JP2000150896A - Thin-film transistor and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reliable thin-film transistor that can be manufactured by a few processes, and its manufacturing method. SOLUTION: In the manufacturing method of a thin-film transistor, photosensitive paste 1 where an element for promoting crystallization is added is formed in an insular shape, the element is selectively added into an amorphous semiconductor film 15a, heat treatment is made, and the amorphous semiconductor film 15a is polycrystallized, thus eliminating the need for a process for forming a photoresist mask, and simplifying a manufacturing process. Also, in the manufacturing method, a photoresist film is not used in an element addition process, thus preventing impurities from being mixed into the amorphous semiconductor film 15a, and hence manufacture a reliable thin-film transistor with superior electric stability by a few processes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor used for an active matrix type liquid crystal display device and the like, and more particularly to a thin film transistor using a crystalline semiconductor and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, thin film transistors (TFTs) have been actively developed for application to image display devices such as flat displays. A thin film transistor used for an active matrix type liquid crystal display device or the like is required to have high mobility, a high on-current / off-current ratio, a high breakdown voltage, a reduction in element size, and the like.

A polycrystalline semiconductor thin film transistor has an advantage that the conductance is larger than that of a thin film transistor using an amorphous semiconductor film. However, the process temperature is usually as high as 1000 ° C., and a polycrystalline semiconductor thin film transistor requires a glass substrate. Is difficult to manufacture. For example,
Corning 7059 glass has a glass strain point of 593 ° C
However, there is a problem in heating at 600 ° C. or more in consideration of increasing the area of the substrate.

Therefore, as a countermeasure against the process temperature, nickel, palladium,
Furthermore, if a small amount of elements such as lead are deposited and then heated, crystallization can be performed at a process temperature of 550 ° C. and a processing time of about 4 hours. Thus, a polycrystalline semiconductor can be obtained at a process temperature of 600 ° C. or less. In order to introduce the above-mentioned metering element (catalytic element) that promotes crystallization, plasma treatment, vapor deposition, and even ion implantation may be used.

However, the presence of a large amount of the above-mentioned catalytic elements in a semiconductor impairs the reliability and electrical stability of a device using such a semiconductor, and is not desirable. That is, the element that promotes crystallization such as nickel (catalytic element) is necessary when crystallizing an amorphous semiconductor, but is preferably not contained as much as possible in the crystallized polycrystalline film. . In order to achieve this object, it is necessary to minimize the amount of the catalyst element required for crystallization and to perform crystallization with the minimum amount of the catalyst element.

Therefore, a conventionally disclosed method of manufacturing a thin film transistor for controlling the addition of a small amount of a catalytic element (Japanese Patent Application Laid-Open No. 7-21635) will be described with reference to FIGS.

First, as shown in FIG. 9A, an amorphous semiconductor film (α-Si) 105 a is formed on a glass substrate 101. Next, as shown in FIG.
13, a required pattern is formed on the amorphous semiconductor film 105a. In this state, for example,
An appropriate amount of an acetate solution containing 100 ppm of nickel is dropped, and spin coating is performed by a spinner 114 at 50 rpm for 10 seconds to form a uniform water film 111 on the entire substrate surface. Next, after maintaining this state for 5 minutes, spin dry is performed at 2000 rpm for 60 seconds using a spinner.

Next, as shown in FIG. 9C, by removing the photoresist film 113 by using a stripping solution or oxygen ashing, a region 112 in which a nickel element is adsorbed is selectively formed. After that, the amorphous semiconductor film 105a is grown into a polycrystalline semiconductor film (P-Si) 105b by performing a heat treatment at 550 ° C. for 4 hours. At this time, as shown in FIG. 9C, the portion 115 into which nickel has been introduced is laterally crystal-grown (laterally grown) into a region into which nickel has not been introduced, and the laterally grown region 11
6 are formed.

