Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B08—CLEANING
  • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
  • B08B7/00—Cleaning by methods not provided for in a single other subclass or a single group in this subclass
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J19/081—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing particle radiation or gamma-radiation
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B33/00—After-treatment of single crystals or homogeneous polycrystalline material with defined structure
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J27/00—Ion beam tubes
  • H01J27/02—Ion sources; Ion guns
  • H01J27/16—Ion sources; Ion guns using high-frequency excitation, e.g. microwave excitation
  • H01J27/18—Ion sources; Ion guns using high-frequency excitation, e.g. microwave excitation with an applied axial magnetic field
• • 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
  • H01J37/30—Electron-beam or ion-beam tubes for localised treatment of objects
  • H01J37/305—Electron-beam or ion-beam tubes for localised treatment of objects for casting, melting, evaporating, or etching
  • H01J37/3053—Electron-beam or ion-beam tubes for localised treatment of objects for casting, melting, evaporating, or etching for evaporating or etching
• • 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
  • H01J2237/30—Electron or ion beam tubes for processing objects
  • H01J2237/31—Processing objects on a macro-scale
  • H01J2237/316—Changing physical properties

Definitions

• the invention relates to a method for surface cleaning and smoothing of material with a single-crystal, polycrystalline or amorphous structure in which the surface is polished to the smallest possible mechanically achievable roughness and then the surface with ions of defined charge and kinetic energy for removal the impurities located on the surface are shot at.
• the materials to be processed are, for example, silicon single crystals for the production of integrated circuits, other semiconductors for the construction of optoelectronic components, metallic or semiconducting single crystals for the development of so-called nanostructures, single crystals as a base for X-ray mirrors made of multilayers, polycrystalline or amorphous Metallic, semiconducting or insulating surfaces in question, which must be atomically clean and smooth in various production processes.
• the material with a surface that was previously mechanically polished to the smallest possible roughness in an ultra-high vacuum is brought to a temperature close to, but clearly below the melting point.
• ⁇ heats in order to heat out all volatile impurities from the inside and to evaporate them from the surface.
• the surface is then subjected to ion bombardment with energies between 200 eV to 10000 eV, preferably 5000 eV, and high flux density between 10 ⁇ A / cm 2 to ⁇ - ⁇ 1000 ⁇ A / cm 2 , the surface and thus with binary impacts and via impact cascades the impurities are also removed by atomization ("sputtering").
• the treatment according to the known method damages the surface, and the ions used, mostly noble gases, penetrate into the sample material, so that aftertreatment of the sample by several cycles of atomization and healing is necessary, which heals the surface damage and the penetrated noble gas atoms outgas so that clean and, in the case of monocrystalline surfaces with low indexing, even flat surfaces can be obtained.
• the heat aftertreatment leads to a pronounced rough surface from an atomic point of view through the formation of microcrystals and, in the case of originally amorphous surfaces, entails the risk of recrystallization.
• the term "clean” is relative to the evidence methods defined, usually reach the detection of egg ⁇ m impurity atom per 1,000 surface atoms correct its limit.
• atomizing or “sputtering”
• recoil atoms are also generated from surface contaminations, which penetrate into the sample material.
• a single cycle thus reduces the impurities on the surface, of which but a fraction is shot into the sample material, which reappears on the surface when removed again. The consequence of this is that the cleaner the surface, the greater the number of cycles and the lower the surface must be removed.
• the invention solves the object in that the surface of the Oberflä ⁇ provided for the cleaning material in a method of the type mentioned at least slaughter ⁇ multiply charged ions of low kinetic energy be ⁇ shot is, the potential energy of the ions according to their high ⁇ Charge causes an interaction with the bound impurities, which causes them to detach, and the kinetic energy given to the ions is only measured in such a way that the ions come closest to the atoms of the surface impurities, but not penetrate into the surface becomes possible.
• cleaning and smoothing is brought about by the interaction of highly charged ions of low kinetic energy with the surface, in contrast to the use of the relatively high kinetic energy for atomization in the previous standard cleaning process.
• the potential energy stored in the uploaded ion is used for cleaning and smoothing and the relatively low kinetic energy of the uploaded ions is only required for the next approach to the surface impurity atoms.
