Objectives

To date, manufacturers have always found it extremely difficult to raise loads in the region of 10 kg for industrial purposes and to hold them in a precise position. Nanometer accuracy was always subject to compromise. The very possibility has come through electromagnetic vertical actuators with pneumatic gravity compensators, which can be integrated into many existing precision drive systems.

Systems of this kind are used for purposes which include semi-conductor technology, for instance in order to position reticles. The jigs needed for measuring and structuring such things as substrates, wafers and reticles usually have an (x,y) stage in order to move the object with extreme precision within a plane.

The problem

These objects are not uniform in height: there is variation in the thickness of wafers and masks or the height of the reticle supports. Besides, the procedures themselves are carried out in different levels. Here one example is the measuring of stacked images behind an exposure mask and another example the structuring of wafer layers. Such layers are often only a few nanometres thick; an entire wafer may have a thickness between 0.7 and 0.9 mm. Rises in temperature of only 0.01 K, for instance, cause such a measurement error when a reticle is being measured that the integrated circuits to be produced with it would fail.

The solution

IMMS has now developed a vertical drive to raise or lower objects with nanometre precision and active control through a range of 10 mm. The raising and lowering is achieved by pneumatic gravity compensation. This controls the amount of force to be applied by the vertical electromagnetic drive by constantly approximating it to zero. As a result there is in effect no current flowing in the actuator coil, which means there is no unwanted source of heat in the measuring space (which would interfere with the necessary precision of measurement by causing expansion of the materials).

The new drive will enable objects to be brought into position with no Abbe error, at much greater accuracy than previously for sampling or processing.

The drives previously on the market, even those working in a vacuum, can now be fitted with this new system and will thus be vastly improved. All that will be necessary is to install three of the new actuators on one platform of a positioning system. The effect will be not only exact manipulation of the height of the load but also extremely sensitive control of the tilt of the platform.