Thereafter, annealing by excimer laser irradiation or the like is performed to further improve the crystallinity of the polycrystalline semiconductor film. Next, as shown in FIG. 9D, the polycrystalline semiconductor film 1
05b is patterned into a predetermined shape. Then, FIG.
As shown in (E), the gate insulating film 106 is formed, and heated at 600 ° C. for about 12 hours to obtain a higher withstand voltage, thereby densifying the gate insulating film 106.

Thereafter, a metal film is formed, and the metal film is patterned into a predetermined shape. As shown in FIGS. 9F and 7, the gate wiring 103 and the gate electrode 10 are formed.
3a is formed. Next, as shown in FIG. 10G, the gate electrode 103a is used as an impurity implantation mask, and a pentavalent element typified by phosphorus (or an octavalent element typified by boron) is used as a dopant. Impurity implantation is performed under the conditions of about 10 KV and a dose of 1 × 10 ¹⁵ / cm ² to 1 × 10 ¹⁷ / cm ² to form an impurity implantation region 119. Thereafter, as shown in FIG. 10H, the region into which the impurities are implanted is activated by irradiation with an excimer laser or the like, so that the source region 104b and the drain region 108b are formed in addition to the channel region.

Next, as shown in FIGS. 10I and 10J, an interlayer insulating film 107 is formed, and the interlayer insulating film 107 and the gate insulating film 106 are simultaneously patterned into a predetermined shape to form a contact. A hole 120 is formed. Thereafter, a metal film is formed, and the metal film is patterned into a predetermined shape, as shown in FIG.
And a source electrode 104a and a drain electrode 108a are formed. Then, the pixel electrode 102 is formed near the thin film transistor 100 shown in FIG. 7 and connected to the drain electrode 108a. The pixel electrode 102 is made of, for example, a transparent conductive film such as ITO (indium tin oxide).

FIG. 7 shows a part of a panel substrate of a liquid crystal display device provided with a large number of thin film transistors 100 each having a polycrystalline semiconductor film manufactured in this conventional example, and FIG. 3 shows a cross section taken along line BB.

As shown in FIG. 9C of the above manufacturing process,
By introducing the nickel element as a catalyst element into the amorphous semiconductor film 105a and performing heat treatment, the lateral growth region 1 grown in the polycrystalline semiconductor film 105b is formed.
In No. 16, needle-like or columnar crystals extend in the growth direction parallel to the surface of the glass substrate 101, and no crystal grain boundaries exist in the growth direction. Therefore, by utilizing the lateral growth region 116, the thin film transistor 10
By forming the zero channel portion, a high-performance thin film transistor can be manufactured.

According to the above-described conventional manufacturing method, as shown in FIG. 5, the source is parallel to the growth direction 43 of the lateral growth region having the lateral growth end 42 shown by the solid elliptical line. When the region 44, the channel region 46, and the drain region 45 are arranged, the direction of crystal growth and the direction of carrier movement can be the same. Therefore, a high mobility thin film transistor having no crystal grain boundary in the carrier moving direction can be realized. On the other hand, as shown in FIG. 6, the source region 54, the channel region 56, and the drain region 55 are substantially perpendicular to the growth direction 53 of the lateral growth region having the lateral growth end 52 indicated by the elliptical solid line.
Is disposed, the grain boundary portion in the electrolytic concentration region at the end of the drain region 55 can be eliminated. Therefore, the density of the grain boundary trap at the end of the drain region can be reduced, and the cause of the characteristic deterioration during the operation of the transistor can be eliminated. Therefore, a thin film transistor having a large on / off current ratio can be manufactured.

However, in the conventional method of manufacturing a thin film transistor, as shown in FIG. 9B, after forming a photoresist mask 113, a solution containing a catalytic element (nickel) is dropped to form a water film 111. Therefore, there is a problem that the number of steps for selectively introducing the catalytic element into the amorphous semiconductor film 105a is increased.

