JP5549834B2 - Thermal spray film and manufacturing method thereof - Google Patents

Description

  The present invention relates to a sprayed film and a method for manufacturing the same, and more specifically, is suitably used in semiconductor manufacturing apparatuses such as a dry etching apparatus and a cleaning apparatus, and halogen-based corrosion such as fluorine-based corrosive gas and chlorine-based corrosive gas. The present invention relates to a thermal sprayed film having high corrosion resistance against reactive gases and plasmas and excellent conductivity, and a method for producing the same.

Conventionally, in the production line of semiconductor devices such as IC, LSI, VLSI, etc., there are processes using halogen-based corrosive gas such as fluorine-based corrosive gas, chlorine-based corrosive gas and their plasma, especially dry etching process. In the cleaning process, corrosion of the components in the semiconductor manufacturing apparatus due to the corrosive gas and plasma is a problem. Therefore, a thermal spray coating such as aluminum oxide or yttrium oxide is used as the corrosion resistant member.
As such a thermal spray coating, a black thermal spray coating of yttrium oxide formed on the surface of a substrate such as a ceramic such as metal or glass is proposed (Patent Document 1). .

JP 2005-256098 A

By the way, the conventional black spray coating of yttrium oxide is certainly excellent in thermal radiation and damage resistance, but it is peeled off during use, and it is peeled off by the black spray coating, causing corrosion and micro cracks that are difficult to see (micro cracks). ) Or the like occurs, the element constituting the base material diffuses, and there is a problem that the base material itself may be damaged or destroyed.
In addition, the black sprayed coating of yttrium oxide has a problem that it cannot be used for a portion requiring electrical conductivity because the yttrium oxide itself is insulative.
Thus, for example, halogen-based corrosive gases such as constituent members in semiconductor manufacturing apparatuses, etching electrodes, and the like, and members that require corrosion resistance and conductivity against these plasmas, are conventionally black yttrium oxide. Thermal spray coating is difficult to cope with, and a film having both halogen-based corrosive gas and corrosion resistance against these plasmas and conductivity has been demanded, but it has not been realized yet.

  The present invention has been made in order to solve the above-described problems, and an object thereof is to provide a halogen-based corrosive gas and a thermal spray film having both corrosion resistance and conductivity with respect to plasma and a method for producing the same. To do.

  The present inventor pays attention to yttrium oxide, which is one of the most excellent corrosion resistance materials in existing ceramics, and further imparts conductivity while maintaining the corrosion resistance of the yttrium oxide to the halogen-based corrosive gas and these plasmas. As a result of intensive studies, the present invention has been completed.

That is, the sprayed film of the present invention is a dense sprayed film including a conductive substance and yttrium oxide formed on a dense sprayed film made of yttrium oxide, and the dense sprayed film contains a conductive substance. 4.0% by volume or more and 12.0% by volume or less, with the balance being yttrium oxide and unavoidable impurities, and the conductive substance segregates at the grain boundaries of the yttrium oxide particles constituting the matrix to form a network structure. It is characterized by forming .

The volume resistance is preferably 0.2 Ω · cm or more and 6.3 Ω · cm or less.
The surface resistance is preferably 0.01Ω / □ or more and 0.70Ω / □ or less.
The conductive material is preferably one or more selected from the group consisting of yttrium, silicon and aluminum.

  In the method for producing a sprayed film of the present invention, yttrium oxide is heated by a first thermal plasma made of a mixed gas containing argon and hydrogen, and a part thereof is melted, and the partially melted yttrium oxide is deposited on the substrate. A coarse sprayed film is deposited, and then the mixture containing yttrium oxide and a conductive material is melted by heating with a second thermal plasma made of a mixed gas containing argon and hydrogen. Depositing a melt with a conductive substance on the dense sprayed film to form a dense sprayed film, and then removing the dense sprayed film and the substrate from the dense sprayed film; .

On the dense sprayed film, yttrium oxide is heated by a third thermal plasma made of a mixed gas containing argon and hydrogen to deposit yttrium oxide partially melted, so that the density of the yttrium oxide is lower than that of the dense sprayed film. A sprayed film may be formed, and then the low-density sprayed film, the dense sprayed film, and the substrate may be removed from the dense sprayed film.
The pressure of one or both of the first and second thermal plasmas and the third thermal plasma is preferably 13 kPa or more and 100 kPa or less.
It is preferable to introduce a gas containing water vapor at the time of the removal.

According to the thermal spray film of the present invention, the conductive material is contained in an amount of 4.0% by volume or more and 12.0% by volume or less, and the balance is yttrium oxide and inevitable impurities, and the conductive material is used as the yttrium oxide constituting the matrix. Since a network structure is formed by segregating at the grain boundaries of the particles , the conductivity is improved without any loss of corrosion resistance against halogen-based corrosive gases such as fluorine-based corrosive gases and chlorine-based corrosive gases and their plasmas. Can be increased.

In addition, since the conductive substance is segregated at the grain boundaries of the yttrium oxide particles constituting the matrix to form a network structure , a small amount of the conductive substance is segregated at the grain boundaries, so that the halogen-based corrosive gas and these The conductivity can be further enhanced without any loss of excellent corrosion resistance against plasma.

  According to the method for manufacturing a sprayed film of the present invention, yttrium oxide is heated by a first thermal plasma made of a mixed gas containing argon and hydrogen, and a part thereof is melted. A coarse sprayed film is deposited thereon, and then a mixture containing yttrium oxide and a conductive material is heated and melted by a second thermal plasma made of a mixed gas containing argon and hydrogen. A melt of yttrium and a conductive material is deposited on the dense sprayed film to form a dense sprayed film, and then the dense sprayed film and the substrate are removed from the dense sprayed film. Thermally sprayed coatings with excellent corrosion resistance against system corrosive gases and their plasmas, as well as excellent electrical conductivity, can be manufactured inexpensively and easily without any changes to existing manufacturing equipment. Rukoto can.

It is sectional drawing which shows the sprayed-film formation apparatus used for the manufacturing method of the sprayed film of one Embodiment of this invention. It is process drawing which shows the manufacturing method of the two-layer sprayed film of one Embodiment of this invention. It is process drawing which shows the manufacturing method of the 3 layer sprayed film of one Embodiment of this invention. It is a scanning electron microscope (SEM) image which shows the cross-sectional structure of the two-layer sprayed film of the reference example 1 of this invention. Is a scanning electron microscope (SEM) image showing the surface of the _Y 2 _O 3 -Y film of Reference Example 1 of the present invention.

