Method for transferring a useful layer onto the front side of a carrier substrate - Patents.com

Abstract

The invention relates to a process for transferring a working layer (15) onto a support substrate (20), the process comprising the steps of: a) providing a donor substrate (10) with a donor layer (12); b) forming a weakened region (14) by implantation of species into the donor layer (12), which, together with its main surface, defines the working layer (15); c) bonding the support substrate (20) to the donor substrate (10); and d) carrying out a heat treatment comprising a first phase and a second phase, the first phase of a first duration comprising a temperature increase to a first temperature and designed to allow maturation of defects generated by the seeds in the weakened region (14) and to prevent initiation of fracture in the weakened region (14), and the second phase of a second duration comprising a holding period at a second temperature lower than the first temperature and initiating fracture along the weakened region (14).

Description

[Technical field]

[0001] FIELD OF THEINVENTION The present invention relates to the field of heterogeneous structures.

[0002] In particular, the present invention relates to a process for transferring a working layer to a support substrate involving SmartCut™ technology.

[0003] More particularly, the process according to the invention relates to a process which makes it possible to reduce the fracture temperature in order to reduce the risk of cracking and / or delamination occurring.

[0004] The process according to the invention is then preferably carried out for the manufacture of a piezoelectric-on-insulator substrate. [Background technology]

[0005] (Technical Background of the Invention) FR 3 068 508 A1 discloses a process for transferring a working layer to a support substrate. In particular, FR 3 068 508 A1 discloses a process for transferring a working layer to a support substrate according to the SmartCut™ process.

[0006] The transcription process described in patent application FR 3 068 508 comprises in this respect the following steps: a0) providing a donor substrate comprising a donor layer located on one side of a handle substrate from a front side to a rear side; b0) implanting a species through the front surface into the donor layer so as to form a weakened area extending along a plane parallel to said front surface and defining, together with said front surface, a working layer; c0) bonding a front surface of the donor substrate to a major surface of a support substrate; d0) carrying out a thermal treatment intended to initiate the propagation of a break wave in the weakened area and then transfer the working layer to the main surface of the support substrate.

[0007] This process is preferably carried out on condition that the materials forming the working layer and the support substrate have different thermal expansion coefficients.More specifically, the process disclosed in FR-A-3068508 proposes the use of a handle substrate made of a material with a thermal expansion coefficient similar to that of the material forming the support substrate, with the aim of reducing the risk of uncontrolled breakage or partial transfer or defects of the working layer.

[0008] Nevertheless, the use of this type of donor substrate remains problematic.

[0009] This is because the interface formed between the donor layer and the handle substrate is sensitive to thermal treatments, and more particularly, this interface may be the site of initiation of cracking and / or delamination of the donor layer.

[0010] It is therefore an object of the present invention to propose a process for transferring a working layer to a donor substrate, which makes it possible to prevent the occurrence of cracks at the interface formed between the donor layer and the handle substrate, and the occurrence of delamination of the donor layer.

[0011] The object of the present invention is achieved by a process for transferring a working layer onto a supporting substrate, the process comprising the following steps: a) providing a donor substrate comprising, starting from a main surface thereof, a donor layer formed from a piezoelectric material and a handle substrate, the donor layer being located on one surface of the handle substrate; b) forming a weakened area parallel to the main surface and defining, together with the main surface, a working layer by implantation of a species into the donor layer; c) bonding the support substrate to the donor substrate such that the donor layer is interposed between the handle substrate and the support substrate; d) carrying out a heat treatment comprising, in this order, a first stage and a second stage, the first stage of a first duration comprising a temperature rise to a first temperature and designed, firstly, to allow maturation of defects generated by seeds in the weakened zone and, secondly, to prevent initiation of fracture in said weakened zone, and the second stage of a second duration comprising a holding period at a second temperature lower than the first temperature and designed to initiate fracture along the weakened zone and thus transfer the working layer to the front surface; and an absolute difference between the first temperature and the second temperature is less than 40°C and more than 30°C.

