Method for preparing silicon nitride film on surface of substrate

Abstract

The invention relates to the technical field of semiconductors, and provides a method for preparing a silicon nitride film on the surface of a substrate. The method comprises the following steps: (1) in a first cavity in a nitrogen atmosphere, providing a hot plate with a process temperature, and preheating a substrate to a preheating temperature at a first interval; the substrate is made of lithium tantalate or lithium niobate; (2) placing the substrate with the preheating temperature on the surface of a hot plate, and heating the substrate to a process temperature; (3) depositing a silicon nitride film on the surface of the substrate with the process temperature; and (4) transferring the substrate on which the silicon nitride film is deposited into a second vacuum cavity for cooling. According to the method, the silicon nitride film is directly deposited on the surface of the lithium niobate or lithium tantalate substrate to obtain the silicon nitride film in a thermal radiation mode through combination of early-stage preheating and later-stage slow cooling under the condition that the lithium niobate or lithium tantalate substrate is complete. The method provided by the invention is simple in process and easy to implement, and has industrial application prospects.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, in particular to the preparation of a silicon nitride film, and in particular to a method for preparing the silicon nitride film on a substrate surface. Background Art

[0002] Lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) are two important ferroelectric crystal materials. Due to their excellent piezoelectric, electro-optical, and acoustic properties, they are widely used in optoelectronics, surface acoustic wave (SAW) devices, integrated optics, and nonlinear optics. As substrate materials, they hold a unique position in the semiconductor and optoelectronics industries.

[0003] However, due to the spontaneously polarized domain structures within lithium niobate and lithium tantalate, domain wall movement during heating can lead to localized stress concentration. Furthermore, lithium niobate and lithium tantalate are trigonal crystals, prone to cleavage along specific crystal planes, and exhibit significant anisotropy in mechanical strength. Furthermore, lithium niobate and lithium tantalate have poor thermal conductivity, with LiNbO3 having a thermal conductivity of only ~5 W / (m·K) and LiTaO3 only ~3 W / (m·K). Therefore, during processing, lithium niobate and lithium tantalate substrates are susceptible to uneven heat distribution due to rapid cooling and heating, generating thermal gradient stress, which in turn triggers thermal shock cracks and leads to fragmentation of the lithium niobate and lithium tantalate substrates. Therefore, lithium niobate and lithium tantalate substrates are typically bonded to silicon nitride layers.

[0004] CN117059631A discloses a heterogeneous optoelectronic fusion integrated chip based on wafer-to-wafer bonding. The integration method includes using an ion doping process to prepare an erbium-doped lithium niobate wafer; using a thin film deposition technology to obtain a silicon nitride film on a silicon wafer; and then using a wafer bonding process to bond the silicon nitride film to the erbium-doped lithium niobate wafer to prepare a silicon nitride-doped lithium niobate electro-optical modulator.

[0005] CN117572673A discloses a method for preparing an optical phase modulator, comprising bonding a lithium niobate single crystal wafer to a silicon nitride waveguide core via a bonding dielectric layer, and reducing insertion loss by providing a slope structure on one or both sides of the bonded lithium niobate single crystal wafer in the length direction of the silicon nitride waveguide core.

[0006] CN118039727A discloses a method for preparing a lithium tantalate-silicon nitride photoelectric chip, comprising: providing a lithium tantalate material on an insulator; the lithium tantalate material on an insulator includes a lithium tantalate thin film layer and a substrate layer disposed above and below; forming a silicon nitride thin film layer on the lithium tantalate thin film layer using a wafer bonding method; removing a portion of the silicon nitride thin film layer to form a patterned silicon nitride thin film layer; forming a metal electrode on the lithium tantalate thin film layer to form a lithium tantalate-silicon nitride photoelectric chip; and separating the metal electrode and the patterned silicon nitride thin film layer. This invention utilizes a wafer bonding method to form a lithium tantalate-silicon nitride heterostructure, avoiding the high-temperature silicon nitride deposition process and ensuring the polarization integrity of the lithium tantalate.

[0007] In the prior art, bonding is often used to achieve the combination of lithium niobate or lithium tantalate and silicon nitride thin film layers, which is a complicated process and difficult to process.

