Semiconductor device and method for producing the same

A method for producing a semiconductor device includes a step of forming a first insulation film, a step of forming a separation layer in a base layer, a step of forming a light-blocking film on the surface of the first insulation film, a step of forming a second insulation film such that the light-blocking film is covered, a step of affixing the base layer provided with the light-blocking film to a substrate, a step of separating and removing along the separation layer a portion of the base layer affixed to the substrate, and a step of forming a semiconductor layer such that at least a portion thereof overlaps with the light-blocking film.

TECHNICAL FIELD

The present invention relates to a semiconductor device used, for example, in a liquid crystal display device or the like, and to a method for manufacturing the same.

BACKGROUND ART

For example, a liquid crystal display device includes a thin film transistor (TFT) substrate on which a plurality of TFTs and pixel electrodes connected thereto are arranged in a matrix, an opposite substrate which is disposed facing this TFT substrate and on which a color filter, a common electrode, and the like are formed, and a liquid crystal layer provided between the opposite substrate and the TFT substrate. A backlight which constitutes the light source is provided on the TFT substrate on the side opposite from the liquid crystal layer. A glass substrate is preferably used as the TFT substrate.

A chemical mechanical polishing (CMP) method has been known as a method for flattening the substrate surface. On a large glass substrate, however, it is difficult to flatten the entire surface with a high degree of accuracy using a CMP method. Therefore, an attempt has been made to perform polycrystallization of amorphous silicon or the like formed on the glass substrate by means of laser annealing and to flatten protrusions or the like at the crystal grain boundary.

Furthermore, in order to stabilize the characteristics of the TFTs formed on the glass substrate, blocking light from a backlight by forming a back-gate layer or light-blocking film (Patent Document 1) has been known.

Meanwhile, as shown inFIG. 15, which is a sectional view, Patent Document 2 discloses that a light-blocking film102is formed in advance on a transparent support substrate101, an insulation layer103covering the light-blocking film102is formed and flattened, and the surface of an embedded oxide film105formed on a monocrystalline silicon substrate104is affixed to the surface of this insulation layer103.

Moreover, Patent Document 3 discloses the following. Namely, recessed and protruding portions are formed on the surface of a semiconductor substrate, and after an insulation layer is formed thereon, an opening for forming a back-gate electrode is formed in a specified region of the insulation layer over the protruding portion, and a back-gate insulation film and a conductive material layer are then formed on the entire surface including the interior of the opening, after which a back-gate electrode is formed inside the opening by polishing the conductive material layer. Subsequently, an interlayer film is formed on the entire surface, the semiconductor substrate and a support substrate are affixed together with the interlayer film being interposed, and the semiconductor substrate is polished from the back surface and flattened so as to expose the insulation layer at the bottom of the recessed portion formed in the surface of the semiconductor substrate. By doing so, an attempt was made to produce SOI-type semiconductor devices having a back-gate electrode at a low cost using a substrate affixing method.

RELATED ART DOCUMENTS

Patent Documents

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

However, with the aforementioned Patent Document 1, in cases where the light-blocking film is formed on the backlight side of the silicon layer, a step difference formed by this light-blocking film affects the silicon layer, which makes it difficult to perform laser annealing of this silicon layer with a high degree of accuracy. As a result of the flatness of the silicon surface being impaired by this step difference and protrusions or the like at the crystal grain boundary, it is difficult to make the gate insulation film thinner. Therefore, the threshold voltage cannot be controlled with a high degree of accuracy, and the power-supply voltage becomes high. As a result, it becomes difficult to reduce the power consumption of the semiconductor device.

Furthermore, if polycrystallization of the silicon layer is performed by laser annealing, leakage current caused by crystal defects occurring in this silicon layer becomes too great to ignore. This leakage current also becomes a factor for inhibiting the reduction in the power consumption of the semiconductor device.

