Abrading – Abrading process – With critical temperature modification or control of work or...
Reexamination Certificate
2001-05-10
2004-01-27
Arbes, Carl J. (Department: 3729)
Abrading
Abrading process
With critical temperature modification or control of work or...
C451S007000, C451S056000, C451S287000, C451S444000
Reexamination Certificate
active
06682404
ABSTRACT:
TECHNICAL FIELD
The present invention relates to methods and apparatus for conditioning of polishing pads used in planarizing substrates.
BACKGROUND OF THE INVENTION
Chemical-mechanical planarization (“CMP”) processes remove material from the surface of semiconductor wafers or other substrates in the production of microelectronic devices and other products. CMP processes typically planarize and/or polish the surface of the substrate in the fabrication of integrated circuits by moving the substrate across a polishing medium to remove material from the substrate surface.
FIG. 1
is a schematic view that illustrates a conventional CMP machine
10
with a platen
20
, a wafer carrier
30
, a polishing pad
40
, and a planarizing liquid
44
on the polishing pad
40
. The platen
20
is typically connected to a drive assembly
26
to rotate the platen
20
(indicated by arrow A) or reciprocate the platen
20
back and forth (indicated by arrow B). Additionally, the wafer carrier
30
generally has a lower surface
32
to which one or more wafers
12
may be attached, or the wafers
12
may be attached to resilient pads
34
positioned between the wafers and the lower surface
32
. The wafer carrier
30
is generally attached to an actuator assembly
36
to impart axial and/or rotational motion to the wafers
12
(indicated by arrows C and D, respectively), or the wafer carrier
30
may be a weighted, free-floating wafer holder (not shown).
The polishing pad
40
and the planarizing liquid
44
may separately, or in combination, define a polishing medium that mechanically and/or chemically removes material from the surface of a wafer. The polishing pad
40
may be a conventional polishing pad made from a continuous phase matrix material (e.g. polyurethane), or it may be a new generation abrasive polishing pad made from abrasive particles fixedly dispersed in a suspension medium. Conversely, the planarizing liquid
44
may be a conventional CMP slurry with abrasive particles, or it may be a planarizing solution without abrasive particles. In general, abrasive slurries are used with conventional non-abrasive polishing pads and planarizing solutions are used with abrasive polishing pads.
To planarize the wafers
12
with the CMP machine
10
, the wafer carrier
30
presses the wafers
12
face-downward against the polishing medium. More specifically, the wafer carrier
30
generally presses the wafers
12
against the planarizing liquid
44
on a planarizing surface
42
of the polishing pad
40
, and at least one of the platen
20
or the wafer carrier
30
moves relative to the other to move the wafers
12
across the planarizing surface
42
. As the wafers
12
move across the planarizing surface
42
, material is removed from the face of the wafers. The process is conventionally conducted at platen temperatures of approximately 85° F. to 105° F. to facilitate any chemical interaction between the polishing medium and the wafer
12
. Conventional wisdom is that processing at higher temperatures may cause undesirable chemical interactions between the polishing medium and the wafer
12
. Furthermore, where ammonia-based slurries are used, higher temperatures may cause the ammonia to evaporate, creating undesirable odors and potentially shifting the pH of the slurry by an unacceptable amount.
In the competitive semiconductor industry, it is desirable to maximize the through-put of finished wafers and to produce a uniform, planar surface on each wafer. The through-put of CMP processing is a function of several factors, one of which is the rate at which the thickness of the wafer decreases as it is being planarized (the “polishing rate”). The polishing rate affects the through-put because the polishing period per wafer decreases with increasing polishing rates and it is easier to accurately endpoint CMP processing with a consistent polishing rate. Thus, it is desirable to have a high, consistent polishing rate.
One manufacturing concern with CMP processing is that the through-put may drop because the act of planarizing wafers alters the condition of the polishing pads. More specifically, slurry and particles from the wafer and pad build up on the planarizing surface of the polishing pad and form waste matter accumulations that may cover portions of the planarizing surface. The accumulations may take the form of a hard glaze coating on the planarizing surface which reduces contact between the wafer and the planarizing surface. The polishing rate accordingly changes during CMP processing, which may make it more difficult to quickly planarize a wafer or endpoint the CMP process. Thus, the waste matter accumulations may reduce the through-put of CMP processing.
CMP processes must also consistently and accurately produce a uniform, planar surface on the wafer because it is important to accurately focus the image of circuit patterns on the surface of the wafer. As the density of integrated circuits increases, it is often necessary to accurately focus the critical dimensions of the circuit pattern to within a tolerance of approximately 0.1 &mgr;m. Focusing circuit patterns to such small tolerances, however, is very difficult when the surface of the wafer is not uniformly planar. Thus, planarizing processes must create a highly uniform, planar surface.
Another problem with CMP processing is that the waste matter accumulations reduce the uniformity of the polishing rate across the planarizing surface of a polishing pad. The waste matter accumulations do not build up uniformly across the planarizing surface of the polishing pad, and thus the polishing rate may vary unpredictably across the polishing pad. As a result, the surface of a polished wafer may not be uniformly planar.
The problems associated with waste matter accumulations are exacerbated when the planarizing surface simultaneously planarizes a large number of wafers or when the planarization rate is increased. For example,
FIG. 1
illustrates a single wafer carrier
30
to which are attached several wafers
12
, each of which contributes waste matter accumulations to the planarizing surface. In other conventional CMP machines, multiple wafer carriers, each with multiple wafers, further increase the rate at which waste matter accumulates on the planarizing surface. As the number of wafers planarized by a given planarizing surface increases, the rate at which waste matter accumulates on the planarizing surface also increases, decreasing wafer through-put and wafer uniformity.
In light of the problems associated with waste matter accumulations on polishing pads, it is necessary to periodically remove the waste matter accumulations from the planarizing surfaces so that the polishing pads are brought back into a desired state for planarizing substrates (“conditioning”). For example, U.S. Pat. No. 5,456,627 issued to Jackson et al. discloses an apparatus for conditioning a rotating, circular polishing pad with a rotating end effector that has an abrasion disk in contact with a polishing surface of the pad. The end effector described in U.S. Pat. No. 5,456,627 moves along a radius of the polishing pad surface at a variable velocity to compensate for the linear velocity of the polishing pad surface. Additionally, U.S. Pat. No. 5,456,627 discloses maintaining a desired contact force between the end effector and the polishing pad surface with a closed feedback loop in which a load transducer generates a signal with an amplitude proportional to the applied force. A computer then uses the signal from the load transducer to operate an actuator that moves the end effector in a direction so that the output of the load transducer is substantially equal to the desired contact force.
Another conventional conditioning method and apparatus, which is disclosed in U.S. Pat. No. 5,081,051 issued to Mattingly et al., uses an elongated blade with a serrated edge that is engaged with a portion of a circular, rotating polishing pad. The blade disclosed in U.S. Pat. No. 5,081,051 is pressed against a polishing path on the planarizing surface of the polishing pad t
Arbes Carl J.
Dorsey & Whitney LLP
Phan Thiem D
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