Further, in the above conventional example, since the photoresist film 113 is in direct contact with the surface of the amorphous semiconductor film 105a, impurities are mixed into the amorphous semiconductor film 105a,
The film quality of the amorphous semiconductor film 105a is deteriorated. This deterioration of the film quality has a problem that reliability and electrical stability of the thin film transistor are impaired.

Therefore, a blocking layer is provided between the amorphous semiconductor film 105a and the photoresist film 113. In the blocking layer, a region facing the portion 115 for introducing the catalytic element is opened, and then the catalytic element is removed. A method of dropping the contained solution may be considered. According to this method, the photoresist film 113 can be prevented from directly touching the amorphous semiconductor film 105a, but the step of forming the blocking layer is an additional step, and the number of steps is increased.

[0018]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thin film transistor which can be manufactured with a small number of steps and has high reliability, and a method for manufacturing the same.

[0019]

In order to achieve the above object, a method for manufacturing a thin film transistor according to the first aspect of the present invention comprises:
A semiconductor film forming step of forming an amorphous semiconductor film over an insulating substrate or over an insulating film formed over the substrate; and a method of adding an element which promotes crystallization to the amorphous semiconductor film. Forming a conductive paste in an island shape, selectively adding a small amount of the element promoting the crystallization to the amorphous semiconductor film, and performing a heat treatment to convert the element to the amorphous semiconductor film. An element diffusion step of diffusing and introducing into the semiconductor film to polycrystallize the amorphous semiconductor film.

In the method of manufacturing a thin film transistor according to the first aspect of the present invention, a photosensitive paste to which an element that promotes crystallization is added is used, the photosensitive paste is formed into an island shape, and the element is selectively amorphous. The amorphous semiconductor film is added to the amorphous semiconductor film and subjected to a heat treatment to polycrystallize the amorphous semiconductor film.

Therefore, according to the manufacturing method of the present invention, the two steps of forming a photoresist mask in the conventional example and then dropping a solution containing a catalyst element are performed by a photosensitive method using an element which promotes crystallization. It can be done in one step of forming the paste into islands. Therefore, the manufacturing process can be simplified and the cost can be reduced.

Further, according to the manufacturing method of the present invention, since the photoresist film is not used in the element addition step, the photoresist film does not directly contact the surface of the amorphous semiconductor film unlike the conventional method. Therefore, even if a blocking layer is not provided between the amorphous semiconductor film and the photoresist film, no impurity is mixed into the amorphous semiconductor film, and the amorphous semiconductor film can be formed without increasing the number of steps. Degradation of the quality semiconductor film can be prevented. Therefore, according to the present invention, a thin film transistor having high reliability and high electrical stability can be manufactured with a small number of steps.

In the thin film transistor according to the second aspect of the present invention, an element promoting crystallization is added to the amorphous semiconductor film formed on the insulating substrate or on the insulating film formed covering the substrate. A polycrystalline semiconductor thin film that is polycrystallized by heating after the photosensitive paste is formed in an island shape is provided, and a source and a drain are formed in the polycrystalline semiconductor thin film.

According to the thin film transistor of the second aspect of the present invention, the photoresist film is not used in the element adding step, so that the photoresist film does not directly contact the surface of the amorphous semiconductor film unlike the related art. . Therefore, even if a blocking layer is not provided between the amorphous semiconductor film and the photoresist film, no impurity is mixed into the amorphous semiconductor film, so that the amorphous semiconductor film can be formed in a simple process. Deterioration of film quality can be prevented. Therefore, according to the present invention, it is possible to provide a thin film transistor having high reliability and high electrical stability, which can be manufactured in a small number of steps.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

An embodiment of a method of manufacturing a thin film transistor according to the present invention will be described with reference to FIGS.

In this embodiment, first, as shown in FIG. 3A, an amorphous semiconductor film (α-Si) 15a is formed on a glass substrate or a substrate 11 formed of an insulating film. 3
The film is formed to a thickness of about 0 to 150 nm. Next, FIG.
As shown in FIG. 1, a photosensitive paste 1 containing only 100 ppm of nickel as a catalyst element for promoting crystallization.
Is applied and photolithography is performed to form a predetermined island shape. In this photolithography, exposure can be performed at an exposure amount of 100 to 700 mJ / cm ² , and development can be performed with an aqueous solution of sodium carbonate 0.5 to 1%.

