A process for depositing a silicon nitride film on an indium phosphide substrate and a silicon nitride film

Abstract

This application belongs to the field of semiconductor technology and provides a process method for depositing a silicon nitride thin film on an indium phosphide substrate and the silicon nitride thin film itself. The process method includes the following steps: providing an indium phosphide wafer as a substrate; depositing a silicon nitride thin film on the surface of the indium phosphide wafer using plasma-enhanced chemical vapor deposition (PECVD); during the deposition of the silicon nitride thin film, the process parameters include: deposition temperature ≤300℃; cavity pressure ≤1 Torr; RF power ≤100W. In this application, the low deposition temperature suppresses the thermal decomposition and phosphorus desorption of the indium phosphide wafer; the low RF power significantly reduces the bombardment damage to the wafer surface by plasma; the low deposition pressure shortens the mean free path of ions, weakens the bombardment intensity, improves the thickness uniformity within and between wafers, and enhances the density of the silicon nitride thin film. With the synergy of these three factors, a dense, damage-free, high-quality silicon nitride thin film can be deposited on the indium phosphide wafer, ensuring the optoelectronic / RF performance of the device.

Description

Technical Field

[0001] This application belongs to the field of semiconductor technology, specifically relating to a process method for depositing silicon nitride thin films on indium phosphide substrates and the silicon nitride thin films themselves. Background Technology

[0002] Indium phosphide (InP), as an important III-V compound semiconductor material, possesses characteristics such as high electron mobility, moderate bandgap, and excellent photoelectric conversion efficiency, and has broad application prospects in high-speed electronic devices, fiber optic communication, and infrared detection. Silicon nitride (SiN) x Thin films are often used as passivation layers, insulating layers, or masking layers for InP-based devices, and have a significant impact on device performance and reliability.

[0003] However, InP materials inherently possess characteristics such as the high volatility of phosphorus at high temperatures and sensitivity to surface conditions, making them extremely sensitive to process temperature, plasma conditions, and interface states. When depositing silicon nitride thin films on InP substrates using conventional high-temperature or high-power plasma-enhanced chemical vapor deposition (PECVD), the following problems arise: 1) Substrate thermal decomposition: High deposition temperatures lead to the volatilization of phosphorus on the InP substrate surface, causing an imbalance in the substrate's stoichiometry and introducing numerous defects; 2) Low interface quality: High-temperature and high-energy plasma environments easily form interface defects at the interface, reducing interface quality; 3) Plasma damage: High-energy ions generated by high-power radio frequency discharge bombard the substrate surface, easily causing lattice damage; 4) High film stress: Silicon nitride films deposited by conventional PECVD typically have high internal stress, easily leading to film cracking or substrate warping.

[0004] For example, patent CN114023846A discloses a method for reducing the dark current of indium phosphide-based detectors, including the following steps: providing an InP substrate, growing N-type InP on the InP substrate, forming a mask layer by a light-absorbing layer, an undoped InP layer, and a photolithographic mask, and then diffusing to form P-type InP; forming a P-type electrode by electron beam evaporation or magnetron sputtering, and forming an N-type electrode on the back side; wherein the chip dicing path is covered by the mask layer. The mask layer is a silicon nitride thin film or a silicon dioxide thin film. This technical solution has the following shortcomings: 1) High deposition temperature, which easily leads to thermal damage and indium atom precipitation; 2) High deposition pressure, resulting in a loose and insufficiently dense thin film; 3) High plasma power, which easily causes ion bombardment damage.

[0005] Therefore, how to deposit a dense, damage-free, high-quality silicon nitride thin film on an indium phosphide substrate is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this application aims to provide a process for depositing silicon nitride thin films on indium phosphide substrates, as well as the silicon nitride thin film itself. This application utilizes plasma-enhanced chemical vapor deposition (PECVD) under low deposition temperature, low cavity pressure, and low radio frequency power conditions. These three factors work synergistically to: firstly, the low deposition temperature effectively suppresses thermal decomposition and phosphorus desorption of the indium phosphide wafer, protecting the contact between the pre-epitaxial structure and the metal, and reducing thermal mismatch stress between the film and the substrate; secondly, the low radio frequency power significantly reduces plasma bombardment damage to the substrate surface, avoiding physical sputtering etching of the wafer surface and the induction of interface charges and interface states, enabling precise control of the silicon nitride thin film composition and stress, and preventing over-oxidation of the wafer surface by active particles; finally, the low cavity pressure shortens the mean free path of ions, weakens the bombardment intensity, effectively suppresses dust generation, significantly improves the thickness uniformity within and between wafers, and enhances the density of the silicon nitride thin film. Therefore, under the synergistic effect of the above three factors, the mean free path of electrons is significantly increased under low pressure. Combined with low RF power, sufficient gas ionization rate can be achieved, avoiding the ion bombardment damage caused by the forced increase of RF power to ensure ionization in conventional processes. Simultaneously, the low-temperature environment suppresses particle nucleation in the gas phase, reducing defects in the thin film. Low temperature avoids thermal decomposition of indium phosphide from a thermal effect perspective, low RF avoids lattice bombardment damage from an ion energy perspective, and low pressure reduces the high-speed impact of large-mass particles from a particle transport perspective. Together, these three factors construct a damage-free deposition environment, perfectly suited to fragile compound semiconductor substrates like indium phosphide. The improved transport directionality of active groups under low pressure, combined with gentle ion bombardment under low RF, can fill the porosity during thin film growth under low-temperature conditions, avoiding the problems of loose films and excessively high hydrogen content in conventional low-temperature processes. Ultimately, a high-density silicon nitride thin film approaching the level of high-temperature deposition is obtained. In summary, this application can deposit a dense, damage-free, high-quality silicon nitride thin film on indium phosphide wafers, thereby ensuring the optoelectronic / RF performance of the device. To achieve this objective, this application adopts the following technical solution: In a first aspect, this application provides a process method for depositing a silicon nitride thin film on an indium phosphide substrate, the process method comprising the following steps: Indium phosphide wafers are provided as substrates.

