Coating processes – Coating by vapor – gas – or smoke – Mixture of vapors or gases utilized
Reexamination Certificate
2001-10-23
2004-06-01
Chen, Bret (Department: 1762)
Coating processes
Coating by vapor, gas, or smoke
Mixture of vapors or gases utilized
C117S088000
Reexamination Certificate
active
06743475
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a process for producing aluminum oxide films by an ALD type process. According to the preferred process the aluminum oxide films are produced at low temperatures by bonding a metal compound on a substrate and converting said metal compound into a metal oxide.
2. Description of Related Art
Dielectric thin films with a high dielectric constant (permittivity) have a number of applications in the field of microelectronics. For example, they may replace the SiO
2
and Si
3
N
4
presently used in DRAM-memories in order to maintain the necessary capacitance as the size of capacitors is reduced.
Al
2
O
3
films suitable for passivating surfaces have previously been prepared by physical processes, such as sputtering. The problem with the films produced by sputtering has been the unevenness of the resulting film, and the pinholes that are formed in the film. These pinholes may form a diffusion path for water through the film.
U.S. Pat. No. 6,124,158 discloses a method of reducing carbon contamination of Al
2
O
3
thin films deposited by an ALD method. The ALD process uses organic aluminum precursors and water. In at least every third cycle, ozone is introduced into the reaction chamber to reduce carbon contaminants. The process has its limits since aluminum oxide films deposited below 190° C. were not dense or reproducible.
ALD methods have also been used for producing Al
2
O
3
films by using aluminum alkoxides, trimethyl aluminum (TMA) or AlCl
3
as the aluminum source material and water, alcohols, H
2
O
2
or N
2
O as the oxygen source material. Al
2
O
3
films from TMA and water have been deposited at temperatures in the range of 150° C. to 400° C. Typically the temperature has been between 150° C. and 300° C. The resulting films had uniform thickness and did not contain any pinholes. However, the density of the film has been questionable at the lower end of the deposition temperature range.
In applications involving organic polymers or low molecular weight organic molecules, such as organic EL displays, the deposition temperature is preferably less than 150° C., while in applications where the substrate is sensitive to water it is not feasible to use water as the oxygen source material. Thus there is a need for a process of producing aluminum oxide films by ALD at low temperatures using an oxygen source other than water.
SUMMARY OF THE INVENTION
The present invention is based on the surprising finding that high-quality aluminum oxide thin film can be grown by an ALD type process at substrate temperatures down to 100° C. Another surprising finding is that ozone can be used in the deposition process without destroying the properties of substrates that contain an organic layer. A dense, pinhole-free thin film layer can be produced very quickly by ALD on the substrate surface, which protects the sensitive materials underneath the surface against the surrounding gas atmosphere.
In accordance with one aspect of the present invention a process is provided for depositing a thin film of aluminum oxide on a substrate by an atomic layer deposition process that comprises a plurality of cycles. Each cycle comprises supplying a first reactant that comprises a gaseous aluminum compound and supplying a gaseous second reactant that comprises a source of oxygen other than water. The second reactant converts the adsorbed portion of the first reactant on the substrate to aluminum oxide. Preferably the substrate is maintained at a temperature of less than 190° C. during the ALD process.
A number of considerable advantages are obtained by means of the preferred embodiments. For example, with the aid of the present invention, it is possible to produce Al
2
O
3
films of good quality at low temperatures.
Dielectric thin films with a dense structure can be used for passivating surfaces that do not tolerate high temperatures. Such surfaces include, for example, polymer films. If a water-free oxygen source is used, surfaces that are sensitive to water can also be passivated.
In addition, dielectric films, including aluminum oxide thin films, with a dense structure can be used as buffer layers between functional films that include at least one organic film. The dielectric film then prevents either reaction or diffusion between the functional films.
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Kattelus, H. et al., “Electrical Properties of Tantalum Based Composite Oxide Films,”Mat. Res. Soc. Symp. Proc., vol. 284, pp. 511-516 (1993).
Kattelus, H. et al., “Layered tantalum-aluminum oxide films deposited by atomic layer epitaxy,”Thin Solid Films, vol. 225, pp. 296-298 (1993).
Kim. Y.K. et al., “Novel capacitor technology for high density stand-alone and embedded DRAMs,”IEEE International Electron Devices Meeting, IEDM (2000), no page numbers.
Kukli, K. et al., Properties of (Nb1-xTax)2O5Solid Solutions and (Nb1-xTax)2O5-ZrO2Nanolaminates Grown by Atomic Layer Epitaxy,NanStructured Materials, vol. 8, No. 7, pp. 785-793 (1997).
Kukli, K. et al., “Properties of Ta2O5-Based Dielectric Nanolaminates Deposited by Atomic Layer Epitaxy,”J. Electrochm. Soc., vol. 144, No. 1, pp. 300-306 (1997).
Kukli, K., “Properties of atomic layer deposited (Ta1-xNbx)2O5solid solution films ant Ta2O5-Nb2O5nanolaminates,”Journal of Applied Physics, vol. 86, No. 10 (1999)m oo 5656-5662.
Lakomaa, E-L. et al., “Surface reactions in Al2O3growth from trimethylaluminum and water by atomic layer epitaxy,”Applied Surface Science, vol. 107, pp. 107-115 (1996).
Ritala, M. et al., “Surface roughness reduction in atomic layer epitaxy growth of titanium dioxide thin films,”Thin Solid Films, vol. 249, pp. 155-162 (1994).
Zhang, H. et al., “High permittivity thin film nanolaminates,”Journal of Applied Physics, vol. 87, No. 4, pp. 1921-1924 (2000).
Kukli et al, “Atomic layer epitaxy growth of aluminum oxide thin films from a novel Al(CH3)2Cl precursor and H2O.”, J. Vac. Sci. Technol. A 15(4), Jul./Aug. 1997, pp. 2214-2218.
Hiltunen et al. “Growth and Characterization of Aluminum Oxide Thin Films Deposited from Various Source Materials by Atomic Layer Epitaxy and Chemical Vapor Deposition Processes”, Materials Chemistry and Physics, 28 (1991) pp. 379-388.
Asikainen Timo
Linnermo Mervi
Skarp Jarmo
ASM International N.V.
Chen Bret
Knobbe Martens & Olson Bear LLP.
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