Next, a heat treatment is performed at 550 ° C. for 4 hours to convert the amorphous semiconductor film 15a into a polycrystalline semiconductor film (P-type).
Si) grown to 15b. At this time, as shown in FIG. 3C, the portion 21 into which the nickel element has been introduced grows laterally toward a region where the nickel element has not been introduced. Thus, a lateral growth region 22 is formed. The catalyst element (nickel) is converted into an amorphous semiconductor film 15a.
And a heat treatment is performed to grow the lateral growth region 15a into the polycrystalline semiconductor film 15b. In the polycrystalline semiconductor film 15b, needle-like or columnar crystals extend in the growth direction in parallel with the surface of the substrate 11, and there are no crystal grain boundaries in the growth direction. Therefore, by using the lateral growth region 22 to form the channel portion of the thin film transistor, FIGS.
As described with reference to, a high mobility thin film transistor and a thin film transistor with a large on / off current ratio can be manufactured.

Next, as shown in FIG. 3D, the photosensitive paste 1 to which the above-mentioned catalytic element (nickel) is added is peeled off with about 1% sodium carbonate aqueous solution. Thereafter, annealing by excimer laser irradiation or the like is performed to further improve the crystallinity of the polycrystalline semiconductor film 15b. Next, the polycrystalline semiconductor film 15b is patterned into a predetermined shape.

Thereafter, as shown in FIG. 3 (E), a gate insulating film 16 is formed, and 600 ° C.
For about 12 hours to densify the gate insulating film 16. Thereafter, as shown in FIG. 3 (F), a metal film is formed,
Further, the metal film is patterned into a predetermined shape to form a gate wiring 13 and a gate electrode 13 as shown in FIG.
a is formed.

Next, as shown in FIG. 4G, a pentavalent element represented by phosphorus (or a trivalent element represented by boron) is used as a dopant by using the gate electrode 13a as an impurity implantation mask. , Acceleration voltage about 10KV, dose amount 1
Impurity implantation is performed under the conditions of × 10 ¹⁵ / cm ² to 1 × 10 ¹⁷ / cm ² to form an impurity implantation region 19. Thereafter, as shown in FIG. 4H, the region into which the impurities are implanted is activated by irradiation with an excimer laser or the like, so that the source region 14b and the drain region 18
b is formed.

Next, as shown in FIGS. 4 (I) and 4 (J),
An interlayer insulating film 17 is formed, and the contact hole 20 is formed by simultaneously patterning the interlayer insulating film 17 and the gate insulating film 16 into a predetermined shape. Thereafter, as shown in FIG. 4K, a metal film is formed, and further, this metal film is patterned into a predetermined shape, and as shown in FIG. 1, the source wiring 14, the source electrode 14a and the drain An electrode 18a is formed.

Then, as shown in FIG. 1, a pixel electrode 12 is formed near the thin film transistor 10 thus obtained so as to be connected to the drain electrode 18b. This pixel electrode 12 is made of, for example, a transparent conductive film such as ITO.

According to the method for manufacturing a thin film transistor of this embodiment, the photosensitive paste 1 to which an element promoting crystallization is added is used, the photosensitive paste 1 is formed in an island shape, and the element is selectively formed. The amorphous semiconductor film 15a is added to the amorphous semiconductor film 15a and subjected to a heat treatment to polycrystallize the amorphous semiconductor film 15a. Therefore, according to this manufacturing method, the two steps of forming the photoresist mask in the conventional example and then dropping the solution containing the catalytic element into an island-shaped photosensitive paste containing an element that promotes crystallization are performed. It can be done in one step of forming. Therefore, the manufacturing process can be simplified and the cost can be reduced.

