JP3439444B2 - Liquid crystal display - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device in which a light shielding film is formed so as to cover a TFT on a TFT (Thin Film Transistor) substrate.

[0002]

2. Description of the Related Art Liquid crystal display devices are widely used as display devices for various information devices. FIG. 17 is a sectional view showing a schematic configuration of an example of a liquid crystal display device. In the liquid crystal display device, as shown in the figure, the TFT 10 that operates as a switching element (driving element) that drives liquid crystal.
0 formed TFT substrate 101 and counter substrate 102
And a liquid crystal 103 sandwiched between the substrates 101 and 102. The TFT 100 has a gate electrode 10
5, a gate insulating film 106, a semiconductor layer 107, a drain electrode 111, a source electrode 112, and the like.

In the liquid crystal display device as described above, T
There is known a structure in which a light shielding film is formed so as to cover the TFT on the FT substrate. FIG. 11 is a plan view showing the structure of a conventional liquid crystal display device of this type, and FIG.
E'and FF 'sectional views taken in the direction of the arrows, and FIGS. 13 and 14 are process diagrams showing the manufacturing method of the liquid crystal display device in the order of processes. In the liquid crystal display device, only the structure of the TFT substrate is shown. In the liquid crystal display device, as shown in FIGS. 11 and 12, a TFT substrate 101 includes a transparent insulating substrate 104 made of glass or the like, and aluminum (Al), chromium (Cr), and the like formed on the transparent insulating substrate 104. The gate electrode 105 made of molybdenum (Mo) or the like, and the gate electrode 1
05 SiO ₂ formed on (silicon oxide) and Si
Gate insulating film 1 made of a laminated film of N _x (silicon nitride)
06, a semiconductor layer 107 made of amorphous silicon (a-Si) formed on the gate insulating film 106, and ohmic layers (n ⁺ -type layers) 10 on both ends of the semiconductor layer 107.
A drain electrode 111 and a source electrode 112 made of Cr, Mo or the like connected via 8d and 108s, a protective film (passivation film) 113 made of SiN _x formed over the entire surface including the semiconductor layer 107, and the semiconductor layer 107.
And a light-shielding film 114 made of amorphous silicon formed on the protective film 113 above. The gate electrode 105, the gate insulating film 106, the semiconductor layer 107,
The drain electrode 111, the source electrode 112, etc.
T110 is configured. A transparent pixel electrode (not shown) made of ITO (Indium-Tin-Oxide) is connected to the source electrode 112. Here, the TFT 110
The light-shielding film 114 formed so as to cover the light-shielding film is provided in order to prevent the leak current flowing in the channel (back channel) of the TFT 110 by blocking the incident light from the counter substrate side.

Next, with reference to FIGS. 13 and 14, a method of manufacturing the liquid crystal display device will be described in the order of steps. First, as shown in FIG. 13A, a transparent insulating substrate 104 made of glass or the like is used, and a film thickness made of Al, Cr, Mo, or the like is 100 to 300 nm over the entire surface by a sputtering method or the like.
After the conductive film is formed, the conductive film is patterned by a well-known photolithography method to form the gate electrode 105.

Next, as shown in FIG. 13B, CVD
By a (Chemical Vapor Deposition) method or the like, SiO ₂ and SiN _X are sequentially formed on the entire surface to form a gate insulating film 106 composed of both laminated films and having a film thickness of 200 to 400 nm. Next, the semiconductor layer 10 made of amorphous silicon and having a film thickness of 100 to 400 nm is formed on the entire surface by the CVD method or the like.
7 is formed, and then n such as P (phosphorus) is formed on the surface of the semiconductor layer.
An n ⁺ type layer 108 is formed by ion implantation of a type impurity.

Next, as shown in FIG. 13C, a film thickness of Cr, Mo, etc. is formed on the entire surface by sputtering or the like.
After forming the conductive film of 0 to 300 nm, the conductive film is patterned by a photolithography method to form the drain electrode 111 and the source electrode 112.

Next, as shown in FIG. 14D, n not covered with the drain electrode 111 and the source electrode 112.
By selectively etching the surface of the ⁺ -type layer 108, a region of the semiconductor layer 107 to be a channel (back channel) is exposed and the TFT 110 is completed.

