Patent Publication Number: US-2015064406-A1

Title: Method for forming fluoride spray coating, and fluoride spray coating covered member

Description:
TECHNICAL FIELD 
     This invention relates to a method for forming fluoride spray coating and a fluoride spray coating covered member. More particularly, the invention relates to a method for forming a fluoride spray coating on a surface of a member for semiconductor working device and the like subjected to a plasma etching process under highly corrosive gas environment through carbide cermet, and also relates to a fluoride spray coating covered member provided by performing this method. 
     RELATED ART 
     As a coating with corrosion resistance formed on a surface of the member for semiconductor working device, a spray coating is useful. For example, in case that the member is subjected to a plasma treatment under an existence of halogen or halogen compound, or in case that the member is used in a field of semiconductor working device wherein fine particles generated by the plasma treatment are required to be cleaned and removed, it is necessary to apply a further surface treatment, and thus there are proposed several conventional techniques. 
     In a working environment of the devices such as dry etcher, CVD and PVD used in the semiconductor working process and the production process of liquid crystal, a higher cleanliness is demanded so as to improve an accuracy of micro-fabrication associated with high circuit integration of a substrate such as silicon and glass. However, since gas or aqueous solution having a strong corrosive nature such as fluoride and chloride is used in various processes for micro-fabrication, the members provided in these devices are fast in corrosive wearing, and as a results, there is a fear of secondary contamination of environment based on the generation of corrosion products. 
     The manufacturing and working process of the semiconductor device is a so-called dry process in which a compound semiconductor made Si, Ga, As, P and so on is mainly used and treated in vacuum or in an atmosphere under a reduced pressure. As an apparatus and a member used in the dry process are included an oxidation furnace, CVD apparatus, PVD apparatus, an epitaxial growing apparatus, an ion implantation apparatus, a diffusion furnace, a reactive ion etching apparatus as well as members and parts accompanied with these apparatuses such as pipes, intake and exhaust fans, vacuum pump, valves and the like. In addition, it is known that the apparatus uses fluorides such as BF 3 , PF 3 , PF 6 , NF 3 , WF 3 , HF, chlorides such as BCl 3 , PCl 3 , PCl 5 , POCl 3 , AsCl 3 , SnCl 4 , TiCl 4 , SiH 2 Cl 2 , SiCl 4 , HCl, Cl 2 , bromides such as HBr, and further strong corrosive reagents and gases such as NH 3 , CH 3 F or the like. 
     In the dry process using these halides, plasma (low-temperature plasma) is frequently used for activation of reaction and the improvement of working accuracy. Under an environment using such plasma, various halides are converted into strong corrosive atomic or ionized F, Cl, Br, l, and provide a large effect to micro-fabrication of semiconductor material. On the other hand, there is a problem that fine particles of SiO 2 , Si 3 N 4 , Si, W and the like, which are removed from the surface of the plasma-treated semiconductor material (especially a plasma etching treatment) through the etching treatment are floated in the treating environment and adhered to the surface of the device during or after the working to considerably deteriorate the quality thereof. 
     As one of these countermeasures for these problems, there is a method wherein the surface of the member for semiconductor manufacturing and working apparatus is subjected to a surface treatment with an anode oxide of aluminum (alumite). And also, there is known a technique wherein an oxide such as Al 2 O 3 , Al 2 O 3 .Ti 2 O 3 , Y 2 O 3  or an oxide in Group IIIa metal of the Periodic Table is applied onto a surface of the member by a spraying method or an evaporation method (CVD method, PVD method), or utilized as a sintered body (Patent Documents 1-5). 
     In recent years, there is known a technique wherein the resistance to plasma erosion is improved by irradiating a laser beam or an electron beam onto a surface of Y 2 O 3  or Y 2 O 3 —Al 2 O 3  spray coating to remelt the surface of the spray coating (Patent Documents 6-9). 
     Moreover, in a field of high-performance semiconductor processing, there is a proposal that YF 3  (yttrium fluoride) is used in a coating-formation condition as a means for improving a cleanness of working environment as well as a material for surpassing plasma erosion resistance of Y 2 O 3  spray coating. For example, there are proposed a method of covering a surface of a sintered body of YAG or the like or an oxide in Group IIIa element of the Periodic Table with YF 3  coating (Patent Documents 10˜11), a method wherein a mixture of Y 2 O 3  or Yb 2 O 3  and YF 3  and the like is used as a coating material (Patent Documents 12-13), a method in which YF 3  itself is coated as a coating material by a spraying method (Patent Documents 14-15). 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     
         
