Semiconductor device manufacturing: process – Having magnetic or ferroelectric component
Reexamination Certificate
1998-10-14
2001-02-27
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Having magnetic or ferroelectric component
C438S239000, C438S256000, C438S386000, C438S399000, C427S100000, C427S372200, C427S376200
Reexamination Certificate
active
06194227
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing, on a substrate, a ferroelectric thin film of a bismuth layer structure, namely, a bismuth (hereinafter “Bi”) layer structured ferroelectric thin film represented by (Bi
2
O
2
)
2+
(A
m
B
n
O
l
)
2−
and, in particular, to a method of producing a Bi layer structured ferroelectric thin film which is capable of compensating and suppressing deviation in composition of the Bi layer structured ferroelectric thin film and which is capable of suppressing degradation in electrical characteristics.
2. Statement of the Problem
Generally, various growing methods, such as organic metal solution coating, chemical vapor deposition (hereinafter CVD), and laser ablation, are known as methods of producing a Bi layer structured ferroelectric thin film. Substrates used therein are typically Si (silicon) substrates having an oxidized surface and a thin layer of high-melting-point precious metal, such as Pt (platinum) or Ir (iridium) deposited on the oxidized Si wafer, or having an oxidized Si layer, a thin film of high-melting-point precious metal, and an appropriate adhesive layer interposed therebetween.
As exemplified in
FIG. 11
, a conventional method of producing a Bi layer structured ferroelectric thin film directly forms a Bi layer structured ferroelectric thin film
6
on the upper surface of a lower electrode
4
of Pt which overlies an adhesive layer
3
of Ti (titanium) deposited on a Si oxide layer
2
.
A typical method for obtaining excellent ferroelectric characteristics in the above-mentioned process is to heat the substrate at a temperature not lower than 750° C. during or after growth of the thin film.
For instance, as described by Watanabe, et. al., in an article entitled “Preparation of Ferroelectric Thin Films of Bismuth Layer Structured Compounds” (Journal of Applied Physics, Volume 34 (1995), Part 1, No. 9B, pp. 5240-5244), organic metal solution is coated and thereafter fired in an oxygen atmosphere at a temperature of 800° C. in a metal-organic decomposition (hereinafter “MOD”) method.
Besides, as described by Hironaka, et. al., in an article entitled “Formation of SrBi
2
Ta
2
O
9
Thin Films by Flash-MOCVD” (Applied Electronics, Technical Meeting on Physical Properties, Nov. 22, 1995, pp. 15-20), thin films are deposited on a substrate by CVD and thereafter post-annealed in an oxygen atmosphere at a temperature of 800° C. in a manner similar to that described above.
In some of the above-mentioned conventional methods of producing a Bi layer structured ferroelectric thin film, the thin films deposited are often subjected to heat treatment to be crystallized. In this case, the resultant Bi layer structured ferroelectric thin film is composed of granular grains and often undesirably includes voids or pores within the thin film. This brings about a problem that the insulation characteristic of the thin film is degraded as compared with other types of ferroelectric thin films.
In addition, the annealing temperature of the Bi layer structured ferroelectric thin film is not lower than 750° C. This results in problems, such as an interdiffusion between Bi used as a constituent element of the ferroelectric thin film and the precious metal used as the lower electrode, an adhesive layer, or the oxidized Si layer, and it spoils the flatness of the substrate. If device elements are formed in the Si substrate, their characteristics may be degraded due to the interdiffusion.
Consideration will be given to the case where a capacitor is formed by the use of a Bi layer structured ferroelectric thin film and is electrically connected to the device element formed in the Si substrate by a polycrystalline Si plug. In this case, the surface of the polycrystalline Si is oxidized by the heat treatment in the oxygen atmosphere at the temperature not lower than 750° C. Such oxidization of the surface of the polycrystalline Si makes an electrical connection impossible.
3. Solution to the Problem
In order to solve the above-mentioned problems, it is an object of the present invention to provide a method of producing a Bi layer structured ferroelectric thin film which is capable of compensating and suppressing deviation in composition of the Bi layer structured ferroelectric thin film, suppressing degradation in electrical characteristics, and achieving a good electrical connection.
A feature of the invention is a method of producing a Bi layer structured ferroelectric thin film comprising steps of: providing a substrate; forming a buffer layer of an oxide film containing Bi (bismuth) on the substrate; and forming a thin film of a Bi layer structured ferroelectric substance, where the Bi layer structured ferroelectric substance is represented by a chemical formula (Bi
2
O
2
)
2+
(A
m
B
n
O
l
)
2−
.
Another feature of the invention is applying a coating of a solution for forming the Bi layer structured ferroelectric substance onto the buffer layer, and then annealing the coating to form the Bi layer structured ferroelectric thin film.
Another feature of the invention is a buffer layer having a thickness not greater than about five percent of a total combined thickness of a layer structure containing the Bi layer structured ferroelectric thin film and the buffer layer.
Another feature of the invention is a preparation temperature of the buffer layer that is lower than a preparation temperature of the Bi layer structured ferroelectric thin film. Preferably, a preparation temperature of the Bi layer structured ferroelectric thin film is not higher than about 650° C.
Another feature of the inventions is a Bi layer structured ferroelectric substance containing constituent elements A and B as represented in the chemical formula (Bi
2
O
2
)
2+
(A
m
B
n
O
l
)
2−
, wherein the buffer layer is represented by a chemical formula selected from the group consisting of “A
x
Bi
y
O
z
” or “B
x
Bi
y
O
z
” and the buffer layer contains only the constituent elements of the Bi layer structured ferroelectric substance.
Another feature of the invention is a thin film of a Bi layer structured ferroelectric substance containing constituent elements A and B as represented in the chemical formula (Bi
2
O
2
)
2+
(A
m
B
n
O
l
)
2−
, whereby the constituent element A is selected from a group consisting of a combination of Sr (strontium) and Ba (barium) and a combination of Sr and Pb (lead), and the constituent element B is at least one selected from the group consisting of Ta (tantalum) and Nb (niobium), and whereby the buffer layer of an oxide thin film comprises a Bi layer structured ferroelectric substance containing both of said constituent elements A and B.
Numerous other features, objects and advantages of the invention will become apparent from the following description when read in conjunction with the accompanying drawings.
REFERENCES:
patent: 5426075 (1995-06-01), Perino et al.
patent: 5434102 (1995-07-01), Watanabe et al.
patent: 5468679 (1995-11-01), Paz de Araujo et al.
patent: 5519234 (1996-05-01), Paz de Araujo et al.
patent: 5784310 (1998-07-01), Cuchiaro et al.
patent: 5824590 (1998-10-01), New
patent: 5833745 (1998-11-01), Atsuki et al.
patent: 5902639 (1999-05-01), Glassman et al.
patent: 0 661 754 A2 (1995-07-01), None
patent: 09142845 (1997-06-01), None
Hu et al., “Effects of a Bi4Ti3O12 buffer layer on SrBi2Ta2O9 thin films prepared by the metal organic solution deposition technique,” International Symposium on Application of Ferroelectrics, p. 1-4 (Aug. 24, 1998).
Hironaka et al., “SrBi2Ta29 Thin Films Formed by Flash-MOCVD,” p. 15-20. Nov., 1995.
Watanabe et al., “Preparation of Ferroelectric Thin Films of Bismuth Layer Structured Compounds,” Jpn. J. Appl. Phys., vol. 34, Part 1, No. 9B, p. 5240-5244 (Sep. 1995).
Duft, Graziano & Forest, P.C.
Ghyka Alexander G.
Niebling John F.
Symetrix Corporation
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