Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
  • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
  • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
  • H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
  • H01L21/306—Chemical or electrical treatment, e.g. electrolytic etching
  • H01L21/3065—Plasma etching; Reactive-ion etching
• • 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
  • H01J37/32137—Radio frequency generated discharge controlling of the discharge by modulation of energy
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
  • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
  • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
  • H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
  • H01L21/3205—Deposition of non-insulating-, e.g. conductive- or resistive-, layers on insulating layers; After-treatment of these layers
  • H01L21/321—After treatment
  • H01L21/3213—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer
  • H01L21/32133—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer by chemical means only
  • H01L21/32135—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer by chemical means only by vapour etching only
  • H01L21/32136—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer by chemical means only by vapour etching only using plasmas
  • H01L21/32137—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer by chemical means only by vapour etching only using plasmas of silicon-containing layers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
  • H01J2237/32—Processing objects by plasma generation
  • H01J2237/33—Processing objects by plasma generation characterised by the type of processing
  • H01J2237/334—Etching

Definitions

• the invention relates to a method for etching structures in an etching body, in particular laterally precisely defined recesses in a silicon body, with a plasma, according to the preamble of the main claim.
• a so-called double pulse technique has already been described in the application DE 199 57 169 AI, in which low-frequency pulsing of a high-frequency modulated carrier signal of high pulse peak power at the substrate electrode in the etching chamber of an inductively coupled plasma etching system suppresses this undesirable pocket formation and at the same time wide process window for the plasma etching process is reached.
• sufficient pocket stability is achieved with aspect ratios of the etched structures from 5: 1 to 10: 1 and reached a certain tolerance towards overetching. In the case of even higher aspect ratios of the trench trenches produced or high overetching times, the formation of pockets cannot be completely suppressed in this process either.
• ICP - “Inductively Coupled Plasma” ICP - “Inductively Coupled Plasma”
• ICP - “Inductively Coupled Plasma” the occurrence of high reflected powers in the associated high-frequency generator, since undefined conditions exist during the ignition of the plasma discharge in the plasma, which require an adaptation of the coupled-in high-frequency power make the plasma impedance very difficult during the transients, so the ignition of the plasma discharge represents a transition from an electrically capacitively coupled to an inductively coupled mode, which leads to impedance mismatches and thus high reflected powers.
• the unpublished application DE 100 51 831.1 already contains a device and a method for Etching of a substrate by means of an inductively coupled plasma has been proposed, in which a static or time-variable magnetic field is provided between the substrate and the ICP source, which is generated via at least two magnet coils arranged one above the other and through which current flows in opposite directions.
• the object of the present invention was to provide a method for etching structures into an etched body with improved pocket stability, in particular with high aspect ratios of the etched structures and high overetch times.
• the method according to the invention has the advantage of a significantly increased pocket stability when etching silicon, for example, in particular when a buried dielectric etching stop layer such as an SiO 2 layer is reached, and an increased tolerance to overetching.
• the intensity of the plasma is modulated or pulsed in such a way that the plasma discharge does not go out during the “discharge pauses” and remains in inductively coupled mode, that is to say that just as much high-frequency power is generated during this period
• the plasma source or the inductively coupled plasma is fed in, as is necessary for maintaining a minimum discharge. Because the plasma does not go out completely during these discharge pauses or pulse pauses, the plasma is subsequently increased to maximum intensity. each time prevents a high reflected power from occurring, since the electrically capacitively coupled start phase of the plasma discharge is largely avoided and the inductively coupled phase of the plasma discharge is started immediately.
• the high-frequency power coupled into the substrate electrode which is done in accordance with the double pulse technique described in DE 199 57 169 AI, is correlated or synchronized with the modulation of the plasma intensity.
• a bipolar plasma consisting of positively and negatively charged ions, that is to say in “after-glow” "Phases, either by recombinations with positively charged ions or by capturing neutral particles, trapping free electrons. Due to the numerical preponderance of the neutral particles surrounding the electrons, the generation of anions by electron capture is the dominant reaction.
