Page 1 of 11
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`(cid:44)(cid:49)(cid:55)(cid:40)(cid:47) EXHIBIT 10(cid:21)(cid:22)
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`

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`US. Patent
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`Apr. 12, 1994
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`Sheet 1 of 4
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`5,302,882
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`Page 2 of11
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`US. Patent
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`Apr. 12, 1994
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`Sheet 2 of 4
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`5,302,882
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`Page 3 of 11
`Page 3 of11
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`US. Patent
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`Apr. 12, 1994
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`Sheet 3 of 4
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`5,302,882
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`Page 4 of 11
`Page 4 of11
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`US. Patent
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`Apr. 12, 1994
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`Sheet 4 of 4
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`5,302,882
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`REACTOR A
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`2
`ply must be largely prevented from reaching the other
`power supply. the mixing products caused by the cou—
`pling of two different frequencies to a non-linear load
`must be attenuated and the radiation emitted by the
`reactor and the various intercOnnections must be mini-
`mized.
`is that the plasmas
`A key feature of most plasmas,
`have “non-linear” impedance characteristics. Non-
`linearity is a mathematical definition signifying that the
`magnitude of the voltage (electric field) in the plasma is
`not directly proportional to the magnitude of the cur-
`rent (magnetic field). Typically,
`the generators em-
`ployed in various plasma systems are designed to gener-
`ate an output of predominantly single-frequency. How-
`ever, because of the non-linearity of the plasma, signals
`at multiples of the fundamental generator frequency are
`generated by the plasma. These multiple frequencies of
`the fundamental frequency are called harmonic fre-
`quencies (or harmonics). The amplitude of the harmon-
`ics affect certain properties of the plasma, such as direct
`current (DC) bias, which impact the particular plasma
`process. The amplitude of the harmonics is determined
`by the interaction of the plasma with the generator and
`the coupling system and is difficult to control simply by
`adjusting the amplitude of the fundamental frequency
`component.
`Plasma non-linearity is a phenomenon which plays an
`important role in causing the plasma conditions to be
`' dependent upon the electrical characteristics of the
`30
`generator, as well as the coupling system, at both the
`operating (fundamental) frequency of the generator and
`at the various harmonic frequencies. That is, if satisfac-
`tory operation of a plasma reactor is achieved for a
`given generator and coupling system, the parameters of
`the generator and the coupling system cannot be readily
`changed without affecting the plasma itself. Thus, gen-
`erally it is impractical, if not possible, to make changes
`to the electrical parameters of the generator and/or the
`coupling system and still be able to reproduce the de~
`sired plasma conditions, simply by readjusting the am-
`plitude of the generator output. Typically, what is re-
`quired is a considerable retuning of the system in order
`to satisfactorily couple the reactor to the generator
`and/or the coupling system to obtain the desired plasma
`conditions.
`Therefore, it is difficult to replace a generator from a
`first manufacturer with a generator from a second man-
`ufacturer and obtain the same plasma conditions, unless
`the electrical parameters of the two generators are iden-
`tical. Similarly, if a change is made to an impedance
`matching network in the coupling system, due to a
`component change for example, the same plasma condi-
`tions cannot be reproduced unless the networks are
`substantially identical. Merely changing the amplitude
`of the generator output will not compensate for the
`impedance differences in the generator and/or the cou-
`pling system.
`An added problem also exists when certain parame-
`ters associated with two systems are not substantially
`identical. If two installations of plasma systems are
`made using identical generators and reactors but differ-
`ent lengths of coaxial cable (wave guides and/or other
`transmission mediums) are utilized in the systems then
`generally identical plasma conditions cannot be repro-
`duced. In actual practice, this lack of reproducibility of
`desired operating plasma conditions under realistic con-
`ditions presents significant difficulties to the user. For
`example, if an RF generator requires service and/or
`
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`5,302,882
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`LOW PASS FILTER FOR PLASMA DISCHARGE
`
`This application is a continuation of US. patent appli-
`cation Ser. No. 756,649, filed Sep. 9, 1991, now aban-
`cloned.
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention relates to the field of plasma
`processing and, more particularly, to the use of plasma
`equipment for modification of materials.
