JPH05160112A - Plasma treatment equipment and method - Google Patents

Abstract

PURPOSE:To perform the treatment of the surface of a semiconductor substrate under the temperature much lower than the ordinary temperature of 1000 deg.C for thermal oxidation treatment, that is, actually at the temperature lower than 30 deg.C by providing means for keeping a constant sample temperature and means for controlling the electric potential of the sample in a sample treatment section. CONSTITUTION:This equipment comprises a sample treatment section 4 for fixing a silicon wafer substrate 5 installed inside a plasma reaction section 2, and a liquid nitrogen introducing tube 6 for introducing the liquid nitrogen for adjusting the temperature of the sample treatment section 4. A power supply section 7 for applying an electric potential to the sample treatment section 4, and an air exhaust section 3 equipped with a pump for maintaining a high vacuum in a plasma generation section 1 and plasma reaction section 2 are also provided. And the plasma reaction section 2 is equipped with water molecule supply means 11 for supplying more than 100 molecules/cm<3> to the reaction section and means for keeping the degree of vacuum constant in the plasma reaction section 2. And the sample treatment section 4 is equipped with means for keeping the sample temperature constant and means for controlling the electric potential of sample.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a plasma processing apparatus and a plasma processing method, and more particularly to an ECR (Electron Cyclo)
tron Resonance: 30 ° C using hydrogen gas plasma and residual water molecules generated by electron cyclotron resonance)
The present invention relates to the following apparatus for plasma processing at low temperature and a method for plasma processing a surface of a sample such as a semiconductor substrate using this apparatus.

[0002]

2. Description of the Related Art In the fabrication of various devices such as semiconductor integrated circuits, surface treatment of semiconductor substrates, for example, fabrication and processing of a surface oxide film of a semiconductor substrate is a very important process. The surface oxide film of a semiconductor substrate is generally produced by the conventional method.
This is performed by a so-called thermal oxidation method in which the surface of a semiconductor substrate is washed with acid, alkali and hydrofluoric acid and then the substrate is heated in an oxygen atmosphere using a thermal diffusion furnace.

Since the rate of oxidation on the surface of the semiconductor substrate is high when the above-mentioned technique is used, it is possible to easily and uniformly form an oxide film having a thickness of several hundred nm or more by controlling the heat treatment temperature and the heat treatment time. is there. On the other hand, however, it is necessary to heat the substrate to 900 ° C. or higher to form the oxide film, and it takes time and technique to stabilize the thermal diffusion furnace at a constant temperature. Further, when the semiconductor substrate is subjected to the thermal oxidation treatment in the thermal diffusion furnace, it is necessary to carefully and sufficiently take the treatment while paying attention to the thermal change of the semiconductor substrate.

On the other hand, as the density of semiconductor elements increases, it becomes necessary to form a thinner oxide film, for example, an ultrathin oxide film having a thickness of 10 nm or less, and a technique for producing an ultrathin oxide film having a thickness of 10 nm or less on a semiconductor substrate is developed. This has become an important issue for new insulating films or capacitor films. For example, with respect to a capacitor film, there is an effect of increasing the charge capacity by reducing the oxide film thickness, and it is required to make the oxide film extremely thin.

[0005]

However, in the above-mentioned prior art, there is a limit to the reduction of the heat treatment temperature and the heat treatment time, and it is substantially impossible to form an ultrathin oxide film having a thickness of 10 nm or less. Further, thermal oxidation treatment at high temperature causes problems such as disorder of the doping layer in the semiconductor substrate. For this reason, there is a demand for a method capable of forming an ultrathin oxide film on a semiconductor substrate at a temperature as low as possible and easily in a short period of time as semiconductor elements become ultra-fine.

