JPH09266171A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the concentration of metallic elements in crystalline silicon film making use of the metallic elements which accelerate the crystallization of silicon. SOLUTION: Nickel elements are introduced into an amorphous silicon film 103, and then the first heat treatment for crystallization is performed. Then, irradiation with a laser beam is performed to diffuse the nickel elements existing partially concentrically. After this, the heat treatment in oxidative atmosphere is performed at a temperature higher than the preceding heat treatment. At this time, HCl, etc., are added to the atmosphere. This way, a thermal oxide film 106 is made. At this time, the gettering of the nickel elements is performed in the thermal oxide film 106. Next, the thermal oxide film 106 is removed. By doing it this way, a crystalline silicon film 107 which has high crystal property with low concentration of metallic elements can be obtained.

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 represented by a thin film transistor. In particular, the present invention relates to a method for manufacturing a semiconductor device using a crystalline silicon thin film formed over a glass substrate or a quartz substrate.

[0002]

2. Description of the Related Art Conventionally, a thin film transistor using a silicon film has been known. This is a technique of forming a thin film transistor by using a silicon film formed on a glass substrate or a quartz substrate.

[0003] Glass substrates and quartz substrates are used for
This is because the thin film transistor is used for an active matrix liquid crystal display. Conventionally, a thin film transistor has been formed using an amorphous silicon film, but in order to obtain higher performance, it is attempted to manufacture a thin film transistor using a crystalline silicon film (called a crystalline silicon film). Has been.

A thin film transistor using a crystalline silicon film can operate at a high speed of two digits or more as compared with a thin film transistor using an amorphous silicon film. Therefore, the peripheral drive circuit of the active matrix type liquid crystal display device, which has been constituted by the external IC circuit so far, can be formed on the glass substrate or the quartz substrate in the same manner as the active matrix circuit.

Such a structure is very advantageous for downsizing the entire device and simplifying the manufacturing process. Further, the structure leads to a reduction in manufacturing cost.

Generally, a crystalline silicon film is obtained by crystallizing an amorphous silicon film by a plasma CVD method or a low pressure thermal CVD method, followed by heat treatment or laser light irradiation. There is.

However, in the case of heat treatment, the crystallization becomes uneven, and it is difficult to obtain the required crystallinity over a wide area at present.

Although the method of irradiating laser light can partially obtain high crystallinity, it is difficult to obtain a good annealing effect over a wide area. In particular, irradiation with laser light under the condition that good crystallinity is obtained tends to be unstable.

On the other hand, the technique described in JP-A-6-232059 is known. This technique is a technique in which a metal element (for example, nickel) that promotes crystallization of silicon is introduced into an amorphous silicon film, and a crystalline silicon film is obtained by heat treatment at a temperature lower than that of the conventional technique.

This technique can uniformly obtain high crystallinity over a wide area as compared with the conventional crystallization method only by heating or crystallization of an amorphous film only by irradiation of laser light.

However, it is difficult to obtain a crystalline silicon film having high crystallinity and its uniformity over a large area required for an active matrix type liquid crystal display device.

Further, since the film contains a metal element, the control of the introduction amount is delicate, and there is a problem in reproducibility and stability (electrical stability of the obtained device).

Further, due to the influence of the residual metal element,
For example, there are problems that the characteristics of the obtained semiconductor device change with time and, in the case of a thin film transistor, the OFF value is large.

That is, the metal element that promotes the crystallization of silicon has a useful role for obtaining a crystalline silicon film, but once the crystalline silicon film is obtained, its existence is numerous. It becomes a negative factor that causes the problem of.

[0015]

An object of the invention disclosed in this specification is to provide a semiconductor device having high characteristics by using a crystalline silicon film having high crystallinity.

Another object of the present invention is to provide a technique for reducing the concentration of a metal element in a crystalline silicon film obtained by utilizing a metal element that promotes crystallization of silicon.

An object of the present invention is to provide a technique capable of enhancing the characteristics and reliability of the obtained semiconductor device.

[0018]

One of the inventions disclosed in the present specification is to introduce a metal element which promotes crystallization of silicon into an amorphous silicon film by intentionally introducing a metal element which promotes crystallization of silicon. A step of crystallizing the crystalline silicon film to obtain a crystalline silicon film; a step of irradiating the crystalline silicon film with laser light or strong light; and a second step in an oxidizing atmosphere containing a halogen element. A step of performing heat treatment to remove or reduce the metal element present in the crystalline silicon film, a step of removing the thermal oxide film formed in the step, and a step of removing the thermal oxide film on the surface of the region. And a step of forming a thermal oxide film by thermal oxidation again.

A step of intentionally introducing a metal element that promotes crystallization of silicon into the amorphous silicon film and crystallizing the amorphous silicon film by the first heat treatment to obtain a crystalline silicon film; Irradiating the crystalline silicon film with laser light or intense light to diffuse the metal element present in the crystalline silicon film in the crystalline silicon film; and in an oxidizing atmosphere containing a halogen element. Second heat treatment to getter the metal element present in the crystalline silicon film into a thermal oxide film to be formed, and a step of removing the thermal oxide film formed in the above process, Forming a thermal oxide film on the surface of the region from which the thermal oxide film has been removed by re-thermal oxidation.

According to another aspect of the present invention, a metal element that promotes crystallization of silicon is intentionally introduced into the amorphous silicon film, and the amorphous silicon film is crystallized by the first heat treatment to form crystalline silicon. A step of obtaining a film, a step of patterning the crystalline silicon film to form an active layer of a semiconductor device, a step of irradiating the active layer with laser light or strong light, and an oxidizing property containing a halogen element. A step of performing a second heat treatment in an atmosphere to remove or reduce the metal element present in the active layer; a step of removing the thermal oxide film formed in the step; And a step of forming a thermal oxide film by thermal oxidation.

According to another aspect of the invention, a step of intentionally and selectively introducing a metal element that promotes crystallization of silicon into the amorphous silicon film and a first step for the amorphous silicon film are provided. A step of performing heat treatment, and performing crystal growth in a direction parallel to the film from the region where the metal element is intentionally and selectively introduced;
A step of irradiating the crystalline silicon film with laser light or intense light to diffuse the metal element present in the crystal-grown region; and a second heat treatment in an oxidizing atmosphere containing a halogen element. The gettering of the metal element existing in the crystal-grown region into the thermal oxide film to be formed, the step of removing the thermal oxide film formed in the step, and the removal of the thermal oxide film. And a step of forming a thermal oxide film on the surface of the region by thermal oxidation again.

According to another aspect of the present invention, a metal element that promotes crystallization of silicon is intentionally introduced into the amorphous silicon film, and the amorphous silicon film is crystallized by the first heat treatment to form crystalline silicon. A step of obtaining a film, a step of patterning the crystalline silicon film to form an active layer of a semiconductor device, a step of irradiating the active layer with laser light or strong light, and an oxidizing property containing a halogen element. A step of performing a second heat treatment in an atmosphere to remove or reduce the metal element present in the active layer; a step of removing the thermal oxide film formed in the step; And a step of forming a thermal oxide film by thermal oxidation, wherein the active layer has an inclined shape whose side surface forms an angle of 20 ° to 50 ° with the underlying surface.

In the invention disclosed in this specification, Fe, Co, N are used as the metal elements for promoting the crystallization of silicon.
i, Ru, Rh, Pd, Os, Ir, Pt, Cu, Au
One kind or a plurality of kinds selected from can be used.

As the oxidizing atmosphere containing a halogen element, one or plural kinds selected from HCl, HF, HBr, Cl ₂ , F ₂ and Br _{2 in} an O ₂ atmosphere or an atmosphere containing O _2. It is possible to select the one to which the kind of gas is added.

