JP2005026389A - Electrode structure on p-type iii-group nitride semiconductor layer and method of forming the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode structure having a stable low resistance and a high adhesive strength on a p-type III-group nitride semiconductor layer. <P>SOLUTION: The electrode structure on the p-type III-group nitride semiconductor layer includes first, second, third, and fourth electrode layers (102, 103, 104, and 105) stacked in this order on the semiconductor layer. The first electrode layer (102) contains at least one kind of metal selected from among a first metal group consisting of Ti, Hf, Zr, V, Nb, Ta, Cr, W, and Sc. The second metal layer (103) contains at least one kind of metal selected from among a second metal group consisting of Ni, Pd, and Co. The third metal layer (104) contains at least one kind of metal selected from among a third metal group consisting of Mo, Ru, Rh, W, and Ir. And, the fourth electrode layer (105) contains at least one kind of metal selected from among a fourth metal group consisting of Au and Al. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement of an electrode structure in a group III nitride semiconductor device represented by a semiconductor laser diode, for example.
[0002]
[Prior art]
Group III nitride semiconductor, for example, In _x Ga _y Al _z A GaN-based compound semiconductor represented by N (where x + y + z = 1, 0 ≦ x <1, 0 <y ≦ 1, 0 ≦ z <1) has a large energy band gap and high thermal stability, and It is also possible to control the band gap width by adjusting the composition. Accordingly, GaN-based semiconductors are expected as materials applicable to various semiconductor devices including light-emitting elements and high-temperature devices. In particular, for a light emitting diode (LED) using a GaN-based material, a device having a light intensity of several cd level in a blue to green light wavelength region has already been developed and put into practical use. In the future, obtaining LEDs for light with a longer wavelength and making LED displays full color, and practical application of laser diodes (LD) using GaN-based materials are becoming the goals of research and development.
[0003]
FIG. 15 is a schematic cross-sectional view showing the structure of a p-type electrode conventionally used in a semiconductor device using a GaN-based material. In this p-type electrode, a Ni layer 502 is deposited on the p-type GaN contact layer 501 and annealed at 500 ° C. for 10 minutes in a nitrogen atmosphere, whereby a diffusion reaction between the p-type GaN contact layer 501 and the Ni layer 502 is achieved. An intermediate layer 504 is formed. A surface electrode layer 503 for wire bonding or device mounting is further laminated on the Ni layer 502. As the material of the surface electrode layer 503, Au or the like is often used.
[0004]
In such an electrode structure, the intermediate layer 504 has an effect of relaxing the Schottky barrier generated at the interface when the p-type GaN contact layer 501 and the Ni layer 502 are in direct contact.
[0005]
[Patent Document 1] Japanese Patent Laid-Open No. 2001-15852
[0006]
[Problems to be solved by the invention]
However, the p-type electrode on the p-type GaN-based contact layer according to the prior art as illustrated in FIG. 15 has instability in ohmic characteristics, and has a relatively high specific contact resistance value of about 10 ^-2 Ωcm ² There is a problem that it is within the range of the degree. For example, the specific contact resistance value required for a p-type electrode of a semiconductor laser is about 10 ^-3 Ωcm ² It is difficult to achieve this with the prior art.
[0007]
Therefore, the present inventor has examined the p-type electrode structure according to the prior art in detail.
[0008]
First, it is understood that the main component of the intermediate layer 504 formed in FIG. 15 is composed of a compound of Ga and Ni (Ga—Ni compound; hereinafter, a compound of element X and element Y is expressed as an XY compound). It was.
[0009]
In addition, the formation of the intermediate layer 504 is easily influenced by the surface state of the p-type GaN contact layer 501 and the annealing temperature, and the in-wafer surface in accordance with the progress of the interface reaction between the p-type GaN contact layer 501 and the Ni layer 502. It became clear that non-uniformity occurred. Such non-uniformity leads to variations in the thickness and element composition ratio of the intermediate layer 504, or variations in the contact condition between the p-type GaN contact layer 501 and the Ni layer 502. It has been found that there is a characteristic distribution in which the contact resistance of the electrode that should be partially increased becomes extremely large, and the contact resistance may be increased when viewed as the whole electrode.
[0010]
It was also confirmed that this non-uniformity was a cause of unevenness on the electrode surface. Due to the non-uniformity of the interfacial reaction between the p-type GaN contact layer 501 and the Ni layer 502 described above, unevenness occurs at the interface or the thickness of the intermediate layer 504 to be formed. As a result, irregularities are formed on the electrode surface. Generally, wire bonding that crimps Al or Au wire to the electrode surface or stem mount that directly welds the electrode surface to the stem is often used as the power supply method for the electrode of the semiconductor element. Then, it became clear that it led to the problem that the bondability of the bonding was lowered, and finally caused the adverse effect of lowering the product yield.
[0011]
Furthermore, it was also found that Ni—N compounds were formed inside the intermediate layer 504 in addition to Ga—Ni compounds as main components. A source of N for the Ni—N compound is a p-type GaN contact layer 501. That is, N atoms in the p-type GaN contact layer 501 are absorbed into the intermediate layer 504, and the vicinity of the surface of the p-type GaN contact layer 501 is transformed into a high-resistance layer (or n-type layer). As a result, the p-type electrode It has also been revealed that it causes high resistance of the structure.
[0012]
In view of the above-mentioned problems in the prior art revealed by the present inventor, the present invention provides an electrode structure having a stable low resistance and high adhesion strength on a p-type group III nitride semiconductor layer at a high yield. The purpose is to do.
[0013]
[Means for Solving the Problems]
The electrode structure on the p-type group III nitride semiconductor layer of the present invention includes a structure including a first electrode layer, a second electrode layer, and a third electrode layer in order from the side in contact with the semiconductor layer. The one electrode layer includes at least one metal element selected from the first metal group consisting of Ti, Hf, Zr, V, Nb, Ta, Cr, W and Sc, and the second electrode layer includes Ni, Pd and At least one metal element selected from the second metal group consisting of Co, and the third electrode layer is at least one metal selected from the third metal group consisting of Mo, Ru, Rh, W and Ir It contains an element.
[0014]
The first electrode layer is a mixed layer and includes a compound of N and at least one metal element selected from the first metal group.
[0015]
The first electrode layer is a mixed layer and includes a compound of Ga and at least one metal element selected from the second metal group.
[0016]
The thickness of the first electrode layer is in the range of 1 to 1000 nm.
[0017]
The thickness of the second electrode layer is in the range of 1 to 1000 nm.
[0018]
Further, the electrode structure on the p-type group III nitride semiconductor layer of the present invention includes a structure including a fifth electrode layer and a third electrode layer in order from the side in contact with the semiconductor layer, and the fifth electrode layer Includes at least one metal element selected from the first metal group and at least one metal element selected from the second metal group, and the third electrode layer is selected from the third metal group. And at least one metal element.
[0019]
The fifth electrode layer is a mixed layer and includes a compound of N and at least one metal element selected from the first metal group.
[0020]
The fifth electrode layer is a mixed layer and includes a compound of Ga and at least one metal element selected from the second metal group.
[0021]
The fifth electrode layer has a thickness in the range of 1 to 1000 nm.
[0022]
The third electrode layer has a thickness in the range of 3 to 500 nm.
[0023]
A fourth electrode layer containing either Au or Al is laminated on the third electrode layer.
[0024]
The fourth electrode layer has a thickness of 50 nm or more.
[0025]
The method for forming an electrode structure on a p-type group III nitride semiconductor layer of the present invention includes at least one selected from the first metal group consisting of Ti, Hf, Zr, V, Nb, Ta, Cr, W, and Sc. A sixth electrode layer made of a kind of metal element is deposited on the semiconductor layer, and a seventh electrode layer made of at least one kind of metal element selected from the second metal group made of Ni, Pd, and Co is formed on the semiconductor layer. Depositing on the seventh electrode layer a third electrode layer deposited on at least one metal element selected from the third metal group consisting of Mo, Ru, Rh, W and Ir. It is characterized by including.
[0026]
The sixth electrode layer to be deposited has a thickness in the range of 1 to 500 nm.
[0027]
The seventh electrode layer to be deposited has a thickness in the range of 5 nm to 1000 nm.
[0028]
The deposited third electrode layer has a thickness in the range of 3 to 500 nm.
[0029]
The method further includes the step of depositing a fourth electrode layer containing either Au or Al on the third electrode layer.
