JP3938450B2 - Barrier film manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the technical field of metal wiring for semiconductor devices, in particular, a barrier film provided between a copper wiring film and an insulating film, a film containing Si, GaAs, etc., and a metal wiring, The present invention relates to a manufacturing method of a barrier film to be prevented and a barrier film between a high dielectric film or a ferroelectric film and an electrode.
[0002]
[Prior art]
In recent years, semiconductor devices are increasingly required to operate at high speed. Therefore, low resistance copper wiring has been studied instead of aluminum wiring.
[0003]
However, copper is an impurity in a semiconductor crystal and has a problem that a diffusion coefficient in a silicon crystal or silicon oxide is large. For this reason, a high-melting-point metal nitride thin film such as a tungsten nitride thin film is used as a barrier film, a barrier film is formed on the surface of a silicon substrate or silicon oxide thin film, and then a copper wiring film is formed on the surface.
[0004]
In order to form the barrier film, a sputtering method, a thermal CVD method, or a PE-CVD method is used. In the sputtering method, a refractory metal is used as a target. In the thermal CVD method, the following reduction is performed. A nitride thin film is formed by the reaction. Equation (1) is for tungsten, and Equation (2) is for titanium.
4WF ₆ + 8NH ₃ → 2W ₂ N + 24HF + 3N ₂ (1)
TiCl ₄ + NH ₃ → TiN + 2HCl + 1 / 2H ₂ (2)
[0005]
When forming a semiconductor device with multilayer wiring, it is necessary to stack copper wiring with an interlayer insulating film in between. However, in semiconductor devices that require high-speed operation, the resistance value of the copper wiring is required to reduce signal transmission delay. In addition, it is necessary to reduce the capacitance value of the interlayer insulating film and the resistance value of the barrier film. Specifically, the barrier film is required to have a low resistance of 200 to 300 μΩcm.
[0006]
The sputtering method can form a low-resistance nitride thin film, but the step coverage is poor, and a barrier film cannot be uniformly formed in a high aspect ratio via hole.
[0007]
On the other hand, in the case of the thermal CVD method, a uniform barrier film can be formed in the via hole, but the low dielectric constant interlayer insulating film has a high dielectric constant when exposed to a high temperature of 500 ° C. or higher. The film formation temperature in the thermal CVD method has an upper limit of 400 ° C. to 500 ° C. At the film formation temperature, for example, in the case of a tungsten nitride thin film, the specific resistance becomes several thousand μΩcm, A low-resistance barrier film cannot be obtained.
[0008]
Even in the CVD method, an MOCVD method using an organic metal or a plasma CVD method can form a barrier film having a low resistance at a low temperature, but the organic metal is expensive, while the plasma CVD method has poor step coverage. There is a problem and it has not been adopted.
[0009]
[Problems to be solved by the invention]
The present invention was created to solve the above-described disadvantages of the prior art, and an object thereof is to provide a barrier film having a low specific resistance and good step coverage.
[0010]
[Means for Solving the Problems]
The inventors of the present invention have analyzed a refractory metal nitride thin film formed by a conventional thermal CVD method and found that the refractory metal atoms are insufficient. For example, in the case of tungsten, the conventional tungsten nitride does not have a stoichiometric composition (W ₂ N), but WxN (x is about 1.5 to 1.6). Such a shortage of metal atoms in the nitride is thought to be a cause of deterioration in crystallinity of the nitride thin film and an increase in resistance.
[0011]
The present invention was created based on the above findings, and in order to bring the composition of the nitride of the refractory metal close to the stoichiometric value, the invention according to claim 1 And a nitrogen-containing reducing gas having nitrogen atoms are introduced into a vacuum atmosphere, and the refractory metal nitride thin film is formed on the substrate placed in the vacuum atmosphere. Then, an auxiliary reducing gas having no nitrogen atoms is introduced into the vacuum atmosphere at a flow rate of 1 to 15 times the flow rate of the source gas to form a barrier film not containing silicon atoms. It is characterized by.
[0012]
The present invention is configured as described above, and introduces a source gas having a refractory metal atom and a nitrogen-containing reducing gas into a vacuum atmosphere, and reduces the source gas with the nitrogen-containing reducing gas to thereby nitride the refractory metal. When precipitating, an auxiliary reducing gas not containing nitrogen atoms is introduced into the vacuum atmosphere so that a high melting point metal is also precipitated.
