EP3939077A1 - Method for transferring a useful layer onto a support substrate - Google Patents

Method for transferring a useful layer onto a support substrate

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Publication number
EP3939077A1
EP3939077A1 EP20713947.8A EP20713947A EP3939077A1 EP 3939077 A1 EP3939077 A1 EP 3939077A1 EP 20713947 A EP20713947 A EP 20713947A EP 3939077 A1 EP3939077 A1 EP 3939077A1
Authority
EP
European Patent Office
Prior art keywords
bonded structure
buried
support substrate
plane
transfer method
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP20713947.8A
Other languages
German (de)
French (fr)
Inventor
Didier Landru
Oleg Kononchuk
Nadia Ben Mohamed
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Soitec SA
Original Assignee
Soitec SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Soitec SA filed Critical Soitec SA
Publication of EP3939077A1 publication Critical patent/EP3939077A1/en
Pending legal-status Critical Current

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Classifications

    • 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
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • 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
    • 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
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/26—Bombardment with radiation
    • H01L21/263—Bombardment with radiation with high-energy radiation
    • H01L21/265—Bombardment with radiation with high-energy radiation producing ion implantation
    • H01L21/26506—Bombardment with radiation with high-energy radiation producing ion implantation in group IV semiconductors
    • 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
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/77—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate
    • H01L21/78—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices
    • H01L21/7806—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices involving the separation of the active layers from a substrate

Definitions

  • TITLE PROCESS FOR TRANSFERRING A USEFUL LAYER ON A
  • the present invention relates to the field of microelectronics. It relates in particular to a method of transferring a useful layer onto a support substrate.
  • a method of transferring a useful layer 3 onto a support substrate 4, shown in FIG. 1, is known from the state of the art; this process described in particular in documents WO2005043615 and WO2005043616 comprises the following steps:
  • the species implanted at the level of the buried fragile plane 2 are at the origin of the development of microcavities.
  • the thermal embrittlement treatment has the effect of promoting the growth and pressurization of these microcavities.
  • additional external forces energy pulse
  • the initiation of a fracture wave in the buried fragile plane 2 is operated, which wave propagates in a self-sustaining manner, leading the transfer of the useful layer 3 by detachment at the level of the buried fragile plane 2.
  • This process can be used for the manufacture of silicon on insulator substrates (SOI - “Silicon on insulator”).
  • the donor substrate 1 and the support substrate 4 are each formed from a silicon wafer, the standardized diameter of which is typically 200mm, 300mm, or even 450 mm for the next generations.
  • One and / or the other of the donor substrate 1 and of the support substrate 4 are oxidized at the surface.
  • SOI substrates must meet very precise specifications. This is particularly the case for the average thickness and the uniformity of thickness of the useful layer 3. Compliance with these specifications is required for the proper functioning of the semiconductor devices which will be formed in and on this useful layer 3. .
  • the architecture of these semiconductor devices requires the availability of SOI substrates having a very low average thickness of the useful layer 3, for example less than 50 nm, and having very good uniformity of thickness of the layer. useful 3.
  • the expected thickness uniformity can be of the order of 5% at most, corresponding to variations typically ranging from +/- 0.3nm to +/- lnm over the entire surface of the useful layer 3.
  • additional finishing steps such as etching or heat treatments for surface smoothing, are carried out after the useful layer 3 is transferred to the support substrate 4, it is important that the surface morphological properties (in particular, thickness uniformity and surface roughness) are as favorable as possible after transfer, to ensure that specifications are maintained finals.
  • certain useful layers 3 may comprise, after transfer, irregular patterns of the marbling type resulting in local variations in thickness, the amplitude of which is of the order of one nm or half a nanometer. These mottles can be distributed over the whole of the useful layer 3, or over only a part. They contribute to the non-uniformity of the useful layer 3.
  • This type of non-uniformity of thickness of the useful layer 3 is very difficult to eliminate by the usual finishing techniques (etching, sacrificial oxidation, heat treatment of smoothing) because the latter are not effective in erasing irregular patterns of this. amplitude.
  • document EP2933828 proposes to put in contact with the assembly to be fractured, an absorbing element to dissipate the acoustic vibrations emitted during initiation and the self-sustaining propagation of the fracture wave.
  • the present invention relates to a method of transferring a useful layer onto a support substrate.
  • the process offers a alternative solution to those of the state of the art, aimed in particular at improving the uniformity of thickness of the useful layers after transfer.
  • the invention relates to a method of transferring a useful layer onto a support substrate, comprising the following steps:
  • a donor substrate comprising a buried fragile plane, the useful layer being delimited by a front face of the donor substrate and the buried fragile plane;
  • the transfer process is remarkable in that the initiation of the fracture wave is carried out while the bonded structure undergoes, at least in its hottest region, a maximum temperature of between 150 ° and 250 ° C.
  • the maximum temperature is between 180 ° C and 220 ° C;
  • step d • the annealing of step d) reaches a maximum plateau temperature of between 300 ° C and 600 ° C;
  • the thermal embrittlement budget is between 40% and 95% of a thermal fracture budget, the thermal fracture budget leading to spontaneous initiation of the fracture wave in the brittle plane buried during annealing;
  • step e • the initiation of step e) is carried out directly after the annealing of step d), before the hottest region of the bonded structure is subjected to a temperature below 150 ° C .;
  • step d) • the annealing of step d) is carried out in heat treatment equipment of horizontal or vertical configuration, suitable for the collective treatment of a plurality of bonded structures, and the initiation of step e) is carried out during removal of glued structures from the equipment;
  • the donor substrate and the support substrate are made of monocrystalline silicon, and in which the buried fragile plane is formed by ionic implantation of light species in the donor substrate, said light species being chosen from hydrogen and helium or a combination hydrogen and helium.
  • FIG. 1 shows a method of transferring a thin film according to the state of the art
  • FIG. 2 presents a transfer method according to the invention
  • FIGS. 3a to 3c show “haze” maps on the surface of useful layers comprising non-uniformities of thickness after transfer;
  • FIG. 4 shows a “haze” map on the surface of a useful layer transferred by a transfer method in accordance with the invention
  • FIG. 5 shows a step of a transfer method according to the invention
  • FIG. 6 presents a graph showing the temperatures and the thermal gradient seen by a bonded structure in a step of a transfer process according to the invention
  • FIG. 7 shows a step of a transfer method according to the invention.
  • the invention relates to a method of transferring a useful layer 3 onto a support substrate 4.
  • the useful layer 3 is so named because it is intended to be used for the manufacture of. components in the fields of microelectronics or microsystems.
  • the useful layer and the support substrate can be of various types depending on the type of component and the intended application. Since silicon is the semiconductor material most used at present, the useful layer and the support substrate can in particular be made of monocrystalline silicon but are of course not limited to this material.
  • the transfer method according to the invention first of all comprises a step a) of supplying a donor substrate 1, from which the useful layer 3 will be obtained.
  • the donor substrate 1 comprises a buried fragile plane 2 (FIG. 2 - a). ).
  • the latter is advantageously formed by ion implantation of light species in the donor substrate 1, at a defined depth.
  • the light species are preferably chosen from hydrogen and helium, or a combination of hydrogen and helium, because these species are favorable to the formation of microcavities around the defined depth of implantation, giving rise to the fragile plane.
  • the useful layer 3 is delimited by a front face 1a of the donor substrate 1 and the buried fragile plane 2.
  • the donor substrate 1 can be formed by at least one material chosen from among silicon, germanium, silicon carbide, compound semiconductors IV-IV, III-V or II-VI, piezoelectric materials (for example, LiNb03 , LiTa03, ...), etc. It may also include one or more surface layer (s) arranged on its front face 1a and / or on its rear face 1b, of all kinds, for example dielectric (s).
  • the transfer process also comprises a step b) of providing a support substrate 4 (FIG. 2 - b)).
  • the support substrate can for example be formed by at least one material chosen from among silicon, silicon carbide, glass, sapphire, aluminum nitride, or any other material capable of being available in the form of a substrate. he can also comprise one or more surface layer (s) of all kinds, for example dielectric (s).
  • the transfer method according to the invention is the manufacture of SOI substrates.
  • the donor substrate 1 and the support substrate 4 are made of monocrystalline silicon, and one and / or the other of said substrates comprises a surface layer of silicon oxide 6 on its front face.
  • the transfer method then comprises a step c) of assembly, according to a bonding interface 7, of the donor substrate 1, at its front face 1a, and of the support substrate 4, to form a bonded structure 5 (FIG. 2 - vs) ) .
  • the assembly can be carried out by any known method, in particular by direct bonding by molecular adhesion, or by thermocompression, or even by electrostatic bonding. These techniques, which are well known from the state of the art, will not be described in detail here. It is nevertheless recalled that, prior to assembly, the donor 1 and support 4 substrates will have undergone cleaning and / or surface activation sequences, so as to guarantee the quality of the bonding interface 7 in terms of defectivity. and bonding energy.
  • a step d) of annealing the bonded structure 5 is then carried out, to apply to said structure 5 a thermal embrittlement budget and bring the buried fragile plane to a defined level of embrittlement. (figure 2 - d)).
  • the time / temperature pairs applied during annealing determine the thermal budget undergone by the bonded structure 5.
  • the temperature range in which annealing can be carried out for this embrittlement of the buried plane 2 depends on essentially of the type of bonded structure 5 (homo-structure or hetero-structure) and of the nature of the donor substrate 1.
  • the annealing of step d) reaches a maximum plateau temperature typically between 200 ° C and 600 ° C, advantageously between 300 and 500 ° C, and even more advantageously between 350 ° C and 450 ° C.
  • the maximum plateau temperature may more generally, for materials used for the donor substrate 1 and / or for the support substrate 4 other than silicon, typically be between 200 ° C and 800 ° C.
  • Annealing may include a temperature rise ramp (typically between 200 ° C. and the maximum plateau temperature) and a plateau at the maximum temperature. In general, such an annealing will have a duration of between a few tens of minutes and several hours, depending on the maximum stage temperature of the annealing.
  • the level of embrittlement of the buried brittle plane 2 is defined by the surface occupied by the microcavities present in the buried brittle plane 2.
  • the characterization of this surface occupied by the microcavities can be perform by infrared microscopy.
  • the level of embrittlement can increase from a low level ( ⁇ 1%, below the detection threshold of the characterization instruments) to more than 80%, depending on the thermal budget applied to the bonded structure 5 during annealing.
  • the thermal embrittlement budget is always kept below a thermal fracture budget, for which the spontaneous initiation of the fracture wave in the buried fragile plane 2 is obtained during annealing.
  • the thermal budget for embrittlement is between 40% and 95% of the thermal budget for fracture.
