JPH1092804A - Manufacture of porous dielectric film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably form a structure having minute air bubbles (cavities) in an organic film, and form a porous dielectric film (permittivity is about 1.2-1.8) whose permittivity is lower than a so-called conventional low permittivity film. SOLUTION: In this method, firstly fluorocarbon resin solvent in solvent is spread on a substrate 11, and a film (organic film 15) is formed. Secondly, the organic film 15 is heat-treated in the following atmosphere, and a porous dielectric film 17 is manufactured; at a temperature higher than the glass transition temperature of fluorocarbon resin and lower than its thermal decomposition temperature, and at a pressure lower than the saturated vapor pressure of the solvent. As the fluorocarbon resin, mixture composed of polytetrafluoroethylene and paradioxole is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing a porous dielectric film. More specifically, the present invention relates to a method for manufacturing a porous dielectric film used as an interlayer insulating film of a semiconductor device having a rule of 0.25 μm or less.

[0002]

2. Description of the Related Art Along with demands for miniaturization, low power consumption, and high speed of a semiconductor device, it has been proposed to lower the dielectric constant of an interlayer insulating film as one of means for realizing the demand. The low dielectric constant films proposed at present lower the dielectric constant by containing carbon atoms and fluorine atoms. At present, those having a dielectric constant of about 1.5 to 2.5 have been realized.

In low dielectric constant materials containing carbon atoms, organic S
OG (relative permittivity = about 3.0 to 3.5), polyimide (relative permittivity = about 3.0 to 3.5), polyparaxylylene (relative permittivity = about 2.4) and the like are known. ing. These materials reduce the density of the material by including carbon atoms, so-called alkyl groups, in the material, and
It is said that by lowering the polarizability of the molecule itself, a low dielectric constant (relative dielectric constant = about 2.4 to 3.5) is achieved. In addition, these materials not only have a low dielectric constant but also have heat resistance indispensable as a material for a semiconductor device. The organic SOG has a siloxane structure, the polyimide has an imide bond, and the polyparaxylylene becomes a polymer of a benzene ring, thereby ensuring heat resistance.

On the other hand, low dielectric constant materials containing fluorine atoms are:
Silicon oxyfluoride (SiOF) (dielectric constant = 3.2-3.
7) is famous. This material has a low dielectric constant due to a decrease in its density by terminating a silicon-oxygen-silicon (Si-O-Si) bond with a fluorine atom and a low polarizability of fluorine itself. I have lowered it. Naturally, this material also has heat resistance that is indispensable as a material for a semiconductor device.

[0005] Recently, there has been proposed a method of reducing the dielectric constant by using boron already used in a conventional semiconductor device without using fluorine harmful to the semiconductor device. The low-k material containing boron atoms, like the low-k material containing fluorine atoms, has a low polarizability of boron itself, shortens the network of Si-O-Si, lowers the density, etc. This causes the dielectric constant to decrease.

It has been proposed to further lower the dielectric constant of a film made of a material having a low dielectric constant as described above. This is because a film is formed using a low dielectric constant material to which a foaming agent has been added, and then the film is subjected to a heat treatment so that bubbles are generated in the film by the action of the added foaming agent. This is a manufacturing method of forming a dielectric film.

[0007]

In the conventional method for producing a porous low dielectric constant film, since a foaming agent is used, the generation of air bubbles becomes unstable, and the fine particles having a size of sub-quarter micron or less are formed in the film. It was not possible to form a structure having fine bubbles into a stable structure.

[0008]

SUMMARY OF THE INVENTION The present invention is a method for producing a porous dielectric constant film which has been made to solve the above-mentioned problems. That is, a fluorocarbon resin dissolved in a solvent is applied on a substrate to form an organic film, and then the organic film is heated in an atmosphere at a temperature higher than the glass transition temperature of the fluorocarbon resin and lower than the thermal decomposition temperature, and at that temperature. This is a manufacturing method in which heat treatment is performed in an atmosphere having a pressure lower than the saturated vapor pressure of the solvent in the atmosphere.

