KR100742240B1 - Method for transferring a thin layer comprising a step of excess fragilization - Google Patents

Abstract

The present invention relates to a method for transferring a thin film 18 from a source substrate 10 to a target support 30, comprising the following steps: a) Injecting an ion or gaseous material into a source substrate, thereby providing a source substrate. Forming a region in the source substrate, called a cleavage zone, defining a thin film 18 in the substrate; b) transferring the source substrate onto the target support to bond the thin film to the target support; c) separating the thin film 18 from the source substrate 10 along the cleavage region. The invention is characterized by including the following method prior to step b): excess fragilization to the cleaved region 16 produced by heat treatment and / or mechanical stress on the source substrate. ) Process to form.

Film transfer, Overbreak, Cleavage area, Overbreak, Source substrate, Target support, Thermal budget

Description

Method for transferring a thin layer comprising a step of excess fragilization

The present invention relates to a method of transferring a thin film of a substrate called a source substrate onto a support called a target substrate.

The invention finds particular application in microelectronics, micromechanics, integrated optics and integrated electronics.

For example, the present invention is a thin film, the material of which is selected in consideration of the specific properties of the material, which is delivered to the support to enable the production of a structure forming a number of stacks. Thus, the advantages of the thin film and the support material can be combined. In particular, the transfer of the membrane can cause parts to be bonded to the same structure as the prior art, which exhibits incompatibilities such as, for example, a significant difference in the coefficient of thermal expansion.

The following is a description of a specific number of materials, the entire contents of which can be found by reference to the materials described after the detailed description of the invention.

Among the methods commonly used for the formation of thin films, in particular splitting methods, the so-called "smart-cut" method is well known and its contents are described in the data (1). .

The "smart-cut" method is inherently based on the method of injecting hydrogen or other gas in neutral or ionic form into the substrate in order to form a cracking fracture zone in the substrate.

In the case of a planar substrate, the cleavage region extends almost parallel to the substrate and is located at a depth determined by the implantation energy within the substrate. The cleavage region thus defines a thin outer film that extends within the substrate to a thickness from the cleavage region to the substrate surface.

The second step involves bonding the source substrate to the target support to merge the thin film with the target support. The thin film may be attached to the target support using an adhesive or / and a bonding layer. It can also be attached through direct aggregation between the surface molecules of the substrate and the target support surface molecules.

However, in the latter case, it is necessary for the surface to be attached to have specific physical properties such as good flatness and low surface roughness.

The final step of the method consists in breaking the substrate along the cleavage region to separate the thin film from the substrate. The film then remains with the target support.

In the case of the method described in the document 1, the fracture (or cleavage) of the substrate is due to the energy supplied by the heat treatment method.                 

Implant conditions define the cleavage region and dominate the separation of the thin film from the substrate.

It is now observed that if the cleavage region breaks too well from the substrate after the implantation step, deformation occurs on the surface of the thin film, although this is desirable for separation. Deformation appears in the form of blisters and is a barrier to attaching the membrane to the target support.

This embrittlement can be coupled with annealing to connect high-dose or low dose ion implantation. Therefore, overbreaking can result in blistering on the surface much more easily because the cleavage zone is near the surface.

In some applications it is desirable to make a self-supported thin film, that is, the thin film can be separated from the source substrate before being attached to the support.

In particular, the thin films thus separated can then be transferred to other target supports, for example, target supports which do not have to be attached to the source substrate before the thin films are separated because the thermal expansion coefficients are similar to each other.

On this subject, reference may be made to data (2), which suggest methods from data (1).

Data (2) suggests a method that enables the separation of its mother substrate from self-supporting thin films. For this purpose, the injected gas species need to be found at a sufficient depth and / or after the injection step, the structure of the thin film is made to be able to separate without blister at the height of the injection zone. A layer of material is deposited.

A description of the technique of forming a thin film by breaking the substrate is described in detail in the material (3), which includes a crush (heat) heat treatment of the substrate by applying mechanical bending, tension, or shear force. It is proposed to complete.

In document (4), which describes a method based on the principle established by the material (1), the thermal budget used to cause the fracture of the source substrate is determined by all thermal treatments applied to the source substrate from implantation to fracture. It is suggested that it depends on the thermal budget.

