Created by Mattias Torstensson Chalmers（由这张Torstensson查尔默斯）.pdfVIP

Created by Mattias Torstensson Photolithography 1 Created by Mattias Torstensson Photoresist Photoresist is a light sensitive liquid used to form thin film. There are several types of photoresists and we will look into some of them, to see how to use them and how they work. The main thing with photoresists is that they change chemically when exposed of light of high energy. The chemical reaction is different in various resists, but generally, they become either more or less acidic. The more acidic the resist are easier it is to remove with an alkali solution such as photoresist developer or NaOH. Because of this property, we can form the photoresist into patterns. The resist that becomes more acidic while exposed is called positive, because the exposed resist is removed. Likewise, the resist that becomes less acidic is called negative resist. Thin film photoresist Whenever use of photoresist is necessary it has to be applied as a thin film. The reason is that the total energy needed for exposure is dependent of the thickness of the film. Therefore, for high resolution a thin and smooth film is necessary. Thin film photoresist is created with a high-speed spinner that can rotate the sample with a specific velocity for a specific time. All resists have specific rotation vs. thickness dependence and it is necessary to control and decide rotation speed (see grap h 1 for the thickness dependence of S-1813, which is the resist we are going to use). Grap h 1.Thicknessdependence for s-1813 Soft and hard-bake of photoresists can be different depending on the type of resist. All photoresists need to be dried (soft baked) before exposure, but some needs special care, so it is always a good idea to check out datasheet before usage (at Chalmers these can be found at http://fy.ch