SiGe Thin Films Research Articles

Electrode contact study for SiGe thin film operated at high temperature

A study on the electrode contact of the sputtered SiGe thin film is reported for application of devices working at high temperature. Surface morphological characterization with optical microscope and AFM (atomic force microscope) together with the electrical characterization by TLM measurements (transmission line method) were performed before and after aging at 500 °C for 24 h using various sputtered multilayer electrodes, Ti/Au/Ti, Ta/Pt/Ta and Ti/Pt/Ti, on 300-nm B-doped SiGe thin film deposited by magnetron sputtering and furnace crystallisation at high temperature. After aging at 500 °C for 24 h, the Ti/Au/Ti multilayer electrodes seriously degraded to be non-ohmic contact, showing rough surface morphology. The Ti/Pt/Ti metal layers showed the lowest specific contact, resistivity before and after aging, 1.46 × 10 −3 Ω cm 2 and 1.68 × 10 2 Ω cm 2 respectively.

SiGe 집적회로 내의 다결정 SiGe 박막 저항기의 특성 분석

RF 및 고속 아날로그 특성 및 제조 공정의 용이성에 의하여 고속 유무선통신 및 초고주파 분야에서 많이 이용되고 있는 SiGe 집적회로에서, SiGe 박막 저항기의편차를 줄여 집적회로의 신뢰성을 높이는 것이 중요하다. 본 논문에서는 실리콘계 박막 저항기 제조 후 발생하는 불균일한 저항 값 분포의 원인 규명과 그 해결 방안에 대하여 고찰한다. SiGe 박막 저항기의 실리사이드가 존재하는 컨택 영역에서 Ti-B석출물의 영향으로 인하여 저항 값의 불균일성 발생하는데, 이를 최소화하기 위하여는 가능한 최대의 boron 이온을 주입할 필요가 있다. SiGe 저항기와 금속을 배선하기 위한 컨택 홀의 크기가 작을수록 SiGe 층 내에서 돌출부가 컨택 홀의 전체면적을 차지하게 될 확률이 커지게 되어 접촉저항이 비정상적으로 커질 확률 또한 높아지게 되므로, 돌출부가 생성되는 SiGe 저항기의 경우는 컨택 홀의 면적을 크게하여 SiGe 저항기의 편차를 개선하였다. SiGe integrated circuits are being used in the field of high-speed wire/wireless communications and microwave systems due to the RF/high-speed analog characteristics and the easiness in the fabrication. Reducing the resistance variation in SiGe thin film resistors results in enhancing the reliability of integrated circuits. In this paper, we investigate the causes that generate the resistance nonuniformity after the silicon-based thin film resistor was fabricated, and consider the counter plan against that. Because the Ti-B precipitate, which formed during the silicide process of the SiGe thin film resistor, gives rise to the nonuniformity of SiGe resistors, the boron ions should be implanted as many as possible. In addition, the resistance deviation increases as the size of the contact hole that interconnects the SiGe resistor and the metal line decreases. Therefore, the size of the contact hole must be enlarged in order to reduce the resistance deviation.

A comparison of thin film microrefrigerators based on Si/SiGe superlattice and bulk SiGe

Most of the conventional thermal management techniques can be used to cool the whole chip. Since thermal design requirements are mostly driven by the peak temperatures, reducing or eliminating hot spots could alleviate the design requirements for the whole package. Monolithic solid-state microcoolers offer an attractive way to eliminate hot spots. In this paper, we review theoretical and experimental cooling performance of silicon-based microrefrigerators on a chip. Both Si/SiGe superlattice and also bulk SiGe thin film devices have been fabricated and characterized. Direct measurement of the cooling along with material characterization allows us to extract the key factors limiting the performance of these microrefrigerators. Although Si/SiGe superlattice has larger thermoelectric power factor, the maximum cooling of thin film refrigerators based on SiGe alloys are comparable to that of superlattices. This is due to the fact that the superlattice thermal conductivity is larger than bulk SiGe alloy by about 30%.

