JP3201029B2 - Thin film transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor used as a drive circuit of an image input / output device such as a liquid crystal display panel or a contact type image sensor. The present invention relates to a structure for improving heat radiation efficiency of an operation layer in a thin film transistor that can be formed over a substrate.

[0002]

2. Description of the Related Art In order to reduce the size and enhance the function of an image input / output device, a thin film transistor (TFT) capable of simultaneously forming a large number of elements on a large-area substrate is used in a drive circuit of the image input / output device. I have. In order to enable the use of an inexpensive glass plate as the substrate, a poly-Si thin film material having a high mobility and suppressing the TFT fabrication process to 600 ° C. or less is suitable for the operation layer of the thin film transistor. The reason for this is that the heat-resistant temperature of the glass substrate is considered to be about 600 ° C. at the highest in consideration of thermal strain. In addition, in order to secure a high driving capability of the driving circuit of the image input / output device, the mobility of electrons is required. Must be high. That is, as a method of forming a poly-Si thin film material, for example, amorphous silicon (a-Si) is formed on a glass substrate.
Is deposited and annealed with an excimer laser, which is a pulse laser, to obtain a poly-Si thin film.According to this method, an excimer laser that can emit a high-energy but short-pulse beam with ultraviolet light is used. Defects in the film can be reduced, and thermal damage to the glass substrate is less likely to occur.

A conventional method for manufacturing a poly-Si thin film transistor using the above-described excimer laser annealing is described below.
This will be described with reference to FIG. Insulating substrate 1 such as glass
A-Si film 12 is formed by depositing amorphous silicon (a-Si) to a thickness of 1000 angstroms by LPCVD or the like on top 1 (FIG. 5A). Subsequently, the a-Si film 12 is annealed by an excimer laser,
The poly-Si film 13 is formed (FIG. 5B). Next, the operation layer 14 is formed by patterning the poly-Si film 13 into an island shape, and a gate insulating film 15 by depositing SiO ₂ and a gate electrode 16 by depositing and patterning poly-Si are sequentially formed ( FIG. 5 (c)). Subsequently, ion implantation is performed using the gate electrode 16 as a mask, and activation annealing is performed to form a source electrode 17a and a drain electrode 17b.
An interlayer insulating film 18 is formed by depositing O2 or the like (FIG. 5).
(D)). Subsequently, formation of a contact hole 19, formation of a wiring 20 by deposition and patterning of a metal film, and formation of a passivation film 21 by deposition of SiN or the like are performed, respectively, and a thin film transistor (poly-Si TFT) using a polysilicon thin film as an operation layer is performed. (FIG. 5)
(E)).

[0004]

Problems to be Solved by the Invention The poly-Si TFT manufactured by the above process is different from a TFT formed directly on a silicon (Si) substrate having a good thermal conductivity and has a low thermal conductivity. It is formed on a substrate 11. When a glass substrate is used as the insulating substrate 11, its thermal conductivity is 0.014 w / cm · deg, which is two orders of magnitude lower than that of the Si substrate. There was a problem. For example, in a liquid crystal display, etc., po
When a drive circuit composed of a ly-Si TFT is formed on the same glass substrate as the liquid crystal display, a relatively large current flows in the drive circuit, so that power consumption increases. However, since the thermal conductivity of the glass substrate is small, TF
The heat generated in the channel region of the T operation layer 14 is not easily dissipated, and the channel temperature of the TFT tends to increase.

In a specific example, the channel width is 50 μm.
m, channel length 10 μm, field effect mobility 60 cm ²
/ V · s, n-type poly-SiTF with threshold voltage V _TH of 2V
When the channel of T was made conductive and a voltage was applied between the source electrode and the drain electrode so as to consume about 40 mV, the surface temperature of the poly-Si TFT was 170 to 21.
It was confirmed that the temperature reached 0 ° C. This temperature increase accelerates the deterioration of the TFT due to the electric stress, and particularly leads to characteristic deterioration such as an increase in the threshold voltage. Therefore, poly-S
iTFT is faster than amorphous-Si TFT.
Despite being capable of high-current operation, sufficient reliability could not be ensured when fabricated on an insulating substrate such as a glass substrate having low thermal conductivity.