Moreover, in the aforementioned Patent Document 2, it is necessary to polish the insulation film that covers the light-blocking film by means of a CMP method on the other-side support substrate to which the semiconductor substrate is affixed. But it is extremely difficult to flatten the insulation film with good accuracy using a CMP method over the entire surface of the support substrate that has been increased in size in recent years. In addition, it is difficult to reduce the film thickness with good accuracy by directly polishing the thick semiconductor substrate affixed to the support substrate by means of a CMP method. Furthermore, in cases where the semiconductor layer of a TFT is formed in the form of an island, alignment at the time of affixing this semiconductor layer and a light-blocking film together becomes very difficult.

In addition, in the aforementioned Patent Document 3, an opening for a back-gate electrode is formed, and a back-gate insulation film and a conductive material layer are then formed on the entire surface including the interior of the opening, after which a back-gate electrode is formed inside the opening by polishing the conductive material layer. However, in cases where one side of the back-gate electrode is sufficiently longer than the thickness of the back-gate electrode layer, a similar recessed portion appears in the surface of the back-gate electrode layer, and if a planarization treatment is performed by means of CMP or the like, the back-gate electrode layer also ends up being ground down. As a result, it is very difficult to control the thickness of the back-gate electrode layer.

The present invention was devised in light of such points, and an object thereof is to improve the characteristics of an element having a semiconductor layer as much as possible while forming a light-blocking film that is disposed to face the semiconductor layer.

Means for Solving the Problems

In order to achieve the object described above, a method for producing a semiconductor device according to the present invention includes: a step of forming a first insulation film having a flat surface on the surface of a base layer; a step of forming a separation layer in the interior of the base layer by ion implantation of a separation substance into this base layer; a step of forming a light-blocking film on the surface of the first insulation film; a step of forming a second insulation film having a flat surface on the base layer such that the light-blocking film is covered; a step of affixing the base layer provided with the light-blocking film to a substrate, using the flat surface of the second insulation film; a step of separating and removing along the separation layer a portion of the base layer affixed to the substrate via the second insulation film; and a step of forming a semiconductor layer that constitutes a semiconductor element from the base layer remaining on the substrate such that at least a portion of this semiconductor layer overlaps with the light-blocking film.

It is also possible to include a step which is performed prior to the step of forming the first insulation film and which is for forming a protruding region that will become the semiconductor layer by etching the surface of the base layer on the side on which the first insulation film is to be formed, wherein in the light-blocking film formation step, the light-blocking film is formed so as to overlap with at least a portion of the protruding region.

It is also possible to include a step of forming a gate insulation film on the first insulation film so as to cover the semiconductor layer, and a step of forming a gate electrode on the surface of the gate insulation film so as to overlap with a portion of the semiconductor layer.

The light-blocking film may constitute a back-gate electrode.

The separation substance may be hydrogen or an inert element.

The base layer may be a monocrystalline silicon layer.

The substrate may be a glass substrate.

Furthermore, the semiconductor device according to the present invention includes: a second insulation film formed on a substrate and having a first recessed portion; a light-blocking film formed inside a first recessed portion of the second insulation film and having a surface that constitutes the same plane as the surface of the second insulation film; a first insulation film covering the surfaces of the light-blocking film and the second insulation film; and a semiconductor layer formed on the surface of the first insulation film, at least a portion of which overlaps with the light-blocking film.

The first insulation film may have a second recessed portion in an area overlapping with the light-blocking film, and the semiconductor layer may be formed inside the second recessed portion of the first insulation film and have a surface that constitutes the same plane as the surface of this first insulation film.

The semiconductor device may include: a gate insulation film that covers the surfaces of the semiconductor layer and the first insulation film; and a gate electrode formed on the surface of the gate insulation film so as to overlap with a portion of the semiconductor layer.

The light-blocking film may constitute a back-gate electrode.

The base layer may be a monocrystalline silicon layer.

The substrate may be a glass substrate.

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

When the aforementioned semiconductor device is to be produced, a first insulation film having a flat surface is first formed on the surface of a base layer such as a monocrystalline silicon layer, for example. Next, a separation layer is formed in the interior of the base layer by ion implantation of a separation substance, e.g., hydrogen or an inert element, into the base layer. Next, a light-blocking film is formed on the surface of the first insulation film. The light-blocking film may constitute a back-gate electrode.

