JP4364611B2 - Method for manufacturing crystalline semiconductor film - Google Patents

Description

  The present invention relates to a laser irradiation apparatus used for crystallization of a semiconductor film. Further, the present invention relates to a laser irradiation method using the laser irradiation apparatus and a method for manufacturing a semiconductor device.

  A thin film transistor using a polycrystalline semiconductor film (polycrystalline TFT) has a mobility that is two orders of magnitude higher than that of a TFT using an amorphous semiconductor film, and a pixel portion of a semiconductor display device and its peripheral drive circuit are formed on the same substrate. It has the advantage that it can be integrally formed on top. The polycrystalline semiconductor film can be formed over an inexpensive glass substrate by using a laser annealing method.

  Lasers are roughly classified into two types, pulse oscillation and continuous oscillation, depending on the oscillation method. A pulsed laser typified by an excimer laser has an output energy of laser light per unit time of about 3 to 6 digits higher than that of a continuous wave laser. Therefore, the beam spot (region where the laser beam is actually irradiated on the surface of the object to be processed) is shaped by an optical system so as to be a rectangular shape of several centimeters square or a linear shape having a length of 100 mm or more, and a semiconductor film It is possible to efficiently irradiate the laser beam and increase the throughput. For this reason, it has become the mainstream to use a pulsed laser for crystallization of the semiconductor film.

  Here, “linear” does not mean “line” in a strict sense, but means a rectangle (or oval) having a large aspect ratio. For example, an aspect ratio of 2 or more (preferably 10 to 10000) is called a linear shape, but the linear shape is still included in a rectangular shape.

  However, the semiconductor film crystallized using pulsed laser light in this way is formed by aggregating a plurality of crystal grains, and the positions and sizes of the crystal grains are random. Compared with the inside of a crystal grain, the interface (crystal grain boundary) of a crystal grain has innumerable recombination centers and trap centers due to an amorphous structure or crystal defects. When carriers are trapped in this trapping center, the grain boundary potential rises and becomes a barrier against the carriers, so that there is a problem that the carrier transport property is lowered.

  With the above problem in the background, by irradiating the semiconductor film while scanning a continuous wave laser in one direction, a crystal is continuously grown in the scanning direction, and a single crystal extending long along the scanning direction In recent years, a technique for forming a collection of crystal grains made of has attracted attention. By using the above method, it is considered that a semiconductor film having almost no crystal grain boundary can be formed at least in the channel direction of the TFT.

By the way, it is preferable that the absorption coefficient of the laser beam with respect to the semiconductor film is larger because the semiconductor film can be efficiently crystallized. The absorption coefficient varies depending on the material and thickness of the semiconductor film. When crystallizing a silicon film with a thickness of several tens to several hundreds of nanometers normally used in a semiconductor device with a YAG laser or a YVO ₄ laser, the second harmonic having a shorter wavelength than the fundamental wave has a higher absorption coefficient and is more efficient. Crystallization can be performed.

However, the laser beam converted into the harmonic wave has lower energy than that of the fundamental wave, and it is difficult to increase the beam spot area and increase the throughput. In particular, this tendency is remarkable in a continuous wave laser because the output energy of laser light per unit time is lower than that of a pulsed laser. For example, in the case of an Nd: YAG laser, the conversion efficiency from the fundamental wave (wavelength: 1064 nm) to the second harmonic (wavelength: 532 nm) is around 50%. In addition, since the nonlinear optical element that converts to harmonics is extremely low in resistance to laser light, for example, a continuous wave YAG laser can output a fundamental wave of 10 kW, whereas an output energy of the second harmonic is only about 10 W. I can't. Therefore, in order to obtain the energy density necessary for crystallization of the semiconductor film, the area of the beam spot must be reduced to about 10 ⁻³ mm ^2, which is inferior to the pulsed excimer laser in terms of throughput. .

  In addition, at both ends of the beam spot in the direction perpendicular to the scanning direction, regions having crystal grains that are significantly smaller than the center of the beam spot and inferior in crystallinity are formed. Even if a semiconductor element is formed in this region, high characteristics cannot be expected. Therefore, in order to alleviate the restrictions on the layout of the semiconductor element, it is important to reduce the proportion of the region with poor crystallinity in the entire region irradiated with the laser light.

  In view of the above-described problems, an object of the present invention is to provide a laser irradiation apparatus capable of dramatically expanding the area of a beam spot and reducing the proportion of a region with poor crystallinity. It is another object of the present invention to provide a laser irradiation apparatus that can increase throughput while using continuous wave laser light. Another object of the present invention is to provide a laser irradiation method using the laser irradiation apparatus and a method for manufacturing a semiconductor device.

  The laser irradiation method of the present invention irradiates a region continuously melted by a first pulsed laser beam of higher harmonics with a second laser beam of continuous oscillation. Specifically, the first laser beam has a wavelength (830 nm, preferably about 780 nm or less) that is approximately the same as or shorter than that of visible light. When the semiconductor film is melted by the first laser light, the absorption coefficient of the second laser light to the semiconductor film is dramatically increased, and the second laser light is easily absorbed by the semiconductor film.

FIG. 8A shows the value of the absorption coefficient (cm ⁻¹ ) of the amorphous silicon film with respect to the wavelength (nm) of the laser beam. FIG. 8B shows the value of the absorption coefficient (cm ⁻¹ ) of the polycrystalline silicon film with respect to the wavelength (nm) of the laser beam. The measurement was obtained from the extinction coefficient obtained with a spectroscopic ellipsometer. From FIGS. 8A and 8B, it is considered that when the absorption coefficient is 1 × 10 ⁴ cm ⁻¹ or more, the semiconductor film can be sufficiently melted by the first laser beam. In order to obtain an absorption coefficient in this numerical range, in the case of an amorphous silicon film, it is considered that the wavelength of the first laser beam is preferably 780 nm or less. Note that the relationship between the wavelength of the first laser beam and the absorption coefficient varies depending on the material of the semiconductor film, crystallinity, and the like. Therefore, the wavelength of the first laser beam is not limited to this, and the wavelength of the first laser beam may be set as appropriate so that the absorption coefficient is 1 × 10 ⁴ cm ⁻¹ or more.

