Abrading – Abrading process – Utilizing fluent abradant
Reexamination Certificate
2000-04-28
2003-07-22
Eley, Timothy V. (Department: 3724)
Abrading
Abrading process
Utilizing fluent abradant
C451S041000, C451S050000, C451S057000, C451S058000, C451S063000
Reexamination Certificate
active
06595831
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to methods and apparatuses for polishing workpieces such as semiconductor wafers, and relates in particular to a polishing apparatus for processing a surface of a so-called “device wafer” including various elements, wiring patterns, or patterned irregularities formed thereon, into a flat mirror surface.
2. Description of the Related Art
In recent years, the integration density of semiconductor devices has become progressively higher, which leads to finer interconnecting wirings and smaller integrated devices. In a manufacturing process for such semiconductor wafers, it is sometimes necessary to provide a step for removing films formed on a device wafer surface by polishing to planarize the surface.
Such process is necessary in the following cases:
(1) In a case of polishing a wafer having multi-layered circuits,
i) materials such as SiO
2
, SiOF, and CF for planarizing inter-layer films are polished,
ii) W, Al or Cu is polished after embedding plugs, or
iii) Al or Cu is polished after embedding wirings.
(2) In a case of manufacturing MOSFET (Metal Oxide Semiconductor Field Effect Transistor),
i) polycrystalline Si is polished after forming shallow trenches, or
ii) SiO
2
is polished after forming various electrodes.
One of the available planarization methods is a chemical-mechanical polishing (CMP) process using an apparatus as shown in FIG.
22
. The polishing apparatus comprises a turntable
9
having a polishing cloth (pad)
3
, and a top ring assembly
10
. The top ring assembly
10
comprises a top ring
13
for holding a semiconductor wafer
20
, a top ring shaft
48
for providing the top ring
13
with rotational forces and pressing forces, and a ball
47
forming a universal joint for tiltably coupling the top ring
13
to the top ring shaft
48
. The top ring
13
comprises an elastic mat
42
at a bottom surface to hold the wafer
20
through the mat
42
. The top ring
13
has a cylindrical retainer ring
16
on its outer periphery to hold the wafer
20
so that the wafer
20
does not disengage from the bottom surface of the top ring
13
while polishing.
By such construction, the wafer surface is polished into a mirror surface while the wafer
20
is between the turntable
9
and the top ring
13
; a certain pressure is applied by the top ring assembly
10
between the wafer
20
and polishing cloth
3
; the turntable
9
and the top ring
13
are respectively rotated; and a polishing solution (slurry) Q including abrasive particles is supplied to the top surface of the polishing cloth
3
.
One of the problems of the conventional chemical mechanical polishing (CMP) process is that, during the initial stage of polishing the device wafer having patterned irregularities, raised regions of the surface structure are preferentially removed, but depressed regions are also gradually removed. Therefore, irregularities of the surface are difficult to eliminate. This is because the combined use of the relatively soft cloth and the slurry solution containing abundant free abrasive particles applies chemical mechanical polishing effects not only to the raised regions but also to the depressed regions of the semiconductor surface structure.
FIG. 23
illustrates such problems of the conventional CMP; showing irregularities caused by a raised region and depressed region of a surface film on the vertical axis, and relative time on the horizontal axis. This graph shows that, after a relative polishing time of 1, the raised regions are polished from a thickness of about 27,000 angstroms to 16,000 angstroms, and the depressed regions are also polished from 20,000 angstroms to 16,000 angstroms, and thus the irregularities are eliminated.
FIG. 24A
shows surface profiles in an initial stage,
FIG. 24B
in a middle stage, and
FIG. 24C
in a final stage of polishing. As illustrated in these drawings, irregularities are very difficult to be removed, that is, step height reduction rate is small, and consequently, such polishing is a time-consuming operation.
Another problem relates to “a pattern dependency” of polishing due to a combination of the relatively soft polishing cloth and the slurry containing abundant abrasive particles. The pattern dependency is a difficulty in obtaining a completely flat surface, resulting from an already existing unevenness pattern on the unpolished surface. This is caused by the polish rate difference between the coexisting fine and coarse irregularities on the polished surface. The locations with fine irregularities are polished at a higher rate than the locations with coarse irregularities, thus resulting in a large-scale surface unevenness on the polished workpiece surface.
Also, an “edge wear” problem may occur, in which an outer periphery (edge) is more intensively polished than the inner region of the workpiece surface, because the polished workpiece is plunged into the elastic polishing cloth.
Another problem is that the polished workpiece is shaped like a dish due to selective polishing of the edge portions. This is caused by uneven distribution of the polishing solution supplied between the polishing cloth and workpiece from the outside to the central region, resulting in that the central region of the polished surface is supplied with a smaller amount of abrasive particles.
Furthermore, as described above, this method consumes a large quantity of suspension (slurry) including abundant expensive abrasive particles, so that environmental problems and a processing cost are also large.
Thus, a method has been developed, which uses a so-called fixed abrasive polishing tool (such as an abrading plate) which comprises cerium-oxide (CeO
2
) or other abrasive particles bound in a binder comprised of phenol resin, etc. This method uses an abrading plate harder than the conventional polishing cloth, which allows to preferentially polish the raised portions of the uneven surface, while leaving the depressed portions unpolished. Consequently, thus, absolute flatness of the polished surface can be obtained easily. Furthermore, the fixed abrasive polishing tool can provide a self-stopping function, depending on its composition, in which the polishing rate is remarkably lowered when the surface becomes flat after being rid of the irregularities. Thus, it can automatically stop further substantial polishing to avoid excessive polishing. Also, since it is not necessary to use a suspension (slurry) containing a large amount of abrasive particles, the environmental problems and processing cost can be lowered.
However, polishing using a fixed abrasive polishing tool has the following problems. That is, although a flat surface without scratches is necessary to produce a wafer suitable for producing devices thereon, the use of the hard tools causes the creation of many scratches on the polished surface of the workpiece while providing a highly flat surface.
Therefore, conventional fixed abrasive polishing tools for polishing the semiconductor wafers were allowed to have a limited choice of binder materials, and have been used in a narrowly balanced composition range of the abrasive particles, the binder and porosity. However, the device wafers to be polished comprise patterns of various materials such as: a silicon substrate, polycrystalline silicon films, oxide films, nitride films, and wiring layers comprised of aluminum or copper. Thus, it has been practically difficult to prepare various fixed abrasive polishing tools corresponding to the various polished subjects for preventing scratches while obtaining a stable removal rate with a small step height reduction rate.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a polishing method and apparatus capable of concurrently establishing a stable removal rate, a small step height reduction rate, and a reduction of defects on the polished surface for various kinds of polished subjects, while providing fewer environmental problems and requiring lower processing costs.
Such problems are solved by a
Hirokawa Kazuto
Hiyama Hirokuni
Matsuo Hisanori
Shimizu Noburu
Wada Yutaka
Ebara Corporation
Eley Timothy V.
Wenderoth , Lind & Ponack, L.L.P.
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