JP2004165184A - Method of manufacturing laser irradiation equipment and semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein a device for shielding a laser beam in accordance with the movement of a scanning stage is provided so as to enable the laser beam to irradiate only a substrate, but the irradiation traces of the laser beam left on the substrate become not rectilinear but wavy reflecting on vibrations when the vibrations of the device are conducted to an optical system that forms a beam spot and the scanning stage where the substrate is installed. <P>SOLUTION: Laser irradiation equipment employs a shutter which uses as a power source a motor whose rotational acceleration change is continuous, so that vibrations originating from the shutter can be eliminated, and the irradiation traces of the laser beam on the substrate become rectilinear. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a laser irradiation apparatus that activates a semiconductor film or the like after crystallization or ion implantation using a laser beam. The present invention belongs to the technical field of a laser irradiation apparatus that irradiates a semiconductor film in a polycrystalline or nearly polycrystalline state with a laser to improve the crystallinity of the semiconductor film. A semiconductor device refers to an electro-optical device and an electric device typified by a liquid crystal display device, and the present invention belongs to a technical field of a method for manufacturing the semiconductor device.
[0002]
[Prior art]
In recent years, the technology for forming a TFT on a substrate has been greatly advanced, and application development to an active matrix type semiconductor display device has been advanced. In particular, a TFT using a polycrystalline semiconductor film has higher field-effect mobility (also referred to as mobility) than a TFT using a conventional amorphous semiconductor film, and thus can operate at high speed. Therefore, an attempt has been made to control a pixel, which has been conventionally performed by a drive circuit provided outside a substrate, by a drive circuit formed on the same substrate as the pixels.
[0003]
As a substrate used for a semiconductor device, a glass substrate is considered more promising than a single crystal silicon substrate in terms of cost. Since a glass substrate is inferior in heat resistance and easily deformed by heat, when a polysilicon TFT is formed on a glass substrate, laser annealing is used for crystallization of a semiconductor film in order to avoid heat deformation of the glass substrate.
[0004]
The characteristics of laser annealing are that the processing time can be significantly reduced compared to the annealing method using radiant heating or conduction heating, and that the semiconductor substrate or semiconductor film is selectively and locally heated to provide almost thermal It is said that no damage is caused.
[0005]
Here, the laser annealing method refers to a technique for recrystallizing a damaged layer or an amorphous layer formed on a semiconductor substrate or a semiconductor film, or a technique for crystallizing an amorphous semiconductor film formed on a substrate. pointing. In addition, the technology includes a technique applied to planarization and surface modification of a semiconductor substrate or a semiconductor film.
Lasers used for laser annealing are roughly classified into two types, pulse oscillation and continuous oscillation, depending on the oscillation method. In recent years, it has been found that the diameter of crystals formed in a semiconductor film is larger when a continuous wave laser is used than in a pulsed laser in crystallization of a semiconductor film. When the crystal grain size in the semiconductor film is increased, the number of grain boundaries entering the TFT channel region formed using the semiconductor film is reduced, so that the mobility is increased and the device can be used for developing a device with higher performance. For this reason, continuous wave lasers have begun to be spotlighted.
[0007]
Further, in performing laser annealing of a semiconductor or a semiconductor film, a laser beam emitted from a laser oscillator is applied to a surface to be irradiated in a linear or elliptical shape having an aspect ratio of 10 or more (referred to as a linear shape in this specification). A method is known in which a beam spot is scanned on an irradiation surface by processing with an optical system such that With the above method, the substrate can be efficiently irradiated with laser light, and mass productivity can be increased. Therefore, it is industrially favorably used (for example, see Patent Document 1).
[0008]
[Patent Document 1] Japanese Patent Application Laid-Open No. 8-195357
[Problems to be solved by the invention]
In order to efficiently perform laser annealing of a semiconductor film formed on a substrate, a beam spot shape emitted from a continuous wave laser oscillator is processed into a linear shape using an optical system, and the linear beam spot is processed. A method of irradiating a substrate is used.
