JP2000068518A - Manufacture of thin-film transistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a thin-film transistor, which can manufacture a thin-film transistor of top-gate structure having excellent characteristics on an insulating substrate having a low heat-resisting temperature such as a plastic substrate. SOLUTION: After a polycrystal Si film 15 is formed on a plastic substrate 11 through a buffer layer 12, a gate electrode 18 comprising an Si film is formed on the film 15. By introducing impurities into the polycrystal film 15 with the gate electrode 18 as a mask, a source region 19 and a drain region 20 are formed. From the upper side of the gate electrode 18, an ultraviolet pulse-laser beam 21 by excimer laser is applied. The gate electrode 18 is locally heated, and a gate insulating film 16 undergoes heat treatment. At the same time, the impurities in the gate electrode 18, the source region 19 and the drain region 20 are electrically made active.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thin film transistor, and more particularly to a method for manufacturing a thin film transistor (TFT) having a so-called top gate structure on a substrate having low heat resistance.

[0002]

2. Description of the Related Art In recent years, polycrystalline silicon (Si) TFTs formed on a glass substrate have been used for pixels and drivers in liquid crystal displays. This polycrystalline Si
TFTs also hold promise for use in semiconductor memories. However, the characteristics of the polycrystalline SiTFT are still insufficient at present, and further improvement in characteristics is required.

When a polycrystalline Si TFT is manufactured on a glass substrate, a silicon dioxide (SiO ₂ ) film used as a gate insulating film is formed at a low temperature of about 400 ° C. or less due to the heat resistance temperature of the glass substrate. There is a need to. Further, when a plastic substrate having a lower heat-resistant temperature is used, it is necessary to lower the deposition temperature of the SiO ₂ film to about 200 ° C. or less.

[0004]

However, when an SiO ₂ film as a gate insulating film is formed at a temperature of 200 ° C. or less, the obtained SiO ₂ film has a poor film quality including a large number of defects, and has a low active property. The characteristics of the interface with the polycrystalline Si film as a layer are also poor. After the formation of this SiO ₂ film, 400
Defects in the interface between the defect and the SiO ₂ film and the polycrystalline Si film in the SiO ₂ film is removed by at ℃ about temperatures above heat treatment is performed, the SiO ₂ film quality and SiO ₂ film and the polycrystalline S
Although it is possible to improve the characteristics of the interface with the i-film,
This is not possible when using a plastic substrate having a heat-resistant temperature of about 200 ° C. or less. For these reasons,
Heretofore, it has not been possible to manufacture a polycrystalline SiTFT having good characteristics on a plastic substrate.

Accordingly, an object of the present invention is to provide a method of manufacturing a thin film transistor capable of manufacturing a thin film transistor having a good top gate structure on an insulating substrate having a low heat resistance temperature such as a plastic substrate.

[0006]

Means for Solving the Problems The present inventor has made intensive studies in order to solve the above-mentioned problems of the prior art. The outline is described below.

The present inventor prepared a sample as shown in FIG. 1 and measured the CV (capacitance-voltage) characteristics in order to evaluate the quality of the SiO ₂ film used as the gate insulating film. As shown in FIG. 1, this sample was prepared by forming a SiO ₂ film 2 on a conductive Si substrate 1 by reactive sputtering at a substrate temperature of 200 ° C. in an atmosphere in which oxygen (O ₂ ) was introduced into helium (He). Is formed, and an electrode 3 is formed thereon.
And an electrode 4 is formed on the back surface of the Si substrate 1. FIG. 2 shows the results of measuring CV characteristics using this sample. The measurement frequency is 10 kHz.
As is clear from FIG. 2, the CV characteristics are shifted, and the shape of the curve is not good. This is because the SiO ₂ film 2 formed at a low temperature of 200 ° C. contains a lot of defects, and the SiO ₂ film 2
This is because the interface with the i-substrate 1 is also damaged.