         Patent Document 1: JP-A-H06-36583 
         Patent Document 2: JP-A-H09-69554 
         Patent Document 3: JP-A-2001-164354 
         Patent Document 4: JP-A-H11-80925 
         Patent Document 5: JP-A-2007-107100 
         Patent Document 6: JP-A-2005-256093 
         Patent Document 7: JP-A-2005-256098 
         Patent Document 8: JP-A-2006-118053 
         Patent Document 9: JP-A-2007-217779 
         Patent Document 10: JP-A-2002-293630 
         Patent Document 11: JP-A-2002-252209 
         Patent Document 12: JP-A-2008-98660 
         Patent Document 13: JP-A-2005-243988 
         Patent Document 14: JP-A-2004-197181 
         Patent Document 15: JP-A-2002-037683 
         Patent Document 16: JP-A-2007-115973 
         Patent Document 17: JP-A-2007-138288 
         Patent Document 18: JP-A-2007-308794 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     A fluoride spray coating has an excellent halogen resistance but has a drawback that an adhesion with substrate is worse. From an experience of the inventors, since a fluoride spray coating covered to a substrate surface has a less ductility and a small surface energy, there is a phenomenon that a crack is generated and a local peeling-off occurs. However, a countermeasure for eliminating the above drawback is not referred in any of the above Patent Documents. This cause is assumed to be the followings. That is, since fluoride (YF 3 , AlF 3  and the like) is not thought to be adapted to Japanese Industrial Standards (JIS) and International Organization for Standardization (ISO) that are a basis of a spray and working technique, a working standard method for a fluoride spray coating is not defined, and thus a spraying is performed on the basis of the same standard as that of metal (alloy), ceramics and cermet material and the like. 
     In the spray working, a substrate surface is generally subjected to a roughening before the spray working. In the Japanese Industrial Standards (JIS), the following blast roughening treatment methods are defined for each of coating materials. 
     (1) Metal coating: In JIS H8300 “Thermal spraying of zinc, aluminum and alloy thereof—Thermal spray working standard”, oxide is removed from a steel substrate by using blast-furnace slag, steel slag and the like defined by JIS Z0312 for oxide (scale) removal, and then the oxide removed surface is subjected to a roughening treatment by using a cast-iron grid defined by JIS Z0311 or a fused alumina (Al 2 O 3 ) grid defined by JIS Z0312. 
     (2) Ceramic coating: In JIS H9302 “Ceramic thermal spray working standard”, after the blast treatment for removing the oxide is performed, the treated surface is subjected to a roughening treatment by artificial abrasives (Al 2 O 3 , SiC) defined by JIS R6111. 
     (3) Cermet coating: In JIS H8306 “Cermet thermal spraying”, it is defined that a roughening treatment is conducted by using the cast-iron grid manufactured in accordance with JIS G5903 or the artificial abrasives manufactured in accordance with JIS R6111. 
     As mentioned above, in the thermal spraying field, the blast materials used for the blast roughening treatment to the substrate surface and its roughened condition are severely defined for each of the coating materials. Moreover, as for the substrate roughening treatment disclosed in each of the Patent Documents relating to the fluoride spray coating, a treatment condition and an extent of roughening are not disclosed. Even if it is disclosed, only the blast material is disclosed, and it is not a disclosure of a method for improving an adhesion of the fluoride spray coating (Patent Documents 14, 16). In Patent Documents 17, 18, a roughening by corundum (Al 2 O 3 ) is only disclosed. In fact, in these Patent Documents and known documents relating to the fluoride spray coating, there is no disclosure about a roughening treatment as a countermeasure for improving an adhesion of the coating and a formation of an intermediate layer such as an undercoat layer, and also there is no disclosure about a surface roughness. 
     Further, in these Patent Documents, a process for forming the fluoride spray coating directly onto the substrate surface is employed, and there is no ingenuity for an adhesion of the fluoride spray coating, for example, there is no intermediate layer such as the undercoat layer formed prior to a formation of the fluoride spray coating. This is assumed as a cause for frequently generating a peel-off of the coating under an actual use environment. 
     An object of this invention is to provide a fluoride spray coating covered member which a firm adhesion of a fluoride spray coating is performed by interposing carbide cermet on a substrate surface, and its advantageous manufacturing method. 
     Solution for Problems 
     This invention found out that an employ of new spray coating formation techniques from the following viewpoints is advantageous so as to overcome the above problems that the conventional technique has. 
     (1) In order to improve an adhesion property of a fluoride spray coating, a preliminary treatment technique of a substrate surface is important. Particularly, prior to forming a fluoride spray coating onto the substrate surface, it is effective to form an intermediate layer (preliminary treatment) such as an undercoat layer of carbide cermet or a primer part in which carbide cermet particle is stuck as piles and is sparsely scattered on the substrate surface. Since the intermediate layer of carbide cermet formed by this preliminary treatment has a good match with a fluoride (between fluorine and carbon), it is beneficial for increasing adhesion strength of a fluoride spray coating as a topcoat. 
     (2) As one of the above preliminary treatments, an undercoat layer is formed onto the roughened substrate surface after a blast treatment by a high velocity spraying of carbide cermet. In this case, after forming a state such that a part of primary particles blown to the substrate surface is stuck as piles to the substrate surface and is upstanding, a coating-formation is performed by repeating the blowing treatment successively. After that, it is advantageous to form a fluoride spray coating according to a conventional means on the undercoat layer formed in a film-shaped manner. 
     (3) Moreover, as another preliminary treatment, after forming a non-film shaped primer part (adhesion area ratio: about 8-50%) wherein a carbide cermet particle is stuck as piles and is sparsely upstanding to the substrate surface by blowing a carbide cermet material at high velocity (150-600 m/sec.) in addition to a roughening of the substrate surface by a blast treatment, it is advantageous to improve an adhesion property of a fluoride spray coating by forming a fluoride spray coating through a primer part. 
     (4) In this case, prior to a formation of the undercoat layer or the primer part of carbide cermet, it is advantageous to perform a blast roughening treatment using particles such as Al 2 O 3  and SiC to the substrate surface, which is compliant with a ceramic spray coating working standard defined by JIS H9302. 
     (5) Basically, after roughening the substrate surface by a blast treatment, the non-film shaped primer part having a structure that at least a part of the tip portion of carbide cermet spray particles flying at a high velocity is stuck as piles and is sparsely upstanding to the substrate surface, is formed by blowing a carbide cermet material such as WC—Co and WC—Ni—Cr at a high velocity (spraying number: not more than 5 times) by means of a spray gun used in a high-velocity flame spraying method or a low-temperature thermal spraying method. Then, it is preferable to form the film-shaped undercoat layer wherein carbide cermet spray particles are deposited by repeating this state successively (spraying number: not less than 6 times). Then, a fluoride spray coating is formed by a conventional spraying method using a plasma flame or a combustion flame of fossil fuel as a heat source through such an intermediate layer (primer part or undercoat layer). 
     (6) After forming the intermediate layer (primer part and undercoat layer) by spraying successively a carbide cermet material at a high velocity to the substrate surface to which a roughening treatment is performed, it is preferable to preheat the substrate at a temperature of 80° C.-700° C. and then to perform a spraying of a fluoride spray material by means of methods such as atmospheric plasma spraying method, reduced-pressure plasma spraying method and high-velocity flame spraying method. 
     The invention developed according to the above viewpoints is a method for forming a fluoride spray coating characterized in that an undercoat layer of carbide cermet, which covers a substrate in a film-shaped manner while a tip portion of carbide cermet particles is embedded in the substrate, or a non-film shaped primer part of carbide cermet, is formed by spraying a carbide cermet material by using a spray gun for a high velocity spraying to a surface of the substrate to which a roughening treatment is performed, and after that, a fluoride spray coating material is sprayed onto the undercoat layer or the primer part. 
     Moreover, the invention proposes a fluoride spray coating covered member comprising: a substrate, a surface of which is subjected to a roughening treatment; a carbide cermet layer coated to a surface of the substrate; and a fluoride spray coating formed thereon, characterized in that the carbide cermet layer is a film-shaped undercoat layer wherein a part of carbide cermet particles is embedded in the substrate to make a thickness thicker or a primer part of non-film shaped structure having a construction that a tip portion of spray particles is stuck as piles and is sparsely upstanding, by blowing carbide cermet particles having a particle size of 5-80 μm which is made of one or more metal carbides selected from Ti, Zr, Hf, V, Nb, Cr, Mn, W and Si and 5-40 mass % of one or more metals or alloys thereof selected from Co, Ni, Cr, Al and Mo by using the spray gun for a high velocity spraying. 
     In addition, in the invention the following constructions are preferable solution means: 
     (1) The undercoat layer of carbide cermet is a layer with a film-shaped structure having a layer thickness of 10 μm-150 μm, in which, at a side of a substrate surface, a tip portion of a part of the carbide cermet particles is embedded in the substrate and a thickness is made thicker by increasing a spraying number;
 
(2) The primer part of carbide cermet is made by a non-film shaped structure having such a state that a tip portion of spray particles is stuck as piles and is sparsely upstanding, at a portion of area ratio 8-50% with respect to a substrate surface;
 
(3) The undercoat layer and the primer part of carbide cermet are formed in such a manner that a spray treatment, in which particles having a particle size of 5-80 μm which is made of one or more metal carbides selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and Si and 5-40 mass % of one or more metals or its alloys selected from Co, Ni, Cr, Al and Mo are sprayed by using the spray gun for a high velocity spraying at a flying velocity of 150-600 m/sec., is repeated at 6 times or more in case of the undercoat layer and at 5 times or less in case of the primer part;
 
(4) The substrate is preheated to 80-700° C. prior to a spraying of fluoride particles;
 
(5) A spray method of fluoride is any one spray method selected from atmospheric plasma spraying method, reduced-pressure plasma spraying method and high-velocity flame spraying method;
 
(6) Any of Al and its alloy, Ti and its alloy, carbon steel, stainless steel, Ni and its alloy, oxide, nitride, carbide, silicide, carbon sintered body and plastics, a surface roughness of which is controlled to be Ra: 0.05-0.74 μm and Rz: 0.09-2.0 μm by a blast roughening treatment in which abrasives such as Al 2 O 3  and SiC are blown, is used as the substrate;
 
(7) The fluoride spray coating is formed in such a manner that fluoride particles having a particle size of 5 μm-80 μm made of a fluoride of one or more materials selected from a group of: Mg in Group IIa of the Periodic Table; Al in Group IIIb of the Periodic Table; Y in Group IIIa of the Periodic Table; and lanthanide metals of Atomic Numbers 57-71 in the Periodic Table such as La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu are blown to the substrate surface to be a coating thickness of 20 μm-500 μm; and
 
(8) The fluoride spray coating has a thickness of 20-500 μm.
 
