JP2004039660A - Method for manufacturing polycrystalline semiconductor film, method for manufacturing thin film transistor, display device, and pulse laser annealing device - Google Patents

Abstract

Provided are a method for manufacturing a polycrystalline semiconductor film and a method for manufacturing a thin film transistor, which can obtain a polycrystalline semiconductor film having high uniformity, high productivity, and excellent characteristics. Further, a pulse laser annealing apparatus for this purpose is provided.
An amorphous semiconductor film forming step of forming an amorphous semiconductor film on an insulator, and melting and recrystallization by irradiating the amorphous semiconductor film with a pulse laser and a continuous wave laser A polycrystalline semiconductor film forming step of forming a polycrystalline semiconductor film by forming the polycrystalline semiconductor film. Further, a method of manufacturing a thin film transistor using the same is provided. Further, a pulsed laser oscillator for outputting a pulsed laser, a continuous wave laser oscillator for irradiating a continuous wave laser, and shaping the pulsed laser and the continuous wave laser to the same portion of an amorphous semiconductor film on an insulator. And an optical system for irradiating.
[Selection diagram] FIG.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a polycrystalline semiconductor film, a method for manufacturing a transistor, a display device, and a pulse laser annealing device.
[0002]
[Prior art]
In order to manufacture a high-definition liquid crystal display (LCD: Liquid Crystal Display) or a small liquid crystal display integrated with a driving circuit in which peripheral circuits are formed on the same substrate, a polycrystalline silicon thin film transistor (poly-Si TFT: Polycrystalline Silicon Silicon). Thin-Film transistors) have been studied. This polycrystalline silicon thin film transistor has a structure in which an active layer made of polycrystalline silicon having high field effect mobility is formed on an insulating substrate such as glass or quartz. This polycrystalline silicon is obtained by first forming an amorphous silicon layer on an insulating substrate by a CVD method, and then recrystallizing the amorphous silicon layer. Various manufacturing methods of the polycrystalline silicon thin film transistor have been studied. Above all, the laser annealing method has been actively studied because the beam shape is made linear so that large-area amorphous silicon on a large-area substrate can be easily recrystallized.
[0003]
In this laser annealing method, the amorphous silicon layer is irradiated with a pulsed laser to heat the amorphous silicon to a melting point, and then cool and crystallize to obtain polycrystalline silicon. Here, as the pulse laser, an excimer laser having an ultraviolet wavelength using XeCl (oscillation wavelength 308 nm), KrF (oscillation wavelength 249 nm), ArF (oscillation wavelength 193 nm), or the like is mainly used. The excimer laser is used in this way because the power is large and the light absorption of the amorphous silicon is large at a wavelength in the ultraviolet region, so that only the amorphous silicon is heated to the melting point and the substrate is not damaged. That's because.
[0004]
The characteristics of the polycrystalline silicon thin film transistor obtained by this laser annealing mainly include defects existing in the crystal grain boundaries of polycrystalline silicon, impurities segregated in the crystal grain boundaries, or crystal defects such as twins existing in the crystal grains. Is known to be limited by Therefore, in order to manufacture a thin film transistor with high characteristics, it is important to increase the crystallinity of polycrystals to reduce crystal grain boundaries and to improve the crystallinity of each polycrystalline crystal grain. Therefore, in the laser annealing method, a large power excimer laser is irradiated to polycrystallize the polycrystal.
[0005]
[Problems to be solved by the invention]
If a polycrystalline silicon thin film transistor having better characteristics than before can be obtained by the above-described laser annealing method using a pulsed laser without deteriorating uniformity or productivity, it can be effectively used for a liquid crystal display device or the like. It is clear. In general, as one method of forming polycrystalline silicon having good characteristics, the recrystallization speed is reduced by cooling, the melting recrystallization time is made as long as possible, and each crystal of the polycrystalline silicon is further crystallized. Is considered an effective means. However, it is extremely difficult to use such a method of extending the melting crystal time in the laser annealing method.
