JP5453892B2 - Nitride semiconductor device - Google Patents

Description

  The present invention relates to a group III nitride semiconductor device.

  An n-channel nitride semiconductor device is being developed. The n-channel nitride semiconductor device includes a p-type nitride semiconductor layer as a current regulating layer. The p-type nitride semiconductor layer usually contains Mg (magnesium) as a p-type impurity. In this nitride semiconductor device, Mg contained in the p-type nitride semiconductor layer may diffuse to other regions adjacent to the p-type nitride semiconductor layer. When Mg diffuses to other regions, the device characteristics of the nitride semiconductor device deteriorate.

  Patent Document 1 discloses a technique for preventing Mg from diffusing from a p-type nitride semiconductor layer in an n-channel nitride semiconductor device. In this technique, a single crystal AlN (aluminum nitride) film is grown on the surface of a p-type nitride semiconductor layer containing Mg by using an MOCVD method (metal organic chemical film forming method). Mg is difficult to pass through the AlN film. For this reason, the AlN film becomes an Mg diffusion preventing film, and Mg is prevented from diffusing to an adjacent region.

JP 2008-21756 A

  In the technique of Patent Document 1, since AlN is stacked on a p-type nitride semiconductor layer, an n-type nitride semiconductor layer is formed on AlN. For this reason, AlN and the n-type nitride semiconductor layer are heterojunctioned, and a two-dimensional electron gas layer (hereinafter referred to as 2DEG) is formed at the junction, thereby degrading the characteristics of the semiconductor device. For example, HEMT (High Electron Mobility Transistor) is known as a group III nitride semiconductor device. In HEMT, 2DEG is formed at the heterojunction interface by heterojunction of two nitride semiconductor layers having different band gaps. By running the electrons using the 2DEG, the mobility of the electrons can be increased and a high-speed operation can be realized.

  In the HEMT, an n-type first nitride semiconductor layer and a second nitride semiconductor layer heterojunctioned on the first nitride semiconductor layer are formed on the p-type nitride semiconductor layer. In some cases, GaN (gallium nitride) and AlGaN (aluminum gallium nitride) are used as the first nitride semiconductor layer. When the technique disclosed in Patent Document 1 is used for this HEMT, AlN, GaN, and AlGaN are stacked on the p-type nitride semiconductor layer. The difference in band gap between AlN and GaN is large, and not only between GaN and AlGaN, but also AlN and GaN heterojunction. For this reason, 2DEG may also be formed between AlN and GaN. In this case, even if the nitride semiconductor device is turned off, 2DEG formed on both the front and back surfaces of GaN does not disappear completely, and a leak current may flow in the 2DEG. For this reason, good normally-off characteristics cannot be ensured.

  The present invention has been created in view of the above problems. The present invention provides a group III nitride semiconductor device capable of preventing diffusion of magnesium from a p-type nitride semiconductor layer and ensuring good semiconductor device characteristics.

  The present invention relates to an n-channel nitride semiconductor device. The nitride semiconductor device includes a p-type first nitride semiconductor layer containing magnesium and an n-type or i-type second nitride semiconductor layer formed on the surface of the first nitride semiconductor layer. Yes. Aluminum is contained in a range facing at least the surface of the first nitride semiconductor layer. Aluminum is contained, for example, by an ion implantation method or the like. Aluminum may be contained at least in a range facing at least the surface of the first nitride semiconductor layer, and may reach the back surface of the first nitride semiconductor layer.

  In the nitride semiconductor device described above, the uniformity of the crystal structure of the region containing aluminum in the first nitride semiconductor layer (hereinafter referred to as the Al-containing region) is reduced. For this reason, the lattice constant of the Al-containing region is small, and it is difficult for Mg to pass through. As a result, the Al-containing region functions as an Mg diffusion preventing film. Furthermore, since the electrons are affected by Al scattering in the vicinity of the Al-containing region, the electron mobility is lowered. For this reason, 2DEG hardly occurs between the Al-containing region and the second nitride semiconductor layer. In the nitride semiconductor device described above, Mg diffusion from the p-type nitride semiconductor layer can be prevented and good semiconductor device characteristics can be ensured.

