JP2001257362A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reliability of a semiconductor device, by forming a proper contact between its wiring and its semiconductor layer. SOLUTION: The semiconductor device has a semiconductor film 8 formed on an insulation substrate, where its thickness is not larger than 1,500 Å and its main component is silicon, a wiring connected electrically with the semiconductor film, and a film connected electrically with the semiconductor film via the wiring, whose main component is a conductive oxide. The wiring has a first layer 11 which has titanium as its main component, a second layer 15 having aluminum as its main component, and a third layer 16 having titanium as its main component. The first layer 11 is brought into contact with the semiconductor film 8. The second layer 15 is formed between the first layer 11 and the third layer 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic circuit which is formed on an insulating substrate, has a thin semiconductor layer such as silicon, such as a thin film transistor, and needs to connect the semiconductor layer to a wiring. .

[0002]

2. Description of the Related Art Conventionally, in a thin film device such as a thin film type insulated gate type field effect transistor (TFT), a semiconductor thin film such as silicon used as an active layer is 1500.
It was about Å thick. Therefore, when an electrode was formed on such a semiconductor thin film, a sufficient contact was formed even by directly adhering a metal such as aluminum similarly to the conventional IC technology. In such a contact portion, usually, aluminum and a semiconductor component such as silicon are chemically reacted with each other to form aluminum and aluminum.
Although silicide such as silicide is formed, there was no problem because the thickness of the semiconductor layer was sufficiently larger than the thickness of silicide.

[0003]

However, recent studies have shown that the thickness of the active layer is less than 1500.
It has been clarified that when the thickness is reduced to about 0 to 750 °, the characteristics of the TFT are further improved. However, when an electrode is formed on such a thin semiconductor layer (active layer), good contact cannot be obtained by the conventional method. This was because the thickness of the silicide grew to about the same as the thickness of the semiconductor layer, and the electrical characteristics of the contact were significantly deteriorated. Then, such a contact deteriorated remarkably when stress such as voltage application for a long time was applied.

Further, in order to improve the characteristics of the TFT, it is necessary to perform a heat treatment in a hydrogen atmosphere at a temperature of 400 ° C. or less, typically 200 to 350 ° C., after forming the electrode with the semiconductor layer. However, in a TFT whose semiconductor layer has a thickness of 1500 ° or less, the formation of silicide remarkably progresses due to such a heat treatment, and there is a problem that the characteristics of the TFT deteriorate.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to obtain a good contact between a wiring and a semiconductor layer which can withstand a heat treatment of at least 300 ° C. It aims to improve.

[0006]

The present invention is formed on an insulating substrate and has a thickness of 1500 ° or less, preferably 100 °.
The present invention relates to an electronic circuit having a semiconductor layer whose main component is silicon of 750 ° or less. For example, if the thickness of the active layer is 15
An electronic circuit having a TFT of less than or equal to 00 is an object of the present invention. The effect of the present invention is more remarkable as the thickness of the semiconductor layer is smaller.

According to a first configuration of the present invention, the thin film semiconductor layer as described above is formed in close contact with an insulating substrate such as glass or through an insulating film, and a part or all of the semiconductor layer is formed. , A first layer containing titanium and nitrogen as main components is in close contact with each other, and a second layer mainly composed of aluminum is formed on the upper surface of the first layer. A wiring is formed by the second layer. At this time, substantially all of the lower surface of the second layer is in close contact with the first layer. Further, a third layer containing titanium and nitrogen as main components may be further provided on the second layer.

According to a second structure of the present invention, the thin film semiconductor layer is formed in close contact with an insulating substrate such as glass or through an insulating film, and titanium is partially or entirely formed on the semiconductor layer. No. 1 contained as main component
And a second layer mainly composed of titanium and nitrogen is closely adhered to the upper surface of the first layer, and furthermore, aluminum is mainly composed to the upper surface of the second layer. A third layer is formed, and a wiring is formed by the first to third layers.
Needless to say, another layer may be formed on the third layer.

