JP2010165744A - Semiconductor device and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce changes in the thickness of a semiconductor layer which is made to be polycrystalline, while simplifying processes. <P>SOLUTION: A semiconductor device 1 includes: a lightproof film 14 which is formed in a flat surface of a substrate 11; a flat layer 15 which is formed in the substrate 11 by directly covering the lightproof film 14 and includes a planarized surface; and a semiconductor layer 16 which is formed on the flat layer 15 so as to overlap the lightproof film 14 and is made to be polycrystalline. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a semiconductor device used for, for example, a liquid crystal display device and a manufacturing method thereof.

  For example, in a liquid crystal display device, a TFT substrate (thin film transistor) and a plurality of pixel electrodes connected thereto are arranged in a matrix, a TFT substrate is arranged opposite to the TFT substrate, and a color filter, a common electrode, and the like are formed. And a liquid crystal layer provided between the counter substrate and the TFT substrate. On the opposite side of the counter substrate from the liquid crystal layer, a backlight as a light source is provided. It is also known that an optical sensor made of a PIN photodiode is formed on a TFT substrate so that the liquid crystal display device has functions such as a touch panel.

  A glass substrate is preferably used as the TFT substrate. When an optical sensor is formed on a glass substrate, it is necessary to provide a light-shielding film so that backlight light does not enter the optical sensor. For TFTs, it is effective to provide a light-shielding film that blocks light from the backlight in order to prevent leakage current and light degradation (see, for example, Patent Document 1).

  Patent Document 1 discloses manufacturing a TFT by forming a relatively wide recess in a glass substrate, forming a light shielding film on the bottom of the recess, and then forming a semiconductor layer with a smaller area than the light shielding film. ing.

  Further, in Patent Document 2, as shown in FIG. 14 which is an enlarged cross-sectional view, a relatively wide recess 102 is formed in a glass substrate 101 and then a light shielding film 103 is embedded in the recess 102. It is disclosed that the surface of 103 and the surface of the glass substrate 101 are flattened. The light shielding film 103 and the glass substrate 101 are covered with an insulating layer 104. A semiconductor layer 105 is formed on the surface of the insulating layer 104 with a smaller area than the light shielding film 103. The semiconductor layer 105 is covered with a gate insulating film 106, and a gate electrode 107 is formed on the surface of the gate insulating film 106. Thus, the TFT 110 is formed on the light shielding film 103.

  Further, Non-Patent Document 1 discloses a method of obtaining a high on-current by combining a lateral crystal and a double gate structure, and Non-Patent Document 2 combines a lateral crystal and a bottom gate structure, A method is disclosed in which a polysilicon TFT can be produced simply by adding a laser device to a conventional amorphous silicon production line.

JP 2002-108244 A JP 2006-190836 A

Japanese Journal of Applied Physics 43 (2004) pp.L790-L793 Society for Information Display (SID) 08 DIGEST pp.1066-1069

  However, as a result of extensive research, the inventor formed a semiconductor layer with a larger area than the light-shielding film and the lower electrode formed on the substrate, and when the semiconductor layer was annealed, the thickness of the semiconductor layer became non-uniform. It was found that there is a problem that the yield decreases.

  That is, as shown in FIG. 12 which is an enlarged cross-sectional view, the light shielding film or the lower electrode 103 is formed relatively small on the glass substrate 101. The light shielding film or lower electrode 103 is covered with an insulating layer 104. A non-single-crystal semiconductor layer 105 (amorphous silicon or the like) is formed on the surface of the insulating layer 104 with a larger area than the light-shielding film or the lower electrode 103. The semiconductor layer 105 is formed in a convex shape reflecting the thickness of the light shielding film or the lower electrode 103.

  When the semiconductor layer 105 is scanned with the CW laser beam 112 for lateral crystallization, as shown in FIG. 13, the thickness of the semiconductor layer 105 is greatly changed in the vicinity of the step of the insulating layer 104. There is a possibility that disconnection may occur in the portion, leading to a decrease in yield.

  Furthermore, even if the semiconductor layer 105 is patterned to a smaller area than the light-shielding film or the lower electrode 103 after annealing, the thickness of the film remains unevenly changed, so that the characteristics of the formed element deteriorate. Is inevitable.

  The present invention has been made in view of these points, and an object of the present invention is to reduce the variation in the thickness of the polycrystalline semiconductor layer as much as possible while simplifying the process. is there.