[0008] Therefore, the present inventors, in order to improve the quality of after forming the SiO ₂ film, as shown in FIG. 3, SiO ₂
A silicon (Si) film 5 is formed on the film 2 by sputtering.
The Si film 5 was plasma-doped with impurities, and the Si film 5 was irradiated with an ultraviolet pulsed laser beam from an excimer laser at an energy density of 280 mJ / cm ² . Then, as shown in FIG. 4, the electrode 3 was formed on the Si film 5 and the electrode 4 was formed on the back surface of the Si substrate 1, and the CV characteristics of this sample were measured. FIG. 5 shows the measurement results of the CV characteristics. As is apparent from FIG. 5, rather than shifting the C-V characteristics, the shape of the curve is also good, the SiO ₂ film 2 film quality and the SiO ₂ film 2 and S
It can be seen that the characteristics of the interface with the i-substrate 1 are greatly improved. This is because the heat treatment of the SiO ₂ film 2 is performed by the Si film 5 heated by the irradiation of the pulse laser beam,
Presumably because defect at the interface between the defect and the SiO ₂ film 2 and the Si substrate 1 of SiO ₂ film 2 is removed.

As described above, the Si film 5 is formed on the SiO ₂ film 2, and the Si film 5 is irradiated with a pulsed laser beam and heated, and the SiO ₂ film 2 is subjected to a heat treatment, thereby obtaining the Si film 5.
The quality of the O ₂ film 2 and the characteristics of the interface between the SiO ₂ film 2 and the Si substrate 1 can be improved. Further, according to this method, since only the Si film 5 can be locally heated, the substrate is hardly heated, so that a substrate having a low heat-resistant temperature such as a plastic substrate can be used. Further, since the Si film 5 is used as a material for the gate electrode, it can be easily applied to a normal polycrystalline SiTFT manufacturing process.

The present invention has been devised based on the above-described study by the present inventors.

In other words, in order to achieve the above object, the present invention provides a method of forming a semiconductor thin film to be an active layer and a gate insulating film sequentially on an insulating substrate, and a step of forming a heating member on the gate insulating film. Irradiating, from above the heating member, an energy beam whose energy is absorbed by the heating member.

In the present invention, the gate insulating film is typically a silicon oxide (SiO ₂ ) film or a silicon nitride (SiN _x ) film. Further, the heating member formed on the gate insulating film is typically a gate electrode, but in some cases, a heating member different from the gate electrode (for example,
(A metal or the like) may be formed, the heating member may be removed after the irradiation with the energy beam, and then the gate electrode may be formed. This gate electrode is most typically a silicon film. In addition, typically, after a source region and a drain region are formed by doping a semiconductor thin film with impurities using a gate electrode as a mask, an energy beam is irradiated. By doing so, the quality of the gate insulating film and the characteristics of the interface between the gate insulating film and the semiconductor thin film can be improved by heating the gate electrode, and impurities in the gate electrode, the source region, and the drain region can be improved. Electrical activation can be achieved. In the case where a silicon film containing hydrogen is used, heating by the energy beam irradiation causes not only the effect of the heat treatment but also the diffusion of hydrogen from the silicon film into the semiconductor thin film serving as an active layer. By inactivating the dangling bonds therein, the electrical characteristics of the semiconductor thin film can be improved.

In the present invention, any energy beam may be used as long as the energy can be absorbed by the heating member or the gate electrode. In addition, a charged particle beam, for example, an electron beam or an ion beam can be used. Further, from the viewpoint of preventing the insulating substrate from being heated,
A pulsed energy beam is used. Semiconductor thin film
Most typically, it is a polycrystalline silicon film. Further, as the insulating substrate, a plastic substrate or a glass substrate whose heat-resistant temperature is 200 ° C. or lower can be used.

