In semiconductor manufacturing facilities, a reactor for generating moisture with a structure as shown in FIG. 15 has been widely used. Namely, in FIG. 15, the following character references are used:    A Reactor    B Temperature regulator    H2 Hydrogen gas    O2 Oxygen gas    G Mixed gas    W Moisture gas    L Gap    V Interior space    α Inclination angle of the peripheral edge of a reflector    1 Reactor structural component on the inlet side    1a Gas feed port    2 Reactor structural component on the outlet side    2a Moisture gas take-out port    3a, 3b Reflectors    4 Reflector fixing bolt    5 Spacer    6 Platinum coating catalyst layer comprising a barrier coat 7 and a platinum coat 8 mounted on its outer surface    9 Barrier coat mounted on the inner surface of the reactor structural component on the inlet side    10 Barrier coat mounted on the outer surface of the reflector    11 Welded portion    12 Fixing hole for the sheath-type thermometer    13 Heater    15 Heater press    15 Cooler    15a Heat dissipation fin    15b Substrate
A mixed gas G produced by mixing hydrogen gas H2 and oxygen gas O2 is fed from the gas feed port 1a to the interior space V, and when the gases contact with a platinum coating catalyst layer 6 mounted on the inner surface of the reactor structural component on the outlet side 2, the reactivity of the hydrogen and oxygen is activated by catalytic action. The activated hydrogen and oxygen react at the appropriate speed without causing an explosive combustion reaction within the atmosphere, below the combustion temperature of hydrogen, and the high purity moisture gas V produced flows out from the moisture take-out port 2a. 
It may be necessary to raise the temperature of the interior space V of the reactor A higher than at least 200° C. in order that the afore-mentioned reactivity of the hydrogen and oxygen is activated and to maintain the stable reaction of both hydrogen and oxygen. To achieve this end, a plane-shaped heater 13 is provided on the outer side of the reactor structural component on the outlet side 2, and the reactor A is heated by the plane-shaped heater when the reactor A starts up. FIG. 16 shows the relationship between the temperature of the reactor A and the reaction rate of the hydrogen.oxygen. When the temperature of the reactor exceeds approximately 200° C., the reaction rate of the hydrogen.oxygen becomes the value of approximately 98% or more regardless of the mixture ratio of both hydrogen and oxygen.
While the reaction of the afore-mentioned hydrogen and oxygen proceeds, the reactor A is heated by the reaction heat, and then the reactor's temperature goes up. In order to restrain the afore-mentioned explosive combustion reaction of the hydrogen and oxygen, it is necessary that the temperature of the interior space V is held at a temperature lower (for example, 400˜450° C.) than the lowest limit ignition temperature (approximately 560° C., and the limit ignition temperature goes up higher than 560° C. depending on the mixing ratio of hydrogen and oxygen) of the hydrogen gas (or hydrogen containing gas).
Accordingly, with this kind of conventional reactor for generating moisture, such measures as limiting the flow rate (namely, the volume of moisture gas W generated), improving the cooling performance of a cooler 15, or increasing the heat capacity of a reactor A, are implemented. When such measures as these are employed, it becomes possible to produce high purity moisture gas at the low cost, and stably and continuously with this kind of reactor for generating moisture. Thus, such reactors are widely and practically used.
However, in recent years there is seen a trend to downsize the apparatus for generating moisture while providing a bigger volume of moisture generation, which has been demanded in the field of semiconductor manufacturing facilities. For example, when the bore of a wafer becomes larger, the volume of moisture required for each treatment process increases. Accordingly, there has been a strong demand for more volume of moisture generation than that presently obtained by a conventional moisture generating apparatus having a dimensional volume similar to that of the conventional ones that are produced.
However, when downsizing of semiconductor manufacturing facilities is required, the moisture generating apparatus has to meet a severe restriction placed upon its volume/dimension. Because of this reason, it is nearly impossible for the cooling performance of the reactor A to be improved by means of upgrading the cooling fan though improvements such as making the heat dissipation fin 15a of the cooler 15 higher and increasing the number of heat dissipation fins slightly. Similarly, it is very difficult to upgrade a reactor A in view of the afore-mentioned restrictions on its volume. For example, the structurally allowable dimensions of a reactor A for generating moisture having a large flow rate of more than 10 SLM (“Standard Liter per Minute”) are similar to the values of dimensions (outer diameter 228 mm, thickness 37 mm and height of a heat dissipation fin 25 mm) of the conventional reactor for generating moisture which has a maximum volume of moisture generation of 5 SLM.
Therefore, for a conventional reactor equipped with a cooler 15 provided with the structure shown in FIG. 15, there is no way at all to meet the requirement of increasing the volume of moisture generated in view of the restrictions in its volume/dimension including that volume/dimension of the cooler 15. Thus, a conventional reactor equipped with a cooler 15 fails to increase the volume of moisture that may be generated safely and easily.
Patent Document 1: TOKU-KAI No. 2001-48501
Patent Document: 2: INTERNATIONA DISCLOSURE WO-01/94254A