EUV Mask Aerial Image Measurement Using Coherent Light and Sensor Array
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Solution Overview
Problem
Current semiconductor manufacturing processes for EUV masks are costly and time-consuming due to the need for complex optical systems and multiple evaluation steps to inspect and correct defects, which affects wafer yield.
Innovation Solution
A high-performance aerial image measuring system for EUV masks utilizing a scanning-type microscope with a coherent EUV light generating portion, including a high-power laser output unit, pin-hole, graphene filter, zirconium filter, x-ray spherical mirror, zone-plate lens, and sensor array detector, capable of emulating inclined illuminating systems without a complex optical setup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a complex optical system is used to measure aerial images of EUV masks, then measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses a sensor array to directly detect and record the aerial image pattern without requiring a complete optical reproduction system. The sensor array captures the light distribution pattern directly, creating a digital copy of the aerial image that can be analyzed computationally, thereby avoiding the need for complex optical path replication
Solution Approach 2:
The patent replaces complex mechanical optical systems with a combination of a simple illumination source, condenser lens, and sensor array. The aerial image measurement is achieved through direct optical projection onto the sensor array, eliminating the need for complex intermediate optical components and mechanical adjustment systems
2Reliability
If multiple evaluation steps are performed to inspect and correct mask defects, then defect detection reliability is improved, but manufacturing time and cost increase
Solution Approach 1:
The patent performs aerial image measurement during the mask fabrication process itself, before the mask is finalized and sent for wafer exposure. This preliminary measurement allows defects to be detected and corrected early in the manufacturing flow, preventing defective masks from proceeding to costly wafer-level processes
Solution Approach 2:
The patent creates a multi-functional measurement system that can evaluate multiple aspects of mask quality (aerial image formation, pattern fidelity, defect detection) through a single integrated apparatus, eliminating the need for multiple separate inspection equipment and process steps
3Adaptability or versatility
If a scanning-type microscope system is used to measure aerial images, then adaptability to various illuminating conditions is improved, but measurement time increases
Solution Approach 1:
The patent uses a scanning approach where the mask or sensor array is moved periodically across the measurement field, allowing aerial images under different illuminating conditions to be captured sequentially. This periodic scanning enables comprehensive evaluation of various illumination scenarios while maintaining efficient measurement throughput
Solution Approach 2:
The patent employs a dynamic scanning mechanism that allows rapid repositioning and reconfiguration of the measurement system. The ability to quickly move the mask or sensor array enables the system to adapt to different measurement requirements and illuminating conditions without significant time penalty, achieving versatility through dynamic rather than static configuration
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 system reduces costs and time by enabling efficient measurement of aerial images under various illuminating conditions, improving optical efficiency and wafer yield by accurately evaluating defect corrections on EUV masks before wafer exposure.
Implementation Method 1
a high-power laser output unit including a flat mirror and a spherical mirror, which are used to focus a high-power femto-second laser on a gas cell; a coherent EUV light generating portion including the gas cell, which is used to generate a coherent EUV light from light output from the laser output unit
Implementation Method 2
an x-ray spherical mirror configured to focus a coherent EUV light on a zone-plate lens and thereby to improve optical efficiency
Implementation Method 3
a zone-plate lens placed between the stage and the x-ray spherical mirror to focus a reflected portion of the coherent EUV light on a region of the reflection-type EUV mask
Implementation Method 4
an x-ray flat mirror placed between the zone-plate lens and the x-ray spherical mirror to guide and reflect a beam, which is focused by the x-ray spherical mirror, to the zone-plate lens
Implementation Method 5
an order sorting aperture (OSA) placed on the stage and configured to transmit only a first-order diffraction light of the focused coherent EUV light
Implementation Method 6
a detector portion placed on the stage and composed of a sensor array, which is configured to sense an energy distribution of the coherent EUV light according to an angle of a reflected portion of the coherent EUV light
Implementation Method 7
a pin-hole, a graphene filter, and a zirconium (Zr) filter configured to remove a high-power laser beam from the generated EUV light
Data Source
AI summary
A system of measuring an image of a pattern in a scanning type EUV mask may include a high-power laser output unit including a flat mirror and a spherical mirror, which are used to focus a high-power femto-second laser on a gas cell; a coherent EUV light generating portion generating a coherent EUV light; a pin-hole, a graphene filter, and a zirconium (Zr) filter; a stage; an x-ray spherical mirror configured to focus a coherent EUV light; a zone-plate lens placed between the stage and the x-ray spherical mirror; an x-ray flat mirror placed between the zone-plate lens and the x-ray spherical mirror; an order sorting aperture (OSA) placed on the stage and configured to transmit only a first-order diffraction light of the focused coherent EUV light; and a detector portion placed on the stage.