Thermal Oxidation Of Silicon Research Articles

Оптические свойства тонких пленок SiO-=SUB=-x-=/SUB=- (x<2), полученных обработкой термического диоксида кремния в водородной плазме

Using the methods of ellipsometry, quantum chemical modeling, and photoluminescent spectroscopy, the optical properties and composition of thin films of thermal silicon oxide processed in a hydrogen electron-cyclotron resonance plasma are studied. It has been established that treatment of films in plasma leads to their depletion in oxygen and the formation of non-stoichiometric oxide SiOx <2. By comparing the experimental spectral dependence of the refractive index with the theoretically calculated from the first principles, the values ​​of the parameter x in the obtained SiOx films are determined. It was shown that an increase in the processing time of thermal SiO2 in hydrogen plasma leads to an increase in the refractive index of the film, as well as the degree of depletion of the film with oxygen. For the studied films, the dependence of the value of the parameter x on the treatment time in a hydrogen plasma is constructed.

Crystalline characteristics and solar-blind photodetecting performances of β-Ga2O3 film grown on silicon thermal oxide wafer using an EBV method

With an EBV technique and post-annealing method, solar-blind photodetectors of β-Ga2O3 film were fabricated on silicon thermal oxide wafers.

One-step growth of wafer-scale monolayer tungsten disulfide via hydrogen sulfide assisted chemical vapor deposition

Wafer-scale monolayer WS2 has been widely investigated. Here, we report a repeatable and low-cost one-step chemical vapor deposition method for the direct growth of a 4-in. monolayer WS2 film on a thermal oxide silicon wafer by using WO3 and H2S gas as precursors. H2S gas exhibits a high vulcanization ability and can effectively reduce the growth temperature of WS2 to 825 °C. The growth process follows a self-limiting growth to form a monolayer polycrystalline film, which is merged via many stable small-angle grain boundaries. The wafer-scale monolayer WS2 film shows uniform and high-quality electrical properties. This method helps promote the future production and application of wafer-scale monolayer sulfide.

Permanent Stiffness Reduction by Thermal Oxidation of Silicon

Stiffness in compliant micro mechanisms can negatively affect performance. Current methods for stiffness reduction in micro electro mechanical systems (MEMS) consume power, have a large footprint or are relatively complex to manufacture. In this paper stiffness is reduced by static balancing. A building block commonly used for stiffness reduction in large scale compliant mechanisms is made compatible with MEMS. Preloading required to create negative stiffness is obtained from residual film stress by thermal oxidation of silicon. Instead of buckling a plate spring by moving its end points, a SiO2 film 1900 nm to 2500 nm thick will stretch micro-beams 24 $\mu $ m wide, while the end points are fixed. To show efficacy of our method, the building block is coupled with a simple linear stage. However, the building block can readily be combined with other compliant micro mechanisms to reduce their stiffness. Statically balanced MEMS will enable novel designs in low-frequency sensor technology, low-frequency energy harvesting and pave the way to autonomous micro-robotics. We show a stiffness reduction of a factor 9 to 46. The balancing effect remained after SiO2 removal, due to plastic deformation of the beams. [2019-0023]

Passivation of Detector‐Grade Float Zone Silicon with Atomic Layer Deposited Aluminum Oxide

Silicon radiation and particle detectors are traditionally passivated with thermal silicon dioxide. It has been shown that aluminum oxide (Al2O3) films provide better surface passivation due to their high negative charge, but studies on Al2O3 surface passivation are usually performed on low‐resistivity substrates. Herein, the passivation of high‐resistivity, detector‐grade float zone silicon (FZ‐Si) with Al2O3 is studied, with a specific emphasis on the effect of post‐annealing temperature on carrier lifetimes and film properties. It is confirmed that Al2O3 provides excellent surface passivation also on high‐resistivity FZ‐Si substrates, with a low interface defect density of around (2–4) × 1011 cm−2 eV−1 and a high negative oxide charge of 1 × 1012 to 3 × 1012 q cm−2, when post‐annealed at temperatures of up to 450–500 °C. In addition, high‐resistivity samples are studied for the phenomenon of bulk lifetime degradation occurring at typical post‐annealing or metal sintering temperatures, which has been reported for low‐resistivity FZ‐Si. At post‐annealing temperatures of >500 °C, reduced bulk lifetimes are observed if the substrates did not receive high‐temperature treatment prior to surface passivation. Furthermore, it is noticed that n‐type samples exhibit lower bulk lifetimes even when a high‐temperature treatment is performed, which indicates a connection between FZ‐Si bulk lifetime degradation and doping type.

