JP2009123737A - Method of depositing silicon oxide film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon oxide film which substantially has no oxygen defect and which has a stable electrical characteristic. <P>SOLUTION: The method of depositing a silicon oxide film using a sputtering sets a substrate on which a target material and a silicon oxide film are deposited in a chamber for forming a gas plasma state and uses introduction gas containing ozone gas as gas which is introduced into the chamber. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for depositing a silicon oxide film such as a silicon dioxide film used in various electronic circuit devices or display devices.

Conventionally, chemical vapor deposition (CVD), plasma CVD, sputtering, and the like have been used as deposition methods for various thin films used in electronic circuit devices, display devices, and the like.
Among them, the sputtering method is a method of irradiating a target material with ions in a gas plasma atmosphere, and depositing target constituent atoms or molecules which are dissociated and released by obtaining the kinetic energy on a substrate disposed oppositely. The sputtering method can be deposited at a lower temperature than other methods, and thus has been widely used as a relatively simple method.

  In the case of a silicon dioxide film, which is a typical thin film, a high-purity quartz plate is used as the target material, and sputtering is performed in a high-frequency plasma of argon gas without heating the substrate to an insulating film with excellent uniformity and density. It can be deposited on any substrate.

  In addition, silicon is used as a target material, and by sputtering in oxygen-containing plasma, flying silicon atoms and oxygen atoms are reacted to deposit a silicon dioxide film on the substrate.

A typical application of a silicon dioxide film is a gate insulating film of a silicon thin film transistor used for pixel selection in a liquid crystal display device.
Since a high electric field of 10 ⁵ V / cm or more is usually applied to the gate insulating film, the silicon dioxide film is required to have extremely stable electrical characteristics as well as film uniformity.

  The silicon dioxide film deposited by the conventional sputtering method has a problem that the electrical characteristics are not as stable as those of the silicon thermal oxide film because the inclusion of carrier traps due to microscopic defects is inevitable. Therefore, it cannot be used for applications of electronic circuits that handle minute signals. In order to have an electrically stable structure, it is required to have a stoichiometric composition of silicon dioxide, in particular, a thin film without oxygen vacancies.

Generally, oxygen vacancies or inclusion of unbonded silicon atoms is unavoidable depending on the sputtering method in the argon gas plasma, and therefore oxygen gas is mixed in the introduced argon gas to compensate for the oxygen vacancies (see Non-Patent Document 1). .
There, 70% argon and 30% oxygen are used. However, although this means has an effect of filling oxygen vacancies by mixing oxygen gas, it is difficult to completely fill the oxygen vacancies, so it is not a practical technique.

  Further, supplementation of deficient oxygen proceeds by heat treatment in an oxidizing atmosphere after thin film deposition, but it has been difficult to completely eliminate oxygen vacancies. For this reason, the silicon dioxide film deposited by the sputtering method has not been put into practical use as a gate insulating film of a thin film transistor requiring high reliability without fluctuation in electrical characteristics.

Furthermore, the problem of oxygen deficiency due to the sputtering method also exists in other oxide films such as a silicon oxynitride film used for an electronic circuit device or a display device.
JP 61-172340 A JP-A-6-21242 JP-A-9-213800 T. Serikawa et al, Jpn.J.Appl.Phys., 45, 4358 (2006)

  An object of the present invention is to provide a method for depositing a silicon oxide film that is substantially free of oxygen vacancies and has stable electrical characteristics.

