Abstract:
A method of utilizing dual-layer photoresist to form black matrixes and spacers on a control circuit substrate is provided. The dual-layer photoresist is composed of a layer of black resin and a layer of transparent photoresist. The black resin, of which optical density is greater than three, is mainly used to achieve the effect of black matrix. The transparent photoresist is mainly used to satisfy the needed cell gap between two transparent substrates.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention relates to a structure of a color liquid crystal display (LCD) and a method of producing the same. More particularly, the present invention relates to a method of utilizing dual-layer photoresist to form black matrixes and spacers on a control circuit substrate and the LCD structure fabricated by the same method. 
   2. Description of Related Art 
   Liquid crystal is a material having properties between those of crystal and liquid. The alignment of the liquid crystal molecules varies with external stimulation such as an electrical field generated by an applied voltage. Hence, this feature of the liquid crystal molecules can be utilized to create a display unit. 
   Liquid crystal material was discovered in 1888, and applications thereof first appeared in 1963. However, the value of the commercial application was not proved until Sharp in Japan developed a liquid crystal display applied in a calculator. Japanese companies have continued to develop the technology and improve the product&#39;s function. Development and improvement have made the liquid crystal display widely applicable. 
   The thin-film-transistor (TFT) array substrate and the color filter substrate are fabricated separately and then are assembled in current technology for producing a color thin film transistor liquid crystal display (TFT-LCD). As a result of the limitations of assembling precision, the aperture ratio of the TFT-LCD cannot be effectively increased. Based on the limitations described above, the latest developments have led to a color filter layer being formed on a TFT array substrate by photolithography to form a color filter on array (COA) substrate. The subsequent process is only to assemble the COA substrate and a transparent indium tin oxide (ITO) substrate, with no precision limit on the assembling step. Therefore, the aperture ratio of the TFT-LCD can be greatly increased to decrease the power consumption. This is the application trend for future portable products. 
   The black matrixes and photoresist spacers have to be separately formed by two photolithography steps for a TFT-LCD made by the COA technique described above. If the black matrixes and the photoresist spacers are formed by only one photolithography step, only black resin of the negative photosensitive type can be used and the thickness of black resin needed is at least 5 μm. However, the light transmittance and the photosensitivity of the black resin are reduced and the required exposure dose is about 250 mj/cm 2 . In comparison with black resin, the required exposure dose is only about 19 mj/cm 2  for a common transparent photoresist. Therefore, a very long exposure time is needed for patterning the black resin to form an ideal pattern, and the throughput of the stepper is seriously affected. Moreover, spacers are in charge of maintaining the distance between two transparent substrates; hence certain requirements exist on the shape and the height of the spacers. Consequently, the process margin for developing the black resin of the negative photosensitive type is very narrow. 
   SUMMARY OF THE INVENTION 
   It is therefore an objective of the present invention to pattern the black resin and the transparent photoresist by only one photo mask to form black matrixes and spacers simultaneously. 
   It is another objective of the present invention to provide a method of forming black matrixes and spacers on a control circuit substrate by double layers of photoresist to increase the throughput of products. 
   It is still another objective of the present invention to provide a method of forming black matrixes and spacers on a control circuit substrate by dual-layer photoresist to increase the process margin. 
   It is also another objective of the present invention to provide a color LCD made by the method mentioned above. 
   In accordance with the foregoing and other objectives of the present invention, a method of utilizing dual-layer photoresist to form black matrixes and spacers on a control circuit substrate is provided. A control circuit, made of control devices and a chessboard-like circuit having supporting areas, is located on a control circuit substrate. A passivation layer is located on the control circuit, and contact windows are formed therein to expose electrodes of the control devices, respectively. This method comprises the following steps. A color filter layer and pixel electrodes are sequentially formed on the control circuit substrate. The pixel electrodes electrically connect to the electrodes of the control devices through the contact windows, respectively. A first photoresist is formed on the control circuit substrate and then is soft-baked. The thickness of the first photoresist is large enough to make the optical density of the first photoresist be greater than 3. A second photoresist is formed on the first photoresist and then is soft-baked. Next, the second photoresist and the first photoresist are patterned to form spacers, respectively on the supporting areas, and black matrixeses, respectively on the control devices. The second photoresist and the first photoresist are hard-baked. 
