JP2002311453A - Liquid crystal display device and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device having increased auxiliary capacitance and TFTs to which characteristics are given in compliance with operation rates and to provide a manufacturing method therefor. SOLUTION: The liquid crystal display device is used, including a TFT substrate 18 provided with a plurality of auxiliary capacitance parts A and a plurality of TFTs (16, 17). A gate insulation film 19 which constitutes a second TFT 17 is constituted by successively laminating an oxidized film 7, a nitride film 8 and an oxidized film 9. A gate insulation film 20 which constitutes a first TFT 16 and an insulation film 21 which constitutes the auxiliary capacitance part A are constituted by laminating the oxidized film 7 and the nitride film 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a MIS (Metal Ins
The present invention relates to a liquid crystal display device having a gate insulating film having a (ulator semiconductor) structure and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been used as information terminals such as personal computers and mobile phones, and as display devices such as viewfinders for video cameras and digital cameras, and their development and commercialization have been actively pursued. I have. In particular, a thin film transistor liquid crystal display device (hereinafter, referred to as a “TFT liquid crystal display device”) driven by a thin film transistor (hereinafter, referred to as a “TFT”) has a feature that high contrast and stable and uniform display can be obtained. Indeed, demand is increasing.

Next, a conventional liquid crystal display device and a method of manufacturing the same will be described with reference to the drawings. 4 and 5
FIG. 4 is a cross-sectional process diagram showing a conventional liquid crystal display device and a method for manufacturing the same, and FIGS. 4A to 5G show a series of manufacturing steps.

[0004] First, as shown in FIG. 4A, a silicon oxide film (SiO ₂ film) 42 and a polysilicon film 43 are sequentially formed on a glass substrate 41. Silicon nitride film 42
Is formed so as to have a thickness of 500 nm to 600 nm by a chemical vapor deposition (CVD) method. The silicon oxide film 42 becomes an undercoat. The polysilicon film 43 is formed on the silicon oxide film 42 by CV
An amorphous silicon film having a thickness of about 50 nm to 80 nm is formed by the method D, dehydrogenated by low-temperature annealing (temperature: 400 ° C. to 500 ° C., time: about 1 hour), and ELA is applied to the amorphous silicon film.
(Excimer Laser annealing) method.

[0005] Next, as shown in FIG. 4 (b), a resist 44 is applied, is patterned by a photolithography technique, and is further subjected to RIE (Reactive Ion Etching).
g) a polysilicon film 43 by an etching method such as a method.
Is patterned. 43 'is a patterned polysilicon film. Thereafter, the resist 44 is removed.

Next, as shown in FIG. 4C, a resist 45 is applied and patterned so that the ion-implanted region is exposed. Further, pentavalent ions (P, As) are ion-doped at about 1.0 × 10 ¹⁵ / cm ^{2 to} 5.0 × 10 ¹⁵ / cm ² . In the example of FIG. 4C, P ions are doped. By this ion doping, the polysilicon film 43 ′ exposed from the resist 45 becomes an auxiliary capacitance layer.

Then, as shown in FIG. 4D, an insulating film 47 and a metal electrode 48 are formed, and an N-type LDD (Lightly Doped Drain) layer 49 is formed by ion doping. The insulating film 47 is formed by a silicon oxide film (SiO 2) having a thickness of 60 nm to 120 nm by a CVD method.
₂ film). Insulating film 4
7 becomes a gate insulating film of the TFT. The metal electrode 48 is formed on the insulating film 47 by sputtering using Mo,
Thickness composed of W, Ti, etc. is 150 nm to 300 nm
Is formed by forming a metal electrode film and patterning it by a photolithography technique and an etching technique. The formation of the N-type LDD layer 49 is 5
1.0 × 10 ¹³ ions / cm ^{2 of} valence ions (P, As)
Being performed by ion doping with 5.0 × 10 ^{1 3} / cm ² or so. Note that P ions are also doped in the example of FIG.

