JPH10150200A - Thin film transistor and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify a process for manufacturing a thin film transistor so as to lessen the transistor in manufacturing cost by a method wherein a heat- resistance high-molecular film is formed on an insulating substrate, an insulating film is formed on the heat-resistant high-molecular film, a semiconductor film is formed on the insulating film, and the semiconductor film is melted by irradiation with a laser beam and crystallized. SOLUTION: A heat-resistant high-molecular film 2 is formed on a transparent insulating substrate 1, an inorganic insulating film 3 is formed thereon, and an amorphous semiconductor thin film 4 is formed thereon. The amorphous semiconductor film 4 is subjected to an annealing treatment by irradiation with a pulse laser beam 5 so as to obtain a polycrystalline semiconductor thin film 6. At this point, the heat-resistant high-molecular film 2 is much lower in thermal conductivity than the inorganic insulating film 3, so that the temperature of the heat-resistant high-molecular film 2 is restrained from rising higher than its melting point as a whole. Therefore, the heat-resistant high-molecular film 2 is capable of functioning effectively as a heat insulating material as kept free from an adverse effect such as melting in an annealing treatment carried out at high temperatures.

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 having a structure in which a semiconductor thin film formed on an insulating substrate via a lower layer is annealed by using a pulse laser, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a high-energy, short-wavelength, short-pulse laser (pulse laser) has been used to melt and crystallize a semiconductor thin film such as amorphous or crystalline silicon. 2. Description of the Related Art Semiconductor thin films are receiving attention as materials for thin film transistors (TFTs), which are active elements of active matrix type liquid crystal display elements. This is because carrier mobility is higher than that of a thin film transistor using an amorphous semiconductor thin film.
This is because it has a high value of 0 times or more, and has an advantage that glass can be used as the insulating substrate.

In general, a method of heating a semiconductor thin film by irradiation with a pulse laser is called a laser annealing method. As described above, a laser annealing method used for crystallization of a semiconductor thin film specifically includes a silicon oxide film or a nitride film formed on a transparent insulating substrate such as quartz or glass having a thickness of about 1 mm as a base layer. An insulating film such as silicon is formed, a semiconductor thin film such as amorphous silicon or polycrystalline silicon is formed thereon, and the semiconductor thin film is melted and crystallized by irradiating the semiconductor thin film with a pulse laser. Things.

The characteristics of the above-mentioned thin film transistor become better as the grain size of the semiconductor crystal in the semiconductor thin film becomes larger.
Therefore, in crystallization of a semiconductor thin film by a laser annealing method, the solidification rate of the melted semiconductor thin film may be reduced in order to increase the grain size of the semiconductor crystal and improve the characteristics of the thin film transistor.

[0005] The solidification rate of a molten semiconductor thin film is inversely proportional to the ratio of the stored thermal energy to the outflow rate of this thermal energy. Therefore, the solidification rate of the melted semiconductor thin film can be reduced by increasing the thermal energy stored in the entire object to be irradiated with the pulse laser, including the insulating substrate of the base layer.

As one of the methods for increasing the thermal energy of the entire object to be irradiated by the pulse laser, there is a method of increasing the energy density of the pulse laser to be irradiated. However, since the insulating substrate having a thickness of about 1 mm serves as a huge heat bath, the outflow speed of the accumulated thermal energy is large, and the solidification speed of the molten semiconductor thin film cannot be significantly reduced.

Therefore, conventionally, in the above-mentioned laser annealing method, a structure exhibiting a heat insulating effect is provided between the insulating substrate and the semiconductor thin film, and the thermal conductivity on the side of the insulating substrate serving as a base layer of the semiconductor thin film is reduced. There has been proposed a method in which the flow rate of thermal energy accumulated in an object to be irradiated with a laser beam is reduced by reducing the flow rate, and the solidification rate of a molten semiconductor thin film is reduced.

One of them is disclosed, for example, in Japanese Patent Application Laid-Open No. 6-29321 and Japanese Patent Application Laid-Open No. 6-16358.
In Japanese Patent Application Laid-Open No. 9-209, a hollow portion for heat insulation is formed between an insulating substrate and an insulating film, and a semiconductor thin film formed thereon is annealed by a pulsed laser, and the above-described hollow portion is formed. A method for reducing the solidification rate of a melted semiconductor thin film by the heat insulating effect is disclosed.

Further, as another method using a structure exhibiting the above-mentioned heat insulating effect, a report of the Subcommittee on Applied Electronic Properties, 199
On January 1st, pp. 1-6, a hole is partially formed in an insulating substrate, and a silicon oxide film is formed so as to cover the hole. A method of annealing a semiconductor thin film formed on a silicon oxide film with a pulse laser has also been reported. According to this method, the amorphous silicon film formed on the silicon oxide film is melted by pulsed laser irradiation, and the solidification rate of the melted amorphous silicon film is increased by the heat insulating effect of the air layer in the bridge portion. Is to be reduced.