   According to a preferred embodiment of the present invention, the first photoresist is black resin and the second photoresist is transparent photoresist. When the first photoresist is non-photosensitive black resin, the second photoresist is positive or negative photosensitive photoresist. The thickness of the non-photosensitive black resin is about 0.2–1.5 μm to let the optical density of the black resin be greater than 3. The method of patterning the first and the second photoresist comprises the following steps. The second photoresist is exposed and then is developed by a developer solution. The developer solution is also used to remove the first photoresist uncovered by the second photoresist during developing the second photoresist. 
   According to another preferred embodiment of the present invention, the first photoresist is a black resin and the second photoresist is a transparent photoresist. When the first photoresist is a negative photosensitive black resin, the second photoresist is negative photosensitive transparent photoresist. The thickness of the negative photosensitive black resin is about 1–2 μm to let the optical density of the black resin be greater than 3. The second and the first photoresist are patterned by photolithography. 
   In accordance with the foregoing and other objectives of the present invention, a method of utilizing dual-layer photoresist to form black matrixes and spacers on a control circuit substrate is provided. A control circuit, made of control devices and a chessboard-like circuit having supporting areas, is located on a control circuit substrate. A passivation layer is located on the control circuit, and contact windows are formed therein to expose electrodes of the control devices, respectively. This method comprises the following steps. A color filter layer and pixel electrodes are sequentially formed on the control circuit substrate. The pixel electrodes electrically connect to the electrodes of the control devices through the contact windows, respectively. A first photoresist is formed on the control circuit substrate and then is soft-baked. A second photoresist is formed on the first photoresist and then is soft-baked. The thickness of the second photoresist is large enough to make the optical density of the second photoresist be greater than 3. Next, the second photoresist and the first photoresist are patterned to form spacers, respectively on the supporting areas, and black matrixeses, respectively on the control devices, by photolithography. The second photoresist and the first photoresist are hard-baked. 
   According to another preferred embodiment of the present invention, the first photoresist is transparent photoresist and the second photoresist is black resin. When the second photoresist is a negative photosensitive black resin, the first photoresist is negative photosensitive transparent photoresist. The thickness of the negative photosensitive black resin is about 1–2 μm to let the optical density of the black resin be greater than 3. 
   In accordance with the foregoing and other objectives of the present invention, a color liquid crystal display is provided. The color liquid crystal display comprises a first transparent substrate, a control circuit, a passivation layer, a color filter layer, pixel electrodes, first photoresist layers, second photoresist layers, a second transparent substrate, a common electrode, and a liquid crystal layer. The control circuit, made of control devices and a chessboard-like circuit having supporting areas, is located on the first transparent substrate. A passivation layer is located on the control circuit, and contact windows are located therein to expose electrodes of the control devices, respectively. A color filter layer and pixel electrodes are sequentially located on the control circuit substrate. The pixel electrodes electrically connect to the electrodes of the control devices through the contact windows, respectively. The first photoresist layers are respectively located on the supporting areas and the control devices. The second photoresist layers are respectively located on the first photoresist layers. The common electrode is on a surface, which faces the first transparent substrate, of the second transparent substrate. The liquid crystal layer is located between the first and the second transparent substrates. 
   According to a preferred embodiment of the present invention, the first photoresist is black resin and the second photoresist is transparent photoresist. When the first photoresist is non-photosensitive black resin, the second photoresist is positive or negative photosensitive photoresist. The thickness of the non-photosensitive black resin is about 0.2–1.5 μm to let the optical density of the black resin be greater than 3. The method of patterning the first and the second photoresist comprises the following steps. The second photoresist is exposed and then is developed by a developer solution. The developer solution is also used to remove the first photoresist uncovered by the second photoresist during developing the second photoresist. 
