Environmental control apparatus

A substrate holder containing semiconductor substrates is held in an air-tight container for conveyance which is placed over the entrance of a chamber. The gas drawn by a first fan for circulating gas through the bottom wall of the chamber flows through a first duct for circulating gas so as to be cleaned by a first high-efficiency filter and to be supplied into the chamber again in a horizontal laminar flow. The clean gas is supplied into the chamber in a vertical laminar flow from a second duct for circulating gas which has a second fan for circulating gas and a second high-efficiency filter.

BACKGROUND OF THE INVENTION 
The present invention relates to an environmental control apparatus and, 
more particularly, it relates to an environmental control apparatus to be 
mounted in a device fabrication apparatus which requires a clean 
environment in producing such plate-like devices as semiconductor and 
liquid-crystal devices. 
Since the fabrication processes for semiconductor, liquid-crystal, or like 
devices require a clean environment, it is necessary that an apparatus for 
producing these devices is placed in a clean environment. Hence, the 
device fabrication apparatus mentioned above is typically installed in 
such a clean room as shown in FIG. 15. 
A variety of clean rooms are shown in pp.93-97 of "Clean Room Handbook" 
published by Japan Air Cleaning Association. Among them, the clean room 
shown in FIG. 15 is cited from FIG. 2.2.13 in p.96 of the same book. In 
FIG. 15, the device fabrication apparatus 51 is disposed in a clean area 
52, for it requires a clean environment in producing plate-like devices. 
The air blown into a ceiling area 54 by a blowing fan 53 is cleaned by a 
high-efficiency filter 55, so as to be supplied to the clean area 52. The 
air exhausted from the clean area 52 to an underfloor area 5B flows 
through a first duct 57, while a conditioned air introduced from outside 
flows through a second duct 58, both of which are blown into the ceiling 
area 54 by the blowing fan 53. 
However, the provision of such a clean room in the aforesaid device 
fabrication system is disadvantageous in that the resulting system becomes 
larger in scale and hence requires a heavy investment. Moreover, a huge 
amount of maintenance cost is necessary in order to clean the entire clean 
room and to maintain a specified degree of cleanliness therein. 
In view of the foregoing, there has recently been proposed an environmental 
control apparatus to be mounted in a device fabrication apparatus which 
requires a clean environment in producing devices, though the drawings 
thereof are omitted here. 
The environmental control apparatus comprises an air-tight chamber 
containing a clean air, an entrance formed in the chamber through which 
devices are carried into the chamber, an exit formed in the chamber 
through which the devices are carried out of the chamber toward the device 
fabrication apparatus, and a means for conveying the devices in the 
chamber from the entrance to the exit. 
As smaller device features are defined in such devices as semiconductor and 
liquid-crystal devices, a higher degree of cleanliness has been required 
in the environment in which the device fabrication apparatus for producing 
these devices is placed. 
However, the conventional environmental control apparatus mentioned above 
is disadvantageous in that it requires a clean-air supplying device to 
supply a clean air into the chamber and that small impurities generated in 
the chamber are not removed. 
SUMMARY OF THE INVENTION 
In view of the foregoing, an object of the present invention is to provide 
an environmental control apparatus which does not require a clean-air 
supplying means for supplying a clean air into the air-tight chamber in 
order to clean the air in the air-tight chamber and which can remove 
extremely small impurities which are generated in the air-tight chamber. 
To attain the above object, the present invention proposes the provision of 
a means for circulating gas which has a fan for circulating the gas in the 
air-tight chamber and a high-efficiency filter for cleaning the 
circulating gas so as to supply the clean gas in a laminar flow parallel 
to the surface of the devices. 
A first environmental control apparatus according to the present invention 
aims at an environmental control apparatus to be mounted in a device 
fabrication apparatus which requires a clean environment in producing 
plate-like devices, comprising: an air-tight chamber; an entrance provided 
in said air-tight chamber through which devices are carried in said 
air-tight chamber, said devices being in a first position; an exit 
provided in said air-tight chamber through which the devices are carried 
out of said air-tight chamber toward said device fabrication apparatus, 
said devices being in a second position different from said first 
position; means for conveying the devices in said air-tight chamber TO 
from said entrance to said exit while changing the position of the devices 
from said first position to said second position; first means for 
circulating gas which is provided outside said air-tight chamber and which 
has a fan for circulating the gas in said air-tight chamber and a 
high-efficiency filter for cleaning the circulating gas so as to supply 
said air-tight chamber with the clean gas in a laminar flow parallel to 
the surface of the devices in said first position; and second means for 
circulating gas which is provided outside said air-tight chamber and which 
has a fan for circulating the gas in said air-tight chamber and a 
high-efficiency filter for cleaning the circulating gas so as to Supply 
said air-tight chamber with the clean gas in a laminar flow parallel to 
the surface of the devices in said second position. 
