JP4713759B2 - Manufacturing method of semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor device used for a liquid crystal display or the like.
[0002]
[Prior art]
2. Description of the Related Art A plasma chemical vapor deposition apparatus (hereinafter referred to as a “P-CVD apparatus”) that uses plasma has been conventionally used when forming a semiconductor film on a substrate surface in a film forming process in a semiconductor manufacturing process. Among them, a so-called parallel plate type P-CVD apparatus in which electrodes are arranged opposite to each other at the top and bottom in a vacuum chamber is used in many cases because it is suitable for a relatively large-diameter process.
[0003]
In the P-CVD apparatus, when a thin film such as a semiconductor film is formed on the substrate surface, a process of removing the thin film formed in a vacuum chamber other than the substrate is performed. For this purpose, plasma discharge is generated while sealing a gas containing fluorine in the vacuum chamber, and the thin film formed in the vacuum chamber is vaporized by reacting fluorine and silicon and exhausted. . By performing such treatment, the inside of the vacuum chamber can be cleaned without releasing the vacuum chamber to atmospheric pressure, the processing amount per unit time can be increased, and a film is formed on the substrate other than the substrate of the vacuum chamber. It is possible to reduce the number of particles in the vacuum chamber by peeling off the thin film.
[0004]
Such a plasma gas cleaning method is disclosed in Japanese Patent Laid-Open Nos. 62-214175 and 63-267430. The plasma gas cleaning method disclosed in these documents is a method in which after depositing a predetermined thin film in a P-CVD apparatus, NF ₃ gas is introduced into the vacuum chamber to remove deposits in the chamber. It is.
[0005]
In the former method (hereinafter referred to as “first conventional example”), fluorine is further removed by using a mixed gas of hydrogen and nitrogen as plasma. Similarly, in the latter method (hereinafter referred to as “second conventional example”), hydrogen plasma treatment is performed to remove fluorine.
[0006]
Further, another plasma gas cleaning method is also disclosed in Japanese Patent Laid-Open Nos. 2-2240267 and 11-224858. In the former method (hereinafter referred to as “third conventional example”), the inside of the CVD apparatus is cleaned with a plasma gas using a fluorine-containing gas after film formation, and after the cleaning process, the CVD apparatus is previously vacuumed. In this method, the inner wall of the tank is coated with a plasma silicon nitride film, and then a predetermined thin film is formed by the CVD method. This has a technical feature in that the amount of fluorine contained in a thin film such as a SiO ₂ film or a PSG film is reduced.
[0007]
On the other hand, in the latter method (hereinafter referred to as “fourth conventional example”), after a film containing fluorine is introduced and plasma gas cleaning is performed, the inside of the vacuum chamber is made of a plasma silicon nitride film. In this method, a coating process and a hydrogen plasma process are sequentially performed. By doing so, it is possible to reduce the amount of fluorine in the thin film formed by the CVD method, as in the third conventional example.
[0008]
[Problems to be solved by the invention]
However, by cleaning the inside of the vacuum chamber with a gas containing fluorine, fluorine atoms that did not react with the thin film formed on the vacuum chamber wall, and the vacuum chamber without being exhausted in the gas exhausting step after cleaning The fluorine atoms staying inside are taken into a thin film such as a semiconductor film formed on the substrate.
[0009]
By using such a semiconductor film as a thin film transistor (hereinafter referred to as “TFT”) for a liquid crystal display device or the like, a phenomenon occurs in which an OFF current in the TFT is increased as compared with a TFT using a semiconductor film that does not incorporate fluorine atoms. . In addition, the increase in the OFF current causes a problem that an image quality abnormality such as an image burn-in phenomenon in the liquid crystal display device may occur.
[0010]
In addition, in a TFT using a semiconductor film that has taken in fluorine atoms, the amount of change in Vt with time increases by applying a DC voltage, and unevenness occurs due to a difference in the amount of partial change. There was also a problem that it may cause display abnormality.
[0011]
Further, the above-described conventional cleaning method in the CVD apparatus still has the following problems. First, the method according to the first conventional example has a problem that the cleaning process takes a long time. That is, in the method according to the first conventional example, the processing time in a normal CVD apparatus is about 30 minutes, and in the case of mass production of semiconductor devices on a substrate, the processing time becomes long. Production costs will increase significantly.
[0012]
Further, in the method according to the second conventional example, the cleaning process time is further increased as compared with the case where the method according to the first conventional example is used, and therefore, the productivity of the semiconductor device is significantly reduced. .
[0013]
The methods according to the third conventional example and the fourth conventional example have a problem that the influence of fluorine remaining in the vacuum chamber of the CVD apparatus cannot be completely eliminated. That is, an increase in the OFF current causes an image quality abnormality such as an image burn-in phenomenon in the liquid crystal display device, and a change amount of Vt with time increases, and unevenness is caused by a difference in partial change amount. This causes a problem of causing a display abnormality such as occurrence, and this phenomenon becomes prominent particularly when thin films stacked in a CVD apparatus are continuously deposited.
[0014]
In order to solve the above problems, the present invention provides a method for manufacturing a semiconductor device that can reliably eliminate fluorine atoms remaining after plasma gas cleaning when using a P-CVD method. Objective.
