FR2751131A1 - METHOD OF MANUFACTURING A DISPLAY DEVICE WITH A LIQUID CRYSTAL ACTIVE MATRIX AND STRUCTURE OF THE DISPLAY DEVICE ACCORDING TO THIS PROCESS - Google Patents

Abstract

The present invention relates to the structure of a liquid crystal display device and a method of manufacturing such a structure, in which a thin film transistor is used as a switching element; it particularly relates to a method of manufacturing a first substrate of a liquid crystal display device, using an organic material such as BCB (benzocyclobutene) and PFCB (perfluorocyclobutane) as an insulating layer and a protective layer. The introduction of an organic layer in the thin film transistor leads to problems in the characteristics of the liquid crystal display device. The invention therefore provides a plasma treatment, with a gas containing O2, N2, N or F, applied to the semiconductor layer and to the organic gate insulation layer, which prevents the detachment of the layers, and the layers. charge traps at the interface, comprising the semiconductor layer, so that the open rate of the display device can be improved, without influencing the transmission characteristic of the thin film transistor.

Description

METHOD FOR MANUFACTURING DISPLAY DEVICE A

  LIQUID CRYSTAL ACTIVE MATRIX AND STRUCTURE OF THE

  DISPLAY DEVICE MADE ACCORDING TO THIS METHOD

  The present invention relates to a liquid crystal active matrix display (AMLCD) device having a thin film transistor (TFT) as a

  switching element, and more particularly the manufacturing process.

  of the thin-film transistor and the structure of the thin-film transistor

manufactured according to this method.

  In a conventional active matrix liquid crystal display device, such as that shown in FIG. 1, the structure of the device comprises two substrates (a first and a second substrate) that form arrayed pixels. On the first substrate 3, each pixel electrode is disposed at intersections of gate bus lines 17 and data bus lines 15. Gate bus lines 17 are formed in the horizontal direction and include gate electrodes ( not shown), protruding from the lines. On the other hand, data bus lines (15) are formed in the vertical direction and include data electrodes (not shown) projecting from these lines. At the intersections between the grid bus lines and the data bus lines are thin-film transistors 8, and provide contact

  electric with pixel electrodes 4.

  On the second substrate 2, layers of color filters 38 and an electrode

common 37 are formed.

  The first and second substrates are arranged opposite one another, aligned, and are assembled. The volume formed between the substrates is filled with a crystal material

  liquid 40 to complete the liquid crystal active matrix display panel.

  A polarization film 1 is formed on the outer face of the substrates, before assembly, and the references 11 and 11 'in FIG.

transparent glass.

  The structure and the manufacturing process of the first substrate 3, which is concerned

  by the present invention are described in detail with reference to FIGS. 2 and 3.

  FIG. 2 is a top view showing the structure of a conventional active matrix liquid crystal display device, and FIG.

  cross section along the line 3-3 of Figure 2.

  In a conventional method of manufacturing an active matrix liquid crystal display device, the structure of the display device is as follows. Transparent glass substrate 11 is formed with grid bus lines 17 in the horizontal direction, and gate electrodes 17a projecting from these I.1.1, 141, k 7 1) ((- 25 June 19) 97-1115 lines Grid electrode can be anodized to improve insulation performance and to prevent formation of mounds on the surface On substrate 11, including gate electrode 17a, forms a gate insulating layer 23, using an inorganic material, such as SiNx or SiO2, forming on the portion of the gate insulating layer 23 above the gate electrode 17a, a semiconductor layer 22, using amorphous silicon (a-Si). On the amorphous silicon semiconductor layer, distinct ohmic contact layers 25 are formed using n + doped amorphous silicon. included on the ohmic contact layer 25, a data bus line 15, in the direction v and a source electrode 15a connected to the data bus line 15 and a drain electrode 15b at a distance from the source electrode 15a. At the same time, the source electrodes 15a and

  15b are in electrical contact with the ohmic contact layer corresponding thereto.

  ponding. A protective layer 26 is then formed using an inorganic material such as SiNx to cover the substrate, including the source and drain electrodes 15a and 15b. A pixel electrode 4 is formed using a transparent conductive material, such as tin-indium oxide (ITO), above the protective layer, which provides electrical contact with the drain electrode 15b to the 'Entrance

  a contact hole 31 formed in the protective layer 26.