  • a step e) of initiation of a fracture wave along the buried brittle plane 2 is then carried out, by applying a stress to the buried brittle plane 2 of the bonded structure 5 (figure 2 - e)).
  • the fracture wave After initiation, the fracture wave propagates in a self-sustaining manner, leading to the separation of the bonded structure 5 at the level of the buried fragile plane 2.
  • a self-sustaining propagation reflects the fact that once initiated, the wave of The fracture propagates by itself, without the application of any external stress and over the entire extent of the buried fragile plane 2, so as to completely detach the useful layer 3 from the donor substrate 1 and to transfer it to the support substrate 4. We obtain thus a transferred set 5a and the remainder 5b of the donor substrate 1 (FIG. 2 - f)).
  • the external stress is advantageously local and can be of mechanical origin or of any other origin such as, for example, localized heating carried out by a laser or an input of energy by ultrasound.
  • the transfer method provides that the initiation of the fracture wave in step e) is performed by application of 'a external stress to the buried brittle plane 2 while the bonded structure 5 is subjected, at least in its hottest region (or typically, in its hottest point), to a maximum temperature of between 150 ° and 250 ° C.
  • the invention therefore provides that the region of the bonded structure 5 undergoing the highest temperatures (its hottest region) sees a temperature between 150 ° C. and 250 ° C.
  • the initiation of the fracture is effected when the maximum temperature to which the bonded structure 5 is subjected, locally in its hottest region or uniformly over its entire extent, is within this temperature range.
  • the aforementioned maximum temperature is between 180 ° C and 220 ° C, preferably around 200 ° C.
  • the energy stored in the system is sufficient to guarantee a self-sustaining and stable propagation of the fracture wave.
  • the Applicant has observed that when the excess energy released during the fracture is too great, regular patterns of large amplitude can appear and degrade the uniformity of thickness of the useful layer 3 after transfer. This can be for example the case, when the fracture budget is applied to a bonded structure 5 and that a fracture wave initiates spontaneously at the annealing stage temperature (eg 400 ° C). Too much energy stored and released during the propagation of the fracture wave is therefore also problematic with respect to the uniformity of thickness of the useful layer 3 after transfer.
  • the energy stored in the system depends on the one hand on the level of embrittlement of the buried fragile plane 2 and on the other hand on the temperature at which the fracture wave is initiated and will propagate.
  • the transfer method according to the invention makes it possible to initiate the fracture wave when the energy stored in the system is, on the one hand, sufficient to guarantee a self-sustaining and stable propagation (thus limiting the appearance of patterns irregular), and secondly, little excess to limit the amplitude of regular patterns also degrading the uniformity of thickness.
  • FIGS. 3a, 3b and 3c show "haze" maps on the surface of useful layers 3 after a fracture, respectively spontaneous, mechanical initiated at room temperature and mechanical initiated with a maximum temperature undergone by the bonded structure. of 100 ° C. Note that the initiation of the aforementioned mechanical fractures was made by local mechanical stress exerted on the bonded structures 5 and generating a stress in the buried brittle plane 2. In each case, regular (figure 3a) or irregular patterns are noted. ( Figures 3b and 3c) of the marbling type which degrade the thickness uniformity of the useful layer 3 after transfer (between 0.5 and 1.5 nm in amplitude).
  • FIG. 4 shows a “haze” map on the surface of a useful layer 3 transferred by a transfer process according to the invention: that is to say after a fracture initiated while the bonded structure 5 is undergoing, at less in its hottest region, a temperature of 200 ° C, by a local mechanical stress exerted on the bonded structure 5 generating a stress in the buried fragile plane 2. No pattern, neither regular nor irregular of the marbling type is present, the thickness uniformity of the useful layer 3 is thus greatly improved.
  • the initiation of step e) is carried out directly after the annealing of step d), before the hottest region of the bonded structure 5 is subjected to a temperature below 150 ° C.
  • the initiation is carried out when the bonded structure 5 (at least at the level of its hottest region) experiences a maximum temperature less than or equal to 250 ° C and before it experiences a maximum temperature of 150 ° C.
  • step e) of initiation of the fracture wave when the bonded structure 5 leaves the heat treatment equipment 20 used for annealing, in a controlled exit zone 23 in which the bonded structure 5 is subjected to a maximum temperature greater than 150 ° C. and less than or equal to 250 ° C. (FIG. 2 - e)).
  • the annealing of step d) can be carried out in heat treatment equipment 20 of horizontal or vertical configuration, suitable for the collective treatment of a plurality of bonded structures 5; the initiation of step e) is then carried out when the bonded structures 5 leave the equipment 20, in the exit zone 23 where the maximum temperature undergone by the structures 5 is controlled within the range required for initiation of the fracture wave.
  • the external constraint to trigger the initiation of the fracture wave is advantageously applied to the bonded structures 5 successively, as they pass through the controlled exit zone 23.
  • the initiation of step e) is carried out after the hottest region of the bonded structure 5 has undergone a temperature below 150 ° C.
  • the bonded structure 5 is maintained in a controlled atmosphere between the end of the annealing of step d) and the moment of the initiation of the fracture wave which will require that the bonded structure 5 is brought back to a maximum temperature. between 150 ° C and 250 ° C.
  • controlled atmosphere is meant here a dry atmosphere having less than 0.1% humidity.
  • step d) when the annealing of step d) exhibits a temperature rise ramp up to 400 ° C, then a temperature drop ramp down to 150 ° C before the bonded structure returns to ambient temperature 5 , the latter is maintained in a dry atmosphere until step e) of initiation of the fracture wave.
  • the application of a stress to the buried fragile plane 2 corresponds to the application of a local mechanical stress on the bonded structure 5, in particular on the periphery. of said structure, so as to initiate the fracture wave.
  • the local mechanical stress can be achieved by inserting a bevel 10, facing the bonding interface 7 of the bonded structure 5, between chamfered edges respectively of the donor substrate 1 and of the support substrate 4 of said bonded structure 5. This has for effect of generating a stress in tension in the buried brittle plane 2.
  • the local mechanical stress is exerted in a region of the bonded structure 5 undergoing lower temperatures, when a temperature gradient exists on the bonded structure 5 during step e). Said region is hereinafter called the cold region, as opposed to the hottest region of the bonded structure 5 mentioned above.
  • a thermal gradient exists in general on each bonded structure 5 ( Figures 5 and 6). This gradient is generally due to the geometry of the furnace and to the presence of a system for maintaining the bonded structures 5, which influence the heat dissipation. For example, in the case of a furnace of horizontal configuration 20, in which the bonded structures
  • the local mechanical stress is exerted on the bonded structure 5 when the temperature gradient is of the order of 80 ° C, ie 80 ° C +/- 15 ° C.
  • the Applicant has observed that a temperature gradient of 80 ° C + / - 10 ° C undergone by the bonded structure 5 at the time of initiation of the fracture wave helped to improve the uniformity of thickness of the useful layer 3 after transfer.
  • the transfer method according to the invention can be used for the manufacture of SOI substrates in which the useful layer 3 is very thin, in particular between a few nanometers and 50 nm.
  • donor 1 and support 4 substrates in monocrystalline silicon each in the form of a wafer 300 mm in diameter.
  • the donor substrate is covered with a layer of silicon oxide 6 50 nm thick.
  • the buried fragile plane 2 is formed in the donor substrate 1 by co-implantation of hydrogen and helium ions under the following conditions:
  • H implantation energy 38 keV, dose 1E16 H / cm2,
  • He implantation energy 25 keV, dose 1E16 He / cm2.
  • the buried fragile plane 2 is located at a depth of approximately 290 nm, from the surface 1a of the donor substrate 1. It delimits, with the oxide layer 6, a useful layer 3 of approximately 240 nm.
  • the assembly of the donor substrate 1 and the support substrate 4 is made by direct bonding by molecular adhesion, to form the bonded structure 5.
  • the donor 1 and support 4 substrates Prior to assembly, will have undergone cleaning and / or sequences. known surface activation, so as to guarantee the quality of the bonding interface 7 in terms of defectivity and bonding energy.
  • a furnace 20 of horizontal configuration is used to collectively perform the annealing of a plurality of bonded structures such as that described above.
  • This type of equipment heat treatment 20 comprises a loading shovel 21 which supports nacelles 22 in which the bonded structures 5 are positioned (FIG. 7).
  • the loading shovel 21 moves between a retracted position, in which the bonded structures 5 are inside the oven 20, and an extended position, in which they are outside the oven 20.
  • a system of bevels 10 can be positioned on each nacelle 22, below the bonded structures 5.
  • the loading shovel 21 moves in the retracted position for carrying out the annealing.
  • the annealing includes a temperature rise ramp from 200 ° C to 380 ° C, a plateau at 380 ° C for 2 minutes and a temperature drop ramp down to 225 ° C.
  • the loading shovel 21 moves to its extended position.
  • each bonded structure 5 will pass through an outlet zone 23 in which it will see a maximum temperature (in its hottest region) of between 150 ° C and 250 ° C.
  • a support device 11 located above the bonded structures 5 will exert a supporting force successively on each bonded structure 5, so that the bevel 10 below it s 'inserts, facing the bonding interface 7, between the chamfered edges of the assembled substrates of the bonded structure 5 (FIG. 7).
  • the insertion of the bevel 10 generates a local stress and in tension at the level of the buried fragile plane 2 making it possible to initiate the fracture wave in each bonded structure 5, successively, as they pass under the device. support 11.
  • the initiation of the fracture wave is thus carried out for each bonded structure 5 while the latter is subjected to a maximum temperature of between 150 ° C and 250 ° C, preferably around 200 ° C.
  • the exit zone 23 in which the initiation of the fracture wave is operated corresponds to a zone in which each bonded structure 5 undergoes, in its hottest region (the upper region H) a maximum temperature of the order of 200 ° C, its central region C seeing an intermediate temperature of the order of 180 ° C and its lower region B seeing a temperature of the order of 130 ° C.
  • the bevel 10 being, in the example illustrated in FIG. 7, placed in the lower part of each bonded structure 5, the initiation also takes place in the cold region (lower region B: that which is subjected to the lowest temperatures) of the bonded structure 5.
  • the SOI substrate is obtained after transfer (transferred assembly 5a) and the remainder 5b of the donor substrate 1. A very good uniformity of thickness of the useful layers 3 transferred is obtained.
  • Finishing steps applied to the transferred assemblies 5a include chemical cleanings and at least one high temperature smoothing heat treatment.
  • the SOI substrates comprise a useful layer 3 with a thickness of 50 nm, the non-uniformity of final thickness of which is of the order of 0.45 nm.
  • SOI substrates in which the useful layer 3 comprises regular or irregular patterns after fracture may have final thickness non-uniformities greater than or equal to 0.7 nm.

