Method of chemical mechanical polishing aluminum containing metal layers and slurry for chemical mechanical polishing

A semiconductor processing method of chemical mechanical polishing an aluminum containing metal layer on a semiconductor substrate includes, a) providing a chemical mechanical polishing slurry comprising H.sub.3 PO.sub.4 at from about 0.1% to about 20% by volume; H.sub.2 O.sub.2 at from about 1% to about 30% by volume, H.sub.2 O, and a solid abrasive material; and b) chemical mechanical polishing an aluminum containing metal layer on a semiconductor substrate with the slurry. Such process and slurry are also usable in chemical mechanical polishing of other layers, such as Ti, TiN and TiW materials. Such enables chemical mechanical polishing of a barrier metal/aluminum layer composite in a single polishing step, leading to increased controllability and resulting increased throughput. With respect to aluminum containing metal layers, the H.sub.2 O.sub.2 is understood to cause oxidation to aluminum oxide, which is subsequently removed by both chemical and mechanical action the result of the polish and slurry. Oxidizing agents other than H.sub.2 O.sub.2 are contemplated.

TECHNICAL FIELD 
This invention relates to methods of chemical mechanical polishing aluminum 
containing metal layers and to slurries used in chemical mechanical 
polishing. 
BACKGROUND OF THE INVENTION 
Metal films are used in semiconductor technology to wire together various 
components formed on a semiconductor wafer. Metal in semiconductor 
processing can also be used to function as gate electrodes in MOS 
structures, and as electrodes in thin film capacitors. Elemental aluminum 
and its alloys have been the traditional metals utilized. Aluminum has 
emerged as the most important material for such applications because of 
its low resistivity, superior adhesion to SiO.sub.2, ease of patterning, 
and high purity. 
One technique of metal wiring comprises the patterning and etching of a 
trough and contact within a thick layer of insulating material, such as 
SiO.sub.2. Thereafter, a thin layer of a barrier metal, such Ti, TiW or 
TiN, is provided atop the insulating layer and within the trough and 
contacts which leads to electrical connection sites which are 
elevationally lower within the wafer. The barrier metal functions to 
separate silicon from aluminum which will be deposited subsequently. After 
barrier metal deposition, a layer of elemental aluminum or an aluminum 
alloy is deposited to completely fill the trough and contacts. The trough, 
which was created prior to metal deposition, defines the desired metal 
patterning such that a planar metal removing technique down to the surface 
of the insulating layer will leave remaining desired patterned 
electrically conductive metal lines. 
One such planarizing technique is chemical mechanical polishing. When 
chemical mechanical polishing is used to form metal lines by the above 
technique, it is referred to as a damascene process. However to date, 
chemical mechanical polishing of aluminum and its alloys has not been well 
understood or developed. Accordingly, a need remains for improved chemical 
mechanical polishing techniques and chemical mechanical polishing slurries 
for aluminum and its alloys, as well as other materials.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
This disclosure of the invention is submitted in furtherance of the 
constitutional purposes of the U.S. Patent Laws "to promote the progress 
of science and useful arts" (Article 1, Section 8). 
In accordance with one aspect of the invention, a semiconductor processing 
method of chemical mechanical polishing an aluminum containing metal layer 
on a semiconductor substrate comprises: 
providing a chemical mechanical polishing slurry comprising H.sub.3 
PO.sub.4 at from about 0.1% to about 20% by volume; H.sub.2 O.sub.2 at 
from about 1% to about 30% by volume, H.sub.2 O, and a solid abrasive 
material; and 
chemical mechanical polishing an aluminum containing metal layer on a 
semiconductor substrate with the slurry. 
In accordance with another aspect of the invention, a chemical mechanical 
polishing slurry for polishing an aluminum containing metal layer 
comprises: 
H.sub.3 PO.sub.4 at from about 0.1% to about 20% by volume; H.sub.2 O.sub.2 
at from about 1% to about 30% by volume, H.sub.2 O, and a solid abrasive 
material. 
Such slurry material has also been discovered to facilitate chemical 
mechanical polishing of titanium containing layers, such as elemental 
titanium or TiN, and is expected to be utilizable in chemical mechanical 
polishing of still other materials. Preferably, the concentrations of 
H.sub.2 O.sub.2 and H.sub.3 PO.sub.4 in the slurry are from about 3% to 
about 9% by volume, and from about 3% to about 10% by volume, 
respectively. Also preferably, the H.sub.3 PO.sub.4 is present at less 
than 6% by volume of the mixed slurry to minimize noxious fumes. Any 
suitable chemical mechanical polishing abrasive particles could be 
utilized in the slurry, such as alumina, silica or a titanium oxide. 
The disclosed and claimed chemical mechanical polishing processes and 
slurry are understood to differ, at least in part, from other such 
processes and slurries in the combination of H.sub.2 O.sub.2 and 
phosphoric acid. Such facilitates a planar removal mechanism of the metal 
which is understood to occur chemical in a chemical mechanical polishing 
technique as follows: 
EQU 2Al+3H.sub.2 O.sub.2 .fwdarw.Al.sub.2 O.sub.3 +3H.sub.2 
O.fwdarw.2Al(OH).sub.3 2Al(OH).sub.3 +3H.sub.2 
O.fwdarw.2Al(OH.sub.2).sub.3 (OH).sub.3 
EQU 2Al(OH.sub.2).sub.3 (OH).sub.3 +H.sub.3 PO.sub.4 .fwdarw.[Al(H.sub.2 
O).sub.6 ].sup.+++ PO.sub.4 .quadbond.[Al(H.sub.2 O).sub.6 ].sup.+++ 
PO.sub.4 .quadbond..fwdarw.AlPO.sub.4 +6H.sub.2 O 
Hydrogen peroxide is understood to oxidize aluminum to a solid layer of 
Al.sub.2 O.sub.3. This oxidized layer is then both chemically and 
mechanically removed by the combined action of, a) mechanical polishing, 
and b) phosphoric acid etching illustrated by the above equations which 
ultimately forms aqueous soluble AlPO.sub.4. The above equations would 
seemingly indicate that H.sub.2 O.sub.2 would be a good chemical etchant 
for aluminum, but this was not found to be so. Utilization of H.sub.2 
O.sub.2 alone or in the composition of the described and claimed slurry 
results in no appreciable removal of metal, absent the chemical mechanical 
polishing action. 
