JP2001284594A - Thin-film transistor and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide TFT where the crystal grain size in a polycrystal silicon film of an active layer is large and constant while light is prevented from being irradiated to a joint surface with an electric field concentrated. SOLUTION: On a glass substrate 10, a light-shielding film 100 of chromium and an insulating film 101 are formed, over which an amorphous silicon film 13 is laminated, which is irradiated with laser beam to provide a polycrystal silicon film 13. The polycrystal silicon 13 has an LDD structure, over which a gate insulating film 12 and a gate electrode 11 are formed. Here, the light- shielding film 100 is so formed as to even cover an LDD region 13LD.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor (hereinafter, referred to as a thin film transistor) having an active layer of a polycrystalline semiconductor film obtained by polycrystallizing an amorphous semiconductor film by laser irradiation.
It is called "TFT". ) And a display device provided with the same.

[0002]

2. Description of the Related Art Conventionally, for example, a liquid crystal display (LCD) having a TFT for driving liquid crystal in a display pixel portion and a TFT for a peripheral drive circuit portion provided around the display pixel portion for driving the TFT. Crystal Display, LC
D ". Research and development of TFT as a switching element of a display device are being advanced.

Hereinafter, a conventional TFT will be described.

FIG. 5 is a sectional view of a conventional TFT.

As shown in FIG. 1, chromium (C) is deposited on an insulating substrate 10 made of quartz glass, non-alkali glass or the like.
An opaque material such as r) is deposited, and the opaque material is left in a region to be an active layer later to form the light shielding film 100. An insulating film 1 such as a SiN film or a SiO ₂ film is formed on the light shielding film 100.
01 is formed. Then, an active layer 13 made of a polycrystalline silicon film obtained by irradiating the amorphous silicon film with a laser beam to be polycrystallized is formed.
_A gate insulating film 12 composed of _two films or the like is formed. Further, a gate electrode 11 made of a refractory metal such as Cr and molybdenum (Mo) is formed thereon in this order.

In the active layer 13, impurity ions are implanted into both sides of the channel 13c using the channel 13c and the gate electrode 11 as a mask, and a resist or the like including the gate electrode 11 and partially covering both sides of the gate electrode 11 is used. Is used as a mask to implant impurity ions into the active layer. As a result, a low-concentration impurity region 13LD is provided on both sides of the gate electrode 11, and a source 13s and a drain 13d, which are high-concentration impurity regions, are further provided outside the region. Do
A TFT having a ped drain structure is formed.

An interlayer insulating film 15 is formed on the entire surface of the gate insulating film 12 and the gate electrode 11 in the order of a SiO ₂ film, a SiN film and a SiO ₂ film, and is provided corresponding to the drain 13d. The drain electrode 16 is formed by filling the contact hole with a metal such as aluminum (Al). Further, a flattening insulating film 17 made of, for example, an organic resin and flattening the surface is formed on the entire surface. Then, a contact hole is formed at a position corresponding to the source 13s of the planarization insulating film 17, and an ITO (Indium Thin Oxid) contacting the source 13s through the contact hole.
e) A display electrode 18 which also serves as the source electrode 14 is formed on the planarizing insulating film 17.

[0008]

However, as shown in FIG. 6, the interface between the low-concentration region 13LD of the LDD region and the source region 13S or the drain region 13d, which is the high-concentration region, has different impurity concentrations. Since the TFTs are in contact with each other, there is a difference in resistance. When the TFT is in an off state, an electric field concentrates near the interface. When light enters there, T
There is a disadvantage that the off current of the FT is increased. That is, as shown in the drawing, the off-state current is not large because the light-shielding film 100 covers the region up to the LDD region, but the off-state current increases sharply in the region beyond the LDD that is not shielded by the light-shielding film. I have.

FIG. 6 shows the relationship between the amount of overlap of the light-shielding film with the semiconductor film and the current ratio in the case where the light-shielding film is provided when it is not provided. In the figure, the LDD region is formed up to 1.25 μm. It can be seen that the current ratio is lowered when the area exceeds that range.

After the amorphous silicon film is formed, when the amorphous silicon film is irradiated with a laser beam to form an active layer of a polycrystalline silicon film, heat generated by the laser beam irradiation is reduced by a light shielding film made of metal. The polycrystalline silicon film 1 on the light-shielding film 100 polycrystallized by laser light irradiation because it is easy to escape
The grain size of the third channel 13c is 13LD, 13d, 13 of the polycrystalline silicon film which does not overlap with the other light shielding films 100.
The grain size of s, that is, the grain size of the polycrystalline silicon film on the glass substrate 10 becomes smaller.