Next, as shown in FIG. 14 (e), a film thickness of SiN _x or the like is formed on the entire surface by a sputtering method or the like.
A protective film 113 having a thickness of 400 nm is formed. Next, CVD
After forming a conductive film made of amorphous silicon and having a film thickness of 200 to 400 nm on the entire surface by a method or the like, the conductive film is patterned to form a light shielding film 114 to complete the TFT substrate 101 of FIGS. 11 and 12. .

According to the conventional liquid crystal display device manufactured by the above manufacturing method, as shown in FIGS. 11 and 12, since the light shielding film 114 exists above the TFT 110, the counter substrate is formed. The incident light from the side is blocked by the light shielding film 114 and does not enter the TFT 110.
The leak current due to 0 can be prevented or the increase of the leak current can be suppressed, and therefore the leak characteristics of the TFT 110 can be improved. A liquid crystal display device having a structure in which a light-shielding film is formed so as to cover the TFT in order to prevent light from entering the TFT in this manner has been generally known from the past, and is disclosed in, for example, Japanese Patent Laid-Open No. 2000-131716. There is. In the liquid crystal display device disclosed in the publication, not only a light-shielding film is formed above the TFT, but also a light-shielding film is formed below the TFT to prevent light from entering the TFT from the counter substrate side. Return light that enters the TFT from the back side of the TFT substrate is also prevented.

[0010]

However, in the conventional liquid crystal display device, even if the light-shielding film is formed so as to cover the TFT formed on the TFT substrate, the TFT as the switching element is turned off. There is a problem that the leak characteristic of the TFT is deteriorated in the region where the gate voltage is low.

FIG. 15 is a diagram for explaining the leak characteristic of the TFT of the conventional liquid crystal display device shown in FIGS. 11 and 12.
The same (a) shows the TFT 11 formed on the TFT substrate 101.
0 is a cross-sectional view showing 0, and FIG. 4B is a view showing a difference in leak characteristic of the TFT 110 depending on the presence or absence of the light shielding film 114. In FIG. 15B, the vertical axis represents the leak current I and the horizontal axis represents the gate voltage Vg.
0 is shown as an example of measurement under the condition that light is not irradiated (for example, the TFT 110 is housed in a dark room). A shows the leak characteristic of the TFT with the light-shielding film, B shows the leak characteristic of the TFT without the light-shielding film, and the drain voltage V
The example is shown in which d is fixed at +10 V and applied. Figure 15
As is apparent from (b), in the conventional liquid crystal display device,
In the region where the gate voltage Vg is low (−14 V to −20 V) where the TFT 110 is off as a switching element, the leakage current of the characteristic A with the light shielding film increases and the leakage current is larger than that of the characteristic B without the light shielding film. It shows that the leakage characteristics are deteriorated as the size increases. In addition, the rising threshold voltage (Vth) of the current characteristic is also low.

Originally, especially in the region where the gate voltage Vg is low, the TFT serving as a switching element is turned off, so that the leak current should be substantially zero. Nevertheless, it is considered that there is some cause that the leak current of the characteristic A with the light-shielding film is increased especially in the region where the gate voltage Vg is low. Therefore, it is desired to clarify the cause.

The present invention has been made in view of the above circumstances, and when a light-shielding film is formed on a TFT substrate so as to cover the TFT, the TF is increased even in a region having a low gate voltage.
An object of the present invention is to provide a liquid crystal display device capable of improving the leak characteristic of T.

[0014]

In order to solve the above-mentioned problems, the invention according to claim 1 is such that a liquid crystal is sandwiched between a TFT substrate and a counter substrate, and light is shielded so as to cover the TFT on the TFT substrate. It relates to a liquid crystal display device which film is formed, prior to
The light shielding film is formed so as to extend to the periphery of the TFT.
And the gate is provided with
Overlap with the gate electrode through the insulating film including the insulating film.
The gate insulating film.
It is characterized in that it is connected to the capacitance electrode formed on the top .

A second aspect of the present invention relates to the liquid crystal display device according to the first aspect, wherein the light shielding film and the gate electrode are provided.
The capacitance formed between the light-shielding film and the TFT is
Than the capacitance formed between the source and drain electrodes
It is characterized by being configured to be large .

