Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
2000-03-10
2002-03-12
Banks, Derris H. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S009000, C451S010000, C451S041000, C451S063000, C451S287000, C451S288000
Reexamination Certificate
active
06354907
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a polishing apparatus for polishing an article such as a semiconductor wafer, and in particular, relates to a polishing apparatus provided with an attitude controller for controlling an attitude of a turntable which is provided with a polishing surface and/or a carrier for carrying an article to be polished and bringing it into contact with the polishing surface of the turntable.
With recent rapid progress in technology for fabricating high-integration semiconductor devices, circuit wiring patterns have been becoming increasingly fine, with spaces between wiring patterns also decreasing. As wiring spacing decreases to less than 0.5 microns, the depth of focus in circuit pattern formation in photolithography and the like becomes shallower. Accordingly, surfaces of semiconductor wafers on which circuit pattern images are to be formed by a stepper are required to be polished by a polishing apparatus to an exceptionally high degree of surface flatness or planarization. As one method for effecting such planarization, for example, a chemical/mechanical polisher (CMP) has recently been used, in which polishing is carried out while a polishing solution having a predetermined chemical composition is supplied.
FIG. 26
shows such a conventional polisher for polishing a semiconductor wafer. The polisher includes a turntable
52
provided on its upper surface with a polishing cloth
51
and a wafer carrier
54
for holding a semiconductor wafer
53
. In a polishing operation, the turntable and the wafer carrier are independently rotated about their axes by motors (not shown) while the wafer
53
is engaged with the polishing cloth
51
and an abrasive liquid Q is supplied through a nozzle
57
provided above the turntable. However, during polishing, if the polishing cloth
51
does not engage with the wafer
53
under a uniform pressure across respective engaging surfaces, the wafer fails to be polished evenly. To solve this problem, the conventional polishing apparatus is provided with a universal joint comprising a ball bearing
56
between the wafer carrier
54
and a drive shaft
55
for pressing the wafer
53
against the polishing cloth
51
while drivingly rotating the wafer carrier
54
. The universal joint enables the wafer
54
to tilt about the ball bearing
56
in response to inclinations in the polishing surface of the polishing cloth
51
. Consequently, the polishing surface of the polishing cloth
51
and the polished surface of the wafer
53
held by the wafer carrier
54
are kept in a parallel relation with each other, whereby pressure between the wafer and the polishing cloth is kept even across the entire surface of the water. Japanese Patent Application 06198561 A discloses such a universal joint.
However, as stated above, since the drive shaft presses the wafer
53
against the polishing cloth
51
under a pressure F, a friction force &mgr;F, in which &mgr; is a friction coefficient, is generated and this causes a rotational moment M=&mgr;FH, in which H is a height of the center of the ball bearing
56
relative to the upper surface of the polishing cloth
51
. The wafer
53
is thus inclined downward in a direction opposite to the direction D in which the polishing cloth
51
on the turntable
52
passes under the wafer
53
, with the result that the wafer
53
is subject to an uneven pressure imposed by the polishing cloth
51
. To make the rotational moment M zero, it is necessary to make the above-noted height H zero. There is proposed an apparatus in which the center of tilting is positioned at a level of engagement between a wafer and a polishing cloth.
In theory, if the center of tilting lies on a surface where the polishing cloth and the wafer engage with each other, the rotational moment M which tends to tilt the wafer carrier will become zero and thus the wafer carrier can be kept parallel to the turntable. However, in practice, the polishing surface or upper surface of the polishing cloth on the turntable is not exactly even across its entire area which gives rise to a change in inclination of the polishing surface which is in contact with the wafer when the turntable is rotated. As a consequence of such a change in inclination of the polishing surface, the wafer carrier tends to tilt excessively under its inertia moment resulting in unstable tilting. Consequently, the wafer is unable to be engaged with the polishing cloth under a uniform pressure.
JP 1058308A discloses a polishing apparatus which is provided with an electromagnetic bearing including an electromagnetic thrust bearing device and an electromagnetic radial bearing device for bearing a drive shaft of a wafer carrier with an electromagnetic force, and an attitude controller for controlling the attitude of the drive shaft to keep the wafer carrier parallel to a turntable.
However, since in the polishing apparatus in accordance with JP 1058308A, the drive shaft of the wafer carrier is designed to be supported only by the electromagnetic bearing under the influence of the electromagnetic force generated thereby, it involves the following problems:
1) It is necessary for the thrust bearing device to be capable of generating a large magnetic force to press a wafer against the polishing cloth.
2) In terms of design, a motor for actuating the wafer carrier is required to be accommodated in a housing which also houses the electromagnetic bearing, and thus the size of the housing becomes large.
3) The wafer carrier is required to be movable up and down so as to load and unload a semiconductor wafer. This means that the wafer carrier, the electromagnetic bearing and the motor noted above are required to be moved as a unit and thus a mechanism for moving the unit also becomes large.
The present invention aims to solve the problems 1)-3) outlined above and, specifically, to provide a polishing apparatus which includes an attitude controller for controlling an attitude of a wafer carrier and/or a turntable so that the wafer or an object to be polished can be engaged with a polishing cloth on a turntable with a uniform pressure being exerted across its entire area.
SUMMARY OF THE INVENTION
In view of the above-described circumstances, an object of the present invention is to provide a polishing apparatus with an attitude controller for controlling an attitude of a turntable and/or a carrier for carrying an article to be polished, whereby the article is engaged with a polishing surface on the turntable under a uniform pressure thereby being polished to a very high degree of flatness.
In accordance with one aspect of this invention, there is provided a polishing apparatus comprising a turntable having a polishing surface that comes into sliding contact with an object to be polished, a support for tiltably supporting the turntable, and, an attitude controller for controlling an attitude or orientation of the turntable. The attitude controller may control the attitude of the turntable by controlling an angle of tilting of the turntable relative to the support by virtue of an electromagnetic force. The polishing apparatus may include a stationary frame, and the attitude controller may comprise an electromagnetic device fixedly provided on the stationary frame of the polishing apparatus, and an armature fixedly provided on the turntable and adapted to be moved by virtue of an electromagnetic force generated by the electromagnetic device. The attitude controller may comprise a cylinder device provided under the turntable and fixed to a stationary frame of the polishing apparatus and engaged with a lower surface of the turntable so that the cylinder device controls the attitude of the turntable by extension and retraction thereof.
In accordance with another aspect of the present invention, there is provided a polishing apparatus comprising a turntable having a polishing surface, a carrier for holding an article to be polished in a sliding contact relation with the polishing surface, a pressing device connected to the carrier and adapted to press th
Kimura Norio
Okumura Katsuya
Satoh Ichiju
Banks Derris H.
Ebara Corporation
McDonald Shantese
Wenderoth , Lind & Ponack, L.L.P.
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