JP2005210097A - Method and device for depositing group-iii nitride material on silicon substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel method for depositing a group-III nitride material on a silicon substrate. <P>SOLUTION: The present invention relates to a device having a substrate including a silicon substrate having a porous top layer, a second layer on the top layer formed of a Ge material, and the other layer on the second layer formed of a group-III nitride material. Further, the present invention relates to a method, an intermediate layer or a template device highly suitable to the epitaxial growth of a group-III nitride layer of high quality. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for growing a group III nitride material on a silicon substrate and an apparatus obtained by the method. The invention also relates to a device having an epitaxial layer with improved quality.

  Due to the lack of commercial GaN substrates, today GaN heterostructures are grown primarily on sapphire or SiC. Since Si is a very attractive substrate, it has shown increasing interest. Its main advantage is that the thermal conductivity is acceptable (half the thermal conductivity of SiC) and is available in large volumes and large wafer sizes. Compared to sapphire and SiC substrates, the most important advantage of Si is that it is very low cost.

  Kuykendall (Nanoletter 2003, Vol. 3, No. 8, 1063-10) discloses forming GaN nanowires on silicon and sapphire substrates, for example, by MOCVD.

  However, there is no direct description regarding growing a high quality epitaxial GaN layer directly on Si.

  Due to the large lattice mismatch between Si and GaN, the dislocation density of the GaN layer increases. This high dislocation density can be dramatically reduced by applying a suitable growth method developed for growing GaN on sapphire.

  Due to the large difference in thermal expansion coefficient between GaN and Si, a large tensile stress is induced in the GaN film while cooling from the growth temperature to room temperature, thereby causing cracks in the GaN layer. The crack phenomenon is a problem for a layer having a film thickness of 1 μm or more, and this adversely affects the performance of the optoelectronic device.

  Another problem with growing GaN directly on a Si substrate is the so-called meltback etching process of Ga and Si. At high temperatures, Ga and Si form an alloy. This alloy causes a strong and fast etching reaction, which destroys the substrate and the GaN layer. This results in a very rough surface.

  Another problem is that an oxide is formed on the Si substrate and requires special attention. Special care is, for example, careful cleaning to grow GaN on the substrate immediately before introducing the sample into the reactor.

  Another problem with growing GaN on Si is that the substrate is curved. When a GaN layer is formed on Si, the stress generated in the GaN layer subsequently generates stress in the Si substrate. For this reason, deformation of the Si substrate or so-called “curvature” occurs.

  In patent application WO 03/054939, Aixtron discloses a method of growing a III-V substrate on a non-III-V substrate such as a silicon substrate. An III-V buffer layer or III-V germination layer is grown on the substrate by MOCVD.

  For the growth of active GaN layers, Boufaden et al. Suggests using thin AlN layers to improve wetting properties between GaN and porous Si / Si substrates (Microelectronic Journal 34 (2003)). 843-848). The AlN layer reduces the lattice mismatch between GaN and Si to 2.5%. Orita et al. Have proposed an AlN buffer layer between a porous Si layer (PS) and a GaN epitaxial layer in US-A-6344375.

Various methods for reducing cracking and threading dislocation are described in `` GaN-based devices on Si layers (A. Krost, A. Dadgar, Phys. Stat. Sol. (A), Vol. 194, Issue 2, 2002, pp.361
-375) ".

Various means proposed to solve the above problems can be classified into two categories. One that uses a completely in-situ growth method and one that requires an ex-situ process step. This ex-situ process continues to the next growth step. The former group is based on stress engineering and prevents cracking and reduces the threading dislocation density present in the active GaN layer as much as possible. The former group uses an appropriate seed layer, super layer, or intermediate layer. The latter group aims to control the geometric distribution of thermal cracks and threading transition defects. ELOG, Pendeo, Cantilever Epitaxy (Cantilever
Epitaxy) can all be a high quality region, while other methods concentrate all the threading transitions and / or cracks that generate stress in one place.
WO03 / 054939 US-A-6344375 Nano Letter 2003, Vol. 3, No. 8, 1063-10 Microelectronic Journal 34 (2003) 843-848 (Phys.Stat.Sol. (A), Vol.194, Issue2,2002, pp.361-375)

  It is an object of the present invention to provide a novel method for growing a group III nitride material on a silicon substrate to overcome the problems of conventional solutions.

  Another object of the present invention is to provide an apparatus including a high-quality group III nitride epitaxial layer.

  It is a further object of the present invention to provide a suitable intermediate template device for the growth of the high quality group III nitride epitaxial layer.

In the first invention,
A substrate comprising a silicon substrate having a porous top layer;
A second layer of Ge material disposed on the top layer;
A device comprising a second layer of III-nitride material on the second layer.

  The term “porous top layer” is used herein to refer to, among other top layers, not only a top layer consisting essentially of porous silicon (PS), but also a two-dimensional or sub-patterned pattern. It also means a top layer made of artificially made porous material, such as a castellated top layer.

  Such a “porous top layer” provides a rough, woven, non-planar, preferably 3D structured surface, and a supple skeleton. There may be voids, bubbles, or inclusions under such a porous top layer. By closing the pores on the surface of the porous uppermost layer, voids, bubbles, inclusions, micropores, or the like can be formed.

