JP2013211415A - Laser annealing device and laser annealing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser annealing device and a laser annealing method, capable of improving utilization efficiency of laser energy and efficiently performing anneal processing.SOLUTION: A laser annealing device for irradiating an amorphous silicon film 5 with a laser beam and performing anneal processing comprises: a first pulse laser 6 which generates a first laser beam Lof a constant wavelength having a constant pulse width; a second pulse laser 7 which generates a second laser beam Lhaving a longer pulse width and wavelength than the first laser light L; synthesizing means 8 for synthesizing the first laser beam Land the second laser beam Linto the same optical axis; and control means 3 for controlling a generation timing of the first laser beam Land the second laser beam Lby the action on the first pulse laser 6 and the second pulse laser 7. The control means 3 controls the first pulse laser 6 so that the first laser light Lis generated at a predetermined timing within a pulse width of the second laser beam L.

Description

  The present invention relates to a laser annealing apparatus for performing an annealing process by irradiating an amorphous silicon film with a laser beam, and more particularly to a laser annealing apparatus and a laser annealing method capable of performing an annealing process efficiently by improving the utilization efficiency of laser energy. It is concerned.

  A conventional laser annealing apparatus irradiates each of a plurality of films to be annealed formed in an island shape on a main surface of a substrate with laser light that moves intermittently, and the plurality of films to be annealed have desired characteristics. The film to be annealed is formed into a film, and the film to be annealed is annealed by irradiating the film to be annealed with a spot-like laser beam a plurality of times (see, for example, Patent Document 1).

JP 9-45632 A

  However, in such a conventional annealing apparatus, the laser beam to be irradiated is a single wavelength ultraviolet laser beam. Therefore, when the amorphous silicon film is melted by the laser beam irradiation, the absorption rate of the ultraviolet laser beam is increased. There was a problem of lowering. Therefore, the amorphous silicon film is not sufficiently melted to the deep part, and polysiliconization may be insufficient.

  In addition, when a plurality of spot-like laser beams are generated from one laser beam generated by one light source device so that annealing can be performed at a plurality of locations of the film to be annealed simultaneously, laser beam irradiation is performed. Since energy is reduced, a large light source device with larger laser energy is required, and there is a problem that the manufacturing cost of the annealing device increases.

  To deal with these problems, it is conceivable to anneal the film to be annealed with a plurality of shots of laser light, but there is a problem that the annealing process efficiency is lowered and the tact time of the annealing process is increased.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a laser annealing apparatus and a laser annealing method that can cope with such problems and improve the efficiency of laser energy utilization so that annealing can be performed efficiently.

  In order to achieve the above object, a laser annealing apparatus according to the present invention is a laser annealing apparatus that performs annealing by irradiating an amorphous silicon film with a laser beam, the first laser beam having a constant pulse width and a constant wavelength. A first pulse laser that generates a second laser beam that generates a second laser beam having a longer pulse width and wavelength than the first laser beam, the first laser beam, and the second laser beam. Combining means for combining laser light with the same optical axis, and control means for controlling the generation timing of the first and second laser lights by acting on the first and second pulse lasers, The control means controls the first pulse laser so that the first laser light is generated at a predetermined timing within a pulse width of the second laser light.

  With such a configuration, the control means controls the first pulse laser to generate a first laser beam having a fixed wavelength and a fixed wavelength, and controls the second pulse laser to control the first laser beam. The second laser light having a longer pulse width and wavelength than the first laser light is generated, and the first laser light and the second laser light are synthesized on the same optical axis by the synthesizing means to form the first and second on the amorphous silicon film. Annealing treatment is performed by irradiating the laser beam. At this time, the control unit controls the first pulse laser so that the first laser beam is generated at a predetermined timing within the pulse width of the second laser beam.

  Preferably, the control means controls the first pulse laser so that the generation timing of the first laser beam can be adjusted within the pulse width of the second laser beam.