It is said that when a material having a glass transition temperature such as a fluorocarbon resin exceeds the glass transition temperature of the material, molecules constituting the organic film start Brownian motion. Then, when the Brownian motion is started, molecules constituting the organic film start vibrating greatly, and microscopic (for example, sub-quarter micron size or less) voids are formed in the organic film. Therefore, the solvent in the organic film is easily released to the outside through the void. Also, the deformation of the organic film is facilitated. At this time, if the atmosphere surrounding the organic film is set to a pressure lower than the saturated vapor pressure of the solvent, the solvent is vaporized. That is, the solvent is eliminated from the constituent molecules of the organic film. At that time, small bubbles (cavities) are generated in the organic film. This is because the volume of the solvent rapidly expands with the elimination of the solvent. In other words, in order to evaporate the solvent, it is necessary that the volume expansion force of the solvent is larger than the external pressure. Therefore, the atmosphere surrounding the organic film is set to a pressure lower than the saturated vapor pressure of the solvent in the temperature atmosphere. The pressure atmosphere surrounding the organic film may be lower than the saturated vapor pressure of the solvent, but the lower limit is actually an industrial vacuum. This industrial vacuum is a pressure atmosphere that can be reached by vacuuming with a vacuum pump.

On the other hand, if the atmosphere surrounding the organic film is a pressure atmosphere higher than the saturated vapor pressure of the solvent, the solvent does not evaporate. In the case of a material having a glass transition temperature, such as a fluorocarbon resin, when the temperature is lower than the glass transition temperature of the material, since the molecules constituting the organic film do not cause Brownian motion, the solvent existing inside the material is Does not evaporate.

When the above principle is applied to an organic film formed by applying a fluorocarbon resin dissolved in a solvent,
A so-called low dielectric constant film having a dielectric constant of about 1.5 can be realized. As the fluorocarbon-based resin, a mixture of polytetrafluoroethylene and paradioxole (what is called amorphous Teflon, for example, manufactured by DuPont: Teflon AF (trade name)) is used. In addition, as a solvent for the amorphous Teflon, a fluorocarbon-based solvent (for example, Fluorinert (trade name) manufactured by 3M) is used. Further, the glass transition temperature varies in the range of about 150 ° C. to 300 ° C. depending on the type of fluorocarbon resin. Therefore, the substrate temperature is preferably maintained at a temperature higher than the glass transition temperature of the fluorocarbon resin, for example, by about 20 ° C. to 30 ° C. so that the Brownian motion in the organic film becomes active. Furthermore, the heat treatment atmosphere is, for example, a general vacuum pump (a rotary pump, a dry pump, etc.)
, A pressure atmosphere lower than the vapor pressure of the solvent is obtained. Therefore, the solvent is easily volatilized, and bubbles (cavities) of sub-quarter micron size or less are generated in the organic film due to the volatilization power.

In this way, by forming a structure having fine bubbles (cavities) of sub-quarter micron size or less in the organic film, the organic film having a dielectric constant lower than that of the conventional low dielectric constant film can be stabilized. It is formed in a state where it is formed.
Therefore, in order to stably form bubbles (cavities) in the organic film, a material having a glass transition temperature is required to be higher than the glass transition temperature and lower than the thermal decomposition temperature of the material as in the above-described manufacturing method of the present invention. Needs to be left in a state of being heated to a low temperature and in an atmosphere at or below the vapor pressure of the solvent.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of the first embodiment of the present invention will be described below.
This will be described with reference to the manufacturing process diagram of FIG.

As shown in FIG. 1A, a silicon oxide film 12 is formed on a substrate (for example, a silicon
It is formed to a thickness of 00 nm. The method of forming the silicon oxide film 12 includes, for example, monosilane (SiH ₄ ) and oxygen (O
₂₎ a chemical vapor deposition using a raw material gas (hereinafter CVD
It is done by the method). Alternatively, it is performed by a plasma CVD method using tetraethoxysilane (TEOS) and oxygen (O ₂ ) gas as source gases.

Next, a metal wiring 13 is formed on the silicon oxide film 12. First, a wiring layer (not shown) is formed of aluminum containing silicon by, for example, sputtering. Then, a resist pattern (not shown) is formed on the wiring layer in a region where the metal wiring is to be formed by lithography. Subsequently, the wiring layer is etched using the resist pattern as a mask to form the metal wiring 13 made of the wiring layer.

Next, a silicon oxide film 14 covering the metal wiring 13 is formed to a thickness of, for example, 100 nm on the silicon oxide film 12 by a plasma CVD method using tetraethoxysilane and oxygen as source gases. . This film thickness is a film thickness on the metal wiring 13, and is formed thinner in the so-called trench portion between the metal wirings 13. The silicon oxide film 14 has a function of protecting the metal wiring 13 from gas (for example, carbon fluoride (CxFy)) released from a fluorocarbon film to be formed later. Therefore, it is not always necessary.