As described above, there is a disadvantage that the crystal grain size of the polycrystalline silicon film is different depending on whether it is on a light-shielding film made of metal or on a glass substrate.

When the laser energy is increased to increase the grain size of the channel region, the grain size on the glass becomes smaller on the contrary, so that the crystal grain size of the channel region cannot be increased. If the particle size is small, there is a disadvantage that the grain boundaries increase, the electric field mobility decreases, and the TFT characteristics deteriorate.

Also, the resistance value of the LDD region into which impurities are implanted at a low concentration varies greatly depending on the crystal grain size in the polycrystalline silicon film and is unstable.
In the case where the LDD region is not completely covered in the middle of the D region, the crystal grain size changes in the LDD region, so that there is a disadvantage that the sheet resistance changes greatly and the TFT characteristics also changes. .

The present invention has been made in view of the above-mentioned conventional drawbacks, and it is intended to prevent light from being irradiated to a junction surface where an electric field is concentrated, and to prevent a polycrystalline silicon film serving as an active layer from being irradiated with light. An object is to provide a TFT having a large crystal grain size and uniformity.

[0015]

The TFT of the present invention has a light-shielding film made of an opaque metal on an insulating substrate, and a non-single-crystal semiconductor film is irradiated with laser light on the light-shielding film. A TFT having an LDD structure including a polycrystallized semiconductor film and a gate electrode formed with the polycrystalline semiconductor film and an insulating film interposed therebetween, wherein the light-shielding film overlaps the gate electrode in a plane. And a low-concentration region provided on both sides of the channel region.

Further, the TFT of the present invention has a light-shielding film made of an opaque metal on an insulating substrate, and a non-single-crystal semiconductor film is irradiated with laser light to form a polycrystal on the light-shielding film. TF having an LDD structure including a semiconductor film and a gate electrode formed with the polycrystalline semiconductor film and an insulating film interposed therebetween
T, wherein the length of the light-shielding film in the channel length direction is a sum of a channel length of a channel region that is planarly overlapped with the gate electrode and a length of a low-concentration region provided on both sides of the channel region. Is larger than

Further, the above-mentioned TFT is a TFT in which an end portion of the light-shielding film overlaps a source region or a drain region formed outside the low-concentration region.

Further, the display device of the present invention has a light-shielding film made of an opaque metal on an insulating substrate, and a non-single-crystal semiconductor film is irradiated with a laser beam on the light-shielding film to form a polycrystal. A thin film transistor having an LDD structure having a semiconductor film formed and a gate electrode formed with the polycrystalline semiconductor film and an insulating film interposed therebetween, wherein the light-shielding film is planar with the gate electrode. And a thin-film transistor that covers a channel region superimposed on the thin film and low-concentration regions provided on both sides of the channel region in a planar manner.

Further, the display device of the present invention includes a light-shielding film made of an opaque metal on an insulating substrate, and irradiates a non-single-crystal semiconductor film with laser light on the upper layer of the light-shielding film to form a polycrystal. A thin film transistor having an LDD structure having a semiconductor film formed and a gate electrode formed with the polycrystalline semiconductor film and an insulating film interposed therebetween, wherein a width of the light shielding film in a channel length direction is: A thin film transistor is provided which is larger than the sum of the channel length of a channel region overlapping the gate electrode in a plane and the length of a low concentration region provided on both sides of the channel region.

Further, the above-mentioned display device is a display device including a thin film transistor in which an end of the light-shielding film overlaps a source region or a drain region formed outside the low-concentration region.

[0021]

Embodiments of the present invention will be described below.

FIG. 1 is a plan view of a TFT according to the present invention, and FIG. 2 is a cross-sectional view when the TFT is used for an LCD.
In the case of the present embodiment, a TFT having a so-called double gate electrode structure having two gate electrodes is shown.

A light-shielding film 100 made of Cr is formed on an insulating substrate 10 made of quartz glass, non-alkali glass, or the like. At this time, the region where the light shielding film 100 is formed is a region where the active layer 13 is formed later. On this light-shielding film 100, an insulating film 101 made of a SiO ₂ film, a SiN film or the like is formed. Next, a gate electrode 11 made of a high melting point metal such as Cr or Mo is formed, and a SiO ₂ film, SiN
Gate insulating film 1 composed of a single film or a laminate thereof
2, and an active layer 13 made of an amorphous silicon film is deposited. Thereafter, the amorphous silicon film 13 is irradiated with a laser beam to be melted and recrystallized to be polycrystallized, thereby being modified into a polycrystalline silicon film 13. Thereafter, the polycrystalline silicon film 13 is etched into an island shape.

