Cryogenic vacuum pump system having a cryopanel and a heat absorbing unit

A cryogenic vacuum pump system in which a pump out system such as a cryotrap 13, with which gas is subjected to vacuum pump out by condensing or adsorbing said gas on a cryopanel which has been cooled to a very low temperature, is used, and a radiant heat absorbing baffle 18 which has been subjected to a blackening surface treatment is established up stream of, or around, the cryopanel 15. The radiant heat which is absorbed by the radiant heat absorbing baffle is released outside the chamber. The total thermal load on such a cryotrap is greatly reduced.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention concerns a cryogenic vacuum pump system, and in 
particular it concerns the improvement of a cryogenic vacuum pump system 
of the capture pump type in which some of the gas or each type of gas is 
condensed or adsorbed on a panel which has been cooled to a very low 
temperature, such as a cryotrap or cryopump. 
2. Description of Related Art 
Conventional cryogenic vacuum pump systems of this type have had the vacuum 
pump fitted directly to a chamber which is to be subjected to vacuum pump 
out. A direct cryopump 52 is sometimes fitted to the chamber 51 which is 
to be subjected to vacuum pump out, as shown in FIG. 3. The cryopump 52 
has two stage panels. The first stage panel is cooled down to about 50K to 
120K (usually about 80K) in order to condense water gas. The second stage 
panel is cooled down to lower than 20K to condense nitrogen gas, oxygen 
gas, argon gas and the like and adsorb hydrogen gas. Or, a direct cryotrap 
(53-55) and a turbo-molecular pump 56 are attached to the chamber 51 as 
shown in FIG. 4. In FIG. 4, the cryotrap includes a cooling panel 53 on 
which the water gas is condensed in a cylindrical container 55 and the 
cryogenic refrigerator 54 which cools the cooling panel 53 to a very low 
temperature of 50K to 120K (usually about 80K). The cryotrap is used 
together with the turbo-molecular pump 56. In FIG. 4, 57 is the auxiliary 
pump of the turbo-molecular pump 56 and, in FIG. 3 and FIG. 4, 58 is a 
heating body such as a heater. The heating body 58 is used to heat the 
vacuum chamber and release the water molecules which are attached to the 
wall to enable an even lower pressure to be achieved. Alternatively, the 
heating body 58 is used to heat the substrate in the vacuum chamber to a 
temperature of from one hundred to a few hundred degrees celsius in a film 
deposition process, such as sputtering. 
Conventionally, a panel on which many kinds of gases are condensed or 
adsorbed (for example, the cooling panel 53, referred to hereinafter as a 
cryopanel) has been included in a cryogenic vacuum pump system in which a 
very low temperature is used, such as the cryopump 52 of FIG. 3 or the 
cryotrap (only water) of FIG. 4. The surface temperature of the cryopanel 
must be set to a level at which the many kinds of gases which are to be 
removed from the vacuum chamber are condensed or adsorbed, set i.e. to a 
temperature below the saturated vapor pressure temperature. In other 
words, if the cryopanel is not below this temperature then no vacuum 
pumping capacity can be realized. 
In a conventional cryogenic vacuum pump system, a cryotrap or cryopump, 
which is furnished with a cryogenic refrigerator which has an adequate 
cooling capacity to cool the cryopanel to below this temperature under the 
influence of the effect of the heat which is generated, for example, for 
heating the substrate, in the chamber which is being subjected to vacuum 
pump out, has been used. 
OBJECTS AND SUMMARY 
The thermal load on the cryopanel, which is to say the heating of the 
cryopanel, is generally determined as being the sum of three types of 
thermal loading, namely radiant heat from the cryopanel surroundings, 
thermal conduction due to gas molecules, and the heat of condensation of 
the gas. These thermal loadings differ according to the construction of 
the cryogenic vacuum pump system which is being used and the conditions 
under which it is being used. Of these thermal loadings, the thermal 
conduction and heat of condensation are not very great since the system is 
initially at a vacuum environment. On the other hand, thermal radiation 
from the surroundings depends on the conditions under which the cryogenic 
vacuum pump system is being used, and it can be from ten to a hundred 
times greater than the other thermal loading factors. 