  In the “porous uppermost layer”, at least a part (preferably substantially all) of the pores are open on the surface of the uppermost layer, but at least a part of the pores may be closed on the surface. In another embodiment, all pores may be closed and voids, bubbles, inclusions or micropores may be formed in the substrate.

  In one embodiment of the first invention, there is provided the device described in the previous embodiments, wherein the porous top layer is at least partially closed such as a void, an enclosure, a bubble or a micropore. Disclosed is an apparatus characterized by having an open pore.

  A porosity gradient may be present in the porous top layer according to a preferred embodiment of the present invention. Preferably, the pore size and / or the amount of pores increases in a direction away from the surface of the top layer.

  A top layer having at least two porosity is preferred. This means here that at least two sub-substrates with different porosity are present in the top layer. This difference is in the size and / or amount of the pores.

  You may have a laminated body which has a high porosity and a low porosity. A layer having a high porosity and a layer having a low porosity may be interchanged. High porosity compared to the presence of small size pores and / or small amounts of pores (low porosity) means that there are large pores and / or large amounts of pores. Means that. Methods for making high porosity and low porosity layers are known in the art.

  For example, it is preferable to form a separated layer so as to be in contact with the silicon substrate under a high porosity sub-substrate by high-temperature annealing in a hydrogen atmosphere. This separated layer is a layer having a high porosity and is mechanically very fragile. This layer can easily be broken by a small mechanical force, ie by sonication or pulling (see eg EP1132952).

  The porous uppermost layer according to the present invention generally has a porosity of 10% to 90%. This porous uppermost layer generally has a thickness of between 10 nm and 10 μm, and between 10 nm and 3 μm.

  The “porous top layer” according to the invention may be relaxed again after growth. Furthermore, the epitaxial layer may be separated from the sub-substrate by releasing the stress.

  The “layer made of Ge material” means a layer made of a material containing at least Ge.

  In a preferred embodiment of the first invention, there is disclosed an apparatus described in the previous embodiments, wherein the second layer is made of a SiGe material (a material containing at least SiGe). ing. This second layer may be a SiGe layer. The composition of the layer of Ge material, preferably SiGe material, is arbitrary but has a concentration gradient. The Ge concentration in the second layer material (with a concentration gradient) is preferably increased in a direction away from the substrate.

  A preferred embodiment of the first invention discloses an apparatus according to any of the previous embodiments, wherein the group III nitride material contains at least GaN. A preferred embodiment of the first invention discloses an apparatus according to any of the previous embodiments, wherein the group III nitride material is GaN.

  In another embodiment, the group III nitride material may contain at least AlN or may be AlN. In addition, for example, a group III nitride epitaxial layer containing at least AlGaN can be grown.

  A preferred embodiment discloses a device as described in any of the previous embodiments, wherein the second layer is in direct contact with the top layer. In a preferred embodiment, the device described in the previous embodiments is disclosed wherein a group III nitride layer such as a GaN layer is in direct contact with the second layer.

  In one embodiment of the first invention, the device according to any of the previous embodiments, wherein the second layer (which is made of a Ge material such as SiGe) is 1 nm to Disclosed is an apparatus having a film thickness between 1000 nm or 2000 nm, preferably between 1 nm and 500 nm, more preferably between 1 nm and 300 nm, and even more preferably between 10 nm and 200 nm. ing.

  The thickness of the Ge material layer is preferably 1 nm to 100 nm, 1 nm to 50 nm, 1 nm to 20 nm, 1 nm to 15 nm, 1 nm to 10 nm. The thickness of the layer containing the Ge material is preferably 1 nm to 20 nm, more preferably 5 nm to 15 nm, and most preferably 6 nm to 12 nm.

  In a preferred embodiment according to the present invention, there is provided an apparatus according to the present invention, wherein the uppermost layer is a porous uppermost layer according to the present invention, and the second layer is made of a SiGe material (for example, a SiGe layer). An apparatus is disclosed in which the further layer is a GaN layer. The layer made of SiGe material (for example, SiGe layer) is preferably in direct contact with the uppermost layer. The GaN layer is preferably in direct contact with the second layer. The film thickness of the second layer of the embodiment described herein is preferably between 1 nm to 2 μm, 1 nm to 1000 nm, 1 nm to 500 nm, 1 nm to 300 nm, 10 nm to 200 nm.

  The pores in the uppermost layer may be open pores, or a combination of closed pores and open pores may exist. In another particular preferred embodiment according to the invention, the porous top layer according to the invention comprises at least partly closed pores, the second layer is made of SiGe material (for example SiGe layer), The device is characterized in that the other layer is a GaN layer. Substantially all pores (70%, 80%, 90% or more than 95% of the pores) may be closed pores.

  Specific examples of closed pores include, but are not limited to, bubbles, inclusions, voids or micropores. Compared with the diameter of the first end of the pore in the porous Si substrate, the micropore has a small diameter that decreases in size. This is for example due to the annealing step prior to the growth of the group III nitride layer. The temperature of the annealing process is higher than the temperature of the process of growing the group III nitride material. The growth temperature of GaN is 500 to 1300 ° C, about 1100 ° C, and about 1050 ° C. On the other hand, the temperature for annealing is 1050 ° C. or higher, 1100 ° C. or higher, preferably 1100 ° C. to 1200 ° C.

