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  • H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
  • H01L21/76—Making of isolation regions between components
  • H01L21/762—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers
  • H01L21/7624—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using semiconductor on insulator [SOI] technology
  • H01L21/76251—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using semiconductor on insulator [SOI] technology using bonding techniques
  • H01L21/76254—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using semiconductor on insulator [SOI] technology using bonding techniques with separation/delamination along an ion implanted layer, e.g. Smart-cut, Unibond
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  • H01L21/02365—Forming inorganic semiconducting materials on a substrate
  • H01L21/02436—Intermediate layers between substrates and deposited layers
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  • H01L21/02612—Formation types
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  • H01L21/02636—Selective deposition, e.g. simultaneous growth of mono- and non-monocrystalline semiconductor materials
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  • H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
  • H01L21/76—Making of isolation regions between components
  • H01L21/762—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers
  • H01L21/7624—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using semiconductor on insulator [SOI] technology
  • H01L21/76248—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using semiconductor on insulator [SOI] technology using lateral overgrowth techniques, i.e. ELO techniques
• • H—ELECTRICITY
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  • H01L33/005—Processes
  • H01L33/0093—Wafer bonding; Removal of the growth substrate
• • 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
  • Y10S117/00—Single-crystal, oriented-crystal, and epitaxy growth processes; non-coating apparatus therefor
  • Y10S117/915—Separating from substrate

Definitions

• the present invention relates to the production of gallium nitride (GaN) films by epitaxy with reduced defect densities.
• Nichia produced a laser diode from III-V nitrides. Such a result showed that one could obtain a laser emission in a heteroepitaxial structure where the density of dislocations obtain a laser emission during 10000 hours provided that it reached 10 8 to 10 10 cm "2.
• Nichia demonstrated that the structure could be provided with a layer of good quality GaN. These were GaN layers developed using ELO (Epitaxial Lateral Overgrowth) lateral overgrowth technology.
• the nitride-based components III-V are produced by heteroepitaxy on substrates such as sapphire, SiC,
• the sapphire commonly used as a substrate does not have a cleavage plane, which implies that in a laser diode structure with based on GaN epitaxied on sapphire, it is difficult to manufacture reflective facets.
• a substrate such as sapphire exhibiting both a lattice parameter disaggregation and a thermal expansion coefficient is responsible for the very high dislocation density in the heteroepitaxial layers of GaN / sapphire.
• a known variant of growth technology is based on vapor phase epitaxy by organometallic pyrolysis (EPVOM) according to a process which is now well established (on sapphire): treatment of the surface of the sapphire, nucleation at low temperature of a layer of GaN or AIN, annealed to the final growth temperature of this nucleation layer and high temperature growth of GaN (1000-1100 ° C).
• EVOM organometallic pyrolysis
• the nucleation layer at low temperature is no longer necessary, a layer of AIN at high temperature is first produced before the deposition of GaN.
• the density of dislocations remains appreciably of the order of approximately 5 ⁇ 10 8 cm "2 .
• dislocations the density of extended defects: dislocations, stacking faults, inversion domains, nanotubes reaches 5.10 8 cm “2.
• Dislocations propagate in the direction of growth and emerge on the surface where they can be identified by atomic force microscopy (AFM) or cathodoluminescence (CL). These dislocations are harmful from several points of view.
• AFM atomic force microscopy
• CL cathodoluminescence
• the dislocations disrupt the ordering of the MQWs and cause a non-homogeneous light emission.
• the metals used for ohmic contacts can also diffuse through these dislocations and nanotubes.
• the overgrowth by lateral epitaxy (ELO) with numerous variants constitutes one of the most relevant methods for reducing the density of dislocations by several orders of magnitude, that is to say less than about 10 7 cm "2 .
• GaN single crystals can be obtained by growth in solution at high temperature (1800K) under hydrostatic pressure (1.5 GPa). But, although of very good crystalline quality (density of dislocations less than 10 4 cm "2 ), the surface of these crystals does not exceed 1 cm 2 and the mode of production does not meet global needs.
• the drawback remains that the density of dislocations is around 10 7 cm "2. More precisely, a very thick layer (approximately 500 ⁇ m) is produced on sapphire by avoiding the formation of cracks. For thicknesses of this order, the density of dislocations decreases until around 10 7 cm “3 . Then, the substrate is separated either by mechanical abrasion or by laser separation (LLO).
• LLO laser separation
• ions are implanted by bombardment creating in the semiconductor, at a depth close to the average depth of penetration of these ions, a layer of microcavities (or bubbles).
