FR3147042A1 - METHOD FOR TRANSFERRING A SEALING LAYER - Google Patents

Abstract

The invention relates to a method for transferring a layer onto a support substrate, the method comprising: a) a step of forming cavities in a support substrate, said cavities opening onto a main face; b) a step of transferring a sealing layer intended to seal all of the cavities formed during step a); step a) being carried out such that all of the cavities are distributed regularly over a main area of the main face, and such that said main face comprises a peripheral crown devoid of cavities and inside which the main area is circumscribed, the peripheral crown extends from the edge of the support substrate over a length L less than a predetermined length Lp below which the sealing layer is free of non-transferred areas at the peripheral crown. Figure 16

Description

METHOD FOR TRANSFERRING A SEALING LAYER FIELD OF THE INVENTION

The present invention relates to the field of substrates and/or micro-electromechanical systems, in particular to the field of membrane-based devices.

In particular, the present invention relates to a method of transferring a layer to collectively seal a plurality of cavities formed on a support substrate.

More particularly, the transfer method according to the present invention is intended to limit the appearance of areas, called non-transferred areas, likely to appear at the level of an outline of the support substrate.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

Layer transfer processes are now widely implemented when it comes to forming suspended membranes and/or sealing cavities.

In this regard, such methods may include performing the following steps:

Ai) a step of providing a donor substrate 1 ( ) and a support substrate 2 ( ) provided with a plurality of cavities 3 opening onto a main face 4 of said support substrate 2;

Bi) a step of assembling the donor substrate 1 and the recipient substrate 2 so as to seal the cavities 3 ( ) ;

Ci) a step of thinning the donor substrate 1 so as to retain only a part of said substrate 1, called the sealing layer 5.

The thinning step Ci) can be carried out according to a first aspect by means of mechanical etching ("Grinding" according to the Anglo-Saxon terminology) and/or chemical etching, definitively consuming the donor substrate ( ).

Furthermore, the uniformity of the sealing layer at the end of step Ci) is very dependent on the technique used during step Ci) and remains difficult to control.

In order to overcome the problems related to uniformity and obtaining thin membranes, the so-called "Smart-Cut™" approach, described in document EP533551, can be considered. This approach makes it possible to transfer a sealing layer by detaching the latter from the donor substrate, at a fracture zone. The fracture zone formed by implantation and/or amorphization makes it possible to delimit a relatively thin sealing layer.

However, the implementation of this process, without other considerations, leads to the formation of defects, and more particularly to the appearance of non-transferred areas or holes ("void" according to Anglo-Saxon terminology) crossing the sealing layer. gives an example. In particular, the is a photograph of a hole appearing in an area near the edge of the sealing layer and diametrically opposite the notch of the support substrate. These holes hamper the overall efficiency of the process considered and are also a source of contamination.

An aim of the present invention is to provide a method of sealing a plurality of cavities with a sealing layer limiting the appearance of defects in said sealing layer.

BRIEF DESCRIPTION OF THE INVENTION

The aim of the invention is achieved by a method of transferring a layer onto a main face of a support substrate, the method comprising:

a) a step of forming cavities in a support substrate, said cavities opening onto a main face of said support substrate;

b) a step of transferring a layer, called a sealing layer, from a donor substrate, covering the main face and intended to seal all of the cavities formed during step a);

step a) being carried out so that all of the cavities are distributed regularly over a zone, called the main zone, of the main face, and so that said main face comprises a peripheral crown devoid of cavities and inside which the main zone is circumscribed, the peripheral crown extends from the edge of the support substrate over a length L less than a predetermined length Lp, said predetermined length Lp being a length below which the sealing layer is free of zones not transferred at the level of the peripheral crown.

According to one embodiment, step a) of forming the cavities comprises the following sub-steps:

a1) a sub-step of forming a peripheral mask covering the peripheral crown, and intended to protect said peripheral crown from physical or chemical etching;

a2) a sub-step of forming a main mask covering the main area and at least partially the peripheral mask, the main mask comprising openings defining the positioning and size of the cavities intended to be formed;

a3) an etching sub-step leading to the formation of cavities in the main zone.

a4) a sub-step of removing the main mask and the peripheral mask in order to expose the entire main face to the external environment.

According to one implementation method, the peripheral mask is produced by a photolithography process using a negative photosensitive resin.

According to one implementation method, the main mask is produced by another photolithography process using a photosensitive resin.

