Vertical heat treatment apparatus

A vertical heat treatment apparatus includes a casing, a vertical heat treatment furnace provided in the casing, a substrate holding unit mounted in the casing for holding substrates to be heat-treated in the vertical heat treatment furnace, a loading/unloading unit having a wafer boat for supporting the substrates, the loading/unloading unit being adapted to put the substrates in and take the same out of the vertical heat treatment furnace, and a transportation robot for moving the substrates between the substrate holding unit and the wafer boat. The vertical heat treatment apparatus further includes a clean air supplying unit for supplying clean air sideways to the wafers supported by the wafer boat when the loading/unloading unit is at an unloading position, a and duct for introducing air from the outside of the apparatus. The clean air supplying unit is provided with an air filter disposed opposed to the wafer boat. Air in a clean room whose pressure is set to be higher than the pressure in the casing is introduced into the clean air supplying unit through the duct.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a vertical heat treatment apparatus used for 
manufacturing semiconductors. 
2. Description of the Related Art 
As a higher density has been required for semiconductor elements, more 
accurate heat treatment has come to be required for semiconductor devices. 
Wafers heat-treated in a reaction vessel in a heat treatment furnace such 
as a vertical or horizontal furnace is unloaded outside of a heat 
treatment path. When the reaction tube is uncovered soon after the heat 
treatment has been carried out, convention occurs in the reaction tube due 
to the temperature difference between the interior of the reaction tube 
and the outside thereof. It is necessary to keep the wafer atmosphere at a 
high temperature clean in order to increase the yield of wafers which are 
heat-treated accurately. 
Japanese Laid-open Patent Application Publications No. 61-111524 and No. 
62-146265 and Japanese Laid-open Utility Model Publication No. 62-8633 
disclose apparatuses for making clean air flow sidewise onto wafers 
unloaded from a vertical heat treatment furnace. Japanese Laid-open Patent 
Application Publication No. 62-36817 discloses an apparatus for making air 
flow downward onto wafers unloaded from a horizontal heat treatment 
furnace. Further, Japanese laid-open Utility Model Application No. 
64-26833 discloses an apparatus for making air side-flow at the unloading 
position of a horizontal heat treatment furnace. 
In those conventional apparatuses, air supplied by a motor fan or the like 
is cleaned by passing through a filter and is made to flow onto wafers. 
The following must be considered when clean air is supplied to the 
unloading position by means of a fan. When air to be supplied is 
circulated in a room, the temperature in the room is raised. In order to 
avoid this, air must be introduced into the room from another room by 
means of a fan. Since the unloading position is provided in a so-called 
maintenance room, pressure difference is provided between the maintenance 
room and the surrounding clean room such that the pressure in the clean 
room is positive. When, therefore, air in the utility zone is introduced 
into the clean room by the fan, an excessive load is exerted on the fan 
due to the pressure difference. Because the pressure difference is varied 
according to user's preference, the amount of air sent by a fan having the 
same blowing capacity changes and air cannot be sent in some cases. 
SUMMARY OF THE INVENTION 
The object of this invention is to provide a vertical heat treatment 
apparatus in which loads exerted on a fan are reduced by improving a duct 
for supplying air to the fan such that air is kept clean at an unloading 
position. 
The object of this invention is attained by a vertical heat treatment 
apparatus which comprises a casing provided with a vertical treatment 
furnace, substrate holding means also housed in the casing for holding 
substrates to be heat-treated in the vertical heat-treatment furnace, 
substrate supporting means for supporting substrates, loading/unloading 
means for putting the substrate in and taking the same out of the vertical 
heat treatment furnace, transmitting means for transporting the substrates 
between the substrate holding means and the substrate supporting means, 
clean air supplying means for sideways supplying clean air to the 
substrates supported by the substrate supporting means when the 
loading/unloading means is at an unloading position, the clean air 
supplying means being provided with an air filter disposed opposed to the 
substrate supporting means, and a duct for conducting air into a clean 
room at a pressure higher than that in the casing into the clean air 
supplying means. 
