JPH09249851A - Reduction of relative permittivity of polymer thin film and formation of interlaminar insulating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide methods for forming both a polymer thin film having stable characteristics and an interlayer insulating film in a simple process. SOLUTION: A diamine and a diisocyanate as raw material monomers are evaporated in a vacuum to carry out the vapor deposition polymerization thereof on a substrate to form a low-molecular weight polyurea film, which is then irradiated with ultraviolet rays and heat-treated to perform cross-linking reaction and provide a high molecular weight. Thereby, the relative permittivity of the polyurea film is reduced. 4,4'-Diaminodiphenylmethane(MDA) is used as the diamine and 4,4'-diphenylmethane diisocyanate(MDI) is used as the diisocyanate. As a result, the relative permittivity of an interlayer insulating film 23 can be reduced to 3.08.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing the relative dielectric constant of a polymer thin film used as, for example, an interlayer insulating film of a semiconductor device.

[0002]

2. Description of the Related Art Conventionally, as an interlayer insulating film of a semiconductor device, an SOG (Spin on Glass) film or a CV
A SiO ₂ film formed by the D method (Chemical Vapor Deposition method: Chemical Vapor Deposition) is mainly used. The relative permittivity of the interlayer insulating film formed by these methods is about 4, but recently, a reduction in the relative permittivity of the interlayer insulating film has become a major issue due to the progress of high integration of LSI, and the relative permittivity is increased. An interlayer insulating film having a rate of 4 or less is required.

In order to meet such demands, in recent years, a SiOF film obtained by adding fluorine to a SiO ₂ film formed by a plasma CVD method has been proposed. According to this film, the relative dielectric constant of an interlayer insulating film is improved. It can be suppressed to about 3.7 to 3.2.

[0004]

However, such a conventional technique has the following problems. That is, while the SiOF film formed by the above-mentioned plasma CVD method can achieve a low relative dielectric constant, the film characteristics greatly differ depending on the film forming method and the film forming conditions, and the desorption and the hygroscopicity of fluorine in the film are large. It has been pointed out that the dielectric constant deteriorates due to the instability of the film, and it is difficult to apply it as a low dielectric constant material in the future.

Further, a power source for generating plasma, supply of gas or liquid material, equipment for removing reaction gas, etc. are required, resulting in high cost.

On the other hand, since the SOG film formed by the spin coating method is formed by baking at a temperature near 400 ° C. to remove the organic solvent and performing a dehydration polymerization reaction, there are problems such as generation of water and a large number of steps. is there.

The present invention has been made in order to solve the problems of the prior art as described above, and a method for lowering the relative dielectric constant of a polymer thin film having stable characteristics in a simple process and forming an interlayer insulating film. It is intended to provide a method.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, irradiating a low molecular weight polyurea film formed by vapor deposition polymerization with ultraviolet rays to perform heat treatment, It has been found that the relative permittivity of the polyurea film can be lowered, and the present invention has been completed.

That is, according to the first aspect of the invention, diamine and diisocyanate as raw material monomers are evaporated in a vacuum, and these are vapor-deposited and polymerized on a substrate to form a polyurea film having a low molecular weight. A method for lowering the relative dielectric constant of a polymer thin film is characterized in that the relative dielectric constant of the polyurea film is reduced by subjecting this polyurea film to irradiation of ultraviolet rays and heat treatment to crosslink and increase the molecular weight.

In this case, as the starting material diamine, 4,4'-diaminodiphenyl ether, 4,4'-diamino 3,3'-dimethyldiphenylmethane, 4,4'-diaminodiphenylmethane 4,4'-diaminodiphenyl sulfide is used. Etc. can be used, and as the other raw material monomer diisocyanate, methylenediphenyl 4,4′-diisocyanate, 3,3′-dimethyldiphenyl 4,4′-diisocyanate, etc. can be used.

Particularly, when 4,4'-diaminodiphenylmethane (MDA) is used as the diamine and 4,4'-diphenylmethane diisocyanate (MDI) is used as the diisocyanate, the effect is obtained. Target.

The wavelength of ultraviolet rays to be irradiated for lowering the relative dielectric constant is i-line (365 nm), KrF excimer laser (248 nm), ArF excimer laser (193n).
m) or the like having a selected wavelength can be used.

The heat treatment is carried out at a temperature of about 200 ° C. and a time of about 30 minutes. In this case, the processing atmosphere may be air or vacuum.

