CN112151355B - Method for manufacturing gallium nitride self-supporting substrate - Google Patents
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Abstract
The invention provides a method for manufacturing a gallium nitride self-supporting substrate, which comprises the following steps: 1) forming a gallium nitride template layer on a sapphire substrate; 2) epitaxially growing a first gallium nitride layer for the first time; 3) separating the sapphire substrate from the gallium nitride template layer to obtain a thin gallium nitride self-supporting substrate; 4) removing the bottom layer part with the worst crystal quality in the thin gallium nitride self-supporting substrate; 5) epitaxially growing a second gallium nitride layer for the second time to obtain a thick gallium nitride self-supporting substrate; 6) and polishing, trimming and chamfering the thick self-supporting substrate to obtain the final gallium nitride self-supporting substrate. According to the invention, after the first epitaxy, the bottom layer part with the worst crystal quality is removed, and the second epitaxy is carried out after the bottom layer part is removed, so that the dislocation density can be effectively reduced in the second epitaxy thickening process, the stress of the gallium nitride self-supporting substrate is reduced, the cracking rate in the second epitaxy thickening process is reduced, and the overall manufacturing yield of the self-supporting substrate is improved.
Description
Technical Field
The invention belongs to the field of semiconductor material manufacturing, and particularly relates to a method for manufacturing a gallium nitride self-supporting substrate.
Background
In order to realize the preparation of electronic and electric devices with excellent performances such as high frequency, high efficiency, high power and the like, the development of third-generation wide bandgap semiconductor materials represented by gallium nitride is accelerated at the end of the twentieth century. Due to its excellent properties, gallium nitride (GaN) can be widely studied and applied in the preparation of semiconductor devices operating under other special conditions, such as high-power high-frequency devices. The crystal quality of the GaN epitaxial layer is the fundamental guarantee for realizing high-performance GaN-based devices. The adoption of the GaN single crystal substrate to realize homoepitaxy is a main way for improving the crystal quality of the GaN epitaxial layer and a GaN-based device.
At present, the preparation technology of the gallium nitride self-supporting substrate becomes one of the biggest obstacles on the advancing path, and the preparation technology generally adopts a heteroepitaxy gallium nitride film on a sapphire substrate, and then adopts a Laser Lift-off Technique (Laser Lift-off Technique) to separate the gallium nitride film from the sapphire, so as to obtain the self-supporting gallium nitride substrate. In the epitaxial growth process of gallium nitride, stress exists in the epitaxial film, the thickness of the gallium nitride film grown on sapphire can only be below 400 microns due to the stress, the gallium nitride film grows too thick and is easy to crack, and therefore the thickness of the self-supporting gallium nitride substrate obtained after laser stripping is too thin to be ground and polished to obtain the required epitaxial surface.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a method for fabricating a gan self-supporting substrate, which is used to solve the problem of cracking caused by large residual stress in the epitaxial process in the prior art and improve the overall yield of the fabrication.
To achieve the above and other related objects, the present invention provides a method for fabricating a gan self-standing substrate, the method comprising the steps of: 1) providing a sapphire substrate, and forming a gallium nitride template layer on the sapphire substrate; 2) epitaxially growing a first gallium nitride layer on the gallium nitride template layer for the first time; 3) separating the sapphire substrate from the gallium nitride template layer by using a laser lift-off process to obtain a thin gallium nitride self-supporting substrate; 4) removing the bottom layer part with the worst crystal quality in the thin gallium nitride self-supporting substrate; 5) epitaxially growing a second gallium nitride layer on the thin gallium nitride self-supporting substrate obtained in the step 4) for the second time to obtain a thick gallium nitride self-supporting substrate; 6) and polishing the thick self-supporting substrate to obtain a final gallium nitride self-supporting substrate.
Optionally, step 1) depositing the gallium nitride template layer by using a metal organic chemical vapor deposition process, wherein the thickness of the gallium nitride template layer is between 2 microns and 10 microns.