   According to another preferred embodiment of the present invention, the first photoresist is a black resin and the second photoresist is a transparent photoresist. When the first photoresist is a negative photosensitive black resin, the second photoresist is negative photosensitive transparent photoresist. The thickness of the negative photosensitive black resin is about 1–2 μm to let the optical density of the black resin be greater than 3. The second and the first photoresist are patterned by photolithography. 
   According to this preferred embodiment of the present invention, the first photoresist is transparent photoresist and the second photoresist is black resin. When the second photoresist is a negative photosensitive black resin, the first photoresist is negative photosensitive transparent photoresist. The thickness of the negative photosensitive black resin is about 1–2 μm to let the optical density of the black resin be greater than 3. 
   In the foregoing, the invention utilizes the much-improved light transmittance and photosensitivity properties of the transparent photoresist rather than those of the black resin to decrease the thickness needed by black resin used in the prior arts. Hence, the exposure time needed for the black resin used in the prior arts can be greatly reduced to increase greatly the product throughput. 
   It is to be understood that both the foregoing general description and the following detailed description are examples, and are intended to provide further explanation of the invention as claimed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
       FIG. 1  is a vertical view of a control circuit substrate according to one preferred embodiment of this invention; 
       FIGS. 2 and 3  are cross-sectional diagrams of utilizing dual-layer photoresist to form black matrixes and spacers on a control circuit substrate in  FIG. 1  according to a preferred embodiment of this invention; and 
       FIGS. 2 and 4  are cross-sectional diagrams of utilizing dual-layer photoresist to form black matrixes and spacers on a control circuit substrate in  FIG. 1  according to another preferred embodiment of this invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
   As stated above, this invention provides a method of utilizing dual-layer photoresist to form black matrixes and spacers on a control circuit substrate and the LCD structure fabricated by the same method to increase greatly the product throughput. 
     FIG. 1  is a vertical view of a control circuit substrate according to one preferred embodiment of this invention. In  FIG. 1 , a control circuit, such as a thin film transistor (TFT) array, is formed on a transparent substrate  100 . Each TFT in the TFT array comprises gate  110 , source  120  and drain  130 . Each gate  110  electrically connects to a gate line  115  made by a first metal layer. Each source  120  electrically connects to a data line  125  made by a second metal layer. The data lines  125  cross over the gate lines  115  to define pixels  135 . Red (R), green (G) and blue (B) color filters are respectively formed on each pixel  135  later, and each TFT is respectively formed in a corner of each pixel  135 . Hence, a control circuit substrate is formed. 
   The black matrixeses are formed on the areas  145  above the TFTs to prevent photocurrent occurring during the “off” state of the TFTs. The spacers are formed on opaque areas such as supporting areas  140  on the gate lines  115 . The material of the gate lines  115  and the data lines  125  is metal, which is an opaque material. Therefore, black matrixeses need not be formed on the gate lines  115  and the data lines  125  to compartment adjacent pixels  135 . In  FIG. 1 , the relative positions of the pixel electrodes  190  formed later and the TFT are also displayed. The subsequent processes are described in the following embodiments 1–2. 
   Embodiment 1: 
     FIGS. 2 and 3  are cross-sectional diagrams of utilizing dual-layer photoresist to form black matrixes and spacers on a control circuit substrate in  FIG. 1  according to a preferred embodiment of this invention. The labels A and B in  FIGS. 2 and 3  indicate the cross-sectional views of the cross-sectional lines AA′ and BB′, respectively. The TFT structures are not drawn in the Parts A in  FIGS. 2 and 3  to simplify the pictures. 
