Plasma Etching Behavior of YOF Coating Deposited by Suspension Plasma Spraying in Inductively Coupled CHF3/Ar Plasma
Round 1
Reviewer 1 Report
Line 11: After “deposition” for 6 min ?
Line 30: I am not sure that the Damascene process is known to all readers.
Line 46 and 51: YF3 particles or “molecules”? Particles could be rather large. What about YF and YF2 radicals?
Line 49: … “already contains” fluorine, its reactivity with the fluorine-containing plasma is reduced?
Line 52: which “resistance” (erosion?) properties?
Line 71: why “raw” material? Sentence regarding YOF suspension properties should be placed next. Start with: the YOF suspension consists of YOF particles with an average size of 3 micro-m dispersed/solved in de-ionized water …
Line 90-92, table 1, and elsewhere: what is an “atomizing” gas? Nitrogen is a molecular gas. Anyhow, what is the purpose of N2 and H2 and why is the gas flow not indicated in figure 1?
Line 92: Plasma “gun”? The “gun” was moved at a speed of 1 m/s, really? Over which distance? Indicate plasma jet-substrate distance in figure 1.
Line 100: what kind of pumping was utilized?
Line 101: “plasma gas” sounds pretty strange. Delete “plasma”.
Line 157-160: sounds pretty complicated. Is there a difference between Y5O4F7 and YOF particles? How is it possible that YF3 “molecules?” form? It appears likely that small YF and/or YF2 but also Y, O, F, and YO radicals form in a plasma.
Line 196: figure 6(b)?
Line 218: figure 7(b) and “7(c)”.
Line 224-232: what makes the Y-3d5/2 peaks from Y-O to appear at 157 eV in figure 7(b) and at 158.5 eV in figure 7(c)?
Line 279: “The high erosion (?) resistance” of the YOF coating …
Author Response
Replies to comments of reviewer # 1
Comment 1: Line 11: After “deposition” for 6 min?
Answer: Thanks to the comment, we corrected the ‘coating’ to ‘deposition’.
Comment 2: Line 30: I am not sure that the Damascene process is known to all readers.
Answer: I agree with your comment. The Damascene process is so specific technology that most of readers cannot understand. So, we eliminated the ‘Damascene process’ term as follows.
Old: In the semi-conductor manufacturing process, dry etching of dielectric SiO2 and cleaning processes have increased due to the multi-level interface connection and the Damascene process [1].
New: In the semi-conductor manufacturing process, dry etching of dielectric SiO2 and cleaning processes have increased due to the multi-level interface connection [1].
Comment 3: Line 46 and 51: YF3 particles or “molecules”? Particles could be rather large. What about YF and YF2 radicals?
Answer: In response to the comment, we revised the manuscript by referring to [ref 12] as follows.
[ref 12]: Kim, D.-M.; Jang, M.-R.; Oh, Y.-S.; Kim, S.; Lee, S.-M.; Lee, S.-H. Relative sputtering rates of oxides and fluorides of aluminum and yttrium. Surface and Coatings Technology 2017, 309, 694-697.
Old: Although Y2O3 is known to be more resistant to plasma than SiO2 and Al2O3, it would not be the best plasma-resistant material because YF3 particles are generated as contaminants in the process of the Y2O3 surface being converted to a YxOyFz layer due to the reaction with plasma [11,12].
New: Although Y2O3 is known to be more resistant to plasma than SiO2 and Al2O3, it would not be the best plasma-resistant material because fluoride particles whose chemical composition is close to YF3 are generated as contaminants in the process of the Y2O3 surface being converted to a YxOyFz layer due to the reaction with plasma [11,12].
Comment 4: Line 49: … “already contains” fluorine, its reactivity with the fluorine-containing plasma is reduced?
Answer: In response to the comment, we revised the manuscript as follows.
Old: Since yttrium oxyfluoride (YOF) has fluorine, it would not react with the fluorocarbon plasma gas.
