NOVELTY - The apparatus (1) has a seal chamber (2) including a chamber body (6) provided with an opening (5). A lid unit (7) is provided rotatably with respect to the body. A liquid seal structure (8) liquid-seals between the lid unit and the body. The chamber includes an internal space sealed from an outside of the chamber. A rotating unit (32) rotates the lid unit. A substrate holding/rotating unit (3) holds and rotates a substrate i.e. wafer (W), in the space of the chamber. A treatment liquid supplying unit (4) supplies treatment liquid to the substrate rotated by the holding/rotating unit.    USE - Apparatus for treating a substrate e.g. semiconductor wafer, and glass substrate, for applications and for performing a wafer cleaning process i.e. residual polymer removing process, on a front surface i.e. major surface, of the substrate. Uses include but are not limited to LCD devices applications, plasma display devices applications, Field Emission Display (FED) devices applications, optical disks applications, magnetic disks applications, magneto-optical disks applications, photo masks applications, and solar cells applications.    ADVANTAGE - The apparatus properly treats the substrate to perform the wafer cleaning process on the front surface of the substrate in the seal chamber in an effective manner, so that volume of the internal space can be reduced, thus controlling an atmosphere in the chamber by sealing the internal space of the chamber. The treatment liquid supplying unit supplies the treatment liquid to the substrate rotated by the holding/rotating unit, where an interior wall region of the apparatus is located at a lower position than the substrate holding/rotating unit located at a chamber cleaning position, so that the treatment liquid removed from the interior wall of the seal chamber is prevented from splashing over and adhering to the substrate holding/rotating unit during cleaning of the interior wall of the seal chamber, thus suppressing contamination of the substrate holding/rotating unit. The apparatus includes gas seal structure placed closer to the internal space of the seal chamber than the liquid seal structure, and any region of an outer surface of an nozzle arm is advanced into the seal chamber after seal gas is supplied when the nozzle arm is moved into the seal chamber, so that the seal liquid applied to the outer surface of the nozzle arm by the liquid seal structure is removed by the seal gas of the gas seal structure, thus reliably preventing an ingress of the seal liquid in the internal space of the seal chamber.    DETAILED DESCRIPTION - The substrate holding/rotating unit is spin chuck. The chamber body is generally hollow cylindrical chamber body. The opening of the body is an upper opening. The treatment liquid supplying unit is treatment liquid nozzle. The treatment liquid is chemical agent or rinse liquid.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic sectional view of a substrate treatment apparatus.    Wafer (W)    Substrate treatment apparatus (1)    Seal chamber (2)    Substrate holding/rotating unit (3)    Treatment liquid supplying unit (4)    Opening of chamber body (5)    Chamber body (6)    Lid unit (7)    Liquid seal structures (8, 13)    Rotating unit (32)