Abrading – Machine – Rotary tool
Reexamination Certificate
2001-06-06
2002-05-21
Morgan, Eileen P. (Department: 3723)
Abrading
Machine
Rotary tool
C451S443000
Reexamination Certificate
active
06390902
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention provides a chemical-mechanical polishing system, and more particularly, a chemical-mechanical polishing system of multi-conditioner arrangement.
2. Description of the Prior Art
The manufacturing of integrated circuits involves applying micro-circuit structures to form a set of whole devices, of which the method is highly precise and consists of multiple steps. With the trend of integrated circuit devices towards smaller size and larger integration, more process steps are necessary in order to achieve the multilevel structure on the semiconductor wafer. A multilevel metallization process is used extensively in the VLSI/ULSI process, whereby a plurality of metal interconnect layers and low dielectric constant materials are used to link each of the semiconductor devices on the semiconductor wafer and complete the whole stacked loop structure. However, these metal lines and semiconductor devices result in severe surface topography of integrated circuits that leads to difficulty in subsequent deposition or pattern transfer processes. Therefore, both the protruding deposition layer and uneven surface profile of the semiconductor wafer need to be removed by a planarization process.
Chemical-mechanical polishing (CMP) is the most commercially applied planarization technique. Chemical-mechanical polishing is similar to that of mechanical polishing in its use of the “blade” principle, of which adequate chemical additives react with the surface of the semiconductor wafer to polish the uneven surface profile of the wafer to achieve planarization. If the various process parameters are properly controlled, the CMP process can provide more than a 94% flatness of the polished surface. Therefore, the semiconductor industry has adopted the CMP process for its sub-micron semiconductor processes, since better planarization is obtained for the surface of the semiconductor wafer.
Please refer to FIG.
1
.
FIG. 1
is the schematic diagram of the structure of the CMP system
10
according to the
42
prior art. The prior art CMP system
10
comprises a polishing table
12
with a first rotational motor for controlling rotational speed, a polishing pad
14
on the polishing table
12
for polishing the surface of the semiconductor wafer
18
, at least one wafer carrier head
16
positioned on the polishing pad
14
, and a vertical driving motor and a second rotational motor for controlling the vertical movement and rotational speed of the carrier head
16
, respectively. The wafer carrier head
16
is for holding a semiconductor wafer
18
so the front face of the semiconductor wafer
18
is downward and contacts with the polishing pad
14
. A slurry supplier
20
above the CMP system
10
is connected to the system for supplying the slurry required for polishing the semiconductor wafer
18
. A conditioner
22
positioned between the two neighboring wafer carrier head
16
on the polishing pad
14
, controlled by a third driving motor, distributes the slurry on the surface of the polishing pad
14
, as well as removes the polishing residue remaining on the polishing pad
14
.
The water-based slurry basically comprises both an abrasive and a chemical additive. The abrasive additive is a colloidal Silica or dispersed Alumina. The size distribution of these large, solid polishing particles in the slurry is 0.1~2.0 &mgr;m. The chemical additive is mostly a mixture of a potassium hydroxide (KOH) solution and ammonia water (NH
4
OH), used to corrode the surface of the semiconductor wafer and allow for easy removal of the corroded material. However, the composition of the slurry is dependent on the type of materials used during the CMP process.
The CMP process first involves horizontally fixing a semiconductor wafer
18
on the carrier head
16
. The semiconductor wafer
18
is placed with the surface to be polished facing the surface of the polishing pad
14
. The surface of the semiconductor wafer
18
is polished by both the rotation of the polishing pad
14
in a first direction
26
and the self-rotation of the carrier head
16
in a second direction
28
. Concurrently, the slurry supplier device
20
evenly dispenses the slurry on the rotating polishing pad
14
, whereby contact of the slurry with the surface of the semiconductor wafer
18
results in a chemical reaction between the slurry and the surface material to allow for easy removal of the reacted material. The semiconductor wafer
18
is also simultaneously pressed downward to allow for mechanical polishing of its surface. The polishing rate at the protrusion of the semiconductor wafer
18
surface is greater than that of the rest of the surface, to result in the overall planarization of the surface of the semiconductor wafer
18
. During the polishing process, the surface material of the semiconductor wafer
18
is removed at a rate of several thousand angstroms per minute.
However, an increase in the quantity of wafers polished leads to a large accumulation of chemically-reacted byproduct on the polishing pad
14
. As a result, the polishing pad
14
becomes unpolished and abraded to decrease both the polishing rate and lifetime of the CMP
10
system. Thus, a method to maintain both the lifetime of the CMP system
10
and the polishing rate involves restoring in-situ the polishing pad
14
by having the conditioner
22
remove the byproduct resulting from surface polishing in order to allow the polishing pad
14
to maintain a state suitable for continued wafer polishing.
In
FIG. 1
, the conditioner
22
has a rough surface and its material, such as a diamond abrasive, is dependent on the properties of the polished material. The conditioner
22
sweeps over the polishing pad
14
from left to right according to a third direction
24
in order to remove the byproduct resulting from polishing and to maintain the surface texture of the polishing pad
14
. Since there are a plurality of carrier heads
16
on the polishing pad
14
, the single conditioner
22
needs to remove the byproducts resulting from polishing of all the semiconductor wafers
18
, to result in the following disadvantages: (1) Since there is only one conditioner
22
for a plurality of carrier heads
16
, the polishing pad
14
requires extensive and frequent treatment to prevent the single conditioner
22
from being unable to completely remove the polishing byproduct, and hence the lifetime of the diamond abrasive of the polishing pad
14
and the conditioner
22
greatly decreases; (2) Following restoration in-situ of the polishing pad
14
, the carrier head
16
contacting the polishing pad
14
earliest has a different polishing rate than the carrier head
16
contacting the polishing pad
14
latest to result in a difference in polishing rate between different wafers of the same batch; and (3) Since the single conditioner
22
uses a left and right sweeping method, spatial coverage is strict and limited.
SUMMARY OF THE INVENTION
It is therefore a primary objective of the present invention to provide a multi-conditioner arrangement of a CMP system so as to resolve the above-mentioned problems.
In the preferred embodiment of the present invention, the CMP system comprises a polishing table, a polishing pad positioned on the polishing table, a plurality of carrier heads on the polishing pad for supporting semiconductor wafers, and a plurality of conditioners positioned between the two neighboring carrier head
16
on the polishing pad
14
for maintaining the surface texture of the polishing pad. Herein, the plurality of conditioners
42
and the plurality of carrier heads are positioned in a one-to-one arrangement, each conditioner producing a back and forth motion in a radiant direction.
It is an advantage of the present invention that both the one-to-one arrangement of the carrier head o the conditioner and the back and forth motion of the conditioner results in the increase in the lifetime of the polishing pad, the decrease in the difference in wafer to wafer polishing rate, and an increase
Chang Ruoh-Haw
Kuo Hung-Yu
Liao De-Can
Liu Yao-Hung
Hsu Winston
Morgan Eileen P.
United Microelectronics Corp.
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