Further, by introducing a gas having an oxygen atom in the structure such as a dilution gas and an oxygen gas together with the raw material gas, the barrier property is improved as compared with the case where the gas having an oxygen atom in the structure is not introduced. A nitride film having a lower resistance can be formed.
[0013]
When a refractory metal nitride is deposited at a low temperature, the refractory metal in the nitride thin film is insufficient, but the refractory metal atoms deposited with the auxiliary reducing gas supplement the shortage, so the resulting nitride The thin film has a stoichiometric composition or a composition ratio in which the content of the refractory metal is larger than the stoichiometric composition ratio.
[0014]
The amount of metal deposited may be smaller than the amount of nitride deposited, but the auxiliary reducing gas has a lower reactivity than the nitrogen-containing reducing gas, so it needs to be introduced more than the amount of precipitation. .
[0015]
On the other hand, if the introduction amount of the auxiliary reducing gas is too large, the content of the refractory metal becomes too large, and the characteristics of the refractory metal are closer to those of the nitride thin film. In addition, when an auxiliary reducing gas containing Si is used, there is a problem that the Si content in the nitride thin film increases. Accordingly, there is an appropriate range for the introduction amount of the nitrogen-containing reducing gas, the auxiliary reducing gas, the dilution gas, and the gas having oxygen atoms in the structure.
[0016]
For example, the introduction amount of ammonia gas (nitrogen-containing reducing gas) to tungsten hexafluoride gas (raw material gas) is set to 1.0, 2.6, and 5.0 times, and silane gas (auxiliary reducing gas) to ammonia gas. The amount of introduction was changed.
[0017]
The results are shown in the graph of FIG. The horizontal axis shows the amount of silane gas introduced when the amount of ammonia gas introduced is 1.0, and the vertical axis shows the specific resistance of the formed tungsten nitride thin film.
[0018]
From this graph, the introduction amount of the nitrogen-containing reducing gas is 1 or more times the introduction amount of the raw material gas, and the introduction amount of the auxiliary reducing gas is 2 to 10 times the introduction amount of the nitrogen-containing reducing gas. It can be seen that a range is desirable.
[0019]
Moreover, since the practical specific resistance of the barrier film is about 200 to 300 μΩ · cm, from this graph, the nitrogen-containing reducing gas is introduced in a flow rate range of 1 to 5 times the flow rate of the source gas, It can be seen that the auxiliary reducing gas is preferably introduced in a flow rate range of 2 to 5 times the flow rate of the nitrogen-containing reducing gas.
[0020]
FIG. 6 shows the content of elements contained in each refractory metal nitride when the flow rate ratio of the source gas and the auxiliary reducing gas is changed when forming the refractory metal nitride. Here, WF ₆ is used as the raw material gas, and SiH ₄ is used as the auxiliary reducing gas. Here, 1.5 sccm of oxygen gas is introduced.
[0021]
It can be seen from this graph that when the value of SiH ₄ / WF ₆ is 15 or more, Si is contained in the refractory metal nitride (WN here). Further, it is shown that a W _x N film is formed when the value of SiH ₄ / WF ₆ is 1 to 15 times.
[0022]
FIG. 7 is an Auger spectroscopic analysis result of a tungsten nitride thin film formed at a film forming temperature of 400 ° C. according to the present invention. The sputtering time on the horizontal axis indicates the depth from the surface. A lot of tungsten is contained (the tungsten atom is about 4.0 with respect to 1 nitrogen atom), and the effect of introducing the auxiliary reducing gas is understood.
Since the barrier film was oxidized when taken out into the atmosphere, oxygen was observed on the surface. Although silicon appears to be present in the film, it is below the measurement limit and is a measurement error.
[0023]
As described above, if the content of the refractory metal in the nitride thin film is made larger than the stoichiometric composition ratio in a range where the barrier property can be maintained, the specific resistance can be reduced.
In the CMP process, high adhesion between the nitride thin film and the substrate surface is required, but before forming the barrier film, plasma of one or more gases of argon gas, nitrogen gas, helium gas, or the plasma and plasma state When the substrate surface is cleaned with a plasma containing a mixture of hydrogen and nitrogen, the nitride thin film formed on the surface does not peel off even when a load of 1 kg per 1 cm ² is applied in the taping test, and adhesion that can be used in the CMP process is obtained. It is done.
