JP2010100913A - Apparatus and method for depositing thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely deposit a high purity thin film from a raw material activated by using plasma. <P>SOLUTION: In a plasma-assisted reactive thin film deposition apparatus, a coil 4 for generating plasma is constituted of a substance comprising elements constituting a thin film to be deposited or covered with the substance. A plasma is generated in a chamber 10 by the coil 4 for generating plasma, and the element of a raw material evaporated from a crucible 6 for an evaporation source and the element of a gas introduced from a gas introduction port 7 are allowed to react in a plasma atmosphere and vapor-deposited on the surface of a substrate 2 together with the elements of the substance emitted by sputtering of the surface of the coil 4 for generating plasma. Thereby, a desired thin film can be deposited. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a thin film forming apparatus for forming a high purity thin film and a thin film forming method using the thin film forming apparatus.

  When a thin film is formed by reacting two or more kinds of raw materials in a vacuum chamber, it is necessary to supply high energy for reacting the raw materials except for the case of using a highly reactive special raw material. For example, neutral molecules can be dissociated by collision of electrons in non-equilibrium plasma with raw materials, and thin films can be efficiently formed at low temperatures using generated radicals and ions.

  However, in a conventional apparatus for forming a thin film by reacting using a material activated with plasma, a plasma generating coil (antenna or induction electrode) is provided in the vacuum chamber of the thin film forming apparatus (internal electrode type). ) In the case of the generated plasma, the radicals, ions or electrons of the inert gas (such as Ar) introduced to generate the raw material or plasma collide with the plasma generating coil, and the molecules of the material constituting the coil Sputtering is performed, and the molecule is taken into the thin film as an unintended impurity, so that a high-purity thin film cannot be formed.

Further, when the plasma generating coil is provided outside the vacuum chamber of the thin film forming apparatus (external electrode type), the plasma density is lowered, and the rate of activation of the raw material to be reacted is lowered. A thin film could not be formed.
A method for forming a thin film by providing a plasma generating coil or electrode in a vacuum chamber and reacting two or more kinds of raw materials by using plasma is disclosed in Patent Documents 1 and 2, for example. There are a sputtering method and a plasma CVD method as disclosed in Patent Documents 3 and 4.

In the reactive sputtering method, the kinetic energy of the particles used as the raw material for the thin film generated by sputtering the target is large, which damages the substrate and the film already formed on the substrate before the particles are attached. End up.
Furthermore, since the rate at which the plasma generating coil collides with and sputters the material constituting it is large, even if the coil is protected with the same material as the thin film, it is difficult to control the crystallinity of the thin film, Further, the deterioration of the plasma generating coil is quick.

  The reactive sputtering method described in Patent Documents 1 and 2 is a method for producing an insulating compound film from a metal film that has already been formed using a high-frequency plasma such as oxygen or nitrogen. However, in this case, if compounding is performed up to a deep region, it is necessary to increase the output of the high frequency, and the particles collide with the surface of the thin film being formed to cause damage. Since particles generated by sputtering adhere, the film thickness increases and it becomes difficult to control the film thickness.

In the plasma CVD method as described in Patent Documents 3 and ₄ , a gas (TiCl ₄ , SiH _4, Zn (C ₂ H ₅ ) _2, etc.) that is a constituent material of a thin film is decomposed using plasma, Since this is a method of depositing a thin film through excitation and a chemical reaction on the surface of the substrate, a reactive material is used as a raw material. For this reason, the source gas remaining after the film formation and the compound produced by the reaction are easily taken into the thin film as impurities. Moreover, the purity of the reactive material used as a raw material is lower than that of metal or the like, and impurities are easily contained. Therefore, it is difficult to produce a high-purity thin film.

Japanese Patent No. 4002317 Japanese Patent Laid-Open No. 10-324969 Japanese Patent No. 3473121 JP-A-2-301564

Therefore, it is very difficult to form a high-purity thin film in an apparatus for forming a thin film by reacting activated materials using plasma, and this has not been realized.
The present invention has been made in view of such a current situation, and provides a thin film forming apparatus and a thin film forming method capable of producing a high-purity thin film by reacting a raw material activated using plasma. With the goal.

