WO2000044038A1 - Processus cvd ameliore par plasma pour la croissance rapide de films en semiconducteur - Google Patents

Processus cvd ameliore par plasma pour la croissance rapide de films en semiconducteur Download PDF

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WO2000044038A1
WO2000044038A1 PCT/US2000/001904 US0001904W WO0044038A1 WO 2000044038 A1 WO2000044038 A1 WO 2000044038A1 US 0001904 W US0001904 W US 0001904W WO 0044038 A1 WO0044038 A1 WO 0044038A1
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process according
reactant gas
substrate
reaction chamber
region
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PCT/US2000/001904
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Walter J. Varhue
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University Of Vermont And State Agricultural College
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    • 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
    • C30B25/10—Heating of the reaction chamber or the substrate
    • C30B25/105—Heating of the reaction chamber or the substrate by irradiation or electric discharge
    • 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
    • C30B29/06—Silicon
    • 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
    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02367—Substrates
    • H01L21/0237—Materials
    • H01L21/02373—Group 14 semiconducting materials
    • H01L21/02381—Silicon, silicon germanium, germanium
    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02521—Materials
    • H01L21/02524—Group 14 semiconducting materials
    • H01L21/02532—Silicon, silicon germanium, germanium
    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/0257—Doping during depositing
    • H01L21/02573—Conductivity type
    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02612—Formation types
    • H01L21/02617—Deposition types
    • H01L21/0262—Reduction or decomposition of gaseous compounds, e.g. CVD

Definitions

  • the invention relates to the epitaxial growth of semiconductor films and in particular to the rapid growth of silicon-based and germanium-based films.
  • Si is typically deposited on blanket Si substrates by the high temperature pyrolysis of one ofthe chlorosilane precursors, such as dichloro silane.
  • chlorosilane precursors such as dichloro silane.
  • silane SiH 4 as a precursor reduces the required substrate temperature.
  • the use of a plasma assisted deposition process has the ability to reduce the substrate temperature for this growth process even further.
  • the associated gaseous discharge assists in the creation ofthe precursors to film growth, such as SiH, SiH 2 and SiH 3 , and also assists in the removal of impediments to film growth, e.g., hydrogen on the substrate surface.
  • the movement of chemical species on the growth surface is enhanced by the energetic particle flux to the surface, which in general assists in the overall growth process. It is known that growth of epitaxial layers at lower substrate temperatures reduces unwanted autodoping, dopant diffusion and the creation of crystal defects.
  • the ability to epitaxially deposit Si-based and Ge-based films at reduced substrate temperatures would improve the quality of semiconductor devices, would simplify the process used to fabricate such devices, and would make possible the fabrication of new device structures.
  • Chemical vapor deposition is a process in which chemical species in the vapor phase react on a heated substrate surface to produce a solid material film.
  • Plasma assisted chemical vapor deposition is a specific variety of a CVD process in which energetic electrons in a gaseous discharge are used to assist in the production of reactive chemical species, principally in the gas. These species then participate in the deposition process. Further, energetic ion bombardment ofthe substrate surface may be included to aid in the growth process.
  • the '609 patent does not emphasize the role of energetic ion bombardment of he substrate surface during the growth process, which, as discussed below, is a key aspect in achieving low temperature growth of Si-based films.
  • the invention concerns a process for depositing epitaxial Si, Ge, Si ⁇ Ge j . ⁇ and Si ⁇ Ge y C j . ⁇ .y films on Si or Ge wafer substrates ("wafers") at low substrate temperatures, i.e., below 650 ° C, and at high deposition rates, i.e., greater than 150 A/min, and as high as 500 A/min or greater.
  • the deposition process is assisted by a gaseous discharge which acts to increase the deposition rate and to reduce the required substrate temperature.
  • An exemplary gas discharge is an electron cyclotron resonance plasma, but this process in practice is not limited to such, and is extendable to other known plasma generating mechanisms, such as transformer coupled, inductively coupled, helicon, helical resonator, and remote or magnetically enhanced RF processes where energetic ion bombardment of the substrate surface is possible.
