| Summary: | 博士 === 國立清華大學 === 材料科學工程學系 === 87 === Abstract
Interfacial reactions of Ti and Cu thin films on Si-Ge Alloys on Silicon and Germanium have been studied by cross-sectional and planview transmission electron microscopy, Auger electron spectrometer, sheet resistance and X-ray diffractometer.
The growth kinetics of a-interlayer in UHV deposited polycrystalline Ti thin films on germanium and epitaxial Si1-xGex(x= 0.3, 0.4 and 0.7) on (001)Si has been studied by XTEM. Amorphous interlayers, less than 2 nm in thickness, were observed to form in all as-deposited samples. The growth was found to follow a linear growth law initially in sample annealed at 300-375, 300-400 oC for Ti/Ge and Ti/Si0.3Ge0.7 and 350-430 oC for Ti/Si0.6Ge0.4 and Ti/Si0.7Ge0.3, respectively. The growth then slows down and deviates from a linear growth behavior. The activation energy for the linear growth of a-interlayer was found to be 1.0, 0.95, 0.85 and 0.7 eV for Ti/Si0.7Ge0.3, Ti/Si0.6Ge0.4, Ti/Si0.3Ge0.7 and Ti/Ge, respectively.
Theoretical calculation has been carried out to determine the driving force for the interfacial reaction. Negative free energy of mixing, which provides the driving force for the formation of a-interlayer, was obtained for all systems over a wide range of composition. The results indicated that the formation of the a-interlayer between Ti thin film and substrates is favored thermodynamically over the physical mixture. The mobility of atomic diffusion during the growth of a-interlayer is also considered to play an important role in determining the maximum thickness of a- interlayer.
Thin films of Ti5(Si1-yGey)3, C49- and C54-Ti(Si1-zGez)2 were observed in the Ti/Si1-xGex (x ≦ 0.4) systems. On the other hand, thin films of Ti6(Si1-yGey)5 and C54-Ti(Si1-zGez)2 were found in the Ti/Si1-xGex (x ≧ 0.7) systems. The relationship of x ＞ y ＞ z was found. The appearance temperature of low-resistivity C54-Ti(Si1-zGez)2 was decreased with the Ge concentration. The agglomeration temperature of C54-Ti(Si1-zGez)2 was also decreased with the Ge concentration. The resistivities of C54-Ti(Si1-zGez)2 were measured to be 15-20 mW/cm. The segregation of Si1-wGew (w ＞ x) was found in all samples annealed above 800 oC. The effects of thermodynamic driving force, kinetic factor and composition of micro-area are discussed.
Epitaxial Cu and epitaxial z-Cu5Ge were found to form in as-deposited Cu/e-Ge/(111)Ge and Cu/e-Ge/(111)Si, respectively. In Cu/(001)Ge system, textured Cu was found to form in the other systems. Poly-e1-Cu3Ge and poly-e1-Cu3(Si1-xGex) were the only phases in annealed Cu/Ge and (Cu/e-Ge/Si and Cu/Si-Ge alloy) systems, respectively. They were found to agglomerate at 550 °C. The room-temperature oxidation of substrate in the presence of Cu3(Si1-xGex) was found only in the Cu/Si0.7Ge0.3 systems. From the sheet resistance measurement, e1-Cu3Ge has the lowest resistivity of 7 mW-cm in the 400 °C annealing samples. The sheet resistance of e1-Cu3(Si1-xGex) was found to increase with the Si content.
In e1-Cu3Ge/TiN systems, low-resistivity and stable e1-Cu3Ge was performed at 150-550 oC. On the other hand, the segregation of Ge was been found in the e1-Cu3Ge/SiO2 samples annealed at 500 oC. The segregation of Ge caused the higher resistivity of e1-Cu3Ge on SiO2 than that on TiN systems. Passivation and adhesion layers for Cu have been formed by annealing of Ge(5 nm)/Cu(100 nm)/Ge(1-5 nm)/TiN(100 nm)/SiO2(100 nm)/(001)Si at 150-550 oC in a nitrogen ambient. Ge reacted with Cu and formed inert and low electrical resistivity e1-Cu3Ge as a passivation layer and adhesion layer, respectively. The thickness of these layers was 1.5-8.0 nm. The thermal stability of Cu has been improved by the thin e1-Cu3Ge interposing layer above 450 oC. Adhesion results obtained from a scratch test showed that Cu/e1-Cu3Ge/TiN exhibited good adhesion in the 450 oC annealed samples. Passivation results were stable up to 500 oC. The behavior of the adhesion properties was related to the interfacial reaction.
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