[0007] A silicon nitride thin film was deposited on the surface of the indium phosphide wafer using plasma-enhanced chemical vapor deposition.

[0008] The process parameters for depositing the silicon nitride thin film include: Deposition temperature ≤300℃; cavity pressure ≤1Torr; RF power ≤100W.

[0009] This application utilizes plasma-enhanced chemical vapor deposition (PECVD) under low deposition temperature, low cavity pressure, and low RF power conditions. These three factors work synergistically to achieve the following: First, the low deposition temperature effectively suppresses the thermal decomposition and phosphorus desorption of the indium phosphide wafer, protecting the contact between the pre-epitaxial structure and the metal, and reducing the thermal mismatch stress between the thin film and the substrate. Second, the low RF power significantly reduces the bombardment damage to the substrate surface by the plasma, avoiding the etching of the wafer surface by physical sputtering and the induction of interface charges and interface states. This enables precise control of the silicon nitride thin film composition and stress, and prevents the over-oxidation of the wafer surface by active particles. Finally, the low cavity pressure shortens the mean free path of ions, weakens the bombardment intensity, effectively suppresses dust generation, significantly improves the thickness uniformity within and between wafers, and enhances the density of the silicon nitride thin film. Therefore, under the synergistic effect of the above three factors, the mean free path of electrons is significantly increased under low pressure. Combined with low RF power, sufficient gas ionization rate can be achieved, avoiding the ion bombardment damage caused by the forced increase in RF power to ensure ionization in conventional processes. Simultaneously, the low-temperature environment suppresses particle nucleation in the gas phase, reducing defects in the thin film. Low temperature avoids thermal decomposition of indium phosphide from a thermal effect perspective, low RF avoids lattice bombardment damage from an ion energy perspective, and low pressure reduces the high-speed impact of large-mass particles from a particle transport perspective. Together, these three factors construct a damage-free deposition environment, perfectly suited to fragile compound semiconductor substrates like indium phosphide. The improved transport directionality of active groups under low pressure, combined with gentle ion bombardment under low RF, can fill the porosity during thin film growth under low-temperature conditions, avoiding the problems of loose films and excessively high hydrogen content in conventional low-temperature processes. Ultimately, a high-density silicon nitride thin film approaching the level of high-temperature deposition is obtained. In summary, this application can deposit dense, damage-free, high-quality silicon nitride thin films on indium phosphide wafers, thereby ensuring the optoelectronic / RF performance of the device.

[0010] In this application, the deposition temperature is ≤300℃, for example, it can be 300℃, 280℃, 260℃, 240℃, 220℃, 200℃ or 150℃, etc.

[0011] In this application, the cavity pressure is ≤1 Torr, for example, it can be 1.0 Torr, 0.8 Torr, 0.6 Torr, 0.5 Torr, 0.3 Torr, 0.1 Torr or 0.05 Torr, etc.

[0012] In this application, the radio frequency power is ≤100W, for example, it can be 100W, 90W, 80W, 70W, 60W, 50W, 30W or 10W, etc.

[0013] In some embodiments, the deposition temperature is 200°C to 300°C, for example, it can be 200°C, 220°C, 240°C, 260°C, 280°C or 300°C.

[0014] In this application, the low deposition temperature of 200℃~300℃ can further suppress the thermal decomposition and phosphorus desorption of indium phosphide wafers, protect the contact between the pre-epitaxial structure and the metal, and reduce the thermal mismatch stress between the thin film and the substrate.

[0015] In some embodiments, the deposition time of the silicon nitride thin film is 150s-450s, for example, it can be 150s, 200s, 250s, 300s, 350s, 400s or 450s.

[0016] In some embodiments, the cavity pressure is 0.1 Torr to 1 Torr, for example, it can be 0.1 Torr, 0.2 Torr, 0.4 Torr, 0.6 Torr, 0.8 Torr or 1.0 Torr, preferably 0.5 Torr to 1 Torr.

[0017] In this application, a low cavity pressure of 0.1 Torr to 1 Torr can further shorten the mean free path of ions, weaken the bombardment intensity, suppress the generation of dust (gas phase particles), significantly improve the thickness uniformity inside and between wafers, and improve the density of silicon nitride films.

