JP3289681B2 - Method for forming semiconductor thin film, pulsed laser irradiation device, and semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for driving elements or driving circuits such as displays and sensors.
For example, the present invention relates to a method for forming a silicon thin film of a crystalline silicon thin film transistor and a pulse laser irradiation apparatus.
Further, the present invention relates to a semiconductor device including such a semiconductor thin film.

[0002]

2. Description of the Related Art A thin film transistor (TF) is formed on a glass substrate.
As typical techniques for forming T), a hydrogenated amorphous semiconductor TFT technique and a polycrystalline silicon TFT technique are known. In the hydrogenated amorphous semiconductor TFT technology, the maximum temperature during the manufacturing process is about 300 ° C., and a carrier mobility of about 1 cm ² / Vsec is realized. In the polycrystalline silicon TFT technology, for example, using a quartz substrate and using a high-temperature process similar to that of an LSI at about 1000 ° C., a carrier mobility of 30 to 1 is used.
A performance of 00 cm ² / Vsec has been obtained. In TFT technology that can realize these high carrier mobilities,
For example, in the case of application to a liquid crystal display, the peripheral drive circuit section can be simultaneously formed on the same glass substrate together with the pixel TFT for driving each pixel, so that the formation process cost can be reduced and the size can be reduced. There is an advantage that you can.

Incidentally, hydrogenated amorphous semiconductor TF
In the case of the T technique, since the highest manufacturing process temperature is as low as about 300 ° C., an inexpensive low softening point glass can be used.
Because of the high temperature process of ° C, such inexpensive low softening point glass cannot be used. Therefore, for the purpose of lowering the temperature of the process, research and development of a low-temperature formation technique of a polycrystalline silicon film using a laser crystallization technique have been conducted.

FIG. 17 shows a schematic configuration of a conventional pulsed laser irradiation apparatus for realizing low-temperature formation of a polycrystalline silicon film using a laser crystallization technique. In this pulse laser irradiation apparatus, a laser beam supplied from a pulse laser light source 11 is an optical path defined by three mirrors 12 and an optical element group such as a beam homogenizer 14 installed to make spatial intensity uniform. 17, the light reaches the silicon thin film 16 on the glass substrate 15 which is the irradiation object.

[0005] In the case of this pulse laser irradiation apparatus, since one irradiation range is small, an arbitrary position on the substrate can be irradiated with laser light by moving the glass substrate on the xy stage 17. Further, the glass substrate with the silicon thin film accommodated in the cassette is transferred onto the xy stage 17 and the glass substrate 15 on the xy stage 17 is moved.
Is mechanically performed by the substrate transfer mechanism.

In the above-described pulse laser irradiation apparatus, a part of the irradiation system or a whole optical system may be moved instead of the xy stage 17. Further, it is also possible to combine a movable optical element group and a stage. Further, the laser irradiation may be performed in a vacuum chamber or in a high-purity gas atmosphere in a vacuum chamber.

[0007] As a laser crystallization technique, a method of irradiating a plurality of pulses with a certain delay time is disclosed in "Ryoichi.
Ishihara et al. “Effects of light pulse duration
on excimer laser crystallization characteristics o
f silicon thin films ”, Japanese journal of applie
d physics, vol. 34, No. 4A, (1995) pp1759 ". According to this known document, the crystallization solidification rate of molten silicon in the laser recrystallization process is 1 m / s.
ec, and it is stated that the solidification rate must be reduced in order to obtain good crystal growth. Specifically, immediately after the solidification of the molten silicon in the irradiation process of the first laser pulse is completed, the second laser pulse is irradiated, and the second irradiation causes recrystallization with a lower solidification rate. It is disclosed to obtain a process.

[0008]

As described above, it is necessary to reduce the solidification rate in order to obtain good crystal growth. For this reason, conventionally, the irradiation of the second laser pulse requires a low solidification rate. A method of obtaining a crystallization process has been adopted. However, this conventional method has the following problems because it does not consider excessive supercooling in the melting and recrystallization process.

