阅读说明：本技术 具有n掺杂中间层的半导体基板 (Semiconductor substrate with n-doped intermediate layer ) 是由 弗洛里安·唐迪耶 于 2019-12-18 设计创作，主要内容包括：本发明涉及一种制造第13族氮化物的单晶半导体材料的方法,其包括以下步骤：a)通过外延生长在起始基板上沉积第一层第13族氮化物,优选GaN,b)供应n掺杂剂气体和在第一层上通过外延生长沉积第二层第13族氮化物,优选GaN,所述沉积包括材料凹陷区域,c)停止供应掺杂剂气体,并在前一掺杂层上通过外延生长沉积第三层第13族氮化物,优选GaN。(The present invention relates to a method for manufacturing a group 13 nitride single crystal semiconductor material, comprising the steps of: a) depositing a first layer of a group 13 nitride, preferably GaN, on a starting substrate by epitaxial growth, b) supplying an n-dopant gas and depositing a second layer of a group 13 nitride, preferably GaN, on the first layer by epitaxial growth, said deposition comprising a material recess region, c) stopping the supply of the dopant gas and depositing a third layer of a group 13 nitride, preferably GaN, on the previous doped layer by epitaxial growth.)

1. A method of fabricating a group 13 nitride single crystal semiconductor material, comprising the steps of:

a) a first layer of a group 13 nitride, preferably GaN,

b) supplying an n-dopant gas and depositing a second layer of a group 13 nitride, preferably GaN, on the first layer by epitaxial growth, the deposition including a recessed region of material,

c) the supply of the dopant gas is stopped and a third layer of a group 13 nitride, preferably GaN, is deposited by epitaxial growth on the previously doped layer and in the recessed regions of the second layer, so that the recessed regions of the second layer are filled by the deposition of the third layer.

2. The manufacturing method according to claim 1, wherein the n-dopant gas contains at least one chemical element of group 14 of the periodic table.

3. The manufacturing method according to claim 2, wherein the chemical element of group 14 of the periodic table is: germanium from a solid source, GeCl₄Germane, tetramethylgermanium and isobutylgermane and their derivatives; and/or the presence of a gas in the gas,

silicon, formed from solid sources, silane, dichlorosilane, silicon tetrachloride and derivatives thereof.

4. Manufacturing process according to one of the preceding claims, in which the n-dopant gas is mixed in the gas phase with a flow of gallium chloride.

5. Manufacturing method according to one of the preceding claims, wherein the epitaxial growth deposition step is carried out by HVPE.

6. The manufacturing method according to one of the preceding claims, further comprising a step of separating the starting substrate to obtain a free-standing group 13 nitride single crystal semiconductor material.

7. A method of fabricating a group 13 or III nitride wafer, comprising:

-manufacturing a free-standing group 13 nitride single crystal semiconductor material according to the preceding claim; the material comprises:

a group 13 nitride layer, preferably a GaN layer, doped with an n-dopant of a predetermined thickness and having a material recess region;

an undoped group 13 nitride layer, preferably a GaN layer, disposed on the doped layer and in the material recess region of the doped layer;

-performing a correction by removing to obtain an n-doped layer according to a given thickness to form a group 13 or III nitride wafer.

8. Method for manufacturing a group 13 or III nitride wafer according to the preceding claim, further comprising a wafer selection step comprising the sub-steps of:

-performing raman spectroscopy to identify a less doped or undoped region of the wafer, called the minimum doped region;

identification of non-radiative defects by cathodoluminescence, to select maximum threading dislocation density or TDD greater than 1X10⁸cm^-2A wafer confined to an area within a circle of 20 μm diameter, the center of the circle coinciding with the center of each of the least doped regions.

9. A group 13 nitride single crystal semiconductor material, comprising:

-a first layer of a group 13 nitride, preferably GaN, having permanent defect regions corresponding to voids or pits of decreasing cross-section in a direction opposite to the growth direction;

-a second layer of a group 13 nitride, preferably GaN, doped with n-dopant of predetermined thickness and having a recessed region of material coinciding with the permanent defect region of the first layer;

a third layer of undoped group 13 nitride, preferably GaN, arranged on the doped layer and in the material recess regions of the doped layer, the recess regions of the second layer being filled by deposition of the third layer.

10. Monocrystalline semiconductor material according to the preceding claim, wherein the thickness of the second n-doped layer is between 100 and 2000 microns.

11. Monocrystalline semiconductor material according to one of claims 9-10, wherein the first layer has a thickness between 100 and 1000 microns.

12. Monocrystalline semiconductor material according to one of claims 9-11, wherein the third layer has a thickness between 200 and 5000 microns.

13. Monocrystalline semiconductor material according to one of claims 9-12, wherein the ratio of the thickness of the second layer to the thickness of the first layer is between 0.1 and 20.

