KR101123009B1 - Method for etching group iii nitride semiconducotr - Google Patents

Abstract

The present invention relates to a method of etching a group III nitride semiconductor, and an embodiment of the present invention provides a method for bringing a surface of a group III nitride semiconductor into contact with an etching solution containing the same group III element as the group III constituent elements of the nitride semiconductor. And, etching the nitride semiconductor with the etching solution, separating the etching solution from the surface of the nitride semiconductor, and exposing the surface of the nitride semiconductor to a gas containing a hydrogen element. A method of etching a group nitride semiconductor is provided.

When the etching method of the group III nitride semiconductor according to the present invention is used, the surface uneven structure of the group III nitride semiconductor can be formed more finely and roughly, and when the group III nitride semiconductor is used in a light emitting device or a light receiving device, light extraction The efficiency can be improved.

Melt back etching, group III nitride semiconductor, irregularities

Description

Etching method of group III nitride semiconductors {METHOD FOR ETCHING GROUP III NITRIDE SEMICONDUCOTR}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of etching a group III nitride semiconductor, and more particularly, to a melt-back etching method capable of forming an uneven structure having a very high roughness on the surface of a group III nitride semiconductor.

Group III nitride semiconductors such as gallium nitride (GaN) have attracted attention as materials for semiconductor devices that emit green or blue light. The blue laser diode LD is applied to high density optical disks and displays, and the blue light emitting diode LED is applied to displays and lighting.

Group III nitride semiconductor substrates for LD and LED are manufactured by vapor deposition or the like, and surface defects such as pits and irregularities are generated on the surface of the group III nitride semiconductor substrate immediately after crystal growth. Therefore, when manufacturing a semiconductor element using a group III nitride semiconductor substrate, it is necessary to treat the surface of the substrate by etching or the like before epitaxial growth.

However, group III nitride semiconductors are chemically and thermally very stable, which makes surface processing and etching difficult. As the etching method of the group III nitride semiconductor, there are a wet method and a dry method. Wet etching uses KOH, H ₃ PO _4, etc., and the surface flatness is not good due to the characteristic that the defective portion is preferentially etched. Dry etching has a method such as ICP-RIE, CAIBE, etc., there is a problem that the surface damage by the plasma collision is large.

On the other hand, Y. Kaneko et al. Reported that GaN can be etched by contacting the GaN substrate with liquid Ga at high temperature [Y. Kaneko et al., Melt-back etching of GaN, Solid-State Electronics Vol. 41, No. 2, pp. 295-298, 1997]. This method is a method of reversely utilizing liquid phase epitaxy (LPE), which is a method of etching GaN by contacting GaN with an unsaturated Ga solution. This etching method is called melt-back etching.

In the melt back etching according to the report, the liquid Ga is raised to a constant temperature and then maintained for a predetermined time, and then the GaN is etched by contacting the upper surface of the GaN substrate with the liquid Ga at a predetermined temperature. However, this method has a very low etching rate. In addition, in order to maintain a constant temperature for a long time, the temperature stability of the reaction is very important, but in practice, there is a problem that can not achieve a good surface quality due to the temperature unevenness of the reactor.

In order to solve this problem, the present inventor has proposed a melt back etching method for etching a nitride semiconductor while increasing the temperature of the etching solution in Korea Patent No. 10-0691625. However, in the case of the registered patent, a nitride semiconductor having excellent surface quality may be obtained, but when employed in a light emitting device or a light receiving device, a nitride semiconductor having a very rough surface uneven structure is required. Accordingly, in the nitride semiconductor used in the optical device, a melt back etching method capable of obtaining a rough surface uneven structure is required in order to improve external light extraction efficiency.

An object of the present invention is to provide a method for etching a group III nitride semiconductor capable of forming an uneven structure with an improved surface roughness of the group III nitride semiconductor.

In order to achieve the above object, one embodiment of the present invention,

Contacting a surface of the group III nitride semiconductor with an etching solution containing a group III element identical to the group III constituent elements of the nitride semiconductor, etching the nitride semiconductor with the etching solution, and etching the nitride solution with the nitride solution It provides a method of etching a group III nitride semiconductor comprising the step of separating at the surface of the semiconductor and the surface of the nitride semiconductor to a gas containing a hydrogen element.

