JP2001320060A - Thin-film transistor and active matrix type display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin-film transistor which is excellent in electric characteristics. SOLUTION: This thin film transistor is provided with a gate electrode, a gate insulating film making contact with it, and a crystallized semiconductor film making contact with the gate insulating film. Here, the semiconductor film comprises an impurity region, and the gate electrode has a region overlapped via the impurity region and the gate insulating film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a polycrystal (microcrystal).
The present invention relates to a method for manufacturing a silicon thin film transistor.

[0002]

2. Description of the Related Art One of the methods for obtaining a polycrystalline (microcrystalline) silicon film is to form a deposited amorphous silicon (hereinafter referred to as "a-
There is a method in which a-Si is crystallized by irradiating a laser to a film (referred to as “Si”), which is generally well known. Laser-crystallized thin-film transistors using this technology have better electrical properties such as field-effect mobility than amorphous-silicon thin-film transistors (hereinafter a-Si TFTs). It is used for peripheral drive circuits.

[0003] A typical method for producing a laser crystallized thin film transistor is firstly to use amorphous silicon as a starting film.
The (a-si) film is crystallized by irradiating the film with a laser, and then the device structure is processed by a series of manufacturing processes. Performing the crystallization step at the beginning or in the middle of the manufacturing process is the main feature of the conventional manufacturing method.

[0004]

When a thin film transistor is manufactured by such a manufacturing method, the following problems occur. (1) By performing laser crystallization as part of the manufacturing process, the electrical characteristics of the TFT cannot be evaluated until the device is completed, and it is difficult to control it. (2) Since laser crystallization is performed at the beginning or in the middle of TFT fabrication, it is impossible to correct various electrical characteristics after the device structure is completed, and the yield of the entire circuit system deteriorates.

The present invention proposes a new method of fabricating a polycrystalline (microcrystalline) thin film transistor to solve the above problems.

[0006]

SUMMARY OF THE INVENTION The present invention provides a method for crystallization of a channel formation region and activation of a source / drain ohmic contact region by laser irradiation after completion of a device structure. A structure in which a part of the drain region on the channel forming region side is exposed to the incident laser light, or the source / drain region is located on the laser light incident side with respect to the source / drain electrodes, and the both regions Is used, a thin film transistor having a structure in which a part thereof is in contact with the laser light incident side of the channel formation region.

The activation of the source / drain regions means that the P-type or N-type characteristics are obtained by adding a Group III or Group V impurity atom to the intrinsic a-Si film by various methods. In order to obtain better P-type or N-type characteristics, it means that energy is applied to a region to which an impurity is added to activate the impurity and improve the conductivity of the film.

FIG. 1 shows that an impurity a-Si layer serving as a source / drain region and an intrinsic a-Si layer serving as a channel forming region are effectively crystallized and activated by laser irradiation after a device structure is completed. T of the present invention that enables
1 shows the structure of FT.

In FIG. 1A, the distance between the source electrode 9 and the drain electrode 10 on the TFT island is made larger than the distance between the source region 11 and the drain region 12 so that the source and the source are irradiated by laser from above the substrate. Activation and crystallization of the drain regions 11 and 12 and the channel formation region 5 are enabled.

At this time, by irradiating a laser beam having a sufficient energy value, an intrinsic region for forming a channel formation region is obtained.
A portion of the a-Si layer 5 below the source region and the drain region is also crystallized, and a channel having excellent characteristics can be obtained. Further, since the interface between the gate insulating film 4 and the channel formation region is below the channel formation region, the interface characteristics do not deteriorate due to the incidence of the laser, so that the characteristics of the device do not deteriorate.

The UV light often used for a laser light source is S
Since iO ₂ can be transmitted, laser irradiation can be performed from the passivation film 13 if the passivation film 13 is silicon oxide (SiO ₂ ).

[0012] Thereby, it is possible to prevent the upper surface of the a-Si film from being disturbed by laser irradiation. That is, if the passivation film is silicon oxide, the passivation film
A cap layer commonly used when laser crystallization of a-Si film is the same as the silicon oxide film formed on the a-Si film targeted for laser irradiation to prevent disturbance of the upper surface of the film during laser irradiation It plays a role and makes it possible to obtain a high-quality laser crystallized film.

