The interfacial reactions in the Zr/Si system were studied by in-situ cross-section TEM including high resolution mode. The reactions consisted of formation of an amorphous interlayer followed by the nucleation and growth of crystalline ZrSi2- The development of the amorphous layer was found to involve two different stages. The ZrSi2 was also found to grow layer-by-layer into the Si via a ledge mechanism.

CVD WSix films have been widely employed for ultra thin gate and bit-line applications. Recently, for sub 0.5 μm technologies based on CVD WSix polycide gates and interconnects, efforts have been made to replace the silane-based deposition chemistry with that based on dichlorosilane (DCS) reduction of tungsten hexafluoride (WF6). Fluorine-contaminated gate oxides and poor film adhesion and cracking (especially after high temperature annealing/oxidation) are main characteristics of silane-based WSix which could be detrimental for fine geometries of sub 0.5 |im technologies. In this paper, the composition and structure of DCS-based CVD WSix films were studied. WSix films were deposited on 200 mm, implanted polysilicon substrates; silicide film thickness ranging from 60 to 200nm. A high temperature furnace anneal and oxidation cycle was used to examine post-oxidation film properties. SIMS, RBS and X-ray diffraction (XRD) were used to determine film composition profile, structure and texture on both as-deposited and annealed/oxidized films. Si/W uniformity through the depth of the film, for both W-rich and Si-rich interfaces, and its impact on film adhesion and cracking were studied. Also, WSix step coverage for sub 0.5 μm polycide topographies were examined.

Based on 2μm-wide CoSi2-n+- and TiSi2-n+-polycide structures with a l00nm-thick silicide and a standard AlSi-metallization a comparison between conventional and the high accelerated SWEAT-test was carried out. Supported by simulations different parameters (e.g. activation energie EA) were determined by time-to-failure-measurements. Because of comparable results out of both different tests the SWEAT-test will be prefered due to short time-to-test. Also it will be shown that both silicide systems have an about three times higher activation energy for the inducing of EM-based “open”-failures than the tested standard AlSi-metallization. The failure-rate was less than 100 FIT for both polycides but because of process advantages the CoSi2-polycide should be a promissing metallization to improve the reliability of single and/or multilevel-metallization.

This paper reports on two types of voiding which occur in Al lines in integrated circuits.

The first type of voiding occurs in high-temperature processes during chip fabrication, in which the thermal stress is expected to be compressive. Ultrahigh voltage electron microscopy (UHVEM) observations of the voids and voiding process show interrelations between the evolution and morphology of voids and grain-boundaries.

The other type of voiding occurs at low temperatures where highly tensile thermal stress develops in Al lines. This type of voiding occurs in accelerated life tests and actual operation. The results of accelerated life tests of intentionally oxygen-contaminated samples are described. Voids observed in low-oxygen samples are mostly large-angle-wedge-shaped and induce essentially no open failures in the early-failure period. In high-oxygen samples, crack-like voids occur, and parallel-slit-like voids also occur. These narrow voids result in high open-failure rates in the early-failure period.

In this paper results of recently developed high resolution resistometric electromigration techniques will be described, with particular attention to the behaviour of narrow, near-bamboo metal lines. After a discussion on recent theoretical results published in the literature, a diffusion model correlating mechanical stress and electromigration will be adopted to describe experimental results of relative resistance change both during and after electromigration. The good agreement between experimental data and simulations must not hide that something must still be understood about the physical mechanism leading to resistance changes during electromigration experiments.

Stress-voiding or stress migration (SM), and electromigration (EM) are urgent problems in ULSI microcircuits with features in the submicron range. Severe stress-voiding arises in multilevel metallizations because of the high constraint offered by the refractory metal layers, the ceramic insulation, and the rigid contact and via structures which prevent plastic relaxation of the thermally induced stresses. Also, W-plugs and/or refractory barrier layers block entirely the EM flux, resulting in an enhanced probability of EM damage. We review the physical bases of a recently introduced unified SM and EM model [1,2]. We apply the model to an interconnect line confined by vias at both ends and derive equations which explicitly show the effects of external conditions and microstructural parameters on the evolution of SM and EM damage. Particularly we analyze the effects of Cu depletion on void growth rate at vias. We also show how the shifts in the line resistance are related to void growth. Finally we demonstrate that the model predictions compare well with the recently published experimental EM data.

