JPH09172179A - Fabrication of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film transistor(TFT) which is high in electric field mobility and low in a leak current in its OFF mode, by selectively forming out an insulating substrate crystalline grains having large crystal boundaries with much less grain boundary. SOLUTION: Deposited on an insulating substrate 1 is an amorphous silicon thin film 3a, on which a film 4, which is smaller in specific heat than the amorphous silicon thin film, is selectively formed so that channel formation zones of a channel region 6 are exposed on the thin film 3a. Thereafter, the substrate is subjected to an irradiation of laser light 5 from its rear side to crystallize the amorphous silicon thin film 3a. A crystalline silicon thin film 3 is subjected to an etching process with use of the film 4 having a small specific heat as a mask to cause the channel region 6 to be formed as a thin film. The film 4 having the small specific heat is made of preferably heat resistive Cr, Ta, Ti, Nb, Ni, Mo or W, or an alloy thereof or silicide thereof. These materials have selectivities for etching of the crystalline silicon thin film.

Description

Detailed Description of the Invention

[0001]

[0001] The present invention relates to an insulating substrate,
TECHNICAL FIELD The present invention relates to a method for manufacturing a semiconductor device in which a plurality of semiconductor devices having an active region made of a crystalline semiconductor thin film are formed, and in particular, a semiconductor that can be used for manufacturing a polycrystalline silicon thin film transistor used in an active matrix liquid crystal display device or the like. The present invention relates to a method of manufacturing a device.

[0002]

2. Description of the Related Art In recent years, an active matrix type liquid crystal display device has been attracting attention as a display having advantages of thinness, light weight and low power consumption. Among them, there is great expectation for a technique of forming a polycrystalline silicon thin film transistor (hereinafter referred to as a TFT) as a liquid crystal driving element on an inexpensive low melting point glass substrate due to demands for large area, high resolution, low cost, and the like. It is sent.

A polycrystalline silicon TFT using a polycrystalline silicon thin film in the active region of the TFT has a high electric field effect mobility, and thus has been widely studied to realize a high resolution liquid crystal display device. As a technique for producing this polycrystalline silicon thin film on a low melting point glass substrate at a low temperature of about 600 ° C., after depositing an amorphous silicon thin film on the substrate, 600
A solid phase growth method is known in which heat treatment is performed for several hours to several tens of hours at a temperature of about ° C to crystallize. In addition, JP-A-6-349
As disclosed in Japanese Unexamined Patent Publication No. 97, Japanese Unexamined Patent Publication No. 6-69128 or Japanese Unexamined Patent Publication No. 6-140321, after depositing an amorphous silicon thin film on a substrate, laser light or the like is irradiated to expose the portion. A laser crystallization method or the like has also been proposed in which an amorphous silicon film is instantly melted and recrystallized.

The TFT using the polycrystalline silicon thin film obtained by these methods as an active region has a high field effect mobility, but has a problem that a large leak current is generated when it is turned off. Therefore, as disclosed in Japanese Patent Publication No. 6-69094, a method of reducing the thickness of the entire polycrystalline silicon thin film in which an active region of a TFT is provided, Japanese Patent Publication No. 5-34837 or Japanese Patent Laid-Open No. 6-34837. -1
As disclosed in Japanese Unexamined Patent Publication No. 63900, there is proposed a method of making the film thickness of the channel region thinner than that of other portions.

[0005]

When manufacturing a polycrystalline silicon TFT using a polycrystalline silicon thin film having a high field effect mobility as an active region, there are the following problems. A first problem is to form a polycrystalline silicon thin film having a large grain size and uniform over the entire surface of the insulating substrate at a low temperature. The second problem is to reduce the leak current when the TFT manufactured using the polycrystalline silicon thin film is turned off. The reason is as follows.

The polycrystalline silicon thin film is an aggregate of silicon single crystal grains having a certain size distribution, and a crystal grain boundary is formed at a portion where the single crystal grains are in contact with each other.
The electrical characteristics of a polycrystalline silicon thin film depend on the crystal grain size and the lattice defect density of crystal grain boundaries. Therefore, in the case of manufacturing a semiconductor device, it is desirable that the active region is constituted by a single crystal grain or a crystal grain having a large grain size with few crystal grain boundaries as much as possible. In particular, if a large number of crystal grain boundaries exist in the active region, a leak current will flow along the crystal grain boundaries and the characteristics of the TFT will be significantly impaired, which is not desirable.

Of the above two problems, the first method of forming a polycrystalline silicon thin film having a uniform large grain size over the entire surface of the insulating substrate at a low temperature is mainly achieved by the solid phase described above. It is roughly divided into a growth method and a laser crystallization method.

The solid phase growth method is a method in which an amorphous silicon thin film is deposited on an insulating substrate and polycrystallized by low temperature heat treatment at about 600 ° C., but it takes several hours to several tens of hours for crystallization. Since it takes a long time, there is a problem that the throughput in the manufacturing process is extremely poor. There is also a problem that the field effect mobility of the obtained polycrystalline silicon thin film is small. On the other hand, the laser crystallization method is a method of depositing an amorphous silicon thin film on an insulating substrate and irradiating a laser beam or the like to instantly melt and recrystallize the amorphous silicon film to form a polycrystalline film. It is a method of crystallization, and crystallization can be performed in a short time. Further, the obtained polycrystalline silicon thin film has high field effect mobility. For this reason, many research institutions are currently conducting active research and development toward the practical use of the laser crystallization method.

However, the above laser crystallization method has the following problems. As shown in FIGS. 9A and 9B, the laser light used for crystallization has an intensity distribution in which the central portion is strong and becomes weaker toward the peripheral portion. This intensity distribution tends to become more prominent as the diameter or width of the beam spot of the irradiated laser light becomes smaller, as indicated by the broken line in FIG. 9B. Therefore, in the amorphous silicon thin film in the region irradiated with the laser light, a temperature distribution occurs in which the central part has the highest temperature and the temperature decreases toward the peripheral part, corresponding to the intensity distribution of the laser light. Therefore, non-uniform crystal nuclei are generated in the amorphous silicon thin film in the region irradiated with the laser beam, and the crystal grains grow irregularly from the crystal nuclei. As a result, crystal grains of large grain size and crystal grains of small grain size are mixed and grown, and it is difficult to obtain uniform crystal grains over the entire surface of the substrate.