In order to solve the above-mentioned problems, the present invention provides the following silicon oxide film deposition method. The silicon oxide film in the present invention includes an oxide film such as a silicon nitride oxide film in addition to the silicon dioxide film and the silicon oxide film.
(1) A silicon oxide film formed by sputtering, wherein a substrate on which a target material and a silicon oxide film are deposited is placed in a chamber for forming a gas plasma state, and an introduction gas containing ozone gas is used as a gas to be introduced into the chamber. Deposition method.
(2) The method for depositing a silicon oxide film by sputtering according to (1), wherein the gas introduced into the chamber is a mixture of rare gas and ozone gas.
(3) The method for depositing a silicon oxide film by sputtering according to (1) or (2), wherein the gas introduced into the chamber is further mixed with a gas containing nitrogen atoms.
(4) The method of depositing a silicon oxide film by sputtering according to any one of (1) to (3), wherein the gas plasma state is generated by applying a high frequency.
(5) The method for depositing a silicon oxide film by sputtering according to any one of (1) to (3), wherein the plasma state is generated by applying a DC voltage.
(6) The method for depositing a silicon oxide film by sputtering according to any one of (1) to (5), wherein the target material is quartz.
(7) The method for depositing a silicon oxide film by sputtering according to any one of (1) to (5), wherein the target material is silicon.
(8) The silicon oxide film formed by sputtering according to any one of (1) to (7), wherein the substrate is a substrate on which silicon or a silicon film is deposited, and the surface is previously oxidized by ozone gas. Deposition method.
(9) After depositing a silicon oxide film on the substrate by the method of depositing a silicon oxide film by sputtering according to any one of (1) to (8), the substrate temperature is approximately the same as the substrate temperature at the time of depositing the silicon oxide film Alternatively, a method for depositing a silicon oxide film, wherein the substrate is heated at a temperature higher than the temperature.

  According to the present invention, plasma is generated by directly introducing ozone gas or ozone-containing gas into the sputtering atmosphere, so that radicals of oxygen atoms that are more active than in the case of oxygen gas alone can be generated, and oxygen in the deposited film can be generated. Defects can be greatly reduced, and an electrically stable and dense silicon oxide film can be obtained.

First, the principle of the present invention will be described.
In the sputtering method, thin film deposition is performed in a gas plasma atmosphere. When oxygen is contained in the introduced gas, oxygen plasma or an excited state of oxygen is generated.

Oxygen molecules become oxygen radicals according to the following equation when excited by plasma.
O ₂ → O [ ³ P] + O [ ³ P] (1)
O ₂ → O [ ¹ D] + O [ ³ P] (2)
The activation energies necessary for the excitations (1) and (2) are 5.12 eV and 7.08 eV, respectively, and (1) is dominant when the plasma is not dense.

On the other hand, in the case of ozone, it is as follows.
O ₃ → O [ ³ P] + O ₂ (3)
O ₃ → O [ ¹ D] + O ₂ (4)
The energies required for the excitations (3) and (4) are 1.06 eV and 4.00 eV, respectively, which are much smaller than those in (1) and (2). Even with oxygen plasma, there is a possibility that ozone is generated by the synthesis reaction in the reverse direction of (3) or (4), but the amount is small.

Here, it is known that O [ ³ P] is a stable state and O [ ¹ D] is an active excited state. The activation energies are 0.14 eV and 0.8 eV, respectively, and the difference greatly affects the oxidation reaction particularly at low temperatures.

The value of the rate ratio O [ ¹ D] / O [ ³ P] of the oxidation reaction by O [ ¹ D] or O [ ³ P] is as follows.
1.2 × 10 ¹² (300K) (5)
3.4 × 10 ⁵ (600K) (6)
4.0 × 10 ³ (1400K) (7)
For these reasons, by introducing ozone into the plasma chamber instead of oxygen, a large amount of O [ ¹ D], which is in an active excited state, can be used effectively, and the oxidation reaction can be promoted.
When a silicon substrate is used, a large amount of active O [ ¹ D] reacts directly with the silicon substrate, so that a silicon dioxide surface layer can be formed.

When depositing the silicon dioxide film, which is most frequently used in electronic circuit devices or display devices, by sputtering, the reaction with silicon atoms can be promoted using O [ ¹ D]. Can be deposited.

Also, when the target material is quartz, the silicon-oxygen bond that forms the quartz is broken by ion bombardment in the plasma, and each atom flies, so silicon atoms are deposited in the process of depositing the film on the substrate. And O [ ¹ D] can be used effectively.

  When the substrate on which the thin film is deposited is silicon, it is indispensable to complete the bonding of the silicon atoms and oxygen atoms on the surface in order to form a stable interface. It is effective to oxidize. It is clear that the same effect can be obtained when another oxide film such as a silicon oxynitride film is deposited by sputtering.

  Thin film deposition by sputtering is performed in a gas plasma atmosphere. A constant gas pressure is required to generate the gas plasma. For this reason, gas components other than the required composition are mixed in the thin film being deposited. Also in the present invention, ozone is mixed as an impurity although it is a trace amount. Such impurity components do not necessarily have to be removed, but in order to remove them, a process of heating the substrate for a certain period of time at a temperature equal to or higher than the deposition temperature after film deposition is effective.

