JP4752214B2 - Surface treatment method of AlN crystal for epitaxial layer formation - Google Patents

Description

The present invention relates to a surface treatment method of an AlN crystal for forming an epitaxial layer used for a substrate of a semiconductor device such as a light emitting element, an electronic element, or a semiconductor sensor .

  A group III nitride crystal such as an AlN crystal is very useful as a material for forming a substrate of a semiconductor device such as a light emitting element, an electronic element, or a semiconductor sensor.

  Conventionally, as a method of forming an AlN crystal substrate from an AlN crystal, a method of slicing the AlN crystal to a predetermined thickness and then polishing the surface has been adopted. In particular, chemical mechanical polishing (hereinafter referred to as chemical mechanical polishing) is described below. CMP) has been widely performed (see, for example, Patent Documents 1 to 3).

  Here, the conventional CMP performs the surface of the AlN crystal by pressing the AlN crystal against the polishing pad while supplying a slurry containing abrasive grains having low hardness below the AlN crystal as the object to be polished to the polishing pad. However, since the AlN crystal is hard and poor in reactivity, the conventional CMP is very inefficient and inefficient.

On the other hand, when the surface of the AlN crystal is ground or polished by mechanical grinding or mechanical polishing using abrasive grains having a hardness higher than that of the AlN crystal, a thick work-affected layer is formed in the surface side region of the AlN crystal, or the surface of the AlN crystal Since the roughness becomes large, the surface of the group III nitride crystal layer epitaxially grown on the AlN crystal surface becomes uneven and becomes clouded, and a high-quality semiconductor device cannot be formed.
US Pat. No. 6,596,079 US Pat. No. 6,488,767 International Publication No. 03/043780 Pamphlet

In order to efficiently obtain an epitaxial layer forming AlN crystal substrate that can be used in a semiconductor device, the present invention efficiently forms a surface of an epitaxial layer forming AlN crystal that has a good morphology on the epitaxial layer forming AlN crystal. An object is to provide a processing method.

The present invention relates to an AlN crystal surface treatment method for forming an epitaxial layer for chemically and mechanically polishing the surface of an AlN crystal, wherein the abrasive grains of the slurry used for chemical mechanical polishing have a hardness higher than that of the AlN crystal. and high high-hardness abrasive grains, seen including a low hardness low hardness abrasive grains below the AlN crystal is a surface treatment method of the pH of the slurry is 5 or less or 8 or more at which the epitaxial layer forming the AlN crystal.

The surface treatment method of the epitaxial layer forming AlN crystal of the present invention, the surface of the AlN crystal mechanical grinding or mechanical polishing, chemical as the surface of the mechanically ground or mechanically polished the AlN crystals described above It can be mechanically polished.

In the surface treatment method of the epitaxial layer forming AlN crystal according to the present invention, when the thickness of the affected layer after the chemical mechanical polishing of the AlN crystal and 100nm or less, to the surface roughness Ry and 5nm or less The surface roughness Ra can be 0.5 nm or less .

In the surface treatment method for epitaxial layer forming AlN crystal according to the present invention, the AlN crystal after the chemical mechanical polishing can be heat-treated.

As described above, according to the present invention, it is possible to efficiently form a good surface morphology of the epitaxial layer forming the AlN crystal, an epitaxial layer for forming AlN crystal substrate that can be used in semiconductor devices efficiently Obtainable.

  The AlN crystal surface treatment method according to the present invention is an AlN crystal surface treatment method for chemically and mechanically polishing the surface of an AlN crystal 1 with reference to FIG. The abrasive grains 16 of the slurry 17 used for CMP include high-hardness abrasive grains having a hardness higher than that of the AlN crystal 1 and low-hardness abrasive grains having a hardness lower than that of the AlN crystal 1.

  Here, CMP refers to chemically and mechanically polishing an object to be polished using a slurry in which abrasive grains are dispersed. For example, CMP is fixed on a surface plate 15 with reference to FIG. While rotating the polishing pad 18 around the rotation shaft 15c, the slurry 17 in which the abrasive grains 16 are dispersed on the polishing pad 18 is supplied from the slurry supply port 19, and the AlN crystal 1 is fixed on the crystal holder 11. The surface of the AlN crystal 1 can be chemically and mechanically polished by placing the weight 14 and pressing the AlN crystal 1 against the polishing pad 18 while rotating about the rotation axis 11c.

  In CMP, by using abrasive grains obtained by mixing the above-mentioned high-hardness abrasive grains and low-hardness abrasive grains, a surface with good morphology can be formed on the AlN crystal while maintaining a high polishing rate. The polishing rate is high only with high-hardness abrasive grains, but the morphology of the crystal surface is poor, and the polishing rate is extremely low only with low-hardness abrasive grains, making CMP substantially difficult.

  From the above viewpoint, the abrasive volume of the slurry is preferably such that the mixing volume ratio of the high hardness abrasive grains to the low hardness abrasive grains is high hardness abrasive grains: low hardness abrasive grains = 5: 95 to 70:30, 15: More preferably, it is 85-50: 50.

  In the AlN crystal surface treatment method according to the present invention, the grain size of the high-hardness abrasive grains is preferably 1 μm or less. Since the surface of the AlN crystal is mechanically removed by the high-hardness abrasive grains, it becomes possible to polish. Therefore, by reducing the particle diameter of the high-hardness abrasive grains, the depth of scratches and irregularities formed on the surface of the AlN crystal Can be made smaller and the surface can be flattened. From this point of view, the particle size of the high-hardness abrasive grains is more preferably 0.5 μm or less.