[0012] In one embodiment, step d) also comprises a strengthening step preceding the first step, carried out at a temperature (called strengthening temperature) lower than the first temperature, the strengthening step intended to strengthen the bonding energy of the interface formed between the support substrate and the donor substrate during the execution of step c).

[0013] In one embodiment, the first stage includes, in that order, an increase in temperature, a hold period at the first temperature, and a decrease in temperature to the second temperature.

[0014] In one embodiment, the first stage is adjusted according to the conditions of the ongoing seed injection of step b).

[0015] In one embodiment, the relative difference between the thermal expansion coefficients of the materials forming the handle substrate and the support substrate, respectively, is less than 10%.

[0016] In one embodiment, the handle substrate comprises a bulk substrate having an intermediate layer on one side thereof, the intermediate layer being interposed between the donor layer and the bulk substrate, preferably the intermediate layer comprising a polymeric material.

[0017] In one embodiment, the first temperature is less than 300°C, preferably less than 250°C, and even more preferably less than 220°C.

[0018] In one embodiment, the absolute difference between the first temperature and the second temperature is less than 40°C and more than 30°C.

[0019] In one embodiment, the second duration is less than 6 hours, preferably less than 4 hours.

[0020] In one embodiment, the second temperature is less than 180°C, preferably less than 170°C.

[0021] In one embodiment, the species comprises at least one element selected from hydrogen ions, helium ions.

[0022] In one embodiment, the piezoelectric material is LiTaO 3 , LiNbO 3 , LiAlO 3 , BaTiO 3 , PbZrTiO 3 , KNbO 3 , BaZrO 3 , CaTiO 3 , PbTiO 3 , KTaO 3 It includes at least one element selected from:

[0023] In one embodiment, the bonding step c) is preceded by a step of forming a layer of dielectric material on the donor layer and / or on the front side of the support substrate.

[0024] In one embodiment, the joining step c) comprises molecular bonding.

[0025] Other features and advantages will become apparent in the following description of a process for transferring a working layer onto a support substrate according to the invention, given by way of non-limiting example with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0026] [Figure 1A] FIG. 1A is a schematic illustration of step a) of the process according to the invention, more specifically, FIG. 1A shows a donor substrate along a cross section perpendicular to a main surface of said donor substrate. [Figure 1B] FIG. 1B is a schematic illustration of step b) of the process according to the invention, more specifically, FIG. 1B shows a donor substrate along a cross section perpendicular to a main surface of said donor substrate, the arrows indicating the implantation of species through the main surface to form a weakened region. [Figure 1C] FIG. 1C is a schematic illustration of step c) of the process according to the invention, more specifically, FIG. 1C shows the assembly formed by a donor substrate and a support substrate along a cross section perpendicular to a main surface of said donor substrate. [Figure 1D] FIG. 1D is a schematic diagram of a first stage of step d) of the process according to the invention, and more specifically, FIG. 1D shows the maturation of defects in a weakened area of ​​the assembly formed by a donor substrate and a support substrate along a cross section perpendicular to the main surface of the donor substrate. [Figure 1E] FIG. 1E is a schematic diagram of a second stage of step d) of the process according to the invention, and more particularly, FIG. 1E shows a break resulting in peeling of the working layer from the donor layer for the purpose of transferring it onto the front side of a supporting substrate. [Diagram 2] FIG. 2 is a schematic illustration of a donor substrate along a cross section perpendicular to a main surface of said donor substrate according to one particular embodiment of the present invention; more particularly, according to this embodiment, the handle substrate comprises a bulk substrate on one side of which an intermediate layer is present such that the intermediate layer is interposed between the bulk substrate and the donor layer. [Diagram 3] FIG. 3 is a graphical representation of a heat treatment that may be carried out in the context of the present invention, more specifically, the horizontal axis indicates time t in hours and the vertical axis indicates temperature T° in degrees Celsius. [Figure 4A] FIG. 4A is a graphical representation of a heat treatment, called the first treatment, that may be carried out to determine the parameters for carrying out step d), more specifically, the horizontal axis showing time in hours and the vertical axis showing temperature in degrees Celsius. [Figure 4B]FIG. 4B is a graphical representation of a heat treatment, called the second treatment, that may be carried out to determine parameters for carrying out step d), more specifically, the horizontal axis showing time in hours and the vertical axis showing temperature in degrees Celsius. [Figure 4C] FIG. 4C is a graphical representation of a heat treatment, called the third treatment, that may be performed to determine parameters for carrying out step d), more specifically, the horizontal axis showing time in hours and the vertical axis showing temperature in degrees Celsius. [Diagram 5] FIG. 5 shows a donor substrate comprising a layer of dielectric material, referred to as the first layer, located on the donor layer. [Figure 6] FIG. 6 shows a support substrate that includes a layer of dielectric material (eg, silica), referred to as the second layer, located on the front side of the support substrate. Detailed Description of the Invention