According to a third aspect of the present invention, a thin film semiconductor layer is formed in close contact with an insulating substrate such as glass or through an insulating film, and a part or all of the semiconductor layer contains titanium. The first layer containing nitrogen as a main component adheres closely, and further, on the upper surface of the first layer,
A second layer containing titanium and nitrogen as main components is in close contact with each other, and a third layer containing aluminum as a main component is formed on the upper surface of the second layer. A wiring is formed by layers, and the ratio of titanium to nitrogen in the first layer (titanium / nitrogen) is larger than that in the second layer.

In any structure, the thin film semiconductor in the portion where the first layer is in close contact exhibits N-type or P-type conductivity, and the impurity concentration in that portion is preferably 1 × 10 ¹⁹ to 10 × 10 ¹⁹ .
It is 1 × 10 ²⁰ cm ⁻² . The introduction of the impurity may be performed by using a known ion implantation method or a plasma doping method. When such impurity ions are accelerated and introduced to high energy, the dose amount is 0.8 × 1.
0 ¹⁵ to 1 × 10 ¹⁷ cm ⁻² is preferable. Alternatively, by a laser doping method using laser irradiation in an impurity gas atmosphere (Japanese Patent Application No. 3-283981, filed on October 4, 1991, or Japanese Patent Application No. 3-290719, filed on October 8, 1991). Good. Further, the sheet resistance of that portion is preferably 1 kΩ / □ or less.

Further, silicon oxide may be formed in close contact with the lower part of the thin film semiconductor. At this time, the same impurity as that contained in the thin film semiconductor may be contained in the silicon oxide film.

In the first layer of the first structure, the ratio of titanium and nitrogen, which are the main components, may be different depending on the thickness. Further, in addition to titanium and nitrogen, other elements such as silicon and oxygen may be contained as main components. For example, of the first layer, a portion near the semiconductor layer is mainly composed of titanium and silicon, and a portion near the second layer has titanium and nitrogen as main components. For example, a ratio of titanium to nitrogen (nitrogen / titanium) ) May be a value close to the stoichiometric ratio (0.8 or more), and the component may change continuously in the middle.

In general, a stoichiometric material composed of nitrogen and titanium (titanium nitride) has excellent barrier properties and a function of preventing the diffusion of aluminum and silicon. However, the material has a high contact resistance with silicon, It is not preferable to use for forming a contact. On the other hand, a stoichiometric material composed of titanium and silicon (titanium silicide, titanium silicide) has a low contact resistance with a semiconductor containing silicon as a main component and is advantageous in forming an ohmic contact. It is easy to diffuse, for example, aluminum in the second layer diffuses through the first layer to form aluminum silicide in the semiconductor layer.

The complicated layer structure as described above is made to solve such a problem. That is, titanium nitride having an excellent barrier property and substantially stoichiometric ratio is used for a portion in contact with the second layer to prevent aluminum of the second layer from entering the first layer, while A good ohmic contact can be obtained by forming titanium-silicide having a substantially stoichiometric ratio in a portion in contact with.

In forming titanium silicide, even if silicon is not intentionally added at the time of film formation, titanium reacts with silicon in the semiconductor layer to automatically form titanium silicide.
A silicide is formed. Therefore, for example, the same effect can be obtained by depositing titanium with a small amount of nitrogen in a portion near the semiconductor layer and titanium with a large amount of nitrogen in the portion near the second layer.

In any case, titanium and nitrogen are main components in the first layer as a whole. Preferably, the ratio of titanium to nitrogen (nitrogen / titanium) in the first layer is between 0.5 and 1.2. Further, such a material containing titanium and nitrogen as main components can obtain ohmic contact with a conductive oxide such as indium / tin oxide, zinc oxide, and nickel oxide. On the other hand, when aluminum and such a conductive oxide form a bond, a thick aluminum oxide layer is formed at the joint, and good contact cannot be obtained. Previously, a layer of chromium was formed between aluminum and the conductive oxide, but chromium is toxic and an alternative material was required. The material containing titanium and nitrogen as main components used in the present invention is also excellent in this respect. Hereinafter, the configuration of the present invention will be described in detail with reference to examples.

