摘要:

The characterization of the surface properties of ZrC films grown by thermally evaporating ZrC onto room temperature W(100)and W(110) and then annealing, are reported. These films as deposited have no long range order as determined by low energy electron diffraction, but heating to above 1800 K produces well‐ordered layers. During annealing the ZrC(100) face forms on W(100), and the ZrC(111) face forms on W(110). Work functions as low as 2.75 eV have been measured on these films after initial heating, but final values are 3.85 eV for ZrC(100), and from 4.40 to 4.80 eV for ZrC(111), depending on the C contamination of the W(110) substrate. From thermal desorption spectra desorption energies were also calculated. Possible mechanisms for the ZrC crystalline ordering during annealing are discussed.

ISSN:0734-2101    

DOI:10.1116/1.578703

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

We studied the influence of a thin Fe interface layer between W and the substrate Si and of a surface W–oxide on the formation kinetics of WSi2. Auger depth profiling, Rutherford backscattering spectrometry and x‐ray diffraction have been used to investigate the reaction between the layers and the Si substrate. W layers with a thickness of 20 nm were deposited by electron beam evaporation on HF dipped Si(100) samples. If deposition and subsequent annealing are performed in ultrahigh vacuum, the complete conversion of a W layer into tetragonal WSi2occurs within 1 h at 800 °C. The intercalation of a 5 nm‐thick Fe layer between the W layer and the substrate reduces the conversion temperature to 650 °C. Ironsilicide is formed at a relatively low temperature. This silicide acts as a medium through which Si can easily diffuse towards the surface, thus maintaining a fast Si supply to the W layer. This experiment indicates that reactions at the metal/Si interface are rate determining in the formation of WSi2. Both with and without an Fe intermediate layer, the reaction proceeds via the migration of Si to the film surface followed by the formation of WSi2at the surface. Continuation of the reaction occurs from the surface to the substrate. Furthermore, we found that the presence of a native oxide layer at the W surface retards the reaction between W and Si. Oxygen migrates via the open structure of the W film to the interface where it probably forms a thin SiO2layer that hampers the transport of Si into the W film.

ISSN:0734-2101    

DOI:10.1116/1.578722

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

Transmission electron microscopy (TEM), cross‐sectional TEM, scanning TEM with energy dispersive x‐ray analysis, and Auger electron spectroscopy were used to investigate the nature of rate‐controlling interfacial reactions in epitaxial Al/Ti1−xAlxN thin‐film couples. TiN and NaCl‐structure Ti1−xAlxN layers, 120 nm thick, with compositionsx=0.1 and 0.2 were grown on MgO(001) substrates by ultrahigh vacuum reactive magnetron cosputter deposition in N2discharges. Epitaxial Al films, 200‐nm‐thick, were then grown in Ar on top of the nitride layers during the same vacuum cycle. The reaction paths for Al/TiN and Al/(Ti,Al)N interactions during anneals atTa=600 °C fortaup to 150 min was similar, but the extent of reaction was dramatically decreased by the substitution of (Ti,Al)N barrier layers for TiN. The primary mobile species during annealing was Ti which penetrated into the Al layers and reacted to form the ordered tetragonal intermetallic phase Al3Ti while Al segregation resulted in the formation of a narrow metastable zincblende structure AlN layer at the Al/nitride interface. The room‐temperature resistivity of 1‐μm‐thick nitride layers varied from 15 μΩ cm for TiN to 60 μΩ cm for Ti0.8Al0.2N.

ISSN:0734-2101    

DOI:10.1116/1.578277

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

Thin films of GaN have been achieved via gas source molecular beam epitaxy with and without substrate illumination from a 500 W Hg arc lamp. X‐ray photoelectron spectroscopy showed a nominally stoichiometric GaN film without contaminants regardless of illumination. Illumination and Ga cell temperature changed the texture of the polycrystalline GaN from (0001)∥(100) to (0001)∥(111) and back again. Near single crystal films were deposited with an orientation relationship ofw‐GaN (0001)∥β‐SiC (100) and (101̄0)∥(011̄). Resulting films were characterized by scanning electron microscopy as well as x‐ray and electron diffraction.

ISSN:0734-2101    

DOI:10.1116/1.578700

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

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 Å. 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.

ISSN:0734-2101    

DOI:10.1116/1.578712

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

The silicon–fluoride reaction layer formed on silicon surfaces when etched in low pressure discharges of CF4and SF6has been characterized using ellipsometry in real time and x‐ray photoemission spectroscopy (XPS) after sample transfer in vacuum. By comparing reactive ion etching (sheath voltageVs=50–500 eV) and plasma etching (Vs≂30 eV) over the pressure range 10–250 mTorr and by using different rf power levels, the effects of ion bombardment on the SiFxlayer were examined. The thickness of the SiFxlayer depends primarily on the sheath voltage of the discharge, which determines the maximum energy of the bombarding ions. For low ion bombardment etching the apparent thickness of the SiFxlayer is ≂0.5 nm. It increases up to ≂1.7 nm as the sheath voltage is increased. Nondestructive profiling of the SiFxlayer was performed by angle‐resolved photoemission to determine the variation of the various fluorosilyls (SiF, SiF2, SiF3, and SiF4) as a function of depth. SiF3has the highest intensity at the surface of the SiFxlayer and drops off rapidly in relative importance as the reacted layer is probed deeper. At the largest depth, SiF becomes the dominant species. SiF2and SiF4are also peaked at the surface, but their relative importance is always smaller than that of SiF and SiF3. The initial stages of fluorination of the Si surface were monitored in real time using ellipsometry. Within the first seconds of exposure to the plasma, a damaged Si layer is introduced which is subsequently fluorinated and partly consumed. The steady‐state SiFxlayer thus formed and present on the crystal during etching is stable when the discharge is terminated. This finding validates the use of postplasma XPS analysis for the study of the SiFxlayer. The ellipsometric measurements demonstrate that an increase in the sheath voltage of the discharge results in increased surface damage and deeper fluorination of the Si surface. These results are in conflict with the predictions of several models of ion‐enhanced etching and indicate that ion‐induced mixing and generation of damage may play an important role in ion‐enhanced etching reactions.

