Metallic thin film on sige si substrates 6

Chapter High Temperature Reaction between Ni and Si(001), Ge(001) and Si0.8Ge0.2 (001) Virtual Substrates Chapter High Temperature Reaction between Ni and Si(001), Ge(001) and Si0.8Ge0.2(001) Virtual Substrates 6.1 Introduction In Chapter 6, we will use XPS to monitor different Ni silicides, germanides and germanosilicides formation when ultra-thin Ni films (~2-6Å) were deposited on hydrogen-terminated Si(001), Ge(001) and Si0.8Ge0.2(001) substrates and annealed insitu to different temperatures in vacuum Atomic force microscope (AFM) will also be used to study the surface morphology evolution along annealing and to correlate the observation with XPS results In particular, we will investigate the effect of annealing temperature on the Ni intensity, compound phases and their stability 6.2 The effects of temperature when annealing Ni/H-terminated Si(001), Ge(001) and Si0.8Ge0.2(001) surfaces In this set of experiments, ~ 15% Ni was deposited on a series of H-terminated Si(001), Ge(001) and Si0.8Ge0.2(001) substrates at room temperature, which is equivalent to ~2-6 Å of Ni layer according to the growth rate measurement derived from Chapter Each sample was then annealed directly to the target temperatures ranging from 100oC to 620oC for hour The Ni 2p3/2, Si 2p and Ge 3d spectra were collected as a function of annealing time And the typical spectra after one hour annealing at various temperatures are shown in Fig 6.1, 6.2 & 6.3 for Si(001), Ge(001) and Si0.8Ge0.2(001) substrates, respectively 210 Chapter High Temperature Reaction between Ni and Si(001), Ge(001) and Si0.8Ge0.2 (001) Virtual Substrates It can be seen from Fig 6.1 that when 6Å Ni was deposited on H-Si(001) surface at RT, binding energy (B.E.) of Ni 2p3/2 was at 853.8±0.1 eV, which corresponds to Ni in Ni2Si environment5 This is understandable as Ni initially forms a NiSi-like layer at the interface and further growth of Ni to 6Å result in a formation of Ni-rich-silicide-like layer From 100oC onwards, annealing the samples resulted in a shift in the binding energy to a higher value At 200oC, Ni 2p3/2 displayed a signature value of 854.0±0.1 eV, which was attributed to NiSi phase5,209 Between 400oC and 620oC, Ni 2p3/2 peak stayed around 854.5±0.1 eV, a value corresponding to Ni in the bulk NiSi2 crystal structure The high temperature annealing facilitates Ni diffusion into Si lattice and the subsequent reaction with Si, therefore the silicide phase has gradually developed from a Ni-rich Ni2Si phase to a Si-rich NiSi2 phase as the annealing temperature increased x22.00 o 620 C x1.75 o 400 C x1.41 o 300 C x1.16 o x1.00 o 500 C Intensity (a.u.) Intensity (a.u.) x7.46 620 C x1.00 500 C x1.00 400 C x1.00 300 C x1.00 200 C x1.00 100 C o o o o 200 C o o x1.10 100 C x1.00 RT 858 857 856 855 854 853 852 851 850 Binding Energy (eV) (a) o x1.00 102 RT 101 100 99 98 97 Binding Energy (eV) (b) Fig 6.1 Normalized (a) Ni 2p3/2 and (b) Si 2p spectra collected at normal photoelectron emission during annealing at different temperatures after depositing ~6 Å Ni on the Hterminated Si(001) surface at RT 211 Chapter High Temperature Reaction between Ni and Si(001), Ge(001) and Si0.8Ge0.2 (001) Virtual Substrates Hence, NiSi2 is a more stable phase at high temperature, which started to form at 400oC This formation temperature is much lower