Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
  • H01J37/32082—Radio frequency generated discharge
  • H01J37/321—Radio frequency generated discharge the radio frequency energy being inductively coupled to the plasma
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P10/00—Bonding of wafers, substrates or parts of devices
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32431—Constructional details of the reactor
  • H01J37/32623—Mechanical discharge control means
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P50/00—Etching of wafers, substrates or parts of devices

Definitions

• This invention relates to inductively-coupled plasma (ICP) sources used in the processing of semiconductors.
• the invention is particularly applicable to high-density inductively-coupled plasma (HDICP) sources in- which RF energy is inductively coupled through a dielectric material that is protected by a slotted deposition baffle to energize a plasma for depositing an electrically conductive material onto, or etching an electrically conductive material from, a semiconductor wafer.
• HDICP high-density inductively-coupled plasma
• ICP sources employ an antenna that couples RF energy into a working, or processing, gas in a vacuum chamber, thus exciting a plasma in the gas.
• Such sources further employ an electrically insulating window or other electrically insulating material barrier between the antenna and the processing zone.
• a window where used, may provide a barrier between atmospheric air and the vacuum of tlie chamber.
• the ICP source is an integral part of tire vacuum chamber that contains the working or processing gas that is used for processing of the semiconductor wafers.
• a dielectric window or other electrically insulating structure has to be protected from plasma to avoid building-up conductive coatings on the surface of tlie insulating material that could prevent efficient RF power delivery into the plasma.
• Surface protection of the insulating material is provided by a structural device, namely, a deposition baffle placed between the plasma and the insulating material.
• the electrically insulating material is referred to hereafter as a window.
• a window is typically formed of a dielectric material such as ceramic. Deposition baffles made of slotted shields are described in U.S.
• iPVD physical vapor deposition
• U.S. Patents Nos. 5,800,688 and 5,948,215 using cylindrical sources
• U.S. Patent Nos. 6,080,287 and 6,287,435 using planar flat and three- dimensional antennae.
• a deposition baffle device or shield in a plasma processing system serves several purposes.
• Such a shield can provide protection, from plasma radiation, contamination and sputtering, for a dielectric window when the antenna is placed at the atmospheric side of the window, and for the antenna itself when the antenna is placed in the vacuum.
• a shield may prevent the deposition of a conductive coating onto the surface of the dielectric window.
• the baffle or shield device is generally preferred to be opaque to the electrostatic fields but transparent to the electromagnetic fields, so that the device prevents electrostatic coupling of RF energy from tlie antenna to the plasma but allows magnetic coupling of the energy for the excitation of plasma. From the coupling efficiency standpoint, it is desirable to minimize tlie image currents on the shield so that energy is not wasted in joule heating of the shield.
• a single design for a deposition baffle or shield cannot fully optimize all these aspects at once and so involves many trade-offs of these various requirements.
• a shield that produces the least loss and is most transparent to electromagnetic fields is no shield at all.
• a perfect electrostatic and particle shield would entail complete enclosure of the antenna or dielectric window within a grounded case to separate it from the plasma environment, allowing no coupling at all. Optimization of a shield design is even more difficult when utilizing an antenna with a complex shape and structure rather than one in the form of a simple RF snip.
• a uniform spatial coupling efficiency is desirable for a deposition baffle, particularly in plasmas used for processing oflarge diameter semiconductor wafers, because of a need for symmetric (at least, aziniuthally uniform) RF power coupling into the plasma inside the chamber.
• Non-symmetric plasma tends to produce more contamination and erosion of hardware parts near the plasma source, including producing an irregular target sputter etch rate due to aziniuthally non-uniform ion flux, which thereby produces a non-uniform etc or deposition.
• overall dimensions of a processing apparatus must be limited to several tens of centimeters, as there are requirements or at least preferences to keep a small footprint for the processing tool. Size limitations prevent enough space for using large components to keep the ends, edges and other irregular structural features away from critical locations.
