Robotics: Semiconductor Industry Prepares for 450mm Wafers (Part 2)
Semiconductor Industry Prepares for 450mm Wafers
The semiconductor industry hasbeen manufacturing products using 300mm diameter wafers for more than 10 years. The push to transition to 450mm wafers, while it provides a huge benefit in available area for chips, is causing tool and robotics vendors to reexamine, and in many cases redesign systems to cope with the emerging standard.
I’ve been involved with the semiconductor industry since the 1980s and I remember when the 200mm wafer became the standard. I was running the engineering group at Electroglas and we were scrambling to extend our prober to deal with Intel’s insistence that they were not going to buy any prober that was not 200mm compatible. As it turned out, we were early to the table. The EG Model 3001 prober became available in 1986 but real acceptance of 200mm wafers did not happen until the early 1990s.
Fast forward to 2000. I’m working for PRI/Equipe Automation doing wafer handling front ends and I was visiting the Semiconductor Equipment Manufacturing International (SEMI) headquarters on a 300mm wafer-related issue. There, I saw on the wall a sample 450mm wafer. My first thoughts were “How were we going to contend with these manhole-sized wafers?” and “How much trouble were we in?”
Figure 1: Wafer Scale Comparison
Evolution of Wafers
As Figure 1 shows, 450mm wafers are just the latest in a long line of wafer sizes stretching back to the 1970s. It is interesting to note that just because Samsung and TSMC are working in 300mm wafers doesn’t mean that somewhere in the world is some small fab or lab still cranking out 100mm wafers full of jelly-bean parts like 2N2222 transistors (yes, those are still around). All that production equipment has to go somewhere.
As it turns out, the transition from pipe dream to reality for 450mm has been slow, to say the least. Advances in semiconductor device technology like Vertical MOS FET transistor architecture are improving chip density on current 300mm production and pushing out the need for the bigger wafers. Even so, current projections are for roll out in the 2017-2018. That’s just around the corner and even though these transitions have been traditionally later than projected it’s more than time to consider what will your company do to contend with the next (really) big thing.
450mm Wafers and the Issues Wafer-Handling Robots Face
Robot Wafer Reach Needs to be in the 750mm Range to Accomodate 450mm Wafers
Figure 2: Simple Robot to Chamber Layout
Figure 2 shows a wafer-handling robot moving a 450mm wafer into a process chamber. It has to contend with clearing a load lock as well as placing the wafer on the receiver within the process chamber. The robot reach has to be in the 750mm range and perhaps even more. This means longer arms, stiffer bearings and joints to prevent cantilever sag, and possibly a new end-effector design to deal with the increased mass and flexibility of the new wafer.
Robot Designers and Semiconductor Test Equipment Companies Await Finished Standards
There are SEMI standards for the new wafers
. and cassettes but they are still being revised. This is forcing robot designers and semiconductor test equipment companies to take a bit of a gamble on the fact that key dimensions are going to remain stable. Presently, wafer thickness is specified at 925um +/- 25um. This puts the weight of a 450mm wafer around 343g, as opposed to the 113g weight of a 300mm wafer. Robot motion profiles will have to change to assure that wafers don’t “flap” as they are swung around by the robot.
End Effectors (EE) to transfer the wafers need to be longer and stiffer. They also have to be thin enough to operate with margin in the gap between slots of a cassette or FOUP. The current spec puts the gap at 10mm. And the wafers droop when supported by their edges, as much as 940 +/- 20 mm . Plan for a little margin and this leaves about 7mm at most for the wafer plus end effector stack. Plan for an EE at least 300mm long supporting a mass of 343g and perhaps 5mm thick. That’s a real challenge for your company’s ME team.
450mm Wafers Cause Engineers to Rethink Handling
Of course, systems will also get larger as a consequence of the move to 450mm. The Figure 2 example results in a minimalistic system at least 1.7m across without framing or skins. Not so obvious might be the human factors issues related to 450mm wafers. A cassette of 25 wafers could easily weigh 20-25lbs. Operators are not likely to be carrying those around. Even handling a single wafer manually may be a dicey proposition. Does your company need to provide a transport helper as part of your system? Even something as mundane as an optical probe mark inspection microscope may not be practical if an operator has to lean out across a large system to get their eyes up to the eyepieces.
Time to Take Stock of Automation Equipment
If your company has not already done so, you may wish to consider treating the emergence of 450mm wafers to a Failure Mode Effects and Analysis (FMEA) survey for your flagship tool. An experienced systems engineer or a consulting firm can help set this up and bring an unbiased assessment to light. In the end, changes resulting from the move to 450mm wafers will be a matter of when, not if.
 SEMI M1-0414 Specification for Polished Single Crystal Silicon Wafers  450 mm silicon wafers challenges – wafer thickness scaling, Goldstein, m and Watanabe, M., ECS Transactions, 16 (6) 3-13 (2008) 10.1149/1.2980288