JPH09116166A - Manufacture of thin film semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently repair the defects of a semiconductor film and a gate insulating film caused by laser annealing. SOLUTION: To manufacture a film semiconductor device, preprocessing is performed first, and a treatment including the film growth is executed at need on an insulating substrate 1. Next, film growth processing is performed to form a noncrystalline semiconductor film 4 on the insulating substrate 1. Subsequently, crystallization processing is performed, and a laser beam 5 is applied to crystallize the semiconductor film 4, thus it is made into the active layer of a film transistor. In after processing, processing including film growth is performed onto the semiconductor film 4 to complete the film transistor. At this time, restoration processing performed before advancing into the after processing after the crystallization process, whereby the defects of the film transistor caused by the application of laser beam is repaired. For example, the insulating substrate 1 is exposed in hydrogen plasma 6 to terminate the defects of the semiconductor film 4 and the gate insulating film 3 in hydrogen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thin film semiconductor device in which thin film transistors are integrated and formed on an insulating substrate. More specifically, the present invention relates to a laser annealing technique for a semiconductor thin film that becomes an active layer of a thin film transistor.

[0002]

2. Description of the Related Art A thin film semiconductor device is suitable for a drive substrate of an active matrix type liquid crystal display panel and is under active development. With the increase in size of liquid crystal display panels, low-temperature processes that can use low-cost glass substrates have attracted attention. In particular, research and development of low-temperature processing of polycrystalline silicon thin film transistors, which have excellent operating characteristics, have been actively conducted. At this time, it is essential to establish a laser annealing technique capable of converting amorphous silicon into polycrystalline silicon. This will be briefly described with reference to FIG. FIG. 4 shows a cross-sectional structure of a bottom gate type thin film transistor manufactured by a low temperature process, which is formed for switching pixel electrodes. A gate electrode 202 made of metal or the like on an insulating substrate 201 such as glass
Are formed by patterning. The gate electrode 202 is covered with a gate insulating film 203. A semiconductor thin film 204, which becomes an active layer of the thin film transistor, is formed thereon in an island shape. This semiconductor thin film 204 is 600
Amorphous silicon formed at a low temperature at a temperature of ℃ or less is converted into polycrystalline silicon by laser annealing.
A channel stopper 205 is patterned and formed thereon in alignment with the gate electrode 202. Ions are doped with impurities using the channel stopper 205 as a mask to form a source region S and a drain region D. Laser annealing is performed again to activate the impurities introduced into the semiconductor thin film 204. The bottom gate type polycrystalline silicon thin film transistor thus obtained is covered with an interlayer insulating film 206 made of PSG or the like. A wiring electrode 207 is patterned on the interlayer insulating film 206 and electrically connected to the source region S via a contact hole. The pixel electrode 208 is also patterned and electrically connected to the drain region D through the contact hole.

[0003]

As described above, in the low temperature process, the semiconductor thin film is crystallized and the impurities are activated by the laser annealing for irradiating the laser beam. That is, the amorphous silicon film formed at a low temperature is locally heated by laser annealing and converted into polycrystalline silicon in the cooling process to form a thin film transistor having high carrier mobility. Further, the impurities injected into the polycrystalline silicon are activated by the laser annealing again, and the resistance of the source region and the drain region is reduced. Conventionally, excimer laser light is used in laser annealing. However, the excimer laser light is short wavelength ultraviolet light. For example, XeCl
The wavelength of the excimer laser light is 308 nm, and the wavelength of the KrF excimer laser light is 248 nm. For this reason, although the energy density is high and efficient laser annealing can be performed, the crystal structure of the semiconductor thin film is likely to be damaged, and a defect level is induced. This induced defect level causes the threshold value of the thin film transistor to fluctuate, resulting in instability in operating characteristics. Particularly, in the case of the bottom gate structure, the gate insulating film 203 is formed prior to the semiconductor thin film 204, and since this is also irradiated with the excimer laser light, the interface and the inside of the gate insulating film are damaged and defects are induced. To be done. Therefore, the conventional manufacturing process has a problem that the operating characteristics of the thin film transistor are adversely affected.

