Patent Application
20200219762
This application claims priority from French Patent Application No. 19 00127 filed on Jan. 7, 2019. The content of this application is incorporated herein by reference in its entirety.
The field of the invention is that of methods for transferring a layer from a donor substrate to a receiver substrate which implement a fracturing along an embrittlement plane formed in the donor substrate. The invention more particularly relates to the control of the fracturing process.
Smart Cut™ technology is a well-known technique bien for enabling the transfer of thin layers of materials, for example semiconductor materials. According to this technique, ionic species such as hydrogen or helium are implanted in a donor substrate in order to form therein an embrittlement plane. The donor substrate is thereafter placed in contact with a receiver substrate, for example by direct bonding. This technique next resorts to the development of defects generated during the implantation to lead to fracturing. This development involves an energy input, generally achieved by means of a thermal treatment, in order to enable the formation of a confined layer of cavities and micro-fissures within which a fracture wave is going to initiate and propagate. This wave is going to progressively extend all along the embrittlement plane leading to the separation of the superficial thin layer delimited by this embrittlement plane and the remainder of the substrate.
The document WO 2018/029419 A1 discloses that the interaction between the propagation of the fracture wave and acoustic vibrations emitted during the initiation and/or the propagation of the fracture wave leads to the formation of periodic patterns of variations in thickness and/or roughness of the transferred layer, which extend over the whole surface of this layer. In other words, the fracture wave is deviated vertically from its progression plane according to the instantaneous stress state of the material that it traverses, this stress state being influenced by the acoustic wave.
The absence of precise control of the localisation of the initiation of the fracture wave leads to a variability between transferred thin layers, notably in terms of roughness and/or thickness, a variability which necessitates the implementation of more stringent controls and/or specific post-fracture treatments.
In order to limit this variability, it is thus sought to initiate the fracture wave in a standardised manner. In the document WO 2018/029419 A1 cited previously, for this purpose zones are created, localised on the wafer, where the fracture preferentially initiates. Such a creation may notably consist in:
The invention proposes a complementary or alternative technique to the aforementioned techniques of confinement of the localisation of the initiation of the fracture wave in a target zone of the embrittlement plane. More particularly, it relates to a method for transferring a thin layer from a donor substrate to a receiver substrate, the donor substrate comprising an embrittlement plane delimiting the thin layer and a bulk part of the donor substrate, the method including the following steps:
Certain preferred but non-limiting aspects of this method are the following:
Other aspects, aims, advantages and characteristics of the invention will become clearer on reading the following detailed description of preferred embodiments thereof, given as a non-limiting example, and made with reference to the appended drawings in which:
The invention relates to a method for transferring a thin layer from a donor substrate to a receiver substrate. The donor substrate may be a silicon substrate, or be made of any other material, semiconductor or not. As examples, it may be silicon-germanium, germanium or a III-V material.
The method includes a step of formation in the donor substrate of an embrittlement plane delimiting the thin layer and a bulk part of the donor substrate. This embrittlement plane is formed by implantation of species, typically hydrogen and/or helium, carried out in a uniform manner (notably in dose) on the whole of the donor substrate. Thus, the dose of implanted species is uniform over the whole extent of the embrittlement plane and the embrittlement plane has an uniform capacity to initiate a fracture wave over its whole extent.
The method includes the placing in contact of the donor substrate and the receiver substrate to form an assembly to fracture. This formation may be carried out by direct assembly, for example by molecular adhesion. Then, following the placing in contact, the method includes the initiation and the propagation of the fracture wave along the embrittlement plane, which leads to the detachment of the thin layer from the donor substrate and to its transfer onto the receiver substrate. This initiation and propagation of the fracture wave includes a so-called embrittlement thermal treatment applied to the assembly to fracture. This thermal treatment embrittles the donor substrate at the level of its embrittlement plane 2, and supplies sufficient energy so that the fracture wave, once initiated, propagates in a self-sustaining manner.
In a first alternative embodiment, the thermal treatment is sufficient on its own to initiate the fracture wave. In a second alternative embodiment, the method includes an additional localised energy input, after or during the embrittlement thermal treatment, to initiate the fracture wave. This energy may be of mechanical or thermal origin or of any other origin. It may involve for example a localised heating carried out by a laser, or an input of energy by ultrasounds.
According to the invention, the initiation of the fracture wave is spatially controlled by reducing, or even inhibiting, the capacity of one or more target zones of the embrittlement plane to initiate the fracture wave. To do so, the method includes, before the placing in contact of the donor and receiver substrates, the application to the donor substrate of a treatment of localised reduction of the capacity of the embrittlement plane to initiate the fracture wave. This spatially selective reduction means that the initiation of the fracture wave is localised in a region of the embrittlement plane different from the target zone(s) which have a probability of initiation of the fracture wave made less by said treatment. And as will be detailed hereafter, in an embodiment, the localised reduction of the capacity to initiate the fracture wave is carried out so as to reduce the probability of initiation of the fracture wave by a target zone without this same target zone forming an obstacle to the propagation of the fracture wave.
A methodology is described hereafter for determining the operating conditions of a treatment of the donor substrate making it possible to reduce or even to inhibit the capacity of a target zone of the embrittlement plane to initiate the fracture wave.
