JPH0927453A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin film transistor having the same characteristics as transistors formed on a silicon wafer. SOLUTION: An amorphous silicon thin film is patterned into a shape shown by the number 102 in the figure, and crystal growth as shown by the number 103 is performed from the region 101 where nickel silicide has been formed. In this crystal growth it is possible to form a region regarded as a single crystal region as shown by the number 104 by heating the thin film and irradiating it with scanned laser light. The single crystal region 104 is patterned into a shape shown by the number 401 to form the active layer of a thin film transistor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention disclosed in this specification relates to a method for manufacturing a semiconductor device using a thin film semiconductor having crystallinity.

[0002]

2. Description of the Related Art In recent years, a transistor (referred to as a thin film transistor or a TFT) using a thin film semiconductor formed on a glass or quartz substrate has been receiving attention. This is a technology in which a thin film semiconductor is formed on the surface of a glass substrate or a quartz substrate to a thickness of several hundred to several thousand liters and a transistor (insulating gate type field effect transistor) is formed using this thin film semiconductor.

As an application range of thin film transistors, an active matrix type liquid crystal display device is known.
In this, a thin film transistor is arranged as a switching element in each of hundreds of thousands or more of pixels arranged in a matrix to perform display with high image quality.

As a thin film transistor used in such an active matrix type liquid crystal display device, a thin film transistor using an amorphous silicon thin film has been put into practical use.

However, a thin film transistor using an amorphous silicon thin film has a problem that its characteristics are low.
For example, when a higher display function of an active matrix liquid crystal display device is desired, the characteristics of a thin film transistor using an amorphous silicon film are too low.

In addition to pixel switching,
By configuring the peripheral drive circuit also with thin film transistors,
Although it has been proposed to construct an integrated liquid crystal display system integrated on a single substrate, a thin film transistor using an amorphous silicon thin film constitutes a peripheral drive circuit due to its low operating speed. Can not do it. Particularly in a thin film transistor using an amorphous silicon thin film, it is difficult to put the P-channel type into practical use, and there is a fundamental problem that a CMOS circuit cannot be constructed (characteristics are too low to be put into practical use).

Further, a technique of integrating an integrated circuit for processing or storing image data and the like on the same substrate as the pixel region and the peripheral drive circuit has been considered, but an amorphous silicon thin film is used. The thin film transistor cannot form an integrated circuit capable of processing image data because of its low characteristics.

On the other hand, as a thin film transistor having characteristics far superior to those of a thin film transistor using an amorphous silicon thin film, a technique of forming a thin film transistor using a crystalline silicon film is known. This technique uses heat treatment and laser light irradiation after the amorphous silicon film is formed,
This utilizes a phenomenon in which an amorphous silicon film is transformed into a crystalline silicon film. A crystalline silicon film obtained by crystallizing an amorphous silicon film generally has a polycrystalline structure or a microcrystalline structure.

When a thin film transistor is formed by using a crystalline silicon film, compared with the case where an amorphous silicon film is used,
Much higher characteristics can be obtained. For example, when viewed from the mobility which is one index for evaluating the characteristics of the thin film transistor, the thin film transistor using the amorphous silicon film has a mobility of 0.5 to 1 cm ² / Vs or less (in the case of N channel type). In a thin film transistor using a crystalline silicon film, an N-channel type is about 100 cm ² / Vs or more, P
It is possible to obtain a channel type device having a size of about 50 cm ² / Vs or more.

[0010]

However, the crystalline silicon film obtained by crystallizing the amorphous silicon film has a polycrystalline structure and has various problems due to crystal grain boundaries. For example, there is a problem in that the withstand voltage of the thin film transistor is greatly limited because there are carriers that move through the crystal grain boundaries. In addition, there is a problem that characteristics change or deterioration is likely to occur when high speed operation is performed. In addition, since there are carriers that move through the grain boundaries, the thin film transistor is turned off.
There is a problem that the off-current (leakage current) at the time increases.

Further, when the active matrix type liquid crystal display device is to be constructed in a more integrated form, it is desired to form not only the pixel region but also the peripheral circuit on one glass substrate. In such a case, in order to drive hundreds of thousands of pixel transistors arranged in a matrix, the thin film transistors arranged in the peripheral circuit are required to be able to handle a large current.

In order to obtain a thin film transistor which can handle a large current, it is necessary to adopt a structure having a large channel width. However, a thin film transistor using a crystalline silicon film has a problem that it cannot withstand use in a peripheral circuit even if its channel width is widened because of a withstand voltage problem. In addition, there is a problem that the threshold value varies greatly and is not practical.

Even if an integrated circuit for processing image data is made up of a thin film transistor using a crystalline silicon film, a practical integrated circuit (conventional integrated circuit) cannot be used because of the problems of fluctuations in threshold value and changes in characteristics over time. Cannot be obtained instead of an IC).

As a means for solving various problems in a thin film transistor using such an amorphous silicon thin film and a thin film transistor using a polycrystalline silicon thin film or a microcrystalline silicon thin film, a region that can be regarded as a single crystal is formed of an amorphous silicon thin film. A technique of forming a thin film transistor in a specific region and using this region is known. By using this technique, characteristics comparable to those of a transistor (MOS type transistor) formed on a single crystal silicon wafer can be obtained.

This technique is disclosed in Japanese Patent Laid-Open No. 2-14091.
The one described in Japanese Patent No. 5 is publicly known. In this technique, as shown in FIG. 2A, a region 201 to be a seed crystal is formed.
And then heat treatment is performed to cause crystal growth as indicated by an arrow 203 from the region 201 to be a seed crystal, and a region to be an amorphous silicon film patterned into a shape 202. Is to crystallize.