• a heat treatment of the semiconductor thus implanted produces a rearrangement of the structure, and the pressure induced by the microbubbles allows a separation of a thin film from the rest of the semiconductor.
• the object of the invention is to propose a method for producing a GaN film separated from its substrate, which is simple, rapid and inexpensive, and which provides a GaN film of increased quality.
• the GaN can be doped or not. Mention may in particular be made, as doping substances, of magnesium, zinc, beryllium, calcium, carbon, boron and silicon.
• GaN film separated from its substrate or “self-supported GaN film” is used.
• the subject of the invention is a method for producing a self-supported film of gallium nitride (GaN) from a substrate, by deposition of GaN by epitaxy, characterized in that the deposition of GaN comprises at minus a step of lateral epitaxial overgrowth (ELO) and in that it comprises a step of separation of a part of the GaN layer from its substrate by embrittlement by implantation of ions in the GaN layer directly.
• the invention relates to a process for producing a gallium nitride (GaN) film as described above, characterized in that it comprises the following successive steps:
• the step or steps of lateral epitaxial growth of GaN can be carried out in the vapor phase, for example using EPVOM, HVPE or even SVT or liquid (LPE) techniques.
• This method makes it possible in particular to place the embrittlement zone in a precisely desired zone because the GaN deposited during the resumption of epitaxy does not hinder the implantation of ions.
• This process also makes it possible to use the high temperatures of the resumption of epitaxy as being the useful heat treatment to ensure the rearrangement of the structure.
• This process finally makes it possible to obtain spontaneous separation after the various epitaxy phases, and heat treatments, namely from the resumption of growth until cooling at the end of the resumption phase of epitaxy.
• This method has the particular advantage of not requiring large doses of implantation ions but also of providing GaN films of homogeneous and controlled thickness, namely in particular very thin, of the order of 0.1 ⁇ m. .
• the invention also relates to any GaN film capable of being obtained by this process.
• the GaN film thus obtained can have a thickness varying from 100 to 5000 ⁇ m.
• the GaN film obtained can have a thickness of at least 0.1 mm.
• the range of thickness that can be targeted is therefore very wide.
• gallium nitride films having a thickness of more than 50 ⁇ m; these films are part of the invention.
• An optoelectronic component is also proposed, and in particular a laser diode, a UV light-emitting diode, a photodetector or a transistor, characterized in that it is provided with a GaN film capable of being obtained by the process of the invention.
• the initial substrates can have a thickness of a few hundred micrometers, generally of the order of 200 ⁇ m and can be chosen from sapphire, ZnO, SiC, LiAI02, LiAI02, LiGa0 2 , MgAI0, Si, GaAs, AIN or GaN.
• the substrates can be treated before any deposition of GaN by nitriding.
• a lateral epitaxial overgrowth in the vapor phase is preferably carried out in order to minimize, from the start of the process of the invention, the defect density.
• EPVOM a lateral epitaxial overgrowth in the vapor phase
• the dielectric masks useful during step (i) can be made of silicon nitride (SiN), SiO 2 or W.
• the dielectric is deposited according to techniques well known to those skilled in the art.
• the prior deposition of the thin layer of GaN (before the deposition of the dielectric as a mask) can be preceded by the deposition of a nucleation layer by formation of a very thin film of silicon nitride so as to obtain spontaneous patterns or islands of GaN.
• a nucleation layer by formation of a very thin film of silicon nitride so as to obtain spontaneous patterns or islands of GaN.
• the step of etching a dielectric mask is eliminated by virtue of the spontaneous formation of GaN patterns in the form of islets, playing the same role. More precisely, this second alternative can be described as follows: The substrate is covered with a thickness of silicon nitride of the order of a few atomic planes, in other words of the order of 10 nm to 20 nm in thickness.
• the deposition of SiN from silane and ammonia can last 360 seconds instead of 30, the SiN layer thus formed, is, as shown by the analysis in very high resolution electron microscopy presented in the aforementioned article, discontinuous; therefore, a SiN mask is formed spontaneously on a nanometric scale, which induces an ELO process.
• a layer of GaN called a continuous buffer layer, is deposited. The thickness of this layer can be between 10 and 100 nm.
• the temperature during this operation can be between 500 and 700 ° C.
• An annealing is then carried out at high temperature between 900 and 1150 ° C.
• the buffer layer is converted from a continuous layer to a discontinuous layer formed of GaN patterns, or in other words of GaN patterns in the form of islands.
• the zones where the silicon nitride is exposed then function as a mask and the GaN patterns function as the GaN zones located in the openings made ex situ in the mask.