Next, a second insulation film having a flat surface is formed on the aforementioned base layer so as to cover the light-blocking film. Next, the base layer having the light-blocking film formed thereon is affixed to a substrate, for instance, a glass substrate or the like, using the flat surface of the aforementioned second insulation film. Next, a portion of the base layer affixed to the substrate via the second insulation film is separated and removed along the aforementioned separation layer. Next, a semiconductor layer that constitutes a semiconductor element is formed from the base layer remaining on the substrate such that at least a portion of this semiconductor layer overlaps with the aforementioned light-blocking film.

Furthermore, prior to the step of forming the first insulation film, it is also possible to form a protruding region which will become the aforementioned semiconductor layer by etching the surface of the base layer on the side on which the first insulation film is to be formed. In this case, in the light-blocking film formation step, the light-blocking film is formed so as to overlap with at least a portion of the protruding region.

Moreover, following the formation of the semiconductor layer, a gate insulation film may be formed on the first insulation film so as to cover this semiconductor layer. In this case, a gate electrode is formed on the surface of the gate insulation film so as to overlap with a portion of the semiconductor layer.

Thus, with the aforementioned production method, by using monocrystalline silicon instead of polysilicon as the material for the base layer, it is possible to solve the problems of reducing the thickness of the gate insulation film caused by difficulty in laser annealing and impairment of flatness of the silicon surface due to the step difference from the lower-layer light-blocking film, protrusions at the crystal grain boundary, and the like, and the threshold voltage in the semiconductor layer can be controlled with a high degree of accuracy, which makes it possible to reduce the power consumption of the semiconductor device.

In addition, because the separation substance can be ion implanted into the base layer prior to the formation of the light-blocking film, it is possible to make the ion implantation depth uniform in the base layer and to form the separation layer at a position of a constant depth.

Furthermore, because the light-blocking film is formed in advance on the base layer before affixing this base layer to the substrate, the difficulty in the alignment between the light-blocking film and the semiconductor layer is reduced, thus allowing a desired range of the semiconductor layer to be covered more easily by the light-blocking film. Moreover, the light-blocking layer and back-gate layer are formed on the side of the base layer before affixing to the substrate and are flattened in advance by CMP, so CMP is not used on the substrate after affixing to this substrate, thus facilitating the affixing in the subsequent step.

In addition, because the semiconductor layer can be composed of monocrystalline silicon, it becomes possible to prevent the occurrence of leakage current caused by crystal defects. Therefore, the light-blocking film disposed to face the semiconductor layer can be formed with good accuracy, and the characteristics of an element having this semiconductor layer can be improved significantly.

Effects of the Invention

With the present invention, it is possible to form a light-blocking film disposed to face the semiconductor layer with good accuracy and to significantly improve the characteristics of an element having this semiconductor layer.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described in detail below with reference to the figures. Note that the present invention is not limited to the following embodiments.

<<Embodiment 1 of the Invention>>

FIGS. 1 to 8show Embodiment 1 of the present invention.

FIG. 1is a plan view showing main parts of a semiconductor device in the present Embodiment 1.FIG. 2is a sectional view along the line II-II inFIG. 1.FIG. 8is a plan view showing main parts of a liquid crystal display device.

—Structure of Liquid Crystal Display Device—

As shown inFIG. 8, a liquid crystal display device1includes a TFT substrate11, an opposite substrate12disposed facing this TFT substrate11, and a liquid crystal layer (illustration omitted) provided between the TFT substrate11and the opposite substrate12.

The liquid crystal display device1has a display region17in an area where the TFT substrate11and the opposite substrate12overlap with each other. A plurality of pixels19are arranged in a matrix in the display region17.

The TFT substrate11is constructed from a glass substrate21used as a transparent substrate and has a circuit region18in an area where there is no overlapping with the opposite substrate12. In the circuit region18, a circuit such as a driver for the drive control of each of the aforementioned pixels is directly fabricated into the glass substrate21that constitutes the TFT substrate11. The driver of this circuit region18has a TFT5which will be described later.

