JPH11233501A - Plasma film formation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a CF film which has a high thermal stability and less F gas elimination, by making a film forming gas containing C4 F8 gas and acetylene gas in plasma state, and forming a fluorine added carbon film on a substrate to be processed. SOLUTION: Ar gas is introduced into a first vacuum chamber 21 from a gas nozzle 31. From gas introducing pipes 51 and 52, C4 F8 gas and acetylene gas (C2 H2 ) are respectively introduced into a second vacuum chamber 22 through a film forming gas supply part 5. Then, Ar gas is activated and concentrated by electron cyclotron resonance caused by interaction between a magnetic field generated by a major electromagnetic coil 26 and an auxiliary electromagnetic coil 27 and microwaves from a high frequency power supply part 24. Then, C4 F8 gas and C2 H2 gas are activated (made into plasma) by the generated plasma flow, an activation seed (plasma) is formed, and a CF film having strong bond and high thermal stability is formed on a semiconductor wafer 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a fluorine-containing carbon film having high thermal stability which can be used, for example, as an interlayer insulating film of a semiconductor device.

[0002]

2. Description of the Related Art In order to increase the degree of integration of semiconductor devices, techniques such as miniaturization of patterns and multi-layering of circuits have been devised. One of them is a technique of multi-layer wiring. In order to form a multilayer wiring structure, a conductive layer is connected between the nth wiring layer and the (n + 1) th wiring layer, and a thin film called an interlayer insulating film is formed in a region other than the conductive layer.

A typical example of this interlayer insulating film is Si
Although there is an O ₂ film, it has been required in recent years to lower the relative dielectric constant of the interlayer insulating film in order to further increase the operation speed of the device, and the material of the interlayer insulating film has been studied. . That is, the SiO ₂ film has a relative dielectric constant of about 4, and efforts are being made to excavate materials smaller than this. One of them is S having a relative dielectric constant of 3.5.
While the realization of iOF films has been promoted, the present inventor has proposed a fluorine-added carbon film (hereinafter referred to as “CF
Film)). When forming the CF film, for example, thermal CVD (Chemical Vapor)
(Deposition) or plasma CVD is used.

Accordingly, the present inventor has used a plasma apparatus which generates plasma by electron cyclotron resonance, and uses, for example, a gas containing a compound gas of carbon (C) and fluorine (F) and a hydrocarbon gas as a film forming gas. In order to realize a CF film having a high adhesion and a high hardness, the process conditions described above were reduced.

[0005]

However, the CF film still has the following problems. FIG. 6 shows a part of a circuit portion formed on the wafer.
3, 14 are conductive layers made of W (tungsten), 15 is a conductive layer made of Al (aluminum), 16 is P, B
Is an SiO ₂ film, and 17 is an n-type semiconductor region. The process temperature for forming the W layer 13 is 400 to 450 ° C., and at this time, the CF films 11 and 12 are heated to the process temperature. However, when the CF film is heated to such a high temperature, a part of the CF bond is broken, and mainly the F-based gas is desorbed. Examples of the F-based gas include F, CF, CF _{2 and the} like.

[0006] When the F-based gas is desorbed in this manner, the following problem occurs. a) Corrosion of metal wiring such as aluminum and tungsten. b) The insulating film also has a function of pressing down the aluminum wiring to prevent swelling of the aluminum, but the degassing weakens the pressing by the insulating film, resulting in swelling of the aluminum wiring and an electrical defect called electromigration. Is more likely to occur. c) Cracks are formed in the insulating film, and the insulation between the wirings is deteriorated. If the degree is large, the next wiring layer cannot be formed. d) The relative permittivity rises when there is much F loss.

The present invention has been made under such circumstances, and has as its object to form an insulating film made of a CF film having a strong bond and high thermal stability, for example, an interlayer insulating film of a semiconductor device. It is to provide a method that can do this.