  Next, a silicon oxide film deposition method according to the present invention will be described in detail by exemplifying a silicon dioxide film deposition method. A schematic cross-sectional view of an apparatus for carrying out the present invention is shown in FIG.

  In FIG. 1, 1 is a vacuum chamber made of SUS. 2 and 3 are a cathode and an anode for applying a voltage, respectively. High-frequency power is input between both electrodes. In the case of a capacitively coupled plasma generator as shown in FIG. 1, an electrode in which an ion sheath is formed longer is called a cathode for convenience. A gas exhaust port 4 is connected to a vacuum pump. 5 is a gas inlet. A silicon disk 6 as a target material is placed in contact with the cathode 2. A clean surface silicon substrate 7 is disposed in contact with the anode 3.

From the gas inlet 5, 6 sccm of a mixed gas containing oxygen gas containing 15% ozone gas flows in, and the chamber pressure is adjusted to 0.65 Pa. The distance between the silicon disk 6 and the silicon substrate 7 is 5 cm. 7 may be another material substrate on which a silicon film is deposited. Stable plasma is generated in the chamber by applying high frequency power of 13.56 MHz at a power density of 2.26 W / cm ² . Under this condition, a silicon dioxide film 8 is deposited on the silicon substrate 7 to a thickness of 51.7 nm per hour. This silicon dioxide film 8 is a silicon oxide film excellent in film thickness uniformity and structural density.
Needless to say, the generation of plasma is not limited to high-frequency power, and a DC voltage can be used.

  Subsequently, the silicon substrate on which the silicon dioxide film is deposited is heated at 450 ° C. for 30 minutes. As the atmosphere, an inert gas such as argon or a vacuum atmosphere is suitable. Subsequent to the sputtering process, annealing may be performed in an ozone atmosphere. By performing heat treatment at the deposition temperature or higher, ozone, oxygen molecules, or oxygen atoms mixed in excess from the stoichiometric composition are released, and the deposited film becomes dense.

  A manufacturing process of a silicon thin film transistor on a silicon substrate on which a silicon dioxide film is deposited by applying the present invention will be sequentially described with reference to FIG.

In (1), 9 is a glass substrate and 10 is a polycrystalline silicon film of 50 nm. As the polycrystalline silicon film 10, a film having carrier mobility comparable to that of a silicon single crystal can be generated by crystallizing an amorphous silicon film by means such as laser irradiation.
In (2), the polycrystallized silicon film 10 is formed in a pattern like 11 by means of photolithography and etching.
In (3), according to the present invention, a silicon dioxide film 12 is deposited to a thickness of 10 nm by high frequency sputtering under the conditions described in paragraph 0024.
In (4), a low-resistance polycrystalline silicon film doped with phosphorus at a high concentration is deposited and formed into a pattern to form a gate electrode 13.
In (5), the exposed portion of the silicon dioxide film 12 is continuously etched to expose the surface of the polycrystalline silicon film 10 as indicated by 14.
In (6), phosphorus is ion-implanted and the low-resistance source and drain regions 15 are formed by activation heat treatment at 900 ° C. for 30 minutes. This heat treatment process also serves to densify the sputter deposited silicon dioxide film.
In (7), a silicon dioxide film cover film 16 is deposited to a thickness of 200 nm according to the present invention.
In (8), contact windows 17 with the source, drain and gate regions are formed by means of photolithography and etching.
In (9), aluminum is deposited to a thickness of about 1 μm and patterned by means of photolithography and etching to form a source extraction electrode 18, a drain extraction electrode 19 and a gate extraction electrode 20. To complete.

FIG. 3 shows the depth profile of the binding energy of oxygen atoms in the deposited film measured by X-ray photoelectron spectroscopy.
Reference numeral 21 denotes a silicon dioxide film formed by sputtering using oxygen plasma containing 25% ozone, which is compared with the silicon dioxide film 22 when only oxygen is introduced. 23 is a result of a silicon dioxide film obtained by thermally oxidizing a silicon single crystal for comparison. Note that the binding energy of oxygen atoms in a silicon dioxide film obtained by thermally oxidizing a silicon single crystal is substantially constant regardless of the depth.
21 has a bond energy of oxygen atoms that is closer to 23 than 22, that is, is close to a silicon thermal oxide film.