The impurity concentration in this specification is SIMS.
It is defined as the minimum value of the measurement values measured by (secondary ion analysis method).

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION As a preferred embodiment of the invention disclosed in this specification, an amorphous silicon film is first formed, and this amorphous silicon film is crystallized from silicon typified by nickel. Is crystallized by the action of a metal element that promotes the formation of a crystalline silicon film. This crystallization is performed by heat treatment.

This heat treatment is carried out within the range of 550 ° C. to 750 ° C. The temperature of this heat treatment is 6
It is preferable to carry out at a temperature of 20 ° C. or higher.

In the crystallized state by the above heat treatment, the crystalline silicon film contains the metal element.

Here, laser light irradiation is performed to promote crystallization of the obtained crystalline silicon film, and at the same time, nickel element existing in the film is further diffused (dispersed) in the film.

In the crystallized state in the first heat treatment, the nickel element exists as a lump to some extent. Therefore, by irradiating the above laser light, the nickel element can be dispersed to some extent in a state where gettering is likely to occur later.

After the irradiation of laser light, heat treatment is performed in an oxidizing atmosphere containing HCl to form a thermal oxide film on the surface of the crystalline silicon film.

At this time, the metal element is gettered by the action of chlorine in the thermal oxide film, and the concentration of the metal element in the crystalline silicon film is lowered. At this time, the elemental nickel is vaporized and removed to the outside by the action of chlorine.

The heat treatment for gettering the nickel element is preferably performed at a higher temperature than the heat treatment for crystallization. The temperature is 60
It is preferable to carry out at a temperature higher than 0 ° C, more preferably 640 ° C or higher. Further, the upper limit is suitably a temperature of 750 ° C. or lower.

As a result of the heat treatment for performing the above gettering, a thermal oxide film containing nickel element at a high concentration is formed. By removing this thermal oxide film, a crystalline silicon film having high crystallinity and a low concentration of the metal element can be obtained.

[0035]

【Example】

[Embodiment 1] In this embodiment, a configuration for obtaining a crystalline silicon film on a glass substrate by using nickel element will be described.

In this embodiment, first, a crystalline silicon film having high crystallinity is obtained by the action of nickel element.

Then, laser light irradiation is performed. By irradiating with this laser beam, the crystallinity of the film is enhanced, and nickel elements that are locally concentrated are diffused in the film. That is, the mass of nickel is extinguished.

Then, an oxide film containing a halogen element is formed on the crystalline silicon film by a thermal oxidation method. At this time, the nickel element remaining in the obtained crystalline silicon film is gettered into the thermal oxide film by the action of the halogen element. At this time, since the nickel element is dispersed and present by the previous irradiation of the laser beam, gettering effectively progresses.

Further, as a result of gettering, the thermal oxide film containing nickel element at a high concentration is removed. By doing so, a crystalline silicon film having high crystallinity and a low nickel element concentration is obtained on the glass substrate.

The manufacturing process of this embodiment will be described below with reference to FIG. First, Corning 1737 glass substrate (strain point 66
A silicon oxynitride film 102 is formed as a base film on (7 ° C.) 101 to a thickness of 3000 Å.

The silicon oxynitride film is formed by the plasma CVD method using silane, N ₂ O gas and oxygen as source gases. Alternatively, a plasma CVD method using TEOS gas and N ₂ O gas is used.

The silicon oxynitride film has a function of suppressing diffusion of impurities (a large amount of impurities are contained in the glass substrate at the manufacturing level of a semiconductor) from a glass substrate in a later step. There is.

In order to maximize the function of suppressing the diffusion of impurities, the silicon nitride film is optimum. However, the silicon nitride film is not practical because it peels off from the glass substrate due to the stress. Alternatively, a silicon oxide film can be used as the base film.

It is an important point that the base film 102 has a hardness as high as possible. This is concluded from the fact that, in the durability test of the finally obtained thin film transistor, the hardness of the base film is higher (that is, the etching rate thereof is lower) is more reliable. The reason is considered to be due to the effect of shielding impurities from the glass substrate during the manufacturing process of the thin film transistor.

Further, it is effective to contain a trace amount of a halogen element represented by chlorine in the base film 102. By doing so, in a subsequent step, the metal element that promotes crystallization of silicon existing in the semiconductor layer can be gettered by the halogen element.

Further, it is effective to add hydrogen plasma treatment after forming the base film. Further, it is effective to perform plasma treatment in an atmosphere in which oxygen and hydrogen are mixed.
This is effective in removing the carbon component adsorbed on the surface of the base film and improving the interface characteristics with the semiconductor film formed later.

Next, an amorphous silicon film 103, which will later become a crystalline silicon film, is formed to a thickness of 500Å by a low pressure thermal CVD method.
The low pressure thermal CVD method is used because the crystalline silicon film obtained later is superior in film quality. Specifically, the film quality is dense. In addition, reduced pressure thermal CVD
As a method other than the method, a plasma CVD method can be used.

The amorphous silicon film produced here preferably has an oxygen concentration in the film of 5 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁹ cm ⁻³ . This is because oxygen plays an important role in the subsequent gettering step of the metal element (metal element that promotes crystallization of silicon).

However, it should be noted that if the oxygen concentration is higher than the above concentration range, crystallization of the amorphous silicon film is hindered.

Further, the other impurity concentrations, for example, the nitrogen and carbon impurity concentrations are preferably as low as possible. Specifically, 2 × 1
It is necessary to set the concentration to 0 ¹⁹ cm ^-3 or less.

The upper limit of the thickness of this amorphous silicon film is 2000.
It is about Å. This is because it is disadvantageous that the film is too thick in order to obtain the effect of the subsequent irradiation of laser light. The disadvantage of the thick film is that most of the laser light applied to the silicon film is absorbed on the surface of the film.

The lower limit of the thickness of the amorphous silicon film 103 is
Although it depends on the film forming method, it is practically about 200 Å.

Next, nickel element is introduced to crystallize the amorphous silicon film 103. Here, 10ppm
The nickel element is introduced by applying a nickel acetate solution containing nickel (by weight) to the surface of the amorphous silicon film 103.

As a method of introducing the nickel element, a sputtering method, a CVD method, a plasma treatment or an adsorption method can be used in addition to the method using the above solution.

The method using the above solution is simple,
It is also useful in that the concentration of the metal element can be easily adjusted.

By applying the nickel acetate solution, a water film of the nickel acetate solution is formed as indicated by 104 in FIG. 1 (A). After obtaining this state, the extra solution is blown off using a spinner (not shown). Thus, the nickel element is held in contact with the surface of the amorphous silicon film 103.

Considering residual impurities in the subsequent heating step, it is preferable to use nickel sulfate instead of the nickel acetate salt solution. This is because the nickel acetate salt solution contains carbon, which may be carbonized in the subsequent heating step and remain in the film.

The amount of nickel element introduced can be adjusted by adjusting the concentration of nickel element in the solution.

Then, in the state shown in FIG.
A heat treatment is performed at a temperature of 550 ° C. to 650 ° C. to crystallize the amorphous silicon film 103 to obtain a crystalline silicon film 105. This heat treatment is performed in a reducing atmosphere.

The temperature of this heat treatment is preferably a temperature below the strain point of the glass substrate. Corning 173
Since the strain point of the 7 glass substrate is 667 ° C., it is preferable that the upper limit of the heating temperature here is about 650 ° C. with a margin.

Here, the atmosphere for this heat treatment is changed to hydrogen.
% Nitrogen atmosphere. The heating temperature is 620 ° C.
And The heating time is 4 hours.

In the crystallization process by the above heat treatment, the atmosphere is made to be a reducing atmosphere in order to prevent oxides from being formed during the heat treatment process. Specifically, nickel reacts with oxygen to form Ni
This is to prevent O _{X from} being formed on the surface of the film or in the film.

