JP2001235767A - Method of forming nitride film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming a nitride film by using a plasma enhanced chemical vapor deposition(PECVD) suitable for a plastic LCD substrate such that a nitride film of high quality having good stability and excellent dielectric characteristics can be formed on a LCD substrate at a low temperature (less than 225 deg.C). SOLUTION: A standard gas for the formation of a nitride film consisting of a nitrogen-containing gas and a silicon-containing gas in an almost same gas ratio as that of the gas conventionally used for the formation of a nitride film by PECVD at a high temperature (over 325 deg.C) is introduced into a chamber 16 while a flow of at least one kind of rare gas selected from elements in the second to sixth periods of the group 18 in the long-form period table into the chamber 16, so as to form a nitride film on a LCD substrate 12 by using PECVD. As for the rare gas, argon (Ar) is especially preferable, and Ne, Kr and Xe are preferable. Thus, a nitride film having 3 to 5 NH/SiH (measured by FT-IR) is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of forming (depositing) a nitride film on a substrate of a liquid crystal display (LCD), and more particularly to a method of forming a nitride film on a substrate of a thin film transistor liquid crystal display (TFT-LCD). The present invention relates to a method for forming a film.

[0002]

2. Description of the Related Art Liquid crystal displays (LCDs) used in active matrix displays are typically:
It has a pair of transparent panels (substrates) parallel to each other that are sealed at the periphery. In the interior space between these panels,
Liquid crystal material is injected. One panel is a substrate provided with a large number of individually drivable thin film transistors (TFTs) for controlling transparent electrodes. Each TFT is connected to each other by a conductive wiring to control a circuit. In a typical TFT, a gate line on a substrate includes a gate insulating film, a channel semiconductor layer, source / drain regions,
A bottom gate structure (inverted stagger structure) covered with a transparent electrode and another layer is employed. Conventionally, a silicon nitride film, also called a nitride film or a gate nitride film, has been used as the gate insulating film.

One of the methods used for forming a gate nitride film and other films on a TFT-LCD is plasma enhanced chemical vapor deposition (PECVD).
icalVapor Deposition). PE on a glass substrate
The film forming temperature when forming a nitride film as a gate insulating film and an a-Si: H (hydrogenated amorphous silicon) layer used as a channel of a TFT using CVD is higher than 300 ° C. Since glass can withstand process temperatures of 600 ° C. or higher, if a glass substrate is used, 3
PECVD process temperatures between 25 ° C and 450 ° C do not cause manufacturing problems.

[0004] The market trend of personal computers is as follows.
From the popular desktop type of glass LCD panel,
They are moving to mobile or handheld products, which may use plastic displays. Because plastics are lightweight, moldable, bendable, and able to withstand impact forces, plastic displays have become a popular alternative to displays for handheld personal computers (PCs) and other portable devices. It is attractive as an option.

However, the maximum process temperature of a plastic LCD substrate must be lower than the temperature at which the plastic softens. The maximum process temperature is approximately 175-200 ° C., depending on the plastic used. PE for plastic substrate used for LCD
It is necessary to lower the process temperature of CVD to a temperature lower than 325 ° C. or higher for PECVD when a glass substrate is used.

[0006] PECVD in the manufacture of TFT-LCD
Other reasons for lowering the process temperature during film formation include switching to a plastic substrate, reducing power consumption, improving the handling of the apparatus, and improving the manufacturing throughput.

[0007]

However, PECVD in the step of forming a gate nitride film or another nitride film.
When the process temperature is lowered from a temperature exceeding 300 ° C. to 200 ° C., the quality of a film to be formed changes. As the film formation temperature is lowered, the hydrogen content in the formed nitride film increases, the amount of water absorption increases, and the dielectric properties of the nitride film decrease. These cause a decrease in the channel mobility of the TFT device. An increase is also observed with respect to the fluctuation of the threshold voltage of the TFT device. These and other disadvantages have previously deterred the use of plastic substrates and low temperature fabrication processes in TFT-LCD fabrication.

[0008] LCDs transparent at temperatures lower than about 325 ° C or higher used in conventional PECVD processes
It would be advantageous if TFTs could be fabricated on a substrate.

Further, when a nitride film such as a TFT gate nitride film or a nitride film for a passivation (passivation) layer is formed on an LCD substrate, PECV at a temperature of about 200 ° C. or less.
It would be advantageous if D could be used to form a nitride film exhibiting substantially the same dielectric properties and thermal stability as a nitride film formed at 325 ° C. or higher.

[0010] The conventional PECVD equipment is used at a low temperature (about 200 ° C or less) and at a high temperature (ie, about 30 ° C).
If a TFT gate nitride insulating film or another nitride film can be formed on an LCD substrate using the same film forming gas used for forming the nitride film at 0 ° C. or higher,
It would be convenient.

Accordingly, an object of the present invention is to provide a plasma enhanced chemical vapor deposition method (PE) capable of forming a high quality nitride film having excellent dielectric properties and thermal stability even at a low film forming temperature.
Provided is a method of forming a nitride film used for an active element on a liquid crystal display (LCD) using CVD, and more particularly, to a method of forming a nitride film used for an active element on a plastic liquid crystal display (LCD). It is another object of the present invention to provide a method for forming a nitride film which is suitable as the above.

