Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/055—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 20% but less than 30%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B23/00—Obtaining nickel or cobalt
  • C22B23/06—Refining
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/02—Making non-ferrous alloys by melting
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/053—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 30% but less than 40%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/056—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 10% but less than 20%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/058—Alloys based on nickel or cobalt based on nickel with chromium without Mo and W
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
  • C23C14/34—Sputtering
  • C23C14/3407—Cathode assembly for sputtering apparatus, e.g. Target
  • C23C14/3414—Metallurgical or chemical aspects of target preparation, e.g. casting, powder metallurgy

Definitions

• the present invention relates to a method for reducing the oxygen content and oxide inclusion content in cobalt to produce a low-oxygen cobalt sputter target having a low oxide inclusion content, and to the sputter target assemblies made therefrom.
• Cathodic sputtering is widely used for depositing thin layers, or films, of materials from sputter targets onto desired substrates.
• a cathode assembly including the sputter target is placed together with an anode in a chamber filled with an inert gas, preferably argon.
• the desired substrate is positioned in the chamber near the anode with a receiving surface oriented normally to a path between the cathode assembly and the anode.
• a high voltage electric field is applied across the cathode assembly and the anode.
• Electrons ejected from the cathode assembly ionize the inert gas.
• the electrical field then propels positively charged ions of the inert gas against a sputtering surface of the sputter target. Material dislodged from the sputter target by the ion bombardment traverses the chamber and deposits to form the thin layer, or film, on the receiving surface of the substrate.
• cobalt (Co) sputter targets sputter deposition of cobalt thin films is a crucial step in forming thin and uniform cobalt suicide films.
• a typical CoSi 2 salicide (a self-aligned suicide) process involves sputter deposition of Co thin films on silicon wafers, followed by rapid thermal processing (RTP) to form CoSi at intermediate temperatures, and sequentially to form CoSi 2 at elevated temperatures.
• RTP rapid thermal processing
• cobalt suicides have low resistivity, excellent chemical stability, inertness to nitrogen and low formation temperature and are considered an alternative to TiSi 2 for use as a contact in ultra-large scale integration (ULSi).
• Cobalt ingots from which cobalt targets typically are made, contain a certain amount of oxide inclusions such as cobalt oxides, cobalt-titanium oxides, etc. These oxide inclusions, or metal defects, cause arcing during sputtering deposition and create metal particles on the substrate (i.e. silicon wafers) onto which the cobalt is sputtered thereby significantly reducing the yields of the cobalt metallization.
• oxide inclusions such as cobalt oxides, cobalt-titanium oxides, etc.
• wppm weight parts per million
• the present invention provides a method to reduce the oxygen content and the oxide inclusion content in cobalt to produce a low-oxygen cobalt sputter target having a low oxide inclusion content, and to the sputter target assemblies produced therefrom.
• the method for reducing the oxygen content and the oxide inclusion content in cobalt are separate processes which may be combined in successive order to produce a low-oxygen cobalt sputter target having a low oxide inclusion content.
• the reduction in oxygen content preferably is performed prior to reducing the oxide inclusion content. Accordingly, the artisan will appreciate that one process can be performed without the other depending upon whether a reduction in oxygen or oxide inclusions is preferred in a desired cobalt sputter target.
• Reducing the oxygen content and oxide inclusion content in cobalt to produce low- oxygen cobalt sputter targets having low oxide inclusion contents reduces the arcing and the metal defects found with conventional high-oxygen cobalt sputter targets during sputtering.
• the method for reducing the oxygen content in cobalt to produce a low-oxygen cobalt sputter target includes the steps of providing cobalt (eg. electrolytic deposit cobalt melting stock).
• the cobalt stock can be either low (eg. 3N5) or high-purity cobalt (eg. 4N5, 5N5, and 6N).
• a degassing agent, preferably carbon, more preferably carbon graphite powder, is mixed with the cobalt wherein the carbon, preferably, is present in an amount of 50-150 wppm of the mixture. The mixture is heated and degassed.
