JPH05167075A - Thin film transistor and formation of its protective insulating film - Google Patents

Abstract

PURPOSE:To reduce the number of times of heating in a fabrication process and prevent any hillock from being produced even though a lower electrode and a lower wiring are formed with an Al alloy by forming a protective insulating film covering the surface with a silicon nitride film formed at low temperature. CONSTITUTION:A protective insulating film 10 is formed by a process wherein a room temperature substrate 1 is transferred into a film formation chamber and just thereafter plasma discharge is produced in an atmosphere of process gas to deposit an SiN film on the substrate 1. Thus, there is formed at low temperature the protective insulating film 10 which is formed finally in the fabrication of a thin film transistor. There is accordingly reduced the number of times of heating to several hundreds of degrees centigrade a gate electrode and a gate wiring being a lower electrode and a lower wiring respectively in the fabrication process of the thin film transistor. Thus, the gate electrode and the gate wiring can be formed with an Al alloy containing a little amount of high melting point metal.

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 and a method for forming the protective insulating film.

[0002]

2. Description of the Related Art A thin film transistor (TFT) includes a stagger type, an inverse stagger type, a coplanar type, and an inverse coplanar type. These thin film transistors are formed on an insulating substrate made of glass or the like, and the surface thereof is covered with a protective insulating film.

The protective insulating film has a transistor characteristic due to a short circuit between upper wirings of thin film transistors (for example, data wiring in an inverted staggered thin film transistor) due to adhesion of dust or the like, or adhesion of moisture or contamination by heavy metal ions such as Na ions. The protective insulating film is provided to prevent deterioration and is generally the same silicon nitride film as the gate insulating film and the interlayer insulating film.

The above-mentioned silicon nitride film is formed by a plasma CVD apparatus. Generally, the silicon nitride film is formed by this plasma CVD apparatus after preheating the substrate in a preheating chamber. The film is transferred to a chamber and heated to a predetermined film forming temperature, and then the process gas (S
This is performed by a method of causing plasma discharge in an i H ₄ + NH ₃ + N ₂ ) atmosphere to deposit silicon nitride on the substrate.

Conventionally, the gate insulating film, the interlayer insulating film and the protective insulating film of the above-mentioned thin film transistor have a substrate temperature (surface temperature) of about 250-27.
The film is formed at 0 ° C. The silicon nitride film formed at such a substrate temperature has a dense film quality and a good withstand voltage.

On the other hand, in the thin film transistor, it is desirable to minimize the resistance of the gate wiring and the data wiring in order to improve the operating characteristics. Therefore, the electrodes and wiring of the thin film transistor are inexpensive and have low resistance.
It is formed of an Al-based alloy containing a refractory metal such as (tantalum). The source and drain electrodes are n
It may be formed of a metal such as Cr (chromium) having a good ohmic contact with the type semiconductor layer.

As described above, the electrodes and wirings are formed of the above Al-based alloy because the pure Al film is heated to several hundreds of degrees Celsius to roughen the film surface and generate sharp protrusions called hillocks. In particular, when the lower electrode and the lower wiring (for example, the gate electrode and the gate wiring in the inverted stagger type thin film transistor) are formed of pure Al, a gate insulating film, an interlayer insulating film, or the like is formed thereon by a plasma CVD apparatus. At that time, hillocks are generated on the surfaces of the lower electrode and the lower wiring, and defects such as cracks are generated in the gate insulating film and the interlayer insulating film due to the influence of the hillocks, so that the upper and lower electrodes and wirings are short-circuited.

However, when Al contains a refractory metal such as Ti or Ta, surface roughness during heating is suppressed. Therefore, if the electrodes and wirings are made of the above Al-based alloy, the gate insulating film is formed. It is possible to prevent hillocks from being generated on the surfaces of the electrodes and the wirings during film formation of the interlayer insulating film and the like, and to prevent short circuit between the upper and lower electrodes and between the wirings. In addition,
The surface roughness during heating of the Al-based alloy can be more effectively suppressed as the content of the refractory metal is increased. However, since the resistance of the Al-based alloy is increased when the content of the refractory metal is increased, It is desirable that the content be as low as possible within the range where hillocks are not generated during the manufacturing process of the thin film transistor.

