Plasma processing method and plasma processing apparatus
At a time point T 0 when starting a process, a duty ratio of a high frequency power RF 1 to which power modulation is performed is set to be an initial value (about 90%) which allows plasma to be ignited securely under any power modulating conditions. At the substantially same time of starting the process, the duty ratio of the high frequency power RF 1 is gradually reduced from the initial value (about 90%) in a regular negative gradient or in a ramp waveform. At a time point t 2 after a lapse of a preset time T d , the duty ratio has an originally set value D s for an etching process. After the time point t 2 , the duty ratio is fixed or maintained at the set value D s until the end (time point T 4 ) of the process.
1. A plasma processing method of generating plasma by an electric discharge of a processing gas between a first electrode and a second electrode which are provided to face each other within an evacuable processing vessel that accommodates therein a substrate to be processed, which is loaded into or unloaded from the processing vessel, and of performing a plasma process on the substrate held on the first electrode under the plasma, the plasma processing method comprising:
performing a power modulation on a first power having a frequency suitable for plasma generation in a pulse shape such that a first period during which the first power is turned on or set to be a first level and a second period during which the first power is turned off or set to be a second level lower than the first level are alternately repeated at a regular pulse frequency in the plasma process; and
setting a duty ratio in the power modulation of the first power to be an initial value for plasma ignition, and then, reducing the duty ratio from the initial value to a set value for the plasma process gradually or in a step shape during a preset transition time,
wherein the reducing of the duty ratio in the power modulation of the first power is started at the same time of starting application of the first power to either one of the first electrode and the second electrode, and
wherein the first power has a frequency of about 13.56 MHz or higher.
2. The plasma processing method of claim 1 ,
wherein the initial value of the duty ratio is set to be about 85% to about 95%.
3. The plasma processing method of claim 1 ,
wherein the transition time is set to be about 0.5 second to about 3.0 seconds.
4. The plasma processing method of claim 1 , further comprising:
applying a negative DC voltage to the second electrode,
wherein an absolute value of the DC voltage during the second period is set to be larger than an absolute value of the DC voltage during the first period in synchronization with the power modulation of the first power.
5. The plasma processing method of claim 1 , further comprising:
applying a second power having a frequency suitable for ion attraction into the substrate from the plasma to the first electrode continuously at a preset constant power without performing the power modulation thereon,
wherein the second power has a frequency of about 13.56 MHz or lower.
6. The plasma processing method of claim 5 ,
wherein the applying of the second power to the first electrode is started after starting the reducing of the duty ratio in the power modulation of the first power.
7. The plasma processing method of claim 1 , further comprising:
applying a negative DC voltage to the second electrode only during the second period in synchronization with the power modulation of the first power.
8. The plasma processing method of claim 7 ,
wherein the applying of the DC voltage to the second electrode is started after starting the reducing of the duty ratio in the power modulation of the first power.
9. The plasma processing method of claim 7 , further comprising:
applying a second power having a frequency suitable for ion attraction into the substrate from the plasma to the second electrode only during the first period in synchronization with the power modulation of the first power,
wherein the second power has a frequency of about 13.56 MHz or lower.
10. The plasma processing method of claim 9 ,
wherein the applying of the second power to the second electrode is started after starting the reducing of the duty ratio in the power modulation of the first power.