Preparation methods of epitaxial wafers and epitaxial wafers

Abstract

This application relates to a method for preparing an epitaxial wafer and the epitaxial wafer itself. The preparation method includes: providing a sapphire substrate; performing an epitaxial growth process to epitaxially grow a GaN epitaxial layer on the sapphire substrate under heating conditions to obtain an epitaxial wafer; wherein the heating temperature of the heating conditions fluctuates, first increasing and then decreasing, depending on the epitaxial growth time or the epitaxial growth thickness, to reduce the temperature change of the epitaxial surface during the epitaxial growth process. This improves the quality of the epitaxial wafer.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and in particular to a method for preparing an epitaxial wafer and the epitaxial wafer itself. Background Technology

[0002] Epitaxy is the process of growing a layer of material with the same crystal orientation and a well-integrity lattice on a substrate with a specific crystal orientation. Epitaxial wafers are often the foundation for manufacturing semiconductor devices; therefore, the quality of epitaxial wafers greatly affects the electrical parameters, yield, and stability of the devices. Thus, the epitaxial growth quality of epitaxial wafers is of paramount importance.

[0003] During epitaxial wafer growth, the quality of the epitaxial growth is closely related to the growth temperature. Changes in the growth temperature alter the growth pattern of the epitaxial layer, thereby affecting process stability and crystal quality. Currently, a method for preparing epitaxial wafers has been proposed in this field, which involves heating the substrate during the epitaxial growth process to meet the actual growth temperature requirements. While the quality of epitaxial wafers prepared using this method has improved, it still does not meet the requirements.

[0004] Therefore, how to further improve the quality of epitaxial wafers has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] In view of this, the present application provides a method for preparing an epitaxial wafer and an epitaxial wafer to solve at least one problem existing in the background art.

[0006] In a first aspect, embodiments of this application provide a method for preparing an epitaxial wafer, the method comprising:

[0007] Provide sapphire substrates;

[0008] An epitaxial growth process is performed to grow a GaN epitaxial layer on the sapphire substrate under heating conditions to obtain an epitaxial wafer;

[0009] The heating temperature of the heating conditions fluctuates, first increasing and then decreasing, depending on the epitaxial growth time or the epitaxial growth thickness, in order to reduce the temperature change of the epitaxial surface during the epitaxial growth process.

[0010] In conjunction with the first aspect of this application, in an optional embodiment, the heating temperature of the heating conditions exhibits a fluctuating change of first increasing and then decreasing with the epitaxial growth time, and the change of the heating temperature is determined based on historical temperature change patterns.

[0011] The historical temperature variation pattern refers to the variation of the first temperature with the epitaxial growth time. The first temperature is the temperature of the epitaxial surface during the historical epitaxial growth process. The heating temperature has an opposite trend to the first temperature. The epitaxial growth rate of the GaN epitaxial layer is the same as the historical epitaxial growth rate during the historical epitaxial growth process.

[0012] In conjunction with the first aspect of this application, in an optional embodiment, the heating temperature of the heating conditions exhibits a fluctuating change with the epitaxial growth thickness, first increasing and then decreasing, and the change in heating temperature is determined based on historical temperature change patterns.

[0013] The historical temperature variation pattern refers to the variation of the first temperature with the epitaxial growth thickness, where the first temperature is the temperature of the epitaxial surface during the historical epitaxial growth process, and the heating temperature has an opposite trend to the first temperature.

[0014] In conjunction with the first aspect of this application, in an optional embodiment, the heating temperature of the heating conditions exhibits a fluctuating change, first increasing and then decreasing, as the epitaxial growth time increases, including:

[0015] During the time period from 0 to t1, the heating temperature increases with the epitaxial growth time;

[0016] During the time period from t1 to t2, the heating temperature decreases with the epitaxial growth time;

[0017] Wherein, the epitaxial growth rate of the GaN epitaxial layer is less than or equal to 200 nm / h, the range of t1 is 270 min to 290 min, the range of t2 is 510 min to 530 min, and the range of the difference between the highest and lowest heating temperatures is 40°C to 50°C.

[0018] In conjunction with the first aspect of this application, in an optional embodiment, the heating temperature of the heating conditions exhibits a fluctuating change, first increasing and then decreasing, with respect to the epitaxial growth thickness, including:

[0019] Within the thickness range of 0 to h1, the heating temperature increases with the epitaxial growth thickness;

[0020] Within the thickness range of h1 to h2, the heating temperature decreases with the epitaxial growth thickness;

[0021] Wherein, h1 ranges from 900nm to 967nm, h2 ranges from 1700nm to 1767nm, and the difference between the highest and lowest heating temperatures ranges from 40℃ to 50℃.

[0022] In conjunction with the first aspect of this application, in an optional embodiment, the heating temperature of the heating conditions exhibits a fluctuating change with the epitaxial growth time, first increasing and then decreasing, and the heating temperature rise rate ranges from 0 to 0.5 °C / min; and / or, the heating temperature cools down at a rate ranging from 0 to 0.6 °C / min.

[0023] In conjunction with the first aspect of this application, in an optional embodiment, the heating temperature of the heating conditions exhibits a fluctuating change with the epitaxial growth thickness, first increasing and then decreasing, and the heating temperature rise rate ranges from 0 to 1.5 °C / nm; and / or, the heating temperature cools down in the range of 0 to 1.8 °C / nm.

[0024] In conjunction with the first aspect of this application, in an optional embodiment, the heating temperature of the heating conditions exhibits a fluctuating change of first increasing and then decreasing with the epitaxial growth time, and the heating temperature rise rate exhibits a change of first increasing and then decreasing with the epitaxial growth time; and / or, the heating temperature cools down rate exhibits a change of first increasing and then decreasing with the epitaxial growth time.

[0025] In conjunction with the first aspect of this application, in an optional embodiment, the heating temperature of the heating conditions exhibits a fluctuating change of first increasing and then decreasing with the epitaxial growth thickness, and the heating rate of the heating temperature exhibits a change of first increasing and then decreasing with the epitaxial growth thickness; and / or, the cooling rate of the heating temperature exhibits a change of first increasing and then decreasing with the epitaxial growth thickness.

[0026] In conjunction with the first aspect of this application, in an optional embodiment, the heating temperature of the heating conditions exhibits a fluctuating change, first increasing and then decreasing, as the epitaxial growth time increases, and the heating temperature fluctuates periodically with the epitaxial growth time.

[0027] In conjunction with the first aspect of this application, in an optional embodiment, the heating temperature of the heating conditions exhibits a fluctuating change with the epitaxial growth thickness, first increasing and then decreasing, and the heating temperature fluctuates periodically with the epitaxial growth thickness.

[0028] In conjunction with the first aspect of this application, in an optional embodiment, the epitaxial growth process includes molecular beam epitaxy.

[0029] In conjunction with the first aspect of this application, in an optional embodiment, after providing the sapphire substrate, the fabrication method further includes: fixing the sapphire substrate below a base;

[0030] A heating device is provided above the base, and the heating device is used to provide the heating temperature.

[0031] In conjunction with the first aspect of this application, in an optional embodiment, a back metal layer is formed on the sapphire substrate;

[0032] The epitaxial growth of a GaN epitaxial layer on the sapphire substrate includes: epitaxially growing a GaN epitaxial layer on the side of the sapphire substrate away from the back metal layer.

[0033] In conjunction with the first aspect of this application, in an optional embodiment, after providing the sapphire substrate, the fabrication method further includes: fixing the sapphire substrate in a base;

[0034] A heating device is provided on the side of the base away from the sapphire substrate. The heating device is used to provide the heating temperature to compensate the temperature of the epitaxial surface.

[0035] The projection of the heating device overlaps the projection of the sapphire substrate along the thickness direction of the sapphire substrate.

[0036] In conjunction with the first aspect of this application, in an optional embodiment, after providing the sapphire substrate, the fabrication method further includes: fixing the sapphire substrate in a base;

[0037] A temperature measuring device is provided on the side of the base facing the sapphire substrate. The temperature measuring device is used to monitor a second temperature, which is the temperature of the epitaxial surface during the epitaxial growth process.

[0038] The preparation method further includes: adjusting the rate of change of the heating temperature based on the second temperature.

[0039] In conjunction with the first aspect of this application, in an optional embodiment, the temperature measuring device includes an infrared thermometer;

[0040] The base is a rotating base;

[0041] The infrared thermometer's measuring optical path forms a measuring spot on the sapphire substrate that is off-center from the center of the sapphire substrate.

