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`Samsung Exhibit 1011
`Samsung Electronics Co., Ltd. v. Daniel L. Flamm
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`

`
`EP 0 665 575 A1
`
`The present invention relates to plasma—based processing systems.
`Etching operations are frequently used in the formation of modern semiconductordevices. Typically, layers
`within device structures are formed by depositing a thin film layer of material on the semiconductor substrate,
`forming a photoresist mask on the thin film layer, and then removing the material left exposed by the photoresist
`mask in an etching step. A number of characteristics of the reactive ion etching (RIE) technique make it better
`suited to the extreme demands of modern device processing than many of other etching techniques. Because
`of the high level of directional selectivity achieved with reactive ion etching, its use enables device structures
`of greater density to be formed. In addition, the relatively low temperatures at which RIE is performed make
`such process steps compatible with even the later stages of device processing.
`The process of forming a photoresist mask and then etching to remove material is repeated many times
`in the formation of semiconductor devices. Thus, the etching process has a substantial impact on the proc-
`essing time required to produce semiconductor devices, as well as on the yields for those processes. As with
`many of the processing steps employed to form modern semiconductor devices, there is a need to reduce the
`time needed for etching steps so that process through put can be increased. There is a similar need to improve
`the reliability and predictability of etching processes.
`Reactive ion etching, and the related technique of magnetically enhanced reactive ion etching (MERIE),
`removes that portion of a thin film layer not protected by a photoresist mask through a combination of physical
`bombardment, chemical etching and chemical deposition. In these reactive ion etching processes, a chemical
`etchantfrom a plasma created above the etching substrate is transferred to and then absorbed onto the surface
`of the material to be etched. Ion bombardment provides additional energy to bring the absorbed etchant species
`to a higher energy state and to accelerate the surface reaction. Chemical etchants are typically chosen so that
`etching occurs predominantly at the exposed portions of the thin film layer rather than on the surfaces of the
`photoresist mask. Reacted material, which is typically volatile,
`is removed from the surface of the device
`through a vacuum exhaust line. An RIE or MERIE system typically uses a single, RF-powered cathode for gen-
`erating a capacitively coupled plasma. Accordingly, the etching system walls, including the top lid, are typically
`grounded in such a system to define the extent ofthe RF field and the region in which a plasma is generated.
`Optimizing the reactive ion etching environment typically includes optimizing the operational pressure
`within the etching chamber. When chlorine chemistry (e.g., based on Clz), fluorocarbon chemistry, or other,
`similar chemistry is used in the etching system, it is desirable to operate at relatively high pressures (between
`about 100 mi||iTorr and about 250 mi||iTorr) to obtain a good balance between the effects of physical bombard-
`ment and chemical etching. When chemically strong etchants, such as SF6 or NF3, are used, lower pressure
`operation is desirable. Higher operating pressures can increase both the density of etchants within the plasma
`and the rate of transport of etchants to the surface of the etching substrate. In many circumstances, higher
`operating pressures may improve the selectivity between the photoresist mask and the material being etched.
`Higher operating pressures require a correspondingly higher level of RF power in put to maintain a suitable DC
`bias to obtain good etch profiles. RIE and MERIE systems also exhibit greater stability and reduced etch re-
`sidues at higher operating pressures.
`Two types of cathode structures are typically used to deliver RF power into reactive ion etching systems.
`The "isolated cathode" structure uses a cathode separated from the chamber walls primarily by insulation. Al-
`though this cathode structure is simple and relatively reliable, the RF power input to the cathode may couple
`to the chamber wall through vacuum, giving rise to an undesirable secondary plasma. Asecond type of cathode
`structure places a shielding structure between the cathode and the walls of the etching system. In typical im-
`plementations of this "shielded cathode" design, a shield, typically in the form of a grounded cylinder, is placed
`around the cathode. An insulating cylinder, also typically cylindrical, physically and electrically separates the
`cathode from the shield. The grounded shield prevents the creation of a secondary plasma between the cath-
`ode and the walls of the etching chamber. Under some conditions, however, arcing may occur between the
`RF-powered cathode and the grounded shield. In particular, high operating pressure and high RF input power
`often causes arcing, probably because of the high potential drop overthe short distance between the powered
`cathode and the grounded shield. The thinner plasma sheath associated with high pressure, high input power
`operation may make the generation of a secondary plasma more likely in the narrow space between the RF-
`powered cathode and the grounded shield.
