JP5250209B2 - Cleaning method for plasma CVD apparatus - Google Patents

Description

  The present invention relates to a method for cleaning a plasma CVD apparatus.

  Carbon nanotubes can be used for semiconductor multilayer wiring, gate channel wiring of field effect transistors, and the like due to their electrical properties. The carbon nanotube is produced by an arc discharge method or a CVD method.

As a CVD method for producing carbon nanotubes, for example, a substrate on which a transition metal layer such as Ni, Fe, and Co is formed is placed in a vacuum chamber, and a carbon supply gas and hydrogen gas are introduced into the vacuum chamber. Then, there is a plasma CVD method in which plasma is generated by a plasma generating means, and a gas dissociated by the plasma is brought into contact with the surface of the substrate to cause vapor growth of carbon nanotubes on the substrate. As an apparatus for carrying out such a plasma CVD method, a mesh-like shielding means is provided between the substrate and the plasma generation region so that the substrate is not exposed to plasma in a vacuum chamber having the plasma generation means. Those are known (for example, see Patent Document 1).
Japanese Patent Laying-Open No. 2005-350342 (Claim 9, FIG. 1, etc.).

  By the way, when carbon nanotubes are grown using the plasma CVD apparatus as described above, if the carbon nanotubes are grown on a large number of substrates and the integration processing (growth) time becomes long, the mesh-like shielding means can be quickly Reaction by-products and the like will adhere. There is a problem in that this deposit may be deposited as an impurity on the substrate and inhibit the growth of the carbon nanotubes. Further, there is a problem that the mesh is insulated by the deposits and charge-up is likely to occur.

  In this case, if only the mesh is removed from the plasma CVD apparatus and polished, or immersed in chemicals, the vacuum chamber needs to be opened to the atmosphere, so that there is a problem that it takes time until the apparatus is restarted.

  Therefore, an object of the present invention is to provide a cleaning method for solving the problems of the prior art and removing the deposits attached to the mesh of the plasma CVD apparatus without removing the mesh from the plasma CVD apparatus.

Cleaning method of the plasma CVD apparatus of the present invention, a plasma generating means for Ru plasma is generated in a vacuum chamber, a substrate stage provided at the bottom of the vacuum chamber, and is disposed to face the substrate stage, in the generated plasma In a cleaning method of a plasma CVD apparatus provided with a shielding member that shields plasma so that a substrate is not exposed , an oxygen atom- containing gas is introduced into a vacuum chamber , plasma is generated by a plasma generating means , and a positive voltage is applied to the shielding member. The shielding member is cleaned by applying a DC voltage of 10 V to 200 V and attracting oxygen ions in plasma to the shielding member. According to this, the deposit | attachment adhering to the shielding member can be removed easily. By attracting oxygen ions to the shielding member, a higher cleaning effect can be obtained.

In the present invention, it is preferable to use oxygen gas, ozone gas, nitrogen monoxide gas, water vapor gas, or air as the oxygen atom-containing gas . According to this, since sufficient oxygen ions required for cleaning can be obtained, cleaning can be performed more efficiently.

  According to the cleaning method of the plasma CVD apparatus of the present invention, it is possible to easily remove the deposits without opening the vacuum chamber to the atmosphere.

  A plasma CVD apparatus 1 that is an object of the cleaning method of the present invention will be described with reference to FIG. The plasma CVD apparatus 1 includes a vacuum chamber 11, and a vacuum exhaust means 12 such as a rotary pump or a turbo molecular pump is provided at the bottom of the vacuum chamber 11.

  A gas introducing means 2 is provided on the ceiling of the vacuum chamber 11 so that a gas for growing carbon nanotubes can be introduced into the vacuum chamber 11. The gas introducing means 2 includes a shower head 21, and this shower head 21 communicates with a gas source (not shown) via a gas pipe 22. Here, as the gas source, a source gas source for growing carbon nanotubes, a dilution gas source for diluting the source gas, and a cleaning gas source for cleaning are provided.

  A microwave cavity 31 is provided in the upper part of the vacuum chamber 11 as the plasma generating means 3, and the microwave oscillated from the microwave cavity 31 enters the vacuum chamber 11 through the waveguide 32 and the quartz window 33. The gas introduced and introduced into the vacuum chamber 11 by the gas introduction means 2 is brought into a plasma state.

  A substrate stage 4 on which the substrate S to be processed is placed is provided at the bottom of the vacuum chamber 11 so as to face the shower head 21.

