Abrading – Abrading process – Combined abrading
Reexamination Certificate
2002-10-28
2004-08-17
Hall, III, Joseph J. (Department: 3723)
Abrading
Abrading process
Combined abrading
C451S008000, C451S011000, C451S036000, C451S041000, C451S060000, C451S286000, C451S287000, C451S288000, C438S690000, C438S691000, C438S692000, C438S693000
Reexamination Certificate
active
06776696
ABSTRACT:
The present invention relates to a chemical mechanical polishing process used in semiconductor manufacturing. More particularly, the present invention relates to a continuous chemical mechanical polishing process for polishing multiple conductive and non-conductive layers on a semiconductor substrate.
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 polishing (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 or platen while pressure is applied. The combination of the mechanical effects of the abrasive particles from the applied pressure and imposed relative velocity, and the chemical effects that result from a 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 type of layers are interlayer dielectrics (ILD), such as, silicon oxide and silicon nitride. The second type of layers are 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 Proceedings
, 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.
Currently, the CMP process, and in particular the copper CMP process, is a two step process, primarily because the tantalum (Ta) barrier is difficult to polish at high removal rates. In the first step of the two-step process, the substrate to be polished is positioned on a platen. While applying mechanical forces to the platen (i.e., downwardly applied force and/or rotational speed), the slurry, in combination with the mechanical forces, polishes the copper layer rapidly, until the desired copper removal is achieved. Typical copper removal rates are from 5000 to 10000 Å/min for a commercial step 1 slurry. Prior to performing the second step, it is necessary to stop the CMP process after the first step, remove the substrate from the platen and position it on another platen and/or change the slurry composition to change metal selectivity. Once the appropriate changes are made, the second step is performed where the copper removal rate is significantly reduced and the tantalum layer is polished. One approach is outlined in the U.S. Pat. No. 6,083,840 to Mravic et al. where copper, tantalum and oxide removal rates are almost equal to get the best topography. Inherent with the two-step process is limited throughputs and high cost of ownership, which includes, for example, consumable costs, cost of the tool and metrology, cost of slurry distribution, and cost of waste treatment. In a two step process, one may end up using two separate platens, two separate pads, two slurries, and different filters and waste treatments, all of which contributes to excess costs and time consumption.
In a conventional copper CMP two step process, a polishing machine with three platens may be used. A wafer is placed on a first platen that polishes copper only with a step 1 slurry at high rates. After a rinsing step, the wafer is then transferred to a second platen that polished tantalum with a step 2 slurry. After another rinse, the wafer is transferred to a third platen for a buff clean. The time per wafer is about 3 minutes total or about 20 wafers per hour. On a single platen machine, such as one sold by Strasbaugh or Ebara, all steps of the process noted above have to be done on the same platen. As a result, throughput is further reduced since the single platen and associated equipment must be changed for each step, rather than just moving the wafer to a different platen already set up for the desired task, such as on the three platen machine described above. The common drawback, despite the type of system used, is that the polishing process must be stopped several times to allow for process changes.
U.S. Pat. No. 6,114,249 to Canaperi et al. (Canaperi) discloses a CMP polishing process for polishing a material in a multiple material substrate. A slurry is used to polish a first layer until a major portion of the first layer is removed. Triethanolamine is added to the slurry without interrupting the polishing of the substrate to increase the selectivity of the slurry towards the first material layer being polished. the polishing continues until the first material layer is completely removed fro
Jenkins Richard J.
Mahulikar Deepak
Hall, III Joseph J.
McDonald Shantese L.
Ohlandt Greeley Ruggiero & Perle L.L.P.
Planar Solutions LLC
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