14. The single crystal semiconductor material of one of claims 9-13 wherein the n-dopant content of the second layer is greater than 1x10¹⁸cm^-3And less than 2X 10¹⁹cm^-3。

15. A group 13 or III nitride wafer made according to the method of claim 7 and comprising:

-a group 13 nitride layer, preferably a GaN layer, doped with n-dopants and having a material recess region;

-an undoped group 13 nitride layer, preferably a GaN layer, arranged in the material recess region of the doped layer;

the upper surface of the wafer includes:

-a first doped region corresponding to the upper surface of the doped layer, the free carrier density of which is greater than 1.0 x10 as measured by the hall effect¹⁸cm^-3(ii) a And

-a less doped or undoped second regionCorresponding to the upper surface of the undoped layer arranged in a material recess region of the doped layer, the free carrier density of said second region being less than 8 x10 as measured by the Hall effect¹⁷cm^-3Preferably less than 5X 10¹⁷cm^-3。

16. Group 13 or III-nitride wafer according to the preceding claim, wherein the first doped region comprises a chemical element of group 14 of the periodic table, the chemical element of group 14 of the periodic table being: germanium from a solid source, GeCl₄Germane, tetramethylgermanium and isobutylgermane and their derivatives; and/or

Silicon, formed from solid sources, silane, dichlorosilane, silicon tetrachloride and derivatives thereof.

17. A group 13 or III nitride wafer according to any of claims 15-16, wherein the dopant content of the first doped region is greater than 1x10¹⁸cm^-3And less than 2X 10¹⁹cm^-3。

18. A group 13 or III nitride wafer according to any of claims 15-17, wherein the first doped region has an oxygen O concentration of less than 2.0 x10¹⁸cm^-3。

19. A group 13 or III nitride wafer according to claim 18, wherein the cumulative concentration of oxygen O atoms and n dopants in the crystal is less than 1.0 x10¹⁹cm^-3。

20. A group 13 or III nitride wafer according to any of claims 15-19, wherein the area of the second region is less than 5%, even less than 2% of the area of the wafer.

21. A group 13 or III nitride wafer according to any one of claims 15 to 20, wherein the crystal quality is measured by: the full width at half maximum of the X-ray diffraction (XRD) peak of (002) line near angle ω under symmetric conditions for GaN plane (0001) is below 130 arcsec, preferably below 100 arcsec, more preferably below 90 arcsec, or even below 60 arcsec; and a full width at half maximum of an X-ray diffraction (XRD) peak of 201 line near angle ω of GaN film (0001) under the tilt condition, which is less than 240 arcsec, preferably less than 140 arcsec, or even less than 100 arcsec.

22. A group 13 or III nitride wafer according to any of claims 15-21, wherein the wafer has an average resistivity of less than 25mohm.

23. Use of a group 13 or III nitride wafer according to one of claims 15-22 as a substrate for the manufacture of optoelectronic components such as light emitting diodes, laser diodes, vertical transistors for power electronics, horizontal transistors for power electronics or telecommunications (radio frequency), current rectifier diodes or sensors.

Technical Field

The present invention relates to the general technical field of manufacturing substrates and wafers of semiconductor material based on elements of groups 13 and 15 of the periodic table of the elements, such as gallium nitride GaN.

These wafers serve as a means for fabricating semiconductor structures such as Light Emitting Diodes (LEDs), Laser Diodes (LDs), vertical transistors for power electronics, horizontal transistors for power electronics or telecommunications (radio frequency), current rectifier diodes or sensors.

Background

The current processes for manufacturing semiconductor material substrates based on nitrides of group 13 or IIIA elements rely on vapor deposition techniques, in particular heteroepitaxy, which consists in growing a crystal (for example a gallium nitride GaN crystal) on a starting substrate of different nature (for example a sapphire substrate).

These methods involve injection systems from at least two different gaseous components that are capable of interacting prior to deposition.

Well-known methods may be mentioned, for example:

metal Organic Vapour Phase Epitaxy (MOVPE),

-Hydride Vapour Phase Epitaxy (HVPE),

-Closed Space Vapor Transport (CSVT) extensions,

ceramic vapor deposition, etc.

The so-called 3D growth process or e.g. three-dimensional lateral growth allows the dislocation density to be reduced to less than 107/cm²。

Under three-dimensional growth conditions, the HVPE growth front has a face perpendicular to the growth front and a face oblique to the growth front. As regards the planes perpendicular to the growth front, these are the planes formed by the basal planes (0001). It is known that these faces contain less oxygen than the various inclined faces that may be present (non-basal face, index hkil, where h ≠ 0 and k ≠ 0 and i ≠ 0). This difference in n-type doping results in some regions being more resistant or having different optical properties than others. After shaping to obtain a two-dimensional surface, for example by rectification and/or polishing, inhomogeneities in the optical and/or electrical properties can be observed.

Furthermore, the crystal lattice may have macroscopic inclusions with a size greater than 10 μm, consisting mainly of twins, domain inversions or even polycrystals.

Furthermore, whatever the process in the 3D or 2D growth mode, the inevitable presence of defects or contaminations on the starting substrate may lead to material depressions, called pits, larger than 100 μm. Defects of this type, in particular permanent voids or pits, have a decreasing cross section in the direction opposite to the growth direction and increase in width and depth with increasing thickness of the deposit. These voids form large inverted pyramids hundreds of microns wide. At the apex of these voids, the crystalline matrix may exhibit crystal defects and a high dislocation density.