Japanese Patent Application Laid-Open No. Hei 6-132306 discloses that two types of inorganic insulating films having different thermal conductivities are used as a lower layer of a semiconductor thin film, and an inorganic insulating film having a lower thermal conductivity is disposed on an upper side.
An inorganic insulating film having high thermal conductivity but low permeability of impurities is formed on the lower side, and the semiconductor thin film formed thereon is annealed by a pulse laser, and a heat insulating effect of the upper inorganic insulating film is used. A method for reducing the solidification rate of a semiconductor thin film is disclosed.

Further, Japanese Patent Application Laid-Open No. 6-140324 discloses that two types of inorganic insulating films having different thermal conductivity are formed on an insulating substrate so as to be alternately arranged in stripes or mosaics. Annealing the semiconductor thin film formed by using a pulsed laser to increase the grain size of the resulting semiconductor crystal by utilizing the difference in crystal growth rate between the low temperature region and the high temperature region caused by the difference in thermal conductivity Such a method is also disclosed.

[0012]

However, none of the above-mentioned methods can improve the characteristics of the obtained thin film transistor, simplify the manufacturing process, and reduce the manufacturing cost. .

In other words, according to the above method and the above method, although the hollow portion is formed in the lower layer of the semiconductor thin film, the diameter of the semiconductor crystal can be increased by the heat insulating effect of the hollow portion. Since an etching process is required, the manufacturing process cannot be said to be simple, the manufacturing process becomes complicated, and the manufacturing cost increases. In addition, the thin film transistor obtained by this method is considered to have a problem in strength due to the presence of the cavity.

In the above-mentioned method, similarly to these methods, it is necessary to form a hole in the silicon substrate in order to form a bridge-like silicon oxide film. Therefore, although the grain size of the semiconductor crystal obtained by the heat insulating effect of the bridge portion can be increased, the manufacturing process is not simple and the manufacturing cost may increase. Further, it is considered that a thin film transistor obtained by the above-described hole provided in the silicon substrate causes a problem in strength similarly to the above.

Further, in the above method,
Unlike the method, the manufacturing process is simple because there is no need to provide a special structure such as a cavity or the like, but the heat insulating effect of the inorganic insulating film is low even if its thermal conductivity is low. Because it is inferior to the heat insulation effect of the hollow part of
The obtained semiconductor crystal does not have a sufficient grain size.

Further, in the above method, two types of inorganic insulating films are formed so as to be alternately arranged in stripes or mosaics. Although the diameter can be increased, the manufacturing process is the same as in the above methods (1) to (4).
It is not easy.

On the other hand, impurities such as phosphorus, arsenic, and boron are implanted as ions into the semiconductor thin film crystallized as described above according to the P-type and N-type. As a method of electrically activating the semiconductor thin film, there is a laser annealing method in which a pulse laser is applied to the semiconductor thin film to perform an annealing process.

In this case, the surface temperature of the semiconductor thin film irradiated with the pulse laser is usually 600 ° C. or higher, and particularly when the semiconductor thin film is made of silicon, the surface may be melted. With the change, the surface temperature becomes 1000 ° C. or more. At this time, if hydrogen is contained in the semiconductor thin film, the hydrogen moves rapidly inside the crystalline semiconductor thin film, and in some cases, jumps out of the semiconductor thin film so as to be bumped. The crystallinity of the semiconductor thin film will be impaired.

When the semiconductor thin film exceeds its melting temperature, the injected impurities (phosphorus, arsenic, boron, etc.)
It becomes easy to diffuse to the intrinsic region where the impurity is not implanted.
As a result, formation of a normal junction surface between the source and drain portions and the gate portion of the crystalline semiconductor thin film in the thin film transistor is prevented, and the characteristics of the thin film transistor deteriorate.

Further, when the impurity is activated at a temperature of about 600 ° C., the impurity existing at the position of the disordered crystal lattice in the implanted state or the silicon atom of the semiconductor thin film recovers the crystallinity. However, at the same time, the rate of forming lattice defects such as dislocations also increases, and as a result, the recovery of the crystallinity of the entire semiconductor thin film is insufficient. Become.

On the other hand, in the case of impurity activation performed at a low temperature of 600 ° C. or less, defects on the crystal lattice such as point defects are reduced, and the proportion of the implanted impurity occupying a normal position in the crystal lattice is reduced. Increase. Therefore, the recovery of the crystallinity of the crystalline semiconductor thin film in this case is better than the case where the annealing treatment is performed at a high temperature of 600 ° C. or more.

However, when the semiconductor thin film is annealed with a pulse laser having a normal energy density, the semiconductor thin film is heated to a high temperature of 600 ° C. or more as described above, and conversely, the energy density of the pulse laser is reduced. If the annealing is performed, the thermal energy stored in the semiconductor thin film immediately flows out, so that the activation time of the impurity is shortened and sufficient activation cannot be obtained.