In the present invention configured as described above, the heating member is locally heated by the irradiation of the energy beam, and the interface between the gate insulating film and the gate insulating film and the semiconductor thin film is formed by the heated heating member. As a result of local heating and heat treatment, defects in the gate insulating film and defects at the interface between the gate insulating film and the semiconductor thin film are removed. Therefore, for example, even if the gate insulating film is formed at a temperature of 200 ° C. or less, the quality of the gate insulating film after the energy beam irradiation and the interface between the gate insulating film and the semiconductor thin film are good. As a result, the heat resistance temperature of the insulating substrate is 200 ° C.
Even if the following plastic substrate or the like is used, a thin film transistor with favorable characteristics can be manufactured.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIGS. 6 to 12 show a method of manufacturing a polycrystalline Si TFT having a top gate structure according to an embodiment of the present invention.

In this embodiment, first, as shown in FIG. 6, a buffer layer made of, for example, an SiO ₂ film, a SiN _x film, or a laminated film thereof is formed on a plastic substrate 11 having a heat-resistant temperature of about 200 ° C. or less. The film 12 is formed at a temperature lower than the heat resistant temperature of the plastic substrate 11. Here, as the plastic substrate 11, for example, a substrate made of polyethylene sulfone (PES) (heat resistance temperature is about 200 ° C.), polyethylene terephthalate (PET) (heat resistance temperature is about 100 ° C.), or the like can be used. Next, an amorphous S
An i (a-Si) film 13 is formed at a temperature equal to or lower than the allowable temperature limit of the plastic substrate 11. The thickness of the a-Si film 13 is, for example, 30 to 100 nm. These buffer layers 1
2 and the a-Si film 13 are formed, for example, by a plasma enhanced CVD (PECVD) method or a low pressure CVD (L
A PCVD) method, an evaporation method, or the like can be used.

Next, the a-Si film 13 is crystallized by irradiating an ultraviolet pulse laser beam 14 with, for example, an excimer laser and heating (laser annealing).
As shown in FIG. 7, a polycrystalline Si film 15 is formed. This polycrystalline Si film 15 becomes an active layer. Since the pulse laser beam 14 is almost completely absorbed by the a-Si film 13, the plastic substrate 11 is hardly heated. Here, as the excimer laser, for example, Xe
A Cl excimer laser (wavelength 308 nm), a XeF excimer laser (wavelength 351 nm), a KrF excimer laser (wavelength 248 nm), an ArF excimer laser (wavelength 193 nm), or the like can be used.

Next, as shown in FIG.
A gate insulating film 16 made of, for example, an SiO ₂ film or a SiN _x film is formed on the plastic substrate 11 at a temperature equal to or lower than the allowable temperature limit of the plastic substrate 11. The thickness of the gate insulating film 16 is, for example, about 100 nm. The gate insulating film 16 may be formed by a reactive sputtering method, a PECVD method, an evaporation method, or the like, or may be formed by plasma oxidizing or plasma nitriding the surface of the polycrystalline Si film 15. Next, a gate electrode forming a is formed on the gate insulating film 16.
-Forming the Si film 17 at a temperature equal to or lower than the heat resistant temperature of the plastic substrate 11; For forming the a-Si film 17, a sputtering method, a PECVD method, an LPCVD method, an evaporation method, or the like can be used.

Next, as shown in FIG. 9, after the a-Si film 17 is patterned into a predetermined shape by lithography and etching to form a gate electrode 18, the gate insulating film 16 is formed by using the gate electrode 18 as a mask. The gate electrode 18 is etched in a self-aligned manner.

Next, as shown in FIG. 10, an impurity is doped into the polycrystalline Si film 15 by using the gate electrode 18 as a mask by a plasma doping method or an ion implantation method at a temperature lower than the allowable temperature limit of the plastic substrate 11. , A source region 19 and a drain region 20 are formed in a self-aligned manner with respect to the gate electrode 18. Here, as an impurity, an n-type impurity such as phosphorus (P) is used when manufacturing an n-channel polycrystalline SiTFT, and a p-type impurity such as boron (B) is used when manufacturing a p-channel polycrystalline SiTFT. Is used.

