JP2003133331A - Thin-film transistor and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin-film transistor and its manufacturing method, by which leakage current can be reduced in a liquid crystal display device driven by laser crystallized polycrystalline silicon thin-film transistor. SOLUTION: This polycrystalline silicon thin-film transistor is formed on a light-shielding metal layer and an insulation film that are provided to reduce optical leakage current. A recessed part is formed therein, to partly thin the lower insulation film of a drain region 9. When applying laser crystallization, a silicon thin film 2 is solidified earlier than other regions 1 and 2, so that it functions as a nucleus-forming site and a silicon thin film 3 made of single crystal or uniform grain boundary can be formed, thus reducing leakage currents.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a functional device such as a display, a sensor and a printing device and a semiconductor device such as a memory and a CPU, and more particularly to a thin film transistor formed on an insulator and a method for manufacturing the thin film transistor.

[0002]

2. Description of the Related Art Conventionally, hydrogenated amorphous silicon T has been used as a typical technique for forming a thin film transistor (abbreviated as TFT) on an insulating substrate such as a glass substrate.
FT technology and polycrystalline silicon TFT technology have been developed and put to practical use.

The hydrogenated amorphous silicon TFT technology has a maximum temperature in the manufacturing process of about 300 ° C. and realizes carrier transfer with a mobility of about 1 cm ² / Vsec. Therefore, the technique is used as a switching transistor of each pixel in an active matrix type liquid crystal display (appropriately referred to as AM-LCD). In such a case, the thin film transistor is a driver integrated circuit arranged around the screen. (IC or LSI formed on a single crystal silicon substrate). Further, in the AM-LCD, since a TFT is formed as a switching element for each pixel, crosstalk is reduced and a good image is obtained as compared with a passive matrix LCD that sends an electric signal for driving a liquid crystal from a peripheral driver circuit. It has the feature that quality can be obtained.

On the other hand, the polycrystalline silicon TFT technology has a mobility of about 30 to 100 cm ² / Vsec, for example, by using a high temperature process similar to an LSI having a maximum temperature of about 1000 ° C. in a manufacturing process using a quartz substrate. It has achieved high carrier movement. Therefore, when the technique is applied to, for example, a liquid crystal display, the pixel TFT for driving each pixel and its peripheral drive circuit section can be simultaneously formed on the same glass substrate. In addition, with the miniaturization and higher resolution of liquid crystal displays, AM-LCD
There was a problem that the connection pitch between the substrate and the peripheral driver integrated circuit was narrowed, and it could not be dealt with by the tab connection or wire bonding method, but this problem was solved, the cost of the manufacturing process was reduced, and the product was downsized. I was able to

However, the polycrystalline silicon TFT technology is
When using the high temperature process as described above, it is not possible to use the inexpensive low softening point glass used in the process of hydrogenated amorphous silicon TFT technology. Therefore, in order to lower the maximum temperature of the manufacturing process of the polycrystalline silicon TFT, a low temperature forming technique of the polycrystalline silicon film applying the laser crystallization technique has been researched and developed.

Generally, this laser crystallization technique is shown in FIG.
This is realized by the pulse laser irradiation device having the configuration shown in. Laser light as an energy beam emitted from a pulsed laser light source passes through an optical path defined by a group of optical elements such as a mirror and a beam homogenizer for spatially homogenizing the light intensity, and a glass substrate as an irradiation target. 5
Reach the top silicon film. Since the irradiation range of the laser light is usually smaller than the glass substrate, the glass substrate is xy
Laser irradiation is performed at an arbitrary position by moving the stage. Note that, instead of the xy stage, a method of moving the above-mentioned optical element group or a method of moving both the optical element group and the stage is also adopted.

The laser-crystallized polycrystalline silicon film thus formed by laser irradiation is used for a thin film transistor as shown in FIG. The thin film transistor shown in the figure has a channel region 7, a source region 8, a drain region 9 and an LDD (Lightly doped drain) on a glass substrate 5 covered with a substrate coat layer 19.
in) region 14 is formed, and the gate electrode 10 is formed via the gate insulating film. Then, silicon dioxide 4 is further laminated, and wiring is performed by the metal 11 formed in the contact hole.

In this thin film transistor, carriers are moved and off-leak current flows due to a high-density trap level existing at a crystal grain boundary in a polycrystalline silicon semiconductor, and an LDD region 14 serving as an offset gate region is formed. Are prevented by.