That is, even in the case where the impurities implanted into the semiconductor thin film are activated by such an annealing process, the thermal conductivity on the side of the insulating substrate serving as a base layer of the semiconductor thin film can be reduced to reduce the thermal conductivity. It is desired to reduce the outflow rate of the stored thermal energy.

In the above methods (1) to (4), the heat insulating effect is enhanced by the structure provided between the semiconductor thin film and the insulating substrate in order to increase the crystal grain size of the semiconductor thin film. In the activation, it is considered that the outflow speed of the accumulated thermal energy is reduced due to the heat insulating effect, and the activation time can be increased to some extent.

Further, it is considered that this method cannot extend the activation time of impurities because the heat insulating effect is not so excellent as described above. further,
Also, the method described above is intended only to obtain a semiconductor crystal having a larger particle size, and thus it cannot be considered that the heat insulating effect of the entire inorganic insulating film is particularly excellent.

By the way, in the above-mentioned thin film transistor, a slight current called a leak current flows in a direction opposite to the pn junction of the thin film transistor at a reverse voltage lower than the breakdown voltage due to extra light irradiation. First, a phenomenon occurs in which a drain current is generated even when the gate voltage is 0V. Therefore, the on / off ratio of the current flowing through the thin film transistor becomes small, and the characteristics of the thin film transistor deteriorate. The deterioration of the characteristics of the thin film transistor adversely affects the driving of the pixels of the liquid crystal panel, and the image quality of a display image on the obtained liquid crystal panel also deteriorates.

Therefore, conventionally, a light-shielding film has been formed on a thin film transistor to block light irradiation and suppress the generation of the leak current. However, a step of further forming a light-shielding film is added to the manufacturing process of the thin film transistor, which makes the manufacturing process of the thin film transistor more complicated.

[0028]

In order to solve the above-mentioned problems, a method for manufacturing a thin film transistor according to the present invention comprises forming a heat-resistant polymer film on an insulating substrate, and forming the film on the heat-resistant polymer film. An insulating film is formed, a semiconductor thin film is formed on the insulating film, and the semiconductor thin film is irradiated with a laser to melt and crystallize the semiconductor thin film.

The thin film transistor of the present invention is characterized in that a heat-resistant polymer film is formed below a semiconductor thin film provided on an insulating substrate with an insulating film interposed therebetween.

The heat conductivity of the heat-resistant polymer film is 0.1 to
It is 0.3 W / m · K, which is very low as compared with the thermal conductivity of 1.51 W / m · K of quartz glass often used as an insulating substrate. Therefore, according to the above-described method and structure for manufacturing a thin film transistor, the semiconductor thin film is irradiated with a laser by irradiating the semiconductor thin film with the heat insulating effect of the heat-resistant polymer film provided between the insulating substrate and the insulating film. When the thin film is melted and crystallized, most of the thermal energy of the melted semiconductor thin film is accumulated in the insulating film, thereby lowering the solidification rate of the melted semiconductor thin film compared to conventional ones.
A thin film transistor including a semiconductor thin film having a larger semiconductor crystal grain size can be obtained.

At this time, the heat insulating effect of the above-mentioned heat-resistant polymer film is almost the same as that in the method of forming the cavity shown in the first and second embodiments, and the semiconductor having the same particle size as these. Crystals are obtained and have comparable properties.

However, as compared with the above method and the method described above, in the method for manufacturing a thin film transistor of the present invention, the heat-resistant polymer film functioning as a heat insulating material can be easily formed by coating on an insulating substrate. The manufacturing process is not complicated as in the case of the hollow portion in the above methods (1) to (4), and the manufacturing process can be simplified and the cost can be reduced.

According to the method of manufacturing a thin film transistor of the present invention, it is preferable that the activation of the impurity injected into the melted and crystallized semiconductor thin film is performed by laser irradiation.

According to this, when activating the impurities in the semiconductor thin film, the annealing temperature of the semiconductor thin film is suppressed to a lower temperature by setting the laser intensity to a lower value and performing the annealing process. Because of the heat insulating effect of the heat-resistant polymer film, the outflow of the thermal energy accumulated in the semiconductor thin film can be suppressed, so that the temperature of the semiconductor thin film is kept almost constant.

As a result, the annealing for activating the impurities can be performed at a low temperature of 600 ° C. or less for a long time, the crystallinity of the semiconductor thin film is maintained, and the impurities are removed from the intrinsic region of the semiconductor thin film. Can be suppressed and impurities can be efficiently activated.

According to the method of manufacturing a thin film transistor of the present invention, it is more preferable to use polyimide for the heat-resistant polymer film.

Among the heat-resistant polymers, polyimide is particularly excellent in heat resistance and has a heat deformation temperature of 306 ° C. or more.
The thermal conductivity is also 0.15 W / m · K, which is a very low value as compared with quartz glass, and functions as an excellent heat insulating material.
Therefore, by using the polyimide as the heat-resistant polymer film, the heat energy accumulated in the semiconductor thin film by the irradiation of the pulse laser is prevented from flowing out to the insulating substrate, and the annealing treatment is more effectively performed. be able to.