  The laser irradiation apparatus of the present invention also includes a first laser oscillator that pulsates the first laser light having a wavelength shorter than or equal to visible light, and a second laser oscillator that continuously oscillates the second laser light that is a fundamental wave. have. The shape and position of the beam spot of the first laser beam and the beam spot of the second laser beam are controlled by the corresponding first and second optical systems, respectively. The first laser beam and the second laser beam are overlapped with each other by the two optical systems. Furthermore, the laser irradiation apparatus of the present invention has means for controlling the relative positions of the beam spot of the first laser beam and the beam spot of the second laser beam with respect to the object to be processed.

  As a result, the portion melted by the first laser beam moves in the semiconductor film while being maintained in the molten state by the irradiation of the second laser beam that is continuously oscillating, so that it continuously grows in the scanning direction. Crystal grains are formed. By forming single crystal grains extending in the scanning direction, it is possible to form a semiconductor film having few crystal grain boundaries at least in the channel direction of the TFT.

  The time during which the molten state can be maintained is determined by the balance between the output of the pulsed laser and the continuous wave laser. If the semiconductor film is irradiated with the next pulsed laser within a time during which the molten state can be maintained, annealing of the semiconductor film can be continued while the molten state is maintained. In an extreme case, once the semiconductor film is melted with a pulse laser, there may be a condition in which the molten state can be maintained only by irradiation with the fundamental wave. In this case, it is only necessary to irradiate only one shot of the pulse laser and then maintain the molten state with a continuous wave laser.

  Since higher harmonics have lower energy, the first laser beam is most preferably the second harmonic when the wavelength of the fundamental wave is about 1 μm. However, the present invention is not limited to this, and the first laser beam only needs to have a wavelength of visible light or less. In the second laser beam, the output power is more important than the absorption coefficient to the semiconductor film for the purpose of assisting energy with respect to the first laser beam. Therefore, it is most desirable to use a fundamental wave as the second laser light. However, the present invention is not limited to this, and the second laser beam may be a fundamental wave or a harmonic wave.

  When the fundamental wave is used for the second laser light, it is not necessary to convert the wavelength, and thus it is not necessary to suppress energy in consideration of deterioration of the nonlinear optical element. For example, the second laser beam can have an output that is 100 times or more (for example, an output of 1000 W or more) compared to a continuous-wave laser of visible light or less. Therefore, the complexity of the maintenance of the nonlinear optical element can be eliminated, the total energy of the laser light absorbed by the semiconductor film can be increased, and a crystal having a larger particle diameter can be obtained.

  In pulse oscillation, the energy of the oscillated laser light per unit time is higher than in continuous oscillation. Moreover, in the harmonic and the fundamental wave, the energy of the harmonic is lower, and the energy of the fundamental wave is higher. In the present invention, a laser beam having a wavelength of harmonics or less than visible light is pulsed oscillation, and the fundamental laser beam is continuously oscillated. Compared to a configuration in which the oscillation is continuous oscillation and the fundamental wave is pulse oscillation, it is possible to secure a large area where the harmonic beam spot and the fundamental beam spot overlap each other.

  The overlap of two beam spots formed by two lasers will be described by taking a continuous wave YAG laser and a pulsed excimer laser as examples.

  FIG. 1A shows a state in which a beam spot 10 of a continuous wave YAG laser having a fundamental wave and a beam spot 11 of a continuous wave YAG laser having a second harmonic are superimposed. The fundamental YAG laser can obtain an output energy of about 10 kW, and the second harmonic YAG laser can obtain an output energy of about 10 W.

Assuming that the energy of the laser beam is absorbed by 100% of the semiconductor film, the crystallinity of the semiconductor film is improved by setting the energy density of each laser beam to 0.01 to 100 MW / cm ^2. Can do. Therefore, here, the energy density is 1 MW / cm ² .

The shape of the beam spot 10 of a continuous wave YAG laser having a fundamental wave is assumed to be rectangular, the length in the minor axis direction is L _X1 , and the length in the major axis direction is L _Y1. For this purpose, L _X1 is 20 μm to 100 μm. For example, when L _X1 = 20 μm, L _Y1 = about 50 mm, and when L _X1 = 30 μm, L _Y1 = 30 mm is appropriate.

Further, assuming that the shape of the beam spot 11 of a continuous wave YAG laser having harmonics is rectangular, the length in the short axis direction is L _X2 , and the length in the long axis direction is L _Y2 , the above energy density is satisfied. For this purpose, L _X2 is 20 μm to 100 μm. For example, when L _X2 = 10 μm, L _Y2 = 100 μm is appropriate.

  The area of the region where the beam spot 10 of the continuous wave YAG laser having the fundamental wave overlaps with the beam spot 11 of the continuous wave YAG laser having the second harmonic wave is such that the beam spot 11 completely overlaps the beam spot 10. It is equivalent to the area of the beam spot 11.

Next, FIG. 1B shows a state where a beam spot 10 of a continuous wave YAG laser having a fundamental wave and a beam spot 12 of a pulsed excimer laser are overlapped. A pulsed excimer laser can obtain an output energy of about 1 J per pulse. If the pulse width is about 30 ns, the output per unit time is 30 MW. Accordingly, assuming that the shape of the beam spot 12 of the pulsed excimer laser is rectangular, the length in the minor axis direction is L _X3 , and the length in the major axis direction is L _Y3 , in order to satisfy the above energy density. L _X3 is 20 μm to 500 μm. For example, when L _X3 = 400 μm, L _Y3 = 300 mm is appropriate.

  Assuming that the beam spot 10 of the continuous wave YAG laser having the fundamental wave overlaps with the beam spot 12 of the pulsed excimer laser, the beam spot 10 completely overlaps the beam spot 12. This corresponds to the area of the spot 10.

  Therefore, rather than making both the first laser beam and the second laser beam oscillate continuously as shown in FIG. 1A, the first laser beam oscillates continuously and the second laser beam oscillates as in the present invention. When the pulse oscillation is used, it is possible to greatly expand the overlapping region of the two laser beams, and the throughput can be further increased.

  Note that the number of laser beams is not limited to two, but may be two or more. A plurality of first laser beams having harmonics may be used, or a plurality of second laser beams may be used.

  By making the beam spot linear, the width of the beam spot in the major axis direction of the region where crystal grains crystallized in the scanning direction gather can be made as wide as possible. That is, it can be said that the ratio of the area occupied by all the beam spots in the region of poor crystallinity formed at both ends of the long axis can be reduced. However, in the present invention, the shape of the beam spot is not limited to a linear shape, and there is no problem even if it is rectangular or planar as long as sufficient annealing can be performed on the irradiated object.

