US 9,804,493 B2  6  5  HO  OH  The graphene derivative may contain a large number of  hydrophilic groups. The number of hydrophilic groups con› tained in a graphene derivative may be determined, for  example, by neutralization determination. Such determina- tion may be difficult if the water-solubility of a graphene  derivative is low. The hydrophilicity of a graphene deriva› tive may be evaluated by determining the oxygen content of  the graphene derivative. Carboxyl groups and hydroxyl  groups are introduced by an oxidization reaction, and the  number of carboxyl groups and hydroxyl groups contained  in a graphene derivative may be assumed to be proportional  to the oxygen content of the graphene derivative.  The content of the graphene derivative in the composition  for forming a topcoat layer may be controlled according to  the optical and gas-barrier characteristics desired of the  topcoat layer, and may be about 0.01 to about 10 wt%, for  example, about 0.5 to about 5 wt %, based on the total  weight of the composition. The graphene derivative may  function as a film-forming component by itself, rather than  as an additive used in combination with a film-forming  polymer for the topcoat layer, and in the composition for  forming a topcoat layer, all the solid contents may be  attributed to the graphene derivative.  According to the present example embodiment, the oxy› gen content of a graphene derivative may be equal to or  greater than about 1 wt %, for example, equal to or greater  than about 3 wt %, or equal to or greater than about 5 wt %.  Maintaining oxygen content within this range may help  provide sufficient solubility to an alkali developer, e.g., a  2.38% aqueous tetramethyl ammonium hydroxide (TMAH)  solution, which may be used in a resist pattern formation  process.  The composition for forming a topcoat layer according to  an embodiment contains a solvent, which may uniformly  dissolve or disperse the above graphene derivative and, may  include, polymers and additives. Examples of the solvent  include:  mono-alcohols, such as, methyl alcohol, ethyl alcohol,  isopropyl alcohol, and methyl isobutyl carbinol;  polyols, such as, ethylene glycol and glycerol;  alkyl ethers of polyols, such as, ethylene glycol monom› ethyl ether, ethylene glycol monoethyl ether and propylene  glycol monomethyl ether;  According to the present example embodiment, oxygen  content may be equal to or less than about 30 wt %, for  example, equal to or less than about 15 wt%, or equal to or 50  less than about 10 wt %.  If  oxygen content is excessively  high, the graphene skeleton may be damaged to a large  extent by an oxidization reaction, which may lead to reduc› tion in extreme UV light transmission effect. The oxygen  content of a graphene derivative may be determined by 55  Energy Dispersion X-ray Spectroscopy (EDS) or Wave› length Dispersion X-ray Analysis (WDS).  alkyl ether acetates of polyols, such as, ethylene glycol  monomethyl ether acetate and ethylene glycol monoethyl  ether acetate;  The weight average molecular weight of the above gra› phene derivative may be, for example, about 1000 to about  20000, or about 2000 to about 5000, and the composition for  forming a topcoat layer may have favorable coatability.  Various kinds of graphene derivatives and graphene  oxides as mentioned above are commercially available.  Examples include TimesGraph™ (manufactured by of  TimesNano Co.), G-Gosi and Sol-GoGo (manufactured by  Graphos Co.), Rap Go and Rap b Go (manufactured by  NiSiNa Materials Co.).  The composition for forming a topcoat layer may com› prise only the graphene derivative and the solvent. The  Some organic solvents highly dissolve resist patterns.  If  such solvents are used, such solvents may be mixed with  solvents having low solvency to resist patterns, for example,  with water.  lactate; and water (for example, that may have low solvency  to resist patterns).  ethers, such as, diethyl ether and dibutyl ether;  cyclic ethers, such as, tetrahydrofuran;  hydrocarbons having 12 or less carbon atoms, such as,  n-hexane, n-octane, and cyclohexane;  aromatic hydrocarbons, such as, benzene and toluene;  ketones, such as, acetone and methyl ethyl ketone;  esters, such as, methyl acetate, ethyl acetate, and ethyl 