[0027] To simplify the following description, the same reference numbers are used for elements that are the same or perform the same functions in various presented embodiments of the prior art or processes.

[0028] The figures are schematic and not to scale for ease of reading, in particular the thicknesses of the layers are not to scale relative to the lateral dimensions of these layers.

[0029] The present invention relates to a process for transferring a working layer onto the front side of a supporting substrate.

[0030] In particular, the process comprises performing steps a) to d), more particularly step a) comprises providing a donor substrate, the donor substrate comprising, starting from a main surface thereof, a donor layer formed from a piezoelectric material and a handle substrate.

[0031] Step b) comprises implanting species into the donor layer to form weakened regions which run parallel to the main surface and which together with the main surface define a working layer.

[0032] Step c) involves bonding the donor layer to the front side of the supporting substrate.

[0033] Step d) comprises a heat treatment comprising, in this order, a first phase and a second phase: the first phase of a first duration comprises a temperature rise to a first temperature and is designed, firstly, to initiate maturation of the defects generated by the seeds in the weakened zone and, secondly, to prevent initiation of fracture in said weakened zone, and the second phase comprises a holding period at a second temperature lower than the first temperature and is of a second duration such as to initiate fracture along the weakened zone and thus transfer the working layer onto the front surface.

[0034] 1A-1E are schematic illustrations of the various steps performed in a process for transferring a working layer onto the front side of a support substrate according to the present invention.

[0035] 1A is a representation of step a), which comprises the provision of a donor substrate 10. In this regard, starting from a main surface 11, the donor substrate 10 comprises a donor layer 12 made from a piezoelectric material and a handle substrate 13. In other words, the donor layer 12 is located on one side of the handle substrate 13.

[0036] The formation of the donor substrate 10 may, for example, include the steps of bonding a piezoelectric substrate onto the surface of a handle substrate and thinning the piezoelectric substrate to form a donor layer, in that order. The formation of the donor substrate 10 may also include a step of heat treatment intended to strengthen the bonding interface formed between the donor layer and the handle substrate 13. The above formation of the donor substrate 10 is given by way of example only and is therefore not intended to limit the scope of the invention.

[0037] The piezoelectric material forming the donor layer 12 is LiTaO 3 , LiNbO 3 , LiAlO 3 , BaTiO 3 , PbZrTiO 3 , KNbO 3 , BaZrO 3 , CaTiO 3 , PbTiO 3 , KTaO 3may include at least one element selected from:

[0038] The handle substrate 13 may comprise any type of material, more specifically a semiconductor material such as silicon, or an insulating material such as glass.

[0039] In one particular embodiment, the handle substrate may include a bulk substrate 13a with an intermediate layer 13b on one side of the bulk substrate 13a, as shown in Figure 2. More specifically, the intermediate layer 13b is interposed between the bulk substrate 13a and the donor layer 12 in this particular embodiment.

[0040] The bulk substrate 13a may comprise any type of material, more specifically a semiconductor material such as silicon, or an insulating material such as glass.

