Method for manufacturing elementary cells to be characterised

Abstract

The invention relates to a method comprising the following steps: a) using a stack comprising, successively, a first substrate (1), a bonding interface (IC) sensitive to a wet medium and / or to mechanical vibrations, and a second substrate (2); b) forming cavities (3) within the second substrate (2) that define elementary cells (CE), wherein the cavities (3) each have a bottom that extends a distance away from the bonding interface (IC), and wherein the second substrate (2) maintains an intermediate zone between the bottom and the bonding interface (IC); c) applying laser radiation to the bottom of each cavity (3) so as to: - locally perform an ablation (A) of the intermediate zone, the bonding interface (IC), and a first portion of the first substrate (1); - retain a second portion (11) of the first substrate (1) in the continuation of the ablation (A), suitable for maintaining the mechanical strength of the elementary cells (CE); d) remove the second portion (11) of the first substrate (1).

Description

[0001] PROCESS FOR MANUFACTURING ELEMENTARY CELLS TO BE CHARACTERIZED

[0002] Technical field

[0003] The invention relates to the technical field of methods for manufacturing elementary cells to be characterized for microelectronics. Each elementary cell is derived from divisions (generally vertical) of a stack, the stack successively comprising a first substrate, a bonding interface, a second substrate. Each elementary cell is therefore a division of a stack, the division successively comprising a part of the first substrate, a part of the bonding interface, a part of the second substrate.

[0004] The invention finds its application in particular in the measurement of the adhesion energy of the bonding interface of an elementary cell, that is to say the energy necessary to separate the parts of the first and second substrates from the bonding interface.

[0005] State of the art

[0006] A method for manufacturing elementary cells to be characterized, known from the state of the art, comprises the steps:

[0007] A) using a stack successively comprising a first substrate, a bonding interface, a second substrate; the bonding interface being sensitive to a humid environment and / or to mechanical vibrations;

[0008] B) cut the stack in a direction perpendicular to the bonding interface with a saw so as to obtain elementary cells.

[0009] Such a prior art method is not entirely satisfactory insofar as the execution of step B) is likely to lead to degradation of the bonding interface due to:

[0010] (i) exposure of the bonding interface to moisture from the saw cooling waters when the saw reaches the bonding interface;

[0011] (ii) the subjection of the bonding interface to significant mechanical vibrations linked to the operation of the saw (with a blade generally made of diamond) when the saw reaches the bonding interface.

[0012] Such degradation of the bonding interface can locally lead to detachments of the second substrate, which will impact the reliability of the characterization of the elementary cells, particularly when it comes to measuring the adhesion energy of the bonding interface.

[0013] Statement of the invention

[0014] The invention aims to remedy all or part of the aforementioned drawbacks. To this end, the subject of the invention is a method for manufacturing elementary cells to be characterized, comprising the steps: a) using a stack successively comprising a first substrate, a bonding interface, a second substrate; the bonding interface being sensitive to a humid environment and / or to mechanical vibrations; b) forming cavities within the second substrate delimiting elementary cells, the cavities each having a bottom extending at a distance from the bonding interface, the second substrate retaining an intermediate zone extending between the bottom of each cavity and the bonding interface; c) applying laser radiation to the bottom of each cavity so as to:

[0015] - locally obtain ablation of the intercalary zone, of the bonding interface, and of a first part of the first substrate;

[0016] - retaining a second part of the first substrate, extending in the extension of the ablation, and adapted to maintain mechanical strength of the elementary cells delimited during step b); d) removing the second part of the first substrate so as to separate the elementary cells delimited during step b).

[0017] Thus, such a method according to the invention makes it possible, thanks to step c) not requiring cooling water, to avoid exposure of the bonding interface to a humid environment as in step B) of the prior art when the saw reaches the bonding interface. In addition, step c) does not lead to subjection of the bonding interface to mechanical vibrations as in step B) of the prior art when the saw reaches the bonding interface. Such a method according to the invention therefore allows better preservation of the bonding interface compared to the prior art, so that the reliability of the characterization of the elementary cells is increased.