Optionally, in the step 2), the first epitaxial growth is performed on the gallium nitride template layer by using a hydride vapor phase epitaxy process to form the first gallium nitride layer, and the thickness of the first gallium nitride layer is between 250 micrometers and 400 micrometers.
Optionally, in the step 4), the bottom layer part with the worst crystal quality in the thin gallium nitride self-supporting substrate is removed by a physical method or a chemical method, and the thickness of the removed bottom layer part is between 25 microns and 150 microns.
Optionally, the removal rate of the bottom layer portion with the worst crystal quality in the thin gallium nitride free-standing substrate is between 20 microns/hour and 100 microns/hour.
Optionally, the physical method includes one of laser ablation removal and plasma etching, and the chemical method includes one of phosphoric acid etching and alkali etching.
Optionally, the laser used for laser ablation comprises one of a gas laser, a solid-state laser and a semiconductor laser.
Optionally, the laser power is 2-15W.
Optionally, the etching gas used for plasma etching includes Cl 2 And BCl 3 。
Optionally, before the chemical method is performed to remove the bottom layer portion with the worst crystal quality in the thin gallium nitride self-supporting substrate, a step of forming an etching protection layer on the upper surface of the thin gallium nitride self-supporting substrate is further included.
Optionally, in step 5), a hydride vapor phase epitaxy process is used to perform a second epitaxial growth on the thin gallium nitride self-supporting substrate to form the second gallium nitride layer, where a thickness of the second gallium nitride layer is between 400 microns and 1000 microns.
Optionally, in step 6), the thick self-supporting substrate is polished for multiple times by using a grinding and polishing device, and then trimming and chamfering are performed to obtain a final gallium nitride self-supporting substrate, wherein the thickness of the final gallium nitride self-supporting substrate ranges from 300 micrometers to 1000 micrometers.
As described above, the method for manufacturing a gan self-supporting substrate of the present invention has the following advantages:
according to the method for manufacturing the gallium nitride self-supporting substrate, after the first epitaxy, the bottom layer part with the worst crystal quality is removed by adopting an optimized removal method, and the second epitaxy is performed after the removal, so that the dislocation density can be effectively reduced in the process of the second epitaxy thickening, the stress of the gallium nitride self-supporting substrate is reduced, the sheet cracking rate in the process of the second epitaxy thickening is reduced, and the overall manufacturing yield of the self-supporting substrate is improved.
The invention can further reduce the dislocation density and stress in the self-supporting substrate by configuring the epitaxial thickness and removing the thickness in each step, and the gallium nitride self-supporting substrate suitable for industrial production and manufacture is manufactured, thereby having wide application prospect in the field of manufacturing semiconductor materials and devices.
Drawings
Fig. 1 to 6 are schematic structural views showing steps of a method for manufacturing a gan self-standing substrate according to embodiment 1 of the present invention.
Fig. 7 to 12 are schematic structural views showing steps of a method for manufacturing a gan self-standing substrate according to embodiment 2 of the present invention.
Fig. 13 to 18 are schematic structural views showing steps of the method for manufacturing a gan free-standing substrate according to embodiment 3 of the present invention.
Fig. 19 to 24 are schematic structural views showing steps of a method for manufacturing a gan self-standing substrate according to embodiment 4 of the present invention.
Description of the element reference
101 sapphire substrate
102 gallium nitride template layer
103 first gallium nitride layer
1031 bottom layer part of the lower layer
1032 Top layer portion of lower layer
104 upper layer of the first gallium nitride layer
105 second gallium nitride layer
301 acid-resistant photoresist
302 alkali-resistant photoresist
Detailed Description
The following embodiments of the present invention are provided by way of specific examples, and other advantages and effects of the present invention will be readily apparent to those skilled in the art from the disclosure herein. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
As in the detailed description of the embodiments of the present invention, the cross-sectional views illustrating the device structures are not partially enlarged in general scale for convenience of illustration, and the schematic views are only examples, which should not limit the scope of the present invention. In addition, the three-dimensional dimensions of length, width and depth should be included in the actual fabrication.
