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topic 13109

Electropolishing copper by using phosphoric acid




An ongoing discussion from 1996 through 2018

1996

Q. I should have written down precisely, but let me ask you once more, using H2S04 bath with additives, in anode, rack copper, and in cathode non-dissolvable stainless steel. Specimen with current density 10 A/dm2 for anodic copper polishing, we measured the gloss meter in advance and after electro polishing, but I've got different results. The gloss figure drops (meaning not polished). Instead in the cathode, the stainless steel became plated with copper. That's my question/problem. Moreover, would you advise copper bath contents for copper plating? Thanks. Looking forward to your reply.

(Miss) Sae.y.oh
- Korea Industrial Technology Research Institute


1996

A. Hi, Miss Sae. According to the Electroplating Engineering Handbook, commercial electropolishing of copper is done in phosphoric acid, or modified phosphoric acid (U.S. Patent 2,366,714) or phosphoric-chromic acid (U.S. Patent 2,347,039).

According to the Metals Handbook, phosphoric-chromic acid is used at 18V and 30-40 A/dm2 (much higher than you are using), 65 °C.

The Metal Finishing Guidebook lists three different approaches, only one of which contains sulfuric acid, and that solution also contains chromic acid and acetic acid. I think a sulphuric acid bath is unsuitable for electropolishing copper. Good luck.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey


1996

Q. More questions about copper electro-polishing: I use copper busbar (conductors); does it relate to the results?

(Miss) Sae.y.oh
- Korea Industrial Technology Research Institute


A. Hi. I don't think the material of the busbar is effecting this process. I think your current density and the chemicals you are using are leading to copper plating onto the anodes instead of polishing the copper.

Still, electropolishing may not give as glossy a result as mechanical polishing. The reason for electropolishing is smoothness and freedom from microscopic burrs and clods of copper. A mechanically polished surface will always look like a plowed field at sufficient magnification, because that's what it is. A properly electropolished surface will resemble gentle ocean swells because the asperities will all have been dissolved away. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



2000

Q. I am a human resources manager in a small manufacturing facility that has only recently brought our electro-polishing in-house. My problem is that our employees are developing health-related problems even though all of our testing indicates that we are well below any risk levels. Specifically, I am interested in hearing from other companies who do electro-polishing in-house to see if they have experienced similar problems. We have, of course, provided personal protective equipment.

Betty T [last name deleted for privacy by Editor]
- Irwin, Pennsylvania


A. Hi Betty. Asking for feedback is fine, and I hope you get some. But still, I think you should retain an experienced plating consultant or industrial hygienist in your situation. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



2002

Q. Hi, professors,

I found one paper "Electrochemical Planarization of ULSI Copper" by Robert J. Contolini, Solid State Technology, June, 1997. It is an interesting method for planarization of ULSI. But after 1997, I cannot find any papers about the electropolishing of copper. So I want to know what is the shortcoming of this method in planarization? Why a lot of people seek a way by using Chemical mechanical planarization?

Feng Liang
- College Station, Texas



To minimize your searching efforts and to offer multiple viewpoints, we've combined some threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



2002

Q. I am a chemical engineer. I want to know more information about the Electropolishing of copper by using phosphoric acid.

I am doing my master degree on electropolishing of copper the copper used in experiment is a commercial copper, I am asking about any kind of copper... and about phosphoric acid ...this is the experiment which they asked of me for my masters.

Many thanks,

Rania Raafat Roushdi Eldin
- Alexandria, Egypt


ASM Metals Handbook
0-15V 0-5A

2002

A. ASM's Metals Handbook, Vol. 5 =>
says 85 percent orthophosphoric acid plus 5 wt percent to saturation chromic acid at 55-65 C and 15-30 A/dm. That should be a start.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey


2002

Q. Dear Sir,

I have the some question as yours. Have you started the polishing? Can you tell me what was going on?

Thanks,

Ji Luo
- Canada


2006

A. I completed my MS in 2000. You do not need chromic acid to electropolish copper. You can also use lower or higher concentration of phosphoric acid. The trick is to locate where (what voltage region) electropolishing occurs.

