Pump-Probe Alignment Measurement for Buried Marks
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Solution Overview
Problem
Current optical alignment methods in lithographic apparatuses face challenges in accurately measuring the position of alignment marks, especially when these marks are buried under varying layers of opaque materials, as the measurement radiation beam cannot penetrate through, leading to inaccuracies in overlay control for smaller product features.
Innovation Solution
An apparatus utilizing a separate pump radiation delivery system to generate mechanical waves, such as acoustic waves, which can propagate through opaque layers, allowing for indirect measurement of alignment marks by probing the surface with measurement radiation, enabling accurate positioning even when marks are beneath the top surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical alignment methods are used to measure alignment marks, then measurement can be performed on exposed marks, but measurement becomes impossible when marks are buried under opaque layers
Solution Approach 1:
The patent introduces pump radiation as an intermediary that generates mechanical waves to mediate between the measurement radiation and the buried alignment marks. The mechanical waves propagate through opaque layers that block direct optical measurement, enabling indirect detection of alignment mark positions beneath the surface.
Solution Approach 2:
The patent replaces direct optical measurement with a mechanical wave-based measurement system. Instead of using measurement radiation to directly detect alignment marks, the system uses pump radiation to generate mechanical waves that propagate through the substrate and interact with buried marks, converting an optical measurement problem into a mechanical wave propagation and detection problem.
2Measurement precision
If measurement radiation beam is used to detect alignment marks, then direct measurement is possible, but the beam cannot penetrate through opaque layers
Solution Approach 1:
The patent introduces pump radiation as an intermediary that generates mechanical waves to mediate between the measurement radiation and the buried alignment marks. The mechanical waves propagate through opaque layers that block direct optical measurement, enabling indirect detection of alignment mark positions beneath the surface.
Solution Approach 2:
The patent changes the physical state and propagation characteristics of the measurement signal. Instead of using electromagnetic radiation that is blocked by opaque layers, the system converts the signal into mechanical waves that can propagate through these layers, fundamentally changing the transmission parameter from optical to mechanical domain.
3Device complexity
If traditional optical alignment systems are used, then the system structure is simple, but measurement accuracy deteriorates when marks are buried
Solution Approach 1:
The patent merges two previously separate systems: a pump radiation system for generating mechanical waves and a measurement radiation system for detecting surface vibrations. By combining these systems into a unified pump-probe arrangement, the patent enables measurement of buried alignment marks while maintaining reasonable system complexity through integrated control and coordinate registration.
Solution Approach 2:
The patent creates a multi-functional alignment system that can measure both exposed and buried alignment marks using the same apparatus. The system universally handles different mark depths and positions by adjusting the pump and measurement radiation parameters, eliminating the need for separate measurement systems for different mark types.
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 allows for precise determination of alignment mark positions, enhancing accuracy and overcoming the limitations of traditional optical methods by using a pump-probe arrangement that can penetrate opaque layers, thus improving overlay control in lithographic processes.
Implementation Method 1
a pump radiation source operable to produce pump radiation; and a pump radiation delivery system operable to irradiate at least a part of the top surface of the object with the pump radiation so as to produce a mechanical response in the object
Implementation Method 2
an alignment measurement system measures the position of an alignment mark by irradiating it with a measurement radiation beam, receiving at least a portion of the measurement radiation beam scattered from the alignment mark
Data Source
AI summary
An apparatus for determining a characteristic of a feature of an object comprises: a measurement radiation source; a measurement radiation delivery system; a measurement system; a pump radiation source; and a pump radiation delivery system. The measurement radiation source is operable to produce measurement radiation and the measurement radiation delivery system is operable to irradiate at least a part of a top surface of the object with the measurement radiation. The measurement system is operable to receive at least a portion of the measurement radiation scattered from the top surface and is further operable to determine a characteristic of the feature of the object from at least a portion of the measurement radiation scattered from the top surface. The pump radiation source is operable to produce pump radiation and the pump radiation delivery system is operable to irradiate at least a part of the top surface of the object with the pump radiation so as to produce a mechanical response (for example an acoustic wave) in the object.