The form for implementing the sprayed film of this invention and its manufacturing method is demonstrated.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

"Sprayed film"
The sprayed film according to the present embodiment is a sprayed film containing yttrium oxide (Y ₂ O ₃ ) and a conductive substance.
This thermal spray film contains 4.0% by volume or more and 12.0% by volume or less of conductive material, preferably 4.0% by volume or more and 10.0% by volume or less, more preferably 4.0% by volume or more and 8% by volume or less. It is preferable that the content is 0.0 vol% or less, and the balance is yttrium oxide and inevitable impurities.
The conductive material is preferably one or more selected from the group of yttrium (Y), silicon (Si), and aluminum (Al).

  Here, the reason why the content of the conductive material is limited to 4.0% by volume or more and 12.0% by volume or less is that when the content is less than 4.0% by volume, there is too little conductive material, This is because sufficient electrical conductivity cannot be imparted to the material, and therefore good electrical conductivity cannot be expressed. On the other hand, when the content exceeds 12.0% by volume, good electrical conductivity is exhibited. Although it is possible, the corrosion resistance to halogen-based corrosive gases and their plasma is lowered, which is not preferable.

The density of the sprayed film is preferably 90% or more of the theoretical density, more preferably 92% or more of the theoretical density, and still more preferably 95% or more of the theoretical density.
Here, the reason why the density of the sprayed film is set to 90% or more of the theoretical density is that when the density is less than 90% of the theoretical density, the amount of minute vacancies and defects in the film increases, so that the film quality is improved. This is because, as a result, a dense sprayed film cannot be obtained, and therefore the corrosion resistance against halogen-based corrosive gases and their plasmas is reduced.

In this sprayed film, yttrium oxide constitutes matrix-like particles, and the conductive material segregates at the grain boundaries of the yttrium oxide particles constituting the sprayed film to form a network structure.
In this case, the conductive material segregates at the grain boundaries of the network structure, so that the conductive material forms a continuous network path in the sprayed film, and therefore the content of the conductive material. Despite being low, the corrosion resistance to halogen-based corrosive gases and their plasmas is excellent, and excellent conductivity is exhibited.

  Since this conductive material is present at the grain boundaries of the yttrium oxide particles constituting the matrix, the individual particles of metal yttrium are small, and even if they are exposed to halogen-based corrosive gases and their plasmas, The generation of coarse particles due to metal yttrium is suppressed and does not cause generation of particles.

The sprayed film of this embodiment has not only excellent corrosion resistance against halogen-based corrosive gases and their plasmas, but also has a conductivity of about 1 × 10 ³ Ω / □ to 1 × 10 ⁶ Ω / □. Therefore, the conductivity can be further improved without deteriorating the corrosion resistance of the halogen-based corrosive gas and these plasmas.

"Method of manufacturing sprayed film"
FIG. 1 is a cross-sectional view showing a sprayed film forming apparatus used in the method for manufacturing a sprayed film of the present embodiment. In the figure, 1 is a chamber, 2 is a substrate holder that is disposed in the chamber 1 and supports the substrate 4, Reference numeral 3 denotes a plasma torch which is provided in the upper part of the chamber 1 and forms a thermal plasma 5 on the substrate 4.

The substrate holder 2 supports the substrate 4 and moves and rotates within a predetermined range. The substrate holder 2 is movable in the vertical direction and the horizontal direction and is rotatable about an axis.
Above the substrate holder 2, a heat insulating plate 6 for preventing the molten / unmelted particles scattered from the thermal plasma 5 from being deposited on the substrate 4 and maintaining the temperature of the substrate 4 in a predetermined temperature range. The heat insulating plate 6 is provided with a thermocouple 7 for measuring (monitoring) the temperature in the vicinity of the substrate 4.

The plasma torch 3 supplies a powder raw material through a tube 13 to the torch 11 for forming the thermal plasma 5, a probe 12 for introducing a powder raw material, argon gas, water vapor, etc. into the torch 11. A powder supplier 14 to which the probe 12 is fixed, a plasma gas source 16 for supplying plasma gas to the torch 11 via the introduction flange 15, and the chamber 1 via the probe 12 and the torch 11. An argon gas source 17 for supplying argon gas therein, a water vapor source 18 for supplying water vapor together with a carrier gas into the chamber 1 via the probe 12 and the torch 11, and a work coil 19 provided outside the torch 11. The work coil 19 is provided with a high-frequency power source 20 for supplying a high-frequency current.
A radiation thermometer 22 for measuring (monitoring) the temperature of the thermal plasma 5 on the substrate 4 is provided outside the window 21 provided on the side wall of the chamber 1.

Next, a method for manufacturing the sprayed film of this embodiment using this sprayed film forming apparatus will be described.
Here, a method for manufacturing a two-layer sprayed film will be described first, and then a method for manufacturing a three-layer sprayed film will be described.

(1) Method for producing two-layer sprayed film First, a predetermined amount of yttrium oxide is charged into the powder feeder 14 and the substrate 4 is placed on the substrate holder 2. This yttrium oxide is preferably in the form of powder or granules.
Next, the inside of the chamber 1 is evacuated by a vacuum pump (not shown). When the inside of the chamber 1 reaches a predetermined pressure, for example, 1 kPa or less, a plasma gas, for example, argon gas is supplied from the plasma gas source 16 into the torch 11. Introduce. Then, a high-frequency current is passed through the work coil 19 by the high-frequency power source 20 and plasma is ignited to form the thermal plasma 5 in the torch 11 and the chamber 1.

Next, argon and hydrogen are respectively introduced into the torch 11 from the plasma gas source 16 at a predetermined flow rate, and the atmosphere in the torch 11 is made a mixed gas atmosphere containing argon and hydrogen. Argon and hydrogen may be mixed in advance at a predetermined volume ratio, and the mixed gas may be introduced into the torch 11 at a predetermined flow rate.
Next, the pressure in the chamber 1 and the torch 11 is gradually increased to a predetermined pressure, for example, 13 kPa (about 98 Torr) or more and 100 kPa (about 750 Torr) or less, and at the same time, the output of the plate power (not shown) is increased and lowered. Thermal plasma 5 is generated in the torch 11 and the chamber 1 by plate power, and the substrate 4 is heated by the thermal plasma 5.

