KR20170091965A - Method for growth of single crystalline AlN - Google Patents

Method for growth of single crystalline AlN Download PDF

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KR20170091965A
KR20170091965A KR1020160012916A KR20160012916A KR20170091965A KR 20170091965 A KR20170091965 A KR 20170091965A KR 1020160012916 A KR1020160012916 A KR 1020160012916A KR 20160012916 A KR20160012916 A KR 20160012916A KR 20170091965 A KR20170091965 A KR 20170091965A
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aln
single crystal
metal layer
substrate
grown
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KR1020160012916A
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Korean (ko)
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신인수
윤의준
박용조
이동현
김종명
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서울대학교산학협력단
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    • H01L21/28158—Making the insulator
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    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
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    • H01L21/2855—Deposition of conductive or insulating materials for electrodes conducting electric current from a gas or vapour, e.g. condensation of conductive layers on semiconductor bodies comprising elements of Group IV of the Periodic System by physical means, e.g. sputtering, evaporation
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    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
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    • H01L2924/049—Nitrides composed of metals from groups of the periodic table
    • H01L2924/0503—13th Group
    • H01L2924/05032—AlN
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    • H01L2924/1032—III-V
    • H01L2924/10323—Aluminium nitride [AlN]

Abstract

There is provided a method for growing monocrystalline AlN using a PVD method such as sputtering even at a low temperature such as room temperature. According to another aspect of the present invention, there is provided a method of growing a single crystal AlN, comprising: forming a metal layer on a substrate to reduce a difference in lattice constant between the substrate and AlN; And growing monocrystalline AlN by PVD on the metal layer.

Description

[0001] The present invention relates to a method for growing single crystalline AlN,

The present invention relates to a method for growing AlN, and more particularly, to a method of growing a single crystal AlN with a quality that can be used as a buffer layer necessary for manufacturing a compound semiconductor device by a PVD (physical vapor deposition) method.

AlN can be used as a nitride semiconductor itself, and is widely used as an electromagnetic device such as a surface acoustic wave (SAW), and is widely used as a buffer layer for growing compound semiconductors such as GaN, AlGaN, and InGaN. AlN must be grown to a single crystal in order to be used for this purpose.

In order to produce single crystal AlN, epitaxial growth is required in which a material is grown along a lattice of a different substrate such as Si. In order to induce such epitaxial growth, sufficient energy is required for the atoms to follow the substrate lattice. Thus, a thin film of a single crystal is manufactured through equipment capable of providing high temperature or high energy such as metal organic chemical vapor deposition (MOCVD) do. AlN films are formed at about 1000 ~ 1200 ℃ for MOCVD and about 800 ~ 1000 ℃ for MBE (molecular beam epitaxy).

In this way, extreme growth conditions such as high temperature through a complicated system are required for epitaxial growth of AlN thin film, and this growth condition not only lowers the economical efficiency of AlN thin film growth but also has a lot of additional problems. In order to solve these problems, efforts have been made to grow a buffer layer by using a separate device other than MOCVD. As one of the alternatives, AlN growth using PVD method is under study.

However, in the case of general DC sputter, the energy that can be given to the atom is too low. Moreover, when growing at room temperature, AlN does not grow into a single crystal because there is no thermal energy supplied. As a result, the AlN buffer layer is produced by a special system which can grow at high temperature or give high energy due to the limit of epitaxial growth at low temperature. However, such a growth condition reduces the advantage of PVD rather than PVD, so there is a problem that the advantage of fabricating the buffer layer by the PVD method is eliminated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for growing single crystal AlN using a PVD method such as sputtering even at a low temperature such as room temperature.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. It will also be readily apparent that the objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

According to another aspect of the present invention, there is provided a method of growing a single crystal AlN, comprising: forming a metal layer on a substrate to reduce a difference in lattice constant between the substrate and the AlN; And growing monocrystalline AlN by PVD on the metal layer.

In the present invention, it is preferable that the lattice constant difference between the metal layer and the AlN is smaller than the lattice constant difference between the substrate and the AlN.

The metal layer may be at least one of Al, Ti, Mg, Cd, Ag, and Au.

The metal layer may be formed by a PVD method.

The single crystal AlN may be grown by depositing AlN along the lattice of the metal layer.

