EP0377445A2 - Procédé et dispositif pour la génération de faisceaux d'ions à grande section transversale - Google Patents

Procédé et dispositif pour la génération de faisceaux d'ions à grande section transversale Download PDF

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Publication number
EP0377445A2
EP0377445A2 EP90100045A EP90100045A EP0377445A2 EP 0377445 A2 EP0377445 A2 EP 0377445A2 EP 90100045 A EP90100045 A EP 90100045A EP 90100045 A EP90100045 A EP 90100045A EP 0377445 A2 EP0377445 A2 EP 0377445A2
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EP
European Patent Office
Prior art keywords
gas
ions
voltage
ion beams
ion
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP90100045A
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German (de)
English (en)
Other versions
EP0377445B1 (fr
EP0377445A3 (fr
Inventor
Joachim Dr. Janes
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Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Original Assignee
Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
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Publication of EP0377445A2 publication Critical patent/EP0377445A2/fr
Publication of EP0377445A3 publication Critical patent/EP0377445A3/fr
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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J27/00—Ion beam tubes
    • H01J27/02—Ion sources; Ion guns
    • H01J27/08—Ion sources; Ion guns using arc discharge
    • H01J27/10—Duoplasmatrons ; Duopigatrons

Definitions

  • the invention relates to a method and a device for generating ion beams with a large beam cross section.
  • the ion beam generated is used for dry etching of semiconductor surfaces.
  • high-resolution dry etching processes with a high degree of anisotropy and dimensional accuracy are becoming increasingly important.
  • the ratio of vertical to lateral etching rate must be so large that the underetching of the structures is smaller than the line width errors caused by lithography processes.
  • the RIE (Reactive Ion Etching) method uses reactive ions for dry etching, which lead to chemical reactions on the surface.
  • the ions are made available by an etching plasma that burns over the semiconductor surface.
  • RIE reactive Ion Beam Etching
  • the semiconductor surface is bombarded with a beam of reactive ions.
  • the advantage of this procedure is that that the disruptive influence of ion generation on the etching reactions on the semiconductor surface is largely eliminated. This is achieved in that the generation of the ions and the etching take place separately from one another by accelerating the ions out of the source onto the surface to be etched.
  • US 30 05 931 discloses an ion source, for example for use in a nuclear fusion apparatus with magnetic mirrors.
  • This ion source is especially designed for the generation of neutral plasmas and is unsuitable for the RIBE process because of the radiation cross section of the ion current and the complex construction.
  • the ion beam In order to achieve a high anisotropy in the etching process, the ion beam must have only a small beam divergence. It must have a high ion current density to ensure high etch rates. The ion energy must be low in order to keep the surface damage and the surface temperature low. In order to be able to structure the entire surface of a wafer, the ion beam must have a beam cross section that is as large as possible.
  • hot filament is unsuitable for the use of reactive gases because the hot filament is etched away over time, which severely limits the operating life of the source.
  • Some ion sources avoid the hot filament used to create the plasma. There, for example, high-frequency discharges or microwave discharges are used for ionization.
  • the object of the invention is to provide a method and a device for generating ion beams with a large beam cross section, which deliver ion beams of high current density, low ion energy and low beam divergence for the creation of the smallest structures on semiconductor surfaces and on heatable filaments for ion generation and on grid electrodes for extraction of the ions.
  • This object is achieved in that the gas to be ionized with the aid of a pulsed molecular jet nozzle system and is ionized in a pulsed high-voltage gas discharge that the ions perpendicular to the direction of the molecular beam and perpendicular to the direction of the high-voltage discharge with synchronously pulsed electrical or Magnetic fields are accelerated and that the non-ionized process gas is removed from the reaction chamber with a pump.
  • the ions must be accelerated so that the beam has as little divergence as possible. It is ideal to accelerate along parallel electric field lines, such as are realized in a plate capacitor.
  • Known methods for generating ion beams try to come close to this ideal by using an extraction grid, which results in the disadvantages described above.
  • the homogeneity of the acceleration field is achieved by timing the method steps 1a to 1c carried out in pulse mode.
  • the acceleration field is only switched on when the ions to be accelerated are no longer in areas in which the field is inhomogeneous, but instead fly through areas whose field lines point parallel to the direction of flight.
  • the pulsed acceleration of the ions in the acceleration fields arranged one behind the other means that ions of the same mass but with different charge states have the same energy when they strike the surface to be etched and therefore induce the same energy-dependent processes.
  • the neutral reaction products are removed from the reaction chamber with the aid of vacuum pumps.
  • a further development according to claim 5 is characterized in that the discharge of the high voltage pulse for plasma generation takes place effectively and uniformly.
  • the discharge gas is pre-ionized with the aid of a peak discharge or with the aid of UV light.
  • a particularly advantageous device for performing the method is characterized in the independent claim 6.
  • the ions are accelerated in a pulsed electric field, which is built up between a potential disc and a series of metal cylinders.
  • the ions are accelerated with the aid of magnetic fields which are generated by a coil system.
  • any field can be used to accelerate the ions, which can exert a pulse on the ions.
  • the aperture field which carries out a selection of the molecules according to their direction of flight, is replaced by a slit aperture.
  • This will make the beam divergence for certain applications only narrowed in one direction.
  • This variant is also characterized by easier adjustability and cheaper production.
  • the pulsed gas supply allows the disturbing background gas pressure in the reaction chamber to be reduced.