[0008]

Means for Solving the Problems] The plasma film forming method of the for the invention, C ₄ F ₈ into plasma the deposition gas containing a gas and acetylene gas, fluoridation mosquitoes on a substrate to be processed by the plasma - It is characterized in that a bon film is formed. At this time, it is preferable that the flow rate ratio between the C ₄ F ₈ gas and the acetylene gas is 4/7 ≦ C ₄ F ₈ gas / acetylene gas ≦ 1.

In the present invention, C ₄ F ₈ gas, acetylene gas and hydrogen gas are used as the film forming gas, and the flow rate ratio between C ₄ F ₈ gas and acetylene gas is 0.7 ≦ C ₄ F ₈ gas. / Acetylene gas ≦ 4/3, and the flow ratio of a mixed gas of C ₄ F ₈ gas and acetylene gas to hydrogen gas is 1
≦ the mixed gas / hydrogen gas ≦ 3.

[0010]

FIG. 1 shows an example of a plasma processing apparatus used in an embodiment of the present invention. This apparatus has a vacuum vessel 2 made of, for example, aluminum or the like. This vacuum vessel 2 is located above and communicates with a first cylindrical vacuum chamber 21 for generating plasma below the first vacuum chamber 21. The first vacuum chamber 21 is connected to a second vacuum chamber 22 having a larger diameter than the first vacuum chamber 21. The vacuum vessel 2 is grounded and has a zero potential.

An upper end of the vacuum vessel 2 is opened, and a transparent window 23 made of a material such as quartz, which transmits microwaves, is provided in this portion in an airtight manner. Is to be maintained. Outside the transmission window 23, a waveguide 25 connected to a high-frequency power supply unit 24 for generating a microwave of 2.45 GHz, for example.
The microwave generated by the high-frequency power supply unit 24 is guided by the waveguide 25 in, for example, the TE mode, or the microwave guided by the TE mode is transmitted by the waveguide 25 in the TM mode. To the first window through the transmission window 23.
Can be introduced into the vacuum chamber 21.

A gas nozzle 31 is provided on a side wall of the first vacuum chamber 21, for example, which is uniformly arranged along a circumferential direction of the first vacuum chamber 21, and a plasma generating gas source such as an Ar gas source (not shown) is provided on the gas nozzle 31. It is connected so that Ar gas can be evenly and uniformly supplied to the upper part in the first vacuum chamber 21.

A mounting table 4 for a semiconductor wafer (hereinafter, referred to as “wafer”) 10 is provided in the second vacuum chamber 22 so as to face the first vacuum chamber 21. The mounting table 4 is provided with an electrostatic chuck 41 on the surface thereof. The electrode of the electrostatic chuck 41 has a DC power supply (not shown) for attracting a wafer and a bias voltage for drawing ions into the wafer. The high frequency power supply unit 42 is connected so as to apply the voltage.

On the other hand, the upper part of the second vacuum chamber 22, that is, the first
A ring-shaped film-forming gas supply unit 5 is provided in a portion that communicates with the vacuum chamber 21.
For example, two kinds of film forming gases are supplied from, for example, gas supply pipes 51 and 52, and the mixed gas is supplied to a gas hole 53 on the inner peripheral surface.
Is supplied to the inside of the vacuum container 2.

A ring-shaped main electromagnetic coil 26, for example, is disposed as a magnetic field forming means close to the outer periphery of the side wall which partitions the first vacuum chamber 21 and is disposed below the second vacuum chamber 22. On the side is a ring-shaped auxiliary electromagnetic coil 27
Is arranged. Exhaust pipes 28 are respectively connected to the bottom of the second vacuum chamber 22 at, for example, two positions symmetric with respect to the central axis of the vacuum chamber 22.

