# Patent

## Title
Method for forming tantalum nitride film

## Abstract

A tantalum nitride film-forming method comprises the steps, according to the CVD technique, of introducing a raw gas consisting of a coordination compound constituted by an elemental tantalum (Ta) having a coordinated ligand represented by the general formula: N═(R, R′) (in the formula, R and R′ may be the same or different and each represents an alkyl group having 1 to 6 carbon atoms) and a halogen gas into a film-forming chamber to thus form a film of a halogenated compound represented by the following general formula: TaNx(Hal)y(R, R′)z (in the formula, Hal represents a halogen atom), reacting the halogenated compound film with a hydrogen atom-containing gas by the introduction thereof into the chamber to thus form a tantalum nitride film rich in tantalum atoms. The resulting tantalum nitride film has a low resistance, low contents of C and N, and a high compositional ratio: Ta/N, can ensure high adherence to the electrical connection-forming film and can thus be useful as a barrier film. Moreover, tantalum particles are implanted in the resulting film according to the sputtering technique to thus further enrich the film with tantalum.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application is a National Stage entry of International Application Number PCT/JP2006/304073, filed Mar. 3, 2006. The disclosure of the prior application is hereby incorporated herein in its entirety by reference.
TECHNICAL FIELD
The present invention relates to a method for forming a tantalum nitride film and, in particular, to a method for forming, according to the CVD technique, a tantalum nitride film useful as a barrier film for distributing wire-forming film or electrical connection-forming films.
BACKGROUND ART
Recently, there has increasingly been desired for the development of a technique which permits the more finely processing step with respect to the thin film-forming technique used in the field of the semiconductor and this results in the occurrence of a variety of related problems.
In an example of the technique for forming electrical connections of a thin film in a semiconductor device, copper has mainly be used as a material for the electrical connection because of its low resistivity. However, it is technically difficult to etch copper and copper may easily penetrate or diffuse into the underlying layer such as an insulating film and accordingly, a problem arises such that the reliability of the resulting device is lowered.
To solve this problem, such diffusion of the copper has conventionally been prevented by forming a metal thin film (or a conductive barrier film) on the inner wall surface of the interlayer-connecting holes in a multi-layered electrical connection structure according to, for instance, the CVD technique; and then forming a layer for making the electrical connections by the application of a copper thin film on the conductive barrier film so that the resulting copper thin film never comes in direct contact with the underlying insulating film such as a silicon oxide film (see, for instance, Japanese Un-Examined Patent Publication 2002-26124 (Claims and the like)).
In this case, it has been required that fine contact holes, trenches or the like each having a high aspect ratio should be plugged or filled up with a thin barrier film while ensuring a high rate of step-coverage, in response to the foregoing demands for the use of electrical connections having a multi-layered structure and a further miniaturized pattern.
DISCLOSURE OF THE INVENTION
Problems that the Invention is to Solve
In the case of the foregoing conventional technique, a problem arises, such that it is difficult to form a tantalum nitride (TaN) film having a low resistance and useful as a barrier layer, according to a CVD technique, while ensuring the adherence to the Cu film used for forming electrical connections. To solve this problem, it would be necessary to develop a film-forming process which can eliminate organic groups such as alkyl groups present in the raw gas used in the process through the cleavage thereof, which can thus reduce the content of C atoms and simultaneously break the linkages between Ta and N and which can thus increase the compositional ratio: Ta/N.
Accordingly, it is an object of the present invention to solve the foregoing problems associated with the conventional techniques and more specifically to provide a method for forming a tantalum nitride film, according to the CVD method, which has a low resistance, whose contents of C and N atoms are low, which has a high compositional ratio: Ta/N, which can ensure sufficiently high adherence to the electrical connection-forming film (such as Cu electrical connection-forming film) and which is thus useful as a barrier film.
Means for the Solution of the Problems
The tantalum nitride film-forming method according to the present invention comprises the steps, according to the CVD technique, of simultaneously introducing a raw gas consisting of a coordination compound constituted by an elemental tantalum (Ta) having a coordinated ligand represented by the general formula: N═(R, R′) (in the formula, R and R′ may be the same or different and each represents an alkyl group having 1 to 6 carbon atoms) and a halogen gas into a film-forming chamber to thus form a film of a halogenated compound represented by the following general formula: TaNx(Hal)y(R, R′)z (in the formula, Hal represents a halogen atom) on a substrate, and then reacting the foregoing halogenated compound film with a hydrogen atom-containing gas by the introduction thereof into the chamber, to remove N atoms bonded to Ta atoms in the film through cleavage, to remove the halogen atoms and/or the R(R′) groups bonded to N atoms in the film and to thus form a tantalum nitride film rich in tantalum atoms. In this respect, if the number of carbon atoms included in the foregoing coordination compound exceeds 6, a problem arises such that the carbon content of the resulting film increases.
