Coating processes – Coating by vapor – gas – or smoke – Mixture of vapors or gases utilized
Reexamination Certificate
2001-01-26
2003-02-25
Meeks, Timothy (Department: 1762)
Coating processes
Coating by vapor, gas, or smoke
Mixture of vapors or gases utilized
C427S255310, C427S255320, C427S255400, C117S103000, C117S108000, C117S939000, C117S944000
Reexamination Certificate
active
06524651
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to oxidized film structures, including crystalline metal oxides epitaxially grown on such structures for electronic, optical, and magnetic applications.
DESCRIPTION OF RELATED ART
New epitaxial metal oxide thin film microstructures on substrates such as silicon could offer a variety of improved properties that are necessary in future microelectronics, including improved dielectric, optical, electronic, and magnetic properties. For example, as device scaling continues in the existing silicon-based complementary metal oxide semiconductor (CMOS) industry, SiO
2
is approaching its fundamental limits as the gate dielectric. Alternative gate materials with higher dielectric constants than SiO
2
are needed. The alkaline earth metal oxide of SrTiO
3
(STO) is a promising material for this purpose because of its high bulk dielectric constant. However, direct growth of this oxide on Si is especially difficult because Si is highly reactive with oxygen, forming amorphous SiO
2
, or glassy silicates. Additionally, extensive interdiffusion or chemical reactions can degrade the properties of the oxide and/or the underlying silicon. It is therefore critical to produce a stable interfacial template on Si that sustains high temperatures in an oxygen environment for the subsequent single-crystal film growth.
A method of growing the alkaline earth metal oxide of BaTiO
3
(BTO) on Si has been reported by McKee et al (1) (Appl. Phys. Lett. 59 (7) p. 782-784, Aug. 12, 1991). The high temperature method includes first reacting Ba metal with a clean Si surface at a temperature greater than 840° C. to form a (2×1) barium silicide submonolayer. The authors state that this barium silicide (discussed in detail by Make, R. A. and Walker, F. J., Appl. Phys. Lett. 63 (20), p. 2818-2820, Nov. 15, 1993) plays a critical role as an interfacial template between silicon and the subsequently epitaxially-grown oxide layers of BaO and BTO. Make et al (1) report growing a BaO layer on this template at temperatures ranging from room temperature to 800° C. by the simultaneous or cyclic exposure of the barium silicide film to Ba metal and oxygen at partial pressures of 10
−7
Torr to 10
−4
Torr and that “the cyclic growth conditions are most important in optimizing the surface and film quality.” BTO is then grown on this BaO layer by the shuttering of Ti and Ba cells at one monolayer intervals in an oxygen partial pressure of 2.5×10
−7
Torr.
U.S. Pat. No. 5,482,003 (Mckee and Walker) similarly discloses a high temperature method for depositing an epitaxial layer of alkaline earth oxide upon another layer having an ordered face-centered-cubic lattice structure (e.g., Si) or an alkaline earth oxide having a sodium chloride-type lattice structure (e.g., BaO, SrO, CaO, and MgO). The method includes the steps of cleaning a silicon substrate using the Modified RCA technique, forming a stable silicide layer by depositing a submonolayer of a mixture of Ba and Sr at a temperature greater than 850° C. in an ultrahigh vacuum, oxygen-free environment (10
−10
Torr to 10
−9
Torr), lowering the temperature to between 200° C. and 300° C. at which point a further mixture of Ba and Sr is deposited until the surface is covered by about one monolayer of the metal mixture, then increasing the pressure of the ultrahigh vacuum to between 1×10
−6
Torr to 5×10−6 Torr with the introduction of oxygen and then exposing the metal-covered surface to this oxygen and additional amount of the metal mixture to epitaxially grow alkaline earth metal oxide on the silicon surface. Further layers of oxide are subsequently grown on this layer. A similar method for growing STO on Si (100) has also been reported by Mckeee et al (2) (Phys. Rev. Lett. 81 (14), p. 3014-3017, Oct. 5, 1998).
