Patent Application
20180118562
The present invention relates according to claim 1 to a method for producing a multi-component wafer, in particular a MEMS wafer, according to claim 14 to a use of a substrate as donor wafer and bonding wafer in a multi-component production method, in particular a MEMS wafer production method, and according to claim 15 to a multi-component wafer, in particular a MEMS wafer.
In many technical fields (for example microelectronics or photovoltaic technology) materials such as silicon, germanium or sapphire are often used in the form of thin slices and plates (what are known as wafers). As standard, wafers of this kind are currently produced by sawing from an ingot, wherein relatively large material losses (“kerf loss”) are incurred. Since the used starting material is often very costly, it is highly sought to produce wafers of this kind with less material consumption and therefore more efficiently and more economically.
By way of example, with the currently conventional methods, almost 50% of the used material is lost as “kerf loss” in the production of silicon wafers for solar cells alone. Considered globally, this corresponds to an annual loss of more than 2 billion euros. Since the costs of the wafer account for the largest share of the cost of the finished solar cell (over 40%), the costs of solar cells could be significantly reduced by corresponding improvements in the wafer production.
Methods which dispense with the conventional sawing and for example can directly split off thin wafers from a thicker workpiece by use of temperature-induced stresses appear to be particularly attractive for wafer production of this kind without kerf loss (“kerf-free wafering”). These include in particular methods as described for example in PCT/US2008/012140 and PCT/EP2009/067539, where a polymer layer applied to the workpiece is used in order to produce these stresses.
Particularly high material losses occur with the production of multi-component wafers, for example what are known as MEMS wafers (microelectromechanical systems wafer). The production of wafers of this kind presupposes the use of a number of very thick starting wafers, the production of which generally already causes significant material losses. The great thickness of the starting wafer is required because only in this way can bow and warp be kept low enough. In the case of MEMS wafers, a starting wafer is usually used to cover an oxide layer on a further starting wafer, at the same time establishing an integrally bonded connection. Once the integrally bonded connection has been established, there is always a machining treatment of the starting wafer in order to significantly reduce the thickness thereof to the smaller size necessary for use, thus resulting in turn in material losses.
The object of the present invention is therefore to reduce the material consumption in multi-component wafer production, in particular MEMS wafer production.
The aforementioned object is achieved in accordance with the invention by a method according to claim 1. The method according to the invention for producing a multi-component wafer, in particular a MEMS wafer, preferably comprises at least the following steps:
The method according to the invention preferably comprises at least the following steps: providing a bonding wafer, wherein at least one surface portion of the bonding wafer is formed by an oxide layer, providing a donor wafer, wherein the donor wafer is thicker than the bonding wafer, bringing the donor wafer into contact with the surface portion of the bonding wafer that is formed by the oxide layer, forming a multilayer arrangement by connecting the donor wafer and the bonding wafer in the region of the contact, producing modifications in the interior of the donor wafer for predefining a detachment region for separating the multilayer arrangement into a separation part and a connection part, wherein the production of the modifications takes place before the formation of the multilayer arrangement or after the formation of the multilayer arrangement, separating the multilayer arrangement along the detachment region as a result of a weakening of the multilayer arrangement brought about by the production of a sufficient number of modifications or as a result of production of mechanical stresses in the multilayer arrangement, wherein the connecting part remains on the bonding wafer, and wherein the split-off separation part has a greater thickness than the connection part. Additionally or alternatively, individual steps or groups of steps of the aforementioned method can be replaced or supplemented by the following steps: providing a bonding wafer, wherein at least one surface portion of the bonding wafer is formed by an oxide layer, providing a donor wafer, wherein the donor wafer is thicker than the bonding wafer, bringing the donor wafer into contact with the surface of the bonding wafer that is formed by the oxide layer, forming a multilayer arrangement by connecting the donor wafer and the bonding wafer in the region of the contact, arranging or producing a stress-producing layer on at least one exposed planar surface of the multilayer arrangement, thermally treating the stress-producing layer in order to produce mechanical stresses within the multilayer arrangement, wherein the stresses in the portion of the multilayer arrangement formed by the donor wafer are large enough that a crack forms in the donor wafer, by means of which the donor wafer is split into a separation part and a connection part, wherein the connection part remains on the bonding wafer, and wherein the split-off separation part has a greater thickness than the connection part.
This solution is advantageous since the donor wafer is not reduced by machining of the connection portion, and instead is divided by a crack into two parts, thus resulting in a separation part, which can be used further. This makes it possible for the starting wafers, or the bonding wafer and the donor wafer, to be connected to one another, and more specifically each can have a great thickness, but without having to experience the material losses known from the prior art.
Further preferred embodiments are the subject of the following parts of the description and/or the dependent claims.
In accordance with a preferred embodiment of the present invention, the method according to the invention comprises the step of cleaning the separation part and/or the step of converting the separation part into a further bonding wafer by treatment of at least one surface portion, and preferably the entire surface, of the separation part. The bonding wafer thus produced is then particularly preferably provided as a further bonding wafer to be brought into contact with a further donor wafer. This embodiment is advantageous since the starting wafer is used in succession as a donor wafer, i.e. firstly as a donor wafer, and as a bonding wafer, i.e. after the use as donor wafer.
The treatment, in accordance with a further preferred embodiment of the present invention, comprises an SiOx process, whereby an oxidation of the at least one surface portion of the bonding wafer is effected. This embodiment is advantageous since the oxide layer necessary for a multi-component wafer, in particular a MEMS wafer, is produced easily in a defined manner. Here, it is conceivable that a multiplicity of wafers or separation parts are treated in a treatment space in succession or at the same time for production of the oxide layer(s).