New: Since yttrium oxyfluoride (YOF) has fluorine, it would not react with the fluorocarbon plasma gas. Shiba et al. [9] reported that the surface crystallinity of YOF, which is a fluorine-based material, was not changed while that of Y2O3 was changed by the penetration and reaction with fluorocarbon plasma gas.
Comment 5: Line 52: which “resistance” (erosion?) properties?
Answer: In response to the comment, we revised the manuscript as follows.
Old: Shiba et al. [9] reported that the resistance properties of YOF for various plasma gases were superior to those of Y2O3 through X-ray diffractometry (XRD) and X-ray photoelectron spectrum (XPS) analyses, although those materials were deposited by ion plating.
New: Shiba et al. [9] also reported that the resistance to erosion of YOF for various plasma gases was superior to that of Y2O3 through X-ray diffractometry (XRD) and X-ray photoelectron spectrum (XPS) analyses, although those materials were deposited by ion plating.
Comment 6: Line 71: why “raw” material? Sentence regarding YOF suspension properties should be placed next. Start with: the YOF suspension consists of YOF particles with an average size of 3 micro-m dispersed/solved in de-ionized water …
Answer: Considering the comment, we revised the manuscript as follows.
Old: Commercially available Y5O4F7 suspension (Nippon Yttrium Co., Ltd., Omuta, Fukuoka, Japan) was used as a raw material. A YOF coating was prepared using a suspension plasma spraying (SPS) system, which had triple anodes and cathodes with coaxial feeding (Mettech’s Axial III, Northwest Mettech Corp., North Vancouver, BC, Canada). The solvent of the Y5O4F7 suspension was deionized water and Y5O4F7 particles with an average size of 3 µm were dispersed in the solvent with a solid concentration of 10 wt.%.
New: Commercially available Y5O4F7 suspension (Nippon Yttrium Co., Ltd., Omuta, Fukuoka, Japan), which consists of Y5O4F7 particles with an average size of 3 µm dispersed in de-ionized water with a solid concentration of 10 wt.%, was used as a feedstock material. A YOF coating was prepared using a suspension plasma spraying (SPS) system, which had triple anodes and cathodes with coaxial feeding (Mettech’s Axial III, Northwest Mettech Corp., North Vancouver, BC, Canada).
Comment 7: Line 90-92, table 1, and elsewhere: what is an “atomizing” gas? Nitrogen is a molecular gas. Anyhow, what is the purpose of N2 and H2 and why is the gas flow not indicated in figure 1?
Answer: Atomizing gas doesn’t mean ‘atomic gas’ or ‘molecular gas’. It is a term commonly used in plasma spray coating. And, because the explanation on the role of N2 and H2 is somewhat lengthy, we inserted a reference (our previous paper: Lee, J.; Lee, S.; Han, H.N.; Kim, W.; Hwang, N.-M. Yttrium Oxyfluoride Coatings Deposited by Suspension Plasma Spraying Using Coaxial Feeding. Coatings 2020, 10, 481.) illustrated well about the role of the gases. Considering the comments, we revised the Figure 1 and the manuscript as follows.
Old: The SPS coating was carried out under the following conditions; the flow rate of argon as a primary gas was set to 90 standard liters per minute (slm), and the flow rates of nitrogen and hydrogen as secondary gases were set to 54 and 36 slm, respectively, to induce the generation of a plasma arc with an arc current of 230 A. The feeding rate of the suspension was 45 standard cubic centimeters per minute (sccm), and the flow rate of nitrogen atomizing gas was 30 sccm. The atomizing gas turned out to affect the quality of the YOF coating because it makes the droplet size of the suspension smaller and thus the particles in the droplet melt more easily [14].
New: The SPS coating was carried out under the following conditions; the flow rate of argon as a primary gas was set to 90 standard liters per minute (slm), and the flow rates of nitrogen and hydrogen as secondary gases were set to 54 and 36 slm, respectively, to induce the generation of a plasma arc with an arc current of 230 A. The role of gases is illustrated in our previous paper [11]. The feeding rate of the suspension was 45 standard cubic centimeters per minute (sccm), and the flow rate of nitrogen atomizing gas was 30 sccm. The atomizing gas, which is injected to the feeding flow and splits the suspension droplets into small ones, turned out to affect the quality of the YOF coating because it makes the droplet size of the suspension smaller and thus the particles in the droplet melt more easily [14, 15].