  • a first aspect ofthe invention is a process of epitaxially growing a Group IV semiconductor film, comprising the steps of first, providing a substrate having a surface made of a material comprising one of Si or Ge in a reaction chamber under vacuum. Then, heating the substrate to a temperature between 300 °C and 650 °C, then introducing into the reaction chamber a first reactant gas containing at least one of Si and Ge, while simultaneously bombarding the surface with energetic ions having a flux ratio of about between 0.5 and 5 eV/adatom.
  • the first reactant gas may be silane and the substrate made of Si, in which case the semiconductor film grown is Si.
  • the first reactant gas may be germane and the substrate made of Ge, in which case the semiconductor film grown is Ge.
  • compounds of Si, Ge and C may be formed by introducing silane, germane and methane reactant gases in the appropriate ratios, as described in detail below.
  • a second aspect ofthe invention is the process as described above, wherein the energetic ions are formed from at least one member of the group of elements and compounds consisting of He, Ar, Ne, Kr, SiH, SiH 2 , and SiH 3 .
  • a third aspect of the invention is a process for making a pn junction diode in a reaction chamber under vacuum.
  • the process comprises the steps of first, providing a Si substrate with a surface and heating the substrate to a temperature between 300°C and 650 °C, and then introducing a first reactant gas containing Si into the reaction chamber and simultaneously forming a first region ofthe pn junction by bombarding the surface with energetic ions having a flux ratio of about between 0.5 and 5 eV/adatom, while introducing one of an n-type or a p-type dopant.
  • the next step is then forming a second region ofthe pn junction atop the first region immediately following the previous step.
  • the final step is then forming an electrical contact between the first region and the second region.
  • FIG. 1 is cross-sectional schematic diagram ofthe ECR-PECVD reactor apparatus used to practice the process ofthe present invention
  • FIG. 2 is a flow diagram ofthe steps for epitaxially growing a Si film, a Ge film, a Si ⁇ Ge ⁇ _ ⁇ film or a Si ⁇ Ge y C ⁇ _ film according to the present invention
  • FIG. 3 is a plot ofthe growth rate dependence of epitaxial Si films deposited at 450° C and two different levels of silane flow as a function of microwave power level;
  • FIG. 4 is a plot ofthe growth rate dependence of epitaxial Si films deposited at 550° C and 275 W of microwave power as a function of silane flow rate;
  • FIG. 5 is a plot showing the extrapolated growth rate as a function of microwave power level at saturated silane flow rates
  • FIG. 6 is a plot showing the extrapolated growth rate as a function of silane flow rates at saturated microwave power levels
  • FIG. 7 is an X-ray rocking curve spectrum for an epitaxial Si sample prepared using the process of the present invention.
  • FIG. 8 is a Rutherford backscatter channeling spectrum for the epitaxial Si sample referred to in FIG. 7;
  • FIG. 9 is a plot ofthe growth rate dependence of epitaxial Si ⁇ Ge ⁇ _ ⁇ films deposited at 450 °C and a silane/germane flow rate of (7.5 sccm/1.5 seem) as a function of microwave power level;
  • FIG. 10 is an X-ray rocking curve spectrum for an epitaxial Si ⁇ Ge ⁇ _ ⁇ sample prepared using the process ofthe present invention.
  • FIG. 1 1 is a plot of a Rutherford backscatter channeling spectrum for the sample referred to in FIG. 10;
  • FIG. 12 is a flow diagram ofthe process steps for making a pn junction according to the present invention
  • FIG. 13 is a cross-sectional diagram of a first embodiment of a pn junction diode fabricated using the process steps ofthe present invention as set forth in FIG. 12.
  • FIG. 14 is a cross-sectional diagram of a first embodiment of a pn junction diode fabricated using the process steps ofthe present invention, wherein the metal contacts are co-planar;
  • FIG. 15 is a plot of the characteristic I-V curve for the pn junction diode of FIG. 13.
  • the present invention is a process to rapidly grow high quality epitaxial Si, Ge, Si ⁇ Ge ⁇ _ ⁇ and Si ⁇ Ge y C j. films at low substrate temperatures, i.e., below 650° C, and at high deposition rates, i.e., greater than 150 A/min.
  • the current process has been developed for use in an electron cyclotron resonance (ECR) PECVD reactor.
