JP3218534B2 - Method of forming insulating film - Google Patents

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 an insulating film, and more particularly to a method for forming an insulating film having a low dielectric constant used as an interlayer insulating film in a highly integrated semiconductor integrated circuit device.

[0002]

2. Description of the Related Art In recent years, interlayer insulating films used for multilayer wiring have been reviewed from the viewpoint of high integration or high speed of semiconductor integrated circuit devices. In particular, the SiO ₂ film has been widely used as an interlayer insulating film of a semiconductor integrated circuit device from the viewpoints of stability and easiness of film formation, but the parasitic capacitance has increased with the progress of miniaturization in recent years. Is in question.

Conventionally, when forming an interlayer insulating film and the like, a low-temperature film forming method has been used in consideration of the influence on an aluminum wiring layer and the like. For example, tetraethylorthosilicate (TEOS: Tetra-Ethyl-Ortho-S) is used.
ilicate), that is, SiO by plasma enhanced chemical vapor deposition (PCVD) using (C ₂ H ₅ O) ₄ Si
_A method for forming _two films has been proposed (see JP-A-6-240559 and JP-A-6-140386).

[0004] Of the above, an SiO ₂ film is used in a manufacturing process of a polysilicon thin film transistor (poly-SiTFT) used for a viewfinder, a CCD, a liquid crystal projector, or the like, which is required to have a large area exceeding 300 mm. In the formation, the volume flow ratio of O ₂ or a mixed gas of O ₂ and He to TEOS is set to be 50 times or more. By selecting such a flow ratio, the center of the large-area substrate can be formed in the film formation process. Even in the portion, impurities are quickly removed from the substrate surface without staying, and uniform film quality can be obtained.

However, when such a method of depositing an SiO ₂ film is used as a method of depositing an interlayer insulating film of a monolithic semiconductor integrated circuit device such as a memory or a logic, the coverage of the interlayer insulating film due to a wiring step is reduced. Is not applicable in practice.

[0006] Further, in the latter case of the above-mentioned prior art (Japanese Unexamined Patent Publication No.
JP) is 140,386, aims to reduce the moisture cause characteristic deterioration of the element, the flow rate of O ₂ with respect to 330cc / min flow rate of TEOS 730Cc / min, i.e., the volumetric flow ratio of O ₂ to TEOS Is approximately 2.2 times.

However, since the SiO ₂ film formed by the PCVD method has a high dielectric constant of about 4.1, the parasitic capacitance between the wiring layers is relatively large, and as the miniaturization progresses, the interval between the wiring layers becomes narrower. The parasitic capacitance further increases, and the parasitic capacitance causes a signal propagation delay. Therefore, there is a problem that the operation speed is not improved even if the elements are miniaturized.

In order to solve such a problem, a material having a small dielectric constant may be used as the interlayer insulating film. As the dielectric constant decreases, the parasitic capacitance decreases and the signal propagation delay also decreases.

In recent years, as a method for obtaining an insulation film having such a low dielectric constant, when forming the SiO ₂ film by a PCVD method, SiO ₂ containing fluorine by adding a gas containing fluorine atoms in the raw material gas Film, ie SiOF
It has been reported that a film is formed (Fukada, Akahori, Ex
tended Abstracts of the19
93 International Conferen
ce on Solid State Devices
and Materials, Makuhari, 1
993, pp. 158-160, Usami, Shimokawa, Yoshimura,
Id., Pp. 161-163, and Mizuno, Hara et al. 510-512 see), the SiOF film in dielectric constant is less than 4.1 of the conventional SiO _2, it has attracted attention as an interlayer insulating film for next-generation semiconductor integrated circuit device.

[0010] However, the SiOF film in this case is also made of PCV.
Similar to the SiO ₂ film obtained by the method D, the SiOF film has a high hygroscopicity, and has a disadvantage that the dielectric constant is unstable and the dielectric constant increases with time even if a low dielectric constant SiOF film is obtained first. That is, since the dielectric constant of water itself is very large at 80,
Hygroscopicity causes an increase in the dielectric constant.

