Reactive Gas Partial Pressure Research Articles

Low-frequency modulation of pulsed d.c. or r.f. discharges for controlling the reactive magnetron sputtering process

Pulsed d.c. discharges (20–60 kHz) and r.f. discharges (13.56 Mhz) are known to prevent electric instabilities due to arcing when highly insulating compounds are deposited by reactive magnetron sputtering. This paper shows how a low-frequency modulation (1–10 Hz) of these discharges can overcome the difficulty due to the instability of the sputtering process itself with its associated hysteresis effect caused by the rapid transition between a clean target and a target poisoned by reaction products with the reactive gas. This new, simple and economical method does not need the use of a complex fast feedback control system of the reactive gas partial pressure. The application of this method will be particularly illustrated by the deposition of amorphous alumina films.

The effects of oxygen content on electrical and optical properties of indium tin oxide films fabricated by reactive sputtering

We have investigated the depth profile of the oxygen content of indium tin oxide (ITO) films fabricated by reactive sputtering. The oxygen content was determined by means of 16O(α,α) 16O resonant backscattering. The effect of the oxygen partial pressure of reactive gas on the oxygen content of the films was investigated. From the depth profile of oxygen, it was found that the oxygen compositions of the films, especially in the surface region, changed with the oxygen partial pressure. Also it was found that the electrical and optical properties of the ITO films changed with the oxygen partial pressure. The correlation between the oxygen content and the electrical and optical properties is discussed.

The structural characteristics of VO x films prepared by He-introduced reactive RF unbalanced magnetron sputtering

Vanadium oxide (VO x , x=0∼2.5) films with several different structures were deposited using reactive unbalanced magnetron sputtering; a metallic vanadium target was used. Helium gas was introduced to the deposition process to cause Penning ionization, which was enhanced by the ‘unbalanced’ magnetic field arrangement at the cathode. The transition region corresponding to the oxidation of a target surface was observed at the lower reactive gas (oxygen) partial pressure. A thermochromic film, rutile VO 2, and its metastable phase, VO 2(B), were successfully deposited at 400°C by controlling the oxygen and helium partial pressures. The plasma diagnostics, examined by optical emission mcitoring, revealed that the relative electron temperature was also increased by the Helium introduction, which should result in an increasing plasma potential close to the substrate surface and hence an increase in the ion-bombardment energy during the film growth.

Reactive Sputter Deposition of Superhard Polycrystalline Nanolayered Coatings

AbstractNanometer-scale multilayer nitride coatings, also known as polycrystalline nitride superlattice coatings, such as TiN/NbN or TiN/VN with hardnesses exceeding 50 GPa, are deposited by highrate reactive sputtering. The high hardness is achieved by carefully controlling several deposition parameters in an opposed cathode, unbalanced magnetron sputtering system: the target power, the reactive gas partial pressure, the substrate bias voltage and current density, and the substrate rotation speed. Target power controls the deposition rate and the thickness for each layer in conjunction with the reactive gas partial pressure at each target, which also affects the composition of each layer, and the substrate rotation speed. Split partial pressure control is necessary when each layer requires a different partial pressure to be stoichiometric. Fully dense, well-adhered coatings with the highest hardness are deposited when the negative substrate bias exceeds -130 V and the substrate ion current density is 4–5 mA cm−2. The work on polycrystalline superlattice coatings is being extended into oxide systems. Oxide coatings can now be sputter deposited using pulsed dc power, which prevents arcing on both the target and the substrate. Pulsed dc power along with partial pressure control of the reactive gas leads to significantly higher deposition rates for the oxide films compared to sputtering with conventional rf power.

