FR2747233A1 - METHOD OF MANUFACTURING A LIQUID CRYSTAL DISPLAY DEVICE - Google Patents

Abstract

The subject of the invention is a method for manufacturing an LCD on a substrate, the method comprising the steps of: forming a thin film transistor on the substrate; - Formation of an organic insulating layer 110 above the thin film transistor; - transformation of the surface of the organic insulating layer 110 into an inorganic insulating layer 115. The method avoids the drawbacks of detachment of the pixel electrode, or cracks at the contact hole on the organic insulating layer. The steps of forming the organic insulating layer and of transforming the surface of the organic insulating layer can be carried out in a continuous step making it possible to increase the yield and to limit the treatment steps.

Description

METHOD FOR MANUFACTURING A DEVICE

LIQUID CRYSTAL DISPLAY

  The present invention relates to a method of manufacturing a liquid crystal display (LCD) device and more particularly to a method of manufacturing an LCD having a thin film transistor (TFT) as

switching element.

  In an LCD using TFTs as switching elements. TFTs are integrated to control and control each pixel. As shown in Fig. 1, in a conventional LCD having a TFT matrix. substantially rectangular pixel electrodes 12 are arranged in rows and columns on a substrate 1. Grid lines 13 are formed along the rows and lines of data.

  14 are formed along the columns.

  Fig. 2A is a top view showing a portion of the elements of an LCD having a thin film transistor array. As shown in Figure 2A. a gate electrode 23 is formed on the substrate and a plurality of

  data lines 14 and grid lines 13, perpendicular to each other.

  are formed on the substrate. Thin-film transistors are formed near each point of intersection of the grid lines 13 and the

  14. Each transistor has a gate 23 and a source 24 and a drain 34.

  Figure 2B is a cross-sectional view along line I-1 of Figure 2A. As shown in Figure 2B. a gate electrode 23 made of Ta is formed on the substrate I. A gate insulating layer 21 made of SiNx is formed over the entire surthce, including on the gate electrode 23, and a semiconductor layer 22 constituted by The amorphous silicon layer 21 is formed on the gate insulating layer 21. An ohmic contact layer 33 made of n-doped amorphous silicon is formed on the semiconductor layer. Electrodes of

  source 24 and drain 34 in MB are formed on the ohmic contact layer 33.

  Then. an organic layer 10 of an organic material is shaped, as

passivation layer.

  The organic material has a smoother surface profile than inorganic materials. In this way, when the organic material is deposited on the surface of the LCD which has an irregular surface due to the multilayer elements, it is possible to smooth the uneven surface. In this way defects such as nonuniform orientations or misalignments of the liquid crystal molecules due to unevenness of the surface can be reduced. In addition, a higher opening rate can be achieved by increasing the area of

pixel electrodes.

  Then. an inorganic insulating layer 15 of SiO2 or SiNX is formed on the organic passivation layer 10. A contact hole is formed and finally a pixel electrode 12 of a transparent conductive material such as tin oxide

and indium (ITO) is formed.

  As described above. the passivation layer of the classic LCD presents

  a layered structure with organic and inorganic insulating layers 10. 1 5.

  The inorganic insulating layer 15 is formed above the organic passivation layer 10 to improve the adhesion properties of the LTO layer on the passivation layer. This results from the fact that the organic passivation layer does not

  does not necessarily provide good adhesion for the ITO layer.

  There are two ways to form the organic and inorganic layers 15. A first is to sequentially deposit the organic and inorganic layers. and structure them simultaneously. The second is to deposit and structure the organic passivation layer first, and then to form the insulating layer

Inorganic.

  First of all, the first method has the following disadvantage. The treatment for structuring the organic and inorganic insulating layers comprises the use of an organic solution, such as, for example, a mixture of N-methylpyrrolidone ("NMP"). of alcohol and amine to remove the photosensitive agent. Then. from this, the insulating layer may swell or expand. because such an organic solution can penetrate through the interface between the layer

  organic passivation and the inorganic isolation layer.

  Then. the second method also has a drawback in that two

  steps are needed to structure and form the insulating layer. In addition.

  the drain electrode can dissociate itself from the fact that the differences of the thermal expansion coefficients of the organic and inorganic insulating layers can

  produce cracks in the area of the contact hole.

  Consequently. The present invention relates to a method of manufacturing a liquid crystal display device which substantially alleviates one or more of

  problems due to the limitations and disadvantages of the prior art.

  An object of the present invention is to provide a method of manufacturing a

  Thin-film transistor that avoids the above-mentioned problems.

