Rotatable Wedge Prism for Overlay Error Correction in Projection Optical Systems
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Solution Overview
Problem
In the manufacturing of microdevices such as semiconductor devices and liquid-crystal display devices, deviations between the scanning direction of the mask stage and the substrate stage during pattern transfer lead to inaccuracies in overlay, resulting in patterns of parallelogram shape instead of rectangular shape, causing deviations in the overlay of upper-layer patterns.
Innovation Solution
A projection optical system with rotatable wedge prisms is used to transform the pattern shape from rectangular to parallelogram, allowing for precise alignment and correction of overlay errors by rotating the wedge prisms around the Y-axis direction, enabling the projection optical system to match the shape of the lower layer on the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a scanning exposure apparatus is used to transfer patterns onto a substrate, then continuous pattern transfer is achieved, but deviations between mask stage and substrate stage scanning directions cause parallelogram-shaped patterns instead of rectangular patterns, resulting in overlay inaccuracies
Solution Approach 1:
A wedge prism is introduced as an intermediary optical element in the projection optical system. This wedge prism transforms the rectangular pattern image into a parallelogram-shaped pattern that matches the actual shape formed by scanning exposure on the substrate, thereby enabling accurate overlay between sequentially formed patterns.
Solution Approach 2:
The wedge angle of the prism is specifically designed and adjusted to transform the rectangular pattern into a parallelogram with the exact geometric parameters needed to compensate for scanning direction deviations. By changing the optical path parameters through the wedge prism, the pattern shape is modified to match the substrate's actual pattern geometry.
2Manufacturing precision
If the pattern shape is transformed to match the lower layer using a wedge prism, then overlay accuracy is improved, but the optical system complexity increases
Solution Approach 1:
The wedge prism serves multiple functions simultaneously: it transforms the pattern shape from rectangular to parallelogram, compensates for scanning direction deviations, and maintains the overall optical path efficiency. This multi-functionality reduces the need for additional separate correction mechanisms.
Solution Approach 2:
Instead of implementing complex mechanical correction systems or multiple adjustment mechanisms, a simple, inexpensive wedge prism is used to achieve the pattern transformation. This single optical element provides the necessary correction without requiring complex control systems or multiple moving parts.
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 solution improves overlay accuracy by transforming the pattern shape to match the previously formed layer, ensuring high-accuracy exposure and reducing overlay deviations to less than 0.3 nm, maintaining imaging performance and correcting for scanning direction deviations.
Implementation Method 1
at least one first wedge prism each of an entrance surface and an exit surface of which has a plane and in which a predetermined first wedge angle is made between the plane of the entrance surface and the plane of the exit surface
Data Source
AI summary
A projection optical system PL for forming an image of a first plane M on a second plane P has at least one first wedge prism 4 each of an entrance surface and an exit surface of which has a plane and in which a predetermined first wedge angle is made between the plane of the entrance surface and the plane of the exit surface, and when a coordinate system is so defined that a Z-axis direction is set along a direction of a normal to the first plane M, an X-axis direction along a direction of an intersecting line between the plane of the entrance surface and the plane of the exit surface, and a Y-axis direction along a direction perpendicular to the Z-axis direction and the X-axis direction, the first wedge prism 4 is arranged rotatably substantially around the Y-axis direction.