JPH02228043A - Semiconductor device and manufacture thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor device and a method for manufacturing the same, and particularly to a semiconductor device suitable for an active matrix type liquid crystal display device and a method for manufacturing the same.

(Prior Art) In recent years, active matrix type liquid crystal displays have rapidly progressed toward higher image quality and larger screens while incorporating peripheral circuits.

In this type of liquid crystal display, TPTs are formed in a matrix on a transparent insulating substrate such as a glass substrate so that one thin film transistor (hereinafter abbreviated as TPT) corresponds to one pixel.

Plasma CV is applied to the part that functions as the active layer of TPT.
Amorphous silicon formed by D or polycrystalline silicon formed by low pressure CVD (LPGVD) is used, but TPT for liquid crystal displays
Polycrystalline silicon (poly-8) is often used because high carrier mobility and low leakage current are required.

Hereinafter, a conventional method for manufacturing TPT will be described.

The polycrystalline silicon film formed by the LPCVD method is
Since the crystallinity of the film is not sufficient at temperatures below 600° C., a step of improving the crystallinity by heat treatment is required. However, in the case of glass substrates with a low strain temperature, the processing temperature is limited by the strain point (approximately 600°C) and sufficient crystallinity cannot be obtained, so in recent years,
A method of improving crystallinity during recrystallization by irradiating a silicon film with a laser beam that is absorbed by the surface to melt only the surface layer has been implemented.

Once the polycrystalline silicon serving as the active layer is formed in this way, islands are cut to form a TPT in a photo-etching step, and a gate insulating film and a gate electrode are further formed. Subsequently, portions of the polycrystalline silicon that will become source/drain regions and the gate electrode are doped with impurities.

Here, heat treatment is performed to activate these impurities, but in this case as well, as above, heat treatment cannot be performed at a temperature of 600°C or higher, so laser light is irradiated to activate the impurities. I do.

(Problems to be Solved by the Invention) Generally, in the formation of amorphous silicon by plasma CVD, since the glass substrate is installed flatly, the amorphous silicon film is formed only on the surface of the glass substrate during its lifetime. In forming a polycrystalline silicon film by the LPCVD method, a large number of glass substrates are placed vertically in parallel, so that polycrystalline silicon films are formed on both sides of the glass substrates.

In this way, when polycrystalline silicon films are formed on both sides of a glass substrate, the polycrystalline silicon film on one side is cut into islands using a photo-etching process to arrange a large number of TPTs in a matrix. When activating the source/drain region, when irradiating an energy beam such as a laser beam, the energy beam is absorbed in the region where polycrystalline silicon remains like an island, that is, the TPT formation region, but in other regions. In the region, the energy beam passes through the glass substrate.

Since the energy beam that passed through the glass substrate still has a large light intensity, it heats the polycrystalline silicon deposited on the back side of the glass substrate, and its temperature greatly exceeds the strain temperature of the glass substrate. There are cases where this happens.

When the temperature of polycrystalline silicon exceeds the strain temperature of the glass substrate, the glass substrate in contact with the polycrystalline silicon also exceeds the strain temperature, causing unevenness on the glass substrate in that area, which eventually causes This causes cloudiness on the screen of a liquid crystal display device.

An object of the present invention is to solve the above-mentioned problems and realize a semiconductor device in which unevenness is prevented from occurring on a glass substrate, and if the semiconductor device according to the present invention is used as an active matrix substrate for a liquid crystal display device, An object of the present invention is to provide a semiconductor device and a method for manufacturing the same that can realize a high-quality display device that does not cause clouding on the screen.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a thin film semiconductor device in which a large number of TPTs are arranged adjacent to each other on the surface of a transparent insulating substrate. The feature is that any of the measures shown in 3) or an appropriate combination of these measures is taken.

(1) A substrate having a high absorption coefficient for an energy beam irradiated to activate impurities in the source/drain region is used as the transparent insulating substrate.

