JPH01241862A - Manufacture of display device - Google Patents

Abstract

PURPOSE:To manufacture a thin film transistor having high performance by using an inexpensive glass substrate of a resin substrate by crystallizing an amorphous silicon film by irradiating it with a pulse laser, and forming source, drain regions by impurity doping by laser radiation. CONSTITUTION:An a-Si:H film 3 is crystallized by irradiating it with a pulse laser beam 5 to form a polycrystalline Si film 6 at an ambient temperature. The film 6 is patterned to form an insular pattern, and an aluminum film 8 is formed on a film 7. The films 8, 7 are patterned, and a gate bus line 9 and a gate electrode 10 are formed. With the film 7 as a mask the film 4 is etched to expose the film 6. After a phosphorus P film 11 is, for example, formed on a whole surface, the surface is radiated with the beam 5 by a XeCl excimer laser. The P is doped in a self-aligning manner to the electrode 10 in the film 6, and an n<+> type source region 12 and an n<+> type pixel electrode 13 used also as a drain region are, for example, formed in a self-aligning manner.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a display device, and is suitable for application to, for example, manufacturing an active matrix type liquid crystal display.

[Summary of the invention]

The present invention provides a method for manufacturing an active matrix display device in which pixel electrodes are turned on and off by thin film transistors, including a step of forming an amorphous silicon film on a transparent substrate, and a step of forming an amorphous silicon film on the amorphous silicon film. a step of crystallizing by irradiating and heating with a pulsed laser beam, a step of forming a gate insulating film and a gate electrode on the crystallized silicon film, and a step of forming a gate insulating film and a gate electrode on the crystallized silicon film. After depositing impurities or in a gas containing impurities, the crystallized silicon film is irradiated with a second pulsed laser beam to diffuse the impurities into the crystallized silicon film, thereby forming the source of the thin film transistor. forming a drain region and a drain region. As a result, a high-performance thin film transistor can be manufactured using an inexpensive glass substrate or resin substrate, and the source region and drain region of this thin film transistor can be formed in self-alignment with the gate electrode. Further, the manufacturing process of the display device can be simplified.

[Conventional technology]

2. Description of the Related Art Active matrix type liquid crystal displays are conventionally known in which display is performed by turning on and off picture element electrodes using thin film transistors formed in each picture element. FIGS. 5A and 5B show an example of a conventional active matrix type liquid crystal display. As shown in FIGS. 5A and 5B, in this liquid crystal display, ITO (Indium Tin) is placed on a transparent glass substrate 101.
a pixel electrode 102 consisting of 0xide), a thin film transistor T for turning on/off the pixel electrode 102, a gate lotus line 103, and a source lotus line 1.
04 is formed. The thin film transistor 'F is
Gate electrode 105, SiO□ film (or SiN film) integrally formed with the gate lot line 103
It consists of a gate insulating film 106, an intrinsic (i-type) hydrogenated amorphous silicon (a-5i:H) film 107, and a source region 108 and a drain region 109 made of an n-type a-3i:H film. ing. In this case, the source region 108 is connected to the source pass line 104, and the drain region 109 is connected to the picture element electrode 102 by a metal wiring 110 such as aluminum (AI). In addition, in FIG. 5A, the gate insulating film 106, the a-5i:H film 107, the source region 1
08 and the drain region 109 are omitted.

In addition, as a prior art document related to the present invention, oxygen (0
) or JP-A-612490 relating to a liquid crystal display element in which pixel electrodes are formed in a semiconductor layer containing nitrogen (N) atoms
Publication No. 80 is mentioned.

[Problem to be solved by the invention]

The thin film transistor T in the conventional active matrix liquid crystal display described above is a-3i: H
p 107. This a-5i:I
(The film 107 can be formed on the non-heat resistant glass substrate 101 by using the plasma CVD method. However, the mobility of carriers (electrons) in this a-5i:H film 107 is sufficiently high. I can't say that. Also,
Since the source region 108 and drain region 109 of this thin film transistor T cannot be formed in a self-aligned manner with respect to the gate electrode 105, these source regions 10
8 and the drain region 109 and the gate electrode 105 are not aligned accurately. Furthermore, a large number of lithography steps are required from the formation of the picture element electrode 102 to the formation of the source lot line 104 and the wiring 110, making the manufacturing process complicated.

Therefore, an object of the present invention is to provide a method for manufacturing a display device that can produce a high-performance thin film transistor with high carrier mobility using an inexpensive glass substrate or resin substrate.

Another object of the present invention is to provide a method for manufacturing a display device in which a source region and a drain region of a thin film transistor can be formed in a self-aligned manner with respect to a gate electrode.

