Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F7/00—Constructional parts, or assemblies thereof, of cells for electrolytic removal of material from objects; Servicing or operating
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S204/00—Chemistry: electrical and wave energy
  • Y10S204/12—Electrochemical machining

Definitions

• the invention relates to an electrochemical etching system, in particular a CMOS-compatible etching system for etching silicon wafers, and a method for etching an etching body according to the type of the independent claims.
• Electrochemical etching systems for example for the production of porous silicon or for the surface porosification of silicon, usually consist of a 2-chamber system, between which a silicon wafer to be etched is clamped as a partition and the two chambers are electrically coupled or connected to one another only by the afer . Furthermore, electrodes for power supply are usually attached in both chambers, which usually consist of platinum.
• Such an etching system is detailed, for example, and its essential details have already been described by Fujiyama et al. in US 5,458,755.
• CMOS Complementary Metal Oxide Semiconductor
• the electrochemical etching system according to the invention for etching an etching body and the one carried out with it has the advantage over the prior art that it enables contamination-free electrochemical etching of an etching body, said etching body at least superficially being etched
• Etching method with such an etching cell is very advantageously used at least one of these electrodes at least with its side facing the etching body as a sacrificial electrode.
• Electrode which are connected as a cathode or anode and are electrically connected to the etching body via a suitable electrolyte, is the same material as the etching material of the etching body to be etched. It is enough it is when the etching body has, at least on the surface, the etching material to be etched or consists of this on the surface and when the first and / or second electrode has at least a surface of a corresponding electrode material or consists of this on the surface.
• the etching material of the etching body is at least weakly electrically conductive, silicon preferably being used as the etching material or a silicon wafer being used as the etching body. It is also advantageous if the first electrode material and the second electrode material of the first and second electrodes are a CMOS-compatible material and in particular not an element selected from the group consisting of platinum, gold, iridium, rhodium, palladium, silver or copper.
• the etching system according to the invention is thus particularly suitable for the production of porous silicon on a silicon wafer, contamination of the wafer with non-silicon substances such as platinum or palladium being prevented, for example, by using silicon electrodes.
• CMOS-compatible material is understood in accordance with the general usage in semiconductor technology to mean a material that does not adversely affect the electrical properties of a circuit generated thereby.
• a material contaminating the etching body is to be understood in particular as a CMOS poison or a material which forms deep impurities in the etching body when it is embedded, i.e. impurities whose energy levels lie in the middle of the gap between the conduction band and the valence band of the material to be etched, and the with it cause a high transition matrix element for the recombination of electrons and holes in the etching body (“recombination seed”).
• Electrodes are particularly advantageous compounds from the group of the at least weakly conductive compounds of the elements silicon, carbon, nitrogen, oxygen, titanium, aluminum, boron, antimony, tungsten, cobalt, tellurium, germanium, molybdenum, gallium, arsenic and selenium, in particular SiC , SiN, TiN, TiC, MoSi 2 and GaAs, in question, as well as pure electrode materials made of the elements silicon, titanium, tungsten, molybdenum and carbon, in particular graphite.
• the materials generally used as contact materials in semiconductor technology are also suitable as electrode materials, since these do not diffuse deeply into the etching body when it strikes the etching body and thus during the etching, but rather on the surface, for example with the formation of suicides, with the
• Etching bodies react or are bound locally and thus remain limited to the surface of the etching body. In this sense, they do not contaminate the etching body and do not impair its electronic properties, in particular with regard to its use in one or its compatibility with a CMOS-compatible production line.
• the first electrode and / or the second electrode and / or the etching body are also advantageously flat, in particular in the form of wafers, the electrodes for use as sacrificial electrodes also being very advantageously much thicker than the actual etching body, so that they can be processed, freed of contamination and reused if necessary. This advantageously extends the exchange cycles of the electrodes.
• the electrochemical etching cell is advantageously constructed in such a way that a first chamber and a second chamber are provided, each of which is at least partially filled with an electrolyte and which are spatially separated from one another by a separating device.
• Each of the two chambers is connected to an electrode in an electrically conductive manner via an electrolyte, the