[0011] Such absorption of moisture by the PCVD film not only results in an increase in the dielectric constant but also adversely affects the semiconductor device itself, and thus has a problem that the reliability of the semiconductor device is reduced. .

Therefore, the present inventors have proposed a low frequency (250 k
Hz) and a high frequency (13.56 MHz), and using tetraethyl orthosilicate (TEOS: Tetra-Ethyl-Orth) as a source gas.
o-Silicate), oxygen and C ₂ F ₆ when forming a SiOF film, it is proposed to optimize the applied amount of low frequency power and control the moisture absorption of the SiOF film by the PCVD method. (Japanese Patent Application No. 6-45920).

[0013]

However, when a two-frequency power supply is used, depending on the type of the semiconductor device, a low-frequency voltage is applied to the transistor which is formed in the semiconductor substrate before the formation of the interlayer insulating film. This method was not always the best method because it may cause deterioration of characteristics.

Accordingly, it is an object of the present invention to provide a PCVD-SiOF film having a low dielectric constant and having characteristics stable over time without applying a low frequency which affects the transistor characteristics.

[0015]

SUMMARY OF THE INVENTION The present invention provides a plasma chemistry
In the method for forming an insulating film using a vapor phase growth method, the insulating film
Tetraethylorthosilicate as a source gas for forming
Salt, oxygen and C _TwoF₆And using tetra
Oxygen gas volume flow to chill ortho silicate gas
The ratio is 20 to 40 times.

Further, the present invention is tetraethyl orthosilicate, oxygen, and, in the raw material gas consisting of C ₂ F _6, C ₂ F against tetraethylorthosilicate gas
₆ is characterized in that the volume flow ratio is 5 to 7 times.

[0017]

In the method of forming an insulating film using plasma enhanced chemical vapor deposition, tetraethylorthosilicate, oxygen,
And a low-permittivity PCVD-SiOF film having stable characteristics over time by increasing the volume flow ratio of oxygen gas to tetraethyl orthosilicate gas in the source gas of C ₂ F ₆ by 20 to 40 times. Can be obtained.

The lower limit of the volume flow ratio of 20 times is determined by the stability of the change with time. If the ratio is less than 20 times, the change with time increases and the dielectric constant at the time of film formation becomes 3.5 to 3.5.
Even if it is as low as about 3.7, it will be about 4 after several days, and there is not much difference from the conventional PCVD-SiO ₂ film.

Further, the upper limit of the volume flow rate ratio, 40 times, is a practical level of deposition rate and coverage (s
Step coverage: Step coverage
When the ratio exceeds 40 times, the film forming speed becomes slow, and the coverage with respect to the wiring step is reduced, so that it is not practical.

Further, by increasing the volume flow ratio of C ₂ F ₆ to tetraethyl orthosilicate gas in the source gas consisting of tetraethyl orthosilicate, oxygen and C ₂ F ₆ by 5 to 7 times, It is possible to obtain a PCVD-SiOF film having a low dielectric constant, which has less hygroscopicity and has more stable characteristics over time.

The lower limit of the volume flow ratio of 5 times is determined by the obtained dielectric constant. If it is less than 5 times, the dielectric constant at the time of film formation becomes 3.7 or more, and the subsequent change with time is taken into consideration. Then, since it becomes 3.8 or more, the effect of preventing signal propagation delay is reduced.

The upper limit of the volume flow ratio of seven times is determined by the stability of the change with time. If it exceeds seven times, for example, in the case of eight times, the dielectric constant at the time of film formation is 3 times. .
Although it has a very low dielectric constant of 5, it becomes about 4 after several days, and there is not much difference from the conventional PCVD-SiO ₂ film.

[0023]

FIG. 1 is a schematic structural view of a plasma enhanced chemical vapor deposition apparatus (PCVD apparatus) used for carrying out the present invention.
First, a basic manufacturing method of the present invention will be described with reference to FIG.