The PVD method for single crystal AlN growth may be a reactive DC sputter using an Al target and an N 2 source. Alternatively, an RF sputter using an AlN target may be used.

The metal layer and the single crystal AlN may be deposited by a process of continuously depositing in one chamber.

The single crystal AlN may be grown at room temperature.

After the step of growing the single crystal AlN, annealing may be performed in a nitrogen, ammonia, or oxygen atmosphere to change the metal layer.

In the present invention, a single-crystal AlN thin film that can be used as a buffer layer can be grown at room temperature using a PVD method such as DC sputtering instead of MOCVD. Since the sputter itself is an inexpensive and simple device compared to MOCVD, the cost of maintaining and managing MOCVD can be reduced. Also, growing at room temperature can solve various problems caused when grown at high temperature. As described above, the sputtering method that grows at a low temperature has advantages in terms of cost and time as compared with the equipment that has been used before, and can effectively replace the AlN thin film grown in the conventional MOCVD and the like.

According to the present invention, it is difficult to grow a single crystal since a single crystal AlN quality is simple and economical and a certain level or more. Therefore, the growth method according to the present invention can be used as a new technique in a nitride semiconductor industry which grows at a high temperature. From the viewpoint of application of buffer layer such as GaN, AlN thin film is affected by GaN grown in the same chamber. Therefore, maintenance cost of growing equipment is very serious to grow AlN thin film at present. However, according to the present invention, since such a problem can be solved, there is a great industrial advantage.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the description of the invention given below, serve to further augment the technical spirit of the invention. And should not be construed as limiting.
1 is a flow chart of a single crystal AlN growth method according to the present invention.
FIG. 2 is a schematic view showing a section of a single crystal AlN according to the flow chart of FIG. 1. FIG.
3 is a diagram for further explaining the single crystal characteristics of AlN according to the present invention.
FIG. 4 is a graph comparing gas supply times according to an embodiment of the present invention and a comparative example. FIG.
5 is XRD and phi scan comparative data of the example and the comparative example according to the present invention.
Figure 6 is a TEM image and FFT spot results of an embodiment and a comparative example according to the present invention.
7 is an enlarged TEM image of an embodiment of the present invention and a comparative example.
8 is a diagram showing the difference in lattice constant between Al and AlN.
9 is an XPS result showing the change in the case where the ammonia atmosphere annealing is further performed for the embodiment according to the present invention.
10 is a photograph of a substrate (a), a surface and a cross-sectional SEM photograph (c), and a phi scan data when GaN is grown according to the embodiment of the present invention. (A) a substrate photograph, (b) a surface and cross-sectional SEM photograph, and (c) phi scan data.
12 is phi scan data of the embodiment according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood, however, that the embodiments of the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

Therefore, the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

Hereinafter, the present invention will be described in detail with reference to the drawings, but the scope of the present invention is not limited thereto.

FIG. 1 is a flow chart of a single crystal AlN growing method according to the present invention, and FIG. 2 is a schematic view showing a section of a single crystal AlN according to the flow chart of FIG.

1 and 2, first, a metal layer 20 is formed on a substrate 10 (step s10).

In the case of the substrate 10, any substrate may be used as long as it is a substrate having the same symmetry as the AlN 30, such as a silicon substrate, a sapphire substrate, or a SiC substrate, which are generally used in nitride semiconductors.

The metal layer 20 is provided between the metal layer 20 and the AlN 30 to reduce the lattice constant difference between the substrate 10 and the AlN 30. The metal layer 20 has a lattice constant difference between the substrate 10 and the AlN 30, It is preferable that the difference in lattice constant between the two is small. The metal layer 20 is preferably at least one of Al, Ti, Mg, Cd, Ag, and Au. These metals can be determined by considering the crystal structure and lattice constant, and these metals can be stacked in two layers (for example, Al / Ti bilayers) or several layers. This metal layer 20 can be formed by the PVD method.

Then, the single crystal AlN 30 is grown on the metal layer 20 by the PVD method (step s20). When AlN is deposited and grown along the lattice of the metal layer 20, the AlN 30 is grown as a single crystal.

According to the method of the present invention, by inserting the metal layer 20 between the substrate 10 and the AlN 30, the AlN 30 has a single crystal characteristic. Fig. 3 is a diagram for further explaining this single crystal characteristic.

