WO2003052176A2

WO2003052176A2 - Method for making crystalline semiconductor substrates

Info

Publication number: WO2003052176A2
Application number: PCT/FR2002/004372
Authority: WO
Inventors: Pierre Ferret; Guy Feuillet; Eric Jalaguier
Original assignee: Commissariat A L'energie Atomique
Priority date: 2001-12-17
Filing date: 2002-12-16
Publication date: 2003-06-26
Also published as: FR2833619A1; WO2003052176A3

Abstract

The invention concerns a method for crystal growth of a first material from a substrate comprising an initial layer (20) of the first material, coated with a layer (10) of a second material, the second material enabling, in liquid state, diffusion of atoms in the composition of the first material; said method consists in melting the second material layer and growing a layer of the first material on the initial layer by subjecting the second material to a reactive gas of the first material. The invention is characterized in that it consists in forming the substrate by bonding or depositing a thin film of the second material on a layer of the first material. The invention is useful for making SiC substrates.

Description

METHOD FOR MANUFACTURING SEMICONDUCTOR SUBSTRATES

CRYSTALLINS.

Technical Field The present invention relates to a method for manufacturing crystalline semiconductor substrates, and in particular monocrystalline substrates. It is aimed in particular at the production of solid semiconductor ingots such as SiC, CdTe, GaN, AIN or other materials for which obtaining ingots of good crystalline quality is difficult.

State of the art

Documents (1) to (3), the references of which are specified at the end of this description illustrate techniques for manufacturing substrates.

The manufacture of monocrystalline semiconductor substrates for the microelectronics industry generally involves the drawing of solid ingots, the slicing of the ingots and then the polishing of the wafers. This constantly improved manufacturing technique is particularly suitable for silicon. It makes it possible to obtain circular slices with a diameter of 300 mm and a very high crystallographic quality.

For other semiconductor materials, on the other hand, it is almost impossible to control the crystal quality over the entire length and over the entire diameter of an ingot. The thermodynamic parameters governing the ingot drawing process cannot be maintained or controlled in such a way as to obtain substrates of large diameter and of good crystalline quality.

In addition, for certain materials such as SiC, AIN, GaN, it is impossible to obtain, at pressures and temperatures ordinarily accessible, a liquid phase suitable for drawing ingots.

For the production of substrates in these materials, other manufacturing techniques are envisaged. For example, for the manufacture of SiC substrates, a so-called Lely method is used. This method essentially consists in subliming a charge of granular SiC at a temperature of the order of 2300 ° C. and condensing it on a seed whose temperature is maintained above 2100 ° C. Other substrates, made of materials such as

GaN, are obtained by heteroepitaxy of a thin film on a heterosubstrate. The term “heterosubstrate” is understood to mean a substrate made of a given material and serving as an epitaxy support for the formation of a layer made of a material different from the material of the substrate. For example, sapphire can be used as a support material for GaN heteroepitaxy.

During the manufacture of such substrates, difficulties are encountered linked to the propagation of crystalline defects, such as dislocations. Dislocations may indeed propagate in the layer formed by heteroepitaxy, and alter its crystalline quality. Furthermore, the heterosubstrate, or possibly adaptation layers which it is provided with, can constitute electrical barriers. parasites. These prohibit, for example, contacting the rear side.

The document (1) mentioned above, indicates yet another method of manufacturing substrates, derived from the previous one, and aimed essentially at the production of substrates of silicon carbide (SiC). This method essentially consists in growing by heteroepitaxy a thin layer of SiC on a silicon substrate, then using the layer of SiC as an epitaxy crucible in liquid phase. The silicon in the substrate is then used as a bath and as a source of growth material. However, in order to obtain a layer of SiC of acceptable quality, the method comprises complex and delicate operations consisting in particular of carrying out growth initiation spikes. Obtaining a final substrate free of dislocations remains, moreover, uncertain.

Yet another technique for manufacturing substrates consists in transferring by molecular bonding a thin layer of a given semiconductor material onto a substrate of a different material. This technique does not however allow the renewal of the semiconductor material of the donor substrate and therefore does not solve the problem of its manufacture.