[0018] The manufacturing of elementary cells is carried out in three stages to divide the stack and obtain elementary cells. In a first stage, the cavities are formed during step b) so as to maintain an intermediate zone between the bottom of each cavity and the bonding interface. The intermediate zone makes it possible to protect the bonding interface, for example from cooling water or mechanical vibrations when step b) is carried out by cutting with a saw to form the cavities. In a second stage, the bonding interface is ablated during step c) by laser ablation not requiring cooling water and not generating strong mechanical vibrations. Such laser ablation makes it possible to better preserve the properties of the bonding interface compared to the state of the art. In a third stage, the removal of the second part of the first substrate at the end of step d) makes it possible to obtain the elementary cells.

[0019] The method according to the invention may comprise one or more of the following characteristics.

[0020] According to a characteristic of the invention, step c) is carried out in a dry atmosphere.

[0021] Thus, an advantage provided is to avoid exposure of the bonding interface to water molecules when the laser ablation of step c) reaches the bonding interface.

[0022] According to a characteristic of the invention, the laser radiation is applied during step c) in a direction perpendicular to the bonding interface.

[0023] Thus, one advantage provided is to optimize the useful volume of the elementary cells manufactured.

[0024] According to a characteristic of the invention, the laser radiation applied during step c) is pulsed radiation having a fluence and a pulse duration adapted to obtain an ablation of the intercalary zone, of the bonding interface, and of the first part of the first substrate.

[0025] Thus, an advantage provided by the pulsed nature of laser radiation is to limit heat transfer in the vicinity of the ablation in order to preserve the bonding interface.

[0026] According to a characteristic of the invention, step c) is carried out so that the first part of the first substrate is ablated to a thickness of between 5 μm and 30 μm, preferably between 10 μm and 20 μm. According to a characteristic of the invention, the cavities are formed during step b) by a technique chosen from:

[0027] - cutting the second substrate with a saw;

[0028] - physical etching of the second substrate with a plasma;

[0029] - chemical etching of the second substrate with an etching agent.

[0030] The choice of technique may depend on the characteristics of the material of the second substrate and the operating time required to carry out step b).

[0031] According to a characteristic of the invention, the cavities formed during step b) extend in a direction perpendicular to the bonding interface.

[0032] Thus, one advantage provided is to optimize the useful volume of the elementary cells manufactured.

[0033] According to a characteristic of the invention, step b) is carried out so that the distance between the bottom of each cavity and the bonding interface is between 5 pm and 30 pm, preferably between 10 pm and 20 pm.

[0034] Thus, an advantage provided is to effectively protect the bonding interface, for example from cooling water or mechanical vibrations when step b) is carried out by cutting with a saw to obtain the cavities.

[0035] According to a characteristic of the invention, each cavity formed during step b) has a width greater than or equal to 50 μm.

[0036] Thus, one advantage provided is to facilitate the subsequent execution of step c).

[0037] According to a characteristic of the invention, the second part of the first substrate is removed during step d) by a technique chosen from:

[0038] - a cleavage propagating a crack resulting from the ablation of the first part of the first substrate during step c);

[0039] - cutting with a saw or a laser;

[0040] - physical engraving with plasma;

[0041] - chemical etching with an etching agent.

[0042] The choice of technique may depend on the characteristics of the first substrate material and the operating time required to perform step d). Definitions

[0043] - By "elementary cell" is meant a unitary structure, partially representative of a structure of an electronic chip, and resulting from divisions of a stack successively comprising a first substrate, a bonding interface, a second substrate. The elementary cell is partially representative of a structure of an electronic chip in the sense that a thin layer generally replaces the second substrate in the case of an electronic chip.

[0044] - By "comprising successively" is meant that the elements of the stack are arranged one on top of the other in a defined order from bottom to top under normal conditions of use, i.e. following the normal to the surface of the first and second substrates. The expression "comprising successively" does not exclude the presence of additional elements (e.g. a dielectric layer, an interconnection structure) interposed between the first substrate and the bonding interface and / or between the bonding interface and the second substrate. An interconnection structure is a stack of interconnection levels, comprising metal tracks embedded in a dielectric material.

[0045] - By "substrate" is meant a self-supporting physical support, made of a basic material from which a device for microelectronics (electronic, optical, mechanical, etc.) can be formed. A substrate can be a slice (also called a "wafer") which is generally in the form of a disc cut from an ingot of a crystalline material.

[0046] - By “bonding interface” we mean the contact zone between the first and second substrates allowing them to bond.