Magnetron sputtering has been used extensively to deposit interconnect layer, diffusion barrier layer, adhesion layer and anti-reflection layer in semiconductor production. As the dimension of VLSI devices get smaller, it is becoming increasingly difficult to deposit these metal layers into high aspect ratio contacts and vias using conventional sputtering method. Coherent sputtering, where a perforated plate (collimator) is placed between the sputtering target and wafer, improves bottom coverage and step coverage. In the recent years, coherent sputtering has been used to deposit titanium, titanium nitride and aluminum films. However, the existence of collimator changes the deposition processes and properties of the deposited films. In this article, we will discuss some of the properties of coherent deposition.

Simulation of the physical vapor deposition (PVD) of titanium nitride (TiN) in micronscale contacts was performed using EVOLVE, a physically-based model of non-continuum mass transport. Simulations of uncollimated TiN PVD using a sub-unity sticking coefficient of 0.6 provide accurate model predictions of experimental data. Using this value in simulations of PVD with a 1:1 aspect ratio collimator results in a significant underprediction of titanium nitride deposition in the feature bottom in comparison to the experimental results. This under-prediction was compensated for empirically by adjusting a “beaming” coefficient to produce good model predictions of the experimental data.

The adsorption and thermal behavior of tetrakis-(dimethylamido)-titaniurn (TDMAT), Ti[NMe2]4, were investigated by surface spectroscopic techniques in the temperature range 100-1100K. A metallic Ti substrate readily dissociates TDMAT even below 300 K, producing a carbon-rich interface. When the substrate is exposed to a continuous flux of TDMAT at growth temperatures (550-700K), deposition of carbon-rich TiCxNy films readily occurs with a high precursor reactive sticking coefficient. With the addition of sufficient NH3 flux, we demonstrate the existence of a direct surface-reaction-driven deposition mechanism which involves reaction(s) between adsorbed TDMAT and NHX species on the film surface and thus leads to growth of substantially cleaner TiNx films. This growth mechanism dominates at low pressures (≤10-4Torr) where gas-phase reaction between the precursor gases becomes insignificant.

The economics of manufacturing is driving the use of larger wafer sizes. At the same time smaller device geometries place more stringent requirements on film properties. Maintaining tight control of metal film properties in larger reactors presents unique challenges in the development of manufacturing worthy processes. This paper presents the development of a CVD tungsten process that was necessitated by the requirement for stable deposition uniformity with the conversion of wafer sizes from 6“ to 8”. The scaled up version of the 6“ process was rendered obsolete in the 8” tool due to unacceptable drifts in deposition uniformity.

Fluorine build up in the reaction chamber from the silane (SiH4) and hydrogen (H2) reduction of tungsten hexafloride (WF6) was identified to be the main cause for the process instability. We discuss how the problem was identified and how the new process was developed. Data on the uniformity of deposited films, collected over several hundred wafers with the old process and the new process show the new process to be superior. Device yield and electrical parameter data show the new process to be at least as good as the previous process.

Chemical vapor deposition (CVD) of tungsten nucleation films is typically done using silane (SiH4) reduction of tungsten hexafluoride (WF6). For SiH4/WF6 flow ratios of ≤ 1, pure tungsten of bulk density and resistivity is deposited. Upon increasing the ratio to 2, nearly 40 at.% Si is incorporated in tungsten films. At a ratio of 3, hexagonal WSi2 is deposited, and at ratios of > 6 WSi2 along with silicon is deposited. A maximum in deposition rate is obtained for WSi2 at the ratio of 3, and the deposition rate drops as more silicon is being deposited. The step coverage of films drops dramatically as one moves away from pure W films. The deposition of these films takes place without any incubation time.

