JP5026248B2 - Method for producing amorphous silicon thin film - Google Patents

Description

  The present invention relates to the technical field of forming an amorphous silicon thin film.

  In the technical field of liquid crystal display panels, in order to improve display speed and display quality, an active matrix driving method using thin film transistors has recently become the mainstream in place of the simple matrix driving method.

  The thin film transistor can be formed on any of an a-Si (amorphous silicon) thin film, a poly-Si (polysilicon) thin film, or a single crystal Si thin film. From the viewpoint of cost and productivity, the a-Si thin film is first formed on the substrate. After a dehydrogenation process is performed in a subsequent process, a technique is employed in which the a-Si thin film is changed to a poly-Si thin film by laser annealing.

Reference numeral 101 in FIG. 7 is a prior art a-Si thin film forming apparatus, which has a transfer chamber 110 as a center, a charging / unloading chamber 111 and a preheating chamber 112 around it, and a reaction chamber 115 _{1. Four} to 1154 are arranged.

In this a-Si thin film forming apparatus 101, the transfer chamber 110, the preheating chamber 112, and the reaction chambers 115 _{1 to} 115 ₄ are evacuated in advance, and a predetermined number of substrates are mounted in the charging / unloading chamber 111. evacuated, and the substrate is carried into the preheating chamber 112 by the substrate transfer robot 119 disposed in the transport chamber 110, after being heated to a predetermined temperature, it is carried into the desired reaction chamber 115 _{1-115 4} After the a-Si thin film is formed by the plasma CVD method, it is returned to the charging / unloading chamber 111.

  Then, after an a-Si thin film is formed on all the substrates mounted in the charging / unloading chamber 111 and returned to the charging / unloading chamber 111, the substrate is taken out from the charging / unloading chamber 111 into the atmosphere, and a heat treatment (not shown) is performed. After performing dehydrogenation in the apparatus, the a-Si thin film was laser annealed to form a poly-Si thin film.

When a poly-Si thin film is manufactured by laser annealing the a-Si thin film as described above, if a-Si thin film contains a large amount of hydrogen, the a-Si is converted into poly-Si. Furthermore, there is a disadvantage that hydrogen blows out and the surface of the poly-Si thin film becomes a crater. Therefore, in general, the hydrogen concentration in the a-Si thin film is reduced to about 1.0 atomic% (Si: 5 × 10 ²² pieces / cm ₃ , H: about 5 × 10 ²⁰ pieces / cm ³ ). It is said that it is necessary to let them.

When dehydrogenating an a-Si thin film, the residual hydrogen concentration can be lowered as the a-Si thin film is heated to a higher temperature. However, if the temperature is too high, the a-Si thin film partially becomes poly-Si during the dehydrogenation process. However, there is a problem that a high-quality poly-Si thin film cannot be obtained even if laser annealing is performed thereafter. Accordingly, the temperature of the dehydrogenation process must be lowered, but there is a problem that the dehydrogenation process for that purpose takes a long time.
Japanese Patent Laid-Open No. 06-342757 Japanese Unexamined Patent Publication No. 07-2221035 JP 09-082662 A Japanese Patent Application Laid-Open No. 08-083765 Japanese Patent Laid-Open No. 10-106950

  The present invention was created to solve the above-mentioned disadvantages of the prior art, and an object thereof is to provide an a-Si thin film forming method with a short dehydrogenation processing time.

In general, when an a-Si thin film is formed, a substrate is placed in a vacuum atmosphere, a source gas such as SiH ₄ gas, Ar gas, H ₂ gas or a dilution gas is introduced, and plasma is generated to form a silicon layer on the substrate surface. It is formed by growing.

  The a-Si thin film formed by using such a plasma CVD method contains a large amount of hydrogen. For example, the a-Si thin film formed at 300 ° C. contains 10 to 20 atomic%. In that case, if the substrate on which the a-Si thin film is formed is heated, the hydrogen in the a-Si thin film is reduced. When releasing hydrogen by heating, it is necessary to heat for a long time.

  The inventors of the present invention have found that dehydrogenation treatment can be performed in a short time if the substrate on which the a-Si thin film is formed is immediately heated without being exposed to the atmosphere.

