Method for firing copper paste

• US 10,433,427 B2
• Filed: 06/02/2015
• Issued: 10/01/2019
• Est. Priority Date: 06/16/2014
• Status: Active Grant

• Current Assignee: Material Concept, Inc. (JX Metals Corp)
• Original Assignee: Material Concept, Inc. (JX Metals Corp)
• Inventors: Koike, Junichi, Sutou, Yuji, Ando, Daisuke
• Primary Examiner(s): Penny, Tabatha L
• Application Number:
  US15/319,549
• Publication Number:
  US 20170135221A1
• Time in Patent Office: 1,582 Days
• Field of Search: 4273761
• CPC Class Codes: B05D 3/02 by baking B05D3/04 takes precedence
• CPC Class Codes: B05D 3/04 by exposure to gases
• CPC Class Codes: B22F 1/065 Spherical particles
• CPC Class Codes: B22F 1/103 containing an organic binding agent comprising a mixture of, or obtained by reaction of, two or more components other than a solvent or a lubricating agent
• CPC Class Codes: B22F 2201/01 Reducing atmosphere
• CPC Class Codes: B22F 2201/013 Hydrogen
• CPC Class Codes: B22F 2201/02 Nitrogen
• CPC Class Codes: B22F 2201/03 Oxygen
• CPC Class Codes: B22F 2998/10 Processes characterised by the sequence of their steps
• CPC Class Codes: B22F 2999/00 Aspects linked to processes or compositions used in powder metallurgy
• CPC Class Codes: B22F 3/10 Sintering only
• CPC Class Codes: B22F 3/1007 Atmosphere B22F3/1021 takes precedence
• CPC Class Codes: B22F 3/1017 Multiple heating or additional steps B22F3/101 takes precedence
• CPC Class Codes: H01B 1/00 Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
• CPC Class Codes: H01B 1/22 the conductive material comprising metals or alloys
• CPC Class Codes: H01B 13/00 Apparatus or processes specially adapted for manufacturing conductors or cables
• CPC Class Codes: H01B 5/02 Single bars, rods, wires, or strips
• CPC Class Codes: H01B 5/14 comprising conductive layers or films on insulating-supports
• CPC Class Codes: H01L 21/4867 Applying pastes or inks, e.g. screen printing H01L21/486 takes precedence
• CPC Class Codes: H05K 2203/1157 Using means for chemical reduction
• CPC Class Codes: H05K 2203/1476 : Same or similar kind of process performed in phases, e.g. coarse patterning followed by fine patterning
• CPC Class Codes: H05K 3/1291 : Firing or sintering at relative high temperatures for patterns on inorganic boards, e.g. co-firing of circuits on green ceramic sheets

Abstract

To provide a method for firing a copper paste, which improves sinterability of copper particles for the purpose of forming a copper wiring line that is decreased in the electrical conductivity. A method for firing a copper paste, which comprises: an application step wherein a copper paste is applied over a substrate; a first heating step wherein the substrate is heated in a nitrogen gas atmosphere containing from 500 ppm to 2,000 ppm (inclusive) of an oxidizing gas in terms of volume ratio after the application step, thereby oxidizing and sintering copper particles in the copper paste; and a second heating step wherein the substrate is heated in a nitrogen gas atmosphere containing 1% or more of a reducing gas in terms of volume ratio after the first heating step, thereby reducing the oxidized and sintered copper oxide.

Claims

1. A method for firing a copper paste, the method comprising:

an application step of applying a copper paste to a substrate, the copper paste comprising copper particles, a binder resin, and a solvent;

after the application step, a first heating step of heating the substrate at 350°

C. or more and 500°

C. or less in a nitrogen gas atmosphere containing 500 ppm or more and 2000 ppm or less of oxidizing gas in a volume ratio, and oxidizing and sintering the copper particles in the copper paste; and

after the first heating step, a second heating step of heating the substrate at 400°

C. or more and 550°

C. or less in a nitrogen gas atmosphere containing 1% or more reducing gas in a volume ratio, and reducing the oxidized and sintered copper oxide,

wherein a mass percent of the binder resin in an organic vehicle contained in the copper paste is more than 0.05% and less than 17.0%,

wherein the binder resin is one or more selected from a group consisting of cellulose resin, acrylic resin, butyral resin, alkyd resin, epoxy resin and phenol resin,

wherein the copper particles in the copper paste are oxidized by oxidation in the first heating step, and cuprous oxide is formed in a continuous shape so as to cover the copper particle surface, and

wherein the oxide of copper particles formed by the first heating step includes cuprous oxide and cupric oxide, and heating is carried out such that an amount of the cuprous oxide is larger than an amount of the cupric oxide,

wherein an electrical resistivity of a copper wiring obtained after the second heating step is 6 μ

Ω

cm or less.

2. The firing method according to claim 1, wherein the first and second heating steps maintain the gas atmosphere by allowing gas to continuously flow in a firing furnace.

3. The firing method according to claim 2, wherein a flow rate of the gas which is allowed to continuously flow is 0.05 liter/min or more and 0.5 liter/min or less with respect to a volume of the firing furnace, 1×

10<sup>−

6</sup> m³.