JP3149034B2 - 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 whose surface is covered with a protective insulating film.

[0002]

2. Description of the Related Art Thin film transistors (TFTs) include a staggered type, an inverted staggered type, a coplanar type, and an inverted coplanar type.

FIG. 5 is a sectional view of a conventional thin film transistor. Here, the thin film transistor formed on a substrate of an active matrix liquid crystal display device is shown.
Note that this thin film transistor is of an inverted stagger type.

The thin film transistor includes a gate electrode G formed on a transparent insulating substrate 1 made of glass or the like, a gate wiring (not shown) connected to the gate electrode G, and the gate electrode G and the gate wiring. A gate insulating film (transparent film) 2 to cover, an i-type semiconductor layer 3 formed on the gate insulating film 2, and a source formed on the i-type semiconductor layer 3 via the n-type semiconductor layer 4 It comprises an electrode S, a drain electrode D, and a data line DL connected to the drain electrode D.

The i-type semiconductor layer 3 is made of a-Si, and the n-type semiconductor layer 4 is made of a-type semiconductor doped with an n-type impurity.
The n-type semiconductor layer 4 is separated at a portion corresponding to a channel region (a region between the source electrode S and the drain electrode D) of the i-type semiconductor layer 3.

The source electrode S and the drain electrode D are covered with an interlayer insulating film 5 formed thereon, and a data line DL connected to the drain electrode D is formed on the interlayer insulating film 5. I have. This data wiring DL
Is connected to the drain electrode D at a contact hole 5 a provided in the interlayer insulating film 5.

Reference numeral 6 denotes an ITO formed on the gate insulating film 2.
The pixel electrode 6 is connected to the source electrode S by forming an end portion of the pixel electrode 6 on the source electrode S.

The surface of the thin film transistor is covered with a protective insulating film 7 together with the data wiring DL. This protective insulating film 7 is provided in order to prevent the data wirings DL from being short-circuited due to the adhesion of dust or the like, and to prevent the transistor characteristics from being deteriorated due to the adhesion of moisture or heavy metal ions such as Na ions. This protective insulating film 7
Is the same as that of the gate insulating film 2 and the interlayer insulating film 5 in the related art.
It is an iN (silicon nitride) film.

The above-mentioned SiN film is formed by a plasma CVD apparatus.
In general, the iN film is formed by preheating the substrate 1 in a preheating chamber, transferring the substrate 1 to a film forming chamber, heating the substrate 1 to a predetermined film forming temperature, and then performing plasma processing in a process gas atmosphere. It is performed by a method of causing a discharge to deposit SiN. In general, the SiN film is formed at a substrate temperature (surface temperature) of about 250 to 270 ° C. The SiN film formed at such a substrate temperature has a dense film quality.
Has good dielectric strength.

On the other hand, in the thin film transistor, it is desirable to reduce the resistance of the gate line and the data line DL as much as possible in order to improve the operation characteristics. Therefore, the electrodes and wirings of the thin film transistor are made of Al (aluminum) which is inexpensive and have low resistance, and Ti (titanium).
It is formed of an Al-based alloy containing a high melting point metal such as Al or Ta (tantalum). The source and drain electrodes S and D are formed of the above-described Al-based alloy or Cr (chromium).

As described above, the electrodes and wirings are formed of an Al-based alloy containing a high melting point metal. When a pure Al film is heated to several hundred degrees centigrade, the surface of the film is roughened and a sharp hillock is formed. In particular, when the lower electrode and the lower electrode, ie, the gate electrode D and the gate wiring, are formed of pure Al, the gate insulating film 2 and the interlayer insulating film 5 are formed thereon by a plasma CVD apparatus. Hillocks occur on the surfaces of the gate electrode G and the gate wiring during the film formation, and defects such as cracks occur in the gate insulating film 2 and the interlayer insulating film 5 due to the influence of the hillocks. And the source and drain electrodes S and D) and the upper and lower wirings (gate wiring and data wiring DL) are short-circuited.

