Harmotec Non-Contact Pick-up Tool Handles Thin Wafers
Kenji Tsuda, Asia Contributing Editor -- Semiconductor International, 2/6/2008 5:35:00 AM
Thinner wafers are required for system-in-a-package (SiP) and multi-chip package (MCP) solutions to cram multiple chips in a thin form factor package. However, as wafer diameters increase, thinned wafers break more easily.
Harmotec Corp. (Tokyo) has developed non-contact wafer pick-up tools for very thin (20 μm) 300 mm wafers.
The pick-up tools are offered with three types of 300 mm wafer supports, including ring, horseshoe and round form factors, suitable for holding fragile wafers. Stress on a wafer is claimed to be 1/360th that of conventional supporters that were not able to pick up such thin wafers. The pick-up tools can be used with wafer transport machines.
The stress-free pick-up tool is based on cavities 1-2 cm in diameter. A sidewall hole is formed around the bottom of a cavity to allow air to flow. When dry nitrogen flows in the sidewall hole, the air flows in whirls in the cavity and then moves outside. When a wafer is brought near the cavity, the wafer is attracted to the cavity, but is not touched by it. The air flows horizontally along the wafer surface because of a negative pressure inside the cavity caused by the whirls. The negative pressure attracts the wafer, but the horizontal air flow prevents the wafer from contact.
The wafer never touches the cavity, otherwise the dry nitrogen might not flow to the outside. With conventional pick-up tools, if a 300 mm wafer is ground down to a thickness of <100 μm , the wafer may undulate like a potato chip. With the Harmotec pick-up tool, the wafer remains flat because of attraction to the cavity. The products have cushions taller than the cavities to adjust the wafer flatness.
The company is targeting applications including single-package, multiple-chip memories, LCD drivers to mount on a flexible printed circuit board (PCB), fragile compound semiconductor wafers, power IC wafers, and through-silicon via (TSV) wafers.
