Cleaning agents comprising beta-diketone and beta-ketoimine ligands and a process for using the same

This invention is a residue-free cleaning process for removing metal-containing contaminants from a surface of a substrate of the type used in manufacturing semi-conductor devices. The process comprises contacting the substrate with an effective amount of a cleaning agent comprising a .beta.-diketone or .beta.-ketoimine dispersed in an atmosphere capable of oxidizing the metal-contaminants at a temperature sufficient to form volatile metal-ligand complexes on the surface of the substrate. The volatile metal-ligand complexes are sublimed from the surface of the substrate leaving essentially no residue.

TECHNICAL FIELD 
The present invention relates to cleaning agents comprising an effective 
amount of a .beta.-diketone or .beta.-ketoimine ligand dispersed in an 
oxidizing atmosphere and a process for cleaning metal-containing 
contaminants from the surface of a substrate of the type used in 
manufacturing semi-conductor devices. 
BACKGROUND OF THE INVENTION 
The electronics industry is striving to further miniaturize circuitry while 
increasing the complexity of the same. In order to meet this goal, the 
individual electrical devices such as transistors and resistors and the 
interconnects between such devices must be fabricated on an increasingly 
small scale. As device and interconnect dimensions approach one-half to 
one-quarter of a micron, the cleanliness of the electronic assembly 
impacts performance and reliability. 
Typical contaminants residing on the surface of semi-conductor devices 
include metal oxides and metal halides formed during the fabrication of 
the electronic device and corrosive chlorides deposited on such assemblies 
through various handling operations. These contaminants can weaken or 
embrittle the electrical connectors causing a physical failure and current 
leakages. Consequently, improved cleaning agents and processes for 
cleaning semi-conductor devices during their fabrication are required in 
order to more effectively remove harmful metal-containing contaminants. 
BRIEF SUMMARY OF THE INVENTION 
The present invention relates to cleaning agents comprising an effective 
amount of a .beta.-diketone or .beta.-ketoimine ligand dispersed in an 
oxidizing atmosphere and a process for cleaning metal-containing 
contaminants from the surface of a substrate of the type used in 
manufacturing semi-conductor devices. 
The process for removing metal-containing contaminants from the surface of 
a semi-conductor substrate comprises contacting a portion of the substrate 
to be cleaned with an effective amount of a .beta.-diketone or 
.beta.-ketoimine cleaning agent dispersed in an atmosphere capable of 
oxidizing the metal-containing contaminants at a temperature sufficient to 
form a volatile metal-ligand complex on the surface of the substrate. The 
volatile metal-ligand complex is easily sublimed from the surface of the 
substrate leaving essentially no residue of the cleaning agent on the 
substrate which might later cause problems during subsequent manufacturing 
steps. 
Cleaning agents suitable for removing metal-containing contaminants from 
the surface of the substrates defined herein comprise a .beta.-diketone or 
.beta.-ketoimine represented by the formula: 
##STR1## 
wherein: R.sub.1 and R.sub.3 are independently selected from a linear or 
branched non-fluorinated, partially-fluorinated or fully fluorinated 
alkyl, alkenyl or aryl group having from 1 to about 8 carbon atoms; 
R.sub.2 is a hydrogen atom, a fluorine atom or a linear or branched 
non-fluorinated, partially-fluorinated or fully fluorinated alkyl or 
alkenyl group having from 1 to about 8 carbon atoms; and 
Y is selected from an oxygen atom; N--R.sub.4 wherein R.sub.4 is selected 
from a non-fluorinated, partially fluorinated, or fully fluorinated alkyl, 
aryl, aralkyl or hydroxyalkyl group having from 1 to about 10 carbon 
atoms, or Y is 
##STR2## 
wherein: R.sub.5, R.sub.6 and R.sub.7 are independently selected from a 
hydrogen atom, a fluorine atom or a linear or branched non-fluorinated, 
partially fluorinated or fully fluorinated alkyl or alkenyl group having 
from 1 to about 8 carbon atoms; and 
R.sub.8 is a linear or branched non-fluorinated, partially fluorinated or 
fully fluorinated alkylene, alkenylene, phenylene, alkylphenylene or 
hydroxyalkylene group having from 1 to about 8 carbon atoms; 
wherein the ligand is dispersed in an atmosphere capable of oxidizing the 
metal-containing contaminants to a corresponding metal oxide compound 
which is capable of reacting with the selected .beta.-diketone or 
.beta.-ketoimine to form a volatile metal-ligand complex. 
