No abstract

B diffusion measurements are used to probe the basic nature of self-interstitial 'point' defects in Ge. We find two distinct self-interstitial forms -a simple one with low entropy and a complex one with entropy ~30 k at the migration saddle point. The latter dominates diffusion at high temperature. We propose that its structure is similar to that of an amorphous pocket -we name it a morph. Computational modelling suggests that morphs exist in both self-interstitial and vacancy-like forms, and are crucial for diffusion and defect dynamics in Ge, Si and probably many other crystalline solids.A vast array of crystalline material properties arises from the behavior of atomic-scale 'point'defects, yet these defects are poorly understood. Knowledge of simple point defects -single atoms added interstitially to, or missing from, an otherwise undisturbed lattice -is well established from quantum theoretical calculations and low-temperature experiments, but diffusion experiments hint that more complex entities may be involved at high temperatures relevant to industrial processing [1][2][3][4][5]. This Letter provides the first definitive evidence for these elusive complex defects and presents a specific physical model for their structure and diffusion. 2 Recent interest in Ge-based nano-electronics has led to basic studies on diffusion [5][6][7][8][9] and implantation defects [10,11] in crystalline Ge. Most dopants in Ge are found to diffuse by vacancy mechanisms, with activation energies below that of vacancy-mediated self-diffusion (≈ 3.1 eV), but boron diffusion is an exception with an activation energy of ≈ 4.65 eV [6,12].Experiments [5,[7][8][9] show that boron diffuses via the reaction B + I  BI, where 'B' represents substitutional boron, 'I' the self interstitial, and 'BI' a mobile dopant-interstitial complex. The energetics involved is illustrated in Figure 1.The reduction in free energy on forming BI enables it to migrate a mean projected distance λ before dissociating to B and I. The mean number of jumps before dissociation depends on the energy difference between migration and dissociation of BI and the diffusional entropies of I and BI. In general,A is the impurity (here, boron), X the point defect driving AX diffusion (here, I), a the capture radius for the forward reaction, f AX the diffusion correlation factor (~1), E AX , S AX , E self,X , S self,X the activation energies and entropies of impurity diffusion and self-diffusion via the species AX and Fig. 1. Schematic of total energy versus configuration for the reaction mediating B diffusion in Ge. Also shown are energies inferred from previous experiments. E BI and E self,I are the respective energies of BI and I at their migration saddle points, relative to that of substitutional B. Under RED conditions (dashed curve) the fitted values of E λ shift 0.025 eV in the negative direction. This could be accounted for by a reduction of 0.05 eV in the migration energy of BI under H irradiation. T (°C)4To test this idea we have repeated the experiments...

Stacked multichannel or nanowire CMOS transistors are foreseen as viable options in future technology nodes. Superior electric performances and a relative immunity to short channel effects have already been demonstrated in such devices. They rely on (i) the epitaxy of SiGe/Si superlattices, (ii) the anisotropic etching of the source and drain (S/D) blocks and the channels, and (iii) the high degree of selectivity that can be achieved when laterally etching the SiGe sacrificial layers. The voids left by the removal of SiGe are then conformally filled by HfO2/TiN/poly-Si gates, leading to the formation of multichannel devices. Doping elements can be included in situ in the SiGe layers during the epitaxial step in order to achieve a proper S/D doping after annealing. Precise knowledge of the diffusion behavior of all species is then crucial to understand and tailor final device performance. In this work, we investigated the properties of intrinsic or in situ doped (with B, C, or P) SiGe/Si superlattices upon annealing, using several characterization techniques, such as x-ray diffraction, x-ray reflectivity, time-of-flight-secondary ion mass spectrometry, and dark-field electron holography; as well as diffusion simulation tools such as S-Process. The combined analysis and simulation approaches allowed a complete characterization of the studied structures upon annealing. In the first step, the diffusion of both germanium and dopants was observed experimentally and quantified with simulation. Their diffusion mechanisms were also studied. In the second step, the evolution of the strain distribution upon annealing was experimentally monitored and simulated to quantify the strain relaxation in such structures.

In this study, TiN/La 2 O 3 /HfSiON/SiO 2 /Si gate stacks with thick high-k (HK) and thick pedestal oxide were used. Samples were annealed at different temperatures and times in order to characterize in detail the interaction mechanisms between La and the gate stack layers. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) measurements performed on these samples show a time diffusion saturation of La in the high-k insulator, indicating an La front immobilization due to LaSiO formation at the high-k/interfacial layer. Based on the SIMS data, a technology computer aided design (TCAD) diffusion model including La time diffusion saturation effect was developed.

No abstract