In accordance with a further preferred embodiment of the present invention, the donor wafer has a first thickness D1, the bonding wafer has a second thickness D2, the separation part has a third thickness D3, and the connection part has a fourth thickness D4, wherein the thickness D1 is greater than the sum of the thicknesses D3 and D4, and wherein the sum of the thicknesses D3 and D4 is greater than the thickness D3, and wherein the thickness D3 is greater than the thickness D2 by a thickness DL. The thickness D2 is here preferably greater than 300 μm and preferably greater than 400 μm or 500 μm or 600 μm or 700 μm. this embodiment is advantageous since very stable elements, such as the bonding wafer, the donor wafer and/or the separation part, can be used, whereby these elements for example withstand the mechanical stresses occurring during an optional polishing step. Elements or wafers of such thickness also form much smaller warps and bows than thinner wafers.
The thickness DL, in accordance with a further preferred embodiment of the present invention, is less than 200 μm, in particular less than 100 μm, for example less than 90 μm or less than 80 μm or less than 70 μm or less than 60 μm or less than 50 μm, and is preferably removed as a result of polishing and/or etching steps or is as large as the material portions removed by means of polishing and/or etching treatment. This embodiment is advantageous since a thickness necessary for the surface treatment is provided, which thickness is sufficient to create a planar surface and at the same time only causes extremely small material losses.
In accordance with a further preferred embodiment of the present invention, the method according to the invention comprises the step of producing modifications for predefining the course of the crack. The modifications are preferably produced before the multilayer arrangement is formed or after the multilayer arrangement is formed. The modifications are preferably produced by means of laser beams or ion radiation in the interior of the donor wafer. The laser beams are preferably emitted from a LASER device, wherein the LASER device is preferably a picosecond laser or a femtosecond laser. Additionally or alternatively, it is conceivable that the modifications are local cracks in the crystal lattice and/or material portions in the interior of the donor wafer that have been converted into another phase as a result of a treatment.
The LASER device, in accordance with a further preferred embodiment of the present invention, comprises a femtosecond LASER (fs LASER), and the energy of the LASER beams of the fs LASER is preferably selected in such a way that the propagation of damage of each modification in the top layer and/or the sacrificial layer is less than 3 times the Rayleigh length, preferably less than the Rayleigh length, and particularly preferably less than a third of the Rayleigh length and/or the wavelength of the LASER beams of the fs LASER is selected in such a way that the absorption of the top layer and/or of the sacrificial layer is less than 10 cm−1 and preferably less than 1 cm−1 and particularly preferably less than 0.1 cm−1 and/or the individual modifications are produced in each case as a result of a multi-photon excitation brought about by the fs LASER.
In accordance with a further preferred embodiment of the present invention, the laser beams for producing the modifications penetrate a surface of the donor wafer which is part of the connection part or belongs to the portion which is thinner than the other portion once the donor wafer has been divided into two portions as a result of the formation of a crack. This embodiment is advantageous since the laser beams have to move less far through a solid body than if they had to move through the other portion. In particular, an energy saving on the part of the laser is hereby possible, and an undesirable heating of the donor substrate as a result of the production of the modification is preferably reduced.
The method according to the invention preferably comprises the steps of arranging or producing a stress-producing layer on at least one exposed surface of the multilayer arrangement and the step of thermally treating the stress-producing layer in order to produce the mechanical stresses within the multilayer arrangement, wherein the stresses in the portion of the multilayer arrangement formed by the donor wafer are so great that a crack forms in the donor wafer along the detachment region, by means of which crack the donor wafer is split into the separation part and the connection part, wherein the stress-producing layer comprises or consists of a polymer, in particular polydimethylsiloxane (PDMS), wherein the thermal treatment is performed in such a way that the polymer experiences a glass transition, wherein the stress-producing layer is temperature-controlled, in particular by means of liquid nitrogen, to a temperature below room temperature or below 0° C. or below −50° C. or below −100° C. or below −110° C., in particular to a temperature below the glass transition temperature of the stress-producing layer.
This embodiment is advantageous since it has been found that, due to the thermal treatment of the stress-producing layer, in particular by utilisation of the property changes of the material of the stress-producing layer occurring with the glass transition, the forces necessary to initiate and form a crack can be produced in a donor substrate. Furthermore, by means of the thermal treatment of the stress-producing layer, it is possible to very precisely control, in time, the moment at which the solid-body layer will be separated or the time at which the multilayer arrangement will be divided.
The mechanical stresses can be produced additionally or alternatively by on the whole mechanical vibrations and/or temperature variations and/or pressure changes, in particular atmospheric pressure changes.
The substrate or the donor wafer preferably comprises a material or a material combination from one of the main groups 3, 4 and 5 of the Periodic Table of Elements, such as Si, SiC, SiGe, Ge, GaAs, InP, GaN, Al2O3 (sapphire), AlN, or consists of one or more of these materials. The substrate or the donor wafer particularly preferably comprises a combination of elements occurring in the third and fifth group of the Periodic Table of Elements. Conceivable materials or material combinations are for example gallium arsenide, silicon, silicon carbide, etc. Furthermore, the substrate or the donor wafer can comprise a ceramic (for example Al2O3—aluminium oxide) or can consist of a ceramic, preferred ceramics being for example perovskite ceramics (such as Pb—O—, Ti/Zr-containing ceramics) in general, and lead magnesium niobates, barium titanate, lithium titanate, yttrium aluminium garnet, in particular yttrium aluminium garnet crystals for solid-body LASER applications, SAW (surface acoustic wave) ceramics, such as lithium niobate, gallium orthophosphate, quartz, calcium titanate, etc., in particular. The substrate or the donor wafer thus preferably comprises a semiconductor material or a ceramic material, or the substrate or the donor wafer particularly preferably consists of at least one semiconductor material or a ceramic material. It is also conceivable that the substrate or the donor wafer comprises a transparent material or partially consists of or is made of a transparent material, such as sapphire. Further materials which can be considered here as solid-body material alone or in combination with another material are for example “wide band gap” materials, InAlSb, high-temperature superconductors, in particular rare earth cuprates (for example YBa2Cu3O7).