• the electronic interaction of uploaded ions with the surface of the material influences on the one hand the electronic state of the ion by electron exchange between the surface and the ion and on the other hand the trajectory (trajectory) of the ion by the attractive force of the image charge, which is the same for electrically conductive surfaces the effective charge of the ion in front of the surface.
• Atomic position of the surface resonantly captures electrons from the surface in highly excited states and is thus neutralized itself, where d is the mean lattice spacing of the atoms in the surface plane. Since these electrons originate from the conduction band or valence band of the surface material, the resonance energy is determined by the binding energy of these bands. This "suction" of electrons from the surface weakens local bonds of weakly bound (physisorbed) impurity atoms or molecules to such an extent that they are desorbed. As a result, the surface is cleaned of physisorbed impurity atoms or molecules before the incident, originally highly charged ion reaches the immediate vicinity (z ⁇ d) of the surface atoms.
• the limit initial energy of the uploaded ions must be chosen between 5 "q and 55" q eV in order to determine the total reflection of the ions on the surface and thus negligible atomization, i.e. ensure non-destructive treatment of the surface.
• Total reflection the distances of the closest approach z O between the surface atoms and the ion are between 0.5 and 2.0 ao. These are distances at which the original uploaded, on the way from up to zO, however, ion neutralized in outer shells can trap electrons directly from filled, inner shells of the surface atoms in its own, still partially empty, inner shells. This is due to quasi-resonant electron exchange processes or an interatomic Auger neutralization, which occur with a probability close to 1 for each individual ion at the reversal point of its trajectory if the ion comes close enough to a surface atom. This latter condition is just as important for the claimed process as the total reflection condition.
• the low energy of the incident ions may not only be selected according to the criterion of total reflection,
• each low-energy, originally charged ion at the reversal point of its trajectory in front of the surface extracts at least one, if not more, inner shell electrons from an impurity atom or molecule located there, so that this impurity atom or molecule desorbs with a high probability . Little is known quantitatively about this probability. However, it can be assumed for incident ions with a charge q> 5 close to 1, since the presence of one or more inner shell holes in one impurity atom leads to the coulombic repulsion of the impurity atom from the surface atom bond (cf. ML Knotek and PJFeibelman, Surf. Sci. 90, 1979, pp. 78-90).
• an area of 1 cm 2 can be cleaned in about 20 s if a monolayer is contaminated with Ar ⁇ ion beams that are technically feasible today.
• the claimed method can already be used during the first thermal outgassing and evaporation treatment, since the slow, charged ions are reflected by the surface and thus none or represent a completely negligible additional thermal load on the sample. This means a further considerable increase in productivity of the claimed method compared to the standard method, since the long time it takes to degas the sample can be fully used for cleaning. After the sample has cooled, a clean surface is immediately available and, in the case of single-crystal material, even a flat surface is available for further processing, since during the slow cooling from the outgassing phase the slight surface damage in the uppermost surface areas was sufficient ⁇ len.
• the listed advantages of the invention specified in claim 1 are based essentially on the fact that the non-destructive cleaning and smoothing of surfaces takes place essentially through the potential energy stored in the charged ions in contrast to the use of kinetic energy in the previous standard method.
• the invention specified in claim 1 will lead to a significant reduction in cleaning times and thus to a decisive increase in productivity in all production processes, where clean surfaces in the atomic dimension are already required, which will often compensate for the additional investment costs of the claimed process .
• FIG. 1 shows a schematic structure of a first arrangement with which surface cleaning and smoothing can be carried out
• Figure 2 shows a second embodiment
• FIG. 5 a specialization of the first two embodiments.
• FIG. 1 shows a schematic representation of a device set-up for carrying out the method, as can be set up using means known today.
• Ions through an entrance aperture 5 into a double-focusing sector magnet 6 or another ion-optical component for the purpose of q / m separation, so that ions of a single charge state, for example Ar +6 or Ne s " " " " , are focused through the exit aperture 7.
• the sector magnet 6 also eliminates all the electrons present in the ion beam, which, owing to their sometimes high kinetic energy in the plasma 1 'of the ion source 1, can leave this plasma against the extraction voltage and are thus superimposed on the ion beam also acts as a differential pump aperture, so that the ions into a pressure zone 8 of 10 ⁇ v Pa occur and there are decelerated from a first braking lens 9 from (20000 + U) "q eV to (1000 + U)" q eV and focused by a second differential pump aperture 10. This allows the construction of a second braking lens 11 and a surface 12 to be cleaned in an ultra high vacuum of 10 _s Pa.