In an embodiment of the present disclosure, exposing the surface of the group III nitride semiconductor to a gas containing a hydrogen element may be performed at a condition of 600 ° C. or more, and more preferably, the surface of the group III nitride semiconductor is hydrogenated. The step of exposing to a gas containing an element may be performed at conditions of 800 ° C. or higher.

In an embodiment of the present disclosure, the etching of the nitride semiconductor may be performed while increasing the temperature of the etching solution while the etching solution is in contact with the surface of the nitride semiconductor.

In one embodiment of the present invention, the gas containing a hydrogen element may be at least one of H ₂ gas and HCl gas.

In an embodiment of the present disclosure, the method may further include exposing the surface of the nitride semiconductor to a gas containing a hydrogen element before contacting the nitride semiconductor to the etching solution.

In one embodiment of the present invention, after the step of exposing the surface of the nitride semiconductor to a gas containing a hydrogen element may further comprise the step of reducing the temperature inside the reactor equipped with the nitride semiconductor. In this case, the step of reducing the temperature inside the reactor equipped with the nitride semiconductor is preferably carried out so that the temperature inside the reactor is 600 ℃ or less.

In one embodiment of the present invention, it is preferable to give a temperature gradient to the etching solution in contact with one end of the nitride semiconductor and the etching solution in contact with the other end.

In one embodiment of the present invention, the nitride semiconductor is GaN, the etching solution may be a Ga solution.

In one embodiment of the present invention, the temperature of the etching solution in the step of etching the nitride semiconductor may be 900 ~ 1050 ℃.

In one embodiment of the present invention, the group III element may be one element selected from the group consisting of Ga, Al and In.

On the other hand, in the case of another embodiment of the present invention,

Contacting the surface of the group III nitride semiconductor with an etching solution containing the same group III element as the group III constituent elements of the nitride semiconductor, and etching the nitride semiconductor with the etching solution in a gas atmosphere containing hydrogen element And separating the etching solution from the surface of the nitride semiconductor in a gas atmosphere containing a hydrogen element.

In one embodiment of the present invention, the step of contacting the surface of the nitride semiconductor with the etching solution is carried out under a condition of 600 ℃ or less in a gas atmosphere containing hydrogen element, the step of etching the nitride semiconductor is 600 ℃ or more conditions Can be run as.

In one embodiment of the present invention, etching the nitride semiconductor may be performed while increasing the temperature of the etching solution.

In an embodiment of the present disclosure, the method may further include reducing a temperature inside the reactor equipped with the nitride semiconductor before separating the etching solution from the surface of the nitride semiconductor.

In one embodiment of the present invention, the step of reducing the inside of the reactor equipped with the nitride semiconductor may be performed so that the temperature inside the reactor is 600 ℃ or less.

In one embodiment of the present invention, the gas containing a hydrogen element may be at least one of H ₂ gas and HCl gas.

In an embodiment of the present disclosure, after the separating of the etching solution from the surface of the nitride semiconductor, the method may further include forming an inside of the reactor equipped with the nitride semiconductor in an N ₂ gas or NH ₃ gas atmosphere.

When the etching method of the group III nitride semiconductor according to the present invention is used, the surface uneven structure of the group III nitride semiconductor can be formed more finely and roughly, and when the group III nitride semiconductor is used in a light emitting device or a light receiving device, light extraction The efficiency can be improved.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. In addition, the embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art. Therefore, the shape and size of the elements in the drawings may be exaggerated for clearer explanation, elements represented by the same reference numerals in the drawings are the same elements.