Since the first environmental control apparatus comprises the first and 
second means for circulating gas which have the fan for circulation and 
high-efficiency filter so as to supply the clean gas into the chamber, the 
amount of the gas to be cleaned is small, for the gas in the chamber is 
the only gas to be cleaned, resulting in the reduction in cost. 
The first means For circulating gas supplies the clean gas in a laminar 
flow parallel to the surface of the devices in the first position in which 
they are carried in the air-tight chamber, while the second means for 
circulating gas supplies the clean gas in a laminar flow parallel to the 
surface of the devices in the second position in which they are to be 
carried out toward the device fabrication apparatus, so that the clean gas 
supplied into the chamber does not stagnate or form a turbulent flow over 
the main surface of the devices, for a laminar flow parallel to the main 
surface of the devices always streams over the main surface of the devices 
even when the position of the devices is changed. This can prevent the 
phenomenon that extremely fine dust which has passed through the 
high-efficiency filter adheres to the main surface of the devices, so that 
the production yield of the devices such as semiconductor and 
liquid-crystal devices is improved. 
In the first environmental control apparatus, said first and second means 
for circulating gas preferably have a physical or chemical adsorbent for 
removing a gaseous impurity from the circulating gas. 
Thus, the air-tight chamber is supplied with the extremely clean gas which 
does not contain gaseous impurities, so that the production yield of the 
devices is further improved. 
In the first environmental control apparatus, at least one of said first 
and second means for circulating gas preferably has an inert-gas supplying 
means for supplying an inert gas into said air-tight chamber. 
Thus, the inert gas is supplied in a laminar flow parallel to the surface 
of the devices, so that the gas flow in the air-tight chamber is not 
disturbed by the supply of the inert gas. Hence, the phenomenon that 
extremely fine dust adheres to the main surface of the devices can be 
prevented. 
In the first environmental control apparatus, said first and second means 
for circulating gas preferably have a gas conditioning means for 
regulating the temperature or humidity of the circulating gas. 
Thus, the temperature or humidity of the gas supplied into the air-tight 
chamber can be regulated to the optimum value, so that a film formed on 
the device can surely have the optimum quality and thickness even when 
Film quality and thickness are affected by temperature or humidity. 
A second environmental control apparatus according to the present invention 
aims at an environmental control apparatus to be mounted in a device 
fabrication apparatus which requires a clean environment in producing 
plate-like devices, comprising: an air-tight chamber; an entrance provided 
in said air-tight chamber through which devices are carried in said 
air-tight chamber; an exit provided in said air-tight chamber through 
which the devices are carried out of said air-tight chamber toward said 
device fabrication apparatus, said devices staying in the same position 
since they were carried in through said entrance; means for conveying the 
devices in said air-tight chamber from said entrance to said exit while 
keeping the devices in the same position throughout the conveyance since 
they were carried in through said entrance; and means for circulating gas 
which is provided outside said air-tight chamber and which has a fan for 
circulating the gas in said air-tight chamber and a high-efficiency filter 
for cleaning the circulating gas so as to supply said air-tight chamber 
with the clean gas in a laminar flow parallel to the surface of the 
devices. 
Since the second environmental control apparatus comprises the means for 
circulating gas which supplies the air-tight chamber with the clean air in 
a laminar flow parallel to the surface of the device, the amount of gas to 
be cleaned is small and the clean gas supplied to the air-tight chamber 
does not stagnate or form a turbulent flow over the main surface of the 
device. Hence, the phenomenon that the extremely fine dust that has passed 
through a high-efficiency filter adheres to the main surface of the device 
can be prevented. 
In the second environmental control apparatus, said means for circulating 
gas preferably has a physical or chemical adsorbent for removing a gaseous 
impurity from the circulating gas. 
In the second environmental control apparatus, said means for circulating 
gas preferably has an inert-gas supplying means for supplying an inert gas 
into said air-tight chamber. 