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Abstract

The invention relates to a method for transferring an useful layer onto a support substrate, said method involving the following steps: a) providing a donor substrate comprising a buried fragile plane, the useful layer being delimited by a front face of the donor substrate and the buried fragile plane; b) providing a support substrate; c) joining the donor substrate by its front face to the support substrate over a bonding interface to form a bonded structure; d) annealing the bonded structure to apply a weakening thermal budget thereto and bringing the buried fragile plane to a defined break-off level; e) initiating a fracture wave in the buried fragile plane by applying stress to the bonded structure, the fracture wave self-propagating along the buried fragile plane to lead to the transfer of the useful layer onto the support substrate. The transfer method is characterized in that the fracture wave is initiated while the bonded structure is subjected to a maximum temperature of 150° to 250°C.

Description

DESCRIPTION DESCRIPTION
TITRE : PROCEDE DE TRANSFERT D'UNE COUCHE UTILE SUR UN TITLE: PROCESS FOR TRANSFERRING A USEFUL LAYER ON A
SUBSTRAT SUPPORT SUBSTRATE SUPPORT
DOMAINE DE L' INVENTION FIELD OF THE INVENTION
La présente invention concerne le domaine de la microélectronique. Elle concerne en particulier un procédé de transfert d'une couche utile sur un substrat support. The present invention relates to the field of microelectronics. It relates in particular to a method of transferring a useful layer onto a support substrate.
ARRIERE PLAN TECHNOLOGIQUE DE L' INVENTION TECHNOLOGICAL BACKGROUND OF THE INVENTION
On connaît de l'état de la technique un procédé de transfert d'une couche utile 3 sur un substrat support 4, représenté sur la figure 1 ; ce procédé décrit notamment dans les documents W02005043615 et W02005043616 comprend les étapes suivantes :A method of transferring a useful layer 3 onto a support substrate 4, shown in FIG. 1, is known from the state of the art; this process described in particular in documents WO2005043615 and WO2005043616 comprises the following steps:
• la formation d'un plan fragile enterré 2 par implantation d'espèces légères dans un substrat donneur 1 de manière à former une couche utile 3 entre ce plan et une surface du substrat donneur ; • the formation of a buried fragile plane 2 by implantation of light species in a donor substrate 1 so as to form a useful layer 3 between this plane and a surface of the donor substrate;
• puis, l'assemblage du substrat donneur 1 sur un substrat support 4 pour former une structure collée 5 ; • then, the assembly of the donor substrate 1 on a support substrate 4 to form a bonded structure 5;
• l'application d'un traitement thermique à la structure collée 5 pour fragiliser le plan fragile enterré ; • the application of a heat treatment to the bonded structure 5 to weaken the fragile buried plane;
• et enfin, l'initiation d'une onde de fracture par une impulsion d'énergie appliquée au niveau du plan fragile enterré 2 et la propagation auto-entretenue de l'onde de fracture dans le substrat donneur 1, le long dudit plan fragile enterré 2. • and finally, the initiation of a fracture wave by an energy pulse applied to the level of the buried fragile plane 2 and the self-sustaining propagation of the fracture wave in the donor substrate 1, along said fragile plane buried 2.
Dans ce procédé, les espèces implantées au niveau du plan fragile enterré 2 sont à l'origine du développement de microcavités. Le traitement thermique de fragilisation a pour effet de favoriser la croissance et la mise sous pression de ces microcavités. Par l'intermédiaire d'efforts extérieurs additionnels (impulsion d'énergie), appliqués après le traitement thermique, l'initiation d'une onde de fracture dans le plan fragile enterré 2 est opérée, laquelle onde se propage de manière auto entretenue, menant au transfert de la couche utile 3 par détachement au niveau du plan fragile enterré 2. Un tel procédé, permet notamment de diminuer la rugosité de surface après transfert . In this process, the species implanted at the level of the buried fragile plane 2 are at the origin of the development of microcavities. The thermal embrittlement treatment has the effect of promoting the growth and pressurization of these microcavities. By the intermediary of additional external forces (energy pulse), applied after the heat treatment, the initiation of a fracture wave in the buried fragile plane 2 is operated, which wave propagates in a self-sustaining manner, leading the transfer of the useful layer 3 by detachment at the level of the buried fragile plane 2. Such a method makes it possible in particular to reduce the surface roughness after transfer.
Ce procédé peut être utilisé pour la fabrication de substrats de silicium sur isolant (SOI - « Silicon on insulator ») . Dans ce cas, le substrat donneur 1 et le substrat support 4 sont chacun formés d'une plaquette de silicium dont le diamètre normalisé est typiquement de 200mm, 300mm, voire même 450 mm pour les prochaines générations. L'un et/ou l'autre du substrat donneur 1 et du substrat support 4 sont oxydés en surface. This process can be used for the manufacture of silicon on insulator substrates (SOI - “Silicon on insulator”). In this case, the donor substrate 1 and the support substrate 4 are each formed from a silicon wafer, the standardized diameter of which is typically 200mm, 300mm, or even 450 mm for the next generations. One and / or the other of the donor substrate 1 and of the support substrate 4 are oxidized at the surface.
Les substrats SOI doivent respecter des spécifications très précises. C'est particulièrement le cas pour l'épaisseur moyenne et l'uniformité d'épaisseur de la couche utile 3. Le respect de ces spécifications est requis pour le bon fonctionnement des dispositifs semi-conducteurs qui seront formés dans et sur cette couche utile 3. SOI substrates must meet very precise specifications. This is particularly the case for the average thickness and the uniformity of thickness of the useful layer 3. Compliance with these specifications is required for the proper functioning of the semiconductor devices which will be formed in and on this useful layer 3. .
Dans certains cas, l'architecture de ces dispositifs semi- conducteurs nécessite de disposer de substrats SOI présentant une épaisseur moyenne de la couche utile 3 très faible, par exemple inférieure à 50 nm, et présentant une très bonne uniformité d'épaisseur de la couche utile 3. L'uniformité d'épaisseur attendue peut être de l'ordre de 5% au maximum, correspondant à des variations allant typiquement de +/- 0,3nm à +/- lnm sur toute la surface de la couche utile 3. Même si des étapes complémentaires de finition, comme des gravures ou des traitements thermiques de lissage de surface, sont réalisées après que la couche utile 3 soit transférée sur le substrat support 4, il est important que les propriétés morphologiques de surface (en particulier, uniformité d'épaisseur et rugosité de surface) soient les plus favorables possibles après transfert, pour garantir la tenue des spécifications finales. In certain cases, the architecture of these semiconductor devices requires the availability of SOI substrates having a very low average thickness of the useful layer 3, for example less than 50 nm, and having very good uniformity of thickness of the layer. useful 3. The expected thickness uniformity can be of the order of 5% at most, corresponding to variations typically ranging from +/- 0.3nm to +/- lnm over the entire surface of the useful layer 3. Even if additional finishing steps, such as etching or heat treatments for surface smoothing, are carried out after the useful layer 3 is transferred to the support substrate 4, it is important that the surface morphological properties (in particular, thickness uniformity and surface roughness) are as favorable as possible after transfer, to ensure that specifications are maintained finals.
La demanderesse a observé que, lorsque l'initiation de l'onde de fracture est réalisée après le traitement thermique, à température ambiante, par une impulsion d'énergie appliquée au plan fragile enterré 2, certaines couches utiles 3 peuvent comporter, après transfert, des motifs irréguliers de type marbrure se traduisant par des variations locales d'épaisseur dont l'amplitude est de l'ordre du nm ou du demi-nanomètre. Ces marbrures peuvent être réparties sur la totalité de la couche utile 3, ou sur une partie seulement. Elles contribuent à la non-uniformité de la couche utile 3. The Applicant has observed that, when the initiation of the fracture wave is carried out after the heat treatment, at room temperature, by an energy pulse applied to the buried fragile plane 2, certain useful layers 3 may comprise, after transfer, irregular patterns of the marbling type resulting in local variations in thickness, the amplitude of which is of the order of one nm or half a nanometer. These mottles can be distributed over the whole of the useful layer 3, or over only a part. They contribute to the non-uniformity of the useful layer 3.
Ce type de non-uniformité d'épaisseur de la couche utile 3 est très difficile à éliminer par les techniques usuelles de finition (gravure, oxydation sacrificielle, traitement thermique de lissage) car ces dernières ne sont pas efficaces pour gommer des motifs irréguliers de cette amplitude. This type of non-uniformity of thickness of the useful layer 3 is very difficult to eliminate by the usual finishing techniques (etching, sacrificial oxidation, heat treatment of smoothing) because the latter are not effective in erasing irregular patterns of this. amplitude.
Pour limiter l'amplitude de motifs périodiques de variation d'épaisseur de la couche mince après fracture, le document EP2933828 propose de mettre en contact avec l'ensemble à fracturer, un élément absorbant pour dissiper les vibrations acoustiques émises lors de l'initiation et la propagation auto entretenue de l'onde de fracture. To limit the amplitude of periodic patterns of variation in thickness of the thin layer after fracture, document EP2933828 proposes to put in contact with the assembly to be fractured, an absorbing element to dissipate the acoustic vibrations emitted during initiation and the self-sustaining propagation of the fracture wave.
OBJET DE L' INVENTION OBJECT OF THE INVENTION
La présente invention concerne un procédé de transfert d'une couche utile sur un substrat support. Le procédé propose une solution alternative à celles de l'état de la technique, visant notamment à améliorer l'uniformité d'épaisseur des couches utiles après transfert. The present invention relates to a method of transferring a useful layer onto a support substrate. The process offers a alternative solution to those of the state of the art, aimed in particular at improving the uniformity of thickness of the useful layers after transfer.
BREVE DESCRIPTION DE L' INVENTION BRIEF DESCRIPTION OF THE INVENTION
L'invention concerne un procédé de transfert d'une couche utile sur un substrat support, comprenant les étapes suivantes : The invention relates to a method of transferring a useful layer onto a support substrate, comprising the following steps:
a) la fourniture d'un substrat donneur comportant un plan fragile enterré, la couche utile étant délimitée par une face avant du substrat donneur et le plan fragile enterré ; a) providing a donor substrate comprising a buried fragile plane, the useful layer being delimited by a front face of the donor substrate and the buried fragile plane;
b) la fourniture d'un substrat support ; b) providing a support substrate;
c) l'assemblage, selon une interface de collage, du substrat donneur, au niveau de sa face avant, et du substrat support, pour former une structure collée ; c) assembly, according to a bonding interface, of the donor substrate, at its front face, and of the support substrate, to form a bonded structure;
d) le recuit de la structure collée pour lui appliquer un budget thermique de fragilisation et amener le plan fragile enterré jusqu'à un niveau de fragilisation défini ; d) annealing of the bonded structure to apply a thermal embrittlement budget to it and bring the fragile buried plane to a defined level of embrittlement;
e) l'initiation d'une onde de fracture dans le plan fragile enterré par application d'une contrainte à la structure collée, l'onde de fracture se propageant de manière auto-entretenue le long du plan fragile enterré pour mener au transfert de la couche utile sur le substrat support. e) initiation of a fracture wave in the buried brittle plane by applying a stress to the bonded structure, the fracture wave propagating in a self-sustaining manner along the buried brittle plane to lead to the transfer of the useful layer on the support substrate.
