ICMCTF1999 Session FP: FP Posters

The importance of characterizing the structure and morphology of vacuum deposited films increases because of the advances in miniaturization and structural design. The bulk properties of a thin film are mainly determined by the evolution of the active surface during growth.

In this paper we present a system for the morphological investigation of the active surface of the growing film. An Atomic Force Microscope (AFM) is located in a measurement-chamber which is kept at high vacuum. Samples can be transferred to the measurement chamber by a transportable load-lock which can easily be attached to various sputter-deposition chambers. The samples are mounted on a specially designed heatable substrate holder which can be inserted into the measurement chamber. The AFM-measurements are performed with the sample still mounted on the substrate holder. Therefore it is possible to study the film surface at various stages of film growth since the sample is continuously kept under vacuum conditions. The system performance is evaluated by studying the surfaces of Al-films up to 5 micron thickness. Special attention is paid to differences in the evolution of the film surface with and without the growth interruption required for the AFM-measurements.

This work was supported by the Austrian "Fonds zur Foerderung der Wissenschaftlichen Forschung", Grant Nr: P-122 81-PHY.

A finite element simulation that models the various processes that give rise to residual stresses in Ion Assisted Physical Vapour Deposited (IAPVD) Films has been developed at the University of Salford. The residual stress field in an IAPVD film comprises two main components: a thermal stress, which forms as the system cools to room temperature; and an intrinsic stress field which is the result of a number of processes that occur during deposition. Tensile stresses arise as a result of material attraction across certain sizes of void in the evolving coating. At the same time compressive stresses are occurring due to the creation of interstitial atoms and/or the entrapment of inert gas atoms. There is some debate as to which effect is predominant in the generation of the compressive stresses, but the pattern of the relationships between ion and atom energies, substrate temperature, and residual stress level is of the same form for each. Thus the computer model is valid for both processes.

The presence of residual stresses in IAPVD coatings can be beneficial, e.g. fatigue characteristics can be improved by inducing compressive residual stress. However, it can be highly undesirable, as in the case where the variation in stress across the thickness of the coating causes the coating to attempt to curl up and thereby peel away from the substrate.

Clearly it is desirable to be able to control very closely the residual stress fields that arise in IAPVD coatings. Because of the large number of processes contributing to the buildup of the residual stresses an experimental program to provide sufficient data for design purposes would be very expensive and impractical. A parametric study utilising the computer model is a more cost-effective way of providing an invaluable tool for the tailoring of residual stresses in IAPVD films.

This paper presents preliminary results from the finite element model and details of the validation of the model against experimental data.

The residual stress in fiber textured films is hardly determined by the commonly used x-ray stress measurement i.e. sin²ψ method, because the method was constructed on the assumption the specimen was an isotropic elastic polycrystalline material. In recent years, several researchers have deduced the x-ray stress measurements in fiber textured films like [111], [100] and [110] in accordance with Hooke's law in the crystal reference frame.

In this paper, the relation between the stress and the measured lattice strain by the x-ray diffraction is reviewed for the fiber textured films in terms of elasticity analysis. The x-ray stress determination is introduced the weighted average around the normal direction of the x-ray diffraction plane for measured strain values. Moreover, the stress determination by the x-ray diffraction was experimentally applied to titanium carbide films with the <110> fiber texture, which were evaporated on steels by chemical vapor deposition (CVD). The determination was tried to verify and discussed in terms of the stress for TiC films.

Some parts in a gasoline engine such as piston lings and liners are required to possess material characteristics of the heat-resistance, the corrosion-resistance and the wear-resistance. In order to cope with the problem, chromium plating has been used so far in this field. Ni-Co-P/α-Si₃N₄ composite plating is anew developed technique to the above purpose.

The purpose of this study is to make clear the state of residual macro-and micro stresses by measuring residual phase stresses in both matrix (Ni-Co-P alloy) and α-Si₃N₄ particles by means of the method of x-ray stress measurement.