The above-mentioned Formula I represents three distinct types of ligands 
which are each suitable for practicing the cleaning process of the present 
invention. Each of the three types is characterized by the definition of 
the Y group. When Y is an oxygen atom, the ligand is a .beta.-diketone. 
When Y is N--R.sub.3, the ligand is a .beta.-kitoimine. Finally, when Y is 
represented by the structure according to Formula II, the ligand comprises 
two .beta.-ketoimines bridged by an organic functionality. 
The invention offers numerous advantages over conventional wet-cleaning 
methods because the instant cleaning process can be conducted in-situ, 
meaning that the substrate does not have to be exposed to the clean room 
environment thereby avoiding recontamination via exposure to other 
contaminants. Moreover, the cleaning agents leave essentially no residue 
on the surface of the electronic assembly which might interfere with 
subsequent manufacturing steps. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention relates to cleaning agents and a process for cleaning 
metal-containing contaminants from the surface of a substrate of the type 
used in manufacturing semi-conductor devices. The invention offers 
numerous advantages over conventional wet-cleaning methods because the 
instant cleaning process can be conducted in-situ, meaning that the 
substrate does not have to be exposed to the clean room environment 
thereby avoiding recontamination via exposure to other contaminants. 
Moreover, the cleaning agents leave essentially no residue on the surface 
of the substrate which might interfere with subsequent manufacturing 
steps. 
The cleaning process according to this invention comprises contacting a 
portion of the contaminated substrate with an effective amount of a 
.beta.-diketone or .beta.-ketoimine cleaning agent dispersed in an 
atmosphere capable of oxidizing the metal-containing contaminants at a 
temperature sufficient to form a volatile metal-ligand complex on the 
surface of the substrate. The volatile metal-ligand complex is then 
sublimed from the surface of the substrate. The process substantially 
reduces the amount of metal-containing contaminants residing on the 
substrate's surface which can interfere with the depositing of conducting 
metals, lithographic printing and other operations conducted during the 
process of making semi-conductor devices. 
A broad range of substrates are suitable for practicing the present 
invention and include any substrate having metallic-containing surface 
contaminants wherein the substrate itself does not react with the ligands 
defined herein. Representative substrates include, but are not limited to 
silicon, silicon oxide, borophosphosilicate glass, phosphosilicate glass 
and strontium titanate. 
The instant cleaning process which utilizes the .beta.-diketone and 
.beta.-ketoimine ligands disclosed herein can be used to remove various 
metal-containing contaminants including metal oxides represented by the 
formula MO, MO.sub.2, MO.sub.3, M.sub.2 O and M.sub.2 O.sub.3 and metal 
halides represented by the formula M.sup.+n X.sup.-n, wherein n is 1, 2 or 
3 and X is a halogen selected from Cl, Br or I. 
Cleaning agents suitable for removing the above-mentioned metal-containing 
contaminants from the surface of the enumerated substrates comprise a 
.beta.-diketone or .beta.-ketoimine represented by the formula: 
##STR3## 
wherein: R.sub.1 and R.sub.3 are independently selected from a linear or 
branched non-fluorinated, partially-fluorinated or fully fluorinated 
alkyl, alkenyl or aryl group having from 1 to about 8 carbon atoms; 
R.sub.2 is a hydrogen atom, a fluorine atom or a linear or branched 
non-fluorinated, partially-fluorinated or fully fluorinated alkyl or 
alkenyl group having from 1 to about 8 carbon atoms; and 
Y is selected from an oxygen atom; N--R.sub.4 wherein R.sub.4 is selected 
from a non-fluorinated, partially fluorinated, or fully fluorinated alkyl, 
aryl, aralkyl or hydroxyalkyl group having from 1 to about 10 carbon 
atoms, or Y is 
##STR4## 
wherein: R.sub.5, R.sub.6 and R.sub.7 are independently selected from a 
hydrogen atom, a fluorine atom or a linear or branched non-fluorinated, 
partially fluorinated or fully fluorinated alkyl, alkenyl or aryl group 
having from 1 to about 8 carbon atoms; and 
R.sub.8 is a linear or branched non-fluorinated, partially fluorinated or 
fully fluorinated alkylene, alkenylene, phenylene, alkylphenylene or 
hydroxyalkylene group having from 1 to about 8 carbon atoms. 
wherein the ligand is dispersed in an atmosphere capable of oxidizing the 
metal-containing species. 
