A graphite boat for improving surface morphology of a thin film material and a method for growing a thin film

Abstract

The application belongs to the technical field of epitaxial growth of thin film materials, and particularly relates to a graphite boat for improving surface morphology of thin film materials in horizontal liquid phase epitaxial growth and a growth method of thin films. By using the graphite boat and the growth method of epitaxial thin films provided by the application, macroscopic ripple defects of the epitaxially grown thin film materials caused by solute convection and mercury pressure difference during the preparation of the thin film materials by horizontal liquid phase epitaxy can be eliminated, the uniformity and flatness of the thickness and components of the thin film materials are improved, and the imaging "ghost" phenomenon of the detector is improved.

Description

Technical Field

[0001] This invention belongs to the field of epitaxial growth technology of thin film materials, and relates to a graphite boat for improving the surface morphology of thin film materials and a method for growing thin films, specifically a graphite boat for improving the surface morphology of horizontal liquid phase epitaxially grown thin film materials and a method for growing thin films. Background Technology

[0002] Mercury cadmium telluride (Hg) 1-x Cd x Mercury cadmium telluride (MCH) materials have the characteristics of adjustable band gap, large optical absorption coefficient, long carrier lifetime, high electron mobility, and high operating temperature. Its excellent performance makes MCH a very important material for manufacturing infrared focal plane array devices and has been the first choice for preparing infrared detectors for many years.

[0003] Horizontal push-boat liquid phase epitaxy (LPE) technology for growing mercury cadmium telluride (HCdT) thin films has gained widespread application due to its advantages such as low mother liquor consumption and easy composition control. The graphite boat is the most critical component in the horizontal LPE growth process, and its structural design directly determines the quality of the grown film. However, HCdT epitaxial films grown using the existing horizontal push-boat LPE process often exhibit macroscopic ripple defects on their surface. On a 10-micrometer-thick crystal surface, ripples with a height difference of at least 3 micrometers can appear. These surface ripples not only affect the interconnection process of large-scale chips but also cause "ghosting" phenomena in detector imaging, severely impacting the detection of point source targets in detector components. Therefore, reducing the surface undulation height difference and improving the horizontal epitaxial ripple phenomenon are crucial for chip fabrication processes and detector imaging quality.

[0004] Currently, the theory of macroscopic ripple formation in horizontal liquid phase epitaxy mainly includes two aspects: First, the uniformity of the temperature field affects the convection of the mother liquor during epitaxy, with solute convection becoming dominant. Solute convection is a spatially inhomogeneous and time-dependent phenomenon, and this inhomogeneity leads to differences in crystallization points and composition, thus causing macroscopic ripple defects. Second, the uniformity of mercury pressure above the mother liquor is affected. Factors such as the design of the mercury protection source and the airtightness of the graphite boat can influence the mercury pressure difference above the mother liquor, affecting the uniformity of film thickness and composition.

[0005] Current reports indicate that to improve the macroscopic ripples in horizontal liquid phase epitaxy and reduce their adverse effects on chip fabrication processes and detector imaging quality, planarization processes are typically used to polish the surface of epitaxially grown mercury cadmium telluride (HCdT) thin films. While polishing can improve the surface smoothness of the epitaxial film, it cannot address the compositional differences in different parts of the epitaxial film caused by solute convection. This means it cannot improve the "ghosting" phenomenon in detector imaging caused by these compositional differences. Furthermore, polishing inevitably causes some surface damage to the epitaxial film material, severely impacting the performance of the detector chip.

[0006] To improve the macroscopic ripple phenomenon in epitaxial thin films, existing technologies include modifications to the structure of graphite boats. Many graphite boat designs exist to improve mercury pressure uniformity, but simply controlling mercury pressure uniformity cannot solve the macroscopic ripple defect. Only by simultaneously controlling the differences in crystallization points and composition caused by mother liquor thermal convection can the macroscopic ripple defect be effectively mitigated and the "ghosting" phenomenon in detector imaging improved.

[0007] Therefore, there is a need to provide a technical solution to address the aforementioned technical problems existing in the prior art. Summary of the Invention

[0008] This invention provides a graphite boat for improving the surface morphology of horizontal liquid phase epitaxial growth thin film materials and a method for growing thin films, which can at least solve some of the problems existing in the prior art.

[0009] To address the aforementioned technical problems, according to one aspect of the present invention, the present invention provides the following technical solution:

[0010] A horizontal liquid phase epitaxial graphite boat, wherein the graphite boat includes a mother liquor cover plate, a heat insulation cover plate, a mother liquor plate, and a substrate plate; the mother liquor cover plate is disposed above the mother liquor plate, the substrate plate is provided with a substrate groove for placing a substrate, the mother liquor plate is provided with a mother liquor groove for placing mother liquor, the heat insulation cover plate is disposed on the mother liquor groove, the mother liquor plate is located above the substrate plate and the two are slidably disposed relative to each other.

