Initial Wafers Research Articles

Spatial arrangements and types of dislocations in interfacial networks obtained by Si(001) wafer bonding at low twist angle: A TEM characterization

Two interfacial dislocation networks were obtained in a Si–Si material system by wafer bonding process for low twist angles around 0.2°. For one sample, one of the two initial wafers was rotated with an additional angle of 90° before the bonding. TEM analyses of samples prepared for planar and transverse views show different characteristics in terms of spatial arrangement and dislocation types. Long climbing segments slightly deviated from the [100] axis and short segments a/2<101> are arranged in the dislocation network obtained with an additional rotation and at the lowest twist angle (Ψ = 0.18°) from a <110> axis. Long screw segments a/2<110> and short partial Shockley segments are arranged in the dislocation network obtained without any additional rotation at the highest twist angle (Ψ = 0.27°) from a <110> axis. In both cases, the long and short segments form elongated hexagonal patterns, which are accurately ordered in one set paving the <100> directions or randomly ordered in two perpendicular sets paving the <110> directions, respectively. The results are discussed taking into account the arangement of the surface miscut steps in the initial wafers before the bonding.

Diffusion of Magnesium in Czochralski Silicon

The diffusion of magnesium in monocrystalline dislocation‐free Czochralski silicon (Cz–Si) with an oxygen concentration of (3–4) × 1017 cm−3 is studied. Initial silicon wafers are doped with Mg by using the sandwich technique. The impurity diffusion profiles are investigated in n‐Si samples by the differential conductivity method. The diffusivity of electrically active magnesium in the temperature range of 1,100–1,250 °C is two to three orders of magnitude lower than the values observed at doping high‐purity silicon crystals grown by the float‐zone method (Fz–Si). The diffusion in Cz–Si is retarded through the trapping of diffusing Mg atoms by oxygen‐related traps. The observed high value of the activation energy of Mg diffusion in investigated samples (4.1 eV) is due—along with the migration energy of interstitial magnesium in the crystal lattice (1.83 eV) —to the significant binding energy of Mg atoms with traps (2.27 eV). A study of the temperature dependence of the Hall effect in bulk‐doped samples reveals two types of deep double donors: interstitial Mg atoms and MgO complexes.

Tuning electrical properties in Ga2O3 polymorphs induced with ion beams

Ion beam fabrication of metastable polymorphs of Ga2O3, assisted by the controllable accumulation of the disorder in the lattice, is an interesting alternative to conventional deposition techniques. However, the adjustability of the electrical properties in such films is unexplored. In this work, we investigated two strategies for tuning the electron concentration in the ion beam created metastable κ-polymorph: adding silicon donors by ion implantation and adding hydrogen via plasma treatments. Importantly, all heat treatments were limited to ≤600 °C, set by the thermal stability of the ion beam fabricated polymorph. Under these conditions, silicon doping did not change the high resistive state caused by the iron acceptors in the initial wafer and residual defects accumulated upon the implants. Conversely, treating samples in a hydrogen plasma converted the ion beam fabricated κ-polymorph to n-type, with a net donor density in the low 1012 cm−3 range and dominating deep traps near 0.6 eV below the conduction band. The mechanism explaining this n-type conductivity change may be due to hydrogen forming shallow donor complexes with gallium vacancies and/or possibly passivating a fraction of the iron acceptors responsible for the high resistivity in the initial wafers.

Stability of Cernox® temperature sensors stored at room temperature over a 29-year period

