Near-field terahertz time-domain spectroscopy for in-line electrical metrology of semiconductor integration processes for memory

Monitoring electrical properties in semiconductor integration processes is crucial in identifying electrical defects that determine the reliability and performance of metal oxide semiconductor field-effect transistors. A non-destructive in-line metrology technique using terahertz (THz) waves was developed to observe electrical properties between semiconductor integration processes. By combining near-field microprobes with THz time-domain spectroscopy (TDS), sub-10 μm resolution was achieved, enabling the measurement of on-chip micro-patterns. The system was integrated into a memory production line and demonstrated consistent results with conventional destructive methods. The TDS signal correction method effectively suppressed signal variations in unwanted layers. The results of non-invasive THz TDS measurements of tungsten films deposited by three different processes were consistent with those obtained by four- point probe method. We also non-destructively detected differences in THz transmission at the gate-oxide/Si-substrate interface due to the infiltration of nitrogen species after the thermal nitridation process at nitridation temperatures ranging from 670 to 730 °C, which were consistent with the results of secondary ion mass spectrometry. Our in-line near-field THz TDS will predict electrical performance immediately after the process, allowing for rapid correction of production conditions.