Lithographic Height Sensor Adjustable Reference
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Solution Overview
Problem
Conventional height sensors in lithographic apparatuses require fine control of the substrate position to maintain accurate height measurements, limiting their applicability due to a narrow range of height variations they can measure, and increasing the grating pitch to widen this range would degrade measurement accuracy.
Innovation Solution
A height sensor with an adjustable reference height system that automatically adjusts during measurements, using movable optical elements or a multi-element detector to maintain measurement accuracy across a wider range of substrate heights without changing the incidence angle, allowing for accurate height measurements without precise substrate positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the grating pitch is increased to widen the measurement range, then the range of height variations that can be measured is increased, but the measurement accuracy is degraded
Solution Approach 1:
The height sensor measures height at multiple discrete locations across the substrate rather than attempting to measure the entire substrate height range at a single location. By segmenting the measurement into multiple positions, the sensor can maintain high accuracy at each location while collectively covering a broad range of height variations across the substrate surface.
Solution Approach 2:
The system dynamically adjusts the measurement location across the substrate surface by moving the substrate or sensor, rather than using a fixed measurement position. This allows the sensor to adapt to different height regions by relocating the measurement point, maintaining accuracy without requiring a large grating pitch.
2Measurement precision
If fine control of substrate position is implemented to maintain measurement accuracy, then measurement precision is improved, but the complexity and cost of the positioning subsystem is increased
Solution Approach 1:
Instead of requiring fine control of the entire substrate position, the system segments the control requirement to only the measurement location. By moving only the measurement point to different locations across the substrate, the system achieves accurate measurements without needing to precisely control the position of the entire substrate during measurement.
Solution Approach 2:
The invention extracts the measurement function from a fixed position on the substrate and relocates it to multiple different positions. By taking the measurement capability to various locations rather than keeping the substrate stationary with fine control, the system reduces positioning complexity while maintaining measurement accuracy.
3Measurement precision
If fine control of substrate position is implemented to maintain measurement accuracy, then measurement precision is improved, but the cost of the positioning subsystem is increased
Solution Approach 1:
The system segments the expensive fine-control requirement to only the measurement location rather than the entire substrate. By using simpler positioning for the measurement point and allowing the substrate to be positioned more coarsely, the overall system cost is reduced while maintaining measurement precision.
Solution Approach 2:
The invention extracts the fine-control requirement from the substrate positioning system and applies it only to the measurement location. This separation allows the use of less expensive positioning mechanisms for the substrate while maintaining accurate measurements through precise positioning of only the measurement point.
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
Enables accurate height measurements across a broader range of substrate heights without compromising sensitivity, relaxing the need for fine substrate control and reducing the complexity and cost of the positioning subsystem.
Implementation Method 1
a projection unit to project a measurement beam on the substrate, the projection unit comprising: a projection grating arranged to impart the measurement beam with a substantially periodic radiation intensity; a detection unit, typically comprising two or more detection elements, to receive the measurement beam after reflection on the substrate
Data Source
AI summary
A lithographic apparatus (LA) applies a pattern to a substrate (W). The lithographic apparatus includes a height sensor (LS), a substrate positioning subsystem, and a controller configured for causing the height sensor to measure the height (h) of the substrate surface at locations across the substrate. The measured heights are used to control the focusing of one or more patterns applied to the substrate. The height h is measured relative to a reference height (zref). The height sensor is operable to vary the reference height (zref), which allows a wider effective range of operation. Specifications for control of the substrate height during measurement can be relaxed. The reference height can be varied by moving one or more optical elements (566, 572, 576, 504 and/or 512) within the height sensor, or moving the height sensor. An embodiment without moving parts includes a multi-element photodetector (1212).