Oxygen is added in the gettering step which will be described later.
When combined with nickel, it makes a great contribution to nickel gettering. However, it has been found that the combination of oxygen and nickel at this crystallization stage inhibits crystallization. Therefore, in this crystallization process by heating, it is important to suppress the formation of oxides as much as possible.

The oxygen concentration in the atmosphere in which the heat treatment for crystallization is performed is in the ppm order, preferably 1 pp.
It is necessary to be m or less.

In addition to nitrogen, an inert gas such as argon can be used as the gas occupying most of the atmosphere for performing the heat treatment for crystallization.

After the crystallization step by the above heat treatment, the nickel element remains as a lump to some extent. This has been confirmed by observation with a TEM (transmission electron microscope).

The cause of the fact that nickel exists in a certain amount of lumps is not clear, but it is considered to be related to some crystallization mechanism.

Next, laser light irradiation is performed as shown in FIG. Here, a KrF excimer laser (wavelength 248 nm) is used. Here, a method of irradiating while scanning a laser beam having a linear beam shape is adopted.

By irradiating with this laser beam, nickel element, which has been locally concentrated, is dispersed to some extent in the film 105 as a result of the crystallization by the above-mentioned heat treatment. That is, it is possible to eliminate the solidified nickel element and disperse the nickel element.

Next, another heat treatment is performed in the step shown in FIG. This heat treatment is performed to form a thermal oxide film for gettering the nickel element. Here, this heat treatment is performed in an atmosphere containing a halogen element. Specifically, heat treatment is performed in an oxygen atmosphere containing 5% HCl. (Fig. 1 (D))

In this step, the nickel element (or other metal element that promotes crystallization of silicon) intentionally mixed in the initial stage for crystallization is added to the crystalline silicon film 105.
This is a process for removing it from the inside. This heat treatment is performed at a higher temperature than the heat treatment performed to perform the above-described crystallization. This is an important condition for effective gettering of nickel element.

This heat treatment is carried out at a temperature of 600 ° C. to 750 ° C. after satisfying the above conditions. The gettering effect of nickel element in this step can be remarkably obtained when the temperature is higher than 600 ° C.

In this step, the nickel element dispersed by the above-mentioned laser light irradiation is effectively gettered into the oxide film.

The upper limit of the heat treatment temperature is limited by the strain point of the glass substrate used. It should be noted that heat treatment at a temperature above the strain point of the glass substrate used will deform the substrate.

HCl is preferably mixed in a proportion of 0.5% to 10% (volume%) with respect to oxygen. It should be noted that when the concentration is higher than this concentration, the surface of the film will be roughened to have irregularities on the order of the film thickness.

When the heat treatment is performed under such conditions, as shown in FIG.
Thermal oxide film 106 containing chlorine as shown in FIG.
Is formed. Here, the heat treatment time is 12 hours,
The film thickness of the thermal oxide film 106 is 100 Å.

By forming the thermal oxide film 106, the thickness of the crystalline silicon film 103 becomes about 450 Å.

In this heat treatment, the heating temperature is 60
In the case of 0 ° C to 750 ° C, the treatment time (heating time) is 10 hours to 48 hours, typically 24 hours.

Of course, this processing time may be set at a proper time depending on the film thickness of the oxide film to be obtained.

In this step, the nickel element is gettered to the outside of the silicon film by the action of the halogen element. Here, due to the action of chlorine, nickel element is gettered in the formed thermal oxide film 106.

In this gettering, oxygen existing in the crystalline silicon film plays an important role. That is, the gettering effect of chlorine acts on nickel oxide formed by the combination of oxygen and nickel, and the gettering of nickel element effectively progresses.

As described above, if the concentration of oxygen is too high, it becomes a factor that hinders the crystallization of the amorphous silicon film 103 in the crystallization process shown in FIG. However, as mentioned above, its presence plays an important role in the nickel gettering process. Therefore, it is important to control the oxygen concentration existing in the amorphous silicon film that is the starting film.

Here, an example is shown in which Cl is selected as the halogen element and HCl is used as the method of introducing it. Gases other than HCl include HF, HBr, Cl
_One or more kinds selected from ₂ , F ₂ and Br ₂ can be used. In general, a halogen hydride can be used.

The content (volume content) of these gases in the atmosphere is 0.25 to 5% for HF, 1 to 15% for HBr, 0.25 to 5% for Cl ₂ , and F ₂ If
It is preferably 0.125 to 2.5%, and Br ₂ is preferably 0.5 to 10%.

If the concentration is lower than the above range, no significant effect can be obtained. If the concentration is higher than the above range, the surface of the silicon film will be roughened.

Through this step, the nickel element concentration can be reduced to 1/10 or less of the initial concentration. This means that the nickel element can be reduced to 1/10 or less as compared with the case where no gettering with a halogen element is performed. This effect can be obtained similarly even when another metal element is used.

Further, in the above process, nickel element is gettered in the oxide film to be formed, so that the nickel concentration in the oxide film is naturally higher than that in other regions.

Further, it is observed that the nickel element tends to be high in the vicinity of the interface between the silicon film 105 and the thermal oxide film 106. It is considered that this is because the region where gettering is mainly performed is on the oxide film side near the interface between the silicon film and the oxide film. It is considered that the gettering progresses near the interface due to the presence of stress and defects near the interface.

Then, the oxide film 106 containing a high concentration of nickel is removed. The oxide film 106 is removed by wet etching using buffer hydrofluoric acid (other hydrofluoric acid-based etchant) or dry etching.

Thus, as shown in FIG. 1 (E), a crystalline silicon film 107 having a reduced nickel content can be obtained.

Since the vicinity of the surface of the obtained crystalline silicon film 107 contains a relatively high concentration of nickel element,
It is effective to further advance the etching of the oxide film 106 to slightly overetch the surface of the crystalline silicon film 107.

Further, it is effective to irradiate the laser beam again after removing the thermal oxide film 106 to further promote the crystallinity of the obtained crystalline silicon film 107. That is, it is effective to irradiate the laser beam again after the gettering of the nickel element is performed.

In this embodiment, an example in which a KrF excimer laser (wavelength 248 nm) is used as the laser light used is shown. However, an XeCl excimer laser (wavelength 308 nm) or another type of excimer laser may be used.

Instead of laser light, for example, ultraviolet light or infrared light may be irradiated.

[Embodiment 2] This embodiment is an example in which Cu is used as the metal element for promoting crystallization of silicon in the structure shown in Embodiment 1. In this case, as a solution for introducing Cu, cupric acetate (Cu (CH ₃ C
OO) ₂ ) or cupric chloride (CuCl ₂ 2H ₂ O) may be used.

[Embodiment 3] This embodiment relates to an example in which crystal growth of a form different from that of Embodiment 1 is performed. This embodiment relates to a method called lateral growth for performing crystal growth in a direction parallel to a substrate by using a metal element that promotes crystallization of silicon.

FIG. 2 shows the manufacturing process of this embodiment. First,
Corning 1737 glass substrate (quartz substrate may be used) 2
01 as a base film 202 and a silicon oxynitride film 3000
The film is formed to a thickness of Å.

Next, an amorphous silicon film 203 serving as a starting film of the crystalline silicon film is formed to a thickness of 600 Å by a low pressure thermal CVD method. The thickness of this amorphous silicon film is preferably 2000 Å or less as described above.

The plasma CVD method may be used instead of the low pressure thermal CVD method.

Next, a silicon oxide film (not shown) is formed to a thickness of 1500 Å and patterned to form 2
A mask indicated by 04 is formed. This mask is 205
An opening is formed in a region indicated by. This opening 20
5 is formed in the region where the amorphous silicon film 20 is formed.
3 is exposed.

