JP3468781B2 - Method for manufacturing thin film transistor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thin film transistor using polycrystalline silicon.

[0002]

2. Description of the Related Art In a polycrystalline silicon thin film transistor used in a liquid crystal display device, various methods are used to increase the mobility of polycrystalline silicon in a channel portion formed on an insulating substrate and improve its characteristics. There is. Here, in order to increase the mobility and improve the characteristics of polycrystalline silicon, it is necessary to increase the crystal grain size. For example, after ion-implanting silicon or the like to make it amorphous, solid-phase growth or laser irradiation by heat treatment is performed. For example, a method of growing larger crystal grains is adopted by crystallization, etc.

Further, generally, the structure of the polycrystalline silicon thin film transistor is a coplanar type, and a thermal oxide film is used as a gate insulating film. This thermal oxide film is formed by thermally oxidizing polycrystalline silicon, but it is difficult to control the film thickness of the thermal oxide film. That is, since the oxidation rate of polycrystalline silicon varies depending on the orientation of the crystal grains, the oxide film thickness differs for each crystal grain.

Thin film transistors are becoming smaller,
A thin film transistor in which the grain size of polycrystalline silicon is small is formed. When a thin film transistor having such a grain size of polycrystalline silicon is formed, there arises a problem that the characteristics vary depending on the orientation of crystal grains forming each transistor. FIG. 11 shows the variation of the threshold voltage of the polycrystalline silicon thin film transistor in the same substrate, which varies in the range of 4.0 to 6.5V.

Such a problem is caused by using polycrystalline silicon having a large crystal grain size. 7 to 10 show polycrystalline silicon formed on an insulating substrate. FIG. 7 shows a small crystal grain size, and FIG. 8 shows a large crystal grain size. 9 and 10 are respectively shown in FIG.
9 shows a state where the polycrystalline silicon shown in FIG. 8 is thermally oxidized. Then, in FIG. 9, a film having a small grain size is thermally oxidized, so that a small unevenness is formed, but the film is flattened as a whole. On the other hand, in FIG. 10, the thermally-oxidized crystal grains are large, and the unevenness after the oxide film is formed is also as large as the crystal grains.

[0006]

From the above results, it is understood that the problem of threshold voltage variation does not occur when the particle size is reduced. However, the mobility of a polycrystalline silicon thin film transistor is proportional to its crystal grain size, and reducing the grain size causes deterioration of transistor characteristics.

An object of the present invention is to provide a method for manufacturing a thin film transistor in which the thermal oxide film is made uniform without lowering the mobility of polycrystalline silicon.

[0008]

The present invention relates to a method of manufacturing a thin film transistor in which a thin film of polycrystalline silicon is used for an active layer, a thin film forming step of forming an amorphous silicon thin film on an insulating substrate, A patterning step of patterning the amorphous silicon thin film into a predetermined shape, and the amorphous silicon thin film is thermally oxidized at a thermal oxidation temperature of 800 ° C. or higher for a deposition time of 6 hours or less to form a thermal oxide film to be a gate insulating film. as well as, a thermal oxidation step of polycrystallizing the amorphous silicon thin film into a polycrystalline silicon thin film, a silicon Io
Is injected to amorphize the polycrystalline silicon thin film to
And amorphization process of the amorphous silicon thin film is obtained by and a recrystallization step of recrystallizing the amorphous sheet <br/> silicon thin film.

