PVD Backside Gas Cooling for Uniform Deposition
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Solution Overview
Problem
Sputtering systems face inefficiencies when processing large rectangular workpieces or those not in direct thermal contact, as they often result in non-uniform deposition and material wastage due to incomplete coverage and inadequate cooling.
Innovation Solution
A circular rotating pallet with an XY stage for precise positioning within a circular PVD chamber, combined with a magnet system for controlled plasma shaping and backside gas cooling to ensure uniform deposition and effective thermal management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a large rectangular workpiece is placed on a rotating pallet with multiple targets, then the workpiece can be processed, but the center portion of the panel cannot be positioned under any target resulting in non-coverage of the middle area
Solution Approach 1:
The patent introduces an XY stage that enables dynamic positioning of the rotating pallet in addition to its rotational movement. This dynamic adjustment allows the pallet to be shifted so that the center portion of large workpieces can be positioned under targets during processing, ensuring complete coverage and uniform deposition across the entire workpiece surface.
2Area of stationary object
If targets are positioned directly above the corners of a rectangular workpiece for sputtering, then corner areas can be covered, but sputtering material is wasted when the workpiece is not directly below the entire target
Solution Approach 1:
The XY stage enables dynamic positioning of the pallet during the sputtering process. By adjusting the pallet position, the system can optimize the alignment between targets and workpiece areas being processed, ensuring that sputtering material is deposited only where needed on the workpiece surface, thereby minimizing material waste while maintaining complete coverage.
3Temperature
If the pallet cools workpieces through direct thermal contact, then cooling is effective, but workpieces not in direct contact with the pallet surface cannot be cooled
Solution Approach 1:
The patent introduces a gas cooling system that uses a coolant gas flowing through channels in the pallet and exiting through openings to cool workpiece back surfaces. This pneumatic cooling method extends cooling capability to workpieces that are not in direct thermal contact with the pallet, such as packaged IC chips mounted on substrates, thereby enhancing both cooling efficiency and adaptability.
4Adaptability or versatility
If multiple wafers are mounted on the pallet with spaces between them, then individual wafer processing is enabled, but sputtered material is wasted if it lands between the wafers
Solution Approach 1:
The XY stage enables dynamic positioning of the pallet during sputtering of multiple wafers. By adjusting the pallet position, the system can optimize target alignment with the wafer array, minimizing gaps between wafers from the perspective of the targets. This reduces sputtered material waste while maintaining the ability to process multiple individual wafers simultaneously.
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 allows for complete coverage of large workpieces and efficient material use by positioning the pallet and magnets to align with targets, and provides effective cooling to prevent overheating, resulting in improved deposition uniformity and thermal control.
Implementation Method 1
The metal pallet is cooled using a liquid coolant flowing in the pallet. The pallet then cools flat wafers that are directly in contact with the pallet surface.
Implementation Method 2
A backside gas cooling technique is used to cool the back surface of a workpiece. A coolant gas flows through channels in the pallet and exits through openings in the pallet. The openings are positioned to align with the back surface of a workpiece not in direct thermal contact with the pallet, allowing the gas to cool the workpiece back surface.
Implementation Method 3
Sputtering is sometimes referred to as physical vapor deposition, or PVD. In a sputtering operation, thin films comprising materials such as Al, Au, Cu, and Ta are deposited in a vacuum on the workpieces.
Data Source
AI summary
A circular PVD chamber has a plurality of sputtering targets mounted on a top wall of the chamber. A pallet in the chamber is coupled to a motor for rotating the pallet about its center axis. The pallet has a diameter less than the diameter of the circular chamber. The pallet is also shiftable in an XY direction to move the center of the pallet beneath any of the targets so all areas of a workpiece supported by the pallet can be positioned directly below any one of the targets. A scanning magnet is in back of each target and is moved, via a programmed controller, to only be above portions of the workpiece so that no sputtered material is wasted. For depositing a material onto small workpieces, a cooling backside gas volume is created between the pallet and the underside of sticky tape supporting the workpieces.