The opening 205 has an elongated rectangular shape having a longitudinal direction in the depth direction and the front direction of the drawing. It is appropriate that the width of the opening 203 is 20 μm or more. The length in the longitudinal direction may be formed to a required length.

Then, 10 p in terms of weight as shown in Example 1.
A nickel acetate solution containing pm of nickel element is applied. Then, spin drying is performed using a spinner (not shown) to remove an excess solution.

In this way, a state in which the nickel element is held in contact with the exposed surface of the amorphous silicon film 203 as shown by the dotted line 206 in FIG. 2A is realized.

Next, heat treatment is performed at 640 ° C. for 4 hours in a nitrogen atmosphere containing hydrogen of 3% and containing oxygen as little as possible. Then, crystal growth proceeds in a direction parallel to the substrate 201 as indicated by 207 in FIG. This crystal growth proceeds from the region of the opening 205 into which nickel element has been introduced toward the periphery. The crystal growth in the direction parallel to the substrate is called lateral growth or lateral growth.

Under the conditions shown in this embodiment, this lateral growth can be performed over 100 μm or more. Thus, a silicon film 208 having a laterally grown region is obtained. In the region where the opening 205 is formed, crystal growth progresses in the vertical direction called vertical growth from the surface of the silicon film toward the base interface.

Then, the mask 204 made of a silicon oxide film for selectively introducing the nickel element is removed. Thus, the state shown in FIG. 2C is obtained. In this state, a vertically grown region, a laterally grown region, and a region (which has an amorphous state) where crystal growth has not reached exist in the silicon film 208.

In this state, the nickel element is unevenly distributed in the film. In particular, the nickel element is present at a relatively high concentration in the region where the opening 205 has been formed and in the tip portion of the crystal growth indicated by 207.

After obtaining the state shown in FIG. 2C, laser light irradiation is performed. Here, irradiation with a KrF excimer laser is performed as in the first embodiment.

In this step, the unevenly distributed nickel element is diffused to obtain a state in which gettering is easily performed in the subsequent gettering step.

After the laser light irradiation is completed, a heat treatment is performed at 650 ° C. for 12 hours in an oxygen atmosphere containing 3% of HCl.
Do time. In this step, an oxide film 209 containing nickel element in high concentration is formed. At the same time, the nickel element concentration in the silicon film 208 can be relatively reduced. (Fig. 2 (D))

Here, the thermal oxide film indicated by 209 is 1
It is deposited to a thickness of 00Å. This thermal oxide film contains a high concentration of nickel element gettered by the action of chlorine. Further, by forming the thermal oxide film 209, the crystalline silicon film 208 has a film thickness of about 500 Å.

Next, the thermal oxide film 209 containing a high concentration of nickel element is removed.

The crystalline silicon film in this state has a concentration distribution such that nickel element exists in a high concentration toward the surface of the crystalline silicon film. This state is due to the fact that the nickel element was gettered into the thermal oxide film when the thermal oxide film 209 was formed.

Therefore, after removing the thermal oxide film 209, it is useful to further etch the surface of the crystalline silicon film to remove the region where the nickel element is present at a high concentration. That is, by etching the surface of the crystalline silicon film in which nickel element is present at a high concentration, a crystalline silicon film with a reduced nickel element concentration can be obtained. However, in this case, it is necessary to consider the film thickness of the finally obtained silicon film.

Next, patterning is performed to form a pattern 210 composed of a lateral growth region.

The concentration of nickel element remaining in the pattern 210 composed of the lateral growth region thus obtained can be made lower than that in the case of the first embodiment.

This is because the concentration of the metal element contained in the lateral growth region is low in the first place. In particular,
It is possible to easily set the concentration of nickel element in the pattern 209 formed of the lateral growth region to the order of 10 ¹⁷ cm ⁻³ or less.

Further, when the thin film transistor is formed by utilizing the lateral growth region, as compared with the case of utilizing the vertical growth region (the entire surface is vertically grown in the case of the first embodiment) as shown in the first embodiment, One having higher mobility can be obtained.

It is useful to remove the nickel element existing on the surface of the pattern by further performing etching after forming the pattern shown in FIG. 2 (E).

Then, after forming a pattern of 210, a thermal oxide film 211 is formed. The formation of this thermal oxide film is 6
A heat treatment is performed in an oxygen atmosphere at 50 ° C. for 12 hours to form a film having a thickness of 200 Å.

This thermal oxide film will later become a part of the gate insulating film if it constitutes a thin film transistor.

After that, if a thin film transistor is to be manufactured, the thermal oxide film 211 is covered and the plasma CV is further applied.
A silicon oxide film is formed by the D method or the like to form a gate insulating film.

[Embodiment 4] In this embodiment, a thin film transistor arranged in a pixel region of an active matrix liquid crystal display device or an active matrix EL display device is manufactured by utilizing the invention disclosed in this specification. Here is an example.

FIG. 3 shows the manufacturing process of this embodiment. First,
A crystalline silicon film is formed on the glass substrate by the process shown in the first or third embodiment. When a crystalline silicon film is obtained with the configuration shown in Example 1, the state shown in FIG. 3A is obtained by patterning the crystalline silicon film.

In the state shown in FIG. 3A, 301 is a glass substrate, 302 is a base film, and 303 is an active layer composed of a crystalline silicon film. After obtaining the state shown in FIG. 3A, plasma treatment is performed in a reduced pressure atmosphere in which oxygen and hydrogen are mixed. This plasma is generated by high frequency discharge.

By this plasma treatment, the active layer 303
The organic matter present on the exposed surface of is removed. To be precise, the oxygen plasma oxidizes the organic substances adsorbed on the surface of the active layer, and the hydrogen plasma further reduces and vaporizes the oxidized organic substances. Thus the active layer 3
Organic matter present on the exposed surface of 03 is removed.

The removal of this organic substance is very effective in suppressing the presence of fixed charges on the surface of the active layer 303. The fixed charge resulting from the presence of the organic substance hinders the operation of the device and causes the instability of the characteristics, and reducing the presence thereof is very useful.

After removing the organic substances, thermal oxidation is performed in an oxygen atmosphere at 640 ° C. to obtain a 100 Å thermal oxide film 3.
00 is formed. This thermal oxide film has high interface characteristics with the semiconductor layer and will later form a part of the gate insulating film. Thus, the state shown in FIG. 3A is obtained.

After obtaining the state shown in FIG. 3A, a silicon oxynitride film 304 forming a gate insulating film is formed to a thickness of 1000 Å. As a film forming method, a plasma CVD method using a mixed gas of oxygen, silane and N ₂ O or a plasma CVD method using a mixed gas of TEOS and N ₂ O is used.

This silicon oxynitride film 304 is a thermal oxide film 30.
Together with 0, it functions as a gate insulating film.

It is effective to contain a halogen element in the silicon oxynitride film. That is, by fixing the nickel element by the action of the halogen element, the function of the gate insulating film as the insulating film is affected by the effect of the nickel element (other metal element that promotes crystallization of silicon) existing in the active layer. It can be prevented from falling.

The use of the silicon oxynitride film has the significance that the metal element is less likely to enter the gate insulating film due to its dense film quality. When a metal element enters the gate insulating film, its function as an insulating film deteriorates, which causes instability and variations in the characteristics of the thin film transistor.

A commonly used silicon oxide film can be used as the gate insulating film.

After the silicon oxynitride film 304 which functions as a gate insulating film is formed, an aluminum film (not shown) which later functions as a gate electrode is formed by the sputtering method. 0.2% by weight of scandium is contained in this aluminum film.

The reason why scandium is contained in the aluminum film is to suppress the generation of hillocks and whiskers in the subsequent steps. Hillocks and whiskers mean that abnormal heating of aluminum occurs due to heating, and needle-like or prickle-like protrusions are formed.

