Vertical resist image profile

The development process produces final three-dimensional resist images. This is a critical process as a sinusoidal latent image generated by exposure must be converted to a step function in order to produce resist images with vertical wall profiles. Thus, it is important to understand the dissolution behavior of resist films in a developer (especially aqueous base). 

Figure 2.4. The latent image in the resist has essentially the shape indicated because of the sloping nature of the free space image and the absorption of the resist film. Depending on the processing conditions, either negatively sloped undercut profiles) vertical profiles or positively sloped profiles can be obtained.

Lin (83) studied the MRS resist (RD2000N) to determine the effect of optical density on performance. Resist images were delineated by 222-nm KrCl and 308-nm XeCl excimer laser radiation as shown in Figure 3.72. At 308 nm, nearly vertical resist profiles were produced. This result provides... 

As mentioned earlier, the COMA positive resists tend to have higher optical absorption at 193 nm than polymethacrylate and COBRA systems, which would produce a tapered image profile. To overcome this potential problem, the T-top formation by absorption of base into the top layer (see above) has been intentionally incorporated in the lithographic process (amine gradient process) [281]. Poly(acrylic acid-co-methyl acrylate) and L-proline were dissolved in water and spin-cast on a COMA resist. During PEB the amine in the overcoat diffuses into the COMA resist layer and compensates for the acid gradient caused by illumination, providing a vertical profile. 

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