Generally, the chamber 51 which is to be subjected to vacuum pump out with 
a cryogenic vacuum pump system is made of a metal such as stainless steel 
or aluminum. Most recently the surface of these metal materials has in 
many cases had the microscopic surface roughness reduced in particular, 
which is to say that it has been provided with a mirror-like finish, in 
order to reduce the amount of gas which is released from the walls of the 
chamber 51. When a process which requires a high temperature is carried 
out inside such a chamber 51, the infrared radiation emitted by the 
heating body 58 is repeatedly reflected within the mirror surface like 
chamber and eventually reaches the cryopanel which is inside the cryopump 
52 or the cryotrap. Even in those cases where the cryopanel in the 
cryogenic vacuum pump system is arranged in such a way that it does not 
receive infrared radiation from the heating body 58 directly, the radiant 
heat due to the infrared radiation is repeatedly subjected to mirror 
surface reflection by the walls of the chamber 51 and so reaches the 
cryopanel. This imposes a very large thermal loading on the cryopanel. 
Most recently, the number of applications where a high temperature process 
such as that described above is required in particular has tended to rise. 
On the basis of the facts outlined above, the thermal loading on the 
cryopanel due to thermal radiation from the surroundings is markedly 
increased in a conventional cryogenic vacuum pump system. A cryogenic 
refrigerator which has a large cooling capacity is required on account of 
this increase in the thermal load. With the conventional cryogenic vacuum 
pump systems, problems have arisen in that there are disadvantages in 
respect of the high cost, and in respect of the complicated shape and 
large size of the apparatus. 
A purpose of the present invention is to provide cryogenic vacuum pump 
systems with which the problems referred to above are resolved and with 
which the incidence of infrared radiation on the cryopanel is reduced, 
even in those cases where there is a large amount of infrared radiation 
within the chamber which is being subjected to vacuum pump out. 
Moreover, another aim of the invention is to provide cryogenic vacuum pump 
systems with which a cryotrap or cryopump in which a cheap cryogenic 
refrigerator which has a small cooling capacity and which is small size is 
used can be used. 
In one embodiment of the present invention, a cryogenic vacuum pump system 
has a radiant heat absorbing baffle fitted on the up-stream side from the 
cryopanel in the flow of gas which is being pumped out, in order to 
realize the abovementioned aims. The cryogenic vacuum pump system utilizes 
a cryotrap or cryopump in which the gas is condensed or adsorbed on a 
cryopanel and vacuum pump out is achieved. 
In the embodiment described above, the radiant heat absorbing baffle is 
fitted between the chamber which is being subjected to vacuum pump out and 
the cryopanel. The radiant heat absorbing baffle absorbs the infrared 
radiation which is being radiated onto the cryopanel from the chamber and 
then releases the heat outside the cryogenic vacuum pump system. The 
radiant heat absorbing baffle greatly reduces the total thermal loading on 
the cryopanel inside the cryotrap or cryopump. 
A distinguishing feature of the abovementioned embodiment is that the 
radiant heat absorbing baffle is preferably made with a metal which has 
good thermal conductivity. The efficiency with which the absorbed heat is 
released out of the system is increased by raising the conductivity with 
respect to the heat which has been absorbed by said baffle, and the 
infrared radiation emissivity of the baffle is reduced. 
Another distinguishing feature of the abovementioned embodiment is that the 
radiant heat absorbing baffle preferably has a surface which has been 
subjected to a blackening surface treatment. Black chrome plating is 
especially desirable. The radiant heat absorbance of the baffle is 
increased by such a surface treatment. 
Another feature of the abovementioned embodiment is that the radiant heat 
absorbing baffle is preferably cooled by means of cooling water. It is 
possible in this way to release the radiant heat outside the chamber 
precisely. 
Yet another feature of the abovementioned embodiment is that the radiant 
heat absorbing baffle is cooled by means of a heat exchanger element. It 
is possible in this way to release the radiant heat outside the chamber 
precisely. 
In another embodiment of the present invention, a cryogenic vacuum pump 
system has a radiant heat absorbing baffle, which is connected with good 
thermal contact to a chamber which has good thermal conductivity, which is 
to be subjected to vacuum pump out established on the upstream side from 
the cryopanel in the flow of gas which is being pumped out. The heat which 
is absorbed by the radiant heat absorbing baffle is conducted to the 
chamber and heat exchange takes place between the walls and the air. The 
heat which has been absorbed is released out of the cryogenic vacuum pump 
system in this way. Water cooling of the radiant heat absorbing baffle is 
not required in those cases where the chamber which is being subjected to 
vacuum pump out is made of a material such as aluminum which has good 
thermal conductivity. 
In the embodiment described above, the radiant heat absorbing baffle is 
preferably formed as one with the chamber, and the inner wall surface of 
the chamber is preferably subjected to a blackening surface treatment. The 
infrared radiation is absorbed at the inner surface of the walls of the 
chamber. This is suitable in cases where the amount of infrared radiation 
is comparatively small. 
