Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2001-03-28
2003-11-04
Morgan, Eileen P. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S285000, C451S287000, C451S398000
Reexamination Certificate
active
06641461
ABSTRACT:
FIELD OF INVENTION
This invention pertains generally to systems and devices for polishing and planarizing substrates, and more particularly to a chemical mechanical planarization or polishing (CMP) apparatus having edge, center and annular zone control of material removal.
BACKGROUND
Chemical Mechanical Planarization or Polishing, commonly referred to as CMP, is a method of planarizing and polishing semiconductor and other types of substrates. Planarizing a surface of a semiconductor substrate or wafer between certain processing steps allows more circuit layers to be built vertically onto a device. As feature size decreases, density increases, and the size of the semiconductor wafer increase, CMP process requirements become more stringent. Substrate to substrate process uniformity as well as uniformity of planarization across the surface of a substrate are important issues from the standpoint of producing semiconductor products at a low cost. Thus, as the size of structures or features on the semiconductor substrate surface have been reduced to smaller and smaller sizes, now typically less than 0.2 microns, the problems associated with non-uniform planarization have increased.
Many reasons are known in the art to contribute to uniformity problems. These include the manner in which pressure is applied to the backside of the substrate during planarization, edge effect or non-uniformities near the edge of the substrate arising from the typically different interaction between the polishing pad at the edge of the substrate as compared to at the central region, and non-uniform deposition of metal and/or oxide layers that might desirably be compensated for by planarizing or adjusting the material removal profile during polishing. Efforts to simultaneously solve these problems have not heretofore been completely successful.
With respect to the nature of the substrate backside polishing pressure, conventional machines typically use hard backed polishing heads to press the substrate against a polishing surface. That is, the polishing heads have a hard receiving surface that presses directly against the backside of the semiconductor substrate. As a result any variation in the receiving surface of the head, or the presence of any material trapped between the substrate and the receiving surface results in a non-uniform application of pressure to the backside of the substrate. Thus, the front surface of the substrate typically does not conform to the polishing surface resulting in planarization non-uniformities. Moreover, such hard backed head designs often must utilize a relatively high polishing pressure (for example, pressures in the range of between about 6 psi and about 8 psi) to provide any reasonable degree of conformity between the substrate and the polishing surface. However, such relatively high pressures can deform the substrate causing too much material to be removed from some areas of the substrate and too little material from others.
Attempts have been made to remedy the above problems with hard backed polishing heads by providing a soft insert between the receiving surface and the substrate to be polished in an attempt to provide some flexibility in an otherwise hard backed system. This insert is commonly referred to as a wafer insert or more simply an insert. The use of inserts is problematic because they frequently result in process variation leading to substrate-to-substrate variation. This variation is not constant or generally deterministic. One element of the variation is the absorption of water or other fluids such as slurry used in the polishing process. Because the amount of water absorbed by the insert tends to increase over its lifetime, there is frequently process variation from substrate-to-substrate. These process variations may be controlled to a limited extent by preconditioning the insert by soaking the insert in water prior to use and by replacing the insert before its characteristics change beyond acceptable limits. This tends to make the initial period of use more like the later period of use, however, this can increase equipment maintenance costs and decrease process throughput. Moreover, unacceptable process variations are still observed due to, for example, variations in the thickness of the insert, wrinkling of the insert and material being trapped between the hard backed head and the insert or the insert and the substrate.
Moreover, use of inserts also requires a fine control of the entire surface to which the insert is adhered as any non-uniformity, imperfection, or deviation from planarity or parallelism of the head surface would typically be manifested as planarization variations across the substrate surface. For example, in conventional heads, an aluminum or ceramic plate is fabricated, then lapped and polished before installation in the head. Such a complex manufacturing process increases the costs of the head and of the machine, particularly if multiple heads are provided.
To overcome the above problems with hard backed polishing head and polishing heads, some attempts have been made in recent years to utilize soft backed heads, however, they have not been entirely satisfactory. One type of soft backed head is described in U.S. Pat. No. 6,019,671, to Shendon, hereby incorporated by reference. Referring to
FIG. 1
, a prior art soft backed polishing head
10
typically includes a carrier
12
having a subcarrier
14
with a lower surface
16
on which the substrate
18
is held during the polishing operation, and a retaining ring
20
circumferentially disposed about a portion of the subcarrier. The subcarrier
14
and the retaining ring
20
, via a backing ring
22
, are suspended from the carrier
12
by a flexible gasket
24
so that they can move vertically and are able to float on the polishing surface (not shown) during the polishing operation. Small mechanical tolerances are provided between the subcarrier
14
and the retaining ring
20
and adjacent elements to accommodate minor angular variations during the polishing operation with little friction and no binding. During the polishing operation a pressurized fluid is admitted into chambers
26
,
28
, formed by the flexible gasket
24
and the carrier
12
to force the subcarrier
14
and the retaining ring
20
against a polishing surface (not shown). A flexible member
30
or membrane stretched across the lower surface
16
of the subcarrier
14
forms a lower chamber
32
or cavity which is pressurized via a passageway
34
to further press the substrate
18
against the polishing surface.
A primary advantage of a soft backed polishing head
10
lies in the fact that the soft material of the flexible member does not distort the substrate as it is pressed against the polishing pad. As a result, conformity of the substrate front surface to the polishing pad can be achieved at lower polishing pressures and without distortion, providing both improved polishing uniformity and planarization.
While a significant improvement over hard backed heads with or without inserts, prior art soft backed polishing heads are not wholly satisfactory for a number of reasons. One problem with this approach is that it does nothing to reduce or eliminate the non-uniformities due to material trapped between the flexible member and the substrate. Moreover, the use of the flexible member can actually increase non-uniformities by introducing new variables, such as variation in the thickness or flexibility of the flexible member across its surface and possible wrinkling of an improperly installed flexible member.
Another problem with prior art soft backed polishing head is a reduction in polishing performance due to interference by the flexible member with other components of the polishing head. For example, as shown in
FIG. 1
, during the polishing operation a side or skirt portion
36
of the flexible member
30
can deform or bow out due to the pressure applied to the lower chamber
32
. This deformation can reduce or eliminate altogether the small mechanical tolerances provided between the subcarrier
14
an
Hansen David A.
Kajiwara Jiro
Moloney Gerard S.
Wang Huey-Ming
Ananian R. Michael
Morgan Eileen P.
Multi Planar Technologyies, Inc.
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