[0018] In some embodiments, the radio frequency power is 30W to 100W, for example, it can be 30W, 40W, 50W, 60W, 70W, 80W, 90W or 100W.

[0019] In this application, the low radio frequency power of 30W~100W can further reduce the bombardment damage of plasma to the substrate surface, avoid the etching of the wafer surface layer by physical sputtering and the induction of interface charge and interface state, realize the precise control of silicon nitride film composition and stress, and prevent active particles from over-oxidizing the wafer surface.

[0020] In some embodiments, before the silicon nitride thin film deposition, a hot plate rise step, a preheating step, and a stabilization step are performed sequentially.

[0021] In some embodiments, the specific steps of the hot plate raising step include: The temperature of the hot plate carrying the indium phosphide wafer is set to 200℃~300℃ (e.g., 200℃, 220℃, 240℃, 260℃, 280℃, or 300℃, etc.), and the hot plate is raised so that the vertical distance between the hot plate and the spray plate is 800mil~1000mil, for example, 800mil, 850mil, 900mil, 950mil, or 1000mil, etc.

[0022] In this application, the purpose of introducing the hot plate rise step is to avoid the indium phosphide wafer directly contacting the hot plate, which would cause a sudden temperature change and lead to indium phosphide wafer fragmentation.

[0023] In some embodiments, the preheating step includes the following specific steps: Inert gas is introduced into the reaction chamber, and the chamber pressure is controlled at 5 Torr-8 Torr (e.g., 5 Torr, 5.5 Torr, 6 Torr, 6.5 Torr, 7 Torr, 7.5 Torr, or 8 Torr, etc.) for preheating.

[0024] In this application, the purpose of introducing a preheating step is to bring the temperature of the indium phosphide wafer close to that of the hot plate before it comes into contact with the hot plate. It is worth noting that the preheating step can lay the foundation for subsequent film deposition.

[0025] In some embodiments, the specific steps of the stabilization step include: A working gas is introduced into the reaction chamber, the chamber pressure is controlled to be ≤1 Torr, and the heating plate is moved so that the vertical distance between the heating plate and the spray plate is 200mil-400mil (e.g., 200mil, 250mil, 300mil, 350mil, or 400mil, etc.). The working gas includes a reaction gas, which comprises a gaseous nitrogen source and a gaseous silicon source. For example, the gaseous nitrogen source may be ammonia, and the gaseous silicon source may be silane.

[0026] In this application, the purpose of introducing the stabilization step is to stabilize the environment inside the cavity; it is worth noting that this step adjusts the position of the hot plate so that the wafer can be moved to the process position for processing after the preheating is completed.

[0027] It should be noted that the process parameters for the stabilization step are the same as those for silicon nitride thin film deposition. For example, the chamber pressure for the stabilization step is the same as the chamber pressure for silicon nitride thin film deposition.

[0028] In some embodiments, after the silicon nitride thin film deposition, a post-processing step is performed, the specific steps of which include: Stop supplying the vapor silicon source and continue RF operation.

[0029] In this application, the above-mentioned post-processing step is performed after the silicon nitride thin film deposition, which helps to reduce the surface roughness of the silicon nitride thin film.

[0030] In some embodiments, the process method includes the following steps: (1) Hot plate rise step: An indium phosphide wafer is placed in the reaction chamber of a plasma-enhanced chemical vapor deposition (PECVD) apparatus. The temperature of the hot plate carrying the indium phosphide wafer is set to 200°C to 300°C. The hot plate is then raised so that the vertical distance between the hot plate and the spray plate is 800 mil to 1000 mil.

[0031] (2) Preheating step: Inert gas with a flow rate of 2000 sccm to 3000 sccm (e.g., 2000 sccm, 2200 sccm, 2400 sccm, 2600 sccm, 2800 sccm, or 3000 sccm, etc.) is introduced into the reaction chamber, and the chamber pressure is controlled at 5 to 8 Torr for preheating for 30 to 90 seconds.

[0032] The inert gas includes nitrogen and / or argon.

[0033] (3) Stable step: A working gas is introduced into the reaction chamber, and the chamber pressure is controlled at 0.5 Torr to 1 Torr. The hot plate is moved so that the vertical distance between the hot plate and the spray plate is 200 mil to 400 mil.

[0034] The working gas includes a reactive gas and an inert gas. The reactive gas includes a gaseous nitrogen source and a gaseous silicon source. The flow rate of the gaseous nitrogen source is 40 sccm to 100 sccm (e.g., 40 sccm, 50 sccm, 60 sccm, 70 sccm, 80 sccm, 90 sccm, or 100 sccm, etc.), and the flow rate of the gaseous silicon source is 10 sccm to 50 sccm (e.g., 10 sccm, 15 sccm, 20 sccm, 25 sccm, 30 sccm, 40 sccm, or 50 sccm, etc.). The inert gas includes nitrogen, and the flow rate of the inert gas is 300 sccm to 700 sccm (e.g., 300 sccm, 350 sccm, 400 sccm, 450 sccm, 500 sccm, 600 sccm, or 700 sccm, etc.).

