Thin epitaxial Si films as a passivation method for Ge(100): Influence of deposition temperature on Ge surface segregation and the high-k/Ge interface quality (original) (raw)
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Experimental and theoretical study of Ge surface passivation
Microelectronic Engineering, 2007
The integration of Ge channels in high performance integrated circuits requires the passivation of the (100)Ge surface prior to gate dielectric deposition. Two promising approaches are discussed here, namely: i) the deposition of an ultrathin epi-Si layer, followed by its partial oxidation prior to high-k dielectric deposition, and ii) the exposure of the Ge surface to H 2 S, resulting in the formation of Ge-S bonds. The insights that can be gained by combining physico-chemical analysis of Ge surfaces and/or electrical properties of Ge-devices, with first-principles simulations are highlighted.
ECS Journal of Solid State Science and Technology, 2020
In this work we study the epitaxial Si growth with Si2H6 for Ge surface passivation in CMOS devices. The Si-caps are grown on Ge in the hydrogen desorption limited regime at a nominal temperature of 400 °C. We evaluate the process window for the interface state density and show that there is an optimal Si-cap thickness between 8 and 9 monolayers for Dit < 5·1011 cm−2 eV−1. Moreover, we discuss the strong impact of the Si-cap growth time and temperature on the interface state density, which arises from the Si thickness dependence on these growth parameters. Furthermore, we successfully transfer a TmSiO/Tm2O3/HfO2 gate stack process from Si to Ge devices with optimized Si-cap, yielding interface state density of 3·1011 eV−1 cm−2 and a significant improvement in oxide trap density compared to GeOx passivation.
Physical review. B, Condensed matter, 1996
We used the XPD ͑x-ray photoelectron diffraction͒ and AED ͑Auger electron diffraction͒ from Ge core levels to probe the crystalline structure of 3 and 6 ML of Ge epitaxially grown by molecular-beam epitaxy on the Si͑001͒ surface. In order to check the film tetragonal distortion and the pseudomorphic growth morphology, we used two different temperatures of the substrate during the deposition: room temperature and 400°C. Evidence for an interfacial intermixing has been found by means of the observation of the angular behavior of the intensity of the emitted electrons. We also investigated the effects of Sb as a surfactant on such an interface. In this case indications of a laminar growth of strained Ge overlayer with reduced intermixing is obtained when 1 ML of Sb is predeposited on the substrate. Furthermore making use of a multiple-scattering approach to reproduce the experimental XPD patterns, a higher amount of accessible information on the morphology of the interface, beyond the determination of the strain content, is obtained.
Journal of Crystal Growth, 2010
Using a low temperature/high temperature strategy, we have grown thin (0.27 mm) and thick (2.45 mm) Ge layers on Si(0 0 1) substrates that we have submitted to various constant temperature (750 1C) or cyclic (750 1C/890 1C) H 2 anneals, the objective being to identify those yielding the smoothest surfaces, the lowest threading dislocations densities (TDDs) and the highest near infra-red optical absorptions. The best trade-off for thin layers was 750 1C, 60 min H 2 anneals. Using longer duration 750 1C anneals and especially 750 1C/890 1C cyclic anneals indeed yielded rougher surfaces and vastly degraded optical absorption (deleterious formation of GeSi alloys). By contrast, short 750 1C/890 1C thermal cyclings yielded the best metrics in thick Ge layers (while being at the same time the best in terms of throughput): root mean square surface roughness around 0.8 nm, TDD around 10 7 cm À 2 , slightly tensily-strained layers (which a plus for optical absorption as the absorption edge is shifted to higher wavelengths), a limited penetration of Si into Ge (and thus absorption coefficients at 1.3 and 1.55 mm almost equal to those of as-grown layers), etc. We have also described the low temperature (450 1C/525 1C) process that we have developed to passivate Ge surfaces thanks to SiH 4 prior to gate stack deposition. Si layer thickness should be below 20Å in order to have conformal deposition. A transition of the growth front to 3 dimensions has indeed been evidenced for 20Å and higher.