Melt back etching is etching the surface of a group III nitride semiconductor with an etching solution containing the same group III elements as the group III member elements of the semiconductor. Group III nitrides include GaN, AlN, InN, GaInN, AlGaN, AlGaInN, and the like. The Group III liquid solution according to the present invention may be composed of a Group III single element such as Ga, Al, In, or may be a liquid solution containing other elements in Group III elements such as GaIn, GaAl, GaAs, AlGaIn, and the like. In particular, in order to easily control the etching rate of the group III nitride semiconductor, it is advantageous to use a mixed solution in which another element is added to the group III element as in the latter. In the case of the present invention, in the melt back etching method of such a group III nitride semiconductor, the inside of the reactor is formed in a gas containing a hydrogen element, for example, H ₂ gas or HCl gas atmosphere, before and after or during the etching to form the uneven surface of the nitride semiconductor. The structure can be made rougher. In the following description, the GaN surface is etched using the Ga solution as the etching solution.

FIG. 1 is a process flowchart illustrating a method of etching a group III nitride semiconductor according to an embodiment of the present invention, and FIG. 2 is a view illustrating a change in etching temperature over time in the process of FIG. 1. 3 is a schematic view showing an etching apparatus that can be applied in the etching method of FIG.

First, as the first step S11, H ₂ gas is exposed on the surface of a group III nitride semiconductor, such as GaN, and HCl gas may be used instead of H ₂ gas, or both gases may be used. In the case of the conventional melt back etching, N ₂ or NH ₃ gas is injected into the reactor before the nitride semiconductor is brought into contact with the etching solution so that the surface thereof is not etched. In contrast, in the present embodiment, the surface of the nitride semiconductor is exposed to H ₂ gas before the etching solution is applied, thereby forming a hole-like structure on the surface of the nitride semiconductor. Holes formed on the surface are several hundred nm in size, which may be because defects or pits on the surface of the nitride semiconductor are preferentially decomposed by H ₂ gas.

Thus, in order to form a hole in the surface of the nitride semiconductor, it is necessary to maintain appropriate temperature conditions, for example, 600 ° C. or higher in addition to the H ₂ gas atmosphere, and more preferably 800 ° C. or higher. In this case, referring to FIG. 2, T1 corresponds to 600 ° C. and T2 corresponds to 850 ° C. FIG. 4 is an electron micrograph showing a GaN surface exposed for 1 hour in a 850 ℃ H ₂ gas atmosphere. As shown in FIG. 4, holes may be formed on the surface of the nitride semiconductor by forming an appropriate temperature condition and an H ₂ gas atmosphere before full melt back etching.

Next, as a second step S12, in the case of a solution containing a group III element of the nitride semiconductor, that is, GaN, the Ga solution is brought into contact with the surface of the nitride semiconductor. In this case, even if the solid phase Ga is used, it may be changed to liquid Ga during the temperature increase process inside the reactor. Thereafter, as a third step S13, the GaN surface is etched using a Ga solution which is an etching solution. In the case of the present etching step (S13), it may be carried out while maintaining a constant temperature as in the general melt back etching, but when increasing the temperature of the etching solution as in the patent (10-0691625) proposed by the present inventors, nitrogen The etching rate can be improved due to promoting diffusion of (N) and suppressing nitrogen saturation of the etching solution.

Given the specific process conditions, the surface etching of the nitride semiconductor proceeds for 1 hour until the etching solution is raised to 910 ° C (T3) at a temperature of 850 ° C (T2) at 1 ° C / min. The temperature of the Ga etching solution for etching the GaN substrate is at least 720 占 폚, more preferably in the range of 750-1200 占 폚. In Ga etching solution, GaN is known to decompose at 720 ° C, but considering the etching rate, 750 ° C or more is preferable. In addition, when the temperature of the etching solution exceeds 1200 ° C, the surface shape of the GaN substrate is not good. More preferably, the temperature of the Ga solution in the GaN substrate etching step is in the range of 900-1050 ° C.

On the other hand, in this etching step, as in the first step (S11), it is possible to maintain the inside of the reactor in the H ₂ gas atmosphere. In addition, by giving a temperature gradient to the solution in contact with one end of the nitride semiconductor and the solution in contact with the other end can induce convection to further increase the etching rate.

