Many readers have probably wondered why NAND flash fabs are so enormous. Although DRAM fabs used to be the largest, running around 60,000 wafers per month, NAND flash fabs now put that number to shame, running anywhere from 100,000-300,000 wafers per month. Why are they so huge?
The reason is that you need to run that many wafers to reach the optimum equipment balance. The equipment must be balanced or some of it will be sitting idle, and with some tools costing $50 million (immersion scanners) you want to minimize their idle time to the smallest possible number. I am sure that this is a tough problem, although I have never had to solve it myself.
The most important reason that so much attention is focused on this is that the cost of the wafer depends on the efficiency of the fab. If you built a $13 billion NAND flash fab that produced 90,000 wafers per month instead of 100,000 wafers per month, then the amount of investment per wafer would be 10% higher. That can make a significant difference to Continue reading “Why are NAND Flash Fabs so Huge?”