By selecting the wavelength of the laser or the material of the glass substrate so that the laser can pass through the glass substrate 1, the base insulating film 2 formed on the glass substrate to prevent impurities from entering the glass substrate and the gate insulating film are formed. If the film is made of a material that transmits laser (for example, silicon oxide), the gate electrode 3 is made smaller than the width between the source and drain electrodes to irradiate the laser from the lower part of the substrate to thereby form an impurity region below the source and drain electrodes. Can be crystallized and activated, and a greater improvement in various properties can be obtained. If the base film and the gate insulating film are silicon oxide films,
They also act as a cap layer at the same time, and can prevent disturbance of the surface below the film.

FIG. 1B shows a further development of the structure shown in FIG. 1A and enables more effective laser activation for the source region and the drain region.

In FIG. 1B, the source region 11 and the drain region 12, which are impurity regions, are located above the source electrode 9 and the drain electrode 10, respectively, and are in contact with the upper side of the channel forming region 5. Since the laser irradiation on the source / drain region can be completely performed only by irradiation from above, a structure capable of obtaining a greater improvement in various characteristics and a range of controllable values as compared with FIG. Has become. By irradiating a laser beam having a sufficient energy value as in FIG. 1A, the lower part of the source region and the drain region in the intrinsic a-Si layer 5 serving as a channel forming region is crystallized. A channel having good characteristics can be obtained. Further, since the interface between the gate insulating film 4 and the channel formation region is below the channel formation region, the interface characteristics do not deteriorate due to the incidence of the laser, so that the device characteristics do not deteriorate. If the passivation film is silicon oxide, it acts as a cap layer at the time of laser irradiation, and disturbs the laser irradiation on the upper surface of the impurity a-Si film as the source / drain region and the intrinsic a-Si film as the channel formation region. Can be prevented.

FIGS. 1C and 1D show FIGS. 1A and 1B, respectively.
The channel is formed upside down with the channel formation region and source by irradiating the laser mainly from the bottom of the substrate by selecting the laser wavelength or the material of the glass substrate so that the laser can pass through the glass substrate. -It enables crystallization and activation of the drain region.

FIG. 1C shows a completely inverted structure of FIG. 1A, and similarly to FIG.
By making the distance between the gate electrode and the drain electrode 10 larger than the distance between the source region 11 and the drain region 12, activation and crystallization of the source / drain region and the channel formation region 5 by laser irradiation from the lower part of the substrate are enabled. .

At this time, by irradiating a laser beam having a sufficient energy value, the intrinsic property of forming a channel forming region is obtained.
A portion of the a-Si layer 5 below the source region and the drain region is also crystallized, and a channel having excellent characteristics can be obtained. In addition, since the interface between the gate insulating film and the channel formation region is above the channel formation region, the interface characteristics are not deteriorated by the incidence of the laser from below, so that the device characteristics are not reduced.

Further, if the underlying film 2 formed on the glass substrate 1 in order to prevent impurities from being mixed from the glass substrate is a silicon oxide film, it acts as a cap layer, and serves as a source / drain region and a channel forming region. Disturbance on the lower surface of the a-Si film can be prevented. Passivation film 1
When the gate insulating film 3 and the gate insulating film 4 are made of a material that transmits laser, for example, silicon oxide, the gate electrode 3 is made smaller than the width between the source and drain electrodes to irradiate the laser from above the substrate and the upper side of the source and drain electrodes. Can be crystallized and activated, and further improvement in various characteristics can be obtained. At that time, if the passivation film and the gate insulating film are silicon oxide, they simultaneously act as a cap layer, and a-
Disturbance on the upper surface of the Si film can be prevented.

FIG. 1D shows a further development of the structure shown in FIG. 1C and enables more effective laser activation for the source region and the drain region.

In FIG. 1D, a source region 11 and a drain region 12, which are impurity regions, are located below the source electrode 9 and the drain electrode 10, respectively, and are in contact with both sides below the channel forming region 5. Therefore, the laser irradiation on the source / drain regions can be completely performed only by irradiation from the lower part, so that a greater improvement in various characteristics and a wider range of controllable values can be obtained as compared with FIG. It has a structure that can be. By irradiating a laser beam having a sufficient energy value in the same manner as in FIG. 1C, a portion above the source region and the drain region in the intrinsic a-Si layer serving as a channel formation region is crystallized, and a favorable A channel having characteristics can be obtained.