Therefore, conventionally, an attempt is made to partially provide a metal film on the upper or lower portion of the amorphous silicon thin film to make the temperature distribution uniform by irradiating the laser beam, or a partially provided metal film. Laser light to block the amorphous silicon thin film in the part where the metal film is not formed, then remove the metal film and irradiate the laser light again to obtain uniform crystal grains, or There has been proposed a method of making the intensity distribution of laser light uniform by a statistical method.

According to these methods, it is possible to obtain crystal grains having a uniform grain size, but the temperature distribution of the amorphous silicon thin film in the region irradiated with the laser beam becomes almost uniform, and the amorphous silicon thin film is A large number of crystal nuclei are generated inside.
For this reason, the growth surfaces of the respective crystal grains collide with each other and the crystal growth is saturated immediately, making it difficult to obtain crystal grains of large grain size.

In the laser crystallization method, the surface of the amorphous silicon thin film irradiated with the laser beam is likely to have irregularities due to explosive vaporization of hydrogen in the amorphous silicon thin film, and the irregularities cause the irregularities to form an insulating film. This is a major factor that influences the interface state density with respect to and the superiority of the TFT characteristics.

Of the above-mentioned two problems, as a method for solving the second problem of reducing the leak current when the TFT is turned off, which will be described later, a low-concentration impurity region is formed in a region adjacent to the source region and the drain region. LDD (Lightl
y Doped Drain) structure, an offset gate structure that forms a region to which impurities are not added between a channel region and a source region and a drain region, or the polycrystalline silicon thin film itself which is an active region of a TFT is thinned. Methods etc. have been proposed. Among these methods, in the LDD structure and the offset gate structure, a method of controlling the impurity concentration in the low concentration impurity region and a method of controlling the offset length have not been established, and a large number of TFTs having uniform characteristics are formed on the insulating substrate. Not easy to do. On the other hand, the method of reducing the film thickness of the active region itself may cause some variation in the film thickness of the active region on the insulating substrate, but the control is far more difficult than the LDD structure or the offset gate structure. It's easy. According to this method,
Since the film thickness of the active region itself is reduced, the contact with the source electrode or the drain electrode may be defective. For this reason, conventionally, by thinning only the channel region, the leak current when the TFT is turned off is reduced and the contact with the source region or the drain region is kept good.

However, in the method of reducing the film thickness of the active region, no consideration has been given to the crystallinity and grain boundaries of the active region, particularly the channel region. for that reason,
By reducing the film thickness of the active region itself, there is a problem that the leak current when the TFT is turned off is reduced and the ON current of the TFT is also reduced.

The present invention has been made to solve the problems of the prior art as described above, and it is possible to form a crystal having a uniform large grain size, and the number of crystal grain boundaries in the channel region or the active region is extremely reduced. An object of the present invention is to provide a method for manufacturing a semiconductor device, which can increase the field effect mobility and can reduce the leak current when off.

[0016]

According to a method of manufacturing a semiconductor device of the present invention, a semiconductor device having an active region made of a crystalline semiconductor thin film on an insulating substrate, and a part of the active region is used as a channel region. And a step of forming an amorphous semiconductor thin film on the substrate, exposing at least a channel region forming portion of the amorphous semiconductor thin film, and the amorphous semiconductor thin film on the amorphous semiconductor thin film. A step of selectively forming a film made of a material having a smaller specific heat capacity than
A step of crystallizing the amorphous semiconductor thin film to obtain a crystalline semiconductor thin film by irradiating a laser beam from the side opposite to the amorphous semiconductor thin film forming side of the substrate; and a specific heat capacity higher than that of the amorphous semiconductor thin film. A step of removing a film made of a small material,
Processing the crystalline semiconductor thin film into the shape of the active region, whereby the above object is achieved.

A method of manufacturing a semiconductor device according to the present invention is a method of manufacturing a semiconductor device in which an active region made of a crystalline semiconductor thin film is provided on an insulating substrate and a part of the active region is used as a channel region. A step of forming an amorphous semiconductor thin film on the substrate, a step of processing the amorphous semiconductor thin film into a shape of an active region, and a step of forming at least a channel region forming portion of the amorphous semiconductor thin film having the shape of the active region. Exposing and selectively forming a film made of a material having a smaller specific heat capacity than the amorphous semiconductor thin film on the amorphous semiconductor thin film in the shape of the active region, and forming the amorphous semiconductor thin film on the substrate Irradiating a laser beam from the side opposite to the side to crystallize the amorphous semiconductor thin film in the shape of the active region to obtain a crystalline semiconductor thin film in the shape of the active region; Also And a step of removing a film made of a material having a small heat capacity, the object is achieved.

In the method of manufacturing a semiconductor device of the present invention,
A step of etching and thinning a channel region forming portion of the crystalline semiconductor thin film may be included by using a film made of a material having a smaller specific heat capacity than the amorphous semiconductor thin film as a mask.

In the method of manufacturing a semiconductor device of the present invention,
A step of etching and thinning a channel region forming portion of the crystalline semiconductor thin film having the shape of the active region may be included by using a film made of a material having a smaller specific heat capacity than the amorphous semiconductor thin film as a mask.

In the method of manufacturing a semiconductor device of the present invention,
As a film made of a material having a smaller specific heat capacity than the amorphous semiconductor thin film, Cr, Ta, Ti, Nb, Ni, Mo,
You may make it form the film which consists of at least 1 material selected from W, these alloys, and these silicides.

In the method of manufacturing a semiconductor device of the present invention,
As a film made of a material having a smaller specific heat capacity than the amorphous semiconductor thin film, a film having a selective ratio in etching with respect to the crystalline semiconductor thin film is formed, and the film made of a material having a small specific heat capacity is removed. In doing so, the etching may be selectively performed.

