JPH04304428A - Manufacture of active matrix liquid crystal display - Google Patents

Abstract

PURPOSE:To obtain the active matrix liquid crystal display which eliminates the deformation of a low substrate, has superior quality such as a small color irregularity and small variation in response speed, and uses thin film transistors. CONSTITUTION:The active matrix liquid crystal display has a lower substrate where plural thin film transistors which are connected in matrix are formed and a silicon nitride film 42 as a surface protection film is formed thereupon, an upper substrate where a transparent electrode is formed, and a liquid crystal layer sandwiched between them; and film formation conditions are so adjusted as to minimize the curvature of the lower substrate and the silicon nitride film 42 as the surface protection film is formed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an active matrix liquid crystal display using thin film transistors.

0002

[Prior Art] Conventionally, technologies in this field include:
For example, there was one described in JP-A-63-284522. Thin film transistor TFT
(lm Transistor) Since liquid crystal displays have characteristics such as light weight, low power consumption, high definition, and large capacity, they have recently started to form a large market. In particular, as the area of liquid crystal panels increases,
Uniformity of in-plane properties becomes a major problem.

FIG. 3 is a sectional view of a main part showing the structure of a conventional active matrix liquid crystal display (AMLCD). As shown in this figure, an α-SiTFT substrate, which will become the lower substrate of the AMLCD, is placed on a first transparent insulating substrate 1 containing chromium (Cr), tantalum (Ta), and molybdenum (M).
o) A metal layer made of aluminum (Al) is formed to a thickness of about 0.1 to 0.3 μm by sputtering or vapor deposition,
Thereafter, the gate electrode 2 is formed by processing into a predetermined shape by photolithography etching.

[0004] Next, a gate metal oxide film 3, which will become a first gate insulating film, is formed to a thickness of 0.1 to 0.5 μm by an anodic oxidation method. Next, a silicon nitride film (SiNx) 4, which will serve as a second gate insulating film, is deposited to a thickness of 0.1 to
0.4μm, amorphous silicon film (n- -α-Si) was formed by PCVD method using SiH4 gas as the main component.
The film thickness is 0.05 μm to 0.2 μm, SiH4 gas and P
By the PCVD method using H3 gas as the main component, n+ −
An α-Si layer of 0.01 to 0.1 μm is deposited on the entire surface of the substrate.

Next, aluminum (Al), chromium (
Cr), nichrome (NiCr), etc.
The source electrode 7 and the drain electrode 8 are formed by forming a film with a thickness of about 0.3 to 1.0 μm by sputtering or vapor deposition and processing it into a predetermined shape. Then, the α-Si semiconductor layers 5 and 6 are formed into a predetermined island shape by photolithography and reactive ion etching. After that, the semiconductor layer 5
The unnecessary ohmic layer 6 in the upper channel portion is removed by dry etching using RIE mainly containing CF4 and O2.

Next, an intermediate insulating film 9 made of a silicon nitride film (SiNx) or the like is formed by the PCVD method. Thereafter, a contact hole 10 for electrical connection between the source and a transparent electrode ITO film to be formed next is formed in a predetermined portion of the intermediate insulating film. Then, ITO film (In2 O3 +S
nO2) to 0.1 μm by sputtering or vapor deposition.
By forming a film to a certain extent and processing it into a predetermined shape, a transparent electrode 11 that becomes a display electrode is formed.

Finally, an insulating film made of silicon nitride (SiNx) or the like is formed by the PCVD method and processed into a predetermined shape to form the surface protective film 1 of the lower substrate.
form 2. The above α-Si TFT with transparent electrode is
By dimensionally arranging them, an α-SiTFT array substrate is completed. An organic film made of polyimide having a thickness of 0.1 μm is formed on this TFT array substrate, and an alignment treatment film 13 is formed by rubbing the organic film. Thereafter, in order to form and maintain uniform cell spacing, spacers 14 having a diameter of 3 to 10 μm are sprinkled on the alignment film 13 to complete the lower substrate.

On the other hand, the upper substrate (counter electrode side) is formed as shown below. That is, the film thickness is 0 on the transparent insulating substrate 15.
．． A counter transparent electrode 16 made of an ITO film of about 1 μm,
It is formed into a predetermined shape by sputtering or vapor deposition and processing. Next, a black matrix layer 17 is formed to prevent light leakage and improve contrast. An organic film made of polyimide having a thickness of about 0.1 μm is formed on this counter electrode, and a rubbing process is performed to form an alignment film 18.

Furthermore, a sealing layer 19 with a thickness of 5 to 20 μm is formed by a thick film screen printing method using a material in which a spacer is mixed into a polymeric insulating material (such as an epoxy material).
By forming a predetermined pattern, the upper substrate is completed. When the upper and lower substrates are completed, the upper and lower substrates are aligned with a sealing layer in between, and after bonding, they are fixed under pressure and the sealing layer is heated and cured. Furthermore,
After the inside of the seal layer is vacuum degassed, liquid crystal 20 is injected through a predetermined injection port.

Finally, by sealing the injection port and pasting the polarizing film 21 in a predetermined position, a liquid crystal display using α-SiTFT is completed.