  Next, when the temperature of the substrate 4 reaches a predetermined temperature, for example, 600 ° C. to 1000 ° C., which is a temperature range below the melting point of yttrium oxide, powder or granules from the probe 12 into the torch 11 using argon gas as a carrier gas. Yttrium oxide is supplied. Since this yttrium oxide has a low plate power, it does not melt sufficiently even when it passes through the thermal plasma 5, and a part of it is deposited on the substrate 4 in an unmelted state. Further, since the temperature of the substrate 4 is also equal to or lower than the melting point of yttrium oxide, yttrium oxide that is partially unmelted is deposited without melting. Therefore, as shown in FIG. 2A, a dense sprayed film 31 having poor adhesion to the substrate 4 and a density of less than 90% of the theoretical density is formed on the substrate 4. .

Next, a predetermined amount of a mixture of yttrium oxide and a conductive substance, that is, a mixed powder or mixed granule of yttrium oxide and a conductive substance is charged into the powder feeder 14.
The conductive material is preferably one or more powders or granules selected from the group of yttrium, silicon, and aluminum.

  Next, the plate power is increased stepwise, and when the temperature of the coarse sprayed film 31 reaches a predetermined temperature, for example, a temperature equal to or higher than the melting point of the conductive material, argon gas is used as a carrier gas from the probe 12 into the torch 11. A mixed powder or mixed granule of yttrium oxide and a conductive substance is supplied. Since this mixed powder or mixed granule of yttrium oxide and a conductive substance has a high plate power, the conductive substance is sufficiently melted when passing through the thermal plasma 5, and the yttrium oxide and the conductive substance are A sufficiently melted melt is formed, and the melt of the yttrium oxide and the conductive material is deposited on the coarse sprayed film 31. Therefore, as shown in FIG. 2B, a dense sprayed film 32 made of yttrium oxide having a high density of 90% or more of the theoretical density and a conductive material is formed on the dense sprayed film 31. It will be.

  Next, the supply of the mixed powder or mixed granule of yttrium oxide and the conductive material is stopped, the plate power is lowered stepwise, and the temperature of the dense sprayed film 32 becomes a temperature lower than the melting point of the conductive material. Then, using argon gas as a carrier gas, water vapor is supplied from the probe 12 into the chamber 1 to oxidize the surface of the dense sprayed film 32. Next, the inside of the chamber 1 is cooled, and the temperature of the substrate 4 on which the dense sprayed film 32 is formed is lowered to the room temperature. In this cooling process, due to the difference in thermal expansion between the dense sprayed film 32 and the substrate 4, as shown in FIG. 2C, the dense sprayed film 32 is peeled off from the substrate 4 together with the dense sprayed film 31. Thus, a two-layered sprayed film 33 composed of a sprayed film 32 and a dense sprayed film 31 is formed.

The cooling rate in this cooling process is not particularly limited as long as the two-layer sprayed film 33 including the dense sprayed film 32 and the dense sprayed film 31 can be separated from the substrate 4 due to a difference in thermal expansion. In the case of a sprayed film containing yttrium oxide and metal yttrium, the temperature is about 20 ° C./min to 100 ° C./min.
When the temperature of the dense sprayed film 32 is lowered to room temperature, the inside of the chamber 1 is opened to the atmosphere, and the two-layered sprayed film 33 and the substrate 4 are taken out. As described above, the two-layered sprayed film 33 including the dense sprayed film 32 and the dense sprayed film 31 which are independent films from the substrate 4 is obtained.
Further, when the dense sprayed film 31 is removed from the two-layered sprayed film 33 by cutting or grinding, a dense sprayed film 32 which is an independent sprayed film is obtained.

(2) Manufacturing method of three-layer sprayed film The above-described method is exactly the same until the dense sprayed film 32 is formed on the dense sprayed film 31.
Here, after the dense sprayed film 32 is formed on the dense sprayed film 31, a predetermined amount of yttrium oxide is charged into the powder supplier 14.

  Next, when the plate power is lowered stepwise and the temperature of the dense sprayed film 32 falls to a predetermined temperature, for example, a temperature below the melting point of the conductive material, argon gas is used as a carrier gas from the probe 12 to the inside of the torch 11. Is supplied with powdered or granular yttrium oxide. Since this yttrium oxide has a relatively low plate power, it does not melt sufficiently when passing through the thermal plasma 5, and a part of it is deposited on the dense sprayed film 32 in an unmelted state. Therefore, as shown in FIG. 3A, a low-density sprayed film 41 made of yttrium oxide with insufficient melting and less than 90% of the theoretical density is formed on the dense sprayed film 32. .

  Next, the supply of yttrium oxide is stopped, the plate power is lowered stepwise, and when the temperature of the low-density sprayed film 41 becomes a temperature equal to or lower than the melting point of the conductive material, the probe 12 Then, water vapor is supplied into the chamber 1 to oxidize the surface of the low density sprayed film 41. Next, the inside of the chamber 1 is cooled, and the temperature of the substrate 4 on which the low density sprayed film 41 is formed is lowered to the room temperature. In this cooling process, due to the difference in thermal expansion between the sprayed films 31, 32, 41 and the substrate 4, as shown in FIG. 3B, a coarse sprayed film 31, a dense sprayed film 32, and a low density sprayed film 41. The three-layer sprayed film 42 made of is peeled off from the substrate 4.

When the temperature of the low-density sprayed film 41 is lowered to room temperature, the chamber 1 is opened to the atmosphere, and the three-layered sprayed film 42 and the substrate 4 are taken out. As described above, the three-layered sprayed film 42 including the dense sprayed film 31, the dense sprayed film 32, and the low-density sprayed film 41, which are films independent of the substrate 4, is obtained.
Further, when the dense sprayed film 31 and the low-density sprayed film 41 are removed from the three-layered sprayed film 42 by cutting, grinding, or the like, a dense sprayed film 32 that is an independent single sprayed film is obtained.

  According to the sprayed film of the present embodiment, since it contains yttrium oxide and one or more conductive substances selected from the group of yttrium, silicon, and aluminum, fluorine-based corrosive gas, chlorine-based corrosion In addition to maintaining corrosion resistance to halogen-based corrosive gases such as reactive gases and these plasmas, conductivity can be increased.