Thermal budgets are known as a combination of the duration of heat treatment / temperature at which the heat treatment takes place.

In some applications, it is necessary to combine a thin film of a source substrate with a target support whose thermal expansion coefficient is different from that of the source substrate.

In these applications, it is generally desirable to have the structure obtained by combining the source substrate and the target support to receive only enough thermal budget to ensure that the thin film is separated from the source substrate.

One solution to this problem consists in modifying the injection conditions by injecting an excessive amount of injection material. In fact, such excessive implantation makes it possible to reduce the thermal budget for separation fracture (fracture) formation.

대신에

이면 여러 시간 동안 진행되는 열처리 온도는 400℃로부터 280℃로 낮출 수 있다.For example, the source substrate is a silicon wafer and the amount of hydrogen ions implanted

Instead of

Afterwards, the heat treatment temperature for several hours may be lowered from 400 ° C. to 280 ° C.

However, the solution of injecting excessive amounts is not always satisfactory because of the difference in coefficient of thermal expansion that may exist between the substrate and the support. In fact, the thermal budget required for separation is quite high, which causes separation of the substrate and the support and / or breaking of the substrate and / or the support bulk.

Another solution to avoid separating the thin film and target support in conditions where there is a differential thermal expansion effect consists in thinning the source substrate prior to the fracture (cracking) step.

This solution, however, has the disadvantage of adding a thinning process and costly materials, as shown in the data (5).

As discussed above in reference to material (3), the use of mechanical forces to separate the source substrate from the thin film also allows the fracture thermal budget to be reduced, particularly in the case where the materials in contact with one another have different coefficients of thermal expansion. In this case, it is possible to reduce the fracture thermal budget. However, it is not always possible to apply a mechanical force to the source substrate and / or the target support, especially if the material used is a well broken material or if the cleavage area is not sufficiently broken by ion implantation.                 

In conclusion, as mentioned above, thin film separation and transfer techniques involve certain limitations and compromises. This restriction is imposed, in particular, on the type of material used to make the source substrate, thin film and target support.

It is an object of the present invention to present a method of delivering thin films which does not exhibit any difficulties or limitations in the processes described above.

One particular object of the present invention is to provide a process for reducing thermal budgets and forming separation fractures in thin films, even without thermal exposure.

Another object of the present invention is to provide a modified method of delivering a thin film to a target support, in which case the material of the thin film and the target support show different coefficients of thermal expansion.

Another object of the present invention is to provide good adhesion to the target support, with or without an adhesion aid (adhesive agent), and to allow formation of a crack area that breaks very well, thereby providing an excellent surface state (no blister) of the source substrate. It suggests a method of delivery that is maintained.

Finally, another object of the present invention is to provide a delivery method in which a thin film having a free surface having a small surface roughness can be formed on the target support even after the film is delivered.

In order to achieve the above object, it is an object of the present invention to propose a method for delivering a thin film of a source substrate to a target support, more precisely including a step which will be described later.

a) implanting ions or gases into the source substrate to form a region, called a cleavage region, that defines the thin film on the source substrate,

b) attaching the source substrate to the target support to interlock the thin film to the target support,

c) separating the thin film from the source substrate along the cleavage region,

According to the invention, prior to step b) above, the following steps are included:

Forming a film having a thickness with the material between the cleavage region and the substrate surface, the film having a thickness that is thicker, equal or similar to the limiting thickness for the film to self-support, and

Forming an overbroke in the cleavage region by applying heat treatment and / or mechanical force to the source substrate.

According to the first embodiment of the present invention, the forming of the film having a thickness consists of performing the injection step of a) so that the cleavage region can be formed at the above thickness, and the film is formed by the thin film. do.

According to a second embodiment of the present invention, the forming of the film having a thickness consists of performing a step of forming a film called a thicker on the thin film, whereby the thin film and the thickness layer are formed. This forms a film.

The limit thickness of the film is the thickness that allows the structure to be made rigid to allow separation of the film in the cleavage region without the presence of surface blisters. This is the limit thickness that allows the film to self-support. This thickness depends not only on the mechanical properties of the materials, but also on the conditions of separation in step c), for example, an increase in temperature in the heat treatment process.

