Semiconductor device manufacturing: process – Chemical etching – Combined with the removal of material by nonchemical means
Reexamination Certificate
2000-08-31
2002-05-07
Powell, William A. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Combined with the removal of material by nonchemical means
C156S345420, C216S038000, C216S084000, C216S085000, C438S693000, C438S745000
Reexamination Certificate
active
06383934
ABSTRACT:
TECHNICAL FIELD
The present invention relates to selected planarizing liquids for chemical-mechanical planarization of microelectronic substrates.
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-device substrates and substrate assemblies.
FIG. 1
schematically illustrates a CMP machine
10
having a platen
20
. The platen
20
supports a planarizing medium
40
that can include a polishing pad
41
having a planarizing surface
42
on which a planarizing liquid
43
is disposed. The polishing pad
41
may be a conventional polishing pad made from a continuous phase matrix material (e.g., polyurethane), or it may be a new generation fixed-abrasive polishing pad made from abrasive particles fixedly dispersed in a suspension medium. The planarizing liquid
43
may be a conventional CMP slurry with abrasive particles and chemicals that remove material from the wafer, or the planarizing liquid may be a planarizing solution without abrasive particles. In most CMP applications, conventional CMP slurries are used on conventional polishing pads, and planarizing solutions without abrasive particles are used on fixed abrasive polishing pads.
The CMP machine
10
can also include an underpad
25
attached to an upper surface
22
of the platen
20
and the lower surface of the polishing pad
41
. A drive assembly
26
rotates the platen
20
(as indicated by arrow A), and/or it reciprocates the platen
20
back and forth (as indicated by arrow B). Because the polishing pad
41
is attached to the underpad
25
, the polishing pad
41
moves with the platen
20
.
A wafer carrier
30
is positioned adjacent the polishing pad
41
and has a lower surface
32
to which a substrate
12
may be attached via suction. Alternatively, the substrate
12
may be attached to a resilient pad
34
positioned between the substrate
12
and the lower surface
32
. The wafer carrier
30
may be a weighted, free-floating wafer carrier, or an actuator assembly
33
may be attached to the wafer carrier to impart axial and/or rotational motion (as indicated by arrows C and D, respectively).
To planarize the substrate
12
with the CMP machine
10
, the wafer carrier
30
presses the substrate
12
face-downward against the polishing pad
41
. While the face of the substrate
12
presses against the polishing pad
41
, at least one of the platen
20
or the wafer carrier
30
moves relative to the other to move the substrate
12
across the planarizing surface
42
. As the face of the substrate
12
moves across the planarizing surface
42
, material is continuously removed from the face of the substrate
12
.
CMP processes should consistently and accurately produce a uniformly planar surface on the substrate to enable precise fabrication of circuits and photo-patterns. During the fabrication of transistors, contacts, interconnects and other features, many substrates develop 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 processing the substrate because non-uniform substrate surfaces significantly increase the difficulty of forming sub-micron features. For example, it is difficult to accurately focus photo-patterns to within tolerances approaching 0.1 &mgr;m on non-uniform substrate surfaces because sub-micron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes are often used to transform a topographical substrate surface into a highly uniform, planar substrate surface.
In the competitive semiconductor industry, it is also highly desirable to have a high yield in CMP processes by producing a uniformly planar surface at a desired endpoint on a substrate as quickly as possible. For example, when a conductive layer on a substrate is under-planarized in the formation of contacts or interconnects, many of these components may not be electrically isolated from one another because undesirable portions of the conductive layer may remain on the substrate over a dielectric layer. Additionally, when a substrate is over-planarized, components below the desired endpoint may be damaged or completely destroyed. Thus, to provide a high yield of operable microelectronic devices, CMP processing should quickly remove material until the desired endpoint is reached.
The planarity of the finished substrate and the yield of CMP processing is a function of several factors, one of which is the rate at which material is removed from the substrate (the “polishing rate”). Although it is desirable to have a high polishing rate to reduce the duration of each planarizing cycle, the polishing rate should be uniform across the substrate to produce a uniformly planar surface. The polishing rate should also be consistent to accurately endpoint CMP processing at a desired elevation in the substrate. The polishing rate, therefore, should be controlled to provide accurate, reproducible results.
In certain applications, the polishing rate depends on the chemical interaction between the substrate and the planarizing liquid. For example, the polishing rate can depend on the rate at which material at the surface of the substrate is hydrolyzed. The rate at which the hydrolysis reaction proceeds can be dependent on several factors, including the pH of the planarizing liquid adjacent to the substrate. In some CMP operations, the pH of the liquid can vary as the planarization process proceeds. For example, the pH can decrease as material from the substrate and the polishing pad is released into the planarizing liquid. As the pH level decreases, the polishing rate can also decrease because the rate at which the hydrolysis reaction proceeds can decrease. Furthermore, as the hydrolysis reaction rate decreases, the mechanical interaction between the polishing pad and the substrate can dominate the chemical interaction and can increase the likelihood for forming scratches in the surface of the substrate.
Another factor affecting the overall planarity of the substrate assembly is the wetted surface area of the polishing pad. If the polishing pad develops localized dry spots, the polishing pad can be more likely to scratch the substrate because the dry spots are less chemically active than the wetted regions, and therefore the mechanical interaction between the polishing pad and the substrate can dominate the chemical interaction at the dry spots, as discussed above.
One conventional approach to maintaining the pH of the planarizing liquid is to planarize a metal-containing substrate with a conventional polishing pad without fixed-abrasive particles in combination with an acidic or neutral pH slurry containing a suspension of abrasive particles and a chemical buffering agent. However, this approach has several drawbacks. For example, the acidic or neutral pH is not suitable for planarizing substrates containing certain materials, such as oxides. Furthermore, the polishing rate can be influenced by the distribution of the planarizing liquid
43
between the substrate
12
and the planarizing surface
42
of the polishing pad
41
. The distribution of the planarizing liquid
43
may not be uniform across the surface of the substrate
12
because the leading edge of the substrate
12
can wipe a significant portion of the planarizing liquid
43
from the polishing pad
41
before the planarizing liquid
43
can contact the other areas of the substrate
12
. The nonuniform distribution of planarizing liquid
43
under the substrate
12
can cause certain areas of the substrate
12
to have a higher polishing rate than other areas because they have more contact with the chemicals and/or abrasive particles in the planarizing liquid
43
. The surface of the substrate
12
may accordingly not be uniformly planar and in extreme cases, some devices may
Hofmann James J.
Joslyn Michael J.
Lee Whonchee
Sabde Gundu M.
Micro)n Technology, Inc.
Perkins Coie LLP
Powell William A.
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