• the implantation of ions during step (ii) can be implemented during a single step or successive steps.
• the implantation energies can vary from 80 to 160 keV.
• the implantation ions can be chosen from H + , ions of rare gases such as helium, neon, krypton and xenon as well as boron, which can be used alone or in combination. H + ions are preferred as implantation ions in the context of the present invention.
• the temperature during implantation can vary between 4K and 1000K.
• this temperature can be maintained at room temperature during the implantation of H + ions in a GaN layer.
• the heat treatment temperature at which the crystal rearrangement takes place which corresponds to the temperature of the epitaxy, can vary from 900 to 1150 ° C.
• dose of implantation ions when this is the H + ion, the preferred dose is between 10 16 and 10 17 H + cm "2 ions.
• the implantation depth varies from 50 nm starting from from the free surface to the GaN / initial substrate interface.
• the epitaxy recovery step (iii) can be implemented by epitaxy in EPVOM, HVPE, CSVT or even LPE (epitaxy in liquid phase - liquid epitaxy phase). We prefer during this step to implement HVPE technology.
• the spontaneous separation in step (iv) takes place due to the thermal cycle (resumption of epitaxy at high temperature and cooling) which the layer of GaN ELO undergoes during step (iii) after implantation.
• the thickness ratio of the layer and the substrate can preferably be greater than 0.5 for spontaneous separation.
• Figure 1 is a representation of a first stage of two-stage lateral epitaxial overgrowth
• FIG. 2 is a representation of a second step of this lateral epitaxial overgrowth
• FIG. 3 is a representation of a step of implanting H + ions in an ELO layer
• FIG. 4 is a representation of a step of resumption of epitaxy in HVPE; - Figure 5 is a representation of a spontaneous ELO layer separation step.
• the first step consists of GaN growth by lateral epitaxial overgrowth on a sapphire substrate by EPVOM;
• the second step consists of implanting hydrogen;
• the third stage consists of a resumption of epitaxy in HVPE.
• the first step is shown diagrammatically in FIGS. 1 and 2: after having epitaxied a layer of GaN, referenced 2, on a sapphire substrate, referenced 1, a deposition of SiN is carried out in situ (masks 3) then, on this dielectric layer, 3bis openings are etched by photolithography in well defined crystallographic directions [1-100] or [11-20] GaN. Finally, we resume growth which first gives a selective epitaxy 4.
• This assembly formed by a GaN ELO 5 layer and the sapphire substrate 1 is implanted by H + ions (FIG. 3) so that a weakening zone 6 is created in the ELO layer 5 at a depth between 50 nm and 5 ⁇ m.
• the ions are implanted at doses between 1 ⁇ 10 15 and 1 ⁇ 10 17 cm “2 .
• the ELO 5 layer therefore constitutes a privileged cleavage zone.
• This layer weakened by the implantation of H + is then taken up by HVPE epitaxy. More precisely, after implantation, the weakened but entire ELO structure is placed on the substrate holder of an HVPE reactor. 10 to 500 ⁇ m of GaN are deposited to form a layer 7 (FIG. 4).
• HVPE technology is very widely documented and the resumption of epitaxy in HVPE is carried out here according to the state of the art.
• a first effect is that the ELO 5 layer is thickened without losing its crystalline qualities (no new dislocation or crack is generated).
• a second effect is that the dislocation density is further reduced when resuming epitaxy in HVPE, by a factor at least equal to 2.
• a third effect is that the overall layer 5,7 thus obtained spontaneously separates from its initial substrate of sapphire 1 during thermal cycle which, because of the difference in thermal expansion coefficients of sapphire 1 and of the GaN layers 5, 7 generates constraints, and a self-supported GaN film 8 of ELO quality is thus obtained.
• This self-supporting GaN film presents a surface where, as is common in HVPE, we observe growths in the form of hexagonal pyramids, and on a rear face, constituted by the fracture zone, we can indeed identify geometric patterns corresponding to the starting ELO structure.
• An ELO quality self-supported GaN film was thus obtained, that is to say with a dislocation density of less than 10 7 cm "2 .
• FIG. 6 shows the reflectivity curve measured in situ in real time during the growth of "spontaneous ELO" during step (i).
• Snapshots (a), (b) and (c) are scanning electron microscopy images of the GaN islets ranging from their spontaneous formation to their coalescence. This particular embodiment is illustrated by example 2 below.
• the GaN films obtained according to the process of the present invention can be polished and used as high quality films for the manufacture of GaN-based components (electronic or optoelectronic such as laser diodes, light emitting diodes, photodetectors, transistors ).