• Non-uniform target erosion shortens the life of a target and thus increases the cost of ownership of the tool.
• a non- uniform erosion rate may produce an oval or other irregular pattern in the film deposited on the substrate formed by a varying thickness of the deposited film on the substrate.
• An important property of a deposition baffle is its transparency to electromagnetic fields. Slots allow azimutlial magnetic flux, which is produced by currents flowing in the conductors of an antenna that encircle the conductors in planes normal to the conductors, to pass through the baffle. An electric field is induced across the gaps between adjacent slots of the baffle that border the slots, which is in a direction such that it supports ExB movement of flux from the gap and away from the antenna.
• the transmission coefficient may reach values up to the 0.8 - 0.9 range.
• An electrically conductive deposition baffle can produce two adverse effects on antenna-to-plasma coupling properties: (1) magnetic shielding of the antenna current /,,, and (2) possible significant ohmic losses Both effects aie stiongei when magnetic flux lioimal to the suiface of the baffle is mci eased
• Electrostatic shielding pi ovided by a deposition baffle between the coil and the piocessing zone m the chamber makes it difficult to ignite plasma in an ICP leactoi, especially at low piess es
• new pioceduies have to be developed to piovide plasma ignition that is safe foi the opeiatmg personnel, will not damage the haidwaie and will not mteifeie with the piocess or damage the substrates being piocessed
• An objective of the piesent invention is to lemove azimuthal non-umfoimity in a plasma in ICP piocessing systems, andpaiticulaily to eliminate local eiosion of the taiget and piovide moieumfoim deposition on the subshate m ICP-iPVD systems by lemovmg such azimuthal plasma non-uniformities
• Anotliei objective of the piesent invention is to optimize tlie tiansfer function of a deposition baffle m an ICP piocessing system to piovide moie uniform distubution of the RF powei bemg hansfened into plasma tlnougli the baffle
• Still another objective of the piesent mvention is to miprove window protection fiom coating contamination
• a fuithei objective of the piesent invention is to aznnutlially lmpiove the cooling of a deposition baffle, and paiticulaily to theieby leduce flaking of deposited matenal mside of slots m the baffle
• a still furthei objective of the piesent invention is to piovide both ignition of the plasma and a safe ignition procedure at low powei and low piessuie conditions
• a deposition baffle in an ICP leactoi is const ucted with diffeieiit featiues and geometiies in the side of the slot facing the chambei oi plasma side of the baffle than on the side of the slot facing the window side of the baffle
• the effects of the ends of the slots of the baffle aie distributed evenly ovei the suiface of the baffle by electrically conductive budges acioss the slots of the baffle Piefeiably, such budges aie pi ovided on the chamber side of the baffle, that is the side that faces towaid the plasma, wheie then limiting effects on the tianspaiency of the baffle to magnetic fields aie minimized
• an mcieased tianspaiency to RF is pi ovided by an increased number of the slots In inci easing the numbei of slots, the slot liumbei and configiuation can be selected so that the lesonant fieqiiency of the coil- baffle RF cucuit is close to that of the RF eneigy souice poweimg the coil
• the budges By placing the budges on the plasma side of the deposition baffle they partially eliminate the letuin current path on the window side of the baffle and avoid being seen diiectly by the antenna, minimizing mtei fei ence between the bi ldges and the antenna Fui ther, the bridges enhance RF gi ound of the centi al poi tion of the shield, enhance shielding of tlie window fiom pai tides coming m a duection paiallel to the slots, and cieate theimal channels m a duection noimal to the slots Moieover, the budges help compress the RF magnetic field m the plasma side of the deposition baffle Further, the pattern of the budges lies and is distiiaded ovei the plane of the deposition baffle, which gives them a uniform effect on conditions m plasma [0027] Fuithei, the antenna and deposition baffle aie setup m appioximate lesonance as a
• plasma ignition may be carried out with DC power of 4-5 watts at 65 mTorr and 9-10 watts at 20 niTorr.
• ICP power is also applied just above the "backward threshold" power for H-E transition.
• the backward threshold for H-E transition is typically less than about 300 W for pressure in the range of from 20 to 100 mTorr. Accordingly, the ICP power can be set to 300 W or higher before ignition, but preferably not more than
