# Patent

## Title
Nanowire and planar transistors co-integrated on utbox SOI substrate

## Abstract

Fabrication of a microelectronic device on a semiconductor on insulator type substrate, the device being provided with a transistor of a given type, the channel structure of which is formed from semiconducting bar(s), a dielectric area different from the insulating layer of the substrate being provided to replace the insulating layer, facing the transistor channel structure, specifically for this given type of transistor.

## Background
TECHNICAL FIELD
This invention relates to the field of microelectronics and is particularly applicable to producing of transistors for which the channel semiconducting structure is in the form of a plurality of parallel adjacent semiconducting nanowires on a semiconductor on insulator type substrate.
In particular, it can be used to make different types of transistors on a single semiconductor on insulator substrate in which one or several regions have been modified.
The invention is applicable for example to the use of finFET or trigate type transistors co-integrated on the same semiconductor on insulator substrate as FDSOI type planar gate transistors.
PRIOR ART
New transistor structures for which the channel is formed from one or several parallel semiconducting bars have been developed, particularly to increase the integration density in comparison with conventional MOSFET transistors.
For example, transistors of the type commonly called “finFET” comprise a channel formed from one or several semiconducting bars or fins in the form of adjacent nanowires that extend parallel to the substrate on which this or these nanowires are arranged.
Document “Spacer FinFET: nanoscale double-gate CMOS technology for the terabit era” by Choi et al., Solid-State Electronics, vol. 46, pp. 1595-1601, 2002) gives an example disclosure of a method for making a finFET transistor with small nanowires obtained by etching through a mask in which the patterns called “spacers” are formed by conforming deposition of a layer in contact with a sacrificial pad that is thinner than the critical dimension of the pad.
The gate structure of nanowire transistors is usually non-planar and is designed so as to encase the nanowire(s), and particularly to extend over the side faces of the nanowires.
For example, the transistor of the type commonly called “Trigate” has a partially encasing gate structure around one or several nanowires arranged in contact with the flanks of the nanowire(s) and on their top face.
Document U.S. Pat. No. 6,914,295 B2 discloses an example of a method for making such a tri-Gate transistor.
Unlike a planar gate structure for which the gate extends only in a direction parallel to the channel, the gate-channel contact surface is improved which has the main advantage of reducing leakage currents when the transistor is in the blocked or “off” state. Thus, shorter gate lengths can be obtained than with planar gate architectures, while maintaining exactly the same electrical performances.
Furthermore, in the field of planar gate structure transistors, transistors of the type commonly called FDSOI (FDSOI for “Fully Depleted Silicon On insulator”), made on a semiconductor on insulator type substrate have the advantage over conventional MOS transistors that they can have a threshold voltage VT that can be modulated by electrostatic coupling also referred to as capacitive coupling.
This is done by varying the potential applied to the semiconducting support layer of the semiconductor on insulator type substrate on which these transistors are formed.
The coupling between this support layer and the transistor channel can be obtained by using an SOI substrate with a thin or ultra-thin layer of buried oxide (BOX).
However, this insulating layer may not be suitable for nanowire transistors.
The problem arises of finding a new method for making a transistor structure with semiconducting nanowires that is capable of co-integrating this structure on a semiconductor on insulator type substrate, with one or several transistors of a different type and particularly planar transistors.
PRESENTATION OF THE INVENTION
This invention makes use of a microelectronic device on a semiconductor on insulator type substrate including the formation of at least one channel structure of at least one first type of transistor, said structure being formed by one or several adjacent semiconducting bars, on a given dielectric area that is different from the remainder of the insulating layer of the substrate.
A semiconductor on insulator type substrate means a substrate with a semiconducting support layer, an insulating layer on said support layer and said thin semiconducting layer being supported on said insulating layer.
To obtain the given dielectric area, the material in said insulating layer of the substrate is firstly removed in a region in which said semiconducting bars are located.
A replacement by a given dielectric material can then be made so as to make a replacement dielectric area different from the remainder of said insulating layer of the substrate, the thickness and composition of which may be adapted specifically to the first type of transistor.
Thus, this invention relates to a method for making a microelectronic device including steps as follows:
a) make one or several semiconducting bars, designed to form at least one transistor channel or several transistor channels of a first type, by etching through an opening in a first mask facing a given region of a thin semiconducting layer of a semiconductor on insulator substrate,
b) remove an area from said insulating layer of said substrate in extension of said opening so as to expose said semiconducting bars.
The semiconducting bars are also called “nanowires” when their critical dimension is less than 1 μm.
The insulating layer is based on a material with a first dielectric constant k1. According to one possible embodiment, the material of the insulating layer may be SiO2.
Advantageously, the method also comprises a step after step b) consisting of depositing a given dielectric material facing said opening to replace said area of said insulating layer removed in b). The thickness and/or composition of this replacement dielectric material are different from the thickness and/or composition of said area of said insulating layer removed in step b).
Thus, a specific dielectric area is formed facing the semiconducting bars different from the initial insulating layer of the semiconductor on insulator type substrate.
Advantageously, the given dielectric replacement material is a dielectric material with a composition and thickness that are selected to enable electrostatic or capacitive coupling between said support layer and said conducting bars.

