Abrading – Machine – Rotary tool
Reexamination Certificate
1998-12-28
2001-03-27
Rose, Robert A. (Department: 1723)
Abrading
Machine
Rotary tool
C451S041000
Reexamination Certificate
active
06206769
ABSTRACT:
TECHNICAL FIELD
The present invention is related to mechanical and chemical-mechanical planarization of substrates, and more particularly, to a method and apparatus for consistently stopping planarization of substrate at a desired endpoint.
BACKGROUND OF THE INVENTION
Chemical-mechanical planarization (“CMP”) processes remove material from the surface of a semiconductor wafer in the production of integrated circuits.
FIG. 1
schematically illustrates a 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 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 fixed-abrasive polishing pad made from abrasive particles fixedly dispersed in a suspension medium. The planarizing liquid
44
may be a conventional CMP slurry with abrasive particles and chemicals that remove material from the wafer, or the planarizing liquid
44
may be a planarizing solution without abrasive particles.
The CMP machine
10
also may have an under-pad
25
attached to an upper surface
22
of the platen
20
and the lower surface of the polishing pad
40
. A drive assembly
26
rotates the platen
20
(as indicated by arrow A), or it reciprocates the platen
20
back and forth (as indicated by arrow B). Since the polishing pad
40
is attached to the under-pad
25
, the polishing pad
40
moves with the platen
20
.
The wafer carrier
30
has a lower surface
32
to which a wafer
12
may be attached, or the wafer
12
may be attached to a resilient pad
34
positioned between the wafer
12
and the lower surface
32
. The wafer carrier
30
may be a weighted, free-floating wafer carrier, or an actuator assembly
36
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 wafer
12
with the CMP machine
10
, the wafer carrier
30
presses the wafer
12
face-downward against the polishing pad
40
. While the face of the wafer
12
presses against the polishing pad
40
, at least one of the platen
20
or the wafer carrier
30
moves relative to the other to move the wafer
12
across the planarizing surface
42
. As the face of the wafer
12
moves across the planarizing surface
42
, material is continuously removed from the face of the wafer
12
.
In the competitive semiconductor industry, it is desirable to consistently stop CMP processing of a run of wafers at a desired endpoint and to produce a uniform, planar surface on each wafer. Accurately stopping CMP processing at a desired endpoint is important to maintaining a high throughput of planarized wafers because the thickness of the planarized layer on the wafer must be within an acceptable range. It will be appreciated that if the thickness of the planarized layer is not within its acceptable range, the wafer must be re-planarized until it reaches a desired endpoint. Additionally, it is important to accurately produce a uniform, planar surface on each wafer to enable precise circuit and device patterns to be formed with photolithography techniques. The critical dimensions of many photo-patterns must be focused within a tolerance of approximately 0.1 &mgr;m. Focusing photo-patterns to such small tolerance, however, is difficult when the planarized surface of the wafer is not uniformly planar. Therefore, two primary objectives of CMP processing are stopping planarization at a desired endpoint and producing a highly uniform, planar surface on each wafer.
CMP processing involves many operating parameters that affect the planarity of the surface on the wafer and the ability to stop CMP processing at the desired endpoint. The rate at which material is removed from the surface of the wafer (the “polishing rate”) often varies across the face of a wafer and from one wafer to another. The most common parameters that affect the polishing rate of a wafer are: (1) the relative velocity gradient between the wafer and the polishing pad across the face of the wafer; (2) the distribution of slurry across the surface of the wafer; (3) the composition of materials across the wafer; (4) the topography of the wafer; (5) the parallelism between the face of the wafer and the surface of the polishing pad; (6) the temperature gradient across the face of the wafer; and (7) the condition of the planarizing surface of the polishing pad. The polishing rate may vary across the face of the wafer because any one of the operating parameters may change during planarization. Moreover, the polishing rate may vary from one wafer to another because it is difficult to identify and correct changes in specific operating parameters. Thus, it is difficult to consistently stop CMP processing at a desired endpoint on a wafer by estimating the time-to-polish using the polishing rate of previous wafers.
One desirable technique of endpointing CMP processing is the stop-on-feature (“SOF”) wafer design. A typical SOF wafer has a polish-stop layer at a desired endpoint on the wafer and a cover layer over the polish-stop layer. The polish-stop layer is made from a material that has a low polishing rate relative to the polishing rate of the cover layer; high regions of the cover layer are accordingly removed faster than lower, exposed portions of the polish-stop layer. The objective of the polish-stop layer, therefore, is to prevent or slow further polishing beyond the high point of the polish-stop layer.
Although SOF wafers are a promising technique to endpoint CMP processing, they may not consistently stop CMP processing at a desired endpoint in some applications. In conventional SOF wafers, the polishing rate of the polish-stop layer is less than that of the cover layer because the polish-stop layer is harder than the cover layer (to inhibit mechanical removal) and/or the polish-stop layer has a lower etch rate in the planarizing solution than the cover layer (to inhibit chemical removal). Although the polishing rate of the polish-stop layer is lower than the cover layer, material is still generally removed from the exposed portions of the polish-stop layer. The removal of material from the polish-stop layer is a particularly acute problem for thin polish-stop layers because exposed portions of thin polish-stop layers may be completely removed from the wafer, thereby destroying the structure protected by the polish-stop layer. The removal of material from the polish-stop layer also reduces the uniformity of the planarized surface. Therefore, conventional SOF wafers may not consistently stop CMP processing at a desired endpoint with conventional CMP processing methods.
SUMMARY OF THE INVENTION
In one embodiment of the invention, material is removed from a substrate with an abrasive medium on a planarizing surface. As a material is removed from the substrate, the abrasive medium is selectively inhibited from contacting a first exposed area at the desired endpoint on the substrate while it still contacts a second area on the substrate that is not yet at the endpoint. In this embodiment of the invention, therefore, polishing substantially stops at the first area on the substrate but continues at the second area on the substrate.
In a preferred embodiment of the invention, a semiconductor substrate has a hydrophobic polish-stop stratum at a desired endpoint of the substrate, and a hydrophilic cover layer on the hydrophobic polish-stop stratum. To remove material from the surface of the semiconductor substrate, the hydrophilic layer is pressed against a hydrophobic planarizing surface of a polishing pad in the presence of an abrasive slurry, and at least one of the semiconductor substrate or the polishing pad is moved with respect to the other to impart relative motion therebetween. As material is removed from the hydrophilic layer, a portion of the hydrophobic stratum is often exposed at a first area on the substrate. The hydrophobic stratum at the first area and the hydrophobic planarizing surface substantially inhibit the abrasiv
Dorsey & Whitney LLP
Micro)n Technology, Inc.
Rose Robert A.
LandOfFree
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