Polishing pad and polisher

Details Polishing pad and polisher Polishing pad and polisher

2002-02-15

2003-04-08

Morgan, Eileen P. (Department: 3723)

Abrading

Precision device or process - or with condition responsive...

With indicating

C451S006000, C451S010000, C451S041000, C451S285000, C451S287000, C451S526000

Reexamination Certificate

active

06544104

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a polishing pad for chemical mechanical polishing.
BACKGROUND ART
In manufacturing a semiconductor device, a step of forming an conductive film over the surface of a wafer is followed by a step of forming a wiring layer by photolithography, etching or the like and a step of forming an inter-layer insulation film over the wiring layer. These steps produce non-uniformity of the wafer surface. As fineness of wiring is increased and multi-layered wiring is used in recent years for higher density semiconductor integrated circuits, a technique for planarizing a non-uniform wafer surface has been important.
Methods for planarizing a non-uniform wafer surface include what is known as a chemical mechanical polishing (CMP) method. In the CMP method, slurry in which abrasive grains are dispersed in a liquid is used as a polishing solution, the surface of the wafer to be polished is pressed against the polishing surface of a polishing pad and polished.
A polisher for use by the CMP method is provided with, for instance a polishing table
2
for supporting a polishing pad
1
, a supporting base
6
for supporting an object (wafer)
5
of polishing and a feed mechanism
10
for the polishing solution as illustrated in FIG.
1
. The polishing pad
1
is fixed to the polishing table
2
with a double-sided adhesive tape or otherwise. The polishing table
2
and the supporting base
6
are so arranged that the polishing pad
1
and the object
5
be opposite each other, and provided with rotation axes
8
and
9
, respectively. On the supporting base
6
side, there is provided a pressing mechanism for pressing the object
5
against the polishing pad
1
.
In polishing a wafer surface by the CMP method, it is required to detect, without having to interrupt the progress of polishing, the end point of polishing (the point of time at which the surface structure and the insulating layer thickness of the wafer achieve their respectively desired states). As a way of detecting this end point of polishing, the wafer surface can be irradiated with a laser beam through a polishing pad and the beam reflected from the wafer can be monitored.
The reflected beam from the wafer having an insulating film on the surface contains an interference light resulting from interference between a first reflected light reflected by an insulating film face present on the wafer surface and a second reflected light reflected by a boundary face between the insulating film and a silicon substrate. This interference light has an intensity matching the phasic relationship between the first reflected light and the second reflected light, and this phasic relationship represents the thickness of the insulating film over the silicon substrate. Therefore, the end point of polishing can be detected by monitoring the reflected light from the wafer and analyzing the interference light.
This method for detecting the end point of polishing is described in, for instance, in Japanese Patent Laid-Open No. 9-7985 (U.S. Pat. No. 5,964,643), WO 99/64205 (internationally disclosed after the priority date of the present application), Japanese Patent Laid-Open No. 10-83977 (U.S. Pat. No. 5,893,796), U.S. Pat. No. 6,045,439 and National Publication of International Patent Application No. 11-512977 (U.S. Pat. No. 5,605,760).
Detection of the end point of polishing by this method requires light transmission areas in the polishing pad. A laser beam is brought to incidence on the wafer surface through the light transmission areas of the polishing pad, lights having passed these light transmission areas, out of the reflected lights from the wafer are directed toward a detector.
The references cited above also describe how these light transmission areas are provided. For instance, a through hole is bored in part of the polishing pad, a hole penetrating the table in its thickness direction is bored continuously from the through hole in the pad, and window members, such as transparent sheets, plugs or the like are fitted to these continuous holes. As these window members, members of a uniform structure consisting of quartz, polyurethane or the like (members having no intentionally designed distribution of refractive index) are used.
However, these methods according to the prior art have need for some improvement in the point of view of the efficiency of bringing reflected lights from the wafer to incidence on the photo detector.
As polishing of a wafer cannot completely eliminate non-uniformity on the wafer surface even if the polishing is done to the end point, the reflected lights from the wafer are scattered. If the face of the window member toward the polishing face is more depressed than the polishing face itself, the polishing solution having accumulated in this more depressed part further scatters the reflected lights from the wafer. If the face of the window member toward the polishing face is made level with the polishing face, the face of the window member toward the polishing face may also be polished depending on its material, resulting in further scattering of the reflected lights from the wafer by the face to be polished.
Therefore, even if a light normal to the polishing face is brought to incidence through the window member, the reflected lights from the wafer will not be aligned to the direction normal to the polishing face. As a result, when these reflected lights enter the window member of a uniform structure, part of these reflected lights will be absorbed by, for instance, the inner face of the through hole in the table and fail to reach the detector.
It is conceivable to expand the light transmission area to bring the reflected lights from the wafer to incidence on the photo detector efficiently, but an expansion of the light transmission area would reduce the polishing face of the polishing pad correspondingly. Thus, it is not preferable to expand the light transmission area because it would adversely affect the uniformity of polishing.
To add, WO 99/64205 describes an arrangement in which a laser beam is brought to incidence and reflected lights are received by an optical fiber, one end of this optical fiber is inserted into a through hole bored in the polishing pad, and the other end is connected to a light receiver for detecting the end point of polishing. Thus, in this example, no window member is fitted in the light transmission area of the polishing pad.
An object of the present invention is to make a transparent window member (provided in the light transmission area of a polishing pad for detecting the end point of polishing by a CMP method) a composition which enables reflected lights from a wafer to be efficiently brought to incidence on a photo detector, even if the size of the transparent window member is small.
DISCLOSURE OF THE INVENTION
In order to solve the problems noted above, the present invention provides a polishing pad for chemical mechanical polishing having a polishing area and a light transmission area consisting of a transparent window member within a pad surface, wherein the window member has areas of a high refractive index and areas of a low refractive index in its window face, and each of the areas is alternately arranged in stripes in a cross section normal to the window face.
When a light is brought to incidence on the light transmission area of the polishing pad from one window face, the light travels in the thickness direction of the polishing pad mainly in the areas having a high refractive index while being reflected by the boundary between the areas having a high refractive index and the areas having a low refractive index, and is emitted from the other face. Thus, even if the light coming incident on this light transmission area is not uniform in direction, the light is transmitted substantially in the lengthwise direction of the aforementioned stripes within the light transmission area.
Therefore, this light transmission area, where the incident light is not uniform in direction, can make the degree of diffusion of the light emitted from the lig

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