  However, since the first substrate of the active matrix liquid crystal display device leads to thin film transistors and bus lines having surfaces with shoulders or steps as shown in FIG. pixel 4 is formed at a distance from the line of

  gate bus 17, the data bus line 15 and the thin-film transistor.

  This results from the fact that an inorganic material such as SiNX or SiO2 is used to

  the gate insulation layer 23 or for the protective layer 26.

  In addition, the thin-film lines and transistors having shoulders cause problems in the manufacture of liquid crystal active matrix display devices. In particular, when forming an anchor film on a surface having shoulders, the initial anchoring of the liquid crystal becomes uniform, which reduces the quality of the display device due to defects in

  friction on areas with shoulders of the anchor film.

  In order to overcome these problems, an organic material having good planarity enhancing characteristics is used for the gate insulating layer 23 or the protective layer 26. The reduction of the performance of the liquid crystal display device is then limited. eliminating the defects of R15600 \ 14637 DO (-25 jin 1'97 -2/15 friction and one can obtain an improvement of the rate of opening because the

  4 pixel electrodes can cover the bus lines.

  The introduction of an organic material into a thin-film transistor structure, however, causes other problems. The characteristic of the on state of a thin-film transistor becomes unstable, with a shift of the curve in the negative direction (FIG. 5) due to charges trapped on the surface of the transistor.

  the semiconductor layer 22 in contact with the organic layer.

  In order to avoid such problems, the surface of the semiconductor layer is plasma treated using oxygen or nitrogen gas, so as to form on the surface Si-O or Si-bonded structures. N stable. In this way, the interface problems between the semiconductor layer and the organic protective layer,

  as trapped charges and detachments can be eliminated. In a similar way

  the surface of a gate insulating layer which is in contact with the semiconductor layer and made of organic material can also be plasma treated.

  to avoid interface problems.

  An object of the present invention is therefore to provide an active matrix liquid crystal display device with a stable thin film transistor, using

  a protective layer and / or an organic insulation layer.

  Another object of the present invention is to manufacture the first substrate of a

  active-matrix liquid crystal display device comprising a processing step

  to the plasma of the semiconductor layer 22, using oxygen or nitrogen gas before the deposition of the organic protective layer 26, which exhibits

  a dielectric constant less than 3.0.

  Yet another object of the present invention is to manufacture the first

  substrate of a liquid crystal display device using a step of processing

  of the organic grid insulation layer 23 formed in BCB, in addition to the plasma treatment step of the semiconductor layer, using

  nitrogen or fluorine as the plasma gas.

  The invention relates to a method for manufacturing a liquid crystal display device having a thin-film transistor comprising a gate electrode 1 1 7a projecting from a gate line 117. a protective layer 123 covering a gate electrode, a semiconductor layer 122, an ohmic contact layer 125, a drain electrode 115b and a source electrode 115a protruding from a data bus line 115, and a second protective layer 126 covering the semiconductor layer, the method comprising the steps of: - surface treatment of the semiconductor layer 122; and - forming the second protective layer 126 on the treated surface of the

  layer 1 36b of the semiconductor layer 122, using an organic material

Picnic.

  It is clear that the above general description and the detailed description of

  following are given as examples only and are intended only to provide

  explanation of the invention as claimed.

  The attached drawings, which are included to ensure a better understanding

  of the invention and form part of the description, illustrate the modes of

  of the invention and, in connection with the description, make it possible to explain the

principles of the invention.