[0030]
The fourth electrode layer has a thickness of 50 nm or more.
[0031]
N is deposited after the sixth electrode layer, the seventh electrode layer, the third electrode layer, and the fourth electrode layer are deposited. ₂ The method further includes a step of heat-treating the electrode structure at a temperature within a range of 300 to 700 ° C. in an atmosphere, an Ar atmosphere, or a vacuum.
[0032]
Next, the operation of the electrode structure according to the structure of the present invention will be described.
[0033]
According to the present invention, the electrode structure on the p-type group III compound semiconductor layer includes first, second, third, and fourth electrode layers sequentially stacked on the semiconductor layer, and the first electrode layer includes: Including at least one selected from the first metal group consisting of Ti, Hf, Zr, V, Nb, Ta, Cr, W, and Sc, and the second electrode layer is a second metal made of Ni, Pd, and Co The third electrode layer includes at least one selected from the group, the third electrode layer includes at least one selected from the third metal group consisting of Mo, Ru, Rh, W, and Ir, and the fourth electrode layer includes Au, Al It is characterized by including either.
[0034]
In such an electrode structure, for example, Hf contained in the first electrode layer is a metal used in the n-type electrode structure for the n-type GaN layer, and if the Hf layer is formed alone on the p-type GaN layer, it is shot. Act as a key electrode. However, for example, by using a small amount of Hf uniformly as the first electrode layer at the interface between the second electrode layer containing Ni and the p-type GaN layer, this small amount of Hf causes almost no Schottky effect, and the interfacial reaction accelerator. It became clear that it acts as.
[0035]
As a result of this interfacial reaction promoting action, in the p-type electrode structure, the annealing temperature applied to obtain a good ohmic contact can be lowered by about 100 to 200 ° C. compared to the conventional case, and the specific contact resistance value is small and high. It was found that adhesion strength can be obtained.
[0036]
Further, in the reaction at the interface between the second electrode layer and the p-type GaN layer, non-uniformity such as variation in the thickness of the intermediate layer formed by the reaction or variation in the element composition ratio may occur. It was found that the uniformity of the interfacial reaction can be improved by forming the electrode layer on the second electrode layer.
[0037]
Taking Mo as an example of the metal used for the third electrode layer, this metal has a high melting point of about 2600 ° C. and is thermally stable. Moreover, it is difficult to form a compound or an intermediate layer easily with the metal group used for the second electrode layer and the metal group used for the fourth electrode layer. Therefore, even after a heat treatment step or the like, the structure below the second electrode layer and the fourth electrode layer are blocked by the third electrode layer, and the laminated structure can be maintained without being mixed with each other.
[0038]
On the other hand, for example, Pd used for the second electrode layer diffuses to the p-type GaN layer side through a heat treatment step or the like to form a Pd—Ga compound layer, but the formation of the Pd diffusion direction is below the electrode. It is made uniform compared with the case where there is no Mo layer. As a result, the Pd—Ga compound layer can be formed uniformly in thickness and elemental composition ratio.
[0039]
As described above, by including the third electrode layer in the electrode structure in the present invention, the interface reaction between the second electrode layer and the p-type group III compound semiconductor layer can be made uniform. Contact resistance can also be kept uniformly low. Further, since the unevenness caused by the interfacial reaction can be suppressed to be extremely small, the unevenness of the electrode surface can be reduced, the deterioration of bondability can be prevented, and the production yield can be kept high.
[0040]
The thickness of the first electrode layer is in the range of 1 to 500 nm, the thickness of the second electrode layer is 5 nm or more, the thickness of the third electrode layer is in the range of 3 to 500 nm, and the fourth The thickness of the electrode layer is preferably 50 nm or more.
[0041]
According to the invention, the electrode structure on the p-type group III compound semiconductor layer includes fifth, third, and fourth electrode layers sequentially stacked on the semiconductor layer, and the fifth electrode layer is the first electrode layer. At least one metal element selected from one metal group and at least one metal element selected from the second metal group, and the third electrode layer is at least one selected from the third metal group And the fourth electrode layer is characterized by containing either Au or Al.
[0042]
In such an electrode structure, the fifth electrode layer is a mixed layer, and besides the simple metal belonging to the first metal group and the second metal group, the compound of the metal belonging to the first metal group and Ga, The compound of the metal and N which belong to a 2nd metal group is included. As a result, the effect of promoting the interface reaction by the metal belonging to the first metal group and the effect of forming the ohmic electrode by the metal belonging to the second metal group can be obtained at the same time.
[0043]
In addition, the presence of the third electrode layer suppresses mixing of the upper fourth electrode layer and the lower fifth electrode layer, thereby maintaining the laminated structure, and the metal elements belonging to the second metal group and the p-type group III The reaction with the nitride semiconductor layer is made uniform, and the contact resistance in the electrode surface can be kept uniformly low. At the same time, the unevenness of the electrode surface originating from the unevenness caused by the interfacial reaction is also reduced, which improves bondability and contributes to an improvement in production yield.
[0044]
The thickness of the fifth electrode layer is preferably in the range of 1 to 1000 nm, the thickness of the third electrode layer is preferably in the range of 3 to 500 nm, and the thickness of the fourth electrode layer is preferably 50 nm or more. .
[0045]
In the method for forming an electrode structure on a p-type group III compound semiconductor layer according to the present invention, a sixth electrode layer made of a metal element belonging to the first metal group is deposited on the semiconductor layer, and the second metal group is formed. A seventh electrode layer made of a metal element belonging to the third metal layer is deposited on the sixth electrode layer, a third electrode layer made of a metal element belonging to the third metal group is deposited on the seventh electrode layer, and the fourth metal group The method includes a step of depositing a fourth electrode layer containing a metal element belonging to the third electrode layer on the third electrode layer.
[0046]
Here, the sixth electrode layer and the seventh electrode layer have the following relationship between the first electrode layer and the second electrode layer in the description relating to the electrode structure. That is, when a heat treatment process is performed on the stacked structure in which the sixth electrode layer, the seventh electrode layer, the third electrode layer, and the fourth electrode layer are sequentially deposited as described above, the sixth electrode layer and the semiconductor layer undergo a compound reaction. As a result, a metal nitride of the sixth electrode layer is formed, and a part of the seventh electrode layer and the semiconductor layer also undergo a compound reaction to form a metal Ga compound of the seventh electrode layer. Thereby, a 1st electrode layer is formed as a layer containing these nitrides and compounds. At this time, the seventh electrode layer remaining without reacting constitutes the second electrode layer as it is. That is, the sixth electrode layer and the seventh electrode layer have a relationship of a laminated structure in the previous stage in which the first electrode layer and the second electrode layer are formed by heat treatment.
[0047]
Depending on the progress of the reaction by the heat treatment, the film thickness ratio between the sixth electrode layer and the seventh electrode layer, and the selection of the elements of the sixth electrode layer and the seventh electrode layer, the first electrode layer and the second electrode layer are stunned. In some cases, the fifth electrode layer is formed by mixing together, but the fifth electrode layer includes both the first electrode layer and the second electrode layer, and thus has the respective properties. The effect of the present invention is still exhibited.
[0048]
As a heat treatment step for forming the electrode structure as described above, N ₂ A process under a temperature in the range of 300 to 700 ° C. in an atmosphere, an Ar atmosphere, or a vacuum is suitable.
[0049]
DETAILED DESCRIPTION OF THE INVENTION
As specific examples of the embodiment of the present invention, the following Examples 1 to 14 were tried, and the matters related to them and the semiconductor elements mounted with them were also examined. Example 1 relates to an Au / Mo / Ni / Hf electrode structure including an Hf layer, a Ni layer, a Mo layer, and an Au layer sequentially stacked on a p-type GaN contact layer. The present invention relates to an Au / Mo / Pd / Hf electrode structure using a Pd layer instead of a Ni layer.
[0050]
Example 3 relates to an Au / Mo / Ni / Ti electrode structure including a Ti layer, a Ni layer, a Mo layer, and an Au layer sequentially stacked on a p-type GaN contact layer. The present invention relates to an Au / Mo / Pd / Ti electrode structure using a Pd layer instead of the Ni layer in Example 3.
[0051]
Example 5 relates to an Al / Mo / Ni / Hf electrode structure including an Hf layer, a Ni layer, a Mo layer, and an Al layer sequentially stacked on a p-type GaN contact layer, and Example 6 is an example. 5 relates to an Al / Mo / Pd / Hf electrode structure in which a Pd layer is used instead of the Ni layer.
