Most foundries do not offer microlens for pixels larger than 8um. It appears that CSEM Muttenz (Switzerland) has a microlens process for pixels as large as 25um, possibly more. The microlens described in OSA paper "Measurement and modeling of microlenses fabricated on single-photon avalanche diode arrays for fill factor recovery" by Juan Mata Pavia, Martin Wolf, and Edoardo Charbon.
"A quartz mold was utilized to imprint the microlenses in a sol-gel polymer on top of the SPAD array. The polymer used for the fabrication of the microlenses was ORMOCER. In the manufacturing process the polymer is deposited on top of the imager, the mold is then brought into contact with the polymer and pressure is applied. The polymer is then UV cured and thermally stabilized in an oven."