JPH10125614A - Laser irradiating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser irradiating device with which laser beams of large pulse width and which is downsized. SOLUTION: A laser irradiating device is provided with laser light sources 11 and 12, a timing controlling device 20, total reflection mirrors 21, 22, 23 and 25, a selective reflection mirror 24 and a laser beam forming part 30. The timing controlling device 20 controls the timing, so that the timing of pulse generation of the laser light source 12 may be later than the pulse-generating timing of the laser light source 11 by a specified time. The laser beam 61 from the laser light source 11 and the laser beam 62 from the laser light source 12 reach in sequence the selective reflection mirror 24 and become a single laser beam 63 of large pulse with which a taught is irradiated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laser irradiation apparatus, and more particularly to a laser irradiation apparatus used in a semiconductor manufacturing process or the like. The laser irradiation apparatus of the present invention is used as various laser irradiation apparatuses such as a laser irradiation apparatus for laser annealing and a laser irradiation apparatus for introducing strain for gettering. The crystallization technology used will be described as an example.

[0002]

2. Description of the Related Art In recent years, as the density of semiconductor integrated circuits has increased, research has been carried out to improve the degree of integration in the horizontal direction by miniaturizing the dimensions of each element of the semiconductor integrated circuit. Form an insulating film over the entire surface of the structure,
In addition, a three-dimensional structure in which a semiconductor thin film is provided on the insulating film and an element is formed using the semiconductor thin film has been actively researched and developed. In particular, a polycrystalline silicon film formed on the insulating film, etc. Is being studied by using a laser beam to recrystallize or crystallize an amorphous silicon film.

[0003] In the field of semiconductor integrated circuits, it has become an important issue to reduce the electrical capacitance between each element or wiring portion of the semiconductor integrated circuit and the substrate silicon as the circuit speed increases. Compared with the pn junction isolation that has been widely used, the parasitic capacitance can be reduced by using the silicon film formed on the insulating film. In this sense, a crystallization technique using a laser beam, that is, a laser crystallization technique, has attracted attention.

In addition, among the flat image display devices, research on an active matrix type liquid crystal display device has been particularly advanced, and an image quality equal to or higher than that of a CRT type image display device has been obtained. In order to achieve high-definition image quality and reduce manufacturing costs, it is necessary to configure a driving circuit for a thin film transistor of a pixel on the same insulating substrate as the pixel. In order to form a drive circuit on the same insulating substrate as a pixel, a technique of irradiating a silicon thin film with a laser beam and crystallizing the silicon thin film is important.

Up to now, a method of irradiating a continuous-wave argon laser beam has been studied, and a conventional integrated circuit has been optimized by optimizing a silicon substrate structure, optimizing a laser beam structure, or optimizing a laser beam scanning method. Crystalline materials that can be used for the purpose of fabrication have been obtained. However, there is a problem that the processing time required for annealing with an argon laser is still long for the purpose of forming a semiconductor integrated circuit. Therefore, laser recrystallization using an excimer pulse laser having a large beam energy has been studied in order to shorten the laser annealing time.

[0006] In the field of active matrix type liquid crystal displays, crystallization of silicon thin films by excimer laser is being studied.

[0007]

However, in crystallization using a pulsed laser, the pulse width of the laser to be oscillated is determined by the performance of the laser oscillating device. There is a problem that the size of the polycrystalline particles constituting the silicon thin film is restricted by the laser oscillator, and a crystalline silicon thin film having sufficient properties cannot be obtained. In the crystallization of a silicon thin film by irradiation with a pulse laser, it is necessary to raise the temperature of the silicon thin film to a temperature equal to or higher than the melting point, and crystallize the silicon thin film.
As reported in PP55 "Transient temperature distribution in silicon film during pulsed laser annealing", a pulse width of a certain value or more is required to melt a silicon thin film. Therefore, when the pulse width of the pulse laser is small due to the performance of the laser oscillator, it is necessary to increase the pulse width by some method.

In laser annealing, when the energy of a laser electromagnetic wave is incident on a silicon thin film, the energy changes to thermal energy, the temperature of the silicon thin film rises, and crystallization is achieved by rearrangement of silicon atoms. Therefore, in crystallization by a laser beam, there is a problem in the efficiency of converting electromagnetic wave energy of laser into heat energy.

In a XeCl excimer laser having a wavelength of 308 nm, the pulse width is about 30 to 50 ns, which is much smaller than the time required for heat to be conducted from the surface of the silicon thin film to the inside of the silicon thin film. XeCl in the silicon thin film
The penetration length of the laser is about 10 nm, and the thermal conductivity of the silicon thin film is small. Therefore, only a part of the electromagnetic wave energy of the laser that has reached the surface of the silicon thin film is converted into heat energy required for crystallization of the silicon thin film, and the remaining energy is vaporized, ionized, and converted into plasma on the silicon thin film surface. , And so on.

