JP2009044007A - Laser irradiation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser irradiation device capable of excellently growing a semiconductor crystal. <P>SOLUTION: A controller 7 controls a first laser irradiating mechanism 1 and a second laser irradiating mechanism 2 so that a body 6 to be irradiated may be irradiated with a peak of first pulse laser light being delayed behind a peak of second pulse laser light by a delay time td satisfying T-0.15tw≤td≤T+0.3tw while a material to be heated is irradiated with the second pulse laser light on condition that T=(3.0×10<SP>-3</SP>)×ρ×C×λ/(4π×k×h), where ρ is the density (kg/m<SP>3</SP>) of the material to be heated, C the specific heat (J/kg×K) of the material to be heated, (k) the attenuation coefficient of the second pulse light to the material 6b to be heated, (h) heat transmissivity (W/m<SP>2</SP>×K) in heat transmission from the material 6b to be heated to a stage, λ the wavelength (m) of the second pulse laser light, and tw a half-value width of a time-base waveform of the second pulse laser light. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laser irradiation apparatus used for crystallization of a semiconductor film.

  Conventionally, a laser annealing technique for crystallizing an amorphous semiconductor thin film is known as a technique for producing a crystalline thin film used for a high performance TFT (Thin Film Transistor). As an example of the laser annealing technique, there is a technique for crystallizing an amorphous semiconductor thin film by irradiating an irradiation object with a plurality of lasers. In order to realize such a laser annealing technique, a laser irradiation apparatus is used.

  Such a laser irradiation apparatus is a first laser that irradiates an irradiated object with a first pulse laser beam having a wavelength that is absorbed by the semiconductor material when the irradiated object is composed of a semiconductor material and a heated material. An irradiation mechanism and a second laser irradiation mechanism that irradiates the irradiation object with a second pulse laser beam having a shape that has a wavelength that is absorbed by the material to be heated and has a peak in the time axis waveform.

  Among the laser irradiation apparatuses described above, in particular, a laser irradiation apparatus in which a carbon dioxide laser is used as the second pulse laser light and an excimer laser is used as the first pulse laser light is widely known.

  This method is a method for efficiently increasing the crystal length by using a carbon dioxide laser as an assist laser. Further, the irradiation timings of the carbon dioxide laser and the excimer laser are various as disclosed in the following patent documents.

  For example, Japanese Patent Application Laid-Open No. 11-307450 discloses a laser irradiation apparatus that irradiates an irradiated object with a carbon dioxide gas laser after irradiating the irradiated object with an excimer laser.

  Japanese Patent Laid-Open No. 6-291034 discloses a method of irradiating an object to be irradiated with an excimer laser after preheating of the object to be irradiated by irradiation with a carbon dioxide gas laser.

Japanese Patent Application Laid-Open No. 56-142630 discloses a method of irradiating an object to be irradiated with a carbon dioxide gas laser and an excimer laser completely simultaneously.
JP-A-11-307450 Japanese Patent Laid-Open No. Hei 6-291034 JP-A-56-142630

  The present inventors have used two types of lasers using the laser irradiation devices disclosed in JP-A-11-307450, JP-A-6-291034, and JP-A-56-142630. An experiment was conducted in which the irradiated object was irradiated and the crystal length of the semiconductor thin film was observed.

  From the results of the experiments by the inventors, when the irradiated object is irradiated with the carbon dioxide laser and the excimer laser at the irradiation timing as described in JP-A-11-307450 and JP-A-6-291034, It is clear that only a polycrystalline semiconductor thin film having the same size as that obtained by crystallization of an irradiated object can be obtained with an excimer laser alone, that is, a polycrystalline semiconductor thin film having a sufficient crystal length cannot be obtained. Became. In other words, from the experimental results, according to the method of irradiating the irradiated object with the excimer laser before starting the irradiation of the carbon dioxide laser or after ending the irradiation of the carbon dioxide laser, a desired giant crystal can be obtained. It turned out to be difficult.

  Further, from the results of experiments by the present inventors, according to a method of irradiating an object to be irradiated with an excimer laser and a carbon dioxide gas laser almost simultaneously, as described in JP-A-56-142630, two types of irradiation It has been clarified that the crystal length of the obtained polycrystalline semiconductor differs depending on the slight deviation of the laser irradiation timing.

  The reason why the above experimental results can be obtained is considered to be that the shape of the laser pulse and the state of heat radiation from the irradiated object differ depending on the type of laser light.

  Therefore, the irradiation timings of the two types of lasers should be set in consideration of the pulse shape of the laser and the state of heat radiation from the irradiated object, respectively. However, conventionally, the irradiation timings of the two types of lasers are set without considering the laser pulse shape and the state of heat radiation from the irradiated object.

  Therefore, the present inventors have developed the irradiation timing of the first laser beam having a wavelength that is absorbed by the semiconductor material, the wavelength that is absorbed by the material to be heated, and the time for growing the semiconductor crystal satisfactorily. It is considered that a method for appropriately setting the irradiation timing of the second laser light having a shape in which the axial waveform has a peak is necessary.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a laser irradiation apparatus capable of favorably growing a semiconductor crystal.