In this invention, air is introduced from the clean room, whose pressure is 
set at a value higher (that is, a positive pressure) than the pressure at 
the unloading position in the casing, into the casing via the duct and the 
air filter. This arrangement easily allows air to flow from the clean room 
at a higher pressure into the casing at a lower pressure. Clean air flows 
sidewise onto the substrates disposed at the unloading position such that 
excessive loads are not applied to the blower fan. When a vertical heat 
treatment apparatus is used, the air conducting duct can be set in the 
bottom portion of the casing in which various devices are housed, and thus 
the duct can be provided without increasing the setting space. 
Additional objects and advantages of the invention will be set forth in the 
description which follows, and in part will be obvious from the 
description, or may be learned by practice of the invention. The objects 
and advantages of the invention may be realized and obtained by means of 
the instrumentalities and combinations particularly pointed out in the 
appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
This invention will be explained with reference to preferred embodiments 
with reference to the accompanying drawings. 
As shown in FIG. 1, a vertical heat treatment apparatus 1 is installed in a 
utility zone 3 disposed adjacent a clean room 2 for manufacturing 
semiconductors. In general, the floor of the clean room 2 is formed with a 
net 4 for passing dust or the like. Air communication between the clean 
room 2 and the utility zone 3 is interrupted by a vertical partition wall 
5. The front portion of the vertical heat treatment apparatus 1 
communicates with the clean room 2 through an opening formed in the 
partition wall 5. 
Referring to FIG. 1 again, the vertical heat treatment apparatus 1 has a 
casing 6, the interior of which is divided by a partition plate 7 into a 
loading room 8 and an unloading room 9, and a heat treatment furnace 10 is 
mounted in the loading room 8. 
In the heat treatment furnace 10 is provided a reaction tube 11 made of 
material such as quartz glass on which a heat treatment gas is hard to 
react and which shows high heat resistance. Wound around the reaction tube 
11 is a coiled heater 12 for heating the interior of the reaction tube 11 
to a required temperature, for example, which is selected among 
600.degree. to 1,200.degree. C., in a spaced relation from the tube 11 at 
a predetermined distance so that the heater 12 is not in contact with the 
tube 11. The reaction tube 11 is connected to a gas source by means of a 
gas supplying pipe (not shown). On the upper portion of the reaction tube 
11 is connected an air exhaust pipe 13 which is connected to a vacuum pump 
(not shown) which reduces the pressure in the reaction tube 11 to a 
predetermined level and exhausts a heat treatment gas. 
In the unloading room 9 are provided a boat elevator 14, a transportation 
robot 15 and a cassette holding unit 16. 
The boat elevator 14 comprises a wafer boat 17 which receives as many 
number of substrates (for example, 100 to 150 semiconductor wafers 28) as 
can be heat-treated in the reaction tube 11 at a time so as to be arranged 
vertically at a required space, and a lift mechanism 18 for transporting 
the wafer boat 17 into and from the reaction tube 11. The lift mechanism 
18 is provided with a guide rod 19 extending vertically and a motor (not 
shown) for vertically moving a first arm 20 slidably mounted on the guide 
rod 19. A second arm 21 is rotatably mounted on the forward portion of the 
first arm 20. Operations such as positioning, setting the timing or the 
like for transporting the wafer are automatically performed in accordance 
with prememorized programs. 
Referring to FIGS. 1 and 2, a heat insulating tube or heat keeping tube 30 
is provided on the lower end of the wafer boat 17. On the lower end of the 
heat insulating tube 30 for keeping the temperature of the wafers 28 to a 
predetermined value is formed a flange 31 which contacts the lower surface 
of the opening 11a of the reaction tube 11 and seals the same when the 
wafer boat 17 is lifted. The flange 31 is disposed on the forward portion 
of the second arm 21. The wafer boat 17 comprises four supporting members 
22 made of heat-resisitive and corrosion-resistive material such as quartz 
glass and fixing members 23 for fixing them together. Each of the 
supporting members 22 is formed with a plurality of grooves 22a engaging 
the wafers 28 to receive them. The wafers 28 are loaded in the heat 
treatment furnace 10 from its bottom by means of the boat elevator 14, 
heat-treated by means of such as a CVD film forming process and unloaded 
to a position (an unloaded position) shown at A. The boat elevator 14 
includes a motor (not shown) for rotating the first arm 20 in the 
directions shown by an arrow .theta..sub.2 (FIG. 2) and a motor (not 
shown) for rotating the wafer boat 17 in the directions depicted by an 
arrow .theta..sub.3 (FIG. 2). 
