Method of recovering and reproducing substrates and method of producing semiconductor wafers

A method of recovering a first substrate, including the steps of: sticking a second substrate on a semiconductor layer epitaxially grown on the first substrate; and separating the semiconductor layer and the first substrate. Furthermore, a method of reproducing a first substrate, including the step of surface processing the first substrate separated. Furthermore, a method of reproducing a first substrate, including the step of homoepitaxially growing the first substrate surface processed. Furthermore, a method of producing a semiconductor wafer, including the step of epitaxially growing a semiconductor layer on a first substrate. Thus a group III nitride or similar, expensive substrate can be used to efficiently and economically, epitaxially grow a group III nitride or similar semiconductor layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods of efficiently recovering and reproducing substrates and methods of efficiently producing semiconductor wafers. More specifically, the present invention relates to methods of recovering and reproducing a first substrate having a semiconductor layer formed thereon and methods of producing semiconductor wafers including the steps of sticking a second substrate on the semiconductor layer and separating the first substrate from the semiconductor layer.

2. Description of the Background Art

To grow a group III nitride semiconductor such as AlxGayIn1-x-yN, wherein 0≦x, 0≦y, and x+y≦1, a sapphire substrate is currently, generally used (seeGroup III Nitride Semiconductor, edited by Isamu Akasaki, Kabushiki Kaisha Baifukan, Dec. 8, 1999, pp. 93-102, or Naoki Shibata, “Fabrication of LED Based on III-V Nitride and its Applications”,Journal of the Japanese Association for Crystal Growth, JACG, vol. 29, No. 3, 2002, pp. 283-287). A sapphire crystal and a group III nitride crystal, however, do not match in lattice constant, and to use a sapphire substrate to epitaxially grow a group III nitride semiconductor layer it is necessary to initially deposit a group III amorphous layer on the sapphire substrate as a low-temperature deposited buffer layer and subsequently deposit the group III nitride semiconductor layer on the buffer layer, which results in reduced production efficiency.

If the above substrate is a group III nitride substrate, then the group III nitride semiconductor layer can epitaxially grown directly on the group III nitride substrate. (See S. Porowski et al., “Thermodynamical properties of III-V nitrides and crystal growth of GaN at high N2pressure”,Journal of Crystal Growth178, Elsevier Science B. V., 1997, pp. 174-188). The group III nitride substrate, however, is difficult to grow in liquid phase, and accordingly need to be grown in vapor phase. This cannot provide a large bulk crystal and is significantly costly.

SUMMARY OF THE INVENTION

The present invention contemplates a method of recovering and reproducing substrates and a method of producing semiconductor wafers that allow a group III nitride or similar, expensive substrate to be used to efficiently and economically, epitaxially grow a group III nitride or similar semiconductor layer.

The present invention in one aspect provides a method of recovering a first substrate, including the steps of: sticking a second substrate on a semiconductor layer epitaxially grown on the first substrate and; and separating the semiconductor layer and the first substrate.

The present invention in another aspect provides a method of reproducing a first substrate, including the steps of: sticking a second substrate on a semiconductor layer epitaxially grown on the first substrate; separating the semiconductor layer and the first substrate; and surface-processing the first substrate separated. In addition to the above steps the present method of reproducing the first substrate can include the step of homoepitaxially growing the first substrate surface-processed.

The present invention in still another aspect provides a method of producing a semiconductor wafer, including the steps of: sticking a second substrate on a semiconductor layer epitaxially grown on a first substrate; and separating the semiconductor layer and the first substrate. In addition to the above steps the present method of producing the semiconductor wafer can include the steps of:

surface-processing the first substrate separated; and epitaxially growing a semiconductor layer on the first substrate surface-processed. Furthermore in addition to the above step the method can include the steps of: surface-processing the first substrate separated; homoepitaxially growing the first substrate surface-processed; and epitaxially growing a semiconductor layer on the first substrate homoepitaxially grown.

Thus in accordance with the present invention the first substrate that is expensive and poor in productivity can efficiently be recovered and reproduced and a semiconductor wafer can efficiently and economically be produced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention in an embodiment will be described with reference to the drawings specifically.

In accordance with the present invention a first substrate is recovered by a method in an embodiment, as follows. With reference toFIGS. 1 and 2, a first substrate10underlies an epitaxially grown semiconductor layer11and a second substrate20is stuck thereon. Then, with reference toFIG. 3, semiconductor substrate11and the first substrate10are separated. Thus the first substrate can efficiently be recovered.

