A reagent with a purity far higher than that of premium grade is called a high-purity reagent. It is developed on the basis of universal reagents and is a pure reagent produced by special methods for specialized purposes. High purity reagents control the impurity content, while reference reagents control the main content. Reference reagents can be prepared using standard solutions, but high-purity reagents cannot be used for the preparation of standard solutions (except for elemental oxides).
At present, there is no unified and clear specification internationally. In China, except for a few products that have established national standards, the quality standards for most high-purity reagents are still very inconsistent, and there are different names such as high-purity, ultrapure, ultrapure, spectral pure, electronic pure, etc. The purity of the product is generally represented by 9. Therefore, in the specification column, mark 2 9s, 3 9s, 4 9s, and so on. According to this principle, high-purity substances can be divided into:
The total impurity content shall not exceed 1.5 × 10-2%, with a purity of 3.5 9s (99.95) abbreviated as 3.5N
The total impurity content shall not exceed 1.0 × 10-2%, with a purity of 4 9s (99.99) abbreviated as 4.0N
The total impurity content shall not exceed 1.0 × 10-3%, with a purity of 5 9s (99.999) abbreviated as 5N
The inspection of the purity or impurity content of high-purity reagents or elements is generally determined by methods such as atomic absorption spectroscopy, atomic emission spectroscopy, chromatography, mass spectrometry, colorimetric chemical analysis, etc. The anion specifications are generally based on the reagent grade standards, and products without grade standards are formulated by the production unit itself. According to different uses, high-purity reagents are further divided into several categories:
Ordinary purification reagents
It refers to some high-purity elemental metals, oxides, metal salts, etc., commonly used in atomic energy industrial materials, electronic industrial materials, semiconductor basic materials, etc. Metal elemental oxides are used to prepare standard solutions and serve as standard substances. This type of reagent often requires a content between 4N-6N.
Ultra clean electronic pure reagent
Ultra clean and high-purity reagents are specialized chemicals in the manufacturing process of integrated circuits (ICs), 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 increasing demand for IC integration, the Semiconductor Industry Association has recently introduced reagent quality standards at the levels of Semic7 (suitable for 0.8-1.2 micron process technology) and Semic8 (suitable for 0.2-0.6 micron process technology). On the basis of the existing MOS grade and BV-I grade reagents, China has also developed standards for BV-II and BV-III grade reagents (equivalent to Semic7). My research institute has also developed various MOS level, BV-I level, BV-II level, and some BV-III level reagents, with particle size (0.5 particle size) ≤ 25-100 pieces/ml and total metal impurities ≤ 10-3-10-5%