Subsequently, impurity ions such as phosphorus (P) are implanted into the polycrystalline silicon film 13 using the gate electrode 11 as a mask to form a low concentration region 13LD of impurity ions.
Further, impurity ions are implanted again using the gate electrode 11 and a resist or the like which partially covers both sides of the gate electrode as a mask. As a result, a low impurity concentration region 13LD and a source region 13s and a drain region 13d which are high impurity concentration regions are formed in the polycrystalline silicon film 13. Active layer 1
A gate insulating film 12 of SiO ₂ film and SiN film on 3
Is formed thereon, and a gate electrode 11 made of a high melting point metal such as Cr and molybdenum (Mo) is sequentially formed thereon. Further, a SiO ₂ film and S on the gate electrode and the gate insulating film 12 are formed.
An interlayer insulating film 15 consisting of three layers, iN film and SiO ₂ film, is deposited. Then, a contact hole is formed at a position corresponding to the drain region 13d of the interlayer insulating film 15, and a metal such as Al is filled therein to form a drain electrode 16.

The drain electrode 16 and the interlayer insulating film 15
A planarizing insulating film 17 for planarizing the surface is formed thereon, and a contact hole is formed at a position corresponding to the source region 13s of the planarizing insulating film 17, the interlayer insulating film 15, and the gate insulating film 12. Is filled with a transparent material such as ITO, and the display electrode 18 serving also as the source electrode 14 is planarized.
7.

Thereafter, as shown in FIG. 2, the alignment film 1 for aligning the liquid crystal 35 on the flattening insulating film 17 and the display electrode 18.
By forming 9, a so-called TFT substrate 10 is completed.

The counter electrode substrate 30 facing the TFT substrate 10 has regions exhibiting respective colors such as red (R), green (G), blue (B), and a black matrix provided between these colors. A counter electrode substrate 30 on which a color filter 31 on which a color filter 32 is disposed, a protective film 34 thereof, and an alignment film 19 are sequentially formed, and the periphery of the TFT substrate 10 and the counter electrode substrate 30 are bonded with a seal adhesive. The liquid crystal 35 is filled in the space between the two substrates to complete the LCD.

Here, the formation region of the light shielding film 100 will be described.

FIG. 3 is an enlarged view in which the vicinity of the TFT of FIG. 1 is enlarged.

As shown in FIG. 3, the gate electrodes 11a, 1
On both sides of 1b, a low concentration region (hereinafter, referred to as an “LDD region”) 13LD (subscripts a, b, c, and d are provided) is provided.

At this time, the light-shielding film 100
Are the LDD regions 13LD and the gate electrodes 11a and 11d.
b. Also, the light shielding film 100
Is located outside the LDD region 13LD, that is, between the drain electrode 16 and the LDD region 13LDa on the gate electrode 11a side, and between the source electrode 14 and the LDD region 13LDd on the gate electrode 11b side. Is formed. LDD region 13LD is provided between gate electrode 11a and gate electrode 11b.
b, 13LDc and the LDD regions 13LDb and 13LDc
LDc.

As described above, the LDD region 13LD, especially L
By covering the region between the DD region 13LD and the source region 13s and the drain region 13d,
As shown in FIG. 2, even when light L is incident on the junction surface between the LDD region and the source region 13s and the drain region 13d, the light L is blocked by the light shielding film 100. There is no irradiation on the joint surface. Therefore, it is possible to prevent an increase in off-state current of the TFT due to light irradiation on the bonding surface.

Further, during polycrystallization by laser light irradiation, the heat of the laser light is absorbed by the light-shielding film below the amorphous silicon film, and the crystal grain size overlaps with the light-shielding film of the active layer. Becomes smaller. That is, the crystal grain size was different depending on whether it was on the light shielding film or the glass substrate.

For this reason, conventionally, if the laser energy is increased to increase the particle size of the channel region, the particle size on the glass will be conversely reduced.
The crystal grain size of the channel region cannot be increased, and when the crystal grain size is small, the grain boundaries increase, the electric field mobility decreases, and the TFT characteristics deteriorate, and impurities are implanted at a low concentration. The resistance value of the LDD region fluctuates greatly depending on the size of the crystal grain in the polycrystalline silicon film and is unstable.
When the region is not completely covered, the crystal grain size changes in the LDD region, so that there is a drawback that the fluctuation of the sheet resistance increases and the fluctuation of the TFT characteristics also increases.