• a synergetic effect of both DC and ICP powers ignites and sustains a plasma at very low power and voltage levels. After ignition both ICP and DC power can be set to process operating levels, or DC power can be switched-off sustaining plasma by ICP power only.
• FIG. 1 is a cut-away perspective view of an iPVD apparatus, illustrating components ofthe prior art
• FIG.1 A is diagrammatic perspective view of a section ofthe apparatus of Fig.1 showing instantaneous
• Fig. I B is a view, similar to Fig. 1 A illustrating such vectors in the center of a deposition baffle;
• Fig. 1C is a view, similar to Fig. IB illustrating such vectors at the ends ofthe slots ofthe deposition baffle;
• Fig. 2 A is a three-dimensional plot of the RF power density distribution in the chamber oftlie apparatus of Fig. 1 without a deposition baffle;
• Fig.2B is a three-dimensional plot ofthe RF power density distribution in tlie chamber ofthe apparatus of Fig. 1 with a deposition baffle;
• Fig. 3A is a perspective view showing the window side of a deposition baffle according to one embodiment ofthe present invention.
• Fig. 3B is a perspective view showing the chamber side of a deposition baffle of Fig. 3A;
• Fig. 3C is a cross-sectional view through tlie deposition baffle of Fig. 3B taken at line 3C-3C;
• Fig.4A is a bottom view showing the chamber side of a deposition baffle of Figs.3 A-D, showing one slot pattern;
• Fig. 4B is a bottom view, similar to Fig. 4A, showing a deposition baffle having an alternative slot pattern;
• Fig.4C is a bottom view, similar to Figs.4A and 4B, showing a deposition baffle having an alternative slot pattern;
• Fig.5A is a cross-sectional electromagnetic energy density diagram tlnougli the source ofthe apparatus of Fig. 1;
• Fig. 5B is a cross-sectional electromagnetic energy density diagram, similar to Fig. 5A, through the one embodiment of a source according to tlie present invention
• Fig. 5C is a cross-sectional electromagnetic energy density diagram, similar to Fig. 5B, through another embodiment of a source according to the present invention
• Fig. 5D is a three-dimensional plot oftlie power density distribution similar to Fig.2B h the chamber ofthe apparatus having the source Fig. 5 A;
• Fig. 5E is a three-dimensional plot oftlie power density distribution similar to Fig.5D in the chamber ofthe apparatus having the source of Fig. 5B;
• Fig. 5F is a three-dimensional plot ofthe power density distribution similar to Figs. 5D and 5E in the chamber ofthe apparatus having the source of Fig. 5C;
• Fig. 6A is a bottom view showing the chamber side of a deposition baffle of Fig. 5B;
• Fig. 6B is a top view showing the wmdow side of a deposition baffle of Fig. 6A;
• Fig. 6C is a fragmentary top view ofthe deposition baffle of Figs. 6A and 6B;
• Fig.6D is a fragmentary perspective view ofthe deposition baffle of Figs.6A-6C taken along line 6D-
• Fig. 6E is a fragmentary perspective view of a portion of tlie deposition baffle of Figs. 6A-6D;
• Fig. 7A is a graph showing peak voltage as a function of ICP power for various plasma ignition conditions
• Fig. 7B is a three-dimensional graph showing DC power as a function of ICP power and pressure
• Fig. 7C is a graph of DC and ICP plasma ignition power in a PVD system according to certain principles ofthe present invention.
• Fig. 7D is a graph of DC and ICP plasma ignition power in a PVD system according to certain principles ofthe present invention.
• the apparatus 10 includes a vacuum chamber 11 bounded by a chamber wall 14 and having a semiconductor wafer 12 supported for processing therein on an upwardly facing substrate support 13.
• An ionized sputter material source 15 is situated in the top ofthe chamber
• the target 11 includes a frusto-conical magnetron sputtering target 16 with an RF energy source 20 situated in an opening 17 in the center ofthe target 16.
• the source 20 includes an RF coil or antenna 21 connected to tlie output of an RF power supply and matching network 22.
• the coil 21 is located in atmosphere 18 outside oftlie chamber 11 , behind a dielectric window 23 that forms a part of the wall 14 of the chamber 11 that isolates a processing gas maintained at a vacuum inside ofthe chamber 11 from the atmosphere outside ofthe chamber 11.
• baffle 30 Inside of the window 23 is a deposition baffle 30 of electrically conductive material having, in the embodiment shown, a plurality of parallel linear slots 31 therethrough.
• the baffle 30 is metal.
• the baffle 30, between each pair of adjacent slots 31, is in the form of an elongated slat 32.
• the coil 21 has a plmality of parallel conductor segments 24 that lie close to the outside ofthe window 23 and interconnected by return segments 25 configured so that the ciuxents / admir in the segments 24 flow in the same direction and generate the magnetic field 2? react (Fig.1 A) that excites a high density plasma 40 within tlie chamber 11.