FIG. 8 shows a temperature change (time history curve) of crystallization and solidification of molten silicon in the laser recrystallization process when the starting material is a-Si. Referring to the temperature change shown in FIG. 8, the temperature of silicon increases with the irradiation of the laser energy, and further increases after the melting point a of a-Si. Then, when the supply of energy by laser irradiation falls below a value required for temperature rise, cooling starts. In this cooling process, at the solidification point b of the crystal Si, solidification is completed after a solidification time t, and thereafter, the crystal Si is cooled to the ambient temperature. The average value of the solidification rate in this case is represented by the following equation.

From the above equation, if the silicon film thickness is constant, it is effective to increase the solidification time to reduce the solidification rate. I understand. Therefore, if the process maintains an ideal state of thermal equilibrium, the solidification time can be extended by increasing the laser irradiation energy.

However, as pointed out in the above-mentioned known documents, an increase in irradiation energy causes the film to become amorphous and microcrystalline. In a practical melting / recrystallization process, an ideal temperature change as shown in FIG. 8 is not exhibited, and a stable state is reached through a temperature overheating process during heating and a supercooling process during cooling. In particular, when the cooling rate at the time of cooling is high and excessive supercooling is performed, an amorphous solid is formed by cooling and solidifying without crystallization near the freezing point. In addition, in the formation of a thin film, as described in the above-mentioned known literature, a microcrystalline body may be formed instead of an amorphous state depending on conditions. Since this microcrystal has a smaller grain size than a polycrystalline thin film or a single crystal thin film, there are many crystal grain boundaries having a large grain boundary potential,
For example, when applied to a thin film transistor, the on-current decreases,
Alternatively, the off-leak current increases.

An object of the present invention is to provide a semiconductor capable of forming a crystalline silicon thin film through a melting and recrystallization process which is closer to an ideal thermal equilibrium process without causing the above-mentioned amorphization or microcrystallization. An object of the present invention is to provide a method for forming a thin film and a pulsed laser irradiation apparatus.

A further object of the present invention is to provide a semiconductor device having a semiconductor thin film formed by the method for forming a semiconductor thin film.

[0014]

A method for forming a semiconductor thin film according to the present invention is a method for forming a semiconductor thin film containing silicon as a main component, the method comprising at least one melting and solidification process by light irradiation energy. The maximum cooling rate in the final solidification process is set to 1.6 × 10 ¹⁰ ° C./sec or less.

In the above case, the melting and solidifying step includes a first melting and solidifying step by irradiating a first pulse light and a second melting and solidifying step by irradiating a second pulse light whose light intensity is smaller than that of the first pulse light. And the irradiation of the second pulsed light is performed after the temperature of the semiconductor thin film reaches the maximum temperature in the first melt-solidification process and before the solidification is completed. It may be.

In the above case, the first and second pulse lights may reach the maximum light emission intensity within 50 nsec from the start of light emission, and the light emission time may be 100 nsec or more.

Further, the first and second pulsed lights are:
The pulse waveform may have a plurality of peaks.

The first pulsed laser irradiation apparatus of the present invention comprises:
Formed on an insulating substrate or an insulating thin film, silicon and Rupa Rusureza source to irradiate a semiconductor thin film mainly, the pulsed light emitted from the pulsed laser light source into first and second pulsed light Dividing means for dividing,
The second pulse light is configured to be irradiated after the temperature of the semiconductor thin film reaches a maximum temperature in a melting and solidifying process by irradiation of the first pulse light and before the solidification is completed. And the second pulsed light
The maximum cooling rate in the heating-cooling process depends on the first
Maximum cooling rate obtained from the heating-cooling process using only lusic light
It is characterized by being controlled to be smaller than

In the above case, a filter means may be provided in the optical path of the second pulsed light so that the light intensity is smaller than that of the first pulsed light.

It is preferable that the pulsed light supplied from the pulsed laser light source reaches the maximum light emission intensity within 50 nsec from the start of light emission, and the light emission time is 100 nsec or more.

