JPH10135472A - Semiconductor device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent failure due to, e.g. breaking of wire over an active layer end portion. SOLUTION: A convex-type semiconductor layer 106 having a flange 107 is formed by thinning only the edges of an island-shaped semiconductor layer 104 to be an active layer. Then, thermal oxidation processing is performed on the convex-type semiconductor layer 106 so as to form a thermal-oxidized film 108. At this time, the flange 107 is completely thermal-oxidized and becomes a part of the thermal-oxidized film 108. By this method, a completely flat active layer 109 can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD [0001] The invention disclosed in the present specification is:
The present invention relates to a semiconductor device using a thin film semiconductor having crystallinity and a manufacturing method thereof. In particular, it relates to the configuration of an active layer of a semiconductor device.

[0002]

2. Description of the Related Art In recent years, a technique for manufacturing a thin film transistor (TFT) on an insulating substrate has been rapidly developed. A TFT is a switching element having a laminated structure of metal / insulating film / semiconductor, and a silicon film (silicon film) is generally used as a semiconductor.

This silicon film functions as an active layer of a TFT. Until now, an amorphous silicon film (amorphous silicon film) has been mainly used. Films (polysilicon films) are becoming mainstream.

[0004] When further high-speed operation is required, various means have been used to enhance the crystallinity of the active layer. In particular, it is known that heat treatment at about 700 to 1000 ° C. is very effective in reducing internal defects in the crystalline silicon film and improving the consistency of interatomic bonds.

Further, a technique of performing thermal oxidation at a high temperature on an active layer and using a thermal oxide film formed on the surface of the active layer as a gate insulating film in the process forms a good Si / SiO ₂ interface. It is known.

Therefore, when performing the above-described steps, the crystalline silicon film is processed into an island-shaped semiconductor layer which is to become an active layer later, and is then heated at a high temperature of 700 to 1000 ° C. Will be done. By this step, a thermal oxide film is formed on the surface of the active layer, but a major problem arises here.

The problem is a phenomenon in which the edge of the island-like semiconductor layer is oxidized from the back side during the thermal oxidation step, and the island-like semiconductor layer is lifted up by the thermal oxide film.

This situation will be schematically described with reference to FIG. As shown in FIG. 3A, when the island-shaped semiconductor layer 301 is formed, the quartz substrate 302 is also slightly etched, so that a recessed portion is formed below an end (see an enlarged view) of the island-shaped semiconductor layer 301. 303 are formed.

Then, as shown in FIG. 3B, at the same time as the formation of the thermal oxide film 304, the back surface of the island-shaped semiconductor layer 301 exposed by the undercut portion 303 is oxidized. Normally, when a silicon film is thermally oxidized, it expands to about twice the volume of the thermally oxidized silicon film.
The thermal oxidation reaction proceeds in such a way that a wedge is driven into the boundary between
The island-shaped semiconductor layer 301 is gradually lifted.

Therefore, when the cross section of the island-shaped semiconductor layer 301 after the thermal oxidation is observed, the end of the island-shaped semiconductor layer 301 rises, and the edge of the thermal oxide film 304 is locally steep.

When a conductive film 305 serving as a gate electrode or a gate wiring is formed thereon in this state, as shown in FIG. 3C, defects such as disconnection due to deterioration of coverage at the end of the island-shaped semiconductor layer 301 are caused. Will occur.

[0012]

The above-mentioned problem is caused by the fact that the thermal oxidation reaction proceeds from the undercut portion formed at the end of the island-shaped semiconductor layer. An object of the present invention is to provide a means for solving the above-described problems based on that point.

[0013]

The gist of the present invention is to keep in mind that the edge of the active layer is lifted by the phenomenon shown in FIG.
An object of the present invention is to make the edge of the active layer thinner in advance to make the step after thermal oxidation gentle, and to prevent a failure such as disconnection of a wiring material later.

At the same time, the active layer ends (more precisely, FIG.
By completely transforming the protruding portion 107 shown in (C) into a thermal oxide film, the purpose is to reduce the leak current due to the defect at the end of the active layer and to improve the breakdown voltage of the gate insulating film at the end of the active layer. .