(2) Before forming polycrystalline silicon, which will become the active layer of the TPT, on at least the back side of the surface of the glass substrate that is irradiated with the energy beam, prepare a material with a low absorption coefficient for the energy beam and high thermal insulation, such as A 5i02 film is deposited in advance.

(3) The silicon film on the back surface of the glass substrate to which the energy beam is irradiated is removed in advance before the energy beam is irradiated.

(Function) The above means works as follows. That is, if a substrate with a high absorption coefficient for the irradiated energy beam is used as the transparent box edge substrate, the energy beam will be absorbed by the glass substrate. The energy intensity is gradually absorbed and attenuated in the thickness direction, and when it reaches the silicon film on the back side,
The intensity will be 50-80% of the initial energy beam. Therefore, the temperature rise of the silicon film on the back surface is suppressed.

The means (2) above operates as follows. That is,
By forming a base film with a small absorption coefficient for the energy beam and high thermal insulation on the back side of the surface that is irradiated with the energy beam, the energy beam irradiated on the front surface will pass through the substrate and the base film. After that, even if the silicon film on the back surface is heated, conduction of the heat to the substrate is blocked by the base film, so that the temperature rise of the glass substrate is suppressed.

The means (3) above operates as follows. That is,
If the silicon film on the back side of the surface that is irradiated with the energy beam is removed in advance, the energy beam that has passed through the substrate can be
It is not absorbed in any part of the thin film semiconductor device and is emitted to the outside.

Therefore, the substrate is not heated and its temperature rise is suppressed.

(Example) An example of the present invention will be described below. FIG. 1 is a cross-sectional view for explaining a semiconductor device and its manufacturing method as an embodiment of the first invention.

In the figure, the glass substrate 1-1 has an absorption coefficient ε of 3 c+a-' for ultraviolet light having a wavelength of 308n-, and a thickness of 1+
This is the u+ substrate. The absorption coefficient ε in this case is defined as the intensity of ultraviolet light incident on the glass substrate is Io1, and the intensity of the incident light after passing through the glass substrate is 1. Board thickness (am
) is defined as (-εX) I-IXexp.

In this example, first, a 5i02 film 2-1 serving as a base film is deposited on the surface of the glass substrate 1-1 to a thickness of approximately 4000 nm by an atmospheric pressure CVD (APCVD) method [see FIG. a)].

Next, TPT was
The polycrystalline silicon film 3-1 functioning as the active layer of
02 film 2-1.

At this time, as described above, in the LPCVD method, the silicon film 3-2 is similarly deposited on the back surface of the glass substrate 1-1.

Next, about 2,000 layers of 5i02 film 20, which is a cap film, is deposited on the surface of the silicon film 3-1 by the APCVD method, and then XeCl
8 nn+) at an intensity of 300 taJ/c4 to crystallize the polycrystalline silicon film 3-1 to obtain a polycrystalline silicon film with excellent crystallinity [FIG. 4(b)].

Next, after removing the cap film, the polycrystalline silicon film 3-
By cutting 1 into islands in the photo-etching process,
Island-shaped polycrystalline silicon films 21 are arranged in a matrix on glass substrate 1-1.

Next, a 5i02 film 7 for a gate insulating film is deposited on the surface.
Approximately 2,000 layers of silicon film 8 were deposited by CVD method, and approximately 300 layers of silicon film 8 for gate electrode was deposited by LPCVD method.
Deposit 00 people.

Next, after the 5i02 film 7 for the gate insulating film and the silicon film 8 for the gate electrode are buttered by a photo-etching process, the island-shaped polycrystalline silicon film 2
1, the portion 4 that becomes the source/drain region of TPT
, 5, and the gate electrode 8 by, for example, ion implantation, phosphorus ions 12 are implanted at an energy of 30 KeV.
Input X1015 [same figure (C)].

Furthermore, after about 2000 layers of 5i02 film 9, which will become a passivation film, are deposited by the APCVD method, XeC
The impurities are activated by irradiation with an excimer laser 11 at an intensity of 250 IIIJ/c [FIG. 4(d)].

