Method for preparing semiconductor device using gallium nitride as epitaxial layer

Abstract

The disclosed embodiments provide a method for fabricating a semiconductor device using gallium nitride as an epitaxial layer, comprising: depositing a laser absorption layer on a deposition surface of a substrate; patterning the laser absorption layer to form a patterned structure, and depositing a gallium nitride epitaxial layer on the patterned structure; and irradiating the laser absorption layer from the bottom surface of the substrate with a lift-off laser, such that the upper surface temperature of the irradiated area adjacent to the gallium nitride epitaxial layer is higher than the thermal decomposition temperature of gallium nitride. The laser absorption layer serves as a functional layer for absorbing the lift-off laser. Thermal decomposition of the adjacent gallium nitride epitaxial layer is achieved by heating the laser absorption layer to the thermal decomposition temperature of gallium nitride. Furthermore, the photon energy of the lift-off laser is less than the bandgap of gallium nitride. Therefore, no matter how the lift-off laser is focused, it will not be absorbed by the gallium nitride epitaxial layer, and the corresponding epitaxial layer will not generate heat.

Description

Technical Field

[0001] The present disclosure relates to the technical field of semiconductor manufacturing processes, and in particular to a method for manufacturing a semiconductor device using gallium nitride as an epitaxial layer. Background Art

[0002] Because the finished substrate material (such as polyimide) cannot withstand the high temperature of sputtering deposition and evaporation process, the light-emitting diode (LED) manufacturing process requires a high-temperature resistant rigid material such as glass, sapphire, and silicon as a substrate carrier. After the preparation is completed, it is peeled off from the substrate through a peeling process and then transferred to the base material through a transfer process.

[0003] Laser lift-off (LAS) is the most widely used process for LED lift-off. For LED devices with gallium nitride (GaN) epilayers deposited on sapphire substrates, the LSL process uses a laser with a specific photon energy (greater than the GaN outer electron bandgap of 3.4eV and less than the sapphire substrate's outer electron bandgap of 6.2eV) to irradiate the GaN epilayer from the sapphire side. The laser light passes through the sapphire substrate (because the laser photon energy is less than the sapphire substrate's bandgap, it cannot be absorbed by the sapphire) and strikes the GaN epilayer. It is then absorbed by the surface GaN layer directly in contact with the substrate. The surface layer, having absorbed the laser energy, rapidly heats to its decomposition temperature and decomposes into gallium and nitrogen, with the nitrogen escaping. Subsequent heating melts the gallium (melting point is 30°C), and mechanical lift-off is then performed to separate the LED from the sapphire substrate.

[0004] In addition, in order to reduce the defect density of the gallium nitride epitaxial layer and improve the yield and quality of LED devices, the existing technology grows the gallium nitride epitaxial layer on a patterned substrate. However, when growing the epitaxial layer on a patterned substrate, the contact area at the side wall of the pattern is large but the positive projection area is small, and the use of the aforementioned laser lift-off process will bring negative problems. Specifically, in order to achieve complete lift-off of the gallium nitride at the side wall of the patterned substrate, higher laser energy irradiation is required. However, due to the interface between the patterned substrate and the gallium nitride, the reflected laser will illuminate the top of the patterned substrate. When a higher laser energy is used, the laser energy received at the top of the pattern is too high and becomes an extremely hot area. Since the top of the patterned substrate is close to the LED functional layer, the high-density heat in the extremely hot area will be transferred to the functional layer, causing thermal failure of the functional layer. Summary of the Invention

[0005] The present disclosure provides a method for preparing a semiconductor device using gallium nitride as an epitaxial layer, comprising:

[0006] Depositing a laser absorption layer on a deposition surface of the substrate, wherein the band gap of the laser absorption layer is smaller than the band gap of gallium nitride, and the melting point temperature of the laser absorption layer material is greater than the decomposition temperature of gallium nitride;

[0007] Performing patterning on the laser absorption layer to form a patterned structure, wherein the patterned structure includes repeated pattern areas formed by the laser absorption layer and non-patterned areas located between the repeated pattern areas and formed by the substrate surface;

[0008] depositing a gallium nitride epitaxial layer on the patterned structure;

[0009] A lift-off laser is used to irradiate the laser absorption layer from the bottom surface of the substrate, so that before the irradiated area of ​​the laser absorption layer reaches the melting point temperature of the laser absorption layer material, the upper surface temperature of the irradiated area adjacent to the gallium nitride epitaxial layer is higher than the thermal decomposition temperature of gallium nitride; the photon energy of the lift-off laser is greater than or equal to the band gap width of the laser absorption layer but less than the band gap width of gallium nitride.

[0010] Optionally, before patterning the laser absorption layer, the method further includes:

[0011] The maximum edge distance is determined based on a target temperature when the root of the edge of the graphic area is irradiated by the peeling laser, a thermal decomposition temperature of gallium nitride, and a thermal conductivity, wherein the target temperature is less than the melting point of the laser absorption layer, and the maximum edge distance is the maximum set distance between the edge of the graphic area and the geometric center of the non-graphic area;

[0012] determining a process edge distance based on a maximum edge distance, the process edge distance being less than the maximum edge distance;

[0013] Determining a repetition period of the patterned structure based on a preset projection size of the patterned area and the process edge distance, and manufacturing a pattern mask based on the repetition period and the preset projection size of the patterned area;

[0014] The patterning of the laser absorption layer to form a patterned structure includes: patterning the laser absorption layer based on the pattern mask to form the patterned structure.