  • a high vacuum pump maintains a pressure difference between the gas supply space and the reaction space, which almost completely removes the particles from the reaction space at the end of the flight path of the molecular jet.
  • the advantages achieved with the invention are, in particular, that the point of origin of the ions and the acceleration region are spatially separated from one another. This prevents reactive radicals, which are formed in the gas discharge by fragmentation of the mother molecules and have a disruptive effect on the etching process, from reaching the surface to be etched.
  • the surface reactions that are used to create structures on semiconductor surfaces are not only spatially but also temporally separated from the generation of the ions. If the ions hit the semiconductor surface after passing through the acceleration path, the high-voltage discharge has already ended. An influence of the high voltage discharge is therefore excluded. Since the kinetic energy of the ions is determined exclusively by the acceleration process, this energy can be set for the respective application regardless of the ion formation process.
  • the use of metal cylinders to accelerate the ions excludes surface reactions such as sputtering processes within the beam cross section. So that becomes a Interference factor switched off, which significantly reduces the quality of the ion beam when using extraction grids.
  • the beam divergence which occurs in the case of extraction gratings is controlled in the device according to the invention by a suitable choice of the distances and diameters of the metal cylinders and the height and duration of the potential pulses which are applied to the cylinders and the potential plate.
  • Another advantage of the invention is that an interaction of interfering neutral particles and reaction products with the ions and the surface reactions is negligible, since these particles are removed from the region of the semiconductor surface by a voltage pulse or by pumping.
  • a large-area ion source which supplies an ion current with low divergence, the parameters of which, such as ion energy and ion current density, can be set independently of one another. It is suitable for RIBE processes for the production of extremely small structures in the sub- ⁇ range on semiconductor surfaces, such as will be required for future 64 MBit memory, for example.
  • FIG. 1, 2 and 3 show the essential components of a device for carrying out the method according to the invention, FIG. 2 showing the section labeled AB in FIG. 1 and FIG. 3 the section labeled CD. All components are housed in a vacuum chamber 10.
  • a gas line 15 is connected to a reservoir of the process gas.
  • an extraction voltage of, for example, -100 V is applied between the potential disk 4 and the first metal cylinder approximately 50 nsec later for a period of one microsecond (negative voltage on the metal cylinder).
  • a voltage of -150 V is applied to the second cylinder for approximately 20 nsec.
  • the ions fly through the zone of homogeneous field distribution between the metal cylinders.
  • the other potentials are 0 V.
  • a voltage of -150 V is applied to the second metal cylinder for 50 nsec and a voltage of -200 V to the third in order to further accelerate the ions in the direction of sample 7.
  • the numerical values mentioned serve only as examples and do not constitute any restriction. The actual values to be selected depend on the type of ion to be accelerated and the design of the acceleration device.
  • the switching times and pulse lengths must be selected so that the electrical fields are only switched on when the ions move in areas in which the field distribution is approximately homogeneous.
  • the field distribution between the potential plate 4 and the first metal cylinder is shown in FIG. 4a, that between two metal cylinders in FIG. 4b. Only in the areas 24 directly on the potential plate and the areas 25 between the Cylinders, the field distribution is almost homogeneous. The acceleration process must therefore be limited to these areas. The accelerated ions then hit the surface of the sample 7 and are available there for etching processes.
  • FIG. 5 shows the high-voltage discharge device and the nozzle field 13 in a spatial representation
  • FIG. 6 shows the nozzle field and the aperture field 12 in detail
  • FIG. 7a shows a nozzle
  • FIG. 7b shows an aperture (peeler).
  • the nozzle array 13 has many nozzle openings 16 with a cross section of approximately 50 ⁇ m to 100 ⁇ m, which are arranged in a row.
  • the openings 18 of the aperture field lie opposite the nozzle openings.
  • the gas expands from the small nozzle openings into the evacuated room, creating a highly directed jet.
  • the diaphragm field is replaced by a narrow slit diaphragm.
  • the pulsed gas supply is synchronized with the pulsed high-voltage discharge in such a way that a directed particle beam is only generated when the high-voltage discharge is also ignited.
  • the device for high voltage discharge is shown in Fig. 8.
  • the opposite Electrodes 1 arranged horizontally e.g. made of stainless steel, which are attached to a Teflon holder 2, are connected to a charging or discharging circuit.
  • a capacitor C1 is charged in the discharge circuit via a high voltage supply HV. By closing the switch S, the stored energy is transferred to a charging capacitor C2.
  • a thyratron serves as a switch, which switches to transmission when a trigger pulse, which is synchronized with the pulsed molecular jet nozzle 14, is placed on the grating of the tyratron S.
  • the charge of the capacitor C2 then flows onto the electrodes 1 and the high-voltage discharge ignites.
  • the inflowing gas is pre-ionized by means of a metal tip 23 by tip ionization in order to ensure an effective and uniform discharge between the electrodes 1.
  • the gas is removed by photoionization, e.g. pre-ionized with an excimer laser or with a UV lamp, or by a high-frequency discharge.
  • photoionization e.g. pre-ionized with an excimer laser or with a UV lamp
  • a high-frequency discharge e.g. pre-ionized with an excimer laser or with a UV lamp
  • the acceleration device with the potential plate 4
  • the metal cylinders 5 the sample 7 and the suction electrodes 6 for charged particles.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Combustion & Propulsion (AREA)
  • Electron Sources, Ion Sources (AREA)
  • ing And Chemical Polishing (AREA)
  • Drying Of Semiconductors (AREA)
EP90100045A 1989-01-05 1990-01-02 Procédé et dispositif pour la génération de faisceaux d'ions à grande section transversale Expired - Lifetime EP0377445B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3900252A DE3900252C1 (fr) 1989-01-05 1989-01-05
DE3900252 1989-01-05

