WO2011131847A1

WO2011131847A1 - Microtechnology proven for transferring at least one layer

Info

Publication number: WO2011131847A1
Application number: PCT/FR2010/050767
Authority: WO
Inventors: Aurélie Tauzin; Anne-Sophie Stragier
Original assignee: Commissariat A L'energie Atomique Et Aux Energies Alternatives
Priority date: 2010-04-21
Filing date: 2010-04-21
Publication date: 2011-10-27
Also published as: EP2422365B1; EP2422365A1; JP5577456B2; JP2013526030A

Abstract

A microtechnology proven for transferring at least one layer comprising steps in which: a first substrate 20 is prepared comprising a porous layer 11 buried under a useful surface at a non-zero distance; a weakened region 13 is formed by ion implantation between this porous layer and this useful surface; the first substrate is bonded to a supporting substrate 30; a mechanical stress is applied to cause separation at the porous layer so as to obtain, on the one hand, a remnant of the first substrate and, on the other hand, a separated layer rigidly connected to the supporting substrate and comprising a bared surface; processing steps are carried out on the bared surface of the separated layer; the separated layer is bonded, by way of the surface to which the processing steps were applied, to a second supporting substrate ; and a heat treatment is applied to cause separation at the weakened region so as to obtain, on the one hand, a remnant of the separated layer which is rigidly connected to the second supporting substrate and, on the other hand, a remnant of this separated layer which is rigidly connected to the first supporting substrate.

Description

Method for transferring at least one micro-technological layer

State of the art

The invention generally relates to the transfer of a layer from a first substrate to a second substrate, then optionally to a third substrate, etc. Various transfer techniques are known to date.

The "Eltran ®" process describes a thin film transfer process based on the formation of a fragile layer in a first substrate, technological steps applied to a surface portion of this substrate such as oxidation, epitaxy, circuit production, etc. the bonding of the first weakened substrate by this surface portion on a support substrate (by molecular or anodic bonding or via adhesives) and the fracture caused at the level of the layer, for example by the application of mechanical stresses. This fragile layer is in principle a porous layer, generally obtained by anodizing the material from a free face; this porous layer is typically located at the surface at the time of its formation. Inasmuch as it is frequently necessary later that this porous layer be buried at a non-zero depth of the surface, it is known to recrystallize a part of this porous layer whose thickness, starting from the free surface determines the depth of the residual porous layer. However, most often, the starting substrate is supplemented by the epitaxial deposition of an additional layer (hence the name of the process, which derives from "Epitaxial Layer Transfer".) Usually, the material constituting the substrate silicon is the starting material and the second substrate is at least electrically insulating surface, so that after transfer of the layer of the starting substrate which overcomes the porous layer, silicon on insulator ("SOI") is obtained.

Another transfer method is known as the "Smart Cut® Process"; it is a thin film transfer process based on the implantation of gaseous ions, the bonding of the substrate implanted on a support substrate and the possible realization of technological steps, and finally the fracture caused at the level of the implanted zone, for example by a heat treatment and / or by application of mechanical stresses.

It is easily understood that in the development of microtechnological components, that is to say, electronic components, optical, mechanical, etc. the dimensions of which are smaller than one millimeter or even one micron, it may be necessary to carry out several transfers so as to proceed with the technological steps at the various depth levels necessary. However, to avoid an imprecise control of where the fracture occurs, it has seemed useful so far to define stages of development such that there is only one fragile area, at a time given within a given structure (that is, a set of substrates or layers assembled by any suitable means, but it is understood that such a precaution runs counter to the concern for productivity that imposes in the industrial world.

Technical problem and presentation of the invention

The subject of the invention is a method for transferring microtechnological layers allowing a greater speed of production and a greater flexibility in the choice of the technological steps to be carried out.