[0015] Optionally, determining the maximum edge distance based on a target temperature of the edge root of the graphic region when irradiated by the peeling laser, a thermal decomposition temperature of gallium nitride, and thermal conductivity includes:

[0016] The maximum edge distance is determined based on the target temperature of the edge root of the pattern area when irradiated with the lift-off laser, the thermal decomposition temperature and thermal conductivity of gallium nitride, and the interface thermal resistance between the laser absorption layer and the gallium nitride epitaxial layer.

[0017] Optionally, the graphic area is a frustum or a pedestal with an upper surface;

[0018] Before patterning the laser absorption layer, the method further comprises: depositing a blocking layer on the laser absorption layer,

[0019] The patterning of the laser absorption layer to form a patterned structure includes: patterning the post-deposition blocking layer and the laser absorption layer to obtain the patterned structure, and retaining the post-deposition blocking layer on the upper surface of the patterned area;

[0020] or,

[0021] After forming the patterned structure and before depositing the gallium nitride epitaxial layer on the patterned structure, depositing the post-deposition blocking layer on the upper surface of the patterned region;

[0022] The post-deposition blocking layer is used to block the deposition of gallium nitride on the upper surface of the pattern area during the deposition process of the gallium nitride epitaxial layer.

[0023] Optionally, the post-deposition barrier layer is a silicon dioxide deposition layer.

[0024] Optionally, depositing a laser absorption layer on the substrate includes: depositing a laser absorption layer of a target thickness on the substrate;

[0025] The target thickness is set so that the temperature of the upper surface of the irradiated area adjacent to the gallium nitride epitaxial layer is higher than the thermal decomposition temperature of gallium nitride before the irradiated area reaches the melting point temperature of the laser absorption layer material;

[0026] The target thickness is determined based on the following parameters: the melting point temperature, thermal conductivity and spectral absorption characteristics of the laser absorption layer material, the thermal decomposition temperature of gallium nitride, the wavelength characteristics of the stripping laser, and the control parameters of the laser light source that outputs the stripping laser.

[0027] Optionally, before depositing the gallium nitride epitaxial layer and subsequent functional layers on the patterned structure, the method further comprises depositing an aluminum nitride buffer layer at least on a non-patterned area of ​​the patterned structure;

[0028] or,

[0029] Before depositing the laser absorption layer on the deposition surface of the substrate, the method further includes: depositing an aluminum nitride buffer layer on the deposition surface of the substrate;

[0030] Depositing the laser absorption layer on the deposition surface of the substrate includes: depositing the laser absorption layer on the surface of the aluminum nitride buffer layer;

[0031] The non-patterned area formed during the patterning process of the laser absorption layer is the surface of the aluminum nitride buffer layer.

[0032] Optionally, the laser absorption layer is formed by depositing the following materials on the deposition surface of the substrate: gallium arsenide, indium phosphide or silicon.

[0033] Optionally, the wavelength range of the lift-off laser is determined according to the spectral absorption characteristics of the material forming the laser absorption layer.

[0034] Optionally, the substrate is a substrate made of sapphire or silicon carbide.

[0035] The method for fabricating a semiconductor device with a gallium nitride epitaxial layer provided by the disclosed embodiments employs a laser absorption layer as a functional layer to absorb the ablation laser. Thermal decomposition of the adjacent gallium nitride epitaxial layer is achieved by heating the laser absorption layer to the thermal decomposition temperature of gallium nitride. Furthermore, the photon energy of the ablation laser is less than the bandgap of gallium nitride. Therefore, no matter how the ablation laser is focused, it will not be absorbed by the gallium nitride epitaxial layer, and the corresponding epitaxial layer will not generate heat. This eliminates the problem of the ablation laser being focused on top of the patterned structure, which causes excessive heating of the gallium nitride in the corresponding area, as is the case with conventional process incompatibility. This reduces the probability of thermal failure in the functional area of ​​the semiconductor device. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0037] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without inventive work, including:

[0038] Figure 1 It is a schematic diagram of the structure of a conventional semiconductor device before laser lift-off;

[0039] Figure 2 is a flow chart of a method for manufacturing a semiconductor device provided by an embodiment of the present disclosure;

[0040] Figure 3 This is a schematic structural diagram of a device before laser lift-off is implemented according to an embodiment of the present disclosure;

[0041] Figure 4 is a bottom schematic diagram of a graphical structure in one embodiment;

[0042] Figure 5 This is a schematic diagram of the overall structure of the device before laser stripping in Scheme 2. DETAILED DESCRIPTION

[0043] The following describes embodiments of the present disclosure in more detail with reference to the accompanying drawings. Although certain embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be construed as limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present disclosure. It should be understood that the drawings and embodiments of the present disclosure are for illustrative purposes only and are not intended to limit the scope of protection of the present disclosure.

[0044] The term "including" and its variations used in this document are open inclusions, that is, "including but not limited to". The term "based on" means "based at least in part on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; the term "some embodiments" means "at least some embodiments". The relevant definitions of other terms will be given in the description below. It should be noted that the concepts of "first", "second", etc. mentioned in this disclosure are only used to distinguish different devices, modules or units, and are not used to limit the order or interdependence of the functions performed by these devices, modules or units.

[0045] To address the problem in existing patterned GaN semiconductor devices, when laser irradiation causes the GaN epitaxial layer near the functional layer to overheat during debonding, potentially leading to thermal failure of the functional layer, the present invention provides a novel method for manufacturing semiconductor devices using GaN as the epitaxial layer. In practical applications, the semiconductor device described in the present invention can be an LED or other device that uses GaN as the epitaxial layer and is debonded from the substrate using a laser debonding process.