• These cunents I s are stiongei at the ends 33 of the slots 31 so as to compress the magnetic flux lines into slot 31 as lllustiated ui Fig.
• Thickness dimensions ofthe baffle 30 at the slots also play a lole m RF magnetic field tianspaiency of the baffle 30
• a gieater thickness of the shield 30 may coiitiibute to cunents that result in dominant contribution to olimic losses and mcieased shielding ofthe RF magnetic field fhiough tlie baffle 30
• slots 31 of tlie shield 30 aie typically pi ovided with slot stractuie piesentmg no lme-of-sight path fiom the plasma to the wmdow
• Such slots may, foi example, be chevion shaped oi have some othei suitable shape to accomplish this Foi simplicity
• m Fig. 1A a lectangulai cioss section is schematically shown
• baffle 30 causes the powei density distribution 42 to be modified to the distiibution 42a by the fonriula
• K BAFFLE ( ⁇ Y,Z) x P ANTENNA (X, Y,Z)
• K BAFFLE (X, Y,Z) represents the effects of olrmic losses, slot geometry and edge effects on the EM field. It represents azimuthal asymmetry ofthe plasma source. Hot spots closely located to the ends 33 of slots 31 produce locally more intense plasma. This can result in enlianced erosion ofthe target, which shortens the life ofthe target and thus increases the cost of ownership ofthe tool. Moreover, such non-uniform erosion rate may produce an oval pattern in film deposited on the substrate due to the varying thickness of deposited film on tlie substrate.
• an approach ofthe present invention is to distribute tlie edge effect over the baffle by intentionally creating the edge effect across the deposition baffle surface. Furthermore, by creating this effect on the side ofthe baffle 30 that faces toward the plasma 40, adverse effects of this approach are minimized. This is achieved by connecting individual slats together with metallic bridges in certain positions and thereby emulating "quasi ends" of slots 31 at various points along the slots 31.
• Steps taken by the present invention provide a deposition baffle 30a with increased transparency to the RF magnetic field from the coil and provide bridges 34 in a way that does not significantly increase return cunents across the slots, as illustrated, for example, in Figs. 3A-3D.
• Increased transmission of RF magnetic fields through the deposition baffle device is achieved in part by providing an increased number of tlie slots.
• the baffle 30 of the prior art source 20 of Figs. 1-lC has thirteen (13) slots 31.
• the RF magnetic field from the coil penetrates through the deposition baffle device through slots increased in number to, for example, sixteen (16), as illustrated in Fig. 3A.
• Such penetration is approximately proportional to the number ofthe slots 31a, increasing by 24% when changing the number of slots from 13 to 16 and by 43% when increasing tlie number of slots from 13 to 20.
• a baffle transmission coefficient can be defined as a ratio of average RF electromagnetic energy at the chamber side ofthe deposition baffle to the value at the input antemia side of the baffle that increases with the number of slots.
• the width of the slots 31a remains the same as the slots 31 , as a reduction in slot width increases ohmic losses in deposition baffle.
• the positions and extent ofthe bridges 34 can affect tlie coupling of power from the antenna 21 into the plasma 40.
• the bridges 34 are, for example, limited to portions ofthe slots 3 la on the chamber side oftlie deposition baffle 30a, as shown in Figs.3C and 3D, thereby restricting the return current paths by avoiding paths on the coil side of the baffle 30a.
• the antemia 21 does not directly "see" bridges 34 that are on the opposite side of tlie shield 30a from tlie coil, avoiding much ofthe potential interference between the bridges 34 and antemia 21.
• Bridges 34 on the chamber side oftlie baffle 30a are farther from the antenna 21, approximately ! _ the thickness of baffle 30a farther, where they have less interference with the antemia 21.
• the bridges 34 provide enlianced RF grounding of the central portion of the shield, reducing the inductance ofthe baffle structure, which can improve, and will not detract from, the performance ofthe baffle.
• the bridges 34 also enhance shielding ofthe window from particles coming in a direction parallel to slots 31a, and the bridges create thermal channels in a direction normal to the slots 31a, thus providing the heat flow in a direction normal to the slots, improved radial heat flow, and more effective cooling of baffle.
• the RF magnetic field from the antemia is not directly affected by addition ofthe bridges 34 in the slots 31 a on tlie chamber side of shield 30a.
