JP2751851B2 - Method for producing fluorinated amorphous carbon 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 producing a fluorinated amorphous carbon film used as an insulating material for a semiconductor device, a high-density mounting substrate and the like.

[0002]

2. Description of the Related Art As the wiring width and wiring interval of a semiconductor device and its mounting substrate are reduced in the future, the wiring stray capacitance and the wiring resistance will increase. As a result, an increase in wiring delay causes a problem in high-speed operation of the semiconductor device. In general, the wiring delay is proportional to the square root of the dielectric constant of the insulating material, so it is possible to reduce the wiring delay by using an insulating material having a low relative dielectric constant. Has been done. Conventionally, SiO ₂ has been mainly used for an interlayer insulating film of a semiconductor device. A high-density plasma is used to improve a film forming rate, and a bias voltage is applied to a substrate to improve a filling characteristic in a wiring pattern. A method of applying and manufacturing has been established. However, the relative dielectric constant of the SiO ₂ film manufactured by this method is about 4, and
It is desired to develop a method for depositing a film having a relative dielectric constant of less than that. Therefore, as a next-generation low dielectric constant interlayer insulating material,
Fluorinated amorphous carbon materials having a relative dielectric constant of 3 or less are considered promising. As a method for producing the fluorinated amorphous carbon material, a chemical vapor deposition method using plasma has conventionally been used, and a production method using a parallel plate type low density plasma has been mainly used. Proceedings of the 55th Annual Conference of the Japan Society of Applied Physics No. 3.21a-G-11 (September 19, 1994) describes an example in which the relative permittivity is reduced to 3 or less by fluorinating a polyimide resin by a fluorine plasma treatment.

[0003]

The interlayer insulating material between wirings has a dielectric constant as low as possible, has good pattern embedding characteristics, and has a deposition rate of at least 0 in order to increase the production volume per unit time. .1 μm / min is required. SiO currently used
_{(2) The} inter-layer insulating film is a film that satisfies the requirements of the above-described insulating materials for pattern embedding characteristics and deposition rate by using high-density plasma and applying a bias power to the substrate. Has been obtained. However, the relative permittivity is about 4 and it is difficult to reduce it below that value. Therefore, when a fluorinated amorphous carbon film having a relative dielectric constant of 3 or less is used as another insulating material,
Although the value of the relative dielectric constant is low, the film formation rate and the buried flatness were inferior to those of the SiO ₂ film.

The film formation rate of the conventional fluorinated amorphous carbon film is low and the buried flatness is poor because the film is formed by low-density plasma, and the decomposition rate of the raw material monomer by the plasma is low. This is because the fluorinated carbon radical density that contributes to film formation is small. Therefore, film thickness 1μ
It takes 30 minutes or more to deposit the m 2 film, and for practical use, it is necessary to increase the film formation rate at least twice or more. In a conventional parallel plate type low-density plasma source, an amorphous carbon film cannot be deposited only with a raw material such as a fluorocarbon gas. Is deposited. Then, the added hydrogen bonds with carbon atoms and is taken into the film, and the degree of crosslinking of the film is reduced, so that heat resistance is deteriorated. Therefore, development of a new technique for forming a film without adding hydrogen is required. Although the film structure of the amorphous carbon film changes greatly due to ion irradiation, in the case of the conventional parallel plate type, the energy of ions irradiated due to self-bias applied to the substrate is large, and the amorphous carbon film In principle, it is difficult to control the ion energy to the optimum energy value for the deposition of GaN, and the burying flatness is deteriorated.

An object of the present invention is to solve these problems by using a different plasma source instead of the parallel plate type, and to obtain a low dielectric constant fluorinated compound exhibiting good filling characteristics at a high film forming rate. An object of the present invention is to provide a method for manufacturing an amorphous carbon film.

[0006]

In the present invention, in order to solve the above-mentioned problems, C _x F _y (x = 1-4, y = 4-
8) A fluorinated amorphous carbon film is manufactured using only gas and high-density plasma in which the substrate on which the film is deposited exists outside the plasma generating portion. When such a high-density plasma source is used, the radical density contributing to the film formation can be increased, so that the film formation speed can be increased. Further, since the substrate is provided outside the plasma generation unit, the ion energy applied to the substrate can be suppressed to be small, and the fluorinated amorphous carbon film can be deposited without adding a hydrogen source. Further, high-frequency power is applied to the substrate to be deposited to control and optimize the potential of the substrate, thereby changing ion energy and controlling film quality such as heat resistance and film flatness.

