Method for creating a stress state in a semiconductor layer

Abstract

Title: Method for Creating a Stress State in a Semiconductor Layer The invention relates to a method for creating a uniaxial stress state (C3, C3') in a semiconductor layer (13). Said method comprises: - Providing a stack comprising a support (10), the semiconductor layer (13), and an interposed fusible layer (11), - Forming a stress-donating layer (14) on the semiconductor layer (13), - Partially altering the stress-donating layer (14), modifying a first stress state (C1) of the layer (14) to obtain a second stress state (C2) in a single direction (y), - Melting the fusible layer (11f), such that the stress-donating layer (14) transfers the second stress state (C2, C2') into the semiconductor layer (13) by relaxation. Figure for the abstract: Fig. 7

Description

Title of the invention: Method for creating a stress state in a semiconductor layer technical field

[0001] The present invention relates to the field of microelectronics and, more particularly, to that of processes for mechanically deforming or constraining a semiconductor layer. A particular application concerns the fabrication of Complementary Metal-Oxide-Semiconductor (CMOS) transistors on a fully depleted silicon-on-insulator (FDSOI) substrate. STATE OF THE ART

[0002] In this area, it is desirable to increase the mobility of load carriers to achieve the best compromises between performance and energy consumption.

[0003] The mobility of electrons can typically be increased (respectively decreased) by a mechanical stress in tension (respectively in compression) of the semiconductor material in which they pass, whereas the mobility of holes can conversely be increased (respectively decreased) when the semiconductor is in compression (respectively in tension).

[0004] Thus, to improve transistor performance, their channel region can be made from a semiconductor material subjected to tensile or compressive mechanical stress. Typically, for N-type silicon channel transistors (where electrons are the majority carriers), the most favorable configurations are a biaxial tensile channel or a uniaxial tensile channel along the direction of electron transport if the uniaxial stress is greater than or equal to 1.4 GPa. For P-type silicon-germanium channel transistors (where holes are the majority carriers), the most favorable configuration is a uniaxial compressive channel along the direction of electron transport.

[0005] Document FR3120738 Al discloses an indirect method for modifying the stress state of a semiconductor layer. This method is based on the use of a fusible layer interposed between the semiconductor layer to be deformed and the substrate. A stress-donating layer is also deposited on the semiconductor layer to be deformed. A heat treatment is then performed to melt the fusible layer. The stress-donating layer then imposes a biaxial deformation on the semiconductor layer. This biaxial deformation of the The semiconductor layer remains after the fusible layer solidifies and the stress-donating layer is removed. To obtain uniaxial stress, the semiconductor layer is then typically cut into strips so that the stress relaxes along the width of the strips. Only the stress along the length of the strips remains.

[0006] This strip cutting process consumes material. This material loss results in a reduced integration density.

[0007] One objective of the present invention is to overcome the limitations of this known method.

[0008] In particular, an object of the present invention is to propose a method of realizing integration of a uniaxial stress state in a semiconductor layer, allowing for a higher integration density. SUMMARY

[0009] To achieve this objective, according to one embodiment, a method for creating a uniaxial stress state in a semiconductor layer is provided, said method comprising at least: • A supply of a stack comprising a substrate, the semiconductor layer and a so-called fusible layer interposed between the substrate and the semiconductor layer, • The formation of a stress-donating layer on the semiconductor layer, • A definition of patterns after formation of the stress-donating layer, • The formation, based on these patterns, of regions surrounded by trenches extending into the semiconductor layer, • A partial alteration of the stress donor layer at said regions, configured to modify a first stress state of said stress donor layer so as to obtain a second stress state primarily along a determined direction, • At least partial melting of the fusible layer, so that the stress-donating layer transfers at least in part, by relaxation, the second stress state into the semiconductor layer, so that the semiconductor layer exhibits a uniaxial stress state along said determined direction.

[0010] Thus, unlike the known process mentioned above, the transformation from an initial stress state, in this case the first stress state, which is typically a biaxial stress state, to a uniaxial stress state, in this case the second stress state, occurs prior to the melting of the fusible layer, upstream of the transfer of the stress state into the semiconductor layer. The stress state transferred from the stress-donating layer during melting is thus directly a uniaxial stress state. No further stress-modification steps are required in the semiconductor layer after this transfer. In particular, the material-intensive semiconductor layer cutting steps are eliminated.

[0011] Transferring a uniaxial stress state according to the invention also makes it possible to increase the thickness of a semiconductor layer free of crystal defects. In the known process, the transferred stress state is a biaxial stress state. For a given stress intensity, the critical thickness of the material (at which plastic stress relaxation occurs, generating crystal defects) is greater when the stress is uniaxial than when it is biaxial. Directly transferring a uniaxial stress state into the semiconductor layer thus makes it possible to obtain a crystal-defect-free semiconductor layer that is thicker than that achievable by the known process.

[0012] Furthermore, modifying the stress state upstream of the transfer offers more possibilities in terms of stress state engineering. The modification can typically be configured to produce a uniaxial compressive stress state or a uniaxial tensile stress state, which is no longer possible after transfer by simple cutting of the semiconductor layer as in the prior art.

[0013] The modification of the first stress state into a second uniaxial stress state is achieved by partial alteration of the stress-donating layer. This alteration can advantageously be carried out by conventional microelectronic steps, such as localized implantation or trench etching in the stress-donating layer.

[0014] Consequently, and advantageously, the method for achieving a uniaxial stress state in a semiconductor layer according to the present invention allows, in particular, for material savings and greater versatility compared to the previously described known method. By implementing the method according to the present invention, the integration density can be advantageously increased.

