Method and system for the removal and/or avoidance of contamination in charged particle beam systems

Method for preventing or removing contamination of a charged particle transmitting aperture in a charged particle beam system arranged in a vacuum chamber, the charged particle beam system comprising:

• a charged particle beam generator for generating a beam of charged particles;
• a charged particle optical column for projecting the beam of charged particles onto a target, said charged particle optical column comprising a charged particle optical element for influencing the beam of charged particles,
• said charged particle optical element comprises said charged particle transmitting aperture for transmitting and/or influencing said beam of charged particles, and a vent hole providing a flow path from a first side to a second side of said charged particle optical element;
• a vacuum pump for maintaining a vacuum in said vacuum chamber;
• a source for providing a cleaning agent;
• a conduit connected to said source and arranged for introducing said cleaning agent from said source towards said charged particle optical element;
• the method comprising the following steps:
• introducing said cleaning agent from said source via said conduit towards said charged particle optical element comprising said charged particle transmitting aperture while a beam of charged particles generated by said charged particle beam generator is present at or near said charged particle optical element;
• and
• maintaining a vacuum in said vacuum chamber using said vacuum pump,
• wherein the step of maintaining a vacuum comprises providing a flow or movement of species at least through said charged particle optical element via said vent hole to said vacuum pump