    
    
        According to one possible embodiment of the method, the given dielectric replacement material has a dielectric constant k2 such that k2>k1.
    
    


In particular, this given replacement dielectric material may be SixNy or a “high-k” type dielectric.
Advantageously, at least one isolation trench may be made between said given region and said other region in the thin semiconducting layer. This isolation trench may be of the STI (Shallow Trench Isolation) type.
Advantageously, the semiconducting bar(s) is (are) formed in step a) by etching the thin semiconducting layer through one or several blocks of a second mask partially covering said opening of said first mask and made by:

    
    
        forming one or several sacrificial pads with critical dimension Dc1 given on said given region,
        forming one or several blocks with critical dimension Dc2<Dc1 in contact with the flanks of said pad(s),
        removing said sacrificial pad(s).
    
    


Thus, small semiconducting bars can be made.
The method may further include deposition of a hard mask layer on said first mask and in said opening, before production of said mask.
In this case, production of said second mask may also include anisotropic etching of the hard mask layer through said blocks with critical dimension Dc2.
The blocks of the second mask may have one end supported on the first mask and that is outside a region delimited by said opening of said first mask. This arrangement can be used to facilitate subsequent removal of the second mask.
According to one possible embodiment of the method, in step b) another area of said insulating layer facing another region of said thin semiconducting layer may be protected by said first mask and kept.
Facing this other area, at least one transistor of a second type, different from said first type, may be provided.
Said other area of said insulating layer that was kept may have a thickness and a composition adapted to the second type of transistor.
Thus, according to the invention, co-integration of transistors of the first type for which the channel is formed by adjacent parallel bars facing said specific dielectric area, and at least one transistor of a second type, different from the first type, may be made facing said intact conserved area of said insulating layer.
The transistor of the first type may for example be a tri-gate or finFET type transistor with an encasing gate structure, while the transistor(s) of the second type may for example be made from MOS transistors with a planar gate structure.
Advantageously, said insulating layer of the substrate may be thin or ultra-thin with a thickness of less than 20 nm. Thus, according to one possible embodiment, the transistor(s) of the second type may for example be of the FDSOI type.
According to another aspect, this invention also relates to a microelectronic device provided with:

    
    
        a substrate comprising a thin semiconducting layer supported on an insulating layer, said insulating layer being supported on a semiconducting support layer,
        at least one first transistor of a first type comprising a region adapted to form a channel formed from one or several adjacent bars in and/or on said thin semiconducting layer and an encasing gate arranged on said bars and around the lateral faces of said bars, said channel of said first transistor being arranged above and facing a modified area of the substrate, or on a modified area of the substrate or on a modified area of the substrate based on a dielectric material different from the material in the insulating layer.
    
    


The dielectric constant k2 of the given dielectric material in the modified area of the substrate may be such that k2>k1 where k1 is the dielectric constant of the material of said insulating layer.
The given dielectric material of the modified area of the substrate may also have a composition and thickness selected to enable capacitive coupling between said channel of said first transistor and said semiconducting support layer.
This in particular makes it possible to modulate the threshold voltage of said first transistor.
The insulating layer of the substrate may be based on SiO2 and its thickness may be less than 25 nm or 20 nm. Thus, the substrate may have an UTBOX type of insulating layer.
Advantageously, the device may comprise at least one second transistor, the channel area of which is formed in a region of the thin semiconducting layer arranged on and in contact with said insulating layer of the substrate.
The composition and thickness of the insulating layer may be designed to enable capacitive coupling between the channel of said second transistor and said semiconducting support layer of said substrate.
Advantageously, the device may further comprise at least one other transistor, in which the channel area is formed in a semiconducting region arranged on and in contact with the semiconducting support layer of the substrate.