According to the method for manufacturing a sprayed film of the present embodiment, a dense sprayed film 31 and a dense sprayed film 32 are sequentially formed on the substrate 4 to form a two-layered sprayed film 33, or a densely sprayed film. 31, a dense sprayed film 32, and a low-density sprayed film 41 are sequentially formed to form a three-layered sprayed film 42. Thereafter, water vapor is supplied into the chamber 1, and the dense sprayed film 32 or the low-density sprayed film is sprayed. Since the surface of the film 41 is oxidized, the two-layered sprayed film 33 including the dense sprayed film 32 and the dense sprayed film 31, or the dense sprayed film 31, the dense sprayed film 32, and the low density sprayed film 41 are used. The three-layered thermal sprayed film 42 can be manufactured inexpensively and easily without any modification to the existing manufacturing apparatus.
Further, the dense sprayed film 31 is removed from the two-layered sprayed film 33 by cutting or grinding, or the densely sprayed film 31 and the low-density sprayed film 41 are cut or ground from the three-layered sprayed film 42. The dense sprayed film 32, which is an independent single sprayed film, can be easily obtained by removing the film by, for example.

Hereinafter, although this invention is concretely demonstrated by the reference examples 1 and 2, Examples 1-4, 7-11, and a comparative example, this invention is not limited by these Examples.

( Reference Example 1 )
The sprayed film of Reference Example 1 was produced using the sprayed film forming apparatus shown in FIG.
First, as a substrate, ring-shaped carbon (manufactured by Nippon Carbon Industry Co., Ltd.) having an outer diameter of 130 mm, an inner diameter of 90 mm, and a thickness of 4 mm is used, and a commercially available yttrium oxide granule having a particle size of 45 μm or less (manufactured by Japan Yttrium Co., Ltd.) ) And metal yttrium (made by Japan Yttrium Co., Ltd.) having a particle size of 500 μm or less are prepared, and the yttrium oxide granules are mixed with metal yttrium so that the metal yttrium content is 3% by volume. A mixture of yttrium and metal yttrium was made.

Next, the yttrium oxide granules were filled in the powder supplier 14, and the ring-shaped carbon was disposed at a predetermined position on the substrate holder 2 in the chamber 1.
Next, the inside of the chamber 1 was evacuated by a vacuum pump (not shown), and after confirming that the inside of the chamber 1 became 1 kPa or less, argon gas was introduced into the torch 11 from the argon gas source 17. Then, a high-frequency current was applied from the high-frequency power source 20 to the work coil 19 to ignite plasma in the torch 11, and thermal plasma 5 was generated in the torch 11 and the chamber 1.

Next, argon gas 80 L / min and hydrogen gas 10 L / min are supplied from the plasma gas source 16 into the torch 11 and the chamber 1, and the pressure in the torch 11 and the chamber 1 is gradually increased to 40 kPa (about 300 Torr). Pressure was used.
At the same time, the plate power was increased to 15 kVA, and the thermal plasma 5 generated in the torch 11 and the chamber 1 was applied to the ring-shaped carbon on the substrate holder 2 and heated. Here, the substrate holder 2 was rotated at a rotational speed of 55 rpm while reciprocating in the horizontal direction between 45 mm and 65 mm in the X-axis direction (direction perpendicular to the paper surface in FIG. 1).

  Next, when the surface temperature of the ring-shaped carbon monitored by the thermocouple 7 (distance from the ring-shaped carbon is 10 mm) rises to about 660 ° C., argon gas is used as a carrier gas and the probe 12 enters the thermal plasma 5. Yttrium oxide granules were supplied at 2.7 g / min, and the yttrium oxide granules that passed through the thermal plasma 5 were sprayed on the surface of the ring-shaped carbon for 4.5 minutes. Since the plate power in this thermal spraying is in a low state, the yttrium oxide granules that have passed through the thermal plasma 5 were deposited on the surface of the ring-shaped carbon with insufficient melting. As a result, on the surface of the ring-shaped carbon, the adhesion with the ring-shaped carbon was poor, and a dense sprayed film having a density as low as 75% of the theoretical density was formed.

Next, while supplying yttrium oxide granules at 2.7 g / min, the plate power was increased by 1 kVA per minute to 30 kVA. At this time, the temperature of the coarse sprayed film rose to about 800 ° C.
Next, the supply of yttrium oxide granules was stopped, and the powder supplier 14 was filled with the mixture of yttrium oxide and metal yttrium.
Then, the supply of the mixture of yttrium oxide and metal yttrium was started, and the supply amount was adjusted from 0 g / min to 2.7 g / min over 5 minutes.

Next, the plate power is increased stepwise by 2 kVA every minute to 40 kVA, and at the same time, the supply amount of the mixture of yttrium oxide and metal yttrium into the thermal plasma 5 is increased by 0.06 g per minute. The supply rate of the mixture was 3.0 g / min, and this state was maintained for 100 minutes.
Since the plate power in this state is high, the mixture of yttrium oxide and metal yttrium that has passed through the thermal plasma 5 is sufficiently melted, and the melt of yttrium oxide and metal yttrium is deposited on the coarse sprayed film. It was. As a result, a dense sprayed film having a density as high as 96.8% of the theoretical density was formed on the surface of the dense sprayed film.

  Next, the supply of the mixture of yttrium oxide and metal yttrium was stopped, the plate power was lowered by 2 kVA every 5 minutes, and the dense sprayed film was gradually cooled. While monitoring the surface temperature of the dense sprayed film with the thermocouple 7, when the surface temperature reached about 850 ° C., argon gas was used as a carrier gas, and water was contained in the torch 11 and the chamber 1 from the probe 12. Gas was supplied to oxidize the surface of the dense sprayed film. When the surface temperature of the dense sprayed film reached about 300 ° C., the sprayed film peeled off from the ring-shaped carbon due to the difference in thermal expansion coefficient between the ring-shaped carbon and the sprayed film.

Next, the thermal plasma 5 was turned off, and when the surface temperature of the dense sprayed film was lowered to room temperature (25 ° C.), the inside of the chamber 1 was opened to the atmosphere, and the sprayed film and the ring-shaped carbon were taken out.
Through the above process, a sprayed film having a two-dimensional structure in which a Y ₂ O ₃ film (rough sprayed film) and a Y ₂ O ₃ —Y film (dense sprayed film) are stacked is obtained.
FIG. 4 is a scanning electron microscope (SEM) image showing the cross-sectional structure of this sprayed film, which is a cross section obtained by cutting the sprayed film embedded in the resin with a diamond cutter.