In the second environmental control apparatus, said means for circulating 
gas preferably has a gas conditioning means for regulating the temperature 
or humidity of the circulating gas.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, embodiments of the present invention will be 
described below. 
FIGS. 1 to 5 show an environmental control apparatus A1 according to a 
first embodiment of the present invention. 
As shown in FIG. 1, the environmental control apparatus A1 is mounted in a 
vertical electric furnace serving as a device fabrication apparatus. 
The environmental control apparatus A1 comprises an air-tight chamber 10 in 
the shape of a rectangular parallelepiped. The top wall 10a of the chamber 
10 is formed with an entrance 12 through which horizontal semiconductor 
substrates C in a first position as devices are carried into the chamber 
10. The bottom wall 10b of the chamber 10 is formed with an exit 14 
through which the vertical semiconductor substrates C in a second position 
are carried out of the chamber 10 toward the vertical electric furnace B1. 
The semiconductor substrates C are held in a substrate holder 16 with a 
U-shaped cross section, and the substrate holder 16 is further held in an 
airtight container 18 for conveyance, so that the semiconductor substrates 
C held in the air-tight container 18 are placed over the entrance 12 of 
the chamber 10. 
In the chamber 10 is provided an elevator 20 with a carriage 20a. When the 
carriage 20a descends, the bottom portion of the air-tight container 18 
(which is detachable from the main body of the air-tight container 18 and 
is locked to the main body in time of conveyance) is detached from the 
main body of the air-tight container 18 to be placed on the carriage 20a 
which descends in the chamber 10. Along with the bottom portion of the 
air-tight container 18, the substrate holder 18 disposed thereon and the 
semiconductor substrates C in the substrate holder 16 also descend. The 
elevator 20 is provided with an arm 22 for holding substrates. The arm 22 
can contract or stretch, can axially rotate, can perform tilt movements, 
and can ascend and descend. When the holder 18 has descended, the arm 22 
holds it, rotates it 90.degree. so that the semiconductor substrates C 
therein become vertical, and places the holder 16 over the exit 14 of the 
chamber 10. The elevator 20, carriage 20a, and the substrate holding arm 
22 described above constitute a means for conveying the semiconductor 
substrates C in the chamber 10 from the entrance 12 to the exit 14 while 
changing its position from the first position to the second position. 
Below, the method of conveying the substrate holder 16 in the chamber 10 
from the entrance 12 to the exit 14 will be described with reference to 
FIGS. 6 to 9. 
First, when the carriage 20a of the elevator 20 is allowed to descend, the 
bottom portion of the air-tight container 18 for conveyance is detached 
from the main body thereof to be placed on the carriage 20a which descends 
in the chamber 10 together with the substrate holder 16, as shown in FIGS. 
6 and 7. 
Next, as shown in FIG. 8, the arm 22 holds the substrate holder 16 and 
changes its position so that the semiconductor substrates C, which are 
held horizontal in the holder 16, become vertical. 
Subsequently, as shown in FIG. 9, the arm 22 is stretched downward so as to 
place the substrate holder 16 over the exit 14 of the chamber 10. The 
substrate holder 16 placed over the exit 14 is carried into the vertical 
electric furnace B1 by the conveyance system of the vertical electric 
furnace B1. 
As shown in FIGS. 1 to 5, the chamber 10 is connected to a first duct 24 
for circulating gas which is provided outside the chamber 10 and which 
extends downwardly from the bottom wall 10b of the chamber 10, bends in 
the right direction of FIG. 1, and then bends again upwardly. The first 
duct 24 has a fan 28 for circulating the gas in the chamber 10 and a first 
high-efficiency filter 28 for cleaning the circulating gas. The first 
high-efficiency filter 28 is attached to the side wall 10c of the chamber 
10, so that the gas which has passed through the first high-efficiency 
filter 28 is supplied into the chamber 10 in a laminar flow parallel to 
the surface of the semiconductor substrates C in the horizontal position. 
The first duct 24 for circulating gas, first fan 28 for circulating gas, 
and first high-efficiency filter 28 described above constitute a first 
means for circulating gas. 
The chamber 10 is also connected to a second duct 30 for circulating gas, 
which is provided outside the chamber 10 and which extends downwardly from 
the bottom wall 10b of the chamber 10, bends in the left direction of FIG. 