However, in the conventional example, even if the pattern shown by 202 is to be grown from the region of the region 201 to be the seed crystal, as shown in FIG. It is carried out at the same time, and it is impossible to grow crystals uniformly. That is, seeds for crystal growth are also formed in the region indicated by 204, and crystal growth is performed in a plurality of modes, so that a polycrystalline state in which crystal grain boundaries exist is obtained. I will end up. Also,
With the crystallization method by heat treatment, the required area cannot be grown.

An object of the present invention is to solve the above problems and to efficiently form a region that can be regarded as a single crystal by using an amorphous silicon film formed on a substrate having an insulating surface as a starting film. To provide. Another object is to provide a thin film transistor that is not affected by crystal grain boundaries. Another object is to provide a thin film transistor having a high breakdown voltage and capable of handling a large current. Another object is to provide a thin film transistor without deterioration or fluctuation of characteristics. Another object is to provide a thin film transistor having characteristics similar to those of the case where a single crystal semiconductor is used.

[0018]

In order to solve the above problems, the main invention disclosed in the present specification is to provide a layer of a metal element which is in contact with the surface of an amorphous silicon film and promotes crystallization of silicon. A step of selectively forming, and a step of irradiating the amorphous silicon film with laser light while moving it in a direction in which the area of the amorphous silicon film gradually increases to form a region that can be regarded as a single crystal, And the irradiation of the laser beam is performed in a state where the amorphous silicon film is heated.

Another aspect of the invention is a step of selectively forming a layer of a metal element in contact with the surface of the amorphous silicon film to promote crystallization of silicon, and a step of gradually forming a region in contact with the layer of the metal element. Patterning the amorphous silicon film into a shape in which the area increases, patterning the amorphous silicon film into a shape in which the area gradually increases from the region in contact with the layer of the metal element, And irradiating the crystalline silicon film with laser light while moving in the direction in which the area gradually increases to form a region that can be regarded as a single crystal. It is characterized in that it is performed in a heated state.

In the above structure, the amorphous silicon film is formed on a substrate having an insulating surface such as a glass substrate or a quartz substrate. The amorphous silicon film is formed by a plasma CVD method or a reduced pressure heat CV.
It is formed by method D.

The metal elements that promote the crystallization of silicon include Fe, Co, Ni, Ru, Rh, Pd, Os and I.
One or more kinds selected from r and Pt can be used.

To selectively form the metal element layer, the metal element layer may be formed on the surface of the amorphous silicon film and patterned. Further, as a method for forming a layer of a metal element (also referred to as a layer containing a metal element), a solution containing a metal element is applied to the surface of an amorphous silicon film, and then a heat treatment is applied to form an amorphous layer. The most preferable method is to form a nickel silicide layer on the surface of the silicon oxide film.

In the above structure, "the step of patterning the amorphous silicon film from the region in contact with the layer of the metal element into a shape in which the area thereof gradually increases" means 1 in FIG.
There may be mentioned a step of patterning the shape indicated by 02. The shape 102 shown in FIG. 1A has a shape in which the area gradually increases from the portion where the layer 101 in contact with the metal element is provided at an angle θ.

In the above structure, "a step of forming a region which can be regarded as a single crystal by irradiating the amorphous silicon film with a laser beam while moving in a direction in which the area gradually increases"
Can include the step shown in FIG. In the step shown in FIG. 1B, laser light is irradiated while scanning (moving or scanning) in a direction indicated by an arrow so that crystal growth is sequentially performed from a region 101 in a direction indicated by an arrow 103 in FIG. The state is shown in which the region 104 that can be regarded as a single crystal is formed. As the laser light, for example, excimer laser light can be used.

The region that can be regarded as a single crystal is a region in which no crystal grain boundary (line defect or plane defect) exists. The region that can be regarded as a single crystal can be called a monodomain region. Since there are point defects in the region that can be regarded as a single crystal (monodomain region), hydrogen or halogen element for neutralization 1 × 10 ¹⁷ cm ^{−3 to} 5 × 1
It is contained at a concentration of 0 ¹⁹ cm ^-3 .

In the region which can be regarded as a single crystal, a metal element which promotes crystallization of silicon is contained at a concentration of 1 × 10 ¹⁴ to 1 × 10 ¹⁹ atoms cm ^-3 . These concentrations are SIM
It is defined as the minimum value based on the data obtained by S (secondary ion analysis method).

The measurement of the metal element concentration by SIMS at a concentration of 1 × 10 ¹⁶ atom cm ⁻³ or less is
It is difficult at present. However, it is possible to roughly estimate the concentration of the metal element in the region that can be regarded as a single crystal, from the concentration of the metal element in the solution used when introducing the metal element. That is, the concentration of the metal element in the solution and the SIM
The concentration not measured by SIMS can be roughly estimated based on the relationship with the concentration of the metal element finally remaining in the silicon film measured by S.

Further, in the region which can be regarded as this single crystal,
Carbon and nitrogen atoms are 1 × 10 ¹⁶ atoms cm ^{−3 to} 5 × 1
It is contained at a concentration of 0 ¹⁸ atoms cm ⁻³ and oxygen atoms are contained at a concentration of 1 × 10 ¹⁷ atoms cm ^{−3 to} 5 × 10 ¹⁹ atoms cm ⁻³ . This is because the amorphous silicon film formed by the CVD method was used as the starting film.

According to another aspect of the invention, a step of selectively forming a layer of a metal element in contact with the surface of the amorphous silicon film to promote the crystallization of silicon and a heat treatment are performed to contact the metal element. Crystal growth from the region in the surface direction of the film; forming the crystal growth region in a pattern in which the area gradually increases in the crystal growth direction; and increasing the area gradually. Forming a region which can be regarded as a single crystal by irradiating laser light while moving in a direction of moving the laser light, and irradiating the laser light is performed while heating the silicon film at a temperature of 400 ° C to 600 ° C. Is characterized by.