After forming the aluminum film, a dense anodic oxide film (not shown) is formed. This anodic oxide film is 3%
Ethylene glycol solution containing tartaric acid is used as an electrolytic solution. That is, in this electrolytic solution, by performing anodization with the aluminum film as the anode and platinum as the cathode,
An anodized film having a dense film quality is formed on the surface of the aluminum film.

The film thickness of the anodic oxide film having a dense film quality (not shown) is about 100 Å. This anodic oxide film has a role of improving the adhesiveness with the resist mask formed later.

The thickness of this anodic oxide film can be controlled by the applied voltage during anodic oxidation.

Next, a resist mask 306 is formed. Then, the aluminum film is patterned into a pattern indicated by 305. Thus, the state shown in FIG. 3B is obtained.

Here, anodic oxidation is performed again. here,
A 3% oxalic acid aqueous solution is used as the electrolytic solution. By performing anodization in this electrolytic solution using the aluminum pattern 305 as an anode, a porous anodic oxide film 308 is formed.

In this step, the anodic oxide film 308 is selectively formed on the side surface of the aluminum pattern due to the existence of the resist mask 306 having high adhesiveness on the upper portion.

This anodic oxide film can be grown to a thickness of several μm. Here, the film thickness is 600
0 °. The growth distance can be controlled by the anodic oxidation time.

Then, the resist mask 306 is removed.
Further, a dense anodic oxide film is formed again. That is,
Anodization is again performed using the above-mentioned ethylene glycol solution containing 3% tartaric acid as an electrolytic solution. Then
Due to the electrolytic solution entering the porous anodic oxide film 308, an anodic oxide film having a dense film quality is formed as indicated by 309.

The film thickness of the dense anodic oxide film 309 is 10
00 °. This film thickness is controlled by the applied voltage.

Here, the exposed silicon oxynitride film 304 and the thermal oxide film 300 are etched. This etching uses dry etching. Then, a porous anodic oxide film 308 is formed by using a mixed acid obtained by mixing acetic acid, nitric acid, and phosphoric acid.
Is removed. Thus, the state shown in FIG. 3D is obtained.

After obtaining the state shown in FIG. 3D, impurity ions are implanted. Here, P (phosphorus) ions are implanted by a plasma doping method in order to manufacture an N-channel thin film transistor.

In this step, regions 311 and 315 that are heavily doped and 312 that are lightly doped are used.
And 314 are formed. This is because part of the remaining silicon oxide film 310 functions as a semi-transparent mask, and part of the implanted ions is shielded there.

Irradiation with laser light or intense light activates the region into which the impurity ions have been implanted. Thus, the source region 311, the channel formation region 313, the drain region 315, and the low concentration impurity region 312 are formed.
And 314 are formed in a self-aligned manner.

Here, what is indicated by 314 is LDD.
This is a region called a (lightly doped drain) region.
(FIG. 3 (D))

The thickness of the dense anodic oxide film 309 is set to 2
When the thickness is made thicker than 000Å or more, the offset gate region can be formed outside the channel formation region 313 with the thickness.

Although the off-gate region is formed also in this embodiment, it is not shown in the drawing because its size is small and its contribution is small and the drawing is complicated.

Next, as the interlayer insulating film 316, a silicon oxide film,
Alternatively, a silicon nitride film or a stacked film thereof is formed. The interlayer insulating film may be formed by forming a layer made of a resin material on a silicon oxide film or a silicon nitride film.

Then, contact holes are formed, and a source electrode 317 and a drain electrode 318 are formed. Thus, the thin film transistor shown in FIG. 3E is completed.

[Embodiment 5] This embodiment relates to a method of forming the gate insulating film 304 in the structure shown in the practical example 4. When a quartz substrate or a glass substrate having high heat resistance is used as the substrate, a thermal oxidation method can be used as a method for forming the gate insulating film.

The thermal oxidation method can make the film quality dense and is useful in obtaining a thin film transistor having stable characteristics.

That is, the oxide film formed by the thermal oxidation method is one of the most suitable as the gate insulating film because it is dense as an insulating film and can reduce the movable charges existing therein.

As a method of forming the thermal oxide film, an example of performing heat treatment in an oxidizing atmosphere at a temperature of 950 ° C. can be mentioned.

At this time, it is effective to mix HCl or the like in the oxidizing atmosphere. By doing so, the metal element existing in the active layer can be fixed simultaneously with the formation of the thermal oxide film.

It is also effective to mix N ₂ O gas in an oxidizing atmosphere to form a thermal oxide film containing a nitrogen component. Here, by optimizing the mixing ratio of N ₂ O gas, it is possible to obtain a silicon oxynitride film by a thermal oxidation method.

In this embodiment, especially the thermal oxide film 3 is used.
00 need not be formed.

[Embodiment 6] This embodiment shows an example in which a thin film transistor is manufactured by a process different from that shown in FIGS.

FIG. 4 shows the manufacturing process of this embodiment. First,
A crystalline silicon film is formed on the glass substrate by the process shown in the first or third embodiment. Then, by patterning it, the state shown in FIG.

After the state shown in FIG. 4A is obtained, plasma treatment is performed in a mixed reduced pressure atmosphere of oxygen and hydrogen.

In the state shown in FIG. 4A, 401 is a glass substrate, 402 is a base film, and 403 is an active layer composed of a crystalline silicon film. A thermal oxide film 400 is formed again after removing the thermal oxide film for gettering.

After obtaining the state shown in FIG. 4A, a silicon oxynitride film 404 forming a gate insulating film is formed to a thickness of 1000 Å. As a film forming method, a plasma CVD method using a mixed gas of oxygen, silane and N ₂ O or a plasma CVD method using a mixed gas of TEOS and N ₂ O is used.

The silicon oxynitride film 404 constitutes a gate insulating film together with the thermal oxide film 400. Note that a silicon oxide film can be used instead of the silicon oxynitride film.

After the silicon oxynitride film 404 which functions as a gate insulating film is formed, an aluminum film (not shown) which later functions as a gate electrode is formed by the sputtering method. 0.2% by weight of scandium is contained in this aluminum film.

After forming the aluminum film, a dense anodic oxide film (not shown) is formed. This anodic oxide film is 3%
Ethylene glycol solution containing tartaric acid is used as an electrolytic solution. That is, in this electrolytic solution, by performing anodization with the aluminum film as the anode and platinum as the cathode,
An anodized film having a dense film quality is formed on the surface of the aluminum film.

The film thickness of the anodic oxide film having a dense film quality (not shown) is about 100Å. This anodic oxide film has a role of improving the adhesiveness with the resist mask formed later.

The film thickness of this anodic oxide film can be controlled by the applied voltage during anodic oxidation.

Next, a resist mask 405 is formed. Then, the aluminum film is patterned into a pattern 406.

Here, anodic oxidation is performed again. here,
A 3% oxalic acid aqueous solution is used as the electrolytic solution. In this electrolytic solution, anodic oxidation is performed using the aluminum pattern 406 as an anode to form a porous anodic oxide film 407.

In this step, the anodic oxide film 407 is selectively formed on the side surface of the aluminum pattern due to the existence of the resist mask 405 having high adhesion on the upper portion.

This anodic oxide film can be grown to a thickness of several μm. Here, the film thickness is 600
0 °. The growth distance can be controlled by the anodic oxidation time.

Then, the resist mask 405 is removed.
Further, a dense anodic oxide film is formed again. That is,
Anodization is again performed using the above-mentioned ethylene glycol solution containing 3% tartaric acid as an electrolytic solution. Then
Since the electrolytic solution enters the porous anodic oxide film 407, an anodic oxide film having a dense film quality is formed as indicated by 408. (Fig. 2 (C))

Here, the first impurity ion implantation is performed. This step may be performed after removing the resist mask 405.