A method of growing STO on Si has been reported by Eisenbeiser et al (Appl. Phys. Lett. 76 (10) p. 1324-1326, Mar. 6, 2000) and Yu et al (1) (Mater. Res. Soc. Symp. Proc. 567 p.427-433, 1999). Eisenbeiser et al discloses a method using lower temperatures and having fewer steps than the Make et al methods. In Eisenbeiser et al, metallic Sr was reacted with the silicon oxide on the surface of a silicon substrate at a temperature greater than 700° C. under high vacuum to produce a 2×1 surface reconstruction. STO was subsequently directly grown on this layer in the temperature range of 200° C. to 800° C. and up to 10
−5
Torr oxygen partial pressure.
Yu et al (2) (J. Vac. Sci. Technol. B 18 (4) p. 2139-2145, July/August 2000) further reports a similar low temperature method of growing STO or BTO on Si. Yu et al (2) discloses a method whereby metallic Ba or Sr was reacted with as-received commercial Si(001) wafers at a temperature below 800° C. at a pressure below mid-10
−10
Torr. BTO and STO films were subsequently deposited at a temperature in the range of 200° C. to 700° C. under up to 10
−5
Torr oxygen partial pressure. U.S. Pat. No. 6,113,690 (Yu et al) discloses another similar method whereby an alkaline earth metal, preferably Ba or Sr, was reacted with a silicon substrate having a silicon dioxide layer at a temperature in the range of 700° C. to 800° C. and a pressure in the range of 10
−10
Torr to 10
−9
Torr.
U.S. Pat. No. 6,022,410 (Yu et a) discloses a low temperature method of forming an ordered Si wafer surface for subsequent thin film epitaxy. The low temperature method includes reacting atomic beams of one or more alkaline earth metals and an atomic beam of Si with a clean Si surface at a temperature in the range of 500° C. to 750° C. to form a single crystal alkaline earth metal silicide layer (e.g., BaSi
2
) on the surface of the silicon substrate.
Accordingly, there is a need for a simplified process that produces a high quality, crystalline oxide structure for semiconductor applications as well as for other electronic, optical, and magnetic applications.
BRIEF SUMMARY OF THE INVENTION
The present invention encompasses a stable oxidized film structure and an improved method of making such a structure, including an improved method of making an interfacial template for growing a crystalline metal oxide structure. The improved method comprises the steps of providing a substrate with a clean surface and depositing a metal on the surface at a high temperature while under a vacuum to form a metal-substrate compound layer on the surface with a thickness of less than one monolayer. The compound layer is then oxidized by exposing the compound layer to essentially oxygen at a low partial pressure and low temperature. The method may further comprise the step of annealing the surface while under a vacuum to further stabilize the oxidized film structure. A crystalline metal oxide structure may be subsequently epitaxially grown by using the oxidized film structure as an interfacial template and depositing on the interfacial template at least one layer of a crystalline metal oxide.
It is an object of the present invention to provide an improved method for making a high quality, robust, and stable oxidized film structure.
It is a further object of the present invention to provide an interfacial template and an improved method for preparing the interfacial template that can sustain high temperatures in an oxygen environment for subsequent epitaxial growth of a crystalline metal oxide structure.
It is a further object of the present invention to provide an improved method for producing an alkaline earth metal oxide structure that can function as a gate material with a higher dielectric constant than SiO
2
for semiconductor applications.
It is a further object of the present invention to provide an improved method for producing an alkaline earth metal oxide structure incorporating a silicon substrate.
It is a further object of the present invention to provide an epitaxy method that can be routinely performed in conventional processing systems or growth chambers.
It is a further object of the present invention to provide an epi
Gan Shupan
Liang Yong
Battelle (Memorial Institute)
May Stephen R.
McKinley Douglas E.
Meeks Timothy
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