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The superiority of dimethylaluminumhydride [(CH 3 ) 2 AlH, DMAH] to dimethylethylaminealane [AlH 3 N(CH 3 ) 2 (C 2 H 5 ), DMEAA] has been investigated from the view point of aluminum chemical vapor deposition (Al CVD) technology in ULSI manufacturing. Both DMAH and DMEAA have the same filling capability such as surface morphology and step coverage. For deposition reproducibility, the smaller activation energy is more suitable for manufacturing. The activation energy of Al deposition is found to be 0.38 [eV] for DMAH and 0.74 [eV] for DMEAA. These results mean the reproducibility of Al thickness using DMAH is superior to that using DMEAA. For safe storage and precise precursor delivery, the precursor should be chemically stable. From the results of measuring the pressure increase in vessel, it has shown that DMAH has superior chemical stability to DMEAA. Manufacturing apparatus such as Al CVD cluster module requires the deposition selectivity that is defined as Al deposition only on the desired areas of wafer surface and not on any parts of cluster module. Using DMAH, Al is deposited on barrier metal surface of silicon wafer, while Al is not deposited on the sealed anodic oxidized aluminum or the synthetic quartz. DMAH has shown excellent selectivity in comparison with DMEAA. Therefore, DMAH is superior to DMEAA as a precursor for the Al CVD technology in ULSI manufacturing.

The (1 1 02) α-Al2O3 surface and the initial nitriding AlN layer are investigated using the atomic-force microscope. The initial nitriding method is to convert the (1 1 02) α-Al2O3 surface to a nanometer-thick AlN single-crystal buffer layer. The epitaxial AlN film is deposited by metalorganic chemical vapor deposition with and without the initial nitriding. Atomic step structure is found to be formed after the H2 annealing. The atomic step structure is maintained during the initial nitriding time up to 5 min. Smooth AlN epitaxial films have been successfully deposited on the 2 inch diameter (1 1 02) α-Al2O3 wafer without any inverse-twin throughout the wafer by keeping the atomic step structure of the initial nitriding buffer layer.

Area-selective AI CVD technology has an excellent potential for filling via and contact holes of multilevel interconnection in Si ULSI. In this article, we discuss the selective AI CVD using metalorganic sources of trimethylaluminum [(CH 3 ) 3 AI, TMA] and dimethylaluminum hydride [(CH 3 ) 2 AIH, DMAH]. In order to deposit AI from TMA, the TMA molecule should be selectively excited into a reactive species of (CH 3 ) 2 AI in the well controlled H 2 /rf plasma. When using DMAH and H 2 , AI can be deposited by low-pressure CVD; the features are (1) single crystal AI on Si surface, (2) filling capability into 0.3 μmΦ/1 μm-deep contact holes, (3) low contact resistivity (2 × 10 −7 Ωcm 2 ) to n + − Si, and (4) erosion free at the Al/Si interface after 450 °C/30 min annealing. As a selective AI growth mechanism on the Si surface, we have proposed and experimentally confirmed a “surface electrochemical reaction model”. In this model, terminated-H on the Si surface reacts with CH 3 -radical of the DMAH molecule to produce volatile CH 4 . The H atom of the DMAH remains on the newly deposited AI surface as a newly terminated-H atom. The terminated-H atom on the surface reacts repeatedly with CH 3 -radical to deposit AI. It is noted that, in the DMAH molecule, two CH 3 -radicals and one H atom are bonded to AI atom, i.e. “asymmetric” structure. Since the different radicals are bonded to the AI atom, AI can be selectively and repeatedly deposited on Si surface. The precursor which has “asymmetric” structure is considered to have an important role for selective growth.

The contribution of surface free electrons to the selective Al CVD using dimethylaluminum hydride (DMAH) and hydrogen has been investigated. As a selective growth mechanism of Al on a Si surface, we have proposed a surface electrochemical reaction model. The most significant points of this model are (1) contribution of free electron to surface reaction, (2) surface terminated-hydrogen, (3) selective reaction between the terminated-H and CH3-radical of DMAH. The nucleation density at the initial growth stage has been found to depend on the carrier density of the Si wafer: The nucleation density dramatically increases when the electron density is larger than 1 × 1015 cm−3. Since the intrinsic carrier density of the Si wafer at a deposition temperature of 270°C is 1 × 1015 cm−3, the increase in the nucleation density means that the free electrons of the Si surface contribute to the surface reaction. Furthermore, with the photo-irradiation of a halogen lamp of a 380–840 nm broad band spectrum and 40 mW/cm2 power, the nucleation density increases and becomes independent of the carrier density of the Si wafer. The dependency of the nucleation density on the carrier density is considered to disappear because of free electrons excited by photo-irradiation. It has been found that the free electrons on the Si surface contribute to the surface reaction. The reaction between terminated-H and CH3-radical have been also confirmed by Al deposition on the Si surface under various hydrogen termination conditions. Therefore, the surface electrochemical reaction model has been experimentally confirmed for the selective Al growth.

High-quality SiO 2 films were conformally deposited on an Al-patterned 6 inch diameter Si wafer at a high deposition rate of 150 nm/min by a photoassisted microwave plasma CVD method using tetraethyl orthosilicate (TEOS) at 250°C. Oxygen gas was excited in a high-density microwave plasma which was generated with cylindrical leaky waveguide and was kept apart from the substrate. Excited oxygen reacted with TEOS gas to generate reactive intermediates. The adsorbed intermediates migrated sufficiently for conformal coverage on the substrate surface and were photoexcited with an extra-high pressure mercury lamp to produce high-quality SiO 2 films. Aluminum steps were successfully planarized with the high-quality SiO 2 film.

Area-selective deposition of metals has the excellent potential for filling via holes in the near future ultra large scale integrated circuits and for fabricating nanometer-scale metal lines in the future atomic and nanometer scale devices. In this article, we discuss area-selective low-pressure chemical vapour deposition of aluminium using dimethylaluminium hydride (DMAH) and hydrogen. By thermal decomposition, 0.3 μmφ deep-submicron via holes with large aspect ratio of more than three are successfully filled by the selective deposition of aluminium. Futhermore, via holes are completely planarized by the selective and the subsequent non-selective deposition, where the deposition mode is changed using a plasma excitation technique. For the selective growth mechanism of aluminium on silicon, we have proposed a “surface electrochemical reaction” model. The most significant point is (1) the catalytic contribution of surface free electrons, (2) surface-terminated hydrogen, and (3) selective reaction between the terminated hydrogen and the methyl radical of DMAH. Based on this model, we have proposed an atomic hydrogen resist process, where the atomic resist is the monolayer-thick terminated hydrogen on the silicon surface. The terminated hydrogen on silicon is desorbed by the electron beam (EB) exposure. The activated silicon surface is oxidized in an air environment. Then, aluminium has been successfully deposited on the remaining hydrogen-terminated region and not deposited on the nanometer-thick oxidized area formed by the EB lithography.

We suggested “gas-beam-flow” condition and “gas-beam-flow” type reactors for epitaxial A1N growth using trimethylaluminum and ammonia. By flow visualization experiments, two gas flows of the sheath and the source were found to be laminar at atmospheric and at low pressures in the “gas-beam-flow” condition. The source gas flowed without touching the reactor wall. Using the “gas-beam-flow” type reactor, we succeeded in growing epitaxial A1N films at low temperature of 690 °C with a superior surface morphology.