Herein, the first substrate10in the present invention refers to an expensive substrate to be recovered, for example including a group III nitride substrate formed of a group III nitride such as AlxGayIn1-x-yN, wherein 0≦x, 0≦y, and x+y≦1. The first substrate is not particularly limited in thickness. When handleability is considered, however, the first substrate preferably has a thickness of no less than 1.5 mm.

Semiconductor layer11epitaxially grown on the first substrate10is not limited to a particular semiconductor layer11. If the first substrate10is a group III nitride substrate, however, then semiconductor substrate11is implemented by a group III nitride semiconductor formed of a group III nitride such as AlxGayIn1-x-yN and epitaxially grown, wherein 0≦x, 0≦y, and x+y≦1. Furthermore, semiconductor layer11is not limited to a single semiconductor layer and may be more than one semiconductor layer deposited in layers.

How semiconductor layer11should epitaxially be grown is not particularly limited. If the group III nitride semiconductor layer is epitaxially grown, it is preferably grown by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE) or the like.

The second substrate20refers to a substrate stuck on semiconductor layer11and may be any general-purpose substrate suitable for sticking on semiconductor layer11. The second substrate20preferably includes a Si substrate, an Al substrate, a Cu substrate, a Cu—W substrate, and the like. The second substrate is not particularly limited in thickness. When handleability is considered, however, the second substrate preferably has a thickness of no less than 300 μm.

How the second substrate20is stuck on semiconductor layer11is not particularly limited. Preferably, the second substrate20is brazed. More specifically, Ag, Ni, Au, Ge, Ti, an alloy thereof, or a similar wax is for example sputtered or vapor-deposited on semiconductor layer11and then melted and the second substrate20is placed thereon and thus stuck together. Alternatively, a paste containing Ag, Ni, Au, Ge, Ti or an alloy thereof is applied on semiconductor layer11and the second substrate20is placed thereon and thus stuck together.

How semiconductor layer11and the first substrate10should be separated is not particularly limited. Preferably, they are separated for example by using a wire saw or an inner, radial blade to mechanically slice the same, or electrolytically etching or similarly, chemically treating the same. In the electrolytical etching, for example the first substrate and the semiconductor layer with a conductive layer previously introduced therebetween are immersed in an electrolyte and a current is passed through the conductive layer to etch the conductive layer to separate the first substrate and the semiconductor layer. For example if the first substrate is a group III nitride substrate and the semiconductor layer is a group III nitride semiconductor layer, the conductive layer is formed of a group III nitride layer heavily doped for example with Si (and providing a specific resistance of approximately 10−2Ω·cm), and approximately 1N of aqueous KOH solution is used with Pt corresponding to a negative electrode and the conductive layer serving as a positive electrode and a current of approximately 1 mA is passed to etch the conductive layer.

Desirably, semiconductor layer11and the first substrate10are separated ideally at an interface of semiconductor layer11and the first substrate10, as shown inFIG. 3. In that case ideally the intermediate product is separated into the second substrate20and semiconductor layer11together forming a semiconductor wafer30, and the first substrate10. In reality, however, a portion of the first substrate can remain on semiconductor wafer30at a surface of semiconductor layer11(not shown) or a portion of the semiconductor layer can remain on a surface of the first substrate10(not shown). Furthermore, if they are mechanically sliced and thus separated, it is difficult to slice them at their interface, and if they are successfully sliced at the interface, semiconductor layer11is often damaged and has a surface with protrusions and depressions, defects in crystallinity, and the like. Accordingly, in reality, to minimize damage to semiconductor layer11, a portion closer to the first substrate10than the interface of semiconductor layer11and the first substrate10is often mechanically sliced. In that case, the intermediate product is separated into the second substrate20, semiconductor layer11and a portion of the first substrate10together forming a semiconductor wafer (not shown), and the remaining, first substrate10. In the present invention, semiconductor wafer30and the first substrate10obtained by separating semiconductor layer11and the first substrate10include any case of the above.

In accordance with the present invention the first substrate is reproduced by a method in one embodiment, as follows: With reference toFIGS. 1 and 2, a first substrate10underlies an epitaxially grown semiconductor layer11and a second substrate20is stuck thereon. Then, with reference toFIG. 3, semiconductor substrate11and the first substrate10are separated. Then, with reference toFIG. 4, the first substrate10separated is surface processed40. Thus the first substrate can efficiently be reproduced.

