Silicon oxide thickness monitoring method
By forming a thickness monitoring structure in a silicon optical device and performing spectral analysis, the accuracy and repetition of the thickness measurement of silicon oxide layer are solved, reducing transmission losses and improving optical performance.
Patent Information
- Application Number
- CN202510124216.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-26
- Publication Date
- 2025-05-23
AI Technical Summary
The prior art has problems such as large error, low accuracy and poor repeatability when monitoring and measuring the thickness of the silicon oxide layer. Especially in the multi-layer thin film measurement and etching of the highly reflective metal layer, it is easy to cause metal to remain on the side wall of the waveguide, affecting device performance.
By sequentially forming a silicon oxide lower cladding, a waveguide layer and a first silicon oxide upper cladding on the substrate, a silicon oxide protective layer and a highly reflective metal layer are deposited, and patterned, a thickness monitoring structure is formed. The second silicon oxide upper cladding is then covered, the thickness is measured by spectral analysis, and the preparation process of the highly reflective metal layer is optimized to avoid metal residue on the side wall of the waveguide.
Accurate measurement of the thickness of the silicon oxide layer is achieved, which reduces the transmission loss of silicon optical devices, improves the optical performance of the device, and solves the problem of residual metal on the sidewave walls.
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Figure CN120028913A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of optical modulation devices, and in particular to a method for monitoring silicon oxide thickness. Background Art
[0002] Heterogeneous integration of lithium niobate materials and waveguide platforms can achieve a modulation bandwidth of more than 1 GHz by utilizing the excellent electro-optical modulation performance of lithium niobate materials. In order to reduce optical loss and power consumption, the thickness of silicon oxide between lithium niobate and the waveguide layer needs to be precisely controlled at 100nm±10nm to achieve advantages such as low cost, low power consumption, and high reliability. The thickness of silicon oxide can be regulated through processes such as chemical mechanical polishing (CMP). In this process, how to monitor the change in silicon oxide thickness and accurately measure it becomes a prominent issue.
[0003] At present, the technical solutions for monitoring and measuring silicon oxide thickness mainly include: (1) evaluating the overall thickness change of silicon oxide by directly measuring the distance between silicon oxide and substrate; (2) calculating the silicon oxide thickness of the waveguide layer by directly measuring the distance between the waveguide layer and silicon oxide, and between the waveguide layer and substrate; (3) directly measuring the silicon oxide thickness on the metal thin layer by preparing a highly reflective metal thin layer on the waveguide layer.
[0004] However, the above methods have the following problems: (1) Directly measuring the distance between silicon oxide and substrate, this solution has large errors for silicon optical devices with thicker silicon oxide layers, and the test results are inaccurate; (2) Measuring the distance between the waveguide layer and silicon oxide, and between the waveguide layer and substrate, still has the problem of low accuracy for multi-layer thin film measurements. At the same time, the measurement results of this method are not repeatable, which affects large-scale mass production; (3) Measuring the thickness change of silicon oxide on the highly reflective metal layer, residual metal is formed on the side wall of the waveguide during the etching process of the highly reflective metal layer, which greatly affects the transmission loss and damages the device performance. Summary of the invention
[0005] In view of this, an embodiment of the present application provides a method for monitoring silicon oxide thickness to achieve the purpose of accurately measuring the silicon oxide thickness above the metal layer, reducing the transmission loss of silicon optical devices, and improving the optical performance of the devices.
[0006] The embodiment of the present application provides the following technical solution: a method for monitoring silicon oxide thickness, comprising:
[0007] forming a silicon oxide lower cladding layer, a waveguide layer and a first silicon oxide upper cladding layer in sequence on the substrate, so that the first silicon oxide upper cladding layer completely fills the gap of the waveguide layer;
[0008] Depositing a silicon oxide protective layer on the waveguide layer, and depositing a high-reflection metal layer on the silicon oxide protective layer;
[0009] Patterning the highly reflective metal layer to form a thickness monitoring structure above the waveguide layer;
[0010] forming a second silicon oxide upper cladding layer, so that the thickness monitoring structure, the waveguide layer and the first silicon oxide upper cladding layer are completely covered by the second silicon oxide upper cladding layer to obtain a silicon optical device to be tested;
[0011] A measuring light beam is emitted to a position on the silicon optical device to be tested corresponding to the thickness monitoring structure and reflected light is received. The thickness of the second silicon oxide upper cladding layer of the silicon optical device to be tested is analyzed and obtained based on the obtained reflected light spectrum.
