Method for manufacturing a semiconductor structure with temporary direct bonding using a porous layer

Abstract

A method for manufacturing a semiconductor structure, including: direct bonding a substrate to be handled with a handle substrate via a bonding layer covering the handle substrate, to form a temporary structure capable of withstanding technological steps; disassembling the temporary structure at the bonding layer to separate the substrate to be handled from the handle substrate; and a prior depositing the bonding layer onto the handle substrate and/or onto the substrate to be handled, the bonding layer including a porous material including, an inorganic matrix and organic compounds connected or not to the matrix, and the disassembling is carried out by providing a thermal budget for disassembly to the intermediate structure, the providing resulting in a spontaneous disassembly of the temporary structure occurring at the bonding layer.

Claims

1. A method for manufacturing a semiconductor structure, comprising: depositing a bonding layer onto a handle substrate and/or onto a substrate to be handled, the bonding layer including a porous material including an inorganic matrix and organic compounds; direct bonding the substrate to be handled with the handle substrate via the bonding layer, to form a temporary structure capable of withstanding technological steps; and disassembling the temporary structure at the bonding layer to separate the substrate to be handled from the handle substrate, wherein the disassembling is carried out by providing a thermal budget for disassembly to the intermediate structure, the providing resulting in a spontaneous disassembly of the temporary structure occurring by splitting within the bonding layer.

2. The method according to claim 1, wherein the disassembling takes place under a controlled atmosphere.

3. The method according to claim 1, wherein the providing the thermal budget for disassembly comprises annealing the temporary structure at a temperature exceeding 600 C. for a duration of more than 10 minutes.

4. The method according to claim 1, further comprising strengthening the bonding implemented by providing a thermal budget for reinforcement to the temporary structure.

5. The method according to claim 1, further comprising, before the disassembling, assembling a free rear side of the substrate to be handled with a receiving substrate.

6. The method according to claim 1, further comprising recycling the handle substrate after the disassembling, the recycling comprising removal of residues of the bonding layer present at a surface of the handle substrate by selective etching.

7. The method according to claim 1, wherein the bonding layer has a porosity in a range of 10% to 80%.

8. The method according to claim 1, wherein the bonding layer is a layer of organosilicon material.

9. The method according to claim 1, wherein the bonding layer is a layer whose porosity is self-generated.

10. The method according to claim 1, wherein depositing the bonding layer comprises depositing a matrix precursor on the handle substrate and incorporating a porogenic agent in the deposited matrix precursor.

11. The method according to claim 1, further comprising, after depositing the bonding layer, modifying the porous material by thermal, chemical, UV, electron beam, or plasma post-treatment.

12. The method according to claim 1, further comprising, after the direct bonding, forming at least one cut in the handle substrate to isolate regions of the handle substrate from each other, the disassembling of the temporary structure resulting in a partial separation of the handle substrate located at one or more of the isolated regions of the handle substrate.

13. The method according to claim 12, further comprising forming a cut in the handle substrate separating a central portion of the handle substrate from a peripheral portion of the handle substrate, the disassembling of the temporary structure resulting in a partial separation of the handle substrate located at the central portion of the handle substrate, whereby the substrate to be handled rests on the peripheral portion of the handle substrate.

14. The method according to claim 13, further comprising thinning the substrate to be handled resting on the peripheral portion of the handle substrate.

15. The method according to claim 1, further comprising, after the direct bonding, forming one or more cuts in the substrate to be handled to isolate regions of the substrate to be handled from each other, the disassembling of the temporary structure resulting in a partial separation of the substrate to be handled located at one or more of the isolated regions of the substrate to be handled.

16. The method according to claim 1, wherein the depositing of the bonding layer is performed by at least one of physical vapor deposition; sol-gel deposition; chemical vapor deposition; or plasma enhanced chemical vapor deposition.

17. The method according to claim 1, wherein the porous material includes at least one of carbonate cycles or carbonate chains.

18. The method according to claim 1, wherein the direct bonding is performed by molecular adhesion without any glue and is performed at ambient temperature and at atmospheric pressure.

