Compositions: coating or plastic – Coating or plastic compositions – Heavy metal compound containing
Reexamination Certificate
2000-10-12
2002-04-16
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Heavy metal compound containing
C438S003000
Reexamination Certificate
active
06372034
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to lead germanium oxide (PGO) thin film materials, and particularly to the spin-coating of PGO ferroelectric thin films in one-transistor applications.
BACKGROUND OF THE INVENTION
Ferroelectric films have attracted great interest in recent years because of their applications in electro-optic, pyroelectric, frequency agile electronic and non-volatile memory devices. The fabrication and characterization of ferroelectric lead germanium oxide thin films (PGO), such as Pb
5
Ge
3
O
11
and Pb
3
GeO
5
, are of current interest. Lead germanite (Pb
5
Ge
3
O
11
) is a relative new member of ferroelectric family. The piezoelectric, dielectric and electric-optic properties of single crystal and polycrystalline materials have been reported in the literature. Pb
5
Ge
3
O
11
is an optically active and ferroelectric material, has a moderate dielectric constant and a small remanent polarization, which make it particularly suitable for ferroelectric non-volatile memory devices such as metal ferroelectric metal oxide silicon (MFMOS), metal ferroelectric metal silicon (MFMS), metal ferroelectric insulators silicon (MFIS), metal-insulator-ferroelectric-silicon (MIPS), metal-insulator ferroelectric insulators silicon (MIFIS), and metal-ferroelectric-silicon (MFS) type memories. Pb
5
Ge
3
O
11
also has potential in thermal detector applications because of its pyroelectric and dielectric characteristics. Pb
3
GeO
5
is a ferroelastic material, which may be used for microelectromechanical systems (MEMS) applications.
Chemical vapor deposition (CVD) is a particularly attractive method for semiconductor industries because it is readily scaled up to production runs and provides very good step coverage. For PGO (Pb
5
Ge
3
O
11
and Pb
3
GeO
5
) films, the content of lead to germanium is very high, i.e., 5:3 and 3:1, respectively. Because of Pb loss in the thermal MOCVD process, an excess Pb concentration and a high oxygen partial pressure must be used to make stoichiometric PGO thin films and avoid the Pb and O deficiency.
The Pb precursors for MOCVD PGO film are liquids or solids that can be sublimed into a gas phase and transported into a reactor. The process window of Pb precursors is very narrow, i.e., the sublimation temperature of the Pb precursors is close to the decomposition and condensation temperature, in which case the reagent may begin to decompose or condense in the reactant lines before reaching the reactor, making it very difficult to control the stoichiometry of the deposited films. The Pb precursor gas easily reacts with oxygen in the gas phase before deposition, which results in large particles and a cloudy film, especially at higher deposition temperatures.
Because of some of the problems associated with MOCVD and known spin coating processes of PGO thin films, other solutions and techniques may be more suitable for deposition of this material in integrated circuit devices by spin coating. There has been some discussion of PGO material suitable for spin coating and of the spin coating process in Kim et al.,
Japanese Journal of Applied Physics
33, pp 2675-2678, 1994; and Lee et al.,
Applied Physics Letters
60, pp 2487-2488, May 18, 1992.
Known techniques for spin coating PGO films are similar to those used for PZT ferroelectric thin films wherein Pb(OCH
3
CO)
2
.3H
2
O is used as the Pb source and Ge(OCH
2
CH
3
)
4
is used as the Ge source. The Ge source, however, is air and moisture sensitive, and as the Pb source contains water, a PGO solution formed in this manner will be unstable, and a Ge gel will generally precipitate from the solution.
SUMMARY OF THE INVENTION
A method of preparing a PGO solution for spin coating includes preparing a 2-methoxyethanol organic solvent; adding Pb(OCH
3
CO)
2
.3H
2
O to the organic solvent at ambient temperature and pressure in a nitrogen-filled gloved box to form Pb in methoxyethanol; refluxing the solution in a nitrogen atmosphere at 150° C. for at least two hours; fractionally distilling the refluxed solution at approximately 150° C. to remove all of the water from the solution; cooling the solution to room temperature; determining the Pb concentration of the solution; adding the 2-methoxyethanol solution to the Pb 2-methoxyethanol until a desired Pb concentration is achieved; combining Ge(OR)
4
, where R is taken from the group of Rs consisting of CH
2
CH
3
and CH(CH
3
)
2
, and 2-methoxyethanol; and adding Ge(OR)
4
2-methoxyethanol to PbO 2-methoxyethanol to form the PGO solution having a predetermined metal ion concentration and a predetermined Pb:Ge molar ratio.
An object of the invention is to provide a PGO solution suitable for spin coating application.
Another object of the invention is to provide a techniques for spin coating a PGO film in a one-transistor application.
This summary and objectives of the invention are provided to enable quick comprehension of the nature of the invention. A more thorough understanding of the invention may be obtained by reference to the following detailed description of the preferred embodiment of the invention in connection with the drawings.
REFERENCES:
patent: 5204314 (1993-04-01), Kirlin et al.
patent: 6242771 (2001-06-01), Hsu et al.
patent: 8-186058 (1996-07-01), None
Caplus 1995:979275, Friedrich et al, “Effect of Structure and chemical modificaton of precursors . . . ”, 1993 (Abstract).*
Caplus 1988:225702, Dekleva et al, “Sol-gel processing of lead titanate in 2-methoxyethanol . . . ”, 1988 (Abstract).*
Iwasaki et al., Applied Physics Letters, 18, 444 (1971) No month provided.
Iwasaki et al., Applied Physics Letters, 43, 4907 (1972) No month provided.
A. Mansingh et al., J. Appl. Phys. 51, 5408 (1980) No month provided.
H. Schmitt et al., Ferroelectrics 56, 142 (1984) No month provided.
Krupanidhi et al., Proceedings of the 3d International Symposium on Integrated Ferroelectrics, 100 (1991). No month provided.
C. J. Peng et al., appl. Phys. Lett. 60, 827 (1992) No month provided.
J. J. Lee et al., Appl. Phys. Lett. 60, 827 (1992) No month provided.
Hsu Sheng Teng
Maa Jer-shen
Zhang Fengyan
Zhuang Wei-Wei
Brunsman David
Krieger Scott C.
Rabdau Matthew D.
Ripma David C.
Sharp Laboratories of America Inc.
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