Film deposition method and film deposition system for depositing a halogen compound film, and magnesium fluoride film

An apparatus for forming a halogen compound film, comprising:

• a vacuum chamber;
• a bias supply electrode disposed in the vacuum chamber and having an obverse side for receiving a substrate thereon;
• an evaporation source for evaporating a film material of the halogen compound film to be formed on the substrate;
• a radio frequency power supply for supplying a radio frequency voltage to the bias supply electrode used as one of electrodes to generate plasma in the vacuum chamber;
• and
• a bias power supply for applying to the bias supply electrode a bias voltage having a frequency ranging between 100 kHz and 2.45 GHz and varying in the form of a wave having a negative mean value and a positive maximum value.

A magnesium fluoride film obtainable by a method comprising the steps of:

• placing a substrate on an obverse side of a bias supply electrode disposed in a vacuum chamber;
• evaporating magnesium fluoride;
• supplying a radio frequency voltage to the bias supply electrode used as one of electrodes to generate plasma in the vacuum chamber;
• and applying to the bias supply electrode a bias voltage having a frequency ranging between 100 kHz and 2.45 GHz and varying in the form of a wave having a negative mean value and a positive maximum value, thereby forming the magnesium fluoride film on the substrate.