On the other hand, the invention of claim 3 evaporates diamine as a raw material monomer and diisocyanate in a vacuum, and vaporizes and polymerizes them on a semiconductor substrate on which metal wiring is formed to form a low molecular weight polyamine. After forming a urea film, this polyurea film is irradiated with ultraviolet rays and heat-treated to form a polymer thin film having a low relative dielectric constant by crosslinking reaction and increasing the molecular weight, thereby forming an interlayer insulating film. Is the way.

In this case, as described in claim 4, in the invention described in claim 3, 4,4'-diaminodiphenylmethane (MDA) is used as the diamine and 4,4'-diphenylmethanediamine is used as the diisocyanate. It is also effective to use isocyanate (MDI).

In the case of the invention according to claim 1 or 2, which has such a constitution, a diamine (for example, 4,4'-diaminodiphenylmethane) as a raw material monomer and a diisocyanate (for example, 4,4'-diphenylmethane) are used in a vacuum. Diisocyanate) and these are vapor-deposited and polymerized on the substrate to form a low molecular weight polyurea film. This polyurea film is an oligomer film and has a relative dielectric constant of about 4. Then, when the polyurea film is irradiated with ultraviolet rays and heat-treated,
At the same time as the molecular weight increases due to the reaction of the unreacted terminal groups, the urea binding portion undergoes a cross-linking reaction, whereby the urea binding portion changes and the relative dielectric constant decreases to around 3.

Then, as in the invention according to claim 3 or 4, a diamine as a raw material monomer (for example,
4,4'-diaminodiphenylmethane) and diisocyanate (for example, 4,4'-diphenylmethane diisocyanate) are evaporated, and these are vapor-deposited and polymerized on the semiconductor substrate on which the metal wiring is formed to form a low molecular weight poly After the urea film is formed, this polyurea film is irradiated with ultraviolet rays and heat-treated to form a polymer thin film by a crosslinking reaction and a high molecular weight, so that it is lower than the SOG film or SiO ₂ film currently used. An interlayer insulating film having a relative dielectric constant (about 3) can be obtained.

As described above, according to the present invention, the baking process of the SOG film by the spin coating method is not necessary and water is not generated. Furthermore, SiO by plasma CVD method
Unlike the F film, the problem of deterioration of characteristics due to film instability does not occur, and simple equipment is sufficient.

[0019]

Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a schematic configuration of an example of a polyurea film forming apparatus for carrying out the present invention.

As shown in FIG. 1, in this device,
First and second processing chambers 1 and 2 are provided, and these first and second processing chambers 1 and 2 are connected via a gate valve 3. The first and second processing chambers 1 and 2 are connected to a vacuum exhaust system such as a vacuum pump (not shown).

A substrate 4 to be processed is provided in the first processing chamber 1.
Is held by the substrate holder 5. The substrate holder 5 is attached to the tip of a transfer arm 6 that is arranged so as to penetrate the outside of the first processing chamber 1. The transfer arm 6 is configured to be movable in the horizontal direction as the transfer motor 7 rotates. That is, a screw portion is formed on the shaft 8 of the transfer motor 7, and a screw portion is also formed on the distal end portion of the transfer arm 6, and the transfer arm 6 moves in the direction of the arrow due to the meshing of these parts. It is configured to enter 2.

An electron beam heating source 9 is arranged below the first processing chamber 1. Aluminum, which is the evaporation material 10, is placed on the electron beam heating source 9. A shutter 11 is provided between the substrate 4 and the electron beam heating source 9,
A film thickness monitor 12 for detecting the film thickness of the thin film formed on the substrate 4 is provided near the shutter 11.

On the other hand, below the second processing chamber 2, evaporation sources 13A and 13B of two kinds of monomers are arranged. Evaporation containers 15A and 15B are provided in the housings 14A and 14B of the evaporation sources 13A and 13B, respectively.
The monomers A and B are respectively injected into the evaporation containers 15A and 15B, and the heaters 16A for heating the monomers A and B are provided in the vicinity of the evaporation containers 15A and 15B. 16B is provided. Further, a partition plate 17 for preventing the vapors of the monomers A and B from mixing with each other is arranged between the evaporation sources 13A and 13B.
On the other hand, the shutter 1 is provided above the evaporation sources 13A and 13B.
8 is provided, and the film thickness monitor 12 is provided near the shutter 18.

When a polyurea film is formed on the substrate 4 using this apparatus, the gate valve 3 is opened and the motor 7
Is rotated to transfer the substrate 4 to the processing chamber 2. Then, with the shutter 18 closed, the pressure in the second processing chamber 2 is set to a predetermined value, and the heater 16A, while measuring the evaporation amount of each raw material monomer A, B by the film pressure monitors 12, 12.
The raw material monomers A and B are heated to a predetermined temperature by 16B.