• the number of negative charge carriers with a mass that corresponds to a multiple of the proton mass is three to four orders of magnitude smaller than the number of positive charge carriers with a mass that corresponds to a multiple of the proton mass
• the number of these negative and positive charge carriers becomes approximately the same in these phases, because as the proportion of free electrons compared to the ions in the plasma decreases, the consequences of the unequal charge carrier masses and charge carrier mobility disappear, the plasma potential approaches previously positive values in the range of some 10 volts a value around 0 V, so that now positive and negative charge carriers can reach the etched body to be processed, for example a silicon wafer, in the same way, which enables optimum charge compensation there even with high aspect ratios.
• the modulation of the plasma intensity as a function of time can advantageously, in addition to a periodically changing high-frequency power coupled into the plasma from the corresponding coil generator, alternatively or additionally also by a periodically changing field strength of a magnetic field acting on the plasma, for example a magnetic field a device according to the type of DE 100 51 831.1.
• FIG. 1 shows a schematic diagram of a plasma etching device for carrying out the method according to the invention
• FIG. 2 explains a first exemplary embodiment of a temporal modulation of the plasma intensity, which is synchronized with the high-frequency pulsed, low-frequency modulated high-frequency power, which is coupled into the substrate electrode
• FIG. 3 explains the structure of the high-frequency pulsed
• FIG. 4 explains a second exemplary embodiment of the modulation of the plasma intensity and its synchronization with the high-frequency power coupled into the substrate electrode
• FIG. 5 explains a third exemplary embodiment also during the low-frequency pulse pauses
• FIG. 6 explains the second exemplary embodiment even during the low-frequency pulse pauses.
• FIG. 1 shows a plasma etching system 5 known from DE 100 51 831.1, with which, for example, an anisotropic plasma etching process in silicon for producing trench trenches in the manner of DE 42 41 045 Cl is carried out.
• an etching chamber 10 a substrate electrode 18 with a substrate 19 arranged thereon, for example a silicon wafer, is provided for this purpose.
• the substrate electrode 18 is electrically connected to a second matchbox 21 for impedance matching and, via it, to a substrate power generator 22.
• a coil 11 is provided which surrounds the etching chamber 10 and which is connected via a first matchbox 12 for impedance matching with a coil generator 13 in
• a high-frequency power is coupled into the etching chamber 10 with the aid of the coil 11 via the coil generator 13 mentioned and the first matchbox 12, so that an inductively coupled plasma 15 is formed there.
• the etching chamber 10 has a gas inlet 14 in its upper region and a gas outlet 20 in its lower region for the supply or removal of process gases, for example alternately etching and passivating gases.
• the etching chamber 10 between the production area of the inductively coupled plasma 15 and the substrate electrode 18 is surrounded by two field coils 16, for which purpose two corresponding spacers 17 are inserted into the side wall of the etching chamber 10, which receive these coils 16.
• the device known from DE 199 27 806 AI or preferably the device known from DE 199 33 842 AI is provided which, for example, as described therein, in the first matchbox 12 or the coil generator 13 is integrated.
• a high-frequency pulsed, low-frequency modulated high frequency is coupled into the substrate 19, as described in DE 199 57 169 AI.
• FIG. 3 explains this high-frequency pulsed, low-frequency modulated high-frequency power, with pulse packets 30 alternating with low frequency and periodic pulse pauses 31 with a frequency of, for example, 1 Hz to 500 Hz, preferably 10 Hz to 250 Hz, preferably 100, periodically alternating in the substrate electrode 18 Hz, with a so-called "duty cycle" of 20% to 80%, preferably 50%, and an average power of preferably 5 watts to 20 watts, for example 10 watts, can be coupled in.
• the low-frequency pulse packets 30 according to FIG.
• the one coupled into the substrate electrode 18 in the process average power in the time average is, for example, 5 watts to 40 watts, in particular 20 watts during the high-frequency clocked pulses 32.
• an individual high-frequency clocked pulse 32 consists of a high-frequency
• a frequency of, for example, 13.56 MHz and a high-frequency power of preferably 100 watts to 1 kWatt, for example 400 watts.
• FIG. 2 explains a first exemplary embodiment of the method according to the invention, the high-frequency pulsed, low-frequency modulated high-frequency power in the substrate electrode 18 being synchronized with the modulation of the plasma intensity in such a way that plasma excitation with minimal power (plasma almost off), that is, on first plasma intensity minimum 41, each coinciding with the low-frequency pulse pauses 31.
