Oxide Removal Process Research Articles

Effect of Post Plasma Oxidation on Ge Gate Stacks Interface Formation

One of the key challenges for Ge gate stack is to achieve an improved interface quality between Ge and the high-K dielectric. In order to overcome this limitation, various interface treatments like ozone pre-gate treatment and ozone ambient annealing (1), nitridation of Ge surface (2),formation of a GeO2 layer between Ge and high-K dielectric using ECR plasma technique (3) and formation of an ultra-thin SiO2/GeO2bilayer have been tried. It has recently been reported that slot plane antenna(SPA) microwave plasma treatment helps to improve the EOT and enhances the oxide quality by reducing impurities and leakage current when the dielectric is exposed during or after deposition (4). Moreover SPA oxidation possesses the unique property of having low electron temperature, which makes it a very low damage process compared to other techniques,either inductively coupled plasma(ICP) and electron cyclotron resonance(ECR) plasma (5). In this study we investigated the impact of SPA plasma oxidation (SPAO) treatment in improving the interface quality when MOS capacitors were fabricated on 300mm p-type Ge substrates. SPAO plasma treatments were performed at different steps in the high-k deposition process. The substrate was initially subjected to a dry chemical oxide removal (COR) process. Subsequently, three different sets of samples were prepared with the exposure of SPAO plasma at following locations (Fig.1): CASE-1: SPAO plasma treatment after Al2O3(1nm)/ZrO2(3.5nm) deposition; CASE-2: SPAO plasma treatment was carried out in between Al2O3(1nm) and ZrO2(3.5nm) deposition; CASE-3: the Ge substrate was exposed to SPAO plasma treatment after COR and prior to Al2O3(1nm)/ ZrO2(3.5nm) layer deposition. Al2O3(1nm) and ZrO2(3.5nm) layers were deposited by atomic layer deposition. Capacitance-voltage at multi-frequencies,current-voltage and conductance measurements were performed at room temperature. Parameters like flatband voltage (Vfb), equivalent oxide thickness(EOT), interface state density(Dit),and leakage current were estimated accurately after quantum mechanical corrections and eliminating the series resistance effect. As shown in Fig. 2 lowest fast interface state density is achieved when SPAO plasma treatment was performed after Al2O3 and prior to ZrO2 deposition (CASE-2). A comparable Dit is also observed when plasma exposure was done after the entire gate stack deposition (CASE-1) (Fig.2). From different experimental results significant degradation to both the dielectric quality and interface was observed when SPAO is performed just after COR (CASE-3).

Analysis of Pulse-Reverse Nb Electropolishing with H2so­­ 4 for Srf Cavities

The performance of superconducting radiofrequency (SRF) cavities is greatly affected by the topography of the interior surface, so it is imperative that the surface be clean metal as smooth as possible. Currently, the 1:10 volume ratio HF (49%) and H2SO4 (96%) electrolyte was widely used for high field SRF cavity production, the problem with using HF is that it is dangerous both to people and to the environment. A new method that has been developed to smooth the surface is pulse reverse electropolishing (EP). This method uses aqueous H2SO­­ 4 as the electrolyte and alternating anodic and cathodic pulses to oxidize the niobium (Nb) and then remove the oxide from the surface [1]. Previous studies have shown that pulse reverse EP effectively polishes the surface of Nb SRF cavities [1,2].. In order to better understand polishing mechanism and optimize the operating parameter for cavity production, systematic electrochemical experiments have been carried out to further explore the oxide removal process, the effect of positive and negative pulse duration, pulse structure, off time between positive and negative pulses, concentration of H2SO­­ 4, and determine optimum polishing parameters for reliable Nb SRF cavity production process, the results will be reported.

Simultaneous desulfurization and denitrification of flue gas by catalytic ozonation over Ce–Ti catalyst

A novel oxidation-removal process for simultaneous removal of NOX and SO2 was developed, which utilized the catalytic ozonation over Ce–Ti catalyst and assisted with a glass made ammonia-based washing tower. Compared with conventional flue gas treatment, the present method acquires non-secondary pollution, minimal waste production and low operating costs. The main byproducts, ammonia sulfate and nitrate, are important fertilizers and industrially raw materials. A maximum removal of 95% for NOX and nearly complete SO2 removal were obtained with the assistance of washing tower under the following experimental conditions: O3 concentration, 8.5mg·L−1; flow of oxidant mixtures, 100mL·min−1; simulated flue gas temperature, 120°C; H2O flow, 2.4mL·min−1; and total gas flow, 400mL·min−1. The reaction mechanisms are discussed, and the final oxidation products are characterized. The experimental results show that the OH radicals from catalytic ozonation have an oxidation-removal effect of NOX and SO2. The multipollutant capacity of the washing tower is largely enhanced with the Ce–Ti catalyst. And the present method performs better stability with the assistance of the washing tower.