[0046] Before analyzing the semiconductor device manufacturing method provided by the embodiment of the present disclosure, the reasons why the existing technology using the patterning process and the laser lift-off technology to manufacture semiconductor devices with gallium nitride as the substrate cannot be adapted are first analyzed.

[0047] Figure 1 This is a schematic diagram of the structure of a conventional semiconductor device before laser stripping. Figure 1 As shown, the prior art adopts the patterning process to produce the patterned structure (the patterned structure is either Figure 1A conical structure (either a frustum-shaped structure or a pyramidal structure) is placed on a substrate, and a gallium nitride buffer layer and subsequent functional layers are deposited on the patterned substrate. To enable the detachment of semiconductor devices from the substrate using a laser lift-off process, conventional techniques employ a laser light source with photon energy greater than the GaN bandgap (3.4 eV) but less than the substrate bandgap to illuminate the semiconductor device from the substrate side. Because the laser photon energy is less than the substrate bandgap, electron transitions in the substrate material cannot occur. Therefore, the substrate does not absorb the laser energy, and the laser light strikes the lower surface of the GaN epitaxial layer, where it is directly absorbed by the GaN and generates heat.

[0048] like Figure 1 As shown, an interface is formed between the substrate and the GaN epitaxial layer. When the laser irradiates the interface between the substrate and the GaN epitaxial layer, part of the laser light is reflected by the interface and directed toward the top area of ​​the patterned structure. Because the patterning process itself inevitably makes the edge of the patterned area a cone structure or a frustum structure with a certain inward curvature, during the process of the stripping laser irradiating the entire patterned structure, the laser light is always reflected to the top of the patterned structure, causing the temperature of the top area to continuously absorb laser energy and form heat accumulation. The aforementioned accumulated heat causes the temperature of the GaN epitaxial layer to exceed its thermal decomposition temperature, and the GaN epitaxial layer at the top of the patterned area remains above the thermal decomposition temperature for a long time. The top area continuously forms the heat dissipation center of the gradient field for heat dissipation, and heat is transferred to the functional layer of the semiconductor device. The aforementioned transferred heat causes the temperature of the functional layer to reach the failure temperature, causing thermal failure of the functional layer.

[0049] Figure 2 This is a flow chart of the method for preparing a semiconductor device according to an embodiment of the present disclosure. Figure 2 As shown, the semiconductor device manufacturing method provided by the embodiment of the present disclosure includes the following S110-S140.

[0050] S110: depositing a laser absorption layer on a deposition surface of the substrate.

[0051] The substrate is used to support the subsequent growth of the gallium nitride epitaxial layer, and is capable of withstanding the high temperatures during the nitriding and epitaxial layer processing and adapting to subsequent processing techniques. In specific implementations, the substrate can be a sapphire substrate or a silicon carbide substrate, preferably a sapphire substrate. In some cases, the substrate can also be a silicon substrate (this consideration takes into account the subsequent preparation process, which will be analyzed later when the subsequent process is introduced).

[0052] The deposition surface of the substrate is the surface used to realize various subsequent functional layers (especially the gallium nitride epitaxial layer). In the case where the substrate is a sapphire substrate, the deposition surface of the substrate can be the C-plane of the sapphire.

[0053] The laser absorption layer is a functional layer used to absorb the ablation laser and increase its own temperature. The laser absorption layer also serves as a functional layer for forming a patterned structure in subsequent processes. In the disclosed embodiments, the laser absorption layer has the following characteristics: (1) the band gap of the material forming the laser absorption layer is smaller than the band gap of gallium nitride; and (2) the melting point of the laser absorption layer is greater than the thermal decomposition temperature of gallium nitride. This section only introduces the material characteristics of the laser absorption layer, and later analyzes the reasons for setting the material characteristics of the laser absorption layer to the aforementioned characteristics.

[0054] In practical applications, based on the aforementioned material property limitations, that is, the bandgap of the laser absorption layer material is smaller than the bandgap of gallium nitride (3.4eV), and the melting point of the laser absorption layer is greater than the thermal decomposition temperature of gallium nitride (approximately 900°C). In practical applications, the laser absorption layer can be made of gallium arsenide (bandgap 1.43eV, melting point 1238°C), indium phosphide (1.34eV, melting point 1070°C), or silicon (1.12eV, melting point 1414°C), or other absorption layers that meet the aforementioned properties. Silicon substrates are rarely used for analysis here. Because the bandgap of silicon is 1.12eV, if silicon is used as the substrate, a material with a smaller bandgap must be used to make the laser absorption layer, making the selection of bandgap materials difficult.

[0055] In a specific implementation, S110 may be performed using an existing or subsequently developed process capable of depositing the aforementioned type of material, so as to achieve the operation of depositing the laser absorption layer on the deposition surface of the substrate.

[0056] S120: performing patterning processing on the laser absorption layer to form a patterned structure.

[0057] The patterned structure is used to achieve lateral epitaxial growth during the subsequent deposition and growth of the GaN epitaxial layer. It reduces dislocation density during the growth process, thereby improving the quality of the epitaxial layer. In the case of LEDs, reducing the dislocation density in the epitaxial layer can reduce non-radiative recombination in the active region, reducing reverse leakage current and thus extending the LED's lifespan. Furthermore, the patterned structure forms a light reflection and refraction mechanism, which increases the probability of light from the flip-chip LED being emitted from the substrate side, thereby improving the LED's light extraction efficiency.

