Carrier provided with a bragg mirror, intended for transfer of a layer by laser splitting

Abstract

Disclosed is a carrier (100) intended to be split by laser radiation, comprising a carrier substrate (Sprt); on the carrier layer, a splitting layer (Sep) formed from an inorganic material of thickness between 10 nm and 100 nm; and a layer (Brg) forming a Bragg mirror, the splitting layer (Sep) being interposed between the carrier substrate (Sprt) and the layer (Brg) forming the Bragg mirror, the carrier being configured in such a way that the carrier substrate is substantially transparent to laser radiation of a certain wavelength, the layer forming the Bragg mirror is substantially reflective with respect to the laser radiation, and the splitting layer (Sep) can absorb some of the laser radiation, such that the carrier can be split into two parts level with the splitting layer (Sep) under the action of the laser radiation.

Description

Support equipped with a Bragg mirror, intended for the transfer of a layer by laser separation TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a support provided with one or more layers to be transferred and intended to be separated from at least part of the support by laser irradiation at a separation layer included in the support, with a view to manufacturing products in the field of semiconductors. TECHNOLOGICAL BACKGROUND

[0002] Among the thin film transfer techniques used in the semiconductor industry, laser lift-off (LLO) has emerged as an effective method for separating a film or a stack of several films or one or more ultra-thin layers from a carrier substrate using a layer, called a separation layer, whose separation or degradation is triggered by a laser.

[0003] Typically, the separation layer is irradiated by laser through the carrier substrate. The separation layer must absorb a sufficient amount of light at the laser wavelength to promote separation or degradation (e.g., by locally melting the separation layer or, for example, by causing its dissociation into its elementary component), while the carrier substrate must be essentially transparent at this wavelength. A balance between laser power, laser wavelength, and material selection (for the separation layer and the carrier substrate) must be found to enable separation while preserving the layer(s) to be transferred from the impact of energy dissipation due to light interaction processes: heat transfer due to absorption in the separation layer or direct absorption by the layer(s) to be transferred.

[0004] US Patent 11,069,865 B2 describes a method for manufacturing a flexible OLED display panel, in which the display panel is manufactured on a glass plate covered with an organic separating layer that strongly absorbs UV radiation. The display panel is detached from the glass plate by a laser separation operation, in which the separating layer, capable of absorbing ultraviolet radiation, is irradiated through the glass plate by a laser operating in the ultraviolet range, facilitating the separation.

[0005] Document US 2021 / 028348 A1 describes a method for separating a composite structure using a light flux.

[0006] Document US 2020 / 381674 A1 describes a method of manufacturing a flexible OLED display comprising a laser irradiation step to delaminate a flexible film from a base.

[0007] Document US 2022 / 406621 A1 describes a manufacturing method comprising a step of peeling off a layer by laser irradiation of an absorbent layer.

[0008] Recent developments have shown that inorganic materials such as TiN can be used as a separation layer in a laser separation process using a laser with a wavelength in the infrared range (around 2000 nm for TiN). Similarly, it is known to use a GaN separation layer on a sapphire support using a laser with a wavelength in the ultraviolet range. These developments open the way to the separation of ultra-thin films or layers with nanometer-level precision, with many potential developments such as 2.5D and / or 3D integration. Limitations remain due to the relatively low absorption rates of thin inorganic films, considering the fact that the separation layer must also be sufficiently thin to allow separation, i.e., a few tens of nanometers thick in the case of TiN or GaN.

[0009] The applicant's objective is to improve the absorption rate of laser irradiation by an inorganic thin film with a view to using this thin film as a separation layer in a laser irradiation layer separation operation (laser lift-off).