[0010]
A method of moving a scanning stage on which a substrate is placed with respect to a beam spot and performing laser annealing on the entire surface of the substrate is often used. In the case of irradiating a laser beam using the above method, it is necessary to provide a device (hereinafter referred to as a shutter) for blocking the laser beam in accordance with the movement of the scanning stage so that the laser beam is irradiated only on the substrate. By providing the shutter, it is possible to irradiate an arbitrary region on the substrate with the laser light, and it is possible to prevent the other region from being irradiated and prevent the apparatus from being damaged by the laser light.
[0011]
When the shutter can be rotated in the reverse direction, for example, by an opening / closing mechanism by rotating a reflection mirror using a solenoid motor (FIG. 1), it is necessary to forcibly stop the rotation of the motor 1101 to completely open and close the shutter. is there. When a projection 1103 is provided on the rotation shaft 1102 of the motor 1101 and the projection 1103 is brought into contact with the stopper 1104 to forcibly stop the rotation, a vibration occurs due to a collision between the stopper 1104 and the projection 1103 when the rotation is stopped. . When the vibration is transmitted to the optical system that forms the beam spot and the scanning stage on which the substrate is installed, the laser irradiation trace formed on the substrate is not linear but has a wave shape reflecting the vibration. When the laser irradiation trace undulates, a portion having an extremely high overlap ratio or a portion not irradiated with laser at all is generated between adjacent laser irradiation traces formed by the reciprocating movement of the scanning stage. Since the TFTs are formed in a regular arrangement on the substrate, the TFTs formed in the above-described portions have poor electric characteristics and cause variations in the electric characteristics.
[0012]
The present invention has been made in view of the above-described problems, and provides a continuous wave laser irradiation apparatus capable of linear laser irradiation and a method for manufacturing a semiconductor device.
[0013]
[Means for Solving the Problems]
The present invention provides a laser irradiation apparatus that uses a shutter whose power source is a motor whose rotation acceleration change is continuous, eliminates vibration generated from the shutter, and enables a laser irradiation trace to be linear. is there. Further, the present invention is a laser irradiation apparatus having a shutter function by changing an optical path using an acousto-optic element utilizing an acousto-optic effect and having no vibration source.
[0014]
FIG. 2 is a schematic diagram of a method for solving the above problem. The reflection mirror 1201 is a disk with a cut in a part. The reflection mirror 1201 rotates around the center of the circle as the rotation axis 1202, and when the laser beam 1206 enters the cut portion 1203, the laser beam passes without hitting the reflection mirror 1201 (1207) and the non-cut portion 1204. Is reflected by the mirror surface (1208), enters the heat sink 1209, and stops traveling. The rotation direction is only one direction, and when the substrate set on the reciprocating scanning stage comes to the laser irradiation position, the laser light 1206 is incident on the cut portion 1203 of the reflection mirror 1201 and the reflection mirror 1201 is moved. The rotation speed is controlled so as to pass.
[0015]
As described above, the rotation of the reflection mirror 1201 is limited to one direction and synchronized with the movement of the scanning stage. By adopting a structure in which rotation is not forcibly stopped, vibration due to the impact of forcibly stopping rotation is eliminated, and vibration transmitted to the optical system and the scanning stage is eliminated. Can be.
[0016]
With the above structure, laser irradiation can be performed without giving vibration to the optical system and the scanning stage, and laser annealing can be performed on the entire surface of the semiconductor film without any gap.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the configuration of the laser irradiation apparatus of the present invention will be described with reference to FIG.
[0018]
The laser irradiation apparatus of the present invention has a laser oscillator 1301 that oscillates laser light. Although FIG. 3 illustrates an example in which one laser oscillator 1301 is provided, the number of laser oscillators included in the laser irradiation device of the present invention is not limited to this number. The beam spots of the respective laser beams output from the laser oscillator may be superimposed on each other and used as one beam spot.
