Abrading – Abrading process – Utilizing fluent abradant
Reexamination Certificate
2001-01-18
2003-08-05
Eley, Timothy V. (Department: 3724)
Abrading
Abrading process
Utilizing fluent abradant
C451S041000, C451S054000, C451S056000, C451S059000, C451S060000
Reexamination Certificate
active
06602112
ABSTRACT:
The present invention relates to dissolution of metal particles that are produced by polishing a semiconductor substrate.
Polishing compositions consist of an aqueous solution, which contains an oxidizing agent, and often times a complexing agent. A polishing composition known as a slurry contains abrasive particles. The part, or semiconductor substrate, is bathed or rinsed in the polishing composition while a polishing pad is pressed against the substrate and the pad and substrate are moved relative to each other. Thus, the lateral motion of the pad relative to the pad results in wear and volumetric removal of the substrate surface.
The metal particles (e.g., copper) fracture and are removed or released from the surface of the substrate by and during polishing of the surface with a polishing pad. Metal particles are most likely to be produced by polishing when the surface is particularly rough. The removed metal particles and other asperities cause a darkening (e.g., graying or blackening) by reaction with the polishing composition, and further darken the polishing pad, thereby interfering with optical wafer loss detectors or optical end point detectors. The metal particles obstruct an optical path through a transparent portion of a polishing pad. The optical path is used by optical detectors that monitor the semiconductor substrate for wafer loss or that monitor for, and detect, complete removal of a layer of metal from a semiconductor substrate, as an indication of a desired end point of the polishing operation, at which end point the polishing operation is substantially slowed or ceased, to prevent overpolishing, meaning excessive removal of material from the semiconductor substrate being polished. Further, the metal particles block or obstruct slurry particles from the surface, which impedes polishing of the surface. Further, the metal particles can scratch the surface being polished by a polishing pad.
It is thus desirable to avoid the presence of metal particles that have been removed from a semiconductor wafer.
It has been found that hydrogen peroxide dissolves metal particles that have been removed from a semiconductor substrate during polishing of the substrate with a polishing pad. The metal particles are dissolved to minimize obstruction of slurry from the surface being polished, and to avoid scratching and other damage to the surface being polished. Further, the metal particles are dissolved to minimize interference with optical wafer loss and end point detectors. Embodiments of the invention will now be described by way of example.
In an embodiment, the hydrogen peroxide solution is used to pre-treat the polishing pad. In this embodiment, the hydrogen peroxide solution is dispensed onto the polishing pad to prepare the pad for polishing. However, just prior to polishing of the substrate, the hydrogen peroxide solution is discontinued, leaving a quantity of hydrogen peroxide on the pad. During the start of polishing of a metal surface on a semiconductor substrate, using the pad and a polishing composition, the metal surface is initially rough, and particles of metal are removed by the polishing operation. Hydrogen peroxide left on the pad dissolves particles of metal that have been removed by polishing. Polishing of the surface is continued, until the surface being polished is smoothed and the production of particles of metal is significantly reduced. Polishing continues after the quantity of hydrogen peroxide dissipates. The quantity of hydrogen peroxide is present for a limited time duration, which is sufficient to dissolve the particles of metal that have been removed from the semiconductor substrate.
According to a further embodiment of the invention, a method for polishing a semiconductor substrate to remove metal, comprises, polishing the semiconductor substrate with a polishing pad and a polishing composition, removing particles of the metal from the semiconductor substrate by said polishing, dispensing hydrogen peroxide onto the polishing pad for a limited time duration to dissolve the particles, and dissolving the particles in the hydrogen peroxide.
According to a further embodiment of the invention, a method includes, monitoring the thickness of the metal on the semiconductor substrate by way of an optical path through at least a portion of the polishing pad that is transparent, and dissolving the particles in the hydrogen peroxide to eliminate obstruction of the optical path by the particles.
In yet another embodiment, the hydrogen peroxide solution is dispensed onto the polishing pad towards the end of the polishing cycle. Metal particles that have darkened by oxidation or by chemical reaction with the polishing composition, are dissolved by the hydrogen peroxide.
The hydrogen peroxide can be controlled by dispensing a hydrogen peroxide solution in conjunction with a CMP polishing composition. Preferably, the method is used as the first step of a two-step copper polishing process. The presence of the hydrogen peroxide dissolves the dark particles that can form during first step copper polishing
A method is provided for chemical-mechanical polishing of semiconductor substrates, comprising dispensing hydrogen peroxide in conjunction with a polishing slurry comprising: water, an optional complexing agent, submicron abrasive particles, and an oxidizing agent.
A method is provided for chemical-mechanical polishing of semiconductor substrates, in conjunction with a polishing composition comprising: water, a complexing agent, and an oxidizing agent. The composition may be a slurry having submicron abrasive particles.
Hydrogen peroxide can be present in a hydrogen peroxide solution at a concentration of about 0.01, 0.1, 1, 2, 3, 4, 5, 10, 15, 20, 25, to 30% by weight. Preferably, hydrogen peroxide is present in the hydrogen peroxide solution at a concentration of about 0.5, 1, 2, or 2.5% by weight, even more preferably about 1% by weight. The hydrogen peroxide solution can be (1) premixed with the polishing composition being used and the resultant mixture dispensed onto the polishing pad, (2) dispensed onto the polishing pad separately from the polishing composition, or (3) dispensed concurrently with the polishing composition (i.e., mixing would occur at the point of dispensing or within the dispensing apparatus). Preferably, the hydrogen peroxide solution is dispensed onto the polishing pad separately from the polishing composition. Such separate dispensing allows for greater control of the presence of hydrogen peroxide. One method of premixing is mixing both solutions together in a chamber and then pumping the resulting solution onto the polishing pad. Premixing can also be accomplished by pumping both solutions simultaneously through the same dispensing channel (e.g., tube).
The flow rate of hydrogen peroxide solution and polishing composition can be varied to maintain the desired ratio of hydrogen peroxide to polishing composition on the polishing surface. It is preferred that the flow rates are equal (e.g., 200 mL/min of hydrogen peroxide solution and 200 mL/min of polishing composition). When using equal flow rates, it is preferred that the hydrogen peroxide solution is 1% by weight hydrogen peroxide. The flow rate of the hydrogen peroxide solution can be varied as the weight % of hydrogen peroxide varies. For example, if a 30% hydrogen peroxide solution, a commercially available concentration, is used, then the flow rate is preferably one thirtieth of the above-noted 200 mL/min (i.e., approximately 7 mL/min). Conversely, if a 0.5% hydrogen peroxide solution is used, then 400 mL/min of hydrogen peroxide solution would preferably be used with 200 mL/min of polishing composition. The above noted flow rates can be used for the premixing, separate, or concurrent dispensing techniques.
Since hydrogen peroxide is an oxidizing agent, its presence can cause damage to the wafer surface if it is dispensed with the polishing slurry for too long of a period. Thus, the wafer is preferably polished for 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 seconds in the presence of the
Burke Peter A.
Gettman David
Lack Craig D.
Sachan Vikas
Thomas Terence M.
Biederman Blake T.
Ramana Anuradha
Rodel Holdings Inc.
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