For convenience in description, spatial relational terms such as "below," "beneath," "below," "under," "over," "upper," and the like may be used herein to describe one element or feature's relationship to another element or feature as illustrated in the figures. It will be understood that these terms of spatial relationship are intended to encompass other orientations of the device in use or operation in addition to the orientation depicted in the figures. In addition, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present.
In the context of this application, a structure described as having a first feature "on" a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed in between the first and second features, such that the first and second features may not be in direct contact.
It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the drawings only show the components related to the present invention rather than being drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of each component in actual implementation may be changed arbitrarily, and the layout of the components may be more complicated.
During epitaxial growth of gallium nitride, there is stress in the epitaxial film, which is mainly lattice mismatch stress and thermal mismatch stress. The lattice mismatch stress is mainly caused by the mismatch of lattice constants of the sapphire substrate and the gallium nitride crystal; the thermal mismatch stress is mainly caused by different thermal expansion coefficients of the two, the gallium nitride epitaxial wafer grows at a high temperature of more than 800 ℃, and after the growth is finished and the temperature is reduced, the contraction ratios of crystal lattices of the two are greatly different, so that the crystal lattices are mutually drawn. The stress causes the thickness of the gallium nitride film grown on the sapphire to be below 400 microns, and the gallium nitride film is excessively thick and is easy to crack, so that the thickness of the self-supporting gallium nitride substrate obtained after laser lift-off is too thin to be ground and polished to obtain a required epitaxial surface. For this purpose, it is necessary to continue epitaxial overgrowth to a sufficient thickness (typically 800 μm or more) on the free-standing gan substrate after laser lift-off. Some "growth stress" is inevitably introduced during the thickening growth. The highest dislocation density is found at the sapphire-gan interface, and the lower the dislocation density inside the interface to the later grown gan, so that there is a gradient of dislocation density from the sapphire-gan interface to the last grown gan surface. Research finds that the dislocation density is more and more difficult to reduce with the increase of the growth thickness of the gallium nitride, and the dislocation density in the upward one hundred micrometers of the sapphire and gallium nitride interface is reduced at a speed much faster than that of the gallium nitride grown later, which means that the dislocation density gradient in the upward one hundred micrometers of the sapphire and gallium nitride interface is much larger than that of the gallium nitride grown later. The larger dislocation density of the sapphire and gallium nitride interface within one hundred microns upwards means that the residual stress inside the layer of gallium nitride is relatively large, the stress limits the final growth thickness of the gallium nitride, and the grown gallium nitride is too thick to crack.
In order to solve the above problems, the present invention provides a method for manufacturing a gan self-standing substrate, the method comprising the steps of:
step 1), providing a sapphire substrate, and forming a gallium nitride template layer on the sapphire substrate; for example, the gallium nitride template layer is deposited using a metal organic chemical vapor deposition process, the gallium nitride template layer having a thickness between 2-10 microns.
Step 2), epitaxially growing a first gallium nitride layer on the gallium nitride template layer for the first time; for example, the first epitaxial growth may be performed on the gallium nitride template layer by using a hydride vapor phase epitaxy process to form the first gallium nitride layer, and the thickness of the first gallium nitride layer is between 250 micrometers and 400 micrometers.
And 3) separating the sapphire substrate from the gallium nitride template layer by utilizing a laser stripping process to obtain the thin gallium nitride self-supporting substrate.
And 4) removing the bottom layer part with the worst crystal quality in the thin gallium nitride self-supporting substrate, wherein the bottom layer part with the worst crystal quality is the part with the highest dislocation density of the thin gallium nitride self-supporting substrate and can comprise the gallium nitride template layer and part of the first gallium nitride layer.
