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(19) United States
(12) Patent Application Publication (io) Pub. No.: US 2002/0167005 Al
Yu et al. (43) Pub. Date: Nov. 14,2002
Patent Application Publication Nov. 14,2002 Sheet 1 of 2 US 2002/0167005 Al
(54) SEMICONDUCTOR STRUCTURE
INCLUDING LOW-LEAKAGE, HIGH
CRYSTALLINE DIELECTRIC MATERIALS
AND METHODS OF FORMING SAME
(75) Inventors: Zhiyi Yu, Gilbert, AZ (US);
Ravindranath Droopad, Chandler, AZ
(US); Corey Overgaard, Phoenix, AZ
OBLON, SPIVAK, McCLELLAND, MAIER &
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON, VA 22202 (US)
(73) Assignee: Motorola, Inc
(21) Appl. No.: 09/853,744
(22) Filed: May 11, 2001
(51) Int. CI.7 H01L 29/12; H01L 21/84;
(52) U.S. CI 257/43; 438/85; 438/86; 438/104;
438/754; 257/347; 257/352;
The present invention provides semiconductor structures and methods for forming semiconductor structures which include monocrystalline oxide films exhibiting both high dielectric constants and low leakage current densities. In accordance with various aspects of the invention, a semiconductor structure includes a monocrystalline semiconductor substrate and one or more stoichiometrically graduated monocrystalline oxide layers. The stoichiometrically graduated monocrystalline oxide layer may include a perovskite material, such as an alkaline-earth metal titanate. Semiconductor devices fabricated in accordance with aspects of the present invention exhibit a high dielectric constant as well as a reduced leakage current density.
Patent Application Publication Nov. 14,2002 Sheet 2 of 2 US 2002/0167005 Al
SEMICONDUCTOR STRUCTURE INCLUDING
LOW-LEAKAGE, HIGH CRYSTALLINE DIELECTRIC MATERIALS AND METHODS OF FORMING SAME
FIELD OF THE INVENTION
 The present invention relates generally to semiconductor structures and devices and to methods for their fabrication and, more specifically, to semiconductor structures and devices and to the fabrication and use of semiconductor structures, devices, and integrated circuits that include high dielectric constant, epitaxial oxide films formed by varying the flux ratio of the elemental components of the oxide during deposition to achieve reduced leakage current density without sacrificing high crystalline quality.
BACKGROUND OF THE INVENTION
 Semiconductor devices often include multiple layers of conductive, insulating, and semiconductive layers. Often, the desirable properties of such layers improve with the crystallinity of the layer. For example, the electron mobility and band gap of semiconductive layers improves as the crystallinity of the layer increases. Similarly, the free electron concentration of conductive layers and the electron charge displacement and electron energy recoverability of insulative or dielectric films improves as the crystallinity of these layers increases.
 Epitaxial growth of single-crystal oxide thin films on single-crystal silicon substrates is therefore of great value in numerous device applications, such as ferroelectric devices, non-volatile high density memory devices, and next-generation metal oxide semiconductor (MOS) devices, for example. Preparation of these films generally requires the formation of an ordered transition layer or buffer layer on the surface of the silicon substrate to facilitate subsequent growth of the single-crystal oxide layer.
 Certain monocrystalline oxides, such as BaO and BaTi03, have been formed on <100>oriented silicon substrates using a BaSi2 (cubic) template by depositing one fourth of a monolayer of barium on the silicon substrate using molecular beam epitaxy (MBE) at temperatures greater than 850° C. See, e.g., R. McKee et al.,Appl. Phys. Lett. 59(7), pp. 782-784 (Aug. 12, 1991); R. McKee et al., Appl. Phys. Lett. 63(20), pp. 2818-2820 (Nov. 15, 1993); R. McKee et al., Mat. Res. Soc. Symp. Proc, Vol. 21, pp. 131-135 (1991); U.S. Pat. No. 5,225,031, issued Jul. 6, 1993, entitled "Process For Depositing An Oxide Epitaxially Onto A Silicon Substrate And Structures Prepared With The Process"; and U.S. Pat. No. 5,482,003, issued Jan. 9, 1996, entitled "Process For Depositing Epitaxial Alkaline Earth Oxide Onto A Substrate And Structures Prepared With The Process." A strontium silicide (SrSi2) interface model with a c(4x2) structure also has been proposed. See, e.g., R. McKee et nl.,Phys. Rev. Lett. 81(14), 3024 (Oct. 5,1998). However, atomic-level simulation of this proposed structure suggests that it likely is not stable at elevated temperatures.
 Growth of SrTi03 on <100>oriented silicon substrates using an SrO buffer layer also has been achieved. See, e.g., T. Tambo et al., Jpn. J. Appl. Phys., Vol. 37, pp. 4454-4459 (1998). However, the SrO buffer layer was comparatively thick (100 A), thereby rendering its applica
tion unsuitable for transistor films, and crystallinity was not maintained throughout the growth of the SrTi03 film.
 Additionally, SrTi03 has been grown on silicon using thick (60-120 A) oxide layers of SrO or TiO. See, e.g., B. K. Moon et al., Jpn. J. Appl. Phys., Vol. 33, pp. 14721477 (1994). As previously noted, however, thick buffer layers are generally not well-suited for MOS transistor applications.
 In gate dielectric applications, high dielectric constant (high-k) films exhibiting low leakage current densities and high crystallinity are highly desirable. However, the inherent tension between these desired electrical and physical characteristics imposes limitations on the suitability of such films for the fabrication of high-quality MOS transistors. For example, while the leakage current density of SrTiO films on a silicon substrate decreases as the Sr/Ti
ratio increases above unity, the crystal structure of such films typically degrades as the Sr/Ti ratio increases above unity. In other words, stoichiometric SrTi03 films (i.e., films where Sr/Ti=l), which generally exhibit a favorably high degree of crystallinity, tend to demonstrate an unfavorably high leakage current density. Thus, since both leakage current density and crystallinity tend to vary in inverse proportion to the stoichiometric ratio of the elemental components of the oxide film, the development of structures and methods which effectively harmonize these competing physical and electrical properties would be highly advantageous for the fabrication of superior semiconductor devices and integrated circuitry.
 It has been suggested that reduced leakage current density in oxide films can be achieved by incorporating foreign dopants, such as silicon in the form of Si02 into Ti02, or by introducing silver into (Ba,Sr)Ti03 films. However, structures formed by such methods are problematic because they involve foreign elements, such as silver, and tend to exhibit elemental diffusion and/or segregation which adversely affect devices fabricated by these methodologies.
 Accordingly, a need exists for semiconductor structures and devices and methods of fabricating semiconductor structures and devices which overcome the shortcomings of the prior art. Thus, there is a need for semiconductor structures and devices including high-k oxide films exhibiting both high crystallinity and low leakage current density. Moreover, a need exists for a method of fabricating epitaxial perovskite films on single-crystal substrates to achieve both low leakage current density and high crystallinity.
BRIEF DESCRIPTION OF THE DRAWINGS
 The present invention is illustrated by way of example, and not of limitation in the accompanying figures, in which like references indicate similar elements, and in which:
 FIGS. 1A-1B illustrate schematically, in cross section, a semiconductor device structure fabricated in accordance with one embodiment of the present invention;
 FIGS. 2A-2B illustrate schematically, in cross section, a semiconductor device structure fabricated in accordance with an alternative embodiment of the present invention;
 FIGS. 3A-3B illustrate schematically, in cross section, a semiconductor device structure fabricated in accordance with yet a further embodiment of the present invention;