[0041] The intermediate layer 13b may comprise an insulating material, more particularly a polymer material, that ensures an adhesive function between the bulk substrate 13a and the donor layer 12.

[0042] The relative difference between the thermal expansion coefficients of the materials forming the handle substrate and the support substrate, respectively, may be less than 10%. The use of such materials makes it possible to reduce stresses likely to occur during the performance of the heat treatment in step d), as described below.

[0043] Step a) is followed by step b), which is illustrated in FIG. 1B.

[0044] More specifically, step b) comprises the formation of a weakened region 14 by implantation of species into the donor layer 12. More specifically, the weakened region extends in a plane parallel to the main surface 11 and together with the main surface 11 defines a working layer 15.

[0045] “Weakened area” is understood to mean an area along which a break wave is likely to propagate so as to cause delamination of the working layer 15 from the donor layer 12 .

[0046] It will be further understood, although not required to be so specified, that the implanted species is selected such that it is capable of inducing, upon thermal activation, first, the maturation of defects within the weakened region, and second, the propagation of a break wave along the weakened region.

[0047] The implantation of the species may more particularly be carried out by ion implantation, more particularly by implantation of hydrogen ions and / or helium ions.

[0048] The implantation conditions, in terms of the dose of implanted species and the implantation energy, determine the thickness of the working layer 15. As an example, LiTaO 3 In the case of the donor layer 12 made of , the implantation energy is 30 keV to 300 keV, and the E 16at / cm 2 ~5 E 17at / cm 2 Dosing this level of hydrogen ions makes it possible to form a working layer 15 having a thickness of 200 nm to 2000 nm.

[0049] The process according to the invention also comprises carrying out step c) (FIG. 1C).

[0050] Step c) involves bonding the donor substrate 10 to a support substrate 20 such that the donor layer 12 is interposed between the support substrate 20 and the handle substrate 13 .

[0051] Thus, as shown in FIG. 1C, step c) involving bonding comprises contacting the main surface 11 with the front surface 21 of a support substrate 20 .

[0052] However, the invention is not limited to this embodiment and it is possible to employ, prior to step c), a step of forming a layer of dielectric material on the donor layer and / or on the front side of the supporting substrate.

[0053] In this regard, FIG. 5 shows a donor substrate 10 comprising a layer of dielectric material (eg, silica) (referred to as first layer 17) located on the donor layer.

[0054] Alternatively or additionally, a layer of dielectric material may be formed on the front side of support substrate 20. In this regard, Figure 6 illustrates support substrate 20 including a layer of dielectric material (e.g., silica), referred to as second layer 22, located on the front side of support substrate 20.

[0055] In such a case, the first layer 17 and / or the second layer 22 should be found interposed between the donor layer and the support substrate at the end of the execution of step c).

[0056] The bonding step c) may comprise a molecular bond which, when the free faces of the donor substrate and the support substrate are in contact, leads to the propagation of a coupling wave, resulting in adhesion between said faces. The invention is not limited to the implementation of molecular bonding only. In this context, it is possible to employ bonding by compression or thermocompression, bonding by an adhesive layer.

[0057] Step c) is then followed by a step d) of a heat treatment intended to initiate a breaking wave along the weakened areas so as to cause detachment of the working layer 15 and, as a consequence, transfer of the working layer onto the front surface 21 of the support substrate 20.

[0058] However, in order to prevent cracking or delamination of the donor layer at the interface formed between the donor layer 12 and the handle substrate 13, the heat treatment is carried out so that the initiation of the break wave occurs at the lowest possible temperature.

[0059] In this connection, the heat treatment comprises two stages, called the first stage and the second stage, respectively.

[0060] FIG. 3 illustrates in graphical form one example of a heat treatment that may be performed during step d).

[0061] More specifically, FIG. 3 shows time along the horizontal axis and temperatures to which the assembly formed by donor substrate 10 and support substrate 20 is exposed along the vertical axis, with the first stage including, in order, an increase in temperature A, a holding period B at the first temperature, and a decrease in temperature C to a second temperature.

