Patent Grant
11731883
The invention relates to a powder suitable for deposition by plasma, to a process for manufacturing such powder, and to a coating obtained by plasma spraying of said powder, more particularly for a semiconductor etch chamber coating.
The internal surfaces of the chambers used to treat (for example by plasma etch) semiconductors, silicon wafers for example, are conventionally protected with a ceramic coating which is applied by plasma spraying. This coating needs to have high resistance to halogen-comprising plasmas or highly corrosive environments. Plasma spraying requires, as a feed powder, a powder which exhibits high fluidity and a particle morphology which allows for appropriate heating during spraying. More particularly, the size of the particles must be sufficient for the particles to penetrate the plasma and for limiting the evaporation losses.
For example, the very fine powders obtained directly by pyrolytic or chemical manufacturing processes are not suitable for plasma spraying without an additional step of consolidation to form more large (and porous) agglomerates, more particularly sintered agglomerates. Since plasma spraying does not result in the melting of all the agglomerates, the resulting coating exhibits porosity. The total porosity of the coating obtained by spraying of sintered agglomerates is typically 2-3%, which would not be appropriate for protecting the internal surfaces of a semiconductor etching chamber. More particularly, the sintered powders described in U.S. Pat. No. 6,916,534, US 2007/077363 or US 2008/0112873 are unable to lead to a very dense coating by thermal spraying. Moreover, the coatings obtained from porous agglomerates result, over time, in the release of particles when they are exposed to corrosive environments.
U.S. Pat. No. 7,931,836 or US 2011/0129399 disclose a particle powder resulting from plasma melting to form liquid droplets which solidify in free fall. In some embodiments, more than 90% of the particles of starting material may be completely or partially converted into liquid form. The bulk density of the resulting powder is between 1.2 and 2.2 g/cm3.
In the application cited above, the powders obtained by grinding a melted mass are not appropriate either, because of impurities which are added during the grinding step.
Rare earth metal oxides and/or hafnium oxide and/or yttrium-aluminum oxides are known to exhibit high intrinsic resistance to chemical attack. However, they have a high melting temperature and low thermal diffusion. It is therefore difficult to obtain a very dense coating from these particles by plasma spraying.
To solve these problems, WO 2014/083544 describes a powder of 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:
the cumulative specific volume of the pores having a radius of less than 1 μm being less than 10% of the bulk volume of the powder,
in which the percentiles Dn 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, the particle sizes being classified by increasing order,
the density P<50 being the bulk density of the fraction of the particles having a size of less than or equal to D50, and the density P being the bulk density of the powder.
This powder can be efficiently sprayed by plasma, with a high productivity, and leads to a very pure and extremely dense coating.
There is nevertheless an ongoing need for a semiconductor etch chamber coating that exhibits increased erosion resistance and a reduced number of defects.
It is an aim of the invention to meet this need while retaining the advantages of the powder of WO 2014/083544.
With this aim, the invention provides a powder (hereinafter “feed powder”) of melted particles (hereinafter “feed 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, for example of Yb2O3 or Y2O3, and/or of hafnium oxide and/or of an aluminum oxide, as percentage by mass based on the oxides, and having:
A feed powder according to the invention is therefore a very pure powder, composed in large part of spherical particles. This powder is notable more particularly for the very low size dispersion of the particles, relative to D10, the small amount of particles having a size of greater than 30 μm, and for a very high relative density.
This latter feature implies a very low, or even substantially zero, amount of hollow particles. The particle size distribution ensures very uniform melting during spraying.
Lastly, a feed powder according to the invention exhibits a high flowability, hence allowing the coating to be manufactured without a complicated feed device.
In the present invention, the term “oxide” may include the simple oxide but also a more complex oxide such as oxyfluoride, an example being yttrium or ytterbium oxyfluoride.
A feed powder in accordance with the invention may also comprise one or more of the following optional features:
The invention further concerns a process for manufacturing a feed powder according to the invention, comprising the following successive steps:
In step b), the injection conditions are different from those described in WO 2014/083544, which, on page 14, recommends gentle injection for limiting the risks of bursting.
The forceful injection of the powder has the advantageous effect of allowing simultaneously a reduction in the median size of the feed powder and a reduction in the proportion of hollow particles. It so makes it possible to obtain a very high relative density.
Preferably, the plasma gun has a power of greater than 40 kW, preferably greater than 50 kW and/or less than 65 kW, preferably less than 60 kW.
Preferably, the plasma gun has a power of between 40 to 65 KW and the ratio of the quantity by mass of granules injected via injection orifice, preferably by each injection orifice, to the surface area of said injection orifice is greater than 10, preferably greater than 15, preferably greater than 16, preferably greater than or equal to 17 g/min per mm2 of surface area of said injection orifice.
The injection orifice, preferably each injection orifice, consists preferably of a channel with a length greater than one time, preferably two times, or even 3 times the equivalent diameter of said injection orifice.
Preferably, the flow rate of the granule powder injected is less than 2.4, preferably less than 2.0 g/min per KW of power of the plasma gun.