Statement of the invention

The object of the invention is to propose a method of manufacturing crystalline substrates, and in particular monocrystalline, which does not have the limitations of the methods mentioned above. One aim is in particular to propose a process suitable for certain semiconductor materials whose physical properties do not allow the implementation of traditional drawing techniques. Another aim is to propose a simple process making it possible to obtain substrates of large diameter and of good crystalline quality.

To achieve these goals, the invention relates more precisely to a crystal growth process in which: a) a substrate is formed comprising an initial layer

(20) of a first material having a crystal coherence, and a layer (10) of a second material, the second material allowing, in the liquid state, the diffusion of atoms entering into the composition of the first material, b ) melting the second material layer and growing a layer of first material ^on a initial layer of first material (20) by subjecting the layer of second material melt, a reactant gas comprising at least one component of the first material.

In accordance with the invention, during step a), the layer of second material is applied, without respecting the crystal coherence, to the initial layer of first material.

The second material is used to form a liquid bath for the growth of the first material. This is akin to growth in the liquid phase. The filler materials for the growth of the first material may in all or part to be supplied by the reactive gas. However, the second material, forming the liquid bath, can also be used as filler material. It is then consumed as the first material grows.

The initial layer of first material, which has a crystal coherence, for example which is monocrystalline, is used to initiate the growth of the first material during step b). More specifically, the face of the thin layer which is in contact with the layer of second material, has the particularity of acting as a growth germ for the first material. This feature is taken advantage of in the process of the invention and thus makes it possible to avoid additional steps such as steps of spike formation or of germ formation.

According to a particular implementation of the method, the layer of second material can be added, for example, by bringing a block of the second material into contact with the layer of first material. The block of second material can be a slice of said second material, obtained, for example, by sawing or cleavage of a donor substrate, and transferred to the initial layer of first material.

The donor substrate can, for example, be cleaved using a technique known under the name "Smart-Cut". This technique consists in implanting light ions in a donor substrate before the transfer of the donor substrate to a target substrate. The shoulder ^ the future thin layer is fixed by the depth implantation. After bonding between the implanted face of the donor substrate and the target substrate, heat treatments, and / or the exercise of mechanical forces, allow coalescence of the implanted species and weaken the donor substrate by promoting cleavage. Cleavage finally makes it possible to detach the remaining part of the donor substrate, leaving the thin layer on the target substrate. We can refer to this subject in the document (2) mentioned above.

The cleavage technique makes it possible to use relatively thin layers of the first material, which saves the donor substrate. The thin layer of the first material has a thickness of the order of a few micrometers, for example of the order of 1 to 10 μ for SiC. Furthermore, the subsequent growth of the first material, in accordance with the method of the invention, makes it possible to produce new substrates for the first material. Some of these can optionally be used later as donor substrates.

The thickness of the new substrates obtained essentially depends on the thickness of the layer of the second material when this material is used as filler material for growth. For example, it is possible to use, in the case of silicon, layers with a thickness of the order of 100 to 1000 μm.

Bringing the block of second material into contact with the initial layer of first material may include direct bonding, by molecular adhesion, or indirect bonding by means of a film of bonding. The bonding film is, for example made of a silicon oxide or nitride Si0 ₂ -Si ₃ N ₄ . It may incidentally have the function of improving the quality of the bonding between the assembled layers. When the ^" bonding is a direct bonding by molecular adhesion, that is to say without addition of material, the molecular bonding can be carried out at ambient temperature after an adequate cleaning of the surfaces to be brought into contact. The bonding forces are Van der Walls type with interatomic distances of a few nanometers These bonds are much weaker than those which would be obtained by heteroepitaxy By heteroepitaxy, we obtain covalent bonds with atomic distances of the order of a few tenths of a nanometer.

According to another possibility of implementing the invention, it is also possible to add the layer of second material, not by bonding a block, but by depositing said material on the initial layer of first material. The deposition of material is distinguished here from an epitaxy. While an epitaxy agrees with the crystal coherence of the support on which it is performed, the deposit remains incoherent. The deposition can take place according to any technique such as sputtering, chemical vapor deposition (CVD), electroplating, etc.