`One preferred embodiment of the present invention is an etching system including a cathode capable of
`exciting a plasma. Ashield structure, which may be maintained at an electrical potential differentfrom the cath-
`ode, is disposed adjacent to and about at least a portion of the cathode. An insulating structure is disposed
`between the cathode and shield. Any gaps within the insulating structure, or between the insulating structure
`and the cathode or shield, which may define a gas conduction path between the cathode and shield, are limited
`over at least a portion of any such gas conduction path to less than the threshold thickness which would allow
`the generation of a secondary plasma.
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`EP 0 665 575 A1
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`Another preferred embodiment of a reactive ion etching system in accordance with the present invention
`includes a cathode coupled to a high frequency power source capable of exciting a plasma. Ashield structure
`is disposed adjacentto at least a portion of the cathode, and the shield structure can be maintained at an elec-
`trical potential different from the cathode. An insulating structure is disposed between the cathode and the
`shield structure so that an edge of the insulating structure extends beyond either a surface of the cathode or
`an edge ofthe shielding structure. The edge ofthe insulating structure has a cap disposed upon it so that the
`cap defines at least a portion of a gas conduction path between the shield structure and the cathode. Aflange
`extends from the insulating structure to interrupt the gas conduction path.
`In another preferred embodiment of the present invention, a cathode is coupled to a high frequency power
`source capable of exciting a plasma. Ashield structure is disposed adjacent to at least a portion of the cathode,
`and the shield structure is maintained at an electrical potential different from the cathode. An insulating struc-
`ture is disposed between the cathode and the shield structure so that an edge of the insulating structure ex-
`tends beyond either a surface of the cathode or an edge of the shielding structure. Acap structure is disposed
`adjacent to an edge of the cathode and is fitted to the insulating structure so that the cap structure is separated
`from the insulating structure by a sufficiently thin gap so that a secondary plasma is not generated within said
`gap at operating pressures in excess of 150 milliTorr. In a further aspect of this preferred embodiment, a gap
`equal to or less than 20 thousandths of an inch separates the cap structure from the edge of the insulating
`structure.
`
`In yet another preferred embodiment of the present invention, a cathode is coupled to a high frequency
`power source capable of exciting a plasma. Ashield structure is disposed adjacent to at least a portion of the
`cathode, and the shield structure is maintained at an electrical potential different from the cathode. An insu-
`lating structure is disposed between the cathode and the shield structure so that an edge of the insulating
`structure extends beyond either a surface of the cathode or an edge of the shielding structure. The etching
`system further includes means for restricting plasma conduction between the cathode and the shield structure
`at operating pressures of 150 milliTorr or greater.
`The following is a description of some specific embodiments of the invention, reference being made to
`the accompanying drawings, in which:
`Fig. 1 is a cross section of a prior art reactive ion etching system;
`Fig. 2 is a detailed view of a portion of the reactive ion etching system of Fig. 1;
`Fig. 3 is a detailed view of a portion of a reactive ion etching system in accordance with the present in-
`vention; and
`Fig. 4 is a cross section of a reactive ion etching system in accordance with the present invention.