As shown in FIG. 3A, when the AlN 30 is directly deposited on the substrate 10 at a low temperature, the out-of-plane aligns in the same direction (in the same orientation) (Random orientation) in a randomly aligned polycrystalline state. As a result, the AlN pattern on the top surface is represented by a polycrystal.

On the other hand, when the metal layer 20 is inserted as in the present invention, the AlN 30 is aligned not only in the out-of-plane direction but also in the in-plane direction as shown in FIG. 3 (b) same orientation). As a result, the AlN pattern on the upper surface was expressed as polycrystalline.

In step s20, the PVD method for single crystal AlN 30 growth may be performed using a reactive DC sputter using an Al target and an N 2 source, or using an RF sputter using an AlN target It is possible.

If the metal layer 20 is formed by the PVD method in step s10, step s10 and step s20 may be performed in-situ. That is, the metal layer 20 and the single crystal AlN 30 can be continuously deposited in one chamber.

At this time, the deposition temperature is preferably room temperature, and the single crystal AlN (30) may be grown at room temperature, but the temperature may be slightly increased as required. Experimental results show that single crystal AlN grows at room temperature.

The optimum conditions can be met by adjusting the deposition conditions in steps s10 and s20, for example, conditions that can be adjusted by sputtering such as pressure, DC power, and gas flow rate.

After the step of growing the single crystal AlN 30, a step of changing the metal layer 20 by annealing in a nitrogen, ammonia, or oxygen atmosphere may be further performed. This step is a subsequent process that can be selectively performed depending on the application. The metal layer 20 may be nitrided or oxidized in combination with N or O from these gases and may also be nitrided or oxidized by the material of the AlN 30 or substrate 10 during annealing.

For example, if sapphire / Ti / AlN is grown as a substrate 10 / metal layer 20 / AlN 30 structure and then annealed in an ammonia atmosphere, TiN x may be formed due to the nitridation of Ti to be used as a conductive thin film . As another example, if annealing is performed in an oxygen atmosphere, TiO x can be formed and used as a semi-insulating thin film.

There has been an attempt to grow monocrystalline AlN by the PVD method. However, the major difference between the present invention and these is whether or not the metal layer 20 is formed.

The biggest problem in growing AlN thin films of single crystals at low temperature by PVD method is the absence of thermal energy due to low temperature. Under such limited energy, it is difficult for epitaxial growth of AlN to follow the lattice of the substrate. The present invention is characterized in that the metal layer 20 is interposed between the substrate 10 and the AlN 30 in a manner different from the conventional technique in which energy is additionally supplied to AlN atoms by a high temperature method, By lowering the energy required to follow the lattice, the single crystal AlN 30 can be obtained even at low energy, that is, at low temperature.

The metal layer 20 is a major factor that reduces the difference in lattice constant and allows the single crystal AlN 30 to grow at a low temperature. In the conventional technologies, single crystal AlN growth was achieved at low temperature using PVD, and there is no report as a buffer layer. Basically, PVD is used. It is known that a high temperature condition is used to make a single crystal, or a modified sputter which can give a high energy instantaneously. However, the present invention is applicable to a general sputtering process because it can be performed at room temperature, and there is a great difference in that a single crystal can be formed even at a low temperature. However, in the present invention, a metal layer such as Ti is first deposited, and then AlN is deposited to allow the AlN to be epitaxially grown along the substrate.

As in the present invention, if the single crystal AlN thin film can be grown at a low temperature by using PVD, it can be expected that advantages of manufacturing the buffer layer using PVD can be utilized. Sputtering is a much simpler structure than the MOCVD and MBE systems used for conventional AlN thin films and is much cheaper in terms of cost. Also, as shown in the following experimental example, the growth time can be shortened compared to the existing technology, and the large area can be enlarged. In particular, since a single crystal can be grown at a low temperature, there is no need for an additional system such as a heater in a sputterer, and there is a great advantage in cost and time in raising the temperature. .

Hereinafter, the present invention will be described in more detail by explaining experimental data.

Al layer  If used: Si (111) / Al / AlN

Table 1 summarizes the growth conditions of Example 1 and Comparative Example 1.

Figure pat00001

In Example 1, an Al layer was formed on an Si (111) substrate prior to growing AlN. In Comparative Example 1, AlN was directly grown on a Si (111) substrate without forming such an Al layer . DC sputtering. The DC power was 600 W, the pressure was 1 mTorr, and the Ar / N 2 ratio was 1: 1.

