Patent Grant
11453956
This disclosure relates to techniques for processing materials in supercritical fluids. Embodiments of the disclosure include techniques for material processing in a capsule disposed within a high-pressure apparatus enclosure. The methods can be applied to growing crystals of GaN, AlN, InN, and their alloys, including, for example, InGaN, AlGaN, and AlInGaN, and others for the manufacture of bulk or patterned substrates. Such bulk or patterned substrates can be used for a variety of applications including optoelectronic devices, lasers, light emitting diodes, solar cells, photoelectrochemical water splitting and hydrogen generation devices, photodetectors, integrated circuits, and transistors, among other devices.
Large area, high quality crystals and substrates, for example, nitride crystals and substrates, are needed for a variety of applications, including light emitting diodes, laser diodes, transistors, and photodetectors. In general, there is an economy of scale with device processing, such that the cost per device is reduced as the diameter of the substrate is increased. In addition, large area seed crystals are needed for bulk nitride crystal growth.
There are known methods for fabrication of large area gallium nitride (GaN) crystals with a (0 0 0 1) c-plane orientation. In many cases, hydride vapor phase epitaxy (HVPE) is used to deposit thick layers of gallium nitride on a non-gallium-nitride substrate such as sapphire, followed by the removal of the substrate. These methods have demonstrated capability for producing free-standing c-plane GaN wafers 50-75 millimeters in diameter, and it is expected that GaN wafers with diameters as large as 100 millimeter can be produced. The typical average dislocation density, however, in these crystals, about 106-108 cm−2, is too high for many applications. Techniques have been developed to gather the dislocations into bundles or low-angle grain boundaries, but it is still very difficult to produce dislocation densities below 104 cm−2 in a large area single grain by these methods, and the relatively high concentration of high-dislocation-density bundles or grain boundaries creates difficulties such as performance degradation and/or yield losses for the device manufacturer.
The non-polar planes of gallium nitride, such as {1 0 −1 0} and {1 1 −2 0}, and the semi-polar planes of gallium nitride, such as {1 0 −1 ±1}, {1 0 −1 ±2}, {1 0 −1 3}, and {1 1 −2 ±2}, {2 0 −2 1} are attractive for a number of applications. Unfortunately, no large area, high quality non-polar or semi-polar GaN wafers are generally available for large scale commercial applications. Other conventional methods for growing very high quality GaN crystals, for example, with a dislocation density less than 104 cm−2 have been proposed. These crystals, however, are typically small, less than 1-5 centimeters in diameter, and are not commercially available.
Legacy techniques have suggested a method for merging elementary GaN seed crystals into a larger compound crystal by a tiling method. Some of the legacy methods use elementary GaN seed crystals grown by hydride vapor phase epitaxy (HVPE) and polishing the edges of the elementary crystals at oblique angles to cause merger in fast-growing directions. Such legacy techniques, however, have limitations. For example, legacy techniques do not specify the accuracy of the crystallographic orientation between the merged elementary seed crystals they provide a method capable of producing highly accurate crystallographic registry between the elementary seed crystals and the observed defects resulting from the merging of the elementary seed crystals.
Conventional techniques are inadequate for at least the reason of failing to meaningfully increase the available size of high-quality nitride crystals while maintaining extremely accurate crystallographic orientation across the crystals.
This disclosure provides a method for growth of a large-area, gallium-containing nitride crystal. The method includes providing at least two nitride crystals having a dislocation density below about 107 cm−2 together with a handle substrate. The nitride crystals are bonded to the handle substrate. Then, the nitride crystals are grown to coalescence into a merged nitride crystal. The polar misorientation angle γ between the first nitride crystal and the second nitride crystal is greater than about 0.005 degree and less than about 0.5 degree and the azimuthal misorientation angles α and β are greater than about 0.01 degree and less than about 1 degree. A semiconductor structure can be formed on the nitride crystals as desired.
In another embodiment, the disclosure includes the steps above, and also includes methods of providing a release layer and a high quality epitaxial layer on each of the two nitride crystals. The epitaxial layers are grown to cause coalescence of the two nitride crystals into a merged nitride crystal. The polar misorientation angle γ between the first nitride crystal and the second nitride crystal is less than 0.5 degree and azimuthal misorientation angles α and β are less than 1 degree.
The disclosed methods can provide a crystal that includes at least two single crystal domains having a nitride composition and characterized by a dislocation density within each of the domains of less than 107 cm−2. Each of the at least two single crystal domains is separated by a line of dislocations with a linear density greater than 50 cm−1 and less than 5×105 cm−1. The polar misorientation angle γ between the first domain and the second domain is less than 0.5 degree and the azimuthal misorientation angles α and β are less than 1 degree.
In a first aspect, crystals comprising at least two single crystal domains having a nitride composition are disclosed comprising: a first domain having a first thickness, a first lateral dimension, and a second lateral dimension, wherein the first lateral dimension and the second lateral dimension define a plane that is perpendicular to the first thickness, and each of the first lateral dimension and the second lateral dimension is greater than about 2 millimeters; and a second domain having a second thickness, a third lateral dimension and a fourth lateral dimension, wherein the third lateral dimension and the fourth later dimension define a plane that is perpendicular to the second thickness, wherein each of the third lateral dimension and the fourth lateral dimension is greater than about 2 millimeters; wherein each of the at least two single crystal domains are characterized by a dislocation density of less than 107 cm−2, are separated by a line of dislocations with a linear density between about 50 cm−1 and about 5×105 cm−1, and a polar misorientation angle γ between the first domain and the second domain is greater than about 0.005 degrees and less than about 0.5 degrees and misorientation angles α and β are greater than about 0.01 degrees and less than about 1 degree.
In a second aspect, method of fabricating a crystal are disclosed, comprising: providing at least two crystals, each of the at least two crystals characterized by a dislocation density below about 107 cm−2; providing a handled substrate; bonding the at least two crystals to the handle substrate; and growing the at least two crystals to cause a coalescence into a merged crystal; wherein the merged crystal comprises a first domain and a second domain characterized by a polar misorientation angle γ between the first domain and the second domain is greater than about 0.005 degrees and less than about 0.5 degrees and the misorientation angles α and β between the first domain and the second domain are greater than about 0.01 degrees and less than about 1 degree.