As shown in FIG. 2, the transportation robot 15 has a drive block 24 having 
five wafer supporting arms 25 arranged in parallel to each other at 
intervals each corresponding to the thickness of a wafer 28. The distal 
end of each arm 25 is fixed to the corresponding one of sliders 26 
provided on the drive block 24. Each slider 26 engages longitudinally 
extending slide grooves 27 formed in the drive block 24 so as to be 
slidable back and forth along the slide grooves 27. A driving mechanism 
(not shown) for reciprocating the sliders 26 in the lengthwise directions 
is housed in the drive block 24 such that one of the supporting arms 25 
can be reciprocated or all of them can be moved back and forth 
simultaneously. 
The transportation robot 15 is provided with a lift mechanism 32 which has 
a guide rod 33 extending vertically and a motor (not shown) for moving an 
arm 34 slidably mounted on the lift mechanism 32 vertically along the 
guide rod 33. On the forward end of the arm 34 is provided a rotary drive 
mechanism 35 for rotating the drive block 24 mounted thereon through 
200.degree. or more in the directions shown by an arrow .theta..sub.1. 
The cassette holding unit 16 includes a cassette loader 36 on which are 
loaded eight wafer cassettes 16a to 16h, each cassette capable of 
receiving a plurality of (for example, twenty-five) semiconductor wafers 
28. The wafer loader 36 is rotated by means of a motor (not shown) in 
either direction shown by an arrow .theta..sub.4. With this arrangement, 
therefore, the wafer cassette holder unit 16 is rotated in a direction 
shown by .theta..sub.4 such that the wafer cassettes 16a to 16h are 
directed toward the transportation robot 15 and then the supporting arms 
25 are moved forward or rearward, thereby taking out wafers 28 from the 
wafer cassettes or moving the wafers 28 to the wafer boat 17. 
A structure for keeping clean the atmosphere of the unloading room 9 of the 
casing 6 will now be explained. 
As shown in FIG. 1, a filter unit 37 and a fan 38 are provided in a 
partition wall 7 of the casing 6 over the wafer cassette holding unit 16 
such that the loading room 8 communicates with the unloading room 9 
through the unit 37 and the fan 38. The fan 38 supplies clean air to the 
unloading room 9 at an air flow rate of 9.9 m.sup.3 /min, for example. 
Heated exhaust air in the unloading room 9 is sent out through the air 
exhaust pipe 13 at an air flow rate of 2 m.sup.3 /min, for example. A HEPA 
filter, an ULPA filter or the like is used as the filter unit 37. Clean 
air filtered by the filter unit 37 is supplied onto the wafers 28 in the 
process of the transportation of them so as to prevent dust from being 
attached to the wafers 28. 
A structure for keeping clean the atmosphere in the vicinity of the 
unloading position A under the heat treatment furnace 10 will now be 
explained. 
An openable back door 41 is hinged by means of a hinge 39 to the lower 
portion of the lateral side of the casing 6 at which the rear wall of the 
boat elevator 14 is disposed. The maintenance of the unloading room 9 of 
the casing 6 can be carried out by opening the back door 41. The back door 
41 is made hollow so as to open to the unloading room 9. At a position 
opposed to the unloading position A in the hollow portion of the back door 
41 is provided a clean module 40 which comprises a fan 42 for delivering 
clean air, a filter 44 and a heat reflector or a heat reflecting plate 50. 
The filter 44 is, for example, a HEPA filter made of electrostatically 
shielded resin and is used for cleaning air delivered by the fan 42. The 
air flow capacity of the clean module 40 is 1.1 m.sup.3 /min, for example, 
and the air flow speed at the filter 44 can be adjusted to 0.1 to 1.0 
m/sec, for example. In this embodiment, the distance between the front 
face of the module 40 and the ends, opposed thereto, of the unloaded 
wafers 28 is set to 150 mm and the air flow speed at the filter 44 is 
adjusted to 0.3 m/sec. 
