CLBO Non-Critical Phase Matching for Sub-213nm DUV Generation
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Solution Overview
Problem
Current semiconductor inspection systems face challenges in achieving high throughput and resolution with light sources that provide adequate deep ultraviolet (DUV) light energy, particularly at wavelengths below 213nm, due to inefficiencies and limitations in frequency conversion processes, which result in short lifetimes, high costs, and instability.
Innovation Solution
A method involving the generation of fundamental frequency laser energy at approximately 998nm, conversion to 2nd and 4th harmonic frequencies, and subsequent mixing using non-critical phase matching in Cesium Lithium Borate (CLBO) crystals to produce DUV light energy, along with the use of fiber laser amplifiers and photonic crystal fibers to enhance power handling and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional frequency conversion methods are used to generate DUV light below 213nm, then light wavelength is reduced, but frequency conversion efficiency is low and crystal lifetime is short
Solution Approach 1:
The patent changes the phase matching parameter from critical to non-critical by orienting the optical axis perpendicular to the propagation direction. This parameter change eliminates walk-off effects and enables efficient frequency conversion at wavelengths below 213nm without the energy losses associated with conventional methods
Solution Approach 2:
The patent uses composite frequency conversion crystals combining CLBO and BBO materials. CLBO provides non-critical phase matching for wavelengths below 213nm, while BBO supplements the conversion process. This composite approach achieves high conversion efficiency that neither crystal could achieve alone
2Illumination intensity
If conventional frequency conversion crystals are used at wavelengths below 213nm, then DUV light is generated, but crystal lifetime is short and damage threshold is low
Solution Approach 1:
The patent employs a composite crystal system where CLBO and BBO are used together. CLBO is specifically selected for its high damage threshold and stability at wavelengths below 213nm, while BBO handles other wavelength ranges. This material composition extends crystal lifetime by distributing stress and damage risks across different materials with complementary properties
3Illumination intensity
If conventional DUV laser sources are used, then light wavelength is achieved, but device size is large and cost is high
Solution Approach 1:
The patent changes the fundamental laser wavelength parameter to 1064nm, which allows the use of established, compact solid-state laser technology. This parameter choice enables a smaller, more cost-effective laser source compared to conventional approaches that would require specialized laser systems for direct DUV generation
4Illumination intensity
If conventional DUV laser sources are used, then light wavelength is achieved, but average power is low and stability is poor
Solution Approach 1:
The patent changes the operating wavelength parameter to 1064nm where high-power, stable solid-state laser technology is well-established. This enables the system to achieve high average power and excellent temporal stability in the fundamental beam, which translates to stable DUV output after frequency conversion, overcoming the power and stability limitations of conventional DUV laser sources
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 the production of high-efficiency, long-lasting, and cost-effective DUV light sources with improved stability and damage thresholds, suitable for high-speed semiconductor inspection systems.
Implementation Method 1
converting a portion of the fundamental frequency laser energy to 2nd and 4th harmonic frequencies and mixing the harmonics using non-critical phase matching in Cesium Lithium Borate (CLBO) to produce deep ultraviolet (DUV) light energy
Implementation Method 2
use of fiber laser amplifiers and photonic crystal fibers to enhance power handling and stability
Implementation Method 3
use of fiber laser amplifiers and photonic crystal fibers to enhance power handling and stability
Data Source
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AI summary
A laser illuminator and illumination method for use in an inspection system, such as a semiconductor wafer inspection system or photomask inspection system is provided. The design comprises generating fundamental frequency laser energy at different fundamental wavelengths, such as 998nm, converting a portion of the fundamental frequency laser energy to 2nd harmonic frequency laser energy, further converting the 2" harmonic frequency laser energy to 4th harmonic frequency laser energy, and mixing the 4th harmonic frequency laser energy with a portion of the fundamental frequency laser energy to produce laser energy at a sum frequency. Mixing is accomplished by non-critical phase matching in a crystal of Cesium Lithium Borate (CLBO). Alternately, the design may employ shifting a portion of the fundamental frequency laser energy to laser energy at a Raman line and/or mixing the 2nd harmonic frequency laser energy with a portion of the fundamental frequency laser energy to produce 3rd harmonic frequency laser energy.