[0015] For this purpose, the structure of the invention disclosed in this specification includes a step of forming an island-shaped semiconductor layer made of a silicon film on a substrate having an insulating surface, and a method in which only an end of the island-shaped semiconductor layer is intentionally formed. At least a step of processing into a convex semiconductor layer having a protrusion at the end, and a step of thermally oxidizing the convex semiconductor layer to completely transform the protrusion into a thermal oxide film. It is characterized by having.

Specifically, only the semiconductor layer remaining after the convex semiconductor layer is thermally oxidized is finally used as an active layer.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG.
After patterning 2 into the island-shaped semiconductor layer 104, the end of the island-shaped semiconductor layer 104 is exposed, and only the exposed portion 105 is selectively etched.

A thermal oxidation step is performed on the convex semiconductor layer 106 thus formed, and a thermal oxide film 108 constituting part or all of the gate insulating film is formed later.

In the thermal oxidation step, the protruding portion 107 is lifted by thermal oxidation from the back surface as described in the conventional example. However, since the film thickness is small, a disconnection failure of the wiring which has been a problem in the past is caused. It does not form as much step. In addition, since the oxide film is finally completely transformed into a thermal oxide film, the end of the active layer 109 can be surely protected.

[0020]

【Example】

[Embodiment 1] FIGS. 1 and 2 show a manufacturing process of a semiconductor device using the present invention. First, a substrate 101 having an insulating surface with excellent heat resistance is prepared. As such a substrate,
A substrate in which a base film such as a silicon oxide film is formed over a quartz substrate, a sapphire substrate, a silicon substrate, or the like can be used.

Next, a crystalline silicon film 102 is
To form The crystalline silicon film 102 may be formed to a thickness of 500 to 1000 ° using a low pressure thermal CVD method or a plasma CVD method. In this embodiment, the film is formed to have a thickness of 750 mm in consideration of the film loss due to the subsequent thermal oxidation.

In addition to the method of forming the crystalline silicon film 102 directly, a method of forming an amorphous silicon film and then crystallizing the film by heat treatment or laser treatment may be used. Furthermore, when crystallizing by heat treatment,
A metal element that promotes crystallization may be added.

Next, a resist mask 103 for processing (patterning) the crystalline silicon film 102 into an island-shaped semiconductor layer serving as a prototype of an active layer later is arranged. At this time, it is preferable to form a thin oxide film on the surface of the crystalline silicon film 102 in advance. This oxide film is used as a resist mask 103
To prevent the crystalline silicon film 102 from being contaminated with a resist material (organic substance).

Thus, the state shown in FIG. 1A is obtained. When the state illustrated in FIG. 1A is obtained, the island-shaped semiconductor layer 104 is formed by first dry etching. The etching conditions in this embodiment are as follows: RF power: 300 W Gas pressure: 800 mTorr Etching gas: CF ₄ 43 sccm, O ₂ 59 sccm

Next, after the island-shaped semiconductor layer 104 is formed,
The inside of the chamber of the etching apparatus is switched to an oxygen atmosphere, and ashing (carbonization) of the resist mask 103 is performed.
It is retracted by a distance of 0.5-1.5 μm (preferably 1.0 μm). Then, as shown in FIG. 1B, the island-shaped semiconductor layer 1 is formed.
The end 105 of the substrate 04 is exposed as much as the resist mask 104 has receded.

Then, dry etching is performed again in the state shown in FIG.
Is etched. At this time, the end portion 105 is not completely removed, but 100 to 500 mm, typically 200 to 300 mm.
It is an important configuration in the present invention that the film is left with a film thickness of about the same level.

Thus, the convex semiconductor layer 106 is formed. The convex semiconductor layer 106 has a length of 0.1 to 1.5 μm at its end.
m and a structure having a protrusion 107 having a thickness of 100 to 500 mm. Note that in this state, the recessed portion 303 as shown in FIG. 3A has been formed at the end of the convex semiconductor layer 106. (Fig. 1 (C))

Next, after the resist mask 103 remaining on the convex semiconductor layer 106 is removed with a dedicated stripper,
Heat treatment is performed in an oxidizing atmosphere at 〜1100 ° C. (950 ° C. in the present embodiment) for 0.1 to 1 hr (0.5 hr in the present embodiment).