Further, according to this manufacturing method, since the photoresist film is not used in the element adding step, the photoresist film does not directly contact the surface of the amorphous semiconductor film as in the related art. Therefore, there is no need to provide a blocking layer between the amorphous semiconductor film and the photoresist film, and no impurities are mixed into the amorphous semiconductor film 15a. Deterioration of the film quality of the crystalline semiconductor film 15a can be prevented. Therefore,
According to this manufacturing method, a thin film transistor with high reliability and high electrical stability can be manufactured with few steps.

Many thin film transistors 10 are formed on a part of the panel substrate of the liquid crystal display device shown in FIG. FIG. 2 shows a cross section taken along line AA of FIG. As shown in FIG. 1, the thin film transistor 10 is connected to pixel electrodes 12 arranged in a matrix on a substrate 11, and is formed as a switching element that controls supply of an image signal to each pixel electrode 12. Further, on the substrate 11, a large number of scanning signal lines (gate lines) 13 for supplying image signals and many data signal lines (source lines) 14 are arranged so as to intersect in a plane. The scanning signal line 13 is formed integrally with the gate electrode 13a. On the other hand, the data signal line 14
Are formed integrally with the source electrode 14a.

As shown in FIG. 2, in the thin film transistor 10, a gate insulating film 16, a gate electrode 13a, and an interlayer insulating film 17 are sequentially formed on a polycrystalline semiconductor film (P-Si) 15b. In two contact holes 20,
It has a structure in which a source electrode 14a and a drain electrode 18a are formed. The polycrystalline semiconductor film 15b has a channel region, and a source region 14b and a drain region 18b on both sides of the channel region.
3a. The drain electrode 18a is
It is connected to the image electrode 12 in the vicinity.

In the thin-film transistor 10, the photosensitive paste 1 containing an element (nickel) that promotes crystallization is formed in an island shape on the amorphous semiconductor film 15a, and then the polycrystalline poly-crystal is formed by heating. A crystalline semiconductor thin film 15b was provided, and a source region 14b and a drain region 18b were formed in the polycrystalline semiconductor thin film 15b. According to the thin film transistor 10, since the photoresist film is not used in the element addition step, the photoresist film does not directly contact the surface of the amorphous semiconductor film as in the related art. Therefore, even if a blocking layer is not provided between the amorphous semiconductor film and the photoresist film, no impurity is mixed into the amorphous semiconductor film, so that the amorphous semiconductor film can be formed in a simple process. Deterioration of film quality can be prevented. Therefore, according to the thin film transistor 10, a thin film transistor with high reliability and high electrical stability, which can be manufactured in a small number of steps, can be realized.

In the above embodiment, nickel is used as an element for promoting crystallization, but another element (such as palladium) may be used.

[0040]

As is apparent from the above description, the method of manufacturing a thin film transistor according to the first aspect of the present invention uses a photosensitive paste to which an element promoting crystallization is added, and forms the photosensitive paste in an island shape. The above element is selectively added to the amorphous semiconductor film, and heat treatment is performed, so that the amorphous semiconductor film is polycrystallized.

Therefore, according to the manufacturing method of the present invention, the two steps of forming a photoresist mask in the conventional example and then dropping a solution containing a catalyst element are performed in a photosensitive method in which an element promoting crystallization is added. It can be done in one step of forming the paste into islands. Therefore, since the amorphous semiconductor film can be polycrystallized at a low temperature for a short time, the manufacturing process can be simplified and the cost can be reduced.

Further, according to the manufacturing method of the present invention, the photoresist film is not used in the element addition step, so that the photoresist film does not directly contact the surface of the amorphous semiconductor film unlike the related art. Therefore, even if a blocking layer is not provided between the amorphous semiconductor film and the photoresist film, no impurity is mixed into the amorphous semiconductor film, and the amorphous semiconductor film can be formed without increasing the number of steps. Degradation of the quality semiconductor film can be prevented. Therefore, according to the present invention, a thin film transistor having high reliability and high electrical stability can be manufactured with a small number of steps.