Therefore, as a structure for releasing the heat generated in the channel region, for example, a heat radiation layer formed of a material having good thermal conductivity is interposed between the glass substrate and the active layer (semiconductor active layer). It is conceivable to diffuse the heat in the horizontal direction to increase the heat radiation area to the substrate, prevent the temperature from rising, and improve the heat radiation efficiency. The material of the heat dissipation layer should have good thermal conductivity and sufficient adhesion to the substrate in order to be applicable to the manufacturing process of poly-Si TFT. Are required, and the film does not contain impurities that impair the TFT characteristics. As a heat radiation layer made of a substance having a good thermal conductivity, there are an amorphous Si film, a diamond thin film, an Al ₂ O ₃ film, and the like, but at present, there is no material that satisfies all the above conditions.

That is, for example, when the heat dissipation layer is formed of a diamond thin film, the diamond thin film itself becomes a source of contamination, and the surface flatness is deteriorated. Further, when the heat radiation layer is formed of an Al ₂ O ₃ film, there is a problem that the adhesion to the substrate is low and the heat radiation layer is peeled off, and impurities in the film are mixed into the operation layer of the poly-Si TFT. Further, when an amorphous Si film is used, the thermal conductivity is lower than those of the two films, so that it is necessary to increase the film thickness. As a result, the surface flatness is deteriorated and the TFT characteristics are adversely affected. Furthermore, in the case of obtaining poly-Si by annealing with an excimer laser in the process of manufacturing a poly-Si TFT, the solidification rate when the amorphous silicon melted by the laser is solidified increases due to the presence of the heat dissipation layer. Was confirmed. For this reason, there has been a problem that only poly-Si having a small crystal grain size can be obtained. Therefore, in the structure in which the heat dissipation layer is interposed, a highly reliable device having good characteristics without adversely affecting the fabrication process of the poly-Si TFT is provided.
It was difficult to obtain a poly-Si TFT.

The present invention has been made in view of the above circumstances, and provides a structure of a thin film transistor capable of increasing the heat radiation efficiency of the TFT without adversely affecting the TFT portion in the process of manufacturing the poly-Si TFT. With the goal.

[0009]

[MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
According to the first aspect of the present invention, an insulating substrate or an insulating film is provided.
Thin film using formed polysilicon thin film as working layer
In the transistor (poly-Si TFT), the TFT side
Ridge-shaped heat radiation laminated after TFT formation
It is characterized by having a layer.

According to a second aspect of the present invention, there is provided a semiconductor device comprising: an insulating substrate;
Uses the polysilicon thin film formed on the insulating film as the operating layer.
Used thin film transistor (poly-Si TFT)
And formed by laminating after forming the TFT at the lateral position of the TFT.
Heat radiation layer, and the heat radiation layer is exposed through metal wiring.
Connected to the silicon thin film, the metal wiring was connected
The feature is that the polysilicon thin film part is a high resistance area
are doing.

[0011]

[0012]

[0013]

[0014]

According to the present invention, since the heat radiation layer is laminated after the TFT is formed, in the process of manufacturing the poly-Si TFT,
The presence of the heat dissipation layer does not adversely affect the TFT portion.

The heat radiation layer is formed on the side of the TFT.
The heat radiation layer is made of the same material as the TFT wiring material.
And it can be formed in the same process, especially to provide a new process
The heat radiation layer can be formed without any.

According to the first aspect of the present invention, the heat radiation layer is formed in a ridge shape.
As a result, the surface area exposed to the atmosphere can be increased.
The heat radiation effect can be enhanced.

According to the second aspect of the present invention, the heat radiation layer is a heat conducting layer.
Connected to a polysilicon thin film through a metal wiring with good efficiency.
The heat generated in the operating layer is directly transmitted to the heat dissipation layer
Can be done.