BRIEF DESCRIPTION OF THE DRAWINGS
This invention will be better understood after reading the description of example embodiments given purely for information and that are in no way limitative, with reference to the appended drawings in which:
FIG. 1 shows an example of a microelectronic device implemented according to the invention on a semiconductor on insulator substrate, including an adjacent nanowire transistor supported on a first insulating region and a planar gate structure transistor supported on a second insulating region forming part of the insulating layer of said substrate ;
FIGS. 2A-2O, 3A-3L, 4A-4J show an example of a method according to an example embodiment of a microelectronic transistor device provided with at least one nanowire transistor and at least one planar gate structure transistor co-integrated on an SOI substrate;
FIGS. 5A-5C, and 6A-6B show an example embodiment of a microelectronic transistor device provided with at least one nanowire transistor on a dielectric area replacing the insulating layer of an SOI substrate of a substrate and at least one other transistor on a semiconducting region replacing the thin semiconducting layer and the insulating layer of the SOI substrate;
FIG. 7 shows parameter variation curves illustrating a variation of the threshold voltage of a nanowire transistor on a dielectric area of silicon nitride or on a silicon oxide area as a function of its gate length;



Identical, similar or equivalent parts of the different figures have the same numeric references to facilitate comparison between different figures.
The different parts shown in the figures are not necessarily all at the same scale, in order to make the figures more easily readable.
DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS
FIG. 1 shows a microelectronic device formed from a semiconductor on insulator substrate including a semiconducting support layer 100, a thin insulating layer 101 arranged on and in contact with the semiconducting support layer 100 and a thin semiconducting layer 104 arranged on and in contact with the insulating layer 101.
In a first region of the substrate, a transistor T1 of a given type, for example a MOSFET FDSOI, comprises a channel C1 and source regions S1 and drain regions D1 formed in said thin semiconducting layer 104. The gate G1 of this transistor has a planar structure in the sense that it is in the form of an area extending parallel to the principal plane of the substrate and parallel to the area of the channel C1.
The principal plane of the substrate is defined herein and throughout the remainder of the description as being a plane passing through the substrate and parallel to the [O; {right arrow over (i)}; {right arrow over (j)}] plane of the [O; {right arrow over (i)}; {right arrow over (j)}; {right arrow over (k)}] coordinate system shown in FIG. 1.
The area of the channel C1 of the transistor T1 is arranged on and in contact with an area of said insulating layer based on a dielectric material 102 with dielectric constant k1 and separated from the support layer 100 by this area.
The area of the insulating layer 101 separating the channel C1 from the support layer 100 is designed in this example to have a composition and thickness such that capacitive coupling can be set up between the channel C1 and said semiconducting support layer. This coupling may be such that a variation of the potential applied on the layer 100 causes a variation in the threshold voltage VT1 of the transistor T1, for example of the order of 100 mV.
The insulating layer 101 may for example be based on SiO2 and its thickness may be less than 20 nm.
In a second region of the substrate separated from the first region by shallow trench isolation STI type trenches 160, a different type of transistor T2 for example a transistor commonly called a “finFET” or of the type commonly called “triGate” comprises a channel C2 formed from a plurality of semiconducting bars or nanowires made by etching said thin semiconducting layer 104, and that are therefore adjacent in a plane parallel to the principal plane of the substrate. The gate G2 of this transistor T2 has an encasing structure and it covers the lateral faces (in this example faces orthogonal to the [O; {right arrow over (l)}; {right arrow over (k)}] plane) and the top face of the nanowires (in this example a face parallel to the [O; {right arrow over (i)}; {right arrow over (j)}] plane).
The channel C2 of the transistor T2 is arranged on and in contact with a area based on a dielectric material 142 different from the material 102 in the area facing which the first transistor T1 is located with a dielectric constant k2 such that k2>k1.
The area of dielectric material 142 separating the channel C2 from the support layer 100 in this example is designed to have a composition and thickness that enable capacitive coupling between this channel C2 and said semiconducting support layer.
The dielectric constant k2 of the dielectric material 142 is greater than the dielectric constant k1 of the dielectric material 102 to enable better capacitive coupling between the channel C2 and the substrate.
The area of the dielectric material 142 may for example be based on Si3N4 or a high-k type dielectric material such as HfO2 or HfSiOxNy with a thickness less than 25 nm or 20 nm.