[0008] Next, as shown in FIG.
Form one. The N + layer 51 is formed by applying a resist 50, patterning the resist 50 by photolithography, and then adding pentavalent ions (P, AS) to the resist 50 by 1.0.
It is performed by ion doping at about × 10 ¹⁵ / cm ^{2 to} 4.0 × 10 ¹⁵ / cm ² . In addition,
Also in the example of FIG. 5E, P ions are doped. Thereby, an N-type TFT (Thin Film Transistor)
r) A region and an auxiliary capacitance region can be obtained.

Next, as shown in FIG. 5F, a P + layer 53 is formed. The P + layer 53 is formed by applying a resist 52, patterning the resist 52 by photolithography, and further adding trivalent ions (B) to 0.3 × 10 ^15.
This is carried out by ion doping at a rate of about ^1.5 / cm ^{2 to} 5.0 × 10 ¹⁵ pieces / cm ² . FIG.
In the example of (f), B ions are doped. Thereby, a P-type TFT region can be obtained.

In the example of FIG. 5F, the N + layer 51,
A heat treatment is performed to activate the P + layer 53 and the N-type LDD layer 49. The heat treatment is performed at 600 ° C.
RTA (Rapid thermal annealing) method in which heat treatment is performed at a temperature of ８００800 ° C. for 30 seconds to 60 seconds, and a method of performing heat treatment at a temperature of 400 ° C. to 600 ° C. for 1 hour to 3 hours in an oxygen atmosphere or a nitrogen atmosphere. Can be

Thereafter, as shown in FIG. 5G, an interlayer film 54, a contact plug 55 and an Al electrode 56 are formed. The interlayer film 54 is formed with a thickness of 20 by the CVD method.
This is performed by forming a silicon nitride film (SiO ₂ film) of 0 nm to 500 nm. The contact plug 55 is formed by forming a contact hole in the interlayer film 54 so that the drain electrode portion and the source electrode portion of the TFT are exposed, and filling the contact hole with a Ti / Al alloy or Al by sputtering. Is being done.
The Al electrode 56 is formed by forming an Al metal film, patterning a resist thereon, and etching it. FIG. 5 (g)
In the example of A, the portion A indicates an auxiliary capacitance portion, and the portion B
Indicates a TFT unit.

Thereafter, a transparent electrode or the like (not shown) is provided to complete the TFT substrate. Liquid crystal is sealed between the TFT substrate and a filter substrate (not shown) provided with a color filter or the like, thereby completing a liquid crystal display device. The conventional liquid crystal display device and the manufacturing method described above are described in Flat Panel Display 1999 (Nikkei BP 1).
(December 14, 999), pages 132 to 139.

[0013]

By the way, in the above-mentioned liquid crystal display device, an auxiliary capacitance portion A is provided as shown in FIG. Since the auxiliary capacitance section A is intended to improve the image quality by increasing the charge holding performance, it can be said that it is preferable to increase the capacitance of the auxiliary capacitance section A as much as possible.

However, in the above-mentioned liquid crystal display device,
The thickness of the insulating film 47 is constant in the auxiliary capacitance portion A and the TFT portion B. Therefore, it is difficult to increase the capacitance of the auxiliary capacitance portion A by adjusting the thickness of the insulating film 47. Therefore, the only way to increase the capacitance of the auxiliary capacitance unit A is to increase the area of the auxiliary capacitance unit A, but in this case, the aperture ratio is reduced.

Further, in the circuit operation of the TFT on the TFT substrate, there are a TFT having a large number of operations and a TFT having a small number of operations in consideration of an operation rate (duty ratio). Generally, TFTs with many operations are required to have high reliability. For this reason,
It is considered that giving characteristics corresponding to the operation rate to each TFT is preferable in terms of improvement of image quality of the TFT liquid crystal display device, production cost, and the like.

However, in the above-described liquid crystal display device, a TFT that requires high reliability and a normal TFT are stably formed separately because an oxide film is used as a gate insulating film, so that an etching selectivity is low. It is difficult because it cannot be taken.

