Process for fabricating a piezoelectric or semiconductor structure
Patent Information
- Application Number
- EP2023750656
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-07-07
- Filing Date
- 2023-07-07
- Publication Date
- 2025-05-14
AI Technical Summary
The manufacturing process of semiconductor or piezoelectric structures often results in bonding imperfections, such as 'edge bonding voids,' due to differences in thermal expansion coefficients and surface roughness, which can lead to deformation and reduced quality of the final multilayer structure.
A method involving mechanical-chemical polishing and peripheral material removal using an ion beam to improve surface flatness, combined with the formation of a weakening zone by hydrogen or helium implantation, ensures better bonding between donor and recipient substrates, minimizing thermal deformation and voids.
This approach enhances the quality of bonding, reducing the occurrence of voids and improving the mechanical and thermal stability of the multilayer structure by ensuring precise surface flatness and controlled material transfer.
Smart Images
Figure 1.1
Abstract
Description
[0001] DESCRIPTION
[0002] TITLE: Method of manufacturing a semiconductor or piezoelectric structure
[0003] TECHNICAL FIELD
[0004] The invention relates to a method of manufacturing a semiconductor or piezoelectric structure.
[0005] STATE OF THE ART
[0006] The transfer of an active layer, i.e. intended for the formation of components for electronic, optical or optoelectronic devices, onto a support substrate via an electrically insulating layer, is widely used in the microelectronics industry.
[0007] In some situations, the active layer is obtained by thinning a donor substrate, said thinning being achieved by material removal, such as grinding. To improve the surface condition of the active layer before bonding, it is generally necessary to carry out chemical mechanical polishing (CMP).
[0008] This is the case in particular for the manufacture of a radiofrequency (RF) device, such as a resonator or filter, on a substrate successively comprising, from its base towards its surface, a support substrate, generally made of a semiconductor material such as silicon, an electrically insulating layer and a piezoelectric layer.
[0009] The piezoelectric layer is typically obtained by transferring a thick substrate made of piezoelectric material onto a supporting substrate.
[0010] Transferring the piezoelectric layer involves bonding the thick piezoelectric substrate to the support substrate, followed by thinning the thick piezoelectric substrate, so that only a thin piezoelectric layer of the desired thickness for RF device fabrication is left on the support substrate.
[0011] For good adhesion of the piezoelectric substrate to the support substrate, an oxide layer (for example, a silicon oxide) is generally formed on each of the two substrates, and said substrates are bonded via said oxide layers. The oxide layer formed on the surface of the support substrate can be formed by thermal oxidation. For example, if it is a silicon substrate, a silicon oxide layer can be formed. However, thermal oxidation has several disadvantages. It may be incompatible with certain materials, for example, with charge trapping layers made of polycrystalline silicon. In addition, thermal oxidation generates oxide layers that do not allow good diffusion, for example, of lithium or hydrogen.
[0012] Thus, the deposition of an oxide layer by PECVD is often preferred to thermal oxidation. The oxide layer can then be polished, for example by chemical-mechanical polishing.
[0013] To strengthen the oxide-oxide bond between the piezoelectric substrate and the support substrate, it is known to carry out, after bonding, a consolidation annealing. Said consolidation annealing is typically carried out at a temperature between 100 °C and 300 °C.
[0014] However, since the piezoelectric material and the support substrate material have very different thermal expansion coefficients, the implementation of such annealing can cause significant deformation of the assembly.
[0015] To overcome this type of problem, it is known to use a pseudo-donor substrate, i.e. a heterostructure in which the piezoelectric substrate is bonded to a handling substrate (“handle substrate” in English).
[0016] The manufacturing process of the pseudo-donor substrate generally comprises several steps. Thus, a layer of thick piezoelectric material is bonded to the handling substrate. Then, the layer of piezoelectric material is thinned and possibly trimmed. Finally, the free surface of the thinned layer of piezoelectric material is polished, for example in a chemical-mechanical polishing (CMP) process and possibly covered with a thin layer of oxide so as to achieve the oxide-oxide bonding described above.
[0017] After bonding said donor pseudo-substrate and the support substrate, the piezoelectric substrate is held between the handling substrate and the support substrate. The choice of materials and thicknesses of the handling substrate and the support substrate makes it possible to ensure a certain symmetry of the thermal expansion coefficients, and thus to minimize the deformation of the assembly during the application of heat treatments. However, when implementing such a method for manufacturing a piezoelectric-on-insulator type structure, the applicants observe bonding imperfections between the donor pseudo-substrate and the support substrate, in the form of holes, called "edge bonding voids" in English, in which bonding does not occur at the periphery of the substrates.
[0018] BRIEF DESCRIPTION OF THE INVENTION
[0019] An aim of the invention is to improve, during the manufacture of an active layer on insulator type structure, the bonding process between a donor substrate and a receiving substrate, the surface to be bonded of the donor substrate and / or the surface to be bonded of the receiving substrate having been polished prior to said bonding.
