JPH04372934A - Manufacture of array substrate for liquid crystal display device - Google Patents

Abstract

PURPOSE:To easily form a taper and provide a large screen for an active matrix type liquid crystal display device with high precision by laminating an aluminum metal and a molybdenum metal in sequence, applying etching machining with the mixed acid of phosphoric acid, acetic acid and nitric acid, then removing the upper molybdenum metal. CONSTITUTION:An aluminum film 31 is accumulated on an insulating substrate 21 by sputtering, and a molybdenum film 32 is accumulated on it by sputtering. A scanning line pattern containing a gate electrode is formed on the laminated film by photolithography, and the aluminum/molybdenum laminated film is etched with the mixed acid of phosphoric acid, acetic acid and nitric acid to manufacture a scanning line pattern. Side etching is applied to molybdenum due to the difference in the etching rate, and a gradual taper is formed. The mixed acid with the mixing ratio for etching only molybdenum is used to remove only the molybdenum film 32, and the scanning line pattern of a molybdenum/tantalum film 33 is formed on the aluminum film 31.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an array substrate for a liquid crystal display device, and more particularly to a method for forming scanning lines.

0002

[Prior Art] A thin film transistor (TFT) array is
Applied to active matrix type liquid crystal display elements, it is much superior to other liquid crystal display elements in terms of high contrast ratio and response speed, and is attracting attention as it is seen as the favorite for flat panel display devices. In addition, amorphous silicon (a-Si) is often used as a semiconductor material for TFT arrays, but structurally, a gate insulating layer is provided on the gate electrode.
A so-called reverse staggered type is often adopted in which a semiconductor layer and source/drain electrodes are provided on top of the semiconductor layer.

FIG. 3 is a sectional view showing the main parts of an inverted staggered TFT array. In FIG. 3, a gate electrode 2 made of, for example, a molybdenum tantalum (MoTa) alloy and a scanning line integrated therewith are patterned on a glass substrate 1. Next, gate insulating films 3, 4, a-Si
After the film 5 and the protective film 6 are laminated and patterned, a low resistance amorphous silicon (n+ a-Si) film 7 is formed. Next, ITO (indium tin oxide film)
A display electrode 8 is formed. Thereafter, a drain electrode 9 and a source electrode 10 integrated with the signal line are patterned to complete the TFT array.

0004

[Problems to be Solved by the Invention] As the display portion of a liquid crystal display device becomes larger or has higher definition, the scanning line becomes longer, and the width of the scanning line increases in order to keep the aperture ratio of the pixel almost constant. Due to the thinning of the scanning line, the resistance of the scanning line increases. As a result, the waveform of the scanning signal is distorted, causing a signal propagation delay. This appears as non-uniformity of the image, leading to a reduction in image quality. Therefore, it is necessary to reduce the resistance of the scanning line. The scanning line resistance value is diagonal 14
According to simulations, when the screen size is 800 x 1000 pixels (800 scanning lines), approximately 0.
Must be 3Ω/□ or less. Aluminum (Al), which is a low-resistance metal, can be used as the scanning line material, but if it is used alone, hillocks will occur during the heat treatment process during the manufacturing process, which will greatly deteriorate the interlayer insulation between the scanning line and the signal line. There is. In addition, in an inverted staggered TFT, various films are formed on the gate, and it is desirable that the film is tapered to prevent breakage at a step portion such as a wiring made of these films. In the conventional gate electrode, a pattern is formed by dry etching after forming a MoTa film, but in order to form a taper, it is necessary to devise gas conditions, gas pressure, etc.

[0005]

[Means for Solving the Problems] The present invention manufactures an array substrate for a liquid crystal display device in which scanning lines and signal lines are formed in a matrix on an insulating substrate, and TFTs and display electrodes are arranged at the intersections of the scanning lines and signal lines. This is about a method in which, when forming a scanning line, Al metal and molybdenum (Mo) metal are sequentially laminated, etched with a mixed acid of phosphoric acid, acetic acid, and nitric acid, and then the upper layer of Mo metal is removed. We are prepared. Further, in this step, after removing the upper layer Mo metal, other metals such as MoTa alloy, tantalum (Ta) metal, titanium (Ti) metal, and chromium (Cr) are applied on the Al metal.
It may be coated with metal or the like.

[0006]

[Operation] In this invention, regarding taper processing,
For example, this is possible by using a mixed acid solution of phosphoric acid, acetic acid, and nitric acid with a mixing ratio such that the etching rate of Mo is higher than that of Al. Thereafter, in order to prevent the Mo oxide film from peeling off, only Mo is etched, and the scan line is made only of Al, thereby making it possible to form a low-resistance wiring. Furthermore,
By layering other metals (MoTa, Ta, etc.) on this Al, hillock prevention and chemical resistance treatment can be achieved. The array substrate formed in this way has no problem with interlayer insulation, and since other metals are present on Al, Al
Because hillocks do not occur, short circuits between layers such as scanning lines and signal lines do not occur. In addition, the Al film thickness was set to 200n.
m, when the film thickness of other metals such as MoTa is 100 nm, the wiring resistance is about 9 when the MoTa film thickness is 300 nm.
The resistance is reduced to 1/1, and the resistance can be lowered.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be explained below with reference to the drawings.

