JP2004103689A - System and method for depositing film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a semiconductor thin film depositing system and method for forming the gate insulating film of an FET, or the like, on a semiconductor wafer, or the like, in which the film is formed while eliminating defects and impurities by controlling the quantity of a material gas being supplied to a film deposition chamber such that the material gas is not supplied excessively nor deficiently. <P>SOLUTION: The system for depositing a thin film on the surface of a semiconductor comprises a means for supplying a material gas, a chamber for depositing a film through the chemical reaction of the material gas, and a means for exhausting the material gas in the film deposition chamber wherein a gas monitoring means is provided between the film deposition chamber and the exhausting means. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor thin film forming apparatus and method for forming a gate insulating film of an FET (field effect transistor) on a single crystal substrate such as a semiconductor wafer.
[0002]
[Prior art]
In recent years, as a technique for forming a thin film (for example, Al ₂ O ₃ ) using a metal oxide or the like having a large dielectric constant as a raw material on a Si substrate or the like as a semiconductor wafer, a method of directly laminating aluminum oxide to form a film ( For example, Patent Literature 1) and an ALD (Atomic Layer Deposition) method are available. In the ALD method, for example, trimethyl aluminum (TMA: Al (CH ₃ ) ₃ ) or the like is used as a raw material, and water (H ₂ O) is alternately sprayed onto a Si substrate to form a film.
[0003]
Generally, as a property of a thin film formed on a semiconductor wafer, the amount of electric charge accumulated on the thin film is proportional to the dielectric constant (ε) of the thin film itself and the area (A) of the wafer, and the thickness of the thin film itself It is known that it is inversely proportional to (d). Therefore, in recent years, there has been a strong tendency to reduce the area of the wafer, and means for reducing the film thickness have been used in order to maintain or increase the amount of charge accumulated on the thin film. However, there is a limit to miniaturization of the film thickness, and therefore, a thin film having a higher dielectric constant is required.
[0004]
The gate insulating film which is a target of the film forming apparatus and the film forming method of the present invention is for forming a thin film (High-k film) such as a metal oxide having a large dielectric constant on a semiconductor wafer. Even if the semiconductor chip is made smaller (thinner), the quality of the semiconductor chip is not deteriorated, and miniaturization of the semiconductor chip can be realized.
[0005]
In addition, after a gate insulating film is formed on a Si substrate as a semiconductor wafer, a high-temperature heat treatment performed in a transistor forming process causes the Si substrate and the gate insulating film to react with each other. An SiO ₂ film (ε = 3.9) or a silicate film having a low dielectric constant may be present as an interface layer. Therefore, by forming a barrier layer in advance at the interface, it is common to prevent the formation of an interface layer having a low dielectric constant at the interface of the wafer even when the high-temperature heat treatment performed in the transistor forming process is performed. Has been done.
[0006]
A conventional method of forming a gate insulating film of a metal oxide or the like will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes a film forming chamber for spraying a source gas onto a semiconductor wafer (for example, a Si substrate) to form a thin film, 2 denotes a container containing liquid TMA (trimethyl aluminum), and 3 denotes water (H). ₂ O). The TMA and water are vaporized by bubbling Ar gas injected into 2 and 3 as a carrier gas and supplied to the film forming chamber 1. Here, the flow rate of the Ar gas as a carrier gas is controlled by the flow meters 4 and 4, and as a result, the amounts of TMA and water supplied to the film formation chamber 1 are controlled. Most of the raw material gas supplied to the film forming chamber is discharged by the pressure reducing means 5. In the film forming chamber 1, a Si substrate heated to a constant temperature (for example, about 300 degrees C.) is horizontally held, and a supplied source gas (TMA, water) is alternately blown onto the Si substrate. FIG. 2 is a graph showing a supply state of TMA and water supplied by the gas flow meters 4 and 4. In FIG. 2, it is assumed that the supply of TMA and water is controlled by ON / OFF switching. In FIG. 2, specifically, the supply ON time is about 0.5 seconds, and the supply OFF time is about 1.0 seconds.