[0008] Therefore, there is an urgent need to provide a method for directly preparing a silicon nitride film on the surface of lithium niobate or lithium tantalate. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention provides a method for depositing a silicon nitride thin film on a substrate surface. This method utilizes thermal radiation, combining preheating with slow cooling, to deposit the silicon nitride thin film directly on the substrate surface while maintaining the integrity of the lithium niobate or lithium tantalate substrate. The method is simple, easy to implement, and has promising prospects for industrial application.

[0010] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a method for preparing a silicon nitride film on a substrate surface, the method comprising:

[0012] (1) In a first chamber with a nitrogen atmosphere, a hot plate having a process temperature is provided, the hot plate is spaced a first distance apart, and the substrate is preheated to a preheating temperature;

[0013] The substrate is made of lithium tantalate or lithium niobate;

[0014] (2) placing the substrate at the preheating temperature on a hot plate surface, and heating the substrate to a process temperature;

[0015] (3) depositing a silicon nitride film on the surface of the substrate at the process temperature;

[0016] (4) The substrate on which the silicon nitride film is deposited is transferred to a second vacuum chamber for cooling.

[0017] In the present invention, the distance between the substrate and the hot plate is achieved by adjusting the vertical positions of the two in the cavity. When the substrate is placed in the first cavity, the substrate is supported by the ejector pins and is located above the hot plate. The distance between the hot plate and the substrate of the present invention is actually the distance from the top of the hot plate to the bottom of the substrate.

[0018] The present invention preheats substrates spaced a first distance apart using a hot plate at a process temperature. This preheating process utilizes thermal radiation at a moderate heating rate, preventing the lithium niobate or lithium tantalate substrate from fragmenting due to rapid thermal expansion. Furthermore, the use of nitrogen as a medium ensures more uniform heating. Furthermore, after the silicon nitride film is deposited, the substrate with the silicon nitride film is directly transferred to a second vacuum chamber for cooling. Cooling in a vacuum environment relies solely on thermal radiation, resulting in a gradual cooling process and preventing sudden cooling that could result in fragmentation of the lithium niobate or lithium tantalate substrate.

[0019] Preferably, the first distance is 30mil~80mil.

[0020] Preferably, the process temperature is 10°C to 30°C higher than the preheating temperature.

[0021] Preferably, the process temperature is 150°C to 260°C.

[0022] Preferably, the nitrogen gas has an inlet flow rate of 800 sccm to 1200 sccm.

[0023] Preferably, in step (1), the substrate is kept at the preheating temperature for more than 30 seconds, preferably 30 seconds to 60 seconds.

[0024] Preferably, in step (2), the substrate is kept at the process temperature for more than 45 seconds, preferably 45 seconds to 120 seconds.

[0025] Preferably, the method for depositing a silicon nitride film comprises:

[0026] At the process temperature, a precursor gas is introduced into the first cavity to deposit a silicon nitride film by plasma enhanced chemical vapor deposition; the precursor gas includes silane, ammonia and nitrogen.

[0027] Preferably, after the precursor gas is introduced, it is stabilized for 45 seconds to 100 seconds before plasma enhanced chemical vapor deposition is performed.

[0028] Preferably, the flow rate of the silane is 30 sccm to 50 sccm.

[0029] Preferably, the flow rate of the ammonia gas is 30 sccm to 50 sccm.

[0030] Preferably, the flow rate of the nitrogen gas is 1400 sccm-1500 sccm.

[0031] Preferably, during the deposition process, the pressure in the first chamber is 1 torr to 1.5 torr.

[0032] Preferably, the power of the plasma enhanced chemical vapor deposition is 100W~200W.

[0033] Preferably, the plasma enhanced chemical vapor deposition time is 30s to 50s.

[0034] Preferably, the method further comprises vacuuming after the deposition of the silicon nitride film is completed.

[0035] Preferably, the temperature inside the second vacuum chamber is 20°C to 40°C.

[0036] Preferably, the cooling time in the second vacuum chamber is 100s to 200s.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The present invention utilizes thermal radiation to deposit a silicon nitride thin film directly on the surface of an intact lithium niobate or lithium tantalate substrate, combining preheating in the early stages with slow cooling in the later stages. The method provided by the present invention is simple, easy to implement, and has promising prospects for industrial application. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention pertains; the terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention; the terms "including" and "having" and any variations thereof in the present invention are intended to cover non-exclusive inclusions.

