Showing papers in "Journal of Vacuum Science and Technology in 1993"

Langmuir probe measurements of a radio frequency induction plasma

Abstract: In this work a planar, radio frequency induction plasma source is characterized in terms of ion density, electron temperature, and plasma potential using a single Langmuir probe in oxygen and noble gases. Probe measurements of density were also verified using microwave interferometry. Measured argon ion densities increase nearly linearly with power from 1×1011 cm−3 at 300 W rf power to 6×1011 cm−3 at 1.2 kW at 1×10−3 Torr. Krypton ion densities are also linear with power but saturate above 1 kW at a density of 2×1012 cm−3 at 1×10−3 Torr. Electron temperatures increase with decreasing pressure from 3 eV at 26×10−3 Torr to 7 eV at 0.3×10−3 Torr. Plasma potentials are typically 15–30 V and increase with decreasing pressure. Ion saturation current in oxygen at 5×10−3 Torr is 2.5% uniform over diagonals of 20 cm when a magnetic multipole bucket is used to confine the plasma. Ion generation energy cost in argon is 100–250 W/A.

CO adsorption on Pd(111) and Pd(100): Low and high pressure correlations

Abstract: The adsorption of CO on Pd(111) and Pd(100) have been studied using infrared reflection–absorption spectroscopy over a wide range of CO pressures and temperatures. A strong dependence of CO adsorption on the initial conditions was found for Pd(111) while CO adsorption on Pd(100) was essentially independent of the conditions of adsorption. Initial isosteric heats of adsorption of 30 and 38 kcal/mol were determined for Pd(111) and Pd(100), respectively. For Pd(111) and equilibrium phase diagram was constructed on the basis of the infrared (IR) data. The excellent correspondence among IR data for the single crystal Pd surfaces and a supported Pd catalyst suggests that the Pd particles in the supported catalyst consist primarily of low index [(111) and (100)] crystal faces.

Novel radio‐frequency induction plasma processing techniques

Abstract: A novel plasma source combining rf inductive drive and multipole plasma confinement has been constructed to process advanced semiconductor materials. Measurements show a linear dependence of density with input power. Ion current efficiencies of 1 A per 150–300 W of input power can be achieved in argon, with lower efficiencies in electronegative gases. Applying an rf bias to a substrate immersed in the plasma allows the sheath voltage to be controlled between 8 and 300 V. Insight into the rf induction process can be gained by a simple circuit model, which represents the induction process with a transformer. The physical quantities describing the transformer can be obtained from numerical calculation of the fields of the induction coil. This plasma source can etch thin films at rates exceeding 1 μm/min.

Analytical electron microscopy and Raman spectroscopy studies of carbon nitride thin films

Abstract: Deposition of carbon nitride thin films on Si(100) and polycrystalline Zr substrates was performed by dc magnetron sputtering of a graphite target under a pure nitrogen ambient. The resulting carbon nitride films (CNx) are primarily amorphous with a small volume fraction of nanocrystallites. Both energy‐dispersive x‐ray analysis and electron energy loss spectroscopy measurements showed that the amorphous matrix has uniform nitrogen‐to‐carbon ratios ∼0.4–0.8 depending on deposition conditions. Carbon and nitrogen K edge structures obtained from electron energy loss spectroscopy studies suggest that the amorphous carbon nitride matrix is primarily sp2 bonded. Apart from the carbon–nitrogen stretching vibration, Raman spectra of CNx films closely resemble those of diamondlike carbon films. Intensity and peak width changes of Raman features in the 1300–1600 cm−1 range due to inorganic carbon (D and G peak) under different deposition conditions are explained in terms of the extent of structural disorder in the...

Electronic and phonon mechanisms of vibrational relaxation: CO on Cu(100)

Abstract: Stochastic dynamics simulations of vibrational relaxation rates are reported for a carbon monoxide molecule adsorbed on the (100) face of copper. A recently developed ‘‘molecular dynamics with electronic friction’’ scheme that self‐consistently incorporates both phonon and nonadiabatic electron–hole (e‐h) pair mechanisms of energy dissipation is employed. Lifetimes of the C–O stretch, the CO‐surface stretch, the frustrated rotation, and the frustrated in‐plane translation are examined as a function of temperature between 0 and 450 K. e‐h pair dissipation plays a significant role for all modes above 150 K. For the C–O internal stretching mode, the e‐h pair mechanism dominates and the lifetime depends weakly on temperature. The frustrated rotational (bending) mode is calculated to have the shortest lifetime at all temperatures, and the temperature dependence is weak. The e‐h pair contribution is again largest although the phonon contribution is significant. The CO‐surface stretch and the frustrated in‐plane...