Further, since the polysilicon thin film portion where the metal wiring is connected is a high resistance region, it is possible to share the heat dissipation layer in each TFT.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. Amorphous silicon (a-Si) is deposited on an insulating substrate 11 such as glass to a thickness of 1000 Å at 500 ° C. by an LPCVD method or the like to form an a-Si film 12 (FIG. 1A). Then, this a-Si
The film 12 is annealed with a KrF excimer laser (248 nm oscillation, pulse width 20 nsec, energy density 450 mJ / cm ² ) to form a poly-Si film 13 (FIG. 1).
(B)). Note that the poly-Si film 13 may be formed by annealing with another laser, a solid phase growth method, or the like. Then, poly
The active layer 14 is formed by patterning the -Si film 13 into an island shape, and SiO ₂ is deposited to a thickness of 1000 Å by LPCVD to form the gate insulating film 15. Next, poly-S is applied to a thickness of 3000 angstrom.
i is deposited and patterned to form a gate electrode 16 on the gate insulating film 15 located on the operation layer 14 (FIG. 1).
(C)). Subsequently, by ion implantation using the gate electrode 16 as a mask, phosphorus (P) is used for an n-channel TFT, and boron (B) is used for a p-channel TFT.
Is implanted as a dopant, and activation annealing is performed to form a source electrode 17a and a drain electrode 17b. next,
SiO ₂ is deposited to a thickness of 7000 Å by LPCVD to form an interlayer insulating film 18. Furthermore,
The formation of a contact hole 19, the formation of a wiring 20 by deposition and patterning of a metal film, and the formation of a passivation film 21 by deposition of SiN or the like are performed (FIG. 1).
(E)).

A thin film transistor (poly-Si TFT) using the polysilicon thin film as the operation layer 14 in the above process
After fabrication, the pressure was 4 mT at room temperature by sputtering.
orr, C under a condition of 2A DC bias to a thickness of 1 μm.
Then, a heat radiation layer 30 is formed so as to cover at least the upper part of the TFT by depositing u (FIG. 1F). The thermal conductivity of Cu is 40
Since it is as high as 0 W / m · K, the heat radiation efficiency can be improved. That is, in the conventional structure, the operation layer 1
The Joule heat generated in Step 4 must be transmitted through the glass (insulating) substrate 11 having a thermal conductivity of 1 W / m · K or less, the gate insulating film 15 and the interlayer insulating film 18 formed of SiO ₂ ,
Although the generated heat tends to be accumulated in the operation layer 14, in the above embodiment, the heat radiation layer 3
Since heat can be released from zero, the heat radiation effect can be improved.

The conditions described in the specific example of the conventional example (an n-type poly-type transistor having a channel width of 50 μm, a channel length of 10 μm, a field effect mobility of 60 cm ² / V · s, and a threshold voltage V _TH of 2 V).
When the heat dissipation effect was compared using a SiTFT and the power consumption was about 40 mV), the surface temperature of the poly-SiTFT was 100 ° C. or less, and the heat dissipation efficiency could be improved. Further, the TFT was not deteriorated by the deposition and formation of the heat radiation layer 30. This is because the heat radiation layer 30 is TFT
This is because it is formed at the final stage of the fabrication process of the above, and the surface properties of the heat radiation layer 30 and the denaturation due to the heat treatment do not affect the characteristics of the TFT.

The poly-Si TFT manufactured by the above process
(Channel width / channel length = 50 μm / 6 μm) under the following conditions, and a threshold voltage V before and after the stress is applied.
The change in _TH was evaluated. The poly-Si TFT used was a p-channel type. When -20 V was applied to the gate electrode and the drain electrode for 32000 seconds so as to be in a conductive state, as shown in Table 1, depending on the presence or absence of the discharge layer 30, before and after the stress was applied. The threshold voltage has changed.

[0023]

[Table 1] Threshold voltage V before and after stress Before _TH stress After stress Sample 1 (without Cu heat dissipation layer) -2.0V -9.5V Sample 2 (with Cu heat dissipation layer) -2.0V -4.0V

In Sample 1 having no heat radiation layer, the channel temperature increased due to the application of the stress to make the conductive state, and the threshold voltage V _TH deteriorated by 7.5 V (variation width). On the other hand, in Sample 2 having the heat dissipation layer, the rise in the channel temperature can be reduced, so that it was confirmed that the fluctuation of the threshold voltage V _TH was small.

Next, the poly-SiTF in the conductive state
The relationship between the power consumption of T and the variation width of the threshold voltage _VTH will be described with reference to FIG. In the figure, the solid line is for the present embodiment, and the dotted line is for the conventional structure. In the conventional poly-Si TFT, as the power consumption increases, the surface temperature in the operation layer of the poly-Si TFT increases, and the fluctuation width of the threshold voltage _VTH greatly increases. According to the poly-Si TFT of this embodiment, the fluctuation width of the threshold voltage V _TH can be reduced. If the power consumption is 20 mW or less, the variation width of the threshold voltage V _TH can be suppressed to 1 V or less. Since the actual operation of the drive circuit is AC drive, its power consumption is 20 m per transistor.
W or less, and according to the structure of the poly-Si TFT of the above embodiment, a highly reliable poly-Si TFT can be obtained.