  In a preferred embodiment of the present invention, there is provided a device according to the present invention, wherein the second layer is a layer made of Ge or a layer made of a SiGe layer with a concentration gradient, and another layer is GaN. Disclosed is a device characterized by being a layer. The Ge concentration in SiGe with a concentration gradient is preferably increased in a direction away from the substrate.

  The device described in any of the previous embodiments preferably further comprises an intermediate layer (third layer). This intermediate layer exists between the second layer (a layer made of a Ge material, such as a SiGe material) and the group III nitride layer (another layer). This intermediate layer is preferably arranged to act as a base for the growth of the group III nitride layer or as a layer from which the growth of the group III nitride layer starts. This intermediate layer is preferably a kind of nucleation layer. The intermediate layer may be a layer having a film thickness in the range of 1 nm to 200 nm, 1 nm to 100 nm, 1 nm to 50 nm. The intermediate layer may be a flat continuous layer or a discontinuous layer having, for example, islands. This intermediate layer may be an AlN layer.

  In another embodiment according to the present invention, there is provided an apparatus according to the present invention, wherein the second layer is a layer made of Ge or a layer made of SiGe with a concentration gradient, and the intermediate layer is An apparatus is disclosed, which is a layer made of AlN, and the other layer is a GaN layer. The Ge concentration in SiGe with a concentration gradient is preferably increased in a direction away from the substrate. In another embodiment of the present invention, an apparatus is disclosed in which the second layer is a layer made of SiGe and the other layer is AlN.

  The present invention relates to a FET, LED, laser diode, HEMT (High Electron Mobility Transistor) or heterojunction bipolar transistor comprising a device according to the invention described in any of the previous embodiments.

  A particular embodiment of the first invention discloses an apparatus as described in any of the previous embodiments, wherein an electronic circuit is integrated on the silicon substrate. The device may include an optoelectronic device or FET formed in the group III nitride layer.

A second invention is a method of fabricating a device comprising a group III nitride material on silicon,
Providing a silicon substrate including a porous top layer (as defined);
Contacting a Ge-containing material with the silicon substrate having the porous top layer, thereby forming a Ge material layer (second layer) on the top layer;
Contacting a silicon substrate having a Ge material layer with a Group III element-containing material and an N-containing material, thereby forming another layer of Group III nitride material on the second layer (see FIG. 1).

  In a preferred embodiment of the second invention, the method according to any of the previous embodiments, wherein the method includes adding a group III element-containing material and an N-containing material to a silicon substrate having a Ge material layer. Disclosed is a method characterized by including a step of thermally annealing a layer of Ge material (an optional step of FIG. 1) prior to the contacting step. The step of thermally annealing is preferably performed at a temperature between 500 ° C. and 1300 ° C., and more preferably performed at a temperature between 500 ° C. and 1100 ° C.

  The step of contacting the Ge-containing material with the silicon substrate having a porous top layer is performed by plasma vapor deposition (PECVD), thermal evaporation, closed space vapor transport, or molecular beam epitaxy. It is preferable to do.

After the growth of the second layer, the intermediate device may be stored for a predetermined period of time (ie, hours, weeks, months, years). It is not necessary to store this device under a protective atmosphere (N ₂ atmosphere or the like). A method as described in any of the previous embodiments, wherein the intermediate device is stored after the step of forming the second layer on the top layer.

  The step of bringing the group III element-containing material and the N-containing material into contact with a silicon substrate including a layer of Ge material is preferably performed by a metal organic chemical vapor deposition (MOCVD) process. This step is generally performed at a temperature between 500 ° C. and 1300 ° C., a temperature between 1000 ° C. and 1100 ° C., and preferably at 1050 ° C. In another embodiment, the step of bringing a group III element-containing material and an N-containing material into contact with a silicon substrate having a Ge material layer is performed by molecular beam epitaxy (MBE) or hydride vapor phase epitaxy (HVPE).

  In another embodiment, the annealing step may be performed prior to the step of bringing the group III element-containing material and the N-containing material into contact with the silicon substrate having the Ge material layer. A stable layer can be formed by the annealing process. For example, the porous top layer and second layer structures may be changed during the annealing step. As a result, during the step of contacting the group III element-containing material and the N-containing material with a silicon substrate having a layer of Ge material, the underlying layer may change in structure (such as, but not limited to, pores). Less susceptible to structural changes). Also, after the annealing step, the second layer will be a layer made of SiGe.

  A preferred embodiment of the second invention discloses the method described in any of the previous embodiments, wherein the group III element is Ga. Most preferably, the group III nitride is GaN. The group III nitride material may be AlN or AlGaN.

  In another preferred embodiment of the second invention, the method according to any of the previous embodiments, wherein the group III element is Al and the group III nitride is AlN. The method of doing is disclosed.

  In a preferred embodiment of the second invention, the method according to any of the previous embodiments, wherein the method comprises contacting a Ge-containing material with a silicon substrate having the porous top layer. And a step of forming an intermediate layer between the step of bringing a group III element-containing substance and an N-containing substance into contact with the silicon substrate having the Ge material layer described above. Here, it is preferable to form an intermediate AlN layer.

  The AlN layer may be grown by MOCVD at a high temperature such as between 900 ° C. and 1200 ° C. in an MOCVD reactor. In another embodiment, the AlN layer may be grown at a low temperature, such as between 400 ° C. and 900 ° C., between 500 ° C. and 800 ° C., followed by a thermal annealing step.

