Wafer measurement technology reduces contamination risks
11/01/2004
BY CHRIS ANDERSON
BEAVERTON, Ore. — CyberOptics Semiconductor (www.cyberoptics.com) has introduced WaferSense ALS technology, designed to provide real-time measurement data to fab managers and engineers without having to shut down process equipment to take measurements.
The ALS (Auto Leveling Sensor) wafer-like device can move through process equipment and transmit information wirelessly to ensure that all stations are level and coplanar. It can be placed in cassettes, FOUPs, on end effectors, aligners, in load locks and in process chambers. CyberOptics says its technology is designed to provide precise pitch and roll measurements that can be logged to relate coplanarity with yield, and to determine the tool adjustments needed for best yields.
Because the WaferSense device works under a vacuum within a tool, it inhibits contamination by eliminating the need to open up the equipment to make critical semiconductor process measurements.
"Most cleanrooms in the world today are not Class 1 or better; they are minienvironment fabs running Class 100 or Class 1,000, and people really hate to open them up because you are exposing them to a potentially very dirty environment," says Ken Goldstein, principal of Cleanroom Consultants, Scottsdale, Ariz. "In some cases, the difference is three, four or even five orders of magnitude between the surrounding cleanroom and inside the pod or cassette."
As a result, Goldstein says, measurements that required exposing the equipment to both the relatively "dirty" environment outside tool and the potential contamination limited the number of times these vital measurements were taken.
Goldstein adds, "What I really like about this [WaferSense] is the in situ measurement capability. In the past, our measurements were always nearby but never actually inside the pod, cassette, or next to the wafer that was being worked on. This appears to be a step in the right direction."
CyberOptics offers its 9-mm thick device in three sizes, for 150-mm, 200-mm and 300-mm production environments. Because WaferSense ALS is run through the process like a regular wafer, it is constructed of non-off-gassing material and contains its own HEPA filter. In addition to the disk-like tool, the ALS package comes with LevelView software and a Bluetooth wireless connection that attaches to a laptop's USB port. The software provides a graphic representation of measurements taken inside process equipment, and data can be stored to establish go/no-go parameters and to coincide with optimal process performance.
"The ALS can move around a tool, go where the wafers go and sense what the coplanarity and leveling is at stations inside," says Evelyn Brosnan, vice president of marketing for CyberOptics. "This will cut down on the time needed to take measurements and automate the process."
With a base price of around $6,995, CyberOptics claims WaferSense ALS can pay for itself in as little as two months if only used on a single tool, citing throughput and labor savings. The company also contends that its technology may eventually provide vital measurement information that can lead to regular machine adjustments and, in turn, improvements in yield.
Goldstein also sees potential for a wireless device to get new fabs up and running quicker: "At the end of construction, the fab people are almost always invariably in a rush and wanted the machine installed 48 hours ago. If this [technology] speeds this up by giving rapid results and readings on leveling, that might help—because leveling is something that is going to require opening and closing the machine each time to take the measurements. If this [device] can do it all at once, it will save time and money."
In late summer, SensArray (www.sensarray.com) introduced a wireless temperature measuring device embedded in a silicon wafer that also moves through process equipment during production (see "Embedded temperature metrology design reduces wafer contamination," CleanRooms, September 2004, page 1).