In the above embodiment, Cu is used as the material of the heat radiation layer 30. However, a material having good thermal conductivity and easy to deposit and process, for example, is generally used in the production of semiconductor devices. Mo (The thermal conductivity is 140 W / m
K), Al (thermal conductivity is 240 W / m · K), Au (thermal conductivity is 320 W / m · K), and the like. Also,
In the case where the heat radiation layer 30 is formed, if there is a concern about the influence on the lower layer or oxidation of the heat radiation layer, a barrier layer such as a TiN film is disposed below or above the heat radiation layer. In addition, a diamond film or an AIN film other than a metal film may be used for the heat radiation layer 30 as long as there is no problem in the production process of the poly-Si TFT. Further, a semiconductor film having high thermal conductivity, for example, single crystal Si (having a thermal conductivity of 170 W / m · K) may be used. Also, poly-Si (having a thermal conductivity of 20 W / m · K) can be used. That is, the material of the heat radiation layer 30 needs to have a thermal conductivity of 10 W / m · K or more, preferably 100 W / m · K or more in order to reduce the film thickness to some extent. Thermal conductivity 100W / m ・ K
Above, a sufficient heat radiation effect can be provided even if the thickness of the heat radiation layer 3 is 1 μm or less. If there is no problem in the production process, the discharge layer may be formed under the protective film. In this case, however, a material that meets various conditions such as moisture resistance required for the protective film must be found.

FIGS. 3 and 4 show another embodiment of the present invention.
This will be described with reference to FIG. Amorphous silicon (a-Si) is deposited at 500 [deg.] C. on an insulating substrate 11 made of glass or the like to a thickness of 1000 angstrom by an LPCVD method or the like to form an a-Si film. Subsequently, this a-Si film was coated with a KrF excimer laser (248 nm oscillation, pulse width 2).
Anneal at 0 nsec and an energy density of 450 mJ / cm ² to form a poly-Si film. Next, the poly-Si film is patterned into an island shape to form the operation layer 14 and the connecting portion 40 continuous with the operation layer 14, and further, SiO ₂ is deposited to a thickness of 1000 Å by LPCVD to form the operation layer 14.
And a gate insulating film 15 extending to a side position (right side in the drawing) of the connection portion 40 is formed. next,
Deposit poly-Si to a thickness of 1000 angstroms,
The gate electrode 16 is formed on the gate insulating film 15 located on the operation layer 14 by patterning.

Next, a dopant is implanted by ion implantation using the resist 41 covering the gate electrode 16 and the connection portion 40 as a mask, and activation annealing is performed to form a source electrode 17a and a drain electrode 17b (FIG. 3A, FIG.
(A)). SiO ₂ is deposited to a thickness of 9000 angstroms by the plasma CVD method, and an interlayer insulating film 18 is formed to cover the TFT and extend to the side position (the right side in the drawing) of the TFT. The gate insulating film 15 and the interlayer insulating film 18 are patterned, and the gate insulating film 15 and the interlayer insulating film 18 on the side of the TFT are removed at intervals of 3 μm to form a plurality of square holes 42. Subsequently, the gate insulating film 15 and the interlayer insulating film 18 are patterned to form contact holes 19 located on the source electrode and the drain electrode.
Contact holes 43 located on the connection portions 41 are respectively formed. Next, a hydrogen plasma process is performed to
The dangling bonds at the interface between the semiconductor and the gate insulating film 15 are terminated with hydrogen to reduce the defect state density.

Aluminum (Al) is deposited to a thickness of 3000 angstroms and patterned by a photolithography method to form a wiring 20 connected to the source electrode 17a and the drain electrode 17b. At the time of this patterning, a rectangular heat dissipation layer 44 having a lead portion 45 covering the contact hole 43 formed at an end is formed.
It is configured to cover. If there is no problem in yield, the heat radiation layer 44 and the wiring 20 may be formed of different metals. The heat radiation layer 44 is formed in a ridge shape so that the surface becomes uneven due to the presence of the square holes 42. Further, a passivation film 21 of a deposited film of SiN or the like is formed so as to cover the whole. The passivation film 21 is provided with an opening 46 for exposing the heat radiation layer 44 to the atmosphere.

