Method of limiting lacunary distribution in a heterostructure

Technical field and prior art

p0001The present invention relates to the field of semiconductor plates, also called "wafer". The invention relates more particularly to semiconductor plates made from heterostructures comprising a first layer of semiconductor material on a second layer or a substrate in another generally insulating material. Such heterostructures can be, for example, type SiGe / Si, that is to say comprise a layer of silicon-germanium (SiGe) on a silicon substrate.

p0002In the case of a type heterostructure SiGe / Si, the latter can be used directly to form a layer of semiconductor material such as in a SiGeOI type structure (silicon-germanium (SiGe) on insulator) or be used as the epitaxial layer in particular for forming a strained silicon layer as in the embodiment of a structure sSOI type (strained silicon on insulator).

p0003Heterostructures type SiGe / Si or with a strained silicon layer (sSi) are relevant today more and more marked in the field of semiconductors. In fact, such structures, thanks to the presence of germanium or so due to the constraint of the material, exhibit interesting electrical characteristics as standard structures made of silicon. The quality of surface films of these semiconductor structures is of great importance. In particular, the absence of defects and contaminants on the surface or so in thickness are parameters to optimize, in view of the manufacture of future components.

p0004If for example the production of a type of sSOI substrate in the Smart Cut ™ technology (particularly described in the document <patcit id="pcit0001" dnum="US5374564A"><text>US 5374564</text></patcit> or in the article by <nplcit id="ncit0001" npl-type="s"><text>AJ Auberton-Hervé et al. entitled "Why can Smart-Cut Change the Future of Microelectronics?", Int. Journal of High Speed ​​Electronics and Systems, Vol.10, No.1, 2000, p.131-146</text></nplcit>), A first step is to realize a donor substrate formed by a type of heterostructure Si / SiGe / sSi (Figure 1A). The manufacture of the donor substrate comprises, after growing a SiGe buffer layer on a silicon support substrate, achieving a layer of relaxed SiGe through the SiGe buffer layer. then forming a layer of strained silicon (sSi) on the relaxed SiGe layer. The concentration of Ge in the relaxed layer is typically of the order of 20%, but can reach up to 100% depending on the desired degree of stress in the silicon film.

p0005Once the layer of sSi formed and according to the Smart Cut ™ technology, implanting atomic species in the relaxed SiGe layer at a settlement area and in intimate contact we put the face of the layer with sSi a supporting substrate (typically a Si substrate). Then cleaves the SiGe layer at the implantation zone to transfer the portion between the surface subjected to implantation and the implantation zone (ie the layer of? Si and part of the layer relaxed SiGe) on the receiver substrate.

p0006After removal of the remaining SiGe remaining above the layer of? Si, ​​a sSOI structure is thus obtained with a layer of? Si on one side of the support substrate (Figure 1B).

p0007Achieving sSOI structure according to the Smart Cut ™ technology is particularly described in the document <patcit id="pcit0002" dnum="US6953736B"><text>US 6953736</text></patcit>.

p0008This type of manufacturing process involves treatments that lead to degradation resulting from the diffusion of germanium elements within the structure (2A to 2C). Indeed, it was observed that the heat treatments involved in the formation on the donor substrate of the strained silicon layer and the oxide layer (Figure 2B) and / or the transfer layers and SiGe sSi ( 2C), contribute to the diffusion of germanium elements in the strained silicon layer. Smart Cut ™ technology requires heat treatments such as the densification of the deposited oxide, the heat treatment of "splitting" or weakening, any post heat treatment "splitting" before the etching (pre-stabilization of reinforcement the bonding interface at about 800 ° C for several hours). These heat treatments are important and can not be limited to avoid the spread of particular elements germanium concentration exceeds 20%.

p0009The diffusion of a germanium fraction of the elements of the SiGe layer in the layer of? Si causes a lack of demarcation between the SiGe layer and the? Si, ​​which causes problems to perform selective etching. Accordingly, the passage area of ​​a SiGe to a silicon region (eg. Change in concentration of Ge from 40% to 0%) does not occur abruptly but extends over a certain thickness by diffusion of germanium in the strained silicon layer adjacent.

