DETERMINATION OF OXYGEN IN SEMICONDUCTOR SILICON BY GAS FUSION ANALYSIS GFA - HISTORICAL AND FUTURE TRENDS -

摘要

Interstitial oxygen is a relevant component of defect engineering. During Czochralski (CZ) crystal pulling, the silicon melt corrodes the quartz wall of the crucible to silicon monoxide (SiO). In that volatile form, oxygen will be partly included in the silicon ingot, partly removed by an inert gas flow from the crystal puller. The oxygen [O_i] occupies interstitial position, increases the mechanical stability of the silicon wafer and, by designed heat treatment i.e. precipitation, facilitates gettering of metallic contamination from the active device zone of the wafer. Due to gettering defect density e.g. density of stacking faults (SF) can be reduced. The characteristic [O_i] concentration range is 10~(16) to 10~(17) [atoms/cm~3] for CZ and ≤5·10~(15) [atoms/cm~3] for float zone (FZ) silicon ingots. The analyst must be able to determine [O_i] in practical range of 10~(17) down to 10~(15) [atoms/cm~3]. In the last two decades Gas Fusion Analysis (GFA) became the routine method of oxygen analysis of heavily doped silicon materials in which the free carrier absorption interferes with the infrared absorption of Si - O. GFA is a carrier gas heat extraction method for oxygen in alloys or in pure metallic substances. In case of silicon a silicon chip (～500 mg) is melted in a small pure graphite double-crucible under helium carrier gas flow at ～1600℃. The graphite reduces the silicon oxide in the melt and converts it to CO and CO_2. A catalyst oxidizes the CO to CO_2 and the oxygen concentration in the carrier gas can be determined by infrared absorption in a special gas cell.