Further, since the interface between the gate insulating film 4 and the channel formation region is above the channel formation region, the interface characteristics are not deteriorated by the incidence of the laser, so that the characteristics of the device are not reduced. If the underlying film is silicon oxide, it acts as a cap layer at the time of laser irradiation, and the lower surface of the impurity a-Si film serving as the source / drain region and the intrinsic a-Si film serving as the channel forming region are disturbed by the laser irradiation. Can be prevented.

With the above structure, a-Si
Activation and crystallization of the source / drain region and the channel formation region by laser irradiation after the completion of the device structure of the thin film transistor can be performed.

As described above, laser irradiation is not performed before or during processing of a device structure.
The device is processed by the complete a-Si TFT process, and the device structure is completed, that is, the formation of the impurity semiconductor layer, the intrinsic semiconductor layer, the gate insulating film, the formation of the source / drain regions, the source, drain, and gate electrodes, and After completing the process including the formation of the passivation film (passivation film) or the formation of circuit wiring, the laser is applied to the source / drain region and channel formation region of one or more a-Si TFTs. Irradiates the crystallization of the channel formation region of the thin film transistor or the source
Activation and crystallization of the drain region are performed. At this time, if the electrodes and wiring are made, any a-Si TFT on the substrate
It is possible to perform laser irradiation until the optimum value is obtained while monitoring the electrical characteristics of the laser in real time. Alternatively, a thin film transistor having desired characteristics can be obtained by repeating a process of measuring electric characteristics after laser irradiation.

In this way, a plurality of a-Si TFTs are manufactured on the same substrate by the same manufacturing process, and after the device structure is completed, any one or a plurality of a-Si TFTs are converted into TFTs having arbitrary electric characteristics. It becomes possible. That is, it is possible to manufacture TFTs having different electric characteristics on the same substrate by irradiating a laser after completing the device structure.

In addition, a plurality of a-Si TFTs are manufactured on the same substrate by the same manufacturing process and the device structure is completed, and any one or a plurality of the a-Si TFTs is subjected to laser crystallization. A polycrystalline silicon thin film transistor (hereinafter referred to as "poly-SiTFT") can be used to create a system in which both a-SiTFT and poly-SiTFT are mixed on the same substrate without dividing the process of manufacturing the device structure It becomes possible.

Further, since the laser irradiation is performed in a very short time, the temperature of the substrate hardly rises.
It is possible to fabricate poly-Si TFTs at low temperatures (room temperature to 400 ° C.), thereby making it possible to fabricate large-area poly-Si TFT systems at low cost without using expensive glass such as quartz glass. .

Hereinafter, examples using the present invention will be described.

[0029]

[Embodiment 1] In this embodiment, an a-Si TFT and a poly-Si TFT in an integrated LCD (liquid crystal display) system are used.
A mixed system of SiTFT (polycrystalline silicon thin film transistor) will be described. The integrated LCD system as shown in FIG.
0 and the peripheral circuit TFT portion 31 are required. The requirements for the operation speed are completely different for the two types of TFTs, and for the pixel driving type, a mobility of about 1 cm ² / Vs is sufficient, but the TFT for the peripheral circuit operates at high speed ( Several MHZ)
Is required. For this reason, the pixel TFT is made of a-Si material,
It is desirable that the TFT for the peripheral circuit is made of a poly-Si material.

According to the present invention, a system as shown in FIG.
It can be manufactured at once without dividing by TFT.

FIG. 3 is a schematic diagram schematically illustrating a method of manufacturing a TFT. In this embodiment, a TFT having the structure shown in FIG. 1A, that is, an inverted staggered structure is used. Of course, other structures may be used. In FIG. 3A, silicon oxide (SiO ₂ ) as a base film 2 is formed on a glass 1 such as quartz glass which can withstand a heat treatment at an inexpensive temperature of 700 ° C. or less, for example, about 600 ° C. by using a magnetron RF (high frequency) sputtering method. The film is formed to a thickness of 1000 to 3000 °, in this example, 2000 °. The film forming conditions were a 100% oxygen atmosphere, a film forming temperature of 150 ° C., an output of 400 to 800 W, and a pressure of 0.5 Pa. Quartz or single crystal silicon was used as a target.
The deposition rate was 30 to 100 ° / min.