`The present invention generally relates to reactive ion etching (RIE) systems and magnetically enhanced
`reactive ion etching (MERIE) systems. For convenience, these systems will be collectively referred to herein
`as reactive ion etching (RIE) systems. Prior art RIE systems are typically unable to maintain the higher oper-
`ating pressures that are desirable for greater operating stability, improved etching rates, improved selectivity,
`and reduced residue levels. The present inventor has identified what is believed to be the primary mechanism
`for electrical breakdown in the shielded cathode configuration of prior art RIE systems. Apparently, a mech-
`anical fitting becomes sufficiently loose during normal operation so as to allow ionized gas to flow between
`the system cathode and a grounded shielding structure within the system. By lengthening or restricting the
`path along which the ionized gas (i.e., the plasma) must travel to conduct electricity, the likelihood that break-
`down will occur by this mechanism can be greatly reduced, allowing for higher pressure operation in a shielded
`cathode RIE system. In a preferred embodiment of the present invention, the plasma conduction path can be
`interrupted by extending an insulating flange to divert plasma flow away from the normal conduction path be-
`tween the cathode and the shielding structure. In another preferred embodiment of the present invention, the
`plasma conduction path is restricted by reducing the size of the gap between the insulating structure and the
`clamping ring structure used to hold the etching substrate in place. By substantially improving the machining
`tolerances for this mechanical joint, the likelihood of creating a sufficient plasma conduction path to allow arc-
`ing to occur is greatly reduced.
`Fig. 1 illustrates a prior art RIE system in cross section. The illustrated etching system consists of an etch-
`ing substrate 10 disposed on a support structure 12. Most often, the etching substrate 10 is a semiconductor
`wafer at some intermediate stage of processing. The etching substrate is preferably mounted in a temporary
`but rigid manner with respect to the support structure 12. For example, the support structure may be an elec-
`trostatic chuck that holds the etching substrate in place by inducing a large electrostatic attraction between
`the dielectric etching substrate and a charge established within the electrostatic chuck. Alternatively, the etch-
`ing substrate may be held in place by a clamping ring 14, as illustrated in Fig. 1.
`During etching operations, the support structure 12 preferably acts as a cathode for the etching system.
`Generally, the anode for the system is primarily the upper surface 16 (i.e., the lid) of the etching chamber, but
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`EP 0 665 575 A1
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`the walls 17 of the etching chamber also act as part of the system anode. Both the lid 16 and the walls 17 of
`the etching chamber are preferably grounded. In operation, a molecular gas such as BCI3, Clz, HBr, SF6, CZF6
`or CF4 is introduced to the region between the cathode 12 and the lid 16 of the etching chamber. RF power is
`applied to the cathode 12, so that the RF power capacitively couples to and excites the molecular gas, partially
`or completely ionizing the gas to create a plasma. The molecular gas is chosen so that it ionizes to yield an
`etchant species that is suitable to etch the desired material from the surface of the etching substrate 10. The
`difference between the surface area of the cathode 12 and the surface area of the lid 16 and walls 17 of the
`
`etching chamber (collectively the system anode) means that the etching system's RF circuit is asymmetric.
`Consequently, when RF power is applied to the cathode, a DC bias will be induced on the cathode. This induced
`DC bias is typically negative and tends to accelerate positive ions toward the etching substrate. An additional
`DC field may also be applied to further accelerate the ionized etchant gases toward the etching substrate 10.
`The induced and applied DC fields improve the etching rate by increasing the transport of etchant to the surface
`of the etching substrate 10 and by increasing the kinetic energy of the etchant molecules reaching the surface
`of the etching substrate.
`High plasma density and high ionization levels are favorable to improved etching rates. Producing a high
`density plasma or a high ionization level requires very high input power levels. As a practical matter, the plasma
`for etching must be contained within a well-defined region of the processing chamber. If the plasma is not ade-
`quately contained, there may be insufficient power density to maintain the plasma, even if powerful RF gen-
`erators are used to excite the plasma. To facilitate the formation of a stable plasma, a number of measures
`are taken within the processing environment to contain both the plasma itself as well as the electric field used
`to create the plasma. Often, the lid 16 ofthe etching chamber and the support structure 12 are spaced closely
`together and the plasma gases may be physically confined in other manners. For example, a ring 8 may extend
`from the clamping ring 14 to partially confine the plasma gas within the region adjacent to the etching substrate
`10.
