Reagents whose purity is much higher than that of superior grade are called high-purity reagents. Developed on the basis of general reagents, it is a reagent with high purity produced by special methods for special purposes. The high-purity reagent controls the content of impurities, and the reference reagent controls the main content. The reference reagent can be prepared with the standard solution, but the high-purity reagent cannot be used for the preparation of the standard solution (except for the elemental oxide).
At present, there is no unified and clear specification in the world. In addition to formulating national standards for a few products, the quality standards of most high-purity reagents are not unified, and there are also different names such as high-purity, ultra pure, ultra pure, spectral pure, electronic pure, etc. Generally, the purity of the product is represented by 9. Therefore, in the specification column, two 9s, three 9s, four 9s, and so on. According to this principle, high-purity substances can be divided into:
The total content of impurities is not more than 1.5 × 10 -2%, its purity is 3.5 9 (99.95), abbreviated as 3.5N
The total content of impurities is not more than 1.0 × 10 -2%, its purity is 4 9 (99.99), abbreviated as 4.0n
The total content of impurities is not more than 1.0 × 10 -3%, its purity is 5 9s (99.999), abbreviated as 5N
The purity or impurity content of high-purity reagents or high-purity elements are generally determined by atomic absorption spectrometry, atomic emission spectrometry, chromatography, mass spectrometry, colorimetric chemical analysis and other methods. In principle, the anion specification shall refer to the reagent superior standard, and the products without superior standard shall be formulated by the production unit itself. According to different uses, high-purity reagents are divided into several categories:
Common purified reagent:
It refers to some high-purity elemental metals, oxides, metal salts, etc., which are commonly used in atomic energy industrial materials, electronic industrial materials, semiconductor basic materials, etc. the oxides of metallic elemental substances are used to prepare standard solutions and as standard substances. The content of such reagents is often required to be between 4n-6n.
Ultra clean electronic pure reagent:
Ultra clean and high purity reagents are special chemicals in integrated circuit (IC) manufacturing process, which are used in silicon wafer cleaning, lithography and corrosion processes. The requirements for soluble impurities and solid particles in this high-purity reagent are very strict. In order to meet the needs of the continuous improvement of IC integration, the semiconductor industry association has recently introduced reagent quality standards at the level of semi7 (suitable for 0.8-1.2 micron process technology) and semi8 (suitable for 0.2-0.6 micron process technology). Based on the original MOS grade and bv-i grade reagents, China has formulated bv-ii and bv-iii grade reagent standards (equivalent to semi7). Our institute also develops a variety of MOS grade, bv-i grade, bv-ii grade and some bv-iii grade reagents, with particle size (0.5 particle size) ≤ 25-100 / ml, and total metal impurities ≤ 10 -3-10 - 5%
Photoresist high purity reagent:
Lithography is a surface processing technology, which plays an important role in the manufacturing of semiconductor electronic devices and integrated circuits. In order to realize selective corrosion on the surface, a kind of photosensitive resin material with anti-corrosion effect is used as the anti-corrosion coating, which is called resist and is commonly known as photoresist in China. Photoresists are divided into "positive" photoresists and "negative" photoresists according to their solubility. According to the different exposure light sources and radiation light sources used, they can also be divided into UV, far UV, electron beam, X-ray and other photoresists.
Photoresist is a key reagent for micro pattern processing, which requires low moisture and low content of metal impurities (≤ 10 -6)
Grinding and polishing high purity reagent:
It refers to the high-purity reagent used for grinding and polishing the surface of silicon wafer. It is also divided into grinding powder (aluminum oxide) and grinding fluid (water and oil), which can grind the surface to achieve micron level machining accuracy. This kind of reagent requires small particle size (nanometer), high purity, and metal impurities generally require 2.0 × 10 -4 — 5 × 10 -5 ﹪
Liquid crystal high purity reagent:
Liquid crystal is a kind of electronic chemical material, which refers to the organic matter that presents an intermediate phase between solid phase and liquid phase in a certain temperature range. It has both liquid fluidity and crystalline anisotropy. Sometimes it is called the fourth state.
There are many kinds of liquid crystals, which are most widely used. The most promising ones are TN (low-grade), STN (medium and high-grade) and TFT (high-grade). The monomer liquid crystals composed of TN, STN and TFT mainly include aromatic esters, biphenyls, phenylcyclohexanes, Ferroelectrics and fluorinated liquid crystals, which are the main objects of use and development today and in the future. This kind of high-purity reagent requires high content (≥ 99%), low moisture content (≤ 10 -6), and less metal impurities (≤ 10 -6).
With the unique optical and electronic characteristics of liquid crystal, it can be used to check the defects of aircraft, candidate satellites and other devices, and in medicine to diagnose cancer, tuberculosis and other diseases.