TheFIGS. 1-3steps are as has been described above. Semiconductor layer11and the first substrate10are separated and if the first substrate10has a surface with protrusions and depressions or defective in crystallinity (not shown) or has a surface with the semiconductor layer partially remaining thereon (not shown), then, with reference toFIG. 4, the first substrate10can be surface processed40. How the first substrate10should be surface processed is not particularly limited. A polishing paper may be used to mechanically polish the substrate. Alternatively, polishing slurry and a polishing pad may be used to chemically, mechanically polish the substrate. Alternatively, liquid-phase etching, vapor-phase etching, or other similar chemical techniques may be employed. If the first substrate is a group III nitride substrate and undergoes liquid-phase etching, the substrate is for example brought into contact with etchant of a liquid at least containing Na, Li or Ca.

In accordance with the present invention the first substrate is reproduced by the method in another embodiment, as follows: With reference toFIGS. 1 and 2, the first substrate10underlies an epitaxially grown semiconductor substrate11and the second substrate20is stuck thereon. Then, with reference toFIG. 3, semiconductor layer11and the first substrate10are separated. Then, with reference toFIG. 4, the first substrate10separated is surface-processed40. Then, with reference toFIG. 5, the first substrate10surface processed is homoepitaxially grown. InFIG. 5, the first substrate10asurface processed and thus reduced in thickness that is homoepitaxially grown provides a homoepitaxially grown portion10bto provide the first substrate10reproduced with its original thickness. Thus a first substrate maintained in mechanical strength and excellent in handleability can efficiently be reproduced.

The first substrate is homoepitaxially grown when the first substrate is reduced in thickness and hence mechanical strength and handleability. For example, if the first substrate is a group III nitride substrate, then preferably it is homoepitaxially grown when it attains a thickness of no more than 0.6 mm. The homoepitaxial growth can be stopped when the first substrate recovers its original thickness or more.

How the first substrate10should homoepitaxially be grown is not particularly limited. If the first substrate10is a group III nitride substrate, HVPE, MOCVD, MBE or the like is preferably employed.

In accordance with the present invention a semiconductor wafer is produced by a method in an embodiment, as follows: With reference toFIGS. 1 and 2, the first substrate10underlies epitaxially grown semiconductor layer11and the second substrate20is stuck thereon. Then, with reference toFIG. 3, semiconductor layer11and the first substrate10are separated. Thus semiconductor wafer30can efficiently be produced. Furthermore, by changing the second substrate20to be stuck, semiconductor wafer30having stuck thereto a substrate accommodating the application of interest, can efficiently be produced.

Note that the first substrate10and semiconductor substrate11are separated and if semiconductor wafer30obtained has semiconductor layer11having a surface with a portion of the first substrate remaining thereon (not shown) or semiconductor layer11having a surface with protrusions or depressions, defective in crystallinity, and/or the like (not shown), then a surface processing similar to surface processing40applied to the first substrate10as described above can be performed. This processing is not limited to any particular method. A polishing paper may be used to mechanically polish the substrate. Alternatively, polishing slurry and a polishing pad may be used to chemically, mechanically polish the substrate. Alternatively, liquid-phase etching, vapor-phase etching, or other similar chemical techniques may be employed. If the first substrate is a group III nitride substrate and undergoes liquid-phase etching, the substrate is for example brought into contact with etchant of a liquid at least containing Na, Li or Ca.

In accordance with the present invention a semiconductor wafer is produced by the method in another embodiment, as follows: With reference toFIGS. 1 and 2, the first substrate10underlies an epitaxially grown semiconductor substrate11and the second substrate20is stuck thereon. Then, with reference toFIG. 3, semiconductor layer11and the first substrate10are separated. Then, with reference toFIG. 4, the first substrate10separated is surface-processed40. Then, with reference again toFIG. 1, a semiconductor layer11is epitaxially grown on the first substrate10surface processed. Thus theFIGS. 1-4steps are performed and theFIG. 1step is then again formed. The steps cyclically performed as described above allow semiconductor wafer30to be produced further efficiently.

In accordance with the present invention a semiconductor wafer is produced by the method in still another embodiment, as follows: With reference toFIGS. 1 and 2, the first substrate10underlies an epitaxially grown semiconductor substrate11and the second substrate20is stuck thereon. Then, with reference toFIG. 3, semiconductor layer11and the first substrate10are separated. Then, with reference toFIG. 4, the first substrate10separated is surface-processed40. Then, with reference toFIG. 5, the first substrate10surface processed is homoepitaxially grown. Then, with reference again toFIG. 1, a semiconductor layer11is epitaxially grown on the first substrate10homoepitaxially grown. Thus theFIGS. 1-5steps are performed and theFIG. 1step is then again formed. The steps cyclically performed as described above allow semiconductor wafer30to be produced further efficiently.

