permeable element, ensuring uniform current density across the wafer substrate, combined with an auxiliary cathode and insulating shield to control current distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If electrical contact is made only at the edge region of the wafer substrate, then the plating tooling structure is simplified, but the plating thickness becomes non-uniform due to the terminal effect
Solution Approach 1:
The cathode structure is segmented into multiple regions: the substrate holder with edge contact and the auxiliary cathode positioned to contact the central region. This segmentation allows independent control of current distribution to different areas of the wafer, enabling uniform plating thickness while maintaining a relatively simple overall structure.
Solution Approach 2:
The auxiliary cathode acts as an intermediary element that introduces an additional current path through the electrolyte to the central region of the substrate. This mediator compensates for the high resistance drop in the seed layer by providing an alternative current route, thereby achieving uniform plating without complicating the direct contact structure.
2Productivity
If the wafer size is increased from 300 mm to 450 mm, then the productivity and capacity are improved, but the terminal effect becomes more pronounced leading to greater plating non-uniformity
Solution Approach 1:
The solution introduces a spatial dimension by positioning the auxiliary cathode at a specific distance below the substrate plane. This three-dimensional arrangement creates an additional current path that spans the increased wafer diameter, allowing uniform current distribution across larger 450 mm wafers without sacrificing the benefits of increased wafer size.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves uniform metal thickness distribution on large wafers by compensating for the resistance drop, ensuring consistent plating across the substrate, even as the seed layer conductivity changes during the electroplating process.
Implementation Method 1
the potential at the edge of the seed layer is significantly greater than at the central region of the seed layer, which is referred to as the 'terminal effect'. Without appropriate means of resistance and voltage compensation, this large edge-to-center voltage drop leads to a non-uniform plating thickness distribution
Implementation Method 2
a plating chamber, a substrate holder, an ionically resistive ionically permeable element, and an anode chamber housing an anode. The plating chamber is configured to contain an electrolyte while electroplating metal onto a substrate
Data Source
AI summary
Methods, systems, and apparatus for plating a metal onto a work piece are described. In one aspect, an apparatus includes a plating chamber, a substrate holder, an anode chamber housing an anode, an ionically resistive ionically permeable element positioned between a substrate and the anode chamber during electroplating, an auxiliary cathode located between the anode and the ionically resistive ionically permeable element, and an insulating shield with an opening in its central region. The insulating shield may be movable with respect to the ionically resistive ionically permeable element to vary a distance between the shield and the ionically resistive ionically permeable element during electroplating.