`2. Prior Art
`Plasma processing equipment is used extensively in
`the industry for the modification of materials. These
`modifications include etching and deposition of films
`for fabrication of microelectronic circuits and semicon-
`ductor devices. The modifications also may include
`implantation of chemical species that change the fric-
`tion and wear properties of surfaces.
`A plasma is a gas (or a gas mixture) which is ener-
`gized so that it is partially decomposed into species that
`are electrically charged. A variety of techniques are
`known for energizing the gas. One commonly used
`technique is the energizing of the gas by imposing an
`electric field on the gas from an external source. A
`common practice is to use high frequency alternating-
`current (AC) fields to energize or excite the gas. For
`example, radio-frequency (RF) fields are generated at
`frequency ranges near 10 MHz. At still higher frequen-
`cies, in the order of 1000 MHz, microwave fields are
`generated. In some instances, these electric fields are
`utilized in combination with magnetic fields which are
`used for the purpose of confining the plasma. Electron
`cyclotron resonance (ECR) plasma processing is one
`technique for controlling the plasma with the use of
`electric and magnetic fields.
`The plasma is typically retained in a chamber of a
`processing equipment and isolated from the surround
`ing ambient and this plasma usually contains species that
`undergo chemical reactions. The plasma chamber and
`its gas-handling equipment are typically referred to as a
`reactor. The source of the electrical power that ener-
`gizes the plasma is commonly referred to as a generator.
`Usually, there are a number of components, including
`cables, wave guides,
`inductors, capacitors, matching
`network, tuner and/or an impedance transforming net-
`work coupling the generator to the reactor. These com-
`ponents are included in a system sometimes referred to
`as a coupler or a coupling system. The generator and
`the coupling system together comprise the AC source
`that energizes the plasma.
`Various schemes have been devised in the prior art
`for coupling the generator, coupler, and the reactor to
`' operate as a plasma processing system for example, in
`US. Pat. No. 4,824,546 (Ohmi) an RF power source is
`coupled to a vacuum vessel through a matching circuit
`in order to provide a sputtering apparatus for forming
`an insulating thin film. Band reject filters are provided
`to permit only high frequencies to be supplied.
`Another example is disclosed in US. Pat. No.
`4,579,618 (Celestine et al.) in which two power sources
`are each coupled through a matching network to a
`plasma reactor. A filter/combiner is coupled between
`the low frequency power supply and the high frequency
`power supply. The filter/combiner serves three pur-
`poses which are unique to a single electrode, dual fre-
`quency plasma reactor. The power of each power sup-
`
`Page 6 of 11
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`5,302,882
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`4
`that the present invention may be practiced without
`these specific details. In other instances, well-known
`processes and structures have not been described in
`detail in order not to unnecessarily obscure the present
`invention.
`
`Prior Art
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`Referring to FIG. 1, a prior art plasma reactor system
`is shown. A generator 10 for providing an alternating
`current electric field to energize or excite the gas (or gas
`mixture) to form the plasma is coupled to reactor 12
`through a coupler 11. The generator 10 is typically of
`RF or microwave frequency in which the desired oper-
`ating (fundamental) frequency is selected. The ampli-
`tude of the output of generator 10 is adjustable.
`Reactor 12 includes the equipment containing the
`plasma chamber, as well as its gas handling apparatus.
`The plasma gas (or gas mixture) is introduced into the
`chamber for it to operate on a target device. The target
`device for whose properties are to be modified is also
`present in the chamber. The coupler 11 can be of a
`variety of couplers utilized in coupling generator 10 to
`reactor 12. For example, coupler 11 can be a blocking
`capacitor or an impedance matching network. Al-
`though shown as coupler 11 it also includes the com-
`plete coupling system, including the various transmis—
`sion cables, wave guides, connectors, etc., which com-
`prise the transmission medium between generator 10
`and reactor 12. The purpose of the coupler 11 is to
`match the impedance, as well as other circuit parame-
`ters, between the generator 10 and reactor 12, in order
`to provide for an efficient transfer of electrical energy
`from generator 10 to reactor 12.
