Multilevel Metal (MLM) technology has been driven by the need for ever faster switching speed. In the simplest considerations, this need has been described by the RC time constant applied to the metal interconnect runner embedded in a dielectric medium:

Electron Cyclotron Resonance (ECR) plasma etching of a variety of III-V devices, including heterojunction bipolar transistors (HBTs), and lasers will be reviewed. In many of these devices, the metal contacts also perform as self-aligned, dry etch masks, so that mask erosion must be addressed. Sidewall smoothness is also an issue for most etched mesa lasers, and conditions for achieving the requisite smoothness will be discussed. The use of stencil masks for pattern transfer of large (∼100μm) features during cluster-tool, single wafer integrated processing raises the possibility of a completely in-situ fabrication technology without the need for lithography. The dry etching of a variety of ohmic and Schottky metallizations and also of dielectrics deposited in a low pressure, rapid thermal CVD system lays the foundation for integrated III-V device processing.

This paper reviews specific contact resistivity pc values obtained theoretically and experimently for a range of semiconducting materials. Techniques of obtaining pc values in terms of measurement, accuracy and reproducibility are then considered and matched to the semiconducting materials previously covered.

A combined thermodynamic/kinetic methodology was presented to give a rational approach to the metallization of n-GaAs when a reciprocal system of GaAs-MδsGa-MsM'-MAs exists. Fortunately, for many quaternary systems consisting of Ga-M-M'-As, such a reciprocal system does exist. This methodology may be used either for Schottky enhancement or ohmic contacts to n-GaAs. Two examples were used to illustrate the approach and preliminary results were given.

This paper reviews some of the problems limiting broad manufacturing implementation of chemical mechanical polishing (CMP) as a planarization process for interlevel dielectrics. We examine the mechanism whereby polish rates tend to decrease as the polish pad ages, and propose an explanation based on slurry transport. We review a simple theory which provides an understanding in terms of basic mechanical principles of how CMP produces its planarizing effect. Finally, we demonstrate a method capable of providing a quantitative measure of planarity.

Tungsten (W) films were deposited onto InP in a cold wall, rapid thermal low-pressure chemical vapor deposition (RT-LPCVD) reactor, from a tungsten hexafluoride (WF6) gas reduced by hydrogran (H2). W films of thickness 50 to 450 nm were deposited in the temperature range of 350° to 550°C, pressure range of 0.5 to 4.5 Torr and deposition rates up to 4 nm/sec with an apparent activation energy of about 1.12 eV. The film stress varied depending upon the deposition pressure, from low compressive for deposition at 0.5 Torr to moderate tensile for deposition at about 4.5 Torr. The films were aged at temperatures as high as 300°C for about 800 hr and exhibited an excellent mechanical stability. Post-deposition sintering of the W films at temperatures up to 600°C led to reduction of the resistivity with a minimum value of about 55μΩ-crn as a result of heating at 500°C. Conditions for both selective and blanket deposition were defined, and a dry etching process for further geometrical definitions of the films was developed, providing etch rates of 40 to 50 nm·sec-1. This report reflects the first attempt to deposit W films onto III-V semiconductor at a very high rate by means of RT-LPCVD.

Tungsten (W) films were deposited on the front surface of float-zone (FZ) Si wafers, from tungsten hexafluoride (WF6) by low pressure chemical vapor deposition (LPCVD). The back surface conditions of the Si wafers was the major concern of this study. Various back surface coatings were investigated, tungsten, thermal SiO2 and LPCVD-Si3N4. Isothermal heat treatments were performed in an argon flow furnace at 760°C for 8 to 30 min. The silicide formation was monitored by Rutherford backscattering spectrometry (RBS). No difference in the silicidation rate was found on the wafers with a back surface oxide layer as compared to that of the reference wafers with no back surface coating. However, for wafers with the back surface covered with Si3N4 or W, a retarded silicidation rate was observed. This phenomenon appeared to be insensitive to the presence of a cap layer (PECVD-SiO2) on the W films before annealing. A model including the behavior of point defects is proposed to provide an explanation to this observation.

The study of the wafer atmosphere during processing has become a key practice in understanding interactions of the process gases with the wafer, internal chamber surfaces and other process gases. For today's ULSI fabrication, Low Pressure Chemical Vapor Deposition (LPCVD) of tungsten has become common for sub-micron contact and via filling and was the chosen process for this investigation. The wafer atmosphere during key process steps of the tungsten LPCVD process has been characterized by mass spectrometry. During the tungsten LPCVD process studied, the TiN surface was first conditioned for tungsten deposition by generating active nucleation sites. This is followed by the actual deposition. After the deposition, wafer backside etch with NF3 plasma, wafer removal and an in situ chamber clean with NF3 and H2 plasmas performed. This paper discusses the mass spectral analysis of the tungsten LPCVD process during the nucleation, backside etch and in situ chamber clean process steps. Additionally, this paper describes benefits of in situ gas analysis.