When the pulse width is short and the thickness of the silicon thin film is 100 nm or more, the IEEE TRANSACTIONS ON
As reported in DEVICES, VOL.36, NO.12, PP2868-2872, the silicon thin film crystallizes only up to about 50 nm in thickness from the surface, and thermal energy cannot be obtained on the insulating film side deep from the surface. There was a problem that crystallization did not proceed.

Conventional annealing by a pulse beam is shown in FIG.
This was performed using an optical system as shown in FIG. In this optical system, the laser beam 261 emitted from the laser oscillator 211 passes through the laser beam forming unit 230 that improves the spatial intensity distribution of the beam 261 and reaches the surface of the sample 240. This optical system has a drawback that the pulse width of the laser beam depends on the laser oscillator 211 and the beam cannot be improved to a required pulse width.

In order to solve this problem and obtain a beam having a required pulse width, the present inventor has proposed a laser irradiation apparatus shown in FIG.

The laser irradiation apparatus 101 includes two laser light sources 111 and 112. By providing an optical path difference L to the laser light from the two laser light sources, the sample 14
The pulse width of the laser light irradiated to 0 is improved.

The pulse width of a currently typical XeCl excimer laser is 30 to 50 ns. Pulse width is 50 ns
Then, if the optical path difference L is 15 m, the speed of light is 3000
Since it is 00 kms ⁻¹ , the laser beam from the laser light source 112 reaches the partially transmitting mirror 121 with a delay of 50 ns from the laser beam from the laser light source 111. Therefore, the laser beam emitted from the laser light source 111 and the laser beam emitted from the laser light source 112 are temporally continuous beams, and after being reflected by the total reflection mirror 122, pass through the laser beam forming unit 130 and pass through the sample stage. The sample 140 on 150 is reached. In this case, the pulse width obtained on the sample surface is 100 ns.

In this manner, the laser light sources 111, 1
A laser beam having a pulse width larger than that of the laser beam oscillated at 12 is obtained on the surface of the sample 140 to be irradiated with the laser, and the energy of the laser can be converted to thermal energy much more efficiently. A crystalline silicon thin film can be manufactured.

However, in this conventional laser irradiation apparatus, as described above, the optical path difference L is required to be as large as 15 m, which leads to an increase in the size of the laser irradiation apparatus.

Accordingly, it is an object of the present invention to provide a laser irradiation apparatus which can obtain a laser beam having a large pulse width and is downsized.

[0018]

According to the present invention, there is provided a first laser light source for oscillating a first laser beam, and a second laser light source for oscillating a second laser beam. A second laser light source different from the first laser light source, and a second laser light source oscillated by the second laser light source after a lapse of a predetermined time after oscillation of the first laser beam by the first laser light source. Timing control means for controlling the timing between the pulse oscillation of the first laser light source and the pulse oscillation of the second laser light source, and the first laser beam and the second laser beam. An optical system capable of irradiating the same irradiated portion of an irradiation object is provided.

According to this configuration, a predetermined time difference can be provided between the first laser beam and the second laser beam, whereby the pulse width of the laser beam reaching the irradiated portion of the object to be irradiated can be provided. Can be substantially increased.

Further, in order to provide a predetermined time difference between the first laser beam and the second laser beam, the timing between the pulse oscillation of the first laser light source and the pulse oscillation of the second laser light source is set. Since the controllable timing control means is used, there is no need to provide an optical path difference between the optical path of the first laser beam by the first laser light source and the optical path of the second laser beam by the second laser light source. As a result, the laser irradiation device can be downsized.

Preferably, the first laser beam and the second laser beam are of the same type.

Preferably, the first laser beam and the second laser beam are excimer laser beams.

Preferably, the first laser beam and the second laser beam are YAG laser beams.

Further, it is preferable that the second laser beam is irradiated before the predetermined processing by the first laser beam ends.

In this case, the predetermined processing may be performed even if a part of the pulse of the first laser beam and a part of the pulse of the second laser beam do not always overlap with each other. It is preferable that a part of the pulse of the first laser beam and a part of the pulse of the second laser beam temporally overlap.

The first laser beam and the second laser beam
In order to irradiate the same irradiated portion of the object to be irradiated with the laser beam, the first laser beam and the second laser beam are not collected on the same optical path until reaching the irradiated portion. Separate optical paths can be used, but preferably
An optical system that focuses the first laser beam and the second laser beam on the same optical path is used. With this configuration, after the light beams are collected on the same optical path, the number of optical paths becomes one, so that the subsequent optical system may be provided for one optical path, and the device configuration is correspondingly simplified.