Referring to FIG. 1, this PCVD apparatus includes a shower head type upper electrode 4 connected to a reaction chamber 1, a raw material gas supply pipe 2, and a 13.56 MHz high frequency power supply 3, and a mounting table for a substrate 5 to be processed. Lower electrode 6 also serving as ground and vacuum pump 7
The main part is constituted by the exhaust port 8 connected to the exhaust port 8. The substrate 5 to be processed and the lower electrode serving as the mounting table are heated by:
Lamp heating with a lamp (not shown) placed outside the reaction chamber 1 is used.

The source gas supply pipe 2 has a pipe 9
It is connected to C ₂ F ₆ gas cylinder 10 via, C ₂ F ₆ gas flow rate is controlled by the mass flow controller 11. Further, an O ₂ cylinder 13 is connected via a pipe 12, and the O ₂ gas flow rate is controlled by a mass flow controller 14. Further, a TEOS (tetraethyl orthosilicate) source is connected via a pipe 15.

This TEOS source is a liquid TEOS 16
And the compressed H
The pipe 15 for feeding e is connected to the TEOS source so that the pipe 15 is inserted into the liquid TEOS 16.

When supplying TEOS, compressed He is fed from the pipe 18 at a pressure of 0.5 to 1.0 kg / cm ² , and liquid TEOS is fed into the pipe 15.
The supply amount of EOS is controlled by a liquid mass flow controller 19 provided in the pipe 15.

The liquid TEOS whose flow rate is controlled by the liquid mass flow controller 19 is vaporized in the vaporizer 20 to become a TEOS gas. This vaporizer 20 includes a pipe 21
And a He cylinder 22 is connected via a pipe 24 and TE
He serving as a carrier gas for stabilizing the supply amount of the OS gas
The gas flow rate is controlled by the mass flow controller 23.

The He gas controlled by the mass flow controller 23 is sent into the vaporizer 20 via the pipe 24 and is sent into the reaction chamber 1 via the pipe 2 together with the TEOS gas. A heater 25 is provided in the pipe 2, and TEOS vaporized by heating the pipe 2 to 100 ° C.
Is not liquefied again in the pipe 2.

The method of directly supplying a vaporized gas without using a bubbler is called direct injection, and the flow rate of the TEOS gas in the present invention is the flow rate in such a gas state (including the flow rate of the carrier gas). Not flow rate).

At the same time as the supply of the TEOS gas, the piping 9
And supply C ₂ F ₆ gas and O ₂ via pipe 12,
Plasma is generated by applying high frequency power between the shower head type upper electrode 4 and the lower electrode 6 by the high frequency power supply 3, and an SiOF film is deposited on the substrate 5 to be processed.

Next, various experiments using the PCVD apparatus will be described.
The experimental results will be described with reference to FIGS.
Based on the number of various manufacturing conditions suitable as an embodiment of the present invention based on
Review the value range. FIG. 2 shows TEOS gas, C_TwoF₆Gas and He gas
At a flow rate of 30 sccm and 210 sccm (C
_TwoF₆And TEOS gas flow ratio, ie, C_TwoF ₆/ TE
OS = 7) and 500 sccm, and O_TwoGas flow
300, 450, 600, 1200, 1350 sc
cm, a SiOF film was deposited, and the resulting S
Temporal change of dielectric constant by leaving iOF film in air
It shows the results of the measurement of chemical conversion.

In this case, the applied power is 1.80 W /
cm ² , the film forming pressure is 5 Torr, and the temperature of the mounting table is 400 ° C. And under these conditions 2
With a deposition rate of 000-2700 ° / min, 6000 °
Was deposited.

As is apparent from FIG. 2, the gas flow ratio C ₂
When F ₆ / TEOS is 7, the dielectric constant at the time of film formation is about 3.6.
And there is almost no dependence on the O ₂ flow rate. However, when left in the air, the dielectric constant gradually increases by absorbing moisture in the air.

The flow rate of O ₂ is 300 sccm (O ₂ and TE
The gas flow ratio of OS, that is, O ₂ / TEOS = 10, and the flow rate of O ₂ is 450 sccm (O ₂ / TEOS = 1)
In the case of 5), the change with time is large, and when left for 7 days, it increases to about 4.0 to 4.2.
There is no difference from the O ₂ film, and it has no practical meaning.