19. The method according to claim 1, wherein the disassembling takes place under one of a nitrogen atmosphere and mixed N.sub.2O.sub.2 atmosphere.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Other aspects, purposes, advantages and characteristics of the invention shall be better understood upon reading the following detailed description given of the non-limiting preferred embodiments of the invention, provided for illustration purposes with reference to the appended figures, in which:

(2) FIGS. 1a-1d show a first embodiment of the method according to the invention;

(3) FIGS. 2a-2f show a second embodiment of the method according to the invention, wherein a layer of the substrate to be handled is transferred onto a receiving substrate;

(4) FIGS. 3a-3c show a third embodiment of the method according to the invention, wherein the disassembly of the temporary structure results in a partial separation of the handle substrate;

(5) FIG. 4 shows the variation in bonding energy depending on the temperature of a consolidating annealing process applied to the temporary structure.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS

(6) The invention discloses a method for manufacturing a semiconductor structure using a handle substrate to support a substrate to be handled.

(7) A semiconductor structure is understood to be any structure that is used to manufacture a device with semiconductors. A semiconductor structure can include conductive, semi-conductive and/or non-conductive materials. It can be a layer that optionally comprises microcomponents, regardless of whether said microcomponents are finished or semi-finished.

(8) A handle substrate is understood to be a composite structure, the function of which is to provide a temporary mechanical support for a substrate or a structure. The handle substrate is, for example, a silicon substrate.

(9) A substrate to be handled is understood to be a substrate that is temporarily assembled with a handle substrate and on which treatments can take place, in particular FEOL or BEOL (Back End Of the Line) technological steps. It can be, for example, a substrate comprising finished or semi-finished microcomponents to be transferred onto a receiving substrate.

(10) A description of the method according to the invention is firstly provided with reference to FIGS. 1a to 1d, which show a first embodiment.

(11) In a first step shown in FIG. 1a, a bonding layer 3 made of a porous material is deposited onto the handle substrate 2.

(12) In a second step shown in FIG. 1b, the substrate to be handled 1 undergoes direct bonding with the handle substrate 2 via the bonding layer made of a porous material 3 coating the handle substrate.

(13) Direct bonding is understood to be bonding by molecular adhesion of the surfaces placed in contact with each other, without the use of any specific material such as glue. Direct bonding can take place at ambient temperature and at atmospheric pressure. It can be preceded by prior treatment of the bonding surfaces, for example chemical treatment intended to make said bonding surfaces hydrophilic or treatment intended to reduce the roughness thereof.

(14) Alternatively, the bonding layer made of porous material can be deposited onto the substrate to be handled 1 or on both sides, i.e. both on the substrate to be handled 1 and on the handle substrate 2.

(15) As shown in FIG. 1b, the bonding layer 3 can be coated with an additional layer 4 intended to ease bonding, for example in the form of a silicon oxide surface layer. Similarly, an additional layer 5 can coat the substrate to be handled 1.

(16) After direct bonding has taken place (FIG. 1c), a temporary structure 6 is obtained, formed from the stack of the substrate to be handled 1 assembled with the handle substrate 2 via the bonding layer 3.

(17) Said bonding is strong enough to allow the temporary structure 6 to withstand high-temperature technological steps (for example at 600 C.), which is not possible when bonding is performed using polymer or metal layers. These technological steps can in particular include the formation of at least one portion of a microtechnological component and/or the formation of at least one insulating layer.

(18) In one possible embodiment of the invention, a step of strengthening the bonding can be implemented by providing a so-called thermal budget for reinforcement to the temporary structure 6. This reinforcement of the bonding can be obtained by, annealing for a duration exceeding 10 minutes at a temperature lying in the range 100 C. to 600 C.

(19) This reinforcement takes place to allow subsequent technological steps to be performed, in particular those having higher thermal budgets. The reinforcement advantageously corresponds to a first heat treatment of the intermediate structure, implemented prior to the subsequent technological steps. However, said subsequent technological steps can also contribute to the thermal budget for reinforcing the mechanical strength of the bonding.

(20) With reference to FIG. 1d, in particular once the different technological steps have been performed, the temporary structure 6 is disassembled at the bonding layer made of porous material 3 in order to separate the substrate to be handled 1 from the handle substrate 2.

(21) This disassembly takes place by providing a so-called thermal budget for disassembly to the intermediate structure 6, said providing resulting in the spontaneous disassembly, without the application of mechanical stress, of the temporary structure occurring at the bonding layer made of porous material 3.

(22) Disassembly can take place under a controlled atmosphere, for example for a bonding layer made of an organosilicon material under a nitrogen or mixed N.sub.2 and O.sub.2 atmosphere, in order to control the reaction between said atmosphere and the bonding layer 3, and thus better control the disassembly conditions (higher or lower temperature, longer or shorter duration, etc.).

