Suspension for filling via holes in silicon and method for making the same
View Patent ↗A metallization process and material system for metallizing either blind or through vias in silicon, involving forming a low coefficient of thermal expansion composite or suspension, relative to pure metals, such as copper, silver, or gold, and filling the via holes in the silicon with the paste or suspension. The suspensions sinter with minimal bulk shrinkage, forming highly conductive structures without the formation of macroscopic voids. The selected suspension maintains a coefficient of thermal expansion closer to that of silicon.
1. A suspension for filling via holes in silicon, comprising a pre-sintered binder-free, high-solids loading paste including a conductive material and a low CTE additive material, wherein said suspension is binder-free within said via prior to, and after, subjecting said suspension to a sintering process, and such that upon sintering, said conductive material densifies prior to said low CTE additive material said silicon substrate and paste at a temperature for densification of said metal but prior to densification of said low CTE additive material.
2. The suspension of claim 1 further comprising having a portion of said suspension include solids in the amount of 50 to 55 volume percent.
3. The suspension of claim 1 including having said conductive material comprise a metal powder.
4. The suspension of claim 3 wherein said metal powder comprises copper, silver or gold powder.
5. The suspension of claim 1 wherein said suspension including solvents and dispersants.
6. The suspension of claim 1 wherein said suspension includes a high-solids loading of approximately greater than 50 volume percent.
7. The suspension of claim 1 wherein said suspension has a viscosity below approximately 1000 centipoise.
8. The suspension of claim 1 including said low CTE additive comprising a conductor, an insulator, or mixture of both.
9. The suspension of claim 1 wherein said low CTE additive material comprises silica, corderite, spodumene, borosilicate glasses, mullite, beta eucryptite, tungsten, magnesium aluminosilicate, or molybdenum.
10. The suspension of claim 1 wherein said suspension includes said low CTE additive material in a range of 20-80 volume percent, corresponding with an amount of said conductive material in the reciprocal range of 20-80 volume percent.