[0015]
[Means for Solving the Problems]
The method of manufacturing a semiconductor device according to the present invention in order to achieve the above object, in order to remove the film deposited on the walls of the vacuum chamber, and row Cormorant step a plasma gas cleaning by introducing a gas containing fluorine, the A step of evacuating the gas in the vacuum chamber after performing plasma gas cleaning, and an amorphous semiconductor thin film mainly composed of silicon on the wall of the vacuum chamber using the plasma chemical vapor deposition method after the gas evacuation a step for forming a film of, after the film formation, the steps of loading a substrate into the vacuum chamber, after the substrate loading, composed mainly of silicon on the base plate by using a plasma chemical vapor deposition method and forming a non-crystalline semiconductor thin film, and in the step of forming the amorphous semiconductor thin film on the substrate, the S iH ₄ concentration that put the source gas for forming the pre-Symbol amorphous semiconductor thin film 10% or more 5 % Or less, and the first S iH ₄ concentration in the step S iH ₄ concentration in the step of forming a film of the amorphous semiconductor thin film on the walls of the vacuum chamber to form said amorphous semiconductor thin film before SL on the substrate. It is characterized by being twice or more.
[0016]
With this configuration, it is possible to more reliably eliminate the fluorine atoms remaining in the processing layer, and it is possible to avoid the occurrence of the image quality abnormality that has occurred in the liquid crystal display device.
[0017]
A method of manufacturing a semiconductor device according to the present invention is a step of performing film formation of the amorphous semiconductor thin film on the walls of the vacuum chamber, it is preferable to carry out a plurality of times the film formation. This is because the remaining fluorine atoms can be eliminated more reliably.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a method for manufacturing a semiconductor device according to an embodiment of the present invention will be described with reference to the drawings. First, FIG. 3 is a schematic configuration diagram of a P-CVD apparatus used in the method for manufacturing a semiconductor device according to the present invention.
[0019]
FIG. 3 shows a cross-sectional structure of a vacuum chamber of a general P-CVD apparatus, and process gas diffusion is performed while heating the substrate 3 disposed on the lower electrode 4 using a heater 6 for heating a normal substrate. The gas diffused by the plate 5 is filled into the vacuum chamber 2, the inside of the vacuum chamber is adjusted to a constant pressure by a valve attached to the gas exhaust port 8, and the RF power source 1 is connected between the upper electrode 5 and the lower electrode. This is an apparatus for forming a thin film on a substrate while decomposing a filling gas with plasma generated by supplied high-frequency power.
[0020]
Next, a process flow in the semiconductor device manufacturing method according to the embodiment of the present invention will be described with reference to FIG. In FIG. 1, first, the film adhering to the wall of the vacuum chamber 2 is removed by performing plasma gas cleaning (step S11). This is because a gas containing fluorine atoms such as NF ₃ is filled in the vacuum chamber 2 and a high frequency voltage such as 13.56 MHz is applied to activate the gas containing fluorine atoms such as NF ₃ , and this activity is activated. The gas containing the fluorine atom and the film adhering to the wall of the vacuum chamber 2 are vaporized by causing a chemical reaction, and exhausted from the gas exhaust port 8 to remove the fluorine atom.
[0021]
Next, in order to replace the inside of the vacuum chamber 2 with N ₂ gas, it was generated by reacting with the gas containing fluorine remaining in the plasma gas cleaning (step S11) and the film adhering to the wall of the vacuum chamber 2. The fluoride gas is exhausted (step S12). This aims to reduce the influence on the next process.
[0022]
And just before carrying in the board | substrate 3 in the vacuum chamber 2, it forms into a film in the vacuum chamber 2 by maintaining a predetermined degree of vacuum, enclosing gas, and performing plasma discharge (step S13). In this step, at least the formation of an a-Si thin film is included, and the SiH ₄ concentration of the mixed gas forming the a-Si thin film is 1.2 times or more the concentration normally used for forming the semiconductor layer To form a film. The SiH ₄ concentration in the deposition gas of a-Si: H that is usually used as a semiconductor layer is 10% or more and 50% or less. It has characteristics.
[0023]
Thus, by increasing the SiH ₄ concentration of the mixed gas, fluorine atoms that did not react with the thin film formed on the wall of the vacuum chamber 2 and the vacuum chamber 2 without being exhausted in the gas exhaust step after cleaning. It becomes possible to reduce the staying fluorine atom.
[0024]
And the process similar to step S13 is repeated at least twice or more (step S14). This makes it possible to remove the remaining fluorine atoms more reliably.
[0025]
After removing the remaining fluorine atoms, the substrate 3 to be formed is carried in (step S15), and a desired film is formed on the substrate 3 (step S16). In the film formation in step S16, an a-Si film having a lower SiH ₄ concentration than the a-Si film formed in steps S13 and S14 is formed. Finally, the substrate 3 on which film formation has been completed is lifted from the lower electrode 4 and carried out of the vacuum chamber 2 (step S17).
