JP4364481B2 - Method for manufacturing thin film transistor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a thin film transistor, and belongs to all technical fields in which the thin film transistor can be used. That is, a technical field related to a display typified by LCD (liquid crystal display), ELD (electroluminescence display) or FED (field emission display) or a technical field related to a sensor typified by a CMOS sensor or the like. It belongs to the technical field related to all semiconductor devices to be mounted.
[0002]
[Prior art]
A thin film transistor is a semiconductor element that performs a switching operation by controlling carriers (electrons or holes) moving in an active layer made of a semiconductor, and a silicon film is generally used as the semiconductor. In particular, in recent years, the development of forming an active layer of a thin film transistor by forming a polycrystalline silicon film (also referred to as a polysilicon film) on an inexpensive glass substrate has attracted attention. When producing a polycrystalline silicon film on a glass substrate, there is a limitation due to the heat resistance of the glass substrate, so how to obtain a polycrystalline silicon film with high crystallinity at low temperatures is the key to improving the characteristics of thin film transistors. .
[0003]
Under such circumstances, a crystallization technique using laser light irradiation has been developed as a technique for forming a polycrystalline silicon film on a glass substrate at a low temperature. Crystallization by laser light irradiation (hereinafter referred to as laser crystallization) is a technology that instantaneously melts and recrystallizes the amorphous silicon film by absorbing the energy of the laser light. Since the processing is completed within an extremely short time, it is possible to easily form a polycrystalline silicon film on a glass substrate without affecting the substrate.
[0004]
Recently, a technology to obtain a highly crystalline polycrystalline silicon film using continuous wave laser light has been announced (Ultra-high Performance Poly-Si TFTs on a Glass by a Stable Scanning CW Laser Lateral Crystallization; A. Hara, F. Takeuchi, M. Takei, K. Yoshino, K. Suga and N. Sasaki, AMLCD'01 Tech.Dig., 2001, pp. 227-230). In this technology, a continuous wave laser beam is scanned on an amorphous silicon film, a temperature difference is formed in the film by moving the solid-liquid interface of the semiconductor, and the silicon film is crystallized using the temperature difference. Technology. However, if the scanning speed is low, the film itself bumps and disappears, and if the scanning speed is high, the movement speed of the solid-liquid interface is exceeded, resulting in insufficient crystallization. Have.
[0005]
[Problems to be solved by the invention]
The present invention has been made in view of the above problems, and forms a temperature difference in a silicon film by a simpler method, forms a highly crystalline silicon film using the temperature difference, and forms a semiconductor film. It is an object of the present invention to provide a technique for manufacturing a thin film transistor with good switching characteristics, in which an active layer is used. It is another object of the present invention to provide a technique for manufacturing a semiconductor device with high operating performance in which thin film transistors according to the present invention are integrated.
[0006]
It is another object of the present invention to provide a laser crystallization technique using a gate electrode in order to form a temperature difference in a semiconductor film by the above simple method.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, a method for manufacturing a thin film transistor according to the present invention uses a difference in absorption rate of laser light between an amorphous silicon film and a crystalline silicon film, and selectively crystallizes the amorphous silicon film. In forming a crystalline silicon film, a metal film (preferably a gate electrode) provided on a part of the amorphous silicon film is used as a mask. Specifically, a mask made of a metal film is provided on the amorphous silicon film, and laser light is irradiated from above the mask, that is, from above the amorphous silicon film (first laser light irradiation). After crystallizing a part of the amorphous silicon film and then removing the mask or from below the amorphous silicon film, laser light is irradiated again (second laser light irradiation) to crystallize in the previous step. The remaining amorphous portion (a part of the amorphous silicon film) is laterally grown (also referred to as lateral growth) with the remaining portion as a nucleus.
[0008]
As described above, when utilizing the difference in the absorption rate of the laser light between the amorphous silicon film and the crystalline silicon film, the light source of the laser light used for the second irradiation is 400 to 600 nm (preferably 450 to 550 nm). ), Typically a solid-state laser (typically Nd: YAG laser or Nd: YVO) _Four It is preferable to use a second harmonic such as a laser or an argon laser. In particular, when the second harmonic of the solid laser is used, the amorphous part can be preferentially melted, and as a result, a temperature difference is easily formed between the amorphous part and the crystalline part. be able to. This is because, as shown in FIG. 5, the wavelength dependency of the absorption coefficient is different between the amorphous silicon film and the crystalline silicon film. That is, from FIG. 5, in the wavelength region of 400 to 600 nm, crystalline silicon (denoted as poly-Si) clearly has an absorption coefficient (denoted as α) compared to amorphous silicon (denoted as a-Si). Is small. Since this tendency is the same for the silicon germanium (SiGe) film, the present invention can provide the same effect even when the silicon germanium film is used as the semiconductor film.
