Movable Reflective Element for Focus Measurement in Inspection Systems
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current inspection methods in lithographic processes face challenges in accurately focusing the target structure on a substrate for precise measurements of critical dimensions and overlay errors, particularly due to the limitations of existing focus adjustment mechanisms that can interfere with measurement operations.
Innovation Solution
An inspection apparatus is developed, incorporating a focus measurement optical system with a movable reflective element and a control system that adjusts the reflective element along the beam path to determine if the substrate is in focus, allowing for simultaneous focusing and measurement operations by using non-overlapping illumination shapes for the focusing and measurement beams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a focus measurement optical system uses a beam path that overlaps with the measurement beam path, then focus measurement can be performed, but the focus measurement interferes with measurement operations
Solution Approach 1:
The optical system is divided into separate beam paths: a first beam path for focus measurement and a second beam path for measurement operations. This segmentation allows both functions to operate simultaneously without interference, as the beams are spatially separated throughout the optical system.
Solution Approach 2:
The focus measurement beam is directed through a different spatial dimension or angle relative to the measurement beam. By using a separate beam path configuration, the system accommodates both beams without overlap, effectively adding a spatial dimension to resolve the conflict.
2Measurement precision
If focus adjustment mechanisms are added to improve focusing accuracy, then measurement precision improves, but device complexity increases
Solution Approach 1:
The objective lens serves multiple functions: it performs both the measurement operation and the focus measurement. The same optical components are utilized for both purposes, eliminating the need for separate dedicated focus adjustment mechanisms and reducing overall system complexity.
Solution Approach 2:
The system uses itself to perform focus measurement. The objective lens and optical path are configured to enable the system to automatically determine focus conditions without requiring external or additional complex adjustment mechanisms, making the system self-diagnostic for focus conditions.
3Device complexity
If the inspection beam and focus measurement beam share the same optical path, then device complexity is reduced, but measurement accuracy deteriorates due to interference
Solution Approach 1:
The optical system is segmented into distinct beam paths: the inspection beam follows one path while the focus measurement beam follows a separate path. This segmentation prevents beam interference while maintaining relatively simple device architecture through efficient use of shared optical components where applicable.
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 enables accurate and efficient focus adjustment, allowing for precise measurements of critical dimensions and overlay errors without interfering with measurement operations, thereby improving the accuracy and throughput of lithographic processes.
Implementation Method 1
an inspection optical system configured to direct an inspection beam onto a surface of a substrate, the inspection optical system comprising an objective
Implementation Method 2
the focus measurement optical system comprising a movable reflective element configured to receive the focus measurement beam
Data Source
AI summary
An inspection apparatus includes an inspection optical system configured to a direct an inspection beam onto a surface of a substrate, the inspection optical system having an objective, a focus measurement optical system configured to receive a focus measurement beam, redirected by the substrate, from the objective, the focus measurement optical system having a movable reflective element configured to receive the focus measurement beam, and a control system configured to cause movement of the reflective element with a direction component along a beam path of the focus measurement beam and configured to determine whether the substrate surface is in the focus of the objective based on the focus measurement beam.