Next, as shown in FIG. 1 (2), a fluorocarbon resin dissolved in a fluorocarbon solvent is applied on the silicon oxide film 14 on the substrate 11 by a spin coating method. Organic film 15
Was formed. As the fluorocarbon resin, a polytetrafluoroethylene resin which is a material represented by the chemical formula [1], for example, having a glass transition temperature of 160 ° C.
And Teflon AF (trade name) manufactured by DuPont and generally called amorphous Teflon having a thermal decomposition temperature of 450 ° C. This fluorocarbon resin has the chemical formula (1)
Any structure may be used as long as it has the structure shown in FIG. Also, as this fluorocarbon solvent,
As an example, a product called Fluorinert (trade name) manufactured by 3M was used. The spin coating conditions were, for example, a rotation speed of 3000 rpm.

[0018]

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Then, as shown in FIG. 1C, the pressure atmosphere is lower than the saturated vapor pressure of the solvent at that temperature atmosphere (however, the pressure atmosphere is higher than the industrial vacuum), for example, an atmosphere of 10 Pa, and Baking is performed for 5 minutes at 200 ° C., which is higher than 160 ° C., which is the glass transition temperature of Teflon AF, and lower than 420 ° C., which is its thermal decomposition temperature. By this baking, the organic film 15
About 99% of the solvent in the solvent evaporates. Then, as the solvent is volatilized, fine bubbles (cavities) 16 having a sub-quarter micron size or less are formed inside the organic film 15.

Further, as shown in FIG. 1 (4), as a pressure atmosphere lower than the saturated vapor pressure of the solvent (however, a pressure atmosphere higher than the industrial vacuum), for example, an atmosphere of 10 Pa and a glass of Teflon AF Transition temperature (160 ° C)
Anneal at 400 ° C. above and below its pyrolysis temperature (450 ° C.) for 30 minutes. Due to this annealing, the organic film 15 is formed into bubbles (cavities) 1
The solvent is completely volatilized and cured in the state of forming 6,
It becomes the porous dielectric film 17. This porous dielectric film 17
Has a relative dielectric constant of about 1.2 to 1.8.

Thereafter, oxidation is performed on the porous dielectric film 17.
A silicon film 18 is formed to a thickness of 500 nm. This acid
The method for forming the silicon nitride film 18 is, for example, a method using monosilane (S
iH _Four) And oxygen (O_Two) And chemical gas used as source gas
By a phase growth (hereinafter referred to as CVD) method. Or, Tet
Laethoxysilane (TEOS) and oxygen (O_Two) Source gas
By the plasma CVD method used for the source gas.

In the manufacturing method of the first embodiment, the organic film 15 formed by applying a fluorocarbon resin dissolved in a solvent is formed in an atmosphere at a temperature higher than the glass transition temperature of the fluorocarbon resin and lower than its thermal decomposition temperature. In addition, since the heat treatment is performed in a pressure atmosphere lower than the saturated vapor pressure of the solvent in the temperature atmosphere, the solvent is volatilized from the organic film 15 and fine bubbles having a size of sub-quarter micron or less are formed in the organic film 15. A porous dielectric film 17 having (16) is formed.

The mechanism by which the air bubbles (cavities) 16 are formed is the same as that described in the section of the operation. That is, by baking at a temperature exceeding the glass transition temperature, the molecules constituting the organic film 15 start Brownian motion, and the molecules start to vibrate greatly. For this reason, microscopic voids (for example, sub-quarter micron size or less) are formed in the organic film 15, and the solvent in the organic film 15 passes through the voids to be easily released to the outside. At this time, since the pressure atmosphere on the surface side of the organic film 15 is a pressure (10 Pa) lower than the saturated vapor pressure of the solvent, the solvent is vaporized. At this time, since the volume of the solvent expands rapidly, the bubbles (cavities) 16 are generated in the organic film 15. Note that the pressure atmosphere surrounding the organic film 15 may be lower than the saturated vapor pressure of the solvent, but the lower limit is actually an industrial vacuum. This industrial vacuum is a pressure atmosphere that can be reached by evacuation with a vacuum pump.

By adjusting the baking temperature, the size of the bubbles (cavities) 16 can be controlled. For example, when the temperature is lowered, the bubble (cavity) 16 becomes smaller, and when the temperature is raised, the bubble (cavity) 16 becomes larger. And, in order to form the bubble (cavity) 16 stably,
The baking is preferably performed at a temperature about 20 ° C. to 30 ° C. higher than the glass transition temperature of the fluorocarbon resin. In other words, the molecules in the organic film 15 suitably start Brownian motion in that temperature range, and thereby, bubbles (cavities) 16 having a size of sub-quarter micron or less are easily generated. Incidentally, conventionally, the organic film 15 has been baked so as not to form bubbles. The baking temperature was within the glass transition temperature + 10 ° C. On the other hand, if the baking temperature is too high, the bubbles (cavities) 16 become large, so that the quality of the porous dielectric film 18 is deteriorated.