[0042] Secondly, embodiments of this application provide a method for preparing an epitaxial wafer, the method comprising:

[0043] Provide a first substrate;

[0044] A first epitaxial growth process is performed to epitaxially grow a first heteroepitaxial layer on the first substrate under a first heating condition to obtain a first epitaxial wafer;

[0045] During the execution of the first epitaxial growth process, a first temperature is monitored to obtain the historical temperature variation law of the first temperature with the epitaxial growth time or epitaxial growth thickness. The first temperature is the temperature of the epitaxial surface during the first epitaxial growth process.

[0046] Provide a second substrate;

[0047] A second epitaxial growth process is performed to epitaxially grow a second heteroepitaxial layer on the second substrate under a second heating condition to obtain a second epitaxial wafer;

[0048] The second heating condition is determined based on the historical temperature change pattern in order to reduce the temperature change of the epitaxial surface during the second epitaxial growth process.

[0049] Wherein, the second substrate and the first substrate are the same type of substrate; the first epitaxial growth process and the second epitaxial growth process are the same type of epitaxial growth process, and the process conditions are the same; the first heteroepitaxial layer and the second heteroepitaxial layer are the same type of heteroepitaxial layer.

[0050] In conjunction with the second aspect of this application, in an optional embodiment, both the first epitaxial growth process and the second epitaxial growth process include molecular beam epitaxy (MBE).

[0051] In conjunction with a second aspect of this application, in an optional embodiment, after providing the second substrate, the fabrication method further includes: fixing the second substrate below a base;

[0052] A heating device is provided above the base, and the heating device is used to provide the second heating condition.

[0053] In conjunction with a second aspect of this application, in an optional embodiment, a back metal layer is formed on the second substrate;

[0054] The step of epitaxially growing a second heteroepitaxial layer on the second substrate includes: epitaxially growing the second heteroepitaxial layer on the side of the second substrate away from the back metal layer.

[0055] In conjunction with a second aspect of this application, in an optional embodiment, after providing the second substrate, the fabrication method further includes: fixing the second substrate in a base;

[0056] A heating device is provided on the side of the base away from the second substrate, and the heating device is used to provide the second heating condition;

[0057] The projection of the heating device overlaps the projection of the second substrate along the direction of the thickness of the second substrate.

[0058] In conjunction with a second aspect of this application, in an optional embodiment, after providing the second substrate, the fabrication method further includes: fixing the second substrate in a base;

[0059] A temperature measuring device is provided on the side of the base facing the second substrate. The temperature measuring device is used to monitor a second temperature, which is the temperature of the epitaxial surface during the second epitaxial growth process.

[0060] The preparation method further includes: adjusting the second heating conditions based on the second temperature.

[0061] In conjunction with a second aspect of this application, in an optional embodiment, the temperature measuring device includes an infrared thermometer;

[0062] The base is a rotating base;

[0063] The temperature measuring spot formed by the temperature measuring optical path of the infrared thermometer on the second substrate is off-center from the center point of the second substrate.

[0064] In conjunction with the second aspect of this application, in an optional embodiment, both the first substrate and the second substrate comprise a sapphire substrate; both the first heteroepitaxial layer and the second heteroepitaxial layer comprise a GaN epitaxial layer;

[0065] The second heating temperature under the second heating condition exhibits a fluctuating change, first increasing and then decreasing, depending on the epitaxial growth time or the epitaxial growth thickness.

[0066] Thirdly, embodiments of this application provide an epitaxial wafer prepared using the epitaxial wafer preparation method described in any one of the first and second aspects above.

[0067] The method for preparing an epitaxial wafer provided in the first aspect of this application controls the heating temperature to fluctuate with the epitaxial growth time or thickness during the heteroepitaxial growth of GaN on a sapphire substrate, first increasing and then decreasing. This improves the compatibility between the heating conditions and the growth pattern of GaN material heteroepitaxially on sapphire material, better compensates for the temperature loss of the epitaxial surface during growth, reduces the temperature change of the epitaxial surface, and makes the temperature of the epitaxial surface meet the growth temperature conditions of the optimal growth mode, thereby improving the quality of the epitaxial wafer.

[0068] The epitaxial wafer preparation method provided in the second aspect of this application first performs the same epitaxial growth process on the same substrate to grow the same heteroepitaxial layer, thereby obtaining the growth law of the heteroepitaxial layer on the substrate, that is, the historical temperature change law of the epitaxial surface temperature with the epitaxial growth time or epitaxial growth thickness. Then, in subsequent preparation, the temperature change of the epitaxial surface can be predicted according to this law, the heating conditions can be accurately controlled, the adaptability of heating conditions and growth law is improved, and the temperature of the epitaxial surface meets the growth conditions of the optimal growth mode, thereby improving the quality of the epitaxial wafer.

[0069] The epitaxial wafer provided in the third aspect of this application is prepared by the epitaxial wafer preparation method described in either the first or second aspect. Therefore, during the epitaxial growth process, the temperature change of the epitaxial surface is reduced, which meets the growth conditions of the optimal growth mode, and the epitaxial wafer has higher crystal quality.

[0070] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0071] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0072] Figure 1 A schematic flowchart illustrating the method for preparing an epitaxial wafer according to an embodiment of this application;

[0073] Figure 2 Electron microscopy images of GaN epitaxial layers in related technologies;

[0074] Figure 3 This is an electron microscope image of the GaN epitaxial layer in the embodiments of this application;

[0075] Figure 4 This is a diffraction pattern of a GaN epitaxial layer in a related technology;

[0076] Figure 5 This is a diffraction pattern of the GaN epitaxial layer in the embodiments of this application;

[0077] Figure 6 This is a cross-sectional structural schematic diagram of the epitaxial device provided in an embodiment of this application;

[0078] Figure 7 This is a curve showing the change of the first temperature with the thickness of the epitaxial growth.

[0079] Figure 8 A comparison graph showing the curves of the first temperature, the second temperature, and the heating temperature as a function of the epitaxial growth thickness;

[0080] Figure 9 This is a graph showing the change of the first temperature with epitaxial growth time.

[0081] Figure 10 A comparison graph showing the curves of the first temperature, the second temperature, and the heating temperature as a function of epitaxial growth time;

[0082] Figure 11 This is a schematic flowchart illustrating the method for preparing an epitaxial wafer according to an embodiment of this application. Detailed Implementation

[0083] Exemplary embodiments of the present application will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application may be implemented in various forms and should not be limited to the specific embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present application and to fully convey the scope of the disclosure of the present application to those skilled in the art.

[0084] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this application. However, it will be apparent to those skilled in the art that this application can be practiced without one or more of these details. In other instances, to avoid confusion with this application, some technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and structures described in detail.

[0085] In the accompanying drawings, for clarity, the dimensions of layers, areas, and elements, as well as their relative dimensions, may be exaggerated. The same reference numerals denote the same elements throughout.

[0086] It should be understood that when an element or layer is referred to as "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, and / or portions, these elements, components, areas, layers, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, component, area, layer, or portion from another element, component, area, layer, or portion. Therefore, without departing from the teachings of this application, the first element, component, area, layer, or portion discussed below may be referred to as a second element, component, area, layer, or portion. And the discussion of a second element, component, area, layer, or portion does not imply that the first element, component, area, layer, or portion necessarily exists in this application.

[0087] Spatial relation terms such as “below,” “under,” “below,” “below,” “above,” “above,” etc., are used herein for convenience of description to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, then the element or feature described as “below” or “below” other elements or features will be oriented “above” other elements or features. Therefore, the exemplary terms “below” and “under” can include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or otherwise) and the spatial descriptive terms used herein will be interpreted accordingly.

[0088] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0089] To fully understand this application, detailed steps and structures will be presented in the following description to illustrate the technical solution of this application. Preferred embodiments of this application are described in detail below; however, in addition to these detailed descriptions, this application may have other implementation methods.

[0090] Figure 1 A schematic flowchart of the method for preparing an epitaxial wafer provided in this application embodiment is shown in the figure. The preparation method includes:

[0091] Step S101: Provide a sapphire substrate;

[0092] Step S102: Perform an epitaxial growth process to grow a GaN epitaxial layer on a sapphire substrate under heating conditions to obtain an epitaxial wafer; wherein, the heating temperature of the heating conditions fluctuates with the epitaxial growth time or the epitaxial growth thickness, first increasing and then decreasing, in order to reduce the temperature change of the epitaxial surface during the epitaxial growth process.

[0093] Therefore, during the heteroepitaxial GaN epitaxial layer process on the sapphire substrate, the heating temperature exhibits a fluctuating change of first increasing and then decreasing with the epitaxial growth time or epitaxial growth thickness. Accurate control of the heating temperature reduces the temperature change of the epitaxial surface, ensuring that the temperature meets the optimal growth temperature conditions, thereby guaranteeing the quality of the epitaxial wafer.

