Coating processes – Coating by vapor – gas – or smoke – Mixture of vapors or gases utilized
Reexamination Certificate
1998-12-14
2004-09-07
Chen, Bret (Department: 1762)
Coating processes
Coating by vapor, gas, or smoke
Mixture of vapors or gases utilized
C427S126300, C427S081000
Reexamination Certificate
active
06787186
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of controlled chemical vapor deposition (CVD) of a metal oxide ceramic layer, and more particularly, to additives for stabilization and efficiency enhancement of CVD processes for forming bismuth oxide ceramics, such as in the form of thin layers or films on semiconductor substrates for use in fabricating microelectronic semiconductor devices, for example, ferroelectric capacitors, and the like.
BACKGROUND OF THE INVENTION
In fabricating microelectronic semiconductor devices and the like on a wafer substrate or chip, such as of silicon, to form an integrated circuit (IC), etc., various metal layers and insulation layers are deposited in selective sequence. To maximize integration of device components in the available substrate area to fit more components in the same area, increased IC miniaturization is utilized. Reduced pitch dimensions are needed for denser packing of components per present day very large scale integration (VLSI), e.g., at sub-micron (below 1 micron, i.e., 1,000 nanometer or 10,000 angstrom) dimensions.
Recently, ceramic phases with bismuth oxide (bismuth trioxide, Bi
2
O
3
) as a component have found widespread interest for application in semiconductor memories. In this regard, bismuth titanate (Bi
4
Ti
3
O
12
), strontium bismuth tantalate (SBT, SrBi
2
Ta
2
O
9
) and strontium bismuth titanate (SrBi
4
Ti
4
O
15
) possess ferroelectric properties, which make these ceramic materials interesting for applications in non-volatile memories, e.g., FeRAMs (ferroelectric random access memories).
Ferroelectric materials, such as strontium bismuth tantalate (SBT, SrBi
2
Ta
2
O
9
), also called an Aurivillius phase ferroelectric or mixed bismuth oxide layer structure, exhibit electric polarization in the absence of an externally applied electric field, such that the direction of polarization may be reversed by an electric field. Thus, ferroelectric capacitors are able to change their direction of polarization under an applied electric field, for instance, to switch between a “1” or a “0”value or state as might be required in a given IC system.
Very thin layers or films of ferroelectric ceramic materials are required for the above noted purposes, which materials, in addition, show a high conformality to the surface structure of the substrate. Moreover, it is necessary to produce these films rapidly and inexpensively. In practice, only a CVD process can meet all of these requirements.
Some examples of the fabrication of ferroelectric devices are shown in the following prior art.
U.S. Pat. No. 5,478,610 (Desu et al.), issued Dec. 26, 1995 (Desu Patent I), and its continuation in part U.S. Pat. No. 5,527,567, issued Jun. 18, 1996 (Desu Patent II), disclose a method of fabricating a layered structure oxide ferroelectric thin film by CVD involving chemical reaction between volatile organo metal compounds, such as alkyls, alkoxides, &bgr;-diketonates or metallocenes of the metal elements to be deposited, and gases such as oxygen, to produce a non-volatile solid that deposits on a substrate. For example, after such a film is deposited on a substrate having a thin surface layer of a metal, e.g., Pt, and then ferroannealed, a second thin layer of the metal is deposited, followed by a second ferroanneal, for forming a ferroelectric capacitor in which the first metal layer is the bottom electrode, the second metal layer is the top electrode and the deposited ceramic oxide film is the dielectric separating the two metal layers.
The Desu Patents I and II contemplate depositing a SrBi
2
(Ta
x
Nb
2−x
)O
9
or BaBi
2
(Ta
x
Nb
2−x
)O
9
film on a substrate by pulsed laser deposition (PLD). This involves using as preferred precursors Ba(thd)
2
(Ba-tetramethyl heptadione), Sr(thd)
2
(Sr-tetramethyl heptadione), Bi(thd)
3
(Bi-tetramethyl heptadione), Ta(OC
2
H
5
)
5
(Ta-ethoxide) and Nb(OC
2
H
5
)
5
(Nb-ethoxide) in stoichiometric ratios in a solvent that is an 8:2:1 mixture in moles of tetrahydrofuran (C
4
H
8
O), isopropanol (C
4
H
10
O) and tetraglyme (C
10
H
22
O
5
), while the substrate is heated to a high temperature of at least 450° C. as claimed.