The invention proposes for this purpose a method for transferring at least one layer comprising steps in which:

a first substrate is prepared comprising a porous layer buried beneath a useful surface at a non-zero distance,

an embrittled zone is formed by ion implantation between this porous layer and this useful surface,

the first substrate is bonded to a support substrate, a detachment is caused at the level of the porous layer, by application of a mechanical stress, so as to obtain, on the one hand, a residue of the first substrate and, on the other hand, a detached layer integral with the support substrate. and having a bare surface,

technological steps are carried out on the exposed surface of the detached layer,

the layer detached by the surface to which technological steps have been applied is glued to a second support substrate,

- detachment is caused at the weakened zone, by applying a heat treatment, so as to obtain, on the one hand, a residue of the detached layer which is integral with the second support substrate and on the other hand , a residue of this detached layer which is integral with the first support substrate.

The invention thus proposes a method for producing a dismountable structure comprising, at a given moment, two buried fragile zones, which allow a double layer transfer by a controlled mechanical or thermal separation, with the possibility of carrying out certain technological steps between the two separations. It should be noted that these two buried zones are formed successively within the same set; it is not only a bonding of two substrates each of which has previously been subjected to a weakening treatment, regardless of the embrittlement treatment of the other.

It will be noted that the invention allows a good control of the fracture site by the realization, in an appropriate order, of fragile zones having sufficiently different characteristics so that, by application of differentiated stresses, it is possible to guarantee that the fractures of these zones fragile occur in a well-determined order compatible with a good efficiency of the process of elaboration.

According to advantageous features of the invention, possibly combined:

the zone weakened by implantation is at a distance from the useful surface of the first substrate which is greater than the distance between this zone embrittled and the porous layer, for example more than double; an inverse relationship is possible; this makes it possible to form both a thin layer and a thick layer (in the sense of micro-technology),

the first substrate is prepared by anodizing a starting substrate so as to make it porous on the surface and then by epitaxially growing a dense layer from this porous layer,

the porous layer is formed of at least two porous sub-layers having different porosities,

the porous sub-layer of lesser porosity is closer to the free surface than the other,

the porous layer has a thickness of at least one micron, which allows a good localization of the mechanical energy at the moment of detachment,

the layer separating the porous layer from the free surface is made of monocrystalline material; it is for example silicon, or germanium (or a Si-Ge alloy), or in AsGa, or other materials of microtechnology,

the layer separating the porous layer from the free surface has a thickness of at least 2 microns, which contributes to obtaining, after the second detachment (at the level of the weakened zone), two useful layers,

the weakened zone is formed by implantation of at least one gaseous species (in fact other options are possible, notably with implantation of species causing the formation of precipitates which can be rendered liquid, when detachment is desired) ,

at least one hydrogen is implanted; alternatively, or in addition, at least helium is implanted,

detaching at the level of the porous layer by localized application of mechanical energy,

the technological steps comprise the formation of at least a part of a micro-technological component; these are, for example, deposition steps at low temperature, cutting to delimit for example vignettes, screen printing and more generally technological steps generating strong mechanical constraints but not requiring high thermal budgets (temperature and duration).

the detachment is caused at the level of the fragile zone by the application of a combined heat treatment, or not, with an application of mechanical energy,

the remainder of the first substrate is used as the first substrate during a new cycle of implementation of the process,

- Technological steps are also applied to each part of the loose layer which are separated during the detachment at the weakened zone; this makes it possible to continue in parallel two microstructure processing processes, resulting in increased productivity.

Objects, characteristics and advantages of the invention will emerge from the description which follows, given by way of nonlimiting illustrative example, with reference to the appended drawings in which:

FIG. 1 is a schematic view of a starting substrate,

FIG. 2 is a schematic view of this substrate after formation of a porous layer by anodization,

FIG. 3 is a diagrammatic view after deposition of a surface layer,

FIG. 4 is a schematic view after embrittlement by ion implantation,

FIG. 5 is a schematic view after assembly with an intermediate substrate, by molecular bonding,

FIG. 6 is a schematic view of the upper part of the assembly of FIG. 5, after separation along the porous layer,

FIG. 7 is a schematic view after formation of components on the face exposed by the separation along the porous layer, FIG. 8 is a schematic view after assembly with a final substrate, along the exposed face, and

FIG. 9 is a schematic view of the assembly formed in FIG. 8, after separation along the weakened layer.