Furthermore, although illustration is omitted, a TFT as a switching element and a pixel electrode connected thereto are respectively arranged for each pixel on the TFT substrate11. Gate wiring32and source wiring35are further connected to each of these TFTs. The end portions of such gate wiring32and source wiring35are led out to the circuit region18and are connected to the aforementioned driver or the like.

The opposite substrate12, though illustration is omitted, is constructed from a glass substrate used as a transparent substrate, and a color filter, common electrode, and the like are formed thereon on the side of the TFT substrate11. Meanwhile, a backlight (illustration omitted) that is the light source is provided on a side of the TFT substrate11, that is opposite from the opposite substrate12.

A semiconductor device10in the present embodiment is used as a multifunction circuit such as a driver formed directly in the glass substrate21that constitutes the aforementioned TFT substrate11. As shown inFIG. 1, the semiconductor device10includes the glass substrate21and a device part D that is formed on the glass substrate21at a high density and with a high degree of accuracy.

Note that a transparent substrate such as the glass substrate21is preferable for the substrate21when the semiconductor device10is applied to a liquid crystal display device that performs transmissive display, but when applied to a display device other than that, other substrates, such as a monocrystalline silicon semiconductor substrate, can be used as the substrate21.

The device part D has a second insulation film22affixed by self-bonding to the glass substrate21, a TFT5which is an element formed on the second insulation film22, and a light-blocking film24disposed between the TFT5and the glass substrate21. That is, the device part D is affixed by self-bonding to the glass substrate21via the second insulation film22. The TFT5is constructed, for example, of a PMOS transistor that is a semiconductor element.

Note that a single TFT5is shown inFIG. 2, but the device that is formed is not limited to this. An NMOS transistor can, of course, be similarly employed, as well as other elements such as a bipolar transistor or diode. Furthermore, there is no limit on the number thereof; it can be one to several millions.

Here, the structure of the semiconductor device10is described in detail with reference toFIGS. 1 and 2.

The second insulation film22formed on the surface of the glass substrate21has a first recessed portion23formed in the surface thereof on the side opposite from the glass substrate21. The aforementioned light-blocking film24is formed inside the first recessed portion23, and the surface of this light-blocking film24constitutes the same plane as the surface of the second insulation film22.

The light-blocking film24is formed from a high-melting-point metal, such as Mo, TiN, or W, for example, and is constructed so as to function as a back-gate electrode as well. Furthermore, it is designed such that the characteristics of the TFT5can be varied dynamically by adjusting the potential of the back-gate electrode. Note that it is also possible to provide a back-gate electrode instead of the light-blocking film24.

The surfaces of the light-blocking film24and second insulation film22are directly covered by a first insulation film25. Moreover, a second recessed portion26is formed in the surface of the first insulation film25on the side opposite from the aforementioned second insulation film22in an area overlapping with the light-blocking film24. A semiconductor layer27is formed inside the second recessed portion26, and the surface of the semiconductor layer27constitutes the same plane as the surface of the first insulation film25. As a result, the semiconductor layer27is formed in the form of an island in the surface of the first insulation film25. The semiconductor layer27is formed such that at least a portion thereof overlaps with the light-blocking film24. In addition, it is sufficient if at least the channel region in the semiconductor layer27overlaps with the light-blocking film24.

In the present embodiment, the semiconductor layer27is also referred to as a base layer. A base layer15is a layer of semiconductor, for example, monocrystalline silicon semiconductor or the like. Note that besides the monocrystalline silicon semiconductor layer, the base layer15can be constructed to contain at least one element selected from a group including group IV semiconductor, group II-VI compound semiconductor, group III-V compound semiconductor, group IV-IV compound semiconductor, mixed crystal semiconductor containing congeners of these, and oxide semiconductor.

As will be described later, a portion of the base layer15is separated and removed along a separation layer that is formed by ion implantation of a separation substance such as hydrogen. Then, the thickness of the base layer15is reduced as a result of a portion thereof being separated and removed by a heat treatment.

The surfaces of the semiconductor layer27and the first insulation film25are directly covered by a gate insulation film28. A gate electrode29is formed on the surface of the gate insulation film28so as to overlap with a portion of the semiconductor layer27.