According to the second pulse laser irradiation apparatus of the present invention, the first and second pulse laser light sources for irradiating a semiconductor thin film containing silicon as a main component formed on an insulating substrate or an insulating thin film are provided. The temperature of the semiconductor thin film reaches a maximum temperature in a melting and solidifying process by irradiation of pulsed light emitted from the first pulsed laser light source, and the second solidifying is performed until the solidification is completed. The pulsed light emitted from the pulsed laser light source is configured to be irradiated, and the pulsed light is emitted from the second pulsed laser light source.
The maximum cooling rate in the heat-cooling process is
The maximum cooling obtained from the heating-cooling process using only the laser light source
It is controlled so as to be lower than the reject speed .

In the above case, the detecting means for detecting the pulsed light emitted from the first pulsed laser light source, and the light emission of the first and second pulsed laser light sources based on the detection timing of the detecting means. Further comprising a light emission control means for controlling, the light emission control means, after the temperature of the semiconductor thin film reaches the highest temperature in the melting and solidification process by irradiation of pulse light emitted from the first pulse laser light source, Until the solidification is completed, the pulse light emitted from the second pulse laser light source may be controlled to be irradiated.

In the above case, it is preferable that the pulse light supplied from the second pulse laser light source has a light intensity smaller than that of the pulse light supplied from the first pulse laser light source. Further, the first and second
The pulse light supplied from the pulse laser light source reaches the maximum light emission intensity within 50 nsec from the start of light emission, and
It is desirable that the light emission time be 100 nsec or more.

A semiconductor device according to the present invention is characterized in that a semiconductor thin film formed by any one of the above-described methods for forming a semiconductor thin film is provided on an insulating substrate or an insulating thin film. (Operation) As shown in FIG. 16, the solidification process is repeated again by inputting additional energy, and amorphousization and microcrystallization by rapid cooling in the previous solidification process are once initialized. This re-solidification process occurs because the energy input before is preserved (this storage is a short time of the order of nanoseconds, so there is little effect of heat conduction to the substrate and radiation to the atmosphere). it is conceivable that. Also, as can be seen from FIG. 16, the cooling rate in the solidification process due to the additional energy input is lower than the cooling rate in the solidification process before that. Therefore, good crystal growth can be expected by paying attention to the cooling rate after the end of the secondary heating by the re-input energy.

As described above, since the cooling process before that is initialized by the finally input energy, the cooling rate in the final solidification process governs the crystallization. As will be described in detail later, the maximum cooling rate in the final solidification process is 1.
It has been experimentally found that good crystallization can be obtained at a temperature of 6 × 10 ¹⁰ ° C./sec or less. In the present invention,
The maximum cooling rate in the final solidification process is 1.6 × 10
^{Since the} temperature is controlled to ¹⁰ ° C./sec or less, no amorphization or microcrystallization occurs.

[0026]

Next, embodiments of the present invention will be described with reference to the drawings.

<First Embodiment> FIG. 2 shows an emission pulse waveform of a pulse laser beam used in this embodiment. This emission pulse waveform has three main peaks, and the emission time is about 1
20 nsec. This light emission pulse waveform is a laser light emission pulse (with a pulse width of 21.m) described in the above-mentioned known document.
Since the light emission time is five times or more longer than that of a 4 nsec rectangular pulse, the solidification rate as described in the above-mentioned known document can be reduced even with single pulse irradiation.

A XeCl laser (wavelength: 308 nm) having an emission pulse waveform as shown in FIG. 2 is irradiated at an irradiation intensity of 450 mJ / cm ² onto an SiO ₂ substrate having a silicon film having a thickness of 75 nm formed on the substrate surface. FIG. 3 shows a temperature-time curve of silicon obtained from a numerical calculation at the time of laser recrystallization in the case of performing the above. In FIG. 3, the solid line is the temperature of the silicon thin film, the broken line is the substrate temperature about 100 nm below the silicon / substrate interface, and the dashed line is about 1 μm from the silicon / substrate interface.
The lower substrate temperature is shown.