Electromagnetic fields in a radio-frequency induction plasma

Abstract: The electromagnetic fields which drive a radio‐frequency induction plasma are both modeled and measured. The plasma source consists of a planar, square coil separated from a low pressure plasma chamber by a 2.54‐cm‐thick quartz window. A small loop antenna, which is sealed in a pyrex tube, is immersed in the discharge to determine the magnitude and direction of the rf magnetic field. The measured B field is primarily radial and axial. Typical rf field strengths vary from 2 to 7 G for rf powers of 0.1–1 kW. The radial B field decays exponentially in the axial direction. The skin depth of the electromagnetic field is 1.6–3.6 cm which is consistent with Langmuir probe measured ion densities (typically 3×1011 cm−3) in argon. Invoking Maxwell’s equations to deduce the rf electric field from the measured B field, we find the E field to be primarily azimuthal. Peak field strengths increase from 100 V/m at 100 W to 200 V/m at 600 W where they saturate for higher powers. Finally, we present a 3D finite element solution for the fields produced by this plasma source which employs a cold, collisionless plasma model to relate the relative plasma permittivity er to the electron plasma frequency, ωpe, using er=1−(ωpe/ω)2. The measured fields support this numerical solution.

Ultrahigh vacuum metalorganic chemical vapor deposition growth and in situ characterization of epitaxial TiO2 films

Abstract: In a two‐chamber ultrahigh vacuum system, epitaxial TiO2 thin films have been deposited by metalorganic chemical vapor deposition on single crystal oxide substrates over a temperature range of 250–800 °C, using titanium (IV) isopropoxide as the precursor. During the initial stage of epitaxial film deposition, the growing surface quickly planarized and the film’s orientations was determined by the substrate structure. This substrate influence is manifested in the growth of anatase (the low temperature phase of TiO2) on (001) SrTiO3, at high deposition temperatures (800 °C), whereas on either (0001) or (1102) Al2O3 sapphire, epitaxial rutile (the high temperature phase) is formed. In situ Auger electron spectroscopy analyses, before and after growth, revealed a film composition identical to that of a bulk TiO2 standard. No carbon contamination was detected in films grown throughout the deposition temperature range. The decomposition mechanism of this precursor that leads to the absence of incorporated carb...

Deposition of crystalline binary nitride films of tin, copper, and nickel by reactive sputtering

Abstract: Crystalline binary nitride films of tin, copper, and nickel were prepared by reactive sputtering in a nitrogen plasma generated in a dc glow discharge. The chemical composition and thermal behavior of the films were established. The films were characterized by additional physicochemical techniques. Tin nitride, Sn3N4 has an electrical resistivity of 0.02 Ω cm and decomposes into the elements at a maximum rate at 615 °C. The thermal decomposition of Cu3N takes place at 465 °C, while Ni3N decomposes at 405 °C in a stepwise fashion through an intermediate stage at 305 °C. Tin, copper, and nickel nitride decompose into the elements. Nickel nitride crystallized in a new cubic phase with a lattice parameter of 0.446 nm.

Surface composition of AlN powders studied by x‐ray photoelectron spectroscopy and bremsstrahlung‐excited Auger electron spectroscopy

Abstract: The surfaces of AlN powders, which are particularly sensitive to moisture and atmospheric oxygen, are characterized by x‐ray photoelectron spectroscopy (XPS). The powders used were exposed to ambient air and then heat treated at 100 °C in air, argon, or nitrogen gas. Bremsstrahlung‐excited Auger electron spectroscopy was used in combination with XPS to distinguish aluminum hydroxide from aluminum nitride on powder surfaces. The Auger peaks due to aluminum hydroxide and aluminum nitride were successfully resolved. The predominant surface oxygen‐containing species was found to be aluminum hydrate with a composition near Al(OH)3, AlOOH, or a mixture of them, depending on the heat treatment employed. Such data are useful in understanding the feedstock surface chemistry involved in the fabrication of AlN ceramics.