Figures 1 to 9 show schematically the method of the invention.

Begin (see Figure 1) by preparing, in any suitable manner, a starting substrate 10, having a useful face 10A. This substrate may be solid or be formed of a support on which is formed a working layer. In fact, in the following, only the upper part of the substrate 10 is solicited by the method.

Then, under the usable face 10A, a porous layer 11 is formed (see FIG. 2). This layer 1 1 is typically formed by anodizing the surface portion of the substrate 10; alternatively, it may be formed by deposition, for example by evaporation, of an additional layer, directly porous or made at least partially porous by a suitable treatment. Such a porous layer can thus be formed by compacting metal powders or by controlled deposition of porous silicon according to the technique described in the article "Microfabrication Using One-Step LPCVD Porous Polysilicon Films" by Dougherty et al. - Journal of Microelectromechanical Systems, Vol. 12, No. 4, August 2003 pp. 418-424.

According to yet another variant not shown, the porous layer is itself formed of several layers having different porosities.

The material of at least the portion intended to form the porous layer is advantageously made of silicon, since it is a material of which the treatment conditions to be applied to generate a given porosity are well known; however, alternatively, the constituent material of this portion may be:

- more generally a semiconductor material (InP, GaAs,

Ge, ...); in fact, the semiconductors can be made porous by anodization, a metal (aluminum, copper, steel, nickel, titanium, etc.) deposited by spray ("spray") or by compacting a powder of these metals,

an oxide, for example a glass by rotation, sometimes called "SOG" (spin on glass) abbreviated (it is a technique of realization notably described in the document US6919106) or an oxide obtained by the deposit and the oxidation of a metal layer.

On this porous layer, a surface layer 12 is then produced (see FIG.

A first multilayer substrate, generally noted, having a porous layer buried at a non-zero distance under a free surface 20A has thus been prepared.

This layer is advantageously formed by epitaxial growth according to the crystallographic characteristics of the constituent material of the porous layer, so that this layer 12 has a density much higher than that of the porous layer, in practice close to 100%, similar to that of the part of the substrate located under the porous layer. Alternatively, this layer 12 may consist of a surface portion of the porous layer which is recrystallized. As a variant, this layer 12 may be made by depositing a polycrystalline material (for example silicon) and crystallization of this layer by appropriate annealing.

This superficial layer, located between the porous layer and the free surface of the substrate of FIG. 3, is homogeneous here by being formed of a single layer; alternatively, this layer may be formed of several sublayers, including a thermal oxide layer (constituting the free surface), or a bonding layer for the rest of the process.

This first substrate 20 is then subjected to ion implantation (see Figure 4) so as to weaken the surface layer 12 in a zone 13 located at a given depth, noted d1; this implantation, and the resulting embrittlement, is therefore performed above the level of the porous layer, at a non-zero distance thereof, denoted d2. The relative proportions between these distances d1 and d2 can be chosen according to the needs. The thickness d1 of the upper part 12A of the layer 12 situated above the weakened zone 13 is in this case substantially greater than that d2 of the lower part 12B located under this weakened zone 13 but above the porous layer 11 ; it can therefore be said that, in the example considered, the fragile zone delimits within the layer 12 a thin layer 12A and a thick layer 12B.

The implantation performed for the formation of the weakened zone 13 is in practice carried out with hydrogen, or another gaseous species, in particular from rare gases, or a combination of such species; it is advantageously a co-implantation of hydrogen and helium.

Preferably, the surface layer 12 has an overall thickness of at least 2 microns, preferably with a thickness sufficiently greater than this value of 2 microns so that the weakened zone is itself at least 2 microns from the porous layer.

At this stage, there is thus a first substrate which comprises two fragile zones of different natures, namely a fragile layer 11 located at depth, which is porous, and a weakened zone 13 which is closer to the surface, obtained by implantation.

It is possible, before or after the implantation step, to perform technological steps (see below about layer 17).