A source region 409 and a drain region 411 are formed by the implantation of the impurity ions. Also 4
Impurity ions are not implanted in the region 10.

Then, the porous anodic oxide film 307 is removed using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. Thus, the state shown in FIG. 4D is obtained.

After obtaining the state shown in FIG. 4D, the impurity ions are implanted again. The impurity ions are formed under light doping conditions rather than the initial impurity ion implantation conditions.

In this step, the lightly doped region 41 is formed.
2 and 413 are formed. The region indicated by 414 becomes the channel formation region. (FIG. 4 (D))

Irradiation with laser light or intense light activates the region into which the impurity ions have been implanted. Thus, the source region 409, the channel formation region 414, the drain region 411, and the low concentration impurity region 412.
And 413 are formed in a self-aligned manner.

Here, LDD is indicated by 413.
This is a region called a (lightly doped drain) region.
(FIG. 4 (D))

Next, a silicon oxide film is formed as an interlayer insulating film 414,
Alternatively, a silicon nitride film or a stacked film thereof is formed. The interlayer insulating film may be formed by forming a layer made of a resin material on a silicon oxide film or a silicon nitride film.

Then, contact holes are formed, and a source electrode 416 and a drain electrode 417 are formed. Thus, the thin film transistor shown in FIG. 4E is completed.

[Embodiment 7] This embodiment relates to an example in which an N-channel type thin film transistor and a P-channel type thin film transistor are configured in a complementary type.

The structure shown in this embodiment can be used, for example, in various thin film integrated circuits integrated on an insulating surface. Further, it can be used, for example, in a peripheral drive circuit of an active matrix type liquid crystal display device.

First, as shown in FIG. 5A, the glass substrate 5
On 01, a silicon oxide film or a silicon oxynitride film is formed as a base film 502. It is preferable to use a silicon oxynitride film.

Further, an amorphous silicon film (not shown) is formed by the plasma CVD method or the low pressure thermal CVD method. Further, the amorphous silicon film is transformed into a crystalline silicon film by the method shown in the first embodiment.

Then, plasma treatment is performed in a mixed atmosphere of oxygen and hydrogen. Further, the obtained crystalline silicon film is patterned to obtain active layers 503 and 504. Thus, the state shown in FIG.

Here, in order to suppress the influence of carriers moving on the side surface of the active layer, in the state shown in FIG. 5A, 65% in a nitrogen atmosphere containing 3% HCl.
Heat treatment is performed at 0 ° C. for 10 hours.

If a trap level exists on the side surface of the active layer due to the presence of a metal element, the OFF current characteristic is deteriorated. Therefore, the treatment shown here is performed to reduce the level density on the side surface of the active layer. It is useful to keep.

Further, the thermal oxide film 5 constituting the gate insulating film
00 and a silicon oxynitride film 505 are formed. Here, if quartz is used as the substrate, it is desirable to form the gate insulating film with only the thermal oxide film by using the above-mentioned thermal oxidation method.

Then, an aluminum film (not shown) for forming a gate electrode later is formed to a thickness of 4000 Å. Other than the aluminum film, a metal that can be anodized (for example, tantalum) can be used.

After forming the aluminum film, an extremely thin and dense anodic oxide film is formed on the surface thereof by the method described above.

Next, a resist mask (not shown) is placed on the aluminum film to pattern the aluminum film. Then, anodic oxidation is performed using the obtained aluminum pattern as an anode to form porous anodic oxide films 508 and 50.
9 is formed. The thickness of this porous anodic oxide film is, for example, 5000 Å.

Further, the anodic oxidation is performed again under the condition that the dense anodic oxide film is formed to obtain the dense anodic oxide films 510 and 511.
To form Here, the film thickness of the dense anodic oxide films 510 and 511 is set to 800 Å. Thus, the state shown in FIG. 5B is obtained.

Further, the exposed silicon oxide film 505 and the thermal oxide film 500 are removed by dry etching.
The state shown in (C) is obtained.

After obtaining the state shown in FIG. 5C, the porous anodic oxide films 508 and 509 are removed by using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. Thus, the state shown in FIG. 5D is obtained.

Here, resist masks are alternately arranged so that P ions are implanted into the left thin film transistor and B ions are implanted into the right thin film transistor.

By implanting the impurity ions, the source region 514 and the drain region 517 having a high concentration of N type are formed.
Are formed in a self-aligned manner.

Further, a region 515 having a weak N type, which is lightly doped with P ions, is formed at the same time. Also,
The channel formation region 516 is formed at the same time.

The region having a weak N type indicated by 515 is formed because the remaining gate insulating film 512 exists. That is, P that has passed through the gate insulating film 512
This is because some of the ions are shielded by the gate insulating film 512.

Further, according to the same principle, the source region 521 and the drain region 518 having strong P type are formed in a self-aligned manner. Further, the low concentration impurity region 520 is formed at the same time. In addition, the channel formation region 519 is formed at the same time.

When the dense anodic oxide films 510 and 511 have a large film thickness of 2000 Å, the offset gate region can be formed in contact with the channel forming region with that thickness.

In the case of this embodiment, the dense anodic oxide film 51 is used.
Since the film thicknesses of 0 and 511 are as thin as 1000 Å or less, their existence can be ignored.

Then, laser light or intense light is irradiated to anneal the region into which the impurity ions are implanted.

Then, as shown in FIG. 5E, a silicon nitride film 522 and a silicon oxide film 523 are formed as an interlayer insulating film. Each film thickness shall be 1000Å. Note that the silicon oxide film 523 may not be formed.

Here, the thin film transistor is covered with the silicon nitride film. Since the silicon nitride film is dense and has good interface characteristics, the reliability of the thin film transistor can be improved by adopting such a structure.

Further, an interlayer insulating film 524 made of a resin material is formed by spin coating. Here, the thickness of the interlayer insulating film 524 is 1 μm. (FIG. 5E)

Then, a contact hole is formed, and the source electrode 52 of the left N-channel type thin film transistor is formed.
5 and the drain electrode 526 are formed. At the same time, the source electrode 527 and drain electrode 5 of the thin film transistor on the right side
26 is formed. Here, 526 is commonly arranged.

In this way, a thin film transistor circuit having a complementary CMOS structure can be formed.

In the structure shown in this embodiment, a thin film transistor is covered with a nitride film and further covered with a resin material. This structure can be made highly durable so that mobile ions and moisture do not easily enter.

Further, when a multilayer wiring is further formed, it is possible to prevent a capacitance from being formed between the thin film transistor and the wiring.

[Embodiment 8] This embodiment shows an example in which the nickel element is directly introduced into the surface of the base film in the step shown in Embodiment 1. In this case, the nickel element is held in contact with the lower surface of the amorphous silicon film.

In this case, the nickel element is introduced after the formation of the base film, and the nickel element (the metal element concerned) is first held in contact with the surface of the base film. As a method for introducing the nickel element, a sputtering method, a CVD method, or an adsorption method can be used in addition to the method using a solution.

[Embodiment 9] This embodiment is a crystal obtained by irradiating a laser beam in the state of FIG. 2 (E), the state of FIG. 3 (A) or the state of FIG. 4 (A). It is characterized in that the crystallinity of an island pattern made of a conductive silicon film is improved.

When laser light is irradiated in the states of FIG. 2E, FIG. 3A and FIG. 4A, a predetermined annealing effect can be obtained with a relatively low irradiation energy density.

It is considered that this is because the laser energy is applied to a small area, so that the energy efficiency used for annealing is increased.

[Embodiment 10] This embodiment relates to a configuration in which the patterning of the active layer of the thin film transistor is devised in order to enhance the annealing effect by the irradiation of laser light.

