JPH0513442A - Semiconductor substrate - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides a semiconductor substrate having a structure in which an electrode made of a conductive thin film is formed on an insulating substrate, an insulating film covering the electrode, and a semiconductor film recrystallized on the electrode. It is an object of the present invention to provide a semiconductor substrate having an electrode capable of enlarging the area of a recrystallized semiconductor film without using a complicated laser optical system. According to the present invention, in a semiconductor substrate having an electrode made of a conductive thin film on an insulating substrate, an insulating film covering it, and a semiconductor film recrystallized thereon, at least two types of electrodes having different light reflectances are used. Of the conductive thin film, or an electrode transparent to the beam, and an electrode made of a conductive thin film opaque to the beam formed so as to cover a part of the transparent electrode. .

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a semiconductor substrate for providing a thin film transistor formed on an insulating substrate.

[0002]

2. Description of the Related Art Control of temperature distribution is important in order to single-crystallize polycrystalline Si or amorphous Si on an insulating substrate such as quartz by beam annealing. Generally, the power distribution of the laser beam is almost Gaussian, so if the irradiation is continued as it is, the crystal growth proceeds from the peripheral part to the central part of the beam irradiation region, and a large single crystal is generated to generate many nuclei. Hard to get. In order to reduce crystal nuclei during melting and solidification, it is necessary to increase the temperature distribution in the Si layer in the peripheral portion. There are roughly three methods for obtaining such temperature distribution. (1) A method of changing the intensity distribution of a laser beam by an optical system or multiple laser light sources. (2) A method in which the absorption of laser light is changed by an antireflection film or a light absorption film provided on the sample surface. (3) A method of changing the temperature distribution depending on the sample shape and structure. The advantage of (1) is that the sample preparation process is simple, and the disadvantages are the controllability of the beam shape and temporal instability.
(2) and (3) are superior in terms of controllability as the precision of the processing technology is improved, but they have the disadvantage that the process of sample preparation is complicated.

[0003]

In view of the above problems of the prior art, an object of the present invention is to provide an electrode composed of a conductive thin film on an insulating substrate, an insulating film covering the same, and a simple structure without using a complicated laser optical system. An object of the present invention is to provide a semiconductor substrate having a structure capable of enlarging a single-crystallized area of a recrystallized semiconductor film when a semiconductor substrate having a structure of a recrystallized semiconductor film is manufactured.

[0004]

According to the present invention, there is provided (1) a layer of a conductive thin film having at least two kinds of light reflectance with respect to a beam formed on an insulating substrate, or (2) a conductive thin film opaque to the beam. A part of which is transparent to the beam, an insulating film formed so as to cover the electrode, and a recrystallized semiconductor film formed by beam annealing on the insulating film. Semiconductor substrate.

As described in the section of the prior art, semiconductors such as polycrystalline (or amorphous) silicon on an insulating substrate such as quartz are monocrystallized by beam annealing. However, as shown in FIG. 1A, when a beam-annealing semiconductor layer, for example, an Si layer 4 has an electrode 1 opaque to the beam, the Si layer is absorbed by the opaque electrode 2 to absorb the beam. The temperature distribution during the beam annealing of No. 4 is as shown in FIG. In such a temperature distribution, crystal growth proceeds from the periphery of the irradiation region to the center, and due to the generation of a large number of nuclei, the respective growth surfaces meet and a large single crystal cannot be obtained.

In the prior art, as shown in FIG. 2, an insulating substrate 1 has a Si layer 4 and a laser antireflection film 5 thereon. As a result, the temperature distribution of the laser irradiation portion of the Si layer 4 becomes higher in the peripheral portion, but it is necessary to optically design the film thickness of the antireflection film 5 according to the laser wavelength used for annealing in this method. Further, there is a drawback that a process of applying and / or removing an antireflection film is required, and the process is complicated.

