JP3083066B2 - Active matrix substrate manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing an active matrix substrate provided with a thin film switching element.

[0002]

2. Description of the Related Art In recent years, for a display device using a liquid crystal, a higher definition display image has been demanded. In particular, the so-called active matrix display panel that uses thin film switching elements to drive pixels can relatively easily increase the number of pixels and increase gray levels compared to other types of liquid crystal display panels. It is being advanced.

[0005] In general, a thin film switching element used for an active matrix type display panel has a capacity of five.
Thin-film transistors (TFTs) using amorphous silicon (a-Si) for large panels larger than inches and mainly polysilicon (p-Si) for smaller panels smaller than inches
Is used.

[0004] TFTs require high speed because it is necessary to write electric charges to the pixels within a few microseconds. Techniques for obtaining a p-Si thin film that can be sufficiently used for such an operation include the following. That is, (1) p-Si deposited by thermal decomposition of silane gas under reduced pressure is 600
A so-called long-time annealing method in which annealing is performed for a long time at about C to obtain p-Si having a grain size of about several microns to improve carrier mobility. (2) A hydrogen-rich film (for example, a nitride film formed by a plasma CVD method) is deposited on p-Si deposited by thermally decomposing silane gas under reduced pressure, and hydrogen in the film is removed by heat treatment. This is a so-called hydrogenation method in which carrier mobility is improved by coupling to traps at polysilicon grain boundaries.

[0005]

However, the above-mentioned conventional method has the following technical problems to be solved. That is, (1) Long-time annealing method: Since long-time processing is required, the throughput is poor, and the cost is inevitably high in mass production. (2) Hydrogenation method: In this method, hydrogen diffusion is generally performed by depositing a nitride film and then performing heat treatment at, for example, 450 ° C. for about 30 minutes in a hydrogen gas. However, hydrogen escapes due to diffusion. Efficient hydrogenation cannot be performed. In these cases,
High-speed driving cannot be performed because the leakage current of the transistor increases and the on-off characteristics deteriorate.

A main object of the present invention is to provide a display device capable of displaying a high pixel and high definition image using a p-Si TFT having sufficiently high carrier mobility and excellent on-off characteristics. .

[0007]

Means for Solving the Problems The present invention has been made by intensive studies in order to solve the above-mentioned problems, and has the following configuration. That is, in the method for manufacturing an active matrix substrate of the present invention, a pixel electrode provided corresponding to an intersection of a plurality of signal lines and a plurality of scanning lines, and a switching transistor connected to the pixel electrode are arranged on a supporting substrate. Forming a silicon nitride film on the supporting substrate by using a low pressure CVD method, and forming a polysilicon layer constituting the transistor on the silicon nitride film in the method for manufacturing an active matrix substrate formed by: Forming a silicon nitride film on the polysilicon layer using a plasma CVD method, and the plasma
350 ° C. to 550 after forming a silicon nitride film by the CVD method
Performing an annealing treatment at a temperature of 10 ° C. for 10 minutes to 5 hours.

According to the present invention, it is possible to provide an active matrix substrate in which the on / off characteristics of the transistor are efficiently improved by the annealing effect. When a liquid crystal display device is formed using the active matrix substrate thus obtained, the switching transistor has improved on / off characteristics, and can display an image with high definition, high gradation, and high contrast.

[0009]

EXAMPLES The present invention will be described in detail below with reference to specific examples, but the present invention is not limited to these examples.