Further, the invention according to claim 3 relates to a liquid crystal display device in which liquid crystal is sandwiched between a TFT substrate and a counter substrate, and a light-shielding film is formed so as to cover the TFT on the TFT substrate. the TFT substrate, the semiconductor layer is a drain electrode and a source electrode disposed on the surface through a gate insulating film covering the gate electrode is formed, a protective film covering the surface of the semiconductor layer including the drain electrode and the source electrode
The light-shielding film is formed via the insulating film , and the light-shielding film has an overhanging portion formed so as to extend to the periphery of the TFT, and the overhanging portion forms the gate insulating film.
It is formed so as to overlap the gate electrode through the insulating film containing it, and is formed on the gate insulating film.
It is characterized in that it is connected to a capacitor electrode that is connected .

The invention according to claim 4 relates to the liquid crystal display device according to claim 3, wherein the light-shielding film and the gate electrode are provided.
The capacitance formed between the light-shielding film and the TFT is
A capacitor formed between the source and drain electrodes
It is characterized in that it is configured to be larger than the quantity .

[0018]

[0019]

[0020]

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Prerequisites First, the experimental results that led to the completion of the present invention will be described. As a result of experiments, the inventor of this application has found that when a light-shielding film is formed on a TFT substrate so as to cover the TFT, the TFT as a switching element is turned off, especially in a region where the gate voltage is low. Is deteriorated because + is applied to the drain electrode
It was clarified that the cause is that the voltage is substantially applied to the light shielding film via the capacitance of the protective film. Therefore, by eliminating the influence of the capacitance, the leak characteristic of the TFT can be improved even in a region where the gate voltage is low. Hereinafter, the principle of the present invention will be described based on experimental results.

Experimental Results A conductive needle (probe) was applied to the light shielding film 114 of the TFT 110 shown in FIG. 15 (a), and a test voltage Vbg was forcibly applied. As shown in FIG. 16 (a), the test was conducted. Voltage V
Each leak characteristic as shown in C to E was obtained according to the value of bg. Here, C indicates the leak characteristic of the TFT at the test voltage Vbg = 0V (ground), and D indicates the test voltage Vbg =
The leak characteristics of the TFT at + 5V are shown, and E shows the leak characteristics of the TFT at the test voltage Vbg = + 10V. On the other hand, F indicates the leak characteristic of the TFT without the light shielding film.

As is clear from FIG. 16A, in the region where the gate voltage Vg is low (-1V to -20V), in which the TFT 110 as a switching element is off,
The leak current is the smallest in the characteristic C (test voltage Vbg = 0V) with the light-shielding film.
(Test voltage Vbg = + 5V), characteristic E (test voltage Vbg = +
The leak current increases in the order of 10V). That is, it was confirmed that when the light shielding film 114 is formed so as to cover the TFT 110, the leakage current tends to increase as the test voltage Vbg applied to the light shielding film 114 increases.

The fact is that even when the light-shielding film 114 is provided so as to cover the TFT 110, when a large voltage is applied to the light-shielding film 114 for some reason, especially in a region where the gate voltage Vg is low, It shows that the leak current increases.

From the above results, in the conventional liquid crystal display device, as shown in FIG. 16B, no voltage is applied to the light shielding film 114 under the condition that the TFT 110 is not irradiated with light. That is, the reason why the leak current increases especially when the TFT 110 is off and the gate voltage Vg is low is that it is formed between the light-shielding film 114 and the source / drain electrodes 111 and 112 facing each other with the protective film 113 interposed therebetween. The positive voltage (for example, 10 V described above) applied to the drain electrode 111 is affected by the generated capacitance C1 and the capacitance C1 is applied.
It is presumed that the cause is that it is substantially applied to the light shielding film 114 via Then, the light shielding film 114
By the + voltage applied to the semiconductor layer 107, charges are induced in the back channel 109A of the semiconductor layer 107, and the leak current increases. Therefore, by devising such that the voltage applied to the light-shielding film 114 becomes small, electrons induced in the back channel are eliminated, and the gate voltage Vg
It becomes possible to prevent the leak current even in a low region.

