Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2002-10-09
2004-06-15
Morgan, Eileen P. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S036000, C438S692000, C438S693000, C156S345110, C156S345120
Reexamination Certificate
active
06749488
ABSTRACT:
The present invention relates to a chemical mechanical polishing slurry system used in semiconductor manufacturing. More particularly, the present invention relates to a chemical mechanical polishing slurry system that has a lower incidence of defects.
BACKGROUND OF THE INVENTION
Semiconductors are typically made up of millions of active devices that are connected together via metal interconnections to form circuits and components. The active devices are interconnected by a well-known multilayer interconnect process. In a typical interconnect process, alternating layers of metal and dielectric are put on the silicon wafer by a variety of processes. After each layer is applied, a means is used to remove excess amounts of these layers and to assure both local and global planarity of the surface in preparation for the application of the next layer.
A common process used to accomplish these goals is chemical mechanical planarization (CMP). In this process, an aqueous solution containing various chemicals and suspended abrasive particles, namely, a slurry, is interposed between the wafer and a moving pad while pressure is applied. The combination of the mechanical effects of the abrasive particles, applied pressure, imposed relative velocity and the chemical effects which result from chemical reaction between the material being polished and constituents in the solution result in a synergistic enhancement of the polishing rate or material removal rate. That is, the material removal rate is higher than that produced by either the mechanical effects or chemical effects alone.
There are two general types of layers that can be polished. The first layer is interlayer dielectrics (ILD), such as, silicon oxide and silicon nitride. The second layer is metal layers, such as, tungsten, copper, aluminum, etc., which are used to connect the active devices.
In the case of CMP of metals, the chemical action is generally considered to take one of two forms. In the first mechanism, the chemicals in the solution react with the metal layer to continuously form an oxide layer on the surface of the metal. This generally requires the addition of an oxidizer to the solution, such as, hydrogen peroxide, ferric nitrate, etc. Thereafter, the mechanical abrasive action of the particles continuously and simultaneously removes this oxide layer. A judicious balance of these two processes obtains optimum results in terms of removal rate and polished surface quality.
In the second mechanism, no protective oxide layer is formed. Instead, the constituents in the solution chemically attack and dissolve the metal, while the mechanical action is largely one of mechanically enhancing the dissolution rate by such processes as continuously exposing more surface area to chemical attack, raising the local temperature (which increases the dissolution rate) by the friction between the particles and the metal, enhancing the diffusion of reactants and products to and away from the surface by mixing, and by reducing the thickness of the boundary layer.
A number of systems for chemical-mechanical polishing of copper have been disclosed. Kumar et al. in an article entitled “Chemical-Mechanical Polishing of Copper in Glycerol Based Slurries” (
Materials Research Society Symposium Proceeding
, 1996) disclose a slurry that contains glycerol and abrasive alumina particles. An article by Gutmann et al. entitled “Chemical-Mechanical Polishing of Copper with Oxide and Polymer Interlevel Dielectrics” (
Thin Solid Films
, 1995) discloses slurries based on either ammonium hydroxide or nitric acid that may contain benzotriazole (BTA) as an inhibitor of copper dissolution. Luo et al. in an article entitled “Stabilization of Alumina Slurry for Chemical-Mechanical Polishing of Copper” (
Langmuir
, 1996) discloses alumina-ferric nitrate slurries that contain polymeric surfactants and BTA. Carpio et al. in an article entitled “Initial Study on Copper CMP Slurry Chemistries” (
Thin Solid Films
, 1995) disclose slurries that contain either alumina or silica particles, nitric acid or ammonium hydroxide, with hydrogen peroxide or potassium permanganate as an oxidizer.
There are a number of theories as to the mechanism for chemical-mechanical polishing of copper. An article by Zeidler et al. (
Microelectronic Engineering
, 1997) proposes that the chemical component forms a passivation layer on the copper, changing the copper to a copper oxide. The copper oxide has different mechanical properties than metallic copper, such as, density and hardness, and passivation changes the polishing rate of the abrasive portion. The above article by Gutmann et al. discloses that the mechanical component abrades elevated portions of copper and the chemical component then dissolves the abraded material. The chemical component also passivates recessed copper areas minimizing dissolution of those portions.
Planar Solutions has developed a basic slurry for the CMP of copper, tantalum and TEOS layers. This is described in a publication titled “Development of a 1:1:1 TA: Copper layer: TEOS layer slurry for Tantalum layer polishing” in the proceedings of the CMP MIC conference, February 1999. In a two step process to CMP the copper layer, in the first step the slurry polishes the copper layer rapidly, while in the second step, the slurry polishes the tantalum layer, the copper layer, and the TEOS layer simultaneously. The prior art slurry was designed to have no selectivity towards these layers and the topography performance was excellent. The topography has been reported to be in the 100-300 Å range. However, the prior art slurry has two distinct disadvantages associated with it, namely, defectivity and oxide thinning or total copper loss.
The defectivity issue revolves around several chatter mark defects revealed in the copper layer after CMP. After polishing with the prior art slurry, the polished substrate, when viewed at 200×magnification at nine sites, had several hundred chatter mark defects (hereafter referred to as a normalized defectivity of 100). The chatter mark defects were deep and were cosmetically unacceptable.
The oxide thinning is primarily associated with the high removal rate of the TEOS layer. The prior art slurry removed the TEOS layer more rapidly than the tantalum layer or the copper layer. For example, typical removal rates were TEOS layer: 1500 Å/min, tantalum layer: 600 Å/min, and copper layer: 900 Å/min. As a result of the high oxide thinning, thicker TEOS layers will have to be deposited, which will result in subsequent increased costs.
The present invention overcomes the disadvantages of the current metal slurry compositions so that defectivity and oxide thinning or total copper loss are significantly reduced and/or eliminated. The present invention also provides many additional advantages, which shall become apparent as described below.
SUMMARY OF THE INVENTION
The present invention relates to a novel CMP slurry composition used for polishing metals comprising (a) a dispersion solution comprising an abrasive; and (b) an oxidizer. The slurry composition has a large particle count of less than about 150,000 particles having a particle size greater than 0.5 &mgr;m in 30 &mgr;L of slurry, which is achieved by filtering the slurry composition prior to use. By controlling the particle size of the abrasive dispersion, through either filtration of the dispersion itself or the slurry composition before use, defectivity and oxide thinning/total copper loss problems are significantly reduced and/or eliminated. Also, the inclusion of a chemical activity enhancer, such as, an amine and a corrosion inhibitor, results in the appropriate copper removal rate without increasing static etch rates, which cause increased topography.
The slurry composition may also comprise at least one other component selected from the group consisting of: acids, chelating agents, fluorine-containing compounds, buffering agents, salts, and biological agents.
DETAILED DESCRIPTION OF THE INVENTION
It has been found that by reducing the number of abras
Jenkins Richard J.
LaFollette Larry A.
Mahulikar Deepak
Pasqualoni Anthony Mark
Morgan Eileen P.
Ohlandt Greeley Ruggiero & Perle L.L.P.
Planar Solutions LLC
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