Pure copper is 99.99% so most pure commercial coppers will work. Beware of not duplicating other theses since there are many.

Kam Dianatkhah
- Chanler, Arizona


November 5, 2012

Q. Hello all,

I want to know how we can Electropolish the copper in phosphoric acid without adding any chrome?

I will be glad very much for helping me on this topic.

Mohamed Khalaf
- Cairo, Egypt



New applications of electropolishing technique in semiconductor industry

2003

Q. I am work on electropolishing research project in my company. I am looking for new applications of electropolish technique in semiconductor process or equipments except the valves and gas delivery system. Could anyone give me any ideas?

Thanks,

Chang [last name deleted for privacy by Editor]
- Taipei, Taiwan


2003

A. There was a bit of work in Copper electropolishing integrated with chemical-mechanical-polishing in the dual damascene copper/low-k plated interconnect system. Applied Materials, Novellus, and Semitool all considered it during process infancy but I don't think it has ever been implemented as a process.

Dave Kinghorn
Dave Kinghorn
Chemical Engineer
SUNNYvale, California




Removal of copper phosphate after electropolishing of copper in phosphoric acid

2003

Q. I'm trying to electropolish polycrystalline copper electrode by using 50% phosphoric acid. After polishing is finished, I have problem removing the layer of copper phosphate. Could you at least direct me to a source where I could find the solution for my problem.

Darko Grujicic
University of Idaho - Moscow, Idaho, USA


2003

A. Dear Mr. Grujicic,

You may want to try a different electropolishing solution for your copper piece as follows;
DeIonized Water - 100 parts
Sulfuric Acid - 21 parts
o-Phosphoric Acid 85% - 78 parts

A stainless steel cathode is normally used. You may have to play with the current densities a bit and gently agitate the piece for about 30 seconds. You may also have to vary the time slightly for best results. Rinse thoroughly in deionized water followed by a rinse in methanol or ethanol. Dry the piece carefully.

Good Luck,

Jim Sivertsen
- Alden, New York, USA



Electropolishing of copper in orthophosphoric acid solution

(2005)

Q. Hi, I need your help to find a theoretical data about electropolishing of copper, I need it to finish my graduation project, I've done my experimental part of the project, the main aim of my project is to find the effect of concentration, anode diameter & temperature on the limiting current so the rate of electropolishing.
Electropolishing of horizontal copper cylinder in orthophosphoric acid.

Joe Elshamy
Alex. university, Faculty of engineering - Alexandria, Cairo


"Electroplating Engineering Handbook"
by Larry Durney

from Abe Books
or
info on Amazon

(2005)

A. With the experimental work done, what results did you get, Joe?

You probably now need to do a computerized search of the published literature. You might try a literature search on Metal Finishing Information Service, which has abstracted most of the world's metal finishing periodicals. But I see on the net a reference to an article "Electrolytic polishing of copper in orthophosphoric acid", (Australia. Council for Scientific and Industrial Research. Division of Tribophysics. Physical metallurgy report) by R. W. K Honeycombe, and maybe you can track down a copy of that. There is a lot about electropolishing, but only a little about electropolishing of copper, in ASM Metals Handbook Vol. 5 "Surface Engineering" and the Electroplating Engineering Handbook =>

Good luck!

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



Electropolishing Reactions

2006

Q. Hello, my name is Regina, I'm still freshmen and doing some laboratory project about electropolishing of copper with aqueous phosphoric acid as electrolyte. What I want to ask are , the double layers that formed in anode, and the presence of solid Cu and CuO in cathode (where do they come from). I have search through many sites,and books, but often their description are either too little or to difficult because I just need to know the chemical reaction that happens during electropolishing. Thank You for your help...

Maria Regina Hartnoto
student - Indonesia


2006

A. See the book, Electrolytic & Chemical Polishing of Metals, by W. J. McG. Tegart (1956) and download 'The Electrolytic Polishing of metals. Application to Copper and Niobium' by V.Palmieri,
http://srf2003.desy.de/talks/Palmieri/Tutorial%20Palmieri.pdf

The figure on page 50 of Palmieri's tutorial is quite informative. Note also that during electropolishing, the anodic rate of oxide formation = rate of oxide dissolution by the acid.

