Ryan Del Re

EUV Resists based on Tin-Oxo Clusters

We have studied the photolysis of tin clusters of the type [(RSn)12O14(OH)6] X2 using extreme ultraviolet (EUV, 13.5 nm) light, and developed these clusters into novel high-resolution photoresists. A thin film of [(BuSn)12O14(OH)6][p-toluenesulfonate]2 (1) was prepared by spin coating a solution of (1) in 2-butanone onto a silicon wafer. Exposure to EUV light caused the compound (1) to be converted into a substance that was markedly less soluble in aqueous isopropanol. To optimize the EUV lithographic performance of resists using tin-oxo clusters, and to gain insight into the mechanism of their photochemical reactions, we prepared several compounds based on [(RSn)12O14(OH)6] X2. The sensitivity of tin-oxide films to EUV light were studied as a function of variations in the structure of the counter-anions (X, primarily carboxylates) and organic ligands bound to tin (R). Correlations were sought between the EUV sensitivity of these complexes vs. the strength of the carbon-carboxylate bonds in the counteranions and vs. the strength of the carbon-tin bonds. No correlation was observed between the strength of the carboncarboxylate bonds in the counter-anions (X) and the EUV photosensitivity. However, the EUV sensitivity of the tinoxide films appears to be well-correlated with the strength of the carbon-tin bonds. We hypothesize this correlation indicates a mechanism of carbon-tin bond homolysis during exposure. Using these tin clusters, 18-nm lines were printed showcasing the high resolution capabilities of these materials as photoresists for EUV lithography.

Platinum and palladium oxalates: positive-tone extreme ultraviolet 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 (L2M(CO3) and L2M(C2O4); 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 mononuclear organometallic compounds. In particular, (dppm)Pd(C2O4) (dppm=1,1-bis(diphenylphosphino)methane) (23) prints 30-nm dense lines with Esize of 50  mJ/cm2. 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, (dppm)Pd(C2O4) (23) and (Ph2EtP)2PdC2O4 (27). Our experiments suggest the loss of CO2 and the formation of a zerovalent L4Pd complex upon exposure to light. We have identified dppm2Pd(δ(P)23.6) as the main photoproduct for (23) and (Ph2EtP)4Pd (δ(P)32.7) as the main photoproduct for (27).

High-sensitivity molecular organometallic resist for EUV (MORE)

We have developed organometallic carboxylate compounds [RnM(O2CR’)2] capable of acting as negativetone EUV resists. Overall, the best and fastest resists contain antimony, are pentavalent and the carboxylate group contains a polymerizable olefin (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 molecules of the type RnM(O2CR’)2 where we have studied seven R groups, four main group metals (M), and three polymerizable carboxylate groups (O2CR’). We found that the greatest predictor of sensitivity of the RnSb(O2CR’)2 resists is their level of polymerizable olefins. We mathematically define the polymerizable olefin loading (POL) as the ratio of the number of olefins vs. the number of non-hydrogen atoms. Linear and log plots of Emax vs. POL for a variety of molecules of the type R3Sb(O2CR’)2 lend insight into the behaviour of these resists.

Low-line edge roughness extreme ultraviolet photoresists of organotin carboxylates

Abstract. Pure thin films of organotin compounds have been lithographically evaluated using extreme ultraviolet lithography (EUVL, 13.5 nm). Twenty compounds of the type R2Sn(O2CR′)2 were spin-coated from solutions in toluene, exposed to EUV light, and developed in organic solvents. Exposures produced negative-tone contrast curves and dense-line patterns using interference lithography. Contrast-curve studies indicated that the photosensitivity is linearly related to the molecular weight of the carboxylate group bound to tin. Additionally, photosensitivity was found to be linearly related to free radical stability of the hydrocarbon group bound directly to tin (R=phenyl, butyl, and benzyl). Dense-line patterning capabilities varied, but two resists in particular show exceptionally good line edge roughness (LER). A resist composed of an amorphous film of (C6H5CH2)2Sn(O2CC(CH3)3)2 (1) achieved 1.4 nm LER at 22-nm half-pitch patterning and a resist composed of (C6H5CH2)2Sn(O2CC6H5)2 (2) achieved 1.1 nm LER at 35-nm half-pitch at high exposure doses (600  mJ/cm2). Two photoresists that use olefin-based carboxylates, (C6H5CH2)2Sn(O2CCH⏧CH2)2 (3) and (C6H5CH2)2Sn(O2CC(CH3)⏧CH2)2 (4), demonstrated better photospeeds (5  mJ/cm2 and 27  mJ/cm2) but worse LER.

Organometallic carboxylate resists for extreme ultraviolet with high sensitivity

Abstract. We have developed organometallic carboxylate compounds [RnM(O2CR′)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 RnM(O2CR′)2 where we have studied seven R groups, four main group metals (M), and three polymerizable carboxylate groups (O2CR′). The sensitivity of these resists was evaluated using Emax or dose to maximum resist thickness after exposure and development. We found that the greatest predictor of sensitivity of the RnSb(O2CR′)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 Emax versus POL for a variety of molecules of the type R3Sb(O2CR′)2 lend insight into the behavior of these resists.

Low-LER tin carboxylate photoresists using EUV

Pure thin films of organotin compounds have been lithographically evaluated using extreme ultraviolet lithography (EUVL, 13.5 nm). Twenty-one compounds of the type R2Sn(O2CR’)2 were spin-coated from solutions in toluene, exposed to EUV light, and developed in organic solvents. Exposures produced negative-tone contrast curves and dense-line patterns using interference lithography. Contrast-curve studies indicated that the Emax values were linearly related to molecular weight when plotted separately depending upon the hydrocarbon group bound directly to tin (R = butyl, phenyl and benzyl). Additionally, Emax was found to be linearly related to free radical stability of the hydrocarbon group bound directly to tin. Dense-line patterning capabilities varied, but two resists in particular show exceptionally good line edge roughness (LER). A resist composed of an amorphous film of (C6H5CH2)2Sn(O2CC(CH3)3)2 (13) achieved 1.4 nm LER at 22 nm half-pitch patterning and a resist composed of (C6H5CH2)2Sn(O2CC6H5)2 (14) achieved 1.1 nm LER at 35 nm half-pitch at high exposure doses (600 mJ/cm2). Two photoresists that use olefin-based carboxylates, (C6H5CH2)2Sn(O2CCH=CH2)2 (11) and (C6H5CH2)2Sn(O2CC(CH3)=CH2)2 (12), demonstrated much improved photospeeds (5 mJ/ cm2 and 27 mJ/cm2) but with worse LER.

EUV resists comprised of main group organometallic oligomeric materials

We present the synthesis and preliminary lithographic evaluation of Molecular Organometallic Resists for EUV (MORE) that contain post transition metals. These post transition metal nuclei have high EUV optical density so they can utilize a high fraction of the incident photons. We will describe two technical approaches for EUV resist platforms that contain bismuth. Approach 1: Combination of organometallic compounds with photoacid generators. Approach 2: Combination of high-oxidation state metal-center oligomers that utilize carboxylate anions bound to the metal centers.

Positive-tone EUV resists: complexes of platinum and palladium

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 (L2M(CO3) and L2M(C2O4); 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 first positive-tone EUV resists based on mono-nuclear organometallic compounds. In particular, (dppm)Pd(C2O4) (dppm = 1,1-Bis(diphenylphosphino)methane) (25) prints 30-nm dense lines with Esize of 50 mJ/cm2. 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.