Although the oxidizing atmosphere is formed in an atmosphere mainly containing oxygen, it is effective to mix a halogen element in order to remove a metal element in the silicon film.

By this heat treatment, the convex semiconductor layer 106 is thermally oxidized, and a thermal oxide film 108 is formed on its surface. In this embodiment, only the thermal oxide film 108 formed in the step shown in FIG. 1D is used as it is as a gate insulating film. Of course, an insulating film may be stacked on the thermal oxide film 108 by a vapor phase method, and the stacked film may be used as a gate insulating film.

In this state, the active layer 109 which will later constitute the source region, the channel formation region and the drain region is defined. According to the conditions of the present embodiment, since a thermal oxide film of about 500 ° is formed (the crystalline silicon film of about 250 ° is reduced), the thickness of the active layer 109 is about 500 °.

The most characteristic point of the present invention is that the protrusion 107 made of a silicon film is completely thermally oxidized through the thermal oxidation step, and the thermal oxide film (FIG. 1D) has a shape as shown in FIG. (A gate insulating film) 108 is formed.

That is, the projecting portion 107 finally becomes a part of the gate insulating film, and the end of the gate insulating film 108 extends to a region 0.1 to 1.5 μm away from the side surface of the active layer 109. . It is obvious that the shape of the gate thermal oxide film shown in FIG. 1D is different from the shape of the conventional thermal oxide film.

Of course, during the thermal oxidation step, the recessed portion (not shown) formed at the end of the convex semiconductor layer 106 (the end of the protruding portion 107) has the same phenomenon as described in the conventional example. Causes the silicon film to be lifted upward. However, in the structure of the present invention, the region that has been lifted up eventually becomes a complete thermal oxide film, so that the active layer 109 is composed of only a completely flat semiconductor layer.

According to the structure of the present invention, as shown in FIG. 1D, the thermal oxide film 108 is formed in a step-like manner (a large step difference in height does not occur in the gate insulating film). There is no possibility of causing a disconnection failure of the gate electrode (gate wiring).

The island-shaped semiconductor layer 104, which is a prototype of the active layer 109, is formed by dry etching. At this time, plasma damage remains on the edge of the island-shaped semiconductor layer 104. Normally, this plasma damage can cause a leak current of the TFT, but in the case of this embodiment,
Since the edge of the island-shaped semiconductor layer 104 is completely thermally oxidized, plasma damage is also removed at the same time.

The state shown in FIG. 1D is obtained as described above. After the state shown in FIG. 1D is obtained, an aluminum film (not shown) for forming a gate electrode is then formed by 2500.
A film is formed to a thickness of Å by a sputtering method. The aluminum film contains 0.2% by weight of scandium to prevent hillocks and whiskers.

In this embodiment, a material mainly composed of aluminum is used as a material for forming a gate electrode (including a gate line), but other materials such as tungsten, tantalum, molybdenum and the like can also be used. Further, a crystalline silicon film provided with conductivity may be used as a gate electrode.

Next, as shown in FIG. 2A, the aluminum film is patterned to form an island-shaped aluminum film pattern 109 serving as a prototype of the gate electrode. Note that a resist mask (not shown) used for patterning is left as it is.

Then, an aluminum film pattern 109 is formed.
Is performed to form a porous anodic oxide film 110 on the side surface of the aluminum film pattern 109. This technique is described in JP-A-7-135318.

After the formation of the porous anodic oxide film 109, the dense anodic oxide film 111 is formed by using the technique described in the publication.
To form At the same time, the gate electrode 112 is defined. The dense anodic oxide film 111 functions to protect the surface of the gate electrode 112 in a later step and to suppress generation of hillocks and whiskers.