  A laser irradiation apparatus according to one aspect of the present invention includes a stage that can hold an irradiation object including a semiconductor material and a material to be heated, a wavelength that is absorbed by the semiconductor material, and a peak in a time axis waveform thereof. A first laser irradiation mechanism capable of irradiating an object with a first pulsed laser beam having a shape. Further, the laser irradiation apparatus includes a second laser irradiation mechanism capable of irradiating the irradiated object with a second pulse laser beam having a wavelength that is absorbed by the material to be heated and having a peak in the time axis waveform. And a control device for controlling the first laser irradiation mechanism and the second laser irradiation mechanism.

  In the control device described above, the peak time of the first pulse laser beam is the delay time td that satisfies the condition of T−0.15tw ≦ td ≦ T + 0.3tw while the second pulse laser beam is irradiated on the material to be heated. Only the first laser irradiation mechanism and the second laser irradiation mechanism are controlled so that the irradiation object is irradiated with a delay from the peak of the second pulse laser beam. In this case, the delay time td is determined using the following parameters.

ρ (kg / m ³ ): density of the material to be heated C (J / kg · K): specific heat of the material to be heated k: extinction coefficient of the second pulse laser beam with respect to the material to be heated h (W / m ² · K): Heat transmittance in heat transfer from heated material to stage λ (m): Wavelength of second pulse laser beam tw (s): Half width of time axis waveform of second pulse laser beam T = (3. 0 × 10 ⁻³ ) · ρ · C · λ / (4π · k · h)
According to said structure, the laser irradiation apparatus which can grow a semiconductor crystal favorably is obtained.

  Further, the control device assumes that the center time in the half width of the time axis waveform of the second laser pulse light is tc, and the peak time of the time axis waveform of the second laser pulse light is tpk, tpk ≧ tc. In this case, the peak of the first pulse laser beam is irradiated from the peak of the second pulse laser beam with a delay time td that satisfies the condition of 0 ≦ td ≦ 0.3tw, and is irradiated to the irradiation object. As described above, the first laser irradiation mechanism and the second laser light irradiation mechanism may be controlled.

  Further, the control device assumes that the center time in the half width of the time axis waveform of the second laser pulse light is tc, and the peak time of the time axis waveform of the second laser pulse light is tpk ≦ tpk ≦ In the case of tc, the peak of the first pulse laser beam is delayed from the peak of the second pulse laser beam by the delay time td that satisfies the condition of T−0.15 tw ≦ td ≦ T + 0.15 tw. The first laser irradiation mechanism and the second laser irradiation mechanism may be controlled so that the object is irradiated.

  A laser irradiation apparatus according to another aspect of the present invention includes a stage capable of holding an irradiation object including a semiconductor material and a material to be heated, a wavelength that is absorbed by the semiconductor material, and a peak in a time axis waveform thereof. A first laser irradiation mechanism capable of irradiating an object with a first pulsed laser beam having a shape. The laser irradiation apparatus includes a second laser irradiation mechanism capable of irradiating the irradiated object with a second pulsed laser beam having a wavelength that is absorbed by the material to be heated and having a peak in the time axis waveform; And a control device that controls the first laser irradiation mechanism and the second laser irradiation mechanism.

  In the above-described control device, the peak of the first pulse laser beam is at time te that satisfies the condition of Tp−0.15 tw ≦ te ≦ Tp + 0.15 tw while the second pulse laser beam is irradiated on the material to be heated. The first laser irradiation mechanism and the second laser irradiation mechanism are controlled so that the irradiated object is irradiated. In this case, the time te is determined using the following parameters.

ρ (kg / m ³ ): density of the material to be heated C (J / kg · K): specific heat of the material to be heated k: extinction coefficient of the second pulse laser beam with respect to the material to be heated h (W / m ² · K ): Heat transmittance in heat transfer from heated material to stage λ (m): wavelength of second pulse laser light Function P (t) (t: time): shape of time axis waveform of second pulse laser light Time constant T _L : T _L = (3.0 × 10 ⁻³ ) · ρ · C · λ / (4π · k · h) × M: (M is a constant)
Δt: Arbitrary minute time Tp: L (t) = (P (t) / h) · {1−exp (−Δt / T _L )} + L (t−Δt) · exp (−Δt / T _L ) Time at which a peak is given in the evaluation function L (t) represented by the recurrence formula tw (s): half-value width of the time-axis waveform of the second pulse laser beam Even with the above configuration, the semiconductor crystal can be grown well. A laser irradiation apparatus that can be obtained is obtained.