[0019]
The laser can be appropriately changed depending on the purpose of processing. In the present invention, a known laser can be used. As the laser, a continuous wave gas laser or solid state laser can be used. As a gas laser, Ar laser, include a Kr laser, a solid state laser, YAG laser, YVO ₄ laser, YLF laser, YAlO _{3 laser,} Y 2 _{O 3} laser, a glass laser, ruby laser, alexandrite laser, Ti: sapphire Laser and the like. Note that there are Nd, Cr, Yb, and the like as dopant substances for the laser medium, and harmonics with respect to the fundamental wave can be obtained by using a nonlinear optical element.
[0020]
Furthermore, after converting the infrared laser light emitted from the solid-state laser into a green laser light by using a non-linear optical element, an ultraviolet laser light obtained by another non-linear optical element can also be used.
[0021]
Laser light emitted from the laser oscillator 1301 enters a shutter 1302 provided on an optical path.
[0022]
Laser light that has entered the inside of the shutter from the entrance port reaches the reflection mirror 1303. The rotation speed is controlled so that the reflection mirror 1303 makes one rotation while the reciprocating X-axis stage 1305 completes one-way operation from the start of operation. Hereinafter, the laser irradiation position is a position where the laser beam is irradiated on the substrate 1307 provided on the stage when the shutter 1302 is not provided. The laser irradiation position is such that the X-axis stage is disposed substantially at the center of the X-axis stage, and the distance from the laser irradiation position to the movement start position of the X-axis stage is the same as the distance from the laser irradiation position to the end position. And The reflection mirror is rotated in the direction indicated by the arrow in FIG. When the front end of the substrate 1307 comes to the laser irradiation position, the incident position of the laser beam to the reflection mirror 1303 is at the cut portion a, and when the rear end of the substrate end 1307 comes to the laser irradiation position. Then, the rotation of the motor is controlled so that the incident position of the laser beam on the reflection mirror 1303 is at the cut portion b. Here, when the X-axis stage is moved, the end on which the laser light of the substrate first strikes is the front end, and the other end is the rear end.
[0023]
The present invention includes an optical system 1304 which shapes a beam spot on a substrate 1307 which is a surface to be irradiated with laser light emitted from a laser oscillator 1301 into a linear shape. The shape of the laser light emitted from the laser oscillator differs depending on the type of laser. In the case of a YAG laser, the shape of the emitted laser light is circular if the rod shape is cylindrical, and rectangular if the rod shape is a slab type. Note that the laser beam emitted from a slab-type laser has a greatly different beam spread angle in the vertical and horizontal directions, and thus the beam shape changes greatly depending on the distance from the exit. By shaping such a laser beam with an optical system, a laser beam having a desired size can be formed.
[0024]
When a plurality of laser oscillators are used, one beam spot may be formed by overlapping the beam spots output from each laser oscillator using the optical system.
[0025]
By performing laser annealing using the laser irradiation apparatus of the present invention, a TFT with reduced variation in electrical characteristics can be obtained.
[0026]
Hereinafter, a method for manufacturing a semiconductor device of the present invention using the laser irradiation apparatus of the present invention will be described. First, a 127 × 127 × 0.7 mm glass substrate (Corning 1737) is prepared as a substrate. This substrate has sufficient durability at temperatures up to 600 ° C. A 200-nm-thick silicon oxide film is formed as a base film on the glass substrate. Further, an amorphous silicon film is formed thereon with a thickness of 55 nm. The film formation is performed by a sputtering method. Alternatively, the film may be formed by a plasma CVD method.