Ken Vlach
- Goleta, California
contributor of the year

Finishing.com honored Ken for his countless carefully
researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work
which the finishing world continues to benefit from.




Explaining experimental phenomena observed during electropolishing process

2006

Q. I am an undergraduate student in Singapore. I am currently working on a report regarding electropolishing process.Electrolysis is used in the experiment. I would like to know the scientific reason for what I observed during and after the experiment. I observed light blue solution on the protecting disk, there are also gas bubbles produced and lastly the reddish-brown precipitate produced also. Thanks a lot.

Donald Lee Gee Chiew
Student - Singapore


2006

A. What are the anode & cathode materials? What is the electrolyte?
Bubbles are normal -- hydrogen forms at the cathode, and oxygen at the anode. Trap a small amount in an inverted beaker and very carefully test with a match.

A wild guess re the observed colors: copper dissolves into sulfuric acid as blue copper sulfate, and plates out as reddish, metallic slime at the cathode.

Ken Vlach
- Goleta, California


2006

Q. Hi, just to add on to the details of my question.The cathode is actually stainless steel, the anode is copper. The electrolyte used is H3PO4 in H2O. Therefore the chemical reaction behind the observations are? Thanks.

Donald Lee Gee Chiew [returning]
- Singapore


2006

A. Cu (+2) in aqueous solutions forms a blue color.

Usual practice in electropolishing copper is to also use copper for the cathode.

The overall reaction is Cu (anode) --> Cu (cathode). The devil is in the details. My understanding of Cu electropolishing is limited, but goes as follows.
Cu metal in ambient air is covered by cuprite, Cu2O.
Acid solutions of < pH 4 dissolve cuprite, according to the Pourbaix diagram.
Phosphoric acid reacts with and adsorbs to the bare Cu, possibly as Cu3(PO4)2.3H2O, copper (II) phosphate trihydrate. When DC electricity is applied, the electrodes become polarized (charge accumulates on the surface), especially at high points on the surface (like tiny lightning rods into the solution) where anodic oxidation then occurs [2Cu --> 2Cu(+) + 2 e(-)], forming Cu2O. As an equal amount of current must flow through the solution and cathode; ergo, a cathodic reduction reaction. The initial reaction is 2 H(+) + 2 e(-) --> H2 (gas). After enough dissolved Cu(+2) is in solution, the cathode reaction becomes Cu(+2) + 2 e(-) --> Cu (metal).
The phosphoric acid chemically dissolves any Cu2O formed into solution, Cu2O + 2 H(+) --> 2 Cu(+2) + H2O, whilst new Cu2O continues to form electrochemically on the high points of the anode. This continued loss of Cu from the high points levels the surface of the anode, creating the polishing.

A more complete explanation would discuss diffusion through the boundary layer of chemical species more or less adsorbed to the Cu. Also, with excessive voltage ('overvoltage'), the diffusion and dissolution processes cannot keep up with the electrical current, and the excess current is expended in the dissociation of water, with 1/2 O2(gas) formed at the anode per H2(gas) formed at the cathode.

Ken Vlach
- Goleta, California



Bubble traces observed in electropolishing copper

2006

Q. Hello, I am a student in a University in Hong Kong. I am now using electropolishing to prepare some samples of copper about 1.5mm thick for nano-indentation. However, I always find that I have got some trace of bubble on the surface (they are just very small bubble and I suppose they are not pitting that caused by over amount of current)

The solution I use is a mixture of phosphoric acid (85%), alcohol (95%), distilled water (in 2:1:1, actually I founnd it in the ASM handbook). I suspect that the bubbles are caused by the dissolved oxygen and hydrogen in the solution during the electropolishing process. Am I right? How can I get rid of these bubbles?

Johnny Lu
A student in University of Hong Kong - Hong Kong


2006

A. Agitate the solution vigorously to both insure fresh material at the interface, and to dislodge the gas bubbles, Johnny. Good luck.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



2007

Q. I am Jae Wook Shin a graduate student.
I was trying to electropolish single crystal Cu(100) using 85% phosphoric acid.
I need atomistically smooth surface to grow epitaxial film of Ni on it.