In another embodiment of the present invention, a cryogenic vacuum pump 
system has a radiant heat absorbing part which has been subjected to a 
blackening surface treatment established around the cryopanel. Black 
chrome plating is preferred for the blackening surface treatment. A 
"radiant heat absorbing part" is a part which comprises conceptually the 
execution of a blackening surface treatment on the inner surface of the 
container in which the cryopanel is housed, or the arrangement of parts 
which have been subjected to a blackening surface treatment around the 
cryopanel. Such a cryogenic vacuum pump system does not involve the use of 
a radiant heat absorbing baffle with which the radiant heat is shielded 
from the panel. It is suitable in those cases where the amount of infrared 
radiation is comparatively small. 
In the embodiment described above, the radiant heat absorbing part is 
preferably the inner surface of the chamber, which is to say the nipple, 
in which the cryopanel is installed. 
In the embodiment described above, the cryopanel is preferably subjected to 
a surface treatment which reduces its thermal absorption properties. 
Lustrous nickel plating is especially desirable. 
As is clear from the description above, the following effects may result 
from the present invention. 
Because a radiant heat absorbing baffle is established on the upstream side 
from the cryopanel in a cryotrap or cryopump, the radiant heat which is 
radiated from the chamber which is being subjected to vacuum pump out onto 
the cryopanel is absorbed with a high probability by the baffle. The 
effect of the radiant heat on the cryopanel is reduced and so the thermal 
loading on the cryopanel is reduced. Hence, a cheap cryogenic refrigerator 
of low cooling capacity and small size can be used to cool the cryopanel. 
A radiant heat absorbing part may be established using a blackening surface 
treatment around the cryopanel, and so the radiant heat which impinges on 
the cryopanel is absorbed with a high probability by this radiant heat 
absorbing part. This is especially suitable in cases where the amount of 
radiant heat which is being generated is comparatively small and the 
thermal load on the cryopanel can be reduced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments of the present invention are described below with 
reference to the drawings. 
An outline cross-sectional drawing of one embodiment of a cryogenic vacuum 
pump system of the present invention is shown in FIG. 1, and a plan view 
of the radiant heat absorbing baffle is shown in FIG. 2. The cryogenic 
vacuum pump system of this embodiment has a water cooled type radiant heat 
absorbing baffle 18 fitted to the cryotrap 13 which, in the main, 
selectively removes water. 
In FIG. 1, the chamber 11 is being subjected to vacuum pump out. The 
heating body 12, for example a heater, is arranged inside the chamber 11 
close to the opening 11a in the bottom wall of the chamber 11, and the 
cryotrap 13 is fitted on the outside of the opening 11a. The cryotrap 13 
comprises a cylindrical chamber 14, a cryopanel 15, a radiant heat 
absorbing panel 18 and a cryogenic refrigerator 16. The cylindrical 
chamber 14 is made with a greater axial length than a conventional 
cylindrical chamber in order to accommodate the radiant heat absorbing 
baffle 18 and the cryopanel 15. 
The radiant heat absorbing baffle 18 is arranged at a location within the 
cylindrical chamber 14 above the cryopanel 15. Hence, the radiant heat 
absorbing baffle 18 is arranged between the above mentioned heating body 
12 and the cryopanel 15. The radiant heat absorbing baffle 18 is arranged 
on the upstream side of the cryopanel 15 in terms of the flow of gas which 
is being pumped out. In this embodiment, the radiant heat absorbing baffle 
18 is connected to a cooling water pipe 19 for cooling purposes. 
A cryogenic refrigerator 16 is arranged outside the cylindrical chamber 14. 
The cryogenic refrigerator 16 is connected to the cryopanel 15 inside the 
cylindrical chamber 14 via a thermal conductor 17. The cryogenic panel 15 
is cooled to a prescribed very low temperature by the cryogenic 
refrigerator 16. 
A turbo-molecular pump 20 is fitted below the cryotrap 13, and an auxiliary 
pump 21, for example a mechanical vacuum pump, is also provided. 
The radiant heat absorbing baffle 18 comprises the three circular radiant 
heat absorbing baffles 18a to 18c which are arranged concentrically, and 
two supports 18d which intersect in the form of a cross, as shown in FIG. 
2. The supports 18d support the radiant heat absorbing baffles 18a to 18c 
concentrically and make connections which have good thermal conductivity 
between the radiant heat absorbing baffles. The outside radiant heat 
absorbing baffle 18c is connected in a way which provides good thermal 
conduction to the aforementioned water cooling pipe 19. The water cooling 
pipe 19 has the effect of releasing externally the heat which has been 
absorbed from the radiant heat absorbing baffles 18 by means of a flow of 
cooling water which is supplied from outside. 
