Fluorine assisted stripping and residue removal in sapphire downstream plasma asher

A method for removing material from a substrate. A plasma is generated in a plasma generating and discharge device including a sapphire plasma tube. At least one fluorine-containing compound is introduced into the plasma. A forming gas is introduced into the plasma. The plasma is directed toward the material to be removed from the substrate.

FIELD OF THE INVENTION 
The invention relates to a method and apparatus for removing materials from 
a substrate. In particular, the present invention relates to removing 
materials from substrates in semiconductor manufacturing processes. 
BACKGROUND OF THE INVENTION 
Several steps in the manufacture of semiconductor devices require the 
removal of photoresist (PR) and other materials from substrates. The 
"removal" of PR is synonymous with "ash," "burn," "strip," and "clean." 
One example of a substance that may be removed is a residue that may 
remain on a silicon wafer after an etching step is completed. Such residue 
is frequently composed of a polymeric material that may be present in the 
form of "veils" and is caused by over etching during etch processes. 
One way to remove PR and other materials such as those described above is 
by directing a plasma stream at the substrate with the attached substance. 
In some cases, the substance is removed from the substrate by the 
"afterglow" of the plasma rather than the plasma itself. 
One gas that may be used in generating the plasma to strip the substrates 
is oxygen. In order to increase the effectiveness and/or efficiency of 
processes for removing materials from a substrate, a source of fluorine 
may be added to the oxygen. 
A problem inherent in utilizing a fluorine-containing substance is 
degradation of the plasma generating/discharge device by the fluorine. For 
example, plasma generating and discharge devices typically include a tube 
through which the plasma flows. Microwave or radio-frequency energy is 
introduced into the tube to excite the gas and form the plasma. Typically, 
the tube is made of quartz. It was observed that fluorine was particularly 
destructive to the quartz tubes. Therefore, quartz tubes were replaced by 
sapphire tubes in order to overcome the corrosive effects of fluorine. 
Although the sapphire plasma discharge tube included in the plasma 
generating and discharge devices overcame the significant degradation of 
the quartz tubes, ash rates of photoresist utilizing the sapphire tube 
were markedly lower than ash rates observed when utilizing the quartz 
tubes. 
One reason for the decreased efficiency of ash by an oxygen plasma 
generated with a plasma generating and discharge device that includes a 
sapphire tube is that oxygen atoms in the plasma may be lost at the 
surface of the sapphire to a much greater degree than at the surface of 
the quartz. 
SUMMARY OF THE INVENTION 
The present invention was developed through efforts to overcome the 
above-described as well as other problems. 
Accordingly, one object of the present invention is to provide a method and 
apparatus that reduces the recombination/loss rate of oxygen atoms on the 
surface of a sapphire tube in a plasma generating and discharge device 
and, hence, increases the effectiveness/efficiency of standard ashing 
processes. 
An additional object of the present invention is to provide a method and 
apparatus for removing materials from a substrate utilizing an oxygen 
plasma with at least one added fluorine-containing compound while 
maintaining minimal oxide loss. 
A further object of the present invention is to provide a method and 
apparatus for removing material from a substrate utilizing forming gas. 
A still further object of the present invention is to increase the 
effectiveness of residue removal from a substrate. 
In accordance with these and other objects and advantages, aspects of the 
present invention provide a method for removing material from a substrate. 
According to the method, a plasma is generated in a plasma generating and 
discharge device including a sapphire plasma tube. At least one 
fluorine-containing compound is introduced into the plasma. A forming gas 
is introduced into the plasma. The plasma is directed toward the material 
to be removed from the substrate. 
Other aspects of the present invention provide a device for removing 
material from a substrate. The device includes a plasma generating and 
discharge device including a sapphire plasma tube. The device also 
includes a source of at least one gas for introducing the at least one gas 
into the plasma generating and discharge device for forming a plasma. At 
least one source of at least one fluorine-containing compound is provided 
for introducing at least one fluorine-containing compound into the plasma 
generating and discharge device. At least one source of at least one 
forming gas is also provided for introducing the at least one forming gas 
into the plasma. The device also includes apparatus for directing the 
plasma toward the material to be removed from the substrate. 
Still other objects and advantages of the present invention will become 
readily apparent by those skilled in the 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.

DETAILED DESCRIPTION OF THE INVENTION 
As discussed above, the present invention provides an enhanced process for 
removing photoresist and other materials from a substrate. It has been 
unexpectedly discovered that a combination of techniques may be utilized 
to increase the efficiency and effectiveness of ash and residue removal. 
The present invention in part was developed after an investigation of the 
"memory effect" in which ash rates continued to be enhanced after the 
cessation of flow of fluorine-containing compound(s) into the plasma. The 
memory effect may be a result of residual fluorine, fluorine seasoning of, 
or remaining in and/or on, all surfaces exposed to it, including chamber 
walls and the plasma tube of a plasma generating and discharge device. 
This residual fluorine will provide the effects of fluorine addition to 
the plasma without actual fluorine being added to the plasma for one or 
more additional wafers being processed after the addition of fluorine has 
ceased. 
The techniques included in the method of the present invention include 
generating an oxygen plasma in a plasma generating and discharge device 
that includes a sapphire plasma discharge tube, adding at least one source 
of fluorine to the oxygen plasma, and introducing a source of forming gas 
to the oxygen plasma. By utilizing a combination of these techniques, it 
has been unexpectedly discovered that ash rates may be increased 
significantly while maintaining plasma tube integrity. 