Many cryogenic applications critically depend upon accurate temperature measurement for success. In certain applications, including aerospace missions, temperature sensor components are procured years in advance of the mission’s launch date in order to accommodate installation and ground-based testing. Once installed there is little opportunity for recalibration, so the stability of the sensor stored at room temperature over extended time periods becomes vitally important. One of the most common cryogenic temperature sensor types used in aerospace applications is the Cernox Resistance Temperature Sensor manufactured by Lake Shore Cryotronics, Inc., and has been commercially available since 1993. For 29 years a set of 35 sensors manufactured from two of the initial production wafers has been stored at room temperature in ambient atmosphere. These sensors have been periodically recalibrated over the 1.4 K to 325 K or 4 K to 325 K temperature range as appropriate to provide an estimate of the long-term stability of these sensors when stored at room temperature. Data for each temperature sensor were analyzed in terms of equivalent temperature shift between each subsequent calibration and its initial calibration in 1992. The data show that the overall 29-year average stability for devices from these two Cernox wafers roughly follows a stability of ±10 mK for temperatures below 10 K and 0.07% of temperature for temperatures above 10 K. Data for an additional nine Cernox devices from an actual JWST production build lot showed they all exhibited stabilities better than ±8 mK for T < 10 K and (ΔT/T) < ±0.075% for T > 10 K.

Spectral Ellipsometry as a Method of Investigation of Influence of Rapid Thermal Processing of Silicon Wafers on their Optical Characteristics

One of the possible ways of improvement of the surface properties of silicon is the solid phase recrystallization of the surface silicon layer after the chemical-mechanical polishing with application of the rapid thermal treatment with the pulses of second duration. The purpose of the given paper is investigation of influence of the rapid thermal treatment of the initial silicon wafers of the various doping level and reticular density on their optical characteristics by means of the spectral ellipsometry method.The investigation results are presented by means of the spectral ellipsometry method of the rapid thermal processing influence on the initial silicon wafers (KDB12 orientation &lt;100&gt;, KDB10 orientation &lt;111&gt; and KDB0.005 orientation &lt;100&gt;) of the various level of doping and reticular density influence on their optical characteristics: refraction and absorption ratios. Influence was confirmed of the silicon reticular density on its optical characteristics before and after the rapid thermal processing. It was shown, that reduction of the refraction and absorption ratios in the center of the Brillouin zone for the silicon samples with the high Boron concentration after the rapid thermal processing as compared with the low doped silicon. In the area of the maximum absorption peak, corresponding to the energy of the electron exit from the silicon surface (4.34 eV) the refraction indicator of the high doped silicon becomes higher, than of the low doped silicon, which is determined by the high concentration of the vacant charge carriers on the silicon surface in this spectral range.It was established, that the spectral area 3.59–4.67 eV, corresponding to the work of the electrons, exiting the silicon surface, the most informative way shows the difference of the 3 optical parameters of silicon of the different orientation, and for evaluation of influence of the silicon doping level on its optical characteristics the most informative is the spectral range of 3.32–4.34 eV.

Smoothing surface roughness using Al2O3 atomic layer deposition

Al2O3 atomic layer deposition (ALD) was used to smooth the roughness on silicon wafers obtained prior to chemical mechanical polishing (CMP). The initial silicon wafers had an average RMS surface roughness of 3.3 nm as determined by atomic force microscopy (AFM) measurements. AFM line scans also measured an average lateral spacing of ≈490 nm between the surface asperities. The RMS roughness decreased and the average lateral spacing increased progressively with number of Al2O3 ALD cycles. After 3000 Al2O3 ALD cycles that deposit an Al2O3 film thickness of 370 nm, the RMS roughness reduced to 1.5 nm and the average lateral spacing between the surface asperities increased to ≈890 nm. Additional Al2O3 ALD cycles produced little change in the RMS roughness or average lateral spacing. The efficiency of the smoothing decreased when the lateral distance between the surface asperities was much larger than the Al2O3 ALD film thickness. Power spectral density (PSD) analysis revealed that the ALD smoothing was most effective for surface topographical features with lateral spacings in the range of 10s to 100s of nanometers. Reflectivity studies of silver films deposited on the silicon wafers also demonstrated that Al2O3 ALD smoothing improved the optical performance of reflective mirrors.

