원거리 플라즈마 원자층 증착법으로 형성된 루세늄 중간층을 이용한 니켈 실리사이드의 열 안정성 개선에 관한 연구

Abstract

As the device feature size reduces, the contact resistance increases severely in Ultra-large scale integrated (ULSI) circuits. Thus, the metal silicide such as TiSi2, CoSi2 and NiSi have been used to lower the contact resistance in source/drain (S/D) regions and gate electrodes in metal-oxide-semiconductor field effect transistors (MOSFETs). Recently, nickel silicide (NiSi) has been increasingly used as contact materials due to low resistivity, low thermal budget, less silicon consumption and no linewidth dependence in sub-50nm CMOS technologies. However, one major drawback of NiSi is the thermal instability (e.g., the phase transition from the low resistivity phase (NiSi) to the high resistivity phase (NiSi2) as well as the agglomeration of films at high temperatures). Hence, many studies have been made in attempts to enhance the thermal stability of NiSi. The purpose of this study was to investigate the effects of a thin Ru interlayer on the thermal and morphological stability of NiSi. Since noble metals have good chemical and thermal stability, these materials are applicable for improvement of the thermal stability of NiSi. Ru is one of the most attractive noble metals in respect of cost and physical properties. Ru and Ni thin films were deposited sequentially to form a Ni/Ru/Si bi-layered structure, without breaking the vacuum, by remote plasma atomic layer deposition (RPALD) on a p-type Si wafer. After annealing at various temperatures, the thermal stabilities of the Ni/Ru/Si and Ni/Si structures were investigated by various analysis techniques. The results showed that the sheet resistance of the Ni/Ru/Si sample was consistently lower compared to the Ni/Si sample over the entire temperature range. Although both samples exhibited the formation of NiSi2 phases at an annealing temperature of 800 °C, as seen with glancing angle X-ray diffraction (GAXRD), the peaks of the Ni/Ru/Si sample were observed to have much weaker intensities than those obtained for the Ni/Si sample. Moreover, the NiSi film with a Ru interlayer exhibited a better interface and improved surface morphologies compared to the NiSi film without a Ru interlayer. These results show that the phase transformation of NiSi to NiSi2 was retarded and that the smooth NiSi/Si interface was retained due to the activation energy increment for NiSi2 nucleation that is caused by adding a Ru interlayer. Hence, it can be said that the Ru interlayer deposited by RPALD can be used to control the phase transformation and physical properties of nickel silicide phases.