In this embodiment, the porous anodic oxide film 110 is used.
Is 0.7 μm, and the thickness of the dense anodic oxide film 111 is 900 μm.

Next, after the dense anodic oxide film 111 is formed, in this state, impurity ions for forming source / drain regions are implanted. N-channel type TF
To produce T, P (phosphorus) ions are implanted, and P
If a channel type TFT is manufactured, B (boron) ions may be implanted.

In this step, a source region 113 and a drain region 114 to which impurities are added at a high concentration are formed.

Next, the porous anodic oxide film 110 is selectively removed by using a mixed acid obtained by mixing acetic acid, phosphoric acid, and nitric acid, and then impurity ions are implanted again. This ion implantation is performed at a lower dose than when the source / drain regions are formed. (Fig. 2 (C))

Then, low-concentration impurity regions 115 and 116 having a lower impurity concentration than the source region 113 and the drain region 114 are formed. And the gate electrode 112
The region indicated immediately below by 117 becomes a channel forming region in a self-aligned manner.

The low-concentration impurity region 116 disposed between the channel formation region 117 and the drain region 114
Is particularly called an LDD (lightly doped drain region) region and has an effect of relaxing a high electric field formed between the channel forming region 117 and the drain region 114.

Further, after the above-described impurity ion implantation step, the region where the ion implantation has been performed is annealed by irradiating laser light, infrared light or ultraviolet light. This process activates the added ions and recovers the damage caused to the active layer during the ion implantation.

In this case, it is effective to carry out the hydrogenation treatment in a temperature range of 300 to 350 ° C. for 0.5 to 1 hour. In this step, dangling bonds generated by desorption of hydrogen from the active layer are terminated with hydrogen again. By performing this step, hydrogen is added to the active layer at a concentration of 1 × 10 ¹⁵ to 1 × 10 ²¹ atoms / cm ³ .

When the state shown in FIG. 2C is obtained, an interlayer insulating film 118 is formed next. Interlayer insulating film 118
Is composed of a silicon oxide film, a silicon nitride film, a silicon oxynitride film, an organic resin film, or a stacked film of these films.

It is preferable to use a silicon nitride film as the interlayer insulating film 118 because the hydrogen added in the previous step can be prevented from being re-emitted to the outside of the device. In addition, when polyimide, which is an organic resin film, is used, since the relative dielectric constant is small, the parasitic capacitance between the upper and lower wirings can be reduced. Further, since the film can be formed by the spin coating method, the film thickness can be easily increased, and the throughput can be improved.

Next, a contact hole is formed in the interlayer insulating film 118, and a source electrode 119 and a drain electrode 120 are formed. Further, by performing heat treatment in a hydrogen atmosphere at 350 ° C., the entire device is hydrogenated, and the TFT shown in FIG. 2D is completed.

Although the TFT shown in FIG. 2D has the simplest structure for explanation, a desired TF is appropriately obtained by making some changes and additions to the manufacturing process procedure of this embodiment.
It is easy to adopt a T structure. For example, in an active matrix display device, a pixel T
In the case of manufacturing an FT, an interlayer insulating film may be provided over the source / drain electrodes again from the state shown in FIG. 2D and a pixel electrode connected to the drain electrode 120 may be provided thereover.

Further, the TFT manufactured by implementing the present invention
Has a structure different from that of a TFT manufactured by a general method. The features are described below.

By practicing the present invention, a thermal oxide film (gate insulating film) 108 and an active layer 109 having the shapes shown in FIG. 1D can be obtained. Since a generally known thermal oxide film is formed only on the surface of the active layer as a matter of course, the shape of the thermal oxide film 108 shown in FIG. 1D is a great feature obtained only when the present invention is used.

FIG. 5A shows an active layer 501 and a thermal oxide film 50 formed on a substrate 51 by a known method.
2. FIG. 5B shows an active layer 503 and a thermal oxide film 504 formed on the substrate 52 according to the present invention.
It is.

First, the first feature of the present invention is shown in FIG.
In FIG. 5, the surface shape (main surface shape) of the active layer 501 and the surface shape of the thermal oxide film 502 are substantially the same.
(B) has a completely different surface shape.

