JP3225694B2 - Method for forming silicon nitride film and CVD apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention relates to Oyo method for forming a silicon nitride film Beauty C VD device.

[0002]

2. Description of the Related Art In a manufacturing process of an LSI, a high-temperature heat-treating low-pressure CVD method is often used for forming wirings and transistors, forming an interlayer insulating film of wirings, and the like. As a feature of the apparatus used for the low-pressure CVD, that is, the low-pressure CVD apparatus, a plurality of wafers can be processed in one batch, so that the throughput is high (100 to 150 wafers can be processed per batch), and Since the reaction on the wafer surface is used, the distribution in the wafer surface is very good, and the coverage for steps is also good.

[0003] In addition, the low-pressure CVD method covers a wide variety of film types that can be formed, such as formation of a polycrystalline Si-based thin film using SiH ₄ gas or the like, and formation of a SiO ₂ film using a TEOS (tetraethoxysilane) -based gas. The formation of a Si ₃ N ₄ film using SiH ₂ Cl ₂ and NH ₃ gas is performed.

The Si ₃ N ₄ film has a very high dielectric constant and is used as an insulating film or a dielectric film of a capacitor such as a DRAM. FIG. 4A shows an example of the structure of this capacitor. In this capacitor, Si ₃ on the lower electrode 101 made of Si substrate or a polycrystalline Si film
An N ₄ film 102 is formed, and an upper electrode 104 made of a polycrystalline Si film is formed on a SiO ₂ film 103 for reducing leakage current formed by oxidizing the surface of the Si ₃ N ₄ film 102. ing. In this case, a dielectric film is formed by the Si ₃ N ₄ film 102 and the SiO ₂ film 103.

[0005] In recent years, as LSI elements have become finer, the dielectric film of the above-mentioned capacitor has become thinner, and the requirements thereof have become particularly severe. The capacitance of the capacitor is given by C = ε (S / d), where ε is the dielectric constant of the dielectric film, d is its film thickness, and S is the electrode area.
This is because, in order to secure the capacitance C, it is necessary to reduce the film thickness d for miniaturization of the capacitor, that is, reduction of the electrode area S. At present, a Si ₃ N ₄ film used as a dielectric film can be formed with a film thickness of about 6 to 7 nm, but further study on thinning is proceeding.

[0006]

As described above, as the thickness of the Si ₃ N ₄ film used as the dielectric film of the capacitor is reduced, the capacitance C increases. Is reduced. This phenomenon, in the surface oxidation of the Si ₃ N ₄ film 102 above process, when the Si ₃ N ₄ film 102 is thin, not only on the surface thereof is oxidized, will be oxidized to the lower electrode 101 In addition, as a result, the distance d between the electrodes substantially increases, and as a result, the capacitance C decreases. FIG. 4B shows an example of the structure of the capacitor at this time. In FIG. 4B, reference numeral 105 denotes a Si formed on the lower electrode 101.
₂ shows an O ₂ film. Although the mechanism of the deterioration of the oxidation resistance of the Si ₃ N ₄ film described above is not clear, it is supposed that the film has poor oxidation resistance in the initial growth stage of the Si ₃ N ₄ film. Therefore, it is an issue to prevent the oxidation resistance of the Si ₃ N ₄ thin film from deteriorating.

Japanese Patent Application Laid-Open No. Sho 60-236214 discloses a laser CVD method for growing a film by irradiating visible laser light onto a substrate on which nuclei have been formed by ultraviolet irradiation. Japanese Patent Application Laid-Open No. 62-7122 discloses a method of manufacturing a Si-based thin film while irradiating a solid beam in a discharge plasma and irradiating a laser beam. A pre-excitation light CVD method is disclosed, and JP-A-62-224923 discloses an ECR plasma CVD method followed by a light CVD method.
A method for forming a thin film by the method is disclosed in
No. 19 discloses a method of forming an amorphous Si thin film by high-frequency plasma discharge and light irradiation by preliminarily decomposing a raw material gas, and Japanese Unexamined Patent Publication No. Hei 3-159991 discloses a silicon nitride film formed by plasma generation by microwaves and photoexcitation. Are disclosed, but neither of these discloses or suggests the configuration of the present invention. Therefore, an object of the present invention is to form a silicon nitride film having good oxidation resistance and good film quality.
Suitable for silicon nitride film forming method and its implementation
And to provide a a C VD devices.

[0008]

In order to achieve the above object, the present invention provides a silicon nitride film formed on silicon by using a nitrogen-based gas and a silicon-based gas by a low pressure CVD method. In the method for forming a film, a step of introducing a photoexcited nitrogen-based gas into a reaction chamber and a step of introducing a silicon-based gas into the reaction chamber in a non-excited state after starting introduction of the photoexcited nitrogen-based gas into the reaction chamber And a process.