[0036] In addition, the flow rate of O ₂ is 600sccm (O ₂
When / TEOS = 20) or more, the change with time is small, and the increase in the dielectric constant tends to be saturated around 4 days after standing in the air, and falls to about 3.75 or less.

As described above, when the flow rate of O ₂ is set to be at least 20 times as large as that of TEOS, a film having a low dielectric constant which is stable with time can be obtained, but the flow rate of O ₂ is 1350 sccm (O ₂ / TE
Becomes the OS = 45) or more, the deposition rate is too small, and, coverage (step Kavareji) it becomes worse for the wiring step, than practical problems arise, O ₂
It is determined that a flow rate of 1200 sccm (O ₂ / TEOS = 40) is appropriate as the upper limit.

Next, referring to FIG. 3, TEOS gas, C
The flow rates of the ₂ F ₆ gas and the He gas are each set to 30 seconds.
ccm, 150 sccm (C ₂ F ₆ / TEOS = 5),
And 500 sccm, the flow rate of the O ₂ gas is 300,
450, 600, 1200 sccm
The result when an OF film is deposited and the obtained SiOF film is left in the air will be examined.

The other conditions in this case are the same as those in FIG. 2, the applied power is 1.80 W / cm ² , the film forming pressure is 5 Torr, and the temperature of the mounting table is 400 ° C.
It is. And, under these conditions, 2700-3000Å /
A 6000 ° thick SiOF film was deposited at a deposition rate of 10 minutes.

In this case, the dielectric constant at the time of film formation is slightly higher at about 3.7, but almost no dependence on the O ₂ flow rate is observed as in the case of FIG. Then, the dielectric constant gradually increases by absorbing moisture in the atmosphere.

Also in this case, the flow rate of O ₂ is 300
When the flow rate of sccm (O ₂ / TEOS = 10) and the flow rate of O ₂ is 450 sccm (O ₂ / TEOS = 15), the change with time is large, and when left for 7 days, it is 4.0 to 4.2. To the extent that there is no difference from the PCVD-SiO ₂ film, and it has no practical significance.

The flow rate of O ₂ is set to 600 sccm (O ₂
When (TEOS = 20) or more, the change with time is small, and the increase in the dielectric constant tends to be saturated from about 4 days after standing in the atmosphere, and falls to about 3.8 or less.

As described above, when the flow rate of O ₂ is set to be 20 times or more larger than that of TEOS, a film having a low dielectric constant whose change with time is stable can be obtained. However, when the flow rate of O ₂ is increased, as in FIG. Since the film formation rate becomes too low, the step coverage becomes worse, and a practical problem arises,
The flow rate of ₂ is 1200 sccm (O ₂ / TEOS = 40)
Is determined to be appropriate as the upper limit.

If the flow rate of C ₂ F ₆ is less than 5 times that of TEOS, the concentration of fluorine in the SiOF film decreases, so that the dielectric constant at the time of film formation becomes higher than 3.7.
Considering subsequent changes over time, the meaning of adding fluorine is daunted, so that the lower limit of the flow rate of C ₂ F _{6 to} TEOS is 5 times.

Next, referring to FIG. 4, TEOS gas, C
The flow rates of the ₂ F ₆ gas and the He gas are each set to 30 seconds.
ccm, 240 sccm (C ₂ F ₆ / TEOS = 8),
And 500 sccm, the flow rate of the O ₂ gas is 300,
The results when the SiOF film is deposited while changing it to 600 and 1350 sccm and the obtained SiOF film is left in the air will be examined.

The other conditions in this case are the same as those in FIG. 2, the applied power is 1.80 W / cm ² , the film forming pressure is 5 Torr, and the temperature of the mounting table is 400 ° C.
It is. And, under these conditions, 1900-2100 ° /
A 6000 ° thick SiOF film was deposited at a deposition rate of 10 minutes.

In this case, the dielectric constant at the time of film formation is as low as about 3.5, and there is almost no dependence on the O ₂ flow rate as in the case of FIG. The dielectric constant is gradually increased by absorbing moisture in the atmosphere.

