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Carrier mobilities and concentrations were measured for different p- and n-type silicon materials in the temperature range 0.3–300 K. Simulations show that experimentally determined carrier mobilities are best described in this temperature range by Klaassen’s model. Freeze-out reduces the carrier concentration with decreasing temperature. Freeze-out, however, depends on the dopant type and initial concentration. Semi-classical calculations are useful only for temperatures above 100 K. Otherwise quantum mechanical calculations are required.

A significant increase of the drain current is verified if defined numbers and types of dislocations are present in the channel of MOSFETs. For pMOSFETs, analysed here, an enhancement by a factor of eight exists if mixed dislocations are placed in the channel. The drain current increase is caused by higher concentration and higher mobility of holes on dislocations. It is shown that cores of mixed dislocations possess uniaxial compressive strain components in the order of e ≅ –0.1 which are significantly higher than in the strain field surrounding a dislocation. The exceptional high uniaxial strain results in dramatic alterations of the silicon band structure. Upward shifts of the upper valence bands appear forming a quantum wire. The generation of the quantum wire forces hole confinement along dislocations and generates a one-dimensional hole gas (1DHG). Confinement and energy quantization are assumed to be most important for the increased carrier transport along dislocations. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dislocations are basic crystal defects and represent one-dimensional native nanostructures embedded in a perfect crystalline matrix. Their structure is predefined by crystal symmetry. Two- dimensional, self-organized arrays of such nanostructures are realized reproducibly using specific preparation conditions (semiconductor wafer direct bonding). This technique allows separating dislocations up to a few hundred nanometers which enables electrical measurements of only a few, or, in the ideal case, of an individual dislocation. Electrical properties of dislocations in silicon were measured using MOSFETs as test structures. It is shown that an increase of the drain current results for nMOSFETs which is caused by a high concentration of electrons on dislocations in p-type material. The number of electrons on a dislocation is estimated from device simulations. This leads to the conclusion that metallic-like conduction exists along dislocations in this material caused by a one-dimensional carrier confinement. On the other hand, measurements of pMOSFETs prepared in n-type silicon proved the dominant transport of holes along dislocations. The experimentally measured increase of the drain current, however, is here not only caused by an higher hole concentration on these defects but also by an increasing hole mobility along dislocations. All the data proved for the first time the ambipolar behavior of dislocations in silicon. Dislocations in p-type Si form efficient one-dimensional channels for electrons, while dislocations in n-type material cause one- dimensional channels for holes.

The influence of GBs contained in the channel of MOS-FETs - fabricated in thin SOI layers - is demonstrated. The drain current measured at room temperature increases about 50 times for nFETs and about 10 times for pFETs, respectively, as compared to reference devices. The observations might be interpreted as a strong increase of the mobility of charge carriers. Moreover, the observed stepwise changes of the drain current at 5 K may point to Coulomb blockades.

Dislocations exhibit a number of exceptional electronic properties resulting in a significant increase of the drain current of metal-oxide-semiconductor field-effect transistors (MOSFETs) if defined numbers of these defects are placed in the channel. Measurements on individual dislocations in Si refer to a supermetallic conductivity. A model of the electronic structure of dislocations is proposed based on experimental measurements and tight binding simulations. It is shown that the high strain level on the dislocation core—exceeding 10% or more—causes locally dramatic changes of the band structure and results in the formation of a quantum well along the dislocation line. This explains experimental findings (two-dimensional electron gas and single-electron transitions). The energy quantization within the quantum well is most important for supermetallic conductivity.