Further, a test piece having a size of 20 mm × 20 mm × 2 mm was cut out from a sprayed film having a two-layer structure in which the Y ₂ O ₃ film and the Y ₂ O ₃ —Y film were laminated, and the surface of the test piece was cut. Were observed with a scanning electron microscope (SEM).
FIG. 5 is a scanning electron microscope (SEM) image showing the surface of the Y ₂ O ₃ —Y film of this test piece. The grain boundary around the Y ₂ O ₃ particles (white portion in the figure) (black in the figure). It can be seen that yttrium segregates in (part) and forms a network structure.
Table 1 shows the amount of metal yttrium added to this sample, the density (relative density:%) relative to the theoretical density of the dense sprayed film, the surface resistance, and the volume resistance.

( Example 1 )
Except that the content of metal yttrium in the mixture of yttrium oxide and metal yttrium was 4% by volume, a Y ₂ O ₃ film (roughly sprayed film) and Y ₂ O were formed on the surface of the ring-shaped carbon in accordance with Reference Example 1. A sample of Example 1 on which a _3- Y film (dense sprayed film) was formed was produced.
Table 1 shows the amount of metal yttrium added to this sample, the density (relative density:%) relative to the theoretical density of the dense sprayed film, the surface resistance, and the volume resistance.

( Example 2 )
Except that the content of metal yttrium in the mixture of yttrium oxide and metal yttrium was 8% by volume, a Y ₂ O ₃ film (roughly sprayed film) and Y ₂ O were formed on the surface of the ring-shaped carbon according to Reference Example 1. A sample of Example 2 on which a _3- Y film (dense sprayed film) was formed was produced.
Table 1 shows the amount of metal yttrium added to this sample, the density (relative density:%) relative to the theoretical density of the dense sprayed film, the surface resistance, and the volume resistance.

( Example 3 )
Except that the content of metal yttrium in the mixture of yttrium oxide and metal yttrium was 10% by volume, a Y ₂ O ₃ film (roughly sprayed film) and Y ₂ O were formed on the surface of the ring-shaped carbon in accordance with Reference Example 1. A sample of Example 3 on which a _3- Y film (dense sprayed film) was formed was produced.
Table 1 shows the amount of metal yttrium added to this sample, the density (relative density:%) relative to the theoretical density of the dense sprayed film, the surface resistance, and the volume resistance.

( Example 4 )
Except that the content of metal yttrium in the mixture of yttrium oxide and metal yttrium was set to 12% by volume, a Y ₂ O ₃ film (roughly sprayed film) and Y ₂ O were formed on the surface of the ring-shaped carbon according to Reference Example 1. A sample of Example 4 in which a _3- Y film (dense sprayed film) was formed was produced.
Table 1 shows the amount of metal yttrium added to this sample, the density (relative density:%) relative to the theoretical density of the dense sprayed film, the surface resistance, and the volume resistance.

( Reference Example 2 )
Except that the content of metal yttrium in the mixture of yttrium oxide and metal yttrium was 13% by volume, a Y ₂ O ₃ film (coarse sprayed film) and Y ₂ O were formed on the surface of the ring-shaped carbon according to Reference Example 1. A sample of Reference Example 2 on which a _3- Y film (dense sprayed film) was formed was produced.
Table 1 shows the amount of metal yttrium added to this sample, the density (relative density:%) relative to the theoretical density of the dense sprayed film, the surface resistance, and the volume resistance.

  According to Table 1, if the yttrium content is less than 4% by volume, the volume resistance is high and sufficient electrical conductivity is not exhibited. On the other hand, if the yttrium content exceeds 12% by volume, the relative density Was found to be lower than 90%.

(Example 7)
After the metal yttrium content in the mixture of yttrium oxide and metal yttrium was 4% by volume, and the supply amount of the mixture of yttrium oxide and metal yttrium into the thermal plasma 5 was 3.0 g / min, the chamber 1 The Y ₂ O ₃ film (coarse sprayed film) and Y on the surface of the ring-like carbon according to Reference Example 1 except that the pressure inside the torch 11 and the pressure inside the torch 11 are reduced to 5 kPa every 5 minutes to 30 kPa (about 218 Torr). A sample of Example 7 in which a ₂ O ₃ —Y film (dense sprayed film) was formed was produced.
Table 2 shows the amount of metal yttrium added to this sample, the density (relative density:%) with respect to the theoretical density of the dense sprayed film, and the volume resistance.

(Example 8)
After the metal yttrium content in the mixture of yttrium oxide and metal yttrium was 8% by volume, and the supply amount of the mixture of yttrium oxide and metal yttrium into the thermal plasma 5 was 3.0 g / min, the chamber 1 The Y ₂ O ₃ film (coarse sprayed film) and Y on the surface of the ring-like carbon according to Reference Example 1 except that the pressure inside the torch 11 and the pressure inside the torch 11 are reduced to 5 kPa every 5 minutes to 30 kPa (about 218 Torr). A sample of Example 8 in which a ₂ O ₃ —Y film (dense sprayed film) was formed was produced.
Table 2 shows the amount of metal yttrium added to this sample, the density (relative density:%) with respect to the theoretical density of the dense sprayed film, and the volume resistance.

Example 9
After the metal yttrium content in the mixture of yttrium oxide and metal yttrium was set to 12% by volume, and the supply amount of the mixture of yttrium oxide and metal yttrium into the thermal plasma 5 was set to 3.0 g / min, the chamber 1 The Y ₂ O ₃ film (coarse sprayed film) and Y on the surface of the ring-like carbon according to Reference Example 1 except that the pressure inside the torch 11 and the pressure inside the torch 11 are reduced to 5 kPa every 5 minutes to 30 kPa (about 218 Torr). A sample of Example 9 in which a ₂ O ₃ —Y film (dense sprayed film) was formed was produced.
Table 2 shows the amount of metal yttrium added to this sample, the density (relative density:%) with respect to the theoretical density of the dense sprayed film, and the volume resistance.

  When Table 2 and Table 1 were compared, it was found that the volume resistance decreased as the pressure during thermal spraying decreased even when the yttrium content was equal.