Thermal desorption of ultraviolet–ozone oxidized Ge(001) for substrate cleaning

Abstract: X‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), and reflection high‐energy electron diffraction (RHEED) have been used to show that 30 min exposures of a degreased and deionized‐water‐rinsed Ge(001) wafer to ultraviolet (UV)–ozone in laboratory air is sufficient to remove C contamination and form a nonpermeable passive amorphous GeO2 layer with a thickness of ≂1.8 nm. Subsequent annealing in ultrahigh vacuum (UHV) at ≥390 °C for ≥30 min resulted in desorption of the oxide layer and the exposure of a clean well‐ordered Ge(001)2×1 surface. No impurities, including C and O, were detected by either XPS or AES. EELS spectra from the clean surface showed well‐defined peaks corresponding to transitions involving dangling bonds, surface states, and surface plasmons. Shorter UV–ozone exposures (i.e., <30 min) often resulted in residual C contamination while incomplete oxide removal was obtained at lower oxide desorption temperatures. Ge overlayer...

Simple source of atomic hydrogen for ultrahigh vacuum applications

Abstract: A simple doser for atomic hydrogen is described. It basically consists of a tungsten capillary which on the outlet is heated by electron bombardment to 1800–2000 K. This temperature is sufficient to achieve nearly total H2 dissociation under relevant working pressures. The performance of the atomic hydrogen source was tested by H adsorption studies on Cu(110). The saturation coverage on this surface could be achieved with a nominal exposure which was smaller by a factor of ∼10−3 as compared to conventional methods of dissociation on a hot filament. The higher efficiency of the present H source greatly reduces the risk of sample contamination.

Experimental data and theoretical modeling of gas flows through metal capillary leaks

Abstract: Metal capillary tubes are commonly used as leak elements to admit known flows of gases into vacuum systems for calibration of vacuum gaging equipment. In many instances it is desired to generate flow rates over a range of three or more decades, preferably with a single leak element. The generation of flow rates over wide ranges is possible with metal capillary leaks, but in most cases the conductance of the leak element will need to be measured as a function of the relevant pressures due to the changing of the flow regimes. Many fits to experimental data and theoretical models exist for predicting the flow rate through tubes, but their validity is not well established. In this study, measured conductances of stainless steel tubes for flow rates of 10 −8 to 10 −14 mol s −1 with several inert gases are compared with various experimental and theoretical models of gas flow in the molecular, viscous and transition flow regimes. Characteristics of crimped metal capillaries are also examined over this range of flows.

Copper deposition by electron cyclotron resonance plasma

Abstract: An electron cyclotron resonance plasma reactor has been built in order to study the filling of high aspect‐ratio features on semiconductor devices with metal. The reactor produces a plasma of copper which is nearly 100% ionized at the substrate, without the use of any buffer or carrier gas. The ion flux is dependent on both the feed rate of copper neutrals into the plasma region, and on the microwave power absorbed in the plasma. Solid filling of features having aspect ratios as high as 4.2 is demonstrated, and a simple model is derived to explain the fill characteristics.

Dry and wet etching characteristics of InN, AlN, and GaN deposited by electron cyclotron resonance metalorganic molecular beam epitaxy

Abstract: The dry etching characteristics of thin film InN, AlN, and GaN epitaxial layers deposited using metalorganic group III sources (trimethylindium, trimethylamine alane, and triethylgallium) and electron cyclotron resonance (ECR) plasma excited atomic nitrogen in a metal organic molecular beam epitaxy (MO‐MBE) chamber have been examined using CCl2F2/Ar, BCl3/Ar, and CH4/H2/Ar discharges. In a hybrid ECR‐rf system, the Cl‐based chemistries readily etch GaN and AlN, while addition of F to the discharges dramatically reduces the etch rate of AlN. Slow, smooth etching of InN is achieved with the CH4/H2/Ar chemistry. Controlled rates of ∼200 A min−1 are obtained for all three materials at moderate dc biases (≤−200 V), low pressure (1 mTorr), and low microwave power (200 W). The dc bias and pressure dependence of the etching have been systematically studied. GaN films can be wet chemically etched in 30–50% NaOH solutions, AlN in HF and InN in HCl:HNO3 solutions.