  The invention provides a method of manufacturing an LCD on a substrate. the method comprising the steps of: - forming a thin-film transistor on the substrate; - formation of an organic insulating layer above the thin film transistor; transforming the surface of the organic insulating layer into an inorganic layer. This method may further comprise the steps of: - forming a structure in a photosensitive agent over the organic insulating layer; etching the organic insulating layer so as to form a contact hole above the source and the drain of the transistor; elimination of the photosensitive agent; - converting the surface of the organic insulating layer by forming an inorganic layer on the surface of the organic insulating layer by combustion with oxygen; and forming a pixel electrode in contact with the source or the drain of

  transistor through the contact hole.

  The organic insulating layer advantageously comprises at least one material chosen from fluorinated polyimide, teflon, cytope, fluoropolyarylether, fluorinated parylene, PFCB (perfluorocyclobutane) and BCB (benzocyclobutene). The method may further include the steps of: - forming a thin-film transistor having a gate, a gate isolation layer, a source and a drain on the substrate; - forming a data line connected to the transistor source; - formation of a data line connected to the gate of the transistor; forming an organic insulating layer above the thin-film transistor, the organic insulating layer comprising at least one material chosen from fluorinated polyimide, teflon, cytope, fluoropolyarylether, fluorinated parylene, PFCB (perfluorocyclobutane) and BCB (benzocyclobutene); forming a structure in a photosensitive agent above the organic insulating layer; etching the organic insulating layer so as to form a contact hole above the source of the transistor - removing the photosensitive agent; transforming the surface of the organic insulating layer into an inorganic layer by combustion with oxygen; and forming a pixel electrode in contact with the source or the drain of the

  thin-film transistor through the contact hole.

  The step of removing the photosensitive agent preferably comprises a

oxygen combustion.

  This oxygen combustion step is advantageously continued continuously until the photosensitive agent is removed and the layer is removed.

  the inorganic layer is formed on the surface of the organic insulating layer.

  In one embodiment, the organic insulating layer comprises at least one structure with a silicon bond. The step of removing the photosensitive agent by combustion with oxygen and

  the step of forming an inorganic layer can be carried out continuously.

  The step of removing the photosensitive agent advantageously comprises a

wet attack treatment.

  This wet etching treatment step includes, for example, wet etching treatment using a mixture of alcohol, acetone, HNO 3, and H 2 SO 4. It is furthermore possible to provide the steps of: forming a thin film transistor having a gate, a gate isolation layer and a source, a drain on the substrate; - forming a data line connected to the source of the transistor; - forming a gate line connected to the gate of the transistor; forming a passivation layer above the transistor, the passivation layer comprising at least one material chosen from fluorinated polyimide, teflon, cytope, fluoropolyarylether, fluorinated parylene, PFCB (perfluorocyclobutane) and BCB (benzocyclobutene); and - performing a plasma treatment of the passivation layer, using

a gas comprising oxygen.

  The passivation layer preferably comprises a structure with a

silicon bond.

  The step of performing a plasma treatment advantageously forms a

  inorganic layer on the surface of the passivation layer.

  Other advantages and features of the invention will appear from the

  description which follows or will result from the implementation of the invention. Objects and

  advantages of the invention can in particular be obtained thanks to the structure

  described in the description, the claims and the drawings. It is understood that the

  general description above, as well as the following detailed description are not

  specimens, and are intended to better explain the invention.

  The attached figures, which form a part of this description,

  show embodiments of the invention, and serve with the written description

  to explain the principles of the invention. In these figures: - Figure 1 is a circuit diagram of a conventional LCD; Fig. 2A is a large scale top view showing thin-film transistors and pixel electrode portions in the conventional LCD; FIG. 2B is a cross-sectional view along line II of FIG. 2A, FIGS. 3A to 3F are cross-sectional views showing the steps of a method of manufacturing a crystal display device. liquid according to a first embodiment of the present invention; and - Figures 4A to 4D are cross-sectional views showing the steps of a method of manufacturing a liquid crystal display device according to a

  second embodiment of the present invention.

  Reference is now made in detail to the preferred embodiments of

  the present invention, the examples of which are illustrated in the accompanying drawings.

  First Preferred Embodiment As shown in FIG. 3A, a metal such as aluminum is deposited over the entire surface of a substrate 111, and is structured to form a grid line and a gate electrode 123. A gate insulation layer 121 is deposited on the entire surface of the substrate on which the metal layer has already been

  structured as shown in Figure 3A.

