Inside AMD - Touring Fab 30

A Quick Tour through Fab 30

As we mentioned earlier, getting AMD to open up the doors of Fab 30 was almost unheard of and thus we did not expect to be able to talk about, much less see anything on our tour. Thankfully we were given a short but very informative tour through a part of AMD’s manufacturing that you rarely hear about – the Materials Analysis Labs. Because of AMD’s strict policies we were not able to bring you any pictures from within Fab 30, but we’ll try our best to describe exactly what we saw in words.

A picture outside Fab 30 as we left in the snow, this was the farthest inside we could use our camera

You often hear about manufacturing yields and improving them, but very rarely do you get an idea of all of the work that goes into the actual process of improving them. Before we can explain how AMD’s Material Analysis Labs contribute to improving yields at Fab 30, you have to have a good understanding of exactly what improving yields means for AMD.

Obviously the higher AMD’s yields the more CPUs they can ship and the faster their CPUs can potentially be, but AMD’s own Ehrenfried Zschech had a much better way of explaining it. If the yields at Fab 30 were to drop 10% for just 8 hours, the drop in yield would cost AMD a cool $1 million. And remember we’re only talking about yields dropping for a matter of hours, if the defects causing the yields to decrease aren’t found and eliminated the loss could be devastating. Manufacturing yields are the life line of any fab-based microprocessor manufacturer, and considering the bullish comments from AMD on their yields at Fab 30 it worked out very well that we’re able to take you through some of the “how” behind detecting defects and turning them around into a way of improving yields.

The Materials Analysis Labs have two major tasks – to find defects and then to analyze them. The discovery of defects takes us to the Sample Preparation Lab, where silicon wafers are sent for defect detection and then prepped for analysis by the Materials Analysis Labs.

The wafers are sent from manufacturing to the Sample Preparation Lab along with a sheet of paper that contains information on what tests the folks in manufacturing want run on the wafers. What inspires manufacturing to suspect something has gone awry with the process and ship a wafer here? If there are any changes in yield, sudden or not, it is time to get to the bottom of why. Remember those calculations from before, a 10% drop in yield for just 8 hours costs $1M; we’re not talking about small sums of money here.

Once the wafers are in the hands of the engineers in AMD’s Sample Preparation Lab they are cut, polished and individual cores can be isolated if necessary. The Lab also can “decorate” wafers in order to make certain structures within the silicon more visible, which helps in the Materials Analysis Labs later on.

The wafers that make it to the Sample Preparation Lab aren’t necessarily made up of fully functional CPUs, in fact they are usually test structures. A test wafer is made up of a number of chips just like a mass production wafer, but instead of the chips being individual CPU cores the test wafer has a set of test structures printed on the wafer itself. The test structures can be lots of gates or an incredible amount of vias (vias are tiny wires that connect the various layers of a CPU) in order to stress the manufacturing process. Improving the yield on these test wafers directly improves the yield on producing actual CPUs, the test structures simply make for better test candidates.

The Sample Preparation Lab gets about 2 to 3 new defects to analyze per month, but what’s interesting to note is that not all of these defects influence yield. Granted there are some defects that will lower production yields but there are others that are simply smaller pieces of a much larger puzzle, and resolving those defects will pave the way for bigger defects to be taken care of.

Although it may not seem all that exciting, the work that goes on in the Sample Preparation Lab is critical to the defect analysis and fine tuning of AMD’s manufacturing process. Without good samples to work with, the engineers in the Materials Analysis Lab can’t produce any good results with which to diagnose defects. As one AMD employee put it, preparing the samples is 80% of the equation; now let’s take a look at the remaining 20%.