Classifications

• • 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
  • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
  • C30B25/02—Epitaxial-layer growth
• • 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
  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/02—Elements
  • C30B29/08—Germanium
• • 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
  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/10—Inorganic compounds or compositions
  • C30B29/52—Alloys

Definitions

• the present invention relates generally to a process for obtaining a layer of monocrystalline germanium on a substrate of monocrystalline silicon.
• Silicon is the basic compound of microelectronics. It is currently available on the market in slices of 200 mm in diameter. The limits in terms of performance of integrated circuits are therefore ultimately those linked to the intrinsic properties of silicon.
• Germanium (Ge) which is part of column IV of the Periodic Table of the Elements is a semiconductor. It would potentially be more interesting than Si because, (i) it has a higher electronic mobility, (ii) it absorbs well in the field of infrared radiation, (iii) its lattice parameter is greater than that of Si, which authorizes hetero-epitaxy with semiconductor materials from columns III-V of the periodic table.
• germanium does not have a stable oxide and there are no large diameter germanium wafers on the market or at prohibitive prices.
• Si ⁇ . ⁇ Ge ⁇ alloys have already been grown on monocrystalline Si substrates. The alloys obtained rarely exceed 50% germanium levels in the alloy.
• Si ⁇ . ⁇ Ge ⁇ on silicon by exceeding the critical thickness for a given composition but by adjusting the deposition parameters of the layers so that the dislocations emitted do not propagate vertically but bend to propagate in the plane of the layer for then evaporate on the edges of the plate. Growth therefore takes place from layers increasingly enriched in germanium, the germanium gradient being able to be carried out in stages or continuously.
• Each layer is, after deposition, subjected to an in situ annealing in hydrogen at 1095 or 1050 ° C. For comparison, similar sequences of layers were deposited, but without annealing.
• a 300 nm layer of Ge ⁇ Si ⁇ _ ⁇ of the same composition as the upper buffer layer is also deposited thereon.
• Samples which have not been subjected to intermediate annealing have an emerging dislocation density of 10 6 cm “2 , while the annealed sample has an emerging dislocation density of 10 3 - 10 4 cm “ 2 .
• a deposition method has also been proposed making it possible to form on a silicon substrate layers of Si l ⁇ Ge ⁇ (x varying from 0 to 1), which can go up to a layer of pure Ge and having a low density of dislocations. emerging.
• the essential characteristic of this process consists, during chemical vapor deposition, of constantly modifying the flow of active gases (SiH 4 and GeH, for example) at the same time as the deposition temperature is varied.
• active gases SiH 4 and GeH, for example
• the dislocations emitted are quickly rejected and evacuated in order to gradually relax the growing layer.
• the latter process therefore has the advantages of a smaller thickness of intermediate layer to obtain a surface layer of relaxed substrate, a density of defects (emerging dislocations) of
• the present invention therefore relates to a new method of depositing a layer of pure monocrystalline germanium on a substrate of monocrystalline silicon, which does not require the deposition of an intermediate layer with a concentration gradient.
• the present invention also relates to such a deposition process providing low densities of residual emerging dislocations, less than 10 3 defects / cm 2 at the surface.
• the present invention also relates to such a process, making it possible to obtain a layer in a very short time and of small thickness (approximately 10 minutes for a layer of pure Ge of ⁇ m).
• the method of forming on a monocrystalline silicon substrate a layer of pure monocrystalline germanium comprises:
• thermostabilization of the monocrystalline silicon substrate at a first predetermined stabilized temperature (T,) from 400 ° C to 500 ° C, preferably from 430 ° C to 460 ° C;
• the method of forming on a monocrystalline silicon substrate a layer of pure monocrystalline germanium comprises after step (c) and before step (d):
• - (c 2 ) a step of chemical vapor deposition at the third predetermined temperature (T 3 ) of an alloy Si, _ ⁇ Ge ⁇ where x> 0.9, until an intermediate layer of Si alloy, _ ⁇ Ge ⁇ having a predetermined thickness;
• - (c 3 ) a transition step in which, at the third predetermined temperature (T 3 ), one passes from the chemical vapor deposition of the alloy Si ⁇ _ ⁇ Ge ⁇ to a chemical vapor deposition of pure Ge;