Le procédé de transfert est remarquable en ce que l'initiation de l'onde de fracture est opérée alors que la structure collée subit, au moins dans sa région la plus chaude, une température maximale comprise entre 150° et 250°C. The transfer process is remarkable in that the initiation of the fracture wave is carried out while the bonded structure undergoes, at least in its hottest region, a maximum temperature of between 150 ° and 250 ° C.
Selon d'autres caractéristiques avantageuses et non limitatives de l'invention, prises seules ou selon toutes combinaisons techniquement réalisables : • la température maximale est comprise entre 180°C et 220 °C ; According to other advantageous and non-limiting characteristics of the invention, taken alone or in any technically feasible combinations: • the maximum temperature is between 180 ° C and 220 ° C;
• le recuit de l'étape d) atteint une température de palier maximale comprise entre 300°C et 600°C ; • the annealing of step d) reaches a maximum plateau temperature of between 300 ° C and 600 ° C;
• le budget thermique de fragilisation est compris entre 40% et 95% d'un budget thermique de fracture, le budget thermique de fracture menant à une initiation spontanée de l'onde de fracture dans le plan fragile enterré au cours du recuit ; • the thermal embrittlement budget is between 40% and 95% of a thermal fracture budget, the thermal fracture budget leading to spontaneous initiation of the fracture wave in the brittle plane buried during annealing;
• l'initiation de l'étape e) est opérée directement après le recuit de l'étape d) , avant que la région la plus chaude de la structure collée ne subisse une température inférieure à 150 °C ; • the initiation of step e) is carried out directly after the annealing of step d), before the hottest region of the bonded structure is subjected to a temperature below 150 ° C .;
• le recuit de l'étape d) est effectué dans un équipement de traitement thermique de configuration horizontale ou verticale, adapté pour le traitement collectif d'une pluralité de structures collées, et l'initiation de l'étape e) est opérée lors de la sortie des structures collées de l'équipement ; • the annealing of step d) is carried out in heat treatment equipment of horizontal or vertical configuration, suitable for the collective treatment of a plurality of bonded structures, and the initiation of step e) is carried out during removal of glued structures from the equipment;
• l'application d'une contrainte au plan fragile enterré correspond à l'application d'une sollicitation mécanique locale sur la structure collée, en particulier sur la périphérie de ladite structure ; • the application of a stress to the buried fragile plane corresponds to the application of a local mechanical stress on the bonded structure, in particular on the periphery of said structure;
• la sollicitation mécanique locale est réalisée par insertion d'un biseau, en vis-à-vis de l'interface de collage de la structure collée, entre des bords chanfreinés respectivement du substrat donneur et du substrat support de ladite structure collée ; • the local mechanical stress is carried out by inserting a bevel, opposite the bonding interface of the bonded structure, between edges chamfered respectively of the donor substrate and of the support substrate of said bonded structure;
• la sollicitation mécanique locale est exercée dans une région de la structure collée subissant des températures moindres lorsqu'un gradient de températures existe sur la structure collée lors de l'étape e) ; • the local mechanical stress is exerted in a region of the bonded structure undergoing lower temperatures when a temperature gradient exists on the bonded structure during step e);
• la sollicitation mécanique locale est exercée sur la structure collée lorsque le gradient de température est de l'ordre de 80°C ; • the local mechanical stress is exerted on the bonded structure when the temperature gradient is of the order of 80 ° C;
• le substrat donneur et le substrat support sont en silicium monocristallin, et dans lequel le plan fragile enterré est formé par implantation ionique d'espèces légères dans le substrat donneur, lesdites espèces légères étant choisies parmi l'hydrogène et l'hélium ou une combinaison d'hydrogène et d'hélium. • the donor substrate and the support substrate are made of monocrystalline silicon, and in which the buried fragile plane is formed by ionic implantation of light species in the donor substrate, said light species being chosen from hydrogen and helium or a combination hydrogen and helium.
BREVE DESCRIPTION DES FIGURES BRIEF DESCRIPTION OF THE FIGURES
D'autres caractéristiques et avantages de l'invention ressortiront de la description détaillée de l'invention qui va suivre en référence aux figures annexées sur lesquelles : Other characteristics and advantages of the invention will emerge from the detailed description of the invention which will follow with reference to the appended figures in which:
La figure 1 présente un procédé de transfert d'une couche mince selon l'état de la technique ; FIG. 1 shows a method of transferring a thin film according to the state of the art;
La figure 2 présente un procédé de transfert conforme à l'invention ; Les figures 3a à 3c présentent des cartographies de « haze » en surface de couches utiles comportant des non-uniformités d'épaisseur après transfert ; FIG. 2 presents a transfer method according to the invention; FIGS. 3a to 3c show “haze” maps on the surface of useful layers comprising non-uniformities of thickness after transfer;
La figure 4 présente une cartographie de « haze » en surface d'une couche utile transférée par un procédé de transfert conforme à l'invention ; FIG. 4 shows a “haze” map on the surface of a useful layer transferred by a transfer method in accordance with the invention;
La figure 5 présente une étape d'un procédé de transfert conforme à l'invention ; FIG. 5 shows a step of a transfer method according to the invention;
La figure 6 présente un graphe montrant les températures et le gradient thermique vus par une structure collée dans une étape d'un procédé de transfert conforme à l'invention ; FIG. 6 presents a graph showing the temperatures and the thermal gradient seen by a bonded structure in a step of a transfer process according to the invention;
La figure 7 présente une étape d'un procédé de transfert conforme à 1 ' invention . FIG. 7 shows a step of a transfer method according to the invention.
DESCRIPTION DETAILLEE DE L' INVENTION DETAILED DESCRIPTION OF THE INVENTION
Dans la partie descriptive, les mêmes références sur les figures pourront être utilisées pour des éléments de même type. Les figures sont des représentations schématiques qui, dans un objectif de lisibilité, ne sont pas à l'échelle. En particulier, les épaisseurs des couches selon l'axe z ne sont pas à l'échelle par rapport aux dimensions latérales selon les axes x et y ; et les épaisseurs relatives des couches entre elles ne sont pas nécessairement respectées sur les figures. Notons que le repère (x,y,z) de la figure 1 s'applique à la figure 2. In the descriptive part, the same references in the figures may be used for elements of the same type. The figures are schematic representations which, for the sake of readability, are not to scale. In particular, the thicknesses of the layers along the z axis are not to scale with respect to the lateral dimensions along the x and y axes; and the relative thicknesses of the layers between them are not necessarily respected in the figures. Note that the reference (x, y, z) of figure 1 applies to figure 2.
L'invention concerne un procédé de transfert d'une couche utile 3 sur un substrat support 4. La couche utile 3 est ainsi nommée car elle est destinée à être utilisée pour la fabrication de composants dans les domaines de la microélectronique ou des microsystèmes. La couche utile et le substrat support peuvent être de natures variées selon le type de composant et l'application visés. Le silicium étant le matériau semi- conducteur le plus utilisé actuellement, la couche utile et le substrat support peuvent en particulier être en silicium monocristallin mais ne sont bien-sûr pas limités à ce matériau. The invention relates to a method of transferring a useful layer 3 onto a support substrate 4. The useful layer 3 is so named because it is intended to be used for the manufacture of. components in the fields of microelectronics or microsystems. The useful layer and the support substrate can be of various types depending on the type of component and the intended application. Since silicon is the semiconductor material most used at present, the useful layer and the support substrate can in particular be made of monocrystalline silicon but are of course not limited to this material.
Le procédé de transfert selon l'invention comprend tout d'abord une étape a) de fourniture d'un substrat donneur 1, duquel sera issu la couche utile 3. Le substrat donneur 1 comporte un plan fragile enterré 2 (figure 2 - a) ) . Ce dernier est avantageusement formé par implantation ionique d'espèces légères dans le substrat donneur 1, à une profondeur définie. Les espèces légères sont préférentiellement choisies parmi l'hydrogène et l'hélium, ou une combinaison d'hydrogène et d'hélium, car ces espèces sont favorables à la formation de microcavités autour de la profondeur définie d'implantation, donnant lieu au plan fragile enterré 2. La couche utile 3 est délimitée par une face avant la du substrat donneur 1 et le plan fragile enterré 2. The transfer method according to the invention first of all comprises a step a) of supplying a donor substrate 1, from which the useful layer 3 will be obtained. The donor substrate 1 comprises a buried fragile plane 2 (FIG. 2 - a). ). The latter is advantageously formed by ion implantation of light species in the donor substrate 1, at a defined depth. The light species are preferably chosen from hydrogen and helium, or a combination of hydrogen and helium, because these species are favorable to the formation of microcavities around the defined depth of implantation, giving rise to the fragile plane. buried 2. The useful layer 3 is delimited by a front face 1a of the donor substrate 1 and the buried fragile plane 2.
Le substrat donneur 1 peut être formé par au moins un matériau choisi parmi le silicium, le germanium, le carbure de silicium, les semi-conducteurs composés IV-IV, III-V ou II-VI, les matériaux piézoélectriques (par exemple, LiNb03, LiTa03,...), etc. Il peut en outre comporter une ou plusieurs couche (s) superficielle ( s ) disposée (s) sur sa face avant la et/ou sur sa face arrière lb, de toutes natures, par exemple diélectrique ( s ) . The donor substrate 1 can be formed by at least one material chosen from among silicon, germanium, silicon carbide, compound semiconductors IV-IV, III-V or II-VI, piezoelectric materials (for example, LiNb03 , LiTa03, ...), etc. It may also include one or more surface layer (s) arranged on its front face 1a and / or on its rear face 1b, of all kinds, for example dielectric (s).
Le procédé de transfert comprend également une étape b) de fourniture d'un substrat support 4 (figure 2 - b) ) . The transfer process also comprises a step b) of providing a support substrate 4 (FIG. 2 - b)).
Le substrat support peut par exemple être formé par au moins un matériau choisi parmi le silicium, le carbure de silicium, le verre, le saphir, le nitrure d'aluminium, ou tout autre matériau susceptible d'être disponible sous forme de substrat. Il peut également comporter une ou plusieurs couche (s) superficielle ( s ) de toutes natures, par exemple diélectrique ( s ) . The support substrate can for example be formed by at least one material chosen from among silicon, silicon carbide, glass, sapphire, aluminum nitride, or any other material capable of being available in the form of a substrate. he can also comprise one or more surface layer (s) of all kinds, for example dielectric (s).
