Powder for coating an etch chamber

Abstract

A powder of melted particles, more than 95% by number of the particles exhibiting a circularity of greater than or equal to 0.85. The powder including more than 99.8% of a rare earth metal oxide and/or of hafnium oxide and/or of an aluminum oxide, as percentage by mass based on the oxides. The powder has a median particle size D.sub.50 of less than 15 μm, a 90 percentile of the particle sizes, D.sub.90, of less than 30 μm, and a size dispersion index (D.sub.90−D.sub.10)/D.sub.10 of less than 2, and a relative density of greater than 90%. The D.sub.n percentiles of the powder are the particle sizes corresponding to the percentages, by number, of n %, on the cumulative distribution curve of the size of the particles in the powder and the particle sizes are classified by increasing order.

Claims

1. A powder of melted particles, more than 95% by number of said particles exhibiting a circularity of greater than or equal to 0.85, said powder comprising more than 99.8% of a rare earth metal oxide and/or of hafnium oxide and/or of an aluminum oxide, as percentage by mass based on the oxides, and having: a median particle size D.sub.50 of less than 15 μm, a 90 percentile of the particle sizes, D.sub.90, of less than 30 μm, and a size dispersion index (D.sub.90−D.sub.10)/D.sub.10 of less than 2; a relative density of greater than 90%, the D.sub.n percentiles of the powder being the particle sizes corresponding to the percentages, by number, of n %, on the cumulative distribution curve of the size of the particles in the powder, the particle sizes being classified by increasing order.

2. The powder as claimed in claim 1, exhibiting a percentage by number of particles having a size of less than or equal to 5 μm which is greater than 5%, and/or a median particle size D.sub.50 of less than 10 μm, and/or a 90 percentile of the particle sizes, D.sub.90, of less than 25 μm, and/or a 99.5 percentile of the particle sizes, D.sub.99.5, of less than 40 μm, and/or a size dispersion index (D.sub.90−D.sub.10)/D.sub.10 of less than 1.5.

3. The powder as claimed in claim 1, in which the median size of the particles, D.sub.50, is less than 8 μm.

4. The powder as claimed in claim 1, comprising, as percentage by mass based on the oxides, more than 99.8% of Yb.sub.2O.sub.3 and/or Y.sub.2O.sub.3 and/or Y.sub.3Al.sub.5O.sub.12 and/or of an yttrium oxyfluoride.

5. A process for manufacturing a powder as claimed in claim 1, said process comprising the following steps: a) granulating a particulate charge so as to obtain a granule powder having a median size D′.sub.50 of between 20 and 60 microns, the particulate charge comprising more than 99.8% of a rare earth metal oxide and/or of hafnium oxide and/or of an aluminum oxide, as percentage by mass based on the oxides; b) injecting said granule powder, via a carrier gas, through at least one injection orifice to a plasma jet generated by a plasma gun, under injection conditions which give rise to the bursting of more than 50% of the granules injected, as percentage by number, so as to obtain molten droplets, the flow rate of the granule powder injected being less than 2 g/min per KW of plasma gun power, and the ratio of the quantity by mass of granules injected via said injection orifice, preferably by each injection orifice, to the surface area of said injection orifice being greater than 16 g/min per mm.sup.2 of surface area of said injection orifice; c) cooling said molten droplets, so as to obtain a feed powder as claimed in any one of the preceding claims; d) optionally, performing particle size selection on said feed powder.

6. The process as claimed in claim 5, in which the injection conditions are determined such as to bring about the bursting of more than 70% of the granules injected, as percentage by number.

7. The process as claimed in claim 6, in which the injection conditions are determined such as to bring about the bursting of more than 90% of the granules injected, as percentage by number.

8. The process for manufacturing a powder as claimed in claim 5, in which, in step b), the injection conditions are adapted to bring about a degree of granule bursting identical to a plasma gun having a power of 40 to 65 KW and generating a plasma jet in which the quantity by mass of granules injected via each injection orifice, in g/min per mm.sup.2 of the surface area of said injection orifice, is greater than 10 g/min per mm.sup.2.

9. The process as claimed in claim 8, in which the quantity by mass of granules injected via each injection orifice, in g/min per mm.sup.2 of the surface area of said injection orifice, is greater than 15 g/min per mm.sup.2.

10. The process for manufacturing a powder as claimed in claim 5, in which said injection orifice defines an injection channel having a length at least one time greater than the equivalent diameter of said injection orifice.

