Plasma processing method

1. A plasma processing method for plasma-etching a polysilicon film, the plasma processing method comprising:

plasma-etching the polysilicon film using a mixed gas of a halogen gas, a fluorocarbon gas, an oxygen gas, and a carbonyl sulfide gas,

wherein the halogen gas is a Cl 2 gas or a HBr gas,

wherein a silicon oxide film is a mask material for forming a hole or a groove in the polysilicon film layer to be etched, and

wherein the silicon oxide film does not extend into the polysilicon film etched layer.

2. The plasma processing method according to claim 1 , wherein

the fluorocarbon gas is at least one gas selected from a CHF 3 gas, a CF 4 gas, a C 4 F 8 gas, a C 5 F 8 gas, a C 4 F 6 gas, a CH 2 F 2 gas, and a CH 3 F gas.

3. The plasma processing method according to claim 1 , wherein

a proportion of a flow rate of the carbonyl sulfide gas relative to a flow rate of the mixed gas is a value in a range of 15% to 35%.

4. The plasma processing method according to claim 1 , wherein

a pressure in a processing chamber in which the polysilicon film is plasma-etched is set to a pressure in a range of 3 Pa to 10 Pa.

5. The plasma processing method according to claim 1 , wherein

a temperature of a sample stage placed with a sample on which the polysilicon film is formed is set to 50° C. or lower.

6. The plasma processing method according to claim 1 , wherein

the fluorocarbon gas is a CHF 3 gas.

7. The plasma processing method according to claim 1 , wherein

the polysilicon film is plasma-etched while supplying a radio frequency power of 2000 W or more to a sample stage placed with a sample on which the polysilicon film is formed, or while applying a peak-to-peak radio frequency voltage of 1800 V or more to the sample stage.

8. The plasma processing method according to claim 7 , wherein

the radio frequency power is subjected to pulse modulation, and

a value of a duty ratio of the pulse modulation is in a range of 10% to 40%.