Here, the high-hardness abrasive grains are not particularly limited as long as they have higher hardness than AlN crystals, but diamond, SiC, Si ₃ N ₄ , BN, Al ₂ O ₃ , Cr ₂ O ₃ , ZrO Abrasive grains containing at least one material selected from the group consisting of ₂ are preferable. By using high-hardness abrasive grains containing such materials, the polishing rate in CMP of the surface of the AlN crystal can be increased.

The low hardness abrasive grain is not particularly limited as long as it is an abrasive grain having a hardness lower than that of the AlN crystal, but SiO ₂ , CeO ₂ , TiO ₂ , MgO, MnO ₂ , Fe ₂ O ₃ , Fe ₃ O _{4. , NiO, ZnO, CoO 2,} Co 3 O 4, CuO, Cu 2 O, GeO 2, CaO it is abrasive grains comprising at least one material selected from the group consisting of _{Ga 2 O 3, in 2 O} 3 Is preferred. By using low-hardness abrasive grains containing such a material, the morphology of the surface formed by CMP of AlN crystals can be improved.

The abrasive grains are not limited to oxides containing a single metal element, but are oxides containing two or more metal elements (for example, those having a structure such as ferrite, perovskite, spinel or ilmenite). Also good. Also, nitrides such as AlN, GaN and InN, carbonates such as CaCO ₃ and BaCO ₃ , metals such as Fe, Cu, Ti and Ni, and carbon (specifically, carbon black, carbon nanotube, C60, etc.) It can also be used.

  Here, the pH of the slurry 17 is preferably 5 or less or 8 or more. The polishing rate in CMP can be increased by bringing an acidic slurry having a pH of 5 or less or a basic slurry having a pH of 8 or more into contact with the AlN crystal and etching the surface of the AlN crystal. From this viewpoint, the pH of the slurry 17 is more preferably 3 or less or 10 or more.

  In the AlN crystal surface treatment method according to the present invention, the surface of the AlN crystal can be mechanically ground or mechanically polished, and the surface of the mechanically ground or mechanically polished AlN crystal can be chemically and mechanically polished. By combining mechanical grinding or mechanical polishing before CMP, it is possible to increase the polishing rate of the AlN crystal surface and form an AlN crystal surface with good morphology.

  Here, with mechanical grinding, referring to FIG. 2, for example, a grinding stone 22 in which abrasive grains are hardened with a bond is fixed to a grinding stone base metal 23 and rotated around its rotating shaft 23c, while being attached to the crystal holder 21. It means smoothing while scraping the surface of the AlN crystal 1 by sending it to the surface of the AlN crystal 1 which is fixed and rotating around the rotating shaft 21c. With mechanical polishing, referring to FIG. 3, for example, while rotating the surface plate 15 around its rotating shaft 35c, slurry in which abrasive grains 36 are dispersed is supplied onto the surface plate 35, and the AlN crystal 1 The surface of the AlN crystal is smoothed by pressing the AlN crystal 1 against the surface plate 35 while placing the weight 34 on the crystal holder 31 on which is fixed and rotating it around the rotation shaft 31c. . In mechanical polishing, instead of using a slurry in which abrasive grains are dispersed, although not shown, the surface of the AlN crystal is polished by pressing a grindstone in which the abrasive grains are hardened with a bond against the AlN crystal while rotating. It is also possible.

  In the AlN crystal surface treatment method according to the present invention, referring to FIG. 1, the thickness of the work-affected layer 1a after CMP of the AlN crystal 1 is preferably 100 nm or less. By setting the altered layer after CMP of the AlN crystal to 100 nm or less, an epitaxial layer having good morphology (referred to as a layer formed by epitaxial growth hereinafter) can be formed on the AlN crystal. From this viewpoint, the thickness of the work-affected layer is more preferably 10 nm or less.

In the AlN crystal surface treatment method according to the present invention, the surface roughness Ry of the AlN crystal after CMP is preferably 5 nm or less. In the present application, the surface roughness Ry is extracted from the roughness curved surface by a 10 μm square (100 μm ² ) as a reference area in the direction of the average surface, and the height from the average surface of the extracted portion to the highest peak and the lowest. The sum of the depth to the bottom of the valley. By setting the surface roughness Ry after CMP of the AlN crystal to 5 nm or less, an epitaxial layer having a good morphology can be formed on the AlN crystal. From this viewpoint, the surface roughness Ry is more preferably 1 nm or less.

In the AlN crystal surface treatment method according to the present invention, the surface roughness Ra of the AlN crystal after CMP is preferably 0.5 nm or less. In the present application, the surface roughness Ra is a 10 μm square (100 μm ² ) extracted as a reference area in the direction of the average surface from the roughness curved surface, and the absolute value of the deviation from the average surface of the extracted portion to the measurement curved surface is the total. Then, it means the value averaged by the reference area. By setting the surface roughness Ra of the AlN crystal after CMP to 0.5 nm or less, an epitaxial layer having a good morphology can be formed on the AlN crystal. From this viewpoint, the surface roughness Ry is more preferably 0.1 nm or less.