[0011] As a preferred embodiment of the horizontal liquid phase epitaxial graphite boat of the present invention, the graphite boat further includes a base plate, and the substrate plate is disposed above the base plate.

[0012] As a preferred embodiment of the horizontal liquid phase epitaxial graphite boat of the present invention, the mother liquor plate is further provided with a mercury source protection tank, which is symmetrically arranged on both sides of the mother liquor tank.

[0013] As a preferred embodiment of the horizontal liquid phase epitaxial graphite boat of the present invention, wherein: a heat insulation tank is provided around the mother liquor tank, and the heat insulation cover plate includes a top wall and side walls extending downward from the top wall around the perimeter. The top wall is located above the mother liquor tank, and the side walls are inserted into the heat insulation tank.

[0014] As a preferred embodiment of the horizontal liquid phase epitaxial graphite boat described in this invention, the material of the heat-insulating cover plate is selected from quartz or alumina heat-insulating materials.

[0015] As a preferred embodiment of the horizontal liquid phase epitaxial graphite boat of the present invention, the heat insulation cover plate adopts an integral design, the side wall of the heat insulation cover plate is a hollow structure, or the thickness of the side wall is greater than the thickness of the top wall.

[0016] In a preferred embodiment of the horizontal liquid phase epitaxial graphite boat described in this invention, the top dimension of the mother liquor tank is larger than the bottom dimension.

[0017] As a preferred embodiment of the horizontal liquid phase epitaxial graphite boat of the present invention, the bottom edge of the mother liquor tank is provided with a stepped structure.

[0018] As a preferred embodiment of the horizontal liquid phase epitaxial graphite boat described in this invention, the bottom dimension of the mother liquor tank is equal to or slightly smaller than the dimension of the substrate tank.

[0019] To solve the above-mentioned technical problems, according to another aspect of the present invention, the present invention provides the following technical solution:

[0020] A method for preparing thin film materials using the above-mentioned horizontal liquid phase epitaxial graphite boat includes the following steps:

[0021] S1: Heat the horizontal epitaxial furnace to the temperature at which the mother liquor is homogenized;

[0022] S2: The horizontal epitaxial furnace is cooled in sections to near the crystallization point of the mother liquor, so that the temperature zones of the graphite boat present a certain temperature gradient from left to right, pushing the mother liquor plate so that the mother liquor tank is located above the substrate.

[0023] S3: Growth ends. Push the mother liquor plate to move the mother liquor tank away from the substrate.

[0024] As a preferred embodiment of the method for preparing thin film materials using the above-mentioned horizontal liquid phase epitaxial graphite boat described in this invention, the horizontal epitaxial furnace has three or more individually temperature-controlled zones.

[0025] As a preferred embodiment of the method for preparing thin film materials using the above-mentioned horizontal liquid phase epitaxial graphite boat described in this invention, during the growth process, a faster cooling rate is used in the higher temperature zone and a slower cooling rate is used in the lower temperature zone, so as to ensure that the temperature gradient is opposite to that at the end of the growth process.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. The horizontal liquid-phase epitaxial graphite boat provided by this invention uses heat-insulating materials such as quartz or alumina inserted around and above the mother liquor tank. The hollow or thickened design of the insulation cover reduces heat diffusion from the graphite boat, thereby improving the temperature uniformity between the center and the periphery of the mother liquor and mitigating thermal convection. Simultaneously, mercury source protection tanks on both sides of the mother liquor tank provide mercury vapor to compensate for the mercury pressure above the mother liquor. The insulation cover allows mercury vapor generated by the mercury sources on both sides to slowly flow into the mother liquor from all sides, eliminating the mercury pressure difference caused by direct flow of mercury vapor from both sides. This improves the thickness and compositional uniformity of the epitaxial film, overcoming the shortcomings of existing technologies that only control mercury pressure, which cannot completely solve the macroscopic ripple defects of the epitaxial film. Ultimately, this eliminates macroscopic ripple defects in the epitaxially grown film, improves the "ghosting" phenomenon in detector imaging, and enhances the growth quality of the epitaxial film.

[0028] 2. The graphite boat of the present invention is used to prepare epitaxial thin films. During the growth of the epitaxial thin film, a three-zone cross temperature control method is adopted to control the movement of the mother liquor heat convection center position through temperature field control, thereby further reducing macroscopic ripple defects and significantly optimizing the epitaxial flatness of the grown mercury cadmium telluride thin film.

