JP2002050768A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device which has proper display properties. SOLUTION: This semiconductor device has a plurality of first gate wirings, a plurality of source wirings which cross the plural first gate wirings, and a plurality of picture elements surrounded with the first wirings and the source wirings. A thin-film transistor provided in each of the plural picture elements includes a first gate electrode, a first insulating film on that first gate electrode, a semiconductor layer on that first insulating film, a second insulating film on that semiconductor layer, and a second gate electrode on the second insulating film. The first gate electrode is an electrode, which is extended from the first gate wiring. The above second gate electrode is electrically connected to the first gate wiring for each plural pixel elements mentioned above. The plural source wirings are provided on the interlayer insulator on the above second gate electrode, and they also cross the plural first gate wirings via only the first insulating film and the above interlayer insulator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulated gate transistor (TFT) formed on an insulating material such as glass or a material obtained by forming an insulating film such as silicon oxide on a silicon wafer and the like. The present invention relates to a manufacturing method, and further relates to a semiconductor device such as an integrated circuit in which a plurality of such TFTs are formed. The TFT according to the present invention is characterized in that an amorphous semiconductor or a crystalline semiconductor such as polycrystal is used as an active layer. The present invention particularly relates to the glass transition point (strain temperature,
(Also referred to as a strain point) is effective for TFTs formed on a glass substrate having a temperature of 750 ° C. or lower, but is also used when provided on an insulating film formed on another high melting point glass substrate or a single crystal semiconductor wafer. it can. The semiconductor device according to the present invention
It is used for a driving circuit such as an active matrix such as a liquid crystal display or an image sensor, or a three-dimensional integrated circuit provided with several integrated circuit layers.

[0002]

2. Description of the Related Art Conventionally, TFs have been used for driving active matrix type liquid crystal display devices and image sensors.
It is widely known to form a T (thin film transistor). In these TFTs, a film-shaped semiconductor deposited by a vapor phase growth method such as a CVD (chemical vapor deposition) method or a sputtering method can be used as it is, or can be thermally annealed.
It is used after annealing treatment such as laser annealing. The semiconductor obtained in this manner is in an amorphous state or a polycrystalline state in many cases.

[0003]

Recently, when a device having a long gate wiring, such as a large-capacity matrix, is manufactured, a signal delay or a pulse distortion is caused by the resistance of the gate wiring. Became a problem. Also,
Since a semiconductor used for an active layer (channel formation region) is usually in a non-single-crystal state, a portion where a gate electrode is not provided (for example, a lower portion in a top gate type,
A channel is formed unintentionally on the upper side of the bottom gate type), which causes a problem that a leak current occurs. Furthermore, especially when an amorphous semiconductor is used,
The high sheet resistance of the source / drain cannot be ignored. The present invention aims to solve one or more of these problems.

[0004]

According to the TFT of the present invention, first (lower) and second (upper) gate electrodes are formed above and below a semiconductor active layer, and between the first gate electrode and the semiconductor layer,
And a first insulating film and a second insulating film (which function as a gate insulating film) are provided between the second active layer and the semiconductor layer, respectively, and the second gate electrode is
An anode oxide film of a material constituting the gate electrode is formed on the upper surface and the side surfaces by the anodic oxidation treatment.

For this reason, the second gate electrode must be made of a material that can be anodized, for example, a metal containing aluminum, titanium, and tantalum as main components.
These metals may be alloys. In the following text, unless otherwise specified, for example, aluminum includes not only pure aluminum but also one containing 10% or less of additives. The same applies to titanium and other metals.

In the present invention, the first gate electrode is the second gate electrode.
Is always kept at the same potential as that of the gate electrode. For that purpose, the first gate electrode needs to have a contact so as to be electrically connected to the second gate electrode, and the first gate electrode is etched by etching the first insulating film and the second insulating film. Extending from the first gate electrode (first gate wiring)
It is also characterized in that a contact hole is formed in the contact hole.
Further, the present invention is characterized in that the first gate wiring and the second gate wiring are formed substantially overlapping. However, there may be a case where the second gate wiring does not exist partially on the first gate wiring, or vice versa. In particular, when the first gate wiring and the second gate wiring overlap with each other, the step becomes large. Therefore, at a place where the first gate wiring and the second gate wiring intersect with a wiring in an upper layer, only one of the two wirings is formed for the purpose of reducing the step. Designing to intersect with the wiring is effective in preventing disconnection at the intersection.

Further, the semiconductor device is characterized by having a source / drain formed in a self-aligned manner using the second gate electrode and the anodic oxide on the side surface thereof as a mask. The source / drain is formed using a method of irradiating accelerated impurity ions such as ion doping, or a method such as thermal diffusion or laser diffusion. In addition, the TFT of the present invention is characterized in that a silicide region is provided by covering the source / drain or by silicidizing a part thereof. In particular, TF using an amorphous semiconductor
In T, since the source / drain is also made of an amorphous material or an equivalent material, the sheet resistance becomes 1
It was extremely high at 0 kΩ / □ or more. However, by providing silicide in this region, the substantial sheet resistance is 1000Ω / □ or less, and under more preferable conditions,
100 Ω / □ or less.

In the present invention, the fact that the second gate electrode is covered with the anodic oxide is important in the silicidation step. That is, silicidation is performed as follows. First, the semiconductor insulating layer is exposed by etching the second insulating film using the second gate electrode covered with the anodic oxide as a mask. Then, a metal film for forming silicide is formed. When silicon is used as the semiconductor, the metal material for forming silicide is a material that can form an ohmic or low ohmic contact close to ohmic with N-type or P-type silicon. It is desired. For example, molybdenum (Mo), tungsten (W), platinum (Pt),
Chromium (Cr), titanium (Ti), cobalt (Co) and the like are suitable. At this stage, the exposed portion of the semiconductor active layer and the metal film are in close contact with each other.