[0020] To this end, the invention proposes a method for manufacturing a semiconductor or piezoelectric structure, comprising the following successive steps:
[0021] (a) providing a donor substrate comprising a semiconductor or piezoelectric layer,
[0022] (b) providing a receiving substrate,
[0023] (c) treatment of a free surface of the donor substrate and / or a free surface of the recipient substrate,
[0024] (d) bonding the donor substrate to the recipient substrate, said at least one treated surface being at the interface between the donor substrate and the recipient substrate, and
[0025] (e) transfer of a portion of the semiconductor or piezoelectric layer (5) from the donor substrate to the receiving substrate, the treatment of the free surface of the donor substrate and / or of the free surface of the receiving substrate comprising the following successive steps:
[0026] (c1) chemical-mechanical polishing,
[0027] (c2) material removal in a peripheral region of the polished surface.
[0028] The removal of material in a peripheral region of the surface to be bonded of one and / or the other of the substrates which has been previously polished, makes it possible to improve the flatness of said surface prior to bonding so that the quality of the bonding is improved.
[0029] According to other optional features of the invention taken alone or in combination when technically possible:
[0030] - at the end of the step of chemical-mechanical polishing of the donor substrate and / or the recipient substrate (c1), the polished surface has a relief at the periphery of said substrate, so that the step of removing material (c2) in the peripheral region of said surface is carried out to flatten said relief,
[0031] - the removal of peripheral material is carried out by abrasion by an ion beam focused on an area of the periphery of the polished semiconductor or piezoelectric layer, the ion beam scanning the entire periphery of said periphery,
[0032] - the removal of peripheral material is carried out after recording the topographic profile of the polished surface by profilometry and implemented so that the modified profile after removal of material has only one maximum and that said maximum is the most central point of the polished surface of the modified profile,
[0033] - the portion of the semiconductor or piezoelectric layer of the donor substrate to be transferred to the receiving substrate is delimited by forming a weakening zone prior to bonding (d) of the donor substrate to the receiving substrate, so that the transfer of said portion to the receiving substrate comprises the detachment of the donor substrate along the weakening zone,
[0034] - the weakening zone in the donor substrate is formed by implantation of hydrogen and / or helium,
[0035] - the donor substrate comprises a piezoelectric layer, the surface of the donor substrate to be treated and bonded being a free surface of the piezoelectric layer and the portion of the transferred donor substrate being a portion of the piezoelectric layer,
[0036] - the supply of the donor substrate includes the following successive steps:
[0037] (a1) bonding a thick piezoelectric layer onto a handling substrate,
[0038] (a2) thinning the thick piezoelectric layer by its face opposite the handling substrate, so that the chemical-mechanical polishing (c1) is carried out on the free surface of the thinned piezoelectric layer, opposite the handling substrate,
[0039] - the thick piezoelectric layer has a thickness of between 100 pm and 2 mm, preferably a thickness of between 200 pm and 1 mm and in that the thinned and polished piezoelectric layer has a thickness of between 1 pm and 100 pm, preferably a thickness of between 5 pm and 50 pm,
[0040] - the provision of the donor substrate further comprises a step (a3) of removing a peripheral portion of the donor substrate prior to the chemical-mechanical polishing (c1) of the free surface of the thinned piezoelectric layer,
[0041] - the donor substrate comprises a semiconductor layer, the surface of the donor substrate to be treated and bonded being a free surface of the semiconductor layer and the portion of the transferred donor substrate being a portion of the semiconductor layer,
[0042] - the method further comprises a step of forming an oxide layer on the free surface of the piezoelectric or semi-conductor layer, so that the bonding (d) of the donor substrate to the recipient substrate is carried out via said oxide layer,
[0043] - the oxide layer formed on the surface of the polished piezoelectric or semiconductor layer has a thickness of between 10 nm and 10 pm, preferably a thickness of between 30 nm and 5 pm,
[0044] - step (c) comprises a treatment of the free surface of the piezoelectric or semi-conductor layer of the donor substrate and in which the formation of the oxide layer on said free surface is carried out after said treatment step (c) and prior to bonding (d),
[0045] - the provision of the receiving substrate (b) comprises the formation of an electrically insulating layer, preferably an oxide layer, the surface of the receiving substrate to be treated and bonded being a surface free of the electrically insulating layer,
[0046] - the electrically insulating layer formed on the surface of the receiving substrate has a thickness of between 10 nm and 10 pm, preferably a thickness of between 30 nm and 5 pm,
[0047] - the electrically insulating layer is formed by plasma-enhanced chemical vapor deposition (PECVD),
[0048] - the material removal step (c2) is carried out on the entire polished surface of the receiving substrate,
[0049] - the quantity of material to be removed locally from the surface of the electrically insulating layer during the step of removing material from the surface of said electrically insulating layer is determined from thickness measurements of said electrically insulating layer by ellipsometry and / or reflectometry.