• the subject of the invention is also the substrate after separation of the gallium nitride layer by implantation of ions, comprising part of the GaN directly deposited on the substrate during step (i) of the method according to the invention, as a new substrate which can be used for recovery by epitaxy of GaN.
• the use of the substrate after separation of the gallium nitride layer by implantation of ions, comprising a part of the GaN directly deposited on the substrate during step (i) of the method according to the present invention, as a new substrate for a recovery by epitaxy of GaN also forms part of the invention.
• a horizontal or vertical reactor is used for the EVPOM epitaxy.
• a vertical reactor is used, with a cylindrical growth chamber 55 mm in diameter to receive a 2 "substrate.
• a layer of GaN by EPVOM is deposited on a sapphire substrate with a thickness of 250 ⁇ m to 430 ⁇ m using a special procedure which makes it possible to spontaneously obtain islets by a treatment consisting in covering the substrate with a film of silicon nitride, of which the thickness is of the order of 0.1 nm.
• a substrate, in particular made of sapphire is brought to a temperature of approximately 1050-1120 ° C. to be nitrided by exposure to a flow of NH 3 for approximately 10 minutes.
• a very thin film of silicon nitride is formed on the surface, the film being obtained by reaction between NH 3 and silane SiH 4 for a time long enough to limit the thickness of the film to that of an atomic plane.
• the operating conditions are as follows:
• the gaseous vehicle is a mixture of nitrogen and hydrogen in equal proportions (4 sl / min).
• the ammonia is introduced with a flow rate of 2 sl / min while the silane, in diluted form at 50 ppm in hydrogen, is introduced with a flow rate of 50 scc / min.
• the typical reaction time between NH 3 and SiH 4 is of the order of 30 seconds. The successive stages are followed by laser reflectometry.
• a layer of gallium nitride with a thickness of 20 to 30 nm is deposited on the dielectric film.
• the precursor of gallium is trimethylgallium (TMGa).
• TMGa trimethylgallium
• the deposition layer is made at low temperature, of the order of 600 ° C.
• patterns or islands of GaN of very good crystal quality are obtained and retaining an epitaxy relationship with the substrate thanks to the very thin thickness of the layer of silicon nitride.
• the patterns or islands of GaN are isolated from each other by zones where the layer of silicon nitride is exposed.
• the characteristic heights of the islands are of the order of 240 nm.
• the zones where the silicon nitride layer is exposed function as a mask for ELO, and the patterns or islands of GaN as well spontaneously formed are analogous to point ELO patterns. Deposition of a thin layer of undoped gallium nitride prior to the ELO step
• a thin layer of GaN 2 ⁇ m thick is deposited by vapor phase epitaxy by pyrolysis of organometallics.
• the source of gallium is Trimethylgallium (TMGa) and the source of nitrogen is ammonia.
• a thin layer of silicon nitride is deposited as a dielectric mask using SiH 4 and NH 3 with flow rates of 50 sccm and 2 slm respectively. Although extremely thin, this layer of SiN has proven to be a perfectly selective mask. Engraving by photolithography and reactive ion attack is then carried out to produce linear openings of 3 ⁇ m spaced 7 ⁇ m apart. The linear openings are advantageously oriented in the direction [10-10] of GaN, although the variant of the method described in this example can be carried out for other linear orientations, in particular [11-20].
• Resumption by epitaxy on the cleared areas is carried out by GaN unintentionally doped under operating conditions such that the growth speed in the direction of the patterns sufficiently exceeds the growth speed in the direction normal to the inclined flanks of said patterns . Under such conditions, the growth anisotropy leads to the disappearance of the facet (0001).
• the first phase of the implementation of the ELO process ends when the disappearance of the facet (0001) of the GaN pattern is ensured. At the end of the first step, the GaN patterns took the form of bands whose section is triangular.
• the second stage of ELO consists of resuming epitaxy by modifying the growth conditions to change the growth anisotropy so that it becomes favorable for the planerization of GaN patterns.
• the GaN patterns develop with an expansion of the facet (0001) (which reappears at the top of each pattern) while the surface of the lateral facets decreases.
• the second step ends when the sides have disappeared, the upper surface of the deposit formed by the coalesced patterns is flat.
• This structure is implanted by H + ions in a step (ii) and taken up in HVPE as follows:
• the ELO layer After having undergone implantation of hydrogen ions in doses of between 1 ⁇ 10 15 and 1 ⁇ 10 17 cm 2 , the ELO layer is reused as a substrate and placed in a HVPE reactor in order to obtain a thickness of GaN sufficient to produce 1 spontaneous separation effect.