However, if Al contains a high melting point metal such as Ti or Ta, the surface roughness during heating is suppressed, so that if the electrodes and wirings are formed of the Al-based alloy, the gate insulating film The formation of hillocks on the surfaces of the electrodes and wiring during the deposition of the second and interlayer insulating films 5 and the like can be prevented, and short circuits between upper and lower electrodes and wiring can be eliminated. The surface roughness of the Al-based alloy during heating can be effectively suppressed by increasing the content of the refractory metal. However, when the content is increased, the resistance of the Al-based alloy is increased.
The content of the high melting point metal is desirably as small as possible within a range that does not cause hillocks during the manufacturing process of the thin film transistor.

[0013]

However, as described above, in the conventional thin film transistor in which the protective insulating film is the same as the SiN film as the gate insulating film and the interlayer insulating film, the lower electrode and the lower wiring contain a high melting point metal. A large amount
Unless it is formed of an l-based alloy, there is a problem that the above-mentioned short circuit occurs between upper and lower wirings and between electrodes in the process of manufacturing a thin film transistor.

That is, for example, in the inverted staggered thin film transistor shown in FIG. 5, after forming a gate electrode G and a gate wiring on a substrate 1, a gate insulating film 2, an i-type semiconductor layer 3 and an n-type semiconductor layer 4 are formed. , A source and drain metal film are sequentially formed, and then the metal film and the n-type semiconductor layer 4 and the i-type semiconductor layer 3 are patterned into the outer shape of the transistor element region. Are patterned into the shapes of the source and drain electrodes S and D. Thereafter, an interlayer insulating film 5 is formed, a contact hole 5 a is formed in the interlayer insulating film 5, and a data hole is formed on the interlayer insulating film 5. It is manufactured by forming a metal film for wiring, patterning the metal film to form a data wiring DL, and then forming a protective insulating film 7 thereon.

The pixel electrode 6 is formed by patterning the metal film for source and drain and the n-type semiconductor layer 4 into the shape of the source and drain electrodes S and D, and then forming a transparent conductive film such as ITO. The transparent conductive film is formed by patterning.

In this manufacturing method, the film formed by the plasma CVD apparatus is composed of the gate insulating film 2, the i-type and the n-type.
Type semiconductor layers 3 and 4, an interlayer insulating film 5, and a protective insulating film 7. The gate insulating film 2, the interlayer insulating film 5, and the protective insulating film 7 (all of which are SiN films) are about 250 to 2
The film is formed at a substrate temperature of 70 ° C., and the i-type and n-type semiconductor layers 3 and 4 are formed at a substrate temperature of about 250 ° C.
The metal film for source and drain, the metal film for data wiring, and the transparent conductive film are approximately 100
The film is formed at a substrate temperature of ° C.

Therefore, in the manufacture of the above-mentioned inverted stagger type thin film transistor, the gate electrode G and the gate wiring, which are the lower electrode and the lower wiring, are formed by the gate insulating film 2,
Each time the i-type and n-type semiconductor layers 3 and 4, the interlayer insulating film 5, and the protective insulating film 7 are formed, the semiconductor device is repeatedly heated to several hundred degrees Celsius.

When the gate electrode G and the gate wiring are repeatedly heated to several hundred degrees Celsius in this manner, for example, even if no hillocks are generated in the gate electrode G and the gate wiring until the interlayer insulating film 5 is formed, Hillocks are generated in the gate electrode G and the gate wiring when the last protective insulating film 7 is formed,
Due to the influence of the hillock, a defect occurs in the gate insulating film 2 or the interlayer insulating film 5, and a short circuit occurs between upper and lower electrodes and between wirings.

Therefore, in the conventional thin film transistor,
The lower electrode and the lower wiring must be formed of an Al-based alloy having a high refractory metal content so that hillocks are not generated even when a protective insulating film to be formed last is formed. The resistance of the lower electrode and the lower wiring increases, and the operating characteristics of the thin film transistor deteriorate.