[0009]

However, the conventional thin film transistor in which the protective insulating film is formed under the same film forming conditions as the gate insulating film and the interlayer insulating film is a transistor which is formed even when the protective insulating film is formed. The substrate is high (about 250
Since it is heated to ~ 270 ° C), the lower electrode and the lower wiring of the thin film transistor are made of Al containing a large amount of refractory metal.
If it is not formed of a system alloy, there is a problem that the above-mentioned short circuit occurs between the upper and lower wirings and between the electrodes in the manufacturing process of the thin film transistor.

That is, for example, in an inverted stagger type thin film transistor, generally, after forming a gate electrode and a gate wiring on a substrate, a gate insulating film, an i type semiconductor layer made of i type a-Sl (amorphous silicon), and n An n-type semiconductor layer made of n-type a-Sl doped with a type impurity,
The source and drain metal films are sequentially formed, and then the source and drain metal films, the n-type semiconductor layer, and the i-type semiconductor layer are patterned into the outer shape of the transistor element region, and the metal film and the n-type semiconductor layer are formed. After patterning and in the shape of source and drain electrodes, an interlayer insulating film is formed, a contact hole is formed in the interlayer insulating film, and then a wiring metal film is formed on the interlayer insulating film. The metal film is patterned to form a data line, and a protective insulating film is formed on the data line.

In this manufacturing method, the gate insulating film, the i-type and n-type semiconductor layers, the interlayer insulating film, and the protective insulating film are formed by the plasma CVD apparatus, and the gate insulating film and the interlayer insulating film are formed. The protective insulating film (both of which is a silicon nitride film) is formed at a substrate temperature of about 250 to 270 ° C. as described above, and the i-type and n-type semiconductor layers are about 25.
The film is formed at a substrate temperature of 0 ° C. The source / drain metal film and the wiring metal film are formed at a substrate temperature of about 100 ° C. by a sputtering device.

Therefore, in manufacturing the above-mentioned inverted stagger type thin film transistor, the gate electrode and the gate wiring, which are the lower electrode and the lower wiring, are formed of the gate insulating film, the i-type and n-type semiconductor layers, the interlayer insulating film, and the protective insulating film. Each film is repeatedly heated to several hundred degrees Celsius.

When the gate electrode and the gate wiring are repeatedly heated to several hundreds of degrees Celsius in this way, for example, until the interlayer insulating film is formed, the gate electrode and the gate wiring are protected by the final protection even if hillocks are not generated. Hillocks are generated in the gate electrode and the gate wiring when the insulating film is formed, and the hillocks cause defects in the gate insulating film and the interlayer insulating film, which causes a short circuit between the upper and lower electrodes and wiring. ..

Therefore, in the conventional thin film transistor,
The lower electrode and the lower wiring must be formed of an Al-based alloy with a high content of refractory metal so that hillock does not occur even when the protective insulating film that is finally formed is formed. The resistance of the lower electrode and the lower wiring becomes high, which deteriorates the operating characteristics of the thin film transistor.

An object of the present invention is to reduce the number of times the lower electrode and the lower wiring are heated to several hundreds of degrees Celsius in the manufacturing process, and to make the lower electrode and the lower wiring from an Al-based alloy having a low content of refractory metal. Prevents hillocks from forming even when formed, prevents short circuits between upper and lower electrodes and between wirings,
Moreover, it is an object of the present invention to provide a thin film transistor capable of improving the operating characteristics by reducing the resistance of the lower electrode and the lower wiring, and at the same time to provide a method for forming the protective insulating film.

[0016]

The thin film transistor of the present invention is characterized in that the protective insulating film covering the surface thereof is a silicon nitride film formed at a low temperature.

The method for forming a protective insulating film according to the present invention is
In a method of forming a protective insulating film made of a silicon nitride film by a plasma CVD apparatus, the transistor forming substrate is placed in a film forming chamber in a state where the temperature is room temperature, and the film forming is started immediately after that. Is.

[0018]

According to the thin film transistor of the present invention, since the protective insulating film which is finally formed in the manufacturing process 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 is reduced. be able to. If the lower electrode and the lower wiring are heated to a few hundreds of degrees Celsius in this manner, hillocks are generated even if the lower electrode and the lower wiring are made of an Al-based alloy having a low refractory metal content. Therefore, a defect due to the influence of the hillocks is not generated in the gate insulating film and the like, so that a short circuit between the upper and lower electrodes and wiring can be prevented. Further, since the lower electrode and the wiring thereof can be formed of an Al-based alloy having a low refractory metal content, 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.