Further, in the thin film transistor according to the second aspect of the present invention, an element which promotes crystallization is added to the amorphous semiconductor film formed on the insulating substrate or on the insulating film formed covering the substrate. After the photosensitive paste was formed into an island shape, a polycrystallized polycrystalline semiconductor thin film was provided by heating, and a source and a drain were formed in the polycrystalline semiconductor thin film.

According to the thin film transistor of the second aspect of the present invention, the photoresist film is not used in the element addition step, so that the photoresist film does not directly contact the surface of the amorphous semiconductor film unlike the conventional case. . Therefore, even if a blocking layer is not provided between the amorphous semiconductor film and the photoresist film, no impurity is mixed into the amorphous semiconductor film, so that the amorphous semiconductor film can be formed in a simple process. Deterioration of film quality can be prevented. Therefore, according to the present invention, it is possible to provide a thin film transistor having high reliability and high electrical stability, which can be manufactured in a small number of steps.

[Brief description of the drawings]

FIG. 1 is a plan view showing a part of a panel substrate of a liquid crystal display device in which a large number of thin film transistors of the present invention are formed.

FIG. 2 is a cross-sectional view of the thin film transistor taken along line AA in FIG.

FIG. 3 is a process diagram showing a first half of a manufacturing process of the thin film transistor.

FIG. 4 is a process chart showing a latter half of a manufacturing process of the thin film transistor.

FIG. 5 is a diagram showing the direction of crystal growth and the arrangement of the source, drain, and channel regions of the thin film transistor, and is a layout diagram in which no crystal grain boundary exists in the carrier moving direction.

FIG. 6 is a diagram showing the direction of crystal growth and the arrangement of source, drain, and channel regions of a thin film transistor, and is an arrangement diagram in which the density of grain boundary traps at the drain end is reduced.

FIG. 7 is a plan view showing a part of a panel substrate of a liquid crystal display device in which a large number of conventional thin film transistors are formed.

8 is a cross-sectional view of the thin film transistor taken along line BB in FIG.

FIG. 9 is a process chart showing a first half of a manufacturing process of the thin film transistor.

FIG. 10 is a process chart showing a latter half of a manufacturing process of the thin film transistor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Catalyst element containing paste, 10 ... Thin film transistor,
11: glass substrate, 12: pixel electrode, 13: gate wiring, 13a: gate electrode, 14: source wiring, 14a ...
Source electrode, 14b, 44, 54 ... source region, 15a ...
Amorphous semiconductor film, 15b polycrystalline semiconductor film, 16 gate insulating film, 17 interlayer insulating film, 18a drain electrode, 18b, 45, 55 drain region, 19 impurity implantation region, 20 contact hole , 21,41,51 ...
Catalyst element introduction region, 22, 43, 53 ... lateral growth region, 46, 56 ... channel region, 42, 52 ... lateral growth end.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F052 AA01 BB07 DA02 FA01 JA01 JA10 5F110 AA05 CC02 FF36 GG02 GG13 GG15 HJ01 HJ04 HJ12 HJ23 NN02 PP03 PP23 PP24 PP34 QQ04

Claims (2)

[Claims] A semiconductor film forming step of forming an amorphous semiconductor film over an insulating substrate or an insulating film formed over the substrate; and promoting crystallization on the amorphous semiconductor film. Forming an island-shaped photosensitive paste to which the element is added, and selectively adding a trace amount of the element promoting the crystallization onto the amorphous semiconductor film; An element diffusion step of diffusing and introducing into the amorphous semiconductor film and polycrystallizing the amorphous semiconductor film. 2. A photosensitive paste containing an element that promotes crystallization is formed in an island shape on an amorphous semiconductor film formed on an insulating substrate or an insulating film formed over the substrate. A thin film transistor comprising a polycrystalline semiconductor thin film that has been polycrystallized by heating, and a source and a drain formed in the polycrystalline semiconductor thin film.