Process for preparing a structured substrate for direct bonding
The method for preparing structured substrates with a protective layer and controlled adhesion enables effective direct bonding by preserving surface quality and avoiding degradation, addressing the challenges of existing methods.
Patent Information
- Application Number
- FR2024003966
- Authority / Receiving Office
- FR · FR
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-04-17
- Publication Date
- 2025-10-24
- Estimated Expiration
- 2044-04-17
AI Technical Summary
Existing methods for preparing structured substrates for direct bonding, particularly those with Cu/SiO2 hybrid surfaces, face issues such as surface degradation due to aggressive cleaning processes, which compromise bonding quality, and edge rounding during polishing, leading to poor bonding results.
A method involving the use of a protective layer with lower adhesion energy than the substrate layer, allowing for resin removal without damaging the surface, followed by bonding a temporary substrate and separating it to achieve a structured substrate suitable for direct bonding, using techniques like laser irradiation or plasma etching to form pads and chips.
Preserves the quality of the substrate surface, ensuring effective direct bonding by avoiding surface degradation and edge rounding, while maintaining the integrity of the structured substrate for subsequent applications.
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Abstract
Description
Title of the invention: Method for preparing a structured substrate for direct bonding Technical field
[0001] The present description relates generally to the field of microelectronics, and more particularly, to a method for preparing a structured substrate which can be used for direct bonding. Prior art
[0002] In the field of microelectronics, the bonding of structured substrates is particularly interesting. For example, it may involve bonding a Cu / SiO2 hybrid surface onto another structured Cu / SiO2 hybrid surface having pads (or steps). The structuring is generally carried out by photolithography / etching steps.
[0003] More particularly, as shown in Figures 1A to 1E, such a structured substrate can be produced according to the following method: - providing a substrate 10, having been previously polished, comprising a support substrate 11 covered by a hybrid layer 12 Cu / SiO2 ([Fig. 1 A]), - deposit a layer of resin 20 on the substrate 10 ([Fig.lB]), - forming openings in the resin layer 20 ([Fig.lC]), - etching the hybrid layer 12 and a part of the support substrate 11 through the openings, whereby a structured substrate 10 is obtained ([Fig.lD]), - removing the resin 20 ([Fig.lE]).
[0004] The structured substrate 10 can then be bonded with another substrate 30 comprising a support substrate 31 and a Cu / SiO2 hybrid layer 32 ([Fig. 1F]).
[0005] Direct bonding assembly processes require careful preparation of the surfaces of the substrates to be joined. Their surface condition is essential for successful bonding and chemical and particulate contamination must be avoided.
[0006] It is therefore important to be able to completely remove the resin.
[0007] Plasma cleaning processes combined with wet cleaning can be implemented to remove all contamination.
[0008] However, these cleaning processes are relatively aggressive, which can degrade the quality of the surface to be bonded (in particular its roughness). This is particularly true for surfaces comprising copper, typically Cu / SiO2 hybrid surfaces.
[0009] Cleaning the resin can therefore damage the hybrid surface which has been previously polished by chemical-mechanical polishing.
[0010] The bonding of the two substrates is then of poor quality.
[0011] Furthermore, it is impossible to polish the surface again because the structuring means that the polishing process would round off the edges of the pads and prevent bonding in these areas. Summary of the invention
[0012] There is a need for a method for preparing a structured substrate of interest that can subsequently be used for direct bonding, the method having to make it possible to obtain good quality substrate surfaces. This need is particularly important for substrates having Cu / SiO2 hybrid surfaces.
[0013] This aim is achieved by a method for preparing a structured substrate of interest for direct bonding comprising the following steps: a) providing a substrate of interest comprising a support substrate and a thin layer, b) bonding a protective layer onto the thin layer by direct bonding, c) depositing a resin onto the protective layer, and forming openings in the resin, d) etching the protective layer, the thin layer and part of the thickness of the support substrate through the openings in the resin, so as to form pads in the substrate of interest, e) bonding a temporary substrate and the substrate of interest, f) separating the temporary substrate from the substrate of interest, whereby the protective layer is separated from the substrate of interest and a structured substrate of interest for direct bonding is obtained, in which process either the resin is removed between step d) and step e) and the adhesion energy between the protective layer and the thin layer is lower than the adhesion energy between the temporary substrate and the protective layer, or the resin is removed during step f) and the adhesion energy between the protective layer and the thin layer is lower than the adhesion energy between the resin and the protective layer.
