Alain E. Kaloyeros

Advanced multilayer metallization schemes with copper as interconnection metal

Abstract Advanced metallization schemes are needed to take advantage of the miniaturization of microelectronic devices which are performing at increasingly high speeds. The demands on metallization center around (a) the increased resistance with lower cross-sectional areas and longer interconnect lengths and (b) stability with the surroundings during processing and use under high current densities and thin film stresses. A threefold attack is being pursued to solve these problems, which also duplicate the issues in packaging of these fast chips with large numbers of inputs and outputs: first is to make use of copper as the interconnection metal; second is to use a multilevel metallization scheme; finally there is a need for a low dielectric constant dielectric. In this paper we present a review of progress made in addressing the first two schemes together with a brief discussion of the third. Copper, a heretofore undesired metal in silicon integrated circuits, seems to show promise, with appropriate processing constraints, of fulfilling the projected needs of ultra-large-scale and giga-scale integration and perhaps even of packaging.

Low-temperature metal-organic chemical vapor deposition (LTMOCVD) of device-quality copper films by microelectronic applications

Copper films for potential use in multilevel metallization in ULSIC’s were produced by low temperature (250–350° C) metal-organic chemical vapor deposition (LTMOCVD) in atmospheres of pure H2 or mixture Ar/H2 from the β-diketonate precursor bis(1,1,1,5,5,5-hexafluoroacetylacetonato) copper(ll), Cu(hfa)2. The films were analyzed by x-ray diffraction (XRD), Rutherford backscattering (RBS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDXS). The results of these studies showed that the films were uniform, continuous, adherent and highly pure—oxygen and carbon contents were below the detection limits of AES. Four point resistivity measurements showed that the copper films had very low resistivity, as low as 1.9 μΩcm for the films deposited in pure hydrogen atmosphere. Our preliminary results seem to indicate that LTMOCVD is a very attractive technique for copper multilevel metallizations.

Tantalum Nitride Films Grown by Inorganic Low Temperature Thermal Chemical Vapor Deposition Diffusion Barrier Properties in Copper Metallization

Key findings are presented from a systematic study which evaluated the performance of chemical vapor deposited (CVD) nitrogen-rich tantalum nitride (TaN x , x ∼ 1.8) films as a diffusion barrier in copper (Cu) based metallization schemes. For this purpose, 3800 A thick Cu films were grown by physical vapor deposition (PVD) on 550 A thick TaN x films which were deposited by low temperature (<425°C) thermal CVD (TCVD) using tantalum pentabromide (TaBr 5 ), ammonia, and hydrogen as coreactants. The resulting stacks were annealed in argon ambient at 450, 500, 550, and 650°C for 30 min each, along with similar PVD Cu/PVD TaN x bilayers of identical thickness. Both types of pre- and postannealed stacks were characterized by X-ray photoelectron spectroscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry, nuclear reaction analysis for hydrogen profiling, X-ray diffraction, stack sheet resistance measurements, and Secco chemical treatment and etch-pit observation by scanning electron microscopy. The resulting findings showed that the PVD TaN x films provided an excellent barrier against Cu diffusion throughout the annealing window investigated. Altematively, the TCVD TaN x films exhibited similar stability up to 550°C. Barrier failure occurred, however, at temperatures between 550 and 600°C, as revealed by the formation of etch pits after Secco etch treatment. The failure of the TCVD TaN x films could not be attributed to bromine incorporation, given that residual bromine (∼0.5 atom %) in the TCVD TaN x films was highly stable against thermal diffusion in the temperature window investigated. Instead, the higher thermal stability of the PVD TaN x was attributed to differences in film microstructure and crystalline phase, or the location of excess nitrogen within the film matrix.

Low temperature plasma-assisted chemical vapor deposition of tantalum nitride from tantalum pentabromide for copper metallization

In this article, the authors report the development of a new low temperature plasma-assisted chemical vapor deposition (PACVD) process for the growth of low resistivity, cubic tantalum nitride (TaNx) for incorporation as a diffusion barrier/adhesion promoter in emerging ultralarge-scale integrated (ULSI) multilevel metallization (MLM) schemes. TaNx films were produced in a low density plasma using tantalum pentabromide, hydrogen, and nitrogen as coreactants. The films were grown at substrate temperatures of 350–450 °C, reactor working pressures of 0.9–1.6 Torr, hydrogen flow rates between 250 and 1500 sccm, nitrogen flow rates of 100–600 sccm, and plasma power ranging from 10 to 60 W, corresponding to a power density of 0.06–0.33 W/cm2. The films were subsequently characterized by Auger electron spectroscopy, Rutherford backscattering spectrometry, x-ray diffraction, atomic force microscopy, four-point resistivity probe, and cross-sectional scanning electron microscopy. These studies indicated that the Ta...

The Effects of Processing Parameters in the Chemical Vapor Deposition of Cobalt from Cobalt Tricarbonyl Nitrosyl

This paper reports the development of a thermal chemical vapor deposition process for pure cobalt from the source precursor cobalt tricarbonyl nitrosyl for incorporation in integrated circuit silicide applications. Studies were carried out to examine the underlying mechanisms that control Co nucleation and growth kinetics, including the effects of key process parameters on film purity, texture, morphology, and electrical properties. For this purpose, systematic variations were implemented for substrate temperature, precursor flow, hydrogen reactant flow, and deposition time (thickness). Resulting films were analyzed by Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, X-ray diffraction, four-point resistivity probe, scanning electron microscopy, and atomic force microscopy. These investigations identified an optimized process window for the growth of pure Co with resistivity of 9 ± 2 μΩ cm, smooth surface morphology, and root-mean-square surface roughness at or below 10% of film thickness.