When the activation of the portions that will become the source/drain regions is completed in this way, holes for contacting the source/drain regions are formed in the passivation film 9, and then aluminum for electrodes is sputtered, and the electrodes 10-1 .10-2 is formed.

Subsequently, after forming a transparent electrode ITO (not shown), which will serve as a lead line for driving the TPT, by sputtering, the polycrystalline silicon film 3-2 is removed by etching [FIG. 4(e)]. This polycrystalline silicon film 3-2 may be removed in a previous step, but since this polycrystalline silicon film 3-2 also functions as a protective film for the Baccara substrate 1-1, it is removed in the final step. This is desirable.

After that, prepare a glass substrate laminated with a polarizing plate, a color filter, and a transparent electrode, and place a T between the two glass substrates.
A liquid crystal display device is completed by sealing in N liquid crystal.

FIG. 4(1) shows the X explained in relation to FIG. 1(d) above.
It is a diagram showing the relationship between the distance X from the surface of the glass substrate 1-1 in the thickness direction and the laser light intensity I, and the relationship between the distance X and the temperature T when eCl excimer laser 11 is irradiated. The same reference numerals as in Figure 1 represent the same or equivalent parts.

As is clear from the figure, the intensity (2) of the laser beam that has reached the inside of the glass substrate is attenuated in accordance with the distance X from the surface in the thickness direction. Therefore, even if the laser light that has passed through the glass substrate 1-1 is absorbed by the silicon film 3-2, the silicon M3-2 will not be heated that much because its energy is small.

In the case of this example, since the absorption coefficient of the glass substrate is larger than that of the conventional technique, the temperature rise of the entire glass substrate due to direct irradiation with laser light is somewhat larger than that of the conventional technique. However, because the intensity of the laser beam reaching the silicon film 3-2 is low, the temperature of the silicon film 3-2 is only sufficiently lower than the strain temperature Tc of the glass substrate 1-1. It is not heated and does not cause damage to the glass substrate 1-1.

FIG. 2 is a cross-sectional view for explaining a semiconductor device and its manufacturing method as an embodiment of the second invention.

In this embodiment, the glass substrate 1-2 is a glass substrate similar to that of the prior art, which has a small absorption coefficient for ultraviolet light with a wavelength of 308 ng.

This embodiment is characterized in that first, a 5i02 film 2-1.2-2, which will serve as a base film, is deposited to a thickness of approximately 4000 nm on both sides of the glass substrate 1-2 by APCVD. [Image (a)].

Thereafter, a TPT as shown in FIG. 2(e) is completed by the same manufacturing method as in the embodiment shown in FIG. 1.

In this embodiment, as in the embodiment shown in FIG. 1, in the step shown in FIG. 1, XeCl excimer laser is irradiated to And the impurities in the gate electrode 8 are activated.

Note that after the laser beam irradiation, the electrodes 10-1, 10-2
The method for forming the above is the same as in the case of the first invention.

FIG. 4(2) shows the relationship between the distance X from the surface of the glass substrate 1-2 in the thickness direction and the laser light intensity ■ when irradiated with the XeCl excimer laser 11 in FIG. 2(d),
2 is a diagram showing the relationship between distance X and temperature T. FIG.

As is clear from the figure, also in this example, the intensity I of the laser beam that has reached the inside of the glass substrate is attenuated according to the distance X from the surface to the thickness direction.
Since the absorption coefficient of −2 is small, the pillars are not attenuated in the embodiment shown in FIG. Because of the large amount of energy generated, the silicon film 3-2 is heated to an extent exceeding the strain temperature Tc of the glass substrate 1-2.

However, in the case of this embodiment, 5i0, which functions as a thermal insulator, is provided between the glass substrate 1-2 and the silicon film 3-2.
2 film 2-2 is formed, the silicon 1i1
The heat of 3-2 is not transmitted to the glass substrate 1-2. Therefore, the glass substrate 1-2 will not be damaged.