[0035] (4) Deposition step: Turn on the RF power supply, set the RF power to 30W~100W, and perform deposition for 150s~450s.

[0036] (5) Post-processing step: Stop supplying the vapor silicon source and continue radio frequency for 5s to 20s (e.g., 5s, 8s, 10s, 12s, 15s, 18s, or 20s).

[0037] (6) Turn off the radio frequency power supply and keep the gaseous nitrogen source and inert gas introduced for 5s~20s (e.g., 5s, 8s, 10s, 12s, 15s, 18s or 20s, etc.) to complete the purging of the reaction chamber. Then turn off all gas sources and pump the pressure of the reaction chamber to the background vacuum.

[0038] Take a wafer and obtain an indium phosphide wafer with a silicon nitride thin film deposited on it.

[0039] It should be noted that the background vacuum refers to the ultimate vacuum level that the chamber can achieve; the smaller this value, the higher the vacuum level. Typically, PECVD processes require a background vacuum <1×10⁻⁶. -2 Torr is used to ensure that the deposited silicon nitride film is not contaminated by residual atmosphere, thereby guaranteeing the purity and density of the film.

[0040] Secondly, this application provides a silicon nitride thin film, which is obtained using the process described in the first aspect.

[0041] In some embodiments, the thickness of the silicon nitride film is 100nm~300nm, for example, it can be 100nm, 120nm, 150nm, 180nm, 200nm, 220nm, 250nm, 280nm or 300nm, etc.

[0042] It should be noted that the thickness can be measured using an ellipsometry. The testing method is as follows: 25 test points are selected evenly, with the edge of the test point distribution area 5 mm away from the edge of the silicon nitride film (i.e., 5 mm edge is removed). The thickness value of each point is recorded, and the arithmetic mean is taken as the thickness of the silicon nitride film.

[0043] In some embodiments, the thickness uniformity of the silicon nitride film is <2%, for example, it can be 1.9%, 1.7%, 1.5%, 1.2%, 1.0%, 0.8%, 0.5%, or 0.3%, etc. It should be noted that thickness uniformity refers to the consistency of the silicon nitride film thickness at different locations on the indium phosphide wafer surface, reflecting the uniformity of the film thickness distribution. The smaller the thickness uniformity value, the more uniform the thickness distribution of the silicon nitride film on the wafer surface. The thickness uniformity of the silicon nitride film can be tested using an ellipsometry. The test method is as follows: 25 test points are uniformly selected for thickness testing, with the edge of the test point distribution area 5 mm away from the edge of the silicon nitride film (i.e., 5 mm edge trimmed), and the thickness value at each point is recorded. The thickness uniformity is calculated according to the following formula: Where STD is the standard deviation of the thickness values ​​at 25 test points, and Average is the arithmetic mean of the thickness values ​​at 25 test points.

[0044] The silicon nitride thin film prepared in this application has a thickness uniformity of <2%, indicating that the silicon nitride thin film has good thickness consistency on the surface of the indium phosphide wafer and the film layer is uniformly distributed, which is beneficial to ensuring the consistency of device performance and improving the reliability and yield of the device.

[0045] In some embodiments, the refractive index of the silicon nitride film is 1.8 to 2.2, for example, it can be 1.80, 1.85, 1.90, 1.95, 2.00, 2.05, 2.10, 2.15 or 2.20.

[0046] It should be noted that the refractive index can be measured using an ellipsometer. The test method is as follows: 25 test points are selected evenly for refractive index measurement. The edge of the test point distribution area is 5 mm away from the edge of the silicon nitride film (i.e., 5 mm is removed from the edge). The test wavelength is 633 nm and the incident angle is 65°. The refractive index values ​​of each point are recorded, and their arithmetic mean is taken as the refractive index of the silicon nitride film.

[0047] In some embodiments, the internal stress of the silicon nitride film is -500MPa to 100MPa, for example, it can be -500MPa, -400MPa, -300MPa, -200MPa, -100MPa, 0MPa, 50MPa or 100MPa, etc.

[0048] It should be noted that internal stress refers to the force per unit area generated within the silicon nitride film. When the internal stress is positive, it is represented as compressive stress; when the internal stress is negative, it is represented as tensile stress. Internal stress can be measured using a stress meter. The testing method is as follows: 20 points are evenly selected along a straight line passing through the center of the wafer for stress testing. The edge of the test point distribution area is 5 mm away from the edge of the silicon nitride film (i.e., 5 mm edge-removed). This straight line is perpendicular to the line perpendicular to the flat edge.

[0049] In some embodiments, the etching rate of the silicon nitride film in a buffered hydrofluoric acid solution at 20°C-22°C (e.g., 20°C, 21°C, or 22°C) is <50 nm / min, for example, it can be 45 nm / min, 40 nm / min, 35 nm / min, 30 nm / min, 25 nm / min, 20 nm / min, 10 nm / min, or 5 nm / min.

