Dual Endpoint Detection for Photomask Etching
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Solution Overview
Problem
In the manufacturing of integrated circuits, accurately determining the etching endpoints for both the photoresist layer and the absorber layer in photomasks is challenging due to varying etch rates and thickness differences, which complicates process control and can lead to defects in the photomask fabrication.
Innovation Solution
The method involves optical monitoring at specific regions of the photomask to collect and analyze optical signals, using radiation with wavelengths greater than 400 nm to determine the thickness loss of both the photoresist and absorber layers, allowing for precise endpoint determination and enhanced process control during the etching process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical monitoring is performed to determine endpoint data during etching, then process control is improved, but different materials in the film stack generate different endpoint data making accurate determination difficult
Solution Approach 1:
The patent segments the endpoint detection by assigning different wavelengths to different layers: a first wavelength (e.g., 193 nm) is used to detect the absorber layer endpoint, while a second wavelength (e.g., 248 nm or 365 nm) is used to detect the photoresist layer endpoint. This segmentation allows each wavelength to be optimized for its specific layer, resolving the confusion caused by mixed material signals.
Solution Approach 2:
The patent changes the optical parameter (wavelength) to match the specific optical properties of each material layer. By selecting wavelengths that are absorbed or transmitted differently by the absorber layer and photoresist layer, the system can distinguish between the two materials and determine their respective endpoints accurately despite their different etch rates and optical characteristics.
2Reliability
If radiation is directed to monitor both photoresist layer and film stack, then endpoint data can be obtained, but different thickness variations generate different reflective or transmissive signals interfering with accurate endpoint determination
Solution Approach 1:
The patent segments the measurement process by using wavelength-specific detection: the first wavelength monitors the absorber layer thickness and endpoint, while the second wavelength monitors the photoresist layer thickness and endpoint. This eliminates the interference problem by ensuring each wavelength measures only its target layer.
Solution Approach 2:
The patent introduces wavelength-specific optical detection as an intermediary mechanism between the etching process and endpoint determination. By using wavelength-selective optics and detectors tuned to specific wavelengths, the system can isolate the optical signals from each material layer, preventing signal interference and enabling accurate simultaneous monitoring of both layers.
3Measurement precision
If single wavelength monitoring is used during etching, then process monitoring is simplified, but accurate endpoint detection for both photoresist layer and absorber layer cannot be achieved
Solution Approach 1:
The patent implements a multi-functional optical monitoring system where a single etching process chamber is equipped with multiple wavelength detection capabilities. The system can simultaneously or sequentially use different wavelengths to monitor both the absorber layer and photoresist layer, making the monitoring system universal for detecting endpoints of multiple different materials without requiring separate etching chambers or processes.
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 enables accurate and reliable endpoint detection for both layers, improving etch rate monitoring and process control, thereby reducing defects and ensuring consistent photomask quality.
Implementation Method 1
directing radiation having a wavelength greater than 400 nm to an area of the absorber layer covered by the patterned photoresist layer during the etching process, collecting an optical signal transmitted through the area of the absorber layer covered by the patterned photoresist layer
Data Source
AI summary
The present invention provides a method and apparatus for etching a photomask substrate with enhanced process monitoring, for example, by providing for optical monitoring at certain regions of the photomask to obtain dual endpoints, e.g., etch rate or thickness loss of both a photoresist layer and an absorber layer. By monitoring transmissity of an optical beam transmitted through areas having photoresist layer and etched absorber layer at two different predetermined wavelength, dual process endpoints may be obtained by a signal optical detection.