[0009]

However, the above-mentioned laser-crystallized polycrystalline silicon thin film has a crystal grain size of several n depending on the intensity of the laser to be irradiated, the pulse width, the number of pulses, and the like.
The film has a crystal grain size of (nano) m to several μm, and it is difficult to uniformly form these crystal grains at a desired place. Particularly, in the laser crystallization method using an excimer laser, crystal nucleation occurs in an extremely short time of the order of nanosecond in the heating recrystallization process by absorption of laser, so that crystal grains are formed uniformly at a desired location. It was very difficult. The same applies not only to the laser crystallized polycrystalline silicon thin film, but also to a polycrystalline silicon thin film by solid phase growth or a method of directly depositing and forming a polycrystalline silicon thin film on a glass substrate.

Therefore, in each thin film transistor, since the state of the crystal grain boundaries is not uniform, each off leak current varies, and even if the off leak current is evenly offset by the LDD region, the variation in off leak current of each thin film transistor is not improved. There is a problem in that the off-leakage current cannot be accurately reduced.

As a technique related to the above problem, a thin film transistor disclosed in Japanese Patent No. 2525707 capable of reducing an off leak current by providing a low concentration offset gate region (LDD region) in a channel region. A semiconductor integrated circuit having the same has been proposed. As described above, this technique cannot accurately reduce the off-leakage current because the state of the crystal grain boundaries of each thin film transistor is not uniform. In particular, in the laser crystallization method using an excimer laser, It is not possible to control the state of crystal nuclei generated in the process,
The above problems cannot be solved.

Similarly, as a technique related to the above problem,
There is proposed a semiconductor device disclosed in Japanese Patent Laid-Open No. 9-293870, in which an electrically conductive film having a high thermal conductivity is formed between a glass substrate and an electrically insulating alkali metal ion blocking film. Although this technology is a technology that can manufacture a thin film transistor with high mobility by obtaining polycrystalline silicon having crystal nuclei having a specific orientation by cooling and solidifying molten silicon almost uniformly, reduction of off-leakage current Moreover, the position control of the crystal nuclei cannot be performed accurately, and the above problems cannot be solved.

In this technique, the laminated structure of the TFT is
・ ・ ・ Electrical conductive film / insulating film / gate electrode / insulating film / silicon film having high thermal conductivity, and the configuration of the present invention (... electrically conductive film / insulating film / silicon having high thermal conductivity). Film / insulating film / gate electrode ...), and the present invention is also different from the object and effect.

The present invention has been made to solve the above problems, and fundamentally eliminates the off-leakage current due to the trap level of the crystal grain boundary by eliminating the crystal grain boundary by single crystallization of the silicon thin film. Along with the reduction, by forming these crystal grains in a desired place and uniformly, it is possible to reduce the variation in the off-leakage current of each thin-film transistor, and to provide a thin-film transistor and a manufacturing method thereof that more accurately reduce the off-leakage current. To do.

[0015]

In order to achieve the above object, a thin film transistor according to a first aspect of the present invention is a thin film transistor formed on a substrate with an insulator interposed between the substrate and the insulator. A cooling film made of a material having a higher thermal conductivity than the insulator is provided between the cooling film and the cooling film, and the cooling film is locally formed on at least one of a drain region, a channel region and a source region formed on the insulator. It is a close configuration.

As a result, the thin film transistor, when a crystalline silicon thin film is manufactured by irradiating a silicon thin film formed on an insulator with an excimer laser, an active region (drain) of a semiconductor locally close to a cooling film is formed. Region, channel region and source region), a crystal nucleus is formed in a part of
Recrystallization starts around these crystal nuclei, and solidification proceeds toward the part where cooling is delayed. Therefore, by epitaxially growing a silicon thin film in the vicinity of crystal nuclei, a silicon thin film composed of a single crystal or uniform crystal grain boundaries can be formed. By using this silicon thin film for a thin film transistor, the thin film transistor can be The off-leakage current due to the trap level can be fundamentally reduced, and the off-leakage current of each thin film transistor can be reduced more accurately.

According to a second aspect of the present invention, in the thin film transistor according to the first aspect, at least one of the drain region, the channel region and the source region, or at least one of the cooling films is close to the other. It is as a configuration.

As described above, the thin film transistor has many choices regarding the structure of the cooling film and the semiconductor active region (drain region, channel region, and source region).
The degree of freedom in design is increased, and optimal design can be performed.