[0029] 3. The improved graphite boat structure of the present invention and the control method for epitaxial thin film growth using the graphite boat eliminate the need for subsequent polishing and planarization processes to improve the flatness of the epitaxial thin film, thus avoiding surface damage caused by the positive subtraction polishing process and improving the process quality and performance of chip fabrication and detector chips. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the cross-sectional structure of the graphite boat of the present invention;

[0032] Figure 2This is a schematic diagram showing the movement of the graphite boat during the epitaxial film growth process of the present invention.

[0033] Figure 3 This is a schematic diagram of the temperature control curve during the epitaxial film growth process of the present invention;

[0034] Figure 4a Surface morphology of epitaxial material grown using the unmodified process;

[0035] Figure 4b This is a surface morphology diagram of the epitaxial material grown using the improved process of this invention.

[0036] Explanation of icon numbers:

[0037] 1-Mother liquor cover plate, 2-Insulation cover plate, 3-Mother liquor plate, 4-Substrate plate, 5-Bottom plate, 31-Mother liquor tank, 32-Mercury source protection tank, 33-Insulation tank, 41-Substrate tank.

[0038] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0039] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0041] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0042] This invention provides a graphite boat and a method for growing thin films to improve the surface morphology of horizontal liquid phase epitaxial growth thin film materials. It can eliminate macroscopic ripple defects in the epitaxially grown thin film materials caused by solute convection and mercury pressure differences during the horizontal liquid phase epitaxial growth process, improve the thickness, composition uniformity and flatness of the thin film material, and improve the "ghosting" phenomenon in detector imaging.

[0043] Example 1

[0044] A horizontal liquid phase epitaxial graphite boat includes a base plate 5, a substrate plate 4, a mother liquor plate 3, a heat-insulating cover plate 2, and a mother liquor cover plate 1. The mother liquor cover plate 1 covers the mother liquor plate 3, and the substrate plate 4 is disposed above the base plate 5. The substrate plate 4 has a substrate groove 41 for placing the substrate. The mother liquor plate 3 has a mother liquor groove 31 for placing the mother liquor, and a heat-insulating groove 33 is disposed around the mother liquor groove 31. The heat-insulating cover plate 2 includes a top wall and side walls extending downward from the top wall around the perimeter. The heat-insulating cover plate 2 covers the mother liquor groove 31, with the top wall positioned above the mother liquor groove and the side walls inserted into the heat-insulating groove. The mother liquor plate 3 is located above the substrate plate 4, and the two are slidably disposed relative to each other.

[0045] The mother liquor plate 3 is also equipped with a mercury source protection tank 32, which is symmetrically arranged on both sides of the mother liquor tank 31, which helps to ensure the uniformity of the mother liquor temperature.

[0046] The insulation cover 2 adopts an integrated design. The side walls of the insulation cover 2 are hollow, or the thickness of the side walls is greater than the thickness of the top wall. The material of the insulation cover 2 is selected from heat-insulating materials, preferably quartz or alumina. Both the selection of the insulation cover material and the design of the insulation structure are aimed at improving the insulation performance of the mother liquor tank. This reduces heat diffusion from the graphite boat structure to the outside, improves the uniformity of the mother liquor temperature, and allows compensating mercury vapor to flow from around the mother liquor into the tank, ensuring the uniformity of mercury pressure.

[0047] The top dimension of the mother liquor tank 31 is larger than the bottom dimension, which can further ensure the uniformity of the mother liquor temperature above the extended region.

[0048] The bottom edge of the mother liquor tank 31 is provided with a stepped structure, and its bottom size is equal to or slightly smaller than the size of the substrate tank 41. This can prevent the mother liquor from entering the back side of the substrate, causing liquid contamination on the back side of the substrate and affecting the substrate deposition quality.

[0049] Example 2

[0050] A method for preparing thin film materials using the above-mentioned horizontal liquid phase epitaxial graphite boat includes the following steps:

[0051] S1: Heat the horizontal epitaxial furnace to the temperature at which the mother liquor is homogenized;

[0052] S2: The horizontal epitaxial furnace is cooled in sections to near the crystallization point of the mother liquor, so that the left, middle and right sections of the graphite boat present a certain temperature gradient, which pushes the mother liquor plate and makes the mother liquor tank located above the substrate.

[0053] S3: Growth ends. Push the mother liquor plate to move the mother liquor tank away from the substrate.