[0052]
Example 7 relates to an Al / Mo / Ni / Ti electrode structure including a Ti layer, a Ni layer, a Mo layer, and an Al layer sequentially stacked on a p-type GaN contact layer. Example 8 is an example. 7 relates to an Al / Mo / Pd / Ti electrode structure in which a Pd layer is used instead of the Ni layer.
[0053]
Example 9 relates to an Al / Ir / Ni / Hf electrode structure including an Hf layer, an Ni layer, an Ir layer, and an Al layer sequentially stacked on a p-type GaN contact layer. Example 10 is an example. The present invention relates to an Al / Ir / Pd / Hf electrode structure in which a Pd layer is used instead of the 9 Ni layer.
[0054]
Example 11 relates to an Al / Ir / Ni / Ti electrode structure including a Ti layer, a Ni layer, an Ir layer, and an Al layer sequentially stacked on a p-type GaN contact layer. Example 12 is an example. The present invention relates to an Al / Ir / Ni / Hf electrode structure using a Pd layer instead of the 11 Ni layer.
[0055]
Example 13 relates to an Au / Ir / Ni / Hf electrode structure including an Hf layer, a Ni layer, an Ir layer, and an Au layer sequentially stacked on a p-type GaN contact layer. Example 14 is an example. The present invention relates to an Au / Ir / Pd / Hf electrode structure using a Pd layer instead of 13 Ni layers.
[0056]
Examples 15 to 18 relate to an AlGaN-based semiconductor laser device on which the electrode structure shown in Example 1 and Example 2 is mounted.
(Example 1)
Example 1 will be described with reference to the schematic cross-sectional view of FIG.
[0057]
First, a p-type GaN layer was formed on a sapphire substrate as a contact layer 101 of a p-type group III nitride semiconductor included in an arbitrary semiconductor device. In order to form the p-type GaN 101, a GaN layer doped with Mg was epitaxially grown by metal organic chemical vapor deposition (MOCVD). The p-type GaN layer 101 has 10 ¹⁹ / Cm ³ Mg is added and N ₂ After the p-type treatment by annealing in the atmosphere, the p-type GaN layer 101 is 1.5 × 10 6 ¹⁷ / Cm ³ The carrier concentration was shown.
[0058]
Thereafter, the sapphire substrate is placed in an electron beam (EB) vacuum deposition apparatus, and a sixth electrode layer 102 made of Hf having a thickness of 5 nm and a seventh electrode layer made of Ni having a thickness of 15 nm are formed on the p-type GaN contact layer 101. 103, a third electrode layer 104 made of Mo with a thickness of 15 nm and a fourth electrode layer 105 made of Au with a thickness of 200 nm were deposited. Finally, the entire electrode structure on the sapphire substrate is N ₂ By annealing at about 450 ° C. in an atmosphere, the electrode structure according to the first embodiment was completed.
[0059]
In FIG. 2, the electrode structure completed using the present invention is shown in a schematic cross-sectional view. When the electrode structure after annealing at 450 ° C. in Example 1 was examined in detail, a p-type GaN layer 101 and a mixture layer of a Hf—N compound and a Ni—Ga compound were sequentially formed on the sapphire substrate from the bottom. It was revealed that the first electrode layer 102A, the second electrode layer 103 (= seventh electrode layer) made of Ni, the third electrode layer 104 made of Mo, and the fourth electrode layer 105 made of Au were made.
[0060]
The thickness of the mixture layer was about 10 nm, which was about twice the thickness of the Hf layer before the heat treatment. On the other hand, almost no Hf—N compound and Ni—Ga compound were detected in the electrode cross-sectional structure before annealing. From this, it is considered that these two types of compounds of Hf—N and Ni—Ga are formed by a reaction during the annealing process.
[0061]
As described above, the Ni—N compound formed between the p-type GaN contact layer 501 and the Ni layer 502 in the conventional electrode structure shown in FIG. 15 causes the resistance and instability of the electrode structure. It becomes. However, in Example 1, since the Hf layer (sixth electrode layer 102) exists before the annealing process, first, in the initial stage of the annealing process, the Hf − is between the p-type GaN layer 101 and the Hf layer. N compounds are formed. Since N for the Hf—N compound is mainly supplied from the p-type GaN layer 101, the surface of the p-type GaN layer 101 is in an excessive state of Ga. The excess free Ga and Ni from the Ni layer (seventh electrode layer 103) directly react to form a Ni—Ga compound in the mixture layer (first electrode layer 102A). By passing through such a reaction process, the high resistance layer (or n-type layer) associated with the formation of the Ni—N compound is obtained in Example 1 without impairing the stoichiometric composition ratio of the surface of the p-type GaN layer 101. It is considered that the ohmic reaction between the p-type GaN contact layer 101 and the metal electrode can be promoted without forming a).
[0062]
By the way, since Hf and N easily react with each other, the Hf—N compound contained in the first electrode layer 102A made of the above-mentioned mixture is formed between the p-type GaN layer 501 and the Ni layer 502 in FIG. Compared with the intermediate layer 504 made of a Ni—Ga compound generated by the reaction, it is generated by annealing at a lower temperature. And in the presence of Ga freed by depletion of N by Hf, the Ni-Ga compound formation reaction is also an annealing temperature lower than the temperature required for Ni to break the bond between Ga and N and react with Ga. It tends to occur. That is, the annealing necessary for obtaining the ohmic property of the electrode structure of Example 1 can be performed at a lower temperature than the conventional electrode structure shown in FIG.
[0063]
FIG. 3 is a graph that proves this fact. In this graph, the horizontal alloy temperature (° C.) represents the annealing temperature for making the electrode structure ohmic, and the vertical axis contact resistance (Ωcm ² ) Represents the resistance after the ohmic treatment.
[0064]
As can be seen from FIG. 3, in the conventional Au / Ni electrode structure, as indicated by the black circles, the contact due to the interface reaction between the p-type GaN contact layer 501 and the Ni layer 502 from the annealing temperature of 400 ° C. While a significant decrease in resistance begins to occur, in the Au / Mo / Ni / Hf electrode structure of Example 1, a significant decrease in contact resistance starts from an annealing temperature of 350 ° C. as represented by a white circle. The reaction between Hf of the sixth electrode layer and N in the p-type GaN contact layer 101 at a lower temperature than in the past, and further, Ga in the p-type GaN contact layer 101 and Ni in the seventh electrode layer 103 It can be seen that the reaction is starting to occur. Such being able to be ohmicized by annealing at a relatively low temperature enables improvement in temperature control accuracy during the electrode manufacturing process and simplification of the process, which is a very beneficial advantage in the production process.
[0065]
As can also be seen from FIG. 3, the Au / Mo / Ni / Hf electrode structure of Example 1 has a smaller contact resistance in the annealing temperature range of 350 to 600 ° C. than the conventional Au / Ni electrode structure. ing. Also, the annealing temperature at which the minimum contact resistance can be obtained is 500 ° C. in the conventional Au / Ni electrode structure, whereas it is 450 ° C. lower than that in the Au / Mo / Ni / Hf electrode structure of Example 1. is there. This is because the Hf layer is interposed in Example 1, which is caused by the deviation of the stoichiometric composition ratio on the surface of the p-type GaN layer 501 seen in the conventional electrode structure or the generation of Ni-N compounds. This is considered to be due to the effect of suppressing the formation of the high resistance layer (or n-type layer).
[0066]
FIG. 4 shows the ohmic properties after annealing in the Au / Mo / Ni / Hf electrode structure before annealing in Example 1 by changing the thicknesses of the Hf layer and Ni layer in various ways. Shows the results. In the graph of FIG. 4, the horizontal axis represents the film thickness (nm) of the Hf layer, and the vertical axis represents the film thickness (nm) of the Ni layer. A black circle mark represents a case where a contact resistance smaller than that of a conventional Au / Ni electrode was stably obtained, and a x mark represents a case where a clear improvement effect was not obtained as compared with the conventional case.
