JP2648746B2 - Insulating film formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for forming an insulating film, in particular, very useful for the formation of an oxide thin film such as SiO ₂ film used for the gate insulating film of a TFT (thin film transistor) Method and apparatus.

[0002]

2. Description of the Related Art In recent years, in order to obtain a high-quality liquid crystal display, an electrode structure including three-terminal elements such as an a-SiTFT (amorphous silicon thin film transistor) has been widely used. Has been put to practical use. However, a-Si TFT
The field effect mobility of the electrons at
There is a limit in using a TFT for displaying a large screen and high definition required for a high-definition television.
This is because when the number of scanning lines increases, the writing time per scanning line becomes shorter, so that it is necessary to increase the response speed of the TFT. Must be reduced, and as a result, it is necessary to improve the performance of the TFT.

In order to overcome this limitation, poly-Si (polysilicon) having high electron mobility is used.
-SiTFT has been proposed to be used as a liquid crystal display electrode.
It is used for displays, liquid crystal projectors, etc. This poly-Si TFT is manufactured by using an LSI process, and when a gate insulating film is formed on a substrate by a thermal oxidation method, a process temperature of 1000 ° C. or more is applied. Therefore, expensive quartz glass having high heat resistance is used for this substrate. At present it is inevitable. It is indispensable that the poly-Si TFT is inexpensive in order to be used for large-screen OA equipment, consumer equipment, and the like. It is hoped that it can be manufactured.

As a method of forming a SiO ₂ film by a low-temperature process, there are a P (plasma) -CVD method, a sputtering method,
A CR (Electron Cyclotron Resonance) -CVD method is known. In particular, in the ECR-CVD method, since the operating pressure at the time of film formation is as low as 10 ⁻³ Torr or less and the plasma density is high, a large amount of ions are deposited on the substrate at the time of film formation.
It is incident with higher energy than VD. Thus P-
Since the CVD method uses the kinetic energy of ions at the time of film formation, there is an advantage that a SiO ₂ film can be obtained at room temperature or a substrate temperature as low as about 200 ° C.
However, at the same time, there is a problem that damage due to high energy ions occurs in the SiO2 film, and the leak current in a low electric field region increases.

On the other hand, conventional atmospheric pressure CVD
According to the method or the low-pressure CVD method, the film formation rate is extremely slow below 600 ° C., which is the heat-resistant temperature of an inexpensive glass substrate, and it is industrially impossible to apply these methods to an inexpensive glass substrate. there were. There is also a method of using a higher order silane such as disilane or trisilane and nitrous oxide or a highly reactive oxygen gas to obtain a SiO ₂ film at a relatively low temperature by a thermal CVD method. It was difficult to obtain a good quality film. Also, according to this method, a large area substrate
There is also a problem that in order to form the O ₂ film uniformly, nitrous oxide having low reactivity must be used instead of oxygen gas.

In general, a gate insulating film is required to have a small leakage current and a large withstand voltage as an insulating film.
In addition to this, it is required that the fixed electric density and the interface state density be small. However, as described above, in order to obtain a high-quality SiO ₂ film satisfying such characteristics by a conventional method, a thermal process at 900 ° C. or higher had to be used. This means that the energy required at the time of film formation is converted into heat, kinetic energy by ions or light.
Because they relied on a single means. As a result, a single means had to be used.
One of the reasons is that it is difficult to manufacture an apparatus capable of uniformly introducing a large area with another energy source such as plasma or light while performing the above-described process to form a film.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to reduce damage to an insulating film due to high energy ions and to obtain a high quality insulating film by heating a substrate at 650 ° C. or lower. EC that can be done
An object of the present invention is to provide a method and an apparatus for forming an insulating film using R plasma.