In this case, the flow rate of O ₂ is 13
Even if it is 50 sccm (O ₂ / TEOS = 45), the change with time is large and becomes 3.9 when left for 7 days.
Further, since there is no saturation tendency in the increase in the dielectric constant, it is assumed that the value will increase to 4.0 or more when the substrate is further left. Therefore, there is no difference from the PCVD-SiO ₂ film, and fluorine is intentionally added. There is no point in doing it.

[0049] Thus, large changes over time when the flow rate is more than 8 times the TEOS of C ₂ F ₆ is because ultimately not SiOF film having a low dielectric constant is obtained, C ₂ F ₆ to TEOS 7 times is suitable as the upper limit.

Therefore, the experimental results shown in FIGS.
Judging jointly, O against TEOS_TwoVolume flow ratio of
Is preferably 20 to 40 times, and
C _TwoF₆Is preferably 5 to 7 times.

Next, the stability of the dielectric constant was measured by changing other conditions, and the results were shown in FIGS.
Consider with reference to 0. First, FIG. 5 shows that the applied power (1
(3.56 MHz), the dependence of the applied power on the O ₂ flow rate at which the stability of the dielectric constant of the SiOF film was obtained was measured. At this time, the deposition conditions were TEOS gas, C
The flow rates of ₂ F ₆ gas and He gas are each 30 sc
cm, 210 sccm (C ₂ F ₆ / TEOS = 7) and 500 sccm, the film formation pressure was 5 Torr, and the mounting table temperature was 400 ° C.

The stability in this case is about the stability when the O ₂ flow rate in FIG. 2 is 600 sccm, and as shown in FIGS. 2 to 4, the greater the O ₂ flow rate, the higher the stability. It is clear that the stable O ₂
It shows the lower limit of the flow rate.

In this experiment, the applied power was 1.54 W / cm ^{2 to} 2.0.
5 W / cm ^2, which was changed within a practical range used normally, but the obtained result was 1.54 W / cm ^{2 to} 2.0 W / cm ^2.
600 sccm to 700 s in the range of 5 W / cm ²
ccm and almost no dependence on applied power was observed. Therefore, the value of 20 to 40 times the O ₂ / TEOS ratio is a value range that is established substantially irrespective of the applied power.

Next, FIG. 6 will be described. FIG. 6 shows the dependency of the O ₂ flow rate on the film forming pressure at which the dielectric constant of the SiOF film can be stabilized when the film forming pressure during film formation is changed. The deposition conditions at this time were as follows: the flow rates of TEOS gas, C ₂ F ₆ gas, and He gas were 30 sccm, 2
10 sccm (C ₂ F ₆ / TEOS = 7) and 50
0 sccm, the applied power is 1.80 W / cm ² , and the mounting table temperature is 400 ° C. The meaning of the stability in this case is the same as in the case of FIG.

Referring to FIG. 6, in this experiment, the film formation pressure was set to 3.0 Torr to 8.0 T.
However, the obtained result was about 600 sccm in the range of 3.0 Torr to 8.0 Torr, showing no dependency on the film forming pressure. Therefore, the above-mentioned O ₂ / TEOS ratio is 20 times to 4 times.
The value of 0 is a numerical value range that is substantially independent of the film forming pressure.

Next, FIG. 7 will be described. FIG. 7 shows that the flow rate of C ₂ F ₆ / TEOS is 500
When the ratio was fixed at 7 and the total flow rate of both gases was changed, the dependence of the O ₂ flow rate on the stability of the dielectric constant of the SiOF film was measured. As for film conditions, the film forming pressure is 5 Torr, and the applied power is 1.80 W / c.
m ² , and the mounting table temperature is 400 ° C. The meaning of the stability in this case is the same as in the case of FIG.