The H atom-containing gas is converted into radicals thereof by the action of heat or plasma within the film-forming chamber and the resulting radicals are reacted with the resulting halogenated compound film to thus form a tantalum nitride film rich in tantalum atoms.
The method comprising the foregoing steps permits the formation of a tantalum nitride film which has a low resistance, whose contents of C and N atoms present in the resulting film are reduced, which has a high compositional ratio: Ta/N, which can ensure sufficiently high adherence to the electrical connection-forming film (such as Cu electrical connection-forming film) and which is thus useful as a barrier film.
It is preferred that the foregoing raw gas is the gas of at least one coordination compound selected from the group consisting of penta-dimethylamino-tantalum (PDMAT), tert-amylimido-tris(dimethylamide) tantalum (TMMATA), penta-diethyl-amino-tantalum (PEMAT), tert-butylimido-tris(dimethylamide) tantalum (TBTDET), tert-butyl-imido-tris(ethyl-methylamide) tantalum (TBTEMT), Ta(N(CH3)2)3(NCH2 CH3)2 (DEMAT) and TaX5 (X represents a halogen atom selected from chlorine, bromine and iodine).
The foregoing halogen gas is desirably at least one member selected from the group consisting of fluorine, chlorine, bromine and iodine gases. The use of such a halogen gas would permit the formation of the foregoing compound represented by the general formula: TaNx(Hal)y(R, R′)z.
The hydrogen atom-containing gas is desirably at least one member or gas selected from the group consisting of H2, NH3 and SiH4 gases.
The foregoing tantalum nitride film-forming method would permit the formation of a low-resistant tantalum nitride film enriched with tantalum, which satisfies the following requirement: the compositional ratio of tantalum to nitrogen in the film: Ta/N≧2.0.
According to the present invention, there is also provided a method for forming a tantalum nitride film which comprises the steps of forming a tantalum nitride film according to the foregoing method; and then implanting tantalum particles into the resulting tantalum nitride film according to the sputtering technique which makes use of a target containing tantalum as the principal constituent. The method would permit the formation of a tantalum nitride film which is further rich in tantalum and which sufficiently satisfies the following requirement: the compositional ratio of tantalum to nitrogen in the film: Ta/N≧2.0.
The sputtering step is desirably carried out while controlling the DC power and the RF power in such a manner that the DC power is low, while the RF power is high.
EFFECTS OF THE INVENTION
The present invention thus permits the formation of a tantalum nitride film, according to the CVD technique, which has a low resistance, whose contents of C and N atoms are low, which has a high compositional ratio: Ta/N, which can ensure sufficiently high adherence to the electrical connection-forming film (such as a Cu electrical connection-forming film) and which is thus useful as a barrier film.
The present invention also permits the formation of a tantalum nitride film which is further enriched with tantalum by the implantation of tantalum in the tantalum nitride film, which is formed according to the foregoing CVD technique, by the PVD technique such as the sputtering method.
In addition, the present invention likewise permits the formation of an electrical connection-forming film on the foregoing barrier film, with excellent adherence to the latter and good evenness.
BEST MODE FOR CARRYING OUT THE INVENTION
According to the present invention, a low-resistant tantalum nitride film having low contents of C, N, a high compositional ratio: Ta/N, may be obtained, according to the CVD technique such as the thermal or plasma enhanced CVD technique, by reacting the raw gas consisting of the foregoing tantalum-containing coordination compound and a halogen gas on a substrate arranged in the vacuum chamber serving as a film-forming chamber to thus form a film of a compound represented by the general formula: TaNx(Hal)y(R, R′)z and then reacting the halogenated compound film with radicals generated through the activation of an H atom-containing gas introduced into the vacuum chamber by the action of heat or plasma, i.e. radicals such as H radicals derived from H2 gas or NH3 gas and NHx radicals derived from NH3 gas.
The raw gas, the halogen gas and the hydrogen atom-containing gas such as those listed above may directly be introduced into the vacuum chamber or they may likewise be introduced into the same in combination with an inert gas such as N2 gas or Ar gas. Regarding the amounts of these reactants, it is desirable that the halogen gas is used in a small amount relative to the raw gas, for instance, at a flow rate of not more than about 5 sccm per 5 sccm of the raw gas, while the hydrogen atom-containing gas is used in an amount, relative to the raw gas, higher than that of the halogen gas likewise relative to the raw gas, for instance, at a flow rate ranging from 100 to 1000 sccm (amount converted to that of H2) per 5 sccm of the raw gas.
