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Rotary Table Tackles Big Wafers

Rotary Table Tackles Big Wafers

The RotoRing300(TM) direct-drive rotary table from IntelLiDrives adapts linear motor technology, coupled with air bearings, to provide faster and reportedly more accurate handling of the largest (300-mm) semiconductor wafers. These improvements are on a more compact, stiffer platform.

According to company VP and engineer Greg Kane, typical direct-drive rotary tables "can only move plus or minus 10 degrees , but the RotoRing rotates 360 degrees at up to 100 rpm." Thus, large angle wafer rotation can be done with the table, eliminating the need to align a wafer carrier before placement on the table, thereby increasing throughput. An XY table that carries the rotary table is used for linear Cartesian alignment. The large open center allows equipment above and below the table to extract the integrated circuit dies cut vertically and horizontally from the wafer.

Previous rotary tables use a mechanical transmission such as a rack-and-pinion, worm drive, or belt, which Kane says lack positioning stiffness and accuracy. While he adds a worm drive could fully rotate a table, its speed is in single-digit rpm and is costly. Belt drives can rotate completely as well but the low belt stiffness and high inertia of any table result in slow speeds. In processing smaller 8-inch wafers these characteristics could be tolerated and it wasn't until advent of the large semiconductor wafers that a large rotary table was needed, Kane says.

The RotoRing is essentially a linear motor with its track curved to form a ring. Sixteen RotoLinear(TM) motor modules within the ring form the motor, but up to 24 can be installed for greater torque. The proprietary architecture uses a grooved, passive ferromagnetic structure in the top ring and the stationary brushless motor modules in the fixed lower section. Modulating the modules creates a rotating magnetic flux to turn the ring.

Tight toleranced radial and axial air bearings allow only a 25-micron air gap, resulting in a small package with a low center of gravity for reduced dynamic inertia effects on motion (i.e. greater stiffness). The 14-inch diameter center opening is round to within 10 microns and in rotation, its vertical and horizontal runout are less than 10 microns.

Kane says interest in RotoRing technology is coming from general automation applications as well. These could include, for example, processes that need increased access to indexed parts afforded by a large center opening such as dispensing adhesives to an array of points. IntelLiDrives Inc., Enter 509

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