Referring to
Nitride crystal 101 may comprise regions characterized by a relatively high concentration of threading dislocations separated by one or more regions characterized by a relatively low concentration of threading dislocations. The concentration of threading dislocations in the relatively high concentration regions may be greater than about 106 cm−2, 107 cm−2, or in certain embodiments, greater than about 108 cm−2. The concentration of threading dislocations in the relatively low concentration regions may be less than about 106 cm−2, 105 cm−2, or in certain embodiments, less than about 104 cm−2. The thickness of nitride crystal 101 may be between about 10 microns and about 100 millimeters, or in certain embodiments, between about 0.1 millimeter and about 10 millimeters. Crystal 101 may have a first lateral dimension and a second lateral dimension, the lateral dimensions defining a plane that is perpendicular to the thickness of the nitride crystal 101, where each of the first lateral dimension and the second lateral dimension may be at least about 0.5 millimeter, 1 millimeter, 2 millimeters, 4 millimeters, 5 millimeters, 10 millimeters, 15 millimeters, 20 millimeters, 25 millimeters, 35 millimeters, 50 millimeters, 75 millimeters, 100 millimeters, 150 millimeters, or in certain embodiments, at least about 200 millimeters. Surface 105 may be characterized by a crystallographic orientation within 5 degrees, within 2 degrees, within 1 degree, within 0.5 degree, within 0.2 degree, within 0.1 degree, within 0.05 degree, within 0.02 degree, or in certain embodiments, within about 0.01 degree of the (0 0 0 1) Ga-polar plane, the (0 0 0 −1) N-polar plane, the {1 0 −1 0} non-polar plane, or the {1 1 −2 0} non-polar a-plane. Surface 105 may be characterized by a (h k i l) semi-polar orientation, where i=−(h+k) and l and at least one of h and k are nonzero.
In certain embodiments, the crystallographic orientation of surface 105 is within 5 degrees, 2 degrees, 1 degree, 0.5 degree, 0.2 degree, 0.1 degree, 0.05 degree, 0.02 degree, or in certain embodiments, within 0.01 degree of any one of the {1 1 −2 ±2} plane, the {6 0 −6 ±1} plane, the {5 0 −5 ±1} plane, the {40 −4 ±1} plane, the {3 0 −3 ±1} plane, the {5 0 −5 ±2} plane, the {7 0 −7 3} plane, the plane, the {2 0 −2 ±1} plane, the {3 0 −3 ±2} plane, the {4 0 −4 ±3} plane, the {5 0 −5 ±4} plane, the {1 0 −1 ±1} plane, the {1 0 −1 ±2} plane, the {1 0 −1 ±3} plane, the {2 1 −3 ±1} plane, or the {3 0 −3 ±4} plane. Nitride crystal 101 may have a minimum lateral dimension of at least two millimeters, but it can be four millimeters, one centimeter, two centimeters, three centimeters, four centimeters, five centimeters, six centimeters, eight centimeters, or in certain embodiments at least ten centimeters. In other embodiments, crystal 101 is characterized by a cubic crystal structure. In some embodiments, crystal 101 has a cubic diamond structure and is selected from diamond, silicon, germanium, and silicon germanium. In other embodiments, crystal 101 is characterized by a cubic zincblende structure and is selected from cubic BN, BP, BAs, AlP, AlAs, AlSb, β-SiC, GaP, GaAs, GaSb, InP, InAs, ZnS, ZnSe, CdS, CdSe, CdTe, CdZeTe, and HgCdTe. In certain embodiments, the crystallographic orientation of surface 105 is within 5 degrees, 2 degrees, 1 degree, 0.5 degree, 0.2 degree, 0.1 degree, 0.05 degree, 0.02 degree, or in certain embodiments within 0.01 degree of one of the {1 1 1} plane, the {1 1 0} plane, the {1 0 0} plane, the {3 1} plane, and the {2 1 1} plane.
In some embodiments, nitride crystal 101 is grown by hydride vapor phase epitaxy (HVPE) according to known methods. In other embodiments, nitride crystal 101 is grown by molecular beam epitaxy (MBE) or metalorganic chemical vapor deposition (MOCVD). Nitride crystal 101 may be grown on a heteroepitaxial substrate such as sapphire, silicon carbide, or gallium arsenide. In some embodiments, nitride crystal 101 is grown by a flux or high temperature solution method. In one specific embodiment, nitride crystal 101 is grown in a solution comprising gallium metal at a temperature between about 1,400 degrees Celsius and about 1,600 degrees Celsius and a nitrogen pressure between about 10 kbar and about 30 kbar. In some embodiments, nitride crystal 101 is grown ammonothermally. In certain embodiments, nitride crystal 101 is characterized by an atomic impurity concentration of hydrogen (H) greater than about 1×1016 cm−3, greater than about 1×1017 cm−3, or greater than about 1×1018 cm−3. In certain embodiments, a ratio of the atomic impurity concentration of H to an atomic impurity concentration of oxygen (O) is between about 1.1 and about 1000, or between about 5 and about 100. In some embodiments, nitride crystal 101 is characterized by an impurity concentration greater than about 1015 cm−1 of at least one of Li, Na, K, Rb, Cs, Mg, Ca, F, and Cl. In some embodiments, nitride crystal 101 is characterized by an impurity concentration greater than about 1014 cm−1 of at least one of Be, Mg, Ca, Sr, Ba, Sc, Y, a rare earth element, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W. In certain embodiments, nitride crystal 101 is characterized by an impurity concentration of O, H, carbon (C), Na, and K between about 1×1016 cm−3 and 1×1019 cm−3, between about 1×1016 cm−3 and 2×1019 cm−3, below 1×1017 cm−3, below 1×1016 cm−3, and below 1×1016 cm−3, respectively, as quantified by calibrated secondary ion mass spectrometry (SIMS). In another embodiment, nitride crystal 101 is characterized by an impurity concentration of O, H, C, and at least one of Na and K between about 1×1016 cm−3 and 1×1019 cm−3, between about 1×1016 cm−3 and 2×1019 cm−3, below 1×1017 cm−3, and between about 3×1015 cm−3 and 1×1018 cm−3, respectively, as quantified by calibrated secondary ion mass spectrometry (SIMS). In still another embodiment, nitride crystal 101 his characterized by an impurity concentration of O, H, C, and at least one of F and Cl between about 1×1016 cm−3 and 1×1019 cm−3, between about 1×1016 cm−3 and 2×1019 cm−3, below 1×1017 cm−3, and between about 1×1015 cm−3 and 1×1017 cm−3, respectively, as quantified by calibrated secondary ion mass spectrometry (SIMS). In some embodiments, nitride crystal 101 is characterized by an impurity concentration of H between about 5×1017 cm−3 and 1×1019 cm−3, as quantified by calibrated secondary ion mass spectrometry (SIMS). In certain embodiments, nitride crystal 101 is characterized by an impurity concentration of copper (Cu), manganese (Mn), and iron (Fe) between about 1×1016 cm−3 and 1×1019 cm−3.