`As was earlier described in the background of the
`invention, a particular reactor 12 is coupled to operate
`with a particular generator 10 and coupler 11. In order
`to obtain the desired plasma conditions, considerable
`amount of tuning is required to obtain those desired
`plasma conditions in reactor 12. During operation of the
`system in FIG. 1, the amplitude of generator 10 can be
`adjusted to vary the plasma conditions in reactor 12.
`A significant disadvantage of the prior art plasma
`system of FIG. 1 is that the desired plasma conditions
`typically cannot be reproduced readily, if any signifi-
`cant characteristic of the generator 10 and/or the cou-
`pler 11 is changed. If, for example, another generator is
`substituted in place of generator 10 and/or another
`. coupler is substituted for coupler 11, then in most in-
`stances, unless the new generator and/or coupler is
`50
`identical in electrical characteristics to the one substi-
`tuted, the desired plasma conditions typically cannot be
`reproduced in reactor 12 without further adjustment.
`In order to obtain the desired plasma conditions
`again, the system of FIG. 1 must be retuned to accom-
`modate the new generator and/or coupler. Thus, the
`system of FIG. 1 must necessarily depend on the partic-
`ular generator 10 and coupler 11 to be tuned to operate
`with reactor 12. In the event a component having differ-
`ent electrical characteristics is to be substituted, consid-
`erable amount of time and effort are required to retune
`the system. Thus, anytime generator 10 and/or coupler
`11 require repair and/or service, the plasma system will
`necessarily require a complete “shut-down” while the
`reactor is reconfigured and retuned to the new system.
`In practice, the lack of reproducibility of desired plasma
`conditions in reactor 12 provides for an inflexible sys-
`tem which may pose economic hardship to the user of
`the plasma equipment.
`
`65
`
`3
`corrective repair, it can only be replaced with another
`identical RF generator without undue tuning and ad-
`justment.
`Accordingly, it is appreciated that a plasma system
`which is flexible in design to accommodate a multitude
`of generator sources, as well as coupling systems, such
`that the reactor could repeatedly reproduce desirable
`plasma operating conditions, will provide for an im—
`provement over the prior art.
`SUMMARY OF THE INVENTION
`
`The present invention describes an isolator for isolat-
`ing a plasma reactor from its electrical energy source.
`The isolator is a low-pass electrical filter which permits
`the passage of the fundamental frequency of an electri-
`cal energy source supplying electrical energy to the
`reactor, but blocks transmission of harmonic frequen-
`cies. Because the plasma operates with non-linear impe-
`dance characteristics and the amplitudes of these har-
`monics affect properties of the plasma, the plasma con-
`ditions are usually dependent upon the electrical char-
`:acteristics of the generator, as well as the entire cou-
`pling system. However, by attenuating and substantially
`preventing the harmonics from interacting with the
`generator and with the coupling circuitry that couples
`the generator to the isolator, this dependence is elimi-
`nated. The reactor is made to operate substantially inde-
`pendent of the effects in the change of the generator
`and/or the coupling system due to the harmonic isola-
`tion and permits substitution of the generator and/or
`the coupling system without undue hardship in tuning
`the system to reproduce the desired plasma conditions.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram of a prior art plasma reactor
`showing a generator and a reactor coupled by a cou-
`pler.
`FIG. 2 is a block diagram of a plasma reactor system
`of the present invention utilizing an isolator to isolate
`the reactor from the generator and the coupler.
`FIG. 3 is a circuit schematic diagram of a low-pass
`filter which is utilized as one embodiment for the isola-
`tor of FIG. 2.
`FIG. 4 is a graphic representation of a frequency
`response curve Vour/Vm of an ideal filter and mea-
`sured .values for the circuit of FIG. 3.
`FIG. 5 is a block diagram showing four different
`plasma system arrangements with and without the isola-
`tor of the present invention which were used in provid-
`ing experimental results.
`FIG. 6 is a graphical representation of DC Bias volt-
`age measured for the eight systems shown in FIG. 5.
`FIG. 7 is a graphical representation of plasma volt-
`ages measured for the eight systems shown in FIG. 5.
`FIG. 8 is a graphical representation of plasma cur-
`rents measured for the eight systems shown in FIG. 5.