  In order to achieve the above object, a semiconductor device according to the present invention includes a substrate having a flat surface throughout, a light shielding film or a lower electrode formed on the flat surface of the substrate, and the light shielding film or A flat layer is formed on the substrate directly covering the lower electrode, and has a flattened surface, and on the flat layer so as to overlap at least a part of the light shielding film or at least a part of the lower electrode. And a polycrystallized semiconductor layer.

  A thin film transistor and a photodiode are formed over the substrate, and the thin film transistor and the photodiode may each include the semiconductor layer.

  The flat layer may be composed of an SOG film.

  The surface of the flat layer may be flattened by a CMP method.

  The semiconductor layer may be laterally crystallized.

  Further, in the method for manufacturing a semiconductor device according to the present invention, a step of forming a light-shielding film or a lower electrode on a flat surface of the substrate having a flat surface over the entire surface, and a flat surface of the substrate, Forming a flat layer directly covering the light-shielding film and having a planarized surface; overlying at least a part of the light-shielding film or at least a part of the lower electrode on the flat layer; A step of forming a semiconductor layer with an area larger than that of the light-shielding film or the lower electrode, and a step of polycrystallizing the semiconductor layer by laser annealing.

  In the step of forming the flat layer, the flat layer may be formed by applying an SOG film to the flat surface of the substrate.

  In the step of forming the flat layer, the flat layer may be formed by planarizing the surface of the insulating film formed on the flat surface of the substrate by a CMP method.

  A plurality of the polycrystalline semiconductor layers may be formed, and a thin film transistor and a photodiode each having the polycrystalline semiconductor layer may be formed.

  In the step of laser annealing the semiconductor layer, the semiconductor layer may be laterally crystallized.

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

  In manufacturing the semiconductor device, first, a light shielding film or a lower electrode is formed on a flat surface of a substrate having a flat surface throughout. Next, a flat layer is formed on the flat surface of the substrate, which directly covers the light shielding film or the lower electrode and has a flattened surface.

  This flat layer can be formed by applying a flattening film such as an SOG film on the flat surface of the substrate. Further, it can be formed by planarizing the surface of the insulating film formed on the flat surface of the substrate by a CMP method.

  Next, a semiconductor layer is formed on the flat layer so as to overlap the light shielding film or the lower electrode and to have a larger area than the light shielding film or the lower electrode. Thereafter, the semiconductor layer is crystallized by laser annealing. Thus, the semiconductor device is manufactured. In particular, when the semiconductor device has a thin film transistor and a photodiode disposed so as to overlap the light shielding film or the lower electrode, it can be preferably manufactured.

  Therefore, according to the present invention, since the semiconductor layer is formed on the flat planarized layer, the variation in the thickness of the laser annealed semiconductor layer is reduced, and the thickness of the polycrystalline semiconductor layer is made uniform. Is possible. Further, since it is not necessary to form a predetermined recess in the substrate, the process can be facilitated.

  According to the present invention, a flat layer is formed on the flat surface of the substrate so as to cover the light shielding film or the lower electrode, and the semiconductor layer formed on the flat layer so as to overlap the light shielding film or the lower electrode is subjected to laser annealing. Since polycrystallization is performed, the thickness of the polycrystallized semiconductor layer can be made uniform while facilitating the process without the need to form a predetermined recess in the substrate.

FIG. 1 is a cross-sectional view showing a schematic structure of a TFT included in the semiconductor device of the first embodiment. FIG. 2 is a cross-sectional view showing a schematic structure of a photodiode included in the semiconductor device of the first embodiment. FIG. 3 is a cross-sectional view showing a light shielding film formed on a glass substrate. FIG. 4 is a cross-sectional view showing a flat layer formed on a glass substrate. FIG. 5 is a cross-sectional view showing the semiconductor layer formed on the surface of the flat layer. FIG. 6 is a cross-sectional view showing a semiconductor layer to be laser annealed. FIG. 7 is a cross-sectional view showing a semiconductor layer formed in a predetermined pattern. FIG. 8 is a cross-sectional view showing an insulating film formed on a glass substrate. FIG. 9 is a cross-sectional view showing a flat layer formed on a glass substrate. FIG. 10 is a cross-sectional view showing a schematic structure of a TFT included in the semiconductor device of the third embodiment. FIG. 11 is a cross-sectional view showing a schematic structure of a TFT included in the semiconductor device of the third embodiment. FIG. 12 is a cross-sectional view showing a semiconductor layer formed on a conventional insulating layer. FIG. 13 is a cross-sectional view showing a conventional semiconductor layer to be laser annealed. FIG. 14 is a cross-sectional view showing the structure of a conventional TFT.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiment.