In the method for manufacturing a semiconductor device according to the present invention,
As a film made of a material having a smaller specific heat capacity than the amorphous semiconductor thin film, a film having a selective ratio for etching with respect to the crystalline semiconductor thin film is formed, and a selective film is used for etching the channel region. Alternatively, the etching may be performed.

Hereinafter, the operation of the present invention will be described.

In the present invention, a material having a smaller specific heat capacity than the amorphous semiconductor thin film is formed so that the amorphous semiconductor thin film is formed on the insulating substrate and at least the channel region forming portion is exposed thereon. And a laser beam is irradiated from the back surface side of the substrate (the side opposite to the side on which the amorphous semiconductor thin film is formed).

Since there is a difference in the crystal growth distance during recrystallization between the region where the film made of a material having a small specific heat capacity is formed and the exposed portion where the film is not formed, the crystal growth distance is selectively applied to the insulating substrate. It is possible to obtain crystals with a good large grain size and very few grain boundaries. Since the film made of a material having a small specific heat capacity is formed so that at least the channel region forming portion is exposed, the crystal grain boundaries of the channel region are reduced and the leak current at the time of OFF can be reduced. Further, since the laser beam is irradiated from the back surface side of the substrate, the unevenness on the surface of the semiconductor thin film is reduced, and the interface state density with the gate insulating film can be reduced.

Furthermore, when the channel region forming portion of the crystalline semiconductor thin film is etched using the film made of a material having a small specific heat capacity as a mask, the channel region is thinned while maintaining good contact with the source electrode and the drain electrode. be able to.

Materials having a smaller specific heat capacity than the amorphous semiconductor thin film are heat-resistant materials such as Cr, Ta, Ti and N.
It is desirable to use at least one material selected from b, Ni, Mo, W, their alloys and their silicides. This is because these materials have heat resistance.

Further, when a film having a selection ratio for etching the crystalline semiconductor thin film is formed as a film made of a material having a small specific heat capacity, etching for thinning the channel region and a small specific heat capacity are performed. Selective etching can be performed in the etching for removing the film made of the material.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1A is a cross-sectional view for explaining the steps until a crystalline semiconductor thin film is obtained by the method for manufacturing a semiconductor device of the present invention, and FIG. 1B is a plan view thereof. Further, FIG. 1C is a cross-sectional view showing a TFT manufactured by partially using the crystalline semiconductor thin film finally obtained by the method for manufacturing a semiconductor device of the present invention.

First, as shown in FIG. 1A, a base film 2 and an amorphous silicon thin film which will later become a crystalline semiconductor thin film 3 are sequentially deposited on an insulating substrate 1, and an amorphous silicon thin film is further deposited thereon. A material having a smaller specific heat capacity than the silicon thin film, for example, the metal film 4 is selectively arranged at a predetermined interval. At this time, the amorphous silicon thin film is in a state where the metal film 4 is not formed at least on the channel region forming portion and is exposed in a slit shape.

Next, the amorphous silicon thin film is crystallized by irradiating the laser beam 5 from the back side of the substrate to form the crystalline silicon thin film 3. At this time, as shown in FIGS. 1A and 1B, in the exposed portion where the metal film 4 is not provided, the crystal grain boundaries 13 are extremely small, and good crystal grains having a large grain size can be obtained. As shown in FIG. 1C, by using this good crystal grain portion as the active region of the TFT, particularly the channel region 6, a TFT having a high field effect mobility and particularly a small leak current when turned off is realized. It becomes possible to do.

As a result of experiments conducted by the present inventors, a case where a metal film is provided on the entire surface of the amorphous silicon thin film and a laser beam is irradiated from the back surface side of the substrate, and a case where the insulating film of the insulating substrate is not provided It was found that the crystallinity of the obtained crystalline silicon thin film was different from that when the laser beam was irradiated from the back surface side.

FIG. 2 is a graph showing the time change of the temperature of the amorphous silicon thin film irradiated with laser light. When the metal film is not provided, the amorphous silicon thin film irradiated with the laser light is once heated to a melting point (melting temperature) or higher and melted, as shown by a curve b in FIG. It is gradually cooled, during which crystallization progresses. The longer the time required for this cooling, the larger the crystal grains obtained, and the better the crystallinity. However, when a metal film is provided on the entire surface of the amorphous silicon thin film, the amorphous silicon thin film irradiated with laser light is once heated to a melting point or higher as shown by a curve a in FIG. Is melted,
Since the heat flows out or is absorbed by the metal film, it is cooled at once. Therefore, crystallization is completed in a short time, and large crystal grains cannot be obtained.

From the above results, as a result of further intensive studies by the present inventors, the following findings were found. FIG.
As shown in FIG. 3A, a film 4 made of a material having a smaller specific heat capacity than that of the amorphous silicon thin film is selectively (partially) provided on the amorphous silicon thin film 3. As shown, a temperature distribution can be generated in the amorphous silicon thin film in the portion irradiated with the laser light. As a result, it becomes possible to grow crystals from a single nucleus, and it is possible to obtain uniform and large-sized crystal grains with extremely few crystal grain boundaries.

In FIG. 3A, in the spot where the laser beam is irradiated, the irradiated laser beam is applied to the amorphous silicon thin film in a portion where the film 4 made of a material having a small specific heat capacity is not formed. Be absorbed. On the other hand, in the portion where the film 4 made of a material having a small specific heat capacity is formed, the irradiated laser light is once absorbed by the amorphous silicon thin film, but the heat is a film made of a material having a small specific heat capacity. It is cooled down at once because it is leaked or absorbed into. Therefore, the temperature distribution of the amorphous silicon thin film within the laser light irradiation range immediately after the laser light irradiation is in a state in which high temperature regions and low temperature regions are alternately repeated, as shown in FIG. 3B. . The crystallization of the amorphous silicon thin film in the low temperature region is completed in a short time, but the crystallization of the amorphous silicon thin film in the high temperature region gradually progresses, and the crystal growth distance is amorphous in the low temperature region. It becomes longer than the crystal growth region of the silicon thin film. As a result, it is possible to selectively obtain large-sized crystal grains having very few crystal grain boundaries in a portion where a film made of a material having a small specific heat capacity is not formed. Then, this portion is used as an active region of the TFT, particularly as a channel region.

