A composite photoresist comprises a photoresist material and a filler material dispersed within the photoresist material, wherein the filler material includes a plurality of nanoparticles. The photoresist material may comprise an acrylic-based photoresist, a novolak-based photoresist, a polyhydroxystyrene-based photoresist, a SLAM, or a BARC. The filler material may comprise base-soluble styrene-butadiene rubber nanospheres, nitrile-butadiene rubber nanospheres, polystyrene-based nanoparticles, acrylic-based nanoparticles, or inorganic nanoparticles. The nanoparticles may have an average diameter that is between around 10 nm and around 1000 nm and may have a loading in the photoresist material that is between around 5% and 50%. The composite photoresist may be used to form die-side metal bumps for use in a C4 connection that have a roughened sidewall surface but a smooth top surface.