[0012]

In order to solve the above-mentioned problems, a method of forming a nitride film according to the present invention uses a plasma enhanced chemical vapor deposition method to form a nitride film used for an active element of a liquid crystal display. A) placing a plastic liquid crystal display substrate having a film-forming surface on which a nitride film is to be formed in a reaction chamber, at a temperature not exceeding a thermal deformation temperature of the plastic liquid crystal display substrate. Heating the liquid crystal display substrate; b)
In the same reaction chamber where the substrate is placed, while applying sufficient energy to generate a gas plasma, a gas flow of a nitrogen-containing gas, a gas flow of a silicon-containing gas, and a second group of Group 18 of the long period type periodic table are used. Generating a gas plasma in the reaction chamber by introducing a gas flow of at least one rare gas selected from elements of six periods into the reaction chamber;
c) forming a nitride film on the film-forming surface by plasma enhanced chemical vapor deposition using the gas plasma generated in the step b), thereby forming a stable nitride film on the film-forming surface; And a process.

According to the above method, in the step c), large energy is given to the film forming surface by the rare gas ions generated in the step b). This allows
A nitride film having an NH / SiH ratio (ratio of the number of N—H bonds to the number of Si—H bonds) measured by FT-IR in the range of 3 to 5 can be formed at a low film formation temperature. As a result, a high-quality nitride film having excellent dielectric properties and thermal stability can be formed while preventing deformation and opacity of the plastic LCD substrate. In addition, by suppressing the film formation temperature, power consumption can be reduced, the handleability of the apparatus can be improved, and the manufacturing throughput can be improved.

Further, according to the above method, by generating plasma in the same reaction chamber where the substrate is placed, energy can be more effectively given to the substrate, and the diffusion length of the active species moving around the film formation surface can be increased. Can be extended.

In the specification of the present application, "nitride film"
Denotes a silicon nitride film.

In the above method, the LCD substrate is
Preferably, the heating is performed at a temperature of 200C or lower, and the above method is particularly effective at a temperature of 200C or lower. The nitrogen-containing gas (NCG) used in the above method is
Preferably, it contains NH ₃ and N ₂ . In the above method, the flow rate of the at least one rare gas introduced into the chamber during the formation of the nitride film may be 5 to 20 times the flow rate of the silicon-containing gas (SiCG) introduced into the chamber. Preferably it is within the range of 2 times. Also,
In the above method, the flow rate of the nitrogen gas (NCG) introduced into the chamber when the nitride film is formed is in a range of 4 to 25 times the flow rate of the silicon-containing gas (SiCG) introduced into the chamber. Is preferably within the range. Further, the silicon-containing gas (SiCG) is preferably SiH ₄ .

According to these preferred embodiments, a high quality nitride film can be formed more reliably.

In order to solve the above-mentioned problems, a method of forming a nitride film according to the present invention uses a plasma-enhanced chemical vapor deposition method.
A method for forming a nitride film used for an active element of a liquid crystal display, comprising the steps of: a) placing a liquid crystal display substrate having a film formation surface on which a nitride film is to be formed in a reaction chamber;
Heating the liquid crystal display substrate at a temperature of 225 ° C. or lower, and b) applying N to the same reaction chamber in which the substrate is placed while applying sufficient energy to generate gas plasma.
The gas flow of the nitride film forming gas including the gas flow of H _3, the gas flow of N ₂ , and the gas flow of SiH ₄ is at least one rare gas selected from the elements of the second to sixth periods of Group 18 of the long period type periodic table. Generating a gas plasma in the reaction chamber by introducing the gas flow into the reaction chamber together with the gas flow; and c) forming the film deposition surface by plasma enhanced chemical vapor deposition using the gas plasma generated in the step b). Forming a nitride film thereon, and thereby forming a stable nitride film on the film formation surface.

According to the above method, in the step c), a large energy is given to the film forming surface by the rare gas ions generated in the step b). This allows
A nitride film having a NH / SiH ratio (ratio of the number of N—H bonds to the number of Si—H bonds) measured by FT-IR of 3 to 5 at a low film formation temperature of 225 ° C. or less can do. As a result, reduction in power consumption, improvement in handleability of the device, and improvement in manufacturing throughput can be achieved. Further, even when a plastic LCD substrate having lower heat resistance than a glass LCD substrate is used, a high quality nitride film having excellent dielectric properties and thermal stability is formed while preventing deformation and opacity of the plastic LCD substrate. be able to.

Further, according to the above method, by generating plasma in the same reaction chamber where the substrate is placed, energy can be more effectively given to the substrate, and the diffusion length of the active species moving around the film formation surface can be increased. Can be extended.

In the above method, the NH in the step b) is used.
₃ / SiH ₄ ratio is in the range of 2 / 1-12 / 1, and the flow rate of the airflow of N ₂ in the above step b), the total flow rate of airflow is introduced into the chamber 30% to 80% of It is preferable that it is within the range. Further, in the step c) of forming the nitride film in the above method, the internal pressure of the chamber is set to 67.
Pa (0.5 Torr) to 400 Pa (3.0 Torr)
r) N is introduced into the chamber so as to fall within the range of r).
Preferably, the method includes a step of maintaining a flow rate of H ₃ , N ₂ , SiH ₄ , and at least one rare gas.
Further, in the above method, it is preferable that the level of energy applied to the chamber for generating gas plasma is in the range of 0.4 W to 4.0 W per square centimeter of the substrate surface. Further, the NH ₃ / N ₂ / SiH ₄ ratio in the above step b) is about 5/13/1.
It is preferred that Further, in the above method, the flow rate of the gas flow of at least one kind of rare gas introduced into the chamber at the time of forming the nitride film is determined by the flow rate of the Si gas introduced into the chamber.
Is preferably in the range 5 to 20 times the air flow of the flow rate of H _4.