Embodiment 1 of the Invention
1 to 7 show Embodiment 1 of the present invention.

  FIG. 1 is a cross-sectional view showing a schematic structure of a thin film transistor (hereinafter abbreviated as TFT) 12 included in the semiconductor device 1 of the first embodiment. FIG. 2 is a cross-sectional view showing a schematic structure of the photodiode 13 included in the semiconductor device 1 of the first embodiment.

  FIG. 3 is a cross-sectional view showing the light shielding film 14 formed on the glass substrate 11. FIG. 4 is a cross-sectional view showing the flat layer 15 formed on the glass substrate 11. FIG. 5 is a cross-sectional view showing the semiconductor layer 16 formed on the surface of the flat layer 15. FIG. 6 is a cross-sectional view showing the semiconductor layer 16 to be laser annealed. FIG. 7 is a cross-sectional view showing the semiconductor layer 16 formed in a predetermined pattern.

-Structure of semiconductor device-
The semiconductor device 1 is configured as a device including a TFT 12 and a photodiode 13 formed on a glass substrate 11 as an insulating substrate. Although not shown, the semiconductor device 1 configures a display panel of a liquid crystal display device, for example.

  Although not shown in the figure, the liquid crystal display device includes a TFT substrate on which a pixel electrode and a TFT as a switching element connected thereto are formed for each of a plurality of pixels, a counter substrate disposed to face the TFT substrate, A liquid crystal layer is provided between the TFT substrate and the counter substrate.

  The TFT substrate is configured as an active matrix substrate, and a driver for driving the plurality of pixels is directly formed in the non-display area. The TFT 12 in this embodiment constitutes, for example, this driver. The plurality of photodiodes 13 are also formed on the TFT substrate as optical sensors.

(Configuration of TFT and photodiode)
The semiconductor device 1 has a glass substrate 11 as a transparent substrate, and a TFT 12 and a photodiode 13 formed on the glass substrate 11. Moreover, the glass substrate 11 comprises the said TFT substrate, and has the flat surface over the whole. As for the glass substrate 11 of this embodiment, the both surfaces are formed flat over the whole.

  A light shielding film 14 is formed in an island shape on the flat surface of the glass substrate 11. The light shielding film 14 is made of a metal film such as Mo. Further, the light shielding film 14 can function as a lower electrode of the TFT 12 by forming a contact hole later and conducting.

  Further, the glass substrate 11 is formed with a flat layer 15 that directly covers the light shielding film 14 and has a flattened surface. The flat layer 15 is made of a flattening film such as an SOG (Spin on glass) film.

  As shown in FIGS. 1 and 2, the semiconductor layer 16 constituting each of the TFT 12 and the photodiode 13 is formed on the surface of the flat layer 15 so as to overlap the light shielding film 14. For example, the area of the semiconductor layer 16 may be smaller than the area of the light shielding film 14 so that light can be reliably shielded. The entire semiconductor layer 16 is formed flat along the surface of the flat layer 15. The semiconductor layer 16 has a channel region 17, a source region 18 and a drain region 19. The semiconductor layer 16 is made of polycrystallized silicon and is particularly laterally crystallized.

  A gate insulating film 20 that directly covers the semiconductor layer 16 is formed on the surface of the flat layer 15. Here, as shown in FIG. 1, the TFT 12 has a gate electrode 21 formed on the surface of the gate insulating film 20 and facing the channel region 17 of the semiconductor layer 16. An interlayer insulating film 22 that directly covers the gate electrode 21 is formed on the surface of the gate insulating film 20. On the other hand, the photodiode 13 does not have a gate electrode, and an interlayer insulating film 22 is laminated directly on the surface of the gate insulating film 20.

  Note that another film such as a silicon oxide film or a silicon nitride film may be formed on the surface of the flat layer 15, and the film may be interposed between the flat layer 15 and the semiconductor layer 16.