The present invention, according to claim 9, also relates to a use of a substrate as donor wafer and bonding wafer in a multi-component wafer production method, in particular a MEMS wafer production method. The substrate is preferably arranged as donor wafer on a further bonding wafer, which has an oxidation layer, wherein the donor wafer is divided by being split into a connection part and a separation part as a result of the propagation of a crack, and wherein the separation part serves as bonding wafer after treatment in an oxidation process, in particular an SiOx process, wherein the bonding wafer is connected to a further donor substrate in order to form a multilayer arrangement.
The present invention also relates to a multi-component wafer, in particular a MEMS wafer, according to claim 10. The multi-component wafer according to the invention comprises at least one bonding wafer, wherein at least one surface portion of the bonding wafer is formed by an oxide layer, a connection part split off from a donor wafer as result of the propagation of a crack, wherein the connection part is arranged in an integrally bonded manner on a surface portion formed by the oxide layer, and wherein the bonding wafer is a portion, processed by means of an oxidation treatment, in particular an SiOx treatment, of a separation part separated from a donor wafer.
The multi-component wafer according to the invention can be referred to alternatively for example as a MEMS wafer or as a silicon-on-insulator wafer or as a multilayer wafer or as wafer with inner bonding layer. It is merely essential here that an oxide layer is created or produced or formed or brought about or arranged as insulator layer or bonding layer or etching stop layer between two further layers or material portions. The further layers or material portions particularly preferably form on the one hand the bonding wafer and on the other hand the donor wafer. The bonding wafer and the donor wafer, in the portions neighbouring the insulator layer or bonding layer or etching stop layer, preferably consist of the same material and/or of a semiconductor material. However, it is also conceivable that the bonding wafer and the donor wafer, in the portions neighbouring the insulator layer or bonding layer or etching stop layer, consists of different materials, in particular of one or more semiconductor materials, or comprises these materials. The oxide layer, which particularly preferably serves as insulator layer or bonding layer or etching stop layer, preferably has a thickness, in particular an average thickness or a minimum thickness or a maximum thickness, of at least or precisely or at most 1.25 μm or 1.5 μm or 1.75 μm or 2 μm or 2.25 μm or 2.5 μm or 2.75 μm or 3 μm or 4 μm or 5 μm or 6 μm or 7 μm or 7.5 μm or 8 μm or 9 μm or 10 μm.
The method according to the invention preferably comprises one or more of the following steps: providing a donor substrate or a multilayer arrangement, producing modifications in the interior of the donor substrate or the multilayer arrangement by means of LASER beams, wherein, by means of the modifications, a detachment region is predefined, along which the solid-body layer is separated from the donor substrate or the multilayer arrangement, removing material of the donor substrate or of the multilayer arrangement starting from a surface extending in the peripheral direction of the donor substrate towards the centre of the donor substrate or the multilayer arrangement, in particular so as to produce a peripheral indentation, wherein the detachment region is exposed by the material removal, separating the solid-body layer from the donor substrate or the multilayer arrangement, wherein the donor substrate or the multilayer arrangement is weakened in the detachment region by the modifications in such a way that the solid-body layer detaches from the donor substrate or the multilayer arrangement as a result of the material removal or, after the material removal, such a number of modifications are produced that the donor substrate or the multilayer arrangement is weakened in the detachment region in such a way that the solid-body layer detaches from the donor substrate or the multilayer arrangement or a stress-producing layer is produced or arranged on a surface of the donor substrate or multilayer arrangement, which surface is oriented at an incline relative to the peripheral surface and in particular is planar, and mechanical stresses are produced in the donor substrate or in the multilayer arrangement by a thermal treatment of the stress-producing layer, wherein a crack for separation of a solid-body layer is created by the mechanical stresses and propagates, starting from the surface of the donor substrate or multilayer arrangement exposed by the material removal, along the modifications.
This solution is advantageous since an edge of the donor substrate or the multilayer arrangement, in the region of which modifications for further forming of the detachment region can be produced only in a very complex manner, can be removed or reduced or modified. A radial material removal is thus hereby provided, as a result of which the distance of the peripheral surface from the detachment region is reduced.
Further preferred embodiments are the subject of the dependent claims and/or the following parts of the description.
The detachment region predefined by the modifications, in accordance with a further preferred embodiment of the present invention, is further distanced from the peripheral surface of the donor substrate before the material removal than after the material removal. This embodiment is advantageous since the detachment region thus can be easily produced and yet is still preferably adjacent to the outer peripheral surface of the donor substrate after the material removal.
The modifications for predefining the detachment region, in accordance with a further preferred embodiment of the present invention, are produced before the material removal, and, by means of the material removal, a reduction of the distance of the detachment region to less than 10 mm, in particular to less than 5 mm and preferably to less than 1 mm, is achieved at least at specific points, or the modifications for predefining the detachment region are produced after the material removal, wherein the modifications are produced in such a way that the detachment region is distanced, at least at specific points, by less than 10 mm, in particular less than 5 mm, and preferably less than 1 mm, from a surface exposed by the material removal. At least individual modifications of the detachment region are particularly preferably part of the surface of the donor substrate that is exposed by the material removal and that is peripheral at least in part, preferably completely.
In accordance with a further preferred embodiment of the present invention, the material is removed by means of ablation beams, in particular ablation LASER beams, or ablation fluids, or an indentation with an asymmetrical design is produced by the material removal, or the material removal is performed at least in portions in the peripheral direction of the donor substrate as a reduction of the radial extent of the donor substrate, in the entire region between the detachment region and a surface of the donor substrate distanced homogeneously from the detachment region.