In the above-mentioned constitution, "the step of performing heat treatment to perform crystal growth in the plane direction of the film from the region in contact with the metal element" can be exemplified by the constitution shown in FIG. 5 (B). In this step, the amorphous silicon film 501 is removed from the region 502 where the layer of the metal element serving as a seed of the crystal is formed.
As indicated by 03, a state is shown in which crystal growth is performed in the plane direction of the film (direction parallel to the substrate on which the film is formed).

In the above structure, as the "step of forming the region where the crystal growth is performed in a shape in which the area gradually increases in the crystal growth direction", there is a step shown in FIG. it can. FIG. 6A shows a state in which a pattern having a shape in which the area thereof gradually increases as shown by 505 in the direction in which the crystal growth by heating shown by arrow 503 is performed is shown.

In the above structure, as a "step of forming a region which can be regarded as a single crystal by irradiating with laser light while moving in the direction in which the area is gradually increased", a step shown in FIG. 6B can be mentioned. This step is a step of irradiating with a laser beam while scanning it in a direction in which the area of the pattern indicated by 505 gradually increases.

In the method using a metal element for promoting crystallization, there are roughly two methods for introducing such a metal element. One of them is to use a metal element as a very thin film by using a "physical forming method" such as a sputtering method or an electron beam evaporation method to form the surface of the amorphous silicon film (or the base film of the amorphous silicon film). It is a method of forming a film on the surface). In these methods, the metal element is introduced into the amorphous silicon film by forming a film of the metal element in contact with the amorphous silicon film.

When this method is used, there is a problem that it is difficult to precisely control the concentration of the metal element introduced into the film.

Further, in order to limit the introduction amount, when forming the film as an extremely thin thin film having a thickness of several tens of liters or less, it is difficult to form a perfect film, and the film of the metal element is an island. Will be formed on the surface to be formed. That is, a discontinuous layer of metal elements is formed.

When the amorphous silicon film is crystallized by using the nonuniform layer of the metal element, the island-shaped regions forming the nonuniform layer are crystallized by seeds (or nuclei). And crystallization progresses. In the crystalline silicon film which has been crystallized under such a condition, a large amount of amorphous component remains. This can be confirmed by observation with an optical microscope or an electron micrograph, and measurement by Raman spectroscopy. It has also been confirmed that the metal component is present in the crystalline silicon film in a partially aggregated state.

The crystalline silicon film finally becomes a semiconductor region. However, the region where the metal component of the crystalline silicon film is present in a partially aggregated state serves as a recombination center of electrons and holes in the semiconductor region. Such recombination centers cause a very bad characteristic such as an increase in leak current of the thin film transistor.

In order to prevent the formation of the non-uniform layer, it is possible to solve it by using, for example, a molecular epitaxy method (MBE method) or the like. However, at present, it is only realized in a limited area.

As described above, the so-called "physical forming method" of forming a thin film of a metal element is not preferable as the method of introducing the metal element. In contrast to the "physical forming method", there is a "chemical forming method" in which a solution containing a metal element that promotes crystallization of silicon is used. In this method, the metal element is included in a solution, and the solution is applied to the surface of an amorphous silicon film or the surface of an oxide film on which the amorphous silicon film is formed by spin coating or the like. .

When the solution contains a metal element, each molecule can be sufficiently dispersed in the solution. Then, this solution is dropped on the formation surface to which the metal element is added and spin-coated by rotating at a rotation speed of 50 to 500 rotations / minute (RPM) to disperse the metal element on the entire formation surface. Let it exist. That is, it is possible to form a uniform layer (continuous layer) on the surface without forming island-shaped regions by metal particles.

When heating or laser light irradiation is performed in this state, the metal element that promotes crystallization of silicon can be atomically diffused into the semiconductor through the oxide film, so that crystal seeds are positively created. Instead, it can be diffused to uniformly crystallize the whole. As a result, it is possible to prevent metal elements from being partially concentrated and to leave a large amount of amorphous components, and uniform and dense crystal growth can be performed.

When the solution is spin-coated at low speed, the metal components in the solution existing on the surface are likely to be supplied on the semiconductor film in an amount more than necessary for solid phase growth. Therefore, this low speed rotation 100
After rotating the substrate at 0 to 10000 revolutions / minute, the rotation speed is increased and typically the substrate is rotated at 2000 to 5000 revolutions / minute. Then, all excess metal components are blown out of the surface of the substrate, and an appropriate amount of metal components can be supplied.

In order to control the amount of metal component introduced, the concentration of the metal element in the solution may be controlled. This method is very useful because the concentration of the metal element finally introduced into the silicon film can be accurately controlled.

As the usable solution, several kinds of solutions can be used depending on the metal element used.
Typically, a metal compound having a solution form can be used. Below, the example of the metal compound which can be utilized for the method using this solution is shown.

(1) When Ni is used as a metal element As a nickel compound, nickel bromide, nickel acetate,
Nickel oxalate, nickel carbonate, nickel chloride, nickel iodide, nickel nitrate, nickel sulfate, nickel formate, nickel oxide, nickel hydroxide, nickel acetylacetonate, 4-cyclohexyl butyrate nickel, 2-ethylhexanoate nickel At least one type of material can be used.

It is also possible to use a mixture of Ni and at least one selected from benzene, toluene xylene, carbon tetrachloride, chloroform, ether, trichloroethylene and freon which are nonpolar solvents.

