The lack of high-temperature thermodynamically stable contacts has been a limiting factor for III-V compound semiconductor metallization. The instability of metal/semiconductor contacts at higher temperatures arises due to factors such as thermodynamic instability at the interface, lack of chemical inertness especially to oxygen containing ambients and a large lattice mismatch to the substrate. Our studies of two rare-earth compounds, dysprosium phosphide (DyP) and dysprosium arsenide (DyAs), demonstrate their potential to address the above problems. The growth and characterization of these two materials and their heterostructures will be presented.

Both the DyP and DyAs epilayers were grown using MBD. DyP has an excellent room temperature lattice match to GaAs with a mismatch of about 0.01%, whereas DyAs has a lattice mismatch to GaAs on the order of about 2.4%. Consistent high quality DyP and good quality DyAs epilayers, as characterized by TEM, XRD, AES and AFM were obtained for growth temperatures between 500°C and 600°C. The growth rate was about 0.5 μm/hr and and the RMS roughness of the epilayer surface was typically about 0.5 nm and 1.3 nm for Dyp and DyAs, respectively.

Electrical characterization of DyP and DyAs include variable temperature Hall measurements, four point probe, TLM, I-V and C-V measurements. Results show that both DyP and DyAs epilayers are n-type with electron concentration between 3–4 × 1020cm−3 and 2–3×1021cm−3, respectively. The room temperature mobility and resistivity of DyP are 300 cm2/Vsec and 60 μ Ω cm, respectively. The room temperature mobility of DyAs is about 50 cm2/Vsec. DyP forms a Schottky barrier to GaAs with a barrier height of 0.81eV and DyAs forms a weak Schottkyt barrier to GaAs. All relevant data will be presented along with schemes for using DyP and DyAs as potential interconnects to III-V compound semiconductors.

In-situ depositions and reactions are utilized in the study of phase formation from solid phase reactions. We report on the formation of epitaxial GaAs and the formation of NiAs or Ni2Ga3 by the exposure of Ni3GaAs to As4 or Ga fluxes. In-situ annealing of Ni on MBE-grown GaAs leads to Ni3GaAs, and subsequent reaction with As4 or Ga drives regrowth of GaAs. The structures were analyzed by RBS, XRD, TEM, and in-situ electrical measurements.

Epitaxial layers of the intermetallic β-CoGa cubic phase were grown at low temperature on (100)GaAs by metal-organic molecular beam epitaxy (MOMBE) using GaEt3 and CpCo(CO)2 as vapor sources. The film composition and the lattice mismatch on (100)GaAs may be adjusted by controlling the molecular beam pressure ratio. The growth on a Co-saturated GaAs surface leads to the formation of bi-phased CoGa-CoAs films whereas epitaxial single-phased β-CoGa layers are grown on a Ga-terminated GaAs surface with the simple cube on cube orientation [100](001 )CoGa//[100](001)GaAs. Annealing experiments under inert atmosphere have shown that MOMBE CoGa films are thermally stable on GaAs until ca. 823 K. Ohmic and Schottky CoGa/GaAs contacts have been made depending on the doping of the substrate by this process.

Inspecting and understanding the thermal stability of metal contacts in the context of reliability testing on high power transistors (especially in the GaAs technology) often necessitates to view atomic concentration profiles at deep interfaces. One common method for this purpose is the combined Auger spectroscopy/ion etching technique, where the region to be investigated is etched sequentially (with a “low” etch rate, typically in the Å/second regime) and Auger electron spectra (AES) are recorded at each step of the etching process. The 3 major resolution drawbacks of this approach are first that it is time-consuming, second that the spatial resolution is limited (atomic profiles on contact regions with lateral dimensions smaller that I R~m are difficult to obtain) and third that the interface of interest is “smoothed” during the etch process. The third point yields atomic concentration profiles with an apparent inter-mixing, which sometimes hinders observation of the details of interest for the interface under investigation.