It is well known that aluminum is a very soft material, and that scratches 
are easily generated on aluminum films during conventional, prior art 
chemical mechanical polishing processes. The formation of Al.sub.2 O.sub.3 
by the above reaction results in a material which is significantly harder 
than aluminum, and thereby substantially reduces or eliminates the amount 
of scratches which otherwise might be generated by a chemical mechanical 
polishing process. 
Oxidizing agents other than H.sub.2 O.sub.2 would also be useable in 
chemical mechanical polishing of an aluminum containing metal layer by the 
above oxide formation and removal technique. Accordingly in another 
aspect, the invention includes a semiconductor processing method of 
chemical mechanical polishing an aluminum containing metal layer on a 
semiconductor substrate comprising the following steps: 
providing a chemical mechanical polishing slurry comprising H.sub.3 
PO.sub.4 at from about 0.1% to about 20% by volume; an oxidizing agent 
capable of oxidizing aluminum to aluminum oxide; H.sub.2 O; and a solid 
abrasive material; 
applying the slurry onto an aluminum containing metal layer on a 
semiconductor substrate; 
polishing the aluminum containing metal layer having the applied slurry; 
reacting the aluminum of the metal layer with the oxidizing agent of the 
slurry to form aluminum oxide; and 
chemically and mechanically removing aluminum oxide from the wafer with the 
slurry and polishing action. 
The invention was reduced to practice utilizing a commercial H.sub.3 
PO.sub.4 etching solution which comprised sixteen parts H.sub.3 PO.sub.4, 
and one part each of HNO.sub.3, CH.sub.3 COOH and deionized water, by 
volume. This material was combined with water and alumina abrasive 
particles of a concentration of 2 gm/l to produce a 3.4% H.sub.3 PO.sub.4 
solution, by volume, slurry. A damascene construction filled and covered 
with an aluminum alloy of Al-Si(1%)-Cu(0.5%) was chemical mechanical 
polished on a polishing pad with such slurry, and resulted in a polishing 
rate from 0.5 to 0.9 K.ANG./min. Under the same conditions, but utilizing 
the same solution with 6% H.sub.2 O.sub.2 by volume substituted in place 
of an equivalent amount of H.sub.2 O, the polishing rate was significantly 
increased for 2.0 to 3.0 K.ANG./min., and as well resulted in a scratch 
free polished Al-Si(1%)-Cu(0.5%) surface. 
Such slurry has also been discovered to be utilizable in chemical 
mechanical polishing Ti and TiN layers at a significantly faster rate than 
where no H.sub.2 O.sub.2 is present. Specifically, chemical mechanical 
polishing of Ti and TiN layers without H.sub.2 O.sub.2 resulted in removal 
rates of 200 to 500 .ANG./min. When H.sub.2 O.sub.2 was added to the same 
slurry and polishing was conducted under the same conditions, the removal 
rate increased to 1000 to 2000 .ANG./min. Accordingly, the described 
slurry enables a composite layer of elemental aluminum or an aluminum 
alloy and underlying barrier layer to be chemical mechanical polished 
within a single chemical mechanical polishing step, whereas most prior art 
processes would require multiple process steps for complete removal of the 
aluminum and barrier metal from the underlying insulating material. 
In such a preferred process, the contact/vias and interconnect troughs 
would fir be etched into SiO.sub.2, typically using a reactive ion etch. 
Thereafter, a barrier layer of Ti, TiN or TiW would be provided, such as 
by using a sputtering or chemical vapor deposition technique. Thereafter, 
an aluminum alloy, such as Al-Si(1%)-Cu(0.5%) or others, would be 
deposited, such as by chemical vapor deposition or sputtering. The subject 
slurry would then be utilized to chemical mechanical polish the alloy and 
barrier metal layer composite in a single step. 
The utilization of H.sub.2 O.sub.2 in the above-described manner for the 
barrier layer increases its polishing rate over that using H.sub.3 
PO.sub.4 alone to be very close to the chemical mechanical polishing rate 
of the aluminum alloy. Such results in enhanced controllability by 
minimizing or reducing the over polishing time required for clearing up 
any metal residue, thus improving throughput on the process. For example, 
with the described slurry, a 10,000 Angstrom (1 micron) thick aluminum 
layer can be completely polished in less than four minutes, thus 
increasing throughput. Utilizing an H.sub.3 PO.sub.4 acid slurry alone, 
throughput was determined to only be six wafers per hour. Yet with the new 
process and slurry, the throughput was improved to 12 to 20 wafers per 
hours. 
In compliance with the statute, the invention has been described in 
language more or less specific as to structural and methodical features. 
It is to be understood, however, that the invention is not limited to the 
specific features described, since the means herein disclosed comprise 
preferred forms of putting the invention into effect. The invention is, 
therefore, claimed in any of its forms or modifications within the proper 
scope of the appended claims appropriately interpreted in accordance with 
the doctrine of equivalents.