• the heating occurs above the melting point of the cobalt, preferably about 50 to 400 degrees F above the melting point, to form a melted cobalt mixture wherein the carbon and initial oxygen content react to produce a second lower oxygen content. Without the addition of the carbon, the oxygen content would increase.
• the solidified cobalt now is suitable for shaping into a desired sputter target or is ready for oxide inclusion reduction.
• the oxide inclusion reduction method involves reducing oxide inclusions at a certain oxygen level, preferably no greater than 1000 wppm, by using certain fabrication and heat treatment steps. These steps include first providing cobalt having an initial oxide inclusion content, an initial oxygen content, and defining a first thickness.
• the cobalt can be either low (eg. 3N5) or high-purity cobalt (eg. 4N5, 5N5, and 6N). Accordingly, the cobalt may comprise the solidified cobalt from the oxygen reduction method.
• the cobalt is heated at a temperature below its melting point, preferably at about 2000 degrees F.
• the cobalt then is hot pressed such that the pressure reduces the first thickness to form a hot pressed cobalt defining a second thickness.
• the hot pressed cobalt then is heated at a temperature below the melting point thereof, preferably at about 1800 degrees F.
• the cobalt is hot rolled such that the rolling further reduces the second thickness to form a hot rolled cobalt defining a third thickness.
• the oxide inclusions are broken into extremely small particles. These particles then dissociate to cobalt and oxygen.
• the dissociated oxygen is dissolved by cobalt. Accordingly, the hot rolled cobalt contains a second oxide inclusion content lower than the initial oxide inclusion content. The rolled cobalt now is suitable for shaping into a desired sputter target.
• one object of the invention is to provide a method for reducing the oxygen content and the oxide inclusion content in cobalt to produce low-oxygen cobalt sputter targets having low oxide inclusion contents.
• Another object of the invention is to reduce the arcing and metal defects associated with high-oxygen cobalt sputter targets during sputtering.
• Another object of the invention is to produce a sputter target assembly having a low-oxygen cobalt sputter target with a low oxide inclusion content.
• Fig. 1 is a graph showing arc counts during cobalt sputtering as a function of oxygen content in cobalt targets
• Fig. 2 is a graph showing the resultant oxygen and carbon contents in cobalt ingots as a function of added carbon powder
• the present invention relates to producing cobalt having a low- oxygen and a low oxide inclusion content for use as a sputter target thereby reducing the arcing and metal defects during sputtering commonly associated with high- oxygen cobalt sputter targets.
• the method for reducing the oxygen content and the oxide inclusion content in cobalt are separate processes which may be combined in successive order to produce a low-oxygen cobalt sputter target having a low oxide inclusion content.
• the reduction in oxygen content method preferably is performed prior to reducing the oxide inclusion content. Accordingly, the artisan will appreciate that one process may be performed without the other depending upon whether a reduction in oxygen or oxide inclusions is preferred.
• the method for reducing the oxygen content in cobalt to produce a low-oxygen cobalt sputter target includes the first step of providing cobalt (eg. electrolytic deposit cobalt melting stock).
• cobalt eg. electrolytic deposit cobalt melting stock.
• the cobalt stock can be either low (eg.
• High-purity cobalt eg. 4N5, 5N5, and 6N
• Low-purity cobalt stock can be purchased from Falcon Bridge, a Norwegian company, and the high-purity stock can be purchased from Japan Metals Chemicals (JMC) located in Japan.
• JMC Japan Metals Chemicals
• a degassing agent preferably carbon, more preferably carbon powder
• a high-purity carbon powder is most preferred to avoid contamination by impurities.
• One such type of high-purity carbon powder is HP 6N graphite powder which can be purchased from Alfa located in the USA.
• the mixing can be performed in a crucible, preferably made of zirconium oxide, wherein the carbon is present in a preferred amount of 50-150 wppm of the mixture, more preferably 50-100 wppm.
• the mixture is placed into a furnace and heated and degassed.
• the degassing is performed via vacuum with the vacuum having a pressure of about 5 x 10 -5 to 1 x 10 -4 Torr.
• the heating occurs above the melting point of the cobalt, preferably about 50 to 400 degrees F above the melting point, for about Vz hour to form a melted cobalt mixture wherein the carbon and initial oxygen content react to produce a second lower oxygen content.