An object of the present invention is to solve the above-mentioned problems, to provide a liquid crystal display device having a TFT capable of increasing an auxiliary capacitance portion and having characteristics corresponding to an operation rate, and a method of manufacturing the same. And

[0018]

In order to achieve the above object, a liquid crystal display device according to the present invention is a liquid crystal display device including a TFT substrate provided with a plurality of auxiliary capacitance portions and a plurality of TFTs, A first TFT having a gate insulating film formed by sequentially stacking an oxide film and a nitride film, and a second TFT having a gate insulating film formed by sequentially stacking an oxide film, a nitride film and an oxide film And an auxiliary capacitance portion having an insulating film formed by sequentially stacking an oxide film and a nitride film is provided on the TFT substrate. In such a liquid crystal display device, the oxide film is a silicon oxide film,
Preferably, the nitride film is a silicon nitride film.

Next, in order to achieve the above object, a liquid crystal display device according to the present invention comprises a first TFT having a gate insulating film formed by sequentially stacking an oxide film and a nitride film; A second TFT having a gate insulating film formed by sequentially stacking a nitride film and an oxide film, and an auxiliary capacitance portion having an insulating film formed by sequentially stacking an oxide film and a nitride film were provided. A method for manufacturing a liquid crystal display device including a TFT substrate, comprising: sequentially stacking an oxide film, a nitride film, and an oxide film on a glass substrate constituting the TFT substrate; Removing the upper oxide film in a region where the auxiliary capacitance portion is provided.

[0020]

(Embodiment 1) Hereinafter, a liquid crystal display device and a method of manufacturing the same according to the present invention will be described with reference to the drawings. FIG. 1 is a view showing a part of a liquid crystal display device according to the present invention, and parts other than the TFT substrate 18 are omitted. 2 and 3 are cross-sectional process diagrams showing a method for manufacturing the liquid crystal display device according to the present invention shown in FIG. 1, and FIGS. 2 (a) to 3 (h) show a series of manufacturing steps.

First, the liquid crystal display of the present invention will be described with reference to FIG. As shown in the example of FIG. 1, the liquid crystal display device of the present invention includes a TFT substrate 18 provided with a plurality of auxiliary capacitance units and a plurality of TFTs. Note that, in the example of FIG. 1, only one auxiliary capacitance unit A is illustrated as the auxiliary capacitance unit. The TFT is composed of the first TFT 16 and the second TFT 16.
Only the TFT 17 is shown, and the first TFT 16 and the second TFT 17 constitute one TFT section B.
The auxiliary capacitance part A and the TFT part B are arranged in a matrix on the TFT substrate as a set.

As shown in the example of FIG.
Is formed by sequentially stacking an oxide film 7 and a nitride film 8. On the other hand, the gate insulating film 19 constituting the second TFT 17 has the oxide film 7,
A nitride film 8 and an oxide film 9 are sequentially laminated.
Further, the insulating film 21 forming the auxiliary capacitance portion A is made of the oxide film 7.
And a nitride film 8 are sequentially laminated.

For this reason, the structure in which the nitride film, which is denser and more excellent in insulation than the oxide film, is sandwiched between the oxide films and the gate insulating film 19 has a large thickness and the electric field used in practice is reduced. The second TFT 17 has higher reliability than the first TFT 16. On the other hand, since the first TFT 16 has a thinner gate insulating film 20 than the second TFT 17, the first TFT 16 has high performance in terms of response characteristics and on-current. Further, in the auxiliary capacitance section A, since the insulating film 21 can be made thinner, the capacitance can be increased as compared with the conventional case.

6 is an N + layer, 11 is a metal electrode, 12
Is an N-type LDD layer, 13 is an interlayer film, 14 is a contact plug, and 15 is an Al electrode. As described above, according to the liquid crystal display device of the present invention, the characteristics according to the operation rate can be changed by the TFT.
, And at the same time, the auxiliary capacity can be increased as compared with the related art, so that the image quality can be improved.

Next, a method of manufacturing the liquid crystal display device of the present invention shown in FIG. 1 will be described step by step with reference to FIGS. First, as shown in FIG.
A silicon oxide film (SiO ₂ film) 2 and a polysilicon film 3 are sequentially formed thereon. Silicon nitride film is formed by CVD
It is performed so that the thickness becomes 500 nm to 600 nm by the method. The polysilicon film 3 is formed by the silicon nitride film 2
An amorphous silicon film having a thickness of about 50 nm to 80 nm is formed thereon by a CVD method, dehydrogenated by low-temperature annealing (temperature: 400 ° C. to 500 ° C., time: about 1 hour). This is performed by applying an ELA (Excimer Laser annealing) method.