[0014] According to a particular embodiment, step b) is carried out by bonding to the substrate of interest a transfer substrate comprising a support substrate and the protective layer, then removing the support substrate.
[0015] According to a particular embodiment, the thin layer is a Cu / SiO2 hybrid layer comprising a thin layer of silicon oxide in which copper pads are formed.
[0016] According to a particular embodiment, the protective layer is made of SiO2.
[0017] According to a particular embodiment, the adhesion energy between the protective layer and the thin layer is at least 0.5 J / m2 lower than the adhesion energy between the temporary substrate and the protective layer, or the adhesion energy between the protective layer and the thin layer is at least 0.5 J / m2 lower than the adhesion energy between the resin and the protective layer.
[0018] According to a particular embodiment, the steps of the method are carried out at a temperature less than or equal to 150°C.
[0019] According to a particular embodiment, the method comprises a singulation step during which the substrate of interest is separated into several parts, at the level of cutting paths positioned between the pads, in order to form chips of interest, the singulation step preferably being carried out by means of a laser irradiation step, a plasma etching step or a saw cutting step.
[0020] According to a particular embodiment, the laser irradiation step is carried out, between step d) and step e) or between step e) and step f), the laser irradiation leading to the formation of weakened zones at the cutting paths, and the substrate of interest is glued to a stretchable adhesive film, the stretchable adhesive film being stretched, after the laser irradiation step, so as to separate the chips of interest at the weakened zones.
[0021] According to a particular embodiment, the plasma etching step is carried out, between step d) and step e), the substrate of interest being bonded to an adhesive film during the plasma etching step and during steps e) and f).
[0022] According to a particular embodiment, the plasma etching step is carried out between step e) and step f), the substrate of interest being bonded to an adhesive film during step f). Brief description of the drawings
[0023] These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:
[0024] [Fig.lA], [Fig.lB], [Fig.lC], [Fig.lD], [Fig.lE] and [Fig.lF], previously described, schematically represent different steps of a method for manufacturing a substrate of interest according to the prior art;
[0025] [Fig.2A], [Fig.2B], [Fig.2C], [Fig.2D], [Fig.2E], [Fig.2F] and [Fig.2G] schematically represent different steps of a method of manufacturing a substrate of interest according to a particular embodiment;
[0026] [Fig.3A], [Fig.3B], [Fig.3C], [Fig.3D], [Fig.3E] and [Fig.3F] schematically represent different steps of a method of manufacturing a substrate of interest according to another particular embodiment;
[0027] [Fig.4A], [Fig.4B], [Fig.4C], [Fig.4D], [Fig.4E], [Fig.4F], [Fig.4G], [Fig.4H] and [Fig.4I] schematically represent different steps of a method of manufacturing a substrate of interest according to another particular embodiment;
[0028] [Fig.5A], [Fig.5B], [Fig.5C], [Fig.5D], [Fig.5E], [Fig.5F], [Fig.5G] and [Fig.5H] schematically represent different steps of a method of manufacturing a substrate of interest according to another particular embodiment; and
[0029] [Fig.6A], [Fig.6B], [Fig.6C], [Fig.6D], [Fig.6E], [Fig.6F], [Fig.6G], [Fig.6H] and [Fig.61] schematically represent different steps of a method of manufacturing a substrate of interest according to another particular embodiment. Description of the embodiments
[0030] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.
[0031] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed.
[0032] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be connected by means of one or more other elements.
[0033] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made unless otherwise specified to the orientation of the figures.
[0034] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%.
[0035] Although the description particularly refers to structured substrates having a Cu / SiO2 hybrid bonding surface, the method can be applied to other structured substrates.