[0062] The first stage (shown in FIG. 1D ) of first duration d1 involves a temperature increase to a first temperature T1 and is designed, firstly, to allow maturation of defects 16 generated by seeds in the weakened region and, secondly, to prevent the initiation of fracture within said weakened region.

[0063] "Maturation of defects" is understood to mean the formation and growth of bubbles in the plane of the weakened area. This maturation is activated by the input of thermal energy.

[0064] A second stage (shown in FIG. 1E) of second duration d2 includes a holding period at a second temperature T2 lower than the first temperature T1 and is designed to initiate fracture along the weakened regions and thus transfer the working layer onto the front surface.

[0065] Although not necessarily so specified, it is understood that the second stage is performed consecutively with the first stage.

[0066] Step d) may be carried out in a batch oven, more particularly under a controlled atmosphere, more particularly under an inert atmosphere. The invention is not limited to the implementation in a batch oven. More particularly, a rapid thermal processing furnace may also be used.

[0067] The use of a two-step heat treatment allows the initiation of the break wave, and therefore the transfer of the working layer 15 onto the support substrate 20, at a lower temperature than currently contemplated by the state of the art.

[0068] The first step may preferably be preceded by a step of strengthening the interface formed during bonding between the donor substrate and the support substrate, in this context, the strengthening step being carried out at a temperature, referred to as the strengthening temperature Ts, which is lower than the first temperature.

[0069] Although not necessarily so specified, it is understood that the first phase is adjusted according to the conditions of the injection of the seeds during the performance of step b).

[0070] More specifically, the conditions of the heat treatment, more specifically the first temperature T1, the second temperature T2, the first duration d1 and the second duration d2, may be determined empirically.

[0071] In this context, by way of example, Figures 4A to 4C are graphical representations of the different heat treatments to which the batch of 25 assemblies obtained at the end of step c) were subjected. During the execution of each of these heat treatments, the inventors identified the moment of detection of the initiation of a fracture likely to occur in each of the assemblies.

[0072] Thus, FIG. 4A illustrates in graphical form a heat treatment, referred to as the first heat treatment, where the first and second temperatures are 200° C. and 160° C., respectively, and the first and second durations are 7 minutes and 6 hours, respectively.

[0073] FIG. 4B illustrates in graphical form a heat treatment, referred to as the second heat treatment, which differs from the first heat treatment in that the second temperature and second duration are 170° C. and 4 hours, respectively.

[0074] FIG. 4C illustrates in graphical form a heat treatment, referred to as the third heat treatment, which differs from the first heat treatment in that the first and second durations are 20 minutes and 4 hours, respectively.

[0075] During the first run, the inventors observed that 8 assemblies out of 25 present in the heat treatment oven did not suffer fracture.

[0076] On the other hand, the use of a second, higher temperature (170° C.) during the second treatment (FIG. 4B) allows the initiation of a break wave inside each of the 25 assemblies in the second stage of said treatment. However, the initiation of a break wave in two of the 25 assemblies was only observed after the end of the holding period in the second stage. The conditions prevailing during this second annealing are not capable of providing the necessary stability for the process according to the invention.

[0077] The use of a longer maturation period (first stage) during the implementation of the third treatment resulted in the initiation of the break wave during the first stage (more specifically during the temperature reduction C). A heat treatment of this nature does not allow the stabilization of step d).

[0078] Based on these results, the inventors believe that the optimal heat treatment parameters for the implantation conditions employed are as follows: Temperature T1=200℃, Duration d1 = 15 minutes, Temperature T2=170℃, Duration d2 = 4 hours.

[0079] The above principles therefore make it possible to determine optimal heat treatment conditions for carrying out step d).

[0080] It is preferred if the first temperature T1 is less than 300°C, preferably less than 250°C, even more preferably less than 220°C.