A more specific embodiment of the present invention will be described below.

(Embodiment 1) FIGS. 4A to 4C are cross-sectional views showing steps in a method of manufacturing a semiconductor device according to Embodiment 1. In this embodiment, a glass substrate is used as the insulating substrate. This is because the following Embodiments 2 to 2
The same applies to 4.

First, as shown in FIG. 4A, a low pressure CVD (Chemical Vapor) is formed on a glass substrate 1.
An insulating film such as a SiO ₂ film is formed as the base film 2 by a deposition method, a plasma CVD method, a sputtering method, or the like.

Then, a non-doped amorphous silicon thin film 3a as an amorphous semiconductor thin film is deposited thereon to a thickness of 10 to 40 nm, for example, about 30 nm by a low pressure CVD method or a plasma CVD method.

Then, the glass substrate 1 in this state is subjected to CVD.
It is made of a material having a smaller specific heat capacity than the amorphous silicon thin film so that at least a channel region forming portion is exposed to a predetermined region on the amorphous silicon thin film 3a by taking out from a chamber of an apparatus or the like. A film, for example, a metal film 4 is selectively formed. This metal film 4
Has a role of absorbing heat from the amorphous silicon thin film,
If the film thickness is extremely thin, the effect is small, so about 100-50
A film thickness of about 0 nm is necessary. In this embodiment, about 3
It was deposited to a film thickness of 00 nm and patterned into a predetermined shape. Further, the pattern interval of the metal film 4 is set to be equal to or more than the width of the channel region of the TFT, but considering the alignment error when patterning the gate electrode or the like in a later process, the pattern of the metal film 4 is taken into consideration. It is preferable to set the interval of a little wider than the width of the channel region. In this embodiment, the pattern interval of the metal film 4 is 5 μm to 1 μm.
The thickness is 0 μm, for example, about 8 μm. The pattern interval of the metal film 4 is appropriately determined according to the shape and size of the TFT to be manufactured, and the pattern interval of the metal film is 2 μm to 3 μm.
Even if it is as small as μm or as large as 20 μm to 30 μm, the effect of the present invention is not impaired. It is preferable that the pattern of the metal film 4 has a stripe shape because it is easy to control the positions of the crystal grain boundaries, but the island shape as shown in FIGS. 5A and 5B can also obtain the same effect. As the material having a smaller specific heat capacity than the amorphous silicon thin film, it is preferable to use heat-resistant Cr, Ta, Ti, Nb, Ni, Mo, W, alloys thereof, silicides thereof, or the like.

In the above steps, no problem occurs even if a step such as heat treatment is added between the step of forming the base film 2 and the step of forming the amorphous silicon thin film 3a.
For example, after forming the base film 2 on the glass substrate, heat treatment or the like may be performed to densify the base film 2 and improve the film quality, and then the amorphous silicon thin film 3a may be formed. Further, the effect of the present invention is not impaired even if a process other than heat treatment is added between the film forming processes.

After that, as shown in FIG. 4B, the amorphous silicon thin film 3a is crystallized into the crystalline silicon thin film 3 by irradiating the laser beam 5 from the back surface side of the glass substrate 1. The laser light 5 used is a XeCl excimer laser (wavelength 308 nm), a KrF excimer laser (wavelength 248 nm), an ArF excimer laser (wavelength 1
93 nm), XeF excimer laser (wavelength 353n
m) and the like can be used. When a quartz substrate is used as the insulating substrate, the absorption of laser light by the substrate is slight, but when a glass substrate having a low melting point is used as in the present embodiment, it may depend on the substrate depending on the wavelength of the laser light. Since large absorption of laser light occurs, it is preferable to use XeCl excimer laser, XeF excimer laser, or the like, which has relatively little absorption. The irradiation condition of the laser light is determined by the film quality and film thickness of the film irradiated with the laser light. In this embodiment, the energy density is 200 to 400 mJ / cm ² , for example, 25 in consideration of the loss due to the absorption of the laser light 5 by the insulating substrate 1 and the base film 2.
Irradiation was performed at about 0 mJ / cm ² . At the time of laser light irradiation, the substrate may be heated to about 200 to 400 ° C. Depending on the optical system such as a lens, the shape of the laser beam may be a spot shape of several mm square to several cm square, or a long shape with the long side of several cm to tens of cm and the short side of several mm. It can be processed and any laser light may be used.
By this laser irradiation, the amorphous silicon thin film 3a is crystallized to become the crystalline silicon thin film 3, and good crystal grains with a large grain size and very few crystal grain boundaries are obtained in the exposed portion where the metal film 4 is not provided. To be Further, since the laser light is emitted from the back surface side of the glass substrate, it is possible to avoid adverse effects such as roughening of the surface of the semiconductor thin film and occurrence of unevenness.

Next, as shown in FIG. 4C, the metal film 4
Get rid of. The removal of the metal film 4 is performed by, for example, the metal film 4
When Ti is used as the material, it can be removed using an etching solution in which EDTA (ethylenediaminetetraacetic acid) + H ₂ O ₂ (hydrogen peroxide) + NH ₃ (ammonia) are mixed at a mixing ratio of 1: 24: 8. . Also, as the metal film 4, M
When o is used, an etching solution in which H ₂ SO ₄ (sulfuric acid) + HNO ₃ (nitric acid) + H ₂ O are mixed at a mixing ratio of 1: 1: 3 or HF (hydrogen fluoride) + HNO ₃ + CH ₃ COO
It can be removed using an etching solution in which H (acetic acid) is mixed at a mixing ratio of 1:20:30. The crystalline silicon thin film is hardly etched by these etching solutions. Therefore, when removing the metal film 4, it is not necessary to form a resist mask for protecting the channel region. The above etching solution is shown as an example, and other etching solutions may be used. C as a metal film
Even when r, Ta, Nb, Ni, W, an alloy containing Ti and Mo, or a silicide thereof is used, by etching under an optimum condition using an etching solution suitable for each metal film. , Ti and Mo can be removed in the same manner.