p0010Also, the selective etching of germanium at this layer must be extended over a long duration to remove all present germanium. This excessive extension of the etching leads to the formation of a rough surface post etching, or even to the formation of HF defects, because the withdrawal of the entire transitional zone containing germanium leads to Overwriting the strained silicon layer, in particular level defect or area of ​​weakness (dislocations, crystal defects, impurities or contaminants, nonuniformities in thickness) in the transferred layer (called "HF" defect defects in the semiconductor active layer of the sSOI structure, here the ? Si layer, which extend from the surface of this layer into the buried oxide and whose presence can be revealed by an after treatment decoration halo in a bath of hydrofluoric acid (HF)).

p0011Due to the fineness of the active layer of strained silicon (of the order of 200 Å to SiGe to 20% Ge), it is important to be able to control with great precision the quality of this layer.

p0012Studies have shown a direct relationship between the distribution of species within SiGe structures and the presence of point defects gaps type and / or interstitials.

p0013As shown in Figure 3A, a point defect gap type corresponds to a site A (gap) of a lattice 10 which is not occupied. The diffusion mechanism making use of point defects such gaps (incomplete mechanism) is the occupation of a loophole by a neighboring atom 11 that can "jump" on this site, showing a gap site he just leave the site B in Figure 3B. Therefore, in a type of heterostructure Si / SiGe, the presence of gaps in the crystal lattice combined with the application of heat treatment will cause a chain of hops between the gaps movement of germanium atoms in the structure and thus achieve dissemination, distribution called "deficient in fashion."

p0014An interstitial point defect type is an interstitial atom jumping from interstitial site in interstitial site (ie websites between substitutional sites in the crystal lattice). One speaks in this case of direct interstitial mechanism. However, when considered the atom may be in substitutional and interstitial position, the diffusion mechanism becomes an interstitial mechanism called "indirect" (or "interstitialcy"). In this case, as illustrated in Figures 4A to 4C, when an atom critsallin 22 of a network 20 is positioned in a substitution site, it can not "jump" so that an interstitial 21 comes into position close (Figure 4A ) and the hunting of its site (Figure 4B), putting himself in the interstitial position (Figure 4C). 22 The atom can then "jump" to any site neighbor substitutional, thereby creating an interstitial default.

p0015In the document <nplcit id="ncit0002" npl-type="s"><text>Griglione et al. "Diffusion of Ge in Si 1-x Ge x / Si single quantum wells in inert and oxidizing ambients", JAP, 88, 3, 1366-1372, August 2000</text></nplcit>The authors studied the diffusion of germanium in a heterostructure Si / SiGe / Si in an oxidizing atmosphere and in an inert atmosphere (Ar / N₂). The results show that the germanium diffusion profiles are the same regardless of the natur e of the environment and the applied temperature.

p0016According to this document, it appears that the presence of gaps mainly promotes the diffusion of germanium while the presence of interstitial has no major role in this broadcast.

p0017This diffusion phenomenon in patchy fashion was also observed in heterostructures other than type SiGe / Si. For example, in a heterostructure formed of an alloy layer of antimony (Sb), for example If_xsb_there or a layer doped with antimony on a silicon substrate, the elements antimony diffuse almost entirely by incomplete path in the silicon. Similarly, in a heterostructure formed of a tin alloy layer (Sn), for example If_xsn_there or a layer doped with tin on a silicon substrate, the tin provides approximately 60% to 80% by lacunar mode in the silicon substrate.

p0018In general, diffusion in metals is mainly in incomplete mode.

p0019In the case of manufacturing a structure, for example sSOI, according to the technology Smart Cut®, the atomic species implantation step to form an embrittlement layer for the detachment of the implanted layer increases the number gaps present in the layer. Indeed, during the implantation step, nano-bubbles are created in the implanted layer and will evolve into agglomerates gaps during the different annealing applied during the manufacturing process according to the Smart Cut technology while creating @ supersaturation gaps in the substrate. In the case of implanting a layer of germanium, germanium, which broadcasts mainly in "incomplete" mode, will then be positioned in the gaps to spread within the structure.

