Dark-Field Overlay Metrology Using Twice-Diffracted Light
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Solution Overview
Problem
As feature sizes in semiconductor devices decrease and density increases, existing overlay metrology systems face challenges in providing sensitive and accurate measurements of small alignment errors between layers, necessitating improved metrology techniques.
Innovation Solution
An overlay metrology system utilizing twice-diffracted light is developed, which includes optical assemblies to redirect light twice towards a metrology target, blocking zero-order diffraction and using non-zero-order diffraction for imaging, thereby enhancing sensitivity through doubled phase-shift measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional overlay metrology systems are used, then the system structure is simple, but the measurement sensitivity is insufficient for small feature sizes
Solution Approach 1:
The optical path is segmented into multiple distinct stages: first diffraction at the sample, re-direction through optical assemblies, and second diffraction at the sample. This segmentation allows each stage to be optimized independently, achieving doubled phase-shift measurement capability while maintaining manageable system complexity through modular design
Solution Approach 2:
The measurement approach transitions from single-pass to multi-pass optical path, adding a temporal/dimensional dimension to the measurement process. By directing light twice towards the metrology target with re-direction in between, the system extracts additional phase information that doubles the measurement sensitivity without simply increasing the number of components linearly
2Manufacturing precision
If feature size decreases, then device density increases, but measurement accuracy becomes more difficult to maintain
Solution Approach 1:
The system changes the optical parameters by utilizing twice-diffracted light paths, which doubles the phase-shift measurement capability. This parameter change in the optical measurement process enables detection of smaller alignment errors that would be invisible to conventional single-pass systems, directly addressing the difficulty of measuring alignment errors at smaller feature sizes
3Measurement precision
If zero-order diffraction is included, then light intensity is high, but measurement precision is reduced due to lack of phase-shift
Solution Approach 1:
The system extracts and isolates the non-zero-order diffraction components while excluding the zero-order diffraction from the measurement path. By using masks or optical elements to separate the diffraction orders, the system retains only the phase-containing non-zero orders that provide measurement precision, while discarding the zero-order light that would dilute the phase signal
Solution Approach 2:
Optical assemblies act as intermediaries between the sample and detector, selectively transmitting non-zero-order diffraction light while blocking zero-order light. These intermediary elements enable the system to achieve high measurement precision by mediating the separation of useful phase information from useless intensity-only information
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 achieves twice the sensitivity of conventional methods by leveraging doubled phase-shifts from twice-diffracted light, improving accuracy in overlay measurements.
Implementation Method 1
one or more optical assemblies to re-direct the light back towards the sample
Implementation Method 2
re-direct the light back towards the metrology target
Implementation Method 3
a first diffraction, a re-direction, and a second diffraction of the one or more illumination beams directed twice towards the metrology target
Data Source
AI summary
An overlay metrology system and method are disclosed. The overlay metrology system may be configured for twice-diffracted light. The overlay metrology system may include a controller. The controller may be configured to receive an image of a metrology target of a sample based on twice-diffracted light associated with one or more illumination beams in accordance with a metrology recipe. The twice-diffracted light may be based on a first diffraction, a re-direction, and a second diffraction of the one or more illumination beams directed twice towards the metrology target. The controller may be configured to generate one or more metrology measurements of the sample based on the image in accordance with the metrology recipe and based on a double-phase-shift of the twice-diffracted light associated with the one or more illumination beams.