JP3291149B2 - Method for producing crystalline thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a crystalline thin film having a large crystal grain size.

[0002]

2. Description of the Related Art In recent years, thin films such as silicon have been used as electrical functional films in semiconductor devices, solar cells, and the like. When a semiconductor element is formed using this silicon thin film, it is known that the film quality of the silicon thin film affects the characteristics of the element. For example, a polycrystalline silicon film has a higher electron mobility than an amorphous silicon film, and a polycrystalline silicon film having a larger crystal grain size has a higher electron mobility. Further, a single crystal silicon thin film is more ideal.

Therefore, a polycrystalline thin film or a single crystal thin film having good characteristics and a large crystal grain size is formed on a substrate, and these are used to form a thin film transistor (TFT) for a liquid crystal display, a semiconductor device having a three-dimensional structure, and a semiconductor for a solar cell. Attempts have been made to improve device characteristics by forming devices and the like.

[0004] As a method of forming a polycrystalline silicon thin film on an insulating substrate or a semiconductor substrate, for example, an amorphous silicon thin film deposited by vacuum deposition or vapor phase chemical reaction (CVD) is thermally annealed to be solid-phase grown. There is a recrystallization method.

Further, by irradiating a thin film formed on a substrate with a laser beam, an electron beam, or an ion beam in a heating atmosphere of about 400 to 450 ° C., the thin film is locally melted and recrystallized to reduce the crystal grain size. There are also ways to make it bigger.

[0006]

However, in the conventional recrystallization treatment by thermal annealing, a large amount of crystal nuclei near the interface between the insulating film on the insulating substrate or semiconductor substrate and the amorphous silicon thin film during the thermal annealing. Therefore, there is a problem that only a polycrystalline silicon thin film having an extremely small particle size of about several μm can be obtained.

In laser annealing, as shown in FIG. 2A, when an amorphous silicon thin film 32 deposited on an insulating substrate 30 is irradiated with a laser beam 40 simultaneously with heating,
The temperature of the central portion 34 irradiated with the laser light 40 becomes the highest. Then, cooling is performed from the peripheral portion 36 to generate a crystal nucleus, and the crystal nucleus grows toward the central portion 34. Therefore, a polycrystalline silicon thin film having a relatively large particle size is formed at the central portion 34. However, as shown in FIG. 2B, since the density of crystal nuclei generated in the peripheral portion 36 is high, polycrystals having a large grain size are not formed in the central portion 34, and there is a limit in increasing the grain size. Also, annealing of an electron beam or an ion beam has the same problem as the laser annealing.

Japanese Patent Laid-Open Publication No. Hei 1-320291 proposes a method for forming a single crystal silicon thin film on a substrate. In this method, when depositing a thin film on a substrate, the substrate is simultaneously irradiated with an ion beam of an inert gas such as Ar ⁺ ion from two predetermined directions to form a single-crystal silicon thin film. When irradiating with Ar ⁺ ions, the acceleration energy is set to 20 to 25 eV, and when irradiating with Ne ⁺ ions, the acceleration energy is set to 30 to 40 eV, thereby irradiating the substrate and the deposited polycrystalline thin film without sputtering. It states that a single crystal silicon thin film can be formed on a substrate.

However, in this method, a microcrystal having a specific crystal axis is grown by irradiating an ion beam from two specific directions. Therefore, the irradiation direction of the ion beam and the like had to be controlled accurately.
Further, when the present applicant irradiates the substrate with Ar ⁺ ions at an acceleration energy of 40 eV during the deposition of the silicon thin film,
Only a polycrystalline silicon thin film having an extremely small particle size of about several μm was obtained.

As described above, in any of the conventional methods for producing a crystalline thin film, there is a problem that a crystalline thin film having good characteristics and a large grain size cannot be obtained.

The present invention has been made to solve the above problems, and has as its object to provide a method for forming a crystalline thin film having a large grain size on a substrate.