Comme énoncé précédemment, une application intéressante du procédé de transfert selon l'invention est la fabrication de substrats SOI. Dans ce cas particulier, le substrat donneur 1 et le substrat support 4 sont en silicium monocristallin, et l'un et/ou l'autre desdits substrats comporte une couche superficielle d'oxyde de silicium 6 sur sa face avant. As stated above, an interesting application of the transfer method according to the invention is the manufacture of SOI substrates. In this particular case, the donor substrate 1 and the support substrate 4 are made of monocrystalline silicon, and one and / or the other of said substrates comprises a surface layer of silicon oxide 6 on its front face.
Le procédé de transfert comprend ensuite une étape c) d'assemblage, selon une interface de collage 7, du substrat donneur 1, au niveau de sa face avant la, et du substrat support 4, pour former une structure collée 5 (figure 2 - c) ) . The transfer method then comprises a step c) of assembly, according to a bonding interface 7, of the donor substrate 1, at its front face 1a, and of the support substrate 4, to form a bonded structure 5 (FIG. 2 - vs) ) .
L'assemblage peut être réalisé par toute méthode connue, notamment par collage direct par adhésion moléculaire, ou par thermocompression, ou encore par collage électrostatique. Ces techniques bien connues de l'état de la technique ne seront pas décrites en détail ici. On rappelle néanmoins que, préalablement à l'assemblage, les substrats donneur 1 et support 4 auront subi des séquences de nettoyages et/ou d'activation de surface, de manière à garantir la qualité de l'interface de collage 7 en termes de défectivité et d'énergie de collage. The assembly can be carried out by any known method, in particular by direct bonding by molecular adhesion, or by thermocompression, or even by electrostatic bonding. These techniques, which are well known from the state of the art, will not be described in detail here. It is nevertheless recalled that, prior to assembly, the donor 1 and support 4 substrates will have undergone cleaning and / or surface activation sequences, so as to guarantee the quality of the bonding interface 7 in terms of defectivity. and bonding energy.
Dans le procédé de transfert selon l'invention, une étape d) de recuit de la structure collée 5 est alors effectuée, pour appliquer à ladite structure 5 un budget thermique de fragilisation et amener le plan fragile enterré jusqu'à un niveau de fragilisation défini (figure 2 - d) ) . Les couples temps / température appliqués au cours du recuit déterminent le budget thermique subi par la structure collée 5. In the transfer method according to the invention, a step d) of annealing the bonded structure 5 is then carried out, to apply to said structure 5 a thermal embrittlement budget and bring the buried fragile plane to a defined level of embrittlement. (figure 2 - d)). The time / temperature pairs applied during annealing determine the thermal budget undergone by the bonded structure 5.
La gamme de températures dans laquelle le recuit peut être opéré pour cette fragilisation du plan enterré 2 dépend essentiellement du type de structure collée 5 (homo-structure ou hétéro-structure) et de la nature du substrat donneur 1. The temperature range in which annealing can be carried out for this embrittlement of the buried plane 2 depends on essentially of the type of bonded structure 5 (homo-structure or hetero-structure) and of the nature of the donor substrate 1.
A titre d'exemple, dans le cas d'un substrat donneur 1 et d'un substrat support 4 en silicium, le recuit de l'étape d) atteint une température de palier maximale typiquement comprise entre 200°C et 600°C, avantageusement entre 300 et 500°C, et encore plus avantageusement entre 350°C et 450°C. By way of example, in the case of a donor substrate 1 and a support substrate 4 in silicon, the annealing of step d) reaches a maximum plateau temperature typically between 200 ° C and 600 ° C, advantageously between 300 and 500 ° C, and even more advantageously between 350 ° C and 450 ° C.
La température de palier maximale pourra plus généralement, pour des matériaux utilisés pour le substrat donneur 1 et/ou pour le substrat support 4 autres que le silicium, être comprise typiquement entre 200°C et 800°C. The maximum plateau temperature may more generally, for materials used for the donor substrate 1 and / or for the support substrate 4 other than silicon, typically be between 200 ° C and 800 ° C.
Le recuit peut comporter une rampe de montée en température (typiquement entre 200 °C et la température de palier maximale) et un palier à la température maximale. En général, un tel recuit va avoir une durée comprise entre quelques dizaines de minutes et plusieurs heures, en fonction de la température de palier maximale du recuit. Annealing may include a temperature rise ramp (typically between 200 ° C. and the maximum plateau temperature) and a plateau at the maximum temperature. In general, such an annealing will have a duration of between a few tens of minutes and several hours, depending on the maximum stage temperature of the annealing.
Le niveau de fragilisation du plan fragile enterré 2 est défini par la surface occupée par les microcavités présentes dans le plan fragile enterré 2. Dans le cas d'un substrat donneur 1 en silicium, la caractérisation de cette surface occupée par les microcavités peut s'effectuer par microscopie infrarouge. The level of embrittlement of the buried brittle plane 2 is defined by the surface occupied by the microcavities present in the buried brittle plane 2. In the case of a donor substrate 1 made of silicon, the characterization of this surface occupied by the microcavities can be perform by infrared microscopy.
Le niveau de fragilisation peut augmenter depuis un niveau faible (<1%, sous le seuil de détection des instruments de caractérisation) jusqu'à plus de 80%, en fonction du budget thermique appliqué à la structure collée 5 au cours du recuit. Le budget thermique de fragilisation est toujours maintenu en- deçà d'un budget thermique de fracture, pour lequel on obtient l'initiation spontanée de l'onde de fracture dans le plan fragile enterré 2, au cours du recuit. Préférentiellement, le budget thermique de fragilisation est compris entre 40% et 95% du budget thermique de fracture. Dans le procédé de transfert selon l'invention, une étape e) d'initiation d'une onde de fracture le long du plan fragile enterré 2 est ensuite opérée, par application d'une contrainte au plan fragile enterré 2 de la structure collée 5 (figure 2 - e) ) . Après initiation, l'onde de fracture se propage de manière auto-entretenue, menant à la séparation de la structure collée 5 au niveau du plan fragile enterré 2. Une propagation auto entretenue traduit le fait qu'une fois initiée, l'onde de fracture se propage par elle-même, sans application de contrainte extérieure et sur toute l'étendue du plan fragile enterré 2, de manière à détacher complètement la couche utile 3 du substrat donneur 1 et à la transférer sur le substrat support 4. On obtient ainsi un ensemble transféré 5a et le reste 5b du substrat donneur 1 (figure 2 - f) ) . The level of embrittlement can increase from a low level (<1%, below the detection threshold of the characterization instruments) to more than 80%, depending on the thermal budget applied to the bonded structure 5 during annealing. The thermal embrittlement budget is always kept below a thermal fracture budget, for which the spontaneous initiation of the fracture wave in the buried fragile plane 2 is obtained during annealing. Preferably, the thermal budget for embrittlement is between 40% and 95% of the thermal budget for fracture. In the transfer method according to the invention, a step e) of initiation of a fracture wave along the buried brittle plane 2 is then carried out, by applying a stress to the buried brittle plane 2 of the bonded structure 5 (figure 2 - e)). After initiation, the fracture wave propagates in a self-sustaining manner, leading to the separation of the bonded structure 5 at the level of the buried fragile plane 2. A self-sustaining propagation reflects the fact that once initiated, the wave of The fracture propagates by itself, without the application of any external stress and over the entire extent of the buried fragile plane 2, so as to completely detach the useful layer 3 from the donor substrate 1 and to transfer it to the support substrate 4. We obtain thus a transferred set 5a and the remainder 5b of the donor substrate 1 (FIG. 2 - f)).
La contrainte extérieure est avantageusement locale et peut être d' origine mécanique ou de toute autre origine comme par exemple un chauffage localisé réalisé par un laser ou un apport d'énergie par ultrason. The external stress is advantageously local and can be of mechanical origin or of any other origin such as, for example, localized heating carried out by a laser or an input of energy by ultrasound.
On rappelle que, en appliquant le procédé de transfert de l'état de la technique énoncé en introduction en référence à la figure 1, consistant en l'initiation mécanique de l'onde de fracture à température ambiante, la demanderesse a observé des motifs irréguliers de type marbrure dégradant l'uniformité d'épaisseur de la couche utile 3 après transfert. La demanderesse a identifié que ces motifs irréguliers étaient liés à une instabilité de la propagation de l'onde de fracture du fait d'une trop faible énergie emmagasinée dans le système [structure collée 5 / plan fragile enterré 2] . It will be recalled that, by applying the transfer method of the state of the art stated in the introduction with reference to FIG. 1, consisting in the mechanical initiation of the fracture wave at room temperature, the applicant has observed irregular patterns. of the marbling type degrading the uniformity of thickness of the useful layer 3 after transfer. The Applicant has identified that these irregular patterns were linked to an instability in the propagation of the fracture wave due to too little energy stored in the system [bonded structure 5 / buried fragile plane 2].
Pour pallier ces problèmes et améliorer l'uniformité d'épaisseur de la couche utile 3 après transfert, le procédé de transfert selon la présente invention prévoit que l'initiation de l'onde de fracture à l'étape e) est opérée par application d'une contrainte extérieure au plan fragile enterré 2 alors que la structure collée 5 subit, au moins dans sa région la plus chaude (ou typiquement, en son point le plus chaud) , une température maximale comprise entre 150° et 250°C. Dans la pratique, il existe souvent un gradient de température sur la structure collée 5, l'invention prévoit donc que la région de la structure collée 5 subissant les plus hautes températures (sa région la plus chaude) voit une température comprise entre 150°C et 250°C. En d'autres termes, l'initiation de la fracture est opérée lorsque la température maximale que subit la structure collée 5, localement dans sa région la plus chaude ou uniformément sur toute son étendue, est comprise dans cette gamme de température. Avantageusement, la température maximale précitée est comprise entre 180°C et 220°C, préférentiellement autour de 200°C. To overcome these problems and improve the uniformity of thickness of the useful layer 3 after transfer, the transfer method according to the present invention provides that the initiation of the fracture wave in step e) is performed by application of 'a external stress to the buried brittle plane 2 while the bonded structure 5 is subjected, at least in its hottest region (or typically, in its hottest point), to a maximum temperature of between 150 ° and 250 ° C. In practice, there is often a temperature gradient on the bonded structure 5, the invention therefore provides that the region of the bonded structure 5 undergoing the highest temperatures (its hottest region) sees a temperature between 150 ° C. and 250 ° C. In other words, the initiation of the fracture is effected when the maximum temperature to which the bonded structure 5 is subjected, locally in its hottest region or uniformly over its entire extent, is within this temperature range. Advantageously, the aforementioned maximum temperature is between 180 ° C and 220 ° C, preferably around 200 ° C.