It is an object of the present invention to reduce the number of times the lower electrode and the lower wiring are heated to several hundred degrees Celsius in the manufacturing process, and to make the lower electrode and the lower wiring an Al-based alloy having a low refractory metal content. Even if formed, hillocks are prevented from occurring, preventing short circuits between upper and lower electrodes and wiring,
In addition, it is an object of the present invention to provide a thin film transistor capable of improving operating characteristics by reducing the resistance of a lower electrode and a lower wiring.

[0021]

The thin film transistor of the present invention comprises a gate electrode, a gate insulating film, a semiconductor layer,
A protective insulating film covering the surface of the element region where the source and drain electrodes are formed by oxidizing a metal film formed on the element region.
A metal oxide film formed by the treatment is characterized.

[0022]

The protective insulating film made of a metal oxide film can be formed by forming a metal film and oxidizing the metal film. In addition, the metal film can be formed at a low substrate temperature of about 100 ° C. by a sputtering apparatus, and the metal film can be oxidized without heating the substrate.

Therefore, according to the thin film transistor of the present invention, since the protective insulating film can be formed at a low temperature, the number of times the lower electrode and the lower wiring are heated to several hundred degrees Celsius in the manufacturing process can be reduced. If the number of times the lower electrode and the lower wiring are heated to several hundred degrees Celsius is small, hillocks are generated even if the lower electrode and the lower wiring are formed of an Al-based alloy having a low content of a high melting point metal. Therefore, a defect due to the influence of the hillock does not occur in a gate insulating film or the like, and thus a short circuit between upper and lower electrodes and a wiring can be prevented. Further, since the lower electrode and its wiring can be formed of an Al-based alloy having a low content of a high melting point metal, the resistance of the lower electrode and the lower wiring can be reduced, and the operating characteristics of the thin film transistor can be improved.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings, taking a thin film transistor formed on a substrate of an active matrix liquid crystal display element as an example.

FIG. 1 is a sectional view of the thin film transistor of this embodiment. In addition, the thin film transistor of this embodiment
Since it is of an inverted stagger type and the configuration of the transistor element portion is the same as that of the conventional thin film transistor shown in FIG. 5, the description thereof will be omitted by attaching the same reference numerals to the drawings.

In the thin film transistor of this embodiment, the gate insulating film 2 and the interlayer insulating film 5 are SiN films formed by a plasma CVD apparatus, and the protective insulating film 11 is a metal oxide film. The film 11 is formed by forming a metal film made of pure Al or an Al-based alloy containing a trace amount of a high melting point metal (Ti, Ta, etc.) and oxidizing the metal film. In this embodiment,
The data line DL connected to the drain electrode D is formed of the metal film serving as the protective insulating film 11, and the data line DL is formed by partially leaving the metal film without being oxidized. .

The thin film transistor is manufactured by the following steps.

[Step 1] A gate metal film made of an Al-based alloy containing a high melting point metal is formed on a substrate 1 by a sputtering apparatus, and the gate metal film is patterned to form a gate electrode G and a gate wiring. To form

[Step 2] Next, the gate insulating film (SiN)
Film) 2, an i-type semiconductor layer (i-type a-Si layer) 3, and an n-type semiconductor layer (n-type a-Si layer) 4 are successively formed by a plasma CVD apparatus, and further thereon. And the source,
A drain metal film (an Al alloy film containing Cr or a high melting point metal) is formed by a sputtering apparatus.

[Step 3] Next, the source and drain metal films, the n-type semiconductor layer 4 and the i-type semiconductor layer 3 are patterned into the outer shape of the transistor element region, and the source and drain metal films and the n-type The semiconductor layer 4 is patterned into source and drain electrodes S and D.

[Step 4] Next, a transparent conductive film such as ITO is formed by a sputtering apparatus, and the transparent conductive film is patterned to form a pixel electrode 6.