Further, in a method of manufacturing a thin film transistor in which a polycrystalline silicon thin film is used for an active layer, a thin film forming step of forming an amorphous silicon thin film on an insulating substrate, and forming the amorphous silicon thin film into a predetermined shape. A patterning step of patterning is performed, and the amorphous silicon thin film is thermally oxidized to form a thermal oxide film serving as a gate insulating film, and the amorphous silicon thin film is converted into a polycrystalline silicon thin film having a crystal grain size of 1 μm or less. a thermal oxidation step of crystallizing, Siri
Amorphous the polycrystalline silicon thin film by implanting conion
Amorphization process to form an amorphous silicon thin film,
And a recrystallization step of recrystallizing the amorphous silicon thin film.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The present invention, an amorphous silicon thin film is formed on an insulating substrate, gate insulating the amorphous silicon thin film by thermally oxidizing
A thermal oxide film to be an edge film is formed . Uniform thermal oxide film for the amorphous silicon thin film grain size when thermally oxidized is small Ru is formed. Further, by a large particle size by recrystallizing the amorphous silicon thin film, the interface between the recrystallization thermal oxide film maintaining flatness, increase the grain size by recrystallization,
Since the mobility of polycrystalline silicon can be increased to improve the characteristics, it is possible to obtain a thin film transistor having a small variation in threshold voltage and a high mobility. Further, by polycrystallizing the amorphous silicon thin film into a polycrystalline silicon thin film having a crystal grain size of 1 μm or less, the thermal oxide film thickness can be precisely controlled . Further, an amorphous silicon thin film thermal oxidation temperature 800 ° C.
As described above, the thermal oxidation temperature is lower than 800 ° C. or lower because the thermal oxidation film is formed by thermal oxidation in the film forming time of 6 hours or less.
Alternatively, the generation of a crystal film that occurs when the thermal oxidation time exceeds 6 hours is suppressed, the crystal grain size is maximized to exceed 1 μm, and the change in oxide film thickness is prevented.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to the manufacture of an n-channel MOS thin film transistor (TFT) shown in the drawings.

In FIG. 1, (a) shows amorphous silicon (amorphous silicon) 12 as a non-single-crystal silicon thin film on an insulating substrate 11 at a film forming temperature of 5 by an LP-CVD apparatus.
It shows a state in which 1700Å film is formed at 50 ° C. In addition,
The non-single-crystal silicon thin film is not limited to amorphous silicon, and polycrystalline silicon (p-Si) having a small grain size may be used. Further, FIG. 2 shows a state in which a polycrystalline silicon thin film having a small grain size is formed on the insulating substrate 11. To form a polycrystalline silicon thin film having this small grain size, LP-CV is used.
Direct film formation by D equipment or LP-CVD
An amorphous silicon thin film is formed by an apparatus, a plasma CVD apparatus, a sputtering apparatus, or the like, and heat-treated at a high temperature for a short time to recrystallize it into smaller crystal grains.

The amorphous silicon 12 thus formed is patterned into a predetermined island shape and then thermally oxidized at 900 ° C. in a dry oxygen atmosphere.

Further, as shown in FIG. 1B, the thermal oxide film 13
Is deposited to 500 Å. Amorphous silicon 12 is crystallized during the formation of this thermal oxide film 13, but becomes polycrystalline silicon 14 having a small grain size because of high temperature and short time. In other words, the polycrystalline silicon having a small grain size is in the same state as the thermally oxidized state, and the thermal oxide film 13 is formed to have a uniform film thickness. Further, FIG. 3 shows a state in which the polycrystalline silicon thin film having a small grain size shown in FIG. 2, which is a non-single-crystal silicon thin film, is thermally oxidized. Since the grain size is small, a uniform thermal oxide film 13 is formed. ing. Note that the polycrystalline silicon thin film having a small grain size is not thermally oxidized as described above, but an amorphous film formed on an insulating substrate by an LP-CVD apparatus, a plasma CVD apparatus, a sputtering apparatus, or the like as described above. By thermally oxidizing the silicon thin film as it is, and simultaneously performing solid phase growth at high temperature for a short time during the thermal oxidation, polycrystalline silicon 14 having a small grain size shown in FIG.
And a uniform thermal oxide film 13 may be obtained.

Here, the mobility is 3 as a property of polycrystalline silicon in which the thermal oxide film 13 is formed by thermal oxidation.
It is preferably 0 cm ² / Vsec or less and the crystal grain size is 1 μm or less. As long as these conditions are satisfied, there is no significant change in the thickness of the thermal oxide film 13 as described above.
13 Thickness can be precisely controlled.