Pour une initiation de l'onde de fracture faite lorsque au moins la région la plus chaude de la structure collée 5 est à une température supérieure à 150°C, l'énergie emmagasinée dans le système, et notamment l'énergie emmagasinée dans le plan fragile enterré 2 du fait de la présence d'espèces gazeuses sous pression dans les microcavités, est suffisante pour garantir une propagation auto-entretenue et stable de l'onde de fracture. Opérer l'initiation alors que la structure collée 5 subit une température maximale inférieure à 250°C limite l'énergie emmagasinée dans le système, de sorte que l'excès d'énergie relâchée lors de la fracture (c'est-à-dire l'énergie qui n'a pas été consommée pour rompre la matière) ne conduise pas à la formation d'autres types de motifs à la surface de la couche utile 3 transférée. En effet, la demanderesse a observé que lorsque l'excès d'énergie relâchée lors de la fracture est trop important, des motifs réguliers de grande amplitude peuvent apparaitre et dégrader l'uniformité d'épaisseur de la couche utile 3 après transfert. Cela peut être par exemple le cas, lorsque le budget de fracture est appliqué à une structure collée 5 et qu'une onde de fracture s'initie spontanément à la température de palier du recuit (par exemple 400 °C) . Trop d'énergie emmagasinée et relâchée lors de la propagation de l'onde de fracture est donc également problématique vis-à-vis de l'uniformité d'épaisseur de la couche utile 3 après transfert. L'énergie emmagasinée dans le système dépend d'une part du niveau de fragilisation du plan fragile enterré 2 et d'autre part de la température à laquelle l'onde de fracture est initiée et va se propager. Le procédé de transfert selon l'invention permet d'initier l'onde de fracture lorsque l'énergie emmagasinée dans le système est, d'une part, suffisante pour garantir une propagation auto-entretenue et stable (limitant ainsi l'apparition de motifs irréguliers), et d'autre part, peu excédentaire pour limiter l'amplitude de motifs réguliers dégradant également l'uniformité d'épaisseur. For initiation of the fracture wave made when at least the hottest region of the bonded structure 5 is at a temperature greater than 150 ° C, the energy stored in the system, and in particular the energy stored in the plane fragile buried 2 due to the presence of gaseous species under pressure in the microcavities, is sufficient to guarantee a self-sustaining and stable propagation of the fracture wave. Perform the initiation while the bonded structure 5 is subjected to a maximum temperature of less than 250 ° C limits the energy stored in the system, so that the excess energy released during the fracture (i.e. the energy which was not consumed to break up the material) does not lead to the formation of other types of patterns on the surface of the useful layer 3 transferred. In fact, the Applicant has observed that when the excess energy released during the fracture is too great, regular patterns of large amplitude can appear and degrade the uniformity of thickness of the useful layer 3 after transfer. This can be for example the case, when the fracture budget is applied to a bonded structure 5 and that a fracture wave initiates spontaneously at the annealing stage temperature (eg 400 ° C). Too much energy stored and released during the propagation of the fracture wave is therefore also problematic with respect to the uniformity of thickness of the useful layer 3 after transfer. The energy stored in the system depends on the one hand on the level of embrittlement of the buried fragile plane 2 and on the other hand on the temperature at which the fracture wave is initiated and will propagate. The transfer method according to the invention makes it possible to initiate the fracture wave when the energy stored in the system is, on the one hand, sufficient to guarantee a self-sustaining and stable propagation (thus limiting the appearance of patterns irregular), and secondly, little excess to limit the amplitude of regular patterns also degrading the uniformity of thickness.
A titre d'exemple, les figures 3a, 3b et 3c présentent des cartographies de « haze » en surface de couches utiles 3 après une fracture, respectivement spontanée, mécanique initiée à température ambiante et mécanique initiée avec une température maximale subie par la structure collée de 100°C. Notons que l'initiation des fractures mécaniques précitées a été faite par sollicitation mécanique locale exercée sur les structures collées 5 et générant une contrainte dans le plan fragile enterré 2. On remarque, dans chacun des cas, des motifs réguliers (figure 3a) ou irréguliers (figures 3b et 3c) de type marbrures qui dégradent l'uniformité d'épaisseur de la couche utile 3 après transfert (entre 0,5 et l,5nm d'amplitude) . Ces motifs ont été rendus apparents par la mesure de bruit de fond diffus (« haze » selon la terminologie anglo-saxonne communément employée) correspondant à l'intensité de la lumière diffusée par la surface de la couche utile 3, à l'aide de l'outil d'inspection Surfscan™ de la société KLA-Tencor. La figure 4 présente une cartographie de « haze » en surface d'une couche utile 3 transférée par un procédé de transfert conforme à l'invention : c'est-à-dire après une fracture initiée alors que la structure collée 5 subit, au moins dans sa région la plus chaude, une température de 200°C, par une sollicitation mécanique locale exercée sur la structure collée 5 générant une contrainte dans le plan fragile enterré 2. Aucun motif, ni régulier, ni irrégulier de type marbrure n'est présent, l'uniformité d'épaisseur de la couche utile 3 est ainsi fortement améliorée . By way of example, FIGS. 3a, 3b and 3c show "haze" maps on the surface of useful layers 3 after a fracture, respectively spontaneous, mechanical initiated at room temperature and mechanical initiated with a maximum temperature undergone by the bonded structure. of 100 ° C. Note that the initiation of the aforementioned mechanical fractures was made by local mechanical stress exerted on the bonded structures 5 and generating a stress in the buried brittle plane 2. In each case, regular (figure 3a) or irregular patterns are noted. (Figures 3b and 3c) of the marbling type which degrade the thickness uniformity of the useful layer 3 after transfer (between 0.5 and 1.5 nm in amplitude). These patterns were made apparent by measuring diffuse background noise ("haze" according to commonly used Anglo-Saxon terminology) corresponding to the intensity of the light scattered by the surface of the useful layer 3, using KLA-Tencor's Surfscan ™ inspection tool. FIG. 4 shows a “haze” map on the surface of a useful layer 3 transferred by a transfer process according to the invention: that is to say after a fracture initiated while the bonded structure 5 is undergoing, at less in its hottest region, a temperature of 200 ° C, by a local mechanical stress exerted on the bonded structure 5 generating a stress in the buried fragile plane 2. No pattern, neither regular nor irregular of the marbling type is present, the thickness uniformity of the useful layer 3 is thus greatly improved.
Selon une première variante avantageuse, l'initiation de l'étape e) est opérée directement après le recuit de l'étape d) , avant que la région la plus chaude de la structure collée 5 ne subisse une température inférieure à 150°C. Par exemple, lorsque le recuit de l'étape d) présente une rampe de montée en températures jusqu'à 400°C, puis une rampe de descente en températures, l'initiation est opérée lorsque la structure collée 5 (au moins au niveau de sa région la plus chaude) subit une température maximale inférieure ou égale à 250°C et avant qu'elle ne subisse une température maximale de 150 °C. According to a first advantageous variant, the initiation of step e) is carried out directly after the annealing of step d), before the hottest region of the bonded structure 5 is subjected to a temperature below 150 ° C. For example, when the annealing of step d) exhibits a temperature rise ramp up to 400 ° C., then a temperature fall ramp, the initiation is carried out when the bonded structure 5 (at least at the level of its hottest region) experiences a maximum temperature less than or equal to 250 ° C and before it experiences a maximum temperature of 150 ° C.
En pratique, on pourra notamment prévoir l'étape e) d'initiation de l'onde de fracture lorsque la structure collée 5 sort de l'équipement de traitement thermique 20 utilisé pour le recuit, dans une zone de sortie contrôlée 23 dans laquelle la structure collée 5 subit une température maximale supérieure à 150 °C et inférieure ou égale à 250°C (figure 2 - e) ) . En particulier, le recuit de l'étape d) peut être effectué dans un équipement de traitement thermique 20 de configuration horizontale ou verticale, adapté pour le traitement collectif d'une pluralité de structures collées 5 ; l'initiation de l'étape e) est alors opérée lorsque les structures collées 5 sortent de l'équipement 20, dans la zone de sortie 23 où la température maximale subie par les structures 5 est contrôlée dans la gamme requise pour l'initiation de l'onde de fracture. La contrainte extérieure pour déclencher l'initiation de l'onde de fracture est avantageusement appliquée aux structures collées 5 successivement, au fur et à mesure de leur passage dans la zone de sortie contrôlée 23. In practice, it is possible in particular to provide for step e) of initiation of the fracture wave when the bonded structure 5 leaves the heat treatment equipment 20 used for annealing, in a controlled exit zone 23 in which the bonded structure 5 is subjected to a maximum temperature greater than 150 ° C. and less than or equal to 250 ° C. (FIG. 2 - e)). In particular, the annealing of step d) can be carried out in heat treatment equipment 20 of horizontal or vertical configuration, suitable for the collective treatment of a plurality of bonded structures 5; the initiation of step e) is then carried out when the bonded structures 5 leave the equipment 20, in the exit zone 23 where the maximum temperature undergone by the structures 5 is controlled within the range required for initiation of the fracture wave. The external constraint to trigger the initiation of the fracture wave is advantageously applied to the bonded structures 5 successively, as they pass through the controlled exit zone 23.
Selon une deuxième variante, l'initiation de l'étape e) est opérée après que la région la plus chaude de la structure collée 5 ait subi une température inférieure à 150°C. Dans ce cas, la structure collée 5 est maintenue en atmosphère contrôlée entre la fin du recuit de l'étape d) et le moment de l'initiation de l'onde de fracture qui nécessitera que la structure collée 5 soit ramenée à une température maximale comprise entre 150 °C et 250°C. Par atmosphère contrôlée, on entend ici une atmosphère sèche présentant moins de 0,1% d'humidité. Par exemple, lorsque le recuit de l'étape d) présente une rampe de montée en températures jusqu'à 400°C, puis une rampe de descente en températures jusqu'à 150 °C avant un retour à température ambiante de la structure collée 5, cette dernière est maintenue en atmosphère sèche jusqu'à l'étape e) d'initiation de l'onde de fracture . According to a second variant, the initiation of step e) is carried out after the hottest region of the bonded structure 5 has undergone a temperature below 150 ° C. In this case, the bonded structure 5 is maintained in a controlled atmosphere between the end of the annealing of step d) and the moment of the initiation of the fracture wave which will require that the bonded structure 5 is brought back to a maximum temperature. between 150 ° C and 250 ° C. By controlled atmosphere is meant here a dry atmosphere having less than 0.1% humidity. For example, when the annealing of step d) exhibits a temperature rise ramp up to 400 ° C, then a temperature drop ramp down to 150 ° C before the bonded structure returns to ambient temperature 5 , the latter is maintained in a dry atmosphere until step e) of initiation of the fracture wave.