Further, the second feature of the present invention is that FIG.
In FIG. 5B, the distance (contact distance) of the region 53 where the substrate 51 and the thermal oxide film 502 are in contact corresponds to the thickness of the thermal oxide film 502, but the distance of the region 54 in FIG. 503.

The third feature of the present invention is that the active layer 50
The point is that the end of the thermal oxide film exists in a region 0.1 to 1.5 μm away from the side surface of No. 3. Of course, when only the thermal oxide film functions as the gate insulating film as in the first embodiment, it can be said that the end of the gate insulating film exists in the above-described region.

A fourth feature of the present invention is that a region where a protrusion is present before the thermal oxidation step is manufactured by a known method in that a gate insulating film is present or its film thickness is different. This is different from the TFT.

For example, when only a thermal oxide film is used as a gate insulating film, in the present invention, a gate insulating film (thermal oxide film) is provided in a region where a protrusion is present (a region of 0.1 to 1.5 μm from the side surface of the active layer). Although there is a thermal oxide film, a known method is not used.

Further, for example, when a gate insulating film is formed of a laminated film of a thermal oxide film and an insulating film formed by a vapor phase method, the thickness of the gate insulating film varies depending on the location. This will be briefly described.

FIG. 6A shows a structure in which a gate insulating film having a structure in which an insulating film 505 is laminated by a vapor phase method in FIG. 5A is used. FIG. 6B shows a structure in which a gate insulating film in which an insulating film 505 is stacked in FIG. 5B is used.

6A and 6B, regions 55 and 56 where the gate insulating film overlaps with the active layers 501 and 503 are defined as first regions, and regions 57 and 58 where they do not overlap are defined as second regions. Since the thickness of the thermal oxide film is extremely smaller than the length of the active layer, the thickness of the thermal oxide film on the side surface of the active layer is ignored.

At this time, in FIGS. 6A and 6B, the thickness of the gate insulating film in the first regions 55 and 56 is determined by the thickness of the laminated film. That is, in this first region, there is no difference between the present invention and the known method.

However, in the gate insulating film formed by a known method, the thickness in the second region 57 is determined only by the thickness of the insulating film 505, whereas in the case of the gate insulating film of the present invention, the second The region 58 has two regions, that is, a region composed of a laminated film and a region composed of only the insulating film 505. In other words, the second region 58 includes at least two regions having different thicknesses.

The first to fourth features as described above are structural features which are inevitably generated by implementing the present invention, and serve as a proof that the present invention has been used.

[Embodiment 2] In the embodiment 1, the resist receding step as shown in FIG. 1B was performed in order to provide a protruding portion at the end of the island-shaped semiconductor layer. May be. That is, the steps shown in FIGS. 1B and 1C can be alternately repeated to form a step-like island-shaped semiconductor layer.

With the structure shown in this embodiment, a structure is obtained in which the level difference of the thermal oxide film (gate insulating film) changes gradually. Needless to say, by increasing the number of repetitions of the steps shown in FIGS. 1B and 1C, the end portion of the island-shaped semiconductor layer approaches a tapered shape.

Therefore, according to the structure of this embodiment, the coverage of the gate electrode (gate wiring) is further improved.

[Embodiment 3] In this embodiment, an example in which an active layer is formed by means different from that in Embodiment 1 will be described. The description will be made with reference to FIG. 4 up to the point where the active layer and the gate insulating film are formed.

First, as shown in FIG.
01, and a base film 402 is prepared thereon. Here, a silicon oxide film is used as the base film 402. Next, an amorphous silicon film (not shown) having a thickness of 500 mm is formed.

After the formation of the amorphous silicon film, see JP-A-6-2325
The amorphous silicon film is crystallized using the techniques described in Japanese Patent Application Laid-Open No. 09-244103 and Japanese Patent Application Laid-Open No.
Get. The technique described in the above publication relates to a crystallization means for adding a metal element (typically, nickel) which promotes crystallization.

