METHOD FOR TRANSFERRING A USEFUL LAYER OF CRYSTALLINE DIAMOND ONTO A SUPPORTING SUBSTRATE

Abstract

Method for transferring a useful layer onto a supporting substrate, comprising the successive steps: a) providing a donor substrate made of crystalline diamond; b) implanting gaseous species, through the first surface of the donor substrate, according to a given implantation dose and implantation temperature suitable for forming a graphitic flat zone; c) assembling the donor substrate to the supporting substrate by direct adhesion; d) applying thermal annealing according to a thermal budget suitable for fracturing the donor substrate along the graphitic flat zone; the annealing temperature being greater than or equal to 800° C.; the implantation temperature is: above a minimum temperature beyond which bubbling of the implanted gaseous species occurs on the first surface when the donor substrate is submitted, in the absence of a stiffening effect, to thermal annealing according to said thermal budget, below a maximum temperature beyond which the given implantation dose no longer allows formation of the graphitic flat zone.

Claims

1. A method for transferring a useful layer onto a supporting substrate, comprising the successive steps: a) providing a donor substrate, made of crystalline diamond, and comprising a first surface; b) implanting gaseous species, comprising ionized hydrogen atoms, through the first surface of the donor substrate, according to a given implantation dose and a given implantation temperature designed to form a graphitic flat zone within the donor substrate, the useful layer being delimited by the graphitic flat zone and the first surface of the donor substrate; c) assembling the donor substrate to the supporting substrate by direct adhesion with the first surface of the donor substrate; d) applying thermal annealing to the assembly obtained at the end of step c), according to a thermal budget designed to fracture the donor substrate along the graphitic flat zone, so as to expose the useful layer; the thermal budget having an annealing temperature greater than or equal to 800° C.; wherein the given implantation temperature, designated T, complies with: T>T.sub.min, where T.sub.min is a minimum temperature beyond which bubbling of the implanted gaseous species occurs on the first surface of the donor substrate when the donor substrate is submitted, in the absence of a stiffening effect, to thermal annealing according to a thermal budget identical to that in step d), T.sub.min being predetermined as a function of the given implantation dose, the given implantation temperature at which step b) is carried out being strictly above 250° C.; and T<T.sub.max, where T.sub.max is a maximum temperature beyond which the given implantation dose no longer allows formation of the graphitic flat zone within the donor substrate.

2. The method according to claim 1, wherein the thermal budget of the thermal annealing applied in step d) has an annealing temperature between 800° C. and 1200° C.

3. The method according to claim 1, wherein the thermal budget of the thermal annealing applied in step d) has an annealing time between 30 minutes and 7 hours.

4. The method according claim 1, wherein the given implantation temperature at which step b) is carried out is strictly below 500° C.

5. The method according to claim 1, wherein the given implantation temperature at which step b) is carried out is strictly below 400° C.

6. The method according to claim 1, wherein step b) is carried out in such a way that the given implantation dose is strictly above 10.sup.17 at.Math.cm.sup.−2.

7. The method according to claim 1, wherein the gaseous species are implanted in step b) according to an implantation energy above 30 keV.

8. The method according to claim 1, wherein step b) is the only implantation step of the gaseous species through the first surface of the donor substrate.

9. The method according to claim 1, comprising a step c′) consisting of applying thermal annealing to the assembly obtained at the end of step c), according to a thermal budget designed to reinforce the bonding interface between the first surface of the donor substrate and the supporting substrate without initiating fracture of the donor substrate along the graphitic flat zone; step c′) being carried out before step d), thermal annealing being applied in step d) to the assembly obtained at the end of step c′).

10. The method according to claim 1, wherein step c) is preceded by a step c.sub.0) consisting of forming a surface layer on the first surface of the donor substrate, step c.sub.0) being carried out after step b), the surface layer being a layer of oxide or a metallic layer; the donor substrate being assembled to the supporting substrate in step c) by direct adhesion with the surface layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Other features and advantages will appear in the detailed account of different embodiments of the invention, the account being provided with examples and references to the accompanying drawings.

[0052] FIGS. 1 (1a to 1e) comprises schematic sectional views illustrating steps of a first embodiment of a method according to the invention.

[0053] FIGS. 2 (2a to 2e) comprises schematic sectional views illustrating steps of a second embodiment of a method according to the invention.

[0054] FIGS. 3 (3a to 3e) comprises schematic sectional views illustrating steps of a third embodiment of a method according to the invention.

[0055] It should be noted that the drawings described above are schematic, and are not necessarily to scale, for legibility and to make them easier to understand. The sections are made along the normal to the first surface of the donor substrate.

DETAILED ACCOUNT OF THE EMBODIMENTS

[0056] Elements that are identical or provide the same function will bear the same references for the various embodiments, for simplification.

