JPH1039330A - Liquid crystal display device and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device which obviates the occurrence of unequal display without requiring a large investment. SOLUTION: This device includes plural pixels and plural thin-film transistors for respectively driving these plural pixels and has a display screen manufactured by depositing thin films by using a stepper and a mask having patterns by a photoengraving method. In such a case, this display screen is divided to the plural display regions divided by using the contour lines of any among the contour lines A, B and C of the film thickness distribution at the time of depositing the thin films. The display screen is so formed as to exhibit uniform characteristics by changing the sizes of the patterns of the mask by each of the plural display regions.

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 (hereinafter, simply referred to as LCD) and a method of manufacturing the same. More particularly, the present invention relates to an LCD having a large area for a display substrate, a high image quality of an LCD, and an LCD corresponding to a process apparatus capable of realizing such a large area and high image quality, and a method of manufacturing the LCD.

[0002]

2. Description of the Related Art A conventional liquid crystal display device will be described with reference to FIG. FIG. 4 is a plan view of a display substrate used in a conventional liquid crystal display device. In FIG. 4, reference numeral 1 denotes a glass substrate, and an area surrounded by abcd is an LCD display area. A, B, and C are contour lines of a film thickness (hereinafter, referred to as a deposit film thickness) distribution in which one thin film used for forming a thin film transistor (hereinafter, referred to as a TFT) is deposited. Here, the display substrate refers to a substrate in which a TFT, a source wiring, a gate wiring, a pixel electrode, and a storage capacitor are provided over a transparent substrate such as glass.

[0003] Since all the TFTs in the conventional LCD display screen have the same conditions, all the TFTs are designed to have the same size and shape. In addition, the values of the storage capacities (hereinafter referred to as Cst values) of the respective pixels are all designed to be the same. For example, a mask used in a photolithography method in an exposure machine of a mirror projection system (photolithography is performed with one mask for each layer in a plurality of layers) has a pattern having the same shape in a display screen. I have.

[0004]

With the recent increase in LCD screen size, it is inevitable to use the display substrate up to the end. However, for example, when using a CVD apparatus in which the distribution of the deposited film thickness in the display screen is poor (that is, the deposited film thickness is not uniform over the entire display screen), the electrical characteristics of the TFT are different between the center of the screen and the edge of the screen. Therefore,
LCD display unevenness may occur.

[0005] Further, in recent years, the life cycle of one model of LCD is short and the price is decreasing. On the other hand, the manufacturing equipment is increasing year by year. Very difficult to maintain.

The present invention eliminates such display unevenness of the LCD, can cope with an increase in the area of the display substrate, and can cope with the high image quality of the LCD without requiring a large investment in the conventional manufacturing apparatus. It is an object of the present invention to provide a liquid crystal display device which can be used.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an array substrate (display substrate) having a constant value so that the display characteristics of an LCD are uniform even if the film thickness is uneven. ) In-plane TFT design parameters (eg, channel width (W), channel length (L), or W / L value), overlap capacitance between gate electrode and drain electrode (hereinafter referred to as Cgd value), or The overlap capacitance with the source electrode (hereinafter, referred to as Cgs value) and the Cst value are changed to optimal values for each area after dividing the display screen into a plurality of areas.

Further, the pattern size of the mask at the time of photolithography, which was conventionally set to a constant value, is changed to an optimum value for each region after the display screen is divided into a plurality of regions at the same time.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the LCD according to the present invention will be described with reference to the drawings.

Embodiment 1 FIG. 1 is an explanatory diagram of Embodiment 1 of a display substrate used for a liquid crystal display device of the present invention. In FIG. 1, the same portions as those in FIG. 4 are denoted by the same reference numerals. In the present invention, a pixel means a pixel electrode, a gate electrode (including a gate electrode line), and a source electrode (including a source electrode line).

In order to equalize the display characteristics on the surface of the LCD, pixel charging characteristics (characteristics of pixel potential when an electric signal is input to a pixel electrode) related to driving of a liquid crystal material, field-through voltage characteristics ( TF for pixel voltage holding characteristics (characteristics of holding an input electric signal) or the like for pixel voltage holding characteristics (characteristics of breakthrough voltage generated by Cgd)
It is necessary to make the design parameters of the T array uniform within the display screen.