• the cycle ratio of 1: 1 shown in FIG. 2, that is to say the ratio of the time duration of the first plasma intensity maxima 40 to the time duration of the first plasma intensity minima 41, can otherwise only be seen as an example. Rather, for reasons of plasma excitation efficiency, it is expedient to excite the plasma 15 as long as possible and to blank it out for as short a time as possible, i.e. it is advantageous to set a ratio of well below 1: 1 when scanning the excitation or the plasma intensity in order to avoid that the required peak pulse powers of the high-frequency power to be coupled into the plasma 15 become enormous large. For example, for an average power at the coil 11 of 3 kW to 5 kW with a pulse duty factor of 1: 1, 6 kW to 10 kW peak power are already required in order to achieve the desired time average.
• the time duration of the first plasma intensity maxima 40 and the subsequent first plasma intensity minima 41 is equal to the time duration of the low-frequency pulse packets 30 or the subsequent low-frequency pulse breaks 31.
• the intensity of the plasma 15 during the first plasma intensity minima 41 is chosen to be so low that the plasma 15 does not go out during these plasma intensity minima.
• FIG. 4 shows a second exemplary embodiment of a synchronization of the modulation of the plasma intensity with the high-frequency pulsed, low-frequency modulated high-frequency power in the substrate electrode 18.
• two or more high-frequency clocked pulses 32 on the substrate electrode 18 is enclosed by a second plasma intensity maximum 40 l , and the plasma 15 is switched to a “low” mode during the subsequent high-frequency pulse pause 33, that is to say the plasma intensity reaches a second plasma intensity minimum 41 which is chosen to be so low that the plasma 15 does not go out at this time, so that two or more high-frequency clocked pulses 32 always fall into a second plasma intensity maximum 40 'before the high-frequency clocked pulse pause 33 coincides with the second plasmin intensity minimum 41 v falls.
• the advantage of the exemplary embodiment according to FIG. 4 compared to the exemplary embodiment according to FIG. 2 is that in the case of FIG. 4, fewer charges can be accumulated in the trench trenches produced during the relatively long "on" times of the comparatively low-frequency modulation of the plasma intensity comparatively few high-frequency pulsed pulses 32, for example a maximum of 20, coincide with the second plasma intensity maximum 40 v , only relatively few electrical charges are accumulated in the trench trenches during this time before a discharge occurs again during a subsequent second plasma intensity minimum 41 % .
• the high-frequency power coupled into the inductively coupled plasma 15 is again between 3 kW and
• FIG. 5 explains a third exemplary embodiment for a time synchronization of a modulation of the intensity of the plasma 15 with the high-frequency pulsed, low-frequency modulated high-frequency power, which is coupled into the substrate electrode 18.
• the temporal modulation of the intensity of the plasma 15 according to FIG. 4 is maintained even during the low-frequency pulse pause 31.
• the term “relatively long” in relation to the decay time of the anion concentration in the plasma 15 after its breakdown or the transition of the plasma intensity to the second plasma intensity minimum 41 It is to be understood that the plasma 15 is raised and lowered again and again so that the phases of a plasma breakdown with the associated increased anion concentration are repeated continuously.
• the low-frequency pulsed pause 31 is used more effectively, not only once at the beginning a plasma breakdown with an increased concentration of anions is generated, which then quickly subsides, measured in terms of the duration of the low-frequency pulse pause 31, but such phases are always provided for the discharge of the trench trenches produced in the etching body
• the low-frequency pulse pauses 31 are now no longer just that
• this state can be intercepted and kept at the limit of the inductively coupled operating mode, so that the increased power of the coil generator 13 increases the electron density in the plasma 15 to the value of a stable operating state.
• the forward power P F ⁇ r w rd of the coil generator 13 is coupled in the plasmin intensity minima 41, 41 ⁇ with the power P Ref i ected reflected in the coil generator 13 according to:
• V a gain factor of the control loop, for which the following preferably applies: V >> 1.
• control factor V is preferably set here to values that are significantly greater than 1, for example to values between 5 and 10, and in addition, as a setpoint value setting (Ps o ii), a value is set as close as possible or even slightly below the value required for a limit operation of the plasma 15, ie an intensity just above the extinction of the plasma 15, is required.
