Mechatronic design of a 3 DOF long stroke motion stage

• particles on the reticle - repeat for each die on the wafer

• particles on the wafer - can kill the action of dies

current state-of-the-art

+high resolution inspection and metrology capabilities

-slow, limited to small areas of interest

challenges of SEM

• high resolution → smaller field of view

• high vacuum environment

• very sensitive to variations in external magnetic field

LoS - SS concept

• inside the vacuum chamber

• Lorentz actuator in SS

• linear roller guides in LoS

• active cooling with water

• magnetic fields

→ costs

LoS outside chamber with piezoelectric short stroke

+magnetic fields reduced, motors in ambient, reduction of cooling hoses, motor cables in vacuum

-position dependent behvaior, only rotary vacuum moton feedthrough

→ ferrofluid seal - uses a magnetic fluid placed around a rotating shaft by a ring of permanent magnets = vacuum (has friction)

requirements of the new system

• reach wafer position

• accurately position it under SEM

• fit inside vacuum chamber

• LoS actuation outside of the chamber

• high voltage and magnetically compatible materias

• bigger lifetime and sevice intervals

• not higher costs

high-speed dynamically balanced robotic manipulator

• favorable dynamics due to symmetry

• only rotational bearings

• vaccum compatible components

• dynamic balance using passive counterweights

• workspace matches purpose

→ dual purpose: actuatos in-plane DoF (x, y, Rz) and constraints out-of-plane DoF (z, Rx, Ry)

kinematics of the high-speed dynamically balanced robotic manipulator

Uses a Jacobian matrix (position dependent) for actuators:

• velocity

• relative changes in position

• torque (force)

singularities

In a singularity, Jacobian matrix loses rank

0=singularity

1=equal in all directions

three arms vs four arms

• fourth arms add out-of-plane stiffness, creates symmetry, less out-of-plane rotations

• eliminates singularities with LoS inside the chamber

• good dynamics

• less position dependent (no worst case)

kinematic design (first order modelling)

what dimensions? where to place motors? can we reach all positions? does it fit inside the chamber?

parameters: vertical displacement due to gravity, torque index, accuracy index, relative angle between arms

• vary link length and actuator placement

• high eigenfrequency = good overall results

→ only configurations that fit inside chamber and cover workspace

→ minimal position dependent vertical deflections due to gravity

→ minimal position dependent eigenfrequency

→ minimal position dependent torque

design considerations in vacuum and SEM environments

• outgassing

• virtual leaks

• chamber deformation

• ferromagnetic properties

• bearings design

carrier-arm connection

• analogy to giving a hand

• carrier compliant in torsion

• mismatch in constraints due to angle between Ry, car and Ry, arm

linkage 2

• compliant in torsion to avoid overconstraint

tolerances

• on bearing and components lead to Ry rotations, resulting in z

• sensitivity matrix - to calculate required vertical actuator displacement

dynamic balancing

• trade-off torque/mass/size

• divide mass carrier over 4 arms

• eigenfrequency decreases due to addition of required balance mass