[0050] It should be noted that the etching rate refers to the reduction in film thickness per unit time when etching a silicon nitride film in a buffered hydrofluoric acid solution (such as a mixture of 40% ammonium fluoride solution and 49% hydrofluoric acid solution at a volume ratio of 10:1) at 20℃-22℃. The room temperature etching rate can be obtained using an ellipsometry. The testing method is as follows: 25 test points are uniformly selected to measure the initial thickness of the silicon nitride film. The edge of the test point distribution area is 5mm from the edge of the sample (i.e., 5mm edge removed). The thickness values ​​at each point are recorded, and the arithmetic mean is taken as the initial thickness. Then, the sample is completely immersed in the buffered hydrofluoric acid solution, and the immersion start time is recorded. After immersion for a certain period, the sample is removed, immediately rinsed with deionized water, and dried with nitrogen. The same method is used again to test the thickness at each point, and the values ​​before and after are calculated. The arithmetic mean is taken as the etching difference, i.e., the etching rate.

[0051] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0052] Compared with the prior art, this application has the following advantages: This application utilizes plasma-enhanced chemical vapor deposition (PECVD) performed under low deposition temperature, low deposition pressure, and low radio frequency (RF) power conditions. These three factors work synergistically to: First, the low deposition temperature effectively suppresses thermal decomposition and phosphorus desorption of the indium phosphide wafer, protecting the contact between the pre-epitaxial structure and the metal, and reducing thermal mismatch stress between the thin film and the substrate. Second, the low RF power significantly reduces plasma bombardment damage to the substrate surface, avoiding physical sputtering etching of the wafer surface and the induction of interface charges and interface states. This enables precise control of the silicon nitride thin film composition and stress, and prevents over-oxidation of the wafer surface by active particles. Finally, the low deposition pressure shortens the mean free path of ions, weakens the bombardment intensity, effectively suppresses dust generation, significantly improves the thickness uniformity within and between wafers, and enhances the density of the silicon nitride thin film. Therefore, under the synergistic effect of the above three factors, the mean free path of electrons is significantly increased under low pressure. Combined with low RF power, sufficient gas ionization rate can be achieved, avoiding the ion bombardment damage caused by the forced increase in RF power to ensure ionization in conventional processes. Simultaneously, the low-temperature environment suppresses particle nucleation in the gas phase, reducing defects in the thin film. Low temperature avoids thermal decomposition of indium phosphide from a thermal effect perspective, low RF avoids lattice bombardment damage from an ion energy perspective, and low pressure reduces the high-speed impact of large-mass particles from a particle transport perspective. Together, these three factors construct a damage-free deposition environment, perfectly suited to fragile compound semiconductor substrates like indium phosphide. The improved transport directionality of active groups under low pressure, combined with gentle ion bombardment under low RF, can fill the porosity during thin film growth under low-temperature conditions, avoiding the problems of loose films and excessively high hydrogen content in conventional low-temperature processes. Ultimately, a high-density silicon nitride thin film approaching the level of high-temperature deposition is obtained. In summary, this application can deposit dense, damage-free, high-quality silicon nitride thin films on indium phosphide wafers, thereby ensuring the optoelectronic / RF performance of the device. Attached Figure Description

[0053] Figure 1 This is a thickness distribution diagram of the silicon nitride thin film prepared in Example 1.

[0054] Figure 2 This is a thickness distribution diagram of the silicon nitride thin film prepared in Example 2.

[0055] Figure 3 This is a thickness distribution diagram of the silicon nitride thin film prepared in Example 3. Detailed Implementation

[0056] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0057] The scope of this application can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form a valid range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this application. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this application. In this application, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0058] In this application, "at least two combinations" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or at least two combinations" means any one of the listed items, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this application. In this application, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this application, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0059] In this application, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond those listed unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this application, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this application. The term "embodiment" as used in this application means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art can explicitly and implicitly understand that the embodiments described in this application can be combined with other embodiments that do not conflict with existing technologies. The ordinal numbers "first," "second," "third," and "fourth," etc., used in this application in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect," are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0060] In this application, the order in which the steps are written in the methods described in the various embodiments does not imply a strict execution order. The actual execution order of each step should be determined according to its function and possible internal logic. Unless otherwise specified, all steps in this application can be executed in the order they are written, or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any order without conflict, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0061] Example 1 This embodiment provides a process for depositing a silicon nitride thin film on an indium phosphide substrate, the process comprising the following steps: (1) Hot plate rise step: An indium phosphide wafer is placed into the reaction chamber of a single-cavity monolithic plasma-enhanced chemical vapor deposition (PECVD) apparatus. The temperature of the hot plate carrying the indium phosphide wafer is set to 300°C. The hot plate is then raised so that the vertical distance between the hot plate and the spray plate is 900 mil.

[0062] (2) Preheating step: Nitrogen gas at a flow rate of 2500 sccm is introduced into the reaction chamber, and the chamber pressure is controlled at 6.5 Torr for 60 seconds of preheating.

