Method for transferring the sealing layer
The method addresses non-uniformity and void formation in sealing layers by using photolithography and controlled fracture techniques to create a cavity-free peripheral ring, ensuring defect-free sealing in electromechanical microsystems and film-based devices.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-02-26
- Publication Date
- 2026-04-10
AI Technical Summary
Existing layer transfer methods in electromechanical microsystems and film-based devices suffer from non-uniformity and the formation of non-transfer zones or voids in the sealing layer, leading to performance issues and contamination.
A method involving the use of photolithography to create a peripheral mask and main mask on a carrier substrate, followed by controlled etching and molecular bonding to transfer a sealing layer that covers cavities, while ensuring a cavity-free peripheral ring to prevent voids, using a weakened plane in the donor substrate for controlled fracture.
The method effectively limits the occurrence of defects in the sealing layer, enhancing the uniformity and integrity of the sealing process, thereby improving device performance and reducing contamination risks.
Smart Images
Figure 2026511002000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of electromechanical microsystems and / or substrates, particularly to the field of film-based devices.
[0002] <0OO0007>In particular, the present invention relates to a method of transferring a layer intended to seal a plurality of cavities formed on a carrier substrate in one go.
[0003] More specifically, the transfer method according to the present invention is intended to limit the appearance of a zone called a non-transfer zone, which is likely to appear on the contour of the carrier substrate.
Background Art
[0004] The layer transfer method is widely used today when forming a suspension film and / or when sealing a cavity.
[0005] In this regard, such a method may include the following steps, namely Ai) providing a donor substrate 1 (FIG. 1) and a carrier substrate 2 provided with a plurality of cavities 3 opening on a main surface 4 of the carrier substrate 2 (FIG. 2); Bi) assembling the donor substrate 1 and the receiver substrate 2 so as to seal the cavities 3 (FIG. 3); Ci) thinning the donor substrate so as to preserve only a part of the substrate 1 called a sealing layer 5.
[0006] The thinning step Ci) is carried out, according to a first aspect, using mechanical grinding and / or chemical etching and can permanently thin the donor substrate (FIG. 4).
[0007] [[ID=3B]]Furthermore, the uniformity of the sealing layer at the end of step Ci) strongly depends on the technique used during step Ci) and is difficult to control.
[0008] To overcome problems related to uniformity and thin film acquisition, the "Smart-Cut" approach described in European Patent No. 533551 may be used. This approach allows for the transfer of the encapsulation layer by separating it from the donor substrate along a fracture zone. The fracture zone formed by injection and / or amorphousization allows for the definition of a relatively thin encapsulation layer.
[0009] However, implementing this method without considering other factors can lead to defect formation, more specifically, the appearance of non-transfer zones or voids through the encapsulation layer. Figure 5 illustrates an example of this. In particular, Figure 5 is a photograph of a void appearing near the edge of the encapsulation layer and in a zone directly opposite the notch in the carrier substrate. These voids negatively impact the overall performance of the method in question and can also be sources of contamination. [Overview of the project] [Problems that the invention aims to solve]
[0010] One object of the present invention is to propose a method for sealing multiple cavities with a sealing layer that limits the occurrence of defects in the sealing layer. [Means for solving the problem]
[0011] The object of the present invention is a method for transferring a layer onto the main surface of a carrier substrate, a) A step of forming a cavity in a carrier substrate, wherein the cavity opens to the main surface of the carrier substrate, b) A step of transferring a layer called a sealing layer from the donor substrate to cover the main surface and sealing all of the cavities formed in step a), Step a) is achieved by a method such that all cavities are regularly distributed across a zone referred to as the main zone of the main surface, and the main surface has no cavities and comprises a peripheral ring inside which the main zone is circumscribed, the peripheral ring extending from the edge of the carrier substrate over a length L less than a predetermined length Lp, the predetermined length Lp being a length below which the sealing layer does not contain a non-transfer zone within the peripheral ring.
[0012] According to one embodiment, step a) forming the cavity is a sub-step, namely, a1) A sub-step of forming a peripheral mask to cover the peripheral ring and protect the peripheral ring from physical grinding or chemical etching, a2) A sub-step comprising forming a main mask that covers the main zone and at least partially covers the peripheral mask, wherein the main mask includes openings that define the position and size of the cavity to be formed, a3) Etching sub-process to form a cavity in the main zone, a4) A sub-step that removes the main mask and peripheral mask to expose the entire main surface to the external environment.
[0013] According to one embodiment, the peripheral mask is fabricated using a photolithography process that utilizes a negative-type photosensitive resin.
