JP4448664B2 - Method and apparatus for forming thin film material - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for forming a thin film material.
[0002]
[Prior art]
Gallium nitride has already been developed as a light emitting device and has been put to practical use. It has been pointed out that the temperature control of the substrate is important because the method for producing a gallium nitride semiconductor thin film when used as a light-emitting element is already known.
Usually, in order to form a high-quality thin film, it is necessary to cause a chemical reaction on the substrate surface by keeping the substrate temperature at a high temperature of 300 ° C. or higher and supplying a toxic gas such as ammonia (Patent Document). 1 etc.). That is, high substrate temperature has been considered an essential element for active reaction and the realization of uniform thin film materials.
[0003]
However, in the case of manufacturing a thin film material at a higher temperature than the ordinary temperature as in the previous process, due to the difference in the thermal expansion coefficient of GaN and the substrate, a number in the process of lowering the gallium nitride thin film to room temperature There was a problem that the characteristics of the semiconductor deteriorated. Due to this problem, a uniform and high-quality gallium nitride semiconductor is not supplied, so that the field of use as a high-speed and high-thermal-conductivity semiconductor material possessed by the gallium nitride semiconductor has been limited.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 5-206520
[Problems to be solved by the invention]
In view of the above circumstances, an object of the present invention is to provide a thin film material forming apparatus capable of forming a thin film material on a substrate at low temperatures without generating a toxic gas or the like.
[0006]
[Means for Solving the Problems]
Therefore, the inventors of the present invention have intensively studied in order to solve the above various problems , and as a result, in depositing gallium nitride on the substrate surface, a plasma state different from the thermal equilibrium system is used, and a thin film is formed. The kinetic energy possessed by the sputtering gas for sputtering the constituent material or the atoms / molecules of the sputtered material, and the excitation energy of neutral excited atoms / molecules generated in the plasma, are used for the chemistry of the gallium nitride. by using as a source of reactive energy, based on the inference of the thin film can be formed while maintaining the substrate at room temperature, was optimum Tsu completed the present invention.
[0012]
Forming apparatus of a thin film material of the present invention, the substrate was fixed to a substrate fixing means provided in the interior of the container to allow sealing in a vacuum state, holds the liquid or solid metal material forming the film facing the substrate The material holding means is provided, the sputtering gas introduced into the container is ionized by the discharge mechanism to generate discharge plasma, and the surface of the material is sputtered by irradiating charged particles in the discharge plasma. In a thin film material forming apparatus for forming a thin film by depositing neutral particles and excited particles of the material on the substrate,
A partition plate in which a through hole having approximately the same area as the substrate is formed is attached to the inside of the container to be divided into a substrate housing portion and a plasma generating portion, and the substrate housing portion is concentric with the through hole of the partition plate. In addition, a substrate fixing means for fixing the substrate in parallel with a gap with respect to the partition plate is disposed, and the electrode provided at the bottom of the plasma generating unit is used as a cathode, while the inner wall surface of the plasma generating unit is used as an anode. And a discharge mechanism for ionizing the sputtering gas introduced into the plasma generator by disposing the electrode between the pair of electrodes, and concentrically with the through hole of the partition plate above the cathode. A material holding means for holding the material, and a negative bias voltage applying means for accelerating the ion attraction in the discharge plasma by setting the material surface held by the material holding means to a negative potential,
A magnetic field generator that generates a parallel DC magnetic field on the substrate surface that is fixed to the substrate fixing means across the through hole is disposed around the through hole of the partition plate,
The plasma guided from the plasma generator to the through hole of the partition plate by adjusting the discharge power supplied to the discharge mechanism and the negative bias voltage applied to the material surface by the negative bias voltage applying means. The flow rate of neutral and excited neutral particles to the substrate is controlled, and the amount of high energy electrons in the plasma incident on the substrate is controlled in cooperation with a DC magnetic field traversing the through hole. It is characterized by being configured to suppress.
[0013]
In the thin film material forming apparatus, the inner peripheral surface of the through hole provided in the partition plate is a tapered surface that expands from the substrate housing portion side to the plasma generating portion side in the container .