[0041] In the description of the present invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the technical features indicated. In the description of the embodiments of the present invention, the meaning of "plurality" is more than two, unless otherwise specifically defined.

[0042] In one embodiment, the present invention provides a method for preparing a silicon nitride film on a substrate surface, the method comprising:

[0043] (1) In a first chamber with a nitrogen atmosphere, a hot plate having a process temperature is provided, the hot plate is spaced a first distance apart, and the substrate is preheated to a preheating temperature;

[0044] The substrate is made of lithium tantalate or lithium niobate;

[0045] (2) placing the substrate at the preheating temperature on a hot plate surface, and heating the substrate to a process temperature;

[0046] (3) depositing a silicon nitride film on the surface of the substrate at the process temperature;

[0047] (4) The substrate on which the silicon nitride film is deposited is transferred to a second vacuum chamber for cooling.

[0048] The present invention preheats substrates spaced a first distance apart using a hot plate at a process temperature. This preheating process utilizes thermal radiation at a moderate heating rate, preventing the lithium niobate or lithium tantalate substrate from fragmenting due to rapid thermal expansion. Furthermore, the use of nitrogen as a medium ensures more uniform heating. Furthermore, after the silicon nitride film is deposited, the substrate with the silicon nitride film is directly transferred to a second vacuum chamber for cooling. Cooling in a vacuum environment relies solely on thermal radiation, resulting in a gradual cooling process and preventing sudden cooling that could result in fragmentation of the lithium niobate or lithium tantalate substrate.

[0049] In the present invention, the distance between the hot plate and lithium niobate or lithium tantalate affects the heating rate of the substrate and the final preheating temperature. A suitable distance can ensure preheating at a moderate heating rate while ensuring that the substrate is preheated to a sufficient preheating temperature to prevent sudden heating fragments caused by excessive temperature differences when placed on the surface of the hot plate.

[0050] In some embodiments, the first distance is 30 mil to 80 mil, for example, 30 mil, 40 mil, 50 mil, 60 mil, 70 mil or 80 mil, including but not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0051] In the present invention, the difference between the process temperature and the preheating temperature should not be too large to prevent the preheated substrate from being suddenly heated and fragmented when placed on the hot plate surface. At the same time, it should not be too small, otherwise it will lead to a long heating time, resulting in waste of resources and not conducive to cost saving.

[0052] In some embodiments, the process temperature is 10°C to 30°C higher than the preheating temperature, for example, 10°C, 15°C, 20°C, 25°C or 23°C, including but not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0053] In some embodiments, the process temperature is 150°C to 260°C, for example, 150, 175°C, 200°C, 225°C, 250°C or 260°C, including but not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0054] In some embodiments, the nitrogen gas flow rate is 800 sccm to 1200 sccm, for example, 800 sccm, 900 sccm, 1000 sccm, 1100 sccm or 1200 sccm, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0055] In some embodiments, the substrate in step (1) is maintained at the preheating temperature for more than 30 seconds, preferably 30 seconds to 60 seconds, for example, 30 seconds, 35 seconds, 40 seconds, 45 seconds, 50 seconds, 55 seconds or 60 seconds, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0056] In some embodiments, the substrate in step (2) is maintained at the process temperature for more than 45 seconds, preferably 45 seconds to 120 seconds, for example, 45 seconds, 50 seconds, 60 seconds, 70 seconds, 80 seconds, 90 seconds, 100 seconds, 110 seconds or 120 seconds, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0057] In some embodiments, the method of depositing a silicon nitride film includes:

[0058] At the process temperature, a precursor gas is introduced into the first cavity to deposit a silicon nitride film by plasma enhanced chemical vapor deposition; the precursor gas includes silane, ammonia and nitrogen.

[0059] In some embodiments, after the precursor gas is introduced, it is stabilized for 45 seconds to 100 seconds, for example, it can be 45 seconds, 50 seconds, 55 seconds, 60 seconds, 65 seconds, 70 seconds, 75 seconds, 80 seconds, 85 seconds, 90 seconds, 95 seconds or 100 seconds, including but not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, and then plasma enhanced chemical vapor deposition is performed.