Next, as a fourth step (S14), the Ga solution is separated from the nitride semiconductor, that is, GaN. Thereafter, as a fifth step S15, the GaN surface is exposed to H ₂ gas again to further improve surface roughness. In the case of this step S15, the same condition as that of the first step S11, which is a step of forming an H ₂ gas atmosphere before etching, may be performed. That is, the GaN surface may be exposed to H ₂ gas for 1 hour in an 850 ° C. H ₂ gas atmosphere. Subsequently, the etching process was terminated by lowering the temperature inside the reactor to room temperature, thereby obtaining a surface structure as shown in the electron micrograph of FIG. 5.

The above-described process will be described in more detail with reference to the etching apparatus of FIG. 3.

The etching apparatus of FIG. 3 includes a reactor 40, an etching solution storage unit 10, a substrate storage unit 20, and a waste liquid storage unit 30 in the reactor 40. The reactor 40 has a gas inlet formed on one side and a gas outlet formed on the other side, and includes a heating member 41. Various heating means (heater etc.) etc. can be employ | adopted as the heating member 41. FIG. The etching solution storage unit 10 is disposed above the reactor 40 and configured to store the etching solution 1. The substrate storage unit 20 is configured to accommodate the semiconductor substrate 3 and to be disposed below the etching solution storage unit 10 in the reactor 40. The waste liquid storage unit 30 is disposed below the substrate storage unit 20.

In the etching apparatus, an etching solution outlet is formed on a lower surface of the etching solution storage unit 10, and an etching solution inlet is formed on an upper surface of the waste solution storage unit 30. When the inlet of the upper surface of the substrate storage unit 20 coincides with the outlet of the etching solution storage unit by the rotation of the substrate storage unit 20, the etching solution 1 flows into the substrate storage unit 20. In addition, when the outlet of the lower surface of the substrate storage unit coincides with the inlet of the waste liquid storage unit 30 by the rotation of the substrate storage unit 20, the etching solution flows into the waste liquid storage unit 30. In FIG. 3C, the etching solution inlet and outlet of the substrate storage unit 20 are illustrated.

Referring to the operation of the etching apparatus, first, the GaN substrate 3 is mounted on the substrate storage portion 20 as shown in FIG. 3A, and the liquid Ga 10 is injected into the solution storage portion 10. Since the liquid Ga 10 is in a solid state at about 20 ° C. or less, solid Ga may be used. The solid Ga is converted into a liquid phase at an elevated temperature. After the temperature raising process, the gas atmosphere in the reactor is made into a H ₂ gas atmosphere at a temperature of about 850 ° C., so that holes are formed in the GaN substrate 3 before the liquid Ga 10 and the GaN substrate 3 contact each other.

Subsequently, as shown in FIG. 3B, the liquid Ga 1 of the solution storage portion 10 is sent to the substrate storage portion 20 and brought into contact with the GaN substrate 30. Subsequently, etching is performed while increasing the temperature of the liquid Ga. For example, the GaN substrate 3 can be etched while the temperature inside the reactor is raised to a constant slope. At this time, etching of the GaN substrate can be performed while maintaining the gas atmosphere with H ₂ gas. The diffusion rate of N in the liquid Ga increases as the temperature increases within the etching temperature range. When N decomposed from the surface of GaN facing the liquid Ga escapes from the liquid Ga, the N out of the liquid Ga exits the reaction tube in various forms depending on the gas flowing inside the reaction tube.

Subsequently, as shown in FIG. 3C, when the etching is completed, the liquid Ga 1 of the substrate storage unit 20 is sent to the waste liquid storage unit 30 while maintaining the H ₂ gas atmosphere inside the reactor. Accordingly, a finer uneven structure may be formed on the surface of the GaN substrate 30 having the etched surface.

FIG. 6 is a flowchart illustrating a method of etching a group III nitride semiconductor according to another embodiment of the present invention, and FIG. 7 illustrates a change in etching temperature over time in the process of FIG. 6. In this case, as in the previous embodiment, the etching apparatus of FIG. 3 can also be applied to the etching method of FIG.

First, as a first step S21, the Ga solution is brought into contact with the GaN surface. In the case of this embodiment, unlike the previous embodiment, the GaN surface is not exposed to H ₂ gas before contacting the Ga solution, and even if exposed, the hole by H ₂ gas is maintained by maintaining the temperature inside the reactor at 600 ° C. or lower. Avoid formation at high rates. In this case, even if solid Ga is used, liquid Ga can be obtained by raising the temperature inside the reactor to 600 ° C (T1).