One of the steps in the preparation of nitride crystal 101 can be lateral growth from a seed crystal. Referring to
In certain embodiments, nitride crystal 101 may be substantially free of stacking faults. The concentrations of threading dislocations and stacking faults can be quantified on polar (±c-plane) and nonpolar (e.g., m-plane) and a range of semipolar planes, on both HVPE GaN and ammonothermal GaN, by etching in a molten salt comprising one or more of NaOH and KOH, or in a solution comprising one or more of H3PO4 and H3PO4 that has been conditioned by prolonged heat treatment to form polyphosphoric acid, and H2SO4, at temperatures between about 100 degrees Celsius and about 500 degrees Celsius for times between about 5 minutes and about 5 hours; where the processing temperature and time are selected so as to cause formation of etch pits with diameters between about 1 micrometer and about 25 micrometers. Large area nonpolar and semipolar nitride crystals that are substantially free of stacking faults, that is, where the stacking fault concentration is below about 103 cm−1, below about 102 cm−1, below about 10 cm−1, or below about 1 cm−1, may be prepared by extended ammonothermal lateral growth from a seed crystal to form a wing or sector followed by separation of the laterally-grown wing or sector from the seed and removal of residual defective material from the laterally-grown wing or sector.
Referring again to
In some embodiments, at least one edge, at least two edges, or at least three edges of nitride crystal 101 are as-grown. In some embodiments, at least one edge, at least two edges, or at least three edges of nitride crystal 101 are cleaved. In some embodiments, at least one edge, at least two edges, or at least three edges of nitride crystal 101 are diced, sawed, ground, lapped, polished, and/or etched, for example, by reactive ion etching (RIE) or inductively-coupled plasma (ICP). In one specific embodiment, one or more edges of the surface of crystal 101 are defined by etching one or more trenches in a larger crystal. In some embodiments, at least one edge, at least two edges, or at least three edges of nitride crystal 101 have a {1 0 −1 0} m-plane orientation. In one specific embodiment, nitride crystal 101 has a substantially hexagonal shape. In another specific embodiment, nitride crystal 101 has a substantially rhombus or half-rhombus shape. In still other embodiments, nitride crystal 101 is substantially rectangular. In one specific embodiment, nitride crystal 101 has a (0 0 0 1)+c-plane edge and a (0 0 0 −1)-c-plane edge. In another specific embodiment, nitride crystal 101 has two {1 1 −2 0} edges. In yet another specific embodiment, nitride crystal 101 has two {1 0 −1 0} edges. In still another specific embodiment, crystal 101 has a cubic crystal structure and at least one edge, at least two edges, or at least three edges have a {111} orientation. In yet another, specific embodiment, crystal 101 has a cubic zincblende crystal structure and at least one edge, at least two edges, or at least three edges have a {110} orientation.
Referring to
Referring to
In certain embodiments, the release layer 107 comprises nitrogen and at least one element selected from Si, Sc, Ti, V, Cr, Y, Zr, Nb, Mo, a rare earth element, Hf, Ta, and W. A metal layer may be deposited on the base crystal, to a thickness between about 1 nm and about 1 micron by sputtering, thermal evaporation, e-beam evaporation, or the like. The metal layer may then be nitrided by heating in a nitrogen-containing atmosphere such as ammonia at a temperature between about 600 degrees Celsius and about 1,200 degrees Celsius. During the nitridation process the metal partially de-wets from the base crystal, creating nano-to-micro openings through which high quality epitaxy can take place. The nitridation step may be performed in an MOCVD reactor, in an HVPE reactor, or in an ammonothermal reactor immediately prior to deposition of a high quality epitaxial layer.
In certain embodiments, the release layer 107 comprises AlxInyGa1-x-yN, where 0≤x, y, x+y≤1, but may not have an optical absorption coefficient larger than that of nitride crystal 101. In a particular embodiment, nitride crystal 101 comprises GaN and release layer 107 comprises Al1-xInxN, where x is approximately equal to 0.17 so that the release layer is lattice-matched to nitride crystal 101, also known as the nitride base crystal.