• the bridges 34 affect the compression ofthe RF magnetic field on the chamber side ofthe deposition baffle 30a, creating local spots of increased RF field magnitude.
• the planar bridge pattern in the plane ofthe deposition baffle 30a provides a uniform affect on the plasma, offsetting other non-uniformities that are intrinsic to the system. Finite element simulation and analysis will aid in optimizing the placement ofthe bridges 34.
• Three examples of deposition baffles 30a, 30b and 30c are shown in Figs. 4A-4C, respectively, having respective slot variations 31a, 31b and 31c.
• the resonance frequency of the antenna 21 and deposition baffle, treating the antemia and baffle as a parallel LRC circuit is affected by the number of slots 31a and other baffle geometry. For example, increasing the number of slots from 13 to 16 and adding the bridges, dropped the resonance frequency of such a circuit from 19 MHz to 15 MHz, much closer to excitation frequency (13.56 MHz). Further reduction of resonance frequency to 13.56 MHz can be achieved by further similar adj ustment, whereby RF inductive coupling through the shield would be greatest, and maximal RF power would be coupled from the coil into the plasma.
• the slots 31 typically are configured so that no line-of-sight path is available from the plasma, through the baffle 30 and onto the window 23.
• chevron-shaped or other suitably shaped slots 31 are provided, and such slots typically have a width W of several millimeters, for example, 3-6 mm. But even with no line-of-sight path, at pressures of 20 mTorr and above, a certain amount of metal vapor can penetrate tlirough the slots of the deposition baffle and contaminate the dielectric window.
• Elimination ofthe stray plasma 43 is achieved by providing a baffle 30d having modified slot structure 31d, as illustrated in Fig. 5B.
• the slots 31d each contain a blade 37 within the slot 31d on the dielectric- window side of the baffle 30d.
• the position of tlie blade 37 which is fomied integrally of the conductive material ofthe baffle 30d, relative to the conductors 24 ofthe antemia 21, can create return current paths in tlie baffle 30d and affect the impedance ofthe coil 21.
• the blades 37 By making the blades 37 thin, such as in the form of narrow slats or lamellas with a thickness around 1 mm or less, placed within the slots 31 d close to the dielectric window 23, with minimal connection to the body ofthe baffle 30d, such return paths are minimized.
• the RF magnetic field B adequately penetrates the slots 3 Id having the blades 37.
• blades 37 are placed in the window side leg ofthe otherwise chevron-shaped slots 31d as shown in Fig. 5B.
• the blades 37 enhance physical shielding ofthe window 23 from particles coming from the stray plasma 43.
• the blades 37 are connected to a robust portion ofthe body ofthe deposition baffle 30d, with blade connection points 38 that are immersed into the bottom or middle side ofthe deposition baffle 30d, away from antemia 21, closer to the plasma side ofthe baffle 30d.
• the antenna 21 therefore "does not see", to any significant degree, these blade connections 38 that are in the bottom/middle portion of baffle 30d, thereby avoiding interference between the blade connections 38 and the antenna 21.
• the blades 37 are connected to tlie body of the deposition baffle 30d, thus they are cooled by the thermal channels created tlirough the blade connections 38.
• the blade connections 38 are in a direction normal to the slots 3 Id.
• tlie positions ofthe blade connections 38 provide only weak return cunent paths for ciuxents on the coil side ofthe baffle 30d.
• the blades 37 are not limited in use to only chevron-shaped slots, but can be incorporated into other slot types in a manner similar to that described above.
• the concept of adding the blades 37 to the slots 31 can be combined with the bridges 34 of Figs.3 A-3D and 4A-4C to achieve the advantages of both such features.
• tlie blades 37 where such blades are kept thin and their connections 38 are placed in tlie chamber side ofthe shield structure where their effect is partially shielded by the body of deposition baffle 30d itself.
• the blade connections 38 also lie in the plane ofthe deposition baffle itself, which provides uniform conditions the plasma.
• the pattern ofthe blades 37 can be optimized to a particular system by conducting simulations. Several blade pattern examples are described below, but the possible patterns for various applications is not limited only to those shown. [0087] For example, the average electromagnetic energy density pattern 45 a for RF energy transferred through a deposition baffle 30 ofthe apparatus of Fig. 1, having regular chevron slots 31 , is illustrated in Fig.
• FIG. 5A The energy density pattern 45b for energy transferred through the baffle 30d, having chevron slots 3 Id that include blades 37 on the wmdow side thereof, is illustrated i Fig. 5B.