As an example, the bottom layer part with the worst crystal quality in the thin gallium nitride self-supporting substrate can be removed by a physical method or a chemical method, the thickness of the removed bottom layer part is between 25 microns and 150 microns, and the removal rate of the bottom layer part with the worst crystal quality in the thin gallium nitride self-supporting substrate is between 20 microns/hour and 100 microns/hour. The physical method comprises one of laser ablation removal and plasma etching, the laser used for the laser ablation comprises one of a gas laser, a solid laser and a semiconductor laser, and more preferably, the power of the laser can be selected to be 2-15W. The etching gas selected for plasma etching comprises Cl 2 And BCl 3 . The chemical method comprises one of phosphoric acid corrosion and alkali corrosion, and the method further comprises the step of forming a corrosion protection layer on the upper surface of the thin gallium nitride self-supporting substrate before the chemical method is carried out to remove the bottom layer part with the worst crystal quality in the thin gallium nitride self-supporting substrate.
And 5) carrying out secondary epitaxial growth on the thin gallium nitride self-supporting substrate obtained in the step 4) to obtain a thick gallium nitride self-supporting substrate, for example, carrying out secondary epitaxial growth on the thin gallium nitride self-supporting substrate by adopting a hydride vapor phase epitaxy process to form the second gallium nitride layer, wherein the thickness of the second gallium nitride layer is between 400 and 1000 micrometers.
And 6) polishing the thick self-supporting substrate for multiple times to obtain a final gallium nitride self-supporting substrate. For example, the thick self-supporting substrate may be polished multiple times by a grinding and polishing apparatus, and then trimmed and chamfered to obtain a final gallium nitride self-supporting substrate having a thickness in the range of 300-1000 μm.
Example 1
As shown in fig. 1 to fig. 6, the present embodiment provides a method for manufacturing a gan free-standing substrate, comprising the following steps:
as shown in fig. 1, step 1) is first performed to provide a sapphire substrate 101, and gallium nitride with a thickness of 4-6 microns is epitaxially grown on the sapphire substrate 101 by MOCVD, so as to serve as a gallium nitride template layer 102 to be subsequently grown.
As shown in fig. 2 and fig. 3, step 2) is then performed to obtain a sapphire/gallium nitride composite substrate by performing HVPE (hydride vapor phase epitaxy) on the gallium nitride template layer 102 to obtain a first gallium nitride layer with a total first epitaxial thickness of 250-400 μm, where the first gallium nitride layer includes a lower layer 103 and an upper layer 104.
As shown in fig. 4, step 3) is performed, and Laser lift-off (LLO for short) is performed: the sapphire/gallium nitride composite substrate is turned over so that the sapphire substrate 101 faces upwards, a laser is used for irradiating a sapphire/gallium nitride interface at a high temperature of 800 ℃ in a nitrogen atmosphere, the sapphire substrate and gallium nitride in the sapphire/gallium nitride composite substrate are separated, and the thin gallium nitride self-supporting substrate is obtained and comprises a gallium nitride template layer 102 and first gallium nitride layers 103 and 104.
The laser is one of a gas laser, a solid laser and a semiconductor laser, and the wavelength of the laser can be 355 nanometers or 266 nanometers.
As shown in fig. 5, step 4) is then performed, and the worst crystal quality portions of the thin gallium nitride free-standing substrate obtained in step 3) are removed by using a laser, the removed portions including the template layer 102 of gallium nitride layer and the underlying portions 1031 of the underlying layer 103 of the first gallium nitride layer, the total thickness of the removed portions being 25-150 μm, the removal rate being 20-100 μm/hr, for example, 20 μm/hr, and the remaining gallium nitride layer portions including the top portion 1032 of the underlying layer of the first gallium nitride layer and the upper portion 104 of the first gallium nitride layer, during which the template layer 102 of gallium nitride is ablated prior to the underlying portions 1031 of the underlying layer 103 of the first gallium nitride layer. In the embodiment, the laser is adopted to remove the part with the worst crystal quality in the thin gallium nitride self-supporting substrate, and the method has the advantages of simple process, low process cost and high process efficiency.