[0015] Another aspect of the invention relates to a method for manufacturing a transistor comprising implementing the method for creating a uniaxial stress state according to the invention. According to this manufacturing method, the transistor comprises a channel region formed in the semiconductor layer exhibiting the uniaxial stress state.

[0016] The other objects, features and advantages of the present invention will become apparent from an examination of the following description and accompanying drawings. It is understood that other advantages may be incorporated. BRIEF DESCRIPTION OF THE FIGURES

[0017] In particular, the aims, objects, features and advantages of the invention will become clearer from the detailed description of at least one embodiment thereof, which is illustrated by the following accompanying drawings in which:

[0018] [Fig.1] Fig.1 illustrates in cross-section a stacking according to an embodiment of the present invention.

[0019] [Fig.2] [Fig.2] illustrates in top view the stacking illustrated in [Fig.1], according to an embodiment of the present invention.

[0020] [Fig.3] The [Fig.3] illustrates in cross-section a process step (formation of isolation trenches and regions) according to an embodiment of the present invention.

[0021] [Fig.4] [Fig.4] illustrates in top view the process step (formation of isolation trenches and regions) illustrated in [Fig.3], according to an embodiment of the present invention.

[0022] [Fig.5] The [Fig.5] illustrates in cross-section a process step (formation of bands implanted in the stress donor layer) according to an embodiment of the present invention.

[0023] [Fig.6] The [Fig.6] illustrates in top view the process step (formation of bands implanted in the stress donor layer) illustrated in the [Fig.5], according to an embodiment of the present invention.

[0024] [Fig.7] The [Fig.7] illustrates in cross-section a process step (partial melting of the fusible layer) according to an embodiment of the present invention.

[0025] [Fig.8] [Fig.8] illustrates in top view the process step (partial melting of the fusible layer) illustrated in [Fig.7], according to an embodiment of the present invention.

[0026] [Fig.9] The [Fig.9] illustrates in cross-section a step of the process (removal of the stress-donating layer) according to an embodiment of the present invention.

[0027] [Fig. 10] [Fig. 10] illustrates in top view the process step (removal of the stress-donating layer) illustrated in [Fig. 9], according to an embodiment of the present invention.

[0028] [Fig. 11] The [Fig. 11] illustrates in cross-section a process step (formation of relaxation trenches in the stress donor layer) according to another embodiment of the present invention.

[0029] [Fig. 12] [Fig. 12] illustrates in top view the process step (formation of relaxation trenches in the stress donor layer) illustrated in [Fig. 11], according to another embodiment of the present invention.

[0030] [Fig. 13] The [Fig. 13] illustrates in cross-section a step of the process (filling the insulation trenches) according to another embodiment of the present invention.

[0031] [Fig. 14] [Fig. 14] illustrates in top view the process step (filling of the isolation trenches) illustrated in [Fig. 13], according to another embodiment of the present invention.

[0032] [Fig. 15] The [Fig. 15] illustrates in cross-section a process step (removal of the stress-donating layer) according to another embodiment of the present invention.

[0033] [Fig. 16] [Fig. 16] illustrates in top view the process step (removal of the stress-donating layer) illustrated in [Fig. 15], according to another embodiment of the present invention.

[0034] [Fig. 17] The [Fig. 17] illustrates the dependence of the deformation obtained in a 10 nm silicon film on 20 nm buried oxide on the Young's modulus and the stress of a 100 nm thick stress donor layer, according to an embodiment of the present invention.

[0035] The drawings are given by way of example and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications. In particular, the thicknesses of the different layers and the dimensions of the different patterns are illustrated by diagrams that are not representative of reality. DETAILED DESCRIPTION

[0036] Before proceeding to a detailed review of embodiments of the invention, optional features that may be used in combination or alternatively are listed below:

[0037] According to one example, the method further comprises filling the trenches to form isolation trenches after melting the fusible layer and before removing the stress-donating layer. This allows certain regions of the semiconductor layer to be confined between the isolation trenches to prevent relaxation, typically along the y-direction of uniaxial stress, of the semiconductor layer regions after removal of the stress-donating layer. This allows, for example, an increase in the uniaxial stress state. This allows, for example, limiting stress losses during the transfer of the stress state in the semiconductor layer.

[0038] According to one example, the partial alteration comprises the implantation of ions in a portion of the stress-donating layer, forming implanted bands oriented along the determined direction. These implanted bands extend over an entire dimension of the stress-donating layer along the determined direction. This implantation typically occurs through the entire thickness of the stress-donating layer. The width of the implanted bands is preferably less than or equal to half the thickness of the stress-donating layer. Typically, if the bands If the implanted bands aim to relax the stress-donating layer along the x-direction, their x-width is preferably chosen to be as small as possible (this minimum width is typically determined by the resolution of the lithography equipment used to create the mask defining the bands to be implanted). If the implanted bands aim to induce a uniaxial compression state along the y-direction in the stress-donating layer, their x-width can be chosen to be on the order of half the thickness of the stress-donating layer, or even on the order of one-third of its thickness. The y-length of the implanted bands is typically much greater, i.e., at least ten times greater, than the thickness of the stress-donating layer. This limits or prevents relaxation of the stress-donating layer along the y-direction.

[0039] According to one example, the regions have a dimension along the determined direction significantly greater than the thickness of the stress-donating layer, typically at least six times greater than the thickness of the stress-donating layer. This allows for optimization of the uniaxial stress transfer along the determined direction in the semiconductor layer.

[0040] According to one example, the implanted ions are argon-based. The stress state of the stress-donating layer is thus modified without exposing the underlying semiconductor layer. The semiconductor layer therefore remains protected from other process steps, typically during the formation, filling, and planarization of the insulation trenches.