  In the nitride semiconductor device of the present invention, the impurity concentration of aluminum contained in the range facing the surface of the nitride semiconductor layer is higher than the impurity concentration of magnesium contained in the range facing the surface of the nitride semiconductor layer. Is preferred. In this case, the lattice constant of the Al-containing region is further reduced by increasing the impurity concentration of aluminum. This makes it more difficult for Mg to pass through the Al-containing region. For this reason, the effect of preventing diffusion of Mg can be enhanced.

  According to the nitride semiconductor device of the present invention, diffusion of magnesium from the p-type nitride semiconductor layer can be prevented. Furthermore, good semiconductor device characteristics can be ensured.

1 is a sectional view of a group III nitride semiconductor device 100 according to Example 1. FIG. 2 shows a step (1) of a method for manufacturing the group III nitride semiconductor device 100. 2 shows a step (2) of a method for manufacturing the group III nitride semiconductor device 100. 3 shows a step (3) of a method for manufacturing the group III nitride semiconductor device 100. FIG. Step (4) of the method for manufacturing the group III nitride semiconductor device 100 will be described. Step (5) of the method for manufacturing the group III nitride semiconductor device 100 will be described. Step (6) of the method for manufacturing the group III nitride semiconductor device 100 will be described. Step (7) of the method for manufacturing the group III nitride semiconductor device 100 will be described. Sectional drawing of the group III nitride semiconductor device 200 which concerns on Example 2 is shown.

Hereinafter, embodiments of the present invention will be described in detail.
(Mode 1) A fourth nitride semiconductor layer is stacked on the second nitride semiconductor layer. The second nitride semiconductor layer is n-type GaN. The fourth nitride semiconductor layer has a general formula of Al _X Ga _Y In _1-XY N (where 0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ 1−X−Y ≦ 1). According to this embodiment, a heterojunction interface can be formed between the second nitride semiconductor layer and the fourth nitride semiconductor layer.
(Mode 2) An Al-containing region is formed in a part of the range facing the surface of the first nitride semiconductor layer. According to this embodiment, it is possible to prevent Mg from diffusing into the second nitride semiconductor layer from the end portion in the range facing the surface of the first nitride semiconductor layer.
(Mode 3) The depth of the Al-containing region does not reach the back surface of the first nitride semiconductor layer. According to this embodiment, it is possible to prevent the breakdown voltage of the group III nitride semiconductor device from decreasing.

FIG. 1 is a sectional view of a nitride semiconductor device 100 according to the first embodiment. The semiconductor device 100 is an n-channel vertical semiconductor device having a HEMT structure. That is, the drain electrode 22 is formed on the back surface, and the pair of source electrodes 10a and 10b are formed on the front surface, and current flows in the vertical direction. The nitride semiconductor device 100 includes a nitride semiconductor substrate 2. The nitride semiconductor substrate 2 is made of n ⁺ -type GaN. A third nitride semiconductor layer 4 is stacked on the surface of the nitride semiconductor substrate 2. The third nitride semiconductor layer 4 is made of n ⁻ type GaN. A pair of first nitride semiconductor layers 6 a and 6 b are provided on the surface of the third nitride semiconductor layer 4. The first nitride semiconductor layers 6a and 6b are made of p ⁺ -type GaN containing Mg. Al-containing regions 8a and 8b are formed in a part of the range facing the surface of the third nitride semiconductor layer 4 and the range facing the surface of the first nitride semiconductor layers 6a and 6b. The Al-containing regions 8a and 8b contain Al. A second nitride semiconductor layer 14 is stacked on the surface of the third nitride semiconductor layer 4 and the surfaces of the first nitride semiconductor layers 6a and 6b. The second nitride semiconductor layer 14 is made of n ⁻ type GaN. Further, the impurity concentrations of the third nitride semiconductor layer 4 and the second nitride semiconductor layer 14 are equal. A fourth nitride semiconductor layer 16 is stacked on the surface of the second nitride semiconductor layer 14. The fourth nitride semiconductor layer 16 is made of n ⁻ type AlGaN. The fourth nitride semiconductor layer 16 has a larger band gap than the second nitride semiconductor layer 14. The fourth nitride semiconductor layer 16 is heterojunction with the second nitride semiconductor layer 14.