(23) Providing the thermal budget for disassembly can take place by annealing for a duration exceeding 10 minutes at a temperature exceeding 600 C. In one possible embodiment, the thermal budget for reinforcement and the thermal budget for disassembly can be combined into a single thermal budget. Said thermal budget therefore acts to reinforce the mechanical strength of the intermediate structure, then to disassemble said structure.

(24) Disassembly thus takes place by splitting within the bonding layer 3 made of porous material, and not within one of the substrates. The substrate to be handled and the handle substrate are therefore not damaged.

(25) After splitting has occurred, the handle substrate 2 is present on the one hand, coated with a portion 3 originating from the split of the bonding layer 3, and the substrate to be handled is present on the other hand, also coated with a portion 3 originating from the split of the bonding layer 3. Said portions 3, 3 have be seen to have identical thicknesses, whereby the split takes place in the middle of the thickness of the bonding layer 3. The handle substrate 2 can be easily recycled via a recycling step comprising the removal of the residues 3 of the porous bonding layer present at the surface of the handle substrate after the disassembly step. This removal step has the advantage of being possible by selective etching, which is less expensive than a CMP operation. The residues 3 present on the substrate to be handled 1 can be removed in a similar manner by selective etching. Alternatively, a CMP operation can be performed when looking to reduce the surface roughness of the porous material (without fully removing the latter) and continue the manufacturing process for the substrate to be handled.

(26) It should be noted that this method is simpler and less expensive than the methods of the prior art. The ability to disassemble the structure is provided by the simple deposition of a single layer, and does not require any prior weakening operation (for example by mechanical means or ion implantation) for one of the substrates or the bonding layer.

(27) The bonding layer made of porous material 3 used within the scope of the invention is made of a porous inorganic matrix (metal, dielectric, semi-conductive and more particularly in the examples given below, a matrix containing SiO bonds) and organic compounds connected or not to the matrix (carbonate cycles, carbonate chains). It could therefore be, for example, a porous layer of organosilicon material SiOC(H).

(28) This composition choice allows the assembly to be spontaneously disassembled by a twofold mechanism. Under the effect of heat treatment, the porous material densities at the periphery of the wafer, thus creating a sealed area at the edge of the wafer. The gases present in the porous material then become trapped within the temporary structure 6. The expansion of said trapped gases with the temperature results in a spontaneous split forming within the porous layer.

(29) This bonding layer made of porous material also has the special ability to change under treatment, for example under heat treatment, chemical treatment or UV treatment. The porosity of the bonding layer can therefore be adjusted or created using such a treatment (in the case of deposition via a porogenic approach). This change can be mechanical (for example densification or change to the porosity state) or chemical (for example production or desorption of gaseous species).

(30) The bonding layer made of porous material 3 can be deposited by physical means (for example: PVDor Physical Vapor Depositionand its derivatives), radical means (for example: sol-gel and its derivatives), or chemical means (for example: CVDor Chemical Vapor Depositionand its derivatives), and more particularly in the examples given below, by PECVD (Plasma Enhanced Chemical Vapor Deposition).

(31) The bonding layer made of a porous material 3 can be a layer whose porosity is self-generated by steric hindrance on certain groups such as cyclic groups (example matrix precursors: trimethyltrivinylcyclotetrasiloxane (V3D3) or tetramethylcyclotetrasiloxane (TMCTS)), methyl groups or carbon derivative groups (example matrix precursors: hexamethyldisiloxane (HMDSO), bistrismethylsilylmethane (BTMSM), methylsilane (1MS), dimethylsilane (2MS), trimethylsilane (3MS), bis (trimethylsiloxy)methylsilane (BTMS), methyltrimethoxysilane (MTMS)).

(32) The bonding layer made of a porous material 3 can also be a layer whose porosity is generated by a porogenic approach according to which organic porogenic agents are introduced during the deposition of the matrix precursor and then removed by heat treatment, UV treatment or by electron beam (e-beam).

(33) Porogenic agents can be chemically bonded to the matrix precursor (for example: vinyltrimethylsilane (VTMS), divinyldimethylsilane (DVMS), tetravinylsilane (TVS), diphenylmethylsilane (DPMS)), or can be co-deposited with the matrix precursor (example porogenic agents: diethoxymethylsilane (DEMS), cyclohexene (CHO), decamethyl-cyclopentasiloxane (DMCPSO), 1-hexene, bicyclohexadiene (BCHD), cyclopentene oxide (CPO)).