Next, as shown in FIG. 11, an impurity in the gate electrode 18, the source region 19 and the drain region 20 is electrically activated by irradiating an ultraviolet pulse laser beam 21 by, for example, an excimer laser. At the same time, the gate insulating film 16 and the interface between the gate insulating film 16 and the polycrystalline Si film 15 are heated and heated by the heated gate electrode 18, and defects in the gate insulating film 16 and the polycrystalline silicon Defects at the interface with the Si film 15 are removed. Further, by the irradiation of the pulse laser beam 21, the a-Si film 17 constituting the gate electrode 18 is crystallized to become a polycrystalline Si film. Since the pulse laser beam 21 is almost completely absorbed by the gate electrode 18, the plastic substrate 11 is hardly heated. As the excimer laser, the same one as described above can be used. Furthermore, a for forming the gate electrode 18
-When a film containing hydrogen is used as the Si film 17,
At the time of heating by irradiation with the pulsed laser beam 21, hydrogen in the Si film forming the gate electrode 18 diffuses into the polycrystalline Si film 15 and dangling existing at crystal grain boundaries in the polycrystalline Si film 15 and the like. By inactivating the bond, electrical characteristics can be improved.

Next, as shown in FIG.
9 and the source electrode 22 on the drain region 20 respectively.
And a drain electrode 23 are formed. The source electrode 22 and the drain electrode 23 are formed of, for example, aluminum (Al). The source electrode 22 and the drain electrode 23 may be formed by forming an Al film on the entire surface of the substrate by, for example, an evaporation method or a sputtering method, and then patterning the Al film into a predetermined shape by lithography and etching. Alternatively, it may be formed by a lift-off method.

As described above, on the plastic substrate 11,
A polycrystalline Si TFT having a top gate structure is manufactured.

As described above, according to this embodiment,
Polycrystalline S at a temperature lower than the heat resistant temperature of the plastic substrate 11
Since the gate insulating film 16 and the gate electrode 18 are formed on the i film 15 and the source region 19 and the drain region 20 are formed in the polycrystalline Si film 15 and then the pulse laser beam 21 is irradiated, the following process is performed. Advantages can be obtained. That is, the gate electrode 18 is heated by irradiation with the pulsed laser beam 21 to heat-treat the gate insulating film 16 and the interface between the gate insulating film 16 and the polycrystalline Si film 15. Defects in the formed gate insulating film 16 of poor quality or the gate insulating film 1
6 can be modified by removing defects at the interface between the gate insulating film 16 and the polycrystalline Si film 15 to improve the quality of the gate insulating film 16 and the characteristics of the interface between the gate insulating film 16 and the polycrystalline Si film 15. be able to. As a result, the polycrystalline S having good characteristics is formed on the plastic substrate 11 having a heat resistant temperature of about 200 ° C. or less.
An iTFT can be manufactured. Further, by irradiating the pulsed laser beam 21, the electrical activation of the impurities in the gate electrode 18, the source region 19, and the drain region 20 can be simultaneously performed, so that the process for electrically activating the impurities is separately performed. And the increase in the number of manufacturing steps can be suppressed.

As described above, one embodiment of the present invention has been specifically described. However, the present invention is not limited to the above-described embodiment, and various modifications based on the technical idea of the present invention are possible. is there.

For example, the numerical values, processes, materials, structures, and the like described in the above-described embodiment are merely examples, and different numerical values, processes, materials, structures, and the like may be used as needed.

Specifically, for example, in the above-described embodiment, an Al film is also formed on the gate electrode 18 when the source electrode 22 and the drain electrode 23 are formed so that the resistance of the gate electrode 18 is reduced. You may.