In the AlN crystal surface treatment method according to the present invention, the density of scratches having a depth of 2 nm or more from the surface after CMP of the AlN crystal is preferably 1 × 10 ⁴ pieces / mm or less. . By setting the density of scratches having a depth of 2 nm or more from the surface after CMP of the AlN crystal to 1 × 10 ⁴ pieces / mm or less, an epitaxial layer having a good morphology can be formed on the AlN crystal.

In the AlN crystal surface treatment method according to the present invention, the density of pits (holes) having a depth of 50 nm or more from the surface after CMP of the AlN crystal is 1 × 10 ³ pieces / mm ² or less. preferable. By setting the density of pits having a depth of 50 nm or more from the surface after CMP of the AlN crystal to 1 × 10 ³ pieces / mm ² or less, an epitaxial layer having a good morphology can be formed on the AlN crystal. .

In the AlN crystal surface treatment method according to the present invention, the thickness of the surface oxide layer of the AlN crystal after CMP is preferably 3 nm or less. The thickness of the surface oxidation layer, ellipsometry, XPS (X-ray photoelectron spectroscopy), AES (Auger electron spectroscopy) or RBS (Rutherford back scattering method) can be evaluated by. By setting the surface oxide layer of the AlN crystal after CMP to 3 nm or less, an epitaxial layer having a good morphology can be formed on the AlN crystal. From this viewpoint, the thickness of the surface oxide layer is more preferably 2 nm or less.

As for the amount of impurities on the surface of the AlN crystal after CMP, the atomic number of elements having an atomic number of 19 or more is 1 × 10 ¹² atoms / cm ² or less, and the atomic numbers excluding O (oxygen) and C (carbon) are the same. The atoms of the elements 1 to 18 are preferably 1 × 10 ¹⁴ atoms / cm ² or less. Moreover, it is preferable that O atom and C atom are 40 atomic% or less respectively with respect to the atom of all the elements which exist in the AlN crystal surface. The Al atoms and N atoms on the AlN crystal surface are preferably 40 atom% to 60 atom%, respectively, with respect to the sum of Al atoms and N atoms present on the AlN crystal surface. Here, the amount of atoms of an element having an atomic number of 19 or more and the atoms of elements having an atomic number of 1 to 18 excluding O and C can be evaluated by TXRF (total reflection X-ray fluorescence analysis). The amount of O, C, Al and N atoms can be evaluated by XPS, AES, or the like. By setting the AlN crystal surface to the above-described chemical composition, an epitaxial layer having a good morphology can be formed on the AlN crystal.

Furthermore, in the AlN crystal surface treatment method according to the present invention, it is preferable to heat-treat the AlN crystal after CMP. By such heat treatment, the values of the surface roughness Ry and the surface roughness Ra of the AlN crystal after CMP can be further reduced. This heat treatment is performed at about 900 ° C. to 1100 ° C. in a non-oxidizing atmosphere, more preferably in a reducing atmosphere (specifically, an N ₂ gas atmosphere, an NH ₃ gas atmosphere, an H ₂ gas atmosphere, etc.). Is preferable.

  The AlN crystal substrate according to the present invention is an AlN crystal substrate obtained by the AlN crystal surface treatment method described above. Since the AlN crystal substrate obtained by the above surface treatment method is thin even if there is no work-affected layer and the surface is flattened, an epitaxial layer having a good morphology can be formed thereon. . Specifically, the AlN crystal substrate according to the present invention is obtained by slicing an AlN crystal grown by various methods in parallel to a predetermined surface as necessary, and then mechanically grinding or polishing by the above method. It is obtained by polishing the surface chemically and mechanically by the above method.

  The AlN crystal growth method is not particularly limited, but from the viewpoint of efficiently growing a large bulk AlN crystal, a vapor phase growth method such as a sublimation method or an HVPE (halide or hydride vapor phase epitaxial growth) method. Is preferably used.

  The AlN crystal substrate according to the present invention has a surface roughness Ry of 1 nm or less. By using the AlN crystal surface treatment method described above, an AlN crystal substrate having a very flat surface with a surface roughness Ry of 1 nm or less, which has not been obtained conventionally, is obtained. An epitaxial layer having a very good morphology can be formed on such an AlN crystal substrate.

  The AlN crystal substrate according to the present invention has a surface roughness Ra of 0.1 nm or less. By using the AlN crystal surface treatment method described above, an AlN crystal substrate having a very flat surface with a surface roughness Ry of 0.1 nm or less, which has not been obtained conventionally, is obtained. An epitaxial layer having a very good morphology can be formed on such an AlN crystal substrate.

The AlN crystal substrate according to the present invention has a scratch density of 1 × 10 ⁴ / mm or less with a depth of 2 nm or more from the surface. By using the AlN crystal surface treatment method described above, an AlN crystal substrate having a surface with few scratches with a scratch density of 1 × 10 ⁴ pieces / mm or less, which has not been obtained conventionally, can be obtained. An epitaxial layer with good morphology can be formed on such an AlN crystal substrate.

In the AlN crystal substrate according to the present invention, the density of pits having a depth from the surface of 50 nm or more is 1 × 10 ³ pieces / mm ² or less. By using the AlN crystal surface treatment method described above, an AlN crystal substrate having a surface with few pits and a density of the pits of 1 × 10 ³ pieces / mm ² or less, which has not been obtained conventionally, can be obtained. An epitaxial layer with good morphology can be formed on such an AlN crystal substrate.