Referring to
The high quality epitaxial layer 109 has the same crystallographic orientation as nitride crystal 101, to within about 0.5 degree, within 0.2 degree, within 0.1 degree, within 0.05 degree, within 0.02 degree, or within 0.01 degree, and very similar crystallographic properties. High quality epitaxial layer 109 may be between 0.1 micron and 50 microns thick, comprises nitrogen and may have a surface dislocation density below 107 cm−2. In particular embodiments, high quality epitaxial layer 109 comprises GaN or AlxInyGa(1-x-y)N, where 0≤x, y≤1 and is characterized by high crystallographic quality. High quality epitaxial layer 109 may be characterized by a surface dislocation density less than about 107 cm−2, less than about 106 cm−2, less than about 105 cm−2, less than about 104 cm−2, less than about 103 cm−2, or less than about 102 cm−2. High quality epitaxial layer 109 may be characterized by a stacking-fault concentration below 103 cm−1, below 102 cm−1, below 10 cm−1 or below 1 cm−1. High quality epitaxial layer 109 may be characterized by a symmetric x-ray rocking curve full width at half maximum (FWHM) less than about 300 arc sec, less than about 200 arc sec, less than about 100 arc sec, less than about 50 arc sec, less than about 35 arc sec, less than about 25 arc sec, or less than about 15 arc sec. In some embodiments, the high quality epitaxial layer is substantially transparent, with an optical absorption coefficient below 100 cm−1, below 50 cm−1, below 5 cm−1, or below 1 cm−1 at wavelengths between about 700 nm and about 3,077 nm and at wavelengths between about 3,333 nm and about 6,667 nm. In some embodiments, the high quality epitaxial layer is substantially free of low angle grain boundaries, or tilt boundaries. In other embodiments, the high quality epitaxial layer comprises at least two tilt boundaries, with the separation between adjacent tilt boundaries not less than 3 mm. The high quality epitaxial layer may have impurity concentrations of O, H, C, Na, and K below 1×1017 cm−3, 2×1017 cm−3, 1×1017 cm−3, 1×1016 cm−3, and 1×1016 cm−3, respectively, as quantified by calibrated secondary ion mass spectrometry (SIMS), glow discharge mass spectrometry (GDMS), interstitial gas analysis (IGA), or the like.
Referring again to
Referring to
Referring to
Referring to
An adhesion layer 113 may be deposited on surface 115 of handle substrate 117. Adhesion layer 113 may comprise at least one of SiO2, GeO2, SiNx, AlNx, or B, Al, Si, P, Zn, Ga, Si, Ge, Au, Ag, Ni, Ti, Cr, Zn, Cd, In, Sn, Sb, Tl, W, In, Cu, or Pb, or an oxide, nitride, or oxynitride thereof. Adhesion layer 113 may further comprise hydrogen. The adhesion layer 113 may be deposited by thermal evaporation, electron-beam evaporation, sputtering, chemical vapor deposition, plasma-enhanced chemical vapor deposition, electroplating, or the like, or by thermal oxidation of a deposited metallic film. The thickness of adhesion layer 113 may, for example, between about 1 nanometer and about 10 microns, or between about 10 nanometers and about 1 micron. Adhesion layer 113 may comprise a non-homogenous composition. In some embodiments, adhesion layer 113 comprises a stack of thin films of varying compositions or a film of graded or continuously-varying composition. In some embodiments, adhesion layer 113 or at least one thin film contained within adhesion layer 113 is laterally non-uniform. In some embodiments, adhesion layer 113 or at least one thin film contained within comprises an array of dots, squares, rectangle, lines, a grid pattern, or the like. The composition of adhesion layer 113 may be chosen so as to undergo nascent melting at a temperature below about 300 degrees Celsius, below about 400 degrees Celsius, or below about 500 degrees Celsius. The composition of adhesion layer 113 may be chosen so as to have a melting point above about 600 degrees Celsius, above about 700 degrees Celsius, above about 800 degrees Celsius, or above about 900 degrees Celsius. The composition and structure of adhesion layer 113 may be chosen so as to undergo nascent melting at a temperature below about 300 degrees Celsius, below about 400 degrees Celsius, below about 500 degrees Celsius, or below about 600 degrees Celsius, then, following a thermal treatment at a temperature below the solidus temperature, to remain unmelted, or with a volume fraction of melt below about 20%, below about 10%, or below about 5%, at a temperature above about 600 degrees Celsius, above about 700 degrees Celsius, above about 800 degrees Celsius, or above about 900 degrees Celsius. In some embodiments, an adhesion layer is deposited on surface 105 of nitride crystal 101 or on surface 111 of high quality epitaxial layer 109 (not shown). The adhesion layer(s) may be annealed, for example, to a temperature between about 300 degrees Celsius and about 1,000 degrees Celsius. In some embodiments, an adhesion layer is deposited on surface 105 of crystal 101 and annealed prior to forming an implanted/damaged layer by ion implantation. In some embodiments, at least one adhesion layer is chemical-mechanically polished. In a particular embodiment, the root-mean-square surface roughness of at least one adhesion layer may be below about 0.5 nanometer, or below about 0.3 nanometer over a 20×20 μm2 area. As shown in
Referring to
The positional and orientational accuracy of the placement of nitride crystal 101 with respect to handle substrate 117 may be precisely controlled. In one specific embodiment, nitride crystal is placed on handle substrate 117 by a pick and place machine, or robot, or a die attach tool. Nitride crystal 101 may be picked up by a vacuum chuck, translated to the desired position above handle substrate 117 by a stepper-motor-driven x-y stage, re-oriented, if necessary, by a digital-camera-driven rotational drive, and lowered onto the handle substrate. The positional accuracy of placement may be better than 50 microns, better than 30 microns, better than 20 microns, better than 10 microns, or better than 5 microns. The orientational accuracy of placement may be better than 5 degrees, better than 2 degrees, better than 1 degree, better than 0.5 degree, better than 0.2 degree, better than 0.1 degree, better than 0.05 degree, better than 0.02 degree, or better than 0.01 degree. In another specific embodiment, block 112, attached to nitride crystal 101, is placed in a kinematic mount. The kinematic mount establishes orientational accuracy with respect to handle substrate 117 that is better than 1 degree, better than 0.5 degree, better than 0.2 degree, better than 0.1 degree, better than 0.05 degree, better than 0.02 degree, or better than 0.01 degree. Nitride crystal 101, block 112, and the kinematic mount may then be positioned with respect to handle substrate 117 with submicron accuracy using an x-y stage similar to that in a stepper photolithography tool, using stepper motors in conjunction with voice coils. In some embodiments, the azimuthal crystallographic orientations of crystal 101 and handle substrate 117 are equivalent to within about 10 degrees, within about 5 degrees, within about 2 degrees, or within about 1 degree.
Nitride crystal 101 may be pressed against handle substrate 117 with a pressure between about 0.001 megapascals and about 100 megapascals. In some embodiments, van der Waals forces or capillarity associated with nascent melting of the adhesion layer(s) are sufficient to obtain a good bond and very little or no additional applied force is necessary. Nitride crystal 101 and handle substrate 117 may be heated to a temperature between about 30 degrees Celsius and about 950 degrees Celsius, between about 30 degrees Celsius and about 400 degrees Celsius, between about 30 degrees Celsius and about 200 degrees Celsius to strengthen the bond. In some embodiments, heating of nitride crystal 101 and handle substrate 117 is performed while they are placed in mechanical contact and/or mechanically loaded against one another.
