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hydrophilicity of exposed portions 206a (in other words, the polymers become more hydrophobic), decreasing solubility of exposed portions 206a to a developer. Alternatively, in some implementations, the exposure process and/or the PEB process increase hydrophilicity of exposed portions 206a (in other words, the polymers become more hydrophilic), increasing solubility of exposed portions 206a to the <level- aper. 

In FIG. 2D, a developing process is performed on resist layer 206, thereby forming patterned resist layer 206’. In the depicted embodiment, a negative tone development (NTD) process is performed to remove unexposed portions 206b of resist layer 206. For example, an NTD developer 210 is applied to resist layer 206 that dissolves unexposed portions 206b, leaving patterned resist layer 206’ having opening(s) 212 defined therein between exposed portions 206a (collec› tively referred to as a resist pattern). In some implementa› tions, a rinsing process is performed after the developing process, for example, to remove any residue and/or particles from workpiece 200. In some implementations, a post› development baking (PDB) process is performed, for example, to ensure structural stability of patterned resist layer 206’. 

NTD developer 210 includes a new and improved com› position that overcomes RLS tradeoff barriers discussed herein, particularly those associated with EUV lithography, providing improved patterning fidelity. NTD developer 210 includes an organic solvent 214 that is an ester acetate derivative having a log P value greater than 1.82. For example, organic solvent 214 is represented by R$_{1}$COOR$_{2}$ , where R$_{1 }$ and R$_{2 }$ are hydrocarbon chains having four or less carbon atoms. In some implementations, organic solvent 214 is represented by formula (I): 

where Ri, R$_{2}$ , or both R 1 and R$_{2 }$ are propyl functional groups. In some implementations, R$_{1 }$ is ethyl and R$_{2 }$ is 2-methylpropyl (also referred to as isobutyl), such that organic solvent 214 is represented by the formula (II): 

In some implementations, R$_{1 }$is isopropyl and R$_{2 }$ is n-propyl, such that organic solvent 214 is represented by formula (III): 

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In some implementations, R$_{1 }$is n-propyl and R$_{2 }$ is isopropyl, such that organic solvent 214 is represented by formula (IV): 

In some implementations, R$_{1 }$ and R$_{2 }$ are selected to balance hydrophobicity and hydrophilicity of NTD developer 210, such that organic solvent 214 has a log P value greater than 1.82. For example, in some implementations, R$_{1 }$ and R$_{2 }$ are not polar functional groups. In some implementations, NTD developer 210 further includes another organic solvent, such as n-butyl acetate (n-BA), such that NTD developer 210 includes co-solvents. A ratio between organic solvent 214 and n-BA is determined by characteristics of resist layer 206, such as desired solubility, molecular weights of the polymer, PAG, and/or other resist components, molecular weight dispersity, polarity of monomers, monomer sequences, other suitable resist characteristics, or combinations thereof. In some implementations, NTD developer 210 further includes additives, surfactants, and/or other suitable developer com- ponents. 

Organic solvent 214 increases hydrophobicity of NTD developer 210, such that NTD developer 210 unable to penetrate ( or minimally penetrate) exposed portions 206a, yet is hydrophilic enough to effectively penetrate and remove unexposed portions 206b, resulting in minimal (to no) swelling of exposed portions 206a. Opening(s) 212 are thus defined by relatively smooth edges and/or sidewalls of exposed portions 206a, such that the resist pattern of pat› terned resist layer 206’ exhibits minimal LER/LWR and improved resist contrast, significantly enhancing lithogra› phy resolution. The improved LER/LWR and resist contrast is achieved at lower exposure dosages, such as those achiev- able by current EUV technologies. NTD developer 210 having organic solvent 214 thus improves sensitivity of resist layer 206 without sacrificing resolution and/or LERI LWR, thereby breaking the RLS tradeoff. Accordingly, NTD developer 210 is particularly useful for EUV lithography, the target lithography technology for sub-10 nanometer IC fabrication, which typically requires higher sensitivity. Dif› ferent embodiments disclosed herein offer different advan- tages and no particular advantage is necessarily required in all embodiments. 

NTD developer 210 performs superior to conventional NTD developers including n-BA solvents and/or derivatives thereof, which dissolve resist materials too easily and/or penetrate exposed portions of resist materials (thereby increasing LER and/or pattern deformation). FIG. 3 includes a graph 250 having EUV contrast curves, such as an EUV contrast curve 260 and an EUV contrast curve 270, for resist layers developed using different developers according to various aspects of the present disclosure. EUV contrast curves correlate post-development remaining resist thick- ness (%) (y-axis) as a function of a logarithm of exposure dose (Eop) (in millijoules (mJ)) (x-axis). EUV contrast curve 260 and EUV contrast curve 270 were obtained by exposing a resist layer, such as resist layer 206, to various exposure doses of EUV radiation and developing the resist layer using different developers. EUV contrast curve 260 corresponds with a resist layer developed by conventional NTD developers, such as n-BA solvents and/or derivatives thereof, having organic solvents with log P values greater than 1.82. EUV contrast curve 270 corresponds with a resist layer developed by NTD developers disclosed herein, such as NTD developer 210 including organic solvent 214 having 

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