Organometallic Chemical Vapor Deposition of Palladium under Very Mild Conditions of Temperature in the Presence of a Low Reactive Gas Partial Pressure

Palladium thin-film deposition was carried out from the known precursors Pd(η3-C3H5)(Cp), and Pd(η3-C3H5)(hfa), where Cp is (η5-C5H5), cyclopentadienyl ligand and hfa is (CF3COCHCOCF3), hexafluoroacetylacetonato ligand. The use of a reactive gas such as dihydrogen led to unexpected low temperatures of deposition (30−60 °C). XPS and electron microprobe analyses revealed that low levels of carbon are incorporated to the palladium films. X-ray analyses showed crystalline deposits and scanning electron microscopy revealed grains of 300−1000 nm. Gas-phase analyses by mass spectrometry and GC/MS of deposition residues were realized to clarify the reaction mechanisms. Such a deposition process leads to metallic palladium with a good purity level.

Properties of thin films of magnetic materials produced from DC Magnetron sputtering; the effects of substrate bias and the partial pressure of reactive gases

The manner in which the coercivity, permeability and resistivity of films of Fe- M- X ( M : Ta, Hf, Zr, Nb; X: N, C, Ar;) and Permalloy varied because of particular conditions during DC magnetron sputter deposition has been determined. The effects of reactive gases and substrate bias during the sputtering process were studied and the measured values for H c′ μ and ϱ were compared with the results from formulae derived from gas impurity pinning and scattering theory. For Fe- M- X films, the coercivity could be modified from 1.2 Oe to 0.4 Oe and the permeability from 3 × 10 3 to 8.5 × 10 3 (1 MHz) by altering the partial pressure of nitrogen between 2 × 10 −5 Torr and 1 × 10 −4 Torr. The coercivity of Permalloy films could be adjusted from 8 Oe to 0.5 Oe and their permeability altered from 200 to 820 (1MHz) by changing the substrate bias between 0V and − 100V.

Ionized magnetron sputter deposition of amorphous carbon nitride thin films

Carbon nitride thin films were prepared using an ionized magnetron sputtering system. An inductively coupled rf plasma was generated in the region between the sputtering source (high purity graphite) and the substrate table. An argon–nitrogen mixture was used as the sputtering gas. Sputtered atoms which pass through the radio frequency (rf) plasma may be ionized, and the degree of ionization depends on several processing variables, such as the gas total pressure, reactive gas partial pressure, and applied rf power. Pulsed substrate bias voltage was varied up to −500 V. Chemical bonding and composition of the deposited films were studied by infrared and Auger electron spectroscopy, respectively. An ultramicroindentation system was used to measure the hardness. Nitrogen was found to be bonded to carbon in various configurations. The dependence of the nitrogen-to-carbon ratio and film hardness on the deposition conditions was studied. Under optimum conditions, films with nitrogen-to-carbon ratio ∼0.3–0.4 and hardness up to 16–17 GPa were made. These values are similar to those obtained without the rf plasma. There is no correlation between the film hardness and the nitrogen-to-carbon ratio.

The effects of substrate bias and reactive gas partial pressure on the resistivity of sputtered ITO films

High quality indium tin oxide (ITO) films were deposited on k 9 glass in a dc magnetron triode system using reactive sputtering in Ar+ O 2 with a negative substrate bias. The target was an alloy of 83wt% and 17%wt% Sn. A film of resistivity of 3.0×10 −4 Ω cm and 85% average transmittance in the visible region was prepared at a film thickness of 1100 Å. The effect of the deposition parameters on the electrical and optical properties of the film has been studied theoretically and experimentally. It was found that the base bias voltage strongly influenced the ITO film resistivity and transmittance during deposition and the optimum for the bias voltage was about −40 to −60 V. The oxygen partial pressure was varied from 8×10 −2 Pa to 10 −2 Pa and if the oxygen pressure was higher than the optimum region, the resistivity of the ITO film increased, black matter of InO and SnO appeared and the transmittance of the ITO film decreased. The equation and curve for the resistivity variation with base bias voltage and the reactive gas partial pressures are given. The effect of annealing on the resistivity of the ITO film was studied and the optimum conditions for post-deposition annealing were 500°C and 30 min in an air environment of 6×10 −3 Pa.