[0017]

[Embodiment 1] FIGS. 1 and 2 show this embodiment. FIG. 1 shows a procedure for manufacturing an electronic circuit having a TFT. The description of the general steps is omitted. First, an underlying silicon oxide film 2 having a thickness of 500 to 1500 に
Preferably, the amorphous silicon film 3 and the protective layer 4 are formed to a thickness of 500 to 750 °. And this is 450-60
The amorphous silicon film was crystallized by annealing at 0 ° C. for 12 to 48 hours. It goes without saying that this crystallization step may use means such as so-called laser annealing. (Fig. 1 (A))

Next, the silicon film is patterned to form an island-shaped semiconductor region 5, which is covered with a thickness of 500
A silicon oxide film 6 having a thickness of １1500Å, preferably 800８００1000 Å was formed and used as a gate oxide film. further,
An aluminum gate wiring / electrode 7 was formed, and this was anodized to form an aluminum oxide film around it. As described above, Japanese Patent Application No. 4-3863 discloses a technique using anodic oxidation for a top gate type TFT.
7 (filed on January 24, 1992). Gate electrode is silicon, titanium, tantalum, tungsten,
It goes without saying that it may be made of a material such as molybdenum. Thereafter, using the gate electrode as a mask, an impurity such as phosphorus is implanted by means such as a plasma doping method, and an impurity region (doped silicon region) 8 is formed in alignment with the gate electrode portion 7. Further, the impurity region 8 was recrystallized by means such as thermal annealing and laser annealing to obtain the source and drain of the TFT. (FIG. 1 (B))

Further, an interlayer insulator (silicon oxide) 9 and a conductive transparent oxide, for example, ITO (indium tin oxide) are deposited, and the ITO film is patterned, which is used for an active matrix type liquid crystal display device. The pixel electrode 10 was formed. Then, a contact hole was formed in the interlayer insulator 9 to expose a part of the impurity region (source, drain). Then, a first layer containing titanium and nitrogen as main components and a second layer made of aluminum were formed by a sputtering method. The method was performed as follows.

First, titanium was set as a target in a sputtering chamber, and a film was formed in an argon atmosphere. The sputtering pressure was 1 to 10 mTorr. Then, first, a layer containing titanium as a main component and containing almost no nitrogen was formed to a thickness of 50 to 500. Next, nitrogen was introduced into the sputter chamber in addition to argon, and a sputter film was formed in this atmosphere. As a result, an approximately stoichiometric titanium nitride layer having a thickness of 200 to 10
00 ° was formed. At this time, the proportion of nitrogen in the sputtering atmosphere was set to 40% or more. It should be noted that the deposition rate by sputtering varies significantly depending on the partial pressure of nitrogen in addition to the sputtering pressure. For example, in an atmosphere containing only argon and an atmosphere containing 20% or more of nitrogen, the former is generally 3 to 5 times.
Double deposition rate is fast. As for the atmosphere during sputtering, ammonia, hydrazine, or the like may be used instead of nitrogen. Furthermore, it is known that the resistivity of a film obtained by the partial pressure of nitrogen during sputtering changes. However, since it is used as a wiring material, it is desirable that the resistance is low. Needless to say, adopt it. For example, an atmosphere of 100% nitrogen and nitrogen 4
In an atmosphere of 0%, the former had a lower resistivity.
Further, the typical resistivity was 50 to 300 μΩ · cm.

In the above steps, if the thickness of the titanium layer containing almost no nitrogen, which is formed first, is too large, the lower semiconductor layer reacts and good contact cannot be obtained. As a result of the study by the present inventors, it has been found that the thickness of the titanium layer is preferably smaller than the thickness of the semiconductor layer.

