WO2024170751A1 - Method for forming a weakened zone in a semiconductor substrate - Google Patents

Abstract

The present disclosure relates to a method for forming a weakened zone (5) in a semiconductor substrate (6), successively comprising the following steps: a. forming a screen layer (4) having a non-planar controlled profile on a first face (61) of the substrate, b. implanting species through the screen layer and the first face (61) of the substrate to form the weakened zone, the profile of the screen layer being selected to compensate for a non-uniformity in the implantation depth of the species so that the weakened zone (5) is substantially located in a plane parallel to the first face (61).

Description

TITLE: METHOD FOR FORMING A WEAKENING ZONE IN A SEMICONDUCTOR SUBSTRATE

TECHNICAL AREA

The present disclosure relates to a method for forming a weakening zone in a semiconductor substrate. This method advantageously finds its application in the manufacture of substrates of the semiconductor-on-insulator type. The manufacture of such semiconductor components can in particular be used for the manufacture of waveguides.

STATE OF THE ART

The manufacture of components in the field of microelectronics, optics and/or optronics, and more particularly the manufacture of waveguides, uses substrates of the semiconductor-on-insulator type. Such substrates comprise, from their rear face to their front face, a support substrate, an electrically insulating layer and a monocrystalline semiconductor layer, called the active layer. The active layer of such substrates is generally, but not limited to, made of silicon, and the substrate is called a silicon-on-insulator (SOI) substrate.

Processes called Smart Cut™, known in the state of the art, make it possible to manufacture semiconductor substrates on insulators. They include in particular a step of implanting species through a surface of a donor substrate in order to create a weakening zone at a desired thickness thereof.

Conventionally, the electrically insulating layer is formed on the donor substrate, in particular by oxidation, and the implantation of species is carried out in the donor substrate through the oxide layer. The implanted species must then be able to cross the electrically insulating layer, as well as the desired depth of the donor substrate in order to form the active layer of the SOI substrate.

When the desired electrically insulating layer and/or active layer is particularly thick, it is difficult in practice to impart enough energy to the implanted species to pass through the electrically insulating layer and the desired depth of the donor substrate. In this case, it is known to manufacture the SOI substrate with so-called "reverse" bonding: the electrically insulating layer is then formed on a receiving substrate, intended to receive the donor substrate by bonding, rather than on the donor substrate itself, and the implantation is done directly through the surface of the donor substrate, without the species having to pass through the electrically insulating layer. Following implantation, the implanted donor substrate is bonded to the electrically insulating layer arranged on the receiving substrate, then the donor substrate is detached along the weakening zone on the receiving substrate.

However, following the implantation step, the inventors found that the uniformity of the implantation depth of the species is degraded. This non-uniformity of depth implantation results in a non-uniformity in the thickness of the active layer, which adopts a typically concave or convex profile, which is detrimental to the quality of the components subsequently formed in this active layer.

Some state-of-the-art methods have attempted to correct the profile of the active layer after its transfer to the receiving substrate.

Single-wafer cleaning (SWC) is a notable method. This involves cleaning the semiconductor-on-insulator substrate by distributing a chemical etching agent at its center, which then spreads by centrifugal effect due to rotation of the substrate around a central axis. This makes it possible to obtain a higher silicon consumption rate by etching at the center of the substrate than at its edges, and thus to correct a convex active layer profile. However, these correction methods are only effective for limited depths, of the order of a nanometer, and the use of several SWC steps to treat highly convex surfaces is very costly. In addition, these methods do not allow the correction of a concave active layer profile, i.e. one with a greater thickness in its peripheral region than in its central region.

Another post-implantation correction method is to form a sacrificial electrically insulating layer on the active layer after its transfer to the recipient substrate. If the oxide formation consumes the active layer at different rates at its center and edges, such a method can then correct concave or convex implantation profiles. However, this consumption rate is difficult to control, which compromises the accuracy of such methods. In addition, the formation of the sacrificial oxide layer often requires subjecting the substrate to complex temperature variations, which precludes the implementation of such methods on an industrial scale.

EXPOSED

It is therefore necessary to develop implantation methods that allow to obtain a uniform implantation depth over the entire surface of the substrate, or in other words to form a flat weakening zone, parallel to a main surface of the substrate, and that can be implemented more easily than the methods mentioned above. It is also necessary to develop implantation methods that allow to precisely correct any implantation profile obtained, depending on the implantation conditions used.