  More preferably, the first pulse laser generates the first laser beam having a wavelength of 355 nm or 532 nm, and the second pulse laser generates the second laser beam having a wavelength of 1064 nm. Is desirable.

  In addition, the laser annealing method according to the present invention uses the same light for the first laser light having a constant pulse width and having a constant wavelength, and the second laser light having a pulse width and wavelength longer than those of the first laser light. A laser annealing method for synthesizing an axis and irradiating an amorphous silicon film to perform annealing, wherein the second laser beam is generated and irradiated to the amorphous silicon film, and the first laser beam is irradiated to the amorphous silicon film. And irradiating the amorphous silicon film with a predetermined timing within the pulse width of the second laser light.

  Preferably, the first laser beam has a wavelength of 355 nm or 532 nm, and the second laser beam has a wavelength of 1064 nm.

  According to the present invention, even if the amorphous silicon film is melted by the irradiation of the first laser beam and the absorption rate of the first laser beam is decreased, the second laser beam having a wavelength longer than that of the first laser beam. As the amorphous silicon film is melted by absorbing the laser light, the amorphous silicon film can be annealed to a deep portion. Therefore, the laser energy utilization efficiency can be improved and the annealing process can be performed more efficiently than when only the ultraviolet laser beam is used in the prior art.

It is a front view which shows embodiment of the laser annealing apparatus by this invention. It is a top view which shows one structural example of the 2nd pulse laser used in the said embodiment. FIG. 6 is an explanatory diagram showing generation of a long-pulse second laser beam by controlling an applied voltage of a Pockels cell of a Q switch in the second pulse laser, (a) is a graph showing normal control, (b) ) Is a graph when the applied voltage is gradually decreased. FIG. 4 is a graph showing a laser pulse generated when the applied voltage is controlled so that one inflection point occurs in the gradually decreasing gradient of the applied voltage in FIG. It is a top view which shows one structural example of the laser attenuator used in the said 2nd pulse laser. It is explanatory drawing which shows a mode that the energy of the specific time in the laser beam of 1 pulse by the said laser attenuator is selectively reduced, (a) shows the state before reduction, (b) shows the state after reduction. Show. It is explanatory drawing which shows an example of the pulse waveform of the 1st and 2nd laser beam used in the said embodiment, (a) shows a 1st laser beam, (b) shows a 2nd laser beam. . It is a graph which shows the relationship between the wavelength of various inorganic materials, and a light absorption coefficient. In the laser annealing method of this invention, it is explanatory drawing which shows the laser energy which acts effectively for an annealing process, (a) is a 1st laser beam at the predetermined timing within the pulse width of a 2nd laser beam. FIG. 5B shows the case where the first and second laser beams are generated simultaneously.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a front view showing an embodiment of a laser annealing apparatus according to the present invention. This laser annealing apparatus performs annealing treatment by irradiating an amorphous silicon film with laser light, and includes a light source device 1, an illumination optical system 2, and a control means 3.

  The light source device 1 generates laser light for annealing the amorphous silicon film 5 formed on the substrate 4, and combines the first pulse laser 6 and the second pulse laser 7. And means 8.

Here, the first pulse laser 6 generates the _first laser light L ₁ having, for example, a pulse width W ₁ of 20 nsec and a wavelength λ ₁ of 355 nm or 532 nm. This is a known YAG laser generated by wavelength conversion from a fundamental wave of 1064 nm. In the following description, the case where the first laser beam L ₁ is a laser beam with λ ₁ = 355 nm will be described. The first pulse laser 6 is not limited to a YAG laser, and may be an excimer laser or the like as long as it generates laser light with a short wavelength. Here, the case of a YAG laser will be described. .

The second pulse laser 7 generates the _second laser light L ₂ having a longer pulse width and wavelength than the first laser light L _1. For example, the pulse width W ₂ is 350 nsec and the wavelength λ ₂ is 1064 nm. This is a YAG laser that generates a laser beam. The second pulse laser 7 is not limited to the YAG laser, and may be, for example, a CO ₂ laser as long as it generates laser light having a long wavelength. Here, the case of the YAG laser will be described. To do.