Исследование диодов Шоттки на основе массива кремниевых волокон, полученных сухим криогенным травлением

We consider arrays of vertically aligned nanowires obtained by dry cryogenic etching of silicon wafers with n = 1016 cm-3 and 1017 cm-3, 6 µm in height and 1.7 µm and 1.2 µm in diameter, respectively. It has been demonstrated that the deposition of gold forms a Schottky diode with an ideality coefficient of 1.1-1.3 and a barrier height of 0.6-0.7 eV to these arrays. It is shown that the experimental curves of the capacitance-voltage characteristics of such structures can be analyzed using a model that takes into account the contribution to the capacitance from all surfaces of the nanowires. This made possible to numerically estimate the concentration profile of free charge carriers in the array of nanowires, which showed good numerical agreement with the doping level in the initial wafers.

Peculiarities of electronic structure and composition in ultrasound milled silicon nanowires

The combined X-ray absorption and emission spectroscopy approach was applied for the detailed electronic structure and composition studies of silicon nanoparticles produced by the ultrasound milling of heavily and lowly doped Si nanowires formed by metal-assisted wet chemical etching. The ultrasoft X-ray emission spectroscopy and synchrotron based X-ray absorption near edges structure spectroscopy techniques were utilize to study the valence and conduction bands electronic structure together with developed surface phase composition qualitative analysis. Our achieved results based on the implemented surface sensitive techniques strongly suggest that nanoparticles under studies show a significant presence of the silicon suboxides depending on the pre-nature of initial Si wafers. The controlled variation of the Si nanoparticles surface composition and electronic structure, including band gap engineering, can open a new prospective for a wide range Si-based nanostructures application including the integration of such structures with organic or biological systems.

INFLUENCE OF RAPID THERMAL TREATMENT OF INITIAL SILICON WAFERS ON THE ELECTROPHYSICAL PROPERTIES OF SILICON DIOXIDE OBTAINED BY PYROGENOUS OXIDATION

For investigation of the influence exerted by rapid thermal treatment of initial silicon wafers on the electrophysical properties of silicon dioxide obtained by means of the pyrogenous oxidation the analysis methods of volt-farad characteristics and the scanning probe electrometry were used. The obtained results demonstrate reduction of both stress of the flat zones and the charge density on the silicon-silicon dioxide boundary on the wafers, which were subjected to rapid thermal treatment. The alterations of the surface potential on the wafer area registered by means of the method of scanning probe electrometry correspond to the diminishing operation of the electrons, leaving the surface and serve as justification of the assertion that the properties of the silicon-silicon dioxide boundary improve after rapid thermal treatment of initial silicon wafers owing to the substantial enhancement of the homogeneity of microstructure of the surface layer of silicon dioxide.

Reliability Express Control of the Gate Dielectric of Semiconductor Devices

The key element determining stability of the semiconductor devices is a gate dielectric. As its thickness reduces in the process of scaling the combined volume of factors determining its electrophysical properties increases. The purpose of this paper is development of the control express method of the error-free running time of the gate dielectric and study the influence of the rapid thermal treatment of the initial silicon wafers and gate dielectric on its reliability.The paper proposes a model for evaluation of the reliability indicators of the gate dielectrics as per the trial results of the test MDS-structures by means of applying of the ramp-increasing voltage on the gate up to the moment of the structure breakdown at various velocities of the voltage sweep with measurement of the IV-parameters. The proposed model makes it possible to realize the express method of the reliability evaluation of the thin dielectrics right in the production process of the integrated circuits.On the basis of this method study of the influence of the rapid thermal treatment of the initial silicon wafers of the KEF 4.5, KDB 12 wafers and formed on them by means of the pyrogenic oxidation of the gate dielectric for the error-free running time were performed. It is shown, that rapid thermal treatment of the initial silicon wafers with their subsequent oxidation results in increase of the error-free running time of the gate dielectric on average from 12.9 to 15.9 years (1.23 times greater). Thermal treatment of the initial silicon wafers and gate dielectric makes it possible to expand the error-free running time up to 25.2 years, i.e.1.89 times more, than in the standard process of the pyrogenic oxidation and 1.5 times more, than under application of the rapid thermal treatment of the initial silicon wafers only.