According to the above embodiment, the heat radiation layer 44 is formed of Al having a high thermal conductivity (heat conductivity of 240 W / m · K).
Is directly connected to the operation layer 14 by the
The Joule heat generated in Step 4 is transmitted to the heat radiation layer 44 and is radiated to the atmosphere, so that the heat radiation effect can be improved. As a result, the temperature rise of the TFT can be suppressed,
It is possible to prevent characteristic deterioration such as threshold value fluctuation. In addition, since the heat radiation layer 44 can be formed in the same step with the same material as the material of the TFT wiring 20, the discharge layer 44 can be formed without particularly providing a new step, and the manufacturing process can be simplified. Further, since the heat radiation layer 44 is formed in a ridge shape, the surface area in contact with the air can be increased, and the heat radiation efficiency can be improved. In addition, a connection portion 40 in a high-resistance region where no dopant is injected exists between the heat radiation layer 44 and the wiring 20, and the contact resistance is as high as 100 MΩ. Prevents the TFT from affecting the operation of the TFT. Therefore, in the above embodiment, the heat radiation layer 44 is formed for each TFT. However, the heat radiation layer 44 can be shared by a plurality of TFTs, and as a result, the area occupied by the heat radiation layer 44 is reduced. Thus, downsizing can be achieved.

[0031]

According to the thin film transistor of the first aspect,
Since the heat radiation layer is formed in a ridge shape on the side of the TFT,
The surface area that touches the surface can be widened,
Heat can be efficiently dissipated, improving the heat dissipation effect.
Can be

According to the thin film transistor of the second aspect, T
The thermal conductivity of the heat dissipation layer formed on the side of the FT is
Connection to polysilicon thin film through good metal wiring
With this, the heat generated in the operation layer is directly transmitted to the heat dissipation layer.
As a result, the heat radiation effect can be improved.

[0033]

[0034]

Further, since the polysilicon thin film portion where the metal wiring is connected is a high resistance region, it is possible to share the heat dissipation layer in the TFT, it is possible to reduce the area occupied by the heat dissipation layer.

[Brief description of the drawings]

FIGS. 1A to 1F are cross-sectional views illustrating a manufacturing process for explaining a manufacturing process of a poly-Si TFT according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between power consumption by a poly-Si TFT according to an example and a variation width of a threshold voltage VTH.

FIGS. 3A to 3E are cross-sectional views illustrating a manufacturing process for explaining a manufacturing process of a poly-Si TFT according to another embodiment of the present invention.

4 (a) to 4 (d) show poly in the embodiment of FIG.
FIG. 18 is an explanatory plan view of the manufacturing process for explaining the manufacturing process of the -SiTFT;

FIGS. 5A to 5E show a conventional poly-SiTF.
It is a manufacturing process figure for explaining the manufacturing process of T.

[Explanation of symbols]

11: insulating substrate, 12: a-Si film, 13: poly
-Si film, 14: working layer, 15: gate insulating film, 1
6 ... gate electrode 17a ... source electrode 17b ... drain electrode 18 ... interlayer insulating film 19 ... contact hole 20 ... wiring 21 ... passivation film 3
0: heat dissipation layer, 40: connection part, 42: square hole, 43
... contact hole, 44 ... heat dissipation layer, 45 ... lead-out part, 46 ... opening

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-133036 (JP, A) JP-A-3-295267 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 29/786

Claims (2)

(57) [Claims] In a thin film transistor (poly-Si TFT) using a polysilicon thin film formed on an insulating substrate or an insulating film as an operation layer, the thin film is formed in a ridge shape by laminating after forming the TFT at a lateral position of the TFT.
A thin film transistor comprising: a heat dissipation layer . 2. A method according to claim 1, wherein said insulating film is formed on an insulating substrate or an insulating film.
Thin film transistor using polysilicon thin film as working layer
(Poly-Si TFT), formed by laminating after TFT formation at the side position of TFT
A heat radiation layer is provided, and the heat radiation layer is connected to a polysilicon thin film via a metal wiring.
The polysilicon thin film portion to which the metal wiring is connected is highly resistive.
A thin film transistor having a resistance region.