This new photoresist system extends the capability of the ESCAP platform previously discussed. (1) This resist material features a modified. ESCAP type 4-hydroxystyrene-t-butyl acrylate polymer system which is capable of annealing due to the increased stability of the t-butyl ester blocking group. The resist based on this polymer system exhibits excellent delay stability and enhanced etch resistance vs. previous DUV resists, APEX and UV2HS. Improved stabilization of chemically amplified photoresist images can be achieved through reduction of film volume by film densification. When the host polymer provides good thermal stability the sofi bake conditions can be above or near the Tg (glass transition) temperature of the polymer. The concept of annealing (film densification) can significantly improve the environmental stability of the photoresist system. Improvements in the photoacid generator, processing conditions and overall formulation coupled with high NA (numerical aperture) exposure systems, affords linear lithography down to 0.15 mu m for isolated lines with excellent post exposure delay stability. In this paper, we will discuss the UV4 and UV5 photoresist systems based on the ESCAP materials platform. The resist based on this polymer system exhibits excellent delay stability and enhanced etch resistance vs. APEX-E and UV2HS. Due to lower acrylate content, the Rmax for this system can be tuned for feature-type optimization. We will demonstrate sub-0.25 mu m deep trench has been discussed by several authors, (14,15) this level requires a fairly thick photoresist layer due to the aggressive mask open etch. The photoresist is required to print a contact hole, line and a contact hole next to each other. The line has a dimension of 0.20 mu m and each contact hole is 0.35 mu m for a total pitch of 0.55 mu m. Approximately 0.95 mu m of photoresist is required for this level. The major problem encountered with UV2HS is the rounding or film loss of the resist island in the overexposed direction. (16) Therefore, we have investigated the use of UV4 for this level. Figure 14 are lithe and etched images of the deep trench with UV4 photoresist through focus. Figure 16 is a plot of linewidth after etch vs dose for both UV4 and UV2 materials, from this plot we can see there is little difference in the dose latitude for either material. Figure 15 is UV4 and UV2 through dose after etch and from these micrographs it's difficult to differentiate between the two materials.