<u>Summary of the Invention</u>

p0020The invention aims to remedy for the dissemination of the problem in incomplete fashion elements in a heterostructure.

p0021To this end, the invention provides a method of manufacturing a heterostructure comprising at least a first layer of semiconductor material on a second layer of a different material than the first layer, the elements of said semiconductor material being capable of diffusing into the second layer in incomplete mode, characterized in that it comprises an ion implantation step of the first layer to form an embrittlement layer at a predetermined depth in said first layer, said implantation step causing forming gaps in the first layer and an enrichment step interstitial defects in the first layer so as to limit diffusion of said elements of said first layer, the enrichment step being carried out before or after said ion implantation step .

p0022Enriching, that is to say supersaturating and the semiconductor layer interstitial defects, there is a significant amount of void to fill many gaps additional sites (supersaturation) from ion implantation for forming the embrittlement layer. This prevents the diffusion path lacunar elements of semiconductor material of the first layer in this layer and in the second adjacent layer, even during subsequent heat treatments.

p0023According to one aspect of the invention, the first layer is a layer of silicon-germanium (SiGe) and the second layer is a silicon substrate, the ion implantation step being performed in the SiGe layer to form a layer of embrittlement to a predetermined depth in said SiGe layer, said SiGe layer being enriched in interstitial defect in the enrichment step.

p0024Enriching (ie in supersaturating) and the SiGe layer interstitial defects is compensated supersaturation gaps created by ion implantation to form the embrittlement layer. Interstitial gaps will come to occupy the sites and prevent therefore the diffusion path germanium lacunar elements of the SiGe layer in this layer and in adjacent layers, even during subsequent heat treatments. Therefore, one can form a silicon layer on the strained SiGe layer thus treated without risk of diffusion of germanium elements in the strained silicon layer.

p0025According to a first implementation of the invention, the enrichment step in interstitial defects in the SiGe layer may be performed by ion implantation of silicon atoms in the SiGe layer.

p0026The implantation energy and the implantation dose in the ion implantation of silicon atoms in the SiGe layer are chosen so as to form a silicon-enriched layer which lies between the embrittlement layer and the surface of the SiGe layer and having a maximum concentration of silicon atoms between 1.10²⁰ and 5.10²¹ atoms / cm³.

p0027According to another embodiment of the invention, the enrichment step in interstitial defects in the SiGe layer can be achieved by oxidation of the surface of the SiGe layer.

p0028The method of the present invention can be used for forming a sSOI type structure. In this case, the SiGe layer is a relaxed SiGe layer on a silicon substrate and the method further comprises:<ul><li>a step of forming a strained silicon layer on the SiGe layer,</li><li>a step of bonding the strained silicon layer on a support substrate,</li><li>a detachment step by cleavage of the SiGe layer at the embrittlement layer,</li><li>selective etching step of the remaining SiGe remaining above the layer of strained silicon layer after detachment.</li></ul>

p0029When the formation of interstitial defects in the SiGe layer is obtained by ion implantation, the implantation may be performed before or after the implantation step for forming the embrittlement layer, but also before or after the step of forming the strained silicon layer on the SiGe layer.

p0030When the formation of interstitial defects in the SiGe layer is obtained by oxidation of the surface of the SiGe layer, the oxidation can be performed before or after the step of forming the strained silicon layer on the SiGe layer and, in all cases, before the implantation step for forming the embrittlement layer.

BRIEF DESCRIPTION OF FIGURES

p0031<ul><li>1A and 1B show the manufacture of a sSOI type structure according to the Smart Cut ™ technology,</li><li>2A to 2C show the diffusion of germanium within the sSOI type structure during its manufacture,</li><li>3A-3B illustrate an example of the diffusion mechanism linked to deficiencies of point defects type</li><li>4A-4C illustrate an example of the diffusion mechanism linked to interstitial point defects of type</li><li>5A to 5D show the nano-bubbles in a silicon layer after ion implantation of helium and their evolution in gaps type defects after application of heat treatment,</li><li>6A to 6G are schematic sectional views showing the construction of a structure of sSOI accordance with an embodiment of the invention,</li><li>Figure 7 is a flowchart of the steps used in Figures 6A to 6G,</li><li>8A to 8H are schematic sectional views showing the embodiment of a structure of the sSOI according to another embodiment of the invention,</li><li>FIG 9 is a flowchart of steps performed in Figures 8A to 8H.</li></ul>