[0050] BRIEF DESCRIPTION OF THE FIGURES
[0051] Other characteristics and advantages of the invention will emerge from the detailed description which follows, with reference to the appended drawings, in which:
[0052] - figure 1 represents a sectional view of a multilayer structure of the piezoelectric type on insulator prepared according to an embodiment of the method according to the invention comprising the bonding of a donor substrate on a receiving substrate,
[0053] - Figure 2 represents a sectional view of the donor substrate,
[0054] - Figure 3 represents a sectional view of a step in the preparation of the donor substrate comprising the bonding of a thick piezoelectric layer on a handling substrate,
[0055] - Figure 4 represents a sectional view of a step in the preparation of the donor substrate comprising the thinning of the thick piezoelectric layer bonded to the handling substrate, - Figure 5 represents the peripheral relief observed on the surface of the thinned piezoelectric layer opposite the handling substrate after an additional step of chemical-mechanical polishing,
[0056] - figure 6 represents a sectional view of the receiving substrate,
[0057] - figure 7 represents a sectional view of a step in the preparation of the receiving substrate comprising the bonding of an electrically insulating layer on a support substrate,
[0058] - Figure 8 shows a sectional view of the formation of a weakening zone in the thinned piezoelectric layer of the donor substrate,
[0059] - figure 9 represents a sectional view of the bonding of the donor substrate to the recipient substrate,
[0060] - Figure 10 represents a sectional view of the formation of a weakening zone in the thinned piezoelectric layer of the donor substrate, the donor substrate further comprising an oxide layer previously formed on the free surface, possibly polished and flattened, of the thinned piezoelectric layer,
[0061] - Figure 11 represents a sectional view of the bonding of the donor substrate to the receiving substrate, the donor substrate when the donor substrate further comprises the oxide layer on the thinned piezoelectric layer on the side opposite the handling substrate.
[0062] For readability reasons, the drawings are not necessarily drawn to scale.
[0063] DETAILED DESCRIPTION OF EMBODIMENTS
[0064] The invention relates to a method of manufacturing multilayer components comprising transferring an active layer from a donor substrate to a recipient substrate.
[0065] To improve the bonding quality between the donor substrate and the receiving substrate during the implementation of said transfer, it may be beneficial to carry out, prior to said bonding, a chemical-mechanical polishing of at least one of the two surfaces forming the bonding interface if the roughness of said surface is too great to induce good bonding. This is for example the case if one of the bonding surfaces was formed during the thinning of a layer by grinding. However, the multilayer structures resulting from such a process have numerous holes at their periphery, at the level of their bonding interface, which reduce the quality of the bonding between the transferred active layer and the receiving substrate. The inventors have observed that, during the manufacture of such multilayer structures, microdrops of condensation water remain blocked at the periphery of the substrates, at the time of bonding of said substrates, at the limit of the propagation of the bonding wave.The inventors suspect that these microdrops of condensation cause the holes visible in the final multilayer structures.
[0066] The inventors also observed that the free surfaces of the substrates that have been polished by chemical-mechanical polishing have a relief, in the form of an excess thickness, on their periphery. The inventors propose that it is this peripheral relief that blocks the condensation water on the periphery of the substrates during their bonding, which generates the holes observed in the final multilayer structure.
[0067] In this respect, the invention relates to a method for manufacturing a multilayer structure comprising the transfer of an active layer from a donor substrate onto a receiving substrate, at least one of the two bonding interfaces having been polished prior to bonding the two substrates, the method further comprising a step of removing peripheral material on at least one of the two polished surfaces.
[0068] In the following, a particular embodiment of the invention is described, in which a multilayer structure of the piezoelectric type on insulator 10 is prepared, shown in FIG. 1, the structure successively comprising, from its rear face to its front face:
[0069] - a support substrate 1,
[0070] - an electrically insulating layer 2, preferably an oxide layer,
[0071] - a piezoelectric layer 3.
[0072] For example, the piezoelectric layer 3 is made of a material such as lithium tantalate (LiTaOs), lithium niobate (LiNbOs), barium titanate (BaTiOs) and / or lead zirconate titano (PZT). The piezoelectric layer 3 has a thickness of between 50 nm and 20 pm, preferably a thickness of between 100 nm and 10 pm.
[0073] The electrically insulating layer 2 may comprise an oxide, a nitride and / or a silicon carbide (SiO x , SiO x N y , If N x , SiC x , SiO x C y), x and y being real numbers between 0 and 2, and / or polymers. The electrically insulating layer has a thickness between 10 nm and 10 pm, preferably a thickness between 30 nm and 5 pm. Finally, the support substrate 1 is for example a substrate of silicon (Si), sapphire, alumina (AI2O3), aluminum nitride (AIN), glass, quartz, mullite, molybdenum (Mo), tungsten (W), indium phosphide (InP), gallium arsenide (GaAs) and / or silicon carbide (SiC). The support substrate 1 has a thickness between 10 pm and 2 mm, preferably a thickness between 200 pm and 1 mm.
[0074] Such piezoelectric-on-insulator structures 10 find applications in the field of radiofrequency components and filters.
[0075] In this particular embodiment, the method according to the invention comprises the provision of a donor substrate 11 comprising a piezoelectric layer to be transferred 3, the provision of a receiver substrate 12 comprising the support substrate 1 and the electrically insulating layer 2, and the transfer of the piezoelectric layer to be transferred 3 from the donor substrate 11 onto the receiver substrate 12, the electrically insulating layer 2 being at the bonding interface (see figure 9).
[0076] According to this embodiment, the donor substrate 11 shown in FIG. 2 is a heterostructure commonly referred to as a pseudo-donor substrate which comprises, from its rear face to its front face:
[0077] - a handling substrate 4,
[0078] - a thinned piezoelectric layer 5 in which the piezoelectric layer to be transferred 3 onto the receiving substrate 12 will be delimited,
[0079] - optionally, an electrically insulating layer 6, preferably an oxide layer.