[0036] All given adhesion energies are determined by the double lever method with imposed displacement (as explained in the article by Foumel et al. 'Measurement of bonding energy in an anhydrous nitrogen atmosphere and its application to Silicon direct bonding technology', Journal of Applied Physics 111, 104907 (2012)).
[0037] We will now describe in more detail the method of preparing a structured substrate of interest 100 or chips of interest 150 with reference to FIGS. 2A to 2G, 3A to 3F, 4A to 41, 5A to 5H and 6A to 61.
[0038] The method comprises at least the following steps: a) providing a substrate of interest 100 comprising a support substrate 110 and a thin layer 120 (figures 2A, 3A, 4A, 5A, 6A), b) covering the thin layer 120 with a protective layer 220 (figures 2C, 3C, 4C, 5C, 6C), c) depositing a resin 300 on the protective layer 220, and forming openings in the resin 300, d) etching the protective layer 220, the thin layer 120 and a portion of the thickness of the support substrate 110 through the openings in the resin, so as to form pads 135 in the substrate of interest 100 (figures 2D, 3D, 4D, 5D, 6D), e) bonding a temporary substrate 400 to the substrate of interest 100 (figures 2F, 3E, 4F, 5F, 6F), f) separating the temporary substrate 400 from the substrate of interest 100 (Figures 2G, 3F, 4G, 5G, 61).
[0039] The method may further comprise an additional step during which the substrate of interest 100 is separated into several parts to form chips of interest 150 (FIGS. 4H, 5F, 6H). This additional step may be carried out between step c) and step d), between step d) and step e), or after step e).
[0040] The protective layer 220 (also called etch stop layer) has a relatively low adhesion EadhO (typically less than 1 J / m2). It is easily separated from the substrate of interest 100 during step f): it is removed at the same time as the temporary substrate 400. At the end of step f, a structured substrate of interest 100 is obtained which can be used for direct bonding.
[0041] To ensure low EadhO adhesion, the process temperatures used during the process will preferably be lower than 150°C and / or the bonding is a direct bonding with low adhesion, such as a bonding involving a hydrophobic silicon surface.
[0042] In this method, the protective layer 220 is held on the thin layer 120 of the substrate of interest 100 by means of a direct bonding method. There is no need to use glue or polymer. The surface of the thin layer 120 is thus preserved.
[0043] The method further comprises a step during which the resin 300 is removed.
[0044] According to a first embodiment, represented for example in FIGS. 2A to 2G, 4A to 41, 5A to 5H and 6A to 61, the resin 300 is removed between step d) and step e) in order to make the protective layer 220 accessible. During step e), the temporary substrate 400 is bonded to the cleaned surface of the protective layer 220.
[0045] The resin 300 can be removed by means of plasma oxidation and wet cleaning steps. The protective layer 220 protects the thin layer 120 during this step.
[0046] The temporary substrate 400 may be formed from a solid substrate or it may be a solid substrate 410 covered by an adhesive layer 420. The use of an adhesive layer 420 makes it possible to be very tolerant with regard to the quality of the surface of the barrier layer. The bonding adhesion between the temporary substrate 400 and the protective layer 220 Eadh1 is strong (typically greater than 1.5 J / m2). The energy Eadh1 is greater than the energy Eadh0. Thus, during step f), the detachment of the temporary substrate 400 will lead to the opening of the weakest adhesion interface: this is the interface between the protective layer 220 and the thin layer 120 of the substrate of interest 100. The surface of the substrate of interest 100 is released and is compatible with a direct bonding method.
[0047] According to a second embodiment, represented for example in FIGS. 3A to 3F, the resin 300 is removed during step f).
[0048] As for the first embodiment, the temporary substrate 400 may be a solid substrate or comprise a solid substrate 410 covered by an adhesive layer 420, which makes the bonding very tolerant to the surface condition of the resin 300. The adhesion Eadh2 between the resin 300 and the protective layer 120 is strong (typically greater than 1.5 J / m2). It is greater than Eadh0. The detachment of this substrate 400 will lead to the detachment of the interface between the protective layer 220 and the surface of the substrate of interest 100. The surface of the substrate of interest 100 is released and is compatible with a direct bonding method. The protective layer 220 and the resin are removed at the same time as the temporary substrate 400.