After the first layer 11 is formed in this manner, the aluminum (containing 1% silicon) film 12 of the second layer is again formed by sputtering to a thickness of 2000 to 50%.
00 ° was formed. Then, these layers were patterned by photolithography. First, the second layer made of aluminum was etched with an etchant such as phosphoric acid (for example, a mixed acid of phosphoric acid, acetic acid, and nitric acid). Then, while leaving the resist on this aluminum film,
The first layer was etched with buffered hydrofluoric acid or hydrofluoric acid. At this time, care must be taken because the over-etching may damage the interlayer insulating film and the like. Note that etching may be performed with a mixed solution of hydrogen peroxide (H ₂ O ₂ ) water and ammonia water (NH ₃ OH) using the aluminum selectively left as a mask. In this case, there is no effect on the interlayer insulating film. However,
Since organic materials such as photoresist are oxidized,
Be careful.

The above etching step may be a dry etching process. It is preferable to use, for example, carbon tetrachloride (CCl ₄ ) as an etching gas because the second layer and the first layer can be continuously etched without damaging silicon oxide or the like. After forming the wiring extending from the impurity region in this manner, annealing was performed in a hydrogen atmosphere at 300 ° C. to complete the TFT.

Now, the circuit thus formed has a portion that needs to be connected to the outside. FIG. 2 (A)
Shows a state in which external connection wirings 19 are formed from the integrated circuit 18 formed on the substrate 17 toward the peripheral portion of the substrate. In such an electronic circuit, electrical contact may be made mechanically by a contact fitting such as a socket in a region 20 surrounded by a dotted line in the drawing.

Alternatively, in a liquid crystal display device as shown in FIG. 2B, in order to supply power and signals to circuits 22 to 24 for driving an active matrix region 25 on a substrate 21, dotted lines in the drawing are used. Electrical contact is made in the area 27 enclosed by. Although connection such as wire bonding is permanent and highly reliable, it takes a considerable amount of time and effort to manufacture, and is not particularly suitable for connecting many terminals. Thus, mechanical contact may be advantageous in some cases.

However, in this case, it is required that the wiring surface at the contact portion is sufficiently strong and that the adhesion between the base and the wiring is good. Aluminum is not suitable for the purpose, but a material containing titanium as a main component is suitable because it has good adhesion to materials such as silicon, silicon oxide, and aluminum, and has a high hardness of the coating film. At that time, nitrogen may not be contained at all, or may be contained up to the stoichiometric ratio. In this embodiment, only the contact portion of the first layer 12 is etched to expose the second layer. In this embodiment, a portion of the first layer that is in contact with the second layer is titanium nitride having a stoichiometric ratio.
Then, the contact fitting 13 with the titanium nitride exposed was pressed to form a contact. (Fig. 1 (C))

Alternatively, as shown in FIG. 1D, a third layer made of titanium nitride is superposed on the first layer 14 and the second layer 15.
May be formed, and a contact fitting may be brought into contact with the third layer. In this case, there is no need to etch a part of the second layer as shown in FIG. 1C, and the patterning step can be omitted. Further, as shown in FIG. 1E, an ITO film may be formed after a wiring having a layer containing nitrogen and titanium as main components of the present invention is first patterned. In any case, in this embodiment, a good contact is obtained because the ITO film is made of a material containing nitrogen and titanium as main components. This applies not only to ITO but also to oxide conductors in general.

V _D − of the TFT obtained as described above
And I _D characteristic (curve a), and V _D -I _D characteristic of a TFT having an ordinary Al / Si contacts for reference (curve b) is shown in FIG. TFT manufactured by the conventional method (curve b
), Kink was observed around V _D ０0, and the contact resistance did not show ohmic contact. However, such an abnormality was not observed in the TFT (shown by curve a) manufactured in this example. , Normal MOSFET characteristics were shown.