[0007]
Here, the chemical reaction that occurs when a source gas is blown onto a semiconductor wafer (for example, a Si substrate) in the film forming chamber 1 is described by Equation 1.
(Equation 1)
Si—H + Al— (CH ₃ ) ₃ → Si—Al— (CH ₃ ) ₂ + CH ₄ }
In the above formula 1, Si-H represents a hydrogen-terminated Si substrate, and this H atom reacts with one of the CH ₃ groups of TMA, and Al— (CH ₃ ) ₂ is formed on the surface of the Si substrate. It represents the connection. Note that the above-described hydrogen termination can be performed by reacting a strong acid such as HF with the Si substrate.
[Patent Document 1]
JP 2001-220294 A
[Problems to be solved by the invention]
As shown in FIG. 2, TMA and water are alternately supplied to the film formation chamber 1, but the amount of gas to be supplied is adjusted empirically by an apparatus worker and supplied to the film formation chamber. This has been done in the past. For this reason, when the supply amount of the gas is not appropriate, for example, when the supply amount of the source gas is insufficient, a defect may occur in a film formed on the Si substrate, and when the source gas is Is supplied to the substrate, there is a problem that impurities are mixed in a film formed on the Si substrate. When defects or impurities are present in such a film, the electrical characteristics of the thin film are significantly reduced.
[0009]
FIG. 3 is a diagram illustrating a state in which the source gas is uniformly adsorbed on the Si substrate and a state in which the source gas is non-uniformly adsorbed. In (1) of FIG. 3, reference numeral 10 denotes a Si substrate, 20 denotes an aluminum atom in aluminum, and 21 denotes an oxygen atom. In this state, it can be seen that the source gas is uniformly adsorbed on the Si substrate. In FIG. 3B, part A indicates a state in which a defect occurs due to insufficient TMA, and part B indicates a state in which a defect and an impurity CH ₃ are mixed due to an excessive amount of TMA entering the film forming chamber 1. ing.
[0010]
[Means for Solving the Problems]
The present invention has been made in view of the above problems, and in claim 1, a gas supply means for supplying a source gas, a film forming chamber for forming a film of the source gas by a chemical reaction, An apparatus for forming a thin film on a surface of a single crystal substrate, comprising an exhaust unit for exhausting a source gas in a film forming chamber, and a gas for monitoring a gas discharged from the film forming chamber. It is characterized by providing monitoring means. Further, the gas monitoring means may be a gas analyzer (claim 2) or a gas mass spectrometer (claim 3).
[0011]
In claim 4, a gas supply means for supplying a source gas, a film forming chamber for forming a film of the source gas by a chemical reaction, and an exhaust means for exhausting the source gas in the film forming chamber are used. A film forming method for forming a thin film on a surface of a single crystal substrate, comprising a gas monitoring means for monitoring a gas discharged from the film forming chamber, and responding to a signal from the gas monitoring means. To change the supply amount of the raw material gas. In this case, the supply amount of the source gas may be changed by controlling the gas supply time (claim 5), and the gas monitoring means may be an analyzer (claim 5). 6), It may be a gas mass spectrometer (claim 7).
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, one embodiment of the present invention will be described. FIG. 4 shows an embodiment according to the present invention, in which 11 is a film forming chamber, 12 and 13 are containers containing liquid TMA and water (H ₂ O), respectively, and 14 and 14 are carrier gases. It is a flow meter for adjusting the flow rate of Ar gas as a gas. Most of the source gas supplied to the film forming chamber is exhausted by an exhaust unit (for example, a decompression pump) 5.
[0013]
Reference numeral 16 denotes a gas analyzer as a gas monitoring means, which is provided in a path through which the raw material gas supplied to the film forming chamber is exhausted by the exhaust means 5. Here, it is assumed that a gas mass spectrometer is used as one of the embodiments. The gas mass spectrometer 16 is for detecting a substitution reaction of the following formula 1 that occurs when TMA is adsorbed on a hydrogen-terminated Si substrate. Here, when the substitution reaction of Formula 1 occurs, methane CH ₄ is generated, and this methane CH ₄ is detected by the gas monitoring means (gas mass spectrometer) 16.
