LOW-TEMPERATURE METHOD FOR TRANSFER AND HEALING OF A SEMICONDUCTOR LAYER

Abstract

The invention relates to a method for creating a substrate of the type semiconductor on insulator, comprising the following steps:

a) providing a donor substrate comprising a monocrystalline support substrate, a smoothing layer and a semiconductor layer, the smoothing layer forming an etch stop layer with respect to the material of the support substrate;

a′) implantation of ion species through the semiconductor layer so as to form a fragilization plane;

b) creating an assembly by placing the donor substrate and a receiver substrate in contact;

c) transferring the semiconductor layer and at least a part of the smoothing layer by detachment along the fragilization plane:

wherein the semiconductor layer of the donor substrate provided in step a) is monocrystalline and in that it further comprises the following steps: before step b), amorphization of at least a part of the semiconductor layer to form an amorphous layer; during or after step c), recrystallization in solid phase of the amorphous layer to form a transferred monocrystalline semiconductor layer.

Claims

1. Method for creating a substrate of the type semiconductor on insulator, comprising the following steps: a) providing a donor substrate comprising a monocrystalline support substrate, a smoothing layer and a semiconductor layer, the smoothing layer forming an etch stop layer with respect to the material of the support substrate; a′) implantation of ion species through the semiconductor layer so as to form a fragilization plane; b) creating an assembly by placing the donor substrate and a receiver substrate in contact; c) transferring the semiconductor layer and at least a part of the smoothing layer by detachment along the fragilization plane: wherein the semiconductor layer of the donor substrate provided in step a) is monocrystalline and wherein the method further comprises the following steps: before step b), amorphization of at least a part of the semiconductor layer to form an amorphous layer; during or after step c), recrystallization in solid phase of the amorphous layer to form a transferred monocrystalline semiconductor layer.

2. Method according to claim 1, wherein said recrystallisation is followed by an amorphization of the transferred monocrystalline semiconductor layer to form a new amorphous layer and by a recrystallization in solid phase of the new amorphous layer to form a new transferred monocrystalline semiconductor layer.

3. Method according to claim 1, further comprising a removal of a layer rich in interstitial atoms present on the surface of the transferred monocrystalline semiconductor layer.

4. Method according to claim 3, wherein said removal comprises plasma-assisted oxidation followed by chemical etching.

5. Method according to claim 1, wherein the amorphization of at least a part of the semiconductor layer comprises the amorphization of the entirety of the semiconductor layer.

6. Method according to claim 1, wherein the amorphization of at least a part of the semiconductor layer comprises the joint amorphization of the semiconductor layer and of the smoothing layer.

7. Method according to claim 1, wherein the donor substrate provided in step a) further comprises an intermediate layer and a thinning layer interposed between the intermediate layer and the semiconductor layer, the thinning layer forming an etch stop layer with respect to the material of the semiconductor layer and wherein step d) further comprises the successive carrying out of a selective etching of the smoothing layer with respect to the intermediate layer, of a selective etching of the intermediate layer with respect to the thinning layer and of a selective etching of the thinning layer with respect to the semiconductor layer.

8. Method according to claim 7, wherein the amorphization of at least a part of the semiconductor layer comprises the joint amorphization of the semiconductor layer and of at least a part of the thinning layer.

9. Method according to claim 7, wherein the amorphization of at least a part of the semiconductor layer comprises the joint amorphization of the semiconductor layer, of the thinning layer and of at least a part of the intermediate layer.

10. Method according to claim 7, wherein the amorphization of at least a part of the semiconductor layer comprises the joint amorphization of the semiconductor layer, of the thinning layer, of the intermediate layer and of at least a part of the smoothing layer.

11. Method according to any one from claim 1, wherein during the step a′) of implantation of ion species, the fragilization plane is formed in the support substrate, and wherein the method further comprises, after step c) of transferring, the following step: d) carrying out a selective etching of said part of the support substrate with respect to the smoothing layer.

12. Method according to claim 11, wherein step d) further comprises performing of selective etching of the smoothing layer.