[0010] To achieve this aim, one aspect of the invention is a support for laser separation, comprising a support substrate; a separation layer on the support layer, formed of an inorganic material with a thickness of between 10 nm and 100 nm; and a Bragg mirror forming layer, the separation layer being interposed between the support substrate and the Bragg mirror forming layer, the support being configured in such a way that the support substrate is substantially transparent to laser radiation of a certain wavelength, the Bragg mirror forming layer is substantially reflective with respect to the laser radiation, and the separation layer can absorb a part of the laser radiation, so that the support can separate into two parts at the separation layer under the action of the laser radiation, wherein the Bragg mirror forming layer (Brg) is formed of a stack of first layers (LL ) with low refractive indices alternating with second layers (L H) with high refractive indices, the high refractive indices being higher than the low refractive indices, the layers with low refractive indices are either (i) made of silicon oxide for layers with high refractive indices made of a material chosen from polycrystalline silicon, titanium nitride, titanium oxide, silicon nitride, and aluminum oxide, or (ii) made of silicon nitride or aluminum oxide for layers with high refractive indices made of polycrystalline silicon, and the layer forming the Bragg mirror has a thickness of between 0.1 µm and 10 µm or the layer forming the Bragg mirror is made of a number of pairs of layers each comprising one of the layers with a low refractive index and one of the layers with a high refractive index, the number of pairs being between 2 and 10.

[0011] The presence of the Bragg mirror behind the separation layer allows the laser irradiation used during a separation operation to be reflected back towards the latter, the laser source being located on the side of the support layer. As a result, the overall absorption rate of this irradiation by the separation layer is considerably increased. Increasing the absorption rate of the separation layer is very beneficial, particularly in the case of a thin inorganic layer, because it allows the laser irradiation to separate layers with minimized light intensity, thus reducing potential damage to the layer(s) to be transferred and / or the support substrate.Furthermore, the use of an inorganic separating layer makes it possible to separate extremely thin layers and / or with nanometric lateral precision, all the more easily since the inorganic layer is thin and therefore difficult to absorb a sufficient quantity of light energy to cause separation.

[0012] Another advantage is that, according to the invention, this optimization can be achieved without resorting to metals traditionally used to form a reflective layer such as copper or aluminum, which are often poorly compatible, or even completely incompatible, with so-called front-end manufacturing processes, where the atoms of these metals behave as impurities with prohibitive consequences on the manufactured semiconductor devices.

[0013] According to additional non-limiting characteristics of the support according to the invention, considered individually or according to any technically feasible combination:

[0014] - the number of pairs can be between 2 and 4;

[0015] - the layer forming the Bragg mirror can have a thickness of between 2 µm and 4 µm and a reflectivity greater than 90%;

[0016] - the layer forming the Bragg mirror can have a thickness of less than 3µm and a reflectivity of greater than 90%;

[0017] - the layer forming the Bragg mirror can be designed to reflect laser radiation belonging to the infrared range;

[0018] - the support substrate may be formed from monocrystalline silicon;

[0019] - the support may further comprise at least one of (i) a first thermal insulation layer interposed between the support substrate and the separation layer and (ii) a second thermal insulation layer interposed between the separation layer and the layer forming the Bragg mirror;

[0020] - one or more of the thermal insulation layers may be formed from silicon dioxide; and

[0021] - all thermal insulation layers can be formed from silicon dioxide.

[0022] The invention extends to a structure comprising the support according to the invention as well as a transfer layer on the support, the layer forming a Bragg mirror being interposed between the transfer layer and the separation layer.

[0023] The structure according to the invention, considered individually or in any technically feasible combination:

[0024] - the structure may further comprise a third thermal insulation layer interposed between the transfer layer and the layer forming the Bragg mirror;

[0025] - one or more of the thermal insulation layers may be formed from silicon dioxide; and

[0026] - all thermal insulation layers can be formed from silicon dioxide. BRIEF DESCRIPTION OF THE FIGURES

[0027] Other characteristics and advantages of the invention will emerge from the detailed description of the invention which follows with reference to the appended figures in which:

[0028] Represents a structure according to the invention;

[0029] Represents the structure according to the claim being separated; and

[0030] This is a graph representing the reflectivity of Bragg mirrors. DETAILED DESCRIPTION OF THE INVENTION

[0031] First embodiment

[0032] A first embodiment of the present invention is described by means of Figures 1 and 3 and the associated passages below.

[0033] Figures 1 and 2 illustrate a structure Strc consisting of a support 100 and a transfer layer Tr, intended to be separated from at least a part of the support 100, which will for example have been able to support it during its manufacture.