<u>detailed discussion of embodiments of the invention</u>

p0032The present invention provides a broadcast of the control method in lacunar elements mode, such as germanium atoms, in a layer of semiconductor material (eg. Layer of silicon-germanium (SiGe)) to restrict movement of these elements in the semiconductor layer, thereby preventing their passage into the layers adjacent to the semiconductor layer.

p0033The present invention applies generally to all types of heterostructures comprising a layer of semiconductor material containing elements capable of diffusing in patchy fashion in this layer and adjacent layers as a result of ion implantation resulting in the formation of gaps favoring the diffusion of elements deficient mode, for example during subsequent heat treatments. The invention can be applied, for example, heterostructures formed of an alloy layer of antimony (Sb), for example If_xsb_there or a layer doped with antimony on a silicon substrate, or to heterostructures formed a tin alloy layer (Sn), for example If_xsn_there or a layer doped with tin on a silicon substrate

p0034The invention applies in particular to the heterostructure containing at least one layer of silicon-germanium 5SiGe) on a silicon substrate and the germanium concentration is between 1% and 100%. This type of layer generally contains gaps type defects promotes diffusion of germanium atoms in the SiGe layer and the adjacent layers. Such layers are equal to the SiGe layers having undergone or for undergoing ion implantation (implantation species He and / or H) to form a zone of weakness for cleavage (fracture).

p0035The invention relates in particular to any type of donor substrates comprising a relaxed SiGe layer used for forming a strained silicon layer (sSi) and more particularly to such donor substrates which the SiGe layer has a significant content of germanium and that are more sensitive to diffusion due to their higher concentration of germanium. The SiGe layer in these substrates typically contains between 20% and 50% germanium but this concentration up to 100% depending on the strain of the desired? Si layer.

p0036In general, shortcomings type of defects (hereinafter called "gaps") but also interstitial type defects (hereinafter called "interstitial") are present within the layers of SiGe. However, there is a state of equilibrium between the vacancy concentration Cv and interstitial concentration Ci in the same substrate. This equilibrium can then be defined by the formula Cv = Ci x constant.

p0037During the implementation steps (eg, implantation of hydrogen and / or helium), conducted to create a zone of weakness to allow transfer layers according to the Smart Cut ™ technology, this balance is changed. Nano-bubbles are created in the SiGe layer and will evolve gaps agglomerates during different annealing applied during the manufacturing process while creating a supersaturation of gaps in the substrate. Germanium which broadcasts mainly in "incomplete fashion" will then be positioned in the gaps to diffuse into the substrate.

p0038Figure 5A shows the presence of agglomerates of gaps 31 obtained after implantation in a silicon substrate 30, helium ions (conditions of the facility: implantation energy = 32 keV, dose He = 1.10¹⁶ atoms / cm²). Figures 5B-5D show, after annealing at 350 ° C for 3 minutes 30 implanted silicon substrate, the processing of nano-bubbles type defects "platelets" horizontal 32 in the {100} planes (planes cubic structure) (figures 5B and 5C) and type defects "platelets" vertical 33 in the planes {010} (Figure 5D).

p0039These objects ( "platelets"), which are filled with gas in the first stage of their development, will dissolve by issuing gaps. These gaps sources objects were also observed in substrates SiGe or germanium.

p0040In order to prevent the migration of gaps and, therefore, the diffusion of germanium, the present invention proposes to enrich the substrate containing the SiGe layer so as to compensate interstitial supersaturation gaps recombinantly gaps / interstitial pairs.

p0041The enrichment of interstitial substrate can be achieved by different techniques.

p0042According to a first technique, the enrichment is accomplished by ion implantation.

p00436A to 6G and 7 describe an implementation of the first technique applied during the production of a plate ( "wafer") type sSOI by the Smart Cut ™ technology.

