Apparatus for thermal control of variously sized articles in vacuum

A semiconductor processing apparatus for surface processing of a semiconductor substrate, comprising

• a vacuum chamber for maintaining a evacuated environment for surface processing of a substrate, and
• a substrate support platform for supporting said substrate within said vacuum chamber, said substrate support platform being configured for thermal control of said substrate by delivery of a gas from a gas source to a region between said substrate and said substrate support platform, and comprising:
• a substrate engaging surface,
• a holder arranged to retain a substrate adjacent said engaging surface,
• a first channel in said engaging surface for introducing a thermal transfer gas to a first region of said engaging surface and distributing said gas within said first region when a substrate is retained adjacent said engaging surface, said first region including that part of the surface of said substrate engaging surface surrounded by said first channel or surrounded by any opening or channel in said substrate engaging surface connected to said first channel through a gas flow connection in said substrate support platform,
• a second channel in said engaging surface for introducing a thermal transfer gas to a second region of said engaging surface and distributing said gas within said second region when a substrate is retained adjacent said engaging surface, said second region including that part of the surface of said substrate engaging surface surrounded by said second channel or surrounded by any opening or channel in said substrate engaging surface connected to said second channel through a gas flow connection in said substrate support platform,
• wherein there is no gas flow connection between said channels through said substrate support platform, and no gas flow connection between said first channel and any part of said second region through said substrate support platform.