`FIG. 9 is a graphical representation of phase differ-
`ences for plasma voltages and currents measured for the
`eight systems shown in FIG. 5.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`An apparatus and method for providing an isolator
`for a plasma reactor is described. In the following de-
`scription, numerous specific details are set forth, such as
`specific circuits, reactors, processes, etc, in order to
`provide a thorough understanding of the present inven-
`tion. However, it will be obvious to on skilled in the art
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`5
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`Present Invention
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`5,302,882
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`6
`of FIG. 3 as curve 29. As is noted, the fundamental
`frequency is set at 13.56 MHz. As is also noted in the
`graph of FIG. 4 the second harmonic frequency of
`27.12 MHz is well below the —3 db point. Thus, by
`utilizing a low-pass filter for isolator 19, the harmonic
`‘ signals generated by the reactor 12 are largely pre-
`vented from interacting with the generator 10 and/or
`coupler 11. The fundamental
`frequency component
`from generator 10 is passed through coupler 11 and
`through the isolator 19 to energize the plasma in reactor
`12. The desired operating conditions can be readily
`achieved by adjusting the amplitude of generator 10.
`, Accordingly, substitution of generator 10, coupler 11
`and/or other components in the transmission medium
`can be easily compensated by adjusting the amplitude of
`generator 10 to obtain the desired plasma conditions in
`reactor 12. The harmonics generated by the reactor 12
`are essentially “trapped” by isolator 19 and are substan-
`tially prevented from interacting with generator 10 and
`coupler 11.
`It is appreciated then that reactor 12 can be readily
`coupled to a variety of generators, couplers, and/or
`transmission medium, wherein the desired plasma con-
`ditions can be readily reproduced by simply adjusting
`the frequency of the generator 10 to the desired funda-
`mental frequency and adjusting the amplitude of the
`electrical signal from generator 10.
`
`Experimental Results
`Referring to FIG. 5, block diagrams for four different
`plasma systems with and without the isolator 19 are
`shown. These eight different arrangements provided
`the experimental results illustrated in FIGS. 6—9. In
`Configuration 1, generator 31 is coupled to reactor 33
`(designated also as “Reactor A”), wherein blocking
`capacitor 35 is utilized as part of coupler 11. In Configu-
`ration II, a second generator 32 is coupled to reactor 33
`through the blocking capacitor 35. In Configuration III,
`generator 32 is coupled to a second reactor 34 (desig-
`nated also as “Reactor B") through the blocking capaci-
`tor 35. In Configuration IV, generator 32 is coupled to
`the same reactor 34, but a matching network 36 is uti-
`lized instead of blocking capacitor 35. These four con-
`figurations which do not include isolator 19 are desig-
`nated as lo, Ho, 1110, and IVo and represent four different
`prior art arrangements. With the same four configura-
`tions, isolator 19 (shown as dotted in FIG. 5) is now
`included and represent four arrangements 1;, 111:, III};
`and IV;.
`The results of the four configurations with and with-
`out the filter of the present invention are shown in the
`resultant graphs of FIGS. 6—9. All data represent dis-
`charges in argon gas at 100 mTorr pressure and 200
`volts peak—to-peak excitation at fundamental frequency
`of 13.56 MHz. In the particular example, the first gener-
`ator 31 is model SG-1250 manufactured by R. D. Mathis
`Co., while the second generator 32 is model ACG—S
`manufactured by ENI Power Systems. The matching
`network 36 is “Matchwork MW-S”, also from ENI
`Power Systems.
`Referring to FIGS. 6-9, in all four of these graphs,
`the results obtained from the first two configurations (I
`and II) pertaining to reactor A are shown on the left
`half portion of the diagram, while configurations III
`and IV, pertaining to reactor B are shown on the right
`half portion of the diagram. FIG. 6 shows the measure-
`ment of the DC Bias voltage in each of the configura-
`tions. FIG. 7 shows the magnitude of the Fourier coeffi-
`
`5
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`Referring to FIG. 2, a plasma reactor system of the
`present invention is shown. The apparatus of the pres-
`ent invention is comprised of the same prior art genera-
`tor 10, coupler 11 and reactor 12. However, isolator 19
`of the present invention is inserted between coupler 11
`and reactor 12. The purpose of isolator 19 is to isolate
`the reactor 12 from the electrical energy generating
`source and transmission medium provided by generator 10
`10 and coupler 11.
