JP2013128009A - Nitride semiconductor device manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a nitride semiconductor device including a p-type GaN-based nitride semiconductor layer having low resistance in a bulk region and low resistance in a surface.SOLUTION: A nitride semiconductor device manufacturing method comprises: (a) a step of annealing a semiconductor substrate having a p-type GaN-based nitride semiconductor layer doped with a p-type impurity in an oxygen-containing atmosphere to activate the p-type impurity; and (b) a step of irradiating a surface of the p-type GaN-based nitride semiconductor layer with ultraviolet in an atmosphere not containing oxygen to increase a surface carrier concentration.

Description

  Embodiments described herein relate generally to a method for manufacturing a nitride semiconductor device.

  A GaN-based nitride semiconductor has a wide band gap and has characteristics of emitting ultraviolet light and blue light. The band gap can be adjusted by adding Al or In as a group III element. AlGaInN is called a GaN-based nitride semiconductor or nitride semiconductor.

  For example, an n-type layer, a light-emitting layer, and a p-type nitride semiconductor layer are grown on a sapphire substrate. For example, the p-type layer and a part of the light-emitting layer are etched to expose the n-type layer. By forming an electrode on the surface of the n-type layer, a GaN-based nitride semiconductor light emitting device can be produced.

  After growing a nitride semiconductor layer on the sapphire substrate, an electrode is formed on the surface of the p-type layer, and a support substrate having good thermal conductivity such as Si is bonded thereon, and then an excimer laser such as KrF is applied from the sapphire substrate side. Is also performed to remove the sapphire substrate. The Si support substrate is bonded to the p-side electrode by eutectic, for example.

  Nitride semiconductors have the property of becoming n-type without being doped with impurities. Si is often used as an n-type impurity. Mg, Zn and the like are well known as p-type impurities in nitride semiconductors. However, a p-type impurity such as Mg has a low degree of activation and a high resistance state as it is doped.

  In order to activate p-type impurities, a method of irradiating an electron beam is known (for example, Patent Document 1). However, the electron beam needs to be scanned on the crystal surface and is effective only in the vicinity of the surface.

Various methods of annealing have been proposed for activating p-type impurities. For example, Japanese Patent Laid-Open No. 05-183189 discloses that the resistivity can be reduced by annealing a GaN layer doped with p-type impurity Mg in a nitrogen atmosphere at a temperature of 400 ° C. or higher. Preferably, in order to suppress the GaN of N escapes, or pressurize the N _2, to form a cap layer, in order to achieve low resistance, annealing temperature to be 700 ° C. or higher, it is described.

  Japanese Patent Laid-Open No. 2002-57161 discloses that annealing a GaN layer to which Mg is added at 200 ° C. to 400 ° C. for 100 minutes or more in the air atmosphere activates Mg and can lower the electrical resistivity. To do. It is described that the same tendency was observed even when the atmosphere was changed to an oxygen atmosphere, an oxygen-hydrogen atmosphere, an oxygen-water vapor atmosphere, an oxygen-hydrogen-water vapor atmosphere, an inert gas atmosphere, or the like.

There has also been a proposal of activating p-type impurities (Mg) in GaN by irradiating ultraviolet rays together with annealing (for example, Patent Documents 4 to 7). Japanese Patent Application Laid-Open No. 07-97300 states that the carrier concentration is quadrupled by heating the Mg-doped GaN to 650 ° C. by resistance heating in an N ₂ atmosphere and irradiating ultraviolet rays having a wavelength of 200 nm to 350 nm from the Hg lamp. Describe. Japanese Patent Application Laid-Open No. 11-126758 discloses that Mg-doped GaN is heated to 300 ° C. to 1000 ° C. in an N ₂ atmosphere and irradiated with ultraviolet rays having energy higher than the band gap from an Hg—Xe lamp. Japanese Patent Laid-Open No. 11-238692 discloses that Mg-doped GaN is heated to 200 ° C. or higher, preferably 400 ° C. or higher, and irradiated with ultraviolet rays having a band gap energy or higher in an atmosphere not containing hydrogen. Japanese Patent Application Laid-Open No. 2000-31084 discloses that heat treatment is performed in an N ₂ atmosphere or air, and ultraviolet rays having a band gap energy or more are irradiated. It is disclosed that resistance type linear characteristics can be obtained in the N ₂ atmosphere, but linear characteristics cannot be obtained in the atmosphere.