The heat reflector 50, which has a function to reflect, on its surface, 
heat rays such as infrared rays or the like, reflects radiant heat from 
the wafers 28 soon after they are loaded on the wafer boat 17 and prevents 
the temperature rise of the filter 44. Three embodiments of the heat 
reflectors 50 are shown in FIGS. 3 to 5. 
The heat reflector 50 shown in FIG. 3 comprises a punched metal plate (heat 
reflecting plate) 52 made of stainless steel (SUS) and punched with a 
plurality of air through holes 52a. 
The heat reflector 50 shown in FIG. 4 comprises a first punched metal plate 
(heat reflecting plate) 54 made of stainless steel (SUS) and a second 
punched metal plate 56 provided in parallel to the first punched metal 
plate 54. Both plates 54 and 56 are formed with punched air through holes 
54a and 56a displaced vertically from each other. From the surface of the 
first punched metal 54 extend hoods 54b for supplying air onto the wafers 
28 in a laminated and side-flow state. 
The heat reflector 50 as shown in FIG. 5 comprises a single thick metal 
plate (heat reflecting plate) 58. It has a plurality of air holes 58a 
penetrating therethrough from its rear surface at the side of the filter 
44 to its front surface. From the front surface of the plate 58 extend a 
plurality of hoods 58b communicating with the front openings of the air 
holes 58a. 
The shape of the surface of the heat reflecting plate is not limited to a 
plane defined by a plate as described above, but may take any shape so 
long as it can exhibit a proper heat reflecting characteristic. The heat 
reflecting plate may be made of aluminum (Al). 
Air is introduced into the hollow portion of the back door 41 from the 
clean room 2 in which the degree of the clean state of air is maintained 
to about class 10. In order to do so, a horizontal duct 62 is provided in 
the bottom portion of the casing 6 or under the casing 6. The duct 62 has 
an opening 64 communicating with the clean room 2 and another opening 66 
communicating with the hollow portion of the back door 41. A pre-filter 
(not shown) can be provided at the opening 66. 
In general, the pressure in the clean room 2 is made higher than the 
pressure in the utility zone 3 (that is, the pressure in the clean room 2 
is set to a positive pressure with respect to the pressure in the utility 
zone 3) such that air in the clean room 2 smoothly flows in the back door 
41 through the duct 62. An opening (not shown) may be formed in the lowest 
partition wall of the casing 6 so as to effect communication between the 
casing 6 and the duct 62, and a further opening (not shown) may be formed 
in the partition wall of the casing 6 between the casing 6 and the clean 
room 2 for communicating therebetween. 
The operation of the heat treatment apparatus of the first embodiment of 
this invention will now be explained. 
Five semiconductor wafers 28 are taken out of one of the wafer cassettes 
16a to 16h in the cassette holding unit 16 by means of the five supporting 
arms 25 of the transportation robot 15 and moved onto the wafer boat 17. A 
test wafer or a dummy wafer can be moved onto the wafer boat 17 by using 
one of the supporting arms 25. The transportation of the wafers 28 are 
repeated until a required number of the wafers 28 are loaded on the wafer 
boat 17. Thereafter, the heat insulating tube 30 and the wafer boat 17 are 
moved into the reaction tube 11 of the heat treatment furnace 10 and the 
wafers 28 are heat-treated by using a CVD film formation process. 
After the heat treatment has been completed in the reaction tube 11, the 
boat elevator 14 is lowered and the heat insulating tube 30 and the wafer 
boat 17 is unloaded at the unloading position A. Since the temperature of 
the wafers 28 and the boat 17 is very high just after the heat treatment, 
dust is attached to the wafers 28 and the yield is reduced unless the 
atmosphere at the unloading position A is not clean. 
In this embodiment, however, clean air flow sidewise onto the wafers at the 
position disposed opposite to the unloading position A, whereby the 
atmosphere at the unloading position A can be kept clean. Air flows 
sidewise from the clean room 2 disposed adjacent the casing 6. Since the 
pressure in the clean room 2 is made higher than the pressure in the 
casing 6, air is smoothly conducted in the back door 41 through the duct 
62 and can be circulated smoothly without exerting excessive loads on the 
fan 42 in the clean module 40. The air which has flowed in the door 41 
blows out through the filter 44 by means of the fan 42 and is rendered to 
make air flow sidewise onto the wafers 28 disposed at the unloading 
position A. 