  • ECR electron cyclotron resonance
  • the critical deposition conditions of adatom flux and energetic ion bombardment are also possible in other plasma reactor configurations, such as helicon, transformer coupled, helical resonator, magnetically enhanced and remoted PECVD, where the addition of substrate biasing can duplicate the conditions described herein below.
  • reactor apparatus 10 comprises a primary reaction chamber 14 enclosing a primary interior region 18, and a secondary elongate chamber 22 enclosing a secondary interior region 28 open to region 18.
  • a quartz liner (not shown) is preferably provided in chamber 22. The latter also includes an outer wall 30 and an end portion 32 made of quartz.
  • a gas ring 36 is located between regions 18 and 28.
  • Apparatus 10 further includes within region 18 a substrate holder 40 capable of holding a wafer W or other substrate having a surface WS, and a radiative heater 42 arranged adjacent the substrate holder so as to be able to heat the wafer.
  • Radiative heater 42 may be, for example, a boron- nitride coated radiative heater.
  • Wafer W is preferably made of Si or Ge for growing Si and Ge based alloy films. Growth of high concentration alloy films on the opposing substrate, e.g. Si on Ge or Ge on Si requires first depositing a suitable buffer layer (e.g., a layer of Si or Ge grown at a different temperature) on the wafer surface.
  • a suitable buffer layer e.g., a layer of Si or Ge grown at a different temperature
  • Apparatus 10 further includes DC magnets 44 surrounding outer wall 30 of chamber 22, and a microwave radiation source 46 outside of chamber 14 and adjacent end portion 32. When, activated, magnets 44 produce magnetic field lines L, as shown. Also included in apparatus 10 is an argon (Ar) gas source 50 in fluid communication with interior regions 18 and 28, and a hydrogen (H 2 ) gas source 56 in fluid communication with interior region 18. Further included is a silane gas source 60a, germane gas source 60b, and methane gas source 60c (e.g., hydride gases), each in fluid communication with interior region 18. Mass flow controllers 66-70 are included between each of gas sources 50, 56 and 60a-60c, respectively, and the interior regions to which each respective gas source is in fluid communication.
  • Ar argon
  • H 2 hydrogen
  • silane gas source 60a, germane gas source 60b, and methane gas source 60c e.g., hydride gases
  • apparatus 10 further includes a load-lock chamber 76 connected to main chamber 14.
  • Load-lock chamber 76 has an interior region 80 separated from interior region 18 by a gate valve 82.
  • Chamber 76 includes a load lock door 83 for allowing placement of wafer W within interior region 80, and a load lock arm 84 for holding and loading the substrate onto wafer holder 40.
  • Apparatus 10 also preferably includes a RF sputter gun 88 arranged in chamber 14.
  • RF sputter gun 88 includes a sputtering target 90 which faces wafer surface WS of substrate W.
  • Sputtering target 90 may be made of Sb or other suitable material for doping the film to be deposited on surface WS of wafer W.
  • wafer W is prepared.
  • This preparation includes cleaning surface WS such that it is free of any oxide and is H-terminated, meaning that a layer of H atoms is site- absorbed to the atoms at wafer surface WS.
  • This may be accomplished using one of a number of different techniques, such as submersing wafer W in a dilute (1 : 10) solution of HF.
  • Preparation of wafer W may also include degreasing in trichloroethane, followed by a rinse in methanol and then DI water prior to etching in a dilute HF solution. It is preferable that, after wafer W is inserted into the HF solution, it not be exposed to an oxygen-containing ambient. If it is, it will require a subsequent in-situ cleaning step to remove the regrown oxide layer.
  • step 104 wafer W is inserted into region 80 of load lock chamber 76 through load lock door 83. With load lock door 83 and gate valve 82 closed, load lock chamber 76 is evacuated, preferably to a desired vacuum level pressure of about 10 "5 Torr or less (i.e., even greater vacuum) .
  • wafer W is heated (e.g., to about 400 °C) in the load lock chamber to remove excess H,0 vapor that may have deposited on wafer surface WS.
  • step 108 wafer W is transferred from region 80 in loadlock chamber 76 to interior region 18 of primary reaction chamber 14 and is placed in substrate holder 40. During this step, it is preferable to flow inert gas into region 18 to limit the flow of other gases from the load-lock chamber into this region. At this point, chamber 14 is continuously being pumped down to the desired vacuum level.