• the q / m-selected ions are decelerated from (1000 + U) «q eV to Uq eV and hit the surface 12 with low energy, which in the present case is a silicon single crystal for chip production "wafer").
• a heater 13 according to one of the known technical embodiments is to be provided for the thermal treatment of the surface. Depending on the application, other vacuum conditions and other acceleration and deceleration conditions can also be used.
• Example 2 corresponds to that in essential details
• Embodiment 1 except for the omission of a q / m separation unit. Accordingly, the entire mixture of charge states extracted from the ion source 1, here e.g. Xe ions, with U »q eV on the surface 12, which here e.g. is a platinum (111) single crystal surface. This increases the total particle flow to the surface and thus the cleaning performance, but on average lowers the probability of desorption per impurity or surface atom hit, since depending on the ion source, high proportions of only single and double charged ions are contained in the particle stream.
• the ion source here e.g. Xe ions
• U »q eV on the surface 12
• This increases the total particle flow to the surface and thus the cleaning performance, but on average lowers the probability of desorption per impurity or surface atom hit, since depending on the ion source, high proportions of only single and double charged ions are contained in the particle stream.
• ions contribute less to the cleaning performance than highly charged ones, since the surface atoms they hit are less likely to desorb than surface atoms hit by uploaded ions. It is therefore important to use ion sources which can produce particle streams with an optimal average charge state.
• the optimal is Nominally and technically defined, because the technical complexity of the ion source construction can be adapted to the lowest charge state of an ionized element, with which efficient cleaning and smoothing performance according to the invention can be achieved.
• Example 3 corresponds in substantial detail to embodiment 1, except for the fact that the entire structure from the ion source to the surface to be cleaned is listed in ultra-high vacuum technology and therefore the differential pump orifices 7 and 10 are omitted. This enables the greatest purity of the system with freely selectable vacuum values.
• Example 4 corresponds essentially to that
• Embodiment 2 except for the fact that the entire structure from the ion source to the one to be cleaned
• a mixture of charge states here from eg As ions, is extracted from the plasma 1 'of the ion source 1 with U «q eV directly in the direction of the material surface 12, here eg a GaAs single crystal, where 0 ⁇ U ⁇ K 60 V .
• Corresponding magnetic field coils or permanent magnet structures 14, 15 are provided for this.
• this exemplary embodiment can only be used where magnetic stray fields do not interfere with the further processing of the surface. If freedom from magnetic fields is required for the further processing of the surface, the surface must be cleaned and smoothed locally with the example 5 from the further processing.
• Example 7 builds on the exemplary embodiments 1-4 and uses 12 ion optical elements 16 shortly in front of the surface, which sharply focus the ion beam, here, for example, Zr ions, and a controlled electrical Tro-magnetic guides 17 enable this focus on the surface or a sharp image of a partially permeable mask 18 on the surface 12, here, for example, amorphous Rh 25Zr "75.
• a predetermined cleaning pattern can thus be projected onto the surface
• FIG. 5 only one possibility is given for the electromagnetic control or guidance 17 of an ion beam focus and for the imaging of a partially transparent mask on the surface.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Plasma & Fusion (AREA)
• Combustion & Propulsion (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Physics & Mathematics (AREA)
• General Health & Medical Sciences (AREA)
• Health & Medical Sciences (AREA)
• Analytical Chemistry (AREA)
• Toxicology (AREA)
• Crystallography & Structural Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Physical Vapour Deposition (AREA)
• Cleaning In General (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)

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• 1992
  • 1992-01-08 DE DE4200235A patent/DE4200235C1/de not_active Expired - Fee Related
  • 1992-12-31 EP EP93901733A patent/EP0620870A1/de not_active Withdrawn
  • 1992-12-31 US US08/256,436 patent/US5849093A/en not_active Expired - Fee Related
  • 1992-12-31 AU AU32586/93A patent/AU3258693A/en not_active Abandoned
  • 1992-12-31 WO PCT/EP1992/003015 patent/WO1993014250A2/de not_active Ceased
  • 1992-12-31 JP JP5512112A patent/JPH07502863A/ja active Pending

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