The temperature of the foregoing two reactions may be one which can initiate these reactions and it is, for instance, not more than 300° C. and preferably 150 to 300° C. for the halogenation reaction between the raw gas and the halogen gas; and it is, for instance, not more than 300° C. and preferably 150 to 300° C. for the reaction between the product of the foregoing halogenation reaction with the radicals. On the other hand, the pressure within the vacuum chamber is desirably in the range of from 1 to 10 Pa for the first halogenation reaction and in the range of from 1 to 100 Pa for the subsequent film-forming reaction.
As has been discussed above, the coordination compound is one constituted by an elemental tantalum (Ta) having a coordinated ligand represented by the general formula: N═(R, R′) (in the formula, R and R′ may be the same or different and each represents an alkyl group having 1 to 6 carbon atoms). The alkyl group may be, for instance, a linear or branched one such as a methyl, ethyl, propyl, butyl, pentyl or hexyl group. The coordination compound is in general one constituted by an elemental tantalum (Ta) having 4 or 5 coordinated ligands represented by the formula: N—(R, R′).
The foregoing method of the present invention may be carried out by, for instance, introducing a raw gas and a halogen gas into a vacuum chamber serving as a film-forming chamber to halogenate the raw gas with the halogen gas to thus form, on the substrate, a film composed of a compound represented by the formula: TaNx(Hal)y(R, R′)z according to the CVD technique; and then introducing a hydrogen atom-containing gas into the chamber and reacting radicals derived from the hydrogen atom-containing gas by the action of heat or plasma with the foregoing halogenated product to thus form a tantalum nitride film; and thereafter the process may be repeated over predetermined times, or the foregoing halogenation reaction is repeated over desired times and then the halogenation product is reacted with the radicals.
The tantalum nitride film-forming method of the present invention may be carried out using any film-forming apparatus inasmuch as the apparatus permits the practice of the so-called CVD technique. For instance, an embodiment of the method of the present invention will hereunder be described in detail while using the plasma CVD film-forming apparatus as shown in FIG. 1.
The plasma CVD apparatus as shown in FIG. 1 comprises a vacuum chamber 1 serving as a film-forming chamber, a vacuum evacuation system 2 is connected to the side wall of the vacuum chamber and an electrode 3 is arranged above the vacuum chamber in a state insulated from the chamber. A high frequency power source 4 is connected to the electrode 3 and arranged at the exterior of the chamber 1 so that a high frequency power can be applied to the electrode to thus generate plasma within the vacuum chamber. A stage 6 for placing a substrate provided with a built-in heating means 5 such as a heater is positioned below or at the lower part of the vacuum chamber and is disposed in such a manner that the substrate-mounting face thereof is horizontal with and opposed to the electrode face.
The electrode 3 is provided with a gas chamber 7 therein and a plurality of holes 8 serving as shower nozzles are formed on the face thereof opposite to the substrate-mounting stage 6, or the electrode is so designed that a gas is introduced into the vacuum chamber through the holes to thus supply the gas onto the substrate surface and accordingly, this electrode may serve as a shower plate.
The gas chamber 7 is connected to one end of a gas-introducing system 9 and the other end of the gas-introducing system is connected to a plurality of bombs (not shown) each filled with, for instance, the raw gas, the halogen gas or the hydrogen atom-containing gas. In this case, the gas chamber 7 may be connected to a plurality of gas-introducing systems 9 connected to separate bombs respectively. The apparatus is so designed that the flow rate of each gas can be controlled with a mass flow controller, although this is not clearly shown in this figure.
In addition to the introduction of the raw gas into the vacuum chamber using a gas bomb filled with the raw gas, it is also possible to accommodate the foregoing tantalum-containing organometal compound in a container which has been heated and maintained at a desired temperature, supply an inert gas such as Ar gas as a bubbling gas to the container through, for instance, a mass-flow controller for the sublimation thereof and to thus introduce the sublimated raw gas together with the bubbling gas into the vacuum chamber; or alternatively, the raw gas, which has been vaporized through a vaporizer, may likewise be introduced into the vacuum chamber.
The following is the description of an embodiment of the tantalum nitride film-forming method according to the present invention which is carried out using the plasma-enhanced CVD type film-forming apparatus as shown in FIG. 1.
First of all, the vacuum evacuation system 2 is put into operation to evacuate the vacuum chamber 1 to a predetermined pressure (for instance, 10−4 to 10−5 Pa), a substrate S is placed on the substrate-mounting stage 6 and then the heating means 5 is switched on to heat the substrate to a desired temperature (for instance, a temperature ranging from 150 to 300° C.). Then a raw gas and a halogen gas are introduced into the gas chamber 7 through the gas-introducing system 9 and supplied towards the surface of the substrate S through the holes 8. The substrate S is not restricted to any particular one, but it may be any known one which is provided with an underlying adhesive layer on the insulating layer and whose surface has been subjected to a pre-treatment such as a degassing treatment.