According to these preferred embodiments, a high quality nitride film can be formed more reliably.

In each of the above methods, at least one rare gas used together with NCG and SiCG is:
It is preferably at least one rare gas selected from Ne, Ar, Kr, and Xe, and particularly preferably contains Ar.

According to these preferred embodiments, a high quality nitride film can be formed more reliably.

In each of the above methods, the step b) is performed.
Will generate multiple types of ions including rare gas ions,
In the step c), the ions impart energy to the substrate surface. In the step b), the energy imparted to the substrate surface by one rare gas ion is changed by the energy of the other ions to the substrate surface. Is preferably larger than the energy given to

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. Here, a case will be described in which the present invention is applied to a thin film transistor liquid crystal display which is one type of active matrix liquid crystal display. A thin film transistor liquid crystal display has a large number of pixel electrodes on a transparent substrate such as a plastic substrate or a glass substrate as one of a pair of substrates sandwiching liquid crystal, and active elements for driving these pixel electrodes ( A substrate (active matrix substrate) on which a large number of thin film transistors as switching elements and wirings are formed is provided. Here, a case where a nitride film is formed as a gate insulating film of a thin film transistor or a passivation film formed over a thin film transistor and its wiring by using the method of the present invention will be particularly described.

FIG. 1 illustrates a plasma enhanced chemical vapor deposition (PEC) process on a substrate such as a liquid crystal display (LCD) substrate 12.
FIG. 1 is a schematic diagram of a suitable PECVD apparatus 10 for performing film formation by VD). The LCD substrate 12 is preferably a plastic substrate made of a transparent plastic material. On the LCD substrate 12, a thin film transistor (T
FT), interconnected wires and the like made of a conductive material such as metal are formed. Suitable plastic substrates used for the LCD substrate 12 are "Polyethersulfone PES", commercially available from Amoco, and Amoc.
o) "UDEL polysulfone" commercially available from
And DuPont and Eastma
n) A substrate made of any one of “PET” (polyethylene terephthalate) commercially available from the company. This low temperature deposition technique of nitride film is particularly suitable as a method of forming a TFT on a plastic substrate, but the method of the present invention is applied to a glass substrate or other suitable type of transparent LCD.
It can also be used for film formation on a substrate.

As used herein, the term "low temperature" is about 200
Temperature below 225 ° C or below 225 ° C. This is approximately equal to the heat distortion temperature of the plastic used for the plastic LCD substrate. About 200 ° C
Plastic substrates heated to higher temperatures tend to deform and become opaque, which makes them uncommercially useable. The heat distortion temperature of the plastic suitable for the LCD substrate 12 is, for example, according to the manufacturer's specifications, for example,
(1) Thermal deformation temperature of polyethersulfone PES = 20
4 ° C., (2) Thermal deformation temperature of UDEL polysulfone = 17
4 ° C., (3) PET heat distortion temperature = 190 ° C. The term "thermal deformation temperature of the LCD substrate" as used herein refers to the case where the thermal deformation temperature of the LCD substrate is determined as in the case of processing a plastic LCD substrate (when the temperature is approximately in the range of 170C to 250C). When the thermal deformation temperature of the LCD substrate is not determined, as in the case of processing a non-plastic LCD substrate, it means 225 ° C. or less. As used herein, the term “high temperature” refers to a temperature higher than about 300 ° C. or conventional PECVD for forming a gate nitride film on a glass substrate.
It refers to a temperature of 325 ° C. or higher, which is the process temperature of the process.

The PECVD apparatus 10 has a PECVD chamber (reaction chamber; hereinafter, abbreviated as a chamber) 16 having a size suitable for holding at least one LCD substrate (hereinafter, abbreviated as a substrate) 16. including. Substrate 12 is held on chuck 20 in chamber 16. The interior 22 of the chamber 16 is evacuated or pressurized by a suitable pump and valve device, shown schematically as a pump 26 in FIG. The individual substrates 12 can also be moved from outside to inside, from inside to outside of the chamber 16 by a suitable handler 30 through a gate valve 32 provided on the chamber wall (the wall of the chamber 16). Thus, the individual substrates 12 can be removed from the chamber 16 after being moved onto the chuck 20 for film formation.

The plurality of selected gases used in the PECVD process are supplied to respective gas supply devices 80, 82, 84, and 80, which are shown in FIG.
From 86, controlled by valve 42, is introduced into chamber 16 through a suitable manifold system 36. These gases are introduced into the chamber 16 through a so-called shower head 46. Shower head 4
Numeral 6 is for spraying these gases as required.

The chuck 20 can be heated to any desired temperature. For heating the chuck 20, a heating element schematically shown as a heater 50 is provided. The heater 50 and the chuck 20 are made of PEC
It is used to set the temperature of the substrate 12 during the VD processing.

Plasma energy is supplied to the chamber 16 from a high frequency (HF) source (RF source) 52. The HF source 52 typically has an HF power (RF
Power) is supplied to the shower head 46 so that the shower head 46 emits HF power. The frequency of the HF plasma energy used in the PECVD chamber 16 is 13.56 megahertz (MHz) according to industry standards, but the present invention is not limited to any particular value of high frequency (HF).

