Room Temperature Photoluminescence Characterization of Interface Quality of SiN/SiO2/Si Prepared under Various Deposition Techniques and Conditions

Various types of stacked dielectric films are used in complimentary metal-oxide-semiconductor (CMOS) devices in gates, capacitors and device isolation structures. They are also used as insulating materials between conductors, as inter-metal dielectrics (IMD) and inter-layer dielectrics (ILD). The preparation technique, structure and properties of dielectrics strongly influence the quality of the dielectrics/Si interface. Nominally, similar dielectrics/Si structures, even prepared by the same technique, often show different electrical properties depending on subtle differences in process conditions (hidden variables). Monitoring of physical dimensions and chemical compositions of dielectrics often miss unexpected variations in electrical properties. Non-contact electrical property characterization techniques lack lateral resolution and often results in impairment of the dielectrics/Si interface due to strong external electric fields from the measurement process. Alternative dielectrics/Si interface characterization techniques, which can provide insights into electrical properties without external electric field, would be very useful as a complimentary process and material quality monitoring technique.

In this study, we have investigated the effect of SiN film deposition techniques on the interface quality of the resulting SiN/SiO₂/Si using spectroscopic room temperature photoluminescence (RTPL) under multiwavelength excitation. The sample preparation procedures are as follows. First, ultra thin (~2.2 nm thick), gate oxide quality, thermal oxide films were grown on 300 mm Si(100) wafers. Nominally 5.0 nm thick SiN films were grown on ~2.0 nm thick SiO₂/Si wafers using conventional low pressure chemical vapor deposition (LPCVD) and atomic layer deposition (ALD) under various nitrogen source flow conditions. The film thickness was measured (after SiO₂ film deposition) before and after SiN deposition using ellipsometry.  Figure 1 (a) and (b) show RTPL spectra measured at the center of seven different SiN/SiO₂/Si wafers under 650 nm excitation and showing maximum RTPL intensity under 650 nm and 827 nm excitation. Significantly large RTPL intensity variations were measured among the seven SiN/SiO₂/Si wafers. The SiN film deposition conditions have modified the underlying SiO₂/Si interface characteristics. Non-contact RTPL measurements are very sensitive to the thin film deposition techniques and conditions. It is effective as a complimentary dielectrics/Si process and interface characterization and monitoring technique.