(Invited) Passivation Schemes for Ge High-K Metal Gate MOSFETs on Si for VLSI Production

As Si Metal Oxide Semiconducting Field Effect Transistors (MOSFETs) have continued to scale Short Channel Effects (SCE) have become exacerbated by the inability to continue scaling the Equivalent Oxide Thickness (EOT) of the device significantly beyond what was realized with the introduction of High K Metal Gate (HKMG) MOSFETs at the 45nm technology node. Since EOT scaling has not kept pace with the gate length (Lg) scaling needed to continually increase the transistor drive current, device makers have instead elected to introduce FinFET and Tri-Gate transistors with inherently better electrostatic control in order to realize reasonable SCE in the device. High mobility channel materials, such as Ge, are attracting increasing interest due to the possibility of realizing increased performance even without scaling the Lg of the device (1). Ge is particularly attractive for use as a channel material for P-type MOSFETs (PMOSFETs) due to its high hole mobility and Si processing compatibility. In fact, we have demonstrated experimental PMOSFET devices with hole mobilities significantly higher than what can be obtained on Si, Fig. 1. However, a significant remaining challenge to incorporating Ge into VLSI production is obtaining a stable and well-passivated dielectric/semiconductor interface using tooling and substrates compatible with current 300mm Si VLSI High Volume Manufacturing (HVM) in order to achieve reasonable device performance at sub 1nm EOTs (2). In this paper we will report progress on surface passivation and functionalization of Ge channel surfaces, as well as High K dielectric layer growth by Atomic Layer Deposition (ALD) and the resulting electrical properties measured by fabricated MOSFETs and Metal Oxide Semiconducting Capacitors (MOSCAPs). The Ge channel devices were formed on 300 mm Si wafers using Ge grown by an epitaxial process including a graded SiGe buffer layer. We have utilized a TEL CertasTMChemical Oxide Removal (COR) process (3), which uses dry HF and ammonia, rather than traditional wet cleaning, to remove Ge native oxides without damaging or roughening the fragile Ge surface. We have also studied Ge oxide interface layer formation by plasma oxidation using a Slot Plane Array (SPA) antenna (4) utilizing in-line X-ray Photoelectron Spectroscopy (XPS) to measure Ge and high K oxide thickness on monitor wafers fashioned by the same Ge epitaxial process used to make the electrical devices and compared it to the equivalent Si oxidation process, Fig. 2. Various other passivation and interface schemes were investigated and will be discussed, contrasted and compared including ozone oxidation, Al oxide passivation/interface layers, SPA plasma nitridation, and thin amorphous Si passivation layers. We have utilized Hf oxide grown by a previously reported ALD process (5) as the High K dielectric for our devices, and TiN as the metal gate. Our results show that Ge channel devices can be fabricated on 300mm Si substrates using Si VLSI-compatible toolsets and infrastructure and resulting in reasonable device characteristics, Fig. 3. Thus, Ge channel MOSFETs are found to be a promising technology for use in HVM at future VLSI technology nodes.

Direct growth of ZnSe and CdSe on (100) InAs substrates

AbstractZnSe and CdSe layers have been grown on InAs substrates using molecular beam epitaxy (MBE) without the need for a III‐V and II‐VI dual chamber system. This paper reports on the optimisation of a chemical oxide removal process using sulphur passivation. This removes the need for conventional in vacuo oxide removal under As overpressure that is used to prevent the formation of high densities of In droplets. X‐ray and photoluminescence characterisation of the samples confirms single crystal growth. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Simultaneous removal of NOX and SO2 from coal-fired flue gas by catalytic oxidation-removal process with H2O2