In some embodiments, at least the surface region of bonded nitride crystal 101 having implanted/damaged region 103 and handle substrate 117 are heated to a temperature between about 200 degrees Celsius and about 800 degrees Celsius or between about 500 degrees Celsius and about 700 degrees Celsius to cause micro-bubbles, micro-cracks, micro-blisters, or other mechanical flaws within region 103. In one specific embodiment, surface 105 or high quality epitaxial layer 109 is heated by means of optical or infrared radiation through handle substrate 117, and the distal portion of crystal 101, which may be in contact with block 112 (not shown), may remain less than about 300 degrees Celsius, less than about 200 degrees Celsius, or less than about 100 degrees Celsius. In some embodiments, mechanical energy may be provided instead of or in addition to thermal energy. In some embodiments, an energy source such as a pressurized fluid is directed to a selected region, such as an edge, of bonded nitride crystal 101 to initiate a controlled cleaving action within region 103. After the application of energy, the distal portion of nitride crystal 101 is removed, leaving a proximate portion of nitride crystal 101 bonded to handle substrate 117. In some embodiments, distal portion of nitride crystal 101 remains bonded to block 112 (not shown). In some embodiments, the newly exposed surface of distal portion of nitride crystal 101 is polished, dry-etched, or chemical-mechanically polished. Care is taken to maintain the surface crystallographic orientation of the newly exposed surface of distal portion of nitride crystal 101 the same as the original orientation of surface 105. In some embodiments, an adhesion layer is deposited on the newly exposed surface of distal portion of crystal 101. In some embodiments, the adhesion layer is chemical-mechanically polished.
Referring to
In some embodiments, multiple release layers and high quality epitaxial layers are present in the wafer-bonded stack. In this case laser illumination is preferably applied through the handle substrate, and the fluence controlled so that substantial decomposition takes place only within the release layer closest to the handle substrate and the remaining release layers and high quality epitaxial layers remain bonded to the nitride crystal after liftoff.
After separation of the high quality epitaxial layer from the nitride crystal, any residual gallium, indium, or other metal or nitride on the newly exposed back surface of the high quality epitaxial layer, on nitride crystal 101, or on another newly-exposed high quality epitaxial layer still bonded to nitride crystal 101 may be removed by treatment with at least one of hydrogen peroxide, an alkali hydroxide, tetramethylammonium hydroxide, an ammonium salt of a rare-earth nitrate, perchloric acid, sulfuric acid, nitric acid, acetic acid, hydrochloric acid, and hydrofluoric acid. The surfaces may be further cleaned or damage removed by dry-etching in at least one of Ar, Cl2, and BCl3, by techniques such as chemically-assisted ion beam etching (CAIBE), inductively coupled plasma (ICP) etching, or reactive ion etching (RIE). The surfaces may be further treated by chemical mechanical polishing.
In some embodiments, traces of the release layer may remain after laser liftoff or etching from the edges of the release layer. Residual release layer material may be removed by photoelectrochemical etching, illuminating the back side of the high quality epitaxial layer or the front side of nitride crystal 101 or of the front side of the outermost high quality epitaxial layer still bonded to nitride crystal 101 with radiation at a wavelength at which the release layer has an optical absorption coefficient greater than 1,000 cm−1 and the high quality epitaxial layer is substantially transparent, with an optical absorption coefficient less than 50 cm−1.
Referring to
In still another set of embodiments, the high quality epitaxial layer bonded to the handle substrate is separated from the nitride crystal by means of photoelectrochemical (PEC) etching of the release layer. For example, an InGaN layer or InGaN/InGaN superlattice may be deposited as the release layer. An electrical contact may be placed on the nitride crystal and the release layer illuminated with above-bandgap radiation, for example, by means of a Xe lamp and a filter to remove light with energy greater than the bandgap of the high quality epitaxial layer and/or the nitride crystal.
In one set of embodiments, illustrated schematically in
In yet another set of embodiments, the high quality epitaxial layer bonded to the handle substrate is separated from the nitride crystal by means of selective oxidation followed by chemical etching of the release layer. For example, at least one release layer comprising AlxInyGa1-x-yN, where 0≤x, x+y≤1, 0≤y≤1, or Al0.83In0.17N, lattice matched to GaN, may be selectively oxidized. The selective oxidation may be performed by exposing at least one edge of the Al-containing release layer to a solution comprising nitriloacetic acid (NTA) and potassium hydroxide at a pH of approximately 8 to 11 and an anodic current of approximately 20 μA/cm−2, to about 0.1 kA/cm−2. The oxide layer may then be removed by treatment in a nitric acid solution at approximately 100 degrees Celsius. The time required for lateral etching of the release layer may be reduced by incorporating a pre-formed set of channels in the release layer. In the case that multiple, alternating release layers and high quality epitaxial layers are bonded to nitride crystal 101, transfer may be restricted to the outermost high quality epitaxial layer by utilizing etch channels that penetrate only the outermost high quality epitaxial layer.
Referring to
The placement of the second nitride crystal is performed in such a way that the crystallographic orientations between the from the first nitride crystal and the second nitride crystal, or the high quality epitaxial layers thereupon, are very nearly identical. Referring to
Referring to
In some embodiments, a similar set of nitride crystals or high quality epitaxial layers is wafer-bonded to the back surface of the handle substrate by an analogous procedure to that used to form the tile pattern of nitride crystals or high quality epitaxial layers on the front surface of the handle substrate. In a particular embodiment, the tile pattern on the back surface of the handle substrate is a mirror image of the tile pattern on the front surface of the handle substrate, with the front and back tile patterns in registry.
In one set of embodiments, the at least two nitride crystals or high quality epitaxial layers on the handle substrate are used as a substrate for fabrication of one or more devices.
The two or more tiled high quality epitaxial layers or crystals bonded to the handle substrate may be prepared for lateral growth for epitaxial growth and/or for fusion of the tiled crystals into a single larger crystal. The lateral crystal growth may be achieved by techniques such as molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), ammonothermal crystal growth, or crystal growth from a flux.