Referring to FIG. 3, the temperature of the silicon thin film reaches the maximum temperature about 60 nsec after the second emission peak is almost finished, and the process shifts to the cooling process. However, in this numerical calculation, the value of amorphous silicon is used as the melting and freezing point, and the behavior near the freezing point is different from the actual one. In particular, when a crystallized film is obtained, crystallization is completed at the freezing point of crystalline silicon.

When the temperature reaches the maximum temperature and the cooling process starts, the temperature-time curve starts cooling once with a large slope, but the slope of the temperature-time curve is around 100 nsec where the third peak exists. Very small. After 120 nsec when the light emission completely ends, the solidification is again performed through a rapid cooling process.

In general, in the case of a solidification process from a liquid which has undergone "quenching" which greatly deviates from the thermal equilibrium process, a sufficient solidification time required for forming a crystal structure cannot be obtained. In some cases, microcrystallization occurs. Hereinafter, the relationship between the amorphization, microcrystallization, and irradiation energy will be described.

The maximum cooling rate after the end of light emission obtained from the temperature change curve of the silicon thin film shown in FIG.
FIG. 1 shows the relationship with the irradiation intensity of the Cl laser. This figure 1
From this, it can be seen that the maximum cooling rate after the end of light emission increases as the irradiation intensity increases. FIG. 4 shows that the irradiation intensity of the XeCl laser was 339 mJ / cm ² , 424 mJ / cm ² , 4
Photographs obtained by observing the structure of the silicon thin film after laser irradiation using a scanning electron microscope when the laser irradiation was changed to 70 mJ / cm ² , where (a) to (c) show one shot (one irradiation pulse). , (D) to (f) show the case of three shots (the number of irradiation pulses is three).

As can be seen from FIG. 4, in the case of one shot, although the particle size increases once with the increase in irradiation intensity, microcrystallization occurs under the set irradiation intensity condition of about 470 mJ / cm ² . On the other hand, in the case of three shots, even under the set irradiation intensity condition of about 470 mJ / cm ² , although the microcrystallized region partially remains, unlike the case of one shot, the particle size is dramatically increased. Is recognized. Here, the actual irradiation intensity is about 5 to 10% higher than the set value, especially in the first few pulses of the excimer laser, so that the threshold intensity at which microcrystallization occurs is 500 mJ / c.
m ² can be estimated.

By applying the above results to the relationship between the maximum cooling rate and the irradiation intensity shown in FIG. 1 and estimating the cooling rate at which microcrystallization occurs under the condition of 500 mJ / cm ² , the microcrystallization is about 1.6 × 10 It can be seen that this occurs at a cooling rate condition of ¹⁰ ° C./sec or more. When the film to be irradiated is a-Si, microcrystallization occurs at an irradiation intensity of about 500 mJ / cm ² or more. When the film to be irradiated is poly-Si, the cooling rate is 1. applying 6x10 ¹⁰ ℃ / sec, microcrystallization occurs at an irradiation intensity of about compared to 500mJ / cm ² 30mJ / cm ² large 530mJ / cm ² in the case of a-Si.

From the above, the cooling rate is set to 1.6.
By controlling the following x ¹⁰ 10 ℃ / sec, microcrystalline, can prevent amorphous, it is possible to obtain a good crystal growth process.

<Second Embodiment> Here, a description will be given of a cooling rate that can prevent microcrystallization and amorphization when the number of irradiation pulses is two (first pulse and second pulse).

(1) Relationship between delay time of second pulse and maximum cooling rate and minimum cooling rate: The irradiation intensity of the first pulse is 450 mJ / cm ^2, and the irradiation intensity of the second pulse is 1
50 mJ / cm ^2, and the delay time of the second pulse with respect to the first pulse is 100, 200, and 300 nsec, respectively.
The calculation results of the temperature-time change curve in the case of
FIG. 5-7, the solid line indicates the temperature of the silicon thin film, the broken line indicates the substrate temperature about 100 nm below the silicon / substrate interface, and the dashed line indicates the substrate temperature about 1 μm below the silicon / substrate interface. Here, the thickness of the silicon layer is set to 75 nm, amorphous silicon is used as a material condition used for calculation, and a material constant of silicon dioxide is used for the substrate. Also, as shown in FIG. 8 described above, the cooling process after the completion of the total energy irradiation, which is defined in the same manner as the maximum cooling speed obtained from the portion having the largest inclination and the minimum cooling speed obtained from the portion having the smallest inclination. FIG. 9 shows the relationship between the maximum cooling speed and the minimum cooling speed in the above and the delay time of the second pulse.

