Patent ID: 7156923

Claim:
A silicon nitride film forming system comprising: a reaction vessel for holding a workpiece therein and provided with a first heating unit for heating the workpiece at a process temperature; a gas supply pipe for carrying hexachlorodisilane and ammonia into the reaction vessel; an exhaust pipe connected to the reaction vessel and provided with a second heating unit for heating the exhaust pipe at a temperature high enough to gasify ammonium chloride; an exhaust system for exhausting gas from the reaction vessel through the exhaust pipe and thereby setting the pressure in an interior of the reaction vessel at a predetermined pressure; and a control unit for controlling the exhaust system to set the pressure in the interior of the reaction vessel at the predetermined pressure and for controlling the supply of hexachlorodisilane and ammonia through the gas supply pipes into the reaction vessel, the control unit causing the gas supply pine to carry hexachlorodisilane and ammonia into the reaction vessel, and the first heating unit to set a temperature of the interior of the reaction vessel to a temperature causing the thermal decomposition of hexachlorodisilane to form a silicon nitride film on the workpiece by reacting the hexachlorodisilane and the ammonia in the reaction vessel, causing the gas supply pipe to further supply ammonia into the reaction vessel after the silicon nitride film has been formed, causing the second heating unit to heat the exhaust pipe at a temperature capable of gasifying ammonium chloride, and causing the exhaust pipe to discharge the ammonia from the reaction vessel such that the ammonia reacts with a Si—CI—N—H compound in the exhaust pipe to produce a Si—N—H compound to preclean inside of the exhaust pipe.