[0080] The piezoelectric material of the piezoelectric layer 3 and the material of the support substrate 1 have very different thermal expansion coefficients. Deposition of a layer of piezoelectric material without a handling substrate on the support substrate, with an electrically insulating layer at the interface, would expose the resulting multilayer structure to significant deformations when carrying out thermal annealing, for example to strengthen the bonding interface between the layer of piezoelectric material and the support substrate.
[0081] The handling substrate 4 is therefore manufactured from a material whose coefficient of thermal expansion is close to that of the material of the support substrate 1 onto which the piezoelectric layer 3 is intended to be transferred. By close, we mean a difference in coefficient of thermal expansion between the material of the handling substrate 4 and the material of the support substrate 1 less than or equal to 5%, and preferably equal to or close to 0%. Suitable materials are for example silicon, sapphire, polycrystalline aluminum nitride, or gallium arsenide. Preferably, the handling substrate 4 is manufactured from the same material as the support substrate 1. In the present invention, we are interested in the coefficient of thermal expansion in a plane parallel to the main surface of the substrates.The handling substrate 4 has a thickness of between 100 μm and 2 mm, preferably a thickness of between 200 μm and 1 mm. Preferably, the handling substrate 4 has a thickness close to that of the support substrate 1, so that the structure obtained after bonding the donor substrate 11 to the receiving substrate 12 is as symmetrical and balanced as possible in terms of mechanical and thermal behavior. A coefficient of thermal expansion and a thickness of the handling substrate 4 close respectively to the coefficient of thermal expansion and the thickness of the support substrate 1 make it possible to minimize the stresses on the multilayer structure and its deformation under the effect of temperature variations.
[0082] The electrically insulating layer 6 is for example a layer of silicon oxide, nitride and / or carbide (SiO x , SiO x N y , SiN x , SiCx , SiO x C y ), x and y being real numbers between 0 and 2, and / or a polymer. The electrically insulating layer 6 has a thickness between 10 nm and 10 pm, preferably a thickness between 30 nm and 5 pm.
[0083] Supply of the donor substrate and possible treatments of a free surface of the donor substrate
[0084] As shown in Figure 3, the formation of the donor substrate 11 comprises bonding a thick piezoelectric layer 8 to a handling substrate 4.
[0085] The thick piezoelectric layer 8 has a thickness of between 100 pm and 2 mm, preferably a thickness of between 200 pm and 1 mm. The thick piezoelectric layer 8 is formed from the piezoelectric material which constitutes the piezoelectric layer 3 in the final piezoelectric-on-insulator structure 10. The thick piezoelectric layer 8 may therefore comprise LiTaOs, LiNbOs, BaTiOs and / or PZT.
[0086] The bonding of the thick piezoelectric layer 8 to the handling substrate 4 is for example carried out using a photopolymerizable adhesive layer previously deposited on an exposed face of the handling substrate 4 or of the thick piezoelectric layer 8. The deposition of the photopolymerizable adhesive layer is advantageously carried out by centrifugal coating, or "spin coating" according to the English terminology. Bonding by a photopolymerizable adhesive layer has the advantage of comprising fewer manufacturing steps than molecular bonding. In addition, the polymer, initially liquid, will fill the flatness defects and partially compensate for the edge fall due to the chamfering of the substrates. Bonding by a photopolymerizable adhesive layer therefore makes it possible to bond the substrates closer to their periphery than molecular bonding.
[0087] Alternatively, the bonding of the thick piezoelectric layer 8 to the handling substrate 4 is carried out by molecular bonding, by bonding by molecular abrasion under ultra-high vacuum or by metal / metal bonding by thermocompression.
[0088] After bonding the thick piezoelectric layer 8 to the handling substrate 4, the thick piezoelectric layer 8 is thinned by its face opposite the handling substrate, as shown in FIG. 4, so that the thinned piezoelectric layer 5 has a thickness of between 1 μm and 100 μm, preferably a thickness of between 5 μm and 50 μm.
[0089] The thinning of the thick piezoelectric layer 8 is for example carried out by coarse grinding, which makes it possible to quickly reduce the thickness of the donor substrate 11. Then, finer grinding can be carried out to continue to reduce the thickness of the donor substrate 11, but by reducing the roughness of the surface of said donor substrate 11.
[0090] Finally, chemical mechanical polishing (CMP) is carried out to smooth the free surface 7 of the thinned piezoelectric layer 5 opposite the handling substrate 4, so as to achieve the desired roughness for bonding the donor pseudo-substrate 11 to the support substrate 12 and thus improve the bonding quality.
[0091] Prior to the chemical-mechanical polishing, the method may further comprise a step of trimming the piezoelectric layer 8, 5. The trimming step may be carried out before, during (for example between two grinding operations of different finenesses) or after the step of thinning the piezoelectric layer 8, 5. The trimming comprises a removal of peripheral material over at least the thickness of the piezoelectric layer 8, 5.
