JOURNAL OF ELECTRONIC MATERIALS
	ABSTRACTS Volume 26, Number 9, September 1997 This Month Featuring: Proceedings of the Symposium on Evolution and Advanced Characterizatin of Thin Film Microstructures from the 1997 TMS Annual Meeting, Orlando, Florida, February 9-13. View September 1997 Table of Contents.

SPECIAL ISSUE PAPERS

Eric P. Kvam
Eric H. Chason
Steve M. Yalisov
Guest Editors

Molecular View of Diamond CVD Growth
C.C. BATTAILE,¹ D.J. SROLOVITZ,¹ and J.E. BUTLER²
1--Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109-2136. 2--Gas/Surface Dynamics Section, Code 6174, Naval Research Laboratory, Washington, DC 20375-0001

KEY WORDS Computer simulation, chemical vapor deposition (CVD), diamond films, Monte Carlo

In this paper, we discuss the simulation of the chemical vapor deposition (CVD) of diamond films on the molecular scale. These simulations are performed using a kinetic Monte Carlo method that combines the surface chemistry that is important to diamond growth with an atomic-scale picture of the diamond surface and its evolving atomic structure and morphology. We address the determination of surface reaction kinetics and growth conditions from experiments and reactor-scale models, and the prediction of polycrystalline film texture and morphology from the molecular-scale results. The growth rates and the concentrations of incorporated point defects as a function of substrate temperature for {100}- and {111}-oriented diamond films are obtained from the molecular-scale growth simulations. The {100} growth rates increase with temperature up to 1200K and then decrease above this value. The {111} growth rates increase with temperature at all of the temperatures studied. The concentrations of point defects in the {100} and {111} films are low at substrate temperatures below 1200K, but increase substantially at higher temperatures. The growth efficiency, measured as the ratio of film growth rate to defect concentration, is maximum between 1100-1200K for both film orientations, suggesting that this temperature range is ideal for CVD diamond growth under the simulated growth conditions.

Surface and Interface Stress Effects on the Growth of Thin Films
R.C. CAMMARATA
Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, MD 21218

KEY WORDS Critical thickness, interface stress, surface stress, thin film

Surface and interface stresses represent the work per unit area to stretch the surface of a solid. These types of stresses are discussed, emphasizing their relevance to thin film growth. In particular, the influence of these parameters on the critical thickness for epitaxy and for intrinsic thin film stress generation are considered.

Real-Time Stress Evolution During Si_1-xGe_x Heteroepitaxy: Dislocations, Islanding, and Segregation
J.A. FLORO,¹ E. CHASON,¹ S.R. LEE,¹ R.D. TWESTEN,¹ R.Q. HWANG¹ and L.B. FREUND²
1--Sandia National Laboratories, Albuquerque, NM 87185-1415. 2--Brown University, Division of Engineering, Providence, RI

KEY WORDS Heteroepitaxy, islanding, roughening, SiGe, strain relaxation, surface segregation

We have used sensitive real-time measurements of film stress during Si_1-xGe_x molecular beam epitaxy to examine strain relaxation due to coherent island formation, and to probe the kinetics of Ge surface segregation. We first describe our novel curvature-measurement technique for real-time stress determination. Measurements of the relaxation kinetics during high temperature Si₇₉Ge₂₁ growth on Si (001) are reported in which formation of highly regular arrays of [501]-faceted islands produce 20% stress relaxation. An island shape transition is also observed that reduces the effective stress by up to 50% without dislocations. Nonuniform composition profiles due to Ge surface segregation during growth of planar alloy films are determined with submonolayer thickness resolution from the real-time stress evolution. Up to two monolayers of Ge can segregate to the growth surface.

Adhesion of CVD TiN on 316L Surgical Stainless Steel Obtained in a Mass Transfer Regime
M.H. STAIA,¹ E.S. PUCHI,¹ and C. JULIA SCHMUTZ²
1--School of Metallurgy and Materials Science, Universidad Central de Venezuela, Apartado 49141, Caracas 1042-A, Venezuela. 2--Swiss Center for Electronics and Microtechnology Incorporated, P.O. Box 41, Neuchatel, Switzerland

KEY WORDS Adhesion, coating, chemical vapor deposition (CVD), microscratch test, TiN

An investigation has been undertaken to study the adhesion of TiN coatings deposited by using the CVD process at 900°C on surgical stainless steel. The microscratch test method (CSEM) was employed to evaluate the coating adhesion. Three scratches were performed at progressive load under the test conditions. The observation of the surface damage by means of an optical microscope allowed the determination of the critical load, defined as the smallest load at which some recognizable adhesive failure event occurs. No acoustic emission detections or frictional force fluctuations could be correlated with the optical observations. An estimate of the work of adhesion was evaluated by using different models presented in the literature and a satisfactory description of the experimental data was obtained by means of the Bull, et al, model which indicated a value of W = 4 J.m^-2. The failure criterion is then correlated with the detailed information obtained by using microscopic observation of the coatings along the scratch channel.

