A vertical heat-treating apparatus for subjecting a plurality of target substrates to a heat treatment at the same time in a semiconductor process system, comprising:
- a process tube forming a pressure-reduced process space for accommodating the target substrates, and having a port at a bottom for loading and unloading the target substrates, and a first flange surrounding said port, said first flange being provided with a looped first mirror surface, and a looped first counter surface arranged around said first mirror surface, said first mirror surface having a surface roughness of Ra=0.06 .mu.m or less;
- a lid configured to open and close said port, and having a second flange for sealing said process space in cooperation with said first flange, said second flange being provided with a looped second mirror surface, and a looped second counter surface arranged around said second mirror surface, said second mirror surface having a surface roughness of Ra=0.06 .mu.m or less, said first and second mirror surfaces facing and contacting each other to form an inner seal for substantially airtightly sealing said process space, said first and second counter surfaces facing each other with a gap therebetween;
- a looped seal member arranged in said gap, and having a looped first sheet in contact with said first counter surface, a looped second sheet in contact with said second counter surface, and a looped connecting portion airtightly connecting said first and second sheets to each other, such that an outer seal is formed by said first and second counter surfaces and said seal member, and a looped buffer space, substantially airtightly closed, is formed between said inner and outer seals;
- a suction mechanism configured to vacuum-stick said first and second sheets onto said first and second counter surfaces, respectively, and including suction holes formed in said first and second flanges to have openings corresponding to said first and second sheets, respectively;
- a buffer exhaust mechanism configured to exhaust and set said buffer space to a pressure-reduced state;
- a holder configured to hold the target substrates to be stacked with a gap therebetween in said process tube, said holder being loaded and unloaded to and from said process tube through said port while holding the target substrates;
- an elevating mechanism configured to move up and down said lid along with said holder, said second flange of said lid being pressed against said first flange of said process tube by said elevating mechanism;
- a heater configured to heat said process tube and arranged around said process space;
- a supply mechanism configured to supply a process gas into said process space;
- and
- a main exhaust mechanism configured to exhaust and set said process space to a pressure-reduced state.