Chemical Vapour Deposition of tungsten on silicon dioxide by means of GeH4 reduction of WF6 is studied. The influence of the ambient gas on the nucleation of tungsten is examined. Experiments have been performed in both Ar and H2 ambient. It is found that an Ar ambient hinders nucleation on silicon dioxide in comparison with a hydrogen ambient. Adhesion of the film and uniformity over the wafer are acceptable for the films deposited in hydrogen ambient.

Material properties are reported of high quality TiN thin films, deposited by a low temperature (400 – 450 C) and low pressure (10 Torr) metalorganic chemical vapor deposition process using tetrakis(diethylamino)Ti and ammonia. Layer resistivities of less than 200 μΩ cm are achieved in 300 to 500 A thick films. The carbon and oxygen content in the films is found to be low (<3% C, <0.5% O). Conformality of the films in small contact holes is sufficient for the films to be applicable as diffusion barrier and adhesion layers in integrated circuit manufacturing at the 0.25 μΩgeneration.

Integration of the MOCVD-TiN films in a Ti/TiN/Al-alloy metallization scheme is also reported. The diffusion barrier performance of the MOCVD-TiN layers is found to exceed that of PVD-TiN layers.

Thin Copper films have been deposited on various substrates by the reduction of copper bis-hexafluoroacetylacetonate, Cu(HFA)2, with hydrogen to investigate the characteristics of the films made at 2–10 torr of total pressure, substrate temperatures of 280–400 °C and precursor temperatures of 55–90 °C. Under the conditions investigated, the highest growth rate was 650 Å/min. and the resistivity of the films was routinely near 2.0 μΩ-cm at 5000 Å or more thickness. Film growth rate depended on precursor concentration and substrate temperature. RBS and AES analysis indicate that the copper deposited at 310–400°C is highly pure. SEM photographs revealed that different structures form depending on substrate kind, the deposition conditions and the deposition time. The surface roughness of the films increased with increasing thickness. The reflectivity of the copper films depends on their thickness and decreases as the grain size increases. The grain sizes in the films were about 0.1–2.0 μm and are correlated with film thickness.

The reaction kinetics of (hfac)CuL were examined in a warm-wall differential reactor. The data are consistent with neutral ligand L dissociation as rate limiting for (hfac)CuVTMS. A strong dependence of film resistivity on (hfac)CuVTMS pressure was observed. Selectivity for tungsten (W) surfaces in the presence of PECVD SiO2 was not observed for (hfac)CuVTMS under the conditions employed.

The chemical vapor deposition of Al-Cu thin films on Si, SiO2, and TiN substrates was examined in a vertical low pressure cold wall reactor using trimethylamine alane (TMAA1) at 20 C as the Al source. The Cu sources bis-(hexafluoroacetylacetonato)copper(H)(CuHFA), (cyclopentadienyl)copper(I) triethylphosphine (CpCuPEt3), and (hexafluoroacetylacetonato)copper(I) trimethylphosphine (HfaCuPMe3), were compared. The Cu content of the films was controlled up to“5 wt% by simply varying the temperature of the Cu source. Codeposited Al-Cu films with excellent conductivity, purity, and adhesion properties were obtained with all Cu sources. Optimal film smoothness was achieved at∼350 C. The compounds differed in the ease of control over the %Cu in the films. CuHFA exhibited a massive parasitic reaction which made control very difficult. The Cu(I) complexes showed very minor parasitic reactions. Analysis of films with high Cu content by SEM-EDS showed clear segregation of Cu and Al, consistent with the low solubility of Cu in Al. Films with >2% Cu appeared homogeneous on a μm scale by both SEM-EDS and SIMS depth profiling. TEM of film cross sections revealed a polycrystalline Al film with small (20–100 Å) Cu-rich particles dispersed throughout the Al grains. These particles exhibited bright field-dark field contrast characteristic of crystalline material.

We present a novel technique to metallize high-aspect-ratio, small-dimension contact holes and via plugs for application to integrated circuits and packaging. The technique uses a laser-assisted process to deposit a thin film of aluminum from DMA1H, which forms a seed layer for subsequent selective CVD. The resistivity of the deposited aluminum is nearly that of the bulk metal, the contact resistivity is good (∼0.03 μΩ-cm2), and the morphology of the deposited film is comparable to that obtained with physical vapor deposition. This process has been used to fill via holes in a SiO2 substrate, and small-diameter (0.7 μm), high-aspect-ratio (3:1), aluminum plugs have been repeatedly formed without the incorporation of voids. A custom-made via chain structure was used to determine the via resistance (plug and contact), which was found to be 0.1 -0.3 Ω. Our technique opens a new process window for void-free high-aspect-ratio via and contact hole filling, and is particularly interesting in that it offers the potential to use aluminum or aluminum-copper in plug metallization.