According to a third aspect of the present invention, in the thin film transistor according to the first aspect, a gate electrode is formed on the channel region and the drain region is close to the cooling film.

As a result, in the thin film transistor, a single crystal or uniform crystal grain boundary is formed in the vicinity of the drain region, that is, in the channel region, so that the off leak current can be effectively reduced. Specifically, by designing single crystal silicon to be formed in the vicinity of the drain end of the thin film transistor, the freak current in the drain region peculiar to polycrystalline silicon can be reduced.

The invention according to claim 4 is the thin film transistor according to any one of claims 1 to 3, wherein:
The cooling film has a light shielding property.

As a result, the thin film transistor can suppress the generation of photocarriers in silicon even under light irradiation conditions and prevent malfunction. Specifically, for example,
A light valve used in a liquid crystal projector exposed to strong light, particularly a thin film transistor for driving a liquid crystal pixel, has a large effect and is suitable.

According to a fifth aspect of the present invention, there is provided a method of manufacturing a thin film transistor, which comprises a step of forming a cooling film having high thermal conductivity on a substrate, and an insulator film having a thermal conductivity smaller than that of the cooling film on the cooling film. And a step of locally thinning this insulator film, a step of forming a semiconductor thin film on this locally thinned insulator film, and irradiating this semiconductor thin film with an energy beam. And a step of performing.

As described above, in the method of manufacturing a thin film transistor according to the present invention, a cooling film is formed, and the silicon thin film is locally cooled by using the cooling film, so that silicon having a single crystal or uniform crystal grain boundaries is formed. A thin film can be formed, and by using this silicon thin film for a thin film transistor, the thin film transistor can fundamentally reduce the off-leakage current due to the trap level of crystal grain boundaries, and also reduce the off-leakage current of each thin film transistor with higher accuracy. be able to.

According to a sixth aspect of the invention of a method for manufacturing a thin film transistor, a step of forming a semiconductor thin film on a substrate, and a cooling film having higher thermal conductivity than the semiconductor thin film is formed and patterned on the semiconductor thin film. The method includes a step, a step of irradiating the semiconductor thin film and the cooling film with an energy beam, and a step of removing at least a part of the cooling film.

As described above, in the thin film transistor, a silicon thin film composed of a single crystal or uniform crystal grain boundaries can be formed by forming a cooling film on the silicon thin film and patterning the thin film. Can be reduced accurately and accurately.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a thin film transistor according to each embodiment and each example of the present invention and a manufacturing method thereof will be described with reference to the drawings. First, the thin film transistor according to the first embodiment of the present invention will be described. [First Embodiment] FIG. 1 is a schematic view of a thin film transistor according to the first embodiment. (A) is a schematic top view in an intermediate step, (b) is a schematic cross-sectional view taken along line AA ( c) shows a schematic sectional view after the final step.

In FIG. 1A, the thin film transistor has silicon thin films 1 to 3 formed as an intermediate step. Specifically, as shown in FIG. 1B, a cooling film is formed on a glass substrate 5. Of tungsten silicide 6, silicon dioxide 4 which is an insulator, and silicon thin films 1 to 3 are sequentially laminated.

The tungsten silicide 6 is a material having a thermal conductivity higher than that of the silicon dioxide 4, and is laminated on almost the entire upper surface of the glass substrate 5. Therefore, the tungsten silicide 6 efficiently transmits this heat and exhibits a cooling effect when the silicon thin films 1 to 3 are irradiated with laser light to be crystallized. In addition, tungsten silicide 6
Is an example of the cooling film, and the cooling film is not limited to the tungsten silicide 6.

The silicon dioxide 4 is laminated on almost the entire upper surface of the tungsten silicide 6, and a concave portion having a substantially square bottom surface is formed on the upper surface. Therefore, the bottom surface of the recess is closer to the tungsten silicide 6 which is the cooling film than the top surface except the recess,
After the irradiation of the laser light is finished, the heat is efficiently transferred to the tungsten silicide 6 to cool it quickly.

The silicon thin films 1 to 3 are silicon dioxide 4
Is formed in a thin film shape so as to cover almost the entire upper surface of the substrate and the recess. On the glass substrate 5 having such a structure, an excimer laser is provided on the silicon layers 1 to 1.
When irradiated under the condition that 3 melts, the silicon layer 1
When 3 is recrystallized, it solidifies in order from a region close to the tungsten silicide 6 having a high thermal conductivity. That is, since the silicon thin film 2 laminated in the concave portion is closest to the tungsten silicide 6 which is the cooling film, heat is efficiently transferred to the tungsten silicide 6 after the irradiation of the laser beam is completed, and the silicon thin film 1 and the other silicon thin films 1 and 3 are not heated. It cools quickly and solidifies quickly.

