FR2967295A1 - PROCESS FOR PROCESSING A MULTILAYER STRUCTURE - Google Patents

Abstract

The invention relates to a method for treating a multilayer structure (211) comprising a plate (208) bonded to a substrate (210), the plate comprising at least one upper layer (202), a lower layer (201) and a buried oxide layer (204) disposed between the upper layer and the lower layer, a bonding oxide layer (206a) being disposed between the plate and the substrate, the method comprising a subsequent step of etching the plate and , before this subsequent step, the following successive steps: a partial mechanical clipping of the upper layer; - a preliminary preliminary chemical etching; a first partial deoxidation by chemical etching with hydrofluoric acid; - a second preliminary chemical etching; and a second partial deoxidation by chemical etching with hydrofluoric acid.

Description

BACKGROUND OF THE INVENTION The present invention relates to the field of producing multilayer semiconductor structures (also called "multilayer semiconductor waters" in English) made by transferring at least one layer onto a final substrate. Such a layer transfer is obtained by bonding, for example by molecular adhesion, a first plate (or initial substrate) on a second plate (or final substrate), the first plate being generally thinned after bonding. The transferred layer may further comprise all or part of a component or a plurality of microcomponents. The present invention applies more particularly to multilayer structures obtained by bonding, and having, at the level of the bonding interface, a low surface energy (less than 1 J / m 2) such as, for example, SOS type structures (for "Silicon On Sapphire", or "Silicon-on-Sapphire" in English). The term SOS refers to multilayer structures comprising a first silicon plate carried on a crystalline sapphire substrate (AI203). SOS is a technology among the family SOI ("Silicon on Insulator" OR "Silicon-On-Insulator" in English). SOS technology is particularly used in radio frequency applications because of its good performance in terms of electrical insulation and heat dissipation.

The invention relates to the problem of fragments of material which appear undesirably on the exposed surface of the transferred layer during the manufacture of a multilayer structure, of the SOS type for example. This phenomenon of contamination has been observed following a technological step involving chemical etching of at least a portion of an SOS multilayer structure. This technological step may correspond, for example, to a chemical etching performed on the first plate of an SOS multilayer structure during a thinning step. This problem of contamination has been particularly observed when it has not been possible to fully stabilize the bonding interface between the two plates of the SOS multilayer structure. The technique frequently used, during the manufacture of multilayer structures for cleaning the surface of a layer transferred after a chemical etching step, consists of performing a rinsing (or cleaning) step by means of a pressurized jet. In general, a jet of water (or any rinsing solution) is manually applied under pressure to the surface of the plate to be cleaned. However, the Applicant has found that the effectiveness of this technique is limited since it only partially eliminates the fragments present on the surface of the plate to be cleaned. Moreover, this rinsing technique requires human intervention, which limits the industrialization of the rinsing step. There is therefore a need today for a method for preventing such material fragments from contaminating a multilayer structure, especially of the SOS type, during its manufacture.

OBJECT AND SUMMARY OF THE INVENTION For this purpose, the present invention provides a method of treating a multilayer structure, the multilayer structure comprising a plate adhered to a substrate at a bonding interface, the plate comprising at least an upper layer, a lower layer and a buried oxide layer disposed between the upper layer and the lower layer, a bonding oxide layer 25 being further disposed between the plate and the substrate, wherein the method comprises a step subsequent etching of the plate, the method further comprising, before the subsequent step of chemical etching, the following successive steps: a partial mechanical trimming of the upper layer; A first preliminary chemical etching to complete the trimming of the upper layer and to expose a peripheral portion of the buried oxide layer; a first partial deoxidation, by chemical etching with hydrofluoric acid, of the exposed peripheral portion 35 of the buried oxide layer; a second preliminary chemical etching to remove a peripheral portion of the lower layer and to expose a peripheral portion of the bonding oxide layer; and a second partial deoxidation, by hydrofluoric acid etching, of the exposed peripheral portion of the bonding oxide layer. Advantageously, the method of the invention makes it possible to eliminate a peripheral portion of the bonding oxide layer and of the buried oxide layer of a multilayer structure (of the SOS type, for example), starting from from which fragments could otherwise become detached during a subsequent chemical etching step and thus contaminate the surface of the structure. The invention makes it possible in particular to minimize the source of the oxide fragments likely to contaminate the exposed surface of a multilayer structure during a subsequent technological step performed with a chemical etching. In addition, the plate may comprise microcomponents. In this document, the term "microcomponents" means any device or pattern resulting from the technological steps performed on the plates of a multilayer structure. It may be in particular active or passive components, simple contacts or interconnections. Partial mechanical cutting may stop at a distance greater than or equal to 40 μm from the bonding interface, and preferably at a distance between 40 μm and 50 μm from the bonding interface. In this way, it is possible to limit the mechanical stresses generated during mechanical trimming at the bonding interface between the plate and the substrate. This makes it possible in particular to avoid the appearance of delaminations at the bonding interface 30 during mechanical trimming. Moreover, the width of the partial mechanical trimming is preferably equal to the width of a low-bonding crown located at the bonding interface. The method of the invention thus makes it possible to eliminate the peripheral portion of the plate which is poorly or poorly bonded to the substrate, this portion being a source of oxide fragments when a chemical etching is subsequently performed. The multilayer structure may have a surface energy of less than 1 3 / m2 at the bonding interface.