Next, an example of the second embodiment will be described with reference to the manufacturing process diagram of FIG.

As shown in FIG. 2A, a silicon oxide film 12 is formed on a substrate (silicon substrate) 11 in the same manner as described with reference to FIG.
After being formed to a thickness of nm, the metal wiring 13 is formed on the upper surface thereof. Further, the metal wiring 1 is formed on the silicon oxide film 12.
3 is formed to a thickness of, for example, 100 nm.

Next, as shown in FIG. 2B, the silicon oxide film 14 is irradiated with plasma using dinitrogen oxide (N ₂ O) gas to activate the surface of the silicon oxide film 14. . That is, oxygen atoms on the surface of the silicon oxide film 14 are removed by plasma irradiation, and dangling bonds are formed. Therefore, the surface of the silicon oxide film 14 becomes a reactive surface. When performing the above plasma irradiation, using a parallel plate type plasma generator as an example,
RF (13.56 MHz) power was set to 300 W to perform the above plasma irradiation.

Next, as shown in FIG.
_Three(CF_Two)_nCH_TwoSiCl_Three, CF _Three(CF_Two)_n
CH_TwoSi (OMe)_ThreeOr CF_Three(CF_Two)_nC
H_TwoSi (OH)_ThreeIt's like the chemical formula
Loose silane coupling agent is applied by spin coating
Apply silane to the surface of activated silicon oxide film 14
The coupling film 21 is formed. In the above chemical formula,
Me represents a methyl group.

Next, as shown in FIG.
A fluorocarbon having a structure represented by a chemical formula [1] dissolved in a fluorocarbon-based solvent (for example, florinate) by a spin coating method in the same manner as described with reference to FIGS. 1 (2) to (4) of the embodiment. A base resin (for example, Teflon AF) is applied on the silicon oxide film 14 activated by applying a silane coupling agent,
For example, an organic film 15 having a thickness of 500 nm was formed. Thereafter, the organic film 15 is baked to form bubbles (cavities) 16 in the organic film 15. Further, the organic film 15 is annealed to form the porous dielectric film 17. Next, a silicon oxide film 18 is formed on the porous dielectric
It is formed to a thickness of nm.

In the second embodiment, the same operation and effect as those described in the first embodiment can be obtained.
After the surface of the silicon oxide film 14 was activated by plasma irradiation, a silane coupling agent was applied, and then the organic film 15 was formed on the silicon oxide film 14. And the adhesiveness with the film is increased.

Next, a third embodiment will be described. The third embodiment differs from the first embodiment or the second embodiment only in the method of forming the porous dielectric film 17. Therefore, here, only the method of forming the porous dielectric film 17 will be described.

As the fluorocarbon resin, use is made of a cyclopolymerized fluorinated polymer resin (for example, Cytop (trade name)) having a structure represented by the chemical formula [2], and a fluorocarbon solvent [for example, 3M Company: Florinert (trade name)]. The fluorocarbon-based resin is not limited to the cyclopolymerized fluorinated polymer-based resin, but may be any material having a structure represented by the chemical formula [2].

[0033]

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First, the above cyclopolymerized fluorinated polymer resin (Cytop) is dissolved in a fluorocarbon solvent (eg, Fluorinert). Then, Cytop dissolved in the above florinate is applied on the substrate by a spin coating method to form an organic film having a thickness of, for example, 500 nm. The spin coating condition is, for example, a rotation speed of 3
000 rpm. Thereafter, as a pressure atmosphere lower than the saturated vapor pressure of the solvent in the temperature atmosphere (but a pressure atmosphere higher than the industrial vacuum), for example, an atmosphere of 10 Pa and a glass transition temperature of CYTOP of 12
Baking is performed for 5 minutes at 150 ° C. at a temperature higher than 0 ° C. and lower than its pyrolysis temperature of 420 ° C. By this baking, about 99% of the solvent in the organic film is volatilized. Then, as the solvent is volatilized, fine bubbles (cavities) of sub-quarter micron size or less are formed inside the organic film.

Further, as the pressure atmosphere lower than the saturated vapor pressure of the solvent (but higher than the industrial vacuum), for example, an atmosphere of 10 Pa and higher than the glass transition temperature of Cytop (120 ° C.) Temperature (4
Annealing is performed at 300 ° C. lower than 50 ° C.) for 30 minutes. By this annealing, the organic film is completely volatilized and hardened in a state in which bubbles (cavities) are formed, and becomes a porous dielectric film. This porous dielectric film has a relative dielectric constant of about 1.2 to 1.8.