     Effect of the Invention 
     According to the invention having the above constructions, the following effects will be expected. 
     (1) If a hard carbide cermet material is blown to a substrate surface at a high velocity, at least a part of primary carbide cermet spray particles is stuck to the substrate surface, and then a thickness becomes gradually thicker by a repetition of sprayings to form an undercoat layer or the primer part. If fluoride particles are sprayed to the thus formed undercoat layer or primer part, the fluoride spray particles adhere onto the undercoat layer of carbide cermet with a high adhesion.
 
(2) Particularly, a fluoride has a weak chemical wettability and less joining property with a metal (aluminum, titanium, cast iron and the like) but has a large chemical affinity with carbide cermet (carbon is an main ingredient). Therefore, a fluoride spray coating having an excellent adhesion can be formed to a surface of the undercoat layer or the primer part having a deposited layer of carbide cermet spray particles as a main ingredient due to a physical function itself or a physical function combined with a chemical affinity function.
 
(3) Since, in the undercoat layer and the primer part of carbide cermet, a part of primary spray particles is first stuck or embedded to the substrate surface and then they become gradually a film-shaped state, a strong compressive residual stress occurs in these substrates, and thus the substrate exhibits a strong resistance to a deformation and a strain. In a member to which the treatment mentioned above is performed, a peeling-off of fluoride spray coating due to mechanical load and vibration of a member covered with a fluoride coating is suppressed during an actual using environment.
 
(4) In addition to the function and effect of the undercoat layer and the primer part of carbide cermet, it is possible to obtain a member having a strong adhesion of respective coatings mutually by forming a fluoride spray coating under a condition that an overall substrate is preheated.
 
(5) Since, in the fluoride spray coating covered member according to the invention, a firm adhesion between the substrate and the fluoride spray coating through carbide cermet can be performed, the fluoride spray coating body exhibits an excellent corrosion resistance (halogen gas resistance) and halogen gas plasma erosion resistance, and it is possible to obtain a member which endures for a long time of use if applied to a semiconductor working member and the like.
 
(6) Since the fluoride spray coating covered member according to the invention has an undercoat layer and a primer part in which a tip portion of spraying particles is embedded in a substrate by strongly spraying a hard carbide cermet particle such as WC—Ni—Cr and Cr 3 C 2 —Ni—Cr into a substrate surface with a high-velocity flame spaying method, it is possible to form a fluoride spray coating having a further strong adhesion on the substrate.
 
     That is, since a fluoride itself has a small surface energy (Al, Ti, Fe and the like) and a weak chemical wettability, a mutual bonding force between fluoride particles or an adhesion between the substrate and the fluoride particle is small, and thus there is a nature that it is sometimes peeled-off. In this point, according to the invention, since a fluoride and a carbide cermet (carbon is a main ingredient) has a strong chemical affinity and a good wettability between them, it is possible to improve a coating adhesion by utilizing their chemical affinity as well as a physical adhesion mechanism of the fluoride spray particles if interposing the undercoat layer and the primer part of carbide cermet. 
     (7) Further, since the undercoat layer of carbide cermet is dense (porosity: 0.1-0.6%) and the primer part of carbide cermet has a structure that a spray particle of carbide cermet is stuck as poles and is sparsely upstanding, there is a function for strongly suppressing a strain and a deformation of the substrate. Therefore, a peeling-off phenomenon of the fluoride spray coating which is liable to occur by a deformation or a vibration of the substrate can be prevented effectively.
 
(8) As explained above, the fluoride spray coating formed by a technique according to the invention can endure a thermal shock due to a repetition of an abrupt temperature variation as well as a physical variation such as a load of micro-vibration and bending stress, and can exhibit an excellent chemical property of primary fluoride spray coating for a long time.
 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flowchart showing a process sequence for carrying out the method according to the invention. 
         FIG. 2  illustrates an initial layer of a substrate surface to which WC-12 mass % Co cermet particles are sprayed sparsely by a high-velocity flame spraying method and a cross sectional SEM image of the same portion: (a) is a view of surface sparsely sprayed with the carbide cermet particles; (b) is an enlarged view of the surface; and (c) is a cross sectional view of a substrate condition prior to forming an undercoat layer sprayed with carbide cermet particles. 
     
    
    