[0034] The transfer layer Tr may for example consist of a layer of semiconductor material such as a layer of monocrystalline silicon bonded to a layer of silicon oxide, or of a layer comprising conventionally manufactured semiconductor components.

[0035] In the embodiment disclosed herein, the support 100 may comprise a support substrate Sprt on which are formed, in this order from the support substrate: a first thermal insulation layer Ins1, a separation layer Sep, a second thermal insulation layer Ins2, a layer Brg forming a Bragg mirror, a third thermal insulation layer Ins3, and the transfer layer Tr.

[0036] The Sprt support substrate may be formed from bulk monocrystalline silicon, for example a silicon wafer.

[0037] The first thermal insulation layer Ins1 and the second thermal insulation layer Ins2 may each be formed from a silicon oxide layer SiO2 with a thickness of between 10 nm and 200 nm.

[0038] The separation layer may be formed from a layer of an inorganic material such as a layer of titanium nitride TiN with a thickness of between 1 nm and 50 nm.

[0039] The third thermal insulation layer Ins3 can be formed from a layer of silicon oxide SiO2 with a thickness between 200 nm and 1000 nm.

[0040] The first, second and third thermal insulation layers may alternatively each be formed of silicon nitride, independently of each other.

[0041] The Brg layer forming the Bragg mirror can be formed from a stack of first L layers L low refractive index n L alternating with second L layers H with high refractive indices n H , high refractive indices n H being higher than the low refractive indices n L The materials forming the low refractive index layers may be chosen so as to obtain low and high refractive indices between 1.25 and 4.1, the differences between these indices preferably being less than 2.85.

[0042] The thicknesses of the alternating layers can be determined according to the following equations 1 and 2:

[0043] Eq. 1

[0044] Eq. 2

[0045] in which H and d L represent the thicknesses of the layers with high and low refractive indices, and λ represents the wavelength of the laser irradiation envisaged to carry out the separation of the layers. The thicknesses of the layers L L and L H can be between 10 nm and 1 µm, thicknesses representing a compromise between a level of uniformity for the thin layers and a thickness that is too great for the layer forming the Bragg mirror as a whole, preferably with a thickness between 1 µm and 10 µm.

[0046] L diapers Lwith low refractive indices can be made of silicon oxide, and the layers with high refractive indices can be made of a material chosen from polycrystalline silicon, titanium nitride, titanium oxide, silicon nitride. Such materials are easy to deposit and widely used in the field of microelectronics, particularly for so-called "Front-End" processes.

[0047] For a structure as described above, the laser irradiation used to carry out the separation is in the infrared range, with a wavelength preferably between 700 nm and 10 µm, more specifically between 1 µm and 5 µm. For other structures based on other materials, the irradiation can be carried out by a laser with a wavelength preferably between 50 nm and 17 µm.

[0048] The ranges of layer thicknesses and refractive indices, and the nature of the support substrate are naturally interrelated, and dependent on the laser irradiation that is planned to be used. It is indeed necessary to ensure that, for the wavelength of the laser that is planned to be used to carry out the separation, the support substrate is substantially transparent, the Bragg mirror reflective, and the separation layer absorbent.

[0049] Laillustrates by means of a graph the importance and relevance of the choice of materials to form the Bragg mirror. The graph of lacomposes 6 curves, each representing the reflectivity, expressed in percents, of a Bragg mirror as a function of its thickness, expressed in micrometers µm. The four curves BrRefl-1 to BrRefl-4 correspond to a laser irradiation of wavelength 2 µm for four Bragg mirrors, whose layers with low refractive indices are made of silicon dioxide SiO2, and the layers with high refractive indices are made respectively of silicon nitride Si3N4, titanium dioxide TiO2, titanium nitride TiN and polycrystalline silicon Poly-Si.The two curves BrRefl-5 and BrRefl-6 correspond to a laser irradiation of wavelength 10 µm for two Bragg mirrors, whose high refractive index layers are made of polycrystalline silicon Poly-Si, and the low refractive index layers are made of silicon nitride Si3N4 and silicon oxide Al2O3 respectively.