In a particular embodiment, the subsequent etching step corresponds to a stage of chemical thinning of the plate. In this case, the treatment process may further comprise, after the first partial deoxidation and before the chemical etching step, a step of mechanical thinning of the plate. Furthermore, the subsequent chemical etching step can be carried out with a solution of TMAH or a solution of KOH. In a particular embodiment, the first preliminary chemical etching is carried out with a TMAH etching solution diluted to 25% by weight and heated to a temperature of 80 ° C., the duration of the first preliminary chemical etching being between 90 and 150 minutes. In a particular embodiment, the first partial deoxidation is carried out with a hydrofluoric acid solution having a concentration of less than or equal to 10% by weight, the duration of the first partial deoxidation being about 280 seconds. The use of a solution of hydrofluoric acid of such a concentration makes it possible to optimize the control of the progress of the deoxidation and to avoid undesirable delaminations which may occur at the interface between the plate and the substrate. In a particular embodiment, the second preliminary chemical etching is carried out with a TMAH etching solution diluted to 25% by weight and heated to a temperature of 800C, the duration of the second preliminary chemical etching being less than or equal to 30 minutes. . In a particular embodiment, the second partial deoxidation is carried out with a hydrofluoric acid solution having a concentration of less than or equal to 10% by weight, the duration of the second partial deoxidation being about 70 seconds.

As indicated above, the use in particular of a hydrofluoric acid solution concentrated to 10% by weight or less is advantageous. Moreover, the plate is for example of the SOI type. In a particular embodiment, the substrate is able to withstand the first and second partial deoxidation or covered with a nitride layer or an oxide layer capable of withstanding the first and second partial deoxidations. Correlatively, the invention relates to a method of manufacturing a multilayer structure comprising the following successive steps: forming a layer of bonding oxide on at least one plate or a substrate; bonding the plate to the substrate by means of the bonding oxide layer so as to form the multilayer structure; annealing of the multilayer structure; the method comprising, after the annealing, the removal of a peripheral portion of the plate according to the treatment method defined above. In a particular embodiment, the forming step is configured so that an oxide layer comprising the bonding oxide layer covers the entire volume of the plate. In this particular mode, a protective oxide layer then protects the upper surface of the plate during the first preliminary etching. This protection is advantageous in that it makes it possible to avoid the presence of acid residues on the upper surface of the plate once the first partial deoxidation has been carried out, these residues being at the origin of undesirable heating when subsequently performs a mechanical thinning. BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the present invention will be apparent from the description given below, with reference to the accompanying drawings which illustrate an embodiment thereof which is not limiting in any way. In the figures: FIGS. 1A to ID are cross-sectional views schematically showing a known embodiment of an SOS multilayer structure; FIG. 2 represents, in the form of a flowchart, the main steps of the method illustrated in FIGS. 1A to 1D; Figures 3a to 3i show, schematically, a method of treatment and a manufacturing method according to a particular embodiment of the invention; and Fig. 4 shows, in flowchart form, the main steps of the methods of the invention according to the embodiment illustrated in Figs. 3a-3i.