Capacitive coupling between the channel C2 and the substrate is such that a modulation of the threshold voltage may be applied. Modulation occurs as soon as the order of magnitude of capacitive coupling between the channel and the substrate becomes the same as the order of magnitude of coupling between the gate and the channel, the substrate then acting as a second gate.
Coupling between the channel C2 and the layer 100 may be such that a variation of potential applied on the layer 100 leads to a variation of the threshold voltage VT2 of the transistor T2 that can be as high as a few tens of mV, for example 100 mV.
FIG. 7 gives an example of a curve 710 of the variation of a parameter commonly called the “body factor” corresponding to a variation of the threshold voltage of a transistor with an arrangement similar to that of transistor T2 but with a single semiconducting bar with a height of the order of 15 nm, a width of the order of 15 nm, depending on a variation of the potential of the layer 100 of the substrate obtained in a case in which the dielectric material 142 is made of silicon nitride with a dielectric constant k=7. For comparison, a curve 720 illustrates the variation of the body factor for this transistor when the dielectric material 142 is replaced by SiO2.
Such a device type may be applied to producing of a high performance low consumption logic circuit.
An example of a method for producing a transistor microelectronic device will be described with reference to FIGS. 2A-2O (in which the device being produced is shown in a cross-sectional view XX′), FIGS. 3A-3L (in which the device being produced is represented in a top view), and FIGS. 4A-4J (in which the device currently being manufactured is shown in a cross-sectional view Y′Y or Z′Z).
The initial material for this method (FIG. 2A) may be a semiconductor on insulator type substrate formed from the support layer 100 based on a semiconducting material, for example silicon, the support layer being covered by the insulating layer 101 based on dielectric material 102 with a dielectric constant k1, for example SiO2, itself covered with the thin semiconducting layer 104.
In particular, the insulating layer 101 may be a thin or ultra-thin layer of the type commonly called “thin-BOX” (Buried Oxide) or “ultra-thin BOX” (UTB), and thus be less than several tens of nanometers thick, or less than 20 nm, for example of the order of 10 nm.
The thin semiconducting layer 104 may for example be based on Ge or SiGe, or Si, particularly with an <100> or <110> orientation and with a thickness that may be less than 20 nm, for example of the order of 12 nm.
In a first region A of the substrate, and particularly of the layer 104, at least one transistor of a given type, for example of the “finFET” or “trigate” type, provided with a channel in the form or several adjacent parallel bars will be made, while in one or several other regions (not shown in FIG. 2A), one or several different types of transistors, for example of the planar gate structure type will be formed.
Firstly, a first mask 106 is formed on the substrate 100 comprising an opening 107 delimiting the first region A and exposing the thin semiconducting layer 104.
For example, the first mask 106 may be based on silicon nitride and its thickness may for example be between several nanometers and several tens of nanometers, for example of the order of 30 nm (FIGS. 2B and 3A).
The next step is to form a so-called “hard mask” layer 109, for example based on a metal such as TiN so as to cover the first mask 106 and the first region A of the thin semiconducting layer 104 exposed through the opening 107, in a conforming manner. The thickness of the hard mask layer 109 is between several nanometers and several tens of nanometers, for example of the order of 10 nm (FIG. 2C).
Then (FIGS. 3B, 2D, and 4A), a sacrificial block is made for example by deposition of a stack of a carbon based layer made by SoC (Spin On Carbon) deposition and Si-Arc and a resin that may for example be insolated using an electron beam (“e-beam”) that will be etched later.
The sacrificial block is composed of first parallelepiped shaped pads 110a, 110b, 110c, 110d, 110e parallel and adjacent to each other, these first pads extending along a first direction (the first direction in this example being the direction of the vector {right arrow over (i)} or the coordinate system [O; {right arrow over (l)}; {right arrow over (j)}; {right arrow over (k)}] given in FIGS. 3B and 2D) parallel to the principal plane of the substrate. The sacrificial block is also composed of two parallelepiped pads 1101, 1102, joining the ends of the first pads 110a, 110b, 110c, 110d, 110e, and extending along a second direction (in this example the direction of the vector {right arrow over (j)}), orthogonal to said first direction.
Some pads 110a, 110b, 110c have a portion formed facing the opening 107 of the mask 106 exposing the first region A of the thin semiconducting layer 104, while the other blocks 110d, 110e, 1101, 1102 are arranged around said first region A and facing the mask 106.