Japanese Patent Laid-Open No. 03-218625 Japanese Patent Laid-Open No. 05-183189 JP 2002-57161 A Japanese Patent Application Laid-Open No. 07-97300 JP 11-126758 A JP-A-11-238692 JP 2000-31084 A

  An object of the embodiment is to provide a method of manufacturing a nitride semiconductor device including a p-type GaN-based nitride semiconductor layer having a low bulk region resistance and a low surface resistance.

  According to one mode of the embodiment, (a) activating a p-type impurity by annealing a semiconductor substrate having a p-type GaN-based nitride semiconductor layer doped with a p-type impurity in an atmosphere containing oxygen; (B) irradiating the surface of the p-type GaN-based nitride semiconductor layer with ultraviolet light in an oxygen-free atmosphere to increase the surface carrier concentration, and the step (b) includes the step (a) A method of manufacturing a nitride semiconductor device that is performed later and recovers the influence of the step (a) is provided.

1A, 1Ba, and 1Bb are cross-sectional views showing a preliminary experiment process, and FIGS. 1Ca and 1Cb are graphs showing the carrier concentration of the p-type layer of the obtained GaN-based nitride semiconductor as a function of depth. When, 2A, 2B, and 2C are cross-sectional views showing the process of the experiment, FIG. 2D is a graph showing the carrier concentration of the p-type layer obtained as a result of annealing in the atmosphere, and 2Ea, 2Eb, and 2Ec are further irradiated with ultraviolet rays. 5 is a graph showing the carrier concentration of the p-type layer obtained as a function of depth. When, 3A to 3F are cross-sectional views illustrating main processes of a method for manufacturing a semiconductor light emitting device including a p-type GaN-based nitride semiconductor layer according to an embodiment. 4A and 4B are cross-sectional views showing an embodiment of a laser including a p-type GaN-based nitride semiconductor layer.

  Japanese Patent Laid-Open No. 05-183189 discloses that in order to suppress the desorption of N from GaN and realize a low resistance p-type region, GaN doped with a p-type impurity is heated at 700 ° C. or higher in a pressurized nitrogen atmosphere. It is taught that it is preferable to anneal. Japanese Patent Laid-Open No. 2002-57161 teaches that the resistivity can be reduced by annealing GaN doped with p-type impurities at 200 ° C. to 400 ° C. for 100 minutes or more in the air atmosphere. It is taught that the same tendency can be obtained even if the active gas is changed. These teachings teach that the atmosphere during annealing is preferably a nitrogen atmosphere or that the atmosphere during annealing does not affect the results. The present inventors conducted a preliminary experiment in order to investigate the influence of the atmosphere during annealing.

  1A to 1Cb are a cross-sectional view for explaining a preliminary experiment and a graph showing the obtained results.

FIG. 1A is a cross-sectional view showing the configuration of a sample that was created. A base layer 52 such as a non-doped GaN layer is grown on the sapphire substrate 51 by metal organic chemical vapor deposition (MOCVD), and a p-type GaN layer 53 doped with Mg is doped thereon, and Mg is doped at a high concentration. A sample 50 on which a p ⁺ -type GaN layer 54 was grown was prepared. When the p ⁺ -type GaN layer 54 is grown thickly, the crystallinity is lowered. Therefore, the p ⁺ -type GaN layer 54 is grown thinly on the surface of the p-type GaN layer 53. The p-type GaN layer 53 and the p ⁺ -type GaN layer 54 may be collectively referred to as a p-type layer. The as-grown p-type region is in a high resistance state. A sapphire substrate on which a GaN-based nitride semiconductor layer is grown may be referred to as a semiconductor substrate.

  FIG. 1Ba shows an annealing process in a nitrogen atmosphere. Sample 50 was placed in an annealing apparatus, and annealing was performed at 700 ° C. for 15 minutes in a nitrogen atmosphere.

  FIG. 1Bb shows an annealing process in an air atmosphere. Sample 50 was placed in an annealing apparatus, and annealing was performed at 700 ° C. for 15 minutes as an air atmosphere.

  The liquid was brought into contact with each sample, and the carrier concentration was calculated from the CV measurement. The distribution in the depth direction of the carrier concentration was measured by measuring while cutting the crystal.

FIG. 1Ca is a graph showing the carrier concentration of a sample annealed in a nitrogen atmosphere as a function of depth. FIG. 1Cb is a graph showing the carrier concentration of a sample annealed in air as a function of depth. A region having a high carrier concentration on the surface will correspond to the p ⁺ -type GaN layer 54, and a region having a substantially constant carrier concentration inside will correspond to the p-type GaN layer 53.

