Detection of trace impurities such as phosphorus and boron in reducing furnace exhaust gas and hydrogen gas after CDI treatment

This boron phosphorus is very difficult to detect. Gas analysis (of exhaust gases, hydrogen) is generally carried out using gas chromatography, and it is very difficult to achieve such a high level of precision. Generally, ICP-MS can be used to detect boron and phosphorus in solid and liquid samples

Polysilicon is zone-melted 1–2 times in an atmosphere to produce single-crystal silicon, after which it is tested. Since Group V impurities represented by phosphorus have not yet volatilized or segregated, the conductivity type should be N-type. The resistivity measured at this time is considered to represent the level of phosphorus, an impurity present in polycrystalline silicon. By using this phosphorus testing rod and conducting tests after 7 times of zone melting in a vacuum, it can be approximately assumed that all Group V impurities such as phosphorus have volatilized, leaving only the impurity boron. Therefore, the conductive type should be P-type. The measured resistivity is considered to represent the level of impurity boron. In the uncompensated condition, the higher the resistivity, the fewer the impurities and the higher the quality ； Conversely, the lower the resistivity, the higher the impurities and the lower the quality. By compensation, it is meant that there are large amounts of both N-type and P-type impurities in the crystal; the effects of these two types of impurities on electrical conductivity cancel each other out. As a result, the resistivity is very high, but this has a negative impact on the quality of the device. Therefore, resistivity cannot fully represent the quality of polysilicon; compensation degree and total impurity concentration also need to be considered.

It must be difficult to detect, right? It’s all detected within the product itself!:P

It is crucial to know in what form phosphorus and boron are present in the exhaust gases; selecting the appropriate sampling points for the process makes it possible to carry out these operations

The question raised by the original poster is indeed quite advanced; I’ve really never heard of any methods for detecting phosphorus and boron in recovered hydrogen. Let’s give it some support!

Detection can be done online or offline; offline detection is relatively easier, and an ICP-MS instrument is required for the detection； Gas chromatographs are commonly used online; however, since they can only detect the relative amount of known gases in a mixture, their accuracy is not high ； Laser chromatography analyzers have emerged now, offering high precision; however, they are not yet widely used as the chromatography technology itself is still underdeveloped. We look forward to the rapid development and widespread application of laser chromatography analyzers! :lol

We use online analytical instruments to measure the concentration of impurity gases in the exhaust gas

Gas chromatography, preferably online analysis, is used with a six-way valve for sample introduction; the sample gas passes through a volumetric tube, and an injection volume of around 5 ml is sufficient to obtain accurate values rather than relative values. The prerequisite is to calibrate the chromatography. It is difficult to determine the composition of polysilicon exhaust gases; it is recommended to use an external standard method for calibration. That is, by accurately measuring a certain volume of pure hydrogen gas, or TCS/STC, and injecting it, the area obtained is directly proportional to the amount injected. In the future, its exact content can be calculated based on the area of the exhaust peak.

Online mass spectrometer. It can quickly measure the gas component content in multiple streams.

Online analysis is only possible for components with high concentrations; impurities such as boron and phosphorus can hardly be detected