[0012]

Means for Solving the Problems To achieve the above object, a method for producing a crystalline thin film according to the present invention comprises the steps of :
Silicon crystal or silicon-based crystal
In the method of manufacturing a crystalline thin film having a large particle diameter, a thin film is formed on the substrate while irradiating rare gas ions having an acceleration energy of 50 to 500 eV when depositing a thin film material on the substrate. After the formation of the thin film, the thin film is subjected to a recrystallization treatment to obtain a crystalline thin film having a large grain size .

[0013]

By irradiating rare gas ions with an acceleration energy of 50 eV or more as in the method for manufacturing a crystalline thin film of the present invention, the thin film is deposited on the substrate in a state where rare gas atoms are incorporated in the deposited thin film. Progresses, and rare gas atoms can remain in the thin film. On the other hand, as in the conventional example,
When Ar ⁺ ions are irradiated at an acceleration energy of 20 eV, it is difficult for Ar ⁺ ions to penetrate 1 nm or more deeply from the surface of the thin film.

The acceleration energy of the rare gas ions is set to 5
When the voltage is set to be equal to or less than 00 eV, problems such as spattering of the thin film, desorption of ions due to local high temperature of the thin film due to ion bombardment, and generation of microcrystals do not occur. On the other hand, when irradiation is performed with Ar ⁺ ions having an acceleration energy of, for example, 1000 eV, one silicon atom per ion is desorbed from the surface of the thin film by a sputtering effect.

As described above, according to the present invention, the acceleration energy of rare gas ions is set within the above-mentioned optimum range,
Preferably, noble gas atoms can be left in the lattice of the thin film. The remaining rare gas atoms are present between the crystal lattices of the thin film without reacting with atoms such as silicon of the thin film material. The remaining rare gas atoms hinder the rearrangement of the crystal lattice of the thin film of silicon or the like during recrystallization by thermal annealing or the like, so that the density of crystal nuclei generated in the thin film is suppressed low.

The rare gas atoms are desorbed from the interstitial space by heating such as recrystallization treatment, but are not completely desorbed, for example, at about 600 ° C. at which the solid phase growth of silicon starts. Therefore, the starting temperature of the solid phase growth of the amorphous silicon thin film increases as the amount of rare gas atoms taken in during the deposition of the thin film increases. Furthermore, desorption of a rare gas atom depends on its atomic radius, and the smaller the radius, the easier it is to desorb. Therefore,
By changing the element of the rare gas ion to be irradiated,
The desorption temperature can be controlled.

Therefore, in the present invention, for example, when the thin film is locally heated during the recrystallization treatment, generation of crystal nuclei starts selectively in a high temperature portion of the thin film. In addition, when the irradiated portion and the non-irradiated portion of the rare gas ion are provided on the thin film, the crystal nuclei generated in the non-irradiated portion grows and the crystal nuclei proceed to the irradiated portion.

As described above, according to the method for producing a crystalline thin film of the present invention, the generation density of crystal nuclei and the position thereof can be controlled as compared with the conventional method. Regardless of the type, a crystalline thin film having a large crystal grain size can be formed on a substrate.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 shows a manufacturing apparatus and a manufacturing method of a crystalline thin film in the present embodiment.

In FIG. 1, a single crystal silicon substrate 10 is disposed as a substrate in a vacuum evaporation tank 28, and an electron beam evaporation apparatus 11 for evaporating a silicon thin film on the silicon substrate 10; Noble gas (argon:
Ar ⁺⁾ electron cyclotron resonance (E ion irradiation
CR) A plasma ion source 20 is provided. Furthermore,
The heater 16 for heating and holding the inside of the tank is provided in the vacuum evaporation tank 28.

The ECR plasma ion source 20 ionizes a rare gas by an arc electrode to generate rare gas ions, and applies a predetermined voltage to an acceleration electrode 22 to accelerate the rare gas ions. The ECR plasma ion source 2
The Faraday cup 26 provided between 0 and the substrate 10 detects the amount of rare gas ions irradiated onto the substrate 10 as an ion current.