A part of each surface of the first nitride semiconductor layers 6a and 6b is provided with a pair of n ⁺ -type source regions 12a and 12b. Each source region 12a, 12b is formed across the second nitride semiconductor layer 14 and the fourth nitride semiconductor layer 16, and the heterojunction interface passes through each source region 12a, 12b. A pair of source electrodes 10a, 10b is in contact with part of the surface of the first nitride semiconductor layers 6a, 6b and in contact with the source regions 12a, 12b at the ends of the first nitride semiconductor layers 6a, 6b. Is provided. The source electrodes 10a and 10b are electrically connected to the second nitride semiconductor layer 14 and the fourth nitride semiconductor layer 16 through the source regions 12a and 12b. The surface of the fourth nitride semiconductor layer 16 is covered with a gate insulating film 18. A gate electrode 20 is provided in a range between the pair of source electrodes 10 a and 10 b on the surface of the gate insulating film 18.

  Next, the operation of the nitride semiconductor device 100 will be described. The nitride semiconductor device 100 is used by applying a voltage between the source electrodes 10 a and 10 b and the drain electrode 22. If no positive voltage is applied to the gate electrode 20, 2DEG is not formed at the heterojunction interface between the second nitride semiconductor layer 14 and the fourth nitride semiconductor layer 16. Further, 2DEG is not formed between the Al-containing regions 8a and 8b and the first nitride semiconductor layers 6a and 6b. Therefore, nitride semiconductor device 100 can ensure good semiconductor device characteristics. When a positive voltage is applied to the gate electrode 16, 2DEG is formed at the heterojunction interface between the second nitride semiconductor layer 14 and the fourth nitride semiconductor layer 16 located between the pair of source regions 14a and 14b. . As a result, the nitride semiconductor device 100 is turned on. The nitride semiconductor device 100 moves electrons using 2DEG. Electron mobility is high and high-speed operation can be realized.

Next, a method for manufacturing the nitride semiconductor device 100 will be described. First, as shown in FIG. 2, an n ⁻ type third nitride semiconductor layer 4 made of GaN is crystallized on the surface of an n ⁺ type nitride semiconductor substrate 2 made of GaN using MOCVD. grow up. The impurity concentration of the nitride semiconductor substrate 2 is 3 × 10 ¹⁸ cm ⁻³ , the impurity to be introduced is Si, and the thickness is 200 μm. The impurity introduced into the third nitride semiconductor layer 4 is Si, and the growing thickness is 6 μm. Next, as shown in FIG. 3, a first silicon oxide film 24 is formed in a range where the first nitride semiconductor layers 6 a and 6 b are not formed on the surface of the third nitride semiconductor layer 4. Next, as shown in FIG. 4, magnesium ions 26 are implanted from the surface using the first silicon oxide film 24 as a mask. The impurity concentration of magnesium ions to be implanted is 1 × 10 ¹⁹ cm ⁻³ and the implantation depth is 0.5 μm. As a result, the p ⁺ type first nitride semiconductor layers 6 a and 6 b are formed in a range that is not covered with the first silicon oxide film 24 in a range facing the surface of the third nitride semiconductor layer 4.

