JP3263894B2 - Active matrix display device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix display device and a method of manufacturing the same. Specifically, the present invention relates to a structure of a driving substrate on which a pixel electrode, a thin film transistor, an auxiliary capacitor, and the like are formed. More specifically, the present invention relates to a three-dimensional structure of an auxiliary capacitor.

[0002]

2. Description of the Related Art FIG. 4 is a schematic partial sectional view showing a general structure of a conventional active matrix type display device. As shown in the figure, the active matrix display device includes a driving substrate 51, a counter substrate 52, and an electro-optical material such as a liquid crystal 53 held between the driving substrate 51 and the counter substrate 52. On the driving substrate 51, a pixel electrode 54, a thin film transistor TFT for driving the pixel electrode 54, and an auxiliary capacitor Cs connected thereto are integrally formed. Thin film transistor TFT is a semiconductor thin film 5
5, a gate insulating film 56 formed thereon, and a gate electrode 57 formed thereon by patterning. On the other hand, the auxiliary capacitance Cs is the first capacitance of the semiconductor thin film 55.
It is composed of an electrode, a dielectric film 58 formed thereon, and a second electrode 59 formed thereon by patterning. These TFT and Cs are covered with the first interlayer insulating film 60. A signal line 61 is formed thereon by patterning. The signal line 61 is covered with a second interlayer insulating film 62, on which the above-described pixel electrode 54 is formed by patterning. On the other hand, the opposite substrate 52 has a black mask 63,
A color filter 64, a counter electrode 65, and the like are provided.

FIG. 5 is a process chart showing a method of manufacturing the active matrix display device shown in FIG. First, in the step (A), a semiconductor thin film 55 made of polycrystalline silicon or the like is formed on a drive substrate 51 made of quartz glass or the like, and patterned in an island shape. Next, in a step (B), an oxide or the like is deposited, and a gate insulating film 56 and a dielectric film 58 are simultaneously formed. Further, a conductive film made of low-resistance polysilicon or the like is formed, and is patterned into a predetermined shape to form the gate electrode 57 and the capacitor electrode 59. Further, impurities are ion-implanted using the gate electrode 57 as a mask, and a drain region D and a source region S are provided in the semiconductor thin film 55. In this manner, the thin film transistor TFT and the auxiliary capacitance Cs are formed integrally. In the case where the liquid crystal is driven by AC using the TFT, the drain region D and the source region S are alternately switched according to the magnetic reversal. Therefore, in the figure, (D) is added beside S, and (S) is added beside D to make sure. Subsequently, the process proceeds to step (C), in which the TFT and Cs are covered with the first interlayer insulating film 60. A signal line 61 is formed thereon by patterning. The signal line 61 is connected to the source region S (D) of the TFT via a contact hole opened in the first interlayer insulating film 60.
Is electrically connected to Then, proceeding to the step (D), the signal line 6
1 is covered with a second interlayer insulating film 62. Further, a contact hole communicating with the drain region D (S) of the TFT is opened. Finally, in a step (E), a transparent conductive film such as ITO is formed on the second interlayer insulating film 62, and is patterned into a predetermined shape to be processed into the pixel electrode 54. Thereafter, although not shown, the opposing substrate is bonded via a predetermined gap, and liquid crystal is sealed in the gap, whereby an active matrix type liquid crystal display device is completed.

FIG. 6 shows an equivalent circuit of the active matrix type liquid crystal display device shown in FIG. The MOS-FE is provided at the intersection of the m gate lines (G1, G2,..., Gm) and the n signal lines (S1, S2,.
A T-type thin film transistor 101, an auxiliary capacitor 102, and a liquid crystal cell 103 forming a pixel are formed. The liquid crystal cell 103 is composed of liquid crystal held between a pixel electrode and a counter electrode. The active matrix type liquid crystal display device having such a structure is driven as follows. That is, selection pulses are sequentially applied to the gate lines G1, G2,..., Gm every horizontal period. During a period in which one gate line is selected, a sampled image signal is supplied to the signal line S1,
S2,..., And Sn are sequentially held and written to corresponding pixels via the thin film transistor 101. The image signal written to the pixel is applied to the liquid crystal cell 103 and the storage capacitor 10.
2 is retained for one field period, and is rewritten to an image signal of the opposite polarity in the next field. Thus, the liquid crystal is AC driven.