   In  FIG. 2 , a passivation layer  150  such as a silicon nitride layer is formed by, for example, chemical vapor deposition (CVD) on the control circuit substrate  105  (i.e. the transparent substrate  100  having the control circuit thereon as shown in  FIG. 1 ). The control circuit substrate  105  comprises, for example, a TFT array substrate. Next, the passivation layer  180  is patterned by, for example, photolithography and etching to form contact windows  152  therein to expose drains  130  (not shown in  FIG. 2 ) of the TFT, respectively. 
   A color filter layer  155  is formed on the control circuit substrate  105 . The color filter is made of red, green and blue colors color filters respectively on pixels  135  (as shown in  FIG. 1 ). In general, the red, green and blue photoresist are respectively patterned by three photolithography steps to form the red, green and blue colors color filters and thus the color filter layer  155 . 
   A transparent conductive layer is formed and then is patterned to form pixel electrodes  160  by, for example, photolithography and etching. The pixel electrodes  160  electrically connect to the drains  130  (not shown in  FIG. 2 ) of the control devices through the contact windows  152 , respectively. A material of the pixel electrodes  160  includes indium tin oxide or indium zinc oxide. 
   In  FIG. 3 , a black resin is formed on the control circuit  105  having the color filter layer  155  and the pixel electrodes  160  located thereon. Then, the black resin is soft-baked. A transparent photoresist is formed on the black resin and then is soft-baked. Next, the transparent photoresist and the black resin are patterned and hard-baked to form black resin layers  165  and transparent photoresist layers  170 . Consequently, black matrixes is formed by stacking the black resin layers  165  and the transparent photoresist layers  170  on Part A, and spacers are formed by stacking the black resin layers  165  and the transparent photoresist layers  170  on Part B. 
   According to a preferred embodiment of this invention, when a material of the black resin layers  165  is non-photosensitive black resin, the material of the transparent photoresist layers  170  is positive or negative photosensitive transparent photoresist. The thickness of the non-photosensitive black resin is about 0.2–1.5 μm so that the optical density of the black resin is greater than 3 to shield the control devices from external light. Moreover, the total thickness of the black resin layers  165  and the transparent photoresist layers  170  is equal to the required spacing between the two transparent substrates of a liquid crystal display. 
   The method of patterning the black resin and the transparent photoresist comprises the following steps. The transparent photoresist is exposed and then is developed by a developer solution. The developer solution is also used to remove the black resin uncovered by the transparent photoresist during developing the transparent photoresist. Since the needed exposure dose for exposing the transparent photoresist is less than that for exposing the black resin, the exposure dose required for the transparent photoresist is much less than that for the black resin alone in the exposure step. In the subsequent developing step, the insoluble transparent photoresist  170  can protect the black resin  165  lying below by being insoluble in the developer solution. Therefore, only one photo mask, i.e. one photolithography process, is needed to form the black matrixes and the spacers simultaneously. 
   According to another preferred embodiment, when a material of the black resin layers  165  is a negative photosensitive black resin, the material of the transparent photoresist layers  170  is also a negative photosensitive transparent photoresist. Therefore, the black resin and the transparent photoresist can be simultaneously patterned by conventional photolithography. 
   The thickness of the non-photosensitive black resin is about 1–2 μm so that the optical density of the black resin is greater than 3 to shield the control devices from external light. Moreover, the total thickness of the black resin layers  165  and the transparent photoresist layers  170  is equal to the required spacing between the two transparent substrates of a liquid crystal display. Similarly, since the exposure dose required for exposing the transparent photoresist is less than that for the black resin, the exposure dose required for the transparent photoresist and the black resin is much less than that for the black resin alone in the exposure step. In the subsequent developing step, the unexposed black resin and the transparent photoresist can be simultaneously dissolved in the developer solution. Therefore, only one photo mask, i.e. one photolithography process, is needed to form the black matrixes and the spacers simultaneously. 