(2) When Fe (iron) is used as a catalytic element A material known as an iron salt, for example, ferrous bromide (Fe)
Br ₂ 6H ₂ O), ferric bromide (FeBr ₃ 6H ₂
O), ferric acetate (Fe (C ₂ H ₃ O ₂ ) ₃ xH ₂ O), ferrous chloride (FeCl ₂ 4H ₂ O), ferric chloride (FeC
l ₃ 6H ₂ O), ferric fluoride (FeF ₃ 3H ₂ O),
Ferric nitrate (Fe (NO ₃ ) ₃ 9H ₂ O), ferrous phosphate (Fe ₃ (PO ₄ ) ₂ 8H ₂ O), ferric phosphate (FeP
At least one selected from O ₄ 2H ₂ O) can be used.

(3) When Co (cobalt) is used as a catalyst element A material known as a cobalt salt as its compound,
For example cobalt bromide (CoBr6H ₂ O), cobalt acetate _{(Co (C 2 H 3 O} 2) 2 4H 2 O), cobalt chloride (CoCl ₂ 6H ₂ O), cobalt fluoride (CoF ₂ x
H ₂ O) and cobalt nitrate (Co (No ₃ ) ₂ 6H ₂ O) may be used.

(4) Ru (ruthenium) as a catalytic element
In the case of using, a material known as a ruthenium salt, for example, ruthenium chloride (RuCl ₃ H ₂ O) can be used as the compound.

(5) When Rh (rhodium) is used as a catalytic element A material known as a rhodium salt as its compound,
For example, rhodium chloride (RhCl ₃ 3H ₂ O) can be used.

(6) Pd (palladium) as a catalytic element
In the case of using, a material known as a palladium salt such as palladium chloride (PdCl ₂ 2H ₂ O) can be used as the compound.

(7) Os (osmium) as a catalytic element
In the case of using, a material known as an osnium salt, for example, osnium chloride (OsCl ₃ ) can be used as the compound.

(8) Ir (iridium) as catalyst element
In the case of using a material known as an iridium salt as its compound, for example, iridium trichloride (IrCl ₃ 3H ₂ O),
A material selected from iridium tetrachloride (IrCl ₄ ) can be used.

(9) When Pt (platinum) is used as the catalyst element As the compound, a material known as a platinum salt, for example, platinum chloride (PtCl ₄ 5H ₂ O) can be used.

(10) When Cu (copper) is used as the catalyst element: The compound is cupric acetate (Cu (CH ₃ COO))
₂ ), cupric chloride (CuCl ₂ 2H ₂ O), cupric nitrate (Cu (NO ₃ ) ₂ 3H ₂ O) can be used.

(11) When gold is used as the catalytic element As the compound, a material selected from gold trichloride (AuCl ₃ xH ₂ O) and gold chloride salt (AuHCl ₄ 4H ₂ O) can be used.

The method using this solution can also be referred to as a method of forming a film of an organometallic compound containing the metal element on the surface to be formed.

It should be noted that the organometallic compound may be uniformly coated and then subjected to ozone treatment (by irradiation with ultraviolet rays (UV) in oxygen). In this case, a metal oxide film is formed, and crystallization proceeds from this metal oxide film. In this case, the organic matter is convenient because it can be oxidized and vaporized and removed as carbon dioxide gas.

Here, an example of using a solution is shown, but as a method capable of obtaining the same effect as in the case of using a solution, a gas of a metal compound, particularly an organometallic compound is CVD.
There is also a method of forming on the surface to be formed by a method. However, this method has a drawback that it is not as simple as the method using a solution.

The crystallization step using the layer of the metal element obtained by the "physical forming method" such as the sputtering method described above is performed by a non-uniform "anisotropic method" using the metal element that promotes crystallization of silicon. It can be said that it is a “crystal growth method”. On the other hand, the crystallization step using the layer of the metal element obtained by the “chemical formation method” using the solution can be referred to as “isotropic growth”.

[0061]

In the method of manufacturing a semiconductor having the above structure, the crystal growth is made uniform by irradiating the laser light in the direction in which the area of the crystal growth seed is gradually increased. And a region that can be regarded as a single crystal can be obtained.

Further, the non-single-crystal silicon film patterned in such a shape that the area thereof gradually increases from the region where the crystal growth seeds are formed is heated and scanned in a direction in which the area gradually increases. By irradiating the laser beam with laser light, crystal growth can be made uniform, and a region which can be regarded as a single crystal can be obtained.

Further, the silicon film crystal-grown in the direction parallel to the substrate is patterned into a shape such that the area thereof gradually increases. Further, while heating the substrate, the silicon film is scanned in the direction of gradually increasing the area of the laser beam. Since the light is irradiated, the crystal can be grown in a single mode,
A region that can be regarded as a single crystal can be obtained.

[0064]

【Example】

[Embodiment 1] In this embodiment, an amorphous silicon film is formed on a glass substrate, and a region which can be regarded as a single crystal is formed based on the amorphous silicon film. 1 and 3 schematically show the manufacturing process of this embodiment.

As shown in FIG. 3, a silicon oxide film 302 is formed as a base film on a glass substrate 301 to a thickness of 3000 Å by a sputtering method or a plasma CVD method. Next, an amorphous silicon film 303 is formed to a thickness of 500Å by plasma CVD method or low pressure thermal CVD method. (Fig. 3
(A))

Next, a solution (nickel acetate salt solution) containing nickel, which is a metal element that promotes crystallization of silicon, is applied by spin coating, and further 300 to 500 is applied.
A nickel silicide layer 304 is formed by heat treatment at a temperature of 400 ° C., here, at 400 ° C. for one hour. (FIG. 3 (B))

Next, the nickel silicide layer 304 is patterned. By using a fluorine-based etchant (for example, buffer hydrofluoric acid), the nickel silicide layer 30 is formed.
4 can be selectively patterned to form an island-shaped nickel silicide layer 101. Further, the amorphous silicon film 303 is patterned. As a result of this patterning, the state shown in FIG. The cross section taken along the line AA ′ in FIG. 1A corresponds to FIG. The angle θ shown by 100 in FIG. 1A is preferably 90 degrees or less.