After a possible preparation of the free surface 20A, the first substrate 20 is then assembled to a second substrate 30, by gluing (see Figure 5) by means of a supply of material, or preferably by molecular bonding preferably. Any thermal annealing may be applied to this set 20 + 30 to consolidate the interface between these substrates.

Then, by applying a mechanical stress, a detachment of the lower part of the initial substrate 10, vis-à-vis the rest of the structure of this Figure 5, at the level of the porous layer 1 1. The remaining part is shown schematically in Figure 6.

If the porous layer 11 is in fact formed of several porous layers of different porosities, the detachment is in practice located within the porous layer having the greatest porosity. The mechanical stress is shown schematically in Figure 5 by a point; this mechanical stress can indeed be applied by an introduced blade acting at the porous mark. Alternatively, the detachment of the lower part of the starting substrate 10 can be caused by the application of a torque to each of the substrates 20 and 30, provided that the weakened zone 13 is able to resist (this is why, it may be preferable to apply the mechanical stress in a localized way, by a point). The applied mechanical energy can also be provided by a high pressure jet directed on the edge of the porous layer, or in the form of ultrasound.

The surface 14 thus exposed can be subjected to a polishing treatment, for example chemical-mechanical, before being the subject of technological steps, that is to say stages involved in the manufacture micro-technological components, such as electronic, mechanical components. The result of such steps is shown schematically in FIG. 7 by the formation of a layer 15 on the free surface 14 exposed as a result of the detachment. In order to avoid inadvertent detachment at the fragile zone 13, the realization of these technological steps must be carried out at a moderate temperature, typically below 500 ° C .; when the realization of these technological steps involves the application of mechanical constraints, it must also be ensured that these constraints remain insufficient to cause detachment at this layer 13. In fact, the knowledge of the technological steps to be accomplished allows the one skilled in the art to identify to what extent he can weaken the zone 13 without risking detachment during these technological steps known in advance. Of course, the technological steps may, in a variant, modify the layer 12B under its surface 14, without necessarily generating the formation of an excess thickness.

The surface 14, with the optional layer 17, is then contiguous to one face of a third substrate 40 (see FIG. 8). This assembly is advantageously carried out by gluing, for example by adding material, or even by molecular bonding, and conventional treatments for this purpose may be applied to promote this collage. Thermal annealing can also be applied to consolidate this bonding (particularly if it is a molecular bonding).

It is then possible to detach the thin layer 12A from the thick layer 12B at the weakened zone 13 (see FIG. 9). This detachment is advantageously obtained by the application of a heat treatment, optionally supplemented by the application of mechanical energy. This heat treatment is chosen at a sufficiently low temperature (in practice between 200 ° C. and 500 ° C.) so as not to risk degrading the result 17 of the technological steps; the lower the temperature, the more useful it may be to add mechanical energy (it may not only be applied locally, at the weakened zone (as for detachment at the porous layer), but also in a global manner by applying forces to the substrates 30 and 40, for example torques or tensile antagonistic forces.

It will be appreciated that the method which has just been described makes it possible to produce:

a structure (40 + 17 + 12B) comprising a technological layer 17 which is buried under a thick layer 12B; - a structure (30 + 12A) comprising a thin layer 12A on a support 30.

Each of these structures can then be the subject of subsequent technological steps, independent or not, while the residual portion of the starting substrate 10 can be recycled for a new cycle as described above. Of course, if the thickness of the layer 12B allows it, it can be provided to use the structure 40 + 17 + 12B as a starting substrate in place of the substrate 10 for a new cycle similar to that just described. .

This method makes it possible to handle relatively thick layers (> 2μηη), homogeneous and of good quality. It makes it possible to carry out technological steps on both sides of the active layer thus produced, by proposing two distinct modes of rupture (mechanical or thermal). The Technological steps can then be applied to the step of Figure 7 or after the step of Figure 9, depending on the thermal or mechanical stresses they induce.