FIG. 6 shows a manufacturing process of the thin film transistor shown in this embodiment. First Corning 1737 glass substrate 6
On 01, a silicon oxide film or a silicon oxynitride film is formed as a base film.

Next, an amorphous silicon film (not shown) is formed to a thickness of 500Å. A low pressure thermal CVD method is used as a film forming method.
This amorphous silicon film later becomes a crystalline silicon film 603 through a crystallization process.

Next, Example 1 (see FIG. 1) or Example 3
The amorphous silicon film (not shown) is crystallized by the method shown in FIG. 2 to obtain a crystalline silicon film. FIG.
The state shown in FIG.

When the state shown in FIG. 6A is obtained, the crystallinity is obtained on the glass substrate in accordance with the steps shown in FIG. 1 for the manufacturing process of Example 1 or FIG. 2 for the manufacturing process of Example 3. A silicon film 603 is formed. That is, the amorphous silicon film is crystallized by heat treatment using nickel element,
A crystalline silicon film 604 is obtained. Note that the heat treatment is 620
It is carried out by heat treatment at 4 ° C. for 4 hours.

After the crystalline silicon film is obtained, a pattern for forming an active layer of a thin film transistor is formed. At this time, the cross-sectional shape of this pattern is as shown by 604 in FIG.

The pattern 604 as shown in FIG. 6B is formed in order to suppress the deformation of the shape of the pattern in the subsequent processing step by irradiation with laser light.

A substrate 701 generally shown in FIG. 7A.
Pattern 70 made of a normal island-shaped silicon film formed on
When 2 is irradiated with the laser light, as shown in FIG. 7B, a convex portion 704 is formed at the edge portion of the pattern 703 after the laser light is irradiated.

It is considered that this occurs because the energy of the irradiated laser light is concentrated on the edge portion of the pattern where there is no escape area for heat.

This phenomenon later becomes a factor of defective wiring which constitutes the thin film transistor and defective operation of the thin film transistor.

Therefore, in the structure shown in this embodiment, the pattern 604 of the active layer has a sectional shape as shown in FIG.

With such a structure, it is possible to prevent the pattern of the silicon film from having a shape as shown in FIG. 7B when the laser beam is irradiated.

Here, it is preferable to set the angle of the portion indicated by 605 to 20 ° to 50 °. It is not preferable to set the angle indicated by 605 to 20 ° or less because the area occupied by the active layer increases and the difficulty of formation increases.
Further, it is also not preferable to set the angle indicated by 600 to 50 ° or more because the effect of suppressing the formation of the shape shown in FIG. 7B is reduced.

The pattern indicated by 604 can be realized by utilizing isotropic dry etching during patterning and controlling the dry etching conditions.

After obtaining a pattern (to be an active layer later) having a shape shown by 603 in FIG. 6B, laser light irradiation is carried out as shown in FIG. 6C. In this process,
The nickel element locally solidified in the pattern 604 can be diffused. Further, its crystallinity can be promoted.

After the irradiation of laser light is completed, heat treatment is performed in an oxygen atmosphere containing 3% of HCl to form a thermal oxide film 606. Here, a thermal oxidation film of 100 Å is formed by performing heat treatment for 12 hours in an oxygen atmosphere of 650 ° C. containing 3% of HCl. (FIG. 6 (D))

By the action of chlorine, this thermal oxide film is
The nickel element contained in the pattern 604 is gettered. At this time, since the solidification of the nickel element is destroyed by the irradiation of laser light in the previous step, gettering of the nickel element is effectively performed.

When the structure shown in this embodiment is adopted,
Gettering is also performed from the side surface of the pattern 604. This is useful in improving the OFF current characteristics and reliability of the finally completed thin film transistor. This is because the presence of nickel element (or a metal element that promotes crystallization of silicon) existing on the side surface of the active layer causes OF
This is because it is greatly related to an increase in F current and instability of characteristics.

After the thermal oxide film 606 for gettering shown in FIG. 6D is formed, the thermal oxide film 606 is removed. Thus, the state shown in FIG. 6E is obtained. When a silicon oxide film is used as the base film 602, there is a concern that the silicon oxide film 602 may be etched in the process of removing the thermal oxide film 606. However, if the thermal oxide film 606 has a thin film thickness of about 100 Å as shown in this embodiment, this does not cause much problem.

After obtaining the state shown in FIG. 6E, a new thermal oxide film 607 is formed. This thermal oxide film contains 100% oxygen.
% Heat treatment in an atmosphere.

Here, the thermal oxide film 607 is formed to a thickness of 100 Å by a heat treatment in an oxygen atmosphere at 650 ° C.

The thermal oxide film 607 is effective in suppressing the surface of the pattern 603 from being roughened during the subsequent irradiation with laser light. The thermal oxide film will later form a part of the gate insulating film. Since the thermal oxide film has extremely good interface characteristics with the silicon film, it is useful to use it as a part of the gate insulating film.

After the thermal oxide film 607 is formed, laser light may be irradiated again. Thus, the concentration of nickel element is reduced, and the crystalline silicon film 604 having high crystallinity is obtained.

Thereafter, the thin film transistor is manufactured by undergoing the steps shown in FIG. 3 or FIG.

[Embodiment 11] This embodiment shows a device for applying heat treatment at a temperature equal to or higher than the strain point of the glass substrate. It is preferable that the step of gettering a metal element that promotes crystallization of silicon in the invention disclosed in this specification be performed at a temperature as high as possible.

For example, when a Corning 1737 glass substrate (strain point 667 ° C.) is used, the temperature at which nickel element gettering is performed by forming a thermal oxide film is 700 ° C. higher than 650 ° C. A ring action can be obtained.

However, when the Corning 1737 glass substrate is used, the heating temperature for forming the thermal oxide film is set to 700.
If the temperature is set to ° C, the glass substrate is deformed.

The present embodiment provides means for solving this problem. That is, in the structure shown in this embodiment, the glass substrate is placed on the surface plate made of quartz whose flatness is guaranteed, and the heat treatment is performed in this state.

By doing so, the flatness of the softened glass substrate is also maintained by the flatness of the surface plate. It is important that the cooling is also performed with the glass substrate placed on the surface plate.

By adopting such a constitution, the heat treatment can be performed even at a temperature equal to or higher than the strain point of the glass substrate.

[0249]

By utilizing the invention disclosed in this specification, there is provided a technique for reducing the concentration of a metal element in a crystalline silicon film obtained by utilizing a metal element that promotes crystallization of silicon. Can be provided.

Further, by utilizing this technique, a thin film semiconductor device having higher reliability and excellent performance can be obtained.

[Brief description of drawings]

FIG. 1 is a view showing a step of obtaining a crystalline silicon film.

FIG. 2 is a diagram showing a process of obtaining a crystalline silicon film.

3A to 3D are diagrams showing steps of manufacturing a thin film transistor.

4A to 4C are diagrams showing steps of manufacturing a thin film transistor.

5A to 5D are diagrams showing steps of manufacturing a thin film transistor.

FIG. 6 is a diagram showing a process of manufacturing an active layer of a thin film transistor.

FIG. 7 is a diagram showing a state in which a pattern made of a crystalline silicon film is irradiated with laser light.