[0067]
As shown in FIG. 4, regarding the film thickness of the Hf layer, when it is in the range of about 1 to 500 nm, the Au / Mo / Ni / Hf electrode structure is changed to the conventional Au / Ni electrode structure. In comparison, a small contact resistance was stably obtained. However, when the Hf layer is thinner than 1 nm, for example, 0.5 nm, the contact resistance after annealing of the Au / Mo / Ni / Hf electrode structure is hardly improved as compared with the conventional Au / Ni electrode structure. This is because, since the Hf layer is too thin, the absolute amount for forming the Hf-N compound in the interface reaction with the p-type GaN layer 101 is insufficient, and the Ni between the Ni layer and the p-type GaN layer 101 is insufficient. It is thought that this reaction becomes dominant. On the other hand, when the Hf layer was thicker than 500 nm, the Au / Mo / Ni / Hf electrode structure did not exhibit ohmic characteristics even when the annealing temperature was increased or the time was increased, and only Schottky characteristics were exhibited. This is considered to be because the Ni layer and the p-type GaN layer 101 are completely blocked because the Hf layer is too thick, and Ni cannot contribute to the reaction.
[0068]
Regarding the thickness of the Ni layer, when it was about 5 nm or more, a smaller contact resistance was stably obtained in the Au / Mo / Ni / Hf electrode structure than in the conventional Au / Ni electrode structure. However, when the Ni layer is thinner than 5 nm and is, for example, 1 nm, the Au / Mo / Ni / Hf electrode structure has insufficient ohmic characteristics even after annealing. This is presumably because the Ni layer is not thick enough so that the entire amount of the Ni layer is consumed to form a compound with Ga. On the other hand, regarding the upper limit of the thickness of the Ni layer, there was no adverse effect on the electrical characteristics of the Au / Mo / Ni / Hf electrode structure even when the thickness was increased to about 1 μm. It was observed that the structure tends to peel off. Therefore, the upper limit of the preferable thickness of the Ni layer is considered to be about 1 μm, considering the adhesion strength which is important when the electrode structure is used in an actual semiconductor device.
[0069]
In addition, regarding the film thickness of the Mo layer (third electrode layer 104), the interface reaction promoting effect between the p-type GaN contact layer 101 and the Ni layer, which is the role of the Hf layer, is made more uniform by setting the film thickness to about 3 nm or more. I was able to. When the thickness of the Mo layer was less than 3 nm, the interface reaction promoting effect tended to be two-dimensionally non-uniform depending on the Hf layer formation conditions and the surface state of the p-type GaN layer 101. On the other hand, when the film thickness of the Mo layer was set to 500 nm or more, there was a problem that was attributed to the film stress of Mo such as peeling of the electrode structure. Therefore, the preferable thickness range of the Mo layer is considered to be in the range of 3 nm to 500 nm.
[0070]
Furthermore, in order to investigate the characteristics of the Au / Mo / Ni / Hf electrode structure of Example 1 in more detail, a Mo / Ni / Hf electrode structure as a comparative example not including an Au layer was also prototyped. However, when this Mo / Ni / Hf electrode structure was left in the atmosphere, a natural oxide film was formed on the surface of the Mo layer. When such an oxide film is present on the outermost surface of the electrode, bondability may be lowered, and in many cases, it is not preferable, for example, when yielding as an electrode of a semiconductor element, the yield is reduced. It is understood that the lamination of the Au layer (fourth electrode layer 105) in Example 1 is effective for preventing the formation of the oxide layer, and it is sufficient that the thickness of the Au layer is about 50 nm or more. It was.
[0071]
On the other hand, the upper limit of the thickness of the Au layer is not limited by the electrical characteristics of the electrode. However, if the Au layer is thicker than 5 μm, the ease of lift-off decreases when a lift-off process is used for patterning the electrodes. Further, from the viewpoint of adhesiveness in the bonding process, it is sufficient that the thickness of the Au layer is 5 μm. Even if it is thicker than that, only the amount of expensive Au used is increased, which is not preferable. Therefore, the preferable upper limit of the thickness of the Au layer is considered to be about 5 μm.
[0072]
Further, as comparative examples for the Au / Mo / Ni / Hf electrode structure of Example 1, an Au / Mo / Hf / Ni electrode structure and an Au / Mo / (HfNi alloy) electrode structure were also prototyped. However, good electrical characteristics as in Example 1 could not be obtained. These facts are illustrated in the graphs of FIGS. 5 and 6 similar to the graph of FIG.
[0073]
In the graph of FIG. 5, the white circle mark and the black circle mark represent the annealing temperature dependence of the contact resistance in the Au / Mo / Hf / Ni electrode structure of the comparative example and the conventional Au / Ni electrode structure, respectively. As shown in this graph, the Au / Mo / Ti / Ni electrode structure of the comparative example has almost improved contact resistance after annealing at any temperature compared to the conventional Au / Ni electrode structure. Will not bring. This is because, even in the Au / Mo / Hf / Ni electrode structure, since the Ni layer is in direct contact with the p-type GaN layer as in the conventional case, a Ni—N compound is generated at the interface, and a high resistance interface layer is generated. It is thought that it is from.
[0074]
In the graph of FIG. 6, black circles and white circles indicate the annealing temperature dependence of contact resistance in the Au / Mo / (HfNi alloy) electrode structure of the comparative example and the Au / Mo / Ni / Hf electrode structure of Example 1, respectively. Represents. In the Au / Mo / (HfNi alloy) electrode structure of the comparative example, the Ni or Ni-concentrated portion in the HfNi alloy layer and the p-type GaN contact layer partially contact and react with each other to form the NiN compound. Tend to generate. Therefore, in the Au / Mo / (HfNi alloy) electrode structure of the comparative example, a high resistance region is partially formed after annealing, and as a result, the contact resistance averaged over the entire electrode is considered to be high.
[0075]
On the other hand, in the Au / Mo / Ni / Hf electrode structure of Example 1, the Hf layer exists almost uniformly between the p-type GaN layer 101 and the Ni layer, and the interface reaction between the two is uniformly promoted. As shown in FIG. 4, a small contact resistance value can be stably obtained as compared with the Au / Mo / (HfNi alloy) electrode structure of the comparative example. That is, it can be seen that the Hf layer formed between the Ni layer and the p-type GaN contact layer 101 plays an important role with respect to the effect of improving the electrical characteristics in the electrode structure of Example 1.
[0076]
In Example 1, regarding the Mg concentration contained in the contact layer 101 of p-type GaN, 1.0 × 10 ¹⁸ ~ 1.0 × 10 ²⁰ / Cm ³ However, it was possible to obtain good ohmic characteristics with the Au / Mo / Ni / Hf electrode structure for any Mg concentration p-type GaN contact layer.
[0077]
In Example 1, an annealing process for ohmic electrode structure is performed in N ₂ Although it was performed in the atmosphere, the annealing treatment may be performed in an Ar atmosphere or in a vacuum. In that case, the optimum annealing temperature is N ₂ Although it changes a little compared with the case of using an atmosphere, it is still lower than the optimum annealing temperature of the conventional Au / Ni electrode structure.
[0078]
Furthermore, in Example 1, since the interface reaction during annealing is reliably generated at a lower temperature than the conventional example and hardly affected by conditions such as temperature, the adhesion strength of the interface often observed in conventional electrodes is insufficient. There is no problem of peeling due to.
(Example 2)
In Example 2, the seventh electrode layer 103 of Example 1 was changed from Ni to Pd.
[0079]
Referring to FIG. 1, also in Example 2, similarly to Example 1, a p-type GaN contact layer 101 doped with Mg was formed on a sapphire substrate. On the contact layer 101, a sixth electrode layer 102 made of Hf with a thickness of 5 nm, a seventh electrode layer 103 made of Pd with a thickness of 15 nm, a third electrode layer 104 made of Mo with a thickness of 15 nm, and a thickness of 200 nm The fourth electrode layer 105 made of Au was deposited by EB vapor deposition. And the entire electrode structure on the sapphire substrate is N ₂ The electrode structure according to Example 2 was completed by annealing at about 550 ° C. in an atmosphere.
[0080]
Referring to FIG. 2, in the electrode structure completed according to Example 2, on the sapphire substrate, a p-type GaN contact layer 101, a first electrode layer made of a mixture of an Hf—N compound and a Pd—Ga compound in order from the bottom. It was revealed that the second electrode layer 103 (= seventh electrode layer) of 102A and Pd, the third electrode layer 104 of Mo, and the fourth electrode layer 105 of Au were formed. The thickness of the first electrode layer 102A made of the mixture was about 10 nm, and was about twice the thickness of the Hf layer (sixth electrode layer 102) before the heat treatment. Note that the Hf—N compound and the Pd—Ga compound were hardly detected in the electrode cross-sectional structure before annealing. From this, it is considered that these two types of compounds of Hf—N and Pd—Ga are formed by the reaction during the annealing process.