DETAILED DESCRIPTION OF THE EMBODIMENT The present invention generally applies to the partial deoxidation of a multilayer structure so as to minimize the source of material fragments likely to appear on the exposed surface of the multilayer structure. the structure during its manufacturing process. The invention applies in particular, but not exclusively, to multilayer structures of the SOS type. An SOS multilayer structure 20 is made by gluing a first plate to a second sapphire plate or substrate constituting the support of the first plate, a layer of bonding oxide being present between the two plates. The plates making up a multilayer structure are generally in the form of slices or "wafers" with a generally circular contour and may have different diameters, in particular diameters of 100 mm, 150 mm, 200 mm or 300 mm. However, it can also be plates of any shape, such as rectangular plates, for example. These plates preferably have a chamfered edge, namely an edge comprising an upper chamfer and a lower chamfer. These chamfers are generally rounded. However, the plates may have chamfers or edge-shaped of different shapes such as a bevel shape. The role of these chamfers is to facilitate the handling of the plates and to avoid breakage of edges that could occur if these edges were protruding, such breaks being sources of particle contamination of the surfaces of the plates. An example of a known manufacturing method of an SOS multilayer structure is now described with reference to FIGS. 1A-ID and 2. As shown in FIGS. 1A-1D, an SOS multilayer structure 111 is formed by assembling a first plate 108 with a second plate (or substrate) 110 of crystalline sapphire (step Ell). In this example, the first plate 108 corresponds to an SOI structure comprising a buried oxide layer 104 interposed between two silicon layers (the upper layer 102 and the lower layer 101). Generally the lower layer 101 corresponds to the thin layer of the SOI used. The first and second plates 108 and 110 have the same diameter here. They could, however, have different diameters. In the example described here, the entire surface of the first plate 108 is oxidized, before bonding to the second plate 110. This oxidation is carried out by means of a thermal treatment in an oxidizing medium and allows forming an oxide layer 106 (called bonding oxide layer) over the entire surface of the first plate 108 before bonding to the second plate 110. In this case, the oxide layer 106 is a SiO2 layer . A bonding oxide layer 106 is thus found at the bonding interface between the first plate 108 and the substrate 110 and allows better bonding therebetween. According to a first alternative, a layer of bonding oxide may be deposited on the face to be bonded (called the bonding face) of the first plate 108, and this before bonding to the second plate 110. According to another alternative, it is possible to before bonding the two plates 108 and 110, forming a bonding oxide layer on the bonding face of the substrate 110, or alternatively forming a bonding oxide layer on the bonding face of each of the two The above alternatives allow, as in the example of FIG. 1B, to insert a layer of bonding oxide between the two plates 10e 110 before bonding. Moreover, the first plate 108 presents a chamfered edge, namely an edge comprising an upper chamfer 107a and a lower chamfer 107b. The second plate 110 likewise has an edge comprising an upper chamfer 109a and a lower chamfer 109b. In the example described here, the assembly of the first plate 108 and the substrate 110 is achieved by means of the molecular adhesion technique well known to those skilled in the art. Other bonding techniques can however be used, such as anodic bonding, metallic bonding, or adhesive bonding. As a reminder, the principle of molecular bonding is based on the direct contact of two surfaces, that is to say without the use of a specific material (glue, wax, solder, etc.). Such an operation requires that the surfaces to be bonded are sufficiently smooth, free of particles or contamination, and that they are sufficiently close together to allow initiation of contact, typically at a distance of less than a few nanometers. In this case, the attractive forces between the two surfaces are high enough to cause the molecular adhesion (bonding induced by the set of attractive forces (Van Der Waals forces) of electronic interaction between atoms or molecules of the two surfaces to be bonded. ). Note that the first plate 108 may comprise microcomponents (not shown in the figures) at its bonding face with the second plate 110, particularly in the case of the three-dimensional integration technology of components (3D-integration) which requires the transfer of one or more layers of microcomponents on a final support, or in the case of transfer of circuits such as in the manufacture of illuminated imagers on the rear face. Once the step El 1 bonding performed, the multilayer structure 111 undergoes a moderate annealing of the bonding interface reinforcement (for example 1000C to 4000C for 2 hours) which aims to strengthen the bonding between the first plate 108 and the second plate 110 (step E12). In this annealing, the first plate 108 is generally thinned so as to form a transferred layer of a determined epoxy (by about 60 μm) on the support plate 110. This thinning operation generally comprises a step of etching the upper layer 102 opposite to the lower layer 101 turned on the side of the support plate 110. However, the Applicant has observed the appearance of fragments of unwanted materials on the exposed surface. of the first plate 108 following a thinning step involving a chemical phase. An in-depth study made it possible to highlight the mechanism of formation of these fragments. The formation mechanism is described in more detail with reference to FIGS. 1C and 1D, which illustrate an exemplary thinning step of the first plate 108. The thinning step comprises in this example two distinct substeps. The first plate 108 is first thinned mechanically using a grinding wheel or any other tool able to mechanically use the material of the first plate 108 ("grinding" in English) (substep E13). This first sub-step thinning eliminates most of the upper layer 102 so as to retain a residual layer 112 (Figure 1C). A second sub-step of thinning is then performed corresponding to a chemical etching of the residual layer 112 (sub-step E14). During this second substep, the multilayer structure 111 is placed in a bath comprising an etching solution 120 (FIG. In the example described here, the etching solution used is a TMAH solution for etching silicon from the first plate 108. Other etching solutions can however be envisaged, these being chosen in particular as a function of the composition of the first plate to thin. For silicon thinning plates, it is possible, for example, to use a solution of TMAH or a solution of KOH. The buried oxide layer 104 interposed between the layers 101 and 102 of the first plate 108 serves as a stop layer during the chemical etching which is then interrupted at the level of the oxide layer 104. The chemical etching thus makes it possible to However, the Applicant has observed that at the end of the etching, fragments of material 118 were present on the exposed surface of the first plate 108. These fragments 118 typically have a size greater than 2. pm.