(34) In the embodiments given below, the co-deposition by PECVD of a matrix precursor of the type Methyl-Diethoxy-Silane (MDEOS) and of porogenic agents of the type norbornadiene (NBD) takes place under He and O.sub.2 flows. After removal of the porogenic agents, a porous layer is obtained, which layer has an inorganic SiOSi matrix comprising methyl groups or derivatives connected to the matrix by the silicon atom (SiOCH.sub.3).

(35) The removal of the porogenic agents, which takes place by heat treatment, UV treatment or by e-beam, generates a porosity level that varies from 10% to 80% (and more particularly in the examples between 20-30%5%) and also in most cases generates a reduction in thickness (in the range 5% to 25% in the examples). This removal can take place such that the porogenic agents are partially removed or are not removed.

(36) One or more subsequent steps can be implemented in order to modify the porous layer deposited, for example in order to change the porosity level, the chemical composition and/or the quantity of remaining porogenic agents. These steps involve, for example, an additional treatment by heat, UV or e-beam, a chemical treatment (for example HF etching widening the radius of the pores) or plasma treatment. It should be noted that when subjected to heat treatment, for example, the carbon groups (remaining porogenic agents and/or methyl groups) are capable of decomposing into gaseous form. Therefore, the method according to the invention can comprise, after the deposition of the bonding layer made of porous material, a step of modifying the porous material by thermal, chemical, UV, electron beam or plasma post-treatment. It is therefore possible, by engineering the porous material deposited, to change some of the properties thereof, and thus change the temperature at which disassembly occurs. The composition and physical-chemical properties of the porous material are therefore chosen in order to adapt the thermal budget for reinforcing the mechanical strength and for disassembling the temporary structure.

(37) The gases used during the deposition of the porous layer and the gases released during post-treatment of the porous layer deposited can become trapped inside the bonding layer, for example according to the deposition technique used. Therefore, the disassembly phenomenon can be controlled by modulating the quantity of gas produced. Indeed, this is the expansion of the gases trapped as a result of the sealed area at the edge of the wafer that causes the spontaneous disassembly.

(38) One embodiment of the invention with two 200 mm P-doped silicon substrates (100) is described below. The handle substrate is coated in a 300-nm layer of porous SiOCH.sub.3 by the co-deposition of MDEOS+NBD by PECVD under He and O.sub.2. The porogenic agents are removed by UV and heat treatment, which causes a reduction in thickness of about 15%5%. The deposited layer has a chemical composition of about 15%5% of Si, 20%5% of C and O, 45%5% of H and a porosity of about 20%10%. The pore size, measured by ellipsometry-porosimetry, is about 1 nm30%. The substrate to be handled is a blank substrate, not coated with a thermal oxide. The two substrates undergo chemical treatment in order to make the porous SiOCH.sub.3 and silicon surfaces hydrophilic, which surfaces are known to be very hydrophobic. This treatment consists of chemical cleaning of the type O.sub.3+RCA. After these different treatments, the surface roughness is about 5 RMS (Root Mean Square) for the deposited SiOCH.sub.3 porous layer and about 1.5 RMS for the silicon substrate to be handled, which is compatible with direct hydrophilic bonding. The two substrates are therefore bonded by the direct bonding method at ambient temperature and atmospheric pressure in order to form the so-called intermediate structure.

(39) Said intermediate structure can then withstand heat treatments at up to 600 C. without detachment. Annealing then takes place at a higher temperature, at 900 C. for 2 h in a mixed O.sub.2+N.sub.2 atmosphere, and results in the disassembly of said structure by splitting within the porous SiOCH.sub.3 layer. Splitting more particularly takes place in the middle of the porous layer as shown by the thickness measurements taken by ellipsometry. The thickness of the porous layer transferred to the substrate to be handled after splitting is about 100 nm5% and the thickness of the porous layer remaining on the handle substrate is also about 100 nm5%. An area at the edge of the wafer, corresponding to the sealed area, is, visible to, the naked eye. It is 118 nm5% thick on the substrate to be handled. After disassembly, a roughness of 1.8 nm RMS is measured in the central portion of each of the substrates.

(40) In another embodiment of the invention, a cut was made in the intermediate structure after bonding in order to produce bonding strips having a width of 20 mm. Annealing at 900 C. for 2 h, under a mixed O.sub.2+N.sub.2 atmosphere, of said strips results in disassembly by, splitting within the porous material of the bonding layer. Under an N.sub.2 atmosphere disassembly occurs at 1000 C., i.e. at a higher temperature.

