Liquid crystal display device and method of manufacturing the same

[0002] This application claims the benefit of Korean Patent Application No. 1999-19145, filed on May 27, 1999, under 35U.S.C. §119, the entirety of which is hereby incorporated by reference.

[0003] 1. Field of the Invention

[0004] The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device fabricated through four photolithography processes and a method of fabricating the same.

[0005] 2. Description of the Related Art

[0006] As shown in FIG. 1, a typical liquid crystal display (LCD) device has a gate bus line 60 arranged in a transverse direction and a data bus line 70 arranged in a longitudinal direction, a thin film transistor (TFT) formed near a cross point of the gate bus line 60 and the data bus line 70. The TFT has a source electrode 70a,a drain electrode 70b,a gate electrode 60a,and a semiconductor layer 80. The drain electrode 70bis connected to a pixel electrode 40.

[0007] The LCD device described above is completed through five photolithography processes.

[0008] Hereinafter, a method of fabricating the conventional LCD device will be explained in detail. FIGS. 2A to 2E show a process of manufacturing the conventional LCD device, and FIGS. 3A and 3B show a photolithography process to form a gate insulating layer 50, the amorphous silicon (a-Si) layer 80a,and an n-type impurity doped silicon (n⁺ a-Si) layer 80b.Further, FIGS. 4A-4C show a photolithography process to form source and drain electrode 70aand 70b.

[0009] First, a gate electrode 60ashown in FIG. 2A is formed on a transparent substrate 10 during a first photolithography process.

[0010] In the first photolithography process, a metal layer (not shown) of Mo or Cr is deposited on the transparent substrate 10 and then a photoresist is applied on the metal layer. Then, a first photo-mask (not shown) is located over the substrate 10, and light exposure and developing processes are performed to etch the metal layer so that the gate electrode 60ais formed. Finally, the photoresist remaining on the metal layer is removed, leaving the gate electrode 60aon transparent substrate 10 as shown in FIG. 2A.

[0011] Second, a gate insulating layer 50, the a-Si layer 80a,and a n⁺ a-Si layer 80bshown in FIG. 2B are sequentially formed during a second photolithography process, detailed as shown in FIGS. 3A and 3B.

[0012] As shown in FIG. 3A, a photoresist 88 is applied on the n⁺ a-Si layer 80b.After that, light exposure and developing processes are performed using a second photo-mask 100, thereby forming a photoresist pattern 88aas shown in FIG. 3B. The a-Si layer 80aand the n⁺ a-Si layer 80bare simultaneously etched according to the photoresist pattern 88aso that the gate insulating layer 50, the a-Si layer 80a,and the n⁺ a-Si layer 80bare formed. Finally, the photoresist remaining on the n⁺ a-Si layer 80bis removed.

[0013] Third, the source electrode 70aand the drain electrode 70bshown in FIG. 2C are formed during a third photolithography process, detailed as shown in FIGS. 4A-4C.

[0014] As shown in FIG. 4A, a metal layer 170 such as Cr is deposited over the whole surface of the substrate 10 while covering a-Si layer 80aand n⁺ a-Si layer 80b.After that, the positive type photoresist 88 is applied, and then light exposure and developing processes are performed using a third photo-mask 200, thereby forming a photoresist pattern 88aas shown in FIG. 4B. In accordance with the photoresist pattern 88a,a lower metal layer 170 is etched to form the source electrode 70aand the drain electrode 70bas shown in FIG. 4C. Continually, the n⁺ a-Si layer 80bis etched using the metal layer (source and drain electrodes) as a mask. Finally, the photoresist pattern 88aremaining on the source electrode 70aand the drain electrode 70bis removed.

[0015] Fourth, the passivation layer 55 having the contact hole 30 shown in FIG. 2D is formed during a fourth photolithography process.

[0016] An inorganic material such as a nitride or oxide of silicon (SiNx or SiOx, respectively) or an organic material such as bis-benzocyclobutene (BCB) is deposited on the source electrode 70aand the drain electrode 70b.After that, the positive type photoresist (not shown) is applied, and then light exposure and developing processes are performed using a fourth photo-mask (not shown) to form a photoresist pattern. Then, the passivation layer 55 is formed through an etching process. After the etching process, the photoresist pattern remaining on the passivation layer 55 is removed.

[0017] Fifth, the pixel electrode 40 to be connected to the drain electrode 70bshown in FIG. 2E is formed during a fifth photolithography process.