The aforementioned object can be achieved additionally or alternatively by a method for separating solid-body slices from a donor substrate, said method preferably comprising at least the following steps: providing a donor substrate, removing material of the donor substrate starting from a surface extending in the peripheral direction of the donor substrate towards the centre of the donor substrate in order to produce an indentation, wherein the material is removed by means of ablation LASER beams and/or the indentation is produced asymmetrically, producing modifications by means of further LASER beams in the interior of the donor substrate, wherein the modifications are positioned in such a way that they are adjacent to the indentation, wherein the solid-body slice is detached from the donor substrate by the produced modifications or a stress-producing layer is produced or arranged on a surface which is oriented at an incline relative to the peripheral surface and in particular is planar, and mechanical stresses are produced in the donor substrate by a thermal treatment of the stress-producing layer, wherein a crack for separation of a solid-body layer is produced by the mechanical stresses and propagates, starting from the indentation, along the modifications.
The modifications are achieved here preferably using the shortest possible pulses in the smallest possible vertical region by focusing in the material with a high numerical aperture.
During the ablation, the ablation LASER beams are focused on the surface of the material with a lower numerical aperture and often a wavelength absorbed linearly by the material. The linear absorption of the ablation LASER beams at the material surface leads to an evaporation of the material (the ablation), i.e. to a material removal, and not only to a structural change.
This solution is advantageous since an edge region of the donor substrate is processed by means of a material-removing treatment, by means of which the outer edge of the donor substrate is displaced in the region of the plane in which the crack propagates, towards the centre of the donor substrate. The displacement preferably occurs in the direction of the centre to such an extent that all LASER beams can penetrate the donor substrate over the same planar surface, depending on the penetration depth of the LASER beams and/or the angle of the LASER beams to one another.
The indentation surrounds the donor substrate, in accordance with a further preferred embodiment of the present invention, completely in the peripheral direction. This embodiment is advantageous since the crack can be introduced into the donor substrate in a defined manner over the entire periphery of the donor substrate.
In accordance with a further preferred embodiment of the present invention, the indentation runs towards the centre as far as an indentation end that becomes increasingly narrower, in particular in a wedge-like or notch-like manner, wherein the indentation end lies in the plane in which the crack propagates. This embodiment is advantageous since a notch is created by the indentation end, which notch predefines the direction of propagation of the crack.
The asymmetric indentation, in accordance with a further preferred embodiment of the present invention, is produced by means of a grinding tool, which is negatively shaped at least in part in order to make the indentation. This embodiment is advantageous since the grinding tool can be produced in accordance with the edge or indentation to be formed.
In accordance with a further preferred embodiment of the present invention, the grinding tool has at least two differently shaped processing portions, wherein a first processing portion is intended for processing of the donor substrate in the region of the underside of a solid-body slice to be separated and a second processing portion is intended for processing of the donor substrate in the region of the upper side of the solid-body slice to be separated from the donor substrate. This embodiment is advantageous since, in addition to shapings for improved crack formation, shapings for improved handling can also be produced by means of the grinding tool at the same time or at a different time on the donor substrate or on the portions of the donor substrate forming one or more solid-body slices.
In accordance with a further preferred embodiment of the present invention, the first processing portion produces a deeper or larger-volume indentation in the donor substrate than the second processing portion, wherein the first processing portion and/or the second processing portion have/has curved or straight grinding faces. The first processing portion preferably has a curved main grinding face and the second processing portion preferably likewise has a curved secondary grinding face, wherein the radius of the main grinding face is greater than the radius of the secondary grinding face, the radius of the main grinding face is preferably at least twice as large as the radius of the secondary grinding face, or the first processing portion has a straight main grinding face and the second processing portion has a straight secondary grinding face, wherein, by means of the main grinding face, more material is removed from the donor substrate than with the secondary grinding face, or the first processing portion has a straight main grinding face and the second processing portion has a curved secondary grinding face, or the first processing portion has a curved main grinding face and the second processing portion has a straight secondary grinding face.
The grinding tool preferably has a multiplicity of processing portions, in particular more than 2, 3, 4, 5, 6, 7, 8, 9 or 10 processing portions, in order to process a corresponding multiplicity of portions of the donor substrate, which can be associated with different solid-body slices, in a machining or material-removing manner.
In accordance with a further preferred embodiment of the present invention, the ablation LASER beams are produced with a wavelength in the range between 300 nm (UV ablation with frequency-tripled Nd:YAG or other solid-body laser) and 10 μm (CO2 glass laser, often used for engraving and cutting processes), with a pulse length of less than 100 microseconds and preferably less than 1 microsecond, and particularly preferably less than 1/10 of a microsecond, and with a pulse energy of more than 1 μJ and preferably more than 10 μJ. This embodiment is advantageous since the indentation can be produced by means of a LASER device and not by means of a grinding tool, which becomes worn.
The modifications in the donor substrate are produced in a material-dependent manner preferably with the following configurations or LASER parameters: If the donor substrate consists of silicon or the donor substrate comprises silicon, then nanosecond pulses or shorter (<500 ns), a pulse energy in the microjoule range (<100 μJ), and a wavelength >100 nm are preferably used.
In the case of all other materials and material combinations, a pulse <5 picoseconds, pulse energies in the microjoule range (<100 μJ), and wavelengths variable between 300 nm and 2500 nm are preferably used.
It is important here that a large aperture is provided in order to pass deep into the material. The aperture for producing the modifications in the interior of the donor substrate is therefore preferably larger than the aperture for ablation of material by means of the ablation LASER beams for producing the indentation. The aperture is preferably multiple times larger, in particular at least 2, 3, 4, 5 or 6 times larger, than the aperture for ablation of material by means of the ablation LASER beams for producing the indentation. The size of the focus for producing a modification, in particular with regard to the diameter of the focus, is preferably smaller than 10 μm, preferably smaller than 5 μm, and particularly preferably smaller than 3 μm.