[0041] According to one example, the first stress state is substantially zero and the second stress state corresponds to uniaxial compression. The stress-donating layer can be initially relaxed, before alteration. Implanting argon in strips oriented along the determined direction typically makes it possible to generate such uniaxial compression in a stress-donating layer based on SiN, for example.

[0042] According to one example, the first stress state corresponds to biaxial tension and the second stress state corresponds to uniaxial tension. The stress-donating layer, for example, based on SiN, may initially be in biaxial tension before alteration. Implanting argon in bands oriented along the determined direction typically relaxes the stress in these bands. The stress-donating layer then exhibits relaxed bands and a residual stress state of uniaxial tension between the relaxed bands.

[0043] According to one example, the partial alteration includes the formation of relaxation trenches in the stress-donating layer, oriented along the determined direction. It is thus possible to transition from a state of biaxial stress to a state of uniaxial stress by forming relaxation trenches in the stress-donating layer, preferably along the entire thickness of the stress-donating layer.

[0044] According to one example, the relaxation trenches are separated by strips of stress donor layer having a width approximately equal to half the thickness of the stress donor layer.

[0045] According to one example, partial alteration includes the formation of relaxation trenches in the stress-donating layer in some regions, and the implantation of ions in bands of the stress-donating layer in other regions. The two types of partial alteration can thus coexist in different regions of the same plate or wafer.

[0046] In one example, the stack comprises an insulating layer between the semiconductor layer and the fusible layer. In another example, the insulating layer is silica-based. It preferably has a thickness between 10 nm and 25 nm. This architecture typically corresponds to FDSOI technology. The low stiffness of silica, which has a Young's modulus E on the order of 50 GPa, and the limited thickness facilitate the transmission of a stress state between the stress-donating layer and the semiconductor layer.

[0047] According to one example, the stress-donating layer is silicon nitride-based. This material has the advantage of being UV-transparent within a wavelength range suitable for melting the fusible layer. It can also be advantageously used for filling insulation trenches, typically shallow trench insulation (STI) trenches implemented for lateral insulation in FDSOI technology. The steps of filling the insulation trenches and depositing the stress-donating layer can thus be carried out simultaneously, at least partially. This reduces the number of steps and the cost of the process.

[0048] According to a preferred embodiment, the melting is carried out by thermal annealing of the rapid thermal annealing type, typically over the entire extent of the fusible layer, i.e., over the entire wafer. The use of rapid thermal annealing allows for collective heating of the regions formed in the semiconductor layer, regardless of the dimensions of said regions. According to another example, this thermal annealing is carried out using a nanosecond laser, typically by scanning the wafer with the laser beam. The use of a laser allows for a rapid and localized thermal rise of the layer stack to a predetermined temperature, enabling the melting of the fusible layer while preventing unwanted diffusion of atoms within the stack. The thermal budget thus remains limited.According to one example, the laser is a pulsed laser with pulses whose duration is less than one microsecond and preferably between 10 ns and 1000 ns, advantageously between . 20 ns and 500 ns. The laser typically has a wavelength between 100 nm and 550 nm, and preferably between 250 nm and 400 nm.

[0049] According to one example, the fusible layer is amorphous. This makes it possible to lower the melting point of the fusible layer compared to a fusible layer based on the same material in crystalline form. For example, a fusible layer based on crystalline SiGe containing 65% Ge melts around 1100°C, while a fusible layer based on amorphous SiGe containing 65% Ge melts below 1000°C.

[0050] According to one example, the amorphous fusible layer is formed by epitaxy before being amorphized by implantation. This makes it possible to obtain a slightly rough amorphous fusible layer containing little hydrogen.

[0051] In one example, the semiconductor layer is silicon-based or silicon-germanium based, and the fusible layer is silicon-germanium or germanium based and has a higher germanium content than the semiconductor layer. The higher the germanium content, the lower the melting point. Advantageously, the fusible layer melts while the semiconductor layer remains solid. The relative compositions of the fusible and semiconductor layers are typically chosen for this purpose. In another example, the semiconductor layer is silicon-germanium or germanium based, and the fusible layer is silicon-germanium and tin or germanium and tin based. The tin further lowers the melting point of the germanium-based alloys.

[0052] Except where incompatible, technical features described in detail for a given embodiment may be combined with technical features described in the context of other embodiments described by way of example and without limitation. In particular, elements described or illustrated for certain embodiments of the process may be combined to form another embodiment that is not necessarily illustrated or described. Such an embodiment is obviously not excluded from the invention.

[0053] It is specified that, within the framework of the present invention, the terms "on", "overcomes", "covers", "underlying", "opposite" and their equivalents do not necessarily mean "in contact with". Thus, for example, the deposition of a first layer on a second layer does not necessarily mean that the two layers are directly in contact with each other, but means that the first layer at least partially covers the second layer by being either directly in contact with it, or by being separated from it by at least one other layer or at least one other element.

[0054] A layer may also be composed of several sub-layers of the same material or of different materials.

[0055] A substrate, stack, or layer "based" on a material A is understood to mean a substrate, stack, or layer comprising only that material A or that material A and possibly other materials, for example, alloying elements and / or dopant elements. Thus, a silicon-based layer is understood, for example, to be a Si, n-doped Si, or p-doped Si layer.

[0056] The present invention notably enables the creation of a uniaxial stress state in a semiconductor layer. This semiconductor layer typically corresponds to the top layer, called "topSi," of a silicon-on-insulator (SOI) substrate. The invention can be implemented for the fabrication of various microelectronic devices or components based on FDSOI, FinFET (field-effect transistor whose channel is formed in a fin shape), or nanosheet (stack of thin films forming the active layers of transistors) architectures. The invention can also be implemented for the fabrication of various optoelectronic devices or components, for example, lasers, birefringent waveguides, or amplifiers.The invention can be implemented more broadly for the realization of any device comprising a thin semiconductor film exhibiting a uniaxial stress state.