After that, a portion of the semiconductor active layer that is in close contact with the metal film is silicided by thermal annealing or by irradiating a laser or a strong light equivalent thereto. On the other hand, a metal film is formed on the anodic oxide and the insulating film other than the semiconductor layer, but the metal film formed in such a place does not react with these materials. Finally, the unreacted metal film is removed. In the above steps, if the second gate electrode is not covered with the anodic oxide, the metal film formed for silicidation reacts with the gate electrode material, and the metal film is removed. It is highly possible that the gate electrode is also etched in the step of performing this, which is not preferable. Thus, the anodic oxide prevents the metal film from reacting with the gate electrode,
In addition, it functions as an etching stopper.

The anodic oxide also serves to prevent a short circuit between the silicide on the source / drain and the gate electrode. That is, the silicide is provided on substantially the entire surface of the source / drain, and consequently comes close to the gate electrode. Although the source / drain and the gate electrode are separated by the gate insulating film, silicide may be formed once after removing the gate insulating film on the source / drain during the process, so that silicide may come into contact with the gate electrode. Is significantly larger. However,
If the anodic oxide is present on the side surface of the gate electrode, it is possible to prevent the contact between the silicide and the gate electrode, and the anodic oxide can be very dense and have good insulating properties. The probability of a short circuit can be significantly reduced.

A typical process for obtaining the TFT or integrated circuit of the present invention is as follows. First, a first gate wiring is formed on an insulating surface. As a material for the first gate wiring, a heat-resistant material such as silicon, molybdenum, or tungsten is preferable, but another material may be used. Further, the surface may be covered with an anodic oxide.

Second, the first gate wiring is
The first insulating film is formed. This insulating film is the first gate electrode
Function as a gate insulating film. As a semiconductor
When using silicon, for example, silicon nitride or silicon oxide
Silicon, silicon oxynitride (SiO_xN _y) May be used.
Further, it may be a single layer or a multilayer. Third, the first insulating film
An island-shaped semiconductor layer is formed thereon. Even if the semiconductor layer is amorphous
It may be crystalline. Also, only a specific part on the substrate is crystallized.
Semiconductor and the other parts are amorphous semiconductors
Also use local annealing means such as laser annealing
Can be implemented.

Fourth, a second insulating film is formed on the semiconductor layer. This insulating film functions as a gate insulating film for the second gate electrode. When silicon is used as the semiconductor, for example, silicon nitride, silicon oxide, silicon oxynitride (SiO _x N _y ), or the like may be used. Further, it may be a single layer or a multilayer. Fifth, the first and second insulating films are etched to form contact holes for the first gate wiring. Although the frequency of the contact holes varies depending on the type of the integrated circuit, it is desirable to configure one TFT in a ratio of one to two.

Sixth, a second gate wiring is formed on the second insulating film and covering the contact hole.
The second gate line is substantially parallel to the first gate line and preferably has the same shape. In some cases, a second wiring is not provided in a portion that intersects a third wiring to reduce a step. Seventh, an anodic oxide layer is formed on the side and top surfaces of the gate wiring by applying a current to the second gate wiring in an electrolytic solution. At least one type of anodic oxide formed in this step is preferably a so-called barrier type anodic oxide. The barrier type anodic oxide is obtained by anodic oxidation in a substantially neutral electrolytic solution, and is characterized in that the applied voltage increases as the anodic oxide grows. The barrier type anodic oxide has a high withstand voltage and a dense film quality.

Eighth, N-type or P-type impurities are introduced into the semiconductor layer in a self-aligning manner using the second gate wiring and the anodic oxide layer on the side surface thereof as a mask. Prior to the impurity introduction, the semiconductor layer may be exposed by etching the second insulating film, or by means of ion doping or the like, through the second insulating film.
It is also possible to implant impurities. When ion doping or the like is used, it is necessary to activate impurities by annealing such as thermal annealing or laser annealing. The above-described silicidation may be performed before or after the impurity implantation. Ninth, a third wiring connected to at least one of the source / drain or the silicide formed in the semiconductor layer is formed.

[0016]

According to the present invention, the gate wiring can be formed in two layers. For this reason, the resistance of the entire gate wiring can be reduced as compared with the case where the gate wiring is a single layer. That is, in the related art, since the gate wiring has a single layer, it is required to increase the thickness of the gate wiring in order to reduce the resistance of the gate wiring.
For example, the thickness of the conventional normal gate wiring is 3000 to 5
However, in the case of a large-capacity matrix, it was necessary to lower the resistance of the gate wiring, and it was necessary to double the thickness.

However, when the thickness of the single-layer gate wiring is increased, the step is increased, and it is difficult to sufficiently cover the gate electrode and the wiring with the insulating film formed thereon. In particular, when the insulating film is formed by a CVD method at a substrate temperature of less than 420 ° C., for example, a plasma CVD method, the coverage is rapidly deteriorated at a step of 5,000 °, causing a short circuit between layers and the like. . In the present invention, although the thickness of the gate wiring vertically combined is sufficiently large, the above-described problem does not occur because the insulating film is sufficiently covered with each gate wiring.

Furthermore, conventionally, 1
If there is a disconnection in any place, the row becomes a line defect, and all the elements in the row are wasted. However, in the present invention, the upper and lower two layers of gate wiring form contacts at appropriate intervals. As a result, there was no reduction in yield due to disconnection of the gate wiring. Further, in the present invention, since the gate electrodes exist above and below the active layer, an unintentional channel is not formed in the active layer on the opposite side of the gate electrode, and a reduction in leakage current is achieved. In this regard, the present invention is particularly preferable when the crystallinity of the semiconductor active layer is different between the upper side and the lower side. In the case of a crystalline silicon semiconductor, it is generally known that the crystal grows from below, and the interface characteristics between the lower crystalline silicon and the insulating film are compared with those of the upper crystalline silicon and the insulating film. Excellent. Therefore, in such a case, it is preferable that the gate electrode exists below.

