JPH09197435A - Liquid crystal display device and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily control the shape of source, drain electrodes and gate electrodes and to obtain a liquid crystal display device having a good yield at a low cost by constituting a conductive film of a first layer and a second layer consisting of the same material as the material of this first layer and having a higher etching rate. SOLUTION: The conductive film forming the thin-film transistors of the liquid crystal display device and having a tapered shape at its ends includes the first layer and the second layer which consists of the same material as the material of the first layer, is arranged on a liquid crystal side and has the higher etching rate. For example, pixel electrodes 3 consisting of ITO are formed on the undercoating film 2 of an insulating substrate 1 and, further, source electrodes 4 and drain electrodes 5 consisting of Mo-W alloy films are formed. In such a case, the film of the MO-W alloy consisting of 0.28μm film thickness is formed in a sputtering device and the film of the Mo-W alloy of 0.02μm film thickness is formed by raising a discharge voltage. When these films are etched by using a photolithography method, the neat tapers of about 30 deg. are formed by the difference in the etching rate between the upper part and lower part of the Mo-W alloy films.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor of a liquid crystal display device, and more particularly to a conductive film forming the thin film transistor.

[0002]

2. Description of the Related Art Conventionally, a method of forming a conductive film on a substrate by utilizing a sputtering phenomenon has been known. In sputtering, sample atoms near the surface of the target solid get part of the kinetic energy of accelerated particles (mainly ions), are released into a vacuum, and are deposited on the facing substrate. Method. In this method, an inert gas, mainly an argon gas, is decomposed by glow discharge to generate ions, and a DC voltage or a high frequency voltage is used to accelerate the ions. Then, the conductive film is formed by repeating this process.

By applying this method of forming a conductive film to a method of manufacturing a semiconductor device, a thin film transistor (TFT: Thi) is formed.
n Film Transistor) has been put into practical use. In particular, a liquid crystal display device using a TFT has the advantages of portability, thinness, light weight, space saving, high contrast, high image quality, halftone display, and fast response speed.

In recent years, this liquid crystal display device has been required to have low resistance and fine processing of signal electrode materials and gate electrode materials due to the spread of software which requires liquid crystal display devices having large screens and high definition screens and the demands of users. There is. In addition, the use of relatively inexpensive materials is desired for cost reduction. Particularly in the manufacturing process of the liquid crystal display device, simplification of the process and processing technology are important so that the manufacturing can be performed with good yield and low cost.

[0005]

As described above, the TFT
Is very important in terms of yield in processing the source and drain electrodes and the gate electrode. Conventionally, these processes use a photolithography method to form a resist pattern on a thin film and perform etching. However, a taper angle is devised to improve the yield.
Conventionally, it is difficult to form a taper angle in a conductive film, and in the conventional method, for example, etching is performed by previously forming an angle in the resist shape. Thereby, the conductive film is angled. Alternatively, if the etching is performed very slowly, the resist is gradually scraped and angled, and the same effect as described above can be obtained.

However, in the above method, the number of steps for forming an angle on the resist is increased and the productivity is reduced. In addition, it is difficult to work stably even when etching slowly, and productivity is reduced. Therefore, as a method that is often adopted at present, two kinds of conductive films having different etching rates are laminated. At this time, a conductive film having a low etching rate is formed on the lower layer side and a conductive film having a high etching rate is formed on the upper layer side.
In this way, the taper angle is obtained by changing the etching rate.

However, in this method, the number of materials used increases, so that the yield, the productivity, and the cost increase. The present invention has been made in view of the above problems, and it is an object of the present invention to provide a liquid crystal display device that can easily control the shapes of the source and drain electrodes and the gate electrode, can be manufactured at a low cost, and can provide a high yield.

[0008]

According to the present invention, in a conductive film which forms a thin film transistor of a liquid crystal display device and has a tapered end portion, the conductive film is made of the same material as the first layer and the first layer. A liquid crystal display device, comprising: a second layer which is disposed closer to the liquid crystal than the first layer and has an etching rate faster than that of the first layer.