Therefore, the gas supply devices 80, 82, 8
The plurality of types of gases supplied from 4.86 receive plasma energy from the HF generation source 52 at the shower head 46 to generate gas plasma. When the gas plasma is generated, at least a part of each of the molecules (NH ₃ , N ₂ , SiH ₄ , and rare gas molecules) contained in each gas is ionized. Then, the rare gas ions generated by ionizing the rare gas molecules collide with the surface of the substrate 12. Thereby, energy is given to the surface of the substrate 12 by the rare gas ions, and a reaction of generating silicon nitride from nitrogen-containing ions, silicon-containing ions, and the like on the surface of the substrate 12 is promoted.

The shower head 46 accelerates a gas such as a rare gas sent through the manifold system 36 so as to have a flow velocity higher than that in the manifold system 36. The concentration of the rare gas ions decreases with increasing distance from the position where the gas plasma is generated. However, by accelerating the rare gas as described above, the rare gas ions are compared with the case where the rare gas is directly introduced into the chamber 16 from the manifold system 36. Then, the rare gas ions can be more efficiently
2 surface can be reached. Therefore, the substrate 12
More energy can be given to the surface. As a result, a nitride film of even better quality can be formed.

The shower head 46 is designed to blow gas uniformly on the entire substrate 12. As a result, rare gas ions generated by ionization of the rare gas molecules uniformly collide with the entire substrate 12, and large energy is uniformly applied to the entire substrate 12. As a result, a nitride film having a more uniform film quality can be formed.

The present invention provides a process for forming a nitride film on the LCD substrate 12 using the PECVD apparatus 10 at a temperature not exceeding the thermal deformation temperature of the LCD substrate 12. Plastic LCD substrate (plastic LC
If the heat distortion temperature of the D substrate 12) is not disclosed by the manufacturer, the heat distortion temperature of the plastic LCD substrate is set to about 2
The present invention is preferably carried out at a deposition temperature of about 200 ° C. or less, assuming that the temperature is 25 ° C. or less.

FIG. 2 shows each step in the process of the present invention. Each step will be described with reference to FIGS. First, the substrate 12 is placed on the chuck 20 in the PECVD chamber 16 by, for example, the handler 30. The substrate 12 has a film formation surface (surface for receiving a nitride film) on which a nitride film is to be formed, schematically shown as “58” in FIG. Film forming surface 58
May be the upper surface of the substrate 12 or the surface of a layer formed on the LCD substrate 12.
A conductor pattern or the like formed on the CD substrate 12 may be used. For example, when forming a bottom gate type TFT, as is well known to those skilled in the art, a conductor pattern of a gate line is formed on the substrate 12, and a gate nitride film is formed on the conductor pattern. You. Therefore, the film forming surface 58 of the substrate 12 may include the surface of the conductive wiring formed in advance. Further, the method of the present invention can be used to form a nitride film as a passivation layer on a TFT or the like completed on the substrate 12.

The first step shown in FIG. 2 is to heat the substrate 12 at a temperature lower than the thermal deformation temperature of the substrate 12 (Step 7).
0. Alternatively, step 70 is performed when the thermal deformation temperature of the substrate 12 is not determined as described above.
It is defined as the step of heating the substrate 12 at a temperature of less than or equal to ° C. In a preferred embodiment of the present invention, in step 70, the substrate 12 is heated at a temperature of about 200 ° C. or less.

In the next step 76, a nitrogen-containing gas (NC
G), a silicon-containing gas (SiCG), and a gas flow of at least one rare gas selected from elements of the second to sixth periods of Group 18 of the long-period type periodic table from the gas supply unit 40 through the manifold 36 to the chamber 16. (See FIG. 1). The process for forming a nitride film at a low temperature according to the present invention may include at least one process selected from the above-described specific group.
A conventional gas used for forming a nitride film by high-temperature PECVD is used in addition to the rare gas. The NCG, it is possible to use NH ₃ (ammonia) and N ₂ (gaseous nitrogen). Preferred SiCG is SiH
₄ (silane). Here, a gas composed of NH ₃ , N ₂ , and SiH ₄ is referred to as a nitride film forming gas.

Preferred noble gases used in the method of the present invention
Is neon (Ne), argon (Ar), krypton
(Kr), and xenon (Xe). These gases
At least one of the following is used:_Three, N_Two,
And SiH_FourCan be supplied with Ne, A
selected from the group of noble gases consisting of r, Kr, and Xe
When only one rare gas is used together with the nitride film forming gas
As may be imagined, the method of the present invention provides for two or more
Noble gases may be used. As shown in FIG.
Gas supply unit 40 for supplying gas to D chamber 16
Inside, as a gas supply device for supplying each gas, N
H_ThreeSupply NH_ThreeGas supply device 80, N _TwoSupply
N_TwoGas supply device 82, SiH_FourSupplying SiH_Four
Gas supply device 84, and at least one selected from the group above
Also provided is a rare gas supply device 86 for supplying one type of rare gas.
Have been.