Next, as shown in FIG. 2B, a resist 4 is applied, is patterned by a photolithography technique, and is further subjected to RIE (Reactive Ion Etching).
The polysilicon film 3 is patterned by an etching method such as an etching method. 3 'is a patterned polysilicon film. Thereafter, the resist 4 is removed.

Next, as shown in FIG. 2C, a resist 5 is applied and patterned so that the ion-implanted region is exposed. Further, pentavalent ions (P, As) are ion-doped at about 1.0 × 10 ¹⁵ / cm ^{2 to} 4.0 × 10 ¹⁵ / cm ² . In the example of FIG. 4B, P ions are doped. By this ion doping, the polysilicon film 3 ′ exposed from the resist 5 becomes the N + layer 6.

Thereafter, as shown in FIG. 2D, an oxide film 7, a nitride film 8 and an oxide film 9 are sequentially laminated to form an insulating layer. This insulating layer becomes a gate insulating film of the TFT and an insulating film of the auxiliary capacitance portion as described later. In the example of FIG. 2D, the oxide films 7 and 9 are formed of a silicon oxide film (SiO _2).
The nitride film 8 is a silicon nitride film (SiN _x (x
Is a natural number)). These films are formed using a CVD method. The thickness of the oxide film 7 is 10 nm or more.
The thickness of the nitride film 8 is about 5 to 15 nm, and the thickness of the oxide film 9 is about 10 to 30 nm. As described above, by the process shown in FIG.
An ONO structure composed of an O ₂ film / SiN _x film / SiO ₂ film can be obtained.

Next, as shown in FIG. 3E, a resist 10 is applied and is patterned by photolithography. The patterning is performed in a portion other than the portion where the ONO structure obtained above is left, that is, ON.
This is performed so that a region where a TFT (first TFT 16 described later) having a gate insulating film of a structure (SiO ₂ film / SiN _x film) is provided and a region where an auxiliary capacitance portion having an insulating film of an ON structure is provided are exposed. .

Next, as shown in FIG. 3F, etching is performed on a portion exposed from the resist 10.
This etching is selectively performed so that the nitride film 8 is not etched, and only the portion of the oxide film 9 exposed from the resist 10 is removed. Thus, FIGS. 3E and 3F
By the process shown in (1), an ON structure composed of a SiO ₂ film / SiN _x film can be obtained.

Next, as shown in FIG. 3 (g), a plurality of metal electrodes 11 are formed by a photolithography technique and an etching technique, and N 2 is formed by ion doping.
The mold LDD layer 12 is formed. The N-type LDD layer 12 is formed by adding pentavalent ions (P, As) to 1.0 × 10 ¹³ ions / c.
It is performed by ion doping at about m ^{2 to} 5.0 × 10 ¹³ / cm ² . In the example of FIG. 3G, P ions are doped.

In forming the N-type LDD layer 12, P
The thickness of a film serving as a mask when ion doping ions is different between the ONO structure portion and the ON structure portion. For this reason, LSS (Lindhard Scharff Schiott)
According to the theory, by adjusting the ion implantation energy,
Since it is possible to perform the same separation as in the case of performing the ion doping twice, the T
The LDD layer can be separately formed for each FT.

In the example shown in FIG. 3 (g), the N + layer 6, N
A heat treatment is performed to activate the mold LDD layer 12.
As a method of this heat treatment, RTA (Rapid thaw) in which heat treatment is performed at a temperature of 600 ° C. to 800 ° C. for 30 seconds to 60 seconds.
thermal annealing) and a method in which the annealing is performed at a temperature of 400 ° C. to 600 ° C. for 1 hour to 3 hours in an oxygen atmosphere or a nitrogen atmosphere.