According to a method in which one advantage of the present invention is achieved, the present invention also includes producing all or part of the microelectronic element and / or micromechanical element and / or photoelectric element before step b).

Separating the thin film from the source substrate in step c) may occur under conditions of heat treatment, mechanical force or combination thereof.

Now, as a result of the over-breaking step, the thermal budget and / or mechanical forces used in step c) for separate fracturing can be reduced particularly. This has the purpose of ensuring that the adhesion between the thin film and the target support is not broken even if the coefficients of thermal expansion differ between the materials in contact with each other.

Another advantage of the present invention is that by suppressing or reducing the mechanical force exerted on the part being contacted, the contact area can be avoided from deteriorating. This makes separation easier.

It is preferable to note that the overbreak formation step is not limited to the effect of restraint of thermal expansion that differs from each other as long as the overbreak formation step is performed before the step (b) of the source substrate being transferred to the target substrate.

According to another advantageous aspect of the present invention, the overbreaking step comprises a heat treatment step using more than or equal to 50% of the overall thermal budget and preferably more than 60% of the thermal budget to enable separation. .

The overall thermal budget contemplated here is that heat treatment that can be used for the formation of components, as well as heat treatments performed within the rigorous framework of the method according to the invention, for example materials between the thin films between steps a) and b). Consider heat treatment for deposition.

As described above, step c) and over-breaking may include applying a mechanical force.

Such mechanical forces include, for example, forces in the form of mechanical pressure and / or forces in the form of mechanical stress and / or gas pressure.

The heat treatment for separation may be chosen sufficiently to allow the thin film to be separated by a simple distance between the source substrate and the target support during step c) or to be a complete separation by only heat treatment. have.

In the implantation step of a), cavities can be formed in place of the cleavage region in the source substrate.

The cavity (or microcavity or small platelet or microbubble) may exist in other forms. The cavity may be spherical and / or may be flat only to a thickness of several times the interatomic spacing. In addition, the cavities may comprise atoms of a gas derived from the free gas phase and / or implanted ions, in which these gases and / or atoms are attached to the atoms of the material to form walls of the cavity. Or it may contain little or even no gas at all.

The heat treatment that the source substrate undergoes, and in particular the heat-treatment that forms overbreaks, can cause coalescence of all or part of the cavities. This adhesion thus causes overbreaking in the cleavage zone.

In addition, this phenomenon allows the formation of a free surface with a small surface roughness of the thin film after transfer and separation crushing.

A film of thickness formation, for example made of silicon (Si), silicon oxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ) or silicon carbide (SiC), covers all or part of the thin film. Thickness for Forming Film The thickness of the formation film is selected in the range of 3 to 10 mu m, for example for silicon oxide (SiO ₂ ).

It is desirable to point out that the film used as the thickness forming film can also be used in whole or in part for forming electronic, optoelectronic or mechanical elements on the surface of the thin film.

The invention also relates to a method comprising the following steps of transferring a thin film of a source substrate:

a) implanting ions or gas species into a source substrate to form a region, called a cleavage region, that defines the thin film on the substrate,

b) separating the thin film from the source substrate along the cleavage region,

According to the invention, the above method comprises the following steps before step b).                 

Forming a film with a material having a thickness between the cleavage region and the surface of the substrate, the thickness being thicker than or equal to or similar to the limit thickness at which the film can self-support, or

Forming over-breaks in the fracture zone by applying heat treatment and / or mechanical forces on the substrate.

The present invention allows the formation of very important overbreaks that can go up to 80-90% of more complete separations due to the presence of thickness formations. This thickness formation is deposited on the surface for the purpose of increasing the above cracking.

Other features and advantages of the present invention will become more apparent with reference to the accompanying drawings, which are described below. This description is given solely for the purpose of illustration and is not intended to limit the invention.

1 is a schematic cross-sectional view of a source substrate and illustrates a process of implanting ions.

FIG. 2 is a schematic cross-sectional view of the source substrate of FIG. 1 illustrating the formation of a thick film.

FIG. 3 is a schematic cross-sectional view of the source substrate of FIG. 2 and illustrating the overbroken forming step.

4 is a schematic cross-sectional view of the structure in which the source substrate of FIG. 3 is delivered to a target support.                 