Further, the material holding part of the material holding means arranged above the cathode provided in the plasma generating part is provided so as to conceal the cathode from the substrate arranged concentrically with the through hole of the partition plate. It is done.
Furthermore, a gas that individually introduces at least one kind of gas selected from a reactive gas and a rare gas into the plasma generation unit when the material is reactive with the material held in the material holding unit. An introduction part is provided.
[0014]
Further, in the forming apparatus of the present invention, the material constituting the film held by the material holding member is Ga, and the sputtering gas introduced into the plasma generating part is a nitrogen N ₂ gas that can react with the Ga material and a rare gas. The gas is mixed with the gas, discharge plasma of the mixed gas is generated by the discharge mechanism in the plasma generator, and the negative power applied to the material surface by the discharge power and negative bias voltage applying means supplied to the discharge mechanism. By adjusting the bias voltage, neutral particles of Ga material generated by sputtering of the Ga material by charged particles of a mixed gas in the discharge plasma in the plasma generation unit, the excited neutral particles, and the Ga material Includes the emitted secondary electrons and neutral particles of nitrogen gas contained in the discharge plasma of the mixed gas, their excited neutral particles and high-energy electrons When the plasma is guided to the through hole of the partition plate, it controls the flow rate of neutral particles and excited neutral particles in the plasma to the substrate and cooperates with a DC magnetic field that traverses the through hole. A GaN thin film is formed on the surface of the substrate while suppressing the amount of high energy electrons in the plasma incident on the substrate.
[0016]
【The invention's effect】
According to the thin-film material forming apparatus of the present invention, the high-energy excited charged particles contained in the discharge plasma of the sputtering gas generated in the plasma generator are used as the sputtered particles of the material constituting the film. The amount of ions generated and the sputtering of material 7 by increasing the negative bias voltage applied by the negative bias voltage applying means for setting the discharge power and the negative potential of the surface of the material to be supplied to the discharge mechanism provided in the generator 12 Even when the amount is increased, by forming a floating ion layer between the material surface portion and the peripheral edge portion of the through hole of the partition plate, so-called ion sheath, high energy electrons in the plasma constituting the ion sheath can be generated. Sputtered material atom, its excited atom, reactive gas atom and its source The flow rate of the substrate 4 of neutral particles etc. increases, can increase the deposition rate. At the same time, the amount of incident high energy electrons in the plasma on the substrate 4 can be suppressed in cooperation with the DC magnetic field G1, and the substrate is suppressed from heating due to the collision of high energy electrons. A thin film material can be formed while the substrate 4 is kept at a relatively low temperature, and even if the thin film is naturally cooled to room temperature (room temperature) after the thin film is formed, it is possible to avoid problems such as cracks in the formed thin film.
In addition, since a high-energy plasma is used during the film forming process, it is not necessary to use a particularly toxic gas or a dangerous gas, so that a technology preferable in terms of safety can be realized. Since the potential distribution inside the plasma can be controlled appropriately, a thin film with little deterioration can be produced.
[0017]
The inner peripheral surface of the through hole 31 of the partition plate 3 is a tapered surface whose diameter gradually increases from the substrate housing portion 11 side toward the plasma generation unit 12 side. Even if the peripheral surface is sputtered by irradiation of ions in the plasma, the impurity particles of the partition plate 3 return to the plasma side and are difficult to reach the substrate side. Therefore, it is possible to suppress the mixing of impurities into the thin film on the substrate.
Furthermore, since the substrate surface is provided so as to be concealed from the cathode of the discharge mechanism part by the holding part of the material holding means, even if the evaporated particles of the cathode material are released when the discharge mechanism part performs discharge, the evaporated particles Is prevented from entering the substrate surface, and contamination of the cathode material impurities into the thin film can be prevented.
Furthermore, according to the thin film forming apparatus in which at least two or more gas introduction portions are provided in the plasma generation portion of the cylindrical container, one gas introduction portion includes a sputtering gas selected from a rare gas and a constituent of the thin film. At least one reactive gas can be introduced into the plasma generator, and nitrogen-rich black gallium nitride formed on the metal gallium surface in a plasma that is difficult to sputter with nitrogen gas plasma ions is a rare gas such as argon. Thus, metal gallium without a nitride film is exposed on the surface, and gallium atoms are efficiently supplied to the substrate side.