White light emission from amorphous silicon oxycarbide (a-SiCxOy) thin films: Role of composition and postdeposition annealing

The effects of carbon and postdeposition annealing on white luminescence are studied in amorphous silicon oxycarbide (a-SiCxOy) films grown by chemical vapor deposition. The films showed strong room-temperature luminescence in a broad spectral range from blue-violet to near infrared, depending on excitation energy. Photoluminescence (PL) intensity exhibited good correlation with SiOC bond concentration. At low C (<5%), matrix PL was completely quenched after annealing in O2 even at 500 °C. PL was unaffected by O2 annealing at higher C, and could be enhanced when excited by an ultraviolet laser. These findings are correlated to C- and Si-related O defect centers as luminescence sources in a-SiCxOy.

Low temperature metal-organic chemical vapor deposition of tungsten nitride as diffusion barrier for copper metallization

A metal-organic chemical vapor deposition process has been developed for the growth of amorphous tungsten nitride thin films for barrier layer applications in ultralarge scale integration copper interconnect schemes. The process employs tungsten hexacarbonyl, [W(CO)6] and ammonia (NH3) as, respectively, the tungsten and nitrogen sources. Tungsten nitride films were produced within a wide process window, including a substrate temperature of 200–350 °C, W(CO)6 flow rate of 1–20 sccm, reactor pressure of 0.2–0.5 Torr, and NH3 flow rates of 100–500 sccm. The films were analyzed by x-ray photoelectron spectroscopy, cross-section scanning electron microscopy, x-ray diffraction, transmission electron microscopy, four-point resistivity probe, and Rutherford backscattering spectrometry. These studies indicated that the films consisted predominantly of a W2N phase. Films were grown with carbon and oxygen concentrations ⩽5 at. %, even at the lowest processing temperature investigated, where precursor dissociation wo...

Device‐quality copper using chemical vapor deposition of β‐diketonate source precursors in liquid solution

Device‐quality copper films were produced by chemical vapor deposition from copper(II) β‐diketonate precursors using a liquid delivery approach. This liquid delivery method exploits the high solubility of copper(II) β‐diketonate precursors in selected solvents, such as isopropanol and ethanol, to provide highly accurate, reproducible, and controllable flow rates of precursor and solvent mixtures to the reaction zone. The approach was successfully employed to produce high‐quality copper files from predetermined mixtures of bis(hexafluoroacetylacetonato) copper(II) and ethanol or isopropanol. Plasma‐assisted chemical vapor deposition (PA‐CVD) was used with substrate temperatures of 160–170 °C, reactor working pressures of 1.0–1.7 Torr, hydrogen flow rates between 500 and 1200 cc/min, and hydrogen plasma power density ranging from 0.13 to 0.25 W/cm2. The films were subsequently characterized by Rutherford backscattering spectroscopy, cross‐section SEM (scanning electron microscopy), and a four‐point resistiv...

Comparative study of the effects of thermal treatment on the optical properties of hydrogenated amorphous silicon-oxycarbide

Findings are presented from a systematic study of the effects of postdeposition thermal treatment on the optical characteristics of hydrogenated amorphous silicon-oxycarbide (a-SiCxOyHz) materials. Three different classes of a-SiCxOyHz films: SiC-like (SiC1.08O0.07H0.21), Si-C-O (SiC0.50O1.20H0.22), and SiO2-like (SiC0.20O1.70H0.24), were deposited by thermal chemical vapor deposition. The effects of thermal annealing on the compositional and optical properties of the resulting films were characterized using Fourier-transform infrared spectroscopy, x-ray photoelectron spectroscopy, nuclear reaction analysis, and spectroscopic ultraviolet-visible ellipsometry. As the Si-C-O system evolved from a SiC-like to SiO2-like matrix, its refractive index and optical absorption strength decreased, while its optical band gap increased. Thermal annealing between 500 and 1100 °C resulted in hydrogen desorption from and densification of the a-SiCxOyHz films. Concurrently, thermally induced changes were also observed for...

Barrier Properties of Titanium Nitride Films Grown by Low Temperature Chemical Vapor Deposition from Titanium Tetraiodide

Results are presented from a systematic study of the composition, texture, and electrical properties of titanium nitride (TiN) films and their performance as diffusion barrier in multilevel interconnect schemes of ultralarge scale integration (ULSI) computer chip device structures. The films were grown by low temperature (<450°C) inorganic chemical vapor deposition using titanium tetraiodide as source precursor and ammonia and hydrogen as co-reactants. The TiN films were nitrogen-rich., with iodine concentrations below 2 atom percent, displayed resistivities in the range 100 to 150 μΩ cm depending on thickness, and exhibited excellent step coverage with better than 90% conformality in both nominal 0.45 μm, 3:1 aspect ratio and 0.25 μm, 4:1 aspect ratio contact structures. A comparison of the properties of chemical vapor deposited (CVD) TiN with equivalent physical vapor deposited (PVD) TiN showed that reactivity with Al-0.5 a/o Cu alloys was equivalent in both cases. In particular, a 10% increase in the Al-Cu/TiN stack sheet resistance was observed for both types of TiN after a 450°C, 30 min sinter. Similarly, the characteristics of CVD tungsten and reflow plug fills were identical on both types of TiN films. However, barrier performance for CVD TiN in aluminum and tungsten plug technologies was superior to that of PVD TiN, as evidenced by lower contact diode leakage for CVD TiN in comparison with PVD TiN films of equal thickness. This improved barrier performance could be attributed to a combination of factors, which include the nitrogen-rich composition, higher density, and enhanced conformality of the CVD TiN phase in comparison with the PVD TiN. In view of the superior step coverage and diffusion barrier characteristics, the low temperature inorganic CVD route to TiN seems to provide an adequate replacement for conventional PVD TiN in emerging ULSI metallization interconnect schemes.