Method of producing active matrix substrate

1. A method of producing an active matrix substrate in which a plurality of contact holes are formed by a one-mask process so as to reach metal films which are located at different depth positions in an insulating layer, comprising the steps of:

performing dry etching using mixed gas of CHF 3 , CF 4 and O 2 to form the plurality of contact holes and to expose the metal films,

depositing carbonaceous polymer from the CF 4 on surfaces of the contact holes and on surfaces of the metal films exposed through the contact holes, while the carbonaceous polymer is partially removed by the O 2 in the form of CO 2 ;

subjecting the plurality of contact holes to oxygen ashing to further remove the carbonaceous polymer; and

forming a transparent conductive film in the plurality of contact holes,

wherein the metal films are fluorinated and are not etched by dry etching using a fluorine-containing gas.

2. The method according to claim 1 , wherein:

the metal films are a Cr film, an alloy film primarily composed of Cr, an Al film, or an alloy film primarily composed of Al.

3. The method according to claim 1 , wherein:

the gas flow rates of CHF 3 and CF 4 in the mixed gas consisting of CHF 3 , CF 4 and O 2 satisfy a relation of CHF 3 >CF 4 .

4. The method according to claim 1 , wherein:

a duration of time for which the metal films exposed through the contact holes are exposed to plasma in the dry etching falls within a range of 60 to 300 seconds.

5. The method according to claim 1 , wherein:

a duration of time for which the oxygen ashing is performed falls within a range of 120 to 240 seconds.

6. The method according to claim 1 , wherein:

the contact holes and the metal films exposed through the contact holes are over-etched in the dry etching.