[0009]
In the present invention, it is particularly desirable to use a metal having a low thermal conductivity, specifically a metal film having a thermal conductivity of 2.0 W / Kcm or less, preferably 1.0 W / Kcm or less, as the metal film. In this way, since heat radiation at the mask edge portion can be minimized, the crystallinity immediately below the edge portion is not impaired. For example, FIG. 6 shows measurement results obtained by examining three patterns in a case where an aluminum film is used as a mask, a case where a titanium film is used, and a case where no mask is used. In the simulation, the temporal change of the temperature distribution was investigated by transiently solving the heat conduction equation. The laser has a pulse width of 20 ns and an energy density of 100 MJ / cm. ² Calculated as injecting energy. The thermal conductivities of the aluminum film and titanium film were 2.38 W / Kcm and 0.22 W / Kcm, respectively.
[0010]
As a result, it was found that only the curve when using an aluminum film in the vicinity of the boundary between the laser irradiation region and the metal mask region slowly changes in the state 20 seconds after the laser irradiation. That is, since the aluminum film has a high thermal conductivity, the thermal diffusion at the mask edge portion advances and the temperature distribution becomes gentle. The gentle temperature distribution means that the crystal grains are small and the crystallinity is inferior. On the other hand, when a titanium film is used as the metal mask, the temperature distribution is almost the same as when the mask is not provided, and it has been found that the steepness of the temperature distribution can be ensured regardless of thermal diffusion.
[0011]
The metal film having a thermal conductivity of 2.0 W / Kcm or less is typically a metal composed of titanium (Ti), tantalum (Ta) or a nitride thereof (specifically, titanium nitride (TiN)). Alternatively, a metal film made of tantalum nitride (TaN)), chromium (Cr) or platinum (Pt), or a metal film made of tungsten (W), molybdenum (Mo), or tungsten-molybdenum alloy (W-Mo) is used. Can do. In particular, a tantalum nitride film having a thermal conductivity of about 0.10 W / Kcm, a titanium film of about 0.22 W / Kcm, or a titanium nitride film of about 0.28 W / Kcm is desirable.
[0012]
As described above, when the present invention is implemented, a crystalline silicon film with high crystallinity can be formed by a simple means. When the crystalline silicon film is used as at least a channel formation region of a thin film transistor, field effect mobility (mobility) is achieved. ) And S value (subthreshold coefficient) are improved. In addition, a semiconductor device including an integrated circuit using a thin film transistor with improved electrical characteristics such as mobility and S value as an element achieves improvement in operation performance such as improvement in operation speed and improvement in driving ability as a whole.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
This embodiment is an example in which a thin film transistor is manufactured using the present invention. A specific description will be given with reference to FIG.
[0014]
In FIG. 1A, reference numeral 101 denotes a base for manufacturing a thin film transistor, 102 denotes a base film, and 103 denotes an amorphous silicon film. As the substrate 101, any known substrate may be used, but the present invention is particularly useful when a glass substrate or a plastic substrate (including a plastic film) is used as the substrate 101. The base film 102 is used for the purpose of preventing diffusion of mobile ions from the substrate 101 and improving the adhesion of the amorphous silicon film 103, and a known silicon oxide film or silicon nitride film may be used. As the amorphous silicon film 103, an amorphous silicon film, an amorphous silicon germanium film, or another amorphous silicon film mainly containing silicon can be used.
[0015]
Next, in FIG. 1B, 104 is a stopper film and 105 is a mask. The stopper film 104 has a function as an etching stopper for preventing the lower semiconductor film from being etched when the mask 105 is removed later and an effect of improving the adhesion of the mask 105. Specifically, a silicon oxide film, a silicon oxynitride film (indicated by SiON), or an aluminum oxide film can be used. Of course, the stopper film 104 must be a film that transmits laser light to be irradiated later. The mask 105 may be formed using the metal film having low thermal conductivity described above. Note that the object can be achieved as the mask 105 as long as it has a shielding effect against laser light. Therefore, it goes without saying that even a metal film having high thermal conductivity can be applied to the present invention.
[0016]
Next, in FIG. 1C, 106a and 106b are first crystalline silicon regions crystallized by the first laser light irradiation, and 107 is an amorphous silicon region. Since the laser light is reflected or absorbed by the mask 105, the amorphous silicon region 107 remains immediately below, and only the regions irradiated with the laser light become the first crystalline silicon regions 106a and 106b. That is, the first crystalline silicon regions 106a and 106b and the amorphous silicon region 107 are in contact with each other so as to form a boundary immediately below the edge portion of the mask 105. As the laser light, light oscillated from any known laser may be used. Moreover, there is no restriction | limiting in particular in laser irradiation conditions, A practitioner should just determine suitably.