[0011]

[Problem to be solved by the invention] The TFT has an address line,
A large number of transistors are connected in a matrix through data lines, and by driving the thin film transistor matrix, a voltage is applied between the transparent pixel electrode 11 and the opposing transparent electrode 16, and the liquid crystal 20 is driven. Although the optimal value for the thickness d of the liquid crystal 20 varies depending on the liquid crystal material used, it is desirable that the variation in the thickness d within the screen of the liquid crystal display be as small as possible. If the variation in the thickness d is large, color unevenness and variation in response speed occur, causing deterioration of display quality.

[0012] In manufacturing the lower substrate on which the TFT is located,
A film is formed several times on the first transparent insulating substrate. The presence of internal stress in these films causes the lower substrate to deform. For example, as shown in FIG. 4A, when a passivation film of silicon oxide (SiOx) is formed on a substrate under predetermined conditions, the substrate is deformed into an upwardly convex shape. In addition, a silicon nitride film (SiNx) is formed on the substrate.
When a passivation film is formed, the substrate is deformed into an upwardly concave shape.

[0013] In order to solve this problem, Japanese Patent Laid-Open No. 63-2
In No. 84522, the surface protective film of the lower substrate has a two-layer structure consisting of a silicon oxide film (SiOx) and a silicon nitride film (SiNx), and the thicknesses of the two types of films are adjusted so as to eliminate warpage of the entire protective film. However, forming the protective film into a two-layer structure requires a complicated film formation process. In addition, by forming the film on the lower substrate several times until the protective film was formed,
Since the lower substrate may have already been deformed, even if the warpage of the protective film is eliminated, the entire lower substrate remains warped. Therefore, there was a problem in that it was difficult to make the thickness of the liquid crystal layer uniform over the entire screen.

The present invention eliminates the problem of the deformation of the lower substrate of the active matrix liquid crystal display mentioned above, and provides an active matrix liquid crystal display using thin film transistors that has excellent display quality with less color unevenness and variation in response speed. The purpose is to provide a manufacturing method for.

[0015]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a substrate in which a plurality of thin film transistors connected in a matrix are formed, and a silicon nitride film serving as a surface protection film is formed thereon. In a method for manufacturing an active matrix liquid crystal display having a substrate, an upper substrate on which a transparent electrode is formed, and a liquid crystal layer sandwiched between these, film forming conditions are set so that warpage of the lower substrate is minimized. The silicon nitride film serving as the surface protection film is formed by adjusting the temperature.

[0016]

[Operation] As described above, the present invention provides a method for manufacturing a lower substrate of an active matrix liquid crystal display.
When forming a silicon nitride film, which is a surface protective film, the film forming conditions are adjusted to control the direction and magnitude of the internal stress of the protective film, and the stress of the protective film and the stress of the lower substrate are adjusted until the protective film is formed. The film is formed so that the two cancel each other out.

[0017]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing a manufacturing process of a lower substrate of an active matrix liquid crystal display according to an embodiment of the present invention. First, the same techniques as in the prior art are used from the formation of the gate electrode to the formation of the transparent electrode on the lower substrate.

That is, as shown in FIG. 1(a), first, the AM
The α-SiTFT substrate, which becomes the lower substrate of the LCD, is made of chromium (Cr), tantalum (Ta) on the first transparent insulating substrate 31.
), molybdenum (Mo), and aluminum (Al) by sputtering or vapor deposition.
The gate electrode 32 is formed by forming a film with a thickness of about 3 μm and then processing it into a predetermined shape by photolithography etching. Then, a gate metal oxide film 33, which will become a first gate insulating film, is formed to a thickness of 0.1 to 0.5 μm by an anodic oxidation method. After that, plasma C containing NH3 and SiH4 gas as main components
A silicon nitride film (SiNx) 34, which will become the second gate insulating film, is formed to a thickness of 0.1 to 0.4 by VD (PCVD) method.
An amorphous silicon (n--α-Si) film is formed with a thickness of 0.05 μm to 0.2 μm by PCVD method using SiH4 gas as the main component, and SiH4 gas and PH3
By PCVD method using gas as the main component, n+ -α-S
The i-layer is deposited to a thickness of 0.01 to 0.1 μm over the entire surface of the substrate. Next, aluminum (Al), chromium (Cr),
The source electrode 37 is formed by forming a metal layer made of nichrome (NiCr) or the like to a thickness of about 0.3 to 1.0 μm by sputtering or vapor deposition, and processing it into a predetermined shape.
and a drain electrode 38 is formed. Then, by photolithography and reactive ion etching, the α-Si semiconductor layer 35 is
, 36 are formed into a predetermined island shape. After that, the semiconductor layer 3
Unnecessary ohmic layer 36 in the channel part on 5 is replaced with CF4
and O2 as the main components. After that, a silicon nitride film (S
An intermediate insulating film 39 made of, for example, iNx is formed. After that, a contact hole 40 for electrical connection between the source and the transparent electrode ITO film to be formed next is formed in a predetermined part of the intermediate insulating film, and an ITO (In2O3 +SnO2) film is deposited to a thickness of about 0.1 μm by sputtering or vapor deposition. Form a film,
By processing it into a predetermined shape, a transparent electrode 41 that becomes a display electrode is formed.

