JP3602299B2 - Substrate for GaN-based crystal growth, method for producing the same, and application - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a GaN-based crystal substrate that can be preferably used as, for example, a substrate of a GaN-based light-emitting element or other members.
[0002]
[Prior art]
As a general method for growing a thick film of a GaN-based semiconductor material, a buffer layer such as ZnO is formed on a sapphire substrate, and a GaN semiconductor material is grown thereon by a hydride vapor phase epitaxial growth method (hereinafter, “HVPE”). There is a way. As an improvement technique, a method using a substrate of spinel, LGO, LAO, ZnO, SiC, or the like instead of a sapphire substrate, a method using an easily cleavable substrate, or a method of selectively growing a mask on a substrate surface is provided. There is a method to make it.
[0003]
[Problems to be solved by the invention]
However, when the GaN-based semiconductor material grows into a thick film, a large stress is applied to the interface due to the difference in the lattice constant and the thermal expansion coefficient between GaN and the sapphire substrate, and there is a problem that GaN is broken and a large substrate cannot be obtained. Was. Further, there is a problem that only a substrate having an extremely large dislocation density (1 × 10 ⁹ cm ⁻² to 1 × 10 ¹⁰ cm ⁻² ) can be obtained. Here, dislocations are defects that occur when a semiconductor layer is grown on a substrate in a state where lattice constants do not match (lattice mismatch), and these dislocations are crystal defects. When the GaN-based semiconductor material is used for a light-emitting element, it functions as a non-radiative recombination center or functions as a current path and causes a leakage current.
[0004]
An object of the present invention is to provide a preferable method of manufacturing a GaN-based crystal growth substrate capable of obtaining a high-quality GaN-based crystal substrate which is thick and does not include defects such as dislocations, and a GaN-based crystal obtained by the manufacturing method. An object of the present invention is to provide a method for manufacturing a GaN-based crystal substrate using a crystal growth substrate.
[0005]
[Means for Solving the Problems]
The present invention has the following features.
(1) (i) A base substrate on which a GaN-based crystal determined by the chemical formula In _X Ga _Y Al _Z N (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, X + Y + Z = 1) can be grown. Forming a GaN-based crystal thin film layer directly or via a buffer layer on one surface of
(ii) a substrate member made of SiO ₂ , Si, GaAs, GaP, LGO or LAO as a material that can be selectively removed by etching with respect to the GaN-based crystal, and having a thickness usable as a substrate, Laminated by bonding on top,
(iii) exposing the surface on the base substrate side of both surfaces of the thin film layer of the GaN-based crystal,
(iv) Using an amorphous body made of a nitride or oxide of an element selected from Si, Ti, Ta and Zr as a material for the mask layer, and using the mask layer to expose the surface of the exposed GaN-based crystal thin film layer. Providing a mask region and a non-mask region on the surface by partially covering the surface.
(2) The method of manufacturing a GaN-based crystal growth substrate according to (1), wherein the base substrate is a C-plane sapphire substrate.
(3) The GaN-based crystal growth method according to (1), wherein the boundary between the mask region and the non-mask region has at least a line segment in the <1-100> direction of the GaN-based crystal of the thin film layer. Substrate manufacturing method.
(4) Using the GaN-based crystal growth substrate obtained by the manufacturing method according to any one of the above (1) to (3), starting from a non-mask region on the substrate as a starting point and covering GaN until the mask layer is covered. A method of manufacturing a GaN-based crystal substrate, comprising a step of etching and removing a layer of a substrate member in the GaN-based crystal growth substrate after growing the base-crystal layer.