In this experiment, the total flow rate of TEOS gas and C ₂ F ₆ gas was set to 80 (10:70) sccm to 360 (45: 315).
Although it was changed in the range of sccm, the obtained result was 200 scc when the total flow rate was 80 (10:70) sccm.
m ₂ , that is, O ₂ / TEOS = 20, 300 scc when the total flow rate is 120 (15: 105) sccm
m ₂ , ie, O ₂ / TEOS = 20, 600 scc when the total flow rate is 240 (30: 210) sccm
m ₂ O ₂ flow rate, ie, O ₂ / TEOS = 20, and
90 when the total flow rate is 360 (45: 315) sccm
An O ₂ flow rate of 0 sccm, ie, O ₂ / TEOS = 20, was obtained.

That is, since the total flow rate of the TEOS gas and the C ₂ F ₆ gas and the O ₂ flow rate necessary for stabilizing the dielectric constant have a linear relationship, the above-mentioned O ₂ / TEOS ratio is 20 to 40 times.
The double is a numerical range that holds regardless of the total flow rate of the TEOS gas and the C ₂ F ₆ gas.

Referring now to FIG. 8, FIG.
When the flow rate of the He gas is changed while the flow rates of the gas and the C ₂ F ₆ gas are 30 sccm and 210 sccm (C ₂ F ₆ / TEOS = 7), the stability of the dielectric constant of the SiOF film is obtained. The dependency of the O ₂ flow rate on the He gas flow rate was measured. At this time, the deposition conditions were a deposition pressure of 5 Torr, an applied power of 1.80 W / cm ² , and a mounting table temperature of 400 ° C. The meaning of the stability in this case is the same as in the case of FIG.

Referring to FIG. 8, in this experiment, the He gas flow rate was set to 300 sccm to 100 sccm.
0 sccm in a practically used range which is usually used, but the obtained result is 300 sccm to 1000 sccm.
In the range of cm, the O ₂ gas flow required to stabilize the dielectric constant was 600 sccm to 700 sccm, and almost no dependency on the He gas flow was observed. Therefore, 20 to 40 times the above-mentioned O ₂ / TEOS ratio is a numerical value range that is established substantially without relation to the He gas flow rate.

Next, FIG. 9 will be described. FIG. 9 shows a case in which the He gas in the experiment of FIG. 8 is replaced with Ar gas, that is, the flow rates of the TEOS gas and the C ₂ F ₆ gas are each 3
0 sccm and 210 sccm (C ₂ F ₆ / TEOS =
Under the condition of 7), when the flow rate of the Ar gas was changed, the dependency of the O ₂ flow rate at which the dielectric constant of the SiOF film was stable was measured, and the deposition conditions at this time were measured. Means that the film formation pressure is 5 Torr and the applied power is 1.80 W /
cm ² , and the mounting table temperature is 400 ° C. The meaning of the stability in this case is the same as in the case of FIG.

Referring to FIG. 9, in this experiment, the flow rate of Ar gas was set to 300 sccm to 100 sccm.
0 sccm in a practically used range which is usually used, but the obtained result is 300 sccm to 1000 sccm.
In the range of cm, the flow rate of the O ₂ gas required to stabilize the dielectric constant was 600 sccm to 700 sccm, and almost no dependency on the Ar gas flow rate was observed. Therefore, the value of 20 to 40 times the O ₂ / TEOS ratio is a numerical value range that is established substantially independently of the Ar gas flow rate.

Also, when the carrier gas is Ar gas, the same result as that obtained with He gas was obtained because both are inert gases and do not directly participate in the chemical reaction in the film formation process. As long as the inert gas is used as the carrier gas, the 20 to 40 times the O ₂ / TEOS ratio is a numerical range that is satisfied substantially regardless of the type of the carrier gas.

In the experiments shown in FIGS. 5 to 9, C ₂ F ₆
Although the ratio of / TEOS is constant at 7, it can be easily predicted that these experimental results are satisfied even when C ₂ F ₆ / TEOS = 5 to 7, and at least FIGS. These conditions are satisfied in the preferred embodiment shown in FIG.

In the experiments shown in FIGS. 2 to 9, the temperature of the mounting table is constant at 400 ° C., but this 400 ° C. is the optimum temperature in the PCVD method of the present invention. It is meaningless.