We have used a different approach for this aspect of metal contact testing, in which the interface to be studied is first “revealed” by focused ion beam (FIB) micro-sectioning. After this preparation step, chemical images of the interface are directly obtained by high resolution Auger electron spectra mapping. The different operating conditions for the FIB process (orientation of the cross-section with respect to the transistor surface, preliminary procedures to eliminate residual roughness as well as surface contamination) have been optimized in order to produce Auger spectra free of any artifact. The approach is demonstrated on Au/GeNiAu ohmics contacts to the emitter electrode of GaAs-based hererostructure bipolar transistor, designed for high power amplification in the microwave regime. Ultimate spatial resolution of 20 to 30 nm on the Ayuger chemical images is demonstrated on an Auger microscope equipped with a Schottky field emitting tip.

The carbon nanotubes and carbon nanobtube junctions have recently emerged as excellent candidates for use as the building blocks in the formation of nanoscale electronic devices. Single wall carbon nanotubes, as molecular wires, could be used as nanoscale interconnects, where as complex junctions of nanotubes of different chirality can be used as rectifying and transiting devices. It has been shown that pentagon-heptagon defect is responsible for the creation of simple hetero-junctions. Complex junctions, such as 3-termianl T-junctions and Y-junctions require entirely different arrangement of defects. These 3-terminal junctions form prototypes of nanoscale tunnel devices made entirely of carbon. Furthermore, either n-type or p-type doping of the semiconducting portion of these complex junctions should yield Schottky barrier type devices. We also investigate simple wires and junctions of boron and nitrogen (III-V elements) and compare with those of carbon. The structural and electronic properties on nanotubes and nanotube junctions (carbon as well as BN) are studied using a generalized tight-binding molecular dynamics (GTBMD) scheme.

Advances in integrated circuit density, speed and complexity are dependent on lower resistance, finer line width on-chip interconnections. Methods for incorporating copper interconnects into IC fabrication processes have been developed which accomplish this objective but most of these methods use some form of blanket metal deposition that requires mechanical and/or chemical removal of excess material. To date, investigations into the selective deposition of conductor materials for device fabrication have met with limited success. A new process for selectively depositing metallic conductors using inexpensive, organic-based chemical solutions could potentially force a paradigm shift in the deposition of metals for microelectronic applications. Reversing the process currently used for selectively removing impurities from metal bearing waste streams, electrochemically controlled deposition of metals from electrically non-conducting organic solutions on submicron feature sizes is possible. A description of the fundamental electrochemical processes involved and parameter space available to engineer the solution chemistry will be presented along with experimental results from model systems. A discussion of the technology in light of ULSI issues and applications will be included.

Conducting thin films of RuO2 were grown at temperatures down to 623K on glass by metalorganic chemical vapor deposition (MOCVD). Tris-trifluoroacetylacetonate-ruthenium(III) (Ru(tfa)3) served as precursor. Smooth, specular and well adherent films were deposited, if the reaction gas contained water. The films were investigated by X-ray diffraction, SEM, and fourprobe resistivity measurement. Growth kinetics were also studied by in situ ellipsometry. The results are compared with films prepared by d.c. reactive sputtering before and after annealing. The properties of the MOCVD films, in particular the resistivity (ρ down to 72 μΩcm), are comparable to CVD films deposited at much higher temperatures and sputtered films after high temperature annealing.

A novel concept for CMOS transistor gate metallization is described. It is featured with Gate Cloisonné, a process consisting of dielectric deposition over frontend transistors, followed by chemical mechanical polishing to re-expose the gate pattern on a planar dielectric background. Based on this concept, two metallization schemes have been developed. One is self-aligned metal gate process, which allows for low thermal budget gate metallization with element metals such as W and Al, resulting in a very low sheet resistance (< 1 Ω/sq). The other scheme is dual self-aligned silicidation, which enables decoupling of gate silicidation from that of source/drain silicon areas. Titanium based silicidation process is implemented to form thick silicide on narrow polysilicon gates and thin one over active silicon areas. Low gate sheet resistance (≈ 1.9Ω/sq) is achieved with complete suppression of linewidth effects. Both the metallization schemes are a priori scaleable to deep submicron technologies and suitable to fabricating ultra-shallow junction devices with very low gate sheet resistance. Both of them have been implemented in a 0.25-μm CMOS technology.