The stage includes one or more solid materials (thermal conductivity λi (W / m · K), thickness di (m), i ≧ 1), and the laser irradiation apparatus brings the fluid into contact with the one or more solid materials. A cooling mechanism for cooling the stage may be further provided. In this case, if heat is transferred from the material to be heated to one or more solid materials and the heat transfer coefficient from one or more solid materials to the fluid is hw (W / m ² · K), the heat transmittance h It is desirable that (W / m ² · K) be expressed by an equation h = 1 / {Σ (di / λi) + (1 / hw)}. According to this, the laser irradiation apparatus can be efficiently cooled.

In addition, the stage includes one or more solid materials (thermal conductivity λi (W / m · K), thickness di (m), i ≧ 1), and the laser irradiation apparatus makes water contact with the one or more solid materials. A cooling mechanism for cooling the stage may be further provided. In this case, if heat is transferred from the material to be heated to one or more solid materials and the heat of the one or more solid materials is transferred to water, the heat transmittance h (W / m ² · K) is , H = 1 / {Σ (di / λi)}. According to this, the laser irradiation apparatus can be efficiently cooled.

Further, the first pulse laser beam may be an infrared laser, and the material to be heated may be an insulating material containing silicon atoms. The second pulse laser beam may be a carbon dioxide laser. The extinction coefficient k of the carbon dioxide laser with respect to the material to be heated may be 4.6 × 10 ⁻² .

Hereinafter, a laser irradiation apparatus according to an embodiment of the present invention will be described with reference to the drawings.
In designing the laser irradiation apparatus according to the embodiment, the relationship between the irradiation timing of the carbon dioxide laser and the irradiation timing of the excimer laser light in consideration of the heat radiation from the irradiation object and the shape of the carbon dioxide laser pulse irradiated to the irradiation object. Has been determined. In the present embodiment, the pulse shape and pulse width of the excimer laser light are not limited and may be anything.

  The laser irradiation apparatus of this embodiment is effective in the case where a semiconductor film is melted and recrystallized by irradiating the substrate with an excimer laser after the substrate temperature is increased by irradiating the substrate with a carbon dioxide gas laser. Excimer laser irradiation timing is specified. Therefore, as long as the excimer laser irradiates the substrate at a predetermined timing, a common action occurs regardless of the pulse shape of the excimer laser. In addition, since the pulse width of the excimer laser is extremely small (several tens of ns) as compared with the carbon dioxide laser, the difference in the pulse width of the excimer laser does not significantly affect the crystal length. Therefore, even if the difference in the pulse width of the excimer laser is ignored, it is possible to obtain a desired effect if the timing of irradiating the substrate with the excimer laser is defined as a predetermined timing.

  According to the laser irradiation apparatus of the present embodiment, the first pulse laser (excimer laser) having a wavelength that is absorbed by the semiconductor material has a wavelength that is absorbed by the material to be heated and the time axis waveform has a peak. The object to be irradiated is irradiated with a predetermined delay time from the peak of the second pulse laser beam (carbon dioxide laser) having the shape. As a result, giant crystals are obtained. Specifically, the object to be irradiated is irradiated with an excimer laser as an example of the first pulse laser beam at a timing shifted by a predetermined time from the peak of the pulse of the carbon dioxide laser as an example of the second pulse laser beam.

  The predetermined time cannot be determined only by considering only the temperature rise of the irradiated object due to heating by the carbon dioxide laser. More specifically, in order to determine the predetermined time, it is necessary to consider the relationship between the temperature increase of the irradiated object and the crystal growth when the irradiated object is irradiated with the excimer laser. Although it is very difficult to determine the predetermined time described above, in the laser irradiation apparatus of the present embodiment, the predetermined time is set in consideration of the above-described relationship.

  Therefore, according to the laser irradiation apparatus of the present embodiment, the excimer has the most suitable timing for crystal growth of a semiconductor thin film, regardless of the pulse waveform of the carbon dioxide laser or any stage. A semiconductor material can be irradiated with a laser. Therefore, the crystal length can be reliably increased.

Next, the laser irradiation apparatus of this Embodiment is demonstrated using FIG.
As shown in FIG. 1, the laser irradiation apparatus 10 of the present embodiment includes a stage 5 that can hold a substrate 6 as an irradiation object. The substrate 6 includes a semiconductor material 6a and a heated material 6b. The laser irradiation apparatus 10 includes a first laser irradiation mechanism 1 and a second laser irradiation mechanism 2.

  The first laser irradiation mechanism 1 irradiates the substrate 1 with a first pulsed laser beam 10 having a wavelength that is absorbed by the semiconductor material 6 a constituting the substrate 6 and having a time-axis waveform having a peak. In the present embodiment, the first pulse laser beam 10 is an excimer laser or an infrared laser, but other pulse laser beams having a wavelength absorbed by the semiconductor material 6a constituting the substrate 6 may be used. Pulse laser light may be used.