• connection points 38 include connections 38a at the opposite longitudinal ends ofthe blades 37a that extend the full length ofthe shoitei ones of slots 31d, connections 38b at only one end ofthe blades 37b that extend only about one-thud ofthe length ofthe longei ones of slots 31d at an end theieof, and connections 38c at one end ofthe blades 37c that extend about one-thud ofthe length ofthe longer ones of slots 31d nea ⁇ the middle theieof Figs. 6C and 6D show the constiuction ofthe blades 37 in the slots 31d m fiagmentaiy bottom and peispective views
• FIG. 6E An alternative and advantageous incorpoiation of the blades 37 mto the baffle 30d is lllustiated in Fig. 6E, wheiem the connection points 38d of each blade 37 oi blade segment aie small cioss section posts that join the blades 37 along one side edge to a wall ofthe portion ofthe slots 31 d that is adjacent the chambei side oftlie baffle 30d Furthermore, the connections 38c of Fig. 6B and the connections 38d of Fig.
• the slots 3 Id with the blades 37 provide inductive coupling efficiency compaiable to that ofthe chevi on-shaped slots 31 without the blades, oi to withm 95% of oiiginal effectiveness of the slots 31
• the diffeience can be compensated foi by adding moie slots 3 Id into deposition baffle 30d
• the RF powei density distiibution m the chambei can be modeiately affected by the positions oftlie blade connections 38 , but the blade connections 38 do not significantly effect the total power oi electi omagnetic energy ti ansfe ⁇ ed into the plasma Umfoim distribution of blade connections 38 and avoiding closed loops by utilizing single connections only leduces the effects oftlie blade connections 38 onpower density distiibution
• the orientation ofthe blades 37 is not expected to mateiially
• the electrostatic shielding by the depositionbaffle oftlie coil from the chamber makes plasma ignition difficult.
• Plasma in tlie described apparatus is ignited and sustained with very low RF power coupled to the antenna (approximately 300 watts, for example) and a low DC power level at the target of about several watts, e.g. at least 4 W and 9 W at 65 mTorr and 20 mTorr, respectively.
• the separate electrode such as the baffle itself, can be used instead ofthe target for plasma ignition.
• iPVD for example, it is natural to use the target as tlie electrode, where the DC needed for ignition involves only setting power levels.
• etching it is necessary to provide another electrode, such as, for example, a small flat electrode, or wire - cylindrical electrode that would be used for plasma striking.
• the baffle itself can be used if it is not groiuided, or if it can be separated from ground for the short period when it is biased by low power DC.
• a so called "focusing ring" that is often provided to improve etch uniformity can be used.
• Electrodes should be (1) that it is made of low sputtering yield material to not contaminate the process chamber by electrode material (for example Pt, Ni, Mo, W, Ta), (2) that it withstand high temperature, (3) that it provide good electron emission from its surface, and (4) that it be incorporated in a place where it is not exposed directly to the hottest plasma, for example, part ofthe wall, part ofthe internal shield, or deposition baffle.
• electrode material for example Pt, Ni, Mo, W, Ta
• an ICP power is applied at the same time to the antemia at a level just above the "backward threshold" power for H-E transition.
• Such DC power alone is not enough to sustain plasma at such low power levels.
• Such low DC power level provides a very small amount of individual electrons of sufficient energy to strike a plasma by ionizing neutral atoms and producing secondary electrons and ions. However, these secondary electrons do not gain enough energy to produce another ionization act, which is needed for a plasma to be sustained.
• the ICP power alone, at the "backward threshold" level enough to ignite the plasma.
• H-E transition is an event that is typical of inductive discharges, which exhibit two modes of operation (1) the true inductive discharge known as the H mode, and (2) a weak capacitive discharge known as E-mode.
• H-E (or E-H) transition is transition from inductive coupling to capacitive coupling (or vice versa).
• E mode capacitive coupling
• the plasma is excited by the electric field produced by tlie antemia; the RF magnetic fields (H) ofthe antemia are low and do not induce electric fields inside the plasma that would be sufficient to sustain the plasma.
• Plasma density is considered as low density (Ne ⁇ 10 9 - 10 ⁇ c cm “3 ) and is generated by the electric field (E, electrostatic regime) that is related to antemia surface as a capacitive electrode.
• E electrostatic regime