Modeling of time-dependent process changes and hysteresis in Ti-O2 reactive sputtering

Understanding the mechanisms of reactive sputtering is thought to be crucial to obtain a better process control and widen applications of reactive sputtering. A model simulating reactive gas mass balance changes in reactive sputtering is described. The model is based on physical mechanisms involved in target and wall gettering behavior. This enables calculation of time-dependent condition changes that occur until the process reaches a steady state, without assuming how the process reaches a steady state. Another important feature of the model is that hysteresis curves are obtained as a result of the calculation of time-dependent target condition changes. This approach to obtain hysteresis curves is more similar to an actual reactive sputtering process. The proposed model clearly displays changes in target coverage, sputtered flux, and reactive gas partial pressure during compound-layer formation and sputter etching processes as a function of elapsed time. Effects of reactive gas flow rate, pumping speed, and sputtering current on compound-layer formation and sputter etching are also discussed. Hysteresis curves are yielded as a result of compound-layer formation and sputter etching calculations. The obtained curves are in accord with experimental results. Further, the dependence of hysteresis on pumping speed, sputtering current, and the difference of sputtering yields between metallic and compound-covered targets was investigated, resulting in showing a good agreement to that obtained experimentally. Mechanisms of hysteresis formation are also discussed on the basis of obtained results. It is concluded that hysteresis is formed because of the difference of gettering capacity before and after the target surface condition transition.

Microstructural and tribological study of triode magnetron sputtered V-C coatings: influence of partial pressure of reactive gas

Microstructural and tribological study of triode magnetron sputtered V-C coatings: influence of partial pressure of reactive gas

Microstructural and tribological study of triode magnetron sputtered V-C coatings: influence of partial pressure of reactive gas

The fine-scale micrcstructure of V−C coatings has been investigated by transmission electron microscopy (TEM). X-ray diffraction (XRD) has been used to identify the global microstructure. These coatings of thickness a few micrometers were obtained by reactive triode magnetron sputtering in an Ar−C 2H 2 mixture. The major objective has been to examine the way in which a deposition process variable (reactive gas flow) affected the coating microstructure and enhanced the tribological properties. Some difficulties have been encountered in the interpretation and the indexing of XRD profiles. These problems were resolved by the TEM study which illustrated how the carbon content of the coating controls the grain size and crystal structure. The VC grain size decreased with increasing the carbon content in the coating and tended towards a configuration of nanocrystallitcs of VC surrounded by an amorphous carbon matrix. Such structure offers good tribological properties, i.e. low friction coefficient and wear resistance for a dry-wear ceramic—metal test. The microstructure results are presented and discussed briefly in terms of the influence on the hardness, friction and wear.

Excimer laser cleaning and processing of Si(100) substrates in ultrahigh vacuum and reactive gases

We have examined the effect of KrF excimer laser irradiation (248 nm, 20–25 ns) on Si(100) substrates under ultrahigh vacuum conditions and in controlled partial pressures of reactive gases. Surface compositions were determined before and after irradiation using in situ angle resolved x-ray photoelectron spectroscopy. We varied peak power, pulse energy, and halocarbon (CF4) or carbon monoxide (CO) pressures to investigate their effects on oxygen and carbon removal. Energy densities near 500 mJ/cm2 were sufficient to eliminate the carbon contamination; higher energies, which depended on the silicon preparation conditions, were required for oxygen removal. Samples were irradiated by pulses at 480–740 mJ/cm2 in molecular oxygen (O2) environment after cleaning to determine pulse energy and gas pressure requirements for oxide regrowth.