[0081]
In the case of the Au / Pd electrode structure as a comparative example not including the Hf layer, a Pd—N compound is formed between the Pd layer and the GaN contact layer after the annealing treatment. This Pd—N compound causes high resistance and instability of the electrode structure, similarly to the Ni—N compound in the conventional Au / Ni electrode structure. However, in Example 2, the Hf layer existing before the annealing step plays the same role as in Example 1, so that the stoichiometric composition ratio of the surface of the p-type GaN contact layer 101 is not impaired. It is considered that the ohmic reaction between the p-type GaN contact layer 101 and the metal electrode can be promoted without forming a high resistance layer (or n-type layer) associated with the formation of the Pd—N compound. .
[0082]
In the graph of FIG. 7 similar to the graph of FIG. 3, the white circle mark and the black circle mark are respectively in the Au / Mo / Pd / Hf electrode structure before annealing of Example 2 and in the Au / Pd electrode structure of the comparative example. It represents the annealing temperature dependence of contact resistance. As shown in this graph, the Au / Mo / Pd / Hf electrode structure of Example 2 has a smaller contact resistance than the Au / Pd electrode structure of the comparative example in the temperature range of 450 to 700 ° C. Yes. Further, with respect to the annealing temperature at which the contact resistance starts to be significantly reduced by the interface reaction and the annealing temperature at which the lowest contact resistance is obtained, the Au / Mo / Pd / of Example 2 is compared with the Au / Pd electrode structure of the comparative example. In the Hf electrode structure, the temperature is lowered by about 50 ° C. This ability to be ohmicized by lower temperature annealing can be a very beneficial advantage in the electrode manufacturing process, as also described with respect to Example 1.
[0083]
As a result of examination and consideration similar to Example 1 regarding the thickness of each metal layer of Example 2, the preferable thickness of each layer is that Hf layer 102 is 1 nm to 500 nm, and Pd layer (seventh electrode layer 103) is It was found that the thickness was 5 nm to 1 μm, the Mo layer (third electrode layer 104) was 3 nm to 1 μm, and the Au layer (fourth electrode layer 105) was 50 nm to 5 μm.
[0084]
As in the case of Example 1, also in Example 2, the concentration of Mg contained in the p-type GaN contact layer is 1.0 × 10 6. ¹⁸ ~ 1.0 × 10 ²⁰ / Cm ³ However, good ohmic characteristics could be obtained by the Au / Mo / Pd / Hf electrode structure for any Mg-concentrated p-type GaN contact layer.
[0085]
Further, as in the case of Example 1, the annealing process for the ohmicization of the electrode structure of Example 2 described above is N ₂ Although it was performed in an atmosphere, annealing may be performed in an Ar atmosphere or in a vacuum. Even in this case, the optimum annealing temperature is N ₂ Although it changes a little compared with the case of using an atmosphere, it is still lower than the optimum annealing temperature of the Au / Pd electrode structure of the comparative example.
[0086]
Furthermore, in the same way as in Example 1, in Example 2, the interface reaction during annealing is reliably generated at a lower temperature and less affected by conditions such as temperature compared to the Au / Pd electrode of the comparative example. The problem of peeling due to insufficient adhesion strength at the interface, which is often observed in the electrode of the example, does not occur.
[0087]
(Example 3)
Referring to FIG. 1, also in Example 3, similarly to Example 1, a p-type GaN contact layer 101 doped with Mg was formed on a sapphire substrate. On the GaN contact layer 101, a Ti sixth electrode layer 102 having a thickness of 3 nm, a Ni seventh electrode layer 103 having a thickness of 15 nm, a third electrode layer 104 having a thickness of 15 nm, and an Au having a thickness of 200 nm are formed. The fourth electrode layer 105 was deposited by EB vapor deposition. And the entire electrode structure on the sapphire substrate is N ₂ The electrode structure according to Example 3 was completed by annealing at about 400 ° C. in an atmosphere.
[0088]
Referring to FIG. 2, in the electrode structure completed according to Example 3, on the sapphire substrate, a p-type GaN contact layer 101, a first electrode layer made of a mixture of a Ti—N compound and a Ni—Ga compound, in order from the bottom. It has been clarified that it is composed of 102A, a second electrode layer 103 made of Ni, a third electrode layer 104 made of Mo, and a fourth electrode layer 105 made of Au. Note that the Ti—N compound and the Ni—Ga compound were hardly detected in the electrode cross-sectional structure before annealing. From this, it is considered that these two types of compounds of Ti—N and Ni—Ga are formed by a reaction during the annealing process.
[0089]
In the third embodiment, a Ti layer is used in place of the Hf layer that is the first electrode layer in the electrode structure shown in the first embodiment. Ti, like Hf, is an element that easily forms a Ti—N compound by reacting with N when reacting with GaN. Due to this property, even if the Hf layer of Example 1 is replaced with a Ti layer in this example, there is no essential change in the effect brought about by the present invention.
[0090]
In the graph of FIG. 8 similar to the graph of FIG. 3, the white circle mark and the black circle mark indicate contact resistances in the Au / Mo / Ni / Ti electrode structure before annealing of Example 3 and the Au / Ni electrode structure of the comparative example, respectively. It shows the annealing temperature dependence. As shown in this graph, the Au / Mo / Ni / Ti electrode structure of Example 3 has a smaller contact resistance than the Au / Ni electrode structure of the comparative example in the temperature range of 300 to 600 ° C. Yes. Further, with respect to the annealing temperature at which the contact resistance starts to be significantly reduced by the interface reaction and the annealing temperature at which the lowest contact resistance is obtained, the Au / Mo / Pd / In the Hf electrode structure, the temperature is lowered by about 100 ° C. This ability to be ohmicized by lower temperature annealing can be a very beneficial advantage in the electrode manufacturing process, as already described with respect to Example 1 and Example 2.
[0091]
As a result of examination and consideration similar to Example 1 and Example 2 regarding the thickness of each metal layer of Example 3, the preferable thickness of each layer is that the Ti layer (sixth electrode layer 102) is 1 nm to 500 nm, It was found that the Ni layer (seventh electrode layer 103) was 5 nm to 1 μm, the Mo layer (third electrode layer 104) was 3 nm to 1 μm, and the Au layer (fourth electrode layer 105) was 50 nm to 5 μm.
[0092]
As in the case of Example 1 and Example 2, also in Example 3, the concentration of Mg contained in the p-type GaN contact layer is 1.0 × 10 ¹⁸ ~ 1.0 × 10 ²⁰ / Cm ³ However, good ohmic characteristics could be obtained by the Au / Mo / Ni / Ti electrode structure for any Mg-concentrated p-type GaN contact layer.
[0093]
Further, as in the case of Example 1 and Example 2, the annealing process for the ohmicization of the electrode structure of Example 3 described above is N ₂ Although it was performed in the atmosphere, the annealing treatment may be performed in an Ar atmosphere or in a vacuum. Even in this case, the optimum annealing temperature is N ₂ Although it changes a little compared with the case where an atmosphere is used, it still remains lower than the optimum annealing temperature of the Au / Ni electrode structure of the comparative example.
[0094]
Further, in Example 3 as well as in Example 1 and Example 2, the interface reaction during annealing is lower than that of the comparative example of Au / Ni, and is less affected by conditions such as temperature, so it is reliable. Therefore, the problem of peeling due to insufficient adhesion strength at the interface often observed in the electrode of the comparative example does not occur.
[0095]
(Example 4)
Referring to FIG. 1, also in Example 4, similarly to Example 1, a p-type GaN contact layer 101 doped with Mg was formed on a sapphire substrate. On the GaN contact layer 101, a Ti sixth electrode layer 102 having a thickness of 3 nm, a Pd seventh electrode layer 103 having a thickness of 15 nm, a Mo third electrode layer 104 having a thickness of 15 nm, and an Au having a thickness of 200 nm are formed. The fourth electrode layer 105 was deposited by EB vapor deposition. And the entire electrode structure on the sapphire substrate is N ₂ The electrode structure according to Example 4 was completed by annealing at about 500 ° C. in an atmosphere.
[0096]
Referring to FIG. 2, in the electrode structure completed according to Example 4, on the sapphire substrate, a p-type GaN layer contact layer 101, a first electrode made of a mixture of Ti—N compound and Pd—Ga compound in order from the bottom. It was revealed that the layer 102A, the second electrode layer 103 of Pd, the third electrode layer 104 of Mo, and the fourth electrode layer 105 of Au were formed. Note that the Ti—N compound and the Pd—Ga compound were hardly detected in the electrode cross-sectional structure before annealing. From this, it is considered that these two types of compounds of Ti—N and Pd—Ga are formed by a reaction during the annealing process.