A study has shown that these fragments of material are debris from the edges of the first plate. More specifically, because of the presence of chamfered edges on the first and second plates, the bonding force in the vicinity of the periphery of the two plates is limited. Despite the moderate annealing step E12 of reinforcing the bonding interface, an annular portion at the periphery of the first plate 108 situated in the vicinity of the lower chamfer 107b has a poor bonding (or even the total absence of bonding) on the second Plate 110. The Applicant has observed that, during the chemical etching of the thinning step E14, the etching solution 120 tends to etch the edges of the first plate 108 as well as the bonding oxide layer laterally. 106. This lateral etching action notably causes uncontrolled breaks in the bonding oxide layer 106, and more particularly at the peripheral portion of the oxide layer 106 which is exposed to the attack of the solution. This breakage phenomenon thus results in the formation of debris or fragments of oxides 118 (of SiO 2, in the present case) originating, at least in part, from this peripheral portion of the body. These oxide fragments are then deposited in part on the exposed surface of the first thinned plate 108 (FIG. ID) during the chemical etching E14. It should be noted that, under the lateral etching action of the etching solution 120, fragments of oxide, silicon and / or circuit originating from the edges of the first plate 108 are also liable to pollute the exposed surface of the etching solution 120. the latter. The Applicant has therefore developed a treatment process for removing a peripheral portion of the bonding oxide layer 106 from the multilayer structure 111. An example of implementation of the treatment method according to the invention, and more generally, an exemplary implementation of the manufacturing method according to the invention is now described with reference to FIGS. 3a to 3i and 4. FIGS. 3a and 3b show a multilayer structure 211 identical to the structure 111 represented in FIG. 18, namely an SOS multilayer structure obtained at the end of the El 1 bonding and E12 annealing steps as described above. FIG. 3b represents, in more detail, the structure 211 illustrated in FIG. 3a at the peripheral edge of the plates 208 and 210. More specifically, the multilayer structure 211 considered consists of a first plate 208 bonded to a second plate ( or substrate) 210 in sapphire, a bonding oxide layer 206a being disposed at the bonding interface 205 between the two plates 208 and 210. In this example, the first plate 208 is an SOI structure: it is constituted a buried oxide layer 204 (identical to the layer 104) interposed between two silicon layers, namely an upper layer 202 (identical to the layer 102) and a lower layer 201 (identical to the layer 101). In addition, in this example, the bonding oxide layer 206a was obtained by oxidatively forming an oxide layer over the entire volume of the first plate 208 before being bonded to the second plate 210. The portion of this oxide layer followed at the bonding interface 205 is denoted 206a, this part corresponding to the bonding oxide layer which is in contact with the plates 208 and 210. The remaining part of this layer of oxide covering all the surface of the first plate 208 (ie the part other than the bonding layer 206a) corresponds to a protective oxide layer denoted 206b in the remainder of this document. In this particular case, the thickness of the bonding oxide layer 206a and the protective oxide layer 206b is about 500 Å (for Angstroms). In addition, the lower layer 201 and the upper layer 202 respectively have thicknesses of 750 Å and 625 Å. The buried oxide layer 204 has in this example a thickness of about 2000 Å. Note that the second plate 210 is not necessarily sapphire. Alternatively, the plate 210 may, for example, be silicon. This same first plate 208 is not necessarily SOI type but may correspond to any stack of layers comprise a buried layer. As indicated prucedetnment, the invention applies more generally to multilayer structures obtained by gluing, and in particular those having a low surface energy (less than 1 3 / m2) at their bonding interface. In this example, the first plate 208 also includes an upper bevel 207a and a lower bevel 207b identical to the bevels 107a and 107b, respectively. Substrate 210 also includes chamfers similar to chamfers 207a and 207b. Due to the presence of chamfered edges on the first and second plates 208 and 210, the bonding force in the vicinity of the periphery of the two plates is reduced or even zero. Despite the moderate annealing step E12 of reinforcing the bonding interface 205, an annular portion at the periphery of the first plate 208 situated in the vicinity of the lower chamfer 207b has a poor bond (or even the total absence of bonding) on the second plate 210. LC is noted the width of a crown of weak bonding, this ring corresponding to an annular portion of the bonding interface 205 located at the periphery and having a weak bond or poor quality (or the total absence lift-off). In the present case, it is considered that this crown of width LC extends into the space between the chamfered edges of the plates 208 and 210 where the bonding force is zero (total separation of the two plates). By "weak or poor quality bonding" is meant here a region of the bonding interface having a bonding force F less than or equal to a minimum required bonding force (denoted by Fmin). This minimum bonding force Fmin is, for example, set at 700 m 3 / m 2. In addition, in the case considered here, the width LC is, for example, about 2 mm. Moreover, as indicated above with reference to FIGS. 1A and 1B, other embodiments may be implemented to provide a bonding oxide layer 206a between the plates 208 and 210. It will be noted for example that the protective oxide layer 206b is optional. In fact, it is thus possible to form only one bonding oxide layer 35 on the bonding surface of the first plate 208 and / or on the bonding surface of the second plate 210, before bonding the two plates. In addition, when the substrate 210 is made of silicon, for example, it is possible to oxidize the entire surface of the substrate before bonding with the first plate 208. In this case, care should be taken that the protection thus formed on the exposed surface of the substrate 210 is sufficiently thick to withstand the etchings used in the treatment method of the invention. Once the annealing step E12 has been performed, the multilayer structure 211 undergoes a partial mechanical clipping (step E20) of the upper layer 202 ("edge grinding" in English) (see FIG. 3C). During this step E20, a peripheral annular portion of the plate 208 is removed in the vicinity of the upper chamfer 207a with a grinding wheel (or other suitable abrasive tool). To do this, the grinding wheel is applied to the chamfered edge 207a of the plate 208 to remove a peripheral portion of the protective oxide layer 206b at the edge 207a and then an underlying peripheral portion of the top layer. 202. This cutting step E20 is said to be partial because the grinding action is stopped at a distance H from the bonding interface 205 between the first plate 208 and the substrate 210, so that the upper layer 202 exhibits a step-shaped profile (Figure 3C). In general, the mechanical trimming E20 ends at a reasonable distance H from the bonding interface 205 in order to avoid the application of excessive mechanical stresses at the bonding interface 205. partial trimming is performed on a too large depth (ie up to a distance H too short), delaminations are for example likely to appear at the bonding interface 205. Therefore, the height H is generally chosen in such a way that the risk of delamination remains negligible. The height H may be chosen depending in particular on the materials of the first plate 202 and the second plate 210, the bonding force between these two plates and the procedure adopted during the trimming (speed of rotation of the wheel, force of application, type of grinding wheel ...).