     EMBODIMENTS FOR CARRYING OUT THE INVENTION 
     An embodiment of the invention will be explained below with reference to the accompanying drawings.  FIG. 1  is a flowchart showing process sequence for carrying out the method according to the invention. Hereinafter, the invention will be explained according to this process sequence. 
     (1) Substrate 
     As a substrate usable in the invention is Al and its alloy, Ti and its alloy, various alloy steels including stainless steel, carbon steel, Ni and its alloy and so on. In addition, ceramic sintered materials such as oxide, nitride, carbide and silicide, sintered carbon, and organic polymer materials such as plastics can be used. 
     (2) Pretreatment 
     The surface of the substrate is preferable to be pretreated according to operation standard of ceramic sprayed coatings defined in JIS H9302. For example, after removing rusts and fats on the substrate surface, a blast treatment for roughening is performed concurrently with a descale and the like by blowing abrasive particles such as Al 2 O 3  and SiC. The roughness after the blast roughening treatment is preferable to be about Ra: 0.05-0.74 μm and Rz: 0.09-2.0 μm. 
     (3) Formation of a Film-Shaped Undercoat Layer or a Non-Film Shaped Primer Part of Carbide Cermet 
     a. Film-Shaped Undercoat Layer of Carbide Cermet 
     Carbide cermet material having a particle size of 5-80 μm is sprayed at a high velocity to a roughened substrate surface after a blast process with a spray gun by means of a high-velocity flame spraying method or an inert gas spraying method. Accordingly, an operation, which forms a state such that at least a part of tip portions of spray particles is stuck and is embedded to the substrate surface and also a state such that another part of tip portions adheres and is deposited, is performed at plural times (not less than 6 times). In this manner, an undercoat layer, wherein the carbide cermet is gradually made thicker and adheres in a film-shaped manner, is formed. This undercoat layer is formed in a film-shaped state by spraying the carbide cermet material (particle size: 5 μm-80 μm) at a spraying number of about not less than 6 times and not more than 10 times by means of a spray gun for high velocity spraying with a flying velocity of 150-600 m/sec. and preferably 300-600 m/sec. It should be noted that, if a flying velocity of the spraying particles is less than 150 μm, a bitten depth of the particles into the substrate surface is not sufficient and adhesion strength is decreased. On the other hand, when the flying velocity exceeds 600 m/sec., an effect is saturated in the case of using the carbide cermet particles. Moreover, if the spraying number is not more than 5 times, it is difficult to form a uniform film-shaped spray coating. 
       FIG. 2  shows forms of a substrate surface and a section thereof at an initial state in the formation of the undercoat layer of carbide cermet materials i.e. just after the carbide cermet particles are sprayed at a flying velocity of 550 m/sec. by a high-velocity flame spraying method.  FIG. 2(   b ) shows a state that a part of sprayed WC—Co cermet particles adhere to a substrate surface so as to dig thereinto, while the other WC—Co cermet particles are scattered in the substrate at a partially crushed state by collision energy and attached thereto.  FIG. 2(   c ) shows a cross-sectional state when observing a distribution condition of WC—Co cermet particles sprayed to a surface layer portion of the substrate surface at an initial stage before the coating formation. As seen from this photograph, tip portions of part of WC—Co cermet particles are stuck and buried into the substrate surface at the initial stage while the other part becomes simply adhered or buried state. In this manner, more uniform coating is obtained as the spraying number is increased. 
     That is, when the WC—Co spraying material is sprayed further repeatedly (≧6 times) to the substrate surface adhered with WC—Co cermet spraying particles by a high-velocity flame spraying method, WC—Co particles are gradually deposited even onto a non-adhered parts of the substrate surface (black parts of  FIG. 2(   a )), to form a film-shaped undercoat layer of WC—Co cermet particles applied over the whole surface in due course. On the contrary, in the case of general metallic undercoat of Ni—Cr, Ni—Al, or the like widely used in the formation of an oxide ceramic spray coating, particles buried in the substrate as shown in  FIG. 2  are not observed. 
     In the invention, when the undercoat layer of carbide cermet is formed in the substrate surface, the adhesion between the undercoat and the substrate is enhanced by the behavior of hard carbide cermet, while the improvement of the adhesion of undercoat layer/topcoat (fluoride spray coating) i.e. adhesion of the fluoride spray coating is attained by a synergistic effect of a surface roughness of the undercoat layer and a chemical affinity between carbon and fluoride (top coat). 
     Carbide cermet spraying particles being at a state that the particles existing in a lowermost layer of the undercoat layer are stuck into the substrate surface are firmly bonded to the substrate while a large compression strain is applied to the substrate surface, which not only gives a large resistance to mechanical deformation of the substrate but also improves the adhesion between the substrate and the undercoat layer of carbide cermet itself to improve the adhesion to the fluoride spray coating covered thereon. 
     In the invention, the undercoat layer of carbide cermet adhered and deposited onto the substrate surface at a state of burying a part of the spraying particles is particularly effective for the substrate being soft and susceptive to deformation or strain under a load in a use environment such as Al and its alloy, Ti and its alloy, mild steel, various stainless steels and so on, and guarantees the formation of fluoride spray coating having always a stable and high adhesion regardless of kind of substrate material. 
     That is, a fluoride coating is originally poor in the ductility and small in the surface energy and hardly joins to a metal series substrate, so that the peel-off of the coating is easily caused by the generation of a little deformation or strain of the substrate. However, it is possible to suppress external stress or a strain applied to the fluoride coating by the suppression of the substrate deformability due to the burying of carbide cermet particles into the substrate surface and the formation of the undercoat layer of carbide cermet formed thereon. 
     The thickness of the undercoat layer of carbide cermet formed on the substrate surface is preferable within a range of 30-200 μm, particularly preferable within a range of 80-150 μm. When the thickness of the undercoat layer is less than 30 μm, the coating thickness becomes easily uneven, while when it exceeds 200 μm, an effect as the undercoat layer is saturated and is uneconomic. 
     b. Formation of Non-Film Shaped Primer Part by Carbide Cermet 
     Carbide cermet particles having a particle size of 5-80 μm are sprayed onto the substrate surface which is roughened through blasting at a high velocity by a spray gun for high-velocity spraying used in a high-velocity flame spraying method or an inert gas spraying method, whereby tip portions of at least a part of the sprayed hard carbide cermet particles are independently skewed and stuck as piles into the substrate surface. Moreover, according to this method, a portion (primer part), in which the carbide cermet particles adhering to the substrate surface in a sparse pattern are dotted and adhere, is formed. In this case, if the particle size of the carbide cermet particles is less than 5 μm, the amount supplied to a spray gun becomes uneven and the uniform spraying can not be performed. In addition, the amount of skewed particles becomes small and it is impossible to form effective primer part wherein spray particles are effectively dotted and adhered. On the other hand, if the particle size exceeds 80 μm, the skewing effect becomes weakened. 
     Moreover, as is the same as the undercoat layer, the primer part is a part that the carbide cermet material (particle size 5-80 μm) is sprayed to the substrate surface at an area ratio of 8-50% with a spray gun at a flying velocity of 150-600 m/sec, preferably 300-600 m/sec in the spraying number of not more than 5 times, preferably not more than 3 times to adhere the sprayed particles at a state of sparsely sticking as piles. 
     The primer part, wherein carbide cermet spray particles dispersed sparsely in this treating step is dotted, is not completely film-shaped and forms the following structure. That is, as seen from  FIGS. 2(   a ) and  2 ( b ) showing an appearance state when particles of WC-12 mass % Co carbide cermet material are sprayed to a surface of SUS310 steel substrate, a part of the sprayed WC—Co cermet particles is at a state of adhering to 8-50% portions of the substrate surface so as to dig thereinto. Moreover, the other WC—Co cermet particles are dispersedly adhered to the substrate surface at a state of being partially crushed by collision energy, and further a part of the other is at a state of completely burying in the substrate to form a reinforcing layer of carbide cermet in the surface layer of the spray coating. 
       FIG. 2(   c ) is a view observing a distribution state of the sprayed WC—Co cermet particles existing in the surface layer portion of the substrate at section. As seen from this photograph, WC—Co cermet particles are existent at a state of foresting small piles sparsely stuck in the substrate surface and another part thereof is simply adhered or buried. In the invention, when the fluoride particles are sprayed onto the substrate surface at such a state, i.e. onto the primer part (this part does not form a complete layer) of the carbide cermet particles adhered at such state, the fluoride spray coating having high adhesion will be formed by utilizing a mutual interlocking effect i.e. anchoring effect (JIS H8200 Thermal spraying terms) with hard WC—Co cermet particles stuck as piles (fluoride spray particles) or a skewing phenomenon (fluoride particles are skewed and adhere to a tip portion of hard WC—Co cermet particle stuck as piles). 
     In this invention, as for a construction of the primer part of the carbide cermet, an area ratio (area occupying ratio) of carbide cermet particles is shown by means of an image analyzing device using SEM photograph of  FIG. 2(   a ) or  FIG. 2(   b ) when white parts are carbide cermet particles and black parts are an exposed surface of the substrate. That is, in the primer part, a ratio occupied by the spray particles with respect to the surface area of the substrate i.e. an area ratio is to be controlled within a range of 8-50% preferably. This is because, when it is less than 8%, the wedging effect of carbide cermet particles is weak, while when it exceeds 50%, the action mechanism is the same as in an undercoat layer of carbide cermet mentioned later and the wedging effect of the fluoride particles becomes small. In this invention, a state of the substrate surface in which the carbide cermet particles are sprayed at an area ratio of 8-50% to the substrate surface is called as “primer part”. 
     As the carbide cermet spraying material usable in this invention can be used of WC—Co, WC—Ni—Cr, WC—Co—Cr, Cr 3 C 2 —Ni—Cr and the like. Moreover, a percentage of metal ingredient occupied in this carbide cermet is preferably within a range of 5-40 mass %, particularly preferable within a range of 10-30 mass %. The reason is that if a metal ingredient is less than 5 mass %, the hard carbide is made to a small powder and a ratio remaining on the substrate surface becomes small when spraying to the substrate surface strongly. On the other hand, when the metal ingredient exceeds 40 mass %, the hardness and corrosion resistance are deteriorated and the entangling effect with the fluoride particle is decreased, and the substrate is liable to be corroded by a corrosive gas penetrated from through-holes of the fluoride spray coating and also the bonding force of the fluoride spray coating is vanished to induce the peeling-off. 
     The sprayed carbide cermet material is preferred to have a particle size of 5-80 μm, particularly 10-45 When the particle size is less than 5 μm, the supply to the spray gun becomes discontinuous, and the formation of uniform coating is difficult, and the particles are finely crushed and scattered in the collision with the substrate and hardly retains on the substrate surface. While, when the particle size exceeds 80 μm, an effect is saturated and it is difficult to obtain commercially available products. 
     (4) Preheating of Substrate 
     The substrate after the roughening and the substrate after the formation of the undercoat layer of carbide cermet and a primer part wherein spray particles are dotted are subjected to a preheating prior to the fluoride spraying treatment. The preheating temperature is preferable to be controlled in accordance with the nature of the substrate and is recommended to be the following temperature. Moreover, the preheating may be performed as one of pretreatments. 
     (i) Al, Ti and alloys thereof: 80° C.-250° C.
 