Next, as a second step (S22), H ₂ gas is injected into the reactor, and then, the temperature of the etching solution (Ga solution) is 2 ° C./min up to 850 ° C. (T 2) to obtain a rough GaN surface. Increase the temperature. After the temperature increase, 850 ° C. is maintained for 1 hour to stabilize the temperature inside the reactor. When brought into contact with GaN and Ga solution in N ₂ gas atmosphere, it is a problem that it is not in the etching do not easily be released to the N atom external emitted from GaN well up, by creating a H ₂ gas atmosphere further etching of the GaN surface I can promote it.

Next, as a third step (S23), the GaN surface is etched using a Ga solution which is an etching solution. In the case of the present etching step (S13), it may be carried out while maintaining a constant temperature as in the general melt back etching, but when increasing the temperature of the etching solution as in the patent (10-0691625) proposed by the present inventors, nitrogen The etching rate can be improved due to promoting diffusion of (N) and suppressing nitrogen saturation of the etching solution. Specific process conditions are as described in the previous embodiment.

Next, as a fourth step (S24), the Ga solution is separated from GaN, while the H ₂ gas atmosphere is maintained. The step S24 lowers the temperature T3 raised during the melt back etching process to about 600 ° C., for example, to gradually reduce the temperature to −2 ° C./min. In this temperature reduction process, the H ₂ gas atmosphere is maintained, and as described above, etching of the GaN surface can be further promoted. After the Ga solution is separated from GaN, the inside of the reactor can be converted to an N ₂ gas atmosphere so that the GaN surface is not exposed to H ₂ gas. Subsequently, the etching process was terminated by lowering the temperature inside the reactor to room temperature, thereby obtaining a surface structure as shown in the electron micrograph of FIG. 8. Looking at the concave-convex structure of Figure 8, it has a much finer pattern than the concave-convex structure of Figure 9 formed by a general wet etching process. In this case, the uneven structure of FIG. 9 is a surface photograph after etching GaN in 1 mol of KOH solution for 4 hours. Furthermore, it can be seen that the uneven structure of FIG. 8 has a rougher surface than the case of FIG. 5 described above.

The present inventors measured the PL (PHotoluminescence) intensity in order to confirm the optical properties according to the surface roughness of the nitride semiconductor obtained by the present invention, the results are as shown in FIG. The PL intensity can be very usefully used as an index representing the optical properties according to the surface roughness.

In Comparative Example 1, the structure was not etched separately on the outer surface of the LED, and Comparative Example 2 was the structure described with reference to FIG. 9. In Example 1, the uneven structure (FIG. 5) which concerns on embodiment described in FIG. 2 is employ | adopted, and Example 2 employ | adopts the uneven structure (FIG. 8) which concerns on embodiment described in FIG. As shown in FIG. 10, it can be seen that the PL strength of the example is higher than that of the comparative examples, which can be understood as the roughness of the GaN surface. In particular, in the case of Example 2, the light emitting efficiency is excellent compared to other cases, and high efficiency can be expected when employing the light emitting device or the light receiving device.

The present invention is not limited by the above-described embodiments and the accompanying drawings, but is intended to be limited only by the appended claims. It will be apparent to those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. something to do.

FIG. 1 is a process flowchart illustrating a method of etching a group III nitride semiconductor according to an embodiment of the present invention, and FIG. 2 is a view illustrating a change in etching temperature over time in the process of FIG. 1. 3 is a schematic view showing an etching apparatus that can be applied in the etching method of FIG.

4 is an electron micrograph showing a GaN surface exposed for 1 hour in a 850 ℃ H ₂ gas atmosphere.

5 and 8 are electron micrographs of the GaN surfaces obtained according to the first and second embodiments of the present invention, respectively, and Fig. 9 is an electron micrograph of the GaN surfaces obtained according to the prior art.