Further, in the present invention, when a silicide region is provided adjacent to the source / drain, there is an effect in reducing the sheet resistance. In the present invention, in particular, in a device to which light is irradiated from the outside, for example, an apparatus such as a liquid crystal display or an image sensor, the TFT may be irradiated with light. In this case, with respect to the light emitted from the direction of the gate electrode toward the active layer, the gate electrode is less likely to affect the characteristics as a shadow, but the light emitted from the side where the gate electrode does not exist. However, there is a problem in that a photocurrent is generated and the characteristics of the TFT are significantly reduced. In addition, light generally does not enter from only one direction, and it is impossible to control even a small amount of light due to scattering or the like. To solve this problem, a method of forming a light-shielding film on the opposite side of the gate electrode is generally used. However, in the present invention, the gate electrodes exist above and below the active layer, and this serves as a light-shielding film to form the active layer. This has the effect that light that enters can be suppressed.

In the present invention, the thickness and dielectric constant of the first gate insulating film and the thickness and dielectric constant of the second gate insulating film are adjusted so that the dominant gate electrode of the TFT becomes the first gate electrode. It is also possible to use any one of the gate electrode and the second gate electrode. That is, the first gate insulating film and the second gate insulating film are formed of an insulator of the same material, and
When the first insulating film is thinner than the second gate insulating film,
The TFT operates with the first gate electrode at the center. In the opposite case, the second gate electrode becomes dominant. Which of the first gate electrode and the second gate electrode is dominant is more preferably the interface between the active layer and the first insulating film or the interface between the active layer and the second insulating film. The selection may be made in consideration of the above.

There are several variations of the integrated circuit using the present invention. Considering, as an integrated circuit, a monolithic active matrix circuit (peripheral circuit integrated type active matrix circuit) having one type of circuit, roughly divided into an active matrix circuit and a peripheral logic circuit for driving the active matrix circuit, The circuit has a structure using a top gate TFT, and the active matrix circuit has a structure using the TFT of the present invention. In this case, the leakage current of the TFT in the matrix circuit can be reduced, and the source / drain can be formed in a self-aligned manner in the peripheral circuit, so that the parasitic capacitance is reduced. Second, the peripheral circuit is made of a crystalline semiconductor, and the active matrix circuit is made of an amorphous semiconductor. Generally, T using a crystalline semiconductor
The FT has a feature that the operation speed is fast and a TFT using an amorphous semiconductor has a small leak current, and is suitable for a peripheral circuit and an active matrix circuit, respectively.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 Embodiment 1 is shown in FIGS. 1, 2 and 4. FIG. This embodiment describes a manufacturing process and a structure of a monolithic active matrix circuit. The monolithic type active matrix circuit has a block configuration as shown in FIG. 6 and includes an active matrix circuit area 604 on one substrate 601.
And a data driver circuit 60 surrounding the
2, 604 and a scan driver circuit 603 are provided. With respect to the number of data driver circuits and scan driver circuits, various variations other than those shown in FIG. 6 are possible. Data driver circuits, scan driver circuits, and other auxiliary driving circuits are collectively called peripheral circuits. In a peripheral circuit, a complementary MOS circuit is formed using a P-channel TFT and an N-channel TFT, and FIG. 2 shows a process of manufacturing an inverter circuit using the complementary MOS circuit.

FIG. 1 shows an active matrix circuit portion.
FIG. 2 is a cross-sectional view of a typical portion of the peripheral circuit portion, which shows the order of steps in FIGS. 1 and 2 (A), (B),
(C),. . . Correspond to each other, and the same reference numerals in FIGS. 1, 2 and 4 indicate the same components. FIG. 4A shows a state in which the completed matrix circuit is viewed from above, and FIG. 1 shows a cross section taken along the line ABC of FIG. 4A. FIG. 4B is a view similar to FIG.
2 shows an ab cross section of FIG. FIG. 4C is a circuit diagram of an active matrix circuit manufactured in this embodiment. Hereinafter, a manufacturing process of this embodiment will be described with reference to FIGS.

First, a substrate (Corning 7059, 100 m) on which a silicon nitride film (not shown) having a thickness of 1000 ° is formed.
First gate wirings / electrodes 102, 103, 104, and 105 were formed on an insulating surface 101 (mx100 mm).
The gate wiring / electrode was formed by etching a polycrystalline silicon film of which resistance was reduced by doping with phosphorous having a thickness of 3000 °. Polycrystalline silicon film is decompressed C
It was formed by the VD method. In this case, the film was in a polycrystalline state after being formed. In order to obtain a polycrystalline silicon film, in addition to the above method, an intrinsic amorphous silicon film is formed by a plasma CVD method or a low pressure CVD method, and impurities such as phosphorus are introduced into the film by an ion doping method or the like. Further, this may be thermally annealed at 500 to 600 ° C. At the time of thermal annealing, a trace element such as nickel which promotes crystallization may be added.

Although silicon is used in this embodiment, metal silicide may be used instead. Thereafter, a thickness of 3000 to 6000 °, for example, 4000
A silicon nitride film 106 was deposited. This also functions as a gate insulating film. And a thickness of 300 to 1000 mm,
For example, a 500 ° amorphous silicon film is formed by plasma CVD.
Formed by the method. And etch this,
The island-shaped regions 107, 108, and 109 were formed. (Figure 1
(A), FIG. 2 (A)) Further, a silicon nitride film 110 having a thickness of 3000 to 6000 Å, for example, 2000 Å was deposited by a plasma CVD method. This also functions as a gate insulating film. In this state, only the peripheral circuit was irradiated with laser light to crystallize the island-shaped silicon film. Laser is XeCl excimer laser (wavelength 308n)
m) was used. The laser irradiation energy density and the number of pulses were adjusted depending on the film quality of the silicon film and the silicon nitride film 110.