More specifically, the second pulse laser 7, as shown in FIG. 2, downstream the resonator 9, the optical amplifier 10, a laser for attenuator 11, the second traveling direction upstream of the laser beam L ₂ It arranges in this order toward.

  The resonator 9 generates a standing wave by reciprocating a laser beam, and is excited between a front mirror 12 and a rear mirror 13 as a resonator mirror by a flash lamp (not shown) to generate a laser beam. For example, an ND: YAG rod 14 as a laser medium, and a Q switch 18 disposed behind the ND: YAG rod 14 and including a polarizing beam splitter 15, a λ / 4 wave plate 16 and a Pockels cell 17 as polarizing elements, , And is configured.

In this case, the voltage applied to the Pockels cell 17, thereby making it possible to expand the separately be controlled to gradually decrease the control unit is provided with not shown, the second pulse width of the laser beam L _2.

  This will be described below. As shown in FIG. 3A, the applied voltage to the Pockels cell 17 is gradually reduced as shown in FIG. 3B in contrast to the normal control in which the applied voltage to the Pockels cell 17 is suddenly reduced. In the case of such control, the pulse width is expanded from 10 ns to 70 ns, for example. This is because, in the oscillation in the resonator 9, the return output energy from the Q switch 18 gradually increases in the time axis and is lower than the normal energy, so that the extraction of energy in the ND: YAG rod 14 is also slow. The pulse oscillation time in the Q switch 18 is extended, and the output pulse width is increased.

Furthermore, if the applied voltage is controlled so that at least one inflection point as shown in FIG. 4 occurs in the gradually decreasing gradient of the applied voltage to the Pockels cell, the pulse width can be further expanded. Thus, by controlling the voltage applied to the Pockels cell 17, it can be the pulse width _{W 2} to generate a second laser beam _{L 2} of 350Nsec.

  An optical amplifier 10 is provided downstream of the resonator 9. This optical amplifier 10 amplifies and outputs the pulse energy of laser light, and for example, an ND: YAG rod is used.

Further, a laser attenuator 11 is provided downstream of the optical amplifier 10. This laser attenuator 11 reduces the energy of the second laser light L ₂ , and as shown in FIG. 5, as a polarizing element disposed in a crossed Nicol configuration on the optical path of the second laser light L ₂ . Between the first and second polarizing beam splitters 19A and 19B and the first and second polarizing beam splitters 19A and 19B, the optical axis forms 45 ° with respect to the incident linearly polarized light (for example, P-polarized light). A Pockels cell 20 as an electro-optical element that rotates the polarization plane of the laser beam that passes through the inside by application of a voltage, and a control unit 21 that controls an applied voltage value and application timing for the Pockels cell 20; It is configured with.

  As an example, the Pockels cell 20 used in the present embodiment can obtain the effect of a λ / 4 wavelength plate by applying a voltage of up to −3.6 kV, and the first and second Pockels cells 20A and 20B are connected in series. By arranging them side by side and controlling the applied voltage in parallel at a maximum of -3.6 kV, the effect of the λ / 2 wavelength plate can be obtained by combining the first and second Pockels cells 20A and 20B. In this case, when the applied voltage of the first and second Pockels cells 20A, 20B is changed from 0 kV to -3.6 kV, for example, the light transmittance of the laser attenuator 11 changes from 0% to 100%. become.

Further, the laser attenuator 11 can control the voltage applied to the Pockels cell 20 with time, thereby leveling the envelope of one pulse of laser light and making the laser energy uniform along the time axis. For example, when the second laser beam L _{2 of} a long pulse that releases excessive pulse energy within the time t _n as shown in FIG. 6A is input to the laser attenuator 11, for example, this pulse energy is 50 %, The applied voltage to the first and second Pockels cells 20A and 20B within the time t _n is set to −1.8 kV, and after the time t _n elapses, the voltage is controlled to −3.6 kV.

