Metrology Apparatus with Tilted Mirror Beam Selection
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Solution Overview
Problem
Current scatterometers have limitations in measuring smaller targets due to the size of the measurement spot, which is restricted by diffraction effects and positioning accuracy, making it difficult to accurately assess process variations within product features.
Innovation Solution
A metrology apparatus with a first and second radiation source, a beam selection device, and an objective lens to direct and collect angle-resolved spectra, allowing for precise measurement of smaller targets by adjusting the illumination beam's spatial extent and angle range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the target size is reduced to position it amongst product features, then measurement accuracy improves, but the measurement spot size must be reduced which is limited by diffraction effects and positioning accuracy
Solution Approach 1:
The patent implements dynamic adjustment of the illumination beam parameters (spatial extent and angle range) to match the target size. The system can switch between different beam configurations - using a smaller spot size with wider angle range for small in-die targets, and larger spot size with narrower angle range for larger scribe lane targets. This dynamic adaptation resolves the contradiction by making the measurement spot size flexible rather than fixed, allowing accurate measurement of both small and large targets.
Solution Approach 2:
The patent changes the parameters of the illumination beam (spatial extent and angular range) depending on the target characteristics. By adjusting these parameters, the system can optimize the measurement spot size for different target dimensions. For small 5x5 μm in-die targets, the beam is focused to a smaller spot with wider angular acceptance, while for larger 40x40 μm scribe lane targets, the beam is expanded with narrower angular acceptance, thereby resolving the measurement spot size limitation.
2Adaptability or versatility
If a single illumination beam is used, then the device complexity is low, but it cannot simultaneously measure both small in-die targets and large scribe lane targets accurately
Solution Approach 1:
The illumination system is segmented into multiple independent sources, each optimized for specific target types. The first source is configured for measuring small in-die targets with appropriate spot size and angular range, while the second source is optimized for large scribe lane targets. This segmentation allows each source to be independently optimized without compromising the other, resolving the versatility-complexity contradiction by providing specialized measurement capabilities for different target categories.
Solution Approach 2:
The patent creates a multi-functional illumination system that can measure both small in-die targets and large scribe lane targets using a single integrated apparatus. By incorporating multiple illumination sources with different characteristics and providing automated beam selection based on target location and size, the system achieves universal measurement capability across different target types, resolving the contradiction between adaptability and device 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
Enables accurate measurement of smaller targets, improving measurement accuracy by reducing interpolation needs and aligning with product features, thus enhancing process control in lithographic processes.
Implementation Method 1
an objective lens configured to direct the measurement beam onto the target on the substrate and to collect radiation diffracted by the target
Data Source
AI summary
A metrology apparatus includes first (21) and second (22) radiation sources which generate first (iB1) and second (iB2) illumination beams of different spatial extent and/or angular range. One of the illumination beams is selected, e.g. according to the size of target to be measured. The beam selection can be made by a tillable mirror (254) at a back-projected substrate plane in a Kohler illumination setup.