JP3991815B2 - Method for growing zinc oxide crystal film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vapor phase growth method for a semiconductor crystal film, and more particularly to a method for easily and inexpensively growing a zinc oxide crystal film having good crystallinity.
[0002]
[Prior art]
Zinc oxide can be applied to light emitting elements, light receiving elements, piezoelectric elements, transparent conductive electrodes, active elements, and the like. Among these applications, since zinc oxide can have a larger energy band gap than silicon and the like as gallium nitride, it can be used as a semiconductor material for light-emitting elements that can emit short-wavelength light from blue to ultraviolet light. In recent years, the use of has attracted particular attention. Needless to say, a light emitting element capable of emitting light of a short wavelength is preferable from the viewpoint of increasing the recording density on the optical recording medium.
[0003]
As a method for obtaining a zinc oxide crystal film as a semiconductor material, MBE (molecular beam epitaxy) method and MOCVD (metal organic chemical vapor deposition) method are mainly used conventionally. In the MBE method, a zinc oxide crystal film having relatively good crystallinity can be obtained. However, since the MBE method requires an ultra-high vacuum film forming chamber, the MBE apparatus becomes large and expensive in order to obtain an ultra-high vacuum, and the production efficiency is low in film formation under an ultra-high vacuum. There is a problem that a low-cost light-emitting element cannot be realized.
[0004]
On the other hand, since the MOCVD method does not require an ultra-high vacuum in the film formation chamber, the MOCVD apparatus is relatively inexpensive and a zinc oxide crystal film can be grown with good productivity. In the MOCVD method for growing a zinc oxide crystal film, a gas of diethyl zinc as a zinc organic compound and a gas containing oxygen are often used conventionally. However, diethylzinc has high reactivity with oxygen, and it is difficult to grow a zinc oxide crystal film having a good crystal quality.
[0005]
International Publication No. 01/73160 therefore proposes a method for growing a zinc oxide crystal film on a substrate by atmospheric pressure MOCVD using a gas of acetylacetone zinc and oxygen gas, which has a relatively low reactivity with oxygen. ing. On the other hand, Journal of ELECTRONIC MATERIALS, Vol. 30, 2001, pp. 659-661 uses a zinc zinc gas and N ₂ O gas in a MOCVD method to form a zinc oxide buffer layer on a substrate at a relatively low temperature. On top of this, a method of growing a zinc oxide crystal film at a relatively high temperature has been proposed.
[0006]
[Problems to be solved by the invention]
As disclosed in WO 01/73160, a zinc oxide crystal film is directly grown on a substrate by MOCVD using a gas of an organic compound of zinc having a relatively low reactivity with oxygen and oxygen gas. In the method, the crystallinity of the obtained zinc oxide crystal film is not yet improved sufficiently, and further improvement of the crystallinity is desired.
[0007]
On the other hand, as disclosed in Journal of ELECTRONIC MATERIALS, Vol. 30, 2001, pp. 659-661, zinc oxide is used on a substrate at a relatively low temperature by using diethyl zinc gas and N ₂ O gas in MOCVD. In the method of forming a buffer layer and growing a zinc oxide crystal film thereon at a relatively high temperature, the substrate temperature must be changed between the formation of the buffer layer and the formation of the zinc oxide crystal film. The process becomes complicated, and it takes time to adjust the substrate temperature, resulting in a decrease in productivity.
[0008]
The buffer layer is preferably formed under zinc-rich conditions, while the zinc oxide crystal film must be formed under oxygen-rich conditions in order to suppress the generation of oxygen defects. Therefore, it is necessary to change the gas supply amount between the formation of the buffer layer and the zinc oxide crystal film, which complicates the film formation process and requires time to change the conditions.
[0009]
In view of the situation in the prior art, an object of the present invention is to provide a method capable of growing a zinc oxide crystal film having good crystallinity easily and at low cost.
[0010]
[Means for Solving the Problems]
According to the present invention, in a method of sequentially forming a zinc oxide buffer layer and a zinc oxide crystal film on a substrate by vapor phase growth, the zinc oxide buffer layer utilizes a gas of an organometallic compound containing zinc and oxygen. It is formed without the use of other gases including oxygen Te, the zinc oxide crystal film on the zinc oxide buffer layer is formed by using other gases including gas and oxygen of the organometallic compound containing zinc and oxygen Rukoto It is characterized by.
[0011]
In addition, as an organometallic compound, zinc acetylacetonate or its hydrate can be used preferably. Further, the zinc oxide buffer layer and the zinc oxide crystal film can be vapor-phase grown under the same substrate temperature. The substrate temperature is preferably a temperature within the range of 300 ° C to 600 ° C.