According to this method, the second substrate 30 serves as a support and must allow a stiffening effect vis-à-vis the layer 12A to propagate a fracture line at the implanted area without blistering on the implanted surface. In fact, if this layer 12A has a sufficient thickness to be self-supporting, this second substrate can be omitted.

It is understood that the substrates 30 and 40 must be able to withstand a heat treatment in the range of 200-500 ° C.

Advantageously, the detachment step of FIG. 5 may include, in addition to the application of mechanical stresses, a selective chemical etching of the porous layer.

As indicated above, the detachment step of FIG. 9 may consist of a heat treatment alone or in combination with the application of mechanical stresses.

It will be understood that the difference in nature of the fragile layers 1 1 and 13 allows a well controlled release of a detachment within each of them, by a suitable choice of energy forms.

By way of example, if the technological steps of FIG. 17 comprise the formation of an insulating layer while the epitaxial layer 12 is of monocrystalline silicon, the detachment of FIG. 9 leads to the obtaining of a structure of the type "Silicon On Insulator" 40 + 17 + 12B as well as a transfer of a thin layer 12A from the starting substrate 10 to the substrate 20.

Example 1

The starting substrate is a substrate Si (100) doped p + (p = 10mΩ / cm). A double layer of porous Si is formed by electrochemical anodization, in two steps:

[HF] (%) Current Density Anodizing Time

(mA / cm ² ) (sec) Step 1 25 5 60

Step 2 12.5 40 60

A low porosity surface layer (20% of pores) with a thickness of 1.2 μm and a highly porous buried layer (70% of pores) with a thickness of 600 nm, located under the low porosity layer, are thus obtained.

The porous Si substrate is placed in an epitaxy frame, under H2 at

1100 ° C to reconstruct the surface of the low porosity layer. The growth of a monocrystalline Si layer can then be carried out from the reconstructed surface, for example at 1100 ° C. under dichlorosilane. The epitaxial parameters (gas flow, duration) are chosen so that the thickness of the epitaxial layer is 15μηη.

The epitaxial layer is implanted with H + ions under the following conditions: 15keV energy, dose 5E16 / cm ² . Advantageously, implantation is performed by immersion in a hydrogen plasma.

The implanted porous plate is glued on a temporary support, which can be a Si plate, via a low-cost adhesive (ceramic, metallic paste, high-temperature polymer, etc.). The fracture is caused at the level of the highly porous layer, by the application of ultrasound in the range 15-400kHz, 200-6000W. The implanted epitaxial layer is thus transferred to the temporary support. It is possible to carry out technological steps for manufacturing solar cells, such as metallization by screen printing (involving high mechanical stresses). The processed surface is then glued on a low cost final support (ceramic, high temperature plastic, steel, ...) via a low-cost glue, and the fracture is caused at the implanted zone by annealing at 800 ° C. The active layer thus reported can then be processed, for example it is possible to perform surface texturing and deposit an anti-reflection layer, so as to produce a solar cell. The initial substrate and the temporary support can be recycled. Example 2

The starting substrate is a p + doped Si substrate (100) (p = 10 mΩ / cnn). A porous Si layer is formed by electrochemical anodization according to the following protocol:

This gives a moderately porous layer (40% pores) of thickness 3μηη. The porous Si substrate is placed in an epitaxial frame, under H ₂ at 1100 ° C, in order to reconstruct the surface of the weakly porous layer. The growth of a monocrystalline Si layer can then be carried out from the reconstructed surface, for example at 1100 ° C. under dichlorosilane. The thickness of the epitaxial Si layer is chosen to be of the order of 3 μm. The epitaxial layer is implanted with H ⁺ ions under the following conditions: 150keV energy, dose 5 ^E 16 / cm ² . The implanted porous plate is glued on a plate Si covered with a thermal oxide, by molecular adhesion. The fracture is caused at the level of the highly porous layer by the insertion of a blade at the bonding interface. The implanted epitaxial layer is thus transferred to the oxidized plate. It is possible to carry out technological steps involving strong mechanical constraints (engraving, deposits, ...). The processed surface is then bonded to a final support which may be an Si plate by molecular bonding via a planarized oxide. Fracture is caused at the implanted area by annealing at 500 ° C. The epitaxial layer is then separated into two layers of thickness ~ 1, 5μηη: one obtains firstly a process layer reported on a Si substrate, and secondly a conventional SOI substrate. Each layer reported can then be processed, for example, it is possible to carry out conventional steps for manufacturing microelectronic components (doping, deposits, etc.). The initial substrate can be recycled.