[0058] As previously analyzed, the patterned structure in the embodiment of the present disclosure is a structure formed by the laser absorption layer. Specifically, the patterned structure includes a repeated patterned area formed by the non-etched area in the laser absorption layer, and a non-patterned area located between the repeated patterned areas and formed by the substrate surface. In other words, in the process of etching the laser absorption layer for patterning, it is necessary to expose the deposition surface of the substrate in the etched area (in the actual process, etching will be performed (that is, the deposition surface of the substrate will also be etched) to ensure that the deposition surface of the substrate is exposed) for the subsequent growth of the gallium nitride epitaxial layer.

[0059] Similar to the patterned structure formed in the prior art, the repeated pattern area formed by the laser absorption layer in the embodiment of the present disclosure can be a pyramidal structure or a truncated cone structure.

[0060] In practice, the laser absorbing layer can be patterned using either a dry etching process or a wet etching process. Regardless of which etching process is used to pattern the laser absorbing layer, a pattern mask is required. This pattern mask is then used to form a protective adhesive layer on the surface of the laser absorbing layer to protect the non-etched areas.

[0061] Considering that photolithography is a well-known technology in the field of semiconductor manufacturing technology, we will not analyze the photolithography process here. For this solution, the difficulty in patterning the laser absorption layer to form a patterned structure lies in how to make a reasonable pattern mask, which will be analyzed later.

[0062] S130: depositing a gallium nitride epitaxial layer on the patterned structure.

[0063] In a specific implementation, the existing gallium nitride deposition process can be used to realize the preparation of the gallium nitride epitaxial layer. The embodiment scheme of the present disclosure will not be further analyzed. For details, please refer to the existing technical literature.

[0064] The goal of preparing a semiconductor device is not to prepare a GaN epitaxial layer. The goal is to deposit various functional regions on the GaN epitaxial layer to achieve the target function of the semiconductor device. Moreover, the preparation of the aforementioned functional layer requires a substrate support. In actual applications, after preparing the GaN epitaxial layer, subsequent functional regions (including majority-carrier doped regions or doped layers, minority-carrier doped regions or doped layers, and electrode regions) will continue to be prepared on the GaN epitaxial layer according to existing processes. Because the preparation of subsequent functional regions is only a necessary step in the preparation process of some semiconductor devices, but is not a non-core invention of this embodiment, it will not be further analyzed here. For details, please refer to the existing technical literature.

[0065] S140: using a lift-off laser to irradiate the laser absorption layer from the bottom surface of the substrate, so that before the irradiated area of ​​the laser absorption layer reaches the melting point temperature of the laser absorption layer material, the upper surface temperature of the irradiated area adjacent to the gallium nitride epitaxial layer is higher than the thermal decomposition temperature of gallium nitride.

[0066] S140 performs a laser lift-off process. In the embodiment of the present disclosure, the photon energy of the lift-off laser is greater than or equal to the band gap of the laser absorption layer, but less than the band gap of gallium nitride.

[0067] Because the photon energy of the stripping laser is greater than or equal to the band gap width of the laser absorption layer, when the laser is irradiated to the laser absorption layer, the electron transition of the laser absorption layer can be realized and absorbed, causing the laser absorption layer to heat up.

[0068] Because the photon energy of the ablation laser is smaller than the bandgap of GaN, even if the ablation laser passes through the laser absorption layer and strikes the GaN epilayer, it will not be absorbed by the GaN epilayer. This means that the GaN epilayer cannot absorb the laser light and heat up, leading to its own thermal decomposition.

[0069] As previously analyzed, the substrate is made of sapphire or silicon carbide, and the bandgap width of these materials is larger than that of gallium nitride. Therefore, when the ablation laser is irradiated from the bottom surface of the substrate, it is not absorbed by the substrate. Instead, the irradiated laser can penetrate the laser absorption layer and be absorbed by it. In the case of a silicon substrate, the bandgap of the ablation laser is smaller than that of silicon, but not smaller than that of gallium nitride.

[0070] In the disclosed embodiment, after the lift-off laser irradiates the laser absorption layer, it is absorbed by the laser absorption layer, causing the laser absorption layer to heat up. In the disclosed embodiment, before the lift-off laser-irradiated region of the laser absorption layer reaches the melting point of the laser absorption layer (because the lower surface of the laser absorption layer adjacent to the substrate is irradiated first and has the highest laser irradiation energy density, the lower surface of the laser absorption layer generally has the highest temperature), the upper surface temperature of the irradiated region at the interface with the gallium nitride epitaxial layer is higher than the thermal decomposition temperature of gallium nitride.

[0071] Because the temperature of the upper surface adjacent to the GaN epitaxial layer is already higher than the thermal decomposition temperature of GaN, the temperature of the corresponding area adjacent to the GaN epitaxial layer also reaches the thermal decomposition temperature. The GaN in the corresponding area is decomposed into gallium and nitrogen, thus achieving laser lift-off.

[0072] After thermal decomposition of the GaN at the interface with the laser absorption layer is achieved, subsequent processes (such as low-temperature water bath plus mechanical stripping) can be used to peel the GaN epitaxial layer (or semiconductor device) from the substrate.

[0073] As previously analyzed, during the thermal decomposition process at the interface between the GaN epitaxial layer and the laser absorption layer, the laser absorption layer does not melt because the temperature of the laser-irradiated area does not reach the material's melting point. Consequently, the laser absorption layer does not act as a sacrificial layer for debonding. The subsequent laser absorption layer does not adhere to the surface of the debonded epitaxial layer.

