The electrical properties of metal/Si(100) and metal/Ge(100) interfaces formed by the deposition of metal on both n-type and p-type Si(100) and Ge(100) have been studied in the temperature range 77-295 K with the use of current- and capacitance-voltage techniques. Compound formation is found to have very little or no effect on the Schottky-barrier height and its temperature dependence. For silicon, the barrier height and its temperature dependence are found to be affected by the metal. For germanium, on the other hand, the barrier height and its temperature dependence are unaffected by the metal. The temperature dependence of the Si and Ge barrier heights is found to deviate from the predictions of recent models of Schottky-barrier formation based on the suggestion of Fermi-level pinning in the center of the semiconductor indirect band gap.

The electrical and physical properties of the contact between the active channel of high electron mobility transistors (HEMT’s) and the source or drain contacts play an important role in determining the transistor characteristics. This paper considers electrical models that may be applied to the various techniques now available to form these Interconnections. Results of electrical (and some physical) studies with regard to these systems are then discussed and compared where possible with predictions made using the electrical models. The comparisons show that the electrical models provide a useful base to identify the important parameters in these interconnections.

Taper etchable molybdenum (Mo) films are successfully obtained by neon (Ne) sputter deposition. Mo films several hundred nanometer thick are deposited using an RF planar magnetron sputtering system. After photolithography, the Ne-sputtered Mo films are etched with a hydrogen peroxide solution. Films deposited in low pressure Ne show an excellent tapered edge with a taper angle of less than 45°, which can eliminate the step-coverage problem. However, higher-pressure Ne-sputtered films and films sputtered in argon (Ar) show steep edge profiles .

Ne-sputtered Mo films show a drastic change in characteristics depending on the gas pressure. The internal stress is strongly compressive for lower pressures and becomes tensile for higher pressures. According to RHEED patterns, lower pressure sputtered film shows a <110> orientation including a halo which indicates the existence of an amorphous-phase, but higher pressure sputtered films show clear <111> orientations. TEM observations confirm the structural change. Higher pressure Ne-sputtered film and Ar-sputtered film show columnar structures, but low-pressure Ne-sputtered film shows the disordered structure.

Taper etchability of the low-pressure Ne-sputtered Mo films is considered to be due to the structural change, especially the included amorphous-phase.

Thin films of amorphous TiP and TiPN2 alloys were deposited by sputtering of a TiP target in an Ar and N2/Ar mixture, respectively. These alloy films were tested as diffusion barriers between Al and Si as well as between Cu and Si and also in metallizations which included TiSi2 as the contacting layer. Rutherford backscattering spectrometry, x-ray diffraction and electrical measurements were used to determine the barrier effectiveness. We find that TiP and TiPN2 films prevent the interdiffusion and reaction between Al and Si up to 500°C and 600°C for 30 minutes annealing, respectively, and between Cu and Si up to 600°C and 700°C, respectively.

We have investigated the effectiveness of thin tantalum layers as diffusion barriers to copper. Fifty nm Ta films were sputtered onto unpatterned single crystal Si wafers and overlaid with 100 nm Cu. Material reactions in these films were followed as a function of annealing temperature by in-situ resistance measurements, and characterized by by Rutherford Backscattering and cross-section TEM. The effect of the incorporation of nitrogen was explored by reactively depositing Ta(5 at.% N) and Ta2N. Pure Ta prevents Cu - silicon interaction to at least 600 °C. At higher temperatures, reaction of the Si substrate with Ta forms a planar TaSi2 layer. Cu rapidly penetrates to the Si substrate, forming Cu silicide precipitates at the TaSi2 - Si interface. A study performed on the Si/Ta(N)/Cu film had very similar results. Ta2N is an even more effective barrier to copper penetration, preventing Cu reaction with the substrate for temperatures up to at least 700 °C.

The chemical stability of boride thin films with aluminum is investigated. Only two diborides, VB2 and HfB2 have a positive heat of reaction which makes them potential candidates for thermodynamically stable diffusion barriers between Al and Si. Thin films of VB2, and ZrB2 for comparison, prepared by rf sputtering of composite targets were chosen for this study. Multilayer samples of these borides and aluminum were investigated by differential scanning calorimetry to determine if, according to calculations, a reaction between Al and the borides takes place, and to measure the heat of reaction. We find that an exothermic chemical reaction occurs between ZrB2 and Al and that an exothermic crystallization reaction takes place in the VB2 and Al sample. The reaction products were determined using X-ray diffraction.