[0004]

In order to solve the above-mentioned problems of the conventional technique, the following two means are taken. That is, the first
With the above means, the thin film semiconductor device is manufactured according to the following steps. First, a pre-process is performed, and a process including film formation is performed on the insulating substrate as needed. Next, a film forming process is performed to form a non-single crystalline semiconductor thin film on the insulating substrate. Subsequently, a crystallization process is performed and the semiconductor thin film is crystallized by irradiating laser light to form an active layer of a thin film transistor. Finally, in a post process, a process including film formation is performed on the semiconductor thin film. As a characteristic feature, a repairing step is performed after the crystallization step and before proceeding to the subsequent step to repair the defect of the thin film transistor caused by the irradiation of the laser beam. Specifically, in the repairing step, exposure to hydrogen plasma, heating in a hydrogen gas atmosphere, pressurization in a hydrogen gas atmosphere, or simple heating is performed. When forming a thin film transistor having a bottom gate structure, in the previous step, first, a process of patterning a gate electrode and a process of forming a gate insulating film on the gate electrode are performed. Next, in the film forming step, 600
A semiconductor thin film made of amorphous silicon is formed at a film forming temperature of ℃ or less. In the crystallization process, the amorphous silicon is converted into polycrystalline silicon by irradiation with laser light. In the repairing step, defects in the gate insulating film are repaired in addition to defects in the polycrystalline silicon. Finally, in the subsequent step, a process of forming an interlayer insulating film on the polycrystalline silicon and a process of patterning wiring electrodes thereon are performed.

According to the second means of the present invention, the thin film semiconductor device is manufactured by the following steps. First, a pre-process is performed to form a gate electrode on an insulating substrate, and then a gate insulating film is formed thereon. Next, a film forming process is performed to form a semiconductor thin film on the gate insulating film. Then, an implantation process is performed to implant the impurity ions into the semiconductor thin film in a region-selective manner to form the source / drain regions of the thin film transistor. Finally, a post-process is performed to form an interlayer insulating film on the semiconductor thin film, and a wiring electrode is patterned on the interlayer insulating film. Characteristically, after the implantation step and before proceeding to the subsequent step, a protective film is formed on the semiconductor thin film, laser light is irradiated through the protective film to activate impurities, and the gate is irradiated from the laser light. Protect the insulating film. Preferably, the protective film is formed in alignment with the channel region located between the source / drain regions, and selectively reflects the irradiated laser light.

According to the first aspect of the present invention, the defect of the thin film transistor caused by the irradiation of the laser beam is repaired by performing the repair process after the crystallization process and before proceeding to the subsequent process.
This repairing process is mainly a so-called hydrogenation process and introduces hydrogen into the semiconductor thin film to terminate the silicon dangling bond. In the present invention, since this repairing step is carried out immediately after the crystallization step and before the subsequent step, the hydrogenation treatment can be carried out extremely efficiently. Particularly, in the case of the bottom gate structure, not only the defects of the semiconductor thin film but also the defects of the gate insulating film located therebelow can be efficiently repaired, so that the operating characteristics of the thin film transistor are significantly improved. When a repair process is performed in a later step, a channel stopper, an interlayer insulating film, and
Since the wiring electrodes and the like are formed, the progress of the hydrogenation treatment is hindered and the repair cannot be efficiently performed. Similarly, in the second aspect of the present invention, the protective film is formed on the semiconductor thin film after the step of implanting impurities and before proceeding to the subsequent step. Laser light is irradiated through this protective film to activate the impurities. At this time, the protective film effectively shields the gate insulating film from the laser light and prevents the induction of defects.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a process diagram showing a first embodiment of a method of manufacturing a thin film semiconductor device according to the present invention. First, as shown in (A), a pre-process is performed to perform a process including film formation on the insulating substrate 1 made of glass or the like, if necessary. For example, when forming a thin film transistor having a bottom gate structure, the gate electrode 2 made of Mo / Ta or the like is patterned. Furthermore, on the gate electrode 2, S
A gate insulating film 3 made of iN _x or SiO _{2 is} formed. In this example, SiN _x and SiO are formed by plasma CVD.
₂ is continuously formed to form a gate insulating film 3 having a two-layer structure.