A novel oxidation-removal process capable of removing NOX and SO2 simultaneously was proposed, which utilized the injection of OH radicals from H2O2 catalytic decomposition over hematite and assisted with a glass made ammonia-based washing tower. Oxidation experiments were conducted in a quartz reactor within an oil bath. Effects of H2O2 flow, temperature of simulated flue gas, volume ratio and preheated temperature on NOX and SO2 removal efficiencies were investigated. Results indicated that SO2 was cleaned up quite efficiently and the removal efficiency was nearly 100% under all conditions. The NOX removal efficiency depended primarily on H2O2 flow and volume ratio between purged gas and total gas, but temperature of simulated flue gas and preheated temperature had slighter influence on the NOX removal efficiency; The H2O2 flow had a significant interaction with the volume ratio. The ion products in solution were analyzed with ion chromatography (IC), and the material balances for NOX and SO2 were calculated. It showed NOX was removed in the oxidation formation of NO3-, but SO2 was mainly in the formation of SO32-. Results of material balances indicated that the main products of this oxidation-removal process were NO3-, SO32- and SO42-. The reaction pathways of removal of NOX and SO2 with this oxidation-removal process were preliminarily discussed. Meanwhile, compared with air discharge flue gas treatments, the present method had lower initial investment and operating costs.

Simultaneous removal of NOX and SO2 with H2O2 over Fe based catalysts at low temperature

Simultaneous flue gas desulfurization and denitrification are achieved with ˙OH radicals generated from H2O2 catalyzed by Fe based transition metal (Fe, Fe–Al, Fe–Ti, Fe–Si) oxides in the duct, followed by purification with ammonia-based glass made washing tower. The main recovered products are the ammonia nitrate and sulfate, which are important fertilizers. In this oxidation-removal process, 100% SO2 and 74% NOX removal efficiencies are achieved at the simulated flue gas temperature of 120–180 °C under the applied conditions with a space velocity of 36 000 h−1. The experimental results show that the enhancement of Lewis acid benefits the generation of O2 without ˙OH radical production. The increase of Fe3+ bonded with hydroxyl group and points of zero charge value are beneficial to produce ˙OH radicals, thus improving the NOX removal efficiency.

High-Performance Normally-Off ${\rm Al}_{2}{\rm O}_{3}/{\rm GaN}$ MOSFET Using a Wet Etching-Based Gate Recess Technique

This letter reports a normally-OFF Al2O3/GaN gate-recessed MOSFET using a low-damage digital recess technique featuring multiple cycles of plasma oxidation and wet oxide removal process. The wet etching process eliminates the damage induced by plasma bombardment induced in conventional inductively coupled plasma dry etching process so that good surface morphology and high interface quality could be achieved. The fully recessed Al2O3/GaN MOSFET delivers true enhancement-mode operation with a threshold voltage of +1.7 V. The maximum output current density is 528 mA/mm at a positive gate bias of 8 V. A peak field-effect mobility of 251 cm2/V·s is obtained, indicating high-quality Al2O3/GaN interface.

Heterogeneous oxidation of folpet and dimethomorph by OH radicals: A kinetic and mechanistic study

This study investigates the heterogeneous OH oxidation of folpet and dimethomorph, two fungicides identified in the atmosphere of the Champagne-Ardenne region. Kinetic experiments were conducted in the relative mode, using terbuthylazine as a reference compound. The experimental method employed makes use of a simulation chamber coupled to a GC/MS analytical system. Meanwhile, the identification of (4-chlorophenyl)(3,4-dimethoxyphenyl)methanone (CPMPM), a degradation product of the OH oxidation of dimethomorph, is achieved using SPME/GC/MS. Moreover, a degradation mechanism of dimethomorph is proposed, and the heterogeneous OH reactivity of CPMPM is evaluated. The obtained OH reaction rate constants (cm3 molecule−1 s−1) are: kZ-dimethomorph = (2.0 ± 1.2) 10−14, kE-dimethomorph = (1.7 ± 1.2) 10−14, kFolpet = (1.6 ± 0.9) 10−13 and kCPMPM = (1.9 ± 1.0) 10−12. The implicated tropospheric life-times are up to 2 months, which shows that the investigated pesticides are relatively persistent towards oxidation removal processes. CPMPM, the identified product of OH oxidation of dimethomorph, is less persistent with a life time of only 6 days relative to heterogeneous oxidation by OH radicals.

