IC DESIGN FLOW

IC DESIGN FLOW

Where does layout design fit in the overall scheme of things? As defined in Section 1.2, layout design occurs once an engineering drawing is complete. Let us look at layout design in the context of an IC’s complete life cycle and where it fits in the “flow.”

There are many kinds of design flows based on the specific design under development. Let us consider a general conceptual flow through which all product concepts pass on their way to market (Figure 1.1).

1. First, it is normally the marketing department that defines the product to be developed.

2. The definition of the architecture or behavior of the design is the next step.

Circuit design engineers decide the architecture of the chip to perform the market and/or IDEA functions.

3. System simulation is done by a group of engineers who define and verify the definition of the individual blocks to be integrated into the final chip. This step validates that the architecture defined in step 2 is sound and clearly defines manageable blocks to implement further.

4. Circuit design groups perform all the digital and analog simulations to verify the circuit solutions and gate connectivity, as well as the sizes of the gates

(to meet timing specifications). These groups interface with the layout design groups who adapt the circuit to the floor plan of the chip.

5. Layout design is done by engineers and layout designers. Their work consists of laying out polygons. Transistors, substrate connections, connections (using 1 to 6 layers of metal), etc., are implemented for all of the blocks using the schematics generated by the circuit group. The final design going to mass production is the layout of the entire chip.

6. After the first wafers are manufactured, a group of test engineers will try to test the chips. First, they will check if the process parameters are within the acceptable tolerance levels. The following step is to test the chips using an engineering tester in order to find all the specification violations and to try, on the spot, to fix them.

7. If and when all the errors are fixed (process and/or logical), the chip will move to mass production and to market.

Remember that this is a conceptual flow. In reality, there are many feedback loops and iterations of the design as it moves through the different stages. Changes to the design occur as a result of many different factors, including many that arise from layout limitations or constraints. Anticipating these issues or problems before they occur is where understanding the basic fundamentals differentiates great designers from good ones.

Where do we start? From a layout designer’s point of view, the work starts once a schematic or netlist is created. On to Chapter 2.