[0074] Further analysis as above shows that because the laser absorption layer is used as the functional layer to absorb the stripping laser, the laser absorption layer is heated to the thermal decomposition temperature of GaN to achieve thermal decomposition of the adjacent GaN epitaxial layer, and the photon energy of the stripping laser is smaller than the band gap of GaN, so no matter how the stripping laser is focused, it will not be absorbed by the GaN epitaxial layer, and the corresponding epitaxial layer will not generate heat. Figure 1 The lift-off laser shown is focused on the top of the patterned structure, thereby solving the problem of excessive heating of the gallium nitride in the corresponding area, thereby reducing the probability of thermal failure in the functional area of ​​the semiconductor device.

[0075] Figure 3 This is a schematic diagram of the structure of the device before laser lift-off is realized in the embodiment of the present disclosure. Figure 3 Combining the transmission path and absorption process of the lift-off laser, as well as the principle of heat conduction, the closer the repeating pattern area (i.e., the patterned substrate) is to the substrate, the higher the local temperature is, while the farther away from the substrate, the lower the local temperature is. In other words, the area of ​​the patterned structure closest to the functional area of ​​the semiconductor device is actually the area with the lowest temperature. Accordingly, the temperature of the functional area is also lower, and the problem of the gallium nitride epitaxial layer closest to the functional area being the highest, as in the prior art, is avoided.

[0076] In summary, by using a laser absorption layer with a bandgap smaller than the bandgap of gallium nitride but a melting point greater than the thermal decomposition temperature of gallium nitride to produce a repeated pattern area of ​​a patterned structure, and using a stripping laser with a photon energy greater than or equal to the bandgap of the laser absorption layer but less than the bandgap of gallium nitride to perform the stripping process, the negative problems brought by the patterned structure to laser stripping can be solved, which is equivalent to achieving a fusion of the two processes without affecting each other.

[0077] As previously analyzed, prior to patterning the laser absorption pattern, a suitable pattern mask must be produced. This article analyzes the post-process adaptation issues that need to be considered when producing a pattern mask, and the pattern design method for the pattern mask based on the aforementioned post-process adaptation.

[0078] During laser lift-off (LAS) using a lift-off laser, it is necessary not only to lift off the GaN epitaxial layer from the repeating patterned area formed by the laser absorption layer, but also to lift off the GaN epitaxial layer from the non-patterned area (i.e., the substrate deposition surface). As previously analyzed, because the substrate cannot absorb the lift-off laser, it cannot actively generate heat to thermally decompose the GaN directly adjacent to it. Accordingly, the heat source for the thermal decomposition of the GaN adjacent to the substrate deposition surface must come from the adjacent laser absorption layer.

[0079] As previously analyzed, the maximum temperature of the laser absorption layer (or the target temperature during laser irradiation) should be lower than its melting point, while still allowing for thermal decomposition of the GaN directly adjacent to the substrate deposition surface. Furthermore, considering the temperature gradient during heat transfer, the non-patterned area should not be too large. Otherwise, even if the temperature of the laser absorption layer adjacent to the laser irradiation layer reaches its melting point, the GaN directly adjacent to the substrate in the center of the non-patterned area will still not reach its thermal decomposition temperature. Therefore, before executing S120, the following steps S150-S170 can be used to create a patterned mask.

[0080] S150: Determine the maximum edge distance based on the target temperature of the root of the edge of the graphic area when it is irradiated by the lift-off laser, the thermal decomposition temperature of gallium nitride, and the thermal conductivity.

[0081] According to the constraint mentioned above to ensure that the maximum temperature of the laser absorption layer does not reach the melting point temperature, the target temperature should be lower than the melting point temperature of the laser absorption layer.

[0082] The maximum edge distance is the maximum set distance between the edge of the graphic area and the geometric center of the non-graphic area.

[0083] The idea of ​​determining the maximum edge distance in S150 can be simplified to a mathematical model problem in which heat is transferred from a high temperature point to a low temperature point, and the high temperature point has an upper limit constraint of the target temperature and the low temperature point has a lower limit constraint of the temperature (that is, the thermal decomposition temperature of gallium nitride).

[0084] Because heat is transferred through the GaN epilayer, the thermal conductivity of the GaN epilayer must be considered to determine the maximum edge distance. Specifically, finite element analysis software can be used to perform heat conduction simulation analysis, combining the previously set target temperature constraints, the GaN thermal decomposition temperature constraints, and the GaN thermal conductivity parameters, to determine the maximum edge distance.

[0085] In practical applications, considering that heat conduction is three-dimensional (not only conducted along the surface of the non-graphic area, but also conducted toward the substrate and toward the laser absorption layer away from the substrate area), in order to more accurately determine the maximum edge distance, it is also necessary to consider the three-dimensional structure of the edge of the graphic area, the thermal conductivity of the laser absorption layer and the substrate, as well as the aforementioned simulation parameters (target temperature constraint, GaN thermal decomposition temperature constraint and GaN thermal conductivity parameter) to perform heat conduction simulation analysis and determine the maximum edge distance.

[0086] Taking into account that the interface between different materials will form an interface thermal resistance due to the interface characteristics, in the actual heat conduction simulation analysis process, the maximum edge distance can also be determined by considering the target temperature when the root of the edge of the graphic area is irradiated by the peeling laser, the thermal decomposition temperature and thermal conductivity of gallium nitride, and the interface thermal resistance between the laser absorption layer and the gallium nitride epitaxial layer (more preferably, also including the interface thermal resistance between the laser absorption layer and the substrate).

[0087] In practical applications, in addition to using heat conduction simulation analysis, theoretical calculations can be performed based on constraints to determine a roughly reasonable edge distance, and then actual experiments can be conducted to determine whether the aforementioned edge distance is feasible, and then the maximum edge distance can be determined.

[0088] S160: Determine a process edge distance based on the maximum edge distance, where the process edge distance is smaller than the maximum edge distance.