The present invention is intended to solve the above-mentioned problems of the prior art, and the purpose thereof is exemplified as follows. 1) The treatment of the surface of the semiconductor substrate is performed at a temperature lower than about 1000 ° C. at which the thermal oxidation treatment is usually performed, specifically at 30 ° C. or lower. 2) To obtain an oxide film having a thickness equal to or less than an oxide film thickness capable of obtaining a uniform oxide film by a thermal oxidation method, specifically, a uniform oxide film having a thickness of about 10 nm or less. 3) Shortening the oxidation time, specifically obtaining an ultra-thin oxide film by an oxidation treatment for several minutes. 4) To facilitate the production of an ultrathin oxide film and to control the oxide film thickness. 5) To prevent damage to the semiconductor substrate when forming the oxide film.

[0007]

Means for Solving the Problems That is, a plasma processing apparatus of the present invention comprises a plasma generating section for generating hydrogen gas plasma by electron cyclotron resonance, a plasma reaction section for introducing a plasma flow from the plasma generating section, and the plasma. In a plasma processing apparatus comprising a sample processing part installed in a reaction part and an exhaust part for keeping the plasma generation part and the plasma reaction part under high vacuum, the plasma reaction part has 10 ¹⁰ water molecules / cm ³ As described above, a water molecule supply means for supplying to the reaction section and a means for keeping the vacuum degree of the plasma reaction section constant are provided, and the sample processing section has a means for keeping the sample temperature at a constant temperature and a sample potential. It is characterized by comprising means for controlling.

The plasma generating part, the plasma reaction part, the sample processing part and the exhaust part may be the ones usually used in this type of plasma processing apparatus. Further, the water molecule supply means may be any means as long as it can supply water molecules to the plasma reaction part. The sample processing unit has, for example, a sample processing table on which a sample is placed or fixed, and the sample processing table may be a non-movable type, or a movable type, for example, a parallel type or a rotatably movable type so as to transfer plasma to the sample. The contact state may be changed or a plurality of samples may be continuously processed.

In the apparatus of the present invention, an appropriate number of plasma measuring means are arranged at a predetermined position in the sample processing section and / or its vicinity so that the plasma state in the sample processing section and / or its vicinity can be accurately and quickly diagnosed. Then it is convenient.
Examples of the plasma measuring means include plasma gas pressure,
It is composed of measuring instruments for plasma electron temperature, plasma electron density, sample temperature and the like, and concretely, for example, various measuring probes can be mentioned. Further, the water molecule measuring means includes, for example, a mass spectrometer.

The state of the plasma is preferably controlled appropriately by a suitable plasma control means. The plasma control means comprises a device for optimizing, for example, the plasma gas pressure, plasma electron temperature, plasma electron density, sample temperature, etc. Specifically, for example, a gas pressure regulator for adjusting the pressure of the processing gas. Is mentioned.

The information about the plasma measured by the plasma measuring means is analyzed by means such as a computer, and the gas pressure regulator is operated so that the plasma state should be adjusted based on the result.

The means for supplying water molecules to keep the number of residual water molecules in the plasma reaction section at 10 ¹⁰ / cm ³ or more is not particularly limited. For example, a gas containing water molecules in an appropriate amount is supplied to the plasma reaction section. I wish I had it. Usually, it can be achieved by exhausting the inside of the plasma reaction part to 0.13 Pa. The optimum value and upper limit value of the residual water molecules are appropriately determined within the range in which the target plasma treatment can be performed.

Further, the degree of vacuum in the plasma reaction section is set to 0.13.
Stable plasma can be generated by introducing a constant pressure within the range of Pa to 13 Pa, for example, hydrogen gas to about 1.3 Pa. That is, even if the degree of vacuum in the plasma reaction part is less than 0.13 Pa or exceeds 13 Pa, stable plasma cannot be generated, so the value is within the above range.

The plasma treatment time is preferably several minutes. For this purpose, it is necessary to maintain a stable plasma state for 10 minutes or more. As a means for this,
For example, the plasma measuring means, the plasma control means, the computer and the like are appropriately combined and used.

In the sample processing section, -120 ° C to 3
As a means for maintaining the sample temperature at a constant temperature within the range of 0 ° C., for example, a structure capable of cooling the sample processing section using liquid nitrogen may be used. The specific structure of the sample processing unit is optimally selected in consideration of operability and the like within a range in which the sample temperature can be maintained.