(5) Selective etching removal of a GaN-based crystal determined by the chemical formula In _X Ga _Y Al _Z N (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, X + Y + Z = 1) On a substrate member made of possible SiO ₂ , Si, GaAs, GaP, LGO or LAO,
A thin film layer of a GaN-based crystal formed separately from the substrate member is laminated by bonding ,
Further, a mask layer made of an amorphous material made of a nitride or oxide of an element selected from Si, Ti, Ta and Zr is partially laminated on the upper surface of the GaN-based crystal thin film layer. A GaN-based crystal growth substrate, characterized in that:
[0011]
[Action]
In this specification, when the lattice plane of a GaN-based crystal, which is a hexagonal lattice crystal, is designated by four Miller indices (hkil), for convenience of description, if the index is negative, a minus sign is placed before the index. Except for the notation method for the negative exponent, the notation method conforms to the general Miller exponent notation method. Therefore, in the case of a GaN-based crystal, there are six prism surfaces (singular surfaces) parallel to the C axis. For example, one of the surfaces is expressed as (1-100), and the six surfaces are grouped as equivalent surfaces. In this case, it is described as {1-100}. Also, planes perpendicular to the {1-100} plane and parallel to the C axis are equivalently collectively denoted as {11-20}. The direction perpendicular to the (1-100) plane is [1-100], the set of equivalent directions is <1-100>, and the direction perpendicular to the (11-20) plane is [11-20]. A set of directions equivalent to this is denoted as <11-20>. However, in the drawings, when the exponent is negative, the exponent is indicated by adding a minus sign to the exponent, and all the notations of the Miller exponent are followed.
[0012]
The “mask region” and the “non-mask region” are in-plane regions of the GaN-based crystal thin film layer both exposed. The region on the upper surface of the mask layer is regarded as being equal to the mask region, and is used in the description as synonymous.
[0013]
As a countermeasure against cracking of a GaN-based crystal layer caused by a difference in lattice constant and thermal expansion coefficient between a GaN-based crystal (especially, a GaN crystal) and a sapphire crystal substrate, as shown in FIG. Then, a mask layer 2 patterned in a lattice pattern is provided on a base substrate 1, a GaN-based crystal is grown only in the non-mask region 11 where the substrate surface is exposed, and a chip-size GaN is formed on the entire base substrate surface. It has been proposed to prevent cracks by interspersing the system crystal layers 30 (Japanese Patent Laid-Open No. 7-273667).
[0014]
Then, as a result of further research by the present inventors, as shown in FIG. 2B, when the GaN-based crystal layer 30 that has been scattered is further grown, It was confirmed that growth was also performed in the lateral direction from the GaN-based crystal layer 30 onto the mask layer 2. In addition, the growth rate was about the same as that in the thickness direction (C-axis direction), and the crystal orientation dependence was found.
[0015]
Further, the dislocations existing in the GaN-based crystal in the GaN-based crystal layer 30 have a property of being inherited from the base including the base substrate or occurring at any of the growth interfaces and growing together with the crystal growth. As shown in b), it has been found that since there is no underlying layer (growth interface) as a source in the mask region (the region on the mask layer 2), a dislocation-free state is obtained. Further, when the above-described lateral growth is further advanced, as shown in FIG. 2C, the GaN-based crystal completely covers the mask layer 2 and embeds the mask layer, and this region has very few defects. It has been found that a large, thick GaN-based crystal 3 that is flat and free from cracks can be obtained.
[0016]
The GaN-based crystal growth substrate in the figure used for manufacturing the GaN-based crystal shown in FIG. 2 is a laminate of a base substrate 1 and a mask layer 2. Therefore, usually, a crystal substrate having good lattice matching with the GaN-based crystal is formed on the base substrate 1 by a procedure in which the mask layer 2 is subtractively or additively laminated.
[0017]
The present inventors have formed a GaN-based crystal thick film using the GaN-based crystal growth substrate obtained by such a normal lamination method, and have found that the thickness between the base substrate and the GaN-based crystal thick film is low. It has been newly found that warpage occurs in the entire laminate due to the difference in thermal expansion coefficient, and this is a problem to be improved.
[0018]
When the laminate shown in FIG. 2C is manufactured by the normal lamination method as described above, warpage occurs. However, it is difficult to remove the base substrate using a polishing apparatus due to the warpage. It is also difficult to obtain only a crystal layer. In addition, a SiC or sapphire substrate is generally used as the base substrate. However, it is generally difficult to selectively remove such a base substrate from a GaN-based crystal by etching. “Selectively removing a GaN-based crystal by etching” means that even if the same etching process is performed on the GaN-based crystal and another material at the same time, the GaN-based crystal is not removed and only the other material remains. It means that it is removed by etching.