[0024]
In addition, when silicon is contained in the nitride thin film, a refractory metal such as tungsten reacts with silicon at a high temperature to generate a silicon compound such as tungsten silicide, and the specific resistance increases. Since the nitride thin film of the present invention does not contain silicon, no silicon compound is generated and the specific resistance is stable at a small value.
[0025]
For comparison, FIG. 8 shows an Auger spectroscopic analysis result of a tungsten nitride thin film formed at a film forming temperature of 400 ° C. by a conventional CVD method. The number of tungsten atoms is about 1.7 with respect to nitrogen atom 1, and the number of tungsten atoms is small. The specific resistance is as high as 1000 μΩcm or more.
[0026]
The pressure range for forming the refractory metal nitride thin film is suitably 1 Pa to 10,000 Pa, more preferably 1 Pa to 100 Pa.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings.
FIGS. 1A to 1D are process diagrams showing an embodiment of the present invention.
Reference numeral 20 in FIG. 4 (a) indicates a substrate to be processed. The substrate 20 includes a semiconductor substrate 21 made of silicon single crystal, and a base film 22 and an insulating film 23 made of silicon oxide are formed on the surface of the substrate 20. A hole 31 is formed in the base film 22 and the insulating film 23 so that the surface of the semiconductor substrate 21 is exposed on the bottom surface 32.
[0028]
A barrier film is formed on the surface of the substrate 20.
Referring to FIG. 4, reference numeral 50 indicates a CVD apparatus in which the present invention can be implemented. The CVD apparatus 50 has a vacuum chamber 51, and a carry-in / out chamber (not shown) is connected to the vacuum chamber 51. A substrate holder 53 is disposed on the bottom surface side of the vacuum chamber 51, and an electrode 55 is disposed on the ceiling side.
[0029]
When the barrier film is formed on the substrate 20 by the CVD apparatus 50, first, the substrate 20 is loaded into the loading / unloading chamber, the inside of the loading / unloading chamber and the vacuum chamber 51 is set to a vacuum atmosphere, and then between the vacuum chamber 51 and the loading / unloading chamber. The gate valve 52 is opened, and the substrate 20 is carried into the CVD apparatus 50.
[0030]
The substrate holder 53 is provided with a substrate raising / lowering mechanism 54, and the substrate raising / lowering mechanism 54 is operated to place the substrate carried into the vacuum chamber 51 on the substrate holder 53. FIG. 4 shows the substrate in this state.
[0031]
Next, the heater in the substrate holder 53 is energized, and the substrate 20 is heated to a temperature of 300 ° C. or higher and 400 ° C. or lower.
[0032]
The vacuum chamber 51 is provided with a gas introduction system 57. Argon gas and ammonia gas are introduced from the gas introduction system 57 into the vacuum chamber 51 at a predetermined flow rate, and a high-frequency voltage is applied between the substrate holder 53 and the electrode 55. When applied, nitrogen and hydrogen in an ionized state are generated from ammonia gas. At this time, the ionized argon gas becomes a diluent gas, and a plasma in which they are mixed is formed.
[0033]
The insulating film 23 on the surface of the substrate 20 is disposed close to and opposed to the electrode 55, and the surface of the insulating film 23 and the surface of the semiconductor substrate 21 in the hole 31 are exposed to and adhered to the mixed plasma by the generated plasma. Organic matter is decomposed (cleaning).
[0034]
The cleaning conditions here were an ammonia gas flow rate of 75 sccm, an argon gas flow rate of 240 sccm, a pressure of 40 Pa, and a high-frequency power of 100 W. After cleaning for about 50 seconds, the application of the high frequency voltage is stopped and the plasma is extinguished. Although argon gas (Ar gas) is used here, nitrogen gas (N ₂ gas) or helium gas (He gas) may be used instead of argon gas, or a mixed gas thereof may be used. .
[0035]
Next, the ammonia gas flow rate and the argon gas flow rate are changed, and in addition to the ammonia gas and the argon gas, tungsten hexafluoride gas (WF ₆ gas), silane gas, and oxygen gas are introduced into the vacuum chamber 51 from the gas introduction system 57. .