  In the plasma CVD apparatus to be cleaned according to the present invention, a mesh-shaped shielding member 5 is provided between the plasma generation region P and the substrate S to be processed so as to face the substrate stage 4. By providing this shielding member 5, dissociated electrons in the plasma at the time of plasma generation cannot enter the target substrate S side by the sheath region formed on the upper surface of the shielding member 5. The mesh-shaped shielding member 5 is made of metal, for example, made of stainless steel, and the mesh size of the mesh-shaped shielding member 5 is set to 1 to 3 mm. If the size of each mesh is set to be smaller than 1 mm, the gas flow is blocked, and if it is set to be larger than 3 mm, the plasma cannot be blocked.

  The distance between the shielding member 5 and the substrate S to be processed placed on the substrate stage 4 is set in the range of 20 to 100 mm. If it is set within this range, radicals that have passed through the shielding member 5 spread uniformly on the substrate S to be processed, and it is possible to produce uniform carbon nanotubes. When the distance is shorter than 20 mm, radicals that have passed through the shielding member 5 do not spread uniformly on the substrate S to be processed. Further, at a distance exceeding 100 mm, radicals are deactivated before reaching the substrate.

  Further, the shielding member 5 is connected to the voltage applying means 6 so that a voltage can be applied between the shielding member 5 and the ground (vacuum chamber) during cleaning. The shielding member 5 may be configured to share a voltage source with a substrate voltage applying means (not shown) and apply a voltage between the shielding member 5 and the substrate S to be processed.

  A method for forming carbon nanotubes using the plasma CVD apparatus shown in the drawing will be described below.

  First, the substrate to be processed S (a substrate made of a transition metal such as Ni, Fe, Co) is placed on the substrate stage 4, and the vacuum exhaust means 12 is operated to exhaust the vacuum chamber 11 to a predetermined degree of vacuum. In this state, the source gas and the dilution gas are introduced into the vacuum chamber 11. As source gas, carbon atom containing gas, for example, hydrocarbon gas, such as methane and acetylene, or vaporized alcohol can be used. Preferably, methane or the like that does not decompose at a heated substrate temperature. Further, as the dilution gas, at least one of hydrogen, ammonia, nitrogen, or argon can be used.

  Next, the substrate S to be processed is heated to a predetermined temperature by a heating means (not shown) provided on the substrate stage, and the substrate temperature is stabilized. Then, plasma is generated in the vacuum chamber 11 through the quartz window 33.

  Next, a voltage is applied to the substrate to be processed S and the shielding member 5, and only the source gas dissociated by the plasma by the shielding member 5 is allowed to pass through to reach the substrate to be processed S to be contacted. Carbon nanotubes are vapor-phase grown on the surface of the processing substrate S, and carbon nanotubes having an orientation aligned in a direction perpendicular to the processing substrate S are produced on the entire surface of the processing substrate S.

  When carbon nanotubes are produced in this manner, soot and reaction by-products may adhere to the mesh-shaped shielding member 5 when the growth of the carbon nanotubes is repeated many times and the integration treatment time becomes long. This deposit is an insulator and may cause a charge-up at the time of carbon nanotube production, which may inhibit the growth of the carbon nanotube. In addition, this deposit may be deposited on the substrate to inhibit the growth of carbon nanotubes. Therefore, after the carbon nanotubes are grown on one or more substrates, it is necessary to clean the shielding member 5 of the plasma CVD apparatus 1.

  Hereinafter, the cleaning method of the plasma CVD apparatus of the present invention will be described.

  In a plasma CVD apparatus in which carbon nanotubes are grown on one or more substrates, first, the inside of the vacuum chamber 11 is evacuated to the shielding member, and then a cleaning gas is introduced under conditions of 10 to 1000 sccm.

An example of the cleaning gas is an oxygen atom-containing gas. Examples of the oxygen atom-containing gas include O ₂ , O ₃ , NO, and H ₂ O, and a gas containing oxygen such as the atmosphere may be used. However, carbon-containing gases such as CO and CO ₂ are not used as cleaning gases because they can cause deposits. As examples of the oxygen-containing gas, the oxygen ions required for cleaning can be sufficiently formed, and handling terms of good, preferably air, and O ₂ gas, in particular O ₂ gas is preferable.