[0089] After determining the maximum edge distance, it can be determined that if the distance from the center of the non-patterned area to the edge of the repeated patterned area is less than the maximum edge distance, the deposited GaN temperature in the center of the non-patterned area can reach the thermal decomposition temperature, thereby achieving thermal decomposition and separation from the substrate. Accordingly, a value less than the maximum edge distance can be determined as the process edge distance.

[0090] It should be noted that in practical applications, when setting the process edge distance, it is necessary to consider not only the maximum edge distance limitation, but also the defect density control requirements during the deposition of the GaN buffer layer. For relevant content, please refer to existing technical literature and engineering practices.

[0091] S170: Determine a repetition period of the patterned structure based on a preset projection size of the pattern area and a process edge distance, and produce a pattern mask based on the repetition period and the preset projection size of the pattern area.

[0092] Figure 4 FIG. 1 is a bottom schematic diagram of a graphical structure in an embodiment. Figure 4The graphical structure shown in the figure is a hexagonal close-packed structure on the bottom surface, where the circles show the repeated graphic areas formed by the laser absorption layer, and the areas between the circles are non-graphic areas (that is, the areas where the GaN epitaxial layer is deposited). Figure 4 In the structure shown in the figure, after determining the bottom diameter D and process edge distance L of the repeated pattern area, Figure 4 As shown, the repetition period of the graphical structure

[0093]

[0094] After determining the repetition period of the patterned structure, the pattern mask can be made according to the bottom diameter D, the process edge distance L and the repetition period T, so that the pattern mask is Figure 4 The structure in .

[0095] Accordingly, when performing the aforementioned S150-S170, the aforementioned S120 patterning the laser absorption layer to form the patterned structure specifically includes patterning the laser absorption layer based on a pattern mask to form the patterned structure. In a specific implementation, the laser absorption layer can be patterned based on the pattern mask to form the patterned structure using the dry etching process or wet etching process mentioned above.

[0096] Depositing a laser absorption layer on a substrate was previously mentioned in S110. The following analyzes the deposition thickness characteristics of the laser absorption layer. In the disclosed embodiments, the thickness of the laser absorption layer deposited on the substrate is a target thickness. The target thickness is set so that the upper surface temperature of the irradiated area adjacent to the gallium nitride epitaxial layer remains above the thermal decomposition temperature of gallium nitride before the irradiated area reaches the melting point of the laser absorption layer material.

[0097] In some embodiments, various constraints are defined, including the melting point temperature, thermal conductivity, and spectral absorption characteristics of the laser absorption layer material, the wavelength characteristics of the laser used for stripping, and the control parameters of the laser light source that outputs the stripping laser. The control parameters of the laser light source include the spot translation speed, light source power, energy density, and pulse width. Under the aforementioned constraints, the upper limit temperature that can be reached on the lower surface of the laser absorption layer when the laser control parameters are used to control the irradiation of the lower surface of the laser absorption layer can be determined (this upper limit temperature is greater than the thermal decomposition temperature of gallium nitride and less than the melting point temperature of the laser absorption material). Subsequently, a heat conduction calculation is performed based on the upper limit temperature, the thermal conductivity of the laser absorption layer material, and the thermal decomposition temperature of gallium nitride to determine the thickness of the laser absorption layer. In a specific implementation, finite element analysis software can be used for simulation analysis to determine the thickness of the laser absorption layer.

[0098] Similar to the analysis above, in some embodiments, during the simulation analysis using finite element software, heat conduction in all directions is taken into account, and parameters such as the thermal conductivity of the substrate and the three-dimensional shape characteristics of the laser absorption layer after graphic processing may also be considered.

[0099] In specific implementations, in addition to the aforementioned factors, the thickness of the laser absorption layer also needs to consider the quality of the GaN epitaxial layer, the diameter of the repeated pattern area to be formed, the thickness characteristics and tilt angle characteristics of the patterned epitaxial layer.

[0100] The aforementioned scheme assumes that the control parameters of the laser light source have already been determined. In other embodiments, the control parameters of the laser light source may not be limited. Instead, only the material characteristics of the laser absorption material layer, the wavelength characteristics of the lift-off laser, and the quality control parameters for forming the GaN epitaxial layer may be determined. The target thickness is then determined based on these parameters, and the operating parameters of the laser light source are then determined based on the target thickness, the melting point temperature, and the thermal conductivity of the laser absorption material.

[0101] As previously mentioned, in certain embodiments, the patterned region within the patterned structure is a frustum (ideally, a pedestal) having an upper surface. According to the aforementioned process, when depositing the GaN epitaxial layer on the patterned structure at step S130, the GaN epitaxial layer is deposited independently in both the non-patterned region and the patterned region of the patterned structure. As the thickness of the epitaxial layer increases, the combination of the two deposited layers may form stress regions, resulting in a decrease in the quality of the GaN epitaxial layer. To avoid this issue, the GaN epitaxial layer is deposited only from the non-patterned region of the patterned structure. A post-deposition barrier layer is formed on the upper surface of the frustum-shaped patterned region to prevent the GaN epitaxial layer from being deposited.

[0102] In a specific implementation, the post-deposition blocking layer can be a silicon dioxide deposition layer, or other material layer that prevents gallium nitride from depositing to form three-dimensional islands and subsequent film formation structures. In one embodiment, the thickness of the post-deposition blocking layer is set to 1-2 nm.

[0103] The following analyzes how to form a post-deposition barrier layer on the upper surface of the image area (ie, the upper surface of the frustum).