[0018] A metal layer such as indium tin oxide (ITO) is deposited on the passivation layer 55. After that, the positive type photoresist (not shown) is applied, and then light exposure and developing processes are performed using a fifth photo-mask (not shown), thereby forming a photoresist pattern. In accordance with the photoresist pattern, the metal layer is etched so that the pixel electrode 40 is formed. After the etching process, the photoresist pattern remaining on the pixel electrode 40 is removed.

[0019] The photolithography process described above includes the steps of: cleaning a substrate; applying a photoresist; soft-baking the photoresist; aligning a photo-mask; light-exposing the photoresist; developing the photoresist; inspecting the array substrate; hard-baking the photoresist; etching a portion that the photoresist does not cover; inspecting the array substrate; and removing the photoresist.

[0020] Since the photolithography process includes the complex steps described above, as the number of photolithography processes increases, the inferiority rate become greater, leading to a low yield. In other words, reliability of the manufacturing process varies inversely proportional to the number of photolithography processes performed.

[0021] An object of the present invention is to provide a liquid crystal display device fabricated through four photolithography processes.

[0022] Another object of the present invention is to increase yield and to reduce the production cost of TFT fabrication.

[0023] To achieve the above objects, the present invention provides a method of manufacturing a liquid crystal display device including a first photolithography process forming a gate electrode on a substrate; a second photolithography process including: a) depositing sequentially a gate insulating layer, first and second semiconductor layers, and a metal layer; b) applying a first photoresist on the metal layer; c) aligning a first photo mask with the substrate; d) light exposing and developing the first photoresist to produce a first photoresist pattern; e) etching the metal layer using a first etchant, the first etchant ashing the first photoresist pattern on a predetermined portion of the metal layer to produce a second photoresist pattern, thereby exposing the predetermined portion of the metal layer; and f) etching the gate insulating layer, the first and second semiconductor layer, and the predetermined portion of the metal layer using a second etchant according to the second photoresist pattern to form source and drain electrodes, an ohmic contact layer, and an active area; a third photolithography process forming a passivation film and a contact hole; and a fourth photolithography process forming a pixel electrode contacting with the drain electrode through the contact hole.

[0024] The first etchant contains Cl₂/O₂gas and the second etchant contains SF₆/HCl or SF₆/H₂/Cl₂gas. The source and drain electrodes are made of a metal selected from a group consisting of Cr, Mo, Al, and Al alloy, and the first semiconductor layer comprises an amorphous silicon and the second semiconductor layer comprises an amorphous silicon doped with n-type impurity.

[0025] For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which like reference numerals denote like parts, and in which:

[0026] FIG. 1 is a plan view of a conventional liquid crystal display device;

[0027] FIGS. 2A to 2E are cross sectional views taken along line I—I of FIG. 1 showing a process of fabricating the conventional liquid crystal display device;

[0028] FIGS. 3A and 3B are cross-sectional views illustrating a photolithography process corresponding to FIG. 2B;

[0029] FIGS. 4A to 4C are cross-sectional views illustrating a photolithography process corresponding to FIG. 2C;

[0030] FIGS. 5A and 5B, 6A to 6E, 7A and 7B, and 8A to 8C are cross sectional views showing a process of fabricating a liquid crystal display device according to a preferred embodiment of the present invention; and

[0031] FIG. 9 is a plan view illustrating the liquid crystal display device according to the preferred embodiment of the present invention.

[0032] Reference will now be made in detail to the preferred embodiment of the present invention, example of which is illustrated in the accompanying drawings.

[0033] As shown in FIG. 5A, in a first photolithography process, first, a metal layer 160 of Mo or Cr is deposited on a transparent substrate 10. After that, a positive type photoresist (photosensitive layer) 88 is applied on the metal layer 160, and then a first photo-mask 15 is aligned. In the first photo-mask, a region 15arepresents a light shielding area and a region 15brepresents a light transmitting area.

[0034] Referring to FIG. 5B, a gate electrode 60ais formed by etching the metal layer 160 according to a photoresist pattern 88aproduced after light exposure and development of the photoresist 88. After that, the photoresist 88aremaining on the gate electrode 60ais removed.