[0007]

The fluorinated amorphous carbon film produced according to the present invention has C
It is formed by exciting fluorinated carbon-based monomer molecules such as F ₄ , C ₂ F ₆ , C ₃ F ₈ and C ₄ F ₈ with plasma, and reacting radical molecules, ions and the like on the substrate. In general, it is considered that the deposition phenomenon of a film by plasma is caused by a combination of a deposition reaction by a deposition radical or the like and an etching reaction by ions or an etching radical. When a high-density plasma is used as the plasma source, the dissociation rate of the monomer molecules is faster than in the parallel plate type, so that the density of the depositable fluorocarbon radicals is increased, and the deposition reaction is accelerated to increase the film deposition speed. It can be carried out.

In the conventional parallel plate type, the ions are accelerated by the self-bias voltage applied to the substrate.
The etching reaction by ion irradiation is promoted. Therefore, when plasma is generated only with CF-based gas, the etching reaction rate becomes higher than the deposition reaction rate, and no deposition of the fluorinated amorphous carbon film is observed. In this case, in order to deposit a film, fluorine atoms considered as an etching substance must be removed by adding hydrogen gas or the like.
However, in a plasma source that uses high-density plasma such as helicon waves or microwave discharge, and separates a plasma generation unit and a film formation unit, the ion energy can be kept small despite the high ion density. With a high-density plasma source, the etching reaction is suppressed and it is possible to form a film without adding hydrogen gas.Hydrogen atoms that have been taken into the film by the conventional parallel plate type and have deteriorated the heat resistance of the film can be removed. Can be excluded. Further, by applying high-frequency power to the sample to control the potential of the sample, the irradiation ion energy is optimized and the heat resistance and flatness of the film are improved.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and 2 are schematic views of an apparatus for forming a fluorinated amorphous carbon film used in the present invention. 1 is equipped with a helicon wave plasma source, and FIG. 2 is equipped with a microwave plasma source. Samples 101 and 201 are mounted on sample tables 102 and 2 respectively.
02, and the sample stage is located other than the plasma generating section. High frequency power 1 to be supplied to the plasma source on the sample stage
03 or microwave power 203, high-frequency power 104 or 204 can be applied, and a bias voltage can be applied to the sample. The sample stage can be heated and cooled to any temperature. First, the samples 101 and 201 such as a silicon substrate
2, 202, and then CF ₄ , C ₂ F ₆ ,
A fluorinated carbon gas such as C ₃ F ₈ or C ₄ F ₈ is introduced, and a high frequency and a microwave are applied at a degree of vacuum of 10 ⁻³ Torr to cause discharge, thereby generating a fluorocarbon plasma. An amorphous carbon film is deposited by this fluorocarbon plasma.
In the figure, 107 and 207 are magnets, 108 and 206 are vacuum pumps, and 109 and 205 are raw material gas cylinders.

Next, a specific embodiment will be described. In film formation by a conventional parallel plate type, the total gas flow rate was fixed to 50 sccm, by the addition of CH ₄ gas to CF ₄ gas frequency power (1
(3.56 MHz) was applied at 200 W to form a film. FIG.
FIG. 4 is a diagram showing a relationship between a film forming speed, a relative dielectric constant, and a gas flow ratio in a conventional case. The film forming speed and the relative dielectric constant (1 MHz) of the film change depending on the mixing ratio of the raw materials, and have the values shown in FIGS. 3 and 4, respectively. Thus, a film having a relative dielectric constant of 3 or less has been obtained, but there is a manufacturing problem that the number of mass-produced units per unit time is small due to a low film formation rate.

[0011] Therefore, if the amount of radicals contributing to the film formation is increased by using a high-density plasma source, the film formation rate is considered to increase. First, the film formation is performed by using the high-density plasma generated by the helicon wave. Was done. CF for source gas
₄ and C ₂ F ₆ , the hydrogen gas to be diluted is H
₂ was used. The high-frequency power (13.56 MHz) used to generate the helicon wave was kept constant at 2 kW. The temperature of the sample stage was kept at 50 ° C. by cooling. FIG. 5 shows the hydrogen dilution amount dependence of the film formation rate. Curve 1 in the figure is a case where CF ₄ is used, and curve 2 is a case where C ₂ F ₆ is used. The film was formed with the flow rates of the raw material CF ₄ and C ₂ F ₆ gases fixed at 100 sccm. The electron density in this case was 5 ×
10 ¹² / cm ³ and the plasma potential were 20V. As can be seen from the figure, by using helicon plasma, a fluorinated amorphous carbon film could be formed without adding hydrogen. That is, the present inventors have found a method for forming fluorinated amorphous carbon consisting entirely of carbon and fluorine atoms by using a high-density plasma source in which a substrate and a plasma generation unit are separately provided. Furthermore, the film formation rate of the amorphous carbon film is about 1 times lower than that of the parallel plate type.
We established a method to improve it about 0 times.