Influence of the plasma on substrate heating during low‐frequency reactive sputtering of AIN

Abstract: Reports in the literature over the last several years have pointed out the advantages of using low‐frequency power for reactive sputtering. In the 10–100 kHz range the impedance of the poisoned target surface is low enough to prevent the charge accumulation that leads to arcing, while the problems associated with rf power are largely avoided. We have found, however, that for a variety of materials the substrate heating at these frequencies is somewhat higher than that observed during dc reactive sputtering under similar conditions. In order to quantify this, we have calorimetrically compared the incident substrate energies while reactively sputtering AlN with both dc and 35 kHz power. In both cases, the power was delivered simultaneously to two 200 cm2 targets. In one set of experiments, they were operated at a total power of 500 W, a total pressure of 10 mTorr, and a N2/Ar flow ratio of 0.18. These conditions were on the knee of the characteristic flow hysteresis curve for our system, and target voltage ...

In situ scanning tunneling microscopy study of platinum (110) in a reactor cell at high pressures and temperatures

Abstract: With a specialized version of a scanning tunneling microscope which allows us to study in situ the atomic structure of surfaces under variable pressures (ultrahigh vacuum—atmospheric) and temperatures (300–425 K), we have investigated the structures of the initially clean (110) surface of single crystal platinum while in environments of hydrogen, oxygen, and carbon monoxide. The surface in 1.6 atm of hydrogen appears to be dominated by various sizes of nested missing‐row reconstructions. The surface in 1 atm of carbon monoxide, however, does not have the small scale missing‐row reconstructions, but does appear to have flat terraces separated by multiple height steps. The surface in 1 atm of oxygen appears to have enlarged (111) microfacets.

Sustained self‐sputtering using a direct current magnetron source

Abstract: Sustained self‐sputtering of copper and silver targets has been achieved using a direct current magnetron source. The sputtering was carried out successfully without an inert gas at 8×10−6 Torr. A very high deposition rate was obtained in this mode of operation. The possible mechanism and requirements for sustained self‐sputtering are discussed and other potential material candidates are suggested.

Correlation of outgassing of stainless steel and aluminum with various surface treatments

Abstract: A number of important applications of ultrahigh vacuum technology involve the use of vacuum systems which cannot be baked in situ, e.g., materials processing equipment and various designs of accelerators and fusion devices. A choice of vessel material and surface treatment which minimizes outgassing in unbaked systems has obvious advantages. We report on a systematic comparison of outgassing measurements from type 304 stainless steels and type 6061/63 aluminum alloys after various standard and advanced surface treatments. Correlations were made with high‐resolution secondary ion mass spectroscopy and x‐ray photoelectron spectroscopy profiles of the passivation oxide layer and profilometry measurements of the surface roughness. The observed outgassing rates Q obeyed a power law Q=Q 0 t −n where n varied from 0.94 to 1.27. Over the standard observation period (50 h), the outgassing was dominated (≳85%) by H2O. The absolute outgassing rates varied by only a factor of 2.8 for the stainless steels and by a factor of 1.4 for the aluminum alloys, even though the surface roughness differed by more than two orders of magnitude. The high‐value‐added surface treatments (i.e., electropolishing) did not have significantly lower outgassing in comparison to simple detergent washes.

Highly transparent and conductive group IV impurity‐doped ZnO thin films prepared by radio frequency magnetron sputtering

Abstract: Highly transparent and conducting group IV impurity‐doped ZnO thin films have been prepared on low‐temperature substrates below 140 °C by rf magnetron sputtering. Resistivities of 4–8×10−4 Ω cm and an average transmittance above 85% in the visible range were obtained for ZnO films doped with Si, Ge, Ti, Zr, or Hf. The stability of resistivity for use in high‐temperature atmospheres was significantly improved by the impurity doping. On the contrary, the resistivity of ZnO films doped with Sn or Pb was higher than that of an undoped ZnO film, and these films were discolored.

Site requirements of reactions on oxide surfaces

Abstract: The development of structure‐reactivity relationships has been a long‐standing goal of surface science studies. Ironically, though they have been considered much less often than metals, metal oxides appear to offer some of the best opportunities for developing such relationships. The localized electronic structure of oxides permits connections to be drawn from reactivity to the discrete coordination environments and oxidation states of surface cations, and thence to coordination chemistry of metal complexes in solution. Reactions of carboxylic acids on different oxide single crystal surfaces illustrate the roles of surface coordinative unsaturation, oxidation state, and redox properties in determining the surface reactivity of metal oxides.

Particulate temperature in radio frequency glow discharges

Abstract: A spectroscopic technique is described for measuring the temperature of phosphorescent particles suspended in a low pressure rf plasma. The particles are found to be slightly hotter than the neutral gas temperature. This result is consistent with models of particle heating in a low pressure discharge. Also, we report on an entrainment device for introducing the phosphorescent particles (or other types of particles) into a discharge.