That is, if the temperature is much higher than 400 ° C., the aluminum wiring layer, the ohmic electrode, or the
In some cases, the Schottky barrier electrode is adversely affected, so there is naturally an upper limit.
There is naturally a lower limit because the quality of the film such as a decrease in the density of the SiOF film is deteriorated. For example, the mounting table temperature in the PCVD method of the present invention is preferably in the range of 360 ° C. to 420 ° C.

Next, with reference to FIG. 10, an experiment was conducted on why the dielectric constant of the SiOF film was stabilized by optimizing the amount of O ₂ gas added to TEOS, and the results will be discussed.

FIG. 10 shows TEOS: O ₂ : He = 30 sccm: 60.
0 sccm: S with 500 sccm and optimized O ₂ flow rate
iOF film, TEOS: O ₂ : He = 30 sccm: 4
00 sccm: 500 sccm and TDS (Thermal Deso) of the SiOF film without optimizing the O ₂ flow rate
3 shows the results of rption spectroscopy analysis.

This TDS analysis is also referred to as a thermal desorption method, in which a sample to be measured is heated and heated under a high vacuum, and the molecular weight of a gas released at the time of temperature rise indicates that the sample is present in the sample. In the case of an SiOF film, F in the film is hydrogen fluoride (H
FIG. 10 measures the amount of HF released since it is released as F).

As is apparent from the figure, when the temperature of the sample is increased, the outgassing of HF occurs at 700 ° C. or higher in the case of the SiOF film in which the O ₂ flow rate is optimized.
₂ 40 in case of SiOF film whose flow rate is not optimized
Degassing has already begun below 0 ° C., and the amount of degassing also varies greatly.

That is, when the O ₂ flow rate is not optimized
In the case of an OF film, the fluorine atoms in the film suggest that they exist as a simple substance without being bonded to silicon atoms, and this unbonded fluorine atoms cause absorption of moisture (H ₂ O). Probably involved.

When comprehensively judging the above results, O ₂ /
When the TEOS ratio is set to 20 to 40 times, the film forming pressure,
The applied power, the total gas flow rate, the flow rate of the carrier gas, and the low dielectric constant SiOF film whose dielectric constant is stable with time without depending on the type of the carrier gas, at a deposition rate that does not cause any practical problem, In addition, it can be deposited with good step coverage.

By setting the C ₂ F ₆ / TEOS ratio in this case to 5 to 7 times, a SiOF film having a dielectric constant lower than that of the PCVD-SiO ₂ film can be formed stably. The signal propagation delay in the device can be reduced.

In the present invention, C is used as the fluorine source.
₂ F ₆ is used because C ₂ F ₆ is optimal for controlling hygroscopicity and lowering the dielectric constant. That is,
As a fluorine source, C ₄ F ₈ , C ₃ F ₆ , or CHF
Although _3, etc., because these are easy to make the polymer of C and F in high plasma polymerizable, it was deposited SiO
Such a polymer is likely to remain as an impurity in the F film, making it difficult to control the hygroscopicity of the film.

Other sources of fluorine include SiF _{4 and} CF _4, but these gases have low decomposition efficiency in plasma, so that it is difficult to incorporate F into the film, and therefore it is difficult to reduce the dielectric constant. This is because

In the embodiment of the present invention, the PCV using the direct injection method shown in FIG.
Although the D apparatus is used, a PCVD apparatus using a bubbler generally used as a TEOS source may be used, but in this case, it becomes difficult to control the flow rate of the TEOS gas. As the heating means, lamp heating is used, but a resistance heater may be used.

Although the effects in the above description are applied to the case where the present invention is applied to an interlayer insulating film of a semiconductor integrated circuit device, the method of forming an insulating film according to the present invention employs a method of forming an interlayer insulating film of a semiconductor integrated circuit device. The present invention is not limited to the method, but can be applied to other dielectric integrated circuit devices such as an optical IC.

