A batch type substrate processing apparatus for processing substrates of required numbers at once is given as an example of the substrate processing apparatus for processing the substrate such as a silicon wafer and a glass substrate. 
The batch type substrate processing apparatus, for example, a vertical substrate processing apparatus has a vertical processing furnace, and the required processing is applied to the substrate in such a manner that the substrate is contained in a processing chamber of this processing furnace, and the processing chamber is exhausted while heating the substrate and introducing processing gas into the processing chamber, in a state that the processing chamber is sealed hermetically. 
The substrate to be processed is held in multiple stages in a horizontal posture by a substrate holding means (boat), and inserting and releasing the substrate into/from this processing chamber by the boat is performed through a furnace port at the lower end of the processing furnace. 
A processing furnace 1 of a conventional substrate processing apparatus is explained in FIG.  8.  Note that FIG.  8 shows a sectional face of the lower end part of this processing furnace 1. 
A short tube-like metal manifold 3 is provided at the lower side of a heater base 2, a quartz reaction tube 4 is airtightly erected on an upper end of this manifold 3, and a cylindrical heating apparatus 5 is erected on the heater base 2 concentrically with the aforementioned reaction tube 4.  A processing chamber is formed inside the reaction tube 4. 
A furnace port 6 is formed at a lower end opening part of the manifold 3, and this furnace port 6 is airtightly sealed by a seal cap 7.  This seal cap 7 is attached to an elevating platform 8 which goes up and down by a boat elevator not shown, and a rotating means 9 is airtightly provided in the seal cap 7. 
A boat seat 12 is provided at the upper end of a rotation shaft 11 of the rotating means 9, and a boat 13 made of quartz is placed on this boat seat 12. 
This boat 13 has a heat insulating part 14 of a lower part and a substrate holding part 15 placed on this heat insulating part 14, and required numbers of heat insulating boards 16 made of quartz or SiC are loaded on the heat insulating part 14. 
A wafer 17 to be processed is loaded on this substrate holding part 15 in a horizontal posture at a specified pitch. 
When processing is applied to the wafer 17, a specified processing is performed in such a manner that as shown in the figure, the wafer 17 is heated by the heating apparatus 5, with the furnace port 6 airtightly sealed by the seal cap 7, and the processing chamber is exhausted from an exhaust pipe not shown, while introducing the processing gas by a processing gas introducing nozzle 19. 
When a uniform film is deposited on the wafer 17, the temperature in the surface of the wafer needs to be constant. 
However, heat radiation occurs from the upper end part of the heating apparatus 5 or from the furnace port 6, and particularly, the periphery of the manifold 3 is not surrounded by the heating apparatus 5, and further the manifold 3 is made of metal, thus increasing the heat radiation from the furnace port 6. 
Therefore, as described above, the heat insulating part 14 is provided in the boat 13, and the heat insulating board 16 is provided for preventing the heat radiation.  Further, in order to prevent the heat radiation from the seal cap, a heater 18 is sometimes provided between the seal cap 7 and the elevating platform 8. 
Also, in order to heat the wafer 17 from a peripheral edge, the heating apparatus 5 has a temperature distribution in which the temperature is decreased from the peripheral edge of the wafer to the center thereof. 
In a conventional substrate processing apparatus, by providing the heat insulating part 14, the heat radiation from the furnace port 6 is prevented.  However, the heat radiation itself can not be prevented, and therefore a dummy wafer is loaded on the lower part of the substrate holding part 15, and the wafer is processed by a uniformly heating member in the processing chamber.  In addition, by processing the wafer by the uniformly heating member, uniformity among wafers and uniformity in the wafer surfaces are guaranteed. 
However, problems are involved as follows.  When the heat radiation from the furnace port 6 is large, a uniform temperature length (shaft length of the uniformly heating member) becomes short, thus reducing processing numbers of the wafer 17, resulting in deteriorating productivity.  Moreover, when the temperature distribution occurs, in-surface uniformity of a film thickness is deteriorated, thereby inviting the deterioration of a processing quality and yield.