For this purpose, the present disclosure provides a method for forming a weakening zone in a semiconductor substrate, successively comprising the following steps: a. forming a screen layer having a controlled non-planar profile on a first face of the substrate, b. implantation of species through the shield layer and the first face of the substrate to form the weakening zone, the profile of the shield layer being chosen to compensate for a non-uniformity in the depth of implantation of the species so that the weakening zone is substantially included in a plane parallel to the first face.

The formation of a shielding layer with a controlled and non-planar profile makes it possible to compensate for variations in implantation depth that could occur on the implanted surface of the substrate, so as to obtain a substantially flat weakening zone, along a plane parallel to the implanted surface. This produces a superinsulating semiconductor substrate having a flat active layer and in particular allowing the manufacture of better quality components.

According to one implementation of the method, the screen layer has a convex or concave profile.

According to one implementation of the method, the species implanted in the first face of the substrate comprise hydrogen ions and helium ions.

According to one implementation of the method, a distance between any two points of a free surface of the screen layer along an axis normal to the first face is between 0.2 nm and 5 nm.

According to one implementation of the method, the substrate comprises silicon.

According to one implementation of the method, the screen layer comprises an oxide of a semiconductor material, in particular silicon dioxide.

According to one implementation of the method, the screen layer is obtained by thermal oxidation of a surface region of the semiconductor substrate.

According to one implementation of the method, forming the shielding layer by oxidation comprises heating the substrate under a neutral atmosphere to a temperature above an oxidation temperature of the substrate, then cooling the substrate to said oxidation temperature, and applying an oxidizing atmosphere to form the shielding layer.

According to one implementation, the method comprises, before thermal oxidation, a selective application of an oxidizing plasma to an area of the first face of the substrate so as to form an excess thickness of oxide in said area.

According to one implementation, the method comprises, prior to the formation of the screen layer, a calibration of the profile of the screen layer comprising the following steps: - implantation of atoms through a first face of a calibration substrate, so as to create a weakening zone,

- separation of the calibration substrate along the weakening zone into a first part, comprising the first face, and a second part,

- defining a target profile whose shape is substantially identical to a surface of the first part exposed by the separation, the target profile being used to define the profile of the screen layer during its formation.

The present disclosure further relates to a method of manufacturing a semiconductor component of the semiconductor-on-insulator type, successively comprising the steps of:

- supply of a donor substrate and a recipient substrate made of semiconductor material,

- formation of an electrically insulating layer on one side of the receiving substrate,

- forming a weakening zone in the donor substrate by means of the forming method according to any one of the preceding claims, the weakening zone thus formed delimiting a semi-conductor layer,

- removal of the screen layer,

- bonding the first face of the donor substrate to the electrically insulating layer of the recipient substrate,

- separation of the donor substrate at the weakening zone so as to transfer the semiconductor layer from the donor substrate to the recipient substrate.

According to one implementation of the method for manufacturing a semiconductor component, the electrically insulating layer and the shielding layer are formed by heat treatment in the same oven.

According to an implementation of the method for manufacturing a semiconductor component, the electrically insulating layer has a thickness of at least 150 nanometers.

DESCRIPTION OF FIGURES

[Fig. 1] illustrates a typical SOI substrate.

[Fig. 2] illustrates a method of manufacturing a semiconductor component by reverse bonding, known from the state of the art.

[Fig. 3] illustrates a proposed method of forming a weakening zone in a semiconductor substrate. [Fig. 4] illustrates a calibration performed as part of the process of forming a weakening zone in a semiconductor substrate.

[Fig. 5] illustrates a proposed method of fabricating a semiconductor-on-insulator component.

DETAILED DESCRIPTION OF EMBODIMENTS

Figure 1 illustrates a conventional semiconductor-on-insulator (SOI) substrate, successively comprising a base substrate 11 made of semiconductor material, generally silicon, an intermediate layer 2 made of electrically insulating material, in particular silicon oxide, and a layer made of monocrystalline semiconductor material 13, called the “active layer”, also generally formed of silicon. The thickness of the monocrystalline semiconductor layer is typically between 50 nanometers and a few micrometers.