FIG. 6 is a flowchart illustrating a method of etching a group III nitride semiconductor according to another embodiment of the present invention, and FIG. 7 illustrates a change in etching temperature over time in the process of FIG. 6.

10 is a PL intensity measurement result for confirming the optical characteristics according to the roughness of the GaN surface obtained according to the Examples and Comparative Examples of the present invention.

<Description of the symbols for the main parts of the drawings>

1: etching solution 3: GaN substrate

10: etching solution storage portion 20: substrate storage portion

30: waste liquid storage unit 40: reactor

41: heating member

Claims (19)

Contacting the surface of the group III nitride semiconductor with an etching solution containing the same group III element as the group III constituent elements of the nitride semiconductor; Etching the nitride semiconductor with the etching solution; Separating the etching solution from the surface of the nitride semiconductor; And Etching the surface of the nitride semiconductor separated from the etching solution by exposing to a gas containing a hydrogen element; Etching method of a group III nitride semiconductor comprising a. The method of claim 1, Exposing the surface of the group III nitride semiconductor to a gas containing a hydrogen element is carried out under a condition of 600 ° C. or higher. 3. The method of claim 2, And exposing the surface of the group III nitride semiconductor to a gas containing a hydrogen element is carried out under conditions of 800 ° C. or higher. The method of claim 1, Etching the nitride semiconductor is performed while increasing the temperature of the etching solution while the etching solution is in contact with the surface of the nitride semiconductor. The method of claim 1, The gas containing the hydrogen element is an etching method of a group III nitride semiconductor, characterized in that at least one of H ₂ gas and HCl gas. The method of claim 1, And exposing the surface of the nitride semiconductor to a gas containing a hydrogen element prior to contacting the nitride semiconductor with the etching solution. The method of claim 1, And reducing the temperature inside the reactor equipped with the nitride semiconductor after exposing the surface of the nitride semiconductor to a gas comprising a hydrogen element. The method of claim 7, wherein Reducing the temperature inside the reactor equipped with the nitride semiconductor is carried out so that the temperature in the reactor is 600 ℃ or less, characterized in that the etching method of the group III nitride semiconductor. The method of claim 1, And a temperature gradient is applied to the etching solution in contact with one end of the nitride semiconductor and the etching solution in contact with the other end. The method of claim 1, Said nitride semiconductor is GaN, and said etching solution is a Ga solution. The method of claim 1, The etching method of the group III nitride semiconductor, characterized in that the temperature of the etching solution in the step of etching the nitride semiconductor is 900 ~ 1050 ℃. The method of claim 1, The group III element is an etching method of a group III nitride semiconductor, characterized in that one element selected from the group consisting of Ga, Al and In. Contacting the surface of the group III nitride semiconductor with an etching solution containing the same group III element as the group III constituent elements of the nitride semiconductor; Etching the nitride semiconductor with the etching solution in a gas atmosphere containing hydrogen element; And Separating and etching the etching solution from the surface of the nitride semiconductor in a gas atmosphere containing hydrogen element; Etching method of a group III nitride semiconductor comprising a. The method of claim 13, The step of contacting the surface of the nitride semiconductor with the etching solution is carried out under a condition of 600 ° C or less in a gas atmosphere containing hydrogen element, and the step of etching the nitride semiconductor is carried out under the condition of 600 ° C or more Etching method of a group nitride semiconductor. The method of claim 13, Etching the nitride semiconductor is performed while increasing the temperature of the etching solution. The method of claim 13, And reducing the temperature inside the reactor equipped with the nitride semiconductor before separating the etching solution from the surface of the nitride semiconductor. The method of claim 16, The method of etching the inside of the reactor equipped with the nitride semiconductor is performed to etch the group III nitride semiconductor, wherein the temperature inside the reactor is performed to be 600 ° C. or less. The method of claim 13, The gas containing the hydrogen element is an etching method of a group III nitride semiconductor, characterized in that at least one of H ₂ gas and HCl gas. The method of claim 13, After the step of separating the etching solution from the surface of the nitride semiconductor, forming the inside of the reactor with the nitride semiconductor in an N ₂ gas or NH ₃ gas atmosphere further comprising the step of etching a group III nitride semiconductor .

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