[0012]
In the gas phase deposition of acid zinc buffer layer and in the vapor phase growth of the zinc oxide crystal film, the supply amount of the gas of the organic metal compound may be the same.
[0013]
Zinc oxide buffer layer preferably is long allowed-phase gas at 10 to 60 minutes time in the range of. The substrate on which the zinc oxide buffer layer is deposited is preferably made of sapphire.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic cross-sectional view of an MOCVD apparatus that can be preferably used in a method for growing a zinc oxide crystal film according to the present invention. This MOCVD apparatus includes a film formation chamber 1, a substrate 2, a substrate holder 3, a substrate heating heater 4, an oxygen gas supply port 5, a zinc organic compound gas supply port 6, a first valve 7 for adjusting the film formation chamber pressure, Zinc organic compound vaporizing chamber 8, zinc organic compound holding boat 9, zinc organic compound heating heater 10, second valve 11 for adjusting the supply amount of zinc organic compound gas, for adjusting the supply amount of oxygen gas A third valve 12 is included. The first valve 7 is connected to an exhaust pump (not shown). An inert gas as a carrier gas is introduced into the zinc organic compound vaporizing chamber 8. Oxygen gas is introduced into the third valve 12.
[0015]
FIG. 2 shows the molecular structure of zinc acetylacetonate [Zn (C ₅ H ₇ O ₂ ) ₂ ] as an example of a zinc organic compound that can be preferably used in the MOCVD method for growing a zinc oxide crystal film according to the present invention. ing. However, the zinc organic compound that can be used in the method for growing a zinc oxide crystal film of the present invention is not limited to zinc acetylacetonate, and other zinc organic compounds such as zinc acetate dihydrate [Zn (CH ₃ COO) ₂ ], for example. Can also be used.
[0016]
In the MOCVD apparatus of FIG. 1, a zinc oxide buffer layer (not shown) is first deposited on the substrate 2. As the substrate 2, a sapphire substrate whose main surface is an A surface can be preferably used. However, the main surface of the sapphire substrate is not limited to the A surface, and a C surface, an R surface, or the like can also be used.
[0017]
The powdered or pelletized zinc organic compound supplied onto the boat 9 is vaporized by heating with the heater 10. The vaporized zinc organic compound gas is transported from the supply port 6 toward the substrate 2 through the first valve 11 by a carrier gas that is an inert gas such as nitrogen. During the deposition of the zinc oxide buffer layer, oxygen gas is not supplied from the supply port 5.
[0018]
That is, since the zinc organic compound used in the present invention also contains oxygen in addition to zinc, a buffer layer of zinc oxide can be deposited only by supplying the zinc organic compound gas without supplying the oxidizing gas. It can be done. Thus, when only zinc organic compound gas is supplied, without supplying oxygen gas, the zinc oxide buffer layer of zinc rich conditions can be formed.
[0019]
Next, in the MOCVD apparatus of FIG. 1, a zinc oxide crystal film (not shown) is grown on the zinc oxide buffer layer formed on the substrate 2. In growing the zinc oxide crystal film, the zinc organic compound gas is supplied from the supply port 6, and the oxygen gas is also supplied from the supply port 5 through the third valve 12. Thus, zinc in the zinc organic compound gas is completely oxidized, and a zinc oxide crystal film having good crystallinity is grown on the zinc oxide buffer layer.
[0020]
As described above, in the MOCVD method using zinc acetylacetonate or zinc acetate dihydrate gas, a zinc oxide crystal layer can be formed at a relatively low temperature. Therefore, in the present invention, the zinc oxide buffer layer and the zinc oxide crystal film thereon can be formed under the same substrate temperature. However, the substrate temperature in that case is preferably in the range of 300 ° C to 600 ° C. This is because if the substrate temperature is lower than 300 ° C., the zinc oxide crystal film formed on the buffer layer is unlikely to become a single crystal. On the other hand, if the substrate temperature is higher than 600 ° C., oxygen defects are likely to occur in the zinc oxide crystal film formed on the buffer layer.
[0021]
The deposition time of the zinc oxide buffer layer is desirably in the range of 10 minutes to 60 minutes. This is because if the deposition time of the buffer layer is shorter than 10 minutes, the effect of inserting the buffer layer is not recognized, and if it is longer than 60 minutes, the crystallinity of the zinc oxide crystal film grown on the buffer layer is deteriorated. Because.
