Selective removal of etching residues

Etching residue is selectively removed employing a substantially non-aqueous composition containing a fluoride containing compound and certain organic solvents. Preferred compositions also include an anhydride.

TECHNICAL FIELD 
The present invention is concerned with selectively removing etching 
residues from a substrate and particularly selectively removing residues 
without attacking metal also exposed to the composition used for removing 
the residues. In addition, the present invention is concerned with certain 
cleaning compositions that are suitable for removing etching residues. 
BACKGROUND ART 
In the fabrication of microelectronic components, a number of the steps 
involved, for instance, in preparing integrated circuit chips and the 
packaging for the chips (articles to which the chips are attached and 
protected), are etching processes. Accordingly, over the years, a number 
of vastly different types of etching processes to remove material, 
sometimes in selective areas, have been developed and are utilized to 
varying degrees. Moreover, the steps of etching different layers which 
constitute, for instance, the finished integrated circuit chip are among 
the most critical and crucial steps. 
Increasingly, reactive ion etching (RIE), plasma etching and ion milling 
are being used to define the pattern in a substrate and to form vias. For 
instance, in complex semiconductor devices such as advanced DRAMS and 
logic devices with multiple layers of back end of line interconnect 
wiring, reactive ion etching is used to produce vias through the 
interlayer dielectric to provide contact between one level of silicon, 
silicide or metal wiring to the next level of wiring. These vias typically 
expose Al, AlCu, Cu, Ti, TiN, Ta, TaN, silicon or a silicide such as a 
silicide of tungsten, titanium or cobalt. The RIE process leaves a residue 
of a complex mixture that may include re-sputtered oxide material and 
possibly small amounts of organic material from the resists used to 
delineate the vias. 
It would therefore be desirable to provide a selective cleaning procedure 
capable of removing the residues caused by the etching and especially a 
plasma, RIE or ion milling etching. Moreover, it would be desirable to 
provide a selective cleaning procedure capable of removing the etching 
residue that exhibits high selectivity for the residue as compared to 
metal, silicon, silicide and/or interlevel dielectric materials such as 
deposited oxides that might also be exposed to the cleaning composition. 
SUMMARY OF INVENTION 
The present invention is concerned with a method for selectively removing 
etching residues. The process of the present invention comprises 
contacting an article that contains etching residues and metal, silicon, 
silicate and/or interlevel dielectric materials with a cleaning 
composition that contains about 0.05 to about 3 molar of a fluoride 
containing compound and an organic solvent to thereby selectively remove 
the etching residue at a rate greater than the rate for the metal, 
silicon, silicide and/or interlevel dielectric materials. 
In addition, the present invention is concerned with certain preferred 
cleaning compositions that are capable of selectively removing etching 
residues at a rate greater than the rate for the metal, silicon, silicide 
and/or interlevel dielectric materials. The preferred compositions of the 
present invention contain about 0.05 to about 3 molar of a fluoride 
containing compound and an organic solvent. 
The organic solvents employed in the present invention typically have 
relatively high flash point and provide low viscosity compositions. 
Suitable solvents include sulfolanes, oxolanes, esters, ketones, 
aldehydes, lactones, halogenated hydrocarbons, alcohols including mono- 
and polyhydric alcohols, amines and imides. 
Other objects and advantages of the present invention will become readily 
apparent to those skilled in this art from the following detailed 
description, wherein it is shown and described only the preferred 
embodiments of the invention, simply by way of illustration of the best 
mode contemplated of carrying out the invention. As will be realized, the 
invention is capable of other and different embodiments, and its several 
details are capable of modifications in various obvious respects, without 
departing from the invention. Accordingly, the drawings and description 
are to be regarded as illustrative in nature and not as restrictive. 
BEST AND VARIOUS MODES FOR CARRYING OUT INVENTION 
The present invention is concerned with selectively removing etching 
residues and especially residues caused by forming vias by reactive ion 
etching. Moreover, the etching residues are present in an article that 
also includes metal, silicon, silicate and/or interlevel dielectric 
material such as deposited silicon oxides, wherein both the residues and 
the metal, silicon, silicide and/or interlevel dielectric materials will 
come in contact with the cleaning composition. The present invention 
provides for selectively removing the residues at a rate of at least about 
100 times, preferably at least about 250 and most preferably at least 
about 500 times the rate for the metal, silicon, silicide and interlevel 
dielectric materials. The metal is typically copper, copper alloy, 
titanium, titanium nitride, tantalum, tantalum nitride, aluminum and/or 
aluminum alloy. The residues removed according to the present invention 
are preferably those created by reactive ion etching of vias. 
The cleaning compositions employed pursuant to the present invention are 
preferably non-aqueous and contain a compound containing fluoride and an 
organic solvent. The amount of the fluoride containing compound in the 
composition is about 0.05 to about 3 molar, and preferably about 0.2 to 
about 2.5 molar, and most preferably about 0.25 to about 1.5 molar. 
Typical compounds providing a fluoride source according to the present 
invention are hydrofluoric acid, ammonium fluoride, fluoroborates, 