After establishing a predetermined stable pressure in the vacuum chamber 1, a high frequency power source 4 is put into operation to thus make, output, a high frequency AC voltage having a frequency of 27.12 MHz and a power density of 0.2 W/cm2. When this AC voltage is applied to the electrode 3 through the high frequency power source, the plasma of the raw gas and the halogen gas is generated between the electrode 3 which is so designed as to function as a cathode and the surface of the substrate S placed on the substrate holder 6 which is so designed as to function as an anode. The radicals of these raw gas and halogen gas are generated within the plasma and a halogenation reaction takes place on the surface of the substrate S and this results in the formation of a film composed of a compound represented by the formula: TaNx(Hal)y(R)z. After the formation of the halogenated compound film having a desired film thickness, the high frequency power source 4 is switched off and the supply of the raw gas and the halogen gas is stopped.
Then, a hydrogen atom-containing gas is introduced into the vacuum chamber 1 through the gas-introducing system 9 to thus carry out the activation of the gas. More specifically, the procedures similar to those used above are repeated to thus generate plasma of the gas within the chamber, the radicals thereof generated within the plasma are incident upon the surface of the halogenated compound film formed in the foregoing step to thus make them react with one another. This leads to the reduction of the N atom bonded to Ta within the halogenated compound film through the cleavage thereof, the removal of the R(R′) groups, which are bonded to an N atom, remaining in the film through the cleavage thereof and the formation of a tantalum nitride film rich in tantalum. After the formation of a tantalum nitride film having a desired film thickness, the high frequency power source 4 is switched off, the introduction of the hydrogen atom-containing gas is stopped and the substrate S is withdrawn from the vacuum chamber 1.
The tantalum nitride film thus formed according to the foregoing method was analyzed by the AES and as a result, the following results were obtained: the content of C: not more than 2%; the content of N: 33 to 35%; the ratio: Ta/N: 1.9 to 2.0; and the resistivity value thereof: not more than 450 μΩ·cm.
As has been described above, the reactant gases such as the NH3 gas and the hydrogen atom-containing gas are activated in the plasma according to the plasma enhanced CVD technique and therefore, a thin film can be formed even at a relatively low film-forming temperature. Moreover, a tantalum nitride film rich in tantalum can likewise be prepared by the same procedure using the known process conditions according to the thermal CVD technique.
The substrate, on which a tantalum nitride film having a desired thickness has been formed by the foregoing method, may further be treated, if necessary, by applying a voltage to a target, while using a sputtering gas such as Ar gas, to thus generate plasma and sputter the target according to the usual sputtering technique to thus form a metal thin film or an adhesive layer on the side of an electrical connection-forming film (an underlying layer on the side of the barrier film), on the surface of the foregoing tantalum nitride film.
A laminated film is formed on the substrate S through the foregoing steps. Subsequently, the electrical connection-forming film (such as Cu-electrical connection-forming film) is formed on the foregoing adhesive layer on the side of the electrical connection-forming film, according to a known method.
Incidentally, in the method for preparing a tantalum nitride film according to the present invention, it is necessary to carry out a known degassing treatment for the removal of impurities such as gases adhered to the surface of the substrate S prior to the formation of such a barrier film, and an electrical connection-forming film of, for instance, Cu is finally formed after such a barrier film is applied onto the substrate. For this reason, if this film-forming apparatus is incorporated into a composite type electrical connection film-forming apparatus which is so designed that the film-forming apparatus is connected to at least the degassing chamber and an electrical connection film-forming chamber through a conveying chamber capable of being evacuated to a vacuum and that a transportation robot can convey the substrate from the conveying chamber to the film-forming chamber, the degassing chamber and the electrical connection film-forming chamber, a series of steps extending from the pre-treatment step to the electrical connection film-forming step can be implemented in this apparatus.
Tantalum particles are implanted in the tantalum nitride film thus formed according to the PVD technique such as the sputtering technique to be able to thus form a tantalum nitride film further rich in tantalum. For instance, this may be carried out using a known sputtering device wherein a target is positioned upper portion of the vacuum chamber and arranged at the position opposite to the substrate holder.
In the case of such a sputtering device, the target is connected to an electric voltage-applying device for generating plasma which can sputter the surface of the target to thus emit particles composed of the constituent of the target. The target used herein is one mainly comprising the metal constituent element (Ta) of the foregoing raw gas and the electric voltage-applying device is constituted by a high frequency-generating device and an electrode connected to the target. In this respect, it is sufficient to use, as the sputtering gas, a known inert gas such as argon gas or xenon gas.
