Deposition of a coating on an interconnect for solid oxide cell stacks

Abstract

A method for coating an interconnect for a solid oxide cell (SOC) stack comprises providing an interconnect substrate comprising Cr and Fe, coating the interconnect substrate with a first metallic layer by electrodeposition, coating the resulting structure with a second layer of metallic cobalt by electrodeposition and coating the resulting structure with a layer of metallic copper by ion-exchange plating. This way, a metallic copper-cobalt coating is formed on the interconnect.

Claims

1. A method for coating an interconnect for a solid oxide cell (SOC) stack, said method comprising: providing an interconnect substrate comprising Cr and Fe, coating the interconnect substrate with a first metallic layer by electrodeposition, coating a second layer of metallic cobalt over the first metallic layer by electrodeposition, and coating a layer of metallic copper over the second layer of metallic cobalt by ion-exchange plating, thereby forming a metallic copper-cobalt coating on the interconnect.

2. The method according to claim 1, wherein the electrodeposition of the first metallic layer and the second metallic Co layer comprises electroplating.

3. The method according to claim 1, wherein the first metallic layer is either cobalt or nickel.

4. The method according to claim 1, wherein the thickness of the first metallic layer is between 10 and 2000 nm.

5. The method according to claim 1, wherein the thickness of the second metallic Co layer is between 0.5 and 10 m.

6. The method according to claim 1, wherein a different electrolyte is used for the electrodeposition of the first metallic layer and for the electrodeposition of the second metallic Co layer.

7. The method according to claim 1, wherein the ion-exchange plating is carried out in an acidic copper electrolyte.

8. The method according to claim 7, wherein the acidic copper electrolyte comprises 160-230 g/liter CuSO.sub.4.5H.sub.2O, 40-100 g/liter H.sub.2SO.sub.4, optionally with minor addition of sodium chloride in the range of 30-150 mg/liter.

9. The method according to claim 1, where the ion-exchange plating is self-limiting.

10. The method according to claim 9, where the thickness of the metallic copper layer coated over the second layer of metallic cobalt is between 10 and 1000 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described further in the examples which follow below. The examples refer to the Figures, where

(2) FIG. 1 is a process diagram of the prior art method for cobalt electrodeposition,

(3) FIG. 2 is a process diagram of the prior art method for cobalt and copper electrodeposition,

(4) FIG. 3 is a process diagram of electrodeposition and ion-exchange plating of copper according to the present invention, and

(5) FIGS. 4a and 4b show an energy dispersive X-ray spectroscopy (EDX) analysis of a cobalt coating deposited by electroplating according to the invention.

EXAMPLES

Example 1

(6) Co Deposition by Electroplating

(7) FIG. 1 presents a schematic process diagram of the method for the electrodeposition of cobalt that can be considered prior art. An interconnect substrate comprising Cr and Fe 101 is first covered with a strike layer of nickel or cobalt 102. This step is explained as A in FIG. 1. The electrodeposition of the first metallic layer can be done for example by using the Woods process. Other formulations such as the sulfamate strike can also be used for this purpose. The current densities used in the deposition of the first layer should be in the range of 1-10 A/dm.sup.2. The second metallic layer of Co 103 is electrodeposited from a Watts type or another acidic electrolyte (such as chloride, sulfate, sulfamate, ammonium sulfate, fluoroborate and mixtures thereof) with a current density ranging from 0.5 to 5 A/dm.sup.2. This step is explained as B in FIG. 1. The thickness of the second metallic Co layer 103 is between 0.5 m and 10 m, preferably between 1 m and 6 m. EDX (energy dispersive X-ray spectroscopy) analysis reveals that the composition of such a coating is 100% metallic Co as seen in FIGS. 4a and 4b.

Example 2

(8) CoCu deposition by electroplating from alkaline solutions FIG. 2 presents a schematic process diagram of the method for the electrodeposition of cobalt and copper that can be considered prior art. The deposition proceeds according to the method described in Example 1, except that after the electrodeposition of the second metallic Co layer 103, a layer of metallic Cu 104 is deposited by electrodeposition from an alkaline cyanide-based electrolyte solution. This step is explained as C in FIG. 2. The current densities used in the deposition of the Cu layer 104 range from 1 to 6 A/dm.sup.2. The growth of the Cu layer from alkaline cyanide-based electrolyte solutions thus requires external electric field to be applied to the galvanic cell and is not self-limiting in nature.

Example 3

(9) FIG. 3 presents a schematic process diagram of the present invention for electrodeposition of cobalt and ion-exchange plating of copper. An interconnect substrate comprising Cr and Fe 101 is first covered with a strike layer of nickel or cobalt 102. This step is explained as A in FIG. 3. The electrodeposition of the first metallic layer can be done for example by using the Woods process or a sulfamate strike. The current densities used in the deposition of the first layer should be in the range of 1-10 A/dm.sup.2. The second metallic layer of Co 103 is electrodeposited from an acidic electrolyte (such as chloride, sulfate, sulfamate, ammonium sulfate, fluoroborate and mixtures thereof) with a current density ranging from 0.5 to 5 A/dm.sup.2. This step is explained as B in FIG. 3. The thickness of the second metallic Co layer 103 is between 0.5 m and 10 m, preferably between 1 m and 6 m. A third metallic layer of Cu 105 is then deposited onto resulting structure by ion-exchange plating from an acidic solution comprising copper ions. This step is explained as D in FIG. 3. One example of an acidic solution of copper ions is the acid sulfate copper electrolyte, comprising 160-230 g/liter CuSO.sub.4.5H.sub.2O and 40-100 g/liter H.sub.2SO.sub.4, optionally with minor addition of sodium chloride in the range of 30-150 mg/liter. However, the ion exchange reaction will also occur from other types of electrolytes containing Cu.sup.2+ ions in an acidic pH. The ion exchange reaction between copper and cobalt will occur as long as the pH of the solution is low enough to remove the passive cobalt oxide layer on the surface which will initiate the ion exchange reaction. The growth of the Cu layer from acidic electrolyte solutions does not require an external electric field to be applied during deposition. Furthermore, the growth of Cu is self-limiting in nature, resulting in a layer with a thickness of approximately 100 nm to 200 nm. X-ray fluorescence (XRF) measurements of the copper layer as deposited are shown in Table 3 below. In the table, POM is point of measurement and Row is the number of the measured point.

(10) TABLE-US-00003 TABLE 3 XRF measurements of deposited copper layers POM1: m Cu POM2: m Co Row Mean Row Mean 1 0.1 1 5.0 2 0.2 2 3.0 3 0.2 3 2.0 4 0.2 4 2.0 5 0.2 5 2.1 6 0.1 6 3.0 7 0.1 7 4.8 8 0.1 8 4.8 9 0.1 9 1.9 10 0.1 10 1.8 11 0.2 11 3.1 12 0.1 12 5.0

(11) The analysis of the final coated interconnect reveals that the top layer comprises Cu. As a result of the ion-exchange plating of Cu, the surface of the interconnect changes colour from white greyish to the characteristic bronze-brown colour of copper metal.