the first embodiment of this invention in which the temperature of the reaction vessel 3 is raised by decreasing the flow rate of the coolant 6 as shown in fig1 and 2 is described . as a reaction vessel 3 , a quartz glass vessel of a rectangle cross - section with 20 mm in hight and 300 mm in width is used . a susceptor 2 supporting a substrate 1 is mounted in the reaction vessel 3 . a set of infrared type heater 4 is mounted outside the reaction vessel 3 in order to maintain the substrate 1 at a specified temperature . a part of the reaction vessel 3 facing the infrared heater 4 has a transparent structure through which infrared radiation light of the infrared heater 4 penetrates . air as a coolant gas 6a which can be adjusted its flow rate flows through a space formed between the reaction vessel 3 and infrared heater 4 . for the adjustment of this coolant gas 6a , a pump which can change its flow rate by changing an applied voltage or current , or a control valve 7 in its piping system is installed . both of them also can be used simultaneously . as is shown in fig2 a cooling gas flow ratio will be extremly decreased at the pre - heat treatment procedure and etching procedure of the substrate 1 . on the other hand , the cooling gas flow ratio will be increased at the procedure of the insertion of the substrate 1 in the reaction vessel 3 and the procedure from the thin film growth to unloading of the substrate out of the reaction vessel 3 . here , the cooling gas flow ratio is defined as a ratio of flow rate of the cooling gas 6a to the maximum flow rate of the cooling gas piping system . the flow rate of the cooling gas 6a is adjusted by a rotation ratio of an air - pump 8 and / or a degree of opening of the control valve 7 . the flow rate of the cooling gas 6a at 100 % cooling gas flow ratio amounted to 20 m 3 / min . in the case of the measurement of the temperature change of the wall of the reaction vessel by adjusting the cooling gas flow ratio of the cooling gas 6a , it is impossible to measure the temperature of a transparent quartz glass by a radiation thermometer . it is also very difficult to measure it using a thermocouple because a temperature sensing part of the thermocouple will be locally heated by irradiation of infrared light . accodingly , the temperature measurements are carried out by inserting quickly a very fine wire thermocouple into the reaction vessel while infrared heater 4 is extinguished . real temperature of the wall of the reaction vessel can not be measured by this method , but the temperature of the wall of the reaction vessel can be estimated . after the temperature inside the vessel 3 became below 800 ° c ., a substrate 1 was inserted into the reaction vessel 3 and loaded on the susceptor 2 . at this time , the temperature of the wall of the reaction vessel 3 was about 300 ° c . as the substrate 1 , a silicon single crystal substrate doped with boron , having 200 mm in its diameter , resistivity of 0 . 015 ω · cm , and crystal orientation of ( 100 ) was used . after completion of the insertion of the substrate 1 , the cooling gas flow ratio of the cooling gas 6a was set to zero % so as to raise the temperature of the reaction vessel 3 as high as possible , hydrogen gas as a carrier gas of 100 liters / min was introduced and the infrared heater was on . after the temperature of the substrate 1 reached to 1100 ° c ., pre - heat treatment was carried out by keeping its temperature for five minutes , then the surface of the substrate 1 was etched by flowing gas with mixing hcl gas of 1 liter / min . the temperature of the wall of the reaction vessel 3 was about 800 ° c . by the temperature measurement method described above . in these pre - heat treatment and etching procedures , a silicon dioxide thin film ( its thickness about 1 . 5 nm ) formed on the surface of the silicon substrate 1 surface will be exfoliated by the reaction with hydrogen gas or hcl gas , thereafter transferred by a carrier gas . on the other hand , boron doped in the substrate 1 is also vaporized from the surface of the substrate 1 and diffused into the gas phase by the external diffusion and etching . in a conventional procedure , if the temperature of the reaction vessel 3 is kept at low temperature , impurities , silicon monoxide , silicon dioxide , and metallic contaminants which are delivered into gas phase from the substrate during the pre - heat treatment and etching procedure will form an equilibrium condition due to the temperature at the inside wall 3a , and therefore , majority of these impurities will remain on the inside wall 3a until the succeeding procedure of the thin film growth , then gradually , these impurities and contaminants will be continuously delivered , accordingly , it may widen a transient width and also decrease a minority carrier lifetime . on the other hand , in the experiment based on an apparatus of this invention , it was confirmed that the temperature of the wall of the reaction vessel 3 which was not forcibly cooled at the pre - heat treatment was about 800 ° c ., therefore , it was assumed that the impurities and contaminants delivered to the gas phase during the pre - heat treatment and etching procedure of the substrate 1 were hardly adsorbed on the inside wall 3a , but exhausted to outside