An interlayer insulation film30is formed on the gate insulation film28so as to cover the gate electrode29. A contact hole31is formed so as to pass through the interlayer insulation film30at a position above the gate electrode29. Furthermore, gate wiring32is formed on the surface of the interlayer insulation film30and in the interior of the contact hole31.

Moreover, as shown inFIG. 1a contact hole34is formed so as to pass through the interlayer insulation film30and gate insulation film28above the source region (illustration omitted) of the semiconductor layer27, while a contact hole36is formed so as to pass through these films above the drain region (illustration omitted). Then, source wiring35is connected to the source region of the semiconductor layer27via the contact hole34, while the drain region of the semiconductor layer27is connected to drain wiring37via the contact hole36.

Next, a method for manufacturing the aforementioned semiconductor device10will be described with reference toFIGS. 3 to 7.

Here,FIG. 3is a sectional view showing a base layer15on which a protruding region16is formed.FIG. 4is a sectional view showing the base layer15on which a separation layer42is formed.FIG. 5is a sectional view showing the base layer15on which a light-blocking film24is formed.FIG. 6is a sectional view showing the base layer15which is affixed to the glass substrate21and from which a portion thereof is separated and removed.FIG. 7is a sectional view showing the semiconductor layer27formed on the first insulation film25.

First, as shown inFIG. 3, a protruding region16, which will become the semiconductor layer27, is formed by etching the surface of a silicon wafer15that is the base layer15on the side on which the first insulation film25is to be formed. Here, the base layer15is a monocrystalline silicon layer.

Next, as shown inFIG. 4, the first insulation film25having a flat surface is formed on the surface of the base layer15. Specifically, an insulation film is formed so as to cover the protruding region16, after which the surface of this insulation film is flattened by CMP or like method.

Next, as shown inFIG. 4, ion implantation of a separation substance41is performed into the base layer15on which the first insulation film25is formed, thus forming the separation layer42in the interior of this base layer15. Hydrogen is used as the separation substance41. Note that an inert element such as He and Ne can be used in place of hydrogen. Furthermore, it is also possible to use hydrogen and an inert element. In the present embodiment, because the surface of the first insulation film25is flattened, the separation layer42can be formed substantially at a constant depth in the interior of the base layer15.

Next, as shown inFIG. 5, the light-blocking film24is formed on the surface of the first insulation film25. Specifically, a high-melting-point metal layer of Mo, TiN, W, or the like, for example, is formed on the surface of the first insulation film25, and this metal layer is then etched by photolithography to form the light-blocking film24. In this step, the light-blocking film24is formed so as to overlap with at least a portion of the aforementioned protruding region16.

Next, as shown inFIG. 5, the second insulation film22having a flat surface is formed on the base layer15so as to cover the light-blocking film24. Specifically, an insulation film is formed so as to cover the light-blocking film24, and the surface of this insulation film is then flattened by CMP or like method.

Next, as shown inFIG. 6, the base layer15on which a portion of the device part D is formed as a result of the light-blocking film24being provided is affixed to the glass substrate21, using the flat surface of the second insulation film22. At this point, the surface of the second insulation film22is affixed to the surface of the glass substrate21by self-bonding due to van der Waals forces.

Next, as shown inFIG. 6, a portion of the base layer15that is affixed to the glass substrate21is separated and removed along the separation layer42. Specifically, by heating the base layer15that is affixed to the glass substrate21via the second insulation film22to approximately 400 to 600° C., a portion of the base layer15on the side opposite from the glass substrate21with the separation layer42being interposed is separated and removed along the separation layer42.

Next, as shown inFIGS. 6 and 7, the base layer15remaining on the glass substrate21is etched using the first insulation film25surrounding the protruding region16as the etching stopper, thus forming the semiconductor layer27constituting the TFT5as the semiconductor element. Here, this formation is performed such that at least a portion of the semiconductor layer27overlaps with the light-blocking film24. As a result, only the portion of the base layer15that was the protruding region16remains in the form of an island and becomes the semiconductor layer27.