Varying internal parameters in the thermal silicon oxidation

Key parameters of the Arrhenius relation governing the oxide growth during the thermal oxidation of silicon have been found to depend on oxide thickness. The activation energy (Ea) has been found to decrease from 2.22 to 1.87 eV with increasing oxide thickness from 6.5 to 13 nm, whereas the reference formation rate R0 of silicon oxide decreases from 24.5 to 20.6 pm/s in the same thickness interval. The combination of these findings gives a linear course of the logarithm of reference rate vs. activation energy. In other words, the reference rate of oxide formation obeys an exponential dependence on activation energy. Calculations give the relation R0 [pm/s] = 0.916 exp. (11.05 Ea), with Ea in eV. The results have been obtained by a four-step-program.

Stress Characterization of the Interface Between Thermal Oxide and the 4H-SiC Epitaxial Layer Using Near-Field Optical Raman Microscopy.

Stresses induced in the silicon carbide (SiC) epitaxial layer near the interface between thermal silicon oxide and 4H-SiC epitaxial substrate were measured using a near-field optical Raman microscope equipped with a hollow pyramid probe (aperture size: approximately 250 nm). The E2 phonon was observed to undergo a 0.17 cm-1 redshift owing to reduction in oxide-layer thickness from 300 nm to 0 nm; this result was compared against that obtained using a standard Raman microprobe sans the pyramidal probe. The result indicates that the epitaxial layer near the SiO2-4H-SiC interface was maintained under a constant tensile stress of the order of 50 MPa. This agrees well with the result obtained using the finite element method (FEM). Based on results obtained using the said Raman microprobe and Fourier transform infrared (FT-IR) measurements, use of an inhomogeneity formation model at the SiO2-4H-SiC interface has been proposed in this study.

Model for Thermal Oxidation of Silicon

Nanometer-thick silicon oxide films are needed for miniaturization and increase in the working rate of electronic devices. Interpretation of the initial stages of silicon oxidation is necessary for fabrication of such structures. A theoretical model of the thermal oxidation of thin silicon monolayers that takes into account an increase in the stress in the transition (oxide–substrate) layer due to oxygen accumulation therein is proposed.

High resistive state retention in room temperature solution processed biocompatible memory devices for health monitoring applications

AbstractWearable and bio-implantable health monitoring applications require flexible memory devices that can be used to locally store body vitals prior to transmission or to support local data processing in distributed smart systems. In recent years, non-volatile resistive random access memories composed of oxide-based insulators such as hafnium oxide and niobium pentoxide have attracted a great deal of interest. Unfortunately, hafnium and niobium are not low-cost materials and may also present health challenges. In this work, we have explored the alternative of using titanium dioxide as the insulating oxide using a low-cost solution-phase deposition process. Aqueous sol deposited thin films were deposited on standard RCA-cleaned commercial thermal silicon dioxide (500 nm) wafer (500 µm). Patterned bottom contacts Cr/Au (∼200/300 Å) using shadow masks were deposited on the substrate using successive DC sputtering, and thermal evaporation, respectively at 5 X 10-6 Torr. A sol was prepared using titanium (IV) butoxide as precursor hydrolysed under water and ethanol to form a colloidal solution (sol) at 50°C under constant stirring. Powder X-Ray Diffraction (PXRD) scans of calcined (from sol at 750°C) nanoparticles show a mixture of anatase and rutile phases, confirming the composition of the material. The sol was slowly cooled to room temperature before being spin coated at low rotational speeds on to the substrate in multiple steps involving several spin coating and drying steps to form a uniform film. Top contacts (Ag) of thickness (∼500 Å) were deposited on the sol-deposited thin films using thermal evaporation. The resulting devices were coated with a thick layer of polydimethylsiloxane (PDMS) using a 10:1 ratio of base elastomer and curing agent respectively. After drying the PDMS, resistance measurements were carried out. A high resistance state was detected prior to electroforming in the air at ∼5 MΩ which remains nearly unchanged (∼4.3 MΩ) when dipped in a ∼7.4 pH phosphate buffer solution (equivalent to human blood’s pH (reference average value ∼7.4 pH)). Unencapsulated devices (UM1) were further characterized in air using a Keithley 4200-SCS semiconductor parameter analyzer in dual sweep mode to observe repeatable hysteresis behavior with a large difference between trace and retrace R-V characteristics (∼50±3% over a pristine device), which compares favorably with recent data in the literature on high-performance sputtered TiO2 memristors. Unchanged retention ratio using biocompatible device materials and encapsulation suggests that these devices can be used for biomedical implantable sensor electronics.