Use of atomic force microscope for the synthesis of GaAs/AlGaAs heterostructure base one-dimensional structure

Electron transport in low-dimensional structures is often studied using semiconductor heterostructures with two-dimensional electron gas in which insulating regions separating the conducting channel from the gates are synthesized using one of available methods. These structures are distinguished by the high quality of the initial wafers and the necessity to change the surface topology during the study, this making photolithography ineffective. In this work we analyze the technology of insulating grooves that uses atomic force microscope, i.e. the pulse force nanolithography, which allows either treating single samples or forming narrow and deep grooves on semiconductor surfaces to provide good insulation. The experimentally measured transport characteristics of the nanostructures produced using this method confirm channel conductance quantization and the absence of large quantities of introduced defects.

Comparative study of impurities in lithium tantalite and lithium niobate

S 38677 The point defects in ferroelectrics may influence the physical properties of phononic crystals LiTaO3 (LT) and LiNbO3 (LN). The initial wafers, periodically poled (PP) structures of LT with 1-mm-domains, and PP-LN with 0.45-mm-domains are investigated. Photoluminescence (PL) is taken at room temperature 310-nm -excitation. The slit width in optical spectrometer is set to 1 nm. The PL spectra of LT reveal multiple impurities including Fe + ,W, Th, Cs, Kr, Cu, Xe. Unlike PL from LN, there are no lines of the F-center, Ar and some other elements. The intensities of PL-lines in both LT and LN demonstrate a saw-type periodicity along the direction normal to the Z-axis. For instance, the PL line of Fe + defect in LT varies ± 15% with periodicity about 200 ± 40 nm. In the case of PP LT phononic crystals, the difference in Fe + line amplitude remains about the same; however, the periodicity becomes equal to a ferroelectric domain length of 1 mm. There is a difference between the two periodicities of charged defects in PP-LT and PP-LN; the positions of maxima in PL-lines are close to the interdomain walls in PP-LN, but it is not the case for PP-LT. Possible practical applications are discussed.

HVPE homo-epitaxial growth of GaN on porous substrates

The results of experiments on homo-epitaxial growth by hydride vapor phase epitaxy (HVPE) of GaN films on free-standing porous substrates with closed surface porosity are presented. In the course of the studies, we observed a phenomenon of pore–dislocation reaction, which resulted in segmentation and pinning of dislocations within the porous layer in the substrate. This effect gives one an ability to control dislocation propagation on the level of collective effects, when interrelated processes take place, which involve the whole ensemble of structural defects, such as point defects (vacancies), linear defects (dislocations), and volume defects (vacancy associates and pores). As a result of the studies, threading dislocation density was reduced from 5 × 106 cm−2 in the initial free-standing wafers down to 105 cm−2 in the films grown on substrates with the nano-porous structure.

Genesis of initial defects in the process of monocrystalline silicon oxidation with subsequent scribing

The type, density, and distribution of defects in initial and oxidated monocrystalline silicon wafers were studied by modern methods. It was established that disordered silicon and stacking faults are basic defects in near-surface layers of oxidated monocrystalline silicon. It was shown that stacking faults are generated during the oxidation process, and the mechanism of their formation is connected with the defective layered structure of initial silicon wafers. It was established that defects of layered heterogeneity, on the one hand, lead to the formation of stacking faults and, on the other hand, prevent their propagation to the wafer bulk.

Study of the Mechanisms of Oxygen Precipitation in RTA Annealed Cz-Si Wafers

In this paper, the influence of the rapid thermal annealing of single crystalline Cz-Si wafers on the evolution of the concentration of interstitial oxygen as well as oxygen in precipitated oxide phase was investigated by infrared spectroscopy. The wafers were preliminary furnace annealed to create the precipitate seeds. The concentration of interstitial oxygen was shows to decrease considerably as a result of annealing during up to 40 min together with the growth of the concentration of precipitated oxygen. This effect depended on the purity and defect structure of initial wafers. The kinetic model was developed to account for the observed effects based on the modification of the solubility level for interstitial oxygen induced by defects as well as its diffusivity. Obtained results of simulation agree well with the experimental data.

