Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
2003-04-17
2004-06-01
Nazario-Gonzalez, Porfirio (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C556S136000, C556S137000, C427S124000, C427S126500, C427S227000, C427S585000, C427S593000, C106S287180, C106S287240
Reexamination Certificate
active
06743934
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to raw materials for producing ruthenium or ruthenium compound thin films by CVD.
2. Description of the Related Art
In recent years, ruthenium or ruthenium compounds have been being applied as materials for thin film electrodes used in semiconductor devices such as DRAM and FERAM. This is because these materials are extremely excellent in electric properties such as specific resistance, and, for example in DRAM, the use of the materials for the storage electrodes of its capacitors have been examined and is considered to be able to contribute largely to higher density DRAM. And ruthenium or ruthenium compound thin films have been expected to become one of the key materials for thin film electrodes and attracted considerable attention.
As the method for producing ruthenium or ruthenium compound thin films, not only sputtering, but also chemical vapor deposition (hereinafter referred to as CVD) is often used. The reason that CVD is often used is that it makes it easier to produce uniform thin films, in addition, it is superior to sputtering in step coverage.
Ruthenium compounds which have been expected to be materials for use in production of ruthenium or ruthenium compound thin films by CVD and the use of which has been examined include, for example, bis(ethylcyclopentadienyl)ruthenium having the formula shown below. This organic ruthenium compound is obtained by replacing hydrogen atoms of the two cyclopentadiene rings bis(cyclopentadienyl)ruthenium by ethyl groups.
The compound, bis(ethylcyclopentadienyl)ruthenium, has been considered to be qualified as a CVD raw material because it is excellent in handling properties, due to its low melting point and the liquid state at room temperature, and in production efficiency, due to its high vapor pressure.
Further, in recent years, from the viewpoint of reduction of thin film production costs and effective use of resources, introduction of recycling techniques has also been examined for CVD raw materials. In such recycling, it is required to efficiently separate/purify unreacted compounds from used materials. In bis(ethylcyclopentadienyl)ruthenium, the unreacted compound is relatively easy to separate and refine, due to its high vapor pressure and good thermal stability, and its effective recycle is made possible by proper means such as distillation.
In thin film electrodes, it goes without saying that their purity and morphology are important, but on the other hand their adhesion to a substrate is also important. As a substrate for semiconductor devices, SiO
2
or a SiO
2
film is often used, a ruthenium thin film produced from bis(ethylcyclopentadienyl)ruthenium, however, has a problem of relatively low adhesion to SiO
2
. And to cope with this problem, a method has been employed in which a Ru front-end is formed by sputtering before forming a thin film by CVD. However, this leads to increase in the number of processes. Thus, there have been demands for development of organic compounds which, as CVD raw materials, permit the production of thin films having higher adhesion properties.
To meet the demand for higher adhesion properties, organic ruthenium compounds having been proposed in recent years are tris(&bgr;-diketonato)ruthenium having the following formula (for further details of this compound, refer to Japanese Patent Laid-Open No. 2000-212744).
wherein R and R′ represent different alkyl groups with 1 to 4 carbon atoms, respectively.
The above organic ruthenium compounds consist of ruthenium and three &bgr;-diketons coordinated therewith, and their states at room temperature differ depending on their substituents, in other words, there are tris(&bgr;-diketonato)ruthenium in the liquid state and those in the solid states. Since the compounds being in the solid state at room temperature are highly soluble in organic solvents, as long as they are dissolved in an organic solvent, they can be used as CVD raw materials. Thus, both liquid and solid tris(&bgr;-diketonato)ruthenium are said to be possibly used as CVD materials. Since the ruthenium thin films produced from tris(&bgr;-diketonato)ruthenium excel in adhesion to SiO
2
, much hope is placed on these compounds, in this respect.
However, according to the inventors of this invention, in tris(&bgr;-diketonato)ruthenium which are in the liquid state at room temperature (such as tris(2,4-octadionato)ruthenium wherein R
1
is a methyl group and R
2
is a butyl group and tris(6-methyl-2,4-heptadionato)ruthenium wherein R
1
is a methyl group and R
2
is an isobutyl group), their thin film production efficiency is low because of their low vapor pressure, and to ensure a certain efficiency, the heating temperature must be increased at the time of thin film production. At the time of heating, if the vaporization temperature is increased higher than necessary and the raw materials are excessively heated, the compounds tend to decompose even in an inert atmosphere. Therefore, when producing their thin films using a large volume of raw material gas, it is difficult to control the heating of the raw materials. Thus, liquid &bgr;-diketonatoruthenium are unfit for thin film production on large-size substrate and mass production.
Further, if the vapor pressure is low, it is difficult to separate/purify the unreacted compounds from the used raw materials by distillation etc.; and moreover, in the above easy-to-decompose compounds, the amount of the unreacted compounds remaining in the used raw materials is very small, and even if they can be separated, it is impossible to recover them efficiently. Thus the use of these compounds for forming thin films results in higher production costs.
As to the solid tris(&bgr;-diketonato)ruthenium, taking into consideration their recycling, they are not necessarily preferable, even if they can be used as CVD raw materials once they are dissolved in solvents. The reason is that it is often difficult to recover solid matters by distillation once they are dissolved in liquids.
Thus, though tris(&bgr;-diketonato)ruthenium have the advantage of providing thin films with good adhesion, they still have problems of being low in thin film production efficiency due to their low vapor pressure and in possibility of their recycling.
This invention has been made in light of the above described background. Accordingly, an object of this invention is to provide, on the assumption that the raw material compounds for use in production of ruthenium thin films or ruthenium compound thin films by CVD are in the liquid state at room temperature, organic ruthenium compounds which have the advantages the above described compounds have, that is, the advantages of having good thermal stability and high vapor pressure, and hence being fit for recycling and of being able to provide thin films with high adhesion to a substrate. Another object of this invention is to provide a method for producing thin films using the above organic ruthenium compounds.
SUMMARY OF THE INVENTION
To solve the above described problems, the inventors started with the analysis of the course of the formation of thin films in CVD and presumed the constitution of preferable compounds. In CVD, vaporized raw material compounds are carried on a substrate, and decomposed and oxidized on the same so that the object materials as constituents of thin films are deposited as thin films.
In the above described CVD, the process of ruthenium thin film formation consists mainly of two steps. The first step is a step of forming ruthenium crystal nucleuses on a substrate, which is also referred to as latent period or incubation period. In this step, there exists no thin film, but countless crystal nucleuses are dotted on the substrate and grow in the planar direction.
The substantial growth of ruthenium crystal as a thin film occurs in the step next to the first step (the latent period). In the step, the decomposition reaction of the raw material gas is accelerated by the catalytic action of the crystal nucleuses produced in the first step
Sagae Takeyuki
Saito Masayuki
Nazario-Gonzalez Porfirio
Rothwell Figg Ernst & Manbeck P.C.
Tanaka Kikinzoku Kogyo K.K.
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