Another object of the present invention is to provide a method for manufacturing a display device that can simplify the manufacturing process.

[Means to solve the problem]

The present invention provides a thin film transistor (T) with a pixel electrode (1
3) in a method for manufacturing an active matrix display device in which a transparent substrate (1) is turned on/off;
A step of forming an amorphous silicon film (3) on top, a step of crystallizing the amorphous silicon film (3) by irradiating it with a first pulsed laser beam (5) and heating it, and a step of crystallizing the amorphous silicon film (3) by heating it. A process of forming gate insulating films (4, 7) and a gate electrode (1o) on the crystallized silicon film (6), and after depositing impurities on the crystallized silicon film (6) or in a gas containing impurities. By irradiating the crystallized silicon film (6) with a second pulsed laser beam (5) to diffuse impurities into the crystallized silicon film (6), the source region (T) of the thin film transistor (T) is
12) and a step of forming a drain region (13).

[Effect]

According to the above-described means, a thin film transistor can be formed using a crystallized silicon film, so that carrier mobility can be increased. Furthermore, formation of an amorphous silicon film, crystallization thereof, impurity doping for forming a source region and a drain region, etc. can all be performed at a low temperature of about room temperature to 300°C. Therefore, a high performance thin film transistor can be manufactured using an inexpensive glass substrate or resin substrate. Also,
By irradiating the pulsed laser beam, impurity doping is performed in the silicon film in a self-aligned manner with respect to the gate electrode, so that the source region and drain region of the thin film transistor can be formed in a self-aligned manner with respect to the gate electrode. . Furthermore, since the conventional lithography process is not required to form these source and drain regions, the number of lithography processes is reduced by at least this amount, and the manufacturing process can therefore be simplified.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. This embodiment is an example in which the present invention is applied to the manufacture of an active matrix type liquid crystal display.

1A to 1D show a method for manufacturing an active matrix type liquid crystal display according to an embodiment of the present invention in order of steps, and FIG. 2 shows its completed state. In addition, the first
Figures A to 1 are cross-sectional views taken along line Y--Y in Figure 2.

In this embodiment, as shown in FIG. 1A, first, a film of about 300% is deposited on a pre-cleaned transparent glass substrate 1 by, for example, plasma CVD at a substrate temperature of about room temperature to about 300°C. A SiN film 2, for example, an i-type a-3i:H film 3 having a thickness of about 300 to 1000 layers, and a SiN film 4 having a thickness of about 1000 layers, for example, are sequentially formed. The SiN film 2 can prevent contamination from the glass substrate 1.

Next, the entire surface is irradiated with a pulsed laser beam 5 at room temperature, for example. This pulsed laser beam 5 is, for example, X
A pulsed laser beam (wavelength: 308 nm) from an eCl excimer laser can be used, the pulse width of which is, for example, 30 ns, and the irradiation energy density of, for example, 20 nm.
It is 0 to 300 mJ/CIIY. This pulse laser
By irradiating the beam 5, the a-3i:H film 3 is instantaneously heated and crystallized. Thereby, as shown in FIG. 1B, a polycrystalline Si film 6 can be formed at room temperature.

Next, the SiN film 4 and the crystallized Si film 6 are patterned by etching to form a Si film for forming a thin film transistor T and a Si film for forming a picture element electrode 13, which will be described later.
Forms an island-like pattern integrated with the film. Next, a film with a thickness of 1000, for example, is applied to the entire surface by, for example, plasma CVD method.
After forming the 5iOz film 7 with a thickness of 1000 to 2000, for example, an AI film 8 having a thickness of 1000 to 2000 is further formed on the 5iOz film 7, for example, by sputtering or vapor deposition.

Next, the AI film 8 and the 5iOz film 7 are patterned into a predetermined shape by etching to form a gate lot line 9 and a gate electrode 10, as shown in FIG. 1C and FIG. 2. Next, the SiN film 4 is etched using the patterned SiO□ film 7 as a mask, thereby exposing the Si film 6. Note that the SiN film 4 and the SiO□ film 7 after patterning
A gate insulating film is formed by this. Next, for example, a plasma CVD method is used to coat the entire surface with a film of, for example, 100 phosphorus (P).
) After forming the film 11, the entire surface is irradiated with a pulsed laser beam 5 using, for example, a XeC1 excimer laser.

The pulse width of this pulsed laser beam 5 is, for example, 20n.
s, and the irradiation energy density is, for example, 200 to 300
mJ/c+fl. The Si film 6 is instantaneously heated by the irradiation of the pulsed laser beam 5, and as a result, P is formed in the Si film 6 in direct contact with the P film 11 in a self-aligned manner with respect to the gate electrode 10. be doped. Thereby, for example, an n' type picture element electrode 13 which also serves as an n' type source region 12 and a drain region can be formed in a self-aligned manner with respect to the gate electrode 10. The resistivity ρ of the picture element electrode 13 which also serves as the source region 12 and the drain region is 10-2 to 10-'
It can be made as low as Ω·cm.