Change in the state of residual stress due to the manufacturing process was also examined, for which specimens in the state of after plating, heat-treatment for hardening and barrel polishing respectively were prepared and used for the x-ray measurement.

It was found from the present study that the residual stress is the composite plating used in this study varied with not only the manufacturing process but also the thickness of the plating, mean diameter of the second particles (α-Si₃N₄) and their volume fraction. Detail residual stresses, such as the macro-and micro stress and the phase stress in each constituent, for these specimens were obtained in this study.

It has already been possible to deposit diamond film on metals or ceramics by the CVD method, and their industrial applications are discussed so far. For example, with the film coating, many properties of materials such as wear and corrosion resistance are highly improved. However, it is important to establish the optimum film deposition method and condition, and to evaluate the material strength of the film for the industrial use of the diamond thin film without debonding and deformation. Residual stresses generated during CVD process plays important role in debonding and deformation of the film. Thus, measurement of residual stresses in the film is very important in evaluation of the diamond film.

The purpose of this study is to make clear the state of the preferred orientation and the residual stress, which is an avoidable during the growth of the film. These are evaluations are necessary for the application of the diamond film. The experiment was performed using the specimens with different film thickness as well as different surface process on the substrate.

The growth process of thin films is affected by its substrate and the boundary between their and the thickness of the film, so that the structure and the state of the residual stress of thin films depend on the depth from the film surface.

In this study, the method of the measurement of the depth profile of the residual stress with depth using the low x-ray incidence angle method was investigated. A newly developed x-ray instrument was used foe purpose in this study, in which the parallel beam method was used for its x-ray optics. On the analysis of the diffraction data obtained from the experiment, the analysis method in which the effect of the stress gradient with depth was applied. The thin film used for the experiment was Silicon oxide (SiO₂) film deposited on Si wafer.

The transition from aluminum to copper interconnects in semiconductor manufacturing is rapid by progressing. Two primary factors drive this transition are the lower resitivity and the increased electromigration resistance that copper offers relative to aluminum. Copper electroplating is the most techniques for copper metallization for ULSI. The electroplating method has advantages of low processing temperature, short processing time, and simple deposition facilities.

In the present study, the suitability of Al as a seed layer is evaluated. A 30- to 50-nm-thick seed layer by sputtering before copper electroplating was deposited on TiN films. The advantage of Al as a seed layer is well known in ULSI and Al has a good adhesion with TiN. However, this seed layer can not be electroplated directly in the present study because it will be dissolved in acidic copper electroplating solution. The seed layer must be activated by a Pd activation solution. The high-throw electroplating electrolyte was composed of CuSO₄.5H₂O (50-100 g/l), H₂SO₄ (170-200 g/l), HCl (50-100 ppm), and a small amount of additives. The values of applied electrical current were 40-100 mA. Transmission electron microscope and X-ray diffractometry were utilized to investigate the microstructure and crystal orientation. Auger electron spectrocopy was applied to determine the stoichiometry and uniformity along the depth direction. The morphology was studied by a field emission scanning electron microscopy. XRD peaks show clearly a small (002) peak and strong (111) peak of pure Cu films deposited on TiN. The evolution of crystal growth orientation of the copper electroplating can be explained by considering surface energy and strain energy of different crystal planes. The electromigration resistance of copper lines was reported to be strongly influenced by the copper texture. In addition, electroplated copper films can be influenced significantly on Pd activation solution. Therefore, the interfaces of Cu/Pd and Pd/Al are investigated. The surface of as-deposited copper films was rather rough and resulted in the increase resistivity. Bright and smooth surface of copper film can be achieved by chemical mechanical polishing (CMP) technology. The thermal stability of Cu/TiN/Si structure has been investigated.

The continued miniaturization towards sub-quarter micron feature size mandates the search for low dielectric constant interlayer dielectric. SiO₂aerogel films have many excellent properties for intermetal dielectrics due to their unique porous structure formed during supercritical drying process. Nano-porous SiO₂aerogel films have low dielectric permittivity through the incorporation of micropores into the SiO₂network. But from the characteristics of sol-gel derived process, skeletal network of SiO₂aerogel film contains a number of Si-OR (R=alkoxyl group) and Si-OH bonds and adsorbed water as internal species.