[0063] (3) Stable step: Nitrogen gas at a flow rate of 500 sccm, ammonia gas at a flow rate of 70 sccm, and silane gas at a flow rate of 30 sccm are introduced into the reaction chamber. The chamber pressure is controlled at 0.8 Torr. The heating plate is moved so that the vertical distance between the heating plate and the spray plate is 300 mil.

[0064] (4) Deposition step: Turn on the RF power, set the RF power to 50W, and perform deposition for 300 seconds.

[0065] (5) Post-processing step: Stop the flow of the silane and continue the radio frequency for 10 seconds.

[0066] (6) Turn off the radio frequency power supply, keep nitrogen and ammonia gas flowing in for 10 seconds to complete the purging of the reaction chamber, then turn off all gas sources and pump the pressure of the reaction chamber to the background vacuum.

[0067] Take a wafer and obtain an indium phosphide wafer with a silicon nitride thin film deposited on it.

[0068] Example 2 This embodiment provides a process for depositing a silicon nitride thin film on an indium phosphide substrate, the process comprising the following steps: (1) Hot plate rise step: An indium phosphide wafer is placed into the reaction chamber of a single-cavity monolithic plasma-enhanced chemical vapor deposition (PECVD) apparatus. The temperature of the hot plate carrying the indium phosphide wafer is set to 250°C. The hot plate is then raised so that the vertical distance between the hot plate and the spray plate is 800 mil.

[0069] (2) Preheating step: Nitrogen gas with a flow rate of 2000 sccm is introduced into the reaction chamber, and the chamber pressure is controlled at 5 Torr for 30 seconds of preheating.

[0070] (3) Stable step: Nitrogen gas at a flow rate of 300 sccm, ammonia gas at a flow rate of 40 sccm, and silane gas at a flow rate of 10 sccm are introduced into the reaction chamber. The chamber pressure is controlled at 0.5 Torr. The heating plate is moved so that the vertical distance between the heating plate and the spray plate is 200 mil.

[0071] (4) Deposition step: Turn on the RF power, set the RF power to 30W, and perform deposition for 450 seconds.

[0072] (5) Post-processing step: Stop the silane supply and continue radio frequency for 5 seconds.

[0073] (6) Turn off the radio frequency power supply, keep nitrogen and ammonia gas flowing in for 5 seconds to complete the purging of the reaction chamber, then turn off all gas sources and pump the pressure of the reaction chamber to the background vacuum.

[0074] Take a wafer and obtain an indium phosphide wafer with a silicon nitride thin film deposited on it.

[0075] Example 3 This embodiment provides a process for depositing a silicon nitride thin film on an indium phosphide substrate, the process comprising the following steps: (1) Hot plate rise step: An indium phosphide wafer is placed into the reaction chamber of a single-cavity monolithic plasma-enhanced chemical vapor deposition (PECVD) apparatus. The temperature of the hot plate carrying the indium phosphide wafer is set to 200°C. The hot plate is then raised so that the vertical distance between the hot plate and the spray plate is 1000 mil.

[0076] (2) Preheating step: Nitrogen gas with a flow rate of 3000 sccm is introduced into the reaction chamber, and the chamber pressure is controlled at 8 Torr for 90 seconds of preheating.

[0077] (3) Stable step: Nitrogen gas at a flow rate of 700 sccm, ammonia gas at a flow rate of 100 sccm, and silane gas at a flow rate of 50 sccm are introduced into the reaction chamber. The chamber pressure is controlled at 1 Torr. The heating plate is moved so that the vertical distance between the heating plate and the spray plate is 400 mil.

[0078] (4) Deposition step: Turn on the RF power, set the RF power to 100W, and perform deposition for 150 seconds.

[0079] (5) Post-processing step: Stop the silane supply and continue radio frequency operation for 20 seconds.

[0080] (6) Turn off the radio frequency power supply, keep nitrogen and ammonia gas flowing in for 20 seconds to complete the purging of the reaction chamber, then turn off all gas sources and pump the pressure of the reaction chamber to the background vacuum.

[0081] Take a wafer and obtain an indium phosphide wafer with a silicon nitride thin film deposited on it.

[0082] Example 4 The difference between this embodiment and embodiment 1 is that in step (3), the pressure in the cavity is controlled to be 0.7 Torr.

[0083] The remaining process methods and parameters are consistent with those in Example 1.

[0084] Example 5 The difference between this embodiment and embodiment 1 is that the temperature of the hot plate is 260°C; the radio frequency power is 100W; and in step (3), the control cavity pressure is 0.7 Torr.

[0085] The remaining process methods and parameters are consistent with those in Example 1.

[0086] Example 6 The difference between this embodiment and Embodiment 1 is that the temperature of the hot plate is 150°C.

[0087] The remaining process methods and parameters are consistent with those in Example 1.

[0088] Example 7 The difference between this embodiment and embodiment 1 is that in step (3), the pressure in the control chamber is 0.1 Torr.

[0089] The remaining process methods and parameters are consistent with those in Example 1.

[0090] Example 8 The difference between this embodiment and Embodiment 1 is that the radio frequency power is 20W.

[0091] The remaining process methods and parameters are consistent with those in Example 1.