• Etching body at least in some areas, the separating device and very advantageously at the same time the only, at least weakly conductive electrical connection between the two chambers and the electrodes connected as cathode or anode.
• the electrochemical etching cell has, in addition to the two chambers already mentioned, a further third chamber or a further third chamber and a further fourth chamber, each of which is at least partially filled with an electrolyte and each with a further one Separating device are spatially separated from the first chamber or second chamber.
• the electrolyte in the third or fourth chamber is very advantageously only electrically conductively connected to the second or first electrode, which in turn at least in regions acts as a separating device between the third or fourth chamber and the first and second chamber respectively.
• the surface of the first and / or the second electrode which is in particular flat, is only in contact with the electrolyte in contact with the etching body only with its surface facing the etching body, so that mixing of the electrolyte in the third or fourth chamber with the electrolyte in the first or second
• the side of the first and / or second electrode facing away from the electrolyte of the first or second chamber can be provided with a metallization or a doping on the surface at least in regions for easier electrical contacting of the electrodes or, for example, in the case of the electrode being constructed from several layers consist of a metal, which combines the advantage of a simple structural design of the etching cell with the targeted adaptation of the electrode material to the respective etching material without
• an additional bath electrode in particular a platinum or, immersed in an electrolyte located there
• Palladium electrode can be provided for simple electrical contacting of the first or second electrode via the respective electrolyte.
• the electrolytes in the individual chambers of the etching system according to the invention can advantageously also be different from one another, the first and second chambers in which the etching body is actually etched advantageously using hydrofluoric acid or a mixture of hydrofluoric acid and ethanol, and the third and fourth chambers are filled, for example, with dilute sulfuric acid as the contact electrolyte.
• the individual chambers can also very advantageously be filled separately with electrolyte and emptied separately, so that a problem-free exchange of, for example, a contaminated electrolyte in each chamber is possible at any time.
• This also enables a simple exchange of a used or contaminated first or second electrode serving as a sacrificial electrode at any time, quickly and easily.
• first and / or second electrode is advantageously contacted electrically via the electrolyte filled in the third or fourth chamber with a bath electrode located there, and is thus connected to an external voltage supply which impresses a current to the etching system during operation.
• the first and / or the second electrode very advantageously allows the suitability of different electrode materials, such as graphite, for the etching of an etching body to be examined in a simple manner and the electrode materials to be optimized for the respective material of the etching body.
• a tunnel made of non-conductive material in particular polypropylene, can advantageously be provided in a manner known per se.
• Figure 1 shows a first electrochemical etching system
• Figure 2 shows an alternative embodiment of the etching system
• Figure 3 shows a third embodiment of the etching system.
• an electrochemical etching cell 1 shows, as a first exemplary embodiment, an electrochemical etching cell 1 according to the invention with four chambers, a first chamber 19, a second chamber 19, a third chamber 17 and a fourth chamber 18, which are each at least partially filled with an electrolyte.
• the first and second chambers 19, 19 are filled, for example, with a mixture of hydrofluoric acid and ethanol, while the third and fourth chambers 17, 18 are filled, for example, with dilute sulfuric acid as the contact electrolyte.
• the four chambers 17, 18, 19, 19 'thus define four electrolyte regions assigned to the chambers 17, 18, 19, 19', a first electrolyte region 29, a second electrolyte region 29 ', a third electrolyte region 27 and a fourth electrolyte region 28, which are different from one another spatially above
• the first chamber 19 is spatially separated from the second chamber 19 "via a first separating device 31, the first chamber 19 from the third chamber 17 via a second separating device 32 and the second chamber 19" from the fourth chamber 18 via a third separating device 33 spatially separated, so that no exchange of electrolyte between the chambers 17, 18, 19, 19 'occurs.
• the first separating device 31 is formed in a manner known per se by an etching body holder 11 made of Teflon or polypropylene, in which the etching body 15 is partially fitted or inserted, so that it is superficially on the one hand with the electrolyte in the first chamber 19 and on the other hand with the electrolyte 19 ⁇ is in contact in the second chamber.
• the etching body 15 is a flat silicon wafer known per se.
• the second separating device 32 and the third separating device 33 are each formed by an electrode holder 10 made of Teflon, in each of which a second electrode 13 'or a first electrode 13 is inserted in regions, so that on the surface at least in regions, on the one hand, these electrodes are connected with the electrolyte of the third or first chamber 17, 19 x and on the other hand are in contact with the electrolyte of the second and fourth chamber 19 1 , 18.
