US 10,520,820 B2  3  4  layer. For example, CAR materials can generate multiple  chemical reactions upon exposure to radiation, thereby  chemically amplifying a response to the radiation, which  reduces sensitivity (in other words, lower exposure doses are  required for defining the pattern in the resist layer). CAR  materials typically include a polymer that is resistant to an  IC process (such as an etching process), an acid generating  component (such as a photoacid generator (PAG)), and a  solvent component. The PAG generates acid upon exposure  to radiation, which functions as a catalyst for causing  chemical reactions that decrease ( or increase) solubility of  exposed portions of a resist layer. For example, in some  implementations, acid generated from the PAG catalyzes  crosslinking of the polymer, thereby reducing solubility of  the exposed portions.  While CAR materials are configured to minimize sensi› tivity, CAR materials must also satisfy other resist perfor› mance characteristics, in particular, resolution (R) and line  edge roughness (LER). Resolution generally describes an  ability of a resist material to print (image) a minimum  feature size with acceptable quality and/or control, where  resist contrast, resist thickness loss, proximity effects, swell› ing and/or contraction of the resist material (typically caused  by development), and/or other resist characteristics and/or  lithography characteristics contribute to the resolution.  Resist contrast generally refers to an ability of a resist  material to distinguish between light ( exposed) regions and  dark (unexposed) regions, where resist materials with higher  contrasts provide better resolution, resist profiles, and/or  LER. Roughness, such as LER and/or line width roughness  (LWR), generally describes whether a pattern in a resist  layer includes edge variations, width variations, critical  dimension variations, and/or other variations. LER generally  describes deviations in edges of a line, whereas LWR  generally describes deviations of width of a line (for  example, from critical dimension (CDU) width). Improving  one resist performance characteristic (for example, reducing  LER) often comes at the expense of degrading another resist  performance characteristic (for example, increasing sensi› tivity), such that attempts at simultaneously minimizing  resolution, LER, and sensitivity is referred to as RLS  tradeoff. Overcoming the RLS tradeoff presents challenges  to meeting lithography process demands for advanced tech› nology nodes (for example, 14 nanometers, 10 nanometers,  5 nanometers, and below).  Extreme ultraviolet (EUY) lithography, which utilizes  radiation having wavelengths in the EUY range, provides  promise for meeting finer lithography resolution limits,  particularly for sub-10 nm IC manufacturing. However,  higher sensitivity CAR materials are often required at EUY  wavelengths because exposure doses required for meeting  resolution, contrast, and/or LER requirements, along with  throughput requirements (such as wafers per hour (WPH)),  are limited by conventional EUY sources. For example,  since a number of photons absorbed by a volume of a resist  material is proportional to wavelength and an amount of  absorbed energy is proportional to exposure dose, a total  absorbed energy is discretized into fewer photons as wave› length decreases.  It has thus been observed that a volume of  resist material absorbs fewer EUY photons than DUY pho› tons (such as ArF photons) when exposed to the same  exposure dose (for example, about 10 mJ/cm 2 ),  which often  means that less acid will be generated by CAR materials for  catalyzing reactions. In some cases, the volume of resist  material absorbs as much as 14x fewer EUY photons. Such  phenomenon is generally referred to as shot noise. Though  increasing EUY exposure dose can alleviate the shot noise,  thereby improving resolution, contrast, and/or roughness,  such is achieved by increasing EUY source power or  decreasing scan speed (in other words, decreasing through› put, such as wafers per hour (WPH)). Since current EUY  sources are limited to EUY source power of about 80 W and  decreasing throughput is not a viable option for meeting next  generation IC manufacturing requirements, the developing  process is currently being explored for improving sensitivity  of CAR resist materials while still meeting other RLS  characteristics, such as resolution and LER.  There are generally two types of developing processes: a  positive tone development (PTD) process and a negative  tone development (NTD) process. The PTD process uses a  positive tone developer, which generally refers to a devel- aper that selectively dissolves and removes exposed portions  of the resist layer. The NTD process uses a negative tone  developer, which generally refers to a developer that selec› tively dissolves and removes unexposed portions of the  resist layer. PTD developers are typically aqueous base  developers,  such  as  tetraalkylammonium  hydroxide  (TMAH), and NTD developers are typically organic-based  developers, such as n-butyl acetate (n-BA). Both PTD  processes and NTD processes have drawbacks when  attempting to meet lithography resolution demands for  advanced technology nodes. For example, both PTD pro› cesses and NTD processes (particularly those using NTD  developers that include n-BA solvents) have been observed  to cause resist pattern swelling, leading to insufficient con› trast between exposed portions and unexposed portions of  the resist layer (in other words, poor resist contrast) and  resulting in higher than desired LER/LWR and/or low pat› terning fidelity. However, because NTD processes typically  provide better normalized image log-slope (NILS) than PTD  processes, NTD processes have become the focus for  improving resolution for advanced technology nodes. The  present disclosure thus explores NTD developers and cor› responding lithography techniques that can improve sensi› tivity of CAR materials ( specifically, reducing an amount of  exposure dosage required) to EUY radiation without degrad- ing resolution and roughness, thereby overcoming the RLS  tradeoff and achieving high patterning fidelity for advanced  technology nodes.  FIG.  1  is a flow chart of a lithography method  100  for  processing a workpiece (for example, a substrate) according  to various aspects of the present disclosure. In some imple› mentations, method  100  is implemented, in whole or in part,  by a system employing advanced lithography processes,  such as DUY lithography, EUY lithography, e-beam lithog› raphy, x-ray lithography, and/or other lithography to  enhance lithography resolution. At block  102,  a resist layer  is formed over a material layer of a workpiece. In some  implementations, the resist layer is a negative tone resist  layer, and the material layer is a portion of a wafer ( or  substrate). At block  104,  the resist layer is exposed to  radiation, for example, patterned radiation. In some imple› mentations, the resist layer is exposed to patterned EUY  radiation. In some implementations, after exposure, the  resist layer is baked, for example, by a post exposure baking  process. At block  106,  the resist layer is developed using a  developer having an organic solvent having a log P value  greater than 1.82, thereby forming a patterned resist layer.  The organic solvent is an ester acetate derivative represented  by R$_{1}$COOR$_{2}$ ,  where R$_{1 }$ and R$_{2 }$ are hydrocarbon chains  having four or less carbon atoms. In some implementations,  Ri, R$_{2}$, or both R 1  and R$_{2 }$ are propyl functional groups. In  some implementations, R$_{1 }$is n-propyl and R$_{2 }$ is isopropyl. In  some implementations, R$_{1 }$is isopropyl and R$_{2 }$ is n-propyl. In 