[0018]
Furthermore, according to the apparatus of the present invention, a gallium nitride GaN film can be formed under a low temperature condition.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments thereof.
1 and 2 show one embodiment of a thin film material forming apparatus according to the present invention.
[0022]
As shown in FIGS. 1 and 2, this forming apparatus 1 is divided into a substrate accommodating portion 11 and a plasma generating portion 12 by attaching a partition plate 3 inside a container 2 having a cylindrical shape. used for forming the GaN film as a material.
Is disposed substrate fixing means to a substrate accommodating portion 11, the substrate fixing means the deposition surface of the substrate 4 formed of silicon depositing a thin film material such as is fixed toward the plasma generator 12 side, of the substrate receiving portion 11 An exhaust passage 13 is opened in the wall so that the inside can be decompressed to a high vacuum state.
[0023]
The partition plate 3 is formed using stainless steel, boron nitride, quartz glass, or the like, and has a through hole having a minimum diameter portion substantially equal to the surface of the substrate 4 at a portion facing the substrate 4 fixed to the reaction portion 11. 31 is formed, the inner circumferential surface of the through hole 31 is gradually expanded toward the plasma generating portion side, i.e., has a tapered surface. The inclination angle of the tapered surface is not particularly limited, 30 ° to 60 °, and preferably, approximately 45 °.
Further , two permanent magnets M1 are embedded in the peripheral portion of the through hole 31 of the partition plate 3, and the through hole 31 is formed in parallel to the substrate surface in front of the substrate 4 accommodated in the reaction unit 11 in FIG. A transverse DC magnetic field G1 is formed .
[0024]
The partition plate 3 is used to reduce the density of the plasma guided to the through hole 31 , in particular, the charged particle density in the plasma, and preferably has a thickness of about 1 cm or more.
The plasma generator 12, eight permanent magnets M2 around its radially disposed et been as toward the plasma generating section 12 side directs the N and S poles alternately around, indicated by a two-dot chain line Such a magnetic confinement magnetic field G2 is formed inside the plasma generation unit 12 .
[0025]
Further, the plasma generation unit 12 is provided with a material holding means 5 and a cathode 6 constituting one of the discharge mechanisms.
The material holding means 5 has a disc shape and has a support portion 51 provided with a concave portion 53 for receiving the metal gallium 7 as a material on the upper surface via a support portion 52 so that the holding portion 51 is positioned at a substantially central portion of plasma described later. The plasma generator 12 is supported on the bottom 12a.
[0026]
Further, the material holding means 5 is formed of a material such as molybdenum that does not react with the liquid metal gallium on which the holding portion 51 is held, and the outer surfaces of the holding portion 51 and the column portion 52 are for avoiding direct plasma irradiation. It is covered with alumina or quartz glass.
Incidentally, by shortening the distance between the metal gallium 7 on the substrate 4 and the holding portion 51, but the flow of sputtered gallium atoms can increase the proportion which reaches the substrate, and the holding portion 51 and much closer plasma between the partition plate 3 is sandwiched, the plasma density of the front portion of the gallium surface is reduced, because the absolute amount of sputtering is reduced, the flow amount of the gallium atoms will be reduced as a whole. The decrease in plasma density also reduces the flow of excited ions / molecules of nitrogen ions and mixed gas species, so the distance must be set according to the operating pressure, plasma electron temperature, and density. An interval of about 10 cm is appropriate from the mean free path.
[0027]
The cathode 6 is provided at a position where the material holding portion 51 becomes blind with respect to the substrate 4 and discharges between the peripheral wall surface of the plasma generating portion 12 which is an anode constituting one of the discharge mechanisms. ing.
Further, two gas introduction paths 8 having a flow rate adjusting function are opened at the bottom 12 a of the plasma generating unit 12.
[0028]
Next, a method for forming a gallium nitride thin film, which is one embodiment of the method for forming a thin film material of the present invention using this forming apparatus 1, will be described in detail.