In the example considered here, the partial mechanical clipping E20 is carried out so that the height H is greater than or equal to 40 dam, and preferably between 40 pm and 50 dam. Furthermore, it is preferable to configure the partial mechanical clipping E20 so that the width (denoted LD) of the cutout peripheral portion is relatively small. Indeed, the larger the width LD, the more the surface of the final multilayer structure will be reduced, which reduces the commercial value of it. Typically, the trimming width LD is set to be equal to or greater than the LC crown width. In this way, the entire peripheral portion of the plate 208 having a bad bond (or the total absence of bonding) on the substrate 210 will be eliminated at the end of the next step E40 (described in more detail later). After the partial mechanical cutting step E20, a first preliminary chemical etching is performed on the multilayer structure 211 (step E25). During this step E25, the multilayer structure 211 is immersed for a time Ti in an etching solution denoted S1. When the multilayer structure 211 is immersed, the solution S1 mainly etches the exposed peripheral part of the upper layer 202, that is to say the part which is no longer protected on the surface by the protective oxide layer 206b ( see figure 3D). This etching is therefore possible thanks to the etching surface that was previously opened in the upper layer 202 during the partial cutting step E20. The etching action of the solution SI is done primarily vertically, that is to say in the direction of the bonding interface 205. This is explained in particular by the fact that the solution S1 is a solution of chemical attack according to preferential crystalline planes.

The first preliminary chemical etching E25 thus completes the partial clipping performed in the previous step E20. Step E25 makes it possible to eliminate the residual peripheral portion of the upper layer 202 which had not been removed during step E20. The buried oxide layer 204 serves here as a stop layer vis-à-vis the etching action of the solution SI used.

