Methodology for in-situ doping of aluminum coatings

Details Methodology for in-situ doping of aluminum coatings Methodology for in-situ doping of aluminum coatings

2000-06-30

2003-03-18

Meeks, Timothy (Department: 1762)

Coating processes

Direct application of electrical, magnetic, wave, or...

Plasma

C427S252000, C427S255700, C438S680000, C438S681000, C438S687000, C438S688000

Reexamination Certificate

active

06534133

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to conformal doped aluminum coatings on a patterned substrate and a methodology and apparatus to prepare such doped coatings. More particularly, the present invention is directed to the controlled, reproducible growth by thermal or plasma-assisted CVD (PACVD) processes of ultrathin Cu layers which are subsequently used as seed surface for the in-situ thermal or plasma assisted chemical vapor deposition of smooth, void-free, and dense copper-doped aluminum films which conformally coat semiconductor device substrates with patterned holes, vias, and trenches with aggressive aspect ratios (hole depth/hole width ratios).
BACKGROUND OF THE INVENTION
The ever increasing demand for higher density and enhanced performance in deep sub-quarter micron integrated chip (IC) device technologies is placing enormous pressure on intrachip interconnect architecture development. Predictions published in the Semiconductor Industry Association Technology Roadmap for Semiconductors, See The International Technology Roadmap for Semiconductors, 1999 Edition (Semiconductor Industry Association, San Jose, Calif., 1999), indicate that the emerging needs of advanced logic and microprocessor systems could require over ten levels of interconnects. One of the key problems in the generation of these multiple conductor levels involves the fabrication of well-defined and precisely-patterned vertical electrical connections (vias) between different interconnect planes of the chip.
As the traditional building block of the IC interconnects, Al alloys have played a major role in the evolution of the computer age. When alloyed with 0.5 wt % copper, Al exhibits enhanced electromigration resistance while maintaining good electrical conductivity. In addition to its ability for self passivation in air and ease of patternability in chlorine based plasmas, Al bonds well to SiO
2
and diffusion barriers of titanium nitride and titanium. See S. P. Murarka, Metallization: Theory and Practice for VLSI and ULSI (Butterworth-Heinemann, Boston, 1993). In light of these properties, Al based metallizations are predicted not only to continue as the interconnection workhorse of the integrated circuit industry in the foreseeable future, but will extend their role in providing contact and via hole plugs for all wiring levels.
Unfortunately, in the past decade, the deposition of Al alloys into small vertical holes cut into interlevel dielectrics has become increasingly problematic as feature sizes decrease below half micron. Poor metal step coverage and the resulting incomplete filling of vias with physical vapor deposited (PVD) Al alloys generated serious process and reliability concerns. Al reflow and other high temperature Al alloy sputtering, or physical vapor deposition (PVD), processes are presently being explored and implemented as potential low cost alternatives which provide conformal via fill and ease in integration in device fabrication process flow. However, the repetitive exposure to high deposition temperatures required in a multilevel metal (MLM) architecture may adversely affect the device during processing. Secondly, the need for high temperature may greatly restrict the implementation of a number of new low dielectric constant materials into future interconnect architectures. The high temperature excursions could also result in barrier failure, which would be problematic at the contact level and lead to undesirable levels of junction leakage. See P. Singer, Semiconductor International 17 (1994) 57.
