A3-dof Precision Position Sensing Using Linear Hall Sensors

Mask-silicon wafer alignment technology, which is one of the three coretechnologies of lithography machines, has been the focus of the lithographymachines. When the mask table is aligned, the micro-displacement measurement ofthe planar three-freedom of the micro-positioner has a direct impact on the totaloverlay accuracy and the image size of the lithography machine. In order to meetthe measurement requirements when replacing the mask table, this paper designed ameasurement system of the planar three-freedom, which is based on the linear Hallsensor. The main work is as follows:Through the electromagnetic simulation of1-DOF displacement measuringscheme, the magnetic induction intensity spatial distribution form was founded, andthe feasibility of1-DOF measurement scheme was verified. On the basis of itdesigned the planar3-DOF measurement sensor layout, and in order to solve theinconsistency problem between the ideal model for the distribution of magneticinduction intensity measurement and the actual distribution model inconsistencyproblem, put forward a kind of position decoupling method for microtremor3-DOFplane based on ellipse fitting function, by measuring the magnetic field intensity ishigh plane density of sampling, by fitting the distribution model of inductionmagnetic using elliptic function, provided theoretical basis for relationship betweenthe sensor measurements and the worktable position control system; according tothe technical requirements of the task, designed the signal processing card of thelinear Hall sensor based on the FPGA modularly, and achieved the measurementrequirements of high sensitivity, high sampling rate and high transmission rate;built one experimental platform with1-DOF and the other with planar3-DOFrespectively. The resolution and linearity of measurement systems was testedrespectively too, also verified the correctness of the measurement system.The results of the experiment with a1-DOF linear Hall sensor showed thatwhen the distance from the sensor to the surface of the magnetic steel is8.0mm, thedisplacement resolution of the Hall sensor is better than1μm within the range of4mm, the non-linearity is6.06%F.S., after compensation it could be0.08%F.S.. Theresults of the experiment with planar3-DOF showed that within the measurementrange of±2mm, elliptic curves can fit the real distribution of magnetic inductionintensity ideally, the average fitting error is less than1μm; the displacementresolution in the X direction is1μm within the range of4mm, the displacementresolution in the Y direction is1μm within the range of4mm, and the displacementresolution in the Rz direction is1.296″. All the above results of the experiments confirmed that the measurement system of the planar3-DOF which is based on thelinear Hall sensor could meet the expected target.