Embodiments of the present invention will be described below with reference to the drawings based on the above-described experimental results. The description will be specifically made using the embodiments. First Embodiment FIG. 1 is a plan view showing the configuration of a liquid crystal display device according to a first embodiment of the present invention, FIG. 2 is a sectional view taken along arrows AA ′ and BB ′ in FIG. 1, and FIG. 4A to 4D are process diagrams showing the method of manufacturing the liquid crystal display device in the order of processes. The liquid crystal display device of this example is
As shown in FIGS. 1 and 2, the TFT substrate 1 includes a transparent insulating substrate 4 made of glass or the like, and a gate electrode made of Al, Cr, Mo or the like formed on the transparent insulating substrate 4 (hereinafter, also referred to as gate wiring). 5), a gate insulating film 6 made of a laminated film of SiO ₂ and SiN _x formed on the gate electrode 5, and a semiconductor layer 7 made of amorphous silicon formed on the gate insulating film 6. And a drain electrode 11 and a source electrode 12 made of Cr, Mo or the like connected to both ends of the semiconductor layer 7 via ohmic layers (n ⁺ type layers) 8d and 8s, and formed on the entire surface including the semiconductor layer 7. The protective film 13 is made of SiN _x and the light shielding film 14 made of amorphous silicon is formed on the protective film 13 above the semiconductor layer 7. Gate electrode 5,
The TFT 10 is composed of the gate insulating film 6, the semiconductor layer 7, the drain electrode 11, the source electrode 12, and the like. A transparent pixel electrode (not shown) made of ITO is connected to the source electrode 12.

As shown in FIGS. 1 and 2, the light-shielding film 14 has a projecting portion 14A formed so as to extend to the periphery of the TFT 10, and the projecting portion 14A includes the gate insulating film 6 and the protective film 13. It is formed so as to overlap with the gate electrode 5 via. That is, the TFT substrate 1
Is formed with a portion where the light shielding film 14 and the gate electrode 5 face each other with only the gate insulating film 6 and the protective film 13 interposed therebetween. As a result, the capacitor C2 formed between the gate electrode 5 and the light-shielding film 14 which is opposed via the gate insulating film 6 and the protective film 13 having a wide opposed area is opposed via the protective film 13. The light-shielding film 14 and the source / drain electrodes 11,
The capacitance C1 is larger than the capacitance C1 formed between the capacitor 12 and 12, that is, the relation of capacitance C2> capacity C1 is satisfied. With this configuration, as will be described later, it is possible to eliminate the influence of the capacitance C1 and reduce the voltage applied to the light shielding film 14.

The larger the overlapping area between the overhanging portion 14A of the light-shielding film 14 and the gate electrode 5, the more effective it is. However, there is a restriction that it must be formed within the pixel area. No, T as an example
It is formed in substantially the same area as the area of the light-shielding film 14 that covers the FT 10. At least, the overlapping area should be large enough to satisfy the above-mentioned relationship of capacitance C2> capacity C1.

Next, with reference to FIGS. 3 and 4, a method of manufacturing the liquid crystal display device will be described in the order of steps. First, as shown in FIG. 3A, a transparent insulating substrate 4 made of glass or the like is used, and Al, Cr, and
After forming a conductive film of Mo or the like having a film thickness of 100 to 300 nm, the conductive film is patterned by a well-known photolithography method to form the gate electrode 5.

Next, as shown in FIG. 3B, a gate insulating film 6 having a film thickness of 200 to 400 nm formed of both laminated films by sequentially forming SiO ₂ and SiN _x on the entire surface by a CVD method or the like. To form. Next, the film thickness of amorphous silicon is 100 to 400 nm on the entire surface by the CVD method or the like.
After forming the semiconductor layer of
An n-type impurity such as (phosphorus) is ion-implanted to form the n ⁺ -type layer 8 and then patterned.

Next, as shown in FIG. 3C, the film thickness of Cr, Mo, etc. is 100 on the entire surface by sputtering or the like.
After forming a conductive film of about 300 nm, the conductive film is patterned by the photolithography method to form the drain electrode 1.
1 and the source electrode 12 are formed.

Next, as shown in FIG. 4D, the surface of the n ⁺ -type layer 8 which is not covered with the drain electrode 11 and the source electrode 12 is selectively etched, so that the channel of the semiconductor layer 7 ( The TFT 10 is completed by exposing the region to be the back channel).