  Next, plasma is generated by plasma generating means under conditions of oscillation power: 0.5 to 3 kW, and deposits such as soot adhering to the shielding member 5 are etched or oxidized by oxygen ions in the plasma for a predetermined time. To clean. FIG. 2 is a schematic view showing a plasma CVD apparatus during cleaning, and the same reference numerals are assigned to the same components as those in FIG. As shown in FIG. 2, if the pressure in the vacuum chamber 11 is set so that the plasma P ′ spreads over the entire shielding member 5 to which the adhered matter has adhered, the entire shielding member 5 can be cleaned uniformly. is there. Preferably, the pressure is set to about 1/3 to 5 times, more preferably 1/2 to 2 times the pressure (1 to 10 Torr) at the time of carbon nanotube formation. When the pressure in the plasma CVD apparatus is lower than 1/3 of the pressure at the time of formation, the plasma density is thin and there is no cleaning effect. On the other hand, if the pressure is higher than 5 times the pressure at the time of formation, the plasma will be dense and it will be impossible to clean the entire shielding member 5.

  The cleaning time is appropriately set. For example, if the cleaning is performed for 10 to 40 minutes, most of the deposits can be removed.

  During cleaning, it is preferable to apply a positive voltage to the shielding member 5 at 10 to 200V. By applying a positive voltage and attracting oxygen ions in the plasma, the shielding member 5 can be efficiently cleaned.

  In this example, the shielding member 5 of the plasma CVD apparatus 1 shown in FIG. 1 was cleaned to remove the deposits attached to the shielding member.

The vacuum chamber 11 of the plasma CVD apparatus to be cleaned is made of a quartz tube having an inner diameter of 50 mm, and methane gas and H ₂ gas (methane gas: 20 sccm, H ₂ gas: 80 sccm) are pressured from the gas introducing means 2 for 20 minutes. The process of introducing at 0 Torr and generating plasma to form carbon nanotubes on the substrate was repeated 10 times. A brown by-product is attached to the surface of the shielding member 5 of the plasma CVD apparatus 1.

  Air was introduced into the plasma CVD apparatus 1 at 100 sccm, and plasma was generated in the vacuum chamber by the plasma generating means 3 under the conditions of pressure: 2 Torr and oscillation power: 1 kW. After 40 minutes, the plasma generating means was stopped and cleaning was completed.

  When the shielding member was visually confirmed after completion, most of the deposits could be removed by cleaning for 40 minutes.

  In the present embodiment, the same cleaning object as in the first embodiment is used except that the shielding member 5 is cleaned for 20 minutes while applying a potential of +200 V to the ground potential (chamber potential). 1 and the same conditions.

  When the shielding member 5 was visually confirmed after the cleaning was completed, most of the deposits could be removed by cleaning for 20 minutes.

  In this example, the same cleaning object as in Example 2 was cleaned for 10 minutes in an oxygen gas atmosphere while applying a + 200V potential to the shielding member 5 with respect to the ground potential (chamber potential). Except for the above, the conditions were the same as in Example 2.

  When the shielding member was visually confirmed after the cleaning was completed, most of the deposits could be removed by cleaning for 10 minutes.

  According to the present invention, the shielding member can be cleaned without removing the shielding member and without opening the chamber to the atmosphere. Therefore, the present invention can be used in the field of carbon nanotube production.

The schematic diagram for demonstrating the structure of a plasma CVD apparatus. The schematic diagram for demonstrating the plasma CVD apparatus in cleaning.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Plasma CVD apparatus 2 Gas introduction means 3 Plasma generation means 4 Substrate stage 5 Shielding member 6 Voltage application means 11 Vacuum chamber 12 Vacuum exhaust means 21 Shower head 22 Gas pipe 31 Microwave cavity 32 Waveguide 33 Quartz window P Plasma S Covered Processing substrate

Claims (2)

Plasma generating means for generating plasma in the vacuum chamber, a substrate stage provided at the bottom of the vacuum chamber, and a shielding member arranged to face the substrate stage so as to shield the plasma from exposure to the generated plasma In the cleaning method of the plasma CVD apparatus provided with
By introducing an oxygen atom-containing gas into the vacuum chamber, generating plasma by plasma generating means, applying a positive DC voltage of 10 V to 200 V to the shielding member, and attracting oxygen ions in the plasma to the shielding member, A method of cleaning a plasma CVD apparatus, wherein the shielding member is cleaned.   2. The method of cleaning a plasma CVD apparatus according to claim 1, wherein the oxygen atom-containing gas is oxygen gas, ozone gas, nitric oxide gas, water vapor gas, or air.

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