Note the first laser beam, Ar laser of pulse oscillation, Kr laser, an excimer laser, CO ₂ laser, YAG _laser, Y 2 _{O 3} laser, YVO ₄ laser, YLF laser, Y A lO ₃ laser, a glass laser, ruby It can be obtained by using a laser, alexandrite laser, Ti: sapphire laser, copper vapor laser or gold vapor laser.

The second laser beam, Ar laser of continuous oscillation, Kr laser, CO ₂ laser, YAG _laser, Y 2 _{O 3} laser, YVO ₄ laser, YLF laser, Y A lO ₃ laser, alexandrite laser, Ti: sapphire laser Alternatively, it can be obtained by using a helium cadmium laser.

  Note that in the crystallization process of a semiconductor film using a continuous wave laser, the beam spot is processed into an elliptical or rectangular shape that is long in one direction, and the semiconductor film is crystallized by scanning in the short axis direction of the beam spot. Can be increased. The reason why the shape of the laser beam after processing is elliptical is that the shape of the original laser beam is circular or close to it. If the original shape of the laser beam is a rectangular shape, it may be used after it has been processed so that the long axis is further elongated by enlarging it in one direction with a cylindrical lens or the like. In addition, a plurality of laser beams may be processed into an elliptical or rectangular shape that is long in one direction, and connected to create a longer beam in one direction, thereby further increasing the throughput.

  In the present invention, the semiconductor film is melted by irradiation with pulsed first laser light having a wavelength of visible light or less that is easily absorbed by the semiconductor film, and the absorption coefficient of the fundamental wave is increased. By using pulse oscillation for the first laser beam, the area of the beam spot can be drastically increased compared to continuous oscillation. By irradiating the second laser light having the fundamental wave in the melted state, the second laser light is efficiently absorbed by the semiconductor film having an increased fundamental wave absorption coefficient. Therefore, since the long axis of the beam spot can be made long, the throughput of laser crystallization can be increased, and it is effective in relaxing the design rule.

  Further, the region melted by the first laser beam and having an increased absorption coefficient can be moved by scanning the second laser beam, and the region in which crystal grains grown in the scanning direction are spread is provided. Can be formed. Furthermore, even after the irradiation of the first laser beam is interrupted, the region whose absorption coefficient is increased by melting can be moved to one direction to some extent by the scanning of the second laser beam.

  Further, since the second laser beam is used as a fundamental wave, it is not necessary to consider the tolerance of the nonlinear optical element used for the conversion to the harmonic, and the second laser beam is a very high output laser, for example, a harmonic. Can be used having an energy of 100 times or more. And the maintenance complexity due to the alteration of the nonlinear optical element is eliminated. In particular, the advantage of a solid-state laser that can maintain a maintenance-free state for a long time can be utilized.

(Embodiment 1)
The configuration of the laser irradiation apparatus of the present invention will be described with reference to FIG.

Reference numeral 101 denotes a pulse oscillation laser oscillator. In this embodiment, a 6 W Nd: YLF laser is used. The laser oscillator 101 is converted to the second harmonic by a nonlinear optical element in the TEM ₀₀ oscillation mode. Although it is not necessary to limit to the second harmonic in particular, the second harmonic is superior to the higher harmonics in terms of energy efficiency. The frequency is 1 kHz and the pulse width is about 60 ns. In the present embodiment, a solid-state laser having an output of about 6 W is used, but a large-sized laser, such as a XeCl excimer laser, whose output reaches 300 W may be used.

  The nonlinear optical element may be provided in a resonator included in the oscillator, or a resonator including a nonlinear optical element may be provided in addition to the fundamental wave resonator. The former has the advantage that the device becomes smaller and precise control of the resonator length becomes unnecessary, and the latter has the advantage that the interaction between the fundamental wave and the harmonic can be ignored.

Nonlinear optical elements include KTP (KTiOPO ₄ ), BBO (β-BaB ₂ O ₄ ), LBO (LiB ₃ O ₅ ), CLBO (CsLiB ₆ O ₁₀ ), GdYCOB (YCa ₄ O) having relatively large nonlinear optical constants. Crystals such as (BO ₃ ) ₃ ), KDP (KD ₂ PO ₄ ), KB5, LiNbO ₃ , Ba ₂ NaNb ₅ O ₁₅ are used, and in particular, LBO, BBO, KDP, KTP, KB5, CLBO, etc. are used. Thus, the conversion efficiency from the fundamental wave to the harmonic can be increased.

  Since the laser light is normally emitted in the horizontal direction, the first laser light oscillated from the laser oscillator 101 is reflected by the reflecting mirror 102 in the direction in which the angle from the vertical direction (incident angle) is θ1. The direction of travel is changed. In the present embodiment, θ1 = 21 °. The shape of the beam spot of the first laser light whose traveling direction has been converted is processed by the lens 103, and is irradiated on the object 104. In FIG. 2, the reflection mirror 102 and the lens 103 correspond to an optical system that controls the shape and position of the beam spot of the first laser beam.

  In FIG. 2, as the lens 103, a plano-concave cylindrical lens 103a and a plano-convex cylindrical lens 103b are used.

  The plano-concave cylindrical lens 103a has a radius of curvature of 10 mm and a thickness of 2 mm, and is disposed at a position of 29 mm along the optical axis from the surface of the workpiece 104 when the traveling direction of the first laser beam is the optical axis. Has been. Then, the bus line of the plano-concave cylindrical lens 103a and the incident surface of the first laser light incident on the object 104 are perpendicular.

  The plano-convex cylindrical lens 103b has a radius of curvature of 15 mm and a thickness of 2 mm, and is disposed at a position of 24 mm from the surface of the workpiece 104 along the optical axis. The generatrix of the planoconvex cylindrical lens 103b is parallel to the incident surface of the first laser beam incident on the workpiece 104.

  As a result, a first beam spot 106 having a size of 3 mm × 0.2 mm is formed on the workpiece 104.

  Reference numeral 110 denotes a continuous wave laser oscillator which uses a 2 kW, fundamental wave Nd: YAG laser in this embodiment. The second laser light oscillated from the laser oscillator 110 is transmitted through the optical fiber 111 having a diameter of 300 μm. The optical fiber 111 is arranged such that the direction of the exit with respect to the vertical direction is an angle θ2. In this embodiment, θ2 = 45 °. The exit of the optical fiber 111 is disposed at a position 105 mm from the workpiece 104 along the optical axis of the second laser light emitted from the laser oscillator 110, and the optical axis is included in the incident surface. To do.