Thus, the second laser light L ₂ of transmittance that transmits a laser for attenuator 11 within the first time t _n is reduced to 50%, the time t _n after the transmittance is 100%. Therefore, in the long-pulse second laser light L ₂ shown in FIG. _6A , the laser intensity within the first time t _n is reduced by 50%, and the laser intensity after the elapse of time t _n is the original intensity. It will be maintained as it is. As a result, as shown in FIG. 6B, the laser intensity within one pulse becomes substantially constant over the entire width.

  In FIG. 2, reference numeral 22 denotes a polarization beam splitter, reference numeral 23 denotes a beam expander that expands the diameter of the laser beam, and reference numeral 24 denotes a reflection mirror.

A synthesizing means 8 is provided at the junction of the optical path of the first pulse laser 6 and the optical path of the second pulse laser 7. The synthesizing means 8 synthesizes the first laser beam L ₁ and the second laser beam L ₂ with the same optical axis, and transmits the first laser beam L ₁ with λ ₁ = 355 nm, for example. , Λ ₂ = 1064 nm, a dichroic mirror that reflects the second laser light L ₂ .

  An illumination optical system 2 is provided on the downstream side of the light source device 1. The illumination optical system 2 irradiates a predetermined region to be annealed of the amorphous silicon film 5 on the substrate 4 with laser light, and the first fly-eye from upstream to downstream in the laser light traveling direction. The lens 25 includes a first condenser lens 26, a second fly-eye lens 27, a beam scanner 28, and a second condenser lens 29.

  The first fly-eye lens 25 functions as a beam expander that makes the intensity distribution in the cross section of the laser light uniform and expands the light beam of the laser light, and has a plurality of convex lenses in the same plane. Are arranged side by side.

  A first condenser lens 26 is provided so that the front focal point is matched with the rear focal point of the first fly-eye lens 25 on the optical axis. The first condenser lens 26 is for narrowing the divergent laser beam so as to be incident on a second fly-eye lens 27 described later after exiting the first fly-eye lens 25.

  The second fly-eye lens 27 is for uniformizing the intensity distribution in the cross section of the laser light, and a pair of lens arrays each having a plurality of convex lenses arranged in the same plane is a corresponding convex lens. The arrangement is such that the central axes are opposed to each other.

  The beam scanner 28 includes a prismatic first and second electro-optic crystal elements 30 and 31 that perform deflection operations in directions perpendicular to each other, and a laser between the first and second electro-optic crystal elements 30 and 31. The first and second electro-optic crystal elements 30 and 31 are provided with a λ / 2 wavelength plate 32 that rotates the polarization plane of light by 90 ° and matches the crystal axis of the second electro-optic crystal element 31. A pair of electrodes 33A and 33B are provided on opposite surfaces parallel to the optical axis. In this case, the pair of electrodes 33A of the first electro-optic crystal element 30 and the pair of electrodes 33B of the second electro-optic crystal element 31 have a relationship that their mounting positions are shifted from each other by 90 degrees about the optical axis. There is no.

  The second condenser lens 29 is provided such that the front focal point coincides with the rear focal point position on the optical axis of the second fly-eye lens 27, and the laser light irradiated onto the substrate 4 is made parallel light. Fulfills the function.

A control means 3 is provided in electrical connection with the first pulse laser 6 and the second pulse laser 7 of the light source device 1. The control means 3 acts on the first and second pulse lasers 6 and 7 to control the generation timing of the first and second laser beams L ₁ and L ₂ . the laser beam L ₁ is adapted to control the first pulse laser 6 to occur at a second predetermined timing of the laser light L ₂ of the pulse width W _2.

More specifically, the control means 3, so as a first generation timing of the laser beam L ₁ by controlling the first pulse laser 6 can be adjusted in the second inner pulse width W ₂ of the laser beam L ₂ Yes. Thereby, the irradiation energy of the laser beam irradiated to the amorphous silicon film 5 can be appropriately adjusted.