Thereafter, although not shown in the figure, the silicon nitride films 110 and 106 were etched to form a contact hole reaching the first gate wiring. This contact hole is formed between the first gate wiring and the second gate wiring formed thereon.
4A, and corresponds to the contact 145 in FIGS. 4A and 4B. After forming the contact hole,
An aluminum film 111 having a thickness of 3000 to 8000 Å, for example, 5000 Å was formed by a sputtering method. When scandium (Sc) was contained in the aluminum film in an amount of 0.1 to 0.5% by weight, it was effective in suppressing the generation of hillocks. (FIG. 1 (B), FIG. 2 (B))

Next, the aluminum film is etched,
Second gate wiring / electrodes 112, 113, 114, 11
5 was formed. As a result, a contact between the first gate wiring and the second gate wiring was formed through the previously formed contact hole. In this case, it is necessary to design the second gate wiring so that the contact hole is completely covered. This is because if the first gate wiring made of silicon is exposed in the contact hole, a current leaks through the exposed portion in the subsequent anodic oxidation step, and the anodic oxidation reaction does not proceed. It is. (FIG. 1 (C), FIG. 2 (C))

Next, a current was applied to the gate electrode in the electrolytic solution. At that time, an ethylene glycol solution adjusted to pH = 6.8 to 7.2 by adding ammonia to tartaric acid of 3 to 10% was used. A better oxide film was obtained when the temperature of the solution was lower than room temperature around 10 ° C. For this reason, barrier-type anodic oxides 116, 117, 118, and 119 were formed on the upper surface and side surfaces of the second gate wiring / electrode. The thickness of the anodic oxide was proportional to the applied voltage, and an applied voltage of 150 V formed an anodic oxide of 2000 °.
The thickness of the anodic oxide was preferably 1000-3000３. 25 to obtain anodic oxide over 3000 mm thick
A high voltage of 0 V or more is required, which adversely affects the characteristics of the TFT, which is not preferable. (FIG. 1 (D), FIG. 2
(D))

Thereafter, the silicon nitride film 110 was etched by a dry etching method. At this time, since the anodic oxide is not etched, the silicon nitride film 110 is etched in a self-aligned manner, and the gate insulating films 120, 121, 122,
123 were left. (FIG. 1 (E), FIG. 2 (E))

Next, an island shape is formed by ion doping.
A gate electrode portion is formed on the silicon layers 107, 108, and 109.
(That is, the gate electrode and its surrounding anodic oxide film)
N-type and P-type impurities are implanted in a self-aligned manner
And an N-type impurity region (source / drain region) 124,
125, 126, 127, P-type impurity regions 128, 12
9 was formed. As a doping gas, an N-type impurity
Doping with phosphine (PH_Three) Is a P-type impurity
Doping of diborane (B_TwoH₆), Respectively
It was used as a grouping gas. The dose is 5 × 10¹⁴~ 5
× 10^FifteenAtom / cm ^Two, Acceleration energy is 10-30k
eV. Then, a KrF excimer laser (wavelength
248 nm, pulse width 20 nsec) to activate
Activation of impurity ions introduced into the layer was performed.
(FIG. 1 (F), FIG. 2 (F))

Thereafter, an appropriate metal, for example, a titanium film 130 having a thickness of 50 to 500.degree. (FIG. 1 (G), FIG. 2 (G)) and 450
Titanium and silicon are reacted by thermal annealing at ℃ 550 ° C., for example, at 500 ° C. for 10-60 minutes,
Silicide (titanium silicide) regions 131, 132, 13
3, 134, 135 and 136 were formed. Further activation of the doped impurities during this thermal anneal was also performed. Instead of silicidation by thermal annealing, irradiation by laser light or lamp annealing by irradiation with visible light or near-infrared light may be used.

Thereafter, the Ti film was etched with an etching solution in which hydrogen peroxide, ammonia and water were mixed at a ratio of 5: 2: 2. Since the titanium film (for example, the titanium film existing on the silicon nitride film 106 or the anodic oxide film) other than the portion in contact with the exposed active layer remains in a metal state as it is, it can be removed by this etching. On the other hand, since titanium silicide is not etched, it can be left. (Figure 1
(H), FIG. 2 (H))

Further, a silicon oxide film having a thickness of 5000 .ANG. Was formed on the entire surface as a first interlayer insulator 137 by a CVD method. Then, contact holes were formed in the source / drain of the TFT. After forming the first interlayer insulator, 400
Annealed at 10 ° C. for 10 to 30 minutes. Thereafter, aluminum wiring / electrodes 138, 139, 140, 141 were formed. Further, the pixel electrode 142 was also formed by the ITO film. Finally, a thickness of 2000 to 5000 mm, for example, to prevent moisture and mobile ions from the outside from entering the TFT, for example,
A 3000 nm silicon nitride film 143 was formed by a plasma CVD method, a pixel portion 144 was opened, and the ITO film was exposed. (FIG. 1 (I), FIG. 2 (I))

As described above, the wiring intersection 147 in the active matrix circuit and the TFT 14 connected to the pixel
8. The N-channel TFT 149 and the P-channel TFT 150 of the peripheral circuit were completed, and the monolithic active matrix circuit was completed. FIG. 4A is a diagram of a TFT provided in a pixel portion according to the present embodiment as viewed from above. Although the gate line extending from the scan driver looks like a single line in the figure, in actuality, the first gate line 102 is provided below and parallel to the second gate line 112.
Is provided. The first gate line and the second gate line are connected at a contact 145. In the active matrix circuit of this embodiment,
One contact was provided for each TFT.

For this reason, even if there is a disconnection in any of the upper and lower gate wirings, the entire row is not defective. In particular, in this embodiment, as shown in FIG.
Although a contact is provided at a portion where the gate line branches, when providing a pad region (a region with a large wiring width) for forming a contact, a special space is not required at the portion, and a layout is improved. This is because it is advantageous. FIG. 4B shows a cross-sectional structure taken along line ab of FIG. 4A along the gate line. FIG. 4C is a circuit diagram of a matrix in which a plurality of circuits in FIG. 4A are arranged.
In FIG. 4A, the gate line 112 (and 102)
Is also divided into a wiring 146 extending below the pixel electrode in the upper row. This wiring 146 forms a capacitance between the pixel electrode and the wiring 146, and the wiring is formed in parallel with the liquid crystal capacitance formed by the pixel electrode. Exists.