  The second laser irradiation mechanism 2 includes a laser irradiator main body 2a and reflectors 2b, 2c, and 2d. Further, the second laser irradiation mechanism 2 irradiates the substrate 6 with the second pulsed laser light 20 having a wavelength that is absorbed by the heated material 6b constituting the substrate 6 and having a time axis waveform having a peak. can do. More specifically, the second pulse laser beam 20 is emitted from the laser irradiator body 2a. Thereafter, the second pulse laser beam 20 is reflected by each of the reflectors 2b, 2c, and 2d. Further, the second pulse laser beam 20 is irradiated on the substrate 6 on the stage 50. The second laser pulse light 20 is a carbon dioxide laser in the present embodiment, but has a wavelength that is absorbed by the material to be heated 6b constituting the substrate 6 and has a peak in its time axis waveform. Any other pulsed laser beam may be used as long as it is a pulsed laser beam.

  In the present embodiment, the stage 5, the first laser irradiation mechanism 1, and the second laser irradiation mechanism 2 are controlled by the control device 7. Therefore, the control device 7 can control the irradiation timings of the first laser irradiation mechanism 1 and the second laser irradiation mechanism 2.

  In the present embodiment, the control device 7 determines that the peak of the first pulse laser beam 10 is Tp−0.15tw ≦ te ≦ Tp + 0.00 while the second pulse laser beam is irradiated on the material to be heated 6b. The first laser irradiation mechanism 1 and the second laser irradiation mechanism 2 are controlled so that the substrate 6 is irradiated at time te that satisfies the condition of 15 tw.

Here, Tp is L (t) = (P (t) / h) · {1−exp (−Δt / T _L )} + L (t−Δt) · when an arbitrary minute time is Δt. In the evaluation function L (t) represented by the recurrence formula exp (−Δt / T _L ), this is a time when a peak is given. The half width of the time axis waveform of the second pulse laser beam 20 is tw. The time T _L is expressed by an expression of T _L = (3.0 × 10 ⁻³ ) · ρ · C · λ / (4π · k · h) × M.

Further, the parameters used in the above formula are as follows.
ρ (kg / m ³ ) is the density of the material to be heated 6b. C (J / kg · K) is the specific heat of the heated material 6b. k is an extinction coefficient of the second pulse laser beam 20 with respect to the material 6b to be heated. h (W / m ² · K) is a heat transmittance in heat transfer from the heated material 6 b to the stage 5. λ (m) is the wavelength of the second pulse laser beam 20. The function P (t) (t: time) is for expressing the time axis waveform of the second pulse laser beam 20. In the present embodiment, it is assumed that the extinction coefficient k of the carbon dioxide laser with respect to the material to be heated 6b is 4.6 × 10 ⁻² .

Further, the stage 5 has a solid material (thermal conductivity λi (W / m · K), thickness di (m), i ≧ 1) 5i (i = 1, 2, 3,..., N) having one or more. The laser irradiation apparatus 10 may further include a cooling mechanism 100 that cools the stage by bringing the fluid 1000 into contact with one or more solid materials 5i. In this case, when heat is transferred from the material to be heated to one or more solid materials and the heat transfer coefficient from one or more solid materials 5i to the fluid is hw, the heat transmittance h (W / m ^2). K) is represented by the equation h = 1 / {Σ (di / λi) + (1 / hw)}.

When the cooling mechanism 100 brings water into contact with one or more solid materials 5i, heat is transferred from the heated material 6b to the one or more solid materials 5i, and the heat of the one or more solid materials 5i is water. , The heat transmittance h (W / m ² · K) is expressed by the equation h = 1 / {Σ (di / λi)}.

  First, in determining the conditional expression as described above, a model of a heat transfer system from the substrate 1 to the stage 5 was considered. Thereby, the irradiation timing of the excimer laser was quantitatively determined.

  In order to calculate the above conditional expression, the temperature increase model of the heated material 6b by the irradiation of the carbon dioxide laser was defined as follows (see FIG. 2).

P (W / m ² ): Absorption power density of carbon dioxide laser with respect to heated material 6b ρ (kg / m ³ ): Density of heated material 6b C (J / kg · K): Specific heat of heated material 6b da ( m): Depth of heated area of heated material 6b θ (K): Temperature difference between heated area of heated material and θe θe (K): Heat is transferred from substrate 6 to fluid 1000 Temperature h of the subsequent fluid 100 h (W / m ² · K): Heat transmittance in heat transfer from the heated region to the fluid 1000 dt: Minute time A configuration embodying the above model is shown in FIG. .

  In this model, it is assumed that the material to be heated is irradiated with a carbon dioxide laser having a power density P in the configuration as described above. Thereby, the material to be heated is heated and its temperature is increased. Thereafter, heat is released from the material to be heated to the outside by transmission.

  When the material to be heated is actually irradiated with a carbon dioxide laser, a predetermined temperature distribution is generated in the z direction in FIG. However, in this model, it is assumed that the energy of the carbon dioxide laser having the power density P is uniformly applied to the material to be heated. Therefore, it is assumed that the carbon dioxide laser is absorbed only in a region from the main surface to a predetermined depth da. As a result, the region has a uniform temperature. Here, the heating depth da was defined as the depth at which the irradiated laser attenuates to 1 / e (= absorption depth).