• step (c 4 ) a step in which CVD deposition of germanium is continued at said third predetermined temperature (T 3 ) so as to obtain a stack of layers comprising the base layer of germanium, an intermediate layer of alloy Si, _ ⁇ Ge ⁇ and an upper layer of germanium, the thickness of the stack being less than the desired final thickness; and "( c 5) a step in which the temperature of the chemical vapor deposition of germanium is increased from the third predetermined temperature (T 3 ) to a fourth predetermined temperature (T 4 ) from 750 to 850 ° C, preferably 800 to 850 ° C; step (d) being carried out at this fourth predetermined temperature (T 4 ), identical to or different from the second predetermined temperature (T 2 ), but preferably identical.
• any germanium precursor gas such as GeH 4 can be used .
• the germanium precursor gas is diluted with a carrier gas such as hydrogen. Dilution factors can vary from 10 to
• the GeH / H 2 volume ratio is 10%.
• the germanium deposits are preferably made at atmospheric pressure, because when the total pressure is less than 500 hPa, the deposits become rough very quickly and the density of emerging dislocations increases.
• the stage of stabilization of the temperature of the silicon substrate (a) is carried out in the absence of any reactive gas, but in the presence of the carrier gas, generally H 2 .
• H 2 carrier gas is preferably used with a flow rate of approximately 20 l / minute (purified or not).
• the precursor gas is preferably GeH 4 and the flux is generally between 30 and 400 cm 3 / minute under standard conditions, the optimal value being 300 cm 3 / minute (it is obviously acts of nominal flux values of
• durations of the CVD germanium deposition steps are obviously determined as a function of the thickness desired for the final germanium layer.
• a duration of 10 minutes from step (b), 60 seconds from step (c) and 120 seconds from l 'step (d) a final layer of pure monocrystalline germanium of approximately 1 ⁇ m is obtained having an extremely low density of emerging dislocations, which may be less than 10 defects / cm 2 .
• all the steps are also carried out in the presence of a carrier gas, preferably hydrogen and also preferably at atmospheric pressure.
• a carrier gas preferably hydrogen and also preferably at atmospheric pressure.
• the step of lowering the temperature (c,) is carried out in the absence of reactive precursor gases, but in the presence of carrier gas, for example hydrogen.
• CVD germanium deposits are carried out under the same conditions as above.
• CVD deposition of the Si, ⁇ Ge ⁇ alloy layer is carried out using a mixture of germanium and silicon precursor gases in the desired proportions to obtain a deposition of Si, _ ⁇ Ge ⁇ alloy comprising at least 90 % germanium atoms.
• the recommended germanium precursor gas is GeH 4 .
• the recommended silicon precursor gases are SiH 4 , Si 2 H 6 , SiH 2 Cl 2 , SiHCl 3 , SiCl 4 and Si (CH 3 ) 4 , SiH 4 being preferred.
• the intermediate layer of SiGe alloy will generally have a thickness of between 5 and 10 nm, preferably of the order of 10 nm, and obviously the CVD deposition conditions of this layer will be chosen to satisfy the requirements of thickness and germanium content of the layer. In particular, if the germanium content of this intermediate layer of SiGe alloy is less than 90 atom%, the density of emerging dislocations increases.
• the method according to the invention may comprise, prior to step (a) of stabilizing the temperature of the substrate, a step of impregnating the surface of the substrate by CVD deposition in the vapor phase of a layer of silicon at a temperature from 500 to 600 ° C, preferably from 550 ° C.
• This CVD deposition step is also preferably carried out at atmospheric pressure.
• the preferred precursor gas is SiH 4 and, as is well known, the deposition takes place in the presence of a carrier gas, preferably hydrogen.
• the thickness of the impregnation silicon layer is generally from 1 to 5 nm, preferably of the order of 3 nm.
• the surface of the substrate is subjected to a preparation step prior to the implementation of the method according to the invention.
• This preparation step can conventionally be a surface cleaning step, for example any liquid or gas phase process which cleans the silicon surface of metallic and organic residues, such as conventional SCI solutions (NH 4 OH + H 2 0 2 ) and SC 2 (HC1 + H 2 0 2 ) or H 2 S0 4 + H 2 0 2 .
• SCI solutions NH 4 OH + H 2 0 2
• SC 2 HC1 + H 2 0 2
• H 2 S0 4 + H 2 0 2 H 2 S0 4 + H 2 0 2
• the products obtained by the process according to the invention generally have a density of emerging dislocations ⁇ 10 3 / cm 2 and may even be less than 10 defects / cm 2 .
• the method described above limits the appearance of surface roughness, it is still desirable to reduce the surface roughness of the germanium deposit.
• Polishing control is done either in-situ by controlling polishing data like motor current, or ex-situ qualitatively by optical or microscopic observation, and / or quantitatively by atomic force microscopy technique [ measurement of average roughness (rms) or summit / valley].
• heteroepitaxy III-V such as GaAs.
• the layers of Ge obtained can present a slight stress (mesh parameter slightly lower than that of massive Ge) harmful for a subsequent resumption of heteroepitaxy, for example of GaAs on Ge.
