Abrading – Machine – Rotary tool
Reexamination Certificate
1998-12-04
2001-02-13
Eley, Timothy V. (Department: 3723)
Abrading
Machine
Rotary tool
C451S269000
Reexamination Certificate
active
06186877
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to equipment used in fabricating semiconductor devices, and more specifically to equipment for performing chemical mechanical polishing (CMP) of semiconductor wafers.
BACKGROUND OF THE INVENTION
Chemical mechanical polishing (CMP) has become an indispensable step in the fabrication of integrated circuit (IC) devices. In some steps of the fabrication process of ICs, later layers cannot be applied to a semiconductor substrate unless an earlier applied layer presents a planar surface. A CMP process is used to planarize such layers. In a step of the fabrication process, it may be desired to obtain a planar surface on an oxide layer. Alternatively, in a different step in fabricating a semiconductor device, a conformal layer of metal is deposited in blanket manner over a dielectric layer to fill vias therein. Then, by a CMP process, the blanket metal layer is polished down to the surface of the dielectric layer. In such a CMP process, it is important for the removal rates of the metal and dielectric materials to be dissimilar in order that polishing stops at the dielectric so that the metal inside the vias does not become overly “dished”, i.e. overly removed below the upper surface of the dielectric layer, nor does the dielectric layer become overly thinned, either of which may lead to failure at a later time.
Conventionally, the chemical composition of the slurry is selected in order to adjust a removal rate according to the composition of a specific layer and features therein to be planarized. Apart from the chemical composition of the slurry provided to the CMP tool, two mechanical parameters play a critical role in determining the removal rate. These are the rotational velocity between the wafer and the polishing pad, and the downforce applied to press the wafer against the polishing pad. An increase in either the rotational velocity or the downforce results in a higher removal rate. Conversely, a decrease in the rotational velocity or the downforce results in a lower removal rate.
Currently available CMP polishers process only one or at most a few wafers at one time. The number of wafers which can be polished at one time is limited because conventional CMP polishers require the entire surface of each wafer to be placed in contact with the polishing pad. At current 200 mm wafer diameters, some existing CMP tools polish at most two wafers concurrently. A very large CMP polisher can polish as many as five 200 mm wafers on a single large disc-shaped polishing pad at one time.
With reference to
FIG. 14
, CMP is conventionally performed on equipment having a large rotating disc-shaped platen
118
of approximately
60
cm in diameter. A wafer
114
is held face down by a carrier
116
on a pad
119
covering the rotating platen
118
. The wafer
114
is positioned between the outer disc perimeter
121
and an inner circle
123
at a set radius R from the center
125
. Because the rotational velocity of the platen
118
is higher near the outer perimeter
121
of the platen than at the inner circle
123
, the wafer is rotated during polishing in order to reduce position-dependent velocity variations which could result in polishing rate differentials at different locations on the wafer surface. However, despite this practice, a difference in rotational velocity still remains between the outer perimeter of the wafer and points near the wafer center. Consequently, a consistent polishing rate is not achieved between the outer perimeter and the interior surface of the wafer.
Because of this difference in rotational velocity at different wafer locations, it is considered undesirable to perform CMP at rotational velocities greater than 140 rpm. The rotational velocity of the disc platen in conventional CMP polishers is generally kept within a range between 10 and 140 rpm.
At conventional platen rotational velocities of 10 to 140 rpm, a force of at least 5 and up to 9 psi must be applied by a wafer carrier
116
to press the wafer towards the platen
118
(“downforce”) in order to perform CMP to attain even a marginal wafer processing rate. The application of a downforce of 5 to 9 psi is not uncommon to achieve desirable process throughput. A known consequence of high downforce at the wafer/platen interface is a tendency for differentials in the removal rates of different composition features to increase. Higher downforce results in increased dishing of metal features within an oxide layer, and ultimately reduced planarity when polishing layers which contain features of different composition or pattern density.
Wafer throughput is one measure of the desirability of a CMP tool. There are other measures too. Optimally, CMP tools should be inexpensive to own and operate, occupy little space in a semiconductor foundry, polish to adequate and consistent local planarity, as well as global uniformity, and provide high and consistent throughput.
Existing CMP polishers are larger and more expensive than necessary and provide much lower throughput than that which is made possible by the multi-level polishing tool of the present invention disclosed in the following.
It is therefore an object of the present invention to provide a CMP polisher which provides greater throughput than existing CMP polishers.
A further object of the present invention is to provide a CMP polisher which is smaller than existing CMP polishers.
Another object of the present invention is to provide a CMP polisher which is less expensive to own and operate than existing CMP polishers.
Still another object of the present invention is to provide a CMP polisher which processes wafers in a consistent, quality manner.
Another object of the present invention is to provide a CMP polisher which polishes to superior planarity than that provided by existing CMP polishers.
An additional object of the present invention is to provide a fully integrated CMP polisher which performs in-situ post measurements and endpoint detection as well as wafer clean and dry operations.
SUMMARY OF THE INVENTION
These and other objects of the invention are provided by the wafer polishing tool of the present invention. In a first aspect of the invention, the wafer polishing tool includes a polishing platen which is rotatable about a central platen axis, and a wafer carrier which supports a wafer for rotational movement to cause a portion of a surface of the wafer to only intermittently contact a polishing surface of the platen while the wafer rotates.
According to a second aspect of the invention, a wafer polishing tool is provided which includes a polishing platen which is rotatable about a central platen axis, and a wafer carrier which supports a wafer for rotational movement and in uninterrupted contact with the platen over less than the entire surface of the wafer.
According to another aspect of the invention, a wafer polishing tool is provided which includes a plurality of vertically stacked polishing platens which are rotatable about a central platen axis, and a plurality of stacked wafer carriers, wherein each carrier supports a wafer for rotational movement and vertical movement into contact with one of the polishing platens.
According to another aspect of the invention, a wafer polishing tool includes a plurality of vertically stacked polishing platens which are rotatable about a central platen axis, and a wafer carrier pack which imparts rotational motion to a plurality of wafers, wherein the carrier pack maintains the wafers in uninterrupted contact with the platen over less than entire surfaces of the wafers.
Further preferred embodiments of the invention are disclosed herein.
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patent: 4179852 (1979-12-01), Barnett
patent: 4550239 (1985-10-01), Uehara et al.
patent: 4550242 (1985-10-01), Uehara et al.
patent: 5240557 (1993-08-01), Dyer et al.
patent: 5435772 (1995-07-01), Yu
patent: 5554065 (1996-09-01), Clover
patent: 5595522 (1997-01-01), Simpson et al.
patent: 5597443 (1997-01-01), Hempel
patent: 5645472 (1997-07-01), Nagahashi et al.
patent:
Eley Timothy V.
International Business Machines - Corporation
Neff Daryl K.
Nguyen Dung Van
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