[0017]
Next, in FIG. 1D, reference numeral 108 denotes a second crystalline silicon region crystallized by the second laser light irradiation. In FIG. 1D, laser light irradiation is performed after the mask 105 is removed. By this laser light irradiation, the amorphous silicon region 107 is laterally grown with the crystalline silicon regions 106a and 106b serving as nuclei, and the second crystalline silicon region 108 having very high crystallinity is obtained. The laser used here is a solid laser (typically Nd: YAG laser or Nd: YVO). _Four The second harmonic of a laser or the like is desirable. In particular, a continuous wave solid-state laser is used as a light source, and an irradiation region on the semiconductor film moves at a scanning speed (20 to 60 cm / second) within a range where the semiconductor film is not lost and can be crystallized. It is recommended to select such conditions.
[0018]
After passing through the steps shown in FIGS. 1A to 1D, a thin film transistor may be manufactured according to a known manufacturing method. Of course, it is important to use the second crystalline silicon region described above at least for the channel formation region. As described above, by implementing the present invention, it is possible to form a crystalline silicon region having high crystallinity by a simple means. By using the crystalline silicon region as a channel formation region, the field effect mobility can be improved and A thin film transistor having an improved S value is obtained.
[0019]
[Embodiment 2]
This embodiment is an example in which the stopper film 104 and the mask 105 are used as they are as a gate insulating film and a gate electrode of a thin film transistor in Embodiment 1, and the second laser light irradiation direction is different. Features. The specific description is made with reference to FIG. 2, and the same reference numerals as those in FIG. 1 are used as necessary. In addition, since this embodiment is an invention related to the modification of the process sequence in Embodiment 1, the constituent material of the thin film, the laser irradiation conditions, and the like may be combined with Embodiment 1.
[0020]
First, as in Embodiment Mode 1, after the base 101, the base film 102, and the amorphous silicon film 103 are formed (FIG. 2A), a silicon oxide film with a thickness of 50 to 150 nm is formed as the gate insulating film 201. Form. As a material of the gate insulating film 201, a known material may be used, and conditions such as a film thickness may be appropriately set by a practitioner. Further, a gate electrode (functioning as a mask) 202 is formed over the gate insulating film 201. The material of the gate electrode 202 may be the same as that in Embodiment 1 (FIG. 2B).
[0021]
Next, similarly to Embodiment Mode 1, the first laser light irradiation is performed to define the first crystalline silicon regions 106a and 106b and the amorphous silicon region 107 (FIG. 2C). Then, the second crystalline silicon region 203 is formed by irradiating the back surface of the semiconductor film with the second laser light from the substrate 101 side while leaving the gate electrode 202 (FIG. 2D). At this time, the substrate 101 must be made of a material that transmits the laser light irradiated for the second time. Nd: YAG laser or Nd: YVO as the light source of the second laser beam _Four When a laser is used, a general glass substrate can be transmitted without any problem.
[0022]
Then, after the steps shown in FIGS. 2A to 2D, a thin film transistor may be manufactured according to a known manufacturing method as in Embodiment Mode 1. According to this embodiment mode, the field effect mobility and the S value of the thin film transistor can be improved, and the process of removing the mask can be reduced as compared with the first embodiment mode. Productivity can be improved.
[0023]
[Embodiment 3]
This embodiment is an example in which the stopper film and the mask are used as they are as the gate insulating film and the gate electrode of the thin film transistor as in the second embodiment, but the second embodiment is a top-gate thin film transistor (specifically, In this embodiment, the present invention is applied to a bottom gate thin film transistor (specifically, an inverted staggered thin film transistor). A specific description will be given with reference to FIG. Further, since this embodiment is an invention related to the process sequence and the transistor structure modification in Embodiment 1, the constituent material of the thin film, laser irradiation conditions, and the like may be combined with Embodiment 1.
[0024]
First, the gate electrode 302 is formed on the substrate 301. The material described in Embodiment 1 may be used for the gate electrode 302. A gate insulating film 303 and an amorphous silicon film 304 are formed on the gate electrode 302. As the gate insulating film 303, a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a stacked film thereof may be used. In particular, a silicon nitride film is used for the first layer in contact with the substrate 301 and the gate electrode 302. preferable. This is because the effect of preventing the mobile ions and the like from diffusing from the substrate 301 by the silicon nitride film can be expected. The amorphous silicon film 304 may be formed by a known technique, but it is preferable that the gate insulating film 303 be continuously formed in the same apparatus without releasing it to the atmosphere. Note that the base 301, the gate insulating film 303, and the amorphous silicon film 304 are not necessarily limited to the materials shown here (FIG. 3A).