(ii) Iron steel (low alloy steel): 80° C.-250° C.
 
(iii) Stainless steels: 80° C.-250° C.
 
(iv) Ceramic sintered material of oxides, carbides and the like: 120° C.-500° C.
 
(v) Sintered carbon: 200° C.-700° C.
 
     Moreover, the preheating may be conducted in air or under vacuum or in an inert gas, but an atmosphere of oxidizing the substrate material by preheating to produce an oxide film on the surface should be avoided. 
     As a method for forming a fluoride spray coating, atmospheric plasma spraying method, reduced-pressure plasma spraying method, high-velocity flame spraying method and the like are preferably used. 
     (5) Formation of Fluoride Spray Coating (Topcoat) 
     a. Fluoride Spraying Material 
     As a fluoride spraying material used in the invention are included fluorides of Mg in Group Ha of the Periodic Table, Al in Group IIIb of the Periodic Table, Y in Group IIIa of the Periodic Table, and lanthanide metals belonging to Atomic Number 5771 in the Periodic Table. The metal elements of Atomic Number 5771 are 15 sorts of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu). 
     As the fluoride spraying material are used fluoride particles of the above metal adjusted to be a particle size of 5-80 μm. When the spraying material is a fine particles having a particle size of less than 5 μm, there is a drawback that the particles are frequently flied apart without forming the coating in the collision with the substrate surface while when the particle size exceeds 80 μm, the rate supplied to a spraying gun is hardly equalized and the tendency of increasing the pore size of the formed coating becomes remarkable. 
     The spray coating by spraying fluoride spray materials formed on the surface of the substrate or the like after the roughening or after the formation of the undercoat layer or primer part of carbide cermet or further the preheating is sufficient to have a thickness of 20-500 μm, particularly 50-200 μm is preferable. When the coating is thinner than 20 μM, uniform thickness is not obtained, while when the thickness exceeds 500 μm, residual stress in the formation of the fluoride coating becomes large to bring about the decrease of the adhesion force to the substrate and the peeling is liable to be easily caused. 
     b. Characteristics of Fluoride Spray Coating 
     As physicochemical properties of the fluoride itself can be pointed out the followings. That is, the fluoride coating has a chemical stability to a halogen-based gas as compared with a metal coating or a ceramic coating but is weak in the mutual bonding force of fluoride particles constituting the coating and adhesion strength to the substrate because the surface energy is small. Also, since a large residual stress is liable to be generated when forming a coating, a peeling-off of the coating is liable to occur easily and frequently due to a slight deformation of substrate after coating-formation. In addition, since the fluoride is poor in ductility, the coating is “cracked” easily and causes corrosion of the substrate due to internal penetration of an acid or alkali cleaning liquid together with porous portions produced in the above coating formation. Therefore, the fluoride is good in the corrosion resistance but has a problem that the property cannot be utilized as a corrosion resistance coating. 
     In this regard, if the aforementioned of the invention is applied, since the undercoat layer or the primer part of carbide cermet is formed to the substrate surface, adhesion of the coating is further improved, whereby the above problems of the fluoride spray coating can be solved. That is, the effect of preventing the corrosion of the substrate can be seen by the prevention from peeling or cracking of the coating and the prevention from penetration of the cleaning fluid accompanied therewith. 
     Moreover, the fluoride spray coating formed according to the invention can be used as is in a coating-forming state, but is subject to a heat treatment at 250° C.-500° C. after the coating formation, if necessary, whereby the residual stress can be released easily or an amorphous phase can be easily crystallized (orthorhombic crystal phase). In the invention, therefore, the use of these treatments is not particularly limited. The reason why the temperature of the heat treatment is limited to the above range is due to the fact that when it is lower than 250° C., a long time is taken for releasing the residual stress of the coating and the crystallization is also insufficient, while when it exceeds 500° C., there is a possibility for promoting a physicochemical change of the fluoride spray coating. 
     EXAMPLES 
     Example 1 
     In this example, an influence of pretreatment of a substrate surface affected to an adhesion of fluoride spray coating is investigated. 
     (1) Kind of Pretreatment 
     The following pretreatments are performed to one surface of Al3003 alloy (“JIS M 4000”, size: diameter 25 mm×thickness 5 mm) as the substrate. 
     (i) After degreasing, the surface is polished by a wire brush lightly.
 
(ii) After degreasing, a metal undercoat layer of Ni-20 mass % Cr having a thickness of 50 μm is formed by an atmospheric plasma spraying method (flying velocity: 250 m/sec.).
 
(iii) After degreasing, a primer part is formed by blowing WC-12 mass % Co in a sparse pattern (area ratio: 22%) by a high-velocity flame spraying method (flying velocity: 580 m/sec., spraying number: 3 times).
 
(iv) After degreasing, an undercoat layer of carbide cermet of Cr 3 C 2 -18 mass % Ni-7 mass % Cr having a thickness of 30 μm is formed by a high-velocity flame spraying method (flying velocity: 560 m/sec., spraying number: 6 times).
 
(v) After degreasing, a blast roughening treatment is performed to a substrate surface by using Al 2 O 3  abrasive.
 
(vi) After the above blast roughening treatment, a metal undercoat layer made of Ni-20 mass % Cr film having a thickness of 50 μm is further formed by atmospheric plasma spraying method (same as (ii)).
 
(vii) After the above blast roughening treatment, a primer part is further formed by blowing WC-12 mass % Co in a sparse pattern (area ratio: 18%) by a high-velocity flame spraying method (same as (iii)).
 
(viii) After the above blast roughening treatment, an undercoat layer of carbide cermet having a thickness of 30 μm is further formed by blowing Cr 3 C 2 -18 mass % Ni-7 mass % Cr by a high-velocity flame spraying method (same as (iv)).
 