FIG. 3 is a cross-sectional view for explaining a method of manufacturing a semiconductor device, which is an embodiment of the third invention.

In this embodiment, as in the case of the second invention, the glass substrate 1-2 has an absorption coefficient X for ultraviolet light having a wavelength of 308 ns.
This is a substrate similar to that of the prior art, with a small size.

In this embodiment, the process up to the step of depositing the 5i02 film 9, which becomes the padding film by the APCVD method, is the same as the embodiment described above in connection with FIG. After removing the silicon film 3-2, the source/drain region 4.5 is removed.
and Xe for activating impurities in the gate electrode 8.
The feature is that Cl excimer laser is used for irradiation.

Thereafter, a TPT as shown in FIG. 3(e) is completed by the same manufacturing method as in the embodiment shown in FIG. 1.

FIG. 4(3) shows the relationship between the distance X from the surface of the glass substrate 1-2 in the thickness direction and the laser light intensity I, and the distance X when the XeCl excimer laser is irradiated in FIG. 3(d). FIG. 3 is a diagram showing the relationship between T and temperature T.

As is clear from the figure, in this example, the intensity l of the laser light that has reached the inside of the glass substrate 1-2 is attenuated according to the distance 1iitX from the surface in the thickness direction, and then the energy that has passed through the substrate is Since the beam is emitted to the outside without being absorbed in any part of the semiconductor device, the glass substrate 1-2 is not heated and is not damaged.

Although this embodiment has been described as removing the silicon film 3-2 immediately before irradiating with the XeCl excimer laser, the present invention is not limited to this, and the polycrystalline silicon film 3-2 is removed immediately before irradiation with the XeCl excimer laser. It may be removed in any step after forming 1.3-2 and before irradiating the laser beam.

Thus, according to the first to third inventions, the TP
Since it is possible to prevent unevenness from occurring on the glass substrate due to laser light irradiation for activating the source/drain region and gate electrode of T, it is possible to provide a high-quality liquid crystal display device that does not cause clouding on the screen. It becomes like this.

In the above-described embodiment, (1) a glass substrate having a high absorption coefficient for an energy beam irradiated to activate impurities in the source/drain region is used; (2) the glass substrate is , 5i0, which has a small absorption coefficient for the energy beam and has high thermal insulation, is placed on at least the back surface of the surface irradiated with the energy beam.
(3) depositing two films on the glass substrate in advance;
The silicon film on the back side of the side that is irradiated with the energy beam,
be removed before irradiating the energy beam,
Although the embodiment has been described in which any one of these means is used alone, these technical means may be combined as appropriate.

For example, if a semiconductor device is manufactured by combining the technical means (+) and (2) above, the intensity of the laser light for activating impurities is attenuated by the glass substrate 1-1, and furthermore, the attenuation Since the heat of the silicon film 3-2 heated by the laser beam is insulated by the base film 2-2, the temperature of the glass substrate increases more than in the embodiment described with reference to FIG. 1.2. can be suppressed.

Further, in the above-mentioned embodiment, the TP of the glass substrate
Although the base film 2-2 on the side where T is not formed is described as being a silicon dioxide film, it may be made of a material such as silicon nitride as long as it has a low absorption coefficient for energy beams and has thermal insulation properties. It doesn't matter if there is. However, as explained with reference to FIG. 2, transparency is also required if it is not removed when used as a semiconductor device for a liquid crystal display device.

(Effects of the Invention) As described above, according to the present invention, it is possible to prevent unevenness of the glass substrate from occurring due to laser light irradiation for activating the source/drain region and gate electrode of the TFT. Therefore, if the semiconductor device according to the present invention is used as an active matrix substrate for a liquid crystal display device,
It becomes possible to provide a high-quality display device that does not cause clouding on the screen.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a semiconductor device which is an embodiment of the first invention. FIG. 2 is a sectional view of a semiconductor device which is an embodiment of the second invention. FIG. 3 is a sectional view of a semiconductor device which is an embodiment of the third invention. FIG. 4 is a diagram for explaining the temperature rise of the substrate in the first to third inventions. 1-1.1-2...Glass substrate, 2-1. 2-2・
... Base film, 3-1.3-2 ... Polycrystalline silicon, 4
．． 5... Source/drain region, 7... Gate insulating film, 8... Gate electrode