A chromium (Cr) layer 3 serving as a gate electrode is formed thereon by a known sputtering method. The film thickness is 800
Å1000 °, and 1000 ° in this embodiment. This was patterned using a first photomask P1 to obtain FIG. 3 (B). Also, tantalum (Ta) is used as a gate electrode material.
May be used.

When aluminum (Al) is used as the gate electrode material, it is used as the first photomask P1.
After the patterning, the surface may be anodized.

A silicon nitride film (SiN _x ) is formed thereon as a gate insulating film 4 by a PCVD method. The film thickness is 10
It was set to 00 to 5000 °, and 3000 ° in this embodiment. The source gases are silane (SiH ₄ ) and ammonia gas (NH)
₃ ) was used in a ratio of 1: 3. The film forming condition is a film forming temperature of 250.
To 350 ° C., 260 ° C. in this embodiment, RF frequency 13.56 MHz, RF output 80 W, pressure 0.05
Torr and the film formation rate were 80 ° / min.

An intrinsic a-Si layer 5 is formed thereon by a PCVD method. The film thickness is 200 to 1000 °, and in this embodiment, 7
00 °. Silane (SiH ₄ ) is used as a source gas, the film forming temperature is 150 to 300 ° C., in this embodiment, 200 ° C., the RF frequency is 13.56 MHz, the RF output is 35 W, the pressure is 0.5 Torr, and the film forming rate is Was 60 ° / min.

On top of this, an impurity a-Si layer, here an n ⁺ type
The a-Si layer 6 is formed by a PCVD method. The film thickness is 300 ~
The angle was set at 500 °, and in this example, 500 °. Silane is used as a source gas, and phosphine (PH ₃ ) is added in an amount corresponding to 1% of silane to add phosphorus as an N-type impurity. The film forming temperature is 150 to 300 ° C., 200 ° C. in this embodiment, the RF frequency is 13.56 MHz, the RF output is 40 W, the pressure is 0.5 Torr, and the film forming speed is 60 ° /
Minutes

As described above, the gate insulating film 4, the intrinsic a-Si layer 5, and the n ⁺ a-Si layer 6 were formed, and FIG. 3C was obtained. Since these are all formed by a PCVD method, it is effective to form a film continuously using a multi-chamber method. Further, another film formation method, for example, a reduced pressure gas phase method, a sputtering method, an optical CVD method, or the like may be used. Thereafter, dry etching is performed using the second photomask P2 to form a TFT island region as shown in FIG.

Next, a chromium (Cr) layer 7 serving as a source / drain electrode is formed by a sputtering method to obtain FIG. The film thickness is 500 to 1000 °, and 800 ° in this embodiment.
And This is patterned using a third photomask P3. At this time, without removing the resist 8, the n ⁺ a-Si layer is patterned by dry etching to form a channel forming region, a source electrode 9, a drain electrode 10, and a source region 11 and a drain 12 region. Obtain F).

Here, by performing wet etching without removing the resist, over-etching is performed to make the distance between the source and drain electrodes larger than that between the source and drain regions. Thereby, activation and crystallization of the source / drain regions by laser irradiation from above can be performed. Thereafter, the resist is peeled off to obtain FIG.

[0040] The silicon oxide as Pashibeishon film as shown in FIG. 3 (H) on the (SiO ₂₎ by an RF sputtering method described above 1000 to 3000 .ANG, in this embodiment 2
A film was formed to a thickness of 000 mm. A PCVD method or the like may be used. Thus, the device structure of the TFT is completed.

Thereafter, wiring was performed, and laser irradiation was performed from above while connecting and monitoring a measuring instrument. HP-4142B was used for the measuring device. The laser used was an excimer laser, here a KrF excimer laser having a wavelength of 248 nm. Within this wavelength range, UV light can pass through the passivation film above the TFT. Energy E is 200-350 mJ / cm ² , irradiation number 1-5
0 SHOTS, substrate temperature T _S during irradiation is room temperature to 400
° C.

