ALD apparatus and method

A perimeter slot valve in a process vessel having a process-vessel wall comprising:

• a substrate-transport slot through said process-vessel wall;
• a continuous perimeter cavity within said process-vessel wall;
• a continuous perimeter-sealing poppet;
• and
• an actuator for moving said sealing poppet between an open position and a closed position;
• wherein said sealing poppet is moved into said perimeter cavity in said closed position, said sealing poppet is moved out of said perimeter cavity in said open position, said substrate-transport slot is substantially coplanar with a substrate-supporting surface of said substrate holder, said perimeter cavity is substantially coplanar with said substrate-transport slot, said substrate-transport slot defines a substrate-transport channel through said process-vessel wall to said substrate holder when said sealing poppet is in said open position, and said sealing poppet separates said substrate-transport slot from said vessel interior when said sealing poppet is in said closed position;
• wherein said perimeter slot valve comprises:
• a fixed upper perimeter-sealing surface;
• an upper-poppet perimeter-sealing surface corresponding to said fixed upper perimeter-sealing surface;
• an upper peripheral seal;
• a fixed lower perimeter-sealing surface;
• a lower-poppet perimeter-sealing surface corresponding to said fixed lower perimeter-sealing surface;
• and
• a lower peripheral seal;
• wherein said upper sealing surfaces, said lower sealing surfaces, and said peripheral seals are configured to seal said process vessel interior when said sealing poppet is in said closed position.