Chemistry: electrical and wave energy – Processes and products – Vacuum arc discharge coating
Reexamination Certificate
2001-01-25
2002-10-01
Ryan, Patrick (Department: 1745)
Chemistry: electrical and wave energy
Processes and products
Vacuum arc discharge coating
C204S192220
Reexamination Certificate
active
06458255
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to tantalum films having ultra-low resistivity, in the range of about 10 &mgr;&OHgr;-cm, as well as methods for depositing ultra-low resistivity tantalum films. Tantalum films deposited according to the method of the invention can be removed from a semiconductor substrate surface using chemical mechanical polishing (CMP) techniques far more rapidly than previously known tantalum films.
2. Brief Description of the Background Art
As microelectronics continue to miniaturize, interconnection performance, reliability, and power consumption has become increasingly important, and interest has grown in replacing aluminum alloys with lower resistivity and higher reliability metals. Copper offers a significant improvement over aluminum as a contact and interconnect material. For example, the resistivity of copper is about 1.67 &mgr;&OHgr;-cm, which is only about half of the resistivity of aluminum.
One of the preferred technologies which enables the use of copper interconnects is the damascene process. This process for producing a multi-level structure having feature sizes in the range of 0.5 micron (&mgr;m) or less typically includes the following steps: blanket deposition of a dielectric material over a substrate; patterning of the dielectric material to form openings; deposition of a diffusion barrier layer and, optionally, a wetting layer to line the openings; deposition of a copper layer onto the substrate in sufficient thickness to fill the openings; and removal of excessive conductive material from the substrate surface using chemical-mechanical polishing (CMP) techniques. The damascene process is described in detail by C. Steinbruchel in “Patterning of copper for multilevel metallization: reactive ion etching and chemical-mechanical polishing”,
Applied Surface Science
91 (1995) 139-146.
The preferred barrier layer/wetting layer for use with copper comprises a tantalum nitride—tantalum barrier/wetting layer having a decreasing nitrogen content toward the upper surface of the layer. This structure, which provides excellent barrier properties while increasing the <111> content of an overlying copper layer, provides a copper layer having improved electromigration resistance, as described in applicants' copending application Ser. No. 08/995,108. A barrier layer having a surface which is essentially pure tantalum or tantalum including only a small amount of nitrogen (typically less than about 15 atomic percent) performs well as a barrier layer and also as a wetting layer to enhance the subsequent application of an overlying copper layer.
Philip Catania et al. in “Low resistivity body-centered cubic tantalum thin films as diffusion barriers between copper and silicon”, J. Vac. Sci. Technol. A 10(5), September/October 1992, describes the resistivity of thin bcc-tantalum films and &bgr;-tantalum films. The resistivity for bcc-tantalum (&agr;-tantalum) films is said to be on the order of 30 &mgr;&OHgr;-cm, while the resistivity of the &bgr;-tantalum films ranges from about 160-180 &mgr;&OHgr;-cm. A comparison of the effectiveness of thin bcc-Ta and &bgr;-Ta layers as diffusion barrier to copper penetration into silicon shows that the bcc-Ta which exhibits low resistivity also performs well as a barrier layer up to 650° C.
Kyung-Hoon Min et al. in “Comparative study of tantalum and tantalum nitrides (Ta
2
N and TaN) as a diffusion barrier for Cu metallization”, J. Vac. Sci. Technol. B 14(5), September/October 1996, discuss tantalum and tantalum nitride films of about 50 nm thickness deposited by reactive sputtering onto a silicon substrate. The performance of these films as a diffusion barrier between copper and silicon is also discussed. The diffusion barrier layer performance is said to be enhanced as nitrogen concentration in the film is increased.
U.S. Pat. No.3,607,384 to Frank D. Banks, issued Sep. 21, 1971, describes thin film resistors which utilize layers of tantalum or tantalum nitride.