Next, after removing the first silicon oxide film 24, as shown in FIG. 5, the second silicon oxide film 30 is formed in a range where the Al-containing regions 8a and 8b are not formed on the surface of the third nitride semiconductor layer 4. Form. Next, aluminum ions are implanted from the surface using the second silicon oxide film 30 as a mask. The impurity concentration of the implanted aluminum ions is 1 × 10 ²⁰ cm ⁻³ . At this time, the implantation conditions are adjusted so that the implantation depth of the aluminum ions does not reach the back surfaces of the first nitride semiconductor layers 6a and 6b. As a result, Al-containing regions 8a and 8b are formed. Next, annealing is performed at 1100 ° C. in a mixed gas atmosphere of N ₂ and NH ₃ . Next, as shown in FIG. 6, an n ⁻ -type second nitride semiconductor layer 14 is formed to a thickness of 100 nm on the surfaces of the third nitride semiconductor layer 4 and the first nitride semiconductor layers 6a and 6b by MOCVD. To do. The material and impurity concentration of the second nitride semiconductor layer 14 are equal to those of the third nitride semiconductor layer 4. Next, as shown in FIG. 7, an n ⁻ -type fourth nitride semiconductor layer 16 made of Al _0.3 Ga _0.7 N as a material is formed on the surface of the second nitride semiconductor layer 14 using MOCVD. Form. The impurity concentration of the fourth nitride semiconductor layer 16 is 1 × 10 ¹⁶ cm ⁻³ , and the growing thickness is 25 nm.

Next, a third silicon oxide film (not shown) is formed on the surface of the fourth nitride semiconductor layer 16. Next, a part of the third silicon oxide film is removed to expose the fourth nitride semiconductor layer 16 in a range where the source regions 12a and 12b are to be formed. Next, N and Si are successively implanted into the exposed surface of the fourth nitride semiconductor layer 16 using an ion implantation apparatus. The implantation amount of N is 1 × 10 ¹⁶ cm ⁻³ , and the acceleration voltage at the time of implantation is 35 keV. The amount of Si implanted is 1 × 10 ¹⁵ cm ⁻² , and the acceleration voltage at the time of implantation is 65 keV. Next, after removing the third silicon oxide film, as shown in FIG. 8, a fourth silicon oxide film 31 is formed on the entire surface and annealed. The annealing temperature is 1300 ° C. and the annealing time is 5 minutes. As a result, n ⁺ -type source regions 12a and 12b are formed in the region where N and Si are implanted.

  Next, the fourth silicon oxide film 31 covering the surface of the fourth nitride semiconductor layer 16 located outside the source regions 12a and 12b is removed. Next, dry etching is performed until the first nitride semiconductor layers 6 a and 6 b are reached from the exposed surface of the fourth nitride semiconductor layer 16 through the second nitride semiconductor layer 14. Next, all the remaining fourth silicon oxide film 31 is removed. Next, 50 nm of HTO (High-Temperature-Oxide) is formed as the gate insulating film 18 on the entire surface using the CVD method. Next, the gate insulating film 18 formed on the surfaces of the first nitride semiconductor layers 6a and 6b is removed by etching. Next, Ni is deposited on the exposed surfaces of the first nitride semiconductor layers 6a and 6b. Next, a part of the gate insulating film 18 formed on the surface of the source regions 12a and 12b is removed by etching. Next, Ti / Al is vapor-deposited with a thickness of 10 nm / 100 nm on the surface of the exposed source regions 12a and 12b and the surface of Ni formed on the first nitride semiconductor layers 6a and 6b, respectively, and a pair of sources Electrodes 12a and 12b are formed. Similarly, Ti / Al is vapor-deposited with a thickness of 10 nm / 100 nm on the back surface of the nitride semiconductor substrate 2 to form the drain electrode 22. Next, the gate electrode 20 is formed using Ni as a material in a range of the surface of the gate insulating film 18 facing the fourth nitride semiconductor layer 16 located between the pair of source regions 12a and 12b. Thereby, the nitride semiconductor device 100 is completed.

  In the nitride semiconductor device 100, Mg may diffuse into the second nitride semiconductor layer 14 from an end portion in a range facing the surfaces of the first nitride semiconductor layers 6a and 6b. In the nitride semiconductor device 100, since the Al-containing regions 8a and 8b are also formed in part of the range facing the surface of the third nitride semiconductor layer 4, Mg is the surface of the first nitride semiconductor layers 6a and 6b. Diffusion to the second nitride semiconductor layer 14 is prevented. The Al-containing regions 8 a and 8 b are formed only in a part of the range facing the surface of the third nitride semiconductor layer 4, so that there is a gap between the third nitride semiconductor layer 4 and the second nitride semiconductor layer 14. A current path flowing in the vertical direction can be secured. Therefore, nitride semiconductor device 100 can be turned on.