`Isolator 19 is designed to permit the transmission of
`the electrical energy at the fundamental operating fre-
`quency of the generator 10, but to inhibit the transmis-
`sion of higher frequencies, predominantly the harmon- 15
`ics. Therefore, the harmonic content of the electrical
`signal from reactor 12 is significantly prevented from
`reaching coupler 11 and generator 10. Because of the
`harmonic isolation, the plasma in reactor 12 cannot
`interact with, nor respond to changes in, the imped- 20
`ances of generator 10 and coupler 11 at the harmonic
`frequencies. Changes made to generator 10 and/or cou-
`pler 11 can be readily compensated by the adjustment of
`the amplitude of the output signal from generator 10,
`which is for the purpose of adjusting the amplitude of 25
`the fundamental frequency component.
`Thus, substitutions for generator 10 and coupler 11
`can be readily made by non-identical generators and
`Couplers, wherein the desired plasma conditions in the
`reactor 12 can be reproduced by adjusting the ampli- 3O
`tude of the output signal from generator 10. The har-
`monics generated due to the nonlinearity of the plasma
`are prevented from substantially interacting with the
`generator 10 and/or the coupler 11. A variety of inter-
`actions can occur, one such being the change of the 35
`impedance of the generator 10 and/or coupler 11
`caused by the harmonics. Another interaction being the
`feedback of harmonics generated by reactor 12, trans-
`‘mitted to generator 10 and coupler 11, and reflected
`from generator 10 and/or coupler 11, so as to either 40
`strengthen or cancel the harmonics at the reactor 12.
`Although a variety of electrical devices can be uti-
`lized for isolator 19, the preferred embodiment utilizes a
`tuned electrical filter. The tuned electrical filter of the
`preferred embodiment is a low-pass filter and is shown 45
`in FIG. 3. Referring to FIG. 3, the particular low-pass
`filter utilized in the preferred embodiment is a Cheby-
`shev filter, which is comprised of five circuit compo-
`nents 22—26. Two w-sections are utilized between input
`terminals 20 and output terminals 21. The input termi- 50
`nals 20 are coupled to the coupler 11 (actually the trans-
`mission medium), while the output terminals 21 are
`coupled to reactor 12. One of the input terminals 20' and
`one of the output terminals 21 are coupled together to
`operate as an electrical return (typically ground poten- 55
`tial of the electrical system). Capacitor 22 is coupled
`across the input terminals 20, while capacitor 24 is cou-
`pled across the output terminals 21. Two inductors 25
`and 26 are coupled in series between the non-returning
`input and output terminals. A third capacitor 23 is cou- 60
`pled between the junction of the two inductors and the
`return line. In the preferred embodiment, capacitors 22
`and 24 have the values of 220.9 pF, while capacitor 23
`has the value of 310.6 pF. The inductors 25 and 26 each
`have a value of 935.1 nH.
`FIG. 4 shows a graphical representation of the theo-
`retically’designed response of the filter of FIG. 3 as
`curve 18 and the actual measured response of the filter
`
`65
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`8
`an electrical filter coupled between said reactor and
`said first electrical source for passing said fre-
`quency f, but inhibiting harmonics of said funda-
`mental frequency f generated due to a non-linear
`response characteristic of said plasma in said reac-
`' tor from interacting with electrical circuit parame-
`ters of said first electrical source, such that a sec-
`ond electrical source can be readily substituted in
`place of the first electrical source and wherein
`original plasma characteristics can be substantially
`restored by adjusting the amplitude of an electrical
`signal from said second electrical source at fre-
`quency f, but without requiring retuning of said
`second electrical source.
`2. The improvement of claim 1 wherein said electrical
`filter is a low-pass electrical filter.
