3 Dof Positioning of a Capacitive Measurement Electrode Using the Thermal Slider Actuator

CAPACITIVE SENSOR ACTUATION In the semiconductor industry there is a need for controlling the displacement of machine parts such as optical elements with sub-nanometer uncertainty within a motion range of several micrometers. This combination makes capacitive measurement a suitable method to acquire the required displacement data. In order to achieve sufficient sensitivity and linearity the measurement electrode must be around 10 micrometers distance from the measurement target and parallel within a few milliradians. Obtaining this during sensor installation is not feasible and due to inaccessibility manual adjustment afterward is not possible. An actuator incorporated in the sensor can however automatically position the electrode using itself as a sensor. In our application the position stability after alignment must however still be better than 200 pm over a time span of 2 minutes. The thermal slider actuator depicted in Figure 1 was developed at Delft University of Technology as a part of an integrated sensor system design and combines the motion capability with a good mechanical stability.