[0027]

FIG. 1 is a diagram for explaining a laser irradiation apparatus according to one embodiment of the present invention.

The laser irradiation apparatus 1 includes two laser light sources 11 and 12, a timing controller 20, total reflection mirrors 21, 22, 23 and 25, and a selective reflection mirror 24.
And a laser beam forming unit 30. The selective reflection mirror 24 is a mirror having a function of functioning as a total reflection mirror for the laser beam 61 and a function as a mere transparent plate for the laser beam 62. As the selective reflection mirror 24, for example, a polarization beam splitter can be used. In the present embodiment, XeCl excimer laser light sources are used as the laser light sources 11 and 12. It should be noted that a YAG laser can be used instead of the excimer laser.

Next, the operation of the laser irradiation apparatus 1 of the present embodiment will be described with reference to FIGS.

As shown in FIG. 2A, the laser light source 11
From time T1 to the laser beam 6 having the pulse width W1.
1 is emitted, reflected by the total reflection mirror 21, and reaches the selective reflection mirror 24. In addition, the time T
At 3, the laser beam 62 having a pulse width W2 is emitted, reflected by the total reflection mirrors 22 and 23, and again reaches the selective reflection mirror 24. The timing between the pulse oscillation of the laser light source 11 and the pulse oscillation of the laser light source 12 is controlled by the timing control device 20. In the present embodiment, the laser beam 62
Is set to coincide with the end of the laser beam 61 from the laser light source 11. The pulse width W1 of the laser beam 61 and the pulse width W2 of the laser beam 62
And the same.

The laser beam 61 is reflected by the selective reflection mirror 24, and the laser beam 62 is reflected by the selective reflection mirror 24.
And a single laser beam 63 that is temporally continuous and has a pulse width of W3 is reflected by the total reflection mirror 25, and then the spatial intensity distribution is improved by the laser beam forming unit 30 and the sample is The sample reaches the sample on the table.

In the present embodiment, the beginning of the laser beam 62 from the laser light source 12 and the end of the laser beam 61 from the laser 11 are matched, and the pulse width W1 of the laser beam 61 and the pulse width of the laser beam 62 W2
Therefore, the laser beam 6 from the laser light source 11 is
A laser beam 63 having a pulse width W3 almost twice as large as that of the laser beam 62 generated by the laser light source 12 is obtained.

As described above, by providing a predetermined time difference between the pulse oscillation of the laser light source 11 and the pulse oscillation of the laser light source 12, the pulse width of the laser beam 63 applied to the sample 40 is improved. By doing so, it is not necessary to provide the optical path difference L as in the laser irradiation device 101 of FIG. 5, and the laser irradiation device 1 of the present embodiment is downsized.

Next, a case of processing a silicon thin film using the laser irradiation apparatus 1 of the present embodiment will be described.

The penetration length of an electromagnetic wave of a XeCl excimer laser having a wavelength of 308 nm in a silicon thin film is about 10 n.
m. Since the pulse width of the XeCl excimer laser is about 50 ns at the maximum, when this pulse laser is irradiated alone on the sample surface, it is 10 nm from the silicon thin film surface.
Is instantaneously hot, but the heat transfer coefficient of silicon is small and the pulse width of the excimer laser is also small,
Before the energy of the pulsed laser is changed to thermal energy for melting the silicon thin film, the energy is consumed for vaporizing silicon atoms and for turning into plasma in the silicon thin film surface portion. That is, if the temporal width of the pulse laser is short, only the surface of the silicon thin film is melted and crystallized. Therefore, the thickness is 1
In the case of a silicon thin film having a thickness of 00 nm or more, a portion of about 50 nm or more from the surface is not sufficiently crystallized.

On the other hand, if the pulse width of the excimer laser beam reaching the sample surface is doubled to about 100 ns as in this embodiment, for example,
Even if the heat transfer coefficient of silicon is small, it is possible to sufficiently crystallize a silicon thin film having a thickness of about 150 nm.

Even if the thickness of the silicon thin film is small, if the pulse width of the laser beam is small, it is not possible to increase the grain size of silicon, so that sufficient electron or hole mobility cannot be obtained. Therefore, as in this embodiment, when the pulse width of the excimer laser beam reaching the sample surface is doubled to about 100 ns, a silicon film having a large grain size can be obtained, and high mobility can be obtained. become.