[0078]

According to the present invention, tetraethyl ortho
Like (TEOS), oxygen and C_TwoF₆The raw material
Insulating film by plasma-enhanced chemical vapor deposition
During the formation, it reacts with tetraethylorthosilicate gas.
The volume flow ratio of oxygen gas to be increased to 20 to 40 times,
C for tetraethyl orthosilicate gas_TwoF
₆By increasing the volumetric flow ratio of 5 to 7 times,
Obtaining low dielectric constant SiOF film with stable electric conductivity over time
Therefore, this SiOF film is used as an interlayer insulating film.
Signal propagation delay of the semiconductor integrated circuit device
Can be prevented, and the speed of the semiconductor integrated circuit device can be improved.
Reliability can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a plasma enhanced chemical vapor deposition apparatus used for carrying out the present invention.

FIG. 2 is a graph showing the O ₂ stability of the dielectric constant of a SiOF film when the C ₂ F ₆ / TEOS ratio is set to 7 in an embodiment of the present invention.
It is a figure which shows a flow rate dependency.

FIG. 3 is a graph showing the relationship between the C ₂ F ₆ / TEOS ratio and the stability of the dielectric constant of an SiOF film, O ₂ , when the C ₂ F ₆ / TEOS ratio is 5
It is a figure which shows a flow rate dependency.

FIG. 4 is a graph showing the O ₂ stability of the dielectric constant of a SiOF film when the C ₂ F ₆ / TEOS ratio is set to 8 in the embodiment of the present invention.
It is a figure which shows a flow rate dependency.

FIG. 5 is a diagram showing the applied power dependence of the O ₂ flow rate necessary for stabilizing the dielectric constant of the SiOF film when the C ₂ F ₆ / TEOS ratio is set to 7 in the example of the present invention.

FIG. 6 is a graph showing the dependency of the flow rate of O ₂ required for stabilizing the dielectric constant of the SiOF film on the deposition pressure when the C ₂ F ₆ / TEOS ratio is set to 7 in the example of the present invention.

FIG. 7 is a graph showing the total gas flow rate dependency of the O ₂ flow rate necessary for stabilizing the dielectric constant of the SiOF film when the C ₂ F ₆ / TEOS ratio is set to 7 in the example of the present invention.

FIG. 8 is a diagram showing the He gas flow rate dependency of the O ₂ flow rate necessary for stabilizing the dielectric constant of the SiOF film when the C ₂ F ₆ / TEOS ratio is set to 7 in the example of the present invention.

FIG. 9 is a diagram showing the dependence of the O ₂ flow rate required for stabilizing the dielectric constant of the SiOF film on the Ar gas flow rate when the C ₂ F ₆ / TEOS ratio is set to 7 in the example of the present invention.

FIG. 10 is a diagram showing the dependence of the amount of HF outgas on film formation conditions in TDS analysis.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Reaction chamber 2 Source gas supply pipe 3 High frequency power supply 4 Shower head type upper electrode 5 Substrate to be processed 6 Lower electrode 7 Vacuum pump 8 Exhaust port 9 Piping 10 C ₂ F ₆ cylinder 11 Mass flow controller 12 Piping 13 O ₂ cylinder 14 Mass flow controller 15 Piping 16 Liquid TEOS 17 TEOS container 18 Piping 19 Liquid mass flow controller 20 Vaporizer 21 Piping 22 He cylinder 23 Mass flow controller 24 Piping 25 Heater

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-211708 (JP, A) JP-A-6-302593 (JP, A) JP-A-7-90589 (JP, A) JP-A-6-302 168937 (JP, A) Table 6-507942 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01L 21/316 H01L 21/31

Claims (2)

(57) [Claims] 1. A method for forming an insulating film using plasma enhanced chemical vapor deposition, wherein a source gas for forming the insulating film is tetraethylorthosilicate, oxygen, and C.
_A method for forming an insulating film, wherein ₂ F ₆ is used and the volume flow ratio of oxygen gas to tetraethyl orthosilicate gas is 20 to 40 times. 2. A method according to claim 1, wherein said source gas has a volume flow ratio of C ₂ F ₆ to tetraethyl orthosilicate gas of 5%.
2. The method for forming an insulating film according to claim 1, wherein the size is increased by a factor of 7 to 7.