[0057] Several embodiments of the invention implementing successive steps of the embodiment process are described below. Unless explicitly stated, the adjective "successive" does not necessarily imply, although this is generally preferred, that the steps follow each other immediately; intermediate steps may separate them.

[0058] Furthermore, the term "step" refers to the execution of a part of the process, and can designate a set of sub-steps.

[0059] Furthermore, the term "step" does not necessarily mean that the actions carried out during a step are simultaneous or immediately successive. Certain actions of a first step may, in particular, be followed by actions related to a different step, and other actions from the first step may be repeated later. Thus, the term "step" does not necessarily imply unitary actions that are inseparable in time and in the sequence of phases of the process.

[0060] A preferably orthonormal coordinate system, comprising the x, y, z axes, is shown in the accompanying figures. When only one coordinate system is shown on the same sheet of figures, this coordinate system applies to all the figures on that sheet.

[0061] In the present patent application, the thickness of a layer is taken along a direction normal to the principal extension plane of the layer. The height of a device or the depth of a pattern, for example a trench, is taken along the z-direction. Thus, a layer typically has a thickness along z and a trench typically presents a depth along z. The relative terms "on", "overcomes", "under", "underlying" refer to positions taken along the z direction.

[0062] The terms "vertical" and "vertically" refer to a direction along the z-axis. The terms "horizontally" and "horizontally" refer to a direction in the xy plane. The term "lateral" refers to an xz or yz plane. Thus, the lateral sides of the isolation trenches extend parallel to a yz and / or xz plane. Unless explicitly stated otherwise, thickness, height, and depth are measured along the z-axis.

[0063] An element located "in line with" or "directly above" another element means that these two elements are both located on the same line perpendicular to a plane in which extends mainly a lower or upper face of a substrate, that is to say on the same line oriented vertically in the figures.

[0064] The method comprises defining patterns after the formation of the stress-donating layer, and forming regions within the semiconductor layer from these patterns. These patterns and regions are not equivalent to a partial alteration of the stress-donating layer. These patterns and regions are intended to structure the stack, particularly for integration within functional devices such as transistors. The dimensions of these patterns, especially along y and / or x, are much larger than the dimensions of the implanted strips or relaxation trenches, particularly much larger than their thickness or height.

[0065] A state of mechanical stress is generally described by a tensor. In the context of the present invention, only the diagonal components of the tensor, and in particular the components in the xy plane, are considered.

[0066] By mechanical deformation of a semiconductor layer we mean that its material has its crystal lattice parameter(s) lengthened or shortened.

[0067] In the case where the deformed lattice parameter is greater than the so-called "natural" lattice parameter of a crystalline material, the material is said to be under tensile strain. When the deformed lattice parameter is smaller than the natural lattice parameter, the material is said to be under compressive strain or compression.

[0068] These states of mechanical deformation are associated with states of mechanical stress. However, it is also common to refer to these states of deformation as states of mechanical stress. In the remainder of this application, this notion of deformation (strain in Anglo-Saxon terminology) will be generically designated by the term "stress".

[0069] The stress-giving layer is also called a "stressor" according to Anglo-Saxon terminology.

[0070] Melting is understood to mean the transient transition of at least a given thickness of the fusible layer from a solid state to a liquid state. Advantageously, the the fusible layer material has a melting or liquidus temperature lower than the melting or liquidus temperature of the semiconductor material of the semiconductor layer.

[0071] In what follows, the term "absorption" or its equivalents refers to the phenomenon by which the energy of an electromagnetic wave is transformed into another form of energy, for example, heat. In this description, a material is considered absorbing if it absorbs at least 50% of a light radiation, preferably at least 75%, and advantageously at least 90%. It can be characterized by an absorption factor between 0 and 1.

[0072] Furthermore, a layer is said to be transparent when it has a transmission coefficient greater than or equal to 50%, preferably 75%, or even 90% for a central wavelength of the spectral range of the incident electromagnetic radiation.

[0073] To determine the composition and stress state of the different layers, electron microscopy analyses can be carried out, in particular Scanning Electron Microscopy (SEM) or Transmission Electron Microscopy (TEM).

[0074] The chemical compositions of the different layers or regions can be determined using the well-known EDX or X-EDS method, an acronym for "energy dispersive x-ray spectroscopy" which means "energy dispersive analysis of X-ray photons".

[0075] This method is well suited for analyzing the composition of thin layers such as the semiconductor layer and the stress-donating layer. It can be implemented on metallurgical sections within a SEM or TEM.

[0076] Precession electron diffraction (PED) can be implemented within a TEM to determine the stress state of thin layers such as the semiconductor layer. Other electron microscopy or diffraction techniques are also conceivable. Optical spectroscopy techniques, for example Raman spectroscopy, can also be implemented.

[0077] These techniques make it possible in particular to determine the state of stress of the semiconductor layer, and the arrangement and composition of the different layers within the stack.

[0078] A uniaxial voltage semiconductor layer above a "solidified" silicon-germanium based layer (corresponding to a fusible layer), may be indicators of implementation of the process according to the present invention.

[0079] Figure 1 illustrates a stack comprising a support 10, a fusible layer 11, an insulating layer 12, a semiconductor layer 13 and a donor layer constraint or stressor 14.

[0080] The support 10 typically corresponds to a bulk substrate made of monocrystalline silicon. The support 10 typically has a resistivity on the order of 20 Ω·cm. For certain applications, for example for RF applications, the support 10 may have a resistivity greater than or equal to 100 Ω·cm. The stack may include other layers, typically between the substrate 10 and the fusible layer 11. A porous silicon layer or a layer comprising a zone capable of trapping a large quantity of mobile charges (generally referred to as "trap rich") may, for example, be intercalated between the substrate 10 and the fusible layer 11.