Next, after the respective raw material monomers A and B have reached a predetermined temperature to obtain a required evaporation amount, the shutter 1
8 is opened, a polyurea film is vapor-deposited on the substrate 4 at a predetermined deposition rate, and after the deposition, the shutter 18 is closed to cause a polymerization reaction of polyurea on the substrate 4 to form a polyurea film.

After that, the substrate 4 is taken out from the second processing chamber 2, and ultraviolet rays having a wavelength of 230 nm to 500 nm are applied to the entire surface of the polyurea film for a predetermined time and heat treatment is performed to crosslink and increase the molecular weight. Thereby lowering the relative dielectric constant of the polyurea film. In this case, the heat treatment conditions are
The temperature is about 200 ° C. and the time is about 30 minutes. Also,
The processing atmosphere may be air or vacuum.

2A to 2E show an example of a process of forming an interlayer insulating film of a semiconductor device by a vapor deposition polymerization method of a polyurea film according to the present invention. First, as shown in FIG. 2A, a semiconductor substrate 20, a silicon thermal oxide film 21 formed on the surface of the semiconductor substrate 20 and having a window opened in a predetermined position, and a film formed thereon and patterned. A substrate 31 made of, for example, Si having the first-layer wiring 22 subjected to the above is prepared.

On the surface of the substrate 31, a polyurea film is formed over the entire surface to a desired thickness by the vapor deposition polymerization method to form an interlayer insulating film 23, and then the ultraviolet ray 2 is applied to the interlayer insulating film 23.
Irradiation and heat treatment of No. 4 are performed (FIG. 2B) to carry out a crosslinking reaction and a high molecular weight.

Next, a resist film 25 having a predetermined pattern is formed on the surface of the interlayer insulating film 23 (FIG. 2C), and dry etching is performed to expose the interlayer exposed in the window opening portion of the resist film 25. The insulating film 23 is removed (FIG. 2
(d)). Then, after removing the resist film 25 described above,
A wiring thin film is formed on the entire surface and patterned to form the second-layer wiring 26. Then, the wiring 22 of the first layer and the wiring 26 of the second layer are electrically connected at the window opening portion 27 where the interlayer insulating film 23 is removed, and as a result, the semiconductor device 35 having the multilayer wiring is formed. Can be obtained (Fig. 2
(e)).

According to the present embodiment, since the inter-layer insulation film 23 is composed of the polyurea film having a low relative dielectric constant, the inter-layer insulation film 23 is formed between the first layer wiring 22 and the second layer wiring 26. The capacitance of the capacitor formed in 1 becomes small, and the operation speed of the semiconductor device 35 can be improved.

[0031]

EXAMPLES Hereinafter, specific examples of the present invention will be described together with comparative examples. A polyurea film was formed on the substrate 4 using the apparatus shown in FIG. First, in the substrate holder 5, the length 76
A substrate 4 made of, for example, Corning # 7059 having a size of mm × width 26 mm × thickness 1.0 mm is attached, and aluminum as the evaporation material 1 is evaporated by electron beam (E / B) heating of 7 in the processing chamber 1 to monitor the film thickness. 1
The lower electrode is formed on the substrate 4 by vapor deposition so that the thickness is 1000 Å while controlling the evaporation rate at 2.
In this case, the gate valve 3 is closed, the temperature of the substrate 4 is kept at 20 ° C., and the pressure in the first processing chamber 1 during the deposition is set to 3 °.
It was set to × 1 ⁻³ Pa.

Next, the gate valve 3 is opened and the motor 7
Is rotated to convey the substrate 4 to the processing chamber 2, and a polyurea film is deposited on the substrate 4. In this case, 4,4'-diaminodiphenylmethane (MDA) and 4,4'-diphenylmethane diisocyanate (MDI) were used as raw material monomers for forming the polyurea film, and they were used in a high vacuum (3 × 10 ^{− 3} P
In a) MDA is 100.0 ± 0.1 ° C and MDI
In regard to the above, the polyurea film was formed on the substrate 4 by evaporating at a temperature of 70.5 ± 0.1 ° C. and controlling the evaporation rate of each monomer by the film thickness monitor 6. In the case of this embodiment, MD
The composition ratio of A and MDI was controlled so that the stoichiometric ratio was 1: 1.

Then, the substrate 4 is taken out of the apparatus, and 23
The entire surface of the polyurea film was irradiated with ultraviolet rays having a wavelength of 0 nm to 500 nm, and heat treatment was performed to carry out a crosslinking reaction and a high molecular weight. In this case, the UV irradiation time is 30
And the heat treatment temperature was 200 ° C.