[0022]
(Example)
As an example of the present invention, a zinc oxide buffer layer and a zinc oxide crystal film were sequentially formed on the A surface of the sapphire substrate 2 using the MOCVD apparatus of FIG. At that time, the sapphire substrate 2 was set on the substrate holder 3. The film formation chamber 1 was evacuated by a vacuum pump connected via a first valve 7. The sapphire substrate 2 was heated to 550 ° C. by the substrate heating heater 4.
[0023]
On the zinc organic compound holding boat 9, zinc acetylacetonate powder was supplied. The zinc organic compound vaporizing chamber 8 was heated to 100 ° C. by the heater 10, and the zinc acetylacetonate on the boat 9 was vaporized. The vaporized zinc acetylacetonate gas was transported from the supply port 6 toward the substrate 2 through the second valve 11 by a nitrogen carrier gas having a flow rate of 150 sccm. At this time, the first valve 7 was adjusted so that the gas pressure in the film forming chamber 1 was maintained at 8 kPa (60 Torr). In this state, a zinc oxide buffer layer was deposited on the sapphire substrate 2 for 20 minutes.
[0024]
After the zinc oxide buffer layer is formed, oxygen gas having a flow rate of 300 sccm is supplied from the supply port 5 through the third valve 12 while maintaining supply of zinc acetylacetonate gas with a nitrogen carrier gas having a flow rate of 150 sccm. 1 was supplied. In this state, a zinc oxide crystal film having a thickness of 0.8 μm was grown on the buffer layer in 2 hours.
[0025]
(Comparative Example 1)
Except for the difference that the zinc oxide buffer layer was not formed, a zinc oxide crystal film was grown directly on the sapphire substrate 2 under the same conditions as in the above-described example.
[0026]
(Comparison between Examples and Comparative Examples)
3 and 4 show X-ray diffraction rocking curves relating to the (0002) plane of the zinc oxide crystal film grown in the example and the comparative example 1, respectively. That is, in the graphs of FIGS. 3 and 4, the horizontal axis represents the diffraction angle (degrees), and the vertical axis represents the diffraction intensity (au: arbitrary unit).
[0027]
As can be seen from these graphs, the half-value width (FWHM) in the rocking curve of the zinc oxide crystal film of the example is 0.02 degrees, whereas the half-value width in the rocking curve of the zinc oxide crystal film of Comparative Example 1 is 0.02 degrees. Is 0.52 degrees. That is, it can be seen that the zinc oxide crystal film of the example has significantly superior crystallinity as compared with the zinc oxide crystal film of comparative example 1.
[0028]
5 and 6 show PL (photoluminescence) emission spectrum distributions relating to the zinc oxide crystal films grown in the examples and comparative example 1, respectively. That is, in the graphs of FIGS. 5 and 6, the horizontal axis represents the PL emission wavelength (nm), and the vertical axis represents the PL emission intensity (au: arbitrary unit).
[0029]
As can be seen from the graphs of FIGS. 5 and 6, the PL emission intensity of the zinc oxide crystal film of the example is 123a. u. In contrast, the PL emission intensity of the zinc oxide crystal film of Comparative Example 1 is 68a. u. It is. That is, it can be seen that the zinc oxide crystal film of the example has a light emission intensity about twice that of the zinc oxide crystal film of comparative example 1. In addition, in the graph of FIG. 6 relating to Comparative Example 1, light emission in the visible light region due to oxygen defects in the zinc oxide crystal film is seen, but in the graph of FIG. Not. That is, it can be seen that the zinc oxide crystal film of the example also has significantly superior optical characteristics as compared with the zinc oxide crystal film of comparative example 1.
[0030]
(Comparative Example 2)
Similar to the method disclosed in the above-mentioned Journal of ELECTRONIC MATERIALS, Vol. 30, 2001, pp. 659-661, a zinc oxide crystal film of Comparative Example 2 was grown. Also in this comparative example 2, the MOCVD apparatus of FIG. 1 was used. However, in Comparative Example 2, diethyl zinc was used as the zinc organic compound supplied onto the boat 9.
[0031]
During the deposition of the zinc oxide buffer layer, the sapphire substrate 2 having the A surface as the main surface was heated to 400 ° C. The vaporized diethyl zinc gas was supplied from the supply port 6 toward the substrate 2 by a nitrogen carrier gas having a flow rate of 5 sccm. At the same time, oxygen gas having a flow rate of 20 sccm was supplied from the supply port 5 toward the substrate 2. This state was maintained for 20 minutes to form a zinc oxide buffer layer.