[0014] According to one embodiment, the main mask is fabricated using a different photolithography process that utilizes a photosensitive resin.
[0015] According to one embodiment, the layer transfer process results in the formation of an edge ring on the main surface extending over a distance D from the edge of the carrier substrate, the edge ring being a zone where no sealing layer exists, the length L being greater than the distance D and less than the sum of the distances D and H, and H being less than 500 μm, preferably less than 200 μm, and even more preferably less than 100 μm.
[0016] According to one embodiment, the length L is 500 μm to 2500 μm, preferably 500 μm to 1500 μm, more preferably 500 μm to 1000 μm, even more preferably 500 μm to 800 μm, and even more preferably 500 μm to 700 μm.
[0017] According to one embodiment, the cavity is rectangular, and each side thereof has a length of 2 μm to 500 μm, preferably 2 μm to 500 μm, and even more preferably 2 μm to 40 μm.
[0018] According to one embodiment, step b) is performed such that the sealing layer has a thickness of 100 nm to 2000 nm.
[0019] According to one embodiment, step b) includes the following sequence of sub-steps, namely b1) forming a weakened plane within the volume of the donor substrate, the weakened plane defining the sealing layer together with the surface of the donor substrate referred to as the assembly surface; b2) assembling the donor substrate and the carrier substrate by bringing the assembly surface into contact with the main surface; b3) a breaking step intended to initiate a fracture wave along the weakened plane to enable separation of the sealing layer from the donor substrate.
[0020] According to one embodiment, the sub-step b1) of forming the weakened plane includes ion implantation.
[0021] According to one embodiment, the sub-step b2) includes molecular bonding between the assembly surface and the main surface.
[0022] According to one embodiment, the sub-step b3) includes a heat treatment intended to initiate propagation of the fracture wave.
Brief Description of the Drawings
[0023] <( Other features and advantages of the present invention will become apparent from the following detailed description with reference to the accompanying drawings. [Figure 1]FIG. 1 is a schematic view of one of the faces of a donor substrate that can be used when performing a layer transfer method known in the prior art, and the layer transfer method is implemented particularly for sealing a cavity formed on a receiver substrate (shown in FIG. 2). [Figure 2] FIG. 2 is a schematic view of a receiver substrate that can be used when performing a layer transfer method known in the prior art, and the receiver substrate is particularly represented by the face on which the cavity opens. [Figure 3] FIG. 3 is a schematic view of the assembly step Bi) of a layer transfer method known in the prior art, showing the donor substrate and the carrier substrate in a cross-section in a plane perpendicular to the main faces of these two substrates. [Figure 4] FIG. 4 is a schematic view of the thinning step Ci) of a layer transfer method known in the prior art, showing the sealing layer and the receiver substrate in a cross-section in a plane perpendicular to the main face of the receiver substrate. [Figure 5] FIG. 5 is a photograph of voids observed in a sealing layer transferred according to a transfer method known in the prior art. [Figure 6] FIG. 6 is a schematic view of a series of steps performed during the implementation of a method according to an advantageous embodiment of the present invention. [Figure 7] FIG. 7 is a schematic view of a sequence of steps performed during the implementation of an advantageous embodiment of a method according to an advantageous embodiment of the present invention. [Figure 8] FIG. 8 is a schematic view of a carrier substrate having a main face on which a photosensitive negative resin layer is formed, and the carrier substrate is particularly shown in a cross-section in a plane perpendicular to its main face. [Figure 9] FIG. 9 is a schematic view of the irradiation of a resin layer formed on the main face of a carrier substrate, and the carrier substrate is particularly shown in a cross-section in a plane perpendicular to its main face. [Figure 10] FIG. 10 is a schematic view of the development of a negative resin layer after irradiation for crosslinking the negative resin on the peripheral zone, and the peripheral zone extends along a length L from the edge of the carrier substrate, and the carrier substrate is shown in a cross-section in a plane perpendicular to its main face. [Figure 11]Figure 11 is a schematic diagram showing a carrier substrate, on which a photosensitive resin layer covering the main zone and peripheral zone is formed on the main surface, cut by a plane perpendicular to the main surface. [Figure 12] Figure 12 is a schematic diagram of the formation of the main mask on the main surface of the carrier substrate, which is formed to give a pattern on the cavity formed by etching, and the carrier substrate is shown in cross-section in a plane perpendicular to its main surface. [Figure 13] Figure 13 is a schematic diagram of the support substrate with a cavity formed on the surface after etching the main mask and removing the main mask and surrounding zone. The support substrate is shown in cross-section in a plane perpendicular to its main surface. [Figure 14] Figure 14 is a schematic diagram of a carrier substrate onto which the sealing layer is transferred. The sealing layer is transferred to the carrier substrate, in particular, to cover the main surface and seal the cavity. The carrier substrate is shown in cross-section in a plane perpendicular to its main surface. [Figure 15] Figure 15 is a schematic diagram of step b1) of the method according to the present invention, where the arrows represent seed injection through the free surface of the donor substrate, and the donor substrate is shown in cross-section in a plane perpendicular to its free surface. [Figure 16] Figure 16 is a schematic diagram of step b2) of the method according to the present invention, and in particular shows the assembly of the donor substrate and the carrier substrate, both of which are shown in cross-section in a plane perpendicular to the main surface. [Figure 17] Figure 17 is a schematic diagram of step b3) of the method according to the present invention, and in particular shows the fracture sub-step in which the sealing layer is transferred onto the main surface of the carrier substrate, and the carrier substrate is shown in cross-section in a plane perpendicular to the main surface. [Modes for carrying out the invention]
[0024] The present invention relates to a method for transferring a sealing layer onto the main surface of a carrier substrate. In particular, the sealing layer is transferred so as to cover (and seal) a cavity formed in the carrier substrate that opens onto the main surface of the carrier substrate.