All these defects generated during the growth process lead to defects in the final wafer (doping heterogeneity and crystal defects, high dislocation density) which cause failures during the fabrication of electronic and/or optoelectronic devices.

To improve the electronic properties of the substrate, for example, US2006255339a1 discloses a concentration of 0.7 × 10¹⁸To about 3X 10¹⁸/cm³At the same time, an n-doped GaN crystal with a thermal conductivity of at least 1.5W/cm.K, in order to be able to equip devices, in particular diodes with a power of more than 1W. Even though only examples with Si doping are provided in the present application, dopants such as Si, O, Ge, C, etc. may be used alone or in combination.

US20110175200a1 proposes an HVPE growth process in which GeCl is added in a reaction chamber₄The crystals were doped with Ge to obtain more electron-conductive crystals to compensate for the sudden increase in resistivity observed when the growth rate was higher than 450 μm/h. However, such growth rates result in high surface density and lower crystal quality of macroscopic inclusions.

US9461121B2 claims a method of improving n-dopant distribution in GaN crystals, typically by mixing Ga and dopant inputs for vapor phase growth. Uniform introduction into the reactor can be achieved by premixing the dopant and Ga prior to reaction with HCl or mixing the dopant and gallium halide as a single tube within the reaction chamber. The uniformity of dopant concentration is measured by micro-raman, Microwave Detection Photoconduction (MDP) or micro-photoluminescence. The uniformity level and method data indicate that this is clearly an HVPE process with 2D growth and therefore does not provide a solution for the 3D growth process.

There is therefore a need for substrates and wafers of group 13 or III nitride materials, in particular of group 13 or III nitride materials, more in particular wafers and substrates made of GaN, which have a large thickness, generally a thickness greater than 100 microns, even 400 microns or higher, are more uniform and have at the same time:

low surface density of macroscopic inclusions, generally less than 5cm^-2Preferably less than 4cm^-2Or even less than 1cm^-2，

-crystal mass, measured by: the full width at half maximum of the X-ray diffraction (XRD) peak of (002) line near angle ω under the symmetry condition of GaN (0001) plane, which is less than 130 arcsec, preferably less than 100 arcsec, more preferably less than 90 arcsec; and a full width at half maximum of an X-ray diffraction (XRD) peak of a 201 line near an angle ω of the GaN (0001) film under a tilt condition, which is less than 240 arc seconds, preferably less than 140 arc seconds, and

improved electronic properties, typically average resistivity less than 25mohm.cm, even less than 20 mohm.cm.

Disclosure of Invention

In this connection, the object of the invention is a method for producing a single-crystal semiconductor material of group 13 nitride, comprising the following steps:

a) a first layer of a group 13 nitride (preferably GaN) is deposited on the starting substrate by epitaxial growth,

b) supplying an n-dopant gas and depositing a second layer of a group 13 nitride, preferably GaN, on the first layer by epitaxial growth, the deposition including a recessed region of material,

c) the supply of the dopant gas is stopped and a third layer of group 13 nitride (preferably GaN) is deposited by epitaxial growth on the previously doped layer and in the recessed regions of the second layer, so that the recessed regions of the second layer are filled by the deposition of the third layer.

As an illustration, unless otherwise indicated, the concentrations of chemical elements referred to herein are atomic concentrations.

Advantageously, but optionally, the method according to the invention may also comprise at least one of the following features:

the n-dopant gas comprises at least one chemical element of group 14 of the periodic table.

-the chemical elements of group 14 of the periodic table are: germanium from a solid source, GeCl₄Germane, tetramethylgermanium and isobutylgermane and their derivatives; and/or silicon, formed from solid sources, silane, dichlorosilane, silicon tetrachloride, and derivatives thereof.

-the n-dopant gas is mixed in the gas phase with the gallium chloride gas stream.

Epitaxial growth is achieved by HVPE at growth rates lower than 450 μm/h to guarantee a low surface density of macroscopic inclusions and to ensure a satisfactory crystalline quality.

-performing an epitaxial growth deposition step by HVPE.

-a step of separating the starting substrate to obtain a free-standing group 13 nitride single crystal semiconductor material.

-the manufacture of a free-standing group 13 nitride single crystal semiconductor material; the material comprises:

a group 13 nitride (preferably GaN) layer doped with an n-dopant of a predetermined thickness and having a material recess region;

an undoped group 13 nitride (preferably GaN) layer disposed on and in the material recess region of the doped layer;

o is corrected by removal to obtain an n-doped layer according to a given thickness to form a group 13 or group III nitride wafer.

-a wafer selection step comprising the sub-steps of:

performing raman spectroscopy to identify a less doped or undoped region of the wafer, referred to as a minimum doped region;

identification of non-radiative defects by cathodoluminescence, to select a maximum threading dislocation density or TDD of more than 1 × 10⁸cm^-2A wafer confined to an area within a circle of 50 μm diameter, the center of which coincides with the center of each of the least doped regions.

