Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-08-27
2001-09-11
Lefkowitz, Edward (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S648000, C257S618000, C451S008000, C438S689000
Reexamination Certificate
active
06288648
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to a semiconductor wafer polishing apparatus and, more specifically, to an apparatus and method for determining when a semiconductor polishing pad conditioning wheel has reached its useable lifetime and requires replacement.
BACKGROUND OF THE INVENTION
Chemical mechanical planarization (CMP) is an essential process in the manufacture of semiconductor chips today. Dielectric and metal layers used in chip fabrication must be made extremely flat and of precise thickness in order to pattern the sub-micron sized features that comprise a semiconductor device. During CMP, the combination of chemical etching and mechanical abrasion produces the required flat, precise surface for subsequent depositions. The polishing pad is usually made of polyurethane and has small pores to carry the slurry under the wafer. As a result of the polishing process, pad material and slurry residues collect in the pores, plugging them, and reducing the polish rate due to slurry starvation. When the pad becomes clogged, it becomes necessary to “condition” the pad to restore its full functionality. That is, the accumulated material must be removed before it completely clogs the pad and results in a smooth, glazed surface that does not effectively polish the semiconductor wafer. A nickel/chromium conditioning wheel with a surface of diamond abrasives embedded in a nickel/chromium setting alloy is used to condition the pad. The conditioning wheel is pressed against the polishing pad by a conditioning wheel actuator, e.g., a hydraulic/pneumatic arm, and the polishing pad and conditioning wheel are each rotated at prescribed speeds while de-ionized water or slurry is flowed to rinse away abraded material. The diamond elements remove embedded particles, slurry, and polishing byproducts from the polishing pad. The conditioning proceeds until the pad is “re-surfaced” and new pores are exposed.
As the conditioning wheel is rotated against the polishing pad, the wheel, setting alloy, and the diamonds come in contact with the chemical/mechanical slurry. Conditioners for an oxide polisher have a useable lifetime of about 15,000 wafers. On the other hand, conditioners for a tungsten metal polisher have a useable lifetime of only about 5,000 to 7,000 wafers due to the abrasive nature of the metal polishing slurry. Conventionally, a polishing pad would be conditioned with the pad being rotated at a specific rate while the conditioner is rotated at another specified rate, the process continuing for a prescribed time; these parameters thereby constituting a recipe. Especially in metal polishing pads, problems developed when, after conditioning, the polishing pad does not perform up to expectations for polishing the next set of wafers. Of course, the initial analysis was that the pad was the problem, and the obvious solution was to replace the pad. After changing the polishing pad several times after minimal conditioning, it became apparent that the problem must not be the pad but rather that the conditioning wheel is not properly conditioning the pad. To resolve this problem of prematurely changing the pad, an empirical approach was developed to determine when the conditioner needs to be replaced, thus the above stated 5000 to 7000 wafers. This is, of course, only an approximation and almost certainly leads to early or late changing of the conditioner.
While the exact problem of why the conditioner loses effectiveness is not known, it is known that the slurries used to planarize metal layers, especially tungsten, are very corrosive and abrasive. Thus, one plausible explanation for the conditioner's loss of effectiveness is that the chemicals of the slurry may attack the nickel/chromium setting alloy and, over time, may loosen the diamond crystals, causing them to fall out of the polishing surface. Of course, this reduces the effective surface area of the conditioning wheel and slows the conditioning process. Alternatively, it may be that particles from the pad, used slurry, and metal particles are collecting between the diamond crystals, and building up until the crystals are ineffective. The end result is that the present methods are imprecise in determining when a change of the conditioning wheel is required.
Accordingly, what is needed in the art is an apparatus and method for determining with some precision when a conditioning wheel has served its useful life and requires replacement.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides a method of manufacturing an integrated circuit using a conditioning wheel status indicator with a polishing apparatus having a conditioning wheel and a polishing pad. In one embodiment, the conditioning wheel status indicator comprises a drive motor, an ammeter, and an indicator. The drive motor is coupled to the conditioning wheel and configured to rotate the conditioning wheel against the polishing pad at a prescribed rotation rate. The ammeter is coupled to the drive motor and configured to measure a current of the drive motor. The current registered is a nominal current when the conditioning wheel is new. The indicator is coupled to the ammeter and configured to register an excess current, which exceeds the nominal current, when the conditioning wheel has incurred an undesirable degree of wear.
Thus, in a broad sense, the present invention provides an apparatus and a method for determining when a polishing pad conditioning wheel has reached its useable lifetime. The useable lifetime is indicated by an increase in the amount of amperage needed to maintain rotation of the conditioning wheel at the prescribed rotation rate.
In another embodiment, the conditioning wheel status indicator further comprises a tachometer that is coupled to the drive motor and configured to measure a rotation rate of the drive motor. In a further aspect, the conditioning wheel status indicator further comprises a feedback loop coupled to the tachometer and to the drive motor. The feedback loop is configured to maintain the rotation rate at the prescribed rotation rate.
In an alternative embodiment, the excess current is about twice the nominal current. The excess current, in a more specific aspect, is about 1.7 times the nominal current.
In yet another embodiment, the conditioning wheel status indicator further comprises a platen tachometer, a platen motor, a platen ammeter, and a platen excess-amperage indicator. The platen motor is coupled to a polishing platen of the polishing apparatus and to the platen tachometer. The platen motor is configured to rotate the polishing platen at a prescribed platen rotation rate. The platen ammeter is coupled to the platen motor and configured to measure a platen motor current of the platen motor. The platen motor current is a nominal platen motor current when the conditioning wheel is new. The platen excess current indicator is coupled to the platen ammeter and is configured to register an excess platen motor current, which exceeds the nominal platen motor current, when the conditioning wheel has incurred an undesirable degree of wear.
In another embodiment, the conditioning wheel status indicator further comprises an excess current sensor and a rejection indicator light. The excess current sensor is configured to sense the current and to illuminate the rejection indicator light when the current equals or exceeds the excess current.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should
Easter William G.
Maze John A.
Miceli Frank
Yan Yifeng W.
Lefkowitz Edward
Lucent Technologies - Inc.
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