According to one embodiment, the layer transfer step leads to the formation of an edge crown on the main face and which extends over a distance D from the edge of the support substrate, said edge crown being an area on which the sealing layer is absent, the length L being greater than the distance D and less than the sum of the distance D and a distance H, H being less than 500 micrometers, advantageously less than 200 micrometers, even more advantageously less than 100 micrometers.

According to one embodiment, the length L is between 500 micrometers and 2500 micrometers, advantageously between 500 micrometers and 1500 micrometers, still advantageously between 500 micrometers and 1000 micrometers, even more advantageously between 500 micrometers and 800 micrometers, still even more advantageously between 500 micrometers and 700 micrometers.

According to one embodiment, the cavities are rectangular in shape and each side has a length of between 2 micrometers and 500 micrometers, advantageously between 2 micrometers and 500 micrometers, even more advantageously between 2 micrometers and 40 micrometers.

According to one embodiment, step b) is carried out so that the sealing layer has a thickness of between 100 nm and 2000 nm.

According to one embodiment, step (b) comprises the following sequence of sub-steps:

b1) a step of forming a weakening plane in the volume of the donor substrate, the weakening plane delimiting with one face, called the assembly face, of the donor substrate, the sealing layer;

b2) a step of assembling the donor substrate and the support substrate by bringing the assembly face and the main face into contact;

b3) a fracture step intended to initiate a fracture wave along the weakening plane allowing the detachment of the sealing layer from the donor substrate.

According to one implementation method, sub-step b1) of forming a weakening plan includes an implantation of species.

According to one embodiment, sub-step b2) comprises molecular bonding of the assembly face with the main face.

According to one embodiment, sub-step b3) comprises a heat treatment intended to initiate the propagation of the fracture wave.

Other characteristics and advantages of the invention will emerge from the detailed description which follows with reference to the appended figures in which:

There is a schematic representation, by one of its faces, of a donor substrate capable of being implemented during the execution of a layer transfer method known from the state of the art, the layer transfer method being implemented in particular for the sealing of cavities formed on a recipient substrate (represented in ) ;

There is a schematic representation of a receiving substrate capable of being implemented during the execution of a layer transfer method known from the state of the art, the receiving substrate is in particular represented by a face at the level of which cavities open;

There is a schematic representation of step Bi) of assembly of a layer transfer method known from the state of the art, on this , the donor substrate and the support substrate are represented according to a section plane perpendicular to the main faces of these two substrates;

There is a schematic representation of the thinning step Ci) of a layer transfer method known from the state of the art, on this , the sealing layer and the receiving substrate are represented according to a section plane perpendicular to the main faces of the receiving substrate;

There is a photograph of a hole observed in a sealing layer transferred using a transfer method known in the prior art;

There is a schematic representation of the sequence of steps performed during the implementation of the method according to an advantageous embodiment of the present invention;

There is a schematic representation of the sequence of steps performed when implementing an advantageous embodiment of the method according to an advantageous embodiment of the present invention;

There is a schematic representation of a support substrate on a main face of which a photosensitive negative resin layer is formed, the support substrate is in particular represented according to a section plane perpendicular to its main face;

There is a schematic representation of the exposure of the resin layer formed on the main face of the support substrate, the support substrate is in particular represented according to a section plane perpendicular to its main face;

There is a schematic representation of the development of the negative resin layer after exposure, and in order to crosslink said negative resin on a peripheral zone, said peripheral zone extending over a length L from the edge of the support substrate, the support substrate is shown along a section plane perpendicular to its main face;

There is a schematic representation of a support substrate on a main face of which a photosensitive resin layer is formed covering the main area and the peripheral area, the support substrate is represented according to a section plane perpendicular to its main face;

There is a schematic representation of the formation of the main mask on the main face of the support substrate, said main mask being formed to impose patterns on the cavities intended to be formed by etching, the support substrate is represented according to a section plane perpendicular to its main face;

There is a schematic representation of a support substrate on one face of which cavities are formed after a step of etching through the main mask and removal of said main mask and the peripheral zone, the support substrate is represented according to a section plane perpendicular to its main face;

There is a schematic representation of the support substrate and on which a sealing layer is transferred, in particular the sealing layer is transferred there to cover the main face and in order to seal the cavities, the support substrate is represented according to a section plane perpendicular to its main face;