[0036]
Since the reactivity of ammonia gas is higher than that of silane gas, tungsten hexafluoride gas becomes a source gas and ammonia gas becomes a nitrogen-containing reducing gas, and the reduction reaction of the source gas proceeds. Since the ammonia gas contains nitrogen, tungsten nitride is deposited on the surface of the insulating film 23 and the surface of the semiconductor substrate 21 in the hole 31 by the reduction reaction as expressed by the above formula (1).
[0037]
The silane gas introduced into the vacuum chamber 51 also has a reducing property. However, since the reactivity is lower than that of ammonia gas, it becomes an auxiliary reducing gas (auxiliary reducing gas). Further, since the silane gas has no nitrogen atom, the raw material gas is reduced by a reaction such as the following formula (3) to deposit metallic tungsten.
WF ₆ +3/2 SiH ₄ → W + 3/2 SiF ₄ + 3H ₂ (3)
[0038]
When metallic tungsten is deposited, it is taken into the growing tungsten nitride thin film. Therefore, since tungsten metal is supplied during the growth of the tungsten nitride thin film, the shortage of tungsten when growing at a low temperature is compensated, and the composition close to the stoichiometric composition or the stoichiometric composition ratio. In addition, a barrier film (tungsten nitride thin film) having a high content of refractory metal is formed.
[0039]
As an example of the growth conditions of the tungsten nitride thin film, the substrate temperature is 380 ° C., the source gas flow rate is 5 sccm, the nitrogen-containing reducing gas flow rate is 13 sccm, the auxiliary reducing gas flow rate is 39 sccm, the argon gas flow rate is 240 sccm, the oxygen gas introduction amount is 1.5 sccm, The pressure is 40 Pa.
[0040]
When the reduction reaction of the source gas with the nitrogen-containing reducing gas and the auxiliary reducing gas is performed for a predetermined time, a tungsten nitride thin film is formed on the surfaces of the insulating film 23 and the semiconductor substrate 21 as shown by reference numeral 24 in FIG. The
[0041]
Next, when the introduction of the nitrogen-containing reducing gas is stopped and the flow rate of the auxiliary reducing gas is increased, the raw material gas is reduced by the auxiliary reducing gas, and metallic tungsten is deposited. Reference numeral 25 in FIG. 1C denotes a metal tungsten thin film grown on the surface of the nitride thin film 24.
[0042]
As an example of the formation conditions of the metal tungsten thin film 25, the substrate temperature is 380 ° C., the source gas introduction amount is 20 sccm, the auxiliary reducing gas introduction amount is 5 sccm, the dilution gas (argon gas) introduction amount is 240 sccm, and the pressure is 40 Pa.
[0043]
The nitride thin film 24 has a high barrier property against copper, but has a higher specific resistance than a refractory metal. On the other hand, refractory metal thin films such as the metal tungsten thin film 25 have a lower specific resistance than the nitride thin film 24, although the barrier property against copper is low.
[0044]
Therefore, when the nitride thin film 24 is used as a barrier film and a refractory metal thin film is laminated thereon as described above, the specific resistance can be reduced while maintaining a high barrier property against copper.
Conversely, a nitride thin film may be formed on the refractory metal thin film, or a single nitride thin film may be formed.
[0045]
After the tungsten thin film 25 is grown for 20 to 30 seconds under the above conditions, the substrate 20 is taken out of the CVD apparatus 50, and a copper thin film is grown on the surface of the refractory metal thin film 25 by a plating method or a sputtering method. The code | symbol 26 of FIG.1 (d) has shown the copper thin film.
[0046]
After the copper thin film 26 is formed, the surface is polished by a CMP method, and the copper thin film 26, the nitride thin film 24, and the metal thin film 25 on the insulating film 23 are polished and removed. A film 27 is formed. A nitride thin film 24 exists between the wiring film 27 and the semiconductor substrate 21 and between the insulating film 23 so that copper does not diffuse.
[0047]
Next, as shown in FIG. 2 (f), two layers of base films 41 and 43 and insulating films 42 and 44 are alternately laminated, and the surface of the wiring film 27 is opened as shown in FIG. 2 (g). , Forming holes and grooves. Reference numeral 32 in FIG. 5G denotes a groove or a hole. The wiring film 27 is exposed at the bottom of the groove or hole 32.