  The shape of the beam spot of the second laser light emitted from the optical fiber 111 is processed by the lens 112 and irradiated to the object 104. In FIG. 2, the optical fiber 111 and the lens 112 correspond to an optical system that controls the shape and position of the beam spot of the second laser light.

  In FIG. 2, as the lens 112, a planoconvex cylindrical lens 112a and a planoconvex cylindrical lens 112b are used.

  The plano-convex cylindrical lens 112a has a radius of curvature of 15 mm and a thickness of 4 mm, and is disposed at a position of 85 mm from the surface of the workpiece 104 along the optical axis of the second laser beam. The direction of the generatrix of the planoconvex cylindrical lens 112a is perpendicular to the incident surface.

  The planoconvex cylindrical lens 112b has a radius of curvature of 10 mm and a thickness of 2 mm, and is arranged at a position of 25 mm from the surface of the workpiece 104 along the optical axis of the second laser beam.

  As a result, a second beam spot 105 having a size of 3 mm × 0.1 mm is formed on the workpiece 104.

  In this embodiment, a substrate over which a semiconductor film is formed as the object to be processed 104 is placed so as to be parallel to a horizontal plane. For example, the semiconductor film is formed on the surface of a glass substrate. The substrate on which the semiconductor film is formed is a glass substrate having a thickness of 0.7 mm, and is fixed to the suction stage 107 so that the substrate does not fall during laser irradiation.

  The suction stage 107 can be moved in the X and Y directions in a plane parallel to the workpiece 104 by a single-axis robot 108 for X-axis and a single-axis robot 109 for Y-axis.

  In the case of annealing a semiconductor film formed on a substrate that is transparent to laser light, in order to achieve uniform laser light irradiation, the plane is perpendicular to the irradiation surface, and When any one of a surface including a short side or a surface including a long side when the shape of the beam is regarded as a rectangle is defined as an incident surface, the incident angle φ of the laser beam is the short side included in the incident surface or Φ ≧ arctan (W / 2d) is satisfied when the length of the long side is W, the thickness of the substrate that is installed on the irradiation surface and has a light transmitting property to the laser beam is d. Is desirable. If multiple laser beams are used, this argument needs to hold for each laser beam. When the locus of the laser beam is not on the incident surface, the incident angle of the projection of the locus onto the incident surface is φ. When laser light is incident at this incident angle φ, the reflected light from the surface of the substrate and the reflected light from the back surface of the substrate do not interfere with each other, and uniform laser light irradiation can be performed. In the above discussion, the refractive index of the substrate was considered as 1. Actually, in many cases, the refractive index of the substrate is around 1.5, and if this value is taken into consideration, a calculated value larger than the angle calculated in the above discussion can be obtained. However, since the energy of the beam spot is attenuated as it approaches the end of the beam spot, the influence of the interference in this portion is small, and the effect of interference attenuation can be sufficiently obtained by the above calculated value. It is preferable that both the first laser beam and the second laser beam satisfy the above inequality, but this discussion is about an extremely short coherent laser such as an excimer laser. There is no problem even if the above inequality is not satisfied. The above inequality for φ is applied only when the substrate is transparent to laser light.

  Generally, a glass substrate has translucency with respect to a fundamental wave having a wavelength of about 1 μm or a green second harmonic. In order for this lens to satisfy the inequality, the planes of the planoconvex cylindrical lens 103b and the planoconvex cylindrical lens 112b are shifted in the direction perpendicular to the incident plane, and the plane is perpendicular to the surface of the workpiece 104 including the minor axis of the beam spot. The incident angles φ1 and φ2 may be provided to satisfy the inequality. In this case, if the first beam spot 106 has an inclination of φ1 = 10 ° and the second beam spot 105 has an inclination of φ2 = 5 °, no interference occurs.

Note that the first laser beam and the second laser beam are preferably in a TEM ₀₀ mode (single mode) obtained from a stable resonator. In the case of the TEM ₀₀ mode, the laser beam has a Gaussian intensity distribution and has excellent light collecting properties, so that the beam spot can be easily processed.

  When a substrate on which a semiconductor film is formed is used as the workpiece 104, for example, a silicon oxynitride film having a thickness of 200 nm is formed on one surface of a glass substrate having a thickness of 0.7 mm, and a semiconductor film is formed thereon. An amorphous silicon (a-Si) film having a thickness of 70 nm is formed using a plasma CVD method. Further, in order to increase the resistance of the semiconductor film to the laser, thermal annealing at 500 ° C. for 1 hour is performed on the amorphous silicon film. In addition to thermal annealing, crystallization using a catalytic metal may be performed. The optimum laser light irradiation conditions are substantially the same for both the semiconductor film subjected to thermal annealing and the semiconductor film crystallized using a catalytic metal.

  Then, the workpiece 104 (the substrate on which the semiconductor film is formed) is scanned in the short axis direction of the second beam spot 105 using the uniaxial robot 109 for the Y axis. At this time, the outputs of the laser oscillators 101 and 102 are set to specification values. By scanning the workpiece 104, the first beam spot 106 and the second beam spot 105 are scanned relative to the surface of the workpiece 104.

  When the semiconductor film is melted in the region where the first beam spot 106 is hit, the absorption coefficient of the continuous-wave second laser light into the semiconductor film is dramatically increased. Accordingly, single crystal grains grown in the scanning direction are formed in a state where the crystal growth in the scanning direction is spread over a region having a width of 1 mm to 2 mm corresponding to the long axis of the second beam spot 105 extending in the scanning direction.

  Note that in the semiconductor film, the region where the first beam spot 106 and the second beam spot 105 are overlapped is irradiated with a fundamental wave whose absorption coefficient is increased by the first laser beam of the second harmonic. It is maintained by a certain first laser beam. Therefore, even if the irradiation of the first laser beam of the second harmonic is interrupted, the semiconductor laser is melted and the absorption coefficient is increased by the first laser beam that is the fundamental wave thereafter. . Therefore, even after the irradiation of the first laser beam of the second harmonic is interrupted, the region where the melting coefficient and the absorption coefficient are increased can be moved in one direction to some extent by scanning. Crystal grains grown toward the surface are formed. Then, in order to continuously maintain the region with the increased absorption coefficient in the scanning process, it is desirable to re-irradiate the first laser beam of the second harmonic and replenish the energy.

