Single-layer resists

Figure 6. SEM photograph of a 0.2 m wide pattern using an SPP single-layer resist. A 1.0 um thick SPP layer was exposed to X-rays In vacuum at 160 mJ/cm followed by a flood exposure and then dip-developed in a 0.8 wt% TMAH solution for 60 s at 25°C.

Figure 1. Gas phase functionalization scheme for single-layer resists.

A photooxidative scheme has been developed to pattern sub half-micron images in single layer resist schemes by photochemical generation of hydrophilic sites in hydrophobic polymers such as poly(styrene) and chlorinated poly(styrene) and by selective functionalization of these hydrophilic sites with TiCU followed by O2 RIE development. Sub half-micron features were resolved in 1-2 pm thick chlorinated poly(styrene) films with exposures at 248 nm on a KrF excimer laser stepper. The polymers are much more sensitive to 193 nm (sensitivity 3-32 mJ/cm2) than to 248 nm radiation (sensitivity -200 mJ/cm2) because of then-intense absorption at 193 nm. 

As for negative deep UV resist, O Toole et al. have exhibited half-micron pattern resolution in 0.5 micron film thickness using the new resist and PIE process (10). The pattern profiles, however, were re-entrant, due to the large photo absorption and the applications to single-layer-resist system have not been presented (11). 

We achieved high aspect ratio sub-half-micron pattern fabrication in 1.0 micron film thickness using this new resist. We are convinced that this new resist could make possible simple and efficient single-layer-resist system for KrF excimer laser lithography. 

Although the single-layer negative resists commonly utilized are simple, they typically do not resolve narrow (0.5 ftm) gaps between wide lines or pads due to proximity effects from backscatter from the substrate during electron beam (E-beam) exposure. Further, there are variations in linewidth which occur when images are written in a single-layer resist which overlies steps in the substrate. 

Although single-layer resists are preferred from the viewpoint of simplicity of the process, two- or three-layer resists are also promising [103]. These resists have an advantage... 

The formulation of a single-layer resist that can meet beyond-state-of-the-art demands is an arduous task. To date, very few such materials have been advertized, and their field performance is yet to be proven. The difficulty lies in the fact that requirements of sensitivity, etch resistance, and planarization are mutually exclusive. For example, thinner resists capable of higher resolution sacrifice substrate etching protection and planarization. Consequently, the focus of lithographers lately has centered upon multilevel-resist processes that distribute desirable resist properties among several different organic and inorganic layers. 

Bnm single layer resists with antineflective coatings... 

Fig. 4. Polynucleotide array fabrication processes using polymeric photoresists. Left. A single layer resist process. Right A bilayer process using a protective underlayer...

Bol, 1.1. High Resolution Optical Lithography Using Dyed Single-Layer Resist In Proceedings of Kodak Microelectronics Seminar-Interface 84 Eastman Kodak Rochester, NY, 1984. 

Single layer resist with negative profile... 

Fig. 4.9. Schematics for successful liftoff procedures showing a negative profile in a single-layer resist and the undercut achievable with a two-layer resist...

Fig. 4.9). In a single-layer resist system this is achieved by either a slight overexposure or a slightly longer development time. 

A terpolymer of ter/-butyl methacrylate (TBMA), methyl methacrylate (MMA), and methacrylic acid (MAA) was initially developed as a chemically amplified thick laser resist for circuit board fabrication [ 180]. The terpolymer containing 1 wt% of di(ferf-butylphenyl)iodonium trifluoromethanesulfonate (triflate) has demonstrated excellent imaging at 193 nm when developed with a dilute (0.01 N) TMAH aqueous solution [181]. This terpolymer single layer resist was employed for exposure tool testing. 

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