The critical dimension Dc1 of the pads 110a, 110b, 110c, 110d, 110e, 1101, 1102 forming the sacrificial block may for example be of the order of 20 nm (the critical dimension being defined in this case and throughout this description as being the smallest dimension of an element measured in a plane parallel to the principal plane of the substrate, i.e. parallel to the [O; {right arrow over (i)};{right arrow over (j)}] plane given for example in FIG. 3B).
The next step is to make a conforming deposition of a material 121 that may be dielectric, and for example based on silicon nitride and in particular covers the flanks or side faces of these pads 110a, 110b, 110c, 110d, 110e, and 1101, 1102. The thickness of the deposited material 121 may for example be of the order of 10 nm.
Mask blocks 123 also called “spacers” 123 are formed by partial removal of the material 121 in contact with the side flanks of the sacrificial block and surrounding it. The critical dimension Dc2 of these spacers 123 may for example be of the order of about ten nanometers, less than the critical dimension Dc1 of the pads forming the sacrificial block and that may be approximately equal to the deposited thickness of the material 121 (FIGS. 3C, 2E, 4B). The spacers 123 may be made by etching and stopping on the hard mask layer 109. For example, in this case, in which the spacers 123 are based on nitride and the hard mask layer 109 is based on metal such as TiN, this etching may be done by means for example of a N2O2 plasma.
The next step is removal of the sacrificial block, while the spacers 123 are kept (FIGS. 3D, 2F, 4C). O2 plasma etching may be done for this purpose.
The patterns of spacers 123 in the hard mask layer 109 are then reproduced (FIGS. 3E, 2G, 4D). Thus, hard mask blocks 125 are formed in this layer 109 prolonging the spacers 123. These blocks 125 on which the spacers 123 are supported have dimensions and particularly a critical dimension, equal to approximately Dc2 of the spacers 123. This step may be done using anisotropic etching of the hard mask layer 109, for example using BCl3/Cl2. This thus exposes the first mask 106 again, together with the first region A of the thin semiconducting layer 104 of the substrate.
The blocks 125 on which the spacers 123 are placed form a second mask 126 arranged above the first mask 106, of which portions are located facing and partially covering the opening 107 of the first mask 106.
The next step can be to reproduce the patterns of the second mask 126 in the thin semiconducting layer 104 (FIGS. 3F, 2H, 4E), so as to form semiconducting bars 1301, 1302, 1303, 1304, 1305, 1306, also called “wires” (or nanowires if their critical dimension is less than 1 μm), or “fins” with a critical dimension Dc3 less than Dc2. The critical dimension Dc3 of the semiconducting bars 1301, 1302, 1303, 1304, 1305, 1306 can thus be such that Dc3≈Dc2 and is of the order of several nanometers, for example of the order of 10 nm. The adjacent semiconducting bars 1301, 1302, 1303, 1304, 1305, 1306, may be distributed for example at a pitch of the order of 35 nm.
In order to perform this step, anisotropic etching is done through the first mask 106 and the second mask 126 stopping on the thin insulating layer 101 of the substrate. This etching may be done for example using CF4 and HBr/O2.
The second mask 126 can then be removed. To achieve this, the spacers 123 can firstly be removed (FIGS. 3G, 2I, 4F), for example by HF etching.
Then (FIGS. 3H, 2J, 4G), FIG. 4G in this case showing a cross sectional view ZZ′ shown in FIG. 3H), the blocks 125 are removed from the hard mask layer 109 to keep only the semiconducting bars 1301, 1302, 1303, 1304, 1305, 1306.
The next step is to remove the thin insulating layer 101 of the substrate facing the first region A and through the opening 107 of the first mask 106 (FIGS. 3I, 2K, 4H). This removal may for example be done by chemical etching using HF. After this removal, a portion of the semiconducting bars 1301, 1302, 1303, 1304, 1305, 1306 located in the first region A is exposed. The semiconducting bars 1301, 1302, 1303, 1304, 1305, 1306 are thus suspended and held in place by areas of the thin semiconducting layer 104 that are not etched and are located outside the first region A delimited by the opening 107 of the first mask 106. The exposed portions of the semiconducting bars 1301, 1302, 1303, 1304, 1305, 1306 have top face 131, bottom face 132 and lateral face 133, 134 exposed in line with opening 107.
A dielectric material 142 different from the material 102 in the thin insulating layer 101 can then be deposited. The dielectric constant k2 of the dielectric material 142 may in particular be greater than the dielectric constant k1 of the thin insulating layer 101 of the substrate. For example, the deposited dielectric material 142 may be a silicon nitride or a type of material commonly called a “high-k” material. The deposition may possibly be made so as to fill in the opening 107 in the hard mask 106 and possibly surround the semiconducting bars 1301, 1302, 1303, 1304, 1305, 1306. In this case, a polishing step commonly called “planarisation” or CMP (Chemical Mechanical Polishing) is done to remove the dielectric material 142 located above the top face of the first mask 106 (FIGS. 3J, 2L, 4I).
The dielectric material 142 is then partially removed so as to expose the top face 131 and side faces 133, 134, of the semiconducting bars 1301, 1302, 1303, 1304, 1305, 1306.