[Step 5] Next, an interlayer insulating film (SiN film)
5 is formed by a plasma CVD apparatus, and a contact hole 5 a corresponding to the drain electrode D is formed in the interlayer insulating film 5.

[Step 6] Next, a protective insulating film 11 and a metal film to be the data wiring DL are formed on the interlayer insulating film 5, and the protective insulating film 11 is formed by patterning and oxidizing the metal film. The thin film transistor is completed by forming the data wiring DL.

FIG. 2 shows a process of forming the protective insulating film 11 and the data wiring DL. The protective insulating film 11 and the data wiring DL are formed as follows.

[Step 6-1] First, as shown in FIG. 2A, pure Al or Al containing a trace amount of a high melting point metal is used.
A metal film 10 made of a system alloy is formed by a sputtering device.

[Step 6-2] Next, as shown in FIG. 2B, the metal film 10 is patterned by photolithography into a shape corresponding to the transistor element region and the data wiring formation portion.

[Step 6-3] Next, as shown in FIG. 2C, a resist mask M is formed on the metal film 10 so as to cover the data wiring formation portion.
Is oxidized to oxidize the region of the metal film 10 other than the data wiring formation portion over the entire film thickness, and this oxidized region is used as an oxide film 10a.

The oxidation treatment of the metal film 10 is performed by, for example, anodic oxidation. In this anodic oxidation, the substrate 1 on which the metal film 10 is formed is immersed in an electrolytic solution so that the metal film 10 faces a counter electrode (platinum electrode) in the electrolytic solution. Is used as a cathode and a voltage is applied between the two electrodes. As described above, when a voltage is applied between the metal film 10 and the counter electrode in the electrolytic solution, a region (a region in contact with the electrolytic solution) of the metal film 10, which is an anode, which is not covered with the resist mask M, causes a chemical reaction. Then, the oxidized region of the metal film 10 becomes an oxide film 10a.

In this case, the metal film 10 is oxidized from the surface side. The oxidation depth is mainly determined by the applied voltage. Therefore, if the applied voltage is set according to the thickness of the metal film 10, The oxidized area of the metal film 10 can be oxidized over its entire thickness. In addition, the energization of the metal film 10 in the anodic oxidation can be performed using the non-oxidized region 10b of the data wiring formation portion covered with the resist mask M as a current path.

[Step 6-4] Next, the resist mask M is peeled off, and the anodic oxidation treatment of the metal film 10 is performed again. As shown in FIG. The surface of the formation portion (the portion covered with the resist mask M in [Step 6-3]) is oxidized, and this portion is also used as the oxide film 10a. Note that the anodizing treatment at this time is performed with the applied voltage set lower than that in the above-mentioned anodizing treatment in [Step 6-3]. In this case, the metal film 1
Since the other part of 0 is already an oxide film 10a,
The metal film 10 is oxidized only on the surface of the data wiring formation portion (the upper surface and both side surfaces in a linear portion other than the transistor element region).

As described above, the region other than the data line forming portion of the metal film 10 patterned in a shape covering the transistor element region and the data line forming portion is oxidized over the entire film thickness. Is oxidized, the non-oxidized region 10b left in the data wiring forming portion of the metal film 10 becomes the data wiring DL, and the oxide film 10a on the surface of the data wiring DL and all other regions becomes the protective insulating film. It becomes 11.

As described above, in the thin-film transistor of the above embodiment, the protective insulating film 11 covering the surface is made of a metal oxide film, and the protective insulating film 11 made of the metal oxide film is formed as described above. It can be formed by forming the metal film 10 and oxidizing the metal film 10.
Further, the metal film 10 is about 100
The film can be formed at a low substrate temperature of about ° C, and the oxidation treatment of the metal film 10 can be performed without heating the substrate 1.

Therefore, according to the thin film transistor, since the protective insulating film 11 can be formed at a low temperature, the number of times the lower electrode and the gate electrode G, which is the lower wiring, and the gate wiring are heated to several hundred degrees Celsius in the manufacturing process. Can be reduced. If the number of times the gate electrode G and the gate wiring are heated to several hundred degrees Celsius is small, the gate electrode G and the gate wiring can be formed of an Al-based alloy having a low refractory metal content.