Next, a method of manufacturing a crystalline thin film by a manufacturing apparatus as shown in FIG. 1 will be described.

An oxide film is previously formed on the surface of the silicon substrate 10 by thermal oxidation. Then, the silicon substrate 10 on which the oxide film is formed is heated and maintained at 150 ° C. in a vacuum deposition tank 28 maintained at about 10 ⁻¹⁰ Torr. The heating at 150 ° C. is performed to remove impurities such as oxygen from the surface of the oxide film of the silicon substrate 10 to clean the oxide film.

In a heating state at 150 ° C., an electron beam is irradiated to the evaporation source 12 using the electron beam evaporation apparatus 11, and silicon (Si) atoms 14 are applied to the surface of the silicon substrate 10.
Deposition was performed at a rate of 05 nm / s for 90 minutes. The amount of Si to be sputtered is detected by an atomic absorption evaporation monitor 13 provided between the evaporation source 12 and the substrate 10, and the amount of electron beam irradiation is controlled based on the detection result of the monitor 13 to control the amount of silicon. The amount of sputtering is controlled.

Further, 150 V is applied to the accelerating electrode 22 of the ECR plasma ion source 20 simultaneously with the deposition of the silicon atoms 14 by using argon (Ar) as a rare gas.
Ar ⁺ ions were accelerated with an acceleration energy of 50 eV, and the silicon substrate 10 was irradiated with the Ar ⁺ ions at an ion current of 5 μA / cm ² . And silicon atom 1
This irradiation with Ar ⁺ ions was performed until the deposition of No. 4 was completed.

After the deposition, thermal annealing (recrystallization treatment) was performed, and the silicon substrate 10 was heated to 750 ° C. in the vacuum deposition tank 28 and held for 30 minutes.

After completion of the recrystallization treatment, the silicon substrate 10 is cooled to room temperature, taken out into the atmosphere, and immersed in a Secco etching solution as a sample to perform a surface treatment. Observed. As a result, the silicon thin film was a large polycrystal having a crystal grain size of about 10 to 100 μm. The used Secco
The composition of the etchant was 2 ml of 49% HF, 0.15
1 ml of M K ₂ Cr ₂ O ₂ .

As described above, the density of crystal nuclei generated during the recrystallization process can be reduced by irradiating the silicon thin film during vapor deposition with the acceleration energy of argon ions at 150 eV, which is about 10 to 100 μm. A large polycrystalline silicon thin film can be manufactured.

The amount (remaining amount) of rare gas atoms taken into the thin film during deposition by the irradiation of rare gas ions is determined when the concentration is in the range of 5 × 10 ¹⁹ cm ⁻³ to 1 × 10 ²² cm ^−3. In addition, generation of crystal nuclei during the recrystallization process (for example, thermal annealing) can be limited. The remaining amount of the rare gas atoms can be easily controlled by the acceleration energy of the rare gas ions and the substrate temperature (annealing temperature). And
If the amount of rare gas atoms taken in during thin film deposition is large,
Since the generation of crystal nuclei is hindered accordingly, the starting temperature of the solid phase growth of the amorphous silicon thin film can be increased. Furthermore, the desorption temperature from the thin film can be controlled by changing the kind of the rare gas ions to be irradiated.

Therefore, when the sample substrate 10 is locally heated during the recrystallization process, generation of crystal nuclei starts from a high temperature portion. Further, when the thin film has an irradiated portion and a non-irradiated portion of the rare gas ion, a crystal nucleus generated in the non-irradiated portion grows and proceeds to the irradiated portion.

As described above, according to the method for producing a crystalline thin film of the present embodiment, the density of crystal nuclei generated in a vapor-deposited thin film can be controlled over a wide range, and a crystal having a significantly larger crystal grain size than the conventional method can be obtained. It is possible to produce high quality thin films.