[0019]
In the present invention, when manufacturing a GaN-based crystal growth substrate, first, a GaN-based crystal thin film is provided on the first crystal substrate, and then a separately formed substrate member is joined to laminate. Next, after the first crystal substrate is removed by polishing and turned inside out and a substrate member having a GaN-based crystal thin film layer on its surface as a new base substrate, a special procedure is performed. A mask layer is formed to obtain a GaN-based crystal growth substrate.
[0020]
During the above process, a special procedure of removing the first crystal substrate by polishing and turning it over is important, but in addition, (1) the temperature at which the substrate member is not warped using, for example, water glass. It is important that (2) a material that can be selectively etched away from the GaN-based crystal is used as the material of the substrate member. Due to the above feature (1), warpage in the intermediate step is avoided, and the first crystal substrate can be polished and removed. According to the feature (2), even if a thick film layer of a GaN-based crystal is finally formed and the whole is warped, the substrate member can be removed by etching, and the thick film layer of the GaN-based crystal without the warp can be obtained. Is obtained.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the method of manufacturing a substrate for growing a GaN-based crystal according to the present invention, first, as shown in FIG. 1A, a thin film layer a2 of a GaN-based crystal is directly or directly formed on one surface of a base substrate S1 as shown in FIG. Is formed via a buffer layer a1. The base substrate S1 is a crystal substrate on which a GaN-based crystal can be grown. Next, the substrate member S2 is joined and laminated on the GaN-based crystal thin film layer a2. Further, as shown in FIG. 1B, the base substrate S1 and the buffer layer a1 are removed by polishing to expose one surface a21 of the GaN-based crystal thin film layer a2. In this state, a laminate of the GaN-based crystal thin film layer a2 and the substrate member S2 is newly regarded as a base substrate 1 (hereinafter, this newly regarded base substrate is referred to as a “new base substrate”), and FIG. As shown in ()), the mask layer 2 is partially provided on the thin film layer surface a21 of the GaN-based crystal of the new base substrate 1 to form the mask region 12 and the non-mask region 11, and the GaN-based crystal growth according to the present invention is performed. Obtain a substrate.
[0022]
The base substrate may be any substrate as long as a GaN-based crystal can be grown. For example, sapphire, quartz, SiC, or the like, which has been widely used when growing a GaN-based crystal, may be used. Among them, the sapphire C-plane, A-plane, and 6H-SiC substrate, particularly the C-plane sapphire substrate are preferable.
[0023]
The GaN-based crystal includes In _X Ga _Y Al _Z N (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, both the target crystal layer to be formed as a thick film on the thin film layer and the mask layer). X + Y + Z = 1) is a binary or more semiconductor crystal determined by (1). In particular, GaN is useful as a thick film layer.
[0024]
When a thin film layer of a GaN-based crystal is formed on a base substrate surface via a buffer layer, the buffer layer is formed using a known buffer layer material such as AlN, GaN, InN, or a compound thereof, or ZnO, MgO. It may be formed by a technique.
[0025]
As a preferred example of the base substrate S1 to the GaN-based crystal thin film layer a2 shown in FIG. 1A, a buffer layer a1, such as GaN or AlN, is formed on a C-plane sapphire substrate S1 by MOVPE, and then a GaN or GaAlN thin film An example in which the layer a2 is sequentially formed. By such a combination, the density of dislocations newly generated in the thin film layer a2 and further in the target thick film layer of the GaN-based crystal can be kept low, and relatively good crystallinity can be obtained even on the non-mask region. Can be obtained.
[0026]
The material of the substrate member should be a material that can be used as a substrate, can support the thin film layer a2 at the start of the growth of a thick GaN-based crystal layer described later, and can be selectively etched away from the GaN-based crystal. For example, SiO ₂ , Si, GaAs, GaP, LGO, LAO, etc. may be used.
[0027]
In particular, when SiO ₂ , Si, or the like, in which a GaN-based crystal cannot substantially grow, is used as the material of the substrate member, the obtained GaN-based crystal growth substrate can be selectively removed by etching with respect to the GaN-based crystal. And a special structure in which a thin film layer of a GaN-based crystal is laminated on a substrate made of a material that cannot substantially grow a GaN-based crystal, and a mask layer is partially laminated thereon. It becomes a substrate.
[0028]
The thickness of the substrate member is not limited, but may be any thickness that can become a new substrate after the first crystal substrate is polished and removed, and is preferably 100 μm or more.