[0081] The fusible layer 11 is preferably based on a single-crystal or polycrystalline SiGe alloy, the Ge content of which is chosen such that the liquidus of the alloy is significantly lower than that of the rest of the stack, and in particular lower than the liquidus or melting point of the semiconductor layer 13. A melting / liquidus temperature difference between the semiconductor layer 13 and the fusible layer 11 of 50°C or more, and preferably 80°C or more, is typically required. Thus, the composition of the fusible layer 11 is chosen relative to the composition of the semiconductor layer 13.

[0082] For example, when the semiconductor layer 13 is made of silicon, the fusible layer 11 can have a germanium content of between 30%at and 99%at, advantageously between 40%at and 70%at.

[0083] If the semiconductor layer 13 contains germanium, the fusible layer 11 may contain tin. This helps to maintain an acceptable melting / liquidus temperature difference between the semiconductor layer 13 and the fusible layer 11.

[0084] The fusible layer 11 can be formed by epitaxy or by chemical vapor deposition (CVD) on the support 10. The fusible layer 11 typically has a thickness of between 5 nm and 20 nm.

[0085] When the semiconductor layer 13 is formed directly in contact with the fusible layer 11 by epitaxy, the fusible layer 11 is preferably single-crystal. The thickness of the fusible layer 11 is preferably less than its critical thickness for plastic relaxation (see, for example, in the case of a SiGe-based fusible layer 11 on a Si-based support 10, the paper "Critical thickness for plastic relaxation of SiGe on Si(001) revisited" by JM Hartmann et al. published in the Journal of Applied Physics 110, 083529 (2011)). This avoids the formation of dislocations in the semiconductor layer 13 during the growth of the semiconductor layer 13 on the fusible layer 11.

[0086] According to one possibility, the fusible layer 11 is amorphous. This allows the melting point of the fusible layer 11 to be lowered, compared to a crystalline fusible layer 11 of the same chemical composition. For example, a fusible layer with SiGe based in crystalline form with a Ge concentration of 65%at melts around 1100°C, while a fusible layer based on amorphous SiGe with the same Ge concentration of 65%at melts below 1000°C.

[0087] The amorphous fusible layer 11 can be formed in two steps. The first step consists of epitaxially attaching the fusible layer 11 in crystalline form to the support 10. The second step consists of amorphizing the fusible layer 11 by ion implantation. This makes it possible to obtain a slightly rough amorphous fusible layer containing little hydrogen.

[0088] The implantation conditions for the amorphization of at least a portion of the thickness of the fusible layer 11 can be defined using a simulation tool, for example, using C-TRIM type software (CTRIM stands for "Crystal Transport of Ions in Matter") employing algorithms based on the Monte Carlo method. For the specific case of a Si semiconductor layer 13 and a SiGe fusible layer 11, Si ions can be used, for example. The implanted dose is calculated to induce amorphization of the SiGe fusible layer. A typical dose range for SiGe is between 1.5 eL⁴ and 3 eL⁴ at / cm². The amorphization depth preferably extends through the entire thickness of the fusible layer 11.

[0089] The insulating layer 12 is optional. It can be of the "buried oxide" or "BOX" type (meaning "Buried Oxide" in English) in a SOI ("Silicon On Insulator") architecture. It is preferably silica-based and typically has a thickness e^ between 10 nm and 25 nm. The low stiffness of silica, which has a Young's modulus E on the order of 50 GPa, and the limited thickness facilitate the transmission of a stress state between the stress-donating layer 14 and the semiconductor layer 13. This configuration is advantageous in the case of an FDSOI architecture. For certain applications, for example, in the case of a structure with high vertical capacitance, the insulating layer 12 can alternatively be based on a material with high permittivity. In this case, the insulating layer 12 can be based on alumina A12O3 or on a silicon-hafnium oxy-nitride HfSiON with thicknesses e^ between 5 nm and 25 nm.

[0090] The semiconductor layer 13 is typically intended to form one or more active areas of a microelectronic device. The semiconductor layer 13 is based on a doped or intrinsic semiconductor material. It may have P-type or N-type doping, depending on the application.

[0091] According to one example, the semiconductor layer 13 is made of single-crystal silicon and has a thickness of between 5 nm and 20 nm. To fabricate the corresponding SOI substrate, a low-temperature fabrication sequence can advantageously be used, for example as disclosed in document FR3116940 Al or in document FR3125631 A1, incorporated herein by reference. Such a low-temperature fabrication sequence makes it possible to remain below the liquidus temperature of the fusible layer 11 during the formation of the semiconductor layer 13. Such a low-temperature fabrication sequence can be implemented in particular when the fusible layer 11 contains more than 60% Ge, or when it is desirable for it to remain amorphous before melting and transfer of the stress state into the semiconductor layer 13.

[0092] According to another example, the semiconductor layer 13 is based on a SiGe alloy with a Ge atomic fraction between 10% and 60%. In this case, the semiconductor layer 13 preferably has a thickness less than the critical thickness, typically between 5 nm and 20 nm. When such a semiconductor layer 13 is used, the fusible layer 11 typically has a higher Ge content and possibly contains Sn.

[0093] According to another example, the semiconductor layer 13 comprises a plurality of alternating single-crystal layers of silicon and silicon-germanium. The silicon-germanium layers typically comprise between 20 and 60% Ge. Each of the single-crystal layers typically has a thickness of between 5 nm and 10 nm. Such a semiconductor layer 13 notably allows the formation of "nanosheet" type transistors.