Some Further Microstructural Characteristics of Face-Centered Cubic Polycrystalline Metal Thin Films
VARUN V. SINGH,¹ ALEXANDER H. KING,¹ and GIRISH DIXIT²
1--Department of Materials Science and Engineering, State University of New York at Stony Brook, Stony Brook, NY 11794-2275. 2--Semiconductor Process and Device Center, Texas Instruments, Inc., 13536 N. Central Expressway, Dallas, TX 75243

KEY WORDS Aluminum,gold, grain boundaries, grain boundary character distribution, texture, thin films

We have made detailed observations of gold thin films and commercial aluminum-copper alloy films, using transmission electron microscopy. All of the films embody a strong <111> fiber texture. We have measured the misorientation distributions for the grain boundaries in these films, and also determined the "grain boundary character distribution" in terms of the coincident site lattice model. We show that in spite of their apparent similarity, these films embody significant differences in terms of these measures.

Local Textures and Grain Boundaries in Voided Copper Interconnects
R.R. KELLER,¹ J.A. NUCCI,² and D.P. FIELD³
1--National Institute of Standards and Technology, Materials Reliability Division, 325 Broadway, Boulder, CO 80303. 2--Cornell University, School of Electrical Engineering, Phillips Hall, Ithaca, NY 14853. 3--TexSEM Laboratories, Inc., 226 West 2230 North #120, Provo, UT 84604

KEY WORDS Copper, grain boundary, texture, thin films

We have characterized grain boundary structures and local textures in stress voided copper lines. Grain boundary misorientations as well as the tilt and twist character of boundaries were measured using electron backscatter diffraction in the scanning electron microscope in conjunction with focused ion beam images. We have summarized data for a number of boundaries immediately adjacent to voids and made comparisons to boundaries from regions that remained intact. These data were acquired from the same lines, and so represent measurements from material with identical histories. Significant local variations in microstructure were observed. Local <111> textures of grains near voids were of lower strength than those away from voids. Grain boundaries intersecting voids were of higher angle character and had significant twist components. These results suggest that local regions associated with more favorable kinetics are more susceptible to void formation and growth.

Elastic Modulus Measurement of Thin Film Using a Dynamic Method
YOUNGMAN KIM
Department of Metallurgical Engineering, Chonnam National University, Kwangju, 500-757, Korea

KEY WORDS Beam vibration theory, elastic modulus, thin film

A two layer composite model was developed using a beam vibration theory and the model was applied for measuring the Young's modulus of thin films. The Ti coated Si wafer composites were produced by radio frequency magnetron sputtering and used to test the developed model. The measured film modulus using a dynamic method was checked with that using the static method utilizing the pure bending of a cantilever composite beam. The film modulus values measured in both methods were in good agreement. The film modulus values for the specimens with different film thicknesses were also in good agreement when they were measured by the same method.

Evolution of Grain Structure in Thin Film Reactions
K. BARMAK,¹ J.M. RICKMAN,¹ and C. MICHAELSEN²
1--Department of Materials Science and Engineering, Lehigh University, 5 East Packer Avenue, Bethlehem, PA 18015. 2--Institute for Materials Research, GKSS Research Center, D-21502 Geesthacht, Germany

KEY WORDS Grain structure, microstructure, niobium/aluminum, polycrystalline, thin film reactions, thin films, titanium/aluminum

In this paper, we examine, both experimentally and theoretically, the kinetics of formation and microstructure of product phases in thin film reactions, using the Nb/Al and Ti/Al systems as our prototypes. The results of calorimetry and microscopy studies are interpreted using simple kinetic and morphology models. In particular, the kinetic models employed here focus on the nucleation and growth components of the phase formation process and the morphology models provide a starting point for the classification of product grain structures.