Further, according to the present invention, in the step of forming the conductive film of the thin film transistor, the film forming rate is relatively slow at the beginning.
The final stage is a method of manufacturing a liquid crystal display device, which is performed relatively quickly.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. First, FIG. 3 shows a cross-sectional view of a liquid crystal display device which is an embodiment of the present invention. The liquid crystal display device of this embodiment includes an array substrate 23, a counter substrate 24 facing the array substrate 23 with a predetermined gap, and the array substrate 23.
And a liquid crystal 25 filled between the counter substrate 24 and the counter substrate 24.

The array substrate 23 is formed on the surface of the insulating substrate 1 made of glass, which faces the counter substrate 24, by a thin film transistor (TFT).
and the pixel electrode 3, and an alignment film 26 made of, for example, a low temperature cure type polyimide resin is provided on the pixel electrode 3. A polarizing plate 27 is attached to the opposite surface of the insulating substrate 1.

On the other hand, in the counter substrate 24, a common electrode 28 made of indium tin oxide (ITO) is formed on a surface of the insulating substrate 31 facing the array substrate 23, and a common electrode 28 is formed on the common electrode 28. Similarly to the array substrate 23, the alignment film 2 made of polyimide resin is used.
9 are provided. Further, a polarizing plate 30 is attached on the opposite surface of the counter substrate 24. The alignment films 26 and 29 of the array substrate 23 and the counter substrate 24 are rubbed with a cloth or the like in a predetermined direction so that the alignment axes are twisted by about 90 degrees.

The rubbing directions of the alignment films 26 and 29 are set so that the good viewing angle direction faces the front. Also, in this liquid crystal display device, illumination is performed from the outside of either the array substrate 23 or the counter substrate 24.

Next, in FIG. 1A, a thin film transistor (TFT: T) formed on the array substrate 23 of the liquid crystal display device.
FIG. 3 shows a cross-sectional view of a thin film transistor). The figure (b) shows the conductive film (source electrode 4 or drain electrode 5 or gate electrode 10 etc.) in the figure (a).
It is an enlarged view of a part.

First, the TFT in this embodiment is called a positive stagger type, and its structure will be shown first. On the insulating substrate 1 made of glass or the like, a silicon oxide film (SiO 2
_An undercoat film 2 made of ( _X film) is formed.

A pixel electrode 3 made of ITO is formed thereon in a predetermined shape, and a source electrode 4 and a drain electrode 5 made of a molybdenum-tungsten (Mo-W) alloy film are further formed thereon. . At this time, the taper angles of the source electrode 4 and the drain electrode 5 are about 30 degrees with respect to the substrate surface.

Furthermore, amorphous silicon (a-S
A semiconductor layer 6 made of i) is formed, and a first gate insulating film 7 made of a silicon nitride film (SiN _x film) is formed on the semiconductor layer 6.
And a second gate insulating film 8 made of a silicon oxynitride film (SiON film) is formed. Further, a third gate insulating film 9 made of a silicon nitride film (SiN _x film) is formed.

A gate electrode 10 composed of two layers of an aluminum film (Al film) and a molybdenum film (Mo film) is formed thereon. The gate electrode 10 has a taper angle of about 45 degrees with respect to the substrate surface.

A silicon nitride film (SiN _x
A protective film 11 made of a film is formed. Then this T
The manufacturing process of the FT will be described in detail.

First, the insulating substrate 1 made of glass is 350
By heating to ℃, silane (SiH ₄ ) and nitrous oxide (N ₂
Ox) gas is introduced, and an undercoat film 2 made of SiO _{x is formed} by a plasma CVD method by glow discharge.
To a thickness of 0.5 μm.

Subsequently, ITO is deposited to a thickness of 0.1 μm. Next, a Mo—W alloy film is formed to a thickness of 0.3 μm by a sputtering method, and the shape of the pixel portion, the signal line, the source electrode 4, and the drain electrode 5 is left together with the above-mentioned ITO by the photolithography method. Etching is performed to form the source electrode 4 and the drain electrode 5 having a predetermined shape. Here, the source electrode 4 and the drain electrode 5 are formed so that the taper angle is about 30 degrees, and details of this forming process will be described later.

Next, this substrate is heated to 350 ° C., a gas for forming a semiconductor layer consisting of silane (SiH ₄ ) and hydrogen (H ₂ ) is introduced, and a-Si is converted to 0.2% by plasma CVD.
A film is formed to a thickness of 1 μm.