Embodiment 2 FIGS. 3 and 5 show this embodiment. This embodiment describes a manufacturing process and a structure of an active matrix circuit. Although the present embodiment relates to a method for manufacturing an active matrix circuit, the same process is applied to a peripheral circuit when a monolithic type active matrix circuit is manufactured. FIG. 3 is a sectional view of the active matrix circuit. 3 and 5 indicate the same items. FIG. 5A shows the completed matrix circuit viewed from above, and FIG. 2 shows the ABC circuit of FIG. 5A.
2 shows a cross section of FIG. FIG. 5B is a view similar to FIG.
2A shows a cross section taken along ab. FIG. 5C is a circuit diagram of an active matrix circuit manufactured in this embodiment. Hereinafter, a manufacturing process of this embodiment will be described with reference to FIGS.

First, a substrate (Corning 7059, 100 m) on which a silicon nitride film (not shown) having a thickness of 1000 ° is formed.
First gate wirings / electrodes 202 and 203 were formed on an insulating surface 201 (mx100 mm). The gate wiring / electrode was formed by forming a 3000 nm thick tungsten film by a sputtering method and etching the tungsten film. In addition to tungsten, a heat-resistant metal such as molybdenum or titanium may be used.

Thereafter, a thickness of 3
A silicon nitride film 204 having a thickness of 000 to 6000Å, for example, 4000Å is deposited. This also functions as a gate insulating film. And a thickness of 300 to 1000 mm, for example, 800
The amorphous silicon film of Å was formed by the plasma CVD method. And a small amount of nickel is added to this,
It was crystallized by annealing at 580 ° C., for example, 550 ° C. Further, the silicon film was irradiated with laser light to improve the crystallinity of the silicon film. Laser is XeCl
An excimer laser (wavelength 308 nm) was used. The laser irradiation energy density and the number of pulses were adjusted according to the quality of the silicon film. And etch this,
An island-like region 205 was formed. (FIG. 3 (A))

Further, a thickness of 3
A silicon oxide film 206 having a thickness of 2,000 to 6000 °, for example, 1000 ° is deposited. This also functions as a gate insulating film. Thereafter, although not shown in the figure, the silicon nitride film 204
Then, the silicon oxide film 206 was etched to form a contact hole reaching the first gate wiring. This contact hole corresponds to the contacts 223 and 224 in FIGS. 5A and 5B. After forming the contact hole, the thickness of 3000 to
8000 °, eg, 5000 ° aluminum film 20
7 was formed. (FIG. 3B) Next, the aluminum film is etched to form second gate wirings / electrodes 208 and 22.
1, 222 were formed. In this embodiment, a portion on which a source line 216 extending from the driver is formed is shown in FIG.
The second gate wiring was not formed on the first gate wiring 202 in (C). (See FIG. 3C, and FIG. 5A for the gate wirings 221 and 222.)

As a result, a contact between the first gate wiring and the second gate wiring was formed through the contact holes 223 and 224 formed earlier. In this embodiment,
As described above, since the second gate wiring is not provided in a portion where the source line 216 exists, two contact holes are provided with the source line interposed therebetween.
Two contacts were formed for one FT. (FIG. 3 (C)) Next, in the electrolytic solution, a current is applied to the gate electrode, and anodic oxidation is performed in the same manner as in the first embodiment. An anodic oxide 209 was formed. The thickness of the anodic oxide was 1500 °. (FIG. 3 (D))

Thereafter, the silicon oxide film 206 was etched by a wet etching method. As an etchant, a mixed solution of hydrofluoric acid, ammonium fluoride and acetic acid was used. This etchant is a silicon oxide film, especially plasma C
The etching rate is large for a silicon oxide film formed by the VD method, and sufficiently small for aluminum oxide, silicon, and silicon nitride. Therefore, only the silicon oxide film 206 could be selectively etched in a self-aligned manner using the gate electrode portion (that is, the gate electrode and the anodic oxide film around the gate electrode) as a mask. The gate insulating film 210 was left between the gate wiring / electrode and the island-shaped silicon layer. (FIG. 3 (E))

Next, P-type impurities are implanted into the island-shaped silicon layer 205 in a self-aligned manner by using the gate electrode portion as a mask by ion doping.
1, 212 were formed. Dose amount is 1 × 10 ^{14 to} 5 × 1
0 ¹⁵ atoms / cm ² , acceleration energy 10-30 keV
And For example, if the dose is 2 × 10 ¹⁴ atoms / cm ² ,
The acceleration voltage was set to 20 kV. Thereafter, irradiation with a KrF excimer laser (wavelength: 248 nm, pulse width: 20 nsec) was performed to activate the impurity ions introduced into the active layer. (FIG. 3 (F))

Thereafter, a titanium film 213 having a thickness of 50 to 500 ° was formed on the entire surface by a sputtering method. (FIG. 3
(G)) and 450-550 ° C., for example, 500 ° C.
For 10 to 60 minutes, the titanium and silicon were reacted to form silicide (titanium silicide) regions 214 and 215. Thereafter, the unreacted Ti film was etched with an etching solution in which hydrogen peroxide, ammonia, and water were mixed at a ratio of 5: 2: 2. (FIG. 3 (H),)

Thereafter, an aluminum wiring / electrode 216 serving as a source line was formed. That is, in the present embodiment, since the second gate wiring does not exist at the intersection of the source line and the gate line, the first insulating film (thickness 4000)
(珪 素 silicon nitride) 204 can be used as an interlayer insulator, and the number of film forming steps can be reduced as compared with the case of Example 1. Further, the thickness is set to 2000 to 5000 so that moisture and mobile ions from the outside do not enter the TFT.
A silicon nitride film 217 having a thickness of, for example, 3000 is formed by a plasma CVD method. Finally, a pixel electrode 218 was formed using an ITO film. (FIG. 3 (I))

As described above, the wiring intersection 226 in the active matrix circuit and the TFT 22 connected to the pixel
7 is completed. FIG. 5A is a diagram of the TFT provided in the pixel portion according to the present embodiment as viewed from above. The gate line extending from the scan driver is the first gate line 2
02 and second gate lines 221 and 222. However, the part 2 where the source line and the gate line intersect
In 26, no second gate line is provided. The first gate line and the second gate line are connected to a contact 223,
At 224, it is connected. In the active matrix circuit of this embodiment, two contacts are provided for one TFT.