X‐ray fluorescence measurements of x‐ray absorption near edge structure at the Si, P, and S L edges

Abstract: High‐resolution (≤0.2 eV) x‐ray absorption near edge structure (XANES) spectra have been recorded at the Si, P, and S 2p edges of several compounds using microchannel plates to detect the ultrasoft x‐ray fluorescence after 2p excitation or ionization. The fluorescence yield (FY) XANES of SiO2, Si, InP, FeS2, and Na2S2O3 are of at least as good quality as the XANES recorded using total electron yield (TEY), despite the extremely small fluorescence yield. The FY spectra obtained show two significant advantages over the TEY spectra. First, the FY XANES is much more bulk sensitive; and second the resolution of the FY spectra is usually considerably better.

Growth of III-V materials by metalorganic molecular-beam epitaxy

Abstract: Metalorganic molecular‐beam epitaxy (MOMBE) is a hybrid growth technique which combines the gaseous sources of metalorganic chemical vapor deposition with the ultrahigh vacuum growth environment of molecular‐beam epitaxy. This combination greatly alters the growth chemistry relative to that obtained in the parent techniques and hence often mandates the development and use of novel matrix and dopant sources. This paper will discuss how the unique chemistry of MOMBE may be exploited for growth of various III–V materials, paying particular attention to the effect of source chemistry on impurity uptake, dopant control, and uniformity. It will also review variations of the basic MOMBE process, such as electron cyclotron resonance‐MOMBE, which allow for growth of nitrogen based materials. Finally the future of this growth technique will be assessed and the key issues which must be resolved in order for this method to achieve its full potential will be discussed.

Scanning tunneling microscopy and atomic force microscopy studies of biomaterials at a liquid–solid interface

Abstract: We have compared the scanning tunneling microscopy (STM) and atomic force microscopy (AFM) using a clean gold surface under electrochemical potential control, finding that the STM usually yields higher resolution, although this may be a consequence of better production methods for STM tips. New methods for tethering DNA molecules to substrates have yielded many excellent AFM images of DNA, even under water. The highest resolution has been obtained with specially sharpened tips, but recent work suggests that this may not be necessary. Control of contamination, and tip–sample interactions (i.e., adhesion) are also important factors. We describe a scheme of magnetic control of AFM cantilevers which should overcome the mechanical instability that places a lower limit on contact force. This should permit active control of interaction forces with the instrument operated in water. We illustrate local force measurements made under water with examples of the measurements of the microelastic properties of bone and ...

Deposition system for the synthesis of modulated, ultrathin-film composites

Abstract: We have initiated a program using elemental superlattices as probes of the early stages of solid‐state reactions. The main advantage of using superlattices as reactants is the ability to tailor their structure on an angstrom length scale to control reaction kinetics. Consequently, we designed and constructed a computer‐controlled and monitored ultrahigh‐vacuum chamber for the preparation of elemental superlattices. This system is capable of manufacturing three sets of three samples in one evacuation cycle. Up to six different elements can be incorporated into each sample. Elements can be deposited from independently controlled electron‐beam sources, Knudsen, or evaporation cells. The sample drive mechanism combined with source shutters and computer control permit complex layer‐repeat units within the composite. Layer thicknesses can be controllably varied from 4 A upward. Various attributes of the chamber include its modular design, multiple layer thickness control options, reproducibility and quality of samples, flexibility, and extensive computer monitoring during sample preparation.

Copper metalorganic chemical vapor deposition reactions of hexafluoroacetylacetonate Cu(I) vinyltrimethylsilane and bis (hexafluoroacetylacetonate) Cu(II) adsorbed on titanium nitride

Abstract: Cu is receiving increasing attention as a replacement for Al in future Si ultra‐large‐scale integrated circuits due to its lower resistivity and potentially better reliability in terms of electromigration resistance and stress‐induced voiding. Metalorganic chemical vapor deposition (MOCVD) of Cu offers the advantages of conformal coverage and selective growth. Whatever the means of deposition, a diffusion barrier and adhesion layer such as TiN is required. To understand the nucleation mechanisms of Cu film growth on TiN during MOCVD, we have studied the thermal decomposition of two metalorganic precursors, hexafluoroacetylacetonate Cu(I) vinyltrimethylsilane [CuI(hfac)(vtms)], and bis (hexafluoroacetylacetonate) Cu(II) [CuII(hfac)2] by x‐ray photoelectron spectroscopy and temperature programmed desorption mass spectrometry in an ultrahigh vacuum (UHV) system.Experiments were carried out on polycrystalline air‐exposed (i.e., oxidized) TiN and N2 ion beam sputter‐cleaned TiN. These surfaces are representati...

