Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
2003-01-22
2004-06-22
Nazario-Gonzalez, Porfirio (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C556S136000, C106S001280, C106S217200, C427S587000, C427S593000
Reexamination Certificate
active
06753437
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a raw material used for the production of an iridium- or iridium compound-thin film by CVD method, and a production method thereof.
2. Description of the Related Art
In recent years, iridium or noble metals such as iridium have been used as thin film electrode materials for various types of semiconductor devices such as DRAM or FERAM. This is because these noble metals have a low specific resistance, and therefore they have excellent electric properties when they are used as electrodes. Especially, iridium and an oxide thereof are used as electrodes for FERAM.
Chemical vapor deposition method (hereinafter referred to as CVD method) is commonly used to produce a thin film used for thin film electrodes, as well as sputtering method. CVD method enables the production of a homogeneous thin film, and this method is superior to sputtering method especially in step coverage (an ability to cover steps). Particularly, in order that memory devices such as the above DRAM or FERAM have a large capacity, it is attempted to change the structure from a two-dimensional multi-layer film to a three-dimensional multi-layer film. The formation of such a complicated electrode structure requires step coverage and a film formation control ability, which are stricter than the previous ones. The CVD method is likely to become a major production process of thin film electrodes, since it can meet a recent requirement for higher densification of circuits and electronic components.
Properties generally required for a raw-material used for CVD method are that it has a low melting point and so it is in a liquid state at ordinary temperature, and that it has a high vapor pressure. Compounds previously known to be used as raw materials for iridium films and iridium compound thin films which are produced by CVD method are broadly divided into &bgr;-diketone iridium compounds and cyclooctadiene iridium compounds.
The &bgr;-diketone iridium compound is a complex of iridium and a &bgr;-diketone organic compound. As &bgr;-diketone organic compounds used as raw materials for CVD, several organic iridium compounds represented by the undermentioned formula have ever been known. Although these iridium compounds are solid at ordinary temperature, they have a melting point (approximately 140° C. to 270° C.) which is significantly lower than that of the previously known iridium compounds. Moreover, these iridium compounds have a high sublimation property and a high vapor pressure at low and medium temperature, and there is a clear difference between the vaporization temperature and the decomposition temperature. Therefore, these iridium compounds are considered to be extremely advantageous in the production of a film by CVD according to sublimation method (for the details of &bgr;-diketone iridium compounds used as raw materials for CVD, please refer to Japanese Patent Laid-Open Nos. 9-49081 and 8-85873).
wherein each of R and R′ is any one of CH
3
, CF, CF
3
, C
2
H
5
, C
2
F
5
, C
3
H7, C
3
F
7
and C(CH
3
)
3
.
On the other hand, the cyclooctadiene iridium compound is a compound obtained by coordinating cyclooctadiene and a cyclodiene derivative with iridium. Examples of cyclooctadiene iridium compounds known to be used as raw materials for CVD include methylcyclopentadienyl(1,5-cyclooctanedione)iridium, ethylcyclopentadienyl(1,5-cyclooctanedione)iridium and others, which are represented by the following formula:
wherein R represents any one of hydrogen, a methyl group and an ethyl group.
These cyclooctadiene iridium compounds have a further lower melting point (approximately 25° C. to 40° C.). Of these, ethylcyclopentadienyl(1,5-scyclooctanedione)iridium is liquid at ordinary temperature and therefore it has the advantage of being vaporized without using the sublimation method (for the details of cyclooctadiene iridium compounds, please refer to Japanese Patent Laid-Open No. 11-292888 and J. Vac. Sci. Technol. A 18(1) 10-16 (2002)).
However, the present inventors point out that these organic iridium compounds have problems in terms of the industrial production efficiency and applicable range of iridium thin films, which are described below.
Concerning &bgr;-diketone iridium compounds, the previously known &bgr;-diketone iridium compound is in a solid state at ordinary temperature, although it has a low melting point. Accordingly, the sublimation method is applied to form a thin film using the &bgr;-diketone iridium compound as a raw material for CVD. However, vaporization by the sublimation method is an unstable process, and it is relatively difficult to keep constant the vaporized amount obtained by sublimation. Moreover, even though the vaporized amount can be controlled, it is difficult to maintain the vaporized compound in a gaseous state, and there may be cases that raw material gas is returned to a solid state and attached to the inner surface of a piping in the step of transporting the gas from a raw material container to a substrate. As a result, there may be a risk that the film production rate becomes unstable and the morphology of a thin film deteriorates.
In contrast, a cyclooctadiene iridium compound, another known organic iridium compound, is liquid at ordinary temperature, and so a thin film can be produced by the vaporization of the compound by heating without applying the sublimation method. However, according to the present inventors' studies, this cyclooctadiene iridium compound has poor reactivity with oxygen, and so, even though film production is carried out in an oxygen atmosphere, an iridium oxide thin film cannot be produced, but a pure iridium thin film is produced instead. Taking into consideration the fact that it is iridium oxide that is considered to be applied as a thin film electrode for FERAM, it cannot but say that the applicable range of the cyclooctadiene iridium compound is narrow.
The present invention was made against the above described background. It is the object of the present invention to provide an iridium compound used as a raw material for CVD for producing an iridium- or iridium compound-thin film, wherein the iridium compound has a low melting point, it is in a liquid state at ordinary temperature, and it can stably be vaporized and has good reactivity with oxygen, so that an iridium oxide thin film as well as an iridium thin film can be produced from the compound; and a production method thereof.
SUMMARY OF THE INVENTION
As a result of intensive studies by the present inventors directed toward the above object, they have found the object can be achieved with the use of tris(2,4-octanedionato)iridium that is one type of &bgr;-diketone iridium, thereby completing the present invention.
That is to say, the present invention relates to a raw material for CVD comprising an organic iridium compound as a main ingredient, wherein the organic iridium compound consists of tris(2,4-octanedionato)iridium represented by the following formula:
This tris(2,4-octanedionato)iridium is one form of &bgr;-diketone iridium, and it is liquid at ordinary temperature. Accordingly, this compound easily vaporizes when it is used in the production of a film, and raw materials can quantitatively be supplied by means such as gas bubbling or a liquid mass flow controller. Moreover, this organic iridium compound has good stability, having a low possibility that it has phase change or decomposition during the process of being transported to a substrate. Thus, the use of the iridium compound of the present invention enables the formation of a thin film at a stable film production rate and the efficient production of a morphologically good thin film.
Furthermore, this tris(2,4-octanedionato)iridium has relatively good reactivity when it is heated on a substrate, and iridium oxide can be deposited by reaction in an oxygen atmosphere. Accordingly, the iridium compound of the present invention is preferably used as a raw material for producing an iridium oxide thin film, and this compound has an applicab
Sagae Takeyuki
Taniuchi Jun-ichi
Nazario-Gonzalez Porfirio
Rothwell Figg Ernst & Manbeck P.C.
Tanaka Kikinzoku Kogyo K.K.
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