Substrate Transfer Orientation Adjustment for Lithography Overlay Accuracy
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Solution Overview
Problem
In lithographic projection apparatuses, the transfer of substrates between substrate holders with burls introduces overlay errors due to local image shifts caused by the uneven surface, which complicates achieving the required accuracy for high-density device manufacturing.
Innovation Solution
A method and system for transferring substrates between substrate holders using transfer data, where the second holder has a surface with burls, and a processor adjusts the substrate's orientation based on burl position data and previous substrate holder data to minimize position and orientation errors, ensuring accurate placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the substrate is fixed to the substrate table using burls, then the substrate can be securely clamped and positioned, but the substrate bends over the burls causing local image shifts and overlay errors
Solution Approach 1:
The patent measures the position and orientation of the substrate relative to the burls before the lithographic exposure process. By performing this measurement in advance, the system can calculate compensation values that will correct for the substrate bending over the burls, thereby maintaining overlay accuracy despite the mechanical clamping requirement
Solution Approach 2:
The patent changes the parameters used for positioning and alignment by introducing compensation based on measured position and orientation data. Instead of relying solely on mechanical precision, the system adjusts the exposure parameters to account for the substrate's actual position and orientation relative to the burls, thereby compensating for bending-induced image shifts
2Ease of operation
If the substrate is positioned on the substrate table with burls, then the backside can be clamped securely, but the local image shift varies between exposures introducing overlay errors
Solution Approach 1:
The patent implements a feedback mechanism where the position and orientation of the substrate relative to the burls is measured and used to calculate compensation values. This feedback loop allows the system to adjust for variations in substrate positioning and bending, ensuring consistent overlay accuracy across multiple exposures despite the use of burls for clamping
3Reliability
If the substrate backside is pressed against a solid surface, then the substrate is securely held, but particulate contamination distorts the image
Solution Approach 1:
The patent applies local quality by using burls that create discrete contact points rather than a continuous solid surface. This localized contact approach secures the substrate while leaving most of the backside surface free from direct contact, thereby minimizing the area where particulate contamination could cause image distortion
Data Source
AI summary
The invention relates to a method of transferring a substrate from a first substrate holder to a second substrate holder in a lithographic projection apparatus by using a transfer unit on the basis of transfer data available thereto. The second substrate holder has a surface provided with a first plurality of burls. In the method, a memory encoded with burl position data and substrate position data is provided. Subsequently, a substrate is provided on the first substrate holder. The position error and orientation of the substrate is then measured. On the basis of the burl position data, substrate position data and orientation as measured orientation adjustment data are calculated. The orientation of the substrate is subsequently adjusted in accordance with the orientation adjustment data. The substrate is then transferred from the first substrate holder to the second substrate holder by the transfer unit and placed on the second substrate holder.