Next, a method for forming an interlayer insulating film made of a CF film on the wafer 10 to be processed by using the above-described apparatus will be described. First, a gate valve (not shown) provided on the side wall of the vacuum vessel 2 is opened, and a wafer 10 having, for example, aluminum wiring formed on its surface is loaded from a load lock chamber (not shown) by a transfer arm (not shown) and placed on the mounting table 4. Then, the wafer 10 is electrostatically attracted by the electrostatic chuck 41. Subsequently, after closing the gate valve to seal the inside, the internal atmosphere is evacuated from the exhaust pipe 28 and evacuated to a predetermined degree of vacuum.
Ar gas is introduced into the first vacuum chamber 22 at a predetermined flow rate, and a film forming gas is introduced from the film forming gas supply unit 5 into the second vacuum chamber 22 at a predetermined flow rate.

Here, the present embodiment is characterized by a film forming gas, and the film forming gas is a gas containing C and F as a gas containing C and F.
₄ F ₈ gas, acetylene gas as the hydrocarbon gas (C ₂
H ₂ gas) is used, and these gases are supplied from the gas introduction pipes 51 and 52 through the film forming gas supply unit 5 into the vacuum vessel. Then, the inside of the vacuum vessel 2 is maintained at a predetermined process pressure, and the high-frequency power supply unit 42 applies 13.
A bias voltage of 56 MHz and 1500 W is applied.

On the other hand, 2.45 GH from the high frequency power supply 24
z, 2000 W high frequency (microwave)
Through to the ceiling of the vacuum vessel 2 where the transmission window 23
And is introduced into the first vacuum chamber 21. In the vacuum vessel 2, a main electromagnetic coil 26 and an auxiliary electromagnetic coil 27 are provided.
As a result, a magnetic field from the upper part of the first vacuum chamber 21 to the lower part of the second vacuum chamber 22 is formed.
The magnetic field strength becomes 875 gauss near the lower part of.

Thus, the interaction between the magnetic field and the microwave causes electron cyclotron resonance.
The r gas is converted into plasma and the density is increased. The generated plasma flow is transmitted from the first vacuum chamber 21 to the second vacuum chamber 2.
C ₂ F ₈ which flows into 2 and is supplied here.
The gas and C ₂ H ₂ gas are activated (plasma) to form active species (plasma), and a CF film is formed on the wafer 10. When an actual device is manufactured, the CF film is thereafter etched in a predetermined pattern.
For example, a W film is buried in the groove to form a W wiring.

The CF film formed by such a method has a strong bond and high thermal stability. That is, even if the temperature becomes high, the escape of the F-based gas is small. Here, an experimental example performed to examine the thermal stability of the CF film formed by the above-described method will be described. Using the plasma processing apparatus shown in FIG. 1, an Ar gas of 30 sccm and a C ₄ F ₈ gas of 40 sc
cm ₂ , C ₂ H ₂ gas is introduced at a flow rate of 30 sccm to form a CF film on the wafer 10, and a change in weight of the formed CF film at a high temperature, for example, 425 ° C. is measured at 425 ° C. in an N ₂ gas atmosphere. The temperature was maintained for 2 hours and checked by an electronic balance. This weight change is an index of the thermal stability of the thin film, and the smaller the value of the weight change, the less the F-based gas escapes and the higher the thermal stability. The microwave power and the bias power were 2000 W and 1500 W, respectively.

As a comparative example, the change in weight was measured in the same manner when a CF film was formed by introducing C ₂ H ₄ gas as a hydrocarbon gas at a flow rate of 30 sccm instead of C ₂ H ₂ gas. At this time, the conditions for forming the CF film were all the same as in the above-described embodiment.

As a result, the change in weight of the CF film is C ₂ H ₂
When gas is used, it is 2.68%, whereas C ₂ H
_{When 4} gases are used, it is 4.3%, so C ₄ F
It was recognized that the change in the weight of the CF film was reduced by the combination of the ₈ gas and the C ₂ H ₂ gas, the release of the F-based gas was reduced, and the thermal stability was increased.