FIG. 4 is a graph comparing gas supply times of two samples in terms of time. In Example 1, unlike Comparative Example 1, an Al shutter was opened before N 2 was supplied and sputtered with Ar against an Al target, Was performed for 5 seconds. ≪ tb >< TABLE > After this step, N 2 was started to be supplied while maintaining the other conditions so as to form an Al layer and a continuous process, and AlN was grown for 15 minutes.

FIG. 5 shows XRD and phi scan comparison data of the results (Example 1) and the results of the application (Comparative Example 1) that were obtained by applying the Al layer.

First, both the Si (111) and AlN (0002) peaks appear in Example 1 and Comparative Example 1 when XRD results (2 theta scan) of (a) and (b) are observed. (c) and (d), six peaks appear in AlN only when the Al layer is applied as in Example 1, and no peaks appear in Comparative Example 1. It can be seen from this that only in the case of Example 1, AlN was grown as a single crystal.

FIG. 6 is a TEM image and an FFT spot result of the results (Example 1) and the results of applying the Al layer (Comparative Example 1).

Referring to FIGS. 6 (a) and 6 (b), it can be seen that AlN is grown along the Al layer in the first embodiment. Referring to FIGS. 6 (d) and 6 (e), in the case of Comparative Example 1, AlN is grown along the Si substrate. (c) and (f). As shown in (c), in the case of Example 1, a clean FFT spot is formed and single crystal AlN is grown. On the other hand, (f) shows that polycrystalline characteristics are shown when the Al layer is not applied.

FIG. 7 is an enlarged cross-sectional TEM image of Example 1 and Comparative Example 1. FIG. 7A is an enlarged TEM photograph of the Al layer portion in Example 1. FIG. It is confirmed that the Al layer is epitaxially grown between AlN and Si. It is expected that the remaining Al layer will reduce the lattice constant between AlN and Si and help the epitaxial growth of AlN more easily. That is, when the Al layer is sandwiched between Si and AlN, AlN grows along the lattice of the Al layer, and eventually epitaxial growth occurs.

FIG. 7 (b) is an enlarged TEM image of the interface between Si and AlN in Comparative Example 1. FIG. As in the case of Comparative Example 1, when AlN is grown on Si, it can not follow the lattice of Si, and epitaxial growth does not occur. As a result, it can be seen that it has grown to polycrystalline AlN.

8 is a diagram showing the difference in lattice constant between Al and AlN.

As shown in Fig. 8, Al < 011 > // AlN

Figure pat00002
: The lattice constant difference is 8.5% and Al
Figure pat00003
// AlN
Figure pat00004
: The lattice constant difference is 6%. This is Si
Figure pat00005
// AlN
Figure pat00006
: The value is smaller than that of the lattice constant difference of 19%. The reason why the AlN can be made single crystal by inserting the Al layer between Si and AlN is that the difference in lattice constant between Al and AlN is smaller than the difference in lattice constant between AlN and Si.

In summary, both Example 1 and Comparative Example 1 have AlN deposition under the same energy, but AlN is grown on Al in Example 1 and on Si in Comparative Example 1. The difference between the lattice constants of AlN and Si is about 19%, so energy required to overcome this lattice constant difference is required for AlN to grow along the lattice of Si. However, since this energy can not be given at room temperature, Comparative Example 1 does not grow into a single crystal. However, when the AlN is grown after the Al is deposited on the Si, the difference in lattice constant is about 8%. As a result, Example 1 epitaxially grows into single crystal under the same energy.

As described above, since the difference in lattice constant is reduced by inserting the Al layer and the energy required for forming the single crystal is lowered, the AlN can be grown as a single crystal even at room temperature.

9 is an XPS result showing the change in the case where the ammonia atmosphere annealing is further performed for Example 1. Fig.

Before the ammonia annealing, the Al-Al peak was observed and the existence of the Al layer was confirmed. However, after the ammonia annealing, the Al layer did not exist because there was no Al-Al peak. And the Al layer is changed to AlN by annealing. Therefore, it has been proved that the metal layer can be changed according to the conditions at the time of annealing.

Experiments to grow GaN on AlN of Example 1 and Comparative Example 1 also proceeded.