De manière avantageuse, pour l'une ou l'autre des variantes énoncées, l'application d'une contrainte au plan fragile enterré 2 correspond à l'application d'une sollicitation mécanique locale sur la structure collée 5, en particulier sur la périphérie de ladite structure, de façon à amorcer l'onde de fracture. A titre d'exemple, la sollicitation mécanique locale peut être réalisée par insertion d'un biseau 10, en vis-à-vis de l'interface de collage 7 de la structure collée 5, entre des bords chanfreinés respectivement du substrat donneur 1 et du substrat support 4 de ladite structure collée 5. Cela a pour effet de générer une contrainte en tension dans le plan fragile enterré 2. Advantageously, for one or the other of the stated variants, the application of a stress to the buried fragile plane 2 corresponds to the application of a local mechanical stress on the bonded structure 5, in particular on the periphery. of said structure, so as to initiate the fracture wave. For example, the local mechanical stress can be achieved by inserting a bevel 10, facing the bonding interface 7 of the bonded structure 5, between chamfered edges respectively of the donor substrate 1 and of the support substrate 4 of said bonded structure 5. This has for effect of generating a stress in tension in the buried brittle plane 2.
Préférentiellement, la sollicitation mécanique locale est exercée dans une région de la structure collée 5 subissant des températures moindres, lorsqu'un gradient de températures existe sur la structure collée 5 lors de l'étape e) . Ladite région est appelée par la suite région froide, par opposition à la région la plus chaude de la structure collée 5 énoncée précédemment. Reprenant par exemple le cas de la première variante précitée, lorsqu'une ou plusieurs structure (s) collée (s) 5 sort (ent) de l'équipement de traitement thermique 20 dans lequel a été effectué le recuit, un gradient thermique existe en général sur chaque structure collée 5 (figures 5 et 6) . Ce gradient est en général dû à la géométrie du four et à la présence d'un système de maintien des structures collées 5, qui influencent la dissipation thermique. Par exemple, dans le cas d'un four de configuration horizontale 20, dans lequel les structures colléesPreferably, the local mechanical stress is exerted in a region of the bonded structure 5 undergoing lower temperatures, when a temperature gradient exists on the bonded structure 5 during step e). Said region is hereinafter called the cold region, as opposed to the hottest region of the bonded structure 5 mentioned above. Taking for example the case of the first variant mentioned above, when one or more bonded structure (s) 5 comes out of the heat treatment equipment 20 in which the annealing was carried out, a thermal gradient exists in general on each bonded structure 5 (Figures 5 and 6). This gradient is generally due to the geometry of the furnace and to the presence of a system for maintaining the bonded structures 5, which influence the heat dissipation. For example, in the case of a furnace of horizontal configuration 20, in which the bonded structures
5 sont placées verticalement dans des nacelles 22, lesquelles sont supportées par une pelle de chargement 21, on observe que la région inférieure B des structures collées 5 (c'est-à-dire la plus proche de la pelle de chargement 21) est plus froide que la région supérieure H des structures collées 5. La sollicitation mécanique locale est alors préférentiellement exercée dans la région inférieure B de la structure collée 5. 5 are placed vertically in nacelles 22, which are supported by a loading shovel 21, it is observed that the lower region B of the bonded structures 5 (i.e. the one closest to the loading shovel 21) is more cold than the upper region H of the bonded structures 5. The local mechanical stress is then preferentially exerted in the lower region B of the bonded structure 5.
De manière encore avantageuse, la sollicitation mécanique locale est exercée sur la structure collée 5 lorsque le gradient de température est de l'ordre de 80°C, soit 80°C +/-15°C. Le figureStill advantageously, the local mechanical stress is exerted on the bonded structure 5 when the temperature gradient is of the order of 80 ° C, ie 80 ° C +/- 15 ° C. The figure
6 présente le gradient de température mesuré sur une structure collée 5, après sa sortie du four, en région supérieure H, centrale C et inférieure B. 6 shows the temperature gradient measured on a bonded structure 5, after it has left the oven, in the upper region H, central C and lower B.
La demanderesse a observé qu'un gradient de température de 80 °C + /— 10 ° C subi par la structure collée 5 au moment de l'initiation de l'onde de fracture participait à améliorer 1 ' uniformité d'épaisseur de la couche utile 3 après transfert. The Applicant has observed that a temperature gradient of 80 ° C + / - 10 ° C undergone by the bonded structure 5 at the time of initiation of the fracture wave helped to improve the uniformity of thickness of the useful layer 3 after transfer.
Exemple d'application : Example of application:
Le procédé de transfert selon l'invention peut être utilisé pour la fabrication de substrats SOI dont la couche utile 3 est très mince, en particulier comprise entre quelques nanomètres et 50nm. The transfer method according to the invention can be used for the manufacture of SOI substrates in which the useful layer 3 is very thin, in particular between a few nanometers and 50 nm.
Prenons l'exemple de substrats donneur 1 et support 4 en silicium monocristallin, se présentant chacun sous forme de plaquette de 300mm de diamètre. Le substrat donneur est recouvert d'une couche d'oxyde de silicium 6 de 50nm d'épaisseur. Le plan fragile enterré 2 est formé dans le substrat donneur 1 par co implantation d'ions d'hydrogène et d'hélium dans les conditions suivantes : Let us take the example of donor 1 and support 4 substrates in monocrystalline silicon, each in the form of a wafer 300 mm in diameter. The donor substrate is covered with a layer of silicon oxide 6 50 nm thick. The buried fragile plane 2 is formed in the donor substrate 1 by co-implantation of hydrogen and helium ions under the following conditions:
• H : énergie d'implantation 38 keV, dose 1E16 H/cm2, • H: implantation energy 38 keV, dose 1E16 H / cm2,
• He : énergie d'implantation 25 keV, dose 1E16 He/cm2.• He: implantation energy 25 keV, dose 1E16 He / cm2.
Le plan fragile enterré 2 se situe à une profondeur d'environ 290 nm, à partir de la surface la du substrat donneur 1. Il délimite, avec la couche d'oxyde 6, une couche utile 3 d'environ 240 nm. The buried fragile plane 2 is located at a depth of approximately 290 nm, from the surface 1a of the donor substrate 1. It delimits, with the oxide layer 6, a useful layer 3 of approximately 240 nm.
L'assemblage du substrat donneur 1 et du substrat support 4 est fait par collage direct par adhésion moléculaire, pour former la structure collée 5. Préalablement à l'assemblage, les substrats donneur 1 et support 4 auront subi des séquences de nettoyages et/ou d'activation de surface connues, de manière à garantir la qualité de l'interface de collage 7 en termes de défectivité et d'énergie de collage. The assembly of the donor substrate 1 and the support substrate 4 is made by direct bonding by molecular adhesion, to form the bonded structure 5. Prior to assembly, the donor 1 and support 4 substrates will have undergone cleaning and / or sequences. known surface activation, so as to guarantee the quality of the bonding interface 7 in terms of defectivity and bonding energy.
Un four 20 de configuration horizontale est utilisé pour réaliser collectivement le recuit d'une pluralité de structures collées 5 telles que celle décrite ci-dessus. Ce type d'équipement de traitement thermique 20 comprend une pelle de chargement 21 qui supporte des nacelles 22 dans lesquelles sont positionnées les structures collées 5 (figure 7) . La pelle de chargement 21 se déplace entre une position rentrée, dans laquelle les structures collées 5 sont à l'intérieur du four 20 et une position sortie, dans laquelle elles sont à l'extérieur du four 20. A furnace 20 of horizontal configuration is used to collectively perform the annealing of a plurality of bonded structures such as that described above. This type of equipment heat treatment 20 comprises a loading shovel 21 which supports nacelles 22 in which the bonded structures 5 are positioned (FIG. 7). The loading shovel 21 moves between a retracted position, in which the bonded structures 5 are inside the oven 20, and an extended position, in which they are outside the oven 20.
Un système de biseaux 10 peut être positionné sur chaque nacelle 22, en-dessous des structures collées 5. La pelle de chargement 21 se déplace en position rentrée pour la réalisation du recuit. Le recuit comprend une rampe de montée en température de 200 °C à 380°C, un palier à 380°C de 2 min et une rampe de descente en température jusqu'à 225°C. A system of bevels 10 can be positioned on each nacelle 22, below the bonded structures 5. The loading shovel 21 moves in the retracted position for carrying out the annealing. The annealing includes a temperature rise ramp from 200 ° C to 380 ° C, a plateau at 380 ° C for 2 minutes and a temperature drop ramp down to 225 ° C.
A l'issue du recuit, la pelle de chargement 21 se déplace vers sa position sortie. After annealing, the loading shovel 21 moves to its extended position.
Comme illustré sur la figure 6, à partir du moment où chaque structure collée 5 sort du four 20, la température qu'elle subit décroit. Chaque structure collée 5 va transiter dans une zone de sortie 23 dans laquelle elle verra une température maximale (dans sa région la plus chaude) comprise entre 150°C et 250°C. Dans cette zone de sortie 23, un dispositif d'appui 11 situé au- dessus des structures collées 5 va venir exercer une force d'appui successivement sur chaque structure collée 5, de sorte que le biseau 10 en-dessous de celle-ci s'insère, en vis-à-vis de l'interface de collage 7, entre les bords chanfreinés des substrats assemblés de la structure collée 5 (figure 7) . L'insertion du biseau 10 génère une contrainte locale et en tension au niveau du plan fragile enterré 2 permettant d' initier l'onde de fracture dans chaque structure collée 5, successivement, au fur et à mesure de leur passage sous le dispositif d'appui 11. As illustrated in FIG. 6, from the moment each bonded structure 5 leaves the oven 20, the temperature to which it is subjected decreases. Each bonded structure 5 will pass through an outlet zone 23 in which it will see a maximum temperature (in its hottest region) of between 150 ° C and 250 ° C. In this exit zone 23, a support device 11 located above the bonded structures 5 will exert a supporting force successively on each bonded structure 5, so that the bevel 10 below it s 'inserts, facing the bonding interface 7, between the chamfered edges of the assembled substrates of the bonded structure 5 (FIG. 7). The insertion of the bevel 10 generates a local stress and in tension at the level of the buried fragile plane 2 making it possible to initiate the fracture wave in each bonded structure 5, successively, as they pass under the device. support 11.
