JPH06232113A - Deposition of insulating film for semiconductor device - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance and step coverage of an insulating film by a method wherein a silicon oxide film is deposited, then, a film, which is continuously made to make a transition from the silicon oxide film to a silicon nitride film, is deposited and a silicon nitride film is deposited thereon. CONSTITUTION:In the case of a silicon nitride film, nitrogen gas N, which is one part of reaction gas, or in the case of a silicon oxide film, oxygen gas 0, which is one part of the reaction gas, is introduced into a plasma producing chamber 11 via a gas introducing tube 14, coils 30 for cyclotron resonance are arranged on the periphery of the chamber 11 and a D.C. magnetic field of a prescribed intensity is generated. After the silicon oxide film is deposited, the flow rate of the oxygen gas is decreased without charging the flow rate of silicon gas and the nitrogen gas is added and the flow rate of the nitrogen gas is increased. For example, the oxygen gas is continuously changed from 32cc/min to 0cc/main. In respect to the nitrogen gas it is continuously changed from 0cc/min to 300cc/min. Thereby, a high-practicability protective film can be obtained to an integrated circuit device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a deposition method for depositing an insulating film, particularly an insulating protective film, by a plasma CVD method on a wafer surface on which a semiconductor device such as an integrated circuit is formed.

[0002]

2. Description of the Related Art Almost all insulating films currently used in integrated circuits and the like are formed by a plasma CVD method using plasma discharge. However, in this plasma CVD method,
In order to obtain a good film quality or to secure the coverage of the step portion caused by wiring or the like, the temperature of the substrate is set to 40
It is necessary to heat up to about 0 ° C. Therefore, there is a problem in that the wiring and elements formed on the substrate may be damaged by the residual thermal stress during the temperature rise and fall.

Therefore, recently, electron cyclotron resonance (EC) which can obtain an insulating film of good quality even if the substrate temperature is low
R) Plasma method is beginning to be used. This is to generate plasma by utilizing the fact that the energy of microwave is absorbed by electrons with high efficiency by the electron cyclotron resonance phenomenon, and the plasma density becomes about two orders of magnitude higher than that of the normal plasma CVD method. Therefore, the substrate temperature is 20
An insulating film having a relatively good film quality can be deposited even at a temperature as low as 0 ° C. or lower, and the thermal stress on the wafer can be reduced and its damage can be prevented.

In such an ECR plasma CVD method, high-density plasma is generated in the plasma generation chamber, and this plasma is then drawn into the gas-phase reaction chamber, whereby the reaction gas is placed in this chamber while undergoing gas-phase reaction. An insulating film is deposited on the wafer. The plasma generation chamber is, for example, a cavity resonator for microwaves having a frequency of 2.45 GHz. A part of the reaction gas is introduced into the plasma generation chamber to be ionized by microwaves, and further, a specific intensity of, for example, 875 gauss DC A high-density plasma is generated by applying a magnetic field to cause electron cyclotron resonance in the ionized gas. In the gas phase reaction chamber, a reaction gas is subjected to a gas phase reaction in a plasma atmosphere drawn from the plasma generation chamber, and the reaction product is deposited as an insulating film on the wafer surface at 200 ° C., for example.

To deposit a silicon nitride film used as a protective film, nitrogen is introduced into the plasma generation chamber and silane is introduced into the gas phase reaction chamber. The silicon oxide film used as an interlayer insulating film can be deposited by introducing oxygen into the plasma generation chamber and silane into the gas phase reaction chamber.

[0006]