[0027]
The substrate on which the film has been formed is placed in a nitrogen atmosphere at 450 ° C. for one hour. This step is a step for reducing the hydrogen concentration in the amorphous silicon film. If the amount of hydrogen in the film is too much, the film cannot withstand the laser energy, so this step is performed. The concentration of hydrogen in the film is suitably on the order of 10 ²⁰ / cm ³ . Here, 10 ²⁰ / cm ³ means that there are 10 ²⁰ hydrogen atoms per 1 cm ³ .
[0028]
In this embodiment, the laser oscillator uses a coherent manufactured LD pumped solid state YVO ₄ laser. The YVO ₄ laser is a continuous wave laser. The YVO ₄ laser maximum energy 10W of the oscillation wavelength is 532 nm.
[0029]
The laser beam irradiation is performed, for example, while scanning the stage on which the irradiation surface 1307 shown in FIG. 3 is placed in a linear short axis direction. At this time, the energy density of the beam spot on the irradiation surface and the scanning speed may be appropriately determined by the practitioner.
[0030]
Thus, the laser annealing step is completed. By repeating the above steps, a large number of substrates can be processed. Using the substrate, for example, an active matrix liquid crystal display can be manufactured according to a known method.
[0031]
In the above example, an amorphous silicon film is used as the non-single-crystal semiconductor film, but it can easily be estimated that the present invention can be applied to other non-single-crystal semiconductors. For example, a compound semiconductor film having an amorphous structure such as an amorphous silicon germanium film may be used as the non-single-crystal semiconductor film. Alternatively, a polycrystalline silicon film may be used as the non-single-crystal semiconductor film.
[0032]
【Example】
(Example 1)
In this embodiment, an example of the laser irradiation apparatus described in the embodiment will be described. Laser light emitted from the laser oscillation device passes through a shutter, and the laser light passing through the shutter is formed into a linear beam using a spherical lens. Laser annealing is performed by irradiating a linearly formed beam spot on a scanning stage on which a substrate is placed. The laser light reflected by the reflection mirror in the shutter may be made incident on the heat sink to reduce damage to the device due to the reflected light. Further, an air cooling and a water cooling mechanism may be added to the heat sink.
[0033]
When irradiating a substrate that transmits laser light, such as a glass substrate, with laser light, reflected light from the substrate surface and light reflected from the back surface of the substrate may cause interference fringes on the irradiated object on the substrate. The laser beam may be incident from an oblique direction.
[0034]
The scanning stage has a stroke length of 500 mm, accelerates from a stopped state at an acceleration of 1000 mm / sec ² , reaches 50 mm / sec in 0.5 sec, and moves 250 mm at a constant speed. After moving at a constant speed, the motor decelerates at an acceleration of 1000 mm / sec ² and stops. After stopping for 1.0 second, the return movement starts. Consider a case in which a laser beam is radiated by 100 mm in the substrate during a one-way operation using a scanning stage that moves in accordance with the above-mentioned standard, and the laser beam is radiated on both the forward path and the return path.
[0035]
Here, a description will be given of a reflection mirror in the case of performing laser irradiation with the above specification. The time required from the start of the one-way operation of the X-axis stage to its completion is 2.5 seconds. Laser irradiation time is 0.2 seconds when the X-axis stage is at a constant speed of 50 mm / sec. If the reflection mirror makes one rotation at the same speed while the scanning stage performs a one-way operation, the reflection mirror only needs to be cut at an angle of 28.8 °. FIG. 4 shows the speed distribution of the X-axis stage and the opening / closing state of the shutter.
[0036]
After the one-side operation is completed, the Y-axis stage is moved by the laser irradiation width that is possible by one-side operation of the laser irradiation. The movement of the Y-axis stage may be performed within a stop time after the end of the one-sided operation of the X-axis stage. By adjusting the number of scans to the standard of the substrate, laser annealing can be performed on the entire surface of the substrate without any gap.
[0037]
(Example 2)
In the present embodiment, an example will be described in which the method of controlling the rotation of the reflection mirror in the first embodiment is changed. The apparatus configuration is the same as that of the first embodiment except for the method of rotating the reflection mirror.