[0049] The substrate of interest 100 provided in step a) is preferably a plate.
[0050] The substrate of interest 100 comprises a front face and a back face. The front face corresponds to the face that you wish to prepare for direct bonding.
[0051] The substrate of interest 100 comprises a support substrate 110 and a thin layer 120. The support substrate 110 is, for example, a substrate made of semiconductor material (preferably, Si, Ge, SiC, AsGa), sapphire or silica.
[0052] The substrate of interest 100 provided in step a) may be an SOI ('Silicon on Insulator') substrate, i.e. comprising a support substrate successively covered by a thin layer of buried oxide and a layer of silicon.
[0053] It may also be a solid substrate 110 made of semiconductor material covered with a dielectric layer 120, in particular an oxide layer (silicon oxide in particular).
[0054] The thin layer 120 is, for example, a metal layer, an oxide layer (in particular, a silicon oxide layer), a layer of a III / V or IV / VI material, a layer of germanium, SiC, silicon or sapphire.
[0055] Preferably, the thin layer 120 is a hybrid layer, formed from at least two materials. Preferably, it is a Cu / SiO2 hybrid layer comprising a silicon oxide matrix in which copper portions (pads) have been formed. The copper pads have, for example, a side of 2 μm.
[0056] The upper face of the thin layer 120 corresponds to the surface which is structured and prepared for direct bonding.
[0057] During step b), the thin layer 120 of the substrate of interest 100 is covered by a protective layer 220.
[0058] The protective layer 220 may be a silicon oxide layer, a silicon layer (also called a hydrophobic silicon layer, i.e. a layer in which the silicon has Si-H terminations), a nitride layer (such as aluminum nitride), or a polymer layer. It may also be a layer composed of several materials with, for example, silicon covered with a silicon oxide layer.
[0059] According to a preferred embodiment, the protective layer 220 is bonded by direct bonding to the substrate of interest 100. This makes it possible to have intimate contact between the protective layer 220 and the thin layer 120 of the substrate of interest 100.
[0060] This embodiment can be carried out according to the following steps: i) bonding to the substrate of interest 100 a transfer substrate 200 comprising a support 210 and the protective layer 220 (figures 2B, 3B, 4B, 5B, 6B), ii) removing the support 210 from the transfer substrate 200, so as to form an assembly comprising the substrate of interest 100 covered by the protective layer 220 (figures 2C, 3C, 4C, 5C, 6C).
[0061] During step i), the temporary substrate 200 and the substrate of interest 100 are assembled by direct bonding. Direct bonding can be carried out at atmospheric pressure (i.e. 1013.25 hPa) or under vacuum (of the order of 1 hPa).
[0062] Prior to step i), the transfer substrate 200 will advantageously be trimmed. Trimming the edge of the plate 200 makes it possible to avoid possible edge problems, in particular if step ii) is carried out by thinning.
[0063] The trimming can be carried out, for example, by photolithography / etching or by mechanical trimming using a diamond saw. The width of the trimming is included, for example, between 1 and 5 mm and / or its depth included, for example, between 100 and 250 pm.
[0064] Step ii) can be carried out by thinning.
[0065] Step ii) may be carried out using a laser detachment technique. ('laser lift-off'). For example, the support 210 may be formed from a transparent substrate covered with a removal layer.
[0066] A silicon support 210 can be used with the Nanocleave® technology from EVGroup® for laser detachment.
[0067] The support substrate 210 of the temporary substrate 200 can be used in a new bonding / etching cycle. Cleaning is advantageously carried out between each use.
[0068] For example, it is possible to recycle it by implementing an oxygen plasma treatment followed by wet cleaning.
[0069] At each use, a new protective layer can be, if necessary, formed on the support substrate 210 before being reused.
[0070] During step c), a resin 300 is deposited on the protective layer 220. Openings are formed in the resin at the level of the cavities 130 of the substrate of interest 100 that it is desired to form. The resin 300 acts as a mask.
