There's a detailed article "Recollections of Early Chip Development at Intel". For the first 10 years, Intel drew schematics and layout by hand. In 1974 they started digitizing on a Calma GDS I system. For the 8086, they spent two weeks manually matching the schematics against the drawn plots looking for errors and found 20 errors.
They cut out the drawings on sheets of Rubylith to create the masks. The earliest chips used a "Coordinatograph", a tool where you'd manually enter the coordinates from the drawing and it would move the cutter appropriately. Then they moved to a Xynetics plotter with a knife. The Rubylith sheets would be sent to the mask vendor, who would photographically reduce it down to mask size.
Intel had simulation tools, but they could only simulate 5-20 transistors at a time. So they could only simulate small, critical chunks like parts of the ALU.
In case you haven't seen it (although I'm sure you have), Now The Chips Are Down had a rare look inside an Intel fab in the 1970s: https://en.wikipedia.org/wiki/Now_the_Chips_Are_Down There are copies of the film on the internet.
They cut out the drawings on sheets of Rubylith to create the masks. The earliest chips used a "Coordinatograph", a tool where you'd manually enter the coordinates from the drawing and it would move the cutter appropriately. Then they moved to a Xynetics plotter with a knife. The Rubylith sheets would be sent to the mask vendor, who would photographically reduce it down to mask size.
Intel had simulation tools, but they could only simulate 5-20 transistors at a time. So they could only simulate small, critical chunks like parts of the ALU.
https://www.intel.com/content/dam/www/public/us/en/documents...