In this study are reported results on the processing of nickel thin films by metal-organic chemical vapor deposition starting from nickelocene, at atmospheric and reduced pressures, and at temperatures varying between 150 °C and 300 °C. Films present a Volmer-Weber type nodular morphology. Nodules are composed of small crystallites, the mean size of which is about 50 nm. Carbon (up to 10 at. % depending on processing conditions) is incorporated at interstitial rather than intergranular position in the films. High operating pressure favors carbonfree films. An analysis of the gas phase reaction by mass spectrometry is presented in order to understand the mechanisms of the carbon contamination of the deposits.

The identification of viable diffusion barrier/adhesion promoter material and associated deposition processes is a critical factor in the successful development of structurally and electrically reliable copper based metallization schemes. As feature sizes continue shrinking, such materials are expected to delivery enhanced performance at increasingly thinner layers to allow maximum space utilization by the actual conductor. In this respect, Ta and W based binary and ternary nitrides present promising solutions in view of their hardness, chemical inertness, and thermal stability to high temperatures. Additionally, their availability in amorphous form provides the added benefit of inherent absence of grain boundaries, which usually serve as a primary diffusion path. This paper presents finds from the development of low0temperature (,350°C) CVD processes for the growth of ultrathin Ta, W, Ta-Si, and WSinitride layers for sub−0.18 micron device structures. These processes employ novel inorganic and metal-organic source precursors which allow for the in-situ, one-step, growth of binary and ternary nitrides from appropriate mixtures of the corresponding source precursors. Results will also be discussed from diffusion barrier studies which established performance metris for the applicability of such materials in copper interconnect technologies.

TiN films deposited by CVD utilizing TiCl4 and NH3 are widely used in ULSI processes. The residual chlorine in the film is one of the major issues of TiCl4 based chemistry [1–5]. We have examined the kinetics of TiN-CVD using TiCl4 and NH3 as precursors to determine method for controlling the residual chlorine concentration.

We analyzed the deposition rate profiles obtained from a simple tubular isothermal reactor. Deposition was performed over the temperature range from 300°C to 500°C and with varying initial concentrations of TiCl4 and NH3. We found that the deposition rate was independent of the TiCl4 concentration at higher concentrations. The deposition rate was proportional to the TiCl4 concentration in the low concentration range. This phenomenon can be well explained by a Langmuir-Hinshelwood type mechanism. Examination of the deposition rate dependence on the concentration of NH3 showed that both the maximum deposition rate at high TiCl4 concentrations and the first order kinetic rate constant in the lower TiCl4 concentration range were proportional to the NH3 concentration. These results indicate that the deposition was controlled by the Eley-Rideal mechanism. The residual chlorine concentration was found to be proportional to the surface coverage factor of adsorbed TiCl4. We conclude that the best way to obtain good quality TiN films can be obtained theoretically through these kinetic studies.

Titanium nitride films are used in a variety of applications in the semiconductor industry, but the stoichiometry and homogeneity of the films can be difficult to control and characterize. The National Institute of Standards and Technology (NIST) is developing a TiN thin film on silicon to be used as a physical and chemical standard for the semiconductor industry. A prototype 100 nm thick film has been manufactured by dual ion beam deposition. NIST is characterizing the film by x-ray interferometry for thickness and density, neutron depth profiling for nitrogen content and homogeneity as a function of depth, neutron activation analysis for titanium content, and x-ray fluorescence spectromety, electron probe microanalysis, grazing incidence x-ray photoelectron spectroscopy, and transmission electron microscopy for homogeneity and composition. The intent of this research is to create a TiN film of known thickness, density, stoichiometry, and homogeneity that can be used by the semiconductor industry as a primary, traceable standard for characterization of industry thin films. The intent of the standard is to promote more accurate characterization and improved TiN manufacturing capabilities as well as to aid manufactures in more easily employing ISO 9000 related traceability and quality assurance practices.

A novel type of diffusion barrier, consisting of a conducting layer whose surface is enriched with silicon nitride, was developed. The new barrier was prepared by thermal decomposition of a metal-organic precursor, tetrakis(dimethylamino) titanium (TDMAT), followed by in-situ silane anneal and subsequent surface nitridation. It combines the conformality and conductivity advantages of the underlying diffusion barrier with the good barrier properties of silicon nitride. The new barrier films were characterized by sheet resistance measurement, secondary electron micrographs (SEM) and x-ray photoelectron spectroscopy (XPS). The thermal stability of Cu/capped barrier/Si multilayer structures was demonstrated.