With this, crystallization and activation can be performed by irradiating a laser to the channel forming region and / or the source / drain region while monitoring, and the TFT shown in FIG. As described above, various characteristics of the TFT were obtained.
Since a huge number of TFTs for driving the pixel matrix, for example, 640.times.400 = 256,000 TFTs, all have to be made to have the same characteristics, it is very difficult to improve the yield. By using, defective TFTs having greatly different characteristics can be significantly reduced, and the yield can be significantly improved.

By sufficiently irradiating the peripheral circuit TFT portion 31 in FIG. 2 with laser light, the characteristics are remarkably improved, and before the laser irradiation, the field effect mobility μ ₁ is 0.5 to 0.8 cm. ² / vs, threshold voltage V
_{Although the th1} was 10 to 20 V, after the laser irradiation, the field effect mobility μ ₂ was 10 to 100 cm ² / vs, the threshold voltage V _th2 was 5 to 7 V, and the characteristics were greatly improved. Sufficient high-speed operation was obtained as a TFT for a peripheral circuit of the device. The channel formation region formed by the a-Si film is crystallized and poly-Si with high carrier mobility
It was a film and had sufficient characteristics as a poly-Si TFT.

Thereafter, the ITO (Injum ™) is placed on the substrate.
Tin oxide) was formed to a thickness of 0.1 μm by a sputtering method, and a pixel electrode was formed using a photomask. This I
TO was formed at room temperature to 150 ° C. and achieved by annealing at 200 to 400 ° C. in oxygen or atmosphere. If the pixel electrode is not deteriorated by the laser, the TFT may be irradiated with laser after the pixel electrode is formed.

A polyimide precursor was printed on the substrate by an offset method, and baked at 350 ° C. for 1 hour in a non-oxidizing atmosphere, for example, nitrogen. Thereafter, a known rubbing method was used to modify the surface of the polyimide, and at least initially, a means for aligning liquid crystal molecules in a certain direction was provided. Thus, one substrate of the liquid crystal display device was obtained.

The other substrate has an I
TO was formed to a thickness of 1 μm using a sputtering method, and a counter electrode was formed using a photomask. This ITO is at room temperature
A film was formed at 150 ° C. and achieved by annealing at 200 to 300 ° C. in oxygen or air to obtain a second substrate.

A polyimide precursor was printed on the substrate by an offset method, and baked at 350 ° C. for 1 hour in a non-oxidizing atmosphere, for example, nitrogen. Thereafter, a known rubbing method was used to modify the surface of the polyimide, and at least initially, a means for aligning liquid crystal molecules in a certain direction was provided.

Thereafter, the nematic liquid crystal composition is sandwiched between the two substrates, external wiring is performed, and a polarizing plate is mounted on the outside.
A transmissive liquid crystal display was obtained. The obtained liquid crystal display device was no inferior to those in which a pixel matrix driving TFT and a peripheral driving circuit were separately manufactured.

As described above, in order to crystallize and activate the channel formation region and the source / drain region by laser irradiation after the completion of the device structure, the passivation film on the laser light incident side, here, the upper part of the substrate is made of UV light. Is required to be transmitted. In addition, since the channel which actually operates as a channel in the channel formation region is a portion at the interface with the gate insulating film, the intrinsic a-Si layer serving as the channel formation region is preferably as thin as possible to perform sufficient crystallization.

The a-Si after completion of the device structure in this way
Control of various characteristics of TFT by laser irradiation and poly-
SiTFT conversion is now possible. Also, a-Si TFT and poly-SiT
FT and FT can be made separately. Also many
Circuit system using poly-Si TFT at room temperature to 400 ° C
Thus, it is possible to manufacture at low cost without using expensive glass such as quartz glass.

Embodiment 2 As an application of the present invention, a poly-Si TFT type liquid crystal display device having a redundant circuit configuration was manufactured and will be described.