Engulfment control of platinum nanoparticles into oxidized silicon substrates for fabrication of dense solid-state nanopore arrays

We found that platinum (Pt) nanoparticles, upon annealing at high temperature of 1000 °C, are engulfed into amorphous fused-silica or thermal oxide silicon substrates. The same phenomenon was previously published for gold (Au) nanoparticles. Similar to the Au nanoparticles, the engulfed Pt nanoparticles connect to the surface of the substrates through conical nanopores, and the size of the Pt nanoparticles decreases with increasing depth of the nanopores. We explain the phenomena as driven by the formation of platinum oxide by reaction of the platinum with atmospheric oxygen, with platinum oxide evaporating to the environment. We found that the use of Pt provides much better controllability than the use of Au. Due to the high vapor pressure of platinum oxide, the engulfment of the Pt nanoparticles into oxidized silicon (SiO2) substrates is faster than of Au nanoparticles. At high temperature annealing we also find that the aggregation of Pt nanoparticles on the substrate surface is insignificant. As a result, the Pt nanoparticles are uniformly engulfed into the substrates, leading to an opportunity for patterning dense nanopore arrays. Moreover, the use of oxidized Si substrates enables us to precisely control the depth of the nanopores since the engulfment of Pt nanoparticles stops at a short distance above the SiOx/Si interface. After subsequent etching steps, a membrane with dense nanopore through-holes with diameters down to sub-30 nm is obtained. With its simple operation and high controllability, this fabrication method provides an alternative for rapid patterning of dense arrays of solid-state nanopores at low-cost.

Luminescence of SiO2 layers on silicon at various types of excitation

We present a comparative analysis of Cathodoluminescence (CL), Photoluminescence (PL) and Electroluminescence (EL) spectra measured on Si-SiO2 structures with various thicknesses of SiO2 layer. The spectral distributions of the luminescence depend on the technology of the SiO2 layer formation, on its thickness and the type of excitation. The analysis indicates that CL and EL spectra of the Si-SiO2 structures, grown by thermal oxidation of silicon in a "dry" oxygen, are almost identical in spectral composition. The PL of the Si-SiO2 structures provides additional information about the optically active centers in the SiO2 layer. The PL spectra allow tracking changes in the SiO2 layer while increasing its thickness in more detail than the EL and CL. We suggest that there is a substantial difference in the excitation mechanisms of luminescence by electrons (CL and EL) and photons (PL). Therefore, in general case, the luminescence centers identified in PL cannot be directly used for the interpretation of CL and EL spectra. However, analysis of the PL and EL spectra before and after the field degradation of the Si-SiO2 structure as well as analysis of PL spectra of the oxide layers formed by various technologies shows that the model of luminescence centers proposed for red photoluminescence is acceptable for the red luminescence excited by electrons in Si-SiO2 structure.

Poole–Frenkel Effect and the Opportunity of Its Application for the Prediction of Radiation Charge Accumulation in Thermal Silicon Dioxide

It is proposed that the Poole–Frenkel effect be applied to predict radiation-induced charge accumulation in thermal silicon dioxide. Various conduction mechanisms of thermal silicon dioxide are considered, the conditions of the appearance of the Poole–Frenkel effect in it are determined, and the characteristics of donor centers participating in Poole–Frenkel electrical conductivity are calculated. A donor center level at an energy of 2.34 eV below the conduction-band bottom is determined and the concentration of ionized donor centers of 1.0 × 109 cm–3 at 400 K and a field strength of 10 MV/cm is found. It is concluded that the Poole–Frenkel effect can be applied not for prediction of the absolute value of the radiation-induced charge but for comparison of the samples in terms of the ability to accumulate it.

Experimental Extraction of the Charge Centroid of Holes Trapped in Metal–Oxide–Nitride–Oxide–Semiconductor Memories