[0094] Understandably, the concept of a "growth window" exists in epitaxial growth processes. This "growth window" refers to a range of parameters that, under specific conditions, enable high-quality epitaxial growth. These parameters may include growth temperature, molecular beam flux, and vacuum level. By precisely controlling these parameters, thin film materials with specific crystal structures and properties can be grown on a substrate. The inventors discovered that during heteroepitaxial growth on a substrate, the temperature of the epitaxial surface changes as the thickness of the epitaxial layer varies. This can be understood as a change in growth temperature, which may fall outside the growth window, altering the growth pattern and ultimately negatively impacting crystal quality. For example, in plasma-assisted molecular beam epitaxy (PAMBE), a stepped flow growth pattern is formed under group III-rich growth conditions, where atoms grow layer by layer along the crystal steps, forming a smooth and uniform epitaxial layer. During the epitaxial growth of GaN on sapphire, temperature fluctuations on the epitaxial surface can cause the temperature to drop outside the growth window. This alters atomic migration and adsorption behavior, preventing Ga atoms in some areas from combining with N atoms to form stable compounds. Instead, Ga atoms remain on the epitaxial layer surface in liquid form, evaporating during subsequent processing and leaving pits. In related technologies, the heating temperature remains constant during epitaxial growth, but the surface temperature varies significantly with growth time or thickness, causing the temperature to drop outside the growth window. Please refer to [reference needed]. Figure 2 At a magnification of 720μm × 540μm, pits left by the evaporation of droplets after residue can be observed (e.g. Figure 2 (As shown in the middle circle). In this embodiment, during the epitaxial growth process, the heating temperature is controlled to first increase and then decrease with the epitaxial growth time or thickness. This makes the heating conditions more compatible with the growth pattern of heteroepitaxial GaN material on sapphire material, better compensates for the temperature loss of the epitaxial surface during growth through heating temperature, reduces the temperature change of the epitaxial surface, and ensures that the temperature of the epitaxial surface conforms to the growth window. Atomic migration and adsorption behaviors remain unchanged, and no liquid residue or pits are generated (e.g.). Figure 3 (As shown).

[0095] The crystal quality of the material is further reflected by the full width at half maximum (FWHM) value of X-ray diffraction (XRD). The FWHM in XRD refers to the width of the diffraction peak at half its peak intensity. Specifically, it is the range of diffraction angles where the peak intensity drops to half of its maximum intensity. The FWHM is typically used to characterize the sharpness of the diffraction peak; it is related to factors such as crystal quality, grain size, and stress. A narrower FWHM usually indicates higher crystal quality, larger grains, and fewer defects. X-ray diffraction was performed on a 500 nm thick GaN epitaxial layer epitaxially grown on a sapphire substrate to obtain the material's diffraction curve, as shown below. Figure 4 As shown, in related technologies, the full width at half maximum (FWHM) of a GaN epitaxial layer is 696 arcseconds, such as... Figure 5 As shown in the embodiment of this application, the full width at half maximum (FWHM) of the GaN epitaxial layer is 612 arcseconds. It can be seen that by controlling the heating temperature of the heating conditions during the epitaxial growth process to first increase and then decrease with the epitaxial growth time or the epitaxial growth thickness, temperature compensation is performed, reducing the temperature change of the epitaxial surface, making the temperature of the epitaxial surface conform to the growth window, reducing the FWHM of the GaN epitaxial layer, making the diffraction peaks sharper, and improving the crystal quality of the epitaxial layer.

[0096] In some embodiments, after performing step S101, the fabrication method may further include: fixing a sapphire substrate in a base; providing a heating device on the side of the base away from the sapphire substrate, the heating device being used to provide a heating temperature for temperature compensation of the epitaxial surface; and the projection of the heating device covering the projection of the sapphire substrate along the thickness direction of the sapphire substrate. Thus, by providing a heating temperature through a heating device, and ensuring that the projection of the heating device covers the projection of the sapphire substrate, the heating area of ​​the heating device is at least equal to the area of ​​the sapphire substrate, ensuring heating of the entire sapphire substrate, improving heating efficiency, and making heating more uniform, which is beneficial for ensuring the uniformity of epitaxial growth. The heating device may include a thermocouple.

[0097] In this embodiment, the epitaxial growth process may include molecular beam epitaxy (MBE). Specifically, the epitaxial growth process may include plasma-assisted molecular beam epitaxy (PAE).

[0098] Please refer to Figure 6After performing step S101, the preparation method may further include: fixing the sapphire substrate 100 below the base 300; a heating device 400 is disposed above the base 300, and the heating device 400 is used to provide heating temperature. Understandably, the molecular beam epitaxy (MBE) growth equipment includes an ultra-high vacuum chamber to provide a clean growth environment; a base, also known as a sample stage, to support the substrate; and a molecular beam source, also known as an evaporation source, disposed below the base to generate the required molecular beam or atomic beam. Therefore, after fixing the sapphire substrate below the base, the molecular beam or atomic beam generated by the molecular beam source can be sprayed onto the sapphire substrate for epitaxial growth. In this embodiment, a heating device is installed above the base to provide heating temperature and conduct it to the sapphire substrate. The heating device may include a thermocouple.

[0099] Furthermore, along the thickness direction of the sapphire substrate, the projection of the heating device covers the projection of the sapphire substrate. Therefore, the heating area of ​​the heating device is at least equal to the area of ​​the sapphire substrate, ensuring heating of the entire sapphire substrate, improving heating efficiency, and making the heating more uniform, which is beneficial for ensuring the uniformity of epitaxial growth.

[0100] Optionally, such as Figure 6 As shown, a back metal layer 500 is formed on a sapphire substrate 100; epitaxial growth of a GaN epitaxial layer 200 on the sapphire substrate 100 includes epitaxial growth of the GaN epitaxial layer 200 on the side of the sapphire substrate 100 away from the back metal layer 500. Understandably, in a vacuum cavity, the thermal conductivity of air is greatly reduced, and sapphire, as a transparent wide bandgap material, has low thermal conductivity, so directly heating the substrate may be inefficient. Therefore, this embodiment of the application improves the heating efficiency of the sapphire substrate by forming a back metal layer on the sapphire substrate, utilizing the good thermal conductivity of the metal, and also makes the heating of the sapphire substrate more uniform, which is beneficial to ensuring the uniformity of epitaxial growth.

[0101] The material of the back metal layer may include titanium and / or tungsten. Titanium and / or tungsten have good thermal conductivity and are inexpensive. In this embodiment, the material of the back metal layer is specifically, for example, titanium, which has better ductility and can better accommodate the thermal expansion and contraction of the sapphire substrate during heating and cooling, reducing thermal stress-induced cracks and defects.

[0102] The thickness of the back metal layer can range from 50 nm to 500 nm. Understandably, if the back metal layer is too thick, its ability to adapt to the thermal expansion and contraction of the substrate decreases. Under large temperature changes, the sapphire substrate is prone to cracking or delamination, affecting the quality of the epitaxial wafer. If the back metal layer is too thin, insufficient heat conduction will result in poor heating efficiency and uniformity, affecting the crystal quality of the epitaxial layer. Therefore, controlling the thickness of the back metal layer within this range can achieve a relatively ideal heat conduction effect while avoiding damage to the sapphire substrate. In this embodiment, the thickness of the back metal layer is specifically 500 nm, and the process is more mature.

[0103] Next, step S102 is performed: an epitaxial growth process is carried out, in which a GaN epitaxial layer is epitaxially grown on a sapphire substrate under heating conditions to obtain an epitaxial wafer. The heating temperature fluctuates, first increasing and then decreasing, depending on the epitaxial growth time or thickness, to reduce temperature changes on the epitaxial surface during the growth process. This improves the compatibility between the heating conditions and the growth pattern of heteroepitaxial GaN material on sapphire, better compensating for temperature losses on the epitaxial surface during growth, reducing temperature changes on the epitaxial surface, and ensuring that the temperature of the epitaxial surface meets the optimal growth temperature conditions, thus improving the quality of the epitaxial wafer.

[0104] As one possible specific implementation method, please refer to Figure 7 and Figure 8 The heating temperature exhibits a fluctuating pattern, first increasing and then decreasing, with the epitaxial growth thickness. This temperature variation is determined based on historical temperature variation patterns. These historical temperature variation patterns are defined as the pattern of a first temperature changing with the epitaxial growth thickness, where the first temperature represents the epitaxial surface temperature during the historical epitaxial growth process. The heating temperature shows an opposite trend to this first temperature. Therefore, by obtaining the historical temperature variation pattern based on the epitaxial surface temperature changes during the historical epitaxial growth process, the actual fabrication process can predict the temperature change trend of the epitaxial surface. By applying a heating temperature with an opposite trend, temperature compensation can be performed on the epitaxial surface, thereby reducing temperature fluctuations. Before actual fabrication, the same epitaxial growth process can be performed on the same sapphire substrate as the actual fabrication, growing the same GaN epitaxial layer. During the epitaxial growth process, the epitaxial growth thickness and the epitaxial surface temperature (i.e., the first temperature) are monitored to obtain the historical temperature variation pattern of the first temperature with the epitaxial growth thickness.