[0025]
Next, the first laser light irradiation is performed from the substrate 301 side to the back surface of the amorphous silicon film 304. At that time, since the gate electrode 302 functions as a mask, the first crystalline silicon regions 305a and 305b and the amorphous silicon region 306 are defined (FIG. 3B).
[0026]
Next, second laser irradiation is performed from above the first crystalline silicon regions 305 a and 305 b and the amorphous silicon region 306 to form a second crystalline silicon region 307. At this time, Nd: YAG laser or Nd: YVO is used as the light source of the second laser beam. _Four It is preferable to use the second harmonic of the laser. Further, the second laser light irradiation may be performed after a protective film such as a silicon oxide film is provided over the first crystalline silicon regions 305a and 305b and the amorphous silicon region 306 (FIG. 3). (C)).
[0027]
Then, after the steps shown in FIGS. 3A to 3C, a thin film transistor may be manufactured according to a known manufacturing method as in Embodiment Mode 1. According to this embodiment mode, the field effect mobility and the S value of the thin film transistor can be improved, and the process of removing the mask can be reduced as compared with the first embodiment mode. Productivity can be improved. Furthermore, since the second laser light irradiation can be performed directly on the semiconductor film, there is an advantage that the energy density of the laser light can be easily controlled and the process margin is improved.
[0028]
[Embodiment 4]
According to the first to third embodiments, since the second crystalline silicon region is formed by lateral growth using the two first crystalline silicon regions as nuclei, the two crystalline silicon regions that have grown laterally from each other are formed. Produces a grain boundary (here, refers to a boundary where the laterally grown crystal grains collide) immediately below or just above the gate electrode. This single crystal grain boundary is formed perpendicularly to the direction of carrier movement, and does not adversely affect the electrical characteristics of the thin film transistor. Cannot be denied.
[0029]
Therefore, in this embodiment mode, an example in which the crystal grain boundary is not formed in the channel formation region by dividing the patterning of the gate electrode into twice in Embodiment Mode 2 is described. The specific description will be made with reference to FIG. 4, and the same reference numerals as those in FIGS. 1 and 2 are used as necessary. In addition, since this embodiment is an invention related to the modification of the structure of the gate electrode in the second embodiment, the constituent material of the thin film, the laser irradiation conditions, and the like may be considered in combination with the first and second embodiments. .
[0030]
First, after the state of FIG. 4A is formed in accordance with the procedure of Embodiment Mode 1, a gate insulating film 201 and a conductive film 401 which later forms a gate electrode are formed. For the material of the conductive film 401, Embodiment 1 may be referred to. The length of the conductive film 401 in the horizontal direction toward the paper surface is preferably at least twice as long as the channel formation region. If it is twice or more, it is not necessary to finally form a crystal grain boundary in the channel formation region.
[0031]
Next, first laser light irradiation is performed to define the first crystalline silicon region 402 and the amorphous silicon region 403 (FIG. 4C), and further, the first crystalline silicon region 402 and the non-crystalline silicon region 402 A second laser light irradiation is performed from the back side of the crystalline silicon region 403 to form a second crystalline silicon region 404 (FIG. 4D). At this time, since the distance for lateral growth is limited, this embodiment is effective in manufacturing a thin film transistor in which the length of the channel formation region (the length in the carrier movement direction) is 3 μm or less (preferably 2 μm or less). Technology.
[0032]
Next, the conductive film 401 is patterned again to form the gate electrode 405 (FIG. 4E). After the steps shown in FIGS. 4A to 4E, a thin film transistor may be manufactured according to a known manufacturing method as in Embodiment Mode 1. According to this embodiment, since it is not necessary to form a crystal grain boundary in the channel formation region, it is possible to expect further improvement in field effect mobility in addition to the effects of the first and second embodiments.
[0033]
【Example】
[Example 1]
In this example, steps from the formation of the second crystalline silicon region in accordance with the manufacturing process described in Embodiment 1 to the completion of the thin film transistor are described with reference to FIGS. Note that the manufacturing process shown in this embodiment is a known manufacturing process of a thin film transistor, and does not limit application of the present invention. Any known material can be used as the thin film material constituting the thin film transistor.
[0034]
First, after the state shown in FIG. 1D is obtained in accordance with the steps shown in Embodiment Mode 1 and FIG. 1, a silicon oxide film is formed to a thickness of 150 nm as the gate insulating film 701, and an alloy of tungsten and molybdenum is further formed. A gate electrode 702 to be formed is formed to a thickness of 250 nm (FIG. 7A).
