Abrasive tool making process – material – or composition – With inorganic material – Metal or metal oxide
Reexamination Certificate
2002-10-24
2004-07-13
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
Metal or metal oxide
C051S307000, C051S308000, C106S003000, C252S06251C, C252S062560, C252S062570, C252S062590, C252S06251C, C216S089000, C438S692000, C438S693000
Reexamination Certificate
active
06761747
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is a novel dispersion containing abrasive particles, a method of preparing the dispersion, and methods of using the dispersion.
2. Discussion of the Background
The polishing dispersion plays a central role in the chemical mechanical polishing (CMP process) of oxide and metallic surfaces made from materials having very low dielectric constants, so-called “low-k” surfaces. These dispersions generally contain abrasive particles or mixtures of abrasive particles in addition to other constituents. With the growth of miniaturization in the electronics industry, the demands made on polishing dispersions are continuing to increase.
The use of magnetic dispersions in the CMP process for polishing “low-k” surfaces is described in U.S. Pat. No. 6,083,839. The polishing device has a number of magnetic coils, which can provide the same or different magnetic field strengths, and which may be arranged in spatially different positions. The distance from the magnetic coil to the surface to be polished can also be varied, thereby varying the force effect of the magnetic particles on the surface to be polished.
The disadvantage of the magnetic dispersion described in U.S. Pat. No. 6,083,839 is that it is made up of non-uniform particles, namely a physical mixture of silicon dioxide or cerium oxide and ferromagnetic particles, which have various particle sizes, differing hardnesses, and differing behaviour in an aqueous dispersion. The role of the silicon dioxide or cerium oxide should be that of an abrasive. The ferromagnetic particles, in conjunction with the magnetic coils, cause the particles to move. In practice, an exact separation of the particle properties is not possible. Thus, the ferromagnetic particles also display abrasive properties and tend to re-agglomerate and cause sedimentation in the dispersion. On the other hand, the magnetic effect is transferred only partially to the non-magnetic particles. For that reason U.S. Pat. No. 6,238,279 describes a method to remove magnetic particles, in this case iron oxide particles, before the CMP process is carried out.
A further disadvantage of U.S. Pat. No. 6,083,839 is that the force effect and the movement of the dispersion is substantially generated by the ferromagnetic particles and not by the abrasive particles, which are supposed to remove the surface to be polished. Thus, although the movement of the ferromagnetic particles also causes the abrasive particles to move in the dispersion, the abrasive particles do not experience pressure against the surface. This can lead to reduced or uneven removal of the surface during the polishing process.
In contrast to U.S. Pat. No. 6,083,839, the dispersion of the present invention contains uniform abrasive particles, which in a chemical mechanical polishing process lead to a uniform polishing result. The dispersion of the present invention further provides a substantially higher stability with regard to re-agglomeration and sedimentation than a dispersion containing ferromagnetic particles. Stability is understood to refer both to storage stability and to stability during the polishing process. The particles in the dispersion of the present invention that make up the magnetic and abrasive part of a particle further provide a uniform pressure on the surface to be polished under the application of a magnetic field. This leads to constant removal rates over the entire surface to be polished.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a dispersion that avoids the disadvantages of the prior art.
In a first embodiment, the present invention is a dispersion comprising abrasive particles which are pyrogenically manufactured particles that have superparamagnetic metal oxide domains in a non-magnetic metal or non-metal oxide matrix.
The term “dispersion” means a fine dispersion of the abrasive particles in a medium comprising aqueous and/or organic phases as dispersant.
Pyrogenically manufactured particles are understood to be highly disperse particles that are obtained in the gas phase at elevated temperatures. This is described in more detail in Ullmann's Encyclopedia of Industrial Chemistry, Vol. A23, page 635 ff, 5
th
edition with reference to silicon dioxide.
Domains are understood to be spatially separated superparamagnetic areas in and on the surface of the metal or non-metal oxide matrix. As a consequence of the pyrogenic manufacturing process, the abrasive particles are almost entirely pore-free and have free hydroxyl groups on the surface. These particles have superparamagnetic properties if an external magnetic field is applied. They are not permanently magnetized, however, and display only a low residual magnetization.
The term superparamagnetic refers to the property of materials whereby they have no permanent (equiaxed) alignment of the elementary magnetic dipoles in the absence of the action of external magnetic fields. In the presence of an external magnetic field, however, they have magnetic susceptibilities at a level similar to ferromagnetic materials. Superparamagnetism occurs when the diameter of the crystalline regions in a normally ferromagnetic substance falls below a particular critical value.
The relative amount of superparamagnetic domains in the particles may be between 1 and 99.6 wt. %. Regions of superparamagnetic domains that are spatially separated by the non-magnetic matrix lie within this range. Preferably, the relative amount of superparamagnetic domains is greater than 30 wt. %, particularly preferably greater than 50 wt. %. As the relative amount of superparamagnetic regions increases, the magnitude of the magnetic effect on the particles that can be achieved, also increases.
The superparamagnetic domains preferably comprise the oxides of Fe, Cr, Eu, Y, Sm or Gd, the superparamagnetic properties of which are already known. The metal oxides in these domains can have a uniform structure or various different structures.
In addition, the particles may also have non-magnetic regions. These non-magnetic regions can comprise mixed oxides of the non-magnetic matrix with the domains, for example, iron silicalite (FeSiO
4
). These non-magnetic constituents behave in the same way as the non-magnetic matrix with regard to superparamagnetism. This means that the particles are superparamagnetic as before, but the saturation magnetization falls as the proportion of non-magnetic components increases.
A particularly preferred superparamagnetic domain is iron oxide in the form of gamma-Fe
2
O
3
(&ggr;-Fe
2
O
3
), Fe
3
O
4
, mixtures of gamma-Fe
2
O
3
(&ggr;-Fe
2
O
3
) and Fe
3
O
4
and/or mixtures of the above with non-magnetic compounds containing iron.
The non-magnetic metal or non-metal oxide matrix can include the oxides of metals and non-metals of Si, Al, Ti, Ce, Mg, Zn, B, Zr or Ge. Silicon dioxide is particularly preferred. In addition to the spatial separation of the superparamagnetic domains, the matrix also has the property of stabilizing the level of oxidation of the superparamagnetic domain. Thus, for example, when the superparamagnetic iron oxide phase is magnetite, it may be stabilized by a silicon dioxide matrix.
The pyrogenically manufactured abrasive particles of the dispersion according to the present invention can be particles with superparamagnetic metal oxide domains having a diameter of 3 to 20 nm in a non-magnetic metal or non-metal oxide matrix.
The particles may have a chloride content of 50 to 1000 ppm and a carbon content of below 500 ppm, preferably below 100 ppm.
The particles of the present invention display varying degrees of aggregation, depending on the way in which the pyrogenic process is carried out. Process parameters affecting aggregation may include residence time, temperature, pressure, the partial pressures of the compounds used, and the type and location of cooling after the reaction. A broad spectrum of particle types of from largely spherical to largely aggregated particles can thus be obtained.
The particles of the present inven
Gottfried Heiko
Heberer Stefan
Muehlenweg Heike
Pridoehl Markus
Trageser Berthold
Degussa - AG
Marcheschi Michael
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