A major challenge for the application of strain engineering to enhance the performance of electronic devices is the quantification of strain on the nanoscale. Besides other techniques (Raman spectroscopy, X-ray diffraction) electron beam techniques allow strain analyses with a spatial resolution of a few nanometers and a reasonable strain sensitivity of 1x10 -3 (relative to the lattice constant of silicon). In the present work, we address practical issues in the application of nano-beam electron diffraction (NBED) to probe the strain in strained silicon layers and sub-100 nm structures. The investigated specimens were prepared on biaxially tensile strained silicon-on- insulator substrates with an initial strain of = 0.6% or 0.8%. Results of the NBED experiments were compared to data obtained by other strain measurement techniques; amongst them the strain mapping by peak-pairs analysis of high-angle annular dark field (HAADF) images was especially considered. NBED can be easily performed by use of STEM with a small aperture of the 2 nd condenser lens in the micro- or nanoprobe mode. The NBED principle consists in illuminating a nanometer-sized area of the specimen (being in zone axis orientation) with a nearly parallel electron beam and acquiring series of diffraction patterns at points along previously defined lines. The strain components of interest are generally calculated using a dedicated software package which is based on procedures for the analysis of electron diffraction patterns. The spatial resolution of NBED is determined by the beam diameter to a few nanometers. The

Schottky diodes prepared on silicon bonded wafers with dislocation network (DN) lying parallel to the sample surface at the depth of ∼2 μm were investigated by means of capacitance-voltage (CV), current-voltage (IV) measurements at 80 K under optical illumination. A model of the interpretation of CV and IV data is presented and discussed. It is shown that electron-beam induced current (EBIC) mapping under the proper chosen forward bias voltages allows one to trace the inhomogeneities of the potential barrier at DN. The observed non-uniformity of the DN barrier heights was ascribed to inhomogeneous distribution of small oxide precipitates lying at the dislocation network plane (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on electro-luminescence from metal-insulator-semiconductor diodes (MISLED). MISLEDs prepared on silicon with HfO2 layers of different thicknesses were investigated and their properties compared with such prepared by using SiO2 insulator layer. The role of the insulator layer was studied in view of the efficiency of the band-to-band radiation from silicon. We show that the luminescence efficiency depends on the dielectric constant of the insulator as well as on its ability to conduct carriers by tunnelling. Efficiency enhancement of 3.3 times was detected when the SiO2 insulator was substituted by HfO2 in the MIS emitter. Optimal injection current exists, which leads to a maximal efficiency of the luminescence. The optimal current depends strongly on the thickness of the oxide. We relate the existence of an optimal current with the depth at which the injected minority carriers recombine radiatively. Thus the electric field in the semiconductor and the surface recombination are the factors determining the optimal injection (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Silicon nanowires (NWs) and vertical nanowire-based Si/Ge heterostructures are expected to be building blocks for future devices, e.g. field-effect transistors or thermoelectric elements. In principle two approaches can be applied to synthesise these NWs: the ‘bottom-up’ and the ‘top-down’ approach. The most common method for the former is the vapour–liquid–solid (VLS) mechanism which can also be applied to grow NWs by molecular beam epitaxy (MBE). Although MBE allows a precise growth control under highly reproducible conditions, the general nature of the growth process via a eutectic droplet prevents the synthesis of heterostructures with sharp interfaces and high Ge concentrations. We compare the VLS NW growth with two different top-down methods: The first is a combination of colloidal lithography and metal-assisted wet chemical etching, which is an inexpensive and fast method and results in large arrays of homogenous Si NWs with adjustable diameters down to 50 nm. The second top-down method combines the growth of Si/Ge superlattices by MBE with electron beam lithography and reactive ion etching. Again, large and homogeneous arrays of NWs were created, this time with a diameter of 40 nm and the Si/Ge superlattice inside.

The investigation of regular dislocation networks (DN) formed by direct wafer bonding suggests that the D1 and D2 peaks of dislocation-related luminescence (DRL) in silicon is linked to screw dislocations, whereas edge dislocations are responsible for D3 and D4 DRL peaks. Non-radiative recombination activity in DN could be attributed to edge dislocations and could be related to enhanced ability of these dislocations to getter impurity atoms. Obtained relation of DRL intensity with the density of screw dislocations suggests existence of the optimum twist angle for the wafer-bonding geometry for which the DRL intensity has a maximum. The dependence of DRL intensity on the spacing between screw dislocations has the maximum at about 7 nm. Reported radiative and non-radiative recombination properties of DN present substantial interest not only for possible LED applications in all-Si photonics but also for photovoltaics, since DNs represent a model system for grain boundaries controlling carrier lifetime in microcrystalline-Si material.