Additionally, the techniques of the present invention have been 
demonstrated to remove residues post via etch, oxide etch, poly, nitride, 
implant, and other levels, while not causing additional plasma damage. 
According to the process of the present invention, a plasma generating and 
discharge device such as in U.S. Pat. application Ser. No. 07/626,451 may 
be utilized to generate plasma. Alternatively, any other plasma generator 
capable of generating oxygen plasma for use in applications such as 
removing materials from a substrate by ashing may be utilized. Examples of 
commercially available plasma generating and discharge devices that could 
be utilized to carry out the method of the present invention include the 
FUSION ENHANCED STRIP ASHER and FUSION GEMINI ENHANCED STRIP ASHER, both 
available from Fusion Semiconductor Systems. Other examples of plasma 
generating and discharge devices that may be utilized according to the 
present invention generate a plasma utilizing radio frequency (RF) energy. 
According to the process of the present invention, an oxygen plasma is 
generated in the plasma generating and discharge device while source(s) of 
fluorine-containing compound(s), nitrogen-containing compound(s), and 
hydrogen-containing compound(s) are added to the gas inlet of the plasma 
generating and discharge device. It has been found that the introduction 
of this combination into the plasma generating and discharge device with 
the sapphire plasma tube unexpectedly results in a significantly increased 
rate of removal of certain materials from a substrate. The unexpected 
result achievable according to the present invention of vastly improved 
rate of removal of material from a substrate while not degrading the 
container by utilizing a sapphire plasma tube was not known. 
As discussed above, it was known that utilizing a sapphire plasma tube 
markedly decreased ashing rates. Therefore, although the advantages of 
utilizing oxygen-containing compound(s), fluorine-containing compound(s), 
and nitrogen-containing compound(s) or gases that include oxygen, 
fluorine, and nitrogen may have been known, it was not known to utilize 
this combination of materials in a sapphire plasma tube. 
According to the present invention, at least one oxygen-containing compound 
may be introduced into the plasma generator as molecular oxygen, atomic 
oxygen, ozone, or other oxygen-containing compound such as N.sub.2 O, 
NO.sub.2, NO, CO.sub.2, or CO. The at least one oxygen-containing compound 
may be introduced into the plasma generating and discharge device at a 
rate of from about 200 standard cubic centimeters per minute (sccm) to 
about 4000 sccm. Alternatively, the at least one oxygen-containing 
compound may be introduced into the plasma generating and discharge device 
at a rate of at least about 200 sccm. Similarly, the at least one 
oxygen-containing compound may be introduced into the plasma generating 
and discharge device at a rate of up to about 4000 sccm. Preferably, the 
at least one oxygen-containing compound in the form of O.sub.2 is 
introduced at a rate of from about 1500 sccm to about 2000 sccm. If 
another gas were used, the flow rate would be adjusted to provide an 
equivalent amount of oxygen to the system. 
The flow rate of the at least one oxygen-containing compound preferably 
generates a pressure in the plasma tube of from about 0.5 torr to about 10 
torr. More preferably, the pressure in the process chamber is about 1.5 
torr. 
Lower flow rates could be used if a lower pressure were desired. For 
example, some plasma generating and discharge devices utilizing RF energy 
to generate a plasma may employ lower pressures in the plasma tube. 
However, any flow rates and pressure could be used if the gases of the 
method were utilized in a sapphire plasma tube. 
At least one source of fluorine may be added to the at least one 
oxygen-containing compound in a variety of forms. For example, suitable 
fluorine-containing compounds include CF.sub.4, C.sub.2 F.sub.6, 
CHF.sub.3, CFH.sub.3, C.sub.2 H.sub.2 F.sub.4, C.sub.2 H.sub.4 F.sub.2, 
CH.sub.2 F.sub.2, CH.sub.3 CF.sub.3, C.sub.3 F.sub.8, SF.sub.6, and 
NF.sub.3. 
The amount of fluorine-containing compound(s) added to the 
oxygen-containing compound(s) may vary. For example, according to one 
process of the present invention, the fluorine containing compound(s) is 
added up to about ten percent of the amount of oxygen in a plasma to be 
generated by the plasma generator. In absolute terms, the amount of 
fluorine-containing compound(s) added is up to about 200 sccm. 
Forming gas may be added to the oxygen-containing compound(s) and plasma in 
the plasma generating and discharge device. The forming gas typically is a 
mixture of at least one nitrogen-containing compound and at least one 
hydrogen-containing compound in the form of N.sub.2 and H.sub.2. The 
forming gas may include up to about 10% H.sub.2. The forming gas may be 
added to the plasma generating and discharge device in an amount up to 
about 2000 sccm. 
The nitrogen-containing compound(s) and hydrogen-containing compound(s) of 
the forming gas may be provided by sources of nitrogen and hydrogen other 
than N.sub.2 and H.sub.2 added to the plasma. In one example, NO.sub.2 is 
used as an oxygen source. The nitrogen of the forming gas could be 
provided by the N in the NO.sub.2. Similarly, the hydrogen of the forming 
gas could be provided by CHF.sub.3 used as a fluorine source. 