[0009]

[0010]

[0011]

[0012] The present invention also have a silicon-based gas inlet for introducing nitrogen-containing gas inlet and a silicon-based gas for introducing nitrogen-based gas, nitride on a silicon sheet
In a CVD apparatus for forming a silicon film , a nitrogen-based
The gas inlet, nitrogen prior to introducing the nitrogen-based gas into the reaction chamber
It has a photo-excitation means for photo-exciting the system gas, and after starting introduction of the photo-excited nitrogen-based gas into the reaction chamber using the photo-excitation means from the nitrogen-based gas inlet, the silicon-based gas is introduced from the silicon-based gas inlet. It is characterized in that it is configured to be introduced into the reaction chamber without being excited.

[0013]

[0014]

[0015]

[0016]

According to the method for forming a silicon nitride film of the present invention, since the introduction of the photoexcited nitrogen-based gas into the reaction chamber is started, the silicon-based gas is introduced into the reaction chamber without being excited. In addition, the effect of the excitation of the nitrogen-based gas allows the reaction to be favorably performed even at the initial stage of the growth of the silicon nitride film. Therefore, it is possible to form a silicon nitride film having a good film quality including the initial growth layer on the underlying silicon. Can be. In particular, in the initial growth stage, as a result of the formation of Si-N by a pre photoexcited nitrogen-based gas is promoted, so that the surface of the initial reaction is Si-rich is suppressed, also initial growth layer on the underlying silicon In addition, a silicon nitride film having good oxidation resistance can be formed.

According to the CVD apparatus of the present invention, nitrogen
The system gas inlet, nitrogen prior to introducing the nitrogen-based gas into the reaction chamber
A photo-excitation means for photo- exciting the element-based gas, and after starting introduction of the photo-excited nitrogen-based gas into the reaction chamber from the nitrogen-based gas inlet using the photo-excitation means, silicon is configured so as to introduce into the reaction chamber in a state of not excited silicon-based gas from the system gas inlet may be film quality with good good oxidation resistance to form a good silicon nitride film on the silicon .

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a low pressure CVD apparatus used in the first embodiment of the present invention. As shown in FIG. 1, in this low-pressure CVD apparatus, an inner tube 2 is provided in a reaction chamber 1 capable of evacuating, and a wafer boat 3 is accommodated in the inner tube 2. A plurality of wafers 4 can be placed on the wafer boat 3. A heater 5 is provided outside the reaction chamber 1, and the heater 5 can heat the wafer 4.

A gas excitation chamber 6 is provided below the reaction chamber 1. The upper part of the gas excitation chamber 6 is partitioned by a light transmission window 7 made of, for example, quartz, and a low-pressure mercury lamp 8 is provided in a space above the light transmission window 7.
The low-pressure mercury lamp 8 can irradiate light to the space below the light transmission window 7. In addition, a gas can be introduced into the gas excitation chamber 6 from the outside through the injector 9, and the gas in the gas excitation chamber 6 can be introduced into the inner tube 2 from below through the injector 10. I can do it. On the other hand, apart from this,
The injector 11 is inserted into the inner tube 2 from below.
The gas can be introduced through. Next, a method of forming a Si ₃ N ₄ film using the low-pressure CVD apparatus configured as described above will be described.

[0020] First, the wafer 4, for example, a silicon wafer in advance and heated to a predetermined temperature, introducing NH ₃ gas from the injector 9 into the gas excitation chamber 6 in its state by the heater 5, a low-pressure mercury lamp in the NH ₃ gas The light is excited by irradiating light with 8, and the excited NH ₃ gas is introduced into the inner tube 2 in the reaction chamber 1 from below. As a result, the inner tube 2 is filled with excited species such as NH ₂ and H generated by decomposition of NH ₃ molecules. Next, SiH ₂ Cl ₂ gas is introduced from below into the inner tube 2 in the reaction chamber 1 from the injector 11,
An Si ₃ N ₄ film is formed. Here, as an example of the growth conditions, temperature 760 ° C., pressure 0.2 Torr, SiH
₂ Cl ₂ flow rate 20 sccm, NH ₃ flow rate 200 sccc
m, the flow rate of N ₂ as a carrier gas is 80 sccm.

According to the first embodiment, the NH ₃ gas, which is one of the reaction gases, is excited by light irradiation in the gas excitation chamber 6 as described above, and then is introduced into the inner tube 2 in the reaction chamber 1. introduced, Si ₃ by separately reacting the SiH ₂ Cl ₂ gas introduced into the inner tube 2 from this
Since the N ₄ film is formed, Si ₃ N having good oxidation resistance
_Four films can be formed. And this method is DR
By applying the present invention to the formation of a Si ₃ N ₄ film as a dielectric film of a capacitor such as an AM, the oxidation resistance of the film can be increased. Therefore, the surface of the Si ₃ N ₄ film is oxidized to reduce leakage current. At this time, it is possible to prevent the lower electrode from being oxidized, thereby increasing the distance between the electrodes and reducing the capacitance of the capacitor. Here, the growth mechanism of the Si ₃ N ₄ film will be considered.

First, ordinary SiH ₂ Cl ₂ gas and N
The mechanism of the growth of the Si ₃ N ₄ film using H ₃ gas is shown in FIG.
As shown in FIG. 2A, an insertion reaction of SiCl ₂ , which is a decomposed species of SiH ₂ Cl ₂ , occurs in the N—H bond, and a Si—N bond is formed as shown in FIG. 2B. After the formation of the Si—N bond, a reaction in which HCl is eliminated occurs, as shown in FIG. 2C. Next, as shown in FIG. 2D, an Si—N bond is formed by bonding NH ₂ to the formed Si—Cl surface. By repeating this, a Si ₃ N ₄ film is formed.

