fig1 is a schematic drawing illustrating a rie unit according to one embodiment of the present invention . rie unit 10 includes a treatment chamber 12 , the interior of which is in fluid connection with a vacuum system ( not shown ). in treatment chamber 12 , a susceptor assembly or support 16 is provided for supporting a semiconductor wafer 14 mounted on the support . susceptor assembly 16 is connected to a high frequency power source 20 through a matching device 18 and functions as a cathode . above susceptor assembly 16 , an electrode 22 is arranged at a predetermined distance from assembly 16 . electrode 22 is grounded so as to function as an anode . electrode 22 is made as a hollow structure , including an inner space 24 communicating with a reactive gas supply source ( not shown ) by way of a pipe 26 . a reactive gas supplied from the reactive gas supply source to inner space 24 of electrode 22 is introduced into treatment chamber 12 through a number of small holes 28 formed on the bottom surface of the electrode . when the inside of treatment chamber 12 is reduced in pressure to , for example , 10 - 2 torr ( 1 . 33 × 10 3 kpa ) or less , a reactive gas is introduced into the treatment chamber . the reactive gas may be , but is not limited to , cf 4 . a high frequency voltage is applied between electrode 22 and susceptor assembly 16 , igniting the reactive gas to its plasma state and producing activated species such as ions and radicals . since susceptor assembly 16 is given a negative voltage , the activated species such as the produced ions are forced in a direction toward susceptor assembly 16 and to etch semiconductor wafer 14 on the susceptor assembly . a temperature control apparatus 30 according to the present invention includes a cooling substance , e . g ., liquid nitrogen , supply device 34 for supplying liquid nitrogen into a temperature control space 32 formed in susceptor assembly 16 . liquid nitrogen supply device 34 in the embodiment illustrated in the drawing preferably includes a gas - liquid separator 36 , into which liquid nitrogen is introduced , disposed outside of treatment chamber 12 , and a flash disc 38 disposed in temperature control space 32 . gas - liquid separator 36 and flash disc 38 are connected with each other by a vacuum - jacketed pipe 40 so that nitrogen in the gasliquid separator is sent to the flash disc in liquid phase only , thereby maintaining a very low temperature . flash disc 38 has a number of liquid injection holes ( not shown ) formed on its top surface , as seen in fig1 where the liquid nitrogen sent to the flash disc is caused to flash upwards from the liquid injection holes . vacuum - jacketed pipe 40 includes an electromagnetic valve 42 . electromagnetic valve 42 is preferably controlled by control signals from a controller 44 . controller 44 may be , but is not limited to , a microcomputer . temperature control apparatus 30 also includes a high temperature nitrogen gas supply device 46 for supplying high temperature nitrogen gas into temperature control space 32 of susceptor assembly 16 . high temperature nitrogen gas supply device 46 includes a nitrogen gas tank 48 preferably disposed outside of treatment chamber 12 into which nitrogen gas is introduced . a heating device 50 , such as an electric heater , is disposed inside nitrogen gas tank 48 in order to heat nitrogen gas introduced therein to a high temperature . high temperature nitrogen gas supply device 46 includes a nitrogen gas release disc 52 disposed in temperature control space 32 . nitrogen gas release disc 52 and nitrogen gas tank 48 are connected with each other by an insulated pipe 54 . insulated pipe 54 preferably includes a solenoid valve 56 . solenoid valve 56 is also controlled by controller 44 . temperature sensors 58 , 60 are provided for sensing the temperature of susceptor assembly 16 and are connected to controller 44 . in the illustrated embodiment , temperature sensors 58 , 60 are disposed at two places , i . e ., in the vicinity of a wafer - supporting face 62 of susceptor assembly 16 and in the vicinity of temperature control space 32 . controller 44 calculates the temperature of wafer - supporting face 62 based on at least the temperature signals from temperature sensors 58 , 60 . controller 44 includes an input device 64 connected thereto for setting a desired treatment temperature . input device 64 may be , but is not limited to , a keyboard . a treatment temperature control method will now be described with reference to fig1 . in this method , treatment temperature refers to a temperature of wafer supporting face 62 of susceptor assembly 16 . when it is desired that the treatment temperature be a particular temperature , e . g ., - 100 ° c ., in order to enhance the anisotropy of etching , a set treatment temperature of - 100 ° c . is input from input device 64 . after the desired temperature has been set , controller 44 calculates the temperature of wafer - supporting face 62 of the susceptor assembly 16 based at least upon signals from temperature sensors 58 , 60 . if the temperature of wafer - supporting face 62 is calculated to be over the set temperature ( e . g ., - 100 ° c . ), a solenoid valve control signal will be produced to open solenoid valve 42 and to leave solenoid valve 56 closed . when solenoid valve 42 has been