If the second gate wiring is not provided at the portion where the source line and the gate line intersect as in this embodiment, it is obvious from FIG. 3I that the step in the optical sub is reduced. Can be smaller. Therefore, the probability of disconnection of the source line is reduced, which contributes to an improvement in yield. FIG. 5B shows a cross-sectional structure taken along line ab of FIG. 5A along the gate line. FIG. 5C is a circuit diagram of a matrix in which a plurality of circuits in FIG. 5A are arranged. FIG.
In (A), a gate line 222 (and 202) is separated into a wiring 225 extending below a pixel electrode in an upper row, and forms a capacitor between the gate line 222 and the pixel electrode.

Embodiment 3 This embodiment is shown in FIG. FIG. 7A shows a portion of the active matrix circuit centering on a transistor, and FIG. 7B shows a peripheral circuit portion. In this embodiment, in the active matrix circuit, the TFT has a structure having the upper and lower gate electrodes of the present invention, whereas in the peripheral circuit, a top gate type TFT is used.
FT. In order to obtain such a structure, in the present embodiment, the first gate wiring is provided only in the active matrix region. Hereinafter, the drawings will be described.

In the active matrix circuit area, first gate electrodes / wirings 301 and 302 are formed. Except for the portion where the first gate wiring 301 intersects with the third wiring 307 as in the second embodiment, A second gate line / electrode 303 coated with anodic oxide was provided. In the present embodiment, the first gate insulating film (the first gate electrode 3
02 and an active layer) and a second gate insulating film (an insulating film between the second gate electrode 303 and the active layer) are both made of silicon oxide. The thickness was 1800 °. Therefore, in the active matrix circuit, the influence of the first gate electrode 302 was large. The structures of the source / drain and the silicide of the TFT were the same as those of the other embodiments. (FIG. 7A) On the other hand, in the peripheral circuit region, the first gate electrode / wire was not provided, and only the second gate wire / electrode 304, 305 covered with anodic oxide was provided. As described above, the thicknesses of the first and second gate insulating films were different from each other, but the effect could not be observed because the first gate electrode did not exist in the peripheral circuit. (FIG. 7
(B))

A first interlayer insulator 306 was formed of a 2000-nm-thick silicon nitride film so as to cover the second gate wirings / electrodes 303-305. Then, a contact hole was formed in the first interlayer insulator 306. At this time, in the TFT of the active matrix circuit, a contact hole was formed not only in the one connected to the source line (third wiring) 307 but also in the one connected to the pixel electrode 312. After that, third wirings 307 to 310 were formed.
As the wiring material, a multilayer film of titanium (thickness 500 °) and aluminum (thickness 4000 °) was used. Aluminum contained 1% silicon. (FIG. 7
(A), FIG. 7 (B))

Further, the second interlayer insulator 311 has a thickness of 3
Formed by silicon oxide of 000 °. Then, in the active matrix circuit, a contact hole was formed in a portion where a contact between the pixel electrode and the TFT was formed. This contact hole was formed inside the contact hole previously provided. Finally, the pixel electrode 3
12 were provided. (FIG. 7B) As described above, the TFT of the active matrix circuit
316, wiring intersection 315, N-channel type T of peripheral circuit
The FT 313 and the P-channel TFT 314 are completed.

Embodiment 4 This embodiment is shown in FIG. FIG. 8A shows a portion of the active matrix circuit centering on a transistor, and FIG. 8B shows a peripheral circuit portion. In the present embodiment, as in the third embodiment, the top gate type TFT is used in the peripheral circuit, but the first gate wiring is also left in the peripheral circuit region, and the wiring intersection is the first wiring and the third wiring. Are crossed. Hereinafter, the drawings will be described. In the active matrix circuit area, the first
Gate electrodes / wirings 401 and 402 are formed, and the first gate wiring 401 is replaced with the third wiring 407 as in the second embodiment.
Except for the part that intersects with
Gate wiring / electrode 404 was provided. In this embodiment, the first gate insulating film (the insulating film between the first gate electrode 402 and the active layer) is a silicon nitride film, and the second gate insulating film (the second gate electrode 404 and the active layer The insulating film between them is made of a silicon oxide film, and the thickness of the former is 4000
Å, the thickness of the latter was 1200１. Considering the dielectric constant, the contributions of the first gate electrode and the second gate electrode were almost the same. The structures of the source / drain and the silicide of the TFT were the same as those of the other embodiments. (FIG. 8A)

On the other hand, in the peripheral circuit region, the first gate electrode was not provided in the TFT portion.
The first gate wiring 403 is provided in other portions. Then, the second gate wiring / electrodes 405 and 406 covered with the anodic oxide were provided in the TFT portion.
No second gate wiring was provided at the portion where the third wiring 409 intersected with the third wiring. This is similar to Example 2
This is for reducing the level difference of the wiring in the same manner as described above. (FIG. 8
(B)) Then, third wirings 407 to 410 were formed thereon. At this time, in the active matrix circuit and the peripheral circuit, the first gate wirings 401 and 403 and the third wirings 408 and 409 are separated from each other by a first gate insulating film formed over the first gate wiring. (FIG. 8
(A), FIG. 8 (B))

Thereafter, the interlayer insulator 411 is formed to a thickness of 3000.
Å was formed by silicon nitride. In the active matrix circuit, a contact hole was formed in a portion where a contact between the pixel electrode and the TFT was formed, and the pixel electrode 412 was provided. (FIG. 8B) As described above, the TFT of the active matrix circuit
414, wiring intersection 413, N-channel type T of peripheral circuit
FT415 and P-channel type TFT416 were completed.