For the formation of SOI substrates whose active layer 13 is particularly thick and/or whose intermediate layer 2 is particularly thick, i.e. which has a thickness greater than or equal to 200 nm, it is known to use a Smart-Cut™ process by reverse bonding, illustrated in FIG. 2 and comprising the steps:

- formation of an electrically insulating layer 2 on a receiving substrate 7,

- implantation of species in a donor substrate 6, so as to form a weakening zone 5 in this substrate,

- bonding the donor substrate 6 to the recipient substrate 7, the electrically insulating layer 2 being arranged between the two substrates,

- separation of the donor substrate along the weakening zone, so as to transfer an active layer 13 from the donor substrate 6 onto the recipient substrate 7.

The active layer 13 thus obtained often has a thickness that is not uniform over its entire length, that is to say that the weakening zone 5 is not flat. A difference in thickness of a few nanometers is generally observed between different zones of the active layer 13. By thickness, we mean the direction normal to the plane formed by a first face 61 of the substrate e through which the implantation of species is carried out. Figure 2 illustrates a convex implantation profile, resulting in a convex transferred active layer 13, but depending on the implementation of the reverse bonding method, other non-planar implantation profiles can be obtained.

The present disclosure provides a method for forming the weakening zone 5 which makes it possible to improve the thickness uniformity of the active layer 13. In its general embodiment, illustrated in FIG. 3, the method successively comprises: - a step 102 of forming a screen layer 4, having a controlled non-planar profile, on a first face 61 of a substrate intended to form the donor substrate 6,

- a step of implanting species 103 through the screen layer 4 and the first face 61 of the substrate 6 in order to form the weakening zone 5.

The method optionally comprises a step 104 of removing the screen layer 4 before bonding the donor substrate to the recipient substrate. This removal can for example be carried out by chemical etching with an etching agent suitable for etching the screen layer without attacking the material of the donor substrate.

By “controlled” profile, it is meant that the profile of the screen layer 4 thus formed has a predefined thickness profile, so as to compensate for any non-uniformity in the depth of implantation of the species, and so as to obtain a weakening zone 5 which is substantially included in a plane parallel to the first face 61. Subsequently, the “non-compensated” profile will be called the weakening zone profile 5 resulting from an implantation of species without compensation.

An advantage of the proposed method is to compensate for a non-planar weakening zone profile 5 without requiring consumption of the semiconductor active layer after its transfer. Indeed, the known weakening zone formation methods which implement compensation of its profile, such as single-plate cleaning or the formation of a sacrificial oxide layer described above, involve consumption of the transferred active layer occurring after the bonding and layer transfer steps. In comparison, the proposed method makes it possible to perform the compensation during the species implantation step, i.e. before the active layer transfer, so as to obtain a substantially planar active layer profile without requiring consumption of the active layer. It is indeed necessary to take into account the volume ratio between silicon and silicon dioxide which is 0.44, that is to say that the formation of a silicon oxide layer of 0.1 nm thickness consumes 0.044 nm of silicon of the transferred active layer. Consequently, to standardize, after the bonding and transfer steps, the thickness of a convex transferred active layer having a determined excess thickness at the center relative to the edge, it is necessary to form an oxide layer having a thickness corresponding substantially to twice the excess thickness to be removed. On the contrary, thanks to the proposed method, the implantation profile being in accordance with the profile of the screen layer, a convex screen layer having a thickness corresponding substantially to the excess thickness to be avoided is sufficient.

Although the active layer obtained by a reverse bonding process can have different irregular thickness profiles, it is common for the uncompensated profile to be concave (the active layer is thicker at its edges than at its center) or convex (the active layer is thicker at its center than at its edges).

Thus, according to one implementation of the method, the screen layer 4 has a convex or concave profile, so as to precisely compensate for the non-compensated convex or concave profile generated by the implantation of species. Indeed, a concave screen layer 4 (i.e. whose thickness is greater at the edge than at the center) makes it possible to compensate for an implantation which would result, without compensation, in a concave active layer 13, and a convex screen layer 4 (i.e. whose thickness is greater at the center than at the edge) makes it possible to compensate for an implantation which would result, without compensation, in a convex active layer 13 - it is this latter case which is illustrated in FIGS. 2 and 3.