[0104] In some embodiments, after executing the aforementioned S110 and before executing S120, a post-deposition blocking layer is deposited on the upper surface of the laser absorption layer. Accordingly, the patterning step S130 specifically includes patterning the post-deposition blocking layer and the laser absorption layer to obtain a patterned structure. Because the post-deposition blocking layer is deposited before the patterning, the post-deposition blocking layer in the non-patterned area can be etched away during the patterning etching process, while the post-deposition layer in the patterned area is covered by the photoresist and is not etched away.

[0105] In other embodiments, a post-deposition barrier layer may be deposited on the upper surface of the patterned area before forming the patterned structure in step S120 and depositing the gallium nitride epitaxial layer on the patterned structure in step S130. In the aforementioned post-deposition process, to ensure that the deposited post-deposition barrier layer is aligned with the upper surface of the patterned area, a corresponding pattern mask is prepared. Using the pattern mask and photoresist manufacturing process, a barrier layer is applied to the non-patterned area to prevent the deposition of the post-deposition barrier layer.

[0106] Existing processes have determined that the substrate (e.g., sapphire) and GaN have a lattice mismatch. Directly depositing GaN onto a sapphire substrate results in a high number of dislocation defects in the GaN epilayer. To address this issue, an aluminum nitride buffer layer can be formed between the substrate and the GaN epilayer. The following describes how to prepare this aluminum nitride buffer layer.

[0107] In some embodiments, after executing S120 and before executing S130, an aluminum nitride buffer layer may be deposited on at least the non-patterned region of the patterned structure. Specifically, if the patterned region is a pyramidal structure, the aluminum nitride buffer layer may be deposited on the entire surface of the patterned structure. If the patterned region is a frustum-conical structure, the aluminum nitride buffer layer may be deposited only on the non-patterned region.

[0108] Alternatively, in some embodiments, when depositing the aforementioned dioxide deposition layer, an aluminum nitride buffer layer can be first deposited on the entire surface of the patterned structure, and then a blocking layer can be deposited on the upper surface of the patterned area to cover the aluminum nitride buffer layer deposited on the upper surface of the patterned area.

[0109] In some other embodiments, an aluminum nitride buffer layer may be deposited on the substrate before performing the aforementioned S110, and a laser absorption layer may be deposited on the aluminum nitride buffer layer during S110. Accordingly, during the patterning of the laser absorption layer in S120, the aluminum nitride buffer layer is exposed in the non-patterned area.

[0110] In order to understand this scheme more intuitively, some preparation schemes that have been experimentally verified are analyzed below.

[0111] Option 1

[0112] In solution 1, the substrate is a sapphire substrate, the laser absorption layer is gallium arsenide, and the graphic area in the graphic structure is a frustum.

[0113] The corresponding fabrication process is as follows: an aluminum nitride buffer layer (20nm), a gallium arsenide laser absorption layer (300nm), and a post-deposition blocking layer (2nm) are sequentially deposited on a sapphire substrate. The post-deposition blocking layer and laser absorption layer are then etched using a photolithography process (with a patterned mask period of 3μm), exposing the aluminum nitride buffer layer and reducing the base diameter of the truncated cone to 2.8μm. Finally, a gallium nitride buffer layer is deposited on the patterned structure, and functional layers and conductive electrodes are prepared to form the LED device. Finally, a laser light source with an energy density of 400mJ / cm2, a pulse width of 10-20μs, and an emission wavelength of 600-700nm is irradiated on the substrate in a spiral inward-rotating manner, causing the gallium arsenide absorption layer to reach a maximum temperature of 1200°C and the interface temperature of the gallium nitride epitaxial layer and the laser absorption layer to exceed 900°C. This results in high-temperature thermal decomposition of the gallium nitride, enabling the LED device to be peeled off the substrate. Preliminary calculations determined that, under the aforementioned constraints, the maximum GaAs laser absorption layer thickness is 400nm. In Scheme 1, the GaAs laser absorption layer is set to 300nm, enabling thermal decomposition and exfoliation at the interface between the GaN epitaxial layer and the laser absorption layer. Preliminary calculations determined that the process edge distance used in Scheme 1 is 174nm, which is less than the maximum edge distance, thus enabling thermal decomposition at the interface between the GaN epitaxial layer and the aluminum nitride buffer layer.

[0114] Option 2

[0115] In the second solution, the substrate is a sapphire substrate, the laser absorption layer is gallium arsenide, and the graphic area in the graphic structure is a cone. Figure 5 This is a schematic diagram of the overall structure of the device before laser stripping in Scheme 2.

[0116] The corresponding preparation process is as follows: a gallium arsenide laser absorption layer (700nm) is deposited on a sapphire substrate. Subsequently, a photolithography process is used to etch the post-deposition barrier layer and laser absorption layer (with a patterned mask period of 1.1um) to expose the sapphire substrate, and the bottom diameter of the pyramidal pattern area is made to be 1.0um. Finally, an aluminum nitride buffer layer (20um) and a gallium nitride buffer layer are sequentially deposited on the patterned structure, and functional layers and conductive electrodes are prepared to form an LED device. Finally, a laser light source with an energy density of 900mJ / cm2, a pulse width of 50-60us, and an emission laser wavelength of 600-700nm is used to irradiate the substrate in a spiral inward rotation manner, so that the maximum temperature of the gallium arsenide absorption layer reaches 1200℃, and the interface temperature of the gallium nitride epitaxial layer and the laser absorption layer is greater than 900℃, thereby causing the gallium nitride to thermally decompose at high temperature, thereby achieving the peeling of the LED device from the substrate. Preliminary calculations determined that, under the aforementioned constraints, the maximum GaAs laser absorption layer thickness is 800nm. In Scheme 2, the GaAs laser absorption layer is set to 700nm, enabling thermal decomposition and stripping of the GaN epitaxial layer. The process edge distance used in Scheme 1 is approximately 135nm, less than the maximum edge distance, thus enabling thermal decomposition at the interface between the GaN epitaxial layer and the aluminum nitride buffer layer.