The thermal oxidation conditions for obtaining the polycrystalline silicon 14 are preferably high temperature thermal oxidation for a short time, for example, 800 ° C. or higher and a film formation time of 6 hours or less. That is, if the thermal oxidation temperature is lower than 800 ° C,
This is because generation of crystal nuclei is suppressed, the crystal grain size is maximized to exceed 1 μm, and the oxide film thickness may be changed. Further, even if the thermal oxidation time exceeds 6 hours, the crystal grain diameter may exceed 1 μm and be maximized, and the thickness of the thermal oxide film 13 may change.

[0017] After this, the dose amount of silicon ions over the thermal oxide film 13 5 × 10 ¹⁵ pieces / cm ^2, implanted at an acceleration voltage 150 keV, completely amorphized channel polycrystalline silicon
To form an amorphous silicon thin film . And this is 600 ℃
Then, heat treatment is performed for 60 hours in the nitrogen atmosphere to recrystallize the silicon in the channel portion as shown in FIG. Since this heat treatment is performed at a relatively low temperature for a long time, it is recrystallized as large grain polycrystalline silicon 15.

[0018] Figure 4, the small particle size polycrystalline silicon 14 as shown in FIG. 3, implanting ions, such as silicon which does not affect the characteristics of the thin film transistor, amorphous and amorphous
It shows a state in which a silicon thin film is formed . Then, by subjecting the thus-amorphized material to a heat treatment at a temperature of about 600 ° C. for a long time, as shown in FIG. It is crystallized.

In order to recrystallize into a state of large grain size as shown in FIG. 5, not only the solid phase growth by the heat treatment as described above but also the state of FIG. May be crystallized by laser annealing or re-crystallized by rapid thermal annealing with infrared rays.

By any of the methods, the interface between the recrystallized polycrystalline silicon 15 and the thermal oxide film 13 maintains the same flatness as that of the thermally oxidized polycrystalline silicon 14 having a small grain size, and is recrystallized. As a result, the grain size can be increased, the mobility of the polycrystalline silicon 15 can be increased, and the characteristics can be improved.

By the steps up to this point, the thermal oxide film 13 having a uniform film thickness and the polycrystalline silicon 15 having a large particle diameter can be obtained, and the thermal oxide film can be obtained without lowering the mobility of the polycrystalline silicon thin film transistor. 13 can be made uniform.

In the subsequent steps, a normal n-channel M
This is the same as the manufacturing process of the OSTFT. That is, FIG.
As shown in (d), LP-CVD is used as the gate electrode 16.
The polycrystal silicon 15 was heated to 650 ° C at a temperature of 4,000 Å
A film is formed and patterned. Thereafter, as shown in FIG. 1 (e), in order to form the source and drain regions in a self-aligned manner, P ions are dosed by 1 × 10 5 by an ion implantation device.
¹⁶ pieces / cm ² and an acceleration voltage of 55 keV are injected.

Next, as shown in FIG. 1 (f), the interlayer insulating film 1
7, the silicon oxide film is formed by LP-CVD equipment.
This layer insulation film is formed at 4000 ℃ at 30 ℃.
A contact hole 18 is patterned in 17. afterwards,
As shown in FIG. 1 (g), in order to form an aluminum (Al) electrode 19, 7500 aluminum is sputtered by a sputtering device.
Å The n-channel MOSTFT manufacturing process is completed by forming a film and patterning.

FIG. 6 shows the variation of the threshold voltage of the polycrystalline silicon thin film transistor manufactured according to the above embodiment. As is clear from FIG. 6, the threshold voltage is 5.0 to
It is concentrated around 5.5V, and the variation is smaller than the variation of the conventional device in FIG. In addition, the field effect mobility of the transistor was 100 cm ² / Vsec when the above example was not used, but no change was observed in the above example.

In the above embodiment, an amorphous silicon thin film was used for the first layer of polycrystalline silicon 15. However, instead of this, polycrystalline silicon formed by an LP-CVD apparatus at 650 ° C. The same effect was obtained by using. Also, n
Although the channel MOSTFT has been described, it is also effective for the p-channel MOSTFT.