  In these drawings: FIG. 1 is a perspective view showing the structure of a conventional active matrix liquid crystal display device; FIG. 2 is a view from above showing the structure of a conventional active matrix liquid crystal display device;

  FIG. 3 is a cross-sectional view showing the structure of a device

  active matrix liquid crystal display system, with reference to line III-III of FIG. 2;

  FIG. 4 is a perspective view showing a surface with shoulder

  ments, an intersection between a grid bus line and a data bus line; FIG. 5 shows the curves of the on state of a thin-film transistor using an organic protective layer; Fig. 6 is a cross-sectional view of a plasma treatment apparatus; FIG. 7 is a diagram showing the chemical structure of a semiconductor layer having unsaturated bonds on its surface; FIG. 8 is a diagram showing the chemical structure of a semiconductor layer, after a treatment of the plasma surface, using oxygen or nitrogen gas; FIG. 9 shows the curves of the on state of a thin-film transistor using an organic protective layer, after a plasma treatment according to the present invention; Fig. 10 is a top view showing the structure of an active matrix liquid crystal display device according to the present invention; FIGS. 11 and 12 are cross-sectional views showing the steps of manufacturing a first substrate of a liquid crystal display device with a matrix of 14/1960. active according to the present invention, along lines VV of the figure; FIGS. 13 to 15 are cross-sectional views showing a first

  substrate of an active matrix liquid crystal display device, with different

  thin-film transistor structures according to the present invention, along line V-V of FIG. 10; FIG. 16 is a cross-sectional view showing another first substrate of an active matrix liquid crystal display device according to FIG.

  present invention along the line 5-5 of FIG.

  Reference is now made to the details and preferred embodiments of the present invention, the examples of which are illustrated in the accompanying drawings. The organic material for the protective layer or the gate insulation layer

  can be selected from BCB and PFCB.

  However, the examples are given in connection with the manufacture of the first substrate of an active matrix liquid crystal display device using BCB

  having a relative dielectric constant of less than 3.0 and a bonding structure

Si-O sounds.

  The importance of the plasma treatment of the semiconductor layer, prior to the deposition of the organic layer, according to the present invention, is described by explaining the

  formation of the semiconductor layer.

  As shown in FIG. 6, when a silane gas (SiH4) is introduced and discharged into a plasma apparatus 150, a plasma comprising SiH3 +, SiH22 + and H + is formed. The reaction of the plasma gas causes the deposition of an amorphous silicon a-Si: H 122 on the substrate 100. The semiconductor layer of a-Si: H has the chemical structure shown in FIG. 7, which comprises a

  bonding defect formed of unsaturated bonds on the surface.

  When the semiconductor layer 122 comprising such a bonding defect is coated with an organic protective layer, by spinning, the unstable surface of the semiconductor layer causes a weak bonding capacity with the organic layer, and a detachment of the organic layer. In addition, unsaturated bonds on the surface of the semiconductor layer cause charge traps for the electrons, which shifts the characteristic curves of the thin film transistor's on state in the direction of the negative voltages, as shown in FIG. This leads to an unstable TFT which undesirably drives the circuit to a voltage which is lower than the voltage making the

transistor passing.

  Thus, the surface 136 of the semiconductor layer is treated with plasma, with

  oxygen or nitrogen gas, in order to prevent defects in the connections and

  41, () 2 - iS997- 515 of the semiconductor layer of the organic layer disposed thereon Surface treatment of the semiconductor layer with oxygen or nitrogen gas leads to a stable bonding structure, such as Si-N or Si-O, as shown in Figure 8. Accordingly, when an organic layer is deposited on the surface 136 of the semiconductor layer 122 having bonds If -O or Si-N, a stable bond is obtained between the semiconductor layer and the organic layer, which eliminates the problem of detachment at the interface and

  ensures steady transistor passing characteristics.

  The experimental results of the passing characteristic of the transistor after depositing an organic protective layer such as BCB on the semiconductor layer, shows that the characteristic curve after treatment with plasma (C2) with oxygen gas or hydrogen shows a transmission characteristic of the improved thin-film transistors, without offset (d) with respect to the characteristic curve without plasma treatment (C1) as is

shown in Figure 2.

EXAMPLE 1

  The method of manufacturing the first substrate of an active matrix liquid crystal display device is explained with reference to Fig. 10, and shows a plan view of the first substrate of a matrix liquid crystal display device. in accordance with the present invention, taken in conjunction with FIG. 11 which shows a

  cross-sectional view along the line V-V of Figure 10.