13. Method according to claim 1, wherein during step a′) of implantation of ionic species, the fragilization plan is formed in the smoothing layer.

14. Method according to claim 1, comprising, before the amorphization of at least a part of the semiconductor layer, the formation on the semiconductor layer, by thermal oxidation at a temperature lower than 800° C., of a dielectric layer having a thickness between 5 nm and 25 nm, said dielectric layer being in step b) at the interface of the donor and receiver substrates placed in contact.

15. Method according to claim 14, wherein said formation further comprises, after the amorphization of at least a part of the semiconductor layer, a thickening of the dielectric layer.

16. Method according to claim 1, further comprising, after the formation of the amorphous layer and before said implantation, the deposition of one or more layers on the donor substrate.

17. Method according to claim 1, wherein the receiver substrate integrates a level of microelectronic components.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Other aspects, goals, advantages and features of the invention will be clearer upon reading the following detailed description of preferred embodiments of the latter, given as a non-limiting example, and made in reference to the appended drawings in which:

[0042] FIGS. 1 to 8 illustrate one possible embodiment of the method according to the invention;

[0043] FIGS. 9 and 10 illustrate the implementation of a new sequence of amorphization/recrystallization;

[0044] FIGS. 11 and 12 illustrate a first amorphization alternative;

[0045] FIG. 13 illustrates another amorphization alternative;

[0046] FIG. 14 shows another possible embodiment of the donor substrate with double etch stop layers;

[0047] FIG. 15 shows a first possible amorphization of the donor substrate of FIG. 14;

[0048] FIG. 16 shows a second possible amorphization of the donor substrate of FIG. 14.

DETAILED DESCRIPTION

[0049] The invention relates to a method for creating a substrate of the type semiconductor on insulator by transfer of a semiconductor layer onto a receiver substrate, a dielectric layer being present at the interface.

[0050] In a preferred use of the invention, the method allows to design a 3D device with superimposed microelectronic components with a receiver substrate that integrates components already manufactured on a first level. The semiconductor layer to be transferred is a layer made amorphous that is recrystallised in the monocrystalline state and can be used as an active layer for the manufacturing of components on a level superimposed on the first level. The semiconductor layer to be transferred can constitute for example a channel region for one or more transistors.

[0051] One possible implementation of the method according to the invention is illustrated by FIGS. 1 to 8. In reference to FIGS. 1 and 2, the method starts with the providing of a monocrystalline support substrate 10. A smoothing layer 11 and a monocrystalline semiconductor layer 12 are formed, for example successively as shown in FIG. 2, by epitaxy on the monocrystalline support substrate. A donor substrate 1 is thus formed which comprises the monocrystalline support substrate 10, the smoothing layer 11 and the monocrystalline semiconductor layer 12, the latter being arranged on the surface of said substrate.

[0052] The smoothing layer 11 forms an etch stop layer with respect to the material of the support substrate 10 and the material of the monocrystalline semiconductor layer 12. For this purpose, the smoothing layer 11 is made from a material having a chemical composition different than that of the support substrate and of the monocrystalline semiconductor layer, and the choice of the materials can be made according to the nature of the etching agent and the desired selectivity.

[0053] According to a preferred embodiment, the support substrate 10 comprises a first material identical to that of the monocrystalline semiconductor layer 12 and the smoothing layer 11 comprises a second monocrystalline material different from the first material. The first material is typically silicon, and the second material can be silicon-germanium.

[0054] The thickness and the concentration of germanium in the smoothing layer 11 are chosen in such a way as to obtain a pseudomorphous layer, i.e. having a thickness smaller than the critical thickness for plastic relaxation, which limits the risk of generating crystalline defects such as dislocations. Thus, the thickness of the smoothing layer is typically between 5 and 120 nm. According to a specific embodiment of the invention, the concentration of germanium in the smoothing layer is between 20 and 40%. The thickness of the monocrystalline semiconductor layer 12 is between 5 and 40 nm.