  Contact holes 23 are formed through the interlayer insulating film 22 and the gate insulating film 20 at positions above the source region 18 and the drain region 19. A source electrode 24 electrically connected to the source region 18 through the contact hole 23 and a drain electrode electrically connected to the drain region 19 through the contact hole 23 are formed on the surface of the interlayer insulating film 22. 25 are formed.

-Manufacturing method-
Next, a method for manufacturing the semiconductor device 1 will be described. In the method for manufacturing the semiconductor device 1 in the present embodiment, the TFT 12 and the photodiode 13 having the polycrystalline semiconductor layer 16 are formed.

  First, as shown in FIG. 3, a light shielding film 14 is formed on a flat surface of a glass substrate 11 having a flat surface throughout. For example, a metal film such as a Mo film is formed on the surface of the glass substrate 11 by a sputtering method or the like to a thickness of about 30 to 500 nm, for example, 100 nm, and the metal film is patterned into an island shape by photolithography.

  In this embodiment, glass is used as the material of the substrate 11, but the present invention is not limited to this. In addition to the glass, an insulating film having high translucency such as quartz or plastic is used. Is possible.

  Also, as the light shielding film 14, in the present embodiment, the first conductive film is TaN and the second conductive film is W. However, the present invention is not particularly limited. For example, Ta, W, Ti, Mo, The light shielding film 14 may be formed of an element selected from Al, Cu, Cr, Pd, Nd, or the like, or an alloy material or compound material containing the element as a main component. Further, these metal films may be used as the lower electrode instead of the light shielding film. When used as a light-shielding film, the film thickness is such that the light from the backlight can be sufficiently shielded. When it is used only as the lower electrode, it can be thinned to such an extent that it is not disconnected.

  Next, as shown in FIG. 4, a flat layer 15 is formed on the flat surface of the glass substrate 11 so as to directly cover the light shielding film 14 and to have a flattened surface. That is, by applying an SOG film, which is a flattening film, to the flat surface of the glass substrate 11 by spin coating, the flat layer 15 is formed to a thickness that can be flattened to about 100 nm to 1 μm, and is heated to a curing temperature.

  A base protective film made of an insulating material such as a silicon oxide film, a silicon nitride film, or a silicon nitride oxide film can be further stacked on the SOG film. It is a film for preventing damage to the substrate due to heat generation during diffusion or laser irradiation, and may be omitted if there is no such risk. The thickness of the base protective film is about 50 nm to 2 μm as a whole, including the case where it is formed of a multilayer film having a plurality of layers.

  Subsequently, as shown in FIG. 5, the semiconductor layer 16 is formed on the flat surface of the flat layer 15 so as to overlap the light shielding film 14 and to have an area larger than the light shielding film 14. The semiconductor layer 16 is made of, for example, a non-single crystal semiconductor such as amorphous silicon, and is formed flat over substantially the whole.

  The semiconductor layer 16 is formed by, for example, an LPCVD method, a plasma CVD method, a sputtering method, or the like, and is formed of a non-single-crystal semiconductor thin film having a thickness of about 30 nm to 250 nm, for example, 50 nm. Examples of the non-single crystal semiconductor thin film 16 include amorphous silicon, polycrystalline silicon, amorphous germanium, polycrystalline germanium, amorphous silicon / germanium, polycrystalline silicon / germanium, amorphous silicon / carbide, and polycrystalline silicon. Examples thereof include crystalline silicon carbide. When the non-single crystal semiconductor thin film 16 is formed by a plasma CVD method or the like, a dehydrogenation treatment at about 400 ° C. to 600 ° C. may be performed thereafter.

  Further, an insulating film such as a silicon oxide film, a silicon nitride film, or a silicon nitride oxide film having a thickness of about 2 nm to 100 nm, or a laminated film thereof may be formed on the non-single crystal semiconductor thin film 16.

  Next, as shown in FIG. 6, the semiconductor layer 16 is scanned while being irradiated with laser light 27, and the semiconductor layer 16 is laser annealed to be polycrystallized. At this time, it is preferable to laterally crystallize the semiconductor layer 16 using CW laser light as the laser light.

  Here, a laser beam (laser light) for crystallizing a non-single-crystal semiconductor thin film will be described.

  When the polycrystalline semiconductor film 16 is crystallized, various laser beams can be used. In this embodiment, as an example, a continuous wave laser beam emitted from a laser oscillator is used.

  Lasers can be classified into solid state lasers, semiconductor lasers, and gas lasers.