Then, after placing, in the sputtering chamber, the substrate on which the tantalum nitride film serving as a barrier layer is formed by the foregoing method, an inert gas such as Ar gas is introduced into the sputtering chamber while inducing discharges to thus sputter the target mainly comprising tantalum as a constituent component of the raw gas and to implant tantalum particles as the sputtering particles in the thin film formed on the substrate. Thus, tantalum originated from the target can be implanted in the thin film on the surface of the substrate according to the sputtering technique and therefore, the content of tantalum in the barrier film can further be increased to thus give a tantalum nitride film rich in tantalum and having a desired low resistance value. In this respect, as the raw gas is an organic tantalum compound, the decomposition thereof is accelerated and impurities such as C and N are expelled from the barrier layer when the constituent element (tantalum) is incident upon the surface of the substrate according to the foregoing sputtering technique and as a result, this results in the formation of a low resistant barrier film having a quite low content of impurities.
This sputtering operation is not carried out for the formation of a laminated tantalum film, but for the implantation of tantalum particles in the tantalum nitride film through the bombardment thereof to remove C and N through sputtering and to improve the quality of the film. Accordingly, it is needed that this sputtering must be performed under such conditions that any tantalum film is not formed or they permit the etching of the tantalum nitride film with tantalum particles. To this end, it would, for instance, be necessary that the sputtering step is carried out while controlling the DC power and the RF power in such a manner that the DC power is low and the RF power is high. For instance, such sputtering conditions which are never accompanied by the formation of any tantalum film can be established when the DC power is set at a level of not more than 5 kW, while the RF power is set at a high level, for instance, a value ranging from 400 to 800 W. In this connection, the RF power is dependent upon the DC power and therefore, these DC and RF powers are appropriately adjusted so as to control the extent of the improvement of the film quality. In addition, the sputtering temperature may be one usually adopted and it may, for instance, be one identical to that used for the formation of the tantalum nitride film.
After the formation of such a barrier film having a desired thickness on the foregoing substrate S according to the foregoing procedures, it is, if necessary, also possible that a sputtering gas such as Ar gas is introduced into the chamber and a voltage is applied to the target by putting the voltage-applying device into operation to thus generate plasma and then the target is sputtered according to any known sputtering technique to thus form a metal thin film or an adhesive layer on the side of the electrical connection-forming film (an underlying layer on the barrier film side) on the surface of the foregoing barrier film.
A laminated film is thus formed on the substrate S through the foregoing steps. Subsequently, the electrical connection-forming film is formed on the foregoing adhesive layer on the side of the electrical connection-forming film according to any known method.
FIG. 2 is a schematic diagram showing the structure of a composite type electrical connection film-forming apparatus equipped with the film-forming apparatus as shown in FIG. 1.
This composite type electrical connection film-forming apparatus 100 is composed of a pre-treatment section 101, a film-forming section 103 and a relay section 102 connecting these sections. Either of these sections should be maintained under desired vacuum atmospheric conditions prior to the implementation of each treatment.
First of all, in the pre-treatment section 101, a substrate free of any treatment and arranged in a transfer chamber 101a is introduced into a degassing chamber 101c by putting, into operation, a conveyer robot 101b for the pre-treatment section. The un-treated substrate is heated in the degassing chamber 101c to thus subject the substrate to a degassing treatment by, for instance, the evaporation of the moisture present on the surface thereof. Then the degassed substrate is transferred to a reduction-treating chamber 101d by the action of the conveyer robot 101b. In this reduction-treating chamber 101d, the substrate is subjected to an annealing treatment in which the substrate is heated while supplying a reducing gas such as hydrogen gas to the chamber to thus remove metal oxides of the underlying electrical connections through the reduction.
After the completion of the annealing treatment, the substrate is withdrawn from the reduction-treating chamber 101d and then transferred to the relay section 102 by the action of the conveyer robot 101b. The substrate is then delivered to a conveyer robot 103a for the film-forming section 103 in the relay section 102.
The substrate thus delivered to the conveyer robot 103a is then introduced into a film-forming chamber 103b by the action of the robot 103a. This film-forming chamber 103b corresponds to the film-forming apparatus 1 described above. In the film-forming chamber 103b, a barrier film and an adhesive layer are formed on the substrate as a laminate film, the substrate provided thereon with the laminate film is then withdrawn from the film-forming chamber 103b and introduced into an electrical connection film-forming chamber 103c by the action of the conveyer robot 103a, in which an electrical connection-forming film is applied onto the foregoing barrier film (or onto the adhesive layer, if an adhesive layer is formed on the barrier film). After the formation of the electrical connection-forming film, the substrate is transferred from the electrical connection film-forming chamber 103c to a transfer chamber 103d by putting the conveyer robot 103a into operation. Thereafter, the substrate is withdrawn from the transfer chamber 103d. 