(Embodiment 1) A description will be given with reference to FIGS. 1 (a) to 3 (e). 1 (a) to 3 (e),
Reference numeral 101 denotes a support substrate, for example, a silicon substrate.
The support substrate 1 is a base of a semiconductor substrate that sandwiches liquid crystal between the support substrate 1 and the support substrate. Reference numeral 102 denotes a silicon nitride film formed on the support substrate 1 by a low pressure CVD method. This film has a tensile stress.
After forming an oxide film 103 on the silicon nitride film 102, depositing a polysilicon 104, the polysilicon 104 is thermally oxidized to form a gate insulating film 105. Further, a gate 106 is formed by depositing polysilicon, and a source 108 and a drain 109 of the transistor are formed by ion implantation. In this example, the source 108 and the drain 109 are offset by a mask so as to provide an interval between the source 108 and the drain 109 so as to improve the source-drain breakdown voltage of the transistor and reduce the leakage current. Further, the low-concentration electric field relaxation layer 1 is formed by gate self-alignment by low-concentration ion implantation.
09 is formed. Next, after depositing the PSG film 110, a silicon nitride film 111 is deposited by a plasma CVD method. Next, a contact 112 is formed, and further, metal wirings 113 and 114 are formed to perform wiring with each electrode of the transistor. Through the above steps, the shape shown in FIG. Thereafter, a further upper layer is formed according to the function of the display device. Then, on the substrate obtained in FIG.
A pixel electrode connected to the drain of the transistor, a signal line connected to the source of the transistor, a scanning line connected to the gate of the transistor, an alignment film, and the like are formed to obtain a semiconductor substrate which sandwiches a liquid crystal layer together with an opposite substrate. Regarding this semiconductor substrate, a film having a tensile stress, that is, a plasma CVD film, is formed further below a wiring layer constituting a signal line or a scanning line located at the lowest position with respect to the liquid crystal layer.
A silicon nitride film 111 is provided by a method. In order to improve the characteristics of the polysilicon transistor, it is effective to implant hydrogen atoms into the polysilicon, which can reduce the off current and increase the on current. In this example, the plasma C
Hydrogen atoms are diffused from the silicon nitride film 111 into the polysilicon layer 104 by the VD method to improve the characteristics of the transistor. It is effective to perform the annealing at 350 ° C. to 550 ° C. for about 10 minutes to 5 hours. For example, the annealing can be performed at 450 ° C. for about 30 minutes. Also, heat history from other steps can be used. Prolonging the annealing time is effective. The annealing step can be performed at any time after the silicon nitride film 111 is formed. However, it is desirable to perform annealing at a time when other processes are not adversely affected. In this example, the silicon nitride film 111 is deposited on the PSG film 110 by the plasma CVD method, but may be deposited anywhere as long as hydrogen can diffuse into the polysilicon 104. For example, the PSG film 110 may be replaced with a silicon nitride film 111. In this example, since the silicon nitride film 102 formed by the low pressure CVD method is below the polysilicon layer 104, hydrogen is prevented from being further diffused downward, and hydrogen is efficiently injected into the polysilicon layer 104. Can be. As a result, a thin film transistor with small off-state current and large on-state current could be realized. When the semiconductor substrate thus obtained is applied to a liquid crystal display device,
Since the size of the transistor can be reduced, the definition of the panel can be improved by increasing the number of pixels. Further, the off-state current can be reduced, so that the contrast and the gradation can be improved.

In the present invention, the transistor disposed on the supporting substrate so as to be connected to the pixel electrode is preferably a thin film transistor (TFT).

(Embodiment 2) A description will be given with reference to FIGS. 4 (a) to 7 (f). This embodiment is an example in which the present invention is applied to a transmission type liquid crystal display device. The support substrate 201 is, for example, a silicon substrate. After forming the oxide film 202 by thermal oxidation,
A silicon nitride film 203 is formed by a low pressure CVD method,
An SG film 204 is deposited to obtain the shape shown in FIG. Next, a transistor is formed by steps similar to those of the first embodiment. 205 is polysilicon, 206 is a gate insulating film, and 207 is a gate electrode. 208 is a source,
209 is a drain, 210 is a low concentration electric field relaxation layer, 211
Is a PSG film. 212 is a contact, 213, 21
4 is a metal wiring. After forming the insulating film 215, a metal film 216 is formed. The metal film 216 only needs to have conductivity and light-shielding properties, and as a material, for example, Ti, TiN, Al, or the like can be appropriately used. Next, a silicon nitride film 217 is formed by the plasma CVD method, and annealing is performed to diffuse hydrogen atoms from the silicon nitride film 217 to the polysilicon 205 by the plasma CVD method, thereby improving the characteristics of the transistor. Further, after opening the through hole 218, a pixel electrode 219 for applying a voltage to the liquid crystal is formed so as to be connected to the wiring 214. The pixel electrode 219 is a transparent electrode in this embodiment, and employs ITO. The metal film 216 is fixed at a potential around the display portion, and functions to form a capacitance between the metal film 216 and the pixel electrode 219 to stabilize the pixel electrode potential. In the present embodiment, since there is a merit that the capacitance between the pixel electrode 219 and the metal film 216 is larger than when an oxide film is used because the film is a nitride film, the place of the nitride film 217 is replaced with another insulating film layer. It is also possible. Although not shown in the figure, a polyimide film is formed thereon and rubbed to obtain a semiconductor substrate which is one substrate of the liquid crystal display device. A liquid crystal is sandwiched between the semiconductor substrate and the counter substrate to obtain a liquid crystal display device. The opposing substrate is composed of a supporting substrate, a transparent electrode, and a rubbed polyimide film. Further, by disposing the color filter in the counter substrate or on the semiconductor substrate provided with the pixel electrode, a liquid crystal display device compatible with color display can be obtained. Further, by etching the back surface of the substrate 201, the pixel display unit is made transparent (220 in the figure), thereby forming a transmissive display device. At this time, the oxide film 202 plays a role of an etch stop. In the method of thinning the film by etching the back surface as in the present embodiment, it is important to balance the stress of the film in the thinned portion. When there is a stress in the direction in which the film extends, there is a problem that the thin film portion becomes wrinkled. In addition, there is a problem that the film is cracked when the film tension is too strong. Low-pressure CVD is used as the material in the direction in which the film is stretched.
Although there is a silicon nitride film formed by the CVD method, if there is a silicon nitride film formed by the low pressure CVD method between the polysilicon layer 205 and the silicon nitride film layer 217 formed by the plasma CVD method, hydrogen is diffused during annealing. And the characteristics of the transistor are not improved. Therefore, the configuration according to the present embodiment is effective. In order to finely adjust the stress of the film when the film is thinned, an initial design value is set on the side where the film is slightly bent, and the oxide film 202 is set.
Can be adjusted by etching with a hydrofluoric acid or the like. Although not shown, the drive circuit and the display portion can be formed on a chip by forming the drive circuit in a region of the substrate 201 which is not thinned. The drive circuit can be constituted by a single type MOS, or can be constituted by a CMOS. The drive circuit can also be formed of polysilicon. The process for forming the drive circuit and the process for forming the display unit can be made common among the processes that can be shared, so that the number of masks can be reduced and the process can be simplified.