• the oxygen in the molten cobalt reacts with the carbon particles to form CO 2 and CO gasses, which then become gas bubbles and eventually release from the molten cobalt into the vacuum chamber. Adding carbon significantly decreases the oxygen content. Accordingly, the resultant oxygen and carbon contents strongly depend on how much carbon is used.
• the oxygen content would increase considerably.
• the temperature in the furnace is reduced to about 50 degrees F above the melting point of the cobalt after the initial Vz hour. Then the melted cobalt mixture is poured into a mold while still under vacuum. The temperature of the mold is held below the melting point of the cobalt so that the cobalt can solidify. The melted mixture then cools in the mold for about 2 hours to produce a solidified cobalt having the lower oxygen content.
• Fig. 2 shows the resultant oxygen and carbon contents as a function of added carbon.
• the oxygen content varies from 170 to 410 wppm when there is no degassing agent (i.e. carbon) added.
• the resultant oxygen content in the cobalt ranges from 5 to 30 wppm, and the resultant carbon content in the cobalt ranges from less than 10 to 25 wpm.
• the amount of added carbon is > 150 wppm, there is too much remaining carbon in the cobalt material.
• the high level of remaining carbon also can cause problems during sputtering. Therefore, the optimum carbon addition is from 50 to 150 wppm.
• the solidified cobalt now is suitable for shaping into a desired sputter target or is ready for oxide inclusion reduction.
• this method involves reducing oxide inclusions at a certain oxygen level, preferably no greater than 1000 wppm, by using certain fabrication and heat treatment steps. These steps include providing cobalt having an initial oxide inclusion content, an initial oxygen content, and defining a first thickness.
• the cobalt can be either low (eg. 3N5) or high-purity cobalt (eg. 4N5, 5N5, and 6N) and may comprise the solidified cobalt produced from the above oxygen reduction method.
• the oxide inclusion content typically is measured using optical metallography and scanning electron microscope/energy dispersion spectrum (SEM/EDS).
• the cobalt is heated at a temperature below its melting point, preferably at about 2000 degrees F for about 2 hours.
• the cobalt then is hot pressed such that the pressure reduces the first thickness, preferably by about 50%, in about 1 minute to form a hot pressed cobalt defining a second thickness.
• the hot pressed cobalt then is heated at a temperature below the melting point thereof, preferably at about 1800 degrees F for about 1 hour.
• the cobalt is hot rolled in a roller at room temperature such that the rolling further reduces the second thickness, preferably by about 60-70%, to form a hot rolled cobalt defining a third thickness. Accordingly, at such temperatures and at the stress provided by the press and roller, the oxide inclusions are broken into extremely small particles. These particles then dissociate to cobalt and oxygen. Finally, the dissociated oxygen is dissolved by cobalt. Accordingly, the hot rolled cobalt contains a second oxide inclusion content lower than the initial oxide inclusion content. Notably, after fabrication, the oxide inclusions significantly decrease, if not disappear altogether. The rolled cobalt now is suitable for shaping into a desired sputter target.
• the low-oxygen and low oxide inclusion cobalt produced by the above processes are used as cobalt sputter targets to reduce the arcing and metal defects during sputtering deposition commonly associated with high-oxygen cobalt targets.
• These low-oxygen targets having low oxide inclusions are best used with metallic backing plates comprising copper, aluminum, and alloys thereof.
• the invention thereby is capable of producing sputtering targets comprising Co having less than about 170 wppm of oxygen therein.
• the targets include less than 100 wppm oxygen with amounts of less than 50 wppm oxygen being most preferred. (All pp calculations are based upon the total weight of the target).
• the cobalt/degassing agent admixture that is used in the disclosed process to form lowered oxide inclusion amounts is a Co/C admixture wherein C is present in an amount of about 1-150 wppm based on the weight of the admixture, preferably in an amount of about 50-150 wppm and most preferably about 50 - 100 wppm.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
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• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Physical Vapour Deposition (AREA)

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Citations (5)

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• 2001
  • 2001-08-03 WO PCT/US2001/024396 patent/WO2002012577A1/en active Application Filing
  • 2001-08-03 EP EP01963786A patent/EP1307600A4/de not_active Withdrawn
  • 2001-08-03 KR KR10-2003-7001516A patent/KR20030019645A/ko not_active Application Discontinuation

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