Titanium carbide films were deposited on silicon wafers by laser reactive ablation. A pure titanium target placed inside a methane (CH4) atmosphere was irradiated by a XeCl excimer laser with a fluence of 5 J/cm2 and a repetition rate of 8 Hz. Experiments were performed at different values of the ambient pressure in order to investigate the influence of the deposition parameters on the film properties. Results show that at low pressure values (p< 10-5 mbar) the deposited layers are mainly constituted of metallic titanium whereas for pressure ranging from 10-5 to 10-1 mbar they are formed of titanium carbide (TiC) with small amount of oxides. The stoichiometry and thickness of the titanium carbide films can be controlled by the partial pressure of the atmosphere and the number of laser pulses, respectively.

The results of first-principles calculations of the electronic band structures, equilibrium lattice constants, cohesive energies, bulk moduli, and magnetic moments are presented for the rare-earth pnictides with the rocksalt structure and chemical formula RX, where R = Gd, Er and X = N, P, As. Some of these materials are semimetals and are suitable for metallization of III-V semiconductors. The results for the lattice constants are in good agreement with experimental data. For ErAs, which is closely lattice-matched to GaAs, the calculated magnetic exchange splittings, electron and hole concentrations, Fermi surface cross-sectional areas and cyclotron masses are found to be in satisfactory agreement with the available experimental data.

Thin films of amorphous Si1−xGex:H with x=0, 0.3, 0.6, and 1 were deposited by RF glow discharge at 200-250°C on SnO2/glass substrates. The tin dioxide was reduced by heat treatment at the temperature range of 400-600°C resulting in a layered structure of silicon oxide, tin suboxide and ß-Sn which formed at the a-Si1−xGex:H/SnO2 interface. A strong dependence of the extent of the reduction on the Ge content in the a-Si1−xGex:H films was found: at low temperatures (T≤475°C) the Si-rich layers were more reactive, whereas at T≥475°C the Ge-rich films totally reduced the SnO2. The interfacial reduction process was followed by a drop in the transparency and drastic changes in the sheet resistance of the a-Si1−xGex:H/SnO2 contacts.

PACS: 61.43.Dq; 78.66; 82.65.-i; 82.65.Fr; 82.65.Yh

Thin film bilayers of metal and amorphous chalcogenides have been prepared by evaporation. The metals were silver and zinc, while the chalcogenides were P2Se3 and arsenic sulphides, mainly As2S3. The metals dissolved into the chalcogenide films when illuminated with ultraviolet light or when irradiated with an electron beam. The changes in composition and chemical bonding which were caused by this irradiation, were investigated by x-ray photoelectron spectroscopy. The concomitant structural changes have been investigated by electron diffraction.

After the metal and chalcogenide had intermixed, either due to photon or electron irradiation, the layers became sensitive to an electron beam; this sensitivity depended on the composition of the chalcogenide. Energy-dispersive x-ray microanalysis showed that the electron beam rapidly, but reversibly, depleted the irradiated areas of the dissolved metal. Very fine patterns, of better than half-micron resolution, could be written. By exposing a pure arsenic sulphide film through a shadow mask to ultraviolet light, zinc could be deposited selectively to form fine patterns. Plasma processing developed either kind of pattern reliably, thus rendering the material a dry inorganic resist for photo- and electron-beam-lithography with potential benefits in particular for GaAs.

Nonalloyed, single crystal, oxide free Ge based ohmic contacts are almost atomically abrupt, have a smooth interface, and have the potential to be better understood. Ultra high vacuum electron beam evaporation is used to deposit a single crystal Ge film on GaAs and InGaP substrates. A large grain, highly oriented Au film or a poly crystalline Pd film with more randomly oriented grains was then deposited on the Ge. These films were characterized in the as grown condition by high resolution electron microscopy (HREM), double crystal x-ray diffraction (DXRD), Auger electron spectroscopy (AES), Rutherford back scattering (RBS) and scanning electron microscopy (SEM). The as deposited Ge film grown at 400°C on GaAs and at 350°C on InGaP are epitaxial with a smooth abrupt, oxide free interface. The highly oriented Au film deposited at 100°C had a smooth interface with the Ge with the orientation relationship (100)Au II (100)Ge and [001]Au II [011 ]Ge or [0-1 1 ]Ge.