Next, as shown in (B), a film forming process is performed to form a non-single crystalline semiconductor thin film 4 on the insulating substrate 1. In this example, amorphous silicon is formed by plasma CVD at a film forming temperature of 600 ° C. or less. Subsequently, a crystallization process is performed, and the semiconductor thin film 4 is crystallized by irradiating the laser beam 5 to form an active layer of a thin film transistor. At this stage, the semiconductor thin film 4
Also, considerable defects are induced in the gate insulating film 3. In this example, the amorphous silicon is locally heated by the pulse irradiation of the excimer laser light and converted into polycrystalline silicon in the cooling process.

Subsequently, as shown in (C), a repairing step is performed immediately after the crystallization step and before proceeding to the next subsequent step to repair the defect of the thin film transistor caused by the irradiation of the laser beam. In this example, the insulating substrate 1 is exposed to hydrogen plasma 6 to repair defects. As a result, hydrogen becomes a semiconductor thin film 4
And the defects (dangling bonds) introduced into the gate insulating film 3 and induced in these films are terminated. As described above, in the present invention, the hydrogenation treatment is performed immediately after the crystallization step while the semiconductor thin film 4 is exposed on the surface, so that the defects can be repaired extremely efficiently. In the repairing step, heating in a hydrogen gas atmosphere may be performed instead of exposure to the hydrogen plasma 6. For example, hydrogen in the atmosphere can be introduced into the semiconductor thin film 4 and the gate insulating film 3 by performing the heat treatment at a temperature of 100 ° C. or higher. Alternatively, the defect may be repaired by performing a pressure treatment in a hydrogen gas atmosphere. Furthermore, even if a simple heat treatment is performed, the defects can be repaired to some extent. This heat treatment is performed at 200 ° C. or higher for 10 minutes or longer.

Finally, as shown in (D), a post process is performed,
A process including film formation is performed on the semiconductor thin film 4 to complete a bottom gate type thin film transistor. Specifically, the channel stopper 7 is aligned with the gate electrode 2 and patterned on the semiconductor thin film 4. For example SiO ₂ or Si
After forming a film of N _x with a thickness of 100 nm to 200 nm, a photoresist is applied thereon. Backside exposure is performed using the gate electrode 2 as a mask to pattern the photoresist. Using this photoresist as a mask, SiO ₂ or S
When iN _x is etched, the channel stopper 7 aligned with the gate electrode 2 is obtained. This channel stopper 7
Using the as a mask, the semiconductor thin film 4 is ion-doped with impurities by self-alignment. Thereby, the source region S and the drain region D of the thin film transistor are formed. Further, a channel region where impurities are not implanted is left just below the channel stopper 7. Further, the thin film transistor is covered with an interlayer insulating film 8 made of PSG or the like. A contact hole is opened in this interlayer insulating film 8 by wet etching. Finally, a metal such as aluminum is sputtered on the interlayer insulating film 8 and then patterned into a predetermined shape to form the wiring electrode 9. The wiring electrode 9 is electrically connected to the source region S via a contact hole. In addition, after forming a transparent conductive film such as ITO, the pixel electrode 10 is processed by patterning into a predetermined shape. The pixel electrode 10 is electrically connected to the drain region D. As described above, a thin film semiconductor device suitable for an active matrix liquid crystal display panel or the like is completed. Note that it is also possible to repair the induced defects due to laser light irradiation in the stage of the post process shown in (D). However, in the later step, the channel stopper 7, the interlayer insulating film 8, the wiring electrode 9 and the like are formed on the semiconductor thin film 4, so that the hydrogenation process cannot be efficiently performed. Particularly in the case of the bottom gate structure, it becomes difficult to repair the induced defects in the gate insulating film 3.