According to one implementation of the method, the implanted species comprise hydrogen ions and/or helium ions. The co-implantation of hydrogen ions and helium ions makes it possible in particular to improve the quality of the detachment obtained during the step of separating the active layer.

In order to ensure a variation in thickness of the screen layer which makes it possible to compensate for the non-uniformity of implantation depth, a distance between any two points of a free surface 41 of the screen layer 4 along an axis normal to the first face 61 can be between 0.2 and 5 nanometers.

The step of forming the screen layer 4 can be implemented in several ways. Preferably, the donor substrate 6 comprises a semiconductor material, and the screen layer 4 is an oxide layer of this material, obtained by thermal oxidation of a surface region of the donor substrate 6. Preferably, the donor substrate 6 comprises silicon, and the screen layer 4 comprises silicon dioxide obtained by thermal oxidation of a surface region of the substrate 6.

Thermal oxidation is generally carried out in a furnace, in an oxidizing atmosphere. According to one implementation of the method, the oxidation allowing the formation of the screen layer 4 with a controlled convex profile is carried out in several steps: initially, the substrate 6 is heated in a neutral atmosphere, i.e. non-oxidizing, to a temperature slightly higher than an oxidation temperature of the substrate, generally a few degrees higher than the oxidation temperature, for example to a temperature between 5 and 20°C above the oxidation temperature. The substrate is then cooled in an oxidizing atmosphere until said oxidation temperature is reached, then the substrate is maintained at its oxidation temperature, still in an oxidizing atmosphere. Due to the thermal inertia of the substrate, the substrate is thus cooled more quickly at its edges than at its center, so that the depth of the oxidized surface part of the substrate will be greater at its center than at its edges. This therefore contributes to obtaining a screen layer convex. It will be noted that the step of cooling the substrate under an oxidizing atmosphere aims to control the concavity or convexity of the screen layer 4, while the step of maintaining the substrate at its oxidation temperature makes it possible to control the thickness of the screen layer 4.

Other implementations of the formation of the screen layer 4 can be considered.

For example, an oxide shield layer 4 can be formed by selectively applying an oxidizing plasma to one or more zones of the first face 61 of the donor substrate 6. It will thus be possible to form an excess thickness of oxide in these zones, for example by suitable confinement of the plasma, before implementing conventional thermal oxidation.

According to another implementation, it is possible to form a screen layer 4 of uniform thickness by thermal oxidation of the donor substrate 6, before treating the screen layer 4 so as to form the desired thickness profile. For example, the screen layer 4 can be etched by applying hydrofluoric acid, or according to a cleaning method known from the state of the art, called “RCA clean”, which consists of using a solution of water, hydrogen peroxide and ammonia in order to etch the oxide layer.

The various embodiments mentioned above may optionally be combined.

Thermal oxidation with the controlled temperature profile is particularly advantageous in that it requires only one piece of equipment and one type of treatment to form the controlled profile shield layer.

Prior to the step of forming the screen layer 4, the method may comprise a calibration of the profile of the screen layer 4, so as to allow precise compensation of the implantation profile.

4, a calibration substrate 600 of the same material as the donor substrate is provided, on which an implantation 701 of atomic or ionic species is carried out, through a first face 601 of the calibration substrate 600, so as to create a weakening zone 500. The calibration then comprises a step 702 of separating the calibration substrate into two parts along the weakening zone 500: a first part 602 which comprises the first face 601 and a second part 603. Furthermore, a step of bonding the calibration substrate 600 to a support substrate is preferably provided. The support substrate acts as a mechanical stiffener intended to facilitate the separation of the layer 621 from the calibration substrate 600. The first part 602 then has a profile identical to an active layer 13 which would be obtained in the context of a manufacturing method by reverse bonding, without compensation as proposed. Calibration finally comprises a step 703 of defining a target profile 400 defined substantially by the shape of the surface 621 of the first part 602 along the weakening zone 500, exposed by the separation.