According to another method for manufacturing a thin film transistor of the present invention, it is more preferable to use a material having a light-shielding ability for the heat-resistant polymer film.

When a thin film transistor is used in an image display device, it is necessary to form a light-shielding film in order to suppress generation of a leak current due to light irradiation. The heat resistant polymer film can serve not only as a heat insulating material but also as a light shielding film.
Therefore, a step of providing a light-shielding film for the thin film transistor can be omitted, so that the manufacturing process of the thin film transistor can be simplified and the cost can be reduced.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment 1] An embodiment of the present invention will be described below with reference to FIGS. Note that the present invention is not limited by this. First, the structure of the thin film transistor according to the present embodiment will be described with reference to the cross-sectional view of FIG.

As shown in FIG. 1, in the thin film transistor of the present invention, a heat-resistant polymer film 2 is formed on a transparent insulating substrate 1.
(Having no light-shielding ability), an inorganic insulating film 3 is formed thereon, and a crystalline semiconductor thin film 6 is further formed thereon. This crystalline semiconductor thin film 6 has a source portion 6
s, a drain portion 6d, and an intrinsic region 6c.

A gate insulating film 7 is formed on the intrinsic region 6c of the crystalline semiconductor thin film 6, a gate electrode 8 is formed thereon, and a gate anodic oxide film 9 is further formed thereon. A gate section is configured.

Further, an inorganic insulating film 11 is formed on the crystalline semiconductor thin film 6 including the gate portion, and a source portion 6s and a drain portion of the crystalline semiconductor thin film 6 are formed on a part of the inorganic insulating film 11. Contact hole 12 is formed such that a part of contact hole 6d is exposed.
2, lead electrodes 13 s and 13 d serving as a source wiring and a drain wiring so as to be in contact with the source part 6 s and the drain part 6 d of the crystalline semiconductor thin film 6 through
Are formed.

Next, a method of manufacturing the thin film transistor shown in FIG. 1 will be described with reference to the sectional views of FIGS. 2 to 5 and the process chart of FIG. First, steps corresponding to processes (hereinafter simply abbreviated as P) 1 to P5 in FIG. 6 are shown in FIG.
This will be described with reference to (e).

In FIG. 2A, a heat-resistant polymer film 2 is applied to a thickness of 0.1 to 10 μm on a transparent insulating substrate 1 made of quartz, glass, or the like (P1). It is important that the heat-resistant polymer film 2 has a lower thermal conductivity than the insulating substrate 1.

It is preferable to use a polyimide film as the heat-resistant polymer film 2. Other than this, any film having high heat resistance and a lower thermal conductivity than the insulating substrate 1 may be used. . Further, the above heat-resistant polymer film 2
May be formed in an island shape as shown in FIG. 2A (island formation). Even without this islanding, the effects of the present invention are essentially guaranteed.

As shown in FIG. 2B, an inorganic insulating film 3 made of silicon oxide (SiO ₂ ) or silicon nitride (SiN _x ) is formed on the heat-resistant polymer film 2 to a thickness of 100 to 100 nm.
It is formed to have a thickness of 500 nm (P2). The above-mentioned inorganic insulating film 3 is formed by a normal pressure CVD method, a sputtering method, a low pressure CVD method.
Method, a plasma CVD method, or a remote plasma CVD method may be used.

As shown in FIG. 2C, an amorphous semiconductor thin film 4 is formed on the inorganic insulating film 3 by a plasma CVD method or a low pressure CVD method (P3). As the amorphous semiconductor thin film 4, a silicon semiconductor, a silicon-germanium semiconductor, a silicon semiconductor containing phosphorus or boron, or the like can be used. Further, a semiconductor thin film of not only amorphous but also microcrystalline or polycrystalline may be formed.

For the amorphous semiconductor thin film 4, FIG.
As shown in (d), the crystalline semiconductor thin film 6 made of a polycrystalline semiconductor is annealed by irradiating it with a pulse laser 5.
(P4). In the above laser annealing method, if a pulse laser having a short wavelength is used, the amorphous semiconductor thin film 4 can be efficiently annealed without damaging the transparent insulating substrate 1 as the underlying layer.

Examples of the short-wavelength pulse laser 5 include XeF (wavelength 351 nm) and XeCl (wavelength 30 nm).
8 nm), KrF (wavelength 249 nm), ArF (wavelength 1
Excimer laser such as 93 nm) can be used. In general, annealing a thin film made of an amorphous semiconductor results in a crystalline semiconductor thin film 6 having a large crystal grain size and good characteristics, compared to forming a thin film made of a crystalline semiconductor directly.