  Comparing FIGS. 1Ca and 1Cb, it is clear that the carrier concentration in the bulk considered to correspond to the p-type GaN layer 53 is higher in the sample annealed in the air atmosphere. The difference between the atmospheric atmosphere and the nitrogen atmosphere is that it first contains oxygen. The increase in the carrier concentration in the atmosphere containing oxygen suggests that the carrier concentration can be improved by annealing in an atmosphere containing oxygen. That is, the carrier concentration can be improved by annealing in an atmosphere containing oxygen.

However, the carrier concentration on the p-type layer surface (p ⁺ -type GaN layer 54) of the sample annealed in the air atmosphere is 1.15 × 10 ²⁰ cm ⁻³ , which is the sample annealed in the nitrogen atmosphere. It was also found that the carrier concentration of the p-type layer surface (p ⁺ -type GaN layer 54) was lower than 1.51 × 10 ²⁰ cm ⁻³ .

  It is considered that oxygen in the air atmosphere improves the carrier concentration in the bulk and decreases the carrier concentration on the surface. It has not been investigated what kind of phenomenon occurs, but some chemical change may occur on the surface. Therefore, the present inventors considered to recover the influence of atmospheric annealing on the p-type layer surface. After annealing in the atmosphere, an experiment was conducted in which the surface was irradiated with high-energy ultraviolet (UV) light.

FIG. 2A is a cross-sectional view showing the configuration of the created sample. The configuration is basically the same as the sample shown in FIG. 1A. A base layer 12 such as a non-doped GaN layer is grown on the sapphire substrate 11 by metal organic chemical vapor deposition (MOCVD), and a p-type GaN layer 13 doped with Mg is doped thereon, and Mg is doped at a high concentration. A sample 10 on which a p ⁺ -type GaN layer 14 was grown was prepared. The as-grown p-type region is in a high resistance state.

  FIG. 2B shows an annealing process in the atmosphere. Sample 10 was annealed at 700 ° C. for 15 minutes in an air atmosphere. It is the same process as FIG. 1Bb.

FIG. 2C shows an ultraviolet irradiation process for the sample 10 after annealing. As an ultraviolet light source, an Xe ₂ excimer lamp having a peak wavelength of 172 nm was used, and irradiation with an irradiance of 10 mW / cm ² was performed mainly on the surface of the p-type layer for 5 minutes.

FIG. 2D is a graph showing the carrier concentration of the sample after annealing in air as a function of depth. Although corresponding to the characteristics of FIG. 1Cb, the lots are different, and the thicknesses of the p ⁺ type layer 14 and the p type layer 13 of the sample 10 are different from the thicknesses of the p ⁺ type layer 54 and the p type layer 53 of the sample 50. . The carrier concentration on the surface of the p-type layer was 5 × 10 ¹⁹ cm ⁻³ .

FIG. 2Ea is a graph showing the carrier concentration of a sample irradiated with ultraviolet light having a peak wavelength of 172 nm at a irradiance of 10 mW / cm ² for 5 minutes as a function of depth on the surface of the sample 10 annealed in the air in a nitrogen atmosphere. is there. Compared with FIG. 2D using the same lot, the bulk carrier concentration (resistivity) of the p-type layer is almost the same, and the carrier concentration on the surface of the p-type layer is about 5 × 10 ¹⁹ / cm ³ to 2 × 10 ^20. It greatly increases to / cm ³ . It is considered that ultraviolet irradiation with a peak wavelength of 172 nm showed a function of increasing the carrier concentration. Since ultraviolet rays having a wavelength shorter than 172 nm have higher energy, they are considered to have the same function.

FIG. 2Eb is a graph showing the carrier concentration of a sample irradiated with ultraviolet light having a peak wavelength of 172 nm at a irradiance of 10 mW / cm ² for 5 minutes in a vacuum atmosphere as a function of depth on the surface of the sample 10 annealed in the air. is there. Compared with before ultraviolet irradiation shown in FIG. 2D, the carrier concentration on the surface of the p-type layer is clearly improved from about 5 × 10 ¹⁹ / cm ³ to 9.6 × 10 ¹⁹ / cm ³ . However, the degree of improvement is lower than ultraviolet irradiation in a nitrogen atmosphere.

