Compositions: coating or plastic – Coating or plastic compositions – Heavy metal compound containing
Reexamination Certificate
2003-04-15
2003-12-16
Nazario-Gonzalez, Porfirio (Department: 1621)
Compositions: coating or plastic
Coating or plastic compositions
Heavy metal compound containing
C556S040000, C556S136000, C427S124000, C427S126500, C427S227000, C427S585000, C427S593000, C106S287240
Reexamination Certificate
active
06663706
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to raw materials for use in production of an iridium or iridium compound thin film by CVD and a method for producing the same.
2. Description of the Related Art
In recent years, noble metals such as iridium and ruthenium have been applied as materials for thin film electrodes used in a variety of semiconductor devices. This is because noble metals have low resistivity and exhibit excellent electric properties when they are formed into electrodes. In particular, iridium and the oxides thereof have been used as upper and lower electrodes of FeRAM.
As a method for producing thin films used in thin film electrode applications, while sputtering is widely in use, the application of chemical vapor deposition (hereinafter referred to as CVD) has been examined in recent years. The reason for this is that CVD makes easier the production of uniform thin films, in addition, it is superior to sputtering in step coverage. Furthermore, as a technique for increasing the capacity of memory devices such as DRAM and FeRAM, it is being attempted to provide thin films with three-dimensional multilayer structure, instead of the conventional two-dimensional multilayer structure; however, to form such a complex electrode structure, the technique is required to have stricter step coverage and process controllability than those of the conventional ones. In terms of these demands, CVD has attracted considerable attention.
Known compounds, which are used as raw materials for iridium film or iridium compound thin films produced by CVD, come in two general types, cyclooctadiene iridium compounds and &bgr;-diketone iridium compounds.
Cyclooctadiene iridium compounds consist of: iridium; and a cyclooctadiene and a cyclodiene derivative coordinated therewith, and as raw materials for use in CVD, are known, for example, methylcyclopentadienyl(1,5-cyclooctanedione)iridium and ethylcyclopentadienyl(1,5-cyclooctanedione)iridium having the following formula:
(wherein R is any one selected from the group consisting of hydrogen, a methyl group and an ethyl group.)
The cyclooctadiene iridium compounds are preferable as CVD raw materials in terms of its handling properties because they have low melting points (about 25° C. to 125° C.), and ethylcyclopentadienyl(1,5-cyclooctanedione)iridium is particularly preferable because it is in the liquid state at room temperature (for further details of the cyclooctadiene iridium compounds, refer to Japanese Patent Laid-Open No. 11-292888, J. Vac. Sci. Technol. A18(1) 10-16 (2000)).
On the other hand, &bgr;-diketone iridium compounds consist of: iridium; and &bgr;-diketone organic compounds coordinated therewith. And as raw materials for use in CVD, some &bgr;-diketone organic iridium compounds having the following formula are disclosed in Japanese Patent Laid-Open No. 8-85873:
(wherein R, R′ are independently selected from the group consisting of CH
3
, CF, CF
3
, C
2
H
5
, C
2
F
5
, C
3
H
7
, C
3
F
7
and C(CH
3
)
3
.)
While many of the above &bgr;-diketone iridium compounds are in the solid state at room temperature, though it depends on the types of substituents R, R′, they are considered to be very advantageous when producing thin films by CVD through sublimation thereof. This is because they are highly subliming, their vapor pressures at moderate and low temperatures are high, and there is a clear gap between their vaporization temperatures and decomposition temperatures. Some of the above &bgr;-diketone iridium compounds (tris(2,4-heptanedionato)iridium wherein R=a methyl group and R′=a propyl group, and tris(2,2-dimethyl-3,5-hexanedionato)iridium wherein R=a methyl group and R′=an isobutyl group) are liquid, and these compounds can be formed into thin films by ordinary vaporizing means. Further, the above &bgr;-diketone iridium compounds has the advantages that they are highly reactive with oxygen and they can be formed into both pure iridium thin films and iridium oxide thin films by controlling the oxygen concentration, and the morphology of their thin films is good.
However, according to the inventors of this invention, the known organic iridium compounds have the problems described below in respect to the industrial production efficiency and application scope of iridium thin films.
First, the cyclooctadiene iridium compounds are good in handling properties because they are in the liquid state at room temperature. However, they have a problem of being unable to produce iridium oxide thin films, but producing only pure iridium thin films even if film formation is performed in an oxygen atmosphere, because they are not very reactive with oxygen. Taking into consideration the fact that it is iridium oxide whose application to FeRAM thin film electrodes are under consideration at present, it has to be said that the application scope of the cyclooctadiene iridium compounds is limited.
On the other hand, the application scope of the &bgr;-diketone iridium compounds is not a problem. However, many of the &bgr;-diketone iridium compounds are in the solid state at room temperature, therefore, they have to be formed into thin films using a sublimation technique; but, it is relatively difficult to control the amount of the compounds vaporized through sublimation to a fixed value, since vaporization using a sublimation technique is an unstable process. Further, even if the amount of the compounds vaporized is controlled, it is difficult to keep the vaporized compounds in the gas state, and the raw material gases can sometimes be brought to the solid state during the process of carrying them from their container to a substrate, resulting in their adhesion to the inside of piping. This may cause an unstable film forming rate and deterioration of thin film morphology.
As aforementioned, some &bgr;-diketone iridium compounds are in the liquid state at room temperature, and these can be formed into thin films without using a sublimation technique. However, in the known liquid &bgr;-diketone iridium compounds, their vapor pressures are low, therefore, their thin film production efficiency is low, and to ensure a certain production efficiency, it is necessary to increase the heating temperature during thin film production. If, however, the vaporization temperature is increased higher than necessary, the raw material compounds tend to decompose even in an inert atmosphere. Therefore, when producing their thin films using a large volume of raw material gases, it is difficult to control the heating of the raw material gases. Thus, the liquid &bgr;-diketone iridium compounds are unfit for production of thin films on large-sized substrates and for mass production.
Recently, in the field of CVD, in light of the low use efficiency (the ratio of introduced raw material compounds to those actually contributing to thin film forming reaction) in CVD, application of a recycling technique, in which used raw materials are collected so as to recover unreacted raw materials therefrom, has been examined. This recycling technique consists of: a step of collecting used raw material compounds (gases) discharged from a reactor while bringing the same to the liquid state with a cold trap etc.; and a step of separating/purifying unreacted compounds from the collected compounds by distillation etc. This recycling is, however, difficult to apply to the &bgr;-diketone iridium compounds. The reason is that, in the solid &bgr;-diketone iridium compounds, it is difficult to recover them in the liquid state and it is impossible to purify them by distillation. In the liquid &bgr;-diketone iridium compounds, it is difficult to separate/purify them by distillation etc. because their vapor pressures are low. Thus CVD in which recycling is taken into consideration is difficult to apply to the known &bgr;-diketone iridium compounds; as a result, costs for producing thin films using these compounds rise.
To summarize the problems described so far, the raw material compounds for use in CVD to p
Sagae Takeyuki
Saito Masayuki
Nazario-Gonzalez Porfirio
Rothwell Figg Ernst & Manbeck
Tanaka Kikinzoku Kogyo K.K.
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