Next, as shown inFIG. 2, the gate insulation film28is formed on the first insulation film25so as to cover the semiconductor layer27. The surface of the gate insulation film28is formed to be flat, conforming to the surfaces of the semiconductor layer27and first insulation film25.

Next, as shown inFIGS. 1 and 2, the gate electrode29is formed on the surface of the gate insulation film28so as to overlap with a portion of the semiconductor layer27.

Afterwards, contact holes31,34, and36are formed in the interlayer insulation film30or the like. Subsequently, a metal layer formed on the interlayer insulation film30is patterned by photolithography, thus respectively forming gate wiring32, source wiring35, and drain wiring37. Each of the steps above is performed to complete a semiconductor device10.

Thus, in this Embodiment 1, the separation substance41can first be ion implanted into the base layer15prior to the formation of the light-blocking film24as shown inFIGS. 4 and 5, so the depth of the ion implantation can be made uniform in the base layer15, thus allowing the separation layer42to be formed at a position of a constant depth.

Furthermore, it is designed such that the light-blocking film24is formed in advance on the base layer15before affixing this base layer15to the glass substrate21. Therefore, in addition to eliminating any need for highly precise alignment between the light-blocking film24and the semiconductor layer27during the affixing step, it is possible to cover a desired region of the semiconductor layer27more easily with the light-blocking film24. Moreover, there is no need to perform a CMP treatment in the glass substrate21.

In addition, by virtue of the affixing, the semiconductor layer27can also easily be formed to be flat. Furthermore, because the semiconductor layer27is not formed with a step difference, the gate insulation film28can be made thinner easily. As a result, the threshold voltage in the semiconductor layer27can be controlled with a high degree of accuracy, which makes it possible to reduce power consumption of the semiconductor device10.

Moreover, when forming the island-form semiconductor layer27, the first insulation film25can be utilized as the etching stopper, so the thickness of the semiconductor layer27can be controlled with a high degree of accuracy.

In addition, because the semiconductor layer27is constructed of monocrystalline silicon, it is possible to prevent the occurrence of leakage current caused by crystal defects. As a result, the light-blocking film24that is disposed facing the semiconductor layer27can be formed with high accuracy, and this also enables significant improvement of the characteristics of the TFT5having this semiconductor layer27.

<<Embodiment 2 of the Invention>>

FIGS. 9 to 14show Embodiment 2 of the present invention.

FIG. 9is a sectional view showing main parts of the semiconductor device of the present Embodiment 2. Note that in each of the following embodiments, the same reference characters are assigned to the parts that are the same as inFIGS. 1 to 8, and a detailed description thereof will be omitted.

In the aforementioned Embodiment 1, the semiconductor layer27is formed inside the second recessed portion26formed in the first insulation film25. In the present Embodiment 2, in contrast, the semiconductor layer27is formed on the surface of the flat first insulation film25.

As in the aforementioned Embodiment 1, the semiconductor device10is such that the light-blocking film24is formed inside the first recessed portion23formed in the second insulation film22, and the surface of this light-blocking film24constitutes the same plane as the surface of the surrounding second insulation film22.

In contrast to the aforementioned Embodiment 1, the surface of the first insulation film25provided on the surfaces of the light-blocking film24and second insulation film22is formed to be flat. Then, the semiconductor layer27is formed in the form of an island on the surface of this flat first insulation film25. The surface of the gate insulation film28that covers this semiconductor layer27is formed in a convex shape in an area where the semiconductor layer27is covered. Furthermore, the surface of the gate electrode29that covers this gate insulation film28is also formed in a convex shape, conforming to the gate insulation film28.

The interlayer insulation film30, contact holes31,34, and36, gate wiring32, source wiring35, and drain wiring37are formed in the same manner as in the aforementioned Embodiment 1.

Next, a method for manufacturing the aforementioned semiconductor device10will be described with reference toFIGS. 10 to 14.