Chemical vapor deposition (CVD) of Al presents a viable alternative to PVD due to its inherent ability to grow films conformally on via and trench structures. Efforts to develop CVD Al deposition techniques date as far back as the late 1940s, wherein a variety of chemical sources were used which included Al halide, alkyl, and organometallic sources. See, for example, C. F. Powell, J. H. Oxley, and J. M. Blocher, Jr., Vapor Deposition (Wiley, New York, N.Y., 1966) p. 27; and H. J. Cooke, R. A. Heinecke, R. C. Stern, and J. W. C. Maas, Solid State Technol. 25 (1982) 62. The resulting Al films, regardless of the chemical source used, exhibited extensive surface roughness, high resistivity, and substantial contamination. Attempts to re-investigate these systems for device applications were revived in the mid-1980s. In these cases, evaluations were performed of Al CVD films generated from metal-organic sources such as tri-isobutyl aluminum (TIBA). See, for example, B. E. Bent, R. G. Nuzzo, and L. H. Dubois, J. Am. Chem. Soc. 111 (1989) 1634, H. O. Pierson, Thin Solid Films, 45 (1977) 257; and R. A. Levy, P. K. Gallagher, R. Contolini, and F. Schrey, J. Electrochem. Soc. 132 (1985) 457. In these initial batch process type studies, which used hot wall CVD reactors, carbon contamination, surface roughness, and low deposition rates posed unacceptable process problems. These unsuccessful experiments were prematurely abandoned in favor of more mature and manufacturable CVD tungsten metallization processes.
Tungsten CVD use could probably continue below the 0.1 &mgr;m device technology, as equipment suppliers focus their efforts on enhancing throughput, reducing particles, and improving cost-of-ownership. See P. Singer, Semiconductor International 17 (1994) 57. However, the cost associated with the deposition and etchback of CVD tungsten is substantially higher than of its Al alloy counterpart. Additionally, the use of Al alloy plug, with its approximately 100% lower electrical resistance (R) than its tungsten counterpart, provides the promise of substantially reduced RC delay, where C is the capacitance of the insulator. These expectations have revived interest in the development of a low temperature CVD based process for Al/0.5 at % Cu that is capable of filling small, high aspect ratio holes that are patterned in thermally fragile plastic-like, low dielectric constant organic polymers. Most recent CVD aluminum work has focused on the use of metal-organic precursors of the type diethylmethylaluminum alane or DMEM and dimethylaluminum hydride or DMAH. See, for instance, M. E. Gross, K. P. Cheung, C. G. Fleming, J. Kovalchick, and L. A. Heimbrok, J. Vac. Sci. Technolo. A9 (1991) 1; M. E. Gross, L. H. Dubois, R. G. Nuzzo, and K. P. Cheung, Mat. Res. Symp. Proc., Vol 204 (MRS, Pittsburgh, Pa., 1991) p. 383; W. L. Gladfelter, D. C. Boyd, and K. F. Jensen, Chemistry of Mater. 1 1989) 339; D. B. Beach, S. E. Blum, and F. K. LeGoues, J. Vac. Sci. Technol. A 1989) 3117. The molecular structure of these precursors is distinguished by the presence of aluminum-hydrogen (i.e. Al—H) bonds. This feature provided a clean chemical pathway to eliminate the precursor's hydrocarbon groups at relatively low temperatures to yield pure aluminum films. More specifically, the AlH
3
groups in DMEAA, and the Al—H groups in DMAH permitted pure aluminum film growth at temperatures as low as, respectively, 100° C. and 200° C. This feature made these compounds the candidates of choice in most on-going Al CVD development activities, and led to the successful growth of device-quality aluminum with conformal step coverage for substrates having aggressive holes and trenches (i.e., with a diameter of 0.25 &mgr;m or smaller) and high aspect ratios (i.e., the ratio of hole depth to hole width equal to or greater than about 4:1).
In spite of the recent success of both PVD processing, such as Al reflow, and CVD processing, both thermal and plasma assisted, at the formation of device-quality Al thin films, there exists a critical need for a processing technology to provide doped aluminum films (aluminum with a few percent of other elements, such as copper, carbon, tungsten, tantalum, titanium, palladium, gold, silver, platinum, silicon, germanium, samarium, zirconium, palladium, magnesium, etc.) suitable for ULSI fabrication. Copper doping is needed to significantly enhance aluminum's resistance to electromigation and allow aluminum interconnects to sustain the high current densities (>10
6
A/cm
2
) require

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