The thin film forming apparatus according to the present invention is configured as follows in order to achieve the above object.
A chamber having a gas introduction port and an exhaust port, and a vacuum pump for exhausting the gas in the chamber from the exhaust port,
In the chamber, a substrate mask for holding a substrate as a base for thin film growth, a substrate heating heater for heating the substrate, an evaporation source for supplying a thin film raw material, the evaporation source and the substrate A plasma generating coil disposed between the mask 3 and the mask 3;
The plasma generating coil is made of a material made of an element constituting the thin film to be formed or coated with the material.

  Then, plasma is generated in the chamber by the plasma generating coil, and the plasma generating coil is composed of or covered with a substance composed of an element constituting a thin film to be formed. The element of the raw material evaporated by the evaporation source and the gas element introduced from the gas inlet are activated in the plasma atmosphere while suppressing the incorporation of impurities other than the elements constituting the thin film, A desired thin film is formed by reacting on the surface of the substrate.

The thin film forming method according to the present invention includes the following steps in order to achieve the above object.
In the chamber, an evaporation source filled with a material as a raw material for the thin film and a substrate on which the thin film is deposited are arranged to face each other, and an element constituting the thin film to be formed is formed between the evaporation source and the substrate. A plasma generating coil made of or coated with the material is disposed.

  Then, after the inside of the chamber is depressurized close to vacuum, the substrate and the evaporation source are heated, high frequency power is supplied to the plasma generating coil to generate plasma, and the evaporation source evaporates. The raw material element and the gaseous element introduced into the chamber are activated in a plasma atmosphere, and the surface of the plasma generating coil is sputtered and deposited on the surface of the substrate together with the element of the material ejected. Thus, a desired thin film is formed.

In the thin film forming apparatus and the thin film forming method, the elements constituting the thin film are Zn, Mg, Cd, Ca, Be, Cu, Ag, B, Al, Ga, In, O, N, As, P, Sb, Any one element or a plurality of elements among Si, C, Mn, Ni, and Fe may be used.
More preferably, the material constituting or covering the plasma generating coil is the same material as the thin film to be formed.

  According to the thin film forming apparatus or the thin film forming method of the present invention, it is possible to reduce impurities taken into the thin film at the time of film formation and to produce a desired high-purity thin film.

The best mode for carrying out the present invention will be described below with reference to the drawings.
[Thin film forming equipment]
An embodiment of a thin film forming apparatus according to the present invention will be described in detail with reference to FIG. FIG. 1 is a schematic cross-sectional view showing a configuration of a plasma-assisted reactive thin film forming apparatus as the thin film forming apparatus. This plasma-assisted reactive thin film forming apparatus is an apparatus for forming a ZnO thin film.

The plasma-assisted reactive vapor deposition apparatus shown in FIG. 1 includes a chamber 10 having a gas introduction port 7 and an exhaust port 9, and a gas in the chamber 10 is exhausted from the exhaust port 9 to reduce the pressure in the chamber to a vacuum state. Including a vacuum pump (not shown). A gas is introduced into the chamber 10 from the gas inlet 7. As the gas to be introduced, oxygen (O ₂ : purity 99.99% or more), which is a raw material for a high-purity thin film, or plasma that is not incorporated into the thin film even if it exists in the chamber is generated. Easy high-purity argon (Ar: purity 99.99% or more) is used in addition to oxygen as a raw material for a high-purity thin film. If the purity is lower than this, the impurity concentration in the thin film increases, and electrical characteristics and crystallinity are deteriorated, so that it cannot be used.

  In the chamber 10, a dedicated substrate mask 3 for holding the substrate 2 as a base for thin film growth and a substrate heating heater 1 for heating the substrate 2 are attached, and the temperature of the substrate 2 is confirmed. A temperature sensor 11 is provided. The substrate 2 is a ZnO bulk single crystal substrate. By using a high-purity crystal substrate made of the same element as the thin film, a high-purity and high-quality thin film can be formed.