FIG. 10is a sectional view showing the base layer on which the separation layer is formed.FIG. 11is a sectional view showing the base layer on which the light-blocking film is formed.FIG. 12is a sectional view showing the base layer which is affixed to the glass substrate and from which a portion thereof is separated and removed.FIG. 13is a sectional view showing the base layer whose film thickness is reduced above the first insulation film.FIG. 14is a sectional view showing the semiconductor layer formed on the first insulation film.

First, as shown inFIG. 10, the first insulation film25is formed on the surface of a silicon wafer that is the base layer15. Because the surface of the base layer15is flat, the surface of the first insulation film25is also formed to be flat.

Next, as shown inFIG. 10, the separation layer42is formed by ion implanting a separation substance41into the base layer15on which the first insulation film25is formed. Hydrogen or an inert element (He, Ne, or the like) is used as the separation substance41as in the aforementioned Embodiment 1. Because the surface of the first insulation film25is flat, the separation layer42can be formed substantially at a constant depth in the interior of the base layer15.

Next, as shown inFIG. 11, the light-blocking film24is formed on the surface of the first insulation film25. Specifically, a high-melting-point metal layer of Mo, TiN, W, or the like, for instance, is formed on the surface of the first insulation film25, and this metal layer is then etched by photolithography to form the light-blocking film24.

Next, as shown inFIG. 11, the second insulation film22having a flat surface is formed on the base layer15so as to cover the light-blocking film24. The second insulation film22is formed by flattening by means of CMP or like method the surface of an insulation film that is formed so as to cover the light-blocking film24.

Next, as shown inFIG. 12, the base layer15provided with the light-blocking film24is affixed to the glass substrate21, using the flat surface of the second insulation film22. At this point, the surface of the second insulation film22is affixed to the surface of the glass substrate21by self-bonding due to van der Waals forces.

Next, as shown inFIG. 12, a portion of the base layer15that is affixed to the glass substrate21is separated and removed along the separation layer42. Specifically, by heating the base layer15that is affixed to the glass substrate21to approximately 400 to 600° C., a portion of the base layer15on the side opposite from the glass substrate21with the separation layer42being interposed is separated and removed along the separation layer42.

Next, as shown inFIG. 13, the thickness of the base layer15is reduced to a desired thickness by etching, and the base layer15is then patterned by photolithography or the like in the form of an island, thus forming the semiconductor layer27.

Next, as shown inFIG. 9, the gate insulation film28is formed so as to cover the semiconductor layer27. The surface of the gate insulation film28is formed in a convex shape, conforming to the surface of the semiconductor layer27.

Next, as shown inFIG. 9, the gate electrode29is formed on the surface of the gate insulation film28so as to overlap with a portion of the semiconductor layer27. Afterwards, contact holes31,34, and36are formed in the interlayer insulation film30or the like in the same manner as in the aforementioned Embodiment 1, thus respectively forming the gate wiring32, source wiring35, and drain wiring37. Each of the steps above is performed to complete a semiconductor device10.

In this Embodiment 2, as in the aforementioned Embodiment 1, it is designed such that the light-blocking film24is formed in advance on the base layer15before affixing this base layer15to the glass substrate21. Therefore, in addition to eliminating any need for highly precise alignment between the light-blocking film24and the semiconductor layer27during the affixing step, it is possible to cover a desired region of the semiconductor layer27more easily with the light-blocking film24. Moreover, the separation layer42can be formed at a position of a constant depth of the base layer, and there is no need to perform a CMP treatment in the glass substrate21.

In addition, by virtue of the affixing, the semiconductor layer27can also be formed to be flat easily, so the threshold voltage in the semiconductor layer27can be controlled with a high degree of accuracy. Furthermore, because the semiconductor layer27is constructed of monocrystalline silicon, it is possible to prevent the occurrence of leakage current caused by crystal defects. As a result, the light-blocking film24that is disposed to face the semiconductor layer27can be formed with good accuracy, and the characteristics of the TFT5having the semiconductor layer27can be improved significantly.

INDUSTRIAL APPLICABILITY

As described above, the present invention is useful for a semiconductor device used, for example, in a liquid crystal display device or the like and for a method for producing the same.

DESCRIPTION OF REFERENCE CHARACTERS

22second insulation film

25first insulation film

28gate insulation film