After that, the crystalline silicon thin film 3 is patterned into an island shape so as to become the active region 7 of the TFT.

Subsequently, the gate insulating film 8 and the gate electrode 9 are formed. The gate insulating film 8 is preferably formed at a low temperature when a substrate having a low melting point such as a glass substrate is used. Examples of the method of forming the gate insulating film 8 at a low temperature include a plasma CVD method, a low pressure CVD method, an optical CVD method, and the like, and a method of forming a thermal oxide film on the surface of a semiconductor thin film at a low temperature. As the gate electrode 9, it is preferable to use an Al-based metal that is a low-resistance wiring material. Considering heat resistance and the like, it is preferable to use an Al alloy such as Al-Ti.

After that, the source region 10 and the drain region 10 of the active region 7 are doped with impurity ions by an ion implantation method, a laser doping method, a plasma doping method or the like. When to produce an N-channel transistor P ^+, doping B ⁺ when the making P-channel transistor. At this time, the active region 7 below the gate electrode 9 is not doped with impurities, and TF
It becomes the channel region 6 of T.

Next, the impurities are activated by a method such as laser annealing to stack the interlayer insulating film 11. As the interlayer insulating film 11, a SiO ₂ film with good step coverage by plasma CVD method using organic silane as a material is used.
It is common to stack from 00 nm to several μm. Alternatively, a silicon nitride film may be used.

Further, contact holes are opened in the interlayer insulating film 11 and the gate insulating film 8 to form the source electrode 11 and the drain electrode 11. As the source electrode 11 and the drain electrode 11, an Al-based metal, which is a wiring material having a low resistance like the gate electrode, can be used. In addition, a refractory metal that is more excellent in step coverage than Al may be used.

In the TFT obtained as described above, crystals of good large grain size with extremely few crystal grain boundaries are selectively formed on the substrate, and the interface state density between the active region and the gate insulating film is small. Therefore, the field effect mobility is high and the leak current at the time of off can be reduced.

(Embodiment 2) FIGS. 6A to 6C are sectional views showing steps in the method of manufacturing a semiconductor device according to the second embodiment.

First, as shown in FIG. 6A, the base film 2 and the amorphous silicon thin film 3a are deposited on the glass substrate 1 in the same manner as in the first embodiment.

Next, the insulating substrate is taken out of the chamber of the CVD apparatus, and the amorphous silicon thin film 3a is patterned into an island shape which is the shape of the active region.

Then, a film made of a material having a smaller specific heat capacity than that of the amorphous silicon thin film so that at least a portion where the channel region is formed is exposed in a predetermined region on the amorphous silicon thin film 3a by a sputtering method or the like. , For example, the metal film 4 is selectively formed. The metal film 4 has a role of absorbing heat from the amorphous silicon thin film, and if the film thickness is extremely thin, the effect is small. Therefore, a film thickness of about 100 to 500 nm is necessary. In this embodiment, a film having a thickness of about 300 nm is deposited and patterned into a predetermined shape. Further, the pattern interval of the metal film 4 is set to be equal to or more than the width of the channel region of the TFT, but considering the alignment error when patterning the gate electrode or the like in a later process, the pattern of the metal film 4 is taken into consideration. It is preferable to set the interval of a little wider than the width of the channel region. In this embodiment, the pattern interval of the metal film 4 is set to 5 μm to 10 μm, for example, about 8 μm. The pattern interval of the metal film 4 is appropriately determined depending on the shape and size of the TFT to be manufactured. Even if the pattern interval of the metal film is as small as 2 μm to 3 μm or as large as 20 μm to 30 μm, the effect of the present invention is not obtained. Not damaged. It is preferable that the pattern of the metal film 4 has a stripe shape because it is easy to control the positions of the crystal grain boundaries, but the island shape as shown in FIGS. 5A and 5B can also obtain the same effect. As a material having a smaller specific heat capacity than the amorphous silicon thin film, heat-resistant materials such as Cr and T are used.
It is preferable to use a, Ti, Nb, Ni, Mo, W, alloys of these and silicides thereof.

In the above steps, no problem arises even if a step such as heat treatment is added between the step of forming the base film 2 and the step of forming the amorphous silicon thin film 3a.
For example, after forming the base film 2 on the glass substrate, heat treatment or the like may be performed to densify the base film 2 and improve the film quality, and then the amorphous silicon thin film 3a may be formed. Further, the effect of the present invention is not impaired even if a process other than heat treatment is added between the film forming processes.

Thereafter, as shown in FIG. 6B, the amorphous silicon thin film 3a is crystallized into the crystalline silicon thin film 3 by irradiating the laser light 5 from the back surface side of the glass substrate 1. The laser light 5 used and the irradiation conditions are the same as in the first embodiment. Since the laser light is applied from the back surface side of the glass substrate as in the first embodiment, it is possible to avoid adverse effects such as roughening of the surface of the semiconductor thin film and occurrence of unevenness.

Further, as shown in FIG. 6C, the metal film 4 is removed in the same manner as in Embodiment 1, and a TFT is manufactured in the same manner as in Embodiment 1. However, in this embodiment, since the active region 7 is patterned in advance in an island shape, it is not necessary to pattern the active region 7 again.

In the TFT obtained as described above, crystals of good large grain size with few crystal grain boundaries are selectively formed on the substrate, and the interface state density between the active region and the gate insulating film is small. Therefore, the field effect mobility is high and the leak current at the time of off can be reduced. Further, in this embodiment, since the active region 7 is patterned in advance in an island shape, it is not necessary to form a new resist mask on the active region 7, and the resist mask remains on the channel region 6. Can be avoided. Therefore, the surface of the active region including the channel region can be kept clean and the characteristics can be further improved.

(Third Embodiment) FIGS. 7A to 7D are sectional views showing steps in a method of manufacturing a semiconductor device according to a third embodiment.