  • step 1 wafer W is radiatively heated via heater 42 to a temperature of between about 300 °C and 650 °C.
  • heater 42 it is preferable to flow Ar gas into regions 18 and 28 to aid in pump-down of water vapor outgassing from the inner walls of chambers 14 and
  • step 112 if an oxide is present on the wafer surface WS, its removal is required.
  • This is preferably accomplished by using an Ar/H 2 plasma clean, which involves activating microwave radiation source 46 and DC magnets 44 and then introducing Ar gas from Ar gas supply 40 into interior region 28 and H 2 gas from H 2 gas supply 56 into interior region 18.
  • the length of this plasma clean should be kept short, on the order of 1 minute, to avoid roughening the wafer surface.
  • the duration ofthe cleaning time is determined by the length of time that microwave power is delivered to reactor apparatus 10 with hydrogen flowing.
  • the cleaning process is preferably carried out for about 1 minute.
  • the Ar/H 2 purge prior to the plasma clean is preferably about 2 minutes, with 30 seem of Ar delivered to . region 28 and 20 seem of H 2 delivered to region 18.
  • the pressure in chamber 14 during the cleaning process is preferably between 1 - 10 mTorr.
  • the result of this cleaning process is that wafer surface WS is H 2 -terminated.
  • Other known ex-situ or in-situ cleaning processes that accomplish this end result without the plasma cleaning step may also be used.
  • step 114 the actual process of growing a Si, Ge, Si ⁇ Ge j . ⁇ or Si ⁇ Ge y C ].x . y film on wafer surface WS begins without delay, i.e., such that the glow discharge plasma is not extinguished.
  • the gas composition in the reactor is changed as quickly as possible. This is accomplished by turning off the H 2 flow from H 2 gas source 56, and initiating the flow of gas from one or a combination of gas sources 60a-60c, with Ar, to interior region 18 and continuing the flow of pure Ar from Ar gas source 50 to interior region 28.
  • germane gas is flowed from gas source 60b.
  • silane gas is flowed from gas source 60a.
  • silane and germane are flowed from gas sources 60a and 60b at a desired ratio (e.g., 5.J).
  • methane gas is also flowed from gas source 60c at a desired ratio (e.g., 5:1 :20).
  • a preferred rate of hydride gas flow from sources 60a-60c is between 2 and 30 seem, and a total preferred rate of Ar gas flow into reactor apparatus 10 is between 65 and 80 seem (e.g., by using a mixture of inert gas and reactant gas).
  • gas sources 60a-60c are between 25 - 35 seem from gas source 50 to interior region 28, and between 35 - 45 seem from one or more of gas sources 60a-60c to interior chamber region 18.
  • This gas ratio balances the flow in reactor apparatus 10 to permit the transport of some hydride gas into interior region 28.
  • the gas flow from gas sources 60a-60c may be accomplished in practice by using gas bottles with set mixtures of hydride and Ar compositions. With the changing total gas feed rates into interior regions 18 and 28 of reactor apparatus 10, may be necessary to mechanically readjust the flow rates to maintain a constant reactor pressure from the clean to deposition steps ofthe process.
  • a feed gas for example, silane
  • a gaseous plasma is generated through one of a number of processes to produce energetic electrons, gaseous ions and metastable gaseous atoms.
  • the working gas is Ar, though any inert gas, such as Ne, Kr or He may be used.
  • the silane molecule disassociates into fragments or radicals (i.e. SiH 3 and SiH 2 ) which are the precursor to film growth.
  • the addition of germane or methane produces similar species or reactive radicals in the gas phase ofthe system. These radicals collide with the Si substrate surface and react further on the substrate surface to form a coherent epitaxial thin film.
  • the composition ofthe film can be controlled by the relative composition of hydride gases supplied to the chamber. Other characteristics of the hydride gases, such as the relative ease with which reactive radicals are produced by collision with energetic electrons in the discharge also effect this ratio. For example when depositing a Si x Ge, .x alloy, a silane to germane ratio of (5.J) will produce a film with a Si to Ge ratio of (14: l).
  • the film growth rate using the process ofthe present invention depends mainly on the temperature of wafer W, the microwave power of microwave radiation source 42, and the feed gas flow rates.