[0054]

The effects obtained by the present invention are summarized as follows. First, the resistance of the gate wiring can be reduced by forming the gate wiring in a two-layer structure. Second, by forming the gate wiring into a two-layer structure,
Defects due to disconnection of the gate wiring could be reduced. Third, by providing a silicide region adjacent to the source / drain, the sheet resistance of the TFT could be reduced to 1 kΩ / □ or less or 0.1 kΩ / □ or less.

In addition, in the third embodiment, FIG.
As shown in FIG. 1A, a plurality of source wirings and a plurality of first gate wirings provided in an active matrix circuit intersect with a first gate insulating film and an interlayer insulator interposed therebetween. Since the capacitance formed at the intersecting portion is smaller as the thickness of the dielectric is larger, FIG.
When such a structure is adopted, it is a well-known effect that the parasitic capacitance at the intersection can be reduced.

It can be said that the TFT of the present invention is formed in the same manner when a three-dimensional integrated circuit is formed on a substrate on which a semiconductor integrated circuit is formed, or when formed on glass or an organic resin. In any case, it is characterized in that it is formed on an insulating surface. In particular, the effect of the present invention is remarkable for an electro-optical device such as a monolithic active matrix circuit having peripheral circuits on the same substrate. As described above, the present invention is industrially useful.

[Brief description of the drawings]

FIG. 1 shows a method for manufacturing a TFT according to Example 1.

FIG. 2 shows a method for manufacturing a TFT according to Example 1.

FIG. 3 shows a method for manufacturing a TFT according to Example 2.

FIG. 4 shows a structure of a TFT circuit manufactured according to the first embodiment.

FIG. 5 shows a structure of a TFT circuit manufactured according to the first embodiment.

FIG. 6 shows a block diagram of a monolithic type active matrix circuit.

FIG. 7 shows a structure of a TFT circuit manufactured in Example 3.

FIG. 8 shows a structure of a TFT circuit manufactured in Example 4.

[Explanation of symbols]

Reference Signs List 101 Insulating surface 102 to 105 First gate wiring / electrode (polycrystalline silicon) 106 First insulating film (silicon nitride) 107 to 109 Active layer (silicon) 110 Second insulating film (silicon nitride) 111 Metal film ( Aluminum) 112-115 Second gate wiring / electrode (Aluminum) 116-119 Anodized oxide (Aluminum oxide) 120-123 Gate insulating film 124-129 N-type or P-type impurity region 130 Metal film (Titanium) 131-136 Silicide region (titanium silicide) 137 First interlayer insulator (silicon oxide) 138 to 141 Metal wiring (aluminum) 142 Pixel electrode (ITO) 143 Second interlayer insulator (silicon nitride) 144 Pixel aperture 145 First And contact part of second gate wiring 146 auxiliary capacitance-like wiring 147 source line P-channel type TFT of the N-channel type TFT 0.99 peripheral circuit TFT 149 peripheral circuits provided at intersections 148 pixel electrode of the gate lines

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) H01L 21/336 H01L 29/78 617S 29/41 616S 29/43 29/44 Z 29/46 L 29/78 616A F-term (Reference) 2H092 GA59 JA01 JA25 JA26 JA29 JA33 JA38 JA39 JA42 JA43 JA47 KA04 KA05 KA07 MA05 MA08 MA12 MA24 MA28 MA35 MA37 NA01 4M104 AA09 BB02 BB14 BB16 BB17 BB18 BB25 CC01 CC05 DD37 DD18 CB16 BA16 FF16 BA18 BB16 EA04 EA07 EB05 5F110 AA03 AA26 BB02 BB04 CC02 CC08 DD01 DD02 DD05 DD07 DD14 EE03 EE04 EE05 EE06 EE08 EE09 EE30 EE34 EE44 EE45 FF02 FF03 FF04 FF09 FF24 FF30 GG02 J04 H25 GG13 H04 GG13 NN03 NN04 NN23 NN24 NN35 NN40 NN44 NN46 NN47 NN72 NN73 NN78 PP01 PP03 PP04 PP10 PP29 PP34 QQ11

Claims (18)