Processes according to the present invention may include a plurality of 
steps. In each step, one or more of the materials listed above may be 
included in the plasma generated in the plasma generating and discharge 
device. Other process parameters that may be controlled in the operation 
of the plasma generating and discharge device include the power provided 
to the plasma generating and discharge device and the temperature of the 
substrate. The temperature of the substrate may be varied from to from 
about 20.degree. C. to about 350.degree. C. for different processes. 
According to the present invention, the pressure maintained in the plasma 
generating and discharge device is from about a few millitorr to about 10 
torr. 
Additionally, the power supplied to a microwave plasma generating and 
discharge device may vary from about 500 watts to about 2000 watts. Plasma 
generators using RF to generate plasma may operate at lower power levels. 
In either case, the power supplied to the plasma generating and discharge 
device should be sufficient to result in the enhanced removal of material 
from the substrate, while not causing damage or other unwanted effects to 
the substrate. 
In fact, the oxygen-containing compound(s), nitrogen-containing 
compound(s), hydrogen-containing compound(s), and fluorine-containing 
compound(s) may be added in amounts sufficient to result in the enhanced 
removal of selected material from the substrate, while not causing damage 
or other unwanted effects to the substrate or the apparatus. 
According to one example, a process according to the present invention for 
removing PR may include a first step of generating a temperature of about 
270.degree. C. and a pressure of about 1.5 torr in the plasma generating 
and discharge device while supplying about 2000 watts of power. About 2000 
sccm of oxygen, about 300 sccm of N.sub.2 /H.sub.2, and about 5 sccm of 
CF.sub.4 are supplied to the plasma generating and discharge device. This 
temperature, pressure, power, and gas supply are maintained for the 
minimum time necessary for the plasma generating and discharge device to 
reach 270.degree. C. In a second step, these conditions are held 
substantially constant for about 60 seconds. 
According to an example of a process according to the present invention for 
removing residue, the above two steps are first carried out. Then, a third 
step is carried out in which the power level is decreased, the forming gas 
is eliminated, and about 5% CF.sub.4 is added to the plasma generating and 
discharge device. 
The addition of at least one fluorine-containing material to the oxygen 
plasma may result in generation of more oxygen atoms in the plasma and 
minimize the recombination of oxygen atoms on the tube/chamber surface. 
Fluorine may also cause hydrogen abstraction from the surface of the 
resist being removed thereby leaving the resist more prone to attack by 
oxygen atoms, effectively lowering the activation energy required to 
remove the resist. 
At least one hydrogen-containing compound may be added to the 
oxygen-containing compounds), fluorine-containing compounds), and 
nitrogen-containing compounds) to provide a cleaner residue removal as 
well as to lower activation energy. Furthermore, nitrogen present in the 
mixture may enhance production of oxygen atoms. The present invention also 
permits low temperature residue removal. 
Below are described numerous examples of process according to the present 
invention and investigations that led up to the present invention. The 
examples are means to be illustrative in nature and not exhaustive. 
FIGS. 1-3 represent graphs that demonstrate various resist removal rates 
given different oxygen-containing compound(s) and fluorine-containing 
compound(s) flow rates and power levels, without any external heat source 
to the substrate that material is being removed from. 
FIGS. 4 and 5 represent a table illustrating ash rates and oxide loss rates 
for various processes according to the present invention. 
FIGS. 6-9 represent graphs demonstrating the different ash rates achieved 
utilizing a plasma generating and discharge device with a sapphire plasma 
tube with and without utilizing CF.sub.4 and utilizing an oxygen plasma 
with nitrogen-containing compound(s) and hydrogen-containing compound(s) 
added as well. The processes utilized to produce the results illustrated 
in FIG. 6 included three process steps. The first step included a minimum 
time of about 15 seconds necessary to bring the plasma generating and 
discharge device up to a temperature of 270.degree. C., at a pressure of 
1.5 torr, and supplying the amounts of the gases specified on the 
horizontal axis of the graph. The second and third steps included the same 
process parameters, but were carried out for thirteen seconds. The plasma 
was turned on during the third step, supplying about 1500 watts of power 
to the plasma generating and discharge device. No oxide loss was detected. 
The results shown in FIG. 7 were achieved utilizing the same three steps as 
the processes shown in FIG. 6. However, the amounts of oxygen-containing 
compound(s) and forming gas supplied were about 1700 scam and about 300 
scam, respectively. FIG. 7 shows the results for processes that included 5 
sccm CF.sub.4 or did not include CF.sub.4 at all. 
The results shown in FIG. 8 were achieved utilizing the same three steps as 
the processes shown in FIG. 6. However, the amounts of oxygen-containing 
compound(s) and forming gas supplied were about 2000 scam and about 300 
scam, respectively, to compensate for a larger substrate being treated. 
FIG. 8 shows the results for processes that included 5 scam CF.sub.4 or 
did not include CF.sub.4 at all. 
The results shown in FIG. 9 were achieved utilizing the same three steps as 
the processes shown in FIG. 6 and demonstrates the repeatability of the 
results over a plurality of substrates. However, the amounts of 
oxygen-containing compound(s) , forming gas, and CF.sub.4 supplied were 
about 2000 scam, about 300 scam, and about 5 scam, respectively. 
