JP4262582B2 - Method for forming conductive element and method for forming reflective electrode part of liquid crystal display device - Google Patents

Description

  The present invention relates to a reflective electrode portion in a liquid crystal display device including a reflective electrode portion formed of a laminated film in which an amorphous transparent conductive film such as an IZO film is laminated on a reflective metal conductive film such as an Al film. The present invention relates to a method for forming a conductive element such as a wiring, and particularly relates to a countermeasure for forming a forward tapered conductive element by wet etching.

  In general, as one of liquid crystal display devices used as a color liquid crystal display, a color input device, and the like, there is a transmissive / reflective liquid crystal display device having both a transmissive function and a reflective function.

  In this device, the reflective electrode portion in a reflective liquid crystal display device comprising a TFT substrate having a TFT element portion and a reflective electrode portion, and a color filter substrate (hereinafter referred to as a CF substrate) having a color filter layer and a counter electrode portion. Part of the structure is replaced with a transparent electrode part, and the function as a transmissive liquid crystal display device can be exhibited by irradiating the light of the backlight from the back side of the panel. .

  As the transparent conductive material used for the transparent electrode portion, tin oxide, zinc oxide, indium tin oxide (ITO), indium zinc oxide (IZO), or the like is used. In particular, ITO and IZO are suitable materials having excellent transparency with respect to visible light and suitable conductivity. In a transmissive liquid crystal display device, both transparent electrode portions of a TFT substrate and a CF substrate are made of ITO. Alternatively, it can be composed of IZO. On the other hand, as the reflective metal conductive material used for the reflective electrode part, a reflective metal which is a substance different from the transparent electrode part such as aluminum is used.

  In so doing, each conductive material has its own work function. That is, the work function is different between the transparent electrode portion and the reflective electrode portion, and therefore, a counter-reflection shift occurs in the transmissive / reflective liquid crystal display device in which the transmissive display mode and the reflective display mode can be used together. In general, in the case of a transmission-only type or a reflection-only type, a DC voltage component is not applied to the panel by applying an offset voltage to the panel so that the electrode potential difference between the TFT substrate and the CF substrate is eliminated. However, in the case of the transmissive / reflective type, the offset voltage is only one for all the pixels even though the electrode potential is different between the reflective electrode part and the transparent electrode part. It cannot be set, and the optimum offset voltage can be applied to only one of the reflective electrode portion and the transparent electrode portion. As a result, a DC voltage component is applied to the liquid crystal panel. This causes the rectangular wave of the potential of the electrode portion to be asymmetrical, resulting in a change in luminance (flicker), and a significant reduction in display quality. Become. Further, when a DC voltage component is applied for a long time, the reliability of the liquid crystal is also adversely affected.

  In order to eliminate such a display defect caused by the difference in work function of the electrode material on the TFT substrate side, the work function of the electrode material of the reflective electrode part is matched with the work function of the transparent electrode part. Conceivable.

  Specifically, for example, when the transparent electrode portion is made of an ITO film and the reflective electrode portion is made of an Al film, the work function on the surface of the ITO film is about 4.9 eV. A transparent conductive material (for example, ITO itself or IZO) having a work function substantially the same as that of the film may be stacked on the Al film. Thereby, the work function of the reflective electrode part surface can be made substantially equal to the work function of the transparent electrode part surface. This also causes the reflective electrode portion and the transparent electrode portion to have the same electrode potential, so that no direct current voltage is applied to the liquid crystal, and thus reliability is not adversely affected.

As a technique related to the above, as described in Patent Document 1, in the reflective liquid crystal display device, the work function of the reflective electrode portion made of the Al film on the TFT substrate side is set to the ITO on the CF substrate side. In order to match the work function of a transparent electrode made of a film, an ITO film is laminated on an Al film, and a reflective electrode portion is formed from this ITO / Al laminated film.
JP-A-10-206845 (5th page, FIG. 6)

  By the way, in laminating the transparent conductive material on the Al film, it is conceivable to select IZO as the transparent conductive material. The reason for this is that since IZO is amorphous, it can be etched using the same weak acid etchant as in the case of the Al film. Therefore, by patterning the IZO / Al laminated film by continuous etching, This is because the formation of the reflective electrode portion can be facilitated.