As can be seen from FIG. 9, the maximum cooling rate in the cooling process after the irradiation of the second pulse is as follows.
The cooling rate is lower than the maximum cooling rate in the cooling process when irradiation is performed under the pulse condition (the condition without the second pulse irradiation, that is, the condition with only the first pulse). The minimum cooling rate in the cooling process after the irradiation of the second pulse has a minimum value when the delay condition of the second pulse is about 100 to 200 nsec.
Beyond this delay condition, the minimum cooling rate will increase again. The increase in the minimum cooling rate with the increase in the delay time is as follows. In other words, an increase in the delay time causes an increase in the energy transfer time, that is, an increase in the amount of energy deprived to the substrate. become.

(2) Relationship between the irradiation intensity of the second pulse and the maximum cooling rate: The irradiation intensity of the first pulse was set to 450 mJ / cm.
² and the delay time of the second pulse with respect to the first pulse is 2
00 nsec, and the irradiation intensity of the second pulse is 1
00 mJ / cm ² , 50 mJ / cm ² , 25 mJ / cm
FIGS. 10 to 12 show the calculation results of the temperature-time change curves when changing to ² . In each of FIGS.
The solid line indicates the temperature of the silicon thin film, the broken line indicates the substrate temperature about 100 nm below the silicon / substrate interface, and the dashed line indicates the substrate temperature about 1 μm below the silicon / substrate interface. Here, the thickness of the silicon layer is set to 75 nm, and the material conditions used for the calculation are those of amorphous silicon.
The material constant of silicon dioxide is used for the substrate.

The maximum cooling rate in the cooling process after the completion of the total energy irradiation and the irradiation intensity of the second pulse, which are defined in the same manner as the maximum cooling rate obtained from the portion having the largest inclination as shown in FIG. Is shown in FIG.

Referring to FIG. 13, the maximum cooling rate in the cooling process after the irradiation of the second pulse is determined under the condition that the number of irradiation pulses is 1 (the condition without the second pulse irradiation, ie, the first cooling pulse).
The cooling rate is lower than the maximum cooling rate in the cooling process when irradiation is performed under the condition of only a pulse. In addition, the maximum cooling rate in the cooling process after the second pulse irradiation of each curve in FIGS. 10 to 12 is almost constant as shown in FIG. 13, and this gradually changes from rapid cooling to a gradual cooling process. 5 to 7 described above.

As can be seen from the relationships (1) and (2) described above, the maximum cooling rate in the cooling process after the irradiation of the second pulse is reduced as compared with the case where irradiation is performed only with the first pulse.

When the number of irradiation pulses is two as in the present embodiment, the cooling process based on the energy input before the irradiation of the second pulse, that is, the cooling process after the irradiation of the first pulse, is performed in the following manner. Since the irradiation is initialized by irradiation, the cooling rate in the cooling process after the irradiation of the second pulse controls the crystallization. Therefore, if the delay time of the second pulse and the irradiation intensity are set so that the cooling rate in the cooling process after the irradiation of the second pulse is reduced, good crystal growth can be obtained.

Further, in order to obtain better crystal growth, the first and second pulses are such that the pulse waveform as a whole reaches the maximum value of the light emission intensity within 50 nsec from the start of light emission, and The light emission time should be 100 nsec or more from the start. Then, after reaching the maximum attainment temperature in the melting and recrystallization by the first pulse irradiation, the second pulse light smaller than the irradiation intensity of the first pulse is set to be irradiated until the solidification is completed. It is desirable to do.

<Third Embodiment> Here, a description will be given assuming a normal distribution type emission pulse waveform. FIG. 14 shows a plot of the maximum cooling rate and the minimum cooling rate near the freezing point when a normally distributed light emission pulse is irradiated. The irradiation intensity of the pulse light is set to 600 m so that the complete melting does not occur as the pulse width increases.
J / cm ² . With this setting, 600 ns
Evaluation up to about c is possible.

