Eliminate scratching

Blade-related wafer scratches occur when the robot, extended into the cassette either to extract or return a wafer, directly contacts the topside of a wafer. The dominant cause of wafer scratching is robot droop.

Droop occurs naturally as a robot ages and wears. As droop worsens, the robot end effector uses more of the vertical clearance area between wafers within the cassette. While much of this area is already used by the end effector thickness, additional space is required when robot droop is considered. As blade-to-wafer clearance becomes smaller, wafer scratches become more likely. Due to design and wear issues, droop is unavoidable in the original equipment manufacturer (OEM) robot design.

When robot droop becomes evident, a tool is typically taken out of production and equipment maintenance is performed to realign the robot. Over time, however, robot droop returns and wafer scratching may again occur. As the time interval between robot alignments increases, the risk of wafer scratching also increases and more wafer lots can be affected.

 

Fabworx products use stronger materials and tighter tolerances to eliminate droop and associated wafer scratching:

  • Hub bearing spacers for the 200mm hub are thicker, made of stronger material, and seven times the spring preload is used to create an extremely solid base.
  • Fabworx's proven joint design uses precision-machined components and pressed-fit bearings in elbow and wrist locations to create a tighter, stronger structure.
  • Forearm components are rigidly connected to the wrist to increase stiffness.
  • Fabworx end effectors are stronger and less susceptible to heat-induced warping. Thin profile end effectors provide additional vertical clearance between wafers within the cassette.

 

In December, 2005, Samsung Semiconductor, Inc. and Fabworx Solutions published an article in Solid State Technology magazine detailing the reduction of robot-related wafer scratches and the increase of yield and productivity through using the Fabhp robot.

Fabs operating cluster tools from the 1990s frequently report robot-related wafer scratching as a common source of yield loss. When scratching occurs, the probability of killing a die is nearly 100%. The dominant cause of wafer scratching in these tools is droop, which occurs as the robot ages. Faced with an ongoing yield-loss issue, a 200mm memory fab analyzed defect data to identify droop-related scratching in a set of tools.

After evaluating options, Samsung Austin Semiconductor, LLC installed the Fabhp robot which eliminated scratching and resulted in a payback on investment from higher yields within 10 weeks. Because the Fabhp robot runs at higher speeds, tool productivity also increased by 15%.