The nitride film forming gases NH ₃ , N ₂ and SiH ₄ used in the method of the present invention have a ratio of NH ₃ / N ₂ / Si
Preferably, H ₄ is approximately 5/13/1. Also, the ratio of NH _{3 to} SiH ₄ (NH ₃ / SiH
₄ ) is approximately in the range of 2/1 to 12/1, and the flow rate of the nitrogen gas (N ₂ ) is approximately 30% to 80% of the total flow rate of the airflow introduced into the chamber 16 in step 76. Is within the range.

Also, during step 76, an appropriate plasma power is applied into the chamber 16 (step 8).
8). In the present invention, the plasma power supplied by the HF source 52 has a frequency of 13.56 MHz.
And the energy level is approximately 0.4 W (watt) to 4.0 W per square centimeter of the LCD substrate surface (that is, the surface area of the deposition surface 58 on the substrate 12).
Is preferably within the range. Steps 76 and 88 are performed as shown by the dashed box 90 in FIG.
It is performed simultaneously by the ECVD device 10.

In the method of the present invention, NCG and SiCG are introduced into the chamber 16 together with NCG and SiCG during the step 76 at least one rare gas selected from the elements of the second to sixth cycles of Group 18 of the long-period periodic table. The step of performing The flow rate of at least one noble gas selected from the above group introduced into the PECVD chamber 16 is in the range of 5 to 20 times the flow rate of SiH ₄ introduced into the chamber 16 during the step 76. .

The flow rate of gas introduced into chamber 16 during steps 76 and 88
Internal pressure is approximately 67 Pa (0.5 Torr) to 400
It should be controlled so as to be within the range of Pa (3.0 Torr). As a result of the above process, box 92 in FIG.
As shown by a symbol, a nitride film is formed.

According to the present invention, the PEC is used during the low-temperature deposition of the nitride film.
This was accomplished by experimenting with introducing argon into the VD chamber. It is believed that the use of neon or other noble gases having a higher atomic weight than argon will have the same effect as using argon. It has been found that the use of argon can improve the quality of a nitride film formed by low-temperature PECVD, which is used for a gate insulating film and a passivation layer.

The TFT-LCD according to the present invention has a low nitride film.
According to the results of experiments using the warm PECVD film forming method,
Lugon or other long-period table of the 18th group of the periodic table
Using high temperature PECVD without the addition of periodic rare gas
Compared with nitride films formed by
An oxide film was obtained. The method of the present invention uses the conventional basic PE
The process temperature of the CVD nitride film
At the same time as remarkable reduction, less selected from the above group
Both are obtained by dilution with one kind of rare gas. Above
The exact mechanics that produce excellent results
Not elucidated, but when diluted with Ar
Ar ions (Ar⁺), Formed nitride film
It is considered that energy was given to the surface to be treated. Step
In a plasma atmosphere, a pressure of about 130 Pa (about 1 Torr)
Force causes numerous collisions between the introduced reactants.
You. This collision is caused by Ar ions, SiH_ThreeIon (SiH
_Three ⁺), NH ions (NH⁺), And N ions
(N⁺) Etc. are formed. All this collision
Occur between the molecules of the mean free path of each molecule and
The average collision time is the same. Therefore, in the plasma
The average velocities of all the molecules in the sample are the same.

The reaction table where the ionized species is a nitride film is formed.
Surface (the surface of the LCD substrate 12 where a reaction to form a nitride film occurs)
When it collides with the film forming surface 58), a certain amount of energy is
To the surface. Larger ions are larger
Apply critical energy to the reaction surface. Ion is heavy
The momentum of the ions increases,
To the reaction surface. Nitriding by PECVD described above
In the case of a film forming method, N _TwoMass (expressed in atomic mass units)
Mass of one molecule) is about 28, NH_ThreeHas a mass of about 17, S
iH_FourIs about 32 in atomic mass units of
The mass expressed in atomic mass units of r is about 40. Predetermined
Plasma power, chamber pressure, and substrate temperature
As a result, Ar ions are larger than other ions on the reaction surface.
Give energy. Such a relatively heavy gas (Ar)
The relatively high ion energy of the substrate lowers the substrate temperature
It is thought that the energy lost due to is compensated.
In the above process, a rare gas heavier than neon or Ar
However, these rare gases can be removed by CVD plating during nitride film formation.
Significant energy on the reaction surface when ionized by Zuma
Energy, it acts in the same way as Ar.
available.

Note that even when Ne is used in the above process, the energy given to the substrate surface by one Ne ion is larger than the energy given to the substrate surface by one N ₂ ion. The reason is as follows. Ne is
It can generate plasma with a lower input power than N _2. Since the input power and the electron energy are almost proportional, Ne requires less energy. The energy given to the substrate surface by one ion is equal to (input power) / (mass of one ion), so that the Ne ion having a small mass per one is larger.

The major effect of the energy imparted to the reaction surface by the addition of argon, one or more noble gases, or more than one noble gas is to increase the rate of hydrogen passivation at the reaction surface and, as a result, NH / Si in the silicon nitride film that forms many vacancies on the reaction surface and is formed
The purpose is to improve the H ratio. As is well known in the art, the NH / Si of the gate nitride film measured by FT-IR (Fourier transform infrared spectroscopy)
The H ratio is preferably from 3 to 5. A nitride film having an NH / SiH ratio FT-IR measurement value of 3 to 5 exhibits good dielectric properties. When this good nitride film is used as a gate insulating film of a TFT device, it also contributes to improving the thermal stability of the breakdown voltage (Vt) and the electron mobility (μ) of the completed TFT device.