During a thermal treatment applied to an implanted substrate not assembled to a stiffener, the defects linked to the implantation evolve in the form of cavities which can be behind a blistering or even an exfoliation of the implanted layer. In the field of the invention, it is generally considered that the operating parameters leading to such a blistering/exfoliation of a non-assembled substrate are also going to make it possible to carry out the transfer of a thin layer when the substrate is assembled with a stiffener.
In a possible embodiment of the invention, the localised reduction of the capacity of the embrittlement plane to initiate the fracture wave may include the carrying out of a localised laser annealing of the donor substrate. The Inventors have actually been able to check that by locally irradiating an implanted substrate with a laser beam, it is possible to reduce or even to inhibit blistering/exfoliation phenomena in the irradiated zones whereas these phenomena are observed in a usual manner in the non-irradiated zones. The absence of blistering/exfoliation in the irradiated zones means that these zones cannot initiate a fracture wave.
The operating conditions of such localised laser annealing may be determined as described hereafter on the basis of an exemplary embodiment of the method according to the invention which uses a donor substrate made of silicon having an embrittlement plane formed by implantation of hydrogen and helium with energies in the range 30-40 keV and a total dose (H+He) of the order of 2.1016 ions/cm2. The laser annealing is a laser annealing of the NSLA (Nano Second Laser Annealing) type exploiting to begin with a single irradiation pulse of wavelength 380 nm and of duration (full width at half maximum) of 160 ns. Different regions of the donor substrate are irradiated with an energy fluence going from 0.4 J/cm2 to 3.125 J/cm2 per pitch of 0.025 J/cm2 and the quality of the surface of the donor substrate is evaluated by means of a “haze” measurement corresponding to the intensity of the light scattered by the surface of the layer, using the Surfscan® SP2 inspection tool of the KLA-Tencor Company.
The donor substrate thereby irradiated is subjected to a thermal treatment at 500° C. for two minutes to verify the presence or the absence of blistering at the level of the different irradiated regions, and thus the possibility or not of initiating fracturing.
It may be deduced from the foregoing that within the framework of an irradiation by a single pulse, it is preferable not to have to resort to fluences comprised between 1.6 and 1.9 J/cm2 or to fluences greater than 3 J/cm2 to avoid a surface degradation but rather to favour fluences comprised between 1.9 and 3 J/cm2. Within this latter range, the higher the fluence, the more the phenomenon of blistering is inhibited and thus the more the capacity for initiation of the fracture wave is reduced.
In
It is clear from the foregoing that it is possible to reduce or even to inhibit blistering by using a laser annealing and that it is possible to adapt the fluence and the number of pulses to attain the desired inhibition effect. Returning to the description of the method according to the invention, said method may thus include a localised irradiation of the free face of the thin layer (i.e. its face intended to be placed in contact with the receiver substrate) by one or more laser pulses. It is obviously possible to irradiate several target zones, and even to apply different irradiation parameters (fluence and number of pulses notably) between the target zones.
In a possible exemplary embodiment, during the step of localised reduction of the capacity to initiate the fracture wave, a peripheral crown of the embrittlement plane P, with the exception of a sector of the peripheral crown, is subjected to said reduction. The thickness of the peripheral crown is for example 100 μm to 10 mm, typically 500 μm to 2 mm. The sector occupies a surface comprised between 200×200 μm2 and 20×20 mm2 (which corresponds to an angular opening comprised between around several tenths of degrees and 10 degrees). To do so, and as illustrated by
In another exemplary embodiment, during the step of localised reduction of the capacity to initiate the fracture wave, the whole of the embrittlement plane P is subjected to said reduction with the exception of a zone (for example a central zone which may occupy a surface comprised between 100×100 μm2 and 30×30 mm2) of the embrittlement plane. To do so, and as illustrated by
In another possible exemplary embodiment, during the step of localised reduction of the capacity to initiate the fracture wave, a peripheral crown of the embrittlement plane P present at the edge of the donor substrate is subjected to said reduction of the capacity of initiating the fracture wave. To do so, and as illustrated by
The peripheral target region Rcb preferably covers the crown on the wafer edge which due to a chamfer is not bonded to the receiver substrate and is not transferred thereon. Indeed, in the absence of implementation of the invention, this non-bonded crown is the seat of blistering/exfoliation phenomena during the embrittlement thermal treatment. Defects are then generated which it is advisable to get rid of by a specific post-treatment. With the implementation of the invention, it is possible to reduce or even to eliminate these blistering/exfoliation phenomena at the level of the non-bonded crown and consequently not to have to carry out a specific post-treatment of defects that would be generated by these phenomena.
In another possible embodiment of the invention, the localised reduction of the capacity of the embrittlement plane to initiate the fracture wave may include, before or after the formation of the embrittlement plane, the formation of a localised amorphous zone in the thin layer in line with the zone where the capacity to initiate the fracture wave must be reduced. By localising an amorphous zone in the vicinity of the embrittlement plane, for example at less than 100 nm and advantageously at less than 75 nm or 50 nm from the embrittlement plane, it is possible in fact to limit or even to inhibit bubbling at the level of the zone of the embrittlement plane situated directly in line with this amorphous zone. The amorphous zone is preferably formed after the formation of the embrittlement plane so as not to interfere with this formation. The amorphous zone may be obtained by ion implantation based notably on one or more of the following species: silicon, germanium, phosphorous, arsenic, nitrogen or argon with a dose typically comprised between 1014 and 1016 at/cm2.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1900127 | Jan 2019 | FR | national |
