TWI521607B - Fabricating method of crystalline semiconductor and laser annealing apparatus - Google Patents

Description

Method for producing crystalline semiconductor and laser annealing device

The present invention relates to the manufacture of a crystalline semiconductor suitable for use in the fabrication of polycrystalline or single crystal semiconductor films for thin film transistors in pixel switches or drive circuits for liquid crystal displays or organic electroluminescent (EL) displays. Method and laser annealing device.

A thin film transistor used in a pixel switch or a driving circuit of a liquid crystal display or an organic EL display is subjected to laser annealing using laser as a part of a manufacturing method of a low temperature process. This method is the following method. The non-single-crystal semiconductor film molded on the substrate is irradiated with a laser, and the non-single-crystal semiconductor film is locally heated and melted, and then the semiconductor thin film is crystallized into a polycrystal or a single crystal during cooling. Since the mobility of the carrier in the crystallized semiconductor thin film is improved, the performance of the thin film transistor can be improved.

In the irradiation of the above laser, it is necessary to perform a homogeneous treatment on the semiconductor thin film. In order for the irradiated laser to have a stable illumination energy, it is generally controlled to control the laser output energy to a fixed value. For pulsed lasers, the pulse energy is controlled to a fixed value.

However, excimer gas lasers commonly used in the above-described pulsed lasers oscillate laser light by means of discharge. For a high output energy excimer gas laser, after a first high voltage discharge, multiple discharges due to residual voltage are generated, resulting in the generation of laser light having a plurality of peaks. At this point, the second and subsequent peaks may differ from the first peak characteristics. Therefore, the following pulsed laser oscillating device is proposed: finding a pulse wave of a pulsed laser The ratio of the plurality of maximum values in the shape is set to a predetermined range to keep the characteristics of the crystallization enthalpy fixed (see Patent Document 1).

In the pulsed laser vibration device, the time-varying waveform of the pulsed laser beam includes two or more peak groups, wherein the pulse cluster of the second peak group is compared with the pulsed laser beam group of the first peak group The peak ratio of the beam is set in the range of 0.37 to 0.47.

[Previous Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2001-338892

In the apparatus described in Patent Document 1 described above, the peak ratio is set to be in a stable range, whereby the characteristics of the crystallized crucible are kept constant. However, even if the peak ratio is stabilized within the above range, there is a problem that crystallization and activation of the ruthenium film are inevitably caused to be uniform in the surface of the ruthenium film.

As a result of verifying the above-described peak ratio, the inventors have found that the value of the peak ratio itself contributes more to the crystallization characteristics uniformity than the stabilization of the peak ratio, and the present invention has been completed.

In other words, in the method for producing a crystalline semiconductor according to the present invention, when the amorphous semiconductor is irradiated with a pulsed laser to crystallize the amorphous semiconductor, the pulsed laser has a plurality of peaks in one pulse in a change in intensity with time. In the group, when the amorphous semiconductor is irradiated, the first peak group having the maximum height and the peak intensity value of the second peak group appearing later in the peak group satisfy the (second peak group) / (first peak group) ≦ 0.35 relationship.

Further, the laser annealing apparatus of the present invention includes a laser oscillator that outputs a pulsed laser; an optical system that guides the pulsed laser to an amorphous semiconductor; and a moving device for causing the pulsed laser to the amorphous semiconductor The amorphous semiconductor is relatively moved by scanning and irradiating, wherein the pulse laser outputted by the laser oscillator has a plurality of peak groups in one pulse due to a change in intensity with time, and the peak group has the largest The peak intensity group of the height of the first peak group and the second peak group that appears later satisfy the relationship of (second peak group) / (first peak group) ≦ 0.35.

According to the present invention, since the peak intensity ratio satisfies the above relationship, uniform crystallization characteristics can be obtained when the amorphous semiconductor irradiated by the pulsed laser is crystallized. If the ratio exceeds 0.35, the characteristics of the crystallized semiconductor become uneven.

A peak group may have multiple peaks, and the maximum height in the peak group may represent the peak intensity corresponding to the peak group. In a general excimer laser, a relatively high height of the first peak group occurs at the beginning, and after a very small decrease in intensity (about a fraction of the maximum height), a relatively low height occurs. 2 crest groups, and have two large crest groups. However, a group in which three or more peak groups appear in one pulse can also be used as the present invention.

In addition, one pulse may be outputted by one laser oscillator, or one pulse of two or more laser oscillator outputs may be superposed.