In some embodiments, the handle substrate is suitable for exposure to the epitaxial growth environment without further treatment. In some embodiments, a thermal treatment may be applied to increase the melting point of at least a portion of the adhesion layer(s). In some embodiments, growth may proceed more smoothly, with fewer stresses, if the gaps between adjacent nitride crystals are undercut. Referring to
In some embodiments, the handle substrate and/or the adhesion layer may not be suitable for exposure to the epitaxial growth environment without further treatment. Exposed portions of the handle substrate may be coated with a suitable inert material. Referring to
The etching/patterning and masking steps may be combined. Referring to
The merged nitride crystal may be grown to a thickness greater than 5 microns, greater than 50 microns, greater than 0.5 millimeters, or greater than 5 millimeters. After cooling and removal from the reactor, the merged nitride crystal may be separated from the handle substrate. The inert coating, if present, may be removed from at least a portion of the edge of the handle substrate by scribing, abrasion, etching, or the like. The handle substrate may be dissolved or etched away, for example, by placing in contact with an acid, a base, or a molten flux, preferably in a way that produces negligible etching or other damage to the merged nitride crystal. For example, a glass, silicon, or germanium substrate may be etched away without damaging the merged nitride crystal by treatment in a solution comprising HF and/or H2SiF6. Alternatively, a glass or zinc oxide substrate may be etched away without damaging the merged nitride crystal by treatment in a solution comprising NaOH, KOH, or NH4OH. A gallium arsenide or zinc oxide substrate may be etched away without damaging the merged nitride crystal by treatment in a solution comprising aqua regia or one or more of HCl, HNO3, HF, H2SO4, and H3PO4. A sapphire or alumina substrate may be etched away without damaging the merged nitride crystal by treatment in molten KBF4. After removal of the handle substrate, one or more surface of the merged nitride crystal may be lapped, polished, and/or chemical-mechanically polished. The merged nitride crystal may be sliced (sawed, polished, and/or chemical-mechanically polished) into one or more wafers.
Referring to
Within individual domains, the merged nitride crystal may have a surface dislocation density less than about 107 cm−2, less than about 106 cm−2, less than about 105 cm−2, less than about 104 cm−2, less than about 103 cm−2, or less than about 102 cm−2. The domains may have a stacking-fault concentration below 103 cm−1, below 102 cm−1, below 10 cm−1 or below 1 cm−1. The merged nitride crystal may have a symmetric x-ray rocking curve full width at half maximum (FWHM) less than about 300 arc sec, less than about 200 arc sec, less than about 100 arc sec, less than about 50 arc sec, less than about 35 arc sec, less than about 25 arc sec, or less than about 15 arc sec. The merged nitride crystal may have a thickness between about 100 microns and about 100 millimeters, or between about 1 millimeter and about 10 millimeters. The merged nitride crystal may have a diameter of at least about 5 millimeters, at least about 10 millimeters, at least about 15 millimeters, at least about 20 millimeters, at least about 25 millimeters, at least about 35 millimeters, at least about 50 millimeters, at least about 75 millimeters, at least about 100 millimeters, at least about 150 millimeters, at least about 200 millimeters, or at least about 400 millimeters. The surface of the merged nitride crystal may have a crystallographic orientation within 10 degrees, within 5 degrees, within 2 degrees, within 1 degree, within 0.5 degree, within 0.2 degree, within 0.1 degree, within 0.05 degree, within 0.02 degree, or within 0.01 degree of (0 0 0 1) Ga-polar, (0 0 0 −1) N-polar, {1 0 −1 0} non-polar, or {1 1 −2 0} non-polar a-plane. The surface of the merged nitride crystal may have a (h k i l) semi-polar orientation, where i=−(h+k) and l and at least one of h and k are nonzero. In a specific embodiment, the crystallographic orientation of the merged nitride crystal is within 10 degrees, within 5 degrees, within 2 degrees, within 1 degree, within 0.5 degree, within 0.2 degree, within 0.1 degree, within 0.05 degree, within 0.02 degree, or within 0.01 degree of {11 −2 ±2}, {6 0 −6±1}, {5 0 −5±1}, {40 −4 ±1}, {3 0 −3 ±1}, {5 0 −5 ±2}, {7 0 −7 ±3}, {2 0 −2 ±1}, {3 0 −3 ±2}, {4 0 −4 ±3}, {5 0 −5 ±4}, {1 0 −1 ±1}, {1 0 −1 ±2}, {1 0 −1 ±3}, {2 1 −3 ±1}, or ({3 0 −3 ±4}. The merged nitride crystal has a minimum lateral dimension of at least four millimeters. In some embodiments, the merged nitride crystal has a minimum lateral dimension of at least one centimeter, at least two centimeters, at least three centimeters, at least four centimeters, at least five centimeters, at least six centimeters, at least eight centimeters, at least ten centimeters, or at least twenty centimeters.
In some embodiments, the merged nitride crystal is used as a substrate for epitaxy, forming a semiconductor structure. The merged nitride crystal may be sawed, lapped, polished, dry etched, and/or chemical-mechanically polished by methods that are known in the art. One or more edges of the merged nitride crystal may be ground. The merged nitride crystal, or a wafer formed therefrom, may be placed in a suitable reactor and an epitaxial layer grown by MOCVD, MBE, HVPE, or the like. In a particular embodiment, the epitaxial layer comprises GaN or AlxInyGa(1-x-y)N, where 0≤x, y≤1. The morphology of the epitaxial layer is uniform from one domain to another over the surface because the surface orientation is almost identical.