As has been discussed above in detail, the working efficiency can be improved by the use of an apparatus such as the foregoing composite type electrical connection film-forming apparatus 100, in which a series of steps including the barrier film-forming step and those carried out before and after the barrier film-forming step, or the degassing step and the electrical connection film-forming steps can be carried out in such a single or the same apparatus.
In this connection, the foregoing composite type electrical connection film-forming apparatus 100 is so designed that the pre-treatment section 101 comprises one each of the degassing chamber 101c and the reduction-treating chamber 101d, while the film-forming section 103 comprises one each of the film-forming chamber 103b and the electrical connection film-forming chamber 103c, but the construction of the apparatus 100 is not restricted to this structure.
Accordingly, for instance, the pre-treatment section 101 and the film-forming section 103 may be so designed as to have polygonal shapes, and a plurality of degassing chambers 101c and reduction-treating chambers 101 and a plurality of film-forming chambers 103b and electrical connection film-forming chambers 103c may be arranged on each face, respectively and accordingly, this leads to a further improvement of the throughput capacity of the apparatus.
EXAMPLE 1
In this Example, a tantalum nitride film was prepared using the film-forming apparatus 1 shown in FIG. 1 and using penta-dimethylamino-tantalum (MO) gas as the raw gas, fluorine gas as the halogen gas and NH3 gas as the reactant gas.
After the surface of a substrate S provided thereon with an SiO2 insulating film was subjected to a pre-treatment or a degassing treatment according to a known method, the substrate S was introduced into the vacuum chamber 1 which had been vacuum-evacuated to a pressure of not more than 10−5 Pa by putting the vacuum evacuation system 2 into operation. The substrate used herein is not limited to any particular one, and it may be, for instance, one prepared by applying a voltage to a target, which comprises Ta as a principal constituent, while using Ar gas as a sputtering gas, to thus generate plasma and then sputtering the target according to the usual sputtering technique to thus form an adhesive layer on the side of the substrate.
After the substrate S was conveyed into the vacuum chamber 1 and the substrate S was placed on the substrate-mounting stage 6, it was heated to a temperature of 250° C. with the heater 5. Subsequently, the foregoing raw gas and the foregoing halogen gas were supplied to the gas chamber 7 through the gas-introducing system 9, at flow rates of 5 sccm and 5 sccm respectively, in such a manner that they were guided towards the surface of the substrate, through the hole 8.
After establishing a predetermined stable pressure within the vacuum chamber 1, a high frequency power source 4 was put into operation to thus make, output, a high frequency AC voltage having a frequency of 27.12 MHz and a power density of 0.2 W/cm2, so that the plasma of the raw gas and the halogen gas was generated between the electrode 3 and the surface of the substrate S. The radicals of these raw gas and halogen gas were generated within the plasma and a halogenation reaction was induced on the surface of the substrate S and this resulted in the formation of a film composed of a compound represented by the formula: TaNx(Hal)yRz. After the formation of the halogenated compound film having a desired film thickness, the high frequency power source 4 was switched off and the supply of the raw gas and the halogen gas was stopped.
Then the foregoing H atom-containing gas was introduced into the vacuum chamber 1 through the gas-introducing system 9, plasma was generated within the chamber according to the foregoing procedures, and the radicals generated within the plasma were incident upon the surface of the halogenated compound film formed according to the foregoing method to thus make them react with one another. This reaction permitted the breakage of Ta—N bonds present in the halogenated compound film, or the removal of N atoms and the removal of the R(R′) groups bonded to N atoms through the cleavage thereof. As a result, there was formed a tantalum nitride film rich in tantalum. After the formation of a tantalum nitride film having a desired film thickness, the high frequency power source 4 was switched off, the supply of the H atom-containing gas was interrupted and the substrate S was withdrawn from the vacuum chamber 1.
The composition of the barrier film thus prepared was analyzed and the following results were obtained: the compositional ratio: Ta/N: 1.9; the content of C: not more than 2%; and the content of N: 33%.
In this connection, the same procedures used above were repeated, by way of comparison, except for using a combination of the foregoing raw gas (MO gas) and a halogen gas (fluorine gas); or a combination of the foregoing raw gas and a reactant gas (H2: provided that the step for the irradiation of the H radicals derived from the reactant gas was carried out for 3, 5 and 10 seconds).
The specific resistance (resistivity) ρ (μΩ·cm) was calculated for each of the thin films prepared according to the foregoing methods. More specifically, the resistivity was obtained by measuring the sheet resistance (Rs) according to the four point probe method and determining the film thickness (T) by the SEM, followed by the substitution of these data in the following relation: ρ=Rs·T.
