Ultraviolet photolithography

Perfluoroacetal or perfluoroketal polymethacrylates containing norbornene substituents and having improved transparency were prepared and were suitable for use in photolithography with far-ultraviolet light at a wavelength of 180 nm or shorter. These materials are particularly useful in the formation of a fine resist patterns. 

One of the methods under development at AT T Bell Laboratories for submicron lithography is deep ultraviolet projection photolithography. (O Fine line definition is obtained by use of 248 nm light and a lens of large numerical aperture. Because of the large chromatic aberration of the quartz lens a spectrally line-narrowed krypton fluoride excimer laser is used as a light source. 

The concept of a "minimum feature size is also important in fabrication of microdevices its actual dimensions are determined by the choice of fabrication process. As discussed below, conventional photolithography (405 or 436 nm) is generally limited to features of approximately 1 pm. Deep ultraviolet (UV) (230 to 260 nm) lithography has a minimum feature size of 0.3 pm, and x-ray and e-beam can be used to generate features as small as 0.1pm. 

Individual microelectronic devices consist of numerous layers of carefully patterned thin films. Patterning depends upon the ability to define and draw a two-dimensional pattern on a wafer substrate. Currently, this ability depends on photolithography by optical projection, in which a polymer resist film is deposited on the wafer and subsequently exposed to ultraviolet... 

Femtosecond laser applications, e.g., in electronic or medical technology require microstructuring on uneven substrates. This cannot be achieved by conventional photolithography which only functions on completely flat supporting materials. Ultraviolet lasers (excimer, fourth harmonic Nd YAG) have been widely used for such purposes. However, when high precision is required and substrates are extremely fragile and thermally sensitive, the very low heat effect by subpicosecond laser pulses can avoid this micromachining problem. 

---