[0035]
Next, a source region 703, a drain region 704, a channel formation region 705, and LDD (lightly doped drain) regions 706a and 706b are formed by ion implantation or ion doping using a photoresist (not shown) or the gate electrode 702 as a mask. Form. Needless to say, these impurity regions may be formed by adding phosphorus, arsenic, or boron and then performing heat treatment for activation. Further, a silicon nitride film is provided as the first protective film 707, and heat treatment is performed to hydrogenate the silicon region (FIG. 7B).
[0036]
Next, a silicon oxide film having a thickness of 90 nm is formed as an interlayer insulating film 708 on the first protective film 707, contact holes are formed in the interlayer insulating film 708, and then a titanium nitride film, an aluminum alloy film, and a titanium film are formed. A source electrode 709 and a drain electrode 710 each including a stack are formed. The film thickness may be 40 nm. A silicon nitride film having a thickness of 20 nm is provided as the second protective film 711 so as to cover the source electrode 709 and the drain electrode 710, whereby the thin film transistor shown in FIG. 7C is completed.
[0037]
Since the thin film transistor formed as described above has a crystalline silicon region with high crystallinity as a channel formation region, the field effect mobility is improved and the S value is improved.
[0038]
Note that in the case where the second crystalline silicon region is formed in accordance with Embodiment Mode 2, the gate electrode 202 can be used as it is, and therefore, the steps after FIG. . In the case where the second crystalline silicon region is formed according to Embodiment Mode 4, the steps after FIG.
[0039]
[Example 2]
In this example, a process until a thin film transistor is completed after the second crystalline silicon region is formed in accordance with the manufacturing process described in Embodiment Mode 3 is described with reference to FIGS. Note that the manufacturing process described in this embodiment is an example of a manufacturing process of a thin film transistor having a dual gate structure (a structure in which a channel formation region is sandwiched between two upper and lower gate electrodes), and does not limit the application of the present invention. . Any known material can be used as the thin film material constituting the thin film transistor.
[0040]
First, when the state of FIG. 3C is obtained in accordance with the steps shown in Embodiment Mode 3 and FIG. 3, a silicon oxide film is formed to a thickness of 150 nm as the gate insulating film 801, and an alloy of tungsten and molybdenum is further formed. A second gate electrode 802 is formed to a thickness of 250 nm (FIG. 8A).
[0041]
Next, a source region 803, a drain region 804, a channel formation region 805, and an LDD (lightly doped drain) region 806a by ion implantation or ion doping using a photoresist (not shown) or the second gate electrode 802 as a mask, 806b is formed. Needless to say, these impurity regions may be formed by adding phosphorus, arsenic, or boron and then performing heat treatment for activation. Further, a silicon nitride film is provided as the first protective film 807, and heat treatment is performed to hydrogenate the silicon region (FIG. 8B).
[0042]
Next, a silicon oxide film having a thickness of 90 nm is formed as an interlayer insulating film 808 on the first protective film 807, contact holes are formed in the interlayer insulating film 808, and then a titanium nitride film, an aluminum alloy film, and a titanium film are formed. A source electrode 809 and a drain electrode 810 which are stacked are formed. The film thickness may be 40 nm. A silicon nitride film having a thickness of 20 nm is provided as the second protective film 811 so as to cover the source electrode 809 and the drain electrode 810, whereby the dual-gate thin film transistor shown in FIG. 8C is completed.
[0043]
Since the dual-gate thin film transistor formed as described above includes the first gate electrode 302, the first gate insulating film 303, the channel formation region 805, the second gate insulating film 801, and the second gate electrode 802, it is structurally However, in this embodiment, since the crystalline silicon region having high crystallinity is further provided as the channel formation region, the ON current can be further increased and the S value can be improved.
[0044]
Note that in this embodiment, an example of a dual gate structure in which gate electrodes are provided above and below a channel formation region is shown. However, if the second gate electrode 802 is not provided, a known bottom gate thin film transistor (specifically, Needless to say, an inverted staggered thin film transistor can be manufactured.
[0045]
Example 3
In this example, an example of manufacturing a light-emitting device including an EL element will be described as an example of a semiconductor device obtained by implementing the present invention. FIG. 9 is a cross-sectional view of an active matrix light-emitting device. Note that in this example, the top-gate thin film transistor described in Example 1 (including the manufacturing methods of Embodiments 1, 2, and 4) is described as an example; however, the dual-gate structure or the bottom illustrated in Example 2 is used. A thin film transistor having a gate structure can also be manufactured.
[0046]
In FIG. 9, reference numeral 901 denotes a substrate, which can be a glass substrate, a quartz substrate, a crystallized glass substrate, a plastic substrate (including a plastic film), or another substrate that transmits visible light. A pixel portion 911 and a driver circuit 912 are provided over the substrate 901. Here, the pixel portion 911 will be described first.
