Lens Array Illumination for Broad Band Wafer Inspection
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Solution Overview
Problem
Current optical configurations for wafer inspection, such as diffractive optics for narrow band applications and refractive condenser plus light pipe combinations, face limitations like material dispersion, limited light collection, and non-uniformity, making them unsuitable for broad band applications and high power deep ultraviolet (DUV) inspections.
Innovation Solution
A system utilizing a light source, pupil lenses, a field lens array, and a lens group to generate a uniform far field pattern for wafer inspection, with the field lens array positioned between the pupil lenses and an aperture stop, focusing the pattern to the back focal plane for consistent and uniform illumination across the wafer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If diffractive optics are used for narrow band applications, then uniform illumination can be generated, but material dispersion occurs making them unsuitable for broad band applications
Solution Approach 1:
The patent divides the illumination system into multiple discrete lenses arranged in an array, where each lens processes a portion of the light spectrum independently. This segmentation allows the system to handle broad band electromagnetic spectra without material dispersion, as each lens can be optimized for its specific angular range while collectively covering the full spectrum.
Solution Approach 2:
Each lens in the array is designed with specific local optical properties tailored to its position and function. The lenses have varying focal lengths and optical characteristics that are optimized for their specific role in directing light at different angles, enabling the entire array to achieve uniform broad band illumination without the dispersion issues of diffractive optics.
2Illumination intensity
If refractive condenser plus light pipe combination is used, then illumination can be provided, but light collection solid angle is limited due to condenser numerical aperture
Solution Approach 1:
The patent transitions from a single-axis light collection approach to a multi-dimensional angular distribution system. By arranging lenses in a two-dimensional array with specific spacing and orientation, the system collects light from a much larger solid angle and distributes it uniformly across the wafer surface, overcoming the numerical aperture limitations of traditional condenser systems.
3Illumination intensity
If ellipsoidal reflector followed by light pipe, relay optics, and light pipe is used for broad band, then combined field and pupil can be generated, but device complexity increases
Solution Approach 1:
The patent merges the functions of field generation and pupil formation into a single integrated lens array structure. The array simultaneously creates the illumination field distribution and controls the angular pupil characteristics, eliminating the need for separate ellipsoidal reflectors, multiple light pipes, and relay optics, thus significantly reducing system complexity while maintaining broad band performance.
4Measurement precision
If high power deep ultraviolet inspection is performed, then defect detection capability is improved, but optical component lifetime decreases due to material absorption and optical damage
Solution Approach 1:
The patent employs lenses made from materials that are optimized for UV transmission but have limited lifetime under high power exposure. These lenses are designed to be replaceable and cost-effective, allowing the system to maintain high defect detection accuracy while accepting that the optical components will require periodic replacement due to UV-induced degradation, thus balancing performance with component longevity.
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 provides spatially uniform illumination with consistent angular distribution, suitable for broad band electromagnetic spectra, extending the lifetime of optical components and improving defect detection accuracy under high power density conditions.
Implementation Method 1
a light source configured to generate light
Implementation Method 2
The field lens array is configured to generate a second far field pattern of the light having a cross-sectional shape that is substantially the same as a cross-sectional shape of each individual lens in the field lens array
Implementation Method 3
The lens group is configured to focus the second far field pattern to a back focal plane of the lens group
Data Source
AI summary
Systems configured to provide illumination for wafer inspection performed by a wafer inspection tool are provided. One system includes one or more pupil lenses configured to focus a first far field pattern having a shape different than a shape of light generated by a light source. The system also includes a field lens array positioned between the one or more pupil lenses and an aperture stop. In addition, the system includes a lens group configured to focus a second far field pattern generated by the field lens array to a back focal plane of the lens group. The back focal plane of the lens group is a field plane of a wafer inspection tool at which a wafer to be inspected is placed during wafer inspection.