Alternatively, the present invention can relate to a method for detaching solid-body slices from a donor substrate. Here, the method according to the invention preferably comprises at least the following steps: providing a donor substrate, producing modifications in the interior of the donor substrate by means of LASER beams, wherein the LASER beams penetrate the donor substrate over a planar surface of the donor substrate, wherein the totality of LASER beams is inclined relative to the surface of the donor substrate in such a way that a first portion of the LASER beams penetrates the donor substrate at a first angle to the surface of the donor substrate and at least one further portion penetrates the donor substrate at a second angle to the surface of the donor substrate, wherein the value of the first angle differs from the value of the second angle, wherein the first portion of the LASER beams and the second portion of the LASER beams are focused in the donor substrate in order to produce the modification, wherein the solid-body slice is detached from the donor substrate by the produced modifications or a stress-producing layer is produced or arranged on the planar surface of the donor substrate and mechanical stresses are produced in the donor substrate by a thermal treatment of the stress-producing layer, wherein a crack for separation of a solid-body layer is produced by the mechanical stresses and propagates along the modifications. The donor wafer and/or the LASER device emitting the LASER beams are/is preferably rotated about an axis of rotation during the production of the modifications. Additionally or alternatively to the rotation of the donor wafer, the distance of the LASER beams from the centre of the donor wafer is particularly preferably changed.
The totality of LASER beams, in accordance with a further preferred embodiment of the present invention, is oriented in the same orientation relative to the planar surface of the donor substrate for the production of modifications in the region of the centre of the donor substrate and for the production of modifications in the region of an edge of the donor substrate provided in the radial direction.
This solution is advantageous since the total cross-section of the LASER beam upon entry into the solid body contacts a planar surface, and since homogeneous damage then occurs in the depth. This homogeneous damage can be produced as far as the outer edge of the donor substrate extending in particular orthogonally to the planar surface. The modifications in the edge region of the donor substrate and in the region of the centre of the donor substrate can thus be produced by means of one processing step.
In accordance with a further preferred embodiment of the present invention, the first portion of the LASER beams penetrates the donor substrate at a first angle to the surface of the donor substrate and the further portion of the LASER beams penetrates at a second angle for production of modifications in the region of the centre of the donor substrate and for production of modifications in the region of an edge of the donor substrate provided in the radial direction, wherein the value of the first angle always differs from the value of the second angle. The first angle and the second angle are preferably constant or unchanged or are not actively changed during the production of the modifications. This embodiment is advantageous since
In accordance with a further preferred embodiment of the present invention, the LASER device comprises a femtosecond LASER (fs LASER) or a picosecond LASER (ps LASER), and the energy of the LASER beams of the LASER (fs LASER or ps LASER) is preferably selected in such a way that the propagation of damage of each modification in the top layer and/or the sacrificial layer is less than 3 times the Rayleigh length, preferably less than the Rayleigh length, and particularly preferably less than a third of the Rayleigh length and/or the wavelength of the LASER beams of the fs LASER is selected in such a way that the absorption of the top layer and/or of the sacrificial layer is less than 10 cm−1 and preferably less than 1 cm−1 and particularly preferably less than 0.1 cm−1 and/or the individual modifications are produced in each case as a result of a multi-photon excitation brought about by the fs LASER.
In accordance with a further preferred embodiment of the present invention the LASER beams for producing the modifications penetrate the donor wafer over a surface that is part of the solid-body slice to be separated. This embodiment is advantageous since the donor substrate is heated to a lesser extent, whereby the donor substrate is exposed only to low thermal stresses.
In accordance with a further preferred embodiment of the present invention, the ablation radiation comprises accelerated ions and/or plasma and/or LASER beams and/or is formed by electron beam heating or ultrasound waves and/or is part of a lithographic method (electron beam, UV, ions, plasma) with at least one etching step following a previously executed photoresist coating and/or the ablation fluid is a liquid jet, in particular a water jet of a water jet cutting process.
The stress-producing layer, in accordance with a further preferred embodiment of the present invention, comprises a polymer, in particular polydimethylsiloxane (PDMS), or consists thereof, wherein the thermal treatment is preferably performed in such a way that the polymer experiences a glass transition, wherein the stress-producing layer is temperature-controlled, in particular by means of liquid nitrogen, to a temperature below room temperature (i.e. to a temperature below 20° C.) or below 0° C. or below −50° C. or below −100° C. or below −110° C., in particular to a temperature below the glass transition temperature of the stress-producing layer.
This embodiment is advantageous since it has been found that, due to the thermal treatment of the stress-producing layer, in particular by utilisation of the property changes of the material of the stress-producing layer occurring with the glass transition, the forces necessary to initiate and form a crack can be produced in a donor substrate.
The donor substrate preferably comprises a material or a material combination from one of the main groups 3, 4 and 5 of the Periodic Table of Elements, such as Si, SiC, SiGe, Ge, GaAs, InP, GaN, Al2O3 (sapphire), AIN, or consists of one or more of these materials. The donor substrate particularly preferably comprises a combination of elements occurring in the third and fifth group of the Periodic Table of Elements. Conceivable materials or material combinations are for example gallium arsenide, silicon, silicon carbide, etc. Furthermore, the donor substrate can comprise a ceramic (for example Al2O3—aluminium oxide) or can consist of a ceramic, preferred ceramics being for example perovskite ceramics (such as Pb—, O—, Ti/Zr-containing ceramics) in general, and lead magnesium niobates, barium titanate, lithium titanate, yttrium aluminium garnet, in particular yttrium aluminium garnet crystals for solid-body laser applications, SAW (surface acoustic wave) ceramics, such as lithium niobate, gallium orthophosphate, quartz, calcium titanate, etc., in particular. The donor substrate thus preferably comprises a semiconductor material or a ceramic material, or the donor substrate particularly preferably consists of at least one semiconductor material or a ceramic material. It is also conceivable that the donor substrate comprises a transparent material or partially consists of or is made of a transparent material, such as sapphire. Further materials which can be considered here as solid-body material alone or in combination with another material are for example “wide band gap” materials, InAlSb, high-temperature superconductors, in particular rare earth cuprates (for example YBa2Cu3O7).
The subject matter of patent application DE 2013 205 720.2 with the title: “Method for rounding edges of semiconductor parts produced from a semiconductor starting material, and semiconductor products produced by this method” is hereby incorporated by reference in its full extent in the subject matter of the present description.