There is no intermediate sintering step, and preferably no consolidation between steps a) and b). This absence of an intermediate consolidation step has the advantageous effect of improving the purity of the feed powder. It also facilitates the bursting of the granules in step b).
A process for manufacturing a powder according to the invention may also comprise one or more of the following optional features:
The invention likewise concerns a thermal spraying process comprising a step of plasma spraying of a feed powder according to the invention to a substrate in order to obtain a coating.
The invention likewise concerns a body comprising a substrate and a coating at least partially covering said substrate, said coating comprising more than 99.8% of a rare earth metal oxide and/or of hafnium oxide and/or an aluminum oxide, as percentage by mass based on the oxides, and exhibiting a porosity of less than or equal to 1.5%, said porosity being measured on a photograph of a polished section of said coating, as described below. Preferably, the porosity of the coating is less than 1%.
Preferably, the coating comprises more than 99.9%, more than 99.95%, more than 99.97%, more than 99.98%, more than 99.99%, preferably more than 99.999% 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.
A coating of this kind may be manufactured with a thermal spraying process according to the invention.
The substrate may be a wall of an oven used in the treatment of semiconductors, and more particularly the wall of a plasma etch chamber.
The oven may contain semiconductors, more particularly silicon wafers. The oven may be equipped with chemical vapor deposition (CVD) means or with physical vapor deposition (PVD) means.
The more elongated the shape of the particle, the lower the circularity. This procedure is also described by the user manual for the Sysmex FPIA 3000 (see “detailed specification sheets” at www.malvern.co.uk).
For example, 10% by number of the particles in the powder have a size of less than D10, and 90% of the particles by number have a size of greater than or equal to D10. The percentiles relating to the size may be determined by means of a particle size distribution produced by means of a laser particle sizer.
Similarly, 5% by number of particles in the powder have a circularity less than the percentile C5. In other words, 95% by number of particles in this powder have a circularity greater than or equal to C5.
The 50 percentile is conventionally called the “median” percentile. For example, C50 is typically called “median circularity”. Similarly, the percentile D50 is typically called “median size”. The percentile A50 also refers typically to the “median aspect ratio”.
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:
Process for Manufacturing a Feed Powder
Any known granulation process may be used. More particularly, the skilled person knows how to prepare a slip suitable for granulation.
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.
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.
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.
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
The resulting powder 20 is a “spray-dried only (SDO)” granule powder.
An SDO granule powder 20, for example, as manufactured by the process illustrated in
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.
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.
More particularly, the skilled person is aware that:
are factors which promote the breaking of the granules.
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.
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.
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.
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.
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.
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.
Preferably, the flow rate of the primary gas is greater than 40 l/min, preferably greater than 45 l/min.
Preferably, the ratio between the flow rate of secondary gas, preferably dihydrogen (H2), and the flow rate of plasma-forming gas (composed of the primary and secondary gases) is between 20% and 25%.
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.
The granule powder is injected with a carrier gas, preferably without any liquid.
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.
An advantageous effect of the melting is to reduce the level of impurities.
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.
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
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°.
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.
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.
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.
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.
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.
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.
The collected feed particles 38 may when appropriate be filtered, so that the median size D50 is less than 15 microns.
Table 1 below provides the preferred parameters for manufacturing a feed powder according to the invention.
The features of a column are preferably, but not necessarily, combined. The features of the two columns may also be combined.
The “ProPlasmaHP” plasma torch is sold by Saint-Gobain Coating Solutions. This torch corresponds to the torch T1 described in WO2010/103497.
The examples which follow are provided for purposes of illustration and do not limit the scope of the invention.
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 Y2O3 powder having a median size D50 of 1.2 microns, measured with a Horiba laser particle analyzer, and a chemical purity of 99.999% of Y2O3.
In step a), a binder mixture is prepared by adding PVA (polyvinyl alcohol) binder 2 (see
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.
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).
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%.
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.
In step b), the granules from step a) are injected into a plasma jet 22 (see
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.
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.
The cumulative specific volume of the pores having a radius of less than 1 μm in the granules was 260×10−3 cm3/g.
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.
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.
The invention is of course not limited to the embodiments described and shown.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1850821 | Jan 2018 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/052438 | 1/31/2019 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2019/149854 | 8/8/2019 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6916534 | Wataya et al. | Jul 2005 | B2 |
| 7931836 | Xie et al. | Apr 2011 | B2 |
| 20060116274 | Kitamura et al. | Jun 2006 | A1 |
| 20070077363 | Kitamura et al. | Apr 2007 | A1 |
| 20080112873 | Aoki et al. | May 2008 | A1 |
| 20110129399 | Xie et al. | Jun 2011 | A1 |
| 20130288037 | Sun | Oct 2013 | A1 |
| Number | Date | Country |
|---|---|---|
| 1167565 | Jan 2002 | EP |
| 1239055 | Sep 2002 | EP |
| 2010103497 | Sep 2010 | WO |
| 2014083544 | Jun 2014 | WO |
| Entry |
|---|
| International Search Report corresponding to International Application No. PCT/EP2019/052438 dated Apr. 8, 2019, 6 pages. |
| Number | Date | Country | |
|---|---|---|---|
| 20210115548 A1 | Apr 2021 | US |