[0014]
As described above, when TMA is adsorbed on the Si substrate, a substitution reaction occurs and methane CH ₄ is generated. Therefore, the generation of this methane is monitored by the gas mass spectrometer 16. That is, it is considered that the substitution reaction is being performed on the Si substrate while methane is being generated.
[0015]
Thus, gas analyzer as the gas monitoring means (Gas mass spectrometer) 16, methane CH ₄ continuously detects, when the methane CH ₄ is no longer detected in the film forming chamber 11 (or of a certain concentration (When it becomes the following), a signal is transmitted to the control unit 17. Upon receiving the signal, the control unit 17 transmits a signal to the gas flow meter 14 to stop supplying the TMA gas to the film formation chamber. As a result, the TMA gas supplied into the film formation chamber does not become excessive or insufficient, and it is possible to appropriately prevent defects and impurities from occurring in the film formed on the Si substrate.
[0016]
Next, the substitution reaction when the H ₂ O gas (water vapor) is supplied to the film formation chamber after the TMA gas is supplied to the film formation chamber is expressed by Equation 2.
[Equation 2]
Si—Al— (CH ₃ ) ₂ + 2H ₂ O → Si—Al— (OH) ₂ + 2CH ₄ }
In Equation 2, in the film forming chamber 11 after the supply of the TMA gas, water (H ₂ O) reacts with molecules that have reacted on the Si substrate to become Si—Al— (CH ₃ ) _2, and Si— This shows how Al- (OH) ₂ is formed.
[0017]
Further, Si—Al— (OH) ₂ is bonded to each other, and water (H ₂ O) is discharged to form Al ₂ O ₃ . That is, by repeatedly performing the substitution reaction of Formula 2, a dense, uniform and high-quality Al ₂ O ₃ film is formed on the Si substrate. Further, at this time, as is apparent from Equation 2, since methane (CH ₄ ) is generated while the substitution reaction is being performed, the methane (CH ₄ ) is continuously detected by the gas analyzer 16 to obtain the above-mentioned value. It can be determined whether or not the substitution reaction has been completed. When methane CH ₄ is no longer detected by the gas analyzer 16 (or when the concentration becomes lower than a certain level), a signal is transmitted to the controller 17, and the H ₂ O gas (water vapor) is The supply to the film formation chamber in step (1) is stopped.
[0018]
As described above, since the supply of the TMA gas and the H ₂ O gas is controlled in accordance with the degree of progress of the substitution reaction performed in the film forming chamber 11, the TMA gas and the H ₂ O gas are accurately stored in the film forming chamber 11. H ₂ O gas can be supplied. FIG. 5 shows a relationship between the supply of the source gas of the TMA gas and the H ₂ O gas (steam) by the Ar carrier gas to the film formation chamber 11 and the methane CH ₄ detected by the gas analyzer 16.
[0019]
FIG. 5 shows a case where the substitution reaction is performed on the Si substrate by supplying TMA (see Equation 1) and a case where the substitution reaction is performed when H ₂ O gas (water vapor) is supplied (see Equation 2). The amount of methane detected in (1) is shown in a graph together with ON / OFF of the supply of the source gas such as TMA gas and H ₂ O gas (steam). Also in this case, the supply gas supply ON time is about 0.5 seconds, and the supply OFF time is about 1.0 seconds.
[0020]
Next, a description will be given of an embodiment for detecting that the supply of the TMA gas becomes excessive and the substitution reaction in the film forming chamber 11 is not properly performed.
[0021]
Equation 3 shows a state in which the excessively supplied Al- (CH ₃ ) ₃ is further substituted by the molecules that have undergone a substitution reaction on the Si substrate and have become Si-Al- (CH ₃ ) ₂ .