  • the deposition rate obtained in the process ofthe present invention depends principally on the microwave power level and the flow rate of hydride feed gases.
  • the microwave power levels used should be equal to or greater than 200 W, and preferably between 200 and 350 W. Higher microwave power levels can be used, but the flow of reactive gas needs to be increased accordingly.
  • the deposition time was varied from 5 to 20 minutes and was stopped by terminating the supply of microwave power to reactor apparatus 10. The flow of reactant gases was then halted and the power to radiative heater 42 was turned off. The wafer was allowed to cool in reactor apparatus 10 for approximately 20 minutes, and then was removed to the load lock chamber 76. The pressure in reactor apparatus 10 was about 5 m Torr.
  • the Si growth rate increases essentially linearly to about 300 A/min at a microwave power of about 275 W, and then flattens out, as indicated by curve Cl .
  • the Si growth is reaction-rate limited.
  • the silane gas flow rate is increased to 13.5 seem, the Si growth rate becomes linear with microwave power up to a growth rate of about 475 A /min at a microwave power of about 320 W, and then flattens out, as indicated by curve C2.
  • the Si growth rate increases as a function of silane flow rate, as indicated by curve C3. Also, with reference to FIGS. 5 and 6, it can be seen that the Si growth rate as a function of microwave power (FIG. 5) and silane gas flow rate (FIG. 6) can reasonably be extrapolated to fairly high growth rates of 600 A/min and beyond, as indicated by curves C4 and C5, respectively.
  • the film growth process is continued under the operating conditions of choice within the parameters as described above until a desired film thickness is achieved.
  • the parameters for growing a Ge film are similar to those described above for Si.
  • Chamber 14 needs to be periodically cleaned of residual parti culate residues. Accordingly, in step 120, chamber 14 is cleaned, preferably by operating the Ar ECR plasma with addition of a fluorine or hydrogen containing a gas such as NF 3 or H 2 . The period of this cleaning cycle is on the order of minutes, depending on the frequency and length of use of apparatus 10. Improvement in the thin film material quality maybe obtained by the addition of a post deposition thermal anneal process step. Accordingly, in step 122, wafer W is exposed to a rapid thermal annealing (RTA) step with a suggested temperature of between 1,000 and 1200°C.
  • RTA rapid thermal annealing
  • Pendellosung fringes PF1 indicate high epitaxial quality material.
  • FIG. 8 there are shown two Rutherford backscatter (RBS) channeling spectra S3 and S4, the ratio between the two being known as the "chi min" value. A small chi min value is indicative of high epitaxial quality. In RBS spectra S3 and S4, the calculated "chi min value" is 6%, indicating a high epitaxial film quality.
  • RBS Rutherford backscatter
  • the mechanism for the process of growing Si, Ge, Si ⁇ Ge ⁇ _ ⁇ and Si ⁇ Ge y C,_ ⁇ _ y films according to the present invention is believed to have two key components.
  • the first is the production of reactive species (SiH, SiH 2 , and SiH 3 ) from silane by the plasma discharge.
  • the reactive species GeH, GeH 2 , and GeH 3 are formed from germane. These species are the precursors to film growth.
  • the second is that the energetic ion flux at the growth surface increases the successful utilization of these available reactive chemical species in the growth of an epitaxial film. Accordingly, energetic ion bombardment ofthe growth surface is an important aspect for the film growth process of the present invention.
  • the energetic ion flux in units of (eV) can be characterized as being on the same order of magnitude as the arrival rate of adatoms to the growth surface.
  • the ion energy/adatom flux ratio (hereinafter, "Flux Ratio") required for epitaxial growth is influenced by the substrate temperature, growth rate, vacuum level and alloy composition of the deposited thin film material. This Flux Ratio is preferably between about 0.5 and 5 eV/adatom.
  • the production of reactive species in the gas phase is believed to be another important factor in achieving high Si, Ge, Si ⁇ Ge ⁇ _ ⁇ and Si ⁇ Ge y C,_ ⁇ _ y deposition rates using this technique.
  • the flow rate ofthe silane/ Ar mixture or the germane/ Ar mixture into interior region 18 of main chamber 14 when growing a Si or Ge film exceeds the flow rate to interior region 28 of secondary chamber 22.