According to a particular and advantageous implementation of the method, the first and second materials can be chosen so that the first material is a binary compound of the second material. AT As an illustration, the first material can be chosen from SiC, InP, GaP, GaAs, CdTe, AIN, GaN, and the second material, respectively from Si In, Cd, Te, Al, Ga and their compounds. The second material can advantageously be composed of elements of which at least one does not participate directly in the development of the layer. For example, it may be preferable to deposit AsGa as a second material on a layer of GaN or GaP rather than pure gallium. During the heating, the arsenic evaporates to leave only the molten gallium in which diffuses nitrogen or phosphorus.

The first material remains solid during the growth stage. In other words, the layer of second material is selectively melted. This can take place by suitable heating or, more simply, by using a first material whose melting temperature is higher than that of the second material. This is often the case for the materials targeted by the invention, and for which the conventional drawing methods prove to be difficult to implement.

The melting of the second material can take place in a crucible, or without a crucible. When the wetting of the second material on the first material is well suited, the layer can in fact be maintained on the layer of the first material.

However, the use of a crucible makes it possible to give the final substrate a desired shape. For example, a crucible with flared walls makes it possible to increase the surface of the substrate. It should be noted that the method can be implemented with additions of the second material to compensate for its consumption.

It may also be advantageous to deposit on the free surface of the substrate a layer of an additional material chosen for a particular function such as controlling the temperature or the quality of the surface. For example, a Ge film on Si can play the role of surfactant. Other characteristics and advantages of the invention will emerge from the description which follows, with reference to the figures of the accompanying drawings. This description is given purely by way of non-limiting illustration.

Brief description of the figures

- Figure 1 is a schematic section of an initial substrate formed of an assembly of layers.

- Figures 2 and 3 are schematic sections of crucibles containing substrates comparable to the substrate of Figure 1.

- Figure 4 is a schematic section of the crucible of Figure 2, containing a substrate, and illustrates a step of material growth. - Figure 5 is a schematic section of a substrate as obtained at the end of the growth process.

- Figure 6 is a schematic section of another crucible containing a substrate and illustrates a particular implementation of the method. - Figure 7 is a schematic section of yet another crucible containing a substrate and illustrates yet another particular implementation of the method.

Detailed description of methods of implementing the invention.

In the following description, identical, similar or equivalent parts of the different figures are identified by the same reference signs to facilitate transfer between the figures. Furthermore, and for the sake of clarity of the figures, all the elements are not represented according to a uniform scale. FIG. 1 shows a substrate comprising a thick layer 10 of silicon on which a thin layer of SiC 20 has been transferred. The layer of Si 10 has for example a thickness of the order of 300 μm and the layer of SiC 20 a thickness of the order of 3 μm. The thin layer 20 is transferred to the thick layer 10 by direct bonding. A dashed line 12 represents possible intermediate layers such as oxide and nitride layers. These intermediate layers are not shown in the following figures for reasons of clarity.

FIG. 2 shows the substrate of FIG. 1 which has been placed in a crucible 30 of suitable dimensions. The crucible is, for example, a graphite crucible. The thin layer 20 of SiC is oriented towards the bottom of the crucible 30 and is maintained against the bottom. The maintenance can result from a bonding. Direct bonding can be considered. A bonding using a graphite lacquer, or any other compound containing carbon, can also be retained. The crucible, provided with the substrate, is placed in a reactor allowing temperatures suitable for melting the material of the thick layer 10 to be reached, under a controlled atmosphere. For example, for silicon, the melting temperatures are of the order of 1450-1500 ° C. To simplify the drawing, the reactor is not shown.

FIG. 3 illustrates a variant in which the crucible has dimensions greater than the substrate. The substrate is held in the crucible 30 by a guard ring 32, also made of graphite, which comes to bear on a flange which the thin layer 20 of the substrate forms relative to the thick layer 10.

In a particular case, the crucible can be removed or replaced by a support without side walls.