[0047]
The pixel portion 911 is an area for displaying an image, and includes a plurality of pixels. Each pixel is provided with a TFT (hereinafter referred to as a current control TFT) 902 and an EL element 900 for controlling a current flowing through the EL element. ing. Although only the current control TFT 902 is shown here, a TFT (hereinafter referred to as a switching TFT) for controlling the voltage applied to the gate of the current control TFT is provided.
[0048]
The current control TFT 902 is preferably a p-channel TFT here. Although an n-channel TFT can be used, when a current control TFT is connected to the anode of an EL element as in the structure of FIG. 9, power consumption can be suppressed by using a p-channel TFT. However, the switching TFT (not shown) may be an n-channel TFT or a p-channel TFT.
[0049]
A pixel electrode 903 is electrically connected to the drain of the current control TFT 902. Here, since a conductive material having a work function of 4.5 to 5.5 eV is used as a material of the pixel electrode 903, the pixel electrode 903 functions as an anode of the EL element 910. As the pixel electrode 903, typically, indium oxide, tin oxide, zinc oxide, or a compound thereof may be used.
[0050]
In addition, an EL layer 905 is provided over the insulator 904 at an end portion of the pixel electrode 903. In this specification, the EL layer is a laminate composed of an organic compound or an inorganic compound included in the structure of the EL element, and the light emitting layer has a hole injection layer, a hole transport layer, a hole blocking layer, and an electron injection layer. The generic term of the layer which laminated | stacked the organic compound or inorganic compound which functions as an electron carrying layer or an electron blocking layer. However, the EL layer includes a case where the light emitting layer is used as a single layer.
[0051]
Next, a cathode 906 is provided over the EL layer 905. As a material for the cathode 906, a conductive material having a work function of 2.5 to 3.5 eV is used. As the cathode 906, typically, a conductive film containing an element belonging to Group 1 or 2 of the periodic table or an aluminum alloy may be stacked.
[0052]
In addition, an EL element 910 including the pixel electrode 903, the EL layer 905, and the cathode 906 is covered with a protective film 907. The protective film 907 is provided to protect the EL element 900 from oxygen and water. As a material for the protective film 907, a silicon nitride film, a silicon nitride oxide film, an aluminum oxide film, a tantalum oxide film, or a carbon film (specifically, a diamond-like carbon film) is used.
[0053]
Next, the drive circuit 912 will be described. The driver circuit 912 is an area for controlling the timing of signals (gate signal and data signal) transmitted to the pixel portion 911, and is provided with a shift register, a buffer, a latch, an analog switch (transfer gate), or a level shifter. Here, a CMOS circuit including an n-channel TFT 908 and a p-channel TFT 909 is shown as a basic unit of these circuits.
[0054]
The circuit configuration of the shift register, buffer, latch, analog switch (transfer gate) or level shifter may be a known one. In FIG. 9, the pixel portion 911 and the driver circuit 912 are provided over the same substrate; however, an IC or an LSI can be electrically connected without providing the driver circuit 912.
[0055]
Here, the anode of the EL element 900 is electrically connected to the current control TFT 902; however, a structure in which the cathode of the EL element 900 is electrically connected to the current control TFT may be employed. In that case, the pixel electrode may be formed using the same material as the cathode 906 and the cathode may be formed using the same material as the pixel electrode 903. In that case, the current control TFT 902 is preferably an n-channel TFT.
[0056]
A thin film transistor obtained by implementing the present invention can be used for the current control TFT 902, the switching TFT (not shown), the n-channel TFT 908, and the p-channel TFT 909. In addition, a structure in which the inverted staggered thin film transistor described in Embodiment 2 is formed in the pixel portion 911 and the dual gate thin film transistor described in Embodiment 2 is formed in the driver circuit 912 is also possible.
[0057]
A light-emitting device obtained by implementing the present invention can be formed using a thin film transistor with high switching performance and high operating speed because the field effect mobility of each thin film transistor is high and the S value is improved. Therefore, the operation performance of the light emitting device is improved, and display with good image quality is possible. Note that an electroluminescent display is a display in which a light emitting device provided with an input terminal or an output terminal is incorporated in a housing.
[0058]
Example 4
In this example, an example of manufacturing a liquid crystal display device including a liquid crystal element will be described as an example of a semiconductor device obtained by implementing the present invention. FIG. 10 is a cross-sectional view of an active matrix liquid crystal display device. Note that in this example, the top-gate thin film transistor described in Example 1 (including the manufacturing methods of Embodiments 1, 2, and 4) is described as an example; however, the dual-gate structure or the bottom illustrated in Example 2 is used. A thin film transistor having a gate structure can also be manufactured.
