Lithographic Apparatus Focus Control Using Height Sensor Data
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Solution Overview
Problem
Lithographic manufacturing processes face challenges due to device-specific topography variations and process dependency issues, which affect the accuracy of height sensor data, leading to poor patterning performance and inconsistent results across substrates.
Innovation Solution
A method and apparatus that utilize height sensor data to identify reliable and unreliable areas on a substrate, calculate substitute height data using prior knowledge of device-specific topography, and combine this data for accurate focus control, thereby improving the lithographic apparatus's response to device-specific topography despite variations in process dependency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If height sensor data is used to control focus across the substrate, then focus control is improved, but measurement precision deteriorates in areas with process dependency variations
Solution Approach 1:
The substrate surface is divided into multiple regions based on height sensor data reliability. Regions are segmented into those with reliable height sensor measurements and those with unreliable measurements due to process dependency. This segmentation allows differential processing where reliable regions use direct sensor data while unreliable regions use alternative correction methods, thereby maintaining overall focus control reliability without compromising measurement precision in any specific region.
Solution Approach 2:
An intermediary correction process is introduced that uses prior knowledge of device-specific topography and process dependency characteristics to adjust height sensor data. This intermediary layer acts as a mediator between the raw height sensor measurements and the final focus control decisions, filtering out process dependency artifacts while preserving real topographical information, thus resolving the contradiction between reliability and precision.
2Loss of information
If height sensor measurements are taken across the substrate, then topographical information is obtained, but data reliability deteriorates due to process dependency of the sensor
Solution Approach 1:
Different quality levels are assigned to height sensor data based on local process dependency characteristics. Regions with low process dependency are marked as high quality while regions with high process dependency are marked as low quality. This local quality differentiation allows the system to maintain complete topographical information coverage while explicitly tracking reliability variations across different substrate areas, enabling subsequent selective use of data based on reliability requirements.
Solution Approach 2:
Prior knowledge of device-specific topography and process dependency patterns is obtained and stored before actual height sensor measurements are taken. This preliminary information is used to pre-identify regions where process dependency is likely to affect measurements. By performing this preliminary analysis, the system can prepare appropriate correction strategies in advance, ensuring that when measurements are taken, the reliability issues are already anticipated and can be addressed systematically.
3Manufacturing precision
If focus control is adjusted for device-specific topography, then patterning quality is improved, but process complexity increases due to need for corrections
Solution Approach 1:
The focus control process utilizes parameter changes in the form of pre-characterized process dependency patterns and device-specific topography profiles. Instead of implementing complex real-time analysis and correction algorithms, the system changes parameters by applying pre-determined correction values based on the identified unreliable regions. This approach maintains high patterning quality while avoiding the complexity of dynamic correction processes, as the parameter adjustments are based on prior knowledge and characterization.
Data Source
AI summary
A lithographic apparatus uses a height sensor to obtain height sensor data representing a topographical variation across a substrate. The height sensor data is used to control focusing of a device pattern at multiple locations across the substrate. A controller identifies one or more first areas where height sensor data is judged to be reliable and one or more second areas where the height sensor data is judged to be less reliable. Substitute height data is calculated for the second areas using height sensor data for the first areas together with prior knowledge of expected device-specific topography. The focusing of the lithographic apparatus is controlled using a combination of the height data from the sensor and the substitute height data.