[0025] Therefore, the present invention is a method for transferring a layer onto the main surface of a carrier substrate, a) A step of forming a cavity in a carrier substrate, wherein the cavity opens to the main surface of the carrier substrate, b) A step of transferring a layer called a sealing layer from the donor substrate to cover the main surface and sealing all of the cavities formed in step a), Step a) relates to a method wherein all cavities are regularly distributed across a zone referred to as the main zone of the main surface, and the main surface has no cavities and comprises a peripheral ring inside which the main zone is circumscribed, the peripheral ring extending from the edge of the carrier substrate over a length L less than a predetermined length Lp, the predetermined length Lp being a length below which the sealing layer does not contain a non-transfer zone within the peripheral ring.
[0026] "Excluding non-transfer zones" means zones in the sealing layer that do not contain voids, especially through-voids.
[0027] Figure 6 schematically shows the steps performed during the implementation of this method. In particular, the method according to the present invention includes step a) forming a cavity in a carrier substrate, wherein the cavity opens to the main surface of the carrier substrate.
[0028] Advantageously, as shown in Figure 7, process A) may include the execution of a set of sub-processes. In particular, process a) includes the following sub-processes, namely a1) A sub-step of forming a peripheral mask to cover the peripheral ring and protect the peripheral ring from physical grinding or chemical etching, a2) A sub-step comprising forming a main mask that covers the main zone and at least partially covers the peripheral mask, wherein the main mask includes openings that define the position and size of the cavity to be formed, a3) Etching sub-process to form a cavity in the main zone, a4) A sub-step that removes the main mask and peripheral mask to expose the entire main surface to the external environment.
[0029] More advantageously, as shown in Figure 7, step b) may include the execution of a set of sub-steps. In particular, step b) includes the following sub-steps, namely b1) A step of forming a brittle surface within the volume of a donor substrate, wherein the brittle surface, together with a surface of the donor substrate referred to as the assembly surface, defines a sealing layer. b2) A step of assembling the donor substrate and the carrier substrate by bringing the assembly surface and the main surface into contact, b3) A fracturing step may include initiating a fracturing wave along the weakened surface to enable separation of the encapsulation layer from the donor substrate.
[0030] This invention refers to donor substrates and carrier substrates. According to the principles described herein, it is understood that the substrate includes two surfaces that are essentially parallel to each other and connected by a contour or edge. Furthermore, the contour or edge is circular.
[0031] Furthermore, the substrate may have notches that allow for the determination and / or definition of its crystal orientation.
[0032] The remainder of the disclosure of the present invention is devoted to describing the embodiments shown in Figure 7.
[0033] Sub-step a1) is shown in Figures 8, 9, and 10.
[0034] Figure 8 shows a carrier substrate 10 with a resin layer 12 formed on one surface, referred to as the main surface 11. The resin layer is understood to cover the entire main surface 11. Furthermore, the resin used is preferably M78Y negative resin (sold by JSR Corporation).
[0035] As shown in Figure 9, the irradiation process is performed following the formation of the resin layer 12. In particular, this irradiation process defines a peripheral zone 13 and a central zone 14 surrounded by the peripheral zone 13 in the resin layer 12. Specifically, the peripheral zone 13 extends over a length L from the edge of the carrier substrate 10. In other words, the peripheral zone 13 forms a ring defined on the outside by an outer edge and on the inside by an inner edge, the inner edge being at a distance L from the edge of the carrier substrate 10.