[0055] According to one embodiment, the donor substrate is covered with a dielectric layer. Said dielectric layer can be in particular a layer of an oxide or of a nitride of a semiconductor material. Said dielectric layer will form all or a part of the buried insulating layer of the semiconductor-on-insulator substrate. One possible formation of this dielectric layer on the donor substrate will be described below.

[0056] Alternatively, the donor substrate is not covered with such a dielectric layer and it is its free surface that forms the surface of the donor substrate. In this case, the buried insulating layer of the substrate consists of a dielectric layer formed on the receiver substrate to which the donor substrate is bonded with a view to the transfer of the semiconductor layer.

[0057] In reference to FIG. 3, the method comprises an amorphization of at least a part of the semiconductor layer 12. This amorphization is carried out by ion implantation, for example of Ge or Si ions, the energy and the dose of which are chosen according to the thickness of material to be made amorphous.

[0058] The process of amorphization is known to generate a layer rich in interstitial atoms close to the part made amorphous in the underlying part remaining crystalline. In the example illustrated in FIG. 3, only a surface part of the semiconductor layer 12 is made amorphous (thus forming an amorphous layer 13) and there is a layer rich in interstitial atoms 14 between the amorphous layer 13 and the smoothing layer 11.

[0059] FIG. 4 illustrates the implementation of an implantation of ion species, for example of hydrogen and/or of helium, in the support substrate 10 so as to form a fragilization plane 15 defining a portion (formed from the amorphous layer 13, the layer rich in interstitial atoms 14, the smoothing layer 11 and a part 17 of the support substrate) to be transferred by the Smart Cut™ method.

[0060] The amorphization described above can, alternatively, be carried out after this implantation of ion species to form the fragilization plane.

[0061] When the amorphization is carried out before the implantation of ion species, the method can comprise, after the amorphization and before the implantation, the deposition of one or more layers on the donor substrate, for example of oxide, of nitride, of polysilicon doped or not. This deposition is preferably carried out at a temperature allowing to avoid a recrystallisation of the amorphous layer, for example at a temperature lower than 500° C.

[0062] As an alternative, notably in case of a smoothing layer relatively thick (for example a smoothing layer 11 of SiGe with a germanium concentration between 20 and 25% and having a thickness between 50 and 120 nm), the fragilization plane 15 could be made into the smoothing layer. With this alternative, we thus avoid the need of the first wet etching step of the part 17 of the support substrate which is specify in the following.

[0063] FIG. 5 illustrates the bonding of the donor substrate to the receiver substrate 20, a dielectric layer 21 being at the bonding interface. This dielectric layer 21 can result from the previous formation of a dielectric layer on the donor substrate and/or on the receiver substrate. In a preferred embodiment, the receiver substrate integrates components such as transistors.

[0064] The detachment of the donor substrate along the fragilization plane 15 is then carried out, for example by providing thermal energy. FIG. 6 illustrates the structure obtained after this detachment, the part 17 of the support substrate being located at the surface of said structure.

[0065] After the transfer, the transferred part of the donor substrate undergoes a finishing treatment carrying out a smoothing (reduction of the roughness) and a thinning allowing to reach the desired thickness for the transferred semiconductor layer.

[0066] This finishing treatment comprises a first wet etching of the part 17 of the support substrate, which is located on the surface of the structure obtained after the transfer, said etching being selective with respect to the material of the smoothing layer 11. For example, if the support substrate is made of silicon and the intermediate layer is made of silicon-germanium, the etching agent can based on TMAH or TEAH.

[0067] In the example described here, this finishing treatment comprises a second wet etching of the smoothing layer 11, which is located on the surface of the structure obtained after the first etching of the part 17 of the support substrate, said second etching being selective with respect to the material of the semiconductor layer. For example, if the smoothing layer is made of silicon-germanium and the semiconductor layer is made of silicon, the etching agent can be based on a mixture of CH.sub.3COOH, HF and H.sub.2O.sub.2.

[0068] FIG. 7 illustrates the structure obtained after these etchings. There is the amorphous layer 13 and the layer rich in interstitial atoms 14 supported by the receiver substrate 20. The advantage of this finishing treatment is that it allows to obtain a transferred semiconductor layer having a uniform thickness and a low roughness without involving a thermal budget capable of degrading components that are integrated into the receiver substrate.