After the film formation, the introduction of SiH ₄ gas is stopped while maintaining the glow discharge during the a-Si film formation, and the introduction gas is a
The glow discharge is continued by switching from the Si film forming gas to hydrogen (H ₂ ) gas, helium (He) gas, or nitrogen (N ₂ ) gas. Subsequently, the hydrogen gas is switched to a gas for forming a gate insulating film composed of ammonia (NH ₃ ) and nitrogen (N ₂ ), discharge is maintained, and SiH is again supplied.
₄ is introduced to form a 2 μm SiN _x film. afterwards,
SiH ₄ and N ₂ O gas were introduced while stopping the discharge of SiH ₄ and maintaining the discharge by N ₂ gas to a film thickness of 0.02 μm.
A SiON film made of is formed. And SiH ₄ , N
The introduction of ₂ O gas was stopped and SiH ₄ and NH ₃ gases were introduced while maintaining the discharge only by N ₂ gas to obtain a film thickness of 0.4.
A SiN _x film of μm is formed.

Next, an Al film of 0.3 μm is formed by the sputtering method.
It is formed to a thickness of m, and a Mo film is further deposited thereon. This Al film and the SiN _x film immediately below it are etched by photolithography to form a gate electrode 10 and a third gate insulating film 9 having a predetermined shape together with the gate line. At this time, the third gate insulating film 9 is formed using a fluorine-based gas.
The SiN _x film to be the above is etched to expose the SiON film. _{Thus, a-Si, SiO X,} Si
Leaving the ON structure can facilitate later laser annealing. Although the taper angle of the gate electrode 10 is 45 degrees here, details of this forming process will be described later.

Further, using the gate electrode 10 as a mask, the a-Si film is doped with P ions. In this ion doping, PH ₃ gas diluted to 5% with H ₂ is decomposed by plasma, and the generated ion species are collectively accelerated by electrolysis without mass separation and implanted into the a-Si film. At this time, the dose amount is 3 × 10 ¹⁵ cm ^-2 and the acceleration voltage is 60 kV.
And

Subsequently, a wavelength of 308n is applied from above the substrate.
XeCl excimer laser of 70 m energy density
Irradiate with Jcm ^-2 . ArF, Kr for this laser
In addition to excimer lasers such as F and XeF, YAG (yttrium-aluminum-garnet) lasers and Ar lasers may be used. By this laser annealing, the gate electrode 10 serves as a mask, and only a-Si in the portion doped with P ions is crystallized. Thus, low resistance N-type polycrystalline silicon is formed.

Next, the SiON film, the SiN _x film and the a-Si film are simultaneously patterned into an island shape to form the second gate insulating film 8, the first gate insulating film 7 and the semiconductor layer 6, and the semiconductor layer 6 A source region 12 and a drain region 13 are formed in the.

After that, a protective film 11 made of a SiN _x film is formed on the substrate by the plasma CVD method. Then, the protective film 11 on the peripheral electrode portion, the protective film 11 on the pixel electrode 3 and the Mo—W film are removed by etching by photolithography. In this way, the TFT is formed.

In this embodiment, the TFT is a normal stagger type, but it goes without saying that there are various variations such as an inverted stagger type and a coplanar type. Further, in the present embodiment, the source electrode 4 and the drain electrode 5 are the Al film and the Mo film, and the gate electrode 10 is the Mo—W alloy film, but the material of this conductive film may be replaced with Al, ITO, or the like. Yes, it may change to other materials.

Next, the film formation of the source electrode 4, the drain electrode 5, the gate electrode 10 and the like described above will be described in detail with reference to FIG. 1B and FIG. 2 showing the structure of the sputtering apparatus.

FIG. 2 shows a main structure of a DC magnetron sputtering apparatus for forming the metal film (source electrode 4, drain electrode 5, gate electrode 10, etc.). This sputtering apparatus is a fixed substrate type sputtering apparatus, and a rectangular metal target 15 having a length and width of 30 × 15 cm is installed in the reaction chamber 14. A magnet 17 is arranged below the metal target 15 via a plate 16. Further, a high voltage power supply 18 is connected to the metal target 15 side, and the metal target 15 side is grounded to serve as a cathode. A counter electrode 20 for fixing the insulating substrate 1 is arranged facing the cathode.

