US-12617146-B1 - Atmospheric pressure plasma reduction of copper oxide to copper metal

US12617146B1US 12617146 B1US12617146 B1US 12617146B1US-12617146-B1

Abstract

Copper oxide films can be reduced to copper with an atmospheric pressure argon and hydrogen plasma at temperatures between 25 and 300° C. A 50-nm-thick CuO layer on a Cu-coated Si wafer, 200 mm in diameter, can be fully reduced by the plasma in 200 seconds at 200° C. The activation energy for the reaction can be approximately 3.7 kcal/mol. X-ray photoelectron spectroscopy can show the copper oxide reduced to metallic copper.

Inventors

Joyce Lee
Thomas Scott Williams
Robert F. Hicks

Assignees

SURFX TECHNOLOGIES LLC

Dates

Publication Date: 20260505
Application Date: 20220204

Claims (10)

1 . A method of producing an ionized gas plasma comprising: directing gas flow comprising an inert gas and hydrogen from an inlet through a flow path within a housing to an outlet for plasma comprising reactive hydrogen species; directing the gas flow within the housing between a powered electrode surface of a power electrode and a grounded electrode surface of a ground electrode, the grounded electrode surface closely spaced from the powered electrode surface; delivering radio frequency power coupled to the power electrode and the ground electrode from a power supply to ionize the gas flow and produce the plasma comprising the reactive hydrogen species from the hydrogen; and disposing a copper material within an enclosure near the outlet of the housing to receive the reactive hydrogen species; wherein copper oxide on the copper material is removed by reaction with the reactive hydrogen species to produce copper metal and water vapor.
2 . The method of claim 1 , wherein the outlet of the housing for plasma comprises a linear opening.
3 . The method of claim 2 , wherein the linear opening is at least as wide as the copper material and the copper material is passed at a constant speed relative to and contacting the plasma comprising the reactive hydrogen species.
4 . The method of claim 1 , further comprising translating the housing with the outlet for the plasma comprising the reactive hydrogen species relative to a surface of the copper material such that the entire surface of the copper material is uniformly treated with the reactive hydrogen species from the plasma.
5 . The method of claim 1 , wherein the radio frequency power is delivered at 13.56 or 27.12 MHz.
6 . The method of claim 1 , wherein the power supply includes an auto-tuning network that impedance matches the radio frequency power supply to the plasma to minimize reflected power.
7 . The method of claim 1 , wherein the hydrogen gas is added to the gas flow at a concentration between 0.1 to 5.0 volume % and a fraction of the hydrogen gas dissociates into atoms inside the plasma, and then flows out of the outlet.
8 . The method of claim 1 , wherein the inert gas is selected from the group consisting of argon and helium.
9 . The method of claim 1 , wherein the copper material is a lead frame strip.
10 . The method of claim 1 , wherein the copper material is used in bonding an integrated circuit to a package.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit under 35 U.S.C. § 119(e) of the following U.S. provisional patent application, which is incorporated by reference herein: U.S. Provisional Patent Application No. 63/145,944, filed Feb. 4, 2021, and entitled “ATMOSPHERIC PRESSURE PLASMA REDUCTION OF COPPER OXIDE TO COPPER METAL,” by Lee et al. This continuation-in-part application claims the benefit under 35 U.S.C. § 120 of the following co-pending and commonly-assigned U.S. utility patent application: U.S. patent application Ser. No. 17/016,951, filed Sep. 10, 2020, which application is a continuation of U.S. patent application Ser. No. 16/042,905, filed Jul. 23, 2018, which application is a continuation-in-part of U.S. patent application Ser. No. 15/196,292, filed Jun. 29, 2016, which application is a continuation-in-part of U.S. patent application Ser. No. 14/576,106, filed Dec. 18, 2014 (now U.S. Pat. No. 9,406,485, issued Aug. 2, 2016) and entitled “ARGON PLASMA APPARATUS AND METHODS,” by Cheng et al. which application claims the benefit of U.S. Provisional Patent Application No. 61/917,901, filed Dec. 18, 2013, and entitled “ARGON PLASMA APPARATUS AND METHODS”, by Cheng et al., which applications are all incorporated by reference herein. BACKGROUND OF THE INVENTION 1. Field of the Invention The invention is related to a plasma apparatus and methods of using the plasma apparatus for cleaning, surface activation, etching and deposition on electronic materials. Particularly, the invention is related to copper oxide films reduced to copper using an atmospheric pressure argon and hydrogen plasma. 2. Description of Related Art Ionized gas plasmas have found wide application in materials processing. Plasmas that are used in materials processing are generally weakly ionized, meaning that a small fraction of the molecules in the gas are charged. In addition to the ions, these plasmas contain reactive species that can clean, activate, etch and deposit thin films onto surfaces. The temperature in these weakly ionized gases is usually below 250° C., so that most thermally sensitive substrates are not damaged. The physics and chemistry of weakly ionized plasmas are described in several textbooks. See for example, Lieberman and Lichtenberg, “Principles of Plasma Discharges and Materials Processing”. (John Wiley & Sons, Inc., New York, 1994), and Raizer, Y. P., “Gas Discharge Physics”, (Springer-Verlag, Berlin (1991). According to the literature, weakly ionized plasmas are generated in vacuum at pressures between 0.001 and 1.0 Torr (see Lieberman and Lichtenberg (1994)). Electrical power is applied across two electrodes to break the gas down and ionize it. The electricity may be provided as a direct current (DC), alternating current (AC), radio frequency (RF), or microwave (MW) source. The electrode may be constructed to provide either capacitive or inductive coupling to strike and maintain the plasma. In the former case, two conducting electrodes are placed inside the vacuum chamber filled with a small amount of gas. One of the electrodes is powered, or biased, by the RF generator, while the other one is grounded. In the latter case, the RF power is supplied through an antenna that is wrapped in a coil around the insulating walls of the chamber. The oscillating electric field from the coil penetrates into the gas inducing ionization. Over the past fifteen years, atmospheric pressure plasmas have been developed as an alternative to vacuum plasmas. These plasmas can treat an object of any size and shape, since they do not have to be loaded into a vacuum chamber. This can significantly reduce the cost of the process. A number of different atmospheric pressure plasma devices have been developed (Schutze, et. al., “The atmospheric-pressure plasma jet: A review and comparison to other plasma sources”, IEEE Trans. Plasma Sci. 26, 1685-1694 (1998). These plasmas are governed by how the ionization process is controlled. At atmospheric pressure, the gas density is so high that the ionization reaction can easily run away and generate a high temperature are, which is not useful for materials processing. There are three common types of atmospheric pressure plasmas used to treat materials. These include a dielectric barrier discharge (DBD), a torch, and a radio-frequency, noble gas discharge. The DBD has long been employed to treat rolls of plastic film whereby the material is continuously passed between the electrodes. In some instances, the DBD may be deployed as a downstream device, so that 3-D objects can be treated with the reactive gasses that flow out from between the electrodes. The torch and the RF noble-gas discharge are strictly downstream plasmas. Here, the ions and electrons are confined to the gap between the electrodes, and the substrate is exposed to a beam of neutral reactive species that exits from the source. A robot is used to scan the plasma beam over the substrate surface, which is p