`'3. In a plasma processing apparatus, having a reactor
`for processing a reactive gas and wherein said reactor is
`coupled to a first electrical energy source which pro-
`0 vid‘es an electrical signal at a fundamental frequency f to
`generate an electrical energy field for generation of
`plasma in said reactor, and an electrical filter is coupled
`between said reactor and said first electrical energy
`source for passing said frequency f, but inhibiting har-
`monics of said fundamental frequency f generated due
`to a non-linear response characteristic of said plasma in
`said reactor from interacting with electrical circuit pa-
`rameters of said first electrical energy source, such that
`when a second electrical energy source is substituted in
`place of the first electrical energy source, original
`plasma characteristics are substantially restored by ad-
`justing he amplitude of an electrical signal from said
`second electrical source at said frequency f without
`requiring retuning of said second electrical energy
`source.
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`4. The apparatus of claim 3 wherein each of said
`electrical energy sources is comprises of an electrical
`generator and a coupling means for electrically cou-
`pling said electrical generator to said reactor.
`5. The apparatus of claim 4 wherein said electrical
`filter is a low-pass electrical filter.
`6. The apparatus of claim 5 wherein said low-pass
`filter is a Chebyshev filter.
`7. A plasma processing apparatus for processing a
`reactive gas and in which said apparatus is coupled to a
`first electrical energy source which provides an electri-
`cal signal at a fundamental frequency f to generate an
`electrical energy field for generation of plasma in said
`apparatus comprising:
`a reactor for processing said reactive gas therein;
`an electrical filter coupled between said reactor and
`said first electrical energy source for passing said
`frequency f, but inhibiting harmonics of said funda-
`mental frequency f generated due to a non-linear
`response characteristic of said plasma in said reac-
`tor from interacting with electrical circuit parame-
`ters of said first electrical energy source, such that
`when a second electrical energy source is substi-
`tuted in place of the first electrical energy source,
`original plasma characteristics are substantially
`restored by adjusting the amplitude of an electrical
`signal from said second electrical source at said
`frequency f without requiring retuning of said sec-
`ond electrical energy source.
`8. The apparatus of claim 7 wherein each of said
`electrical energy sources is comprises of an electrical
`generator and a coupling means for electrically cou-
`pling said electrical generator to said reactor.
`
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`5,302,882
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`7
`cients of the fundamental (V1) and the second harmonic
`(V2) of the plasma voltage in each of the four configura-
`tions with and without the filter. FIG. 8 shows the
`magnitude of the Fourier coefficient of the plasma cur-
`rent at the fundamental (II) and at the second harmonic
`frequency (12) in each of the four configurations with
`and without the filter. FIG. 9 shows the phase qb of the
`Fourier coefficients of the voltages V1, V2 and current
`12. The phase of the current 11 is not indicated on the
`graph simply because the selected value for the phase of
`I] is chosen as zero degrees.
`Notice that in FIG. 6, for Reactor A, the DC Bias
`voltage of the reactor is measured at approximately 155
`volts for configuration 10 (without the filter). When
`generator 31 is substituted by a different generator 32,
`which is the condition shown in Configuration 110, the
`DC Bias voltage in the reactor drops to approximately
`129 volts. However, when the isolator 18, in the form of
`the low-pass Chebyshev filter is used, the same DC bias,
`approximately 138 volts,
`is measured regardless of
`which generator 31 or 32 is used to energize the reactor
`(Configurations Ipand 11;). This illustrates the fact that
`the presence of isolator 19 of the present
`invention
`permits for the substitution of the generator 32 for 31,
`but wherein such substitution does not appreciably
`change the DC Bias voltage of Reactor A. Similar re-
`sults are shown for Reactor B in comparing conditions
`shown in IIIFand IVFof FIG. 6.
`In FIG. 7, it is noted that the plasma voltage V] at the
`fundamental frequency is fairly uniform with and with-
`out the isolator 19. However,
`the second harmonic
`content varies significantly when the filter of the pres-
`ent invention is not utilized (Compare 10 and Ho; and
`compare 1110 and 1V0). This fact is significantly noted in
`lo and 110, wherein the plasma voltage of the second
`harmonic (V2) varies from 50 volts to 15 volts. When
`the filter is utilized, the disparity of the values of the
`second harmonic voltage is reduced significantly.