Effects of HF solution in the electroless deposition process on silicon surfaces

Abstract: We have investigated the influence of HF concentration on the initial stages of electroless deposition for various metals (Al, Au, Cu, Sn, and Pd) onto silicon using atomic force microscopy. As the HF concentration in the plating solution increased, the rate of metal deposition correspondingly increased for Au, Cu, and Pd. In the case of Au and Cu, uniformly sized nuclei comprised the first deposited layer. However for Al and Sn, deposition occurred only at sporadic sites on the surface and was independent of HF concentration. For all of the metal ion studied, deposition initiated preferentially at flaws on the surface. The electroless process indicates a direct displacement mechanism which results in the simultaneous dissolution of Si as the metal ion is reduced at the surface. For all the metal ions deposited in this manner, metal adhesion to the Si surface was poor.

Controlling the plasma chemistry of silicon nitride and oxide deposition from silane

Abstract: We have studied the chemistry of glow discharge plasma‐enhanced chemical vapor deposition (PECVD) by using vibrating quartz crystal deposition rate monitoring at 200–300 °C and line‐of‐sight mass spectrometry of orifice‐sampled reactive neutral species. In the deposition of dielectric films from silane plus a large excess of oxidant (NH3, N2, or N2O), the key process factor is the ratio of plasma power to silane supply rate. When enough of the oxidant is activated by the plasma, it completely converts the silane to films which have no excess Si and no Si–H bonding. The critical ratio can be detected by the disappearance of Si2H6 byproduct or by the presence of excess activated oxidant. Nitride deposited from N2 is electrically leaky due to porous microstructure even when deposited using excess activated oxidant. Conversely, nitride deposited from NH3 is nonporous, and when deposited using excess activated oxidant it has a surprisingly low electron trapping rate which is at least as low as that achievable ...

Etching rate characterization of SiO2 and Si using ion energy flux and atomic fluorine density in a CF4/O2/Ar electron cyclotron resonance plasma

Abstract: SiO2 and Si etching in a CF4/O2/Ar plasma has been carried out in an electron cyclotron resonance etcher over a wide range of conditions. The etch rate has been compared with the ion energy flux to the wafer surface, JiEi, and the atomic fluorine density in the gas phase, nF. It is found that the etch rate can be divided into two regimes by a critical value of nF/(JiEi), the ratio of the atomic fluorine density to the ion energy flux. The critical value can be determined from a contour plot of the etch rate as a function of the ion energy flux and the atomic fluorine density. The critical value of nF/(JiEi) for Si is higher than that for SiO2. For nF/(JiEi) higher than the critical value, the SiO2 etch rate linearly increases with the ion energy flux, and the Si etch rate shows a nonlinear increase with the ion energy flux. For nF/(JiEi) lower than the critical value, both SiO2 and Si etch rates linearly increase with the atomic fluorine density.

Low‐pressure ion nitriding of AISI 304 austenitic stainless steel with an intensified glow discharge

Abstract: Low‐pressure ion nitriding of AISI 304 austenitic stainless steel was conducted in the present study by intensifying the glow discharge. Plasma intensification was produced by thermionic emission and by utilizing a triode glow discharge system. The results showed that under the intensified plasma conditions, effective nitriding can be accomplished at relatively low temperatures. The nitride layer had a dense structure, high purity and an ultrafine microstructure with a grain (nucleus) size less than 80 A. The nitriding treatment produced a thin layer of high nitrides (FeN and Fe2N) followed by a diffusion controlled layer of (Fe,Cr)3N. X‐ray and electron‐diffraction analysis showed that all nitrides were hexagonal in crystal structure. The intensified plasma treatment caused a significant increase in the nitride layer growth kinetics. The enhancement of the nitrogen diffusion was attributed to the higher surface concentration of vacancies due to the energetic particle bombardment and to grain boundary diffusion in the nitride phase. A simplified diffusion model is developed to estimate the effective nitrogen diffusivity under the intensified plasma ion nitriding.