In a circuit system using a very large number of poly-Si TFTs, such as a poly-Si TFT type liquid crystal display device, it is very difficult to make all the TFTs operate completely. For this reason, some redundant configuration is often adopted. As one of the redundant configurations of the a-Si TFT for driving the pixel matrix in the a-Si TFT type liquid crystal display device, a plurality of, for example, two TFTs are connected in parallel, and two TFTs are connected.
By operating both FTs, there is a method in which even if one of them does not operate for some reason, the other TFT operates to improve the yield. However
ON current of poly-Si TFT is about 0.1 per TFT.
There is also mA, which is about 100 times that of about 1 μA of a-Si TFT,
Operating twice as many TFTs for redundancy purposes is a huge waste of power and one TF per pixel.
It is desired to operate at T.

On the other hand, laser-crystallized poly-Si TFT
In a circuit system, exactly the same circuit is used for poly-Si TFT
And make it possible to connect them in parallel.First, one circuit is operated, and when it does not work properly, or when it does not work properly at the time of operation check, the other circuit In the case of a redundant configuration in which both circuits are switched, laser crystallization was applied to both circuits.
The laser irradiation time must be doubled, the energy consumption also doubled, and the working time is prolonged and the cost of the product is increased.

The above problems can be solved by using the method according to the present invention.

FIG. 4 shows a redundant configuration p using the present invention.
1 shows an oly-Si TFT type liquid crystal display device. As shown in FIGS. 4 and 5, in this liquid crystal display device, all the TFTs in the pixel matrix driving TFT portion 20 and the shift register circuit 21 in the peripheral circuit have a redundant configuration.
The pixel matrix driving TFT has a redundant configuration of two TFTs, and the shift register circuit has two identical circuits.

First, all the TFTs to be subjected to redundancy are manufactured with the structure according to the present invention as shown in FIG. 1, and after the device structure is completed, it can be operated as a poly-Si TFT by irradiating a laser. . The TFT was manufactured in the steps shown in FIG. 3 as described in Example 1. The process was advanced to the state before the formation of the passivation film and the formation of the pixel electrode, that is, FIG.

FIG. 5 shows an arrangement of the pixel matrix driving TFTs. As shown here, the TFT is an a-Si TFT, and the two TFTs are connected in parallel. First, out of the two TFTs connected to all the pixel electrodes, one of the two TFTs, here, 23 TFTs is irradiated with a laser to obtain a poly-Si TFT. Here, a measuring instrument was connected and an operation check was performed. If there is no abnormality here, the process proceeds to the next step. Since the redundant TFT 24 is an a-Si TFT, the operating current is about two orders of magnitude smaller than that of the poly-Si TFT, so that the effect can be substantially ignored. The threshold voltage is pol
Since the voltage of the y-Si TFT is 0 to about 10 V and the voltage of the a-Si TFT is about 10 to about 20 V, only the laser-crystallized poly-Si TFT operates without parallel operation.

If there is a malfunctioning TFT, a-Si TFT on the redundant side of the TFT, here 24 TFTs
Then, laser irradiation was performed to obtain a poly-Si TFT, and if necessary, wiring to the TFT on the non-redundant side, here, the point A was burned off with a laser, thereby easily switching to the redundant side.

In this way, when there is no need to switch to the redundant side, the number of poly-Si TFTs that drive one pixel while taking a redundant configuration with two TFTs becomes substantially one, and the number of poly-Si TFTs becomes two. The power consumption was reduced to about half that of the method of connecting the SiTFTs in parallel to realize a redundant configuration. Also, switching to the redundant TFT can be performed by one or several laser irradiations, and a very simple and efficient method can be realized.

Next, the redundant circuit of the shift register is also 2
Two identical circuits were made in parallel, and the TFT was made as an a-Si TFT until the electrodes were connected after the state of FIG. 3 (H). The connection and switching may be made later by a connector or the like. The laser crystallization is first performed on one of the circuits, here, all the TFTs in the 21 circuits, an operation check is performed by connecting a measuring instrument, and if the operation is normal, the process proceeds to the next step.

When both circuits are connected in parallel,
Since the TFT in the redundant circuit is an a-Si TFT, the operating current is
The effect is substantially negligible because it is about two orders of magnitude smaller than poly-Si TFTs. Also, the threshold voltage of the poly-Si TFT is 0 to about 10 V, whereas the a-Si TFT is about 10 to about 20 V, so that only the laser-crystallized poly-Si TFT operates without parallel operation. Become.