Patterned amorphous silicon film 303
Has a shape as shown by 102 in FIG.
And, at one end thereof, an island-shaped nickel silicide layer 1 is formed.
01 is formed.

Next, as shown in FIG. 3D, KrF excimer laser light is irradiated while moving in the direction of 305. The laser light is processed into a linear beam having a longitudinal direction perpendicular to the scanning direction. Also, the sample is 4
It is heated to a temperature of 00 ° C to 600 ° C. By irradiation with laser light, crystal growth is performed in a direction shown by an arrow 103 from a region where the nickel silicide layer 101 is formed, and a region which can be regarded as a single crystal as shown in FIG. ) 104 is formed. Note that FIG. 3E corresponds to a cross section taken along line BB ′ in FIG.

[Embodiment 2] This embodiment is an example of forming a thin film transistor using the region which can be regarded as a single crystal shown in FIG. FIG. 4 shows a manufacturing process of the thin film transistor shown in this embodiment. First, as shown in FIGS. 1C and 4A, a region which can be regarded as a single crystal is patterned to form an active layer 401 of a thin film transistor. C in FIG. 1 (C)
The cross section cut along -C 'corresponds to FIG.

Next, a silicon oxide film 402 which functions as a gate insulating film is formed to cover the active layer 401 to a thickness of 1000 Å. Further, a film containing scandium and containing aluminum as a main component is formed to a thickness of 7,000 Å by an electron beam evaporation method, and patterned to form the gate electrode 403. Next, anodic oxidation using the gate electrode 403 as an anode is performed in an electrolytic solution to form an oxide layer 404. (FIG. 4 (B))

Next, impurity ions are doped to form impurity regions. Here, phosphorus ions are doped. At this time, the gate electrode 403 and the surrounding oxide layer 404 serve as a mask, and phosphorus ions are implanted into the regions 405 and 408. The regions 405 and 408 become the source region and the drain region. Then, in this step, the channel formation region 407 and the offset gate region 4 are formed.
06 will be formed in a self-aligned manner. (FIG. 4
(C))

Next, as the interlayer insulating film 409, a silicon oxide film having a thickness of 6000 Å is formed by the plasma CVD method, contact holes are further formed, and then the source electrode 410 and the drain electrode 411 are made of aluminum.
And are formed. Finally, heat treatment is performed in a hydrogen atmosphere at 350 ° C. to perform hydrogenation, so that the thin film transistor illustrated in FIG. 4D is completed.

[Embodiment 3] In this embodiment, a crystal is grown by heating by the action of a metal element that promotes crystallization of silicon, and a laser beam is irradiated to the region to obtain a single crystal. The present invention relates to a structure for forming a region that can be regarded (mono domain region).

5 and 6 show the configuration of this embodiment. First, an amorphous silicon film (not shown) is formed to a thickness of 500 Å by plasma CVD or low pressure thermal CVD. Although not shown, a glass substrate having a silicon oxide film formed on its surface is used as the substrate.

A nickel acetate solution is applied to the surface of the amorphous film to form a nickel layer or a nickel-containing layer. By patterning, a region indicated by 502 is formed into a rectangular shape having a 3 μm square. And
By adding heat treatment at 550 ° C. for 4 hours, 5
In the region indicated by 02, nickel diffuses from the nickel layer formed on the surface of the region and is crystallized to be a seed for crystal growth. Since the region indicated by 502 is a small region, the region 502 can be transformed into a region which can be regarded as a single crystal in this step.

Next, an amorphous silicon film 501 is formed so as to cover the area indicated by 502. In this state, the amorphous silicon film 5
A state in which a layer 502 containing a metal element (nickel in this embodiment) that promotes crystallization of silicon is formed in contact with a part of 01 is realized.

Next, 400 ° C. to 600 ° C., here 550
Heat treatment is performed at a temperature of ℃ for 4 hours. In this step, the crystal growth proceeds in all directions starting from the region 502 which becomes the seed of crystal growth. This crystal growth progresses two-dimensionally in a direction parallel to the substrate, so that microscopically, the crystal grows in a needle shape or a column shape, and the crystalline silicon film 504 is obtained. The crystal growth indicated by 503 can proceed over 100 μm and the heating temperature required for the growth is 6
Since the temperature is 00 ° C. or lower, there is an advantage that an inexpensive glass substrate having a low strain point can be used.

After the crystal growth shown in FIG. 5B, the crystalline silicon film 504 is patterned into a shape as shown by 505 in FIG. 6A. An enlarged version of the pattern indicated by 505 in FIG. 6A is shown in FIG. 6B.

Further, laser light is irradiated after crystallization by heating. By irradiating a linear laser beam while scanning along the direction indicated by arrow 507, 508
Crystal growth progresses as shown by. During the irradiation with the laser light, the sample is heated to a temperature of 550 ° C. As the laser light, KrF excimer laser light is used. In addition, laser light having a linear shape in a direction perpendicular to the scanning direction is used. The linear laser light is a laser light beam having a width of several millimeters and a length of several tens of centimeters and having a longitudinal direction perpendicular to the moving direction of the laser light.

