In the manufacture of an electronic device such as a semiconductor device, a plasma processing is performed on a processing target object by using a plasma processing apparatus. In general, the plasma processing apparatus includes a processing vessel, a gas supply system, a first electrode, a second electrode, a first high frequency power supply and a second high frequency power supply. The gas supply system is configured to supply a gas into the processing vessel. The first electrode and the second electrode are disposed with a space within the processing vessel therebetween. The first high frequency power supply is configured to supply a first high frequency power for plasma generation to either one of the first electrode and the second electrode, and the second high frequency power supply is configured to supply a second high frequency power for ion attraction, which has a relatively low frequency, to the second electrode. Generally, in the plasma processing performed in this plasma processing apparatus, the gas is supplied into the processing vessel from the gas supply system, and the first high frequency power from the first high frequency power supply is supplied to either one of the first electrode and the second electrode to generate plasma. The second high frequency power from the second high frequency power supply is supplied to the second electrode, when necessary.
In the plasma processing, a first stage of generating plasma of a first processing gas and a second stage of generating plasma of a second processing gas may be performed alternately. That is, a multiple number of cycles each of which includes the first stage and the second stage may be performed. The first processing gas includes a first gas, and the second processing gas includes the first gas and a second gas added to the first gas. In this plasma processing, the first gas is supplied into the processing vessel over a first period during which the first stage is performed and a second period during which the second stage is performed. Furthermore, the first high frequency power is supplied to either one of the first electrode and the second electrode over the first period and the second period. Further, in the second stage, the second high frequency power is supplied to the second electrode. The supply of the second high frequency power in the second stage is started from the start time point of the second stage. In addition, in the first stage, a supply of the second high frequency power to the second electrode may not be performed, or a second high frequency power having a power lower than that of the second high frequency power supplied in the second stage may be supplied to the second electrode.
Since a gas has a mass, there is required a time period from the time point when the gas supply system starts the supply of the second gas to the time point when the second gas actually reaches the processing vessel. Meanwhile, the second high frequency power is supplied to the second electrode nearly without being delayed at the time point when the supply of the high frequency power from the second high frequency power supply is begun. Accordingly, it happens that the second high frequency power is supplied to the second electrode at a time point when the second gas has not reached the processing vessel yet. To prevent this problem, it is required to reduce a time difference between the time point when the second gas is supplied into the processing vessel and the time point when the second high frequency power is supplied to the second electrode.
Further, there is required a time period from the time point when the output of the second gas from the gas supply system is stopped to the time point when the supply of the second gas into the processing vessel is stopped. Meanwhile, the supply of the second high frequency power to the second electrode is ended nearly without being delayed at the time point when the output of the second high frequency power from the second high frequency power supply is stopped. Accordingly, it happens that the supply of the second high frequency power is ended though the second gas is still being supplied into the processing vessel. To prevent this problem, it is required to reduce a time difference between the time point when the supply of the second gas into the processing vessel is stopped and the time point when the supply of the second high frequency power is stopped.
Further, Patent Document 1 discloses a technique of detecting a time point when the gas has reached the processing vessel by using emission spectrum of plasma within the processing vessel and beginning the supply of the high frequency power at this time point.
Patent Document 1: Japanese Patent Laid-open Publication No. 2013-058749
As a way to solve the aforementioned problems, it may be considered to start the output of the second gas from the gas supply system at a time point prior to a start time point of the supply of the second high frequency power, i.e., prior to a start time point of the second period. Further, it may be considered to stop the output of the second gas from the gas supply system at a time point prior to an end time point of the supply of the second high frequency power, i.e., prior to an end time point of the second period. In these methods, a time difference between the start time point of the second period and the start time point of the output of the second gas from the gas supply system needs to be decided. Further, it is also required to decide a time difference between the end time point of the second period and the end time point of the output of the second gas from the gas supply system. Moreover, these time differences need to be automatically decided according to a recipe.