[0071] During step d), the protective layer 220, the thin layer 120 and a portion of the thickness of the support substrate 110 is etched.
[0072] Pads 135 are thus formed in the substrate of interest 100. The pads 135 are separated by spaces 130.
[0073] The pads 135 form, for example, a square step with a side of 10 mm and a depth of 50 μm.
[0074] During step e), a temporary substrate 400 is bonded with the substrate of interest 100.
[0075] If the resin 300 has been removed between step d) and step e), the temporary substrate 400 is glued onto the protective layer 220.
[0076] If the resin 300 has not been removed, the temporary substrate 400 is bonded to the resin layer 300.
[0077] The temporary substrate 400 comprises a support substrate 410 and a layer 420, preferably an adhesive layer.
[0078] During step f), the temporary substrate 400 is removed. The protective layer 220 and, if applicable, the resin 300 are removed simultaneously. This step is made possible by the differences in adhesion energy involved.
[0079] In order to promote the removal of the protective layer 120, it is possible to carry out an implantation of gaseous species before the bonding of step e). The implantation can be carried out through the protective layer 120 and, potentially, also through the resin layer 300.
[0080] Following this implantation step, thermal annealing can be implemented to diffuse the gaseous species and promote detachment at the interface between the layer of interest 120 and the protective layer 220.
[0081] At the end of step f), structured substrates of interest 100 are obtained (FIGS. 2G and 3F). Their surfaces are ready for direct bonding.
[0082] It is also possible to carry out an additional step during which the substrate of interest 100 is cut or etched, at the spaces 130 between the pads 135, to obtain chips of interest 150 whose surface is ready for direct bonding (as shown in FIGS. 41, 5H and 61).
[0083] The cutting or engraving is carried out over the entire thickness of the substrate 110.
[0084] This step can be carried out before step e) or after step f).
[0085] It can be achieved using different techniques.
[0086] According to a first variant embodiment, shown in Figures 4E to 41, the cutting is carried out by means of a laser (cutting by 'Stealth Dicing').
[0087] Firstly, laser irradiation is carried out between the pads 135 to form weakened zones 140. This step can be carried out, before step e), either by irradiating from the front face of the substrate of interest 100 or by irradiating from the rear face. Alternatively, this laser irradiation step can be carried out after step e), by irradiating the rear face of the substrate of interest. For rear face irradiation (before or after bonding of the substrates), alignment marks or alignment by infrared vision can be implemented.
[0088] After having carried out the irradiation step ([Fig.4E]) and the bonding step ([Fig.4F]) of the substrate of interest 100 with the temporary substrate 400 (or vice versa), the substrate of interest 100 is bonded to a device 500 comprising an adhesive film 510 held by a metal surround ('frame') 520. The temporary substrate 400 is then peeled off in order to remove the protective layer 220 from the front face of the substrate of interest ([Fig.4G]). Then, the stretchable adhesive film 510 is stretched ([Fig.4H]) to cause the fracture of the substrate of interest 100 at the areas weakened 140 by the irradiation. The chips of interest 150 are thus obtained. The chips 150 are then removed from the stretchable film 510.
[0089] According to a second variant embodiment, as shown in FIGS. 5E to 5H and 6G to 6I, the cutting of the substrate 100 is carried out by means of a plasma. This is a so-called deep cutting.
[0090] For example, the deep cutting of the substrate 100, in particular in silicon, can be carried out using a Bosch process.
[0091] According to a first variant embodiment, as shown in FIGS. 5E and 5F, the etching can be carried out from the front face of the substrate of interest 100 just before step e).
[0092] In order to single out the chips 150, the substrate of interest 100 is bonded to a device 500 comprising an adhesive film 510 held by a metal frame 520 ([Fig.5E]). Then the etching step is carried out. The protective layer 220 can act as a hard mask during etching, which makes it possible to reduce the duration of the process.
[0093] The temporary substrate 400 is then glued ([Fig.5F]). When the temporary substrate 400 is peeled off, chips of interest 150 are obtained, fixed on the adhesive film 510 ([Fig.5G]). After separation of the adhesive film 510, the chips are ready for use ([Fig.5H]).