In the present invention, in particular, by optimizing the dimensions of the TFT and the like in each display portion of the LCD using a photolithography mask, the vertical structure of the TFT such as uneven film thickness distribution, ie, the thickness of the TFT It is intended to make the display unevenness due to the dimensional fluctuation of the structure in the direction uniform. Representative examples of TFT design parameters that can be changed using a photolithography mask include a W / L value and a Cgd value (Cgs value) of the TFT that are related to a current Ion flowing when the TFT is turned on.
And the Cst value of the storage capacity.

With respect to the design parameters, the distribution of the deposited film thickness formed on the glass substrate 1 is measured in advance.
In the first embodiment, for example, the thickness of the gate insulating film is set to a deposition thickness. FIG. 1 shows the contour line A of the deposit thickness.
B and C are indicated by dotted lines, and the film thickness is reduced in the order of A to C.

After the thickness of the deposited film is measured, a simulation is performed on the display characteristics of the LCD, or each parameter is measured using a plurality of test LCD cells formed by changing the dimensions of the TFT in advance, that is, changing the parameters. Perform an experiment to measure assignment and display characteristics. Based on the result, the design parameters (W / L value, Cgd value, and Cg value of TFT) for correcting the film thickness distribution in each region in the display screen are obtained.
Design (reset) the optimal value of (st value). Further, photolithography is performed using a mask in which the dimensions of the TFT are determined so as to correspond to the above-mentioned optimum value, and a display substrate in which a thin film is formed in a desired size (dimension) is manufactured.

In the first embodiment, a mask used in a mirror projection type exposure apparatus in which photolithography of each layer is performed with one mask is used because the design value of the mask in the display screen can be changed more easily. Easy to be.
On the other hand, if correction is required only at two corners of the screen, for example, depending on the film thickness distribution, exposure is performed only once in a shot area of that part, that is, when exposure for one screen is divided a plurality of times. By providing an area in addition to a dedicated pattern on a reticle which is a pattern original plate for exposure, it is possible to perform correction by photolithography using a step-type projection exposure apparatus (hereinafter, referred to as a stepper).

In the first embodiment, the thickness of the gate insulating film made of a SiN film is made to be a deposition film thickness. However, for example, a gate electrode made of a chromium (Cr) film or an aluminum (Al) film is used. Like the source electrode,
Any thin film constituting the TFT may be used. In this case, the display screen is divided into a plurality of display areas based on the film thickness distribution of the deposited film when these thin films are deposited. A method of dividing the display screen based on the film thickness distribution will be described below using specific numerical values.

As shown in FIG. 1, a plasma CVD apparatus,
Although the contour lines of the film thickness distribution are different in each of the thin film deposition apparatuses such as the sputtering apparatus, there is a case where the deposited film thickness in the central portion is large and the deposited film thickness in the peripheral portion is small. In the first embodiment, the contour line of the deposition thickness distribution of the gate insulating film has shown an oval shape.

First, the display screen is divided into two display areas by using any one of the contour lines A, B, and C shown in FIG. 1 as a measured contour value. One of the display regions is a region inside any of the contour lines, and the region is a region X using a standard design value,
The other of the display areas is an area outside any one of the contour lines and inside an area surrounded by abcd, and is an area Y requiring correction.

In the first embodiment, the display screen is divided into two display areas, but the display screen may be divided into three or more than two. Even if there are three or more display areas, the screen display characteristics can be made uniform by changing the design parameters for each display area and correcting the design parameters in at least one area.

The method of correcting the design parameters by the contour lines as described above is used not only for the film thickness distribution at the time of forming the thin film according to the first embodiment, but also for the in-plane distribution of the etching characteristics at the time of etching (etching of the semiconductor layer). It can also be applied to the in-plane distribution of the TFT characteristics due to the in-plane distribution of the digging amount.

According to the first embodiment, since only the design dimensions of the mask used in the exposure apparatus need to be changed using the conventional thin film deposition apparatus as it is, a large investment is made in the conventional manufacturing apparatus. It is possible to provide a liquid crystal display device that does not require display irregularities.

Embodiment 2 FIG. A second embodiment according to the present invention will be described with reference to FIG. FIG. 2 is an explanatory diagram of Embodiment 2 of a display substrate used in the liquid crystal display device of the present invention. 2, the same parts as those in FIG. 4 are denoted by the same reference numerals, and 4 is a gate terminal.