Comment 8: Line 92: Plasma “gun”? The “gun” was moved at a speed of 1 m/s, really? Over which distance? Indicate plasma jet-substrate distance in figure 1.
Answer: Plasma gun means plasma torch. ‘Plasma gun’ is commonly used term in plasma spray coating. We used the value of plasma gun speed of 1 m/s by referring this literature [Park, S.-J.; Kim, H.; Lee, S.-M. Solid-State Synthesis of Yttirum Oxyfluoride Powders and Their Application to Suspension Plasma Spray Coating. Korean J. Mater. Res. 2017, 27, 710–715]. In response to the comment, we corrected the Figure 1.
Comment 9: Line 100: what kind of pumping was utilized?
Answer: In response to the comment, we revised the manuscript as follows.
Old: The working pressure in the plasma etching chamber was 20 mTorr. The specimens were exposed to CHF3/Ar plasma for 60 min. The details of plasma etching conditions are shown in Table 2.
New: Dry and turbo molecular pumps were utilized to prepare the vacuum. The working pressure in the plasma etching chamber was 20 mTorr. The specimens were exposed to CHF3/Ar plasma for 60 min. The details of plasma etching conditions are shown in Table 2.
Comment 10: Line 101: “plasma gas” sounds pretty strange. Delete “plasma”.
Answer: In response to the comment, we deleted the ‘plasma’ term.
Comment 11: Line 157-160: sounds pretty complicated. Is there a difference between Y5O4F7 and YOF particles? How is it possible that YF3 “molecules?” form? It appears likely that small YF and/or YF2 but also Y, O, F, and YO radicals form in a plasma.
Answer: In response to the comment, we revised the manuscript.
You can see the detail mechanism in our previous paper [ref 11: Lee, J.; Lee, S.; Han, H.N.; Kim, W.; Hwang, N.-M. Yttrium Oxyfluoride Coatings Deposited by Suspension Plasma Spraying Using Coaxial Feeding. Coatings 2020, 10, 481]. And the volatilization of YF3 mechanism is explained by thermo-gravimetric analysis in reference 21 [Park, S.-J.; Kim, H.; Lee, S.-M. Solid-State Synthesis of Yttirum Oxyfluoride Powders and Their Application to Suspension Plasma Spray Coating. Korean J. Mater. Res. 2017, 27, 710–715.] as following figure.
Old: A possible scenario for the formation of Y2O3 would be as follows. First, Y5O4F7 particles in suspension would be transformed into YOF particles while Y5O4F7 particles volatilize in the form of YF3 in the plasma jet region [20]. Then, some of YOF would be transformed into Y2O3 while the YOF is volatilized in the form of YF3 by sufficient heat energy in the plasma jet region [21].
New: A possible scenario for the formation of Y2O3 would be as follows. First, Y5O4F7 particles in suspension would be transformed into YOF particles while Y5O4F7 particles volatilize in the form of YF3 in the plasma jet region [20]. Then, some of YOF would be transformed into Y2O3 while the YOF is mainly volatilized in the form of YF3 by sufficient heat energy in the plasma jet region [21]. The detailed mechanism is explained in our previous paper [11].
Comment 12: Line 196: figure 6(b)?
Answer: This is modified from Figure 6(b) to Figure 6. We revised the manuscript.
Comment 13: Line 218: figure 7(b) and “7(c)”.
Answer: In response to the comment, we revised the manuscript.
Comment 14: Line 224-232: what makes the Y-3d5/2 peaks from Y-O to appear at 157 eV in figure 7(b) and at 158.5 eV in figure 7(c)?
