Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2001-04-05
2003-05-27
Nguyen, George (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S060000, C106S003000, C051S307000, C216S088000
Reexamination Certificate
active
06568997
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the field of manufacturing semiconductor integrated circuits. In particular, this invention is related to a polishing composition for the chemical mechanical polishing (CMP) of semiconductor substrates.
In the manufacture of integrated circuits, multiple layers of material are successively deposited on a substrate. Typically, a layer of an insulating material, such as, silica, is deposited in pattern that contains a series of troughs and then a metal conductor, such as, copper, is deposited in these troughs to form the circuit or a portion of the circuit. Often, the metal conductor is separated from the insulating material by a buffer material, such as, tantalum nitride. After a layer of material is deposited, the layer must be made flat before a succeeding layer of matter is deposited. The process of removing any excess material and making a layer flat involves controlling the rate of removal of material, such as, metal, buffer material and/or insulating material and is commonly known a “planarization”. This process also involves removing protrusions and those portions of the surface that are above the average surface height of the substrate at a higher rate than the removal of material in the recesses that are below the average surface height of the substrate.
CMP is used to planarize these semiconductor substrates. In a typical CMP process, a polishing pad is pressed against the substrate and is moved across the surface of the substrate while an aqueous liquid polishing composition is interposed between the polishing pad and the surface of the substrate being polished. The CMP process combines chemical action and mechanical action. An oxidizer generally is used in the polishing composition that converts metal on the surface of the substrate to an oxide that sometimes serves as an element of a passivating layer that reduces further reaction of the metal with the polishing composition. Generally, mild abrasives are used in the polishing composition to increase the rate of polishing.
Copper, that is electrolytically deposited to form the circuits of a semiconductor, often does not form a uniform layer but a layer having peaks and valleys that must be planarized before the semiconductor can be used or before another layer of material is applied. Conventional polishing compositions, polishing pads and polishing equipment and techniques result in removal of copper in both the peaks and valleys when only removal of the copper from the peaks is desired. Copper, in comparison to the substrate that usually is silica or some other hard substance, is a relatively soft metal and is easily eroded by polishing and areas of copper that do not require polishing or only require a slight amount of polishing must be protected. By using conventional equipment and techniques, the peaks and valley are polished at an almost equal rate. When polishing a line of a copper circuit of the semiconductor device is continued, more of the center of the line is polished rather than on the edges and the result is a low center that may even break through the copper line of the circuit to the substrate that typically is silica. This problem is commonly known as “dishing”.
Efforts have been made to reduce or eliminate this dishing problem by using various polishing compositions. European Patent Application (EP 0 913 442 A2) attempts to eliminate the problem by using a variety of compositions some of which contain polyacrylic acid. However, the dishing problem was not overcome. The novel composition of this invention significantly reduces the problem of dishing of copper circuits of semiconductor devices.
SUMMARY OF THE INVENTION
This invention is directed to a polishing composition used for the chemical mechanical polishing of semiconductor wafers having a copper metal circuit. The composition has a pH of under 5.0 and comprises the following:
(a) a water soluble 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 an 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 organic polymer particles,
wherein the polymer of the organic polymer particles has a number average molecular weight of at least 500,000 determined by GPC (gel permeation chromatography) and a Tg (glass transition temperature) of at least 25° C.
DETAILED DESCRIPTION OF THE INVENTION
The novel polishing composition of this invention can be used with conventional polishing equipment, known polishing pads and techniques to polish semiconductor wafers having copper circuits. The copper layer on the wafer is polished to remove peaks from the copper layer but little or no polishing occurs in the valleys. Copper is cleared from the surface of the wafer and there is a substantial reduction in dishing of the copper circuits of the wafer in comparison to conventional polishing compositions. The novel polishing composition provides a substantially planar surface that is free of scratches and other defects that commonly result from polishing.
The novel polishing composition of this invention contains organic polymer particles that replace conventional inorganic abrasive particles, such as, silica and alumina. These organic polymer particles do not have the abrasive characteristics of the inorganic abrasive particles but do remove “high spots” of the copper layer of semiconductor circuit and provide a planarized copper layer or copper circuit. Also, the organic polymer particles are selective in that only copper is polished and not other layers of material, such as, tantalum.
The novel 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. It has been found that polishing compositions having a pH over 5 and higher result in a reduction of polishing of copper of the semiconductor wafer.
The novel polishing composition contains about 0.05-2.0% by weight, based on the weight of the composition, of a carboxylic acid polymer comprising polymerized unsaturated carboxylic acid monomers and has a number average molecular weight of about 20,000 to 1,500,000. Blends of high and low number average molecular weight carboxylic acid polymers also can be used and are preferred for many polishing uses. These carboxylic acid polymers generally are in solution but under some circumstances may be in the form of an aqueous dispersion.
The number average molecular weight of the aforementioned polymers are determined by GPC (gel permeation chromatography).
Unsaturated carboxylic acid monomers include unsaturated monocarboxylic acids and unsaturated dicarboxylic acids. Typical unsaturated monocarboxylic acid monomers contain 3 to 6 carbon atoms and include acrylic acid, oligomeric acrylic acid, methacrylic acid, crotonic acid and vinyl acetic acid. Typical unsaturated dicarboxylic acids contain 4 to 8 carbon atoms and include the anhydrides thereof and are, for example, maleic acid, maleic anhydride, fumaric acid, glutaric acid, itaconic acid, itaconic anhydride, and cyclohexene dicarboxylic acid. Water soluble salts of the aforementioned acids also can be used.
The term “poly(meth)acrylic acid”, as used hereinafter, means polymers of acrylic acid or polymers of methacrylic acid.
Particularly useful are poly(meth)acrylic acids having a number average molecular weight of about 20,000 to 150,000, preferably 25,000 to 75,000 and more preferably, 25,000 to 40,000. Blends of high and low number average molecular weight poly(meth)acrylic acids are particularly preferred. In such blends or mixtures of poly(meth)acrylic acids, a low number average molecular weight poly(meth)acrylic acid having a number average molecular weight of 20
Costas Wesley D.
Lack Craig D.
Saucy Daniel A.
Benson Kenneth A.
Biederman Blake T.
Nguyen George
Rodel Holdings Inc.
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