[0105] Understandably, during the epitaxial growth of GaN layers on a sapphire substrate, the epitaxial surface is constantly changing. If the epitaxial growth process is viewed as the formation of countless sequentially stacked GaN material layers, then the surface of each formed GaN material layer becomes the epitaxial surface of the next GaN material layer to be formed. Due to the different thermal conductivity of sapphire and GaN, a heterogeneous interface exists between the sapphire substrate and the GaN epitaxial layer. The interface thermal resistance hinders heat conduction from the substrate. As the thickness of the GaN epitaxial layer increases, the path for heat conduction from the sapphire substrate to the epitaxial surface lengthens, and the heat conduction efficiency decreases. Furthermore, with more GaN material layers participating in the heat conduction from the sapphire substrate, the heat dispersion path increases. Therefore, as the thickness of the GaN epitaxial layer increases, the temperature of the epitaxial surface decreases. Currently, those skilled in the art generally believe that the growth law of heteroepitaxial GaN material on sapphire material is that the temperature of the epitaxial surface monotonically decreases with increasing GaN epitaxial layer thickness, and the above-mentioned principle analysis conclusion has been obtained. However, in actual preparation, when adjusting the heating conditions based on this growth pattern, there are still cases where the temperature of the epitaxial surface does not meet the optimal temperature conditions for the growth mode.

[0106] The inventors of this application discovered through multiple experiments that during the epitaxial growth of GaN layers on sapphire substrates, the temperature of the epitaxial surface exhibits a fluctuating change with the thickness of the epitaxial growth layer, first decreasing and then increasing, rather than a monotonically decreasing or increasing change. Please refer to [reference needed]. Figure 7 and Figure 8 Within the thickness range of 0 to h1, the first temperature decreases with increasing epitaxial growth thickness; within the thickness range of h1 to h2, the first temperature increases with increasing epitaxial growth thickness, thus forming a cycle. This cycle continues in the next cycle until the preset thickness is reached. The temperature of the epitaxial surface exhibits a periodic fluctuation of first decreasing and then increasing with the epitaxial growth thickness, which can also be understood as a cosine-like fluctuation. This yields the actual growth law of heteroepitaxial GaN material on sapphire: the temperature of the epitaxial surface exhibits a fluctuating trend of first decreasing and then increasing with increasing GaN epitaxial layer thickness. Using this actual growth law as a basis for adjusting heating conditions allows for a higher degree of compatibility between the heating conditions and the growth law of heteroepitaxial GaN material on sapphire. It is easy to understand that if the heating conditions are adjusted based on the growth law currently known to those skilled in the art, and combined with the principle that the heating temperature has an opposite trend to the first temperature, the heating temperature will be controlled to increase monotonically with the epitaxial growth thickness. This has a very low degree of compatibility with the actual growth law of fluctuating changes from first decreasing to increasing, making it difficult to effectively compensate for the temperature of the epitaxial surface, and the crystal quality of the epitaxial wafer is still poor.

[0107] Based on obtaining the actual growth pattern as the basis for adjusting the heating conditions, and combined with the principle that the heating temperature and the first temperature have opposite trends, the trend of heating temperature changing with the epitaxial growth thickness can be obtained, such as... Figure 8 As shown, within the thickness range of 0 to h1, the heating temperature increases with the epitaxial growth thickness; within the thickness range of h1 to h2, the heating temperature decreases with the epitaxial growth thickness, exhibiting a fluctuating change of first increasing and then decreasing. Therefore, the obtained pattern of heating temperature variation with epitaxial growth thickness can be input into the epitaxial equipment before the process is executed, and heating conditions can be set. During the process, the current epitaxial growth thickness is monitored, and the heating temperature is adjusted to a value corresponding to the current epitaxial growth thickness, thus enabling more precise temperature compensation.

[0108] Figure 8 Specifically, the temperature of the epitaxial surface changes with the epitaxial growth thickness over a period of time. Compared with the temperature of the epitaxial surface without temperature compensation, i.e., the first temperature, the temperature of the epitaxial surface after temperature compensation, i.e., the second temperature, changes less with the epitaxial growth thickness and the overall trend tends to be gentle. The difference between the maximum and minimum values ​​of the second temperature is in the range of 0℃-4℃. The temperature of the epitaxial surface can be maintained within the growth temperature range of the growth window, the epitaxial growth can maintain the optimal growth mode, and the crystal quality is improved.

[0109] Please continue to refer to this. Figure 8 The heating temperature exhibits a fluctuating change with the epitaxial growth thickness, first increasing and then decreasing. Specifically, within the thickness range of 0 to h1, the heating temperature increases with the epitaxial growth thickness; within the thickness range of h1 to h2, the heating temperature decreases with the epitaxial growth thickness. Here, h1 ranges from 900 nm to 967 nm, h2 ranges from 1700 nm to 1767 nm, and the difference between the highest and lowest heating temperatures ranges from 40°C to 50°C. Therefore, within the thickness range of 0 to h1, increasing the heating temperature by 40°C to 50°C compensates for the gradually decreasing temperature of the epitaxial surface, bringing the temperature back within the growth window. Within the thickness range of h1 to h2, decreasing the heating temperature by 40°C to 50°C reduces the impact on the gradually increasing temperature of the epitaxial surface, maintaining the temperature within the growth window. This approximates flattening the fluctuation curve in the historical temperature variation pattern, reducing temperature changes on the epitaxial surface. Furthermore, a difference between the highest and lowest heating temperatures ranging from 47°C to 50°C is more conducive to compensating for the temperature of the epitaxial surface.

[0110] Optionally, the heating temperature fluctuates periodically with the thickness of the epitaxial growth. Understandably, within one cycle, such as... Figure 8As shown, within the thickness range of 0 to h1, the heating temperature increases with the epitaxial growth thickness; within the thickness range of h1 to h2, the heating temperature decreases with the epitaxial growth thickness. The curve of heating temperature versus epitaxial growth thickness contains multiple such periods, exhibiting periodic fluctuations. Furthermore, the heating temperature exhibits uniform periodic fluctuations with the epitaxial growth thickness.

[0111] Optionally, the heating rate ranges from 0 to 1.5 °C / nm; and / or the cooling rate ranges from 0 to 1.8 °C / nm. Therefore, controlling the heating rate and / or cooling rate within a certain range can reduce thermal stress caused by rapid temperature changes, prevent substrate and epitaxial layer cracking, and avoid problems such as uneven growth and increased defects caused by rapid temperature changes, thus improving the quality of the epitaxial wafer.

[0112] Optionally, the heating rate increases and then decreases with the epitaxial growth thickness; and / or, the cooling rate increases and then decreases with the epitaxial growth thickness. Therefore, as the epitaxial surface temperature begins to decrease, the heating rate gradually increases to quickly compensate for the temperature drop, and then gradually decreases to avoid excessively rapid heating, which could cause large temperature fluctuations and adversely affect epitaxial growth. The cooling rate follows the same principle.

[0113] As another optional specific implementation method, please refer to Figure 9 and Figure 10 The heating temperature exhibits a fluctuating pattern, first increasing and then decreasing, with the temperature variation determined based on historical temperature variation patterns. These historical temperature variation patterns are defined as the variation of a first temperature with epitaxial growth time, where the first temperature represents the epitaxial surface temperature during the historical epitaxial growth process. The heating temperature shows an opposite trend to the first temperature, and the epitaxial growth rate of the GaN epitaxial layer is the same as the historical epitaxial growth rate. Therefore, by obtaining the historical variation pattern of the epitaxial surface temperature during the historical epitaxial growth process, this pattern can be used to predict the temperature change of the epitaxial surface during actual fabrication. By applying a heating temperature with an opposite trend, temperature compensation can be performed on the epitaxial surface to reduce temperature variations. Before actual fabrication, the same epitaxial growth process can be performed on the same sapphire substrate as the actual fabrication, growing the same GaN epitaxial layer. During the epitaxial growth process, the epitaxial growth time and the temperature of the epitaxial surface (i.e., the first temperature) are monitored to obtain the variation pattern of the first temperature with epitaxial growth time.