(Example 10)
As a substrate, ring-shaped carbon (manufactured by Nippon Carbon Industry Co., Ltd.) having an outer diameter of 260 mm, an inner diameter of 200 mm, and a thickness of 12 mm is used, and a commercially available yttrium oxide granule having a particle size of 38 μm or more and 63 μm or less (Nippon Yttrium Co., Ltd.) Manufactured) and metallic aluminum (made by Showa Aluminum Co., Ltd.) having a particle size of 500 μm or less are prepared, and mixed with the yttrium oxide granules so that the metallic aluminum content is 6% by volume, A mixture of yttrium oxide and metallic aluminum was made.

Next, the yttrium oxide granules were filled in the powder supplier 14, and the ring-shaped carbon was disposed at a predetermined position on the substrate holder 2 in the chamber 1.
Next, the inside of the chamber 1 was evacuated by a vacuum pump (not shown), and after confirming that the inside of the chamber 1 became 1 kPa or less, argon gas was introduced into the torch 11 from the argon gas source 17. Then, a high-frequency current was applied from the high-frequency power source 20 to the work coil 19 to ignite plasma in the torch 11, and thermal plasma 5 was generated in the torch 11 and the chamber 1.

Next, argon gas 80 L / min and hydrogen gas 10 L / min are supplied from the plasma gas source 16 into the torch 11 and the chamber 1, and the pressure in the torch 11 and the chamber 1 is gradually increased to 40 kPa (about 300 Torr). Pressure was used.
At the same time, the plate power was increased to 15 kVA, and the thermal plasma 5 generated in the torch 11 and the chamber 1 was applied to the ring-shaped carbon on the substrate holder 2 and heated. Here, the substrate holder 2 was rotated at a rotational speed of 120 rpm while reciprocating in the horizontal direction between 100 mm and 130 mm in the X-axis direction (direction perpendicular to the paper surface in FIG. 1).

  Next, when the surface temperature of the ring-shaped carbon monitored by the thermocouple 7 (distance from the ring-shaped carbon is 20 mm) rises to about 660 ° C., argon gas is used as a carrier gas and the probe 12 enters the thermal plasma 5. Yttrium oxide granules were supplied at 6.0 g / min, and the yttrium oxide granules passed through the thermal plasma 5 were sprayed on the surface of the ring-shaped carbon for 3 minutes. Since the plate power in this thermal spraying is in a low state, the yttrium oxide granules that have passed through the thermal plasma 5 were deposited on the surface of the ring-shaped carbon with insufficient melting. As a result, on the surface of the ring-shaped carbon, the adhesion with the ring-shaped carbon was poor, and a dense sprayed film having a density as low as 85% of the theoretical density was formed.

  Next, increase the supply amount of yttrium oxide granules by 0.45 g per minute to 7.6 g / min, increase the plate power by 1 kVA every minute to 20 kVA, and then supply yttrium oxide granules. The plate power was increased by 1 kVA per minute to 30 kVA while maintaining the amount at 7.6 g / min. The coarse sprayed film and this process increased the thickness of the sprayed film by 0.7 mm.

Next, the supply of yttrium oxide granules was stopped, and the powder supplier 14 was filled with the mixture of yttrium oxide and metal aluminum.
Next, supply of the mixture of yttrium oxide and metal aluminum to the thermal plasma 5 was started, and the supply amount was adjusted from 0 g / min to 4.2 g / min over 5 minutes.

Subsequently, the plate power was increased stepwise by 2 kVA per minute to 40 kVA, and the pressure in the chamber 1 was decreased stepwise by 2 kPa per minute to a pressure of 30 kPa (about 218 Torr). At this time, the surface temperature of the ring-shaped carbon measured with the thermocouple 7 rose to 1010 ° C. Thereafter, this state was maintained for 180 minutes.
Since the plate power in this state is high, the mixture of yttrium oxide and metal aluminum that has passed through the thermal plasma 5 is sufficiently melted, and the melt of yttrium oxide and metal aluminum is deposited on the dense sprayed film. It was. As a result, a dense sprayed film having a thickness of 4.5 mm was formed on the surface of the coarse sprayed film.

  Next, the supply of the mixture of yttrium oxide and metal aluminum was stopped, and the plate power was lowered by 1 kVA every 10 minutes to gradually cool the dense sprayed film. While monitoring the surface temperature of the dense sprayed film with the thermocouple 7, when the surface temperature reached about 750 ° C., argon gas was used as a carrier gas, and water was contained in the torch 11 and the chamber 1 from the probe 12. Gas was supplied to oxidize the surface of the dense sprayed film. When the surface temperature of this dense sprayed film reached about 650 ° C., the sprayed film peeled off from the ring-shaped carbon due to the difference in thermal expansion coefficient between the ring-shaped carbon and the sprayed film.

Next, the thermal plasma 5 was turned off, and when the surface temperature of the dense sprayed film was lowered to room temperature (25 ° C.), the inside of the chamber 1 was opened to the atmosphere, and the sprayed film and the ring-shaped carbon were taken out.
By the above process, a sprayed film having a two-dimensional structure in which a Y ₂ O ₃ film (rough sprayed film) and a Y ₂ O ₃ -Al film (dense sprayed film) are stacked is obtained.

Then removed _Y 2 _{O 3} film lower surface of the sprayed film is ground to a thickness of 1 mm, to obtain a ring-shaped sample of Example 10 consisting of _Y 2 _O 3 -Al film thickness 4.2 mm.
Table 3 shows the amount of metal aluminum added to this ring sample, the density (relative density:%) with respect to the theoretical density of the Y ₂ O ₃ -Al film, and the volume resistance.

  According to Table 3, it was found that metal aluminum also has the same characteristics as metal yttrium.

(Example 11)
As a substrate, ring-shaped carbon (manufactured by Nippon Carbon Industry Co., Ltd.) having an outer diameter of 260 mm, an inner diameter of 200 mm, and a thickness of 12 mm is used, and a commercially available yttrium oxide granule having a particle size of 38 μm or more and 63 μm or less (Nippon Yttrium Co., Ltd.) Manufactured) and metal yttrium having a particle size of 500 μm or less (manufactured by Japan Yttrium Co., Ltd.), respectively, and yttrium oxide granules were mixed with metal yttrium so that the metal yttrium content was 6% by volume, A mixture of yttrium oxide and metal yttrium was made.

Next, the yttrium oxide granules were filled in the powder supplier 14, and the ring-shaped carbon was disposed at a predetermined position on the substrate holder 2 in the chamber 1.
Next, the inside of the chamber 1 was evacuated by a vacuum pump (not shown), and after confirming that the inside of the chamber 1 became 1 kPa or less, argon gas was introduced into the torch 11 from the argon gas source 17. Then, a high-frequency current was applied from the high-frequency power source 20 to the work coil 19 to ignite plasma in the torch 11, and thermal plasma 5 was generated in the torch 11 and the chamber 1.

