CMP 공정을 적용한 BLT 강유전 Capacitor의 전기적 특성

Abstract

(Bi,La)Ti3O12(BLT) thin films have attracted much interest owing to its excellent properties for ferroelectric random access memory (FeRAM) applications such as high fatigue endurance, low processing temperature and large remanent polarization. The patterning of these ferroelectric thin films with a vertical sidewall and without plasma damage is strongly required. Chemical mechanical polishing(CMP) process was firstly proposed to fabricate the ferroelectric capacitor instead of plasma etching process for the vertical profile without plasma damage. In this study, removal rate and within-wafer non-uniformity (WIWNU%) were examined by change of process parameters in BLT-CMP. Surface roughness of BLT thin films after CMP process for the improvement of device-integration was inquired into by atomic force microscopy(AFM). The electrical properties of BLT capacitors fabricated by the CMP process were analysed with change of the process parameters. In particular, the effects of CMP pressure, which mainly affects the removal rate of BLT thin films, were examined on the fabrication of BLT capacitor and its electrical properties. CMP characteristics such as the removal rate and WIWNU% were improved by the increase of CMP pressure ; however, the electrical properties including polarization-voltage(P-V) characteristics of BLT capacitor fabricated by CMP process with the high CMP pressure condition were degraded. The relative Bi content of BLT thin films increased as the increase of CMP pressure in CMP process by the X-ray photoelectron spectroscopy(XPS) analysis, while the relative La content of BLT thin film decreased as the same condition. This means that La was easily removed in high CMP pressure by physical (mechanical) mechanism of CMP process. X-ray diffraction (XRD) analysis confirmed that the structural change was observed in the sample polished by the high CMP pressure. The excellent polarization-voltage(P-V) characteristics with the high remanent polarization and low coercive voltage could be obtained in the metal-ferroelectric (BLT)-metal capacitor polished by the low CMP pressure in CMP damascene process. The good leakage current characteristic was also obtained in this condition. Therefore, the lower CMP pressure must be selected in CMP damascene process for BLT thin film capacitor although the removal rate of BLT thin film was somewhat lower than that in high CMP pressure. This proposal of the application of CMP damascene process to fabricate the BLT capacitor successfully achieved with the better process yield than the plasma etching process with no plasma damage and the vertical sidewall.