ISSN:0734-2101    

DOI:10.1116/1.578717

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

The oxidation of TiN in an oxygen flow at temperatures in the range 300–500 °C has been studied by means of soft x‐ray absorption spectroscopy. The analysis of the experimental results indicates that O progressively displaces N to form TiO2. The process appears to be controlled by the temperature dependence of the oxygen diffusion. Some oxidation is observed to take place even at room temperature. No evidence of oxynitride formation was found in thermally oxidized TiN, instead complete phase separation is observed. The interface between TiO2and TiN seems to be very abrupt. The appearance of a sharp absorption peak in the N 1sspectrum of TiN is believed to be due to nitrogen atoms which are displaced during the oxidation process and remain unbounded within the TiO2matrix. For temperatures above 400 °C, this peak disappears as the interstitial N atoms migrate to the surface and desorb.

ISSN:0734-2101    

DOI:10.1116/1.578718

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

Bonding states and the band bending of S/n‐GaAs (001) and metal/S/n‐GaAs (001) systems are studied by synchrotron radiation photoemission spectroscopy (SRPES). The difference in the surface chemistry between the (NH4)2Sx‐treated GaAs and the sulfur‐chemisorbed GaAs is explained well by the formation of the sulfur‐rich transition layer for the (NH4)2Sx‐treated GaAs. A structural model for the annealed S/GaAs (001) system is proposed, in which the surface is terminated with Ga–S bonds. The barrier height of the Al, Au, and In Schottky contacts on (NH4)2Sx‐treatedn‐GaAs is also determined to be about 0.4, 0.7, and 0.3 eV, respectively, by SRPES for the first time, which are in fairly good agreement withI–Vcharacteristics of the metal/S/n‐GaAs Schottky diodes. It is found that the oxide‐free interface with a sulfur interlayer plays an important role for the metal‐dependent Schottky barrier formation.

ISSN:0734-2101    

DOI:10.1116/1.578719

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

Mixing effects induced in CeO2/TiO2and CeO2/SiO2composite powdered materials by bombardment with Ar+ions of 3.5 keV of kinetic energy have been studied by x‐ray photoelectron spectroscopy (XPS) and the factor analysis method. Characterization of the ceria phase in the original composite samples was carried out by x‐ray diffraction (XRD) temperature programmed reaction, transmission electron microscopy, and extended x‐ray absorption fine structure. The CeO2/SiO2sample is characterized by very small domains (∼25 Å in size) where the cerium has entered the Si–O lattice forming a kind of silicatelike amorphous phase. In CeO2/TiO2the cerium is in a bimodal distribution with small particles of CeO2(30–100 Å in size) and a cerium oxide phase formed by very small particles (d=16 Å) well dispersed on the TiO2grains. XPS showed that either by heating in H2or by Ar+sputtering a Ce4+→Ce3+reduction occurs to an extent which depends on the sample and reduction conditions. The reduction degree, determined from the XPS spectra by the factor analysis method, decreased in the sense CeO2/SiO2≳CeO2/TiO2≳ CeO2, for each sample being always higher after Ar+sputtering than after heating in H2. Adsorption of O2at 373 K on the reduced samples led to their partial reoxidation, to an extent which was dependent on the structure of the cerium in the samples and on the type of the previous reduction treatment. In the case of the CeO2/TiO2sample the high reduction degree obtained by Ar+sputtering can be explained by assuming a mixing of the cerium and titanium oxide phases induced by the ion bombardment. The use of a chemical probe such as the adsorption of O2is proposed as a method to detect the existence of mixing phenomena in composite systems submitted to ion bombardment.

ISSN:0734-2101    

DOI:10.1116/1.578720

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

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 N2ion beam sputter‐cleaned TiN. These surfaces are representative of those found in the traditional stand‐alone and newer integrated metallization processing sequences, respectively. Room temperature dosing of TiN with CuI(hfac)(vtms) is accompanied by rapid desorption of the vtms ligand, leaving chemisorbed CuI(hfac). This CuI(hfac) decomposes upon heating to form CO, CO2and CF4desorption products, leaving about 90% of the Cu on the surface, along with some F and C. CII(hfac)2also dissociatively chemisorbs at room temperature to form CuI(hfac) and an adsorbate with the stoichiometry of hfac. Unlike CuI(hfac)(vtms), a Cu(hfac)‐containing species desorbs upon heating above 75 °C. Near 200 °C this process ceases and decomposition (and possibly some intact desorption) of hfac takes place, leading to desorption of CO, CO2, and CF4. After desorption of all C‐containing species, about 30% of the initially deposited Cu remains on the surface, along with a submonolayer coverage of F. Regardless of the precursor, Cu begins to diffuse into the TiN film, above 280 °C. The results of our studies offer insights into the different mechanisms that may play a role in the nucleation of MOCVD film growth and incorporation of impurities at the interface. Significantly, the disproportionation reaction that dominates the deposition of pure Cu from CuI(hfac)(vtms) at the higher pressures typical of MOCVD does not occur under UHV conditions.  

ISSN:0734-2101    

DOI:10.1116/1.578721

出版商:American Vacuum Society    

年代:1993

数据来源: AIP