Table 1 shows a TF having a nitride film formed by low-temperature PECVD for dilution with Ar according to the present invention.
A TFT device (abbreviated as “LT TFT (Ar dilution)” in the table) and a TFT device manufactured by forming a nitride film using conventional high-temperature PECVD without dilution with Ar (in the table, This is a comparison of characteristics between an "HT TFT" (abbreviated as "HT TFT") and a TFT device (abbreviated as "LT (no dilution)" in the table) manufactured by low-temperature PECVD.

[0051]

[Table 1]

In the above table, Ioff is the voltage (gate voltage) Vg = -10 applied to the gate electrode.
V, the voltage (signal voltage) Vd applied to the drain electrode =
The current value (leakage current) flowing between the source and the drain of the TFT under the condition of 1 V (the condition that the TFT is turned off) is shown, and dVt is 6 hours under the condition of Vg = Vd = 25 V and a temperature of 40 ° C. The change (increment) in the breakdown voltage of the TFT device when held.

As can be seen from Table 1, the characteristics of the TFT formed by using the nitride film according to the present invention as the gate insulating film are almost the same as those of the TFT formed by using the conventional high-temperature process, whereas those of the TFT formed by using the conventional high-temperature process. In a low-temperature process in which no dilution is performed, characteristics of the obtained TFT (thermal stability of breakdown voltage and leak current characteristics) are deteriorated.

Next, a specific experimental example of the process of the present invention will be described.

First, in the AKT PECVD 1600 system, a sample of an LCD substrate having a size of 46.5 cm × 35.5 cm is placed on the chuck 20 and placed on the chuck 20.
Heated at a temperature of 00 ° C.

Next, an NH ₃ , N ₂ , SiH ₄ , and Ar gas stream was supplied at a flow rate of 750 sccm for NH ₃ , 2000 sccm for N ₂ , 150 sccm for SiH ₄ ,
Ar was introduced into the chamber 16 at a flow rate of 2000 sccm. The unit of flow rate “sccm” is 0 ° C., 1
The volume of gas flowing per minute in atm is cc
It is represented by

Also, HF power (13.56 MHz) is applied to the chamber 16 from the high frequency (HF) source 52 at 1550.
Granted at W power level. The pressure of the atmosphere in the chamber 16 was maintained at about 200 Pa (about 1.5 Torr).

Under the above conditions, a nitride film was formed at a film formation rate of 30 to 45 ° / sec. The film was formed for 2 minutes. The final NH / SiH ratio FT-IR measurement at the time the wafer was removed from the chamber was 4.0.

According to the present invention, it has been found that thermal stability, dielectric characteristics, and leak current characteristics can be improved by forming a nitride film by PECVD at a low temperature. The process described above can be varied in many ways within the scope of the invention. For example, the specific film forming temperature and gas ratio shown in the above experimental examples can be changed within the scope of the claims of the present invention. Also, here
The nitride film used as the gate nitride film of the TFT has been mainly described.
It can also be used for other purposes in D manufacturing. For example, the method of forming a nitride film according to the present invention can be used to form a nitride film as a passivation film on an active element by PECVD.

Further, the method for forming a nitride film according to the present invention comprises:
It can be applied to uses other than LCD manufacturing. For example, when the present invention is applied to uses other than LCD manufacturing, the substrate on which the nitride film is formed is not limited to a transparent substrate mainly composed of an insulating substrate such as an LCD substrate, but is formed on an opaque insulating substrate. It may be an opaque substrate on which a conductor layer or a semiconductor layer is formed.

In addition, the above-mentioned method of forming a nitride film includes N
1 selected from the group consisting of e, Ar, Kr, and Xe
A kind of gas may be used, and a mixture of two or more kinds of rare gases selected from the above group may be used.

[0062]

As described above, the method for forming a nitride film according to the present invention comprises the steps of: a) placing a plastic liquid crystal display substrate having a film formation surface on which a nitride film is to be formed in a reaction chamber; Heating the plastic liquid crystal display substrate at a temperature not exceeding the thermal deformation temperature of the liquid crystal display substrate, and b) applying sufficient energy to generate gas plasma to the same reaction chamber in which the substrate is placed, By introducing a gas flow of a nitrogen-containing gas, a gas flow of a silicon-containing gas, and a gas flow of at least one rare gas selected from the elements of Groups 2 to 6 of Group 18 of the long-period periodic table into the reaction chamber. Generating a gas plasma in the reaction chamber; and c) forming a nitrogen gas on the film-forming surface by a plasma chemical vapor deposition method using the gas plasma generated in the step b). Forming a nitrided film, thereby forming a stable nitride film on the film formation surface.

According to the above method, in the step c), large energy is given to the film formation surface by the rare gas ions generated in the step b). This allows
A nitride film having an NH / SiH ratio (ratio of the number of N—H bonds to the number of Si—H bonds) measured by FT-IR in the range of 3 to 5 can be formed at a low film formation temperature. Therefore, the above method has an effect that a high-quality nitride film having excellent dielectric properties and thermal stability can be formed while preventing deformation and opacity of the plastic LCD substrate. In addition, the above-described method also has the effect of reducing power consumption, improving the handleability of the apparatus, and improving the production throughput by keeping the film formation temperature low.

