JP4537610B2 - Liquid crystal display device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device having a gate insulating film having a MIS (Metal Insulator Semiconductor) structure and a method for manufacturing the same.
[0002]
[Prior art]
In recent years, liquid crystal display devices have been used as display devices for information terminals such as personal computers and mobile phones, and viewfinders for video cameras and digital cameras, and their development and commercialization have been actively conducted. In particular, a thin film transistor liquid crystal display device (hereinafter referred to as “TFT liquid crystal display device”) driven by a thin film transistor (hereinafter referred to as “TFT”) has a feature that a high contrast and a stable display can be obtained. In addition, demand is increasing.
[0003]
Next, a conventional liquid crystal display device and a manufacturing method thereof will be described with reference to the drawings. 4 and 5 are cross-sectional process diagrams showing a conventional liquid crystal display device and a manufacturing method thereof, and FIGS. 4A to 5G show a series of manufacturing processes.
[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. The 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 by forming an amorphous silicon film having a thickness of about 50 nm to 80 nm on the silicon oxide film 42 by a CVD method, and performing a dehydrogenation treatment by low-temperature annealing (temperature: 400 ° C. to 500 ° C., time: 1 hour). In addition, the ELA (Excimer Laser Annealing) method is applied to the amorphous silicon film.
[0005]
Next, as shown in FIG. 4B, a resist 44 is applied, this is patterned by a photolithography technique, and the polysilicon film 43 is patterned by an etching method such as RIE (Reactive Ion Etching) method. 43 ′ is a patterned polysilicon film. Thereafter, the resist 44 is removed.
[0006]
Next, as shown in FIG. 4C, a resist 45 is applied and patterned so that the ion implantation region is exposed. Further, pentavalent ions (P, As) are ion-doped at about 1.0 × 10 ¹⁵ ions / cm ^{2 to} 5.0 × 10 ¹⁵ ions / 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 the auxiliary capacitance layer 46.
[0007]
Thereafter, 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 forming a silicon oxide film (SiO ₂ film) having a thickness of 60 nm to 120 nm by a CVD method. The insulating film 47 becomes a gate insulating film of the TFT. The metal electrode 48 is formed by forming a metal electrode film made of Mo, W, Ti, or the like having a thickness of 150 nm to 300 nm on the insulating film 47 by a sputtering technique, and using a photolithography technique and an etching technique. This is done by patterning. The N-type LDD layer 49 is formed by ion doping pentavalent ions (P, As) at about 1.0 × 10 ¹³ ions / cm ^{2 to} 5.0 × 10 ¹³ ions / cm ^2. Yes. In the example of FIG. 4D, P ions are also doped.
[0008]
Next, as shown in FIG. 5E, an N + layer 51 is formed. The N + layer 51 is formed by applying a resist 50 and patterning the resist 50 by a photolithography technique, followed by 1.0 × 10 ¹⁵ ions / cm ^{2 to} 4.0 × 10 5 pentavalent ions (P, AS). ^The ion doping is performed at about ¹⁵ ions / cm ² . In the example of FIG. 5E, P ions are also doped. Thereby, an N-type TFT (Thin Film Transistor) region and an auxiliary capacitance region can be obtained.
[0009]
Next, as shown in FIG. 5F, a P + layer 53 is formed. The P + layer 53 is formed by applying a resist 52, patterning it by photolithography, and further adding trivalent ions (B) from 0.3 × 10 ¹⁵ ions / cm ^{2 to} 5.0 × 10 ¹⁵ ions / This is done by ion doping at about cm ² . In the example of FIG. 5F, B ions are doped. Thereby, a P-type TFT region can be obtained.
[0010]
In the example of FIG. 5F, heat treatment is performed to activate the N + layer 51, the P + layer 53, and the N-type LDD layer 49. As the heat treatment method, a rapid thermal annealing (RTA) method in which heat treatment is performed at a temperature of 600 ° C. to 800 ° C. for 30 seconds to 60 seconds, or a temperature of 400 ° C. to 600 ° C. in an oxygen atmosphere or a nitrogen atmosphere is performed. Examples include a method of performing for 3 hours.