The SI etch solution may correspond to a TMAH solution or to a KOH solution. In the example described here, the solution SI used is a solution of TMAH diluted to 25% and heated to a temperature of about 800C. Those skilled in the art will nevertheless understand that other etching solutions and procedures are conceivable within the scope of the present invention. Moreover, the time Ti is chosen as a function, in particular, of the type of the solution S1 used so that the entire residual peripheral portion not cut off from the upper layer 202 (ie the outer portion 10 not cut off during the step E20) is eliminated. at the end of step E25. In this example, Ti is preferably between 90 and 150 minutes. It should be noted that, during step E25, the etching action of the solution S1 on the protective oxide layer 206b is negligible. This is why, at the end of step E25, there remains in particular the portion 206c of the protective oxide layer 206b, that is to say the portion which covered the upper layer 202 and which had not not eliminated during the partial mechanical cutting step E20. It should be further noted that in this example, the protective oxide layer 206b protects the vast majority of the upper surface of the first plate 202 during the chemical etching step E25. As described in more detail later, this protection makes it possible to improve the step E45 of mechanical thinning to come. However, as already explained, such protection is not essential to carry out the present invention. After step E25, a first partial deoxidation E30 of the multilayer structure 211 is carried out with hydrofluoric acid (HF) (FIG. 3E). During this step E30, the multilayer structure 211 is immersed for a time T2 in an etching solution S2 having a non-zero concentration of CHF2 in hydrofluoric acid. During this step, the hydrofluoric acid solution S2 attacks and eliminates the entire protective layer 206b (FIG. 3E). Thus, the portions of the protective oxide layer 206b located at the plate edge 208 and on the upper surface of the plate 208 are removed in step E30. In addition, during step E30, the solution S2 is introduced between the plates 208 and 210 at the level of the low-sticking ring at the bonding interface 205. The first partial deoxidation E30 thus eliminates a portion accessible peripheral of the bonding oxide layer 206a in the vicinity of the lower bevel 207b. It should be noted that once the portion of the protective oxide layer 206b has been removed at the edge of the plate, the edge of the buried oxide layer 204 is no longer protected with respect to the etching action of the solution S2. Therefore, during this step E30, an exposed peripheral portion of the buried oxide layer 204 is also eliminated, thereby discovering the underlying portion of the lower layer 201. In the example considered here, the CHF2 concentration in hydrofluoric acid amounts to 10% by weight. In addition, the time T2 rises in this example to about 280 seconds. Note that other CHF2 concentrations are however possible. The concentration CHF 2 is preferably less than or equal to 10% (by weight). The time T2 is then set according to the concentration CHF2 (OR conversely) so as to avoid any undesirable detachments at the bonding interface 205. It is indeed necessary to set the parameters T2 and CHF2 in such a way that that the etching with hydrofluoric acid is relatively slow and allows: to precisely control the progress of the deoxidation during step E30, and to limit undesired lateral etching. Excessive CHF2 concentration can make the deoxidation action difficult to control. If T2 is excessive, solution S2 infiltrates too deeply at bonding interface 205 between plates 208 and 210, thereby degrading the quality of bonding between these two plates. Once the first partial deoxidation E30 has been completed, a second preliminary chemical etching E35 is carried out (FIG. 3F). During this step E35, the multilayer structure 211 is imne for a time T3 in an etching solution denoted 53.

During this step, the solution S3 mainly attacks the exposed peripheral portion of the lower layer 201, that is to say the part which is no longer protected on the surface by the buried oxide layer 204. The exposed peripheral portion of the lower layer 201 is thus eliminated during the second preliminary etching E35. This attack is made possible by the etching surface previously opened at the periphery of the lower layer 201 during step E30. In this example, the etching solution S3 is identical to the solution S1, namely a solution of TMAH diluted at 25 ° C. and heated to 80 ° C. As for the step E25, the skilled person will however understand that other types of solution S3 and other operating conditions (temperature) are possible within the scope of the present invention. It will be noted that during this second preliminary chemical etching E35, the upper layer 202 is little or not impaired by the etching action of the solution S3. The duration T3 is indeed relatively limited, and preferably less than or equal to 15 minutes. In addition, in the present case, the thickness of the upper layer 202 is much greater than that of the lower layer 201. It can therefore be considered that the etching action on the upper layer 202 is negligible when the step E35 of etching. In the example considered here, the upper layer 202 thus retains a thickness of about 625 μm at the end of step E35. After step E35, a second partial deoxidation E40 of the multilayer structure 211 is carried out with hydrofluoric acid (FIG. 3G). During this step E40, the multilayer structure 211 is immersed for a time T4 in an etching solution S4 having a non-zero concentration of CHF4 in hydrofluoric acid. In this step, the S4 hydrofluoric acid solution etches and removes the entire exposed portion of the bonding oxide layer 206a, i.e., the peripheral portion which is no longer protected by the lower layer 201 This etching is made possible by the etching surface previously opened on the residual bonding oxide layer 206a during step E35. In the present case, the etching carried out at the edges L-2puses of the buried oxide layer 204 is considered negligible.