  A preferred embodiment of the second invention discloses a method characterized in that the growth of a group III nitride layer such as a GaN layer is performed at two different temperatures between 500 ° C. and 1300 ° C. The first step of the growth step is performed at a lower temperature (eg, a temperature between 400 ° C. and 800 ° C., a temperature between 400 ° C. and 700 ° C., a temperature between 400 ° C. and 600 ° C.), and subsequently , Preferably at higher temperatures (e.g., temperatures between 800C and 1200C, temperatures between 800C and 1100C, temperatures between 800C and 1000C).

  The third invention relates to an apparatus obtained by any of the above methods. Specific examples of the apparatus obtained by any of the above-described methods according to the present invention are given in the section according to the first invention.

A fourth invention is a method for making an intermediate template device for the growth of group III nitride materials,
Preparing a silicon substrate including a porous top layer;
Contacting the silicon-containing material with a porous top layer with a Ge-containing material, thereby forming a second layer of Ge-containing material on the top layer;
And thermally annealing the second layer made of a Ge-containing material.

  Preferred embodiments relating to the method of forming the different layers, their composition and film thickness are described in the first to third aspects of the invention.

  By this method, it is possible to obtain an optimum template device for the growth of the group III nitride material. The template device includes a porous top layer and a silicon substrate having a second layer on the top layer, and the second layer is made of a Ge-containing material. The top layer is arranged such that a group III nitride material grows on the second layer. In a preferred embodiment, at least a part of the uppermost pore may be a closed pore. Yet another invention relates to a template device obtained by the method of forming a template device according to the present invention.

  Another invention of the present invention relates to the use of intermediate template devices for the growth of III-nitride materials. The template device includes a substrate including a porous top layer and a silicon substrate having a second layer on the top layer, and the second layer is made of a Ge-containing material. Preferably, the top layer is arranged so that the group III nitride material grows on the second layer. At least a part of the uppermost pore may be a closed pore or a pore having a reduced diameter. The possible film thickness and / or layer composition, etc. are as shown in the relevant parts of the first and second inventions.

  The present invention is described in detail below. However, it will be apparent to those skilled in the art that several other similar embodiments or other methods for carrying out the invention can be envisaged.

  In the present invention, when a layer is “on” another layer or substrate, it means that the layer is directly on the other layer or substrate, and a layer is “above” the other layer or substrate. When there is, it means that an intermediate layer exists. When a layer is “in direct contact” with another layer or substrate, it means that there is no intermediate layer between the two layers or between the layer and the substrate.

  In the present invention, the group III nitride material is a material containing a nitride of a group III element in the periodic table of elements. The group III nitride material may be GaN. Here, it can be seen that GaN is a material having at least GaN such as, but not limited to, AlN, AlGaN, InGaN, AlInGaN, GaAsPN, and the like. The device described in this invention may include a diamond layer instead of a Group III material.

  The silicon substrate is a substrate containing silicon. In a particular embodiment, the silicon substrate is a silicon wafer. This silicon substrate may include a porous uppermost layer (defined as described above) according to the present invention.

  By the term “castellated”, the cross-section of the substrate at the main surface is characterized by steep hills and valleys, the upper surface of the hills defining a flat trapezoidal surface portion, the trapezoidal surface The parts are separated from each other by a gap formed by a trough. Each of these trapezoidal portions has a minimum lateral width of 1 μm or less, more preferably 200 mm or less, and most preferably 100 mm or less along the upper surface of the trapezoid. Adjacent trapezoids are separated from each other by a gap having a width of at least 30 mm, more preferably 60 mm.

  By the term “two-dimensionally submicron patterned”, the surface is characterized by a flat trapezoid of arbitrary shape, each trapezoidal portion having a minimum lateral width in the direction along the top surface of the trapezoid of less than 1 micron A gap having a lateral width and formed by the groove is located between the trapezoidal portions. This is obtained by nanometer lithography (Applied Physic Letter (1986), vol 48 (10) 676-678) described by Douglas et al.

  In this specification, the term “pore” is extended to “gap”, “valley” or “groove” as described above. The “pore” in the porous uppermost layer according to the present invention may be an open pore or a closed pore, or a combination of an open pore and a closed pore may exist. This pore is a bubble, an inclusion, a void, a macropore, or the like.

In the first invention, a substrate comprising a silicon substrate having a porous top layer;
A second layer of Ge material;
Disclosed is a device comprising another layer of Group III nitride material on the second layer.

  The second layer preferably contains SiGe. The group III nitride material preferably contains at least GaN. The group III nitride material is preferably GaN. In another embodiment, the group III nitride material may contain at least AlN or may be AlN.

  The lattice mismatch between Si and III-nitride material is very large. By adding Ge to Si and performing an annealing process, a SiGe layer having a larger lattice mismatch is formed.

  Also, the difference in thermal expansion coefficient between the two materials (Si and Group III nitride material) is very large, so excessive stress in the Group III nitride layer such as GaN layer during the cooling process after GaN growth Become bigger.

  The difference in thermal stress between Si and Group III nitride material, preferably GaN, will be reduced when a SiGe layer is formed between Si and Group III nitride material. As a result, the occurrence of cracks in the group III nitride material is reduced.