Another object of the present invention is a group 13 nitride single-crystal semiconductor material, comprising:

-a first layer of a group 13 nitride (preferably GaN) having permanent defect regions corresponding to voids or pits of decreasing cross-section in a direction opposite to the growth direction;

-a second layer of a group 13 nitride (preferably GaN) doped with n-dopant of predetermined thickness and having a recessed region of material coinciding with a permanent defect region in the first layer or a defect region formed within the second layer;

a third layer of undoped group 13 nitride (preferably GaN) arranged on the doped layer and in the recessed regions of the material of the doped layer, the recessed regions of the second layer being filled by deposition of the third layer.

Advantageously, but optionally, the monocrystalline semiconductor material according to the invention may also comprise at least one of the following features:

-the thickness of the second n-doped layer is between 100 and 2000 microns:

-the thickness of the first layer is between 100 and 1000 microns:

-the thickness of the third layer is between 200 and 5000 microns;

-the ratio of the thickness of the second layer to the thickness of the first layer is between 0.1 and 20;

-the n-dopant content of the second layer is greater than 1x10¹⁸cm^-3And less than 2X 10¹⁹cm^-3。

Another object of the present invention is a group 13 or III nitride wafer that can be produced according to the above method, and includes:

-a group 13 nitride (preferably GaN) layer doped with n-dopants and having a recessed region of material;

-an undoped group 13 nitride (preferably GaN) layer disposed in the material recess region of the doped layer;

the upper surface of the wafer includes:

-a first doped region corresponding to the upper surface of the doped layer having a free carrier density, measured by the hall effect, of greater than 1.0 x10¹⁸cm^-3(ii) a And

-a second, less doped or undoped, region corresponding to the upper surface of the undoped layer arranged in the material recess region of the doped layer, the free carrier density of said second region being by the hall effectMeasured as less than 8 x10¹⁷cm^-3Preferably less than 5X 10¹⁷cm^-3。

Advantageously, but optionally, the group 13 or III wafer according to the invention may also comprise at least one of the following features:

the first doped region comprises a chemical element of group 14 of the periodic table, which is germanium, from a solid source, GeCl₄Germane, tetramethylgermanium and isobutylgermane and their derivatives; and/or silicon, formed from solid sources, silane, dichlorosilane, silicon tetrachloride, and derivatives thereof.

-the dopant content of the first region is greater than 1x10¹⁸cm^-3And less than 2X 10¹⁹cm^-3。

The first doped region has an oxygen O concentration of less than 2.0X 10¹⁸cm^-3。

By controlling the purity of the group III element precursor and by subjecting the reactor to one or more very thorough purges at a residual pressure of less than 10 Torr, followed by one or more N₂Purging to control oxygen supply and concentration.

-the cumulative concentration of oxygen O atoms and n dopants in the crystal is less than 1.0 x10¹⁹cm^-3。

The area of the second region is less than 5%, or even less than 2% of the area of the wafer.

-crystal mass, measured by: the full width at half maximum of the X-ray diffraction (XRD) peak of (002) line near angle ω under symmetric conditions for GaN (0001) plane, which is less than 130 arcsec, preferably less than 100 arcsec, more preferably less than 90 arcsec, or even less than 60 arcsec; and a full width at half maximum of an X-ray diffraction (XRD) peak of 201 line near angle ω of the GaN (0001) film under tilt conditions, which is less than 240 arcsec, preferably less than 140 arcsec, or even less than 100 arcsec.

The average resistivity of the wafer is less than 25mohm.

Another object of the present invention is the use of a group 13 or III nitride wafer according to one of the preceding features as a substrate for the manufacture of electronic and/or optoelectronic components such as light emitting diodes, laser diodes, vertical transistors for power electronics, horizontal transistors for power electronics or telecommunications (radio frequency), current rectifier diodes or sensors.

The invention also relates to a method for selecting defect regions in a wafer of group 13 nitride single crystal semiconductor material, which defect regions cause defects in the optoelectronic components arranged on or near these regions.

More specifically, another object of the invention is a method for selecting a defective region within a wafer of group 13 nitride single crystal semiconductor material before or after deposition of a photovoltaic element, comprising the steps of:

-performing Raman spectroscopy to identify less doped or undoped regions of the wafer, called minimum doped regions, according to a first step,

or by photoluminescence, preferably by cathodoluminescence, to identify a maximum Threading Dislocation Density (TDD) higher than 1x10⁸cm^-2Is not a radiation defect of (a) a,

-according to a second step, selecting the area inscribed in a circle of diameter 50 μm, the centre of said circle coinciding with the centre of each of the minimum doped areas corresponding to the areas where the photocell defect may be present, so as to facilitate the detection of the defect in the photocell

Avoiding deposition in this selected 50 μm diameter region prior to depositing the photovoltaic element on the wafer, and/or

After depositing the photovoltaic elements on the wafer, the elements deposited in the selected 50 μm diameter region are removed.

Drawings

Other characteristics, objects and advantages of the invention will appear on reading the following detailed description and on reference to the accompanying drawings, given by way of non-limiting example, in which:

[ FIG. 1]

Fig. 1 summarizes the main steps of a substrate manufacturing method according to one embodiment of the invention.

[ FIG. 2]

Figure 2 schematically shows a semiconductor material consisting of a multilayer stack according to one possible embodiment of the invention.

[ FIG. 3]

Fig. 3 illustrates a slice of a free-standing GaN material according to a possible embodiment of the invention comprising, after separation, an undoped first layer or underlayer, an n-doped second layer or underlayer or intermediate layer and an undoped third layer or upper layer.