[0092] Comparative Example 1 The difference between this comparative example and Example 1 is that the temperature of the hot plate is 350°C, that is, the deposition temperature is 350°C.

[0093] The remaining process methods and parameters are consistent with those in Example 1.

[0094] Comparative Example 2 The difference between this comparative example and Example 1 is that in step (3), the pressure in the controlled cavity is 1.5 Torr.

[0095] The remaining process methods and parameters are consistent with those in Example 1.

[0096] Comparative Example 3 The difference between this comparative example and Example 1 is that the radio frequency power is 150W.

[0097] The remaining process methods and parameters are consistent with those in Example 1.

[0098] Comparative Example 4 The difference between this comparative example and Example 1 is that the temperature of the hot plate is 350°C (i.e., the deposition temperature is 350°C), the radio frequency power is 150W, and in step (3), the cavity pressure is controlled to be 1.5 Torr.

[0099] The remaining process methods and parameters are consistent with those in Example 1.

[0100] Performance testing The silicon nitride films prepared by the processes provided in the above embodiments and comparative examples were subjected to the following tests: 1) Thickness; 2) Thickness uniformity; 3) Refractive index; 4) Internal stress; 5) Corrosion rate.

[0101] The test results are shown in Table 1. Figure 1 , Figure 2 and Figure 3 Thickness distribution diagrams of silicon nitride films prepared in Examples 1, 2 and 3 are shown respectively.

[0102] Table 1

[0103] analyze: As shown in Table 1, in Examples 1-5, temperature, pressure, and RF power are all within the protection range of this application. The three factors work together to constrain the process. First, the low deposition temperature effectively suppresses the thermal decomposition and phosphorus desorption of the indium phosphide wafer, protecting the contact between the pre-epitaxial structure and the metal, and reducing the thermal mismatch stress between the thin film and the substrate. Second, the low RF power significantly reduces the bombardment damage of the substrate surface by plasma, avoiding the etching of the wafer surface layer by physical sputtering and the induction of interface charge and interface state, achieving precise control of the silicon nitride thin film composition and stress, and preventing the over-oxidation of the wafer surface by active particles. Finally, the low deposition pressure shortens the mean free path of ions, weakens the bombardment intensity, effectively suppresses the generation of dust, significantly improves the thickness uniformity inside and between wafers, and improves the density of the silicon nitride thin film. Therefore, under the synergistic effect of the above three factors, the mean free path of electrons is significantly increased under low pressure. Combined with low RF power, sufficient gas ionization rate can be achieved, avoiding the ion bombardment damage caused by the forced increase of RF power to ensure ionization in conventional processes. Simultaneously, the low-temperature environment suppresses particle nucleation in the gas phase, reducing defects in the thin film. Low temperature avoids thermal decomposition of indium phosphide from a thermal effect perspective, low RF avoids lattice bombardment damage from an ion energy perspective, and low pressure reduces the high-speed impact of large-mass particles from a particle transport perspective. Together, these three factors construct a damage-free deposition environment, perfectly suited to fragile compound semiconductor substrates like indium phosphide. The improved transport directionality of active groups under low pressure, combined with gentle ion bombardment under low RF, can fill the porosity during thin film growth under low-temperature conditions, avoiding the problems of loose films and excessively high hydrogen content in conventional low-temperature processes. Ultimately, a high-density silicon nitride thin film approaching the level of high-temperature deposition is obtained. In summary, this application can deposit dense, damage-free, high-quality silicon nitride thin films on indium phosphide wafers with excellent film uniformity, thereby ensuring the optoelectronic / RF performance of the device.

[0104] A comparison of Examples 1 and 6-8 reveals that a lower hot plate temperature results in higher hydrogen content and a faster corrosion rate; a lower deposition pressure leads to poorer uniformity and higher stress; and a lower radio frequency power results in poorer uniformity, insufficient ion bombardment of the film, and a porous film. These results indicate that maintaining any two of the three parameters (temperature, pressure, and radio frequency power) at the level of Example 1 still leaves a weak link dominated by the remaining parameters: lower temperature leads to hydrogen residue, lower pressure leads to transport instability, and lower power leads to insufficient densification. Therefore, without precise coordination of these three parameters, the film performance will always deteriorate due to a weakness in one dimension. Only when temperature, pressure, and power simultaneously fall within the range defined in this application can excellent performance in terms of hydrogen content, corrosion rate, stress, uniformity, and densification be achieved.

[0105] A comparison of Example 1 and Comparative Examples 1-3 shows that if the temperature of the hot plate is too high, the uniformity is poor, and the risk of wafer fragmentation is increased; if the deposition pressure is too high, the uniformity deteriorates, the film becomes porous, and the corrosion rate increases; if the RF power is too high, the uniformity deteriorates, the stress increases, and there is ion damage to the substrate. These results indicate that excessive deviation from any parameter will lead to the individual occurrence of the mechanism dominated by that parameter, such as high-temperature thermochemical damage, high-pressure ion transport damage, and high-energy ion bombardment damage, while the other two parameters, even if within their optimized range, cannot compensate for this. Therefore, the three parameters are complementary and indispensable in protecting the deposition environment; any loss of control over any one of them constitutes a performance defect.