[0006]
That is, in the laser annealing method, for example, a method of irradiating an excimer laser to amorphous silicon while heating the entire substrate to a high temperature is proposed as a method for increasing the melt crystallization time to increase the size of polycrystalline silicon. Have been. However, in the case of the method of heating the entire substrate, it is necessary to evacuate the atmosphere for annealing in order to protect the heater and the susceptor for heating the substrate. However, when annealing is performed in a vacuum atmosphere, silicon atoms ablated (ablated) by hydrogen contained in the amorphous silicon film, and silicon atoms evaporated during melting, emit laser light in the annealing chamber. Vacuum deposition is performed inside a window for guiding light, and the transmittance of laser light gradually decreases. As a result, there is a possibility that energy for producing a polycrystalline silicon film sufficient to produce a TFT-LCD with an integrated drive circuit may not reach the substrate. For this reason, unless the windows of the annealing chamber are frequently replaced, the crystallinity in the substrate and between the substrates will be different, the variation in characteristics will be large, and the uniformity and reproducibility will be reduced. Further, if the windows of the annealing chamber are frequently replaced to maintain the transmittance of the laser beam, the operation rate of the apparatus is significantly reduced, and the productivity is reduced. As described above, in the laser annealing method, when the entire substrate is heated by the heater, it is inevitable that problems occur in productivity, uniformity, and reproducibility.
[0007]
Further, in the method of heating the substrate, a problem arises from the viewpoint of damage to the substrate. That is, although a glass substrate is often used in a liquid crystal display device, as is well known, this glass substrate is weaker to heat than a Si substrate or the like. For this reason, when the substrate is heated, the damage to the substrate increases, and the characteristics of the completed polycrystalline silicon may be deteriorated.
[0008]
As described above, it is extremely difficult to obtain polycrystalline silicon having better characteristics than the conventional laser annealing method without lowering the uniformity of the quality of the obtained crystal and the productivity by the laser annealing method.
[0009]
The present invention has been made in view of such a point, and an object of the present invention is to provide a method for manufacturing a polycrystalline semiconductor film and a method for manufacturing a thin film transistor, in which polycrystalline silicon having high uniformity and productivity and high characteristics can be obtained. It is to provide. Another object of the present invention is to provide a pulse laser annealing apparatus used in such a manufacturing method.
[0010]
[Means for Solving the Problems]
The method for manufacturing a polycrystalline semiconductor film of the present invention includes an amorphous semiconductor film forming step of forming an amorphous semiconductor film on an insulator, a pulse laser, a continuous wave laser, And forming a polycrystalline semiconductor film by melting and recrystallizing to form a polycrystalline semiconductor film.
[0011]
Further, the method of manufacturing a thin film transistor according to the present invention is a method of manufacturing a thin film transistor in which an active layer is formed of a polycrystalline silicon film, the method comprising forming an amorphous silicon film on an insulating substrate. And a step of irradiating the amorphous silicon film with a pulsed laser and a continuous wave laser to melt and recrystallize to form a polycrystalline silicon film, thereby forming a polycrystalline silicon film. I do.
[0012]
Further, the pulse laser annealing apparatus of the present invention includes a pulse laser oscillator that outputs a pulse laser, a continuous wave laser oscillator that irradiates a continuous wave laser, and the pulse laser and the continuous wave laser that are shaped and formed on an insulator. And an optical system for irradiating the same portion of the amorphous semiconductor film.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. One of the features of the present embodiment is that an excimer laser which is a pulse laser and an Ar ion laser which is a continuous wave (CW) laser are used in laser annealing. Thereby, the melting and recrystallization time of the amorphous silicon film (30 in FIG. 2) can be prolonged, and a polycrystalline silicon film (32 in FIG. 2) having high characteristics can be obtained.
[0014]
FIG. 1 is a diagram showing a thin film transistor obtained according to an embodiment of the present invention. An undercoat film 20 made of SiN and SiO ₂ is formed on an insulating substrate 10 made of non-alkali glass. On this undercoat film 20, an active layer 33 made of a polycrystalline silicon film (polycrystalline semiconductor film) is formed. The active layer 33 includes ion-doped source / drain regions 34 and 36 and a channel region 35 therebetween. The active layer 33 is covered with a gate insulating film 40 made of SiO ₂ , and a gate electrode 50 is formed on the gate insulating film 40. This gate electrode 50 is further covered with an interlayer insulating film 60 made of SiO ₂ . A contact hole is formed in the interlayer insulating film 60 by etching, and a source / drain electrode 70 connected to the source / drain regions 34 and 36 is formed through the contact hole.
[0015]
Next, a method for manufacturing the thin film transistor of FIG. 1 will be described. 2A to 2D are views showing a method for manufacturing a thin film transistor according to an embodiment of the present invention. In this manufacturing method, a case where a large number of thin film transistors are manufactured on a large substrate of about 400 mm × 500 mm is taken as an example. FIG. 2 is an enlarged sectional view of one of the thin film transistors.