[Equation 3]
Si—Al— (CH ₃ ) ₂ + Al— (CH ₃ ) ₃ → O—Al (CH ₃ ) —Al (CH ₃ ) ₂ + C ₂ H ₆ }
[0022]
With respect to the Si—Al (CH ₃ ) —Al (CH ₃ ) ₂ generated in Formula 3, the substitution reaction shown in Formula 4 further occurs.
(Equation 4)
Si—Al (CH ₃ ) —Al— (CH ₃ ) ₂ + 2H ₂ O → Si—Al (CH ₃ ) —Al— (OH) ₂ + 2CH ₄ }
[0023]
Further, Si—Al (CH ₃ ) —Al— (OH) _{2 of} Formula 4 is bonded to each other and water (H ₂ O) is discharged to partially form Al ₂ O _3. As is evident, in the film where Al ₂ O ₃ is to be formed, methyl (CH ₃ ) groups are mixed as impurities. Therefore, when the substitution reaction as shown in Formula 3 occurs (that is, when the TMA gas is excessively supplied), the ethane C ₂ H ₆ generated at the same time is detected by the gas analyzer 16 so that the TMA gas is excessively supplied. Can be quickly detected. When ethane C ₂ H ₆ is detected by the gas analyzer 16, a signal is transmitted to the control unit 17, the flow meter 14 is operated, and the supply of TMA gas is stopped (turned off) to reduce the excessive supply of TMA. it can.
[0024]
Next, an embodiment in which a barrier layer is formed at the interface between the Si substrate and the gate insulating film will be described with reference to FIG. 6, the same components as those shown in FIG. 4 are denoted by the same reference numerals. Numerals 12 and 13 denote containers containing liquefied TMA and water (H ₂ O), respectively, and numeral 18 denotes a cylinder containing liquefied ammonia (NH ₃ ). By opening the valve of the cylinder 18, vaporized ammonia (ammonia gas) is supplied to the film forming chamber 11. In this embodiment, a case is described in which an Si ₃ N ₄ film is formed as a barrier layer at the interface between a Si substrate and a gate insulating film.
[0025]
Equation 5 shows a reaction equation when ammonia gas (NH ₃ ) is reacted on a hydrogen-terminated Si substrate.
(Equation 5)
Si—H + NH ₃ → Si—NH ₂ + H ₂ ↑
[0026]
As is apparent from Equation 5, as a reaction before the formation of the Si ₃ N ₄ layer as the barrier layer on the Si substrate, when Si—NH ₂ is formed on the Si substrate, hydrogen gas (H ₂ ) Occurs. The H atom of Si—NH ₂ is replaced by the methyl group of Si—Al (CH ₃ ), and as a result, an Al ₂ O ₃ film is formed on the Si ₃ N ₄ layer.
[0027]
That is, since hydrogen gas (H ₂ ) is generated while the substitution reaction is being performed, the hydrogen gas (H ₂ ) is continuously monitored by the gas analyzer 16 to determine whether or not the substitution reaction has been completed. can do. When hydrogen gas (H ₂ ) is no longer detected by the gas analyzer 16 (or when the concentration becomes lower than a certain lower level), a signal is transmitted to the control unit 17, the valve of the cylinder 18 is closed, and the ammonia gas is By stopping the supply of (NH ₃ ) to the deposition chamber, a uniform and defect-free barrier layer can be formed extremely thin. FIG. 7 shows the supply state of the gas and the monitoring state of the generated gas at this time.
[0028]
The switching of supply gas ON / OFF according to the amount of generated gas as described above is performed using the control unit 17, but this is not limited to hardware such as a personal computer (PC). For example, it can be performed by an arithmetic processing unit or the like incorporated in the gas analyzer 16. By storing a program and / or data in which the optimum timing for switching the supply gas in accordance with the amount of generated gas is stored in the control unit 17 or the like, it is automatically and uniformly stored on the semiconductor wafer. Defect-free gate insulating films and barrier layers can be formed. Further, the ON / OFF control of the supply gas may be performed by a means for controlling the supply amount such as a flow meter 14 so as to be changeable, or the ON / OFF of the supply of the gas such as a solenoid valve or an air drive valve. It may be carried out by means for causing it to.