After the ultraviolet irradiation and the heat treatment, the substrate 4 is again inserted into the processing chamber 1, and aluminum is vapor-deposited under the same conditions as in the case of the lower electrode described above to form the upper electrode. A device was created. The relative permittivity of the polyurea film of this device was measured and found to be 3.08. In this case, the value of the relative permittivity is the multi-frequency LCR meter (model 4275) manufactured by Yokogawa Hewlett-Packard Company.
The capacitance C was measured using A) and calculated.

On the other hand, as a comparative example, the upper electrode and the polyurea film were formed by the same method as that of the example, and the lower electrode was formed on the polyurea film without irradiation of ultraviolet rays and heat treatment to obtain a relative dielectric constant. A device for measurement was prepared. When the relative permittivity of the polyurea film of this device was measured by the same method as in the example, it was about 4.0.

As described above, the polyurea film irradiated with ultraviolet rays had a dielectric constant of 3.08 at an irradiation time of 30 minutes, which was lower than that of the unirradiated ultraviolet rays film and the non-heat-treated film. From this, it was clarified that the relative permittivity of the polyurea film can be lowered by irradiating with ultraviolet rays and performing heat treatment.

[0037]

As described above, according to the present invention, since a polymer thin film is formed in a vacuum, a uniform film can be formed on a substrate without the need for a solvent, and the irradiation of ultraviolet rays can be performed. The heat treatment can lower the relative dielectric constant. Therefore, if the interlayer insulating film of the multi-layer wiring is formed using the present invention, the operation speed of the semiconductor device can be improved.

In addition, the polyurea film formed by vapor deposition polymerization is suitable as an interlayer insulating film of a semiconductor device because it can form a pattern like existing resist materials and has excellent step coverage. is there.

On the other hand, according to the present invention, the step of baking the SOG film by the spin coating method is not required and no water is generated, so that the step can be simplified. further,
It is possible to solve the problem of cost increase due to the deterioration of characteristics due to the instability of the film and the increase in complexity of the device like the SiOF film formed by the plasma CVD method.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of a polyurea film forming apparatus for carrying out the present invention.

FIG. 2 is a process chart showing an example of a process of forming an interlayer insulating film of a semiconductor device by a vapor deposition polymerization method of a polyurea film according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... 1st process chamber, 2 ... 2nd process chamber, 3 ... Gate valve, 4 ... Substrate, 5 ... Substrate holder, 12 ... Film thickness monitor, 13A, 13B ... Evaporation source, 15A, 15B ... Evaporation container , 16A, 16B ... Heater, 18 ... Shutter,
20 ... Semiconductor substrate, 21 ... Silicon thermal oxide film, 22 ... Wiring, 23 ... Interlayer insulating film, 24 ... UV, 25 ... Resist film, 26 ... Wiring, 31 ... Substrate, 35 ... Semiconductor device, A,
B ... Raw material monomer

Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location G03F 7/11 H01L 21/95 (72) Inventor Sadayuki Ukishima 5-9-7 Tokodai, Tsukuba, Ibaraki Japan Shin Sky Technology Co., Ltd., Tsukuba Institute for Super Materials

Claims (4)

[Claims] 1. A low molecular weight polyurea film is formed by evaporating diamine and diisocyanate as raw material monomers in a vacuum and vapor-depositing and polymerizing these on a substrate, and then the polyurea film is irradiated with ultraviolet rays. And a heat treatment to reduce the relative permittivity of the polyurea film by cross-linking and increasing the molecular weight of the polyurea film. 2. Use of 4,4′-diaminodiphenylmethane (MDA) as the diamine and 4,4′-diaminodiphenylmethane (MDA) as the diisocyanate.
4. The method for reducing the relative permittivity of a polymer thin film according to claim 1, wherein 4'-diphenylmethane diisocyanate (MDI) is used. 3. A low molecular weight polyurea film is formed by evaporating diamine and diisocyanate as raw material monomers in a vacuum and vapor-depositing and polymerizing these on a semiconductor substrate on which metal wiring is formed. A method for forming an interlayer insulating film, which comprises forming a polymer thin film having a low relative dielectric constant by subjecting a polyurea film to irradiation of ultraviolet rays and heat treatment to cause a crosslinking reaction and a high molecular weight. 4. A diamine is 4,4′-diaminodiphenylmethane (MDA), and a diisocyanate is 4,
The method for forming an interlayer insulating film according to claim 3, wherein 4'-diphenylmethane diisocyanate (MDI) is used.