[0016]
(1) First, as shown in FIG. 2A, an undercoat layer 20 made of SiN and a SiO ₂ film is formed on an insulating substrate (insulator) 10 made of non-alkali glass by a plasma CVD method. An amorphous silicon film (amorphous semiconductor film) 30 is formed thereon. The amorphous silicon film 30 is a thin film having a thickness of 50 nm so that laser annealing described later is easy. Thereafter, annealing at 500 ° C. for one hour is performed to reduce the hydrogen concentration in the amorphous silicon film 30.
[0017]
(2) Next, as shown in FIG. 2 (b), while scanning the substrate, an excimer laser which is a pulse laser, a C.I. W. An amorphous silicon 30 is irradiated with an Ar ion laser, which is a laser, and laser annealing is performed to form a polycrystalline silicon film 32.
[0018]
(3) Next, the polycrystalline silicon film 32 is patterned into an island shape to form an active layer 33 as shown in FIG. Then, a gate insulating film 40 made of a SiO ₂ film is formed on the active layer 33 by a plasma CVD method.
[0019]
(4) Next, a high melting point metal such as Mo or Ta or doped polycrystalline silicon is formed and patterned on the gate insulating film 40, and a gate electrode 50 is formed as shown in FIG. 2D. . Then, using the gate electrode 50 as a mask, a dopant is implanted by an ion doping method to form the source / drain regions 34 and 36 in a self-aligned manner. Thereafter, as can be seen from FIG. 1, an interlayer insulating film 60 made of SiO ₂ is formed, contact holes for the source / drain regions 34 and 36 are formed, and a source / drain electrode 70 made of Al is formed by sputtering. Then, patterning is performed to obtain the polycrystalline silicon thin film transistor of FIG.
[0020]
The method of manufacturing the polycrystalline silicon thin film transistor of FIG. 2 described above has a feature in the step of forming the polycrystalline silicon 32 by the laser annealing method of FIG. 2B. Therefore, a polycrystalline silicon film forming step by the laser annealing method will be described in detail with reference to FIGS.
[0021]
FIG. 3 schematically shows a pulse laser annealing apparatus for converting an amorphous silicon film into a polycrystalline silicon film. This apparatus includes a substrate stage 1. An insulating substrate 10 on which an amorphous silicon film 30 is formed is disposed on the substrate stage 1, and the disposed insulating substrate 10 is moved in the direction of the arrow in the figure. As a result, as described later, the amorphous silicon film 30 is scanned by two types of laser beams. This device also includes a pulse laser oscillator 2 that outputs a pulse laser. The pulse laser from the pulse laser oscillator 2 is shaped by the optical systems 3, 4, and 5, and is applied to the focal plane of the amorphous silicon film 30. More specifically, the pulse laser beam output from the pulse laser oscillator 2 is shaped into a line by the beam homogenizer 3, reflected by the return mirror 4, and passed through the projection lens 5 to the focal plane of the amorphous silicon 30. Is irradiated. In this embodiment, an excimer laser is used as the pulse laser beam. Further, in the pulse laser device of FIG. 3, in addition to the pulse laser oscillator 2, C.P. W. C. Irradiation with laser (continuous wave laser) W. A laser system 90 is provided. C. W. As a laser, an Ar ion laser is used. More specifically, as shown in FIG. W. The laser beam is output from the laser oscillator 91, shaped into a line by the long axis homogenizer 92, reflected by the return mirror 4, and radiated to the focal plane via the projection lens 5. As described above, in the apparatus of FIG. 3, the pulse laser from the pulse laser oscillator 2 and the continuous wave laser from the continuous wave laser oscillator 91 are shaped by the optical systems 3, 4, 5, and 92, and are formed on the insulator 10. The same portion of the amorphous semiconductor film 30 is irradiated.
[0022]
In the pulse laser annealing apparatus shown in FIG. 3, the crystallization is performed by irradiating the substrate 10 with a pulse laser 20 times while scanning the substrate 10. The irradiation atmosphere is nitrogen at normal pressure. However, an atmosphere in which a trace amount of oxygen is mixed with nitrogen, or hydrogen, helium, argon, or the like may be used instead of nitrogen. The pressure in the processing chamber may be a positive pressure state or a reduced pressure state.
[0023]
The excimer laser from the pulse laser oscillator 2 and the C.I. from the laser system 90 (continuous wave laser oscillator 91) in the pulse laser device of FIG. W. FIG. 5 shows a timing chart of laser irradiation. C. W. The laser is irradiated by modulating the amplitude so that the amplitude is small when the pulse laser is irradiated on the insulating substrate 10 and is large when the pulse laser is not irradiated on the insulating substrate 10. By performing such modulation, it is possible to obtain polycrystalline silicon 32 having high characteristics, as described later.