[0059]
In FIG. 10, reference numeral 601 denotes a substrate, which can be a glass substrate, a quartz substrate, a crystallized glass substrate, a plastic substrate (including a plastic film), or another substrate that transmits visible light. A pixel portion 611 and a driver circuit 612 are provided over the substrate 601. Here, the pixel portion 611 will be described first.
[0060]
The pixel portion 611 is a region for displaying an image, and includes a plurality of pixels. Each pixel has a TFT (hereinafter referred to as a switching TFT) 602 for controlling on / off of a voltage applied to the liquid crystal element, and a liquid crystal element. 600 is provided. A pixel electrode 603 is electrically connected to the drain of the switching TFT 602. Here, ITO (compound of indium oxide and tin oxide) is used as the material of the pixel electrode 603. However, when a reflective liquid crystal display device is used, a metal having high reflectivity such as an aluminum alloy may be used. Further, although not shown in the drawing, an alignment film is provided on the pixel electrode 603. Of course, it is not necessary to provide an alignment film as long as an alignment process that does not require a rubbing process is possible. Further, a spacer 604 made of resin is provided on the alignment film (not shown). This can be substituted by spraying spherical spacers.
[0061]
Reference numeral 605 denotes a counter substrate, on which a counter electrode 606 formed of an ITO film and a light shielding mask 607 formed of a chromium film are provided. The light shielding mask 607 is not arranged on the switching TFT of each pixel when a liquid crystal cell is assembled later, and is patterned in advance so that the driving circuit 612 can be shielded from light. Note that an alignment film (not shown) is provided over the counter electrode 606 and the light shielding mask 607.
[0062]
The substrate 601 and the counter substrate 605 are bonded with a sealing material (not shown), and liquid crystal 608 is injected into a region surrounded by the sealing material to complete a liquid crystal display device. A known technique may be used for the assembly process of the liquid crystal cell.
[0063]
Next, the drive circuit 612 will be described. The driver circuit 612 is an area for controlling the timing of signals (gate signal and data signal) transmitted to the pixel portion 611, and is provided with a shift register, a buffer, a latch, an analog switch (transfer gate), or a level shifter. Here, a CMOS circuit including an n-channel TFT 609 and a p-channel TFT 610 is shown as a basic unit of these circuits.
[0064]
The circuit configuration of the shift register, buffer, latch, analog switch (transfer gate) or level shifter may be a known one. In FIG. 10, the pixel portion 611 and the driver circuit 612 are provided over the same substrate; however, an IC or an LSI can be electrically connected without providing the driver circuit 612.
[0065]
A thin film transistor obtained by implementing the present invention can be used for the switching TFT 602, the n-channel TFT 609, and the p-channel TFT 610. Alternatively, a structure in which the thin film transistor having the inverted stagger structure described in Embodiment 2 is formed in the pixel portion 611 and the thin film transistor having the dual gate structure shown in Embodiment 2 is formed in the driver circuit 612 is also possible.
[0066]
The liquid crystal display device obtained by carrying out the present invention should be formed of a thin film transistor with good switching performance and high operating speed because the field effect mobility of each thin film transistor is high and the S value is improved. Therefore, the operation performance of the liquid crystal display device is improved, and display with good image quality is possible. Note that a liquid crystal display is a display in which a liquid crystal display device provided with an input terminal or an output terminal is incorporated in a housing.
[0067]
Example 5
In this embodiment, an example of manufacturing a semiconductor integrated circuit including a sensor will be described as an example of a semiconductor device obtained by implementing the present invention. FIG. 11 is a sectional view of the sensor. Note that in this example, the top-gate thin film transistor described in Example 1 (including the manufacturing methods of Embodiments 1, 2, and 4) is described as an example; however, the dual-gate structure or the bottom illustrated in Example 2 is used. A thin film transistor having a gate structure can also be manufactured.
[0068]
In FIG. 11, reference numeral 501 denotes a substrate, which can be a glass substrate, a quartz substrate, a crystallized glass substrate, a plastic substrate (including a plastic film), or another substrate that transmits visible light. A pixel portion 511 and a driver circuit 512 are provided over the substrate 501. Here, the pixel portion 511 will be described first.
[0069]
The pixel portion 511 is an area for displaying an image, and includes a plurality of pixels. Each pixel includes a TFT 502 (hereinafter referred to as an amplification TFT) 502 and a photoelectric conversion element 500 for amplifying a voltage generated by the photoelectric conversion element. Is provided. A pixel electrode 503 is electrically connected to the drain of the amplification TFT 502. Here, ITO (compound of indium oxide and tin oxide) is used as the material of the pixel electrode 503, but a metal may be used.