with the carrier gas . after the etching procedure was finished , the wall of the reaction vessel 3 was cooled preliminarily for two minutes by adjusting the cooling gas flow ratio of cooling air to 100 %, trichlorosilane as a raw material gas of 10 g / min and diborane gas as a dopant were mixed together into hydrogen gas . accordingly , trichlorosilane introduced into the reaction vessel 3 reacted on the surface of the substrate 1 which was heated at 1100 ° c ., then a thin film 9 was formed thereon , the growth rate was about 3 μm / min . after one minute of the growth , supply of trichlorosilane and diborane was stopped . thereafter , cool - down of the inside of the reaction vessel 3 was conducted by turn - off of the infrared heater 4 , the substrate 1 with the semiconductor crystal thin film 9 was taken out from the reaction vessel 3 , by maintaining 100 % of the cooling gas flow ratio of the cooling gas 6a . the transient width ta of the thin film 9 formed by the procedure and condition described above was compared with the transient width tb of a thin film 9 formed by the conventional condition . as shown in fig5 the transient width ta of the thin film 9 formed by the method of this invention became narrower than the transient width tb formed by the conventional method , and the influence of autodoping phenomenon was drastically improved in the method of this invention . the profile a of the spreading resistance in this invention is steeper than the profile b in the conventional method and the spreading resistance of the profile a itself has a higher resistance value than profile b , therefore , it is clear that the influence of the memory effect was improved by this invention . next , second embodiment of this invention is described . in an etching procedure of the deposited material on the inside wall surface 3a of the reaction vessel 3 , the temperature of the reaction vessel 3 was kept higher temperature by forcible heating than during the procedure of thin film growth . this embodiment is explained by using fig3 and 4 . as the reaction vessel 3 , the same reaction vessel as that used in the first embodiment was employed . a set of graphite plates by which the reaction vessel 3 is forcibly heated was used . in the etching procedure of the deposited material on the inside surface 3a in the reaction vessel 3 , hydrogen gas of 100 liters / min was introduced in the reaction vessel 3 , then the temperature in the reaction vessel 3 was raised to 1150 ° c . by the infrared heater 4 . soon after the temperature was rised to 1150 ° c ., a set of graphite plates 10 which was stored in a compressed state at the exhaust side of the reaction vessel 3 as shown in fig3 ( a ) was inserted into the space between the reaction vessel 3 and infrared heater 4 in the stretched state as shown in fig3 ( b ). thus the set of graphite plates absorbed a thermal energy from the infrared heater 4 , and transmitted the energy to the wall of the reaction vessel 3 , thereby the wall of the reaction vessel was forcibly heated . during this forced heating , the supply of the cooling gas 6a was stopped . the change of the cooling gas flow ratio of the cooling gas 6a in the second embodiment is shown in fig4 for each procedure in this second embodiment . three minutes after the temperature was raised to 1150 ° c ., etching of the inside wall 3a was started by introducing hydrogen gas mixed with hcl gas of 10 liters / min . after flowing of hcl gas for five minutes , hcl gas flow was stopped , thereby only hydrogen gas was flown for another three minutes . then the infrared heater 4 was turned off . the set of graphite plates 10 was returned to the exhaust side , at the same time as the infrared heater was turned off . and cooling gas flow ratio was raised from 0 % to 100 %. after the temperature of the inside of the reaction vessel 3 was dropped to 800 ° c ., the substrate 1 was introduced into the rection vessel 3 for the next gas phase growth procedure . the etching procedure of the deposited material on the inside wall surface 3a of the reaction vessel 3 was performed by the following two methods , one method was for the second embodiment and the other method was for the conventional method . just after etching procedure by each method , the gas phase growth procedure was performed to compare a generation lifetime of the thin film 9 for each method . the substrate 1 used for this comparison was a silicon single crystal substrate consisting of p - type , its resistivity of 10 ω · cm , its lattice plane orientation of ( 100 ), its diameter of 8 inches , and grown by czochralsky method , and a 3 μm thickness of a single crystal thin film was grown on the substrate 1 by an non - doping condition . the generation lifetime was 1000 μsec after the gas phase growth by the second embodiment of this invention , on the other hand , the generation life time was 300 μsec after the gas phase growth by the conventional method . as is described above , the quantity of impurities and contaminants adsorbed on the inside wall of the reaction vessel can be decreased by the method and apparatus for the thin film growth of this invention , and moreover , the impurities and contaminants on the inside wall can be effectively and quickly removed to the non - affected level .