[0057] As illustrated in FIGS. 1 to 3, the invention relates to a method for transferring a useful layer 1 onto a supporting substrate 2, comprising the successive steps:

a) providing a donor substrate 3, made of crystalline diamond, and comprising a first surface 30;
b) implanting gaseous species 4, comprising ionized hydrogen atoms, through the first surface 30 of the donor substrate 3, according to a given implantation dose and a given implantation temperature suitable for forming a graphitic flat zone 5 within the donor substrate 3, the useful layer 1 being delimited by the graphitic flat zone 5 and the first surface 30 of the donor substrate 3;
c) assembling the donor substrate 3 to the supporting substrate 2 by direct adhesion with the first surface 30 of the donor substrate 3;
d) applying thermal annealing to the assembly obtained at the end of step c), according to a thermal budget suitable for fracturing the donor substrate 3 along the graphitic flat zone 5, so as to expose the useful layer 1.

[0058] The thermal budget of the thermal annealing applied in step d) has an annealing temperature greater than or equal to 800° C.

[0059] Step b) is carried out at the given implantation temperature, designated T, complying with:

T>T.sub.min, where T.sub.min is a minimum temperature beyond which bubbling of the implanted gaseous species 4 occurs on the first surface 30 of the donor substrate 3 when the donor substrate 3 is submitted, in the absence of a stiffening effect, to thermal annealing according to a thermal budget identical to that in step d), T.sub.min being predetermined as a function of the given implantation dose; and
T<T.sub.max, where T.sub.max is a maximum temperature beyond which the given implantation dose no longer allows formation of the graphitic flat zone 5 within the donor substrate 3.

Step a)

[0060] Step a) is illustrated in FIGS. 1a, 2a, 3a.

[0061] The first surface 30 of the donor substrate 3 may have a surface area of the order of a few square millimetres. The first surface 30 of the donor substrate 3 may be oriented in terms of crystal planes according to the Miller indices [100]. As a non-limiting example, the donor substrate 3 may have a thickness of the order of 0.5 mm.

Step b)

[0062] Step b) is illustrated in FIGS. 1b and 1c, 2b and 2c, 3b and 3c.

[0063] Step b) is the only implantation step of the gaseous species 4 through the first surface 30 of the donor substrate 3. In other words, the method according to the invention comprises a single step of implantation of the gaseous species 4 through the first surface 30 of the donor substrate 3. The method according to the invention advantageously does not have a step of implantation of non-gaseous species, before step c), in a zone of the donor substrate 3 corresponding to the graphitic flat zone 5.

[0064] The gaseous species 4 may comprise ionized helium atoms, in addition to the ionized hydrogen atoms. In other words, the ionized hydrogen atoms and the ionized helium atoms may be co-implanted in step b).

[0065] The given implantation temperature at which step b) is carried out is advantageously strictly above 250° C., preferably strictly above 280° C. In other words, T.sub.min is between 250° C. and 280° C.

[0066] The given implantation temperature at which step b) is carried out is preferably strictly below 500° C. The given implantation temperature at which step b) is carried out is advantageously strictly below 400° C., preferably strictly below 380° C. In other words, T.sub.max is between 380° C. and 500° C., advantageously between 380° C. and 400° C.

[0067] Step b) is advantageously carried out in such a way that the given implantation dose is strictly above 10.sup.17 at.Math.cm.sup.−2, preferably between 3.10.sup.17 at.Math.cm.sup.−2 and 4.10.sup.17 at.Math.cm.sup.−2.

[0068] The gaseous species 4 are advantageously implanted in step b) according to an implantation energy above 30 keV. Step b) may be carried out in such a way that the useful layer 1 has a thickness between some tens of nanometres and some microns. “Thickness” means a dimension extending according to the normal to the first surface 30 of the donor substrate 3.

[0069] Step b) is advantageously carried out in such a way that the graphitic flat zone 5 extends over the entire surface area of the first surface 30 of the donor substrate 3, to a given depth of the first surface 30. The depth of the graphitic flat zone 5 (starting from the first surface 30 of the donor substrate 3) is mainly determined by the implantation energy.

Step c)

[0070] Step c) is illustrated in FIGS. 1d, 2d and 3d.

[0071] Step c) may be preceded by steps consisting of cleaning or preparing the first surface 30 of the donor substrate 3 (more generally the surface to be bonded), for example to avoid contamination of the first surface 30 with hydrocarbons, particles or metallic elements. As a non-limiting example, it is possible to treat the first surface 30 by means of a dilute solution SC1 (mixture of NH.sub.4OH and H.sub.2O.sub.2) in order to generate chemical surface bonds able to provide good adhesion.