[0114] As described in the aforementioned optional embodiment, the temperature of the epitaxial surface exhibits a fluctuating change with the epitaxial growth thickness, first decreasing and then increasing, rather than a monotonically decreasing or increasing change. Since the epitaxial growth thickness equals the epitaxial growth rate multiplied by the epitaxial growth time, and there is a linear relationship between the epitaxial growth thickness and the epitaxial growth time, when the epitaxial growth rate is constant, the temperature change of the epitaxial surface with the epitaxial growth thickness can be equated to the temperature change with the epitaxial growth time. The fluctuation curve of the epitaxial surface temperature with the epitaxial growth time can also be proportionally viewed as the fluctuation curve of the epitaxial surface temperature with the epitaxial growth thickness. Therefore, when the epitaxial growth rate is constant, the temperature of the epitaxial surface exhibits a fluctuating trend of first decreasing and then increasing with the epitaxial growth time.

[0115] like Figure 9 and Figure 10 As shown, during the time interval from 0 to t1, the first temperature decreases with the epitaxial growth time; during the time interval from t1 to t2, the first temperature increases with the epitaxial growth time, thus forming a cycle. This cycle continues to fluctuate in the next cycle until the preset growth time is reached. The temperature of the epitaxial surface exhibits a periodic fluctuation of first decreasing and then increasing with the epitaxial growth time, which can also be understood as a cosine-like fluctuation. This yields the actual growth law of heteroepitaxial GaN material on sapphire: the temperature of the epitaxial surface exhibits a fluctuating trend of first decreasing and then increasing with the epitaxial growth time. Using this actual growth law as the basis for adjusting heating conditions allows for a higher degree of adaptation between the heating conditions and the growth law of heteroepitaxial GaN material on sapphire. It is easy to understand that if the heating conditions are adjusted based on the growth law currently known to those skilled in the art, and combined with the principle that the heating temperature has an opposite trend to the first temperature, the heating temperature will be controlled to rise monotonically with the epitaxial growth time. This has a very low degree of compatibility with the actual growth law of fluctuating changes from first decreasing to increasing, and it is difficult to effectively compensate for the temperature of the epitaxial surface. As a result, the crystal quality of the epitaxial wafer is still poor.

[0116] Based on the actual growth pattern obtained as the basis for adjusting the heating temperature, and combined with the principle that the heating temperature and the first temperature have opposite trends, the trend of heating temperature changing with epitaxial growth time can be obtained, such as... Figure 10 As shown, during the time period from 0 to t1, the heating temperature increases with the epitaxial growth time; during the time period from t1 to t2, the heating temperature decreases with the epitaxial growth time, exhibiting a fluctuating change of first increasing and then decreasing. Therefore, the obtained pattern of heating temperature variation with epitaxial growth time can be input into the epitaxial equipment before the process is executed, and heating conditions can be set. During the process, the current epitaxial growth time is monitored, and the heating temperature is adjusted to a value corresponding to the current epitaxial growth time, thus enabling more accurate temperature compensation.

[0117] Figure 10 Specifically, the temperature of the epitaxial surface during one cycle is shown to change with the epitaxial growth time. Compared with the temperature of the epitaxial surface without temperature compensation, i.e., the first temperature, the temperature of the epitaxial surface with temperature compensation, i.e., the second temperature, changes less with the epitaxial growth time and the overall trend is relatively flat. The difference between the maximum and minimum values ​​of the second temperature is only in the range of 0℃-4℃. The temperature of the epitaxial surface can be maintained within the temperature range of the growth window, the epitaxial growth can maintain the optimal growth mode, and the crystal quality is improved.

[0118] Please continue to refer to this. Figure 10 The heating temperature exhibits a fluctuating change with the epitaxial growth time, first increasing and then decreasing. Specifically, during the time interval 0 to t1, the heating temperature increases with the epitaxial growth time; during the time interval t1 to t2, the heating temperature decreases with the epitaxial growth time. The epitaxial growth rate of the GaN epitaxial layer is less than or equal to 200 nm / h, with t1 ranging from 270 min to 290 min and t2 ranging from 510 min to 530 min. The difference between the highest and lowest heating temperatures ranges from 40°C to 50°C. Therefore, during the time interval 0 to t1, the heating temperature is increased by 40°C to 50°C to compensate for the gradually decreasing temperature of the epitaxial surface, bringing the temperature back within the growth window. During the time interval t1 to t2, the heating temperature is decreased by 40°C to 50°C to reduce the impact on the gradually increasing temperature of the epitaxial surface, maintaining the temperature within the growth window. This approximates the flattening of the historical temperature variation curve and reduces the temperature change of the epitaxial surface. Furthermore, the difference between the highest and lowest heating temperatures is in the range of 47°C to 50°C, which is more conducive to compensating for the temperature of the epitaxial surface.

[0119] Optionally, the heating temperature fluctuates periodically with the epitaxial growth time. Understandably, within one cycle, such as... Figure 10 As shown, during the time interval from 0 to t1, the heating temperature increases with the epitaxial growth time; during the time interval from t1 to t2, the heating temperature decreases with the epitaxial growth time. The curve of heating temperature versus epitaxial growth time contains multiple such periods, exhibiting periodic fluctuations. Understandably, during heteroepitaxial growth, the temperature of the epitaxial surface fluctuates periodically with the epitaxial growth time, and the fluctuation period is related to the epitaxial growth rate. Therefore, when the heating temperature fluctuates periodically with the epitaxial growth time, under a constant epitaxial growth rate, the heating temperature can further exhibit uniform periodic fluctuations with the epitaxial growth time.

[0120] Optionally, the heating rate ranges from 0 to 0.5 °C / min; and / or the cooling rate ranges from 0 to 0.6 °C / min. Therefore, controlling the heating rate and / or cooling rate within a certain range can reduce thermal stress caused by rapid temperature changes, prevent substrate and epitaxial layer cracking, and avoid problems such as uneven growth and increased defects caused by rapid temperature changes, thus improving the quality of the epitaxial wafer.

[0121] Optionally, the heating rate increases and then decreases with the epitaxial growth time; and / or, the cooling rate increases and then decreases with the epitaxial growth time. Therefore, when the epitaxial surface temperature begins to decrease, the heating rate gradually increases to quickly compensate for the temperature drop, and then gradually decreases to avoid excessively rapid heating, which could cause large temperature fluctuations and adversely affect epitaxial growth. The cooling rate follows the same principle.

[0122] Please refer to Figure 6 Optionally, a temperature measuring device 700 is provided on the side of the base 300 facing the sapphire substrate 100. The temperature measuring device 700 is used to monitor a second temperature, which is the temperature of the epitaxial surface during the epitaxial growth process. The preparation method also includes: adjusting the rate of change of the heating temperature based on the second temperature. Understandably, before executing the process, the operator will set the process conditions in advance, and the equipment can automatically execute according to the process conditions. However, the growth of the epitaxial layer is not only determined by the epitaxial growth process conditions, but is also affected by other factors such as process equipment conditions. In actual execution, the effect of the heating temperature on the temperature change of the epitaxial surface may not be as expected. Therefore, during the epitaxial growth process, the temperature of the epitaxial surface is monitored in real time by a temperature measuring device, and the heating rate and / or cooling rate are adjusted in real time according to the temperature of the epitaxial surface to control the degree of heating and achieve the expected temperature compensation effect. Understandably, when obtaining historical temperature change patterns, a temperature measuring device is also set up to monitor the temperature of the epitaxial surface in historical epitaxial growth processes, i.e., the first temperature. In embodiments where a heating device is located on the side of the substrate furthest from the sapphire substrate, the temperature measuring device can form an interconnected feedback loop with the heating device. Thus, the temperature measuring device can feed back the monitored second temperature to the heating device, which can then adjust the rate of change of the heating temperature. In some specific embodiments, the temperature measuring device can be used to monitor the first temperature during the execution of a historical epitaxial growth process.

[0123] Furthermore, the temperature measuring device may include an infrared thermometer; the base is a rotating base; the temperature measuring beam of the infrared thermometer forms a temperature measuring spot on the sapphire substrate that is offset from the center point of the sapphire substrate. The infrared thermometer emits infrared laser light towards the base. According to the blackbody radiation law, the substrate on the base and the material layer being epitaxially grown will radiate infrared energy outward. The infrared thermometer receives the reflected infrared energy and converts it into temperature. Since the emissivity of a real object may differ from that of an ideal blackbody, the infrared surface emissivity is corrected using the growth principle to obtain the actual temperature. The infrared thermometer may also include an infrared camera, which can acquire the temperature of the entire epitaxial surface.