[0117] It should be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus that includes a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0118] The above are merely specific embodiments of the present disclosure, intended to enable those skilled in the art to understand and implement the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure is not limited to these embodiments, but is to be construed in the broadest manner consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a semiconductor device using gallium nitride as an epitaxial layer, characterized in that: include: Depositing a laser absorption layer on a deposition surface of the substrate, wherein the band gap of the laser absorption layer is smaller than the band gap of gallium nitride, and the melting point temperature of the laser absorption layer material is greater than the decomposition temperature of gallium nitride; Performing patterning on the laser absorption layer to form a patterned structure, wherein the patterned structure includes repeated pattern areas formed by the laser absorption layer and non-patterned areas located between the repeated pattern areas and formed by the substrate surface; depositing a gallium nitride epitaxial layer on the patterned structure; A lift-off laser is used to irradiate the laser absorption layer from the bottom surface of the substrate, so that before the irradiated area of ​​the laser absorption layer reaches the melting point temperature of the laser absorption layer material, the upper surface temperature of the irradiated area adjacent to the gallium nitride epitaxial layer is higher than the thermal decomposition temperature of gallium nitride; the photon energy of the lift-off laser is greater than or equal to the band gap width of the laser absorption layer but less than the band gap width of gallium nitride.

2. The preparation method according to claim 1, characterized in that Before patterning the laser absorption layer, the method further includes: The maximum edge distance is determined based on a target temperature when the root of the edge of the graphic area is irradiated by the peeling laser, a thermal decomposition temperature of gallium nitride, and a thermal conductivity, wherein the target temperature is less than the melting point of the laser absorption layer, and the maximum edge distance is the maximum set distance between the edge of the graphic area and the geometric center of the non-graphic area; determining a process edge distance based on a maximum edge distance, the process edge distance being less than the maximum edge distance; Determining a repetition period of the patterned structure based on a preset projection size of the patterned area and the process edge distance, and manufacturing a pattern mask based on the repetition period and the preset projection size of the patterned area; The patterning of the laser absorption layer to form a patterned structure includes: patterning the laser absorption layer based on the pattern mask to form the patterned structure.

3. The preparation method according to claim 2, characterized in that The determining of the maximum edge distance based on the target temperature of the edge root of the graphic area when irradiated by the peeling laser, the thermal decomposition temperature of gallium nitride, and the thermal conductivity includes: The maximum edge distance is determined based on the target temperature of the edge root of the pattern area when irradiated with the lift-off laser, the thermal decomposition temperature and thermal conductivity of gallium nitride, and the interface thermal resistance between the laser absorption layer and the gallium nitride epitaxial layer.

4. The preparation method according to claim 1, characterized in that The graphic area is a frustum or a pedestal with an upper surface; Before patterning the laser absorption layer, the method further comprises: depositing a blocking layer on the laser absorption layer, The patterning of the laser absorption layer to form a patterned structure includes: patterning the post-deposition blocking layer and the laser absorption layer to obtain the patterned structure, and retaining the post-deposition blocking layer on the upper surface of the patterned area; or, After forming the patterned structure and before depositing the gallium nitride epitaxial layer on the patterned structure, depositing the post-deposition blocking layer on the upper surface of the patterned region; The post-deposition blocking layer is used to block the deposition of gallium nitride on the upper surface of the pattern area during the deposition process of the gallium nitride epitaxial layer.

5. The preparation method according to claim 4, characterized in that The post-deposition barrier layer is a silicon dioxide deposition layer.

6. The preparation method according to claim 1, characterized in that Depositing a laser absorption layer on a substrate includes: depositing a laser absorption layer of a target thickness on the substrate; The target thickness is set so that the temperature of the upper surface of the irradiated area adjacent to the gallium nitride epitaxial layer is higher than the thermal decomposition temperature of gallium nitride before the irradiated area reaches the melting point temperature of the laser absorption layer material; The target thickness is determined based on the following parameters: the melting point temperature, thermal conductivity and spectral absorption characteristics of the laser absorption layer material, the thermal decomposition temperature of gallium nitride, the wavelength characteristics of the stripping laser, and the control parameters of the laser light source that outputs the stripping laser.

7. The preparation method according to claim 1, characterized in that Before depositing the gallium nitride epitaxial layer and subsequent functional layers on the patterned structure, the method further comprises depositing an aluminum nitride buffer layer at least on a non-patterned area of ​​the patterned structure; or, Before depositing the laser absorption layer on the deposition surface of the substrate, the method further includes: depositing an aluminum nitride buffer layer on the deposition surface of the substrate; Depositing the laser absorption layer on the deposition surface of the substrate includes: depositing the laser absorption layer on the surface of the aluminum nitride buffer layer; The non-patterned area formed during the patterning process of the laser absorption layer is the surface of the aluminum nitride buffer layer.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The laser absorption layer is formed by depositing the following materials on the deposition surface of the substrate: gallium arsenide, indium phosphide or silicon.

9. The preparation method according to claim 8, characterized in that: The wavelength range of the lift-off laser is determined according to the spectral absorption characteristics of the material forming the laser absorption layer.

10. The preparation method according to claim 8, characterized in that The substrate is made of sapphire or silicon carbide.

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