   The subsequent fabrication processes are well known by persons skilled in the art. Hence, the cross-sectional diagrams of the fabrication processes are omitted here, and subsequent fabrication processes are described verbally, only. 
   Next, another transparent conductive layer is formed on another transparent substrate as a common electrode. These two transparent substrates are parallel assembled, and the pixel electrodes  160  and the common electrode face each other. The periphery of the two transparent substrates is sealed, and only one opening is left for pouring liquid crystal into the space between the two transparent substrates. After pouring in the liquid crystal to fill the space between the two transparent substrates, the opening is sealed to accomplish the fabrication process of a TFT LCD. 
   Embodiment 2: 
     FIGS. 2 and 4  are cross-sectional diagrams of utilizing dual-layer photoresist to form black matrixes and spacers on a control circuit substrate in  FIG. 1  according to another preferred embodiment of this invention. The labels A and B in  FIGS. 2 and 4  indicate the cross-sectional views of the cross-sectional lines AA′ and BB′, respectively. The TFT structures are not drawn on the Parts A in  FIGS. 2 and 4  to simplify the pictures. Besides, a detailed description of  FIG. 2  has been given above, and hence is omitted here. 
   In  FIG. 4 , a transparent photoresist is formed on the control circuit  105  having the color filter layer  155  and the pixel electrodes  160  located thereon. Then, the transparent photoresist is soft-baked. A black resin is formed on the black resin and then is soft-baked. Next, the black resin and the transparent photoresist are patterned and hard-baked to form transparent photoresist layers  175  and black resin layers  180 . Consequently, black matrixes is formed by stacking the transparent photoresist layers  175  and the black resin layers  180  on Part A, and spacers are formed by stacking the transparent photoresist layers  175  and the black resin layers  180  on Part B. 
   According to another preferred embodiment, when a material of the black resin layers  180  is a negative photosensitive black resin, the material of the transparent photoresist layers  175  is also a negative photosensitive transparent photoresist. Therefore, the black resin and the transparent photoresist can be pattered by conventional photolithography simultaneously. 
   The thickness of the non-photosensitive black resin is about 1–2 μm so that the optical density of the black resin is greater than 3 to shield the control devices from external light. Moreover, the total thickness of the black resin layers  165  and the transparent photoresist layers  170  is equal to the required spacing between the two transparent substrates of a liquid crystal display. Similarly, since the exposure dose required for the transparent photoresist is less than that for the black resin, the exposure dose required for the transparent photoresist and the black resin is much less than that for the black resin alone in the exposure step. In the subsequent developing step, the unexposed black resin and the transparent photoresist can be simultaneously dissolved in the developer solution. Therefore, only one photo mask, i.e. one photolithography process, is needed to form the black matrixes and the spacers simultaneously. 
   The subsequent fabrication processes are well known by persons skilled in the art. Hence, the cross-sectional diagrams of the fabrication processes are omitted here, and subsequent fabrication processes are described verbally, only. 
   Next, another transparent conductive layer is formed on another transparent substrate as a common electrode. These two transparent substrates are parallel assembled, and the pixel electrodes  160  and the common electrode face each other. The periphery of the two transparent substrates is sealed, and only one opening is left for pouring liquid crystal into the space between the two transparent substrates. After pouring in the liquid crystal to fill the space between the two transparent substrates, the opening is sealed to accomplish the fabrication process of a TFT LCD. 
   In light of foregoing, the function of the black matrixes is achieved by black resin having a thickness that makes the optical density of the black resin greater than 3. The function of the spacers is achieved by the transparent photoresist to maintain the required spacing between the two transparent substrates of a LCD. Therefore, the transparent photoresist having much improved properties of light transmittance and photosensitivity can be used to replace most of the black resin to greatly reduce the required thickness of a single black resin layer. Therefore, utilizing this invention can not only decrease the required exposure time but also increase the process margin, and thus the product throughput is greatly increased. 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.