  That is, after the carbon dioxide laser of power density P is uniformly absorbed in the portion from the main surface to the depth da, the temperature of that portion rises to a predetermined temperature (temperature difference θ from the ambient temperature), A model was assumed in which heat was released to the outside.

Based on the above model, the heat balance is described by the following equation.
P (t) dt = ρ · C · da · dθ + h · θdt
By solving this differential equation, the following equation (a) is obtained. (As initial conditions, t = 0 and θ = θ0)
θ (t) = (θ0−P / h) exp (−ht / ρ · C · da) + P / h
= (P (t) / h) {1−exp (−t / T)} + θ0 · exp (−t / T) Expression (a)
Time constant T = ρ · C · da / h Equation (b)
Assuming that θ changes by Δθ after the minute time Δt has elapsed, applying this to equation (a) yields the following equation (1) as an approximate difference equation.

θ (t) = (P (t) / h) {1−exp (−Δt / T)} + θ (t−Δt) · exp (−Δt / T) (1) Equation When described, a difference approximation such as dθ / dt = {θ (t) −θ (t−Δt)} / Δt is executed, and as a result, θ (t) = {ρ · C · da · θ (t -Δt) + P · Δt} / (ρ · C · da + h) (2)
Is obtained. However, in the present embodiment, Expression (1) is used as an approximate expression.

  Further, in order to determine h in the above-described time constant equation (b), as shown in FIG. 3, heat is transmitted from the position of the heated region depth da of the heated material 6 b to the stage 5. A one-dimensional heat conduction model moving with h is used.

The following rules are used in the one-dimensional heat conduction model.
λ1 (W / m · K): Thermal conductivity of heated material d1 (m): Thickness of heated material 6b λ2 (W / m · K): Thermal conductivity of stage 5 d2 (m): Stage 5 Thickness hw (W / m ² · K): heat transfer coefficient in heat transfer from the stage 5 to the fluid 1000 At this time, if the heat transmittance h (W / m ² · K) is da << d1,
h≈1 / {(d1 / λ1) + (d2 / λ2) + (1 / hw)} (3)
It is expressed by the formula.

  From the foregoing, the one-dimensional heat conduction model in the n-layer stacked structure can be expressed by the formula h = 1 / {Σ (di / λi) + (1 / hw)} as described above. Understood.

In the aforementioned model, the depth da of the heated region is defined as the absorption depth.
Absorption depth da is generally da = 1 / α = λ / (4π × k) (4)
It is expressed as

Here, α: absorption coefficient (m ⁻¹ ), λ: incident laser wavelength (m), k: extinction coefficient A relational expression between excimer laser irradiation timing and crystal growth is determined as follows.

  In this embodiment, the substrate 6 is irradiated with a carbon dioxide gas laser to irradiate the excimer laser onto the semiconductor thin film whose temperature is rising as shown by the equation (1). As a result, the semiconductor thin film melts and crystallizes.

  According to this method, when the excimer laser 10 is irradiated, the temperature of the semiconductor thin film is already increased by the irradiation of the carbon dioxide laser 20 as shown in FIG. Therefore, the time required for the semiconductor thin film to change from the molten state to the solidified state after the irradiation of the excimer laser 10 is increased. As a result, it is possible to lengthen the time for crystal growth. Therefore, the crystal length can be increased.

  If the timing te at which the excimer laser is irradiated matches the timing tpeak of the temperature peak specified by the equation (1), the crystal length of the semiconductor material 6a is not maximized. This is because there is a cooling effect by irradiating the carbon dioxide laser, and it is desirable to irradiate the substrate with the excimer laser at a timing before the temperature peak timing tpeak.

  In view of the foregoing, the inventors of the present application conducted an experiment in which an excimer laser was irradiated at various timings to measure the crystal length. From this experimental result, a graph showing the relationship between crystal length and irradiation timing was created. According to this, the graph showing the relationship between the crystal length and the irradiation timing created from the experimental results is almost the same shape as the graph showing the relationship between the crystal length and the irradiation timing specified by the equation of θ (t). I knew that there was. Therefore, the formula showing the relationship between the crystal length and the irradiation timing created from the experimental results is expressed by the same formula as the formula of θ (t), and only the time constant T is different from the formula of θ (t). ing.

Therefore, if the time constant is T _L and M is a constant, the relationship T _L = T × M is established, and the relational expression indicating the crystal length and irradiation timing is as follows:
L (t) = P (t) / h · (1−exp (−Δt / T _L )) + L (t−Δt) ·
exp (−Δt / T _L ) (5)
It is expressed.

T _L = T × M
= (Ρ · C · da) / h × M
= (Ρ · C · λ) / (4π · k · h) × M (6) Equation L (t): Crystal length when irradiated with excimer laser at time t P (t): of carbon dioxide laser Absorption power density for heated material 6b The validity of the above equations (5) and (6) was confirmed by experiments.