Under the manufacturing conditions of the present embodiment described above, the acceleration energy of Ar ⁺ ions is 20 eV,
The silicon thin film was deposited at an ion current of 5 μA / cm ² and recrystallized using thermal annealing in the same manner as in this example. As a result, the crystal grain size of the obtained polycrystalline silicon thin film was about 1 to 10 μm. Met. This hardly has a significant difference from the case where a conventional recrystallization treatment such as thermal annealing is performed without irradiating rare gas ions.

Further, the sample immediately after the deposition is taken out, and
When the argon concentration in the silicon thin film was measured by X-ray photoelectron spectroscopy, the residual argon concentration in the thin film was below the detection limit of the spectrometer. That is, acceleration energy 2
At about 0 eV, it has been confirmed that Ar atoms cannot penetrate into the silicon thin film and remain between the silicon lattices.

Further, the acceleration energy of the Ar ⁺ ion is set to 7
When a silicon thin film was deposited under the conditions of 00 eV and an ion current of 10 μA / cm ² , the silicon thin film had already been microcrystallized at the end of the deposition. Therefore, even if recrystallization treatment such as thermal annealing is performed on the silicon thin film, the crystal cannot be made large. Also, when the argon concentration in the silicon thin film was measured, the residual argon concentration in the thin film was below the detection limit of the spectrometer.

As shown in the above experiment, the acceleration energy of the rare gas ions is larger than 20 eV and 700 eV.
In order to obtain a polycrystalline thin film having a large grain size, a range of less than V, more preferably a range of 50 to 500 eV is necessary.

Embodiment 2 FIG. Next, an example in which a silicon thin film formed on a substrate under the same conditions as in Example 1 is recrystallized by excimer laser annealing will be described.

In this embodiment, as in the first embodiment, Ar ⁺ ions are applied to the silicon substrate 10 at an acceleration energy of 150 e.
V, while irradiating with an ion current of 5 μA / cm ² , a silicon thin film was formed by vapor deposition.

Subsequently, the substrate 10 was heated and held at 400 ° C., and the width of the surface of the silicon thin film was 3 mm from the window of the vacuum vessel.
Was irradiated with an ArF excimer laser to recrystallize the silicon thin film to obtain a sample. The irradiation energy density of the ArF excimer laser was 300 mJ / cm ² , and the number of pulses was 150 shots.

After the recrystallization treatment, the substrate 10 was cooled to room temperature, taken out into the atmosphere to form a sample, subjected to a surface treatment with a Secco etching solution, and the surface was observed with a scanning electron microscope. As a result, in the center of the region irradiated with the ArF excimer laser, polycrystalline silicon having an extremely large grain size of about 100 × 500 μm was formed at the maximum.

Since the excimer laser is absorbed by the thin film portion and does not reach the substrate, the thin film can be selectively annealed without increasing the substrate temperature. Therefore, by using excimer laser annealing for the recrystallization treatment as in this embodiment, even if a low melting point glass substrate is used as the substrate, a large particle size having extremely high characteristics can be formed on the substrate. Can be formed. It should be noted that a polycrystalline thin film having a large grain size can be obtained in the same manner as in the present embodiment by using other laser annealing, electron beam annealing, ion beam annealing, or the like as the recrystallization treatment without being limited to the excimer laser.

As described above, according to this embodiment, a polycrystalline thin film having a large crystal grain size can be formed not only on a single-crystal semiconductor substrate but also on various substrates such as an insulating substrate. Therefore, by using this polycrystalline thin film for an element such as a TFT such as a semiconductor device, a solar cell, or a display element of a liquid crystal display, the characteristics of the element can be improved.

Embodiment 3 FIG. Next, an example of a method for manufacturing a single crystal thin film on a substrate will be described.

First, an oxide film having a thickness of 200 nm was formed on the surface of a single crystal silicon substrate by thermal oxidation. afterwards,
This thermal oxide film was removed in a striped shape having a width of 50 μm by using a resist process. Next, the silicon substrate was heated and maintained at 150 ° C. in the vacuum evaporation tank 28 of FIG.
Deposited at a rate of nnm / s for 90 minutes.