Next, argon gas 80 L / min and hydrogen gas 10 L / min are supplied from the plasma gas source 16 into the torch 11 and the chamber 1, and the pressure in the torch 11 and the chamber 1 is gradually increased to 40 kPa (about 300 Torr). Pressure was used.
At the same time, the plate power was increased to 15 kVA, and the thermal plasma 5 generated in the torch 11 and the chamber 1 was applied to the ring-shaped carbon on the substrate holder 2 and heated. Here, the substrate holder 2 was rotated at a rotational speed of 120 rpm while reciprocating in the horizontal direction between 100 mm and 130 mm in the X-axis direction (direction perpendicular to the paper surface in FIG. 1).

  Next, when the surface temperature of the ring-shaped carbon monitored by the thermocouple 7 (distance from the ring-shaped carbon is 20 mm) rises to about 660 ° C., argon gas is used as a carrier gas and the probe 12 enters the thermal plasma 5. Yttrium oxide granules were supplied at 6.0 g / min, and the yttrium oxide granules passed through the thermal plasma 5 were sprayed on the surface of the ring-shaped carbon for 3 minutes. Since the plate power in this thermal spraying is in a low state, the yttrium oxide granules that have passed through the thermal plasma 5 were deposited on the surface of the ring-shaped carbon with insufficient melting. As a result, on the surface of the ring-shaped carbon, the adhesion with the ring-shaped carbon was poor, and a dense sprayed film having a density as low as 85% of the theoretical density was formed.

  Next, increase the supply amount of yttrium oxide granules by 0.45 g per minute to 7.6 g / min, increase the plate power by 1 kVA every minute to 20 kVA, and then supply yttrium oxide granules. The plate power was increased by 1 kVA per minute to 30 kVA while maintaining the amount at 7.6 g / min. The coarse sprayed film and this process increased the thickness of the sprayed film by about 0.7 mm.

Next, the supply of yttrium oxide granules was stopped, and the powder supplier 14 was filled with the mixture of yttrium oxide and metal yttrium.
Next, supply of the mixture of yttrium oxide and metal yttrium to the thermal plasma 5 was started, and the supply amount was adjusted from 0 g / min to 4.2 g / min over 5 minutes.

Next, the plate power was increased stepwise by 1 kVA every minute to 40 kVA, and simultaneously the pressure in the chamber 1 was decreased stepwise by 2 kPa every minute to a pressure of 30 kPa (about 218 Torr). At this time, the surface temperature of the ring-shaped carbon measured with the thermocouple 7 rose to 1010 ° C. Thereafter, this state was maintained for 180 minutes.
Since the plate power in this state is high, the mixture of yttrium oxide and metal yttrium that has passed through the thermal plasma 5 is sufficiently melted, and the melt of yttrium oxide and metal yttrium is deposited on the coarse sprayed film. It was. As a result, a Y ₂ O ₃ —Y film (dense sprayed film) having a thickness of about 4.5 mm was formed on the surface of the coarse sprayed film.

Then, while continuing to supply the mixture of yttrium oxide and metal yttrium, the plate power is decreased stepwise by 1 kVA every minute to 30 kVA, and at the same time the pressure in the chamber 1 is increased stepwise by 1 kPa every minute. The pressure was 40 kPa (about 300 Torr).
Next, the supply of the mixture of yttrium oxide and metal yttrium was stopped, and the above-mentioned yttrium oxide granules were filled in the powder feeder 14.
Next, the supply of the yttrium oxide granules to the thermal plasma 5 was started, and the supply amount was adjusted from 0 g / min to 4.6 g / min over 5 minutes.

Next, the plate power was reduced stepwise by 0.5 kVA every minute to 20 kVA. At this time, the surface temperature of the dense sprayed film measured with the thermocouple 7 was 700 ° C. Next, thermal spraying was performed for 45 minutes in this state. Thereby, the thickness of the sprayed film increased by about 1.0 mm.
Since the plate power in this thermal spraying is in a low state, the yttrium oxide granules that have passed through the thermal plasma 5 were deposited on the dense thermal sprayed film with insufficient melting. Therefore, a Y ₂ O ₃ film (low density sprayed film) having a density of about 89% of the theoretical density was formed.

  Next, the supply of yttrium oxide granules was stopped, the plate power was decreased stepwise by 1 kVA every 10 minutes, and the surface temperature of the low-density sprayed film was monitored by the thermocouple 7 while the surface temperature was about 750. When the temperature reached 0 ° C., argon gas was used as a carrier gas, and a gas containing water vapor was supplied from the probe 12 into the torch 11 and the chamber 1 to oxidize the surface of this low density sprayed film. When the surface temperature of the low-density sprayed film reached about 650 ° C., the sprayed film peeled off from the ring-shaped carbon due to the difference in thermal expansion coefficient between the ring-shaped carbon and the sprayed film.

Next, the thermal plasma 5 was turned off, and when the surface temperature of the low density sprayed film was lowered to room temperature (25 ° C.), the inside of the chamber 1 was opened to the atmosphere, and the sprayed film and the ring-shaped carbon were taken out.
A three-layer structure in which a Y ₂ O ₃ film (rough sprayed film), a Y ₂ O ₃ —Y film (dense sprayed film), and a Y ₂ O ₃ film (low density sprayed film) are stacked by the above process. As a result, a sprayed coating having an autostereoscopic shape was obtained.

Next, both sides of this sprayed film were ground to a thickness of 1 mm respectively to remove the Y ₂ O ₃ films on both sides, and Example 11 consisting of a Y ₂ O ₃ —Y film (dense sprayed film) having a thickness of 4.2 mm. A ring-shaped sample was obtained.
Table 4 shows the amount of metal yttrium added to the ring sample, the density (relative density:%) relative to the theoretical density of the Y ₂ O ₃ —Y film, and the volume resistance.

Further, the Y ₂ O ₃ film (rough sprayed film), Y ₂ O ₃ —Y film (dense sprayed film) and Y ₂ O ₃ film (low density sprayed film) are laminated. A test piece having a size of 20 mm × 20 mm × 2 mm was cut out from the three-dimensional sprayed film, and the surface of the test piece was observed with a scanning electron microscope (SEM). As a result, the grain boundary layer around the Y ₂ O ₃ particles was observed. It was found that yttrium segregated and formed a network structure.

