|The Initial State and the Symmetry
22th February 2014
Those of us fortunate enough to work in semiconductor manufacturing, find the experience exhilarating. You have thousands of wafers and millions of die going through the manufacturing pipeline everyday and the process is 24x7. Unlike many other types of manufacturing, the semiconductor fabs are run in the integrated mode with very little possibility of rework or error correction. For example if a door in a car assembly line is defective it can be replaced and the reworked car can still be sent through the assembly line. However in integrated manufacturing mode the car with defective door and all the cars in the assembly line, belonging to the same batch, will be scrapped as a rework is not allowed. Therefore a simple mistake can have catastrophic consequences. In fabs the methodology used in production management plays a crucial rule. We can break-down the product management in the following steps:
1. Initialization: The initialization is equivalent to the formation of an initial state specific to the product. Its formation is the most important step in the product introduction into the manufacturing environment. All the information available about the product, the technologies used, and the resources required, is collected and critically reviewed. The planning of the project takes place to the smallest detail, and all the possible failure modes during product life-time are accounted for. More robust the initial state is, more stable the product is during its life-time in a fab.
2. Simplification: In this mode the information gathered is simplified. The noise is reduced and the essential information is highlighted. We can consider this step analogous to the symmetry-breaking. The symmetry-breaking requires removing the ambiguities in the process being handed over to the manufacturing. Most of the time the problems which may affect the product quality, are just below the surface and the slightest lapse in process control can kill the product. The resources are always limited and the dead-lines are suffocating, so the simplification or the symmetry breaking becomes extremely important. A perfect initial state should have no symmetry i.e. no ambiguity.
3. Implementation: The fabs are managed best in preventive mode rather than in fire-fighting mode. Fire dousing is always more expensive and damaging than prevention. The fabs are run by hundreds of technicians, supervisors, engineers, and managers working in unison. It is very important that they are well informed about products and what to come. More information is disseminated among the working units, better are the chances of success. The implementation part can not succeed, without a work-force unaware of the contents of the initial-state. This is the basic principle behind the working in any manufacturing environment in the prevention mode.
4. Feedback: The feedback process is the connection between the real-time situations during manufacturing and the initial-state. The engineering and production data is provided to the initial-state. As a result the initial-state becomes more and more robust. The feedback process is iterative and it is continuous throughout the product life-time. Every effort is made to gather information about the devices in field and their reliability. It improves the quality of the manufacturing of the future products. Every fab has its history and understanding it is one of the most important aspect of the business.
We have described, the essence of a little known but a rather important discipline in the semiconductor manufacturing, called the Process Integration. So a question may be asked, what is the relevance of this methodology to physics or to the contents of this site?
We will be describing the formation of the initial state in nature. The observer will be making measurements of the initial state and the resulting description will be based on the measurements. Rather than trying to describe the initial state from the description, we will develop the description by determining the initial state. Each time we come across the limitations of the observer, we will be looking for the appropriate symmetry to bridge the gap. We will have to keep in mind that nature in its truest form, does not allow any symmetries. If we see a symmetry, that is due to the limitation of the observer's capability. VTS is the strongest symmetry we can think of in our universe, which can not be broken with existing resources.
In the real world the search for missing neutrinos is on. Turns out that neutrinos may not be missing but transformed into another flavour instead. The detectors used earlier were expecting only one flavour rather than three, due to an assumption that the neutrinos were massless. Another example that the book-keeping, is important even in nature.
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