JPH09186336A - Method of manufacturing thin film transistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the bottom gate type polysilicon thin film transistor. SOLUTION: A hydrogen containing true amorphous silicon thin film 25 and a channel protective film forming film 26 comprising a silicon nitride are continuously formed on the surface of the second insulating film 24. Next, the amorphous silicon film 25 is dehydrogenated by irradiating the film 25 with excimer laser in low density in the atmosphere and then the true amorphous silicon thin film 25 is polymerized to form a true polysilicon thin film 27. At this time, this step can be performed simply by changing the energy density of the excimer laser. Besides, after the formation of a channel protective film 26a, a source region 28a and a drain region 28b are formed of a formed n type silicon film. In such a case, both impurity implanting step and activating step can be eliminated.

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, and more particularly to a method of manufacturing a bottom gate type polysilicon thin film transistor.

[0002]

2. Description of the Related Art FIG. 3 shows a manufacturing process of a conventional bottom gate type polysilicon thin film transistor.
3D is a cross-sectional view in each state of the thin film transistor manufactured through the manufacturing process illustrated in FIG. 3. In manufacturing this thin film transistor, first, in the gate electrode forming step A shown in FIG.
As shown in FIG. 3, the gate electrode 2 is formed at a predetermined position on the upper surface of the glass substrate 1. Next, in a two-layer continuous film forming step B shown in FIG. 3, a gate insulating film 3 and an intrinsic amorphous silicon thin film 4 containing hydrogen are continuously formed on the entire upper surface of the glass substrate 1 including the gate electrode 2. Next, in the dehydrogenation step C shown in FIG. 3, in order to prevent hydrogen from bumping and causing defects when high energy is applied by excimer laser irradiation in a later step, heat treatment is performed in an electric furnace for dehydrogenation. By doing so, the hydrogen concentration in the amorphous silicon thin film 4 is reduced.

Next, in a polyizing step D shown in FIG. 3, by irradiating an excimer laser with a high energy density,
The intrinsic amorphous silicon thin film 4 is polyized to form an intrinsic polysilicon thin film 5. Next, in the impurity implantation step E shown in FIG. 3, as shown in FIG. 4B, an impurity implantation mask 6 is formed on a region of the polysilicon thin film 5 which will be the channel region 5a, and the polysilicon thin film 5 is formed. An n-type impurity such as phosphorus is implanted into the entire region except the channel region 5a. After that, the impurity implantation mask 6 is peeled off.
Next, in the activation step F shown in FIG. 3, the n-type impurity implantation region is activated by irradiating the excimer laser with a low energy density. Next, in a channel protective film forming step G shown in FIG. 3, as shown in FIG. 4C, a channel protective film 7 is formed on a region of the polysilicon thin film 5 which will be the channel region 5a.

Next, in a device area forming step H shown in FIG. 3, an unnecessary portion of the polysilicon thin film 5 is removed as shown in FIG. 4 (D). In this state, the central portion of the polysilicon thin film 5 is a channel region 5a made of an intrinsic region, and both sides thereof are a source region 5b and a drain region 5c made of an n-type impurity implantation region.
Next, in the source / drain electrode forming step I shown in FIG. 3, both sides of the upper surface of the channel protective film 7 and the source region 5 are formed.
b, the source electrode 8 and the drain electrode 9 are formed on each upper surface of the drain region 5c. Next, in the overcoat film forming step J shown in FIG. 3, the overcoat film 10 is formed on the entire upper surface. Next, in a hydrogenation step K shown in FIG. 3, dangling bonds of the polysilicon thin film 5 are reduced by performing a hydrogenation process in an electric furnace for hydrogenation or a plasma furnace for hydrogenation. Thus, a bottom gate type polysilicon thin film transistor is manufactured.

[Problems to be Solved by the Invention]

By the way, in the conventional method for manufacturing the bottom gate type polysilicon thin film transistor, as compared with the conventional method for manufacturing the same type, that is, the bottom gate type amorphous silicon thin film transistor, the dehydrogenation step C and the polysiliconization step are performed. Since D, the impurity injection step E, the activation step F and the hydrogenation step K are added, there is a problem that the manufacturing process is complicated. In this case, in particular, since the dehydrogenation electric furnace for the dehydrogenation step C and the excimer laser device for the polyprocessing step D and the activation step F are separate apparatuses, the manufacturing process becomes complicated, It is also a factor of increasing capital investment. An object of the present invention is to simplify the manufacturing process and reduce the equipment investment.