Subsequently, a film was formed using a microwave.
Similarly, CF ₄ and C ₂ F ₆ gases were used as raw materials. FIG. 6 shows the hydrogen dilution amount dependence of the film forming rate. Curve 1 is C
When F ₄ is used, curve 2 is the case where C ₂ F ₆ is used. The gas flow rate and microwave (2.45 GHz) power were set to 100 sccm and 2 kW, similarly to the helicon. The temperature of the sample stage was similarly controlled to 50 ° C. by cooling. The electron density when using microwaves is 2 × 10 ¹² /
cm ³ and the plasma potential was 16V. It was found that a fluorinated amorphous carbon film could be formed without dilution with hydrogen by microwave discharge as well as helicon. The deposition rate was slower for the helicon, but could be increased significantly from the parallel plate type.

As described above, the use of high-density plasma makes it possible to greatly increase the film forming speed as compared with the conventional parallel plate type. It is thought to rise. The reason that fluorinated amorphous carbon films can be deposited without hydrogen dilution is that, with these high-density plasma sources, the energy of ions that are accelerated by the potential difference between the substrate and the plasma and are applied to the film is reduced to a parallel plate type. This is considered to be possible because the etching reaction can be suppressed to a smaller value and the etching reaction can be suppressed.

The case where the film is formed using CF ₄ and C ₂ F ₆ has been described above. However, even when other fluorocarbon gas such as C ₃ F ₈ or C ₄ F ₈ is used, the parallel plate is similarly formed. While film deposition did not occur in the mold, a film was deposited when high-density plasma was used, and the deposition rate was equivalent to that when C ₂ F ₆ was used.

As described above, a method for forming a fluorinated amorphous carbon film without adding hydrogen gas has been established. Subsequently, only CF ₄ and C ₂ F ₆ gases are used without adding hydrogen gas.
Furthermore, a high frequency (400 kHz) was applied to the sample stage to control the potential of the sample, and the effect of changing the energy of ions irradiated on the sample to the quality of the fluorinated amorphous carbon film was examined. The temperature of the sample stage was also 50 ° C. in this case.
In the case of the parallel plate type, since the self-bias voltage is applied to the sample placed on the electrode, it is difficult to control the ion energy by controlling the bias voltage, but high-density plasma such as helicon waves and microwaves is difficult. When the film forming unit and the plasma generating unit are separated from each other, the potential of the sample stage can be controlled by applying high-frequency power to the sample stage, thereby controlling the energy of ions irradiated to the substrate. It becomes possible.

FIG. 7 shows a change in the film forming speed when the high frequency bias power is changed using CF ₄ gas. Curve 1
Is a case where a film is formed using a helicon wave, and a curve 2 is a case where the film is formed using a microwave. As the bias power increases, the film forming speed decreases in both cases, and the power 200
It was found that an amorphous carbon film was not formed in both cases above W. This is considered to be due to the fact that the energy of ions increases with an increase in the power, thereby promoting the etching reaction. In the case of the conventional parallel plate type, the film was not deposited only by the CF-based gas because ions of the energy corresponding to the bias power of 200 W or more were applied by this high-density plasma source. it is conceivable that.
Also for other fluorocarbon gases such as C ₃ F ₈ and C ₄ F ₈ , when the film was formed using high-density plasma, the same phenomenon that the film formation speed was reduced by the application of bias power was observed. Was seen.

The effects of bias power application on the heat resistance, relative dielectric constant, and pattern embedding of the film were evaluated. When heated in a vacuum atmosphere, the temperature at which the film began to decompose and the weight of the film began to decrease, the fluorine content in the film, and the relative dielectric constant (1 MHz) of the film were examined. Table 1 shows the results.