Here, when the amorphous semiconductor thin film 4 made of silicon is annealed by the pulse laser 5,
Although the melting temperature of the amorphous semiconductor thin film 4 reaches about 1000 ° C., the heat-resistant polymer film 2
The inorganic insulating film 3 having a certain degree of heat insulating effect is interposed therebetween, so that the thickness of the inorganic insulating film 3 is adjusted to suppress the degree of heat rise with respect to the heat-resistant polymer film 2, and the above heat resistance The surface of the conductive polymer film 2 on the semiconductor thin film 4 side is 1000
It can be protected from high temperatures approaching ° C.

Further, since the heat conductivity of the heat-resistant polymer film 2 is much lower than that of the inorganic insulating film 3, the temperature of the heat-resistant polymer film 2 as a whole may rise until it reaches melting. There is no. Therefore, the heat-resistant polymer film 2 can effectively function as a heat insulating material without being affected by the high temperature in the annealing treatment using the pulse laser 5 such as melting.

The obtained crystalline semiconductor thin film 6 was
As shown in (e), the crystalline semiconductor thin film 6 is islanded by patterning by etching (P5). At this time, the vertical and horizontal sizes of the crystalline semiconductor thin film 6 are formed so as to be equal to or smaller than the size of the heat-resistant polymer film 2 formed in the lower layer.

Next, steps corresponding to P6 to P9 in FIG. 6 will be described with reference to FIGS. A normal pressure CVD method, a sputtering method, a low pressure CVD method, a plasma CVD method are formed on the islanded crystalline semiconductor thin film 6.
Figure 3
As shown in (a), the gate insulating film 7 is formed to a thickness of 50 to 15 mm.
It is formed to have a thickness of 0 nm (P6). As the gate insulating film 7, silicon oxide, silicon nitride, aluminum oxide (Al ₂ O ₃ ), tantalum oxide (Ta ₂ O ₅ )
And the like, and a combination of these can also be used.

As shown in FIG. 3B, a gate electrode 8 is formed on the gate insulating film 7 by a sputtering method (P7). The gate electrode 8 may be made of tantalum or a metal containing aluminum such as aluminum, aluminum silicon, aluminum titanium, aluminum scandium, or the like. In particular, a metal containing aluminum is preferable because an electrode wiring with lower resistance can be formed.

The gate electrode 8 is anodically oxidized to obtain the structure shown in FIG.
As shown in (c), the gate anodic oxide film 9 is formed to a thickness of 0.0
It is formed to have a thickness of 5 to 1 μm (P8). Further, FIG.
As shown in (d), the gate insulating layer 7 is etched in a self-aligned manner by using the gate electrode 8 and the gate anodic oxide film 9 as a mask, thereby exposing portions of the crystalline semiconductor thin film 6 to become a source portion and a drain portion. (P9). For the above etching, wet etching using an etchant or dry etching using plasma can be used.

Next, steps corresponding to P10 to P12 in FIG. 6 will be described with reference to FIGS.
Impurity ions 10 are implanted into the crystalline semiconductor thin film 6 as shown in FIG. 4A (P10). Phosphorus and arsenic are implanted into an N-type and boron and the like are implanted into a P-type by an ion implanter utilizing plasma, thereby forming a source of the crystalline semiconductor thin film 6 into which the impurity ions 10 have been implanted. The part 6s and the drain part 6d are formed. Here, the portion of the crystalline semiconductor thin film 6 where the impurity ions 10 have not been implanted is hereinafter referred to as an intrinsic region 6c of the crystalline semiconductor thin film 6.

The crystalline semiconductor thin film 6 shown in FIG.
(B) As shown in FIG.
Or a pulse laser 5 whose energy density is reduced to a level at which the impurity ions 10 implanted into the source portion 6s and the drain portion 6d of the crystalline semiconductor thin film 6 are not electrically activated is irradiated. As a result, a dehydrogenation process for removing hydrogen contained in the source portion 6s and the drain portion 6d of the crystalline semiconductor thin film 6, the gate portion, and the like is performed (P11).

By performing the above dehydrogenation treatment, the amount of hydrogen contained in the source portion 6s and the drain portion 6d of the crystalline semiconductor thin film 6 is reduced to 5 × 10 ¹⁹ / cm ³ or less, preferably 5 × 10 ¹⁸ / cm 3. ³ or less.

The source 6s of the crystalline semiconductor thin film 6
In order to electrically activate the impurity ions 10 implanted into the drain portion 6d, as shown in FIG.
Irradiation is performed by irradiating the pulse laser 5 (P1
2). As the pulse laser 5 used for the above-mentioned purpose, a laser having a short wavelength is used, and the source 6s and the drain 6d of the crystalline semiconductor thin film 6 are not damaged without damaging the underlying transparent insulating substrate 1. Can be efficiently activated.

As the short-wavelength pulse laser 5 described above,
The same pulse laser 5 used in the annealing process for crystallizing the amorphous semiconductor thin film 4 can be used. At this time, the energy density of the pulse laser 5 is set lower than that in the case of crystallization of the semiconductor thin film 4 at P4 in FIG.