  The main surface of the AlN crystal substrate is preferably parallel to any one of the C, A, R, M, and S surfaces in the wurtzite structure. Here, the C plane is the {0001} plane and {000-1} plane, the A plane is the {11-20} plane and its equivalent plane, and the R plane is the {01-12} plane and its equivalent plane. , M plane means {10-10} plane and its equivalent plane, and S plane means {10-11} plane and its equivalent plane. By making the main surface of the AlN crystal substrate parallel or nearly parallel to each of the above surfaces in the wurtzite structure, it is easy to form an epitaxial layer with good morphology on the AlN crystal substrate.

  Further, an off angle, which is an angle formed between the principal surface of the AlN crystal substrate and any one of the C, A, R, M, and S surfaces in the wurtzite structure, is 0.05 ° or more. It is preferably 15 ° or less. By providing an off angle of 0.05 ° or more, defects in the epitaxial layer formed on the AlN crystal substrate can be reduced. However, if the off angle exceeds 15 °, a stepped step is easily formed in the epitaxial layer. From this viewpoint, the off angle is more preferably 0.1 ° or more and 10 ° or less.

An AlN crystal substrate with an epitaxial layer according to the present invention has one or more Group III nitride layers formed by epitaxial growth on the AlN crystal substrate. Since the AlN crystal substrate described above is thin with or without a work-affected layer and has a flat surface, the group III nitride layer epitaxially grown thereon has a good morphology. Here, the group III nitride layer is not particularly limited, for example, _{Al x Ga y In 1-xy} N layer (0 ≦ x, 0 ≦ y , x + y ≦ 1) , and the like. The method for epitaxial growth of the group III nitride layer is not particularly limited, and preferred examples include HVPE, MBE (molecular beam epitaxy), and MOCVD (metal organic chemical vapor deposition).

A semiconductor device according to the present invention includes the AlN crystal substrate described above. Since the above AlN crystal substrate is thin even if there is no work-affected layer and the surface is flattened, an epitaxial layer having a good morphology is formed on this Al crystal substrate, and a high-quality semiconductor device can be obtained. Can be formed. Examples of the semiconductor device according to the present invention include light emitting elements such as light emitting diodes and laser diodes, rectifiers, bipolar transistors, field effect transistors, electronic elements such as HEMTs (High Electron Mobility Transistors), temperature sensors, and pressures. sensor, radiation sensor, a visible - etc. semiconductor sensors, such as ultraviolet light detector and the like.

  A semiconductor device according to the present invention is a semiconductor device 400 including the AlN crystal substrate 410 described above with reference to FIG. 4, and includes three or more layers epitaxially grown on one main surface side of the AlN crystal substrate 410. A light emitting element including a semiconductor layer 450, a first electrode 461 formed on the other main surface of the AlN crystal substrate 410, and a second electrode 462 formed on the outermost semiconductor layer of the semiconductor layer 450; A light-emitting element on which the AlN crystal substrate 410 side is the light-emitting surface side, the outermost semiconductor layer side is the mounting surface side, and the semiconductor layer 450 is a p-type semiconductor layer 430. It includes an n-type semiconductor layer 420 and a light emitting layer 440 formed between the p-type semiconductor layer 430 and the n-type semiconductor layer 420. By having the said structure, the semiconductor device which makes an AlN crystal substrate surface side the light emission surface side can be formed.

  Such a semiconductor device is excellent in heat dissipation against heat generation in the light emitting layer, as compared with a semiconductor device in which the semiconductor layer side is the light emitting surface side. Therefore, even when operated with high power, the temperature rise of the semiconductor device is mitigated and light emission with high luminance can be obtained. Further, in an insulating substrate such as a sapphire substrate, it is necessary to take a single-sided electrode structure in which two types of electrodes, an n-side electrode and a p-side electrode, are formed on a semiconductor layer. A double-sided electrode structure in which electrodes are respectively formed on the AlN crystal substrate can be adopted, and a major part of the main surface of the semiconductor device can be a light emitting surface. Furthermore, there is an advantage that the manufacturing process can be simplified, for example, wire bonding is sufficient for mounting a semiconductor device.

Example 1
In this embodiment, the surface of the AlN crystal grown by the sublimation method is mechanically polished and further processed by chemical mechanical polishing.

(1-1) Preparation of AlN crystal An AlN crystal was formed on a C plane ((0001) plane) on the Al atomic plane side of an AlN seed crystal (diameter 50 mm × thickness 1.5 mm) by sublimation as follows. Grown up.

  Referring to FIG. 5, AlN raw material 5 such as AlN powder was housed in the lower part of BN crucible 52, and AlN seed crystal 9 was placed in the upper part of crucible 52 having an inner diameter of 48 mm. The AlN seed crystal 9 is processed flat, and the AlN seed crystal 9 is arranged so that the BN material as the seed crystal protective material 53 is in close contact with the back surface of the AlN seed crystal 9, and the sublimation of AlN from the back surface of the AlN seed crystal 9 Prevented.

Next, the temperature in the crucible 52 was raised by heating the heating body 54 using the high frequency heating coil 55 while flowing N ₂ gas into the reaction vessel 51. During the temperature rise in the crucible 52, the temperature on the AlN seed crystal 9 side of the crucible 52 is set higher than the temperature on the AlN raw material 5 side, and the surface of the AlN seed crystal 9 is cleaned by etching during the temperature rise. Impurities released from the inside of the AlN seed crystal 9 and the crucible 52 during the warming were removed through an exhaust port 52 c provided in the crucible 52.