As described above, the ECR plasma CVD method has a feature that an insulating film can be deposited at a low temperature, but the plasma density generated by the cyclotron resonance causes the cavity resonance mode in the plasma generation chamber and the magnetic field distribution. It has a unique spatial distribution determined by, and tends to decrease from the center to the outside. Therefore, if the film is deposited as it is, the film thickness distribution becomes thick in the central part and thin in the peripheral part. In the case of a silicon nitride film, as a method of correcting this and improving the refractive index distribution at the same time, the present inventor first clarified that the high frequency power supplied to the wafer was set to a unit volume (cm ³ ) of the total gas flow rate, Per unit area (cm ² ) (2.5
~ 8) Introduce silane to be introduced into the vapor phase growth chamber at a flow rate of × 10 ^-3 W with a flow rate distribution such that the flow rate ratio is 3 or more near the boundary between the plasma generation chamber and the vapor phase reaction chamber and near the wafer. I proposed that (Japanese Patent Application No. 2-406170). At the same time, the bias potential of the wafer surface of 100 to 2 required for imparting the step coverage of the film while suppressing the stress in the film to 10 × 10 ⁹ dyne / cm ²
The gas flow rate ratio (nitrogen / silane), the high frequency power per unit volume of the total gas flow rate, and the gas pressure range were given as film forming conditions capable of generating 00V. However, in the case of a silicon nitride film, if it is attempted to maintain good film quality and step coverage, the internal stress of the film cannot be further reduced, and the same result as the above-mentioned thermal stress will result. Therefore, as a method of imparting good film quality and step coverage while further reducing the internal stress of the film with a little delay from the above proposal, the present inventor has a high internal power of 5 × when the high frequency power is reduced. A multilayer film is formed by alternately depositing a silicon nitride film having a density of 10 ⁹ dyne / cm ² or less and a silicon nitride film having an internal stress of 10 × 10 ⁹ dyne / cm ² or more with high frequency power increased. Proposed (Japanese Patent Application No. 3-220)
811). However, as described above, films having different internal stresses tend to peel when the thickness of each layer is large.
It is necessary to form each layer as thin as possible, which causes a problem that it takes time to obtain a desired film thickness.

As described above, the silicon nitride film formed by ECR plasma CVD, which is resistant to chemicals and has high water resistance as a protective film, is used in the semiconductor manufacturing process in view of the magnitude of internal stress or the film forming speed even if it is desired to use it. I haven't arrived. On the other hand, the silicon oxide film formed by the ECR plasma CVD method has much higher water resistance than the silicon oxide film formed by the conventional plasma CVD method as shown in FIG. 2, and is almost comparable to the silicon nitride film. As for the coverage of the step portion, the coating shape can be controlled without impairing the film quality. Moreover, the internal stress of the upper film is not so great as to adversely affect the integrated circuit. However, it is unsuitable as a protective film because it is etched very quickly with respect to chemical resistance, particularly hydrofluoric acid. Note that FIG. 2 shows a phosphor glass (PSG) film deposited on a wafer, a plasma oxide film (P-SiO ₂ ) by a conventional method, and a plasma TEOS (tetra-ethoxy-ortho-silene-silane-based raw material). Gas) oxide film (P-TEOS), ECR oxide film (ECR-
SiO ₂ ), plasma nitride film (P-Si
FIG. 3 is a diagram showing the residual amount of a peak of P═O (double bond between P and O) appearing at 1300 cm ⁻¹ in an infrared absorption spectrum after depositing N) and performing a pressure cooker test. The smaller the remaining amount is, the more water penetrated the insulating film.

The object of the present invention is to show corrosion resistance to corrosive chemicals such as hydrofluoric acid, to provide internal stress that does not adversely affect the integrated circuit in terms of stress, and has excellent step coverage. An object of the present invention is to provide a method for depositing a protective film for an integrated circuit, which does not particularly increase the film forming time.

[0009]

In order to solve the above-mentioned problems, in the present invention, as a method of depositing the insulating protective film for an integrated circuit, a part of the atmospheric gas used for forming the insulating film is partially electron cyclotron. In an apparatus in which an insulating film is to be deposited by making it into plasma by the resonance method and reacting with the remaining gas, first, a silicon oxide film is deposited, and then a transition is continuously made from the silicon oxide film to the silicon nitride film. Film is deposited, and a silicon nitride film is deposited thereon.

In this case, when depositing the silicon oxide film, the film in which the silicon oxide film is continuously transitioned to the silicon nitride film, and the silicon nitride film in this order, it is preferable to deposit them all at the same wafer temperature. In addition, the silicon oxide film,
The transition film and the silicon nitride film are preferably deposited under the following deposition conditions.

Deposition conditions of silicon oxide film: Oxygen gas flow rate: 30 to 40 cc / min Silane gas flow rate: 28 to 36 cc / min Silane / oxygen flow rate ratio: 0.8 to 1.0 Gas pressure in apparatus: 1 to 10 mTorr Microwave power: 400 to 1000 W High frequency power: 1.5 to 3.5 W / cm ² (per unit area of wafer surface) Wafer temperature: 150 to 250 ° C. Deposition condition of silicon nitride film: Nitrogen gas flow rate: 250 to 350 cc / min Silane gas flow rate: 28 to 36 cc / min Gas pressure in equipment: 40-100 mTorr Microwave power: 1200-1800 W High-frequency power: 0.3-1.0 W / cm ² (per unit area of wafer surface) Wafer temperature: 150-250 ° C Transition film: Silicon oxide film The deposition conditions are continuously changed to the deposition conditions of the silicon nitride film, and the silicon nitride film is deposited.