[0018]

[Table 1]

By applying a bias in this manner, it was found that the dielectric constant of the film slightly increased, but the heat resistance of the film was improved in each case. That is, the inventors have found that using high-density plasma and applying high-frequency power to the sample during film formation is effective for improving the heat resistance of the fluorinated amorphous carbon film. It was also found that when the irradiation energy was increased by applying the bias power, the amount of fluorine in the film was reduced. It is considered that when the amount of fluorine in the film decreases, more carbon-carbon bonds are formed in the film, that is, the degree of crosslinking of the film increases. Generally, the heat resistance of a resin material or the like is determined by the crosslinked structure of the film, and it is considered that the improvement of the heat resistance by applying the bias power is due to an increase in the degree of crosslinking of the film. Further, in the parallel plate type of the comparative example in Table 1, it is considered that ions having energy corresponding to that when bias power is applied by high-density plasma are applied to the film, but despite this, the heat resistance of the film is low. This is considered to be because hydrogen gas must be added at the time of film formation, and therefore, hydrogen atoms which are eliminated at a lower temperature are present in the film.

Subsequently, a fluorinated amorphous carbon film was deposited on a silicon substrate on which aluminum wiring was formed by a known fine processing technique, and the filling characteristics of the pattern were examined. Wiring width, wiring interval 0.4μm, wiring height 0.8μ
When a film is formed using a helicon and a microwave using the pattern of
When using any of F ₄ , C ₂ F ₆ , C ₃ F ₈ , and C ₄ F ₈ gases, the pattern could not be completely buried, and voids were observed between the wirings. However, when the film was formed by applying the bias power, in each case, the fluorinated amorphous carbon film could be embedded in the pattern without generating voids. Usually, voids are generated when the deposition rate of the wiring material such as aluminum on the side wall is lower than the deposition rate on the wiring material. The reason that bias power application is effective for improving the burying characteristic is that ions are accelerated by bias power application to selectively promote only the etching reaction occurring on the wiring material, and to reduce the film forming rate between the wiring material side wall and the upper part. This is thought to be to reduce the difference.

The above is an embodiment using a helicon and a microwave. In addition to the above, any other plasma source having a high density and capable of separating a plasma generating portion and a substrate to be deposited into another place can be used. The present invention can be similarly applied to other plasma sources such as an inductive coupling type, and the same effect as the present invention can be obtained.

[0022]

As described above, the present invention is a low dielectric constant insulating material for an insulating film for a multilayer wiring such as a semiconductor device and a mounting substrate. Regarding the method for producing a fluorinated amorphous carbon film, a high-density plasma source can be used to separate a plasma generation unit and a film formation unit to form a high-quality film containing no hydrogen at high speed. The method was established. Furthermore, by applying high-frequency power to the sample during film formation, a method for optimizing ion energy to form a film with high heat resistance and a method for improving the filling characteristics of a fluorinated amorphous carbon film were established. .

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an apparatus for producing a fluorinated amorphous carbon film using a helicon wave plasma source.

FIG. 2 is a schematic diagram of an apparatus for producing a fluorinated amorphous carbon film using a microwave plasma source.

FIG. 3 is a diagram showing a film formation rate of a fluorinated amorphous carbon film when a parallel plate type plasma source is used.

FIG. 4 is a diagram showing a relative dielectric constant of a fluorinated amorphous carbon film when a parallel plate type plasma source is used.

FIG. 5 is a diagram showing the dependence of the film formation rate on the amount of hydrogen added when a helicon wave plasma source is used.

FIG. 6 is a diagram showing the dependence of the film formation rate on the amount of hydrogen added when a microwave plasma source is used.

FIG. 7 is a diagram showing a bias power dependence of a film forming speed.

[Explanation of symbols]

 101 sample 102 sample stand 103 high frequency power supply 104 high frequency power supply 105 quartz tube 106 antenna 107 magnet 108 vacuum pump 109 gas cylinder 110 vacuum tank 201 sample 202 sample table 203 microwave generator 204 high frequency power supply 205 gas cylinder 206 vacuum pump 207 magnet 208 vacuum tank

Claims (3)

(57) [Claims] 1. A method for producing a fluorinated amorphous carbon film using plasma, wherein CF ₄ , C ₂ F ₆ , C ₃ F ₈ ,
Using only a gas selected from C ₄ F ₈ , and using a high-density plasma in which a substrate on which the carbon film is deposited as a plasma source is present outside the plasma generating portion, and using a carbon film other than the power supplied to the plasma. A method for producing a fluorinated amorphous carbon film, characterized in that high-frequency power is also supplied to a substrate on which is deposited. 2. The method for producing a fluorinated amorphous carbon film according to claim 1, wherein a microwave discharge is used for the plasma generator. 3. The method for producing a fluorinated amorphous carbon film according to claim 1, wherein a helicon wave discharge is used for the plasma generator.