[0092] The thick piezoelectric layer 8 has a peripheral chamfer C on each of its main faces (not shown in the figures). The objective of the trimming step is to remove the sharp angle generated by the thinning of the donor substrate 11 at the chamfer when the thickness e of the thinned piezoelectric layer 5 is less than the thickness of the chamfer C of the thinned piezoelectric layer 5 and to generate a right (or obtuse) angle. Indeed, such a sharp angle is likely to break during handling of the donor substrate 11, to generate flaking and to pollute the manufacturing line with debris.
[0093] The trimming can be carried out using an abrasive wheel, for example a diamond wheel, driven in rotation around a Y axis, the donor substrate 11 itself being fixed on a support driven in rotation around an X axis, the Y axis being able to be parallel or perpendicular to the X axis.
[0094] Whatever the technique used, trimming can generate defects that chemical-mechanical polishing will partially resolve.
[0095] The chemical-mechanical polishing makes it possible to obtain a free surface 7 of the thinned piezoelectric layer 5 having a roughness compatible with bonding to the receiving substrate 12. However, at the end of such a chemical-mechanical polishing step, the inventors noticed that the polished surface 7 of the thinned piezoelectric layer 5 has a peripheral relief. Figure 5 reports a profilometric analysis of the surface 7. The profilometric analysis is carried out using a tip whose vertical displacement is recorded during the scanning of the surface 7, so as to obtain the topographic profile of the surface along the path followed by the tip. The profilometry of the surface 7 therefore makes it possible to highlight the previously mentioned peripheral relief (black square in Figure 5).
[0096] The more the profiles deviate from flatness, the more negative the impact on bonding. The method according to the invention therefore comprises a removal of material in the peripheral region of said surface.
[0097] The step of removing material in the peripheral region of the polished surface 7 of the thinned piezoelectric layer 5 is preferably carried out so as to flatten the peripheral relief formed during the chemical-mechanical polishing step. The objective is to prevent, during bonding to the receiving substrate 12, said relief from blocking the condensation water and preventing its elimination under the effect of the propagation of the bonding wave.
[0098] The inventors observe that the peripheral relief can reach several micrometers in thickness and several millimeters in width and that the dimensions of said relief depend on the grinding parameters (such as the rotational speeds of the grinding wheel and the grinding plate, the descent speed and the inclination of the grinding wheel) and the chemical-mechanical polishing parameters (such as the distribution of the pressure applied to the plates, the hydrodynamics of the colloidal mixture used, the relative rotational speed of the polishing head and the plate). It proves very difficult to decorrelate the effect of each of these parameters on the characteristics of the resulting peripheral relief and therefore to identify parameter values that do not lead to the formation of such a relief.The removal of peripheral material according to the invention provides a solution external to the thinning and polishing process which makes it possible to remove the peripheral relief whatever the grinding and chemical-mechanical polishing parameters used.
[0099] The removal of peripheral material can be carried out by abrasion by an ion beam focused on an area of the periphery of the surface 7 of the thinned and polished piezoelectric layer 5, the ion beam scanning the entirety of said periphery. When implementing ion beam abrasion, several parameters can be adjusted, such as the beam width, the angle of incidence, the current (corresponding to the flow of ions constituting the beam), the scanning speed (defining the time during which an area of the surface is located under the beam) and the abrasion speed (corresponding to the material removal speed), in order to very precisely control said removal of peripheral material. It is indeed possible to modulate the abrasion speed down to very low values (of the order of 10' 3 m 3 / s). The combined control of abrasion speed and scanning speed allows for nanometer-level surface profile accuracy.
[0100] Ion beam abrasion is a technique conventionally used to adjust the thickness of a piezoelectric substrate in order to improve its performance. The invention proposes to use this technique to rectify the topology of the substrate surface and improve its flatness. Ion beam abrasion has the advantage of allowing the surface profile to be corrected with sufficient precision to avoid excessive material removal and the formation of a hollow. Indeed, such a hollow would also affect the bonding quality between the donor substrate and the recipient substrate by increasing the width of the peripheral surface on which the substrates are not correctly bonded, a surface which is conventionally formed when bonding two substrates, in particular because of the chamfers that the two substrates have.
[0101] In practice, the topographic profile is recorded beforehand by profilometry. Then, the thickness to be removed is determined so that the modified profile has only one maximum, therefore a point of zero derivative, and that this point is the most central point of the substrate (rightmost point of the profiles in Figure 5). Finally, optionally, the formation of the donor substrate 11 shown in Figure 2 further comprises a step of forming the electrically insulating layer 6 on the free surface 7 of the thinned piezoelectric layer 5, on the side opposite the handling substrate 4. In the case where chemical-mechanical polishing has been carried out followed by removal of a peripheral portion of said surface 7, the electrically insulating layer 6 is preferably formed after these treatments on the thinned piezoelectric layer 5, polished and flattened.
[0102] The electrically insulating layer 6 is preferably formed by plasma-enhanced chemical vapor deposition (PECVD) or by physical vapor deposition (PVD).
[0103] According to an alternative embodiment of the invention not developed here, the donor substrate comprises a semiconductor layer, the surface of the donor substrate to be treated (by chemical-mechanical polishing and by peripheral removal of material) and to be bonded being a free surface of the semiconductor layer and the portion of the donor substrate transferred being a portion of the semiconductor layer. In this embodiment also, the abrasion by laser beam ensures peripheral material removal with very high precision.