We present a process for creating in-plane anisotropic strain in (100) GaAs and GaAs/AlGaAs multiple quantum well (MQW) thin films. The host substrates used for bonding include (100) GaAs, (100) silicon, and lithium tantalate (LiTaO3) with a special crystalline orientation. A mutilayer metallization consisting of Au-Sn (Au: 80 wt% , Sn: 20 wt%, 0.95μm), Ti (500Å) adhesion layer and Pt (500Å) barrier layer is deposited on the thin films and the host substrates. By choosing a proper annealing temperature (380°C) and thickness of eutectic layer, the thin films and the substrates are bonded together. Photoluminescence measurements do not reveal any thermally induced strain in the thin films bonded to GaAs; however, they show the existence of in-plane biaxial strain in the films bonded on Si. Linearly polarized reflectance measurements reveal an optical anisotropy in the MQW bonded to LiTaO3, which possesses an orientation-dependent thermal expansion. This indicates that the in-plane strain in the thin films is induced by the different thermal expansions between the thin films and the substrates. This process can be used to develop a new class of devices with an artificially induced in-plane strain.

Copper films generally exhibit poor adhesion on dielectrics. It has been shown that the addition of refractory metals promotes adhesion via an interfacial reaction or better wetting to the dielectric. We investigate the adhesion of Cu-refractory metal (Cr, Ti) alloy films and bilayers on various silicon oxide substrates (SiO2, PSG, BPSG) after annealing in the temperature range 400-600°C by conventional furnace using N2/H2 forming gas. Rutherford backscattering spectrometry (RBS) was used to determine the interfacial reaction characteristics. The efficacy of a variation of the standard Scotch™ tape testing was evaluated. We found that the combined Scotch™ tape/scribe adhesion test revealed excellent qualitative bonding information and could be correlated well to RBS characterization. We were able to optimize the sample configurations and chemical compositions to achieve the best adhering film.

We investigate the nitridation of chromium films in an NH3 ambient at 500°C. Rutherford backscattering spectrometry using 2.0 MeV He2+ was utilized to determine the compositions of thick reacted layers and to provide calibration for the other techniques. In addition, analysis was performed using the 14N(α,α)14N resonance at 3.72 MeV in order to enhance sensitivity to nitrogen. Sputter-deposited TiN was used as a calibration for the cross section a for this resonance over the energy range 3.05-3.85 MeV and compared to the literature value. We find that analysis just above the peak in the resonance provides excellent sensitivity to N concentration in the nitride layers. This approach may be readily used in conjunction with 2.0 MeV backscattering to determine the overall composition and sample configuration. Auger electron spectroscopy was used to provide more depth sensitivity in compositional profiling and to monitor the oxygen impurity distribution. X-ray diffraction was used to identify phases in both as-deposited and annealed films.

Co-deposited Cu-Cr and Cu-Ti thin films were heated at various temperatures in an ammonia ambient in an environmental cell placed into the column of a transmission electron microscope (TEM). The reaction dynamics were observed in situ and recorded on a videotape using a TV camera with 1/30 second time resolution. Nitridation of chromium and titanium was accompanied by the nucleation and growth of copper particles starting at 370 and 580°C, respectively. It was found that in the Cu-Ti system at a temperatures regime of 370-400°C the growth rate behaves under a parabolic law; namely, the process is controlled by diffusion of Cu through the nitride matrix. However, for the Cu-Cr system at temperatures of 610-630°C two growth regimes were observed. In the initial growth stages, the surface reaction is rate-limiting, while for longer nitridation times, growth is diffusion-controlled.