The method for forming a protective insulating film according to the present invention is
Since the transistor formation substrate is placed in the film formation chamber at a room temperature and the film formation is started immediately after that, the protective insulating film made of a silicon nitride film can be formed at a low temperature.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings by taking a thin film transistor formed on a substrate of an active matrix liquid crystal display device as an example. The thin film transistor of this example is an inverted stagger type.

FIG. 1 is a sectional view of a thin film transistor,
This thin film transistor includes a gate electrode 2 formed on a transparent insulating substrate 1 made of glass or the like, a gate wiring (not shown) connected to the gate electrode 2, and a gate insulation covering the gate electrode 2 and the gate wiring. A film (transparent film) 3, an i-type semiconductor layer 4 formed on the gate insulating film 3, and an n-type semiconductor layer 5 on the i-type semiconductor layer 4.
Source electrode 6 and drain electrode 7 formed through
And a data line 9 connected to the drain electrode 7, the surface of which is covered with a protective insulating film 10.

Reference numeral 11 is a pixel electrode formed of a transparent conductive film such as ITO formed on the gate insulating film 3, and the pixel electrode 11 is formed by stacking its end portion on the source electrode 6. Is connected to the source electrode 6.

The i-type semiconductor layer 4 is formed of i-type a-Si, and the n-type semiconductor layer 6 is n-type a doped with n-type impurities.
Is formed of -Si, and the n-type semiconductor layer 5 is a channel region of the i-type semiconductor layer 4 (source electrode 6 and drain electrode 7).
(The area between and) is separated in the part corresponding to.

The gate electrode 2 and the gate wiring are A
The source and drain electrodes 6 and 7 are formed of an Al-based alloy containing a refractory metal such as Ti or Ta in l.
A metal having a good ohmic contact with the semiconductor layer 5;
For example, it is made of Cr or the above Al-based alloy.

The source and drain electrodes 6 and 7 are covered with an interlayer insulating film 8 formed thereon, and the data wiring 9 connected to the drain electrode 7 is formed on the interlayer insulating film 8. The data wiring 9 is formed of the above Al-based alloy or pure Al, and the data wiring 9 is connected to the drain electrode 7 through a contact hole 8a formed in the interlayer insulating film 8.

The gate insulating film 3 and the interlayer insulating film 8 are also provided.
The protective insulating film 10 and the protective insulating film 10 are both formed of silicon nitride by a plasma CVD apparatus (hereinafter, referred to as Si N).
The gate insulating film 3 and the interlayer insulating film 8 are high temperature SiN films formed at a substrate temperature of about 250 to 270 ° C., and the protective insulating film 10 has a substrate temperature of 100 ° C. or less. It is a low-temperature deposited SiN film.

The thin film transistor is manufactured by the following steps.

[Step 1] A metal film for a gate made of the above Al alloy is formed on the substrate 1 by a sputtering apparatus, and the metal film for a gate is patterned to form a gate electrode 2 and a gate wiring.

[Step 2] Next, the gate insulating film (high temperature SiN film) 3 and the i-type semiconductor layer (i-type a-Si film) 4 are formed.
And n-type semiconductor layer (n-type a-Si film) 5 with plasma C
Films are sequentially formed by a VD device, and a source,
A metal film for drain (Cr or Al alloy film) is formed by a sputtering apparatus.

[Step 3] Next, the source / drain metal film and the n-type semiconductor layer 5 and the i-type semiconductor layer 4 are patterned into the outer shape of the transistor element region, and the source / drain metal film and the n-type semiconductor layer are formed. The semiconductor layer 5 and the source / drain electrodes 6 and 7 are patterned.

[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 the pixel electrode 11.

[Step 5] Next, an interlayer insulating film (high temperature film formation S
iN film) 8 is formed by a plasma CVD apparatus, and a contact hole 8 corresponding to the drain electrode 7 is formed in the interlayer insulating film 8.
a is formed.