  In this experiment, as shown in FIG. 5, the heated material 6b was regarded as an integral structure of silicon, a silicon insulating film, and a glass substrate.

  FIG. 6 shows a pulse waveform when the pulse width of the carbon dioxide laser beam is 600 μs. An experiment was conducted to measure the crystal length while changing the irradiation timing of the excimer laser beam. The resulting crystal length is plotted in FIG. The value of the constant M is determined so that the above equation (5) satisfies the crystal length distribution obtained from the experimental results of FIG.

Here, the density of the glass is ρ = 2510 (kg / m ³ ), the specific heat of the glass is C = 837 (J / kg · K), the heat transmittance is h = 580 (W / m ² · K), The wavelength of the gas laser is λ = 10.6 (μm), and the extinction coefficient k of the carbon dioxide gas laser with respect to glass is 4.6 × 10 ⁻² . These values were substituted into equation (5), resulting in M = 3.0 × 10 ⁻³ . At this time, T _L = 200 μs.

  The validity of the value of M was confirmed by an experiment in which the crystal length of the semiconductor material was measured a plurality of times while changing the transmittance h and the pulse width of the carbon dioxide laser beam.

  FIG. 8 shows a pulse waveform when the pulse width of the carbon dioxide laser is 150 μs.

  Similarly to the above, an experiment was conducted in which the crystal length of the semiconductor material was measured a plurality of times while changing the irradiation timing of the excimer laser light.

  FIG. 9 shows values measured by experiments and values calculated using Equation (5).

Next, the influence when the thickness of the chuck, that is, the heat transmittance h is changed will be described.
The heat transmittance h is changed by changing the thickness of the chuck, that is, the thickness of the stage. With the pulse width of the carbon dioxide gas laser set to 600 μs and 150 μs, the excimer laser was irradiated to the irradiated object at different irradiation timings as described above, and the crystal length of the semiconductor material at each irradiation timing was measured.

  The values measured by the experiment when the pulse width is 600 μs and the values calculated using the equation (5) are plotted in FIG. Moreover, the calculation result of Formula (5) when the pulse width is 150 μs, the value measured by the experiment of the crystal length, and the value calculated by using Formula (5) are plotted in FIG.

  From FIG. 10 and FIG. 11, the experimental result and the calculation result by Formula (5) are substantially in agreement, and the validity of the calculation result by Formula (5) can be confirmed.

  Theoretically, L (t), which is an evaluation function of the semiconductor crystal length, is created from the pulse waveform data of the carbon dioxide laser using Equation (5), and L (t) has a peak value (= It is considered optimal to irradiate the substrate with an excimer laser at the time when the crystal length is maximum. In other words, it is most desirable to create L (t) from the pulse waveform of the carbon dioxide laser and irradiate the substrate with the excimer laser at time t (= Tp) at which L (t) is maximum. However, in the present embodiment, from the viewpoint of practical use, the irradiation timing of the excimer laser light is defined in a range having a predetermined width around the peak value of L (t). Specifically, the excimer laser may be irradiated to the substrate at the irradiation timing te that satisfies the condition of Tp−0.15tw ≦ te ≦ Tp + 0.15tw in consideration of the waveform of the carbon dioxide laser. Experiments have confirmed that a crystal length of 90% or more of the L (t) peak value can be obtained by irradiating the substrate with an excimer laser at the irradiation timing when the above-described conditions are satisfied.

  However, according to the method of creating L (t) each time according to the pulse waveform and determining the irradiation timing, it takes time to create L (t). It cannot be said that it is suitable for practical use. Therefore, as a practical method, another embodiment for defining the irradiation timing of the excimer laser on the basis of the pulse waveform of the carbon dioxide laser will be described below.

  In this embodiment, the overall configuration of the laser irradiation apparatus is the same as that of the above-described embodiment. In the present embodiment, the control device 7 determines that the peak of the first pulsed laser beam 10 is T−0.15tw ≦ td ≦ T + 0.W while the second pulsed laser beam is irradiated on the material to be heated 6b. The first laser irradiation mechanism 1 and the second laser irradiation mechanism 2 are controlled so that the substrate 6 is irradiated with a delay from the peak of the second pulse laser beam 20 by a delay time td defined by 3tw. As a result, it is possible to achieve the object of the invention of growing a giant crystal as in the above-described embodiment.

In the above conditional expression, ρ (kg / m ³ ) is the density of the material to be heated. C (J / kg · K) is the specific heat of the material to be heated. k is an extinction coefficient of the second pulse laser beam 20 with respect to the material to be heated. h (W / m ² · K) is a heat transmittance in heat transfer from the material to be heated to the stage 5. λ (m) is the wavelength of the second pulse laser beam 20. tw is the half width of the time axis waveform of the second pulse laser beam 20.

  Note that the actual pulse waveform of the carbon dioxide laser is not a perfect rectangle, but has various shapes depending on the pulse width. Specifically, the pulse waveform of the actual carbon dioxide laser beam is a waveform having an intensity peak at a timing before the center of the half-value width tw as shown in FIG. 6 when the pulse width is 600 μs. If the pulse width is 150 μs, the waveform has an intensity peak behind the center of the half-value width tw as shown in FIG.