  However, in the above proposed example, when processing is performed by conventional patterning (photosensitive material application, exposure, development, etching), the cross-sectional shape of the end portion of the reflective electrode after etching is exaggerated in FIG. As shown, the end of the IZO film 101 protrudes like a ridge from the end of the Al film 102, and the ridge-shaped portion peels off in a later process to cause leakage between picture elements. This may reduce the yield in manufacturing the liquid crystal display device. This is presumably because IZO is a material that is less easily etched than Al.

  The present invention has been made in view of the above points, and the main object of the present invention is to provide an amorphous conductive film such as an IZO film that is harder to etch than a metal conductive film such as an Al film. In forming a conductive element such as a reflective electrode portion in a liquid crystal display by patterning the laminated film with an etching solution for a metal conductive film, a process for making the amorphous conductive film easy to be etched is added. The patterning can be performed so that the end portion of the amorphous conductive film does not protrude from the end portion of the metal conductive film, and the IZO film is formed when the reflective electrode portion of the liquid crystal display device is formed from the IZO / Al laminated film. In other words, it is possible to prevent a situation in which the edge portion of the film is peeled off and cause a leak between picture elements, and to suppress a decrease in manufacturing yield due to such a leak.

  In order to achieve the above object, in the present invention, the IZO film on the Al film is subjected to plasma treatment in a gas atmosphere containing fluorine, thereby making the IZO film easy to be etched. / Al laminated film was continuously etched.

  Specifically, an amorphous conductive film that can be etched with the same etching solution as the metal conductive film is stacked on the metal conductive film, and then a stacked film including the metal conductive film and the amorphous conductive film is formed. As a method for forming a conductive element that is patterned using the etching solution, a plasma treatment is performed on the amorphous conductive film in a gas atmosphere containing fluorine, and then the etching solution is used. Then, the laminated film is patterned. Here, the “conductive element” is a concept including electrodes and wiring.

  The reflective metal conductive film having the above-described configuration, comprising a pair of substrates and a liquid crystal layer disposed between the substrates, wherein one of the pair of substrates has a light reflecting function and an electrode mechanism. A reflective electrode portion formed from a laminated film in which an amorphous transparent conductive film that can be etched with the same etching solution as the reflective metal conductive film and has a light transmission function and an electrode function is laminated. When applied to the method for forming the reflective electrode portion in the liquid crystal display device provided for each element, a step of forming a reflective metal conductive film and a step of forming an amorphous transparent conductive film on the reflective metal conductive film And a step of performing plasma treatment on the amorphous transparent conductive film in a gas atmosphere containing fluorine, and using the etching solution for the reflective metal conductive film and the amorphous transparent conductive film. Patterning process and It may be so provided.

  In the above case, the amorphous transparent conductive film can be made of an amorphous conductive oxide In—Zn—O containing indium oxide and zinc oxide as main components.

  According to the present invention, a laminated film formed by laminating an amorphous conductive film that is harder to be etched than the metal conductive film is formed on the metal conductive film by using an etching solution common to the metal conductive film and the amorphous conductive film. When forming conductive elements such as electrodes and wiring by etching, the amorphous conductive film is easily etched by performing plasma treatment in a gas atmosphere containing fluorine. Therefore, the conductive element can be formed so that the end portion of the amorphous conductive film does not protrude from the end portion of the metal conductive film in a bowl shape.

  When forming a reflective electrode portion of a liquid crystal display device by etching a laminated film formed by laminating an amorphous transparent conductive film on a reflective metal conductive film with the same etching solution as that for the metal conductive film Since the amorphous transparent conductive film can be easily etched by performing plasma treatment in a gas atmosphere containing fluorine on the amorphous transparent conductive film, The reflective electrode portion can be formed in a forward tapered shape so that the end portion does not protrude from the end portion of the reflective metal conductive film into a bowl shape. Therefore, it is possible to prevent a situation in which the portion of the liquid crystal display device is peeled off and cause a leak between picture elements. Therefore, it is possible to suppress a decrease in yield in manufacturing a liquid crystal display device due to such a leak.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 2 is a plan view showing the configuration of the main part of the liquid crystal display panel of the transflective liquid crystal display device according to the embodiment of the present invention.