According to the present invention, by using the electrode as described in (1) or (2) above, the temperature distribution of the Si layer 4 during beam annealing becomes as shown in FIG. It is possible to set a minimum temperature portion in the central region, which is a bimodal shape, allows crystal growth from a single nucleus, and obtains a single crystal silicon layer in which the positions of crystal grain boundaries are controlled.

[0008]

EXAMPLES The present invention will be described in detail below based on examples. First, the semiconductor substrate (1) will be described. Example 1 FIG. 3 (a) shows that a conductive thin film 21 is deposited on an insulating substrate (quartz substrate or a glass substrate having a SiO ₂ film formed on the surface) 1,
After the resist 6 is applied and developed, a predetermined portion of the conductive thin film 21 is removed by etching. FIG. 3B shows a state in which the conductive thin film 22 is deposited on this. FIG. 3C shows a state in which the resist has been removed by the lift-off method and the development of the resist 6'with a new pattern has been completed. FIG. 3D shows a state in which a predetermined portion of the conductive thin film 21 is removed by etching and the resist is removed. As the conductive thin films 21 and 22, Mo, W,
It is selected from metals such as Ta, Pt, Ti, Au, Al and Cr, or metal oxides such as ITO and SnO ₂ , which are a combination of materials having different light reflectivities with respect to the laser beam, and The light reflectance of the conductive thin film 21 is selected to be lower than the light reflectance of the conductive thin film 22. For example, when the XeCl excimer laser (wavelength 308 nm) is used, the conductive thin film 21 is Au (reflectance about 15%), and the conductive thin film 2
2 selects Pt (reflectance about 43%) or ITO film.
The conductive thin film is deposited by the sputtering method or the vacuum evaporation method. The thickness of the conductive thin films 21 and 22 is 1000 to 3000
Å is preferred. Insulating film 3 (SiO ₂ , S
FIG. 4 shows the state in which the Si layer 4 (polycrystalline Si, amorphous Si, etc.) is further deposited after the deposition of iON, SiN, etc.
It is (a). As a method of depositing the insulating film 3 and the Si layer 4, there are a sputtering method and various CVD methods. Here, plasma CV is used.
The D method will be described. The insulating film 3 uses SiH _{4 as a} source gas.
Or Si ₂ H ₆ , N ₂ O or CO ₂ is used and the substrate temperature is 200
The film thickness is deposited between 1000 and 5000Å between ~ 400 ℃. The Si layer 4 is deposited at a substrate temperature of 200 to 400 ° C. using SiH ₄ or Si ₂ H ₆ as a source gas. Film thickness 300
Set between ~ 3000Å. FIG. 5 shows a step of melting and recrystallizing the Si layer 4 by beam annealing. The sweep direction of the beam spot 7 is the stripe direction of the conductive thin films 21 and 22. When the Si layer 4 is a film containing hydrogen such as a-Si: H, the Si layer 4 is pre-annealed at a temperature between about 500 ° C. and the melting temperature or less to remove hydrogen in the film. This is not necessary in the case of polycrystalline Si produced by the LPCVD method. The beam annealing method is performed by sweeping a laser in a vacuum or an atmosphere of nitrogen or an inert gas. As a result, the Si layer 4 becomes a crystallized Si layer 4'as shown in FIG. The laser irradiation conditions differ depending on the material constituting the present invention and the film thickness thereof, and further on the type of laser used. Pulse width for XeCl excimer laser
It is advisable to carry out under conditions of 100 ns or less and a power density of 10 ⁴ W / cm ² or more. In FIG. 7, the Si layer 8 doped with impurities from FIG. 6 is deposited and patterned, the interlayer insulating film 3 ′ is deposited and patterned, contact holes are formed, and then the source electrode 9 and the drain electrode 10 are formed of Al. The thin film semiconductor device having an inverted stagger structure is shown.