Further, the reaction chamber 14 has a vacuum exhaust device 19
This allows vacuum evacuation. Further reaction chamber 14
A gas introduction device 21 for introducing a sputtering gas into the reaction chamber 14 is provided outside.

A resistance heater 22 for heating the insulating substrate 1 placed on the electrode 20 with an accuracy of ± 10 ° C.
Is provided. Here, two types of film forming conditions for the Mo—W alloy film and the Al film will be individually described.

First, the conditions for forming the Mo-W alloy film will be described. First, the insulating substrate 1 is fixed on the counter electrode 20 of the reaction chamber 14 of the sputtering apparatus, and the reaction chamber 14 is evacuated. The resistance heater 2 provided on the counter electrode 20
After heating the insulating substrate 1 to 150 ° C. by the step 2, the reaction chamber 1
Ar gas as a gas for sputtering is introduced into the No. 4 at a flow rate of 78 sccm to adjust the pressure to 0.51 Pa. Then, 2.7 kW of electric power is supplied from the high voltage power supply 18 to the reaction chamber 1
Then, glow discharge is generated in 4 to form a lower layer Mo—W alloy having a film thickness of 0.28 μm. Then, the discharge is stopped once, and 3.7 kW of power is supplied from the high-voltage power supply 18 to form a Mo—W alloy having a film thickness of 0.02 μm.
FIG. 4 shows the relationship between the discharge power during the film formation of the Mo-W alloy and the etching rate. The etching conditions at this time are
This is a chemical dry etching in which the flow rate of CF ₄ is 180 sccm and the flow rate of O ₂ is 360 sccm.
w. From the figure, the etching rate of the Mo-W alloy increases as the discharge voltage increases. Moreover, the density of the Mo-W alloy becomes coarser by increasing the discharge power.

The conductive film can be formed as described above. In addition, since the film can be formed in a single chamber, the interface between the films is well formed, and the productivity is very excellent. When the Mo-W alloy is etched by the photolithography method by the above method, a clean taper of about 30 degrees is formed due to the difference in etching rate between the upper and lower portions of the Mo-W alloy film.

Next, the conditions for forming the Al film will be described. First, similarly to the above, the insulating substrate 1 is fixed on the counter electrode 20 of the reaction chamber 14 of the sputtering apparatus, and the inside of the reaction chamber 14 is exhausted. Then, the insulating substrate 1 is heated to 150 ° C. by the resistance heater 22 provided on the counter electrode, and then 20 sccc of Ar gas is used as the sputtering gas in the reaction chamber 14.
It is introduced at a flow rate of m to adjust the pressure to 0.2 Pa. Then, the high voltage power supply 18 supplies 4 kW of power to the reaction chamber 14
A glow discharge is generated therein to form a lower Al film having a thickness of 0.28 μm. Then, the discharge was stopped once, and Ar gas as a sputtering gas was added to the inside of the reaction chamber 14 by 6%.
It is introduced at 0 sccm and the pressure is adjusted to 0.7 Pa. Then, the high voltage power supply 18 supplies 4 kW of power to the reaction chamber 1
Then, glow discharge is generated in 4 to form an upper Al film having a film thickness of 0.02 μm. FIG. 5 shows the relationship between the Al film forming pressure and the etching rate. The etching conditions at this time are the same as those in the case of FIG. From FIG. 5, the etching rate of the Al film is increased by increasing the film forming pressure.
Further, the density of the Al alloy becomes coarser by increasing the film forming pressure of the Al alloy.

By etching the Al films laminated by the above method using the photolithography method, it is possible to form a clean taper of about 45 degrees with respect to the substrate surface.

Further, according to this embodiment, when the metal film is formed by the sputtering method, a plurality of thin layers can be formed in one reaction chamber of the sputtering apparatus, so that the interface of each thin layer is kept normal. It can be formed as it is, and the sputtering device can be effectively used. Further, it is possible to reduce the time required for forming the conductive film and provide a manufacturing method with a good yield.

