FAST INDUCTIVE INLINE MEASUREMENT OF THE EMITTER SHEET RESISTANCE IN INDUSTRIAL SOLAR CELL FABRICATION

摘要

Although the eddy-current technique is well known and already used in microelectronics for sheet resistance measurements, at present it has not been reported to be used in PV industry to measure the sheet resistance of emitter layers. This work aims at qualifying this technique for inline process control of emitter layers in solar cell production. Being contactless and allowing transfer rates of up to 2000 wafers/h, the investigated system meets two basic requirements for an inline integration. Due to a robust calibration, the reproducibility of the inductive system is shown to be better than 2.5% over a period of months for standard emitters with 55 Ω/sqr, compared to 10% achieved with common 4-point-probe (4pp) technique. Furthermore, the agreement of results obtained from the inductive and the 4pp technique is investigated within the whole resistivity range of interest and shown to be better than 3% on polished FZ-Si wafers. However, on Cz-Si wafers with damage-etched and textured surfaces significant deviations up to 34% are observed. It is shown that these deviations arise from surface-dependent systematic errors of the 4pp measurements and may be avoided by a special measurement procedure. The agreement of the corrected 4pp data with the inductive data is shown to be better than 5% for all resistivities and surfaces. This demonstrates the accuracy and reliability of the results obtained from the inductive technique.