Process and apparatus for manufacturing MOS device

An apparatus for manufacturing MOS devices from substantially disc-shaped semiconductor wafers, comprising:

• a heat treating furnace, the heat treating furnace including a vertical cylindrical tube with upper and lower open ends, means, mounted within the tube, for holding a semiconductor wafer in a setting position transverse against the longitudinal axis of the tube, a gas feed system connected to the upper open end of the tube and feeding a flow of an oxidizing gas into the tube at an oxidizing step to produce an oxidizing ambient, the gas feed system feeding a flow of an annealing gas to the oxidized semiconductor wafer at an annealing step to produce an annealing ambient, and means, removably mounted to the lower open end of the tube, for closing it, the closing means in a mounted position allowing a gas in the tube to flow outside the tube, the closing means in a removed position allowing the semiconductor wafer to be put into and taken out of the tube;
• means for controlling a first clearance linear speeds (1st CLSs) X which is the flows of the oxidizing and annealing gases defined as ratios of those flow rates to the area of a clearance between the semiconductor wafer and the interior surface of the tube to be fixed at the oxidizing and annealing steps;
• means for controlling a second clearance linear speed (2nd CLS) Y which is the flow of the annealing gas defined as a ratio of that flow rate to the area of said clearance to be fixed throughout the duration of the step of taking the semiconductor wafer out of the tube;
• and
• means for controlling a relation between the 1st CLSs X and the 2nd CLS Y so as to be fixed.

An apparatus for manufacturing MOS devices from substantially disc-shaped semiconductor wafers, comprising:

• (a) a heat treating furnace including
• a cylindrical tube with opposite open ends,
• means, mounted within the tube, for holding the oxidized semiconductor wafer in a setting position transverse against the longitudinal axis of the tube,
• a gas feed system feeding a flow of an annealing gas to the oxidized semiconductor wafer to produce an annealing ambient, and
• means, removably mounted to the other open end of the tube, for closing it, said closing means in a mounted position allowing a gas in the tube to flow outside the tube, said closing means in a removed position allowing semiconductor wafer to be put into and taken out of the tube;
• (b) a sensor mounted to the tube, said sensor detecting the flow rate of the annealing gas in said clearance and producing a second flow rate signal at the annealing step, said sensor detecting the flow rate of the annealing gas in said clearance and producing a third flow rate signal throughout the duration of a step of taking the semiconductor wafer out of the tube;
• (c) means, responsive to the first and second flow rate signals, for controlling first clearance speed (1st CLS) X which is the flow of the annealing gas defined as ratio of that flow rate to the area of said clearance to be at least 30 cm/min;
• (d) means, responsive to the third flow rate signal, for controlling a second clearance linear speed (2nd CLS which is the flow of the annealing gas defined as a ratio of that flow rate to the area of said clearance to be at least 100 cm/min:
• and
• (e) means for controlling a relation between the 1st CLS X and the second CLS Y so that Y.gtoreq.-2.5 X+275.