[0050] For the case of an incident laser with a wavelength of 2 µm, the reflectivity initially increases rapidly with the thickness of the Bragg mirror, reaching a plateau close to perfect reflectivity of 100%. We find that for thicknesses between 4 µm and 10 µm, the reflectivity of the layer is close to 1, at more than 95% reflectivity, for each of the four Bragg mirrors. This is also the case with thicknesses between 1 µm and 10 µm for Bragg mirrors whose high refractive index layers are formed of titanium nitride or polycrystalline silicon. For the latter, we even observe reflectivities exceeding 50% for thicknesses of only 0.5 µm.

[0051] Another way to characterize Bragg mirrors is the number of pairs, each consisting of a high refractive index layer and a low refractive index layer, forming the Bragg mirror in question. Thus, to obtain a reflectivity of more than 90% while limiting the thickness and manufacturing complexity of a Bragg mirror, numbers of pairs of layers between 2 and 10 are sufficient. We can even limit ourselves to numbers of pairs between 2 and 4, or even equal to 2 or 3, for SiO2 / Poly-Si or SiO2 / TiN pairs. Minimizing the number of pairs leads to maximizing the difference between the high and low refractive indices of the two layers forming the pair in question.

[0052] For the case of an incident laser with a wavelength of 10 µm, similar observations can be made to the previous case, with reflectivities initially increasing rapidly with the thickness of the Bragg mirror, reaching a plateau close to the perfect reflectivity of 100%. We note that for thicknesses between 4 µm and 10 µm, the reflectivity of the layer is close to 1, at more than 90% reflectivity, for each of the two Bragg mirrors. Note that the wavelength being longer than in the first case, the thickness of the stack increases mechanically.

[0053] Of course, the choice of materials is made in pairs of materials, a first material with a relatively low refractive index being coupled with a second material with a relatively high refractive index.

[0054] In operation, the separation is carried out at the level of the separation layer, which absorbs the energy of the incident laser irradiation a first time, then a second time following its reflection by the layer forming the Bragg mirror. By absorption, the separation layer is heated locally, possibly causing its decomposition (in the case of a TiN layer, the TiN decomposes into gaseous nitrogen and liquid Ti) and therefore the detachment of the two layers surrounding it from each other. This situation is illustrated by the Ins2 layer detaching from the Ins1 layer following the elimination, or degradation, of the Sep separation layer.

[0055] Preliminary calculations indicate an increase in laser irradiation absorption of at least 15% in the TiN separation layer of the structure described above.

[0056] The local heating caused by laser irradiation can reach 2000°C, and it is necessary to limit the heating of neighboring layers. In particular, the degradation of the layer of interest of the process, which is the transfer layer Tr, must be avoided. The thermal insulation layer Ins3 limits the heating of the layer of interest. For this purpose, the thermal insulation layer Ins3 can be the thickest among the three thermal insulation layers.

[0057] It may also be interesting to limit the heating of the Sprt support substrate, particularly if it is to be reused. This is the role of the Ins1 thermal insulation layer.

[0058] Finally, heating the Bragg mirror can significantly modify its refractive indices. This is the case, for example, if a layer of polycrystalline silicon is used, the structure of which can be transformed by recrystallization by excessive heating, causing it to lose its polycrystalline character and therefore radically modifying its refractive index.

[0059] It should be noted that the thermal insulation layers Ins1, Ins2 and Ins3 are each individually optional, their respective uses having to be examined on a case-by-case basis. In addition, other materials than silicon oxide can be used, although the use of the latter is extremely convenient, due to its physical characteristics and its high compatibility with semiconductor manufacturing processes.

[0060] All the layers mentioned in this description can be formed using thin film deposition processes, well known and mastered in the field of semiconductors.

[0061] Second embodiment

[0062] The first embodiment took as an example the situation of a structure suitable for separation by infrared irradiation, with, for this wavelength range, a transparent support substrate, a reflective Bragg mirror, and an absorbent separation layer. However, other situations can be considered.

[0063] This second embodiment constitutes such a situation: it relates to a structure similar to that of the first embodiment and illustrated by the same figures, but comprising a layer of interest (GaN or other, depending on the intended applications) formed on a sapphire support substrate and comprising a GaN separation layer. In such a case, the materials and thicknesses considered must be adapted to the wavelength of an irradiation passing through the sapphire, that is to say in the ultraviolet range, with a wavelength between 100 nm and 380 nm.