[0029]
Furthermore, in the present description, an example was described in which Al ₂ O ₃ was used for the gate insulating film, a Si ₃ N ₄ film was used for the interface layer, and TMA, H ₂ O, and NH ₃ gas were used as the raw materials as an example. However, the present invention is not limited to only these examples. For example, in the case of forming hafnium oxide HfO ₂ as a gate insulating film, Hf (N (CH ₃ ) ₂ ) ₄ and water H ₂ O may be used as source gases. In this case, the gas generated when the source gas undergoes the substitution reaction on the Si wafer is HN (CH ₂ ) ₂ , and the generated gas is detected by the gas analyzer 16 to form a high-quality gate insulating film. It is possible to form. Table 1 shows the type of the gate insulating film to be formed, the source gas used at that time, and the generated gas in association with each other.
[0030]
The single crystal substrate described here is not limited to a semiconductor wafer such as a Si substrate, but includes a substrate made of strontium titanate (SrTiO ₃ ) or magnesium oxide (MgO). It is.
[0031]
Also, if a gas mass spectrometer is used as the gas analyzer 16 for detecting generated gas, various kinds of gases can be detected and quantified quickly and accurately in real time, which is extremely effective. However, the gas analyzer 16 is particularly limited to a gas mass spectrometer as long as it is an analyzer that can detect generated gas with good response (rapidly), such as an infrared gas analyzer or another analyzer. is not.
[0032]
【The invention's effect】
According to the present invention described above, a gas generated during a reaction performed in forming a thin film (eg, a gate insulating film) performed in a deposition chamber is analyzed by an analyzer such as a gas mass spectrometer. By detecting and measuring, the supply of the source gas can be appropriately controlled, so that a uniform and defect-free film layer can be formed without introducing defects or impurities into the film on the substrate. .
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a general apparatus configuration of a conventional film forming apparatus for a semiconductor wafer or the like.
FIG. 2 is a graph showing a graph in which supply ON / OFF of a source gas is changed with time.
FIG. 3 is a diagram illustrating a state of atoms formed on a wafer.
FIG. 4 is a diagram illustrating an embodiment of a configuration of a film forming apparatus according to the present invention.
FIG. 5 is a diagram illustrating an example of source gas monitoring in the film forming method of the present invention.
FIG. 6 is a diagram illustrating an embodiment in which a barrier layer is formed in the configuration of the film forming apparatus according to the present invention.
FIG. 7 is a diagram illustrating an example of material monitoring when forming a barrier layer in the film forming method of the present invention.
[Explanation of symbols]
11: film forming apparatus, 12: TMA, 13: water, 14: flow control means, 15: exhaust means, 16: gas analyzer, 17: control unit

Claims (7)

A thin film is formed on the surface of a single crystal substrate including a gas supply means for supplying a source gas, a film formation chamber for forming a film of the source gas by a chemical reaction, and an exhaust means for exhausting the source gas in the film formation chamber. An apparatus for forming a film, wherein a gas monitoring means for monitoring a gas discharged from the film forming chamber is provided. 2. The film forming apparatus according to claim 1, wherein said gas monitoring means is a gas analyzer. 2. The film forming apparatus according to claim 1, wherein said gas monitoring means is a gas mass spectrometer. A gas supply unit for supplying a source gas, a film forming chamber for forming a film of the source gas by a chemical reaction, and an exhaust unit for exhausting the source gas in the film formation chamber. A film forming method for forming a thin film, wherein a gas monitoring means for monitoring a gas discharged from the film forming chamber is provided, and a supply amount of a source gas is changed according to a signal from the gas monitoring means. A film forming method characterized by performing the following. 5. The film forming method according to claim 4, wherein the supply amount of the source gas is changed by controlling a gas supply time. 6. The film forming method according to claim 4, wherein the gas monitoring unit is a gas analyzer. The film forming method according to claim 5, wherein the gas analyzer is a gas mass spectrometer.

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