Next, as shown in FIG. 4E, the film thickness of SiN _x or the like is 200 to 200 on the entire surface by a sputtering method or the like.
A protective film 13 having a thickness of 400 nm is formed. Then, a conductive film having a film thickness of 200 to 400 nm made of n ⁺ -type amorphous silicon doped with an n-type impurity such as P (phosphorus) is formed on the entire surface by a CVD method or the like, and then this conductive film is formed. Is patterned to form the light shielding film 14. When the light shielding film 14 is patterned, the overhanging portion 14A is formed so as to overlap the gate electrode 5 which is formed in advance. As a result, a capacitor C2 is formed between the light shielding film 14 and the gate electrode 5 which are opposed to each other via the gate insulating film 6 and the protective film 13. From the above, the TFT of FIG. 1 and FIG.
The substrate 1 is completed.

FIG. 5 is a diagram for explaining the leak characteristics of the TFT of the liquid crystal display device of this example. FIG. 5A is a sectional view showing the TFT 10 formed on the TFT substrate 1, and FIG. 5B is a light shielding film. 14 is a diagram showing a difference in leak characteristic of the TFT 10 depending on the presence or absence of the overhanging portion 14A of FIG. Each leak characteristic is TFT
10 is an example measured under the condition that light is not irradiated. A shows the leakage characteristics of the TFT without the light shielding film overhanging portion 14A, and B shows the TF with the light shielding film overhanging portion 14A.
Shows the leakage characteristics of T, and the drain voltage Vd is +
An example is shown in which the voltage is fixed at 10 V and applied.

As is apparent from FIG. 5B, the liquid crystal display device of this example has the entire gate voltage Vg region (-18 V to 1 V).
9V), the characteristic B with the light-shielding film overhanging portion 14A has a smaller leak current than the characteristic A without the light-shielding film overhanging portion 14A, and the effect of providing the light-shielding film overhanging portion 14A is exerted to improve the leak characteristics. It shows that it is excellent.

The reason why the leak characteristic is improved especially in the region where the gate voltage Vg is low is presumed to be as follows. As in this example, by forming the overhanging portion 14A in the light-shielding film 14 so as to overlap with the gate electrode 5, as described above, the capacitance C
The relationship of 2> capacity C1 is satisfied. Then, in this example, substantially the + voltage from the drain electrode 11 is about to be applied to the light-shielding film 14 via the capacitor C1, and at the same time, the gate electrode 5 via the capacitor C2 is sufficiently large when the TFT is off. -It is thought that a voltage is about to be applied. However, due to the relationship of capacitance C2> capacity C1,
As a result of the-voltage being predominantly applied by the gate electrode 5 via the capacitor C2, the light-shielding film 14 is substantially in a state in which the-voltage of the gate electrode 5 is applied.

Therefore, the charge induced in the back channel 9A of the semiconductor layer 7 located at the position facing the light-shielding film 14 disappears, and the leak current of the TFT 10 does not increase. On the other hand, the charge induced by the negative voltage of the gate electrode 4 flows on the front channel 9B side,
It does not contribute to the increase of leak current. Further, as the leak characteristic is improved, the rising threshold voltage (Vth) of the current characteristic can be increased.

As described above, according to the structure of the liquid crystal display device of this example, the light-shielding film 14 formed so as to cover the TFT 10 on the TFT substrate 1 is formed to extend to the periphery of the TFT 10. 14A, and this overhanging portion 14A is formed so as to overlap the gate electrode 5 with the gate insulating film 6 and the protective film 13 interposed therebetween.
The capacitance C2 formed between the gate layer and the light-shielding film 14 facing each other through the gate insulating film 6 and the protective film 13 is compared with the light-shielding film 14 facing through the protective film 13 and the source / drain electrodes. The capacitance can be formed larger than the capacitance C1 formed between 11 and 12. Therefore, when the light-shielding film is formed on the TFT substrate so as to cover the TFT, the leak characteristic of the TFT can be improved even in the region where the gate voltage is low.