• a platinum electrode or a palladium electrode as bath electrode 34, 34 ⁇ is provided in the third and fourth chamber 17, 18, respectively, which is immersed in the electrolyte located there.
• the bath electrodes 34, 34 are further connected to a voltage source, not shown, which impresses an electrical current into the etching cell 1 in a manner known per se.
• the first electrode 13 or its side facing the etching body 15 is connected as an anode and the second electrode 13 ⁇ or its side facing the etching body 15 is connected as a cathode.
• the first electrode 13 and the second electrode 13 ' consist of a flat silicon wafer or a silicon wafer, which is preferably substantially thicker than the silicon wafer used as the etching body 15.
• the electrodes 13, 13 are preferably selected with regard to the electrode material used in such a way that they consist at least superficially of the same material as the respective surfaces of the etching body 15. This ensures that the material of the first electrode 13 and the material of the second Electrode 13 'does not contaminate the etching body 15 during operation of the etching cell 1 and thus impairs its electrical or catalytic properties after the etching.
• the etching cell 1 When the etching cell 1 is operating, an externally impressed current now flows via the bath electrodes 34, 34 ', the electrolytes, the first and second electrodes 13, 13' and the etching body 15, this being etched at least superficially in a body etching area 14 '.
• the first and second electrodes 13, 13' are at least superficially etched in an etching area 14, ie they serve as sacrificial electrodes in the etching process of the etching body 15 due to their significantly greater thickness
• they are not etched through the etching body 15, but only attacked, etched or removed on the surface or, for example, porosified.
• a loosening of silicon, for example, during the etching, from one of the electrodes 13, 13 'in the electrolyte in the first or second chamber 19, 19' is not critical for the etching body 15, since this consists of the same material and is therefore not contaminated.
• the electrodes 13, 13 ' are preferably connected to the electrode holders 10 via seals and to the etching system 1 via closable windows 16 in the side walls thereof screwed.
• a quick-release fastener known per se is also provided.
• the chambers 17, 18, 19, 19' and the associated electrolyte regions 27, 28, 29, 29 ' can also be filled and emptied separately using corresponding devices known per se .
• FIG. 2 explains a second exemplary embodiment of an etching cell according to the invention.
• This etching cell is essentially analogous to the etching cell 1 according to FIG. 1, but has a different embodiment of the contacting of the electrodes 13, 13 '.
• the third chamber 17 and the fourth chamber 18, the bath electrodes 34, 34 'and the electrolytes located in these chambers 17, 18 can be dispensed with.
• the first electrode 13 and the second electrode 13 ′ are each provided with a metallization 20 known per se on the side facing away from the etching body 15.
• the electrodes 13, 13 'can also be provided with a very high doping on this side, so that good electrical conductivity is ensured.
• the electrodes 13, 13 'can also consist of a laminate which has a metal layer on its side facing away from the etching body 15 or consists of a metal.
• Further embodiments of the electrical contacting of the electrodes 13, 13 ' provide that they are provided in a manner known per se on the side facing away from the etching body 15 with pin, network or surface contacts or, depending on the electrode material, particularly simply that the electrodes 13, 13 'in the first or second chamber 19, 19 'partially directly immersed in the electrolyte and electrically contacted directly at a non-immersed point. They thus serve as sacrificial electrodes instead of the platinum electrodes known from the prior art.
• FIG. 3 a third exemplary embodiment of the etching system according to the invention explained with the aid of FIG. 3, in which, in contrast to FIG. 1, only a tunnel 30 made of non-conductive material, such as polypropylene, is known.
• This tunnel 30 is connected to the etching body holder 11 on both sides and concentrically surrounds, for example, a circular wafer as the etching body 15.
• the tunnel 30 causes one

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Weting (AREA)

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Citations (4)

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• 1999
  • 1999-04-01 DE DE19914905A patent/DE19914905A1/de not_active Ceased
• 2000
  • 2000-03-17 US US09/937,926 patent/US6726815B1/en not_active Expired - Lifetime
  • 2000-03-17 JP JP2000609630A patent/JP4511741B2/ja not_active Expired - Lifetime
  • 2000-03-17 EP EP00922440A patent/EP1181400B1/de not_active Expired - Lifetime
  • 2000-03-17 KR KR1020017012317A patent/KR100698798B1/ko not_active Expired - Lifetime
  • 2000-03-17 WO PCT/DE2000/000857 patent/WO2000060143A1/de not_active Ceased
  • 2000-03-17 ES ES00922440T patent/ES2282103T3/es not_active Expired - Lifetime
  • 2000-03-17 DE DE50014121T patent/DE50014121D1/de not_active Expired - Lifetime

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