Referring to FIG. 14, the half width of the pulse is 1
At about 00 nsec, a steep cooling state is observed. In this case, the maximum cooling rate exceeds 1.6 × ^{10 10} ° C./sec, and enters a region where microcrystallization occurs. When the half width of the pulse is longer than 100 nsec, the maximum cooling rate decreases and approaches the same value as the cooling rate near the freezing point. When the half width of the pulse becomes 600 nsec, the cooling rate further decreases to 1.0 × 10 ⁹ ° C./sec or less.

In the case of having a normal distribution type emission pulse waveform as in this embodiment, by increasing the half width, the increase in the cooling rate is reduced by the irradiation energy in the latter half of the pulse waveform. Therefore, also in the case of the present embodiment, similarly to the case of each of the above-described embodiments, the cooling process before that is initialized by the irradiation energy finally input,
The cooling rate after the end of the irradiation governs the crystallization. Therefore, the maximum cooling rate in the final solidification process is set to 1.0 × 10
^By controlling the temperature to ⁹ ° C./sec or less, good crystallization can be obtained.

As can be seen from the first to third embodiments described above, when a semiconductor thin film containing silicon as a main component is crystallized in at least one melting and solidifying process by light irradiation energy, the final solidifying process is performed. By setting the maximum cooling rate at 1.6 × 10 ¹⁰ ° C./sec or less, favorable crystal growth can be obtained.

When the number of irradiation pulses is two as in the second embodiment, the second pulse light is irradiated with the first pulse light so that its light intensity is smaller than that of the first pulse light. After the temperature of the semiconductor thin film reaches the maximum temperature in the melting and solidification process, the second
By irradiating pulsed light, better crystal growth can be obtained. In this case, it is desirable that the first pulse light and the second pulse light reach the maximum light emission intensity within 50 nsec from the start of light emission, and the light emission time is 100 nsec or more.

Further, if the pulse waveform has a plurality of peaks as described in the first embodiment, better crystal growth can be obtained.

<Pulse Laser Irradiation Apparatus> FIG. 15 shows an embodiment of a pulse laser irradiation apparatus to which the above-described method of forming a semiconductor thin film is applied. This laser irradiation device includes two pulse laser light sources 1a and 1b whose drive pulse waveforms are controlled by a light emission control device 2. Each pulse laser light source 1a, 1b reaches the maximum light emission intensity within 50 nsec from the start of light emission, and the light emission time is 100 nsec.
It is configured to emit the above pulse light. The pulse laser light source 1b has a smaller light intensity of the pulse light than the pulse laser light source 1a.

The laser light supplied from the pulse laser light source 1a is split by the half mirror 3, and the light reflected by the half mirror 3 is provided with a beam homogenizer 6 and mirrors 4a and 4a, which are installed to equalize the spatial intensity. The light reaches a silicon thin film 9 on a glass substrate 8 as an irradiation object through an optical path 7 defined by the optical element group 4b. The light transmitted through one half mirror 3 reaches the optical sensor 5.

The laser light supplied from the pulse laser light source 1b is reflected by the mirror 4c and reaches the half mirror 3, and passes through the half mirror 3 so that the laser light is transmitted along with the laser light supplied from the pulse laser light source 1a. 7 and reaches the silicon thin film 9. The optical sensor 5 detects a laser beam supplied from the pulse laser light source 1a and sends a detection signal to the light emission control device 2. Light emission control device 2
Causes the supply of the laser light from the pulse laser light source 1b to be delayed by a predetermined time from the time when the optical sensor 5 detects the laser light supplied from the pulse laser light source 1a.
Specifically, based on the detection timing of the optical sensor 5, the light emission control device 2 sets the temperature of the silicon thin film 9 after reaching the maximum temperature in the melting and solidifying process by irradiation of the pulsed light emitted from the pulsed laser light source 1a. The pulse light emitted from the pulse laser light source 1b is controlled so as to irradiate the silicon thin film 9 until the solidification is completed. Thereby, laser light irradiation corresponding to the formation of the semiconductor thin film as described above can be realized.