  A metal layer, which can be Al, Al-Ta, Al-Mo, Ta or Ti, capable of being anodized, or Cr, is deposited on a transparent glass substrate 111 and structured so as to form a grid bus line. 117 and a gate electrode 117a derived therefrom, as shown in FIG. When the metal layer is likely to be anodized, an anodized layer 135 is formed on the gate bus line, and on the gate electrode 117a, to improve the insulating properties and to prevent mound formation, as shown in Figure lib. Then the whole surface is coated with an inorganic material such as

  than SiNx or SiO2, to form a grid insulating film, and then successively

  amorphous silicon and n + doped amorphous silicon on the insulating layer.

  123, as shown in Figure 1 1 c.

  The layers of amorphous silicon and n + doped amorphous silicon are structurally

  at the same time to form a semiconductor layer 122 and an ohmic contact layer 125, as shown in FIG. 1b. Next, a metal such as an aluminum alloy is deposited on the ohmic contact layer, and is structured to form data bus lines 115 and the protruding source electrode 115a R 14600 (14637 DO ( The output portion of the electrical contact layer is eliminated by using the drain electrodes 115b and 120b, and the drain electrodes 120b themselves serve as an output. source 115a as a mask, as

shown in Figure 1 the.

  Then, the uncovered portion of the semiconductor layer is plasma treated using oxygen or nitrogen gas, so as to form a surface treatment layer 136. The protective layer of an organic material such as BCB and PFCB is formed on the entire substrate 111, as shown in Figure 11 f. The contact hole 131 is formed so as to expose the drain electrode 11 5b and through the protective layer 126, all of which is formed above the drain electrode 122, as shown in FIG. Then, tin and indium oxide is deposited on the substrate, including the protective layer, and is structured to form a pixel electrode 104, which is in electrical contact with the electrode. 115b and covers the data bus line 115, as the

shows Figure 1 lh.

  This embodiment has been explained using an IOP (ITO on Passivation) structure, ie tin and indium oxide on the passivation layer. pixel is formed on the protective layer. However, this invention can be applied to other thin-film transistor structures, regardless of the sequence of the pixel-forming steps. For example, the pixel electrode may be formed before or after formation of the semiconductor and ohmic contact layers, such as the

show Figures 12a and 12b.

  The embodiment of Figure 12a is similar to that of Figure 1a; however, the pixel electrode 4 is formed on the insulating layer 123, before the

  data bus line 115, the source electrode 115a and the drain electrode 115b.

  The embodiment of Fig. 12b is similar to that of Fig. 1h, however, the pixel electrode 104 is formed on the insulating layer 123, after the

  data bus line, the source electrode 115a, and the drain electrode 115b.

  Further, as shown in FIGS. 13 to 15, this invention can be applied to stacked, coplanar, and self-aligned thin-film transistor structures, and not only to the transistor reverse stack structure

  as shown in Figure 11.

  These different structures are known to those skilled in the art and clearly

  comprehensible with reference to Figures 13 to 15, which form part of this

scription.

  In each of these figures, reference 136a indicates a treatment layer.

  surface treatment according to the present invention.

  Thus, according to the present invention, the pixel electrode 104 may be formed so as to cover a portion of the thin film transistor, such as the gate 117 and the data bus line 115, as shown in FIG. improves the opening rate. In addition, the pixel electrode 104 overlaying the gate bus line 117 may play a role as a storage capacitor electrode.

EXAMPLE 2

  Another example of a method of manufacturing a first substrate of a device

  Active-matrix liquid crystal display is explained with reference to FIG.

  16, which shows a cross-sectional view along the line V-V of FIG.

  A metal layer, comprising Al, Al-Ta, Al-Mo, Ta or Ti (which may be anodized) or Cr, is deposited on a transparent glass substrate 111 and is structured to form a grid bus line and a gate electrode 117a derived therefrom as shown in FIG. 16a. When the metal layer is likely to be anodized, an anodized layer 135 is formed on the gate bus line and the gate electrode 117 to improve the insulating properties and

  to prevent the formation of mounds, as shown in Figure 16b.

  Subsequently, an organic material such as BCB or PFCB is deposited over the entire surface to form a gate insulating layer, and this layer is treated with plasma using a gas containing N 2, N or F, so to form

  a surface treatment layer 136a, as shown in FIG. 16c.