This partial removal may possibly be done until the top face of the remaining areas of the thin insulating layer 101 is reached corresponding to the level of the bottom face 132 of the bars 1301, 1302, 1303, 1304, 1305, 1306. In this case, the thickness of the area of dielectric material 142 produced under and facing the bars 1301, 1302, 1303, 1304, 1305, 1306 is approximately the same as the thickness of the insulating layer 101.
The remaining area of dielectric material 142 then replaces the region of the thin BOX insulating layer 101 that had previously been removed. The area of replacement dielectric material 142 extends particularly along the bars and its thickness and composition are designed to set up capacitive coupling between the substrate 100 and the bars 1301, 1302, 1303, 1304, 1305, 1306. The next step is to remove the first mask 106, for example by HF (FIGS. 2M, 3K, 4J).
The next step is to form isolation areas, for example of the STI type around the first region A and other regions B and D of the thin semiconducting layer 104 in which other transistor structures were made or will be made.
The isolation areas may be made by the formation of trenches 106 around the regions A, B, D, and then by deposition of a dielectric material 161 such as SiO2 in these trenches 160.
FIG. 2O shows a first isolation area that separates the first region A in which the semiconducting bars 1301, 1302, 1303, 1304, 1305, 1306 were made from a second region B in which planar gate structure transistors, for example of the FDSOI type, will be made or are being made.
A second isolation area separates the first region A from a third region D in which one or several other structures or components have been made or will be made.
The steps to deposit a gate dielectric and then a gate material on the semiconducting bars 1301, 1302, 1303, 1304, 1305, 1306 and on the region B of the thin semiconducting layer 104, can then be done followed by etching of this gate dielectric and this gate material.
The result is the formation of transistor gates, and particularly one or several planar type gates that extend parallel to the thin semiconducting layer 104 of the substrate in the second region B and at least one encasing gate arranged around the side faces 133, 134 and on the top face of the semiconducting bars 1301, 1302, 1303, 1304, 1305, 1306.
One variant embodiment is shown in FIGS. 5A-5C and 6A-6B.
For this variant, the initial material may be the semiconductor on insulator type substrate in the previously described example method, formed by the support layer 100 based on semiconducting material covered by the insulating layer 101 based on a dielectric material 102 with a dielectric constant k1, itself covered with the thin semiconducting layer 104.
In a first region A of the layer 104, a given type of transistor, for example a “finFET” or “trigate” type transistor with a channel in the form of adjacent parallel bars will be made, while at least one different type of transistor, for example a planar gate structure type transistor, will be formed in another region B′.
The first step is to form a hard mask layer 201, for example based on a TeOS type silicon oxide, on the thin semiconducting layer 104.
A mask 203, for example based on a photosensitive resin facing the first region A of the thin semiconducting layer 104 is then formed on the hard mask layer 203, the other region B′ being exposed (FIG. 5A).
The next step is to etch the hard mask layer 201, the thin semiconducting layer 104 and the insulating layer 101 through the mask 203.
Thus, the insulating layer 101 in the other region B′ of the substrate is removed, so as to expose an area of the support layer 101 located in this second region of the semiconductor on insulator type substrate (FIG. 5B).
The resin mask 203 can then be removed, and a semiconducting region 204 can then be formed on the exposed area of the support layer 101. This semiconducting region 204 may be made for example by epitaxial growth (FIG. 5C).
In the other region B′ of the substrate, the semiconducting region 204 thus forms a modified bulk substrate type region. This thus forms a semiconductor on insulator type substrate that is modified comprising a semiconducting region 204 supported directly on the support layer 100.
A method like that described above with reference to FIGS. 2A-2O, 3A-3L, 4A-4J can then be used in order to form a transistor channel structure with bars 1301, 1302, 1303, 1304, 1305, 1306 in the first region A (FIG. 6A).
A transistor T2 comprising a channel formed from a plurality of semiconducting bars formed on a area based on dielectric material 142 different from the dielectric material of the insulating layer 101 in the semiconductor on insulator type substrate can then be formed in the first region A.
A planar transistor structure T′1 for which the channel structure is located in the semiconducting region 204 is formed in the other region B′. The regions A and B′ can be co-integrated with a third region D of the insulating semiconductor substrate of which the insulating layer 101 was kept intact. In this third region, a transistor T3 for which the channel is provided in the thin semiconducting layer 104 of the substrate can be formed (FIG. 6B).