  FIG. 9 is a cross-sectional view of the nitride semiconductor device 200 according to the second embodiment. In FIG. 9, the members obtained by adding 30 to the reference numerals in FIG. 1 are the same as the members described in FIG. In the nitride semiconductor device 200, the Al-containing regions 38a and 38b reach the back surfaces of the first nitride semiconductor layers 36a and 36b. This structure can be realized by adjusting the implantation conditions when implanting magnesium ions. In the nitride semiconductor device 200, Al-containing regions 38a and 38b are also provided in the range facing the side surfaces of the first nitride semiconductor layers 36a and 36b. For this reason, Mg is prevented from diffusing from the end of the range facing the surfaces of the first nitride semiconductor layers 36a and 36b. Mg diffuses from the first nitride semiconductor layers 36a, 36b to the second nitride semiconductor layer 44 without forming the impurity-containing regions 38a, 38b in a part of the range facing the surface of the third nitride semiconductor layer 34. This can be prevented.

  In the nitride semiconductor devices of Examples 1 and 2, it is preferable that the depth of the Al-containing region does not reach the back surface of the first nitride semiconductor layer. If the Al-containing region reaches the back surface of the first nitride semiconductor layer, the breakdown voltage of the nitride semiconductor device may be reduced. By forming the Al-containing region so as not to reach the back surface of the first nitride semiconductor layer, it is possible to prevent the breakdown voltage of the nitride semiconductor device from being lowered.

  In the first and second embodiments, the vertical nitride semiconductor device is described. However, a horizontal nitride semiconductor device may be used. Even in a lateral nitride semiconductor device, by providing an Al-containing region in a range facing the surface of the p-type nitride semiconductor layer, Mg diffusion can be prevented and good semiconductor device characteristics can be ensured. .

  In the first and second embodiments, the HEMT is described, but another nitride semiconductor device such as a semiconductor laser may be used. Even in this case, by providing the Al-containing region in the range facing the surface of the p-type nitride semiconductor layer, Mg diffusion can be prevented and good semiconductor device characteristics can be ensured.

As mentioned above, although the Example of this invention was described in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

2, 32: Nitride semiconductor substrate 4, 34: Third nitride semiconductor layers 6a, 6b, 36a, 36b: First nitride semiconductor layers 8a, 8b, 38a, 38b: Al-containing regions 10a, 10b, 40a, 40b : Source electrodes 12a, 12b, 42a, 42b: Source regions 14, 44: Second nitride semiconductor layer 16, 46: Fourth nitride semiconductor layer 18, 48: Gate insulating film 20, 50: Gate electrodes 22, 52: Drain electrodes 100 and 200: Nitride semiconductor device

Claims (3)

N-channel nitridation comprising a p-type first nitride semiconductor layer containing magnesium and an n-type or i-type second nitride semiconductor layer formed on the surface of the first nitride semiconductor layer A semiconductor device,
Aluminum is implanted in a range facing at least the surface of the first nitride semiconductor layer ,
A nitride semiconductor device, wherein the aluminum implantation depth does not reach the back surface of the first nitride semiconductor layer .   The impurity concentration of aluminum contained in the range facing the surface of the first nitride semiconductor layer is higher than the impurity concentration of magnesium contained in the range facing the surface of the first nitride semiconductor layer. The nitride semiconductor device according to claim 1. A method for manufacturing an n-channel nitride semiconductor device,
Forming an n-type or i-type second nitride semiconductor layer on the surface of the p-type first nitride semiconductor layer containing magnesium;
  Injecting aluminum so that the aluminum implantation depth does not reach the back surface of the first nitride semiconductor layer in a range facing at least the surface of the first nitride semiconductor layer;
  A method for manufacturing a nitride semiconductor device, comprising:

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