1.  Field of the Invention
The present invention relates to movable body apparatuses, pattern formation apparatus and exposure apparatus, and device manufacturing methods, and more particularly, to a movable body apparatus equipped with a movable body which substantially moves along a predetermined plane, a pattern formation apparatus which forms a pattern on an object mounted on a movable body, an exposure apparatus which forms a pattern on an object by irradiating an energy beam, and a device manufacturing method which uses the exposure apparatus. 
2.  Description of the Background Art
Conventionally, in a lithography process for manufacturing microdevices (electron devices) such as semiconductor devices, liquid crystal display devices and the like, exposure apparatuses such as a projection exposure apparatus by a step-and-repeat method (a so-called stepper) and a projection exposure apparatus by a step-and-scan method (a so-called scanning stepper (which is also called a scanner) are mainly used. 
With these types of projection exposure apparatus, the position of a stage holding a substrate subject to exposure, such as for example, a wafer, was generally measured using a laser interferometer.  However, due to finer patterns which accompany higher integration of semiconductor devices, requirements in performance is becoming tighter, and for example, as for overlay error, the permissible value of the overall overlay error has become an order of several nm, while the permissible value of a position control error of the stage has also become equal to or less than a sub-nano order, and short-term variation of measurement values which is caused by air fluctuation which occurs due to the influence of temperature fluctuation and/or temperature gradient of the atmosphere on the beam path of the laser interferometer can no longer be ignored. 
Therefore, recently, an encoder with a high resolution which is impervious to air fluctuation when compared with an interferometer has begun to gather attention, and an invention related to an exposure apparatus which uses the encoder in position measurement of a wafer stage and the like has been proposed (refer to, for example, the pamphlet of International Publication 2007/097379 and the like). 
In the exposure apparatus and the like disclosed in the pamphlet of International Publication 2007/097379, position measurement of a wafer stage and the like is performed, using a plurality of encoder heads.  However, when position measurement of a wafer stage and the like is performed using a plurality of encoder heads, malfunction of each encoder head, such as, for example, a mechanical failure and the like may cause an abnormality in the output of the encoder heads.  Meanwhile, in order to achieve a highly precise exposure even in such a case, being able to measure the position of the wafer stage continuously with high precision is required.