Grounded Shield Geometry for Low-Sputter PVD Chambers
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Solution Overview
Problem
In physical vapor deposition (PVD) chambers, the high plasma density and frequency of the RF source lead to undesirable sputtering of the grounded shield, causing contamination and affecting plasma geometry, as the plasma potential difference and ion density result in sputtering of the grounded shield.
Innovation Solution
The design includes a grounded shield with a specific ratio of surface area to height and diameter, and the incorporation of waves on the shield to increase surface area while maintaining the same height, reducing the plasma potential difference and preventing sputtering, along with optimized RF frequencies and pressures to achieve high deposition rates without shield contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high frequency RF power source is used to increase plasma density, then deposition rate is improved, but sputtering of grounded shield increases causing contamination
Solution Approach 1:
The grounded shield is designed with a specific surface area to height ratio (about 2 to about 3) to reduce the plasma potential difference across the shield. By optimizing the surface area relative to height, the shield maintains a more equipotential surface, reducing the electric field strength and ion bombardment energy, thereby minimizing sputtering while allowing high frequency RF operation for high deposition rates
Solution Approach 2:
The invention changes the geometric parameters of the grounded shield, specifically the surface area to height ratio, to alter the plasma-sheath interaction. This parameter change reduces the potential drop across the sheath region near the shield, thereby reducing ion bombardment and sputtering while maintaining the benefits of high frequency RF plasma for high deposition rates
2Productivity
If high plasma density is maintained, then deposition rate increases, but sputtering of grounded shield increases
Solution Approach 1:
The optimized shield geometry with surface area to height ratio of about 2 to about 3 creates a more equipotential surface that reduces the potential difference in the plasma sheath. This reduces ion bombardment energy and prevents excessive sputtering of shield material, allowing high plasma density operation for high deposition rates without significant shield material loss
3Reliability
If grounded shield acts as main current return path, then plasma operation is enabled, but sputtering causes contamination of chamber and substrate
Solution Approach 1:
The grounded shield with optimized surface area to height ratio maintains reliable plasma operation by providing a stable current return path while reducing the potential difference across the sheath. This reduces ion bombardment intensity and minimizes sputtering, thereby preventing contamination of the chamber and substrate while maintaining reliable plasma discharge
Solution Approach 2:
By changing the geometric parameters of the shield (surface area to height ratio), the invention reduces the electric field strength and ion bombardment energy at the shield surface. This allows the shield to continue functioning as the main current return path for reliable plasma operation while minimizing material sputtering and contamination
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 configuration reduces or eliminates sputtering of the grounded shield, allowing for increased deposition rates with high ionization levels and minimized contamination, while maintaining target to substrate spacing and plasma geometry.
Implementation Method 1
an RF power source to form a plasma within the chamber body
Implementation Method 2
the plasma potential can be in the region of a few tens to a few hundred volts positive with respect to the grounded shield. This potential difference coupled with the high plasma-ion density can cause undesirable sputtering of the grounded shield
Data Source
AI summary
Methods and apparatus for physical vapor deposition are provided herein. In some embodiments, a process kit shield for use in a physical vapor deposition chamber may include an electrically conductive body having one or more sidewalls defining a central opening, wherein the body has a ratio of a surface area of inner facing surfaces of the one or more sidewalls to a height of the one or more sidewalls of about 2 to about 3.