Sonoscan's automated double-throughput 300 mm wafer scanner
Monday, 23 May 2011 00:06
The FOUP or FSOB wafer carriers are loaded into two loadports.
Sonoscan has begun shipping its automated 300 mm bonded wafer inspection system that simultaneously scans two wafer pairs and gives users twice the throughput of other systems.
Structural defects in bonded wafers typically consist of disbonds, voids or particle-related gaps between the two wafer surfaces. Less common are cracks in a wafer. In MEMS wafers, the most significant defects are likely to be gaps in the seal surrounding the cavity. To lower costs, it is important to identify and remove devices containing these defects as early as possible in the production process. These defects may cause damage during later process steps.
The AW300™ Series delivers fully automated inspection of 300 mm wafer pairs bonded by virtually any method, including SOI, direct fusion, anodic, glass frit and epoxy bonding. Wafer pairs of 200 mm diameter can also be inspected, but smaller sizes are not available on this model.
The FOUP or FSOB wafer carriers are loaded into two loadports. Next, a robotic arm moves a wafer pair to the wafer aligner and from there to one of two vacuum-assisted stages where acoustic inspection is carried out. The arm then moves a second wafer pair to the other stage.
Sonoscan’s proprietary Waterfall Transducer™ scans the entire surface without immersing the wafer pair in water. This technique avoids false readings resulting from ingression of de-ionized water. The system uses proprietary high-frequency transducers up to 400 MHz, all designed in-house by Sonoscan. Intentional internal features (MEMS seals, for example) and defects are imaged, including features with diameters as small as 5 microns and thicknesses down to 100Å. The acoustic image of wafers bearing metallization can be overlaid onto a wafer map in order to assign defects to individual die.
When scanning is completed, the wafer pair is moved to the wafer dryer, and a new wafer pair is moved onto the stage. While the new wafer pair is being scanned, software performs an automated analysis of the previous pair according to the user’s definitions to determine acceptance or rejection. By scanning two wafer pairs at once, and by performing analysis during imaging of the next wafer set, the AW300 minimizes overall scan time and maximizes throughput.
The overall impact of the AW300 is to speed up the process of improving yield by removing defective wafers or die as early as possible in the production process. For direct bond techniques, users of the system have found that yields can be significantly improved by inspecting at three production stages - after initial bonding by Van der Waals forces, after annealing and after thinning.
Sonoscan, Inc., 2149 E. Pratt Blvd., Elk Grove Village, IL 60007. Phone 847.437.6400; Contact person: Steve Martell, x240; email
; web www.sonoscan.com