Answer: The peak positions of Y-3d5/2 from Y-O by XPS can be seen in the literature [Handbook of X-ray Photoelectron Spectroscopy, Physical Electronics Inc., Minnesota, J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, 1995]. So, the peak position of Y-3d5/2 measured by XPS in our paper was predicted by referring to the previous data. The reason why the Y-O binding energy of Y2O3 and YOF was different is because the crystalline structure between the two materials is different. Y2O3 has a Cubic structure, whereas YOF has a Trigonal structure. Another possibility is, during analysis, insulating samples tend to acquire a steady state charge of as much as several volts. This steady state charge is a balance between electron loss from the surface by emission and electron gain by conduction or by acquisition of slow or thermal electrons from the vacuum. By the extent of charging, any positive charging retards outgoing electrons and tends to make the peaks appear at higher binding energies.
Comment 15: Line 279: “The high erosion (?) resistance” of the YOF coating …
Answer: In response to the comment, we revised the manuscript.
Old: Such high resistance of the YOF coating to fluorocarbon plasma comes from the formation of a strongly fluorinated layer on the surface.
New: Such high erosion resistance of the YOF coating to fluorocarbon plasma comes from the formation of a strongly fluorinated layer on the surface.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The authors of the article with title “Plasma etching behavior of YOF coating deposited by suspension plasma spraying in inductively coupled CHF3/Ar plasma” touch sensible industrial questions connected with sustainability and operating efficiency of the machines by protecting the inner wall of reactors from florocarbon plasma gas by deposit on it yttrium oxyfluoride (YOF) using suspension plasma spraying (SPS).
Study is written using simple and understandable style. Importance of using YOF coating deposited on inner wall of chambers was explained carefully. Authors systematically point the effects of different layers (Al2O3, Y2O3) as a plasma-resistant materials and compare with YOF. The explanations are simple, short and understandable enough without unnecessary details. The Al2O3, Y2O3 and YOF had been characterized by FE-SEM, a noncontact three-dimensional surface profiler NanoView-E1000 and XPS AXIS SUPRA KRATOS were used. It was analized Y 3d and Al 2p. It was prepared dept-profiling of Al2O3, Y2O3 and YOF deposited coatings.
My meaning is that authors were able to show systematical study of YOF coating deposited by SPS technique having excellent plasma-resistance to CHF3/Ar plasma etching. The paper is high quality and fulfill the requirements of journal Coatings.
about the review of the paper in Coatings No: coatings-944137:
How original is the topic?
Usually the YOF was deposited by classical atmospheric plasma spraying (APS). The alternative of APS is suspension plasma spraying (SPS) method which is a new promising processing method using suspensions of sub-micrometer particles as feedstock. The topic is original and important enough for the science and industry.
What does it add to the subject area compared with other published material?
Suspension plasma spraying (SPS) in nowadays becoming a popular method for deposition of ceramic top coats which are widely used in industry. This technique is using for deposition of materials such as alumina, yttria-stabilized zirconia (YSZ), YOF and etc. The current study is based on previous study on the team connected to the deposition of YOF by SPS (Coatings 2020, 10(5), 481; https://doi.org/10.3390/coatings10050481). The focus of the current study is protective properties of YOF coatings deposited by suspension plasma spray (SPS) with coaxial feeding from fluorocarbon plasma etching.
Is the text/concepts clear and easy to read for most readers?
The text/concept is written using simple and understandable style.
Are the conclusions consistent with the evidence and arguments presented?
From chemical point of view, the conclusions are solid enough and easy understandable.
Do they address the main question posed?
The authors lead the study’s story in positive note and accurately shows, by facts extracted from XPS core levels and dept profiles measurements, the best protective role of YOF coatings compare to the alternatives.
Are the figures/tables correct?
The presented figures who represent schematics, FE-SEM pictures and cross section, XPS and XPS depth profiles are correct enough from scientific point of view.
Author Response
Since there are no requests to correct the manuscript, we didn't include the reply.
But, thanks to your helpful comments, we could revise our manuscript better.
Round 2
Reviewer 1 Report
Paper was carefully revised and is now ready for publication.