Stress Relaxation and Thermal Evolution of Film Properties in Amorphous Carbon
J.P. SULLIVAN, T.A. FRIEDMANN, and A.G. BACA
Sandia National Laboratories, Albuquerque, NM 87185

KEY WORDS Amorphous carbon, electrical conductivity, stress relaxation, thermal evolution

A model for the stress relaxation of amorphous carbon films containing high concentrations of fourfold coordinated carbon is presented. The onset of stress relaxation in these materials occurs following thermal annealing at temperatures as low as 100°C, and near full stress relaxation occurs after annealing at 600°C. The stress relaxation is modeled by a series of first order chemical reactions which lead to a conversion of some fourfold coordinated carbon atoms into threefold coordinated carbon atoms. The distribution of activation energies for this process is derived from the experimental measurements of stress relaxation and is found to range from 1 eV to over 3 eV. Permanent increases in the electrical conductivity of the carbon films are also found following thermal annealing. The electrical conductivity is found to be exponentially proportional to the number of additional threefold atoms which are created upon annealing, with the increase in threefold atom concentration being deduced from the stress relaxation model. This indicates that the increase in electrical conductivity and the stress relaxation originate from the same fourfold to threefold conversion process and that electrical transport through these films is dominated by a hopping conduction process.

Glancing-Angle Ion Bombardment for Modification and Monitoring of Semiconductor Surfaces
J.G.C. LABANDA and S.A. BARNETT
Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208-3108

KEY WORDS Ion bombardment, ion scattering, semiconductor surfaces

Using glancing-angle ion bombardment for surface modification rather than conventional near-normal incidence ions has the advantages of reducing damage and implantation projected ranges, reducing channeling, reducing sputtering, and preferentially removing surface asperities leading to flat surfaces. The effect of bombardment conditions on the surface morphology and perfection of GaAs (001), InP (001), and Si (001) surfaces are reported. Air-exposed surfaces were cleaned and smoothened to near atomic flatness without damage under optimal conditions. Sputtering yield, measured using film thicknesses and changes in reflection high-energy electron diffraction oscillations, decreased with decreasing incidence angle. The low sputtering yield and minimal damage make a glancing-angle geometry ideal for real-time characterization by ion scattering spectroscopy. Surface composition measurements on single monolayers of InAs on GaAs showed that the glancing-angle Ar beam did not measurably change the In coverage over relatively long times. A new ion beam monitoring technique was also developed that utilizes the advantages of glancing-angle ions. Specular scattering of 3 keV He ions was observed for incidence angles of 2-6° from GaAs (001). Oscillation in the specularly scattered ion current during GaAs growth were observed with periods corresponding to monolayer growth times. The oscillations allow a simple quantitative interpretation based on scattering by adatoms and step edges.

Mechanisms of Strain Induced Roughening and Dislocation Multiplication in Si_xGe_1-x Thin Films
D.E. JESSON,¹ K.M. CHEN,¹ S.J. PENNYCOOK,¹ T. THUNDAT,² and R.J. WARMACK²
1--Solid State Division, Oak Ridge National Laboratory, TN 37831-6030. 2--Health Sciences Research Division, Oak Ridge National Laboratory, TN 37831-6123

KEY WORDS Heteroepitaxy, interface roughening, SiGe

We discuss the stress driven roughening transition of Si_xGe_1-x thin films. In the case of annealed films, nucleation effects dominate the nature of the surface ripple which formed by a cooperative nucleation mechanism. Individual islands appear to nucleate via multilayer fluctuations. Faceting can however be suppressed at high supersaturations, resulting in a transition with characteristics of the Asaro-Tiller-Grinfeld instability. The relationship between morphological evolution and dislocation nucleation and multiplication is considered.

Spontaneous Lateral Composition Modulation in AlAs/InAs Short Period Superlattices Via the Growth Front
J. MIRECKI MILLUNCHICK,¹ R.D. TWESTEN,¹ S.R LEE,¹ D.M. FOLLSTAEDT,¹ E.D. JONES,¹ S.P. AHRENKIEL,² Y. ZHANG, ²H.M. CHEONG,² and A. MASCARENHAS²
1--Sandia National Laboratory, Albuquerque, NM. 2--National Renewable Energy Laboratory, Golden, CO

KEY WORDS Composition modulation, lateral modulation, superlattices

The spontaneous formation of lateral composition modulation in AlAs/InAs short period superlattices on InP (001) substrates has been investigated. Transmission electron microscopy and x-ray diffraction reciprocal space mapping show that the lateral modulation is very regular, with a periodicity along the [110] direction on the order of 180Å. A surprising result is that this material system also exhibits a lateral modulation along the [] direction, with a periodicity of 330Å. Reflection high energy electron diffraction performed during the deposition revealed that the reconstruction changed from (2 x 1) during the InAs deposition cycle to (1 x 2) during the AlAs cycle, which may be related to the presence of the modulation in both <110> directions. High magnification transmission electron micrographs show that the surface is undulated and that these undulations correlate spatially with composition modulation. Detailed analysis of the images shows that the contrast observed is indeed due to composition modulation. Photoluminescence from the modulated layer is strongly polarized and red-shifted by 220 meV.