Furthermore, as will be described later, the picture element electrode 13 has good transmission characteristics for visible light having a wavelength of 300 to 800 nm. Thereafter, the P film 11 is removed by etching. Note that the impurity doping method as described above is L I M P I
D (Laser Induced Melting
of Predeposited Impurity
This is called the Doping method.

Next, as shown in the first diagram, a film with a thickness of 0.15, for example, is applied to the entire surface.
~1 μm photosensitive glabellar insulating film 14 such as polyimide
After forming the interlayer insulating film 14, a predetermined portion of the interlayer insulating film 14 is removed to form a contact hole 14a. Next, after forming, for example, an A1 film on the entire surface, this A1 film is patterned into a predetermined shape by etching to form source path lines 15. This source bus line 15 is connected to the source region 12 through the contact hole 14a. Next, a liquid crystal alignment film (not shown) is applied to the entire surface.
After forming, annealing is performed at a temperature of, for example, 300 to 400°C as necessary to improve the characteristics of the interface between the SiN film 4 and the Si film 6, and to improve the breakdown voltage of the SiO□ film 7 and interlayer insulating film 14. conduct. Thereafter, the desired liquid crystal display is completed through a liquid crystal filling process and the like.

In the liquid crystal display manufactured in this way, the gate electrode 10 and the SiN films 4 and 5i02
a gate insulating film consisting of film 7; the source region 12;
The drain region which is also used by the picture element electrode 13
A channel thin film transistor T is configured.

Figure 3 shows a as-deposited
-5i: H film (thickness: 550) and this a -3i
: The transmission spectrum of the H film after crystallization by irradiation with a pulsed laser beam is shown, and FIG. 4 shows the wavelength dependence of the absorption coefficient calculated from the transmission spectrum shown in FIG. 3.

As can be seen from Fig. 3, a −5i :H immediately after formation
The membrane allows blue light to pass through it ((), but green and red light easily pass through it, so the color of the membrane appears brown.

On the other hand, after this a-5i:H film is crystallized by irradiation with a pulsed laser beam, the absorption coefficient particularly for blue to green light decreases, as shown in FIG. As can be seen from Figure 3, the Si film after crystallization has a high transmittance even for blue light, so it has a high transmittance for red, green,
A high transmittance of 35 to 45% is obtained for light of the three primary colors of blue. As a result, a white transparent Si film 6 with excellent color in the visible range can be obtained. 35-45% of the above
Although this value of transmittance is lower than that of ITO (see FIG. 3), it is a value that is sufficient for practical use. Note that if a non-reflective film such as a SiN film is formed on the crystallized Si film 6 to suppress reflection, the transmittance can be improved to about 80%, for example.

According to this embodiment, there are various advantages as follows.

That is, by irradiation with the pulsed laser beam 5, a-
3i:) Crystallization of the I film 3 can be performed at room temperature. Further, impurity doping for forming the picture element electrode 13 which serves as both the source region 12 and the drain region can be similarly performed at room temperature by irradiation with the pulsed laser beam 5. Therefore, according to this embodiment, it is possible to manufacture a high-performance thin film transistor T with high carrier (electron) mobility using a low-temperature but inexpensive glass substrate 1 in a low-temperature process ranging from room temperature to 300'C. can. This thin film transistor T allows high speed and larger current switching. Moreover, not only can the Si film for forming the thin film transistor T and the picture element electrode 13 be formed by one lithography process, but also the lithography process can be performed to form the drain region which is also used by the source region 12 and the picture element electrode 13. Since no steps are required, the number of lithography steps is reduced compared to the conventional liquid crystal display described above, and therefore the manufacturing process can be simplified accordingly. Further, since impurities are doped into the Si film 6 in a self-aligned manner with respect to the gate electrode 10, a picture element electrode 13 which also serves as the source region 12 and drain region is formed in a self-aligned manner with respect to the gate electrode 10. be able to.

Furthermore, since the Si film for the thin film transistor T and the picture element electrode 13 are formed of the common thin Si film 6, the surface is flat as a whole, and therefore the gate, hash, and
Disconnection of the line 9 and the source lot line 15 can be prevented.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications can be made based on the technical idea of the present invention.