Thus, the state shown in FIG. 4A is obtained. Next, a resist mask 40 is formed on the crystalline silicon film 403.
4 is provided. The resist mask 404 is formed of the crystalline silicon film 4
At 03, an arrangement is made such that only the region which will be the active layer later is masked. (FIG. 5 (B))

Next, the crystalline silicon film 403 is etched using the resist mask 404 as a mask, and selectively
05 is formed. The etching may be a dry etching method or a wet etching method, but a dry etching method is preferable for controlling the thickness of the crystalline silicon film after the etching.

What is important here is that the crystalline silicon film 503 is not completely removed in this etching step, but is not completely removed.
It is to be kept at a thickness of 0 to 500 mm (preferably 100 to 200 mm). In this embodiment, the region 406 on the bottom of the concave portion 405 is called a bridge-like semiconductor layer.
It is formed with a thickness of Å.

In the structure of the present embodiment, the bridge-like semiconductor layer 406 left here functions to prevent the active layer from being lifted by a thermal oxidation step later.

Thus, the state shown in FIG. 4C is obtained. When the state of FIG. 4C is obtained, the resist mask 4
04 is removed with a dedicated stripper, and then a heat treatment (thermal oxidation step) at 850 ° C. for 30 minutes is performed. (FIG. 4 (D))

By this heat treatment, the crystalline silicon film of 200 ° is thermally oxidized to form a thermal oxide film having a thickness of about 400 °. Therefore, the bridge-like semiconductor layer 406 is completely transformed into a thermal oxide film, and active layers 407 to 409 which are individually insulated and separated are formed. The surface of the active layers 407 to 409
A 400 ° thermal oxide film 410 is formed.

The feature of this embodiment is that the crystalline silicon film 4
That is, there is no step for exposing the base film 402 after the formation of the substrate 03. That is, the phenomenon of undercut of the thermal oxide film under the active layer as described in the conventional example does not occur fundamentally.

[Embodiment 4] The present invention relates to a SIMOX or SOS
It can also be applied to SOI substrates represented by In this case, the crystalline silicon film on the insulating surface is a single crystal silicon film, and it is necessary to apply the contrivance shown in the first embodiment to the single crystal silicon film. In addition, it is easy to apply not only the first embodiment but also the second and third embodiments.

[0082]

By implementing the present invention, it is possible to prevent the semiconductor layer from being raised during thermal oxidation and the accompanying defects such as disconnection of the gate electrode or the gate wiring.

Further, since an active layer having no plasma damage or the like can be formed at an edge portion, an off current (a current flowing when the TFT is off) and a leak current when a TFT is manufactured can be significantly reduced. Can be.

As described above, it is possible to manufacture a semiconductor device having excellent electrical characteristics having both high reliability and low off-current characteristics.

[Brief description of the drawings]

FIG. 1 illustrates a manufacturing process of a semiconductor device.

FIG. 2 illustrates a manufacturing process of a semiconductor device.

FIG. 3 is a diagram for explaining a conventional example.

FIG. 4 illustrates a manufacturing process of a semiconductor device.

FIG. 5 is a diagram for explaining the structural features of the TFT of the present invention.

FIG. 6 is a diagram for explaining the structural characteristics of the TFT of the present invention.

[Explanation of symbols]

 Reference Signs List 101 substrate having insulating surface 102 crystalline silicon film 103 resist mask 104 island-shaped semiconductor layer 105 exposed region 106 convex semiconductor layer 107 protrusion 108 thermal oxide film (gate insulating film) 109 active layer

Claims (18)