[0104] According to this embodiment also, an oxide layer can be formed on the free surface of the semiconductor layer, said layer possibly having been previously treated by chemical-mechanical polishing and removal of peripheral material.
[0105] According to this embodiment, the method makes it possible to obtain a multilayer structure of the semiconductor on insulator type by transferring the semiconductor layer onto a receiving substrate such as the substrate 12
[0106] Supply of a receiving substrate and possible treatments of the free surface of the receiving substrate.
[0107] According to the embodiment detailed here, the receiving substrate 12 shown in FIG. 6 comprises, from its rear face to its front face:
[0108] - a support substrate which forms the support substrate 1 in the final piezoelectric-on-insulator type structure 10,
[0109] - an electrically insulating layer which forms the electrically insulating layer 2 in the final piezoelectric-on-insulator structure 10. The support substrate 1 is therefore made of a material such as silicon (Si), sapphire, alumina (AI2O3), aluminum nitride (AIN), glass, quartz, mullite, molybdenum (Mo), tungsten (W), indium phosphide (InP), gallium arsenide (GaAs) and / or silicon carbide (SiC). The support substrate 1 has a thickness of between 10 pm and 2 mm, preferably a thickness of between 200 pm and 1 mm.
[0110] The electrically insulating layer 2 comprises, for example, an oxide, a nitride and / or a silicon carbide (SiO x , SiO x N y , SiN x , SiC x , SiO x C y), x and y being real numbers between 0 and 2, and / or a polymer. The electrically insulating layer 2 of the receiving substrate has a thickness between 10 nm and 10 pm, preferably a thickness between 30 nm and 5 pm.
[0111] The provision of the receiving substrate 12 comprises the formation of the electrically insulating layer 2 on a free surface of the support substrate 1, so as to obtain the receiving substrate 12. The electrically insulating layer 2 is preferably formed by plasma-enhanced chemical vapor deposition (PECVD). A representation of such deposition is given in FIG. 7. The PECVD process generates significant non-uniformity and roughness that are incompatible with good quality bonding. Furthermore, even if other deposition processes can provide better results in terms of uniformity and roughness, excessive roughness of the electrically insulating layer can also originate from the free surface of the support substrate, for example when the support substrate comprises on its surface a layer of polycrystalline silicon that has not been planarized.
[0112] A chemical-mechanical polishing of the free surface 9 of the electrically insulating layer 2 opposite the support substrate 1 is therefore carried out.
[0113] In this case also, the inventors observe the formation of a peripheral relief on the free surface 9 of the electrically insulating layer 2 at the end of the polishing, said relief being able to reach several hundred nanometers in thickness and several millimeters in width. The inventors further note that these dimensions vary according to the parameters used for implementing the chemical-mechanical polishing, such as the hydrodynamics of the colloidal mixture used, the distribution of the pressure applied to the plates and the relative rotation speed of the head and the chemical-mechanical polishing plate. The method according to the invention therefore comprises, in addition to the chemical-mechanical polishing, a removal of material in the peripheral region. The removal of material in the peripheral region of said surface is preferably carried out to flatten said relief, regardless of the parameters used for implementing the chemical-mechanical polishing.
[0114] Just as previously described, the removal of peripheral material is preferably carried out by abrasion by an ion beam focused on an area of the periphery of the polished surface 9 of the electrically insulating layer 2, the ion beam scanning the entirety of said periphery. In practice, in the same way as for carrying out the flattening of the surface 7 of the thinned and polished piezoelectric layer 5, a topographic profile of the polished surface 9 of the electrically insulating layer 2 is previously recorded by profilometry. Then, the thickness to be removed is determined so that the modified profile has only one maximum, therefore a point of zero derivative, and that this point is the most central point of the substrate.
[0115] Optionally, the removal step is carried out on the entire polished surface 9 of the receiving substrate 12, so as to improve the uniformity of the electrically insulating layer 2. In this case, the quantity of material to be removed locally on the surface 9 of the electrically insulating layer 2 during the step of removing material on said surface 9 can be determined from measurements of the local thickness of said electrically insulating layer 2 by ellipsometry and / or reflectometry.
[0116] Transfer of a portion of the donor substrate to the recipient substrate
[0117] In the following, a portion 3 of the thinned piezoelectric layer 5 is transferred from the donor substrate 11 to the receiving substrate 12.
[0118] For example, the transfer may comprise the formation of a weakening zone in the thinned piezoelectric layer 5, so as to delimit the piezoelectric layer to be transferred 3, the bonding of the donor substrate 11 to the receiving substrate 12, the piezoelectric layer to be transferred 3 being at the bonding interface, and the detachment of the donor substrate 11 along the weakening zone.
[0119] According to a preferred embodiment shown in Figure 8, the weakening zone is formed by implantation of atomic species in the thinned piezoelectric layer 5, the implantation (arrows in Figure 8) being carried out through the free surface 7 of said layer 5. The atomic species are implanted at a determined depth, this depth fixing the thickness of the piezoelectric layer to be transferred 3. The implanted atomic species are preferably hydrogen and / or helium.Subsequently, the bonding of the donor substrate 11 to the receiving substrate 12 as illustrated in FIG. 9, is carried out between the free surface 7 of the thinned piezoelectric layer 5 having been exposed to the implantation and the free surface 9 of the electrically insulating layer 2 of the receiving substrate 12, at least one of the two bonding surfaces 7, 9 having previously undergone the surface treatment previously described, said treatment comprising a chemical-mechanical polishing followed by a peripheral removal of material.