Examples of the solid-state laser include a YAG laser, a YVO ₄ laser, a YLF laser, a YAlO ₃ laser, a glass laser, a ruby laser, an alexandrite laser, and a titanium sapphire laser.

Examples of the gas laser include an excimer laser, an Ar laser, and a Kr laser. In addition, as the active species having a laser action, for example, trivalent ions (Cr ³⁺ , Nd ³⁺ , Yb ³⁺ , Tm ³⁺ , Ho ³⁺ , Er ³⁺ , and Ti ³⁺ ) can be used.

  In addition, a semiconductor laser, a disk laser, or a fiber laser can be used.

  The laser beam used for the laser annealing is preferably converted into a harmonic by a nonlinear optical element when the wavelength of the fundamental wave is longer than 700 nm. For example, it is known that a YAG laser emits a laser beam having a wavelength of 1064 nm as a fundamental wave. The absorption coefficient of the laser beam with respect to the silicon film is very low, and it is difficult to crystallize an amorphous silicon film which is one of the semiconductor films.

  However, this laser beam can be converted to a shorter wavelength by using a nonlinear optical element such as LBO, CLBO, BBO, or CBO. Examples of the harmonic include second harmonic (532 nm), third harmonic (355 nm), fourth harmonic (266 nm), and fifth harmonic (213 nm). Since these harmonics have a higher absorption coefficient than the amorphous silicon film, they can be used for crystallization of the amorphous silicon film.

  The laser oscillation method may be a continuous oscillation type or a pulse oscillation type. In the case of the pulse oscillation type, the crystal is continuously grown in the scanning direction of the laser beam (or stage). It is preferable to use a so-called pseudo continuous wave laser beam which is a high-frequency pulse having a frequency of several tens of MHz or more. Laser beam irradiation conditions (for example, frequency, power density, energy density, beam profile, and the like) are appropriately adjusted in consideration of material properties and thickness, laser beam scanning speed, and the like.

  The polycrystalline semiconductor layer 16 may be a semiconductor layer made of granular crystals having no anisotropy other than the lateral crystals having anisotropy.

Hereinafter, as an example of the present embodiment, the second harmonic (wavelength of 532 nm) of a continuous wave (CW) Nd: YVO ₄ laser used as a laser beam will be described in more detail.

  The laser beam for crystallization is shaped by a beam shaping optical system and a condensing lens according to the laser power and the required size. The beam shaping optical system shapes a beam by a combination of a beam expander, a homogenizer, a diffractive optical element, a Powell lens, an fθ lens, and the like.

  The condensing lens condenses the crystallization beam that has passed through the beam shaping optical system on the surface of the substrate to be processed. Examples of the condensing lens include a cylindrical lens, but it is possible to shape the beam by combining two cylindrical lenses and to omit the beam shaping optical system. The beam shaping optical system and the condensing lens constitute a modified optical system that is an optical system for crystallization. By combining these, the shape of the crystallization beam is shaped into a desired shape such as a linear shape, an elliptical shape, or a rectangular shape, and crystallization is performed.

  The beam width is shaped into a linear shape of several tens of μm to several tens of mm × several μm to 100 μm, for example, 500 μm × 20 μm, and the minor axis direction of the beam is the scanning direction.

The line scanning speed can be about 10 cm to 20 m per second, but here it is fixed at 50 cm / s. The laser power is 10 W, and the substrate size is 730 × 920 mm ² . As a scanning method, the substrate position may be fixed and the laser beam may be scanned, or the stage on which the substrate is placed may be moved for scanning.

  Note that in the case where the substrate to be processed is transparent, the non-single-crystal semiconductor thin film may be irradiated with a laser beam from the back side of the substrate. Further, the laser beam may be scanned only in one direction or may be scanned back and forth. However, as an example of this embodiment, the semiconductor laser is scanned while overlapping the crystallization laser beam little by little. Crystal modification is performed on the entire surface of the layer 16 and, for example, assuming that the width of a band-like lateral crystal formed by one scan is 500 μm, crystallization is performed by reciprocating scan at a pitch of 450 μm. As a result, an overlapping portion of laser beams having a width of 50 μm is generated.

  By irradiation with this continuous wave (CW) laser beam, the non-single-crystal semiconductor thin film is polycrystallized to obtain a polycrystalline semiconductor thin film. The crystal in the polycrystalline semiconductor thin film is 10 to 100 times larger than the granular crystal obtained by pulsed irradiation with a conventional excimer laser, becomes a strip-like crystal elongated in the laser scanning direction, It is also possible to make the length of crystal grains 5 μm or more.