The radiant heat absorbing baffle 18 is preferably made from sheet 
material, such as copper or aluminum, which has good thermal conductivity, 
and the surface is preferably subjected to a blackening surface treatment, 
such as black chrome plating. Black chrome plating provides an infrared 
radiation absorbance of from 92 to 98% and an emissivity of from 0.066 to 
0.12%, and so it is a good absorber of infrared radiation and also has the 
characteristics of allowing virtually no re-irradiation. The infrared 
radiation which has been radiated from the heating body 12 and reflected 
by the inner surface of the walls of the chamber 11 is absorbed with a 
high probability by the radiant heat absorbing baffle 18, which has been 
black chrome plated. 
As shown in FIG. 1, the radiant heat absorbing baffle 18 is arranged on the 
chamber 11 side with respect to the cryopanel 15 inside the cylindrical 
chamber 14 of the cryotrap 13. The infrared radiation which radiates into 
the cylindrical chamber 14 from the chamber 11 reaches the radiant heat 
absorbing baffle, whereupon said baffle absorbs with a high probability 
the infrared radiation which reaches said baffle, and the heat which is 
absorbed is released to the outside of the cryotrap 13 by the water 
cooling pipe 19. The radiant heat absorbing baffle 18 interrupts the 
radiant heat (infrared radiation) originating from the heating body 12 
which is being radiated onto the cryopanel 15. The radiant heat absorbing 
baffle 18 greatly reduces the thermal load which is imposed on the 
cryopanel 15. Hence, it is possible to use a cryogenic refrigerator 16 for 
the cryopanel which has a relatively small cooling capacity when compared 
with a conventional system. 
It has been confirmed by experiment that when the radiant heat absorbing 
baffle 18 and the cryopanel 15 are almost the same size in the embodiment 
described above, it is possible to absorb by means of the radiant heat 
absorbing baffle 18 some 70 to 90% of the infrared radiation which is 
being radiated onto the cryopanel 15. 
In the embodiment described above, the radiant heat absorbing baffle 18 and 
the cryopanel 15 are housed in the same cylindrical chamber 14, but it is 
clear that the same radiant heat absorbing effect as described above can 
be achieved even if they are housed in separate chambers. In those cases 
where a cryopump is used, it is, of course, possible to realize the same 
radiant heat absorbing effect as described above by establishing a radiant 
heat absorbing baffle between the cryopump and the chamber which is to be 
subjected to vacuum pump out. 
The radiant heat absorbing baffle cooling system may involve the use of a 
cooling fluid other than water, or a semiconductor heat exchange type 
cooling element such as a Peltier element. 
In another embodiment, the radiant heat absorbing baffle 18 is fitted 
directly with good thermal contact to the chamber 11 where the chamber 11 
which is to be subjected to vacuum pump out is made of a material which 
has good thermal conductivity, such as aluminum. In this case, even though 
no water cooling system is being used, the heat which is absorbed by the 
radiant heat absorbing baffle 18 is released outside the chamber 11 as a 
result of being conducted into the chamber 11, and the heat is exchanged 
with the atmosphere through the walls of the chamber 11. The radiant heat 
absorbing baffle 18 may be formed as one with the body of the chamber 11. 
In this case, the absorption of the infrared radiation is enhanced by 
subjecting the inner surface of the walls of the chamber 11 to black 
chrome plating. 
Moreover, in another embodiment, in those cases where the amount of 
infrared radiation produced inside the chamber 11 is comparatively small, 
a blackening surface treatment which facilitates the absorption of 
infrared radiation is carried out on the inner surface of the cylindrical 
chamber 14 in which the cryopanel 15 is housed. As a result, a radiant 
heat absorbing part which has been formed by a blackening surface 
treatment is established around the cryopanel 15. Of the radiant heat 
which is directed toward the cryopanel 15, a considerable amount (90% or 
more) is absorbed by said radiant heat absorbing part. The thermal load on 
the cryopanel 15 is greatly reduced as a result of this. There is no need 
to use a radiant heat absorbing baffle which shields the cryopanel 15 from 
the infrared radiation in this embodiment. Moreover, the cryopanel 15 is 
preferably subjected to a surface treatment which reduces its heat 
absorbing characteristics, such as lustrous nickel plating for example. 
The construction is comparatively simple since it can be realized by 
simply carrying out a blackening surface treatment on the inner surface of 
the cylindrical chamber (nipple) of a conventional apparatus, which is to 
say a conventional cryogenic vacuum pump. Moreover, the above mentioned 
radiant heat absorbing part is not limited to the inner surface of the 
cylindrical chamber 14 and, of course, other analogous parts can be used.