Thereafter, as shown in FIG. 3H, an interlayer film 13, a contact plug 14, and an Al electrode 15 are formed. The thickness of the interlayer film 13 is set to 20 by the CVD method.
This is performed by forming a silicon oxide film (SiO ₂ film) of 0 nm to 500 nm. The contact plug 14 is formed by forming a contact hole in the interlayer film 14 so that the drain electrode portion and the source electrode portion of the TFT are exposed, and filling the contact hole with a Ti / Al alloy or Al by sputtering. Is being done.
The formation of the Al electrode 15 is performed by forming an Al metal film, patterning a resist thereon, and etching the resist. The Al electrode 1
6 is connected to a transparent electrode (not shown).

In this way, a TFT substrate on which the auxiliary capacitance portion A and the TFT portion B are formed is formed. This TFT
Liquid crystal is sealed between the substrate 18 and a filter substrate (not shown) to complete the liquid crystal display device according to the present invention.

[0036]

As described above, according to the liquid crystal display device and the method of manufacturing the same according to the present invention, the TF provided on the TFT substrate is provided.
TFTs that can easily make T, have a thin gate insulating film, have excellent response characteristics, and have a large on-current;
High reliability T of ONO structure with nitride film sandwiched by oxide film
The effect that FT and FT can be produced simultaneously can be obtained. Further, since the capacity of the auxiliary capacitor can be increased as compared with the conventional case, the image quality can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a part of a liquid crystal display device according to the present invention.

FIG. 2 is a sectional process view showing a method for manufacturing the liquid crystal display device according to the present invention shown in FIG. 1;

FIG. 3 is a sectional process view showing the method for manufacturing the liquid crystal display device according to the present invention shown in FIG. 1;

FIG. 4 is a sectional process view showing a conventional liquid crystal display device and a method for manufacturing the same.

FIG. 5 is a sectional process view showing a conventional liquid crystal display device and a method for manufacturing the same.

[Explanation of symbols]

 Reference Signs List 1 glass substrate 2 silicon oxide film 3 polysilicon film 3 ′ patterned polysilicon film 4, 5, 10 resist 6 N + layer 7, 9 oxide film 8 nitride film 11 metal electrode 12 N-type LDD layer 13 interlayer film 14 contact plug DESCRIPTION OF SYMBOLS 15 Al electrode 16 1st TFT 17 2nd TFT 18 TFT substrate 19 Gate insulating film which comprises 2nd TFT 20 Gate insulating film which comprises 1st TFT 21 Insulating film which comprises an auxiliary capacitance part A Auxiliary capacitance Part B TFT part

Continuation of the front page F term (reference) 2H092 GA59 JA25 JA34 JA36 JA37 JB61 KA04 KA10 KA11 MA05 MA08 MA13 MA18 MA27 MA29 NA01 NA24 5F048 AC04 BA16 BB09 BB11 BC06 BF16 5F110 AA01 AA07 AA14 BB01 CC02 DD02 FF13FF02FF03FF03FF03FF03FF02FF GG25 GG44 HJ01 HJ04 HJ12 HJ23 HL03 HL06 HL07 HL23 HM15 NN04 NN23 NN35 NN72 NN73 NN78 PP03 PP35 QQ03 QQ11

Claims (3)

[Claims] 1. A liquid crystal display device including a TFT substrate provided with a plurality of storage capacitor portions and a plurality of TFTs, the device including a gate insulating film formed by sequentially stacking an oxide film and a nitride film. 1 TFT, a second TFT having a gate insulating film formed by sequentially stacking an oxide film, a nitride film, and an oxide film, and an insulating film formed by sequentially stacking an oxide film and a nitride film. A liquid crystal display device, wherein an auxiliary capacitance portion is provided on a TFT substrate. 2. The liquid crystal display device according to claim 1, wherein said oxide film is a silicon oxide film, and said nitride film is a silicon nitride film. 3. A first TFT having a gate insulating film formed by sequentially stacking an oxide film and a nitride film, and a gate insulating film formed by sequentially stacking an oxide film, a nitride film and an oxide film. A method for manufacturing a liquid crystal display device, comprising: a TFT substrate provided with a second TFT having an auxiliary capacitance portion having an insulating film formed by sequentially stacking an oxide film and a nitride film. Stacking an oxide film, a nitride film, and an oxide film in this order on a glass substrate, and removing the upper oxide film in a region where the first TFT is provided and a region where the auxiliary capacitance unit is provided. And a method for manufacturing a liquid crystal display device.