     (2) Formation of Fluoride Spray Coating 
     With respect to the substrate surface after the above pretreatments, YF 3  spray coating having a thickness of 100 μm is formed by an atmospheric plasma spraying method. 
     (3) Test Method of Coating Adhesion 
     An adhesion of a coating is measured by a test method of adhesion strength defined in Test method of ceramic spray coating of JIS H8666. 
     (4) Test Results 
     Test results are shown in Table 1. As is clear from these results, the sample piece (No. 1), in which a fluoride spray coating is formed after degreasing the substrate surface only, seldom indicates adhesion force, and the coating is peeled-off at 0.5-1.2 MPa. Moreover, the coating (No. 2) formed on the metal undercoat layer indicates an adhesion force of about 4-5 MPa. However, since a blast roughening treatment is not performed to the substrate surface, some sample pieces show a peeling-off from a boundary between the metal undercoat layer and the substrate. On the other hand, the sample piece (No. 3), in which the primer part of carbide cermet particle is formed, and the sample piece (No. 4), in which the undercoat layer is formed, exhibit a high adhesion force. Therefore, it is confirmed that, even if a blast roughening treatment is omitted, adhesion force required for an actual use can be obtained. 
     Then, since YF 3  coating (No. 5) formed on the blast roughened substrate surface indicates an adhesion force of 4-6 MPa and has a high bonding force as compared with the coating of No. 1, it is confirmed that a blast roughening treatment is effective for a formation of fluoride spray coating. Moreover, an adhesion of the test pieces (Nos. 7 and 8), wherein a primer part or an undercoat layer is formed by spraying carbide cermet particles to a substrate surface, to which a blast roughening treatment is performed, and then a fluoride spray coating is formed thereon, is further increased. Therefore, it is confirmed that these treatments are suitable for the pretreatment method for forming a fluoride spray coating. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Coating Structure 
                 Adhesion 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 No. 
                 Substrate 
                 Pretreatment 
                 Undercoat 
                 Topcoat 
                 MPa 
                 Remarks 
               
               
                   
               
               
                 1 
                 Al3003 
                 Degreasing 
                 None 
                 YF 3   
                 0.5~1.2 
                 Comparative 
               
               
                 2 
                 (Al 
                 Only 
                 Ni—Cr 
                   
                 4~5 
                 example 
               
               
                   
                 alloy) 
                 (Light wire 
                 (50 μm) 
               
               
                 3 
                   
                 brushing) 
                 WC—12Co 
                   
                 13~16 
                 Invention 
               
               
                   
                   
                   
                 Blowing 
                   
                   
                 example 
               
               
                   
                   
                   
                 (Primer part) 
               
               
                 4 
                   
                   
                 Cr 3 C 2 —Ni•Cr 
                   
                 14~19 
                 Invention 
               
               
                   
                   
                   
                 (Undercoat 
                   
                   
                 example 
               
               
                   
                   
                   
                 layer) 
               
               
                   
                   
                   
                 (30 μm) 
               
               
                 5 
                   
                 Blast treatment 
                 None 
                   
                 4~6 
                 Comparative 
               
               
                 6 
                   
                 after 
                 Ni—Cr 
                   
                 7~8 
                 example 
               
               
                   
                   
                 degreasing 
                 (50 μm) 
               
               
                 7 
                   
                   
                 WC—12Co 
                   
                 13~15 
                 Invention 
               
               
                   
                   
                   
                 Blowing 
                   
                   
                 example 
               
               
                   
                   
                   
                 (Primer part) 
               
               
                 8 
                   
                   
                 Cr 3 C 2 —Ni•Cr 
                   
                 14~18 
                 Invention 
               
               
                   
                   
                   
                 (Undercoat 
                   
                   
                 example 
               
               
                   
                   
                   
                 layer) 
               
               
                   
                   
                   
                 (30 μm) 
               
               
                   
               
               
                 (Remarks) 
               
               
                 (1) The coating to be tested is formed by an atmospheric plasma spraying method and has a thickness of 100 μm. 
               
               
                 (2) Three samples are tested per one condition and an adhesion force of coating is indicated by maximum value to minimum value. 
               
               
                 (3) The adhesion strength of the coating is measured by a test method defined at JIS H8666 Test method of ceramic sprayed coating. 
               
            
           
         
       
     
     Example 2 
     In this example, an adhesion of the spray coating is examined when YF 3  spray coating having a thickness of 100 μm is formed to SS400 steel substrate by a reduced-pressure plasma spraying method. 
     (1) Kind of Pretreatment (Roughening, Formation of Intermediate Layer) 
     Pretreatments, that are the same kinds as those of Example 1, are performed. 
     (2) Formation of Fluoride Spray Coating 
     A fluoride spray coating having a thickness of 100 μm is formed by a plasma spraying method (a reduced-pressure plasma spraying method) using YF 3  under reduced pressure environment of Ar gas at 100-200 hPa. 
     (3) Test Method of Coating Adhesion 
     The same test method as that of Example 1 is performed. 
     (4) Test Results 
     Test results are shown in Table 2. As seen from the results, an adhesion of the coating after blast treatment is higher as compared with the case (No. 1) in which YF 3  spray coating is directly formed to the substrate surface, and it is confirmed that an excellent adhesion can be obtained as compared with Al alloy substrate of Example 1. However, even if SS400 steel substrate is used, the cases (Nos. 3 and 7) wherein the primer part is formed by spraying carbide cermet particles and the cases (Nos. 4 and 8) wherein the undercoat layer is formed exhibit further higher adhesion. That is, it is confirmed that the pretreatment method in which the undercoat layer and the primer part are formed by carbide cermet can always form the coating having a high adhesion regardless of effects of substrate kinds. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Coating Structure 
                 Adhesion 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 No. 
                 Substrate 
                 Pretreatment 
                 Undercoat 
                 Topcoat 
                 MPa 
                 Remarks 
               
               
                   
               
               
                 1 
                 SS400 
                 Degreasing 
                 None 
                 CeF 3   
                 0.7~1.3 
                 Comparative 
               
               
                 2 
                 steel 
                 Only 
                 Ni—Cr 
                   
                 4~5 
                 example 
               
               
                   
                   
                 (Light wire 
                 (50 μm) 
               
               
                 3 
                   
                 brushing) 
                 WC—12Co 
                   
                 15~18 
                 Invention 
               
               
                   
                   
                   
                 Blowing 
                   
                   
                 example 
               
               
                   
                   
                   
                 (Primer part) 
               
               
                 4 
                   
                   
                 Cr 3 C 2 —Ni•Cr 
                   
                 16~19 
                 Invention 
               
               
                   
                   
                   
                 (Undercoat 
                   
                   
                 example 
               
               
                   
                   
                   
                 layer) 
               
               
                   
                   
                   
                 (30 μm) 
               
               
                 5 
                   
                 Blast treatment 
                 None 
                   
                 5~8 
                 Comparative 
               
               
                 6 
                   
                 after 
                 Ni—Cr 
                   
                 10~12 
                 example 
               
               
                   
                   
                 degreasing 
                 (50 μm) 
               
               
                 7 
                   
                   
                 WC—12Co 
                   
                 15~18 
                 Invention 
               
               
                   
                   
                   
                 Blowing 
                   
                   
                 example 
               
               
                   
                   
                   
                 (Primer part) 
               
               
                 8 
                   
                   
                 Cr 3 C 2 —Ni•Cr 
                   
                 17~20 
                 Invention 
               
               
                   
                   
                   
                 (Undercoat 
                   
                   
                 example 
               
               
                   
                   
                   
                 layer) 
               
               
                   
                   
                   
                 (30 μm) 
               
               
                   
               
               
                 (Remarks) 
               
               
                 (1) The coating to be tested is formed by a reduced-pressure plasma spraying method and has a thickness of 100 μm. 
               
               
                 (2) Three sample pieces are tested per one condition and an adhesion of coating is indicated by maximum value to minimum value. 
               
               
                 (3) The adhesion strength of the coating is measured by a test method defined at JIS H8666 Test methods for ceramic sprayed coatings. 
               