  As described above, in crystallization of a non-single-crystal semiconductor film, the crystal grain size formed in the semiconductor film is larger when a continuous wave laser or a pseudo continuous wave laser is used than when a pulsed laser is used. When the crystal grain size in the semiconductor layer 16 is increased, the electron mobility of the TFT 12 formed using the semiconductor layer 16 is increased, which is suitable for manufacturing a TFT requiring high-speed driving characteristics.

  Next, the polycrystalline semiconductor layer 16 is patterned by photolithography to form a semiconductor layer 16 having a predetermined shape as shown in FIG.

  Thereafter, a silicon oxide film, a silicon nitride film, or a silicon oxynitride film is used as the gate insulating film 20 so as to directly cover the semiconductor layer 16 on the surface of the flat layer 15. Thus, it is formed to a thickness of about 200 nm or less, for example 80 nm, and the polycrystalline semiconductor film 16 is covered with this gate insulating film 20. If necessary, a small amount of impurity element (boron or phosphorus) is subsequently doped to control the characteristics of the TFT 12 and the photodiode 13.

  In the case of forming the TFT 12, subsequently, as the gate electrode 21, a TaN film as a first conductive film having a thickness of about 10 to 100 nm and, for example, 30 nm, and a first electrode having a thickness of about 50 to 500 nm, for example, 370 nm. A W film as the second conductive film is stacked on each other. The TaN film is formed by sputtering. That is, sputtering is performed in an atmosphere containing nitrogen using a Ta target. Further, the W film is formed by sputtering using a target.

  As an example of the present embodiment, the first conductive film is TaN and the second conductive film is W. However, there is no particular limitation, and Ta, W, Ti, Mo, Al, Cu are not limited thereto. Each conductive film may be formed of an element selected from Cr, Pd, Nd, or the like, or an alloy material or a compound material containing the element as a main component. Alternatively, a semiconductor film typified by polycrystalline silicon or the like may be doped with an impurity such as phosphorus or boron.

  Next, after forming a desired gate electrode shape by photolithography, an interlayer insulating film 22 is formed on the surface of the gate insulating film 20 so as to directly cover the gate electrode 21.

  At this time, in the TFT region, it is preferable that the major axis direction of the crystal of the polycrystalline semiconductor film 16 is the direction in which the current flows. However, this is not the case when a large current is not necessarily required in the pixel region or the like. On the other hand, when forming the photodiode 13, the interlayer insulating film 22 is directly laminated on the surface of the gate insulating film 20 without forming the gate electrode 21.

Next, in the case of forming the NMOS TFT 12, it is patterned into a predetermined pattern using a photoresist, and an n-type impurity P is ion-doped under the conditions of 45 keV and a dose of 5 × 10 ¹⁵ cm ⁻² , for example. Then, an n-type impurity element is added in a concentration range of 1 × 10 ¹⁸ to 1 × 10 ²⁰ . As a result, a high concentration source region and a high concentration drain region are formed in the polycrystalline semiconductor film 16. When the PIN photodiode 13 is formed, the n-type region is similarly ion-doped.

  Note that the acceleration voltage and the dose can be appropriately adjusted according to the thickness of the insulating film and the required characteristics.

Next, in the case of forming the PMOS TFT 12, patterning is performed using a photoresist into a predetermined pattern, and B, which is a p-type impurity, is ionized under the conditions of, for example, 60 keV and a dose of 5 × 10 ¹⁵ cm ^−2. Doping is performed, and a p-type impurity element is added in a concentration range of 1 × 10 ¹⁸ to 1 × 10 ²⁰ . As a result, a high concentration source region and a high concentration drain region are formed in the polycrystalline semiconductor film 16. When the PIN photodiode 13 is formed, the p-type region is similarly ion-doped.

  Next, the mask made of photoresist is removed, and activation of impurities and recovery of crystallinity of the semiconductor layer 16 are performed by heat treatment (450 ° C. to 680 ° C. for about 1 minute to 12 hours). A laser similar to that used in the above may be used.

  Next, an interlayer insulating film made of a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or the like, or a laminated film thereof is formed to a thickness of about 30 nm to 1500 nm by a sputtering method, a plasma CVD method, or the like. Here, a stacked film of a silicon oxide film having a thickness of 50 nm, a silicon nitride film having a thickness of 250 nm, and a silicon oxide film having a thickness of 700 nm is used.