[0094] According to a second variant embodiment, as shown in FIGS. 6F to 61, the deep etching of the substrate of interest 100 can be carried out after step e), from the rear face of the substrate of interest 100. A hard mask will be previously deposited on the rear face of the substrate of interest 100 ([Fig.6G]), before or after bonding with the temporary substrate 400.
[0095] At the end of the etching step, the chips 150 are held by bonding with the temporary substrate 400 ([Fig.6H]). There is no need to use adhesive during this step, which requires less complex equipment and simplifies the process.
[0096] Once the etching is carried out, the hard mask is removed. Then, the rear face of the substrate of interest 100 is fixed on a device 500 comprising an adhesive film 510 held by a metal surround ('frame') 520, then the temporary substrate 400 is peeled off to obtain the chips of interest ([Fig.61]).
[0097] It is possible to mix the last two variants by making a first deep etching on the front face of the support substrate 110 by cleverly using the layer 220 as a hard mask. Since this is a partial etching, there is no need for the adhesive film 510. Then, it is glued to the temporary substrate 400 and the back face of the support substrate 110 can be thinned using the same deep etching technique by having put a hard mask or an etching can be carried out on the entire surface. This last option amounts to thinning the chips until they open into the first partial deep etching. Then, the support substrate 110 is glued to the adhesive film 510 and the temporary substrate 400 is peeled off.
[0098] According to a third variant embodiment, not shown, the cutting is carried out mechanically, in particular by means of a saw.
[0099] The substrate of interest 100 can be cut before or after bonding with the temporary substrate 400.
[0100] When the substrate 100 is cut before bonding with the temporary substrate 400, it is first fixed to a device 500 comprising an adhesive film held by a perimeter, then sawn to obtain the chips of interest 150. The chips 150 are then glued to the temporary substrate, then the latter is peeled off in order to remove the protective layer 220 and obtain the chips of interest 150.
[0101] When the substrate 100 is cut after bonding with the temporary substrate 400, care will be taken not to cut the temporary substrate 400 or a very small thickness of the temporary substrate 400 so as not to weaken it and to maintain functional detachment. This embodiment variant is particularly advantageous because, not only does it allow cutting to be carried out without using an adhesive film but, also, the future front face of the chips of interest 150 will not be disturbed at all by the possible particulate contamination of the cut because the protective bonding is in place. After cutting, the rear face of the substrate of interest 100 is positioned on an adhesive film held by a rim and the temporary substrate 400 is detached. The chips of interest 150 are obtained.
[0102] It is also possible to cut the substrate by implementing cleavage. The cleavage can be initiated by making a notch in the substrate, for example, using a diamond tip.
[0103] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art.
[0104] Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art from the functional indications given above.
[0105] Illustrative and non-limiting examples of different embodiments
[0106] Example 1:
[0107] On a silicon plate of interest, 2 pm copper pads are produced using a Damascene process in a SiO2 matrix. This plate undergoes a chemical-mechanical polishing process to make it compatible with a direct bonding process. A SOI type transfer substrate is used. It comprises a 205 nm silicon film on a 400 nm oxide layer. It is trimmed with a diamond saw to a depth of 250 pm and a width of 1.5 mm. The surface of the transfer substrate is cleaned to make it compatible with a hydrophilic direct bonding process.
[0108] The substrate of interest and the transfer substrate are assembled by direct bonding.
[0109] The transfer substrate is thinned to 50 pm and then the remaining silicon is removed by SF6-based plasma etching. The etching stops at the 400 nm oxide layer. The silicon can also be etched using an aqueous HF / HNO3 solution. Finally, the SiO2 layer is removed by HF-based wet etching.
[0110] A photolithography / etching step is carried out on this structure so as to obtain pads 50 μm thick and 10 mm on each side.
[0111] This structure is bonded to a temporary substrate 400 covered by an adhesive film. For example, this is an adhesive film marketed by Furukawa® under the reference SP5207M-425. It comprises a 5 μm adhesive layer.
