Diffractive Optical Element Alignment Using Infrared Beam
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The alignment of diffractive optical systems in lithographic apparatuses is complex due to the wavelength dependence of diffraction angles, making it difficult to align gratings without vacuum conditions, especially when using soft X-ray radiation, as conventional methods are inadequate for precise orientation and require additional checks under vacuum.
Innovation Solution
A method involving a diffractive optical element with multiple pitches, optimized to diffract alignment and operating beams in the same direction, using an infrared alignment beam to simplify the alignment process at atmospheric pressure, allowing for alignment without vacuum and maintaining alignment accuracy for soft X-ray operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional alignment methods are used for diffractive optical systems with soft X-ray radiation, then alignment can be performed without vacuum conditions, but alignment precision deteriorates due to wavelength dependence of diffraction angles
Solution Approach 1:
An infrared alignment beam is introduced as an intermediary tool to align the diffractive optical element. The infrared beam has a wavelength that is an integer multiple of the soft X-ray wavelength, allowing it to produce diffraction patterns at the same angles as the soft X-ray beam. This intermediary beam enables alignment to be performed at atmospheric pressure using standard optical techniques, while still achieving the precision required for soft X-ray operation.
Solution Approach 2:
The invention changes the wavelength parameter of the alignment beam from soft X-ray range to infrared range. By selecting an infrared wavelength that is an integer multiple of the soft X-ray wavelength, the diffraction angles remain identical according to the grating equation. This parameter change allows alignment to be performed using well-established infrared optical techniques rather than requiring complex soft X-ray alignment procedures.
2Reliability
If a diffractive optical element is optimized for soft X-ray operation, then it achieves high diffraction efficiency for the operating beam, but alignment becomes complex due to wavelength dependence
Solution Approach 1:
The diffractive optical element is designed to serve multiple functions: it maintains high diffraction efficiency for soft X-ray operation while simultaneously serving as an alignment element for infrared beams. By engineering the grating pitch and structure, the element can be aligned using infrared light without compromising its soft X-ray performance. This multi-functionality eliminates the need for separate alignment procedures and reduces overall system complexity.
3Manufacturing precision
If alignment is performed using the operating soft X-ray beam, then alignment precision is maximized, but additional vacuum checks are required increasing time and cost
Solution Approach 1:
Alignment is performed preliminarily using the infrared beam at atmospheric pressure before the system is placed in vacuum for soft X-ray operation. The infrared alignment beam allows all necessary alignment adjustments to be made while the optical system is accessible and can be observed using standard optical equipment. Once aligned with the infrared beam, the system maintains this alignment when operated with soft X-rays, eliminating the need for additional vacuum-based alignment checks and reducing both time and cost.
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 simplifies the alignment process, reduces complexity, and ensures accurate alignment of diffractive optical elements, enhancing the reliability and stability of the optical system while reducing costs by performing alignment only during assembly.
Implementation Method 1
a diffractive optical element optimized to diffract the alignment beam and the operating beam in predetermined directions
Implementation Method 2
using a diffractive optical element with multiple pitches, optimized to diffract alignment and operating beams in the same direction
Implementation Method 3
using an infrared alignment beam to simplify the alignment process at atmospheric pressure
Data Source
AI summary
A method of aligning a diffractive optical system, to be operated with an operating beam, comprises: aligning (558) the diffractive optical system using an alignment beam having a different wavelength range from the operating beam and using a diffractive optical element optimized (552) to diffract the alignment beam and the operating beam in the same (or a predetermined) direction. In an example, the alignment beam comprises infra-red (IR) radiation and the operating beam comprises soft X-ray (SXR) radiation. The diffractive optical element is optimized by providing it with a first periodic structure with a first pitch (pIR) and a second periodic structure with a second pitch (pSXR). After alignment, the vacuum system is pumped down (562) and in operation the SXR operating beam is generated (564) by a high harmonic generation (HHG) optical source pumped by the IR alignment beam’ optical source.