p0044The first step (step S1) comprises forming a heterogeneous structure 103, shown in FIG 6A, a substrate 101 comprising silicon substrate and a relaxed SiGe layer 102 formed from a SiGe buffer layer (not shown). The realization of such a heterogeneous structure is well known in itself and will be described in detail for simplicity. The layer 102 comprises an amount of germanium elements 104 corresponding, for example between 20% and 50% of the composition of the SiGe layer 102. The thickness of the SiGe layer is between 0.1 and 1 micrometer.

p0045According to the invention, elements are located so as to enrich an area between the maximum implantation forming the zone of weakness for cleavage (subsequently formed in step S4) and the interface between the SiGe layer and the sSi. The dose of implanted elements is controlled not to make the amorphous substrate and prevent its relaxation. In this step (Figure 6B) (step S2) is carried out for example ion implantation of 106 silicon atoms 105a (ie implantation of silicon ionized atoms) to obtain a maximum concentration of silicon atoms between 1.10²⁰ and 5.10²¹ atoms / cm³ in the vicinity of the maximum implantation zone 105.

p0046then forming a silicon layer 107 on the layer 102, for example by epitaxy (Figure 6C) (step S3). In accordance with the Smart Cut ™ technology well known, implantation 108, for example helium and / or hydrogen, is formed in the SiGe layer 102 to form a weakened zone 109 (Figure 6D) (step S4). The surface of the layer of? Si 107 is then brought into intimate contact, for example by gluing, with a support substrate or receiver 112 comprising a base substrate 111 for example of silicon with a buried oxide layer 110 (BOX) forming the insulating layer (Figure 6E) (step S5). Alternatively, or in addition, the oxide layer may be formed by deposition on the layer of? Si 107. The thickness of the buried oxide layer ( "buried oxide" (BOX)) typically varies between 500 and 1600 angstroms, and preferably between 1300 and 1500 angstroms.

p0047Then is detached by cleavage ( "splitting") of the SiGe layer 102 at the weakened zone 109 by the implantation of helium and / or hydrogen, leaving a remainder 102a of the layer 102 between the zone of weakness 109 and the interface SiGe layer 102 / layer 107 sSi (Figure 6F, step S6). The cleavage can be caused in particular by annealing at 500 ° C carried out over a period of about 30 minutes.

p0048A finishing step for removing the SiGe remaining 102a (by selective etching, polishing / planarization, etc.) and give a good surface to the layer of sSi is performed (Figure 6G, step S7). It may further comprises forming an insulating layer on the layer of? Si. The finishing step also includes a stabilization annealing at 800 ° C carried out over a period ranging from 30 minutes to 1 hour.

p0049The layout 106 (step S2) may also be performed after the step of forming the strained silicon layer 107 on the layer 102 (step S2 'in Figure 7), or after the implantation step 108 of helium and / or hydrogen produced in the SiGe layer 102 to form the weakened zone 109 (step S2 "in FIG 7).

p0050The layout 106 (step S2, S2 'and S2 ") consists of a silicon atom implantation performed at an implantation energy of between 10 and 150 keV for an implantation dose of between 5.10¹⁴ and 5.10¹⁵ atoms / cm².

p0051Thereby enriching the SiGe layer 102 in interstitial defects by implantation of silicon atom, preventing the distribution of germanium elements within the SiGe layer and consequently their passage through the layer of? Si 107. the selectivity of the etching of the SiGe layer remaining is thereby substantially increased, which can significantly reduce the appearance of defects and degradation of the surface condition of the layer of sSi after etching.

p0052According to a second technique, the interstitial enrichment of the SiGe layer is formed by a step of oxidizing the surface of the substrate. The substrate of the oxidation reaction comprising the SiGe layer will cause the injection of interstitial silicon atoms from the surface, thereby allowing recombination of the gaps created by the implantation of helium and / or hydrogen (creation area of weakness for cleavage) with these interstitial and prevent diffusion of Ge incomplete way.

p00538A to 8H and 9 describe an implementation of the second technique applied during the production of a plate ( "wafer") type sSOI by the Smart Cut ™ technology.

