Periodically Stacked Nonlinear Crystals for VUV Quasi-Phase Matching
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Solution Overview
Problem
Existing methods for creating periodically-poled nonlinear crystals for generating VUV/DUV wavelengths face challenges due to material limitations, such as non-ferroelectricity in strontium tetraborate (SBO) and weak birefringence in lithium triborate (LBO), leading to low efficiency and unpredictable results, while existing lasers like excimer lasers have low pulse repetition rates and use toxic gases, making them unsuitable for semiconductor inspection and metrology.
Innovation Solution
A method involving ion implantation to create damaged layers in SBO or LBO crystals, followed by cleaving and polishing to form thin plates with alternating crystal axes, stacked to achieve quasi-phase-matching, enabling high-power VUV/DUV light generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If excimer lasers are used to generate VUV light, then VUV light can be produced, but the pulse repetition rate is low and toxic gases are used
Solution Approach 1:
The invention changes the fundamental approach from using excimer lasers with fixed low repetition rates to using mode-locked lasers with可调 repetition rates. By changing the laser type and operating parameters, the system achieves repetition rates of 50 MHz or higher while generating VUV light through frequency conversion in periodically poled crystals, thus resolving the contradiction between VUV generation capability and pulse repetition rate
Solution Approach 2:
The invention replaces the mechanical/gas-based excimer laser system with a solid-state mode-locked laser system combined with nonlinear optical frequency conversion. This substitution eliminates the need for toxic gases while achieving higher repetition rates through the properties of mode-locked laser operation and periodically poled crystal structures
2Productivity
If periodically poled crystals are constructed for frequency conversion, then VUV/DUV light generation efficiency is improved, but manufacturing complexity increases
Solution Approach 1:
The invention segments the periodically poled crystal into multiple thin plates with alternating polarity orientations. Each plate can be independently fabricated and then assembled into a stack, simplifying the manufacturing process while maintaining the quasi-phase-matching structure necessary for efficient frequency conversion to VUV/DUV wavelengths
Solution Approach 2:
The invention uses composite structures by stacking multiple crystal plates with different polarity orientations. This composite approach allows the system to achieve the desired periodic poling effect for frequency conversion while using standard crystal growth techniques for each individual plate, reducing overall manufacturing complexity
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 method produces high-power VUV/DUV light efficiently, overcoming previous limitations by ensuring consistent phase-matching and scalability, suitable for semiconductor inspection and metrology applications.
Implementation Method 1
frequency conversion of infrared or visible laser light into the VUV range
Implementation Method 2
the plurality of crystal plates are cooperatively configured to form a periodic structure that achieves quasi-phase-matching
Implementation Method 3
implanting ions of a predetermined energy into a first nonlinear crystal at a uniform depth to generate a damaged or amorphous layer
Implementation Method 4
heating or chemically etching the first nonlinear crystal in order to cleave the first nonlinear crystal at the damaged or amorphous layer
Data Source
AI summary
A method for constructing a periodically-poled nonlinear crystal may include implanting ions in a bulk crystal of strontium tetraborate (SBO) or lithium triborate (LBO) to generate a damaged layer at a predetermined depth, attaching a handle material to the surface of the bulk crystal, cleaving the bulk crystal at the damaged layer to generate a thin plate, and polishing the thin plate to a thickness suitable for quasi-phase-matching (QPM) to generate laser output light having wavelengths in the range of about 120-200 nm. The surfaces of thin plates generated in this way are optically contacted, and resulting stacks are diced and arranged to generate many-layered QPM crystals. Methods, inspection systems, lithography systems and cutting systems incorporating the laser assembly are also described.