[0026]
A phenomenon caused by a processing process using such a P-CVD apparatus will be described with reference to FIG. First, FIG. 2A schematically shows the gas atmosphere in the vacuum chamber 2 after the plasma gas cleaning. In FIG. 2A, fluorine atoms contained in the gas used in the plasma gas cleaning remain, and when film formation on the substrate 3 is performed in this environment, a large amount of fluorine atoms are taken into the semiconductor film. Will end up.
[0027]
By using a semiconductor film that has taken in a large amount of fluorine atoms as a TFT of a liquid crystal display device or the like, a phenomenon occurs in which the OFF current in the TFT increases compared to a TFT that uses a semiconductor film that does not take in fluorine atoms. Then, an increase in the OFF current results in an image quality abnormality such as an image burn-in phenomenon in the liquid crystal display device.
[0028]
In addition, in a TFT using a semiconductor film that has taken in fluorine atoms, the amount of change in Vt with time increases by applying a DC voltage, and unevenness occurs due to a difference in the amount of partial change. It may cause display abnormality.
[0029]
Further, as shown in FIG. 2 (c), in the vacuum chamber 2 using the conventional method, there are few unbonded portions of silicon having a strong binding force with fluorine, and the fluorine atoms remaining in the vacuum chamber 2 It is clear that it is difficult to remove completely.
[0030]
However, by increasing the SiH ₄ concentration as shown in the present embodiment, as shown in FIG. 2 (b), the unbonded portion of silicon increases as compared with FIG. 2 (c) and remains in the vacuum chamber 2. It is possible to remove more fluorine atoms.
[0031]
Such an effect will be described with reference to FIGS. FIG. 4 shows the flow rate ratio of the OFF current to the SiH ₄ concentration ratio. As shown in FIG. 4, it can be seen that when the SiH ₄ concentration ratio is 1.2 or less, the flow rate ratio of the OFF current tends to increase, that is, a phenomenon in which the OFF current increases occurs. Therefore, by increasing the SiH ₄ concentration ratio by 1.2 times or more, it is possible to suppress the increase phenomenon of the OFF current and to avoid the occurrence of the image afterimage phenomenon.
[0032]
FIG. 5 shows the shift ratio of Vt with respect to the SiH ₄ concentration ratio. As shown in FIG. 5, when the SiH ₄ concentration ratio exceeds 1.2, the shift ratio of Vt in the TFT decreases rapidly, so that the amount of change in Vt over time can be suppressed, and unevenness It can be seen that it is possible to avoid display anomalies such as the occurrence of an error. That is, by making the SiH ₄ concentration 1.2 times or more, it is possible to make it difficult to cause display abnormality such as unevenness due to a difference in the partial change amount.
[0033]
As described above, according to the present embodiment, the influence of the fluorine gas remaining in the vacuum chamber of the CVD apparatus can be almost completely removed in a short time, and a liquid crystal display device with good image performance can be obtained. It becomes possible.
[0034]
【The invention's effect】
As described above, according to the method for manufacturing a semiconductor device according to the present invention, the influence of fluorine gas remaining in the vacuum chamber of the CVD apparatus can be almost completely removed in a short time, and the liquid crystal display with good image performance can be obtained. An apparatus can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a process flow in a method of manufacturing a semiconductor device according to an embodiment of the present invention. FIG. 2 is a reaction diagram in a vacuum chamber. FIG. 3 is a schematic configuration diagram of a P-CVD apparatus. Vt for SiH ₄ concentration ratio in the method of manufacturing a semiconductor device according to the embodiment of FIGS. 5A and 5B present invention showing the OFF current amount ratio SiH ₄ concentration ratio in the method of manufacturing a semiconductor device according to the embodiment of the present invention Diagram showing shift ratio 【Explanation of symbols】
1 RF power source 2 Vacuum chamber 3 Substrate 4 Lower electrode 5 Upper electrode and process gas diffusion plate 6 Substrate heater 7 Grounding 8 Gas exhaust port

Claims (2)

To remove the film deposited on the walls of the vacuum chamber, and row Cormorant step a plasma gas cleaning by introducing a gas containing fluorine,
Exhausting the gas in the vacuum chamber after performing the plasma gas cleaning;
After the gas exhaust, a step of forming an amorphous semiconductor thin film mainly composed of silicon on the wall of the vacuum chamber using a plasma chemical vapor deposition method;
A step of carrying the substrate into the vacuum chamber after the film formation;
After the substrate loading, and forming a non-crystalline semiconductor thin film mainly containing silicon on the base plate by using a plasma chemical vapor deposition method, a
In the step of forming the amorphous semiconductor thin film on the substrate, S iH ₄ concentration that put the source gas for forming the pre-Symbol amorphous semiconductor thin film is less than 10% to 50%
Is S iH ₄ concentration of 1.2 times or more in the step S iH ₄ concentration in the step of forming a film of the amorphous semiconductor thin film on the walls of the vacuum chamber to form said amorphous semiconductor thin film before SL on the substrate A method for manufacturing a semiconductor device. In the step of performing film formation of the amorphous semiconductor thin film on the walls of the vacuum chamber, a method of manufacturing a semiconductor device 請 Motomeko 1, wherein a plurality of times the film formation.

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