Reagents whose purity is much higher than that of the prime grade are called high purity reagents. Developed on the basis of general reagents, reagents of the highest purity are produced by special methods for specific use purposes. The high purity reagents control the impurity content, and the reference reagents control the main content. The reference reagents can be prepared with standard solutions, but the high purity reagents can not be used in the preparation of standard solutions (except for elemental oxides).
At present, there is no unified clear specification in the world. In addition to the national standards for a few products, the quality standards of most high-purity reagents are not uniform, and there are different names such as high-purity, ultra-pure, ultra-pure, spectral pure and electronic pure in the name. The purity of the product is generally denoted by 9. Therefore, 2 9s, 3 9s and 4 9s are marked in the specification column. According to this principle, high purity substances can be divided into:
The total impurity content is not more than 1.5×10-2%, and its purity is 3.5 9 (99.95) abbreviated as 3.5N
The total impurity content is not greater than 1.0×10-2%, and its purity is 4 9 (99.99) abbreviated as 4.0N
The total impurity content is not more than 1.0×10-3%, and its purity is 5 9 (99.999) abbreviated as 5N
To test the purity or impurity content of high purity reagents or high purity elements, atomic absorption spectroscopy, atomic emission spectroscopy, chromatography, mass spectrometry colorimetric chemical analysis and other methods are commonly used for determination. In principle, the anion specifications refer to the superior grade standards of reagents, and the products without superior grade standards are formulated by the production unit. According to different uses, the high purity reagents are divided into several categories:
Ordinary purified reagent
It refers to some high purity metal, oxide, metal salts, etc., often used in atomic energy industry materials, electronic industry materials, semiconductor basic materials, metal oxide, used to prepare standard solution and as a standard substance, this kind of reagent often requires content between 4N-6N.
Ultra-clean electron pure reagent
Ultra-clean and high-purity reagents are special chemicals used in the manufacturing process of integrated circuits (IC). They are used in cleaning, lithography and etching of silicon wafers. The soluble impurities and solid particles in this high purity reagent are very strict. In order to adapt to the increasing integration of IC, International semiconductor industry association (SemiconductorIndustryAssociation) recently launched Semic7 (0.8 1.2 micron technology suitable for) and Semic8 (0.2-0.6 micron technology suitable for) level of reagent quality standards. On the basis of the original MOS and BV-I reagents, BV-II and BV-III reagents standards (equivalent to SEMIC7) have been developed in China. Our institute has also developed a variety of MOS grade, BV-I grade BV-II grade and some BV-III grade reagents, the particle size (0.5 particle) ≤25-100 / mL, the total metal impurity ≤10-3 -- 10-5%
Photoresist high purity reagent
Lithography is a kind of surface processing technology, which plays an important role in the fabrication of semiconductor electronic devices and integrated circuits. In order to achieve selective corrosion on the surface, a class of photosensitive resin material with anti-corrosion effect is used as anti-corrosion coating, known as anti-corrosion agent, the domestic general name photoresist. According to the solubility of different photoresist is divided into "positive" photoresist and "negative" photoresist, according to the different exposure source and radiation source, it can be divided into ultraviolet, far ultraviolet, electron beam, X-ray photoresist.
Photoresist is a key reagent for fine graphics processing, which requires low moisture content and low metal impurities (≤10-6).
Grinding and polishing high purity reagents
Refers to a high purity reagent used for grinding and polishing the surface of single silicon wafers. It is divided into grinding powder (aluminum oxide) and grinding fluid (water and oil), can grind the surface to reach micron level processing accuracy. This kind of reagent requires small particle size (nanometer), high purity, 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 is an organic substance that presents an intermediate phase between the solid phase and the liquid phase in a certain temperature range. It has both liquid fluidity and crystalline anisotropy, sometimes called the fourth state.
Liquid crystal variety, the most widely used, the biggest prospect belongs to TN(low grade), STN (high grade), TFT (high grade) type. Monomer liquid crystals composed of TN, STN and TFT mainly include five kinds of aromatic esters, biphenyl, phenylcyclohexane, ferroelectric and fluorine-containing liquid crystals, which are the main objects of use and development today and in the future. These high-purity reagents require a high content (≥99%), a low moisture content (≤10-6), and a low metal impurity content (≤10-6).