Unit of carbon impurity concentration
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Dear everyone: Regarding the unit for the carbon impurity concentration in polysilicon, **the standard specifies the use of 10^16 atoms/cm3, that is, the number of atoms per cubic centimeter. But why do some people still use ppm, which stands for one part per million?** If converted using the **standard units, 1016 atoms/cm3 ≈ 0.086 ppm (with the mass of a carbon atom taken as 1.9927×10-26 kg). Logically speaking, ppm is a dimensionless unit, and carbon is a neutral element for silicon; it does not affect its conductivity type or the number of charge carriers. Such a unit has little practical value, so why do so many people prefer to use it? **The standard is easier to understand and doesn’t have any ambiguities; why then don’t people like it? Everyone, speak up.
However, nowadays measurements are made using PPM or PPB.
This is just a common issue; back in high school chemistry, it was made clear that terms like ppm, ppb, and molar concentration are not professional terms, yet they are still being used everywhere
I checked again just now, and there are important results. at/cm3 is atomic density. In the semiconductor industry, 5e22 silicon atoms per cubic centimeter is used as a standard. ppmw and ppbw refer to concentrations based on mass, where w stands for weight. PPMA and PPBA represent concentrations based on the number of atoms, with a standing for atom. To convert the atomic density of trace impurities in high-purity silicon into a mass concentration (ppmw or ppbw), use the following formula: Atomic density of the impurity × atomic weight of the impurity element / (5e22 × 28) = Mass concentration of the impurity (ppmw or ppbw). To convert the atomic density of trace impurities in high-purity silicon into a concentration based on the number of atoms (ppma or PPBA), use the following formula: Atomic density of the impurity / 5e22 = Atomic concentration of the impurity (ppma or PPBA). What’s crucial here is the standard specified for the number of silicon atoms per cubic centimeter in the semiconductor industry; this is very important. There are slight differences compared to those calculated directly using the amount of substance, but that’s okay – this is engineering after all. 1# wangstudio