The use of the word “substantially” in all cases in which this word is used within the scope of the present invention preferably defines a deviation in the range of 1% to 30%, in particular 1% to 20%, in particular 1% to 10%, in particular 1% to 5%, in particular 1% to 2%, from the definition that would be given without the use of this word.
Further advantages, objectives and properties of the present invention will be explained on the basis of drawings accompanying the following description, in which the solutions according to the invention are illustrated by way of example. Components or elements or method steps of the solutions according to the invention which in the figures coincide at least substantially in terms of their function can be denoted here by the same reference signs, wherein these components or elements do not have to be provided with reference signs or explained in all figures.
In the drawings:
In accordance with this illustration, a bonding wafer 2 is first provided in a first step I., wherein at least one surface portion 4 of the bonding wafer 2 is formed by an oxide layer. A donor wafer 6 is also provided in the first step I., wherein the donor wafer 6 is thicker than the bonding wafer.
In a second step II., the donor wafer 6 is brought into contact with the surface portion 4 of the bonding wafer 2 formed by the oxide layer. This leads to the formation of a multilayer arrangement 8 by connection of the donor wafer 6 and of the bonding wafer 2 in the region of the contact.
In a third step III., modifications 18 are produced in the interior of the donor wafer 6 for predefining a detachment region 11 for separation of the multilayer arrangement 8 into a separation part 14 and a connection part 16, wherein the modifications 18 are produced before the formation of the multilayer arrangement 8 or after the formation of the multilayer arrangement 8.
Step IV. shows the step of separation of the multilayer arrangement 8 along the detachment region 11 as a result of a weakening of the multilayer arrangement brought about by the production of a sufficient number of modifications, wherein the connection part 16 remains on the bonding wafer 2, and wherein the split-off separation part 14 has a greater thickness than the connection part 16.
The separation part 14 is then supplied in a further step to a treatment device 24. The treatment device 24 produces an oxide layer by material application and/or by material conversion, by means of which oxide layer at least one, preferably planar, surface of the separation part 14 is formed.
Before or after production of the oxide layer, a material-removing step is preferably performed, in particular a polishing, lapping, etching and/or chemical-mechanical polishing, by means of which at least one surface or a surface portion of the detachment layer 14 or of the bonding wafer 2 is smoothed, i.e. experiences a roughness reduction at least in part.
By means of the roughness reduction and the oxide layer production, in particular an SiOx process, the separation part 14 is reconfigured into a further bonding wafer 3. This further bonding wafer 3 is then used as bonding wafer 2 in accordance with the method described by steps I-IV.
In step II., the bonding wafer 2 and the donor wafer 6 are connected to one another, in particular integrally bonded to one another. The oxide layer or at least part of the oxide layer of the bonding wafer 2 is hereby directly superimposed or covered by the donor wafer 6. The surface of the oxide layer and the surface of the donor wafer 6, which are connected to one another here, both particularly preferably have a surface finish provided by polishing, lapping, etching and/or chemical-mechanical polishing. The mean roughness Ra is preferably less than 76 μm, or less than 38 μm or less than 12.5 μm or less than 6 μm or less than 3 μm or less than 2.5 μm or less than 1.25 μm or less than 0.5 μm.
In step III., the multilayer arrangement 8, in particular the donor substrate 6, is acted on by LASER beams 20 of a LASER device 22. The LASER beams 20 cause modifications 18 of the material forming the donor wafer 6 to be created or produced in the interior of the donor wafer 6, in particular on account of a multi-photon excitation. A multiplicity of modifications 18 are preferably produced, wherein the individual modifications 18 preferably lie in the same plane. The totality of modifications 18 thus constitutes a precise producible weakening of the donor wafer at 6, which predefines the course of formation of a crack for separating the donor wafer 6 into two parts in the sense of a perforation. The LASER beams 20, in accordance with the shown example, penetrate the donor wafer 6 over a surface of the donor wafer 6 which is part of the thicker part following the splitting of the donor wafer 6 into two parts.
An alternative production of modifications 18 is shown by
In step IV., a stress-producing layer 10 is arranged or produced on a preferably further exposed and particularly preferably planar surface of the bonding wafer 2 and/or on a preferably further exposed and particularly preferably planar surface of the donor wafer 6. The stress-producing layer 10 is here preferably a polymer layer, in particular a layer consisting of PDMS or comprising PDMS.
In step V., the stress-producing layer 10 arranged on the bonding wafer 2 and/or the stress-producing layer 10 arranged on the donor wafer 6 are/is exposed to a thermal treatment, whereby the stress-producing layer 10 contracts and thus introduces mechanical stresses into the multilayer arrangement 8 in such a way that a crack forms and propagates in the region of the modifications 18. The thermal treatment is preferably provided via a cooling device 26, which particularly preferably dispenses a free-flowing substance 28, which cools the stress-producing layer 10. The free-flowing substance 28 is here preferably a fluid and particularly preferably liquid nitrogen. By means of the crack, the donor wafer 6 is split into two parts: a connection part 16 and a separation part 14, wherein the connection part 16 remains on the bonding wafer 2 on account of the integrally bonded connection to the bonding wafer 2, and the separation part 14 is separated. The separation part 14 and the connection part 16 both have a wafer-like design. The separation part 14 is preferably thicker than the connection part 16, the separation part 14 is preferably at least 1.25 times or at least 1.5 times or at least 1.75 times or at least 2 times or at least 2.25 times or at least 2.5 times or at least 2.75 times or at least 3 times or at least 3.25 times or at least 3.5 times or at least 3.75 times or at least 4 times or at least 4.25 times or at least 4.5 times or at least 4.75 times or at least 5 times or at least 5.25 times or at least 5.5 times or at least 5.75 times or at least 6 times or at least 6.25 times as thick as the connection part 16. The thickness of the connection part 16 is preferably determined by the mean distance of the planar surfaces of the connection part 16 from one another. The thickness of the separation part 14 is preferably determined by the mean distance of the planar surfaces of the separation part 14 from one another.
