Particle counter for chemical solution
Inventors
Minakami, Takashi • SHIMMURA, Masaki • Matsuda, Tomonobu
Assignees
Publication Number
US-9823190-B2
Publication Date
2017-11-21
Expiration Date
2035-09-21
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Abstract
A particle counter for chemical solution in this disclosure uses a flow cell through which a chemical solution including particles flows, a laser light, and a light-receiving element array. Scattered light from the particles passing through a detection region on an optical path of the laser light in the flow cell is condensed to the light-receiving element array. The laser light in the center of the detection region has an energy density of 3×108 mW/cm2 or more. Each of plural light-receiving elements (a) is larger in length and width than a spot diameter of the scattered light, and (b) receives the scattered light from a region with a size of 760 μm2 or less included in the detection region. The signal processing unit counts the particles passing through the detection region by use of a threshold corresponding to the smallest measurable particle size of 0.03 μm.
Core Innovation
The invention is a particle counter for chemical solutions that enables counting of particles as small as 0.03 μm. This particle counter employs a flow cell through which the chemical solution with particles flows, a laser light source, and a light-receiving element array. The chemical solution is irradiated perpendicularly to the flow direction with laser light concentrated to an energy density of at least 3×108 mW/cm2 at the center of the detection region. Scattered light from particles passing through this detection region is condensed onto the light-receiving element array, where each light-receiving element is larger in length and width than the spot diameter of the scattered light and receives scattered light from a region of 760 μm2 or less within the detection region.
The particle counter includes a signal processing unit that counts the particles based on outputs from the light-receiving elements using a threshold set according to the smallest measurable particle size of 0.03 μm. The detection system reduces background noise inherent in chemical solutions, which scatter laser light more than water, by using an array of light-receiving elements to reduce noise level and implementing low-pass filtering at the signal processing stage. The design parameters ensure that the sensitivity and signal-to-noise ratio enable counting of ultra-fine particles in chemical solutions, which was previously difficult to achieve with existing particle counters capable only of detecting particles of size 0.04 μm or larger.
Claims Coverage
The patent contains two independent claims covering a particle counter system and its specific features for measuring small particles in chemical solutions.
Particle counting with high energy density laser light and specific light-receiving element array
A particle counter comprising a flow cell for a chemical solution including particles, a laser light source irradiating perpendicularly to the flow, a light-receiving element array with multiple elements each larger than the spot diameter of scattered light, and a condensing optical system. The laser light at the center of the detection region has an energy density of 3×108 mW/cm2 or more. Each light-receiving element receives scattered light from a region of 760 μm2 or less within the detection region. The signal processing unit counts particles by using a threshold corresponding to the smallest measurable particle size of 0.03 μm.
Laser wavelength and chemical solution refractive index specifications
The particle counter wherein the laser light has a wavelength of 532 nm, and the chemical solution has a refractive index ranging from 1.26 to 1.43.
These inventive features collectively provide a particle counter configuration enabling the counting of extremely small particles of size 0.03 μm or less in chemical solutions by optimizing laser energy density, detection optics, and signal processing parameters.
Stated Advantages
Capable of counting particles as small as 0.03 μm in a chemical solution, improving over existing particle counters limited to 0.04 μm.
Enhanced signal-to-noise ratio in chemical solutions by using a light-receiving element array and filtering, reducing background noise from scattering by the chemical solution itself.
Optimized laser energy density and optical design allow sensitive detection while maintaining counting efficiency.
Documented Applications
Counting particles in chemical solutions used for manufacturing semiconductor wafers.
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