[0008]

SUMMARY OF THE INVENTION A method of forming an insulating film according to the present invention has been made to solve the above-mentioned problems, and includes a step of arranging an object to be processed in a processing chamber, and exhausting the processing chamber. Process and introduction of silane into the processing chamber
In the ECR plasma chamber communicating with the processing chamber, N ₂ O
And introducing a microwave having a predetermined frequency into the ECR plasma chamber to generate high-density plasma and guide the high-density plasma to the vicinity of the object in the processing chamber, and Temperature of 400 ° C ~
By maintaining the temperature at 600 ° C. , S
forming an iO ₂ film .

The reactive gas may be a higher silane gas such as silane or disilane, or a gas obtained by adding at least one of nitrogen, oxygen, argon, helium, and hydrogen as a diluent gas. It is preferable to use N ₂ O gas or a gas to which at least one of nitrogen, argon, helium, and hydrogen is added as a diluent gas.

An apparatus used in the method of forming an insulating film according to the present invention comprises:
An object to be processed is arranged inside, and a vacuum vessel capable of holding a vacuum, a means for generating microwaves, and communicating with the vacuum vessel to constitute a microwave cavity resonator and generate the microwave. An ECR plasma chamber for generating a plasma by introducing microwaves, a unit for introducing a reaction gas into the vacuum chamber and an excitation gas into the ECR plasma chamber, and heating the object to be processed to 400 ° C to 600 ° C. Means that can be provided.

The method for forming an insulating film according to the present invention is characterized in that
It can be used to form not only a gate insulating film for a SiTFT but also various insulating films such as a general gate insulating film of a MIS transistor, an insulating film for a capacitor, and an interlayer insulating film. As the insulating film, not only SiO ₂ but also Si ₃ N ₄ , Ta ₂
Various insulating materials such as O ₅ and Al ₂ O ₃ can be used. Further, the gas pressure introduced into the processing chamber and the ECR plasma chamber is maintained at an appropriate value of 1 × 10 ^{−3 to} 5 × 10 ⁻⁴ Torr. The shape of the ECR plasma chamber, the frequency of the microwave introduced into the ECR plasma chamber, the magnetic flux density by the magnetic coil, and the like may use conditions generally used for generating ECR.

[0012]

After an object to be processed such as a poly-Si TFT substrate is set at a predetermined position in the processing chamber and the processing chamber is evacuated, a reaction gas is introduced into the processing chamber, and a reaction gas is introduced into the ECR plasma chamber communicating with the processing chamber. Excitation gas is introduced to a predetermined pressure. Then, a microwave having a predetermined frequency is externally introduced into the ECR plasma chamber through a window made of a material such as quartz that transmits the microwave. This ECR plasma chamber constitutes a microwave cavity resonator.
High-density ECR plasma is generated inside the CR plasma chamber. The electrons in the plasma efficiently absorb the microwave energy due to the resonance of the microwaves with the rotation of the electrons by the magnetic field.

The object to be processed is heated by heating means.
The plasma is heated and maintained at 400 ° C. to 600 ° C. When the plasma reaches the vicinity of the workpiece, the thermal energy due to the heating and the kinetic energy of ions, electrons, and the like in the plasma cause the workpiece to be heated. The reaction gas in the vicinity is activated to cause a chemical reaction, and a desired insulating film such as SiO ₂ is generated on the object to be processed. Since this generation reaction activates the reaction gas by ECR plasma, it is possible to form a film at a lower temperature than in the conventional thermal oxidation method. In addition, since the reaction is performed at a temperature of 400 ° C. to 600 ° C. , it is possible to cause a necessary reaction without significantly increasing the kinetic energy of ions, electrons, and the like in the plasma. Damage due to the impact of ions, high energy electrons, etc. can be minimized.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments. FIG. 1 is a sectional view showing an embodiment of an ECR plasma CVD apparatus for forming an insulating film according to the present invention. In this figure, reference numeral 1 denotes a vacuum vessel having a gas inlet 6 for introducing a reaction gas such as SiH _{4 into a} part thereof, and the vacuum vessel 1 is connected to an exhaust port via a pump valve. . The flow rate of the gas passing through the exhaust port and the gas inlet 6 is configured to be independently controlled by a mass flow controller (not shown) or the like. The vacuum vessel 1 has a double structure with the outer wall 2 so that high-temperature processing can be performed inside the vacuum vessel 1.
The coolant 3 is circulated between them. The inside of the vacuum vessel 1 is made of an inexpensive material on a tray 8 configured to be able to be carried between the inside of the vacuum vessel 1 and the outside (another vacuum system) by a carrying system 7. Poly
-The glass substrate 9 for SiTFT is set. Behind the substrate 9, a heater unit 10 incorporating a Kanthal heater is provided so that the substrate 9 can be heated to at least 650 ° C.