However, since the light-shielding film 100 covers the LDD region 13LD as in the present invention, even when polycrystallization by laser light is performed, the channel region 13LD can be formed.
Since the crystal grain size of c and the LDD region 13LD is the same, the conventional problem does not occur.

As described above, according to the present invention, it is possible to prevent an increase in off-state current due to light irradiation at the junction between the channel 13c and the LDD region 13LD, and to reduce the crystal grain size in both regions 13c and 13LD. It can be uniform.

In addition, it is possible to obtain a display device capable of obtaining a good display.

In each of the above embodiments, the LCD has been described as a display device having the TFT of the present invention. However, the present invention is not limited to this. For example, an organic EL (Electro Luminescence) display device The effects of the present invention can be obtained even when the present invention is adopted as a semiconductor device such as a switching element or a sensor of an organic EL element.

[0039]

According to the present invention, it is possible to prevent the irradiation of light to the junction surface where the field is concentrated and to obtain a TFT having a large crystal grain size in the polycrystalline silicon film as the active layer. it can.

[Brief description of the drawings]

FIG. 1 is a plan view of an LCD showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an LCD showing an embodiment of the present invention.

FIG. 3 is a partially enlarged plan view of the TFT of the present invention.

FIG. 4 is a plan view of a conventional LCD.

FIG. 5 is a cross-sectional view of a conventional LCD.

FIG. 6 is a characteristic diagram showing characteristics of a TFT.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Insulating substrate 11 Gate electrode 12 Gate insulating film 13 Active layer 13s Source 13d Drain 13c Channel 13LD LDD region 15 Interlayer insulating film 17 Flattening insulating film 18 Display electrode 30 Counter electrode substrate 31 Counter electrode 35 Liquid crystal 100 Light shielding film

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H092 JA25 JA31 JA32 JA46 JB42 JB51 JB58 KA04 KA12 KA18 KB25 MA30 NA22 NA24 5F110 AA01 AA06 AA30 BB02 CC02 DD02 DD03 DD13 DD14 DD17 EE04 EE28 FF02 FF03 GG03 GG09 GG09 NN03 NN23 NN24 NN46 NN72 PP03 QQ11 QQ19

Claims (6)

[Claims] 1. A light-shielding film made of an opaque metal is provided on an insulating substrate, and a semiconductor film obtained by irradiating a non-single-crystal semiconductor film with a laser beam to be polycrystallized is formed on the light-shielding film. What is claimed is: 1. A thin film transistor having an LDD structure including a crystalline semiconductor film and a gate electrode formed with an insulating film interposed therebetween, wherein the light-shielding film has a channel region planarly overlapping the gate electrode, and both sides of the channel region. Wherein the low-concentration region provided in the thin film transistor is planarly covered. 2. A light-shielding film made of an opaque metal is provided on an insulating substrate, and a semiconductor film obtained by irradiating a non-single-crystal semiconductor film with a laser beam and polycrystallizing the light-shielding film on the light-shielding film. A thin film transistor having an LDD structure including a crystalline semiconductor film and a gate electrode formed with an insulating film interposed therebetween, wherein a width of the light-shielding film in a channel length direction is equal to a width of a channel region overlapping the gate electrode in a plane. A thin film transistor which is larger than a sum of a channel length and lengths of low concentration regions provided on both sides of the channel region. 3. The thin film transistor according to claim 1, wherein an end of the light-shielding film overlaps a source region or a drain region formed outside the low-concentration region. 4. A light-shielding film made of an opaque metal is provided on an insulating substrate, and a semiconductor film obtained by irradiating a non-single-crystal semiconductor film with a laser beam to form a polycrystal, A display device including a thin film transistor having an LDD structure including a crystalline semiconductor film and a gate electrode formed with an insulating film interposed therebetween, wherein the light-shielding film includes a channel region that overlaps the gate electrode in a plane. A display device comprising: a thin film transistor that covers a low-concentration region provided on both sides of the channel region in a planar manner. 5. A light-shielding film made of an opaque metal is provided on an insulating substrate, and a semiconductor film obtained by irradiating a non-single-crystal semiconductor film with a laser beam to be polycrystallized is provided above the light-shielding film. A display device including a thin film transistor having an LDD structure including a crystalline semiconductor film and a gate electrode formed with an insulating film interposed therebetween, wherein a width of the light shielding film in a channel length direction is planar with respect to the gate electrode. A display device, comprising: a thin film transistor which is larger than a sum of a channel length of a superposed channel region and lengths of low concentration regions provided on both sides of the channel region. 6. The light-shielding film according to claim 4, wherein an end portion of the light-shielding film includes a thin film transistor overlapping a source region or a drain region formed outside the low-concentration region. Display device.