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LED knowledge of photoresist

Photoresist, also known as photoresist, is a photosensitive material used in many industrial processes. Like lithography, a patterned coating can be engraved on the surface of the material.

There are two kinds of photoresists, positive photoresist and negative photoresist.
The forward photoresist is a kind of photoresist, and the portion that shines on the light is dissolved in the photoresist developer, and the portion that is not illuminated is not dissolved in the photoresist developer.

The negative photoresist is a kind of photoresist, and the portion which is irradiated to the light is not dissolved in the photoresist developing solution, and the portion which is not irradiated with light is dissolved in the photoresist developing solution.

Positive-type photoresists and negative-type photoresists are mainly used in the metal electrode evaporation Lift-off process for LED die manufacturing. Since the metal materials used for LED electrodes are not easy to make circuit patterns by etching, Lift-off lithography process, obtaining an overhang photoresist pattern, so that the metal will not be continuously deposited on the photoresist during the evaporation process, and the photoresist will not be used. The photoresist portion of the metal cloth cover is partially pulled up to complete the pattern of the metal electrode.

In the optical exposure mode, the upper layer of the photoresist receives higher energy than the lower layer, so that most of the positive photoresist is imaged as narrow and wide, and cannot be exposed once. That is, the pattern of Overhang is obtained, and the image of the negative photoresist is exactly opposite to the image of the positive photoresist, so the negative photoresist is the best choice for the lift-off process.

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