  As described above, the Ge material layer dramatically reduces thermal stress and does not generate lattice mismatch. In fact, this thermal stress is a major obstacle to growing group III nitride materials such as GaN on Si.

  Transitions may still occur in III-nitride materials such as GaN layers. This problem can be solved by using a very flexible porous Si layer according to the present invention. The porous Si layer according to the invention makes it possible to adapt this substrate to a large lattice mismatch between the silicon and the group III nitride layer, thereby reducing the transition density in the latter layer. . Furthermore, by using the substrate according to the present invention, cracks in the group III nitride layer can be prevented during cooling of the device. Yet another advantage is to prevent “curving” of the substrate.

  The selection of the substrate (silicon having a porous layer according to the present invention) is not a direct matter. This is because porous Si is thermally unstable (it may be deformed at high temperatures) and may absorb moisture from the outside air.

  The Ge material layer is grown at a temperature between 300 ° C. and 800 ° C., preferably at a temperature of 500 ° C. This is in contrast to the high growth temperatures of AlN and GaN that are typically used in this technical field.

  On the other hand, the Ge layer mainly functions as a protective layer for preventing the oxidation of the porous Si according to the present invention. As a result, structural deformation of the porous Si layer is prevented. The GaN layer or AlN layer grown directly on the silicon substrate according to the present invention cannot prevent the oxidation of the porous Si substrate.

  Furthermore, the reduction temperature of Ge is much lower than the critical temperature at which porous Si is recrystallized into bulk Si having voids. On the other hand, the reduction temperature of Si is considerably higher than this transition temperature. Here, the void can be regarded as a micropore in porous Si.

  The Ge intermediate layer prevents nitridation of the Si substrate and does not form any amorphous SiNx material at this interface or only a small amount. The formation of amorphous thin SiNx material is the worst drawback for further epitaxial growth of the device. The Ge intermediate layer also reduces the mixing of Ga and Si, thereby preventing meltback etching.

  The advantageous effect of the second layer of Ge material according to the invention is obtained when a very thin layer containing Ge is applied on the Si substrate having the top layer according to the invention. For example, the uppermost layer is a layer having a film thickness between 1 nm to 20 nm, 5 nm to 15 nm, and 6 nm to 12 nm.

  The device obtained by the method according to the invention is a high quality device.

  The Ge-containing material layer on the Si substrate with the top layer according to the present invention provides a surface that is very suitable for epitaxial growth of Group III nitride semiconductor materials with high quality wide band gap, especially GaN I found out that Compared with growth on a non-porous Si substrate without a Ge layer, it is possible to obtain a high-quality epitaxial layer with good crystallinity, very few cracks, and extremely reduced curved parts. It was.

  Preferred devices according to the present invention are described below.

The first device is
A substrate comprising a silicon substrate having a porous top layer;
A second layer of SiGe-containing material on the porous top layer;
A GaN layer on the second layer.

  The pores in the porous layer may be open pores or a combination of closed pores and open pores.

  In one embodiment of the invention, a SiGe material layer (a material containing at least SiGe) is in direct contact with the top layer. In certain embodiments, the GaN layer is in direct contact with the layer of SiGe material. The second layer is preferably a SiGe layer.

  The film thickness of the layer of SiGe material in the embodiment described here is between 1 nm to 2 μm, 1 nm to 1000 nm, 1 nm to 500 nm, 1 nm to 300 nm, 10 nm to 200 nm.

Other preferred devices are
A substrate comprising a silicon substrate having a porous top layer comprising a pore closed at least in part;
A second layer of SiGe-containing material on the porous top layer;
And another GaN on the second layer. The second layer is preferably a SiGe layer.

  A substrate having a silicon substrate with a pore closed at least in part, for example, a top layer having voids, is formed, for example, after growth and cooling of the GaN layer. During the first step in the GaN growth process (which is an annealing step), the porous silicon layer is converted into bulk Si containing voids.

The present invention discloses an apparatus comprising a III-nitride material layer and a substrate. In one embodiment, the device is
A substrate comprising a silicon substrate having a porous top layer;
A second layer comprising a Ge layer and a SiGe layer with a concentration gradient on the porous top layer;
A GaN layer on the second layer.

  A second layer made of Ge material, for example, a Ge layer or a layer made of SiGe with a concentration gradient, is preferably in direct contact with the uppermost layer. The Ge concentration in the SiGe with the concentration gradient is preferably increased in a direction away from the substrate. The GaN layer is preferably in direct contact with the second layer.

  The porous Si layer and the Ge layer diffuse, resulting in the formation of a SiGe layer, possibly a gradient SiGe layer, at least in the lower part of the layer, ie in the vicinity of the Si substrate.

  The film thickness of the Ge layer or SiGe layer with a concentration gradient in the embodiments described herein is between 1 nm to 1000 nm, 1 nm to 500 nm, 1 nm to 300 nm, 10 nm to 200 nm. More preferably, the film thickness of the Ge layer and the SiGe layer with a concentration gradient is between 1 nm to 100 nm, 1 nm to 50 nm, 1 nm to 20 nm, 1 nm to 15 nm, and 1 nm to 10 nm.