Since self-aligned suicides are beginning to be used routinely in integral ULSI processes, critical processing characteristics need to be investigated. In this paper, three relevant issues concerning processing are discussed, namely, the formation of ultra-thin suicides, the silicidation of laterally confined areas and the thermal stability of silicide/Si structures. The technological aspects of TiSi2 and COSi2 are discussed and related to their materials properties.

In-situ emissivity measurements at a wavelength of 2.4 μα were used to monitor RTP Co silicidation on crystalline and polycrystalline silicon substrates. The influence of various parameters influencing the silicidation reaction was extensively studied. It is shown that particularly the phase transformation from CoSi to the final suicide phase, COSi2, strongly depends on parameters such as background doping level and type of substrate. This is illustrated for As-doped substrates. The method is extremely sensitive for the in-situ detection of the thermal degradation of thin COSi2 films at high temperatures, which is demonstrated for 25 nm COSi2 layers on highly As-doped c-Si substrates.

Copper is being investigated for application as multi-level interconnection metal in silicon ultra-large-scale integration (ULSI). On the other hand, COSi2 is being tested for application as contacts in sub-half micron ULSI circuits. Copper will thus be used on COSi2 to bring the electrical connection to the outside world. In this investigation we have therefore studied the interactions of copper with CoSi2 employing sheet resistance measurements (four-point probe), Rutherford back scattering (RBS), and X-ray diffraction (XRD). In addition the stability of the Schottky diodes, n-Si/CoS2/Cu, has been investigated as a function of the heat treatment in the range of room temperature to 600° C in argon-3% hydrogen mixture gas ambient. Both the measurements of the analytical and electrical characteristics show that Cu on n-Si/CoSi2 is stable at least up to a 30 minutes anneal at 600°C in argon-3% hydrogen medium. These results will be presented and discussed.

Redistribution of boron during the formation of the cobalt suicides Co2Si, CoSi and CoSi2 has been studied. The suicides were formed by solid state reactions of cobalt deposited on boron implanted silicon. The suicide formation was determined by Rutherford backseat tering spectrometry (RBS), and the resulting redistribution of boron was studied using secondary ion mass spectrometry (SIMS). The study shows that the atoms participating in the suicide formation diffuse in the growing suicide without any mutual interference. Boron atoms in the consumed silicon layer redistribute within the formed suicide layer and accumulate at the surface, while boron in the underlying unconsumed silicon is unaltered, and no accumulation due to snowplowing occurs at the silicide/silicon interface.

The thermal stability of COSi2 for thermal budgets suitable for a self-aligned P+ gate MOSFET process using rapid thermal processing was studied. The substrate underlying the suicide has a major impact on suicide degradation. Suicides formed on as-deposited amorphous silicon films and on single crystal Si were found to be stable at least up to 1000°C, whereas suicides formed on as-deposited polysilicon (i.e. conventional polycide) began to degrade at annealing temperatures greater than 800°C. BF2-implant dosages of 1×1015 cm-2 to 2×1016 cm-2 at 20keV in the suicide were found to affect the conventional polycide significantly. With higher implant dosages, the degradation of the conventional polycide is retarded for a 900°C anneal. However, for thermally stable suicides i.e., suicides formed on as-deposited amorphous Si and on single crystal Si, a high dose 2×1016 cm-2 implant increases the sheet resistance slightly from 1.4 Ω/square to 1.6 Ω/square for suicides on as-deposited amorphous Si substrate, and from 1.3 Ω/square to 1.6 Ω/square for suicides on single crystal substrates. A model which involves spheroidization of the suicide, silicon incursion, and indiffusion of Co into polysilicon is proposed to explain the degradation behavior.

The current/voltage characteristics of ion beam synthesised CoSi2/Si (n - type) Schottky barrier diodes implanted with phosphorus to doses between 5 × 1012 and 2 × 1013 ions cm-2are examined after annealing at temperatures in the range 400° - 1000°C. For each dose of implanted phosphorus, the effective barrier height of the CoSi2/Si interface is successively reduced as the anneal temperature increases. The results of Secondary Ion Mass Spectroscopy (SIMS) analysis indicate that these changes are due to an increase in the space charge density at the interface. For lower annealing temperatures the increase in space charge density is attributed to activation of the phosphorus in the tail of the dopant distribution which extends across the CoSi2/Si interface. For higher annealing temperatures larger increases in the space charge density are attributed to a modified dopant distribution resulting from phosphorus diffusion and activation at the interface. For doses of 1 × 1014 P* cm-2and 2×1015P*cm2, ohrnie characteristics are seen after annealing at temperatures of 1000°C and 500°C respectively.