[0005]

SUMMARY OF THE INVENTION Individual liquid crystal cells 103
The larger the pixel capacitance of the device, the more reliably the pixel potential can be held, and therefore, a certain display quality can be secured without causing contrast unevenness. Therefore, when the pixel electrode area is large, it is not necessary to provide an auxiliary capacitance. However, when a pixel is made finer or finer in a small display device, the pixel electrode area is significantly reduced, and an auxiliary capacitor for supplementing the pixel capacitance is indispensable.

Generally, in order to perform stable sampling and holding of an image signal, it is required that the auxiliary capacitance be several times as large as the pixel capacitance. This auxiliary capacity is shown in FIG.
As shown in (1), it has a MOS structure and is formed on a substrate plane. In order to secure a necessary capacitance, it is necessary to increase the electrode area. When the pixel is miniaturized, the ratio of the capacitance electrode increases, so that the aperture ratio (the ratio of the pixel area to the display surface) decreases. In particular, when the pixel area is extremely miniaturized, there is a disadvantage that the aperture ratio is greatly deteriorated due to the auxiliary capacitance.

Generally, in order to increase the capacitance of the auxiliary capacitance, the area of the dielectric film should be increased or the thickness of the dielectric film should be reduced. However, when the area of the dielectric film is increased, the area occupied by the auxiliary capacitance inevitably increases and the aperture ratio deteriorates. That is, the plane area of the auxiliary capacitor and the aperture ratio are in an inversely proportional relationship, and it is difficult to achieve compatibility in an actual pattern design. Therefore, in order to increase the auxiliary capacitance, the thickness of the dielectric film has been reduced as much as possible. Alternatively, the dielectric film is formed using a material having a high dielectric constant. However, these measures have limitations, and the aperture ratio is sacrificed in order to secure the necessary capacitance of the auxiliary capacitance.

As another approach for increasing the capacitance, for example, Japanese Patent Application Laid-Open No. 64-81262 discloses a conventional example using a so-called trench type auxiliary capacitance. As shown in FIG. 7, a groove or trench 10 is formed on the surface of the insulating substrate 104.
5 are formed. On the inner wall of the trench 105, one electrode film 106, the dielectric film 107, and the other electrode film 10
8 are stacked to form a so-called trench capacitance element 109. Compared to the planar opening area of the trench 105,
The effective area of the pair of electrode films 106 and 108 is increased, and only the capacitance value can be increased without increasing the element size. Therefore, when such a trench-type capacitance element 109 is used, the ratio occupying the display surface can be suppressed to a small value, so that a predetermined aperture ratio can be secured even when the pixel is miniaturized. On the other hand, the thin film transistor 110 is a planar type and is formed on the semiconductor thin film 111. Two layers of gate insulating films 112 and 11 are formed on the semiconductor thin film 111.
3, a gate electrode 114 is formed,
The pixel electrode 116 is electrically connected to the drain region (also referred to as a source region) of the thin film transistor 110 via the interlayer insulating film 115. In a source region (also referred to as a drain region) of the thin film transistor 110, a wiring electrode 117 connected to each signal line is provided. A passivation film 118 is coated on the top of these stacked structures.

The use of a trench-type auxiliary capacitor can increase the capacity without sacrificing the aperture ratio to some extent. However, the manufacturing process for forming the trench-type storage capacitor is complicated in many steps, and is considerably disadvantageous as compared with the manufacturing process of the planar storage capacitor shown in FIG.

[0010]

SUMMARY OF THE INVENTION In view of the above-mentioned problems in the prior art, the present invention aims at achieving a three-dimensional auxiliary capacitor without complicating the manufacturing process, and achieving both an increase in the capacity and maintenance of the aperture ratio. Aim. The following measures were taken to achieve this purpose. That is, the active matrix display device according to the present invention has, as a basic configuration, at least a pixel electrode, a driving substrate on which a thin film transistor for driving the pixel electrode and an auxiliary capacitor connected thereto are integrally formed, and at least a counter electrode. An opto-substrate and an electro-optical material held between the two substrates joined via a predetermined gap are provided. The thin film transistor includes a semiconductor thin film having a plane region, a gate insulating film formed on the upper surface of the plane region, and a gate electrode formed on the gate insulating film by patterning. On the other hand, the storage capacitor includes a first electrode formed of a three-dimensional region provided in a part of the semiconductor thin film, a dielectric film formed on an upper surface, a side surface, and a lower surface of the three-dimensional region; And a second electrode formed so as to include the three-dimensional region via a body film. Preferably, the gate insulating film and the dielectric film are formed of an oxide film or a nitride film belonging to the same layer. Further, the gate electrode and the second electrode are made of a conductor film belonging to the same layer.

An active matrix type display device according to the present invention is manufactured by the following steps. First, a base film having a tapered step is formed on one substrate. Next, a semiconductor thin film is formed on the base film and patterned into a predetermined shape to provide a plane region and a region including a step. Subsequently, the base film is etched away from the region including the step to provide a three-dimensional region. Further, an insulating film is formed over the upper surface of the planar region and the upper, lower, and side surfaces of the three-dimensional region. Thereafter, a thin film transistor is provided by patterning a gate electrode on the planar region through the insulating film, and an electrode is formed by patterning the electrode so as to include the three-dimensional region through the insulating film. Is provided. Subsequently, a pixel electrode is formed by connecting to the thin film transistor. Finally, the other substrate on which the counter electrode is formed in advance is bonded to the one substrate, and an electro-optical material is injected into a gap between the two to complete an active matrix display device.

[0012]

According to the present invention, the thin film transistor is formed in the planar region of the semiconductor thin film, while the auxiliary capacitance is formed in the three-dimensional region. In this three-dimensional region, the semiconductor thin film has a side surface and a lower surface in addition to a normal upper surface, and these are continuous. Therefore, the surface area of the semiconductor thin film in the three-dimensional region is significantly increased as compared with the planar region.
By successively depositing a dielectric film on the upper surface, the lower surface, and the side surfaces of the three-dimensional region, the capacitance of the auxiliary capacitance is significantly increased. Further, since the electrodes are provided so as to include the three-dimensional region, the area occupied by the auxiliary capacitance does not increase. In this way, the capacitance of the auxiliary capacitance can be increased without sacrificing the aperture ratio. Further, when forming a three-dimensional auxiliary capacitor, it is not necessary to provide a trench as in the prior art, the manufacturing process is relatively simple, and the load on the process can be reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a partial sectional view showing the structure of an active matrix display device according to the present invention. As shown, the display device includes a driving substrate 1 and a counter substrate 2. These substrates 1 and 2 are joined to each other via a predetermined gap, and an electro-optical material such as a liquid crystal 3 is held in the gap. At least a pixel electrode 4, a thin film transistor TFT for driving the pixel electrode 4, and an auxiliary capacitance Cs connected to the pixel electrode 4 are integrally formed on the driving substrate 1. on the other hand,
A counter electrode 5 is entirely formed on the counter substrate 2.
Also, matching with the TFT and Cs provided on the driving substrate 1 side,
A black mask 6 is formed. Further, a color filter 7 of three primary colors of RGB is provided in alignment with the pixel electrode 4 formed on the drive substrate 1 side.

The thin film transistor TFT includes a semiconductor thin film 8 having a plane region, a gate insulating film 9 formed on the upper surface of the plane region, and a gate electrode 10 formed on the gate insulating film 9 by patterning. I have. This TF
T has a replaceable drain region D and a source region S on both sides of the gate electrode 10. Source area S
The signal line 11 is electrically connected to (D), while the pixel electrode 4 is electrically connected to the drain region D (S). The signal line 11 is patterned on the first interlayer insulating film 12,
The pixel electrode 4 is formed on the second interlayer insulating film 13 by patterning.

On the other hand, the auxiliary capacitance Cs is the semiconductor thin film 8
, A first electrode 15 formed of a three-dimensional region provided in a part of the three-dimensional region, a dielectric film 16 formed on an upper surface U, a side surface W and a lower surface L of the three-dimensional region, and a three-dimensional Electrode 1 formed so as to include the activation region (first electrode 15)
7. Preferably, the gate insulating film 9 and the dielectric film 16 are made of an oxide film or a nitride film belonging to the same layer. Further, the gate electrode 10 and the second electrode 17 are made of a conductor film belonging to the same layer.

Next, referring to the process charts of FIGS. 2 and 3,
A method for manufacturing the active matrix display device shown in FIG. 1 will be described in detail. First, in step (A), one substrate 1
An underlying film 14 having a tapered step is formed thereon.
Specifically, a base film 14 made of an oxide is grown on the substrate 1 made of quartz glass or the like by a chemical vapor deposition method (CVD). Subsequently, predetermined patterning is performed by using a photolithography technique, and isotropic etching is further performed to form a tapered pattern of the base film 14.

Next, proceeding to step (B), a semiconductor thin film 8 is formed on the base film 14, and is patterned into a predetermined shape to provide a plane region and a region including a step. Specifically, the semiconductor thin film 8 made of polysilicon is formed by using, for example, low pressure chemical vapor deposition (LP-CVD). Subsequently, patterning is performed, for example, in an island shape using a photolithography technique.

In the step (C), the underlying film 14 is removed by etching from the region including the step to provide a three-dimensional region X. Specifically, isotropic etching is performed only on the base film 14 using wet etching or dry etching with a high selectivity. By performing the isotropic etching, the base film 14 is removed along the edge of the semiconductor thin film 8 to obtain the eaves-shaped three-dimensional region X.

Next, the process proceeds to the step (D) in FIG. 3, and an insulating film 9 is formed on the upper surface of the planar region of the semiconductor thin film 8. At the same time, the insulating film 16 is continuously formed over the upper surface U, the lower surface L, and the side surface W of the three-dimensional region X. For example, by selectively subjecting the semiconductor thin film 8 to thermal oxidation treatment, the insulating films 9 and 16 can be formed simultaneously. Alternatively, a nitride film may be formed instead of the thermal oxide film. Thereafter, a gate electrode 10 is formed in a pattern on the plane region via the insulating film 9 to form a thin film transistor TFT.
Is provided. In addition, an auxiliary capacitance Cs is provided by patterning the electrode 17 so as to include the three-dimensional region X via the insulating film 16. Specifically, LP- with high step coverage
A polysilicon film is grown using a CVD technique. Since the step coverage is good, the formed polysilicon film can completely fill the three-dimensional region X including the portion below the eaves portion. Subsequently, using a photolithography technique and an etching technique, the polysilicon film is patterned into a predetermined shape to be processed into the gate electrode 10 and the capacitor electrode 17. After that, impurity ions are implanted using the gate electrode 10 as a mask, and a source region S and a drain region D are provided in the semiconductor thin film 8. Thus, the thin film transistor TF
T is completed. Also, the auxiliary capacitance Cs is completed. In particular, since the auxiliary capacitance Cs is provided in the three-dimensional region X, the insulating film (dielectric film) 16 is formed not only on the upper surface U but also on the lower surface L and the side surface W, thereby greatly increasing the capacitance.

Next, in the step (E), the thin film transistor TF
A first interlayer insulating film 12 made of PSG or the like is formed so as to cover T and the storage capacitor Cs. Further, a contact hole communicating with the source region S of the TFT is formed in the first interlayer insulating film 1 using a photolithography technique and an etching technique.
Open to 2. Further, a film of metal aluminum or the like is formed using a sputtering technique, and is patterned into a predetermined shape again using a photolithography technique and an etching technique to be processed into the signal line 11.

Finally, a step (F) is performed, a second interlayer insulating film 13 made of PSG or the like is formed, and the signal line 11 is covered. Subsequently, a contact hole penetrating the second interlayer insulating film 13 and the first interlayer insulating film 12 is opened by using a photolithography technique and an etching technique, and the drain region D of the TFT is exposed. Further, a transparent conductive film such as ITO is formed using a sputtering technique, and the ITO film is patterned into a predetermined shape again using a photolithography technique and an etching technique, and is processed into the pixel electrode 4. After this,
The other substrate on which the opposing electrode is formed in advance is joined via a predetermined gap, and an electro-optical material such as liquid crystal is injected into the gap. Thus, an active matrix liquid crystal display device is completed.

[0022]

As described above, according to the present invention, the three-dimensional region is provided in the semiconductor thin film, and the auxiliary capacitance is formed by using not only the upper surface but also the side surface and the lower surface. Therefore, it is possible to increase the capacitance without increasing the area occupied by the auxiliary capacitance. Therefore, a sufficient capacitance of the auxiliary capacitance can be secured without sacrificing the aperture ratio of the pixel. According to the present invention, since the auxiliary capacitance is formed not only in the horizontal direction but also in the vertical direction, the projected area of the auxiliary capacitance can be reduced as compared with the related art. In addition, when forming the auxiliary capacitor in the three-dimensional region, a normal etching technique or a film forming technique can be applied as it is, so that the load on the manufacturing process can be reduced.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a basic configuration of an active matrix display device according to the present invention.

FIG. 2 is a process chart showing a method for manufacturing the active matrix display device shown in FIG.

FIG. 3 is a process drawing showing the same manufacturing method.

FIG. 4 is a partial cross-sectional view showing a conventional example of an active matrix display device.

FIG. 5 is a process chart showing a method of manufacturing the conventional active matrix display device shown in FIG.

FIG. 6 is a circuit diagram showing a general equivalent circuit of an active matrix display device.

FIG. 7 is a partially cutaway sectional view showing another example of a conventional active matrix display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Driving substrate 2 Counter substrate 3 Liquid crystal 4 Pixel electrode 5 Counter electrode 8 Semiconductor thin film 9 Gate insulating film 10 Gate electrode 14 Base film 15 First electrode 16 Dielectric film 17 Second electrode X Three-dimensional region U Upper surface L Lower surface W Side surface

Claims (4)

(57) [Claims] 1. A drive substrate, on which at least a pixel electrode, a thin film transistor for driving the pixel electrode, and an auxiliary capacitor connected thereto are integrally formed, and a counter substrate, on which at least a counter electrode is formed, joined to each other via a predetermined gap. An active matrix display device including an electro-optical material held between substrates, wherein the thin film transistor has a semiconductor thin film having a planar region, a gate insulating film formed on an upper surface of the planar region, A gate electrode patterned on the gate insulating film, wherein the auxiliary capacitance includes a first electrode formed of a three-dimensional region provided in a part of the semiconductor thin film, and upper and side surfaces of the three-dimensional region And a dielectric film formed on the lower surface, and a second electrode formed so as to include the three-dimensional region via the dielectric film. Rikusu type display device. 2. The active matrix display device according to claim 1, wherein said gate insulating film and said dielectric film are formed of an oxide film or a nitride film belonging to the same layer. 3. The active matrix display device according to claim 1, wherein said gate electrode and said second electrode are made of a conductor film belonging to the same layer. 4. A step of forming a base film having a tapered step on one substrate, and forming a semiconductor thin film on the base film and patterning the semiconductor thin film into a predetermined shape to form a plane region and a region including a step. Providing a three-dimensional region by etching the base film from the region including the step; forming an insulating film over the upper surface of the planar region and the upper, lower, and side surfaces of the three-dimensional region. A step of forming a gate electrode on the planar region through the insulating film to form a thin film transistor, and forming an electrode so as to include the three-dimensional region through the insulating film to form an auxiliary capacitor. Providing, a step of connecting to the thin film transistor to form a pixel electrode, a step of bonding the other substrate on which the counter electrode is formed in advance to the one substrate, and injecting an electro-optical material into a gap between the two. Of manufacturing an active matrix display device that performs the following.