JP4429587B2 - Method for manufacturing semiconductor device - Google Patents

Description

[0001]
BACKGROUND 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 for improving the crystallinity of a semiconductor film by irradiating a semiconductor film in a polycrystalline or near-polycrystalline state with laser. A semiconductor device refers to an electro-optical device and an electric apparatus 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, a technology for forming a TFT on a substrate has greatly advanced, and application development to an active matrix semiconductor display device has been advanced. In particular, a TFT using a polycrystalline semiconductor film has higher electrolytic effect mobility (also referred to as mobility) than a TFT using a conventional amorphous semiconductor film, and thus can operate at high speed. For this reason, attempts have been made to control a pixel, which is conventionally performed by a driving circuit provided outside the substrate, using a driving circuit formed on the same substrate as the pixel.
[0003]
By the way, as a substrate used for a semiconductor device, a glass substrate is considered promising rather than a single crystal silicon substrate in terms of cost. Since a glass substrate is inferior in heat resistance and easily deforms by heat, when a polysilicon TFT is formed on the glass substrate, laser annealing is used for crystallization of the semiconductor film in order to avoid thermal deformation of the glass substrate.
[0004]
The characteristics of laser annealing are that the processing time can be significantly shortened compared to annealing methods using radiation heating or conduction heating, and the semiconductor substrate or semiconductor film is selectively and locally heated to make the substrate almost thermally It has been raised not to damage.
[0005]
The laser annealing method here refers to a technique for recrystallizing a damaged layer or an amorphous layer formed on a semiconductor substrate or semiconductor film, or a technique for crystallizing an amorphous semiconductor film formed on a substrate. pointing. Also included are techniques applied to planarization and surface modification of semiconductor substrates or semiconductor films.
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 crystal grain size formed in a semiconductor film is larger when a continuous wave laser is used than when a pulsed laser is used for 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 by using the semiconductor film is reduced, so that the mobility is increased and it can be used for development of a higher performance device. For this reason, continuous wave lasers are starting to attract attention.
[0007]
In addition, when laser annealing of a semiconductor or a semiconductor film is performed, a laser beam emitted from a laser oscillator is linear or elliptical with an aspect ratio of 10 or more on the surface to be irradiated (described as linear in this specification). A method is known in which a beam spot is scanned with respect to a surface to be irradiated by processing with an optical system. Since the above method can efficiently irradiate the substrate with laser light and increase the mass productivity, it is preferably used industrially (for example, see Patent Document 1).
[0008]
[Patent Document 1]
JP-A-8-195357 [0009]
[Problems to be solved by the invention]
In order to efficiently perform laser annealing of the semiconductor film formed on the substrate, the beam spot shape emitted from the continuous oscillation laser oscillator is processed into a linear shape using an optical system, and the linear beam spot is A method of irradiating the substrate is used.
[0010]
A method of moving the scanning stage on which the substrate is placed with respect to the beam spot and performing laser annealing on the entire surface of the substrate is often used. When laser light is irradiated using the above method, it is necessary to provide a device (hereinafter referred to as a shutter) that blocks the laser light in accordance with the movement of the scanning stage so that the laser light is irradiated only on the substrate. By providing the shutter, it is possible to irradiate laser light to an arbitrary region on the substrate, and it is possible to eliminate irradiation to other regions and prevent damage to the apparatus by the laser light.
[0011]
When the shutter can be rotated in the reverse direction, for example, when an opening / closing mechanism is formed by rotating a reflecting mirror using a solenoid motor (FIG. 1), the rotation of the motor 1101 needs to be forcibly stopped when it is desired to completely open and close the shutter. is there. When a rotation is forcibly stopped by providing a protrusion 1103 on the rotation shaft 1102 of the motor 1101 and applying the protrusion 1103 to the stopper 1104, vibration occurs due to the collision between the stopper 1104 and the protrusion 1103 when the rotation stops. . When the vibration is transmitted to the optical stage 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 shape that reflects the vibration. When the laser irradiation traces undulate, a part having an extremely high overlap rate or a part where no laser irradiation occurs is caused between adjacent laser irradiation traces formed by the reciprocating motion of the scanning stage. Since the TFTs are formed on the substrate with a regular arrangement, the TFTs formed in the above-described portions have poor electrical characteristics and cause variations in electrical characteristics.
