October, 2016
www.us-tech.com
The Next Big Hurdle in Semiconductor Fabrication Continued from previous page
Top-side clamping provides a clear area for reading device bar code data. In addition, top-side
in. (0.76 mm) thickness, which is stiff and strong enough to be supported on three small pins. In instances where the wafer is thinned and
placed on a plastic film, which is mounted to a metal frame, the backside of the wafer cannot be used at all; it is fragile and will be destroyed if lift pins are used. The plastic film on which the wafer is mounted is also thin and fragile. The only mem- ber that can be used to hold or support this assem- bly is the metal frame itself. A mechanical clamp can grip the metal frame
without damaging it and achieve a firm hold. If a chuck is used the frame can be supported by pins as with standard wafers. This method is still in use today, but it requires a mechanism of many parts and still has some drawbacks. When clamping the metal frame at only one edge, the far unsupported end will bend downward and will vi- brate during movement. This makes handling difficult and dangerous, even though the mechanical clamp is secure.
Several machine manufacturers
have developed mechanical clamping devices to hold both ends of the metal frame. These mechanisms can be large and heavy, as well as expen- sive. The frame could be handled using vacuum grip instead of a me- chanical clamp and support it from the bottom. The mid-frame support reduces bending of the metal frame and minimizes vibration. This method also presents problems be- cause the frame holder (cassette) supports the metal frame from below using support rails. This leaves little room to grip the metal frame. For backside capture an articu-
lating support pin mechanism must be used on the chuck to support the
Page 35
clamping eliminates the need for chuck pins, which reduces cost and simplifies the system. En- hanced stability is achieved by the topside vacuum gripping method because the end-effector is made from ceramic which is rigid and lightweight; once the end-effector clamps onto the metal frame the rigidity of the end-effector is transferred to the combination of parts that reduces vibration. Each step forward in the evolution of the
semiconductor industry has brought challenges that have demanded innovative solutions. In some instances the challenges are small and in other in- stances they are monumental. The thinning of wafers may achieve device performance goals, but it requires an entirely new approach to handling. Contact: FJA Industries, Inc., P.O. Box 242,
Top-side gripping end-effector on a metal frame while in a cassette.
Santa Clara, CA 95052 % 408-727-0100 fax: 408-727-2100 E-mail:
gen@fjaind.com Web:
www.fjaind.com r
Need Flex?
End-effector with wafer on chuck.
frame while removing the end effec- tor. There is little extra space to ac- commodate all of these functions and the warpage of the metal frame also plays a role in the security of the hold. These methods are acceptable for structurally rigid wafers, but not for handling the metal frames that support thinned wafers.
Top-Side Wafer Handling We must make a major depar-
ture from the handling methods of the past for rigid wafers. The solu- tion is a new handling process that grips the metal frame from the top, as there is ample room for multiple vacuum pads to ensure a secure hold and safe handling. The entire top is available for clamping except for the area around the bar code. This method permits multiple
vacuum pad locations, allows safe movement of the wafer/metal frame assembly, and does so without the need for chuck support pins, though they can still be used if desired. Hold- ing from the top permits easy entry into the cassette whether the support rails are only below the metal frame or both above and below the frame. Multiple clamping positions can be used for vacuum clamping as desired.
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