FIG. 2Ec shows the carrier concentration of the sample 10 irradiated with ultraviolet light having a peak wavelength of 172 nm with an irradiance of 10 mW / cm ² on the surface of the sample 10 annealed in the air for 3 minutes in the air and then for 5 minutes in the nitrogen atmosphere. It is a graph shown as a function of height. Compared with before ultraviolet irradiation shown in FIG. 2D, the carrier concentration on the surface is clearly improved from about 5 × 10 ¹⁹ / cm ³ to 7.4 × 10 ¹⁹ / cm ³ . However, the degree of improvement is lower than ultraviolet irradiation in a nitrogen atmosphere and ultraviolet irradiation in a vacuum atmosphere. There is a possibility that the oxygen atmosphere may have the same effect as annealing in air. This is referred to as ultraviolet irradiation in an oxygen-free atmosphere, including the case where ultraviolet irradiation is performed in an oxygen-free atmosphere after the ultraviolet irradiation in an oxygen-containing atmosphere.

  From these results, it can be seen that the surface carrier concentration can be improved by annealing a GaN-based semiconductor doped with a p-type impurity such as Mg in an atmosphere containing oxygen and then performing ultraviolet irradiation. It may be desirable for the ultraviolet light to contain components with wavelengths shorter than 172 nm. The atmosphere at the time of ultraviolet irradiation realizes a carrier concentration higher in a nitrogen atmosphere than in a vacuum. Ultraviolet irradiation in an atmosphere containing oxygen is less effective in improving the surface carrier concentration than ultraviolet irradiation in a vacuum.

  Hereinafter, examples based on these experimental results will be described.

As shown in FIG. 3A, the c-plane sapphire substrate 1 is put into a MOCVD apparatus, heated at 1000 ° C. for 10 minutes (thermal cleaning) in a hydrogen atmosphere, and at about 400-500 ° C., trimethylgallium (TMG), Ammonia NH ₃ is supplied to form the GaN low-temperature buffer layer 21, and the low-temperature buffer layer 21 is crystallized by raising the temperature to 1000 ° C. and holding it for 30 seconds. While maintaining the temperature at 1000 ° C., TMG and NH ₃ are supplied to form the non-doped GaN layer 22 with a thickness of about 1 μm. The layers 21 and 22 may be collectively referred to as the foundation layer 2.

TMG, NH ₃ and SiH ₄ are supplied at a temperature of 1000 ° C., and the Si-doped n-type GaN layer 3 is grown to about 5 μm. The temperature is lowered to about 700-800 ° C. to grow the active layer AL. For example, a multiple quantum well structure is formed as the active layer.

As shown in FIG. 3B, nine-period growth is performed with the InGaN well layer WL / GaN barrier layer BL as one period. TMG, trimethylindium (TMI), and NH ₃ are supplied, for example, an InGaN well layer WL having a thickness of about 2.2 nm is grown, and TMG and NH ₃ are supplied, for example, a GaN barrier layer BL having a thickness of about 15 nm is grown. To do. Repeat for 9 cycles.

Returning to FIG. 3A, the temperature is increased to 870 ° C., TMG, trimethylaluminum (TMA), NH ₃ , CP 2 Mg (biscyclopentadienyl magnesium) is supplied, and Mg-doped p-type Al _0.15 Ga _0.85 N electrons A block (cladding) layer 4 is grown to about 20 nm. TMG, NH ₃ and CP2Mg are supplied at the same temperature to grow the Mg-doped p-type GaN layer 5 to about 85 nm, and further, the p ⁺ -type GaN contact layer 6 doped with Mg at a high concentration is grown to about 5 nm. The p-type layer 5 and the p ⁺ -type layer 6 may be collectively referred to as a p-type layer. In this way, a GaN-based nitride semiconductor multilayer for a light emitting diode is formed.

  As shown in FIG. 3C, the grown GaN-based nitride semiconductor stack is annealed at 700 ° C. for 15 minutes in an air atmosphere. An improvement in carrier concentration in the bulk p-type region can be expected. An atmosphere containing oxygen can be used instead of the air atmosphere.

As shown in FIG. 3D, the surface (p-type layer side) of the annealed GaN-based nitride semiconductor stack is irradiated with Xe ₂ excimer lamp light having a peak wavelength of 172 nm at an irradiance of 10 mW / cm ² for 5 minutes. The atmosphere is preferably vacuum or nitrogen. However, an atmosphere containing oxygen for a short time may be used, and then a vacuum or nitrogen atmosphere may be used. Thereafter, an n-side electrode and a p-side electrode are formed by a known method.