opened , liquid nitrogen is transferred from gas - liquid separator 36 to flash disc 38 through vacuum - jacketed pipe 40 and blown onto the top surface of temperature control space 32 by using the pressure of the nitrogen gas in gas - liquid separator 36 as a driving source . since very low temperature liquid nitrogen is directly blown onto susceptor assembly 16 , susceptor assembly 16 is rapidly cooled down and the semiconductor wafer 14 supported thereon is also cooled down . when the temperature of wafer - supporting face 62 has reached the set temperature as determined by controller 44 , controller 44 recognizes , from signals of temperature sensors 58 , 60 , that the set temperature has been reached , and controls solenoid valve 42 so that the flow of liquid nitrogen to flash disc 38 is stopped or significantly decreased . an etching treatment is then carried out in treatment chamber 12 , as described above . turning on high frequency power source 20 , semiconductor wafer 14 is heated by electric discharge , and hence it is necessary for controller 44 to control solenoid valve 42 to send liquid nitrogen to temperature control space 32 to cool susceptor assembly 16 . liquid nitrogen introduced to temperature control space 32 is evaporated at the same time as it is caused to flow from flash disc 38 , from which it is quickly released to the atmosphere by way of a pipe 66 . when it is desired to raise the treatment temperature , a desired temperature is input from input device 64 into controller 44 . after the treatment temperature has been set , controller 44 closes solenoid valve 42 and opens solenoid valve 56 . high temperature nitrogen gas is introduced from nitrogen gas tank 48 into temperature control space 32 through insulated pipe 54 and nitrogen gas release disc 52 . as a result , the temperature of susceptor assembly 16 , and of semiconductor wafer 14 supported thereon , rises . because the liquid nitrogen previously introduced in temperature control space 32 has been discharged by way of pipe 66 , the temperature of susceptor assembly 16 rises rapidly . if the temperature of wafer - supporting face 62 of the susceptor assembly 16 has reached the set temperature , e . g ., 20 ° c ., a control signal will be produced from controller 44 so as to close solenoid valve 46 . etching is then performed in treatment chamber 16 . semiconductor wafer 14 is heated as described above and the temperature of the wafer - supporting face 62 potentially then exceeds the set temperature , e . g ., 20 ° c . if the temperature of wafer - supporting face 62 exceeds the set temperature , controller 44 controls solenoid valve 42 so that liquid nitrogen is introduced into temperature control space 32 to keep the treatment temperature constant . although an illustrative embodiment of the present invention has been described , the present invention is not limited thereto , and variations may be devised without departing from the spirit of the invention . for example , high temperature nitrogen gas supply device 46 is used as a heating device for heating the susceptor assembly 16 . alternatively , an electric heater , e . g ., a heating resistor ( not shown ), may be embedded in susceptor assembly 16 in place of high temperature nitrogen gas supply device 46 . controller 44 then controls the amount of electricity to be fed to this electric heater . although the aforementioned embodiment is of an example where the present invention is applied to a rie unit , a temperature control apparatus according to the present invention also can be applied to other treatment units , for example , a pressure - reduced cvd unit , a spattering unit , or other types of etching units . according to the present invention , wafer - supporting face 62 and support 16 can be cooled down to a desired temperature within a short period of time because liquid nitrogen is used as a cooling substance . the discharge of liquid nitrogen from support 16 can be carried out within a short period of time and the switching operation from the cooling mode to the heating mode can be rapidly carried out because the liquid nitrogen introduced to support 16 is flash evaporated . furthermore , the heating of support 16 also can be performed within a short period of time because there is no liquid nitrogen within temperature control space 32 at the time heating is desired . a temperature control apparatus according to the present invention controls temperature over a large temperature range and within a short period of time . when it is desired to perform successive treatments at different temperatures , the overall treatment duration can be greatly reduced , whereby the treating capacity and productivity of a treatment unit according to the present invention are vastly improved . since different kinds of such treatments have been performed in the prior art devices by using a plurality of treatment units , a treatment unit according to the present invention decreases the number of such treatment units which are required to perform multiple treatments . while the invention has been described in detail with reference to a preferred embodiment thereof , it will be apparent to one of ordinary skill in the art that various changes can be made , and equivalents employed , without depicting from the spirit and scope of the invention .