Modulating Scanning Velocity for Overlay Metrology
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Solution Overview
Problem
Conventional methods for imaging overlay targets on a wafer are time-consuming due to the need for the wafer stage to be stationary, which introduces vibrations and limits throughput, especially in high-magnification microscope-based systems with strict stability and image quality requirements.
Innovation Solution
A method and system that utilize a Time Delay Integration (TDI) sensor to acquire images of overlay targets while the wafer is in motion, with controlled acceleration and deceleration profiles such as linear, triangular, sinusoidal, or dual-frequency sinusoidal patterns to minimize vibrations and optimize movement between targets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the wafer stage is moved to position overlay targets within the field of view, then the overlay targets can be imaged, but system vibrations are introduced that require a waiting period before imaging
Solution Approach 1:
The patent applies dynamics by transitioning from a static imaging approach (wafer stage must be stationary) to a dynamic approach where the wafer stage moves continuously at a constant velocity while the TDI sensor captures images during motion. This eliminates the need for settling time after positioning, as the system is designed to image during movement rather than requiring the stage to be stationary.
Solution Approach 2:
The patent implements continuity of useful action by maintaining constant velocity motion of the wafer stage throughout the imaging process, rather than stopping and starting between targets. The TDI sensor continuously integrates light from moving overlay targets, allowing uninterrupted imaging without settling periods, thus maximizing throughput.
2Productivity
If the acceleration and deceleration of the stage are increased to reduce movement time between targets, then throughput increases, but system vibrations increase requiring longer settling periods
Solution Approach 1:
The patent applies dynamics by maintaining constant velocity motion rather than accelerating and decelerating between targets. This dynamic approach allows the system to move continuously through the wafer at an optimized velocity, eliminating the vibration-induced settling time that would otherwise limit throughput.
Solution Approach 2:
The patent replaces the conventional mechanical positioning system (accelerate-move-decelerate-wait) with an optical-dynamic system using TDI sensor that can capture images during continuous motion. This substitution eliminates the mechanical settling requirement and allows uninterrupted imaging at constant velocity.
3Productivity
If the wafer stage is moved continuously to image multiple overlay targets, then throughput increases, but image quality may deteriorate due to motion blur
Solution Approach 1:
The patent replaces the mechanical positioning system with a TDI sensor-based optical system that is specifically designed to capture sharp images during continuous motion. The TDI sensor synchronizes its charge transfer with the wafer stage velocity, eliminating motion blur that would otherwise occur with conventional stationary sensors during movement.
Solution Approach 2:
The patent applies dynamics by matching the TDI sensor's charge transfer rate to the wafer stage's velocity. This dynamic synchronization allows the sensor to integrate light from moving targets without motion blur, maintaining image quality while enabling continuous motion imaging for high throughput.
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 approach reduces the time required to obtain clear images of overlay targets, increases process throughput, and minimizes system vibrations, leading to improved measurement accuracy and reduced settling times.
Implementation Method 1
utilize a Time Delay Integration (TDI) sensor to acquire images of overlay targets while the wafer is in motion
Implementation Method 2
acquire images of overlay targets on a wafer while the wafer is in motion
Data Source
AI summary
A method for imaging overlay targets on a wafer includes (1) using a sensor to acquire images of overlay targets on a wafer while the wafer is in motion and (2) accelerating and decelerating the wafer to move the overlay targets into alignment with the sensor between acquiring images of the overlay targets. Accelerating/decelerating the wafer may include: (1) accelerating the wafer at a maximum acceleration and then decelerating the wafer at a maximum deceleration, (2) accelerating/decelerating the wafer in a triangular waveform pattern, (3) accelerating/decelerating the wafer in a sinusoidal pattern, or (4) accelerating/decelerating the wafer in a near-sinusoidal pattern (created by combining a pure sinusoidal profile with one or more harmonic profiles). A system is also provided for implementing the above method(s).