[ FIG. 4]

Figure 4 shows a cross section of the wafer after rectification and finishing of the slices of support material.

[ FIG. 5]

Fig. 5 shows raman spectra measured at and around the bottom of the growth pit, respectively.

Detailed Description

Referring to fig. 1 and 2, the main stages of the GaN wafer fabrication method are illustrated.

In the following, the process according to the invention will be described with reference to the fabrication of silicon nitride GaN wafers.

However, it will be apparent to those skilled in the art that the processes described below may be used to grow materials that include group 13 nitride layers other than gallium nitride GaN.

1.Manufacturing method

The process comprises the following steps:

a growth phase 10 of a first layer 5a of a group 13 nitride (preferably GaN);

a stage 20 of formation of a separation zone 4;

a phase 30 of recovering the epitaxy to form a thick layer 5b of undoped GaN, a thick layer 5c of n-doped GaN and a final thick layer 5d of undoped GaN;

a separation stage 40 to obtain GaN crystal 5;

-a rectification phase 45 to remove the thickness of the thick layer of undoped GaN;

a finishing stage 50 to form a GaN wafer from GaN crystal 5.

1.1Growth phase 10

The optional growth phase 10 comprises the formation of a GaN sublayer 5a by lateral overgrowth.

The lateral overgrowth minimizes the defect density contained in the GaN sublayer 5 a.

The method for reducing the dislocation density in the GaN sublayer 5a includes:

initiating an island mode of GaN growth, and then

Promoting the coalescence of the islands to obtain the GaN sublayer 5 a.

Advantageously, the lateral overgrowth is achieved on a starting substrate 1 having a non-zero cutoff angle.

The use of the starting substrate 1 having a non-zero off-angle allows the growth of the first GaN layer 5a having a non-zero off-angle.

The starting substrate 1 may be selected from Si, AlN, GaN, GaAs, Al₂O₃(sapphire), ZnO, SiC, LiAlO₂、LiGaO₂、MgAl₂O₄4H-SiC, or any other type of starting substrate known to the skilled person for achieving gallium nitride growth.

It may have a thickness of several hundred microns, typically 350 microns.

Advantageously, the starting substrate 1 may be treated by nitridation before any deposition step. This improves the quality of the obtained GaN crystal.

The cut-off angle may be comprised between 0.1 and 5 degrees, preferably between 0.2 and 0.8 degrees, even more preferably between 0.3 and 0.6 degrees (in particular to limit stacking errors).

The growth of the GaN sublayer 5a can be realized in different variants. In particular, the lateral overgrowth may be based on:

using a dielectric mask 3b comprising openings 3a in which islands are formed, as described in document WO 99/20816;

using a dielectric layer on which islands are spontaneously formed without openings, as described in document EP 1338683.

1.2.1.First variation of lateral overgrowth

In a first variant, the growth phase 10 is an epitaxial lateral overgrowth (hereinafter ELO).

ELO comprises the step of depositing a thicker planar layer 2 on a starting substrate 1.

The deposition is preferably carried out by Metal Organic Vapour Phase Epitaxy (MOVPE), for example at a temperature comprised between 500 ℃ and 700 ℃, in particular at a temperature of 600 ℃.

The deposition of layer 2 reduces the stress between the starting substrate 1 and the subsequent epitaxial GaN sublayer 5 a. In fact, the deposition of the layer 2 on the substrate 1 ensures a "soft" transition between the substrate 1 and the GaN sublayer 5a (which differ in their crystalline structure).

The deposition of layer 2 further promotes the subsequent separation of GaN crystal 5, as will become apparent from the following description. The layer 2 is for example a GaN layer, an AlN layer or an AlGaN layer.

In another step, a mask 3b including the opening 3a is formed. The openings 3a may be in the form of dots or stripes and define locations for subsequent selective growth of GaN islands.

The mask 3b may be made of a dielectric material (e.g., SiN)_x(SiN、Si₃N₄Etc.) or SiO₂Or TiN). This minimizes defects generated at the edges of the mask, thereby improving the quality of the GaN layer subsequently epitaxial thereon.

The formation of the mask 3b may be performed by any technique known to those skilled in the art. For example, the forming of the mask may include:

depositing the dielectric layer 3a directly on the layer 2 from gaseous silane and ammonia precursors, and

the dielectric layer 3a is etched by photolithography to form the opening 3 a.

A starting substrate 1 covered with a layer 2 and a mask 3b is thus obtained. In addition to improving the quality of the GaN sublayer 5a (by filtering out defects), the mask 3b weakens the interface between the starting substrate 1 and the GaN sublayer 5 a.

Another step consists in forming GaN islands-in-the-sea through the mask openings 3 a. The growth rate along the axis orthogonal to the main plane of the starting substrate 1 remains higher than the lateral growth rate. This results in islands or stripes with triangular cross-sections (depending on the shape of the openings 3 a). In these strips with triangular cross-section, the threading dislocations are bent by 90 °.

Then laterally overgrown to finally form a planar ELO layer. At the end of this process step, a dislocation density of less than 10 is obtained⁸cm^-2The first GaN layer 5 a.