[0036] The irradiation process is carried out such that only the peripheral zone 13 is exposed to light radiation, thereby crosslinking the peripheral zone. In this regard, a mask (not shown) may be used to mask the central zone 14 of the resin layer 12.
[0037] Following irradiation, the resin layer is subjected to a developing process, in which the central zone 14 of the resin layer 12 is removed, exposing the main zone 15 of the main surface 11 to the external environment (Figure 10). It is understood that the developing process covers the peripheral ring 16 of the main surface 11, preserving the peripheral zone 13 inside which the main zone 15 is circumscribed. Furthermore, the resin forming the resin layer 12 is designed to protect the peripheral zone 16 from physical grinding and / or chemical etching.
[0038] Sub-step a2) is shown in Figures 11 and 12.
[0039] Therefore, sub-step a2) first includes forming a resin layer 17 that covers the main zone 15 and the peripheral zone 13 (Figure 11).
[0040] As shown in Figure 12, the resin layer 17 is exposed (or irradiated) to light radiation, particularly ultraviolet radiation, and then developed to form the main mask 17a. The exposure (or irradiation) of the resin layer is carried out using a photolithography apparatus (e.g., a photorepeater) that irradiates the resin layer 17 through a photolithography mask for printing a predetermined pattern. Therefore, after development, the main mask 17a has openings 18 that define the printing of cavities formed by the etching process.
[0041] Sub-processes a3) and a4) are shown in Figure 13.
[0042] In this regard, Figure 13 shows the carrier substrate 10 after the completion of the etching process performed through the main mask 17a, after which the main mask and peripheral zone 13 are removed. In particular, the carrier substrate 10 has a cavity 19 that opens into the main surface 11 of the carrier substrate 10. When the peripheral zone 13 masks the peripheral ring 16, it is understood that the cavity is formed only in the main zone. This is because the peripheral zone 13 protects the peripheral ring 16 from etching, thereby providing a zone without a cavity 19.
[0043] For example, cavity 19 may be rectangular, with each side having a length of 2 μm to 500 μm, preferably 2 μm to 500 μm, and more preferably 2 μm to 40 μm.
[0044] The peripheral ring 16 according to the present invention extends from the edge of the carrier substrate over a length L.
[0045] The method according to the present invention also includes step b) transferring a layer called a sealing layer 21 from a donor substrate 20 to cover the main surface 11 and sealing all of the cavities 19 formed in step a).
[0046] Figure 14 shows an example of this.
[0047] Furthermore, step b) may be performed such that the sealing layer has a thickness of 100 nm to 2000 nm.
[0048] According to one advantageous embodiment, the transfer step b) may be carried out according to the principle shown in Figure 7.
[0049] In particular, step b1) shown in Figure 15 includes the step of forming a weakened surface 23 within the volume of the donor substrate 20. The weakened surface 23, in particular, defines the sealing layer 21 together with a surface of the donor substrate 20 referred to as the assembly surface 24.
[0050] Sub-step b1) forming the weakened surface may include seed injection. The seed may include at least one of the following elements, namely hydrogen and helium.
[0051] Step b) also includes assembly sub-step b2). In particular, as shown in Figure 16, sub-step b2) includes bringing the assembly surface 24 and the main surface 11 into contact. Sub-step b2) may also include initiating the coupling wave. In particular, this coupling wave initiation can be achieved by applying pressure that tends to bring the assembly surface and the main surface closer together. This pressure is usually applied using a pin or a finger on the surface of the donor substrate opposite to the assembly surface and near the notch of the substrate.
[0052] "Near the notch" means being less than 1 cm away from the notch in question.
[0053] This pressure creates localized contact between the mounting surface and the main surface, which is close enough to form a localized weak bond (e.g., a hydrogen bond) between the two surfaces in question. This contact gradually spreads across the entire interface in the form of a bonding wave.
[0054] Therefore, advantageously, sub-step b2) includes molecular bonding between the assembly surface and the main surface.
[0055] Step b) also includes a fracture sub-step b3) intended to initiate a fracture wave along the weakened surface, thereby enabling the sealing layer to be separated from the donor substrate (Figure 17). Advantageously, sub-step b3) may include a heat treatment intended to initiate the propagation of the fracture wave.
[0056] The implementation of the present invention, particularly the provision of a cavity-free peripheral ring 16, limits or prevents the appearance of voids in the sealing layer after the sealing layer has been transferred to the main surface.
[0057] In particular, the inventors observed that by removing the peripheral ring, as defined in the terminology of this invention, voids inevitably appear in the sealing layer. Specifically, the inventors also observed that these voids are essentially located in the region diametrically opposite the coupling wave initiation zone.