[Claims] An active layer made of a crystalline silicon film formed on a substrate having an insulating surface; a gate insulating film formed on the active layer; a gate electrode formed on the gate insulating film; 2. The semiconductor device according to claim 1, wherein the end of the gate insulating film exists in a region which is apart from the side surface of the active layer by 0.1 to 1.5 μm. 2. The semiconductor device according to claim 1, wherein said gate insulating film comprises only a thermal oxide film obtained by thermally oxidizing said active layer. 3. An active layer made of a crystalline silicon film formed on a substrate having an insulating surface, a gate insulating film formed on the active layer, and a gate electrode formed on the gate insulating film. A gate insulating film, wherein the first region overlaps the active layer;
A semiconductor device, comprising: a second region that does not overlap with the active layer; wherein the second region includes at least two regions having different thicknesses. 4. A semiconductor device according to claim 3, wherein, of the regions having at least two different film thicknesses, the region having the larger film thickness is a laminated film of a thermal oxide film and an insulating film formed by a vapor phase method. A semiconductor device characterized by being performed. 5. An active layer comprising a crystalline silicon film formed on a substrate having an insulating surface, a gate insulating film formed on the active layer, and a gate electrode formed on the gate insulating film. Wherein the gate insulating film is formed of an insulating film including a thermal oxide film obtained by thermally oxidizing the active layer, wherein the thermal oxide film has a thickness equal to or greater than the thickness thereof. A semiconductor device, wherein a region which is in contact with the substrate at a distance exists. 6. An active layer comprising a crystalline silicon film formed on a substrate having an insulating surface; a gate insulating film formed on the active layer; a gate electrode formed on the gate insulating film; Wherein the gate insulating film is formed of an insulating film including a thermal oxide film obtained by thermally oxidizing the active layer, and the surface shape of the thermal oxide film is the same as that of the active layer. A semiconductor device having a shape different from a surface shape. 7. A step of forming an island-shaped semiconductor layer made of a silicon film on a substrate having an insulating surface; and intentionally thinning only an end of the island-shaped semiconductor layer to have a projecting portion at the end. A semiconductor device which is manufactured through at least a step of processing into a convex semiconductor layer and a step of thermally oxidizing the convex semiconductor layer to completely transform the protrusion into a thermal oxide film. 8. The method according to claim 7, wherein the thickness of the projection is 10
A semiconductor device having a thickness of 0 to 500 mm. 9. The semiconductor device according to claim 7, wherein said protrusion has a stepped shape or a tapered shape. 10. The semiconductor device according to claim 7, wherein said projection has a length of 0.1 to 1.5 μm. 11. A step of forming an island-shaped semiconductor layer made of a silicon film on a substrate having an insulating surface, and intentionally thinning only an end of the island-shaped semiconductor layer to have a protrusion at the end. A method for manufacturing a semiconductor device, comprising: at least a step of processing into a convex semiconductor layer; and a step of thermally oxidizing the convex semiconductor layer to completely transform the protrusion into a thermal oxide film. 12. A step of forming an island-shaped semiconductor layer made of a silicon film on a substrate having an insulating surface, and intentionally thinning only an end of the island-shaped semiconductor layer to have a projecting portion at the end. A method of manufacturing a semiconductor device, comprising: a step of processing a convex semiconductor layer; and a step of thermally oxidizing the convex semiconductor layer to completely transform the protrusion into a thermal oxide film. A method for manufacturing a semiconductor device, wherein only a semiconductor layer remaining after thermally oxidizing a layer is finally used as an active layer. 13. The method according to claim 11, wherein
The method of manufacturing a semiconductor device, wherein the thickness of the protrusion is 100 to 500 mm. 14. A method for manufacturing a semiconductor device according to claim 11, wherein said projecting portion has a stepped shape or a tapered shape. 15. The method for manufacturing a semiconductor device according to claim 11, wherein the length of said protruding portion is 0.1 to 1.5 μm. 16. The method according to claim 11, wherein
The step of forming the convex semiconductor layer includes: a step of etching the island-shaped semiconductor layer by a dry etching method; and a step of receding a resist mask existing on the island-shaped semiconductor by a dry etching method or a plasma treatment. A method for manufacturing a semiconductor device, which is performed alternately. 17. A step of intentionally forming a concave portion in a silicon film deposited on a substrate having an insulating surface, and thermally oxidizing the silicon film to completely bridge the bridge-like semiconductor layer on the bottom surface of the concave portion. And a step of transforming into a thermal oxide film. 18. The method according to claim 17, wherein the thickness of the concave portion is
A method for manufacturing a semiconductor device, which has a thickness of 100 to 500 mm.