Substrate processing method

A substrate processing method comprising:

• forming a first thin film by supplying a first reactant and a second reactant on a substrate having a patterned structure;
• supplying a third reactant;
• and
• converting the first thin film into a second thin film.

A substrate processing method comprising:

• forming a first thin film of a certain thickness adsorbed on a patterned spin-on-hardmask (SOH) structure by performing a first cycle a plurality of times, the first cycle comprising supplying a silicon-containing source gas on the patterned SOH structure and purging the residue;
• forming a second thin film by changing a chemical composition of the first thin film by performing a second cycle a plurality of times, the second cycle comprising supplying a reaction gas that is reactive with the patterned SOH structure and reactive with the silicon-containing source gas and purging the residue;
• and
• forming a third thin film having the same component as that of the second thin film on the second thin film by performing a third cycle a plurality of times, the third cycle comprising supplying the silicon-containing source gas and supplying the reaction gas.