[0060] In some embodiments, the flow rate of silane is 30 sccm to 50 sccm, for example, 30 sccm, 35 sccm, 40 sccm, 45 sccm or 50 sccm, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0061] In some embodiments, the flow rate of the ammonia gas is 30 sccm to 50 sccm, for example, 30 sccm, 35 sccm, 40 sccm, 45 sccm or 50 sccm, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0062] In some embodiments, the flow rate of the nitrogen gas is 1400 sccm~1500 sccm, for example, it can be 1400 sccm, 1420 sccm, 1440 sccm, 1460 sccm, 1480 sccm or 1500 sccm, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0063] In some embodiments, during the deposition process, the pressure in the first chamber is 1 torr to 1.5 torr, for example, 1 torr, 1.1 torr, 1.2 torr, 1.3 torr, 1.4 torr or 1.5 torr, including but not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0064] In the present invention, during the plasma enhanced chemical vapor deposition process, appropriate power is beneficial to maintaining the integrity of the lithium niobate or lithium titanate substrate. If the power is too high, the risk of fragmentation increases.

[0065] In some embodiments, the power of the plasma enhanced chemical vapor deposition is 100W~200W, for example, it can be 100W, 120W, 140W, 160W, 180W or 200W, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0066] In some embodiments, the plasma enhanced chemical vapor deposition time is 30s to 50s, for example, 30s, 35s, 40s, 45s or 50s, including but not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0067] In some embodiments, the radio frequency system used in the plasma enhanced chemical vapor deposition is AENI, with a frequency of 13.56 MHz.

[0068] In some embodiments, the method further comprises evacuating the silicon nitride film after the deposition is completed.

[0069] In the present invention, in a vacuum environment, the lithium niobate or lithium titanate deposited with the silicon nitride film is cooled gently by thermal radiation, thereby avoiding the risk of fragmentation caused by sudden cooling.

[0070] In some embodiments, the temperature in the second vacuum chamber is 20°C to 40°C, for example, 20°C, 25°C, 30°C, 35°C or 40°C, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0071] Preferably, the cooling time in the second vacuum chamber is 100s to 200s, for example, 100s, 120s, 140s, 160s, 180s or 200s, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0072] Example 1

[0073] This embodiment provides a method for forming a silicon nitride film on a surface of a lithium niobate substrate, the method comprising:

[0074] (1) Nitrogen gas with a flow rate of 1000 sccm was introduced into the vacuum first chamber, and the hot plate was heated to 180°C with a spacing of 50 mils to preheat the lithium niobate substrate to 180°C and maintain it for 45 seconds;

[0075] (2) Heat the hot plate to 200°C, place the preheated lithium niobate substrate on the hot plate surface, heat the lithium niobate substrate to 200°C, and maintain for 90 seconds;

[0076] (3) Silane with a flow rate of 40 sccm, ammonia with a flow rate of 40 sccm, and nitrogen with a flow rate of 1450 sccm were introduced to make the pressure in the first chamber 1.2 torr and stabilize for 90 seconds; using the AENI radio frequency system, adjusting the frequency to 13.56 MHz, plasma enhanced chemical vapor deposition was performed, controlling the deposition power to 150 W, and depositing for 40 seconds; after the deposition was completed, the pressure in the first chamber was evacuated to vacuum;

[0077] (4) The lithium niobate substrate with the silicon nitride film deposited thereon was transferred to a second vacuum chamber at a temperature of 30°C and naturally cooled for 150 seconds, and the preparation was completed.

[0078] Example 2

[0079] This embodiment provides a method for forming a silicon nitride film on a surface of a lithium niobate substrate, the method comprising:

[0080] (1) Nitrogen gas with a flow rate of 800 sccm was introduced into the vacuum first chamber, and the hot plate was heated to 140°C with a spacing of 30 mils. The lithium niobate substrate was preheated to 140°C and maintained for 30 seconds.

[0081] (2) Heat the hot plate to 150°C, place the preheated lithium niobate substrate on the hot plate surface, heat the lithium niobate substrate to 150°C, and maintain for 45 seconds;

[0082] (3) Silane with a flow rate of 30 sccm, ammonia with a flow rate of 30 sccm, and nitrogen with a flow rate of 1400 sccm were introduced to make the pressure in the first chamber 1 torr and stabilize for 45 seconds; using the AENI radio frequency system, adjusting the frequency to 13.56 MHz, plasma enhanced chemical vapor deposition was performed, and the deposition power was controlled to 100 W for 30 seconds; after the deposition was completed, the pressure in the first chamber was evacuated to vacuum;

[0083] (4) The lithium niobate substrate with the silicon nitride film deposited thereon was transferred to a second vacuum chamber at a temperature of 20°C and naturally cooled for 100 seconds, and the preparation was completed.

