This paper compares thermal shrink properties of contact holes and chemical shrink performance for 193 nm
lithography. Pitch dependence, shrink properties, contact hole circularity, sidewall roughness, and process window are
also discussed. Thermal flow process exhibited more pitch dependence than chemical shrink process. Thermal shrink
rate increased substantially at higher bake temperatures. Contact holes in defocused area shrunk non-evenly and DOF
deteriorated upon heating. In chemical shrink process, shrink rate was hardly influenced by mixing bake temperature,
contact holes from center focus to defocus area shrunk evenly preserving effective DOF and MEF became smaller at
smaller CD. Chemical shrink has clear advantages over thermal flow process and sub-70 nm contact holes were obtained with iso-dense overlap DOF 0.25 μm by optimizing resist formulations and process conditions. Application of shrink processes will pave the way for the next generation LSI production.
We will give an account of our investigation on structure property relationships of amines with regards to line width roughness (LWR) and line edge roughness (LER) of a 193 nm alicyclic-acrylate resist. Specifically, we have looked at basicity, molar volume and logD as factors which may have an influence of roughness of 80 nm 1:1 L/S features. For relatively hydrophobic amines (Log D > -1), the lower the hydrophilicity at acidic pH the greater the LER and LWR becomes. Specifically, in this range of Log D, more hydrophobic larger amines, with higher basicity, tend to give worse L/S feature roughness. For amines which are more hydrophilic, the relationship becomes more complex with some amines giving a lower LER while others do not. This appears to be predicated on a delicate balance between basicity, hydrophilicy and size.
Optics contamination is a huge concern for extreme ultraviolet (EUV) lithography. In efforts to protect EUV optics, all materials used in EUV vacuum exposure chambers must be screened prior to use. Photoresists are a concern since a freshly coated wafer will be introduced into the chamber approximately every minute in a high volume production tool. SEMATECH has initiated a resist outgassing program to screen new resists and to learn outgassing characteristics using model compounds. This paper presents outgassing data for commercial resists as well as resists made by university researchers. Several resists made at the University of North Carolina at Charlotte (UNCC) were measured, including polymer-bound photoacid generator (PAG) resists such as poly (HOST-co-EAMA-co-PAG). Previous papers have reported that a large portion of outgassing is due to PAG fragments and deblocking groups. The UNCC resists outgas an order of magnitude less than most commercial resists tested by SEMATECH. This may be due to the low diffusion of the acid-cleavable adamantyl groups after exposure. In addition, fewer PAG species outgassed in the polymer-bound PAG resist than in blend PAG resists.
Extreme UV lithography (EUVL) is one of the most promising NGL technologies for sub-100nm resolution. We are developing polymer bound PAG resists for patterning down to the 32 nm node by EUVL. It has been reported that photoacid generators have limited compatibility with the chemically amplified polymer resist matrix that leads to phase separation, non-uniform acid distribution and migration during the baking process. To alleviate these problems, it is proposed that PAG units be incorporated in the resist chains, rather than adding monomeric PAG in to the resist polymer. The polymer bound PAG resists, poly (4-hydroxystyrene-co-2-ethyl-2-adamantyl methacrylate-co-PAG) were synthesized with different PAG loading (2% to 10.5%) using free radical polymerization. These resists contain the bulky adamantly protecting group to improve lithographic performance. The incorporation of photoacid generators (ionic and covalent) in the main chain of the polymer enhanced sensitivity and contrast compared to conventional PMMA resist and polymer with blend PAG. It was found that the sample with 5% PAG loading in the main chain gave sub 50 nm features using EUV exposure.
A chemically amplified resist, Poly(4-hydroxystyrene-co-tertiarybutylmethacrylate-co-MethacrylphenylPOSS) with different Polyhedral oligosilsesquioxane (POSS) loading has been synthesized by free radical polymerization. The incorporation of POSS units into the resist matrix has been found to affect their RIE resistance in O2 plasma. The thickness of the films were monitored using ellipsometry at various etch intervals to determine the etch rate and selectivity. It was observed that etch rate of these nanocomposite resists were comparable to the standard PHOST and Novolac based resists. HRTEM and HAADF studies showed that the POSS units exhibit a morphology of rectangular crystallites that are responsible for the plasma etch behavior. We have obtained 120 nm (1:1) (Line/Space) feature using 248 nm lithography. The protecting group, tertiary butyl protecting group exhibits acceptable outgassing. Using e-beam lithography, 70nm pattern feature was obtained.
The goal of nanofabrication capabilities that can routinely achieve dimensions of less than 32 nm will require the design of new photopolymers and strategies using wavelengths as short as 13 nm [extreme ultraviolet (EUV)]. Although EUV lithography is a challenging emerging technology that has proven its feasibility to smaller image features, yet it still requires novel photoresists. This communication discusses developments in the synthesis and lithographic performance of positive chemically amplified photoresists incorporating hydroxystyrene and a bulky adamantly protecting group. The incorporation of an ionic PAG unit, phenyl methacrylate dimethysulfonium triflate (PAG), in the resist backbone showed increased sensitivity compared with the analogous blend PAG resist samples. Sub-50 nm patterns were obtained upon extreme UV exposure on ultrathin single layer resist films of the newly synthesized polymer bound PAG resist, poly (4-hydroxystyrene-co-2-ethyl-2-adamantyl methacrylate-co-PAG).