193 nm Laser System for High-Resolution Inspection
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Solution Overview
Problem
Current solid-state and fiber lasers producing sub-200 nm light have low power output, complex designs, and are expensive, making them unsuitable for high-resolution photomask and reticle inspection due to their limitations in repetition rate and stability.
Innovation Solution
A laser system generating light near 193 nm using a fundamental source and multiple frequency conversion stages, including Yb-doped fiber lasers and neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers, to produce harmonic, sum, and other frequencies, with non-linear crystals like CLBO and BBO for efficient frequency conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If excimer lasers are used to generate 193 nm ultraviolet light, then the wavelength requirement for photomask and reticle inspection is met, but the lasers have low repetition rate and very high peak power that could damage samples
Solution Approach 1:
The patent changes the fundamental laser parameters from excimer laser characteristics (low repetition rate, high peak power) to solid-state laser characteristics (high repetition rate, lower peak power) while achieving the same 193 nm wavelength through frequency conversion processes including second harmonic generation and sum frequency generation
Solution Approach 2:
The patent replaces the excimer laser system (gas-based) with a solid-state laser system using nonlinear optical crystals for frequency conversion, substituting a mechanical/gas-based system with a solid-state optical system that provides superior repetition rate and reduced peak power
2Measurement precision
If conventional excimer lasers are used for 193 nm light generation, then the wavelength is suitable for lithography, but fluorine gas is toxic and corrosive resulting in high cost of ownership
Solution Approach 1:
The patent replaces expensive and hazardous fluorine gas consumables with durable solid-state laser components including nonlinear optical crystals (BBO, LBO, KTP) that do not require replacement, eliminating ongoing gas procurement and safety compliance costs
Solution Approach 2:
The patent eliminates the need for toxic fluorine gas environment by using solid-state laser media and nonlinear optical crystals that operate in inert or controlled atmospheric conditions, removing safety hazards and associated infrastructure costs
3Productivity
If solid-state and fiber lasers are used to produce sub-200 nm light, then the repetition rate can be increased, but the power output is low and the design is complex
Solution Approach 1:
The patent segments the frequency conversion process into multiple distinct stages: second harmonic generation stage, sum frequency generation stage, and combination stage, where each stage uses optimized nonlinear optical crystals to progressively convert the fundamental laser wavelength to the target 193 nm wavelength while maintaining high power and repetition rate
Solution Approach 2:
The patent merges multiple frequency conversion processes (second harmonic generation and sum frequency generation) within a unified solid-state laser system, combining the advantages of high repetition rate with sufficient output power by coordinating multiple conversion stages
4Measurement precision
If solid-state lasers with complex designs are used for sub-200 nm output, then frequency conversion can be achieved, but the systems are expensive and unstable
Solution Approach 1:
The patent optimizes critical parameters including crystal orientation angles, temperature control ranges (20-40°C), and pump laser wavelengths to maximize conversion efficiency and stability, using specific nonlinear optical crystals (BBO, LBO, KTP) with known optimal operating parameters for 193 nm generation
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 achieves efficient generation of 193 nm light with high conversion efficiency, stability, and low walk-off, overcoming the limitations of existing lasers by providing a reliable and cost-effective solution for high-resolution inspection applications.
Implementation Method 1
A laser system generating light near 193 nm using a fundamental source and multiple frequency conversion stages, including Yb-doped fiber lasers and neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers, to produce harmonic, sum, and other frequencies, with non-linear crystals like CLBO and BBO for efficient frequency conversion
Data Source
AI summary
An optical inspection system that utilizes sub-200 nm incident light beam to inspect a surface of an object for defects is described. The sub-200 nm incident light beam is generated by combining first light having a wavelength of about 1109 nm with second light having a wavelength of approximately 234 nm. An optical system includes optical components configured to direct the incident light beam to a surface of the object, and image relay optics are configured to collect and relay at least two channels of light to a sensor, where at least one channel includes light reflected from the object, and at least one channel includes light transmitted through the object. The sensor is configured to simultaneously detect both the reflected and transmitted light. A laser for generating the sub-200 nm incident light beam includes a fundamental laser, two or more harmonic generators, a frequency doubler and a two frequency mixing stages.