[0006]

According to the present invention, in a method of manufacturing a thin film transistor using polysilicon having a source, a drain, and a channel region as an active semiconductor layer, a hydrogenated amorphous silicon film is irradiated with an excimer laser as a previous irradiation region. A scan scan for irradiation with 50% or more overlap is performed over the entire region to dehydrogenate and poly-ize the hydrogenated amorphous silicon film.

According to the present invention, the hydrogenated amorphous silicon film is irradiated with the excimer laser by 50% from the previous irradiation area.
By performing the scanning scan with overlapping irradiation, the dehydrogenation step and the polycondensation step can be performed at the same time. Therefore, the manufacturing process can be simplified, and the capital investment can be reduced accordingly. be able to.

[0008]

FIG. 1 shows a manufacturing process of a bottom gate type polysilicon thin film transistor in one embodiment of the present invention, and FIGS. 2 (A) to 2 (C) are respectively manufactured through the manufacturing process shown in FIG. 7A to 7C are cross-sectional views of the thin film transistor in each state. In manufacturing this thin film transistor, first, in a gate electrode forming step A shown in FIG. 1, as shown in FIG. 2A, a gate electrode 22 made of an aluminum-titanium alloy is formed at a predetermined position on the upper surface of a glass substrate 21. To do. Next, in the anodizing step B shown in FIG. 1, by performing anodizing treatment, the first gate insulating film 23 made of aluminum oxide is formed on the surface of the gate electrode 22. Next, as shown in FIG.
In the layer continuous film forming step C, PE-CVD is performed on the entire upper surface of the glass substrate 21 including the first gate insulating film 23 by PE-CVD.
A second gate insulating film 24 made of silicon nitride, an intrinsic amorphous silicon thin film 25 containing hydrogen, and a channel protective film forming film 26 made of silicon nitride are continuously formed.

Next, the dehydrogenation / polyization step D shown in FIG.
In this case, the channel protective film forming film 2 is formed on the hydrogen-containing intrinsic amorphous silicon thin film 25.
Since the film 6 is formed, the dehydrogenation process of the hydrogen-containing intrinsic amorphous silicon thin film 25 can be performed by irradiating an excimer laser having a low energy density in the atmosphere. Therefore, first, when the excimer laser is irradiated with a low energy density in the atmosphere at, for example, about 60 to 150 mJ / cm ² , the hydrogen concentration in the amorphous silicon thin film 25 is reduced, and then the excimer laser is similarly irradiated with a high energy density in the atmosphere, for example. 150-300 mJ / cm
^{When the} irradiation is performed at about ² , the intrinsic amorphous silicon thin film 25 is polyized to form an intrinsic polysilicon thin film 27. As described above, the dehydrogenation step and the polycrystallization step can be continuously performed only by changing the energy density of the excimer laser, so that the manufacturing process can be simplified.

By the way, the irradiation of the excimer laser in the dehydrogenation / polyization process D is performed by scanning irradiation with the laser beam in the form of a narrow strip having a short beam size while overlapping in the width direction of the beam size. To do. In this case, it is important to set the overlap amount to preferably 50% or more, more preferably 90 to 99%. Further, the irradiation of the excimer laser is performed by increasing the low energy density and the high energy density twice or more, preferably by gradually increasing the energy density from the low energy density, for example, by increasing the energy density by about 10 to ²⁰ mJ / cm ^2. It may be performed more than once. Scan As the scanning method,
The scan density is gradually increased in one region to irradiate the excimer laser a plurality of times, and then the scan scanning is performed to shift the region so that it overlaps with the one region by 50% or more and irradiate the excimer laser. There are a method and a method of irradiating the excimer laser with a low energy density over the entire region by scan scanning and then increasing the energy density and irradiating the excimer laser again over the entire region. Note that lamp irradiation may be performed instead of excimer laser irradiation.