  Note that the scanning speed of the first beam spot 106 and the second beam spot 105 is suitably about several cm / s to several hundred cm / s, and is set to 50 cm / s here.

  Next, FIG. 3 shows a scanning path of the first beam spot 106 and the second beam spot 105 on the surface of the workpiece 104. When irradiating the entire surface of the semiconductor film, which is the workpiece 104, with the second laser beam, after scanning in one direction using the Y-axis uniaxial robot 109, the X-axis uniaxial robot 108 is used. The first beam spot 106 and the second beam spot 105 are slid in a direction perpendicular to the scanning direction by the uniaxial robot 109 for the Y axis.

  For example, the semiconductor film is scanned in one direction by the Y-axis uniaxial robot 109 at a scanning speed of 50 cm / s. In FIG. 3, the scanning path is indicated by A1. Next, the first beam spot 106 and the second beam spot 105 are slid along the scanning path in a direction perpendicular to A1 using the uniaxial robot 108 for the X axis. A scanning path by the slide is indicated by B1. Next, the semiconductor film is scanned in one direction by the Y-axis uniaxial robot 109 in the direction opposite to the scanning path A1. The scanning path is indicated by A2. Next, the first beam spot 106 and the second beam spot 105 are slid along the scanning path in a direction perpendicular to A2 using the uniaxial robot 108 for the X axis. A scanning path by the slide is indicated by B2. In this manner, the second laser beam or the first laser beam is irradiated on the entire surface of the workpiece 104 by sequentially repeating the scanning by the Y-axis uniaxial robot 109 and the scanning by the X-axis uniaxial robot 108. be able to.

  It is desirable that the length of the scanning paths B1, B2,... Be 1 mm to 2 mm corresponding to the long axis of the second beam spot 105.

  A region where crystal grains grown in the scanning direction are irradiated with the second laser light is extremely excellent in crystallinity. Therefore, by using this region as a TFT channel formation region, extremely high electric mobility and on-current can be expected. However, when there is a portion of the semiconductor film where such high crystallinity is not required, the portion may not be irradiated with laser light. Alternatively, laser light irradiation may be performed under conditions that do not provide high crystallinity, such as increasing the scanning speed. For example, when scanning is performed at a speed of about 2 m / s, the a-Si film can be crystallized, but a region that is continuously crystallized in the scanning direction as described above is difficult to form. The throughput can be further increased by partially increasing the scanning speed.

  The scanning of the laser beam includes an irradiation system moving type that fixes the substrate as the object to be processed and moves the irradiation position of the laser light, and an object movement type that fixes the irradiation position of the laser light and moves the substrate. And a combination of the above two methods. The laser irradiation apparatus of the present invention uses at least two laser beams of the first laser beam and the second laser beam, so that the object to be processed can be made to have the simplest optical system configuration. Is suitable. However, the laser irradiation apparatus of the present invention is not limited to this, and it is not impossible to make the irradiation system moving type by combining the optical system, or to combine the object moving type and the irradiation system moving type. In any case, it is assumed that the relative movement direction of each beam spot with respect to the semiconductor film can be controlled.

  Note that the optical system in the laser irradiation apparatus of the present invention is not limited to the structure shown in this embodiment mode.

(Embodiment 2)
Next, a laser light irradiation method and a semiconductor device manufacturing method of the present invention will be described with reference to FIGS.

  First, as shown in FIG. 4A, a base film 501 is formed over a substrate 500. As the substrate 500, for example, a glass substrate such as barium borosilicate glass or alumino borosilicate glass, a quartz substrate, a SUS substrate, or the like can be used. In addition, substrates made of plastics typified by PET, PES, PEN, and flexible synthetic resins such as acrylic generally tend to have lower heat-resistant temperatures than the above-mentioned substrates. Any material that can withstand the processing temperature can be used.

  The base film 501 is provided to prevent an alkali metal such as Na or an alkaline earth metal contained in the substrate 500 from diffusing into the semiconductor film and adversely affecting the characteristics of the semiconductor element. Therefore, the insulating film is formed using an insulating film such as silicon oxide, silicon nitride, or silicon nitride oxide that can suppress diffusion of alkali metal or alkaline earth metal into the semiconductor film. In this embodiment, a silicon nitride oxide film is formed to a thickness of 10 to 400 nm (preferably 50 to 300 nm) by a plasma CVD method.

  Note that the base film 501 may be a single layer or a stack of a plurality of insulating films. In the case of using a substrate containing an alkali metal or an alkaline earth metal, such as a glass substrate, a SUS substrate, or a plastic substrate, it is effective to provide a base film from the viewpoint of preventing impurity diffusion. However, when diffusion of impurities does not cause any problem, such as a quartz substrate, it is not necessarily provided.

  Next, a semiconductor film 502 is formed over the base film 501. The thickness of the semiconductor film 502 is 25 to 100 nm (preferably 30 to 60 nm). Note that the semiconductor film 502 may be an amorphous semiconductor or a polycrystalline semiconductor. As the semiconductor, not only silicon but also silicon germanium can be used. When silicon germanium is used, the concentration of germanium is preferably about 0.01 atomic% to 4.5 atomic%.

  Next, as shown in FIG. 4B, crystallization is performed by irradiating the semiconductor film 502 with the first and second laser beams using the laser irradiation apparatus of the present invention.

In this embodiment, a YLF laser having an energy of 6 W, an energy of 6 mJ / p for one pulse, an oscillation mode of TEM _00, a second harmonic (527 nm), an oscillation frequency of 1 kHz, and a pulse width of 60 ns is used as the first laser light. Note that the first beam spot formed on the surface of the semiconductor film 502 by processing the first laser beam with an optical system has a rectangular shape with a minor axis of 200 μm and a major axis of 3 mm, and an energy density of 1000 mJ / cm ^2. And

In this embodiment, a YAG laser having an energy of 2 kW and a fundamental wave (1.064 μm) is used as the second laser light. Note that the second beam spot formed on the surface of the semiconductor film 502 by processing the second laser light with an optical system has a rectangular shape with a short axis of 100 μm and a long axis of 3 mm, and an energy density of 0.7 MW / cm ² .