[0064] Thus, the layer Brg forming a Bragg mirror may consist of alternating layers of SiO2 40 nm thick and layers of Si3N4 26 nm thick, for a total thickness preferably between 1 µm and 10 µm. Where appropriate, the thermal insulation layer(s) Ins1, Ins2 and Ins3 may each consist of a layer of SiO2 or Al2O3 50 nm to 100 nm thick. The separation layer Sep may be formed of a layer of GaN with a thickness between 10 nm and 100 nm. The support substrate Sprt may consist of a sapphire Al2O3 substrate.

[0065] In this case, the laser irradiation used to carry out the separation is in the ultraviolet range, with a wavelength preferably between 200 nm and 400 nm.

[0066] Preliminary calculations indicate an increase in laser irradiation absorption in the separation layer of at least 40% in the GaN separation layer of the structure described above.

[0067] The invention is not limited to the embodiments described above and variations may be made thereto without departing from the scope of the invention as defined by the claims.

Claims

Support (100) provided for separation by laser radiation, comprising:- a support substrate (Sprt);- a separation layer (Sep) on the support layer, formed of an inorganic material with a thickness of between 10 nm and 100 nm; and- a layer (Brg) forming a Bragg mirror, the separation layer (Sep) being interposed between the support substrate (Sprt) and the layer (Brg) forming the Bragg mirror,the support being configured in such a way that:- the support substrate is substantially transparent to laser radiation of a certain wavelength,- the layer forming the Bragg mirror is substantially reflective with respect to the laser radiation, and- the separation layer (Sep) can absorb part of the laser radiation,so that the support can separate into two parts at the separation layer (Sep) under the action of the laser radiation, wherein:- the layer (Brg) forming a Bragg mirror is formed of a stack of first layers (LL ) with low refractive indices alternating with second layers (L H) with high refractive indices, the high refractive indices being higher than the low refractive indices,- the layers with low refractive indices are either (i) made of silicon oxide for layers with high refractive indices made of a material chosen from polycrystalline silicon, titanium nitride, titanium oxide, silicon nitride, and aluminum oxide, or (ii) made of silicon nitride or aluminum oxide for layers with high refractive indices made of polycrystalline silicon, and- the layer forming the Bragg mirror has a thickness of between 0.1 µm and 10 µm, or- the layer forming the Bragg mirror is made of a number of pairs of layers each comprising one of the layers with a low refractive index and one of the layers with a high refractive index, the number of pairs being between 2 and 10. The support according to claim 1, wherein the number of pairs is between 2 and 4. The support according to claim 2, in which the layer forming the Bragg mirror has a thickness of between 2 µm and 4 µm and a reflectivity greater than 90%. The support according to claim 2, in which the layer forming the Bragg mirror has a thickness of less than 3 µm and a reflectivity of greater than 90%. The support according to any one of claims 1 to 4, in which the layer (Brg) forming the Bragg mirror is designed to reflect laser radiation belonging to the infrared range. The support according to any one of claims 1 to 5, in which the support substrate (Sprt) is formed of monocrystalline silicon. The support according to any one of claims 1 to 6, further comprising at least one of (i) a first thermal insulation layer (Ins1) interposed between the support substrate (Sprt) and the separation layer (Sep) and (ii) a second thermal insulation layer (Ins2) interposed between the separation layer (Sep) and the layer (Brg) forming the Bragg mirror. Structure (Strc) comprising the support (100) according to any one of claims 1 to 7 as well as a transfer layer (Tr) on the support (100), the layer (Brg) forming a Bragg mirror being interposed between the transfer layer (Tr) and the separation layer (Sep). The structure according to claim 8, further comprising a third thermal insulation layer (Ins3) interposed between the transfer layer and the layer forming the Bragg mirror. The support according to claim 7 or the structure according to claim 9, one or more of the thermal insulation layers being formed of silicon dioxide. The support according to claim 7 in which the two thermal insulation layers (Ins1, Ins2) are formed of silicon dioxide or the structure according to claim 12 in which the three thermal insulation layers (Ins1, Ins2, Ins3) are formed of silicon dioxide.

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