• the Ge layer could release this constraint during a subsequent rise in temperature, which will have the unfortunate effect of making the surface rough again and therefore of hampering the resumption of III-V heteroepitaxy, for example by creating defects.
• the particularly preferred methods according to the invention comprise a step of stabilizing the germanium layer.
• This stabilization step introduced at the end of growth of the germanium layer (before mechanical-chemical polishing) will have the effect of (1) relaxing the stresses and finding the theoretical mesh parameter of germanium, and (2) stabilizing therefore the structure during subsequent annealing.
• this stabilization step consists of annealing under a hydrogen atmosphere at a temperature ranging from 650 ° C to less than 900 ° C for a sufficient time, generally about 10 minutes or more, to remove the residual stress.
• the duration of the annealing obviously depends on the annealing temperature and the thickness of the germanium layer.
• the annealing temperature is less than 900 ° C because, above 900 ° C, the germanium which makes at 937 ° C, becomes very unstable.
• This stabilization step can be carried out in a conventional multi-plate oven, however it will preferably be carried out in situ (after the growth of the germanium layer) in order to avoid any contamination of carbonaceous and oxygenated species in a single-plate reactor.
• the germanium layer can be polished mechanical-chemical as described previously.
• Figure 1 - a graph of deposition temperatures as a function of time (curve A), as well as graphs of the flow rates of the precursor gases SiH 4 and GeH 4 as a function of time (curves B and C) for the first embodiment of the process according to the invention;
• Figure 2 graphs of the flow rates of the precursor gases SiH 4 (curves B and D) and GeH 4 (curves C and E) as a function of time, as well as a graph of the deposition temperatures as a function of time (curve A); and
• Figure 3 a photomicrograph of a section of a monocrystalline silicon substrate coated, according to the first embodiment of the method of the invention, with a deposit of pure monocrystalline germanium (area observed by electron microscopy on the wafer) y;
• Figure 4 - a microphotograph of a surface of a monocrystalline silicon substrate coated, according to the first embodiment of the method of the invention, with a deposit of pure monocrystalline germanium (area observed by electron microscopy in plan view);
• Figure 5 a profile by atomic force microscopy (AFM) of a layer of Ge re-epitaxied on a layer of germanium obtained according to the method of the invention, but not stabilized; and Figure 6 - an AFM profile of a Ge layer, re-epitaxied on a germanium layer obtained according to the method of the invention, but stabilized.
• AFM atomic force microscopy
• the surface of the wafer is impregnated by chemical vapor deposition of silicon under the following conditions shown diagrammatically in FIG. 1 by curve B and the corresponding part of curve A.
• Total pressure atmospheric pressure
• Deposition temperature 550 ° C
• Precursor gas SiH 4 350 cm 3 / minute
• Carrier gas H 2 20 1 / minute
• Duration of deposition 30 seconds.
• a deposit of a silicon layer of approximately 3 nm is obtained.
• a layer of Ge with a thickness slightly less than 1 ⁇ m is obtained.
• the germanium deposit is maintained at 850 ° C (T 2 ) for 120 seconds to obtain a layer of pure monocrystalline germanium having a thickness of 1 ⁇ m.
• FIG. 3 is a scanning electron micrograph of a section of the deposit obtained and FIG. 4 a plan view of the deposit. These views show the absence of emerging dislocations in the germanium deposit.
• step (c j ) At the end of step (c), the arrival of GeH 4 is suppressed while maintaining the flow of H 2 and the temperature is lowered from 850 ° C to 550 ° C in about one minute.
• SiH flux 10 cm 3 / minute H 2 flux: 20 1 / minute
• Deposition time 120 seconds.
• Si 0 j Ge Q 9 of about 15 nm.
• step (d) This process is repeated by varying the temperature (T 2 ) of step (b) and the final temperature (T 4 ) of step (d).
• the re-epitaxy germanium (II) layer has a thickness of 500 nm.
• the re-epitaxy of the germanium (II) layer can also be done at atmospheric pressure and at a temperature above 670 ° C.
• a layer of germanium (II) was re-epitaxied under the same conditions on a plate obtained in an identical manner but without the annealing step.

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• Chemical & Material Sciences (AREA)
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• Recrystallisation Techniques (AREA)

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• 1998
  • 1998-09-10 FR FR9811313A patent/FR2783254B1/fr not_active Expired - Fee Related
• 1999
  • 1999-09-10 WO PCT/FR1999/002154 patent/WO2000015885A1/fr not_active Ceased
  • 1999-09-10 DE DE69905179T patent/DE69905179D1/de not_active Expired - Lifetime
  • 1999-09-10 US US09/786,996 patent/US6537370B1/en not_active Expired - Fee Related
  • 1999-09-10 EP EP99941731A patent/EP1115920B1/fr not_active Expired - Lifetime
  • 1999-09-10 JP JP2000570400A patent/JP4486753B2/ja not_active Expired - Fee Related

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