  Then, irradiation is performed on the surface of the semiconductor film 502 so as to overlap the first beam spot and the second beam spot, and the two beams are directed in the direction of the white arrow illustrated in FIG. Scan. By melting with the first laser light, the absorption coefficient of the fundamental wave is increased, and the energy of the second laser light is easily absorbed by the semiconductor film. Then, a region melted by irradiation with the second laser beam that is continuous oscillation moves in the semiconductor film, so that crystal grains continuously grown in the scanning direction are formed. By forming single crystal grains extending in the scanning direction, it is possible to form a semiconductor film having few crystal grain boundaries at least in the channel direction of the TFT.

  Note that laser light may be irradiated in an inert gas atmosphere such as a rare gas or nitrogen. Thereby, roughness of the semiconductor surface due to laser light irradiation can be suppressed, and variation in threshold value caused by variation in interface state density can be suppressed.

  By irradiating the semiconductor film 502 with the laser light, the semiconductor film 503 with higher crystallinity is formed.

  Next, as illustrated in FIG. 4C, the semiconductor film 503 is patterned to form island-shaped semiconductor films 507 to 509, and various islands represented by TFTs using the island-shaped semiconductor films 507 to 509 are formed. A semiconductor element is formed.

  For example, in the case of manufacturing a TFT, a gate insulating film is formed so as to cover the island-shaped semiconductor films 507 to 509, although not illustrated. For the gate insulating film, for example, silicon oxide, silicon nitride, silicon nitride oxide, or the like can be used. As a film formation method, a plasma CVD method, a sputtering method, or the like can be used.

  Next, a conductive film is formed over the gate insulating film and patterned to form a gate electrode. Then, a gate electrode or a resist film formed and patterned is used as a mask, an impurity imparting n-type or p-type conductivity is added to the island-shaped semiconductor films 507 to 509, and a source region and a drain region are added. Further, an LDD region or the like is formed.

  A TFT can be formed by the series of steps described above. Note that the method for manufacturing a semiconductor device of the present invention is not limited to the above-described TFT manufacturing process after the formation of an island-shaped semiconductor film. By using a semiconductor film crystallized by the laser light irradiation method of the present invention as an active layer of a TFT, variations in mobility, threshold value, and on-current between elements can be suppressed.

  Note that the first laser light and the second laser light are not limited to the irradiation conditions described in this embodiment mode.

For example, a YAG laser having an energy of 4 W, an energy of 2 mJ / p, a TEM ₀₀ oscillation mode, a second harmonic (532 nm), an oscillation frequency of 1 kHz, and a pulse width of 30 ns may be used as the first laser light. Further, for example, a YVO ₄ laser having an energy of 5 W, an energy of 0.25 mJ / p, a TEM ₀₀ oscillation mode, a third harmonic (355 nm), an oscillation frequency of 20 kHz, and a pulse width of 30 ns is used as the first laser beam. You can also. Further, for example, as the first laser light, a YVO ₄ laser having an energy of 3.5 W, an energy of one pulse of 0.233 mJ / p, an oscillation mode of TEM _00, a fourth harmonic (266 nm), an oscillation frequency of 15 kHz, and a pulse width of 30 ns. Can also be used.

  For example, an Nd: YAG laser having an energy of 500 W and a fundamental wave (1.064 μm) can be used as the second laser light. For example, an Nd: YAG laser having an energy of 2000 W and a fundamental wave (1.064 μm) can be used as the second laser light.

  Further, a crystallization step using a catalytic element may be provided before crystallization with laser light. Nickel (Ni) is used as the catalyst element, but besides that, germanium (Ge), iron (Fe), palladium (Pd), tin (Sn), lead (Pb), cobalt (Co), Elements such as platinum (Pt), copper (Cu), and gold (Au) can be used. When a crystallization process using a laser beam is performed after a crystallization process using a catalytic element, the crystal formed during the crystallization using the catalytic element remains on the side closer to the substrate without being melted by the laser beam irradiation. Then, crystallization proceeds using the crystal as a crystal nucleus. Therefore, crystallization by laser light irradiation tends to progress uniformly from the substrate side toward the surface of the semiconductor film, and the crystallinity of the semiconductor film can be improved more than in the case of only the crystallization process by laser light. The surface roughness of the semiconductor film after crystallization by light can be suppressed. Accordingly, variation in characteristics of semiconductor elements formed later, typically TFTs, can be further suppressed, and off-current can be suppressed.

  Note that after the catalyst element is added and heat treatment is performed to promote crystallization, the crystallinity may be further increased by laser light irradiation, or the heat treatment step may be omitted. Specifically, after adding a catalyst element, laser light may be irradiated instead of heat treatment to improve crystallinity.

  Note that although an example in which the laser irradiation method of the present invention is used for crystallization of a semiconductor film is described in this embodiment mode, the semiconductor film may be used for activation of an impurity element doped.

  The method for manufacturing a semiconductor device of the present invention can be used for a method for manufacturing an integrated circuit or a semiconductor display device. In particular, liquid crystal display devices, light-emitting devices including light-emitting elements typified by organic light-emitting elements in each pixel, semiconductor display devices such as DMD (Digital Micromirror Device), PDP (Plasma Display Panel), and FED (Field Emission Display). When used for a semiconductor element such as a transistor provided in the pixel portion, it is possible to suppress the horizontal stripes due to the energy distribution of the laser light irradiated in the pixel portion from being visually recognized.

Examples of the present invention will be described below.

Example 1
In this embodiment, one mode of a laser irradiation apparatus of the present invention will be described.

  FIG. 5 shows the configuration of the laser irradiation apparatus of this embodiment. In this embodiment, a first laser beam having a wavelength shorter than or equal to that of pulsed visible light is oscillated from a laser oscillator 1520. A continuous oscillation second laser beam is oscillated from two laser oscillators 1500 and 1501.

  In this embodiment, an excimer laser is used as the laser oscillator 1520, the output energy per pulse is 1 J, the pulse width is about 30 ns, and therefore the output per unit time is 30 MW. The laser oscillators 1500 and 1501 are both YAG lasers, and each output energy is 10 kW.

  The first laser light oscillated from the laser oscillator 1520 is reflected by the mirror 1523, collected by the optical system 1524 in a rectangular shape, an elliptical shape, or a linear shape, and irradiated on the object to be processed 1514. In this embodiment, the shutter 1521 for blocking the first laser beam is provided between the laser oscillator 1520 and the mirror 1523, but it is not always necessary to provide the shutter 1521. The optical system 1524 may be any system that can collect the beam spot in a linear, rectangular, or elliptical shape and make the energy distribution uniform.