The future high density multilevel interconnection and packaging requires that the combination of the insulator and conductor layers has a low RC value. Thermal stress and diffusion during processing are issues of great concern in the high density multilevel structures. The problem can be alleviated by a proper choice of materials and processes that do not require high temperature. In this paper we propose to use parylene and its derivatives (dielectric constant 2.3–2.6) as the possible interlayer dielectrics and Cu (bulk resistivity ∼1.7 μ Ω-cm) as the conductor. Parylene can be vapor-deposited and cured at room temperature. The metallization of Cu has been achieved at room temperature using the newly developed partially ionized beam deposition technique. This technique has been shown to grow high quality metal films with low resistivity at low substrate temperatures. The interaction between Cu and parylene, including adhesion and diffusion, is also discussed.

Recent studies have shown that sputter deposited amorphous NixNb1−x (60≤×≤75) alloy films are effective diffusion barriers for operation at temperatures up to 6(X) °C[1]. The thermal stability of the amorphous films has been established on Si and GaAs substrates and may be modified by interactions wilji polycrystalline metal overlayer films. In the current work a detailed microstructural examination by cross-sectional TEM was performed on the annealing behavior of 50 nm polycrystalline Cu films on amorphous Ni60Nb40. Specifically, the development of grooves at the intersection of grain boundaries in the Cu film with both the free surface and the amorphous Ni60Nb40 base was monitored to evaluate the low temperature interfacial diffusion processes. Based upon measurements of the groove dimensions and dihedral angle during vacuum annealing at 450 °C, the surface diffusion coefficient of Cu was determined as 7.4 × 10-20 m2/sec and the surface energy for Cu derived from groove kinetics was in good agreement with other reported determinations. In addition, the grain boundary grooves that were present at the Cu/amorphous Ni60Nb40 interface in the as-deposited condition were observed to be eliminated during annealing. Again, by following the kinetics of groove healing the interfacial diffusivity was determined to be of the order of 10-28m2/sec at 500 °C and the interfacial energy for the amorphous film/Cu surface was estimated to be ≥ 340 mJ/cm2. The benefits of utilizing amorphous Ni-Nb alloys as underlays to retard thermal grooving and electromigration failure in copper arc discussed.

High purity copper has been deposited from trialkyl phosphine complexes of cyclopentadienyl and methylcyclopentadienyl copper(I) by thermal chemical vapor deposition (CVD). Films as thick as 4.4 μm have been deposited at growth rates of up to 2000 Å/min with resistivites typically 2.0 μΩ cm, just slightly higher than bulk copper. Depositions were carried out at substrate temperatures between 150 and 220 °C on a variety of substrates including Si, SiO2, polyimide, and Cr/Cu. At low substrate temperatures, copper film growth appears to show some selectivity for transition metal surfaces. An activation energy of 18 kcal/mole has been measured for film growth on Cu seeded substrates. CVD copper films have been characterized by Auger spectroscopy which showed that carbon and oxygen levels are below the limits of detection. Transmission electron microscopy revealed that the copper grain size was ∼0.6μm and the grain boundaries are free of precipitates. Films show good conformality.

As the focus of integration technology inevitably shifts from the present very large scale integration (VLSI) to ultra large scale integration (ULSI) schemes, thus leading to continuous decrease in circuit dimensions, the limitations of present multilevel metallization technologies become increasingly important. Because of the appreciably higher speeds and more complex multi-functional layering involved in the newest ULSI circuits, the electrical resistance and capacitance of presently used interconnects and their electromigration and stress resistance stand as major limiting factors to signal processing throughput. In this paper, some recent results achieved by the present investigators in their studies of blanket and selective low-temperature metal-organic chemical vapor deposition (LTMOCVD) of copper for potential use in multilevel metallizations in ULSIC’s are presented. The films were produced at 300–400°C in atmospheres of pure H2 or Ar from the β-diketonate precursor bis(6, 6, 7,7, 8, 8, 8-heptafluoro-2, 2-dimethy1-3, 5-octanediono)copper(II), Cu(fod)2. The films were analyzed by x-ray diffraction (XRD), Rutherford Backscattering (RBS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDXS), and four-point resistivity probe. The results of these studies showed that films deposited on metallic substrates were uniform, continuous, adherent, highly pure, and exhibited very low resistivity, as low as 1.8 μΩcm for films deposited in pure H2 atmosphere. Preliminary investigations of selective LTMOCVD of copper showed that selectivity is indeed possible, but is a function of a wide range of parameters that include reactor geometry, substrate type and temperature, working pressure, type of carrier gas, and precursor chemistry.

This paper describes the effect of the ambient atmosphere (air, vacuum and deuterium) during thermal cycling on chromium/polyimide (Cr/PI) interfaces. Cross-section TEM has been employed to reveal the interface microstructure and morphology. The extent of interdiffusion across the metal/polyimide interface was determined by Energy Dispersive Spectroscopy in the STEM. The nature of the mechanical failure was identified by SEM and the locus of failure determined by Auger Electron Spectroscopy. It was observed that in the Cr/Cu/Cr/PI/Si system, tensile cracks form in the metal layers that originate at the Cr/PI interface after thermal cycling in any of the ambient atmosphere. Also, after annealing, the Cr/PI interface remains sharp, with no significant diffusion of Cr across the interface, irrespective of the ambient atmosphere.