More specifically, since the silicon thin film 2 laminated on the bottom surface of the recess is cooled faster than the surroundings, it is solidified at the incubation time t1 and the nucleus generation density n1 to form the first polycrystalline silicon region. . Then, the silicon thin film 3 is solidified (crystallized) in this first polycrystalline silicon region.
The silicon thin film 2 which has started as a nucleus serves as a nucleus to grow crystals toward the side surface and the outer periphery of the recess.

The crystal growth distance at this time is determined by the point of collision with the crystallization region 1 of the second polycrystalline silicon region which solidifies at the incubation time t2 (t1 <t2) and the nucleus generation density n2 (n1n2) (crystal Growth time: t3 = t2-t1). Therefore,
The silicon thin film 3 is formed as single crystal silicon by the time of crystal growth using the first polycrystalline silicon region 2 as a nucleus and colliding with the crystallization region (silicon thin film 1) of the second polycrystalline silicon region.

As described above, the thin film transistor has the silicon thin film 1 in the recrystallization process by the excimer laser.
~ 3 to be cooled uniformly, after a predetermined incubation time, to randomly form crystal nuclei, to prevent the crystal grains from growing randomly around this nucleus, the occurrence of random grain boundaries You can That is, the thin film transistor can be solidified (recrystallized) from a specific place (bottom surface of the recess) in the recrystallization step, and can be solidified toward a portion where cooling is delayed, so that the crystal is
The bottom surface of the recess is used as a nucleus for epitaxial growth in the outer peripheral direction to grow as a single crystal.

The silicon thin films 1 to 3 thus formed
FIG. 1C shows a TFT structure in the case where is used for a thin film transistor (TFT). The thin film transistor continues to have a channel region 7, a source region 8, a drain region 9,
Are formed, and the gate 10, the metal 11 wiring, and the interlayer insulating film 13 are formed via the gate insulating film 12.

Here, the drain region 9 is replaced by the silicon thin film 2
The channel region 7 is formed in accordance with the position of
Is formed of a single crystal layer. Here, the silicon thin film 3
In some cases, crystals may grow from each side of the bottom surface of the recess and crystal grain boundaries may be generated on a diagonal line. However, by forming the drain region, the channel region and the source region in a narrow rectangular shape, It can be excluded.

Therefore, in the thin film transistor, since the number of grain boundaries in the channel region 7 is reduced, it is possible to reduce the leak current due to the grain boundary trap peculiar to polycrystalline silicon. In this way, the incubation time t2, t1
Is adjusted, the crystal growth time (t3 = t2-t1) is lengthened, and the silicon thin film 3 is grown large, whereby the channel region 7 made of a single crystal (having no crystal grain boundary) can be formed. .

As described above, in the thin film transistor according to the first embodiment, a part of the drain region, the channel region, and the source region, which are silicon layers, locally approaches the cooling film made of a material having a high thermal conductivity. Therefore, when recrystallized after being heated by the laser light, that portion becomes a nucleus and the crystal grows as a single crystal toward the periphery. Thereby, the thin film transistor can fundamentally reduce the leak current due to the grain boundary trap.

In the thin film transistor, crystal nucleation occurs in the extremely short time of nanosecond order in the heating recrystallization process by the laser crystallization method using the excimer laser, but the crystal nuclei are formed on the bottom surface of the recess, A silicon thin film composed of a single crystal or uniform crystal grain boundaries can be formed around this crystal nucleus, and the off-leakage current of the thin film transistor can be reduced more accurately.

Further, the description of the thin film transistor in the first embodiment of the present invention also describes the manufacturing method thereof, and in the manufacturing method of this thin film transistor, a single crystal or a uniform crystal is formed by forming a cooling film. By forming a silicon thin film composed of grain boundaries, it is possible to fundamentally reduce the off-leakage current due to the trap level of the crystal grain boundaries, and it is possible to more accurately reduce the off-leakage current of each thin film transistor.

Further, the thin film transistor in the first embodiment is limited to the above-mentioned structure in the structure in which a part of the drain region, the channel region and the source region is locally brought close to the cooling film made of a material having a high thermal conductivity. However, various structures can be used. Next, these structures will be described as application examples of the first embodiment with reference to the drawings.

