Abrasive tool making process – material – or composition – With inorganic material – Metal or metal oxide
Reexamination Certificate
1999-10-22
2002-09-10
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
Metal or metal oxide
C051S307000, C051S308000, C106S003000, C438S692000, C438S693000, C252S079200, C252S079300, C252S079400
Reexamination Certificate
active
06447563
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of semiconductor manufacturing. More particularly it relates to a chemical-mechanical polishing slurry system used in semiconductor manufacturing.
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. Then 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 and enhancing the diffusion of reactants and products to and away from the surface by mixing and by reducing the thickness of the boundary layer.
An ILD slurry typically is a one part system, which usually contains an alkaline fumed silica dispersion containing 12 to 25% fumed silica. Examples of commercial fumed silica dispersions are Cabot SS-25® and Wacker K 1020®. The ILD slurry is then shipped to the customer as a concentrate. The customer then dilutes the slurry by adding water at the point of use.
CMP metal slurries, on the other hand, are two part mixtures consisting of a dispersion and an oxidizer. The dispersion comprises an abrasive, an acid to lower the pH to about 2 to 6, optionally a surfactant which maintains the abrasive in suspension and other chemicals tailored to the metal being polished. An example is a tungsten layer slurry called Biplanar® made by EKC. The dispersion is an acidic dispersion (approximately pH of 3, with 5 to 15% alumina particles). Acids reportedly used in the slurry include carboxylic acids or nitric acid. At the point of use, the dispersion is mixed with an oxidizer, such as hydrogen peroxide or ferric nitrate, to form the slurry that will be used to polish the metal layers.
Metal slurry manufactures typically sell only the acidic dispersion while the customer buys the oxidizer independently and mixes the two parts at the point of use. In this case, the oxidizer is a standard bulk commodity solution that can be mixed with the different customized metal dispersion solutions. The problem with this system is that the customer has to inventory the various types of metal dispersion solutions. Since a semiconductor manufacturer typically uses many different metal layers and consumes many thousands of gallons of dispersions for each layer, controlling, storing and waste treating the inventory can be a formidable problem. For example, if the manufacturer does not forecast appropriately and the dispersion reaches its shelf life, then a large volume of dispersion may have to be disposed of which is very expensive and environmentally unfriendly.
In addition, the shelf life of the metal dispersions are reduced when the solid abrasive is mixed with the many different types of chemicals used in the dispersion. The abrasives tend to react with the chemicals in the dispersion resulting in reduced shelf life. Also, the finer particles tend to agglomerate in the presence of these chemicals. Agglomerates tend to settle in the container resulting in a non-uniform product, which can ultimately lead to serious problems or defects on the surface of the substrate.
Therefore, the present invention modifies the current metal slurry system so that the current problem of inventory control is simplified by standardizing the dispersion and customizing the activator for the particular metal layer being polished.
One advantage of the present invention is that the inventory control of the slurry is greatly simplified since the volume of chemicals that have to be controlled is greatly reduced. The volume of the activator will typically be 5 to 10 times less than the volume of the dispersion. Therefore, instead of controlling a large volume of different dispersions, the manufacturer will only have to control a small volume of different activators. This significantly reduces the amount of inventory space required because the manufacture does not have to stock a large volume of different dispersions. Also, the inventory can be more effectively managed because the manufacturer can quickly and accurately measure the use of the generic dispersion solution and forecast appropriately.
Another advantage of the present invention is that since the aggressive chemicals are removed from the abrasives, the shelf life of the dispersion will be increased. Thus, it is less likely that large volumes of dispersion material will have to be disposed due to the increased shelf life and better forecasting. Conversely, since the activator solution does not have any abrasive, it has a reduced shelf life problems and, therefore, many smaller quantities of the activator solution may be stored whenever necessary.
Still another advantage of the present invention is that by using a standard dispersion, (withoutaggressive chemicals), one can take advantage of all the reliability storage life data already generated on these products. For example, if customers standardize their dispersion using a familiar commercialized product such as Cabot SS-25®, the storage life data is well known and does not have to be generated.
Furthermore, the present invention offers a major advantage for slurry manufacturers because it reduces their inventory. Instead of manufacturing a large variety of metal layer dispersions, the manufacturer only needs to prepare one or two standard dispersions. The chemical supplier, who is the expert in the area, will manufacture the activator solution so that it will be optimized for the metal layers.
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 system used for polishing metals comprising: (a) a dispersion solution comprising an abrasive; and (b)
Arch Specialty Chemicals, Inc.
Marcheschi Michael
Ohlandt Greeley Ruggiero & Perle LLP
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