Study On Solid State Reaction Of Metal/SiGe And Its Contact Characteristics

As the critical dimension of complementary metal-oxide-semiconductor (MOS) devices is continuously scaled down, SiGe has found its applications in modern devices. Strain can be induced in the channel by incorporating SiGe in the substrate or the source/drain (S/D) areas, which enhances the carrier mobility and thus the device performance. The dimensional scaling down also makes the S/D contact a big challenge due to the more dominant parasitic series resistance. Beyond the 45 run technology node, Ni-based silicide is believed to be the most promising contact material. However, the incorporation of Ge into Si substrates results in a new material for contact, Ni gemanosilicde, which shows relatively poor thermal stability. And studies relating to electrical characteristics of NiSiGe/SiGe contact haven't been carried out extensively. With such background, this thesis performed a study on the reaction of the Ni/SiGe system. Various characterization methods were employed to investigate the phase, morphology and electrical properties of the formed germanosilicide on SiGe substrates. The thesis obtained the following results.1. Characterization of Ni(Pt)/SiGe reaction and the contact formedNiSiGe shows quite good phase stability at least up to 800℃but poor thermal stability. Film agglomeration was observed when the temperature increased above 600℃, leading to the increase of the sheet resistance and the deterioration of the Schottky contact of NiSiGe/n-SiGe. By introducing a Pt interlayer, thermal stability of the germanosilicide was improved for about 100℃. A similar Schottky barrier height (SBH) to NiSi/n-Si contact of 0.65 eV was observed for NiSiGe/n-Si0.84Ge0.16 contact. The SBH was adjusted to 0.73 eV by the addition of Pt. The annealing time has a remarkable influence on NiSiGe film when it was under an isothermal annealing at 550℃. Serious degradation of NiSiGe film was found especially when the annealing time exceeded 10 min.2. Study of Ni/SiGe reaction by in situ XRD methodIn situ XRD technique was used to study the Ni/SiGe reaction. A sequential phase growth of Ni2(SiGe), NiSiGe was observed. NiSiGe shows a preferred (130) orientation. Based on the information of the peak positions, Ge segregation was found to occur at a quite low temperature,400℃, which may be related to the long-time thermal stress imposed on the sample. Isothermal annealing was carried out at relatively low temperatures and the information of diffraction peaks indicated a diffusion controlled growth for both phases of Ni2(SiGe) and NiSiGe.3. Extraction of contact resistivity of NiSiGe/p+-SiGeCross bridge Kelvin (CBK) structure was fabricated on p+-SiGe substrate and tested. After correction for the crowding effect and the sharp shrink of diffusion layer thickness underneath NiSiGe due to germanocilicidation, contact resistivity of 10"7Ω·cm2 magnitude was measured.