[0032]
After the formation of the buffer layer, the substrate temperature was increased from 400 ° C. to 700 ° C. and stabilized for 40 minutes. Then, the zinc oxide buffer layer was heat-treated at the 700 ° C. substrate temperature for 30 minutes. Thereafter, while maintaining the substrate temperature of 700 ° C., a zinc oxide crystal film was grown on the buffer layer over 2 hours.
[0033]
In growing the zinc oxide crystal film, the flow rate of the nitrogen carrier gas for transporting the diethylzinc gas was reduced to 1 sccm, and the flow rate of the oxygen gas was increased to 50 sccm. In other words, the zinc-rich gas phase reaction conditions were used when the zinc oxide buffer layer was formed, but the conditions were changed to oxygen-rich gas phase reaction conditions when the zinc oxide crystal film was grown.
[0034]
Regarding the zinc oxide crystal film of Comparative Example 2 obtained in this way, the crystallinity and optical characteristics were examined in the same manner as in the example. The half-value width in the rocking curve of X-ray diffraction was 0.22 degrees, PL emission intensity is 110a. u. Met. That is, it can be seen that the zinc oxide crystal film of Comparative Example 2 has good crystallinity and optical characteristics almost similar to those of the examples.
[0035]
However, in Comparative Example 2, an extra time of 70 minutes is required for the change of the substrate temperature and the heat treatment of the zinc oxide buffer layer compared to the example. In Comparative Example 2, the reaction gas flow rate must be changed and adjusted between the formation of the zinc oxide buffer layer and the growth of the zinc oxide crystal film, and the film formation process is more complicated than in the example. I understand that.
[0036]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a method capable of easily and inexpensively growing a zinc oxide crystal film as a semiconductor material that can be preferably used for, for example, a light emitting device that can emit light having a short wavelength. it can.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an MOCVD apparatus that can be used for vapor phase growth of a zinc oxide crystal film according to the present invention.
FIG. 2 is a chemical structure diagram of zinc acetylacetonate that can be used for MOCVD growth of a zinc oxide crystal film according to the present invention.
FIG. 3 is a graph showing a rocking curve of X-ray diffraction in a zinc oxide crystal film obtained by the growing method of the present invention.
FIG. 4 is a graph showing a rocking curve of X-ray diffraction in a zinc oxide crystal film obtained by a conventional growth method.
FIG. 5 is a graph showing PL measurement results in a zinc oxide crystal film obtained by the growing method of the present invention.
FIG. 6 is a graph showing a PL measurement result in a zinc oxide crystal film obtained by a conventional growth method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Deposition chamber, 2 Substrate, 3 Substrate holder, 4 Substrate heater, 5 Oxygen gas supply port, 6 Zinc organic compound gas supply port, 7 First valve for film formation chamber pressure adjustment, 8 Zinc organic compound vaporization Chamber, 9 zinc organic compound holding boat, 10 heater for heating zinc organic compound, 11 second valve for adjusting the supply amount of zinc organic compound gas, 12 third valve for adjusting the supply amount of oxygen gas .

Claims (7)

In the method of sequentially forming a zinc oxide buffer layer and a zinc oxide crystal film on a substrate by vapor phase growth, the zinc oxide buffer layer may be formed of another metal containing oxygen using a gas of an organometallic compound containing zinc and oxygen. is formed without using a gas, growth of the zinc oxide crystal film of zinc oxide crystal film, wherein Rukoto formed using other gases including gas and oxygen of the organometallic compound containing zinc and oxygen Method.   2. The method for growing a zinc oxide crystal film according to claim 1, wherein the organometallic compound is zinc acetylacetonate or a hydrate thereof.   3. The method for growing a zinc oxide crystal film according to claim 1, wherein the zinc oxide buffer layer and the zinc oxide crystal film are vapor-phase grown at the same substrate temperature.   The method for growing a zinc oxide crystal film according to claim 3, wherein the substrate temperature is a temperature within a range of 300C to 600C. To any one of claims 1 to 4, wherein said a gas supply amount of the organometallic compound in a gas phase growth with a gas phase deposition of the zinc oxide buffer layer and the zinc oxide crystal film identical A method for growing the described zinc oxide crystal film. Method of growing a zinc oxide crystal film according to any one of claims 1 to 5 wherein the zinc oxide buffer layer, wherein provoking long-phase gas for a time period within a range of 10 minutes to 60 minutes. It said substrate method of growing a zinc oxide crystal film according to any one of claims 1 to 6, characterized in that it consists of sapphire.

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