Titanium nitride removal method

Abstract: A method for removing nitride coatings from metal tooling and mold surfaces without damaging the underlying base metal includes placing the nitride coated metal surface into a plasma reactor and subjecting it to a gaseous plasma comprising a reactive fluorine species. The reactive fluorine species may be derived from one or more of many well known gases. An optional step of cleaning the nitride coating is recommended.

Description: Background of the Invention This invention relates, in general, to a method for removing nitride coatings from metal surfaces, and more particularly to a method of removing nitride coatings from metal surfaces employing a gaseous plasma comprising a reactive fluorine species. Metal tooling and mold surfaces are commonly coated for protection, to improve the wear characteristics and to better interact with the materials that the metal surface comes in contact with. Metal tooling and mold surfaces commonly employ chromium coatings for these reasons. However, once the chromium coating starts to wear through, it is extremely difficult to remove so that the metal tooling and mold surfaces may be recoated. One method of removing chromium coatings is reverse plating. However, this will often damage the underlying base metal, especially if the underlying base metal contains chromium itself. Another method used for removing chromium coatings is a wet chemical etch. Wet chemical etches often do not etch uniformly and therefore, the etch may also damage the underlying base metal. When the underlying base metal is damaged, the metal tooling or mold surface often will need to be reworked or will be rendered non-usable. Another coating commonly used with metal tooling and molds is titanium nitride. In addition to improving wear characteristics and increasing metal tooling or mold lifetime, titanium nitride has excellent lubricity and is excellent in conjunction with plastics. However, titanium nitride is also difficult to remove from metal tooling and mold surfaces without damaging the underlying base metal. Various removal methods include wet chemical etching which encounters the same problems with titanium nitride as discussed above with chromium. Also employed is media blast removal. Again, this results in an uneven removal of the titanium nitride and possible damage to the underlying base metal. Japanese Patent Application JP 870028727 having Publication Number JP 63196039 and published on 15th August 1988, teaches a plasma etching method useful in the fabrication of semiconductor devices. This application teaches plasma etching through a contact window to expose a portion of aluminium metallization. A titanium nitride layer is initially disposed on the aluminium metallization and is etched. The titanium nitride layer is plasma etched by including a small quantity of sulphur fluoride reaction gas in a hydrocarbon reaction gas containing fluoric atoms to be used for plasma etching of dielectric layers. This allows the etching rate of the titanium nitride layer to be sharply increased without impairing the etching rate of a dielectric layer. United States Patent 4, 786, 352 issued to David W Benzing on November 22, 1988, teaches an apparatus and method for the in situ cleaning of the interior surfaces of a processing chamber and/or tooling or substrates disposed within the chamber. This patent states that the apparatus and method is most effective in cleaning deposits of silicon dioxide, silicon nitride, organic compounds and other dielectric compounds as well as many types of contaminants. The process disclosed teaches etching such deposits using a gaseous plasma containing a fluorine species. SUMMARY OF THE INVENTION In accordance with the present invention there is provided a method for removing titanium nitride coatings from metal tooling and mold surfaces comprising the steps of: providing a metal tooling or mold surface having a titanium nitride coating disposed thereon; cleaning the titanium nitride coating disposed on the metal tooling or mold surface; placing said titanium nitride coated metal tooling or mold surface into a plasma reactor; and exposing said titanium nitride coated metal tooling or mold surface to a gaseous plasma comprising a reactive fluorine species, whereby the titanium nitride coating is completely removed to expose the metal tooling or mold surface. Detailed Description of the Invention Typically, it is desirable to coat metal tooling and mold surfaces with titanium nitride to protect the base metal, improve the wear characteristics and increase lubricity. Titanium nitride coatings work extremely well on mold plates for use in encapsulating semiconductor devices as well as other types of tools and molds. However, titanium nitride coatings have been extremely difficult to remove from the base metal surfaces without damaging the underlying metal once the nitride surfaces have begun to wear. To remove titanium nitride coatings from metal tooling and mold surfaces without damaging the underlying metal, it is desirable to clean the nitride coating. One way in which this may be done includes first cleaning the nitride coating with acetone followed by an isopropyl alcohol clean. The nitride coating is then subjected to a methanol clean which leaves no residue on the nitride coating. Finally, the nitride coated metal surface is placed into a plasma reactor and subjected to a gaseous plasma consisting of pure oxygen. It should be understood that impurities on the nitride coating will hinder the removal of the nitride coating itself. Once the titanium nitride coating has been cleaned, it is exposed to a gaseous plasma comprising a reactive fluorine species. The reactive fluorine species may be derived from one or more of the gases including CF₄, CHF₃, C₂F₆, SF₆ and other fluorine containing gases. The gaseous plasma may be derived from a single fluorine containing gas, a mixture of fluorine containing gases or a mixture of fluorine containing gases and non-fluorine containing gases. The method for removing nitride coatings from metal tooling and mold surfaces has been shown to work best in a plasma reactor having a barrel configured chamber wherein the chamber pressure is in the range of 66.66 to 666.61 Pa (0.5 to 5.0 torr), the chamber temperature is in the range of 313 to 373 kelvin (40 to 100 degrees centigrade) and the power applied to the plasma reactor is in the range of 100 to 1000 watts. A specific example of a method for removing titanium nitride coatings from metal tooling and mold surfaces includes initially cleaning the titanium nitride coating in the manner disclosed above. Once the titanium nitride coating has been cleaned, the titanium nitride coated metal tooling or mold surface is placed into a plasma reactor having a barrel configured chamber such as a Tegal 965 plasma etcher. The chamber pressure is set to approximately 133.32 Pa (1.0 torr), the chamber temperature is approximately 353 kelvin (80 degrees centigrade) and the power applied to the plasma etcher is approximately 400 watts. The gas from which the plasma is derived is a mixture comprising 91.5% CF₄ and 8.5% O2. It should be understood that the reaction time is dependent upon the amount of the titanium nitride coating disposed on the metal tooling or mold surface. The plasma containing the reactive fluorine species will not damage the underlying metal tooling or mold surface if it is removed within a reasonable amount of time following the complete removal of the titanium nitride coating.