`Similar comparisons can be readily made for the
`plasma current graphs of FIG. 8 and the overall resul-
`tant phase differences of current and voltage phases (4))
`as shown in FIG. 9. These illustrations conclusively
`exemplify the insensitivity of the reactor conditions to
`changes in generator and coupler that is caused by the
`presence of the isolator 19 of the present invention. The
`plasma system operates to provide substantially uniform
`plasma conditions for a giVen reactor even when the
`electrical energy source or the energy transfer medium
`is varied or substituted.
`It is appreciated that although one particular Cheby-
`shev low-pass filter is shown in four experimental con-
`figurations of plasma systems, the type of filter is a mere
`design choice. A variety of other configurations can be
`readily adapted for use with the isolator of the present
`invention. Furthermore, the frequency of operation is a
`design choice and can be readily selected in the RF,
`microwave or other bands. The filter will necessarily be
`designed to reflect the frequency of operation. It is to be
`noted also that the isolator can be designed as part of the
`reactor equipment.
`I claim:
`1. In a plasma processing apparatus, having a reactor
`for processing a reactive gas and wherein said reactor is
`coupled to a first electrical source which provides an
`electrical signal at a fundamental frequency f to gener-
`ate an electrical energy field in said reactor for genera-
`tion of plasma, the improvement comprising:
`
`Page 9 of 11
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`

`

`5,302,882
`
`9
`9. The apparatus of claim 8 wherein said electrical
`filter a low-pass filter.
`10. The apparatus of claim 9 wherein said low-pass
`filter is a Chebyshev filter.
`11. A plasma process of exposing a material to a reac-
`tive gas in a reactor wherein said reactor is coupled to
`a first electrical source which provides an electrical
`signal at a fundamental frequency f to generate an elec-
`trical energy field for generation of plasma in said reac- '
`tor, comprising inserting an electrical filter coupled
`between said reactor and said first electrical source to
`pass said frequency f, but to inhibit harmonics of said
`fundamental frequency f generated due to a non-linear
`response characteristic of said plasma in said reactor
`
`10
`from interacting with electrical circuit parameters of
`said first electrical source, such that when a second
`electrical energy source is substituted in place of the
`first electrical source, original plasma characteristics
`are substantially restored by adjusting the amplitude of
`an electrical signal from said second electrical source at
`said frequency f without requiring retuning of said sec—
`ond electrical energy source.
`12. The process of claim 11 wherein said electrical
`’filter is a low-pass filter.
`13. The process of claim 12 wherein said low-pass
`filter is a Chebyshev filter.
`t
`t
`t
`t
`t
`
`10
`
`15‘
`
`20
`
`25
`
`3O
`
`35
`
`45
`
`SO
`
`55
`
`65
`
`Page 10 of 11
`Page 10 ofll
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`

`

`UNITED STATES PATENT AND TRADEMARK OFFICE
`
`CERTIFICATE OF CORRECTION
`
`PATENTNO : 5,302,882
`DATED
`: April 12, 1994
`
`INVENTOR(S): Paul A. Miller
`
`It is certified that error appears in the above-identified patent and that said Letters Patent
`.
`18 hereby corrected as shown beIow:
`
`Column 1,
`
`line 55, "system for" should be -—system. For——.
`
`Column
`
`line 37, "possible" should be -—impossible--.
`
`Column
`
`line 25,
`
`insert ——,—- after "11“.
`
`Column
`
`line 32, "he" should be --the——.
`
`Column
`
`line 37, "comprises" should be —-comprised——.
`
`Column
`
`line 66, "comprises" should be --comprised—-.
`
`insert -—The United States Government
`line 4,
`Column 1,
`has rights in this invention pursuant
`to Contract
`No. DE—ACO4—89AL58872 between the Department of
`Energy and SEMATECH,
`Inc.—- before "This".
`
`
`
`Signed and Sealed this
`
`Fifth Day of August, 1997
`
`mum
`
`BRUCE LEHMAN
`
`Attesting Ofiicer
`
`Commisxiorzer of Patents and Trademarks
`
`Page 11 of 11
`Page 11 ofll
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`