The line indicated by 24 is the interface between the deposited film and the substrate measured by ellipsometry, and the deposited film thickness is about 35 nm for both 21 and 22.
Looking at the slopes of 21 and 22 near 24, 21 is steeper, indicating that the compositional change of the deposited film near the interface is small.

  The above results show that the implementation of the present invention produces a silicon dioxide film having a low stoichiometric oxygen vacancy uniformly over the depth direction of the deposited film, demonstrating the effect of the present invention. Is.

  FIG. 4 shows the drain current-voltage characteristics of a silicon thin film transistor on a glass substrate manufactured according to the present invention. According to the present invention, the interface between the silicon substrate surface and the silicon dioxide film deposited thereon has substantially no oxygen vacancies that affect the drain current-voltage characteristics, so that the characteristics are extremely stable.

One of the indices indicating the state of the interface is carrier mobility. The prototype silicon thin film transistor uses 400 cm ^2, which is close to the value of a normal MOS transistor using a silicon single crystal despite the use of polycrystalline silicon. / Vs. By implementing the present invention, the performance of the thin film transistor can be increased as compared with the conventional method.

In the above description, the application to the generation of a silicon dioxide thin film as a gate insulating film of a silicon thin film transistor that is required to have the highest performance as an insulating thin film has been disclosed, but the present invention is not limited to this.
That is, it is clear that the conventional method can be widely used as a method for depositing an oxide thin film containing oxygen vacancies, and it can be expected to contribute widely to the electronic equipment industry through the manufacture of various electronic circuit devices or display devices.

  Furthermore, as a gas containing nitrogen atoms in addition to ozone gas, for example, by introducing ammonia gas and performing sputtering, it is possible to deposit a silicon oxynitride film, but other gases are mixed into ozone. It goes without saying that the process is included in the present invention.

It is sectional drawing of the sputtering chamber for demonstrating this invention. It is sectional drawing of the main manufacturing processes of the thin-film transistor manufactured using this invention. It is a result of X-ray photoelectron spectroscopy analysis of a silicon dioxide film deposited on a silicon substrate according to the present invention. It is an electrical characteristic view of a silicon thin film transistor manufactured using the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 Cathode 3 Anode 4 Gas exhaust port 5 Gas inlet 6 Silicon disk 7 Silicon substrate 8 Silicon dioxide film 9 Glass substrate 10 Polycrystalline silicon film 11 Polycrystalline silicon film pattern 12 Silicon dioxide film 13 Gate electrode 14 Exposed portion 15 of polycrystalline silicon film Source and drain region 16 Cover film 17 Contact window 18 Source extraction electrode 19 Drain extraction electrode 20 Gate extraction electrode

Claims (9)

  A method for depositing a silicon oxide film by sputtering, wherein a substrate for depositing a target material and a silicon oxide film is installed in a chamber for forming a gas plasma state, and an introduction gas containing ozone gas is used as a gas to be introduced into the chamber .   2. The method of depositing a silicon oxide film by sputtering according to claim 1, wherein the gas introduced into the chamber is a mixture of rare gas and ozone gas.   The method for depositing a silicon oxide film by sputtering according to claim 1 or 2, wherein the gas introduced into the chamber is further mixed with a gas containing nitrogen atoms.   The method of depositing a silicon oxide film by sputtering according to any one of claims 1 to 3, wherein the gas plasma state is generated by applying a high frequency.   4. The method for depositing a silicon oxide film by sputtering according to claim 1, wherein the plasma state is generated by applying a DC voltage.   6. The method for depositing a silicon oxide film by sputtering according to any one of claims 1 to 5, wherein the target material is quartz.   6. The method of depositing a silicon oxide film by sputtering according to claim 1, wherein the target material is silicon.   8. The method for depositing a silicon oxide film by sputtering according to claim 1, wherein the substrate is a substrate on which silicon or a silicon film is deposited, and the surface is previously oxidized by ozone gas. .   The silicon oxide film is deposited on the substrate by the method of depositing a silicon oxide film by sputtering according to any one of claims 1 to 8, and then the same temperature as the substrate temperature at the time of depositing the silicon oxide film or a temperature thereof. A method for depositing a silicon oxide film, characterized in that a substrate is heated at a higher temperature.

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