In metal-oxide-nitride-oxide-silicon (MONOS)-type memories with an ultrathin tunnel oxide film, electrons and holes are injected from the silicon substrate to the silicon nitride charge trapping film owing to the quantum mechanical tunneling and are trapped in the film. In the previous studies, the constant-voltage carrier injection method has been used to determine the charge centroid of trapped carriers [1-4]. This method requires the application of an auxiliary pulse before injecting carriers. To determine the auxiliary pulse level, another set of measurements of the programming and erasing characteristics is needed in preliminary step. Such a sequence would generate an error in the charge centroid estimation due to the variation of the programming and erasing characteristics among individual memory elements. Therefore, we have developed the constant-current carrier injection (CCCI) method which does not require the application of the auxiliary pulse and any additional measurements [5]. The CCCI method is effective to obtain the accurate charge centroid of trapped carriers. On the other hand, these two methods can be used only in the case that the number of carriers passing through the silicon nitride film during the carrier injection is negligible as compared to that of carriers trapped in the nitride film. Therefore, neither of the two methods is usable with high gate voltages which induce a large number of carriers passing through the nitride film. In the present work, in order to obtain the charge centroid of holes trapped in the silicon nitride film at high gate voltages, we proposed a method based on the analysis of Fowler-Nordheim (F-N) tunneling current through the blocking oxide film. We determined the charge centroid and the density of holes trapped at high gate voltages by means of the proposed method and the CCCI method. Memory capacitors with the blocking oxide (SiOx)/silicon nitride/tunnel oxide stacked films were used in this work. A tunnel oxide film of 2.4 nm in thickness was grown by rapid thermal oxidation of silicon. A 30.4-nm-thick silicon nitride film was deposited at 600 °C in an LPCVD reactor. A blocking oxide film of 17.2 nm in thickness was grown at 400 °C using a PECVD method. The thickness of the blocking oxide film was designed to be sufficiently thick for electrons to obey the F-N tunneling mechanism and to gain a high kinetic energy in the oxide film. High-energy electrons entering the nitride film from the blocking oxide film would pass through the nitride film without interaction with nitride trap centers. Figure 1 shows the charge centroid of holes trapped in the nitride film, which was obtained by means of the analysis of F-N current under negative gate bias and the CCCI method. The charge centroid of trapped holes was initially located near the middle of the nitride film, and moved toward the blocking oxide-nitride interface as the flat-band voltage shift ΔVfb,h increased. Finally, the charge centroid reached 2.3 nm from the blocking oxide-nitride interface after the ΔVfb,h value was saturated. We also have estimated the density of trapped holes. A maximum of the density of trapped holes was determined to be 1.0×1013 holes/cm2 by means of the analysis of F-N tunneling current. The proposed method is useful to determine the maximum density of trapped holes which the charge trapping film in MONOS-type memories can achieve. Acknowledgment- We would like to express gratitude to S. R. A. Ahmed, K. Kato and H. Koizumi for their valuable discussions. This work was partly supported by JSPS KAKENHI Grant Number 26420280.

Fabrication of seeded substrates for layer transferrable silicon films**Project supported by the National Natural Science Foundation of China (Grant No. 11374313) and the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 11504392).

The layer transfer process is one of the most promising methods for low-cost and highly-efficient solar cells, in which transferrable mono-crystalline silicon thin wafers or films can be produced directly from gaseous feed-stocks. In this work, we show an approach to preparing seeded substrates for layer-transferrable silicon films. The commercial silicon wafers are used as mother substrates, on which periodically patterned silicon rod arrays are fabricated, and all of the surfaces of the wafers and rods are sheathed by thermal silicon oxide. Thermal evaporated aluminum film is used to fill the gaps between the rods and as the stiff mask, while polymethyl methacrylate (PMMA) and photoresist are used as the soft mask to seal the gap between the filled aluminum and the rods. Under the joint resist of the stiff and soft masks, the oxide on the rod head is selectively removed by wet etching and the seed site is formed on the rod head. The seeded substrate is obtained after the removal of the masks. This joint mask technique will promote the endeavor of the exploration of mechanically stable, unlimitedly reusable substrates for the kerfless technology.

Knudsen pump produced via silicon deep RIE, thermal oxidation, and anodic bonding processes for on-chip vacuum pumping

This work describes the fabrication and evaluation of the Knudsen pump for on-chip vacuum pumping that works based on the principle of a thermal transpiration. Three AFM (atomic force microscope) cantilevers are integrated into small chambers with a size of 5 mm × 3 mm × 0.4 mm for the pump’s evaluation. Knudsen pump is fabricated using deep RIE (reactive ion etching), wet thermal oxidation and anodic bonding processes. The fabricated device is evaluated by monitoring the quality (Q) factor of the integrated cantilevers. The Q factor of the cantilever is increased from 300 –1150 in cases without and with a temperature difference approximately 25 °C between the top (the hot side at 40 °C) and bottom (the cold side at 15 °C) sides of the fabricated device, respectively. The evacuated chamber pressure of around 10 kPa is estimated from the Q factor of the integrated cantilevers.