The pulse laser 5 having a low energy density and the heat insulating effect of the heat-resistant polymer film 2 provide
The annealing process of the crystalline semiconductor thin film 6 can be performed at a low temperature of 600 ° C. or less for a long time. Thereby, the impurity ions 10 implanted into the crystalline semiconductor thin film 6 are
Prevents the impurity ions 10 from diffusing from the source portion 6s or the drain portion 6d of the crystalline semiconductor thin film 6 to the intrinsic region 6c. Is activated.

Finally, steps corresponding to P13 to P15 in FIG. 6 will be described with reference to FIGS. 5 (a) to 5 (c). As shown in FIG. 5A, an inorganic insulating film 11 is formed on the crystalline semiconductor thin film 6 and the gate portion where the impurities are activated (P13). The inorganic insulating film 11 is
Atmospheric pressure CVD silicon oxide film or TEOS (Tetra-Ethyl-Ortho-Silicate, S
i (OC ₂ H ₅ ) ₄ ) A silicon oxide film formed by a normal pressure CVD method using a gas, a plasma CVD method, or a plasma CV
A silicon nitride film formed at 200 to 250 ° C. by Method D can be used.

As shown in FIG. 5B, a contact hole 12 is formed on the inorganic insulating film 11 (P14).
Finally, as shown in FIG. 5C, a metal thin film is formed on the inorganic insulating film 11 including the contact hole 12 by a sputtering method, and thereafter, is patterned by etching, thereby forming a lead electrode as a source wiring and a drain wiring. By forming 13s and 13d (P15), the thin film transistor of the present invention can be obtained.

Example An example of the above-described thin film transistor according to the present embodiment will be described below with reference to FIGS. First, the transparent insulating substrate 1
A 1.1 mm thick, 5 inch diagonal square glass plate was used, and polyimide was applied thereon as a heat resistant polymer film 2 to a thickness of 0.1 to 10 μm by spin coating. This heat-resistant polymer film 2 is shown in FIG.
The island is formed as shown in FIG.
As shown in (b), the inorganic insulating film 3 has a thickness of 100 to 50.
A 0-nm-thick silicon oxide film was formed by a normal pressure CVD method using monosilane (SiH ₄ ) gas and oxygen gas.

The above-mentioned inorganic insulating film 3 made of silicon oxide
2C, an amorphous semiconductor thin film 4 made of silicon was formed using a monosilane gas and a hydrogen gas at a substrate temperature of 200 to 300 ° C. by a plasma CVD method.

This amorphous semiconductor thin film 4 is compared with FIG.
The pulse laser 5 was irradiated as shown in (d). As the pulse laser 5, an XeCl (wavelength 308 nm) excimer laser was used, and 5 to 20 pulses of a pulse having a pulse half width of 40 ns and an energy density of 200 to 350 mJ / cm ² were irradiated. The amorphous semiconductor thin film 4 made of silicon was melted by the laser annealing method and then solidified to obtain a crystalline semiconductor thin film 6 made of polycrystalline silicon. Further, the crystalline semiconductor thin film 6
Was formed into islands smaller than the heat-resistant polymer film 2 made of polyimide as shown in FIG.

As shown in FIG. 3A, a gate insulating film 7 made of silicon oxide having a thickness of 50 to 150 nm was formed on the crystalline semiconductor thin film 6 made of silicon. The above-described gate insulating film 7 made of silicon oxide was formed by a normal pressure CVD method using a monosilane gas and an oxygen gas, but was formed using a TEOS gas having a good step coverage.
It may be formed by a VD method or a plasma CVD method.

As shown in FIG. 3B, a gate electrode 8 made of aluminum having a thickness of 200 to 500 nm was formed on the gate insulating film 7 by a sputtering method. By anodizing the gate electrode 8, a gate anodic oxide film 9 made of aluminum oxide having a thickness of 0.05 to 1 μm was formed as shown in FIG. The gate insulating film 7 is etched by self-alignment using the gate electrode 8 and the gate anodic oxide film 9 as a mask, and as shown in FIG. 3D, the source portion and the drain portion are formed in the crystalline semiconductor thin film 6 made of silicon. Was exposed.

As shown in FIG. 4A, a portion of the crystalline semiconductor thin film 6 serving as a source portion and a drain portion is ion-implanted using plasma, and phosphorus ions for N-type and P-type ions for N-type. In this case, boron ions are implanted, and the source portion 6 of the crystalline semiconductor thin film 6 made of silicon is implanted.
s and the drain portion 6d were formed.

The source 6 s of the crystalline semiconductor thin film 6 described above
4B, the source portion 6s and the drain portion 6d of the crystalline semiconductor thin film 6 are subjected to dehydrogenation treatment by performing thermal annealing at 300 to 500 ° C. in a nitrogen atmosphere as shown in FIG. Was done.