(Comparative example)
As a substrate, ring-shaped carbon (manufactured by Nippon Carbon Industry Co., Ltd.) having an outer diameter of 130 mm, an inner diameter of 90 mm, and a thickness of 4 mm is used, and a commercially available yttrium oxide granule having a particle size of 38 μm or more and 63 μm or less (Nihon Yttrium Co., Ltd.) Each).

Next, the yttrium oxide granules were filled in the powder supplier 14, and the ring-shaped carbon was disposed at a predetermined position on the substrate holder 2 in the chamber 1.
Next, the inside of the chamber 1 was evacuated by a vacuum pump (not shown), and after confirming that the inside of the chamber 1 became 1 kPa or less, argon gas was introduced into the torch 11 from the argon gas source 17. Then, a high-frequency current was applied from the high-frequency power source 20 to the work coil 19 to ignite plasma in the torch 11, and thermal plasma 5 was generated in the torch 11 and the chamber 1.

Next, argon gas 80 L / min and hydrogen gas 10 L / min are supplied from the plasma gas source 16 into the torch 11 and the chamber 1, and the pressure in the torch 11 and the chamber 1 is gradually increased to 40 kPa (about 300 Torr). Pressure was used.
At the same time, the plate power was increased to 15 kVA, and the thermal plasma 5 generated in the torch 11 and the chamber 1 was applied to the ring-shaped carbon on the substrate holder 2 and heated. Here, the substrate holder 2 was rotated at a rotational speed of 55 rpm while reciprocating in the horizontal direction between 45 mm and 65 mm in the X-axis direction (direction perpendicular to the paper surface in FIG. 1).

Next, the plate power was further increased to 40 kVA, and the ring-shaped carbon was heated by the thermal plasma 5. The surface temperature of the ring-shaped carbon was about 900 ° C.
Next, argon gas is used as a carrier gas, yttrium oxide granules are supplied from the probe 12 into the thermal plasma 5 at 3.7 g / min, and the yttrium oxide granules that have passed through the thermal plasma 5 are deposited on the surface of the ring-shaped carbon 85. Sprayed for a minute. Since the plate power in this thermal spraying is in a high state, the yttrium oxide granules that have passed through the thermal plasma 5 are in a sufficiently melted state, and thus a dense sprayed film is formed on the surface of the ring-shaped carbon.

Next, the supply of yttrium oxide granules was stopped, and the plate power was decreased stepwise by 1 kVA every 5 minutes, so that the temperature of the dense sprayed film and the ring-shaped carbon was gradually decreased. Thereafter, the thermal plasma 5 was turned off, and when the temperature of the dense sprayed film and the ring-shaped carbon was lowered to room temperature (25 ° C.), the inside of the chamber 1 was opened to the atmosphere, and the sprayed film and the ring-shaped carbon were taken out.
Although many cracks were generated on the surface of the sprayed film, the bond between the sprayed film and the ring-shaped carbon was strong, and it was not easy to peel off the sprayed film from the ring-shaped carbon.

  Further, when the sprayed film and the ring-shaped carbon were taken out from the chamber 1, a corrosion odor was felt, but this corrosion odor was thought to be generated near the interface between the sprayed film and the ring-shaped carbon. It is thought that acetylene and yttria were produced by reacting with moisture in the atmosphere.

  Since the thermal spray film of the present invention contains yttrium oxide and a conductive substance, the yttrium oxide can further impart conductivity while maintaining the corrosion resistance of the yttrium oxide to the halogen-based corrosive gas and these plasmas. Therefore, it can be applied to various members that require corrosion resistance and conductivity other than semiconductor manufacturing equipment, such as etching electrodes and dielectric materials for electrostatic chucks, as well as components in semiconductor manufacturing equipment. And its usefulness is very large.

DESCRIPTION OF SYMBOLS 1 Chamber 2 Substrate holder 3 Plasma torch 4 Substrate 5 Thermal plasma 6 Heat insulation board 7 Thermocouple 31 Dense sprayed film 32 Dense sprayed film 33 Two-layered sprayed film 41 Low-density sprayed film 42 Three-layered sprayed film

Claims (8)

A dense sprayed film containing a conductive substance and yttrium oxide formed on a dense sprayed film made of yttrium oxide,
The conductive substance is contained in an amount of 4.0% by volume or more and 12.0% by volume or less, and the balance is yttrium oxide and inevitable impurities. The conductive substance segregates at the grain boundaries of the yttrium oxide particles constituting the matrix. A sprayed coating characterized by forming a network structure . The thermal spray film according to claim 1, wherein the volume resistance is 0.2 Ω · cm or more and 6.3 Ω · cm or less. The thermal spray film according to claim 1 or 2, wherein the surface resistance is 0.01Ω / □ or more and 0.70Ω / □ or less. The thermal spray film according to any one of claims 1 to 3, wherein the conductive substance is one or more selected from the group consisting of yttrium, silicon, and aluminum. The yttrium oxide is heated by a first thermal plasma composed of a mixed gas containing argon and hydrogen to melt a part thereof, and this partly melted yttrium oxide is deposited on the substrate to form a coarse sprayed film. ,
Next, the mixture containing yttrium oxide and the conductive substance is heated and melted by the second thermal plasma made of a mixed gas containing argon and hydrogen, and the melt of the yttrium oxide and the conductive substance is melted into the above-mentioned dense state. Depositing on the sprayed film to form a dense sprayed film,
Next, a method for producing a sprayed coating, comprising removing the coarse sprayed coating and the substrate from the dense sprayed coating. On the dense sprayed film, yttrium oxide is heated by a third thermal plasma made of a mixed gas containing argon and hydrogen to deposit yttrium oxide partially melted, so that the density of the yttrium oxide is lower than that of the dense sprayed film. Forming a sprayed coating,
6. The method for producing a sprayed film according to claim 5 , wherein the low-density sprayed film, the dense sprayed film, and the substrate are removed from the dense sprayed film. The thermal spray film according to claim 5 or 6 , wherein the pressure of one or both of the first and second thermal plasmas and the third thermal plasma is 13 kPa or more and 100 kPa or less. Production method. The method for producing a sprayed film according to claim 5, wherein a gas containing water vapor is introduced during the removal.