An oxygen plasma treatment using inductively coupled plasma to nano-porous SiO₂aerogel film at room temperature was introduced to control the internal surface chemical species for applying to intermetal dielectrics. In this work, the microstructural evolution of SiO₂aerogel through oxygen plasma treatment was investigated using scanning electron microscopy, transmission electron microscopy, small-angle X-ray scattering, and nuclear magnetic resonance. In addition, the changes of chemical species and surface chemical bonding states after the treatment were observed using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Rutherford backscattering spectrometry.

In ultra large scaled integration, as the size of devices in multilevel microelectronics becomes much smaller and their structure more complex, they require lower dielectric constant in the IC fabrications to overcome the interconnection delay which is termed resistance-capacitance delay. Low density SiO₂xerogel film prepared by two-step procedure is a novel material with lower dielectric constant than any conventional SiO₂film by chemical vapor deposition. Theoretically, dielectric constant depends on porosity, for example, dielectric constant of a film with 50% porosity is about 2.5. Therefore, a major issue for xerogel film is the porosity due to its inherent porous nature.

After gelation but before complete drying, the chemistry and structure of a gel may be dramatically altered in aging process. During aging, terminal Si-OR (R=alkoxyl group) and Si-OH groups will continue to condense to form Si-O-Si bonds plus either ROH or H₂O by-products. Consequently, the porosity of SiO₂xerogel thin film prepared using a sol-gel technique could be controlled by aging parameters and an increase in the microstructural strength of the SiO₂xerogel film could be also obtained.

In this work, we investigated the changes in microstructure and properties of SiO₂xerogel films by varying aging parameters such as time, temperature, and solution. The network structure of xerogel film was evaluated using scanning electron microscope (SEM). The density and porosity of xerogel film was deduced from Rutherford backscattering spectrometric analysis and cross-sectional SEM. X-ray photoelectron spectroscopic and Fourier transformed-infrared spectroscopic analyses were also conducted to investigate the composition and surface bondings of the films. From the above analysis, it could be found that the 3-dimensional network structure of the film is changed by aging process. These microstructural changes accompanies the changes in porosity and electrical property of the films.

The etching behavior of SiO₂aerogel film was investigated to know the feasibility of application to integrated circuits as an interlevel dielectric (ILD) material. SiO₂aerogel film has porous structure and its particles are covered with surface terminal chemicals, which can play an unique role unlikely with other SiO₂films. Because of these properties, the etching behavior of this material depends strongly on its microstructure and surface terminal coverages.

In this work, the etching behavior of SiO₂ aerogel was examined with the microstructural and surface chemical points of view. For this, SiO₂ aerogel and thermally grown SiO₂ films were etched with a magnetized inductively coupled plasma using various etching gases. Ar plasma etching was done to reveal the physical effect of the etching. SF₆gas plasma was chosen as a fluorocarbon residue-free etching. An usual C₂F₆gas plasma etching was also carried out to investigate the etching behavior of SiO₂ films with the existence of fluorocarbon polymeric residue. From these experiments, the etching behavior of SiO₂ aerogel film could be interpreted. Before and after the etching procedure, surface morphologies and particle shape were observed using scanning electron microscopy. Surface bonding states were analyzed using Fourier-transformed infrared and X-ray photoelectron spectroscopy. Due to the porous structure and high C, H contents of SiO2₂ aerogel film unlike the other SiO₂ materials, it shows a distinguished unique etching behavior.

For the application of GaAs to high-speed semiconductor devices, the control of surface characteristics of GaAs is very important. There have been a lot of works on S-passivation treatment which improves the electrical properties of GaAs device, i.e. leakage current and breakdown voltage. But the mechanism of passivating GaAs surface is not agreed with each other. Especially, the state of elemental As on the etched surface, which forms a bond with S and finally a passivation layer, is not clear.