Formula III represents three distinct types of ligands which are each 
suitable for practicing the cleaning process of the present invention. 
Each of the three types is characterized by the definition of the Y group. 
When Y is an oxygen atom, the ligand is a .beta.-diketone. When Y is 
N--R.sub.3, the ligand is a .beta.-ketoimine. Finally, when Y is 
represented by the structure according to Formula IIIa, the ligand 
comprises two .beta.-ketoimines bridged by an organic functionality. 
The non-fluorinated, partially fluorinated and fully fluorinated 
.beta.-diketone ligands suitable for use in the present process are 
represented by the formula: 
##STR5## 
wherein: R.sub.1 and R.sub.3 are independently selected from a linear or 
branched non-fluorinated, partially-fluorinated or fully fluorinated 
alkyl, alkenyl or aryl group having from 1 to about 8 carbon atoms; and 
R.sub.2 is a hydrogen atom, a fluorine atom or a linear or branched 
non-fluorinated, partially-fluorinated or fully fluorinated alkyl or 
alkenyl group having from 1 to about 8 carbon atoms. 
In a preferred embodiment according to Formula IV, R.sub.2 is a hydrogen 
atom or a fluorine atom and R.sub.1 and R.sub.3 are independently selected 
from a fully fluorinated linear or branched alkyl group having from 1 to 
about 4 carbon atoms. 
The .beta.-diketones represented by Formula IV are prepared according to 
methods well known in the art. In a preferred embodiment, R.sub.1 and 
R.sub.3 are independently selected from a linear or branched alkyl group 
having from one to about four carbon atoms, each of which can optionally 
be partially or fully fluorinated. Suitable alkyl groups to be fluorinated 
include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl and 
the like. 
The non-fluorinated, partially fluorinated and fully fluorinated 
.beta.-ketoimine ligands of the present invention are represented by the 
Formula: 
##STR6## 
wherein: R.sub.1 and R.sub.3 are independently selected from a linear or 
branched non-fluorinated, partially-fluorinated or fully fluorinated 
alkyl, alkenyl or aryl group having from 1 to about 8 carbon atoms; 
R.sub.2 is a hydrogen atom, a fluorine atom or a linear or branched 
non-fluorinated, partially-fluorinated or fully fluorinated alkyl or 
alkenyl group having from 1 to about 8 carbon atoms; and 
R.sub.4 is selected from a non-fluorinated, partially fluorinated or fully 
fluorinated alkyl, aralkyl or hydroxyalkyl group having from 1 to about 10 
carbon atoms. 
A preferred method for preparing the .beta.-ketoimine ligands disclosed in 
Formula V, particularly the partially or fully fluorinated 
.beta.-ketoimine ligands, is disclosed in U.S. Pat. No. 4,950,790, the 
specification which is specifically incorporated by reference herein. In a 
preferred embodiment, R.sub.1 and R.sub.3 are independently selected from 
a fully fluorinated linear or branched alkyl group having from one to 
about four carbon atoms. Suitable alkyl groups to be fluorinated include 
methyl, ethyl, propyl, isopropyl, butyl, isobutyl and tert-butyl. 
The .beta.-ketoimines are prepared by treating the corresponding 
.beta.-diketone with potassium hydride under conditions sufficient to 
produce the potassium salt of the diketone and subsequently reacting the 
resultant potassium salt of the diketone with a silylchloride such as 
tert-butyldimethylsilylchloride to produce a silylenolether having the 
general formula: 
##STR7## 
wherein: R.sub.9 is a linear or branched alkyl group having from 1 to 
about 4 carbon atoms. The silylenolether described above is then treated 
with a primary monoamine, R.sub.3 NH.sub.2, wherein R.sub.3 is defined 
above, to produce the desired .beta.-ketoimine. 