That is, in the manufacturing process of the thin film transistor of the above embodiment, the gate electrode G and the gate wiring are heated to several hundred degrees Celsius when the gate insulating film 2 and the interlayer insulating film 5 made of the SiN film are formed ( In each case, the substrate temperature is about 2
50 to 270 ° C.) and when the i-type and n-type semiconductor layers 3 and 4 are formed (substrate temperature: about 250 ° C.), and therefore, the high melting point metal content of the Al-based alloy used for the gate electrode G and the gate wiring. May be sufficient as long as it can withstand heating at several hundred degrees Celsius at the time of forming the gate insulating film 2, the i-type and n-type semiconductor layers 3 and 4, and the interlayer insulating film 5.

The gate electrode G and the gate wiring are
When forming a metal film for source and drain, a metal film for data wiring, and a transparent conductive film for pixel electrodes, the protective insulating film 1
The substrate is heated at about 100 ° C. when the metal film 10 is formed by sputtering, and the substrate temperature is about 100 ° C. when the metal film for gate is formed by the sputtering apparatus. Is about the same as the substrate temperature (about 100 ° C.), so that the surfaces of the gate electrode G and the gate wiring are not roughened during the film formation.

According to the above thin film transistor,
Hillocks do not occur even if the gate electrode G and the gate wiring are formed of an Al-based alloy having a low content of a high melting point metal. Therefore, defects due to the hillocks occur in the gate insulating film 2 and the interlayer insulating film 5. The gate electrode G and the source / drain electrodes S, D
And between the gate wiring and the data wiring DL. Further, since the gate electrode G and the gate wiring can be formed of an Al-based alloy having a low content of a high melting point metal, the resistance of the gate electrode G and the gate wiring can be reduced to improve the operation characteristics.

Further, according to the thin film transistor,
Since the metal film 10 serving as the protective insulating film 11 can be formed at a low substrate temperature of about 100 ° C., the source and drain electrodes S and D are heated to several hundred degrees Celsius in the manufacturing process of the thin film transistor. When forming the source and drain electrodes S and D with an Al-based alloy, the content of the refractory metal of the Al-based alloy is determined as follows.
The amount can be further reduced as compared with the Al-based alloy used for the gate electrode G and the gate wiring.

In the above embodiment, the data line DL
When the metal film 10 serving as the protective insulating film 11 is oxidized to become the oxide film 10a, the metal film 10 is partially left unoxidized, and the non-oxidized region 10b of the metal film 10 is Accordingly, unlike the conventional thin film transistor, it is not necessary to form the data wiring metal film and the protective insulating film by the sputtering device and the plasma CVD device, respectively, so that the manufacturing efficiency of the thin film transistor can be improved.

In the above embodiment, the metal film 10 serving as the protective insulating film 11 is oxidized by anodic oxidation treatment for causing a chemical reaction in the electrolytic solution. It may be performed by plasma oxidation that causes a chemical reaction in an atmosphere.

In the above embodiment, the protective insulating film 11 made of a metal oxide film is formed only on the transistor element region and the data wiring DL. However, the metal oxide film obtained by oxidizing Al or an Al-based alloy is used. Is a transparent film, the protective insulating film (metal oxide film) 11 may be formed on almost the entire surface of the substrate 1 so as to cover the pixel electrode 6 as in the second embodiment shown in FIG. In this case, the patterning step of the metal film 10 in the above-described manufacturing method becomes unnecessary, so that the manufacturing efficiency of the thin film transistor can be further improved.

Further, in the thin film transistor of the above embodiment, the data wiring DL is formed on the interlayer insulating film 5 covering the source and drain electrodes S and D, but this data wiring DL is formed on the gate insulating film 2. It may be formed integrally with the drain electrode D. In this case, the interlayer insulating film 5 is eliminated, and the source and drain electrodes S and D and the data wiring DL are formed.
A protective insulating film 11 may be formed on the substrate.