Low temperature oxide desorption in GaAs (111)A substrates

The aim of this work is to study oxide removal processes on GaAs (111) A substrates previous to epitaxial growth. We have studied conventional thermal desorption and processes based on the reduction of surface oxides by deposition of gallium, indium and exposure to atomic hydrogen.We have determined substrate temperatures (Ts) for optimum oxide removal in epi-ready substrates by the different studied processes: Ts=540°C for thermal desorption, Ts=505°C for indium deposition and Ts=400°C for oxide desorption by exposure to atomic hydrogen. All these processes allow for a subsequent good quality epitaxial growth. These results cannot be directly extended to oxide removal in grown samples that have been exposed to air outside the growth chamber. In this case, we have found that only indium deposition and exposure to atomic hydrogen are compatible with regrowth processes.

1/f noise analysis of replacement metal gate bulk p-type fin field effect transistor

The origin of performance difference between gate-first (GF) and replacement metal gate (RMG) fin field effect transistors (FinFETs) is investigated. Although RMG technology has the advantage of low thermal-budget, a 1.5 times lower effective hole mobility is shown for the high-k last (HKL) FinFET. Based on low frequency noise analysis, it is shown that the carrier transport is due to the carrier number fluctuation with correlated mobility fluctuation from the interface states. For HKL FinFETs, about 10 times higher trap density is observed compared to GF and high-k first FinFETs, which is generated during the dummy gate oxide removal process.

Growth of heterostructures on InAs for high mobility device applications

The growth of heterostructures lattice matched to InAs(100) substrates for high mobility electronic devices has been investigated. The oxide removal process and homoepitaxial nucleation depends on the deposition parameters to avoid the formation of surface defects that can propagate through the structure during growth which can result in degraded device performance. The growth parameters for InAs homoepitaxy were found to be within an extremely narrow range when using As4 with a slight increase using As2. High structural quality lattice matched AlAsxSb1−x buffer layer was grown on InAs(100) substrates using a digital growth technique with the AlAs mole fraction adjusted by varying the incident As flux. Using the AlAsxSb1−x buffer layer, the transport properties of thin InAs channel layers were determined on conducting native substrates.

Non-Thermal Plasma and Catalyst System for Simultaneously Oxidizing SO<sub>2</sub> and NO<sub>x</sub>

For the requirements of nitric oxide (NOx) and sulfur dioxide (SO2) removal process in coal-fired power plant, a new non-thermal plasma system combined with catalyst was developed to investigate the effect of parameters such as temperature, atmosphere, residence time, and additives (NH3 and methanol) on NOx and SO2 conversion rate. The results indicated that the new system could greatly promote the NOx conversion rate while it only had a slight influence on the SO2 oxidization rate. Meanwhile, high temperature suppressed the NO oxidization, and promoted the SO2 oxidation. The long residence time was beneficial to the NOx and SO2 oxidization. In the absence of water, the additive of NH3 can improve NO, NOx, and SO2 oxidization rate due to the reactions between NH3 and NOx, or SO2. Contrary to NH3, methonal had a negative effect on NOx and SO2 oxidization.

Development of readout interconnections for the Si-W calorimeter of SiD

The SiD collaboration is developing a Si-W sampling electromagnetic calorimeter, with anticipated application for the International Linear Collider. Assembling the modules for such a detector will involve special bonding technologies for the interconnections, especially for attaching a silicon detector wafer to a flex cable readout bus. We review the interconnect technologies involved, including oxidation removal processes, pad surface preparation, solder ball selection and placement, and bond quality assurance. Our results show that solder ball bonding is a promising technique for the Si-W ECAL, and unresolved issues are being addressed.

Energy dependence of processing and breakdown properties of Cu and Mo

Obtaining basic knowledge of breakdowns is desirable in many fields of physics; however, often the energy absorbed by a breakdown is not known or can vary by large amounts. We have therefore investigated how processing and breakdown properties scale with available energy for two materials, Cu and Mo, in the energy range of about 1 mJ to 1 J. A central result obtained is that there appears to be an optimum energy for processing and thus the highest possible electric field a processed material can sustain without breaking down depends on energy accordingly; what this implies for radio frequency cavity processing is discussed as well. For Cu, both the local field and the field enhancement factor showed only a weak dependence on energy; the average of the local field over the entire energy range investigated was $(9.6\ifmmode\pm\else\textpm\fi{}0.4)\text{ }\text{ }\mathrm{GV}/\mathrm{m}$ at breakdown. For Mo, the local field increased with increasing energy, while the field enhancement factor remained constant at $34\ifmmode\pm\else\textpm\fi{}2$. Finally, a possible explanation of the direct current (DC) processing mechanism---at least in the case of Mo---as an oxide removal process is presented.

