Precise positioning system for UV exposure masks

A high-pre­ci­sion posi­tion­ing sys­tem for use in a dry nitro­gen atmos­phere or vac­u­um has now been devel­oped by Stein­mey­er Mecha­tron­ik GmbH in coop­er­a­tion with August Stein­mey­er GmbH & Co. KG. The mask sys­tem is ide­al­ly suit­ed for use in stan­dard as well as high-res­o­lu­tion UV lith­o­g­ra­phy and enables very fine XY theta align­ment of expo­sure masks with up to 0.03 µrad. Minia­ture ball screws from Alb­stadt are used in it, which meet par­tic­u­lar­ly high require­ments for uni­for­mi­ty of pre­load and run­ning qual­i­ty in the application.

 The three lin­ear axes of the posi­tion­ing sys­tem are par­al­lel-kine­mat­ic in design: two ver­ti­cal axes in the X direc­tion and one trans­verse in the Y direc­tion. The two ver­ti­cal axes gen­er­ate a ver­ti­cal stroke when mov­ing simul­ta­ne­ous­ly and a rota­tion when mov­ing in oppo­site direc­tions. This enables high-pre­ci­sion lin­ear and rota­tion­al posi­tion­ing of the masks down to the sub-microm­e­ter range.

Ball screw meets high requirements

Ground minia­ture ball screws with a spin­dle diam­e­ter of 12 mm from August Stein­mey­er are used in this very pre­cise posi­tion­ing sys­tem. These are equipped with a flanged sin­gle nut with 4‑point con­tact, sin­gle-gear revers­ing and option­al ceram­ic balls. The high geo­met­ric qual­i­ty and sur­face fin­ish of the back­lash-free pre­loaded com­po­nents ensure ide­al syn­chro­niza­tion in the appli­ca­tion and enable the small­est posi­tion­ing incre­ments. The assem­blies under­go appli­ca­tion-ori­ent­ed series test­ing pri­or to deliv­ery. The ser­vice life has been proven in dry nitro­gen atmos­phere and vacuum.

Use in a dry nitro­gen atmos­phere or vac­u­um requires the selec­tion of spe­cial mate­ri­als and lubri­cants. Hard­en­able stain­less steel is there­fore used in the ball screw. In addi­tion, to min­i­mize scat­tered radi­a­tion, all struc­tur­al parts of the mask sys­tem are pro­vid­ed with an anodized coat­ing opti­mized for UV absorp­tion. The ultra­vi­o­let light appli­ca­tion also pro­hibits hydro­car­bons for the com­po­nents and assem­blies of the three-axis mask sys­tem. There­fore, a flu­o­rine com­pound-based lubri­cant is used that is chem­i­cal­ly and phys­i­cal­ly very sta­ble, shows no degra­da­tion under ultra­vi­o­let radi­a­tion and has an extreme­ly low out­gassing rate. It has been spe­cial­ly devel­oped by the user for this appli­ca­tion and adapt­ed for use in pre­loaded ball screws.

Optimal for service and maintenance

For main­te­nance, the expo­sure masks can be moved lat­er­al­ly out of the opti­cal axis into ser­vice posi­tions. If nec­es­sary, a mag­net­i­cal­ly pre­loaded quick-change mech­a­nism ensures that the mask can be replaced quick­ly and eas­i­ly in just a few steps. Main­te­nance of the motors and end-posi­tion sen­sors, which are designed as inter­change­able mod­ules, is just as uncomplicated.

For low-effort inte­gra­tion into the con­trol sys­tem of the machine under series pro­duc­tion con­di­tions, the spec­i­fied band of the no-load torque must be pre­cise­ly set by means of the pre­load dur­ing assem­bly of the ball screw. This is a pre­req­ui­site for sta­ble tun­ing of the con­trol sys­tem and reduces down­times in the event of main­te­nance, since the PID para­me­ters do not have to be found again in the event of replace­ment. The sta­bil­i­ty of the run­ning char­ac­ter­is­tics over the ser­vice life achieved in this way also increas­es oper­a­tional reli­a­bil­i­ty, since the motor con­trol always runs in the opti­mal­ly tuned range, which in turn is the pre­req­ui­site for achiev­ing very small posi­tion­ing incre­ments below micrometers.

The posi­tion­ing sys­tem is avail­able in sev­er­al trav­els to suit dif­fer­ent mask sizes and can also be cus­tomized to suit appli­ca­tions. Clean room or vac­u­um ver­sions are avail­able as options. Appli­ca­tion exam­ples can be found in semi­con­duc­tor image­set­ters, but also in the inspec­tion of masks.