Electroformed stencils for solar cell front side metallization
View Patent ↗A method for providing metallization upon a semiconductor substrate utilizing a stencil having at least one aperture extending from the contact side to the fill side, the contact side of the stencil being substantially flat and forming a sharp edge with a wall of the at least one aperture, the at least one aperture being tapered such that an area of a cross-section of the at least one aperture at the fill side is larger than an area of the cross-section of the at least one aperture at the contact side. A method of forming a stencil for depositing metallization lines on a semiconductor substrate is also disclosed.
1. A method for providing metallization upon a semiconductor substrate, the method comprising:
providing a semiconductor substrate having a surface suitable for printing;
placing a stencil having a contact side, a fill side, and at least one aperture extending from the contact side to the fill side over the semiconductor substrate with the contact side of the stencil in contact with the semiconductor substrate, the contact side of the stencil being substantially flat and forming a sharp edge with a wall of the at least one aperture, a cross-section of the at least one aperture at the contact side having a predetermined width, and the at least one aperture being tapered such that an area of a cross-section of the at least one aperture at the fill side is larger than an area of the cross-section of the at least one aperture at the contact side; and
printing conductive ink through the at least one aperture and onto the semiconductor substrate, the conductive ink being printed in direct contact with the semiconductor substrate.
2. A method for providing metallization upon a semiconductor substrate, the method comprising:
providing a semiconductor substrate having a surface suitable for printing;
placing a stencil having a contact side, a fill side, and at least one aperture extending from the contact side to the fill side over the semiconductor substrate with the contact side of the stencil in contact with the semiconductor substrate, the contact side of the stencil being substantially flat and forming a sharp edge with a wall of the at least one aperture, a cross-section of the at least one aperture at the contact side having a predetermined width, and the at least one aperture being tapered such that an area of a cross-section of the at least one aperture at the fill side is larger than an area of the cross-section of the at least one aperture at the contact side;
printing conductive ink through the at least one aperture and directly onto the semiconductor substrate; and
removing the stencil, wherein after removal of the stencil, the conductive ink adheres to the semiconductor substrate without significant bleedout, such that at least one line of conductive ink has substantially straight edges, and wherein a height to width aspect ratio of the at least one line of conductive ink is greater than about 1:10 after heating and cooling.
3. The method of claim 1 , wherein the semiconductor substrate comprises silicon.
4. The method of claim 1 , wherein the surface of the semiconductor substrate comprises a surface of a photovoltaic device.
5. The method of claim 1 , wherein the conductive ink comprises silver-based ink.
6. The method of claim 1 , wherein the conductive ink has a Malcolm viscosity of less than about Mx 30.
7. The method of claim 1 , wherein the conductive ink has a Malcolm viscosity of less than about Mx 15.
8. The method of claim 1 , wherein the conductive ink has a Malcolm viscosity in the range of from about Mx 05 to about Mx 10.
9. The method of claim 1 , wherein the conductive ink has a viscosity of between about 160 Pa·s and about 260 Pa·s as measured on a Brookfield HBT viscometer (Utility Cup and Spindle) tested at 10 RPM at 25° Celsius.
10. The method of claim 1 , wherein the conductive ink has a viscosity of less than about 140 Pa·s as measured on a Brookfield model HBT cone/plate viscometer tested at 9.6 reciprocal seconds using a 1.565″ cone at 25° Celsius.
11. The method of claim 1 , wherein the conductive ink has a viscosity of between about 70 Pa·s and 110 Pa·s as measured on a Brookfield model HBT cone/plate viscometer tested at 9.6 reciprocal seconds using a 1.565″ cone at 25° Celsius.
12. The method of claim 1 , wherein the conductive ink has a resistivity of less than about 15×10 −6 ohm·cm at room temperature.
13. The method of claim 1 , further comprising aligning the stencil with the semiconductor substrate.
14. The method of claim 1 , further comprising removing the stencil, while leaving the conductive ink substantially adhered to the semiconductor substrate.
15. The method of claim 1 , wherein the conductive ink is at about room temperature when passing through the stencil.
16. The method of claim 1 , wherein the at least one aperture gradually tapers from the fill side to the contact side of the stencil.
17. The method of claim 1 , wherein the conductive ink is forced through the at least one aperture and onto the semiconductor substrate with a squeegee.
18. The method of claim 1 , wherein the conductive ink is forced through the at least one aperture and onto the semiconductor substrate with a material dispensing head.
19. The method of claim 1 , wherein the stencil has a thickness in the range from about 0.025 mm to about 0.2 mm thick.
20. The method of claim 1 , wherein the stencil is a multi-layer stencil.
21. The method of claim 1 , wherein at least one aperture is formed in the stencil by laser cutting.
22. The method of claim 12 , wherein the conductive ink has a resistivity in the range of from about 1.6×10 −6 to about 10×10 −6 ohm·cm at room temperature.
23. The method of claim 14 , wherein the conductive ink adheres to the semiconductor substrate without significant bleedout, such that at least one line of conductive ink has substantially straight edges.
24. The method of claim 14 , wherein the conductive ink is at about room temperature when the stencil is removed.
25. The method of claim 19 , wherein the at least one aperture has a width of about 0.005 mm to about 0.15 mm at the contact side of the stencil.
26. The method of claim 20 , wherein a conductive finger and a conductive busbar are deposited on the semiconductor substrate in one print step, a length dimension of the conductive busbar being non-parallel to a length dimension of the conductive finger, the conductive busbar having at least one of a greater thickness and a greater height than the conductive finger.
27. The method of claim 21 , wherein the stencil is a multi-layer stencil, at least one layer including at least one aperture formed by laser cutting.
28. The method of claim 22 , wherein the conductive ink has a resistivity in the range of from about 2×10 −6 to about 8×10 −6 ohm·cm at room temperature.
29. The method of claim 23 , further comprising heating the at least one line of conductive ink after printing, wherein a secure mechanical and electrical coupling between the at least one line of conductive ink and the semiconductor substrate is formed.
30. The method of claim 29 , wherein a height to width aspect ratio of the at least one line of conductive ink is greater than about 1:10 after heating and cooling.
31. The method of claim 2 , wherein the at least one aperture has a width of about 0.005 mm to about 0.095 mm at the contact side of the stencil.