(7') How to apply photoresist (continued)

When you apply a photoresist over a glass substrate, it is common to deposit metals, such as chromium, over the glass surface or to apply silane-based coupling agent.

An infrared lamp or hot air at 60 to 90°C will be used for drying and removing the solvent after applying a photoresist. However, if you dry it too fast, it dries only the surface and leaves bubbles, which will turn into pinholes later or will result in degraded adhesion. [Fig.1], [Fig.2], and [Fig.3] are the illustration of coating by liquid discharge, spin coating, and dip coating, respectively.

(8) Lithographic exposure and development

Place a negative film on top of the base plate with a photosensitive film applied. To improve the adhesion to masks, put this assembly into vacuum contact lithography equipment for light exposure.

Use a carbon arc lamp, a high-pressure mercury lamp, a xenon lamp, or laser light as the light source for exposure.

The photosensitive area of photoresists covers ultraviolet regions and visible parts. Use vacuum contact to adhere the resist-applied surface to the emulsion-applied surface before exposing them to light. [Fig.4] is an image of vacuum contact lithography equipment.

Process the sensitized base material for photoresist development. This processing dissolves and removes the area not sensitized, and hardens the sensitized part to form an insoluble film adhered to the base material. In other words, a shaped film that is difficult to dissolve will be formed on the surface where no electrodeposition will take place in order to protect this area from the electrolyte.

Organic alkali type seems to be more popular than inorganic alkali type for the developing solution. Make sure to adjust the solution's temperature since it affects the developing speed.

Various developing methods are available, such as dipping the negative into developing solution, exposing the negative to vapor of organic solvent and rinsing it off, spraying the developing solution with a spray gun, etc.

After developing the negative, completely remove the residual solvent on the photoresist. In addition, apply heat treatment using hot air or an infrared heater at 60 to 90°C in order to improve the adhesion performance and chemical resistance. (This process is called "baking".)