Since the crystal growth indicated by 508 does not proceed at a plurality of positions at the same time but is sequentially performed in the same direction as the crystal growth shown in FIG. 5B, a single mode may be adopted. it can. Further, since the crystalline silicon film 505 is formed in a pattern in which the area gradually increases in the crystal growth direction, the crystal growth can be made uniform and one large domain (crystal Grain). This is because the side indicated by 509 is 50
It is also largely suppressed that the edge of the pattern shown by 509 becomes a starting point of the crystal growth and the progress of the crystal growth is made so as to be a direction substantially along the crystal growth direction shown by 8. Have contributed. As described above, the pattern indicated by 505 can be made a region which can be regarded as a single crystal relatively easily.

In the structure shown in the present embodiment, first, crystallization by heating is performed by the action of the metal element that promotes crystallization of silicon, and further the crystal growth proceeds smoothly in the direction in which the crystallization progresses. The patterned amorphous region can be regarded as a single crystal by patterning the silicon film crystallized by the heating and further irradiating the laser beam along the direction of crystal growth while heating. It is characterized by being an area.

[Embodiment 4] This embodiment relates to the shape of the pattern of the region (monodomain region) shown as 102 in FIG. 1 and 505 in FIG. 6 that can be regarded as a single crystal. The characteristic of the shape of the pattern of the region shown by 102 in FIG. 1 and 505 in FIG. 6 is that the area gradually increases in the direction of crystal growth.

This is to prevent crystal grain boundaries from being formed due to the crystal growth progressing from a plurality of regions during the crystal growth and the crystal growth from the plurality of regions colliding with each other. That is, by gradually expanding the crystal growth from a single starting point, uniform crystal growth,
In other words, this is to promote single-mode crystal growth to promote the formation of a region that can be regarded as a single crystal.

In order to carry out uniform crystal growth as described above, the region where crystal growth is performed may be gradually increased from the starting point of crystal growth. In the patterns shown in FIG. 1 and FIG. 6, the area gradually increases from the starting point of crystal growth to a certain distance, and the area does not change from a certain place.

However, an amorphous silicon film or a crystalline silicon film formed in a pattern as shown in FIGS. 7A and 7B may be used to form a region that can be regarded as a single crystal. For example, when an amorphous silicon film is patterned into the shape shown in FIG. 7A, a region 704 is contacted with a layer of a metal element that promotes crystallization of silicon such as nickel or a layer containing this metal element. By providing and irradiating laser light while scanning in the direction indicated by 705, crystal growth can be performed from the region indicated by 704 in the direction indicated by arrow 700. As the laser light, it is preferable to use one having a linear beam shape in a direction perpendicular to the scanning direction.

Further, due to the action of the metal element that promotes the crystallization of silicon from the region indicated by 704, the temperature is increased to 7 by heating.
Crystal growth in the direction indicated by 00, and 701
Then, patterning is performed into a shape as shown by. Further, when the laser beam is irradiated while scanning in the direction indicated by 705 while heating, crystal growth is performed again in the direction indicated by 700, and the region indicated by 701 can be regarded as a single crystal. .

The crystal growth carried out in the direction indicated by 700 by the heat treatment is needle-like or columnar,
It does not form a region that can be regarded as a single crystal. That is,
It is a crystal growth in which a grain boundary exists. However, the crystal growth by the irradiation of the laser beam while moving in the direction indicated by 705 is uniform crystal growth starting from 704 (single-mode crystal growth) and is a monodomain region, that is, a single crystal. To form a region that can be regarded as

Then, patterning is performed to form a region 702, whereby a region forming an active layer of a thin film transistor can be obtained, for example.

Even when the pattern as shown in FIG. 7B is adopted, crystal growth can be performed in the same manner as in the case of FIG. 7A. That is, in FIG. 7 (B),
Patterning the amorphous silicon film into a shape like 706,
The metal element accelerating crystallization of silicon is in contact with the portion 708. In this state, by irradiating the laser light while moving it in the direction indicated by 709, 708
With the region indicated by (7) as the starting point of crystal growth, uniform crystal growth can be performed in the direction indicated by 710.
The region indicated by can be a region which can be regarded as a single crystal. Then, patterning is performed to form a region 707, so that a region forming an active layer of a thin film transistor can be obtained, for example.

The angles indicated by 703 and 711 are 9
It is desirable to set it to 0 degrees or less. This is because this angle is 9
This is because if it is larger than 0 degrees, crystal growth from the edges of the patterns shown by 701 and 706 becomes apparent, and crystal growth is performed in a plurality of modes. (As a result of crystal growth in multiple modes, multiple domains are formed and do not become monodomains.)

[Embodiment 5] In this embodiment, plasma treatment is performed on an amorphous silicon film to promote dehydrogenation (desorption of hydrogen) from the amorphous silicon film. ,
This is characterized by promoting crystallization of the amorphous silicon film.

Here, in the step of FIG. 3A, plasma treatment with hydrogen or helium plasma is performed on the amorphous silicon film. This plasma is
By utilizing the CR condition, hydrogen gas or helium gas in a reduced pressure is turned into plasma, and the amorphous silicon film is exposed to this hydrogen plasma.

During the plasma treatment,
It is important to heat the amorphous silicon film at a temperature below its crystallization temperature. The crystallization temperature of the amorphous silicon film varies depending on the film forming method and film forming conditions of the amorphous silicon film, but it is generally appropriate to consider it to be in the range of 600 ° C to 650 ° C. The lower limit is about 400 ° C. Therefore, the heating temperature range is preferably 400 to 600 ° C.

It is also useful to use the strain point of the glass substrate used as a standard for determining the upper limit of the heating temperature. That is, heating is performed at the highest possible temperature, with the strain point of the glass substrate used as the upper limit. By adopting this method, it is possible to suppress the influence of deformation and contraction of the glass substrate and obtain a predetermined effect.