The reason is presumed as follows. In other words, the C ₂ H ₂ gas has a triple bond between carbon and carbon, and when plasma is formed, decomposition products such as a triple bond, a double bond, and a single bond are generated as shown in FIG. These combine with the decomposition products of C ₄ F ₈ to form a steric structure having triple bonds and double bonds. On the other hand, since C ₂ H ₄ gas is a gas having a double bond, decomposition products of C ₂ H ₄ and C ₄ F ₈ combine to form a three-dimensional structure having a double bond. The bonding force increases as the number of single bonds, double bonds, and triple bonds increases, and it is difficult to cause thermal disconnection and degassing from the CF film. Therefore, it is presumed that the CF film generated by using C ₂ H ₂ gas having double bonds and triple bonds has good thermal stability. Further, H separated from the C ₂ H ₂ gas is combined with F weakly bound in the film to generate HF gas, which is desorbed from the CF film. Since F which is weakly bound in the film is easily desorbed by heat, it is presumed that removal of such F also improves thermal stability.

Subsequently, the present inventors succeeded in developing C ₄ F ₈ gas and C ₂ H
_The following experiment was conducted in order to optimize the flow ratio with the _two gases. Using the plasma processing apparatus shown in FIG. 1, Ar gas was introduced at a flow rate of 30 sccm, C ₄ F ₈ gas was introduced at a flow rate of 40 sccm, and C ₂ H ₂ gas was introduced at a flow rate of 30 sccm to 70 sccm.
The CF film was formed on the wafer 10 by changing the flow rate in the range of m, and the weight change of the formed CF film was examined by the above-described method. At this time, the microwave power and the bias power were set to 2000 W and 1500 W, respectively.

[0025] While results are shown in FIG. 3, thereby C ₂
When the flow rate of the H ₂ gas is 35 sccm or less, the weight change of the CF film is about 2.7%, whereas when the flow rate of the C ₂ H ₂ gas is 40 sccm or more, the weight change is 1.7%.
It was recognized that it became small in the vicinity. Where C ₂
When the flow rate of the H ₂ gas exceeds 75 sccm, film peeling occurs.

Thus, there is an optimum condition for the flow ratio of the C ₄ F ₈ gas and the C ₂ H ₂ gas. When the flow rate of the C ₄ F ₈ gas is 40 sccm, the flow rate of the C ₂ H ₂ gas is 40 s.
ccm to 70 sccm is preferable, that is, 40 sccm / 70 sccm ≦ C ₄ F ₈ gas / C ₂ H
₂ gas ≦ 40sccm / 40sccm (4/7 ≦ C ₄ F
_{When 8} gas / C ₂ H ₂ gas ≦ 1), it was confirmed that the change in weight of the CF film was small, the escape of the F-based gas was reduced, and the thermal stability was increased.

[0027] For this reason, when the flow rate ratio is C ₄ F ₈ gas / C ₂ H ₂ gas ≧ 1, C ₂ H ₂ in the film forming gas
It is considered that the amount of gas is reduced, so that it is difficult to form the three-dimensional structure, thereby reducing the ratio of strong C—F bonds in the CF film.

Next, another example of the present invention will be described. This example is characterized in that C ₄ F ₈ gas, C ₂ H ₂ gas and H ₂ gas are used as a film forming gas. Even with the use of a combination of film forming gases, the thermal stability of the CF film can be improved. These film forming gases are introduced via the film forming gas supply unit 5 in the above-described plasma processing apparatus.

An experimental example will now be described to confirm the effect of this method. Using the plasma processing apparatus shown in FIG. 1, 30 sccm of Ar gas and 40 s of C ₄ F ₈ gas were used.
ccm, C ₂ H ₂ gas at 30 sccm, H ₂ gas at 25 sccm
A CF film was formed on the wafer 10 at a flow rate of sccm, and a change in weight of the formed CF film was examined by the above-described method. At this time, the microwave power and the bias power were set to 2000 W and 1500 W, respectively.

As a result, the change in weight of the CF film was 1.89%, and the change in weight when the CF film was formed using a combination of C ₄ F ₈ gas and C ₂ H ₄ gas as in the above-described comparative example ( 4.3%), C ₄ F ₈ gas, C
It was recognized that the combination of ₂ H ₂ gas and H ₂ gas reduced the change in weight of the CF film, reduced the escape of the F-based gas, and increased the thermal stability.