5 is a schematic cross-sectional view of the structure of FIG. 4 after the source substrate has been broken apart.

The following discussion relates to the transfer of a silicon thin film to a fused silica target support (which is improperly referred to as quartz).

However, the present invention can be used for other solid materials, whether or not they are crystals. Such materials may be dielectric materials, conductive materials, semi-insulating materials, or semiconductors.

Likewise, the target support may be a final or intermediate stage support, such as, for example, a handle, a large substrate or a multilayer substrate.

In particular, the method can be applied to non-semiconductor materials, ferroelectric materials, for example piezoelectric materials such as Rithiumiobate (LiNbO ₃ ), or group III-V semiconductor materials such as gallium arsenide (AsGa) and indium phosphide (InP). It can also be used to deliver the film to silicon or silicon carbide.

1 shows an initial silicon substrate 10. The silicon substrate 10 is implanted with hydrogen ions in the direction indicated by the arrow 12. This injection corresponds to step a1) of the method.

의 도즈와 70 kev의 에너지로 수행되는, 상기한 주입은 기판(10)에 7000Å 정도의 깊이에 미세 공동(14)의 형성을 가능하게 한다.E.g

The implantation, performed at a dose of 70 kev and an energy of 70 kev, allows the formation of the microcavity 14 in the substrate 10 at a depth of about 7000 kV.

This depth also corresponds to the thickness of the membrane 18. The thin film 18 is limited to the surface of the substrate by a region 16, called a cleavage region, which includes a microcavity 14.

Before, or preferably after, the injection step described above, the superficial thin film 18 may be subjected to other treatments, known per se, to form electronic, optical or mechanical elements in the thin film. . These elements are not shown in the drawings for clarity. In this case, these steps are considered for the formation of overbreaking.

Likewise, for the sake of clear interpretation of the drawings, the various layers or features disclosed are not drawn to scale. In particular, very thin films are shown with an exaggerated thickness.

2, which corresponds to the step of using a thickness film during the process, shows the deposition of silicon oxide film 20 on thin film 18 to a thickness similar to or greater than 5 μm. Silicon oxide films are deposited by, for example, plasma-assisted chemical gas-phase deposition at 300 ° C. The thermal budget is selected to prevent blisters from forming in the thickness film formation.

The silicon oxide film 20 acts as a material for forming a thick film of the thin film 18. In other words, it has the purpose of preventing the thin film from deforming under the influence of subsequent heat treatment.

3 corresponds to the overbroken forming step of the present invention. During this step, the substrate is processed for the purpose of breaking the cleavage region 16 even better.

In the illustrated example, heat treatment is performed at a temperature of about 450 ° C. for about 12 minutes.

Such thermal budgets are preferably more than 60% of the thermal budget required to be separated by only annealing. Such formation of overbreak is possible as a film having a sufficient thickness.

During the heat treatment process, it was observed to cause adhesion between the microcavity 14 and the cleavage region 16.

During this process, the thick film 20, covering the thin film 18, prevents deformation of the thin film, in particular the formation of blisters.

In the absence of such a film, a blister will form after about 2 minutes at a temperature of about 450 ° C., which corresponds to only 10% of the heat treatment required for separation.

After the heat treatment step, the surface is polished to improve the roughness of the free surface of the thickness forming film 20 so that molecular gluing can be prepared.

4 shows that the source substrate 10 is delivered to the target support 30, which, unfortunately, is a quartz wafer.

The above transfer is performed by placing the flat surface of the target support into contact with the flat free surface of the thickness forming film 20.

Molecular adhesion to the height of the surfaces placed in contact ensures that the source substrate and the target support are coupled (attached).                 

If such molecular adhesion is not possible due to the physical properties of the material itself or the quality of the surface, the above transfer can take place using a binder or glue.

The intermolecular adhesion can be enhanced by, for example, heat treatment and / or preparation for the surface. In the example described, and because the coefficient of thermal expansion between silicon and quartz is quite different, the above heat treatment is carried out for 20 hours at a relatively low temperature, on the order of 200 ° C.

Such heat treatment can help to cause constraints, for example, fracture of the substrate can be formed along this area.