The dehydrogenated crystalline semiconductor thin film 6 is annealed by irradiating a pulse laser 5 as shown in FIG. 4C, and the source portion of the crystalline semiconductor thin film 6 made of silicon is formed. The impurity ions 10 implanted into 6s and the drain portion 6d were electrically activated. At this time, the XeCl (wavelength 308) is used as the pulse laser 5.
nm) excimer laser and pulse half width 40n
Irradiation was performed at 5 to 100 pulses with a pulse having an energy density of 100 to 300 mJ / cm ² .

On the crystalline semiconductor thin film 6 and the gate portion, as shown in FIG.
An inorganic insulating film 11 made of silicon oxide was formed to have a thickness of 0 to 500 nm.

As shown in FIG.
As described above, the contact hole 12 was formed so that the source part 6s and the drain part 6d of the crystalline semiconductor thin film 6 were partially exposed. Next, the source portion 6 of the crystalline semiconductor thin film 6 made of silicon is formed through the contact hole 12.
An aluminum film is formed by a sputtering method so as to be in contact with the drain electrode 6s and the drain portion 6d. The aluminum film is patterned by etching, and as shown in FIG. By forming 13d, a thin film transistor of the present invention was obtained.

As described above, in the thin film transistor according to the present embodiment, when compared with a thin film transistor having a heat insulating structure manufactured by a conventional method of forming an inorganic insulating film, a heat resistant structure provided on an insulating substrate is used. Due to the heat insulating effect of the conductive resin, the grain size of the silicon crystal in the crystalline semiconductor thin film made of silicon can be further increased.

In the method of manufacturing a thin film transistor according to the present invention, the obtained heat insulating effect is almost the same as that obtained by a conventional method of forming a cavity as a structure having a heat insulating effect. Since the heat-resistant polymer film exhibiting the effect can be easily formed by coating on the insulating substrate, the manufacturing process can be simplified and the cost can be reduced.

Further, in the above method, as compared with the conventional method, the impurity implanted into the crystalline semiconductor thin film made of silicon suppresses the impairment of the crystallinity of the semiconductor thin film, and the impurity is added to the intrinsic region. Suppresses the spread,
It is possible to effectively activate impurities.

[Embodiment 2] Another embodiment of the present invention will be described below with reference to FIG. For convenience of explanation, members having the same functions as the members described in the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted. In addition, the present invention is not limited by this.

In the thin film transistor according to the present embodiment, as shown in FIG. 7, a heat-resistant polymer film 2 'having a light-shielding ability is formed on a transparent insulating substrate 1, and an inorganic insulating film is formed thereon. 3 and a crystalline semiconductor thin film 6 is further formed thereon. The crystalline semiconductor thin film 6 has a source portion 6s, a drain portion 6d, and an intrinsic region 6c.
It has two areas.

A gate insulating film 7 is formed on the intrinsic region 6c of the crystalline semiconductor thin film 6, a gate electrode 8 is formed thereon, and a gate anodic oxide film 9 is further formed thereon. A gate section is configured.

Further, an inorganic insulating film 11 is formed on the semiconductor thin film 6 including the gate portion.
A contact hole 12 is formed in a part of the crystalline semiconductor thin film 6 so that a part of the source part 6s and part of the drain part 6d of the crystalline semiconductor thin film 6 are exposed. Leading electrodes 13s and 13d, which are source wiring and drain wiring, are formed so as to be in contact with source part 6s and drain part 6d.

As described above, the structure of the thin film transistor according to this embodiment is different from the thin film transistor shown in FIG. 1 in that the heat resistant polymer film 2 ′ having a light-shielding function is used instead of the heat resistant polymer film 2. They have the same structure except that they are provided.

The specific method of manufacturing the above-mentioned thin film transistor is described in P1 of FIG. 6 for forming the heat-resistant polymer film 2 ′.
As the heat-resistant polymer film 2 ', a color mosaic CK film (manufactured by Fuji Hunt), which is a black resin having a light-shielding ability as used in a resin black matrix (BM), is used. The same method can be used.

Since the thin film transistor having the above-described structure uses a color mosaic CK film which is a black polymer film as the heat-resistant polymer film 2 ', the heat-resistant polymer film 2' functions as a light-shielding film. However, the light applied to the thin film transistor could be blocked, as shown in FIG. 7, without forming a light shielding film. for that reason,
It was possible to protect the crystalline semiconductor thin film 6 and to suppress the occurrence of a leak current, and to obtain excellent characteristics. In addition, the grain size of the silicon crystal in the crystalline semiconductor thin film made of silicon is larger, so that the manufacturing process is simple and the cost can be reduced.

[0085]

According to the first aspect of the present invention, a method for manufacturing a thin film transistor comprises forming a heat-resistant polymer film on an insulating substrate and forming an insulating film on the heat-resistant polymer film as described above. Then, a semiconductor thin film is formed on the insulating film, and the semiconductor thin film is irradiated with a laser to melt and crystallize the semiconductor thin film.

The thin film transistor according to the fifth aspect of the present invention has a structure in which a heat-resistant polymer film is formed below a semiconductor thin film provided on an insulating substrate with an insulating film interposed therebetween.