Next, the operation of the laser annealing apparatus configured as described above will be described.
First, a stage (not shown) on which a substrate 4 having an amorphous silicon film 5 formed thereon is placed on the upper surface is moved in a two-dimensional direction in a plane parallel to the upper surface to center the region to be annealed on the substrate 4. Is aligned with the optical axis of the illumination optical system 2.

Next, the gradual decrease gradient of the voltage applied to the Pockels cell 17 of the second pulse laser 7 is controlled to be a predetermined gradual decrease gradient by a control unit (not shown), for example, pulse width W ₂ = 350 nsec, wavelength λ _2. = 1064 nm long pulse second laser light L ₂ is generated.

The laser beam L ₂ of the second, after being amplified to a predetermined level by a subsequent optical amplifier 10 by parallel control first and second Pockels cell 20A of the laser for the attenuator 11, the applied voltage 20B, The energy intensity is reduced to an energy intensity necessary and sufficient for the annealing process confirmed in advance by experiments. At the same time, as shown in FIG. 7B, the laser intensity within one pulse is made substantially constant over the entire width. Then, the second laser light L ₂ is reflected by the dichroic mirror of the synthesizing unit 8 and enters the subsequent illumination optical system 2.

On the other hand, the first pulse laser 6 is driven by a certain time delay from the drive of the second pulse laser 7 under the control of the control means 3, and has a pulse width W ₁ = 20 nsec and a wavelength λ ₁ = 355 nm, for example, FIG. first laser light L ₁ of the short pulse as shown in (a) is generated. The first laser light L ₁ passes through the dichroic mirror of the combining unit 8, is combined with the same optical axis as the _second laser light L _2, and enters the illumination optical system 2.

The combined first and second laser beams L ₁ and L ₂ are enlarged in beam diameter by the illumination optical system 2 and made uniform in intensity distribution, and then two-dimensionally on the surface of the substrate 4 by the beam scanner 28. The irradiation position is adjusted by being deflected in the direction. Thereby, the laser beam can be irradiated onto the substrate 4 without interference fringes of the first and second laser beams L ₁ and L ₂ . As a result, the amorphous silicon film 5 in the region to be annealed is melted and recrystallized to change into polysilicon.

Here, the annealing process using the first and second laser beams L ₁ and L ₂ will be described in more detail.
As shown in FIG. 8, it is generally known that the light absorption rate of silicon (Si) decreases as the wavelength of laser light becomes longer. Therefore, generally, when the amorphous silicon film 5 is annealed, an ultraviolet laser beam having a high light absorption rate, for example, a wavelength of 355 nm or the like is used.

  On the other hand, melted silicon is also known to have a low ultraviolet absorption rate. Therefore, when the irradiation energy of the ultraviolet laser beam is not sufficiently high, if the surface of the amorphous silicon film 5 is melted by the irradiation of the ultraviolet laser beam, the absorption rate of the subsequent ultraviolet laser beam is reduced and the amorphous silicon film 5 The case where it cannot fully melt to the deep part may occur. Therefore, there may be a case where the amorphous silicon film 5 cannot be fully polysiliconized to the deep part.

  On the other hand, as shown in FIG. 8, a long-wavelength laser beam having a wavelength of 1064 nm, for example, is difficult to be absorbed by silicon, so that it is generally not used for laser annealing. However, it is also known that long wavelength laser light is easily absorbed by molten silicon.

Therefore, in the present invention, first, the amorphous silicon film 5 is melted by the first laser beam L _{1 having} the short wavelength, and then the amorphous silicon film 5 is melted to the deep portion by the second laser beam L ₂ having the long wavelength. It is what I did.

Specifically, as shown in FIG. 9A, after the second laser beam L ₂ is generated and irradiated to the amorphous silicon film 5, within the pulse width W _{2 of the second} laser beam L ₂ . constant timing, the first generating laser light _{L 1} at timing after t = 100 nsec, for example, from the second laser light _{L 2} of the generation time (rising time of the pulse). In this case, until the first laser beam L ₁ is irradiated, since the amorphous silicon film 5 does not absorb the second laser beam L _2, the amorphous silicon film 5 is not melted. However, by the irradiation of the first laser light L _1, the amorphous silicon film 5 is once melted, then, the amorphous silicon film 5 is melted deeper absorbs the second laser beam L _2. In this case, in the first and second laser beams L ₁ and L ₂ , the energy applied to the annealing process of the amorphous silicon film 5 is the energy in the shaded area in FIG.