Wherein, the laser is one of gas laser, solid laser and semiconductor laser. The wavelength of the laser is less than or equal to 10.8 microns, and the power of the laser is 3.5W.
By removing the bottom layer part with the worst crystal quality, the stress in the reserved thin gallium nitride self-supporting substrate can be greatly reduced, so that the dislocation density can be effectively reduced in the process of secondary epitaxial thickening, the stress of the gallium nitride self-supporting substrate is reduced, and the crack rate in the process of secondary epitaxial thickening is reduced.
As shown in fig. 6, step 5) is performed next, the thin gan self-standing substrate obtained in step 4) is flipped over, and a second gan layer 105 with a thickness of 400-1000 μm is epitaxially grown on the upper layer 104 of the first gan layer by using a Hydride Vapor Phase Epitaxy (HVPE) process, so as to obtain a thick gan self-standing substrate.
And finally, performing step 6), polishing the thick self-supporting substrate obtained in the step 5) by using polishing equipment for multiple times until the thickness is 300-1000 microns, and then performing edge cutting and chamfering treatment to obtain the final gallium nitride self-supporting substrate.
Example 2
As shown in fig. 7-12, the present embodiment provides a method for manufacturing a gan free-standing substrate, comprising the following steps:
as shown in fig. 7, step 1) is first performed to provide a sapphire substrate 101, and gallium nitride with a thickness of 4-6 microns is epitaxially grown on the sapphire substrate 101 by MOCVD to serve as a gallium nitride template layer 102 to be subsequently grown.
As shown in fig. 8 and fig. 9, step 2) is then performed to obtain a sapphire/gallium nitride composite substrate by performing HVPE (hydride vapor phase epitaxy) on the gallium nitride template layer 102 to obtain a first gallium nitride layer with a total first epitaxial thickness of 250-400 μm, where the first gallium nitride layer includes a lower layer 103 and an upper layer 104.
As shown in fig. 10, step 3) is followed by Laser lift-off (LLO): the sapphire/gallium nitride composite substrate is turned over so that the sapphire substrate 101 faces upwards, a laser is used for irradiating a sapphire/gallium nitride interface at a high temperature of 800 ℃ in a nitrogen atmosphere, the sapphire substrate and gallium nitride in the sapphire/gallium nitride composite substrate are separated, and the thin gallium nitride self-supporting substrate is obtained and comprises a gallium nitride template layer 102 and first gallium nitride layers 103 and 104.
The laser is one of a gas laser, a solid laser and a semiconductor laser, and the wavelength of the laser can be 355 nanometers or 266 nanometers.
As shown in fig. 11, step 4) is performed, and the gallium nitride layer 103 with the worst crystal quality in the thin gallium nitride self-supporting substrate obtained in step 3) is completely removed by using an inductively coupled plasma etching method (ICP etching), the removed portion of the gallium nitride template layer 102 and the lower layer 103 of the first gallium nitride layer are removed, the total thickness of the removed portions is 25 to 150 micrometers, the removal rate is 20 to 100 micrometers/hour, for example, 20 micrometers/hour, and the portion of the gallium nitride layer left is the upper layer 104 of the first gallium nitride layer, during which the gallium nitride template layer 102 is etched before the lower layer 103 of the first gallium nitride layer. Wherein, the ICP etching can adopt Cl 2 And BCl 3 Is an etching gas. In the embodiment, the part with the worst crystal quality in the thin gallium nitride self-supporting substrate is removed by adopting an inductively coupled plasma etching method (ICP etching), and the method has the advantages of high process precision, basically no residue and the like.
By removing the bottom layer part with the worst crystal quality, the stress in the reserved thin gallium nitride self-supporting substrate can be greatly reduced, so that the dislocation density can be effectively reduced in the process of secondary epitaxial thickening, the stress of the gallium nitride self-supporting substrate is reduced, and the splitting rate in the process of secondary epitaxial thickening is reduced.