Next, the temperature on the AlN seed crystal 9 side of the crucible 52 is set to 2100 ° C., the temperature on the AlN raw material 5 side is set to 2150 ° C., and AlN is sublimated from the AlN raw material 5. 9, AlN was solidified again to grow an AlN crystal 1. During AlN crystal growth, it continued to flow N ₂ gas to the outside of the crucible 52 in the reaction vessel 51, as the outer gas partial pressure of the crucible 52 in the reaction vessel 51 is about 101.3HPa～1013hPa, N ₂ and controlling the N ₂ gas exhaust amount in the N ₂ gas introduction rate and N ₂ gas exhaust port 51c in the gas inlet 51a. An AlN crystal was grown for 50 hours under the above crystal growth conditions, and then cooled to room temperature (25 ° C.) to obtain an AlN crystal 1.

  The obtained AlN crystal was polycrystallized at the outer periphery of the crystal, but within the range of 42 mm in diameter from the center of the crystal, the half-value width of X-ray diffraction is 200 arcsec or less and can be used as a substrate for semiconductor devices. A single crystal of AlN. The thickness of the AlN crystal was 7.5 mm at the thick part and 4.5 mm at the thin part.

  Next, the obtained AlN crystal was sliced along a plane parallel to the (0001) plane of the AlN seed crystal 9 and the polycrystallized outer peripheral portion was removed to obtain an AlN crystal having a diameter of 42 mm and a thickness of 1.5 mm. A substrate was obtained.

(1-2) Mechanical Polishing of AlN Crystal Surface Substrate Referring to FIG. 3, the C-plane ((000-1) plane) on the N atomic plane side of AlN crystal substrate 1 is attached to a ceramic crystal holder 31 with wax. I attached. A surface plate 35 having a diameter of 300 mm is installed in a lapping device (not shown), and the surface plate 35 is rotated about its rotation axis 35c while supplying slurry in which diamond abrasive grains 36 are dispersed to the surface plate 35. In addition, the AlN crystal substrate 1 is rotated around the rotation axis 31c of the crystal holder 31 while pressing the AlN crystal substrate 1 against the surface plate 35 by placing the weight 34 on the crystal holder 31. The surface (C plane on the Al atomic plane side, (0001) plane) was mechanically polished. Here, a copper surface plate or a tin surface plate was used as the surface plate 35. Two kinds of diamond abrasive grains having an abrasive grain diameter of 6 μm and 2 μm were prepared, and the abrasive grain diameter was gradually reduced as the mechanical polishing progressed. Polishing pressure was ^{200g / cm 2 ~500g / cm 2} , any rotational speed of the AlN crystal 1 and the surface plate 35 was 30Rpm～100rpm. By this mechanical polishing, the surface of the AlN crystal substrate became a mirror surface.

(1-3) CMP of AlN crystal substrate surface
Referring to FIG. 1, the C plane ((000-1) plane) on the N atomic plane side of AlN crystal substrate 1 after the mechanical polishing was attached to a ceramic crystal holder 11 with wax. A polishing pad 18 is installed on a surface plate 15 having a diameter of 300 mm installed in a polishing apparatus (not shown), and a slurry 17 in which abrasive grains 16 are dispersed is supplied to the polishing pad 18, and the rotating shaft 15 c is the center. The polishing pad 18 is rotated, and the AlN crystal substrate 1 is rotated about the rotation axis 11c of the crystal holder 11 while pressing the AlN crystal substrate 1 against the polishing pad 18 by placing the weight 14 on the crystal holder 11. As a result, CMP of the surface of the AlN crystal (C plane on the Al atomic plane side, (0001) plane) was performed. Here, a stainless copper surface plate was used as the surface plate 15. Polishing pressure was ^{100g / cm 2 ~500g / cm 2} , any rotational speed of the AlN crystal 1 and the polishing pad 18 30Rpm～80rpm, polishing time was 120 minutes. Here, the abrasive grains are diamond abrasive grains having a particle diameter of 1 μm as high hardness abrasive grains and colloidal silker (SiO ₂ ) abrasive grains having a particle diameter of 0.1 μm as low hardness abrasive grains in a mixing volume ratio of 5:95. The slurry was adjusted to pH 8 (see Table 1).

  The polishing rate in this CMP was 0.8 μm / hr. The thickness of the work-affected layer of the AlN crystal after CMP was 10 nm, the surface roughness Ry of the AlN crystal surface was 1.1 nm, and the surface roughness Ra was 0.11 nm. Here, the thickness of the work-affected layer in the AlN crystal was evaluated by TEM (transmission electron microscope) observation of a cross section of the crystal broken at the cleavage plane. The surface roughness Ry and the surface roughness Ra of the AlN crystal surface were evaluated by AFM (atomic force microscope) observation within a 10 μm square area of the AlN crystal substrate surface. The work-affected layer refers to a layer in which the crystal lattice formed in the surface side region of the crystal is disturbed by grinding or polishing of the crystal surface, and the presence and thickness of the layer can be confirmed by TEM observation. The thickness of the surface oxide layer of the AlN crystal after CMP was 1 nm, and the ratio of Al atoms to N atoms on the surface of the AlN crystal was 50 atomic% and 50 atomic%, respectively. Here, evaluation of the thickness of the surface acid lower layer and the ratio of Al atom to N atom was performed by XPS.