5 shows step c) of the present invention corresponding to shredding of the source substrate. Such fractures occur along the cleavage region and separate the thin film 18 from the rest of the substrate 10. This remainder can be used again, for example, for delivery of a new thin film.

The thin film 18 is combined with the support 30 with the thickness forming layer 20 therebetween.

In another example, although not shown, if the thickness of the thin film is sufficient to cause no deformation, the thickness forming layer may be omitted. The thin film then contacts the target support directly.

According to an embodiment, mention may be made of using silicon carbide as a substrate, which is implanted with an energy of about 200 KeV to form a film of about 1.5 μm without a thickness forming layer. In this example, overbreaking can be made without a thickness forming layer.                 

Fracture of the substrate can occur by applying mechanical force and / or by heat treatment.

In the described example, a razor blade (not shown) can be inserted by hand at the height of the cleavage region.

<Quotation materials>

(1) FR-A-2 681 472 (US-A-5 374 564)

(2) FR-A-2 738 671 (US-A-5 714 395)

(3) FR-A-2 748 851

(4) FR-A-2 767 416

(5) FR-A-2 755 537

The present invention is particularly well suited to the formation of thin silicon films on fused silica, where a major concern is to make transparent supports with semiconductor films that may include components.

The present invention is applicable to a process of reducing thermal budgets and forming separation fractures in thin films, even without thermal exposure.

The present invention is a modified method of transferring a thin film to a target support, which is also applicable to the case where the materials of the thin film and the target support show different coefficients of thermal expansion.                 

The present invention provides a method of delivery in which a good surface state (no blister) of the source substrate is maintained by enabling adhesion of the target support with or without the adhesion aid (adhesive) to be well adhered to, and to the formation of a very brittle cleavage region. Applicable to

Claims (11)

In the method for transferring the thin film 18 of the source substrate 10 to the target support 30, a) implanting ions or gas species into the source substrate to form a region 16 in the source substrate, called a cleavage region, that defines the thin film 18 on the source substrate, b) transferring the source substrate to the target support and interlocking the thin film with the target support; c) separating the thin film 18 from the source substrate 10 along the cleavage region, wherein the thin film transfer method comprises: Before step b) above: Forming a film having a thickness between the cleavage region and the substrate surface with a material such that the thickness is greater than or equal to the limiting thickness for the film to self-support, and Forming an overbreak of the fractured region comprising heat treatment or application of a mechanical force to the source substrate. The method of claim 1, wherein separating the thin film from the source substrate comprises heat treatment or application of mechanical force. The method of claim 1 or 2, wherein the forming of the overbreak includes heat treatment using a thermal budget that enables the separation. 3. The heat treatment for separation according to claim 2, wherein the heat treatment for separation is sufficient to separate the thin film 18 by simply separating between the source substrate and the target support during the step c), or It is selected to be sufficiently separated by the method of delivery of the thin film. The method of claim 1, wherein the step c) and the formation of the overspray include applying a force in the form of mechanical pressure or mechanical stress or gas pressure. In the method of transferring the thin film 18 of the source substrate 10, a) implanting ions or gas species into the source substrate to form a region 16 on the source substrate, called a cleavage region, which defines the thin film 18 on the source substrate, b) separating the thin film 18 from the source substrate 10 along the cleavage region, wherein the thin film transfer method comprises: Before step b) above: Forming a film having a thickness between the cleavage region and the substrate surface with a material such that the thickness is greater than or equal to the limiting thickness for the film to self-support, and Forming an overbreak in the cleaved region by applying heat treatment or mechanical force to the source substrate. The method of claim 1, wherein the forming of the film having a thickness comprises forming the cleavage region at the thickness by injection of the step a), and then forming the film by the thin film. Thin film delivery method. The method of claim 1 wherein the step of forming a film having a thickness comprises forming a film called a thickness formation 20 on the thin film, such that the thin film and the thickness formation form the film. A delivery method of a thin film. The method of claim 1, further comprising producing all or part of the microelectronic elements or micromechanical elements or photoelectric elements prior to step b). The method of claim 1, wherein the overbreak is caused by heat treatment and applying mechanical force to the source substrate. The method of claim 1, wherein the separation is caused by heat treatment and applying mechanical force.

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