Reference numeral 11 denotes an ECR plasma chamber provided at a position facing the glass substrate 9. The plasma chamber 11 has a gas inlet 5 for introducing an excitation gas such as N ₂ O, and a microwave introduction chamber. Window 12, ECR
Coil 13 for generating a magnetic field in plasma chamber 11
have. The ECR plasma chamber 11 has a structure that constitutes a microwave cavity resonator. The ECR plasma chamber 11 passes through a waveguide (not shown) and a quartz window 12 from a microwave oscillator (not shown) provided outside. When a microwave having a predetermined frequency is introduced into the ECR plasma chamber 11, high-density ECR plasma is generated inside the chamber. The electrons in the ECR plasma cause the rotation of the electrons by the magnetic field generated by the coil 13 and the microwave to resonate, thereby efficiently absorbing the energy of the microwave and having a large kinetic energy. In addition, in order to ensure uniformity of heating inside the vacuum vessel 1 and to prevent heating of other parts, an appropriate position inside the vacuum vessel 1 is used.
A reflector 4 made of a mirror-finished material such as stainless steel is provided.

Next, the operation of the above-mentioned ECR plasma CVD apparatus and an embodiment of a method for forming an insulating film will be described.
First, the inside of the vacuum vessel 1 is evacuated to 1 × 10 ⁻⁶ Torr or less by operating a vacuum pump, and the heater unit 10 is simultaneously operated to 400 ° C.
Heat to a predetermined temperature of 600 ° C. Then, poly
-The tray 8 on which the glass substrate 9 for SiTFT is mounted is transferred from another vacuum chamber to a predetermined position inside the vacuum vessel 1 by the transfer system 7. Next, SiH ₄ gas and N ₂ O gas are introduced into the vacuum vessel 1 and the ECR plasma chamber 11 from the gas introduction ports 6 and 5, respectively. The flow rates are controlled by mass flow controllers, respectively.
By adjusting the variable valve provided in the exhaust unit (not shown) 1x10 ^- maintaining a predetermined pressure between the 3~5x10 ^-4 Torr. Thereafter, a microwave having a predetermined frequency is externally applied through the quartz window 12 to the ECR plasma chamber 11.
To generate high-density ECR plasma.
In this way, when the plasma reaches the vicinity of the glass substrate 9, the reaction gas near the glass substrate 9 is activated by the thermal energy of the heating and the kinetic energy of ions, electrons, and the like in the plasma, and the chemical reaction occurs. This causes a SiO ₂ insulating film to be formed on the glass substrate 9.

FIG. 2 is a graph showing the relationship between the temperature of the glass substrate and the leakage current of the insulating film formed using the above-described apparatus and method. This was measured by forming an SiO ₂ film on a glass substrate 9 for a poly-Si TFT, forming an Al electrode thereon by vapor deposition to form a MOS structure, and applying an electric field of 2 MV / cm thereto. Things. Note that the same gas is used for reference in FIG.
A black circle indicates a leak current when a film is formed at 0 ° C. by a plasma CVD method. Arrows indicate the leakage current of the thermal oxide film obtained by the conventional thermal oxidation method (about 1100 ° C.). As is clear from this graph, the leak current gradually decreases with increasing substrate temperature from the room temperature to around 400 ° C.
When the temperature exceeds 00 ° C., the temperature sharply decreases with an increase in the substrate temperature, and extremely good characteristics are exhibited. According to this,
In the vicinity of a substrate temperature of 600 ° C., SiO having a leak current at 1100 ° C. which is considerably close to a film obtained by a thermal oxidation method
_Two films are obtained. In addition, it can be seen that a better insulating film can be obtained by the method of the present invention at the same temperature as compared with the plasma CVD method. As described above, according to the method of forming an insulating film of the present invention, EC
It can be seen that the ion irradiation by the R plasma and the thermal energy work effectively to produce a synergistic effect.