Fig. 10 is a photograph of a substrate (a), a surface and a cross-sectional SEM photograph (c), and a phi scan data when GaN is grown for Example 1. Fig. (A) a substrate photograph, (b) a surface and cross-sectional SEM photograph, and (c) phi scan data.

As can be seen from a comparison between FIG. 10 and FIG. 11, it can be confirmed that GaN grows mirror-like in the case of Embodiment 1. FIG. Thus, the AlN of Example 1 according to the present invention is of such a quality that can be used as a buffer layer in the growth of single crystal GaN.

The above results are obtained when an Al layer having a smaller lattice constant difference from AlN than the difference in lattice constant between AlN and Si is inserted. Therefore, even when another metal layer satisfying these conditions is inserted, AlN is grown as a single crystal according to the present invention . The following Table 2 summarizes the difference between the lattice constants and the lattice constants for metal materials having a small lattice constant difference with AlN.

Figure pat00007

Ti, Mg, Cd, Ag, and Au have smaller lattice constant difference with AlN than Al. As one example, the lattice constant difference between Ti and AlN is smaller than the difference between the lattice constants between Al and AlN, and thus it is expected that a better quality AlN thin film can be obtained.

Ti layer  When used: Sapphire / Ti / AlN , Si / Ti / AlN

In Example 2, 5 nm of Ti was formed on a Si (111) substrate and 100 nm of AlN was grown. In Example 3, 5 nm of Ti was formed on a sapphire substrate and 100 nm of AlN was grown. Example 1 was produced as described above, and the Ti thickness was 5 nm and the AlN thickness was 100 nm as in Examples 2 and 3.

12 is phi scan data of the first to third embodiments.

As expected through the difference in lattice constants, it can be seen that the AlN thin film is formed with better quality than the Al layer using the Ti layer in practice. It is possible to apply various substrates, and it is expected that a metal layer corresponding to each substrate is also present. Both the Si substrate and the sapphire substrate were found to be better than the Al layer when the Ti layer was formed, but in the case of the Al layer, AlN was deposited better on the Si substrate than on the sapphire substrate.

As a result of the above experimental results, it is confirmed that AlN is grown not only on the Si (111) substrate but also on the sapphire substrate when the AlN is grown at room temperature, but the single crystal AlN is grown even at room temperature by inserting the metal layer. It can be expected that the method according to the present invention would be effective for other substrates having a hexagonal structure.

As described above, in the present invention, single crystal AlN can be grown even at a low energy (room temperature) by lowering the energy for growing AlN into a single crystal by inserting a metal layer that can reduce the difference in lattice constant between the substrate and AlN.

The result of GaN growth by MOCVD on sapphire / Ti (5 nm) / AlN (25 nm) fabricated at room temperature by PVD was similar to the case of using GaN buffer layer (MOCVD) . That is, it can be confirmed that AlN at low temperature made by the method according to the present invention can replace the conventional high-temperature buffer layer.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It will be understood that various modifications and changes may be made without departing from the scope of the appended claims.

10: substrate 20: metal layer 30: single crystal AlN

Claims (10)

Forming a metal layer on the substrate to reduce a difference in lattice constant between the substrate and the AlN; And
And growing monocrystalline AlN on the metal layer by a PVD method. 2. The method of claim 1, wherein a difference in lattice constant between the metal layer and AlN is smaller than a difference in lattice constant between the substrate and the AlN. The method of growing a single crystal AlN according to claim 1, wherein the metal layer is at least one of Al, Ti, Mg, Cd, Ag and Au. The method of claim 1, wherein the metal layer is formed by a PVD process. The method of claim 1, wherein the single crystal AlN is grown by depositing AlN along a lattice of the metal layer. The method according to claim 1, wherein the PVD method uses a reactive DC sputter using an Al target and an N 2 source. The method according to claim 1, wherein the PVD method uses an RF sputter using an AlN target. The method according to claim 1, wherein the metal layer and the single-crystal AlN are continuously deposited in one chamber. The method of growing a single crystal AlN according to claim 1, wherein the single crystal AlN is grown at room temperature. The method of claim 1, further comprising the step of annealing the substrate in a nitrogen, ammonia, or oxygen atmosphere to change the metal layer after growing the single crystal AlN.
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