As shown in fig. 12, step 5) is then performed to flip the thin gan self-standing substrate obtained in step 4), and a second gan layer 105 with a thickness of 400 microns and 700 microns is epitaxially grown on the upper layer 104 of the first gan layer by using a hydride vapor phase epitaxy process HVPE, so as to obtain a thick gan self-standing substrate.
And finally, performing step 6), polishing the thick self-supporting substrate obtained in the step 5) by using polishing equipment for multiple times until the thickness is 300-1000 microns, and then performing edge cutting and chamfering treatment to obtain the final gallium nitride self-supporting substrate.
Example 3
As shown in fig. 13-18, the present embodiment provides a method for manufacturing a gan self-supporting substrate, comprising the following steps:
as shown in fig. 13, step 1) is first performed to provide a sapphire substrate 101, and gallium nitride with a thickness of 4-6 microns is epitaxially grown on the sapphire substrate 101 by MOCVD, so as to serve as a gallium nitride template layer 102 to be subsequently grown.
As shown in fig. 14 and fig. 15, step 2) is then performed to obtain a sapphire/gallium nitride composite substrate by performing HVPE (hydride vapor phase epitaxy) on the gallium nitride template layer 102 to obtain a first gallium nitride layer with a total first epitaxial thickness of 250-400 μm, where the first gallium nitride layer includes a lower layer 103 and an upper layer 104.
As shown in fig. 16, step 3) is performed, and Laser lift-off (LLO for short) is performed: the sapphire/gallium nitride composite substrate is turned over so that the sapphire substrate 101 faces upwards, a laser is used for irradiating a sapphire/gallium nitride interface at a high temperature of 800 ℃ in a nitrogen atmosphere, the sapphire substrate and gallium nitride in the sapphire/gallium nitride composite substrate are separated, and the thin gallium nitride self-supporting substrate is obtained and comprises a gallium nitride template layer 102 and first gallium nitride layers 103 and 104.
The laser is one of a gas laser, a solid laser and a semiconductor laser, and the wavelength of the laser can be 355 nanometers or 266 nanometers.
As shown in fig. 17, step 4) is then performed to spin coat a certain thickness of acid-resistant photoresist 301 on the surface of the gallium nitride layer 104 of the thin gallium nitride self-supporting substrate, and develop the whole, as shown in fig. 17, so as to protect this surface from the subsequent chemical etching process, for example, the photoresist 301 may be a positive or negative photoresist with a thickness greater than 2 microns, so as to ensure its protective effect. The thin composite substrate is then immersed in a hot phosphoric acid solution to remove the portion of the substrate with the worst crystal quality, the removed portion including the template layer 102 of gallium nitride layer and the lower layer 103 of the first gallium nitride layer, the total thickness of the removal is 25-150 microns, the removal rate is 20-100 microns/hour, for example, 50 microns/hour, and the portion of the gallium nitride layer remaining is the upper layer 104 of the first gallium nitride layer, during which the template layer 102 of gallium nitride is etched away before the lower layer 103 of the first gallium nitride layer. Wherein the temperature of the hot phosphoric acid is more than 100 ℃, and the mass concentration is 70-90%. In the embodiment, the hot phosphoric acid solution is adopted to remove the part with the worst crystal quality, so that the removal rate is very high, and the overall process efficiency can be greatly improved.
By removing the bottom layer part with the worst crystal quality, the stress in the reserved thin gallium nitride self-supporting substrate can be greatly reduced, so that the dislocation density can be effectively reduced in the process of secondary epitaxial thickening, the stress of the gallium nitride self-supporting substrate is reduced, and the splitting rate in the process of secondary epitaxial thickening is reduced.
As shown in fig. 18, step 5) is then performed, the photoresist 301 on the surface of the thin gan self-supporting substrate obtained in step 4) is removed, the photoresist is cleaned, and then a second gan layer 105 with the thickness of 400-700 μm is epitaxially grown on the upper layer 104 of the first gan layer by using a hydride vapor phase epitaxy process HVPE, so as to obtain a thick gan self-supporting substrate.