  Subsequently, amorphous silicon and n + doped amorphous silicon are deposited successively on the organic insulation layer 123, and they are simultaneously structured to form a semiconductor layer 122 and an ohmic contact layer 125, as shown in FIG. Figure 16d. Then, a metal such as an aluminum alloy is deposited on the ohmic contact layer and structured to form a data bus line 115, a source electrode 115 Sa projecting from the

  data bus line, and a drain electrode 115b serving as an output terminal.

  The exposed portion of the ohmic contact layer is removed using the source 115a and drain 115b electrodes as a mask, as shown in FIG.

figure 16e.

  Then, the uncovered portion of the semiconductor layer is plasma treated using a gas containing N2, N or F, so as to form a surface treatment layer 136b. Then, a protective layer made of an organic material such as BCB or PFCB is formed on the entire substrate

111, as shown in Figure 16F.

  A contact hole 131 is made so as to discover the drain electrode b, through the protective layer 126, above the drain electrode 115b. as shown in Figure 16g. Then, tin oxide and indium are deposited on the substrate, including the protective layer, and are structured to form a pixel electrode 104, which is in electrical contact with the drain electrode 115b, and

  covers the data bus line 115, as shown in Figure 16h.

  The plasma treatment of the organic grid insulating layer 123, and the semiconductor layer 122, using a gas containing N2, N or F, modifies the surface bonding structures of the layers. organic, so as to stabilize the transmission characteristic of the thin-film transistor, without carrying out a charge trap at the interface between the semiconductor layer 122 and the organic layer, and so as to prevent the detachment or structural defects in the inorganic layers, and, for example, in the layers of metal, ITO or silicon

  amorphous deposits on the organic layer.

  This embodiment is also explained by using an IOP transistor structure (tin oxide and indium on passivation layer, acronym for ITO

  On Passivation) in which the pixel electrode is formed on the protective layer

  However, the invention can be applied to other thin-film transistor structures regardless of the sequence of the pixel-forming steps. For example, the pixel electrode may be formed before or after forming the source and drain electrodes, as shown in the figures

17aetl 17b.

  The embodiment of Figure 17a is similar to that of Figure 16h.

  However, the pixel electrode is formed on the surface treatment layer 136a, before the data bus lines 115, the source electrode 1 1 5a and the electrode

115b drain.

  The embodiment of Figure 17b is similar to that of Figure 16h.

  However, the pixel electrode 104 is formed on the surface treatment layer 136a, after the data bus line, the source electrode 115a and the

drain 115b.

  Thus, while using an organic material such as BCB or PFCB for the gate insulating layer 123 and the protective layer 126, the plasma treatment of the organic insulation layer 123 and the semiconductor layer 122 allows to improve the opening rate of the liquid crystal display device to

  active matrix, with a stabilized thin film transistor.

  Similarly, fluorinated polyimide, teflon, cytop, fluoropolyarylether, or fluorinated paraxylene, each having a constant, can be used as the gate insulating layer or as the passivation layer.

  relative dielectric less than 3, as shown in Table 1.

-1) 1 (- 2q imi 1997 - 9/15

TABLE 1

  Relative dielectric constant of diorganic materials Struc-ure Material Organic constant dielectric 2. 7 C F CFs Polyimide 2.7 CF Co CF] I / CON I p. / CO \ N

fluorinated R-C R-N io - C -

  ## EQU1 ## CF 2 CF 2 CF 2 CF 2 CF 2 CF 2 CF 2 O 2

CF3 - CF3

  2.1 Cytop (CF 2) x 1 -CF 2 -F CF - (CF 2) z, (CF 2) y

BCB 2. 7 CH) CH,

I I

  CH HCH-Si-O-Si CH I CRi CHi (U CHi OR Si-O- Si IIo Me Me |

2.6 O

Fluoroly-

  -arylether 2.4 fluorinated paraxylene - CF2 CF2 14600 14637 DOC 2 ji 1997 10 / 1.n R 14600 \ 14637 DOC - 25 luin 1997 - 1 () / 15

