Also, check LibreSilicon [1], a free and open source semiconductor manufacturing process, currently in development. The target is 1 μm, but the developers said 0.5 μm should be possible. Here's a comprehensive introductory talk [2]. And as usual, the project is on GitHub [3]. If things went well, they said they planned to manufacture an open source RISC-V microcontroller, pin-compatible with Atmel AVR ATTiny.