The pulsed laser described above must satisfy the above-described peak intensity ratio at the output from the laser oscillator. Multiple pulses in one pulse due to changes in intensity over time In the case of a crest group, it is generally impossible to adjust the height of each crest group individually. Therefore, at least the peak intensity ratio satisfies the peak intensity ratio when outputting from the laser oscillator. In addition, the pulsed laser changes the laser waveform by the optical system, and the maximum height of the pulsed laser may be lowered. At this time, since the intensity of the first peak group is lowered, the peak intensity ratio tends to become large. Therefore, when the peak intensity ratio is changed by the optical path, the pulse intensity of the pulse laser emitted from the laser oscillator is made such that the peak intensity ratio of the pulse laser when the amorphous semiconductor is irradiated satisfies the above condition. The ratio is 0.35 or less and is a value (smaller value) for predicting the above change.

The output of the pulsed laser is preferably a pulse energy of 700 mJ or more, and more preferably 850 mJ. When the output of the pulse energy is small, the peak intensity ratio tends to be small, but in the low pulse energy, the adjustment range of the attenuator disposed in the optical path to adjust the transmittance of the laser becomes small.

In the present invention, as the amorphous semiconductor, an amorphous germanium film formed on a substrate is suitable. The substrate is usually a glass substrate. However, the material of the substrate in the present invention is not particularly limited, and may be other materials. The amorphous germanium film is usually formed to have a thickness of 40 nm to 100 nm, but the thickness of the present invention is not particularly limited.

Further, a quasi-molecular laser having a wavelength of 308 nm is preferably cited as a pulsed laser. However, the type of the pulse laser of the present invention is not limited to this.

As described above, according to the present invention, when the amorphous semiconductor is crystallized by irradiating a pulsed laser with an amorphous semiconductor, the pulsed laser has a plurality of peak groups in one pulse in the change with time intensity, and the amorphous When the semiconductor is irradiated, the first peak group having the maximum height among the peak groups is Since the peak intensity value of the second peak group that appears later satisfies the relationship of (second peak group) / (first peak group) ≦ 0.35, it has an effect of obtaining a uniform crystalline semiconductor.

The above described features and advantages of the present invention will be more apparent from the following description.

Hereinafter, an embodiment of the present invention will be described with reference to Fig. 1 .

In the method for producing a crystalline film of the present embodiment, a substrate 8 for use in a flat-panel thin film transistor (TFT) device is formed, and an amorphous germanium film 8a as an amorphous film is formed on the substrate 8. . The amorphous tantalum film 8a is formed on the upper layer of the substrate 8 in a general manner and subjected to dehydrogenation treatment.

However, the present invention is not limited to the type of the substrate 8 to be targeted and the amorphous film formed on the substrate 8.

Fig. 1 shows an excimer laser annealing treatment apparatus 1 used in a method for producing a crystalline film according to an embodiment of the present invention. This excimer laser annealing treatment apparatus 1 corresponds to the laser annealing apparatus of the present invention.

In the excimer laser annealing treatment device 1, an excimer laser oscillator 2 is provided on the vibration removing table 6, and the excimer laser oscillator 2 can output a wavelength of 308 nm, a pulse frequency of 1 Hz to 600 Hz, and a pulse width (full width at Half maximum, FWHM) 20 ns to 50 ns pulsed laser. The excimer laser oscillator 2 has a control circuit 2a that generates a pulse signal.

Further, as shown in FIG. 2, the pulse output from the excimer laser oscillator 2 is laser-pulled at 1 pulse, has two peak groups A, B in time variation, and is relative to the first peak group A having the maximum height. Peak intensity a, The peak intensity b of the peak group B satisfies the condition that b/a is less than 0.35. Since it is not possible to form only the second after-peak and the first peak separately, and it is impossible to control the peak after the second one, it is necessary to output a pulse laser having a lower peak intensity after the second. The pulse laser waveform can be set by the design of the laser oscillation circuit, the energy setting of the laser oscillator, or the gas mixture ratio of the excimer gas laser.

The excimer laser oscillator 2 described above corresponds to the laser oscillator of the present invention.

