BACKGROUND OF THE INVENTION Hitherto, many metals such as tungsten and aluminum have been widely used as interconnecting materials in many electronic devices such as semiconductors. However, an aluminum interconnect (specific resistance: about 2.7 yQ-cm) tends to be hampered by the problem of electromigration, while tungsten has the problem of high resistivity (specific resistance: about 5.4 HQ-cm). Therefore, attempts have been recently made to use copper which is highly conductive (specific resistance: about 1.67 HQ cm) and electromigration resistant, as an interconnecting material in advanced devices such as ultra-large semiconductor integrated circuits.

A metallic interconnect is typically formed by a chemical vapor deposition (CVD) method using a metallorganic precursor compound, and Cu films have previously been

prepared using various organic copper (II) precursors such as Cu (II) (hfac) 2'wherein hfac stands for hexafluoroacetyl- acetonate. However, a CVD process using such Cu (II) precursors requires a high deposition temperature and the resulting Cu film is often contaminated by various impurities.

Organic copper (I) precursor compounds usable in a low- temperature, selective CVD process have been recently described. For example, the use of organocuprous precursors such as (hfac) Cu (I) (VTMS) (VTMS: vinyltrimethylsilane) and (hfac) Cu (I) (ATMS) (ATMS: allyltrimethylsilane) in a low- temperature CVD process to selectively deposit a Cu film on a conductive substrate surface has been disclosed by Norman et al. in U. S. Patent No. 5,085,731 and Electrochemical and Solid-State Letters, 1 (1) 32-33 (1998), respectively.

However, the above CVD process has a low productivity due to the low vapor pressure and the low thermal stability of the organic copper precursors.

U. S. Patent No. 5,098,516 teaches the use of Cu (I)- olefin precursors such as (hfac) Cu (I)-COD (COD: cyclooctadiene) and (hfac) Cu (I)-NBD (NBD: norbonadiene) in a low temperature CVD process. The above Cu (I)-olefin precursors are solids, and they must be sublimed at a temperature below their thermal decomposition temperatures, e. g., about 105 °C for (hfac) Cu (I)-COD. Thus, the CVD process disclosed in U. S. Patent No. 5,098,516 is hampered by the difficulty in handling solid precursors in a mass

production system. Moreover, the CVD of a copper film using, e. g., (hfac) Cu (I) COD requires a relatively high substrate temperature of above 150 °C and the resulting copper film is often of poor quality.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide an organic copper (I) precursor which can be advantageously used in a low-temperature CVD process for the mass production of a contaminant-free copper film.

In accordance with one aspect of the present invention, there is provided an organocuprous compound of formula (I) wherein: R1, R2 and R3 are each independently a C18 alkyl, C1 8 alkoxy, aryl or aryloxy group, R4 and R5 are each independently hydrogen, fluorine, a CnF2n+ or CnH2n+1 group, n being an integer in the range of 1 to 6, R6 is hydrogen, fluorine or a C1-4 alkyl group, and m is 1 or 2, when m is 1, C-C represents C=C, and when m is 2, C-C represents C=C.

In accordance with another aspect of the present

invention, there is provided a process for depositing a copper film on a substrate, which comprises vaporizing the compound of formula (I) and bringing the resulting vapor into contact with the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects and features of the present invention will become apparent from the following description of the invention taken in conjunction with the accompanying drawings, in which: Fig. 1 depicts the thermal decomposition characteristics of the inventive organocuprous precursor ( (hfac) Cu (DMB)), as analyzed by TGA (thermal gravimetric analyzer) and DSC (differential scanning calorimeter); Fig. 2 exhibits the thermal decomposition characteristics of (hfac) Cu (VTMS), as analyzed by TGA and DSC; Fig. 3 shows the vapor pressure changes of the inventive organocuprous precursor ( (hfac) Cu (DMB)) and (hfac) Cu (VTMS) determined with temperature; Fig. 4 illustrates the copper film deposition rate as function of the substrate temperature in a CVD process using the inventive organocuprous precursor ( (hfac) Cu (DMB)), (hfac) Cu (VTMS) and (hfac) Cu (ATMS); and Fig. 5 presents the change in the specific resistance

of the copper film derived from the inventive precursor ( (hfac) Cu (DMB)) with the substrate temperature.

DETAILED DESCRIPTION OF THE INVENTION Among the compounds according to the present invention, preferred are those of formula (I) wherein R1, R2 and R3 are each independently methyl, ethyl, methoxy or ethoxy group, R4 and R5 are each dependently a CnF2n+1 or CnH2n+1 group wherein n is 1 or 4, and R6 is hydrogen.

More preferred compounds of formula (I) according to the present invention are those represented by formula (I-a) and (I-b): wherein R4 and R5 are each dependently a CnF2n+1 or CnH2n+1 group (n is an integer of 1 to 4),'preferably trifluoromethyl group.

When R4 and R5 are each a trifluoromethyl group, the

compound of formula (I-a) may be prepared by reacting 1, 1, 1, 5, 5, 5-hexafluoro-2, 4-pentanedione (Hhfac), 3,3- dimethyl-1-butene (DMB) and cuprous oxide (Cu2O) in the presence of an organic solvent, e. g., diethylether or dichloromethane, at a temperature ranging from 0 to 20 °C under an ambient pressure for 2 to 3 hours. The reactants may be preferably employed in an Hhfac: DMB : Cu2O molar ratio of about 2 : 2 : 1.

Further, the compound of formula (I-b) wherein R4 and R5 are each a trifluoromethyl group may be prepared by using 3,3-dimethyl-1-butyne (i. e., tert-butylacetylene) (TBA) in place of 3,3-dimethyl-1-butene (DMB), in the process for the synthesis of the compound of formula (I-a).