The facile formation of silver dendritic structures in the absence of surfactants and their electrochemical and SERS properties

In this work a simple approach to the creation of highly dispersed electrocatalytically active silver microstructured dendrites on indium tin oxide in the absence of any surface modification or surfactant is presented. It is found that the addition of low concentrations of supporting electrolyte to the AgNO 3 solution dramatically influences the morphology of electrodeposited silver which is independent of both the anion and the cation employed. The silver dendrites are characterized by SEM, XRD, XPS as well as by cyclic voltammetry under alkaline conditions. It is found that the surface oxide formation and removal processes are significantly influenced by the microstructured morphology of the silver electrodeposits compared to a smooth macrosized silver electrode. The facile formation of dendritic silver microstructures is also shown to be beneficial for the electrocatalytic oxidation of both formaldehyde and hydrazine and oxygen reduction. The formation of a continuous film of dendritic silver is also investigated for its SERS activity where the connectivity between the individual dendrites is found to be particularly important.

Nanoimprint lithography patterned GaAs templates for site-controlled InAs quantum dots

We report on the development of a soft UV-nanoimprint lithography (UV-NIL) based process to fabricate nanopatterned templates for epitaxy of site-controlled Stranski–Krastanov grown quantum dots. Surface cleaning and chemical native oxide removal processes are analyzed in detail. The quality of the surface is studied by means of scanning electron microscopy, atomic force microscopy and photoluminescence analysis. To evaluate the suitability of the process for fabricating high optical quality site-controlled quantum dots, we have investigated the photoluminescence signal of the near-surface quantum well and overgrown quantum dots. We present the successful growth of optically active, site-controlled InAs quantum dots, both in the ensemble and single-dot regime, by molecular beam epitaxy on UV-NIL patterned GaAs surfaces using only chemical cleaning prior to the growth.

Ga assisted oxide desorption on GaAs(0 0 1) studied by scanning tunnelling microscopy

Native oxide removal on GaAs wafers under conventional thermal desorption causes severe surface degradation. Recently a new method of Ga assisted oxide removal has reported improved initial surface conditions. A precise dosing of Ga is required to optimise the oxide removal, however the effects of alternate temperatures on the desorption process effects the reaction kinetics. By using selected bias imaging, scanning tunnelling microscopy (STM) can be used to probe the underlying bulk whilst the native oxide is still present. Hence the effects of oxide removal on the surface can be identified during the native oxide desorption. By comparing Ga assisted oxide removal on both vicinal and off cut samples, the Ga adatom kinetics are shown to underpin the oxide removal process and a sample temperature in excess of 500 °C is necessary to optimise the procedure.

Relation between surface roughness and number of cathode spots of a low-pressure arc

A remarkable characteristic of the cathode spot of a low-pressure arc is that it can remove an oxide layer preferentially. Recently, cathode spots of a low-pressure arc have been used for cleaning metal oxide surfaces before thermal spraying or surface modification. Nevertheless, few reports have described the cathode spot movement or the oxide removal process. This experiment was carried out using a Fe+C cathode workpiece and a cylindrical copper anode. The cathode spot movement was recorded using a high-speed video camera. The images were later analysed using plasma image processing. The workpiece surface, which was covered with a 9.67 µm thick oxide, was analysed using laser microscopy after processing. The surface roughness and the number of cathode spots showed no direct relation because the current density per cathode spot did not change according to the number of cathode spots.

Cathode Spot Movement of a Low-Pressure Arc for Removing Oxide Layer

A remarkable characteristic of the cathode spot of a low-pressure arc is that it can remove an oxide layer preferentially. Recently, the cathode spot of a low-pressure arc has been used for cleaning metal oxide surfaces before thermal spraying or surface modification. However, few reports have described the cathode spot movement or the oxide removal process. This experiment was carried out using the SS400 cathode workpiece and a cylindrical copper anode. The cathode spot movement was recorded using a high-speed video camera. The images were later analyzed using plasma image processing. The workpiece surface was covered with a thick oxide of 9.67 mum. The workpiece surface was analyzed using a laser microscope after processing. The cathode spot movement shows differences as the processing time increases and as the oxide layer roughness changes.