[First Application Example] FIG. 2 is a schematic view of a thin film transistor according to the first application example. (A) is a schematic sectional view in an intermediate step, and (b) is a schematic sectional view after a final step. Shows. In FIG. 1A, as a thin film transistor, as a middle step, a tungsten silicide 6 as a cooling film 6, a silicon dioxide 4 as an insulator, and silicon thin films 1 to 3 are sequentially laminated on a glass substrate 5. Here, a groove is formed on the upper surface of the silicon dioxide 4, and the silicon thin film 2 is laminated on the bottom of the groove. Therefore, since the silicon thin film 2 is closest to the tungsten silicide 6, the cooling efficiency is high.

On the glass substrate 5 having such a structure,
When the excimer laser is irradiated under the condition that the silicon layers 1 to 3 are melted, when the silicon layers 1 to 3 are recrystallized, like the thin film transistor of the first embodiment, the silicon thin film 2 close to the tungsten silicide 6 is removed. Solidify,
A silicon thin film 3 composed of a single crystal or uniform crystal grain boundaries is formed.

Subsequently, in the thin film transistor, the channel region 7, the source region 8 and the drain region 9 are formed in the region of the single crystal silicon thin film 3, and the gate 10 and the wiring are formed through the insulating silicon dioxide 4. 11 are formed respectively.

As a result, in the thin film transistor, a single crystal grain or a uniform grain boundary is formed in the drain region 9 and in the vicinity thereof (channel region 7), so that the freak current in the drain region 9 peculiar to polycrystalline silicon is effective. Can be reduced to Here, it is preferable to form the LDD regions 14 on both ends of the channel region 7. By doing so, for example, when two or three crystal grain boundaries are uniformly generated in each channel region 7,
By offsetting this amount, it is possible to prevent the generation of leak current with extremely high accuracy. Other structures and actions are similar to those of the thin film transistor in the first embodiment.

As described above, in the thin film transistor according to the first application example, since the drain region 9, the channel region 7 and the source region 8 are formed of a single crystal layer, the leak current due to the grain boundary trap peculiar to polycrystalline silicon is accurately measured. It can be reduced.

[Second Application Example] FIG. 3 is a schematic view of a thin film transistor according to a second application example. (A) is a schematic sectional view in an intermediate step, and (b) is a schematic sectional view after a final step. Shows. In FIG. 1A, as a thin film transistor, as a middle step, a tungsten silicide 6 as a cooling film 6, a silicon dioxide 4 as an insulator, and silicon thin films 1 to 3 are sequentially laminated on a glass substrate 5. Here, two groove portions are formed in a stripe shape on the upper surface of the silicon dioxide 4, and the silicon thin films 1 to 3 are laminated on the silicon dioxide 4 including the two groove portions. Therefore, the bottom surface of this groove portion is closest to the tungsten silicide 6, so that the cooling efficiency is high.

On the glass substrate 5 having such a structure,
When the excimer laser is irradiated under the condition that the silicon layers 1 to 3 are melted, when the silicon layers 1 to 3 are recrystallized, the tungsten silicide 6 is formed as in the first embodiment.
Is solidified from the silicon thin film 2 laminated on the bottom surface of the groove portion close to, to form a silicon thin film 3 composed of a single crystal or uniform grain boundaries. Here, it is preferable to reduce the width of the upper surface of the convex portion sandwiched between the groove portions. By doing so, when the silicon thin film 3 grown from each groove collides on the upper surface of the convex portion before the polycrystalline silicon thin film 1 is formed, the channel region 7 with few crystal grain boundaries is formed. You can

Subsequently, in the thin film transistor, the channel region 7, the source region 8 and the drain region 9 are formed in the region of the single crystal silicon thin film 3, and the gate 10 and the metal are formed through the insulating silicon dioxide 4. 11 wirings are formed respectively.

By doing so, the thin film transistor forms the source region 8 and the drain region 9 in the single crystal silicon 3 region, and the channel region 7 is a silicon thin film 3 made of a uniform crystal grain boundary containing a single crystal. Therefore, for example, even when used as a pixel driving element of a liquid crystal display, the leak current due to the grain boundary trap peculiar to polycrystalline silicon is eliminated, and the contrast is improved. Other structures and operations are similar to those of the thin film transistor in the first application example.