[0112] The rear face of the substrate of interest is placed on a vacuum table. By inserting a wedge into the bonding, the assembly is dismantled. The opening separates the interface between the substrate of interest and the silicon film from the temporary substrate. A surface of copper pads of 2 μm on each side is obtained on a square step of 10 mm on each side and 50 μm in depth, directly compatible with a direct bonding process.
[0113] Example 2:
[0114] On a silicon plate of interest, 2 pm copper pads are produced using a Damascene process in a SiO2 matrix. This plate undergoes a chemical-mechanical polishing process to make it compatible with a direct bonding process. A SOI type transfer substrate comprises a 205 nm silicon film on a 400 nm oxide layer. This substrate is cut using a diamond saw to a depth of 250 pm and a width of 1.5 mm. The surface of the transfer substrate is cleaned using an HF-based deoxidizing treatment to prepare a hydrophobic direct bond.
[0115] The substrate of interest and the transfer substrate are assembled by direct bonding.
[0116] The transfer substrate is thinned to 50 pm and the remaining silicon is removed by SF6-based plasma etching, which stops at the 400 nm oxide layer. The silicon can also be etched using an aqueous HF / HNO3 solution. Finally, the SiO2 layer is removed by HF-based wet etching.
[0117] A photolithography / etching step is carried out on this structure so as to obtain 50 μm thick pads with sides measuring 10 mm.
[0118] This structure is bonded to a temporary substrate comprising an adhesive such as an adhesive film marketed by the company Furukawa® under the reference SP5207M-425. The adhesive film has a thickness of 5 μm. The rear face of the substrate of interest is then placed on a vacuum table. By inserting a corner into the bonding, the assembly is dismantled. The opening separates the interface between the substrate of interest and the silicon film. A surface of copper pads of 2 μm on each side is obtained on a square step of 10 mm on each side and 50 μm in depth, directly compatible with a direct bonding process.
[0119] Example 3:
[0120] On a silicon plate of interest, copper pads of 2 pm on each side are produced in a SiO2 matrix using a Damascene process. This plate undergoes a process chemical-mechanical polishing to make it compatible with a direct bonding process. 1 pm of SiO2 is deposited by chemical vapor deposition on a temporary silicon substrate. This plate is then cut with a diamond saw to a depth of 250 pm and a width of 1.5 mm. The surface of the transfer substrate is cleaned and then chemical-mechanical polished.
[0121] The substrate of interest and the transfer substrate are assembled by direct bonding. Slt is thinned to 50 pm and the remaining silicon is removed by SF6 plasma etching which stops at the 1 pm oxide layer.
[0122] A photolithography / etching step is carried out on this structure so as to obtain 50 μm thick pads with a side of 10 mm.
[0123] This structure is bonded to a temporary substrate comprising a glass plate on which 10 μm of adhesive marketed under the reference LC5200 has been spread. The bonding is carried out at room temperature by UV exposure. The rear face of the substrate of interest is then placed on a vacuum table. By inserting a wedge into the bonding, the assembly is dismantled. The opening separates the interface between the substrate of interest and the oxide film of the transfer substrate. A surface of copper pads of 2 μm on each side is obtained on a square step of 10 mm on each side and 50 μm in depth, directly compatible with a direct bonding process.
[0124] Example 4:
[0125] On a silicon plate of interest, 2 pm copper pads are produced using a Damascene process in a SiO2 matrix. This plate undergoes a chemical-mechanical polishing process to make it compatible with a direct bonding process. On a silicon transfer substrate, 1 pm of SiO2 is deposited by chemical vapor deposition. This plate is then cut using a diamond saw to a depth of 250 pm and a width of 1.5 mm. The surface of the transfer substrate is cleaned and then chemical-mechanical polished.
[0126] The substrate of interest and the temporary substrate are assembled by direct bonding. The transfer substrate is thinned to 50 pm and the remaining silicon is removed by SF6 plasma etching which stops at the 1 pm oxide layer.