Examples of the etching method include etching with an acid for a SiO ₂ substrate member and etching with a hydrofluoric acid + nitric acid (hydrofluoric nitric acid) for a Si substrate member.
[0029]
The bonding between the substrate member and the thin film layer is preferably performed using water glass as a bonding agent when the substrate member is SiO ₂ . Examples of the water glass include a concentrated aqueous solution of an alkali silicate.
By using the water glass as a bonding agent and bonding the substrate member onto the GaN-based crystal thin film layer at a low temperature of about 85 ° C. to 200 ° C., the base substrate and the substrate member can be laminated without warpage. Become.
When Si, GaAs, or the like is used as the substrate member, the bonding with the thin film layer can be performed by mirror-finish-bonding the two, followed by heating and pressing.
[0030]
The method of removing the base substrate and the buffer layer for exposing one surface (a21 in FIG. 1) of the GaN-based crystal thin film layer can be performed by a general polishing method.
[0031]
Since the mask layer is a layer intended to substantially limit the growth of GaN-based crystals from the surface of the new base substrate, the material constituting the mask layer is substantially from its own surface. It is necessary that the GaN-based crystal cannot grow. As such a material, for example, an amorphous body is exemplified, and as the amorphous body, a nitride or an oxide such as Si, Ti, Ta, or Zr is exemplified. In particular, a SiO ₂ film which is excellent in heat resistance and relatively easy to form and remove by etching can be preferably used.
[0032]
The mask layer is formed so as to cover the entire surface of the substrate by a method such as vacuum deposition, sputtering, or CVD, and then the photosensitive resist is patterned by a normal photolithography technique, and a part of the substrate is exposed by etching. And the like.
[0033]
The boundary line between the mask region and the non-mask region is at least in the <1-100> direction of the GaN-based crystal growing on the new base substrate (= the <1-100> direction of the thin film layer of the GaN-based crystal on the surface layer of the new base substrate). ) Is preferably formed. Thus, the {11-20} plane of the GaN-based crystal is secured as a plane that grows along the upper surface of the mask layer. The {11-20} plane is an unstable face, and is a face that grows faster than the stable {1-100} face.
[0034]
The method of manufacturing a GaN-based crystal substrate according to the present invention is a method of growing a GaN-based crystal using the above-described GaN-based crystal growth substrate, and then removing the substrate member by etching to obtain a GaN-based crystal layer. The etching of the substrate member is as described above. The growth of the GaN-based crystal starts with the non-mask region 11 of the new base substrate 1 shown in FIG. When the growth is continued, the space between the mask layers is filled with the GaN-based crystal as shown in FIG. 2A, and the GaN-based crystal is higher than the upper surface of the mask layer as shown in FIG. 2B. Swell. At this time, the GaN-based crystal starts growing not only in the height direction (C-axis direction) but also in the lateral direction starting from the side surface of the bulging portion. Eventually, it merges with the growing crystal starting from the adjacent non-mask region, and eventually, as shown in FIG. 2C, completely covers the mask layer 2 and continues to grow in the thickness direction. A GaN-based crystal layer 3 is formed.
[0035]
In the GaN-based crystal layer, as shown in FIG. 2C, a portion such as a dislocation may be inherited in a portion on the non-mask region. However, since at least the portion on the mask region is formed by lateral growth starting from the side surface of the bulging portion (the surface on which no defect such as dislocation exists), there is no defect such as dislocation. It is a very high quality crystal. Moreover, the direct contact portion between the GaN-based crystal layer and the new base substrate is only the non-mask region, the contact area is small, and the GaN-based crystal layer is hardly affected by the difference in the coefficient of thermal expansion. There is also an advantage that it can be easily grown.
[0036]
The method of growing the GaN-based crystal is not limited, and examples thereof include HVPE, MOVPE, and MBE. Among them, HVPE is particularly preferable because it has an advantage that the growth rate is very high.
[0037]
【Example】
Example 1
[Manufacture of GaN-based crystal growth substrate]
As shown in FIG. 1A, a 20-nm-thick AlN buffer layer a1 is grown at a low temperature on a C-plane sapphire substrate S1 having a diameter of 2 inches and a thickness of 330 μm using a MOVPE apparatus. A crystalline thin film layer a2 was grown. Further thereon, a 150 μm thick SiO ₂ substrate member S2 was laminated using water glass as an adhesive. Next, lapping and polishing are performed to remove the C-plane sapphire substrate S1 and the AlN buffer layer a1, exposing one surface a21 of the GaN crystal thin film layer a2, and obtaining a new base substrate 1 shown in FIG. 1B. .