[0038]
The response speed of the shutter can be controlled by giving a speed change to the rotation of the reflection mirror. Here, the response speed of the shutter is the time from when the reflection mirror starts to block the laser beam to when it completely blocks the laser beam, or when the reflection mirror starts to pass the laser beam until it completely passes the laser beam. The rotation speed may be controlled according to the condition of a desired response speed. Further, by controlling the rotation speed, the laser irradiation time can be controlled.
[0039]
FIG. 5 shows an example of the rotation speed distribution of the reflection mirror. In this apparatus, laser scanning is performed according to the distribution shown in FIG. The rotation speed of the reflection mirror is controlled by controlling the rotation speed of the motor.
The motor control device may store speed change patterns corresponding to various scanning speeds in advance so that the rotation speed of the motor can be set according to the scanning speed of the X-axis stage.
[0041]
(Example 3)
In this embodiment, an example in which an acousto-optic element is used for a shutter will be described. Except for the shutter, the apparatus configuration is the same as that of the first embodiment.
[0042]
FIG. 6 shows a shutter using an acousto-optic element. In the acousto-optic element 1601, the medium to which the ultrasonic wave is applied has a change in the refractive index due to the photoelastic effect, and the light incident on the medium is diffracted, and the optical path is changed. The diffraction effect is called an acousto-optic effect. The laser light incident on the acousto-optic element is emitted as undiffracted light 1603 when no ultrasonic wave is flowing, and as diffracted light 1602 when the ultrasonic wave is flowing. In this embodiment, the shutter is opened when the non-diffracted light 1603 is emitted, but the shutter may be opened when the diffracted light 1602 is emitted. Since the acousto-optic device is a device using the ultrasonic generator 1604 and the absorber 1605, which are electric devices, it does not generate vibration. Therefore, by using a shutter using the acousto-optic element, laser irradiation can be performed without giving vibration to the optical system and the scanning stage, and thus laser annealing can be performed on the entire surface of the substrate without gaps. Since the acousto-optic device can have a reaction time on the order of 10 ⁻⁶ seconds, a shutter having a very fast reaction time can be used. Further, a shutter using an E / O element may be used instead of the acousto-optic element.
[0043]
【The invention's effect】
With the use of a shutter composed of a continuous reflection mirror and a shutter composed of an acousto-optic element, the rotational acceleration change disclosed in the present invention does not give vibration to the optical system and the scanning stage that form the beam spot, The substrate on the scanning stage can be laser-annealed. When linear and elliptical beam spots emitted from a laser irradiation device using this shutter are scanned on the semiconductor film in the linear and elliptical short side directions, the undulation of the laser irradiation trace due to vibration is generated. Thus, laser annealing can be performed on the entire surface of the substrate without any gap. Therefore, the uniformity of the crystallinity in the substrate plane can be improved. If the present invention is applied to a mass production line of low-temperature polysilicon TFTs, TFTs having high operation characteristics can be efficiently produced.
[0044]
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a conventional laser light shutter.
FIG. 2 is a diagram illustrating a means of the present invention.
FIG. 3 is a diagram showing an example of a laser irradiation apparatus disclosed by the present invention.
FIG. 4 is a diagram showing a change in the speed of an X-axis stage and the opening / closing state of a shutter.
FIG. 5 is a diagram showing a change in the rotation speed of the shutter and the opening / closing state of the shutter.
FIG. 6 is a diagram showing an example in which an acousto-optic element is used for a shutter.