`
`In shielded cathode RIE systems, the RF electric field used to create the plasma is also contained to pre-
`vent power dissipation in ways that do not contribute to the formation of an etching plasma. An example of
`such containment is illustrated in Fig. 1. Ashield structure 18 is disposed around the cathode support structure
`12 to contain the RF driving field. The shield structure 18 is typically disposed as closely as possible to the
`cathode support structure 12 and is generally maintained at ground potential. Accordingly, the shield structure
`18 also acts, to some extent, as an anode for the reactive ion etching system. The close proximity of the shield
`structure 18 to the cathode support structure 12, coupled with the presence of ionized gases from the plasma,
`makes electrical conduction between the shield structure 18 and the cathode support structure 12 likely unless
`appropriate measures are taken. Such electrical conduction is an effective short circuit, allowing the input RF
`power to be drawn away and causing the plasma to break down.
`To prevent conduction between the shield structure 18 and the cathode support structure 12, a dielectric
`insulator 20 is disposed between shield structure 18 and the cathode support structure 12. Often the dielectric
`insulator 20 is formed from quartz because of the durability, toughness and good insulating properties of
`quartz. Other dielectric materials can also be used, including such dielectric ceramics as alumina. For the ge-
`ometry shown in Fig. 1, the dielectric insulator 20 has a cylindrical or pipe-like shape. In addition to providing
`a dielectric insulator 20 between the shield structure 18 and the cathode support structure 12, it is typical to
`use a close fitting cap over the dielectric insulator 20 to further electrically isolate the shield structure 18 and
`the cathode support structure 12. For example, when a clamping ring structure is used, the clamping ring 14
`may be formed with a groove having a rectangular cross section that mates with the edge of the dielectric in-
`sulator 20. Thejoint between the dielectric insulator 20 and the clamping ring 14 illustrated in Fig. 1 is shown
`in greater detail in Fig. 2. Here, and in all ofthe figures discussed herein. the same numbers are used to indicate
`the same or similar components of the illustrated systems.
`Fig. 2 illustrates the mechanical joint between shield structure 18, dielectric insulator 20, cathode support
`structure 12 and clamping ring 14. Achannel 22 having a rectangular cross section is formed in clamping ring
`14 to fit over the edge of the dielectric insulator 20 that extends above the shield structure 18 and the edge
`of the cathode 12. The channel 22 is designed to fit around the edge of the dielectric insulator 20. Using the
`clamping ring 14 as an end cap for the dielectric insulator 20 has the effect of further electrically isolating the
`shield structure 18 from the cathode support structure 12. However, the gap 24 which is left between the chan-
`nel 22 and the edge of the dielectric insulator 20 upon assembly of the clamping ring 14 tothe dielectric insulator
`20, generally has not been well controlled in embodiments ofthe Fig. 1 geometry. Consequently, the typical
`gap 24 has ordinarily been on the order of between about 40 and 60 thousands of an inch.
`Despite the measures taken to electrically isolate the cathode support structure 12 from the shield struc-
`ture 18 and to contain the plasma field within the region in which the etching operation is to be performed,
`existing reactive ion etching systems cannot be reliably operated at high pressures. For example, the use of
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`EP 0 665 575 A1
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`pressures above about 150 milliTorr results in plasma instability and arcing in existing shielded cathode de-
`signs of reactive ion etching systems. Table 1 illustrates the arcing problems of an RIE system of the general
`configuration indicated by Fig. 1. This Table shows the level of DC bias (in Volts) induced on the cathode for
`a variety of different in put RF power levels for a number of different operating pressures. Either two or three
`trials were made at each combination of input RF power and operating pressure. Typical DC biases for non-
`arcing conditions are between -300 V and -500 V. The shaded boxes indicate trials in which arcing was ob-
`served within the 50 second trial period.