The non-fluorinated, partially fluorinated and fully fluorinated bridged 
.beta.-ketoimine ligands of the present invention are represented by the 
formula: 
##STR8## 
wherein: R.sub.1 and R.sub.3 are independently selected from a linear or 
branched non-fluorinated, partially-fluorinated or fully fluorinated 
alkyl, alkenyl or aryl group having from 1 to about 8 carbon atoms; 
R.sub.2 is a hydrogen atom, a fluorine atom or a linear or branched 
non-fluorinated, partially-fluorinated or fully fluorinated alkyl or 
alkenyl group having from 1 to about 8 carbon atoms; 
R.sub.5, R.sub.6 and R.sub.7 are independently selected from a hydrogen 
atom, a fluorine atom or a non-fluorinated, partially fluorinated or fully 
fluorinated alkyl or alkenyl group having from 1 to about 8 carbon atoms; 
and 
R.sub.8 is a non-fluorinated, partially fluorinated or fully fluorinated 
linear or branched alkylene, alkenylene, phenylene, alkylphenylene or 
hydroxyalkylene group having from 1 to about 8 carbon atoms. 
In a preferred embodiment, R.sub.1 and R.sub.3 are independently selected 
from a fully fluorinated linear or branched alkyl group having from one to 
about four carbon atoms and R.sub.2 is a hydrogen atom or a fluorine atom. 
Suitable alkyl groups to be fluorinated include methyl, ethyl, propyl, 
isopropyl, butyl, isobutyl and tert-butyl. 
A preferred method for preparing the bridged .beta.-ketoimine ligands 
according to Formula VI is described in U.S. Pat. No. 4,950,790, the 
Specification which is incorporated by reference herein. These ligands are 
prepared by treating the corresponding .beta.-diketone with potassium 
hydride under conditions sufficient to form the potassium salt of the 
diketone and subsequently reacting the resultant 
tert-butyldimethylsilylchloride to produce a silylenolether represented by 
formula Va. 
The silylenolether is then treated with one equivalent of a primary 
diamine, NH.sub.2 R.sub.3 NH.sub.2 wherein R.sub.3 is defined above to 
produce the desired bridged .beta.-ketoimine. In a preferred embodiment, 
R.sub.1 and R.sub.3 are independently selected from a linear or branched 
alkyl group having from one to about four carbon atoms, each of which can 
optionally be partially or fully fluorinated. Suitable alkyl groups 
include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl and 
the like. 
The ligands of the present invention can exist in two tautomeric forms, 
keto and enol, the structure of the enol form which is easily ascertained 
by those skilled in the art. Reference to the keto form of the 
above-mentioned ligands of this invention shall also expressly include the 
corresponding enol form. 
As previously stated, the cleaning process is conducted in an atmosphere 
capable of oxidizing the metal-containing contaminants, which for the 
purpose of interpreting the specification and appended claims, refers to 
any atmosphere which can convert the subject metal-containing contaminants 
to a corresponding metal oxide which is then capable of reacting with the 
subject ligands to form a volatile metal-ligand complex. Suitable 
atmospheres include, by way of example, oxygen gas, zero-grade air (a 
gaseous mixture containing about 19.5 to 23.5 mol percent oxygen and less 
than 0.5 mol percent hydrocarbons, with the remainder comprising nitrogen, 
sold by Air Products and Chemicals, Inc., Allentown, PA), HCl, Br.sub.2, 
Cl.sub.2, HF and the like. Moreover such oxidizing atmospheres may be 
dispersed in carrier gases such as argon, nitrogen, helium and 
perfluorinated hydrocarbons such as Multifluor.RTM. APF-200 
perfluoroisopropyldecalin, which is commercially available from Air 
Products and Chemicals, Inc., Allentown, Pa. 
The cleaning agents according to the present invention can be applied by 
both machine and manual operations known in the art. The particular 
cleaning agent to be utilized and the appropriate oxidizing atmosphere for 
delivering the cleaning agents to the substrates to be cleaned will depend 
upon numerous factors including the properties of the semi-conductor 
device, the type of metal-containing contaminants to be removed from the 
substrate's surface and the like. 
In order to more fully describe the practice of the present process, a 
general embodiment of the instant process for cleaning the previously 
defined substrates will be discussed. The substrate is placed into an 
infrared furnace, vapor phase machine or other suitable furnace typically 
used in cleaning processes known in the art and heated to the desired 
temperature, typically from about 200.degree. to 300.degree. C. The 
desired .beta.-diketone or .beta.-ketoimine dispersed in the desired 
oxidizing atmosphere (for example, zero-grade air) are passed into the hot 
zone of the selected furnace by conventional techniques. 