  Therefore, it is necessary to vary the irradiation timing of the excimer laser light depending on whether the peak time tpk of the time axis waveform is after or before the central time tc in the half width tw of the time axis waveform. Become.

  More specifically, it is assumed that the center time in the half width tw of the time axis waveform is tc and the peak time of the time axis waveform is tpk.

  In the case where tpk ≧ tc, the control device 7 satisfies the condition that 0 ≦ td ≦ 0.3 tw when the peak of the first pulse laser beam 10 is applied to the material to be heated 6 b with the second pulse laser beam. The first laser irradiation mechanism 1 and the second laser light irradiation mechanism 2 are controlled so that the substrate 6 is irradiated with a delay time td that satisfies the condition, delayed from the peak of the second pulse laser light 20.

  On the other hand, when tpk ≦ tc, the control device 7 indicates that the peak of the first pulse laser beam 10 is T−0.15 tw ≦ W while the second pulse laser beam is irradiated on the material 6b to be heated. The first laser irradiation mechanism 10 and the second laser irradiation mechanism 20 are set so that the substrate 6 is irradiated with a delay time td that satisfies the condition of td ≦ T + 0.15tw, delayed from the peak of the second pulse laser light 20. Control.

  In the laser irradiation apparatus of the present embodiment, as shown in FIG. 12, first, in step 1, the parameters such as ρ, C, k, h, λ, and tw described above are input to the control device 7. . Next, in step 2 and step 3, the control device 7 calculates T and td using the above-described formulas built in a storage area such as a ROM (Read Only Memory). Thereafter, when the user presses the drive switch of the laser irradiation device 10, the control device 7 causes the second laser irradiation mechanism 2 to irradiate the substrate 6 with the second pulse laser light 20 in Step 4. In step 4, the control device 7 sends the first pulse to the first laser irradiation mechanism 1 when the delay time td has elapsed since the second laser irradiation mechanism 2 irradiated the substrate 6 with the second pulse laser light. The substrate 6 is irradiated with laser light.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a figure for demonstrating the structure of the laser irradiation apparatus of embodiment. It is a figure used for calculation of a formula. It is a figure used for description of calculation for calculating heat transmittance. It is a figure which shows the relationship between the pulse waveform of a laser, the temperature of a to-be-heated material, and the crystal length of a semiconductor material. It is a figure which shows an example of the specific structure of a board | substrate and a stage. It is a figure which shows an example of the waveform of a carbon dioxide laser with a pulse width of 600 μs. It is a figure which shows the relationship between the crystal length calculated by the formula, and the crystal length measured in experiment, when a carbon dioxide gas laser with a pulse width of 600 μs is irradiated onto the substrate. It is a figure which shows an example of the waveform of a carbon dioxide laser with a pulse width of 150 μs. It is a figure which shows the relationship between the crystal length calculated by the formula, and the crystal length measured in experiment, when a carbon dioxide gas laser with a pulse width of 150 μs is irradiated onto the substrate. The crystal length calculated by the formula and the crystal measured in the experiment when the substrate is irradiated with a carbon dioxide gas laser having a pulse width of 600 μs under the chuck condition different from the chuck condition in the experiment for obtaining the result of FIG. It is a figure which shows the relationship with length. The crystal length calculated by the calculation formula and the crystal measured in the experiment when the substrate is irradiated with a carbon dioxide gas laser having a pulse width of 150 μs under the chuck condition different from the chuck condition in the experiment for obtaining the result of FIG. It is a figure which shows the relationship with length. It is a flowchart of the control which the control apparatus of a laser irradiation apparatus performs.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 1st laser irradiation mechanism, 2nd 2nd laser irradiation mechanism, 2a Laser irradiation mechanism main body, 2b, 2c, 2d reflector, 5 stage, 6 substrate, 7 control apparatus, 10 2nd pulse laser beam, 20 2nd pulse laser Light, 100 cooling mechanism, 1000 fluid.

Claims (9)