[0024]
In the laser annealing using the pulse laser annealing apparatus of FIG. 3 described above, in addition to the excimer laser from the pulse laser oscillator 2, the C.I. W. Since the laser irradiation is performed, the melting and recrystallization time of the amorphous silicon film 30 can be lengthened, and the polycrystalline silicon film 32 having a large crystal grain size and excellent characteristics can be obtained. The C.I. W. By modulating and irradiating the laser as shown in FIG. 5, a polycrystalline silicon film 32 having higher characteristics can be obtained. Hereinafter, a description will be given with reference to FIGS. 6 and 7 while referring to a comparative example in which the irradiation method of the continuous wave laser 90 is changed.
[0025]
FIG. W. When amplitude modulation of the laser is performed (this embodiment), C.I. W. When the amplitude modulation was not performed with the laser kept constant, and C.I. W. FIG. 9 is a diagram showing an average crystal grain size of a polycrystalline silicon film 32 obtained without laser. The horizontal axis is C.I. The irradiation energy of the W laser and the vertical axis indicate the average crystal grain size of the polycrystalline silicon film 32, respectively. From FIG. W. Compared to the case without the laser, W. It is understood that the characteristics of the polycrystalline silicon film 32 can be improved by irradiating the laser. This is C.I. W. This is because the place where the laser is irradiated is kept in a state where the substrate temperature is higher than that of a normal place, and the time for melting and recrystallizing becomes longer, so that a large crystal grain size can be grown. .
[0026]
Also, as in the present embodiment, C.I. W. By performing laser amplitude modulation, C.I. W. It can be seen that the margin can be expanded to the higher energy side as compared with the case where the laser is fixed. This is C.I. W. If the laser irradiation is always performed at a constant amplitude, the C.I. W. It is analyzed that the temperature becomes too high only at the position where the laser is irradiated, and microcrystals are formed at that position by supercooling. That is, in the present embodiment, C.I. W. By performing the amplitude modulation of the laser, it is possible to suppress the generation of partial microcrystals and to secure the irradiation energy margin of the pulse laser.
[0027]
FIG. 7 shows the thin film transistor (TFT) of FIG. 1 obtained by the manufacturing method (with CW laser) of the present embodiment, and FIG. FIG. 4 is a diagram showing a comparison of electrical characteristics between a thin film transistor obtained by a conventional method without a W laser and a thin film transistor. In the present embodiment (with CW laser), C.W. W. Compared with the case without the laser, the characteristics of the mobility, the threshold value, and the S-factor are C.I. W. It is better than the one without. This is C.I. W. Shows that a large crystal grows by the irradiation, and defects in the crystal grain boundaries and in the crystal grains are reduced. Further, from the characteristics, it is understood that the thin film transistor obtained in the present embodiment has little damage to the glass substrate 10 and hardly deteriorates the characteristics due to the substrate damage. Further, in the manufacturing method of the present embodiment, since a device such as a heater for heating the substrate is not required, there is no need to evacuate the irradiation atmosphere and to reduce the operation rate of the device. Further, uniformity and productivity do not decrease due to the vacuum.
[0028]
As described above, in the present embodiment, in addition to the excimer laser, C.I. W. By irradiating the laser, polycrystalline silicon 32 having high characteristics and high uniformity and high productivity can be obtained.
[0029]
However, as in this embodiment, in addition to the excimer laser, C.I. W. It has been considered difficult to improve the characteristics of the polycrystalline silicon film 32 by irradiating a laser, according to the common general technical knowledge of the related art. Because, C. W. This is because it has been considered that the laser irradiation may cause thermal damage to the glass substrate 10 that is weak to heat, and may lower the threshold value and the S-factor of the thin film transistor. However, according to experiments performed by the present inventors, C.I. W. By using an Ar ion laser as the laser and irradiating the Ar ion laser with amplitude modulation as shown in FIG. 5, a good transistor was obtained as can be seen from FIG. The present inventor considers the reason as follows. That is, the wavelength of the excimer laser is in the ultraviolet light range (about 300 nm or less), while the wavelength of the Ar ion laser is about 500 nm, and both wavelengths are different. When the laser beams having different wavelengths are periodically irradiated as shown in FIG. 5, a specific load on the glass substrate 10 is intensively applied as compared with the case where the laser beam is continuously irradiated at a constant wavelength. Is reduced. As a result, C.I. W. It is analyzed that even if an Ar ion laser, which is a laser, is used, damage to the glass substrate 10 does not become a major problem.