  On the other hand, the second laser light oscillated from the laser oscillators 1500 and 1501 enters the beam expanders 1508 and 1560, respectively. In this embodiment, shutters 1502 and 1503 for blocking the second laser light are provided between the laser oscillators 1500 and 1501 and the beam expanders 1508 and 1560, respectively, but it is not always necessary to provide them.

  The beam expanders 1508 and 1560 can suppress the spread of the incident second laser beam and can adjust the size of the cross-sectional shape of the beam.

  The second laser beams emitted from the beam expanders 1508 and 1560 are expanded in cylindrical lenses 1509 and 1561 so that the cross-sectional shape of the beams becomes rectangular, elliptical, or linear, respectively. Then, the extended second laser light is reflected by mirrors 1510 and 1562, and is incident on the lens 1511. The incident laser light is condensed into a linear shape by the lens 1511 and irradiated to the object 1514 in the laser irradiation chamber 1513. In this embodiment, a cylindrical lens is used as the lens 1511. However, any lens that can make the beam spot rectangular, elliptical, or linear may be used.

  In this embodiment, the mirror 1523 and the optical system 1524 correspond to an optical system corresponding to the first laser beam. Beam expanders 1508 and 1560, cylindrical lenses 1509 and 1561, and mirrors 1510 and 1562 correspond to an optical system corresponding to the second laser beam. By these two optical systems, a first beam spot formed on the surface of the object to be processed 1514 by the first laser light and a second beam formed on the surface of the object to be processed 1514 by the second laser light. Spots can be superimposed.

  FIG. 7 shows an example of the shape and arrangement of each beam spot used in the laser irradiation apparatus shown in FIG. In FIG. 7, 1570 corresponds to the first beam spot, and 1571 and 1572 correspond to the second beam spot. In FIG. 7, the second beam spots 1571 and 1572 are partially overlapped with each other so that their long axes coincide. The first beam spot 1570 is overlapped so as to completely cover the second beam spots 1571 and 1572.

In this embodiment, the short axial length L _X1570 of the first beam spot 1570 400 [mu] m, the longitudinal length L _Y1570 and 110 mm, the energy density and 25 MW / cm ² approximately. When converted to the energy density per pulse, about 100 to 1000 mJ / cm ² is appropriate. The second beam short axis direction of 200μm length L _X1571 spots 1571, the longitudinal length L _Y1571 and 60 mm, the energy density and 0.1 MW / cm ^2. The second beam short axis direction of 200μm length L _X1571 spots 1571, the longitudinal length L _Y1571 and 60 mm, the energy density and 0.1 MW / cm ^2. The second beam spots 1571 and 1572 overlap each other by 20 mm, and the length of the long axes of the second beam spots 1571 and 1572 is 100 mm.

  By combining a plurality of second laser beams in this way, the region where the first laser beam and the second laser beam overlap can be expanded, and the crystalline property occupies the entire region irradiated with the laser beam. The ratio of inferior areas can be reduced.

  In this embodiment, two laser oscillators are used to irradiate the object to be processed with the two systems of the second laser light. However, the present invention is not limited to this, and the second system of the three or more systems is used. The laser beam may be used. The first laser light may also be a plurality of systems.

  In the laser irradiation chamber 1513, the workpiece 1514 is placed on a stage 1515, and the position of the stage 1515 is controlled by three uniaxial robots 1516 to 1518. Specifically, the stage 1515 can be rotated in the horizontal plane by the uniaxial robot 1516 for the φ axis. Further, the stage 1515 can be moved in the X-axis direction in the horizontal plane by the X-axis single-axis robot 1517. Further, the stage 1515 can be moved in the Y-axis direction in the horizontal plane by the single-axis robot 1518 for the Y-axis. The operation of each position control means is controlled by the central processing unit 1519.

  By irradiating the object to be processed in the X direction while irradiating a linear beam spot elongated in the Y-axis direction, a collection of crystal grains elongated in the scanning direction can be formed. The scanning speed may be, for example, 10 to 2000 mm / s, preferably 100 to 1000 mm / s. However, the optimum range of the scanning speed varies depending on conditions such as the film thickness and material of the semiconductor film. Thereby, it is possible to form a single crystal crystal grain that has grown in the scanning direction in a region having a width of 100 mm extending in the scanning direction. The region where the crystal grains grown in the scanning direction are spread is dramatically widened by about 100 times as compared with the case of the conventional technique in which crystallization is performed using only continuous wave laser light. .

  Note that, as in this embodiment, a monitor 1512 using a light receiving element such as a CCD may be provided so that the position of the workpiece 1514 can be accurately grasped.

(Example 2)
A structure of a pixel of a light-emitting device, which is one of semiconductor devices formed using the laser irradiation apparatus of the present invention, will be described with reference to FIGS.

  In FIG. 6, a base film 6001 is formed over a substrate 6000, and a transistor 6002 is formed over the base film 6001. The transistor 6002 includes an active layer 6003, a gate electrode 6005, and a gate insulating film 6004 sandwiched between the active layer 6003 and the gate electrode 6005.

  As the active layer 6003, a polycrystalline semiconductor film crystallized by using the laser irradiation apparatus of the present invention is used. The active layer may be made of silicon germanium as well as silicon. When silicon germanium is used, the concentration of germanium is preferably about 0.01 to 4.5 atomic%. Further, silicon to which carbon nitride is added may be used.

For the gate insulating film 6004, silicon oxide, silicon nitride, or silicon oxynitride can be used. A film in which these layers are stacked, for example, a film in which SiN is stacked on SiO ₂ may be used as the gate insulating film. The gate electrode 6005 is formed using an element selected from Ta, W, Ti, Mo, Al, and Cu, or an alloy material or a compound material containing the element as a main component. Alternatively, a semiconductor film typified by a polycrystalline silicon film doped with an impurity element such as phosphorus may be used. Further, instead of a single conductive film, a conductive film composed of a plurality of layers may be stacked.

  The transistor 6002 is covered with a first interlayer insulating film 6006, and a second interlayer insulating film 6007 and a third interlayer insulating film 6008 are stacked over the first interlayer insulating film 6006. . The first interlayer insulating film 6006 can be formed using a single layer or a stack of silicon oxide, silicon nitride, or silicon oxynitride films by a plasma CVD method or a sputtering method.