With the progress of lower power consumption and higher image quality of LCDs, it is necessary to reduce the electrode line width among the electrode line dimensions, that is, to reduce the electrode line width in order to increase the aperture ratio of the TFT array. However, when the gate electrode line is made thinner, the resistance of the electrode line becomes higher, so that a signal delay occurs at the terminal portion of the gate (gate terminal 4 in FIG. 2). Therefore, a luminance gradient of the screen occurs in the Q portion. In the second embodiment, the display screen is divided so that the plurality of display regions include a region where the luminance gradient occurs and a region where the luminance gradient does not occur, in order to prevent the luminance gradient from occurring due to the thinning of the gate electrode lines. Is what you do.

Next, a method of dividing the display screen based on the luminance gradient will be described.

By making the gate electrode line thinner,
At the end (right end or left end; region Q in FIG. 2) of the display screen, the display luminance tends to decrease. In the second embodiment, the display screen is divided so that the display area is divided into a region where the luminance gradient occurs (region Q) and a region where the luminance gradient does not occur (region P).

Based on the results of an optical characteristic evaluation experiment using an LCD display simulator or a test LCD cell to which design parameters have been assigned in advance, the W / L value, Cgd value, and Cst value of the TFT, which are the design parameters in the region Q in FIG. Values and the like are set again separately from the area P.

As a result, the screen display characteristics (pixel charging characteristics,
The dimensions (W / L values) of the TFTs in the screen in the region P so that the field-through characteristics and the pixel holding characteristics are uniform.
By performing photolithography using a mask whose distribution is changed so that the Cst value becomes a desired value, it is possible to improve the image quality of the LCD. That is, as described above, in the TFT on the input end side, the charging characteristic is suppressed by reducing the W / L value and the like, and by making it equal to the charging characteristic on the terminal end side, a uniform image on display can be obtained. Can be.

In the second embodiment, the display screen is divided into two display areas. However, the display screen is divided into three or more display areas, and design parameters are changed for each display area.
The screen display characteristics can be made uniform by correcting the design parameters in at least one region.

According to the second embodiment, only the design dimensions of the mask used for the exposure apparatus need to be changed using the thin film deposition apparatus conventionally used as it is, which is larger than the conventional manufacturing apparatus. It is possible to provide a liquid crystal display device in which display unevenness does not occur without requiring investment.

Embodiment 3 Embodiment 3 of the present invention will be described with reference to FIG. FIG. 3 is an explanatory diagram of Embodiment 3 of a display substrate used in the liquid crystal display device of the present invention. In FIG. 3, the same parts as those in FIG. 4 are denoted by the same reference numerals, E indicates a boundary line of an area where the resolution is guaranteed, and F indicates a boundary line of an area that can be exposed.

In the third embodiment, a region where the resolution is ensured when a stepper is used to produce a high-definition projection LCD (a region inside the boundary line D, hereinafter referred to as a region R). A method of dividing the display screen using a region where the resolution is not guaranteed (a region outside the boundary line D and inside the boundary line E, hereinafter, referred to as a region S) will be described.

That is, LC for high definition projection
In D, it is necessary to increase the density of pixels and increase the number of display pixels in order to reduce the size of the projector body and increase the definition of display. In a manufacturing method in which a pixel area is exposed with one shot of a stepper, the pixel area must be designed so as to partially protrude from a boundary line D, which is a limit at which the resolution of the stepper is guaranteed, or a region S, which is outside the boundary line D. In other cases, or in the case of a design that requires exposure to the limit of the resolution of the stepper lens, variations in the resist dimensions after exposure inside and outside the guaranteed area become a problem.

For example, when a pattern is designed beyond the above-mentioned area where the resolution is guaranteed, the resolution of the protruding portion is reduced, and the pattern line width becomes slightly larger than the inside, or the pattern of the contact hole is removed. A punched pattern is a pattern in which a hole is formed, that is, a pattern in which a through hole is formed at a desired position in a thin film. At this time, the resist pattern after exposure and development can be made uniform within the LCD display area by narrowing the pattern line width in anticipation of the pattern on the reticle or designing the pattern pattern to be relatively large. For this design, for example, using a test reticle of a stepper, data of fluctuations in resist dimensions and resolution state outside the resolution assurance area may be accumulated and fed back to the production of a product reticle.

A small LC for high-definition projection
In the case of D as well, when luminance unevenness occurs due to gate delay due to the high definition design, it is possible to make the reticle pattern have an in-plane distribution and uniform display as in the case of the large LCD of the second embodiment. it can. The correction of the design value is performed in the same manner as in the second embodiment.