Moreover, in the example considered here, the CFiR concentration of hydrofluoric acid is 10 ° k by weight, so that CHF2 CHF4. In addition, the time T4 rises in this example to about 70 seconds. Note that other CHF4 concentrations are however possible. The concentration CHF4 is preferably less than or equal to 10% (by weight). The time T4 is then fixed as a function of the concentration CHF2 (or vice versa) so as to avoid any undesirable detachments at the bonding interface 205. In the same manner as for the parameters T2 and CHF2 during the step E30 it is necessary to set the parameters T4 and CHF4 so that the etching with hydrofluoric acid is relatively slow during step E40. In this way, it is possible to precisely control the progress of deoxidation. The time T4 is thus chosen so that the solution S4 does not infiltrate too deeply at the bonding interface 205 in order to maintain a good bonding quality between the two plates 208 and 210. As illustrated in FIG. 3G, the edges of the upper layer 202 and the lower layer 204 are aligned at the end of step E40. The realization of steps E20 to E40 thus makes it possible to perform a complete trimming of the first plate 208, this trimming allowing to eliminate a peripheral portion of width LD of the plate 208. In this embodiment, a step of mechanical thinning E45 is then performed on the multilayer structure 211 (Figure 3H). During this step, a grinding wheel (or any other suitable abrasive tool) mechanically thins the upper layer 202. As for the partial mechanical cutting step E20, it is preferable to stop the grinding wheel at a reasonable distance from the ground. bonding interface 205 in order not to apply mechanical stresses that could deteriorate the quality of bonding between the plates 208 and 210.

Typically, the mechanical thinning E45 ends at the distance H previously mentioned so as to retain only a residual portion 212 of the upper layer 202 (Figure 3H). In addition, as indicated above, the majority of the upper surface of the upper layer 202 was protected by the protective oxide layer 206b during the first preliminary etching E25. This protection is advantageous in that it allows the upper layer 202 not to be in contact with the solution S1 during the step E25. In this case, the SI solution is a TMAH solution. However, because of its viscosity, this type of etching solution is generally difficult to rinse once the etching step completed.

In this embodiment, the upper layer 202 is therefore exposed only to the second preliminary etching E35 whose duration T3 is here much lower than Ti. The presence of the protective oxide layer 206b on the entire upper surface of the plate 208 during the step E25 is therefore advantageous in that it makes it possible to limit the amount of TMAH residues likely to be present on the surface. exposed surface of the upper layer 202 during the mechanical thinning step E45. The Applicant has indeed observed that, in step E45, such residues can cause undesirable heating of the grinding wheel, thus reducing its attack efficiency. Once the mechanical thinning step E45 has been completed, a chemical thinning step E50 is carried out in order to finalize the thinning of the first plate 208. During this step 45, the multilayer structure 211 is immersed for a period of time. T5 in an S5 etching solution to remove all the residual upper layer 212. In the example described here, this solution S5 is a solution of TMAH diluted to 25% and heated to 80 ° C. In addition, the time T5 is set between 3 and 4 hours, and is for example 3 hours and 45 minutes. After the chemical thinning step E50, a rinsing step (not shown) is generally performed. Furthermore, as indicated above, the realization of steps E20 to E40 makes it possible to perform a complete trimming of the first plate 208, this trimming making it possible to eliminate a peripheral portion 30 of width LD of the plate 208. However, the width LD is preferably equal to or greater than the width LC of the low-sticking ring at the bonding interface 205. The steps E20 to E40 thus make it possible to eliminate the peripheral portion of the plate 208 which is in the vicinity of this 35 low bonding crown. The elimination of this portion of plate is advantageous because, as shown by the studies of the Applicant, this portion, and more particularly the corresponding portions of the protective oxide layers 206b, bonding oxide 206a and buried oxide 204, are at the origin of the formation of oxide fragments contaminating the surface of the multilayer structure 211 during a chemical etching step. The elimination of the peripheral portions of the layers 204, 206a and 206b thus advantageously makes it possible to considerably reduce the oxide fragments that may deposit on the exposed surface of the structure 211 during chemical thinning E50.

In other words, the invention advantageously makes it possible to minimize the source of the oxide fragments liable to contaminate the exposed surface of a multilayer structure during a subsequent etching step, such as step E50 by example. However, it will be understood that the thinning steps E45 and E50 are not mandatory and may be replaced by any technological step involving chemical etching. Such a step may, for example, be carried out with a solution of TMAH or a KOH solution and may, for example, have the object of forming one or more microcomponents (in the first plate 208 for example). In addition, in an alternative to the embodiment described above, the mechanical thinning step E45 is performed between step E30 and E35. This alternative is advantageous in that it allows the mechanical thinning before the surface of the upper layer 202 comes into contact with the solution S3 during the second preliminary etching E35. In this way, during step E45, any heating of the grinding wheel likely to be caused by the presence of residues (of TMAH, for example) on the surface of the upper layer 202 is avoided. Moreover, the Applicant has found that the mechanical stresses generated during the mechanical thinning step E45 generally lead to an enlargement of the ring at the bonding interface 205. The realization of step E45 before the second partial deoxidation E40 (as required in this alternative) thus optimizes the access of hydrofluoric acid to the bonding interface between the two plates 208 and 210, so as to eliminate as much potential sources of contamination. More generally, the treatment method of the invention is advantageous in that its application parameters (in particular the concentrations CHF2 and CHF4, as well as the etching times T1 to T4) are controllable and reproducible. This technique can be optimized and automated for industrial purposes. Steps E20 to E40 can indeed be integrated, before any step of chemical etching, in a conventional manufacturing process of a multilayer structure, SOS type for example. The sapphire substrate 210 is advantageous in that it is capable of withstanding the successive chemical etchings, namely the etchings carried out during the steps E20 to E40. Note also that the sapphire substrate 210 can contain different types of impurities in the form of traces (titanium, iron, vanadium ...) and in any concentrations. The substrate 210 may however be formed of a material other than sapphire provided that it is resistant to the chemical attacks mentioned above. Alternatively, the substrate 210 may be formed of any material covered with a protective layer (oxide or nitride, for example) sufficiently thick so as not to be completely eliminated at the end of the various etchings implemented in the method of the invention. The substrate 210 may, for example, be covered with an oxide layer whose thickness is of the order of 2000 Å.