[0058] Therefore, according to the present invention, the length L is less than a predetermined length Lp, and if the predetermined length Lp is shorter than that, the sealing layer does not include the non-transfer zone within the peripheral ring.
[0059] Furthermore, the layer transfer process is known to form an edge ring on the main surface extending over a distance D from the edge of the carrier substrate, and this edge ring is a zone where no sealing layer exists. This distance D can be determined experimentally.
[0060] Therefore, 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 the distance H, and H is less than 500 μm, advantageously less than 200 μm, and even more advantageously less than 100 μm.
[0061] Alternatively, the length L is 500 μm to 2500 μm, preferably 500 μm to 1500 μm, also preferably 500 μm to 1000 μm, even more preferably 500 μm to 800 μm, and even more preferably 500 μm to 700 μm.
[0062] The aforementioned length L slows down the coupling wave during the execution of sub-process b2) in the peripheral ring, thereby limiting bubble trapping when the coupling wave reaches and closes in the zone on the diametrically opposite side of the starting point.
[0063] Naturally, the present invention is not limited to the embodiments described, and modifications can be applied thereto without departing from the scope of the invention as defined by the claims.
Claims
1. A method for transferring a layer onto the main surface of a support substrate, a) A step of forming a cavity in a carrier substrate, wherein the cavity opens to the main surface of the carrier substrate, b) A step of transferring a layer called a sealing layer from a donor substrate to cover the main surface and sealing all of the cavities formed in step a), Step a) is a method wherein all of the cavities are regularly distributed across a zone referred to as the main zone of the main surface, and the main surface has no cavities and comprises a peripheral ring inside which the main zone is circumscribed, the peripheral ring extending from the edge of the carrier substrate over a length L less than a predetermined length Lp, the predetermined length Lp being a length below which the sealing layer does not contain a non-transfer zone within the peripheral ring.
2. The step a) of forming the cavity is a sub-step, namely, a1) A sub-step of forming a peripheral mask to cover the peripheral ring and protect the peripheral ring from physical grinding or chemical etching, a2) A sub-step comprising forming a main mask that covers the main zone and at least partially covers the peripheral mask, wherein the main mask includes an opening that defines the position and size of the cavity to be formed, a3) Etching sub-step for forming the cavity in the main zone, a4) The transfer method according to claim 1, comprising a sub-step of removing the main mask and the peripheral mask to expose the entire main surface to the external environment.
3. The transfer method according to claim 2, wherein the peripheral mask is manufactured using a photolithography process that uses a negative-type photosensitive resin.
4. The transfer method according to claim 2 or 3, wherein the main mask is prepared using another photolithography process that uses a photosensitive resin.
5. The transfer method according to any one of claims 1 to 4, wherein the layer transfer step results in the formation of an edge ring on the main surface extending over a distance D from the edge of the carrier substrate, the edge ring being a zone where the sealing layer is absent, the length L being greater than the distance D and less than the sum of the distance D and the distance H, and H being less than 500 μm, preferably less than 200 μm, and more preferably less than 100 μm.
6. The transfer method according to any one of claims 1 to 4, wherein the length L is 500 μm to 2500 μm, preferably 500 μm to 1500 μm, preferably 500 μm to 1000 μm, more preferably 500 μm to 800 μm, and more preferably 500 μm to 700 μm.
7. The transfer method according to any one of claims 1 to 6, wherein the cavity is rectangular, and each side thereof has a length of 2 μm to 500 μm, preferably 2 μm to 500 μm, and more preferably 2 μm to 40 μm.
8. The transfer method according to any one of claims 1 to 7, wherein step b) is performed such that the sealing layer has a thickness of 100 nm to 2000 nm.
9. Step b) is the sequence of the following sub-steps, namely b1) A step of forming a weakened surface within the volume of a donor substrate, wherein the weakened surface, together with a surface of the donor substrate referred to as the assembly surface, defines the sealing layer. b2) A step of assembling the donor substrate and the carrier substrate by bringing the assembly surface and the main surface into contact, b3) The transfer method according to claim 1, comprising a fracturing step intended to enable the separation of the sealing layer from the donor substrate by initiating a fracturing wave along the weakened surface.
10. The transfer method according to claim 9, wherein the sub-step b1) for forming a weakened surface includes seed injection.
11. The transfer method according to claim 9 or 10, wherein sub-step b2) includes molecular bonding between the assembly surface and the main surface.
12. The transfer method according to any one of claims 9 to 11, wherein sub-step b3) includes a heat treatment intended to initiate the propagation of the fracture wave.