(1-4) Heat treatment of AlN crystal substrate The above-mentioned AlN crystal substrate after CMP is placed in an MOCVD apparatus, and NH ₃ gas is flowed at 1 slm (standard flow rate is 1 liter per minute, the same applies hereinafter) ) After raising the temperature to 1000 ° C. while flowing, the AlN crystal substrate was heat-treated by holding HN ₃ gas at 1000 ° C. for 10 minutes while flowing 0.5 slm to 5 slm.

(1-5) Formation of Epitaxial Layer on AlN Crystal Substrate In the MOCVD apparatus, TMA (trimethylaluminum, the same applies hereinafter) gas having a flow rate of 2 slm is applied on the AlN crystal substrate after the heat treatment at 1000 ° C. for 60 minutes. By flowing, an AlN layer having a thickness of 2 μm was formed as an epitaxial layer on the AlN crystal substrate.

  The epitaxial layer had a mirror surface with a surface roughness Ry of 1.2 nm and a surface roughness Ra of 0.13 nm. The results are summarized in Table 1.

(Example 2 to Example 5)
Preparation of an AlN crystal substrate in the same manner as in Example 1, except that the types of the high-hardness abrasive grains and the low-hardness abrasive grains in the abrasive grains, the particle diameter and the mixing ratio, and the pH of the slurry are as shown in Table 1. The surface treatment of the AlN crystal substrate was performed, and an epitaxial layer was formed on the AlN crystal substrate. The results are summarized in Table 1.

(Comparative Example 1)
The surface treatment of the AlN crystal substrate is performed in the same manner as in Example 1 except that only the colloidal silica (SiO ₂ ) abrasive grains having a particle diameter of 0.1 μm, which are low-hardness abrasive grains, are used as the abrasive grains. Formed. The polishing rate of CMP was 0 μm / hr, and polishing did not proceed. The thickness of the work-affected layer of AlN crystals after CMP was 1500 nm. The surface roughness Ry of the AlN crystal surface after CMP was 21 nm, and the surface roughness Ra was 2.0 nm. Further, the epitaxial layer formed on the Al crystal substrate became cloudy, and the surface roughness Ry exceeded 100 nm and the surface roughness Ra exceeded 10 nm. The results are summarized in Table 1.

(Comparative Example 2)
The surface treatment of the AlN crystal substrate was performed in the same manner as in Example 1 except that only high-diameter diamond abrasive grains having a particle diameter of 1 μm were used as the abrasive grains to form an epitaxial layer. The polishing rate of CMP was as large as 3.2 μm / hr, but the thickness of the work-affected layer of AlN crystal after CMP was 500 nm. The surface roughness Ry of the AlN crystal surface after CMP was 12 nm, and the surface roughness Ra was 1.1 nm. Further, the epitaxial layer formed on the Al crystal substrate became cloudy, and the surface roughness Ry exceeded 100 nm and the surface roughness Ra exceeded 10 nm. The results are summarized in Table 1.

  As is apparent from Table 1, by performing CMP using abrasive grains in which high-hardness abrasive grains and low-hardness abrasive grains are mixed, an AlN crystal surface and an epitaxial layer having good morphology were obtained. Here, as the mixing ratio of the low-hardness abrasive grains increases, the polishing rate decreases, but the morphology of the AlN crystal surface is improved.

(Example 6 to Example 11)
Examples 6 to 11 are examples in which the surface of the AlN crystal grown by the HVPE method is mechanically polished and further processed by chemical mechanical polishing.

(2-1) Preparation of AlN crystal An AlN crystal was formed on the C plane ((0001) plane) on the Al atomic plane side of an AlN seed crystal (diameter 50 mm × thickness 0.5 mm) by HVPE as follows. Grown up.

Referring to FIG. 6, AlN seed crystal 9 is arranged on pedestal 62 in reaction vessel 61, and AlCl gas or AlCl ₃ gas is introduced into reaction vessel 61 as Al source gas 7 from Al source gas inlet 61a, nitrogen gas NH ₃ gas was introduced as the nitrogen source gas 8 from the source gas inlet 61b. N ₂ gas was used as a carrier gas for the group III element source gas and the nitrogen source gas. The ratio (molar ratio) of AlCl gas or AlCl ₃ gas to NH ₃ gas is 1: 100, the temperature of the AlN seed crystal is 1000 ° C., and the growth rate of the AlN crystal is adjusted to 20 μm / hr. An AlN crystal 1 having a thickness of 5 mm was grown on the AlN seed crystal 9.

  Next, the obtained AlN crystal was sliced on a plane parallel to the (0001) plane of the AlN seed crystal 9 to obtain an AlN crystal substrate having a diameter of 50 mm and a thickness of 0.5 mm.

(2-2) Mechanical polishing of the AlN crystal substrate surface The mechanical polishing of the AlN crystal substrate was performed in the same manner as in Example 1.

(2-3) CMP of AlN crystal substrate surface
Table 2 shows the surface of the AlN crystal substrate after the mechanical polishing, as shown in Table 2, the types and mixing ratios of the high-hardness and low-hardness abrasive grains in the abrasive grains, the particle diameter of the high-hardness abrasive grains, and the pH of the slurry. Except for this, chemical mechanical polishing was performed in the same manner as in Example 1.

(2-4) Heat treatment of AlN crystal substrate The AlN crystal substrate after the CMP was placed in an MOCVD apparatus, and the AlN crystal substrate was heat-treated in the same manner as in Example 1.