In the case of this laser irradiation apparatus, since the irradiation range is small, the xy stage 10 on which the glass substrate 8 is fixed
Is moved, an arbitrary position on the glass substrate 8 can be irradiated with laser light. Further, instead of the xy stage 10, the above-described optical element group can be moved, or the optical element group and the stage can be combined. Further, laser irradiation may be performed in a vacuum chamber or in a high-purity gas atmosphere in a vacuum chamber.

Further, if necessary, a cassette 11 containing a glass substrate with a silicon thin film and a substrate transport mechanism 12 are provided.
The transfer of the glass substrate with the silicon thin film stored in the cassette onto the xy stage 10 and the storage of the glass substrate on the xy stage 10 in the cassette 11 can also be performed mechanically by a substrate transfer mechanism.

As a method of controlling the delay, in addition to the above, the optical path length of the laser light supplied from the pulse laser light source 1b is changed (to be longer than the optical path length of the laser light supplied from the pulse laser light source 1a). It is also possible to do this.

When two light sources are used as in this embodiment, light sources having different pulse waveforms or light sources having similar pulse waveforms may be used.

Also, instead of using the two light sources as described above, the laser light supplied from one laser light source is divided into two and the optical path length of one laser light is changed. It is also possible to realize a device similar to the irradiation device. Specifically, assuming that the pulse is divided into the first pulse and the second pulse, the second pulse light is applied after the temperature of the semiconductor thin film reaches the maximum temperature in the melting and solidifying process by the irradiation of the first pulse light. Irradiation may be performed before solidification is completed. In this case, it is necessary to provide a filter in the optical path of the second pulsed light so that the light intensity is smaller than that of the first pulsed light.

[0059]

As described above, according to the present invention,
It is possible to provide a crystalline silicon thin film formed through a melt recrystallization process that is closer to an ideal thermal equilibrium process while preventing amorphization or microcrystallization in the laser recrystallization process.

Further, even on a glass substrate having a low softening point, crystalline silicon can be formed through a melting and recrystallization process closer to an ideal thermal equilibrium process.

Further, in a semiconductor device having a semiconductor thin film obtained according to the method of forming a semiconductor thin film of the present invention, for example, when applied to a thin film transistor, it is possible to prevent a decrease in on-current or an increase in off-leakage current. And a device having excellent operation stability can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the relationship between the maximum cooling rate after the end of light emission and the irradiation intensity of a XeCl laser.

FIG. 2 is a diagram showing a pulse waveform used in the method for forming a semiconductor thin film according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a temperature change of a silicon film when a pulse light having an irradiation intensity of 450 mJ / cm ² is irradiated.

FIG. 4 is a drawing-substitute photograph obtained by observing the structure of a laser recrystallized film using a scanning electron microscope, wherein (a) to (c) show one shot (one irradiation pulse number) and (d) ~
(F) shows a case of three shots (the number of irradiation pulses is three).

FIG. 5 shows that the irradiation intensity of the first pulse is 450 mJ / cm ² ,
FIG. 9 is a diagram illustrating a temperature change of the silicon film when the irradiation intensity of the second pulse is 150 mJ / cm ² and the delay time is 100 nsec.

FIG. 6 shows an irradiation intensity of a first pulse of 450 mJ / cm ² ,
FIG. 7 is a diagram showing a temperature change of a silicon film when the irradiation intensity of the second pulse is 150 mJ / cm ² and the delay time is 200 nsec.

FIG. 7 shows that the irradiation intensity of the first pulse is 450 mJ / cm ² ,
FIG. 9 is a diagram illustrating a temperature change of the silicon film when the irradiation intensity of the second pulse is 150 mJ / cm ² and the delay time is 300 nsec.

FIG. 8 is a diagram showing a temperature change of crystallization and solidification of molten silicon in a laser recrystallization process when a starting material is a-Si.