[0047] The bonding may be a direct bonding. A direct bonding is a spontaneous bonding resulting from the direct contact of two surfaces, that is to say in the absence of an additional element such as an adhesive, a wax or a solder. The adhesion comes mainly from the van der Waals forces resulting from the electronic interaction between the atoms or molecules of two surfaces, from hydrogen bonds due to the preparation of the surfaces or from covalent bonds established between the two surfaces. The bonding may be direct between the first and second substrates. When the first substrate and / or the second substrate are coated with a dielectric layer (e.g. an oxide layer) before bonding, the contact zone may be formed by a dielectric layer or two dielectric layers extending between the first and second substrates. The bonding may be direct between a dielectric layer and a substrate, or between two dielectric layers.The bonding can be a hybrid bond. A hybrid bond is a metal-to-metal bond and a dielectric-to-dielectric bond. The hybrid bonding interface can be the contact surface between two interconnect structures.

[0048] The bonding can be a metallic bond (e.g. eutectic bond) or a polymer bond (e.g. epoxy).

[0049] - By "sensitive" we mean that the bonding interface can react chemically with the humid environment and / or can be damaged by mechanical vibrations (impaired adhesion).

[0050] - By "wet environment" we mean an environment containing water molecules in gaseous or liquid form.

[0051] - By "ablation" we mean an ejection of material from a material crossed by laser radiation at a given fluence.

[0052] - By “thickness” is meant a dimension along the normal to the surface of the first and second substrates, or along a direction perpendicular to the bonding interface.

[0053] - By “mechanical strength” we mean that the elementary cells delimited during step b) resist rupture at the end of step c), in response to mechanical stress.

[0054] - By "dry atmosphere" we mean an atmosphere devoid of water molecules in gaseous or liquid form.

[0055] - X and Y values ​​expressed using the expressions "between X and Y" or "between X and Y" are included in the defined range of values.

[0056] Brief description of the drawings

[0057] Other features and advantages will become apparent in the detailed description of various embodiments of the invention, the description being accompanied by examples and references to the attached drawings.

[0058] Figure 1 is a schematic sectional view, illustrating a step a) of a method according to the invention.

[0059] Figure 2 is a schematic sectional view, illustrating a step b) of a method according to the invention.

[0060] Figure 3 is a schematic sectional view, illustrating the start of the execution of a step c) of a method according to the invention.

[0061] Figure 4 is a schematic sectional view, illustrating the end of the execution of a step c) of a method according to the invention. Figure 5 is a schematic sectional view, illustrating a step d) of a method according to the invention.

[0062] It should be noted that the drawings described above are schematic, and are not necessarily to scale for the sake of readability and to simplify their understanding. The sections are made along the perpendicular to the bonding interface (in other words along the normal to the surface of the first and second substrates).

[0063] Detailed description of the implementation methods

[0064] Identical elements or those providing the same function will bear the same references for the different embodiments, for the sake of simplification.

[0065] An object of the invention is a method for manufacturing elementary cells CE to be characterized, comprising the steps: a) using a stack successively comprising a first substrate 1, a bonding interface IC, a second substrate 2; the bonding interface IC being sensitive to a humid environment and / or to mechanical vibrations; b) forming cavities 3 within the second substrate 2 delimiting elementary cells CE, the cavities 3 each having a bottom 30 extending at a distance d from the bonding interface IC, the second substrate 2 retaining an intermediate zone ZI extending between the bottom 30 of each cavity 3 and the bonding interface IC; c) applying laser radiation L to the bottom 30 of each cavity 3 so as to:

[0066] - locally obtaining an ablation A of the intercalary zone ZI, of the bonding interface IC, and of a first part 10 of the first substrate 1;

[0067] - retaining a second part 11 of the first substrate 1, extending in the extension of the ablation A, and adapted to retain mechanical strength of the elementary cells CE delimited during step b); d) removing the second part 11 of the first substrate 1 so as to separate the elementary cells CE delimited during step b).

[0068] Step a)

[0069] Step a) consists of using a stack successively comprising a first substrate 1, an IC bonding interface, a second substrate 2. The stack comes from an assembly of the first and second substrates 1, 2.

[0070] The assembly between the first and second substrates 1, 2 may be a direct bonding between two surfaces of the first and second substrates 1, 2. The first substrate 1 and / or the second substrate 2 may be coated with a dielectric layer, such as an oxide layer, before assembly. Where appropriate, the assembly between the first and second substrates 1, 2 may be a direct bonding via the dielectric layer(s).