  An amorphous silicon layer 122 and an n + 133 doped amorphous silicon layer are then deposited. as shown in Fig. 3B, and are structured to form an amorphous silicon layer 122 and an n + type amorphous silicon layer 133, as shown in Fig. 3C. For example, a chromium layer is deposited and structured to form a source electrode 124 and a drain electrode 134. Next, the exposed portion of the amorphous silicon layer

  n + type 133 is etched, as shown in FIG. 3D.

  Referring to Figure 3E, a passivation layer 110 is formed over the entire surface by coating it with an organic material having a structure with a -Si-O bond. The organic passivation layer may also be an insulating organic layer. An insulating organic layer can be used in place of a

  organic passivation layer in the invention and its various embodiments.

  A photosensitive agent is coated on the passivation layer and is developed. A

  Contact hole 143 is formed using a dry etching method, for example.

  The photosensitive agent is removed by combustion in the presence of oxygen, or cendragc or oxygen attack. An inorganic insulating layer 115 is obtained by oxidizing the surface of the organic passivation layer to transform it into SiO 2 (FIG. 3E). If the organic passivation layer covers the terminals of R 14 '1 ;, INN' - 7ugâ 1-tni 7-5, 12 contact data lines and grid, it can be attacked at the same time as the contact hole is formed using a dry etching method (not shown

on the drawings).

  Then, with reference to FIG. 3F, a layer of tin oxide and indium is deposited. A photosensitive agent is coated and deposited on this layer and developed. A pixel electrode 112 is formed by etching the tin and indium layer following the structure of the developed photosensitive agent. The remainder of the photosensitive agent could be removed by combustion in the presence of oxygen (FIG. 3F). Second Preferred Embodiment Referring to Figure 4A, a metal such as chromium is disposed over the entire surface of a substrate 111 and is structured to form a data line. a source electrode 124 and a drain electrode 134. An amorphous silicon layer, a SiNx layer and an aluminum layer are deposited on the entire surface of the substrate on which the chromium layer has already been structured, as shown in FIG. Figure 4A. These layers are structured so as to form a semiconductor layer 122, a gate insulation layer 121, a line of

  gate, and a gate electrode 123 (FIG. 4B).

  A passivation layer 110 is formed by coating the entire surface of an organic material having a - $ i-O bonded structure.

  Organic passivation layer can also be an insulating organic layer.

  An organic insulating layer may be used in place of an organic passivation layer in the invention and its various embodiments. Many different compounds having the chemical-Si-O bond can be used according to the present invention. An example of such compounds is benzocyclobutene (BCB). A photosensitive agent is coated on the passivation layer and is developed. A contact hole 143 is formed using. for example, a method of dry attack. The photosensitive agent is removed by combustion in the presence of oxygen, or ashing or oxygen attack. An inorganic insulating layer 115 is formed by continuing the oxygen treatment for a time, and thereby transforming the surface of the organic passivation layer 110 into a SiO 2 layer, as shown in Figure 4C. If the organic passivation layer covers the terminals of the grid and data lines, it can be etched at the same time as the contact hole is formed.

  using the dry attack method; this is not shown in the drawings.

  With reference to FIG. 4D, a layer of tin and indium oxide is

  filed. A photosensitive agent is then coated on this layer and developed.

  The pixel electrode 112 is formed by etching the tin oxide and indium layer, following the structure of the developed photosensitive agent. by dry or wet attack. The rest of the photosensitive agent could be eliminated by

  oxygen combustion. as shown in Figure 4D.

  The characteristics of the methods mentioned above according to the present invention are described now. The photosensitive agent is coated on an organic insulation layer. The photosensitive agent is exposed and developed to present the desired structure. using a mask. The organic passivation layer is structured according to the structure of the developed photosensitive agent. using a dry attack method. The remainder of the photosensitive agent can be removed by burning in the presence of O 2, or using a wet etching method. If we use a combustion at 'o2 ,. an inorganic insulating layer 1 can be formed by continuing to attack the organic oxygen passivation layer for a period of time. so as to transform the surface of the organic layer of

SiO2 passivation.

  Consequently. it can be done in a dry attack chamber. in one go, the three steps of (1I) attack the organic passivation layer. (2) removal of the photosensitive agent and (3) combustion. ashing or attack of the organic passivation layer with oxygen. In this way. because these three steps are performed successively at one time in a dry attack chamber. the

  number of process steps is reduced. according to the present invention.

  Alternatively, the photosensitive agent can be removed using wet etching. In that case. a mixture of alcohol, acetone. H2SO4 and HNO3 can be used as a solution for the wet etching process. this being just one of a variety of methods for removing the photosensitive agent. Then. the inorganic insulating layer can be formed on the organic passivation layer by transforming the surface of the organic passivation layer 1 into a SiO 2 layer, by combustion in the presence of oxygen, after removing the agent

  photosensitive layer disposed on the organic passivation layer.

