Optical Height Sensing for Electron Beam Focus Alignment
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Solution Overview
Problem
Current metrology systems for semiconductor wafers face challenges in accurately determining the absolute distance between an electron beam column and the workpiece due to imperfections in metallic L-shaped targets, leading to difficulties in focus alignment and measurement accuracy, especially with large feature sizes and rough machined metal trenches causing scattering and alignment issues.
Innovation Solution
A system comprising a stage, an electron beam column, a light source, a sensor, and a processor that uses a light beam to determine displacement from a nominal distance between the electron beam column and the workpiece, employing mirrors, lenses, and a beam splitter to improve alignment accuracy and focus positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a metallic L-shaped target is machined on the workpiece for mechanical alignment, then alignment in X and Y directions can be achieved, but the roughness, scratches, and non-uniformities from machining cause scattering that negatively affects measurement precision
Solution Approach 1:
The patent replaces the mechanical alignment system (L-shaped metal target with physical trenches) with an optical system. Instead of using machined metal features that cause scattering, the invention uses optical reflection from the workpiece surface combined with sensor detection to determine height and focus position, eliminating the scattering problem inherent in mechanical targets
Solution Approach 2:
The patent introduces an optical intermediary system consisting of a light source, mirrors, and sensors that mediate between the workpiece and the measurement system. This optical intermediary allows height sensing without direct mechanical contact or reliance on machined target features, thereby avoiding the scattering issues caused by rough surfaces
2Ease of manufacture
If large feature sizes are used on the workpiece, then the workpiece can accommodate standard mounting, but large features cannot provide enough pattern complexity for full measurement and evaluation of optical performance
Solution Approach 1:
The patent transitions from two-dimensional pattern analysis on the workpiece surface to three-dimensional height sensing. By measuring the height profile of features rather than relying on in-plane pattern complexity, the system can evaluate optical performance and focus alignment without requiring complex patterns on large features
3Ease of operation
If the target is not on the same height as the workpiece, then mechanical alignment can be simplified, but alignment accuracy and height sensor performance are affected
Solution Approach 1:
The patent implements a feedback-based height sensing system where a light source illuminates the workpiece, mirrors reflect the light, and sensors detect the reflected light position. The system uses this feedback information to determine the height of features relative to the workpiece and adjust the focus position accordingly, maintaining alignment accuracy without requiring the target to be precisely at the same height as the workpiece
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
The system enhances focus alignment and measurement accuracy by determining relative displacement from nominal distance, allowing for precise adjustment of the stage to achieve desired electron beam focus and address variations in workpiece height and curvature, thereby improving overall metrology tool performance.
Implementation Method 1
a light source configured to generate a light beam at the workpiece on the stage; a sensor configured to receive the light beam reflected from the workpiece
Data Source
AI summary
A beam of light is directed at a workpiece on a stage. The workpiece is disposed an absolute distance from an electron beam column. The beam of light that is reflected off the workpiece is received at a sensor. Using the beam of light, a nominal distance between the electron beam column and the workpiece on the stage is determined.