Further, according to the above method, by generating plasma in the same reaction chamber where the substrate is placed, energy can be more effectively given to the substrate, and the diffusion length of the active species moving around the film formation surface can be increased. The effect that it can extend is also produced.

As described above, the method for forming a nitride film according to the present invention comprises the steps of: a) placing a liquid crystal display substrate having a film formation surface on which a nitride film is to be formed in a reaction chamber;
Heating the liquid crystal display substrate at a temperature of 25 ° C. or less, and b) applying NH to the same reaction chamber in which the substrate is placed while applying sufficient energy to generate gas plasma.
_The gas flow of the nitride film forming gas including the gas flow of No. 3, the gas flow of N ₂ , and the gas flow of SiH ₄
A step of generating a gas plasma in the reaction chamber by introducing the gas plasma into the reaction chamber together with a gas flow of at least one rare gas selected from elements having up to 6 cycles; and c) converting the gas plasma generated in the step b). Forming a nitride film on the film formation surface by the used plasma enhanced chemical vapor deposition method, thereby forming a stable nitride film on the film formation surface.

According to the above method, in the step c), a large energy is given to the film formation surface by the rare gas ions generated in the step b). This allows
A nitride film having a NH / SiH ratio (ratio of the number of N—H bonds to the number of Si—H bonds) measured by FT-IR of 3 to 5 at a low film formation temperature of 225 ° C. or less can do. Therefore, the above-described method has an effect that power consumption can be reduced, device handling can be improved, and manufacturing throughput can be improved. Also,
The above method is capable of forming a high quality nitride film having excellent dielectric properties and thermal stability while preventing deformation and opacity of a plastic LCD substrate even when a plastic LCD substrate having lower heat resistance than a glass LCD substrate is used. It also has the effect that it can be formed.

Furthermore, according to the above method, by generating plasma in the same reaction chamber where the substrate is placed, energy can be more effectively given to the substrate, and the diffusion length of the active species moving around the film formation surface can be increased. The effect that it can extend is also produced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a PECVD apparatus for performing the method of the present invention.

2 is a flowchart showing each step of a method for forming a nitride film for a thin film transistor (TFT) at a low temperature (ie, about 200 ° C. or lower) using the PECVD apparatus of FIG.

[Explanation of symbols]

Reference Signs List 10 PECVD apparatus 12 LCD substrate (substrate) 16 PECVD chamber (reaction chamber) 36 Manifold system 40 Gas supply unit 46 Shower head 52 HF generation source 58 Film forming surface 80 NH ₃ gas supply device 82 N ₂ gas supply device 84 SiH ₄ gas Supply device 86 Noble gas supply device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) H01L 21/336 H01L 29/78 619A (72) Inventor John Hersell 98607, Washington, United States of America, Camas, Columbia Summit Drive N. W. 2026

Claims (28)