First, the base film 2 is deposited on the glass substrate 1 in the same manner as in Embodiment 1, and as shown in FIG. 7A, an amorphous semiconductor thin film 3a is formed by a low pressure CVD method or a plasma CVD method. Non-doped amorphous silicon thin film 10
The film is deposited with a film thickness of 0 to 150 nm, for example, about 150 nm.

Next, the glass substrate 1 in this state is taken out of the chamber of the CVD apparatus, and is exposed by a sputtering method or the like so that at least a channel region forming portion is exposed in a predetermined region on the amorphous silicon thin film 3a. A film made of a material having a smaller specific heat capacity than the crystalline silicon thin film 3a, for example, a metal film 4 is selectively formed. This metal film 4
Has a role of absorbing heat from the amorphous silicon thin film,
If the film thickness is extremely thin, the effect is small, so about 100-50
A film thickness of about 0 nm is necessary. In this embodiment, about 3
It was deposited to a film thickness of 00 nm and patterned into a predetermined shape. Further, the pattern interval of the metal film 4 is set to be equal to or more than the width of the channel region of the TFT, but considering the alignment error when patterning the gate electrode or the like in a later process, the pattern of the metal film 4 is taken into consideration. It is preferable to set the interval of a little wider than the width of the channel region. In this embodiment, the pattern interval of the metal film 4 is 5 μm to 1 μm.
The thickness is 0 μm, for example, about 8 μm. The pattern interval of the metal film 4 is appropriately determined according to the shape and size of the TFT to be manufactured, and the pattern interval of the metal film is 2 μm to 3 μm.
Even if it is as small as μm or as large as 20 μm to 30 μm, the effect of the present invention is not impaired. It is preferable that the pattern of the metal film 4 has a stripe shape because it is easy to control the positions of the crystal grain boundaries, but the island shape as shown in FIGS. 5A and 5B can also obtain the same effect. As the material having a smaller specific heat capacity than the amorphous silicon thin film, it is preferable to use heat-resistant Cr, Ta, Ti, Nb, Ni, Mo, W, alloys thereof, silicides thereof, or the like.

In the above steps, no problem occurs even if a step such as heat treatment is added between the step of forming the base film 2 and the step of forming the amorphous silicon thin film 3a.
For example, after forming the base film 2 on the glass substrate, heat treatment or the like may be performed to densify the base film 2 and improve the film quality, and then the amorphous silicon thin film 3a may be formed. Further, the effect of the present invention is not impaired even if a process other than heat treatment is added between the film forming processes.

Subsequently, as shown in FIG. 7B, the amorphous silicon thin film 3a is crystallized into the crystalline silicon thin film 3 by irradiating the laser beam 5 from the back surface side of the glass substrate 1. As the laser beam 5 to be used, the same laser beam as in the first embodiment can be used. The irradiation condition of the laser light is determined by the film quality and film thickness of the amorphous silicon thin film 3a irradiated with the laser light. In this embodiment, the energy density is 200 to 400 mJ / in consideration of the loss due to the absorption of the laser light 5 by the insulating substrate 1 and the base film 2.
Irradiation was performed at cm ² , for example, about 350 mJ / cm ² . At the time of laser light irradiation, the substrate may be heated to about 200 to 400 ° C. The shape of the laser beam may be a spot shape with a length of several mm to several cm depending on an optical system such as a lens, or a long shape with a long side of several cm to tens of cm and a short side of several mm. It can be processed into one, and any laser light may be used. By this laser irradiation, the amorphous silicon thin film 3a is crystallized to become the crystalline silicon thin film 3, and good crystal grains with a large grain size and very few crystal grain boundaries are obtained in the exposed portion where the metal film 4 is not provided. To be Further, as in the first embodiment, since the laser light is emitted from the back surface side of the insulating substrate, it is possible to avoid adverse effects such as roughening the surface of the semiconductor thin film and generating irregularities. Further, in this embodiment, since the amorphous silicon thin film is deposited with a film thickness of about 150 nm, the heat capacity of the film is increased as compared with the case where the amorphous silicon thin film is thinly deposited with a thickness of, for example, about 10 to 40 nm. To do. Therefore, the variation due to the energy density distribution of the laser light is alleviated, and a polycrystalline silicon thin film having better crystallinity can be obtained. Further, since the variation in the energy density distribution of the laser light is alleviated, there is also an advantage that the irradiation condition of the laser light, particularly the fine adjustment of the energy density is not necessary, and the control of the laser light becomes easy.

Thereafter, as shown in FIG. 7C, the exposed portion of the crystalline silicon thin film 3, that is, the portion which will be the channel region 6 of the TFT in a later step is etched to reduce the film thickness. . In the present embodiment, the channel region is 30 to
Etching was carried out to a film thickness of about 50 nm, preferably about 40 nm. This step can be performed by dry etching using CF ₄ (carbon tetrafluoride) + O ₂ gas, for example. Cr, Ta, Ti, N as the metal film 4
When b, Ni, Mo, W, their alloys, or their silicides are used, the amount etched by CF ₄ + O ₂ gas is smaller than that of the polycrystalline silicon thin film, and it is It is possible to secure a sufficient selection ratio. Therefore, when etching the channel region, the metal film 4 can be used as a mask for etching, and there is no need to form a new resist mask.

Next, as shown in FIG. 7D, the metal film 4
Get rid of. For example, when Ti is used as the metal film 4, EDTA (ethylenediaminetetraacetic acid) + H ₂ O
Mixing ratio of ₂ (hydrogen peroxide) + NH ₃ (ammonia) 1: 2
It can be removed using an etching solution mixed at 4: 8. When Mo is used as the metal film 4,
Etching solution prepared by mixing H ₂ SO ₄ (sulfuric acid) + HNO ₃ (nitric acid) + H ₂ O at a mixing ratio of 1: 1: 3 or HF (hydrogen fluoride) + HNO ₃ + CH ₃ COOH (acetic acid) at a mixing ratio of 1:20: It can be removed by using the etching solution mixed in 30. The crystalline silicon thin film is hardly etched by these etching solutions. Therefore, when removing the metal film 4, it is not necessary to form a resist mask for protecting the channel region. The above etching solution is shown as an example, and other etching solutions may be used. Cr, Ta, Nb, N as metal film
Even when i, W, an alloy containing Ti and Mo, or a silicide of these is used, the same etching as Ti and Mo can be achieved by etching under optimum conditions using an etching solution suitable for each metal film. Can be removed.