[Third Application Example] FIG. 4 is a schematic view of a thin film transistor according to a third application example. (A) is a schematic sectional view in an intermediate step, and (b) is a schematic sectional view after a final step. Shows. In FIG. 1A, as a thin film transistor, as a middle step, a tungsten silicide 6 as a cooling film 6, a silicon dioxide 4 as an insulator, and silicon thin films 1 to 3 are sequentially laminated on a glass substrate 5. Here, one groove is formed on the upper surface of the silicon dioxide 4, and the silicon thin films 1 to 3 are laminated on the silicon dioxide 4 including this one groove. Therefore, the bottom surface of this groove portion is closest to the tungsten silicide 6, so that the cooling efficiency is high.

On the glass substrate 5 having such a structure,
When the excimer laser is irradiated under the condition that the silicon layers 1 to 3 are melted, when the silicon layers 1 to 3 are recrystallized, the tungsten silicide 6 is formed as in the first embodiment.
Is solidified from the silicon thin film 2 laminated on the bottom surface of the groove portion, and the silicon thin film 3 made of a single crystal or uniform crystal grain boundaries is formed on both sides of the groove portion. Here, it is preferable to narrow the width of the groove. By doing this,
Since the region where the silicon thin film 1 made of polycrystal is formed is reduced and the silicon thin film 3 made of single crystal or uniform crystal grain boundaries is increased, as a result, the channel region 7 having few crystal grain boundaries is formed. You can

Subsequently, in the thin film transistor, the channel region 7, the source region 8 and the drain region 9 are formed in the region of the single crystal silicon thin film 3, and the gate 10 and the metal are formed through the insulating silicon dioxide 4. 1
One wiring is formed respectively. Other structures and operations are similar to those of the thin film transistor in the first application example.

[Fourth Application Example] FIG. 5 is a schematic view of a complementary MOS (CMOS) using a thin film transistor according to a fourth application example, (a) is a schematic sectional view in an intermediate step, and (b) is a schematic sectional view. Shows a schematic sectional view after the final step. As shown in FIG. 1A, in the CMOS, as an intermediate step, a tungsten silicide 6 having a constant thickness 6, a silicon dioxide 4 having a flat upper surface, and silicon thin films 1 to 3 are formed on a glass substrate 5 having convex portions formed in stripes. Are sequentially laminated.
Therefore, since the silicon thin film 2 above the convex portion is closest to the tungsten silicide 6, the cooling efficiency is high.

Here, the convex portion is provided with a step on the glass substrate in advance, and the tungsten silicide 6 is formed so as to cover the step. The projection is not limited to the processing of the substrate material itself, and may be patterned after depositing a film such as an oxide film or a nitride film, or the projection may be provided on the tungsten silicide 6. .

On the glass substrate 5 having such a structure,
When the excimer laser is irradiated under the condition that the silicon layers 1 to 3 are melted, when the silicon layers 1 to 3 are recrystallized, the tungsten silicide 6 is formed as in the first embodiment.
It is possible to solidify the silicon thin film 2 laminated on the upper surface of the convex portion close to, and form the silicon thin film 3 composed of a single crystal or uniform crystal grain boundaries on both sides of the silicon thin film 2.

Next, in the CMOS using the silicon thin films 1 to 3 thus formed, as shown in FIG. 6, after forming the gate insulating film 12 and the gate electrode 10, by ion implantation, the channel region 7, The source region 8 and the drain region 9 are formed. In addition, by using a resist, phosphorus and boron are separately implanted, so that n ⁺ region 1
5 and p ⁺ region 16 are made separately, and complementary MOS (CMOS)
The circuit is formed. Then, as shown in FIG. 5B, after forming an interlayer insulating film 13 and forming a contact hole, wiring is performed by the metal layer 11. Note that n ⁺ region 1
The portion where 5 and the p ⁺ region 16 contact each other is made of polycrystal, but it is needless to say that a single crystal is preferable.

As described above, in the CMOS circuit using the thin film transistor in the first embodiment, since the channel region 7 can be formed in the single crystal region, the leak current can be reduced, and as a result, the consumed current can be reduced. Can be reduced.

As described above with reference to each application example, the thin film transistor according to the present invention is provided with a cooling film and a semiconductor active region (drain region, channel region and source region).
Since there are many options for the structure of (1), the degree of freedom in designing is increased, optimum designing can be performed, and as a result, a thin film transistor with excellent performance can be provided.