[0071] Alternatively, the first substrate 1 and / or the second substrate 2 may be coated with a metal layer before assembly. The assembly between the first and second substrates 1, 2 may be a metal bonding such as a eutectic bonding via the metal layer(s).

[0072] According to another variant, the first substrate 1 and / or the second substrate 2 may be coated with an interconnection structure, before assembly. The assembly between the first and second substrates 1, 2 may be a hybrid bonding (metal / metal bonding and dielectric / dielectric bonding) via the interconnection structure(s).

[0073] According to another variant, the first substrate 1 and / or the second substrate 2 may be coated with a layer of polymer (e.g. epoxy), before assembly. The assembly between the first and second substrates 1, 2 may be a bonding via the polymer layer(s).

[0074] The IC bonding interface may be sensitive to a humid environment. The IC bonding interface may therefore react chemically with water molecules (usually in liquid or gaseous form) in the humid environment, for example by oxidation when the IC bonding interface comprises metallic materials. The IC bonding interface may be sensitive to mechanical vibrations. In other words, the IC bonding interface may be damaged by mechanical vibrations, leading to impaired adhesion.

[0075] The first and second substrates 1, 2 are each made of a material from which a device for microelectronics can be formed. By way of non-limiting examples, the material can be chosen from silicon, silicon carbide, diamond, sapphire, a III-V material.

[0076] By way of non-limiting example, the first and second substrates 1, 2 may each have a diameter of 200 mm and a thickness of 725 μm.

[0077] Step b)

[0078] Step b) consists of forming cavities 3 within the second substrate 2 so as to delimit elementary cells CE. The cavities 3 each have a bottom 30 extending at a distance d from the bonding interface IC. Step b) is carried out so that the second substrate 2 retains an intermediate zone ZI extending between the bottom 30 of each cavity 3 and the bonding interface IC. The cavities 3 are advantageously formed during step b) by a technique chosen from:

[0079] - cutting the second substrate 2 with a saw;

[0080] - a physical etching of the second substrate 2 with a plasma;

[0081] - chemical etching of the second substrate 2 with an etching agent.

[0082] The cavities 3 formed during step b) advantageously extend in a direction perpendicular to the bonding interface IC.

[0083] Step b) is advantageously carried out so that the distance d between the bottom 30 of each cavity 3 and the bonding interface IC is between 5 pm and 30 pm, preferably between 10 pm and 20 pm. In other words, the intermediate zone ZI has a thickness between 5 pm and 30 pm, preferably between 10 pm and 20 pm.

[0084] Each cavity 3 formed during step b) advantageously has a width 1 greater than or equal to 50 pm. By way of non-limiting example, the width 1 may be between 80 pm and 120 pm.

[0085] By way of non-limiting example, step b) may be performed by cutting the second substrate 2 with a saw equipped with a diamond blade. The blade may have a width of 100 μm. The cutting may be carried out in the second substrate 2 to a depth of around 710 μm. The cutting conditions may be conventional: blade rotation speed set at 20,000 revolutions per minute with a feed rate of 13 mm / s.

[0086] Step c)

[0087] The laser radiation L is applied to the bottom 30 of each cavity 3 during step c) so as to locally obtain an ablation A of the intermediate zone ZI, of the bonding interface IC, and of a first part 10 of the first substrate 1.

[0088] The laser radiation L is applied to the bottom 30 of each cavity 3 during step c) so as to preserve a second part 11 of the first substrate 1, extending in the extension of the ablation A. The second part 11 of the first substrate 1 is adapted to preserve a mechanical strength of the elementary cells CE delimited during step b).

[0089] Step c) is advantageously carried out in a dry atmosphere.

[0090] The laser radiation L is advantageously applied during step c) in a direction perpendicular to the bonding interface IC.

[0091] The laser radiation L applied during step c) is advantageously a pulsed radiation having a fluence and a pulse duration adapted to obtain an ablation A of the intercalary zone ZI, of the bonding interface IC, and of the first part 10 of the first substrate 1. By way of non-limiting example, it is possible to use a laser radiation L whose pulse duration is of the order of a nanosecond (e.g. frequency of 15 kHz) with a power of 3 W. The scanning speed (advancement) of the laser radiation L applied during step c) is adjusted to obtain the desired ablation depth, for example 50 mm / s for an ablation depth of the order of 30 μm.

