Photomask Inspection Using Reusable Z Calibration Map
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The photolithography process in semiconductor manufacturing lacks an efficient method for inspecting photomasks during fabrication, particularly in determining defects and maintaining consistent critical dimension (CD) uniformity, which affects the quality of semiconductor devices.
Innovation Solution
An inspection system that includes a light source, optical module, stage, image sensor, and computing device, capable of generating a Z calibration map to auto-focus and capture images of photomasks, performing two inspection processes to detect defects and categorize them as hard or soft, allowing for targeted repairs and ensuring accurate defect detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional inspection methods are used for photomasks, then the inspection process is simple, but the defect detection accuracy and CD uniformity measurement precision are insufficient
Solution Approach 1:
The system performs preliminary actions by generating a Z calibration map before inspection to establish focus reference data. This pre-calibration enables the inspection system to automatically adjust focus settings for different regions of the photomask, improving measurement precision without requiring complex real-time adjustments during inspection
Solution Approach 2:
The inspection process is segmented into distinct phases: first inspection process for initial defect detection, second inspection process for verification, and Z calibration map generation for focus reference. This segmentation allows each phase to be optimized independently, achieving high precision without proportionally increasing overall system complexity
2Reliability
If multiple inspection processes are performed on photomasks, then defect detection reliability is improved, but the inspection time increases
Solution Approach 1:
The Z calibration map is generated in advance and reused across multiple inspection processes. This preliminary calibration eliminates the need to perform time-consuming focus calibration before each inspection, allowing multiple inspections to be conducted quickly while maintaining high reliability through consistent focus reference
Solution Approach 2:
The system maintains continuous useful action by keeping the Z calibration map available for repeated use during multiple inspection processes. This continuity allows the inspection system to operate efficiently across multiple passes without interrupting the workflow for recalibration, thereby maintaining reliability while minimizing time loss
3Manufacturing precision
If manual focus adjustment is used during inspection, then the system is easier to operate, but the focus consistency and measurement precision deteriorate
Solution Approach 1:
The inspection system performs self-service by automatically adjusting focus based on the Z calibration map without requiring manual intervention. The system autonomously references the pre-generated calibration data to maintain consistent focus across different regions of the photomask, achieving high manufacturing precision while simplifying operation
Solution Approach 2:
The system replaces manual mechanical focus adjustment with an automated optical/electronic focus control mechanism that references the Z calibration map. This substitution eliminates human error in focus adjustment while maintaining ease of operation through automated control
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 enhances the quality control of photomasks by accurately identifying and categorizing defects, improving the precision of semiconductor device fabrication through efficient inspection methods that save time and improve efficiency in the second inspection process by reusing the Z calibration map.
Implementation Method 1
an optical module configured to scan the photomask by focusing an objective lens of the optical module based on the Z calibration map
Implementation Method 2
an image sensor configured to capture images of the photomask while an illuminated light scans the photomask
Data Source
AI summary
In accordance with some embodiments of the present disclosure, an inspection method of a photomask includes performing a first inspection process, unloading the photomask from the inspection system, and performing a second inspection process. In the first inspection process, a common Z calibration map of an objective lens of an optical module with respect to the photomask is generated and stored, and a first image of the photomask is captured by using an image sensor while focusing the objective lens of the optical module based on the common Z calibration map. The photomask is unloaded from the inspection system. In the second inspection process, the photomask is loaded on the inspection system and a second image of the photomask is captured by using an image sensor while focusing an objective lens of an optical module based on the common Z calibration map generated in the first inspection process.