11. The process as claimed in claim 10, in which said length is at least two times greater than said equivalent diameter.

12. The process for manufacturing a powder as claimed in claim 5, in which, in step b), the flow rate of granule powder is less than 3 g/min per kW of plasma gun power.

13. The process as claimed in claim 5, in which the granulation comprises an atomization.

14. A thermal spraying process comprising a step of thermal spraying of a powder as claimed in claim 1.

15. The powder as claimed in claim 1, comprising, as percentage by mass based on the oxides, more than 99.8% of Yb.sub.2O.sub.3 and/or Y.sub.2O.sub.3 and/or Y.sub.3Al.sub.5O.sub.12 and/or of an yttrium oxyfluoride of the formula Y.sub.aO.sub.bF.sub.c in which a is 1, b is between 0.7 and 1.1, and c is between 1 and 1.5.

16. The powder as claimed in claim 1, comprising, as percentage by mass based on the oxides, more than 99.8% of Yb.sub.2O.sub.3 and/or Y.sub.2O.sub.3 and/or Y.sub.3Al.sub.5O.sub.12 and/or of an oxyfluoride selected from YOF and Y.sub.5O.sub.4F.sub.7 or a mixture of these oxyfluorides.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Other features and advantages of the invention will emerge more clearly from the reading of the description which is to follow and the examination of the appended drawings, in which:

(2) FIG. 1 represents schematically step a) of a process according to the invention;

(3) FIG. 2 represents schematically a plasma torch for manufacturing a feed powder according to the invention;

(4) FIG. 3 represents schematically a process for manufacturing a feed powder according to the invention;

(5) FIG. 4 illustrates the technique used to evaluate the circularity of a particle.

DETAILED DESCRIPTION

(6) Process for Manufacturing a Feed Powder

(7) FIG. 1 illustrates one embodiment of step a) of a process for manufacturing a feed powder according to the invention.

(8) Any known granulation process may be used. More particularly, the skilled person knows how to prepare a slip suitable for granulation.

(9) In one embodiment, a binder mixture is prepared by adding PVA (polyvinyl alcohol) 2 to deionized water 4. This binder mixture 6 is then filtered through a 5 μm filter 8. A particulate charge consisting of powdered yttrium oxide 10 (with a purity, for example, of 99.99%) having a medium size of 1 μm is mixed into the filtered binder mixture to form a slip 12. The slip may comprise by mass, for example, 55% of yttrium oxide and 0.55% of PVA, the balance to 100% being made up of water. This slip is injected into an atomizer 14 to give a granular powder 16. The skilled person knows how to adapt the atomizer to obtain the desired particle size distribution.

(10) The granules are preferably agglomerates of particles of an oxide material exhibiting a medium size of preferably less than 3 μm, preferably less than 2 μm, preferably less than 1.5 μm.

(11) Preferably, to manufacture a feed powder in which the particles comprise a mixed oxide or oxyfluoride phase, for example yttrium or ytterbium oxyfluoride, or a YAG or YAP phase, granules are used which preferably already comprise this phase, these being, respectively, granules formed of grains of yttrium or ytterbium oxyfluoride, YAG or YAP.

(12) The granule powder may be sieved (5 mm sieve 18, for example) to remove the possible presence of residues which have fallen from the walls of the atomizer

(13) The resulting powder 20 is a “spray-dried only (SDO)” granule powder.

(14) FIGS. 2 and 3 illustrate one embodiment of the melting step b) of a process for manufacturing a feed powder according to the invention.

(15) An SDO granule powder 20, for example, as manufactured by the process illustrated in FIG. 1, is injected by an injector 21 into a plasma jet 22 produced by a plasma gun 24, for example, of a ProPlasma HP plasma torch. Conventional injection and plasma spraying devices may be used, such as to mix the SDO granule powder with a carrier gas and to inject the resulting mixture into the heart of the hot plasma.

(16) However, the granule powder injected need not be consolidated (SDO), and injection into the plasma jet must be done vigorously, to promote granule breaking. The force of the impacts determines the intensity of bursting of the granules, and hence the median size of the powder manufactured.

(17) The skilled person knows how to adapt the injection parameters for vigorous injection of the granules such that the feed powder obtained at the end of steps c) or d) has a particle size distribution according to the invention.