Example 2 The semiconductor of (2) above will be described below. FIG. 8A shows an insulating substrate (a quartz substrate or a glass substrate having a SiO ₂ film formed on its surface) 1 on which a conductive thin film transparent to a conductive beam is deposited, and the transparent electrode 2 is formed by a photolithography process. 2 shows a state in which a predetermined portion of is removed by etching. Figure 8
(b) shows a state after a metal thin film 2'which is opaque to the beam is deposited thereon and resist development is performed by a photolithography process. Further, FIG. 8C shows a state in which the shape processing of the metal thin film 21 is completed. As the transparent conductive thin film 2, IT
The opaque metal thin film 2'selected from a metal oxide such as O or SnO ₂ is preferably a refractory metal such as Mo, Ta or W, or a silicide compound thereof. For example, ITO and SnO ₂ hardly absorb light with respect to an Ar laser having a wavelength near 500 μm. on the other hand,
W, Mo, Ta, etc. show a light absorption rate of about 30 to 40% for the same laser. To deposit these conductive thin films 2, 2 ',
Sputtering method or vacuum evaporation method is used, and the film thickness is 500
~ 3000Å is preferred. In FIG. 8D, the insulating film 3 (S
It shows a state in which iO ₂ , SiON, SiN, etc. are deposited, and a Si layer 4 (polycrystalline Si, amorphous Si, etc.) is further deposited. As a method of depositing the insulating film 3 and the Si layer 4, there are a sputtering method and various CVD methods. Here, a plasma CVD method will be described. The insulating film 3 uses SiH ₄ or S as a source gas.
i ₂ H ₆ , H ₂ O or CO ₂ is used and the substrate temperature is 200 to 400 ° C.
The film thickness is deposited between 1000 and 5000Å. Also Si
Layer 4 is deposited at a substrate temperature of 200-400 ° C. Film thickness 300
Set between ~ 3000Å. FIG. 8F shows a state in which the Si layer 4 is melted and recrystallized by beam annealing. The beam is swept in the direction of the stripes of the conductive thin films 2 and 2 '. The beam annealing method is vacuum, N ₂ or Ar,
It is performed in an atmosphere of an inert gas such as Ne or He. The Si layer 4 becomes a recrystallized Si layer 4 '. The laser irradiation conditions differ depending on the material constituting the present invention and the film thickness thereof, and further on the type of laser used. In the case of Ar laser, power density 0.1 to 3 W / cm ² , scan (sweep) speed 10 to 10
Perform in the range of 0 mm / sec. In FIG. 8 (f), the Si layer 8 doped with impurities from the state of (e) is deposited and patterned, then the interlayer insulating film 3'is deposited, and after the patterning, contact holes are formed and the source and drain electrodes are made of Al. The formed thin film transistor element of the inverted stagger structure is shown.

[0010]

[Effect] According to the present invention, by using an electrode having a specific structure, for example, the structure shown in FIG. 3 (d) and FIG. 8 (c), the temperature distribution during beam annealing is shown in FIG. 4 (b) or FIG. As shown in (b), the minimum temperature part can be set in the central region irradiated with the beam. Therefore, when a thin film transistor is formed with an inverted staggered structure, a large area single crystal can be formed in a semiconductor layer overlapping with a gate electrode.

[Brief description of drawings]

FIG. 1 (a) is a diagram showing beam annealing of a semiconductor film of a semiconductor substrate using conventional electrodes, which is not according to the present invention. (b) shows the temperature distribution of the semiconductor film when the beam annealing shown in (a) is performed.

FIG. 2 shows a conventional technique in which a temperature distribution of a semiconductor film on a semiconductor substrate is controlled by providing an antireflection film for a laser.

3 (a), (b), (c) and (d) are one-layer electrodes made of a conductive thin film having at least two kinds of light reflectance on an insulating substrate in the production of the semiconductor substrate of the present invention. Each step of the process of providing is shown.

4 (a) is an insulating film 3 (SiO ₂ , SiO ₂ ) on FIG. 3 (d).
N, SiN, etc. are deposited, and the Si layer 4 (polycrystalline S
i, amorphous Si, etc.) is subjected to beam annealing of the semiconductor film of the semiconductor substrate of the present invention before beam annealing. (b) The temperature distribution of the semiconductor film when the beam annealing of (a) is performed is shown.