In this work, cleaned GaAs surface was prepared by wet-etching using acid base solution. An elemental As was produced and remained on the etched GaAs surface irregularly. After S-treatment using (NH₄)₂S_Xsolution, the elemental As disappeared completely and the surface was passivated with sulfur in a monolayer thick, which distributes with crystallographically regular site. The (NH₄)₂S_Xsolution treatment limited a thickness of passivation layer and dissolved elemental As partially. (NH₄)₂S_X vapor was also used to passivate the etched GaAs, with this procedure, the dissolution of elemental As could be eliminated during the passivation. The amount of elemental As could be controlled during the etching before the passivation. The passivation GaAs surface containing various amount of bonds with S were revealed to have different surface structure and chemical bonding state by angle resolved X-ray photoelectron spectroscopic analyses. The surface structure was conformed by low energy electron diffraction observations.

The deposition of thin films or multilayer systems is always accompanied by stress generation both in substrate and in growing film. Stress and adhesion determine the stability of a thin film/substrate composite and thus the life time of a component, since the composite may fail by cracking, delimitation or buckling. Substrate bending, and thus changes in the electric properties of semiconductors, lead again to the defects in fabricated electronic devices or shifts in bandgap in semiconductors.

In this work we have used cantilever technique to measure the stress in cadmium sulfide thin films and have constructed the laser interferometer to perform these measurements. Cadmium sulfide is a promising candidate as material for emitting optoelectronic devices, namely several II-VI compounds have been used in the quantum well structures. Polycrystalline CdS can be applied as wide band gap window material in a CdTe/CdS heterojunction solar cell. The single crystal (100)GaAs has served as substrate material for these multilayer structures. Cadmium sulfide thin films were grown on (100)GaAs by successive ionic layer adsorption and reaction (SILAR) technique from aqueous precursor solutions. The stress of the thin films was characterized by means of laser interferometry, composition morphology by Electron Spectroscopy for Chemical Analysis (ESCA) and by Atomic Force Microscopy (AFM). Correlation between the growth mode and the residual stress level is demonstrated. The changes from three-dimensional to two-dimensional growth of the film results in the change from tensile to compressive residual stress.

The amelioration of ULSI circuit demands the intermetal dielectric materials of low-¥ê(dielectric constants) because these materials permit us to obtain lower power consumption and reduced crosstalk. Porous silica xerogel film which contains large internal surface area, typically in the range of 500~1000 m²/g, is a promising ultra-low dielectric material with high thermal stability for ULSI interconnecting application. However, silica xerogel films were found to have a number of surface coverages which would greatly influence the dielectric constant.

We have investigated the effects of various plasma (H₂, He, O₂, N₂, Ar) treatment on silica xerogel films in order to strengthen the silica xerogel film and improve the surface chemical bonding nature of silica xerogel film. The plasma treatments could reduce the density of silanols (Si-OH) and methyl (-CH₃) groups. The thickness reduction and particle size growth were observed. The partial etching of silica xerogel film was also observed and the etching rate was found to depend on the plasma treatment time and bias-voltage.

This work could reveal the physical, chemical, electrical, and thermal properties of silica xerogel film through curing with various gases plasma. The modification of xerogel film by each plasma is related to the radiation damage and the reconstruction of internal structure during the plasma treatments. The role of reactive gases seems to be very important to improve the quality of silica xerogel film.

We have studied the effect of oxygen pressure (PO₂) during pulsed laser deposition of YBa₂Cu₃O₇-δ (YBCO) using high resolution x-ray diffractometry and topography with synchrotron generated x-rays. In some cases, the rocking curves of the YBCO (005) and (006) diffraction peaks showed multiple peaks characteristic of slightly misoriented crystalline grains in the films, but very narrow peak widths, e.g., full-width at half maximum of 0.13±0.03 degrees. The magnitude of the c-axis lattice parameter was found to be a monotonic function of PO₂; c increased as PO₂ decreased. Based on measurements of the integrated intensities of the (005) and (006), the films were found to be fully oxygenated.¹ Topographs were made on Beamline X23A3 at the National Synchrotron Light Source, Brookhaven National Laboratory. Analyses of these topographs showed that the films fabricated at lower values of PO₂ were uniformly strained. Comparisons of topographs from films made with different values of PO₂ and on both LaAlO₃ and MgO substrates were also made. Those grown on MgO substrates tended to have a much smoother morphology, as compared with those grown on the LaAlO₃ substrates. Additional details of this work will be discussed.