[0011]
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 by forming a silicon nitride film (SiO ₂ film) having a thickness of 200 nm to 500 nm by a CVD method. 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 Ti / Al alloy or Al by sputtering. Has been done. The Al electrode 56 is formed by forming an Al metal film, patterning a resist thereon, and etching in accordance therewith. In the example of FIG. 5G, the part A indicates an auxiliary capacitance part, and the part B indicates a TFT part.
[0012]
Thereafter, a transparent electrode or the like (not shown) is provided to complete the TFT substrate. A liquid crystal display device is completed by, for example, sealing liquid crystal between the TFT substrate and a filter substrate (not shown) provided with a color filter or the like. The above-described conventional liquid crystal display device and manufacturing method are also disclosed in pages 132 to 139 of the flat panel display 1999 (issued on December 14, 1999 by Nikkei BP).
[0013]
[Problems to be solved by the invention]
By the way, in the above-mentioned liquid crystal display device, the auxiliary capacitor portion A is provided as shown in FIG. Since the auxiliary capacity portion A is intended to improve the charge retention performance and improve the image quality, it can be said that it is preferable to increase the capacity of the auxiliary capacity portion A as much as possible.
[0014]
However, in the above-described liquid crystal display device, the thickness of the insulating film 47 is constant in the auxiliary capacitor portion A and the TFT portion B. Therefore, it is difficult to increase the capacity of the auxiliary capacitor portion A by adjusting the thickness of the insulating film 47. Therefore, in order to increase the capacity of the auxiliary capacity part A, the area of the auxiliary capacity part A must be increased, but in this case, the aperture ratio is reduced.
[0015]
Further, in the circuit operation of TFTs on the TFT substrate, there are TFTs with a large number of operations and TFTs with a small number of operations considering the operation rate (Duty ratio). In general, high reliability is required for TFTs that operate frequently. For this reason, it is considered preferable to give each TFT characteristics according to the operating rate from the viewpoint of improving the image quality of the TFT liquid crystal display device, production cost, and the like.
[0016]
However, in the liquid crystal display device described above, the reason why the TFTs that require high reliability and the normal TFTs are stably formed is because the etching selectivity cannot be obtained because the oxide film is used as the gate insulating film. It is difficult to.
[0017]
It is an object of the present invention to provide a liquid crystal display device having a TFT which can solve the above-described problems, increase the number of auxiliary capacitance portions, and have characteristics according to the operation rate, and a method for manufacturing the same.
[0018]
[Means for Solving the Problems]
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 units and a plurality of TFTs, and an oxide film and a nitride film are sequentially stacked. A first TFT having a gate insulating film configured as described above; a second TFT having a gate insulating film configured by sequentially stacking an oxide film, a nitride film, and an oxide film; and an oxide film and a nitride film. A storage capacitor portion having an insulating film that is sequentially laminated is provided on the TFT substrate. In such a liquid crystal display device, it is preferable that the oxide film is a silicon oxide film and the nitride film is a silicon nitride film.
[0019]
Next, in order to achieve the above object, a liquid crystal display device according to the present invention includes a first TFT having a gate insulating film formed by sequentially stacking an oxide film and a nitride film, an oxide film, a nitride film, A TFT substrate provided with a second TFT having a gate insulating film formed by sequentially stacking oxide films, and an auxiliary capacitor having an insulating film formed by sequentially stacking oxide films and nitride films A method of manufacturing a liquid crystal display device including a step of sequentially stacking an oxide film, a nitride film, and an oxide film on a glass substrate constituting the TFT substrate, a region where the first TFT is provided, and an auxiliary capacitance unit And a step of removing the upper oxide film.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
Hereinafter, a liquid crystal display device and a manufacturing method thereof 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 the portions other than the TFT substrate 18 are omitted. 2 and 3 are cross-sectional process diagrams showing a manufacturing method of 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 processes.
[0021]
First, the liquid crystal display device 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 portions and a plurality of TFTs. In the example of FIG. 1, only one auxiliary capacitor unit A is shown as the auxiliary capacitor unit. Further, only the first TFT 16 and the second TFT 17 are shown as the TFT, and the first TFT 16 and the second TFT 17 form one TFT portion B. The auxiliary capacitor part A and the TFT part B are arranged in a matrix on the TFT substrate as a set.