A process has been developed for the deposition of amorphous Ti-Si-N films using reactive ion sputtering of a TiSi target. The Ti-Si-N films have been extensively characterized over a wide range of process parameters. Resistivities of the films less than 300 μΩ-cm have been achieved. Stress measurements on Ti-Si-N films indicate that the film stress changes from tensile to compressive as the nitrogen composition is increased. Near-zero film stresses were achieved by choice of optimum nitrogen N2 flow. SIMS analysis of Cu diffusion through blanket PVD Ti-Si-N (300Å) after an anneal at 390°C/3 hour showed a near overlap of the Cu profile compared to the profile of an unannealed SiO2/PVD Ti-Si-N /Cu film stack, indicating that the Cu did not diffuse significantly through the barrier after anneal. Low contact resistance (0.8 Ω) and low (< 10−11 A) leakage were obtained using a dual inlaid structure with a 300 Å Ti-Si-N processed with optimized conditions. These results showed that Ti-Si-N could be used as a potential barrier for copper metallization.

The Cu metallization in future VLSI technology requires a liner or diffusion barrier. We have studied TaN thin Films of thickness from 5 nm to 3 nm as the diffusion barrier. We deposited sandwiched TaN/Cu/TaN thin films on oxidized Si wafers, annealed them in air with ramping temperature, and measured in-situ resistance changes. Scanning and transmission electron microscopes were used to characterize the surface and microstructure of the thin films and Rutherford backscattering spectrometer (RBS) was used to profile the elemental composition and after oxidation. The oxidation of the Cu sandwiched between TaN films of 5, 10, 20, and 30 nm occurs at 300, 400, 450 and 475°C, respectively. The activation energy of oxidation of Cu with the TaN barrier of 10, 20, and 30 nm are 1.73, 2.13, and 2.26 eV, respectively, but the 5 nm TaN was not calculated due to large data scattering. For comparison, the oxidation temperature and activation energy for bare Cu films in air are 250°C and 0.74 eV, respectively. It suggests that 20 nm of TaN is quite effective as a barrier layer. However, the reaction between Cu and the underlying SiO2/Si layers was also detected in RBS; this may arise as another serious reliability criterion to the system.

Integration of a TiCl4-based chemical vapor deposition (CVD) process for TiN barrier films with Ti underlayers for sub-micron integrated circuit metallization stacks exposes the Ti film to TiCl4 and NH3 adducts of TiCl4 that may etch the Ti in addition to depositing TiN. In this paper we report results of studies on the interactions of TiCl4 with ex situ PVD Ti films during the CVD TiN process. Deposition of TiN on Ti/SiO2/Si using a onestep 650°C process shows evidence of significant etching of the underlying Ti. A two-step process using a reduced TiCl4 flow for the initial deposition reduced the amount of etching but for Ti films over 200Å thick there was significant non-uniformity and peeling at the Ti/SiO2 interface. Pre-treatment of the Ti surface in situ with a 500W, 450 kHz NH3 plasma for 20–60 sec. leads to formation of TiN0.3, which shows a slight protective effect against etching. The same series of experiments with Ti deposited on Si reveals no etching, owing to reaction of the Ti with the Si substrate to form etch-resistant silicides. These results suggest that integration of a TiCl4-based CVD TiN process with an underlying Ti layer may be undesirable unless the surface of the Ti is protected against etching.

Tantalum nitride (TaN) films were deposited by using pentakis(diethylamido)tantalum and ammonia. The activation energies of the surface reaction were obtained with the NH3 flow rate. In addition, the resistivity, composition, crystal structure, and microstructure were systematically studied with the NH3 flow rate from 0 to 25 sccm. The resistivity of the asdeposited film was decreased as the NH3 flow rate was increased, but it was increased at the NH3 flow rate of 25 sccm. The minimum value of resistivity is about 7000 μΩ-cm at the NH3 flow rate of 20 sccm. The carbon content in the film was decreased down to 1 at.% as the NH3 flow rate was increased up to 25 sccm by Auger electron spectroscopy. Rutherford backscattering spectrometry showed that the N/Ta ratio is about 1.75, which is not considerably changed with the NH3 flow rate. In spite of this high nitrogen content in the film, it was revealed that the fcc TaN was formed by x-ray diffractometry and transmission electron microscopy. The etch-pits test showed that 50-nm-thick TaN films deposited at the NH3 flow rate of 0 and 25 sccm prevented the diffusion of Cu into the Si substrate at the annealing condition of 500 °C and 550 °C for 1 hour, respectively. The step coverage was estimated as over 80 % at the NH3 flow rate of 0 sccm and below 10 % with the addition of NH3 in 0.5 μm × 1.5 μm contacts by cross-section scanning electron microscopy.

