Abrasive tool making process – material – or composition – With inorganic material – Clay – silica – or silicate
Reexamination Certificate
2002-09-26
2003-12-30
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
Clay, silica, or silicate
C106S003000, C423S335000, C423S338000, C423S339000
Reexamination Certificate
active
06669748
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a dispersion liquid of silica particles for polishing with the excellent stability in dispersion, a method of producing the same, and a polishing agent comprising the dispersion liquid of silica particles.
BACKGROUND TECHNOLOGY
In a production process of a substrate with a semiconductor integrated circuit provided thereon, as irregularities or steps are generated, for instance, when the circuit is formed on a silicon wafer with metal such as copper, the metallic portion of the circuit is preferentially removed by polishing to eliminate the irregularities or steps on the surface thereof. When aluminum wiring is formed on a silicon wafer and such an oxide film as SiO
2
film is provided as an insulating film thereon, also irregularities are generated due to the wiring, so that the oxide film is polished for flattening.
As one of the polishing methods available for the purpose described above, there has been well known the chemical mechanical polishing method. In this method, a substrate with irregularities thereon is pressed to a rotating polishing pad and also the substrate itself is dipped into a slurry of a polishing agent, when particles for polishing included in the slurry is pressed to the substrate with irregularities thereon and as a result convex metallic sections on the substrate are removed and the surface is flattened. Further polishing in the same manner is performed also for flattening a surface of an oxide film formed on a substrate or for eliminating irregularities on an insulating film (oxide film) formed on a circuit.
In this polishing step, spherical particles each with the average particle diameter of about 200 nm such as those of fumed alumina or fumed silica are used as the particles for polishing. As the polishing agent, together with the particles for polishing as described above, oxidants such as hydrogen peroxide for improving the metal polishing speed, benzotriazole (BTA) for suppressing corrosion or oxidation of metal, or water-based slurry for polishing with a chemical polishing agent such as an acid added therein are used according to a type of the metal to be processed.
In the process for polishing a substrate as described above, it is required that a surface after having been subjected to polishing is a flat one without any irregularity or microscopic flaw, and further the polishing speed should be high. In addition, in the field of semiconductor materials, a degree of circuit integrated has been becoming higher and higher in association with the tendency for size reduction and more sophisticated performance of electric and electronic products, but sometimes the intended performances can not be achieved or troubles may occur due to impurities remaining in the transistor separation layers. Especially when any alkali metal, especially sodium is deposited on a surface of a polished semiconductor substrate or a polished oxide film, the dispersibility is very high, and the alkali metal is trapped in defective sections in the oxide film, and even if a circuit is formed on the semiconductor substrate, sometimes the circuit may be shorted, or the dielectric performance may become lower. Therefore the troubles as described above may occur under some conditions for use thereof or when the semiconductor substrate is used for a long time.
DISCLOSURE OF THE INVENTION
The present invention was made to solve the problems described above, and it is an object to provide a dispersion liquid of silica particles for polishing with a low content of Na ions and also with a specific range of content of ions other than Na ions, a method of producing the dispersion liquid, and a polishing agent comprising the dispersion liquid.
The present invention provides a dispersion liquid of silica particles for polishing with an average particle diameter in the range from 5 to 300 nm, and Na ion content in the silica particle is less than 100 ppm, while content of ions other than Na ions is in the range from 300 ppm to 2 weight %.
The method of producing the dispersion liquid of silica particles for polishing according to the present invention comprises the steps of adding an acidic silicic acid solution into a dispersion liquid of core particles and growing the core particles to obtain a dispersion liquid of silica particles, and the steps are performed to grow the particles under the conditions that a content of Na ions (N
s
) defined by a number of Na ions per square meter of the core particle is less than 50×10
17
pieces/core particle's surface area(m
2
), that a content of ions (N
k
) other than Na ions defined by a number of ions other than Na ions per square meter of the core particle is in the range from 5×10
17
to 2000×10
17
pieces/core particle's surface area(m
2
), and that the ratio of (N
k
)/(N
s
) is 5 or more.
An alkali silicate should preferably be added to the dispersion liquid of core particles before the acidic silicic acid liquid is added thereto.
An polishing agent according to the present invention comprises the dispersion liquid of silica particles.
BEST MODE FOR CARRYING OUT THE INVENTION
Preferable embodiments of the present invention are described below.
1. Dispersion Liquid of Silica Particles for Polishing
A content of Na ions in a silica particle in the dispersion liquid of silica particles for polishing according to the present invention, when calculated as a content of Na in SiO2, is less than 100 ppm, preferably less than 50 ppm, and more preferably less than 20 ppm.
If the Na ion content in a silica particle exceeds 100 ppm, Na remains on a substrate to be polished when the particles are used as a polishing agent, and the residual Na may cause insulation fault or short circuitry in a circuit formed on the semiconductor substrate, which may in turn lower the dielectric constant of a film (insulating film) provided for insulation, and such troubles as increase in impedance, a slower response speed, and increase of power consumption may occur. Further the Na ions may move (disperse) and cause the troubles as described under some specific conditions or when used for a long time.
The silica particle includes ions other than Na ion such as monovalent cations of Li, K, Rb, Cs, NH
4
and others, and bivalent cations of Mg, Ca, Sr, Ba and others. A content of these ions other than those of Na is in the range from 300 ppm to 2 weight %, and preferably in the range from 300 ppm to 1 weight %.
When the content of ions other than Na ions is less than 300 ppm, a quantity of cations on a surface of the silica particle is too small and stability of the silica particle dispersion liquid is poor, which gives some negative effects for such use as the low workability with low cost performance, and even if it is used as a polishing agent or a polishing material, sometimes a sufficient polishing speed can not be obtained. When the content of ions other than Na ions is over 2 weight %, many ions other than Na ions remain on a surface of a substrate and/or an insulating film, and the troubles as described above may occur when it is used for a long time. Of the ions other than Na ions, cations of K, Rb, Cs, and NH
4
each having a larger ion diameter as compared to that of the Na ion are preferable because the ions seldom cause such troubles including insulation fault as described above.
The average particle diameter of the silica particles described above varies according to such factors as the required polishing speed and polishing precision, but it should preferably be in the range from 5 to 300 nm, and more preferably in the range from 10 to 200 nm. When the average particle diameter is less than 5 nm, the silica particle dispersion liquid will generally lack the stability, and further the particle diameter is too small to obtain a sufficient polishing speed. On the other hand, when the average particle diameter exceeds 300 nm, scratches may remain on surfaces of some specific types of substrates or insulating films, and it is impossible to obtain sufficient surface smoothness.
In the dispe
Komatsu Michio
Nishida Hiroyasu
Wakamiya Yoshinori
Watanabe Manabu
Catalysts & Chemicals Industries Co. Ltd.
Kanesaka & Takeuchi
Marcheschi Michael
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