[0054] A horizontal epitaxial furnace has more than three individually temperature-controlled zones. Setting a certain number of controllable temperature zones is beneficial for making appropriate and targeted adjustments to the temperature field and cooling rate according to the differences in the growth thickness of the prepared epitaxial film, thereby ensuring the thickness and uniformity of the composition of the epitaxial film deposition.

[0055] Appendix Figure 3 This is a schematic diagram of the temperature control curves during the epitaxial film growth process in this embodiment. The horizontal axis represents time, and the vertical axis represents temperature. The temperature control curves for the first, middle, and last stages correspond to the attached diagram. Figure 2 Temperature curves for the left, center, and right positions of the graphite boat. After the mother liquor is sufficiently homogenized at high temperature, it is cooled at different rates in three sections to create a temperature gradient between the left, center, and right positions of the graphite boat when the mother liquor is near its crystallization point temperature. The mother liquor plate is then pushed to position the mother liquor tank above the substrate, initiating growth. During the growth stage, the cooling rate is fastest in the first section and slowest in the second, ensuring that the temperature field at the end of growth is opposite to that at the beginning. This change in temperature field during growth shifts the position of the highest temperature point in the mother liquor, reducing temperature unevenness caused by the difference in heat dissipation between the center and the periphery, and further mitigating macroscopic ripple defects caused by temperature differences in the mother liquor.

[0056] During the growth of epitaxial films, by specifically adjusting and controlling the cooling rate in different temperature zones, the growth of epitaxial films in different temperature zones can be made more uniform. A faster cooling rate is used in higher temperature zones, and a slower cooling rate is used in lower temperature zones, ultimately ensuring that the temperature gradient is opposite to that at the beginning of growth when the growth is completed.

[0057] From the appendix Figure 4a As can be seen from the data, the maximum height difference between adjacent ripples in the epitaxial thin film material obtained by the unmodified graphite boat and epitaxial method reaches 4.145 μm; while the maximum height difference between adjacent ripples in the epitaxial thin film material obtained by the graphite boat and epitaxial method improved by this invention is reduced to 1.36 μm, as can be seen from the curve data, and the uniformity of the surface of the epitaxial thin film material is significantly improved.

[0058] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing thin film materials using a horizontal liquid-phase epitaxial graphite boat, characterized in that, The horizontal liquid phase epitaxial graphite boat includes: a mother liquor cover plate (1), a heat insulation cover plate (2), a mother liquor plate (3), and a substrate plate (4); the mother liquor cover plate (1) is placed on top of the mother liquor plate (3), the substrate plate (4) is provided with a substrate groove (41) for placing the substrate, the mother liquor plate (3) is provided with a mother liquor groove (31) for placing the mother liquor, the heat insulation cover plate (2) is placed on the mother liquor groove (31), the mother liquor plate (3) is located above the substrate plate (4), and the two can slide relative to each other; the mother liquor plate (3) is also provided with a mercury source protection groove (32), and the mercury source protection groove (32) is symmetrically arranged on both sides of the mother liquor groove (31); The method includes the following steps: S1: Heat the horizontal epitaxial furnace to the temperature at which the mother liquor is homogenized; S2: The horizontal epitaxial furnace is cooled in sections to near the crystallization point of the mother liquor, so that each temperature zone of the graphite boat presents a certain temperature gradient from left to right, pushing the mother liquor plate (3) so that the mother liquor tank (31) is located above the substrate; S3: Growth ends, push the mother liquor plate (3) to make the mother liquor tank (31) leave the substrate.

2. The method according to claim 1, characterized in that, The graphite boat also includes a base plate (5), and the substrate plate (4) is disposed above the base plate (5).

3. The method according to claim 1, characterized in that, The mother liquor tank (31) is surrounded by a heat insulation tank (33). The heat insulation cover plate (2) includes a top wall and side walls extending downward from the top wall. The top wall is located above the mother liquor tank (31), and the side walls are inserted into the heat insulation tank (33).

4. The method according to claim 3, characterized in that, The insulation cover plate (2) adopts an integrated design. The side wall of the insulation cover plate (2) is a hollow structure, or the thickness of the side wall is greater than the thickness of the top wall.

5. The method according to claim 1, characterized in that, The material of the insulation cover plate (2) is selected from quartz or alumina insulation materials.

6. The method according to claim 1, characterized in that, The top dimension of the mother liquor tank (31) is larger than the bottom dimension.

7. The method according to claim 1, characterized in that, The bottom dimension of the mother liquor tank (31) is equal to or slightly smaller than the dimension of the substrate tank (41).

8. The method according to claim 1, characterized in that: During the growth process, a faster cooling rate is used in the higher temperature zone and a slower cooling rate is used in the lower temperature zone, so that the temperature gradient is reversed at the end of the growth process.

Images