FIG. 3 is a graph showing the relationship between the substrate temperature and the BHF etching rate of the SiO ₂ film formed by the method for forming an insulating film according to the present invention. According to this figure,
The BHF etching rate of the SiO ₂ film formed by using the present invention decreases as the substrate temperature increases, and becomes 400 ° C.
Above C, it approaches a constant value. From this, it is understood that a dense film is formed at a substrate temperature of 400 ° C. or higher.

FIG. 4 shows an ECR plasma CVD of the present invention.
It is sectional drawing which shows another Example of an apparatus. In the above embodiment, only one ECR plasma source is used.
Since the effective film formation area of one plasma source is at most about 200 mm square, a plurality of ECR plasma sources are used side by side as shown in FIG. 4 to uniformly form a film on a substrate having a larger area. Is preferred. In this case, a plurality of micro oscillators may be prepared in accordance with this,
The distribution may be performed by the distributor using only one unit. In FIG. 4, the same components as those in FIG. 1 are denoted by the same reference numerals.

In the above embodiment, the poly-
Although only the case of forming a SiO ₂ gate insulating film for a SiTFT has been described, it goes without saying that the present invention can be used for forming various insulating films such as a gate insulating film of a general MIS transistor, an insulating film for a capacitor, and an interlayer insulating film. It is. Further, according to the present invention, Si ₃ N ₄ , Ta 2
Even if an insulating film other than SiO ₂ such as O ₅ and Al ₂ O ₃ is formed, the same effect as in the case of SiO ₂ can be obtained.

[0021]

According to the present invention, the ECR plasma CV
When the insulating film is formed by the method D, the substrate is heated at 400 ° C. to 6 ° C.
By heating to 00 ° C. and maintaining this temperature , the EC
A dense insulating film can be obtained by the synergistic effect of the energy of the R plasma ion irradiation and the heating energy of the substrate, and the damage to the microscopic film due to the ion irradiation is reduced by the heat energy. An excellent insulating film can be obtained. Further, since the film forming temperature of the insulating film may be 400 ° C. to 600 ° C. , a high-quality insulating film which cannot be obtained conventionally without using expensive quartz glass can be obtained with an inexpensive glass substrate.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of an apparatus for forming an insulating film according to the present invention.

FIG. 2 is a graph showing a relationship between a glass substrate temperature and a leak current of an insulating film formed by using the apparatus and the method of the above embodiment.

FIG. 3 is a graph showing a relationship between a substrate temperature and a BHF etching rate of an insulating film formed by using the apparatus and method of the embodiment.

FIG. 4 is a sectional view showing another embodiment of an apparatus for forming an insulating film according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Vacuum container 4 ... Reflector 5 ... Gas inlet 6 ... Gas inlet 7 ... Transport system 8 ... Tray 9 ... Glass substrate 10 ... Heater unit 11 ... ECR plasma chamber 12 ... Quartz window 13 ... Coil

Claims (1)

(57) [Claims] A step of arranging an object to be processed in a processing chamber; a step of exhausting the processing chamber; a step of introducing silane into the processing chamber; and a step of applying N ₂ O to a predetermined pressure in an ECR plasma chamber communicating with the processing chamber. And introducing a microwave having a predetermined frequency into the ECR plasma chamber to generate high-density ECR plasma, guiding the plasma to the vicinity of the processing object in the processing chamber, and Forming an SiO ₂ film on the object to be processed by maintaining the temperature at 400 ° C. to 600 ° C.