• the temperature rise takes place in a mixed atmosphere of nitrogen (2.5 slm) and ammonia (0.5 slm). As soon as the temperature of
• the first phase of the growth of a thick layer of GaN is then initiated by introducing into the vapor phase a flow rate of 15 sccm of gallium chloride obtained by reaction of 15 sccm of HCl with liquid gallium maintained at a temperature equal to that of the substrate (1030 ° C). As soon as the gallium chloride is brought into contact with the ammonia, there is instantaneous formation of GaN which is deposited on the substrate with a growth rate of approximately 40 ⁇ m per hour with these flow rates.
• the growth thus continues for several hours under these experimental conditions in order to reach a thickness of at least 200 ⁇ m of the GaN layer.
• the growth is then interrupted and while remaining under a flow of ammonia, the experimental parameters are modified in order to reduce the roughness of the surface which is very important under the operating conditions described above.
• the growth temperature is brought to 1050 ° C., the flow of ammonia is increased to 1 slm and the composition of the carrier gas is modified to have a mixture of 1 slm of hydrogen and 1.5 slm of nitrogen. .
• the growth is then definitively completed by diverting the flow of HCI towards the outside and the cooling takes place in an atmosphere consisting only of nitrogen and ammonia with a temperature ramp of 2.5 ° C per minute.
• the temperature of the substrate is below 800 ° C, the ammonia flow can be completely interrupted.
• the separation step (iv) takes place spontaneously by cooling.
• Example 2 a 3 ⁇ 2 "vertical reactor is used where the active gases are distributed by a shower system which makes it possible to separate the gaseous flows of ammonia and trimethylgallium.
• a thin film of silicon nitride is formed on the surface, the film being obtained by reaction between NH 3 and silane SiH for a time long enough to limit the thickness of the film to a few atomic planes.
• the operating conditions are as follows:
• the gaseous vehicle is a mixture of nitrogen and hydrogen in equal proportions (10 sl / min).
• the ammonia is introduced with a flow rate of 8 sl / min while the silane, in the form diluted to 1000 ppm in hydrogen, is introduced with a flow rate of 50 scc / min. Under these conditions the typical reaction time between NH 3 and SiH 4 is of the order of 300 seconds.
• the growth technology is then identical to Example 1:
• the" spontaneous ELO "layer is reused as a substrate and placed in an HVPE reactor in order to obtain a sufficient thickness of GaN to produce the spontaneous separation effect.
• implantation can be carried out at different stages of growth either in the islets, or at an intermediate stage where the islets are not fully coalesced, or after coalescence These three possibilities are indicated by an arrow in Figure 6.
• the resumption of epitaxy takes place in a horizontal HVPE reactor 1 ⁇ 2 "The temperature rise takes place in a mixed atmosphere of nitrogen (2.5 slm) and ammonia (0.5 slm). the temperature of 1030 ° C is reached, the vapor phase is modified, a mixture of 0.5 slm of nitrogen and 2 slm of hydrogen is maintained as a new carrier gas, while the flow of ammonia is reduced to 0 , 4 slm.
• the first phase of the growth of a thick layer of GaN is then initiated by introducing into the vapor phase a flow of 15 sccm of gallium chloride obtained by reaction of 15 sccm of HCl with liquid gallium maintained at a temperature equal to that of the substrate (1030 ° C). As soon as the gallium chloride is brought into contact with the ammonia, there is instantaneous formation of GaN which is deposited on the substrate with a growth rate of approximately 40 ⁇ m per hour with these flow rates.
• the growth is then interrupted and while remaining under a flow of ammonia, the experimental parameters are modified in order to reduce the roughness of the surface which is very important under the operating conditions described above.
• the growth temperature is brought to 1050 ° C., the flow of ammonia is increased to 1 ⁇ m and the composition of the carrier gas is modified to have a mixture of 1 ⁇ l of hydrogen and 1.5 ⁇ m of nitrogen.
• growth is then resumed by introducing a flow rate of 5 sccm of HCl on the liquid gallium leading to a flow rate of 5 sccm of gallium chloride in the vapor phase.
• the growth is continued under these new conditions for approximately 2 hours. Growth is then definitively completed by deriving the flow of
• HCI to the outside and cooling takes place in an atmosphere consisting only of nitrogen and ammonia with a temperature ramp of 2.5 ° C per minute.
• the ammonia flow can be completely interrupted.
• the self-supporting substrate which separated spontaneously during a step (iv) after the thermal cycle, resumption of HVPE growth and cooling has a dislocation density of less than 10 7 cm "2 .

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