Process for forming an electrically conductive structure on a substrate
View Patent ↗A conductive paste composition contains a source of an electrically conductive metal, an alkaline-earth-metal boron tellurium oxide, and an organic vehicle. An article such as a high-efficiency photovoltaic cell is formed by a process of deposition of the paste composition on a semiconductor device substrate (e.g., by screen printing) and firing the paste to remove the organic vehicle and sinter the metal and establish electrical contact between it and the device.
1. A process for forming an electrically conductive structure on a substrate, the process comprising:
(a) providing a substrate having a first major surface;
(b) applying a paste composition onto a preselected portion of the first major surface, wherein the paste composition comprises:
i) a source of electrically conductive metal,
ii) an alkaline-earth-metal boron tellurium oxide wherein the alkaline earth metal, boron, and tellurium cations together comprise at least 70% of the cations present in the oxide, and
iii) an organic vehicle in which the source of electrically conductive metal and the alkaline-earth-metal boron tellurium oxide are dispersed; and
(c) firing the substrate and paste composition thereon, whereby the electrically conductive structure is formed on the substrate.
2. The process of claim 1 , wherein the alkaline-earth-metal boron tellurium oxide comprises:
25 to 72 cation % of Te;
5 to 45 cation % of B;
0 to 30 cation % of Ca;
0 to 30 cation % of Sr;
0 to 30 cation % of Ba;
0 to 10 cation % of Mg;
0 to 25 cation % of Li;
0 to 25 cation % of Na;
0 to 10 cation % of Si;
0 to 12 cation % of Zn; and
0 to 10 cation % of Ti, plus incidental impurities,
and wherein the total content of Ba+Sr+Ca cations is at least 5 cation %.
3. The process of claim 1 , wherein the alkaline-earth-metal boron tellurium oxide further comprises at least one oxide selected from the group consisting of oxides of Al, Li, Na, K, Rb, Cs, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Si, Mo, Hf, Ag, Ga, Ge, In, Sn, Sb, Se, Ru, Bi, P, Y, La and the other lanthanide elements, and mixtures thereof.
4. The process of claim 1 , wherein the source of electrically conductive metal comprises silver powder.
5. The process of claim 1 , wherein the paste composition is lead-free.
6. The process of claim 1 , wherein the substrate comprises an insulating layer present on at least the first major surface and the paste composition is applied onto the insulating layer of the first major surface, and wherein the insulating layer is at least one layer comprised of aluminum oxide, titanium oxide, silicon nitride, SiN x :H, silicon oxide, or silicon oxide/titanium oxide.
7. The process of claim 6 , wherein the insulating layer is penetrated and the electrically conductive metal is sintered during the firing, whereby an electrical contact is formed between the electrically conductive metal and the substrate.
8. An article comprising a substrate and an electrically conductive structure thereon, the article having been formed by the process of claim 7 .
9. The article of claim 8 , wherein the substrate is a silicon wafer.
10. The article of claim 9 , wherein the article comprises a semiconductor device.
11. The article of claim 10 , wherein the article comprises a photovoltaic cell.