[0012]
In view of the above-described problems, the present invention 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 eliminates vibrations generated from the shutter and enables a laser irradiation trace to be linear by using a shutter whose power source is a motor whose rotation acceleration change is continuous. is there. Further, the present invention is a laser irradiation apparatus without a vibration source that uses an acoustooptic element utilizing an acoustooptic effect and has a shutter function by changing an optical path.
[0014]
FIG. 2 shows a schematic diagram of a method for solving the above problem. The reflection mirror 1201 is a disk with a cut in a part. When the reflection mirror 1201 rotates around the center of the circle as the rotation axis 1202 and the laser beam 1206 is incident on the cut portion 1203, the laser beam passes through the reflection mirror 1201 without hitting the reflection mirror 1201 (1207), and the non-cut portion 1204 The laser beam incident on 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 placed on the reciprocating scanning stage reaches the laser irradiation position, the laser beam 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 is synchronized with the movement of the scanning stage. By adopting a structure that does not forcibly stop rotation, there is no generation of vibration due to the impact of forced rotation stop, and there is no vibration transmitted to the optical system and the scanning stage. Can do.
[0016]
With the above structure, laser irradiation can be performed without applying vibration to the optical system and the scanning stage, and laser annealing can be performed on the entire surface of the semiconductor film without gaps.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the structure of the laser irradiation apparatus of this invention is demonstrated using FIG.
[0018]
The laser irradiation apparatus of the present invention includes a laser oscillator 1301 that oscillates laser light. Although FIG. 3 shows an example in which one laser oscillator 1301 is provided, the number of laser oscillators included in the laser irradiation apparatus of the present invention is not limited to this number. The beam spots of the laser beams output from the laser oscillator may be overlapped with 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. Examples of gas lasers include Ar laser and Kr laser, and solid-state lasers include YAG laser, YVO ₄ laser, YLF laser, YAlO ₃ laser, Y ₂ O ₃ laser, glass laser, ruby laser, alexandride laser, and Ti: sapphire. A laser etc. are mentioned. In addition, there exist Nd, Cr, Yb etc. as a dopant substance to a laser medium, The harmonic with respect to a fundamental wave can be obtained by using a nonlinear optical element.
[0020]
Furthermore, after converting infrared laser light emitted from a solid-state laser into green laser light using a nonlinear optical element, ultraviolet laser light obtained by another nonlinear optical element can also be used.
[0021]
Laser light emitted from the laser oscillator 1301 enters a shutter 1302 installed on the optical path.
[0022]
The laser light that has entered the shutter from the entrance reaches the reflection mirror 1303. While the reciprocating X-axis stage 1305 finishes the one-way operation from the start of operation, the rotation speed is controlled so that the reflection mirror 1303 makes one rotation. In the following, the laser irradiation position is a position where the laser beam is irradiated onto the substrate 1307 installed on the stage when the shutter 1302 is not provided. The X-axis stage is arranged so that the laser irradiation position is 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 to the end position. And The reflection mirror is rotated in the direction indicated by the arrow in FIG. When the front end portion of the substrate 1307 comes to the laser irradiation position, the incident position of the laser light on the reflection mirror 1303 comes to the cut portion a, and the rear end portion of the substrate end 1307 comes to the laser irradiation position. In addition, the rotation of the motor is controlled so that the incident position of the laser beam on the reflection mirror 1303 becomes the cut portion b. Here, when the X-axis stage is moved, the end on which the laser beam 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 that shapes a beam spot on a substrate 1307 that is an irradiation surface of a laser beam emitted from a laser oscillator 1301 into a linear shape. The shape of the laser light emitted from the laser oscillator varies 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 is rectangular if it is a slab type. Note that the laser beam emitted from the slab type laser differs greatly in the beam divergence angle in the vertical and horizontal directions, so that the beam shape largely changes depending on the distance from the emission port. By shaping such a laser beam by an optical system, the laser beam can be formed in a linear shape having a desired size.