In this embodiment, the clean module 40 is disposed close to the unloaded 
wafers 28 at the position separated by, for example, 150 mm from them. 
Radiant heat from the wafers 28 or the boat 17 heated to high temperature 
is effectively reflected by the heat reflector 50 disposed in front of the 
filter 44, preventing the rise of the temperature of the filter 44. The 
air through holes 52a formed in the heat reflector 50 as shown in FIG. 3 
enables the clean air blown out through the filter 44 to arrive at the 
wafers 28 in a state in which a laminated flow is retained. 
Since the air through holes 52a in the heat reflector 50 as shown in FIG. 
3, are directed toward the filter 44, their central lines are 
perpendicular to the filter 44. Heat rays such as infrared rays pass 
through the air holes 52a, and thus the heat rays are not reflected at the 
holes 52a. On the contrary, the air through holes 54a and 56a in the heat 
reflector 50 as shown in FIG. 4 are not aligned with each other and the 
central lines of the air through holes 58a of the heat reflector 50 as 
shown in FIG. 5 are inclined with respect to the filter 44. The heat rays 
emitted from the unloaded wafers 28 do not pass through the holes 56a and 
58a, and consequently are reflected at the second plate 56 and the inner 
wall of the hole 58a, assuring of the reflection of the radiant heat from 
the unloaded wafers 28. In both cases, it is preferred that the hoods 54b 
and 58b are added in order to ensure the side flow of air in a laminated 
state. 
Since the clean module 40 is housed in the back door 41, the apparatus 
according to this invention can be made smaller in depth and thus has a 
smaller floor space than the conventional apparatus. 
In FIGS. 6 and 7 illustrate horizontal multi-stage type furnaces provided 
with the clean modules 40 according to this invention. 
FIG. 6 shows a horizontal furnace in which air is made to flow downward at 
the unloading positions A of the wafers 28. Over each unloading position A 
in each stage of the furnace is disposed a clean module 40 provided with a 
fan (not shown) and comprising a filter 44 and a heat reflector 50 as 
shown in either one of FIGS. 3 to 5. Under each clean module 40, an 
exhaust module 70 is provided. 
As seen from FIG. 6, the stages of the horizontal multi-stage furnace are 
independently constructed from one another. Since each clean module 40 has 
a heat reflector 50, the temperature rise of the filter 44 in the module 
40 is prevented even if the heated wafers 28 soon after unloaded are 
disposed adjacent the module 40. 
In the horizontal furnace as shown in FIG. 6, down-flow clean air is caused 
to escape in the horizontal direction by means of the exhaust modules 70, 
and thus the laminated flow of clean air is not disturbed at the unloading 
positions A. The down-flow clean air is not always sucked in downward by 
means of the exhaust modules 70 but it may be exhausted by means of 
exhaust modules provided on the side wall 72 of the casing 6. 
In the embodiment of the multi-stage type furnace as shown in FIG. 7, a 
clean module 40 is provided on that side wall 72 of the casing 6 which is 
opposed to the unloading position A in each stage. Side-flow of clean air 
is supplied onto the wafers 28 soon after they have been unloaded. The 
temperature rise of the filter 44 in each clean module 40 can be avoided 
due to the action of the heat reflector 50 by the same reason as explained 
with respect to the embodiment as shown in FIG. 6. 
The filter 44 and the heat reflector 50 can be replaced by other various 
members having the same functions. In particular, the heat reflector 50 is 
not always made of metal but may be made of resin or the like so long as 
the plate has a heat reflecting film on its surface. 
The air filter according to this invention is not only applied to a heat 
treatment apparatus but is suited to a plasma furnace, an ion-implanting 
apparatus and the like in which the temperature in the vicinity of their 
filter or filters is much raised. 
This invention is not limited to the above-mentioned embodiments but is 
applicable to various modifications so long as they are not departed from 
the scope of this invention.