Posted by Graham Etchells on December 10, 2015
It’s amazing what you find when you clean out your garage. I came across some old photographs of the first CALMA systems I worked on. Boy, have we come a long way since those days.
Those early CALMA Graphic Data Station (GDS) systems that I worked on back in the late 1970’s were considered revolutionary. Why revolutionary? Well before they came along, making the masks for an IC was a real pain. Here’s a brief recap of what you had to do to.
Before GDS the IC layout engineer would have to draw the circuits on large sheets of grid paper, using a different color for each layer of the circuit. Then they would produce a mask of each layer by cutting the shapes into a peel coat material such as Rubylith. To get a rectangle for example you would cut the four edges that made up the rectangle through the top layer of the Rubylith but not through the base layer. The peel coat material would be removed, leaving the rectangle exposed. The sheets were then photographically reduced to the real size of the IC. A stepper was then used to produce the physical masks by replicating the sheets as many times as would fit on a mask that was the real size of the wafer. Typical wafer sizes back then were around 4 inches. As you can imagine this was very time consuming and very error prone.
The GDS system revolutionized this process by enabling the circuit to be precisely digitized and the data stored for output to a plotter to produce check plots. CalComp who made plotters also produced a flatbed style plotter that could be fitted with a cutting head to produce the mask layers on the Rubylith.
This was clearly, a giant leap forward in custom layout productivity.
Over the years the CALMA system evolved to include color displays, a graphical programming language (GPL) and many other features that we today take for granted in a layout tool.
However, even today we still rely heavily on an experienced individual to ensure that the physical implementation of the circuit will actually produce working silicon. In my experience we have yet to see something as revolutionary as those early CALMA systems although there have been some significant improvements over the years.
Over the next few posts I will walk you through the progress we have made that allows us to design today’s complex custom designs.
Oh, by the way – I am Graham Etchells, part of the marketing team for Custom design at Synopsys.