FIG. 20 illustrates the advantage of the increased ash rate according to 
the present invention of adding a trickle of at least one 
fluorine-containing gas, in this case, CF.sub.4, especially at lower 
temperatures. FIG. 21 illustrates temperature variation of ash rate while 
utilizing a 5 scam trickle of CF.sub.4. 
FIG. 22 illustrates a characterization of oxide loss for a process that 
includes two treatment steps during which different process parameters 
were utilized. In the first step, the plasma generating and discharge 
device was turned on for a time sufficient for the device to reach a 
temperature of about 140.degree. C. No power is provided to the plasma 
generating and discharge device. At least one fluorine-containing compound 
in the form of CF.sub.4 is provided to the plasma generating and discharge 
device at a flow rate of about 300 sccm. At least one oxygen-containing 
compound in the form of O.sub.2 is provided to the plasma generating and 
discharge device at a flow rate of about 1700 sccm. The pressure within 
the plasma generating and discharge device is about 1.5 torr. 
According to the second step in the process whose results are shown in FIG. 
22, the plasma generating and discharge device was turned on for about 20 
seconds. About 1500 watts of power is provided to the plasma generating 
and discharge device. At least one fluorine-containing compound in the 
form of CF.sub.4 is provided to the plasma generating and discharge device 
at a flow rate of about 90 sccm. At least one oxygen-containing compound 
in the form of O.sub.2 is provided to the plasma generating and discharge 
device at a flow rate of about 2210 sccm. The pressure within the plasma 
generating and discharge device is about 1.5 torr. 
FIG. 23 illustrates a characterization of nitride etch for a process that 
includes two treatment steps during which different process parameters 
were utilized. In the first step, the plasma generating and discharge 
device was turned on for a time sufficient for the device to reach a 
temperature of about 140.degree. C. No power is provided to the plasma 
generating and discharge device. At least one fluorine-containing compound 
in the form of CF.sub.4 is provided to the plasma generating and discharge 
device at a flow rate of about 300 sccm. At least one oxygen-containing 
compound in the form of O.sub.2 is provided to the plasma generating and 
discharge device at a flow rate of about 1700 sccm. The pressure within 
the plasma generating and discharge device is about 1.5 torr. 
According to the second step in the process whose results are shown in FIG. 
23, the plasma generating and discharge device was turned on for about 60 
seconds. The temperature within the plasma generating and discharge device 
was about 170.degree. C. About 1500 watts of power was provided to the 
plasma generating and discharge device. At least one fluorine-containing 
compound in the form of CF.sub.4 is provided to the plasma generating and 
discharge device at a flow rate of about 300 sccm. At least one 
oxygen-containing compound in the form of O.sub.2 is provided to the 
plasma generating and discharge device at a flow rate of about 1700 sccm. 
The pressure within the plasma generating and discharge device is about 
1.5 torr. 
According to one example of a plasma generating and discharge device 
including a sapphire plasma tube that may be utilized in carrying out 
processes according to the present invention, microwave excitation 
electric field is utilized that is substantially uniform in the azimuthal 
and axial directions of the tube. Such a field will cause substantially 
equal heating of the tube in the azimuthal and longitudinal directions, 
thus obviating cracking. 
The resultant azimuthal and longitudinal uniformity may be provided by 
modes including the rectangular TM.sub.110 mode or the cylindrical 
TM.sub.010 mode, or possibly by a combination of other modes, the 
resultant of which is the desired uniformity. 
In order to create the conditions necessary to excite and support the 
rectangular TM.sub.110 or cylindrical TM.sub.010 modes, such that it is 
the dominant driven mode, it is necessary to use a relatively short 
microwave cavity. This would ordinarily dictate using a correspondingly 
short plasma tube. However, a problem caused by using a short plasma tube 
may be that the longitudinal temperature gradient is too great at the ends 
of the tube where there is a transition from inside the cavity, where 
there is a field, to outside the cavity where there is no field, thus 
causing cracking. 
To solve this problem, a relatively long microwave structure is provided, 
which is divided into lengthwise sections by partitions. The plasma tube 
is fed through a hole in each partition, and thus runs the length of the 
microwave structure, while each of the lengthwise sections is separately 
fed with microwave energy. Each section thus appears to the incoming 
microwave energy to be a separate cavity of relatively short length, thus 
promoting the formation of the correct mode, while the plasma tube is 
relatively long, thus obviating any problems with cracking. 
Microwave energy may be provided having an electric field which is 
substantially uniform in the azimuthal and axial directions of the tube. 
Such an electric field will heat the tube substantially uniformly in the 
azimuthal and axial directions of the tube, which will prevent or minimize 
the formation of temperature stresses due to unequal heating. As used 
herein, the term "azimuthal direction" applies to tubes having both 
circular and non-circular cross-sections, and means the direction which 
follows the periphery of the tube in a plane which is perpendicular to the 
axial direction. 
The rectangular TM.sub.110 and circular TM.sub.010 modes both provide 
substantial azimuthal and axial uniformity for a tube of circular 
cross-section. In FIG. 31, the idealized electric field intensity 
distribution for such modes are depicted (shown in rectangular cavity 22). 
The intensity distribution may be viewed as concentric cylinders having 
azimuthal and axial uniformity with the strength increasing towards the 
center. There is negligible variation in field strength over the 
relatively small radial dimension of the tube. 
