Aerial Image Mask Inspection for CD Error Detection
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Solution Overview
Problem
Current mask inspection technologies, such as SEM and conventional optical inspection equipment, are slow and lack precision, unable to effectively measure optical effects and detect all critical dimension errors across the entire mask surface, leading to wafer defects.
Innovation Solution
A method utilizing a modified optical proximity correction (OPC) algorithm and an aerial image inspection apparatus to rapidly inspect the entire mask surface, extracting an effective mask layout that accounts for optical effects, and simulating the wafer image to detect errors before the exposure process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SEM is used for mask inspection, then measurement precision is improved, but productivity deteriorates due to slow inspection speed
Solution Approach 1:
The mask inspection process is segmented into multiple operational modes: a first operational mode for high-precision inspection of specific regions using SEM, and a second operational mode for rapid full-mask inspection using aerial image inspection. This segmentation allows the system to achieve both high precision where needed and high productivity for overall inspection.
Solution Approach 2:
The inspection system dynamically switches between different operational modes based on inspection requirements. The control unit determines whether to perform full-mask aerial image inspection or targeted SEM inspection, allowing the system to adapt its inspection strategy to optimize both speed and precision for different mask regions and defect types.
2Productivity
If conventional optical inspection equipment is used, then productivity is improved through high-speed full surface inspection, but measurement precision deteriorates due to low resolution
Solution Approach 1:
The inspection system segments the mask into regions inspected by aerial image inspection (for overall coverage and speed) and regions requiring SEM inspection (for high-precision CD error detection). This segmentation allows conventional optical equipment to maintain its speed advantage while precision-critical areas receive enhanced inspection.
Solution Approach 2:
Aerial image inspection serves as an intermediary between conventional optical inspection and SEM inspection. It provides higher precision than conventional optical equipment while maintaining faster speed, and can identify regions that require subsequent SEM inspection, thus bridging the gap between speed and precision requirements.
3Measurement precision
If SEM is used for mask inspection, then measurement precision is improved, but area of inspection deteriorates as only small areas can be inspected
Solution Approach 1:
The mask inspection is segmented into comprehensive aerial image inspection covering the entire mask surface, followed by targeted SEM inspection of specific regions of interest. This segmentation enables the system to achieve both full-area coverage and high-precision optical effects measurement.
Solution Approach 2:
Aerial image inspection is performed as a preliminary step to identify potential defects and regions requiring detailed analysis. This preliminary action allows the system to then focus SEM inspection on specific areas, achieving both full-area coverage and high-precision measurement without the time penalty of inspecting the entire mask with SEM.
4Productivity
If aerial image inspection apparatus is used, then productivity is improved through high-speed full surface inspection, but measurement precision deteriorates due to insufficient CD sensitivity
Solution Approach 1:
The inspection system segments the inspection task by using aerial image inspection for rapid full-mask scanning and control, followed by SEM inspection of identified critical regions. This segmentation allows the system to maintain high productivity through aerial image inspection while achieving high CD sensitivity where needed through selective SEM inspection.
Solution Approach 2:
The system uses feedback from aerial image inspection results to guide subsequent SEM inspection. Regions showing anomalies or requiring verification in the aerial image are flagged for detailed SEM inspection, creating a feedback loop that optimizes the allocation of high-precision inspection resources based on actual inspection needs.
Data Source
AI summary
A method of precisely inspecting the entire surface of a mask at a high speed in consideration of optical effects of the mask. The method includes designing a target mask layout for a pattern to be formed on a wafer, and extracting an effective mask layout using an inspection image measured from the target mask layout using an aerial image inspection apparatus as a mask inspection apparatus. The effective mask layout is input to a wafer simulation tool for calculating a wafer image to be formed on the wafer. Optical effects of the mask are detected by comparing the target mask layout with the effective mask layout.