At the same time as the deposition of silicon atoms, the acceleration energy is 100 eV and the ion current is 5 μA / cm ^2.
The substrate was irradiated with argon (Ar ⁺ ) ions, and this irradiation was performed until the deposition of silicon atoms was completed.

Subsequently, thermal annealing was performed as a recrystallization treatment of the thin film, and the substrate was heated to 750 ° C. in a vacuum evaporation tank 28 and held for 30 minutes.

After the completion of the thermal annealing, the substrate was cooled to room temperature and the substrate was taken out to the atmosphere to obtain a sample. Then, the sample surface was treated with a Secco etching solution, and the surface was observed with a scanning electron microscope. As a result, a region of about 3 mm was formed of single crystal silicon along the striped pattern from which the thermal oxide film had been removed.

As described above, according to the present embodiment, a single-crystal thin film can be formed in a region on an insulating film formed on a single-crystal substrate. In the present embodiment, the recrystallization treatment is not limited to the above-described thermal annealing, but may be performed by laser annealing, electron beam annealing, ion beam annealing, or the like as in the second embodiment.

In the first, second, and third embodiments described above, argon (Ar ⁺ ) ions are described as an example of rare gas ions, but other rare gas ions (Ne ⁺
Ion, Xe ⁺ ion), the same effect can be obtained. That is, by irradiating the target thin film during deposition of the thin film with the acceleration energy in the range of 50 to 500 eV, a polycrystalline thin film or a single crystal thin film having a large grain size can be manufactured.

[0050]

According to the present invention, the substrate is irradiated with the rare gas ions during the deposition of the thin film material at an acceleration energy of the rare gas ions of 50 to 500 eV, and thereafter, the deposited thin film is recrystallized. .

When irradiation with rare gas ions is performed at an acceleration energy of 50 eV or more, the deposition of the thin film proceeds while the rare gas atoms are incorporated into the deposited thin film on the substrate, and the rare gas atoms remain in the thin film. If the acceleration energy is set to 500 eV or less, the thin film itself is sputtered, the surface of the thin film becomes locally high due to ion bombardment, rare gas ions are desorbed, and microcrystals are generated in the thin film. do not do.

As described above, by performing the acceleration energy of the rare gas ions in the optimum range, the present invention preferably allows the rare gas atoms to remain in the lattice of the thin film and to be used for recrystallization by thermal annealing or the like. The crystal nucleus generation density in the thin film can be kept low.

Therefore, according to the method for producing a crystalline thin film of the present invention, it is possible to control the generation density and position of crystal nuclei as compared with the conventional method, and the crystal grain size can be controlled regardless of the type of substrate. Large crystalline thin films can be formed on a substrate.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating a manufacturing apparatus and a manufacturing method of a crystalline thin film according to an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional method for producing a crystalline thin film using laser annealing.

[Explanation of symbols]

Reference Signs List 10 substrate, 11 electron beam evaporation apparatus, 14 silicon atoms, 20 electron cyclotron resonance plasma ion source, 22 acceleration electrode, 24 argon ions.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H01L 31/04 (72) Inventor Koji Kajino 2-1-1 Asahi-cho, Kariya-shi, Aichi AISIN SEIKI CO., LTD. ) Inventor Noriyoshi Shibata 2-4-1 Rokuno, Atsuta-ku, Nagoya-shi, Aichi Japan Fine Ceramics Center Testing Laboratory (72) Inventor Yukari Tani 2-4-1 Rokuno, Atsuta-ku, Nagoya-shi, Aichi Pref. (56) References JP-A-5-275331 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/20

Claims (1)

(57) [Claims] 1. A silicon crystal or a silicon crystal on a substrate.
In the method of producing a large-grain crystalline thin film composed of a crystal mainly composed of silicon, when depositing a thin-film material on a substrate, an acceleration energy of 50% is used.
Forming a thin film on the substrate while irradiating a rare gas ion of ~ 500 eV, and performing a recrystallization treatment on the thin film after forming the thin film;
A method for producing a crystalline thin film, wherein the crystalline thin film has a large grain size .