In step VI, the stress-producing layers 10 are removed from the produced multi-component wafer 1, in particular MEMS wafer 1, by cleaning and are preferably likewise removed from the separation part 14.
The separation part 14 is then fed in a further step to a treatment device 24. The treatment device 24 produces an oxide layer by material application and/or by material conversion, by means of which oxide layer at least one preferably planar surface of the separation part 14 is formed.
Before or after production of the oxide layer, a material-removing step is preferably performed, in particular a polishing, lapping, etching and/or chemical-mechanical polishing, by means of which at least one surface or a surface portion of the detachment layer 14 and/or of the bonding wafer 2 is smoothed, i.e. experiences a roughness reduction at least in part.
Due to the roughness reduction and the oxide layer production, the separation part 14 is reconfigured to form a further bonding wafer 3. This further bonding wafer 3 is then used as bonding wafer 2 in accordance with the method described by steps I-VI.
The present invention thus relates to a method for producing a multi-component wafer 1, in particular a MEMS wafer 1. The method according to the invention preferably comprises at least the following steps: providing a bonding wafer 2, wherein at least one surface portion 4 of the bonding wafer 2 is formed by an oxide layer, providing a donor wafer 6, wherein the donor wafer 6 is thicker than the bonding wafer 2, bringing the donor wafer 6 into contact with the surface portion 4 of the bonding wafer 2 formed by the oxide layer, forming a multilayer arrangement 8 by connecting the donor wafer 6 and the bonding wafer 2 in the region of the contact, arranging or producing a stress-producing layer 10 on at least one exposed planar surface 12 of the multilayer arrangement 8, thermally treating the stress-producing layer in order to produce mechanical stresses within the multilayer arrangement 8, wherein the stresses in the portion of the multilayer arrangement 8 formed by the donor wafer 6 are so great that a crack forms in the donor wafer 6, by means of which crack the donor wafer 6 is split into a separation part 14 and a connection part 16, wherein the connection part 16 remains on the bonding wafer 2, and wherein the split-off separation part 14 has a greater thickness than the connection part 16.
The present invention thus relates to a method for producing a multi-component wafer, in particular a MEMS wafer. The method according to the invention comprises at least the following steps: providing a bonding wafer 2, wherein at least one surface portion 4 of the bonding wafer 2 is formed by an oxide layer, providing a donor wafer 6, wherein the donor wafer 6 is thicker than the bonding wafer 2, bringing the donor wafer 6 into contact with the surface portion 4 of the bonding wafer 2 formed by the oxide layer, forming a multilayer arrangement 8 by connecting the donor wafer 6 and the bonding wafer 2 in the region of the contact, producing modifications 18 in the interior of the donor wafer 6 for predefining a detachment region 11 for separating the multilayer arrangement 8 into a separation part 14 and a connection part 16, wherein the modifications 18 are produced prior to the formation of the multilayer arrangement 8 or after the formation of the multilayer arrangement 8, separating the multilayer arrangement along the detachment region as a result of a weakness of the multilayer arrangement brought about by the production of a sufficient number of modifications or as a result of a production of mechanical stresses in the multilayer arrangement, wherein the connection part 16 remains on the bonding wafer 2, and wherein the split-off separation part 14 has a thickness greater than the connection part 16.
Illustration 2 of
The third illustration shows that a stress-producing layer 114 has been produced or arranged on the surface 116 over which the LASER beams 112 were introduced into the donor substrate 12 for production of the modifications 110. The stress-producing layer 114 is thermally treated or temperature-controlled, in particular cooled, in order to produce mechanical stresses in the donor substrate 12. By means of the thermal treatment of the stress-producing layer 114, the stress-producing layer 114 contracts, whereby the mechanical stresses are produced in the donor substrate 12. The previously produced indentations 16 form notches, through which the mechanical stresses can be conducted in such a way that the crack 120 resulting from the stresses propagates in a targeted manner in the region of crack formation predefined by the modifications 110. The indentation ends 118 therefore are preferably adjacent to the particular region of crack formation predefined by the modifications 110. It is preferably always the case that only precisely the solid-body layer 11 of which the indentation 16 is distanced least far from the stress-producing layer 114 is split off.
Illustration 4 shows a state following crack propagation. The solid-body slice 11 has been split off from the donor substrate 12, and the stress-producing layer 114 initially still remains on the surface 116 of the solid-body slice 11.
Reference sign 128 denotes the side of the solid-body slice 11 which is denoted here as the underside of the solid-body slice 11, and reference sign 130 denotes the side of the solid-body slice 11 which is denoted here as the upper side of the solid-body slice 11.
Illustration 5 shows a method in which the solid-body layer 11 is detached from the donor substrate 12 without a stress-producing layer 114. Here, following production of the indentation 16, so many modifications 110 are preferably produced by means of LASER beams 112, that the solid-body layer 11 detaches from the donor substrate 12. The dashed line Z here preferably characterises a centre or an axis of rotation of the donor substrate 12. The donor substrate 12 is preferably rotatable about the axis of rotation Z.
In accordance with the second illustration of
The grinding tools 122 shown in
The second illustration of
Illustration 3 of
Illustration 4 of
It can also be seen from illustration 5 of
The present invention thus relates to a method for separating solid-body slices 11 from a donor substrate 12. Here, the method according to the invention comprises the following steps:
Providing a donor substrate 12, removing material of the donor substrate 12 starting from a surface 14 extending in the peripheral direction of the donor substrate 2 towards the centre Z of the donor substrate 12 in order to produce an indentation 16, wherein the material is removed by means of ablation LASER beams 18 and/or the indentation 16 is produced asymmetrically, producing modifications 110 in the interior of the donor substrate 12 by means of further LASER beams 112, wherein the modifications 10 are positioned in such a way that they are adjacent to the indentation 16, wherein the solid-body slice 11 is detached from the donor substrate 12 by means of the produced modifications 110, or a stress-producing layer 114 is produced or arranged on a surface 116 of the donor substrate 12, which surface is oriented at an incline to the peripheral surface and in particular is planar, and mechanical stresses are produced in the donor substrate 12 by means of a thermal treatment of the stress-producing layer 114, wherein a crack 120 for separating a solid-body layer 11 is created by the mechanical stresses and propagates, starting from the indentation 16, along the modifications 110.