There is a schematic representation of step b1) of the method according to the present invention, the arrows symbolizing the implantation of species by a free face of the donor substrate, the donor substrate being represented according to a section plane perpendicular to its free face;

There is a schematic representation of step b2) of the method according to the present invention, in particular the illustrates the assembly of the donor substrate with the support substrate which are both represented according to a section plane perpendicular to the principal face;

There is a schematic representation of step b3) of the method according to the present invention, in particular the illustrates the fracture sub-step which leads to transferring the sealing layer onto the main face of the support substrate, the support substrate being represented according to a section plane perpendicular to the main face.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for transferring a sealing layer onto a main face of a support substrate. In particular, the sealing layer is applied to cover (for sealing purposes) cavities formed in the support substrate and opening onto the main face of said support substrate.

Thus, the invention relates to a method of transferring a layer onto a main face of a support substrate, the method comprising:

a) a step of forming cavities in a support substrate, said cavities opening onto a main face of said support substrate;

b) a step of transferring a layer, called a sealing layer, from a donor substrate, covering the main face and intended to seal all of the cavities formed during step a);

step a) being carried out so that all of the cavities are distributed regularly over a zone, called the main zone, of the main face, and so that said main face comprises a peripheral crown devoid of cavities and inside which the main zone is circumscribed, the peripheral crown extends from the edge of the support substrate over a length L less than a predetermined length Lp, said predetermined length Lp being a length below which the sealing layer is free of zones not transferred at the level of the peripheral crown.

“Free from non-transferred areas” means an area of the sealant layer that is free of holes, including through holes.

There schematically represents the steps performed during the implementation of the method. In particular, the method according to the present invention comprises a step a) of forming cavities in a support substrate, said cavities opening onto a main face of said support substrate.

Advantageously, and as illustrated in the , step a) may comprise performing a set of substeps. In particular, step a) may comprise the following substeps:

a1) a sub-step of forming a peripheral mask covering the peripheral crown, and intended to protect said peripheral crown from physical or chemical etching;

a2) a sub-step of forming a main mask covering the main area and at least partially the peripheral mask, the main mask comprising openings defining the positioning and size of the cavities intended to be formed;

a3) an etching sub-step leading to the formation of cavities in the main zone.

a4) a sub-step of removing the main mask and the peripheral mask in order to expose the entire main face to the external environment.

Always advantageously, and as illustrated in the , step b) may comprise performing a set of substeps. In particular, step b) may comprise the following substeps:

b1) a step of forming a weakening plane in the volume of the donor substrate, the weakening plane delimiting with one face, called the assembly face, of the donor substrate, the sealing layer;

b2) a step of assembling the donor substrate and the support substrate by bringing the assembly face and the main face into contact;

b3) a fracture step intended to initiate a fracture wave along the weakening plane allowing the detachment of the sealing layer from the donor substrate.

The present invention refers to a donor substrate and a support substrate. It is understood that a substrate, according to the principles set forth herein, comprises two faces essentially parallel to each other and connected by a contour or an edge. Said contour or edge further describes a circle.

In addition, a substrate may include a notch which in particular makes it possible to identify and/or define its crystalline orientation.

The remainder of the statement of the present invention is devoted to the description of the embodiment illustrated in .

Substep a1) is illustrated in , to the and to the .

So, the represents a support substrate 10 on one face, called the main face 11, from which a resin layer 12 is formed. It is understood that the resin layer completely covers the main face 11. Furthermore, the resin used is advantageously a negative resin of the M78Y type (sold by the company “JSR Corporation”).

The formation of the resin layer 12 is followed by an exposure step as illustrated in . In particular, this exposure step makes it possible to define, in the resin layer 12, a peripheral zone 13 and a central zone 14 circumscribed by the peripheral zone 13. In particular, the peripheral zone 13 extends over a length L from the edge of the support substrate 10. In other words, the peripheral zone 13 forms a ring delimited externally by an external edge and internally by an internal edge, said internal edge being at a distance L from the edge of the support substrate 10.

The exposure step is notably carried out so as to expose only the peripheral zone 13 to light radiation and thus induce crosslinking of the latter. In this regard, a mask (not illustrated) may be implemented to mask a central zone 14 of the resin layer 12.