When the plasma treatment of hydrogen is carried out, hydrogen in the amorphous silicon film is combined with hydrogen ions in the plasma to form hydrogen gas, and as a result, desorption of hydrogen from the film is promoted. Further, when plasma treatment with helium is performed, the bond between hydrogen and silicon in the amorphous silicon film is separated by collision of helium ions. Then, the bond between silicon atoms is promoted, and the order of the arrangement of atoms can be increased. This state can be said to be a quasi-crystalline state, and is a state in which it is extremely easy to crystallize.

In this plasma-treated state,
The amorphous silicon film can be crystallized by applying energy by heating or laser light irradiation.
This crystallization can be performed with extremely high reproducibility because the amorphous silicon film is in a state of being easily crystallized by the effect of the plasma treatment, and the crystallinity can be extremely high. it can. [Embodiment 6] In this embodiment, a portion which becomes a seed for crystal growth is formed at one corner of an amorphous silicon film formed on a glass substrate, and a laser beam is scanned and irradiated from that portion. , A structure for crystallizing the front surface of the amorphous silicon film.

FIG. 8 shows an outline of the crystallization process shown in this embodiment. In FIG. 8, reference numeral 801 denotes a stage for disposing the glass substrate 802, which is configured to be movable in the direction opposite to the direction indicated by the arrow 809. That is, by moving the stage 801, the laser light is relatively scanned in the direction indicated by the arrow 809 and is irradiated onto the glass substrate 802. A heater is built in the stage 801, and the glass substrate 802 placed on the stage can be heated to an arbitrary temperature. Reference numeral 803 denotes a portion which becomes a seed for crystal growth formed by utilizing the nickel element. A method of forming the portion 802 which becomes the seed of crystal growth will be described later.

Numeral 804 is a portion 8 which becomes a seed of the above-mentioned crystal growth.
Is an amorphous silicon film formed so as to cover 03. FIG. 8 shows a state in which this amorphous silicon film 804 is relatively scanned and irradiated with a linear laser beam indicated by 808 in the direction indicated by arrow 809.

When irradiating the laser beam, a linear laser beam 806 emitted from a laser irradiating means (not shown).
Is reflected by a mirror 807 and is irradiated onto the amorphous silicon film 804 as a laser beam 808 which is bent in a direction substantially perpendicular to the stage 801. By moving the stage 801 in the direction opposite to the arrow 809 while irradiating the laser beam 808, the laser beam 808 relatively scans in the direction of the arrow 809. Note that the laser light irradiation is performed by a heater in the stage 801.
The glass substrate 802 is heated to 400 to 600 ° C., for example 500.
The heating is performed at a temperature of ℃.

When laser light is irradiated in the state as shown in FIG. 8, crystallization proceeds from the portion 805 of the amorphous silicon film on the portion 803 where the crystal growth seed is formed. Become. Further, since the scanning direction of the laser beam 808 is set to be substantially parallel to the diagonal line of the glass substrate 802,
Crystal growth gradually progresses in a direction in which the area of the amorphous silicon film 804 gradually increases. Thus, the amorphous silicon film 8
The whole 04 can be regarded as a monodomain region.

A method of forming the portion 803 which becomes a seed for crystal growth will be described below. First, an amorphous silicon film 804 is formed by a plasma CVD method or a low pressure thermal CVD method. And
By patterning this amorphous silicon film 804, a pattern (indicated by 803 in the drawing) which becomes a nucleus of crystal growth is formed. Then, the nickel element is brought into contact with and retained on the surface by spin coating. Then, by heat treatment, crystallization is performed and a portion 803 which becomes a seed for crystal growth is formed. Then, an amorphous silicon film 804 is formed so as to cover the portion 803 that becomes a seed for crystal growth, and a sample state as shown in FIG. 8 is obtained.

[Embodiment 7] This embodiment relates to a structure in which after formation of an active layer constituting a TFT, crystal growth is performed from the corner portion of the active layer, and the active layer is regarded as a single crystal region. FIG. 9 shows a state in which an island-shaped region (active layer) obtained by patterning an amorphous silicon film is crystallized by irradiation with laser light.

In FIG. 9, 901 is a linear laser beam with which the amorphous silicon film is irradiated, 902 is an island-shaped patterned amorphous silicon film, and 903 is a seed for crystal growth. It is a part. 903, which is the seed for crystal growth
The method described in the other embodiments may be adopted as the forming method.

FIG. 9 shows that laser light is relatively scanned in the direction of arrow 905 and irradiated, whereby crystal growth progresses from the corners of the island-shaped region 902, It is shown that an active layer of the TFT is formed in a region that can be regarded as a crystal. In the figure, 904 is an active layer transformed into a region that can be regarded as a single crystal.

When irradiating with laser light, a portion 903 to be a seed for crystal growth is formed in advance at a corner portion of the rectangular active layer, and the laser light 901 is used to form this portion 9.
From 03, scan in the direction of a substantially diagonal line. By doing so, the crystal growth can proceed from the portion 903 which becomes a seed of crystal growth as a starting point, and the area of the active layer can be regarded as a single crystal. You can After the crystallization,
The crystal growth seed portion 903 is preferably removed by etching.

[0107]

According to the method of manufacturing a semiconductor according to the present invention, in a method of irradiating a silicon film with a laser beam to form a region which can be regarded as a single crystal, the region which can be regarded as a single crystal is devised, Since the crystal growth is performed by forming a pattern in which the area gradually increases from the starting point of crystal growth, it is possible to prevent crystal growth from multiple regions, which becomes an obstacle when obtaining a region that can be regarded as a single crystal. You can Further, a so-called mono-domain region that can be easily regarded as a single crystal can be obtained only by devising a pattern shape.

By constructing a thin film transistor using this monodomain region, it is possible to obtain a thin film transistor which is not affected by crystal grain boundaries and has characteristics similar to those of the case of using a single crystal semiconductor. Therefore, it is possible to obtain a thin film transistor which has a high breakdown voltage, can handle a large current, and has no deterioration or fluctuation in characteristics.

