2. Polysilicon and Its Characterization Methods

The purity of polysilicon is usually between 6 N (99.9999%) and 9 N (99.9999999%). This chapter describes the test methods for measuring physical characteristics as well as quantification of elemental impurities in polysilicon materials. Float zone (FZ) process is an important method for converting granular polysilicon and polycrystalline chunk materials to monocrystalline silicon. A monocrystalline silicon rod is used to test the resistivity (n-type or p-type), minority carrier lifetime, carbon, oxygen, donors, and acceptor impurities in the polysilicon materials. Due to technological advancement, the analytical instrument detection limit (IDL) has improved in recent years allowing parts per billion atomic (ppba) to parts per trillion atomic (ppta) impurity detection in polysilicon. Donors (P, As, Sb), acceptors (B, Al), carbon, and oxygen can be measured by low-temperature FT-IR. The concentration of bulk and surface metal impurities (iron, chromium, nickel, copper, zinc, etc.) can be measured using ICP-MS.