[0124] In some other embodiments, the temperature measuring device may include an optical temperature measuring device. The temperature of the epitaxial surface is monitored by measuring the luminescence intensity of the epitaxial surface.

[0125] Understandably, in epitaxial growth equipment commonly used in this field, the substrate support is typically a rotating base to improve the uniformity of epitaxial growth. Since infrared thermometers detect temperature by forming a temperature-measuring spot on an object using a temperature-measuring optical path, and this spot has a small diameter, covering only a small portion of the object, it cannot determine the temperature of the entire object. Considering that the heating temperature of different parts of the substrate may be uneven during epitaxial growth, the temperature-measuring spot formed by the infrared thermometer's optical path on the sapphire substrate is offset from the center point of the sapphire substrate. As the base rotates, the temperature-measuring spot forms at different positions, allowing the infrared thermometer to obtain the temperature at multiple locations on the epitaxial surface. By averaging these locations, the temperature of the epitaxial surface can be more accurately and comprehensively reflected.

[0126] In this embodiment, the base rotates at 20 revolutions per minute. The infrared thermometer performs multiple measurements within 1 minute, and the values ​​obtained from these multiple measurements provide a more accurate assessment of the temperature of the epitaxial surface.

[0127] Please refer to Figure 11 This application also provides a method for preparing an epitaxial wafer, comprising:

[0128] Step S201: Provide a first substrate;

[0129] Step S202: Perform a first epitaxial growth process to epitaxially grow a first heteroepitaxial layer on a first substrate under a first heating condition to obtain a first epitaxial wafer; wherein, during the execution of the first epitaxial growth process, a first temperature is monitored to obtain the historical temperature change law of the first temperature with the epitaxial growth time or epitaxial growth thickness, and the first temperature is the temperature of the epitaxial surface during the first epitaxial growth process.

[0130] Step S203: Provide a second substrate;

[0131] Step S204: Perform a second epitaxial growth process to epitaxially grow a second heteroepitaxial layer on a second substrate under a second heating condition to obtain a second epitaxial wafer; wherein, the second heating condition is determined according to historical temperature change patterns to reduce temperature changes on the epitaxial surface during the second epitaxial growth process; wherein, the second substrate and the first substrate are the same type of substrate; the first epitaxial growth process and the second epitaxial growth process are the same epitaxial growth process and have the same process conditions; the first heteroepitaxial layer and the second heteroepitaxial layer are the same type of heteroepitaxial layer.

[0132] Understandably, this embodiment first performs the same epitaxial growth process on the same substrate to grow the same heteroepitaxial layer, thereby obtaining the growth law of the heteroepitaxial layer material on the substrate material, that is, the historical temperature change law of the epitaxial surface temperature with the epitaxial growth time or epitaxial growth thickness. Then, in actual preparation, the temperature change of the epitaxial surface is predicted according to this law, the heating conditions are accurately controlled, the adaptability of heating conditions and growth law is improved, so as to reduce the temperature change of the epitaxial surface during the epitaxial growth process, so that the temperature of the epitaxial surface meets the growth conditions of the optimal growth mode, and improves the quality of the epitaxial wafer.

[0133] In related technologies, when the epitaxial layer material is mercury cadmium telluride (HCDT), As atoms are doped during the epitaxial process. As doping introduces specific defect structures into HCDT, such as As-Hg complexes and acceptors formed by As occupying Te sites. The concentration and distribution of these defects change with the growth temperature. Therefore, by monitoring the defect concentration of HCDT in real time during epitaxial growth, reflecting the As doping concentration, the change in epitaxial surface temperature can be indirectly inferred, thus obtaining the epitaxial growth law of HCDT and using this growth law to regulate the heating conditions. However, this approach has material limitations; the stringent requirement of a growth temperature of 190±2℃ is extremely rare in other epitaxial materials, making it difficult to apply in other material systems. The solution provided in this application, however, has higher applicability.

[0134] First, step S201 is performed: a first substrate is provided.

[0135] The first substrate can be any suitable semiconductor substrate, such as a bulk silicon substrate, or at least one of the following materials: SiGe, SiC, SiGeC, TnAs, GaAs, InP, or other group III and group V compound semiconductors, including multilayer structures formed from these semiconductors, or silicon-on-insulator (SOI), silicon-germanium-on-insulator (SiGeOI), and germanium-on-insulator (GeOI), or a sapphire substrate, etc. In this embodiment, the first substrate is specifically, for example, a sapphire substrate.

[0136] After performing step S201, the preparation method further includes: fixing a first substrate onto a base; a temperature measuring device is provided on the side of the base facing the first substrate, the temperature measuring device being used to monitor a first temperature, which is the temperature of the epitaxial surface during the first epitaxial growth process. Thus, the temperature of the epitaxial surface during the epitaxial process can be monitored by the temperature measuring device, facilitating the acquisition of historical temperature variation patterns.

[0137] Understandably, since epitaxial growth typically requires a certain temperature to proceed, the epitaxial growth process is usually performed under specific heating conditions, and these conditions generally remain constant throughout the entire epitaxial growth process. Therefore, in this embodiment, a first heating condition is required when performing the first epitaxial growth process. Consequently, a heating device can be provided on the side of the substrate away from the first substrate to provide the first heating condition.

[0138] Next, step S202 is executed: the first epitaxial growth process is executed, and the first heteroepitaxial layer is epitaxially grown on the first substrate under the first heating condition to obtain the first epitaxial wafer; wherein, during the execution of the first epitaxial growth process, the first temperature is monitored to obtain the historical temperature change law of the first temperature with the epitaxial growth time or the epitaxial growth thickness, and the first temperature is the temperature of the epitaxial surface during the first epitaxial growth process.

[0139] Understandably, the concept of a "growth window" exists in epitaxial growth processes. Here, the "growth window" refers to a range of parameters under specific conditions that enable high-quality epitaxial growth. These parameters may include growth temperature, molecular beam flux, and vacuum level. By precisely controlling these parameters, thin film materials with specific crystal structures and properties can be grown on a substrate.

[0140] During epitaxial growth, the epitaxial surface is constantly changing. If we consider epitaxial growth as the formation of countless sequentially stacked material layers, then the surface of each formed material layer becomes the epitaxial surface of the next material layer to be formed. Because a heterogeneous epitaxial layer is formed on the substrate, the thermal conductivity of the substrate and the epitaxial layer may differ. A heterogeneous interface exists between the substrate and the epitaxial layer, and the interface thermal resistance hinders heat conduction from the substrate. As the epitaxial layer thickness increases, the path for heat conduction from the substrate to the epitaxial surface lengthens, reducing heat conduction efficiency. Furthermore, more material layers participate in the heat conduction process, increasing the heat dispersion path. Therefore, the temperature of the epitaxial surface changes with increasing epitaxial growth thickness. Since epitaxial growth thickness = epitaxial growth rate * epitaxial growth time, there is a linear relationship between epitaxial growth thickness and epitaxial growth time. With a fixed epitaxial growth rate, the temperature change of the epitaxial surface with epitaxial growth thickness is equivalent to the temperature change of the epitaxial surface with epitaxial growth time. Therefore, with a fixed epitaxial growth rate, the temperature of the epitaxial surface will also change with increasing epitaxial growth time. The temperature of the epitaxial surface may drop outside the growth window, causing a change in the growth pattern and ultimately having an adverse effect on the quality of the crystal.

[0141] Next, step S203 is performed: a second substrate is provided. The second substrate is the same type of substrate as the first substrate to ensure that the substrate on which the epitaxial growth process is performed is the same.

[0142] In some embodiments, after performing step S203, the fabrication method may further include: fixing a second substrate in a base; providing a heating device on the side of the base away from the second substrate, the heating device being used to provide a second heating condition; and the projection of the heating device covering the projection of the second substrate in the direction along the thickness of the second substrate. Thus, in any epitaxial growth apparatus, by providing a heating device on the side of the base away from the second substrate, a heating temperature can be provided; and the projection of the heating device covers the projection of the second substrate, the heating area of ​​the heating device being at least equal to the area of ​​the substrate, which ensures heating of the entire substrate, improves heating efficiency, and makes heating more uniform, thus helping to ensure the uniformity of epitaxial growth.

[0143] In some embodiments, after performing step S203, the fabrication method may further include: fixing a second substrate below a base; a heating device is disposed above the base, the heating device being used to provide a second heating condition. This heating device can also be used to provide the first heating condition during the first epitaxial growth process, but it is understood that the second heating condition is determined based on historical temperature variation patterns summarized from the first epitaxial growth process, and the first heating condition differs from the second heating condition.