[0097]
In the fourth embodiment, a Ti layer is used in place of the Hf layer that was the first electrode layer in the electrode structure shown in the second embodiment. Ti, like Hf, is an element that easily forms a Ti—N compound by reacting with N when reacting with GaN. Due to this property, even if the Hf layer of Example 2 is replaced with a Ti layer in this example, there is no essential change in the effect provided by the present invention.
[0098]
In the graph of FIG. 9 similar to the graph of FIG. 3, the white circle mark and the black circle mark indicate contact resistances in the Au / Mo / Pd / Ti electrode structure before annealing of Example 4 and the Au / Pd electrode structure of the comparative example, respectively. It shows the annealing temperature dependence. As shown in this graph, the Au / Mo / Pd / Ti electrode structure of Example 4 has a smaller contact resistance than the Au / Pd electrode structure of the comparative example in the temperature range of 400 to 650 ° C. Yes. Further, regarding the annealing temperature at which the contact resistance starts to be significantly reduced by the interface reaction and the annealing temperature at which the lowest contact resistance is obtained, the Au / Mo / Pd / of Example 4 is compared with the Au / Pd electrode structure of the comparative example. The temperature is lowered by about 100 ° C. in the Hf electrode structure. This ability to be ohmicized by lower temperature annealing can be a very beneficial advantage in the electrode manufacturing process, as has already been described with respect to Examples 1-3.
[0099]
As a result of examination and consideration similar to Example 1 to Example 3 regarding the thickness of each metal layer of Example 4, the preferred thickness of each layer is as follows: Ti layer is 1 nm to 500 nm, Pd layer is 5 nm to 1 μm, It was found that the Mo layer was 3 nm to 1 μm and the Au layer was 50 nm to 5 μm.
[0100]
As in the case of Example 1 to Example 3, also in Example 4, the concentration of Mg contained in the p-type GaN contact layer is 1.0 × 10 ¹⁸ ~ 1.0 × 10 ²⁰ / Cm ³ However, good ohmic characteristics could be obtained by the Au / Mo / Pd / Ti electrode structure for any Mg-concentrated p-type GaN contact layer. Further, as in the case of Examples 1 to 3, the annealing process for the ohmicization of the electrode structure of Example 4 described above is N ₂ Although it was performed in the atmosphere, the annealing treatment may be performed in an Ar atmosphere or in a vacuum. Even in this case, the optimum annealing temperature is N ₂ Although it changes a little compared with the case of using an atmosphere, it is still lower than the optimum annealing temperature of the Au / Pd electrode structure of the comparative example.
[0101]
Furthermore, in the same manner as in Examples 1 to 3, in Example 4, the interface reaction during annealing is lower than that of the Au / Pd electrode of the comparative example and is less affected by conditions such as temperature, so that it is ensured. Therefore, the problem of peeling due to insufficient adhesion strength at the interface often observed in the electrode of the comparative example does not occur.
(Examples 5 to 14)
In Examples 1 to 4 described so far, the Au layer has been used as the fourth electrode layer. However, even if the fourth electrode layer is changed to the Al layer, the effect of the present invention is affected at all. is not. This is because Example 5 was changed from the Au / Mo / Ni / Hf electrode of Example 1 and Example 6 was changed from the Al / Mo / Ni / Hf electrode of Example 2 and Au / Mo / Pd / Hf electrode of Example 2. As an Al / Mo / Pd / Hf electrode, as an Example 7 modified from the Au / Mo / Ni / Ti electrode in Example 3, and as an Au / Mo / Pd / Ti electrode in Example 4. It was able to confirm each by producing the Al / Mo / Pd / Ti electrode as Example 8 changed from the electrode.
[0102]
Moreover, although the Mo layer is used as the third electrode layer in all of the above-described first to eighth embodiments, even if the third electrode layer is changed to the Ir layer, the third electrode layer depends on the third electrode layer. There is no change in effect. This is because the Al / Ir / Ni / Hf electrode was changed from the Al / Mo / Ni / Hf electrode in Example 5 and the Al / Mo / Pd / Hf electrode in Example 10 was changed as Example 9. As an Al / Ir / Pd / Hf electrode, as an Example 11 modified from the Al / Mo / Ni / Ti electrode in Example 7, and as an Al / Mo / Pd / Ti electrode in Example 8. It was able to be confirmed by fabricating an Al / Ir / Pd / Ti electrode as Example 12 which was changed from the electrode. Similarly, when Au is used as the fourth electrode layer, the Au / Ir / Ni / Hf electrode is changed from the Au / Mo / Ni / Hf electrode of Example 1, and the Au / Ir / Ni / Hf electrode of Example 2 is changed. An Au / Ir / Pd / Hf electrode was manufactured as Example 14 which was changed from the / Mo / Pd / Hf electrode, and it was confirmed that there was no change in the effect of the third electrode layer.
[0103]
In Examples 1 to 14, Hf or Ti was used as the first metal layer (sixth electrode layer) in direct contact with the p-type GaN contact layer. As a result of further investigation, only Hf and Ti were used. In other words, it has been found that the same effect as that obtained when Hf or Ti is used can be obtained by using a single metal such as Zr, V, Nb, Ta, Cr, W, or Sc or an alloy thereof.
[0104]
Furthermore, in Example 1 to Example 14 described above, Ni or Pd was used as the second metal layer (seventh electrode layer) laminated on the first metal layer (sixth electrode layer). It has been found that the same effect as that obtained when Ni or Pd is used can be obtained by using not only these metals but also three kinds of simple metals including Co and alloys thereof.
[0105]
In Examples 1 to 14, Mo or Ir was used as the third metal layer (third electrode layer) stacked on the second metal layer (seventh electrode layer). As a result, it was found that the same effect as that obtained when Mo or Pt is used can be obtained by using not only Mo and Ir but also a single metal such as Ru, Rh, and W or an alloy thereof.
[0106]
Furthermore, in Example 1 to Example 14, the fifth electrode layer may be formed depending on the formation conditions. For example, instead of the first electrode layer and the second electrode layer, the fifth electrode layer containing Hf, Ni, Hf—Ga compound, and Ni—N compound was formed in Example 1. In this case, the same effect as in Example 1 was obtained. The same applies to Examples 2 to 14.
[0107]
Furthermore, in Examples 1 to 14, the EB vapor deposition method is used for depositing each metal layer. However, other methods such as a sputtering method and a CVD method may be used for the metal layer deposition method. Needless to say.
(Examination of related matters)
When the electrode structures of Examples 1 to 14 described above are applied to an AlGaInN semiconductor laser element, the voltage drop in the electrode portion can be suppressed lower than the conventional electrode structure, and the power consumption of the entire semiconductor laser element can be reduced. It was confirmed that it could be reduced. For example, when the Au / Mo / Ni / Hf electrode of Example 1 and the conventional Au / Ni electrode are applied to a semiconductor laser having a stripe width of 5 μm and a resonator length of 500 μm, the electrode portion at the time of energizing 20 mA is used. The voltage drops were about 0.8 V and about 4 V, respectively, and the excellent effect of the present invention could be clearly confirmed. In addition, the contact resistance can be further reduced by using the Pd layer instead of the Ni layer as in the second embodiment, and accordingly, the voltage drop at the electrode portion of the semiconductor laser element can be further reduced. Was confirmed.
[0108]
(Example 15)
The fifteenth embodiment of the present invention will be described below with reference to FIGS. 10 to 12 schematically showing the element cross section. In the present embodiment, the electrode structure described in the first embodiment is applied to an actual laser device structure. This laser element is manufactured by the following method.
[0109]
First, as shown in FIG. 10, a GaN buffer layer 201, an n-type GaN contact layer 202, an n-type AlGaN cladding layer 203, an n-type GaN light guide layer 204, an InGaN layer on a sapphire substrate 200 having a C-plane crystal plane. The multi-quantum well active layer 205, the p-type GaN light guide layer 206, the p-type AlGaN layer 207, and the p-type GaN contact layer 208 are sequentially epitaxially grown by MOCVD to produce a GaN-based semiconductor multilayer structure.