Although the amorphous silicon film formed by the plasma CVD method contains hydrogen, even if the amorphous silicon film is annealed with a laser beam from a single excimer laser light source, the pulse width is short. Since the annealing time is short, it is difficult for hydrogen to separate and escape sufficiently, and it is also difficult to form polycrystals. Therefore, as in this embodiment, if the pulse width of the excimer laser beam reaching the sample surface is doubled to about 100 ns, the annealing time becomes longer, and as a result, hydrogen can be sufficiently separated and removed. The amorphous silicon film formed by the CVD method can be polycrystallized. According to this plasma CVD method, a silicon thin film can be formed at a lower temperature, so that polycrystalline silicon can be formed on a material having a lower melting point or softening point.

In FIG. 2, the pulse oscillation of the laser light source 11 and the laser light source 12 are adjusted so that the start of the laser beam 62 from the laser light source 12 coincides with the end of the laser beam 61 from the laser light source 11.
Is controlled by the timing control device 20. The first part of the laser beam 62 by the laser light source 12 and the last part of the laser beam 61 by the laser light source 11 are controlled as shown in FIG. By partially overlapping, even when an excimer laser having a pulse waveform that is not completely rectangular is used, the sample can be irradiated with the laser beam 63 that is uniform in time.

In the present embodiment, as shown in FIG. 1, since the laser beam forming section 30 is provided in front of the sample 40, the spatial energy intensity distribution of the pulse laser beam can be made uniform. As a result, a silicon crystal having uniform characteristics can be obtained in a range irradiated with the laser beam.

As described above, with the laser irradiation apparatus 1 of the present embodiment, a recrystallized silicon thin film or a crystalline silicon thin film having good characteristics required for a semiconductor integrated circuit or an active matrix type thin film transistor can be obtained. it can.

In addition, the present invention can be applied to fields such as property modification of metals, formation / decomposition of polymers, chemical reactions, and biological reactions using a pulse laser.

In the above embodiment, the XeCl excimer laser is used as an example. However, the pulse laser is not limited to this, and an excimer laser such as ArF, KrF, or the like may be used.
The present invention can be applied to pulse lasers such as an AG laser and a ruby laser.

[0044]

According to the present invention, a laser beam having a large pulse width can be obtained even if a small laser irradiation device is used.

By increasing the pulse width of the laser beam in this manner, the electromagnetic wave energy of the laser beam can be efficiently converted into thermal energy in the silicon thin film, and crystal defects having a large crystal grain size can be obtained. And a high quality recrystallized or crystallized silicon thin film can be obtained. Further, since the hydrogen-containing amorphous silicon thin film formed by the plasma CVD method can be polycrystallized, the silicon thin film can be formed at a lower temperature.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a laser irradiation apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a laser pulse by the laser irradiation device according to one embodiment of the present invention.

FIG. 3 is a diagram for explaining a laser pulse by the laser irradiation device according to the embodiment of the present invention.

FIG. 4 is a view for explaining a conventional laser irradiation apparatus.

FIG. 5 is a view for explaining a conventional laser irradiation apparatus.

[Explanation of symbols]

 11, 12, 111, 112, 211 laser light source 20 timing controller 21, 22, 23, 25, 122 total reflection mirror 24 selective reflection mirror 121 partial transmission mirror 30, 130, 230 laser beam forming unit 40, 140, 240: sample 50, 150: sample stage 61, 62, 63: laser beam L: optical path difference

Claims (7)

[Claims] A first laser beam for oscillating a first laser beam;
A second laser light source that oscillates a second laser beam, wherein the second laser light source is different from the first laser light source; and a first laser beam generated by the first laser light source After a predetermined time has elapsed after the oscillation of the second laser light source,
Timing control means capable of controlling the timing between the pulse oscillation of the first laser light source and the pulse oscillation of the second laser light source so as to oscillate the laser beam, An optical system capable of irradiating two laser beams to the same irradiated portion of the object to be irradiated. 2. The laser irradiation apparatus according to claim 1, wherein said first laser beam and said second laser beam are the same type of laser beam. 3. The laser irradiation apparatus according to claim 1, wherein said first laser beam and said second laser beam are excimer laser beams. 4. The laser irradiation apparatus according to claim 1, wherein said first laser beam and said second laser beam are YAG laser beams. 5. The laser irradiation apparatus according to claim 1, wherein the second laser beam is irradiated before a predetermined process using the first laser beam is completed. 6. The laser according to claim 1, wherein a part of the pulse of the first laser beam and a part of the pulse of the second laser beam temporally overlap. Irradiation device. 7. The laser according to claim 1, wherein said optical system is an optical system that focuses said first laser beam and said second laser beam on the same optical path. Irradiation device.