FIG. 2 is a process diagram showing a second embodiment of the method of manufacturing a thin film semiconductor device according to the present invention. First, as shown in (A), a pre-process is performed to form the gate electrode 12 on the insulating substrate 11 and further form the gate insulating film 13 thereon. Subsequently, a film forming process is performed to form the semiconductor thin film 14 on the gate insulating film 13.

Next, an injection step is performed as shown in FIG.
Impurity ions are selectively implanted into the semiconductor thin film 14 to form a source region S and a drain region D of the thin film transistor.
To form Specifically, first, a photoresist 15 is applied on the semiconductor thin film 14, and back surface exposure is performed using the gate electrode 12 as a mask. As a result, the photoresist 15 is patterned into a shape matching the gate electrode 12. When the ion doping is performed by self-alignment using the photoresist 15 as a mask, the source region S and the drain region D can be formed. Note that a channel region where impurity ions are not implanted is left just below the photoresist 15.

Next, as shown in (C), a protective film 16 is formed on the semiconductor thin film 14 after the implantation step and before proceeding to the next subsequent step. Further, laser light 17 is passed through this protective film 16.
Is irradiated to activate the impurities implanted in the semiconductor thin film 14. As a result, the resistance of the source region S and the drain region D can be reduced. At this time, the protective film 16 is the gate insulating film 1.
3 is cut off from the laser beam 16 and the gate insulating film 13
It prevents the laser light induced defects from occurring. In this example, the protective film 16 is formed in alignment with the channel region located between the source region S and the drain region D, and selectively reflects the emitted laser light 17. Therefore,
There is no fear that the channel region and the gate insulating film directly below the channel region will be irradiated with laser light, and defects will not be induced. The protective film 16 is made of, for example, SiO ₂ or SiN _x , and is laminated with a thickness of at least 10 nm or more. When the protective film 16 is patterned, the backside exposure technique is used similarly to the channel stopper 7 shown in FIG. The protective film 16 is preferably set to have a thickness of about 150 nm. This thickness can realize an extremely high reflectance for XeCl excimer laser light having a wavelength of 308 nm.

Finally, a post-process is performed as shown in (D),
An interlayer insulating film 18 is formed on the semiconductor thin film 14. Further, the wiring electrode 19 and the pixel electrode 20 are patterned and formed thereon.

As described above, in the first and second embodiments, generation of excimer laser light induced defects is suppressed.
As a result, it is possible to suppress in-plane variation in threshold value and temporal change in the operating characteristics of the thin film transistor. If the induced defect is left as it is, the channel potential is changed by its energy level, ionized atoms, etc., so that the operating characteristics of the thin film transistor become unstable.

FIG. 3 is a schematic perspective view showing an example of an active matrix liquid crystal display panel using a thin film semiconductor device manufactured by the manufacturing method shown in FIG. 1 or 2 as a driving substrate. As shown in the figure, the liquid crystal display panel is composed of a drive substrate 101 made of glass or the like, a counter substrate 102 made of glass or the like, and a liquid crystal 103 held between the two. The pixel array section 104 is provided on the driving substrate 101.
And the drive circuit section are formed integrally. The drive circuit section is divided into a vertical drive circuit 105 and a horizontal drive circuit 106. Further, a terminal portion 107 for external connection is formed at an upper end of a peripheral portion of the drive substrate 101. Terminal section 107 is wiring 1
08 through the vertical drive circuit 105 and the horizontal drive circuit 10
6 is connected. The pixel array unit 104 includes a gate line 109 and a signal line 110 that cross each other. The pixel electrode 11 is provided at the intersection of both lines 109 and 110.
1 and a thin film transistor 112 for driving the same are integrally formed. On the other hand, a counter electrode and a color filter (not shown) are formed on the inner surface of the counter substrate 102.
According to the present invention, since the thin film transistor is formed by a low temperature process, low-cost glass or the like can be used as the driving substrate 101, which can contribute to a large screen of the liquid crystal display panel. Further, since a high-quality polycrystalline silicon thin film transistor can be formed even in the low temperature process, the vertical driving circuit 105 and the horizontal driving circuit 106 in the periphery can be integrally formed by the thin film transistor in addition to the thin film transistor 112 for pixel switching.