The deposition of the insulating film composed of the silicon oxide film, the transition film, and the silicon nitride film is performed by introducing the gas to be plasma and the gas that reacts with the plasma into the same container and It is extremely preferable to position the inside of the container.

[0013]

The method of the present invention focuses on the film quality and the step coverage of the silicon oxide film by the ECR plasma CVD method, and uses a silicon oxide film having low stress and good step coverage as the film at the initial stage of film formation, For the intermediate layer, a film that continuously transitions from a silicon oxide film to a silicon nitride film, and for the film near the surface, a silicon nitride film with strong chemical resistance is deposited by simply changing the gas composition without stopping the plasma. (Of course, the gas pressure and microwave power in the device are continuously changed). This makes it possible to obtain a protective film which has corrosion resistance against corrosive chemicals from the outside and has internal stress that does not adversely affect the integrated circuit in terms of stress.

The above-mentioned respective film thicknesses are about 5000 Å for the silicon oxide film, about 3000 Å for the film that continuously transitions from the silicon oxide film to the silicon nitride film, and about 2000 Å for the silicon nitride film. About 1 μm
It is practically desirable to have a film thickness of. The high frequency bias power applied to the wafer is in the per unit area of the wafer surface appropriate range when 1.5~3.5W / cm ² of silicon oxide film, the 2.0~3.0W / cm ² It is more desirable to set the range. In the case of a silicon nitride film, 0.
A range of 3 to 1.0 W / cm ² is suitable, and a range of 0.5 to 0.
It is more desirable to set it in the range of 7 W / cm ² . In the case of a film that continuously transitions from a silicon oxide film to a silicon nitride film, both high-frequency bias power and microwave power should be continuously changed from the supply power range of the silicon oxide film to the supply power range of the silicon nitride film. Is desirable.

The wafer temperature may be 250 ° C. or lower, and the silicon oxide film and the silicon nitride film may be formed at the same temperature. In depositing the composite film including the silicon oxide film, the transition film, and the silicon nitride film, the gas to be plasmatized and the gas to react with the plasmatized gas are both in the same container, specifically, plasma is generated. If the wafer is introduced into the chamber and the wafer is also positioned in the plasma generation chamber for deposition, the plasma generation chamber has a high plasma density and the deposition rate is higher than the deposition rate in the gas phase reaction chamber in a normal ECR plasma CVD apparatus. It is performed at high speed, and it becomes possible to deposit a single film such as a silicon oxide film or a silicon nitride film in a time equal to or shorter than the normal deposition time.

[0016]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 illustrates an essential part of an ECR plasma CVD apparatus suitable for an insulating film deposition method according to the present invention. The main body of the illustrated apparatus is a vacuum container indicated by reference numeral 10, and the inside is an upper plasma generation chamber 11 in the drawing.
And the lower gas phase reaction chamber 12 is roughly divided.
The microwave MW is injected into the plasma generation chamber 11 from the upper side through the waveguide 20 connected to the upper opening 13 of the plasma generation chamber 11 to cause cavity resonance in the chamber. Further, into the plasma generation chamber 11, nitrogen gas N which is a part of the reaction gas in the case of a silicon nitride film and oxygen gas O in the case of a silicon oxide film are introduced through the gas introduction pipe 14 and around the same. A coil 30 for cyclotron resonance is arranged in the column to generate a DC magnetic field of a predetermined intensity in the vertical direction in the figure. The reaction gas in the chamber is ionized by the microwave MW, and cyclotron resonance of electrons under the action of a magnetic field generates high-density plasma of the reaction gas. This generated plasma is drawn from the plasma generation chamber 11 toward the gas phase reaction chamber 12 by the gradient in the divergent DC magnetic field. Silane S, which is the rest of the reaction gas, is introduced into the gas phase reaction chamber 12 through a gas introduction pipe 15, and the lower portion thereof is connected through an exhaust pipe 16 to a vacuum pump system, which is schematically indicated by vacuum V in the figure. ing. The silane S introduced into the gas phase reaction chamber 12 mixes with the plasma of the reaction gas from above to cause a gas phase reaction, and silicon nitride molecules and silicon oxide molecules are generated as reaction products in a region near the center of the chamber. Occur. At the lower part of the chamber, a wafer 1 on which the above-described reaction product is to be deposited as a silicon nitride film or a silicon oxide film is placed on a wafer table 40. This wafer table 40
Is a vacuum container 10 with a high frequency insulator 41 such as glass.
Supported by the bottom plate of the high frequency bias power supply 50 and the lead 4
2 is connected. The frequency of the power supply 50 is 13.56 MHz, for example. Further, in order to keep the wafer 1 at a predetermined temperature on the wafer table 40, it is preferable to incorporate appropriate heating and cooling means (not shown). When it is desired to arbitrarily control the pressure in the gas phase reaction chamber 12, a gas that does not affect the reaction, such as helium, is introduced into the intermediate portion of the connecting pipe line between the gas phase reaction chamber 12 and the vacuum pump system, and a vacuum is introduced. It is preferable to control by a method of reducing the exhausting capacity of the vacuum pump for the container 10.