In this method of forming a gallium nitride thin film, first, the inside of the container 2 is exhausted through the exhaust passage 13 by a vacuum pump (not shown) until the inside of the container 2 reaches about 0.00001 Pa, and sufficient baking is performed. After removing carbon and oxygen impurities in the container 2, nitrogen gas is introduced while adjusting the flow rate using one gas introduction path 8 to about 0.1 Pa. Further, a rare gas such as argon is introduced through the other gas introduction path 8 while adjusting the flow rate as necessary.
[0029]
Generate discharge the one of a cylindrical container 2 of the cathode 6 bar electrode provided on the bottom portion of the plasma generating section 12, and the inner wall surface of the plasma generating part 12 by applying a DC voltage to the electrode pairs of the anode Then, plasma of the sputtering process gas introduced into the plasma generator 12 is generated.
The generated plasma is confined in the magnetic field caused by the permanent magnet M2 arranged to surrounding the periphery of the inner wall surface of the plasma generating section 12 G2, held in a horizontal state by the holding portion 51 of the material retaining means 5 A plasma part having a high electron temperature (high energy) of 2 eV or more is formed in the central part where the metal gallium Ga 7 is located. Incidentally, confinement of plasma, a permanent magnet M2 mounted is susceptible to improvement in efficiency, not necessarily essential element. With this configuration, the plasma space potential is a positive potential several volts higher than the anode.
[0030]
Then, in addition a negative bias voltage by the DC power supply (not shown) on the surface of metallic gallium 7 to set the said surface faces a negative potential. That is, if the voltage is 100 V or more, ions are attracted from the plasma to the surface portion, and sputtering occurs to generate gallium atoms in a direction perpendicular to the metal gallium surface. By increasing the applied voltage, the flow of generated gallium atoms increases. However, when discharge occurs between the material holding means 5 and the container 2, impurities are generated and contaminate the substrate 4. About 500V is appropriate. The flow of generated gallium atoms reaches the substrate 4 positioned just above the material holding means 5.
[0031]
On the other hand, the plasma generated in the plasma generating section 12, contains excited nitrogen atoms and nitrogen molecules, these active species, the charged particles of the excited high electron temperature, i.e., ions and sputtering gas Along with a part of the excited electrons, it flies toward the substrate, and on the substrate 4, as will be described later, a sputtered gallium metal Ga atom and a chemical reaction with the excited atom form a gallium nitride GaN thin film . To do. Energy required for a chemical reaction at this time is applied from the photons emitted excited energy of nitrogen atoms, the kinetic energy of the sputtered Ga atoms and excited Ga atoms gallium metal material and from them. In addition, when a rare gas is mixed as a sputtering gas in addition to the nitrogen gas as a reactive gas, the rare gas atoms in a metastable excited state can also serve as a reaction energy supply source on the substrate surface.
Moreover, the cylindrical container 2 is divided by the partition plate 3 provided between the plasma generation unit 12 and the substrate housing unit 11 for housing the substrate 4, and the through holes 31 of the partition plate 3 are formed as shown in FIG. 1. The plasma generated in the plasma generating unit 12 is concentrically spaced from the surface of the substrate 4 arranged in the reaction unit 11, and the plasma generated in the plasma generating unit 12 is transmitted only through the through hole 31 of the partition plate 3. A plasma flux flowing toward the side is formed. In addition, since the diameter of the through hole 31 of the partition plate 3 is a tapered surface that gradually increases from the substrate storage unit 11 side toward the plasma generation unit 12 side, ions in the plasma generated by the plasma generation unit 12 even if the sputtered particles and the like is irradiated to the tapered surface, the charged particles generated without entering the substrate receiving portion 11 side, back to the plasma generating section 12 side. That is, with this configuration , the amount of particles (impurities) of the sputtered partition plate 3 deposited on the substrate 4 can be reduced.
[0032]
Further, the permanent magnet M1 provided on the partition plate 3 crosses the through hole 31, that is, a DC magnetic field G1 parallel to the front surface of the substrate 4 is formed, so that the plasma density in the vicinity of the substrate 4 is reduced. The electron temperature is lowered with the density. This is a magnetic filter structure frequently used for a negative ion source of hydrogen, and the amount of ions irradiated on the substrate 4 decreases as the electron density decreases. Further, when a thin film having a high resistivity such as gallium nitride is formed, or when the substrate 4 is an insulator, the surface potential of gallium nitride, which is a deposited thin film material, becomes a floating potential of plasma. As the temperature decreases, the energy of ions reaching the thin film decreases.
