1. Field of the Invention
This invention relates to an X-Y positionable work station and more particularly to a very accurately and quickly positionable work station in a vacuum environment.
2. Description of the Prior Art
Generally, in the known prior art, systems operating in vacuum environments are not required to simultaneously perform to stringent specifications. As such, relatively loose designs are possible which are inaccurate or slow and do not severely stress the components. In the writing of photolithographic patterns on semiconductor workpieces by an electron beam in a vacuum environment, a very accurately positionable X-Y table is required. The table also has to function within a high vacuum environment, presenting stringent lubrication requirements and special material and component limitations. Also, the electron beam is greatly affected by moving magnetic material near the final lens, and by electro magnetic fields created in the vacinity of the lens. These considerations require that the electric drive motor be located outside the vacuum chamber to eliminate the outgassing friction of the brushes, and lubrication problems, as well as to attenuate the electro magnetic field. By placing the motors outside the vacuum chamber, heat transfer from the motor is also facilitated.
At the same time, the requirements for very fast and accurate positioning demand that the prime mover and associated linear actuators conform to prescribed requirements of good design of servo systems. Mandatory characteristics include items such as low friction, low compliance, high rigidity, high stiffness, and low mass, to achieve the maximum mechanical resonent frequency. This requires a minimal backlash linear actuator, and positive coupling between all the drive components, as well as positive coupling to the X-Y stage. Consequently, such items as flexible shafts and couplings are not desirable.
A system having the foregoing characteristics has many interactive parts requiring maintenance, repair, replacement, and diagnosis. A severe problem with prior art systems has been that the entire electron beam (E-beam) column which provides a control for the electron beam, must be lifted up with a crane to provide access to the workpiece positioning apparatus. The prior art teaches no quick and convenient way to remove the X-Y table, to perform necessary maintenence etc., and return the same into the vacuum chamber. Similarly, known techniques for conveniently accessing X-Y tables for maintenance and repair purposes would not be applicable to the highly fast and accurate X-Y positioning apparatus required herein.