FIG. 1 is an equivalent circuit diagram of an active matrix liquid crystal display device using an embodiment of the present invention. In FIG. 1, scanning lines 22 and signal lines 23 are arranged in a matrix on an insulating substrate 21. As shown in FIG. A TF having an a-Si film is provided at the intersection of the scanning line 22 and the signal line 23.
T24 is formed. Further, the drain of the TFT 24 is connected to the signal line 23, and the gate is connected to the scanning line 22. Furthermore, a display electrode 25 of each pixel, a liquid crystal capacitor 26, and an auxiliary capacitor 27 are connected to the source of the TFT 24.

FIG. 2 is a sectional view showing the manufacturing process of the TFT section in this embodiment, and parts corresponding to those in FIG. 1 are given the same reference numerals. Referring to FIG. 2, the manufacturing process will be explained. First, as shown in FIG. 2A, two Al films 31 are deposited by sputtering on an insulating substrate 21 made of glass with a SiOx film formed by plasma CVD, for example.
Deposit 00 nm. At this time, the Al film 31 may be an Al alloy, for example, an Al film containing 1 atomic % of Cu and 0.5 atomic % of Si. Next, on this Al film 31, a Mo film 32 is deposited to a thickness of 50 nm by sputtering. Next, a scanning line pattern including a gate electrode was formed on this laminated film using photolithography, and the Al/Mo laminated film was etched using a mixed acid of phosphoric acid + nitric acid + acetic acid to create a scanning line pattern. do. At this time, side etching occurs in Mo due to the difference in etching rate during etching, forming a gentle taper. Next, Mo of phosphoric acid + nitric acid + acetic acid
As shown in FIG. 2B, only the Mo film 32 is removed using a mixed acid at a ratio that etches only the Mo film 32. Subsequently, a MoTa film 33 is deposited to a thickness of 50 nm on the Al film 31 by sputtering. Next, the MoTa film 33 is etched,
A scanning line pattern consisting of an Al film 31 and a MoTa film 33 is produced.

Subsequently, as shown in FIG. 2(c), an SiOx film 34 and a SiNx film 35 are formed by plasma CVD.
, an a-Si film 36 and a SiNx film 37 are successively deposited. Next, the upper layer SiNx film 37 is patterned,
After the pretreatment, an n+ a-Si film 38 is deposited as a source/drain electrode contact by plasma CVD. Next, the a-Si film 36 is patterned to form a display electrode 25 made of, for example, an ITO film. Subsequently, openings in the pad portions (not shown) of the scanning lines 22 are made using an HF-based etching solution. Next, Al is deposited by sputtering, and this is applied to the signal line 23 and source electrode 39 shown in FIG.
and is formed as the drain electrode 40. After this, RIE (
Reactive Ion Etching)
n+ a-Si facing the channel part of the a-Si film 36
The film 38 is removed, and an array substrate for a liquid crystal display device is completed.

In this example, the scanning line resistance is approximately 1 kΩ when the average scanning line width is 30 μm and the scanning line length is 20 cm, and with the same wiring width and length, the film thickness is 3.
The resistance of the scanning line made of 000 angstrom MoTa film is approximately 9kΩ, so the resistance of the scanning line is 1/1 compared to the conventional one.
We were able to reduce this to 9. Further, by using an etching solution made of a mixed acid of phosphoric acid, nitric acid, and acetic acid that has a high etching selectivity between the Al film 31 and the Mo film 32, it is possible to gently taper the Al film 31 as a scanning line. Furthermore, by protecting the Al film 31 with the MoTa film 33, it was possible to prevent Al hillocks caused by heat treatment. Furthermore, by forming the MoTa film 33 on the Al film 31, the conventionally used MoTa process could be employed in the steps after forming the scanning lines.

0012

Effects of the Invention The present invention has a step of sequentially laminating Al metal and Mo metal, etching with a mixed acid of phosphoric acid, acetic acid, and nitric acid, and then removing the upper layer of Mo metal, thereby achieving low scanning line resistance. It is resistive and has excellent interlayer insulation.
Since a taper can be easily formed, it is possible to increase the screen size and high definition of a liquid crystal display device.

[Brief explanation of drawings]

FIG. 1 is an equivalent circuit diagram of an active matrix liquid crystal display device using an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the manufacturing process of a TFT section in an embodiment of the present invention.

FIG. 3 is a cross-sectional view showing essential parts of a conventional TFT array.

[Explanation of symbols]

21...Insulating substrate 22...scanning line 23...Signal line 24...TFT 25...Display electrode 31...Al film 32...Mo film

Claims (1)

[Claims] 1. A method for manufacturing an array substrate for a liquid crystal display device, in which scanning lines and signal lines are formed in a matrix on an insulating substrate, and thin film transistors and display electrodes are arranged at the intersections of the scanning lines and signal lines. 1. A method for manufacturing an array substrate for a liquid crystal display device, comprising a step of successively stacking the molybdenum metal on the upper layer after etching with a mixed acid of phosphoric acid, acetic acid, and nitric acid.