In some embodiments, the merged nitride crystal is used as a substrate for further tiling. For example, referring to
The merged nitride crystal, or a wafer that has been sliced and polished from the merged nitride crystal or from a boule obtained by bulk crystal growth using the merged nitride crystal as a seed, may be used as a substrate for fabrication into optoelectronic and electronic devices such as at least one of a light emitting diode, a laser diode, a photodetector, an avalanche photodiode, a transistor, a rectifier, a Schottky rectifier, a thyristor, a p-i-n diode, a metal-semiconductor-metal diode, high-electron mobility transistor, a metal semiconductor field effect transistor, a metal oxide field effect transistor, a power metal oxide semiconductor field effect transistor, a power metal insulator semiconductor field effect transistor, a bipolar junction transistor, a metal insulator field effect transistor, a heterojunction bipolar transistor, a power insulated gate bipolar transistor, a power vertical junction field effect transistor, a cascode switch, an inner sub-band emitter, a quantum well infrared photodetector, a quantum dot infrared photodetector, a solar cell, or a diode for photoelectrochemical water splitting and hydrogen generation device. In some embodiments, the positions of the devices with respect to the domain structure in the merged nitride crystal are chosen so that the active regions of individual devices lie within a single domain of the merged nitride crystal.
In other embodiments, the merged nitride crystal, or a wafer sliced and polished from the merged nitride crystal, is used as a seed crystal for bulk crystal growth. In one specific embodiment, the tiled crystal, or a wafer sliced and polished from the merged nitride crystal, is used as a seed crystal for ammonothermal crystal growth. In another embodiment, the tiled crystal, or a wafer sliced and polished from the merged nitride crystal, is used as a seed crystal for HVPE crystal growth.
In still other embodiments, the at least two nitride crystals or high quality epitaxial layers on the handle substrate, non-merged, are used as a substrate for fabrication into optoelectronic and electronic devices such as at least one of a light emitting diode, a laser diode, a photodetector, an avalanche photodiode, a transistor, a rectifier, a Schottky rectifier, a thyristor, a p-i-n diode, a metal-semiconductor-metal diode, high-electron mobility transistor, a metal semiconductor field effect transistor, a metal oxide field effect transistor, a power metal oxide semiconductor field effect transistor, a power metal insulator semiconductor field effect transistor, a bipolar junction transistor, a metal insulator field effect transistor, a heterojunction bipolar transistor, a power insulated gate bipolar transistor, a power vertical junction field effect transistor, a cascode switch, an inner sub-band emitter, a quantum well infrared photodetector, a quantum dot infrared photodetector, a solar cell, and a diode for photoelectrochemical water splitting and hydrogen generation device. The at least one device may flip-chip mounted onto a carrier and the handle substrate removed.
Still further embodiments support method of making and method of use. Any of the embodiments below can be practiced in a variety of variations.
In certain embodiments of the method of
In certain embodiments of the method of
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In certain embodiments of forming a semiconductor on the merged crystal, the semiconductor structure is incorporated into an optoelectronic or electronic device, the optoelectronic or electronic device comprising at least one of wafer sliced and polished from the merged crystal or from a boule obtained by bulk crystal growth using the merged crystal as a seed.
In certain embodiments, the positions of the devices with respect to the domain structure in the merged crystal are chosen so that the active regions of individual devices lie within a single domain of the merged crystal.
Embodiments provided by the present disclosure are further illustrated by reference to the following examples. It will be apparent to those skilled in the art that many modifications, both to materials, and methods, may be practiced without departing from the scope of the disclosure.
A template was prepared using four HVPE-grown bulk GaN crystals wafer-bonded to a handle substrate, also comprising HVPE-grown bulk GaN. The nitride crystals exhibited a crystallographic orientation within 1 degree of the (0 0 0 1)+c-plane (Ga face). The adjoining surfaces of the nitride crystals and the handle substrate were each coated with a 200 Ångstrom Ti layer followed by a 1.5 micron Au layer and wafer-bonded at a pressure of 5.4 MPa and a temperature of 450° C. under vacuum. The gaps between adjacent bonded nitride crystals were approximately 85 microns. The misorientation angles α, β, and γ between the adjacent bonded nitride crystals were all less than 0.1 degrees. The template was degreased, suspended by a silver wire, and placed in a silver capsule with a baffle. Approximately 37.3 g of polycrystalline GaN, 1.27 g of NH4F mineralizer, and 30.4 g of ammonia were also placed in the capsule and the capsule was hermetically sealed. The capsule was placed in an internally-heated high pressure apparatus, heated to a temperature of approximately 675° C. for approximately 68 hours, then cooled, removed, and opened. The gap between the two nitride crystals was closed by newly-grown GaN, causing full coalescence of the crystals. The coalesced nitride crystal was removed from the handle substrate by dissolution of the Ti—Au adhesion layers by soaking in concentrated aqua regia solution. The linear etch pit densities at the coalescence fronts were measured as approximately 1.2×103 cm−1, indicating high-quality boundaries.
A template was prepared using two HVPE-grown bulk GaN crystals bonded to a handle substrate, also comprising HVPE-grown bulk GaN. The nitride crystals exhibited a crystallographic orientation within 1 degree of the (0 0 0 1)+c-plane (Ga face). The adjoining surfaces of the handle substrate and the nitride crystals were coated with a 200 Ångstrom Ti layer followed by a 1.0 micron Au layer. The nitride crystals further had an array of 300 micron diameter Si dots having a height of 0.6 microns, the dots being located at the vertices of a square grid having a period of 1,000 microns in both the x- and y-directions. The handle substrate was then placed on a heated stage at 475° C. and a pick and place tool was used to precisely position the two nitride crystals on the handle substrate. The adjoining surfaces of the nitride crystals and the handle substrate, while precisely aligned, were placed in contact for approximately 30 seconds and a bond was formed. The misorientation angles α and β between the adjacent bonded nitride crystals were less than 0.3 degrees and the misorientation angle γ between the adjacent bonded nitride crystals was less than 0.1 degree. The bonded template was subsequently heated to 275° C. in a nitrogen atmosphere and held for 24 hours. The template was degreased, suspended by a silver wire, and placed in a silver capsule with a baffle. Approximately 43.5 g of polycrystalline GaN, 1.28 g of NH4F mineralizer, and 30.6 g of ammonia were also placed in the capsule and the capsule was hermetically sealed. The capsule was placed in an internally-heated high pressure apparatus, heated to a temperature of approximately 680° C. for approximately 20 hours, then cooled, removed, and opened. The gap between the two nitride crystals was closed by newly-grown GaN, causing full coalescence of the crystals. No pits were identified at the coalescence front by scanning electron microscopy (SEM), indicating a high-quality boundary.