FIG. 5 is a perspective view showing melting and recrystallization of the Si layer 4 by beam annealing. The sweep direction of the beam spot 7 is the stripe direction of the conductive thin films 21 and 22.

FIG. 6 shows that in the semiconductor substrate of the present invention, the Si layer 4 (polycrystalline Si, amorphous Si, etc.) becomes a crystallized Si layer 4 ′ by beam annealing.

FIG. 7 shows an inverted staggered thin film semiconductor device using the semiconductor substrate of the present invention.

8 (a), (b) and (c) In the production of a semiconductor of the present invention, for an electrode transparent to a beam and a beam formed so as to cover a part of the transparent electrode on an insulating substrate. The respective steps of the process for providing an electrode made of an opaque conductive thin film are shown. (d) On top of (c), the insulating film 4 (SiO ₂ , SiO ₂
N, SiN, etc. are deposited, and the Si layer 5 (polycrystalline S
i, amorphous Si, etc.) and beam anneal with this. (e) A state in which the Si layer 5 is melted and recrystallized by beam annealing is shown. (f) The Si layer 8 added with impurities from the state of (e) is deposited, and after patterning, the interlayer insulating film 4'is deposited, and after patterning, contact holes are formed, and source and drain electrodes are formed of Al. 1 shows a thin film transistor element having an inverted staggered structure.

9 shows a temperature distribution of a semiconductor film when the beam annealing shown in FIG. 8 (d) is performed.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Transparent electrode 2'Opaque electrode 2 "Electrode 3 consisting of conductive thin films 21 and 22 having different light reflectances 3 Insulating film 3'Interlayer insulating film 4 Si layer 4'Crystalline Si layer 5 Antireflection film 6 Resist 6'Resist 7 Beam spot 8 Impurity-added Si layer 9 Source electrode 10 Drain electrode

Claims (8)

[Claims] 1. At least two kinds of conductive thin films having different light reflectivities so that the temperature distribution of the semiconductor layer can be set to a minimum temperature portion in the central region by irradiation of the beam and the temperature distribution becomes a bimodal shape. A semiconductor substrate comprising: an electrode on which is arranged; an insulating film formed on the electrode; and a semiconductor film recrystallized by beam annealing on the insulating film. 2. An electrode having at least two kinds of conductive thin films having different light reflectivities, at least a part of the electrodes, wherein each thin film is arranged in stripes along the beam sweeping direction, and on the electrode. A semiconductor substrate comprising the insulating film formed on the substrate and a semiconductor film recrystallized by beam annealing on the insulating film. 3. The conductive thin film is Mo, Ta, W, Ti,
Metal thin film such as Pt, Au, Al, Cr or ITO,
The semiconductor substrate according to claim 1, which is a thin film of a metal oxide such as SnO ₂ . 4. An electrode transparent to a beam, a conductive thin film opaque to the beam formed so as to cover a part of the transparent electrode, and a transparent thin film formed to cover the transparent electrode and the opaque conductive thin film. A semiconductor substrate comprising an insulating film and a semiconductor film recrystallized by beam annealing on the insulating film. 5. The semiconductor substrate according to claim 4, wherein the transparent electrode is ITO or SnO ₂ and the opaque conductive thin film is Mo, W, Ta or its silicide. 6. The semiconductor substrate according to claim 4, wherein at least a part of the opaque electrode has a structure in which stripes are arranged along the beam sweep direction. 7. A conductive thin film of at least two kinds having different light reflectances so that the temperature distribution of the semiconductor layer can be set to a minimum temperature portion in the central region by irradiation of the beam and is bimodal. The thin film transistor element having an inverted staggered structure, wherein the electrode in which the thin film is arranged or at least a part of the electrode constitutes a gate region by the electrode in which thin films are arranged in stripes along the beam sweep direction. 8. A gate region is constituted by an electrode transparent to a beam and an electrode formed of a conductive thin film opaque to the beam formed so as to cover a part of the transparent electrode. And an inverted staggered thin film transistor element.