Electrical characterization of amorphous Al2O3 dielectric films on n-type 4H-SiC

We report on the electrical properties of Al2O3 films grown on 4H-SiC by successive thermal oxidation of thin Al layers at low temperatures (200°C - 300°C). MOS capacitors made using these films contain lower density of interface traps, are more immune to electron injection and exhibit higher breakdown field (5MV/cm) than Al2O3 films grown by atomic layer deposition (ALD) or rapid thermal processing (RTP). Furthermore, the interface state density is significantly lower than in MOS capacitors with nitrided thermal silicon dioxide, grown in N2O, serving as the gate dielectric. Deposition of an additional SiO2 film on the top of the Al2O3 layer increases the breakdown voltage of the MOS capacitors while maintaining low density of interface traps. We examine the origin of negative charges frequently encountered in Al2O3 films grown on SiC and find that these charges consist of trapped electrons which can be released from the Al2O3 layer by depletion bias stress and ultraviolet light exposure. This electron trapping needs to be reduced if Al2O3 is to be used as a gate dielectric in SiC MOS technology.

Эффект Пула--Френкеля и возможность его применения для прогнозирования радиационного накопления заряда в термическом диоксиде кремния

AbstractIt is proposed that the Poole–Frenkel effect be applied to predict radiation-induced charge accumulation in thermal silicon dioxide. Various conduction mechanisms of thermal silicon dioxide are considered, the conditions of the appearance of the Poole–Frenkel effect in it are determined, and the characteristics of donor centers participating in Poole–Frenkel electrical conductivity are calculated. A donor center level at an energy of 2.34 eV below the conduction-band bottom is determined and the concentration of ionized donor centers of 1.0 × 10^9 cm^–3 at 400 K and a field strength of 10 MV/cm is found. It is concluded that the Poole–Frenkel effect can be applied not for prediction of the absolute value of the radiation-induced charge but for comparison of the samples in terms of the ability to accumulate it.

Hydrogen passivation of silicon/silicon oxide interface by atomic layer deposited hafnium oxide and impact of silicon oxide underlayer

HfO2 synthesized by atomic layer deposition (ALD) can be used as a passivation material for photodetectors. This paper shows a significant reduction of density of interface traps at the Si/SiO2 interface using ALD HfO2. This is explained by a chemical passivation effect due to presence of hydrogen from water used in the ALD process. Furthermore, ALD HfO2 layers appear negatively charged which generate an additional field effect passivation. The impact of the SiO2 underlayer is also discussed by comparing a chemical silicon oxide to a standard thermal silicon oxide. It is shown that chemical silicon oxide can act as a reservoir of hydrogen atoms which helps to reduce the density of defects close to the Si/SiO2 interface. This result demonstrates the importance of the surface preparation before the ALD of HfO2 in the passivation scheme. Finally, this work shows the correlation between negatively charged defects and Si–O–Hf bonds at the SiO2/HfO2 interface. A passivation stack composed of chemical oxide permits to reach both a low density of interface traps (∼1.0 × 1011 cm−2 eV−1) and a negative charge density (∼−1.0 × 1011 cm−2). This stack provides both chemical and field effect passivation of the silicon surface.

Three-dimensional vertical Si nanowire MOS capacitor model structure for the study of electrical versus geometrical Si nanowire characteristics

Three-dimensional (3D) Si surface nanostructuring is interesting towards increasing the capacitance density of a metal-oxidesemiconductor (MOS) capacitor, while keeping reduced footprint for miniaturization. Si nanowires (SiNWs) can be used in this respect. With the aim of understanding the electrical versus geometrical characteristics of such capacitors, we fabricated and studied a MOS capacitor with highly ordered arrays of vertical Si nanowires of different lengths and thermal silicon oxide dielectric, in comparison to similar flat MOS capacitors. The high homogeneity and ordering of the SiNWs allowed the determination of the single SiNW capacitance and intrinsic series resistance, as well as other electrical characteristics (density of interface states, flat-band voltage and leakage current) in relation to the geometrical characteristics of the SiNWs. The SiNW capacitors demonstrated increased capacitance density compared to the flat case, while maintaining a cutoff frequency above 1 MHz, much higher than in other reports in the literature. Finally, our model system has been shown to constitute an excellent platform for the study of SiNW capacitors with either grown or deposited dielectrics, as for example high-k dielectrics for further increasing the capacitance density. This will be the subject of future work.

Three-Component Model of an Effective Medium for Determining the Composition of Layers on Silicon Wafers

A proposed model of an effective medium in which a Maxwell–Garnett matrix medium is filled with a Bruggeman medium is used to solve inverse problems of multi-angle ellipsometry to determine the composition of transition layers surrounding a layer of thermal silicon dioxide on a silicon substrate. The volume filling factors of the layer reflect correctly possible structural transformations during the oxidation of crystalline silicon.