• the pulse strategy explained above i. H. the modulation of the plasma intensity and the high-frequency power coupled into the substrate electrode 18 as a function of time in a process according to the type of DE 42 41 045 Cl are used both in the course of the deposition cycles and during the etching cycles. As a rule, however, it is sufficient to restrict them to the etching cycles, since there is a risk of pocket formation only during the etching cycles. In addition, the full generator output is then available during the deposition cycles. In addition, it is also often advantageous to completely switch off the coupling of high-frequency power into the substrate electrode 19 during the deposition cycles.
• a particularly simple modulation of the intensity of the plasma 15 results from the use of an inductively coupled plasma source with a magnet coil arrangement, as described in the application DE 100 51 831.1 and shown in FIG. 1.
• at least two magnetic field coils 16 are arranged between the ICP source, that is to say the inductively coupled plasma 15, and the substrate 19, an upper magnetic field coil 16 facing the ICP source and a lower magnetic field coil facing the substrate 19, which is caused by opposing and im Generally different sized e- flow through electric currents so that they generate magnetic fields that are directed towards one another and generally have different strengths.
• the upper magnetic field coil 16 facing the ICP source is set to a magnetic field strength as is required for optimal plasma generation, while the lower magnetic field coil 16 facing the substrate 19 generates an oppositely directed magnetic field, the strength of which is so is set as is for optimal etch uniformity, i.e. H. an optimal distribution of the energy input over the surface of the substrate 19 is required.
• the use of the magnetic field coils 16 initially has the effect that a plasma 15 with a lower excitation density and electron concentration can be maintained, especially in the limit case of the plasma which is not yet extinguishing, than would be possible without it. This is due to the fact that the generated magnetic field "increases the lifespan" of the electrons in the plasma 15 by reducing wall losses in the source area, so that a desired "ambipolar" plasma with a minimal density of free electrons is particularly good Plasma intensity minima 41, 41 'can be maintained.
• a plasma etching system 5 In order to achieve a modulation of the intensity of the plasma 15, in a plasma etching system 5 according to FIG. 1, not only is the high-frequency power coupled into the plasma 15 by the coil generator 13 via the coil 11, but additionally or alternatively also the strength of the field coils 16 generated magnetic field within the chamber 10 is available.
• coil currents in field coils 16 are first used, which correspond to the target current values of the process. ses according to DE 100 51 831.1, ie for example 10 amperes for the upper field coil 16 and 7 amperes for the oppositely polarized lower field coil 16.
• these currents are then reduced, for example in such a way that both currents in the field coils 16 are synchronously reduced to zero or clocked.
• intermediate values can also be approached, for example 3 amperes for the upper field coil 16 and 2 amperes for the lower field coil 16.
• both coil currents are switched back and forth simultaneously between a high and a low extreme value, as a result of which the same effect is achieved as by reducing the power of the coil generator 13, ie. H. the plasma density collapses when the magnetic coil currents are reduced and reaches the plasma intensity minimum 41, 41 ', with a high anion density arising for a short time from the recombination of electrons and neutral gas particles.
• magnetic coil currents cannot be modulated as quickly as the high-frequency power coupled into the plasma 15.
• only clock frequencies are below
• This finite rate of change can be made particularly simple with the aid of modulation of the magnet coil currents, since only a direct voltage or a direct current with a modulation voltage of finite slope must be superimposed here.
• the alternating voltages or currents at the two field coils 16 are in phase opposition at all times, U 0 ⁇ and U 02 denoting the voltage amplitudes and current amplitudes on each of the two magnetic field coils 16.
• the offset currents or offset voltages U 0ffSet , ⁇ and U 0ffS e t , 2 are each dimensioned such that the occurrence of so-called “beaking effects” in the edge region of the Substrate 19 is still effectively suppressed and thus a homogeneous etching result is achieved over the entire substrate surface.
• the frequency ⁇ is comparatively small according to the above equations, i.e. for example 10 Hz to 50 Hz, and the speed of the first matchbox 12 used in the impedance matching is high enough to follow such a modulation of the plasma intensity, it is even possible in this way to completely avoid the occurrence of reflected powers in the coil generator 13 , and yet significantly suppress unwanted pocket formation. It is only important that the density of the plasma 15 is modulated and that this modulation preferably periodically provides phases of increased anion concentration, which ensure that trench trenches with a high aspect ratio are discharged.

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• 2001
  • 2001-09-14 DE DE10145297A patent/DE10145297A1/de not_active Ceased
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