Method of forming thin film

A method of forming a thin film, comprising:

• injecting a reaction surface pretreatment agent into a chamber to shield a surface of a loaded substrate;
• injecting a precursor compound into the chamber and adsorbing the precursor compound onto the surface of the shielded substrate;
• injecting a ligand substitution agent into the chamber to perform ligand substitution of the adsorbed precursor compound;
• and
• injecting a reaction gas into the chamber to form a thin film,
• wherein the reaction surface pretreatment agent comprises one or more selected from compounds represented by Chemical Formulas 1 to 4 below;
• and
• wherein the ligand substitution agent comprises one or more selected from hydrogen iodide, hydrogen iodide water, methyl iodide, ethyl iodide, propyl iodide, butyl iodide, isopropyl iodide, and tert-butyl iodide;
• wherein, in Chemical Formulas 1 to 4, R1 and R2 are independently H or an alkyl group having 1 to 5 carbon atoms;
• R3, R4, and R5 are independently H or -(Me)z-CH3, wherein Me is a saturated or unsaturated hydrocarbon with 1 to 3 carbon atoms, and z is an integer from 0 to 4;
• R′ and R″ are independently hydrogen, an alkyl group having 1 to 5 carbon atoms, an alkene group having 1 to 5 carbon atoms, or an alkoxy group having 1 to 5 carbon atoms;
• A is oxygen (O), sulfur(S), phosphorus (P), nitrogen (N),—CH, or —CH2;
• B is —OH, —OCH3, —OCH2CH3, —CH2CH3, —SH, —SCH3, or —SCH2CH3;
• X is fluorine (F), chlorine (Cl), bromine (Br), or iodine (I);
• Y is carbon (C) or silicon (Si);
• n is an integer from 1 to 4;
• and
• m is an integer from 0 to 3.