[Step 6] Next, a metal film for data wiring (Al-based alloy or pure Al film) is formed on the interlayer insulating film 8 by a sputtering device, and the metal film is patterned to form the data wiring. 9 is formed.

[Step 7] Next, a protective insulating film (low temperature film formation S
iN film) 10 is formed by a plasma CVD apparatus, and the protective insulating film 10 is formed on the transistor element region and the data wiring 9.
To form a thin film transistor.

FIG. 2 shows a plasma CVD apparatus used for forming the gate insulating film 3, the i-type and n-type semiconductor layers 4 and 5, the interlayer insulating film 8 and the protective insulating film 10.

This plasma CVD apparatus has a preheating chamber 2
1, a film forming chamber 22, and an unloading chamber 23, and can be opened and closed between the substrate receiving port of the preheating chamber 21, the substrate unloading port of the unloading chamber 23, and each chamber 21, 22, 23. A closed door 26 is provided. Further, heaters 27 and 28 are provided in the preheating chamber 21 and the film forming chamber 22, respectively.
Further, a discharge electrode 29 is provided in the film forming chamber 22.
A high frequency power supply 30 is connected to the discharge electrode 29. A process gas introduction pipe 30 and an exhaust pipe 31 are connected to the film forming chamber 22, and exhaust pipes 33 and 34 are connected to the preheating chamber 21 and the take-out chamber 23. Although not shown, in front of the preheating chamber 21, there is provided a substrate loading chamber provided with an openable / closable door at the substrate loading port, and an exhaust pipe is also connected to this substrate loading chamber. There is.

Then, the transistor formation substrate 1 is carried into the substrate loading chamber, and after the loading chamber is evacuated, it is transferred to the film forming chamber 22 through the preheating chamber 21. In this film forming chamber 22, the film A is formed. Is deposited. The substrate 1 on which the film A has been formed is exhausted from the gas in the film forming chamber 22, then transferred from the film forming chamber 22 to the taking-out chamber 23, and taken out from the substrate taking-out port. The transfer of the substrate to each chamber is performed by a transfer device (not shown).

The coating film A formed on the substrate 1 is made of Si.
N film (gate insulating film 3, interlayer insulating film 8, protective insulating film 1
0) or a-Si film (i-type and n-type semiconductor layers 4,
5) and the Si N film is Si H ₄ + NH ₃ + gas N ₂
Is used as a process gas, and the i-type a-Si film is Si H
₄ + gas H ₂ is used as a process gas to form an n-type aS
The i film is formed by using Si H ₄ + PH ₃ + gas H ₂ as a process gas.

The gate insulating film 3 and the interlayer insulating film 8 are transferred from the substrate loading chamber to the preheating chamber 21 for the substrate 1
Is preheated in the preheating chamber 21, and then the substrate 1 is transferred to the film forming chamber 22 so that the substrate temperature (surface temperature) is about 2
The film is heated to 50 to 270 ° C., and thereafter, plasma discharge is caused in a process gas atmosphere to deposit Si 3 N 4 on the substrate 1 to form a film.

FIG. 3 shows the gate insulating film 3 and the interlayer insulating film 8.
The film forming process of the substrate 1 is shown in FIG.
1 for about 40 minutes, and further for about 20 minutes in the film forming chamber 22 to form a film at a film forming temperature (about 250 to 270).
After the temperature is raised to (° C.), a SiN film is deposited for a predetermined film formation time that is determined according to the film thickness of the gate insulating film 3 and the interlayer insulating film 8, and the gas in the film forming chamber 22 is exhausted. It is transferred to the take-out chamber 23 and naturally cooled.

As described above, the gate insulating film 3 and the interlayer insulating film 8 made of the high-temperature formed SiN film formed at a high substrate temperature of about 250 to 270 ° C. have a dense film quality and a good withstand voltage.

The i-type semiconductor layer 4 and the n-type semiconductor layer 5 are also included.
The substrate 1 is preheated in the preheating chamber 21 as in the case of forming the gate insulating film 3 and the interlayer insulating film 8 described above, and the substrate 1 is transferred to the film forming chamber 22 to change the substrate temperature (surface temperature). A film is formed after heating to about 250 ° C.