[0030]
In the embodiment described above, an excimer laser is used as a pulse laser, but a YAG laser or the like can be used as a pulse laser. C.I. W. Although an Ar ion laser was used as the laser, C.I. W. Other lasers can be used as the laser.
[0031]
【The invention's effect】
According to the present invention, in laser annealing for irradiating amorphous silicon with laser to form polycrystalline silicon, C.I. W. Since laser irradiation is performed, polycrystalline silicon having good characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a polycrystalline silicon thin film transistor according to an embodiment of the present invention.
FIG. 2 is a diagram schematically illustrating a method for manufacturing a polycrystalline silicon thin film transistor according to an embodiment of the present invention.
FIG. 3 is a view showing a laser annealing step of the method for manufacturing a polycrystalline silicon thin film transistor according to the embodiment of the present invention.
FIG. 4 is a pulse laser annealing apparatus according to an embodiment of the present invention.
FIG. 5 is a pulse laser annealing apparatus according to an embodiment of the present invention.
FIG. W. When the laser irradiation method is changed, C.I. W. FIG. 4 is a diagram showing a relationship between laser energy of a laser and an average crystal grain size of polycrystalline silicon.
FIG. 7 shows a TFT obtained in the present embodiment and C.I. W. FIG. 4 is a diagram showing a comparison of electrical characteristics between a TFT obtained by a conventional method without using a laser and a TFT obtained by a conventional method.
[Explanation of symbols]
2 pulse laser oscillator 3 beam homogenizer (optical system)
4 Folding mirror (optical system)
5 Projection lens (optical system)
10 Glass substrate (insulator)
Reference Signs List 30 amorphous silicon layer 32 polycrystalline silicon layer 33 active layer 91 continuous wave laser (CW laser) oscillator 92 long axis homogenizer (optical system)

Claims (9)

An amorphous semiconductor film forming step of forming an amorphous semiconductor film on the insulator;
A polycrystalline semiconductor film forming step of forming a polycrystalline semiconductor film by irradiating the amorphous semiconductor film with a pulse laser and a continuous wave laser to melt and recrystallize the amorphous semiconductor film,
A method for manufacturing a polycrystalline semiconductor film, comprising: In the polycrystalline semiconductor film forming step, the amplitude of the continuous wave laser is small when the pulse laser is irradiated on the insulating substrate, and the amplitude is large when the pulse laser is not irradiated on the insulating substrate. 2. The method of manufacturing a polycrystalline semiconductor film according to claim 1, wherein the irradiation is performed with the amplitude modulated in such a manner. A method of manufacturing a thin film transistor in which an active layer is made of a polycrystalline silicon film,
An amorphous silicon film forming step of forming an amorphous silicon film on an insulating substrate,
A polycrystalline silicon film forming step of forming a polycrystalline silicon film by irradiating the amorphous silicon film with a pulse laser and a continuous wave laser to melt and recrystallize the film;
A method for manufacturing a thin film transistor, comprising: In the step of forming the polycrystalline silicon film, the amplitude of the continuous wave laser is small when the pulse laser is irradiated on the insulating substrate, and the amplitude is large when the pulse laser is not irradiated on the insulating substrate. 4. The method for manufacturing a thin film transistor according to claim 3, wherein the irradiation is performed by modulating the amplitude in such a manner. 5. The method according to claim 3, wherein the pulse laser is an excimer laser using XeCl, KrF or ArF, and the continuous wave laser is an Ar ion laser. A display device comprising the thin film transistor according to claim 3. A pulse laser oscillator that outputs a pulse laser,
A continuous wave laser oscillator for irradiating a continuous wave laser,
An optical system that shapes the pulse laser and the continuous wave laser and irradiates the same portion of the amorphous semiconductor film on the insulator,
A pulse laser annealing apparatus characterized by comprising: An amplitude modulator that modulates the amplitude of the continuous wave laser so that the amplitude is small when the pulse laser is irradiated on the insulating substrate and is large when the pulse laser is not irradiated on the insulating substrate. The pulse laser annealing apparatus according to claim 7, wherein: 9. The pulse laser annealing apparatus according to claim 7, wherein said pulse laser is an excimer laser using XeCl, KrF or ArF, and said continuous wave laser is an Ar ion laser.

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