The present invention will more specifically be described with reference to examples.

First Example

With reference toFIG. 1, the first substrate10implemented by a group III nitride, GaN substrate having a thickness of 1.5 mm is used and MOCVD is employed to deposit semiconductor layer11on the GaN substrate heated to 1000° C. Semiconductor layer11is implemented by group III nitride semiconductor layer formed of a p-GaN layer111having a thickness of 150 nm, a p-Al0.2Ga0.8N layer112having a thickness of 60 nm, an In0.2Ga0.8N layer113having a thickness of 3 nm, and an n-GaN layer114having a thickness of 5000 nm deposited successively.

Then, with reference toFIG. 2, on the semiconductor layer111outermost, surface layer or n-GaN layer114, Ag serving as a wax member is sputtered and thus deposited and then melted and the second substrate20implemented by a Si substrate having a thickness of 30 μm is stuck thereon. Then, with reference toFIG. 3, a wire saw is used to separate semiconductor layer111and the first substrate10. More specifically, although not shown, a portion of the first substrate that is 80 μm distant from the interface of the semiconductor layer and the first substrate is sliced with the wire saw parallel to the interface.

Then, with reference toFIG. 4, the first substrate10separated is surface-processed40. More specifically, a liquid of Na serving as etchant is placed on the first substrate10or GaN substrate and a surface plate having a flat surface is pressed against the GaN substrate while it is rotated at 50 rpm for one hour to perform liquid-phase etching. Then, with reference toFIG. 5, the first substrate10or GaN substrate surface-processed to have a thickness of no more than 0.6 mm is heated to 1000° C., and HVPE is employed and GaN, the same material as the GaN substrate, is used to homoepitaxially grow the substrate. When the GaN substrate recovers its original thickness, i.e., 1.5 mm, the homoepitaxial growth is terminated. Note that the substrate or the semiconductor layer is controlled in thickness by the time required to grow the substrate or the semiconductor layer. More specifically, an experiment is previously conducted to obtain a relationship between the time required to grow the substrate or the semiconductor layer and its thickness and for example a time required for growth is determined to allow the GaN substrate to have a thickness of 1.5 mm. The GaN substrate's thickness before the experiment and the growth can be measured with a film thickness meter of contact type. The result is shown in Table 1.

Second Example

Except that the first and second substrates are AlN and Cu substrates, respectively, the wax material is Ni, and the AlN substrate is homoepitaxially grown with AlN used as material, the first substrate has a semiconductor layer deposited thereon, the semiconductor layer has the second substrate stuck thereon, the semiconductor layer and the first substrate are separated, the first substrate separated is surface processed and then homoepitaxially grown, similarly as has been described in the first embodiment. The result is also shown in Table 1.

Third Embodiment

Except that the first and second substrates are InN and Cu—W substrates, respectively, the wax material is Ti, The semiconductor layer and the first substrate are separated with an inner, radial blade and the InN substrate is homoepitaxially grown with InN used as material, the first substrate has a semiconductor layer deposited thereon, the semiconductor layer has the second substrate stuck thereon, the semiconductor layer and the first substrate are separated, the first substrate separated is surface processed and then homoepitaxially grown, similarly as has been described in the first embodiment. The result is also shown in Table 1.

Fourth Example

Except that the first and second substrates are Al0.5Ga0.5N and Al substrates, respectively, the wax member is Au (50 mole %)-Ge (50 mole %), the semiconductor layer and the first substrate are separated with an inner, radial blade, and the Al0.5Ga0.5N substrate is homoepitaxially grown with Al0.5Ga0.5N used as material, the first substrate has a semiconductor layer deposited thereon, the semiconductor layer has the second substrate stuck thereon, the semiconductor layer and the first substrate are separated, the first substrate separated is surface processed and then homoepitaxially grown, similarly as has been described in the first embodiment. The result is also shown in Table 1.

The present invention can recover and reproduce a group III nitride or similar, expensive substrate to form a cyclical semiconductor wafer production process to efficiently and economically produce a semiconductor wafer having a group III nitride semiconductor layer or the like.