  As shown in FIG. 3E, using the resist mask, in the n-side electrode formation region, the p-type layers 6 and 5, the electron blocking layer 4 and the active layer AL are etched from the surface side to expose the n-type layer 3. An n-side electrode 7 with a Ti / Al stack is formed on the n-type layer 3, and a p-side electrode 8 with a Pt / Ag stack is formed on the p-type layer.

  As shown in FIG. 3F, after forming the p-side electrode 8 on the p-type layer, a support substrate 9 such as Si is bonded using an Au—Sn eutectic layer or the like, and the sapphire substrate 1 is peeled off by laser lift-off or the like. Then, the n-type layer 3 is exposed, and the n-side electrode 7 can be formed thereon.

  The p-type layer of GaN-based nitride semiconductor with improved carrier concentration can also be used for a laser.

  FIG. 4A is a cross-sectional view showing the structure of an edge-emitting GaN-based nitride semiconductor laser. On the GaN substrate 31, an n-type GaN contact layer 32, an n-type AlGaN cladding layer 33, a GaN guide layer 34, an active layer AL having a multiple quantum well structure including three well layers, a p-type AlGaN electron blocking layer 36, GaN A stack including a guide layer 37, a p-type AlGaN cladding layer 38, and a p-type GaN contact layer 39 is grown, annealed in an air atmosphere or an atmosphere containing oxygen, and irradiated with ultraviolet light having a peak wavelength of 172 nm in a nitrogen atmosphere. Improve the carrier concentration of the p-type layer. The p-type GaN contact layer 39 and the p-type AlGaN cladding layer 38 are partially etched in a mesa shape. The mesa structure has a width of about 1.5 μm and a length of about 500 μm, for example. The side surface of the mesa structure and the bottom surface of the notch on both sides thereof are covered with an insulating film 40 such as silicon oxide. A p-side electrode 41 such as Pt / Au is formed on the surface of the p-type GaN layer 39, and an n-side electrode 42 such as Ti / Pt / Au is formed on the back surface of the GaN substrate 31. Thereafter, both end faces are cleaved to form a resonator structure.

  FIG. 4B is a cross-sectional view showing the structure of a surface-emitting GaN-based nitride semiconductor laser. The p-side electrodes 46 and 47 are joined to the Si substrate 43 via the eutectic layer 44. For example, the p-side electrode 46 is a Ti / Pt / Au laminated layer, and the p-side electrode 47 is ITO (indium tin oxide). A DBR mirror 45 is provided on the same plane as the p electrodes 46 and 47. The DBR mirror 45 is a dielectric multilayer mirror made of, for example, a GaN / AlN repetitive stack. A p-type GaN contact layer 39, an active layer AL having a multiple quantum well structure including five well layers, and an n-type GaN contact layer 32 via an insulating film 48 such as silicon oxide on the DBR mirror 45 and the p-side electrode 47. , And a DBR mirror 49 and an n-side electrode 42 such as Ti / Pt / Au are arranged on the same plane on the n-type GaN layer 32.

  As a manufacturing process, epitaxial growth is performed from an upper layer to a lower layer on a sapphire substrate, a p-type layer is formed, and then annealing in an atmosphere or an atmosphere containing oxygen is performed, and a peak wavelength of 172 nm is achieved in a nitrogen atmosphere. Ultraviolet irradiation is performed to improve the carrier concentration of the p-type layer. The light reciprocates between the upper and lower DBRs and exits from the upper DBR mirror 46.

  As mentioned above, although this invention was demonstrated along the Example, this invention is not limited to these. Exemplified materials, numerical values have no limiting meaning. It will be apparent to those skilled in the art that various modifications, improvements, substitutions, combinations, and the like can be made.

10,50 samples,
1,11,51 sapphire substrate,
12, 52 Underlayer,
13, 53 p-type GaN layer,
14, 54 p ⁺ type GaN layer,

Claims (3)

(A) activating a p-type impurity by annealing a semiconductor substrate having a p-type GaN-based nitride semiconductor layer doped with a p-type impurity in an atmosphere containing oxygen;
(B) irradiating the surface of the p-type GaN-based nitride semiconductor layer with ultraviolet light in an oxygen-free atmosphere to increase the surface carrier concentration;
Including
The method of manufacturing a nitride semiconductor device, wherein the step (b) is performed after the step (a) and recovers the influence of the step (a).   The method for manufacturing a nitride semiconductor device according to claim 1, wherein the ultraviolet ray in the step (b) includes a component having a wavelength of 172 nm or less.   The method for manufacturing a nitride semiconductor device according to claim 1, wherein the atmosphere in the step (b) is a nitrogen atmosphere.

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