A relatively short cavity favors the formation of modes having azimuthal 
and axial uniformity, which suggests the use of a correspondingly short 
plasma tube. In a practical system, process etch rates are related to 
microwave input power. When an input power that attains an acceptable etch 
rate is used with a short plasma tube, the power density is such that an 
unacceptably large thermal gradient exists at the ends of the tube, which 
may cause cracking. 
This problem is solved by using a microwave enclosure which is partitioned 
into lengthwise sections. Referring to FIG. 32, microwave enclosure 42 is 
a rectangular box which is partitioned into lengthwise sections by 
partitions 44, 45, and 46 having plasma tube 40 passing therethrough. 
While four sections are shown in the embodiment which is illustrated, 
fewer or more sections may be used. Each partition has an opening through 
which the plasma tube passes. Each section is separately fed with 
microwave energy. Thus, each section appears to be a relatively short 
cavity to the incoming microwave energy, promoting the formation of modes 
having azimuthal and axial uniformity, and preventing the formation of 
modes such as the TE.sub.101, TE.sub.102, etc., which do not. However, the 
total length of the plasma tube is relatively long, thus ensuring that the 
power density in the tube is such that the temperature gradient at the 
tube ends is within acceptable limits. 
Outer tube 41 surrounds the plasma tube inside the cavity. The outer tube 
is slightly separated from the plasma tube, and air under positive 
pressure is fed between the two tubes to provide effective cooling of the 
plasma tube. Tube 41 would typically be made of quartz. 
The openings in the partitions 44, 45, and 46 through which the concentric 
tubes are fed are made larger than the exterior dimension of the plasma 
tube. There is microwave leakage through such openings which causes a 
plasma to be excited in the part of the tube that is surrounded by the 
partition. Such leakage helps reduce thermal gradients in the plasma tube 
between regions surrounded by partitions and regions that are not. If an 
outer tube is not used (cooling provided in some other manner), the 
openings in the partitions are sized so that there is a space between the 
plasma tube and the partition to provide such microwave leakage. In the 
embodiment shown in FIG. 32, there is a space between the outer tube and 
the partition. 
FIG. 32 also shows an iris plate 50 which covers the open side of the 
microwave structure, and is effective to feed microwave energy into the 
adjacent sections. Plate 50 is a flat metallic plate having irises 52, 54, 
56 and 58, through which the microwave energy is fed. 
The invention is applicable to devices where either the plasma or the 
afterglow from the plasma is used to remove material. Microwave traps 43 
and 45 are provided at the ends to prevent microwave leakage. Such traps 
may be of the type disclosed in U.S. Pat. No. 5,498,308, which is 
incorporated herein by reference. Air seals/directional feeders 47 and 49 
are provided for admitting cooling air and feeding it to the space between 
the concentric tubes. Air seal/directional feeder 51 is shown at the 
outlet end, and a fourth such unit is present, but is not seen. 
FIG. 33 shows a more complete device as assembled. Magnetron 60 provides 
microwave power, which is fed through coupler 62 to a waveguide supplying 
a TE.sub.10 mode, having mutually perpendicular sections 64 and 66. The 
length of waveguide section 66 is adjustable with moveable plunger 82. The 
bottom plate of waveguide section 66 in FIG. 33 is iris plate 50, which 
couples microwave energy into partitioned microwave structure 42, through 
which the plasma tube extends; thus, a plasma is excited in the gas 
flowing through the plasma tube. 
Referring again to FIG. 33, it is seen that end cap 70 abuts microwave trap 
43, and fitting 72 having a central orifice for admitting gas to the 
plasma tube extends into the end cap. The plasma tube is supported at this 
end by O ring 71 in the end cap. The outer tube 41 is supported at its 
ends by abutment against microwave traps 43 and 45. Spacer 78 is present 
to provide the proper spacing in relation to the process chamber. The 
other end of the plasma tube is located in end member 80, and has an 
orifice 86 for emitting gas into the process chamber. 
The process chamber 84 includes retractable wafer support pins 90 and 91, 
which support wafer 88, to be processed. Chuck 92 is for providing the 
correct heating to the wafer during processing. One or more baffle plates 
may be present above the wafer to promote even distribution of the gas. 
Referring to FIG. 33, an exterior view of the device is shown. The 
reference numerals in FIG. 34 correspond to those which are in the other 
Figures. 
In the preferred embodiment, microwave enclosure 42 is dimensioned to 
support the rectangular TM.sub.110 mode and the enclosure 42 may have a 
square cross section. The dimensions of the cross sections are such that 
the TM.sub.110 mode is resonant. The length of each section is less than 
.lambda..sub.g /2 where .lambda..sub.g is the guide length within the 
cavity of the TE.sub.104 mode. 
In an actual embodiment which was built, the magnetron frequency was 2443 
MHz, the microwave enclosure was 3.475-3.5 inches on each side, and the 
length of each of four sections was 2.875 inches. A sapphire tube having 
an ID of about 0.900" and an OD of about 1.000" was used, and a gas of 85% 
O.sub.2, 5% He, 10% NF.sub.3 was flowed through the tube for removing 
residue of polymeric materials in the form of veils which are caused by 
over etching. The power density was about 36 watts/in.sup.3. 