[0026]

According to the present invention, the gate insulating film can be formed without lowering the mobility of the polycrystalline silicon thin film transistor.
Since as possible out uniform thermal oxide film becomes, can be obtained with less variation TFT characteristics on the same substrate, a thin film transistor having, for example, small variations in the threshold voltage and high mobility. Further, the polycrystalline grain size of the crystalline silicon thin film by a 1μm or less, as possible out precisely control the thermal oxide thickness.

[Brief description of drawings]

FIG. 1 is a process drawing showing an embodiment of a method of manufacturing a thin film transistor according to the present invention.

FIG. 2 is an explanatory diagram showing one step of the above.

FIG. 3 is an explanatory diagram showing another process of the above.

FIG. 4 is an explanatory diagram showing another process of the above.

FIG. 5 is an explanatory diagram showing another process of the above.

FIG. 6 is a graph showing variations in threshold voltage of the polycrystalline silicon thin film transistor of the same.

FIG. 7 is an explanatory diagram illustrating a shape of polycrystalline silicon having a small grain size.

FIG. 8 is an explanatory diagram illustrating a large grain size shape of polycrystalline silicon.

FIG. 9 is an explanatory diagram illustrating the shape of a thermal oxide film having a small grain size of polycrystalline silicon.

FIG. 10 is an explanatory diagram illustrating the shape of a large-grain thermal oxide film of polycrystalline silicon.

FIG. 11 is a graph showing variations in threshold voltage of a conventional polycrystalline silicon thin film transistor.

[Explanation of symbols]

11 insulating board 13 thermal oxide films 14 and 15 of polycrystalline silicon

Continued front page       (56) References JP-A-56-88317 (JP, A)                 JP 62-39070 (JP, A)                 Japanese Patent Laid-Open No. 62-104021 (JP, A)                 JP-A-56-80126 (JP, A)                 JP-A-63-254720 (JP, A)                 JP-A-60-91623 (JP, A)                 JP 63-137412 (JP, A)                 JP-A-61-174621 (JP, A)

Claims (4)

(57) [Claims] 1. A method of manufacturing a thin film transistor, wherein a thin film of polycrystalline silicon is used for an active layer, a thin film forming step of forming an amorphous silicon thin film on an insulating substrate, and the amorphous silicon thin film having a predetermined shape. And a patterning step of patterning the amorphous silicon thin film at a thermal oxidation temperature of 800 ° C. or higher for a film formation time of 6 hours or less to form a thermal oxide film serving as a gate insulating film. A thermal oxidation step of polycrystallizing the thin film into a polycrystalline silicon thin film, and implanting silicon ions to remove the polycrystalline silicon thin film
A method of manufacturing a thin film transistor, comprising: an amorphization step of crystallizing an amorphous silicon thin film and a recrystallization step of recrystallizing the amorphous silicon thin film. 2. A method of manufacturing a thin film transistor using a polycrystalline silicon thin film as an active layer, comprising: a thin film forming step of forming an amorphous silicon thin film on an insulating substrate; and forming the amorphous silicon thin film into a predetermined shape. A patterning step of patterning, and the amorphous silicon thin film is thermally oxidized to form a gate insulating film.
That together form a thermal oxide film, wherein the amorphous silicon thin film thermal oxidation step of the grain size is polycrystalline below the polycrystalline silicon thin film 1 [mu] m, by implanting silicon ions to the polycrystalline silicon thin film non
A method of manufacturing a thin film transistor, comprising: an amorphization step of crystallizing an amorphous silicon thin film and a recrystallization step of recrystallizing the amorphous silicon thin film. 3. A thermal oxidation process, the amorphous silicon thin film thermal oxidation temperature 800 ° C. or higher, according to claim 2, wherein the thermally oxidized below the deposition time of 6 hours, and forming a thermal oxide film Method of manufacturing thin film transistor. 4. A thermal oxidation process, a thin film transistor manufacturing method according to any one of claims 1 to 3, characterized in that in a dry oxygen atmosphere.