In the present invention, it is a first generation timing of the laser beam L ₁ by appropriately adjusting the second inner laser light L ₂ of the pulse width W _2, to be able to adjust the irradiation energy of the laser beam ing. For example, as shown in FIG. 9 (b), when that caused the first laser light L ₁ at the same time as the second generation of the laser beam L _2, the energy applied to the annealing of the amorphous silicon film 5 Is the energy of the hatched area in FIG. 5B, and the irradiation energy can be increased as compared with FIG. Of course, the reverse is also possible.

  In the above-described embodiment, the case where one annealing region on the amorphous silicon film 5 is annealed has been described. However, the present invention is not limited to this. For example, the second condenser lens 29 of the illumination optical system 2 is used. A microlens array having a plurality of microlenses arranged side by side corresponding to a plurality of regions to be annealed is arranged on the light emitting side, and a plurality of synthetic laser beams are generated from one synthetic laser beam, thereby generating a plurality of regions to be annealed May be annealed simultaneously. In this case, since the utilization efficiency of the laser energy is higher than that of the prior art, a pulse laser having a smaller power than that of the prior art can be used.

In addition, while the substrate 4 is transported at a constant speed in a direction crossing the alignment direction of the microlenses, a plurality of regions to be annealed are detected by imaging means in advance and the substrate is detected after the regions to be annealed are detected. The first and second laser beams L ₁ and L ₂ are generated so that the first and second laser beams L ₁ and L ₂ are generated when the plurality of regions to be annealed reach just below the plurality of microlenses of the microlens array. The second pulse lasers 6 and 7 may be controlled. Thereby, the plurality of regions to be annealed in a direction intersecting the transport direction of the substrate 4 can be annealed together and annealed in order in the substrate transport direction to anneal the entire surface of the substrate 4. it can.

3 ... control unit 5 ... an amorphous silicon film 6 ... first pulse laser 7 ... second pulse laser 8 ... synthesis unit L 1 _... first laser beam L 2 _... second laser beam

Claims (5)

A laser annealing apparatus that performs annealing by irradiating an amorphous silicon film with laser light,
A first pulse laser that generates a first laser beam having a constant wavelength and a constant wavelength;
A second pulse laser that generates a second laser beam having a longer pulse width and wavelength than the first laser beam;
Combining means for combining the first laser beam and the second laser beam on the same optical axis;
Control means for controlling the generation timing of the first and second laser beams by acting on the first and second pulse lasers;
With
The laser annealing apparatus characterized in that the control means controls the first pulse laser so that the first laser beam is generated at a predetermined timing within a pulse width of the second laser beam. .   2. The control unit according to claim 1, wherein the control means controls the first pulse laser to adjust the generation timing of the first laser beam within a pulse width of the second laser beam. Laser annealing equipment. The first pulse laser generates the first laser beam having a wavelength of 355 nm or 532 nm,
The second pulse laser generates the second laser beam having a wavelength of 1064 nm.
The laser annealing apparatus according to claim 1 or 2, wherein A first laser beam having a constant pulse width and a constant wavelength and a second laser beam having a pulse width and a wavelength longer than those of the first laser beam are synthesized on the same optical axis and irradiated to the amorphous silicon film. And a laser annealing method for annealing,
Generating the second laser light and irradiating the amorphous silicon film;
Irradiating the amorphous silicon film with the first laser beam generated at a predetermined timing within a pulse width of the second laser beam;
Performing a laser annealing method. The first laser beam has a wavelength of 355 nm or 532 nm,
The second laser beam has a wavelength of 1064 nm.
5. The laser annealing method according to claim 4, wherein: