JP3183294B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thin film semiconductor device comprising a semiconductor element formed on an insulating substrate, and more particularly to a structure of a thin film semiconductor device capable of forming a high-performance circuit with good uniformity.

[0002]

2. Description of the Related Art In recent years, the development of a thin-film semiconductor device using a thin-film active element using a semiconductor film formed on an insulating substrate such as glass as an active layer has been activated. Typical examples include an active matrix type liquid crystal display and a line light sensor for facsimile. With the trend toward higher performance and longer length of these semiconductor devices, higher performance elements are required. For this purpose, it is necessary to form a higher quality polycrystalline or single crystal film at a lower temperature.

As a method for forming a polycrystalline or single crystal film at a low temperature, a so-called laser annealing method for recrystallizing a semiconductor by irradiating a laser beam has conventionally been used. Regarding the laser annealing technique, see, for example, JP-A-57-187.
No. 933, and the like.

[0004]

In the laser annealing technique, it is important to make the device characteristics uniform, that is, to reduce the variation in the crystallinity of the film depending on the location.
Although the above prior art is considered to obtain a semiconductor film having good crystallinity, it does not take into consideration the uniformity of crystallinity. If the element characteristics vary due to differences in crystallinity depending on the location, even if the element alone has good characteristics, if a circuit is composed of multiple elements, the desired circuit operation can not be obtained due to the variation in characteristics between the elements It becomes impossible to offer. The variation in crystallinity when using laser annealing is caused by the variation in cooling rate during recrystallization. The following will be described with reference to FIG.

FIG. 2 shows that a glass substrate 101 having an area of 10
× 50 μm ² and 400 × 400 μm ² amorphous Si
After forming an (a-Si) film 102 and further forming a SiO ₂ film 103 thereon as a capping film,
(A)) XeCl Eskima laser light was applied at 200 mJ / cm ^2.
2 (b), the crystallinity in the film was evaluated by the microscopic X-ray diffraction method (FIG. 2 (c), FIG. 2 (c)).
(d)). As shown in FIG. 3C, the area is 10 × 50 μm.
While the crystallinity in the film is almost uniform in the film of m ^2, the film having a large area of 400 × 400 μm ² shows high crystallinity near the edge of the film but goes to the center of the film. As a result, the crystallinity was reduced, and no crystallization occurred at a position 100 μm or more from the end. This is considered to be because the heat capacity is large such as a film having a large area, and when the power of the laser beam is not sufficiently strong, thermal energy is insufficient to cause crystallization of the film. The reason that crystallization occurs only at the end of the film is considered to be because the heat radiation at the end is suppressed by the SiO ₂ film having poor heat conduction as compared with the center.

In order to crystallize the entire film having a large area, the power of the laser beam may be increased. However, if the power is excessively increased, another problem arises in that the surface of the film having a small area is roughened and peels off. Therefore, it is difficult to achieve uniform crystallinity over all the films by the above-mentioned conventional technology.

FIG. 3 shows an example of a circuit actually formed of a polycrystalline silicon film on an insulating substrate using a conventional laser annealing technique. FIG. 2B is a plan view of the three-stage inverter circuit shown in FIG. Here, the transistors Q ₅ and Q ₆ have a large channel width of 1500 μm in order to obtain a large driving capability. For this reason,
The area Si of the silicon film 201 to be the active layers of Q ₅ and Q ₆
Is 140 × 1500 = 2.1 × 10 ⁵ μm ² and 20 of the smallest silicon film to be the active layer of the transistors Q ₁ and Q _2.
The area is 75 times as large as the area of Si = 2.8 × 10 ³ μm ² . Therefore, when recrystallized by the same laser power between the silicon film 201 to 203 for the above reason, the crystallinity of the variation occurs, resulting in the desired inverter output V _'od can not be obtained.

It is an object of the present invention to solve the problems of the prior art and to utilize a characteristic of a laser annealing method capable of obtaining good crystallinity, and to provide a liquid crystal display device having a high-performance circuit in which variations in crystallinity are suppressed. Is to provide.

[0009]

According to the present invention, a semiconductor film to be laser recrystallized is previously patterned into a plurality of islands in order to reduce variations in crystallinity due to laser annealing, and the area of each island is reduced. 1.6 × 10 ⁵ μm ² or less, and the ratio between the maximum value and the minimum value of the area is 50
An active element is configured as follows.

In the present invention, by controlling the area of the semiconductor film to be recrystallized by laser to 1.6 × 10 ⁵ μm ² or less, the heat capacity of the film is reduced so that the entire film can be uniformly formed even at a relatively low laser power. It can be crystallized. In addition, the ratio of the minimum value to the maximum value of the area of at least one of the films to be recrystallized, which is used as the active layer of the active element, is reduced to 50 or less, so that the difference in heat capacity between the films is reduced to reduce the crystallinity. Variation can be suppressed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows a circuit similar to that shown in FIG. 3 formed on an insulating substrate by the method of the present invention. In the present embodiment, the transistors Q ₅ and Q _{6 at} the output stage of the channel layer 1500 μm are configured by connecting 30 sub-transistors having a channel width of 50 μm separated from each other in parallel. The active layer of each sub-transformer is a silicon film 203 of 40 × 50 μm ² , and these silicon films 203 are thermally insulated. Therefore, when the silicon films 201, 202, and 203 are crystallized by laser irradiation, the heat capacity values of the respective silicon films are close to each other, so that the variation in the crystallinity of the films can be reduced, thereby obtaining good inverter characteristics. Can be

FIG. 4 schematically shows a manufacturing process of the apparatus shown in the first embodiment.

An a-Si film 102 having a thickness of 100 nm is deposited on a glass substrate 101 by a low pressure CVD method. Then this a-
The Si film 102 is separated into a plurality of films by a normal hot etching process. Next, normal pressure CVD as a capping film
A 100 nm SiO ₂ film 103 is deposited by the method. Here, a XeCl excimer laser beam having a wavelength of 308 nm is applied for 200 m.
The Si film is irradiated from above the SiO ₂ film 103 with a power of J / cm ² and recrystallized to obtain a polycrystalline Si film 108. Next, Si
After removing the O ₂ film 103 by hydrofluoric acid treatment, an SiO ₂ film 104, 150 nm as a gate insulating film is subjected to normal pressure CVD, and then a-Si films 105, 150 as gate electrodes.
nm is formed by a low pressure CVD method. Next, the gate Si
After patterning the film 105 and the gate insulating film 104 into a predetermined shape, the gate electrode and the source,
³¹ P ions are implanted into the drain region, and heat treatment is performed at 600 ° C. for 10 hours to obtain a resistance layer. Next, PS as a protective film
A G film 106 is deposited by a normal pressure CVD method, and after opening a contact through hole, an Al electrode 107 is deposited by a sputtering method, and this is patterned to obtain a circuit having the structure shown in FIG.

In this embodiment, the maximum value of the area of the Si film to be recrystallized is 7.0 × 10 ³ μm ² , and the minimum value is 2.8 × 1.
0 ³ μm ² and the ratio of the maximum value to the minimum value is 2.5.
Is configured. If the area ratio is 50 or less, the variation in element characteristics can be suppressed to a level that causes no practical problem. The maximum value of the area of the film is 400 μm ×
When the thickness is 400 μm = 1.6 × 10 ⁵ μm ² or more, uniform crystallization cannot be achieved with a laser power of 200 mJ / cm ² .
The laser power may be increased to uniformly crystallize the film. However, when the laser power is 220 mJ / cm ² or more, recrystallization is caused because surface irregularities occur particularly in a film having a small area and the device characteristics are deteriorated. The area of the Si film is 1.6 ×
It is desirable to set it to 10 ⁵ μm ² or less.

Although the above embodiment relates to a very simple circuit, the structure of the present invention is applicable to various thin film semiconductor devices formed on an insulating substrate. For example, in the case of an active matrix substrate for image display in which a driving circuit is built in on the same substrate, by applying the structure of the present invention to the transistors forming the driving circuit, a transistor having high current driving capability can be uniformly formed. Thus, a drive circuit that can operate at high speed can be configured. Thereby, a larger or higher definition display device is realized.

FIG. 5 shows a display device constructed on an active matrix substrate having the structure of the present invention.

A scanning line 301 and a signal line 302 formed on a glass substrate 101 are formed in a matrix, and a thin film transistor 300 is formed near an intersection of the scanning line 301 and a signal line 302 to drive pixel electrodes formed of transparent electrodes. The scanning wiring 301 and the signal wiring 302 are respectively connected to the scanning driving circuit 30.
4 and the signal side drive circuit 305 to be driven. An opposing electrode 307 made of a transparent electrode and a color filter 3 are formed on a glass substrate 309 opposing the liquid crystal layer 306 therebetween.
08 is formed, and a polarizing plate 310 is provided so as to sandwich the pair of glass substrates 101 and 309. A color liquid crystal display device driven by a thin film transistor is formed by adjusting the amount of light transmitted from the light source at the pixel electrodes and the like. Since the structure of the present invention can improve the performance of the driving circuit, it is suitable for increasing the size and definition of the liquid crystal display device.
A workstation, a high-quality TV, and the like are realized.

The structure of the present invention can be applied not only to the above example but also to a drive circuit for a photoelectric conversion device formed on an insulating substrate, such as a drive circuit for a facsimile line sensor. . According to the present invention, a high-performance drive circuit can be obtained, so that a high-definition, high-sensitivity, high-speed photoelectric conversion device can be realized.

In the above embodiment, the semiconductor film is described as being made of silicon, but the present invention is not limited to this.
It is also applicable to semiconductors other than e, SiGe, GaAs, ZnSe, and the like.

The means for recrystallization is not limited to the XeCl excimer laser light described in the above embodiment, but may be another type of laser such as an Ar laser, an ArF excimer laser, or the like.
It is also possible to use an electron beam or an ion beam.

As described above, according to the present invention, the area of the semiconductor film to be recrystallized by laser is set to 1.6 × 10 ⁵ μm ² or less, and the ratio of the minimum area to the maximum area of the semiconductor film is set to 50.
With the configuration described below, there is an effect that variation in crystallinity of the film is suppressed and a high-performance active element can be formed uniformly.

[0022]

According to the present invention, it is possible to provide a liquid crystal display device having a high-performance circuit in which variation in crystallinity is suppressed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram and a plan view showing an embodiment of the present invention.

FIG. 2 is a diagram for explaining a variation in crystallinity of a film according to a conventional technique.

FIG. 3 is a circuit diagram and a plan view of an example of a conventional technique.

FIG. 4 is a sectional structural view of a process of an embodiment of the present invention.

FIG. 5 is a perspective view showing a structure of a thin film transistor driven liquid crystal display device.

[Explanation of symbols]

101, 309: glass substrate, 102: a-Si film, 1
03: SiO ₂ film, 104: gate insulating film, 105: gate Si film, 106: protective film, 107: Al electrode, 10
8 ... polycrystalline film, 201, 202, 203 ... Si film, 30
DESCRIPTION OF SYMBOLS 1 ... scanning wiring, 302 ... signal wiring, 303 ... thin film transistor, 304 ... scanning side driving circuit, 305 ... signal side driving circuit, 306 ... liquid crystal layer, 307 ... counter electrode, 308 ... color filter, 310 ... deflecting plate.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI H01L 21/336 H01L 29/78 612Z 29/786 618Z (72) Inventor Hidemi Ando 4026 Kujicho, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi, Ltd. Hitachi Research Laboratory (56) References JP-A-59-187396 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/133 550 G02F 1/133 505 G09G 3/36

Claims (3)

(57) [Claims] 1. A liquid crystal display device having a display area and a drive circuit area for driving the display area on the same substrate, wherein the drive circuit area includes a circuit to which at least two or more inverters are connected. The inverter has a thin-film semiconductor element, and the active layer of the thin-film semiconductor element of the last-stage inverter of the circuit connecting the two or more inverters is divided into a plurality of parts. Liquid crystal display device. 2. The active layer of the thin-film semiconductor device comprises one or two or more Si film regions crystallized by laser light, electron beam or ion beam irradiation, and the area of each Si film region is , 1.6 × 10 ⁵ μm ²
2. The liquid crystal display device according to claim 1, wherein the ratio between the maximum value and the minimum value of the area of these regions is 50 or less. 3. The liquid crystal display device according to claim 1, wherein said inverter is configured in a multi-stage connection.