Further, a crucible 6 serving as an evaporation source for supplying a thin film raw material is mounted in the chamber 10. The crucible 6 is filled with zinc (Zn: purity 99.99% or more) as a thin film raw material. If the purity of the zinc is lower than this, the impurity concentration becomes high, and electrical characteristics and crystallinity are deteriorated, so that the zinc cannot be used.
A crucible heater 8 for heating the crucible 6 to evaporate zinc is attached to the crucible 6, and a temperature sensor 12 for confirming the heating temperature is also provided.

  In addition, a rotatable shutter 5 is installed between the crucible 6 and the substrate mask 3 arranged to face each other to prevent the raw material evaporated from the crucible 6 from adhering to the substrate 2 when not intended. A plasma generating coil (also referred to as an antenna) 4 is disposed between the shutter 5 and the crucible 6, and a high frequency (RF) power source 14 shown in FIG. Yes.

  The inside of the chamber 10 is kept in a vacuum state by a vacuum pump (not shown) when the thin film is manufactured. The thin film growth and the degree of vacuum in the chamber 10 are appropriately controlled by a control panel (not shown). Similarly, the output of the plasma generated by the plasma generating coil 4 is appropriately controlled by the control panel.

  FIG. 2 is an enlarged perspective view of the plasma generating coil 4 and a high-frequency power source, and FIG. 3 is a partially enlarged perspective view showing various structural examples by further expanding a part of the plasma generating coil 4. The illustrated plasma generating coil 4 is a plasma generating coil for forming a ZnO thin film.

  The plasma generating coil 4 used in the present invention has a linear or tubular shape as shown in FIG. 2 and is disposed between the crucible 6 serving as an evaporation source and the substrate mask 3, and from the vicinity of the shutter 5 to the crucible 6. It extends spirally to the vicinity, is connected to a high frequency power supply 14, and generates inductively coupled plasma by applying high frequency power. The plasma generating coil 4 has a structure shown in any one of (a) to (d) of FIG.

The coil shown to (a) is comprised with the substance 41 which consists of an element which comprises a thin film.
In the coil shown in (b), the core material 42 is covered with a substance 41 made of an element constituting a thin film.
In the coil shown in (c), a conductive core wire (mesh) 44 is placed inside a low-conductivity substance 43 made of an element constituting a thin film.
In the coil shown in (d), a conductive core wire (hollow pipe) 45 is placed inside a low-conductive substance 43 made of an element constituting a thin film.

  In these cases, it is more preferable that the material 41 constituting or covering the coil is the same material as the thin film because the ratio of atoms contained in the thin film does not change. In this embodiment, since a ZnO thin film is formed, it is preferable that it be composed of or covered with ZnO. However, since the coil must be made of a conductive material, it is necessary to insert a conductive core wire 44 when it is made of a material 43 having low conductivity as shown in FIG.

  In this case, even if the conductive core wire 44 is a substance composed of an element not included in the thin film and an element constituting the thin film, if the composition ratio is different, the surface is sputtered if exposed to the surface. Then, the constituent atoms may be taken into the thin film as unintended impurities or the ratio of atoms contained in the thin film may be changed, so that the conductive core wire 44 is not exposed on the surface. To.

In the thin film forming apparatus shown in FIG. 1, plasma is generated in a chamber 10 by a plasma generating coil 4, and the plasma generating coil is made of a substance made of an element constituting a thin film to be formed, or By being covered with the substance, the raw material element (for example, Zn) evaporated by the evaporation source 6 and the gas introduction port 7 are introduced while suppressing the incorporation of impurities other than the elements constituting the thin film. The gas element (for example, O ₂ ) to be activated is activated in a plasma atmosphere and reacts on the surface of the substrate to form a desired thin film.

[Thin film formation method]
Next, as an embodiment of the thin film forming method according to the present invention, a step of forming a ZnO thin film in detail using the plasma-assisted reactive thin film forming apparatus and a plasma generating coil composed of or coated with ZnO will be described in detail. explain.