Claims (17)

A laser oscillator,
Means for blocking the laser light emitted from the laser oscillator without generating vibration,
An optical system that processes the laser light emitted from the laser oscillator so that the beam spot on the irradiated surface is linear;
A laser irradiation device, comprising: 2. A laser irradiation apparatus according to claim 1, wherein said blocking means is a shutter comprising a disk-shaped reflecting mirror whose rotation acceleration changes continuously. A laser oscillator,
A scanning stage provided with an object to be irradiated with laser light emitted from the laser oscillator,
Means for blocking the laser light,
An optical system for processing a laser beam emitted from the laser oscillator, so that a beam spot on a surface to be irradiated becomes linear,
The means for blocking the laser beam is a shutter composed of a disk-shaped reflection mirror whose rotation acceleration change is continuous, and the rotation speed of the reflection mirror is synchronized with the movement of the scanning stage. Laser irradiation equipment. 2. A laser irradiation apparatus according to claim 1, wherein said means for blocking laser light emitted from a laser oscillator is a shutter comprising an acousto-optic element. 5. The laser irradiation apparatus according to claim 1, wherein the laser oscillator is a continuous wave solid-state laser. In any one of claims 1 to 5, wherein the laser oscillator is a YAG laser of a continuous oscillation, YVO ₄ laser, YLF laser, YAlO _{3 laser,} Y 2 _{O 3} laser, a glass laser, ruby laser, alexandrite laser , Ti: a laser irradiation apparatus characterized in that it is one or more kinds selected from sapphire lasers. 5. The laser irradiation apparatus according to claim 1, wherein the laser oscillator is one or more types selected from a continuous wave Ar laser and a Kr laser. 6. 7. The laser irradiation apparatus according to claim 1, wherein the laser beam is a second harmonic. Place the non-single-crystal semiconductor film formed on the substrate on the scanning stage,
A laser beam shaped into a linear beam spot in the non-single-crystal semiconductor film, scanning in a minor axis direction of the linear beam spot, and annealing the non-single-crystal semiconductor film. A method of making,
When the scanning speed of the linear beam spot does not reach a certain speed, the laser beam is blocked by blocking means,
Directing the linear beam spot from one side of the substrate to the other,
A method for manufacturing a semiconductor device, characterized in that an irradiation mark on the non-single-crystal semiconductor film by the laser beam is scanned and annealed so as to be parallel to each other, and annealing is performed. Place the non-single-crystal semiconductor film formed on the substrate on the scanning stage,
A laser beam shaped into a linear beam spot in the non-single-crystal semiconductor film, scanning in a minor axis direction of the linear beam spot, and annealing the non-single-crystal semiconductor film. A method of making,
When the scanning speed of the linear beam spot does not reach a certain speed, the laser beam is blocked by blocking means,
The linear beam spot is directed from one side of the substrate to the other, or from the other side of the substrate to one side,
The semiconductor device according to claim 1, wherein the laser light is irradiated continuously on the non-single-crystal semiconductor film so that the irradiation marks on the non-single-crystal semiconductor film are parallel to each other, and the laser light is continuously scanned and annealed. Production method. 11. The method for manufacturing a semiconductor device according to claim 9, wherein said blocking means is a shutter comprising a disk-shaped reflecting mirror whose rotation acceleration changes continuously. 12. The method according to claim 11, wherein the rotation of the reflection mirror is synchronized with the movement of the scanning stage. 11. The method for manufacturing a semiconductor device according to claim 9, wherein the laser light is blocked by a shutter including an acousto-optic element. 14. The method for manufacturing a semiconductor device according to claim 9, wherein the laser light oscillator is a continuous wave solid-state laser. In any one of claims 9 to 14, YAG laser oscillator continuous oscillation of the laser light, YVO ₄ laser, YLF laser, YAlO _{3 laser,} Y 2 _{O 3} laser, a glass laser, ruby laser, alexandrite Lee And a method of manufacturing a semiconductor device, which is one or more kinds selected from the group consisting of laser and Ti: sapphire laser. 14. The method for manufacturing a semiconductor device according to claim 9, wherein the laser beam oscillator is one or more types selected from a continuous wave Ar laser and a Kr laser. 16. The method for manufacturing a semiconductor device according to claim 9, wherein the laser beam is a second harmonic.

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