The output side of the excimer laser oscillator 2 is provided with an attenuator 3, and the output side of the attenuator 3 is connected to the optical fiber 5 via the combiner 4. The optical end of the optical fiber 5 is connected to the optical system 7. The optical system 7 includes condensing lenses 70a, 70b and beam homogenizers 71a, 71b and the like. The beam homogenizers 71a and 71b are disposed between the condenser lenses 70a and 70b. In addition to this, the optical system 7 may also include suitable optical components such as mirrors. The present invention is not particularly limited to members in an optical system, and an optical system can be constructed by a suitable optical member. In addition to guiding the pulsed laser, the optical system 7 can modulate the pulsed laser into a suitable laser shape.

The substrate stage 9 on which the substrate 8 is placed is provided in the emission direction of the optical system 7. The optical system 7 is configured to shape a pulsed laser into a rectangular or linear beam shape by the shape of the irradiation surface. The substrate mounting table 9 is movable along the surface direction (XY direction) of the substrate mounting table 9 and has a moving device 10 that moves the substrate mounting table 9 at a high speed in the surface direction.

Next, a method of crystallizing the amorphous tantalum film using the above excimer laser annealing treatment apparatus 1 will be described.

First, the substrate 8 on which the amorphous germanium film 8a is formed is placed on the substrate mounting table 9.

The control circuit 2a generates a pulse signal by outputting a pulse laser of the pulse energy of a predetermined pulse frequency (1 Hz to 600 Hz) and a pulse width (FWHM) of 20 ns to 50 ns. A pulsed laser having a wavelength of 308 nm is output by the excimer laser oscillator 2 based on the pulse signal.

When the pulsed laser output from the excimer laser oscillator 2 reaches the attenuator 3, it is attenuated to a predetermined attenuation rate by passing through the attenuator 3. The attenuation rate is set such that the processing surface causes the pulsed laser to become a predetermined energy density. The attenuator 3 can also vary the attenuation rate.

The pulsed laser whose energy density is adjusted is introduced into the optical system 7 by the optical fiber 5. In the optical system 7, as described above, the pulse laser is shaped into a rectangular or linear beam shape having a short-axis width of 1.0 mm or less by the condenser lenses 70a and 70b, the beam homogenizers 71a and 71b, and the like, and is directed toward the substrate 8. The machined surface is illuminated at a predetermined energy density. In addition, the pulsed laser has two peak groups that change with time in the same manner as the output, and the peak intensity ratio is calculated in the machined surface (the peak intensity of the second peak group) / (the peak intensity of the first peak group) It is 0.35 or less.

The substrate stage 9 is moved by the moving device 10 along the surface of the amorphous germanium film 8a in the direction of the minor axis width of the line beam. Therefore, on the wide area of the surface of the amorphous tantalum film 8a, the above-described pulsed laser is relatively scanned and simultaneously irradiated.

By the irradiation of the pulsed laser light, only the amorphous germanium film 8a on the substrate 8 is heated, and the amorphous germanium film 8a is polycrystallized in a short time.

The crystalline thin film obtained by the above irradiation has a uniform crystallinity of an average crystal grain size of about 350 nm and uniformity. The above crystalline film is suitable for use in an organic EL display. However, the use of the present invention is not limited thereto, and it can also be utilized for other liquid crystal displays or electronic materials.

However, in the above embodiment, the pulsed laser light is relatively scanned by moving the substrate stage, but the optical system for guiding the pulsed laser light can be moved at a high speed to relatively scan the pulsed laser light.

[Example 1]

Examples of the invention are described below.

The output energy (1050 mJ, 950 mJ, 850 mJ) was changed using the same laser oscillator, and the pulse waveform at the time of outputting the pulse laser was shown in FIG. This waveform is a waveform corresponding to the position amount side of the amorphous tantalum film 8a on the substrate 8. Its intensity is expressed as a relative value.

The pulse waveform has a first peak group A and a second peak group B that appears later. When the output energy of the pulsed laser is large (1050 mJ), the maximum height of the first peak group increases as the output energy of the pulsed laser increases, and the height of the second peak group also increases. When the peak intensity of the first peak group is regarded as a and the peak intensity of the second peak group is regarded as b, b/a is 0.418. When the output energy of the pulsed laser is made smaller than the output energy of the above-described pulsed laser (950 mJ), the above ratio becomes 0.374.

As described above, when a pulsed laser having a peak intensity ratio of more than 0.35 is irradiated to the tantalum film, the intensity of the second peak group is relatively high, and the tantalum film is twice dissolved. In other words, when the ruthenium film is melted by the first peak and the ruthenium is crystallized from the liquid to the solid, if the strength of the second peak is high, The solidified ruthenium film is again melted to cause recrystallization. This phenomenon causes unevenness in the tantalum film and impairs the uniformity of crystallization.