[0144] Furthermore, along the thickness of the second substrate, the projection of the heating device covers the projection of the second substrate. Therefore, the heating area of ​​the heating device is at least equal to the area of ​​the substrate, ensuring heating of the entire substrate, improving heating efficiency, and making the heating more uniform, which is beneficial for ensuring the uniformity of epitaxial growth.

[0145] Optionally, both the first and second epitaxial growth processes include molecular beam epitaxy (MBE). The MBE equipment includes an ultra-high vacuum chamber to provide a clean growth environment; a base, also known as a sample stage, to support the substrate; and a molecular beam source, also known as an evaporation source, located below the base to generate the desired molecular or atomic beam. Therefore, after the substrate is fixed below the base, the molecular or atomic beam generated by the molecular beam source can be sprayed onto the substrate for epitaxial growth. In this embodiment, a heating device is installed above the base to provide heating temperature and apply it to the substrate. The heating device may include a thermocouple.

[0146] Optionally, a back metal layer is formed on the second substrate; epitaxially growing a second heteroepitaxial layer on the second substrate includes epitaxially growing the second heteroepitaxial layer on the side of the second substrate away from the back metal layer. It is understood that in a vacuum cavity, the thermal conductivity of air is greatly reduced, and the second substrate is an epitaxial growth substrate, typically made of semiconductor material with low thermal conductivity; directly heating the second substrate may be inefficient. Therefore, embodiments of this application improve the heating efficiency of the second substrate by forming a back metal layer on the second substrate, utilizing the good thermal conductivity of the metal, and also make the heating of the second substrate more uniform, which is beneficial to ensuring the uniformity of epitaxial growth.

[0147] The material of the back metal layer may include titanium and / or tungsten. Titanium and / or tungsten have good thermal conductivity and are inexpensive. In this embodiment, the material of the back metal layer is specifically, for example, titanium, which has better ductility and can better accommodate the thermal expansion and contraction of the substrate during heating and cooling, reducing thermal stress-induced cracks and defects.

[0148] The thickness of the back metal layer can range from 50 nm to 500 nm. Understandably, if the back metal layer is too thick, its ability to adapt to the thermal expansion and contraction of the substrate decreases. Under large temperature changes, the substrate is prone to cracking or delamination, affecting the quality of the epitaxial wafer. If the back metal layer is too thin, insufficient heat conduction will result in poor heating efficiency and uniformity, affecting the crystal quality of the epitaxial layer. Therefore, controlling the thickness of the back metal layer within this range can achieve a relatively ideal heat conduction effect while avoiding damage to the substrate. In this embodiment, the thickness of the back metal layer is 500 nm, and the process is more mature.

[0149] Step S204: Perform a second epitaxial growth process, growing a second heteroepitaxial layer on a second substrate under second heating conditions to obtain a second epitaxial wafer. The second heating conditions are determined based on historical temperature variation patterns to reduce temperature changes on the epitaxial surface during the second epitaxial growth process. The first and second epitaxial growth processes are the same epitaxial growth process with identical process conditions. The first and second heteroepitaxial layers are also the same type of heteroepitaxial layer. Therefore, by performing the same epitaxial growth process on the same substrate beforehand to grow the same heteroepitaxial layer, the historical temperature variation pattern of the epitaxial surface temperature with epitaxial growth time or thickness is obtained. During actual fabrication, this pattern is used to predict temperature changes on the epitaxial surface, accurately control heating conditions, reduce temperature changes on the epitaxial surface during epitaxial growth, and improve the quality of the epitaxial wafer.

[0150] Optionally, a temperature measuring device is provided on the side of the base facing the second substrate. This device monitors a second temperature, which is the temperature of the epitaxial surface during the second epitaxial growth process. The fabrication method further includes adjusting the second heating conditions based on the second temperature. Understandably, operators pre-set process conditions before executing the process, and the equipment can automatically execute according to these conditions. However, the growth of the epitaxial layer is not only determined by the epitaxial growth process conditions but is also affected by other factors such as process equipment conditions. In actual execution, the effect of heating conditions on the temperature change of the epitaxial surface may not be as expected. Therefore, by additionally setting a temperature measuring device, the temperature of the epitaxial surface is monitored in real time during epitaxial growth, and the heating conditions are adjusted in real time based on the epitaxial surface temperature to control the degree of heating and achieve the expected temperature compensation effect. In embodiments where a heating device is provided on the side of the base away from the sapphire substrate, the temperature measuring device can form an interconnected feedback with the heating device. Thus, the temperature measuring device can feed back the monitored second temperature to the heating device, which then adjusts the rate of change of the heating temperature accordingly.

[0151] Furthermore, the temperature measuring device may include an infrared thermometer; the base is a rotating base; the temperature measuring spot formed on the second substrate by the temperature measuring optical path of the infrared thermometer is offset from the center point of the second substrate. The infrared thermometer emits infrared laser light towards the base. According to the blackbody radiation law, the substrate on the base and the material layer being epitaxially grown will radiate infrared energy outward. The infrared thermometer receives the reflected infrared energy and converts it into temperature. Since the emissivity of a real object may differ from that of an ideal blackbody, the infrared surface emissivity is corrected using the growth principle to obtain the actual temperature.

[0152] Understandably, in epitaxial growth equipment commonly used in this field, the substrate support is typically a rotating base to improve the uniformity of epitaxial growth. Since infrared thermometers detect temperature by forming a temperature-measuring spot on an object using a temperature-measuring optical path, and this spot has a small diameter, covering only a small portion of the object, it cannot determine the temperature of the entire object. Considering that the heating temperature of different parts of the substrate may be uneven during epitaxial growth, the temperature-measuring spot formed by the infrared thermometer's optical path on the second substrate is offset from the center point of the second substrate. As the base rotates, the temperature-measuring spot will form at different positions, allowing the infrared thermometer to obtain the temperature at multiple locations on the epitaxial surface. By averaging these locations, the temperature of the epitaxial surface can be more accurately and comprehensively reflected.

[0153] In this embodiment, the base rotates at 20 revolutions per minute. The infrared thermometer performs multiple measurements per minute, obtaining multiple values ​​for a more accurate determination of the epitaxial surface temperature. The infrared thermometer may also include an infrared camera, which can acquire the temperature of the entire epitaxial surface.

[0154] In some other embodiments, the temperature measuring device may include an optical temperature measuring device. The temperature of the epitaxial surface is monitored by measuring the luminescence intensity of the epitaxial surface.

[0155] In some optional specific examples, both the first substrate and the second substrate include sapphire substrates; both the first heteroepitaxial layer and the second heteroepitaxial layer include GaN epitaxial layers; the second heating temperature of the second heating condition exhibits a fluctuating change, first increasing and then decreasing, with the epitaxial growth time or epitaxial growth thickness. Therefore, by first heteroepitaxially growing the first heteroepitaxial layer (GaN epitaxial layer) on the first substrate (sapphire substrate), the historical temperature variation law of the first temperature with the epitaxial growth thickness or epitaxial growth time is obtained, thus acquiring the actual growth law. In subsequent fabrication, the heating conditions are adjusted based on the historical temperature variation law, so that the second heating temperature of the second heating condition exhibits a fluctuating change, first increasing and then decreasing, with the epitaxial growth time or epitaxial growth thickness. This improves the adaptability of the second heating conditions to the growth law, allowing for more effective temperature compensation, reducing temperature changes on the epitaxial surface, and improving the quality of the epitaxial wafer. For a specific example, please refer to the description in the epitaxial wafer fabrication method provided in the foregoing embodiments; further details are omitted here.

[0156] This application also provides an epitaxial wafer, prepared using the epitaxial wafer preparation method provided in any of the foregoing embodiments. Therefore, during the epitaxial growth process, the temperature change on the epitaxial surface is reduced and controlled within the growth window range, meeting the growth conditions of the optimal growth mode, and the crystal quality of the epitaxial wafer is effectively improved.

[0157] It should be understood that the above embodiments are exemplary and are not intended to encompass all possible implementations included in the claims. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of this application that may not be explicitly described. Therefore, the above embodiments only illustrate several implementations of this application and do not limit the scope of protection of this patent application.

Claims

1. A method for preparing an epitaxial wafer, characterized in that, The preparation method includes: Provide sapphire substrates; An epitaxial growth process is performed to grow a GaN epitaxial layer on the sapphire substrate under heating conditions to obtain an epitaxial wafer; The heating temperature under the heating conditions exhibits a fluctuating change, first increasing and then decreasing, with the epitaxial growth time or the epitaxial growth thickness, in order to reduce the temperature change of the epitaxial surface during the epitaxial growth process. The change in heating temperature is determined based on historical temperature change patterns, which are the patterns of first temperature change with epitaxial growth thickness. The first temperature is the temperature of the epitaxial surface during the historical epitaxial growth process, and the heating temperature has an opposite trend to the first temperature.