Electron field emission from nanostructured surfaces of GaN and AlGaN

AbstractThe possibility of high frequency electromagnetic wave generation by field emission based devices has great interest. The wide bandgap materials GaN and AlGaN are very promising for these applications due to low electron affinity and the existence of satellite valleys in conduction band. The results of investigations of the peculiarities of electron field emission from nanostructured surfaces of GaN and AlGaN are presented. Multilayer GaN and AlGaN structures with various levels of layer doping on sapphire and bulk GaN substrates were used as initial wafers. The surface of the upper layers was nanostructured by photoelectrochemical etching in water solution of KOH. Intensive electron field emission into vacuum was observed and explained by low electron affinity and electric field enhancement on surface nanowires. A decrease of the slope in the Fowler‐Nordheim characteristics was revealed. The changing slope suggests a lowering of effective work function. It is caused by electron heating and transfer into an upper satellite valley with lower electron affinity. A theory was developed for the observed phenomena and interpretation of results. It is baseed on electron intervalley transition upon heating and on energy band reconstruction of the surface of the nanowires due to quantum size‐confinement effect. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

P-i-n structures based on high-ohmic gettered gallium arsenide for α particle detectors

It is shown that p-i-n detectors of α particles can be created using high-ohmic (n ∼ 1012 cm−3) gallium arsenide obtained through lanthanide gettering of a low-ohmic (n ∼ 1015 cm−3) initial material wafers.

Comparison of SiGe Virtual Substrates for the Fabrication of Strained Silicon-on-Insulator (sSOI) Using Wafer Bonding and Layer Transfer

Different methods of preparing sSOI wafers have been analyzed. The initial virtual substrate wafers are characterized by a 17 - 20 nm thick strained silicon layer grown either on a thick relaxed SiGe layer on a graded buffer or on a thin SiGe buffer relaxed by He implantation. Bonding and layer transfer experiments using different oxide layers proved that strained silicon layers are completely transferred if designed PE-CVD oxide layers were used. For both types of virtual substrates the oxide layers are deposited on top of the strained silicon and bonded to non-oxidized (blank) silicon wafers. A perfect layers transfer is obtained for virtual substrates having thick SiGe buffer layers (type A) even at 350ºC, while annealing at 450ºC is required for substrates with thin SiGe buffer layers (type B). The lower annealing temperature for substrates of type A is caused by the lower activation energy for blistering. The hydrogen implantation is here into the SiGe. For type B substrates the hydrogen implantation is into the underlying Si requiring a higher temperature for layer splitting (higher activation energy for Si).

Formation of the Buried Insulating Si&lt;sub&gt;x&lt;/sub&gt;N&lt;sub&gt;y&lt;/sub&gt; Layer in the Region of Radiation Defects Created by Hydrogen Implantation in Silicon Wafer

The radiation defects in 10 Ω⋅cm p-type and 4.5 Ω⋅cm n-type Cz Si were created at depth of 0.8-1 µm using 100 keV 2⋅1016 at/cm2 hydrogen implantation at room temperature. Then the introduction of nitrogen into silicon and its diffusion were carried out at different thermodynamic conditions. Finally, the samples were vacuum annealed at 800 oС during 2 h. The state of sample surfaces was studied by SEM. The depth and thickness of SixNy layer and also defect numbers were estimated by RBS method in the channeling mode. The electrical properties of the obtained structures were characterized by the transversal conductance measurements with the keep of a standard LCR-meter at a frequency of 1 MHz using the two-probe method. Our experiments have shown that the above-described method enables one to form the buried SiхNy layer with dielectric properties and the number of defects and nitrogen atoms on the silicon surface and in the near-surface region are comparable with those for the initial silicon wafers.

Electrophysical properties of GaAs layers and the characteristics of fast particle GaAs detectors

Results of complex experiments aimed at finding a relationship between the properties of initial GaAs single-crystal wafers and epitaxial films and the threshold spectrometric characteristics of ionizing radiation detectors are reported.