Next, the substrate 20 is carried into the CVD apparatus 50, and a nitride thin film (tungsten nitride thin film) is formed under the same conditions as the nitride thin film 24 shown in FIG.
Reference numeral 33 in FIG. 2H denotes the nitride thin film, and the grooves or holes 32 and the surfaces of the insulating film 44 and the wiring film 27 are covered with the nitride thin film 33.
[0048]
Next, when the copper thin film 34 is grown by plating or sputtering, as shown in FIG. 3I, the groove or hole 32 is filled with the copper thin film 34.
[0049]
Finally, when the surface is polished by the CMP method, a wiring film 35 is formed by the copper thin film 34 filled in the groove or hole 32 as shown in FIG.
Since the barrier film 33 is disposed between the wiring film 35 and the insulating films 42 and 44, copper does not diffuse into the insulating films 42 and 44.
[0050]
The above describes the case of forming a tungsten nitride thin film using tungsten as the refractory metal, ammonia gas as the nitrogen-containing reducing gas, and silane gas as the auxiliary reducing gas. W (CO) ₆ gas can be used.
[0051]
Further, the present invention includes a case where a refractory metal other than tungsten is used and the nitride thin film is formed as a barrier film. When titanium (Ti) is used as the refractory metal, a titanium halide gas such as TiF ₄ or TiCl ₄ can be used as a raw material gas. When tantalum (Ta) is used as the refractory metal, a tantalum halide gas such as TaCl ₅ can be used as a source gas. Also, Mo or Nb halides can be used as the source gas.
[0052]
As the nitrogen-containing reducing gas having a nitrogen atom, N ₂ H ₄ gas, NF ₃ gas, N ₂ O gas or the like can be used in addition to NH ₃ gas.
[0053]
As the auxiliary reducing gas having no nitrogen atom, H ₂ gas, Si ₂ H ₆ gas, PH ₃ gas, B ₂ H ₆ gas, etc. can be used in addition to SiH ₄ gas.
Moreover, argon gas, nitrogen gas, helium gas, and those mixed gas can also be used as dilution gas.
[0054]
The above-described cleaning condition is an example and can be performed under other conditions. As an example, the same effect was obtained even when the argon gas flow rate was 100 sccm, the pressure was 1.0 Pa, the high frequency power was 150 W, and the cleaning time was 60 seconds.
Further, after cleaning is performed under these conditions, ammonia gas may be further added to the argon gas for cleaning.
[0055]
【The invention's effect】
By the CVD method, a low specific resistance barrier film (nitride thin film of a refractory metal) can be formed at a temperature of 500 ° C. or lower, particularly 350 ° C. to 450 ° C. Therefore, the interlayer insulating film is not damaged.
Further, since the nitride thin film is formed by the thermal CVD method, the step coverage is good.
[Brief description of the drawings]
FIG. 1 (a) to (e): the first half of a process diagram for explaining the method of the present invention. FIG. FIG. 3 (i) to (j): Second half of the process diagram for explaining the method of the present invention. FIG. 4 shows an example of a CVD apparatus capable of carrying out the method of the present invention. and resistivity of the thin film, the element according to the raw material gas, a nitrogen-containing reducing gas, and SiH ₄ / WF ₆ flow rate ratio of the tungsten nitride films formed by the graph 6 present process showing the relationship between the flow rate of the auxiliary reductive gas FIG. 7 is a graph showing the composition in the depth direction of tungsten nitride formed by the method of the present invention. FIG. 8 is a graph showing the composition in the depth direction of the conventional tungsten nitride. Explanation of]
20 ... Substrate 24, 33 ... Nitride thin film (barrier film) 25 ... Metal thin film 27, 35 ... Wiring film

Claims (1)

A raw material gas having a refractory metal in the chemical structure and a nitrogen-containing reducing gas having a nitrogen atom are introduced into a vacuum atmosphere, and a nitride thin film of the refractory metal is formed on the substrate placed in the vacuum atmosphere. A method for producing a barrier film comprising:
An auxiliary reducing gas having no nitrogen atoms is introduced into the vacuum atmosphere at a flow rate of 1 to 15 times the flow rate of the source gas to form a barrier film not containing silicon atoms. A barrier film manufacturing method.

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