Second Embodiment FIG. 6 is a plan view showing the structure of a liquid crystal display device according to a second embodiment of the present invention, and FIG. 7 is a sectional view taken along line CC ′ and DD ′ of FIG. FIGS. 8 and 9 are process diagrams showing a method of manufacturing the liquid crystal display device in the order of processes. The structure of the liquid crystal display device according to the second embodiment of the present invention is greatly different from the structure of the first embodiment described above in that a larger capacitance is formed between the light shielding film and the gate layer. . In the liquid crystal display device of this example, as shown in FIGS. 6 and 7, the TFT substrate 20 has a portion where the light shielding film 14 and the gate electrode 5 face each other with only the gate insulating film 6 interposed therebetween. That is, the light-shielding film 14 has an overhanging portion 14A formed so as to extend to the periphery of the TFT 10, and this overhanging portion 14A
Is formed so as to overlap the gate electrode 5 via the gate insulating film 6, and is connected to the capacitor electrode 15 formed on the gate insulating film 6.

With this structure, since the capacitance electrode 15 and the gate electrode 5 face each other via only the gate insulating film 6, the light shielding film 14 and the gate electrode 5 facing each other via the gate insulating film 6 are formed. The capacitance C3 formed between them can be made larger than the capacitance C2 of the first embodiment, and
The relationship of capacitance C3> capacity C1 is more easily satisfied. Therefore, as in the case of the first embodiment, it is possible to eliminate the influence of the capacitance C1 and reduce the voltage applied to the light shielding film 14. Other than this,
This is almost the same as the first embodiment described above. Therefore, FIG.
9, parts corresponding to the parts shown in FIGS. 1 to 4 are designated by the same reference numerals, and description thereof will be omitted.

Next, with reference to FIGS. 8 and 9, a method of manufacturing the liquid crystal display device will be described in the order of steps. First, as shown in FIG. 8A, a transparent insulating substrate 4 made of glass or the like is used, and Al, Cr, and
After forming a conductive film of Mo or the like having a film thickness of 100 to 300 nm, the conductive film is patterned by a well-known photolithography method to form the gate electrode 5.

Next, as shown in FIG. 8B, a gate insulating film 6 having a film thickness of 200 to 400 nm formed of both laminated films by sequentially forming SiO ₂ and SiN _x on the entire surface by a CVD method or the like. To form. Next, the film thickness of amorphous silicon is 100 to 400 nm on the entire surface by the CVD method or the like.
After forming the semiconductor layer of
An n ⁺ type layer 8 is formed by ion implantation of an n type impurity such as (phosphorus).

Next, as shown in FIG. 8C, the film thickness of Cr, Mo, etc. is 100 on the entire surface by a sputtering method or the like.
After forming a conductive film of about 300 nm, the conductive film is patterned by the photolithography method to form the drain electrode 1.
1 and the source electrode 12 are formed, the capacitor electrode 15 is formed on the gate insulating film 6 around the source electrode 12 at the same time.

Next, as shown in FIG. 9D, the surface of the n ⁺ -type layer 8 which is not covered with the drain electrode 11 and the source electrode 12 is selectively etched to form a channel ( The TFT 10 is completed by exposing the region to be the back channel).

Next, as shown in FIG. 9E, the film thickness of SiN _x or the like is 200 to 200 on the entire surface by a sputtering method or the like.
A protective film 13 having a thickness of 400 nm is formed. A contact hole reaching the capacitance electrode 15 is opened in the protective film 13. Then, a conductive film having a film thickness of 200 to 400 nm made of n ⁺ -type amorphous silicon doped with n-type impurities such as P (phosphorus) is formed on the entire surface by the CVD method or the like, and then this conductive film is formed. The light shielding film 14 is formed by patterning. At the time of patterning the light shielding film 14, the overhanging portion 1 is formed so as to overlap the gate electrode 5 which is formed in advance.
4A is formed. At this time, the overhanging portion 14A and the capacitor electrode 15 are connected via the contact hole. As a result, the capacitor C3 is formed between the light shielding film 14 and the gate electrode 5 which are opposed to each other with the gate insulating film 6 interposed therebetween. As described above, the TFT substrate 1 shown in FIGS. 6 and 7 is completed.