Claims (27)

  1. A method of manufacturing a liquid crystal display device   sensing a thin-film transistor comprising a gate electrode (117a) projecting from a gate line (117), a first protective layer (123) overlying the gate electrode, a semiconductor layer (122) , an ohmic contact layer (125), a drain electrode (1 15b) and a source electrode (1 15a) protruding from a data bus line (115), and a second protective layer (126). ) covering the semiconductor layer, the method comprising the steps of: - surface-treating the semiconductor layer (122); and - forming the second protective layer (126) on the treated surface (136b) of the semiconductor layer (122), using an organic material. 2. The process according to claim 1, wherein the treatment step of   surface is a plasma treatment.   3. The process according to claim 2, wherein the step of treating with   plasma uses at least one gas selected from N2 and O2.   4. The process according to one of claims 1 to 3, wherein the first   protective layer (123) is formed under the semiconductor layer (122), and comprises an organic material.   5. The process according to claim 4, further comprising a step of   surface treatment of the first protective layer (123).   The process according to claim 5, wherein the step of treating   surface is a plasma treatment.   7. The process according to claim 6, wherein the plasma treatment step uses a gas containing at least one of N2, N and F.   8. The process according to one of claims 1 to 7, further comprising a   step of forming a pixel electrode (104) on the first or on the second protective layer.   The method of claim 8, wherein the pixel electrode is in accordance with claim 8, wherein the pixel electrode is   (104) partially overlaps the data bus line (115).   The method of claim 8, wherein the pixel electrode (104) partially overlaps the data bus line (115), and the bus line of gate (117).   The method of claim 8, wherein the pixel electrode   (104) is formed prior to formation of the semiconductor layer (122).   The method of claim 8, wherein the pixel electrode   (104) is formed after formation of the semiconductor layer (122).   The process according to any one of claims 1 to 12, wherein   the organic material comprises an Si-O bonded structure.   14. The process according to any one of claims 1 to 13, wherein   the organic material has a relative dielectric constant of less than 3.0.   15. The process according to any one of claims 1 to 14, wherein   the organic material comprises BCB or PFCB.   16. A liquid crystal display device comprising: a thin-film transistor comprising: a gate electrode (117a) projecting from a gate line (117);   a first protective layer (123) covering the gate electrode; a semiconductor layer (122); an ohmic contact layer (125); a drain electrode and a source electrode (115a) projecting from a data bus line (115); and   a second protective layer (126) covering the semiconductor layer   conductor, a surface of the semiconductor layer having undergone surface treatment.   17. The device according to claim 16, wherein the surface of the   Semiconductor layer is treated by plasma treatment.   18. The device according to claim 17, wherein the treatment according to claim 17, wherein   plasma uses a gas selected from oxygen and nitrogen.   19.- The device according to one of claims 16 to 18, wherein the   first protective layer is formed under the semiconductor layer and comprises an organic material.   20. The device according to claim 19, wherein a surface of the   first protective layer is surface treated.   21. The device according to claim 20, wherein the surface of the   first protective layer is plasma treated.   22. The device according to claim 21, wherein the plasma treatment uses a gas comprising at least N2, N or F.   23.- The device according to one of claims 16 to 22, further comprising   a pixel electrode (104) on the first or second protective layer.   24. The device according to claim 23, wherein the pixel electrode   partially overlaps the data bus line.   The device of claim 23, wherein the pixel electrode   (104) partially overlaps the data bus line and the gate bus line.   The device of claim 23, wherein the pixel electrode   (104) is formed prior to formation of the semiconductor layer (122).   The device of claim 23, wherein the pixel electrode   (104) is formed after formation of the semiconductor layer (122).   28.- The device according to any one of claims 16 to 27, in   wherein the organic material comprises an Si-O bonded structure.   The device of any one of claims 16 to 28, wherein the organic material has a relative dielectric constant of less than 3.0. R 14 (O) t0 \ l46,37 DOC -29 August 1997- 13/15   30.- The device according to any one of claims 16 to 29. in   wherein the organic material comprises BCB or PFCB.   - 14600 \ 14637 DOC - 25 June 1997 - 14/15