  The present liquid crystal display device is disposed between a TFT substrate 10 having a TFT element portion 11 and a picture element electrode 14, a CF substrate (not shown) having a color filter layer and a counter electrode, and the TFT substrate 10 and the CF substrate. 2 is a TFT substrate 10 viewed from the CF substrate side.

  The TFT substrate 10 has a plurality of gate bus lines 12, 12,... Arranged so as to extend in a predetermined direction (left-right direction in FIG. 2), and directions intersecting with the gate bus lines 12, 12,. Have a plurality of source bus lines 13, 13,... Arranged so as to extend in the vertical direction of FIG. These gate bus lines 12, 12,... And source bus lines 13, 13,. The TFT element portion 11 is disposed in the vicinity of each intersection of the gate bus lines 12, 12,... And the source bus lines 13, 13,... And has a source electrode 11a, a gate electrode 11b, and a drain electrode 11c. . The source electrode 11a is connected to the source bus line 13, the gate electrode 11b is connected to the gate bus line 12, and the pixel electrode 14 is connected to the drain electrode 11c. The picture element electrode 14 is composed of a transparent electrode portion 15 arranged in the transmission area of the picture element and a reflection electrode section 16 arranged in the reflection area surrounding the transmission area.

  The laminated structure of the TFT element unit 11 will be described with reference to FIG. 3 showing a cross section taken along line III-III in FIG.

The TFT substrate 10 has a glass substrate 21, and a Ta layer having a layer thickness of about 3000 mm is provided on the glass substrate 21 so as to branch from the gate bus line 12. 11b consists of this Ta layer. A gate insulating film 22 is provided on the gate electrode 11b. The gate insulating film 22 is made of a SiNx layer having a layer thickness of about 3000 mm. A first semiconductor layer 23 is provided on the gate insulating film 22 corresponding to the gate electrode 11b. The first semiconductor layer 23 is composed of a Si layer having a thickness of about 1500 mm. A second semiconductor layer 24 is provided in each range corresponding to the source electrode 11 a and the drain electrode 11 c on the first semiconductor layer 23. These second semiconductor layers 24 are composed of n ⁺ layers having a thickness of about 500 mm. On each second semiconductor layer 24, a Ta / ITO layer having a thickness of about 4500 mm is laminated, and the source electrode 11a and the drain electrode 11c are made of the Ta / ITO layer. In this way, the TFT element portion 11 is configured.

  A laminated structure of the picture element electrode 14 will be described with reference to FIG. 4 showing a cross section taken along line IV-IV in FIG.

  An ITO film 25 is provided at a portion corresponding to substantially the entire region of each pixel so as to be connected to the drain electrode 11c of the TFT element portion 11, and the transparent electrode portion 15 is a transmission region portion of the ITO film 25. It is made up of. On the other hand, an interlayer insulating film 26 is formed in a portion corresponding to the reflection region of each picture element. This interlayer insulating film 26 is made of a SiNx layer having a layer thickness of about 3000 mm. On the interlayer insulating film 26, an unevenness forming insulating film 27 is formed. The unevenness-forming insulating film 27 is made of an organic insulating film having a thickness of about 3 μm. The reflective electrode portion 16 is formed on the unevenness forming insulating film 27. The reflective electrode portion 16 is connected to the transparent electrode portion 15 at a boundary portion with the transmissive region.

  The reflective electrode portion 16 includes an IZO film composed of an Al film 28 as a reflective metal conductive film having a thickness of about 1000 mm and an IZO film 29 as an amorphous transparent conductive film laminated on the Al film 28. / Al laminated film.

  Here, the film thickness of the IZO film 29 is preferably in the range of 10 to 200 mm from the viewpoint of display quality. That is, as an extreme example, if the thickness of the IZO film 29 is several thousand Å, the IZO film 29 absorbs the light to be reflected and causes a reduction in display quality. As described above, in the reflective display mode, the film thickness control of the IZO film 29 is important because the color by the reflective electrode unit 16 directly affects the display quality. Actually, the film thickness dependency of the color was confirmed. When the film thickness exceeded 200 mm, coloring occurred and the display quality was remarkably lowered. Therefore, the thinner the film thickness, the less the coloring and the better the display quality. On the other hand, if the thickness of the IZO film 29 is too thin, this time, the work function (for example, 4.9 eV) on the surface of the reflective electrode portion 16 becomes substantially equal to the work function on the surface of the ITO film 25 in the transparent electrode portion 15. Don't be. Therefore, the thickness dependence of the work function was also confirmed. As a result, when the film thickness was 10 mm, a value almost equal to the work function of the ITO film 25 was obtained.