  Furthermore, hydrogenation is performed by performing heat treatment at 300 ° C. to 550 ° C. for about 30 minutes to 12 hours. This is a process for terminating defects such as dangling bonds in the semiconductor layer 16 with hydrogen contained in the insulating film. Hydrogenation can also be performed by performing heat treatment at 300 ° C. to 450 ° C. in an atmosphere containing hydrogen plasma or 3 to 100% of hydrogen.

  Next, a contact hole 23 that penetrates the interlayer insulating film 22 and the gate insulating film 20 is formed by photolithography. Subsequently, the source electrode 24 and the drain electrode 25 are formed by patterning the metal film deposited on the surface of the interlayer insulating film 22 and the inside of the contact hole 23 by photolithography. Thus, the TFT 12 and the photodiode 13 are formed, and the semiconductor device 1 constituting the TFT substrate of the liquid crystal display device is manufactured.

  As the metal film, for example, a laminated film of Ti having a thickness of 100 nm, Al having a thickness of 350 nm, and Ti having a thickness of 100 nm is formed, and the metal film is formed for a desired source and drain electrode by photolithography. Form into a pattern. As an example of this embodiment, the metal film is a laminated film of Ti / Al / Ti, but is not particularly limited, and is selected from Ta, W, Ti, Mo, Al, Cu, Cr, Pd, Nd, and the like. A laminated structure may be formed as necessary using the above-described elements, or an alloy material or compound material containing the element as a main component.

-Effect of Embodiment 1-
Therefore, according to the first embodiment, the SOG film (flattening film) as the flat layer 15 is formed on the flat surface of the glass substrate 11 so as to cover the light shielding film 14, and the light shielding film 14 is formed on the flat layer 15. Since the semiconductor layer 16 formed so as to overlap is crystallized by laser annealing, it is not necessary to form a predetermined recess in the glass substrate 11 as in the prior art, and the process is facilitated while the process is simplified. The thickness of the semiconductor layer 16 can be made uniform with high accuracy. As a result, the characteristics of the formed TFT 12 and photodiode 13 can be improved, and the yield can be improved. In particular, this effect is remarkable when lateral crystallization of the semiconductor layer 16 is performed using CW laser light.

  Further, the semiconductor layer 16 formed in advance in a large area can be patterned by dividing into individual semiconductor layers 16 after laser annealing while uniforming the thickness in a batch and with high accuracy, so that a semiconductor that has been laterally crystallized, etc. The layer 16 can be formed efficiently and with high accuracy.

  In this embodiment, the semiconductor layer 16 is formed so as to overlap the light shielding film 14, but the area of the semiconductor layer 16 is made smaller than the area of the light shielding film 14 in consideration of misalignment in photolithography. Thus, light can be reliably shielded.

<< Embodiment 2 of the Invention >>
8 and 9 show Embodiment 2 of the present invention.

  FIG. 8 is a cross-sectional view showing the insulating film 30 formed on the glass substrate 11. FIG. 9 is a cross-sectional view showing the flat layer 15 formed on the glass substrate 11. In the following embodiments, the same portions as those in FIGS. 1 to 7 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the first embodiment, the flat layer 15 is made of a flattening film such as an SOG film, whereas the flat layer 15 in the second embodiment is made of an insulating film whose surface is flattened by the CMP method. .

  That is, when manufacturing the semiconductor device 1 of Embodiment 2, the insulating film 30 is formed on the flat surface of the glass substrate 11 so as to directly cover the light shielding film 14 as shown in FIG. At this time, the surface of the insulating film 30 is formed in a convex shape reflecting the shape of the light shielding film 14.

  Next, as shown in FIG. 9, the surface of the insulating film 30 is polished by a CMP method to flatten the surface. As a result, a flat layer 15 having no step is formed. The semiconductor device 1 is manufactured by performing the subsequent steps in the same manner as in the first embodiment.

  Therefore, also in the second embodiment, since the semiconductor layer 16 is formed on the light shielding film 14 on the flat layer 15 flattened by the CMP method, the process can be easily performed as in the first embodiment. However, the thickness of the polycrystalline semiconductor layer 16 can be made uniform with high accuracy. As a result, the characteristics of the formed TFT 12 and photodiode 13 can be improved, and the yield can be improved.