Next, the initial growth process of the Si ₃ N ₄ film will be considered. That is, the initial growth of the Si ₃ N ₄ film is S
Unlike Si ₃ N ₄ grown on i ₃ N ₄ , the underlayer is considered to be the Si surface. Near this surface, SiCl ₂
And the like may be directly bonded to Si on the surface and the film deposition may be promoted by the formation of a Si—Si bond. Therefore, when the thickness of the Si ₃ N ₄ film is small, the oxidation resistance is low. May be inferior. In this case, Si ₃ N
_{4 During} the surface oxidation of the film, Si-O bonds are easily formed,
That is, it is easily oxidized. In addition, since oxygen easily diffuses into the Si—O layer, the underlying polycrystalline Si is easily oxidized. However, in the first embodiment, since the reaction is carried out using the NH ₃ gas previously excited in the gas excitation chamber 6 as described above, the Si—N
The formation of the bond can be promoted, and the Si ₃ N ₄ film can be prevented from becoming Si-rich in the initial growth process. As described above, a Si ₃ N ₄ film having good oxidation resistance is formed.

Next, a second embodiment of the present invention will be described. FIG. 3 shows a reduced pressure CVD used in the second embodiment.
The device is shown. This low-pressure CVD apparatus has the same configuration as the low-pressure CVD apparatus used in the first embodiment, except that a parallel plate electrode 12 for plasma excitation is provided in the gas excitation chamber 6.

Using the low pressure CVD apparatus shown in FIG.
In order to form an i ₃ N ₄ film, NH ₃ is injected from the injector 9.
₃ gas is introduced into the gas excitation chamber 6, plasma is generated by applying high frequency power between the electrodes 12 a and 12 b of the parallel plate electrode 12, and the NH ₃ gas is excited and the NH ₃ gas is introduced into the inner space of the reaction chamber 1. Introduce into tube 2. Next, Si
H ₂ Cl ₂ gas is introduced from the injector 11 into the inner tube 7 in the reaction chamber 1 to form a Si ₃ N ₄ film. Others are the same as those described in the first embodiment. The growth conditions can be the same. According to the second embodiment, similarly to the first embodiment, Si ₃ N _{4 having} good oxidation resistance is used.
A film can be formed.

The reduced pressure CV used in the first embodiment
Although both the D apparatus and the low pressure CVD apparatus used in the second embodiment are of a batch processing type, a single-wafer type low pressure CVD apparatus may be used instead of these apparatuses.

[0027]

As described above, according to the present invention,
A silicon nitride film having favorable oxidation resistance and favorable film quality can be formed.

[Brief description of the drawings]

FIG. 1 shows a reduced pressure CV used in a first embodiment of the present invention.
It is an approximate line figure showing D device.

FIG. 2 is a schematic diagram for explaining a growth mechanism of a Si ₃ N ₄ film.

FIG. 3 shows a reduced pressure CV used in a second embodiment of the present invention.
It is an approximate line figure showing D device.

FIG. 4 is a cross-sectional view illustrating an example of a structure of a capacitor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction chamber 2 Inner tube 4 Wafer 6 Gas excitation chamber 8 Low-pressure mercury lamp 9, 10, 11 Injector 12 Parallel plate electrode

Claims (6)

(57) [Claims] 1. Use of a nitrogen-based gas and a silicon-based gas,
A method of forming a silicon nitride film on silicon by low- pressure CVD, comprising: introducing the photoexcited nitrogen-based gas into a reaction chamber; and reacting the photoexcited nitrogen-based gas with the nitrogen-based gas. Introducing the silicon-based gas into the reaction chamber in a state where the silicon-based gas is not excited after the introduction into the chamber is started. 2. The method for forming a silicon nitride film according to claim 1, wherein NH ₃ is used as said nitrogen-based gas. 3. The method according to claim 1, wherein the silicon-based gas is SiH ₂ Cl.
_{2. The} method for forming a silicon nitride film according to claim 1, wherein ₂ is used. 4. The method for forming a silicon nitride film according to claim 1, wherein a mercury lamp is used as the light excitation means for performing the light excitation. 5. A nitrogen-based gas inlet for introducing a nitrogen-based gas and a silicon-based gas for introducing a silicon-based gas.
Possess a scan inlet forming a silicon nitride film on the silicon
In the CVD apparatus for, to the nitrogen-based gas inlet has a light excitation means for photoexcitation of the nitrogen-based gas before being introduced into the reaction chamber the nitrogen-based gas, from the nitrogen-based gas inlet, said photoexcitation after starting the introduction into the reaction chamber of the photoexcited the nitrogen-based gas using the means, the silicon from the silicon-based gas inlet
A CVD apparatus characterized in that a system gas is introduced into the reaction chamber without being excited. 6. The CVD apparatus according to claim 5, wherein a mercury lamp is used as said light excitation means.