[0035] In a second photolithography process, as shown in FIG. 6A, a gate insulating layer 50 comprising an inorganic material such as SiNx and SiOx, an a-Si layer 80a,an n⁺ a-Si layer 80b,and a single or multi-layered metal layer 170 made of a metal such as Cr, Mo, Al, and Al alloy are sequentially formed on the gate electrode 60a.After that, a positive type photoresist 88 is applied on the metal layer 170 and then a second photo-mask 25 partially executing a diffraction light exposure is aligned. At this time, a region 25arepresents a light shielding area, a region 25brepresents a light transmitting area, and a region 25crepresents a diffraction light exposing area.

[0036] Further, as shown in FIG. 6B, a photoresist pattern 88ais formed by the second photo-mask 25. The region 25ais relatively thick and the region 25cis relatively thin in thickness. Further, the region 25bis completely removed so that a surface of the metal layer 170 is exposed. Specifically, the thickness of the photoresist pattern depends on a pattern shape of the second photo-mask 25.

[0037] Continually, as shown in FIG. 6C, the metal layer 170 is etched by subjecting the array substrate 10 having the photoresist pattern 88ato a first etchant containing Cl₂/O₂gas. When an etching process for the metal layer is completed, a central portion of the photoresist pattern 88ais removed by O₂gas ashing, thereby exposing a central portion of the metal layer 170 corresponding to the central portion of the photoresist pattern 88a.

[0038] And then, as shown in FIG. 6D, the a-Si layer 80aand the n⁺ a-Si layer 80bare etched by a second etchant preferably containing either SF₆/HCl or SF₆/H₂/Cl₂gas. At this time, the metal layer 170 functions as a mask.

[0039] Further, the exposed portion of the metal layer 170 and the central portion of the n⁺ a-Si layer 80bcorresponding to the exposed portion of the metal layer 170 are etched by a third etchant preferably containing Cl₂/O₂gas, thereby forming an ohmic contact layer, and source and drain electrodes 70aand 70b.At this time, the photoresist pattern 88afunctions as a mask.

[0040] Subsequently, as shown in FIG. 9, by the diffraction light exposure as the inventive second photolithography process, the line edge of the source and drain electrodes 70aand 70band the line edge of the semiconductor layer 80 are formed in the shape of curved lines. The dimension “d” represents a distance between the data bus line 70 and the semiconductor layer 80 or the drain electrode 70band the semiconductor layer 80. Since the distance ‘d’ is maintained equally throughout, it is possible to prevent the distance difference due to misalignment during the photolithography process.

[0041] In a third photolithography process, as shown in FIG. 7A, an inorganic material such as SiNx and SiOx or an organic material such as BCB is deposited on the source and drain electrodes 70aand 70bto form a passivation layer 55. After that, the positive type photoresist 88 is applied on the passivation layer 55, and then light exposure and developing processes are executed using a third photo-mask 35, thereby forming a photoresist pattern 88a.In the third photo-mask 35, a region 35arepresents a light shielding area and a region 35brepresents a light transmitting area. Further, in accordance with the photoresist pattern 88a,as shown in FIG. 7B, the passivation layer 55 is etched to form a contact hole 30 and then the photoresist pattern remaining on the passivation 55 is removed.

[0042] In a fourth photolithography process, as shown in FIG. 8A, a metal layer 140 made of ITO is deposited on the passivation layer 55 having the contact hole 30. After that, the positive type photoresist 88 is applied on the metal layer 140, and then the light exposure and developing processes are executed using a fourth photo-mask 45, thereby forming a photoresist pattern 88a.In the fourth photo-mask 45, a region 45arepresents a light shielding area and a region 45brepresents a light transmitting area. Further, in accordance with the photoresist pattern 88a,as shown in FIG. 8B, the metal layer 140 is etched so that the pixel electrode 40 is formed. After etching process, the photoresist pattern 88aremaining on the pixel electrode 40 is removed as shown in FIG. 8C.

[0043] Accordingly, the substantially important components of liquid crystal display device according to the preferred embodiment of the present invention are completed by four photolithography processes described above.

[0044] In the present invention, since the a-Si layer 80a,the n⁺ a-Si layer 80band the source and drain electrodes are simultaneously formed through the same photolithography process, that is, by the diffraction light exposure using the second photo-mask, it is possible to manufacture the LCD device through the four lithography processes, thereby increasing the yield and reducing the production cost by decreasing the inferiority rate due to many photolithography processes.

[0045] It is further understood by those skilled in the art that the foregoing description is a preferred embodiment of the disclosed device and that various changes and modification may be made in the invention without departing from the spirit and scope thereof.