[0094] The stress-donating layer or stressor 14 is preferably based on silicon nitride (SiN). This material has the advantage of being transparent in the UV range, within a wavelength range suitable for melting the fusible layer 11. This material is also widely used for other process steps in the field of microelectronics. It is well-known and perfectly compatible with numerous applications. Moreover, the melting temperature of silicon nitride is around 1900°C, which is strictly higher than that of silicon and most semiconductors used as a semiconductor layer 13 and / or fusible layer 11. The stressor 14 thus remains in the solid state during the stress transfer step involving the melting of the fusible layer 11. The stressor 14 typically has a thickness eu of between 30 nm and 200 nm.

[0095] The stressor 14 can be deposited by CVD onto the semiconductor layer 13. This deposition can be plasma-assisted. According to one possibility, a thin oxide layer, on the order of 1 nm to 5 nm, is formed on the semiconductor layer 13 before the deposition of the silicon nitride-based stressor 14 (not shown). This facilitates the subsequent removal of the stressor 14.

[0096] According to one possibility, the SiN-based stressor 14 is deposited without internal stress. Alternatively, different stress states can be obtained during the SiN deposition. According to one possibility, a SiN-based stressor 14 under tensile stress, ty A pitting stressor up to 1.5 GPa can be formed by CVD deposition. Alternatively, a SiN-based stressor 14 under compressive stress, typically up to -2 GPa or even -3 GPa, can be formed by CVD deposition. Further details on the type of stress depending on the deposition type or conditions can be found in the document "A comparison of the mechanical stability of Silicon nitride films deposited with various techniques" by Pierre Morin et al., published in Applied Surface Science 260 (2012) 69-72, in the case of a silicon nitride-based stressor 14.

[0097] Other materials can be used for the stressor 14, for example Al₂O₃ or Ga₂O₃. The parameters to be considered for the choice of the stressor 14 material are mainly UV transparency (when fusion is performed by laser), the ability to be deposited with a high internal stress, and a relatively low Young's modulus. Figure 17 illustrates the dependence of the strain obtained in a 10 nm thick Si layer on a 20 nm thick buried oxide layer on the Young's modulus E and the initial stress sO of a 100 nm thick stressor. A silicon nitride-based stressor deposited by plasma-assisted CVD (PECVD), typically exhibiting an initial compressive stress of -2 GPa, allows for a Si layer strain of between 1 and 1.5%.

[0098] As illustrated in [Fig. 2], a region of the semiconductor layer to be deformed can be predefined by means of a motif 100. This can be a sequence common to the FDSOI fabrication process for forming active areas of transistors. The motif 100 typically includes a masking element protecting the stack in the region to be preserved.

[0099] As illustrated in Figures 3 and 4, the stack can be structured by etching the exposed areas around the pattern 100. This etching can be performed by dry RIE (Reactive Ion Etching). The etching is typically carried out through the entire thickness of the stack, at least down to the base of the fusible layer 11, typically to a depth of about 200 nm from the top face of the semiconductor layer 13. Trenches 110 surrounding an RI region of the semiconductor layer 13 are thus formed. One or more pattern definition and etching steps can be chained together, for example, in a so-called "double patterning" structure, depending on the target dimensions for the RI region and the lithography equipment used.Different trench depths of 110 can also be achieved, for example within the framework of a so-called "double STI" technology.

[0100] It is advantageous to define RI regions of the largest possible dimension in the y direction to optimize the uniaxial stress transfer along y in the layer Semiconductor 13. One possibility is to provide consecutive active regions of the same conductivity type (N or P) joined along the y-direction (current flow direction) by replacing the separating trenches 110 with inactive gates. Such an arrangement is called "continuous active region" or "continuous RX." In one scenario, the y-dimensional dimension of the RI region is greater than or equal to six times the stressor thickness. This allows the maximum theoretically transferable stress value to be achieved by moving away from the free edge of the RI region. Ultimately, the continuous active region topology makes it possible to obtain more strongly constrained transistor channels, produced from a stressor of a given stress and thickness.

[0101] After structuring, the stressor 14 above the semiconductor layer 13 in the RI region exhibits a biaxial stress state Cl in the xy plane. In [Fig. 4], the biaxial stress state Cl illustrated for the stressor 14 is in compression. As mentioned above, this stress state Cl can alternatively be in tension or zero.

[0102] As illustrated in Figures 5, 6, according to one embodiment, the stressor 14 is altered by the formation of bands 40 directed along y. This alteration modifies the biaxial stress state Cl to produce a uniaxial stress state C2.

[0103] A first method of altering the stressor 14 consists of implanting the bands 40 of the stressor 14 with argon ions. The implantation energy is preferably chosen so that the argon ions remain confined within the thickness eM of the stressor 14 while being distributed homogeneously along the thickness eu of the stressor 14. This implantation typically changes the stress in the bands 40 of the stressor 14 by shifting the initial stress in the direction of compression. The implanted dose, the implantation energy, and the thickness eM of the stressor 14 determine the magnitude of the resulting stress shift. For example, implanting 3x10eL5 at / cm² of argon at 30 keV in a 100 nm layer of silicon nitride causes a stress shift of approximately -4 GPa in the direction of compression. By reducing the argon dose to lxl0el4 at / cm2 at an energy of 30 keV, the shift is close to -1.5 GPa, which is sufficient to relax a stressor 14 initially tensile at 1.5 GPa.

[0104] Implantation is preferably carried out after lithographic masking configured to define and expose stressor 14 bands 40, and mask stressor 14 bands 41.

[0105] According to one possibility, the initial biaxial stress state Cl of the stressor 14 is in tension at 1.5 GPa. The implantation then forms substantially relaxed nitride bands 40. The stress state C2 of the stressor 14 obtained after implantation is overall in uniaxial tension at 1.5 GPa. This is due to the unimplanted stressor 14 bands 41 that have not relaxed along the y direction. The lithography is preferably configured so that the bands 41 have a width Lu along x approximately equal to half the thickness eM of the stressor 14. The bands 40 preferably have a width l40 along x as small as permitted by lithography.