Claims: A method for removing titanium nitride coatings from metal tooling and mold surfaces comprising the steps of: providing a metal tooling or mold surface having a titanium nitride coating disposed thereon; cleaning the titanium nitride coating disposed on the metal tooling or mold surface; placing said titanium nitride coated metal tooling or mold surface into a plasma reactor; and exposing said titanium nitride coated metal tooling or mold surface to a gaseous plasma comprising a reactive fluorine species, whereby the titanium nitride coating is completely removed to expose the metal tooling or mold surface. The method of claim 1 wherein the cleaning step comprises the steps of: cleaning the nitride coating with acetone; cleaning said nitride coating with isopropyl alcohol; cleaning said nitride coating with methanol; and subjecting said nitride coating to a gaseous plasma consisting of oxygen. The method of claim 1 or 2 wherein the exposing step includes exposing the nitride coated metal surface to a reactive fluorine species derived from one or more of the gases in the group comprising CF₄, CHF₃, C₂F₆ amd SF₆. The method of claim 1, 2 or 3 wherein the placing step includes placing the nitride coated metal surface into a plasma reactor having a barrel configured chamber wherein the chamber pressure is in the range of 66.66 to 666.61 Pa (0.5 to 5.0 torr), the chamber temperature is in the range of 313 to 373 Kelvin (40 to 100 degrees centigrade) and the power is in the range of 100 to 1000 watts. The method of claim 4 wherein the placing step includes placing the nitride coated metal surface into a plasma reactor having a barrel configured chamber wherein the chamber pressure is approximately 133.32 Pa (1.0 torr), the chamber temperature is approximately 353 Kelvin (80 degrees centigrade) and the power is approximately 400 watts.

Inventors: CARNEY FRANCIS JOSEPH, CARNEY GEORGE FRANCIS, KNAPP JAMES HOWARD, CARNEY, FRANCIS JOSEPH, CARNEY, GEORGE FRANCIS, KNAPP, JAMES HOWARD
Applicants: MOTOROLA INC, MOTOROLA INC.
Application year: 1990
Main classification: C23G5
IPC codes: C23F4, C23C16, C23G5, B23K10