FIG. 4 shows a third embodiment of the present invention. In the thin-film transistor of this embodiment, a data line DL is formed integrally with a drain electrode D, and a protection film made of a metal oxide film is formed thereon. The insulating film 11 is formed. In this embodiment, the source and drain electrodes S,
When a metal film for forming the protective insulating film 11 for the D and data wirings DL is formed by a sputtering apparatus, the substrate temperature (about 1
(.Degree. C.), the source and drain electrodes S and D and the data wiring DL can be formed of pure Al or an Al-based alloy containing a very small amount of a high melting point metal.

Further, the thin film transistors of the above embodiments are formed on a substrate of an active matrix liquid crystal display element, but the present invention can be widely applied to thin film transistors formed on various circuit boards and the like. Furthermore, the present invention is not limited to the inverted stagger type thin film transistor,
The present invention can be applied to a staggered type, a coplanar type, and a reverse coplanar type thin film transistor.

[0054]

The thin film transistor of the present invention is characterized in that the protective insulating film covering the surface is a metal oxide film, and the protective insulating film made of the metal oxide film is formed by forming a metal film. Can be formed by oxidizing this metal film. Further, the metal film can be formed at a low substrate temperature of about 100 ° C. by a sputtering apparatus, and the metal film can be oxidized without heating the substrate.

Therefore, according to the thin film transistor of the present invention, since the protective insulating film can be formed at a low temperature, the number of times the lower electrode and the lower wiring are heated to several hundred degrees Celsius in the manufacturing process can be reduced. If the number of times the lower electrode and the lower wiring are heated to several hundred degrees Celsius is small, hillocks are generated even if the lower electrode and the lower wiring are formed of an Al-based alloy having a low content of a high melting point metal. Therefore, a defect due to the influence of the hillock does not occur in a gate insulating film or the like, and thus a short circuit between upper and lower electrodes and a wiring can be prevented. Further, since the lower electrode and its wiring can be formed of an Al-based alloy having a low content of a high melting point metal, the resistance of the lower electrode and the lower wiring can be reduced, and the operating characteristics of the thin film transistor can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a thin film transistor showing a first embodiment of the present invention.

FIG. 2 is a process chart of forming a protective insulating film and a data wiring of the thin film transistor.

FIG. 3 is a sectional view of a thin film transistor showing a second embodiment of the present invention.

FIG. 4 is a sectional view of a thin film transistor showing a third embodiment of the present invention.

FIG. 5 is a cross-sectional view of a conventional thin film transistor.

[Description of Signs] 1 ... substrate, G ... gate electrode, 2 ... gate insulating film, 3 ... i
Semiconductor layer, 4 ... n-type semiconductor layer, S ... source electrode, D ...
Drain electrode, 5 ... interlayer insulating film, 5a ... contact hole,
6 ... pixel electrode, DL ... data wiring, 10 ... metal film, 10
a: oxide film, 10b: non-oxidized region, M: resist mask, 11: protective insulating film.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 29/786 H01L 21/316 G02F 1/1368

Claims (3)

(57) [Claims] A gate electrode, a gate insulating film, a semiconductor layer, and a semiconductor layer;
In a thin film transistor in which a surface of an element region where a source electrode and a drain electrode are formed is covered with a protective insulating film, the protective insulating film is formed by oxidation of a metal film formed on the element region.
A thin film transistor comprising a metal oxide film formed by processing . (2) A drain electrode is formed on the element region.
Formed by the non-oxidized region of the metal film
The thin film transistor according to claim 1, wherein: (3) Under the protective insulating film of the thin film transistor
The provided electrode is formed of Al or an Al-based alloy.
The protective insulating film oxidizes Al or an Al-based alloy.
Characterized in that it is formed of oxidized Al oxide.
3. The thin film transistor according to claim 1 or 2.