  • a portion ofthe silane or germane feed gas finds its way to interior region 28 of chamber 22, where it is effectively . activated. This phenomenon is believed to contribute to the observed increase in the Si, Ge, Si ⁇ Ge j. ⁇ and Si ⁇ Ge y C, . ⁇ _ y deposition rate.
  • deposition rate obtained in the process ofthe present invention depends principally on the microwave power level and the flow rate of hydride feed gases.
  • the experimental results presented below show a dependence on these operating parameters.
  • the microwave power levels used should be equal to or greater than 200 W, and preferably between 200 and 350 W. Higher microwave power levels can be used, but the flow of reactive gas needs to be increased accordingly.
  • the deposition time was varied from 5 to 20 minutes and was stopped by terminating the supply of microwave power to reactor apparatus 10. The flow of reactant gases was then halted and the power to radiative heater 42 was turned off. The wafer was allowed to cool in reactor apparatus 10 for approximately 20 minutes, and then was removed to the load lock chamber 76. The pressure in reactor apparatus 10 was about 5 m Torr.
  • the ion flux incident on wafer surface WS during the film growing process ofthe present invention was measured with a Faraday cup.
  • the ion flux was observed to increase with microwave power and decreasing reactor pressure.
  • the energy of an Ar ion incident on the wafer surface WS was also measured with a gridded electrostatic ion energy analyzer. It was found that ion energy increases with increasing microwave power and decreasing reactor pressure.
  • the average magnitude ofthe measured ion energy is on the order ofthe threshold energy known to cause atomic displacements in Si (i.e., 12-13 eV). Assuming a sticking coefficient of 1 , the Flux Ratio can be calculated. This calculation is performed at the point where the growth rate is observed to saturate for increasing microwave power (see FIG. 3).
  • the Flux Ratios are essentially identical.
  • the Flux Ratio obtained by increasing silane flow rate at a substrate temperature of 550 °C is similar, but lower. This lower Flux Ratio is expected, as the increased substrate (wafer) temperature contributes thermal energy to the epitaxial growth process.
  • the exact mechanism by which the higher substrate temperature increases the Flux Ratio is most likely a combination of phenomena, such as an increase in desorption of impurity atoms from the growth surface, as well as an increase in the adatom surface mobility.
  • epitaxial growth at high deposition rates is made possible by the assistance of energetic ion bombardment.
  • the conditions available at 450 °C result in a Flux Ratio equal approximately to 1.0 (eV/adatom).
  • Increasing the vacuum quality above 5xl0 "7 Torr acts to decrease the required Flux Ratio, as the flux of impurity atoms to the surface will be reduced.
  • the required Flux Ratio can be larger than 1.0 if vacuum quality decreases or the substrate temperature is reduced. Even lower substrate temperatures may be desired in certain applications. In these cases, the flux ratio needs to be higher by increasing the microwave power or decreasing the flow rate of one or more reactive gases.
  • the measured Flux Ratio value is lower than what has been predicted using the simple model above.
  • the adatom mass used in this calculation should be a weighted average of Si/Ge atomic masses representing the alloy composition. Assuming a 7% Ge composition, the average Si ⁇ Ge ⁇ . ⁇ adatom has a weighted mass of 31 gr/mole. Using this value in the above relationship yields a Flux Ratio of 1.11 eV/adatom. At this point, the experimentally determined value is bounded above and below by predicted values using simple theoretical considerations.
  • the deposition rate therefore can be increased further by raising the reactant feed rate (silane and germane) and then further by increasing the microwave power level. Results are similar to those observed with the growth of Si.
  • the crystalline quality ofthe Si ⁇ Ge j . ⁇ films has been determined by both high resolution x-ray diffraction and RBS channeling.
  • a representative x-ray diffraction spectrum S5 is shown in FIG. 10 for a film prepared under the following conditions: microwave power (275 W), substrate temperature (450 °C), silane flow rate (7.5 seem), germane flow rate (1.5 seem), Ar flow rate (30 seem upstream, and 40 seem downstream) and a resulting deposition rate of 332 A/min.
  • Pendellosung fringes PF2 are apparent in the diffraction spectrum, indicative of excellent quality.
  • RBS spectra S6 and S7 for this same film is shown in FIG. 1 1.