The treatment method according to the invention is applicable to all types of multilayer structure obtained by bonding, and more particularly to SOS multilayer structures whose plates have chamfered edges (or edge drops of any shape) and / or or that can not be brought to high temperatures in order to perfectly stabilize the bonding interface.

Claims (15)

1. A method of treating a multilayer structure (211), said multilayer structure comprising a plate (208) bonded to a substrate (210) at a bonding interface (205), said plate comprising at least one upper layer (202), a lower layer (201) and a buried oxide layer (204) disposed between the upper layer and the lower layer, a bonding oxide layer (206a) being further disposed between the plate and the substrate, wherein the method comprises a subsequent step (E50) of etching said plate, the method being characterized in that it further comprises, before the subsequent step of chemical etching, the following successive steps: a clipping partial mechanics (E20) of said upper layer; a first preliminary chemical etching (E25) for completing the trimming of said top layer and for exposing a peripheral portion of the buried oxide layer; a first partial deoxidation (E30), by hydrofluoric acid etching, of said exposed peripheral portion of the buried oxide layer; a second preliminary chemical etching (E35) for removing a peripheral portion of said lower layer and for exposing a peripheral portion of the bonding oxide layer; and a second partial deoxidation (E40), by hydrofluoric acid etching, of said exposed peripheral layer of bonding oxide layer. 30 The method of claim 1, wherein the partial mechanical cutting stops at a distance (Fi) from the bonding interface of between 40 μm and 50 μm. 3. The method of claim 1 or 2, wherein the width (LD) of the partial mechanical clipping is equal to the width of a low-bonding crown located at said bonding interface. 4. Method according to any one of claims 1 to 3, wherein the multilayer structure has at the bonding interface a surface energy of less than 1 3 / m2. 5. A process according to any one of claims 1 to 4, wherein the subsequent etching step corresponds to a step of chemically thinning said plate. The method of claim 5 further comprising, after the first partial deoxidation and prior to the chemical etching step, a step (E45) of mechanical thinning of the plate. The method of any one of claims 1 to 6, wherein the subsequent chemical etching step is performed with a solution of TMAH or a solution of KOH. 20 8. Process according to any one of claims 1 to 7, wherein the first preliminary chemical etching is carried out with a TMAH etching solution diluted to 25% by weight and heated to a temperature of 800C, the duration of said first etching Preliminary being between 90 and 150 minutes. The process according to any one of claims 1 to 8, wherein the first partial deoxidation is carried out with a hydrofluoric acid solution having a concentration of less than or equal to 10% by weight, the duration of said first partial deoxidation being about 280 seconds. 10. A process according to any one of claims 1 to 9, wherein the second preliminary chemical etching is carried out with a 2 wt% diluted TMAH etching solution heated to a temperature of 80 ° C, the duration of said second preliminary etching being less than or equal to 15 minutes. 11. A method according to any one of claims 1 to 10, wherein the second partial deoxidation is carried out with a hydrofluoric acid solution having a concentration of less than or equal to 10% by weight, the duration of said second partial deoxidation being About 70 seconds. 10 The method of any one of claims 1 to 11, wherein the plate (208) is of the SOI type. 13. A method according to any one of claims 1 to 12, wherein the substrate is able to withstand said first and second partial deoxidation or coated with a nitride layer or an oxide layer capable of withstanding said first and second partial deoxidations. A method of manufacturing a multilayer structure (211) comprising the following successive steps: forming a bonding oxide layer (206a) on at least one plate (208) or substrate (210); bonding (Ell) said plate to said substrate by means of the bonding oxide layer to form said multilayer structure; annealing (E12) of said multilayer structure; said method being characterized by comprising, after annealing, the removal of a peripheral portion of said plate according to the treatment method defined in any one of 0 claims 1 to The manufacturing method according to claim 14, said formation being configured so that an oxide layer (206a, 206b) comprising the bonding oxide layer covers the entire volume of said plate.