¹ J. Ye and K. Nakamura, Phys. Rev.-B 48, 7554 (1993).

The study of particles of a few nanometers in size has become a rapidly developing field. Metal, semiconductor and ceramic nanoparticles appear in many applications, some in a natural way (i e precipitates in a matrix), and some have been developed with special engineering properties, like quantum dot diode lasers, magnetic devices, etc.. They also appear in catalytic systems, for instance Pt/Alumina, Pt/graphite, etc. In this work we present our efforts towards understanding the contrast present in High-Resolution Transmission Electron Microscopy (HREM) of multiple-phase systems, such as Ni-Pt grown on amorphous substrates. The problem is interesting from the point of view of catalysis where one needs to know whether there has been alloying of the metals at the nano-scale or the phases have been segregated.

Specimens were prepared by sputtering of Pt and Ni in a clean system on amorphous carbon coated grids. In order to obtain alloys, Pt and Ni thin films have been co-sputtered,then reduced in a hydrogen flow to promote the alloying of the particles. HREM characterization was performed using a JEOL 4000EX microscope. Image simulations were performed using a full dynamical calculation with Cerius’ in a Silicon Graphics computer. The particles were constructed by modeling a super-cell of the core-shell type.

Using the techniques mentioned it has been possible to identify a) metal Ni nanoparticles covered by thin graphite surface films. b) Ni nanoparticles covered by a few NiO layers; c) In Pt-Ni co-sputtered particles: Pt core with a NiO film covering the particles; d) Alloying of Ni Pt particles. A good crystallographic guess has to be made of how the shell “covers” the core particle, in order to obtain reasonable results. This can be achieved through careful observation of, for instance, moire fringes.

We are grateful to L. Rendon, C. Zorrilla and L Beltran del Rio for technical help.

In-situ plasma etching was conventionally used to remove the metal oxide from the aluminum surface prior to tungsten deposition. During the plasma etching, however, the outsputtered aluminum oxide and aluminum atoms can be redeposited on the sidewalls of the via and on the surface of dielectric layer, resulting in selectivity loss during the subsequent selective CVD-W.

In this work, we have investigated the effects of new clean solution, hydroxylamine sulfate ((NH₂OH)₂H₂SO₄) mixed with CuSO₄ , on Al via. The results show cleaning effect of the new clean solution is better than that of conventional plasma etching. Low via resistance is obtained if the via is cleaned by this new cleaning solution. Hydroxylamine sulfate is a powerful reducing agent capable of removing aluminum oxide (Al₂O₃) and leave the clean Al surface on the bottom of via. Then, the Cu ion in this new solution will immediately react with clean Al and in-situ form a copper passivated layer on the bottom of via hole. The copper is more stable than aluminum under the environment, and hard to be oxidized. In addition, the thin copper layer is helpful for tungsten nuclearation in via during CVD-W deposition. Therefore, the new clean solution can provide excellent cleaning capability and reduced via resistance for aluminum via.

Silicon nitride (Si₃N₄) is an important VLSI material owing to its high resistivity and breakdown strength and its use in surface encapsulation during ion implantation and annealing. Previous work has focused on films prepared by low-pressure and plasma-enhanced chemical vapour deposition (LPCVD and PECVD), but in the present work the DC electrical properties of films prepared by RF magnetron sputtering were investigated.