than the reported value of 500oC700oC138,142,144-145 We attribute this to the use of ultra-thin Ni film in our work, which facilitates the faster inter-diffusion of Ni & Si to form NiSi2 For the case of 2Å of Ni grown on H-Ge(001), the change of Ni 2p3/2 and Ge 3d B.E after annealed from 100oC to 500oC is shown in Fig 6.2 The B.E of Ni 2p3/2 was at 853.4±0.1 eV at RT Between 100oC and 500oC, Ni 2p3/2 peak remained at 853.5±0.1 eV throughout annealing The close B.E value suggests that only one phase was observed in our experiment from RT to 500oC Because NiGe is also the final phase in Ni-Ge system during annealing and no NiGe2 was observed even after annealing to 700oC (either thin film or bulk)9-10,77,149, the single phase from RT to 500oC was attributed to NiGe, which is the stable phase at high temperatures o 500 C o x11.3 400 C o x4.6 300 C o 200 C x1.4 Intensity (a.u.) Intensity (a.u.) x22.9 500 C x1.0 400 C x1.0 300 C x1.0 200 C x1.0 100 C x1.0 RT o o o o x1.1 100 C x1.0 RT 858 o x1.0 856 854 852 Binding Energy (eV) (a) 850 33 32 o 31 30 29 28 27 26 Binding Energy (eV) (b) Fig 6.2 Normalized (a) Ni 2p3/2 and (b) Ge 3d spectra collected at normal photoelectron emission during annealing at different temperatures after depositing ~2 Å Ni on the H-terminated Ge(001) surface at RT 212 Chapter High Temperature Reaction between Ni and Si(001), Ge(001) and Si0.8Ge0.2 (001) Virtual Substrates For annealing 5Å Ni grown on H-Si0.8Ge0.2(001) from 100oC to 620oC, the change of Ni 2p3/2, Si 2p and Ge 3d B.E is shown in Fig 6.3 The B.E of Ni 2p3/2 was at 853.6±0.1 eV upon deposition at RT When annealing from 100oC to 300oC, the B.E was observed to shift progressively to 853.8±0.1 eV Between the temperature region of 300oC and 500oC, the B.E further shifted from 853.8±0.1 eV to 854.5±0.1 eV Therefore, there is a significant shift in B.E from 300oC to 500oC Similar to the case of annealing Ni/H-Si(001) (Fig 6.1) where the shift of Ni 2p3/2 B.E during annealing was attributed to different Ni silicides phases, the shift of Ni 2p3/2 B.E in the current case can be similarly ascribed to different Ni germanosilicide formation 213 Chapter High Temperature Reaction between Ni and Si(001), Ge(001) and Si0.8Ge0.2 (001) Virtual Substrates 620 C x50.7 500 C o Intensity (a.u.) Intensity (a.u.) x78.8 o o 620 C x1.0 400 C x1.0 300 C o x28.8 x1.0 x1.0 x1.0 200 C 100 C RT o 400 C x4.9 300 C x1.3 200 C x1.1 100 C o RT o x1.0 x1.0 o 500 C x1.0 o 858 857 856 855 854 853 852 851 850 102 o o o 101 Binding Energy (eV) 100 99 98 97 Binding Energy (eV) (b) Intensity (a.u.) (a) o x2.63 620 C x1.22 500 C x1.01 400 C x1.00 300 C x1.07 200 C o o o o o x1.10 x1.24 32 100 C RT 31 30 29 28 27 26 Binding Energy (eV) (c) Fig 6.3 Normalized (a) Ni 2p3/2, (b) Si 2p and (c) Ge 3d spectra collected at normal photoelectron emission during annealing at different temperatures after depositing ~5 Å Ni on the H-terminated Si0.8Ge0.2(001) surface at RT According to the description in Section 1.2.1.5 in Chapter 1, the sequence for Ni germanosilicide formation when annealing thick Ni layer (>10nm) grown on hydrogen-terminated Si1-xGex(001) surface is as follows14-22,152,219,220:  NiSi1− y Gey + Si1− z Gez o o o C  C  −500  C Ni 650→  Ni( Si1− y Gey ) + Si1− z Gez 214 Chapter High Temperature Reaction between Ni and Si(001), Ge(001) and Si0.8Ge0.2 (001) Virtual Substrates where y