Strain on wrinkled bilayer thin film

The authors report strain measurement on bilayer wrinkling silicon-germanium (SiGe) thin film. In combination of atomic force microscopy and ultraviolet micro-Raman measurement, the relationship between the spatial profile and strain distribution is established. Theoretical analysis on the mechanism of strain relaxation shows that, in contrast to self-rolling nanotube, both bending and shearing force play an important role in determining the morphology. The behavior demonstrated in the SiGe system should also exist in a wide range of material systems under various strain situations. This study advances the understanding of nanostructure engineered by strain and has significant implications on the performance of nanodevices.

Silicon-based thin films as bottom electrodes in chalcogenide nonvolatile memories

The effect of the electrical resistivity of a silicon–germanium (SiGe) thin film on the phase transition in a GeSbTe (GST) chalcogenide alloy and the manufacturing aspect of the fabrication process of a chalcogenide memory device employing the SiGe film as bottom electrodes were investigated. While p-type SiGe bottom electrodes were formed using in situ doping techniques, n-type ones could be made in a different manner where phosphorus atoms diffused from highly doped silicon underlayers to undoped SiGe films. The p–n heterojunction did not form between the p-type GST and n-type SiGe layers, and the semiconduction type of the SiGe alloys did not influence the memory device switching. It was confirmed that an optimum resistivity value existed for memory operation in spite of proportionality of Joule heating to electrical resistivity. The very high resistivity of the SiGe film had no effect on the reduction of reset current, which might result from the resistance decrease of the SiGe alloy at high temperatures.

RBF neural networks for solving the inverse problem of backscattering spectra

This paper investigates a new method to solve the inverse problem of Rutherford backscattering (RBS) data. The inverse problem is to determine the sample structure information from measured spectra, which can be defined as a function approximation problem. We propose using radial basis function (RBF) neural networks to approximate an inverse function. Each RBS spectrum, which may contain up to 128 data points, is compressed by the principal component analysis, so that the dimensionality of input data and complexity of the network are reduced significantly. Our theoretical consideration is tested by numerical experiments with the example of the SiGe thin film sample and corresponding backscattering spectra. A comparison of the RBF method with multilayer perceptrons reveals that the former has better performance in extracting structural information from spectra. Furthermore, the proposed method can handle redundancies properly, which are caused by the constraint of output variables. This study is the first method based on RBF to deal with the inverse RBS data analysis problem.

Electron-hole liquid in strained SiGe layers of silicon heterostructures

The electron-hole liquid has been found in strained SiGe thin films of Si/Si1−x Gex/Si heterostructures. The density and binding energy of the electron-hole liquid have been determined. Owing to the presence of internal strains in the SiGe layer, the density and binding energy are significantly smaller than the respective quantities for the electron-hole liquid in a bulk single crystal of the solid solution of the same composition. The critical temperature of the transition from the exciton gas to the electron-hole liquid is estimated using the experimental data. The Mott transition (from the exciton gas to electron-hole plasma) occurs above the critical temperatures for high excitation intensities.

Composition and atomic ordering of Ge/Si(001) wetting layers

A combination of X-ray diffraction with anomalous X-ray scattering at the Ge K edge and specular reflectivity measurements is used to reveal both composition and atomic ordering in Ge:Si wetting layers. By comparing the intensity distribution close to the (400) and (200) surface reflections we show that the Ge wetting layer is composed of a SiGe alloy which exhibits atomic ordering. Due to the Si interdiffusion the wetting layer thickness is larger than the nominal 3 ML Ge deposition. The chemical depth distribution is obtained from X-ray reflectivity measurements and confirms the enhanced Ge interdiffusion. These phenomena evidence the crucial interplay between surface kinetics and intermixing in SiGe thin films and nanostructures on Si(001) substrates.

Control of strain status in SiGe thin film by epitaxial growth on Si with buried porous layer

Single crystalline Si with buried porous layers was utilized as a substrate for the epitaxy of 100-nm-thick Si0.73Ge0.27. Raman spectroscopy revealed that the strain status in SiGe systematically changes according to the variation in the porosity of the substrate and that the strain relaxation in SiGe was found to proceed with increasing porosity. Furthermore, Si was found to be tensilely strained to reduce the compressive strain in SiGe. These results suggest that the appropriate design of the porosity and the thickness of the thin Si layer on the buried porous layer offers an alternative way to control strain status in SiGe.