Further, in order to subject the sample to the intended plasma treatment, a means for controlling the sample potential is required.
The means for controlling the sample potential is preferably a means capable of controlling the DC potential within the range of 0 to 50 V and above the plasma potential of the plasma reaction portion while being insulated from the plasma reaction portion. .. The specific structure of the means for controlling the sample potential may be appropriately selected within the range where the above object can be achieved.

In the plasma processing method of the present invention, the sample is plasma-processed using the plasma processing apparatus of the present invention. At this time, the sample is placed on the surface of the sample processing unit opposite to the surface on which the plasma flow strikes, or the sample is placed at a position other than the plasma emission unit in the plasma reaction unit for plasma processing. That is, the sample can be plasma-treated under milder conditions than by installing the sample in the above-mentioned place.

The material, size and shape of the sample to be treated, the size and shape of the treated portion, etc. are not particularly limited as long as plasma treatment can be performed using the apparatus and method of the present invention. For example, a plate-shaped one such as a silicon substrate is preferable.

[0019]

In the apparatus of the present invention, the plasma reaction part supplies water molecules to the reaction part at least 10 ¹⁰ molecules / cm ³ and means for maintaining the vacuum degree of the plasma reaction part constant. Since the sample processing section is provided with a means for holding the sample temperature at a constant temperature and a means for controlling the sample potential, the target plasma processing becomes possible.

Further, in the method of the present invention, when the sample is plasma-treated under the predetermined conditions by using the plasma processing apparatus of the present invention, the sample is applied to the surface of the sample processing unit opposite to the surface on which the plasma flow strikes. The sample can be plasma-treated under mild conditions by installing the sample or placing the sample in a position other than the plasma emission part in the plasma reaction part and performing the plasma-treatment.

[0021]

The present invention will be described in more detail with reference to the following examples and comparative examples. Note that, for convenience of explanation, the following examples all relate to the oxidation treatment of the silicon wafer substrate, but it goes without saying that the present invention can also be applied to the oxidation treatment of the substrate made of another material.

Embodiment FIG. 1 shows an embodiment of the plasma processing apparatus of the present invention.
This apparatus uses a microwave supplied from a microwave generator 10 and a magnetic field generated by an air-core magnetic field coil 8 to generate plasma by using electron cyclotron resonance, and a plasma flow from the plasma generator 1 Plasma reaction part 2 to be introduced, water molecule supply part 11 connected to plasma reaction part 2 for supplying water molecules into plasma reaction part 2, and hydrogen gas introducing pipe 9 for introducing hydrogen gas into plasma reaction part 2. A sample processing unit 4 for fixing a silicon wafer substrate 5 installed in the plasma reaction unit 2,
A liquid nitrogen introduction tube 6 for introducing liquid nitrogen for adjusting the temperature of the sample processing unit 4, a power supply unit 7 for applying a potential to the sample processing unit 4, the plasma generation unit 1 and the plasma reaction unit 2 are set to a high vacuum. And a measuring device such as a plasma gas pressure measuring probe, a plasma electron temperature measuring probe, a plasma electron density measuring probe, a sample substrate thermometer, and the like. It is equipped with analytical equipment such as a computer and a mass spectrometer for measuring water molecules (these are not shown).

FIG. 2 is a diagram showing the results of mass spectrometry when water molecules are introduced from the water molecule supply unit 11 into the plasma reaction unit 2 of the apparatus of the present invention shown in FIG. 1 and then the pressure is evacuated to 0.13 Pa. is there. A mass of 18 is mainly present in the plasma reaction unit 2.
The residual water molecules are observed as shown in the peak of 1. and the amount reaches about 10 ¹⁰ / cm ³ . Next, hydrogen gas was introduced into the plasma reaction section 2 through the hydrogen gas introduction pipe 9 until the pressure reached 1.3 Pa. Further, a so-called electron cyclotron resonance plasma was generated by applying a magnetic field of 875 Gauss and a microwave of 2.45 GHz to the plasma generating unit 1. As shown in FIG. 1, a silicon wafer substrate 5 was previously attached to the sample processing unit 4 on the surface opposite to the surface on which the plasma flow hits. Further, the sample processing unit 4 is the plasma reaction unit 2
Are insulated from each other, and have a structure in which a DC potential can be applied by the power supply section 7.