[0022]
As shown in the example of FIG. 1, the gate insulating film 20 constituting the first TFT 16 is configured 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 is formed by sequentially laminating the oxide film 7, the nitride film 8, and the oxide film 9. In addition, the insulating film 21 constituting the auxiliary capacitance portion A is configured by sequentially stacking the oxide film 7 and the nitride film 8.
[0023]
For this reason, the second TFT 17 has a structure in which a nitride film denser than the oxide film and excellent in insulating properties is sandwiched between the oxide films, and the gate insulating film 19 is thick and the actual electric field is relaxed. Is more reliable 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. Furthermore, since the auxiliary capacitor A can be configured to have a thin insulating film 21, the capacity can be increased as compared with the conventional case.
[0024]
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 according to the present invention, characteristics according to the operation rate can be given to the TFT, and at the same time, the auxiliary capacity can be increased as compared with the conventional case, so that the image quality can be improved.
[0025]
Next, a method for manufacturing the liquid crystal display device of the present invention shown in FIG. 1 will be described for each step with reference to FIGS. First, as shown in FIG. 2A, a silicon oxide film (SiO ₂ film) 2 and a polysilicon film 3 are sequentially formed on a glass substrate 1. The silicon nitride film is formed by a CVD method so that the thickness becomes 500 nm to 600 nm. The polysilicon film 3 is formed by forming an amorphous silicon film having a thickness of about 50 nm to 80 nm on the silicon nitride film 2 by a CVD method, and performing a dehydrogenation process by low-temperature annealing (temperature: 400 ° C. to 500 ° C., time: 1 hour) In addition, the ELA (Excimer Laser Annealing) method is applied to the amorphous silicon film.
[0026]
Next, as shown in FIG. 2B, a resist 4 is applied and patterned by photolithography, and the polysilicon film 3 is patterned by an etching method such as RIE (Reactive Ion Etching). Reference numeral 3 'denotes a patterned polysilicon film. Thereafter, the resist 4 is removed.
[0027]
Next, as shown in FIG. 2C, a resist 5 is applied and patterned so that the ion implantation region is exposed. Further, pentavalent ions (P, As) are ion-doped at about 1.0 × 10 ¹⁵ ions / cm ^{2 to} 4.0 × 10 ¹⁵ ions / 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.
[0028]
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. As will be described later, this insulating layer becomes a gate insulating film of the TFT and an insulating film of the auxiliary capacitance portion. In the example of FIG. 2D, the oxide film 7 and the oxide film 9 are silicon oxide films (SiO ₂ films), and 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 oxide film 7 has a thickness of about 10 nm to 15 nm, the nitride film 8 has a thickness of about 5 nm to 15 nm, and the oxide film 9 has a thickness of about 10 nm to 30 nm. In this way, an ONO structure composed of SiO ₂ film / SiN _x film / SiO ₂ film can be obtained by the process shown in FIG.
[0029]
Next, as shown in FIG. 3E, a resist 10 is applied and patterned by photolithography. Patterning is a region where a TFT (a first TFT 16 described later) having a gate insulating film of an ON structure (SiO ₂ film / SiN _x film) other than a portion where the ONO structure obtained above is left is left. And a region where the auxiliary capacitor portion having the insulating film having the ON structure is exposed.
[0030]
Next, as shown in FIG. 3F, the portion exposed from the resist 10 is etched. This etching is selectively performed so that the nitride film 8 is not etched, and only the oxide film 9 exposed from the resist 10 is removed. As described above, the ON structure composed of the SiO ₂ film / SiN _x film can be obtained by the steps shown in FIGS.
[0031]
Next, as shown in FIG. 3G, a plurality of metal electrodes 11 are formed by a photolithography technique and an etching technique, and an N-type LDD layer 12 is further formed by ion doping. The N-type LDD layer 12 is formed by ion doping pentavalent ions (P, As) at about 1.0 × 10 ¹³ ions / cm ^{2 to} 5.0 × 10 ¹³ ions / cm ^2. Yes. In the example of FIG. 3G, P ions are doped.