For power-chip cooling devices based on Bi2Te3 thick films, copper is a desirable choice as metallic conductor, because it has high thermal conductivity and low electrical resistivity. On the other hand, Cu shows donor activity in Bi2Te3, and is known for its high diffusivity in bismuth-telluride and the rapid formation of Cu2Te. Therefore, the deployment of a chemically inert, low resistivity diffusion barrier between the Cu metallization layer and the thermoelectric base material is indispensable. In this paper we report on the effectiveness of films of Cr, Pt, and Ta40Si14N46 as diffusion barriers at temperatures up to 350°C for Cu overlayers on Bi2Te3 bulk substrates. The films, each about 100 nm thick, were magnetron-deposited on the Bi2 Te3 followed by about 300 nm thick copper overlayers without breaking vacuum. The samples were annealed in vacuum at temperatures of 200 and 350°C for up to 50 h. The performance of the metals and the tantalum-silicon-nitride films as diffusion barriers for Cu inward and Bi and Te toward diffusion was evaluated by 2.0 MeV4 He backscattering spectrometer and x-ray diffraction. While the Cr and Pt films fail already after hours of annealing at 200°C, the Ta40Si14N46 film remains intact at this temperature after vacuum heat treatment for 50 h, and even at 350°C for 1 h as well. Ta-Si-N, and related ternary materials of this type, have already shown to be highly effective barriers in Cu/Si contacts. This study demonstrates that their field in application extends quite beyond Si-based technology.

Advanced interconnect fabrication may require alternative TiITiN processes, such as an ionized metal plasma (IMP) sputtering technique to deposit Ti/TiN liner for sufficient step coverage in high aspect ratio contacts/vias. Since TiN is also widely used as an anti-reflective coating on top of multilayer metal films, the optical properties of the TiN film are extremely important.

In this paper, both IMP and standard PVD TiN films deposited on an aluminum layer are compared with respect to their lithography performance at exposure wavelengths of 365 nm (i-line) and 248 un (deep ultraviolet, or DUV). The measured optical constants of the two films were found to be very similar. The linewidth response of these two films at 365 nm was comparable; however, with DUV patterning, resist footing was observed on both films; but was especially severe with standard TiN. Differences in resist profile are explained in terms of the surface structure and density of the TiN film. By varying the conditions for deposition of IMP TiN (such as, RF bias, chamber pressure, etc.), the optical properties of the films may be varied. The impact of these varying film properties on DUV lithography is evaluated. Experimentally obtained linewidth response is compared with optical lithography simulations.

The knowledge of the reaction kinetics which can occur at an interface of a couple of materials, remains a crucial issue to establish the structural limits of a diffusion barrier intended for microelectronic structures.

In the past years, the interfacial reactions activated at an interface of a couple of materials, as for example aluminum and titanium, have been analyzed extensively using different experimental tools, as for example: Ruthreford Back Scattering (thickness determination) and Differential Scanning Calorimetry (DSC). Then, these experimental methods were useful to deduce parameters, characterizing the interfacial reactions in bulk samples: apparent activation energies, enthalpy of formation. Because in thin films, the kinetics of the reactions that can be activated at an interface will be different; we studied interfacial reactions in submicronic Al/Ti layers.

Taking advantage of the accuracy of the DSC (reaction rate determinations and detection of earlier stages of intermetallic phase formation), our experimental approach consisted in a series of isothermal and non-isothermal DSC experiments on submicron Al/Ti layered structures. From the reaction rate determination, analytical methods as the Kissinger Ozawa approach were used, to determine the apparent activation energies of the phase formation. Also the results allowed to model and discuss the first steps of the interfacial reaction.