  As the second interlayer insulating film 6007, an organic resin film, an inorganic insulating film, an insulating film including a Si—O bond and a Si—CHx bond formed using a siloxane-based material as a starting material, or the like can be used. In this embodiment, non-photosensitive acrylic is used. As the third interlayer insulating film 6008, a film that hardly transmits a substance that causes deterioration of the light-emitting element such as moisture or oxygen as compared with other insulating films is used. Typically, it is desirable to use, for example, a DLC film, a carbon nitride film, a silicon nitride film formed by an RF sputtering method, or the like.

  In FIG. 6, 6010 is an anode, 6011 is an electroluminescent layer, and 6012 is a cathode. One of the transistors 6002 is a driving transistor that controls current supplied to the light-emitting element 6013, and is connected to the light-emitting element 6013 directly or in series via another circuit element. The electroluminescent layer 6011 has a structure in which a light emitting layer alone or a plurality of layers including a light emitting layer are stacked.

  The anode 6010 is formed on the third interlayer insulating film 6008. An organic resin film 6014 used as a partition is formed over the third interlayer insulating film 6008. In this embodiment, an organic resin film is used as a partition. However, an inorganic insulating film, an insulating film including a Si—O bond and a Si—CHx bond formed using a siloxane-based material as a partition, and the like are used as a partition. Can do. The organic resin film 6014 has an opening 6015, and the light emitting element 6013 is formed by overlapping the anode 6010, the electroluminescent layer 6011, and the cathode 6012 in the opening.

  A protective film 6016 is formed over the organic resin film 6014 and the cathode 6012. As with the third interlayer insulating film 6008, the protective film 6016 is a film that hardly transmits a substance that causes deterioration of the light-emitting element such as moisture and oxygen compared to other insulating films, such as a DLC film, A carbon nitride film, a silicon nitride film formed by an RF sputtering method, or the like is used.

  Also, the end of the organic resin film 6014 in the opening 6015 is rounded so that the electroluminescent layer 6011 formed on the organic resin film 6014 partially overlaps so that there is no hole in the end. Is desirable. Specifically, it is desirable that the radius of curvature of the curve drawn by the cross section of the organic resin film in the opening is about 0.2 to 2 μm. With the above structure, coverage of an electroluminescent layer and a cathode to be formed later can be improved, and a short circuit between the anode 6010 and the cathode 6012 in a hole formed in the electroluminescent layer 6011 can be prevented. Further, by relaxing the stress of the electroluminescent layer 6011, defects called “shrink” in which a light emitting region is reduced can be reduced, and reliability can be improved.

  Note that FIG. 6 illustrates an example in which a positive photosensitive acrylic resin is used as the organic resin film 6014. The photosensitive organic resin includes a positive type in which a portion exposed to energy rays such as light, electrons, and ions is removed, and a negative type in which the exposed portion remains. In the present invention, a negative organic resin film may be used. Alternatively, the organic resin film 6014 may be formed using photosensitive polyimide. When the organic resin film 6014 is formed using negative acrylic, an end portion of the opening 6015 has an S-shaped cross-sectional shape. At this time, it is desirable that the radius of curvature at the upper end and the lower end of the opening is 0.2 to 2 μm.

  A transparent conductive film can be used for the anode 6010. In addition to ITO, a transparent conductive film in which indium oxide is mixed with 2 to 20% zinc oxide (ZnO) may be used. In FIG. 6, ITO is used as the anode 6010. The cathode 6012 can be formed using other known materials as long as the conductive film has a low work function. For example, Ca, Al, CaF, MgAg, AlLi, etc. are desirable.

  Note that FIG. 6 illustrates a structure in which light emitted from the light-emitting element is irradiated to the substrate 6000 side; however, a light-emitting element having a structure in which light is directed to the side opposite to the substrate may be used. In FIG. 6, the transistor 6002 and the anode 6010 of the light-emitting element are connected, but the present invention is not limited to this structure, and the transistor 6002 and the cathode 6001 of the light-emitting element may be connected. In this case, the cathode is formed on the third interlayer insulating film 6008. And it forms using TiN etc.

  Actually, when completed up to FIG. 6, packaging with a protective film (laminate film, ultraviolet curable resin film, etc.) or a translucent cover material that is highly airtight and less degassed so as not to be exposed to the outside air ( (Encapsulation) is preferable. At that time, if the inside of the cover material is made an inert atmosphere or if a hygroscopic material (for example, barium oxide) is arranged inside, the reliability of the OLED is improved.

  Note that although a light-emitting device is described as an example of a semiconductor device in this embodiment, a semiconductor device formed using the manufacturing method of the present invention is not limited thereto.

The figure which shows the magnitude relationship of a beam spot. The figure which shows the structure of the laser irradiation apparatus of this invention. The figure which shows the scanning path | route of a to-be-processed object in the laser irradiation method of this invention. 10A and 10B illustrate a method for manufacturing a semiconductor device. The figure which shows the structure of the laser irradiation apparatus of this invention. Sectional drawing of the light-emitting device produced using the laser irradiation apparatus of this invention. The figure which shows the shape of the beam spot used in the laser irradiation apparatus shown in FIG. The figure which shows the relationship between the wavelength of a laser beam, and an absorption coefficient.

Claims (3)

A semiconductor film formed on a glass substrate is irradiated with a pulsed first linear laser beam having a harmonic of 532 nm and a continuously oscillating second linear laser beam having a fundamental wave of 1064 nm. When doing
While overlapping the beam spot formed on the surface of the semiconductor film by the first linear laser beam and the beam spot formed on the surface of the semiconductor film by the second linear laser beam, the semiconductor film And relatively moving the first linear laser beam and the second linear laser beam,
In the semiconductor film, a molten state of a portion melted by the first linear laser beam is maintained by the second linear laser beam, and crystal growth is performed in the relative movement direction. A method for manufacturing a crystalline semiconductor film. In claim 1,
The method for manufacturing a crystalline semiconductor film, wherein the first linear laser beam is oscillated from a laser oscillator using a YAG laser, a Y ₂ O ₃ laser, a YVO ₄ laser, or a YAlO ₃ laser . In claim 1 or claim 2,
The method for manufacturing a crystalline semiconductor film, wherein the second linear laser beam is oscillated from a laser oscillator using a YAG laser, a Y ₂ O ₃ laser, a YVO ₄ laser, or a YAlO ₃ laser .

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