According to the liquid crystal display device of this example, since the capacitance C3 can be formed larger than the capacitance C2 of the first embodiment as described above, the gate electrode 5 via the capacitance C3 with respect to the light shielding film 14 is formed. -The voltage can be applied more dominantly. Therefore, it is possible to more reliably improve the leak characteristics of the TFT especially in the region where the gate voltage is low.

As described above, also with the configuration of this example, substantially the same effects as those described in the first embodiment can be obtained. In addition, according to the configuration of this example, it is possible to more reliably improve the leak characteristics of the TFT, particularly in the region where the gate voltage is low.

Third Embodiment FIG. 10 is a sectional view showing the structure of a liquid crystal display device according to the third embodiment of the present invention. The structure of the liquid crystal display device according to the third embodiment of the present invention is different from the structure of the second embodiment described above in that a larger capacitance is formed between the light shielding film and the gate layer by the different structure. Is.
The liquid crystal display device of this example has a TFT as shown in FIG.
The light-shielding film 14 and the gate electrode 5 are provided on the substrate 30 as the protective film 1.
The portions facing each other through only 3 are formed. That is, the light-shielding film 14 has an overhanging portion 14A formed so as to extend to the periphery of the TFT 10, and this overhanging portion 14A
Is formed so as to overlap the gate electrode 5 through the protective film 13, while the gate electrode 5 is formed by the gate insulating film 6
It is connected to the capacitance electrode 15 formed on the gate insulating film 6 through the contact hole 17 formed in the.

With this configuration, the capacitance electrode 15 and the light shielding film 1
4 is opposed only to the protective film 13 having a large opposing area, the light shielding film 14 opposed to the protective film 13 via the protective film 13.
The capacitance C4 formed between the gate electrode 5 and the gate electrode 5 can be formed larger than the capacitance C2 of the first embodiment as in the case of the second embodiment, and the relation of capacitance C4> capacity C1 is satisfied. Are satisfied.

To manufacture the liquid crystal display device of this example, in the step of FIG. 8B of the second embodiment, the gate insulating film 6 is formed.
Then, a contact hole 17 is formed in the gate insulating film 6 on the gate electrode 5, and the contact hole 1 is formed.
A conductive film made of Cr, Mo, W (tungsten) or the like may be embedded in the film 7. Then, after forming the semiconductor layer 7 and the n ⁺ -type layer 8, the capacitor electrode 15 may be formed in the step of FIG. 8C. Other than this, it is substantially the same as the above-described first embodiment. Therefore, in FIG. 10, the same numbers are given to the respective units corresponding to the components of FIGS. 6 to 9, and the description thereof will be omitted.

As described above, also with the configuration of this example, substantially the same effect as that described in the second embodiment can be obtained.

The embodiment of the present invention has been described in detail above with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like within the scope not departing from the gist of the present invention. Also included in the present invention. For example, although the light-shielding film is described as an example using amorphous silicon, the material is not limited to this, and other materials such as polycrystalline silicon, Ti (titanium), and Cr can be used as long as they are conductive materials. However,
From the viewpoint of the manufacturing method, it is desirable to use a conductive material capable of forming a film in one step. Further, the gate electrode, the drain electrode, the source electrode and the like are not limited to the metal materials shown in the respective embodiments. Similarly, the gate insulating film, the protective film, etc. are not limited to the insulating materials shown in the respective embodiments.

Further, although an example in which amorphous silicon is used as the semiconductor layer of the TFT formed on the TFT substrate has been described, the present invention is not limited to this, and other semiconductor materials such as polycrystalline silicon may be used. Moreover, the film forming method of each conductive film and each insulating film, and the value of the film thickness are merely examples, and can be arbitrarily changed according to the purpose, application, and the like. Further, the light-shielding film does not have to be connected to the drain or source electrode as long as the light-shielding film forms a capacitance with each other.

[0054]

As described above, according to the configuration of the liquid crystal display device of the present invention, the light shielding film formed so as to cover the TFT on the TFT substrate is formed so as to extend to the periphery of the TFT. Since it has an overhang portion and this overhang portion is formed so as to overlap the gate electrode only through the insulating film, it is formed between the light-shielding film and the gate layer facing each other through the insulating film. The capacitance can be made larger than the capacitance formed between the light-shielding film and the source / drain electrode which are opposed to each other via the insulating film. Therefore, when the light-shielding film is formed on the TFT substrate so as to cover the TFT, the leak characteristic of the TFT can be improved even in the region where the gate voltage is low.

