Vias and method of making
The invention relates to a method of providing a planar substrate with electrical through connections (vias). The method comprises providing a hole in said substrate and a treatment to render the substrate surface exhibiting a lower wettability than the walls inside the hole. The planar substrate is exposed to a molten material with low resistivity, whereby the molten material is drawn into the hole(s). It also relates to a semiconductor wafer as a starting substrate for electronic packaging applications, comprising low resistivity wafer through connections having closely spaced vias.
1. A method of providing a planar substrate with electrical through connections (vias), the method comprising:
a) providing at least one hole in a planar substrate;
b) treating the planar substrate such that a surface of the planar substrate exhibits a lower wettability than walls inside the hole;
c) exposing the planar substrate to a molten material with low resistivity, whereby the molten material is drawn into the hole by capillary force or by wetting force; and
d) providing polysilicon both inside the hole and on restricted portions around the hole defining a pattern of polysilicon.
2. The method of claim 1 , wherein the planar substrate is a semiconductor wafer, preferably selected from silicon, doped silicon, GaAs, InP.
3. The method of claim 1 , wherein the surface of the planar substrate is oxidized or provided with Ti or other suitable material to provide a non-wettable surface or at least a surface having lower wettability than that present in the hole.
4. The method of claim 1 , wherein polysilicon is deposited in the hole.
5. The method of claim 1 , wherein silicon is the native material of the planar substrate.
6. The method of claim 1 , wherein exposing the planar substrate to the molten material includes depositing gold on the polysilicon and heating to a temperature of 363° C. or more to form a eutectic liquid phase between silicon and gold.
7. The method of claim 6 , wherein the gold is provided on the planar substrate in a solid, semi-liquid or liquid state.
8. The method of claim 6 , wherein the gold is provided on the planar substrate by any of sputtering, evaporation, screen-printing or rolling or raking of a paste, attaching a preform and subsequently heat is applied to melt the gold.
9. The method of claim 1 , wherein the hole has a front side opening into which the molten material flows during filling thereof, and a back side opening.
10. The method of claim 9 , wherein the back side opening is smaller than the first opening.
11. The method of claim 9 , wherein the diameter of said back side opening is small enough to reduce the outflow of the molten material but still allows venting of ambient gas present inside the hole.
12. The method of claim 1 , comprising active sucking to draw the molten material into the hole.
13. The method of claim 1 or 6 , comprising patterning the polysilicon to define routing structures.
14. A method of providing a planar substrate with electrical through connections (vias), the method comprising: a) providing at least one hole in a planar substrate; b) treating the planar substrate such that a surface of the planar substrate exhibits a lower wettability than walls inside the hole; c) exposing the planar substrate to a molten material with low resistivity, whereby the molten material is drawn into the hole by capillary force or by wetting force; d) metallizing the entire planar substrate to provide a shielding layer; and e) providing a dielectric layer, such that the final structure is a coaxial lead-through suitable for RF applications.
15. A method of providing a planar substrate with electrical through connections (vias), the method comprising:
a) providing at least one hole in a planar substrate;
treating the planar substrate such that a surface of the planar substrate exhibits a lower wettability than walls inside the hole;
exposing the planar substrate to a molten material with low resistivity, whereby the molten material is drawn into the hole by capillary force or by wetting force; and
making recesses in the planar substrate extending from the hole to other locations on the planar substrate, the recesses being exposed to the same processing as the holes so as to form routing structures on the planar substrate.