As discussed above, the example of a plasma generating and discharge device 
including a sapphire plasma tube described herein finds a particular use 
with plasma tubes which are made of a material which is inclined to crack 
when heated unequally. One example of such materials are those having a 
linear thermal expansion coefficient greater than 7.times.10.sup.-7 
/K.degree. at operating temperature. However, the example of a plasma 
generating and discharge device including a sapphire plasma tube may also 
be used with other plasma tubes made of other material, for example those 
made of quartz, as the uniform field will tend to keep the plasma off the 
tube wall and may provide improved lifetime of the quartz. 
A quartz tube may be used with at least one fluorine-containing gas by 
coating the inside of the tube with a fluorine resistant coating such as 
Al.sub.2 O.sub.3, CaF.sub.2, fluorosilicade glasses AlN, or other fluorine 
resistant coating. 
EXAMPLE 1 
Example 1, on the following page, describes the treatment of photoresist on 
nitride to be stripped using a process according to the present invention. 
The Example includes four different processes described in four tables, 
labeled 1-4. Each process includes three process steps. 
Example 1 
Demonstration of nitride level strip 
ES Asher 
__________________________________________________________________________ 
Time(sec) 
Temp.(deg. C) 
Press. (torr) 
Power(watts) 
O.sub.2 (sccm) 
N.sub.2 H.sub.2 (sccm) 
CF.sub.1 
__________________________________________________________________________ 
MIN 270 1.5 2000 2000 300 8 
60 270 1.5 2000 2000 300 8 
20 270 1.5 2000 2000 300 8 
__________________________________________________________________________ 
MIN: minimum time needed to reach said temperature (18 sec) 
2. 
Time(sec) 
Temp.(deg. C) 
Press. (torr) 
Power(watts) 
O.sub.2 (sccm) 
N.sub.2 H.sub.2 (sccm) 
CF.sub.1 
__________________________________________________________________________ 
MIN 175 1.5 1500 2000 300 5 
60 175 1.5 1500 2000 300 5 
20 OFF 1.5 1250 2185 0 115 
__________________________________________________________________________ 
MIN: 7 sec 
3. 
Time(sec) 
Temp.(.degree. C.) 
Press. (torr) 
Power(watts) 
O.sub.2 (sccm) 
N.sub.2 H.sub.2 (sccm) 
CF.sub.4 
__________________________________________________________________________ 
MIN 175 1.5 2000 2000 300 8 
60 175 1.5 2000 2000 300 8 
20 OFF 1.5 1250 2185 0 115 
__________________________________________________________________________ 
Time(sec) 
Temp.(.degree. C.) 
Press. (torr) 
Power(watts) 
O.sub.2 (sccm) 
N.sub.2 H.sub.2 (sccm) 
CF.sub.4 
__________________________________________________________________________ 
MIN 175 1.5 2000 2000 300 8 
60 175 1.5 2000 2000 300 8 
20 175 1.5 1500 2000 300 8 
__________________________________________________________________________ 
EXAMPLE 2 
Example 2 describes a plurality of different processes performed utilizing 
a plurality of different process steps, to optimize residue removal while 
preventing undercuts and minimizing oxide loss. 
EXAMPLE 2 
__________________________________________________________________________ 
Process 1) 10% CF4 
Wafer number 
__________________________________________________________________________ 
15 
14 
13 
12 
__________________________________________________________________________ 
Time Pressure 
Temp. 
Power 
O2 CF4 H2N2 CF4 
(sec) 
(torr) 
(.degree. C.) 
(watts) 
(sccm) 
(sccm) 
(sccm) 
(sccm)** 
__________________________________________________________________________ 
Min* 1.5 140 1500 
2000 Off 300 5 
120 1.5 140 1500 
2000 Off 300 5 
20 1.5 Off 1000 
2070 230 Off Off 
__________________________________________________________________________ 
*Minimum time to reach required temperature 
**A 50 sccm MFC installed 
Wafer Oxide Loss (.ANG.) 
__________________________________________________________________________ 
1 21 
2 33 
3 33 
4 32 
__________________________________________________________________________ 
Process 2) 5% CF4 
Wafer number 
__________________________________________________________________________ 
11 
10 
9 
8 
__________________________________________________________________________ 
Time Pressure 
Temp. 
Power 
O2 CF4 H2N2 CF4 
(sec) 
(torr) 
(.degree. C.) 
(watts) 
(sccm) 
(sccm) 
(sccm) 
(sccm)** 
__________________________________________________________________________ 
Min* 1.5 140 1500 
2000 Off 300 5 
120 1.5 140 1500 
2000 Off 300 5 
20 1.5 Off 1250 
2185 115 Off Off 
__________________________________________________________________________ 
*Minimum time to reach required temperature 
**A 50 sccm MFC installed 
Wafer Oxide Loss (.ANG.) 
__________________________________________________________________________ 
1 14 
2 15 
3 13 
4 17 
5 17 
6 17 
__________________________________________________________________________ 
Process 3) 4% CF4 
Wafer number 
__________________________________________________________________________ 
6 
4 
__________________________________________________________________________ 
Time Pressure 
Temp. 
Power 
O2 CF4 H2N2 CF4 
(sec) 
(torr) 
(.degree. C.) 