If the circuit does not operate normally, the a-Si TFT in the redundant circuit 22 is irradiated with a laser to perform poly-SiT.
By switching to the FT and, if necessary, wiring to the circuit on the non-redundant side, here, the point B was burned off with a laser, it was possible to easily switch to the redundant side. Of course, connection and switching may be performed with a connector or the like.

Thus, laser crystallization only needs to be performed when it becomes necessary to switch to the redundant side.
Laser irradiation time is halved compared to the manufacturing process in which laser irradiation is performed on all TFTs at the beginning or in the middle of the manufacturing process, and unnecessary energy is not used. Therefore, work time is reduced, costs are reduced, energy is saved, etc. Was realized. Also, the switching operation to the redundant side could be made very simple without complicated wiring work.

This method is not limited to the manufacturing stage,
It can also be used for those that have failed during use, and performance can be restored in a similar manner.

As described above, by using the structure according to the present invention, in the circuit constituted by the poly-Si TFT,
It has become possible to realize an effective redundancy method such as lower power consumption, shorter working time, lower cost, and energy saving.

[0066]

By employing the manufacturing method proposed by the present invention, the following excellent effects were obtained.

According to the present invention, after the device structure is completed, the optimum parameters of the thin film transistor for forming the circuit system can be easily controlled by irradiating the laser while monitoring the electrical characteristics. Accordingly, when a large number of TFTs need to have uniform characteristics, such as a TFT type liquid crystal display device, when the characteristics of the TFTs vary, the method according to the present invention is used to reduce such variations. Can be modified,
Quality and yield were significantly improved.

In addition, the quality and the yield could be simultaneously improved without adding any difficult steps to the device structure.

Further, according to the present invention, it is possible to freely control various electrical characteristics such as the mobility of the thin film transistor on the same substrate, and to crystallize only the necessary TFT to obtain a-
It is now possible to realize a mixed system of SiTFT and poly-SiTFT

Further, since the laser irradiation is performed in a very short time, the substrate temperature is hardly increased,
It is possible to manufacture y-Si TFTs at low temperatures (room temperature to 400 ° C.), thereby making it possible to manufacture large-area poly-Si TFT systems at low cost without using expensive glass such as quartz glass. Was.

A TFT structure according to the present invention and a general TFT structure are formed on the same substrate using a-Si, and laser irradiation is performed on the TFT having the structure according to the present invention.
It goes without saying that a mixed system of T and poly-Si TFT can be realized.

As described above, the present invention can bring a number of advantages in the method of manufacturing a thin film transistor, and has a great industrial effect.

[Brief description of the drawings]

FIG. 1 shows an example of the structure of a thin film transistor of the present invention.

FIG. 2 is a configuration of a liquid crystal display device.

FIG. 3 is a process for manufacturing a thin film transistor.

FIG. 4—Poly-Si TFT driven liquid crystal display device with redundant configuration

5 is a TF for driving a pixel of the liquid crystal display device of FIG.
Redundant configuration of T

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass substrate 2 ... Base film 3 ... Gate electrode 4 ... Gate insulating film 5 ... Channel formation region 9 ... Source electrode 10 ... Drain electrode 11 ... Source region Reference numeral 12: drain region 13: passivation film 20: poly-Si TFT portion for driving a pixel matrix of a poly-Si TFT drive type liquid crystal display device 21: shift register circuit in a peripheral circuit of the liquid crystal display device 22 ..Redundant shift register circuit in peripheral circuits of liquid crystal display device 23... Poly- for driving pixel matrix of liquid crystal display device
SiTFT 24 ・ ・ ・ redundant pixel matrix drive for liquid crystal display device p
oly-Si TFT 30: TFT for driving the pixel matrix of the liquid crystal display device
Part 31: TFT part for peripheral circuit of liquid crystal display device

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[Procedure amendment]

[Submission date] March 26, 2001 (2001.3.2)
6)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 29/78 616V 617J 617M 618Z

Claims (21)