[0070]
A photoelectric conversion layer 504 and a counter electrode 505 are provided over the pixel electrode 503. In this embodiment, the photoelectric conversion layer 504 is a stacked body including a stacked structure of a P-type semiconductor layer, an I-type (intrinsic) semiconductor layer, and an N-type semiconductor layer. It is possible to use. Further, as the counter electrode 505, a transparent ITO film or the like may be used, or a metal film may be used. That is, the electrode material is not particularly limited as long as light is incident from the pixel electrode side or the counter electrode side. Finally, a protective film 505 is provided to cover the photoelectric conversion element 500. As the protective film 505, a silicon nitride film or a silicon oxide film may be used.
[0071]
Next, the drive circuit 512 will be described. The driver circuit 512 is an area for controlling the timing of signals (gate signals and data signals) transmitted to the pixel portion 511 and calculating signals read by the pixel portion 511, and includes a shift register, a buffer, a latch, An analog switch (transfer gate), a level shifter, a correction circuit, or an arithmetic circuit is provided. Here, a CMOS circuit including an n-channel TFT 506 and a p-channel TFT 507 is shown as a basic unit of these circuits.
[0072]
The circuit configuration of the shift register, buffer, latch, analog switch (transfer gate), level shifter, correction circuit, or arithmetic circuit may be a known one. In FIG. 11, the pixel portion 511 and the drive circuit 512 are provided over the same substrate; however, an IC or an LSI can be electrically connected without providing the drive circuit 512.
[0073]
Thin film transistors obtained by implementing the present invention can be used for the switching TFT 502, the n-channel TFT 506, and the p-channel TFT 507. Alternatively, a structure in which the thin film transistor having the inverted stagger structure described in Embodiment 2 is formed in the pixel portion 511 and the thin film transistor having the dual gate structure shown in Embodiment 2 is formed in the driver circuit 512 is possible.
[0074]
A semiconductor integrated circuit obtained by practicing the present invention should be formed of a thin film transistor with good switching performance and high operating speed because the field effect mobility of each thin film transistor is high and the S value is improved. Therefore, it is possible to improve the operation performance of the sensor and to obtain a sensor having high resolution reading performance.
[0075]
【The invention's effect】
By implementing the present invention, a crystalline silicon film with high crystallinity can be obtained by a simple method. Further, by using the crystalline silicon film as a channel formation region of a thin film transistor, the field effect mobility of the thin film transistor can be improved. Improvements and improvements in S value can be achieved. In addition, by using a thin film transistor manufactured using the manufacturing method, the image quality of the light-emitting device or the liquid crystal display device can be improved. Furthermore, by using a thin film transistor manufactured using the manufacturing method, reading resolution as a sensor can be improved.
[Brief description of the drawings]
FIG. 1 is a view showing a method for manufacturing a crystalline silicon film.
FIG. 2 is a view showing a method for manufacturing a crystalline silicon film.
FIGS. 3A and 3B are diagrams illustrating a method for manufacturing a crystalline silicon film. FIGS.
FIGS. 4A and 4B illustrate a method for manufacturing a crystalline silicon film. FIGS.
FIG. 5 is a graph showing the wavelength dependence of absorption coefficients of amorphous silicon and crystalline silicon.
FIG. 6 is a diagram showing a simulation result showing a difference in temperature distribution depending on a metal mask material.
7A to 7C illustrate a method for manufacturing a thin film transistor.
FIG. 8 illustrates a method for manufacturing a thin film transistor.
FIG 9 illustrates a cross-sectional structure of a light-emitting device.
10 is a cross-sectional view of a liquid crystal display device.
FIG. 11 is a diagram showing a cross-sectional structure of a sensor.

Claims (3)

Forming an amorphous silicon film on the substrate;
Forming a gate insulating film on the amorphous silicon film;
Forming a conductive film having a length more than twice the channel formation region on the gate insulating film;
Using the conductive film as a mask, a first laser light irradiation is performed from above the amorphous silicon film to selectively crystallize the amorphous silicon film in a region not masked by the conductive film. Forming a quality silicon region,
Irradiating a second laser beam from below the amorphous silicon film to crystallize the amorphous silicon film to form a second crystalline silicon region laterally grown from the first crystalline silicon region;
A method for manufacturing a thin film transistor, wherein the channel formation region is formed in the second crystalline silicon region so that a lateral growth direction and a carrier movement direction are the same by patterning the conductive film . In claim 1,
A method for manufacturing a thin film transistor, wherein a length of the channel formation region is 3 μm or less. In claim 1 or claim 2,
The method for manufacturing a thin film transistor, wherein the conductive film has a thermal conductivity of 2.0 W / Kcm or less.

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