[0017]

As described above, according to the present invention, laser light induced defects are prevented from remaining in the gate insulating film as much as possible when the semiconductor thin film is crystallized and the impurities are activated by laser annealing. As a result, the operating characteristics of the thin film transistor manufactured by the low temperature process can be stabilized. For example, it is possible to reduce variations in the threshold voltage of the bottom gate type polycrystalline silicon thin film transistor over time and variations in the in-plane distribution. This makes it possible to remarkably improve the image uniformity of a liquid crystal display panel using, for example, a low temperature polycrystalline silicon thin film transistor in a switching element or a peripheral drive circuit.

[Brief description of the drawings]

FIG. 1 shows a first example of a method of manufacturing a thin film semiconductor device according to the present invention.
It is a process drawing showing an embodiment.

FIG. 2 shows a second example of the method of manufacturing a thin film semiconductor device according to the present invention.
It is a process drawing showing an embodiment.

FIG. 3 is a perspective view showing an example of a liquid crystal display panel in which a thin film semiconductor device manufactured according to the present invention is assembled as a drive substrate.

FIG. 4 is a cross-sectional view showing a conventional thin film semiconductor device.

[Explanation of symbols]

 1 Insulating Substrate 2 Gate Electrode 3 Gate Insulating Film 4 Semiconductor Thin Film 5 Laser Light 6 Hydrogen Plasma 8 Interlayer Insulating Film 9 Wiring Electrode 10 Pixel Electrode 16 Protective Film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H01L 29/78 627E

Claims (5)

[Claims] 1. A pre-process of performing a process including film formation on an insulating substrate as necessary, a film forming process of forming a non-single crystalline semiconductor thin film on the insulating substrate, and a laser beam irradiation. What is claimed is: 1. A method of manufacturing a thin film semiconductor device, comprising: a crystallization step of crystallizing the semiconductor thin film into an active layer of a thin film transistor; and a post-step of performing a treatment including film formation on the semiconductor thin film. A method for manufacturing a thin film semiconductor device, comprising: performing a repairing step before performing the subsequent step to repair defects in a thin film transistor caused by irradiation with laser light. 2. The repairing step includes performing exposure to hydrogen plasma, heating in a hydrogen gas atmosphere, pressurization in a hydrogen gas atmosphere, or simple heating. Method of manufacturing thin film semiconductor device. 3. The preceding step includes a step of patterning a gate electrode and a step of forming a gate insulating film on the gate electrode, wherein the film forming step is amorphous at a film forming temperature of 600 ° C. or less. A semiconductor thin film made of silicon is formed, the crystallization step converts the amorphous silicon into polycrystalline silicon by irradiation with laser light, and the repair step adds the gate insulating film in addition to the defects generated in the polycrystalline silicon. 2. The defect produced in the above step is also repaired, and the post-process includes a step of forming an interlayer insulating film on the polycrystalline silicon and a step of patterning a wiring electrode thereon. Method of manufacturing thin film semiconductor device. 4. A pre-process of forming a gate electrode on an insulating substrate and further forming a gate insulating film thereon, a film forming process of forming a semiconductor thin film on the gate insulating film, and the semiconductor thin film. An implantation step of selectively implanting impurity ions into the source / drain regions of the thin film transistor, and a post-step of forming an interlayer insulating film on the semiconductor thin film and further patterning a wiring electrode thereon. A method of manufacturing a thin film semiconductor device, which comprises forming a protective film on the semiconductor thin film after the implantation step and before proceeding to the subsequent step, and irradiating a laser beam therethrough to activate impurities. A method of manufacturing a thin film semiconductor device, comprising protecting the gate insulating film from the laser light. 5. The protective film is formed in alignment with a channel region located between the source / drain regions, and selectively reflects the emitted laser light.
A manufacturing method of the thin film semiconductor device according to the above.