[Claims] A plurality of first gate lines, a plurality of source lines intersecting with the plurality of first gate lines, and a plurality of pixels surrounded by the plurality of source lines and the plurality of gate lines. And a semiconductor device including a thin film transistor and a pixel electrode connected to the thin film transistor in each of the plurality of pixels, wherein the thin film transistor includes a first gate electrode, a first insulating layer on the first gate electrode. A film, a semiconductor layer on the first insulating film, a second insulating film on the semiconductor layer, and a second gate electrode on the second insulating film, wherein the first gate electrode is An electrode extending from one of the plurality of gate lines, the second gate electrode being electrically connected to the first gate line for each of the plurality of pixels, and the plurality of source lines being connected to the second gate line. Interlayer insulation on gate electrode A semiconductor device provided on an object and intersecting with the plurality of first gate wirings only through the first insulating film and the interlayer insulator. A plurality of first gate lines, a plurality of source lines intersecting with the plurality of first gate lines, and a plurality of pixels surrounded by the plurality of source lines and the plurality of gate lines. And a semiconductor device including a thin film transistor and a pixel electrode connected to the thin film transistor in each of the plurality of pixels, wherein the thin film transistor has a first gate electrode, a first insulating film on the first gate electrode. A film, a semiconductor layer on the first insulating film, a second insulating film on the semiconductor layer, and a second gate electrode on the second insulating film, wherein the first gate electrode is An electrode extending from the first gate line, wherein the second gate electrode is electrically connected to the first gate line for each of the plurality of pixels, and a film thickness of the first insulating film is: Thinner than the thickness of the second insulating film The plurality of source lines are provided on an interlayer insulator on the second gate electrode, and the plurality of first gate lines are provided only via the first insulating film and the interlayer insulator. And a semiconductor device intersecting with the semiconductor device. 3. A semiconductor device comprising: a plurality of first gate wirings; a plurality of source wirings intersecting with the plurality of first gate wirings; and a plurality of pixels surrounded by the plurality of source wirings and the plurality of gate wirings. And a semiconductor device including a thin film transistor and a pixel electrode connected to the thin film transistor in each of the plurality of pixels, wherein the thin film transistor has a first gate electrode, a first insulating film on the first gate electrode. A film, a semiconductor layer on the first insulating film, a second insulating film on the semiconductor layer, and a second gate electrode on the second insulating film, wherein the first gate electrode is An electrode extending from the first gate line, the second gate electrode is electrically connected to the first gate line for each of the plurality of pixels, and the first insulating film has a thickness of: Thinner than the thickness of the second insulating film And the first insulating film and the second insulating film have different dielectric constants, and the plurality of source wirings are provided on an interlayer insulator on the second gate electrode; A semiconductor device intersecting the plurality of first gate wirings via only one insulating film and the interlayer insulator. 4. A semiconductor device comprising: a plurality of first gate wirings; a plurality of source wirings intersecting the plurality of first gate wirings; and a plurality of pixels surrounded by the plurality of source wirings and the plurality of gate wirings. And a semiconductor device including a thin film transistor and a pixel electrode connected to the thin film transistor in each of the plurality of pixels, wherein the thin film transistor has a first gate electrode, a first insulating film on the first gate electrode. A film, a semiconductor layer on the first insulating film, a second insulating film on the semiconductor layer, and a second gate electrode on the second insulating film, wherein the semiconductor layer has a channel formation region, A second impurity region including a first impurity region in contact with a channel formation region and a second impurity region in contact with the first impurity region, wherein the second impurity region has a lower resistance value than the first impurity region; First gate power The pole is an electrode extended from the first gate wiring, and overlaps the first impurity region via the first insulating film. The second gate electrode is connected to the plurality of pixels. The plurality of source lines are provided on an interlayer insulator on the second gate electrode, and are electrically connected to the first gate line. A semiconductor device intersecting with the plurality of first gate wirings only through an insulator. 5. A semiconductor device comprising: a plurality of first gate wirings; a plurality of source wirings intersecting with the plurality of first gate wirings; and a plurality of pixels surrounded by the plurality of source wirings and the plurality of gate wirings. And a semiconductor device including a thin film transistor and a pixel electrode connected to the thin film transistor in each of the plurality of pixels, wherein the thin film transistor has a first gate electrode, a first insulating film on the first gate electrode. A film, a semiconductor layer on the first insulating film, a second insulating film on the semiconductor layer, and a second gate electrode on the second insulating film, wherein the semiconductor layer has a channel formation region, A second impurity region including a first impurity region in contact with the channel formation region and a second impurity region in contact with the first impurity region, wherein the second impurity region has a lower resistance value than the first impurity region; First gate power The pole is an electrode extended from the first gate wiring, and overlaps the first impurity region via the first insulating film. The second gate electrode is connected to the plurality of pixels. The first insulating film is electrically connected to the first gate wiring, the first insulating film is thinner than the second insulating film, and the plurality of source wirings are connected to the second gate. A semiconductor device which is provided on an interlayer insulator on an electrode and intersects with the plurality of first gate wirings only via the first insulating film and the interlayer insulator. 6. A semiconductor device comprising: a plurality of first gate wirings; a plurality of source wirings intersecting the plurality of first gate wirings; and a plurality of pixels surrounded by the plurality of source wirings and the plurality of gate wirings. And a semiconductor device including a thin film transistor and a pixel electrode connected to the thin film transistor in each of the plurality of pixels, wherein the thin film transistor has a first gate electrode, a first insulating film on the first gate electrode. A film, a semiconductor layer on the first insulating film, a second insulating film on the semiconductor layer, and a second gate electrode on the second insulating film, wherein the semiconductor layer has a channel formation region, A second impurity region including a first impurity region in contact with a channel formation region and a second impurity region in contact with the first impurity region, wherein the second impurity region has a lower resistance value than the first impurity region; First gate power The pole is an electrode extended from the first gate wiring, and overlaps the first impurity region via the first insulating film. The second gate electrode is connected to the plurality of pixels. The first insulating film is electrically connected to the first gate wiring, the first insulating film is thinner than the second insulating film, and the first insulating film is electrically connected to the second insulating film. The plurality of source wirings are provided on an interlayer insulator on the second gate electrode, and only via the first insulating film and the interlayer insulator. A semiconductor device intersecting with the plurality of first gate lines. 7. The semiconductor device according to claim 4, wherein said second impurity region includes a silicide region. 8. The sheet according to claim 4, wherein the sheet resistance of the second impurity region is 1 kΩ / cm 2.
□ A semiconductor device characterized by the following. 9. The semiconductor device according to claim 1, wherein the semiconductor layer is a crystalline semiconductor layer. 10. The semiconductor device according to claim 1, wherein the second gate electrode includes an aluminum film, a titanium film, a tantalum film, an aluminum alloy film, a titanium alloy film, or a tantalum alloy film. Characteristic semiconductor device. 11. The semiconductor device according to claim 1, wherein the second gate electrode is provided with an anodic oxide film on an upper surface and side surfaces. 12. The semiconductor device according to claim 1, wherein the second gate electrode is an electrode extended from a second gate wiring, and the second gate wiring is the first gate wiring. A semiconductor device provided along the first gate wiring over the gate wiring and electrically connected to the first gate wiring. 13. The semiconductor device according to claim 12, wherein said second gate wiring is electrically connected to said first gate wiring at two places. 14. The method according to claim 12, wherein
The semiconductor device according to claim 1, wherein the second gate line overlaps with one of the plurality of pixel electrodes via an insulating film. 15. The semiconductor device according to claim 1, wherein the plurality of first gate lines are connected to a scan driver circuit. 16. The semiconductor device according to claim 1, wherein said plurality of first gate wirings are covered with an anodic oxide. 17. The semiconductor device according to claim 1, wherein the plurality of thin film transistors are provided on an organic resin. 18. The semiconductor device according to claim 1, wherein the semiconductor device is a liquid crystal display.