And finally, performing step 6), polishing the thick self-supporting substrate obtained in the step 5) for multiple times by using polishing equipment until the thickness is 300-550 microns, and then performing edge cutting and chamfering treatment to obtain the final gallium nitride self-supporting substrate.
Example 4
As shown in fig. 19 to fig. 24, the present embodiment provides a method for manufacturing a gan self-supporting substrate, including the following steps:
as shown in fig. 19, step 1) is first performed to provide a sapphire substrate 101, and gallium nitride with a thickness of 4-6 microns is epitaxially grown on the sapphire substrate 101 by MOCVD, so as to serve as a gallium nitride template layer 102 to be subsequently grown.
As shown in fig. 20 and fig. 21, step 2) is then performed to obtain a sapphire/gallium nitride composite substrate by performing a HVPE (hydride vapor phase epitaxy) process on the gallium nitride template layer 102 to obtain a first gallium nitride layer with a total first epitaxial thickness of 250-400 μm, where the first gallium nitride layer includes a lower layer 103 and an upper layer 104.
As shown in fig. 22, step 3) is performed, and Laser lift-off (LLO for short) is performed: the sapphire/gallium nitride composite substrate is turned over, so that the sapphire substrate 101 faces upwards, a laser is used for irradiating a sapphire/gallium nitride interface at the high temperature of 800 ℃ in a nitrogen atmosphere, the sapphire substrate and gallium nitride in the sapphire/gallium nitride composite substrate are separated, and the thin gallium nitride self-supporting substrate is obtained and comprises a gallium nitride template layer 102 and first gallium nitride layers 103 and 104.
The laser is one of a gas laser, a solid laser and a semiconductor laser, and the wavelength of the laser can be 355 nanometers or 266 nanometers.
By removing the bottom layer part with the worst crystal quality, the stress in the reserved thin gallium nitride self-supporting substrate can be greatly reduced, so that the dislocation density can be effectively reduced in the process of secondary epitaxial thickening, the stress of the gallium nitride self-supporting substrate is reduced, and the splitting rate in the process of secondary epitaxial thickening is reduced.
As shown in fig. 23, step 4) is then performed to spin coat an alkali-resistant photoresist 301 with a certain thickness on the surface of the gallium nitride layer 104 of the thin gan self-supporting substrate, and the entire gallium nitride self-supporting substrate is developed as shown in fig. 23, so that this surface is not affected by the subsequent chemical etching process, for example, the photoresist 301 may be a positive photoresist or a negative photoresist with a thickness greater than 2 μm to ensure its protection. And then immersing the thin composite substrate into a potassium hydroxide solution, removing the part with the worst crystal quality, wherein the removed part comprises the gallium nitride layer template layer 102 and the lower layer 103 of the first gallium nitride layer, the total thickness of the removal is 25-150 micrometers, the removal rate is 20-100 micrometers/hour, for example, the removal rate can be 50 micrometers/hour, the part of the gallium nitride layer which is remained is the upper layer 104 of the first gallium nitride layer, and in the process, the gallium nitride template layer 102 is etched before the lower layer 103 of the first gallium nitride layer. Wherein the temperature of the potassium hydroxide is more than 60 ℃, and the molar concentration is 1-3 mol/L. The embodiment adopts the potassium hydroxide solution to remove the part with the worst crystal quality, has a very high removal rate, and can greatly improve the overall process efficiency.
As shown in fig. 24, step 5) is then performed to remove the photoresist 301 on the surface of the thin gan self-standing substrate obtained in step 4), and the photoresist is cleaned, and then a second 400-micron thick second gan layer 105 is epitaxially grown on the upper layer 104 of the first gan layer by using a hydride vapor phase epitaxy process HVPE to obtain a thick gan self-standing substrate.
And finally, performing step 6), polishing the thick self-supporting substrate obtained in the step 5) by using polishing equipment for multiple times until the thickness is 300-1000 microns, and then performing edge cutting and chamfering treatment to obtain the final gallium nitride self-supporting substrate.