[0039]

According to the present invention, when a conductive film in a thin film transistor of a liquid crystal display device is patterned by etching, the conductive film is made of the same material but the etching rates are partially different, so that the cost is increased. Without it, the end of the pattern can be etched into a clean tapered shape. By thus taperly etching, the coverage of the film formed on the upper layer is improved, and the yield can be improved.

[Brief description of drawings]

FIG. 1A is a sectional view showing a structure of a thin film transistor according to an embodiment of the present invention. (B) is an enlarged view of a conductive film portion in (a).

FIG. 2 is a DC forming a conductive film according to an embodiment of the present invention.
It is a figure which shows the structure of a magnetron sputtering device.

FIG. 3 is a cross-sectional view of a liquid crystal display device according to an embodiment of the present invention.

FIG. 4 is a graph showing the relationship between the discharge power and the etching rate of a Mo—W film.

FIG. 5 is a graph showing the relationship between the film forming pressure and the etching rate of an Al film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Insulating substrate 3 ... Pixel electrode 4 ... Source electrode 5 ... Drain electrode 6 ... Semiconductor layer 7 ... 1st gate insulating film 8 ... 2nd gate insulating film 9 ... 3rd gate insulating film 10 ... Gate electrode 11 ... Protective film 23 ... Array substrate 24 ... Counter substrate 25 ... Liquid crystal 26, 29 ... Alignment film 27, 30 ... Polarizing plate 28 ... Common electrode

Claims (14)

[Claims] 1. A liquid crystal is sandwiched between a pair of substrates, and a conductive film formed on at least one of the pair of substrates and having a tapered end is provided to switch a voltage applied to the liquid crystal. In a liquid crystal display device including a thin film transistor, the conductive film is a first layer, is made of the same material as the first layer, is disposed closer to the liquid crystal than the first layer, and has a higher etching rate than the first layer. A liquid crystal display device comprising: two layers. 2. A liquid crystal is sandwiched between a pair of substrates, and a conductive film formed on at least one of the pair of substrates and having a tapered end is provided to switch a voltage applied to the liquid crystal. In the liquid crystal display device including a thin film transistor, the conductive film is a film in which an etching rate is continuously increased in a direction from a substrate side on which the thin film transistor is formed to a liquid crystal side. apparatus. 3. The liquid crystal display device according to claim 1, wherein the conductive film contains an alloy of molybdenum and tungsten as a main component. 4. The liquid crystal display device according to claim 1, wherein the conductive film contains aluminum as a main component. 5. The liquid crystal display device according to claim 1, wherein the conductive film is a gate electrode of a thin film transistor. 6. The liquid crystal display device according to claim 1, wherein the conductive film is a drain electrode of a thin film transistor. 7. The liquid crystal display device according to claim 1, wherein the conductive film is a source electrode of a thin film transistor. 8. A liquid crystal is sandwiched between a pair of substrates, and a conductive film which is formed on at least one of the pair of substrates and has a tapered end is provided to switch a voltage applied to the liquid crystal. A method of manufacturing a liquid crystal display device including a thin film transistor, the step of forming the conductive film of the thin film transistor,
A method for manufacturing a liquid crystal display device, characterized in that the film forming rate is relatively slow in the initial stage and relatively fast in the final stage. 9. The method of manufacturing a liquid crystal display device according to claim 8, wherein in the step of forming the conductive film, the discharge power at the end of film formation is larger than that at the start of film formation. . 10. The step of forming the conductive film is characterized in that discharge power at the end of film formation is 1.2 to 1.5 times as large as discharge power at the start of film formation. A method for manufacturing a liquid crystal display device according to claim 8. 11. The method of manufacturing a liquid crystal display device according to claim 8, wherein in the step of forming the conductive film, the film forming pressure at the end of the film formation is larger than that at the start of the film formation. Method. 12. The step of forming the conductive film, wherein the film forming pressure at the end of film forming is three to four times as large as the film forming pressure at the start of film forming. Or the method for manufacturing a liquid crystal display device according to any one of 11). 13. The method of manufacturing a liquid crystal display device according to claim 8, wherein the step of forming the conductive film is performed by changing discharge power or film forming pressure in a plurality of steps. . 14. The method of manufacturing a liquid crystal display device according to claim 8, wherein the step of forming the conductive film is performed by continuously changing discharge power or film forming pressure. .