(18) More particularly, the skilled person is aware that: an approximation to 90° of the angle of injection θ between the axis of injection of the granules Y and the axis X of the plasma jet, an increase in the flow rate of powder per mm.sup.2 of surface area of the injection orifice, a reduction in the flow rate of powder, in g/min, per kW of power of the gun, and an increase in the flow rate of the plasma-forming gas

(19) are factors which promote the breaking of the granules.

(20) More particularly, WO2014/083544 does not disclose injection parameters enabling the breaking of more than 50% by number of granules, as described in the examples below.

(21) It is preferable for the particles to be injected rapidly so as to disperse them in a very viscous plasma jet which flows at a very high speed.

(22) When the granules injected come into contact with the plasma jet, they are subjected to forceful impacts, which may break them into pieces. In order to penetrate the plasma jet, the unconsolidated, and more particularly unsintered, granules to be dispersed are injected with a sufficiently high speed to benefit from a high kinetic energy, this speed, however, being limited so as to ensure highly effective bursting. The absence of consolidation of the granules reduces their mechanical strength and therefore their resistance to these impacts.

(23) The skilled person is aware that the speed of granules is determined by the flow rate of the carrier gas and the diameter of the injection orifice.

(24) The speed of the plasma jet is also high. The flow rate of plasma-forming gas is preferably greater than the median value recommended by the constructor of the torch for the anode diameter selected. Preferably, the flow rate of plasma-forming gas is greater than 50 l/min, preferably greater than 55 l/min.

(25) The skilled person is aware that the speed of the plasma jet may be increased using a small-diameter anode and/or by raising the flow rate of the primary gas.

(26) Preferably, the flow rate of the primary gas is greater than 40 l/min, preferably greater than 45 l/min.

(27) Preferably, the ratio between the flow rate of secondary gas, preferably dihydrogen (H.sub.2), and the flow rate of plasma-forming gas (composed of the primary and secondary gases) is between 20% and 25%.

(28) Of course, the energy of the plasma jet, influenced particularly by the flow rate of the secondary gas, must be sufficiently high to cause the granules to melt.

(29) The granule powder is injected with a carrier gas, preferably without any liquid.

(30) In the plasma jet 22, the granules are melted to droplets 25. The plasma gun is preferably regulated so that the melting is substantially complete.

(31) An advantageous effect of the melting is to reduce the level of impurities.

(32) On their exit from the hot zone of the plasma jet, the droplets are rapidly cooled by the surrounding cold air, but also by forced circulation 26 of a cooling gas, preferably air. The air advantageously limits the reducing effect of the hydrogen.

(33) The plasma torch preferably comprises at least one nozzle arranged so as to inject a cooling fluid, preferably air, so as to cool the droplets resulting from the heating of the granule powder injected into the plasma jet. The cooling fluid is preferably injected to downstream of the plasma jet (as represented in FIG. 2), and the angle γ between the path of said droplets and the path of the cooling fluid is preferably less than or equal to 80°, preferably less than or equal to 60° and/or greater than or equal to 10°, preferably greater than or equal to 20°, preferably greater than or equal to 30°. Preferably, the axis of injection Y of any nozzle and the axis X of the plasma jet are secant.

(34) Preferably, the angle of injection θ between the axis of injection Y and the axis X of the plasma jet is greater than 85°, and preferably is approximately 90°.

(35) Preferably, the forced cooling is generated by an assembly of nozzles 28 positioned around the axis X of the plasma jet 22, such as to create a substantially conical or annular flow of cooling gas.

(36) The plasma gun 24 is oriented vertically toward the ground. Preferably, the angle α between the vertical and the axis X of the plasma jet is less than 30°, less than 20°, less than 10°, preferably less than 5°, preferably substantially zero. Advantageously, the flow of cooling gas is therefore perfectly centered with respect to the axis X of the plasma jet.

(37) Preferably, the minimum distance d between the outer surface of the anode and the cooling zone (where the droplets come into contact with the injected cooling fluid) is between 50 mm and 400 mm, preferably between 100 mm and 300 mm.

(38) Advantageously, the forced cooling limits the generation of secondaries, resulting from the contact between very large, hot particles and small particles in suspension in the densification chamber 32. Moreover, a cooling operation of this kind enables a reduction in the overall size of the treatment equipment, more particularly the size of the collecting chamber.

(39) The cooling of the droplets 25 makes it possible to obtain feed particles 30, which can be extracted in the lower part of the densification chamber 32.