  The substrate according to the present invention described in any of the above embodiments is very useful for the epitaxial growth of III-nitride semiconductor materials having a wide band gap of high quality, in particular GaN. In particular, a substrate prepared according to a method comprising an annealing step and / or growing a group III nitride in two steps (performed at a low temperature in the first step and subsequently grown at a higher temperature) and / or Or a substrate comprising a Ge layer is very suitable for these purposes.

  All of the above devices may be at least part of the device area. This device may be part of a FET, LED, laser diode, HEMT or heterojunction bipolar transistor.

  Another invention of the present invention discloses the use of eg Si / pSi / SiGe substrates for the growth of III-nitride materials. Here, pSi represents porous Si according to the present invention. A Si / pSi / SiGe substrate called a template device includes a silicon substrate comprising a porous top layer and a SiGe material layer (second layer) on the top layer. The “Si / pSi / SiGe substrate” actually relates to all the template devices disclosed in the present invention, ie devices having as a second layer a layer of Ge material (preferably a SiGe layer).

  By using the Si / pSi / SiGe substrate according to the present invention for the growth of the group III nitride material, the problems with the conventional problems can be solved. However, the Si / pSi / SiGe substrate of the present invention may be formed and stored, preferably with at least a portion of the pores closed, until the III-nitride material is grown. This storage may be for hours, days, months or longer.

In yet another invention, a method for making the template device described above is disclosed. This method
Preparing a silicon substrate with a porous top layer;
Contacting the silicon substrate having the porous top layer with a Ge-containing substance, thereby forming a second layer of a Ge-containing material on the top layer;
Subsequently, a step of thermally annealing the layer made of a Ge-containing material is included.

  A step of preparing a silicon substrate and a step of bringing a Ge-containing substance into contact with the silicon substrate may be performed, and the resulting substrate may be stored. The step of bringing the group III element-containing material and the N-containing material into contact with the substrate having the Ge material layer may be performed when the apparatus needs to be further processed.

  The annealing step is preferably performed before the step of bringing the group III element-containing substance and the N-containing substance into contact with the silicon substrate having the Ge material layer. In certain preferred embodiments, the Group III element is Ga. In another embodiment, the group III element may be Al.

  The step of thermally annealing the Ge material layer prior to the step of contacting the Ge material layer with a Group III element (eg, Ga) containing material can remove the oxide formed on the Ge layer and is porous. A SiGe material layer, preferably a SiGe material with a concentration gradient, can be formed on the uppermost Si-like layer. The thermal annealing step is preferably performed at a temperature between 500 ° C and 1300 ° C, preferably between 500 ° C and 1100 ° C.

By the step of bringing the Ge-containing material into contact with the silicon substrate having the porous uppermost layer, SiO ₂ can be prevented from being formed on the porous uppermost layer. The newly etched silicon substrate has been contaminated by conventional technology ("Introduction of porous silicon in room temperature" Canham et al., J. Appl. Phys. 70 (1), July 1991, pp422-431). It is known that non-fluorinated hydride surfaces are converted to contaminated natural oxides during long periods of exposure to ambient air, resulting in a continuous change in structural properties.

  The method according to the present invention further includes a step of bringing a group III element-containing material and an N-containing material into contact with the silicon substrate having a Ge layer, thereby forming a group III nitride layer on the second layer. Also good.

  The present invention may further include a step of forming an intermediate (third) layer between the second layer of Ge material and the group III nitride layer (another layer). This intermediate layer is preferably arranged to be useful as a base for the growth of the group III nitride layer or as a layer from which the growth of the group III nitride layer is initiated. This intermediate layer may be a layer having a film thickness of 1 nm to 200 nm, 1 nm to 100 nm, 1 nm to 50 nm. This intermediate layer may be a flat continuous layer or a discontinuous layer with islands. This intermediate layer may be an AlN layer.

  The intermediate layer AlN can induce moderate compressive stress in the GaN layer grown on the AlN. This offsets the large thermal tensile stress due to thermal mismatch during cooling of the heterostructure and further prevents cracking.

  The film thickness of the AlN layer is between 1 nm to 2 μm, 10 nm to 1000 nm, 10 nm to 500 nm. The AlN layer is grown at a temperature between 500 ° C and 900 ° C or between 900 ° C and 1100 ° C.

  The step of bringing the Ge-containing material into contact with the silicon substrate having the porous top layer may be performed by plasma vapor deposition (PECVD), thermal evaporation, closed space vapor transfer, or molecular beam epitaxy.

The growth of the Ge layer generally takes several minutes. After the step of preparing the porous silicon substrate, the substrate having the porous uppermost layer according to the present invention is stored for several seconds, minutes, hours (up to 2 hours) under a protective atmosphere (such as N ₂ atmosphere). Well, a Ge material layer has grown since then.

The wafer may be placed in a metal organic chemical vapor deposition (MOCVD) furnace for contacting the Ge layer with a Group III-containing material and an N-containing material, thereby growing a Group III nitride layer. preferable. Further, this wafer may be put into an MBE furnace or an HVPRE furnace. Prior to growth, the substrate is annealed, for example in an H ₂ atmosphere, thereby removing the oxide. During this annealing step, a stable epitaxial Ge silicide layer is formed.

The group III-containing material may be TMGa (trimethylgallium), while the N-containing material may be NH ₃ . In one embodiment, the step of bringing the G-containing substance and N-containing substance into contact with the Ge material layer may be performed at a temperature between 500 ° C. and 1300 ° C., preferably between 1000 ° C. and 1100 ° C.