The present invention has been created based on the above findings, a first aspect of the present invention, after forming the amorphous silicon thin film by the CVD method on the surface of the substrate in a vacuum atmosphere, before the substrate without being exposed to the air A method for producing an amorphous silicon thin film, wherein the dehydrogenation treatment is performed by raising the temperature to a temperature higher than the temperature at which the amorphous silicon thin film is formed, wherein the amorphous silicon thin film is formed at a substrate temperature of 350 ° C. or more, and the dehydrogenation treatment is performed. Is a temperature in the reaction chamber different from the reaction chamber in which the amorphous silicon thin film is formed, and the amorphous silicon thin film is at a temperature equal to or higher than the formation temperature of the amorphous silicon thin film and lower than the temperature at which the amorphous silicon thin film becomes polysilicon. Amo that is heated at a temperature of 450 ° C. or more and 550 ° C. or less for a time of 5 minutes or more and 20 minutes or less A Fass silicon thin film manufacturing method.

  The method for producing an amorphous silicon thin film of the present invention is configured as described above, and after the amorphous silicon thin film is formed on the surface of the substrate by a CVD method in a vacuum atmosphere, the amorphous silicon thin film is left in the vacuum atmosphere. Dehydrogenation is performed by raising the temperature above the temperature at which the thin film was formed. Therefore, the substrate is not exposed to the atmosphere and the temperature does not decrease, so that the dehydrogenation treatment can be performed in a short time.

  In this case, the dehydrogenation process needs to heat the a-Si thin film to a temperature higher than the formation temperature. However, the higher the dehydrogenation temperature of the a-Si thin film, the lower the hydrogen concentration in the a-Si thin film. be able to.

On the other hand, the plasma CVD apparatus is generally for cleaning using NF ₃ gas, for use at high temperatures, it is necessary to configure the reaction chamber fluorine-resistant corrosion-resistant material. However, there is actually no material that can completely withstand the film forming process and the cleaning process at 450 ° C.

  Therefore, it is desirable to perform PECVD film formation at as low a temperature as possible and to perform dehydrogenation treatment at as high a temperature as possible. However, due to the film quality, the CVD method has a lower temperature of 350 ° C., and the dehydrogenation temperature is 420 ° C. C is the lower limit.

  In addition, when the a-Si thin film is heated at 550 ° C. or higher, partial poly-Si conversion occurs, and thus the temperature of the dehydrogenation treatment is the upper limit. Therefore, the dehydrogenation temperature is 420 ° C. or higher and lower than 550 ° C. (actually 530 ° C. or lower).

  When the dehydrogenation treatment is performed, a heating device capable of infrared irradiation is used, and the a-Si thin film can be irradiated with infrared rays in a vacuum atmosphere while relatively moving the heating device and the substrate. In this case, the entire a-Si thin film forming apparatus can be reduced in size, and the overall processing speed can be improved.

  On the other hand, the dehydrogenation treatment can be performed in a reaction chamber different from the reaction chamber in which the amorphous silicon thin film is formed. In this case, the dehydrogenation treatment can be performed with the substrate stationary.

  In the present invention, the vacuum atmosphere for dehydrogenating the substrate may be low pressure, and an inert gas that does not affect the a-Si thin film such as argon gas or nitrogen gas is introduced into the vacuum atmosphere. Is also included. When a substrate is placed on a hot plate and heated, it is preferable to introduce an inert gas because the temperature controllability of the substrate is improved.

According to the present invention, the processing time of the glass substrate can be greatly shortened.
Since the dehydrogenation process can be performed while moving the glass substrate, the entire apparatus is downsized.

Embodiments of the present invention will be described with reference to the drawings.
Referring to FIG. 1, reference numeral 1 denotes an a-Si thin film forming apparatus to which the present invention can be applied.

This a-Si thin film forming apparatus 1 has a transfer chamber 10, and around the transfer chamber 10, one charging / unloading chamber 11 and a preheating chamber 12 are provided around the transfer chamber 10. Chambers 15 ₁ to 15 ₄ are arranged.

The charging / unloading chamber 11, the transfer chamber 10, and the reaction chambers 15 ₁ to 15 ₄ can be evacuated independently, and the a-Si thin film forming apparatus 1 having the above-described configuration is used to form an a-Si thin film. when forming, advance the advance chambers 10～12,15 _{1-15 4} evacuated. Next, only the inside of the preparation take-out chamber 11 is exposed to the atmosphere, a predetermined number of large-diameter glass substrates having a plate thickness of about 0.5 to 3 mm are arranged, and the door between the atmosphere is closed.

  After the inside of the preparation / extraction chamber 11 is evacuated to a predetermined pressure, the partition with the transfer chamber 10 is opened. A substrate transfer robot 19 is disposed in the transfer chamber 10, and one glass substrate in the preparation take-out chamber 11 is taken out and transferred into the preheating chamber 12.

The glass substrate was heated in the preliminary heating chamber 12, the temperature was raised to forming temperature of the a-Si film, was transported into desired reaction chamber (here, the reaction chamber indicated at 15 _1), the reaction chamber 15 Close the partition between ₁ and the transfer chamber 10.