(40) The densification chamber may be connected to a cyclone 34, the exhaust gases from which are directed to a dust collector 36, so as to separate off very fine particles 40. Depending on configuration, some feed particles in accordance with the invention may also be collected in the cyclone. Preferably, these feed particles can be separated off, more particularly with an air separator.

(41) The collected feed particles 38 may when appropriate be filtered, so that the median size D.sub.50 is less than 15 microns.

(42) Table 1 below provides the preferred parameters for manufacturing a feed powder according to the invention.

(43) The features of a column are preferably, but not necessarily, combined. The features of the two columns may also be combined.

(44) The “ProPlasmaHP” plasma torch is sold by Saint-Gobain Coating Solutions. This torch corresponds to the torch T1 described in WO2010/103497.

(45) TABLE-US-00001 TABLE 1 Preferred features Even more preferred features Step b) Gun High-performance gun ProPlasma HP gun with low wear (for treating the powder without contaminating it) Anode Diameter > 7 mm HP8 anode (diameter of 8 mm) Cathode Doped tungsten cathode ProPlasma cathode Gas injector Partially radial injection ProPlasma HP setup (swirling gas injection) Current 500-700 A 650 A Power >40 kW >50 kW, preferably approximately 54 kW Nature of primary gas Ar or N.sub.2 Ar Flow rate of primary gas >40 l/min, 50 l/min preferably >45 l/min Nature of secondary gas H.sub.2 H.sub.2 Flow rate of secondary gas >20 vol % of the plasma- 25 vol % of the plasma- forming gas mixture forming gas mixture Injection of the granule powder Total flow rate of powder injected <180 g/min <100 g/min (g/min) (3 injection orifices) Flow rate in g/min per kW of power <5 <2 Diameter of injection orifices (mm) <2 mm ≤1.5 mm preferably <1.8 mm Flow rate in g/min per mm.sup.2 of >10 >15 and <20 surface area of injection orifice Type of carrier gas Ar or N.sub.2 Ar Flow rate of carrier gas per injection >6.0 l/min, ≥7.0 l/min orifice Preferably >6.5 l/min Injection angle relative to the X axis >85° 90° of the plasma jet (angle θ in FIG. 2) Distance between an injection orifice >10 mm ≥12 mm and the axis X of the plasma jet Cooling of the droplets Cooling parameters Conical or annular air curtain, oriented in the downstream direction of the plasma jet Angle γ between the direction of In the downstream In the downstream injection of the cooling fluid, from a direction of direction of the plasma nozzle, and the axis X of the plasma the plasma jet, ≥10° jet, ≥30° and <60° jet Total flow rate of the forced cooling 10-70 Nm.sup.3/h 35-50 Nm.sup.3/h fluid Flow rate of the exhaust gas 100-700 Nm.sup.3/h 250-500 Nm.sup.3/h

EXAMPLES

(46) The examples which follow are provided for purposes of illustration and do not limit the scope of the invention.

(47) The feed powders H1, I1 (comparative) and C1 (comparative) were manufactured with a plasma torch similar to the plasma torch shown in FIG. 2 of WO2014/083544, from a pure Y.sub.2O.sub.3 powder having a median size D.sub.50 of 1.2 microns, measured with a Horiba laser particle analyzer, and a chemical purity of 99.999% of Y.sub.2O.sub.3.

(48) In step a), a binder mixture is prepared by adding PVA (polyvinyl alcohol) binder 2 (see FIG. 1) to deionized water 4. This binder mixture is then filtered through a 5 μm filter 8. The yttrium oxide powder 10 is mixed into the filtered binder mixture to form a slip 12. The slip is prepared so as to comprise, as percentage by mass, 55% of yttrium oxide and 0.55% of PVA, the balance to 100% being deionized water. The slip is mixed intensely using a high-shear speed mixer.

(49) The granules G3 are subsequently obtained by atomization of the slip, using an atomizer 14. More particularly, the slip is atomized in the chamber of a GEA Niro SD 6.3 R atomizer, the slip being introduced at a flow rate of approximately 0.38 l/min.

(50) The speed of the rotating atomization wheel, driven by a Niro FS1 motor, is regulated to give the target sizes of the granules 16 (G3).

(51) The flow rate of air is adjusted to maintain the entry temperature at 295° C. and the exit temperature close to 125° C., such that the residue moisture content of the granules is between 0.5% and 1%.

(52) The granule powder is then sieved with a sieve 18 so as to extract the residues from it and to give an SDO granule powder 20.