An important step in the process is illustrated in FIG. 4 which shows the growth of the first material, in this case SiC, on the thin layer 20. The crucible is heated to a temperature sufficient to melt the thick layer 10 of silicon but low enough not to melt the SiC. The thick layer 10 is subjected in the reactor to a reactive gas containing the species necessary for the growth of the first material. The reactive gas is symbolized by arrows in Figure 4. Here it it is a gas such as propane or silane which contains carbon or silicon with which a carrier gas such as hydrogen can be mixed. The supply of silicon is, in the present case, provided essentially by the bath of the thick molten layer. The pressure of the reactive gas is preferably maintained at a value below a limit corresponding to a formation of SiC on the surface of the silicon bath. Passivation of the surface should be avoided. This would risk blocking the diffusion of the carbon element towards the thin layer 20. The partial pressure of propane is for example 1000 Pa.

The growth of the first material takes place from the contact interface between the thin layer and the thick layer, which, as indicated above, behaves like a seed. Crystal growth of SiC from a liquid Si phase is faster than growth in the gas phase. It can reach 100 μm per hour.

In FIG. 4, the reference 22 indicates solid SiC which has grown on the thin layer 20.

During the growth, the silicon of the thick layer 10 is consumed until exhaustion. We then obtain a final substrate as shown in Figure 5, entirely of SiC. The layer 22 of SiC obtained by growth has a crystalline quality comparable to the initial layer 20.

A variant of the process is illustrated in FIG. 6. This shows a crucible 30 with a carbon insert 34 allowing the crucible to be given flared side walls. The flared walls lead to an increase in the diameter of the substrate as the first material grows. It may be advantageous to open the crucible to an angle of 180 ° so as to obtain a substantial gain in the size of the crystal. This variant is shown in FIG. 7. It makes it possible to use initial sections of the first material with a diameter smaller than that of the first material finally obtained.

FIG. 6 also symbolically shows an addition of the second material, in this case silicon, to compensate for the consumption of the material during growth. A silicon block 14 is added to the surface of the thick layer of silicon 10 initially present. The addition can take place before or after the complete transformation of the silicon layer 10 into SiC.

If the silicon initially present is exhausted, a new molecular bonding can take place to fix the silicon block 14 on the substrate obtained, entirely of SiC. The silicon block 14 can also be placed on the remaining silicon of the thick layer

10, in the molten state or not.

CITED DOCUMENTS (1)

WO- 00/31322

(2)

"Silicon carbide on insulator formation by the S art-Cut process" by L. Di Cioccio et al., Materials Science and Engineering B46 (1997) pp. 349-356.

(3) “Semiconductor wafer Bonding: Science and Technology” by Q.Y. TONG and U. GOSELE, A WILEY INTERSCIENCE PUBLICATION, JOHN WILEY S- SONS, INC.

Claims

1. A crystal growth method in which: a) a substrate is formed comprising an initial layer (20) of a first material having a crystal coherence, and a layer (10) of a second material, the second material allowing, the liquid state, the diffusion of atoms entering into the composition of the first material, b) the layer of second material is melted and a layer of the first material is grown on the initial layer of first material (20), subjecting the layer of second material, melted, with a reactive gas comprising at least one component of the first material, characterized in that, during step a), the layer of second material is applied, without respecting the crystal coherence the initial layer of first material.

2. Method according to claim 1, in which the layer of second material is added by bringing a block of the second material into contact with the layer of first material.

3. The method of claim 2, wherein the contacting comprises direct bonding by molecular adhesion.

4. The method of claim 2, wherein the contacting comprises bonding by means of a bonding film (12).

5. Method according to claim 1, in which the second material layer is added by deposition of said material on the initial layer of first material.

6. The method of claim 1, wherein the first material is a compound of the second material.

7. Method according to claim 6, comprising an addition of the second material compensating for a consumption of this material during the growth of the first material.

8. The method of claim 1, wherein the first material has a higher melting temperature than that of the second material.

9. Method according to claim 1, in which the first material is chosen from SiC, CdTe, AlN, InP, GaP, GaAs, GaN, and in which the second material is chosen from Si, Cd, Te, Al, Ga and their compounds.

10. The method of claim 1, wherein the second material comprises at least one component different from the components of the first material.

11. The method of claim 1, wherein the layer of second material is melted in a crucible (30) with flared walls.

12. The method of claim 1, wherein at least one additional layer of a third material is further deposited on the free surface of the first material.