A ZnO single crystal substrate (hereinafter also simply referred to as “substrate”) 2 is attached to a dedicated substrate mask 3 at a predetermined position in the chamber 10 in the plasma-assisted reactive vapor deposition apparatus shown in FIG. A size of 0.5 to 5 mm and a purity of 99.99% or more) is quantitatively packed in the crucible 6. Next, the inside of the chamber 10 is evacuated to about 1.0 to 4.0 × 10 ⁻⁴ Pa by a vacuum pump. If the degree of vacuum is low, the content of impurities in the deposited film increases and crystallinity deteriorates.

  Thereafter, a substrate heating heater power source (not shown) is turned on, the substrate 2 is heated by the substrate heating heater 1, the surface is cleaned at a temperature higher than the film formation temperature, and then the substrate heating temperature is set to the film formation temperature. Adjust to. If the cleaning temperature is low, impurities may be taken into the thin film due to contamination on the substrate surface, so it is necessary to set the cleaning temperature high. After the substrate heating temperature is adjusted to the film formation temperature, the crucible heater 8 is turned on.

Next, oxygen (O ₂ ) to be reacted with Zn is introduced into the chamber 10 from the gas inlet 7 and the radio frequency (RF) power source 14 shown in FIG. 2 is activated to generate plasma by the plasma generating coil 4. . Then, the shutter 5 is opened and film formation is started.

That is, the plasma generating coil is made of a material composed of an element constituting the thin film to be formed or is covered with the material, thereby suppressing the incorporation of impurities other than the elements constituting the thin film. However, the raw material Zn evaporated by the crucible 6 as the evaporation source and the gaseous O ₂ introduced from the gas inlet 7 are activated in the plasma atmosphere and react on the surface of the substrate to form a desired thin film. Is deposited. Thereby, a high-purity zinc oxide (ZnO) thin film can be formed.

  Thereafter, after a thin film is formed to a predetermined thickness, the shutter 5 is closed, heating of the crucible 6 and the substrate 2 is stopped, the high frequency power supply 14 is also turned off, and the introduction of oxygen is also stopped. When the temperature of the substrate 2 and the crucible 6 is lowered, the substrate 2 and the crucible 6 on which the thin film is formed are taken out.

  In this embodiment, even if the surface of the plasma generating coil 4 is sputtered by particles or electrons ionized or excited by plasma during film formation, only the elements constituting the thin film are generated. Even if taken in, it does not become an impurity. It is more preferable if the material constituting the plasma generating coil 4 or the material to be coated is the same material as the thin film to be formed because the ratio of atoms contained in the thin film does not change.

[Evaluation of prepared thin film]
It is generally used as a plasma generating antenna by the impurity concentration in a ZnO thin film prepared by using a stainless steel antenna coated with ZnO as a plasma generating coil by the thin film forming method of the present invention and by a conventional thin film forming method. Evaluation of the impurity concentration in the ZnO thin film produced using the stainless steel antenna which is not coat | covered was performed by the secondary ion mass spectrometry (SIMS) method.

Table 1 shows SIMS measurement results of a ZnO thin film formed on a ZnO single crystal using a stainless steel coil coated with ZnO and a stainless steel coil not coated with ZnO as plasma generating coils. The values in the table indicate the concentrations (atoms / cm ³ ) of Fe, Ni, and Cr contained in the ZnO thin film.

  As can be seen from Table 1, the ZnO thin film prepared using the stainless steel coil not coated with ZnO contains a considerable amount of Fe, Ni and Cr, which are the stainless steel constituent elements of the coil. On the other hand, in a ZnO thin film prepared using a stainless steel coil whose surface is coated with ZnO, the concentrations of Fe, Ni, and Cr are greatly reduced. The values shown in Table 1 indicate that they were below the SIMS detection limit.

  In the above-described embodiment, an example in which a ZnO thin film is formed has been described. Regarding the constituent elements of the thin film, nitrogen-doped ZnO (ZnO: N), AlZnO, ZnMgO, ZnO: C, ZnO: Mn, It has been confirmed that ZnO: Ni, ZnO: Fe, CdO, CdO: Cu, and CdO: N can be formed into a film, and the same II-VI compound or the same group I, III, IV, V, VII It is also considered that a thin film of a compound to which a group VIII element is added can be prepared.