[Brief description of drawings]

FIG. 1 is a plan view showing the configuration of a liquid crystal display device that is a first embodiment of the present invention.

2 is a cross-sectional view taken along arrows AA ′ and BB ′ of FIG.

FIG. 3 is a process chart showing a method of manufacturing the liquid crystal display device in the order of steps.

FIG. 4 is a process diagram showing a method of manufacturing the liquid crystal display device in the order of processes.

FIG. 5 is a diagram illustrating a leak characteristic of a TFT of the liquid crystal display device.

FIG. 6 is a plan view showing the configuration of a liquid crystal display device that is a second embodiment of the present invention.

FIG. 7 is a sectional view taken along the line CC ′ and DD ′ of FIG.

FIG. 8 is a process chart showing the manufacturing method of the liquid crystal display device in the order of processes.

FIG. 9 is a process chart showing the manufacturing method of the liquid crystal display device in the order of processes.

FIG. 10 is a cross-sectional view showing a configuration of a liquid crystal display device which is a third embodiment of the present invention.

FIG. 11 is a plan view showing a configuration of a conventional liquid crystal display device.

12 is a cross-sectional view taken along arrows EE ′ and FF ′ of FIG.

FIG. 13 is a process chart showing the method of manufacturing the liquid crystal display device in the order of steps.

FIG. 14 is a process diagram showing the manufacturing method of the liquid crystal display device in the order of processes.

FIG. 15 is a diagram illustrating a leak characteristic of a TFT of the liquid crystal display device.

FIG. 16 is a diagram illustrating a leak characteristic of a TFT which is the principle of the present invention.

FIG. 17 is a schematic cross-sectional view of a conventional liquid crystal display device.

[Explanation of symbols]

1, 20, 30 TFT substrate 4 Transparent insulating substrate 5 Gate electrode 6 Gate insulating film 7 Semiconductor layer 8 n ⁺ type layers 8d, 8s Ohmic layer 10 TFT 11 Drain electrode 12 Source electrode 13 Protective film (passivation film) 14 Light-shielding film 14A Light-shielding film overhang 15 Capacitance electrode 17 Contact hole

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-10-70277 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 29/786 H01L 21/336 G02F 1 / 1368

Claims (4)

(57) [Claims] 1. A liquid crystal display device in which liquid crystal is sandwiched between a TFT substrate and a counter substrate, and a light shielding film is formed so as to cover the TFT on the TFT substrate, wherein the light shielding film is the TFT. Shaped to extend around
And an overhang formed by the
Through the insulating film including the insulating film
The gate insulating film.
A liquid crystal display device, characterized in that the liquid crystal display device is connected to a capacitor electrode formed on the top . 2. Formed between the light-shielding film and the gate electrode
The generated capacitance is the light-shielding film and the source and drain of the TFT.
It will be larger than the capacitance formed with the rain electrode.
The liquid crystal display device according to claim 1, wherein the liquid crystal display device is configured as described above. 3. A liquid crystal display device in which liquid crystal is sandwiched between a TFT substrate and a counter substrate, and a light-shielding film is formed so as to cover the TFT on the TFT substrate, wherein a gate electrode is provided on the TFT substrate. A semiconductor layer having a drain electrode and a source electrode provided on the surface via a gate insulating film that covers the surface of the semiconductor layer including the drain electrode and the source electrode, and an insulating film as a protective film covering the surface of the semiconductor layer. A light shielding film is formed, and the light shielding film is the TFT.
Of the gate insulating film , and the overhanging part is formed so as to extend to the periphery of the gate insulating film , and the overhanging part is formed so as to overlap with the gate electrode through an insulating film including a gate insulating film. Capacitive electrode formed on
A liquid crystal display device characterized by being connected to . 4. Formed between the light-shielding film and the gate electrode
The generated capacitance depends on the light-shielding film and the source of the TFT.
And the capacitance formed between the drain electrode and the drain electrode.
4. The structure according to claim 3, wherein
The described liquid crystal display device.