On the other hand, the protective insulating film 10 preheats the substrate 1 transferred from the substrate loading chamber to the preheating chamber 21 without preheating (the heater 27 of the preheating chamber 21 is stopped). The substrate 1 having a substrate temperature of room temperature (about 25 ° C.) is transferred to the film forming chamber 22 through the chamber 21, and immediately after that,
Substrate 1 by causing plasma discharge in process gas atmosphere
A film is formed by a method of depositing a SiN film on top.

FIG. 4 shows a process for forming the protective insulating film 10 described above. The substrate 1 is passed through the preheating chamber 21 with the substrate temperature kept at room temperature (passing time is about 30 seconds to 1 minute), and is formed. Immediately after being placed in the film chamber 22, the formation of the protective insulating film 10 is started. In addition, the substrate 1 on which the film formation is completed is formed in the film formation chamber 2
After the gas in 2 is exhausted, it is transferred to the extraction chamber 23.

Even when the protective insulating film 10 is formed, the temperature inside the film forming chamber 22 (gas temperature) is controlled by the heater 28 to a temperature at which plasma discharge can be obtained. The temperature (surface temperature) rises during the formation of the Si 3 N film, but since the rise in the substrate temperature is from room temperature, the substrate temperature is 10 even at the end of the film formation.
It can be kept below 0 ° C. That is, the rise in the substrate temperature during film formation varies depending on the film formation time determined according to the film thickness of the protective insulating film 10, but for example, the film thickness is 200 to 300 n.
The time required to form the SiN film of m is about 10 to 15 minutes, and the substrate temperature does not exceed 100 ° C. in such a film forming time.

Although the dielectric strength of the protective insulating film 10 made of the low-temperature deposited SiN film formed at a low substrate temperature of 100 ° C. or less is not so good, the protective insulating film 10 has data due to adhesion of dust or the like. Since it is intended to prevent the wirings 9 from being short-circuited with each other and to prevent the transistor characteristics from being deteriorated due to adhesion of water or contamination with heavy metal ions such as Na ions, there is no particular problem even if the insulation breakdown voltage is poor.

In the thin film transistor of the above embodiment, since the protective insulating film 10 covering the surface is a SiN film formed at a low substrate temperature of 100 ° C. or lower, the protective insulating film formed last in the manufacture of the thin film transistor. Since the film can be formed at a low temperature, the gate electrode 20 which is the lower electrode and the lower wiring in the manufacturing process of the thin film transistor.
Further, the number of times the gate wiring is heated to several hundreds of degrees Celsius can be reduced. If the number of times the lower electrode and the lower wiring are heated to several hundreds of degrees Celsius is small, the gate electrode 20 and the gate wiring can be formed of an Al-based alloy having a low refractory metal content.

That is, the gate electrode 20 and the gate wiring are heated to several hundreds of degrees Celsius in the process of manufacturing the thin film transistor when the gate insulating film 3 and the interlayer insulating film 8 which are required to have sufficient withstand voltage are formed. Substrate temperature about 2
50 to 270 ° C.) during the film formation of the i-type and n-type semiconductor layers 4 and 5 (substrate temperature of about 250 ° C.). Therefore, the refractory metal content of the Al-based alloy used for the gate electrode 20 and the gate wiring is high. Is the gate insulating film 3 and the i-type and n
It is sufficient that the type semiconductor layers 4 and 5 and the interlayer insulating film 8 can withstand heating at several hundreds of degrees Celsius (no hillock is generated).

The gate electrode 20 and the gate wiring are formed of the metal film for the source and drain, the metal film for the data wiring and the transparent conductive film for the pixel electrode by the sputtering device even when the protective insulating film 10 is formed by the plasma CVD device. The substrate temperature at the time of forming the protective insulating film 10 is 100 ° C. or lower as described above, and the substrate temperature at the time of forming the metal film and the transparent conductive film is about 100 ° C. ,
Since this temperature is about the same as the substrate temperature (about 100 ° C.) when the gate metal film is formed by the sputtering device,
The surfaces of the gate electrode 20 and the gate wiring are not roughened when these are formed.