[0106] As can be seen from the comparison between Example 1 and Comparative Example 4, if the temperature of the hot plate is too high, the deposition pressure is too high, and the radio frequency power is too high, the reaction is in an extremely unstable stage, the uniformity is extremely poor, the stress refractive index is in an abnormal stage, and the probability of generating white powder increases.

[0107] It should be noted that this application illustrates the process method through the above embodiments, but this application is not limited to the above process steps, that is, it does not mean that this application must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to this application, equivalent substitutions of the raw materials used in this application, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of this application.

Claims

1. A process for depositing a silicon nitride thin film on an indium phosphide substrate, characterized in that, The process includes the following steps: Indium phosphide wafers are provided as substrates; A silicon nitride thin film was deposited on the surface of the indium phosphide wafer using plasma-enhanced chemical vapor deposition. The process parameters for depositing the silicon nitride thin film include: Deposition temperature ≤300℃; cavity pressure ≤1Torr; RF power ≤100W.

2. The process method according to claim 1, characterized in that, The deposition temperature is 200℃~300℃; And / or, the deposition time of the silicon nitride film is 150s-450s.

3. The process method according to claim 1, characterized in that, The pressure in the cavity is 0.1 Torr to 1 Torr.

4. The process method according to claim 1, characterized in that, The radio frequency power is 30W~100W.

5. The process method according to claim 1, characterized in that, Before the silicon nitride thin film deposition, the hot plate raising step, the preheating step, and the stabilization step are performed in sequence.

6. The process method according to claim 5, characterized in that, The specific steps of the hot plate lifting step include: The temperature of the hot plate carrying the indium phosphide wafer is set to 200°C to 300°C, and the hot plate is raised so that the vertical distance between the hot plate and the spray plate is 800mil to 1000mil. And / or, the specific steps of the preheating step include: Inert gas is introduced into the reaction chamber, and the chamber pressure is controlled at 5 Torr-8 Torr for preheating; And / or, the specific steps of the stabilization step include: A working gas is introduced into the reaction chamber, the chamber pressure is controlled to be ≤1 Torr, and the hot plate is moved so that the vertical distance between the hot plate and the spray plate is 200mil-400mil; wherein, the working gas includes a reaction gas, and the reaction gas includes a gaseous nitrogen source and a gaseous silicon source.

7. The process method according to claim 6, characterized in that, After the silicon nitride thin film is deposited, a post-processing step is performed, the specific steps of which include: Stop supplying the vapor silicon source and continue RF operation.

8. The process method according to any one of claims 1-7, characterized in that, The process includes the following steps: (1) Hot plate rise step: An indium phosphide wafer is placed in the reaction chamber of a plasma-enhanced chemical vapor deposition (PECVD) apparatus. The temperature of the hot plate carrying the indium phosphide wafer is set to 200°C to 300°C. The hot plate is raised so that the vertical distance between the hot plate and the spray plate is 800 mil to 1000 mil. (2) Preheating step: Inert gas with a flow rate of 2000 sccm to 3000 sccm is introduced into the reaction chamber, and the chamber pressure is controlled at 5 Torr to 8 Torr for preheating for 30 to 90 seconds. The inert gas includes nitrogen and / or argon; (3) Stable step: Introduce working gas into the reaction chamber, control the chamber pressure to 0.5 Torr~1 Torr, and move the heating plate so that the vertical distance between the heating plate and the spray plate is 200mil~400mil; The working gas includes a reactive gas and an inert gas. The reactive gas includes a gaseous nitrogen source and a gaseous silicon source. The flow rate of the gaseous nitrogen source is 40 sccm to 100 sccm, and the flow rate of the gaseous silicon source is 10 sccm to 50 sccm. The inert gas includes nitrogen, and the flow rate of the inert gas is 300 sccm to 700 sccm. (4) Deposition step: Turn on the RF power supply, set the RF power to 30W~100W, and perform deposition for 150s~450s; (5) Post-processing step: Stop supplying the vapor silicon source and continue RF for 5s~20s; (6) Turn off the radio frequency power supply, maintain the gas phase nitrogen source and inert gas flow for 5s~20s to complete the purging of the reaction chamber, then turn off all gas sources and pump the pressure of the reaction chamber to the background vacuum. Take a wafer to obtain an indium phosphide wafer with a silicon nitride thin film deposited on it.

9. A silicon nitride thin film, characterized in that, The silicon nitride thin film is obtained using the process described in any one of claims 1-8.

10. The silicon nitride thin film according to claim 9, characterized in that, The thickness of the silicon nitride thin film is 100nm~300nm; And / or, the thickness uniformity of the silicon nitride film is <2%; And / or, the refractive index of the silicon nitride thin film is 1.8 to 2.2; And / or, the internal stress of the silicon nitride film is -500MPa to 100MPa; And / or, the etching rate of the silicon nitride film in buffered hydrofluoric acid solution at 20°C-22°C is <50 nm / min.

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