Bien-sûr, des outils autres que l'ensemble formé par le système de biseaux 10 et le dispositif d'appui 11 pourraient être mis en œuvre pour opérer l'initiation de l'onde de fracture dans les structures collées 5 conformément à la présente invention. Of course, tools other than the assembly formed by the system of bevels 10 and the support device 11 could be put implemented to effect the initiation of the fracture wave in the bonded structures in accordance with the present invention.
L'initiation de l'onde de fracture est ainsi opérée pour chaque structure collée 5 alors que cette dernière subit une température maximale comprise entre 150°C et 250°C, préférentiellement autour de 200°C. Sur l'exemple de la figure 6, la zone de sortie 23 dans laquelle l'initiation de l'onde de fracture est opérée, correspond à une zone dans laquelle chaque structure collée 5 subit, dans sa région la plus chaude (la région haute H) une température maximale de l'ordre de 200°C, sa région centrale C voyant une température intermédiaire de l'ordre de 180 °C et sa région basse B voyant une température de l'ordre de 130 °C. Le biseau 10 étant, dans l'exemple illustré sur la figure 7, placé en partie inférieure de chaque structure collée 5, l'initiation se fait en outre dans la région froide (région basse B : celle qui subit les températures les plus basses) de la structure collée 5. The initiation of the fracture wave is thus carried out for each bonded structure 5 while the latter is subjected to a maximum temperature of between 150 ° C and 250 ° C, preferably around 200 ° C. In the example of FIG. 6, the exit zone 23 in which the initiation of the fracture wave is operated, corresponds to a zone in which each bonded structure 5 undergoes, in its hottest region (the upper region H) a maximum temperature of the order of 200 ° C, its central region C seeing an intermediate temperature of the order of 180 ° C and its lower region B seeing a temperature of the order of 130 ° C. The bevel 10 being, in the example illustrated in FIG. 7, placed in the lower part of each bonded structure 5, the initiation also takes place in the cold region (lower region B: that which is subjected to the lowest temperatures) of the bonded structure 5.
Suite à la propagation auto-entretenue de l'onde de fracture, on obtient le substrat SOI après transfert (ensemble transféré 5a) et le reste 5b du substrat donneur 1. Une très bonne uniformité d'épaisseur des couches utiles 3 transférées est obtenue. Following the self-sustaining propagation of the fracture wave, the SOI substrate is obtained after transfer (transferred assembly 5a) and the remainder 5b of the donor substrate 1. A very good uniformity of thickness of the useful layers 3 transferred is obtained.
Des étapes de finition appliquées aux ensembles transférés 5a comprennent des nettoyages chimiques et au moins un traitement thermique de lissage à haute température. A l'issue de ces étapes, les substrats SOI comportent une couche utile 3 d'épaisseur 50nm, dont la non-uniformité d'épaisseur finale est de l'ordre de 0,45nm. Notons que comparativement, des substrats SOI dont la couche utile 3 comporte des motifs réguliers ou irréguliers après fracture, peuvent présenter des non- uniformités d'épaisseur finales supérieures ou égales à 0,7nm. Bien entendu, l'invention n'est pas limitée aux modes de mise en œuvre et exemples décrits, et on peut y apporter des variantes de réalisation sans sortir du cadre de l'invention tel que défini par les revendications. Finishing steps applied to the transferred assemblies 5a include chemical cleanings and at least one high temperature smoothing heat treatment. At the end of these steps, the SOI substrates comprise a useful layer 3 with a thickness of 50 nm, the non-uniformity of final thickness of which is of the order of 0.45 nm. It should be noted that, in comparison, SOI substrates in which the useful layer 3 comprises regular or irregular patterns after fracture, may have final thickness non-uniformities greater than or equal to 0.7 nm. Of course, the invention is not limited to the embodiments and examples described, and variant embodiments can be provided without departing from the scope of the invention as defined by the claims.

Claims

REVENDICATIONS
1. Procédé de transfert d'une couche utile (3) sur un substrat support (4), comprenant les étapes suivantes : 1. A method of transferring a useful layer (3) onto a support substrate (4), comprising the following steps:
a) la fourniture d'un substrat donneur (1) comportant un plan fragile enterré (2), la couche utile (3) étant délimitée par une face avant (la) du substrat donneur (1) et le plan fragile enterré (2) ; a) the provision of a donor substrate (1) comprising a buried fragile plane (2), the useful layer (3) being delimited by a front face (la) of the donor substrate (1) and the buried fragile plane (2) ;
b) la fourniture d'un substrat support (4) ; b) providing a support substrate (4);
c) l'assemblage, selon une interface de collage (7), du substrat donneur (1), au niveau de sa face avant (la), et du substrat support (4), pour former une structure collée (5) ; c) the assembly, according to a bonding interface (7), of the donor substrate (1), at its front face (la), and of the support substrate (4), to form a bonded structure (5);
d) le recuit de la structure collée (5) pour lui appliquer un budget thermique de fragilisation et amener le plan fragile enterré (2) jusqu'à un niveau de fragilisation défini ; d) annealing the bonded structure (5) to apply a thermal embrittlement budget to it and bring the buried fragile plane (2) to a defined level of embrittlement;
e) l'initiation d'une onde de fracture dans le plan fragile enterré (2) par application d'une contrainte à la structure collée (5), l'onde de fracture se propageant de manière auto-entretenue le long du plan fragile enterré (2) pour mener au transfert de la couche utile (3) sur le substrat support (4) ; e) initiation of a fracture wave in the buried brittle plane (2) by applying a stress to the bonded structure (5), the fracture wave propagating in a self-sustaining manner along the brittle plane buried (2) to lead to the transfer of the useful layer (3) on the support substrate (4);
Le procédé de transfert étant caractérisé en ce que l'initiation de l'onde de fracture est opérée alors que la structure collée (5) subit, au moins dans sa région la plus chaude, une température maximale comprise entre 150° et 250 °C . The transfer process being characterized in that the initiation of the fracture wave is carried out while the bonded structure (5) undergoes, at least in its hottest region, a maximum temperature of between 150 ° and 250 ° C. .
2. Procédé de transfert selon la revendication précédente, dans lequel la température maximale est comprise entre 180 °C et 220 °C . 2. Transfer method according to the preceding claim, wherein the maximum temperature is between 180 ° C and 220 ° C.
3. Procédé de transfert selon l'une des revendications précédentes, dans lequel le recuit de l'étape d) atteint une température de palier maximale comprise entre 300 °C et 600 °C . 3. Transfer method according to one of the preceding claims, wherein the annealing of step d) reaches a maximum plateau temperature of between 300 ° C and 600 ° C.
4. Procédé de transfert selon l'une des revendications précédentes, dans lequel le budget thermique de fragilisation est compris entre 40% et 95% d'un budget thermique de fracture, le budget thermique de fracture menant à une initiation spontanée de l'onde de fracture dans le plan fragile enterré (2) au cours du recuit. 4. Transfer method according to one of the preceding claims, wherein the thermal budget for embrittlement is between 40% and 95% of a thermal budget for fracture, the thermal budget for fracture leading to spontaneous initiation of the wave. fracture in the buried brittle plane (2) during annealing.
5. Procédé de transfert selon l'une des revendications précédentes, dans lequel l'initiation de l'étape e) est opérée directement après le recuit de l'étape d) , avant que la région la plus chaude de la structure collée (5) ne subisse une température inférieure à 150°C. 5. Transfer method according to one of the preceding claims, wherein the initiation of step e) is performed directly after the annealing of step d), before the hottest region of the bonded structure (5 ) is not subjected to a temperature lower than 150 ° C.
6. Procédé de transfert selon l'une des revendications précédentes, dans lequel le recuit de l'étape d) est effectué dans un équipement de traitement thermique (20) de configuration horizontale ou verticale, adapté pour le traitement collectif d'une pluralité de structures collées (5), et dans lequel l'initiation de l'étape e) est opérée lors de la sortie des structures collées (5) de l'équipement (20) . 6. Transfer method according to one of the preceding claims, wherein the annealing of step d) is carried out in a heat treatment equipment (20) of horizontal or vertical configuration, suitable for the collective treatment of a plurality of bonded structures (5), and in which the initiation of step e) is carried out when the bonded structures (5) are removed from the equipment (20).
7. Procédé de transfert selon l'une des revendications précédentes, dans lequel l'application d'une contrainte au plan fragile enterré (2) correspond à l'application d'une sollicitation mécanique locale sur la structure collée (5) , en particulier sur la périphérie de ladite structure (5) . 7. Transfer method according to one of the preceding claims, wherein the application of a stress to the buried fragile plane (2) corresponds to the application of a local mechanical stress on the bonded structure (5), in particular on the periphery of said structure (5).
8. Procédé de transfert selon la revendication précédente, dans lequel la sollicitation mécanique locale est réalisée par insertion d'un biseau (10), en vis-à-vis de l'interface de collage (7) de la structure collée (5), entre des bords chanfreinés respectivement du substrat donneur (1) et du substrat support (4) de ladite structure collée (5). 8. Transfer method according to the preceding claim, wherein the local mechanical stress is produced by inserting a bevel (10), facing the bonding interface (7) of the bonded structure (5). , between chamfered edges respectively of the donor substrate (1) and of the support substrate (4) of said bonded structure (5).
9. Procédé de transfert selon l'une des deux revendications précédentes, dans lequel la sollicitation mécanique locale est exercée dans une région de la structure collée (5) subissant des températures moindres lorsqu'un gradient de températures existe sur la structure collée (5) lors de l' étape e) . 9. Transfer method according to one of the two preceding claims, wherein the local mechanical stress is exerted in a region of the bonded structure (5) undergoing lower temperatures when a temperature gradient exists on the bonded structure (5). during step e).
10. Procédé de transfert selon la revendication précédente, dans lequel la sollicitation mécanique locale est exercée sur la structure collée (5) lorsque le gradient de température est de l'ordre de 80 °C. 10. Transfer method according to the preceding claim, wherein the local mechanical stress is exerted on the bonded structure (5) when the temperature gradient is of the order of 80 ° C.
11. Procédé de transfert selon l'une des revendications précédentes, dans lequel le substrat donneur (1) et le substrat support (4) sont en silicium monocristallin, et dans lequel le plan fragile enterré (2) est formé par implantation ionique d'espèces légères dans le substrat donneur (1), lesdites espèces légères étant choisies parmi l'hydrogène et l'hélium ou une combinaison d'hydrogène et d' hélium. 11. Transfer method according to one of the preceding claims, wherein the donor substrate (1) and the support substrate (4) are monocrystalline silicon, and wherein the buried brittle plane (2) is formed by ion implantation of light species in the donor substrate (1), said light species being selected from hydrogen and helium or a combination of hydrogen and helium.
EP20713947.8A 2019-03-15 2020-02-26 Method for transferring a useful layer onto a support substrate Pending EP3939077A1 (en)

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