  The undesirable swelling of the insulating layer caused in the conventional method by the penetration of an organic solution such as a mixture of NMP is also avoided. of alcohol and amine through the interface between the organic passivation layer and the inorganic insulating layer, since the inorganic insulating layer is formed by transforming the surface of the organic layer of

passivation into a layer of SiO-).

  I | if.SI. X_I 1 7.1 7 71 In addition. the SiO 2 layer on the top of the insulating layer of the present invention prevents the separation or detachment between the pixel and drain electrodes which may be caused by cracks in the contact hole area resulting from a difference in coefficients of thermal expansion of the organic and inorganic insulating layers. This difference in expansion coefficients

  thermal is overcome by the invention.

  It will be apparent to those skilled in the art that various modifications and variations in the manufacturing method of the present invention can be made without

  as far away from the spirit of the invention.

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Claims (12)

  A method of manufacturing an LCD on a substrate, the method comprising the steps of: - forming a thin film transistor on the substrate (111); - forming an organic insulating layer (110) above the thin film transistor; - deformation of the surface of the organic insulating layer (110) into one inorganic layer (115).   The method of claim 1, further comprising the steps of: forming a structure in a photosensitive agent over the organic insulating layer; etching the organic insulating layer (110) so as to form a contact hole (143) above the source and drain of the transistor; elimination of the photosensitive agent; - converting the surface of the organic insulating layer by forming an inorganic layer on the surface of the organic insulating layer by combustion with oxygen; and forming a pixel electrode (112) in contact with the source (124) or   transistor drain (134) through the contact hole.   3. A process according to claim 2, wherein the organic insulating layer comprises at least one material chosen from fluorinated polyimide, teflon, cytope, fluoropolyarylether, fluorinated parylene, PFCB (perfluorocyclobutane) and BCB (benzocyclobutene).   The method of claim 1, further comprising the steps of: forming a thin film transistor having a gate (123). a gate insulation layer (121), a source (124) and a drain (134) on the substrate; - forming a data line connected to the transistor source; - formation of a data line connected to the gate of the transistor; forming an organic insulating layer (110) above the thin-film transistor, the organic insulating layer comprising at least one material chosen from fluorinated polyimide. teflon, cytope, fluoropolyarylether, fluorinated parylene, PFCB (perfluorocyclobutane) and BCB (benzocyclobutene); forming a structure in a photosensitive agent above the organic insulating layer; etching the organic insulating layer so as to form a contact hole above the source of the transistor - removing the photosensitive agent; transforming the surface of the organic insulating layer into an inorganic layer by combustion with oxygen: and - forming a pixel electrode (1 12) in contact with the source or the drain   of the thin-film transistor through the contact hole.   5.- Method according to one of claims 2 3 or 4 wherein the step   removal of the photosensitive agent comprises oxygen combustion.   The process of claim 5 wherein the oxygen combustion step is continued continuously until the photosensitive agent is removed and the inorganic layer is formed on the surface of the insulating layer. organic.   7. A process according to claim 5 or 6 wherein the insulating layer   organic composition comprises at least one structure with a silicon bond.   8. A process according to claim 5. 6 or 7. wherein the step of removing the photosensitive agent by combustion with oxygen and the step of forming a   inorganic layer are carried out continuously.   9.- Method according to one of claims 2 to 8. wherein the step   removal of the photosensitive agent comprises wet etching treatment.   The process of claim 9 wherein the wet etching treatment step comprises wet etching treatment using an alcohol mixture. of acetone. HNO3. and H 2 SO 4. I. A process according to claim 1, further comprising the steps of: - forming a thin film transistor having a gate (123). a gate insulation layer (121) and a source (124). uni drain (134) on the substrate (l): - formation of a data line connected to the source of the transistor; forming a gate line connected to the gate of the transistor; forming a passivation layer (110) above the transistor. the passivation layer comprising at least one material chosen from fluorinated polyimide, teflon, cytope, fluoropolyarylether, fluorinated parylene, PFCB (perfluorocyclobutane) and BCB (benzocyclobutene); and - performing a plasma treatment of the passivation layer, using a gas comprising oxygen.   12. The process according to claim 11, wherein the passivation layer   comprises a structure with a silicon connection.   The process of claim 11 or 12, wherein the step of performing a plasma treatment forms an inorganic layer on the surface of the passivation layer. # 14, NI -; 'ImN' -, - in 1997- It 12