## Claims

1. A method for making a microelectronic device including the steps as consisting of:
a) making one or several semiconducting bars, designed to form at least one transistor channel or several transistor channels of a first type in a first region of a thin semiconducting layer of a substrate facing an opening in a first mask, said substrate being a semiconductor on insulator type substrate comprising a support layer on which an insulating layer is supported, said thin semiconducting layer being supported on said insulating layer;
b) removing an area from the insulating layer in extension of said opening in said first mask so as to expose said semiconducting bars; and
c) replacing said area removed from said insulating layer by a given dielectric material with a composition and a thickness selected to facilitate capacitive coupling between said support layer and said conducting bars.

2. The method according to claim 1, in which said insulating layer is based on a first material with a first dielectric constant k1, the method also comprising a step consisting of replacing said area of said insulating layer removed in step b) by a given dielectric material with a second dielectric constant k2 such that k2>k1.

3. The method according to claim 1, in which the dielectric material is formed to reach a bottom face of the semiconducting bars located facing the support layer.

4. The method for making a microelectronic device according to claim 1, also comprising at least one step consisting of:
making at least one isolation trench between said given region and said other region in the thin semiconducting layer.

5. The method for making a microelectronic device according to claim 1, said insulating layer being based on SiO2 and being less than 20 nm thick.

6. The method for making a microelectronic device according to claim 1, in which in step b) another area of the insulating layer, located facing a second region in said thin semiconducting layer in which at least another transistor channel of a second type will be formed, is kept.

7. The method for making a microelectronic device according to claim 1, also comprising steps to:
remove another area from the insulating layer so as to expose a given region in the support layer,
growth of a semiconducting region on said given region in the support layer, at least one transistor channel will be formed in said semiconducting region.

8. The method for making a microelectronic device according to claim 1, in which an encasing gate is formed on said bars and around side faces of said bars after step c).

9. The method according to claim 1, in which said one or several semiconducting bar(s) is (are) formed in step a) by etching the thin semiconducting layer through one or several blocks in a second mask partially covering said opening in said first mask, production of the second mask comprising steps consisting of:
forming one or several sacrificial pads with critical dimension Dc1,
forming one or several masking blocks with critical dimension Dc2<Dc1 in contact with the flanks of said sacrificial pad(s),
removing said sacrificial pad(s).

10. The method for making a microelectronic device according to claim 9, in which, making said second mask also comprises the following steps after making said first mask and before step a):
deposit a hard mask layer on said first mask and in said opening,
etch the hard mask layer through said blocks with critical dimension Dc2 so as to form hard mask blocks in extension of said blocks.

11. The method for making a microelectronic device according to claim 9, in which said blocks are arranged so as to be provided with ends supported on said first mask.

12. A method for making a microelectronic device comprising the steps to:
a) make one or several semiconducting bars that will form at least one transistor channel or several transistor channels of a first type in a first region of a thin semiconducting layer of a substrate facing an opening in a first mask, said substrate being a semiconductor on insulator type substrate comprising a support layer on which an insulating layer is supported, said thin semiconducting layer being supported on said insulating layer, wherein said insulating layer has a first dielectric constant k1;
b) remove an area from said insulating layer in extension of said opening in said first mask so as to expose said semiconducting bars; and
c) replace said area removed from said insulating layer by a given dielectric material with a second dielectric constant k2 such that k2 >k1.

13. The method for making a microelectronic device according to claim 12, in which an encasing gate is formed on said bars and around side faces of said bars after step c).