(53) In step b), the granules from step a) are injected into a plasma jet 22 (see FIG. 2) produced with a plasma gun 24. The injection and melting parameters are given in table 2 below.

(54) In step c), to cool the droplets, 7 Silvent 2021L nozzles 28, sold by Silvent, were fixed on a Silvent 463 annular nozzle holder, sold by Silvent. The nozzles 28 are spaced regularly along the annular nozzle holder, so as to generate a substantially conical flow of air.

(55) The collection yield of the collected feed particles 38 is the ratio of the amount of feed particles collected to the total amount of granules injected into the plasma jet.

(56) TABLE-US-00002 TABLE 2 Treatment of the powder Dried by spraying + plasma spraying Granules (particles obtained after spray drying) Granule reference G3 Type of granules Spray-dried yttrium oxide powder Granules D.sub.10 (μm) 23.4 Granules D.sub.50 (μm) 39.0 Granules D.sub.90 (μM) 63.0 Mean bulk density 1.05 Step b): injection Feed rate of granules 120 g/min 90 g/min Flow rate in g/min per KW of power of the gun 2.5 1.9 Number of injection orifices (powder lines) 3 Injection angle θ relative to the axis X of the 80° in downstream dir. 90° (normal plasma jet (FIG. 2) to the jet) Distance of each injector 12 mm 14 mm 12 mm (radially from the axis of the gun) Diameter of the injection orifice of each injector 2.0 mm 1.8 mm 1.5 mm Flow rate of the argon carrier gas per 3.5 l/min 6.0 l/min 7.0 l/min injection orifice Flow rate in g/min per mm.sup.2 of injection orifice 12.7 16 17 surface area Step b): melting Plasma gun ProPlasma HP Diameter of the anode of the plasma gun 8 mm Voltage (V) 74 83 Power (kW) 48 54 Plasma-forming gas mixture Ar + H.sub.2 Flow rate of the plasma-forming gas 48 l/min 67 l/min Proportion of H.sub.2 (secondary gas) in the 25% plasma-forming gas Nature of the primary gas Ar Calculated flow rate of the primary gas 48*(100 − 25)/100% = 50 l/min 36 l/min Intensity of the plasma arc 650 A Step c): cooling Annular cooling nozzles 7 Silvent 2021L nozzles attached to Silvent 463 Total flow rate of cooling air Nm.sup.3/h) 0 42 42 Flow rate of air in the cyclone (Nm.sup.3/h) 650 350 650 Collection yield of feed particles  54%   20%    44% Feed particles collected (feed powder) Reference I1 C1 H1 (inventive) D.sub.10 (μm) 15.7 10.0 7.0 D.sub.50 (μm) 24.9 22.0 11.7 D.sub.90 (μm) 37.2 35.0 17.0 (D.sub.90 − D.sub.10)/D.sub.10 1.4 2.5 1.4 Fraction by number: ≥37 μm  10%   9% <0.5% Fraction by number: ≥30 μm  27%   23% <0.5% Fraction by number: ≤10 μm 1.8% 10.3%    33% Fraction by number: ≤5 μm 0.9%  5.1%     3% Median circularity C.sub.50 0.993 0.982 >0.85 Specific surface area (m.sup.2/g) 0.44 0.57 0.26 Level of impurities measured by GDMS <150 ppm Bulk density measured by mercury 2.37 2.53 Not measured porosimetry at a pressure of 3.5 KPa Calculated bulk density 0.47 0.50 Bulk density measured by mercury 4.25 4.43 4.60 porosimetry at a pressure of 200 MPa Calculated relative density in % 84 88 91 Cumulative specific volume of the pores 13 7 11 having a radius of less than 1 micron 10.sup.−3 cm.sup.3/g of the powder sample)

(57) The cumulative specific volume of the pores having a radius of less than 1 μm in the granules was 260×10.sup.−3 cm.sup.3/g.

(58) The invention thus provides a feed powder having a size distribution and a relative density which endow the coating with a very high density. Furthermore, this feed powder can be efficiently sprayed by plasma, with a high productivity.

(59) The feed powder according to the invention so makes it possible to produce coatings having a smaller concentration of defects. Furthermore, the powder exhibits enhanced flowability in relation to a powder of the same size which has not been plasma-melted, so enabling injection without a complex feed means.

(60) The invention is of course not limited to the embodiments described and shown.