[Explanation of symbols]

101 glass substrate or quartz substrate 102 base film (silicon oxide film or silicon oxynitride film) 103 amorphous silicon film 104 water film of solution containing nickel 105 crystalline silicon film 106 thermal oxide film 107 reduced concentration of nickel element Crystalline silicon film 201 Glass substrate or quartz substrate 202 Base film (silicon oxide film or silicon oxynitride film) 203 Amorphous silicon film 204 Mask made of silicon oxide film 205 Opening 206 Nickel 207 held in contact with the substrate Direction of crystal growth in a direction parallel to the direction 208 silicon film 209 thermal oxide film 210 patterned silicon film 211 thermal oxide film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location H01L 21/336 H01L 29/78 617V 627G (72) Inventor Yasushi Ogata 398 Hase, Atsugi, Kanagawa Prefecture Shares Company Semi Conductor Energy Laboratory (72) Inventor Masahiko Hayakawa 398 Hase, Atsugi City, Kanagawa Prefecture Semi Conductor Energy Laboratory Co., Ltd. (72) Inventor Mitsuaki Nono 398 Hase, Atsugi City, Kanagawa Prefecture Semi Conductor Energy Laboratory Co., Ltd.

Claims (23)

[Claims] 1. A step of intentionally introducing a metal element that promotes crystallization of silicon into an amorphous silicon film and crystallizing the amorphous silicon film by a first heat treatment to obtain a crystalline silicon film. A step of irradiating the crystalline silicon film with a laser beam or an intense light, and a second heat treatment in an oxidizing atmosphere containing a halogen element, and the metal element present in the crystalline silicon film. A step of removing or reducing the thermal oxide film, a step of removing the thermal oxide film formed in the step, and a step of forming a thermal oxide film on the surface of the region from which the thermal oxide film has been removed by thermal oxidation again. A method for manufacturing a semiconductor device having: 2. A step of intentionally introducing a metal element that promotes crystallization of silicon into an amorphous silicon film and crystallizing the amorphous silicon film by a first heat treatment to obtain a crystalline silicon film. Irradiating the crystalline silicon film with laser light or intense light to diffuse the metal element present in the crystalline silicon film in the crystalline silicon film, and oxidizing with a halogen element. A step of performing a second heat treatment in an atmosphere to getter the metal element present in the crystalline silicon film into a formed thermal oxide film; and a step of removing the thermal oxide film formed in the step And a step of forming a thermal oxide film on the surface of the region where the thermal oxide film is removed by thermal oxidation again. 3. A step of intentionally and selectively introducing a metal element that promotes crystallization of silicon into the amorphous silicon film; and a first heat treatment of the amorphous silicon film, A step of performing crystal growth in a direction parallel to the film from a region where the metal element is intentionally and selectively introduced; and a metal element existing in the crystal-grown region by irradiating laser light or intense light And a step of performing second heat treatment in an oxidizing atmosphere containing a halogen element to getter the metal element present in the crystal-grown region into a thermal oxide film to be formed, A step of removing the thermal oxide film formed in the step; and a step of forming a thermal oxide film on the surface of the region where the thermal oxide film is removed by thermal oxidation again, Manufacturing method. 4. The method for manufacturing a semiconductor device according to claim 1, wherein the second processing temperature is higher than 600 ° C. and not higher than 750 ° C. 5. The method for manufacturing a semiconductor device according to claim 1, wherein the gate insulating film is formed by using the thermal oxide film again. 6. The metal element according to any one of claims 1 to 3, wherein Fe, Co, N is used as a metal element for promoting crystallization of silicon.
i, Ru, Rh, Pd, Os, Ir, Pt, Cu, Au
A method for manufacturing a semiconductor device, characterized in that one or more kinds selected from the above are used. 7. The oxidizing atmosphere according to claim 1, wherein the oxidizing atmosphere containing a halogen element is HCl in an O ₂ atmosphere.
_{HF, HBr, Cl 2, F} 2, a method for manufacturing a semiconductor device, characterized in that the gas one or more kinds selected from Br ₂ is one that was added. 8. The oxidizing atmosphere containing a halogen element according to any one of claims 1 to 3, is selected from HCl, HF, HBr, Cl ₂ , F ₂ and Br _{2 in} an atmosphere containing O ₂ . A method for manufacturing a semiconductor device, characterized in that one or more kinds of gases are added. 9. A method for manufacturing a semiconductor device according to claim 1, wherein a gas of a hydride of oxygen and a halogen element is added to the oxidizing atmosphere containing a halogen element. 10. The method for manufacturing a semiconductor device according to claim 1, wherein the second heat treatment temperature is higher than the first heat treatment temperature. 11. A method of manufacturing a semiconductor device according to claim 1, wherein after the thermal oxide film is removed, annealing is performed in a plasma atmosphere containing oxygen and hydrogen. 12. The oxygen concentration contained in the amorphous silicon film according to claim 1, wherein the concentration of oxygen is 5 × 10 ¹⁷ cm ^−3.
˜2 × 10 ¹⁹ cm ⁻³ , a method for manufacturing a semiconductor device. 13. A step of intentionally introducing a metal element for promoting crystallization of silicon into an amorphous silicon film and crystallizing the amorphous silicon film by a first heat treatment to obtain a crystalline silicon film. Patterning the crystalline silicon film to form an active layer of a semiconductor device, irradiating the active layer with a laser beam or strong light, and a second step in an oxidizing atmosphere containing a halogen element. Heat treatment to remove or reduce the metal element present in the active layer, a step of removing the thermal oxide film formed in the step, and a thermal oxidation to the surface of the active layer again. A method for manufacturing a semiconductor device, comprising: a step of forming an oxide film. 14. A step of intentionally introducing a metal element for promoting crystallization of silicon into an amorphous silicon film and crystallizing the amorphous silicon film by a first heat treatment to obtain a crystalline silicon film. Patterning the crystalline silicon film to form an active layer of a semiconductor device, irradiating the active layer with a laser beam or strong light, and a second step in an oxidizing atmosphere containing a halogen element. Heat treatment to remove or reduce the metal element present in the active layer; a step of removing the thermal oxide film formed in the step; and a thermal oxidation of the surface of the active layer by thermal oxidation. And a step of forming an oxide film, wherein the side surface of the active layer forms an angle of 20 ° to 50 °.
A method for manufacturing a semiconductor device, which has an inclined shape having 15. The method of manufacturing a semiconductor device according to claim 13, wherein the gate insulating film is formed by using the thermal oxide film again. 16. The method according to claim 13 or 14,
The upper limit of the first heat treatment temperature and the second heat treatment temperature is 75.
A method for manufacturing a semiconductor device, which is 0 ° C. or lower. 17. The metal element according to claim 13 or 14, wherein Fe, Co, N is used as a metal element for promoting crystallization of silicon.
i, Ru, Rh, Pd, Os, Ir, Pt, Cu, Au
A method for manufacturing a semiconductor device, characterized in that one or more kinds selected from the above are used. 18. The method according to claim 13 or 14,
The oxidizing atmosphere containing a halogen element is characterized in that one or more kinds of gas selected from HCl, HF, HBr, Cl ₂ , F ₂ and Br ₂ are added to the O ₂ atmosphere. Method for manufacturing a semiconductor device. 19. The method according to claim 13 or 14,
Oxidizing atmosphere containing a halogen element, HCl in an atmosphere containing _{O 2, HF, HBr, Cl} 2, F 2, Br 2
A method for manufacturing a semiconductor device, wherein one or more kinds of gases selected from the above are added. 20. The method according to claim 13 or 14,
A method for manufacturing a semiconductor device, wherein oxygen and a hydride gas of a halogen element are added to an oxidizing atmosphere containing a halogen element. 21. In Claim 13 or Claim 14,
A method for manufacturing a semiconductor device, wherein the second heat treatment temperature is higher than the first heat treatment temperature. 22. In Claim 13 or Claim 14,
A method for manufacturing a semiconductor device, which comprises performing annealing in a plasma atmosphere containing oxygen and hydrogen after removing the thermal oxide film. 23. The oxygen concentration contained in the amorphous silicon film according to claim 13 or 14, which is 5 × 10 ¹⁷ cm ^−3.
˜2 × 10 ¹⁹ cm ⁻³ , a method for manufacturing a semiconductor device.