According to the display device obtained in this way, since the ON current of the transistor can be large for the pixel, the size of the transistor can be reduced, and the definition of the panel can be improved by increasing the number of pixels. Further, reduction in off-state current can improve contrast and gradation.

In this embodiment, an example in which a silicon substrate is used as a supporting substrate has been described. However, a liquid crystal display device can be constructed without using a transparent substrate such as a glass substrate as a supporting substrate without reducing the thickness of the display section. It is possible. Also in this case, a liquid crystal display device capable of displaying an image with high definition, high gradation, and high contrast can be obtained by improving the characteristics of the transistor.

In this embodiment, the transmission type liquid crystal display device is shown, but the display device of the present invention can be applied to a reflection type liquid crystal display device. The reflection type is effective for obtaining a high aperture ratio. The silicon nitride film formed by the low pressure CVD method is a film having a tensile stress, but is not limited to the silicon nitride film, but may be a SiON film containing oxygen atoms, a laminated film of a SiON film and a silicon nitride film, or the like. Any film having the following can be applied to the display device of the present invention.

[0016]

According to the present invention, it is possible to provide an active matrix substrate in which the on / off characteristics of the transistor are efficiently improved by the annealing effect. When applied to a transmissive display device in which the active matrix substrate obtained by the present invention is made transparent by etching, a display device having a switching transistor with an excellent on / off characteristic while having a film of an etched portion can be formed. .
This display device can display an image with high definition, high gradation, and high contrast.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one example of a semiconductor substrate applicable to a method for manufacturing an active matrix substrate of the present invention.

FIG. 2 is a schematic view showing one example of a semiconductor substrate applicable to the method for manufacturing an active matrix substrate of the present invention.

FIG. 3 is a schematic view showing one example of a semiconductor substrate applicable to the method of manufacturing an active matrix substrate of the present invention.

FIG. 4 is a schematic view showing one example of a semiconductor substrate applicable to the method of manufacturing an active matrix substrate of the present invention.

FIG. 5 is a schematic view showing one example of a semiconductor substrate applicable to the method for manufacturing an active matrix substrate of the present invention.

FIG. 6 is a schematic view showing an example of a semiconductor substrate applicable to the method of manufacturing an active matrix substrate according to the present invention.

FIG. 7 is a schematic view showing one example of a semiconductor substrate applicable to the method of manufacturing an active matrix substrate of the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Mamoru Miyawaki 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-4-50920 (JP, A) -304428 (JP, A) JP-A-4-298722 (JP, A) JP-A-6-347830 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1368

Claims (3)

(57) [Claims] An active matrix substrate configured by arranging a pixel electrode provided corresponding to an intersection of a plurality of signal lines and a plurality of scanning lines, and a switching transistor connected to the pixel electrode on a support substrate. Forming a silicon nitride film on the support substrate by using a low pressure CVD method, forming a polysilicon layer constituting the transistor on the silicon nitride film, and forming a plasma on the polysilicon layer. Forming a silicon nitride film using a CVD method, and performing an annealing process at a temperature of 350 ° C. to 550 ° C. for 10 minutes to 5 hours after forming the silicon nitride film by the plasma CVD method. A method for manufacturing an active matrix substrate. 2. The method according to claim 1, wherein said support substrate is made of silicon. 3. The method of manufacturing an active matrix substrate according to claim 1, wherein an oxide film is formed between the silicon nitride film formed by the low pressure CVD method and the polysilicon layer.