Abrasive tool making process – material – or composition – With inorganic material
Reexamination Certificate
2002-04-12
2004-01-20
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
C051S308000, C051S309000, C051S298000, C106S003000, C438S690000, C438S692000, C438S693000
Reexamination Certificate
active
06679928
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a polishing composition for chemical mechanical planarization, CMP, to remove a metal layer from a semiconductor substrate, further described as, a semiconductor wafer.
BACKGROUND OF THE INVENTION
Large numbers of semiconductor devices are built from different materials that are successively deposited in successive layers on a wafer of silicon, which provides a semiconductor substrate. The semiconductor devices include semiconductor circuit elements and electrically conducting circuits, further described as, interconnects. The interconnects comprise metal in trenches of precise dimensions. The trenches are recessed in a surface of a dielectric layer on the wafer, also known as, an interlayer. The trenches are manufactured according to known photolithographic etching processes. A barrier film is deposited over the underlying dielectric layer and the trenches. The metal that fills the trenches to provide the interconnects is applied as a layer of metal that is deposited on the underlying barrier film.
CMP is a process performed with a moving polishing pad applied with a downforce against the layer of metal, while an aqueous polishing composition is interposed between the polishing pad and the surface being polished. The layer of metal is removed by a combination of abrasion and chemical reaction. CMP is performed to remove the layer of metal from the underlying barrier film, while minimizing removal of the metal in the trenches, thus, minimizes dishing of the interconnects. Dishing is a name applied to recesses that result from undesired removal of some of the metal in trenches by the CMP operation. Excessive dishing comprises defects in the interconnects.
According to EP 0 913 442, a polishing composition is provided with polyacrylic acid to minimize removal of metal in trenches during CMP, thus, minimizing dishing.
A polishing composition is desired to minimize removal of metal in trenches during CMP, while maximizing a removal rate of the metal layer during CMP.
SUMMARY OF THE INVENTION
The invention resides in a polishing composition, further described as, an aqueous composition, for polishing a semiconductor substrate with both the aqueous composition and a polishing pad applying a downforce, to remove metal from an underlying barrier film on the semiconductor substrate, the aqueous composition comprising:
a pH no higher than 5,
an oxidizer of the metal at said pH to provide ions of the metal,
a complexing agent to dissolve the ions,
a carboxylic acid polymer reactive with the metal while the polishing pad applies a relatively higher downforce on the metal in a metal layer on the underlying barrier film, to provide a relatively high removal rate of the metal layer,
the carboxylic acid polymer being reactive with the metal in trenches while the polishing pad applies a relatively lower downforce on the metal in trenches, which tends to provide a relatively high removal rate of the metal in trenches, and
a combination of a metal corrosion inhibitor and a surfactant, which adsorbs on the metal in trenches on which the relatively lower downforce is applied, to minimize the removal rate of the metal in trenches, as would tend to be provided by the carboxylic acid polymer and the applied downforce without the combination of the metal corrosion inhibitor and the surfactant.
The terminology, surfactant, is interpreted to mean, a surface active agent that adsorbs to a surface and lowers a surface tension of a liquid on the surface. According to an embodiment, a surfactant comprises, an anionic surfactant as distinguished from a cationic surfactant, and as distinguished from a neutral charge surfactant.
According to another embodiment, a surfactant comprises, a sulfonate surfactant comprised of molecules having at least six carbon atoms, as distinguished from a sulfonate comprising molecules having an insufficient number of carbon atoms to exist as a polymer in the polishing composition.
According to another embodiment, a surfactant comprises, an alkali metal organic sulfonate.
According to another embodiment, the aqueous composition comprises, a pH under 5.0 and,
(a) a carboxylic acid polymer comprising polymerized unsaturated carboxylic acid monomers having a number average molecular weight of about 20,000 to 1,500,000 or blends of high and low number average molecular weight polymers of polymerized unsaturated carboxylic acid monomers,
(b) 1 to 15% by weight of an oxidizing agent,
(c) up to 3.0% by weight of abrasive particles,
(d) 50-5,000 ppm (parts per million) of a corrosion inhibitor,
(e) up to 3.0% by weight of a complexing agent, such as, malic acid, and
(f) 0.1 to 5.0% by weight of a surfactant.
DETAILED DESCRIPTION
A polishing composition according to the invention can be used with conventional polishing equipment, known polishing pads and techniques to polish semiconductor wafers having copper circuits that result in clearing of a layer of excess copper from the surface of the wafer with a substantial reduction in dishing of the copper circuits of the wafer. The polishing composition provides a substantially planar surface that is free from scratches and other defects that commonly result from polishing.
The polishing composition is an aqueous composition that has a pH under 5.0 and preferably has a pH of 2.8 to 4.2 and more preferably, a pH of 2.8 to 3.8.
The polishing composition contains 1-15% by weight of an oxidizing agent that serves as an oxidizer of the metal at a pH lower than 5.0. Appropriate oxidizing agents are hydrogen peroxide, iodates, such as, potassium iodate, nitrates, such as, cesium nitrate, barium nitrate, ammonium nitrate, mixtures of ammonium nitrate and cesium nitrate, carbonates, such as, ammonium carbonate, persulfates, such as, ammonium and sodium persulfate, and perchlorates. For example, the polishing composition contains about 5-10% by weight of an oxidizing agent. Preferably, the polishing composition contains about 9% by weight of hydrogen peroxide as the oxidizing agent.
The composition contains up to 3.0% by weight and preferably, 0.1-1.0% by weight of a complexing agent, such as, a dissolved carboxylic acid having two or more carboxyl groups and having a hydroxyl group as disclosed in U.S. Pat. No. 5,391,258. An appropriate complexing agent includes straight chain mono- and dicarboxylic acids and their salts, such as, malic acid and malates, tartaric acid and tartarates, gluconic acid and gluconates, citric acid and citrates, malonic acid and malonates, formic acid and formates, lactic acid and lactates. Polyhydroxybenzoic acid, phthalic acid and salts thereof also can be used. During CMP, the oxidizing agent serves as an oxidizer of the metal at said pH under 5.0 to provide ions of the metal. The complexing agent dissolves the ions, while the polishing pad applies downforce and abrasion to the metal being polished. As a result, the metal layer is removed from the underlying barrier film.
The polishing composition contains 50 to 5,000 ppm (parts per million) of an inhibitor preferably BTA (benzotriazole), or TTA (tolyltriazole) or mixtures thereof. Other inhibitors that can be used are 1-hydroxybenzotriazole, N-(1H-benzotriazole-1-ylmethyl) formamide, 3,5-dimethylpyrazole, indazole, 4-bromopyrazole, 3-amino-5-phenylpyrazole, 3-amino-4-pyrazolecarbonitrile, 1-methylimidazole, Indolin QTS and the like. It is known that the inhibitor, for example, benzotriazole (BTA), adsorbs on the surface of a metal, for example, copper, to inhibit corrosion of the metal, for example, by exposure of the metal to the atmosphere. The inhibitor tends to lower a tendency for the oxidizer of the metal to provide ions of the metal.
The aqueous composition comprises, a carboxylic acid polymer, which maximizes the removal rate of the metal during CMP. It is believed that the carboxylic acid polymer is reactive on the metal similarly as particle abrasives are reactive on the metal, in transferring energy from a polishing pad to the copper metal, which removes the copper metal at an increased removal rate during CMP.
Bian Jinru
Costas Wesley D.
Ghosh Tirthankar
Valentine Karel-Anne
Kita Gerald K.
Marcheschi Michael
Oh Edwin
Rodel Holdings Inc.
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