[0033]
As described above, according to the forming method of the present invention using the forming apparatus 1, by providing the magnetic field G1 across the front of the substrate 4, the amount of ion flow reaching the substrate 4 is kept small, and the substrate surface Therefore, the gallium nitride formed on the substrate 4 can be grown without being damaged by the ion irradiation from the plasma.
[0034]
The present invention is not limited to the above embodiment. For example, a nitrogen gas having a reactive gas with respect to metal gallium Ga may be mixed with a rare gas that promotes sputtering in advance and introduced into the container. In the above embodiment, the plasma central portion is a substantially no magnetic field region. However, as described later, the presence or absence of the no magnetic field portion in the central portion does not greatly affect the effect.
[0035]
In the above embodiment, the thin film material is gallium nitride. However, according to this formation method, for example, zinc oxide or the like can be formed.
The material holding means may be provided with a holding portion position changing mechanism that can change the distance of the material held by the holding portion from the substrate.
[0036]
【Example】
Examples of the present invention will be described in detail below.
[0037]
Example 1
Using the forming apparatus 1, a gallium nitride thin film as a thin film material was obtained under the following forming conditions. And the obtained gallium nitride thin film was not cracked . Further, when the obtained gallium nitride thin film was examined by X-ray diffraction, it showed a single structure as shown in FIG. The angles shown correspond to cubic (1, 1, 1) or hexagonal (0, 0, 0, 2), but cubic images are obtained from an image obtained by a focused ion beam microscope. concluded et al is to have a system. Further, the substrate frontal arrival rate of gallium nitride particles calculated backward from the film thickness is about 10 14 per square centimeter and 10 per second, and almost coincides with the value of the gallium atomic particle bundle calculated from the sputtering rate and the shape factor. Value.
[0038]
[Formation conditions]
Inner diameter of container: 16cm
Container height: 20cm
Partition plate thickness: 2cm
Minimum diameter of partition hole: 5cm
Hole taper: 45 °
Substrate material: Silicon substrate Temperature: 30 ° C (room temperature)
Distance between substrate and gallium: 10 cm
Nitrogen gas pressure in the container: 0.05 Pa
Argon gas pressure in the container: 0.01 Pa
Applied voltage to gallium: 300V
Discharge voltage: 50V
Processing time: 5-6 hours [0039]
The nitrogen gas pressure is determined by observing light emission from the plasma around the gallium surface using a spectroscope, so that the line spectrum intensity emitted from the gallium atoms and the light emission of excited nitrogen atoms / molecules are constant pressure (0.05 Pa). ) Since it has been found that the local maximum takes a moderate value in the vicinity, it was set near this local maximum.
[0040]
(Example 2)
Changes in the excitation spectrum intensities of Ga (417 nm), Ga (403 nm) and N ₂ (391 nm) when the mixing ratio of nitrogen gas and argon gas was changed were measured using a spectroscope, and the results are shown in FIG. It was shown to.
As shown in FIG. 4, with nitrogen gas alone, the maximum potential gallium nitride layer covers the surface when the material holding means and the wall surface of the plasma generating portion do not generate a direct discharge. It drops to about the potential. Therefore, even if a large negative voltage is applied to the gallium holding mechanism, it cannot be removed due to the reduction of sputtering due to nitrogen ions. However, it is understood that when a rare gas such as argon is introduced into the nitrogen plasma, the rare gas ions can remove the nitride layer by sputtering and recover the generation of gallium atoms. In other words, it is useful to use a mixture of nitrogen gas and argon gas, and it can be seen that suitable film forming conditions can be realized.
[Brief description of the drawings]
FIG. 1 is an explanatory view schematically showing one embodiment of a thin film material forming apparatus according to the present invention.
2 is a cross-sectional view taken along line XX of FIG.
3 is an X-ray diffraction data of the gallium nitride thin film obtained in Example 1. FIG.