The film prepared by treating (halogenation) the raw gas (MO gas) with fluorine gas and then irradiating the halogenated product with a reactant gas (H radicals) for 10 seconds was found to have a resistivity value (450 μΩ·cm), lower than that (106 μΩ·cm) observed for the film prepared using MO gas and fluorine gas, that (3×105 μΩ·cm) observed for the film prepared using MO gas, fluorine gas and a reactant gas (irradiated with H radicals for 3 seconds) and that (about 4800 μΩ·cm) observed for the film prepared using MO gas, fluorine gas and a reactant gas (irradiated with H radicals for 5 seconds).
It would be concluded as follows: the foregoing results indicate that as the film obtained using MO gas and a halogen gas includes halogen atoms therein, the resulting film has a high resistivity value, and if the film is treated with H radicals, the resistivity value thereof varies depending on the length of the treating time and the longer the treating time, the lower the resistivity value of the resulting film. This result clearly indicates that if the treatment with H radicals is carried out for a time preferably not less than 10 seconds, halogen atoms and/or R,R′ groups and/or N atoms are effectively removed from the resulting tantalum nitride film.
As has been described above, it would be concluded as follows: the foregoing results indicate that, when forming a film using MO gas, a halogen gas and H atom-containing gas (radicals), part of the Ta—N—R(R′) bonds, or part of the N—R bonds, present in the raw gas molecules are broken by the action of the halogen and R is selectively removed, but the subsequent irradiation with the H radicals permits the breakage of the Ta—N bonds, N-halogen atom bonds and the remaining N—R(R′) bonds (R and R′ are an alkyl group) present in the halogenated Ta-containing compound, that the removal of these halogen atoms, N and C atoms leads to the reduction of the contents of C and N atoms in the resulting film and that, as a result, the resulting film is enriched with tantalum and the resistivity thereof is likewise reduced.
As has been described above, the substrate which has been provided thereon with the tantalum nitride film or the barrier layer having a desired thickness may, if necessary, further be treated by applying a voltage to a target, while using Ar gas as a sputtering gas, to thus generate plasma, then sputtering the target according to the usual sputtering technique to thus form a metal thin film or an adhesive layer on the side of an electrical connection-forming film serving as an underlying layer on the surface of the barrier film.
A Cu-electrical connection-forming film was applied, under the known process conditions, onto the substrate S provided thereon with the laminated film thus formed or on the adhesive layer on the side of the barrier film, if such an adhesive layer had been formed on the substrate. In this respect, it was confirmed that the adhesiveness between each neighboring films was excellent.
EXAMPLE 2
In this Example, tantalum particles were implanted into the tantalum nitride film prepared in Example 1 using a known sputtering device to thus form a tantalum nitride film richer in the tantalum content.
Ar gas as the sputtering gas was introduced into the sputtering device while inducing discharges through the application of an electric voltage through the voltage-applying device to generate plasma within the chamber and the target mainly comprising tantalum was then sputtered to thus implant tantalum particles as the sputtered particles in the thin film formed on the substrate S. The sputtering procedures were carried out under the following conditions: DC power: 5 kW; RF power: 600 W. In addition, the sputtering temperature was set at a level ranging from −30 to 150° C.
Thus, the implantation of the tantalum-containing particles into the thin film through the sputtering technique permitted a further increase in the content of tantalum in the barrier film to thus give a tantalum nitride film rich in tantalum and having a desired low resistance value. In this respect, the decomposition of the thin film was accelerated and impurities such as C and N were expelled from the barrier film by the impact of such tantalum particles on the surface of the substrate S and as a result, this resulted in the formation of a low resistant barrier film having a quite low content of impurities. The thin film thus formed was inspected for a variety of properties thereof and it was found that the ratio: Ta/N was 3.4 and the content of C was not more than 0.1% and that of N was 23%. In addition, the resulting thin film had a specific resistance value of 250 μΩ·cm.
After the formation of such a modified tantalum nitride film having a desired thickness according to the foregoing procedures, it is, if necessary, also possible that a sputtering gas such as Ar gas is introduced into the chamber and a voltage is applied to the target by the operation of the voltage-applying device to thus generate plasma and then the target is sputtered according to the known film-forming process conditions of the sputtering technique to thus form a metal thin film or an adhesive layer on the side of the electrical connection-forming film as an underlying layer on the surface of the barrier film.
A Cu-electrical connection-forming film was applied, under the known process conditions, onto the substrate S provided thereon with the laminated film thus formed according to the foregoing steps or on the adhesive layer on the side of the electrical connection-forming film. In this respect, it was confirmed that the adhesiveness between each neighboring films was excellent.
