Compositions – Etching or brightening compositions
Reexamination Certificate
1999-05-18
2002-11-05
Utech, Benjamin L. (Department: 1765)
Compositions
Etching or brightening compositions
C252S079200, C438S692000, C438S693000
Reexamination Certificate
active
06475407
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polishing composition for selectively polishing a metal film on a semiconductor wafer and a polishing method of using the composition.
2. Description of the Related Art
A typical semiconductor wafer comprises a substrate such as a silicon or gallium arsenide wafer, and a plurality of integrated circuits are formed on the substrate. The integrated circuits are chemically or physically integrated on the substrate by patterning the regions in the substrate and layers on the substrate. The layers are generally formed of a material having any one of a conductivity, an insulating property and a semiconducting property. In order to obtain semiconductor devices at a high yield, it is very important to start from a flat semiconductor wafer. To this purpose, the surface or a certain part of the semiconductor wafer must be often polished.
According to the surface formation by conventional techniques, the upper surface of the wafer is disadvantageously left to have a topography still in a very irregular state such that upheavals, uneven height regions, troughs, trenches and other similar surface irregularities are present. Therefore, the surface must be planalized overall so as to ensure a sufficiently large depth of focus in photolithography and to remove the irregularity and surface defects during various steps in the production process. For attaining flatness on the wafer surface, several polishing methods are known and a chemical/mechanical planalization or polishing (CMP) is used over a wide range in the treatment for rendering the wafer surface flat during various steps in the production of a device, so that the yield, performance and reliability can be improved.
The slurry used for this chemical/mechanical polishing is formed from an acidic or basic solution containing abrasive grains such as silica, alumina, zirconia, ceria or titania.
The CMP technique is essential in the production process of a semiconductor device, particularly in the planalization of an interlayer insulating film for the formation of a multi-layer interconnection, in the formation of a conductive plug which is a metal, or in the formation of flush wiring.
With respect to the slurry for CMP used in the formation of a conductive plug which is a metal film comprising tungsten, aluminum, copper, titanium or an alloy thereof, JP-A-8-83780 (the term “JP-A” as used herein means an “unexamined published Japanese patent application (Kokai)”) discloses an abrasive composition containing a polishing accelerator such as an aminoacetic acid and/or amidosulfuric acid or an oxidizing agent, and a chemical reagent such as benzotriazole, and JP-A-8-197414 discloses a slurry containing a metal oxide particle such as fumed silica or fumed alumina having specific properties.
Conventional slurries for polishing a metal film of a semiconductor device are disadvantageous in that both the polishing rate for a metal film and the ratio (selection ratio) of the polishing rate for a metal film to the polishing rate for an oxide film (insulting layer) such as silica cannot be increased or, even if the polishing rate is high, a large number of scratches are generated on the polished surface.
The object of the present invention is to provide a slurry composition for polishing a metal film on a semiconductor substrate, which ensures a high polishing rate for a metal film, a high selection ratio, and reduction in the generation of scratches on the polished surface, as well as a method for polishing using the above composition.
SUMMARY OF THE INVENTION
As a result of extensive studies to achieve the above-described object, the present inventor has made the present invention.
More specifically, the present invention provides a slurry composition for polishing a metal film on a semiconductor substrate, comprising alumina-type fine particles containing or not containing alumina hydrate, a polishing accelerator and water, the alumina-type fine particles having an a conversion ratio of from 65 to 90% and a specific surface area of from 30 to 80 m
2
/g.
By the present invention, the polishing work can be favored with a high polishing rate for a metal film, particularly a high selection ratio, and reduction in scratches on the polished surface.
DETAILED DESCRIPTION OF THE INVENTION
The alumina-type fine particles containing or not containing an alumina hydrate for use in the present invention are described below.
The alumina-type fine particles can be produced by preparing an alumina sol, forming it into a gel while heating, subjecting the gel to calcination and then firing, and crushing the fired powder in a medium stirring-type grinding machine.
To speak more specifically, a sol-form aqueous solution of a commercially available pseudo boehmite is prepared in a concentration of from 2 to 60 wt % using an inorganic acid such as nitric acid, or an organic acid, or the like. The amount of peptizer added is preferably on the order of from 1×10
−2
to 10
−5
mol/g, and the pH of the solid is preferably on the order of from 3 to 4.
If the amount of the peptizer added is less than 1×10
−5
mol/g, the peptization does not proceed satisfactorily and the fine particles after firing are deteriorated in their properties, whereas if the added amount is excessively large, the sol is abruptly gelled and the fired fine particles are also disadvantageously deteriorated in their properties.
The thus-prepared sol is dried to reduce the water content and is thereby formed into a dry gel. The gel obtained is calcined at from 500 to 800° C. for about 1 hour and then preferably, crashed to have a gain size of about 1 mm or less.
After the calcination, the gel is fired at from 1,000 to 1,600° C., preferably at from 1,100 to 1,300° C., for from 1 to 3 hours. If the firing temperature is less than 1,000° C., the &agr;-alumina conversion ratio is low and for elevating the ratio, a long period of time is necessary, whereas if it exceeds 1,600° C., the fired fine particles may be disadvantageously sintered.
After the firing, the fine particles are preferably wet-treated by crushing or cracking in an ordinary manner, such as pot milling, to have a maximum particle size of 100 &mgr;m or less.
Thereafter, the fine particles are further pulverized by a medium stirring-type grinding machine such as an attritor, a bead mill, a Dynomill, an apex mill or a co-ball mill.
The conditions for the treatment in a medium stirring-type grinding machine are as follows.
(1)
Rotation number:
from 1,000 to 2,000 rpm
(2)
Pulverization time:
from 2 to 24 hours
(3)
Sample concentration:
from 25 to 65 wt %
(4)
Sample amount:
from 1 to 50 times the
mill capacity
(5)
Grinding medium:
(a)
sintered zirconia,
alumina or silicon
nitride ball
(b)
ball size:
from 0.5 to 3 mm&phgr;
(c)
ball amount:
from 70 to 80% of the
mill capacity.
The fine particles obtained by the above-described production process are a mixture of alumina and alumina hydroxide, more specifically, a mixture of &agr;-alumina and an intermediate alumina showing a peak at 2&thgr;=67.3° at the measurement by X-ray diffraction (Cu and K&agr; rays), or alumina-type fine particles containing bayerite in addition to those aluminas.
The alumina-type fine particles have the following properties.
When a peak height (a) at 2&thgr;=68.2° corresponding to a-alumina and a peak height (b) at 2&thgr;=67.3° corresponding to an intermediate alumina are determined by X-ray diffraction measurement with Cu and Ka rays, the value according to the following expression, namely, the a conversion ratio is from 65 to 90%.
a
conversion
ratio
(
%
)
=
a
a
+
b
×
100
The alumina-type fine particles have a BET specific surface area of from 30 to 80 m
2
/g.
The alumina-type fine particles preferably have a maximum grain size of 1.0 &mgr;m or less, more preferably 0.5 &mgr;m. If the maximum grain size exceeds 1.0 &mgr;m, scratches increase on the metal film or insulating film an
Brown Charlotte A.
Showa Denko K.K.
Utech Benjamin L.
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