Silicon-Germanium Heterostructure-on-Insulator Formed by Ge+ Ion Implantation and Hydrogen Transfer

Using bulk silicon can be ended for 32 nm technological nodes. New type of substrates needs for further scaling in CMOS microelectronics. We speculate that these new type of materials will be semiconductor heterostructure on insulator (SHI) compatible with current silicon planar CMOS technology. Joint semiconductor material stack placed on cheap amorphous dioxide is presented. First of all thin film SiGe heterostructure properties is considered. It was obtain using Ge ion implantation in dioxide with followed Ge segregation to the directly bonded interface between silicon and silicon dioxide wafers. The method is also compatible with A3B5 thin film formation.

Micro-Thermoelectric Hydrogen Sensor of Three Different Membrane Structures

We prepared micro-thermoelectric hydrogen sensors (micro-THSs) operating with a combination of the thermoelectric effect of SiGe thin film and Pt-catalyzed exothermic hydrogen oxidation of the catalyst. The membrane area of each sensor was heated by a micro heater. The responses of the micro-THSs with three different types of membranes to hydrogen in air were investigated. The micro-THS with a single membrane, which had a better thermal isolation than those of other membranes, reduced the power consumption of 251 mW and the time required to heat the membrane by 5 s. This micro-THS with a single membrane showed the optimal gas sensing property of voltage signal of 1.13 mV for 1% hydrogen in air with the low detection limit of 50 ppm.

An investigation of the effects of radiation exposure on stability constraints in epitaxial SiGe strained layers

The thermodynamic stability of device-relevant epitaxial SiGe strained layers under proton irradiation is investigated using X-ray diffraction techniques, and compared with its stability constrain under high-temperature annealing. Irradiation with 63MeV protons is found to introduce no significant microdefects into the SiGe thin films, regardless of starting stability condition of the SiGe film, and thus does not appear to be an issue for the use of SiGe HBT technology in emerging space systems. The strain relaxation of SiGe thin film under thermal annealing, however, is sensitive to the composition and thickness of the as-grown samples, as expected, with the subsequent lattice relaxation of the unstable samples occurring at a much higher rate than that of metastable samples.

Micro-Thermoelectric Gas Sensor with P-doped SiGe Thin Film Deposited by Helicon Sputtering

Micro-thermoelectric hydrogen sensor working with the combination of the thermoelectric effect of phosphorus-doped SiGe thin film and the Pt-catalyzed exothermic reaction of hydrogen oxidation has been fabricated. Sensitivity of hydrogen gas of the device was improved by doping the SiGe thermoelectric thin film deposited by helicon sputtering.

Morphological study of polycrystalline SiGe alloy deposited by vertical LPCVD

As device dimensions shrink to the deep-submicron scale, new challenges arises from the very small scale used and even poly crystalline silicon (poly-Si) presents problems as gate electrode. The use of SiGe as gate material can present many advantages over the poly-Si, as it leads to a lower boron penetration and gate depletion. In this paper authors present some morphological studies of polycrystalline SiGe thin films deposited in a vertical LPCVD (Low Pressure Chemical Vapor Deposition) reactor for using as MOS (Metal Oxide Semiconductor) gate electrode.

Growth of high-quality relaxed SiGe films with an intermediate Si layer for strained Si n-MOSFETs

An intermediate Si layer in Si1–xGex film, replacing the conventionally compositional graded buffer layer, was used to fabricate a relaxed SiGe substrate of high quality. The intermediate Si layer changes the relaxation mechanism of the SiGe thin film via the generation of {3 1 1} dislocation loops. The {3 1 1} dislocation loops are formed in the intermediate Si layer to prompt a state of relaxation in the SiGe overlayer, provide the defects for trapping of threading dislocations (TDs) and leave a SiGe top layer with low dislocation density. For the SiGe/Si/SiGe samples, the residual strain and TDs on the top SiGe layer are independent of the SiGe underlayer thickness. With a 700 nm thick Si0.8Ge0.2 overlayer, such a Si0.8Ge0.2/Si/Si0.8Ge0.2 heterostructure with a smooth surface has a TD density of 8.9 × 105 cm−2 and 3% residual strain. Owing to the different main relaxation mechanisms in SiGe films, the surface root mean square roughness of this relaxed buffer with a low density of surface pits was measured to be about 3 nm, which is lower than that of the sample without any intermediate Si layer (13 nm). Relaxation of the SiGe overlayer depends on the thickness of the intermediate Si layer. Optimization on relaxation in the SiGe/Si/SiGe structure with an intermediate Si layer of 50 nm is done. Strained Si n-channel metal-oxide-semiconductor field effect transistors with various buffer layers were fabricated and examined. The effective electron mobility for the strained Si device with this novel substrate technology was found to be 80% higher than that of the Si control device. The SiGe thin films with the intermediate Si layer serve as good candidates for high-speed strained Si devices. The global strain in the Si channel with a SiGe/Si/SiGe buffer is still beneficial for short channel devices.