[Claims] A thin film transistor including a gate electrode, a gate insulating film in contact with the gate electrode, and a crystallized semiconductor film in contact with the gate insulating film, wherein the semiconductor film has an impurity region; A thin film transistor, wherein the gate electrode has a region overlapping with the impurity region via the gate insulating film. 2. A thin film transistor having a gate electrode, a gate insulating film on the gate electrode, and a crystallized semiconductor film on the gate insulating film, wherein the semiconductor film has an impurity region, A thin film transistor, wherein the gate electrode has a region overlapping with the impurity region via the gate insulating film. 3. The thin film transistor according to claim 1, wherein an end of the gate electrode has a portion overlapping with the impurity region via the gate insulating film. 4. The thin film transistor according to claim 1, wherein an end of the impurity region has a portion overlapping with the gate electrode with the gate insulating film interposed therebetween. 5. The thin film transistor according to claim 1, wherein an end of the gate electrode has a portion below the impurity region. 6. The method according to claim 1, wherein
The field effect mobility of the thin film transistor is 10 cm ² /
vs. or more. 7. The method according to claim 1, wherein
The thin film transistor, wherein the thickness of the gate insulating film is 100 to 500 nm. 8. The method according to claim 1, wherein
The thin film transistor has a channel formation region, and the thickness of the channel formation region is 20 to 100 nm. 9. The method according to claim 1, wherein
A thin film transistor, wherein a surface of the gate electrode is anodized. 10. The thin film transistor according to claim 1, wherein chromium, tantalum, or aluminum is used for the gate electrode. 11. The thin film transistor according to claim 1, wherein the impurity region has N-type conductivity. 12. The thin film transistor according to claim 1, wherein the impurity region has a P-type conductivity. 13. The thin film transistor according to claim 1, wherein the impurity region contains phosphorus. 14. The thin film transistor according to claim 1, wherein the semiconductor film is crystallized by laser irradiation. 15. An active matrix display device comprising: a thin film transistor having a gate electrode, a gate insulating film in contact with the gate electrode, a crystallized semiconductor film in contact with the gate insulating film, and a pixel electrode. ,
The active matrix display device, wherein the semiconductor film has an impurity region, and the gate electrode has a region overlapping with the impurity region via the gate insulating film. 16. An active matrix display device comprising: a thin film transistor having a gate electrode, a gate insulating film on the gate electrode, a crystallized semiconductor film on the gate insulating film, and a pixel electrode. An active matrix display device, wherein the semiconductor film has an impurity region, and the gate electrode has a region overlapping with the impurity region via the gate insulating film. 17. A thin film transistor including a gate electrode, a gate insulating film in contact with the gate electrode, a crystallized semiconductor film in contact with the gate insulating film, a pixel electrode, and a first polyimide film. A second substrate having one substrate, a counter electrode, and a second polyimide film;
An active matrix display device including a liquid crystal between the first substrate and the second substrate, wherein the semiconductor film has an impurity region, and the gate electrode includes the impurity region and the gate insulating film. An active matrix type display device having an overlapping area via a substrate. 18. A thin film transistor having a gate electrode, a gate insulating film on the gate electrode, a crystallized semiconductor film on the gate insulating film, a pixel electrode, and a first electrode.
A first substrate having a polyimide film, a counter electrode,
A second substrate having a second polyimide film;
An active matrix display device having a liquid crystal between the substrate and the second substrate, wherein the semiconductor film has an impurity region, and the gate electrode has the impurity region and the gate insulating film interposed therebetween. An active matrix display device having an overlapping region. 19. The active matrix display device according to claim 15, wherein the thin film transistor is used by being connected to a pixel electrode of the active matrix display device. 20. The active matrix display device according to claim 15, wherein the thin film transistor is used for a peripheral driver circuit of the active matrix display device. 21. The active matrix display device according to claim 15, further comprising: a thin film transistor connected to a pixel electrode and a thin film transistor used for a peripheral driver circuit on the same substrate. An active matrix type thin film transistor, wherein the thin film transistor having a region where a gate electrode overlaps with the impurity region via the gate insulating film is a thin film transistor used in connection with the pixel electrode or a thin film transistor used in the peripheral driver circuit. Display device.