FIG. 1
in the '385 patent shows the resistivity for a particular tantalum nitride film as a function of the sputtering voltage and
FIG. 2
shows the resistivity as a function of the nitrogen content of the film. The lowest resistivity obtained under any conditions was about 179 &mgr;&OHgr;-cm.
U.S. Pat. No.3,819,976 to Chilton et al., issued Jun. 25, 1974, describes a tantalum-aluminum alloy attenuator for traveling wave tubes. In the background art section of this patent, there is a reference to tantalum film undergoing a phase transition from beta-tantalum to body-centered-cubic (alpha) tantalum at about 700° C.
U.S. Pat. No.3,878,079 to Alois Schauer, issued Apr. 15, 1975, describes and claims a method of producing thin tantalum films which are body-centered cubic lattices. The films are deposited upon a glass substrate, and
FIG. 2
of the '079 patent shows resistivity for tantalum nitride films as a function of nitrogen content. U.S. Pat. No. 4,000,055 to Kumagai et al., issued Dec. 28, 1976, discloses a method of depositing nitrogen-doped beta-tantalum thin films.
FIG. 2
of the '055 patent also shows the resistivity of the film as a function of the nitrogen content of the film.
U.S. Pat. No. 4,364,099 to Koyama et al., issued Dec. 14, 1982, discloses a tantalum film capacitor having an &agr;-tantalum as a lower electrode, a chemical conversion layer of &agr;-tantalum as a dielectric, and an upper electrode. This references also discusses a phase transition of the tantalum film depending on the nitrogen concentration of the film. When the nitrogen content ranges from about 6 to about 12 percent, the resistivity of the tantalum thin film is said to be advantageously low, although no particular resistivity data is provided.
U.S. Pat. No. 5,221,449 to Colgan et al., issued Jun. 22, 1993, describes a method of making alpha-tantalum thin films. In particular, a seed layer of Ta(N) is grown upon a substrate by reactive sputtering of tantalum in a nitrogen-containing environment. A thin film of &agr;-tantalum is then formed over the Ta(N) seed layer. In the Background Art section of the patent, reference is made to the “Handbook of Thin Film Technology”, McGraw-Hill, page 18-12 (1970), where it is reported that if the substrate temperature exceeds 600° C., alpha phase tantalum film is formed. Further reference is made to an article by G. Feinstein and R. D. Huttemann, “Factors Controlling the Structure of Sputtered Tantalum Films”,
Thin Solid Films,
Vol. 16, pages 129-145 (1973). The authors are said to divide substrates into three groups: Group I, containing substrates onto which only beta-tantalum can be formed (including glass, quartz, sapphire, and metals such as copper and nickel); Group II, containing substrates onto which only alpha (bcc) tantalum can be grown (including substrates coated with 5000 Å thick metal films such as gold, platinum, or tungsten); and Group III, containing substrates which normally produce alpha-tantalum, but which can be induced to yield beta-tantalum or mixtures of alpha and beta by suitable treatment of the surface (i.e., substrates coated with 5,000 Å of molybdenum, silicon nitride, or stoichiometric tantalum nitride, Ta
2
N).
As the feature size of semiconductor devices becomes ever smaller, the barrier/wetting layer becomes a larger portion of the interconnect structure. In order to maximize the benefit of copper's low resistivity, the diffusion barrier/adhesion layer must be made very thin and/or must have low resistivity itself (so that it does not impact the effective line resistance of the resulting metal interconnect structure). As is readily apparent, depending on the device to be fabricated, various methods have been used in an attempt to develop a tantalum film which is a phase when lower resistivity is desired. Typically, small additions of nitrogen have been made to tantalum films to lower the resistivity of the tantalum. This method is difficult to control, as any deviation in the nitrogen content (even±1 scc
Chiang Tony
Chin Barry
Ding Peijun
Applied Materials Inc.
Bean Kathi
Cantelmo Gregg
Church Shirley L.
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