Claims (6)

[Claims] (1) A large number of thin film semiconductor devices each having a polycrystalline silicon film as an active layer are arranged adjacent to each other on a transparent insulating substrate, and energy is transferred to impurities doped in the source/drain regions and gate electrodes of the thin film semiconductor devices. In a method of manufacturing a semiconductor device for a liquid crystal display device in which a beam is irradiated to activate the semiconductor device, at least the side of the transparent insulating substrate on which the thin film semiconductor device is not formed has a low absorption coefficient for the energy beam and has thermal insulation properties. forming a polycrystalline silicon film on both sides of the transparent insulating substrate on which the base film is formed; and cutting the polycrystalline silicon film on the side on which the thin film semiconductor device will be formed into islands. a step of forming a large number of island-like polycrystalline silicon films; a step of forming a thin film semiconductor device using the island-like polycrystalline silicon film as an active layer; A semiconductor device comprising the steps of doping an impurity and activating the impurity by irradiating the impurity with an energy beam, and removing the polycrystalline silicon film on the side where the thin film semiconductor device is not formed. Production method. (2) A large number of thin film semiconductor devices each having a polycrystalline silicon film as an active layer are arranged adjacent to each other on a transparent insulating substrate, and energy is transferred to impurities doped in the source/drain regions and gate electrodes of the thin film semiconductor devices. A method of manufacturing a semiconductor device for a liquid crystal display device in which a beam is irradiated to activate the semiconductor device includes a step of forming a polycrystalline silicon film on both sides of a transparent insulating substrate, and a step of forming a polycrystalline silicon film on the side where a thin film semiconductor device is formed. a step of cutting a silicon film into islands to form a large number of island-like polycrystalline silicon films; a step of forming a thin film semiconductor device using the island-like polycrystalline silicon film as an active layer; doping the drain region and the gate electrode with an impurity and irradiating the impurity with an energy beam to activate the impurity, further comprising a step of forming the polycrystalline silicon film and irradiating the energy beam. 1. A method for manufacturing a semiconductor device, comprising a step of removing a polycrystalline silicon film on a side where a thin film semiconductor device is not formed, between the step of removing the polycrystalline silicon film. (3) A large number of thin film semiconductor devices each having a polycrystalline silicon film as an active layer are arranged adjacent to each other on a transparent insulating substrate, and energy is transferred to impurities doped in the source/drain regions and gate electrodes of the thin film semiconductor devices. In a semiconductor device for a liquid crystal display manufactured by irradiating a beam to activate it, the absorption coefficient ε of the transparent insulating substrate for the energy beam is 2 cm^-^1 or more in the relational expression shown below. A semiconductor device characterized in that it is 30cm^-^1. I=I_0×exp^(^-^ε^x^) However, I_0: Intensity of ultraviolet light incident on the glass substrate I: Light intensity after the incident light passes through the glass substrate x: Thickness of the glass substrate (cm ) (4) The energy beam is made of XeC with a wavelength of 308 nm.
4. The semiconductor device according to claim 3, wherein the semiconductor device is a l excimer laser. (5) A large number of thin film semiconductor devices each having a polycrystalline silicon film as an active layer are arranged adjacent to each other on a transparent insulating substrate, and energy is transferred to impurities doped in the source/drain regions and gate electrodes of the thin film semiconductor devices. In a semiconductor device for a liquid crystal display manufactured by beam irradiation and activation, at least the side of the transparent insulating substrate on which the thin film semiconductor device is not formed has a low absorption coefficient for the energy beam;
A semiconductor device characterized in that a base film having thermal insulation properties is formed. (6) The semiconductor device according to claim 5, wherein the base film is silicon dioxide or silicon nitride.