Growth and characterization of silicon-nitride films by plasma-enhanced chemical vapor deposition

Thin films of silicon nitride were deposited on Si wafers by plasma-enhanced chemical vapor deposition (PECVD). For deposition we designed and made hot wall capacitively coupled PECVD equipment which has a radial flow reactor. Using an RF generator of frequency 13.56 MHz and SiH 4 (5% SiH 4 in N 2) + NH 3 and N 2 as reactive gases and the carrier gas, respectively, we systematically varied the substrate temperature (240–360°C), the partial pressure of reactive gases (0.35 <P SiH 3 P SiH 4 <1.32, 5% of S iH 4 in N 2) and the RF power (20–160 W), as deposition parameters. The characteristics of the films such as composition, deposition rate, refractive index and hydrogen content were investigated by AES, ellipsometry, FTIR spectrometry, nanospec and spectroscopic ellipsometry. As a result of these measurements, well-known characteristics were observed as a function of the substrate temperature and the partial pressure of the reactive gases. However, in our investigation of the RF power dependence of the refractive index of the film, we found that the refractive index increases and then decreases as we increase the RF power. To explain this, we considered the RF power-dependent heating effect in the glow discharge process and the amount of NH radicals which increases with the RF power.

7486. Elemental dependence of angular ejections distributions of sputtered particles from an SiO 2+5 wt% P 2O 5 sintered composite target : T Motohiro and Y Taga,Thin Solid Films, 189, 1990, 103–109

<dm:abstracts xmlns:dm="http://www.elsevier.com/xml/dm/dtd"><ce:abstract xmlns:ce="http://www.elsevier.com/xml/common/dtd" view="all" class="author" id="aep-abstract-id5"><ce:section-title>Publisher Summary</ce:section-title><ce:abstract-sec view="all" id="aep-abstract-sec-id6"><ce:simple-para id="fsabs003" view="all">Various aspects of early vacuum science and technology are discussed in the chapter. The use of vacuum equipment for deposition (and etching) processes introduces problems associated with pumping and disposing of possibly toxic, flammable, and corrosive processing gases, as well as reactive gases used for <ce:italic>in situ</ce:italic> cleaning of vacuum systems. Specialized vacuum equipment and <ce:italic>in situ</ce:italic> chamber plasma-etch-cleaning techniques are developed to address these concerns. With the advent of reactive deposition and hybrid processing, the control of gas composition and mass flow has become an important aspect of vacuum engineering and technology. This includes partial pressure control and gas manifolding in processing chambers. Differentially pumped mass spectrometers can be used to monitor and control partial pressures of gases. Optical emission spectroscopy is also used to control the partial pressures of reactive gases in reactive sputter deposition. Optical emission has been used for many years to detect the end-point in plasma etching for semiconductor processing.</ce:simple-para></ce:abstract-sec></ce:abstract></dm:abstracts>

Time-dependent simulation modelling of reactivesputtering

A time-dependent simulation model of reactive sputtering is proposed. The model deals with time-dependent poisoning of the target surface and hysteresis phenomena. The model is based on the calculation of the time-dependent change in gettering pumping speed and target poisoning speed, yielding the time-dependent change in target coverage and reactive gas partial pressure. By calculating the equilibrium values of the time-dependent change over a range of reactive gas flow rates, hysteresis effects of target coverage and reactive gas partial pressure are investigated as a function of the gas flow rate. The hysteresis results obtained suggest that with the time-dependent model it is possible to evaluate the effect of pumping speed on the transition points and width of hysteresis curves. As compared with experimentally investigated results it is found that the model explains mechanisms of reactive sputtering qualitively.

The use of process modelling for optimum design of reactive sputtering processes

The reactive sputtering process has been successfully described in a quite simple mathematical model in some recent articles. By the use of such a model it has been possible to predict the partial pressure of the reactive gas, the rate and also the composition of the deposited film. In such a complex process it is not easy to experimentally verify all aspects of the model. Numerous experiments have, however, been carried out which support the validity of the model. In this article we will apply this model to investigate the problem of target poisoning. We will calculate the composition of the deposited film, the deposition rate and the poisoning of the target surface. We will mathematically show that by introducing a pressure gradient in the processing chamber it is possible to obtain compound film formation while minimizing the target poisoning effect. This effect has earlier been experimentally observed by several authors. These theoretical findings explain quite satisfactorily the expected improvement in performance of the reactive sputtering of compound films, as far as deposition rate is concerned. However, the most favourable conditions only exist at non-stable processing operating points. To be able to operate the process at optimum conditions a feedback control system for the partial pressure of reactive gas vs. gas mass flow has to be incorporated.