1.2.2.Second variation of lateral overgrowth

In a second variant, the growth phase 10 consists of a global lateral overgrowth (hereinafter ULO) described in document EP 1977028.

ULO includes the step of depositing a nucleation layer on the starting substrate 1.

The nucleation layer is, for example, a very thin silicon nitride SiN film, with about several atomic planes, i.e., about 10nm to 20nm thick. The silane and ammonia based SiN deposition may last 360 seconds.

A continuous buffer layer 2 (e.g., GaN) is then deposited on the nucleation layer. The deposition of the GaN buffer layer 2 filters out crystal defects and thus minimizes the defect density that will occur in the first GaN sublayer 5a of the subsequent epitaxy from the beginning of the process.

The thickness of the GaN buffer layer 2 may be between 10 and 100 nm. The temperature during this operation may be between 500 and 700 ℃.

Annealing is then performed at a high temperature of 900 to 1150 ℃. The profile of the GaN buffer layer 2 undergoes a depth change due to solid phase recrystallization due to mass transfer under the combined effect of the temperature rise, the presence of a sufficient amount of hydrogen in the carrier gas, and the presence of a very thin SiN film. The initially continuous GaN buffer layer 2 is then transformed into a discontinuous GaN pattern layer. Due to the very small thickness of the nucleation layer, a GaN pattern or islands-in-the-sea is obtained with very good crystalline quality and maintaining the epitaxial relationship with the starting substrate.

The exposed regions of silicon nitride SiN then serve as a mask and the GaN pattern serves as GaN regions located in the openings made ex situ in the mask. Then laterally overgrown to finally form a planar ULO layer.

This method, in which the silicon nitride mask is formed spontaneously and involves the same dislocation bending mechanism as in ELO, is identified as "ULO" (or "spontaneous ELO").

1.2Stage 20 of forming separation zone 4

The process also includes a stage 20 of forming the separation zone 4.

This stage 20 of forming the separation zones can be carried out according to different variants. In particular, the stage 20 of carrying out the formation of the separation zones can be:

before the growth phase 10 of the first GaN layer (first variant), or

After a growth phase 10 of the first GaN layer (second variant), or

During the growth phase 10 of the first GaN layer (third variant).

1.2.1.First variant for forming the separation zone 4

In a first variant, the step 20 of forming the detachment zones 4 may consist in depositing a sacrificial intermediate layer before the growth phase 10 of the GaN sublayer 5a, as described in document EP 1699951.

The intermediate layer, which may be Si, ZnO, TiN, SiN, TiC, acts as a sacrificial layer that spontaneously evaporates during the subsequent epitaxial growth phase of the GaN sublayer 5 a.

1.2.2.Second variant for forming a separation zone

In a second variant, the phase 20 of formation of the detachment zones 4 comprises an implantation step carried out after the growth phase 10 of the GaN sublayer 5 a. This implantation allows to create an embrittlement zone in the GaN sublayer 5 a.

Implantation involves bombarding the GaN sublayer 5a with ions to create a microcavity (or foam) layer in the semiconductor at a depth close to the average penetration depth of these ions.

The implanted ions may be selected from tungsten, helium, neon, krypton, chromium, molybdenum, iron, hydrogen, or boron. Preferably, the implanted ions are tungsten ions. They have the special feature of decomposing GaN.

In terms of dose, when the implanted ions are H + ions, the dose of implanted ions may be 10+ to 10¹⁷cm^-2In between, the implantation depth may vary from 0nm to 50nm starting from the free surface of the first GaN sublayer 5a, called the growth plane.

The implantation of the embrittlement ions may be carried out in a single step or in successive steps. During the injection step, the temperature may be between 4K and 1400K.

The implantation may be followed by an annealing phase to cure crystal damage generated during the ion implantation, which may be performed at a temperature comprised between 500 ℃ and 1500 ℃.

1.2.3.Third variant for forming a separation zone

In the third variant, the separation zones 4 can be formed during the growth phase 10 of the GaN sublayer 5 a.

In particular, when the growth phase is carried out according to a first variant embodiment called ELO (i.e. deposition of the dielectric mask 3 b), the phase 20 of forming the detachment zones 4 may comprise implantation of the buffer layer 2 before deposition of the mask 3 b.

This allows to place the separation zone 4 at a precisely desired depth, since the first GaN layer 5a deposited in the ELO step does not "interfere" with the ion implantation.

Of course, the implantation may be performed at different stages of the ELO (or ULO) stage, either within the islands, at intermediate stages where the islands do not completely coalesce, or after the islands completely coalesce.

1.3An epitaxy recovery stage 30

At the end of the growth phase 10 of the GaN sublayer 5a and of the phase 20 of forming the separation zones 4, the process comprises an epitaxial recovery phase 30 to form a thick first undoped GaN layer 5b, a thick second n-doped GaN layer 5c and a thick third undoped GaN layer 5 d.

The process may also start directly at this stage 30 by forming a thick GaN layer 5b, the growth stage 10 and the stage 20 of forming the separation region being optional. In the following, it is considered to apply these phases 10 and 20.