1, then bends again upwardly, and further bends in the right direction of 
FIG. 1 over the chamber 10. The second duct 30 has a second fan 32 for 
circulating the gas in the chamber 10 and a second high-efficiency filter 
34 for cleaning the circulating gas. The second high-efficiency filter 34 
is attached to the top wall 10a of the chamber 10, so that the gas which 
has passed through the second high-efficiency filter 34 is supplied into 
the chamber 10 in a laminar flow parallel to the surface of the 
semiconductor substrates C in the vertical position. The second duct 30 
for circulating gas, second fan 32 for circulating gas, and second 
high-efficiency filter 34 constitute a second means for circulating gas. 
Below, the method of cleaning the inside of the chamber 10 will be 
described with reference to FIGS. 2 to 5. In the drawings, arrows indicate 
the direction of gas circulation. 
First, when the semiconductor substrates C are in the horizontal position, 
the first fan 28 is activated, so that the gas in the chamber 10 is drawn 
by the first fan 26 into the first duct 24. The gas in the first duct 24 
flows upward and passes through the first high-efficiency filter 28, 
whereby particulates are removed from the gas, to be supplied into the 
chamber 10 in a horizontal laminar flow. Since the clean gas streams in a 
horizontal laminar flow over the main surface of the semiconductor 
substrates C in the horizontal position, the extremely small particulates 
mixed in the gas also flow over the semiconductor substrates C and hence 
do not adhere to the main surface thereof. 
Next, when the semiconductor substrates C are in the vertical position, the 
second fan 32 is activated, so that the gas in the chamber 10 is drawn by 
the second fan 32 into the second duct 30. The gas in the second duct 30 
flows upward, passes through the second high-efficiency filter 34, whereby 
the particulates are removed from the gas, to be supplied into the chamber 
10 in a vertical laminar flow. Since the clean gas streams in a vertical 
laminar flow over the main surface of the semiconductor substrates C in 
the vertical position, the extremely small particulates mixed in the gas 
also flow over the semiconductor substrates C along the main surface 
thereof and hence do not adhere to the main surface thereof. 
The transfer of the semiconductor substrates C to the vertical electric 
furnace B1 is thus conducted in the highly clean air-tight space, so that 
the particulates adhering to the main surface can be reduced. 
Below, the environmental control apparatus A2 according to a first 
variation of the first embodiment will be described with reference to FIG. 
10. 
FIG. 10 is a view showing a cross section taken along the line II--II of 
FIG. 1, which corresponds to FIG. 2 of the first embodiment. In the first 
variation, the description of similar elements to those used in the first 
embodiment will be omitted by providing the same reference numerals as 
used in the first embodiment. 
As shown in FIG. 10, an upstream portion of the first high-efficiency 
filter 28 is provided with an impurity adsorbent 38 which is composed of a 
physical or chemical adsorbent for removing gaseous impurities. This 
removes the gaseous impurities from the gas flowing through the first duct 
24, so that the amount of impurities in the gas supplied to the chamber 10 
is reduced to several ten p.p.t. or less. 
The air in general contains various impurities which may adversely affect 
semiconductor devices in its fabrication processes. For example, ammonia 
gas exists in large amount in natural environments as well as it is 
generated by human bodies. The ammonia gas prevents the reaction of a 
chemical amplification resist used in the lithographic process of 
semiconductor fabrication, and changes the dimension of the resulting 
resist pattern. With the environmental control apparatus A2 according to 
the first variation, however, the amount of the gaseous impurities is 
reduced to several ten p.p.t. or less, so that the reaction mentioned 
above is not prevented and hence the production yield of the resulting 
semiconductor devices is greatly improved. 
Below, the environmental control apparatus AS according to the second 
variation of the first embodiment will be described with reference to FIG. 
11. 
FIG. 11 is a view corresponding to FIG. 2 of the first embodiment, which 
shows a cross-sectional structure taken along the line II--II of FIG. 1. 
In the second variation also, the description of similar elements to those 
used in the first embodiment and its first variation will be omitted by 
providing the same reference numerals as used in the first embodiment and 
its first variation. 