• the discharge abmptly shifts from a low-density capacitive mode to a high-density inductive mode as the antenna generates intense RF magnetic fields, in the H electromagnetic regime due to the coil inductance, that induce strong electric fields inside plasma.
• This electric field is not related to any surface of the antemia, but it is strong enough to produce plasma densities in range from Ne -10" - 10' 2 cm "3 .
• the "backward" threshold for H-E transition is the reverse H-E transition threshold on the hysteresis curve.
• the true inductive plasma (H mode) is ignited only in the region above the forward E-H transition on the hysteresis curve and will extinguish in the region below the reverse H-E transition on the hysteresis curve.
• the "backward threshold" for H-E transition is less than 300 W for pressures in the range of from 20 mTorr to 100 mTorr. That means the ICP power should be set at least to 300 W before ignition, but not more than the power that would cause a vacuum tuned antenna to exhibit 5 kV or more of peak-to-peak voltage at one of its ends. For the antenna illustrated, this upper limit is around 500 - 600 W, as illustrated in Fig. 7A. [0098] The reason that 300 watts of ICP power is desirable for plasma ignition is to sustain low voltages in the system and to avoid damage, or by providing softer ignition, reducing the likelihood of arcing, for example, at the atmospheric side ofthe window.
• Atmospheric side arcing occurs at about 3.5 kV/mm for DC voltages.
• this limit is typically lower and depends on many factors.
• 500 - 600 watts of ICP power can be used safely for plasma ignition, but at 1 kW the probability of atmospheric arcing is higher. Therefore, the power should be less than 1 KW, and preferably not more than 500-600 W, particularly for lower pressure operation of, for example, below 20 mTorr.
• 500-600 watts of ICP power can be used safely at pressures above 20 mToix, with 10 mToix probably being the safe lower pressure limit for efficient ICP ignition at low DC power.
• ICP power plasma either may not ignite well or may not be sustained in "true inductive mode".
• Higher ICP powers of up to 600 watts helps ignite an inductive plasma using values of DC power at a target of up to 25-30 watts. But the plasma should not be ignited and sustained by higher DC power at a target only, as this produces voltage spikes in the absence of special electronic controls, as described inLantsmanU.S. PatentNo. 6,190,512, which spikes can produce damage to the equipment and contamination ofthe chamber and substrate by sputtered material. 10 mTorr is the likely limit for efficient ICP ignition at low DC and ICP powers.
• both the DC power and the ICP power causes the plasma to ignite and be sustained at very low power and voltage conditions.
• both ICP and DC power canbe set to process operating levels, or DC power can be switched-off sustaining plasma by the ICP power only.
• the example of power levels required to ignite and sustain plasma in argon gas in a plasma processing system for iPVD are shown in experimental data as plotted in Fig.7B, in which the arrows show from which DC power level plasma is ignited and sustained at two different pressures.
• Ignition and plasma sustaining procedures are shown in Figs. 7C for PVD systems in which there is a target and in Figs. 7D for etch systems or for plasma cleaning processes in which a target is not being used.
• the sequence in Fig. 7C is used for plasma ignition and subsequent ionized PVD processing, while the sequence in Fig. 7D is used for low power ignition and subsequent ICP-only based processes.
• Table 1 The sequence in Fig. 7C is used for plasma ignition and subsequent ionized PVD processing, while the sequence in Fig. 7D is used for low power ignition and subsequent ICP-only based processes.

Landscapes

• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Plasma Technology (AREA)
• Drying Of Semiconductors (AREA)
• Chemical Vapour Deposition (AREA)
• Physical Vapour Deposition (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=27752833

Family Applications (1)

Country Status (7)

Cited By (2)

Families Citing this family (39)

Citations (1)

Family Cites Families (26)

• 2002
  • 2002-02-22 US US10/080,496 patent/US6946054B2/en not_active Expired - Fee Related
• 2003
  • 2003-02-19 KR KR1020047013039A patent/KR100955996B1/ko not_active Expired - Fee Related
  • 2003-02-19 JP JP2003572060A patent/JP4740541B2/ja not_active Expired - Fee Related
  • 2003-02-19 WO PCT/US2003/004830 patent/WO2003073460A1/en not_active Ceased
  • 2003-02-19 AU AU2003211138A patent/AU2003211138A1/en not_active Abandoned
  • 2003-02-19 CN CNB03808953XA patent/CN100440419C/zh not_active Expired - Fee Related
  • 2003-02-20 TW TW092103594A patent/TW589668B/zh not_active IP Right Cessation

Patent Citations (1)

Also Published As

Similar Documents

Legal Events