Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-09-20
2003-08-12
Ngo, Julie (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S038000, C430S312000
Reexamination Certificate
active
06606141
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a manufacturing method of a liquid crystal display device, a manufacturing method of a display device and a liquid crystal display device. More particularly, the present invention relates to a manufacturing method of a liquid crystal display device, a manufacturing method of a display device, and a liquid crystal display device, which are accompanied with improvement of a patterning process.
There has been remarkable progress in popularization of a liquid crystal display (LCD) device used as an image display device for a personal computer or other various monitors. The liquid crystal display device generally comprises: a liquid crystal display panel provided with a drive circuit; and a backlight unit arranged in a backside thereof. The display panel displays an image by controlling light transmitted there through. The display panel comprises a display region constituted of a plurality of sub-pixels arranged in a matrix layout, and an outer peripheral region formed in an outer periphery of the display region. Among the liquid crystal display devices, there is an active matrix LCD device, in which each sub-pixel has a switching element such as a thin film transistor (TFT) and a metal-insulator-metal (MIM).
Since the active matrix LCD can perform a fine gradation display and is high in contrast, it has been widely applied to a high-definition display device or a color LCD. The color LCD is typically formed by filling liquid crystal between an array substrate, in which switching elements and pixel electrodes are formed in an array fashion, and a color filter substrate with color filters. The color LCD device has color filters of R, G and B, each of which is provided for each sub-pixel, and performs a color display by controlling a quantity of light from each sub-pixel. Three sub-pixels of R, G and B from one pixel. It should be noted that each sub-pixel corresponds to one pixel in a monochrome LCD device.
FIG. 1
is a constructional view schematically showing a sub-pixel having a TFT as a switching element. Only the sub-pixel formed on a TFT substrate is shown.
FIG. 1
shows a bottom gate type TFT using amorphous silicon (a-Si) as a semiconductor. Besides the above, there are a bottom gate type TFT using polysilicon as semiconductor, a top gate type TFT and the like. The bottom gate type TFT is a TFT in which a gate of the TFT is disposed below drain/source thereof.
In
FIG. 1
, shows a TFT
11
as a switching element, a gate electrode
12
, a gate insulating layer
13
, an amorphous silicon (a-Si) layer
14
, an ohmic layer
15
improving an ohmic contact between the a-Si layer and electrodes, a source electrode
16
, a drain electrode
17
, and a pixel electrode
18
for applying an electric field to liquid crystal. In the ohmic layer
15
, phosphorous or arsenic is doped as a donor. The gate electrode
12
is connected to a Y-axis-side driver IC (not shown) via a gate line
19
. The source electrode
16
is connected to an X-axis-side driver IC (not shown) via a signal line
20
. It should be noted that, since the TFT
11
is driven by an alternating current, the source and drain electrodes
16
and
17
are sequentially inverted. A reference numeral
21
denotes a storage capacitor improving a retention characteristic of the liquid crystal. The storage capacitor
21
utilizes the gate insulating layer as a dielectric, and is formed between the pixel electrode
18
and a part of the gate line of a sub-pixel adjacent thereto.
Elements on the array substrate are formed by deposition of materials, a photolithography process and an etching process. In the photolithography process, photoresist made of photosensitive resin is coated on the substrate. Coating on the substrate is performed by a spin-coating method or a roll-coating method. The photoresist coated on the substrate is then subjected to a pre-baking process, followed by an exposure process. The exposure is performed by irradiating the substrate with light having a specified pattern by use of a mask called a reticle. The reticle is typically a mask in which the original picture of the pattern is formed of such as chromium on a glass substrate.
As an exposure method, in general, a proximity method, a lens projection method or mirror projection method is used. The proximity method is an exposing method of disposing a substrate for exposure proximately to a mask. Each of the lens projection and mirror projection methods is a method of exposing a substrate with a mask pattern by projecting the pattern on the substrate by use of a lens or a mirror. In each projection method, a pattern on the reticle is often enlarged by about 1.25 times to be projected on a substrate.
Since the full surface of a relatively large substrate cannot be exposed once, the substrate is dividedly exposed in general. It is a method of exposing patterns on a mask onto a substrate, not by exposing the whole substrate all at once but by exposing a plurality of divided regions. Here, the substrate is disposed on an exposure stage, or the reticle is disposed on a reticle stage, and by moving these stages, the substrate and the reticle are aligned. An apparatus for exposing the divided regions as described above is generally called a stepper.
FIG. 2
is a view showing the case of exposing one circuit onto a substrate by dividing the circuit into four regions. As shown in
FIG. 2
, the substrate is divided into four regions, and exposure is performed sequentially for each divided region. While exposing the respective divided regions, the same reticle can be repeatedly used, or alternatively, four different reticles can be used. In the case where a circuit is exposed by dividing the plurality of divided regions, the respective divided regions are different from one another in electrical characteristics due to exposure errors during manufacturing, resulting in a problem that a quantity of transmitted light for the same electric signal differs in each divided region. Such difference of the quantity of transmitted light has sometimes been recognized as a difference of a display color among the divided regions in the color LCD.
In order to solve the problem as described above, the gazette of Japanese Patent Laid-Open No. Hei 11 (1999)-258629 and the gazette of WO No. 95/16276 have proposed that a boundary between the divided regions is made nonlinear. The technologies proposed in these gazettes have an object to make a joint of the divided regions inconspicuous by zigzagging the boundary of the divided regions.
In such divisional exposure, not only the difference in the electrical characteristic for each divided region but also exposure misalignment of the mask pattern on a divisional boundary portion must be taken into consideration. An error in reticle alignment accuracy, distortion, a magnification error, an error in manufacturing a reticle and the like bring an error in jointing the respective divided regions in the divisional boundary portion. In consideration of the jointing error, double exposure is performed for the vicinity of the divisional boundary portion so that parts of the divided regions adjacent to each other overlap. The exposure misalignment causes a change of a patterned shape or a pattern position. A problem caused by the error in jointing the respective divided regions has been described in, for example, the gazette of Japanese Patent Laid-Open No. Hei 2 (1990)-223926. The change in a display characteristic caused by the jointing error becomes particularly significant on an active element such as a TFT. Therefore, the gazette has proposed that an exposure joint be set so as not to overlap the active element such as a TFT.
The inventor of the present invention found out that the setting of the TFT and the divisional boundary portion so as not to overlap each other is not sufficient for solving the problem of the exposure misalignment in the divisional boundary portion. In the conventional exposure method, the divisional boundary portion has been parallel to the signal line, and has b
Ikezaki Mitsuru
Takasugi Shinji
Jennings Derek S.
Ngo Julie
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