EXAMPLE 3
The same film-forming procedures used in Example 1 were repeated except that tert-amylimido-tris(dimethylamino) tantalum was substituted for the penta-dimethylamino-tantalum as the raw gas used in Example 1 to thus form a low-resistant tantalum nitride film rich in tantalum. The resulting film was inspected for a variety of properties thereof and it was found that the ratio: Ta/N was 1.8 and the content of C was 3% and that of N was 35.7%. In addition, the resulting thin film had a specific resistance value of 550 μΩ·cm.
EXAMPLE 4
A film-forming process was conducted according to that used in Example 1 except for using, as the halogen gas, chlorine, bromine or iodine gas in place of the fluorine gas used in Example 1. As a result, there were obtained the results identical to those obtained in Example 1.
INDUSTRIAL APPLICABILITY
The present invention permits the formation, according to the CVD technique, of a tantalum nitride film having a low resistance, whose contents of C and N atoms are low, which has a high compositional ratio: Ta/N, which can ensure sufficiently high adherence to a Cu film and which is thus useful as a barrier film. Accordingly, the present invention can be applied to the thin film-forming process in the field of the semiconductor device.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic block diagram for illustrating an embodiment of a film-forming apparatus used for practicing the film-forming method according to the present invention.
FIG. 2 is a schematic block diagram for illustrating a composite type electrical connection film-forming apparatus provided with a film-forming apparatus, incorporated into the same, used for carrying out the film-forming method according to the present invention.


DESCRIPTION OF SYMBOLS
1 . . . Vacuum chamber; 2 . . . Vacuum evacuation system; 3 . . . Electrode; 4 . . . High frequency power source; 5 . . . Heating means; 6 . . . Substrate-mounting stage; 7 . . . Gas chamber; 8 . . . Hole; 9 . . . Gas-introducing system; S . . . Substrate.

## Claims

1. A method for forming a tantalum nitride film comprising the steps, according to the CVD technique, of simultaneously introducing a raw gas consisting of a coordination compound constituted by an elemental tantalum (Ta) having a coordinated ligand represented by the general formula: N═(R, R′) (in the formula, R and R′ may be the same or different and each represents an alkyl group having 1 to 6 carbon atoms) and a halogen gas into a film-forming chamber to thus form, on a substrate, a film of a halogenated compound represented by the following general formula: TaNx(Hal)y(R, R′)z (in the formula, Hal represents a halogen atom), reacting the halogenated compound film with a hydrogen atom-containing gas by the introduction thereof into the chamber, to remove N atoms bonded to Ta atoms in the film through cleavage, to remove the halogen atoms and/or the R(R′) groups bonded to N atoms in the film through cleavage and to thus form a tantalum nitride film rich in tantalum atoms.

2. The method for forming a tantalum nitride film as set forth in claim 1, wherein the H atom-containing gas is converted into radicals thereof by the action of heat or plasma within the film-forming chamber and the resulting radicals are reacted with the halogenated compound film to thus form a tantalum nitride film rich in tantalum atoms.

3. The method for forming a tantalum nitride film as set forth in claim 1, wherein the raw gas is the gas of at least one coordination compound selected from the group consisting of penta-dimethylamino-tantalum, tert-amylimido-tris(dimethylamide) tantalum, penta-diethyl-amino-tantalum, tert-butylimido-tris(dimethylamide) tantalum, tert-butyl-imido-tris(ethyl-methylamide) tantalum, and Ta(N(CH3)2)3(N(CH2CH3)2)2.

4. The method for forming a tantalum nitride film as set forth in claim 1, wherein the halogen gas is at least one member selected from the group consisting of fluorine, chlorine, bromine and iodine gases.

5. The method for forming a tantalum nitride film as set forth in claim 1, wherein the hydrogen atom-containing gas is at least one gas selected from the group consisting of H2, NH3 and SiH4.

6. The method for forming a tantalum nitride film as set forth in claim 1, wherein the tantalum nitride film is one which satisfies the following requirement: the compositional ratio of tantalum to nitrogen: Ta/N≧2.0.

7. A method for forming a tantalum nitride film comprising the steps of forming a tantalum nitride film according to the method as set forth in claim 1; and then implanting tantalum particles into the resulting tantalum nitride film according to a sputtering technique which makes use of a target containing tantalum as a principal constituent.

8. The method for forming a tantalum nitride film as set forth in claim 7, wherein the sputtering step is carried out while controlling the DC power and the RF power in such a manner that the DC power is low and the RF power is high.

9. The method for forming a tantalum nitride film as set forth in claim 7, wherein the tantalum nitride film, in which the tantalum particles are implanted, is one which satisfies the following requirement: the compositional ratio of tantalum to nitrogen: Ta/N≧2.0.