Embodiment 2 This embodiment will be described with reference to FIG. FIG. 1 conceptually shows a procedure for manufacturing an electronic circuit having a TFT. The description of the general steps is omitted. First, a base silicon oxide film 2 having a thickness of 100 to 1500 Å, preferably 1
Amorphous silicon film 3 of 100 to 750 °, protective layer 4
To form And this is 450 ~ 600 ° C for 12 ~
Annealing was performed for 48 hours to crystallize the amorphous silicon film. It goes without saying that this crystallization step may use means such as so-called laser annealing. (Fig. 1 (A))

Next, the silicon film is patterned to form an island-shaped semiconductor region 5, which is covered with
A silicon oxide film 6 having a thickness of １1500Å, preferably 800８００1000 Å was formed and used as a gate oxide film. further,
An aluminum gate wiring / electrode 7 was formed, and this was anodized to form an aluminum oxide film around it. Thereafter, using the gate electrode as a mask, an impurity such as phosphorus is implanted by means such as an ion implantation method, and an impurity region (doped silicon region) 8 is formed in alignment with the gate electrode portion 7. The dose is 0.8-4 × 10 ¹⁵ cm ⁻² and 1 × 10 ^{19 -1} ×
The dose, the acceleration voltage, and the thickness of the gate oxide film were set so that the impurity concentration became 10 ²¹ cm ^-3 . Further, the impurity region 8 was recrystallized by means such as thermal annealing and laser annealing to obtain the source and drain of the TFT. (FIG. 1 (B))

Further, an interlayer insulator (silicon oxide) 9, an IT
O was deposited and the ITO film was patterned to form a pixel electrode 10 of an active matrix type liquid crystal display device. Then, a contact hole was formed in the interlayer insulator 9 to expose a part of the impurity region (source, drain). Then, a first layer containing titanium and nitrogen as main components and a second layer made of aluminum were formed by DC sputtering. The method was performed as follows.

First, titanium is set as a target in a sputtering chamber, and a film is formed in an atmosphere in which a partial pressure ratio of argon and nitrogen (argon / nitrogen) is 0.3 or less, for example, argon: nitrogen = 4: 1. Was done. The sputtering pressure is 3 mTorr and the DC current is 4.5
A, flow rate of argon is 24 SCCM, flow rate of nitrogen is 6 S
CCM. Then, a lower layer of the first layer having a low nitrogen content was formed to a thickness of 100. The film thus formed had a sufficiently low contact resistance with silicon and ITO.

Next, the nitrogen atmosphere in the sputtering chamber is increased, and the partial pressure ratio of argon and nitrogen (argon / nitrogen) is 0.3 or more, for example, argon: nitrogen = 1:
As No. 1, a sputter film was formed in this atmosphere.
The sputtering pressure and DC current remain at 3 mTorr and 4.5 A, but the flow rate of argon and nitrogen is 15 SC
CM. Through the above steps, the upper layer of the first layer was formed to a thickness of 900. The film thus formed is
Since the contact resistance with silicon was large, it could not be used as a contact, but there was no problem in using it as a wiring material as in this embodiment. It should be noted that the deposition rate by sputtering varies significantly depending on the partial pressure of nitrogen in addition to the sputtering pressure. For example, when argon / nitrogen = 4/1,
In the case of 100 to 120 ° / min and argon / nitrogen = 1/1, it was 30 to 40 ° / min.