The present disclosure also relates to a method of manufacturing a semiconductor-on-insulator type component 10, shown in FIG. 5. This method comprises the following steps:

- the provision of a donor substrate 6 and a recipient substrate 7 comprising a semiconductor material, for example but not limited to silicon,

- the formation of an electrically insulating layer 2 on a face 71 of the receiving substrate. It may in particular be provided that this layer 2 has a thickness of at least 150 nanometers, so as to ensure optimal insulation of the active layer 13 relative to the base 11 of the substrate,

- the formation of a weakening zone 5 in the donor substrate 6 by means of the method according to the present disclosure. This step therefore comprises the formation 102 of the screen layer 4 on the first face 61 of the donor substrate, as well as the implantation 103 of species through this first face. At the end of this step, a planar weakening zone 5 is obtained, substantially parallel to the first face 61,

- the removal 104 of the screen layer 4, so as to expose the first face 61,

- the bonding 105 of the donor substrate 6 on the receiving substrate 7. The first face 61 of the donor substrate is bonded on the receiving substrate 7, the electrically insulating layer 2 being arranged between the two substrates,

- the separation 106 of the donor substrate 6 at the level of the weakening zone 5, so as to transfer a semi-conductor layer from the donor substrate 6 onto the recipient substrate 7. This semi-conductor layer forms the active layer 13 of the SOI substrate.

Claims

1. Method for forming a weakening zone (5) in a semiconductor substrate (6), successively comprising the following steps: a. forming a shielding layer (4) having a controlled non-planar profile on a first face (61) of the substrate, b. implanting species through the shielding layer and the first face (61) of the substrate to form the weakening zone, the profile of the shielding layer being chosen to compensate for a non-uniformity in the depth of implantation of the species so that the weakening zone (5) is substantially included in a plane parallel to the first face (61). 2. Method according to the preceding claim, the screen layer (4) having a convex or concave profile. 3. Method according to any one of the preceding claims, the species implanted in the first face (61) of the substrate comprising hydrogen ions and helium ions. 4. Method according to any one of the preceding claims, a distance between any two points of a free surface (41) of the screen layer (4) along an axis normal to the first face (61) being between 0.2 nm and 5 nm. 5. Method according to any one of the preceding claims, the substrate (6) comprising silicon. 6. Method according to any one of the preceding claims, the screen layer (4) comprising an oxide of a semiconductor material, in particular silicon dioxide. 7. Method according to the preceding claim, the screen layer (4) being obtained by thermal oxidation of a surface region of the semiconductor substrate (6) 8. Method according to the preceding claim, the formation of the screen layer (4) by oxidation comprising heating the substrate (6) under a neutral atmosphere to a temperature above an oxidation temperature of the substrate, then cooling the substrate to said oxidation temperature, and applying an oxidizing atmosphere to form the screen layer (4). 9. Method according to claim 7, comprising, before the thermal oxidation, a selective application of an oxidizing plasma on a zone of the first face (61) of the substrate (6) so as to form an excess thickness of oxide in said zone. 10. Method according to any one of the preceding claims, comprising, prior to the formation of the screen layer (4), a calibration of the profile of the screen layer (4) comprising the following steps: - implantation (701) of atoms through a first face (601) of a calibration substrate (600), so as to create a weakening zone (500), - separation (702) of the calibration substrate along the weakening zone into a first part (602), comprising the first face (601), and a second part (603), - defining (703) a target profile (400) whose shape is substantially identical to a surface (621) of the first part (602) exposed by the separation, the target profile (400) being used to define the profile of the screen layer (4) during its formation. 11. Method for manufacturing a semiconductor component (10) of the semiconductor-on-insulator type, successively comprising the steps of: - supply of a donor substrate (6) and a recipient substrate (7) made of semiconductor material, - formation (101) of an electrically insulating layer (2) on one face (71) of the receiving substrate, - formation (102, 103) of a weakening zone (5) in the donor substrate (6) by means of the forming method according to any one of the preceding claims, the weakening zone (5) thus formed delimiting a semi-conductor layer, - removal (104) of the screen layer (4), - bonding (105) of the first face (601) of the donor substrate (6) to the electrically insulating layer (2) of the recipient substrate (7), - separation (106) of the donor substrate (6) at the weakening zone (5) so as to transfer the semiconductor layer from the donor substrate (6) to the recipient substrate (7). 12. Method according to the preceding claim, in which the electrically insulating layer (2) and the screen layer (4) are formed by heat treatment in the same oven. 13. Method according to any one of claims 11 and 12, the electrically insulating layer (2) having a thickness of at least 150 nanometers.