Laboratory: A Typical Lithography Process

- Place the wafer in a tin plate.

- To make sure that the wafer is completely dry, place the tin plate containing the wafer into the dehydration oven for 30 minutes to "Pre-Bake" it.

- Using teflon tweezers, place the wafer on the wafer chuck in the center of the Photoresist Spinner.

- Using a Nitrogen Gun, blow the wafer surface to remove any dust particles.

- Using an eye dropper, flood the wafer surface with primer to facilitate resist adhesion to substrate.

- Press the spin button which will cause the wafer to spin at ~ 5000 rpm. Centrifugal force will cause excess primer to move away from the center until all wafer is primed and ready to accept resist. Then release spin button.

- No photos could be taken while resist is applied since it is sensitive to light. Actually all lighting in the clean room is covered by yellow filters.

- Give the resist a soft-bake in an oven at temperatures between 90 and 120 °C to semi-harden the resist. Meanwhile setup the mask aligner.

- For each layer there is a separate mask (patterned glass).

- Place the mask in the wafer holder so that the emulsion side of the mask is facing downward toward the wafer.

- Slide the wafer holder into the mask aligner.

- Tighten the two knobs to secure the wafer holder in place.

- Bring the resist-covered wafer back from the soft-bake oven.

- Carefully place the wafer on the wafer chuck of the aligner.

- Carefully slide the wafer chuck into the aligner so that the wafer is positioned under the mask.

- Slowly raise the lever so that the wafer comes into contact with the mask Then press the button marked “Separation” that will cause the wafer ~ 0.5 mm away from the mask without being scratched..

- Adjust the microscope knobs as well as knobs (three) that allow you to move the wafer in horizontal and vertical directions.

- Press expose button. A very bright light will come on inside the aligner. The exposure time is set according to the type of resist (~10 s)

- The type of developer solution used is determined by the type of resist chosen.

- Carefully place the wafer into a chemically resistant carrier.

- Be sure to lock the wafer so that it is firmly secured.

- Immerse the wafer in the developer for the recommended time ( ~ 30 s).

- Immediately after plunge the wafer into the beaker filled with water to stop the development process.

- Use a de-ionized water gun to completely clean the wafer.

- Use nitrogen gun to thoroughly dry the wafer, front and back.

- Inspect the wafer under the microscope to see if the patterns are clear and well defined.

- If everything is OK , place the wafer in the hard-bake oven which should be preheated to the required temperature (120 - 140 °C).