[0084] Example 3

[0085] This embodiment provides a method for forming a silicon nitride film on a surface of a lithium tantalate substrate, the method comprising:

[0086] (1) Nitrogen gas with a flow rate of 1200 sccm was introduced into the vacuum first chamber, and the hot plate was heated to 230°C with an interval of 80 mils to preheat the lithium tantalate substrate to 230°C and maintain it for 60 seconds;

[0087] (2) Heat the hot plate to 260°C, place the preheated lithium tantalate substrate on the hot plate, heat the lithium tantalate substrate to 260°C, and hold for 120 seconds;

[0088] (3) Silane with a flow rate of 50 sccm, ammonia with a flow rate of 50 sccm, and nitrogen with a flow rate of 1500 sccm were introduced to make the pressure in the first chamber 1.5 torr and stabilize for 100 seconds; using the AENI radio frequency system, adjusting the frequency to 13.56 MHz, plasma enhanced chemical vapor deposition was performed, and the deposition power was controlled to 100 W ~ 200 W, and the deposition was carried out for 30 seconds ~ 50 seconds; after the deposition was completed, the pressure in the first chamber was evacuated to vacuum;

[0089] (4) The lithium tantalate substrate with the silicon nitride film deposited thereon was transferred to a second vacuum chamber at a temperature of 40°C and naturally cooled for 200 seconds, and the preparation was completed.

[0090] Example 4

[0091] This embodiment provides a method for preparing a silicon nitride film on the surface of a lithium tantalate substrate. The method is the same as that of Example 1, except that in step (1), the hot plate is heated to 160°C and the lithium niobate substrate is preheated to 160°C, which is 40°C lower than the process temperature.

[0092] Example 5

[0093] This embodiment provides a method for preparing a silicon nitride film on the surface of a lithium tantalate substrate. The method is the same as that of Example 1, except that in step (1), the hot plate is heated to 195°C and the lithium niobate substrate is heated to 195°C, which is only 5°C lower than the process temperature.

[0094] Example 6

[0095] This embodiment provides a method for preparing a silicon nitride film on the surface of a lithium tantalate substrate. The method is the same as that of Example 1, except that the lithium niobate substrate is preheated to 180° C. at intervals of only 20 mils in step (1).

[0096] Example 7

[0097] This embodiment provides a method for preparing a silicon nitride film on the surface of a lithium tantalate substrate. The method is the same as that of Example 1 except that step (1) the lithium niobate substrate is preheated to 180°C and then kept for only 20 seconds before being heated to 200°C.

[0098] Example 8

[0099] This embodiment provides a method for preparing a silicon nitride film on the surface of a lithium tantalate substrate. The method is the same as that of Example 1 except that in step (2), the lithium niobate substrate is heated to 200°C and maintained for only 30 seconds before plasma enhanced chemical vapor deposition is performed.

[0100] Example 9

[0101] This embodiment provides a method for preparing a silicon nitride film on the surface of a lithium tantalate substrate. The method is the same as that of Example 1, except that in step (3), after the precursor gas is introduced, it is stabilized for only 30 seconds before plasma-enhanced chemical vapor deposition is performed.

[0102] Example 10

[0103] This embodiment provides a method for preparing a silicon nitride film on the surface of a lithium tantalate substrate. The method is the same as that of Example 1 except that the power of plasma enhanced chemical vapor deposition in step (3) is 75 W.

[0104] Example 11

[0105] This embodiment provides a method for preparing a silicon nitride film on the surface of a lithium tantalate substrate. The method is the same as that of Example 1 except that the power of plasma enhanced chemical vapor deposition in step (3) is 225 W.

[0106] Comparative Example 1

[0107] This comparative example provides a method for preparing a silicon nitride film on the surface of a lithium tantalate substrate. The method is the same as Example 1 except that step (1) is not performed.

[0108] During the preparation of this comparative example, lithium niobate substrate fragments were found.

[0109] Comparative Example 2

[0110] This comparative example provides a method for preparing a silicon nitride film on the surface of a lithium tantalate substrate. The method is the same as Example 1 except that step (4) is not performed.