[Claims] 1. A method for forming a nitride film used for an active element of a liquid crystal display using a plasma enhanced chemical vapor deposition method, the method comprising: a) having a film formation surface on which a nitride film is to be formed; Put the plastic liquid crystal display substrate in the reaction chamber,
Heating the plastic liquid crystal display substrate at a temperature not exceeding the thermal deformation temperature of the plastic liquid crystal display substrate; and b) applying sufficient energy to generate gas plasma to the same reaction chamber where the substrate is placed. And introducing a gas flow of a nitrogen-containing gas, a gas flow of a silicon-containing gas, and a gas flow of at least one rare gas selected from elements in the second to sixth cycles of Group 18 of the long-period periodic table into the reaction chamber. A step of generating gas plasma in the reaction chamber; and c) forming a nitride film on the film formation surface by plasma enhanced chemical vapor deposition using the gas plasma generated in step b). Forming a stable nitride film on the film-forming surface by the method described above. 2. The method according to claim 1, wherein the step (a) includes a step of heating the substrate at a temperature of 225 ° C. or lower. 3. The method according to claim 1, wherein said step a) includes heating the substrate at a temperature of 200 ° C. or less. 4. The method according to claim 1, wherein the nitrogen-containing gas introduced in step b) comprises NH ₃ and N _2.
The method for forming a nitride film according to the above. 5. The method according to claim 1, wherein the flow rate of the gas flow of the at least one rare gas introduced into the reaction chamber in the step b) is in the range of 5 to 20 times the flow rate of the gas flow of the silicon-containing gas. The method for forming a nitride film according to claim 1. 6. The method for forming a nitride film according to claim 5, wherein the gas flow of at least one rare gas introduced into the reaction chamber in the step b) contains argon (Ar). 7. The method according to claim 1, wherein the flow rate of the nitrogen-containing gas introduced into the reaction chamber in step b) is in the range of 4 to 25 times the flow rate of the silicon-containing gas. 6. The method for forming a nitride film according to claim 5. 8. The method according to claim 1, wherein the silicon-containing gas introduced into the reaction chamber in step b) is SiH ₄ . 9. The gas flow of at least one rare gas introduced into the reaction chamber in the step b) is in the range of 5 to 20 times the gas flow of the silicon-containing gas. 9. The method for forming a nitride film according to claim 8, wherein: 10. The method for forming a nitride film according to claim 9, wherein the gas flow of at least one rare gas introduced into the reaction chamber in the step b) contains argon (Ar). 11. A method for forming a nitride film used for an active element of a liquid crystal display using a plasma enhanced chemical vapor deposition method, the method comprising: a) having a film-forming surface on which a nitride film is to be formed; Placing the liquid crystal display substrate in a reaction chamber and heating the liquid crystal display substrate at a temperature of 225 ° C. or less; b) in the same reaction chamber where the substrate is placed, while applying sufficient energy to generate gas plasma. , NH ₃ gas flow, N ₂ gas flow, and SiH ₄ gas flow, the gas flow of the nitride film forming gas is selected from at least one element selected from the elements in the second to sixth periods of Group 18 of the long period type periodic table. Generating a gas plasma in the reaction chamber by introducing the rare gas stream into the reaction chamber; and c) forming the film by plasma enhanced chemical vapor deposition using the gas plasma generated in the step b). The nitride film is deposited on top, thereby forming method of the nitride film which comprises a step of forming a stable nitride film on the deposition surface. 12. The NH ₃ / SiH ₄ in step b) above.
Ratio is in the range of 2 / 1-12 / 1, and the air flow of the flow rate of N ₂ in the above step b), is within 30% to 80% range of the total flow rate of the air flow to be introduced into the reaction chamber The method for forming a nitride film according to claim 11, wherein: 13. The step (c) of forming the nitride film is performed by introducing NH ₃ , N ₂ , SiH ₄ , and the like into the reaction chamber such that the internal pressure of the reaction chamber falls within a range of 67 Pa to 400 Pa.
13. The method for forming a nitride film according to claim 12, further comprising a step of maintaining a flow rate of at least one kind of rare gas. 14. The level of energy for generating gas plasma applied to said reaction chamber is in the range of 0.4 W to 4.0 W per square centimeter of substrate surface. The method for forming a nitride film according to the above. 15. The NH ₃ / N ₂ / S in step b) above.
iH ₄ ratio, the method of forming the nitride film according to claim 11, wherein the approximately 5/13/1. 16. The flow rate of at least one rare gas introduced into the reaction chamber in the step b) is in the range of 5 to 20 times the flow rate of SiH ₄ gas. Item 12. The method for forming a nitride film according to Item 11. 17. The method for forming a nitride film according to claim 16, wherein the gas flow of at least one rare gas introduced into the reaction chamber in the step b) contains argon (Ar). 18. The method according to claim 11, wherein the level of energy for generating gas plasma applied to the reaction chamber is in the range of 0.4 W to 4.0 W per square centimeter of the substrate surface. The method for forming a nitride film according to the above. 19. The method according to claim 19, wherein the step (c) of forming the nitride film comprises introducing NH ₃ , N ₂ , SiH ₄ into the reaction chamber such that the internal pressure of the reaction chamber falls within a range of 67 Pa to 400 Pa.
12. The method for forming a nitride film according to claim 11, further comprising a step of maintaining a flow rate of at least one kind of rare gas. 20. The method according to claim 11, wherein said step a) includes heating the substrate at a temperature of 200 ° C. or less.
The method for forming a nitride film according to the above. 21. A method for forming a nitride film used for an active element of a liquid crystal display using a plasma enhanced chemical vapor deposition method, comprising the steps of: a) having a film formation surface on which a nitride film is to be formed; Placing the liquid crystal display substrate in a reaction chamber and heating the liquid crystal display substrate at a temperature of 225 ° C. or lower; b) in the same reaction chamber where the substrate is placed, while applying sufficient energy to generate gas plasma. , NH ₃ gas flow, N ₂ gas flow, and SiH ₄ gas flow, together with a gas flow of at least one rare gas selected from the group consisting of Ne, Ar, Kr, and Xe. Generating a gas plasma in the reaction chamber by introducing the gas into the reaction chamber; and c) forming a gas plasma on the film formation surface by a plasma enhanced chemical vapor deposition method using the gas plasma generated in the step b). The nitride film is deposited, thereby forming method of the nitride film which comprises a step of forming a stable nitride film on the deposition surface. 22. The NH ₃ / SiH ₄ in the step b).
Ratio is in the range of 2 / 1-12 / 1, and the air flow of the flow rate of N ₂ in the above step b), is within 30% to 80% range of the total flow rate of the air flow to be introduced into the reaction chamber The method for forming a nitride film according to claim 21, wherein: 23. The step c) of forming a nitride film is performed by introducing NH ₃ , N ₂ , SiH ₄ into the reaction chamber such that the internal pressure of the reaction chamber falls within a range of 67 Pa to 400 Pa.
23. The method for forming a nitride film according to claim 22, further comprising a step of maintaining a flow rate of at least one kind of rare gas. 24. The method according to claim 23, wherein an energy level for generating gas plasma applied to the reaction chamber is in a range of 0.4 W to 4.0 W per square centimeter of the substrate surface. The method for forming a nitride film according to the above. 25. The NH ₃ / N ₂ / S in step b) above.
iH ₄ ratio, the method of forming the nitride film according to claim 21, wherein the approximately 5/13/1. 26. The flow rate of at least one rare gas introduced into the reaction chamber in step b) is in the range of 5 to 20 times the flow rate of SiH ₄ gas. Item 22. The method for forming a nitride film according to Item 21. 27. The method according to claim 26, wherein the gas flow of at least one rare gas introduced into the reaction chamber in the step b) contains argon (Ar). 28. The method of claim 21, wherein said step a) includes heating the substrate at a temperature of 200 ° C. or less.
The method for forming a nitride film according to the above.