The resin layer, after exposure, is subjected to a development step which makes it possible to remove the central zone 14 of the resin layer 12 and thus expose to the external environment a main zone 15 of the main face 11 ( ). It is understood that the development step makes it possible to preserve the peripheral zone 13 which covers a peripheral crown 16 of the main face 11 and in which the main zone 15 is circumscribed. In addition, the resin forming the resin layer 12 is suitable for protecting the peripheral zone 16 from physical and/or chemical etching.

Substep a2) is illustrated in and to the .

Thus, sub-step a2) firstly comprises the formation of a resin layer 17 covering the main zone 15 and the peripheral zone 13 ( ).

As illustrated in the , the resin layer 17 is exposed (or insolated) to light radiation, and in particular ultraviolet radiation, and then developed to form a main mask 17a. The exposure (or insolation) of the resin layer is implemented with photolithography equipment (for example a photo repeater) which insolates the resin layer 17 through a lithographic photomask intended to print predefined patterns. Thus, after development, the main mask 17a comprises openings 18 defining the imprint of cavities intended to be formed by an etching step.

Substeps a3) and a4) are illustrated in .

In this regard, the is a representation of the support substrate 10 at the end of an etching step performed through the main mask 17a and a removal, after etching, of said main mask and of the peripheral zone 13. In particular, the support substrate 10 comprises cavities 19 opening through the main face 11 of the support substrate 10. It is understood that, insofar as the peripheral zone 13 masks the peripheral crown 16, the cavities are formed only at the level of the main zone. Indeed, the consideration of the peripheral zone 13 makes it possible to protect the peripheral crown 16 from etching, and thus to provide an area free of cavities 19.

For example, the cavities 19 may be rectangular in shape and each side may have a length of between 2 micrometers and 500 micrometers, advantageously between 2 micrometers and 500 micrometers, even more advantageously between 2 micrometers and 40 micrometers.

The peripheral crown 16 in accordance with the present invention extends from the edge of the support substrate over a length L.

The method according to the present invention also comprises a step b) of transferring a layer, called a sealing layer 21, from a donor substrate 20, covering the main face 11 and intended to seal all of the cavities 19 formed during step a).

There illustrates an example.

Furthermore, step b) can be carried out so that the sealing layer has a thickness of between 100 nm and 2000 nm.

According to an advantageous embodiment, the reporting step b) can be implemented according to the principles set out in .

In particular, step b1), illustrated in , comprises a step of forming a weakening plane 23 in the volume of the donor substrate 20. The weakening plane 23 delimits in particular with one face, called the assembly face 24, of the donor substrate 20, the sealing layer 21.

Sub-step b1) of forming a weakening plane may comprise an implantation of species. Said species may comprise at least one of the elements chosen from: hydrogen, helium.

Step b) also includes an assembly substep b2). In particular, and as illustrated in , substep b2) comprises bringing the assembly face 24 and the main face 11 into contact. Substep b2) may also comprise initiating a bonding wave. In particular, this initiation of the bonding wave may be obtained by exerting pressure tending to bring the assembly face and the main face closer together. Generally, this pressure is exerted by means of a pin or a finger, on a face of the donor substrate opposite the assembly face, and in the vicinity of the notch of said substrate.

By “in the vicinity of the notch” is meant at a distance of less than one centimeter from said notch.

This pressure has the effect of generating a sufficiently intimate local contact between the assembly face and the main face so as to locally create weak bonds (for example hydrogen bonds) between the two surfaces considered. This intimate contact propagates from near to far over the entire interface in the form of a bonding wave.

Thus, and advantageously, sub-step b2) comprises molecular bonding of the assembly face with the main face.

Step b) also comprises a fracture sub-step b3) intended to initiate a fracture wave along the weakening plane allowing the detachment of the sealing layer from the donor substrate ( ). Advantageously, substep b3) may comprise a heat treatment intended to initiate the propagation of the fracture wave.

The implementation of the invention and in particular the consideration of a peripheral crown 16 devoid of cavities makes it possible to limit, or even prevent, the appearance of a hole in the sealing layer after its transfer to the main face.

In particular, the inventors were able to observe that failure to consider the peripheral crown according to the terms of the present invention inevitably led to the appearance of holes in the sealing layer. In particular, the inventors were also able to observe that these holes were essentially present in a region diametrically opposite the initiation zone of the bonding wave.

Thus, according to the present invention the length L less than a predetermined length Lp, said predetermined length Lp being a length below which the sealing layer is free of non-transferred zones at the peripheral crown.

