Abrading – Precision device or process - or with condition responsive... – With indicating
Reexamination Certificate
1999-09-01
2001-12-04
Rachuba, M. (Department: 3724)
Abrading
Precision device or process - or with condition responsive...
With indicating
C451S056000, C451S060000, C451S041000, C051S308000
Reexamination Certificate
active
06325698
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cleaning method and a polishing apparatus employing such cleaning method, and more particularly to a cleaning method suitable for cleaning substrates that require a high degree of cleanliness, such as semiconductor wafers, glass substrates, or liquid crystal displays, and to a polishing apparatus employing such cleaning method.
2. Description of the Related Art
As semiconductor devices have become more highly integrated in recently years, circuit interconnections on semiconductor substrates become finer and the distances between those circuit interconnections have become smaller. One of the processes available for forming such circuit interconnections is photolithography. In the case where circuit interconnections are formed by the photolithography or the like, it requires that surfaces on which patterns images are to be focused by a stepper be as flat as possible because the depth of focus of the optical system is relatively small.
It is therefore necessary to make the surfaces of semiconductor substrates flat for photolithography. One customary way of flattening the surfaces of the semiconductor substrates is to polish them with a polishing apparatus. As shown in
FIG. 8
, a conventional polishing apparatus
76
comprises a turntable
72
having a polishing cloth
70
thereon, and a top ring
74
for holding a semiconductor substrate W and pressing the semiconductor substrate W against the turntable
72
. In the polishing apparatus, a chemical mechanical polishing (CMP) of the substrate is performed by a combination of chemical polishing with an abrasive liquid and mechanical polishing with abrasive particles contained in the abrasive liquid. An abrasive liquid supply nozzle
78
is provided above the turntable
72
to supply the abrasive liquid Q to the polishing cloth
70
. Further, a dressing device
80
is provided to regenerate, i.e. dress the polishing cloth
70
.
FIG. 9
shows a CMP unit which is constructed as an integral unit having the polishing apparatus
76
shown in FIG.
8
and various devices associated with the polishing apparatus
76
. The CMP unit has a substantially rectangular shape in plan, and the polishing apparatus
76
is disposed at one side of the CMP unit, and load and unload units
84
a,
84
b
for placing wafer cassettes which accommodate semiconductor substrates to be polished are disposed at the other side of the CMP unit. Transfer robots
86
a,
86
b
are movably provided between the polishing apparatus
76
and the load and unload units
84
a,
84
b
so that the transfer robots
86
a,
86
b
are movable along a transfer line C. Reversing devices
88
a,
88
b
for reversing a semiconductor substrate are disposed at one side of the transfer line C, and cleaning apparatuses
90
a,
90
b,
90
c
for cleaning the semiconductor substrate are disposed at the other side of the transfer line C. A pusher
10
is disposed adjacent to the turn table
72
to transfer the semiconductor substrate between the top ring
74
and the pusher
10
by vertical movement thereof.
In the polishing apparatus
76
having the above structure, the semiconductor substrate w is held by the lower surface of the top ring
74
and pressed against the polishing cloth
70
on the turntable
72
. The abrasive liquid Q is supplied from the abrasive liquid supply nozzle
78
onto the polishing cloth
70
and retained on the polishing cloth
70
. During operation, the top ring
74
exerts a certain pressure on the turntable
72
, and the surface of the semiconductor substrate held against the polishing cloth
70
is therefore polished in the presence of the abrasive liquid Q between the surface of the semiconductor substrate w and the polishing cloth
70
by a combination of chemical polishing and mechanical polishing while the top ring and the turntable are rotated. The abrasive liquid Q contains various abrasive particles, and the pH of the abrasive liquid Q is adjusted in accordance with the kind of semiconductor substrates to be polished.
As described above, as semiconductor devices have become more highly integrated, circuit interconnections on semiconductor substrates become finer and the distances between those circuit interconnections have become smaller. Therefore, in the above polishing process, if a particle greater than the distance between interconnections adheres to a semiconductor substrate and thus such particle remains on the product, i.e. semiconductor device, then the particle will short-circuit interconnections on the semiconductor device. Therefore, any undesirable particles on the semiconductor substrate have to be sufficiently smaller than the distance between interconnections on the semiconductor substrate. Such a problem and a requirement hold true for the processing of other substrates including a glass substrate to be used as a mask, a liquid crystal panel, and so on.
In the above-mentioned CMP process, the semiconductor substrate which has been polished is transferred to the cleaning apparatuses
90
a,
90
b
and
90
c.
In the cleaning apparatuses
90
a,
90
b
and
90
c,
for example, a scrubbing cleaning process in which a cleaning member such as a brush or a sponge is used to scrub a surface of the semiconductor substrate while supplying a cleaning liquid such as pure water, and a spinning dry process subsequent to the scrubbing cleaning process are performed, and the abrasive particles or the ground-off particles attached to the semiconductor substrate during the polishing process are removed from the semiconductor substrate.
When pure water (deionized water) is supplied to the semiconductor substrate which has been polished, the pH of the abrasive liquid remaining on the semiconductor substrate changes greatly. Therefore, in some cases, abrasive particles which have been dispersed in the abrasive liquid having an original pH are aggregated together, and adhere to the surface of the semiconductor substrate. For example, in slurry of colloidal silica which is generally used for polishing a SiO
2
layer, silica particles which are abrasive particles are stable in alkali solution having a pH of about 10, and form secondary particles having a diameter of about 0.2, &mgr;m due to aggregation of primary silica particles. If this slurry is rapidly diluted with pure water to lower the pH of the slurry to 7 or 8, then the electric potential on the surfaces of silica particles is rapidly changed by so-called pH shock, and the silica particles become unstable to thus aggregate the secondary particles to form larger aggregates. In this specification, the pH shock is defined as a rapid change of a pH. This holds true for the dressing process of the polishing cloth
70
. To be more specific, when pure water as a dressing liquid is supplied onto the polishing cloth
70
holding the abrasive liquid Q thereon, the pH of the abrasive liquid is rapidly lowered to cause abrasive particles to aggregate. These aggregates remain on the polishing cloth
70
and cause the semiconductor substrate to form scratches in the polishing process.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a cleaning method which can efficiently perform cleaning of substrates which have been polished without causing abrasive particles contained in an abrasive liquid to be aggregated.
Another object of the present invention is to provide a dressing method which can efficiently perform dressing of a polishing surface on a turntable without causing abrasive particles contained in an abrasive liquid to be aggregated on the polishing surface.
Still another object of the present invention is to provide a polishing apparatus employing such cleaning method or dressing method.
According to a first aspect of the present invention, there is provided a method for polishing and then cleaning a substrate. The method comprising polishing a substrate using an abrasive liquid containing abrasive particles, and cleaning a polished surface of the substrate by supplying a cleaning liqui
Hiyama Hirokuni
Kimura Norio
Wada Yutaka
Ebara Corporation
Rachuba M.
Wenderoth , Lind & Ponack, L.L.P.
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