[0111] During the preparation of this comparative example, lithium niobate substrate fragments were found.

[0112] Performance testing:

[0113] The thickness and uniformity of the silicon nitride films prepared in all the above examples were measured using an ellipsometer. The test results are shown in Table 1.

[0114] Table 1

[0115]

[0116] According to the test results in Table 1, the present invention preheats the substrate by using a hot plate at the process temperature at a first distance, using thermal radiation at a gentle heating rate, effectively preventing the lithium niobate or lithium tantalate substrate from fragmenting due to rapid thermal expansion. Furthermore, the use of nitrogen as a medium ensures more uniform heating. Furthermore, after the silicon nitride film deposition is completed, the substrate with the deposited silicon nitride film is directly transferred to a second vacuum chamber for cooling. In a vacuum environment, cooling relies solely on thermal radiation, resulting in a gradual cooling process and avoiding sudden cooling that could lead to fragmentation of the lithium niobate or lithium tantalate substrate.

[0117] According to the test results of Example 1, Example 4 and Example 5, a suitable temperature difference between the preheating temperature and the process temperature is more conducive to improving the uniformity of the substrate temperature, thereby improving the uniformity of the subsequent silicon nitride film deposition.

[0118] According to the test results of Example 1 and Example 6, if the distance between the hot plate and the substrate is too small during the preheating process, the substrate will heat up too quickly, resulting in uneven heating of the wafer, local thickness differences, and poor uniformity.

[0119] According to the test results of Example 1, Example 7 and Example 8, if the target temperature is maintained for only 20 seconds after preheating, or only 30 seconds after reaching the process temperature, the time maintained at the target temperature is too short, which will lead to uneven temperature distribution inside the substrate and reduce the uniformity of the prepared silicon nitride film.

[0120] According to the test results of Example 1 and Example 9, if the stabilization time after the precursor gas is introduced is too short, the precursor gas is unstable, resulting in poor stability of the silicon nitride film.

[0121] According to the test results of Example 1, Example 10 and Example 11, if the power of the plasma enhanced chemical vapor deposition is too small or too large, it is not conducive to improving the uniformity of the silicon nitride film.

[0122] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a silicon nitride thin film on a substrate surface, characterized in that: The method comprises: (1) In a first chamber with a nitrogen atmosphere, a hot plate having a process temperature is provided, the hot plate is spaced a first distance apart, and the substrate is preheated to a preheating temperature; The substrate is made of lithium tantalate or lithium niobate; (2) placing the substrate at the preheating temperature on a hot plate surface, and heating the substrate to a process temperature; (3) depositing a silicon nitride film on the surface of the substrate at the process temperature; (4) The substrate on which the silicon nitride film is deposited is transferred to a second vacuum chamber for cooling.

2. The method according to claim 1, wherein The first distance is 30mil~80mil; and / or, the process temperature is 10° C. to 30° C. higher than the preheating temperature; And / or, the process temperature is 150°C~260°C.

3. The method according to claim 1, wherein The nitrogen gas flow rate is 800 sccm to 1200 sccm.

4. The method according to claim 1, wherein In step (1), the substrate is kept at the preheating temperature for more than 30 seconds.

5. The method according to claim 1, wherein In step (2), the substrate is kept at the process temperature for more than 45 seconds.

6. The method according to claim 1, wherein The method for depositing a silicon nitride film comprises: At the process temperature, a precursor gas is introduced into the first chamber to deposit a silicon nitride film by plasma enhanced chemical vapor deposition; The precursor gas includes silane, ammonia and nitrogen.

7. The method according to claim 6, wherein The flow rate of the silane is 30 sccm to 50 sccm; And / or, the flow rate of the ammonia gas is 30 sccm to 50 sccm; And / or, the flow rate of the nitrogen gas is 1400 sccm to 1500 sccm; And / or, during the deposition process, the pressure in the first chamber is 1 torr to 1.5 torr.

8. The method according to claim 6, wherein The power of the plasma enhanced chemical vapor deposition is 100W~200W; And / or, the plasma enhanced chemical vapor deposition time is 30s~50s.

9. The method according to claim 1, wherein The method further includes evacuating the silicon nitride film after the deposition is completed.

10. The method according to claim 1, wherein The temperature in the second vacuum chamber is 20°C to 40°C; And / or, the cooling time in the second vacuum chamber is 100s to 200s.

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