It will be appreciated that, by teaching to implant directly in the substrate containing the porous layer, the invention makes it possible to manipulate a homogeneous and relatively thick layer and to perform technological steps on both sides of this layer. Active layer is defined between the porous layer and the implanted layer, which leaves a great latitude on the thickness of this layer; this thickness can easily be greater than one micron, or even 10 microns or more (and without resorting to very high implantation energies, which could prove to be expensive).

Claims

1. A method of transferring at least one micro-technological layer comprising steps according to which:

a first substrate (20) is prepared comprising a porous layer (1 1) buried beneath a useful surface (20A) at a non-zero distance,

an embrittled zone (13) is formed by ion implantation between this porous layer and this useful surface,

the first substrate is bonded to a support substrate (30),

- detachment at the level of the porous layer (1 1), by application of a mechanical stress, so as to obtain, firstly, a residue of the first substrate and, secondly, a detached layer (12) integral with the support substrate and having a exposed surface (14),

technological steps (17) are carried out on the exposed surface (14) of the detached layer,

the attached layer is adhered, by the surface to which technological steps have been applied, to a second support substrate (40),

- detachment is caused at the weakened zone (13), by applying a heat treatment, so as to obtain, on the one hand, a residue of the detached layer which is integral with the second support substrate (40) and, on the other hand, a residue of this detached layer which is integral with the first support substrate (30).

2. Method according to claim 1, characterized in that the embrittled zone by implantation is at a distance (d1) from the useful surface of the first substrate which is greater than the distance (d2) between this weakened zone and the porous layer.

3. Method according to claim 1 or claim 2, characterized in that the first substrate (20) is prepared by anodizing a starting substrate (10) so as to render it porous on the surface and then by epitaxial growth. a dense layer (12) from this porous layer.

4. Method according to any one of claims 1 to 3, characterized in that the porous layer is formed of at least two porous sub-layers having different porosities.

5. Method according to claim 4, characterized in that the porous sub-layer of lower porosity is closer to the free surface than the other.

6. Method according to any one of claims 1 to 5, characterized in that the porous layer (1 1) has a thickness of at least one micron.

7. Method according to any one of claims 1 to 6, characterized in that the layer (12) separating the porous layer (1 1) of the free surface (20A) is monocrystalline material.

8. Method according to any one of claims 1 to 7, characterized in that the layer (12) separating the porous layer (1 1) from the free surface (20A) has a thickness of at least 2 microns.

9. Process according to any one of Claims 1 to 8, characterized in that the weakened zone (13) is formed by implantation of at least one gaseous species.

10. Process according to claim 9, characterized in that at least hydrogen is implanted.

1 1. Process according to Claim 9, characterized in that at least helium is implanted.

12. Method according to any one of claims 1 to 1 1, characterized in that it causes the detachment at the porous layer (1 1) by localized application of mechanical energy.

13. Method according to any one of claims 1 to 12, characterized in that the technological steps comprise the formation of at least a portion of a micro-technological component.

14. Method according to any one of claims 1 to 13, characterized in that the technological steps comprise the formation of at least one insulating layer.

15. Method according to any one of claims 1 to 14, characterized in that it causes the detachment at the fragile zone (13) by applying a heat treatment combined with an application of mechanical energy.

16. Method according to any one of claims 1 to 15, characterized in that the residue of the first substrate is used as the first substrate in a new cycle of implementation of the method.

17. Method according to any one of claims 1 to 16, characterized in that it also applies technological steps to each part of the detached layer which are separated during the detachment at the weakened zone.