As described above, the method for manufacturing a gan self-standing substrate according to the present invention has the following advantages:
according to the method for manufacturing the gallium nitride self-supporting substrate, the bottom layer part with the worst crystal quality is removed after the first epitaxy is carried out, the second epitaxy is carried out after the bottom layer part is removed, the dislocation density can be effectively reduced in the process of the second epitaxy thickening, the stress of the gallium nitride self-supporting substrate is reduced, the cracking rate in the process of the second epitaxy thickening is reduced, and the overall manufacturing yield of the self-supporting substrate is improved.
Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (12)
1. A method of fabricating a gallium nitride free standing substrate, the method comprising the steps of:
1) providing a sapphire substrate, and forming a gallium nitride template layer on the whole upper surface of the sapphire substrate;
2) epitaxially growing a first gallium nitride layer on the gallium nitride template layer for the first time;
3) separating the sapphire substrate from the gallium nitride template layer by using a laser lift-off process to obtain a thin gallium nitride self-supporting substrate;
4) removing the bottom layer part with the worst crystal quality in the thin gallium nitride self-supporting substrate, wherein the removed part comprises the lower layer of the gallium nitride template layer and the first gallium nitride layer, and the remained gallium nitride layer part comprises the upper layer of the first gallium nitride layer;
5) epitaxially growing a second gallium nitride layer on the upper layer of the first gallium nitride layer reserved in the step 4) for the second time to obtain a thick gallium nitride self-supporting substrate;
6) and polishing the thick gallium nitride self-supporting substrate to obtain a final gallium nitride self-supporting substrate.
2. The method of claim 1, wherein: step 1) depositing the gallium nitride template layer by utilizing a metal organic chemical vapor deposition process, wherein the thickness of the gallium nitride template layer is between 2 and 10 micrometers.
3. The method of claim 1, wherein: and 2) carrying out the first epitaxial growth on the gallium nitride template layer by adopting a hydride vapor phase epitaxy process to form the first gallium nitride layer, wherein the thickness of the first gallium nitride layer is between 250 and 400 microns.
4. The method of claim 3, wherein: and 4) removing the bottom layer part with the worst crystal quality in the thin gallium nitride self-supporting substrate by adopting a physical method or a chemical method, wherein the thickness of the removed bottom layer part is between 25 and 150 micrometers.
5. The method for producing a gallium nitride free-standing substrate according to claim 4, wherein: the removal rate of the bottom layer part with the worst crystal quality in the thin gallium nitride self-supporting substrate is between 20 and 100 microns/hour.
6. The method for producing a gallium nitride free-standing substrate according to claim 4, wherein: the physical method comprises one of laser ablation removal and plasma etching, and the chemical method comprises one of phosphoric acid corrosion and alkali corrosion.
7. The method according to claim 6, wherein: the laser used for laser ablation comprises one of a gas laser and a solid laser.
8. The method according to claim 7, wherein: the laser power is 2-15W.
9. The method of claim 6, wherein: the etching gas selected for plasma etching comprises Cl 2 And BCl 3 。
10. The method of claim 6, wherein: before the chemical method is carried out to remove the bottom layer part with the worst crystal quality in the thin gallium nitride self-supporting substrate, the method also comprises the step of forming an etching protective layer on the upper surface of the thin gallium nitride self-supporting substrate.
11. The method of claim 1, wherein: and 5) carrying out secondary epitaxial growth on the thin gallium nitride self-supporting substrate by adopting a hydride vapor phase epitaxy process to form the second gallium nitride layer, wherein the thickness of the second gallium nitride layer is between 400 and 1000 microns.
12. The method of fabricating a gallium nitride free-standing substrate according to claim 11, wherein: and 6) polishing the thick gallium nitride self-supporting substrate for multiple times by using grinding and polishing equipment, and then performing trimming and chamfering treatment to obtain a final gallium nitride self-supporting substrate, wherein the thickness range of the final gallium nitride self-supporting substrate is 300-1000 microns.
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