Experimental Procedure In this section, we willdiscuss the basic structure of CMOS or simply MOS. There istow type of coms structure, the NMOS andPMOS transistors. CMOSintegrated circuits are fabricated on thin circular slices of silicon wafers.
here we will cover the NMOS type becauseboth transistors are complementary in nature. in a groundwork way, to any layer thatwe need to pattern. We start out with an unprocessed wafer, asillustration in Figure (1-a). Figure (1-a) a clean bare wafer Figure( 1-b) a p-substrate in the cross-sectional in Figure (1-b) the NMOS transistor is fabricated on a P-type substrate and the PMOStransistor is fabricated in N-well.
afterput the P-type substrate, we grow an oxide on it such as Si02 or glass (seefigure 1-c). However, semiconductor processes must have precisely thickness andpurity of the oxide. Figure( 1-c) The oxidation process The next step of the genericCMOS patterning is adding A light-sensitive layer across the wafer it’s calledas Photoresist layer shown in figure (1-d). notes that the dimensions of thelayers that is oxide, resist, and the wafer, are not drawn to scale.
because the normal thickness of awafer is (typically between 500 µm and 800 µm), while the thickness of a grown oxide or Photoresistlayer is may be only a µm ( ) or even less. When It is formed wemoved to the masking step which is formed from layout program (see figure 1-f),and it use a reticle mask which is known as single mask, however you can seethere is a use of selectively illuminating apply in the areas of the wafer shownfigure (1-g). Figure( 1-f) the masking process