Subsequently, the present inventors carried out C ₄ F by the following method.
_An attempt was made to optimize the flow ratio of _eight gases, C ₂ H ₂ gas, and H ₂ gas. First, the following experiment was conducted in order to optimize the flow ratio of a mixed gas of C ₄ F ₈ gas and C ₂ H ₂ gas (hereinafter referred to as “mixed gas”) and H ₂ gas.

Using the plasma processing apparatus shown in FIG.
While introducing a gas at 30sccm flow rate, set the flow rate ratio of the mixed gas to C ₄ F ₈ gas / C ₂ H ₂ gas = 4/6, and the total amount of the mixed gas and H ₂ gas as 100 sccm, H ₂ A gas is introduced at a varied flow rate in the range of 10 sccm to 60 sccm to form a CF film on the wafer 10,
The weight change of the formed CF film was examined by the method described above. At this time, the microwave power and the bias power are 20
00W and 1500W.

FIG. 4 shows the results. The change in the weight of the CF film is about 2.8% when the flow rate of the H ₂ gas is 20 sccm or less, while the flow rate of the H ₂ gas is 25 s.
At ccm to 50 sccm, it was found to be around 1.7% and smaller. When the flow rate of H ₂ gas is 5
If it exceeds 5 sccm, film peeling occurs.

As a result, there is an optimum condition for the flow ratio of the mixed gas and the H ₂ gas.
When indicated by ₂ gas, the lower limit of the mixed gas / H ₂ gas is 50 sccm / 50 sccm, the upper limit value of the mixed gas / H ₂ gas is 75 sccm / 25 sccm,
That is, it was confirmed that 1 ≦ mixed gas / H ₂ gas ≦ 3.

Next, the following experiment was conducted to optimize the mixing ratio of the mixed gas. Ar gas was introduced at a flow rate of 30 sccm and H ₂ gas was introduced at a flow rate of 30 sccm using the plasma processing apparatus shown in FIG. 1, and the mixed gas was mixed at a mixing ratio of 0.6 ≦ C ₄ F ₈ gas / C ₂ H ₂ gas ≦ 1.6, a CF film is formed on the wafer 10 by changing and introducing the same.
The weight change of the formed CF film was examined by the method described above. At this time, the microwave power and the bias power are 20
00W and 1500W.

FIG. 5 shows the results. The change in the weight of the CF film was 2.9% or more when the mixture ratio was greater than 1.4, whereas the change in the CF film was 0.7 to 4/3 when the mixture ratio was 0.7 to 4/3. In this case, it was recognized that the density was as small as about 1.7% to 2%. If the mixing ratio is smaller than 0.65, film peeling occurs. As a result, there is an optimum condition for the mixing ratio of the mixed gas, and the optimum value of the mixing ratio is 0.7 ≦ C ₄ F ₈ gas / C ₂ H.
It was confirmed that ₂ gas ≦ 4/3.

According to these experiments, C ₄ was used as a film forming gas.
When F ₈ gas, C ₂ H ₂ gas and H ₂ gas are used, the optimal flow ratio of these gases is 0.7 ≦ C ₄ F ₈
Gas / C ₂ H ₂ gas ≦ 4/3, and 1 ≦ mixed gas / H ₂ gas ≦ 3, it was recognized that such a flow ratio reduced the weight change of the CF film, It was confirmed that the release of the F-based gas was reduced and the thermal stability was increased.

As a film forming gas, C ₄ F ₈ gas and C ₂ H
_{When two} gases are used, the optimal flow rate ratio is 4/7 ≦ C
Where ₄ F ₈ gas / C ₂ H ₂ gas ≦ 1, when H ₂ gas is added to these gases, the upper limit of the optimal flow rate ratio is 4/3 and the upper limit is high. Becoming C
It was confirmed that the lower limit flow rate of ₂ H ₂ gas was reduced.