I could electropolish Cu, but quality was not good enough.
There are lots of pits on surface and even faint scatches.

When I increased the polishing voltage O2 bubbles stick to the surface and make more pits or dimples.

Do you have any suggestion of good electropolishing solution and condition for Cu especially for pit free surface?

Thank you very much.

Jae Wook Shin
Student - Providence, Rhode Island, USA



2007

Q. I have made the apparatus but stuck with what voltage range I should use. The electrolyte is phosphoric acid, cathode of copper plate(22 * 10 mm), anode is copper(10 * 11 mm), distance between the electrodes is about 2 cm. What voltage range should I use and for what time?

Jwala Kumar
student - Jamshedpur, Jharkhand, India



To minimize your searching efforts and to offer multiple viewpoints, we've combined some threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



How to electropolish copper

May 12, 2009

Q. Dear sir,
I'm making an electropolisher. Can you give me plans, and can you tell what kind of acids are required?
for POLISH BY CU

ABBAS SHARGH
TEACHER - NISHABUR, IRAN

May 12, 2009

A. Hi, Abbas. Phosphoric acid is probably the most commonly used acid for electropolishing copper. But electropolishing is too complicated to explain in a single paragraph. You can try to glean the info you need from this posting, but it would probably be best to get hold of a copy of the Electroplating Engineering Handbook, which has an excellent chapter on electropolishing. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



April 19, 2015 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I would like to electropolish copper rods to mirror finish. Is it possible?

Abhishek Jainn
Buyer - Delhi, INDIA


June 2015

A. Hi Abhishek. It's certainly possible to electropolish copper, and we have appended your inquiry to a thread dealing with the subject. But electropolishing is rarely a one-step process to get you from raw copper to mirror finished copper, if that is what you are seeking. It's more a way to get from a polished surface to a surface with no microscopic asperities or "tooth".

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



September 9, 2015

Q. What are the reactions taking place at the anode, cathode and in electrolyte solution during electro polishing of Cu in ortho-phosphoric acid. Can anyone help me.

Sudip Nath
- Indore, India


September 2015

A. Hello Sudip. Ken Vlach's response already referred you to an on-line paper that exactly answers your questions. Good luck! Readers: please respect people's efforts by reading the page before asking people to re-post what they've already posted :-)

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



September 21, 2015

Q. Hi.

I have faced a problem while electropolishing copper in 85% orthophosphoric acid. I use an adjustable 30 V- 50 Amps rectifier in a bath containing the working solution and a mesh of stainless steel which holds my specimens. Prior to introducing the pats into the bath, I remove oxides by using HNO3. While electropolishing, the copper surface gradually turns dark; a kind of very adherent black smut which is quite hard to be removed. I have to polish it with very coarse steel wool or any other grit. But after mechanical, time-consuming step, the surface is shiny and the lustre becomes acceptable. Does anyone have any suggestion how can I get rid of the last exhausting step? Or any suggestion how can I dissolve away this black smut?

THANKS

Aref Daneshfar
electropolishing - Isfahan, Iran


October 16, 2015

A. You might try some ferric chloride.

dave wichern
Dave Wichern
Consultant - The Bronx, New York


Electropolishing a brazed stainless 304L/copper 101 part in same bath?

August 3, 2018

Q. My situation: I am looking to polish/clean a part for UHV use. The part is used and is unable to be separated as the copper and stainless are brazed together with a gold/copper alloy. The part is 90 ss/ 10 cu. Is there an electropolishing bath suitable for both of these metals being polished together?

Chris Host
- cherry hill, New Jersey


August 7, 2018

Your Q, A, or Comment:

The common phosphoric/sulfuric electrpolishing bath will do a fine job on the stainless and will smooth and brighten the copper somewhat. You'll need to do some experimentation with times, temperatures and current densities.

But why electropolish? Certainly there are relatively simple cleaning methods for UHV use, no?

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina


August 8, 2018

Q. At 150kV high points will arc.

Christian Masullo [returning]
Host labs LLC - cherry hill



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