[0106] According to another possibility, the initial biaxial stress state Cl of the stressor 14 is relaxed. The implantation then forms compressional nitride bands 40, for example at -1.5 GPa for an implanted dose of lx10e14 at / cm2 at 30 keV. In this case, the stress state C2 of the stressor 14 obtained after implantation is overall uniaxial compression at -1.5 GPa. In this case, the bands 40 preferably have a width l40 along x approximately equal to half the thickness eM of the stressor 14, and the bands 41 preferably have a width Lu along x as small as permitted by lithography.

[0107] This alteration embodiment by implantation has the advantage of keeping the RI region(s) entirely covered by the stressor 14. The stress state of the stressor is thus modified without exposing the underlying semiconductor layer 13. The semiconductor layer 13 therefore remains protected from other process steps, typically during the formation, filling, and planarization of the insulation trenches.

[0108] Apart from the RI regions intended to be subjected to uniaxial stress, the same masking and implantation steps advantageously allow for obtaining fully implanted or completely unimplanted regions, i.e., totally relaxed or under biaxial stress. Furthermore, if lithography allows the definition of bands in several directions of the xy plane, uniaxial stresses in different directions of the xy plane can be obtained. The process therefore advantageously allows for the creation of different uniaxial stress states on certain regions, while simultaneously allowing the creation of biaxial or relaxed stress states in other regions.

[0109] As illustrated in Figures 7 and 8, after alteration of the stressor 14, a heat treatment is applied to the stack. This heat treatment is configured to at least partially melt the fusible layer 11, which becomes a fused layer 1 If. This releases the stresses imposed on the upper layers 12, 13, and 14 by the support 10 and / or the fusible layer 11. The entire set of layers 12, 13, and 14 can thus relax into a lower elastic energy configuration. In particular, the stressor 14 will at least partially relax by transferring all or part of its stress state C2 to the underlying semiconductor layer 13, and possibly to the insulating layer 12. After relaxation, the stressor 14 exhibits a residual stress state C2' lower than the stress state C2, or even substantially zero.Good transfer of the C2 stress state into the semiconductor layer 13 is favored by relatively low Young's moduli for the stressor 14 and / or the insulating layer 12 with respect to the semiconductor layer 13. The residual C2' stress state is then minimized.

[0110] In practice, according to a preferred option, the heat treatment can be carried out by rapid thermal annealing (RTA). This type of RTA advantageously allows for relatively homogeneous heat transfer over the entire extent of the fusible layer at the wafer level, without significant influence from the size of the RI regions. According to another option, the heat treatment is carried out using a laser, in particular by subjecting the stack to one or more laser pulses. The heat treatment conditions disclosed by document FR3120738 A1 are directly applicable to the process according to the invention. At the end of the laser treatment step, the return of the fusible layer 11 to a solid state allows the stress in the semiconductor layer 13 to be fixed.The heat treatment step leading to the temporary melting of the fusible layer 11 thus allows for a modification of the stress state within the semiconductor layer 13. The use of a laser enables a rapid thermal increase of the layer stack to a predetermined temperature, allowing the melting of the fusible layer 11 and the stress modification in the semiconductor layer 13, while limiting the thermal budget used. This prevents unwanted diffusion of atoms within the stack. The use of the laser also allows for rapid cooling of the stack once the laser exposure has ceased. Another advantage of this type of laser beam heat treatment is that the stress state modification can be performed locally, in a spatially targeted manner.

[0111] According to one example, the heat treatment step is carried out using a laser by emitting one or more successive laser pulses, the duration of each pulse being less than one microsecond and preferably between 10 ns and 1000 ns, advantageously between 20 ns and 500 ns. The laser typically has a wavelength between 100 nm and 550 nm and preferably between 250 nm and 400 nm. Longer wavelengths may be preferred to avoid or limit the influence of the size of the RI regions, in the xy plane, on the energy absorbed by the stack and in particular by the fusible layer 11. This ensures homogeneous stress transfer conditions over a wider range of RL region sizes

[0112] The laser wavelength, the laser beam pulse duration and preferably the laser beam energy density are chosen according to the stacking of layers 11, 12, 13, 14, so as to allow the melting, at least locally, of the material of the fusible layer 11 while keeping at least a continuous film of the semiconductor layer 13 in the solid state.

[0113] According to a particular embodiment, an energy density of between 0.01 and 2 J / cm² can be predicted. A person skilled in the art can rely on a combination of simulation tools, for example, as mentioned in the document "LIAB: a FEniCS based computational tool for laser annealing simulation », de Lamagna et al., 2017, to determine the conditions of rapid thermal laser annealing.

[0114] According to one possibility, following a first stress transfer, the stressor 14 can be replaced or modified again, and a second stress transfer involving a second melting of the fusible layer 11 can be carried out. This makes it possible to increase the final stress state of the semiconductor layer 13.

[0115] As illustrated in Figures 9 and 10, after transfer, the stressor 14 can be removed. The semiconductor layer 13 then retains a uniaxial stress state C3. If the stressor 14 was in uniaxial tension, the semiconductor layer 13 is typically in uniaxial compression, as illustrated in [Fig. 10]. In the case of a mesa-based insulation technology, there is no filling of the trenches 110 between RI regions, nor a planarization step.

[0116] According to one possibility, after stress transfer, a long annealing at a temperature below the liquidus of the SiGe fusible layer 11 is carried out. This allows the germanium to diffuse into the support 10. The liquidus temperature of the fusible layer 11 is increased. This prevents the subsequent melting of the fusible layer 11.