Advances in partial-pressure control applied to reactive sputtering

Summary High-rate reactive sputtering (HRRS) requires rapid and careful control of the reactive gas partial pressure to achieve high deposition rates and to maintain stoichiometry in the coating. HRRS of TiN was first achieved with feedback control of the N 2 utilizing a differentially pumped mass spectrometer system to sense the N 2 partial pressure. Recently, a new instrument called the optical gas controller (OGC) that operates at sputtering pressures became available for sensing the partial pressure of the gases in the sputtering atmosphere. The OGC was used during the reactive sputtering of TiO x with partial-pressure control, and the TiO x hysteresis loop exhibited a wide negative slope region which is much larger than the one found during the reactive sputtering of TiN x . Partial-pressure control, compared to mass flow control during oxide reactive sputtering, leads to better control of the process and to a 3.5 times higher deposition rate for highly resistive oxide coatings. With partial-pressure control, the anatase form of TiO 2 has been produced with lattice parameters of a 0 = 3.780 A and c 0 = 9.610 A.

The effect of target-substrate coupling on reactive direct current magnetron sputtering

Summary From a consideration of the reactive gas flow rates and of the reactive gas partial pressure a criterion for process stability in reactive direct current magnetron sputtering is derived. By a discussion of this stability criterion the methods of self-stabilization and stabilization through high pump speed are deduced. If the gas discharge is considered as a getter pump with a reactive gas pressure dependent pumping rate S Dis ( p R ), the stability criterion includes a term — d S Dis /d p R which describes the degiee of target-to-substrate coupling (TSC). From this the method of stabilization through reduction of TSC, i.e. through decoupling, is deduced. The relationship of process stability, TSC and film properties is discussed and exemplified by the system CrSi-O 2 . Coating of large areas and plasma-assisted deposition call for strong TSC, which may be contradictory to the stability criterion. An active closed-loop control circuit, e.g. using the plasma emission intensity signal (PEM control), has to be employed for process stabilization.

Pressure stability in reactive magnetron sputtering

In high rate reactive magnetron sputtering the film deposition results in a substantial pumping rate of the reactive gas. When the depositing film is substoichiometric, the film's consumption of the reactive gas is limited by the arrival rate of that gas and so consumption increases with reactive gas partial pressure. When the film is saturated with gas, the reactive gas consumption is limited by the metal arrival rate. As the reactive gas pressure is increased reaction products form on the target (it is “poisoned”) and the metal flux falls, leading to a decreasing consumption of the reactive gas. At pressures where a stoichiometric film is formed the consumption of the reactive gas by the film will be falling. This can lead to an uncontrollable transition between a metallic and a poisoned target that makes the control of optimum deposition conditions difficult. We have investigated this instability and its causes and our results indicate various means of getting a stable deposition system.

Reactive and chemically assisted ion beam etching of Si and SiO2

Abstract Results are presented for the etching of thermal SiO2 and single crystal Si by two ion beam sources of widely different characteristics, viz. a cold cathode saddle field source and a heated filament source. Reactive ion beam etching in SF6 is described for both sources and chemically assisted ion beam etching (using a specially constructed ring inlet system) in SF6/Ar+ using the heated filament source. Etching rates of Si in the latter mode are dependent on reactive gas partial pressure. Reactive and chemically assisted ion beam etching work in CF4 using the heated filament source is reported. Changes in etch selectivity between Si and SiO2 are observed.