Etching a substrate: processes – Nongaseous phase etching of substrate – With measuring – testing – or inspecting
Reexamination Certificate
2000-06-21
2001-11-20
Mills, Gregory (Department: 1763)
Etching a substrate: processes
Nongaseous phase etching of substrate
With measuring, testing, or inspecting
C216S084000, C216S088000, C438S692000, C438S005000, C438S013000, C438S017000
Reexamination Certificate
active
06319420
ABSTRACT:
TECHNICAL FIELD
The present invention relates to methods and apparatuses for electrically endpointing a chemical-mechanical planarization process.
BACKGROUND OF THE INVENTION
Mechanical and chemical-mechanical planarizing processes (collectively “CMP”) are used in the manufacturing of microelectronic devices for forming a flat surface on semiconductor wafers, field emission displays, and many other microelectronic substrates.
FIG. 1
schematically illustrates a planarizing machine
10
with a platen or table
20
, a carrier assembly
30
, a polishing pad
21
positioned on the table
20
, and a planarizing fluid
23
on the polishing pad
21
. The planarizing machine
10
may also have an under-pad
25
attached to an upper surface
22
of the platen
20
for supporting the polishing pad
21
. In many planarizing machines, a platen drive assembly
26
rotates (arrow A) and/or reciprocates (arrow B) the platen
20
to move the polishing pad
21
during planarization.
The carrier assembly
30
controls and protects a substrate
80
during planarization. The carrier assembly
30
typically has a substrate holder
32
with a pad
34
that holds the substrate
80
via suction. A carrier drive assembly
36
typically rotates (arrow C) and/or translates (arrow D) the substrate holder
32
. The substrate holder
32
, however, may be a weighted, free-floating disk (not shown) that slides over the polishing pad
21
.
The combination of the polishing pad
21
and the planarizing fluid
23
generally defines a planarizing medium
28
that mechanically and/or chemically-mechanically removes material from the surface of the substrate
80
. The polishing pad
21
may be a conventional polishing pad composed of a polymeric material (e.g., polyurethane) without abrasive particles, or it may be an abrasive polishing pad with abrasive particles fixedly bonded to a suspension material. In a typical application, the planarizing fluid
23
may be a CMP slurry with abrasive particles and chemicals for use with a conventional non-abrasive polishing pad. In other applications, the planarizing fluid
23
may be a chemical solution without abrasive particles for use with an abrasive polishing pad.
To planarize the substrate
80
with the planarizing machine
10
, the carrier assembly
30
presses the substrate
80
against a planarizing surface
24
of the polishing pad
21
in the presence of the planarizing fluid
23
. The platen
20
and/or the substrate holder
32
then move relative to one another to translate the substrate
80
across the planarizing surface
24
. As a result, the abrasive particles and/or the chemicals in the planarizing medium
28
remove material from the surface of the substrate
80
.
CMP processes must consistently and accurately produce a uniformly planar surface on the substrate to enable precise fabrication of circuits and photo-patterns. Prior to being planarized, many substrates have large “step heights” that create a highly topographic surface across the substrate. Yet, as the density of integrated circuits increases, it is necessary to have a planar substrate surface at several stages of substrate processing because non-uniform substrate surfaces significantly increase the difficulty of forming sub-micron features or photo-patterns to within a tolerance of approximately 0.1 &mgr;m. Thus, CMP processes must typically transform a highly topographical substrate surface into a highly uniform, planar substrate surface (e.g., a “blanket surface”).
In the competitive semiconductor industry, it is desirable to maximize the throughput of CMP processing by producing a blanket surface on a substrate as quickly as possible. The throughput of CMP processing is a function of several factors, one of which is the ability to accurately stop CMP processing at a desired endpoint. In a typical CMP process, the desired endpoint is reached when the surface of the substrate is a blanket surface and/or when enough material has been removed from the substrate to form discrete components on the substrate (e.g., shallow trench isolation areas, contacts, damascene lines, etc.). Accurately stopping CMP processing at a desired endpoint is important for maintaining a high throughput because the substrate may need to be re-polished if the substrate is “under-planarized.” Accurately stopping CMP processing at the desired endpoint is also important because too much material can be removed from the substrate, and thus the substrate may be “over-polished.” For example, over-polishing can cause “dishing” in shallow-trench isolation structures, or over-polishing can completely destroy a section of the substrate. Thus, it is highly desirable to stop CMP processing at the desired endpoint.
In one conventional method for determining the endpoint of CMP processing, the planarizing period of one substrate in the run is estimated using the polishing rate of previous substrates in the run. The estimated planarizing period for a particular substrate, however, may not be accurate because the polishing rate may change from one substrate to another. Thus, this method may not accurately planarize all of the substrates in a run to the desired endpoint.
In another method for determining the endpoint of CMP processing, the substrate is removed from the pad and the substrate carrier, and then a measuring device measures a change in thickness of the substrate. Removing the substrate from the pad and substrate carrier, however, is time consuming and may delay further processing until the measurement is completed. Thus, this method generally reduces the throughput of CMP processing.
In still another method for determining the endpoint of CMP processing, a portion of the substrate is moved beyond the edge of the pad, and an interferometer directs a beam of light directly onto the exposed portion of the substrate and through a layer of the substrate to detect a thickness of the layer. The substrate, however, may not be in the same reference position each time it overhangs the pad. For example, because the edge of the pad is compressible, the substrate may not be at the same elevation for each measurement. Thus, this method may inaccurately measure the change in thickness of the layer of the wafer.
In yet another method for determining the endpoint of CMP processing, U.S. Pat. No. 5,036,015 discloses detecting the planar endpoint by sensing a change in friction between a wafer and the polishing medium. Such a change in friction may be produced by a different coefficient of friction at the wafer surface as one material (e.g., an oxide) is removed from the wafer to expose another material (e.g., a nitride). In addition to the different coefficients of friction caused by a change of material at the substrate surface, the friction between the wafer and the planarizing medium generally increases during CMP processing because more surface area of the substrate contacts the polishing pad as the substrate becomes more planar. U.S. Pat. No. 5,036,015 discloses detecting the change in friction by measuring the change in current through the platen drive motor and/or the drive motor for the substrate holder.
In still a further method for determining the endpoint of CMP processing, such as is disclosed in U.S. Pat. No. 5,559,428, the chemical composition of the CMP slurry is analyzed to determine when a layer of a first material has been removed to expose a layer of a second, different material. For example, planarization may continue through the first material until the second material is exposed, at which point some of the second material is removed and enters the slurry. The second material and the slurry is identified using instrumentation such as inductively coupled plasma for atomic emission spectroscopy, and the planarization process is halted.
In yet another method for determining the endpoint of CMP processing, such as is disclosed in U.S. Pat. No. 5,321,304, the substrate includes parasitic conductive contacts or terminals buried beneath an insulative layer. When the insulative layer over the contacts has been removed by planari
Dorsey & Whitney LLP
Goudreau George
Micro)n Technology, Inc.
Mills Gregory
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