Structural Stability of Low Temperature Grown InGaAs/GaAs Heterostructure
CHANRO PARK,¹ C.G. PARK,¹ CHAE-DEOK LEE,² and S.K. NOH²
1--Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, Kyungbuk 790-784 Korea. 2--Materials Evaluation Center, Korea Research Institute of Standards and Science

KEY WORDS As precipitate, dislocation generation, low temperature growth

InGaAs/GaAs superlattice was grown by molecular beam epitaxy (MBE) on GaAs (100) substrate at low substrate temperature (250°C). The as-grown superlattice sample was then annealed at various temperatures for 10 min. The as-grown superlattice was pseudomorphic and stable up to 800°C annealing. Annealing at 850°C or higher temperatures, however, caused strain relaxation accompanying with dislocation generation at the As precipitate. Dislocation generation at the As precipitate was influenced by two factors. The one is lattice mismatch between GaAs and As precipitate, and the other is elastic interaction force acting on the As precipitate.

Fatigue-Creep Crack Propagation Path in Solder Joints Under Thermal Cycling
D.R. LIU and YI-HSIN PAO
Ford Research Laboratory, Ford Motor Company, 20000 Rotunda Drive, Dearborn, MI 48121

KEY WORDS Crack propagation, scanning electron microscopy, solder joint, thermal fatigue-creep

The present study investigates the thermal fatigue crack propagation path in a eutectic solder joint between a 2512 leadless chip resistor and a printed wiring board which had experienced thermal cycling between -55 and 125°C. This was achieved through the microstructural examination of fractured surfaces of the joints. Patches of finely spaced striations were observed in a predominant shear strain field in the joints. These striations were attributed to the tensile strain components in the field and used to add the identification of the fatigue crack propagation direction. It was observed that cracks did not simply propagate across the depth of the joint from the inner end (the heel) to the outer end (the toe) in the longitudinal direction, but from a corner point on the free edge of the heel to the center across the joint depth, making an angle of about 70° with respect to the longitudinal direction.

Analysis of Iodine Incorporation in MBE Grown CdTe and HgCdTe
A. PARIKH, S.D. PEARSON, B.K. WAGNER, and C.J. SUMMERS
Quantum Microstructures Laboratory, Georgia Tech Research Institute, Atlanta, GA 30332

KEY WORDS CdTe, HgCdTe, iodine, molecular beam epitaxy (MBE)

A study is reported of the dynamics of dopant incorporation in iodine doped CdTe. Using a mathematical formulation, the iodine doping profiles in CdTe and HgCdTe have been fitted to experiment to obtain material parameters such as the bulk and surface diffusion and the segregation energy. Dopant profile fitting showed that iodine diffusion was insignificant and gave an iodine segregation energy of 0.6 eV and a surface diffusivity enhancement factor of 300 at a growth temperature of 230°C. The model was used to determine the effect of the growth rate and temperature for particular growth conditions.

Electromigration in Aluminum/Silicon/Copper Metallization Due to the Presence of a Thin Oxide Layer
K.A. KOH¹ and S.J. CHUA²
1--Brooktree Pte, No 1. Kallang Sector, #07-04, Kolam Ayer Industrial Park, Singapore 1334. 2--Centre for Optoelectronics, Department of Electrical Engineering, National University of Singapore, Kent Ridge, Singapore 0511

KEY WORDS Al/Si/Cu, electromigration, metallization

The effect of a thin layer of SiO₂ (50 nm) on the electromigration behavior of Al/0.8wt.%Si/0.5wt.%Cu metallization, passivated by spin-on-glass, phosphorus silicate glass and silicon nitride as part of the complementary metal oxide semiconductor technology fabrication process was studied. It is found that voids were formed along the edge of the metallization line as opposed to formation at triple point of grain boundaries. At the same stress current of 1 x 10⁶ A/cm², thicker metallization layer (600 nm) showed an improvement in median time to failure (MTF) (1.4 times) with smaller void size (0.2 to 0.4 µm) over one without an underlying oxide, whereas if the metallization thickness is thin (300 nm), the MTF is degraded (0.6 times) with larger void size formed (0.3 to 1.0 µm).