            
           
         
       
     
     Example 3 
     In this example, an adhesion of YF 3  spray coating formed to SS400 steel substrate by a high-velocity flame spraying method is examined. 
     (1) Kind of Pretreatment (Roughening, Formation of Intermediate Layer) 
     Pretreatments, that are the same as those of Example 1, are performed. 
     (2) Formation of Fluoride Spray Coating 
     A fluoride spray coating having a thickness of 100 μm is formed by a high-velocity flame spraying method using YF 3 . 
     (3) Test Method of Coating Adhesion 
     The same test method as that of Example 1 is performed. 
     (4) Test Results 
     Test results are shown in Table 3. As seen from the results of this table, as is the same results as those of Examples 1 and 2, in the cases (Nos. 3, 4, 7, 8) wherein the undercoat layer and the primer part of carbide cermet are formed according to the invention, it is confirmed that it is always possible to form a fluoride spray coating having a high adhesion regardless of presence or absence of a blast roughening treatment of the substrate. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 Coating structure 
                 Adhesion 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 No. 
                 Substrate 
                 pretreatment 
                 Undercoat 
                 Topcoat 
                 MPa 
                 Remarks 
               
               
                   
               
               
                 1 
                 SS400 
                 Degreasing 
                 None 
                 YF 3   
                 0.6~1.3 
                 Comparative 
               
               
                 2 
                 steel 
                 Only 
                 Ni—Cr 
                   
                 3~4 
                 example 
               
               
                   
                   
                 (Light wire 
                 (50 μm) 
               
               
                 3 
                   
                 brushing) 
                 WC—12Co 
                   
                 10~12 
                 Invention 
               
               
                   
                   
                   
                 Blowing 
                   
                   
                 example 
               
               
                   
                   
                   
                 (Primer part) 
               
               
                 4 
                   
                   
                 Cr 3 C 2 —Ni•Cr 
                   
                 12~13 
                 Invention 
               
               
                   
                   
                   
                 (Undercoat 
                   
                   
                 example 
               
               
                   
                   
                   
                 layer) 
               
               
                   
                   
                   
                 (30 μm) 
               
               
                 5 
                   
                 Blast treatment 
                 None 
                   
                 2~4 
                 Comparative 
               
               
                 6 
                   
                 after 
                 Ni—Cr 
                   
                 4~5 
                 example 
               
               
                   
                   
                 degreasing 
                 (50 μm) 
               
               
                 7 
                   
                   
                 WC—12Co 
                   
                 11~14 
                 Invention 
               
               
                   
                   
                   
                 Blowing 
                   
                   
                 example 
               
               
                   
                   
                   
                 (Primer part) 
               
               
                 8 
                   
                   
                 Cr 3 C 2 —Ni•Cr 
                   
                 14~16 
                 Invention 
               
               
                   
                   
                   
                 (Undercoat 
                   
                   
                 example 
               
               
                   
                   
                   
                 layer) 
               
               
                   
                   
                   
                 (30 μm) 
               
               
                   
               
               
                 (Remarks) 
               
               
                 (1) The coating to be tested is formed by a high-velocity flame spraying method and has a thickness of 100 μm. 
               
               
                 (2) Three sample pieces are tested per one condition and an adhesion of coating is indicated by maximum value to minimum value. 
               
               
                 (3) The adhesion strength of the coating is measured by a test method defined at JIS H8666 Test methods of ceramic spray coatings. 
               
            
           
         
       
     
     Example 4 
     In this example, SUS304 steel is used as a substrate, and an adhesion of three kinds of fluoride spray coatings formed by an atmospheric plasma spraying method is examined. 
     (1) Kind of Pretreatment 
     After a substrate is subjected to a blast roughening treatment by SiC abrasives, WC-12 mass % Co-5 mass % Cr or Cr 3 C 2 -17 mass % Ni-7 mass % Cr is brown onto the roughened surface at a high-velocity as is the same conditions of Example 1 so as to obtain a blowing thickness of 80 μm. 
     (2) Formation of Fluoride Spray Coating 
     A fluoride spray coating having a thickness of 120 μm is formed by an atmospheric plasma spraying method using CeF 3 , DyF 3  and EuF 3 . 
     (3) Test Method of Coating Adhesion 
     The same test method as that of Example 1 is performed. 
     (4) Test Results 
     Test results are shown in Table 4. As seen from the results of this table, it is confirmed that the coating to which the undercoat layer of carbide cermet is formed has an effect for improving an adhesion to the fluoride spray coating such as CeF 3 , DyF 3  and EuF 3 . 
     
       
         
           
               
               
             
               
                   
                 TABLE 4 
               
             
            
               
                   
                   
               
               
                   
                 Adhesion according 
               
               
                   
                 to pretreatment kind 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 Blast 
                   
                 WC—12Co 
                 Cr 3 C 2 —Ni•Cr 
               
               
                   
                   
                 Coating 
                 roughening 
                   
                 (Primer 
                 (Undercoat 
               
               
                 No. 
                 Substrate 
                 material 
                 treatment 
                 None 
                 part) 
                 layer) 
               
               
                   
               
               
                 1 
                 SUS304 
                 CeF 3   
                 perform 
                 4~7 
                 11~12 
                 11~14 
               
               
                 2 
                 steel 
                 DyF 3   
                   
                 5~8 
                 10~14 
                 12~15 
               
               
                 3 
                   
                 EuF 3   
                   
                 4~6 
                 11~13 
                 12~14 
               
               
                   
               
               
                 (Remarks) 
               
               
                 (1) The coating to be tested is formed by an atmospheric plasma spraying method and has a thickness of 120 μm. 
               
               
                 (2) Three sample pieces are tested per one condition and an adhesion of coating is indicated by maximum value to minimum value. 
               
               
                 (3) The adhesion strength of the coating is measured by a method defined at JIS H8666 Test methods of ceramic spraying coatings. 
               
            
           
         
       
     
     Example 5 
     In this example, a primer part of carbide cermet and a fluoride spray coating thereon are formed to a surface of Al alloy substrate (size: width 30 mm×longitudinal 50 mm×thickness 3 mm) by the method adapted to the invention to evaluate a resistance to plasma etching of the spray coating. 
     (1) Substrate: A fluoride spray coating is prepared by: subjecting a surface of Al alloy (A3003 defined by JIS H4000) to a blast roughening treatment; performing a pretreatment for forming a primer part having a sparse pattern (area ratio of 12%) by blowing carbide cermet materials (spraying number: 2 times) at a high velocity (550 m/sec.) according to the invention; and preheating at a temperature of 180° C. 
     (2) Fluoride for coating-formation: YF 3 , DyF 3  and CeF 3  (particle size 5-45 μm) are sprayed to form a coating having a coating thickness of 180 μm by an atmospheric plasma spraying method. Moreover, as a coating of a comparative example, oxide coatings having a thickness of 180 μm respectively, which are formed by the atmospheric plasma spraying method of Y 2 O 3 , Dy 2 O 3  and CeO 2 , are tested. 
     (3) Gas Composition of Plasma Etching Atmosphere and Plasma Output 
     (i) Conditions of atmospheric gas and flow rate
 
(a) F-containing gas: CHF 3 /O 2 /Ar=80/100/160 (flow rate per 1 minute cm 3 )
 
(b) CH-containing gas: C 2 H 2 /Ar=80/100 (flow rate per 1 minute cm 3 )
 
(ii) Plasma irradiation output
 
High-frequency power: 1300 W
 
     Pressure: 4 Pa 
     Temperature: 60° C. 
     (iii) Atmosphere of plasma etching test
 
(a) Performed in a F-containing gas atmosphere
 
(b) Performed in a CH-containing gas atmosphere
 
(c) Performed in an alternately repeated atmosphere of F-containing gas atmosphere for 1 hour CH-containing gas atmosphere for 1 hour
 