`
`DC BIAS (Volts) -- PRIOR ART CONFIGURATION
`
`RF Power Input to Target
`wow
`
`i i
`
`i
`
`:
`
`Previous efforts have been unable to improve upon the performance indicated in Table 1. The present in-
`ventor has identified what is believed to be the most common breakdown path in existing shielded cathode
`reactive ion etching systems. By reducing the likelihood of electrical breakdown along this path, the present
`invention overcomes some of the disadvantages of existing reactive ion etching systems. The resulting system
`has achieved stable operation at considerably higher operating pressures and has achieved greater stability
`at those pressures than has been obtained with existing reactive ion etching systems.
`The present inventor has observed that in existing shielded cathode etching systems, the shield structure
`18 is insufficiently insulated from the cathode support structure 12, giving rise to the arcing and plasma break-
`down indicated in Table 1. The present inventor has determined that, despite the presence of an insulating
`structure 20 and the presence of an isolating clamping ring structure 14, electrical breakdown occurs in shield-
`ed cathode etching systems by plasma conduction between the shield structure 18 and the cathode support
`structure 12. This conduction is mediated by the presence of ionized gas within a gap 24, indicated in Fig. 2,
`between the clamping ring channel 22 and the dielectric insulator 20. In existing RIE systems, the channel 22
`is typically machined so that the gap 24 remains on the order of between 40 and 60 thousandths of an inch.
`Gap 24 may open further during the normal operation ofthe reactive ion etching system due to the differential
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`EP 0 665 575 A1
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`thermal expansion of components of the etching system. During normal operation of the reactive ion etching
`system, all of the components of the etching system are heated to some extent. The heating and the absorption
`of heat need not be uniform between the various components of the system. Thus, different components of
`the system may be heated to different temperatures. The differing temperatures of different system compo-
`nents, as well as the differing thermal expansion coefficients of these different system components, may lead
`even closely fitting mechanical joints to separate in the normal course of operation. Thus, a gap 24 may arise
`between the channel 22 and the edge of the dielectric insulator 20 during normal operation regardless of how
`closely the channel 22 fits around the edge of the dielectric insulator 20 at room temperature.
`Whether the gap arises from poor machining tolerances or because of differential thermal expansion, this
`gap is larger than the threshold width necessary for the generation of a secondary plasma at high operating
`pressures and high input powers. In other words, as the operating pressure and power are increased, the thick-
`ness of the plasma sheath decreases sufficiently so as to fitwithin the gap. If the gap 24 is larger than a thresh-
`old width during operation of the etching system, a gap 24 extending from the shield structure 18 to the cathode
`support structure 12 will eventually contain sufficient ionized gas to maintain conduction between the shield
`and the cathode. When a secondary plasma is generated within the gap 24, arcing occurs and current flows
`between the cathode and the shield, draining the input RF power away from the primary plasma and causing
`the primary plasma to break down.
`The present invention is directed to reducing the possibility of electrical conduction between the shield
`structure 18 and the cathode support structure 12. A preferred embodiment of the present invention is illu-
`strated in Fig. 3, which is an expanded cross sectional view of the junction between a shield structure 18, cath-
`ode support structure 12, clamping ring 14 and dielectric insulator 26. Typically, it is preferred that the joint
`between the clamping ring 14 and the dielectric insulator 26 be machined to higher tolerances than in the prior
`art system. The gap 24 is controlled to within approximately 10 to 20 thousandths of an inch. By maintaining
`higher tolerances between the components ofthe etching system, the gap 24 will be smaller than the threshold
`width necessary to support the generation of a secondary plasma, even for high operating pressures and high
`RF power input.