After correcting the design values, a photograph is taken using a mask whose distribution is changed so that the dimensions (W / L values), Cgd values, Cst values, etc. of the TFTs in the screen in the region S become desired values. By performing the plate making, the screen display characteristics (pixel charging characteristics, field-through characteristics, pixel holding characteristics, etc.) become uniform, and thus the image quality of the LCD can be improved. That is, as described above, the input end T
In the FT, a charging characteristic is suppressed by reducing the W / L value or the like, and a uniform image on display can be obtained by making the charging characteristic equal to the charging characteristic on the terminal side.

According to the third embodiment, since only the design dimensions of the mask used in the exposure apparatus need to be changed using the conventional thin film deposition apparatus as it is, a large investment is made in the conventional manufacturing apparatus. It is possible to provide a liquid crystal display device that does not require display irregularities.

[0037]

According to the liquid crystal display device according to the present invention, the display substrate can be fully used up to the end, and the electrical characteristics of the TFT are not different between the center of the screen and the end of the screen. Therefore, display unevenness of the LCD does not occur.

In the present invention, the division of the display screen is such that the pixel charging characteristics, the field-through voltage characteristics and the pixel voltage holding characteristics, which are the major factors in making the display characteristics uniform, are kept constant. Image quality can be improved.

Also, such LCDs can be manufactured using conventional manufacturing equipment without requiring additional investment.

[Brief description of the drawings]

FIG. 1 is a plan view showing a display substrate according to a first embodiment of the present invention.

FIG. 2 is a plan view showing a display substrate according to a second embodiment of the present invention.

FIG. 3 is a plan view showing a display substrate according to Embodiment 3 of the present invention.

FIG. 4 is a plan view showing a conventional display substrate.

[Explanation of symbols]

 1 glass substrate 4 gate terminal

Claims (12)

[Claims] 1. A display comprising a plurality of pixels and a plurality of thin film transistors each of which drives the plurality of pixels, and formed by depositing a thin film by a photoengraving method using a stepper and a mask having a pattern. A liquid crystal display device having a screen, wherein the display screen is divided into a plurality of display areas, and the size of the pattern of the mask is changed for each of the plurality of display areas so that the display screen has uniform characteristics. A liquid crystal display device comprising: 2. The liquid crystal display device according to claim 1, wherein the plurality of display areas are divided using contour lines of a film thickness distribution when a thin film is deposited. 3. The liquid crystal display device according to claim 1, wherein the plurality of display regions include at least one region having a luminance gradient and at least one region having no luminance gradient. 4. The plurality of display areas include at least one area where the resolution of the stepper used in the photoengraving method is guaranteed, and at least one area where the resolution of the stepper is not guaranteed. The liquid crystal display device as described in the above. 5. A display screen including a plurality of pixels and a plurality of thin film transistors each of which drives the plurality of pixels, and formed by depositing a thin film by a photoengraving method using a stepper and a mask having a pattern. Wherein the display screen is divided into a plurality of display areas, and the display screen is formed so as to exhibit uniform characteristics by changing the dimensions of the plurality of thin film transistors for each of the plurality of display areas. A liquid crystal display device comprising: 6. The liquid crystal display device according to claim 5, wherein the plurality of display areas are divided using contour lines of a film thickness distribution when a thin film is deposited. 7. The liquid crystal display device according to claim 5, wherein the plurality of display regions include at least one region where a luminance gradient is generated and at least one region where a luminance gradient is not generated. 8. The plurality of display areas include at least one area where the resolution of the stepper used in the photoengraving method is guaranteed, and at least one area where the resolution of the stepper is not guaranteed. The liquid crystal display device as described in the above. 9. A method for manufacturing a liquid crystal display device including a plurality of pixels and a thin film transistor for driving each of the plurality of pixels, wherein a step of forming a pattern of a mask using a photoengraving method includes the steps of: A method of manufacturing a liquid crystal display device, comprising dividing a display area into display areas and changing a mask pattern for each display area so that a display screen shows uniform characteristics. 10. The method for manufacturing a liquid crystal display device according to claim 9, wherein the plurality of display regions are regions divided using contour lines of a film thickness distribution when depositing a thin film. 11. The method according to claim 11, wherein the plurality of display areas are at least one.
10. The method of manufacturing a liquid crystal display device according to claim 9, comprising a region where one luminance gradient is generated and at least one region where no luminance gradient is generated. 12. The display area according to claim 9, wherein the plurality of display areas include at least one area where the resolution of the stepper used in the photoengraving method is guaranteed, and at least one area where the resolution of the stepper is not guaranteed. Manufacturing method of the liquid crystal display device described in the above.