     (4) Evaluation Method 
     In an evaluation of the test of plasma erosion resistance, the plasma erosion resistance and environmental pollution resistance are investigated by measuring the number of particles of coating ingredients flied from the coating to be tested by etching treatment. The number of particles is evaluated by measuring time duration until the number of particles having a particle size of not less than 0.2 μm adhered to a surface of silicon wafer having a diameter of 8 inch disposed in a test container reached to 30. 
     (5) Test Results 
     Test results are shown in Table 5. As seen from the results, the oxide based spray coatings (No. 1, 3, 5) of the comparative examples indicate such a situation that the generation of particles is smallest in the CH-containing gas and becomes somewhat large in the F-containing gas, and the time reaching to an acceptable value becomes short. However, it is proved that the number of particles generated becomes further large in the alternately repeated atmosphere of the F-containing gas and the CH-containing gas and the time reaching to an acceptable value becomes very short. This cause is considered due to the fact that the oxide film in the surface of the oxide ceramic coating becomes always unstable and is scattered by a repetition of oxidation function of fluoride gas in the F-containing gas and a reduction function of CH gas. On the other hand, it is considered that the fluoride spray coatings of No. 2, 4 and 6 are maintained in a chemically stable state even in the F-containing gas, in the CH-containing gas and the alternately repeated atmosphere of these gasses, which is considered to suppress the generation of particles. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 5 
               
             
            
               
                   
                   
               
               
                   
                 Time until particle generation amount 
                   
               
               
                   
                 exceeds acceptable value 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Mutual 
                   
               
               
                   
                   
                   
                   
                 repetition of 
               
               
                   
                 Coating 
                 F  
                 CH 
                 gas containing 
                   
               
               
                   
                 to 
                 containing 
                 containing 
                 F and gas 
               
               
                 No. 
                 be tested 
                 gas 
                 gas 
                 containing CH 
                 Remarks 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1 
                 Y 2 O 3   
                 70 
                 120 
                 35 
                 Comparative 
               
               
                   
                   
                   
                   
                   
                 example 
               
               
                 2 
                 YF 3   
                 108 
                 220 
                 82 
                 Invention 
               
               
                   
                   
                   
                   
                   
                 example 
               
               
                 3 
                 Dy 2 O 3   
                 70 
                 120 
                 30 
                 Comparative 
               
               
                   
                   
                   
                   
                   
                 example 
               
               
                 4 
                 DyF 3   
                 98 
                 210 
                 77 
                 Invention 
               
               
                   
                   
                   
                   
                   
                 example 
               
               
                 5 
                 CeO 2   
                 80 
                 78 
                 30 
                 Comparative 
               
               
                   
                   
                   
                   
                   
                 example 
               
               
                 6 
                 CeF 2   
                 101 
                 240 
                 78 
                 Invention 
               
               
                   
                   
                   
                   
                   
                 example 
               
               
                   
               
               
                 (Remarks) 
               
               
                 (1) Coating thickness of the coating to be tested is 180 μm. 
               
               
                 (2) Surface roughness of substrate after blast roughening treatment: Ra 0.4-0.5 μm, Rz 0.7-1.0 μm. 
               
               
                 (3) Formation of coating is performed by an atmospheric plasma spraying method. 
               
            
           
         
       
     
     Example 6 
     In this example is examined a corrosion resistance to a vapor of a halogen based acid in a fluoride spray coating formed on a substrate surface by a method adapted to the invention. 
     (1) Substrate: A substrate of SS400 steel (size: width 30 mm×longitudinal 50 mm×thickness 3.2 mm) is used, and a coating-formation is performed by: subjecting a substrate surface to a blast roughening treatment; forming a primer part having a sparse pattern (area ratio of 28%) of carbide cermet particles on the substrate surface by blowing carbide cermet particles of Cr 2 C 3 -18 mass % Ni-8 mass % Cr at a high velocity by a high-velocity flame spraying method (560 m/sec., spraying number: 3 times); and preheating the substrate to a temperature of 200° C. 
     (2) Fluoride for coating-formation: MgF 2 , YF 3  (particle size: 10-60 μm) are used, and a sample having a fluoride coating with a coating thickness of 250 μm is prepared by a reduced-pressure plasma spraying method. Moreover, as a coating of a comparative example, coatings having a thickness of 250 μm respectively formed by a reduced-pressure plasma spraying method of MgO, Y 2 O 3 , are tested under the same conditions. 
     (3) Corrosion Test 
     (a) A corrosion test by HCl vapor is adopted a method wherein 100 ml of an aqueous solution of 30% HCl is placed in a bottom portion of desiccator for chemical experiment and a sample is suspended in a top portion thereof and exposed to HCl vapor generated from the aqueous HCl solution. A temperature of the corrosion test is 30° C.-50° C., and a time thereof is 96 hours.
 
(b) A corrosion test by HF vapor is conducted by placing 100 ml of HF aqueous solution in a bottom portion of autoclave made of SUS316 and suspending a sample in a top portion thereof. A temperature of the corrosion test is 30° C.-50° C., and an exposing time thereof is 96 hours.
 
     (4) Test Results 
     Test results are shown in Table 6. As seen from the results, a large amount of red rust reached to the surface of the coatings in the oxide based coating of the comparative examples (No. 2, 4). That is, it is considered that, since many through-holes are existent in the oxide coating, a vapor of HCl, HF and the like reaches to an interior of the coating via the through-holes to corrode the SS400 steel substrate, and an iron component as a corroded product reaches to the coating surface via the through-holes to present red rust state. On the other hand, in the fluoride coatings (No. 1, 3) formed according to the invention, a generation of red rust is recognized, but its extent remained to about 30-40% of the comparative example. From the results, it is found that there are through-holes in the fluoride spray coating but they are little as compared with those of the oxide spray coating, and further since the fluoride coating itself has an excellent corrosion resistance, the good corrosion resistance is developed to vapors of comprehensive halogen based acids. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 6 
               
             
            
               
                   
                   
               
               
                   
                 Corrosion 
                   
               
               
                   
                 test results 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 Coating 
                 HCl 
                   
                   
               
               
                 No. 
                 Substrate 
                 material 
                 vapor 
                 HF vapor 
                 Remarks 
               
               
                   
               
               
                 1 
                 SS400 
                 MgF 2   
                 Δ 
                 Δ 
                 Invention example 
               
               
                 2 
                 steel 
                 MgO 
                 x 
                 x 
                 Comparative example 
               
               
                 3 
                   
                 YF 3   
                 Δ 
                 Δ 
                 Invention example 
               
               
                 4 
                   
                 Y 2 O 3   
                 x 
                 x 
                 Comparative example 
               
               
                   
               
               
                 (Remarks) 
               
               
                 (1) The coating to be tested is formed to be a thickness of 250 μm by a reduced-pressure plasma spraying method. 
               
               
                 (2) An area ratio of a sparse pattern by means of Cr 3 C 2 —Ni—Cr carbide particles is 28%. 
               
               
                 (3) Symbols of corrosion test results: x: large generation of red rust Δ: small generation of red rust. 
               
            
           
         
       
     
     INDUSTRIAL APPLICABILITY 
     The technique according to the invention can be applied to a surface treatment of members for precise working apparatus for semiconductors requiring a high resistance to halogen corrosion and plasma erosion. For example, they can be utilized as a corrosion resistant coating such as deposit shield, baffle plate, focus ring, insulator ring, shield ring, bellows cover, electrode and the like disposed in a plasma treating apparatus with a treating gas including halogen and a compound thereof as well as members for chemical plant apparatus in similar gas atmosphere. 
     Moreover, a technique for forming an undercoat layer of carbide cermet to a substrate according to the invention can be applied to a technique for processing a topcoat for metal (alloy) coating, oxide ceramics, plastics and the like.