A template was prepared using three HVPE-grown bulk GaN crystals bonded to a handle substrate, also comprising HVPE-grown bulk GaN. The nitride crystals exhibited a crystallographic orientation that was miscut from the {1 0 −1 0} m-plane by approximately 0.25 degree toward [0 0 0 −1]. The adjoining surfaces of the handle substrate and the nitride crystals were coated with a 200 Ångstrom Ti layer followed by approximately a 20 micron thick Au layer and 3 micron thick AuSn layer on the handle substrate and the nitride crystals, respectively. The handle substrate was then placed on a heated stage at 330° C. and a pick and place tool was used to precisely position the three nitride crystals on the handle substrate. The adjoining surfaces of the nitride crystals and the handle substrate, while precisely aligned, were placed in contact for approximately 30 seconds and a bond was formed. The template was degreased and placed in a silver capsule with a baffle. Approximately 4,815 g of polycrystalline GaN, 172 g of NH4F mineralizer, and 3,608 g of ammonia were also placed in the capsule and the capsule was hermetically sealed. The capsule was placed in an internally-heated high pressure apparatus, heated to a temperature of approximately 680° C. for approximately 100 hours, then cooled, removed, and opened. The gap between the three nitride crystals was closed by newly-grown GaN, causing full coalescence of the crystals. The three nitride crystals were subsequently removed from the handle substrate as one distinct piece. The misorientation angles α and β between the adjacent bonded nitride crystals were between about 0.02 degree and about 0.45 degrees and the misorientation angles γ between the adjacent bonded nitride crystals were about 0.09 degree and about 0.11 degree, respectively. The linear etch pit densities at the coalescence fronts were measured as approximately 6.08×103 cm−1 and 5.84×103 cm−1 for the two coalescence boundaries, indicating high-quality boundaries.
A template was prepared using three HVPE-grown bulk GaN crystals bonded to a handle substrate comprising polycrystalline AlN. The nitride crystals exhibited a crystallographic orientation within about 0.5 degree of {1 0 −1 −1}. The adjoining surfaces of the handle substrate and the nitride crystals were coated with a 200 Ångstrom Ti layer followed by approximately a 20 micron thick Au layer and 3 micron thick AuSn layer on the handle substrate and the nitride crystals, respectively. The handle substrate was then placed on a heated stage at 330° C. and a pick and place tool was used to precisely position the three nitride crystals on the handle substrate. The adjoining surfaces of the nitride crystals and the handle substrate, while precisely aligned, were placed in contact for approximately 30 seconds and a bond was formed. The template was degreased and placed in a silver capsule with a baffle. Approximately 43.5 g of polycrystalline GaN, 2.56 g of NH4F mineralizer, and 30 g of ammonia were also placed in the capsule and the capsule was hermetically sealed. The capsule was placed in an internally-heated high pressure apparatus, heated to a temperature of approximately 655° C. for approximately 51 hours, then cooled, removed, and opened. The gap between the three nitride crystals was closed by newly-grown GaN, causing full coalescence of the crystals. The misorientation angles α and β between the adjacent pairs of bonded nitride crystals were between about 0.03 degree and about 0.26 degree and the misorientation angles γ between the adjacent bonded nitride crystals were about 0.085 degree and less than 0.01 degree, respectively.
A template was prepared using two HVPE-grown bulk GaN crystals bonded to a handle substrate comprising AlN. The nitride crystals exhibited a crystallographic orientation that was miscut from the {1 0 −1 0} m-plane by approximately 0.25 degree toward [0 0 0 −1]. The adjoining surfaces of the handle substrate and the nitride crystals were coated with a 3,000 Ångstrom Ti layer followed by approximately a 20 micron thick Au layer and 3 micron thick AuSn layer on the handle substrate and the nitride crystals, respectively. The handle substrate was then placed on a heated stage at 330° C. and a pick and place tool was used to precisely position the two nitride crystals on the handle substrate. The adjoining surfaces of the nitride crystals and the handle substrate, while precisely aligned, were placed in contact for approximately 30 seconds and a bond was formed. The template was degreased and placed in a silver capsule with a baffle. Approximately 37.54 g of polycrystalline GaN, 2.57 g of NH4F mineralizer, and 30.08 g of ammonia were also placed in the capsule and the capsule was hermetically sealed. The capsule was placed in an internally-heated high pressure apparatus, heated to a temperature of approximately 663° C. for approximately 51 hours, then cooled, removed, and opened. The gap between the two nitride crystals was closed by newly-grown GaN, causing full coalescence of the crystals. The two nitride crystals were subsequently removed from the handle substrate as one distinct piece. The nitride crystals were then placed in a silver capsule with a baffle. Approximately 3,560 g of polycrystalline GaN, 174.1 g of NH4F mineralizer, and 2,637.88 g of ammonia were also placed in the capsule and the capsule was hermetically sealed. The capsule was placed in an internally-heated high pressure apparatus, heated to a temperature of approximately 680° C. for approximately 116 hours, then cooled, removed, and opened. The misorientation angles α and β between the adjacent bonded nitride crystals were approximately 0.03 degree and the misorientation angle γ between the adjacent bonded nitride crystals was approximately 0.04 degree. The linear etch pit densities at the coalescence front was measured as approximately 6.75×103 cm−1, indicating high-quality boundaries.
While the above is a full description of the specific embodiments, various modifications, alternative constructions and equivalents may be used. Therefore, the above description and illustrations should not be taken as limiting the scope of the present invention which is defined by the appended claims.
This application is a continuation of Ser. No. 15/426,770, filed Feb. 7, 2017, which is a continuation of Ser. No. 13/731,453, filed Dec. 31, 2012, now U.S. Pat. No. 9,564,320, which is continuation-in-part of, and claims priority to U.S. application Ser. No. 13/160,307, filed on Jun. 14, 2011, which claims priority to U.S. Provisional Application No. 61/356,489, filed on Jun. 18, 2010; and to U.S. Provisional Application No. 61/386,879, filed on Sep. 27, 2010; each of which is incorporated herein by reference for all purposes.
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