The Desu Patent II also contemplates depositing a strontium bismuth tantalate (SBT, SrBi
2
Ta
2
O
9
) film on a substrate, by a liquid source delivery (LSD) method. This involves using Sr(thd)
2
(Sr-tetramethyl heptadione), Bi(C
6
H
5
)
3
(Bi-triphenyl, BiPh
3
) and Ta(OC
2
H
5
)
5
(Ta-ethoxide) as precursors in such 8:2:1 molar ratio solvent mixture, at a high temperature of 450-800° C., in a two-step method, in which the film is first deposited at 450-600° C. for 5 minutes, and then at 600-700° C. for 30-120 minutes, compared to a one-step method wherein the film is deposited at 650° C.
It is desirable to have a one-step method of forming a metal oxide ceramic layer on a substrate by CVD that can be conducted, inexpensively, rapidly and efficiently under vacuum pressure, especially at a comparatively low deposition temperature, with facilitated thermal decomposition of the precursor organo metal compound to its metal oxide having the same oxidation state as in the precursor compound, and with control of the in situ oxidation state of the deposited metal and the amount of oxygen in the formed layer, while suppressing the formation of volatile intermediates and of vacancies in the formed layer.
SUMMARY OF THE INVENTION
The foregoing drawbacks are obviated in accordance with the present invention by providing a protonating additive substance and/or an activating agent for facilitating a one-step method of forming a metal oxide ceramic layer on a substrate by CVD that can be conducted inexpensively, rapidly and efficiently under vacuum pressure, especially at a comparatively low temperature.
According to a first aspect of the invention, a method of forming a metal oxide ceramic layer on a substrate by CVD is provided, comprising conducting a gaseous flow of a vaporized solution of a precursor organo metal compound in a volatile organic solvent, e.g., plus an oxidizing gas, in the presence of a protonating additive substance in gaseous state, into contact with a surface portion of the substrate under a vacuum pressure at a thermal decomposition temperature effective for converting the precursor compound to its corresponding metal oxide, e.g., having the same oxidation state as in the precursor compound.
The additive substance is present in an amount sufficient for facilitating the thermal decomposition of the precursor compound and for controlling the in situ oxidation state of the deposited metal and the amount of oxygen in the formed layer, e.g., while suppressing the formation of volatile intermediates and of vacancies in the formed layer.
The additive substance may be water, a volatile carboxylic acid compound, a volatile ketone, a volatile amine or ammonia. The carboxylic acid compound may be a volatile carboxylic acid, a volatile carboxylic acid anhydride, a volatile carboxylic acid ester, a volatile carboxylic acid nitrile, a volatile carboxylic acid isonitrile or a volatile carboxylic acid aldehyde. The additive substance is desirably present in an amount of about 0.01-200 mols per mol of the precursor compound.
According to an alternative feature of the invention, the conducting of the gaseous flow is effected in the additional presence of an activating agent in gaseous state in an amount sufficient for producing in situ hydrogen-active compounds for enhancing the converting of the corresponding precursor compound to its metal oxide. The activating agent may be carbon monoxide, hydrogen or a volatile lower aliphatic hydrocarbon having 1-4 carbon atoms or aromatic hydrocarbon, which volatile hydrocarbon is optionally substituted by a bromo, iodo or nitro (—NO
2
) substituent, i.e., so as to provide a volatile brominated lower aliphatic or aromatic hydrocarbon, a volatile iodinated lower aliphatic or aromatic hydrocarbon or a volatile nitro group-containing lower aliphatic or aromatic hydrocarbon.
The decomposition temperature may be about 150-800° C., pref
Advanced Technology & Materials Inc.
Chappuis Margaret
Chen Bret
Hultquist Steven J.
Ryann William F.
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