[0127] Using a resin marketed under the reference TOK® TDMR with a thickness of 1 pm, a photolithography / etching step is carried out on the structure so as to obtain 50 pm thick pads with a side of 10 mm. After etching, the resin is not removed using conventional plasma etching techniques combined with wet cleaning.
[0128] This structure is glued onto a temporary substrate comprising a glass plate on which 10 μm of adhesive marketed under the reference LC5200 has been spread. The bonding is carried out at room temperature by UV exposure. The structure is placed on a vacuum table: the back face of the substrate of interest is vacuumed. By inserting a wedge into the bond, the assembly is dismantled. The opening separates the interface between the substrate of interest and the oxide film coming from the transfer substrate. We obtain a surface of copper pads of 2 pm on a side on a square step of 10 mm on a side and 50 pm in depth directly compatible with a direct bonding process.
Claims
Claims
1. A method for preparing a structured substrate of interest (100) for direct bonding comprising the following steps: a) providing a substrate of interest (100) comprising a support substrate (110) and a thin layer (120), b) bonding a protective layer (220) to the thin layer (120) by direct bonding, c) depositing a resin (300) on the protective layer (220), and forming openings in the resin (300), d) etching the protective layer (220), the thin layer (120) and a portion of the thickness of the support substrate (110) through the openings in the resin, so as to form pads (135) in the substrate of interest (100), e) bonding a temporary substrate (400) and the substrate of interest (100), f) separating the temporary substrate (400) from the substrate of interest (100), whereby the protective layer (220) is separated from the substrate of interest (100) and a structured substrate of interest (100) is obtained for direct bonding,method in which either the resin (300) is removed between step d) and step e) and the adhesion energy between the protective layer (220) and the thin layer (120) is lower than the adhesion energy between the temporary substrate (400) and the protective layer (220), or the resin (300) is removed during step f) and the adhesion energy between the protective layer (220) and the thin layer (120) is lower than the adhesion energy between the resin (300) and the protective layer (220).,
2. Method according to claim 1, characterized in that step b) is carried out by gluing to the substrate of interest (100) a transfer substrate (200) comprising a support substrate (210) and the protective layer (220), then removing the support substrate (210).
3. Method according to one of claims 1 and 2, characterized in that the thin layer (120) is a Cu / SiO2 hybrid layer comprising a thin layer of silicon oxide in which copper pads are formed.
4. Method according to any one of the preceding claims, characterized in that the protective layer (220) is made of SiO2.
5. Method according to any one of the preceding claims, characterized in that the adhesion energy between the protective layer (220) and the thin layer (120) is at least 0.5 J / m2 lower than the adhesion energy between the temporary substrate (400) and the protective layer (220), or in that the adhesion energy between the protective layer (220) and the thin layer (120) is at least 0.5 J / m2 lower than the adhesion energy between the resin (300) and the protective layer (220).
6. Method according to any one of the preceding claims, characterized in that the steps of the method are carried out at a temperature less than or equal to 150°C.
7. Method according to any one of the preceding claims, characterized in that the method comprises a singulation step during which the substrate of interest (100) is separated into several parts, at the level of cutting paths positioned between the pads (135), in order to form chips of interest (150), the singulation step being, preferably, carried out by means of a laser irradiation step, a plasma etching step or a saw cutting step.
8. Method according to claim 7, characterized in that the laser irradiation step is carried out, between step d) and step e) or between step e) and step f), the laser irradiation leading to the formation of weakened zones (140) at the cutting paths, and in that the substrate of interest (100) is glued to a stretchable adhesive film (510), the stretchable adhesive film (510) being stretched, after the laser irradiation step, so as to separate the chips of interest (150) at the weakened zones (140).
9. Method according to claim 7, characterized in that the plasma etching step is carried out, between step d) and step e), the substrate of interest (100) being glued to an adhesive film (510) during the plasma etching step and during steps e) and f).
10. Method according to claim 7, characterized in that the plasma etching step is carried out between step e) and step f), the substrate of interest (100) being glued to an adhesive film (510) during step f).
Citation Information
Patent Citations
Processing Stacked Substrates
US20180182639A1