Lithographic Overlay Correction via Grating Asymmetry Measurement
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Solution Overview
Problem
Lithographic processes face significant alignment and overlay errors due to asymmetry in alignment and overlay gratings, which are not effectively measured by existing Diffraction-Based Overlay (DBO) techniques, leading to inaccuracies in layer alignment and device performance.
Innovation Solution
A method and apparatus that measure the transverse profiles of overlay and alignment markers to correct for asymmetry, using radiation projection and detection systems to determine and adjust the position of alignment markers and measure lateral overlays, thereby improving alignment and overlay accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If Diffraction-Based Overlay (DBO) techniques are used to measure overlay, then measurement speed is improved, but measurement precision deteriorates due to inability to detect asymmetry in gratings
Solution Approach 1:
The system performs preliminary measurement of the transverse profile of the overlay grating using scatterometry before conducting the overlay measurement. This preliminary action characterizes the grating asymmetry in advance, allowing the subsequent overlay measurement to compensate for the detected asymmetry and achieve both speed and precision.
2Speed
If alignment gratings are used for alignment, then alignment speed is improved, but alignment precision deteriorates due to asymmetry in the gratings
Solution Approach 1:
The system measures the transverse profile of the alignment grating and feeds this information back to correct the alignment measurement. The feedback mechanism allows the system to compensate for grating asymmetry by adjusting the reference profile, thereby maintaining both fast alignment speed and high alignment precision.
3Device complexity
If conventional overlay measurement methods are used, then device complexity is reduced, but overlay error increases due to asymmetry effects
Solution Approach 1:
The system changes the measurement parameter from simple intensity-based overlay detection to transverse profile characterization using scatterometry. By measuring the shape and asymmetry of the grating profile, the system can distinguish between actual overlay errors and apparent errors caused by grating asymmetry, achieving higher precision without excessive complexity.
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 alignment and overlay errors by directly addressing asymmetry in gratings, enhancing the precision of layer alignment and improving device yield and performance.
Implementation Method 1
a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured
Implementation Method 2
properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it has been reflected or scattered by the substrate
Data Source
AI summary
Disclosed is a device manufacturing method, and accompanying inspection and lithographic apparatuses. The method comprises measuring on the substrate a property such as asymmetry of a first overlay marker and measuring on the substrate a property such as asymmetry of an alignment marker. In both cases the asymmetry is determined. The position of the alignment marker on the substrate is then determined using an alignment system and the asymmetry information of the alignment marker and the substrate aligned using this measured position. A second overlay marker is then printed on the substrate; and a lateral overlay measured on the substrate of the second overlay marker with respect to the first overlay marker using the determined asymmetry information of the first overlay marker.