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Disclosed is a semiconductor device wherein an insulation layer has a via opening with an aluminum layer in the via opening and in contact with the last wiring layer of the device. There is a barrier layer on the aluminum layer followed by a copper plug which fills the via opening. Also disclosed is

Disclosed is a semiconductor device wherein an insulation layer has a via opening with an aluminum layer in the via opening and in contact with the last wiring layer of the device. There is a barrier layer on the aluminum layer followed by a copper plug which fills the via opening. Also disclosed is a process for making the semiconductor device.

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1. A semiconductor device comprising: a semiconductor substrate having a plurality of wiring layers wherein a last wiring level comprises a conductive material;an insulation layer formed on the last wiring layer, the insulation layer having a via opening formed therein to expose the conductive mater

1. A semiconductor device comprising: a semiconductor substrate having a plurality of wiring layers wherein a last wiring level comprises a conductive material;an insulation layer formed on the last wiring layer, the insulation layer having a via opening formed therein to expose the conductive material in the last wiring layer, the via opening extending to a full thickness of the insulation layer;an aluminum layer in the via opening extending to a height above the full thickness of the insulation layer and the entire via opening, the aluminum layer having a wall and a bottom;a barrier layer formed on the aluminum layer, the barrier layer having a wall and a bottom coextensive with the aluminum layer wall and bottom; anda copper plug formed on the barrier layer and in contact with all of the barrier layer wall and bottom and filling the entire via opening, the copper plug extending to the height above the full thickness of the insulation layer. 2. The semiconductor device of claim 1 wherein the aluminum layer extends over the insulation layer. 3. The semiconductor device of claim 1 wherein the aluminum layer is in contact with the conductive material in the last wiring layer. 4. The semiconductor device of claim 1 wherein the aluminum layer is in direct contact with the conductive material in the last wiring layer. 5. The semiconductor device of claim 1 further comprising a cap layer formed over the copper plug. 6. The semiconductor device of claim 5 wherein the barrier layer has an edge portion between the aluminum layer and the copper plug and the cap layer is formed only over the edge portion of the barrier layer and the copper plug. 7. The semiconductor device of claim 5 wherein the cap layer is selected from the group consisting of cobalt, cobalt/tungsten/phosphorus, and cobalt alloys. 8. The semiconductor device of claim 1 wherein the barrier layer is selected from the group consisting of tantalum/tantalum nitride, titanium, titanium tungsten, titanium nitride and tungsten nitride. 9. The semiconductor device of claim 1 further comprising a dielectric layer formed on the insulation layer and having an opening aligned with the copper plug. 10. The semiconductor device of claim 9 further comprising ball limiting metallurgy formed on the dielectric layer and in the opening. 11. The semiconductor device of claim 1 wherein the copper plug has a wall which makes an angle with respect to the last wiring layer of 45 to 75 degrees. 12. A method of forming a semiconductor device comprising: obtaining a semiconductor substrate having a plurality of wiring layers wherein a last wiring layer comprises a conductive material;forming an insulation layer on the last wiring layer, the insulation layer having a thickness,forming a via opening in the insulation layer to expose the conductive material in the last wiring layer, the via opening extending to the full thickness of the insulation;forming an aluminum layer in the via opening, the aluminum layer extending to a height above the full thickness of the insulation layer and the entire via opening, the aluminum layer having a wall and a bottom;forming a barrier layer on the aluminum layer, the barrier layer having a wall and a bottom coextensive with the aluminum wall and bottom; andforming a copper plug on the barrier layer and in contact with all of the barrier layer wall and bottom and filling the entire via opening, the copper plug extending to the height above the full thickness of the insulation layer. 13. The method of claim 12 wherein the forming of the aluminum layer includes extending the aluminum layer over the insulation layer. 14. The method of claim 12 wherein the aluminum layer is contacting the conductive material in the last wiring layer. 15. The method of claim 12 wherein the aluminum layer is directly contacting the conductive material in the last wiring layer. 16. The method of claim 12 further comprising forming a cap layer over the copper plug. 17. The method of claim 16 wherein the barrier layer has an edge portion between the aluminum layer and the copper plug and wherein forming the cap layer is forming the cap layer only over the edge portion of the barrier layer and the copper plug. 18. The method of claim 16 wherein the cap layer is selected from the group consisting of cobalt, cobalt/tungsten/phosphorus, and cobalt alloys. 19. The method of claim 12 further comprising forming a dielectric layer on the insulation layer and having an opening aligned with the copper plug. 20. The method of claim 19 further comprising forming a ball limiting metallurgy on the dielectric layer and in the opening. 21. A semiconductor device comprising: a semiconductor substrate having a plurality of wiring layers wherein a last wiring level comprises a conductive material;an insulation layer formed on the last wiring layer, the insulation layer having a via opening formed therein to expose the conductive material in the last wiring layer;an aluminum layer in the via opening and includes a portion over an upper surface of the insulation layer, the aluminum layer having a wall and a bottom, the wall having a height that is greater than a height of the upper surface of the insulation layer;a barrier layer formed on the aluminum layer, the barrier layer limited to covering only the wall and bottom of the aluminum layer and not extending beyond the aluminum layer; anda copper plug formed on the barrier layer and in the via opening and filling the entire via opening, the copper plug extending above the height of the upper surface of the insulation layer so as to be coplanar with the portion of the aluminum layer.