Furthermore, it is known that the layer transfer step leads to the formation of an edge crown on the main face and which extends over a distance D from the edge of the support substrate, said edge crown being an area on which the sealing layer is absent. This distance D can be determined experimentally.

Thus, and according to the present invention, the length L is advantageously greater than the distance D and less than the sum of the distance D and a distance H, H being less than 500 micrometers, advantageously less than 200 micrometers, even more advantageously less than 100 micrometers.

Alternatively, the length L is between 500 micrometers and 2500 micrometers, advantageously between 500 micrometers and 1500 micrometers, still advantageously between 500 micrometers and 1000 micrometers, even more advantageously between 500 micrometers and 800 micrometers, still even more advantageously between 500 micrometers and 700 micrometers.

The lengths L previously considered make it possible to slow down the bonding wave during the execution of sub-step b2) at the level of the peripheral crown and consequently limit the trapping of gas bubbles when the bonding wave reaches, to close, a zone diametrically opposite the initiation point.

Of course, the invention is not limited to the embodiments described and variant embodiments can be made without departing from the scope of the invention as defined by the claims.

Claims (12)

Method for transferring a layer onto a main face of a support substrate, the method comprising:
a) a step of forming cavities in a support substrate, said cavities opening onto a main face of said support substrate;
b) a step of transferring a layer, called a sealing layer, from a donor substrate, covering the main face and intended to seal all of the cavities formed during step a);
step a) being carried out so that all of the cavities are distributed regularly over a zone, called the main zone, of the main face, and so that said main face comprises a peripheral crown devoid of cavities and inside which the main zone is circumscribed, the peripheral crown extends from the edge of the support substrate over a length L less than a predetermined length Lp, said predetermined length Lp being a length below which the sealing layer is free of zones not transferred at the level of the peripheral crown. Transfer method according to claim 1, in which step a) of forming the cavities comprises the following sub-steps:
a1) a sub-step of forming a peripheral mask covering the peripheral crown, and intended to protect said peripheral crown from physical or chemical etching;
a2) a sub-step of forming a main mask covering the main area and at least partially the peripheral mask, the main mask comprising openings defining the positioning and size of the cavities intended to be formed;
a3) an etching sub-step leading to the formation of cavities in the main zone.
a4) a sub-step of removing the main mask and the peripheral mask in order to expose the entire main face to the external environment. Transfer method according to claim 2, in which the peripheral mask is produced by a photolithography process using a negative photosensitive resin. Transfer method according to claim 2 or 3, in which the main mask is produced by another photolithography process using a photosensitive resin. Transfer method according to one of claims 1 to 4, in which the layer transfer step leads to the formation of an edge crown on the main face and which extends over a distance D from the edge of the support substrate, said edge crown being an area on which the sealing layer is absent, the length L being greater than the distance D and less than the sum of the distance D and a distance H, H being less than 500 micrometers, advantageously less than 200 micrometers, even more advantageously less than 100 micrometers. Transfer method according to one of claims 1 to 4, in which the length L is between 500 micrometers and 2500 micrometers, advantageously between 500 micrometers and 1500 micrometers, still advantageously between 500 micrometers and 1000 micrometers, even more advantageously between 500 micrometers and 800 micrometers, still more advantageously between 500 micrometers and 700 micrometers. Transfer method according to one of claims 1 to 6, in which the cavities are rectangular in shape and each side has a length of between 2 micrometers and 500 micrometers, advantageously between 2 micrometers and 500 micrometers, even more advantageously between 2 micrometers and 40 micrometers. Transfer method according to one of claims 1 to 7, in which step b) is carried out so that the sealing layer has a thickness of between 100 nm and 2000 nm. Transfer method according to claim 1, wherein step b) comprises the following sequence of sub-steps:
b1) a step of forming a weakening plane in the volume of the donor substrate, the weakening plane delimiting with one face, called the assembly face, of the donor substrate, the sealing layer;
b2) a step of assembling the donor substrate and the support substrate by bringing the assembly face and the main face into contact;
b3) a fracture step intended to initiate a fracture wave along the weakening plane allowing the detachment of the sealing layer from the donor substrate. Transfer method according to claim 9, in which sub-step b1) of forming a weakening plane comprises an implantation of species. Transfer method according to claim 9 or 10, in which sub-step b2) comprises molecular bonding of the assembly face with the main face. Transfer method according to one of claims 9 to 11, in which sub-step b3) comprises a heat treatment intended to initiate the propagation of the fracture wave.