  In another embodiment, the step of bringing the group III-containing substance and the N-containing substance into contact with the Ge material layer may be performed at two different temperatures between 500C and 1300C. The first step of this step may be performed at a lower temperature (eg, a temperature between 400 ° C. and 800 ° C.) followed by a higher temperature (eg, a temperature between 800 ° C. and 1200 ° C.). good.

  A group III nitride material layer can be formed by the step of bringing a group III-containing substance and an N-containing substance into contact with the Ge material layer. In a preferred embodiment, the group III nitride material layer is a material containing at least GaN. In another embodiment, the group III nitride material layer may be a material containing at least AlN.

  In some embodiments, starting from a Si wafer, a porous substrate may be fabricated by methods known to those skilled in the art.

  In an embodiment, the uppermost layer may be formed into a porous shape by anodizing using, for example, concentrated hydrofluoric acid (HF).

Porous Si (pSi) is obtained by anodizing in an HF base solution using a two-electrode apparatus (see FIG. 2). The two electrodes have a silicon working electrode (24) and a platinum counter electrode (23). Acetic acid can be added as a surfactant, thereby effectively removing hydrogen bubbles generated during the formation of pSi, resulting in a more homogeneous pSi layer. During the anodic oxidation of the Si (111) substrate (21), the electrochemical dissolution of the Si element takes place near the interface between the already formed pSi and the Si substrate. Therefore, the thickness of the pSi layer is controlled by the etching time. Appropriate parameters for pore formation are current density, substrate doping type, substrate doping level, electrolyte concentration, and expected wafer illumination. Since holes on the electrode surface are required for silicon dissolution, p-type silicon can be easily etched in the dark, while n-type materials require illuminance. A porous layer having a porosity in the range of 10% to 90% and changing in the range of 10 nm to several μm can be easily obtained. By this process, a homogeneous porous layer can be formed on a large wafer area. FIG. 2 shows an installation for pSi formation. 21 is a silicon substrate, 22 is a Teflon beaker, 23 is a platinum electrode, 24 is a silicon anode, and 25 is a back contact. Certain process conditions are:
Film thickness: 280mm
Resistivity: 0.01Wcm
Chemical solution: 2 hydrofluoric acid / 3 acetic acid
Current density: 75 mA / cm ²
It is. This process results in a 1.7 mm porous Si layer with a porosity of up to 30%. FIG. 4 relates to porous silicon [001] obtained by the method described above. FIG. 5 shows a porous silicon [001] substrate comprising a silicon substrate (53), a low porosity layer (51), and a high porosity layer (52). FIGS. 6a-f show various processes for forming a porous top layer on a silicon [001] substrate, for example by an anodic oxidation reaction in an HF base solution as described in EP1132652. Reference numeral 61 denotes a silicon substrate, 62 denotes a pore, 63 denotes a point of reaction, 64 denotes a hydrogen molecule, and 65 denotes a direction of a hydrodynamic force acted on by the molecule.

After pSi formation, the wafer is rinsed thoroughly in DI water until no trace of electrolyte remains. The substrate is then dried with N ₂ and immediately put into a vacuum system to grow a Ge layer. This means that porous Si is not oxidized. Ge is grown in a plasma CVD system at a suitable temperature of about 500 ° C. Ge will have a film thickness in the range of 10-100 nm. As estimated from the XRD analysis of the PECVD Ge layer, an epitaxial Ge layer is formed on the upper surface of the Si substrate by PECVD. FIG. 3 shows reflectance and XRD measurements. This XRD measurement shows that an epitaxial layer of GaN has grown on the upper surface of pSi (111).

  This step is followed by a degassing and annealing step at 1125 ° C., resulting in the formation of a SiGe layer.

In the next step, the substrate is contacted with TMAl and NH ₃ in a MOCVD furnace, and an AlN intermediate layer is formed at 1100 ° C. (rate: 7.5 nm / min, film thickness 200 nm).

After growing the Ge layer, the substrate is placed in a MOCVD furnace. This substrate is brought into contact with TMGa and NH ₃ at 1020 ° C. (rate 10 nm / min, film thickness 1 μm). The resulting reflectance (FIG. 3a) and XRD measurements (FIG. 3b) show that a smooth GaN epitaxial layer is formed on the top surface of the porous Si (111).

FIG. 1 shows a flowchart illustrating the (essential and optional) steps of the present invention. Optional steps are indicated by dotted lines. FIG. 2 shows a configuration for forming pSi. FIG. 3a shows the reflectivity as a function of time. FIG. 3b shows the XRD measurement. FIG. 4 shows a porous silicon substrate that slopes from a low porosity to a high porosity. FIG. 5 shows a porous silicon substrate comprising a silicon substrate (53), a layer (51) having a low porosity and a layer (52) having a high porosity. FIGS. 6a-f show the various steps in forming a porous top layer on a silicon [001] substrate, for example by anodizing in an HF-based solution as described in EP1132952. Reference numeral 61 denotes a silicon substrate, 62 denotes a pore, 63 denotes a reaction point, 64 denotes a hydrogen molecule, and 65 denotes a direction of a fluid force acting on the molecule.