[0120] The bonding of the donor substrate 11 to the receiving substrate 12 is preferably carried out by molecular adhesion, because it makes it possible to obtain a bond that is strong and mechanically stable at a temperature above 400°C. Such bonding properties are particularly useful when the transfer of the portion 3 of the thinned piezoelectric layer 5 of the donor substrate 11 to the receiving substrate 12 is carried out according to the Smart Cut™ process (which comprises the formation of a weakening zone by implantation of atomic species). Indeed, the Smart Cut™ process generates defects in the substrate that can be healed by high-temperature thermal annealing. Such bonding properties are not achievable by bonding with a polymer or by metal / metal bonding. The vast majority of polymers are completely degraded above 300°C.Metal / metal bonding evolves with temperature (increase in grain size) and most of the time leads to deformation of the substrate, not to mention the diffusion of metal atoms in the layers which disrupts the electrical properties of the initial stack.
[0121] Molecular bonding requires an extremely flat surface because any lack of flatness prevents the two substrates from coming into intimate contact and therefore the formation of a bonding defect which will subsequently cause a gap in the transferred surface. The invention therefore finds a particular advantage in this embodiment and in any embodiment where the bonding between the donor substrate and the recipient substrate is preferably implemented by molecular adhesion.
[0122] In this embodiment, at the time of bonding, the inventors do not observe the formation of microdrops of water at the end of the bonding wave, on the periphery of the substrates.
[0123] After bonding, the donor substrate 11 is detached along the weakening zone. The detachment along the weakening zone can be triggered by a mechanical action and / or an input of thermal energy. The final piezoelectric-on-insulator type structure 10 shown in FIG. 1 is then obtained, comprising, from the rear face to the front face, the support substrate 1, the electrically insulating layer 2 and the transferred piezoelectric layer 3.
[0124] In the case where an oxide layer 6 has been formed on the surface of the donor substrate 10, the implantation of the atomic species shown in FIG. 10 is carried out through the oxide layer 6 and the bonding shown in FIG. 11 is carried out between the free surface 13 of said oxide layer 6 and the free surface 9 of the electrically insulating layer 2 of the receiving substrate 12, so that the oxide layer 6 is transferred at the same time as the piezoelectric layer to be transferred 3. In this embodiment, the electrically insulating layer of the final structure comprises the oxide layer 6 formed on the donor substrate 11 prior to bonding.
[0125] The formation of an electrically insulating layer 6 on the surface of the donor substrate 11 therefore makes it possible to advantageously produce an oxide-oxide bond. In the case where a bond by molecular adhesion is implemented, the bond between two oxide layers can easily be reinforced, simply by bringing said bond to a temperature above 200°C. Furthermore, in an atmosphere having a non-zero hygrometry, the oxide layers make it possible to absorb the water naturally present on their surface and thus prevent this water from forming gas bubbles at the bonding interface when said bond is annealed above 200°C for its reinforcement.
[0126] Alternatively to the Smart Cut™ process described above, layer transfer can be achieved by thinning the donor substrate on its face opposite the face bonded to the support substrate, until the desired thickness for the first semiconductor layer is obtained. However, the Smart Cut™ process is preferred for the transfer of layers with a thickness of less than a micrometer.
[0127] A laser scanning defect detection analysis reveals that the final piezoelectric-on-insulator structure 10 comprises practically no holes between the piezoelectric layer 2 and the electrically insulating layer 3 at the periphery of said structure. When implementing molecular bonding in particular, any particle at the bonding interface generates a hole. Since the periphery is more sensitive to the presence of particles, the few holes still detected at the periphery following implementation of the method according to the invention are attributed, not to microdroplets of water at the end of the bonding wave at the time of bonding of the two layers (they are not observed), but to the presence of particles at the bonding interface.The inventors believe that it is the removal of peripheral material on the bonding surfaces that have undergone polishing that makes it possible to eliminate the relief generated at the edge during said polishing prior to bonding said surfaces, and that consequently, the condensation water is not retained at the periphery of the substrates during the propagation of the bonding wave, which prevents the formation of microdrops. The quality of the bonding is improved since the number of holes is much lower in the final structure.
[0128] The method according to the invention therefore makes it possible to improve the quality of bonding between two substrates in a method where the application of chemical-mechanical polishing of at least one of the two bonding surfaces was necessary prior to said bonding.
Claims
CLAIMS 1. Method for manufacturing a semiconductor or piezoelectric structure (10), comprising the following successive steps: (a) providing a donor substrate (11) comprising a semiconductor or piezoelectric layer (5), (b) providing a receiving substrate (12), (c) treatment of a free surface (7) of the donor substrate (11) and / or of a free surface (9) of the recipient substrate (12), (d) bonding the donor substrate (11) to the recipient substrate (12), said at least one treated surface (7, 9) being at the interface between the donor substrate (11) and the recipient substrate (12), and (e) transfer of a portion (3) of the semiconductor or piezoelectric layer (5) from the donor substrate (11) onto the receiving substrate (12), the treatment of the free surface (7) of the donor substrate (11) and / or of the free surface (9) of the receiving substrate (12) comprising the following successive steps: (c1) chemical-mechanical polishing, (c2) material removal in a peripheral region of the polished surface (7,9).