[0038]
A mask layer composed of a SiO ₂ thin film was formed on the surface of the new base substrate 1 by a sputtering method so as to form a linear stripe pattern, thereby obtaining a GaN-based crystal growth substrate according to the present invention. The mask layer was formed as a band extending in the <1-100> direction, and had a thickness of 0.5 μm, a band width of 5 μm, and a width between bands (width of the non-mask region) of 10 μm.
[0039]
[Formation of GaN crystal layer]
The GaN-based crystal growth substrate was loaded into an HVPE apparatus, and as shown in FIG. 2, a 200 μm GaN crystal layer was formed starting from a non-mask region. The GaN crystal grew also on the mask layer in the lateral direction and completely covered the mask layer.
At this time, the entire laminate was warped.
[0040]
[Removal of substrate member; formation of GaN crystal substrate]
The substrate member was immersed in an aqueous HF solution and removed by etching to obtain a 200 μm-thick GaN crystal substrate including a mask layer therein. The warp of the GaN crystal substrate returned, and the GaN crystal substrate was flat and high quality.
[0041]
【The invention's effect】
The GaN-based crystal growth substrate obtained by the manufacturing method of the present invention has a new base substrate having a substrate member made of a material that can be selectively removed by etching with respect to the GaN-based crystal. Moreover, the substrate member has a wide range of material choices, regardless of whether GaN-based crystals can be grown or not.
After the target GaN-based crystal thick film layer is formed, only the substrate member is removed by etching, whereby the entire GaN-based crystal thick film layer is restored from warping, and a flat, high-quality GaN-based crystal substrate is obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a manufacturing method of the present invention.
FIG. 2 is a diagram showing an example of a state in which a GaN-based single crystal grows on a mask layer.
[Explanation of symbols]
S1 Base substrate a1 Buffer layer a2 Thin film layer of GaN-based crystal S2 Substrate member 2 Mask layer 11 Non-mask region 12 Mask region

Claims (5)

(i) One of the base substrates on which a GaN-based crystal determined by the chemical formula In _X Ga _Y Al _Z N (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, X + Y + Z = 1) can be grown A GaN-based thin film layer is formed directly or via a buffer layer on the surface,
(ii) a substrate member made of SiO ₂ , Si, GaAs, GaP, LGO or LAO as a material that can be selectively removed by etching with respect to the GaN-based crystal , and having a thickness usable as a substrate, Laminated by bonding on top,
(iii) exposing the surface on the base substrate side of both surfaces of the thin film layer of the GaN-based crystal,
(iv) Using an amorphous body made of a nitride or oxide of an element selected from Si, Ti, Ta and Zr as a material for the mask layer , and using the mask layer to expose the exposed surface of the thin film layer of the GaN-based crystal. Providing a mask region and a non-mask region on the surface by partially covering the surface. 2. The method according to claim 1, wherein the base substrate is a C-plane sapphire substrate. 2. The method of manufacturing a GaN-based crystal growth substrate according to claim 1, wherein a boundary between the masked region and the unmasked region has at least a line segment in the <1-100> direction of the GaN-based crystal of the thin film layer. . A GaN-based crystal layer is grown using the GaN-based crystal growth substrate obtained by the method according to any one of claims 1 to 3 until a mask layer is covered starting from a non-mask region on the substrate. Forming a GaN-based crystal substrate on the GaN-based crystal growth substrate by etching. SiO that can be selectively etched away from a GaN-based crystal determined by the chemical formula In _X Ga _Y Al _Z N (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, X + Y + Z = 1) ₂ , on a substrate member made of Si, GaAs, GaP, LGO or LAO,
A thin film layer of a GaN-based crystal formed separately from the substrate member is laminated by bonding ,
Further, a mask layer made of an amorphous material made of a nitride or oxide of an element selected from Si, Ti, Ta and Zr is partially laminated on the upper surface of the GaN-based crystal thin film layer. A GaN-based crystal growth substrate, characterized in that:

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