This epitaxial recovery can be achieved by:

-Metal Organic Vapour Phase Epitaxy (MOVPE);

-Hydride Vapour Phase Epitaxy (HVPE);

-Closed Space Vapor Transport (CSVT) epitaxy; or

-Liquid Phase Epitaxy (LPE).

In this step, the HVPE technique is preferably used, which can obtain three main advantageous effects:

the first effect is that the GaN sublayer 5a is thickened (without generating new dislocations or cracks) without losing its crystalline quality;

a second effect is that during HVPE the dislocation density is further reduced by at least a factor of 2, over 100 μm for GaN growth (0001) (ref. https:// doi.org/10.1143/APEX.5.095503);

a third effect is that the thick GaN layer 5 thus obtained may in some cases allow spontaneous separation from its starting substrate 1 at the separation zones 4 in case of sublimation or mechanical fracture of said zones during HVPE growth.

More precisely, the recovery is performed according to the following procedure: the temperature was raised in a mixed atmosphere of nitrogen gas and ammonia gas and hydrogen gas. Once a stable temperature of about 1000 ℃ is reached, the growth phase of the thick GaN layer is then initiated by introducing a gaseous phase, for example gallium chloride (GaCl). The GaCl and ammonia are partially pyrolyzed in a growth chamber maintained at a temperature of about 1000 c. Thus, monocrystalline GaN deposits gradually form at the nucleation substrate level (formed during the first growth stage).

It is necessary to obtain a GaN layer that is sufficiently thick and therefore sufficiently resistant from a mechanical point of view to avoid cracking of the GaN layer into small pieces during the detachment process and to facilitate its handling without the risk of cracking. Under these experimental conditions, growth was continued for several hours to reach a GaN layer of at least 200 microns thickness, preferably greater than 1 mm.

Growth is then finally completed by transferring the HCl stream to the outside and cooling is performed in an atmosphere consisting of nitrogen and ammonia.

The growth conditions of these first, second and third monocrystalline layers 5b, 5c, 5d are generally such that the growth temperature is between 900 and 1200 c and the growth rate can be between 50 and 500 microns/hour, preferably between 70 and 200 microns/hour.

The thickness of the as-obtained original self-supporting GaN crystal is greater than 200 microns, preferably greater than 1 mm. Its maximum thickness is less than 10 mm, or even less than 5 mm.

The original self-supporting GaN crystal thus obtained has a diameter of more than 50mm, preferably more than 100 mm. Its maximum diameter is less than 250 mm, or even less than 200 mm.

Referring to fig. 3, the layer 5b has permanent defect areas corresponding to voids or pits with a cross-section decreasing in the direction opposite to the growth direction.

Second, a second monocrystalline GaN layer 5c is obtained on layer 5b by doping with an n-doping element, under the same growth conditions, according to the following method:

control of oxygen supply and concentration by controlling the purity of the group III precursor and by performing a very thorough purge of the reactor before growth under vacuum at residual pressure below 500 torr.

-for germanium: from solid sources, GeCl₄Germane, tetramethylgermanium and isobutylgermane and their derivatives. These dopant gases are then vaporized in the reaction chamber. Preferably, these dopant gases may be mixed with the GaCl flow in the gas phase in advance to improve the uniform distribution of the dopant flow in the growth chamber.

-in the case of a gaseous precursor, the gas tank is maintained at a pressure between 1 and 3 bar and a carrier gas (N) is applied at a flow rate between 0.25 and 20sccm₂And/or H₂) And (4) streaming.

For silicon, from silane, dichlorosilane, silicon tetrachloride and derivatives thereof evaporated in the reaction chamber. In dichlorosilane (1%, diluted in 99% N)₂(or H)₂) In (b), a flow rate of between 1 and 20sccm is applied. Preferably, these dopant gases may be mixed in the gas phase with the GaCl flow to improve the uniform distribution of the dopant flow in the growth chamber.

Silicon and germanium may be introduced together to form a 3-dopant system.

Typically, the thickness of the first single-crystal GaN layer 5b is 100 to 1000 μm.

The permanently defective region 6 of the layer 5b causes defects to also propagate into the layer 5 b. Thus, during the growth of the second doped layer 5c, a material depression of the layer 5c is obtained in a depression region coinciding with the defect region of the layer 5 b.

Other forms of material recession may appear to be associated with inclusions or nucleation that locally alter the growth rate without reaching the upper surface of the layer 5b or even 5 c.

In the third step, the supply of the n-dopant gas is stopped and the growth conditions are maintained, thereby obtaining a third single-crystal GaN layer 5d having a thickness of typically 200 to 5000 micrometers on the previously doped layer 5c having a thickness of typically 100 to 2000 micrometers.

The obtained thickness of the single crystal layer and the GaN 5d growth mode allow to fill the recessed regions of layer 5c by depositing this third layer.

1.4Separation stage 40

Separation stage 40 is also carried out, depending on the variant carried out for stage 20 of forming separation zone 4.

In the case of ion implantation, spontaneous detachment phase 40 occurs due to thermal cycling (high temperature epitaxial recovery and cooling) undergone by thickened GaN layer 5, which is caused by the stress generated by the difference in thermal expansion coefficient between starting substrate 1 and thickened GaN layer 5, causing its detachment.