2. Method according to claim 1, in which, at the end of the step of chemical-mechanical polishing of the donor substrate (11) and / or of the recipient substrate (12) (c1), the polished surface (7, 9) has a relief at the periphery of said substrate (11, 12), so that the step of removing material (c2) in the peripheral region of said surface (7, 9) is carried out to flatten said relief.
3. Method according to one of claims 1 or 2, in which the removal of peripheral material is carried out by abrasion by an ion beam focused on an area of the periphery of the polished semiconductor or piezoelectric layer (5), the ion beam scanning the entirety of said periphery.
4. Method according to claim 1 to 3, in which the removal of peripheral material is carried out after recording the topographic profile of the polished surface (7,9) by profilometry and implemented so that the modified profile after removal of material has only one maximum and that said maximum is the most central point of the polished surface (7,9) of the modified profile.
5. Method according to one of claims 1 to 4, in which the portion (3) of the semiconductor or piezoelectric layer (5) of the donor substrate (11) to be transferred onto the receiving substrate (12) is delimited by the formation of a weakening zone beforehand. to the bonding (d) of the donor substrate (11) on the receiving substrate (12), so that the transfer of said portion (3) on the receiving substrate (12) comprises the detachment of the donor substrate (11) along the weakening zone.
6. The method of claim 5, wherein the weakening zone in the donor substrate (11) is formed by implantation of hydrogen and / or helium.
7. Method according to one of claims 1 to 6, in which the donor substrate (11) comprises a piezoelectric layer (5), the surface of the donor substrate to be treated and bonded being a free surface (7) of the piezoelectric layer (5) and the portion of the transferred donor substrate being a portion (3) of the piezoelectric layer (5).
8. Method according to claim 7, in which the provision of the donor substrate (11) comprises the following successive steps: (a1) bonding a thick piezoelectric layer (8) onto a handling substrate (4), (a2) thinning the thick piezoelectric layer (8) by its face opposite the handling substrate (4), so that the chemical-mechanical polishing (c1) is carried out on the free surface (7) of the thinned piezoelectric layer (5), opposite the handling substrate (4).
9. Method according to claim 8, characterized in that the thick piezoelectric layer (8) has a thickness of between 100 pm and 2 mm, preferably a thickness of between 200 pm and 1 mm and in that the thinned and polished piezoelectric layer (5) has a thickness of between 1 pm and 100 pm, preferably a thickness of between 5 pm and 50 pm.
10. Method according to one of claims 8 or 9, in which the provision of the donor substrate (11) further comprises a step (a3) of removing a peripheral portion of the donor substrate (11) prior to the chemical-mechanical polishing (c1) of the free surface (7) of the thinned piezoelectric layer (5).
11. Method according to one of claims 1 to 6, in which the donor substrate (11) comprises a semiconductor layer, the surface of the donor substrate to be treated and bonded being a free surface of the semiconductor layer and the portion of the donor substrate transferred being a portion of the semiconductor layer.
12. Method according to one of claims 7 to 11, characterized in that it further comprises a step of forming an electrically insulating layer (6) on the free surface of the piezoelectric (5) or semi-conductor layer, so that the bonding (d) of the substrate donor (11) on the receiving substrate (12) is produced via said electrically insulating layer (6).
13. Method according to claim 12, characterized in that the electrically insulating layer (6) formed on the surface of the polished piezoelectric or semiconductor layer (5) has a thickness of between 10 nm and 10 pm, preferably a thickness of between 30 nm and 5 pm.
14. Method according to one of claims 12 or 13, in which step (c) comprises a treatment of the free surface (7) of the piezoelectric (5) or semi-conductor layer of the donor substrate (11) and in which the formation of the electrically insulating layer (6) on said free surface (7) is carried out after said treatment step (c) and prior to bonding (d).
15. Method according to one of claims 1 to 14, in which the provision of the receiving substrate (12) (b) comprises the formation of an electrically insulating layer (2), preferably an oxide layer, the surface of the receiving substrate (12) to be treated and bonded being a free surface (9) of the electrically insulating layer (2).
16. Method according to claim 15, characterized in that the electrically insulating layer (2) formed on the surface of the receiving substrate (12) has a thickness of between 10 nm and 10 pm, preferably a thickness of between 30 nm and 5 pm.
17. Method according to one of claims 15 or 16, in which the electrically insulating layer (2) is formed by plasma-enhanced chemical vapor deposition (PECVD).
18. Method according to one of claims 15 to 17, in which the material removal step (c2) is carried out on the entire polished surface (9) of the receiving substrate (12).
19. Method according to claim 18, wherein the quantity of material to be removed locally at the surface of the electrically insulating layer (2) during the step of removing material at the surface (9) of said electrically insulating layer (2) is determined from thickness measurements of said electrically insulating layer (9) by ellipsometry and / or reflectometry.