Characteristics of Si₃N₄/GaAs Metal-Insulator-Semiconductor Interfaces with Coherent Si/Al_0.3Ga_0.7As Interlayers
DAE-GYU PARK,¹ ZHI CHEN,¹ and HADIS MORKOÇ^1,2
1--University of Illinois at Urbana-Champaign, Frederick Seitz Materials Research Laboratory and Coordinated Science Laboratory, 104 South Goodwin Avenue, Urbana, IL 61801. 2--Also at Wright Laboratory, Wright Patterson Air Force Base, OH

KEY WORDS Interfaces, metal-insulator-semiconductor (MIS), Si/AlGaAs interlayers, SiN/GaAs

Si₃N₄/GaAs metal-insulator-semiconductor (MIS) interfaces with Si(10Å)/Al_0.3Ga_0.7As (20Å) interface control layers have been characterized using capacitance-voltage (C-V) and conductance methods. The structure was in situ grown by a combination of molecular beam epitaxy and chemical vapor deposition. A density of interface states in the 1.1 x 10¹¹ eV^-1 cm^-2 range near the GaAs midgap as determined by the conductance loss has been attained with an ex situ solid phase annealing of 600°C in N₂ ambient. A dip quasi-static C-V demonstrating the inversion of the minority-carrier verifies the decent interface quality of GaAs MIS interface. The hysteresis and frequency dispersion of the MIS capacitors were lower than 100 mV, some of them as low as 50 mV under a field swing of about ±2 MV/cm. The increase of the conductance loss at higher frequencies was observed when employing the surface potential toward conduction band edge, suggesting the dominance of faster traps. Self-aligned gate depletion mode GaAs metal-insulator-semiconductor field-effect transistors with Si/Al_0.3Ga_0.7As interlayers having 3 µm gate lengths exhibited a transconductance of about 114 mS/mm. The present article reports the first application of pseudomorphic Si/Al_0.3Ga_0.7As interlayers to ideal GaAs MIS devices and demonstrates a favorable interface stability.

Continuous In Situ Growth Rate Extraction Using Pyrometric Interferometry and Laser Reflectance Measurement During Molecular Beam Epitaxy
J.J. ZHOU,¹ Y. LI,¹ P. THOMPSON,¹ R. CHU,¹ and H.P. LEE,¹ Y.C. KAO, and F.G. CELII
1--Department of Electrical and Computer Engineering, University of California, Irvine, Irvine, CA 92697. 2--Corporate Research and Development, Texas Instruments, Dallas, TX 75265

KEY WORDS Growth rate estimation, in situ monitoring, laser reflectance, molecular beam epitaxy (MBE), pyrometric interferometry

We describe a new, universal, and easy-to-use method for real-time thickness and growth rate extraction based on in situ optical monitoring during molecular beam epitaxy of GaAs/AlAs layered structures. The method is based on a novel least-square phase extraction algorithm and a model-reference comparison scheme. The new method demonstrates a significantly reduced growth rate estimation error (<2%) on both pyrometric interferometry (PI) and laser reflectance (LR) monitored data over conventional methods. Based on preliminary studies, the new method also shows excellent dynamic tracking of growth rate with a thickness resolution of only 30 nm when the growth rate is intentionally changed.

Crystallographic Texture of C54 Titanium Disilicide as a Function of Deep Submicron Structure Geometry
V. SVILAN, K.P. RODBELL, L.A. CLEVENGER, C. CABRAL, JR., R.A. ROY, C. LAVOIE, J. JORDAN-SWEET, and J.M.E. HARPER
IBM T.J. Watson Research Center, Yorktown Heights, NY 10598

KEY WORDS Crystallographic texture, TiSi2, x-ray diffraction

Detailed analysis of the crystallographic texture of C54 TiSi₂ was performed and showed a strong correlation between the geometry of the silicide structures and preferential crystallographic orientation. The study was undertaken on blanket and patterned TiSi₂ films formed in the reaction between 32 nm of Ti and undoped polycrystalline silicon using both in situ x-ray diffraction during heating and post-anneal four-circle pole figure reflection geometry measurements. Full pole figures were taken to determine the distribution of C54 TiSi₂ grain orientations in narrow (0.2 to 1.1 µm) lines which was compared with similar results obtained from unpatterned (blanket) films. While in blanket films we found the presence of weak <311> C54 TiSi₂ crystallographic orientation perpendicular to the sample surface, the <040> preferential orientation dominated in patterned submicron line structures and increased with decreasing linewidth. Using pole figure analysis, we observed strong <040> fiber texture in narrow lines with a slight variation in the tilt of the (040) planes normal in the direction perpendicular to the line (full width at half maximum [FWHM] ~6°), but very little along the length of the line (FWHM ~2°). In addition, a preferred in-plane (azimuthal) orientation of <040> crystals was found which showed that most of the <040> grains had their (004) plane normals oriented parallel with the line direction. These findings support a model of the C49 to C54 TiSi₂ transformation involving rapid growth of certain orientations favored by the one-dimensional geometry imposed by narrow lines.