1. Field of the Invention
The present invention relates to a method of analyzing particles suspended in a liquid, and a liquid-suspended particle analyzer for carrying out the method. More particularly, the present invention relates to a method capable of accurately measuring the particle size of particles having sizes on the order of nanometers (hereinafter, referred to as “nanoparticles”) suspended in a liquid and of determining the particle size distribution of the nanoparticles in a short time, and a liquid-suspended particle analyzer for carrying out the method.
2. Description of the Related Art
In a semiconductor device fabricating process for instance, a silicon wafer is cleaned with cleaning water, such as ultrapure water, to remove contaminants from the surfaces of the silicon wafer. If the cleaning water contains particles, the particles contained in the cleaning water remain and adhere to the surfaces of the silicon wafer after cleaning and drying operations. Such particles cause detrimental effects on the formation of an integrated circuit on the surface of the silicon wafer and reduce the yield of semiconductor devices.
In precision machine manufacturing processes, workpieces are cleaned with a volatile solvent to remove anticorrosive oil coating the workpieces and cutting fluids flowed over the workpiece in machining. If the volatile solvent contains hard particles, such as fine grains of sand and fine fragments of cutting tools, precision-machine parts are contaminated with those hard particles, and precision machines are constructed by assembling such precision-machine parts contaminated with hard particles. When a precision machine thus assembled is operated, the particles adhering to sliding surfaces cause abnormal abrasion and, consequently, the precision machine unable to function properly.
To avoid such problems and to improve the yield and the reliability of products, the cleanliness of the liquid, such as the cleaning water and the volatile solvent, must be monitored and proper measures must be taken to prevent contamination with particles.
Optical methods, such as light scattering methods and light transmission methods, and microscopic methods that analyzes an image formed by an electron beam microscope have been generally used for measuring the particle size and number of particles suspended in liquids, such as cleaning water and volatile solvents, to monitor the cleanliness of the liquids.
Optical methods, such as light scattering methods and light transmission methods, are subject to restrictions on the measurable particle size of particles. Even an optical particle size measuring instrument having the highest sensitivity is capable of measuring particle sizes on the order of submicrometers and incapable of measuring particle sizes below submicrometers. Microscopic methods that analyze an image formed by an electron beam microscope require advanced techniques and need a long time for image analysis.