Bearings – Linear bearing – Combined with seal or guard
Reexamination Certificate
1997-10-17
2004-10-19
Hannon, Thomas R. (Department: 3622)
Bearings
Linear bearing
Combined with seal or guard
C277S431000, C277S913000
Reexamination Certificate
active
06805487
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a holder driving device which is used, for example, in an ion-implantation apparatus of a hybrid scan system, etc., and which drives mechanically a holder holding a substrate to reciprocate linearly in a vacuum vessel, and more specifically, it relates to a unit for preventing moisture in the atmosphere from flowing into its bearing unit using a differential pumping system to thereby prevent the vacuum seal performance of the bearing unit from lowering.
2. Description of the Related Art
For example, an ion-implantation apparatus of a hybrid scan system is designed to scan an ion beam reciprocatingly in a vacuum vessel in one direction, and at the same time to scan a substrate reciprocatingly mechanically in the direction substantially perpendicular to the scanning direction of the ion beam so as to perform uniform ion-implantation in the whole surface of the substrate. A holder driving device for driving a holder holding the substrate linearly and reciprocatingly in the vacuum vessel is used in such an ion-implantation apparatus.
Although it can be considered that a packing such as an O-ring or the like is used for vacuum seal in the portion where a shaft of such a holder driving device is penetrating the vacuum vessel, it is difficult to increase the driving speed of the shaft with such a packing, and it is also necessary to exchange the packing periodically because of abrasion. To this end, there is a case where differential pumping is used. In the above example, the differential pumping means a system where one or more stages of exhaust chambers are provided between the vacuum vessel and the atmosphere, and the exhaust chambers are pumped by a vacuum pump, so that the pressure in the exhaust chambers is set to values between the pressure in the vacuum vessel and the atmospheric pressure. With such differential pumping, the vacuum seal in the above-mentioned penetration portion can be attained without using any packing.
FIG. 5
shows an example of an ion-implantation apparatus of a hybrid scan system having a conventional holder driving device using such differential pumping.
This ion-implantation apparatus is configured so that in a vacuum vessel
4
, an ion beam
2
travelling from the surface of the paper toward the back is made to perform scanning reciprocatingly electrically (that is, by means of an electric field or a magnetic field) in the direction X (for example, the horizontal direction, and that applies to the following description), while a holder
12
holding a substrate
6
(for example, a semiconductor wafer) is made to perform scanning reciprocatingly mechanically in the direction Y substantially perpendicular to the above-mentioned direction X (for example, in the vertical direction, and that applies to the following description) by means of a holder driving device
10
so as to radiate the ion beam
2
over the whole surface of the substrate
6
uniformly to perform ion-implantation therein.
The vacuum vessel
4
is disposed in the atmosphere, and the inside thereof is pumped up to a high vacuum, for example,about 1×10
−6
Torr to 1×10
−7
Torr, by means of a not-shown vacuum pump.
This holder driving device
10
is that which is disclosed in U.S. Pat. No. 4,726,689 and which comprises the above-mentioned holder
12
, a shaft
14
supporting the holder
12
and penetrating the vacuum vessel
4
, a driver (not-shown) provided outside the vacuum vessel
4
and for driving the shaft
14
linearly and reciprocatingly in the direction Y, a gas bearing unit
16
attached to the outside of the vacuum vessel
4
so as to vacuum-seal the portion where the shaft
14
penetrates the vacuum vessel
4
, and a vacuum pump and a compressed gas supply means (both not shown) for this gas bearing unit
16
.
The gas bearing unit
16
is constituted by a combination of a gas bearing and differential pumping. That is, this gas bearing unit
16
has plural stages (four stages in the illustrated example) of exhaust chambers
18
to
21
surrounding the shaft
14
in a housing (also called a sleeve)
17
of the unit
16
. The respective exhaust chambers
18
to
21
are pumped by not-shown four vacuum pumps respectively so that they become higher in the degree of vacuum toward the vacuum vessel
4
side. Consequently, the above-mentioned differential pumping is realized.
This gas bearing unit
16
is further configured so that compressed gas
24
supplied from a not-shown compressed gas supply means is fed through an entrance
22
to a gap with its size managed accurately between a housing
17
and the shaft
14
to form a gas layer which is extremely thin (for example, about 13 &mgr;m or less) in the gap so as to make the axes of the housing
17
and the shaft
14
coincident with each other to thereby make the shaft
14
held without contacting. Thus, gas bearing is realized. The pressure of the compressed gas
24
fed to the entrance
22
is usually about 6 kgf/cm
2
in terms of gauge pressure. Most of the compressed gas
24
fed to the entrance
22
is discharged to the outside through an exhaust port
26
provided between the entrance
22
and the exhaust chamber
21
, and the rest of the gas
24
leaks out to the atmosphere through a gap in the lower end portion of the housing
17
.
In order to improve the vacuum seal performance in the gas bearing unit
16
using such differential pumping, it is generally necessary to adopt and successfully combine methods such as a method in which a gap portion is elongated in the direction along the shaft
14
between the shaft
14
and the housing
17
in order to reduce the conductance between the shaft
14
and the housing
17
, a method in which a number of exhaust chambers are provided to thereby increase the number of stages of differential pumping, and a method in which vacuum pumps which are high in pumping speed are used.
The method using vacuum pumps which are high in pumping speed increases the cost. Either of the method in which a gap portion is elongated and the method in which the number of stages of differential pumping is made large causes the length of the gas bearing unit
16
to be elongated in the direction along the shaft
14
to thereby increase the lengthwise size of the holder driving device
10
.
However, in such an ion-implantation apparatus of a hybrid scan system, beam line height (height from a floor surface
28
to a beam line
3
) H to scan with the ion beam
2
cannot be made so high, because of the limitation of the handling height of the substrate
6
, the maintenance height of an ion source for emitting the ion beam
2
, the total height of the ion-implantation apparatus, and so on. Therefore, the lengthwise size of the holder driving device
10
also has a limit.
Therefore, there is a limit in increasing the number of stages of differential pumping in the gas bearing unit
16
or in elongating the length of the gap portion in the direction along the shaft
14
.
In the gas bearing unit
16
configured under such a limitation, it was found that a good vacuum seal performance is not maintained and resulted in a bad vacuum in the vacuum vessel
4
if the driving rate is increased when the shaft
14
was driven reciprocatingly and linearly as mentioned above, while the degree of vacuum in the vacuum vessel
4
was not influenced when the shaft
14
was not driven.
For example, the maximum rate of scanning the holder
12
mechanically in the direction Y usually reaches about 250 to 300 mm/sec. Even in that case, it is necessary to suppress the deterioration of the degree of vacuum in the vacuum vessel
4
to be not larger than about 10% of the ultimate degree of vacuum (for example, about 1 to 5×
−7
Torr), but this is difficult to realize for the above-mentioned gas bearing unit
16
. In the gas bearing unit
16
, the scanning rate of the holder
12
is limited to about 50 mm/sec in order to suppress the deterioration of the degree of vacuum to be within the above-mentioned range.
In or
Matsuno Tomoyasu
Nagai Nobuo
Nakaya Makoto
Tamura Yoshio
Yuasa Satoru
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Hannon Thomas R.
Nissin Electric Co. Ltd.
LandOfFree
Holder driving unit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Holder driving unit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Holder driving unit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3328739