Al-Si₃N₄-Al sandwich structures were fabricated from a Si₃N₄ target at a discharge power of 100 W using N₂ as the sputtering gas at a pressure of approximately 0.5 Pa. Capacitance was independent of voltage, indicating the absence of a Schottky barrier at the Al/Si₃N₄ interface. Measurements of the capacitance as a function of inverse dielectric thickness implied a relative permittivity value of 6.3. In contrast to results on films prepared using PECVD¹ the samples did not exhibit Poole-Frenkel conductivity and tunnelling at higher voltages, but showed space-charge-limited conductivity (SCLC), dominated by an exponential distribution of trap levels, as indicated by a power-law dependence of current-density J on applied voltage V with an exponent value of typically 3.3. Measurements of J as a function of temperature confirmed the appearance of SCLC and indicated that the bulk trap density was of the order of 2 x 10²⁴ m^-3 as observed in LPCVD and PECVD films², with the appearance of hopping conductivity at low temperatures.

¹M. Tao, D. Park, S.N. Mohammad, D. Li, A.E. Botchkerav, and H. Morko, Philosophical Magazine B, 73, 723 (1996).

²Y.C. Park, W.B. Jackson, N.M. Johnson and S.B. Hagstrom, Journal of Applied Physics, 68, 5212 (1990).

As the device dimensions continue to shrink to 0.25um and below, the interconnect delay becomes a limiting device factor and increases device speed. Low dielectric constant interlayer dielectric (ILD) material such as poly(arylene ether)(PAE) which can offer lower dielectric constant than conventional silicon dioxide insulator are required in the ULSI technology.

In this work, we study the effect of CF₄ plasma treatment of poly(arylene ether) film characteristics. The dielectric constant of poly(arylene ether) film is found to be further reduced with the application of CF₄ plasma treatment. Also, the characteristics of Cu-gate metal- insulator-semiconductor capacitors with poly(arylene ether) dielectrics performed by CF₄ plasma treatment are studied.

There is a growing interest in coating solid surfaces with thin oxocarbosilane-based polymeric films by reactions resulting from ultraviolet radiation in an atmosphere Si, O, H containing a low molecular weight organic compounds. Polymers produced by influence of UV irradiation from a variety of organosilicon monomers have been studied due to the general interest in conventional organosilicon polymers and interest in organosilicon polymer films for silicon-based microelectronics applications (as insulators, composite thin films, wave guides, and separation membranes). Organosilicon monomers are volatile, easy to use, non-toxic, relatively inexpensive, and available from commercial sources.

The chemical structure of films formed by photolyses of disiloxanes depends on the fragmentation of the monomer. This fragmentation depends not only on the chemical composition and structure of the monomer, but also on the polymer deposition process conditions, such as pressure, presence of the buffer gas, current fluence of UV irradiation, etc. By varying these parameters, materials with different chemical compositions and structures can be obtained from the same monomer.

The present report focuses on the relationships between the UV polymerisation conditions and the chemical structure of thin films of ArF laser induced-polymerised series of methyldisiloxanes [(CH₃)_nH_3-nSi]₂O with n = 1-3 in the gas phase. The peculiarities of the solid deposits will be presented by means of UV, FTIR, XPS and SEM techniques.

The photolysis mechanism also will be interpreted in terms of and the importance of contributing steps will inferred from the chemical structure of thin films and distribution of the photolytic products.

The surface kinetics during thin film growth has spurred great interest in the last dacade because of scientific and technological reasons. However, even the growth process of amorphous SiO₂ thin films, which are used extensively in the microelectronic industry as well as in optical coating applications, is still not well understood.

In the present work, the surface morphology of the amorphous SiO₂ thin films, formed by a newly developed ultrahigh vacuum sputering system which deposits thin films with excellent uniformity, is studied by atomic force microscopy. The results show that the hill-like surface of the initial growth is isotropic, homogenous, and smooth. With the increase of growth time, the size of the hill-like structure gradually increases in both the vertical and the lateral directions. It is remarkable that there is a critical thickness, about 100 nm in this case. After the film grows to the critical thickness, further growth leads to a sharp increase in the lateral size, especially the height of the hill-like structures, indicating a roughening transition. The detailed results will be presented.