[0092] Step c) is advantageously carried out so that the first part 10 of the first substrate 1 is ablated to a thickness of between 5 μm and 30 μm, preferably between 10 μm and 20 μm. The total ablated thickness of the intermediate zone ZI and of the first part 10 of the first substrate 1 is between 10 μm and 60 μm, preferably between 20 μm and 40 μm.

[0093] Step d)

[0094] Step d) consists of removing the second part 11 of the first substrate 1 so as to separate the elementary cells CE delimited during step b).

[0095] The second part 11 of the first substrate 1 is advantageously removed during step d) by a technique chosen from:

[0096] - a cleavage propagating a crack resulting from the ablation A of the first part 10 of the first substrate 1 during step c);

[0097] - cutting with a saw or with a laser (“laser dicing” in English);

[0098] - physical engraving with plasma;

[0099] - chemical etching with an etching agent.

[0100] As non-limiting examples, step d) may be performed by cleaving with a 3-point type cleaving plier, or with a wafer expander stretching an adhesive tape applied to the lower surface of the first substrate 1.

[0101] The invention is not limited to the embodiments disclosed. Those skilled in the art are able to consider their technically effective combinations and to substitute equivalents for them.

Claims

CLAIMS 1. Method for manufacturing elementary cells (EC) to be characterized for microelectronics, comprising the steps: a) using a stack successively comprising a first substrate (1), a bonding interface (IC), a second substrate (2); the bonding interface (IC) being sensitive to a humid environment in the sense that the bonding interface (IC) can react chemically with the humid environment, the bonding interface (IC) being obtained by direct bonding or by hybrid bonding between the first and second substrates (1, 2); b) forming cavities (3) within the second substrate (2) delimiting elementary cells (EC), the cavities (3) each having a bottom (30) extending at a distance (d) from the bonding interface (IC), the second substrate (2) retaining an intermediate zone (ZI) extending between the bottom (30) of each cavity (3) and the bonding interface (IC);c) applying laser radiation (L) to the bottom (30) of each cavity (3) in a dry atmosphere free of water molecules in gaseous or liquid form so as to:; - locally obtaining an ablation (A) of the intercalary zone (ZI), of the bonding interface (IC), and of a first part (10) of the first substrate (1); - retaining a second part (11) of the first substrate (1), extending in the extension of the ablation (A), and adapted to retain mechanical strength of the elementary cells (CE) delimited during step b) so that the elementary cells (CE) delimited during step b) resist breaking at the end of step c) in response to mechanical stress; d) removing the second part (11) of the first substrate (1) so as to separate the elementary cells (CE) delimited during step b).

2. Method according to claim 1, in which the laser radiation (L) is applied during step c) in a direction perpendicular to the bonding interface (IC).

3. Method according to claim 1 or 2, in which the laser radiation (L) applied during step c) is pulsed radiation having a fluence and a pulse duration adapted to obtain an ablation (A) of the intercalary zone (ZI), of the bonding interface (IC), and of the first part (10) of the first substrate (1).

4. Method according to one of claims 1 to 3, in which step c) is carried out so that the first part (10) of the first substrate (1) is ablated to a thickness of between 5 μm and 30 μm, preferably between 10 μm and 20 μm.

5. Method according to one of claims 1 to 4, in which the cavities (3) are formed during step b) by a technique chosen from: - cutting the second substrate (2) with a saw; - a physical etching of the second substrate (2) with a plasma; - chemical etching of the second substrate (2) with an etching agent.

6. Method according to one of claims 1 to 5, in which the cavities (3) formed during step b) extend in a direction perpendicular to the bonding interface (IC).

7. Method according to one of claims 1 to 6, in which step b) is carried out so that the distance (d) between the bottom (30) of each cavity (3) and the bonding interface (IC) is between 5 pm and 30 pm, preferably between 10 pm and 20 pm.

8. Method according to one of claims 1 to 7, in which each cavity (3) formed during step b) has a width (1) greater than or equal to 50 μm.

9. Method according to one of claims 1 to 8, in which the second part (11) of the first substrate (1) is removed during step d) by a technique chosen from: - a cleavage propagating a crack resulting from the ablation (A) of the first part (10) of the first substrate (1) during step c); - cutting with a saw or a laser; - physical engraving with plasma; - chemical etching with an etching agent.

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