NOVELTY - A seal mechanism (12) that is disposed between first and second structural members having opposing surfaces, comprises a first seal trench that is formed in a first opposing surface of the first structural member; a first seal member that is housed in the first seal trench, and part of which projects from the first opposing surface; a second seal trench that is formed in a second opposing surface of the second structural member; and a second seal member that is housed in the second seal trench, and part of which projects from the second opposing surface.    USE - A seal mechanism for a substrate processing apparatus (claimed), e.g. an etching processing apparatus as a semiconductor device manufacturing apparatus, an ion implantation processing apparatus, a vacuum transfer apparatus, a heat processing apparatus, an analyzing apparatus, an electron accelerator, a flat panel display manufacturing apparatus, a solar cell manufacturing apparatus, an etching processing apparatus as a physical quantity analyzing apparatus, and a film formation processing apparatus.    ADVANTAGE - The seal mechanism can prevent the occurrence of corrosion and abnormal discharge.    DETAILED DESCRIPTION - A seal mechanism (12) that is disposed between first and second structural members having opposing surfaces, comprises a first seal trench that is formed in a first opposing surface of the first structural member; a first seal member that is housed in the first seal trench, and part of which projects from the first opposing surface; a second seal trench that is formed in a second opposing surface of the second structural member; and a second seal member that is housed in the second seal trench, and part of which projects from the second opposing surface. The first and second seal members are brought into pressure contact with each other. The first seal trench comprises a first seal surface from which aluminum is exposed and with which the first seal member is brought into pressure contact, and a first shut-off surface that is disposed between the first opposing surface and the first seal surface. The first seal member comprises a first covering portion that covers the first shut-off surface when the first seal member is housed in the first seal trench. The second seal trench comprises a second seal surface from which aluminum is exposed and with which the second seal member is brought into pressure contact, and a second shut-off surface that is disposed between the second opposing surface and the second seal surface. The second seal member comprises a second covering portion that covers the second shut-off surface when the second seal member is housed in the second seal trench. INDEPENDENT CLAIMS are included for:    (1) a seal trench that is formed in a predetermined surface of a structural member and houses a seal member;    (2) a seal member that is housed in the seal trench; and    (3) a substrate processing apparatus (10) including the seal mechanism, the seal trench or the seal member.    DESCRIPTION OF DRAWING(S) - The drawing is a cross-sectional view schematically showing the construction of the substrate processing apparatus having the seal mechanism.    Substrate processing apparatus (10)    Chamber (11)    Seal mechanism (12)    Cylindrical susceptor (13)    Semiconductor wafer (W)