According to the above thin film transistor,
Even if the gate electrode 20 and the gate wiring are formed of an Al-based alloy having a low refractory metal content, hillocks do not occur. Therefore, defects due to the influence of the hillocks occur in the gate insulating film 3 and the interlayer insulating film 8. The gate electrode 2 and the source and drain electrodes 6, 6
It is possible to prevent short circuits between the gate wiring and the data wiring and between the gate wiring and the data wiring. Further, since the gate electrode 20 and the gate wiring can be formed of an Al-based alloy having a low refractory metal content, the resistance of the gate electrode 20 and the gate wiring can be reduced and the operating characteristics can be improved.

Further, according to the above thin film transistor,
Since the protective insulating film 10 is a SiN film formed at a substrate temperature of 100 ° C. or lower, the source / drain electrodes 6 and 7 are heated to several hundreds of ° C. in the manufacturing process of the thin film transistor. Therefore, when the source and drain electrodes 6 and 7 are formed of an Al-based alloy, the refractory metal content of the Al-based alloy is used for the gate electrode 20 and the gate wiring. It can be even less than alloys.

Further, since the data wiring 9 formed on the interlayer insulating film 8 is only heated to a temperature of 100 ° C. or lower when the protective insulating film 10 is formed, the data wiring 9 is made of a refractory metal. Al-based alloys and pure Al with a very small content
It is possible to reduce the resistance by forming it.

In the method of forming the protective insulating film, the transistor forming substrate 1 is placed in the film forming chamber 22 at a temperature of room temperature, and the film formation is started immediately after that. The protective insulating film 10 made of a film can be formed at a low temperature.

In the thin film transistor of the above embodiment, the data wiring 9 is formed on the interlayer insulating film 8 covering the source / drain electrodes 6 and 7, but the data wiring is formed on the gate insulating film 3 by the drain. It may be formed integrally with the electrode 6. In that case, the interlayer insulating film 8 is eliminated and the source,
Since the protective insulating film 10 may be formed on the drain electrodes 6 and 7 and the data wiring, the source and drain electrodes 6 and
7 can also be formed of an Al-based alloy or pure Al with a very low refractory metal content.

Further, although the thin film transistor formed on the substrate of the active matrix liquid crystal display element has been described in the above embodiments, 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 reverse stagger type thin film transistor,
It can also be applied to stagger type, coplanar type, and inverse coplanar type thin film transistors.

[0056]

In the thin film transistor of the present invention, since the protective insulating film covering the surface thereof is a silicon nitride film formed at a low temperature, the lower electrode and the lower wiring are heated to several hundred degrees Celsius in the manufacturing process of the thin film transistor. The number of times of heating can be reduced. Therefore, according to the thin film transistor of the present invention, hillock does not occur even if the lower electrode and the lower wiring are formed of an Al-based alloy having a low refractory metal content, so that a short circuit between the upper and lower electrodes and wiring is prevented. In addition, the operating characteristics can be improved by reducing the resistances of the lower electrode and the lower wiring.

The method for forming a protective insulating film according to the present invention is
Since the transistor formation substrate is placed in the film formation chamber at a room temperature and the film formation is started immediately after that, the protective insulating film made of a silicon nitride film can be formed at a low temperature.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram of a plasma CVD apparatus.

FIG. 3 is a diagram showing a film forming process of a gate insulating film and an interlayer insulating film.

FIG. 4 is a diagram showing a film forming process of a protective insulating film.

[Explanation of symbols]

1 ... Substrate, 2 ... Gate electrode, 3 ... Gate insulating film, 4 ... i
-Type semiconductor layer, 5 ... N-type semiconductor layer, 6 ... Source electrode, 7 ...
Drain electrode, 8 ... Interlayer insulating film, 8a ... Contact hole,
9 ... Data wiring, 10 ... Protective insulating film, 11 ... Pixel electrode.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 21/318 B 8518-4M 21/3205 29/40 A 7738-4M

Claims (3)

[Claims] 1. A thin film transistor having a surface covered with a protective insulating film, wherein the protective insulating film is a silicon nitride film formed at a low temperature. 2. The thin film transistor according to claim 1, wherein the protective insulating film is a silicon nitride film formed by a plasma CVD apparatus at a transistor forming substrate temperature of 100 ° C. or lower. 3. In a method of forming a protective insulating film made of silicon nitride by a plasma CVD apparatus, the transistor formation substrate is placed in a film formation chamber at a temperature of room temperature and the film formation is started immediately after that. And a method for forming a protective insulating film.