Next, the lower substrate is inspected for warpage, and the warpage of each board is determined. When forming a surface protective film, by adjusting the film forming conditions, the direction and magnitude of the internal stress of the protective film can be controlled to cancel out the stress of the protective film and the stress of the lower substrate until the protective film is formed. make it fit. That is, when the lower substrate is convex (concave), the silicon nitride film 42 as a surface protective film is formed so that the internal stress of the protective film becomes tensile (compressive) stress, as shown in FIG. 1(b). .

[0020] Here, the film formation method is performed by a 13.56 MHz parallel plate type high frequency plasma CVD method using a mixed gas of four types of SiH4, NH3, N2, and H2 as raw material gases. As specific film forming conditions, Si
The flow rates of H4, NH3, N2, and H2 are each 1
0~100sccm, 30~500sccm, 0~60
0sccm, 0 to 600sccm, high frequency power is 1
00 to 600 W, film forming pressure to 0.1 to 2 torr,
The distance between the electrodes is 30-200mm, and the substrate temperature is 200-200mm.
If the temperature is adjusted to 600°C, SiNx has a nearly stoichiometric composition (N/Si ~1.3, density ~2
．． 8g/cm3), the internal stress ranges from tension to compression,
It can be freely controlled independently of changes in film composition and optical bandgap. Furthermore, the magnitude of the internal stress of the film can also be changed by adjusting the film formation time.

As an example of the correlation between the film forming conditions and the internal stress of the protective film, FIG. 2 shows the correlation between the high frequency power and the internal stress of the film. High frequency power from 100W to 50
When the internal stress of the film is changed to 0W, the tensile stress (+
4dynes/cm2) to compressive stress (-4dynes/cm2)
s/cm2). At this time, as the film forming conditions other than high frequency power, SiH4, NH3
, N2, and H2 flow rates were 20 sccm and 8 sccm, respectively.
0 sccm, 100 sccm, 100 sccm, the film forming pressure was 1.0 torr, the distance between the electrodes was 100 mm, and the substrate temperature was 300°C.

Next, on this TFT array substrate, a pattern shown in FIG.
As shown in c), an organic film made of polyimide having a thickness of 0.1 μm is formed and rubbed, thereby forming an alignment film 43. Note that the above-mentioned TFTs include amorphous silicon TFTs, polycrystalline silicon TFTs, and CdSeT.
Any material can be used for thin film transistors such as FT.

Furthermore, the present invention is not limited to the above embodiments, but various modifications can be made based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0024]

As described above in detail, according to the present invention, by appropriately adjusting the film forming conditions of a silicon nitride film as a protective film of an active matrix liquid crystal display using thin film transistors, The warpage can be minimized.

Therefore, even in an active matrix liquid crystal display having a large screen area, it is easy to make the thickness of the liquid crystal layer within the screen uniform. Therefore, it is possible to obtain excellent display quality with no color unevenness and no variation in response speed.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing a manufacturing process of a main part of a lower substrate of an active matrix liquid crystal display according to an embodiment of the present invention.

FIG. 2 is a diagram showing the correlation between high frequency power and internal stress of the film during formation of a surface protective film of an active matrix liquid crystal display according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view showing the structure of a conventional active matrix liquid crystal display (AMLCD).

FIG. 4 is a diagram showing the deflection of the substrate due to the strain of the SiOx film and the SiNx film.

[Explanation of symbols]

31 First transparent insulating substrate 32 Gate electrode 33 Gate metal oxide film 34 Silicon nitride film (SiNx) 35, 36
α-Si semiconductor layer 37 Source electrode 38 Drain electrode 39 Intermediate insulating film 40 Contact hole 41 Transparent electrode 42 Surface protection film (silicon nitride film) 43
Orientation treatment film

Claims (3)

[Claims] 1. A lower substrate on which a plurality of thin film transistors connected in a matrix are formed, a silicon nitride film serving as a surface protection film is formed thereon, an upper substrate on which a transparent electrode is formed, and a space between these. In the method of manufacturing an active matrix liquid crystal display having a liquid crystal layer sandwiched between the silicon nitride film and the silicon nitride film, the silicon nitride film serving as the surface protection film is formed by adjusting the film forming conditions so that the warpage of the lower substrate is minimized. A method for manufacturing an active matrix liquid crystal display characterized by: 2. The silicon nitride film is formed by plasma CVD.
2. The method of manufacturing an active matrix liquid crystal display according to claim 1, wherein the active matrix liquid crystal display is formed by a method. 3. The silicon nitride film is formed by plasma CVD.
The film was formed using SiH4, NH3 as the film forming conditions.
, N2, and H2 flow rates are each 10 to 100 scc.
m, 30-500sccm, 0-600sccm, 0-
600sccm, substrate temperature 200~600℃, high frequency power 100~600W, and film forming pressure 0.1~600°C.
2. The method of manufacturing an active matrix liquid crystal display according to claim 1, wherein the distance between the electrodes is adjusted to 2 torr and the distance between the electrodes to be 30 to 200 mm.