  • the "chi min" value for this Si ⁇ Ge ⁇ _ ⁇ film is 6 %, a further indication of excellent epitaxial quality.
  • Another piece of information that can be received from this spectrum is the high level of channeling experience from the Ge component ofthe film. This is an indication that the Ge atoms, which amount to 6.9 % of the composition, have assumed lattice site locations.
  • Preparation step 202 includes steps 102 through 114, described above in connection with flow diagram 100 of FIG. 2.
  • step 204 the actual process of growing an electrically doped Si, Ge, Si ⁇ Ge ⁇ . ⁇ and Si ⁇ Ge y C ]. ⁇ .y film on wafer surface WS begins without delay. This is accomplished by turning off the H 2 flow from H 2 gas source 56 and initiating the flow of gas from gas sources 60a-60c and the flow of Ar from Ar gas source 50 to interior region 18 of chamber 14.
  • silane gas is flowed from gas source 60a (step 204a).
  • germane gas is flowed from gas source 60b (step 204b).
  • Si ⁇ Ge j For growing a Si ⁇ Ge j .
  • ⁇ film, silane and germane are flowed from gas sources 60a and 60b at a desired ratio (step 204c).
  • methane gas is also flowed from gas source 60c at a desired ratio (step 204d).
  • the preferred rate of gas flow from sources 60a-60c is between 2 and 20 seem, and the preferred rate of Ar gas flow is between 70 and 80 seem.
  • a n-type dopant is added while the film is first being grown.
  • the starting wafer material is also n-type. This can be accomplished, for example, by co- sputtering during growth using an Sb, RF coupled sputtering gun as sputtering gun 88.
  • a preferred RF sputter gun 88 is 1.5 in. in diameter and is operated at 2 to 12 W of power.
  • the resulting doping concentration depends on film growth rate and RF power supplied to the sputter gun.
  • a typical growth rate is 350 A/min with an anticipated doping concentration of 1x10 cm " .
  • Other options for adding n-type dopant include the addition of a gaseous dopant such as PH
  • the second region 258 of pn junction 250 is formed. This is accomplished by ceasing the operation ofthe n-type sputter gun, and simultaneously, initiating the delivery of a p-type dopant to growth surface 254. This can also be accomplished, for example, by co- sputtering from a p-type dopant source, such as boron. Again, the resulting doping concentration depends on the film growth rate and RF power supplied to the sputter gun. This operation is ended when the desired film thickness has been deposited on growth surface 254. The sample is then removed from the reactor. Doping could also be accomplished by adding a P-type gaseous dopant such as diborane during growth of this layer.
  • a P-type gaseous dopant such as diborane
  • metal contacts 264 and 268 are formed so as to electrically connect to the n-region (here, first region 252) and the p-region (here, second region 258) of pn junction 250.
  • metal contacts 264 and 268 can be made coplanar, which requires diffusing a p-type material into the n-type first region 252 to create a p-type second region 258, and then forming metal contact 264 atop this second side.
  • second "region" 258 is formed in first region 252 by diffusing boron or by forming an alloyed indium contact.
  • the top and back surfaces of wafer W can be metalized to form ohmic contacts between regions 252 and 258.
  • first region 252 can be formed as the n-type region and second region 258 can be formed as the p-type region.
  • the process of growing Si, Ge, Si ⁇ Ge ⁇ _ ⁇ and Si ⁇ Ge y C ⁇ _ ⁇ _ y films according to the present invention will favorably impact the fabrication of integrated circuits which require the deposition of Si, Ge, Si ⁇ Ge j . ⁇ and/or Si ⁇ Ge y C,. x _ y epitaxial thin film materials.
  • the principal advantage ofthe present invention is that the deposition rates are high (i.e., much greater than 50 A/min) and the required substrate temperatures are low (i.e., less that about 650 °C).
  • the present invention will furthermore permit the fabrication of device structures such as heterojunction bipolar transistors that are limited by thermal equilibrium and diffusion.
  • An additional application of the present invention will include the fabrication of devices , such as wavelength specific photodiodes and Si ⁇ Ge ⁇ ⁇ based CMOS devices, which involve the growth of crystalline Si ⁇ Ge j . ⁇ and Si ⁇ Ge y C j. ⁇ .y alloy films on Si substrates.