In addition, III-V group compounds such as GaN, InN and AlN having the same crystal structure as ZnO, mixed crystals such as GaInAlN, and compounds doped with II and IV groups such as GaN: Mg and GaN: Si are also prepared. It is considered possible.
That is, the constituent elements of the thin film are Zn, Mg, Cd, Ca, Be, Cu, Ag, B, Al, Ga, In, O, N, As, P, Sb, Si, C, Mn, Ni, and Fe. Any one or more of these elements can be created.

  The present invention can be applied to a thin film forming apparatus and a thin film forming method for forming various high purity thin films. The thin film produced by the thin film forming apparatus and the thin film forming method according to the present invention can be widely used in electronic devices such as field effect transistors (FETs), semiconductor light emitting elements (LEDs), solar cells, transparent conductive films and the like.

It is a schematic block diagram of the plasma assistance reactive vapor deposition apparatus which is one Example of the thin film formation apparatus by this invention. It is the front view which expands and shows the coil for plasma generation with a high frequency power supply. It is a partial expansion perspective view which expands a part of the antenna for plasma generation, and shows various structural examples.

Explanation of symbols

1: Substrate heating heater 2: Substrate (ZnO single crystal substrate)
3: substrate mask 4: coil for generating plasma 5: shutter 6: crucible (evaporation source) 7: gas inlet 8: crucible heater 9: exhaust port 10: chamber 11, 12: temperature sensor 41: composed of elements constituting a thin film Substance 42: Core material 43: Low-conductivity substance 44 consisting of elements constituting the thin film 44: Conductive core wire (network) 45: Conductive core wire (hollow pipe shape)

Claims (4)

A substrate mask having a gas introduction port and an exhaust port, a vacuum pump for exhausting the gas in the chamber from the exhaust port, a substrate mask for holding a substrate serving as a base for thin film growth in the chamber, and the substrate A substrate heating heater for heating the substrate, an evaporation source for supplying a thin film raw material, and a plasma generating coil disposed between the evaporation source and the substrate mask. The coil is composed of or coated with a material comprising an element constituting the thin film to be formed;
Plasma is generated in the chamber by the plasma generating coil, and the plasma generating coil is made of a material composed of an element constituting the thin film to be formed or is coated with the material, thereby forming a thin film The raw material element evaporated by the evaporation source and the gaseous element introduced from the gas inlet are activated in a plasma atmosphere while suppressing the incorporation of impurities other than the elements constituting the substrate, and the substrate is activated. A thin film forming apparatus configured to form a desired thin film by reacting on the surface of the film.   2. The thin film forming apparatus according to claim 1, wherein the elements constituting the thin film are Zn, Mg, Cd, Ca, Be, Cu, Ag, B, Al, Ga, In, O, N, As, P, Sb. , Si, C, Mn, Ni, Fe One or a plurality of elements. In the chamber, an evaporation source filled with a material that is a raw material for the thin film and a substrate on which the thin film is deposited are arranged to face each other.
Between the evaporation source and the substrate, a plasma generating coil formed of a material made of an element constituting a thin film to be formed or coated with the material is disposed,
After the chamber is evacuated to near vacuum, the substrate and the evaporation source are heated, and high-frequency power is supplied to the plasma generating coil to generate plasma, thereby forming the plasma generating coil. The element evaporated by the evaporation source while suppressing the incorporation of impurities other than the elements constituting the thin film by being composed of or covered with the substance comprising the element constituting the power thin film A thin film formation characterized in that a raw material element and a gas element introduced from the gas inlet are activated in a plasma atmosphere and react on the surface of the substrate to form a desired thin film. Method.   4. The thin film forming method according to claim 3, wherein the elements constituting the thin film are Zn, Mg, Cd, Ca, Be, Cu, Ag, B, Al, Ga, In, O, N, As, P, Sb. , Si, C, Mn, Ni, Fe, or any one or a plurality of elements.

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