fluoroboric acid, tin bifluoride, antimony fluoride, tetrabutylammonium 
tetrafluoroborate, and aluminum hexafluoride. Also, a fluoride salt of an 
aliphatic primary, secondary or tertiary amine can be used. Such have the 
following formula: 
EQU R.sub.1 N(R.sub.3)R.sub.2 
wherein R.sub.1, R.sub.2 and R.sub.3 each individually represents H or an 
alkyl group. 
Typically, the total number of carbon atoms in the R.sub.1, R.sub.2 and 
R.sub.3 groups is 12 carbon atoms or less. The preferred fluoride 
compounds are hydrogen fluoride and ammonium fluoride. 
The hydrogen fluoride is typically added as a 49 weight percent aqueous 
solution. When the fluoride is added as an aqueous composition, it is 
preferred to add a component capable of rendering the composition at least 
substantially non-aqueous. Substantially non-aqueous refers to non-aqueous 
as well as containing water of up to 20 and preferably up to 3% by weight 
of the fluoride content. Such component is referred to herein as a 
dehydrating agent. Suitable dehydrating agents are alkyl anhydrides and 
aryl anhydrides. The alkyl group typically contains 1-8 carbon atoms and 
the aryl group typically contains 6-9 carbon atoms in the ring. The aryl 
groups can be substituted on the ring with an alkyl group containing 1-8 
carbon atoms. Typical anhydrides are acetic anhydride, benzyl anhydride, 
phenyl anhydride. Of course the dehydrating agent must not adversely 
affect to an undesirable extent the cleaning ability characteristics of 
the composition. 
Typically, the amount of the anhydride is at least one anhydride group 
(O.dbd.COC.dbd.O) per H.sub.2 O molecule, and preferably at least about a 
5% excess and more preferably at least about 10% excess of one anhydride 
group per H.sub.2 O molecule. Usually the excess will not be greater than 
about 25%. However, when a small amount of water can be tolerated 
(i.e.--0.1 to 20% and more typically 0.1 to 3% by weight based upon the 
weight of the fluoride content), the anhydride will be used in an amount 
less than one anhydride group per H.sub.2 O molecule to correspond to the 
small amount of water. 
In the alternative, the cleaning composition can be produced by adding the 
fluoride as a non-aqueous component such as by bubbling anhydrous HF gas 
into an organic solvent or by adding an organic fluoride. Also, the 
anhydrous compositions can be prepared by admixing an aqueous solution of 
the fluoride compound with the organic solvent and then heating the 
composition to evaporate water. 
Examples of suitable organic compounds include oxolanes, sulfolanes, 
esters, ketones, aldehydes, lactones, halogenated solvents, amines, imides 
and alcohols. Examples of suitable esters are esters of carbonic acids, 
benzoic acid, phthalic acid, isophthalic acid and terephthalic acid, and 
especially the C.sub.1 -C.sub.6 alkyl esters. Preferred organic solvents 
are propylene carbonate, N-methyl pyrrolidone, gamma butyrolactone, 
methylene chloride, benzyl alcohol, N-formyl morpholine, N-formyl 
piperidine, cyclohexanone, cyclopentanone, methyl benzoate, diglyme, 
2-methyl tetrahydrofuran, and methyl and ethyl esters of phthalic, 
isophthalic or terephthalic acids. The more preferred solvents employed 
pursuant to the present invention are propylene carbonate, 
N-methylpyrrolidone and gamma butyrolactone, ethylene glycol and propylene 
glycol with propylene carbonate being the most preferred. 
Organic solvents employed in the present invention provide for low 
viscosity compositions, which in turn render the compositions more 
workable and providing for better etch uniformity. This is especially so 
when compared to using glycerol. 
In addition, the compositions can include a tertiary amine to facilitate 
removing any photoresist residue that might be remaining after the 
etching. Typical examples are represented by the formula R.sub.4 
N(R.sub.5)R.sub.6 wherein each individually represents alkyl, aryl, 
alkaryl, aralkyl and substituted derivatives such as those containing one 
or more hydroxyl or anhydride groups. The alkyl groups typically contain 
1-12 carbon atoms and the aryl groups typically contain 6-14 carbon atoms. 
Typical tertiary amines are N N,N',N'-tetramethyl ethylenediamine and 
triethanol amine. When present, the tertiary amine is typically present in 
amounts of about 0.05 to about 5 volume percent, and more typically about 
1 to about 3 volume percent. 
The cleaning process of the present invention is typically carried out at 
temperatures of about 20.degree. C. to about 90.degree. C., and preferably 
about 30.degree. C. to about 70.degree. C. Employing increased temperature 
results in increasing the removal rates of the residues but not 
necessarily the rates for the metal, silicon, silicide and interlevel 
dielectric material, thereby increasing the selectivity of removing the 
residues. 
The following non-limiting examples are presented to further illustrate the 
present invention.

EXAMPLE 1 
A cleaning composition is prepared by admixing one part by volume of a 49 
percent by weight aqueous solution of HF with about 28 parts by volume of 
propylene carbonate to provide a 1 molar HF solution in propylene 
carbonate; and acetic anhydride in an amount to provide about 1.5 molar 
solution of the acetic anhydride. A patterned silicon wafer containing 
vias formed by reactive ion etching (RIE) through interlevel dielectric of 
silicon dioxide where the vias expose aluminum conductive units, is 
immersed in the cleaning composition. The cleaning is carried out at a 
temperature of about 35.degree. C. for about 4 minutes. The cleaning 
solution removes the RIE residues without removing any of the aluminum. 
In this disclosure, there are shown and described only the preferred 
embodiments of the invention, but as aforementioned, it is to be 
understood that the invention is capable of use in various other 
combinations and environments and is capable of changes or modifications 
within the scope of the inventive concept as expressed herein.