A gas introduction system (not shown) is connected to each of the reaction chambers 15 ₁ to 15 ₄ so that a desired type of gas can be introduced. In addition, a heater is provided in the placement portion on which the glass substrate that has been loaded is placed, so that the glass substrate can be maintained at a desired temperature.

After the glass substrate is carried in, the silane gas and the argon gas are introduced at a flow rate ratio of 5:95 from the gas introduction system in a state where the glass substrate is placed on the placement unit and heated to 420 ° C. Then, a voltage to the electrodes of the reaction chamber 15 ₁ is applied to generate plasma of the introduced gas, growing a-Si film on the glass substrate surface by the plasma CVD method.

After growing the a-Si thin film to a predetermined thickness (3 00~1000Å), by the substrate transfer robot 19, it is unloaded into the transfer chamber 10 the glass substrate from the reaction chamber 15 _1.
Reference numeral 4 in FIG. 2 denotes the glass substrate, which is in a state of being placed on the tip of the arm 25 of the transfer robot 19.

Infrared heating devices 16 _{1 to} 16 ₄ are arranged at positions near the carry-in / out entrances of the reaction chambers 15 ₁ to 15 _{4 on} the ceiling of the transfer chamber 10, and are carried out from the reaction chambers 15 ₁ to 15 _4. substrate is configured to pass through respectively the position directly below the infrared heating device _161-164.

Each of the infrared heating devices 16 _{1 to} 16 ₄ includes a linear infrared lamp 27 and a reflecting mirror 29, and the reflecting mirror 29 is disposed behind the infrared lamp 27 and is radiated by the infrared lamp 27. It is configured to collect light while reflecting infrared rays.

  A quartz window 21 is airtightly provided immediately below the infrared lamp 27 on the ceiling of the transfer chamber 10, and the infrared light 22 emitted from the infrared lamp 27 is reflected directly or after being reflected by a reflecting mirror 28, and then the quartz window 21. And is irradiated into the transfer chamber 10 so as to be focused linearly.

The glass substrate 4 a-Si thin film is formed at the time of unloading from the reaction chamber 15 within ₁ and keep energizing the infrared heating device 16 ₁ on unloading port of the reaction chamber 15 _1, crow substrate 4 infrared The a-Si thin film at the focal portion is concentrated and heated after passing through the focal position 22.

In each of the infrared irradiation devices 16 _{1 to} 16 ₂ , the longitudinal direction of the infrared lamp 27 is arranged in a direction perpendicular to the carry-out direction of the glass substrate 4, and the linear focus is substantially the same as the carry-out direction of the glass substrate 4. It extends vertically. As a result, when the glass substrate 4 is carried out at a constant speed, the infrared rays 22 are uniformly irradiated from the head to the tail of the glass substrate 4, and the entire glass substrate 4 is heated uniformly.

  In this case, the glass substrate 4 can be heated to a desired temperature by adjusting the input power to the infrared lamp 27 or adjusting the carry-out speed (moving speed) of the glass substrate 4.

The infrared heating device 16 _1, the glass substrate 4 is heated above the substrate temperature (and 550 below ℃ a crystallization temperature of a-Si) when it is formed a-Si film, the a-Si thin film Hydrogen is released. The hydrogen is exhausted out of the a-Si thin film forming apparatus 1 by vacuum exhaust.

In this manner, the a-Si thin film on one glass substrate 4 is dehydrogenated, and the glass substrate 4 is returned to the carry-in / out chamber 11. Then, carries the glass substrate preheating is completed in the pre-heating chamber 12 to an empty reaction chamber 15 _1, it starts the growth of a-Si films.

At this time, the growth process of the a-Si thin film is also performed in parallel in the other reaction chambers 15 ₂ to 15 _{4. When the} formation of the a-Si thin film is completed, the infrared heating devices 16 _{2 to} 16 ₄ are energized, The glass substrate is unloaded at a predetermined speed while being irradiated with infrared rays, dehydrogenated, and returned to the loading / unloading chamber 11.

  As described above, the glass substrate after the dehydrogenation process is returned to the carry-in / out chamber 11. When all the glass substrates mounted in the carry-in / out chamber 11 have returned, the partition between the carry-in / out chamber 11 and the transfer chamber 10 is closed, the carry-in / out chamber 11 is opened to the atmosphere, and the glass substrate is taken out.