  • the equilibrium lattice constant of Si ⁇ Ge ⁇ . ⁇ varies from 5.43 A, for pure Si, to 5.66 A for pure Ge. If the Si ⁇ Ge ⁇ _ ⁇ film is deposited at a high substrate temperature (>600 °C) or to a thickness beyond its pseudomorphic thickness (>300 A), the film will relax with the creation of crystalline dislocations.
  • a process to avoid this thermal relaxation is to deposit the material at a low substrate temperature, i.e., below 600 °C.
  • Examples of device structures that will benefit from this technological advance are bandgap specific Si ⁇ Ge j _ ⁇ and Si ⁇ Ge y C, . ⁇ _ y detectors, heteroj unction bipolar devices, heteroj unction CMOS and abrupt interface Si ⁇ Ge ⁇ . ⁇ and Si ⁇ Ge y C,_ ⁇ _ y superlattices for a variety of quantum well devices.

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Abstract

L'invention concerne un processus de croissance épitaxiale de film en semiconducteur du groupe IV sur une surface (WS) de substrat (W) en matériau à base de Si ou de Ge, dans une chambre de réaction (14) sous vide. Les étapes du procédé sont les suivantes : chauffer le substrat à une température comprise entre 300 °C et 650 °C, introduire dans la chambre de réaction un premier gaz réactif à base de Si ou de Ge, correspondant au matériau qui constitue le substrat, tout en bombardant la surface avec des ions énergétiques dont le rapport de flux est compris entre environ 0,5 et 5 eV/adatom. Le premier réactif peut être du silane et le substrat peut être en Si, moyennant quoi le film en semiconducteur dont la croissance est obtenue est en Si. Selon une variante, le gaz peut être du germane et le substrat peut être en Ge, moyennant quoi le film en semiconducteur dont la croissance est obtenue est en Ge. De même, on peut former des composés de Si, Ge et C en introduisant des gaz réactifs à base de Si, Ge et C, par exemple silane, germane et méthane, selon des rapports appropriés.
PCT/US2000/001904 1999-01-26 2000-01-25 Processus cvd ameliore par plasma pour la croissance rapide de films en semiconducteur WO2000044038A1 (fr)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9136794B2 (en) 2011-06-22 2015-09-15 Research Triangle Institute, International Bipolar microelectronic device
RU2622092C1 (ru) * 2016-07-13 2017-06-09 Федеральное государственное автономное образовательное учреждение высшего образования "Национальный исследовательский Нижегородский государственный университет им. Н.И. Лобачевского" Применение вакуумного осаждения германия из газовой среды германа в качестве способа удаления диоксида кремния с рабочей поверхности кремниевой подложки и способ изготовления монокристаллической плёнки германия на кремниевой подложке, включающий указанное применение
RU2669159C1 (ru) * 2017-12-21 2018-10-08 Федеральное государственное автономное образовательное учреждение высшего образования "Национальный исследовательский Нижегородский государственный университет им. Н.И. Лобачевского" Способ вакуумного эпитаксиального выращивания легированных слоёв германия

Citations (1)

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US4870030A (en) * 1987-09-24 1989-09-26 Research Triangle Institute, Inc. Remote plasma enhanced CVD method for growing an epitaxial semiconductor layer

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4870030A (en) * 1987-09-24 1989-09-26 Research Triangle Institute, Inc. Remote plasma enhanced CVD method for growing an epitaxial semiconductor layer

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9136794B2 (en) 2011-06-22 2015-09-15 Research Triangle Institute, International Bipolar microelectronic device
RU2622092C1 (ru) * 2016-07-13 2017-06-09 Федеральное государственное автономное образовательное учреждение высшего образования "Национальный исследовательский Нижегородский государственный университет им. Н.И. Лобачевского" Применение вакуумного осаждения германия из газовой среды германа в качестве способа удаления диоксида кремния с рабочей поверхности кремниевой подложки и способ изготовления монокристаллической плёнки германия на кремниевой подложке, включающий указанное применение
RU2669159C1 (ru) * 2017-12-21 2018-10-08 Федеральное государственное автономное образовательное учреждение высшего образования "Национальный исследовательский Нижегородский государственный университет им. Н.И. Лобачевского" Способ вакуумного эпитаксиального выращивания легированных слоёв германия

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