Growth of Si[sub 1−x]Gesub x on Si(011)16×2 by gas-source molecular beam epitaxy: Growth kinetics, Ge incorporation, and surface phase transitions
Journal of Applied Physics, 1999
Single crystal Si 1Ϫx Ge x (011) layers with xр0.35 have been grown on double-domain Si͑011͒''16ϫ2'' surfaces from Si 2 H 6 /Ge 2 H 6 mixtures at temperatures T s ϭ400-950°C. D 2 temperature programmed desorption was used to show that the structure of the Si͑011͒''16ϫ2'' surface unit cell, more correctly written as ͓ 2 17 2 1 ͔ since the unit cell vectors are nonorthogonal, is composed of 16 adatoms and eight-bonded dimers with a dangling bond density half that of the 1ϫ1 surface. Si 1Ϫx Ge x (011) overlayers are ''16ϫ2'' when xϽx c (T s) and ''2ϫ8'' with x Ͼx c (T s). The value of x c decreases from Ӎ 0.10 at T s ϭ475°C to 0.08 at 550°C to 0.06 at 650°C. Both the ''2ϫ8'' and ''16ϫ2'' Si 1Ϫx Ge x (011) surface reconstructions gradually and reversibly transform to 1ϫ1 at T s between 650 and 725°C. Film growth kinetics exhibit three distinct regimes. At low temperatures (T s Շ500°C), the film deposition rate R SiGe decreases exponentially with 1/T s in a surface-reaction-limited growth mode for which the rate-limiting step is hydrogen desorption from Si and Ge monohydride phases. R SiGe becomes essentially constant with T s in the intermediate impingement-flux-limited range, T s ϭ500-650°C. At T s Ͼ650°C, R SiGe increases again with T s due initially (T s Ӎ650-725°C) to an increase in the steady-state dangling bond coverage as the surface reconstruction gradually transforms to 1ϫ1. The continued increase in R SiGe at even higher T s is associated with strain-induced roughening. Ge/Si ratios in as-deposited films are linearly proportional to the incident Ge 2 H 6 /Si 2 H 6 flux ratio J Ge 2 H 6 /J Si 2 H 6 and nearly independent of T s indicating that the reactive sticking probabilities of Si 2 H 6 and Ge 2 H 6 have very similar temperature dependencies. R SiGe (J Ge 2 H 6 /J Si 2 H 6 ,T s) in both the surface-reaction-limited and flux-limited regimes is well described by a simple kinetic model incorporating second-order dissociative chemisorption and second-order hydrogen desorption as rate-limiting steps.
Diffusion of Ge below the Si(100) Surface: Theory and Experiment
Physical Review Letters, 2000
We have studied diffusion of Ge into subsurface layers of Si(100). Auger electron diffraction measurements show Ge in the fourth layer after submonolayer growth at temperatures as low as 500 ± C. Density functional theory predictions of equilibrium Ge subsurface distributions are consistent with the measurements. We identify a surprisingly low energy pathway resulting from low interstitial formation energy in the third and fourth layers. Doping significantly affects the formation energy, suggesting that n-type doping may lead to sharper Si͞Ge interfaces.
Effect of Ba termination layer on chemical and electrical passivation of Ge (100) surfaces
Materials Science in Semiconductor Processing, 2006
During the deposition process of high-k gate oxides on Ge, the Ge interface tends to be oxidized to form GeO x , leading to the introduction of interface states which compromise transistor performance. It has been suggested that a Ba termination layer on Ge could fulfill the same passivating role on Ge as reported for Sr on Si. In this paper, we present LEED, UPS and XPS studies on the effect of Ba overlayers on the chemical and electrical passivation of Ge(1 0 0). For 1 ML coverage, the adsorbate phase has (1 Â 1) symmetry, as observed by LEED. Ba is seen to significantly increase the oxidation tendency of the Ge(1 0 0) surface. Using UPS, 1 ML Ba was seen to reduce surface band bending by 200 meV on n-type Ge, suggesting that Ba deposition causes transfer of electrons to the Ge substrate, resulting in a surface dipole. The role of this dipole in oxidation enhancement and possible electronic passivation effects is discussed.
Electronic states of thin epitaxial layers of Ge on Si(100)
Applied Surface Science, 1998
The valence density of states of Ge grown epitaxially on Si(100) is investigated as a function of thickness by yield spectroscopy and photoemission techniques. A double edge is present in the yield data for thicknesses smaller than the lattice relaxation critical thickness. Furthermore, the line-up of the Ge states to the Si valence band varies with overlayer thickness. Photoemission techniques fail to detect this behavior. The causes for the discrepancy are analyzed. © 1998 Elsevier Science B.V.