FIG. 4 is gallium line spectrum data obtained by a spectroscope in which changes in argon concentration and gallium atom production were examined.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Formation apparatus 11 Substrate accommodating part 12 Plasma generating part 2 Container 3 Partition plate 31 Through-hole 4 Substrate 5 Material holding means 6 Cathode 7 Metal gallium Ga (material)
8 Gas introduction path M1, M2 Permanent magnet (magnetic field generating means)
G1, G2 magnetic field

Claims (5)

The substrate is fixed to the substrate fixing means provided inside the container that can be sealed in a vacuum state, and the material holding means for holding the liquid or solid material constituting the film is provided opposite to the substrate, and the inside of the container The sputtering gas introduced into is ionized by the discharge mechanism to generate discharge plasma, and the charged particles in the discharge plasma are irradiated onto the material surface to neutral and excited particles of the material sputtered. In a thin film material forming apparatus for forming a thin film by being deposited on the substrate,
Attach a partition plate formed with a through hole approximately the same size as the area of the substrate inside the container, and divide it into a substrate accommodating portion and a plasma generating portion,
A substrate fixing means for fixing the substrate concentrically with the through hole of the partition plate in the substrate accommodating portion and in parallel with a space from the partition plate is disposed,
While the electrode provided at the bottom of the plasma generation unit is used as a cathode, a discharge is generated between an electrode pair having the inner wall surface of the plasma generation unit as an anode to ionize the sputtering gas introduced into the plasma generation unit. Disposing a discharge mechanism and arranging a material holding means for holding the material concentrically with the through hole of the partition plate above the cathode,
A negative bias voltage applying means for accelerating ion attraction in the discharge plasma by setting the material surface held by the material holding means to a negative potential;
A magnetic field generator that generates a parallel DC magnetic field on the substrate surface that is fixed to the substrate fixing means across the through hole is disposed around the through hole of the partition plate,
The plasma guided from the plasma generator to the through hole of the partition plate by adjusting the discharge power supplied to the discharge mechanism and the negative bias voltage applied to the material surface by the negative bias voltage applying means. The flow rate of neutral and excited neutral particles to the substrate is controlled, and the amount of high energy electrons in the plasma incident on the substrate is controlled in cooperation with a DC magnetic field traversing the through hole. An apparatus for forming a thin film material, characterized by being configured to suppress . 2. The thin film material forming apparatus according to claim 1, wherein an inner peripheral surface of the through hole provided in the partition plate is a tapered surface that expands from the substrate accommodating portion side to the plasma generating portion side in the container . The material holding portion of the material holding means arranged above the cathode provided in the plasma generating portion is provided so as to conceal the cathode from the substrate arranged concentrically with the through hole of the partition plate. The apparatus for forming a thin film material according to claim 1, wherein: A gas introduction unit that individually introduces at least one kind of gas selected from a reactive gas and a rare gas into the plasma generation unit when the material is reactive with the material held in the material holding unit. The apparatus for forming a thin film material according to any one of claims 1 to 3, wherein: The material constituting the film held by the material holding member is Ga, and the sputtering gas introduced into the plasma generation unit through the gas introduction unit is composed of nitrogen N ₂ gas and a rare gas that can react with the Ga material . A mixed gas, a discharge plasma of the mixed gas is generated by a discharge mechanism in a plasma generator, a discharge power supplied to the discharge mechanism and a negative bias voltage applied to the material surface by a negative bias voltage application unit In the plasma generator, neutral particles of the Ga material generated by sputtering of the Ga material by the charged particles of the mixed gas in the discharge plasma, the excited neutral particles, and the Ga material are emitted from the Ga material. Plasma including neutral electrons of nitrogen gas contained in discharge plasma of the mixed gas, excited neutral particles thereof, and high energy electrons When guided to the through hole of the partition plate, the plasma controls the flow rate of neutral particles and excited neutral particles in the plasma to the substrate and cooperates with a DC magnetic field traversing the through hole. by suppressing the incident amount to high-energy electrons of the substrate in the thin film material according to any one of claims 1 to 4, characterized by being configured to form a GaN thin film on the substrate surface Forming equipment .

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