[0024]
When a plurality of laser oscillators are used, one beam spot may be formed by superimposing the beam spots output from the laser oscillators 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 is sufficiently durable at temperatures up to 600 ° C. A silicon oxide film having a thickness of 200 nm is formed on the glass substrate as a base film. Further, an amorphous silicon film is formed thereon to a thickness of 55 nm. Both films are formed by sputtering. Or you may form into a film by plasma CVD method.
[0027]
The film-formed substrate is placed in a nitrogen atmosphere at 450 ° C. for 1 hour. This step is a step for reducing the hydrogen concentration in the amorphous silicon film. If there is too much hydrogen in the film, the film cannot withstand the laser energy, so this step can be entered. The hydrogen concentration in the film is suitably on the order of 10 ²⁰ / cm ³ . Here, 10 ²⁰ / cm ³ means that 10 ²⁰ hydrogen atoms exist per 1 cm ³ .
[0028]
In the present embodiment, an LD-excited solid YVO ₄ laser manufactured by Coherent is used as the laser oscillator. The YVO ₄ laser is a continuous wave laser. The maximum energy of the YVO ₄ laser is 10 W, and the oscillation wavelength is 532 nm.
[0029]
The laser light irradiation is performed, for example, while scanning the stage with the irradiated surface 1307 shown in FIG. 3 in the linear short axis direction. At this time, the practitioner may appropriately determine the energy density of the beam spot on the irradiated surface and the scanning speed.
[0030]
Thus, the laser annealing process is completed. A large number of substrates can be processed by repeating the above steps. For example, an active matrix liquid crystal display can be manufactured according to a known method using the substrate.
[0031]
In the above example, an amorphous silicon film is used as the non-single crystal semiconductor film, but it can be easily 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 for the non-single-crystal semiconductor film.
[0032]
【Example】
Example 1
In this example, an example of the laser irradiation apparatus described in the embodiment is shown. Laser light emitted from the laser oscillation device is passed 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 scanning stage provided with a substrate with a linearly formed beam spot. In addition, it is good also as a structure which reduces the damage to the apparatus by reflected light by making the laser beam reflected by the reflective mirror in the said shutter inject into a heat sink. An air cooling and water cooling mechanism may be added to the heat sink.
[0033]
When laser irradiation is performed on a substrate that transmits laser light, such as a glass substrate, interference fringes may occur on the irradiated object on the substrate due to reflected light from the substrate surface and reflected light from the back surface of 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 stop state with an acceleration of 1000 mm / sec ² , moves to 250 mm at a constant speed after reaching 50 mm / sec in 0.5 sec. After moving at a constant speed, it decelerates at an acceleration of 1000 mm / sec ² and stops. After stopping for 1.0 second, start the return movement. Consider a case in which a laser stage is irradiated by 100 mm within a substrate during a one-way operation using a scanning stage that moves in accordance with the above-mentioned standard, and laser irradiation is performed on both the forward and return paths.
[0035]
Here, the reflection mirror in the case of performing laser irradiation of the above specifications will be described. The time required from the start of the one-way operation of the X-axis stage to the completion is 2.5 seconds. The laser irradiation time is 0.2 seconds when the X-axis stage is at a constant speed of 50 mm / sec. If the reflecting mirror makes one rotation at the same speed while the scanning stage is operating in one way, the reflecting mirror only needs to be cut by 28.8 ° in angle. 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 can be obtained by one-side operation laser irradiation. The movement of the Y-axis stage may be performed within the stop time after the end of one-side operation of the X-axis stage. By matching the number of scans to the standard of the substrate, the entire surface of the substrate can be laser-annealed with no gaps.
[0037]
(Example 2)
In the present embodiment, an example in which the method for controlling the rotation of the reflecting mirror is changed in the first embodiment will be described. 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 reflecting mirror. Here, the response speed of the shutter is the time from when the reflection mirror starts to shield the laser light until it is completely shielded, or the time from when the reflection mirror starts to pass the laser light until it completely passes. The rotation speed may be controlled according to a desired response speed condition. Further, the laser irradiation time can be controlled by controlling the rotation speed.
[0039]
FIG. 5 shows an example of the rotational speed distribution of the reflecting mirror. In this apparatus, laser scanning is performed with the distribution shown in FIG. Note that the rotation speed of the reflection mirror is controlled by controlling the rotation speed of the motor.
