Abrading – Precision device or process - or with condition responsive... – By optical sensor
Reexamination Certificate
1999-03-17
2001-01-30
Hail, III, Joseph J. (Department: 3725)
Abrading
Precision device or process - or with condition responsive...
By optical sensor
C451S007000, C451S010000, C451S041000, C451S053000, C451S288000
Reexamination Certificate
active
06179688
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally pertains to semiconductor processing, and, more particularly, to the polishing of process layers formed above a semiconducting substrate.
2. Description of the Related Art
The manufacture of semiconductor devices generally involves the formation of various process layers, selective removal or patterning of portions of those layers, and deposition of yet additional process layers above the surface of a semiconducting substrate. The substrate and the deposited layers are collectively called a “wafer.” This process continues until a semiconductor device is completely constructed. The process layers may include, by way of example, insulation layers, gate oxide layers, conductive layers, and layers of metal or glass, etc. It is generally desirable in certain steps of the wafer process that the uppermost surface of the process layers be planar, i.e., flat, for the deposition of subsequent layers.
FIGS. 1A and 1B
illustrate a general process for providing such a planar uppermost surface.
FIG. 1A
illustrates a portion of a wafer
10
during the manufacture of a semiconducting device. A layer of insulative material is deposited on the wafer
10
over the substrate
11
and partially etched away to create the insulators
12
. A layer of conductive material
14
, e.g., a metal, is then deposited over the wafer
10
to cover the insulators
12
and the substrate
11
. The layer of conductive material
14
is then “planarized.”
FIG. 1B
illustrates the wafer
10
after the layer of conductive material
14
is planarized to create the interconnects
16
between the insulators
12
.
One process used to planarize process layers is known as “chemical-mechanical polishing,” or “CMP.” In a CMP process, a deposited material, such as the conductive material
14
in
FIG. 1A
, is polished to planarize the wafer for subsequent procession steps. Both insulative and conductive layers may be polished, depending on the particular step in the manufacture.
In the case of metal CMP, a metal previously deposited on the wafer is polished with a CMP tool to remove a portion of the metal to form insulator interconnects such as lines and plugs, e.g., the interconnects
12
in FIG.
1
B. The metal process layer is removed by an abrasive action created by a chemically active slurry and a polishing pad. A typical objective is to remove the metal process layer down to the upper level of the insulative layer, as was the case for the example of
FIGS. 1A and 1B
.
Such a CMP process is more particularly illustrated in
FIGS. 2A and 2B
. A wafer
20
is typically mounted upside down on a carrier
22
. A force (F) pushes the carrier
22
and the wafer
20
downward. The carrier
22
and the wafer
20
are rotated above a rotating pad
24
on the CMP tool's polishing table
26
. A slurry (not shown) is generally introduced between the rotating wafer
20
and the rotating pad
24
during the polishing process. The slurry may contain a chemical that dissolves the uppermost process layer(s) and/or an abrasive material that physically removes portions of the layer(s). The wafer
20
and the pad
24
may be rotated in the same direction or in opposite directions, whichever is desirable for the particular process being implemented. In the example of
FIGS. 2A and 2B
, the wafer
20
and the pad
24
are rotated in the same direction as indicated by the arrows
28
. The carrier
22
may also oscillate across the pad
24
on the polishing table
26
, as indicated by the arrow
29
.
The point at which the excess conductive material is removed and the embedded interconnects remain is called the “endpoint” of the CMP process. The CMP process should result in a planar surface with little or no detectable scratches or excess material present on the surface. In practice, the wafer, including the deposited, planarized process layers, are polished beyond the endpoint to ensure that all excess conductive material has been removed. Polishing too far beyond the endpoint increases the chances of damaging the wafer surface, uses more of the consumable slurry and pad than may be necessary, and reduces the production rate of the CMP equipment. The window for the polish time endpoint can be small, e.g., on the order of seconds. Also, variations in material thickness may cause the endpoint to change. Thus, accurate in-situ endpoint detection is highly desirable.
Current techniques for endpoint detection may be classed as optical reflection, thermal detection, and friction based techniques. Optical reflection techniques encounter higher levels of signal noise as the number of process layers increase, thereby decreasing the accuracy of endpoint detection outside the range where the endpoint can be detected. Optical reflection techniques may also require that the wafer be moved off the edge of the polishing table. This frequently interrupts the polishing process. This may also cause the endpoint to be missed and its detection delayed by perhaps as much as a few seconds, depending on oscillation speed and distance. Thermal techniques suffer from thermal noise caused by variations in the wafer production rate, variations in the slurry, or changes in the pad. Thermal techniques are also adversely impacted by complexity in the thermal variations as the CMP tool warms and cools over the operation cycle and carrier arm oscillations.
Friction-based techniques detect the endpoint by monitoring the power consumed by the CMP tool's carrier motor(s) and detect the endpoint from the changes therein. The electrical current required to rotate the carrier at a given, specified speed is directly affected by the drag of the wafer on the pad. The coefficient of friction is different for a metal sliding on the pad versus an insulating oxide on the pad, and this difference appears as a change in the carrier motor current, and hence the carrier motor power consumption. The carrier motor current is monitored using Hall effect probes or mechanically clamping sensors. Friction-based techniques detect the endpoint from the change in the current or from the slope of the current profile.
Friction-based techniques also have their drawbacks. The power signals from which the endpoint is detected in a friction-based technique are highly susceptible to noise. Noise may be induced by electromagnetic fields emanating from nearby equipment. Also, where the carrier radially oscillates, the rotation of the carrier(s) and the table introduce noise. This noise must be filtered from the power signal. Even with filtering, however, the power signals may have complex shapes that mask the relatively simple change in the current or power caused when the endpoint is reached. When the carrier current profile is complicated, techniques based on a change in the current or slope of the current profile frequently fail due to variations in the profile from run to run or the large amount of noise inherent in the polishing process.
The present invention is directed to a semiconductor processing method and apparatus that addresses some or all of the aforementioned problems.
SUMMARY OF THE INVENTION
The invention, in a first aspect, includes a method and apparatus for detecting the endpoint in a chemical-mechanical polishing process. The first aspect includes a chemical-mechanical polishing tool modified to receive a first and a second data signal; combine the first and second data signals to generate a combined data signal; and detect a peak in the combined data signal, wherein the peak indicates the process endpoint. In a second aspect, the invention is a method and an apparatus for detecting the endpoint in a chemical-mechanical polishing process. The second aspect includes an apparatus implementing a method in which a data signal is received. The data signal is analyzed to detect a peak indicative of the process endpoint in the received data signal. The peak detection includes determining a high value for an initial peak; determining a low value for a following trough; estimating a value for the endpoint pr
Beckage Peter J.
Cho Wonhui
Edwards Keith A.
Lukner Ralf B.
Advanced Micro Devices , Inc.
Hail III Joseph J.
Hong William
Williams Morgan & Amerson
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