After forming the first layer 11 in this manner, the aluminum (containing 1% silicon) film 12 of the second layer is also formed to a thickness of 2000 to 50 by the sputtering method.
00 ° was formed. Then, these layers were patterned by photolithography. First, the second layer made of aluminum was etched with an etchant such as phosphoric acid (for example, a mixed acid of phosphoric acid, acetic acid, and nitric acid). Then, while leaving the resist on this aluminum film,
Hydrogen peroxide (H ₂ O ₂ ) water and ammonia water (NH ₃ O)
The first layer was etched by the mixed solution of H). Since this etchant oxidizes the organic substance, it is the same as performing the final organic cleaning at the same time. After forming the wiring extending from the impurity region in this manner,
Annealing was performed in a hydrogen atmosphere at 300 ° C. to complete a TFT. Further, in the present embodiment, only the contact portion of the first layer 12 was etched to expose the second layer.
Then, the exposed contact fitting 13 of the first layer was pressed to form a contact. (Fig. 1 (C))

[0035]

According to the present invention, a thin source of a TFT,
A good contact at the drain (impurity region) and the like could be formed. This contact has high reliability, and thus has been effective in improving the reliability of the entire electronic circuit. As described above, the present invention is an industrially useful invention.

[Brief description of the drawings]

FIG. 1 shows an example (cross-sectional view) of a circuit having a TFT using the present invention.

FIG. 2 shows an example (top view) of an electronic circuit using the present invention.

FIG. 3 shows the characteristics (a) of a TFT obtained in this example and the characteristics (b) of a TFT obtained by a conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass substrate 2 ... Underlying silicon oxide film 3 ... Silicon film 4 ... Protective film 5 ... Island-shaped semiconductor region 6 ... Silicon oxide film (gate oxide film) 7 ... Gate electrode / wiring (aluminum covered with anodic oxide film) 8 ... impurity region 9 ... interlayer insulator (silicon oxide) 10 ... pixel electrode (ITO) 11 ... first layer (nitridation) 12) second layer (aluminum) 13 ... connection terminal fitting 14 ... first layer (titanium nitride) 15 ... second layer (aluminum) 16 ... third Layer (titanium nitride)

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H01L 21/3205 H01L 21/88 R 21/768 21/90 C 29/78 612C (72) Inventor Mutsumi Yamamoto Atsugi, Kanagawa 398 Hase, Ichimizu Semiconductor Energy Laboratory Co., Ltd.

Claims (6)

[Claims] 1. A semiconductor device comprising: an insulating substrate having a thickness of 150
A semiconductor film containing silicon of 0 ° or less as a main component, a wiring electrically connected to the semiconductor film, and electrically connected to the semiconductor film through the wiring.
A wiring containing a conductive oxide as a main component; the wiring having a first layer mainly containing titanium, a second layer mainly containing aluminum, and a first layer mainly containing titanium. And wherein the first layer is in contact with the semiconductor film, and the second layer is formed between the first and third layers. Semiconductor device. 2. The method according to claim 1, wherein the thickness is 150 formed on the insulating substrate.
A semiconductor film mainly containing silicon of 0 ° or less and having at least a source region, a drain region, and a channel formation region formed between the source region and the drain region; and a gate insulating film formed in contact with the semiconductor film. A film, a gate electrode formed in contact with the gate insulating film, a wiring connected to the source region or the drain region, and electrically connected to the source region or the drain region via the wiring. And a film containing a conductive oxide as a main component. The wiring contains a first layer containing titanium as a main component, a second layer containing aluminum as a main component, and titanium as a main component. A third layer, wherein the first layer is in contact with the source region or the drain region, and the second layer is formed between the first layer and the third layer. To be Characteristic semiconductor device. 3. The semiconductor device according to claim 2, wherein the impurity concentration in the source region and the drain region is 1 × 10 ¹⁹ to 1 × 10 ²¹ cm ⁻³ . 4. The film containing the conductive oxide as a main component,
The semiconductor device according to claim 1, wherein the semiconductor device is in contact with the first layer or the third layer. 5. The semiconductor device according to claim 1, wherein the conductive oxide is indium tin oxide, zinc oxide, or nickel oxide. 6. The thickness of the semiconductor film is 100 ° or more and 75 or more.
The semiconductor device according to claim 1, wherein the angle is 0 ° or less.