2. The method for preparing an epitaxial wafer according to claim 1, characterized in that, The heating temperature under the heating conditions exhibits a fluctuating change, first increasing and then decreasing, as the epitaxial growth time increases. The change in heating temperature is determined based on historical temperature variation patterns. The historical temperature variation pattern refers to the variation of the first temperature with the epitaxial growth time. The first temperature is the temperature of the epitaxial surface during the historical epitaxial growth process. The heating temperature has an opposite trend to the first temperature. The epitaxial growth rate of the GaN epitaxial layer is the same as the historical epitaxial growth rate during the historical epitaxial growth process.

3. The method for preparing an epitaxial wafer according to claim 1, characterized in that, The heating conditions, wherein the heating temperature fluctuates with the epitaxial growth time, first increasing and then decreasing, including: During the time period from 0 to t1, the heating temperature increases with the epitaxial growth time; During the time period from t1 to t2, the heating temperature decreases with the epitaxial growth time; Wherein, the epitaxial growth rate of the GaN epitaxial layer is less than or equal to 200 nm / h, the range of t1 is 270 min to 290 min, the range of t2 is 510 min to 530 min, and the range of the difference between the highest and lowest heating temperatures is 40°C to 50°C.

4. The method for preparing an epitaxial wafer according to claim 1, characterized in that, The heating conditions, wherein the heating temperature fluctuates with the epitaxial growth thickness, first increasing and then decreasing, including: Within the thickness range of 0 to h1, the heating temperature increases with the epitaxial growth thickness; Within the thickness range of h1 to h2, the heating temperature decreases with the epitaxial growth thickness; Wherein, h1 ranges from 900nm to 967nm, h2 ranges from 1700nm to 1767nm, and the difference between the highest and lowest heating temperatures ranges from 40℃ to 50℃.

5. The method for preparing an epitaxial wafer according to claim 1, characterized in that, The heating conditions are such that the heating temperature fluctuates, first increasing and then decreasing, with the epitaxial growth time, and the heating temperature rise rate is in the range of 0-0.5℃ / min; and / or, the heating temperature cools down in the range of 0-0.6℃ / min.

6. The method for preparing an epitaxial wafer according to claim 1, characterized in that, The heating temperature under the heating conditions exhibits a fluctuating change, first increasing and then decreasing, with the epitaxial growth thickness. The heating rate ranges from 0 to 1.5 °C / nm; and / or, the cooling rate ranges from 0 to 1.8 °C / nm.

7. The method for preparing an epitaxial wafer according to claim 1, characterized in that, The heating conditions are such that the heating temperature first increases and then decreases with the epitaxial growth time, the heating rate first increases and then decreases with the epitaxial growth time, and / or the cooling rate first increases and then decreases with the epitaxial growth time.

8. The method for preparing an epitaxial wafer according to claim 1, characterized in that, The heating conditions are such that the heating temperature fluctuates with the epitaxial growth thickness, first increasing and then decreasing; the heating rate increases and then decreases with the epitaxial growth thickness; and / or the cooling rate decreases and then increases with the epitaxial growth thickness.

9. The method for preparing an epitaxial wafer according to claim 1, characterized in that, The heating temperature under the heating conditions exhibits a fluctuating change, first increasing and then decreasing, with the heating temperature fluctuating periodically with the epitaxial growth time.

10. The method for preparing an epitaxial wafer according to claim 1, characterized in that, The heating temperature under the heating conditions exhibits a fluctuating change, first increasing and then decreasing, with the heating temperature fluctuating periodically with the epitaxial growth thickness.

11. The method for preparing an epitaxial wafer according to claim 1, characterized in that, The epitaxial growth process includes molecular beam epitaxy.

12. The method for preparing an epitaxial wafer according to claim 11, characterized in that, After providing the sapphire substrate, the preparation method further includes: fixing the sapphire substrate under the base; A heating device is provided above the base, and the heating device is used to provide the heating temperature.

13. The method for preparing an epitaxial wafer according to claim 11, characterized in that, A back metal layer is formed on the sapphire substrate; The epitaxial growth of a GaN epitaxial layer on the sapphire substrate includes: epitaxially growing a GaN epitaxial layer on the side of the sapphire substrate away from the back metal layer.

14. The method for preparing an epitaxial wafer according to claim 1, characterized in that, After providing the sapphire substrate, the preparation method further includes: fixing the sapphire substrate in a base; A heating device is provided on the side of the base away from the sapphire substrate. The heating device is used to provide the heating temperature to compensate the temperature of the epitaxial surface. The projection of the heating device overlaps the projection of the sapphire substrate along the thickness direction of the sapphire substrate.

15. The method for preparing an epitaxial wafer according to claim 1, characterized in that, After providing the sapphire substrate, the preparation method further includes: fixing the sapphire substrate in a base; A temperature measuring device is provided on the side of the base facing the sapphire substrate. The temperature measuring device is used to monitor a second temperature, which is the temperature of the epitaxial surface during the epitaxial growth process. The preparation method further includes: adjusting the rate of change of the heating temperature based on the second temperature.

16. The method for preparing an epitaxial wafer according to claim 15, characterized in that, The temperature measuring device includes an infrared thermometer; The base is a rotating base; The infrared thermometer's measuring optical path forms a measuring spot on the sapphire substrate that is off-center from the center of the sapphire substrate.

17. A method for preparing an epitaxial wafer, characterized in that, The preparation method includes: Provide a first substrate; A first epitaxial growth process is performed to epitaxially grow a first heteroepitaxial layer on the first substrate under a first heating condition to obtain a first epitaxial wafer; During the execution of the first epitaxial growth process, a first temperature is monitored to obtain the historical temperature variation law of the first temperature with the epitaxial growth time or epitaxial growth thickness. The first temperature is the temperature of the epitaxial surface during the first epitaxial growth process. Provide a second substrate; A second epitaxial growth process is performed to epitaxially grow a second heteroepitaxial layer on the second substrate under a second heating condition to obtain a second epitaxial wafer; The second heating condition is determined based on the historical temperature change pattern in order to reduce the temperature change of the epitaxial surface during the second epitaxial growth process. Wherein, the second substrate and the first substrate are the same type of substrate; the first epitaxial growth process and the second epitaxial growth process are the same type of epitaxial growth process, and the process conditions are the same; the first heteroepitaxial layer and the second heteroepitaxial layer are the same type of heteroepitaxial layer.

18. The method for preparing an epitaxial wafer according to claim 17, characterized in that, Both the first epitaxial growth process and the second epitaxial growth process include molecular beam epitaxy.

19. The method for preparing an epitaxial wafer according to claim 18, characterized in that, After providing the second substrate, the preparation method further includes: fixing the second substrate below the base; A heating device is provided above the base, and the heating device is used to provide the second heating condition.

20. The method for preparing an epitaxial wafer according to claim 18, characterized in that, A back metal layer is formed on the second substrate; The step of epitaxially growing a second heteroepitaxial layer on the second substrate includes: epitaxially growing the second heteroepitaxial layer on the side of the second substrate away from the back metal layer.

21. The method for preparing an epitaxial wafer according to claim 17, characterized in that, After providing the second substrate, the preparation method further includes: fixing the second substrate in a base; A heating device is provided on the side of the base away from the second substrate, and the heating device is used to provide the second heating condition; The projection of the heating device overlaps the projection of the second substrate along the direction of the thickness of the second substrate.

22. The method for preparing an epitaxial wafer according to claim 17, characterized in that, After providing the second substrate, the preparation method further includes: fixing the second substrate in a base; A temperature measuring device is provided on the side of the base facing the second substrate. The temperature measuring device is used to monitor a second temperature, which is the temperature of the epitaxial surface during the second epitaxial growth process. The preparation method further includes: adjusting the second heating conditions based on the second temperature.

23. The method for preparing an epitaxial wafer according to claim 22, characterized in that, The temperature measuring device includes an infrared thermometer; The base is a rotating base; The temperature measuring spot formed by the temperature measuring optical path of the infrared thermometer on the second substrate is off-center from the center point of the second substrate.

24. The method for preparing an epitaxial wafer according to claim 17, characterized in that, Both the first substrate and the second substrate comprise sapphire substrates; both the first heteroepitaxial layer and the second heteroepitaxial layer comprise GaN epitaxial layers; The second heating temperature under the second heating condition exhibits a fluctuating change, first increasing and then decreasing, depending on the epitaxial growth time or the epitaxial growth thickness.

25. An epitaxial wafer, characterized in that, It is prepared by the method for preparing an epitaxial wafer as described in any one of claims 1 to 24.

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