Further, the thin film transistor manufacturing method according to the present invention is, as an application example of the above-described thin film transistor manufacturing method, forming and patterning a cooling film above a semiconductor thin film and irradiating the semiconductor thin film and the cooling film with an energy beam. It is also possible to use a manufacturing method in which crystal nuclei are first formed in the semiconductor thin film below the cooling film. Also by this method of manufacturing a thin film transistor, the thin film transistor,
The same action (forming the silicon thin film 3 formed of a single crystal or a uniform crystal grain boundary) can be obtained, and the off-leakage current can be reduced fundamentally and accurately.

The thin film transistor of the present invention is widely used in various electronic devices. For example, the thin film transistor of the present invention can be used in a semiconductor memory as shown in FIG. This semiconductor memory is composed of memory cells of 2n × 2m bits, and thin film transistors are formed in the memory cells.

Further, for example, the thin film transistor of the present invention can be used for a liquid crystal display (appropriately referred to as a liquid crystal light valve) as shown in FIG. 8, and a schematic of a projector to which the liquid crystal light valve is applied is shown in FIG. The configuration is shown. In FIG. 8, a peripheral drive circuit (data driver, gate driver) drives liquid crystal pixels connected to the active matrix array. Here, the thin film transistor is used for a data driver, a gate driver, and a pixel. In FIG. 9, in the projector, the light generated by the halogen lamp enters the light valve through the dichroic mirror, and the image thereof is projected on the screen through the projection lens. here,
Light valves corresponding to the red, green, and blue components of light are used.

Furthermore, for example, as shown in FIG. 10, the thin film transistor of the present invention can be used in a portable scanner, and more specifically, it is used for driving an amorphous silicon photodiode. The image sensor includes an amorphous silicon photodiode, a shift register including a thin film transistor that controls the main scanning direction, and a read switch.

The portable scanner is equipped with a light source, an image sensor and a fiber array plate, and the document surface image certified from the back surface of the image sensor is image-read using the fiber array plate. Then, the read image signal is read by the roller and the encoder in the moving position in the sub-scanning direction, and the read image signal is output to a computer or a recording device via an external circuit formed on the printed circuit board. It Although the portable scanner as described above is illustrated here, the invention can be applied to an image sensor such as a flatbed scanner, a facsimile, a digital copying machine, or a two-dimensional sensor.

[0065]

As described above, in the thin film transistor of the present invention, when a silicon thin film formed on an insulator is irradiated with an excimer laser to form a crystalline silicon thin film, a thin film is locally formed with a cooling film. Crystal nuclei are formed in a part of the active regions (drain region, channel region, and source region) of the semiconductor that are close to each other, recrystallization starts around these crystal nuclei, and solidification proceeds toward the part where cooling is delayed. .

Therefore, a silicon thin film consisting of a single crystal or uniform crystal grain boundaries can be formed by epitaxially growing a silicon thin film in the vicinity of crystal nuclei. By using this silicon thin film for a thin film transistor, the thin film transistor is The off-leakage current due to the trap levels at the grain boundaries is fundamentally reduced, and
The off leak current of each thin film transistor can be reduced more accurately.

[Brief description of drawings]

1A and 1B are schematic views of a thin film transistor according to a first embodiment, FIG. 1A is a schematic top view in an intermediate step, and FIG. 1B is a schematic cross sectional view taken along the line AA.
(C) has shown the schematic sectional drawing after the last process.

2A and 2B are schematic diagrams of a thin film transistor according to a first application example, FIG. 2A is a schematic sectional view in an intermediate step, and FIG. 2B is a schematic sectional view after a final step.

3A and 3B are schematic views of a thin film transistor according to a second application example, FIG. 3A is a schematic sectional view in an intermediate step, and FIG. 3B is a schematic sectional view after a final step.

4A and 4B are schematic views of a thin film transistor according to a third application example, FIG. 4A is a schematic sectional view in an intermediate step, and FIG. 4B is a schematic sectional view after a final step.

FIG. 5 is a schematic view of a complementary MOS (CMOS) using a thin film transistor according to a fourth application example,
(A) is a schematic sectional view in an intermediate step, and (b) is a schematic sectional view after a final step.

FIG. 6 is a schematic cross-sectional view of a complementary MOS (CMOS) using a thin film transistor according to a fourth application example at an intermediate step.

FIG. 7 is a schematic configuration diagram of a semiconductor memory using a thin film transistor according to the present invention.

