Probe-on-substrate

Probes are directly patterned on a test substrate, thereby eliminating a need for an interposer. Probe contact structures are formed as a two-level structure having a greater lateral dimension for a lower level portion than for an upper level portion. First cavities are formed in a masking layer applied to a test substrate, filling the cavities with a conductive material, and planarizing the top surfaces of the conductive material portions to form lower level portions. Another masking layer is applied over the lower level portions and patterned to define second cavities having a smaller lateral dimension that the lower level portions. The second cavities are filled with at least one conductive material to form upper level portions of the probe contact structures. The upper level portion of each probe contact structure can be employed to penetrate a surface oxide of solder balls.