(watts) 
(sccm) 
(sccm) 
(sccm) 
(sccm)** 
__________________________________________________________________________ 
Min* 1.5 140 1500 
2000 Off 300 5 
120 1.5 140 1500 
2000 Off 300 5 
20 1.5 Off 1500 
2210 90 Off Off 
__________________________________________________________________________ 
*Minimum time to reach required temperature 
**A 50 sccm MFC installed 
Wafer Oxide Loss (.ANG.) 
__________________________________________________________________________ 
1 11 
2 13 
3 12 
4 16 
5 11 
6 15 
__________________________________________________________________________ 
EXAMPLE 3 
Example 3 includes five processes carried out on a Fusion Gemini Enhanced 
Strip tool. Example 3 shows effective ash processes for via, poly, oxide, 
and nitride process levels. Gemini Enhanced Strip processes were 
demonstrated for these process levels that effectively eliminate a wet 
strip step and may require, if necessary, only dry ash followed by a 
deionized water (DI) rinse. 
A Gemini Enhanced Strip (GES) process was developed for the ion implant 
process level that removes all photoresist and implant residue using only 
the dry ash followed by about a five minute DI rinse. No photoresist 
poppers were seen on the sample or in the chamber. 
Descum recipes were demonstrated that removed about 530 .ANG.. It may be 
possible to fine tune the process recipes to even further improve the 
results. However, the process would basically remain the same as described 
herein. The processes may also be shortened to improve total wafer 
throughput. 
FIGS. 10-19 show photomicrographic evidence of the results of the processes 
according to Example 3. 
EXAMPLE 3 
__________________________________________________________________________ 
Time Pressure 
Temp. 
Power 
O2 flow 
CF4 flow 
N2/H2 flow 
CF4 flow 
(sec) 
(torr) 
(deg. C) 
(watts) 
(sccm) 
(sccm) 
(sccm) 
(sccm) 
__________________________________________________________________________ 
MIN 1.5 120 1500 
2000 0 300 8 
45 1.5 120 1250 
2185 210 0 8 
MIN 1.5 270 1500 
2000 0 300 0 
15 1.5 270 1500 
2000 0 300 0 
__________________________________________________________________________ 
Time Pressure 
Temp. 
Power 
O2 flow 
CF4 flow 
N2/H2 flow 
CF4 flow 
(sec) 
(torr) 
(deg. C) 
(watts) 
(sccm) 
(sccm) 
(sccm) 
(sccm) 
__________________________________________________________________________ 
MIN 1.5 140 1500 
2000 0 300 5 
120 1.5 140 1500 
2000 0 300 5 
20 1.5 OFF 1000 
2070 210 0 8 
__________________________________________________________________________ 
Time Pressure 
Temp. 
Power 
O2 flow 
CF4 flow 
N2/H2 flow 
CF4 flow 
(sec) 
(torr) 
(deg. C) 
(watts) 
(sccm) 
(sccm) 
(sccm) 
(sccm) 
__________________________________________________________________________ 
MIN 1.5 175 2000 
2000 0 300 8 
60 1.5 175 2000 
2000 0 300 8 
20 1.5 OFF 1250 
2185 115 0 0 
__________________________________________________________________________ 
Time Pressure 
Temp. 
Power 
O2 flow 
CF4 flow 
N2/H2 flow 
CF4 flow 
(sec) 
(torr) 
(deg. C) 
(watts) 
(sccm) 
(sccm) 
(sccm) 
(sccm) 
__________________________________________________________________________ 
MIN 1.5 175 1500 
2000 0 300 8 
60 1.5 175 1500 
2000 0 300 8 
20 1.5 OFF 1250 
2185 115 0 0 
__________________________________________________________________________ 
Time Pressure 
Temp. 
Power 
O2 flow 
CF4 flow 
N2/H2 flow 
CF4 flow 
(sec) 
(torr) 
(deg. C) 
(watts) 
(sccm) 
(sccm) 
(sccm) 
(sccm) 
__________________________________________________________________________ 
MIN 1.5 140 1500 
2000 0 300 5 
30 1.5 140 1500 
2000 0 300 5 
MIN 1.5 300 1500 
2000 0 300 5 
60 1.5 300 1500 
2000 0 300 5 
__________________________________________________________________________ 
EXAMPLE 4 
Example 4 includes another process combination according to the present 
invention for removing material from a substrate. 
FIG. 26a and FIG. 26b illustrate vias that have been treated with a process 
including parameters substantially similar to those of Example 4. FIG. 24 
illustrates a cross-sectional view of a typical via structure similar to 
the vias shown in FIG. 26a and FIG. 26b and treated according to the 
present invention. FIG. 26a illustrates undercut of the TiN layer in the 
substrate. FIG. 26b illustrates a via that by reducing the treatment time 
by about 15 seconds from that shown in Example 4, the undercutting may be 
eliminated. 
FIG. 25a illustrates a via prior to treatment with the process of Example 
4. As can be seen in FIG. 25a, debris remains in the via. On the other 
hand, FIG. 25b represents vias after treatment with a process according to 
Example 4 followed by a deionized water rinse. 
EXAMPLE 4 
______________________________________ 
Time Pressure 
Temp. Power O.sub.2 flow 
CF.sub.4 flow 
FG flow 
Step (sec) (torr) (deg. C) 
(watts) 
(sccm) 
(sccm) (sccm) 
______________________________________ 
1 75 1.5 off 1500 1350 150 0 
______________________________________ 
EXAMPLE 5 
Example 5 includes another process combination according to the present 
invention for removing material from a substrate. According to Example 5, 
oxide loss can be reduced by utilizing hydrogen in the forming gas to 
scavenge fluorine radicals while utilizing relatively high flows of 
CF.sub.4. Example 5 provides one example of such a process. 