The heat conductivity of the heat-resistant polymer film is very low compared to the heat conductivity of quartz glass, which is often used as an insulating substrate. Thereby, when the semiconductor thin film is irradiated with a laser to be melted and crystallized, almost the thermal energy of the melted semiconductor thin film is accumulated in the insulating film. Accordingly, the solidification rate of the semiconductor thin film is lower than that of the conventional semiconductor thin film, and a thin film transistor having a semiconductor crystal with a larger particle diameter in the semiconductor thin film can be obtained.

The heat insulating effect of the heat-resistant polymer film at this time is almost the same as that of the conventional method of forming a hollow portion, but the heat-resistant polymer film is formed on the insulating substrate. Can be easily formed by applying
The production process is not complicated as in the case of forming a cavity or the like, and the production process can be simplified and the cost can be reduced.

In the method of manufacturing a thin film transistor according to the second aspect of the present invention, in addition to the above structure, the activation of the impurity injected into the melted and crystallized semiconductor thin film is performed by laser irradiation.

In the above structure, the heat insulating property of the heat-resistant polymer film makes it possible to suppress the outflow of thermal energy accumulated in the semiconductor thin film irradiated with the laser. Thus, the annealing process for activating the impurities can be performed at a low temperature for a long time. This has the effect of maintaining the crystallinity of the semiconductor thin film and suppressing the diffusion of the impurity into the intrinsic region of the semiconductor thin film, thereby enabling effective activation of the impurity.

According to a third aspect of the present invention, there is provided a method of manufacturing a thin film transistor according to the first aspect.
In this configuration, polyimide is used for the heat-resistant polymer film.

Among the heat-resistant polymers having low thermal conductivity, the polyimide has particularly high heat resistance and functions as an excellent heat insulating material. Therefore, by using the polyimide as a heat-resistant polymer film, It is possible to prevent the thermal energy accumulated in the semiconductor thin film from flowing out to the insulating substrate by the irradiation of the pulse laser, so that the annealing can be more effectively performed.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a thin film transistor according to the first aspect.
The heat-resistant polymer film is made of a material having a light-shielding ability.

In the above configuration, the heat-resistant polymer film can serve not only as a heat insulating material but also as a light-shielding film.
Therefore, a step of providing a light-shielding film to suppress the occurrence of a leakage current in the thin film transistor can be omitted, and thus the manufacturing process of the thin film transistor can be simplified and the cost can be reduced. Play.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a structure of a thin film transistor according to one embodiment of the present invention.

FIGS. 2A to 2E are cross-sectional views illustrating a process of forming a heat-resistant polymer film and a crystalline semiconductor thin film in the process of manufacturing the thin film transistor.

FIGS. 3A to 3D are cross-sectional views illustrating a process of forming a gate portion on a crystalline semiconductor thin film in the process of manufacturing the thin film transistor.

FIGS. 4A to 4C are cross-sectional views illustrating a process of injecting an impurity into a crystalline semiconductor thin film and activating the same in a process of manufacturing the thin film transistor.

FIGS. 5A to 5C are cross-sectional views illustrating a process of forming an extraction electrode in a crystalline semiconductor thin film activated by implanting impurity ions in the manufacturing process of the thin film transistor.

FIG. 6 is a process chart showing a flow of an entire manufacturing process of the thin film transistor.

FIG. 7 is a cross-sectional view illustrating a structure of a thin film transistor according to another embodiment of the present invention.

[Description of Signs] 1 Insulating substrate 2 Heat-resistant polymer film having no light-shielding ability 2 'Heat-resistant polymer film having light-shielding ability 3 Inorganic insulating film 4 Amorphous semiconductor thin film 5 Pulse laser 6 Crystalline semiconductor thin film 6c Intrinsic region of crystalline semiconductor thin film 6d Drain portion of crystalline semiconductor thin film 6s Source portion of crystalline semiconductor thin film 7 Gate insulating film 8 Gate electrode 9 Gate anodic oxide film 10 Impurity ions 11 Inorganic insulating film 12 Contact hole 13d Drain wiring Lead electrode 13s Lead electrode as source wiring

Claims (5)

[Claims] 1. A heat-resistant polymer film is formed on an insulating substrate,
An insulating film is formed on the heat-resistant polymer film, a semiconductor thin film is formed on the insulating film, and the semiconductor thin film is irradiated with a laser to melt and crystallize the semiconductor thin film. A method for manufacturing a thin film transistor. 2. The method of manufacturing a thin film transistor according to claim 1, wherein the activation of the impurities injected into the melted and crystallized semiconductor thin film is performed by laser irradiation. 3. The method according to claim 1, wherein polyimide is used for the heat-resistant polymer film. 4. The method according to claim 1, wherein the heat-resistant polymer film is made of a material having a light-shielding ability. 5. A thin film transistor wherein a heat-resistant polymer film is formed under a semiconductor thin film provided on an insulating substrate with an insulating film interposed therebetween.