Claims (38)

A substrate comprising a silicon substrate having a porous top layer;
A second layer of Ge material disposed on the top layer;
And another layer of Group III nitride material on the second layer.   The apparatus of claim 1, wherein the second layer is made of a material containing at least SiGe.   3. A device according to claim 1, wherein the second layer is a SiGe layer.   4. The apparatus according to claim 1, wherein the composition of the second layer has a concentration gradient.   The device according to claim 1, wherein the Ge concentration in the material of the second layer increases in a direction away from the substrate.   6. The apparatus according to claim 1, wherein the group III nitride material is GaN or AlN.   The device according to claim 1, wherein the second layer is in direct contact with the porous uppermost layer.   The device according to claim 1, further comprising a third layer disposed between the second layer and the another layer.   The device according to any one of claims 1 to 8, wherein the porous uppermost layer has a closed pore such as a bubble, a void, an inclusion, or a micropore at least partially.   10. A device according to any preceding claim, wherein the porous top layer has a porosity of between 10 and 90%.   The device according to any one of claims 1 to 10, wherein the porous uppermost layer has a film thickness of between 10 nm and 3 µm.   The apparatus according to any one of claims 1 to 11, wherein the second layer has a film thickness between 1 nm and 1000 nm.   Device according to any of the preceding claims, characterized in that the second layer has a thickness between 1 nm and 20 nm, preferably between 5 and 15 nm.   The device according to claim 1, wherein the second layer is a layer made of a SiGe material, and the another layer is a GaN layer.   The porous uppermost layer includes at least partly closed pores such as bubbles, voids, and micropores, the second layer is a layer made of SiGe material, and the other layer is a GaN layer. The device according to claim 1, wherein the device is a device.   The second layer is a layer made of Ge or a layer made of SiGe with a concentration gradient, and the Ge concentration in the SiGe layer with the concentration gradient increases in a direction away from the substrate. The device according to claim 1, wherein the another layer is a GaN layer.   An FET, LED, laser diode, HEMT or heterojunction bipolar transistor comprising the device according to claim 1.   The apparatus according to claim 1, wherein an electrical circuit is integrated in the silicon substrate.   The apparatus according to claim 1, wherein the optoelectronic element or the FET is formed on the group III nitride layer. A method of fabricating a device comprising a group III nitride material on silicon, comprising:
Providing a silicon substrate including a porous top layer (which has already been defined);
Contacting a Ge-containing material with a silicon substrate having the porous top layer, thereby forming a second layer of Ge material on the top layer;
Contacting a silicon substrate having a layer of Ge material with a Group III element-containing substance and an N-containing substance, thereby forming another layer of Group III nitride material on the second layer. And how to.   Prior to the step of contacting the group III element-containing material and the N-containing material with the silicon substrate having the layer of Ge material to form another layer of Group III nitride material, the second layer of Ge material is thermally removed. 21. The method of claim 20, comprising the step of annealing.   The method of claim 21, wherein the thermal annealing step is performed at a temperature between 500C and 1300C.   The method according to claim 21 or 22, characterized in that the thermal annealing step is carried out at a temperature between 500C and 1100C.   The step of bringing the Ge-containing material into contact with the silicon substrate having the porous uppermost layer is performed by plasma vapor deposition, thermal evaporation, closed space vapor transfer, or molecular beam epitaxy. Item 24. The method according to any one of Items 20 to 23.   The method according to any one of claims 20 to 24, wherein the intermediate device is stored after the step of forming the second layer on the uppermost layer.   26. The step of bringing a group III element-containing substance and an N-containing substance into contact with the silicon substrate having the Ge material layer is performed by a metal organic chemical vapor deposition process. The method described in 1.   27. The method of claim 26, wherein the step is performed at a temperature between 500 <0> C and 1300 <0> C.   The method according to claim 26 or 27, wherein the step is performed at a temperature between 1000C and 1100C.   The method according to any one of claims 20 to 28, wherein the group III element is Ga.   30. A method according to any of claims 20 to 29, wherein the group III nitride material is GaN.   The method according to any one of claims 20 to 28, wherein the group III element is Al.   The method according to any one of claims 20 to 28 or claim 31, wherein the group III nitride material is AlN.   Between the step of bringing the Ge-containing material into contact with the silicon substrate having the porous uppermost layer and the step of bringing the Group III element-containing material and the N-containing material into contact with the silicon substrate having the Ge material layer. 33. A method according to any one of claims 20 to 32, comprising the step of forming an intermediate layer such as a layer.   The method according to any one of claims 20 to 33, wherein the step of growing a group III nitride layer such as a GaN layer is performed at two different temperatures between 500C and 1300C.   35. The method of claim 34, wherein the first step of the growth step is performed at a temperature between 400 <0> C and 800 <0> C, followed by a step at a temperature between 800 <0> C and 1200 <0> C. A method for making a template device for growing a III-nitride material comprising:
Preparing a silicon substrate having a porous top layer;
Contacting a Ge-containing material with a silicon substrate having a porous top layer, thereby forming a second layer of Ge-containing material on the top layer;
And a step of thermally annealing the layer made of the Ge-containing material.   37. The template device manufacturing method according to claim 36, further comprising a step of storing the apparatus for a predetermined time after the annealing step. A template device for the growth of group III nitride materials,
Use of a template device comprising a substrate including a silicon substrate having a porous uppermost layer, and comprising a second layer made of a Ge-containing material on the uppermost layer.

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