The RISC-V core is a custom design. It supports the RV32-IMC extensions. More details about the CPU will be published in the ESP32-C3 Technical Reference Manual which is currently being finalised, thanks for being patient.But this no info about what riscV core is it and who is the factory maker of this chip.
The "factory maker" for all Espressif chips to date is TSMC, Espressif is a fabless semiconductor company which means we design our own chips but the silicon is fabricated by a third party foundry.