Further, the crystalline silicon thin film 3 is patterned into an island shape so as to become the active region 7 of the TFT, and the TFT is manufactured in the same manner as in the first embodiment. The manufacturing conditions of the TFT may be the same as in the first embodiment.

In the TFT obtained as described above, crystals having a very large grain size with extremely few crystal grain boundaries are selectively formed on the substrate, and the interface state density between the active region and the gate insulating film is small. Therefore, the field effect mobility is high and the leak current at the time of off can be reduced. Further, in this embodiment, the channel region of the TFT is etched in the film thickness direction to be thinner than the initial film thickness, and the film thickness of the source region and the drain region is formed thicker than the film thickness of the channel region. ing. Therefore, it is possible to sufficiently reduce the leak current when the TFT is turned off without reducing the on-current, and it is possible to secure good contact between the source region and the drain region and the source electrode and the drain electrode.

(Embodiment 4) FIGS. 8A to 8D are cross-sectional views showing steps in a method of manufacturing a semiconductor device according to Embodiment 4.

First, similarly to the third embodiment, the base film 2 and the amorphous silicon thin film 3a are deposited on the glass substrate 1.

Next, the insulating substrate is taken out of the chamber of the CVD apparatus, and the amorphous silicon thin film 3a is patterned into an island shape which is the shape of the active region.

Next, the amorphous silicon thin film 3 is formed by a sputtering method or the like so that at least a channel region forming portion is exposed in a predetermined region on the amorphous silicon thin film 3a.
A film made of a material having a smaller specific heat capacity than a, for example, a metal film 4 is selectively formed. The metal film 4 is used in the first embodiment.
The same material, film thickness, and pattern interval can be used. In this embodiment, the metal film 4 is deposited to a film thickness of about 300 nm, and the pattern interval of the metal film 4 is set to 5 μm to 10 μm, for example, about 8 μm.

Then, as shown in FIG. 8B, the amorphous silicon thin film 3a is crystallized into the crystalline silicon thin film 3 by irradiating the laser beam 5 from the back surface side of the glass substrate 1. As the laser beam 5 to be used, the same laser beam as in the first embodiment can be used. The irradiation condition of the laser light is determined by the film quality and film thickness of the film irradiated with the laser light. In this embodiment, the insulating substrate 1 and the base film 2 are
Energy loss of 200 to 400 mJ / cm ² , for example 300
Irradiation was performed at about mJ / cm ² . At the time of laser light irradiation,
The substrate may be heated to about 200 to 400 ° C. Also,
The shape of the laser beam is several mm square depending on the optical system such as a lens.
Spot-shaped ones with a few centimeters square, and several centimeters on the long side
It can be processed into a long shape having a length of about 10 cm and a short side of about several mm, and any laser light may be used. By this laser irradiation, the amorphous silicon thin film 3a is crystallized to become the crystalline silicon thin film 3, and good crystal grains with a large grain size and very few crystal grain boundaries are obtained in the exposed portion where the metal film 4 is not provided. To be Further, as in the first embodiment, since the laser light is emitted from the back surface side of the insulating substrate, it is possible to avoid adverse effects such as roughening the surface of the semiconductor thin film and generating irregularities. Further, similarly to the third embodiment, since the amorphous silicon thin film is deposited with a film thickness of about 150 nm, the variation due to the energy density distribution of laser light can be reduced.

After that, as shown in FIG. 8C, the portion where the crystalline silicon thin film 3 is exposed, that is, the portion which becomes the channel region 6 of the TFT in a later step is etched to reduce the film thickness. . This step can be performed in the same manner as in the third embodiment.

Next, as shown in FIG. 8D, the metal film 4
Get rid of. This step can be performed in the same manner as in the third embodiment.

After that, the TFT is formed in the same manner as in the first embodiment.
Is prepared. However, in the present embodiment as well, as in the second embodiment, the active region 7 is patterned in advance in an island shape, so that it is not necessary to pattern the active region 7 again.

In the TFT obtained as described above, crystals with a good large grain size having extremely few crystal grain boundaries are selectively formed on the substrate, and the interface state density between the active region and the gate insulating film is small. Therefore, the field effect mobility is high and the leak current at the time of off can be reduced. Further, in this embodiment, the channel region of the TFT is etched in the film thickness direction to be thinner than the initial film thickness, and the film thickness of the source region and the drain region is formed thicker than the film thickness of the channel region. ing. Therefore, it is possible to sufficiently reduce the leak current when the TFT is turned off without reducing the on-current, and it is possible to secure good contact between the source region and the drain region and the source electrode and the drain electrode. Further, in this embodiment, since the active region 7 is patterned in advance in an island shape, it is not necessary to newly form a resist mask on the active region 7, and the resist mask remains on the channel region 6. Can be avoided. Therefore, the surface of the active region including the channel region can be kept clean and the characteristics can be further improved.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above embodiments.

For example, although the glass substrate is used as the insulating substrate in the above embodiment, other insulating substrates such as a quartz substrate and a plastic substrate may be used. The process temperature can withstand a high temperature process of 1200 ° C. for a quartz substrate, but is limited to a low temperature of about 600 ° C. when a glass substrate is used because the strain point is low. On the other hand, it is desirable to use a glass substrate as a substrate having a larger area and a lower cost. The plastic substrate can be used so that heat is not transmitted.

Further, as for the manufacturing process of the TFT after removing the metal film, an example thereof is shown, and other methods may be used.

