Abrading – Precision device or process - or with condition responsive... – By optical sensor
Reexamination Certificate
2003-03-19
2004-07-13
Shakeri, Hadi (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
By optical sensor
C451S029000, C451S285000, C451S060000
Reexamination Certificate
active
06761616
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
The present document is based on Japanese Priority Document JP2002-079163, filed in the Japanese Patent Office on Mar. 20, 2002, the entire contents of which being incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polishing method and a polishing apparatus, and more particularly, to a polishing method and a polishing apparatus which polish a work surface still having unevenness thereon with slurry containing particles.
2. Description of the Related Art
As disclosed in Japanese Patent Application Laid-Open No.11-288906, a CMP (Chemical Mechanical Polishing) method has widely been used conventionally in the process of planarizing a semiconductor wafer substrate.
Especially, an enhanced integration degree of VLSI circuits causes an increase in number of wiring layers, and improving planarization process with CMP method is strongly required. The planarization process can be possible by realizing selective polishing on protrusions of a surface. Conventionally, a polishing pad is pressed to the surface at constant pressure so as to increase the speed at which the protrusions are selectively polished and removed with the aid of pressure distribution difference between the protrusions and depressions. However, since the method cannot produce a sufficient difference in the pressure distribution, there is a limitation on the ability to reduce unevenness. Thus, a method which actively allows a material process in an arbitrary fine region has been needed.
As shown in
FIG. 1
, the conventional CMP method involves adhering and fixing an elastic polishing pad
12
onto a rotating polishing plate
11
. A silicon wafer
13
is fixed to an end face of a polishing head
14
. The silicon wafer
13
is fixed by compression to the polishing pad
12
with its surface to be polished facing downward. Slurry
15
is supplied in this state, and the polishing plate
11
is rotated and the polishing head
14
is also rotated to polish the surface of the silicon wafer
13
.
At this time, since the polishing pad
12
is in contact with the silicon wafer
13
with pressure exerted on each other, the slurry
15
is not sufficiently flowed into the polishing region to result in unstable polishing. To prevent this, the surface of the polishing pad
12
is dressed with a diamond tool or the like so as to make relatively large protrusions and depressions for slurry pools. Thus, because the surface of the polishing pad
12
is made of elastic material, it becomes fuzzy due to the protrusions and depressions for the slurry pools and scratching with the dressing tool.
As shown in
FIG. 2
, the silicon wafer
13
to be polished with the CMP method as shown in
FIG. 1
has regular protrusions and depressions such as wiring pattern
21
of conductive metal at a surface layer and a thin film layer
22
serving as an insulating film made of SiO
2
formed over the protrusions and depressions. Affected by the protrusions and depressions of the wiring pattern
21
, protrusions and depressions are generated at the surface of the thin film layer
22
. In the planarizing process with the CMP method, selectively polishing on only the protrusions
23
of the protrusions and depressions of the thin film layer
22
achieves a surface planarization.
Attempts have been made to bring the polishing pad
12
into contact only with the protrusions on the surface of the silicon wafer
13
to perform polishing by increasing the elasticity of the polishing pad
12
, by way of example. Actually, however, as shown in
FIG. 3
, because the polishing pad
12
is formed of an elastic body which is deformed under pressure and its surface is fuzzy, the surface of the polishing pad
12
contacts not only the protrusions
23
of the thin film layer
22
but also the depressions. In other words, it is difficult to perform selectively polishing on only the protrusions
23
.
For this reason, it is difficult to achieve an ideal planarization process in which largely remove material including only the protrusions
23
as shown by a removed region
24
in
FIG. 4
for selectively removing the protrusions
23
. Specifically, in reality, there exists a problem that the removed region
24
has a substantially uniform thickness regardless of the presence of the protrusions and depressions as shown in
FIG. 5
to substantially uniformly polish the protrusions and depressions of the thin film layer
22
made of SiO
2
formed on the surface of the silicon wafer
13
even with the progression of the polishing, thereby preventing successful planarization.
When planarizing a surface having protrusions and depressions thereon, it is necessary to selectively remove only the protrusions. In typical CMP, however, since the surface of the polishing pad has large protrusions and depressions for holding slurry and is dressed to have fuzz as fibers, the polishing pad is not in contact uniformly with the silicon wafer. When the protrusions are removed with the progression of the polishing, the depressions are also simultaneously removed, although the removing amount is smaller. For this reason, planarization in a short time is difficult in polishing the surface having the protrusions and depressions. Also, even when polishing the surface is performed in a long time, a favorable planarized surface is difficult to achieve although its steps are reduced.
This phenomenon is also seen in processing of an aspheric lens. Specifically, in general, high precision grinding process is performed to form a desired aspheric shape on the surface of a lens, and then a polishing process is performed to remove a surface damage layer and ensure surface roughness as optics device simultaneously.
In the polishing process, even when previously measurements are made to calculate polishing regions and removing amounts at those regions, a shape of the region to be removed through the polishing has a certain area and thus its surroundings are processed at the same time, meaning that regions other than the intended region are subjected to processing. As a result, the polishing process deteriorates the accuracy achieved through the grinding process.
In view of the above-described problems, the present inventors have proposed a method as shown
FIG. 6
, in Japanese Patent Application Laid-Open No. 2000-289444. The method can be carried out local and selective polishing the protrusions
23
of the thin film layer
22
formed on the silicon wafer
13
by selectively irradiating laser light to the protrusions
23
so as to form aggregation trace of particles of the slurry there, and then performing polishing to break the aggregation trace of particles to result in a high concentration of the slurry in a local region.
According to the above-mentioned method, however, most of the polishing time is spent on polishing the aggregation trace, and an only extremely short time is spent on removing the material of the protrusions
23
immediately before the aggregation trace are eliminated. Thus, the method has disadvantages of an insufficient ability of planarization and low efficiency of planarization.
SUMMARY OF THE INVENTION
The present invention has been made in order to solve or alleviate such problems, and there is a need to provide a polishing method and a polishing apparatus which polish a work surface having protrusions and depressions thereon to efficiently achieve a target flat or curved surface by polishing and removing a relatively large material amount of the protrusions.
The present invention relating to the polishing method provides a method of polishing a work surface having protrusions and depressions thereon with slurry containing particles, comprising the steps of:
forming aggregation trace within the depressions by collecting the particles of the slurry through irradiating laser light to the depressions existed adjacent to or in the vicinity of the protrusions where a selectively larger removal material amount is desired during polishing process, whereby regions having the aggre
Kimura Keiichi
Miyoshi Takashi
Rader & Fishman & Grauer, PLLC
Shakeri Hadi
Sony Corporation
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