Just as in the design stage, the layout stage follows the very same rules – with one added complication, the statistical nature of manufacturing the chip. With advances in technology, the lower order effects, so far ignored, come into the picture. The environmental conditions may affect manufacturing; maybe one out of a hundred chips, maybe more. There are also effects that arise from variations in process parameters like the optical proximity effects, random dopant effect, etc. Semiconductor variability is another statistical phenomenon of utmost importance – the effect of too much scaling resulting in unpredictability.
And, not all of these are in the hands of the designer; some depend on the technology or the effectiveness of the tool and its library. So, the designer needs to accommodate a little deviation from what is expected. This could be in terms of timing, power, design tricks that allow small compromises, or precautions for what lies in store during later processes.
The demon called cost
Finally, the one factor that is so trivial, yet pervades the entire process, is the cost of making a single chip. In fact, making it in bulk is a lot cheaper. One needs to keep in mind the returns from it, also the trends and the customer’s interests. More importantly, the perfection in terms of design and testing that is to be achieved before going in for fabrication takes humongous precedence owing to the cost involved. Plus, it is not easy to rectify errors in a chip, once manufactured. One other factor to keep in mind is that it is all not just about manufacturing. Once done, the chip has to stand the test of time and use.
Chip Designing is an art – one that demands thoroughness and leaves no place for doubt. It might seem impossible, but time and again, people have proven that it is not. Still, there is a lot more to uncover, many more marvels to behold.
- [stextbox id=”info” caption=”Pointers to take back:”]
- How good a code is, is decided by how a tool understands it.
- Understand the errors that crop up, debug.
- Make sure the design is functioning correctly.
- Be clear with your design idea.
- Be patient.
- Think outofthebox.
- Know the ins and outs of your design.
- Accommodate for statistical deviations.
- Keep an eye on the cost.