[0032]
In the formation of the N-type LDD layer 12, the thickness of the film serving as a mask when ion doping P ions is different between the ONO structure portion and the ON structure portion. For this reason, according to the LSS (Lindhard Scharff Schiott) theory, by adjusting the ion implantation energy, it becomes possible to perform the same placement as in the case of performing ion doping twice. It is possible to make them separately.
[0033]
In the example of FIG. 3G, heat treatment is performed to activate the N + layer 6 and the N-type LDD layer 12. As the heat treatment method, a rapid thermal annealing (RTA) method in which heat treatment is performed at a temperature of 600 ° C. to 800 ° C. for 30 seconds to 60 seconds, or a temperature of 400 ° C. to 600 ° C. in an oxygen atmosphere or a nitrogen atmosphere is performed. Examples include a method of performing for 3 hours.
[0034]
Thereafter, as shown in FIG. 3H, an interlayer film 13, a contact plug 14, and an Al electrode 15 are formed. The interlayer film 13 is formed by forming a silicon oxide film (SiO ₂ film) having a thickness of 200 nm to 500 nm by a CVD method. 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 Ti / Al alloy or Al by sputtering. Has been done. The Al electrode 15 is formed by forming an Al metal film, patterning a resist thereon, and etching it accordingly. A transparent electrode (not shown) is connected to the Al electrode 16.
[0035]
In this way, a TFT substrate on which the auxiliary capacitor portion A and the TFT portion B are formed is formed. A liquid crystal display device according to the present invention is completed by, for example, enclosing liquid crystal between the TFT substrate 18 and a filter substrate (not shown).
[0036]
【The invention's effect】
As described above, according to the liquid crystal display device and the manufacturing method thereof according to the present invention, it is possible to easily produce TFTs provided on the TFT substrate, the gate insulating film is thin, the response characteristics are excellent, and the on-current is large. It is possible to obtain an effect that a TFT and a highly reliable TFT having an ONO structure in which a nitride film is sandwiched between oxide films can be formed at the same time. In addition, since the capacity of the auxiliary capacity portion 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 diagram showing a manufacturing method of the liquid crystal display device according to the present invention shown in FIG. FIG. 4 is a sectional process diagram showing a conventional liquid crystal display device and a manufacturing method thereof. FIG. 5 is a sectional process diagram showing a conventional liquid crystal display device and a manufacturing method thereof. Explanation of]
DESCRIPTION OF SYMBOLS 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 15 Al electrode 16 First TFT
17 Second TFT
18 TFT substrate 19 Gate insulating film 20 constituting the second TFT Gate insulating film 21 constituting the first TFT Insulating film A constituting the auxiliary capacitor part A auxiliary capacitor part B TFT part

Claims (3)

A liquid crystal display device including a TFT substrate provided with a plurality of auxiliary capacitance units and a plurality of TFTs,
A first TFT having a gate insulating film configured by sequentially stacking an oxide film and a nitride film, and a second TFT having a gate insulating film configured by sequentially stacking an oxide film, a nitride film, and an oxide film And a storage capacitor having an insulating film formed by sequentially stacking an oxide film and a nitride film on a TFT substrate. The liquid crystal display device according to claim 1, wherein the oxide film is a silicon oxide film, and the nitride film is a silicon nitride film. A first TFT having a gate insulating film configured by sequentially stacking an oxide film and a nitride film, and a second TFT having a gate insulating film configured by sequentially stacking an oxide film, a nitride film, and an oxide film And a manufacturing method of a liquid crystal display device including a TFT substrate provided with an auxiliary capacitor portion having an insulating film configured by sequentially stacking an oxide film and a nitride film,
A step of sequentially stacking an oxide film, a nitride film and an oxide film on a glass substrate constituting the TFT substrate;
A method of manufacturing a liquid crystal display device, comprising: at least a step of removing the upper oxide film in a region where the first TFT is provided and a region where the auxiliary capacitor portion is provided.

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