FIG. 3 shows the results of damage to the silicon wafer substrate 5 when a potential is applied to the silicon wafer substrate 5 when the silicon wafer substrate 5 is processed for 3 minutes under the plasma processing conditions shown in FIGS. 1 and 2. Indicates. The damage of the silicon wafer substrate 5 is obtained from the intensity change of the electron channeling pattern. At this time, the plasma potential of the plasma reaction part 2 is about 20 V, and damage can be suppressed by applying a potential higher than this to the silicon wafer substrate 5. However, when a potential of 60 V or higher is applied to the silicon wafer substrate 5, the temperature of the silicon wafer substrate 5 rises due to the influence of electron collision and the like, and the object of the present invention, that is, low temperature plasma oxidation cannot be achieved. Therefore, in order to perform plasma oxidation without damaging the silicon wafer substrate 5, it is desirable to perform plasma oxidation with the potential applied to the silicon wafer substrate 5 in the range of 20V to 50V.

In FIG. 4, among the plasma processing conditions described with reference to FIG. 3, the potential of the silicon wafer substrate 5 is set to 50 V so that the processing can be performed under the condition that the silicon wafer substrate is not damaged by plasma. The effect of the plasma processing time on the production of the plasma oxide film when the substrate temperature of the silicon wafer substrate 5 was set to a low temperature, specifically -100 ° C. by introducing liquid nitrogen from the liquid nitrogen introducing pipe 6 into is there. When the low-temperature plasma oxidation treatment is performed under such conditions, the film thickness of 10 minutes or less is required.
It was confirmed that a plasma oxide film having a thickness of nm or less can be produced.

FIG. 5 shows the effect of the substrate temperature on the production of the plasma oxide film when the plasma treatment time is set to 3 minutes under the conditions shown in FIG. It is understood that the plasma oxide film can be controlled with a film thickness of 10 nm or less by controlling the substrate temperature to a low temperature.

Comparative Example 1 A silicon wafer substrate 5 was plasma-treated in the same manner as in the example described in FIG. 5, except that argon gas was used instead of hydrogen gas. The results are shown in FIG. 5 together with the examples.

Comparative Example 2 The silicon wafer substrate 5 was plasma-treated in the same manner as the example described in FIG. 5 except that oxygen gas was used instead of hydrogen gas. The results are shown in FIG. 5 together with the examples.

Comparing the example with the comparative examples 1 and 2 in FIG. 5, when argon gas is used instead of hydrogen gas, even if it takes a long time to form an oxide film of about 2 nm. The formation of the oxide film does not proceed any further. When oxygen gas is used, the oxidation rate is too high to control the oxide film thickness. On the other hand, when hydrogen gas is used,
The oxide film can be gradually formed in a state where the substrate temperature can be controlled to near room temperature. It should be noted that the oxide film thickness formed near room temperature starts to decrease and becomes 0 at 35 ° C. or higher because
This is due to the phenomenon that the oxide film once formed starts to separate at this temperature. From the above comparative example, the production of the ultrathin oxide film and the film thickness can be performed for the first time by oxidizing the silicon wafer substrate 5 using hydrogen gas while dissociating and activating the residual water molecules in the plasma reaction part 2. It turns out that control of is possible.

[0030]

As described above, in the plasma processing apparatus of the present invention, the plasma reaction portion contains 10 ¹⁰ water molecules / cm ^3.
The sample processing section is provided with a water molecule supply means for supplying to the reaction section and a means for keeping the degree of vacuum of the plasma reaction section constant, and the sample processing section controls the sample potential and a means for keeping the sample temperature at a constant temperature. Therefore, in the plasma oxidation treatment of various samples, for example, in the manufacture of semiconductor devices, a film thickness of 10 n, which is uniform and has a large area on the surface of a silicon wafer substrate at a temperature of 30 ° C. or less, is used.
An extremely thin oxide film having a thickness of about m or less can be produced with high production efficiency. Further, the oxidation treatment time is about several minutes, which is extremely short, and the production efficiency is good.

