Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
2001-10-30
2002-07-02
Hail, III, Joseph J. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S006000, C451S041000, C451S060000, C451S173000, C451S174000, C451S288000
Reexamination Certificate
active
06413146
ABSTRACT:
TECHNICAL FIELD
The present invention relates to polishing apparatus in general, and relates in particular to a polishing apparatus to produce a flat and mirror polished surface on workpieces such as semiconductor wafers.
BACKGROUND ART
With increasing intensity of circuit integration in semiconductor devices in recent years, circuit lines have become finer and interline spacing has also been drastically reduced. With this trend for finer resolution in circuit fabrication, it is now necessary to provide a precision flat substrate surface because of the extreme shallow depth of focus required in optical photolithography using stepper reproduction of circuit layout. One method of obtaining a flat surface is mechano-chemical polishing carried out by pressing wafers held on a carrier against a polishing cloth mounted on a rotating turntable while dripping a solution containing abrasive powder at tile interface of the wafer and the polishing cloth.
FIG. 11
shows a polishing apparatus disclosed in a Japanese Patent Laid-Open Publication, H9-117857. The facility is comprised by a pair of polishing units
101
a,
101
b
disposed symmetrically at one end of a rectangular-shaped floor, and a loading /unloading unit including wafer cassettes
102
a,
102
b
disposed on the opposite end of the floor for storing wafers. Transport rails
103
are disposed along a line joining the polishing units
101
a,
101
b
and the loading/unloading unit, and alongside the rails
103
, there are wafer inverters
105
,
106
surrounded by respective cleaning units
107
a,
107
b
and
108
a,
108
b.
Such a polishing apparatus, comprised by a pair of parallel processing lines arranged on both sides of the rails, is able to handle workpieces polished through a single step process in each line of the facility to improve its productivity. For those workpieces requiring a double step polishing, such as compound semiconductor materials requiring polishing steps using different solutions, after completing a first polishing step through one polishing line
101
a,
the workpieces are cleaned next, and then transferred over to the second line
101
b
to carry out a second polishing step. Thus, such a polishing apparatus is able to carry out a series-operation for workpieces processed in double-step polishing, and a parallel-operation for workpieces processed in single-step polishing.
Transport of workpieces in the parallel polishing process is carried out as follows. After completing a polishing operation of the polishing units
101
a,
101
b,
the top ring (workpiece carrier)
110
rotates and moves over to the workpiece pusher (transfer device)
112
to transfer the polished workpiece. A second robot
104
b
transports the workpiece over to the cleaning units
107
a
or
107
b,
and receives an unpolished workpiece from the inverter
105
,
106
, and transfers it to the workpiece pusher
112
. The top ring
110
receives the unpolished workpieces and moves back to the turntable
109
to begin polishing. A dresser
111
is provided to carry out reconditioning of a polishing cloth.
A polishing unit, such as the one shown in
FIG. 12
, is comprised by a turntable
109
having a polishing cloth
115
bonded to its top surface, and a top ring
113
for holding and pressing a wafer W onto the turntable
109
. Polishing action is produced by rotating and pressing the wafer W by the top ring
113
against the rotating turntable
109
while a polishing solution Q is supplied in the interface between the wafer W and the polishing cloth
115
. The polishing solution Q is held between the surface to be polished (bottom surface) of the wafer W and the polishing cloth
115
while the wafer is being polished.
In such a polishing unit, the turntable
109
and the top ring
113
are rotated at their own independent speeds, and the top ring
113
is positioned, as shown in
FIG. 12
, so that the inner edge of the wafer W will be off from the center of the turntable
109
at a distance “a”, and the outer edge of the wafer W will be at a distance “b” from the periphery of the turntable
109
, respectively. The wafer W is polished in this condition at high rotational speeds so that the surface of the wafer will be polished uniformly and quickly. Therefore, the diameter “D” of the turntable
109
is chosen to be more than double the radius “d” of the wafer W according to the following expression:
D=
2(
d+a+b
).
Polished wafers W are stored in the wafer cassette
102
a,
102
b
after having gone through one or more cleaning and drying steps. Cleaning methods for wafers include scrubbing with brush made of nylon or mohair, and sponges including polyvinyl alcohol (PVA).
One of the problems in the existing polishing apparatus is its productivity. To increase the through-put from such a facility, the efficiency-determining processes involving polishing at the turntable
109
must be raised. However, in the existing technology, one robot
104
b
is required to carry out a multiple duty of removing polished wafers and supplying unpolished wafers to and from two workpiece pushers
112
. This is time-consuming, resulting in idle time for the turntable
109
.
Therefore, there is a need to provide, as a first objective, a polishing apparatus having two parallel processing lines that carries out efficient parallel processing by minimizing the idle time for the turntable and maximizing the through-put.
Furthermore, in the existing polishing apparatus, a high relative speed between the turntable
109
and the top ring
113
is used to achieve effective polishing as well as high flatness of the wafer surface, but this high relative speed may also cause micro-scratch marks on the wafers due to abrasive particles contained in the polishing solution.
To prevent fine scratches, it is possible to consider utilizing two sets of turntables
109
, and carry out polishing in two stages, by changing polishing parameters such as the material and abrasive characteristics of the polishing cloth
115
, rotation speed of the turntable
109
, and polishing solution. However, as mentioned above, the large size of the turntable
109
occupying a large installation space and requiring high capital cost are disadvantages of such an approach, and this type of problem is expected to become more serious in the future, as larger diameter wafers become more common.
On the other hand, it is also possible to consider using one turntable by switching polishing solutions or by reducing the rotational speed to resolve existing problems, but such approaches are not expected to lead to improved productivity, because mixing of solutions may lead to poor performance and polishing time would be lengthened.
Another problem is related to cleaning of the wafers. When the wafers are scrubbed after polishing with abrasive particles, it is difficult to remove particles of sub-micron sizes, and if the adhesion force between the wafer and particles is strong, such cleaning method is sometimes ineffective for removing such particles.
Therefore, there is a need to provide, as a second objective, a compact polishing apparatus that can provide excellent flatness and efficient cleaning.
DISCLOSURE OF INVENTION
These objectives of the present invention are realized in a polishing apparatus comprising: a storage section for storing a workpiece to be polished; at least two processing lines extending substantially in parallel from the storage section, with each line being provided with a cleaning unit and a polishing unit; a temporary storage station disposed between the cleaning unit and the polishing unit and shared by the processing lines; and at least two robotic devices disposed for each of the processing lines for transferring workpieces among the temporary storage station, the polishing unit and the cleaning unit.
Accordingly, each of the robotic devices is used to supply an unpolished wafer placed on the temporary storage station to a polishing unit, and a polished wafer in another polishing unit directly to a cleaning unit. Therefore, replacing of wafers between processe
Katsuoka Seiji
Osawa Hiroyuki
Sakurai Kunihiko
Tsujimura Manabu
Ebara Corporation
Hail III Joseph J.
McDonald Shantese
Wenderoth , Lind & Ponack, L.L.P.
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