We have studied the formation of metal silicides in-situ in an ultra-high vacuum transmission electron microscope. Metals were deposited on in-situ cleaned, reconstructed silicon surfaces and annealed. For the metals Ni and Co, we find that the phase sequence in ultra-thin films is different from that seen in ≈1000 Å thick films, and attribute this to the high surface-to-volume ratio. In general reactions occur at room temperature, to form an epitaxial phase if possible. We report preliminary new results on the formation of Pd2Si.

The importance of self aligned cobalt disilicide technology for gate and interconnection, and contact metallization cannot be overemphasized. Simultaneously, the concept of forming shallow junctions by using the metal or silicide layer as a dopant source is gaining prominence. In this work, we will present and discuss the results of the effect of arsenic, implanted into cobalt films on silicon, on the Co-Si reaction. Arsenic redistribution during the reaction, both during furnace annealing and RTA, and the effect of ion implantation and dose and energy will also be included.

Interaction of thin film Cu and CoSi2 has been studied using Rutherford backscattering spectroscopy and sheet resistance measurements. For temperatures ≤ 600° C. , no measurable diffusion of Cu into CoSi2 is observed.

Growth of monocrystalline CoSi2 on top of (100) Si has been obtained by silicidation of deposited Co films on Si/CoSi2/Si heterostructures formed by ion implantation. The layers are of excellent crystalline quality and the CoSi2/Si interface is atomically flat. The required implanted dose can be reduced, since epitaxial silicidation is possible starting from aligned CoSi2 precipitates in the Si.

The growth of epitaxial CoSi2 by means of SPE on heavily ion implanted Si(111) was investigated with LEED, RBS and TEM. After silicide formation, the dopant distribution in silicide and silicon was determined by means of SIMS. In a self-aligned process epitaxial CoSi2/Si p+ contacts have been produced. The specific contact resistance was found to be lower than for polycrystalline CoSi2 contacts.

The processing of titanium silicide in a multichamber processing system is described. Three processes are included: wafer cleaning, Ti deposition, and annealing. The results are compared to wafers processed in a conventional way with exposure to ambient air between Ti deposition and the annealing step. TEM, RBS and sheet resistance measurements indicate that the films processed without exposure to ambient air have thicker and purer TiN layers as compared to the films with air exposure. Furthermore, integration allows for a wider processing window for the first annealing step. The use of reactive cleaning chemistry prior to Ti deposition results in a smooth silicon surface and therefore uniform silicidation as compared to inert cleaning technology, where redeposit of etched material occurs.

Modelling of temperature dependent current-voltage characteristics of TiSi2/n+/p-Si shallow junctions has been presented here. The formation of shallow pn junctions, by ion implantation of As+ through Ti films evaporated on p-Si substrates has been performed in these experiments. The temperature dependent factors such as band gap narrowing, intrinsic carrier concentration, mobilities and diffusivities are considered in the model.

The Ti-single crystal Si interfaces, before and after annealing in argon, were examined by cross section high resolution transmission electron microscopy (HRTEM) combined for the first time with 2nmΦ probe for energy dispersive spectrometry (EDS). HRTEM shows that there is amorphous alloy formation at the Ti-Si interface. The thickness of the reacted layer is ∼1.7nm for single crystal Si, independent of doping level and impurity species such as As and B, and is ∼2.5nm for back sputter-amorphized Si. After annealing at 430°C for 30min, the thickness of the amorphous alloy increases up to ∼11.5nm. High spatial resolution EDS microanalysis has been obtained. The results show that reliable compositions can be deduced at this level since some of the layers are only about 2nm thick. The amorphous alloy formed at the deposition step was found to be Ti55Si45. After annealing, the composition across the amorphous layer varied from about 70%Si near the substrate to about 30%S1 close to the Ti interface. The substrate interface is atomically flat. Interpretation of the behavior in terms of the metastable Ti-Si phase diagram calculated by Holloway and Bormann will be discussed.

Metal-GeSi reactions have been investigated in the Pt-GeSi and Cr-GeSi systems. Pt started to diffuse into and react with the alloys at 250 °C. The reacted region consisted of a uniform mixture of Pt2Si and Pt2Ge, with the same ratios of Ge to Si as those in the unreacted region. On the other hand, the Cr-GeSi reaction was induced by Ge motion at 375 °C. As a result a two-layer phase separation was observed. A Si-rich ternary layer was sandwiched between a germanide layer and the unreacted alloy