In the case of deposition of a sacrificial interlayer, this separation occurs during epitaxy either by spontaneous evaporation of the interlayer or by mechanical fracture at the level of the so-called sacrificial layer.

In the case of post-growth detachment, a laser may be used to evaporate the sacrificial layer.

A self-supporting GaN crystal 5 as shown in fig. 3 was obtained.

Such crystals, as shown in fig. 3 (non-curved representation), may be curved and have a radius of curvature of typically more than 5 meters and less than 25 meters, preferably less than 20 meters. Furthermore, the crystal 5 has 10⁷cm^-2Or less, preferably less than 5X 10⁶cm^-2The dislocation density of (a).

GaN crystal 5, which has been formed on a starting substrate having a non-zero cutoff angle (or undercut), also has a non-zero cutoff angle, in which the orientation of the crystal plane propagates from one layer to the next. For example, in the case of the sapphire substrate 1 having a cutoff angle of 4 degrees, the growth plane of the crystal 5 has a cutoff angle of 4 degrees, preferably between 0.1 and 1 degree, over the entire surface thereof.

1.5Correction phase 45

Once the GaN crystal 5 is separated from the starting substrate 1, it is corrected.

Current technology allows for controlled removal of layer thicknesses within 10 microns.

1.6Finishing stage 50

Then, a finishing operation is performed to form a GaN wafer whose GaN thin film (0001) has an X-ray diffraction (XRD) peak of (002) line near angle ω under the symmetric condition with a full width at half maximum of less than 130 arc seconds or even less than 90 arc seconds, preferably less than 60 arc seconds.

The back and side surfaces or edges of the wafer are corrected and polished to an acceptable surface finish for the application.

The correction corresponding to the thickness of the second n-doped layer 5c is performed by removal as shown in fig. 3 to form a group 13 or III nitride wafer.

The proposed process is therefore particularly suitable for the manufacture of slices or wafers of semiconductor material, in particular of materials of elements of groups 13 and 15 of the periodic table, more particularly of slices or wafers consisting of group 13 nitrides, preferably GaN, with large dimensions, greater than 5cm, more than 10 cm and even between 15 and 20 cm.

Referring to fig. 4, a slice or wafer of semiconductor material 7 formed according to the method of the invention has:

-a smaller value of n-doped region. Which coincides with the high-density crystalline defect region, in such a way that, in a plane perpendicular to the growth direction, the gallium face comprises a first n-doped region 7a whose free carrier density, measured by the van der Waals method, is greater than 1.0 x10¹⁸cm^-3And a second zone 7b, undoped or less n-doped, corresponding to a depression of the material, for example coinciding with a permanent defect of the above-mentioned first layer, for example a growth pit, the free carrier density of which, measured by the hall effect, is less than 1.0 x10¹⁸cm^-3And are and

a thickness of about 450 μm and

excellent crystal quality such that the full width at half maximum of the X-ray diffraction (XRD) peak of the (002) line near angle ω under symmetric conditions of the (0001) GaN film is less than 130 arcsec or even less than 60 arcsec, and

surface density of macroscopic inclusions less than 5cm^-2Preferably less than 1cm^-2

-average resistivity less than 25mohm.

1.7Selection phase 60

The proposed method may further comprise a wafer selection phase comprising the sub-steps of:

performing raman spectroscopy, with reference to fig. 5, to identify less doped or undoped regions of the wafer, called minimum doped regions, which are located around permanent defect regions.

Measurements were performed on a Thermo DXRxi raman spectrometer. The spectrometer is specially used for rapid Raman imaging, and the maximum acquisition capacity of the spectrometer is 600 spectra/second. In one configuration, the analysis was performed using a 532nm laser at 10mW power. The laser beam is focused on the sample by a microscope providing 50 times magnification;

identification of non-radiative defects by cathodoluminescence, to select maximum threading dislocation density or TDD greater than 1X10⁸cm^-2A wafer confined to an area within a circle of 50 μm diameter, the center of which coincides with the center of each of the least doped regions.

This identification makes it possible to select the area engraved in a disc of 50 μm diameter, the centre of which coincides with the centre of each of the minimum doped areas, corresponding to the area where the photovoltaic element may be defective, in order to avoid such deposition in this selected 50 μm diameter area before the deposition of the photovoltaic element on the wafer and/or to remove the components deposited in this 50 μm diameter selected area after the deposition of the photovoltaic element on the wafer.

According to another possible process, by way of illustration and in contrast to the process described above, the single-crystal material according to the invention is obtained by growth on a starting substrate or seed (for example sapphire) on which a GaN nitride layer has preferably been previously deposited, preferably at least a few microns and less than 10 microns. The growth was carried out in an HVPE type reactor. The epitaxial deposition is performed under the same conditions as in the above-described stage 30, but for a longer time to form a layer of a few millimeters.

The crystal is subjected to a dressing operation and then cut into several slices or wafers, typically 100 to 600 microns thick, using either a loose wire saw (abrasive particles in a slurry that impregnates the wire before cutting) or a fixed wire saw (abrasive particles previously fixed on the wire). The finishing steps (pre-polishing, polishing) are similar to the process described above.