Formation of polycrystalline SiGe thin films by the RF magnetron sputtering method with Ar–H 2 mixture gases

Polycrystalline silicon–germanium (SiGe) films were prepared on corning ♯7059 substrates by an RF magnetron sputtering method. The crystallization temperature of SiGe films could be decreased from 600 to 400 °C due to the introduction of H 2 into the sputtering gases probably because of the enhancement of the surface reaction caused by the hydrogen radicals. The optical absorption coefficients of SiGe films by the Ar–H 2 gas sputtering are similar to those of the single crystalline SiGe, nevertheless much higher values are observed in SiGe films by the Ar sputtering. The dark conductivity of the films decreases from 1.2×10 −2 to 2.1×10 −6 S/cm, and their properties seem closer to the intrinsic properties with the introduction of H 2. These results suggest that the introduction of H 2 into the sputtering gases is effective to decrease the crystallization temperature and to improve the optical and electrical properties of SiGe films.

Silicon‐based narrow‐bandgap thin‐film semiconductor materials: polycrystalline SiGe prepared by reactive thermal CVD

AbstractIn this work, the mechanisms of reactive thermal CVD are discussed and the influences of various deposition parameters on crystallinity, composition, uniformity and reproducibility are clarified. Based on optimization of deposition parameters, we obtained device‐grade polycrystalline SiGe (poly‐SiGe) thin films with high crystallinity of >95%, high uniformity of >80% and high reproducibility of >85% at 450 °C. The results presented in this paper proved that polycrystalline SiGe films deposited by reactive thermal CVD are suitable for device application. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Micro-Thermoelectric Gas Sensor with B- and P-doped SiGe Thin Film deposited by Helicon Sputtering

not Available.

Micro-Thermoelectric Hydrogen Sensors with Pt Thin Film and Pt ∕ Alumina Thick Film Catalysts

Micro-thermoelectric hydrogen sensor (micro-THS) was fabricated to operate with its unique working principle of the combination of the thermoelectric effect of SiGe thin film and the Pt-catalyzed exothermic reaction of hydrogen oxidation. We focused on improving sensitivity and response speed of micro-THS using a new catalyst deposition method. Comparing with the two catalysts of thin and thick film technology, sensitivity of the micro-THS with thick film catalyst was 5 times higher than that of the sensor with Pt thin film catalyst. The of thick film catalyst was large enough for a wide detection range of hydrogen concentration from 25 ppm to 3%, although its size was small, 35% of the Pt thin film one. At operating temperature of 100°C, for the low hydrogen concentration of 25 ppm, clear response of 0.03 mV the micro-THS with thick film catalyst was observed.

Sb surfactant-mediated SiGe graded layers for Ge photodiodes integrated on Si

High-quality SiGe and Ge thin films were grown on Si substrates by molecular-beam epitaxy using a technique that combines SiGe composition grading and Sb surfactant mediation. Both transmission electron microscopy and Schimmel defect etch measurements show that the Sb surfactant-mediated SiGe graded buffer layers have lower dislocation densities than those without an Sb surfactant. A systematic study of Sb surfactant-mediated graded buffers was carried out. The relationship between the threading dislocation densities and the grading rates of the Sb surfactant-mediated SiGe buffer layers was investigated. Moreover, p-i-n Ge photodiodes were fabricated on Si substrates using Sb surfactant-mediated SiGe graded buffer layers. These photodiodes exhibit very low dark current densities of about 0.15mA∕cm2 at the reverse bias of 1 V and high quantum efficiencies of 50%–72%.