The reason for this is that when H ₂ gas is mixed, H generated by the plasma of H ₂ gas is combined with F which is weakly bonded in the film to generate HF gas, and C
Desorbs from F film. Since F which is weakly bound in the film is easily desorbed by heat, it is presumed that removing such F improves thermal stability. Therefore, when H ₂ is mixed, the lower limit flow rate of C ₂ H ₂ is reduced.

In the above, in the present invention, the plasma is ECR
Is not limited to generating plasma by
P (Inductive Coupled Plasu)
The method can also be applied to a case where plasma is generated by a method called ma) that applies an electric field and a magnetic field to a processing gas from a coil wound around a dome-shaped container. Further, for example, 13.56 which is called a helicon wave plasma or the like.
When a plasma is generated by the interaction between a helicon wave of MHz and a magnetic field applied by a magnetic coil, or two parallel cathode-rays called a magnetron plasma or the like are used.
When generating a plasma by applying a magnetic field so as to be almost parallel to the electrode, also apply when generating a plasma by applying high-frequency power between electrodes facing each other called a parallel plate etc. Can be.

[0041]

As described above, according to the present invention, it is possible to obtain a CF film having high thermal stability and small desorption of F-based gas. Therefore, if this CF film is used, for example, as an interlayer insulating film of a semiconductor device, there is no possibility of corroding metal wiring, and undulation and cracking of aluminum wiring can be prevented. With the demand for miniaturization and high-speed of semiconductor devices, the CF film is attracting attention as an effective insulating film having a small relative dielectric constant. Therefore, the present invention aims at practical use of the CF film as an insulating film. This is an effective method.

[Brief description of the drawings]

FIG. 1 is a vertical sectional side view showing an example of a plasma processing apparatus for carrying out a method of the present invention.

FIG. 2 is a schematic diagram for explaining the operation of the method of the present invention.

FIG. 3 is a characteristic diagram showing a relationship between a flow rate ratio of C ₄ F ₈ gas and C ₂ H ₂ gas and a change in weight.

FIG. 4 shows a mixed gas of C ₄ F ₈ gas and C ₂ H ₂ gas and H
FIG. 4 is a characteristic diagram showing a relationship between a flow rate ratio of _two gases and a change in weight.

FIG. 5 shows C ₄ F ₈ when the flow rate of H ₂ gas is constant.
FIG. 3 is a characteristic diagram showing a relationship between a flow rate ratio of gas and C ₂ H ₂ gas and a change in weight.

FIG. 6 is a structural diagram showing an example of the structure of a semiconductor device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Semiconductor wafer 2 Vacuum container 21 1st vacuum chamber 22 2nd vacuum chamber 24 High frequency power supply part 25 Waveguide 26, 27 Electromagnetic coil 28 Exhaust pipe 31 Gas nozzle 4 Mounting table 5 Deposition gas supply part

Claims (3)

[Claims] 1. A plasma film forming method comprising forming a film forming gas containing a C ₄ F ₈ gas and an acetylene gas into plasma, and forming a fluorine-added carbon film on a substrate to be processed by the plasma. . 2. The film forming method according to claim 1, wherein the flow rate ratio of the C ₄ F ₈ gas to the acetylene gas is 4/7 ≦ C ₄ F ₈ gas / acetylene gas ≦ 1. 3. A plasma film forming method for forming a film forming gas containing a C ₄ F ₈ gas, an acetylene gas and a hydrogen gas into plasma and forming a fluorine-added carbon film on a substrate to be processed by the plasma. The flow ratio of C ₄ F ₈ gas to acetylene gas is 0.7 ≦ C ₄ F ₈ gas / acetylene gas ≦ 4/3, and a mixed gas of C ₄ F ₈ gas and acetylene gas, hydrogen gas and A flow rate ratio of 1 ≦ the mixed gas / hydrogen gas ≦ 3.