In Fig. 2, when the output energy of the pulsed laser is further decreased (850 mJ), the ratio becomes smaller than 0.35. The tantalum film will crystallize evenly.

Next, the pulse laser having the peak intensity ratio of 0.374 (comparative example) and the peak intensity ratio of 0.341 (invention example) was irradiated onto the tantalum film by the energy density (E/D) shown in FIG. 3 to be crystallized. A photograph of a scanning electron microscope (SEM) of the obtained polycrystalline germanium film (magnification: 5000 times; instead of a photograph) is shown in FIG.

Although the crystallinity is changed depending on the magnitude of the energy density irradiated on the substrate, it is known that the second peak is compared with the polycrystalline germanium film (comparative example) after the laser pulse having a large intensity of the second peak. The polycrystalline germanium film (inventive example) after the laser pulse having a small intensity is obtained to obtain uniform crystals.

Further, the test material was irradiated by changing the angle of the white light from the oblique direction, and the occurrence of unevenness in irradiation was visually observed. For the energy density as a result of observation invention 337mJ / cm ² and Comparative Example as the energy density of 333mJ / cm ² are shown in FIG. 4. As clearly shown in Fig. 4, in the invention example in which the crystallization was uniform, no unevenness in irradiation was observed regardless of the change in the irradiation angle, but unevenness in irradiation was observed in the comparative example. From this, the crystallization unevenness in the comparative example was known. However, the unevenness of the irradiation was not observed in the inventive materials other than the drawings, and the unevenness of the irradiation was observed in the same manner as described above in the comparative examples.

Although the invention has been disclosed above by way of example, it is not intended to be limiting The scope of the present invention is defined by the scope of the appended claims, and the scope of the invention is defined by the scope of the appended claims. Prevail.

1‧‧‧Excimer laser annealing treatment device

2‧‧‧Excimer laser oscillator

2a‧‧‧Control circuit

3‧‧‧Attenuator

4‧‧‧ combiner

5‧‧‧Fiber

6‧‧‧ Vibration removal table

7‧‧‧Optical system

8‧‧‧Substrate

8a‧‧‧Amorphous film

9‧‧‧Substrate mounting table

10‧‧‧Mobile devices

70a, 70b‧‧‧ concentrating lens

71a, 71b‧‧‧ Beam homogenizer

A‧‧‧The first peak group

B‧‧‧Second peak group

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a laser annealing apparatus according to an embodiment of the present invention.

Fig. 2 is a view showing a pulse waveform of a pulse laser in an embodiment of the present invention.

Fig. 3 is a view showing an SEM photograph of each energy density in an embodiment of the present invention.

Fig. 4 is a schematic view showing a polycrystalline germanium film showing uneven irradiation in an embodiment of the present invention.

A‧‧‧The first peak group

B‧‧‧Second peak group

Claims (2)

A method for producing a crystalline semiconductor, comprising: an amorphous semiconductor formed on a substrate; an amorphous semiconductor having a metal film formed between the substrate and the amorphous semiconductor; and a metal film not formed When the amorphous semiconductor is crystallized by the irradiation of the pulsed laser, the pulsed laser has a plurality of peak groups in one pulse during the change in intensity with time, and when the amorphous semiconductor is irradiated, In the peak group, the peak intensity group having the maximum height and the peak intensity group of the second peak group appearing later satisfy the relationship of (second peak group) / (first peak group) ≦ 0.35. A laser annealing device comprising: a laser oscillator, outputting a pulsed laser; an optical system for guiding the pulsed laser to an amorphous semiconductor formed on an amorphous germanium film on a substrate (the substrate and the amorphous semiconductor Except for an amorphous semiconductor having a region in which a metal film is formed and a region in which a metal film is not formed; and a moving device that causes the pulsed laser to scan and irradiate the amorphous semiconductor to cause the non- The crystal semiconductor is relatively moved, wherein the pulse laser outputted by the laser oscillator has a plurality of peak groups in one pulse in accordance with a change in intensity over time, and the peak group has the largest amplitude when irradiated to the amorphous semiconductor. The peak intensity group of the height of the first peak group and the second peak group that appears later satisfy the relationship of (second peak group) / (first peak group) ≦ 0.35.