FIG. 27a illustrates a via after treatment with a process according to 
Example 5. As shown in FIG. 27a, residue may remain in the via after 
processing with the present invention. However, as illustrated by FIG. 
27b, the residue may be water-removable since FIG. 27b shows a via after a 
deionized water rinse. No undercutting is seen in the vias shown in FIG. 
27a or FIG. 27b. 
EXAMPLE 5 
Oxide loss can also be reduced by using the hydrogen in forming gas to 
scavenge the F radicals while using high CF.sub.4 flows. Recipe V5 is an 
example. 
__________________________________________________________________________ 
Time 
Pressure 
Temp. 
Power 
O.sub.2 flow 
CF.sub.4 flow 
FG flow 
CF.sub.4 flow 
Step 
(sec) 
(torr) 
(deg. C) 
(watts) 
(sccm) 
(sccm) 
(sccm) 
(sccm) 
__________________________________________________________________________ 
1 MIN 
1.5 150 2000 1735 140 425 0 
2 75 1.5 150 2000 1735 140 425 0 
__________________________________________________________________________ 
EXAMPLE 6 
Example 6 includes another combination of process steps according to the 
present invention for removing material from a substrate. According to 
Example 6, about 9% CF.sub.4 may be added to the plasma during step 3. 
FIG. 28a illustrates a substrate of post poly residues after treatment with 
a process according to the present invention. FIG. 28b illustrates residue 
removal after treatment with the process of Example 6 and a deionized 
water rinse. 
EXAMPLE 6 
__________________________________________________________________________ 
8" Gas Flows Step 3-9% CF4 Concentration 
Time 
Pressure 
Temp. 
Power 
O2 CF4 N2H2 CF4 
Step 
(sec) 
(torr) 
(.degree. C.) 
(watts) 
(sccm) 
(sccm) 
(sccm) 
(sccm) 
__________________________________________________________________________ 
1 Min* 
1.5 140 1500 
2000 
Off 300 5 
2 120 1.5 140 1500 
2000 
Off 300 5 
3 20 1.5 Off 1000 
2070 
210 Off 8 
__________________________________________________________________________ 
*Minimum time to reach required temperature 
EXAMPLE 7 
Example 7 includes another combination of process steps according to the 
present invention for removing material from a substrate. According to 
Example 7, about 7.5% CF.sub.4 may be added to the plasma during step 3. 
FIG. 29a illustrates a substrate of post poly residues after treatment with 
a process according to the present invention. FIG. 29b illustrates residue 
removal after treatment with the process of Example 7 and a deionized 
water rinse. 
EXAMPLE 7 
__________________________________________________________________________ 
6" Gas Flows Step 3-7.5% CF4 Concentration 
Time 
Pressure 
Temp. 
Power 
O2 CF4 N2H2 CF4 
Step 
(sec) 
(torr) 
(.degree. C.) 
(watts) 
(sccm) 
(sccm) 
(sccm) 
(sccm) 
__________________________________________________________________________ 
1 Min* 
1.5 140 1500 
1700 
Off 300 5 
2 90 1.5 140 1500 
1700 
Off 300 5 
3 20 1.5 Off 1250 
1850 
150 Off Off 
__________________________________________________________________________ 
*Minimum time to reach required temperature 
EXAMPLE 8 
Example 8 includes another combination of process steps according to the 
present invention for removing material from a substrate. According to 
Example 8, about 3.75% CF.sub.4 may be added to the plasma during step 3. 
FIG. 30a illustrates a substrate of post poly residues after treatment with 
a process according to the present invention. FIG. 30b illustrates residue 
removal after treatment with the process of Example 8 and a deionized 
water rinse. 
EXAMPLE 8 
__________________________________________________________________________ 
6" Gas Flows Step 3-3.75% CF4 Concentration 
Time 
Pressure 
Temp. 
Power 
O2 CF4 N2H2 CF4 
Step 
(sec) 
(torr) 
(.degree. C.) 
(watts) 
(sccm) 
(sccm) 
(sccm) 
(sccm) 
__________________________________________________________________________ 
1 Min* 
1.5 140 1500 
1700 
Off 300 5 
2 70 1.5 140 1500 
1700 
Off 300 5 
3 20 1.5 Off 1500 
1925 
75 Off Off 
__________________________________________________________________________ 
*Minimum time to reach required temperature 
The foregoing description of the invention illustrates and describes the 
present invention. Additionally, the disclosure shows and describes 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, modifications, and environments and is capable of changes or 
modifications within the scope of the inventive concept as expressed 
herein, commensurate with the above teachings, and/or the skill or 
knowledge of the relevant art. The embodiments described hereinabove are 
further intended to explain best modes known of practicing the invention 
and to enable others skilled in the art to utilize the invention in such, 
or other, embodiments and with the various modifications required by the 
particular applications or uses of the invention. Accordingly, the 
description is not intended to limit the invention to the form disclosed 
herein. Also, it is intended that the appended claims be construed to 
include alternative embodiments.