`In some preferred embodiments ofthe present invention, a flange 28 extends from the dielectric insulator
`26 between the clamping ring 14 and the shield structure 18. It is believed that the flange 28 has the effect
`of interrupting the gas conduction path from the shield structure to the cathode support structure. This inter-
`ruption may arise from the flange 28 acting to substantially block the gas conduction path or to divert the gas
`conduction path through a region with a low density of ionized gas and a reduced level of RF power. Because
`little of the plasma excitation field should be present in the region 30 adjacent to the outer edge of the clamping
`ring 14, which is disposed away from the plasma excitation region, no secondary plasma should be generated
`in the region 30. Accordingly, if the flange 28 acts to divert the gas conduction path into the region 30, the
`ionized gas flowing through the channel 22 will be diluted in the region 30, greatly reducing the possibility of
`electrical conduction between the shield structure 18 and the cathode support structure 12. From a different
`perspective, the flange 28 may effectively increase the length of the conduction path between the shield struc-
`ture 18 and the cathode support structure 12, increasing the impedance to electrical conduction between the
`shield 18 and the cathode 12.
`
`Fig. 3 illustrates the flange 28 as extending to be flush with the edge ofthe clamping ring 14, but in practice
`the flange 28 may extend beyond the extent of either the clamping ring 14 or the shield structure 18. The extent
`of the flange 28 is limited by the space available within the reactive ion etching chamber. In some circumstanc-
`es, where either the gas conduction path is sufficiently blocked or diverted, the flange need not extend to be
`flush with either the clamping ring 14 or the shield structure 18. Fig. 3 illustrates a preferred embodiment of
`the present invention in which the flange 28 has a generally rectangular cross section. Other shapes are useful
`in practicing the present invention. The particular shape employed for the flange 28 will often depend on the
`geometry of the edge of the shield structure 18 and of the clamping ring 14. It is preferred that the shape of
`the flange be chosen to divert or block the gas conduction path between the electrode shield 18 and the cath-
`ode support structure 12.
`Fig. 4 illustrates a preferred embodiment of the present invention. Here, the dielectric insulator 26 prefer-
`ably comprises a quartz cylinder with a flange 28 extending outwardly from the surface of the quartz cylinder.
`The flange 28 may be formed by machining the quartz cylinder, or it may be formed by "welding" the flange
`structure to the surface of the quartz by any of the well—known methods for working quartz. Structures other
`than a flange could also be used, so long as the structure functions to interrupt the gas conduction path be-
`tween the shield structure 18 and the cathode support structure 12. In addition, the present invention may
`also be implemented in reactive ion etching systems where a structure other than a clamping ring is used as
`a cap for the dielectric insulator.
`Table 2 illustrates the improved performance achieved by an RIE system in accordance with the present
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`EP 0 665 575 A1
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`invention. As with Table 1, Table 2 shows the level of DC bias (in Volts) induced on the cathode for a variety
`of different input RF power levels for a number of different operating pressures. The numbers in Table 2 are
`averages of three trials made at each combination of input RF power and operating pressure. No arcing was
`observed for any of the combinations of operating pressures and input RF power for any of the trials.
`
`TABLE 2
`
`ti
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`P753?3E
`3 -447E
`EE
`
`3 -324
`
`(mTorr)
`
`700W 750W
`
`800W
`
`8 50W
`
`900W 9 50W
`
`By modifying the reactive ion etching system in accordance with the present invention, higher gas pres-
`sures can be maintained in the processing chamber. Tests on a reactive ion etching system as illustrated by
`Fig. 4 have demonstrated stable operation at gas pressures of 300 milliTorr for a wide range of input powers.
`This represents a marked improvement over the system illustrated by Fig. 1, which demonstrates stable op-
`eration only at pressures of 150 milliTorr or lower. Similarly, the present invention allows reactive ion etching
`systems to operate with higher plasma power inputs and the consequential increase in the density of ionized
`gas. For example, the system illustrated by Fig. 4 demonstrated stable operation at input powers of up to 950
`Watts at gas pressures as high as 300 milliTorr. By contrast, the Fig. 1 system demonstrated stable operation
`only up to about 600 Watts of input power at a gas pressure of only 150 milliTorr. By obtaining such higher
`pressure or higher power operation, a reactive ion etching system in accordance with the present invention is
`capable of attaining higher etching rates, reduced etch residue, better photoresist selectivity, and an overall
`more stable etching process.