  In this embodiment, the semiconductor layer 16 is formed so as to overlap the light shielding film 14, but the area of the semiconductor layer 16 is made smaller than the area of the light shielding film 14 in consideration of misalignment in photolithography. Thus, light can be reliably shielded.

<< Embodiment 3 of the Invention >>
10 and 11 show Embodiment 3 of the present invention.

  10 and 11 are sectional views showing a schematic structure of the TFT 12 included in the semiconductor device 1 of the third embodiment.

  In the first embodiment, the light shielding film 14 is formed on the surface of the glass substrate 11, whereas in the third embodiment, the lower electrode 34 is formed on the surface of the glass substrate 11. .

  That is, the lower electrode 34 is made of the same metal film as the light shielding film 14, but its area is smaller than that of the light shielding film 14 and is a region facing the channel region of the semiconductor layer 16 as shown in FIG. Is formed. The semiconductor layer 16 may be formed on the flat layer so as to overlap at least a part of the lower electrode 34. Thus, the TFT 1 shown in FIG. 10 is configured as a so-called double gate TFT.

  Further, the TFT 1 shown in FIG. 11 has the lower electrode 34, but does not have the gate electrode 21. Accordingly, the TFT 1 shown in FIG. 11 is configured as a so-called bottom gate TFT.

  Therefore, according to the third embodiment, since the semiconductor layer 16 is formed on the lower electrode 34 on the flat layer 15 flattened by the CMP method, the process is performed as in the first embodiment. Although easy, the thickness of the polycrystalline semiconductor layer 16 can be uniformized with high accuracy. As a result, the characteristics of the formed TFT 12 and photodiode 13 can be improved, and the yield can be improved.

  As described above, the present invention is useful for a semiconductor device used in, for example, a liquid crystal display device and a manufacturing method thereof.

1 Semiconductor device
11 Glass substrate
12 TFT
13 Photodiode
14 Shading film
15 Flat layer
16 Semiconductor layer
22 Interlayer insulation film
27 Laser light
30 Insulating film
34 Lower electrode

Claims (10)

A substrate having a flat surface throughout;
A light shielding film or a lower electrode formed on the flat surface of the substrate;
A flat layer directly covering the light shielding film or the lower electrode and formed on the substrate and having a flattened surface;
A semiconductor device comprising: a polycrystalline semiconductor layer formed on the flat layer so as to overlap at least part of the light shielding film or at least part of the lower electrode. The semiconductor device according to claim 1,
A thin film transistor and a photodiode are formed on the substrate,
The thin film transistor and the photodiode each include the semiconductor layer. The semiconductor device according to claim 1 or 2,
2. The semiconductor device according to claim 1, wherein the flat layer is composed of an SOG film. The semiconductor device according to claim 1 or 2,
A semiconductor device, wherein the flat layer has a surface flattened by a CMP method. The semiconductor device according to any one of claims 1 to 4, wherein
The semiconductor device is characterized in that the semiconductor layer is laterally crystallized. Forming a light shielding film or a lower electrode on the flat surface of the substrate having a flat surface throughout;
Forming a flat layer directly covering the light shielding film or the lower electrode and having a flattened surface on the flat surface of the substrate;
Forming a semiconductor layer on the flat layer overlying at least a part of the light shielding film or at least a part of the lower electrode and having a larger area than the light shielding film or the lower electrode;
A method of manufacturing a semiconductor device, comprising: a step of polycrystallizing the semiconductor layer by laser annealing. In the manufacturing method of the semiconductor device according to claim 6,
In the step of forming the flat layer, the flat layer is formed by applying an SOG film to the flat surface of the substrate. In the manufacturing method of the semiconductor device according to claim 6,
In the step of forming the flat layer, the flat layer is formed by flattening the surface of the insulating film formed on the flat surface of the substrate by a CMP method. In the manufacturing method of the semiconductor device according to any one of claims 6 to 8,
Forming a plurality of polycrystalline semiconductor layers,
A method of manufacturing a semiconductor device, comprising: forming a thin film transistor and a photodiode each having the polycrystalline semiconductor layer. In the manufacturing method of the semiconductor device as described in any one of Claim 6 thru | or 9,
A method of manufacturing a semiconductor device, wherein in the step of laser annealing the semiconductor layer, the semiconductor layer is laterally crystallized.

Images