[0117] Figures 11, 12 illustrate another embodiment of the stressor 14 alteration step. According to this embodiment, the stressor 14 is altered by etching relaxation trenches 42 into the thickness eM of the stressor 14. These relaxation trenches 42 preferably have a depth equal to the thickness eM of the stressor 14. They are mainly directed along y and regularly spaced from each other along x. This makes it possible to obtain bands 41 of stressor 14 under uniaxial stress along y. The bands 41 have a width Lu along x approximately equal to half the thickness eM of the stressor 14. The relaxation trenches 42 preferably have a width 142 along x as small as permitted by lithography and etching. These relaxation trenches 42 allow the transformation of the biaxial stress state Cl of the stressor 14 into a uniaxial stress state C2.This embodiment is directly applicable to all types and values ​​of the non-zero biaxial stress state Cl.

[0118] If lithography allows the definition of trenches 42 in several directions of the xy plane, uniaxial stresses in different directions of the xy plane can be obtained. Furthermore, apart from the RI regions intended to be subjected to uniaxial stress, the superposition of trenches 42 along x and y advantageously allows for obtaining totally relaxed regions. Typically, such a grid of trenches 42 is configured to form approximately square stressor blocks 14, with a side length on the order of half the thickness ei4 of the stressor. The process This therefore advantageously allows for the realization of different uniaxial stress states on certain regions, while also permitting the joint realization of relaxed stress states in other regions.

[0119] Figures 13, 14 illustrate another embodiment in which the trenches 110 are filled to form isolation trenches 20, after transfer of the stress state by temporary melting of the fusible layer 11, and before removal of the stressor 14. The RI regions are thus laterally confined between the isolation trenches 20 before removal of the stressor 14. This prevents relaxation through the free edges of the stack.

[0120] As illustrated in Figures 15 and 16, after removal of the stressor 14, the uniaxial stress state C3' in the semiconductor layer 13 is thus increased. According to one possibility, the insulating trenches 20 extend only along yz planes, parallel to the direction of the uniaxial stress. This further promotes the increase in uniaxial stress in the semiconductor layer 13.

[0121] From the examples described above, it is clear that the method for creating a uniaxial stress state in a semiconductor layer according to the invention is particularly advantageous for applications in the field of microelectronics and / or optoelectronics. The fabrication of transistors on such a uniaxially stressed semiconductor layer benefits in particular from a significant increase in charge carrier mobility, especially for FDSOI MOSFET, FinFET, and stacked-channel MOSFET ("nanosheet") architectures.

[0122] The invention is not limited to the embodiments described above. Different combinations of stressor alteration and stack structuring can be envisaged. These steps can be reversed or alternated.

Claims

Claims

1. Method for producing a uniaxial stress state (C3, C3') in a semiconductor layer (13), said method comprising at least: - A provision of a stack comprising a support (10), the semiconductor layer (13) and a fusible layer (11) interposed between the support (10) and the semiconductor layer (13), - A formation of a stress-donor layer (14) on the semiconductor layer (13), - A definition of patterns (100) after formation of the stress-donor layer (14), - A formation, from said patterns (100), of regions (RI) surrounded by trenches (110) extending into the semiconductor layer (13), - A partial alteration of the stress-donor layer (14) at the level of said regions (RI),configured to modify a first stress state (Cl) of said stress-donating layer (14) so ​​as to obtain a second stress state (C2) mainly in a determined direction (y), - An at least partial melting of the fusible layer (1 If), so that the stress-donating layer (14) transfers at least in part, by relaxation, the second stress state (C2, C2') into the semiconductor layer (13), so that the semiconductor layer (13) has a uniaxial stress state (C3) in said determined direction (y).,

2. A method according to the preceding claim further comprising filling the trenches (110) to form isolation trenches (20), after melting the fusible layer (11) and before removing the stress-giving layer (14).

3. A method according to any one of the preceding claims wherein the partial alteration comprises implantation of ions into a portion of the stress donor layer (14) forming im- planted (40) oriented in the determined direction (y), said implanted strips (40) extending over an entire dimension of the stress-giving layer (14) in the determined direction (y).

4. Method according to the preceding claim in which the first stress state (Cl) is substantially zero and the second stress state (C2) corresponds to uniaxial compression.

5. A method according to claim 3 wherein the first stress state (Cl) corresponds to a biaxial tension and the second stress state (C2) corresponds to a uniaxial tension.

6. Method according to any one of claims 1 to 2 in which the partial alteration comprises a formation of relaxation trenches (42) in the stress-giving layer (14), oriented in the determined direction (y).

7. Method according to the preceding claim in which the relaxation trenches (42) are separated by strips (41) of stress-donating layer (14) having a width Lu approximately equal to half the thickness eM of the stress-donating layer (14).

8. A method according to any preceding claim wherein the stack comprises an insulating layer (12) between the semiconductor layer (13) and the fusible layer (11).

9. A method according to any preceding claim wherein the stress-giving layer (14) is based on silicon nitride.

10. A method according to any preceding claim wherein the melting is carried out by thermal annealing of the rapid thermal annealing type or using a nanosecond laser.

11. A method according to any preceding claim wherein the fusible layer (11) is amorphous.

12. Method according to the preceding claim in which the amorphous fusible layer (11) is formed by epitaxy before being amorphized by implantation.

13. A method according to any preceding claim wherein the semiconductor layer (13) is based on silicon or silicon-germanium and the fusible layer (11) is based on silicon-germanium or germanium and has a higher germanium content than the semiconductor layer (13).

14. A method of manufacturing a transistor comprising implementing a method of producing a uniaxial stress state (C3, C3') according to any one of the preceding claims, the transistor comprising a channel region made in said semiconductor layer (13).

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