The compound of formula (I) according to the present invention has good thermostability and high volatility, and in a CVD process for the formation of a copper film on a specified surface of a substrate, it may be conveniently vaporized in a bubbler or evaporator at a temperature ranging from about 15 to 100 °C in a gas delivering system or a liquid delivery system.

The CVD process for the formation of a copper thin film using the inventive organocuprous precursor may be carried out in a conventional manner, e. g., by vaporizing the inventive precursor and conveying the resulting vapor with a carrier gas such as argon to a substrate, e. g., platinum, silica, TiN, TaN, WN, etc., which is preferably heated to a temperature ranging from 100 to 300 °C, more preferably from

150 to 250 °C, under a reduced pressure, e. g., 0.1 to 10 torr.

The thickness of the copper film may be conveniently controlled by adjusting the deposition time.

The copper film obtained according to the present invention is useful as a metallized or seed layer of a semi- conductor device.

The following Examples are intended to further illustrate the present invention without limiting its scope.

Example 1: Synthesis of (hfac) Cu (I) (DMB) 0.5 g (3.5 mmol) of Cu2O and 0.84 g (7.0 mmol) of MgSO4 were charged to a Schlenk flask and thereto was added 30 ml of diethylether which had been previously distilled from sodium benzophenone under an argon atmosphere, and then slowly added 0.59 g (7.0 mmol) of 3,3-dimethyl-1-butene.

The resulting reddish suspension was stirred for 1 hour and cooled to 0 °C, and slowly added thereto with a canula was a solution of 1.46 g (7.0 mmol) of 1,1,1,5,5,5-hexafluoro- 2,4-pentanedione (Hhfac) in diethyl ether. The resulting mixture was stirred at room temperature for 2 hours and, at this time, the color of the mixture turned dark green. The resulting solution was filtered through a bed of CELLITETM and the solvent was removed therefrom under a reduced pressure to obtain 1.74 g of the titled compound as a dark green liquid (yield 70 %).

1H-NMR (CDCl3, ppm) b 6.12 (s, 1H), 5.38 (m, 1H), 4.30 (dd, 2H),

1.15 (s, 9H) C-NMR (CDCl3, ppm) 6 177.83 (q, CF3COCH), 119.73,115.8 (q, CF3), 89.97 (COCHCO), 75.69,35.16,29.99 19F-NMR (TFA, ppm) 6-0.14 (s, 6F) Example 2: Synthesis of (hfac) Cu (I) (TBA) 0.5 g (3.5 mmol) of Cu2O and 0.84 g (7.0 mmol) of MgSO4 were charged to a Schlenk flask and thereto was added 30 ml of diethylether which had been previously distilled from sodium benzophenone under an argon atmosphere, and then slowly added 0.58 g (7.0 mmol) of 3,3-dimethyl-1-butyne.

The resulting reddish suspension was stirred for 1 hour and cooled to 0 °C, and slowly added thereto with a canula was a solution of 1.46 g (7.0 mmol) of 1,1,1,5,5,5-hexafluoro- 2,4-pentanedione (Hhfac) in diethyl ether. The resulting mixture was stirred at room temperature for 2 hours and, at this time, the color of the mixture turned yellow. The resulting solution was filtered through a bed of CELLITETM and the solvent was removed therefrom under a reduced pressure to obtain 1.75 g of the titled compound as a yellow solid (yield 73 %).

H-NMR (CDC13, ppm) 6 6.09 (s, 1H), 4.25 (s, 1H), 1.38 (s, 9H) 13C-NMR (C6D6, ppm) 6 178.57 (q, CF3COCH), 116.52 (q, CF3) 105.25,90.36 (COCHCO), 70.83,31.73,30.63 M. P.: 98-99 °C In order to compare the thermal decomposition

characteristics of the compound synthesized in Example 1 and (hfac) Cu (VTMS) as a prior art precursor, each compound was analyzed with TGA (thermal gravimetric analyzer) and DSC (differential scanning calorimeter), and the results are presented in Figs. 1 and 2, respectively. As can be seen in Fig. 1 and Fig. 2, the thermal decomposition temperature of the inventive organocuprous precursor is higher than that of the prior art precursor, and thus, the inventive precursor has good thermal stability.

The changes in the vapor pressure of the titled compound and (hfac) Cu (VTMS) were determined at various temperatures. The result in Fig. 3 demonstrates that the inventive precursor has a higher vapor pressure than the prior art compound.

Example 3: Deposition of a copper film on a substrate Copper films were deposited on a TiN or SiO2-coated substrate by a CVD process, using the inventive precursor synthesized in Example 1, as well as (hfac) Cu (VTMS) and (hfac) Cu (ATMS) as prior art precursors. Specifically, each compound was fed to a bubbler maintained at 45 °C, and the vapor thereof was conveyed in an argon flow at a rate of 50 sccm to the surface of the substrate positioned in a CVD chamber under a pressure of 0.3 mmHg. The copper film deposition rates depending on the substrate temperature are shown in Fig. 4. The results in Fig. 4 demonstrate that the

inventive precursor forms a copper film at a rate which is about 5-6 times higher than those of the prior art precursors.

On the other hand, the change in the specific resistance of the film deposited using the inventive precursor depends on the substrate temperature, as shown in Fig. 5. It can be seen from Fig. 5 that the specific resistance of the film deposited at a substrate temperature of 150 °C to 250 °C approximately reaches that of bulk copper (about 1.67 pX cm).

While the invention has been described with respect to the above specific embodiments, it should be recognized that various modifications and changes may be made to the invention by those skilled in the art which also fall within the scope of the invention as defined by the appended claims.