(2-5) Formation of Epitaxial Layer on AlN Crystal Substrate In the MOCVD apparatus, an AlN layer having a thickness of 2 μm was formed as an epitaxial layer on the AlN crystal substrate in the same manner as in Example 1. The results are summarized in Table 2.

  In Table 2, referring to Examples 6 to 8, the polishing rate of CMP decreased as the grain size of the high-hardness abrasive grains decreased, but the thickness of the work-affected layer of the AlN crystal substrate, the surface roughness Ry Both the surface roughness Ra and the AlN crystal substrate surface morphology were improved. Further, with reference to Example 9 and Example 10 and Example 8 and Example 11, the polishing rate of CMP was increased by setting the pH of the slurry to 5 to 3 or 8 to 11.

(Example 12 , Reference Example 13, Example 14 to Example 18)
Example 12, Reference Example 13, Examples 14 to 18, the surface of the AlN crystal grown by sublimation, and mechanical grinding, examples of the case of processing by further chemically polished mechanically or It is a reference example .

(3-1) Production of AlN crystal Production of the AlN crystal was carried out by the sublimation method in the same manner as in Example 1.

(3-2) Mechanical Grinding of AlN Crystal Substrate Surface Referring to FIG. 2, the C-plane ((000-1) plane) on the N atomic plane side of AlN crystal substrate 1 is attached to a ceramic crystal holder 21 with wax. I attached. As the grinding machine, an in-feed type was used. As the grindstone 22, a vitrified bond diamond grindstone having an outer diameter of 80 mm and a width of 5 mm was used. While the AlN crystal 1 is fixed to the crystal holder 21 and rotated about the rotation shaft 21c, and the wheel 22 is fixed to the grindstone base 23 and rotated about the rotation shaft 23c, the grindstone 22 is rotated to the AlN crystal. The surface of the AlN crystal (C plane on the Al atomic plane side, (0001) plane) was mechanically ground. Three types of diamond grindstones having an abrasive grain size of 15 μm, 5 μm, and 3 μm were prepared, and the abrasive grain size was gradually reduced as the mechanical grinding progressed. By this mechanical grinding, the surface of the AlN crystal became a mirror surface.

(3-3) CMP of AlN crystal substrate surface
Table 3 shows the surface of the AlN crystal substrate after mechanical polishing, with the types and mixing ratios of the high-hardness and low-hardness abrasive grains in the abrasive grains, the particle diameter of the high-hardness abrasive grains, and the pH of the slurry shown in Table 3. Except for this, chemical mechanical polishing was performed in the same manner as in Example 1. Here, the hardness of the high-hardness abrasive grains is in the order of diamond>SiC> Al ₂ O ₃ > Cr ₂ O ₃ > ZrO ₂ .

(3-4) Heat Treatment of AlN Crystal Substrate The AlN crystal substrate after the CMP was placed in an MOCVD apparatus, and the AlN crystal substrate was heat treated in the same manner as in Example 1.

(3-5) Formation of Epitaxial Layer on AlN Crystal Substrate In the MOCVD apparatus, an AlN layer having a thickness of 2 μm was formed as an epitaxial layer on the AlN crystal substrate in the same manner as in Example 1. The results are summarized in Table 3.

In Table 3 , with reference to Example 12 , Reference Example 13, Example 14 -Example 18, CMP which used the slurry containing the abrasive grain which mixed various high hardness abrasive grains and various low hardness abrasive grains was used. The surface treatment can be performed with a high polishing rate and good AlN crystal surface morphology. Here, as the hardness or grain size of the high-hardness abrasive grains decreased, the AlN crystal work-affected layer, the surface roughness Ry and the surface roughness Ra all decreased, and the morphology of the AlN crystal substrate surface improved.

(Example 19 to Example 24)
In Examples 19 to 24, after an AlN crystal grown by a sublimation method was sliced in various plane orientations to produce an AlN crystal substrate, this AlN crystal substrate was mechanically polished in the same manner as in Example 1, Further, this is an example of chemical mechanical polishing similar to Example 14. The results are summarized in Table 4.

  In Table 4, with reference to Examples 19 to 24, the present invention is applied regardless of whether the principal surface of the AlN crystal substrate is any of the C, A, R, M, and S surfaces. By CMP, it is possible to perform surface treatment with a high polishing rate and good AlN crystal surface morphology. Further, as is clear from Table 4, the surface with the higher polishing rate is in the order of C surface (N atom surface side)> A surface> M surface> S surface> R surface> C surface (Al atom surface side). It was.

(Example 25)
When an AlN crystal was grown by the HVPE method, Si was doped into the AlN crystal to obtain an n-type AlN crystal. The obtained n-type AlN crystal was subjected to mechanical grinding and CMP in the same manner as in Example 15 to obtain an n-type AlN crystal substrate.

Next, referring to FIG. 4, an n-type AlN layer 421 (dopant: Si) having a thickness of 1 μm as n-type semiconductor layer 420 is formed on one main surface of this n-type AlN crystal substrate 410 by MOCVD. ) And a 1 μm-thick n-type Al _0.3 Ga _0.7 N layer 422 (dopant: Si), a light-emitting layer 440, and a p-type Al _0.3 Ga _0.7 N layer 431 (dopant: Mg) as a p-type semiconductor layer 430 A p-type Al _0.2 Ga _0.8 N layer 432 (dopant: Mg) having a thickness of 150 nm was sequentially formed to obtain a light-emitting element as a semiconductor device. Here, the light emitting layer 440 is composed of six barrier layers formed of an Al _0.25 Ga _0.70 In _0.05 N layer having a thickness of 10 nm and a well layer formed of an Al _0.20 Ga _0.75 In _0.05 N layer having a thickness of 10 nm. A multi-quantum well structure in which five layers were alternately stacked was used.