[0069] The method continues with a step of recrystallisation in solid phase (SPER for Solid Phase Epitaxial Regrowth) of the at least a part of the semiconductor layer previously made amorphous, namely the layer 13 in the example described here. As shown in FIG. 8, the layer 13 is thus recrystallised and forms a transferred monocrystalline semiconductor layer 18.

[0070] This recrystallisation can be obtained via annealing at a temperature typically greater than 450° C., preferably less than 650° C., for example at 500° C., for a time that depends on the thickness of the material to be recrystallised. This time is between several minutes for annealing at high temperature for the recrystallisation of a fine layer and a dozen hours for annealing at lower temperature for the recrystallisation of a thicker layer.

[0071] The combination of the amorphization and the recrystallization allows to obtain a monocrystalline transferred layer 18 healed of defects generated by the ion implantation carried out to form the fragilization plane. This healing is obtained without involving a thermal budget capable of degrading components that are integrated into the receiver substrate.

[0072] This step of recrystallisation in solid phase can be implemented in the form of a finishing treatment carried out after detachment of the donor substrate along the fragilization plane as described above. It can also be carried out during the detachment via the providing of thermal energy which is thus provided to the assembly of the donor and receiver substrates. When carried out after detachment, this recrystallisation step can be carried out before or after the etching of the smoothing layer 11. When carried out before this etching, it is implemented at a temperature, for example between 500° C. and 650° C., that allows to not generate dislocations in the smoothing layer.

[0073] After the recrystallisation, as shown in FIG. 8, above the transferred monocrystalline semiconductor layer 18 there is a layer 14′ rich in interstitial atoms. In one possible embodiment, the method comprises a step of removal of this layer 14′ rich in interstitial atoms. This removal step preferably comprises an oxidation of the layer 14′ followed by a removal of the oxidised layer 14′. The oxidation can comprise oxidation chemical, preferably at low-temperature, of the layer 14′. The oxidation can also comprise plasma-assisted oxidation, preferably at low temperature (for example between 400° C. and 450° C.). The removal of the oxidised layer 14′ can comprises chemical etching, for example based on HF.

[0074] In another possible embodiment illustrated in FIGS. 9 and 10, after the recrystallisation and preferably after the etching of the smoothing layer, the method comprises an additional amorphization that leads to the formation of a new surface layer made amorphous 19. This additional amorphization is thus carried out in such a manner as to preserve a crystalline seed near the layer of oxide 21. This additional amorphization is followed by an additional recrystallisation in solid phase that leads to a new transferred monocrystalline thin layer 22.

[0075] In another embodiment illustrated in FIGS. 11 and 12, the method comprises an amorphization of the entirety of the semiconductor layer 12 leading to an amorphous layer 13. This amorphization can be preceded by a selective amorphization of the smoothing layer 11 with respect to the semiconductor layer 12. The selective amorphization of the smoothing layer is made possible by the fact that it is achieved to a lower extent than the amorphization of the semiconductor layer 12.

[0076] In another embodiment illustrated by FIG. 13, the amorphization of at least a part of the semiconductor layer comprises the joint amorphization of the semiconductor layer, of the smoothing layer and optionally of a part of the support substrate 10 in such a way that the layer rich in interstitial atoms 14 is located in the support substrate 10. This layer 14 is later removed by the selective etching of the transferred part of the support substrate using the smoothing layer 11 as a stop layer.

[0077] When the recrystallisation is carried out in the presence of the smoothing layer, there is a risk of the smoothing layer, which is subjected during the recrystallisation to biaxial compressive stresses to preserve the mesh parameter of the material of the semiconductor layer, relaxing its stresses while forming dislocations. These dislocations are capable of propagating in the transferred monocrystalline semiconductor layer 18 and thus of degrading the performance of components that are later created via this layer. To reduce the risk of formation of these dislocations, a finer smoothing layer can be used, having for example a thickness of less than 20 nm, preferably less than 15 nm for a layer having a concentration of germanium of 20%, or a thickness of less than 15 nm, preferably less than 10 nm for a layer having a concentration of germanium of 25%, or a thickness of less than 10 nm, preferably less than 5 nm for a layer having a concentration of germanium of 30%.