[0072] As illustrated in FIG. 3c, step c) may be preceded by a step c.sub.0) consisting of forming a surface layer 6 on the first surface 30 of the donor substrate 3. Step c.sub.0) is carried out after step b). The surface layer 6 is advantageously a layer of oxide or a metallic layer. The surface layer 6 has the role of facilitating subsequent bonding. The layer of oxide may consist of SiO.sub.2. The metallic layer may be made of a metallic material selected from Ti, W. The surface layer 6 may have a thickness between some nanometres and 1 μm.

[0073] Step c) is carried out at a suitable temperature and a suitable pressure depending on the type of bonding employed.

[0074] If there is a surface layer 6 covering the first surface 30 of the donor substrate 3, the donor substrate 3 is assembled to the supporting substrate 2 in step c) by direct adhesion with the surface layer 6.

[0075] In the embodiment illustrated in FIG. 2, the method advantageously comprises a step c′) consisting of applying thermal annealing to the assembly obtained at the end of step c), according to a thermal budget suitable for reinforcing the bonding interface between the first surface 30 of the donor substrate 3 and the supporting substrate 2 without initiating fracture of the donor substrate 3 along the graphitic flat zone 5. Step c′) is carried out before step d). The thermal budget for reinforcing the bonding interface is advantageously less than 10% of the thermal budget for fracture, i.e. the thermal budget applied in step d). It is possible to define a percentage of the thermal budget for fracture. The thermal budget for fracture may be described by a law of the Arrhenius type, relating the fracture time (designated “t”) to the annealing temperature (designated “T.sub.r”, in kelvin):

[00001]$t=A\exp \left(-E_a/{\mathrm{kT}}_r\right)$

where:

[0076] “A” is a constant,

[0077] “E.sub.a” is a constant corresponding to the energy of activation of the mechanism involved in fracture,

[0078] “k” is the Boltzmann constant.

[0079] “E.sub.a” can be determined experimentally starting from two operating points: it is the slope of the straight line “log(t)” as a function of “1/kT.sub.r”.

[0080] “E.sub.a” being known, it is easy to determine, for a given annealing temperature “T.sub.r1”, the time “t.sub.1” required to obtain fracture. By convention, it will be said that the percentage of the thermal budget used corresponds to the percentage of the time “t.sub.1” elapsed at temperature “T.sub.r1”. Thus, for example, to remain at less than 10% of the thermal budget for fracture, a time “t” less than “t.sub.1/10” will be selected for thermal annealing at an annealing temperature “T.sub.r1”.

[0081] The method according to the invention advantageously does not have a step of thermal treatment of the donor substrate 3 obtained at the end of step b), carried out before step c) of assembly to the supporting substrate 2. In other words, the method according to the invention advantageously does not have a step of thermal treatment carried out between step b) and step c).

[0082] As a non-limiting example, the supporting substrate 2 may be made of a material selected from Si, SiC, GaN, polycrystalline diamond.

Step d)

[0083] Step d) is illustrated in FIGS. 1e, 2e and 3e.

[0084] The thermal budget of the thermal annealing applied in step d) advantageously has an annealing temperature between 800° C. and 1200° C., preferably between 800° C. and 1100° C., more preferably between 850° C. and 1000° C.

[0085] The thermal budget of the thermal annealing applied in step d) advantageously has an annealing time between 30 minutes and 7 hours, preferably between 45 minutes and 75 minutes.

[0086] If step c′) is carried out, thermal annealing is applied in step d) to the assembly obtained at the end of step c′).

[0087] Step d) is advantageously carried out in an environment with a controlled atmosphere in order to limit the presence of oxygen, which consumes crystalline diamond by forming oxides (CO, CO.sub.2). As a non-limiting example, step d) may be carried out under high vacuum, such as ultrahigh vacuum below 10.sup.−5 mbar or under a neutral atmosphere (e.g. argon).

Embodiment Example

[0088] The first surface 30 of the donor substrate 3, provided in step a), of monocrystalline diamond, is oriented in terms of crystal planes according to the Miller indices [100]. The donor substrate 3 has a thickness of 0.5 mm. The first surface 30 of the donor substrate 3 has a surface area of 4×4 mm.sup.2.

[0089] Step b) is carried out according to the following conditions:

[0090] the given implantation dose is equal to 3.7.10.sup.17 cm.sup.−2;

[0091] the implantation energy is equal to 150 keV;

[0092] the implantation temperature is equal to 283° C.

[0093] The graphitic flat zone 5 formed at the end of step b) has a thickness of the order of 100 nm, and is located at a depth of the first surface 30 of the order of 800 nm

[0094] Step d) is carried out at an annealing temperature of 1000° C. for 60 minutes.

[0095] The invention is not limited to the embodiments presented. A person skilled in the art is able to consider their technically operative combinations, and substitute them with equivalents.