  As described above, the transflective liquid crystal display device is configured.

  Next, a method for forming the reflective electrode portion of the transmission / reflection type liquid crystal display device configured as described above will be described with reference to cross-sectional views for each step shown in FIG.

  The first step is a reflective electrode portion film forming step. Here, as shown in FIG. 1A, an Al film 28 and an IZO film 29 are sequentially formed on the unevenness forming insulating film 27. Specifically, film formation is continuously performed using a DC magnetron sputtering apparatus. An example of the material for the IZO film 29 is “IZO target” (manufactured by Idemitsu Kosan Co., Ltd.).

In the present embodiment, as the second step, as shown in FIG. 1B, a CF ₄ / O ₂ plasma treatment step in which plasma treatment is performed on the surface of the IZO film 29 in a CF ₄ / O ₂ gas atmosphere. I do. Thereby, the IZO film 29 is easily etched.

Specifically, as an example, the gas flow rate ratio of CF ₄ / O ₂ gas is set to 500 sccm / 0 sccm to 150 sccm / 350 sccm (where 1 sccm is 1 cc / min under the conditions of 0 ° C. and 1013 hPa), and the power is 1000 to 1000 The pressure is 1400 W, the pressure is 150 mTorr (≈20 Pa), the temperature is 60 ° C., and the treatment time is 30 to 120 sec.

  The third and subsequent steps are the same as in the case of conventional photolithography. That is, the third step is a photosensitive material application step, and here, as shown in FIG. 1C, a photosensitive material is applied to a predetermined range on the IZO film 29 to form a resist film 51. Specifically, a positive resist containing a novolac resin is applied to a thickness of approximately 2.0 to 2.4 μm.

  The fourth step is an exposure step. Here, as shown in FIG. 1D, a portion to be removed of the resist film 51 is exposed using a photomask 52. In the case of using a negative resist, on the contrary, the portion to be left of the resist film is exposed.

  The fifth step is a development step. Here, an alkaline solution obtained by diluting TMAH (tetramethylammonium hydroxide) to a concentration of 2.38% is used as a developer. FIG. 1 (e) As shown in FIG. 3, the resist film 51 is developed.

  The sixth step is an etching step. Here, a mixed solution of nitric acid, acetic acid, phosphoric acid and water (weakly acidic etching solution) is used as an etching solution, and as shown in FIG. 1 (f), IZO / Al Etching is performed on the laminated film. At this time, in the conventional case, the end of the IZO film remains in a bowl shape after etching (see FIG. 11), but in this embodiment, the IZO film 29 is easily etched by the process of the second step. Therefore, the IZO / Al laminated film is formed in a forward tapered shape.

  The seventh step is a photosensitive material peeling step. Here, the resist film 51 is peeled off using a peeling solution. FIG.1 (g) has shown the state after peeling.

  Through the above first to seventh steps, the forward taper processing of the reflective electrode portion 16 having the IZO film 29 on the outermost surface is completed.

  Here, the action of “plasma treatment in a gas atmosphere containing fluorine” in the second step will be described. Although details are not yet known, as a result of surface film quality analysis after plasma treatment, IZO It was found that thin fluoride exists on the surface of the film 29. It is considered that the presence of this fluoride increases the hydrophilicity of the surface, weakens the adhesion with the resist, and the IZO film 29 is easily etched. When the contact angle of the surface of the IZO film 29 was measured before and after the plasma treatment, it was 30 ° before the plasma treatment, but changed rapidly to 10 ° after the plasma treatment. Probably, this change in the contact angle is considered as one result indicating that the adhesion to the resist is weakened. Note that changes in the work function of the surface of the IZO film 29 due to residual fluorine on the surface of the IZO film 29 were also investigated, but such changes were hardly recognized. Therefore, it is considered that there is no adverse effect on the display quality in the reflective display mode.