`While the present invention has been described with reference to specific preferred embodiments thereof,
`it will be understood by those skilled in this art that various changes may be made without departing from the
`true spirit and scope of the invention. In addition, many modifications may be made to adapt the invention to
`a given situation without departing from its essential teachings.
`
`Claims
`
`1. An etching system defining a controlled subatmospheric environment containing ionizable gas, and for
`use with a high frequency power source, comprising:
`a cathode within the environment coupled to the high frequency power source and capable of ex-
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`EP 0 665 575 A1
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`citing a plasma;
`a shield structure disposed adjacent to and about at least a portion of said cathode, wherein said
`shield structure may be maintained at an electrical potential different from said cathode; and
`an insulating structure disposed between said cathode and shield structure,
`with any gaps within said insulating structure, or between said insulating structure and said cath-
`ode or shield structure, which may define a gas conduction path between said cathode and shield struc-
`ture being limited over a least a portion of any such path to less than the threshold thickness which would
`allow the generation of a secondary plasma within such a path.
`
`in which said insulating structure between said cathode and
`An etching system as claimed in claim 1,
`shield structure extends outwardly at least to the outer perimeter of said shield structure.
`
`An etching system as claimed in claim 1 or claim 2, wherein the thickness of any said gap is limited to
`less than about twenty thousandths of an inch over at least a portion of said part.
`
`An etching system as claimed in any of claims 1 to 3, wherein the environment is maintained at a pressure
`of less than about 250 mi|liTorr.
`
`An etching system as in any of claims 1 to 3, wherein the environment is maintained at a pressure within
`the range of greater than about 150 mi||iTorr to about 300 mi||iTorr.
`
`An etching system as claimed in claim 5, wherein the power input by said high frequency power source
`to said cathode is in excess of 600 Watts.
`
`An etching system comprising:
`a high frequency power source;
`a cathode coupled to said high frequency power sources so that said cathode is capable of exciting
`a plasma in a region adjacent to said cathode;
`a shield structure disposed adjacent to and enclosing at least a portion of said cathode, wherein
`said shield structure may be maintained at an electrical potential different from said cathode; and
`an insulating assembly disposed between said cathode and said shield structure, said insulating
`assembly having a projecting portion extending at least to the outer perimeter of said shield structure,
`wherein said insulating assembly defines one or more gaps therein, or between said insulating as-
`sembly and said cathode or said shield structure, said one or more gaps comprising at least a portion of
`a gas conduction path between said shield structure and said cathode, and
`wherein said projecting portion of said insulating assembly interrupts said gas conduction path.
`
`The etching system as claimed in claim 7, wherein the thickness of at least a portion of said gas conduction
`path is less than the threshold thickness necessary to allow the generation of a secondary plasma within
`said at least a portion of said gas conduction path.
`
`The etching system as claimed in claim 8, wherein the thickness of at least a portion of said gas conduction
`path is less than about twenty thousandths of an inch.
`
`. The etching system as claimed in any of claims 7 to 9, wherein said insulating assembly substantially
`blocks said gas conduction path between said shield structure and said cathode.
`
`. The etching system as claimed in any of claims 7 to 10, wherein said insulating assembly acts to divert
`said gas conduction path through a region having a low density of ionized gas.
`
`. The etching system as claimed in any of claims 7 to 11, wherein said insulating assembly comprises a
`substantially cylindrical body of dielectric material and wherein said projecting portion of said insulating
`assembly has a generally rectangular cross section.
`
`. The etching system of claim 12 wherein said projecting portion of said insulating assembly extends beyond
`both the perimeter of said cathode and the perimeter of said shield structure.
`
`. An etching system comprising:
`a high f