Silicon design is a hard process. You start by defining design in a hardware description language (HDL) and finish by routing all the wires on the piece of silicon. This used to be done by using proprietary tools and silicon Process Design Kits (PDK) that were unique to silicon manufacturing facilities. Starting from Intel, Samsung, and TSMC, they all have a specific PDK that is used for their silicon manufacturing and it contains all of the specifications for their nodes. It contains design constrains/information on the number of metal layers, how close can two wires be to each other, etc.

In the aim to open-source silicon design and finally allow for fully open silicon design flow, Google has partnered with SkyWater to deliver an open-source PDK that will allow designers to produce silicon on an open platform. Despite being designed for an older 130 nm node, this represents a massive achievement as there was a lack of such a thing before. There is already existing open-source toolchain to create designs, but there wasn't a PDK to port them to. Now, the PDK is available and designers can manufacture 100% open source silicon at SkyWater's facilities. In the GitHub repository listed as a source below, you can find some examples on how you can use the PDK with open source tools as well.