The ligand-saturated oxidizing atmospheric stream may be continuously or 
intermittently delivered into the furnace. The process can be conducted in 
one or two stages. For example the metal-containing contaminants may be 
initially oxidized by subjecting the substrate to the defined oxidizing 
atmosphere followed by treating the substrate with the desired cleaning 
agent at a later time. Alternately, the process may be conducted in one 
stage wherein the metal oxides are formed in-situ followed by the 
immediate reaction of the ligands according to the present invention with 
metal oxides and metal halides residing on the substrate's surface to form 
volatile metal-ligand complexes which are then conveniently sublimed from 
the surface to provide a substrate which is substantially residue free. 
The .beta.-diketone ligands have been experimentally shown to react with 
commonly occurring oxides (CuO, Cu.sub.2 O, PbO, SnO and the like) 
typically residing on the surface of the defined substrates. The resultant 
reaction products have been analytically identified as Cu(HFac).sub.2, 
Pb(HFac).sub.2 and Sn(HFac).sub.2, respectively. Such products are 
sufficiently volatile such that following sublimation, essentially no 
residue remains on the substrate. 
The desired cleaning agent should contain an amount of ligand dispersed in 
an oxidizing atmosphere such that maximum cleaning activity is obtained. 
The term, effective amount, refers to that amount of ligand which provides 
a sufficient amount of cleaning to satisfy the desired application. The 
optimum concentration will vary depending upon the particular cleaning 
ligand used and the metal-containing compounds to be cleaned from the 
surface of the substrate. Typical concentrations range from 1.0% to about 
40.0%, and preferably, from 5.0% to 25.0% of the desired ligand dispersed 
in an oxidizing atmosphere. If the ligand concentration in the oxidizing 
atmosphere is less than about 4.6%, a decreased cleaning action may occur. 
The process can be practiced at temperatures comensurate with those used in 
conventional cleaning processes. Typical temperatures for practicing the 
process range from about 200.degree. to 230.degree. C. The optimum 
reaction time and temperature for practicing the process will vary 
depending upon the particular ligand used, the type and quantity of 
contaminants to be removed and the like. Typical processing time ranges 
from about 5 to 50 minutes. Shorter process times (i.e., &lt;5 minutes) have 
been found to decrease cleaning effectiveness. Furnace pressure typically 
ranges from about 0 to 1.5 psig although the pressure is not critical to 
the practice of the invention. 
The following example is provided to further illustrate an embodiment of 
the present invention and is not intended to restrict the scope of the 
invention. In the following example, temperatures are set forth 
uncorrected in degrees Celsius.

EXAMPLE 
Cleaning Of A Silicon Wafer With Hexafluoroacetylacetone 
A silicon wafer was analyzed by X-Ray fluorescence and Rutherford 
Back-Scattering to determine the amount of gold-, copper-, iron-, 
indium-and chloride-containing contaminants residing on the substrate's 
surface. The wafer was placed at a 30 degree angle in a pyrex.RTM. wafer 
boat. Filtered zero-grade oxygen was bubbled through unpurified 
1,1,1,5,5,5-hexafluoro-2,4-pentanedione, having the common name, 
hexafluoroacetylacetone, referred to herein as HFac (Strem Chemicals, Inc. 
Newburtport) at a rate of 83 sccm or 16.5% HFac in the process stream. The 
silicon wafer was contacted with HFac and heated to 205.degree. C. for 40 
minutes. The results presented in the sole Table demonstrate that the 
cleaning process is extremely effective in removing copper-, iron-, 
chloride- and indium-containing contaminants from the substrate's surface. 
The process demonstrates marginal success in removing gold-containing 
contaminants from the surface. 
Representative ligands suitable for use in the present invention are 
disclosed below wherein the chemical structure and both the IU and 
abbreviated names of the ligands are provided. 
##STR9## 
The present vapor-phase process for cleaning metal-containing contaminants 
from the surface of substrates of the type used in manufacturing 
semi-conductor devices offers numerous advantages over typical wet 
cleaning methods known in the art because the instant cleaning process can 
be conducted in-situ, meaning that the substrate does not have to be 
exposed to the clean room environment thereby avoiding recontamination via 
exposure to other contaminants. Moreover, the cleaning agents leave 
essentially no residue on the surface of the electronic assembly which 
might later interfere with subsequent manufacturing steps. 
Having thus described the present invention, what is now deemed appropriate 
for Letters Patent is set out in the following appended claims.