[0078] With such a fineness, the smoothing layer could be not sufficiently robust for the selective etching of the finishing treatment aimed at both the smoothing and the thinning. One solution to bypass this difficulty involves only conferring a smoothing function onto the smoothing layer 11 and doubling it with a thinning layer 24, also pseudomorphous, dedicated to the thinning allowing to reach the desired thickness for the transferred semiconductor layer. For this purpose, as shown in FIG. 14, the donor substrate further comprises an intermediate layer 23 (for example made of silicon) and said thinning layer 24 (for example made of silicon-germanium) interposed between the intermediate layer 23 and the semiconductor layer 12. The thinning layer 24 forms an etch stop layer with respect to the material of the semiconductor layer. The finishing step thus comprises the successive carrying out of a selective etching of the smoothing layer 11 with respect to the intermediate layer 23, of a selective etching of the intermediate layer 23 with respect to the thinning layer 24 and of a selective etching of the thinning layer 24 with respect to the semiconductor layer 12.

[0079] As show in FIG. 15, the amorphization of at least a part of the semiconductor layer can thus comprise the joint amorphization of the semiconductor layer 12 and of the thinning layer 24 in such a way that the layer rich in interstitial atoms 14 is located between the thinning layer 24 and the smoothing layer 11. The smoothing layer 11 is not made amorphous, it does not have to be recrystallised and does not therefore generate dislocations during the recrystallisation. It can therefore be thicker and/or have a higher concentration of germanium, thus making the selective etching more stable in terms of performance. As for the thinning layer 24, it can be relatively fine since the roughness is already largely compensated for using the smoothing layer. By forming an etch stop layer, it allows to easily eliminate the layer rich in interstitial atoms.

[0080] As shown in FIG. 16, the amorphization of at least a part of the semiconductor layer can also comprise the joint amorphization of the semiconductor layer 12, of the thinning layer 24, of the intermediate layer 23 and of the smoothing layer 11 in such a way that the layer rich in interstitial atoms 14 is located in the support substrate.

[0081] It was shown above that the donor substrate could be covered with a layer of oxide, the latter being in particular intended to form a buffer zone between the bonding interface and the components remaining to be manufactured in the second layer in such a way that the latter have optimal electric characteristics for example such as a low surface-state density at the interface between the active layer and the layer of oxide.

[0082] A first difficulty is due to the presence of the smoothing layer typically made of silicon-germanium which makes it so that an oxidation thermal budget that is too great must not be provided in order to avoid a diffusion of the germanium and a relaxation of the stresses (formation of dislocations) of the layer of silicon-germanium. In practice, the temperature must not exceed 800° C., while preferably being in the range 700-750° C. The kinetics of the oxidation process are thus reduced and obtaining layers thicker than 15 nm can require a prohibitive time.

[0083] Another difficulty is due to the amorphization of a crystalline layer of silicon through a layer of oxide made of SiO.sub.2, this amorphization creating a transition layer at the interface. The thicker the layer of oxide, the greater the quantity of atoms of oxygen present in the layer of silicon and the more the effectiveness of the SPER recrystallisation is reduced.

[0084] In order to bypass these difficulties, the invention proposes in one possible embodiment to form, before the amorphization of at least a part of the semiconductor layer, a fine dielectric layer via a low-temperature heat treatment. This involves for example forming a dielectric layer having a thickness between for example 5 nm ad 25 nm by thermal oxidation at a temperature preferably lower than 800° C. This dielectric layer can then, after the amorphization of at least a part of the semiconductor layer, be subject to a thickening via a deposition of a dielectric at low temperature, for example SiN or SiO.sub.2 deposited by PECVD. This deposition can thus be carried out at a temperature of up to 500° C. if it is carried out before the formation of the fragilization plane by H/He implantation. It can be carried out at a temperature lower than 250° C. in the contrary case.