Patent Number: 
Section: claims

1. A particle attachment preventing method in a substrate processing apparatus including an accommodation chamber configured to accommodate a substrate therein and generate a plasma therein, a mounting table configured to mount the accommodated substrate thereon, a first power supply configured to supply a bias power for attracting the plasma to the mounting table, and a second power supply configured to supply an electron density control power for controlling an electron density above the substrate, the method comprising:adjusting the electron density control power supplied from the second power supply such that the electron density above the substrate gets lower than during a plasma processing, for a preset short period of time after the plasma processing is ended; andmaintaining the bias power supplied from the first power for the preset short period of time,wherein the preset short period of time is about 0.5 to 1.0 second. 2. The method of claim 1, wherein the second power supply is a high frequency power supply for supplying a high frequency power having a frequency that is higher than that of the bias power, andin said adjusting of the electron density control power, the high frequency power supplied from the second power supply is lowered as compared with that during the plasma processing. 3. The method of claim 1, wherein the substrate processing apparatus further includes an opposite electrode facing the mounting table,the second power supply serves as a DC power supply for supplying a DC power to the opposite electrode, andin said adjusting of the electron density control power, the DC power supplied from the second power supply is lowered as compared with that during the plasma processing. 4. The method of claim 1, wherein the substrate processing apparatus further includes an opposite electrode facing the mounting table,the second power supply serves as a high frequency power supply for supplying a high frequency power having a frequency that is higher than that of the bias power and a DC power supply for supplying a DC power to the opposite electrode, andin said adjusting of the electron density control power, the DC power supplied from the second power supply is lowered as compared with that during the plasma processing and the high frequency power supplied from the second power supply is lowered as compared with that during the plasma processing. 5. The method of claim 2, wherein, in said adjusting of the electron density control power, the high frequency power supplied from the second power supply is lowered to about 40% or less of the high frequency power during the plasma processing. 6. The method of claim 4, wherein, in said adjusting of the electron density control power, the high frequency power supplied from the second power supply is lowered to about 40% or less of the high frequency power during the plasma processing. 7. A substrate processing apparatus comprising:an accommodation chamber configured to accommodate a substrate therein and generate a plasma therein;a mounting table configured to mount the accommodated substrate thereon;a first power supply configured to supply a bias power for attracting the plasma to the mounting table; anda second power supply configured to supply an electron density control power for controlling an electron density above the substrate,wherein the electron density control power supplied from the second power supply is adjusted such that the electron density above the substrate gets lower than during a plasma processing, for a preset short period of time after the plasma processing is ended, andthe bias power supplied from the first power supply is maintained for the preset short period of time, andwherein the preset short period of time is about 0.5 to 1.0 second. 8. The apparatus of claim 7, wherein the electron density control power is a power for generating the plasma, anda first region in which the electron density control power is supplied to generate the plasma and a second region in which the substrate is subjected to the plasma processing are identical or adjacent to each other.