A method comprising: - providing a substrate processing apparatus comprising: o a process tunnel, said process tunnel including a lower tunnel wall, an upper tunnel wall, and two lateral tunnel walls, wherein said tunnel walls together bound a process tunnel space that extends in a transport direction and that is configured to accommodate at least one substantially planar substrate that is oriented parallel to the upper and lower tunnel walls; o a plurality of gas injection channels (122, 132), provided in both the lower and the upper tunnel wall, wherein the gas injection channels in the lower tunnel wall are configured to provide for a lower gas bearing, while the gas injection channels in the upper tunnel wall are configured to provide for an upper gas bearing, said gas bearings being configured to floatingly support and accommodate said substrate there between; characterized in that the method further comprises: - providing a substantially rectangular substrate and transporting it through the process tunnel in said transport direction; and in that - the provided semiconductor processing apparatus further comprises a plurality of gas exhaust channels, provided in both said lateral tunnel walls, wherein the gas exhaust channels in each lateral tunnel wall are spaced apart in the transport direction, and wherein a gas exhaust channel density, i.e. a number of gas exhaust channels in said lateral tunnel walls per unit of tunnel length, which unit of tunnel length is equal to a length of the substrate, is in the range of 5-20. - providing a substrate processing apparatus comprising: o a process tunnel, said process tunnel including a lower tunnel wall, an upper tunnel wall, and two lateral tunnel walls, wherein said tunnel walls together bound a process tunnel space that extends in a transport direction and that is configured to accommodate at least one substantially planar substrate that is oriented parallel to the upper and lower tunnel walls; o a plurality of gas injection channels (122, 132), provided in both the lower and the upper tunnel wall, wherein the gas injection channels in the lower tunnel wall are configured to provide for a lower gas bearing, while the gas injection channels in the upper tunnel wall are configured to provide for an upper gas bearing, said gas bearings being configured to floatingly support and accommodate said substrate there between; characterized in that the method further comprises: - providing a substantially rectangular substrate and transporting it through the process tunnel in said transport direction; and in that - the provided semiconductor processing apparatus further comprises a plurality of gas exhaust channels, provided in both said lateral tunnel walls, wherein the gas exhaust channels in each lateral tunnel wall are spaced apart in the transport direction, and wherein a gas exhaust channel density, i.e. a number of gas exhaust channels in said lateral tunnel walls per unit of tunnel length, which unit of tunnel length is equal to a length of the substrate, is in the range of 5-20. o a process tunnel, said process tunnel including a lower tunnel wall, an upper tunnel wall, and two lateral tunnel walls, wherein said tunnel walls together bound a process tunnel space that extends in a transport direction and that is configured to accommodate at least one substantially planar substrate that is oriented parallel to the upper and lower tunnel walls; o a plurality of gas injection channels (122, 132), provided in both the lower and the upper tunnel wall, wherein the gas injection channels in the lower tunnel wall are configured to provide for a lower gas bearing, while the gas injection channels in the upper tunnel wall are configured to provide for an upper gas bearing, said gas bearings being configured to floatingly support and accommodate said substrate there between; - providing a substantially rectangular substrate and transporting it through the process tunnel in said transport direction; and in that - the provided semiconductor processing apparatus further comprises a plurality of gas exhaust channels, provided in both said lateral tunnel walls, wherein the gas exhaust channels in each lateral tunnel wall are spaced apart in the transport direction, and wherein a gas exhaust channel density, i.e. a number of gas exhaust channels in said lateral tunnel walls per unit of tunnel length, which unit of tunnel length is equal to a length of the substrate, is in the range of 5-20.