  As described above, according to the present invention, the dehydrogenation treatment can be performed before the glass substrate on which the a-Si thin film is formed is taken out into the atmosphere. It is only necessary to slightly heat the glass substrate in a heated state immediately after the formation of. Therefore, the heating time of the glass substrate can be very short, and since it is processed in a vacuum atmosphere, hydrogen is easily released, and the processing time is shortened.

FIG. 4 is a graph showing the relationship between the moving speed of the glass substrate when the power of the infrared heating devices 16 _{1 to} 16 ₄ is 150 W and 450 W and the residual hydrogen concentration in the a-Si thin film after the dehydrogenation treatment. As the electric power increases, the residual hydrogen concentration decreases. However, in any case, as the moving speed increases, the glass substrate temperature decreases. As a result, the dehydrogenation treatment becomes insufficient and the residual hydrogen concentration increases. The measurement conditions at this time were an atmospheric pressure around the glass substrate of 5 Pa, a focal width of 5 mm, and a focal length of 400 mm.

In the a-Si thin film forming apparatus 1 described above, the infrared heating devices 16 _{1 to} 16 ₄ are arranged on the inlets of the reaction chambers 15 ₁ to 15 _4. However, when an infrared heating device capable of emitting strong infrared rays is used. Since the moving speed of the glass substrate during the dehydrogenation process can be increased, an infrared irradiation device can be provided only at the upper part of the entrance of the carry-in / out chamber 11 rather than on the entrance of the reaction chambers 15 ₁ to 15 ₄ .

Although the above has described the case where the dehydrogenation treatment is performed while moving the glass substrate, the present invention is not limited thereto. For example, any _{one of the} reaction chambers 15 ₁ to 15 ₄ may be connected to the transfer chamber 10 instead of the dedicated dehydrogenation chamber 18 as shown in FIG.

  In the dehydrogenation treatment chamber 18 shown in FIG. 3, a lamp heater 31 is disposed in the chamber 30 and the glass substrate 4 ′ carried in is heated in a stationary state. Further, instead of the lamp heater 31, the hot plate 32 may be disposed in the chamber 30, and the glass substrate 4 ′ carried in may be placed on the hot plate 30 and heated.

  The residual hydrogen concentrations in the a-Si thin film when the dehydrogenation process is performed using the lamp heater 31 and when the dehydrogenation process is performed using the hot plate 30 are shown in the graphs of FIGS. 5 and 6, respectively.

  The measurement condition of the graph of FIG. 5 using the lamp heater 31 is the case where the atmospheric pressure is 5 Pa, and the input power to the lamp is 200 W and 500 W. It can be seen that at 200 W, sufficient dehydrogenation treatment cannot be performed even if the treatment time is increased.

  The measurement conditions of the graph of FIG. 6 using the hot plate 30 are an atmospheric pressure of 133 Pa (nitrogen gas atmosphere), and a glass substrate temperature of 420 ° C. (hot plate temperature 450 ° C.) and 450 ° C. (hot plate temperature 480 ° C.). It is.

When heating with a hot plate, it is preferable to introduce an inert gas such as nitrogen gas or argon gas in order to increase the thermal conductivity, when using an infrared heating device _161-164 and the lamp heater 31 of the Is not necessarily an inert gas atmosphere.

An example of an a-Si thin film manufacturing apparatus to which the present invention can be applied Enlarged view of the infrared heating device An example of a dedicated dehydrogenation chamber Graph showing the relationship between the moving speed of the substrate and the residual hydrogen concentration Graph showing the relationship between treatment time and residual hydrogen concentration in the case of lamp heating Graph showing the relationship between substrate temperature and residual hydrogen concentration in hot plate heating Example of conventional a-Si thin film production equipment

Explanation of symbols

1 …… a-Si thin film manufacturing equipment 4 …… Substrate 16 ₁ -16 ₄ ...... Heating equipment

Claims (1)

After forming the amorphous silicon thin film by the CVD method on the surface of the substrate in a vacuum atmosphere, the substrate was raised above the temperature at which the formation of the pre-Symbol amorphous silicon thin film without being exposed to the air, an amorphous silicon performing dehydrogenation treatment A thin film manufacturing method,
The amorphous silicon thin film is formed at a substrate temperature of 350 ° C. or higher,
The dehydrogenation treatment is performed in a reaction chamber different from the reaction chamber in which the amorphous silicon thin film is formed. The amorphous silicon thin film is at a temperature equal to or higher than the formation temperature of the amorphous silicon thin film, and the amorphous silicon thin film becomes polysilicon. A method for producing an amorphous silicon thin film, comprising heating at a temperature of 450 ° C. or higher and 550 ° C. or lower, which is a temperature lower than the temperature, for a time of 5 minutes or longer and 20 minutes or shorter.

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