FIG. 9 is a diagram for explaining a relationship between a maximum cooling rate and a minimum cooling rate and a delay time of a second pulse in a cooling process after completion of total energy irradiation.

FIG. 10 shows an irradiation intensity of the first pulse of 450 mJ / c.
m ² and the irradiation intensity of the second pulse are each 100 mJ / c.
FIG. 3 is a diagram showing a temperature change of a silicon film when m ² and its delay time are ²⁰⁰ nsec.

FIG. 11 shows an irradiation intensity of the first pulse of 450 mJ / c.
m ² and the irradiation intensity of the second pulse were each 50 mJ / cm.
² is a diagram showing a temperature change of the silicon film when the delay time is set to ²⁰⁰ nsec.

FIG. 12 shows an irradiation intensity of the first pulse of 450 mJ / c.
m ² and the irradiation intensity of the second pulse were 25 mJ / cm, respectively.
² is a diagram showing a temperature change of the silicon film when the delay time is set to ²⁰⁰ nsec.

FIG. 13 is a diagram for explaining the relationship between the maximum cooling rate and the irradiation intensity of the second pulse in the cooling process after the completion of the total energy irradiation.

FIG. 14 is a diagram showing the relationship between the maximum cooling rate and the minimum cooling rate near the freezing point when a normally distributed light emission pulse is irradiated.

FIG. 15 is a configuration diagram showing one embodiment of a pulsed laser irradiation apparatus to which the method for forming a semiconductor thin film of the present invention is applied.

FIG. 16 is a diagram showing a temperature change of a silicon film when secondary energy is applied.

FIG. 17 is a configuration diagram showing a conventional pulse laser irradiation device.

[Explanation of symbols]

 1a, 1b pulse laser light source 2 light emission control device 3 half mirror 4a, 4b, 4c mirror 5 optical sensor 6 beam homogenizer 7 optical path 8 glass substrate 9 silicon thin film 10 xy stage

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-9-306839 (JP, A) JP-A-9-162121 (JP, A) JP-A-10-12549 (JP, A) JP-A-9-92 213651 (JP, A) JP-A-3-25920 (JP, A) JP-A-6-61172 (JP, A) Jpn. J. Appl. Phys. Vol. 34, Part 1, No. 8A pp. 3976-3981 (1 Jpn. J. Appl. Phys. Vol. 34, Part 1, No. 4A pp. 1759-1764 (1 (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21 / 20

Claims (3)

(57) [Claims] 1. The method according to claim 1, wherein the insulating film is formed on an insulating substrate or an insulating thin film.
Irradiates a semiconductor thin film containing silicon as a main component
First and second pulsed laser light sources,
Melting by irradiation of pulsed light emitted from a laser light source
During the solidification process, the temperature of the semiconductor thin film reaches the maximum temperature.
After the arrival, the solidification of the second
Pulsed light emitted from the pulsed laser light source
The second pulsed laser light source
The maximum cooling rate in the heating-cooling process by
Obtained from the heating-cooling process of only one pulsed laser light source
Controlled to be less than the maximum cooling rate
In the pulse laser irradiation apparatus, the first
Detecting means for detecting pulsed light emitted from the pulsed laser light source, and light emission controlling means for controlling light emission of the first and second pulsed laser light sources based on the detection timing of the detecting means. The light emission control means, after the temperature of the semiconductor thin film reaches the maximum temperature in the melting and solidification process by irradiation of the pulse light emitted from the first pulse laser light source, until the solidification is completed, A pulse laser irradiation device, which controls so as to emit pulse light emitted from the second pulse laser light source. 2. The pulse laser irradiation apparatus according to claim 1 , wherein the pulse light supplied from the second pulse laser light source has a light intensity higher than that of the pulse light supplied from the first pulse laser light source. A pulsed laser irradiation apparatus characterized in that it is also small. 3. The pulse laser irradiation apparatus according to claim 1 , wherein the pulse light supplied from the first and second pulse laser light sources reaches a maximum light emission intensity within 50 nsec from the start of light emission and emits light. Time is 100 ns
A pulse laser irradiation device, wherein the number is not less than c.