[Brief description of drawings]

FIG. 1 shows a method for forming a region which can be regarded as a single crystal.

FIG. 2 shows a conventional method of forming a crystal region.

FIG. 3 shows a method for forming a region which can be regarded as a single crystal.

FIG. 4 illustrates a manufacturing process of a thin film transistor.

FIG. 5 shows a crystal growth process of a silicon film.

FIG. 6 shows a process of forming a region which can be regarded as a single crystal.

FIG. 7 shows a process of forming a region that can be regarded as a single crystal.

FIG. 8 shows a laser irradiation process.

FIG. 9 shows a laser irradiation process.

[Explanation of symbols]

101 nickel silicide layer 103, 203 crystal growth direction 102, 202 patterned amorphous silicon film 104 region regarded as a single crystal 201 crystal growth seed 203 crystal growth direction 204 part where crystal growth starts 301 glass substrate 302 base film (Silicon oxide film) 303 Amorphous silicon film 304 Nickel silicide layer 305 Scanning direction of laser light 401 Active layer composed of monodomain region 402 Gate insulating film 403 Gate electrode 404 Oxide layer 405 Source region 406 Offset gate region 407 Channel forming region 408 Drain region 409 Interlayer insulating film 410 Source electrode 411 Drain electrode 501 Amorphous silicon film 502 Nickel-containing crystal growth seed 503 Crystal growth direction 504 Crystalline silicon film 505 Patterning type Shape 507 laser beam scanning direction 508 crystal growth direction 509 pattern edge

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoshi Teramoto 398 Hase, Atsugi City, Kanagawa Prefecture Inside Semiconductor Energy Research Institute Co., Ltd.

Claims (9)

[Claims] 1. A step of selectively forming a layer of a metal element or a layer containing the metal element in contact with the surface of the amorphous silicon film to promote crystallization of silicon; Irradiating the laser light while moving it in a direction in which the area of the amorphous silicon film gradually increases to form a region that can be regarded as a single crystal. A method for manufacturing a semiconductor device, characterized in that the method is performed in a state of heating. 2. A step of selectively forming a layer of a metal element or a layer containing the metal element that promotes crystallization of silicon in contact with the surface of the amorphous silicon film, and contacting the layer of the metal element Patterning the amorphous silicon film into a shape in which the area gradually increases from the region; and irradiating the amorphous silicon film with laser light while moving in the direction in which the area gradually increases, which can be regarded as a single crystal. And a step of forming a region, wherein the laser light irradiation is performed in a state where the amorphous silicon film is heated. 3. A step of selectively forming a layer of a metal element or a layer containing the metal element in contact with the surface of the amorphous silicon film to promote crystallization of silicon, and heating the amorphous silicon film. A step of performing a crystal growth in a plane direction of the film from a region in contact with the metal element by applying a treatment, and forming the crystal growth region in a pattern in which the area gradually increases in the crystal growth direction. And a step of irradiating with a laser beam while moving in a direction in which the area gradually increases to form a region that can be regarded as a single crystal.
A method for manufacturing a semiconductor device, which is performed at a temperature of 0 ° C. while being heated. 4. A step of exposing the amorphous silicon film to plasma, and selectively forming a layer of a metal element or a layer containing the metal element in contact with the surface of the amorphous silicon film to promote crystallization of silicon. And a step of patterning the amorphous silicon film in a shape in which the area of the amorphous silicon film gradually increases from the region in contact with the layer of the metal element, and the laser light is gradually increased in the area of the amorphous silicon film. Forming a region that can be regarded as a single crystal by irradiating the amorphous silicon film while moving it in a direction in which the laser beam is irradiated while the amorphous silicon film is heated. Method. 5. A step of exposing the amorphous silicon film to plasma, and selectively forming a layer of a metal element or a layer containing the metal element in contact with the surface of the amorphous silicon film to promote crystallization of silicon. And a step of performing heat treatment to perform crystal growth in a plane direction of the film from a region in contact with the metal element, and a region where the crystal growth is performed gradually increases in area in the crystal growth direction. A step of forming a pattern, and a step of irradiating with a laser beam while moving in a direction in which the area gradually increases to form a region that can be regarded as a single crystal. ~ 600 ℃
A method for manufacturing a semiconductor device, which is performed in a state of being heated at the temperature of. 6. The metal element according to claim 1, wherein Fe, Co, Ni, Ru, Rh, Pd, Os, and
A method of manufacturing a semiconductor device, wherein one or more kinds of elements selected from Ir and Pt are used. 7. The concentration of a metal element in a region which can be regarded as a single crystal according to any one of claims 1 to 5, is 1 × 10 5.
¹⁶ cm ^{−3 to} 5 × 10 ¹⁹ cm ⁻³ , a method for manufacturing a semiconductor device. 8. In any one of claims 1 to 5, 1 × 1 hydrogen or halogen element is contained in a region which can be regarded as a single crystal.
A method for manufacturing a semiconductor device, wherein the semiconductor device is contained at a concentration of 0 ¹⁷ cm ^{−3 to} 5 × 10 ¹⁹ cm ⁻³ . 9. The carbon and nitrogen atoms in a region which can be regarded as a single crystal according to any one of claims 1 to 5.
It is contained at a concentration of ¹⁶ atom cm ^{−3 to} 5 × 10 ¹⁸ atom cm ⁻³ , and contains oxygen atoms of 1 × 10 ¹⁷ atom cm ^{−3 to} 5 × 1.
A method for manufacturing a semiconductor device, characterized in that it is contained at a concentration of 0 ¹⁹ atoms cm ⁻³ .