For example, a-SiX instead of a-3i:H film 3
C+-X: H (0<x<1) film, a SIX N1
-X: H (0<x<1) film, a St
An xO+-x:H (0<x<1) film or the like can be used. These a-8iXC1-X :H films,
aSIXNl-X: H film and a-8iXOI-X
Since the :H film has an absorption edge on the shorter wavelength side compared to the a-3i :H film 3, the transmittance can be made higher in the visible range. Note that the concentration of these C1N,0 can be set to, for example, about 1019C'3, which allows the absorption coefficient to be 105CI11-' or less in the visible range.Also, these a-5iXC+-8:H film,
a SIX N1-X” membrane and a-5iXol-
x: The H film contains, in addition to SiH4, C and H2C, respectively, as a reactive gas during growth by plasma CVD method.
It can be formed by using H3, NH3 and NO□. Furthermore, since it is the picture element electrode 13 that needs to have high transmittance, for example, a-5i:I(
After forming the film 3, C, N, or 0 may be added thereto by the LIMPID method described above. Also, this a-S
The i:H film 3 does not necessarily have to be formed by the plasma CVD method, but can also be formed by a sputtering method or a vapor deposition method. Furthermore, as an impurity doping method for forming the picture element electrode 13 which also serves as the source region 12 and the drain region, a gas containing the impurity to be doped (for example, PH3 for n-type impurity, B2 for n-type impurity) is used. C is a method of impurity doping by irradiating a pulsed laser beam in Hb).
ILD (Gas Immersion La5er D
opening) method may also be used.

Further, as the pulsed laser beam 5, for example, XeF
It is also possible to use a pulsed laser beam (wavelength 351 nm) from an excimer laser. Furthermore, instead of the glass substrate 1, for example, polymethyl methacrylate (P
It is also possible to use a substrate made of a transparent resin material such as MMA) or polycarbonate.

Further, in the above-described embodiments, the case where the present invention is applied to the manufacture of liquid crystal displays has been described, but the present invention can be applied to the manufacture of active matrix type display devices other than liquid crystal displays. . For example, if the glabellar insulation film 14 on the picture element electrode 13 in the above embodiment is removed and an electrochromic (EC) material is used instead of liquid crystal as the display material, an active matrix type electrochromic display can be obtained. can be manufactured. Note that a two-dimensional sensor can also be manufactured by using an optical sensor material instead of liquid crystal.

〔Effect of the invention〕

As explained above, according to the present invention, an amorphous silicon film is irradiated with a pulsed laser beam and heated to crystallize it, and a source region and a drain region are formed by impurity doping by irradiation with a pulsed laser beam. This makes it possible to manufacture high-performance thin film transistors using inexpensive glass or resin substrates. Further, since impurities are doped into the silicon film in a self-aligned manner with respect to the gate electrode, the source region and drain region of the thin film transistor can be formed in a self-aligned manner with respect to the gate electrode. Furthermore, since no lithography process is required to form the source and drain regions, the number of lithography processes is reduced by at least this amount, thereby simplifying the manufacturing process.

[Brief explanation of the drawing]

1A to 1D are cross-sectional views for explaining step-by-step a method for manufacturing an active matrix liquid crystal display according to an embodiment of the present invention, and FIG. 2 is a sectional view of FIGS.
A perspective view showing the completed state of the liquid crystal display manufactured by the method shown in the figure, Figure 3 is a-3i immediately after formation:)
A graph showing the transmission spectra of the I film and this a-3i:H film after crystallization by irradiation with a pulsed laser beam. Figure 4 shows the wavelength dependence of the absorption coefficient calculated from the transmission spectrum shown in Figure 3. Graph showing gender, Figure 5A
5 is a perspective view showing an example of a conventional active matrix type liquid crystal display, and FIG. 5B is a sectional view taken along line XX in FIG. 5A. Explanation of main symbols in the drawings ■ = Niglass plate (transparent substrate), 3: a-5i: H film,
6: Crystallized Si film, 9: Gate lot line, 10: Gate electrode, 15: Source bus line, T: Thin film transistor. Agent Patent Attorney Masatoshi Sugiura

Claims (1)

[Claims] A method for manufacturing an active matrix display device in which pixel electrodes are turned on and off by thin film transistors, comprising: forming an amorphous silicon film on a transparent substrate; a step of crystallizing by irradiating and heating with a first pulsed laser beam; a step of forming a gate insulating film and a gate electrode on the crystallized silicon film; and a step of forming a gate insulating film and a gate electrode on the crystallized silicon film. After depositing impurities on the source of the thin film transistor, or by irradiating the crystallized silicon film with a second pulsed laser beam in a gas containing impurities to diffuse the impurities into the crystallized silicon film, 1. A method of manufacturing a display device, comprising: forming a region and a drain region.