[0110]
Subsequently, as shown in FIG. 11, after a dry etching mask 209 is formed on the GaN-based semiconductor multilayer structure, a portion not covered with the dry etching mask 209 is formed by n-type GaN by a reactive ion etching (RIE) method. The contact layer 202 is dug down to form a mesa structure.
[0111]
Next, after the dry etching mask 209 is completely removed, a stripe pattern made of the insulating film 210 is formed on the mesa as shown in FIG.
[0112]
Next, a p-type electrode 211 made of Au / Mo / Ni / Hf is formed on the mesa, and an n-type electrode 212 made of Al / Ti is formed on the n-type GaN contact layer 202 corresponding to the mesa bottom. Note that the laminated film thickness of each electrode metal is 200 nm for Au, 15 nm for Mo, 5 nm for Ni, 5 nm for Hf for the n-type electrode, and 30 nm for Ti for the n-type electrode. Finally, the entire laser device structure is N ₂ In the atmosphere, annealing is performed at about 450 ° C. to complete the laser element.
[0113]
In the laser element of this example manufactured as described above, the variation in the adhesion strength of the p-type electrode for each laser element is suppressed as compared with the conventional laser element having the p-type electrode made of Au / Ni, and the non-defective product. Improved yield of removal. In addition, the annealing temperature performed after the formation of the p-type electrode is 450 ° C., which is about 50 ° C. lower than the conventional temperature, thereby contributing to improvement in temperature control accuracy of the manufacturing process and simplification of the manufacturing process.
[0114]
By changing the p-type electrode structure applied to this example from the electrode structure of Example 1 to the electrode structure of Example 3, the annealing temperature performed after forming the p-type electrode is lowered to 400 ° C. and about 50 ° C. It is possible to improve the temperature control accuracy of the manufacturing process and simplify the manufacturing process.
[0115]
In addition, since the interface reaction between the p-type electrode and the p-type GaN contact layer 208 occurs uniformly over the entire surface, the contact area in which good ohmic characteristics in the electrode-contact layer can be obtained can be increased. As a result, the p-type electrode The contact resistance is reduced. As a result, the operating voltage was reduced compared to a laser element using a conventional Au / Ni electrode as a p-type electrode.
[0116]
(Example 16)
The sixteenth embodiment of the present invention will be described below with reference to FIGS. 10 to 12 schematically showing the element cross section. Compared with the laser element structure described in Example 15, this example has the same structure except that the electrode structure of Example 2 is applied to the p-type electrode.
[0117]
Similar to Example 15, the GaN-based semiconductor multilayer structure shown in FIG. Subsequently, a mesa structure and a stripe pattern shown in FIG. 11 are formed. Next, as shown in FIG. 12, a p-type electrode 211 made of Au / Mo / Pd / Hf is formed on the top of the mesa, and an n-type electrode 212 made of Al / Ti is formed on the n-type GaN contact layer 212 on the bottom of the mesa. . Note that the laminated film thickness of each electrode metal is 200 nm for Au, 15 nm for Mo, 5 nm for Pd, 5 nm for Hf, and 5 nm for Hf for the n-type electrode 212 for the p-type electrode 211, and 30 nm for Ti. Finally, the entire laser device structure is N ₂ In the atmosphere, annealing is performed at about 550 ° C. to complete the laser element.
[0118]
In the laser element of this example manufactured in this way, as in the laser element shown in Example 3, the variation in the adhesion strength of the p-type electrode for each laser element was suppressed, and the yield of good products was improved. Also, the annealing temperature after the formation of the p-type electrode is lower by about 50 ° C. compared to the case where Hf is not included in the p-type electrode, thereby contributing to the improvement of the temperature control accuracy of the manufacturing process and the simplification of the manufacturing process. .
[0119]
In addition, by changing the p-type electrode structure applied to this example from the electrode structure of Example 2 to the electrode structure of Example 4, the annealing temperature performed after the formation of the p-type electrode is lowered to about 500 ° C. and about 50 ° C. It is possible to improve the temperature control accuracy of the manufacturing process and simplify the manufacturing process.
[0120]
In this embodiment, the voltage drop of the p-type electrode part and the operating voltage of the entire laser element are reduced as compared with the case where the Au / Pd electrode is used as the p-type electrode. Further, by using Pd instead of Ni, the operating voltage of the p-type electrode portion and the operating voltage of the entire laser device could be reduced as compared with the laser device shown in Example 15.
[0121]
(Example 17)
Next, a seventeenth embodiment of the present invention will be described with reference to FIGS. 13 to 14, which schematically show element cross sections. The present embodiment is another example in which the electrode structure described in the first embodiment is applied to an actual laser device structure. This laser element is manufactured by the following method.
[0122]
First, as shown in FIG. 13, an n-type GaN buffer layer 301, an n-type AlGaN cladding layer 302, an n-type GaN light guide layer 303, an InGaN multiple layer on an n-type GaN substrate 300 having a [0001] plane orientation. The quantum well active layer 304, the p-type GaN light guide layer 105, the p-type AlGaN layer 306, and the p-type GaN contact layer 307 are sequentially epitaxially grown by MOCVD to produce a GaN-based semiconductor multilayer structure.
[0123]
Subsequently, as shown in FIG. 14, a stripe pattern made of the insulating film 308 is formed on the upper surface of the p-type GaN contact layer 307. Next, a p-type electrode 309 made of Au / Mo / Ni / Hf is formed on the p-type GaN contact layer 307, and an n-type electrode 310 made of Al / Ti is formed on the back surface of the n-type GaN substrate 300. Note that the laminated film thickness of each electrode metal is 200 nm for Au, 5 nm for Mo, 15 nm for Ni, 5 nm for Hf for the n-type electrode 310 for the p-type electrode 309, and 30 nm for Ti for the n-type electrode 310. Finally, the entire laser device structure is represented by N ₂ In the atmosphere, annealing is performed at about 450 ° C. to complete the laser element.
[0124]
In this example, an n-type GaN substrate was used as a substrate on which a semiconductor layer was epitaxially grown. This improves the crystallinity of the epitaxial layer such as reduction in defect density compared to the laser element using the sapphire substrate described in Example 15 and Example 16, and as a result, the characteristics of the laser element of this example are improved. improves. Even when such a GaN substrate is used, by using the electrode structure of the present invention, an effect similar to that of a laser element on a sapphire substrate is exhibited, and a conventional Au / Ni electrode is used as a p-type electrode. In comparison, it was possible to improve the adhesion strength of the p-type electrode, reduce the voltage drop at the p-type electrode portion, and reduce the operating voltage of the entire device.
[0125]
Further, by changing the p-type electrode structure applied to this example from the electrode structure of Example 1 to the electrode structure of Example 3, the annealing temperature after the formation of the p-type electrode is lowered to about 400 ° C. and about 50 ° C. It is possible to improve the temperature control accuracy of the manufacturing process and simplify the manufacturing process.
[0126]
(Example 18)
Next, an eighteenth embodiment of the present invention will be described with reference to FIGS. 13 to 14, which schematically show element cross sections. This example is the same as Example 17 except that the electrode structure described in Example 2 is applied to the p-type electrode. This laser element is manufactured by the following method.
[0127]
First, the GaN-based semiconductor multilayer structure shown in FIG. Subsequently, as shown in FIG. 14, a stripe pattern made of the insulating film 308 is formed on the upper surface of the p-type GaN contact layer 307. Next, a p-type electrode 309 made of Au / Mo / Pd / Hf is formed on the p-type GaN contact layer 307 and an n-type electrode 310 made of Al / Ti is formed on the back surface of the n-type GaN substrate 300. The laminated thickness of each electrode metal is 200 nm for Au, 5 nm for Mo, 15 nm for Pd, 5 nm for Hf, and 5 nm for Hf for the n-type electrode 310 for the p-type electrode 309 and 150 nm for Ti and 30 nm for Ti. Finally, the entire laser device structure is represented by N ₂ In the atmosphere, annealing is performed at about 550 ° C. to complete the laser element.
[0128]
Also in this example, an n-type GaN substrate was used as a substrate for epitaxially growing the semiconductor layer. Further, in this embodiment, the voltage drop of the p-type electrode portion and the operating voltage of the entire laser element are reduced as compared with the case where the Au / Pd electrode is used as the p-type electrode. Further, by using Pd instead of Ni, the operating voltage of the p-type electrode portion and the operating voltage of the entire laser device could be reduced as compared with the laser device shown in Example 17.