p0054The first step (step S10) of forming a heterogeneous structure 203, shown in FIG 8A, a substrate 201 comprising silicon substrate and a relaxed SiGe layer 202 formed from a SiGe buffer layer (not shown). The realization of such a heterogeneous structure is well known in itself and will be described in detail for simplicity. The layer 202 comprises an amount of germanium elements 204 corresponding, for example between 20% and 50% of the composition of the SiGe layer 202. The thickness of the SiGe layer is between 0.1 and 1 micrometer.

p0055According to the invention there is provided an oxidation of the surface of the SiGe layer 202 so as to inject carbon interstitial silicon 205a and to supersaturate the layer with these interstitial silicon atoms in an area 205, the latter being intended to capture gaps introduced during the ion implantation step (Figure 8B) (step S11). A thin oxide layer 206 is then formed on the surface of the SiGe layer 202.

p0056In this step, oxidation of the substrate or heterostructure 203 can be performed, for example, using an annealing carried out between 350 ° C and 450 ° C under an oxygen stream and a duration of between 10 minutes and 1 hour. Such oxidation can inject an equivalent dose of interstitial silicon atoms between 1.10¹³ and 1.10¹⁴ atoms / cm³.

p0057According to the Smart Cut ™ technology well known, implantation 208 helium and / or hydrogen is carried out in the SiGe layer 202 to form a zone of weakness 209 (8C) (step S12).

p0058In the case where the oxidation step is performed before the formation of the stress silicon layer after the heat treatment for oxide formation, a deoxidation step is carried out (by immersion in a hydrofluoric acid bath (HF) for example) to remove the thin oxide layer 206 formed on the surface of the layer 202 (Figure 8D) (step S13).

p0059then forming a silicon layer 207 on layer 202, for example by epitaxy (Figure 8E) (step S14).

p0060The surface of the layer of? Si 207 is then brought into intimate contact, for example by bonding, with a carrier receiver 212 or substrate comprising a base substrate 211 for example, silicon with an oxide layer buried 210 ( "buried oxide" (BOX)) forming the insulating layer (Figure 8F) (step S15). Alternatively, or in addition, the oxide layer may be formed by deposition on the layer of? Si 207. The thickness of the buried oxide layer (BOX) typically varies between 500 and 1600 angstroms, and preferably between 1300 and 1500 angstroms.

p0061then is detached by cleavage ( "splitting") of the SiGe layer 202 at the weakened zone 209 by the implantation of helium and / or hydrogen, leaving a remainder 202a of the layer 202 between the zone of weakness 209 and the interface SiGe layer 202 / layer 207 sSi (Figure 8G, step S16). The cleavage can be caused in particular by annealing at 500 ° C over a period of 30 minutes.

p0062A finishing step for removing the SiGe remaining 202a (by selective chemical etching, polishing / planarization, etc.) and give a good surface to the layer of sSi is performed (Figure 8H, step S17). It may further comprises forming an insulating layer on the layer of? Si. The finishing step also includes a stabilization annealing at 800 ° C carried out over a period ranging from 30 minutes to 1 hour.

p0063The oxidation step (step S11) may also be performed after the step of forming the strained silicon layer 207 on the layer 202 (step S11 'in Figure 9). In this case and contrary to that in which the oxidation is carried out before the formation of the? Si layer 207, the deoxidation step (step S13) is not necessary, an insulating layer, corresponding to a buried oxide (BOX) in the final structure, being subsequently deposited.

p0064Si atoms injected in step S11 (or S11 ') will be placed in interstitial then recombine with the gaps present in the vicinity of the implantation of helium and / or hydrogen. This reduces the flow of gaps in the interface between the SiGe layer and the layer of sSi and, therefore, reduce the spread after the application of subsequent heat treatments (eg formation oxide layer, annealing splitting, stabilization, etc.).

p0065Thereby enriching the SiGe layer 202 in interstitial defects by oxidation, preventing the distribution of germanium elements within the SiGe layer and consequently their passage through the layer of? Si 207. The selectivity of the etching of the remaining of SiGe layer is thereby substantially increased, which will considerably reduce the occurrence of defects and the degradation of the surface condition of the layer of? Si after etching.