(41) Another embodiment of the invention is shown in FIGS. 2a-2f. It implements, by means of two direct bonding operations, the transfer of a thin layer 10 of the substrate to be handled 10 to a receiving substrate 11.

(42) With reference to FIG. 1a, the handle substrate 2 is coated in a 300-mm porous layer 3 of SiOCH.sub.3 deposited by PECVD (MDEOS+NBD under He+O.sub.2). The porogenic agents are removed by UV and heat treatment, which causes a reduction in thickness of about 15%5%. The deposited layer has a chemical composition of about 15%5% of Si, 20%5% of C and O, 45%5% of H and a porosity of about 20%10%.

(43) The substrate to be handled 10 is a non highly-doped substrate that comprises, at the surface thereof, at least one portion derived from FEOL steps. The two substrates 2, 10 undergo chemical treatment in order to make the surfaces thereof hydrophilic. This treatment consists of chemical cleaning of the type O.sub.3+RCA.

(44) With reference to FIG. 2b, the two substrates are bonded by the direct bonding method at ambient temperature and atmospheric pressure. A first a annealing is applied to the intermediate structure 16 at 400 C. for 2 h in order to consolidate and mechanically strengthen the bonding interface.

(45) With reference to FIG. 2c, a thinning of the substrate to be handled takes place on the free rear surface thereof in order to form a thin layer 10. This thinning can take place by mechanical-chemical abrasion or by implementing the Smart Cut method, whereby the substrate to be handled has previously undergone ion implantation.

(46) Then, with reference to FIG. 2d, a second hydrophobic bonding takes place between the free rear side of the thinned substrate to be handled 10 and a receiving substrate 11. The receiving substrate is a doped silicon substrate not compatible with the production of the portion derived from FEOL steps present at the surface of the substrate to be handled.

(47) With reference to FIG. 2e, a second annealing takes place for the whole stack produced by the second bonding at 900 C. for 2 h. The purpose of this heat treatment is to consolidate the bonding interface between the thin layer 10 and the receiving substrate 11 and to separate the handle substrate 2 from the thin layer 2 by splitting within the porous layer 3. Said heat treatment takes place at a temperature that is low enough so as not to cause a too significant release of the doping agents.

(48) Another embodiment of the invention is shown in FIG. 3a-3b. With reference to FIG. 3a, the substrate to be handled 1 undergoes direct bonding with the handle substrate 2 coated with the bonding layer 3 made of porous material. With reference to FIG. 3b, after direct bonding, a step is performed for cutting the handle substrate 2 in order to form cuts therein, isolating regions 20 of the handle substrate from each other. Regions of variable widths (5, 10, 20 and 40 mm) have thus been isolated. Sealed areas will be created at the edge of each region. Therefore, with reference to FIG. 3c, annealing at 900 C. for 2 h results in the partial separation of the handle substrate located at the isolated regions 20 of the handle substrate, in this case the regions having a width of greater than or equal to 20 mm. In smaller regions, the width of the sealed area at the edge of the region and the low quantity of gas trapped inside the region do not allow for spontaneous separation at this region.

(49) This partial separation can be exploited so as to only cause disassembly on one central portion of the temporary structure. To achieve this, a cut, for example annular in shape, is made in the handle substrate that separates said central portion from a peripheral portion of the handle substrate. Therefore, potentially after additional thinning of the substrate to be handled 1, a membrane is produced in said substrate 1, tensioned over the non-disassembled peripheral portion of the handle substrate, for example an annular portion.

(50) Similarly, one or more cuts can be made in the substrate to be handled 1. It is therefore possible to cause said substrate 1 to separate directly in the form of chips.

(51) FIG. 4 shows the variation in bonding energy E, measured using the blade insertion method, as a function of the temperature T of the consolidation annealing process (in this case isothermal annealing for two hours) for SiO.sub.2/Si bonding (shown as dotted lines and measurements identified by diamond shapes) and for Si bonding with an initial porosity of 20% (shown as continuous lines and measurements identified by triangle shapes). Below the disassembly temperature T.sub.D (about 830 C.), the bonding energy E is sufficient to allow numerous high-temperature technological methods to be performed (for example dielectric deposition, or thinning). Moreover, this energy does not dissipate, even when approaching the disassembly temperature.