The present invention thus relates to a method for separating solid-body slices 11 from a donor substrate 12. Here, the method according to the invention comprises the following steps:
producing modifications 110 in the interior of the donor substrate 12 by means of LASER beams 112, wherein a detachment region is predefined by the modifications 110, along which detachment region the solid-body layer 11 is separated from the donor substrate 12 or the multilayer arrangement,
removing material of the donor substrate 12, starting from a surface 14 extending in the peripheral direction of the donor substrate 12 towards the centre Z of the donor substrate 12, in particular in order to produce a peripheral indentation 16, wherein the detachment region is exposed by the material removal, separating the solid-body layer from the donor substrate, wherein the donor substrate is weakened in the detachment region by the modifications in such a way that the solid-body layer 11 is detached from the donor substrate 12 as a result of the material removal or such a number of modifications are produced after the material removal that the donor substrate is weakened in the detachment region in such a way that the solid-body layer 11 is detached from the donor substrate 12 or a stress-producing layer 114 is produced or arranged on a surface 16 of the donor substrate 12, which surface is oriented at an incline to the peripheral surface and in particular is planar, and mechanical stresses are produced in the donor substrate 12 by means of a thermal treatment of the stress-producing layer 114, wherein by means of the mechanical stresses a crack 120 for separating a solid-body layer 11 is created and propagates, starting from the surface of the donor substrate exposed by the material removal, along the modifications 110.
It can also be deduced from illustration 2 of
Illustration 3 of
Illustration 4 of
The present invention thus relates to a method for separating solid-body slices 21 from a donor substrate 22. Here, the method according to the invention comprises the following steps:
providing a donor substrate 22, producing modifications 210 in the interior of the donor substrate 22 by means of LASER beams 212, wherein the LASER beams 212 penetrate the donor substrate 22 over a planar surface 216 of the donor substrate 22, wherein the totality of the LASER beams 212 is inclined relative to the planar surface 216 of the donor substrate 22 in such a way that a first portion 236 of the LASER beams 212 penetrates the donor substrate 22 at a first angle 238 to the planar surface 216 of the donor substrate 22 and at least one further portion 240 of the LASER beams 212 penetrates the donor substrate 22 at a second angle 242 to the planar surface 216 of the donor substrate 22, wherein the value of the first angle 238 differs from the value of the second angle 242, wherein the first portion 236 of the LASER beams 212 and the further portion 240 of the LASER beams 212 are focused in the donor substrate 22 in order to produce the modification 210, wherein the solid-body slice 21 is detached from the donor substrate 22 by the produced modifications 210 or a stress-producing layer 214 is produced or arranged on the planar surface 216 of the donor substrate and mechanical stresses are produced in the donor substrate 22 by means of a thermal treatment of the stress-producing layer 214, wherein a crack 220 for separating a solid-body layer 21 is created by the mechanical stresses and propagates along the modifications 210.
The second illustration of
Illustration 3 of
Illustration 4 of
It can also be seen from illustration 5 of
Alternatively, it is also conceivable that all modifications 210 of the detachment region or the plurality of modifications 210 of the detachment region 211 are produced by the LASER beam 260 inclined at an angle α1 relative to the longitudinal axis L.
Additionally or alternatively, within the sense of the present invention, the modifications 210 in the edge region can be produced by a further LASER beam 262, 264 inclined relative to the longitudinal axis L of the donor substrate 22, wherein this LASER beam preferably penetrates the donor substrate 22 over a peripheral surface of the donor substrate 22. It can be seen from the illustration that a LASER beam 262, for production of the modifications 210 in the edge region, can be introduced into the donor substrate 22 over the peripheral surface for example at an angle α2, which is greater than 0° and smaller than 90°, relative to the detachment region 211. It can also be seen from the illustration that a LASER beam 264, in order to produce the modifications 210, can be introduced into the donor substrate 22 over the peripheral surface of the donor substrate 22 in the direction of extent of the detachment region 211. Here, the LASER beam 264 is preferably inclined at an angle α3, between 80° and 100°, in particular 90° or substantially 90°, relative to the longitudinal axis L of the donor substrate 22.
A modification 210 can thus be produced in the region of the edge by one of the LASER beams 260, 262, 264.
Furthermore, in accordance with the invention, the statements provided with reference to
In accordance with
The present invention therefore relates to a method for separating solid-body slices 21 from a donor substrate 22. The method according to the invention comprises the following steps: providing a donor substrate 22, producing at least one modification 10 in the interior of the donor substrate 2 by means of at least one LASER beam 212, wherein the LASER beam 212 penetrates the donor substrate 22 over a planar surface 216 of the donor substrate 22, wherein the LASER beam 212 is inclined relative to the planar surface 216 of the donor substrate 22, in such a way that it penetrates the donor substrate at an angle that is unequal to 0° or 180° relative to the longitudinal axis of the donor substrate, wherein the LASER beam 212 is focused in the donor substrate 22 in order to produce the modification 210, wherein the solid-body slice 21 is detached from the donor substrate 22 by the produced modifications 210 or a stress-producing layer 214 is produced or arranged on the planar surface 216 of the donor substrate 22 and mechanical stresses are produced in the donor substrate 22 by a thermal treatment of the stress-producing layer 214, wherein a crack 220 for separating a solid-body layer 21 is produced by the mechanical stresses and propagates along the modifications 210.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2015 004 601.2 | Apr 2015 | DE | national |
| 10 2015 006 971.3 | Jun 2015 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/064104 | 6/23/2015 | WO | 00 |