Next, in the channel protective film forming step E shown in FIG. 1, as shown in FIG. 2B, unnecessary portions of the channel protective film forming film 26 are removed,
A channel protection film 26a is formed at a predetermined position on the polysilicon thin film 27. Next, in an n-type silicon film forming step F shown in FIG. 1, an n-type silicon film 28 doped with phosphorus or the like is formed by PE-CVD on the entire upper surface of the polysilicon thin film 27 including the channel protective film 26a. Next, in the device area forming step G shown in FIG.
As shown in (C), unnecessary portions of the n-type silicon film 28 are removed to remove the source region 28a and the drain region 2.
8b is formed, and unnecessary portions of the polysilicon thin film 27 are removed to form a channel region 27a.
That is, the source region 28a and the drain region 28b are formed on both upper surfaces of the channel protective film 26a and on each upper surface of the channel region 27a on both sides thereof. In this case, the channel region 27a is made of intrinsic polysilicon,
The source region 28a and the drain region 28b are made of n-type silicon. As described above, since the source region 28a and the drain region 28b are formed by the formed n-type silicon film, the impurity implantation step and the activation step are unnecessary, and thus the manufacturing process can be simplified. it can. The source region 28a and the drain region 28b may be made of n-type amorphous silicon or n-type polysilicon.

Next, in a source / drain electrode forming step H shown in FIG. 1, a first source electrode 29 and a first drain electrode 30 made of chromium are formed on the respective upper surfaces of the source region 28a and the drain region 28b. Subsequently, a second source electrode 31 and a second drain electrode 32 made of an aluminum-titanium alloy are formed on each upper surface thereof. Next, in the overcoat film forming step I shown in FIG.
An overcoat film 33 is formed on the entire upper surface. Next, FIG.
In the hydrogenation step J shown in (1), the dangling bond in the channel region 27a, the source region 28a, and the drain region 28b is reduced by performing the hydrogenation treatment in the hydrogenation electric furnace or the hydrogenation plasma furnace. Thus,
A bottom gate type polysilicon thin film transistor is manufactured.

By the way, when the manufacturing process shown in FIG. 1 is compared with the manufacturing process of the conventional bottom gate type polysilicon thin film transistor, only the dehydrogenation / polyization process D and the hydrogenation process J are added. Therefore, an excimer laser device for the dehydrogenation / polyization process D and an electric furnace for hydrogenation or a plasma furnace for hydrogenation for the hydrogenation process J are added to the conventional bottom gate type polysilicon thin film transistor manufacturing process line. In addition, the thin film transistor of the present invention can be manufactured by slightly changing the manufacturing process line of the conventional bottom gate type polysilicon thin film transistor and using it as it is. The present invention can also be applied to a p-type polysilicon thin film transistor.

[0014]

As described above, according to the present invention, the dehydrogenation step is performed by the scan scanning in which the hydrogenated amorphous silicon film is irradiated with the excimer laser so as to overlap with the irradiation region of the previous time by 50% or more. It is possible to carry out the polycondensation process at the same time, and therefore, the manufacturing process can be simplified, and accordingly, the capital investment can be reduced.

[Brief description of the drawings]

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

2A to 2C are cross-sectional views in each state of a thin film transistor manufactured through the manufacturing process shown in FIG.

FIG. 3 is a diagram showing a manufacturing process of a conventional thin film transistor.

4A to 4D are cross-sectional views of a thin film transistor manufactured through the manufacturing process shown in FIG. 3 in various states.

[Explanation of symbols]

 22 gate electrode 23 first gate insulating film 24 second gate insulating film 25 amorphous silicon thin film 26 channel protective film forming film 26a channel protective film 27 polysilicon thin film 27a channel region 28 n-type silicon film 28a source region 28b drain region 29th 1 Source Electrode 30 First Drain Electrode 31 Second Source Electrode 32 Second Drain Electrode

Claims (6)

[Claims] 1. A method of manufacturing a thin film transistor using polysilicon having a source, drain, and channel regions as an active semiconductor layer, wherein a hydrogenated amorphous silicon film is irradiated with an excimer laser so as to overlap with a previous irradiation region by 50% or more. A method of manufacturing a thin film transistor, characterized in that the hydrogenated amorphous silicon film is dehydrogenated and poly-processed by performing a scan scan to the whole area. 2. The method of manufacturing a thin film transistor according to claim 1, wherein the excimer laser is overlapped with the previous time by 90% or more. 3. The invention according to claim 1, wherein the excimer laser has an elongated strip beam shape having a short width,
A method of manufacturing a thin film transistor, which comprises scanning in the width direction of the strip beam. 4. The method of manufacturing a thin film transistor according to claim 1, further comprising irradiating an excimer laser a plurality of times and then performing scan scanning. 5. The method of manufacturing a thin film transistor according to claim 4, wherein the irradiation of the excimer laser a plurality of times has the lowest energy density at the beginning. 6. The method of manufacturing a thin film transistor according to claim 1, wherein after scanning and scanning the entire region, the energy density is made higher than in the first scanning and scanning is performed again by irradiating the excimer laser.