The plasma processing method of the present invention uses the plasma processing apparatus of the present invention to perform plasma processing on a sample under predetermined conditions, so that the surface of the sample processing unit opposite to the surface on which the plasma flow strikes the sample. Since the sample is installed or placed in a position other than the plasma emission part in the plasma reaction part for plasma treatment, the plasma oxidation process can be performed under mild conditions, so that an ultrathin oxide film can be easily produced, and It is also possible to control the oxide film thickness. Further, it is possible to prevent damage to the semiconductor substrate when forming the oxide film.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of an embodiment of a plasma processing apparatus of the present invention.

FIG. 2 is a diagram showing a mass spectrometry result when the inside of the plasma reaction part of the apparatus of the present invention shown in FIG. 1 is evacuated to a pressure of 0.13 Pa.

FIG. 3 is a diagram showing the relationship between the silicon wafer substrate potential and the degree of damage to the silicon wafer substrate when the silicon wafer substrate is processed under the plasma processing conditions shown in FIGS. 1 and 2.

FIG. 4 is a diagram showing a relationship between a plasma processing time and an oxide film thickness when a substrate potential of a silicon wafer substrate is 50 V and a substrate temperature is −100 ° C.

5 is a diagram showing a relationship between a substrate temperature and a plasma oxide film thickness when various gases are used and a plasma treatment time is set to 3 minutes under the conditions shown in FIG.

[Explanation of symbols]

 1 Plasma Generation Section 2 Plasma Reaction Section 3 Exhaust Section 4 Sample Processing Section 5 Silicon Wafer Substrate 6 Liquid Nitrogen Introduction Tube 7 Power Supply Section 8 Air-Core Magnetic Field Coil 9 Hydrogen Gas Introduction Tube 10 Microwave Generator 11 Water Molecule Supply Section

Claims (3)

[Claims] 1. A plasma generation part for generating hydrogen gas plasma by electron cyclotron resonance, a plasma reaction part into which a plasma flow is introduced from the plasma generation part, a sample processing part installed in the plasma reaction part, and the plasma generation. In the plasma processing apparatus, which comprises an exhaust unit for maintaining the reaction unit and the plasma reaction unit under a high vacuum, the plasma reaction unit supplies water molecules to the reaction unit in an amount of 10 ¹⁰ / cm ³ or more, and the plasma. It is characterized in that it is provided with means for keeping the degree of vacuum of the reaction part constant, and the sample processing part is provided with means for holding the sample temperature at a constant temperature and means for controlling the sample potential. Plasma processing equipment. 2. The means for controlling the sample potential is capable of controlling the DC potential within the range of 0 to 50 V and above the plasma potential of the plasma reaction part while being insulated from the plasma reaction part. The plasma processing apparatus according to claim 1, which is a different means. 3. A plasma generation part for generating hydrogen gas plasma by electron cyclotron resonance, a plasma reaction part into which a plasma flow is introduced from the plasma generation part, a sample processing part installed in the plasma reaction part, and the plasma generation. In the plasma processing apparatus, which comprises an exhaust part for maintaining the vacuum part and the plasma reaction part under a high vacuum, the plasma reaction part has residual water molecules of 10 ¹⁰ molecules / cm.
^The sample processing section is provided with a means for maintaining the degree of vacuum at ³ or more and the internal vacuum degree at a constant pressure within the range of 0.13 Pa to 13 Pa for 10 minutes or more.
When plasma-treating a sample using a plasma processing apparatus comprising means for holding the sample temperature at a constant temperature within the range of ° C and means for controlling the sample potential,
A plasma processing method, wherein the sample is placed on the surface of the sample processing unit opposite to the surface on which the plasma flow strikes, or the sample is placed at a position other than the plasma emission unit in the plasma reaction unit for plasma processing.