[0129]
Further, by changing the p-type electrode structure applied to the present embodiment from the electrode structure of the second embodiment to the electrode structure of the fourth embodiment, the annealing temperature after the formation of the p-type electrode is lowered to about 500 ° C. and about 50 ° C. It is possible to improve the temperature control accuracy of the manufacturing process and simplify the manufacturing process.
[0130]
In Example 17 and Example 18, a GaN substrate having a {0001} plane orientation was used as the substrate, but the substrate is not limited to this, and in addition to the {0001} plane, {0-100 } Plane, {11-20} plane, {1-101} plane, and {01-12} plane, laser elements having the same characteristics as those of Examples 17 and 18 can be produced. In the present invention, an InGaN multiple quantum well structure is used as the active layer. However, for example, a structure in which As or P is contained in a GaN-based semiconductor may be used as the active layer. In the laser element, the current injection portion of the p-type GaN contact layer uses an electrode stripe structure, but a ridge structure or other structure may be used. Further, the present invention is not limited to the laser element, and the present invention can also be applied to a light emitting element (LED).
[0131]
【The invention's effect】
As described above, according to the electrode structure of the present invention, it is possible to realize an electrode structure having a low resistance and good ohmic characteristics by suppressing a factor of increasing the resistance of the electrode structure with respect to the p-type GaN contact layer. The adhesion strength between the contact layer and the electrode structure is also improved, and the production yield of semiconductor devices can be greatly improved. Further, as a secondary effect of the present invention, the annealing temperature required for ohmic electrode structure can be lowered as compared with the conventional one, which greatly contributes to simplification and easy control in the semiconductor device manufacturing process. can do
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a state immediately after a plurality of metal layers are deposited on a group III nitride semiconductor contact layer in the electrode structure of the present invention.
FIG. 2 is a schematic cross-sectional view showing a state after an ohmic annealing treatment in the electrode structure of the present invention.
3 is a graph showing a relationship between an alloy temperature and contact resistance as ohmic annealing of an electrode structure according to Example 1. FIG.
4 is a graph showing a preferable thickness range of an Hf layer and an Ni layer in the electrode structure of Example 1. FIG.
FIG. 5 is a graph showing a relationship between ohmic alloy temperature and contact resistance in an Au / Mo / Hf / Ni electrode structure of a comparative example and a conventional Au / Ni electrode structure.
6 is a graph showing the relationship between ohmic alloy temperature and contact resistance in a Au / Mo / (HfNi alloy) electrode structure of a comparative example in comparison with Example 1. FIG.
7 is a graph showing the relationship between ohmic alloy temperature and contact resistance in the electrode structure according to Example 2. FIG.
FIG. 8 is a graph showing the relationship between ohmic alloy temperature and contact resistance in the electrode structure according to Example 2;
9 is a graph showing the relationship between the ohmic alloy temperature and the contact resistance in the electrode structure according to Example 2. FIG.
FIG. 10 is a diagram showing a manufacturing process of a laser device having an electrode structure of the present invention formed on a sapphire substrate.
FIG. 11 is a diagram showing a manufacturing process of a laser device having the electrode structure of the present invention formed on a sapphire substrate.
FIG. 12 is a diagram showing a manufacturing process of a laser device having the electrode structure of the present invention formed on a sapphire substrate.
FIG. 13 is a diagram showing a manufacturing process of a laser device having an electrode structure of the present invention formed on a GaN substrate.
FIG. 14 is a diagram showing a manufacturing process of a laser device having an electrode structure of the present invention formed on a GaN substrate.
FIG. 15 is a schematic cross-sectional view showing a conventional electrode structure.
[Explanation of symbols]
101 ... Contact layer
102 ... Sixth electrode layer
102A ... first electrode layer
103 ... 2nd electrode layer or 7th electrode layer
104 ... Third electrode layer
105 ... Fourth electrode layer
200: Sapphire substrate
201: GaN buffer layer
202 ... n-type GaN contact layer
203 ... n-type AlGaN cladding layer
204... N-type GaN light guide layer
205 ... InGaN multiple quantum well active layer
206 ... p-type GaN optical guide layer
207 ... p-type AlGaN layer
208 ... p-type GaN contact layer
209 ... Dry etching mask
210: Insulating film
211 ... p-type electrode
212 ... n-type electrode
300 ... n-type GaN substrate
301 ... GaN buffer layer
302 ... n-type AlGaN cladding layer
303 ... n-type GaN optical guide layer
304 ... InGaN multiple quantum well active layer
305 ... p-type GaN optical guide layer
306 ... p-type AlGaN layer
307 ... p-type GaN contact layer
308 ... Insulating film
309 ... p-type electrode
310 ... n-type electrode

Claims (19)

an electrode structure on a p-type group III nitride semiconductor layer, including a structure including a first electrode layer, a second electrode layer, and a third electrode layer sequentially from the side in contact with the semiconductor layer
The first electrode layer includes at least one metal element selected from the first metal group consisting of Ti, Hf, Zr, V, Nb, Ta, Cr, W, and Sc;
The second electrode layer includes at least one metal element selected from the second metal group consisting of Ni, Pd, and Co;
The electrode structure characterized in that the third electrode layer contains at least one metal element selected from the third metal group consisting of Mo, Ru, Rh, W and Ir. 2. The electrode structure according to claim 1, wherein the first electrode layer is a mixed layer and includes a compound of N and at least one metal element selected from the first metal group. 3. The electrode structure according to claim 1, wherein the first electrode layer is a mixed layer and includes a compound of Ga and at least one kind of metal element selected from the second metal group. 2. The electrode structure according to claim 1, wherein the thickness of the first electrode layer is in a range of 1 to 1000 nm. 2. The electrode structure according to claim 1, wherein a thickness of the second electrode layer is in a range of 1 to 1000 nm. an electrode structure on a p-type group III nitride semiconductor layer, including a structure including a fifth electrode layer and a third electrode layer in order from the side in contact with the semiconductor layer;
The fifth electrode layer includes at least one metal element selected from the first metal group and at least one metal element selected from the second metal group;
The electrode structure, wherein the third electrode layer contains at least one metal element selected from the third metal group. The electrode structure according to claim 6, wherein the fifth electrode layer is a mixed layer and includes a compound of N and at least one metal element selected from the first metal group. The said 5th electrode layer is a mixed layer, It contains the compound of at least 1 type of metal element selected from the said 2nd metal group, and Ga, The Claim 6 or 7 characterized by the above-mentioned. Electrode structure. The electrode structure according to claim 6, wherein the thickness of the fifth electrode layer is in a range of 1 to 1000 nm. The thickness of the said 3rd electrode layer exists in the range of 3-500 nm, The electrode structure in any one of Claim 1 or 6 characterized by the above-mentioned. The electrode structure according to claim 1, wherein a fourth electrode layer containing either Au or Al is laminated on the third electrode layer. The electrode structure according to claim 11, wherein the thickness of the fourth electrode layer is 50 nm or more. A method for forming an electrode structure on a p-type group III nitride semiconductor layer, comprising:
Depositing on the semiconductor layer a sixth electrode layer made of at least one metal element selected from the first metal group consisting of Ti, Hf, Zr, V, Nb, Ta, Cr, W and Sc;
Depositing a seventh electrode layer comprising at least one metal element selected from the second metal group comprising Ni, Pd, and Co on the sixth electrode layer;
An electrode comprising a step of depositing on the seventh electrode layer a third electrode layer made of at least one metal element selected from the third metal group consisting of Mo, Ru, Rh, W and Ir. Structure formation method. 14. The method for forming an electrode structure according to claim 13, wherein the thickness of the sixth electrode layer to be deposited is in the range of 1 to 500 nm. 14. The method of forming an electrode structure according to claim 13, wherein the thickness of the seventh electrode layer to be deposited is in the range of 5 nm to 1000 nm. 14. The method for forming an electrode structure according to claim 13, wherein the thickness of the third electrode layer to be deposited is in the range of 3 to 500 nm. The method for forming an electrode structure according to claim 13, further comprising a step of depositing a fourth electrode layer containing either Au or Al on the third electrode layer. The method of forming an electrode structure according to claim 17, wherein the thickness of the fourth electrode layer is 50 nm or more. After the sixth electrode layer, the seventh electrode layer, the third electrode layer, and the fourth electrode layer are deposited, under a temperature in the range of 300 to 700 ° C. in an N ₂ atmosphere, an Ar atmosphere, or a vacuum. The method for forming an electrode structure according to claim 17, further comprising a step of heat-treating the electrode structure.

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