In the third embodiment, the same operations and effects as described in the first embodiment can be obtained. When the activation treatment by plasma irradiation and the application of the silane coupling agent are performed as in the second embodiment, the same operations and effects as described in the second embodiment can be obtained.

Next, a fourth embodiment will be described. This fourth embodiment differs from the first embodiment or the second embodiment only in the method of forming a porous dielectric film, as in the third embodiment. Therefore, here, only the method for forming the porous dielectric film will be described.

The fluorocarbon resin has the chemical formula [3]
And a fluorocarbon-based solvent [eg, Fluorinert (trade name) manufactured by 3M Company] is used as the solvent. The fluorocarbon-based resin is not limited to the fluorinated polyallyl ether-based resin, and may be any material having a structure represented by the chemical formula [3].

[0039]

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First, the above-mentioned fluorinated polyallyl ether resin (for example, FLARE (trade name)) is dissolved in a fluorocarbon-based solvent (for example, florinate (trade name)). Then, FLARE dissolved in the above florinate is applied on the substrate by a spin coating method to form an organic film having a thickness of, for example, 500 nm. The spin coating conditions were, for example, a rotation speed of 3000 rpm. Thereafter, a pressure atmosphere lower than the saturated vapor pressure of the solvent in the temperature atmosphere (however, a pressure atmosphere higher than the industrial vacuum), for example, 10
Baking is performed for 5 minutes at 350 ° C. in an atmosphere of Pa and at a temperature higher than 260 ° C., which is the glass transition temperature of CYTOP, and lower than its thermal decomposition temperature, 500 ° C.
This baking will result in approximately 99% of the solvent in the organic film.
About% volatilizes. Then, as the solvent is volatilized, fine bubbles (cavities) of sub-quarter micron size or less are formed inside the organic film.

Further, as the pressure atmosphere lower than the saturated vapor pressure of the solvent (but higher than the industrial vacuum), for example, an atmosphere of 10 Pa and higher than the glass transition temperature (260 ° C.) of CYTOP, Temperature (5
Annealing is performed at 450 ° C., which is lower than (00 ° C.), for 30 minutes. By this annealing, the organic film is completely volatilized and hardened in a state in which bubbles (cavities) are formed, and becomes a porous dielectric film. This porous dielectric film has a relative dielectric constant of about 1.2 to 1.8.

The above FLARE has a thermal decomposition temperature of 5
Although a substrate having a temperature of about 00 ° C. is used, in a process of manufacturing a semiconductor device, usually, only a heating step at a temperature of 450 ° C. or lower can be performed in a step after forming an aluminum (Al) wiring. Therefore, the annealing was performed at 450 ° C.

In the fourth embodiment, the same operations and effects as described in the first embodiment can be obtained. When the activation treatment by plasma irradiation and the application of the silane coupling agent are performed as in the second embodiment, the same operations and effects as described in the second embodiment can be obtained.

[0044]

As described above, according to the present invention,
An organic film formed by applying a fluorocarbon resin dissolved in a solvent on a substrate is subjected to a heat treatment in an atmosphere at a temperature higher than the glass transition temperature of the fluorocarbon resin and lower than the thermal decomposition temperature, so that a microscopic A void is formed, and the solvent in the organic film is easily released outside through the void. In addition, since the pressure atmosphere in the temperature atmosphere is lower than the saturated vapor pressure of the solvent, the solvent is vaporized, and small bubbles (cavities) can be generated in the organic film. Therefore, a structure having microbubbles (cavities) in the organic film can be stably formed, and the relative dielectric constant of the porous dielectric film (relative dielectric constant 1) is lower than that of a conventional so-called low dielectric constant film. .2 to 1.8).

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of a first embodiment according to the present invention.

FIG. 2 is a manufacturing process diagram of a second embodiment.

[Explanation of symbols]

 11 Substrate 15 Organic film 17 Porous dielectric film

Claims (2)

[Claims] 1. A method for forming a porous dielectric film, comprising: applying a fluorocarbon resin dissolved in a solvent on a substrate to form an organic film; and forming the organic film on a glass of the fluorocarbon resin. A porous dielectric film, wherein the heat treatment is performed in an atmosphere at a temperature higher than the transition temperature and lower than the thermal decomposition temperature of the fluorocarbon resin, and at a pressure lower than the saturated vapor pressure of the solvent in the temperature atmosphere. Manufacturing method. 2. The method for producing a porous dielectric film according to claim 1, wherein said fluorocarbon resin is made of a mixture of polytetrafluoroethylene and paradioxole.