[0081] It is always preferred if the absolute difference between the first temperature T1 and the second temperature T2 is less than 40° C. and more than 30° C. For example, the second temperature T2 is less than 180° C., preferably less than 170° C.

[0082] It is preferred if the second duration d2 is less than 6 hours, preferably less than 4 hours.

[0083] The implementation of the heat treatment of step d) according to the terms of the invention makes it possible to reduce the temperature of the holding period at which the initiation of the break wave is likely to occur. This aspect makes it possible to reduce the stresses in the interface formed between the donor layer and the handle substrate, and potentially in the intermediate layer, if used.

[0084] In other words, the heat treatment used in the present invention reduces the occurrence of cracks and / or delamination, as explained in the "Technical Background of the Invention" section.

[0085] Of course, the invention is not limited to the described embodiments, and variations in implementation may be applied without departing from the scope of the invention as defined by the claims.

Claims

1. A process for transferring a working layer (15) onto a support substrate (20), comprising: a) providing a donor substrate (10) comprising a donor layer (12) formed from a piezoelectric material and a handle substrate (13), starting from a main surface, the donor layer (12) being located on one surface of the handle substrate (13); b) forming a weakened region (14) parallel to the main surface and defining the working layer (15) together with the main surface by implanting species into the donor layer (12); c) bonding the support substrate (20) to the donor substrate (10) such that the donor layer (12) is interposed between the handle substrate (13) and the support substrate (20); d) subjecting to a heat treatment comprising a first stage and a second stage in this order, the first stage of the first period comprising a temperature increase to a first temperature and being designed to, firstly, allow the maturation of defects generated by the species in the weakened region (14) and, secondly, prevent the initiation of fracture in the weakened region (14), the second stage of the second period comprising a holding period at a second temperature lower than the first temperature and being designed to initiate fracture along the weakened region (14) and thus transfer the working layer (15) onto the support substrate (20). A process comprising the above steps.

2. The process according to claim 1, wherein step d) also includes a strengthening step that precedes the first stage and is carried out at a temperature called a strengthening temperature lower than the first temperature, the strengthening step being intended to strengthen the binding energy of the interface formed between the support substrate (20) and the donor substrate (10) during the execution of step c).

3. The process according to claim 1 or 2, wherein the first stage includes a temperature increase, a holding period at the first temperature, and a temperature decrease to the second temperature in this order.

4. The process according to claim 1 or 2, wherein the first stage is adjusted according to the conditions of the implantation of the species during the execution of step b).

5. The process according to claim 1 or 2, wherein the relative difference in the coefficient of thermal expansion of the materials forming the handle substrate (13) and the support substrate (20) is less than 10%.

6. The process according to claim 1 or 2, wherein the handle substrate (13) comprises a bulk substrate, there is an intermediate layer on one surface of the bulk substrate, and the intermediate layer is interposed between the donor layer (12) and the bulk substrate, and preferably, the intermediate layer contains a polymer material.

7. The process according to claim 1 or 2, wherein the first temperature is less than 300 °C, preferably less than 250 °C, and even more preferably less than 220 °C.

8. The process according to claim 1 or 2, wherein the second period is less than 6 hours, preferably less than 4 hours.

9. The process according to claim 1 or 2, wherein the second temperature is less than 180 °C, preferably less than 170 °C.

10. The process according to claim 1 or 2, wherein the species contains at least one element selected from hydrogen ions and helium ions.

11. The piezoelectric material is LiTaO ３ 、LiNbO ３ 、LiAlO ３ 、BaTiO ３ 、PbZrTiO ３ 、KNbO ３ 、BaZrO ３ 、CaTiO ３ 、PbTiO ３ 、KTaO ３ The process according to claim 1 or 2, which contains at least one element selected from the group consisting of.

12. The process according to claim 1 or 2, wherein a step of forming a layer of dielectric material precedes step c) of bonding, on the donor layer (12) and / or on the front face (21) of the support substrate (20). **Claim 13** The process according to claim 1 or 2, wherein step c) of bonding comprises a molecular bond.

Images