[0080]

As is apparent from the above description, according to the present invention, by forming a film made of a material having a small specific heat capacity selectively on an insulating substrate, the crystal grain boundaries can be extremely reduced. Since a small number of excellent crystals having a large grain size can be formed, the number of crystal grain boundaries in the channel region can be reduced and the leak current when the TFT is off can be reduced. In addition, when the channel region is thinner than the source region and the drain region, the leak current when the TFT is off can be reduced without reducing the on-current. Further, since the semiconductor device can be manufactured at a low temperature, a large area and a low cost can be achieved by using a low melting point glass.

Further, according to the present invention, the channel region can be thinned by etching the crystalline semiconductor thin film using the film made of a material having a small specific heat capacity as a mask. Therefore, while maintaining good contact between the source region and the drain region and the source electrode and the drain electrode, it is possible to further reduce the leak current when off.

Furthermore, by selectively etching the crystalline semiconductor thin film and the film made of a material having a small specific heat capacity, a TFT having excellent characteristics can be manufactured without significantly increasing the manufacturing process.

As described above, according to the present invention, a high-performance semiconductor device, in particular, a semiconductor device or a semiconductor circuit including a high-performance TFT having a high field-effect mobility and a low leak current at the time of off is provided. Since it can be provided, it is an industrially very useful invention.

[Brief description of the drawings]

FIG. 1A is a sectional view for explaining a process for obtaining a crystalline semiconductor thin film by a method for manufacturing a semiconductor device of the present invention, FIG. 1B is a plan view thereof, and FIG. Is
It is sectional drawing which shows TFT manufactured using the crystalline semiconductor thin film finally obtained by the manufacturing method of the semiconductor device of this invention partially.

FIG. 2 is a graph showing a temporal change in temperature of a semiconductor thin film during laser light irradiation.

3A and 3B are diagrams showing a temperature distribution of a semiconductor thin film in the method for manufacturing a semiconductor device of the present invention.

4A to 4C are cross-sectional views showing a manufacturing process of the semiconductor device of the first embodiment.

5A and 5B are diagrams showing an example of the shape of a metal film used in the method for manufacturing a semiconductor device of the present invention.

6A to 6C are cross-sectional views showing the manufacturing process of the semiconductor device of the second embodiment.

7A to 7D are cross-sectional views showing the manufacturing process of the semiconductor device of the third embodiment.

8A to 8D are cross-sectional views showing the manufacturing process of the semiconductor device of the fourth embodiment.

9A and 9B are diagrams showing the intensity distribution of laser light.

[Explanation of symbols]

 1 Glass Substrate 2 Base Film 3a Amorphous Silicon Thin Film 3 Crystalline Silicon Thin Film 4 Film with Small Specific Heat Capacity (Metal Film) 5 Laser Light 6 Channel Region 7 Active Region 8 Gate Insulating Film 9 Gate Electrode 10 Source and Drain Regions 11 Interlayer insulating film 12 Source and drain electrodes 13 Grain boundaries

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 21/308 H01S 3/095 B H01S 3/0953

Claims (7)

[Claims] 1. A method of manufacturing a semiconductor device, comprising an active region made of a crystalline semiconductor thin film on an insulating substrate, wherein a part of the active region is used as a channel region, which is amorphous on the substrate. A step of forming a semiconductor thin film, exposing at least a channel region forming part of the amorphous semiconductor thin film, and selectively forming a film of a material having a smaller specific heat capacity than the amorphous semiconductor thin film on the amorphous semiconductor thin film. A step of forming, a step of irradiating a laser beam from a side of the substrate opposite to the side where the amorphous semiconductor thin film is formed to crystallize the amorphous semiconductor thin film to obtain a crystalline semiconductor thin film, and the amorphous semiconductor A method of manufacturing a semiconductor device, comprising: a step of removing a film made of a material having a smaller specific heat capacity than that of a thin film; and a step of processing the crystalline semiconductor thin film into a shape of an active region. 2. A method of manufacturing a semiconductor device, comprising an active region made of a crystalline semiconductor thin film on an insulating substrate, wherein a part of the active region is used as a channel region, which is amorphous on the substrate. A step of forming a semiconductor thin film; a step of processing the amorphous semiconductor thin film into a shape of an active region; and a step of exposing at least a channel region forming portion of the amorphous semiconductor thin film having a shape of the active region to expose the active region. A step of selectively forming a film made of a material having a smaller specific heat capacity than the amorphous semiconductor thin film on the shaped amorphous semiconductor thin film; and a laser beam from a side opposite to the amorphous semiconductor thin film forming side of the substrate. And crystallization of the amorphous semiconductor thin film in the shape of the active region to obtain a crystalline semiconductor thin film in the shape of the active region, and a material having a smaller specific heat capacity than the amorphous semiconductor thin film. The method of manufacturing a semiconductor device including the step of removing the. 3. The method according to claim 1, further comprising the step of etching the channel region forming portion of the crystalline semiconductor thin film to thin the film by using a film made of a material having a specific heat capacity smaller than that of the amorphous semiconductor thin film as a mask. Manufacturing method of semiconductor device. 4. A step of etching and thinning a channel region forming portion of the crystalline semiconductor thin film in the shape of the active region using a film made of a material having a smaller specific heat capacity than the amorphous semiconductor thin film as a mask. Item 3. A method for manufacturing a semiconductor device according to item 2. 5. A film made of a material having a smaller specific heat capacity than that of the amorphous semiconductor thin film is Cr, Ta, Ti, N.
5. The method for manufacturing a semiconductor device according to claim 1, wherein a film made of at least one material selected from b, Ni, Mo, W, alloys thereof, and silicides thereof is formed. 6. A material having a smaller specific heat capacity than that of the amorphous semiconductor thin film, wherein a film having a selection ratio at the time of etching is formed with respect to the crystalline semiconductor thin film, and the material having a smaller specific heat capacity. The method for manufacturing a semiconductor device according to claim 1, wherein etching is selectively performed when the film made of is removed. 7. A film having a selection ratio in etching with respect to the crystalline semiconductor thin film is formed as a film made of a material having a smaller specific heat capacity than the amorphous semiconductor thin film, and the channel region is etched. The method for manufacturing a semiconductor device according to claim 3, wherein the etching is selectively performed at this time.