Next, as a first electrode 461 on the other main surface of the n-type AlN crystal substrate, a Ti layer with a thickness of 200 nm, an Al layer with a thickness of 1000 nm, a Ti layer with a thickness of 200 nm, and an Au layer with a thickness of 2000 nm Was formed, and the n-side electrode was formed by heating in a nitrogen atmosphere. On the other hand, a stacked structure formed of a 4 nm thick Ni layer and a 4 nm thick Au layer is formed as the second electrode 462 on the p-type Al _0.2 Ga _0.8 N layer 432 and heated in an inert gas atmosphere. As a result, a p-side electrode was formed. After the laminated body was made into a chip, the p-side electrode was bonded to the conductor 482 with a solder layer 470 formed of AuSn. Further, the n-side electrode and the conductor 481 were bonded with a wire 490 to obtain a semiconductor device 400 as a light emitting device.

In this way, a light emitting device is obtained in which the AlN crystal substrate 410 side is the light emitting surface side and the p-type Al _0.2 Ga _0.8 N layer 432 side which is the outermost semiconductor layer of the semiconductor layer 450 is the mounting surface side to the conductor 482. It is done. Moreover, when the emission spectrum of this light-emitting device was measured using the spectroscope, it had a peak wavelength at 330 nm.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a cross-sectional schematic diagram which shows the method of grind | polishing the surface of the AlN crystal | crystallization used for this invention chemically mechanically. It is a cross-sectional schematic diagram which shows the method of carrying out the mechanical grinding of the surface of the AlN crystal used for this invention. It is a cross-sectional schematic diagram which shows the method of carrying out the mechanical polishing of the surface of the AlN crystal used for this invention. It is a cross-sectional schematic diagram which shows one semiconductor device concerning this invention. In this invention, it is a schematic diagram which shows the sublimation furnace which makes an AlN crystal grow by the sublimation method. In this invention, it is a schematic diagram which shows the HVPE apparatus which grows an AlN crystal | crystallization by HVPE method.

Explanation of symbols

1 AlN crystal, 1a Work-affected layer, 5 AlN raw material, 7 Al raw material gas, 8 Nitrogen raw material gas, 9 AlN seed crystal, 11, 21, 31 Crystal holder, 11c, 15c, 21c, 23c, 31c, 35c Rotating shaft, 14, 34 Weight, 15, 35 Surface plate, 16, 36 Abrasive grain, 17 Slurry, 18 Polishing pad, 19 Slurry supply port, 22 Grinding stone, 23 Grinding stone base metal, 50 Sublimation furnace, 51, 61 Reaction vessel, 51a N ₂ Gas inlet, 51c N ₂ gas outlet, 52 crucible, 53 seed crystal protective material, 54 heating element, 55 high frequency heating coil, 56 radiation thermometer, 60 HVPE device, 61a Al source gas inlet, 61b nitrogen source gas introduction Mouth, 61c gas outlet, 62 pedestal, 65 heater, 400 semiconductor device, 410 AlN crystal substrate, 420 n-type semiconductor layer, 421 n-type A N layer, 422 n-type Al _0.3 Ga _0.7 N layer, 430 p-type semiconductor layer, 431 p-type Al _0.3 Ga _0.7 N layer, 432 p-type Al _0.2 Ga _0.8 N layer, 440 light-emitting layer, 450 a semiconductor layer, 461 a first Electrode, 462 second electrode, 470 solder layer, 481, 482 conductor.

Claims (6)

A surface treatment method of an AlN crystal for forming an epitaxial layer for chemically and mechanically polishing the surface of an AlN crystal,
Chemical mechanical abrasive slurry for use in polishing, and high hardness abrasive grains higher hardness than the AlN crystal, viewed contains a low hardness low hardness abrasive grains below the AlN crystal,
A method for surface treatment of an AlN crystal for epitaxial layer formation , wherein the pH of the slurry is 5 or less or 8 or more . Wherein the surface of the AlN crystal mechanical grinding or mechanical polishing, the mechanical grinding or mechanical polishing surface treatment method of the epitaxial layer forming AlN crystal according to claim 1 for polishing chemically mechanically surface of the AlN crystal. The surface treatment method for an AlN crystal for epitaxial layer formation according to claim 1 or 2 , wherein the thickness of the work-affected layer after chemical mechanical polishing of the AlN crystal is 100 nm or less. The surface treatment method of an AlN crystal for epitaxial layer formation according to claim 1 or 2 , wherein the surface roughness Ry after chemical mechanical polishing of the AlN crystal is 5 nm or less. The surface treatment method of an AlN crystal for epitaxial layer formation according to claim 1 or 2 , wherein the surface roughness Ra after chemical mechanical polishing of the AlN crystal is 0.5 nm or less. The method for surface treatment of an AlN crystal for epitaxial layer formation according to any one of claims 1 to 5 , wherein the AlN crystal after chemical mechanical polishing is heat-treated.

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