Process for bonding in an atmosphere of a gas having a negative Joule-Thomson coefficient

Abstract

The present invention relates to a process for direct bonding two substrates, comprising at least: (a) bringing the surfaces to be bonded of said substrates in close contact; and (b) propagating a bonding wave between said substrates, characterised in that said substrates are kept, during step (b), in an atmosphere of a gas having a negative Joule-Thomson coefficient at the temperature and pressure of said atmosphere.

Claims

1. A process for bonding two substrates by molecular adhesion, comprising at least: (a) bringing the surfaces to be bonded of the said substrates into intimate contact; and (b) propagating a bonding front between the said substrates; wherein the said substrates are kept, during stage (b), in a gas atmosphere exhibiting, at the temperature and at the pressure of the said atmosphere, a negative Joule-Thomson coefficient.

2. The process according to claim 1, in which the propagation of the bonding front is initiated by the application of at least one pressure point on at least one of the external faces of the assembly formed by the two juxtaposed substrates.

3. The process according to claim 2, in which the pressure point is applied on the peripheral edge of the exposed surface of at least one of the two juxtaposed substrates.

4. The process according to claim 1, in which the said atmosphere is formed of a gas or gas mixture, the said gas or gases exhibiting, at the temperature and pressure of the said atmosphere, a negative Joule-Thomson coefficient.

5. The process according to claim 1, in which the said atmosphere is formed of a mixture composed (i) of one or more gases exhibiting, at the temperature and at the pressure of the said atmosphere, a negative Joule-Thomson coefficient and (ii) of one or more gases exhibiting, at the temperature and at the pressure of the said atmosphere, a positive Joule-Thomson coefficient, in proportions such that the said mixture exhibits, at the temperature and at the pressure of the said atmosphere, a negative Joule-Thomson coefficient.

6. The process according to claim 1, in which stage (b) is carried out at ambient temperature and at atmospheric pressure.

7. The process according to claim 6, in which the said atmosphere is formed of one or more gases chosen from helium, neon and hydrogen.

8. The process according to claim 6, in which the said atmosphere is formed of a mixture (i) of one or more gases chosen from helium, neon and hydrogen and (ii) of one or more gases exhibiting, at ambient temperature and atmospheric pressure, a positive Joule-Thomson coefficient, in proportions such that the said mixture exhibits, at ambient temperature and atmospheric pressure, a negative Joule-Thomson coefficient.

9. The process according to claim 8, in which said gases exhibiting, at ambient temperature and atmospheric pressure, a positive Joule-Thomson coefficient, are chosen from nitrogen, oxygen and argon.

10. The process according to claim 8, in which the said atmosphere is formed of a mixture (i) of one or more gases chosen from helium, neon and hydrogen with (ii) air, in proportions such that the said mixture exhibits, at ambient temperature and atmospheric pressure, a negative Joule-Thomson coefficient.

11. The process according to claim 6, in which the said atmosphere comprises one or more gases chosen from helium, neon and hydrogen.

12. The process according to claim 1, in which one of the surfaces, indeed even both surfaces, to be bonded of the said substrates is/are subjected, prior to stage (a), to one or more surface treatment stages intended to promote molecular adhesion.

13. The process according to claim 12, in which the surface treatment(s) is/are chosen from a polishing, cleaning and/or hydrophilic or hydrophobic treatment.

14. A process for the formation of a structure comprising a thin layer made of a semiconductor material on a substrate, comprising at least the stages consisting in: (c) having available a donor substrate comprising a part to be transferred comprising at least one thin layer of the said semiconductor material and exhibiting a first bonding surface, and having available a receiving substrate exhibiting a second bonding surface; (d) bonding, by molecular adhesion, the said first surface and the said second surface; and (e) removing the remainder of the donor substrate from the said part bonded to the said receiving substrate; wherein the bonding stage (d) is carried out according to a process comprising at least: (a) bringing the surfaces to be bonded of the said substrates into intimate contact; and (b) propagating a bonding front between the said substrates; wherein the said substrates are kept, during stage (b), in a gas atmosphere exhibiting, at the temperature and at the pressure of the said atmosphere, a negative Joule-Thomson coefficient.

15. The process according to claim 14, in which the said semiconductor material is silicon.

16. The process according to claim 14, in which the part to be transferred comprises, in addition to the said thin layer, another layer of material, the said other layer of material exhibiting the said first bonding surface.

17. The process according to claim 16, in which the said another layer of material is of silicon oxide.

Description

FIGURES

(1) FIG. 1: graphical representation of the variation in the Joule-Thomson coefficient as a function of the temperature for different gases at atmospheric pressure.

(2) FIG. 2: transverse cross sections of the substrate or substrates at the different stages of the Smart Cut process.

(3) It should be noted that, for reasons of clarity, the different elements in FIG. 2 are not drawn to scale, the true dimensions of the different parts not being observed.

(4) The following example is given by way of illustration and without implied limitation of the invention.

EXAMPLE

Bonding by Molecular Adhesion

(5) The bonding by molecular adhesion was carried out between a first silicon wafer carrying a layer of silicon oxide defining a first bonding surface and a second silicon wafer defining a second bonding surface. The wafers are in the form of circular platelets with a diameter from 1 inch (2.54 cm) to 450 mm.

(6) The surfaces to be bonded of the substrates were cleaned beforehand by brushing, then rinsing with ultra-pure water and drying by centrifuging.

(7) The substrates were positioned on the substrate holders of a conventional bonding device (EV 540 Automated Wafer Bonding System from EVG) capable of bringing the surfaces of the said substrates into intimate contact and of initiating the bonding front via the application of a bond pin at a point of the peripheral edge of the exposed surface of one of the substrates.

(8) The bonding device is introduced into a chamber containing a gas atmosphere and in which the automated bonding is carried out by the bonding device.

(9) The bonding process is repeated while varying the nature of the gas atmosphere of the bonding chamber, at ambient temperature and atmospheric pressure. The atmospheres tested are as follows:

(10) 1. air,

(11) 2. nitrogen,

(12) 3. argon, and

(13) 4. helium.

(14) Results

(15) Observation of the bonding interface, using an infrared camera or also by acoustic microscopy, reveals the presence along the edge of the plates of edge void or bubble defects in the case of the plates under an air, nitrogen or argon atmosphere.

(16) On the other hand, in the case of the bonding carried out under a helium atmosphere, no edge void or bubble defect is observed at the periphery of the bonding interface.