As shown in FIG. 11, an upstream portion of the first duct 24 for 
circulating gas is connected to a duct 38 serving as an inert-gas 
supplying means through which an inept gas is introduced into the chamber 
10. The duct 38 for supplying inert gas is provided with a flow-rate 
regulating valve 40 which regulates the flow rate of the inert gas 
supplied into the chamber 10. An downstream portion of the first duct 24 
is formed with an exhaust hole 42 for exhausting a part of the gas flowing 
through the first duct 24. The exhaust hole 42 is provided with a dumper 
44 which opens the exhaust hole 42 when the pressure in the first duct 24 
for circulating gas is higher than the ambient pressure and closes the 
exhaust hole 42 when the pressure in the first duct 24 for circulating gas 
is lower than the ambient pressure. 
When an inert gas, e.g. nitrogen gas, is introduced into the duct 38 for 
supplying inert gas, the nitrogen gas is supplied into the chamber 10 
through the impurity adsorbent 36 and first high-efficiency filter 28, 
thereby replacing the gas in the chamber 10 with the inert gas. 
The environmental control apparatus A3 according to the second variation is 
preferably mounted in a sputtering apparatus which is used in the 
electrode forming process of semiconductor fabrication. In the electrode 
forming process, a material for the electrode is deposited on the 
semiconductor substrate, but if the semiconductor substrate is exposed to 
the ambient air during the deposition of the electrode material, an 
oxidation film is naturally formed on the semiconductor substrate, which 
may change the electric contact resistance between the semiconductor 
substrate and the electrode material. However, if the environmental 
control apparatus A3 according to the second variation is mounted in the 
sputtering apparatus used in the electrode forming process, the growth of 
the natural oxidation film is prevented. Consequently, the characteristics 
of the resultant semiconductor devices are stabilized and the production 
yield of the semiconductor substrates is further improved. 
Below, an environmental control apparatus A4 according to a third variation 
of the first embodiment will be described with reference to FIG. 12. 
FIG. 12 is a view corresponding to FIG. 2 of the first embodiment, which 
shows a cross-sectional structure taken along the line II--II of FIG. 1. 
In the third variation also, the description of similar elements to those 
used in the first embodiment and its first and second variations will be 
omitted by providing the same reference numerals as used in the first 
embodiment and its first and second variations. 
As shown in FIG. 12, the first duct 24 for circulating gas is provided with 
a heat exchanger 48 which is controlled by a controller 48. The controller 
4B and heat exchanger 48 constitute a means for circulating gas whereby 
temperature and humidity of the gas flowing through the first duct 24 can 
be conditioned. 
The environmental control apparatus A4 according to the third variation is 
preferably mounted in a resist coater used in the lithographic process of 
the semiconductor fabrication. Since the film thickness of a resist 
changes depending on temperature and humidity, stringent temperature and 
humidity control is required to provide a resist with a uniform film 
thickness. With the environmental control apparatus A4 according to the 
third variation, however, it is possible to stabilize the lithographic 
process. 
Below, an environmental control apparatus A5 according to the second 
embodiment of the present invention will be described with reference to 
FIGS. 13 and 14. 
FIG. 13 shows the environmental control apparatus A5 according to the 
second embodiment of the present invention and FIG. 14 shows a 
cross-sectional structure thereof taken along the line XIV--XIV of FIG. 
13. In the second embodiment also, the description of similar elements to 
those used in the first embodiment will be omitted by providing the same 
reference numerals as used in the first embodiment. 
In the environmental control apparatus A5 according to the second 
embodiment, the semiconductor substrates C stay in the same position while 
they are carried in the chamber 10 through the entrance 12 and conveyed 
therefrom to the exit 14. 
The environmental control apparatus A5 is mounted in a dry-etching 
apparatus B2 serving as the device fabrication apparatus. Typically, the 
dry-etching apparatus B2 is so designed as to process a single wafer at a 
time. Accordingly, when the substrate holder 18 is placed over the exit 
14, a conveyance arm in the dry-etching apparatus B2 takes semiconductor 
substrates C one by one in the dry-etching apparatus B2. Therefore, the 
substrate holder 16 is placed over the exit 14 so that the semiconductor 
substrates C are in the horizontal position, as shown in FIG. 14. 
The environmental control means A5 according to the second embodiment is 
provided with the first means for circulating gas consisting of the first 
duct 24, the first fan 28, and the first high-efficiency filter 28, for it 
is sufficient to supply the chamber 10 with a clean gas in a horizontal 
laminar flow, similarly to the first embodiment. However, the second means 
for circulating gas provided in the first embodiment is not provided in 
the second embodiment.