We have developed organometallic carboxylate compounds [R n MðO 2 CR 0 Þ 2 ] capable of acting as negative-tone extreme ultraviolet (EUV) resists. The most sensitive of these resists contain antimony, three R-groups and two carboxylate groups, and carboxylate groups with polymerizable olefins (e.g., acrylate, methacrylate, or styrenecarboxylate). Evidence suggests that high sensitivity is achieved through the polymerization of olefins in the exposed region. We have performed a systematic sensitivity study of the molecules of the type R n MðO 2 CR 0 Þ 2 where we have studied seven R groups, four main group metals (M), and three polymerizable carboxylate groups (O 2 CR 0). The sensitivity of these resists was evaluated using E max or dose to maximum resist thickness after exposure and development. We found that the greatest predictor of sensitivity of the R n SbðO 2 CR 0 Þ 2 resists is their level of polymerizable olefins. We mathematically define the polymerizable olefin loading (POL) as the ratio of the number of olefins versus the number of nonhydrogen atoms. Linear and log plots of E max versus POL for a variety of molecules of the type R 3 SbðO 2 CR 0 Þ 2 lend insight into the behavior of these resists.

Abstract. Here, we present platinum and palladium mononuclear complexes with EUV photosensitivity and lithographic performance. Many platinum and palladium complexes show little or no EUV sensitivity; however, we have found that metal carbonates and metal oxalates (L 2 MðCO 3 Þ and L 2 MðC 2 O 4 Þ; M ¼ Pt or Pd) are sensitive to EUV. The metal carbonates give negative-tone behavior. The most interesting result is that the metal oxalates give the first positive-tone EUV resists based on mononuclear organometallic compounds. In particular, (dppm)Pd(C 2 O 4 ) (dppm ¼ 1,1-bis(diphenylphosphino)methane) (23) prints 30-nm dense lines with E size of 50 mJ∕cm 2 . Derivatives of (23) were synthesized to explore the relationship between the core metal and the resist sensitivity. The study showed that palladium-based resists are more sensitive than platinum-based resists. The photoreaction has been investigated for two of our most promising resists, ðdppmÞPdðC 2 O 4 Þ (23) and ðPh 2 EtPÞ 2 PdC 2 O 4 (27). Our experiments suggest the loss of CO 2 and the formation of a zerovalent L 4 Pd complex upon exposure to light. We have identified dppm 2 PdðδðPÞ23:6Þ as the main photoproduct for (23) and ðPh 2 EtPÞ 4 Pd (δðPÞ32:7) as the main photoproduct for (27).

The EUV photoreactivity of platinum and palladium mononuclear complexes has been investigated. Many platinum and palladium complexes show little or no EUV sensitivity, however, we have found that metal carbonates and metal oxalates (L 2 M(CO 3) and L 2 M(C 2 O 4); M = Pt or Pd) are sensitive to EUV. The metal-carbonates give negative tone behavior. The most interesting result is that the metal oxalates give the first positive-tone EUV resists based on mono-nuclear organometallic compounds. In particular, (dppm)Pd(C 2 O 4) (dppm = 1,1-Bis(diphenylphosphino)methane) (25) prints 30-nm dense lines with E size of 50 mJ/cm 2. To improve the lithographic performance of (25), the processing conditions were studied. A bake study showed that bake affected sensitivity and dark loss very little, while dark loss worsened with development time. Derivatives of (25) were synthesized to explore the effect of molecular weight on resist sensitivity, but the study showed no correlation between molecular weight and sensitivity.

Pure thin-films of unimolecular organometallic photoresists were lithographically evaluated using extreme ultraviolet light (EUV, λ = 13.5 nm) and developed using solutions containing carboxylic acids. Optimization of development solutions used with a cobalt-oxalate EUV resist (NP1, 2) led to a switch in lithographic tone from negative to positive. Additional optimization led to an improvement in top loss (35 to 7%) with development in cyclohexanone and 2-butanone, respectively. We saw a drastic improvement in photo-speed (E max = 5 mJ/cm 2) and contrast of the negative-tone imaging with development in certain acidic solutions. Additionally, carboxylic acid solutions provide excellent development conditions for resists that we, in the past, have been unable to successfully develop.

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