Therefore, according to the present embodiment, when the reflective electrode portion 16 is formed by continuously etching the IZO / Al laminated film with the etching solution for the Al film in the transflective liquid crystal display device, the CF for the IZO film 29 is formed. _{Since the} IZO film 29 can be easily etched by plasma treatment in a ₄ / O ₂ gas atmosphere, the forward-tapered reflective electrode portion 16 can be formed. As a result, it is possible to prevent leakage between picture elements due to peeling of the end portion of the IZO film 29 in a state of protruding from the end portion of the Al film 28 in a later process, and thus, due to such leakage. As a result, it is possible to suppress a decrease in yield during manufacturing.

  In the above embodiment, the reflective electrode portion 16 is formed from the IZO / Al laminated film formed by laminating the IZO film 29 on the Al film 28, but the Mo film is disposed below the Al film 28. The IZO film 29 may be laminated on the Al / Mo laminated film obtained in this way, and the reflective electrode portion 16 may be formed from this IZO / Al / Mo laminated film.

  In the above embodiment, Al is used as the material of the reflective metal conductive film. However, other reflective metal conductive materials may be used.

  In the above embodiment, IZO is used as the material for the amorphous transparent conductive film, but other amorphous transparent conductive material (for example, ITO) may be used.

In the above embodiment, CF ₄ / O ₂ gas is used as the atmosphere gas containing fluorine. However, other atmosphere gas (for example, SF ₆ ) may be used.

  In the above embodiment, a mixed liquid (weak acid etching liquid) of nitric acid, acetic acid, phosphoric acid, and water is used during etching. As the etching liquid, a reflective metal conductive film and an amorphous film are used. It can select suitably according to a transparent conductive film. For example, when an ITO film is laminated as an amorphous transparent conductive film on an Al film as a reflective metal conductive film, it can be etched using the same etching solution as in the embodiment.

  Further, in the above embodiment, the case where the reflective electrode portion 16 of the transmission / reflection type liquid crystal display device is formed is described. However, the present invention is not limited to various conductive elements such as a bus line (wiring) of the liquid crystal display device. It can be applied to the formation of In that case, a metal conductive film, an amorphous conductive film, and an etching solution can be appropriately employed as necessary from known ones.

(Experimental example)
Here, an experiment conducted for verifying the presence of fluorine on the surface of the IZO film subjected to the CF ₄ / O ₂ plasma treatment will be described.

Specifically, after an IZO film having a thickness of 1000 mm is formed on an Al film, Sample 1 was subjected to CF ₄ / O ₂ plasma treatment for 180 seconds, and Sample _{2 was} subjected to 60 seconds. AES (Auger Electron Spectroscopy, “Auger Electron Spectroscopy”) survey and AES profile were measured in order while sputtering and etching ions on Samples 1 and 2, and IZO was measured based on the measurement results. The fluoride layer thickness at the surface portion of the film was examined. The measurement conditions of the AES survey and the AES profile were as follows: the primary electron acceleration voltage Ep was Ep = 3.00 keV, and the current Ip flowing through the sample 1 was Ip = 0.0294 μA.

  FIG. 5 shows the AES profile of the sample 1 as the sputtering time elapses, and FIGS. 6 and 7 show the AES surveys at the time of the initial state and when the sputtering time has passed 0.1 min. Here, the “initial state” is a state in which ions are not collided yet when analyzing in the depth direction. 6 and FIG. 7, the horizontal axis represents the energy (unit: eV) of electrons emitted when a primary electron is applied to the sample 1, and the vertical axis represents the number of electrons measured. N is differentiated by electron energy. Based on the measured values of the AES survey (see FIG. 6) at the time of the initial state, the values of Peak-to-Peak are expressed as sensitivity coefficients (Sensitivity) of each element of In, Zn, O, F, and C, respectively. When the concentration of F is calculated with the sum of the values (In (pp), Zn (pp), O (pp), F (pp), C (pp)) obtained by dividing by (Factor) being 100%, 20 It was 33%.

  FIG. 8 shows the AES profile of the sample 2 as the sputtering time elapses, and FIGS. 9 and 10 show the AES surveys at the time of the initial state and when the sputtering time has passed 0.1 min, respectively. In addition, based on the measured value of the AES survey in FIG. 9, the concentration of F at the time of the initial state was calculated as in the case of Sample 1, and it was 18.87%.