A stage capable of holding an irradiated object including a semiconductor material and a heated material;
A first laser irradiation mechanism capable of irradiating the irradiated object with a first pulse laser beam having a shape that has a wavelength absorbed by the semiconductor material and has a peak in the time axis waveform;
A second laser irradiation mechanism capable of irradiating the irradiated object with a second pulsed laser light having a wavelength that is absorbed by the material to be heated and having a peak in the time axis waveform;
A control device for controlling the first laser irradiation mechanism and the second laser irradiation mechanism;
The controller is
The density of the heated material is ρ (kg / m ³ ),
The specific heat of the material to be heated is C (J / kg · K),
The extinction coefficient of the second pulse laser beam with respect to the material to be heated is k,
The heat transmittance in heat transfer from the heated material to the stage is h (W / m ² · K),
The wavelength of the second pulse laser beam is λ (m),
The half width of the time-axis waveform of the second pulse laser beam is tw.
When T = (3.0 × 10 ⁻³ ) · ρ · C · λ / (4π · k · h),
The peak of the first pulse laser beam is the delay time td that satisfies the condition of T−0.15tw ≦ td ≦ T + 0.3tw while the second pulse laser beam is irradiated on the material to be heated. In order to irradiate the irradiated object with a delay from the peak of the second pulse laser beam,
A laser irradiation apparatus for controlling the first laser irradiation mechanism and the second laser irradiation mechanism. The controller is
The center time in the half width of the time-axis waveform of the second laser pulse light is tc,
Assuming that the peak time of the time axis waveform of the second laser pulse light is tpk,
If tpk ≧ tc,
The peak of the first pulse laser beam is delayed from the peak of the second pulse laser beam by a delay time td that satisfies the condition of 0 ≦ td ≦ 0.3tw, and is irradiated to the irradiated object.
The laser irradiation apparatus according to claim 1, wherein the first laser irradiation mechanism and the second laser light irradiation mechanism are controlled. The controller is
The center time in the half width of the time-axis waveform of the second laser pulse light is tc,
If the peak time of the time axis waveform of the second laser pulse light is tpk,
If tpk ≦ tc,
The peak of the first pulse laser beam is delayed from the peak of the second pulse laser beam by a delay time td that satisfies the condition of T−0.15 tw ≦ td ≦ T + 0.15 tw, and is irradiated on the irradiated object. As
The laser irradiation apparatus according to claim 1, wherein the first laser irradiation mechanism and the second laser irradiation mechanism are controlled. A stage capable of holding an irradiated object including a semiconductor material and a heated material;
A first laser irradiation mechanism capable of irradiating the irradiated object with a first pulse laser beam having a shape that has a wavelength absorbed by the semiconductor material and has a peak in the time axis waveform;
A second laser irradiation mechanism capable of irradiating the irradiated object with a second pulsed laser light having a wavelength that is absorbed by the material to be heated and having a peak in the time axis waveform;
A control device for controlling the first laser irradiation mechanism and the second laser irradiation mechanism;
The controller is
The density of the material to be heated is ρ (kg / m ³ ),
The specific heat of the material to be heated is C (J / kg · K),
The extinction coefficient of the second pulse laser beam with respect to the material to be heated is k,
The heat transmittance in heat transfer from the heated material to the stage is h (W / m ² · K),
The wavelength of the second pulse laser beam is λ (m),
The shape of the time axis waveform of the second pulse laser beam is a function P (t) (t: time),
Time _TL is a constant M
T _L = (3.0 × 10 ⁻³ ) · ρ · C · λ / (4π · k · h) × M
Expressed by the formula
When an arbitrary minute time is Δt, L (t) = (P (t) / h) · {1−exp (−Δt / T _L )} + L (t−Δt) · exp (−Δt / T _L ) When the time at which the peak is given in the evaluation function L (t) represented by the recurrence formula is Tp, and the half width of the time-axis waveform of the second pulse laser beam is tw,
The peak of the first pulse laser beam is at the time te that satisfies the condition of Tp−0.15 tw ≦ te ≦ Tp + 0.15 tw while the second pulse laser beam is irradiated on the material to be heated. To irradiate the irradiated object,
A laser irradiation apparatus for controlling the first laser irradiation mechanism and the second laser irradiation mechanism. The stage includes one or more solid materials (thermal conductivity λi (W / m · K), thickness di (m), i ≧ 1);
The laser irradiation apparatus further includes a cooling mechanism that cools the stage by bringing a fluid into contact with the one or more solid materials,
When heat is transferred from the heated material to the one or more solid materials and a heat transfer coefficient from the one or more solid materials to the fluid is hw (W / m ² · K),
The said heat transmittance h (W / m < ² > * K) is represented in any one of Claims 1-4 represented by the formula h = 1 / {(SIGMA) (di / (lambda) i) + (1 / hw)}. Laser irradiation device. The stage includes one or more solid materials (thermal conductivity λi (W / m · K), thickness di (m), i ≧ 1);
The laser irradiation apparatus further includes a cooling mechanism that cools the stage by bringing water into contact with the one or more solid materials,
When heat is transferred from the heated material to the one or more solid materials and the heat of the one or more solid materials is transferred to the water,
The laser irradiation apparatus according to claim 1, wherein the heat transmittance h (W / m ² · K) is represented by an expression h = 1 / {Σ (di / λi)}.   The laser irradiation apparatus according to claim 1, wherein the first pulse laser beam is an infrared laser, and the material to be heated is an insulating material containing silicon atoms.   The laser irradiation apparatus according to claim 7, wherein the second pulse laser beam is a carbon dioxide laser. The laser irradiation apparatus according to claim 8, wherein an extinction coefficient k of the carbon dioxide laser with respect to the material to be heated is 4.6 × 10 ⁻² .

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