Incorporation of optical components into microelectronic devices will significantly improve their performance. Absence of effective Si-based light emitter hampers such integration. In the present work light emitting Si diodes, fabricated by dopant (boron or phosphorous) implantation and annealing are investigated. Different implantation doses and annealing temperatures were employed. The efficiency of the electroluminescence (EL), obtained from such structures was measured and correlated with the fabrication process parameters. As previously reported, the EL of band-to-band radiative transition in Si is strongly influenced, by the dopant implantation dose, i.e. higher doses usually enhance EL. Our results suggest that the effect is mainly related to the increase of minority carrier lifetime in the substrate. Distinct measurements showed that the higher implantation doses lead longer carrier lifetimes in the samples. The correlation between lifetime and the EL efficiency could be satisfactory explained in the frame of a classical model, considering the carrier-injection dependence of the rates of the three main recombination mechanisms in silicon, i.e. multi-phonon, radiative and Auger recombination. We suppose that the increase in the implantation dose improves minority carrier lifetime due to the gettering of impurity atoms from the substrate material to the highly doped emitter region.

The electrical and optical properties of dislocations in Si are reviewed, namely dislocation-related recombination and luminescence, transport of minority and majority carriers along dislocations or the electric field around dislocations. It is shown that Si wafer direct bonding allows well-controlled formation of dislocation networks, giving rise to adjustable dislocation properties. Ideas for novel Si devices utilizing dislocations as active components are presented. In particular, dislocation-based light emitters at about 1.5 μm wavelength are demonstrated. Concepts for dislocation-based conductive channels and fast FETs, manipulators of biomolecules or thermo-electric generators are sketched.

Semiconductor wafer bonding offers a new degree of freedom in the design of material combinations without the common restrictions of the structure of the materials bonded. It is already an established method for the industrial production of advanced substrates (SOI) applied as basic material in high-performance device fabrication. SOI, i.e. a thin device layer on an insulator, is a promising concept for further device developments. The advantages of SOI can be combined with mobility enhancing materials such as strained silicon (SSOI) or germanium on insulator (GOI). The bonding process is not limited to a certain wafer diameter and is applicable to different material combinations which are important to integrate different functions on a chip (system on a chip, SoC). (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dislocation rich regions can be controllably formed at a certain location inside a silicon wafer. We studied the light emission properties of such regions located in an electric field of a p–n junction under different excitation conditions. It was found that the luminescence spectra of the dislocations are significantly influenced by the presence of the junction. The dislocation-related luminescence peak position appears red-shifted due to the built-in electric field. A suppression of that field by photogeneration of carriers or by applying a forward bias voltage at the junction leads to a gradual decrease in the energy position of the peaks. The dependence of the peak position on the electric field was found to be a quadratic function, similar to that observed for semiconductor nanostructures. We show that the shift of the peak position is due to the Stark effect on dislocation-related excitonic states. The characteristic constant of the shift, obtained by fitting the data with the quadratic Stark effect equation, was 0.0186 meV/(kV/cm)2. The observed effect opens new possibilities for integration of a silicon based light emitter, combining the radiation from dislocations with a Stark effect based modulator.

Different methods to introduce strain in thin silicon device layers are presented. Uniaxial strain is introduced in CMOS devices by process-induced stressors allowing the local generation of tensile or compressive strain in the channel region of MOSFETs. Biaxial strain is introduced by growing of thin silicon layers on SiGe buffers and their transfer to oxidized silicon substrates. The latter forms strained silicon on insulator (SSOI) wafers characterized by tensile strain only. Future CMOS device technologies require the combination of the global strain of SSOI substrates with local stressors to increase the device performance.

The paper reviews methods of hydrophobic wafer bonding. Hydrophobic surfaces are obtained by removing the oxide layer from the surfaces of crystalline silicon substrates. Bonding such surfaces causes the formation of a dislocation network in the interface. The structure of the dislocation network depends only on the misalignment (twist and tilt components). The different dislocation structures are discussed. Because wafer bonding offers a method to the reproducible formation of such networks, different applications are possible

Dislocation networks obtained by hydrophobic wafer bonding of Si (100) are investigated. The twist and tilt misorientations induce two interacting dislocation networks. Advanced bonding techniques are applied and optimized allowing to eliminate the tilt and to control the twist misorientation. At very low twist angles the interfaces no longer exhibit regular dislocation networks. Properties of dislocation networks are discussed.

The paper presents a critical analysis of Si light emitters made by ion implantation and describes novel concepts for IR light emitters based on silicon nanostructures that do not need Er doping. It is shown that dislocation networks which can be generated in a well controlled way by wafer direct bonding exhibit promising light emitting properties. The luminescence of the dislocation networks can be tailored by the choice of the misorientation of the bonded wafers. It is demonstrated that efficient D1 emission (1.55 μm) at 300 K or D3 emission (1.3 μm) can be obtained for specific misorientations. An enhancement of the luminescence is observed when applying a bias voltage across the network, caused by a changed occupation of the states at the network. Oxygen in the dislocation network is supposed to increase the intensity of the D1 luminescence. Si nanowires are discussed as another potential candidate for IR emitters. Among other lines, efficient luminescence around 1.55 μm is found at 300 K in nanowires. This emission line is attributed to extended defects within the nanowires.

Si-based light emitters with efficient emission at 1.5 or 1.3 μm are required for on-chip optical interconnection for the ultra large scale integrated circuits in the future. In this paper, we have shown that dislocation networks in Si formed by direct wafer bonding emit a quartet of luminescence D-lines. The D-line spectrum can be tailored by the structure of the dislocation network. The D1 or D3, with a wavelength of 1.5 or 1.3 μm respectively, can be made dominating in the luminescence spectrum. An external bias voltage applied to the bonded interface can significantly enhance the luminescence intensity of D-lines.

In order to investigate the electrical properties at the surface of dislocation rich silicon, we conducted Electrostatic Force Microscopy on cross-sections of samples prepared by Wafer Direct Bonding. The applied methods, namely Scanning Kelvin Probe Microscopy and non-contact Scanning Capacitance Microscopy, yield a distinct contrast at the position of the dislocation area, i.e. the bonding interface, indicating strong electrical activity. For an explanation of the explicit electrostatic potential extracted from the experiment a simple model taking into account only an intrinsic charge distribution at the dislocation area appears to be insufficient. Instead, a more complex approach has to be used considering carrier generation and recombination by additional, dynamic mechanisms. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Uniaxial strain on wafer-level was realised by mechanically bending and direct wafer bonding of Si wafers in the bent state followed by thinning one of the Si wafers by the smart-cut process. This approach is flexible and allows to obtain different strain values at wafer-level in both tension and compression. UV micro-Raman spectroscopy was used to determine the strain in the thin transferred Si layers. Numerical modelling by 3D finite elements of the strain provided a good description of the experimental results.

Direct wafer bonding between high-density-plasma chemical vapour deposited (HDP-CVD) oxide and thermal oxide (TO) has been investigated. HDP-CVD oxides, about 230 nm in thickness, were deposited on Si(0 0 1) control wafers and the wafers of interest that contain a thin strained silicon (sSi) layer on a so-called virtual substrate that is composed of relaxed SiGe (∼4 μm thick) on Si(0 0 1) wafers. The surfaces of the as-deposited HDP-CVD oxides on the Si control wafers were smooth with a root-mean-square (RMS) roughness of 2 nm. After HDP-CVD oxide deposition on the sSi/SiGe/Si substrates, the RMS roughness of the oxide surfaces was also found to be the same, i.e., >2 nm. To use these wafers for direct bonding the RMS roughness had to be reduced below 1 nm, which was carried out using a chemo-mechanical polishing (CMP) step. After bonding the HDP-CVD oxides to thermally oxidized handle wafers, the bonded interfaces were mostly bubble- and void-free for the silicon control and the sSi/SiGe/Si(0 0 1) wafers. The bonded wafer pairs were then annealed at higher temperatures up to 800 °C and the bonded interfaces were still found to be almost bubble- and void-free. Thus, HDP-CVD oxide is quite suitable for direct wafer bonding and layer transfer of ultrathin sSi layers on oxidized Si wafers for the fabrication of novel sSOI substrates.

Tensile strained Si (sSi) layers were epitaxially deposited onto fully relaxed Si0.78Ge0.22 (SiGe) epitaxial layers (4 μm) on silicon substrates. Periodic arrays of 150 nm × 150 nm and 150 nm × 750 nm pillars with a height of 100 nm were fabricated into the sSi and SiGe layers by electron-beam lithography and subsequent reactive ion etching. The strain in the patterned and unpatterned samples was analyzed using high-resolution UV micro-Raman spectroscopy. The 325 nm excitation line used probes strain in Si close to the surface (penetration depth of ∼9 nm). The Raman measurements revealed that the nano-patterning yields a relaxation of strain of ∼33% in the large pillars and ∼53% in the small pillars of the ∼0.95% initial strain in the unpatterned sSi layer.

The paper deals with possibilities of utilizing dislocation structures as active components of devices. The suggested means for controlled formation of dislocations is direct wafer bonding, giving rise to well defined dislocation networks with adjustable properties. It is shown that the networks allow building light emitting diodes based on the D line luminescence of the dislocations. A light emitter at about 1.5 mm wavelength is demonstrated, with an efficiency potential estimated at 1%. Immobilization of biomolecules on Si surfaces by Coulomb interaction with the dislocations in the network is another application discussed. Finally, the potential use of dislocation networks as insulating layers permeable to impurities to be gettered and as three-dimensional buried conductive channels in the Si wafer is addressed.

SiGe offers new advantages in MEMS technologies. The excellent electronic and optoelectronic properties of SiGe alloys are of main interest for MEMS and NEMS. SiGe combines the electronic properties of Si and Ge having different band structures. Bandgap engineering allows the realization of different electronic and optical properties depending on the composition of the alloy and on the strain in the layer. This gives the opportunity to create new components and microsystems using a silicon-based technology and to replace III-V compound materials. Depending on the growth of SiGe layers tensile or compressive stress is caused in the layers making it possible to create prestressed or deformable elements. Strain engineering allows the realization of numerous microsystems. Combining, for instance, thin SiGe and Si layers result in deformable structures used as nanometer-range building blocks for future electronic and mechanical nanodevices.

On-chip optical interconnects require a CMOS-compatible electrically pumped Si-based light emitter at about 1.5 μm. Dislocations in silicon offer a recombination centre for light emission at the desired energy. Here we report on the radiative properties of dislocation networks, created in a well controllable manner at a certain depth of silicon wafers. Dislocation networks, created by ion implantation and annealing, misfit dislocation in SiGe buffers and a novel concept of dislocations created by misoriented direct bonded Si wafers are discussed. We demonstrate that under a specific misorientation a dislocation network with efficient room temperature D1 (1.55 μm) emission might be generated.

Defined placement of biomolecules at Si surfaces is a precondition for a successful combination of Si electronics with biological applications. We aim to realize this by Coulomb interaction of biomolecules with dislocations in Si. The dislocations form charged lines and they will be surrounded with a space charge region being connected with an electric field. The electric stray field in a solution of biomolecules, caused by dislocations located close to the Si surface, was estimated to yield values up to few kVcm � 1 . A regular dislocation network can be formed by wafer direct bonding at the interface between the bonded wafers in case of misorientation. The adjustment of misorientation allows the variation of the distance between dislocations in a range from 10 nm to a few Am. This is appropriate for nanobiotechnology dealing with protein or DNA molecules with sizes in the nm and lower Am range. Actually, we achieved a distance between the dislocations of 10–20 nm. Also the existence of a distinct electric field formed by the dislocation network was demonstrated by the technique of the electron-beam-induced current (EBIC). Because of the relatively short range of the field, the dislocations have to be placed close to the surface. We positioned the dislocation network in an interface being 200 nm parallel to the Si surface by layer transfer techniques using hydrogen implantation and bonding. Based on EBIC and luminescence data we postulate a barrier of the dislocations at the as bonded interface

A new concept for a Si light emitting diode (LED) capable of emitting efficiently at 1.55 μm or at 1.3 pm, respectively, is proposed. It utilizes radiation from a well-defined dislocation network created in a reproducible manner by direct Si wafer bonding. The wavelength of the light emitted from the network can be tailored by adjusting the misorientation between the Si wafers. That way dominance of radiation at 1.55 μm (D1 line) or at 1.3 μm (D3 line) was achieved. There are hints that decoration of the dislocations by oxygen enhances the intensity of the D1 radiation. A critical analysis of the light emitter proposed by W. L. Ng et al. [Nature 410, 192 (2001)] using band-to-band emission is given. Its application at the above wavelengths would require a few microns thick SiGe layer on top of the Si substrate.

Reproducible formation of well-controlled dislocation structures is a prerequisite to use dislocations as an active part of devices. Regular dislocation networks have been formed at the interface by Si wafer direct bonding. The barriers of interface were generally smaller than 100 meV. The temperature dependence of the electron-beam-induced current (EBIC) contrast of the interface indicates a deep state density of a few 10E5 per cm along the dislocation lines in the network. It is also found that the dislocation networks in Si can act as effective channel for carrier transport. Photoluminescence (PL) reveals that the D line spectrum related to the dislocation networks can be tailored by the bonding misorientation. So, the D1 line can be made the dominating feature in the PL spectrum. It is suggested that regular dislocation networks represent an interesting new nanosystem for future applications, such as accommodation biomolecules onto silicon, dislocation-based LED or buried nanowires.

Electroluminescence of B and P implanted samples has been studied. P implantation is found to have a similar effect on light emission as B implant. The band-to-band (BB) luminescence of P implanted diodes is observed to increase by more than one order of magnitude upon rising the temperature and an internal efficiency of 2 % has been reached at 300 K. An efficiency larger than 5% seems to be reachable. The strong BB line emission at 1.1 &m is attributed to high bulk SRH lifetime. The BB line escapes from the substrate below the p-n junction. It is not due to the implantation-related defects/dislocations. The luminescence spectrum can be tailored to achieve dominance of the dislocation-related D1 line at about 1.5 &m. It is observed that a regular periodic dislocation network, formed by Si wafer direct bonding with a specific misorientation, exhibits even at 300 K only D1 photoluminescence. Such a dislocation network is believed to be a serious candidate to gain an efficient Si-based light emitter.

Strained silicon devices provide for an enhanced carrier mobility compared to that of unstrained silicon devices of identical dimensions. The device performance gets even better when using strained silicon on insulator material. We report experimental procedures based on wafer bonding, smart cutting and selective chemical etching to obtain thin strained silicon (∼15 nm) on insulator wafers. The starting material is an 8″ wafer with pseudomorphically grown strained silicon on a so-called virtual substrate as realized by epitaxial chemical vapor deposition of relaxed SiGe (grown with a grading rate of 10% Ge in the SiGe-alloy per 1 μm layer deposition) on a Si(0 0 1) substrate. The starting and bonded wafers are characterized: (i) structurally using transmission electron microscopy, (ii) topographically, using atomic force microscopy and (iii) the strain is quantified using UV-Raman spectroscopy.

The influence of dislocations in the channel of MOS-FETs is analyzed. The drain current at room temperature increases about 50 times for nFETs and about 10 times for pFETs, as compared to reference devices. The observations might be interpreted as a strong increase of the mobility of charge carriers. Moreover, the observed stepwise changes of the drain current at 5 K may point to Coulomb blockades.

A new concept for light emitting diodes in silicon capable of emitting 1.55 µm is reported. It utilizes D1-band luminescence from a dislocation network in silicon.

Studies dealing with the bonding behavior of silicon wafers coated with thermal oxide, plasma-enhanced chemical vapor deposition (PE-CVD) oxide, PE-CVD oxynitride, PE-CVD nitride and low-pressure (LP) CVD nitride are presented. The PE-CVD layers require a chemo-mechanical polishing (CMP) before bonding to reduce the surface roughness. The bonding energies of the wafer pairs with different interface layers are similar to those of bonded hydrophilic silicon wafers. Infrared microscopy of patterned wafer pairs reveals interfaces which are almost free of bubbles. Presumably, the gas, which usually generates such interface bubbles, diffuses into the interface cavities. The tensile strengths of patterned wafer pairs including a PE-CVD oxide or a PE-CVD oxynitride interface layer are about twice as high as for patterned hydrophilic silicon wafer pairs.

Metallic impurities are detrimental to many silicon devices and limit the efficiency of multicrystalline silicon solar cells. Therefore they are a major subject of ongoing research. Photoluminescence spectroscopy is a promising technique for detecting precipitated metals in silicon because of its sensitivity to the minority carrier density and to specific types of defects; however the impact of impurities on the defect luminescence could not be clarified yet. In this letter we examine the role of micron-sized iron and copper precipitates in direct bonded wafers by micro-photoluminescence spectroscopy. Both kinds of precipitates are detectable by means of the reduced band-to-band luminescence. An element-specific effect on the defect luminescence is observed. The results are confirmed by X-ray fluorescence spectroscopy. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In microsystems technologies, frequently complex structures consisting of structured or plain silicon or other wafers have to be joined to one mechanically stable configuration. In many cases, wafer bonding, also termed fusion bonding, allows to achieve this objective. The present overview will introduce the different requirements surfaces have to fulfill for successful bonding especially in the case of silicon wafers. Special emphasis is put on understanding the atomistic reactions at the bonding interface. This understanding has allowed the development of a simple low temperature bonding approach which allows to reach high bonding energies at temperatures as low as 150°C. Implications for pressure sensors will be discussed as well as various thinning approaches and bonding of dissimilar materials.

Multiple internal reflection spectroscopy (MIRS) was applied to analyse atomic bonds at deep (500 μm) interfaces of directly bonded Si/Si wafer pairs. It is shown that under the conditions used the polarized spectra contain information only about the interface layer a few nanometers thick. Examples are given of analysing the Si-H- and SiO-H vibration modes and bands of undissociated water in interfaces of bonded hydrophobic and hydrophilic wafer pairs, respectively, after annealing at temperatures between 200 and 1100 °C. Variations of the bonding behaviour (especially caused by alterations of the Si-H bonds) are discussed.

A new concept for light emitting diodes in silicon capable of emitting 1.55 μm is reported. It utilizes D1-band luminescence from a dislocation network in silicon. The dislocation network is created in a reproducible manner by silicon wafer direct bonding. A MOS-LED on silicon substrate and a novel two-electrode device in a thin SOI layer using p-n junctions are demonstrated. The maximum efficiency is expected to exceed 1% at room temperature.

Dislocations are frequently involved in the growth of nanostructures. On the other hand, dislocations itself are one-dimensional nanostructures with diameters of about 1 nm. The present paper deals with electronic properties of dislocations. In contrast to previous studies, only a few dislocations are measured which excludes interaction with other defects. The characterization of MOSFETs with defined numbers of dislocations proved an increase of the drain current and refers to the presence of electrons on the dislocation core. The number of electrons per dislocation length was extracted from device simulations. Measurements on TFETs refer to trap-assisted tunneling of carriers via dislocations.

The bonding interface of bonded hydrophobic Si pairs has been found to be a strong gettering layer. By thinning one wafer of the pair, the location of the gettering layer with respect to the defect-free Si surface layer where devices are fabricated can be varied from more than 500 μm to deep-submicrons. Secondary ion mass spectrometry and simulation results suggest that F atoms at the interface are primarily responsible for the gettering effect via Au-F ion pairing. It appears that a significant segregation of Au to the hydrophobic bonding interface is observed during annealing at 900 °C. These results are compared to gettering of Au by a hydrophilic bonding interface.

Spatial distribution and properties of oxide were examined in 300 mm nitrogen (N) doped CZ-Si. Experimentally grown materials with N ranging from ∼ 10 13 cm -3 to 10 15 cm -3 were studied by infrared light scattering tomography, scanning infrared microscopy, transmission electron microscopy and electron beam induced current. It was established that an increasing N content improves the uniformity of the radial distribution of precipitates in the bulk of the wafer, the density of precipitates reaching a level of ∼ 10 9 cm -3 . The width of the denuded zone varies in the range from 15 μm to 70 μm depending on radial position and N doping level. Electron microscopy revealed lower oxide precipitate densities of about 10 5 to 10 8 cm -3 . The results are interpreted in terms of existence of agglomerates of nanometer size precipitate muclei and/or by the defect-induced strain relaxation around the precipitates.

Interfaces of bonded hydrophilic and hydrophobic wafer pairs are studied by multiple internal reflection spectroscopy after annealing at 1100°C. Si−Hx and SiO−H stretching modes are still present in bonded hydrophilic wafers. Interfaces of bonded hydrophobic wafers, prepared by joining HF-etched surfaces without defonized water rinsing, are characterized by the dominance of hydrides (SiH, SiH2, SiH3). Their concentration is about 100 times higher than for bonded hydrophilic wafers. Comparison with the ATR-spectra of HF-treated surfaces showed appreciable shifts in the peak positions indicating that Si−H bonds might be involved in the bonding process.

Presently the most prominent silicon materials considered for silicon-on-insulator (SOI) technologies are SIMOX (separation by implanted oxygen) and bonded SOI. The present paper will review recent developments for these two types of approaches for SOI materials with special emphasis on the progress in obtaining ultra thin bonded SOI layers by local plasma etching or an etch-back procedure involving stress compensated boron-germanium doped etch-stop layers.

Single-crystalline silicon films with thicknesses as thin as 2000 A have been prepared on thermally mismatched quartz substrates by a simple wafer-bonding approach. Initial bonding at ≈ 80 °C, storage at room temperature for more than 100 h and multi-temperature (maximum 150 °C) consecutive annealing with a 1 °C min −1 ramping rate have been adopted to strengthen the bond and to prevent debonding at the edge of the bonded pairs during annealing and etching, where thermal shearing and peeling stresses are maximum. Final etching by EDP (ethylenediamine—pyrocatechol—water) effectively reduces the peeling failure of the highly stressed thinned silicon layer, mainly due to a reduced lateral oxide etching rate along the interface. The high carrier mobility in the single-crystalline silicon layer and the transparent and insulating quartz substrate provides a new dimension of freedom in applications.

This article deals with uncertainty in the analysis of strain in silicon nanoscale structures and devices using nanobeam electron diffraction (NBED). Specimen and instrument related errors and instabilities and their effects on NBED analysis are addressed using a nanopatterned ultrathin strained silicon layer directly on oxide as a model system. We demonstrate that zero-loss filtering significantly improves the NBED precision by decreasing the diffuse background in the diffraction patterns. To minimize the systematic deviations the acquired data were verified through a reliability test and then calibrated. Furthermore, the effect of strain relaxation by specimen preparation using a FIB is estimated by comparing profiles, which were acquired by analyzing slices of strained structures in a 220-nm-thick region of the sample (invasive preparation) and the entire strained nanostructures, which are embedded in a thicker region of the same sample (noninvasive preparation). Together with the random deviation, the corresponding systematic shift results in a total deviation of ∼1 × 10−3for NBED analyses, which is employed to estimate the measurement uncertainty in the thinner sample region. In contrast, the strain in the thick sample region is not affected by the preparation; the systematic shift reduces to a minimum, which improves the total deviation by ∼50%.