Publications (3)

Publication Number Publication Date
EP0377445A2 true EP0377445A2 (fr) 1990-07-11
EP0377445A3 EP0377445A3 (fr) 1991-07-03
EP0377445B1 EP0377445B1 (fr) 1994-05-11

Family

ID=6371639

Family Applications (1)

Application Number Title Priority Date Filing Date
EP90100045A Expired - Lifetime EP0377445B1 (fr) 1989-01-05 1990-01-02 Procédé et dispositif pour la génération de faisceaux d'ions à grande section transversale

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EP (1) EP0377445B1 (fr)
DE (2) DE3900252C1 (fr)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2764707A (en) * 1955-07-22 1956-09-25 Richard B Crawford Ion source
DE2942386A1 (de) * 1979-10-19 1981-04-30 Ulrich Dr. 8000 München Boesl Ionenquelle
US4737688A (en) * 1986-07-22 1988-04-12 Applied Electron Corporation Wide area source of multiply ionized atomic or molecular species
WO1988007259A1 (fr) * 1987-03-18 1988-09-22 Hans Oechsner Source d'ions de haute frequence

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3005931A (en) * 1960-03-29 1961-10-24 Raphael A Dandl Ion gun

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2764707A (en) * 1955-07-22 1956-09-25 Richard B Crawford Ion source
DE2942386A1 (de) * 1979-10-19 1981-04-30 Ulrich Dr. 8000 München Boesl Ionenquelle
US4737688A (en) * 1986-07-22 1988-04-12 Applied Electron Corporation Wide area source of multiply ionized atomic or molecular species
WO1988007259A1 (fr) * 1987-03-18 1988-09-22 Hans Oechsner Source d'ions de haute frequence

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
IBM TECHNICAL DISCLOSURE BULLETIN. vol. 17, no. 5, Oktober 1974, NEW YORK US Seite 1379 W.C. KO, R.WINNARD: "HOLLOW CATHODE DISCHARGE ION SOURCE" *

Also Published As

Publication number Publication date
EP0377445B1 (fr) 1994-05-11
EP0377445A3 (fr) 1991-07-03
DE3900252C1 (fr) 1990-05-23
DE59005653D1 (de) 1994-06-16

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