Electroplating Wafer Notch Current Crowding Mitigation
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Solution Overview
Problem
The challenge in electroplating wafers with notches or edge irregularities is current crowding, which leads to non-uniform plating thickness, reducing yield due to thicker films at notches affecting subsequent processing steps, and the need for smaller edge zones to minimize seal coverage, complicating the manufacturing process.
Innovation Solution
Applying a local positive voltage at the notch region using a contact ring with a perimeter voltage ring grounded or at negative voltage, and a notch contact segment at positive voltage, along with a seal design that reduces current crowding by altering the electric field and using a current thief electrode to distribute current uniformly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a seal is used to keep electrolyte away from electrical contacts, then metal ions do not plate out onto the electrical contacts, but the annular band covered by the seal must be as small as possible (currently towards about 1 mm), which complicates the manufacturing process
Solution Approach 1:
The contact ring is divided into separate functional segments: a seal portion that contacts the wafer edge and a voltage application portion that contacts the wafer surface. This segmentation allows the seal to be minimized while still providing effective electrolyte isolation, and enables independent optimization of each function without compromising the other.
Solution Approach 2:
A voltage application portion is introduced as an intermediary element between the seal and the wafer surface. This intermediary structure applies a positive voltage to the wafer surface at the notch location to counteract current crowding, while the seal maintains its electrolyte isolation function. The intermediary allows both functions to be optimized independently.
2Reliability
If a seal with inward protrusion is used at the notch to seal the electrolyte, then the electrolyte is kept away from the notch region, but electric current is concentrated at the notch due to irregular geometry, causing thicker plated film and reduced yield
Solution Approach 1:
A positive voltage is applied locally only at the notch location on the wafer surface, while the rest of the wafer surface remains at ground potential. This local voltage application creates a localized electric field that compensates for the current crowding effect specifically at the notch, without affecting other regions of the wafer. The seal maintains its sealing function while the local voltage ensures uniform plating thickness.
3Productivity
If the edge zone is minimized to reduce seal coverage, then the productive area of the wafer is maximized, but the manufacturing process becomes more complex and difficult to control
Solution Approach 1:
The contact ring is segmented into a seal portion and a voltage application portion, allowing the seal to be minimized to the necessary minimum while the voltage application portion provides the needed electrical control. This segmentation enables maximum wafer utilization while maintaining process control through independent optimization of each function.
Solution Approach 2:
The voltage parameter is changed from a uniform ground potential to a non-uniform distribution where the notch location is at a positive voltage potential while the rest of the wafer is at ground. This parameter change allows precise control of current distribution and plating thickness without requiring a larger seal zone, thereby maintaining both productivity and ease of manufacture.
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 more uniform plating thickness across the wafer, reducing yield loss and simplifying the manufacturing process by minimizing the edge zone required for sealing, thus enhancing the overall efficiency of the electroplating process.
Implementation Method 1
A local positive voltage is applied at the notch region... The positive voltage applied at the notch reduces the current crowding effect at the notch
Implementation Method 2
Electroplating is performed with the wafer, or one side of the substrate, in a bath of liquid electrolyte... Metal ions in the electrolyte deposit or plate out onto the wafer, creating a metal film on the wafer
Data Source
AI summary
An electroplating apparatus has a vessel for holding electrolyte. A head has a rotor including a contact ring for holding a wafer having a notch. The contact ring includes a perimeter voltage ring having perimeter contact fingers for contacting the wafer around the perimeter of the wafer, except at the notch. The contact ring also has a notch contact segment having one or more notch contact fingers for contacting the wafer at the notch. The perimeter voltage ring is insulated from the notch contact segment. A negative voltage source is connected to the perimeter voltage ring, and a positive voltage source connected to the notch contact segment. The positive voltage applied at the notch reduces the current crowding effect at the notch. The wafer is plated with a film having more uniform thickness.