  Next, for each sample, the concentration of F for each elapse of the sputtering time was calculated based on the measured value of the AES survey. As a result, the F concentration decreased to 1% at the time when the sputtering time for Sample 1 passed 0.26 min and at the time when the sputtering time for Sample 2 passed 0.27 min.

  On the other hand, from the AES profiles of Samples 1 and 2, the point where the line indicating the In concentration intersects with the line indicating the Al concentration is regarded as the depth position where the IZO film disappears. When the value of the axis (sputtering time) was read, it was 6.19 min for sample 1 and 6.10 min for sample 2. That is, the time required for etching the IZO film having a thickness of 1000 mm was 6.19 min for sample 1 and 6.10 min for sample 2.

Therefore, in the case of Sample 1 with a CF ₄ / O ₂ plasma treatment time of 180 sec, a fluoride film with a film thickness of 42.00 mm (≈1000 × 0.26 / 6.19) is also treated. In the case of sample 2 having a time of 60 seconds, it is estimated that a fluoride film having a film thickness of 44.26 mm (≈1000 × 0.27 / 6.10) is formed on the surface portion of the IZO film. be able to.

  For reference, the relative concentration of F, which is the ratio of the concentration of F to the concentration of In, is shown in the following table at the time of the initial state and at the time of each 0.1 minute from the start of sputtering. From this table, the relative concentration of F is slightly higher in the sample 1 than in the sample 2, and in all the samples, the F is almost lost when 0.1 min has passed from the start. I know that.

It is sectional drawing which shows typically the state for every process at the time of reflective electrode part formation. It is a top view which shows the principal part of the TFT substrate in the liquid crystal panel of the transflective liquid crystal display device which concerns on embodiment of this invention. It is the III-III sectional view taken on the line of FIG. It is the IV-IV sectional view taken on the line of FIG. It is a characteristic view which shows the AES profile of the sample 1 in an experiment example. FIG. 5 is a characteristic diagram showing an AES survey at the initial sputtering time of Sample 1. FIG. 6 is a characteristic diagram showing an AES survey when 0.1 min has elapsed from the start of sputtering of sample 1. It is a characteristic view which shows the AES profile of the sample 2 in an experiment example. FIG. 6 is a characteristic diagram showing an AES survey at the initial sputtering time of Sample 2. FIG. 6 is a characteristic diagram showing an AES survey when 0.1 min has elapsed from the start of sputtering of sample 2. FIG. 5 is a view corresponding to FIG. 4 schematically showing a tapered shape of a reflective electrode portion obtained by a conventional forming method.

Explanation of symbols

16 Reflective electrode (conductive element)
28 Al film (reflective metal conductive film, metal conductive film)
29 IZO film (amorphous transparent conductive film, amorphous conductive film)

Claims (3)

An amorphous conductive film that can be etched with the same etching solution as the metal conductive film is stacked on the metal conductive film, and then the stacked film composed of the metal conductive film and the amorphous conductive film is used with the etching liquid. A method of forming a conductive element that is patterned by:
A method for forming a conductive element, wherein the amorphous conductive film is subjected to plasma treatment in a gas atmosphere containing fluorine, and then the laminated film is patterned using the etching solution. A pair of substrates and a liquid crystal layer disposed between the substrates, wherein one of the pair of substrates is provided on the reflective metal conductive film having a light reflection function and an electrode mechanism. Reflection of a liquid crystal display device having a reflective electrode portion formed of a laminated film formed by laminating amorphous transparent conductive films that can be etched with the same etching solution as the conductive metal conductive film and have a light transmission function and an electrode function An electrode part forming method comprising:
Providing the reflective metal conductive film;
Providing the amorphous transparent conductive film on the reflective metal conductive film;
Performing a plasma treatment in a gas atmosphere containing fluorine on the amorphous transparent conductive film;
And a step of patterning the reflective metal conductive film and the amorphous transparent conductive film using the etching solution. In the reflective electrode part formation method of the liquid crystal display device of Claim 2,
The method for forming a reflective electrode part of a liquid crystal display device, wherein the amorphous transparent conductive film is made of an amorphous conductive oxide In-Zn-O containing indium oxide and zinc oxide as main components.

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