The motor control device may store in advance speed change patterns according to various scanning speeds so that the rotational 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 as a shutter will be described. The apparatus configuration is the same as that of the first embodiment except for the shutter.
[0042]
FIG. 6 shows a shutter using an acoustooptic device. In the acoustooptic device 1601, the refractive index of the medium to which the ultrasonic wave is applied is changed by the photoelastic effect, and the light incident on the medium is diffracted to change the optical path. The diffraction effect is referred to as an acousto-optic effect. The laser light incident on the acoustooptic device is emitted as non-diffracted light 1603 when no ultrasonic wave is applied, and as diffracted light 1602 when an ultrasonic wave is applied. In this embodiment, the shutter is open when the non-diffracted light 1603 is emitted, but the shutter may be open when the diffracted light 1602 is emitted. The acoustooptic device is an apparatus using an ultrasonic generator 1604 and an absorber 1605, which are electrical devices, and therefore does not generate vibration. Therefore, by using a shutter using the acousto-optic element, laser irradiation can be performed without applying vibration to the optical system and the scanning stage, so that the entire surface of the substrate can be laser-annealed without gaps. Since the acoustooptic device can have a reaction time on the order of 10 ⁻⁶ seconds, a shutter with a very fast reaction time can be used. A shutter using an E / O element may be used instead of the acousto-optic element.
[0043]
【The invention's effect】
By using a shutter composed of a reflective mirror and a shutter composed of an acousto-optic device disclosed in the present invention, the rotational acceleration change is continuous, without giving vibration to the optical system and scanning stage that form the beam spot. The substrate on the scanning stage can be laser-annealed. When the linear and elliptical beam spots emitted from the laser irradiation apparatus using this shutter are scanned in the linear and elliptical short sides of the semiconductor film, the undulation of the laser irradiation trace due to vibration is generated. Therefore, laser annealing can be performed on the entire surface of the substrate without any gap. Therefore, the uniformity of crystallinity within the substrate surface can be improved. If the present invention is applied to a mass production line for low-temperature polysilicon TFTs, TFTs with high operating 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 view for explaining means of the present invention.
FIG. 3 is a diagram showing an example of a laser irradiation apparatus disclosed in the present invention.
FIG. 4 is a diagram showing a change in speed of an X-axis stage and a shutter opening / closing state.
FIG. 5 is a diagram showing a change in shutter rotation speed and the opening / closing state of the shutter.
FIG. 6 is a diagram showing an example in which an acoustooptic device is used as a shutter.

Claims (6)

A method for manufacturing a semiconductor device, which emits laser light from a laser oscillator and irradiates the non-single crystal semiconductor film placed on a scanning stage with the laser light,
When the non-single crystal semiconductor film is irradiated by the disk-shaped reflecting mirror having a cut, the laser light is controlled at the time of non-irradiation,
The laser beam passes through the cut at the time of irradiation,
The laser beam is reflected by the disk-shaped reflecting mirror other than the cut when not irradiated,
The method for manufacturing a semiconductor device, wherein the disk-shaped reflection mirror rotates at a constant speed during the irradiation, and rotates at a constant speed slower than the rotation speed during the irradiation when the irradiation is not performed.   2. The method for manufacturing a semiconductor device according to claim 1, wherein the laser light applied to the non-single-crystal semiconductor film is shaped into a linear beam spot. According to claim 1 or claim 2, wherein the rotation of the reflecting mirror method for manufacturing a semiconductor device characterized by synchronizing the movement of the scanning stage. In any one of claims 1 to 3, the method for manufacturing a semiconductor device the lasers oscillator is characterized in that it is a continuous-wave solid-state laser. In any one of claims 1 to 3, wherein the lasers oscillator is a continuous wave YAG laser, YVO ₄ laser, YLF laser, YAlO _{3 laser,} Y 2 _{O 3} laser, a glass laser, a ruby laser, A method for manufacturing a semiconductor device, wherein the semiconductor device is one or more selected from an alexandride laser and a Ti: sapphire laser. In any one of claims 1 to 3, the method for manufacturing a semiconductor device, characterized in that the lasers oscillator is one or more selected from Ar laser or Kr laser continuous wave.

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