In the method of the present invention, in order to deposit a predetermined insulating film in the above apparatus, the wafer 1 is placed on the wafer stage 40 and the temperature is automatically adjusted to 300 ° C. or lower, usually 150 to 250 ° C. After exhausting the inside of the vacuum vessel 10 sufficiently, oxygen O, which is the first reaction gas, is flown into the plasma generation chamber 11 and silane gas S is flown into the gas phase reaction chamber 12 at a predetermined flow rate.
The pressure in the container with such atmosphere gas is 1 to 10 mTorr
Within the range, preferably 2-5 mTorr.

Then, with the coil 30 excited, the microwave MW is irradiated from the waveguide 20 to the plasma generation chamber 11,
At the same time, 1.5 to 3.5 W / from the high frequency bias power supply 50
A high frequency power of cm ² , preferably 2.0 to 3.0 W / cm ² is applied to the wafer 1. The microwave power is 400-1
Irradiate 000 W, preferably 500 to 800 W. The main conditions for depositing a silicon oxide film are as follows.

[0019] When a silicon oxide film is deposited under the central condition, the deposition rate of the film becomes about 1200Å / min, and the internal stress is 2 × compressive stress.
A film of 10 ⁹ dyne / cm ² or less is obtained. Therefore about 500
To obtain a film thickness of 0Å, a silicon oxide film may be deposited for 4 to 5 minutes. The method of depositing a film that continuously transitions from a silicon oxide film to a silicon nitride film is as follows.

After depositing the silicon oxide film, the flow rate of silane gas is decreased and the flow rate of oxygen gas is decreased and nitrogen gas is added to increase the flow rate. The deposition rate of the film is almost regulated by the silane flow rate, and is about 1200Å / min, so that the deposition time of the intermediate layer is 2 to 3 minutes. During film formation under the central conditions during this period, the oxygen gas is continuously changed from 32 cc / min to 0 cc / min. 0cc / min to 300cc / mi for nitrogen gas
Change continuously up to n. The microwave power is continuously changed from 600 W to 1500 W, and the high frequency power is continuously changed from 600 W to 250 W. Further, the atmospheric gas pressure is also 3 mTorr to 60 mTorr
Change up to. By changing the conditions in this way,
A transition is continuously made from the silicon oxide film to the silicon nitride film. The deposition conditions of the silicon nitride film are as follows.

[0021] The characteristics of the film at this time are such that the deposition rate is about 1100 Å / min, and the internal stress of the film is about 8 × 10 ⁹ dyne / cm ² in terms of compressive stress.
Also, the etching rate for hydrofluoric acid (50%) solution is 2
It is less than 000Å / min.

Although the stress is large, since the film thickness is small, the influence on the entire insulating film is small, and the total film thickness is about 4 × 10.
It can be controlled to ⁹ dyne / cm ² or less. Further, since the dissimilar films are not in contact with each other discontinuously but the quality is continuously changed, there is no need to worry about the film peeling.