[0029]

As described above, according to the present invention,
A heating member is formed on the gate insulating film, and an energy beam whose energy is absorbed by the heating member is irradiated from above the heating member. Therefore, the heating member is locally heated without heating the substrate. The gate insulating film is heat-treated by the heated member to remove defects in the gate insulating film and defects at the interface between the gate insulating film and the semiconductor thin film. In addition, the characteristics of the interface between the gate insulating film and the semiconductor thin film can be improved. Accordingly, a thin film transistor having a top gate structure with favorable characteristics can be manufactured over an insulating substrate such as a plastic substrate having a low heat resistance temperature.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a sample used for measuring CV characteristics.

FIG. 2 is a schematic diagram illustrating measurement results of CV characteristics.

FIG. 3 is a cross-sectional view showing a sample used for measuring CV characteristics.

FIG. 4 is a cross-sectional view showing a sample used for measuring CV characteristics.

FIG. 5 is a schematic diagram illustrating measurement results of CV characteristics.

FIG. 6 is a cross-sectional view for explaining a method of manufacturing a polycrystalline SiTFT having a top gate structure according to one embodiment of the present invention.

FIG. 7 is a cross-sectional view for explaining a method for manufacturing a polycrystalline SiTFT having a top gate structure according to one embodiment of the present invention.

FIG. 8 is a cross-sectional view for explaining a method for manufacturing a polycrystalline SiTFT having a top gate structure according to one embodiment of the present invention.

FIG. 9 is a cross-sectional view for explaining a method of manufacturing a polycrystalline Si TFT having a top gate structure according to one embodiment of the present invention.

FIG. 10 is a cross-sectional view for explaining a method for manufacturing a polycrystalline SiTFT having a top gate structure according to one embodiment of the present invention.

FIG. 11 is a cross-sectional view for explaining a method of manufacturing a polycrystalline Si TFT having a top gate structure according to one embodiment of the present invention.

FIG. 12 is a cross-sectional view for explaining a method for manufacturing a polycrystalline SiTFT having a top gate structure according to one embodiment of the present invention.

[Explanation of symbols]

11: plastic substrate, 12: buffer layer,
13, 17: a-Si film, 14, 21: pulsed laser beam, 15: polycrystalline Si film, 16: gate insulating film, 18: gate electrode, 19: source Region, 20: drain region, 22: source electrode, 23: drain electrode

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takashi Noguchi 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Westwater Jonathan 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo No. Sony Corporation (72) Inventor Setsuo Usui 6-7-35 Kita Shinagawa, Shinagawa-ku, Tokyo F-term within Sony Corporation (reference) 5F052 AA02 BB07 CA09 DA02 DB02 DB03 EA16 FA19 JA01

Claims (11)

[Claims] A step of sequentially forming a semiconductor thin film and a gate insulating film to be an active layer on an insulating substrate; a step of forming a heating member on the gate insulating film; and a step of forming the heating member from above the heating member. Irradiating an energy beam whose energy is absorbed in the thin film transistor. 2. The method according to claim 1, wherein the heating member is made of a metal. 3. The method according to claim 1, wherein the heating member is a gate electrode. 4. The method according to claim 3, wherein the energy beam is applied after forming a source region and a drain region by doping the semiconductor thin film with an impurity using the gate electrode as a mask. A method for manufacturing a thin film transistor. 5. The method according to claim 1, wherein the gate insulating film is a silicon oxide film or a silicon nitride film. 6. The method according to claim 3, wherein the gate electrode is made of a silicon film. 7. The method according to claim 3, wherein said gate electrode is made of a silicon film containing hydrogen. 8. The method according to claim 1, wherein the energy beam is a pulsed laser beam. 9. The method according to claim 1, wherein the semiconductor thin film is a polycrystalline silicon film. 10. The method according to claim 1, wherein the heat-resistant temperature of the insulating substrate is 200 ° C. or less. 11. The method according to claim 1, wherein the insulating substrate is a plastic substrate or a glass substrate having a heat-resistant temperature of 200 ° C. or lower.