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EP-4511873-B1 - METHOD FOR ASSEMBLING TWO SUBSTRATES BY MOLECULAR ADHESION AND STRUCTURE OBTAINED BY SUCH A METHOD

EP4511873B1EP 4511873 B1EP4511873 B1EP 4511873B1EP-4511873-B1

Inventors

  • BROEKAART, MARCEL
  • LOGIOU, MORGANE

Dates

Publication Date
20260513
Application Date
20230412

Claims (17)

  1. Method for assembling by molecular adhesion two substrates each having a main face, at least one of the two substrates being provided with a surface dielectric layer on the main face thereof, the method comprising the following steps: (a) bringing the main faces of the two substrates into contact, then; (b) initiating and propagating a bonding wave between the main faces of the two substrates in order to assemble them together; the method being characterized in that it comprises, prior to the contacting step, a step of preparing the surface dielectric layer for the purpose of introducing a sulfur dose greater than 3.0 E13 at/cm 2 into this layer.
  2. Assembly method according to the preceding claim, wherein the sulfur dose is greater than 3.5 E13 at/cm 2 .
  3. Assembly method according to either of the preceding claims, wherein the step of preparing the surface dielectric layer also has the purpose of introducing a fluorine dose greater than 4.0 E14 at/cm 2 into this layer.
  4. Assembly method according to either claim 1 or claim 2, wherein the preparation step comprises activating the surface dielectric layer by a plasma of a gas comprising sulfur, such as a plasma comprising sulfur hexafluoride.
  5. Assembly method according to the preceding claim, wherein the plasma also comprises oxygen or nitrogen.
  6. Assembly method according to the preceding claim, wherein the activation of the surface dielectric layer is carried out for an activation time of between 15 seconds and 2 minutes.
  7. Assembly method according to the preceding claim, wherein the surface layer is exposed to the oxygen or nitrogen plasma for the duration of the activation, and a controlled quantity of sulfur hexafluoride is mixed with the oxygen or nitrogen for a determined period of the activation time.
  8. Assembly method according to the preceding claim, wherein the determined period is respectively preceded and followed by periods during which the surface dielectric layer is exposed to the plasma formed by an activation gas of oxygen or nitrogen.
  9. Assembly method according to either claim 1 or claim 2, wherein the preparation step comprises preparing a chamber of a plasma activation apparatus by a plasma of a gas comprising sulfur and then, after preparing the chamber, treating the surface dielectric layer in the chamber by a plasma comprising oxygen or nitrogen.
  10. Assembly method according to any of the preceding claims comprising heat treatment of the two substrates assembled together.
  11. Assembly method according to any of the preceding claims, wherein the two substrates are provided with a surface dielectric layer of silicon oxide or silicon nitride on the main face side thereof, and the preparation step is carried out on each of the surface dielectric layers.
  12. Assembly method according to any of the preceding claims, wherein the surface dielectric layer is made of silicon oxide.
  13. Assembly method according to any of the preceding claims comprising a step of cleaning at least one of the main faces of the two substrates, between the preparation step and the contacting step.
  14. Structure (1) comprising a support substrate (2), a buried dielectric layer (3) arranged on and in contact with the support substrate (2) and a so-called "useful" layer (4) on and in contact with the buried layer (3), the structure being characterized in that the buried dielectric layer (3) has a sulfur dose greater than 3.0 E13 at/cm 2 .
  15. Structure (1) according to the preceding claim, wherein the sulfur dose is greater than 3.5 E13 at/cm 2 .
  16. Structure (1) according to the preceding claim, wherein the buried dielectric layer (3) comprises a fluorine dose greater than 4.0 E14 at/cm 2 .
  17. Structure (1) according to any of claims 14 to 16, wherein the buried dielectric layer is made of silicon oxide.

Description

The invention finds its application particularly in the fields of microelectronics, microsystems, and photonics. TECHNOLOGICAL BACKGROUND OF THE INVENTION Molecular adhesion is a process for joining two bodies in which the main faces or surfaces of these two bodies, perfectly clean, flat, and smooth, are brought into intimate contact with each other to promote the development of molecular bonds, such as van der Waals or covalent bonds. The two bodies are then joined without the use of an adhesive. These bonds can be strengthened by applying heat treatment to the joint. This process is used in particular for the manufacture of substrates which find application in the fields of microelectronics, microsystems, photonics... In these fields, the substrates generally have the form of circular wafers of materials which can be single-crystal, poly-crystalline or amorphous, conductive, semiconductive or insulating. In these fields, and to facilitate substrate assembly, it is common practice to form a dielectric layer, typically of silicon oxide, on one or both of the two substrates. This can be done by deposition, possibly followed by a polishing step, or by simple oxidation when the substrate is already formed or contains silicon. It is also common practice to prepare the main surfaces to make them clean (particularly in terms of particles and contaminants) and smooth (to provide a surface roughness typically below 0.5 nm in root mean square value over a 5-micron x 5-micron field of view). It is also sometimes considered to make at least one of these surfaces reactive by applying a plasma, typically oxygen or nitrogen. This surface preparation aims to achieve maximum bonding energy immediately after the assembly step and before any thermal annealing. After preparation, the two substrates are placed one on top of the other, at the level of their principal faces. Applying pressure to either of the two substrates causes the principal faces to come into intimate and localized contact, and this intimate contact propagates over the entire extent of the principal faces in the form of a wave, called a "bonding wave". Patent, technical, and scientific literature abounds with documents explaining the principles and use of such an adhesion process. Reference may be made, in particular, to the publication of Rieutord et al., “Dynamics of a bonding front”, Physical Review Letters, vol. 94, pp. 236101, 2005 . A recurring problem encountered during the deployment of a molecular adhesion process is the appearance of peripheral defects (often referred to as "pits") at the bonding interface, where the bonding wave encounters the substrate edges. When the wave is initiated at a substrate edge, these peripheral defects are located in a peripheral sector, generally positioned on the edge diametrically opposite the wave initiation point. When the wave is initiated in a central area of one of the substrates, these peripheral defects can be located along the entire contour. These defects result from the trapping of gas and/or water at the bonding interface between the two substrates. At these defects, the two substrates are not in contact, and the local adhesion energy is very low, or even nonexistent. These defects, although present, are not necessarily visible directly after the propagation of the bonding wave, but they can be revealed during thermal annealing of the assembly formed by the two substrates joined together. The speed of the bonding wave has been identified as a factor influencing the number of such defects, and reducing this speed generally leads to a reduction in the number of defects, or even their elimination. To this end, various techniques for controlling this speed have been proposed, notably through surface treatment of one or both substrates, particularly by heating ( WO2007060145 It has also been proposed, in order to reduce the speed of the bonding wave, to project a gas jet, possibly hot, towards the point where the bonding wave begins, at the moment of bonding. However, while these treatments can indeed reduce the bonding speed, they are also likely to reduce the adhesion energy, which can be detrimental for certain applications. The document WO2013160841 plans to maintain the substrates, during wave propagation, in a gas atmosphere having, at the temperature and pressure of said atmosphere, a negative Joule-Thomson coefficient, for example helium, neon or hydrogen. Furthermore, the documents US 2006216904 A1 , US 5407506 A And US 2008171443 A1 disclose processes describing a surface treatment of the intermediate bonding layer prior to the bonding step. Regardless of the solution chosen in the state of the art and regardless of the effectiveness of that solution, it constitutes a significant constraint. SUBJECT OF THE INVENTION One aim of the invention is to provide a molecular adhesion assembly method that differs from the existing art and that prevents, or at least limits, the occurrence of "pitted" type defe