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Simplified Tuned Mass Damper For GMR Head and Semiconductor Wafer Positioning Stages

IP.com Disclosure Number: IPCOM000015010D
Original Publication Date: 2002-Jan-01
Included in the Prior Art Database: 2003-Jun-20
Document File: 3 page(s) / 57K

Publishing Venue

IBM

Abstract

Disclosed is a tuned mass damper that can be incorporated into a wafer stage to reduce the oscillations of the wafer stage. A tuned mass damper is designed so that its mass will oscillate at the same frequency

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  Simplified Tuned Mass Damper For GMR Head and Semiconductor Wafer Positioning Stages

Disclosed is a tuned mass damper that can be incorporated into a wafer stage to reduce the oscillations of the wafer stage. A tuned mass damper is designed so that its mass will oscillate at the same frequency

as the object of concern, but 180 degrees out of phase in response to motion of the object. The opposing motions thus act to cancel each other.

As GMR head and semiconductor wafers are processed, various tools must rapidly move the wafer inside the tool to perform one or more operations at several locations on the wafer. Such tools include steppers to expose photo resist, metrology tools to measure feature size, and probers to electrically test devices. Given the high cost of these tools, it is imperative that they be made to perform their operations as quickly as possible.

In these tools, the wafer is typically held to a moving stage by a vacuum and the stage is made to move rapidly within the tool so that a stationary device can perform the desired operation at each location. The speed with which the wafer stage can be made to move and become ready for the desired operation is a key factor in how long the tool takes to process each wafer. After the wafer stage has been moved to a new location and stopped, it will oscillate due to the excitation of the structural modes of the wafer stage by the forces imparted in moving and stopping it. The desired operation cannot begin until these wafer stage oscillations die out with time.

The proposed design is shown in Figure 1, where the tuned mass damper is incorporated into a cavity in the wafer stage. The cavity is completely filled with an incompressible viscous fluid selected to provide the appropriate damping ratio in each axis (the damping ratio is the ratio of critical damping, where, for a second-order spring-mass-damper system, c...