[0023]

As described above, in the method for depositing an insulating film for an integrated circuit according to the present invention, the fact that the insulating film by the ECR method is superior in quality to the conventional plasma method is utilized, and an internal film is formed on the wafer side. A silicon oxide film with low stress and excellent step coverage is deposited, a silicon nitride film with high chemical resistance and high water resistance is deposited on the surface layer, and in the meanwhile, the silicon oxide film continuously changes to the silicon nitride film. By depositing the transitional film, the dissociation between different films is eliminated, and the silicon oxide film and the transition film are made to function as a buffer film for the silicon nitride film having a large internal stress. It is possible to prevent the internal stress acting on the coating material from increasing, and to provide a highly practical protective film for the integrated circuit device.

Further, according to the method of the present invention, since the silicon oxide film, the transition film, and the silicon nitride film can all be deposited at the same wafer temperature, there is no adjustment time of the wafer temperature which takes time to stabilize, and the composite temperature is improved. Despite being a film, there is an advantage that the deposition time does not need to be particularly long. Further, in the method of the present invention, since a considerably wide range is allowed for each deposition condition other than the gas flow rate, a protective film having a target film quality can be easily deposited without difficulty in setting conditions. be able to.

When the gas to be turned into plasma and the remaining gas that reacts with the gas to be turned into plasma are introduced into the same container and the wafer is also placed in the same container, a silicon oxide film and a silicon nitride film are formed. It is known that high-speed film formation is possible in all cases. Naturally, high-speed film formation of a transition film is also possible, and despite the composite film, the deposition time is shortened as a whole, and the slew stop of the apparatus is improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram illustrating an essential part of an ECR plasma CVD apparatus suitable for depositing an insulating film for a semiconductor device, which is the object of the present invention.

FIG. 2 is a diagram showing a comparison of water permeation resistance among a silicon oxide film formed by a conventional plasma CVD method, a TEOS oxide film, a silicon oxide film formed by an ECR plasma CVD method, and a silicon nitride film formed by a conventional plasma CVD method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wafer 11 Plasma generation chamber 12 Gas phase reaction chamber 14 Gas introduction pipe 15 Gas introduction pipe 20 Waveguide 30 Coil (electron cyclotron resonance coil) 40 Wafer stage 50 High frequency bias power supply

Claims (4)

[Claims] 1. A method of depositing an insulating film on a wafer surface on which a semiconductor device is formed by plasma CVD, comprising:
In an apparatus that attempts to deposit an insulating film by converting a part of the atmosphere gas involved in forming the insulating film into plasma by an electron cyclotron resonance method and reacting with the remaining gas, first deposit a silicon oxide film. A method for depositing an insulating film for a semiconductor device, comprising depositing a film in which a silicon oxide film is continuously transitioned to a silicon nitride film, and depositing a silicon nitride film thereon. 2. The method according to claim 1, wherein a silicon oxide film, a film in which a silicon oxide film is continuously changed to a silicon nitride film, and a silicon nitride film are sequentially deposited, all of which are the same wafer. A method for depositing an insulating film for a semiconductor device, characterized by depositing at a temperature. 3. The method according to claim 1, wherein a silicon oxide film and a silicon nitride film are deposited under the deposition conditions described below, respectively, and the silicon oxide film and the silicon nitride film are continuously transitioned. The method for depositing an insulating film for a semiconductor device, wherein the deposition of the film is performed by continuously shifting each deposition condition from the deposition condition of the silicon oxide film to the deposition condition of the silicon nitride film. Deposition conditions of silicon oxide film: Oxygen gas flow rate: 30 to 40 cc / min Silane gas flow rate: 28 to 36 cc / min Silane / oxygen flow rate ratio: 0.8 to 1.0 Gas pressure in equipment: 1 to 10 mTorr Microwave power: 400 to 1000 W High frequency power: 1.5 to 3.5 W / cm ² (per unit area of wafer surface) Wafer temperature: 150 to 250 ° C. Silicon nitride film deposition conditions: Nitrogen gas flow rate: 250 to 350 cc / min Silane gas flow rate: 28 to 36 cc / min Gas pressure in the apparatus: 40 to 100 mTorr Microwave power: 1200 to 1800 W High frequency power: 0.3 to 1.0 W / cm ² (per unit area of wafer surface) Wafer temperature: 150 to 250 ° C. 4. The method according to claim 1, wherein a gas to be plasmatized and a gas that reacts with the gas to be plasmatized are introduced into the same container, and a wafer on which an insulating film is deposited is formed. Place the silicon oxide film in the container,
A method for depositing an insulating film for a semiconductor device, comprising depositing an insulating film made of a silicon nitride film and a film in which a silicon oxide film is continuously transitioned to a silicon nitride film.