FIG. 8 is a schematic configuration diagram of a liquid crystal light valve using a thin film transistor according to the present invention.

FIG. 9 is a schematic configuration diagram of a projector using a thin film transistor according to the present invention.

FIG. 10 is a schematic view of a main part of a portable scanner using a thin film transistor according to the present invention, (a)
Shows a perspective view of the inside, and (b) shows an enlarged sectional view.

FIG. 11 shows a schematic configuration diagram of a pulse laser irradiation device.

FIG. 12 shows a schematic cross-sectional view of a thin film transistor in the prior art.

[Explanation of symbols]

1 silicon thin film 2 silicon thin film 3 silicon thin film 4 silicon dioxide 5 glass substrate 6 tungsten silicide 7 channel region 8 source region 9 drain region 10 gate electrode 11 metal 12 gate insulating film 13 interlayer insulating film 14 LDD region 15 n ⁺ region 16 p ⁺ Area 19 Substrate coat layer

Continued front page    F-term (reference) 5F052 AA02 BB07 DA01 EA11 FA02                       FA04 FA16 FA17 JA01 JA04                 5F110 AA06 BB01 BB02 BB04 BB05                       BB10 CC02 DD02 DD12 DD13                       DD17 DD21 DD25 FF02 GG02                       GG13 GG22 HJ01 HJ13 HL02                       HM02 HM15 NN02 NN23 NN43                       NN46 PP03 PP24 PP36

Claims (9)

[Claims] 1. A thin film transistor formed on a substrate with an insulator interposed between the substrate and the insulator, comprising a cooling film made of a material having higher thermal conductivity than the insulator. Is locally close to at least one of a drain region, a channel region and a source region formed on the insulator, and a portion including the drain region, the channel region and the source region is close to the local region. A thin film transistor, which is a semiconductor film grown from a portion. 2. The thin film transistor according to claim 1, wherein at least one of the drain region, the channel region and the source region, or at least one of the cooling films is close to the other. Thin film transistor. 3. The thin film transistor according to claim 1, wherein a gate electrode is formed on the channel region, and the drain region is close to the cooling film. 4. The thin film transistor according to claim 1, wherein the cooling film has a light shielding property. 5. A step of forming a cooling film having high thermal conductivity on a substrate, a step of forming an insulating film having a thermal conductivity smaller than that of the cooling film on the cooling film, and the step of forming the insulating film. A thin film transistor comprising: a step of locally thinning the film, a step of forming a semiconductor thin film on the locally thinned insulator film, and a step of irradiating the semiconductor thin film with an energy beam. Manufacturing method. 6. A silicon thin film formed on an insulator,
A method of manufacturing a thin film transistor, characterized in that in a step of producing a crystalline silicon thin film by irradiating an excimer laser, solidification is performed from a location that cools quickly and solidification proceeds toward a portion where cooling is delayed. 7. A silicon thin film formed on an insulator,
In a method of manufacturing a thin film transistor including a step of irradiating an excimer laser to form a crystalline silicon thin film, a crystal nucleus is formed in at least a part of a drain region, a channel region, and a source region of the thin film transistor, and the crystal nucleus is re-centered around the crystal nucleus. A method of manufacturing a thin film transistor, comprising a step of solidification progressing toward a portion where crystallization starts and cooling is delayed. 8. A step of forming a cooling film having a high thermal conductivity on a substrate, a step of forming an insulating film having a thermal conductivity smaller than that of the cooling film on the cooling film, and a step of forming the insulating film. In a method of manufacturing a thin film transistor, which includes a step of locally thinning a film, a step of forming a semiconductor thin film on the locally thinned insulator film, and a step of irradiating the semiconductor thin film with an energy beam, A method of manufacturing a thin film transistor, characterized in that the drain region, the channel region, and the source region are formed in a rectangular shape having a narrow width so as not to include a crystal grain boundary. 9. A step of forming a cooling film having a high thermal conductivity on a substrate, a step of forming an insulating film having a thermal conductivity smaller than that of the cooling film on the cooling film, and a step of forming the insulating film. Manufacture of a thin film transistor including a step of locally thinning at least two locations, a step of forming a semiconductor thin film on the locally thinned insulator film, and a step of irradiating the semiconductor thin film with an energy beam In the method, a method for producing a thin film transistor is characterized in that a semiconductor thin film grown from each locally thinned portion is made to collide.