[0012] According to an embodiment of the present application, before depositing the silicon oxide protective layer on the waveguide layer, the method further includes:
[0013] The first silicon oxide upper cladding layer is subjected to chemical mechanical polishing, and the polishing of the first silicon oxide upper cladding layer is stopped when the polishing reaches the waveguide layer, and then the silicon oxide protective layer is deposited on the waveguide layer.
[0014] According to an embodiment of the present application, the waveguide layer is a waveguide layer that has not been patterned.
[0015] According to an embodiment of the present application, after the high-reflective metal layer is patterned, the method further includes:
[0016] The waveguide layer is patterned, and then the second silicon oxide upper cladding layer is formed on the patterned waveguide layer.
[0017] According to an embodiment of the present application, the waveguide layer includes a patterned first waveguide layer and a second waveguide layer in order from bottom to top; before depositing the silicon oxide protective layer on the waveguide layer, it also includes:
[0018] The first silicon oxide upper cladding layer is subjected to chemical mechanical polishing, and the polishing of the first silicon oxide upper cladding layer is stopped when the polishing reaches the second waveguide layer, and then the silicon oxide protective layer is deposited on the second waveguide layer.
[0019] According to an embodiment of the present application, the waveguide layer includes a first waveguide layer and a second waveguide layer from bottom to top; wherein the second waveguide layer is a waveguide layer that has not been patterned.
[0020] According to an embodiment of the present application, the thickness of the silicon oxide protective layer is 30-50 nm.
[0021] According to an embodiment of the present application, the method further includes:
[0022] Forming an etched groove on the first silicon oxide upper cladding layer, wherein the position of the etched groove corresponds to the position of the waveguide layer, and the bottom of the etched groove extends to the waveguide layer;
[0023] The first silicon oxide upper cladding layer except the etching groove is used as the silicon oxide protective layer, and the high-reflection metal layer is deposited on the surface of the first silicon oxide upper cladding layer and the surface of the etching groove.
[0024] According to one embodiment of the present application, the method further includes: performing patterning on the high-reflective metal layer to remove the high-reflective metal layer on the surface of the first silicon oxide upper cladding layer, so that the high-reflective metal layer in the etched groove serves as the thickness monitoring structure.
[0025] According to one embodiment of the present application, the method further includes: forming a second silicon oxide upper cladding layer, and allowing the second silicon oxide upper cladding layer to completely fill the remaining portion of the etched groove, and flattening the second silicon oxide upper cladding layer to obtain the silicon optical device to be tested.
[0026] Compared with the prior art, the beneficial effects that can be achieved by at least one of the above-mentioned technical solutions adopted in the embodiments of this specification include at least the following: in the embodiments of the present invention, a silicon oxide lower cladding layer, a waveguide layer and a first silicon oxide upper cladding layer are sequentially formed on a substrate, so that the first silicon oxide upper cladding layer completely fills the gap of the waveguide layer; a silicon oxide protective layer is deposited on the waveguide layer, and a high-reflection metal layer is deposited on the silicon oxide protective layer; the high-reflection metal layer is patterned to form a thickness monitoring structure above the waveguide layer; a second silicon oxide upper cladding layer is formed, so that the thickness monitoring structure, the waveguide layer and the first silicon oxide upper cladding layer are completely covered by the second silicon oxide upper cladding layer to obtain a silicon optical device to be tested; a measuring light beam is emitted to a position on the silicon optical device to be tested corresponding to the thickness monitoring structure and reflected light is received, and the thickness of the second silicon oxide upper cladding layer of the silicon optical device to be tested is obtained by analyzing the obtained reflected light spectrum. By preparing a highly reflective metal thin layer on the waveguide layer, the thickness of silicon oxide on the metal thin layer is directly measured. In addition, in order to prevent residual metal from being formed on the side wall of the waveguide during the etching of the highly reflective metal layer, thereby affecting the transmission loss and damaging the device performance, the embodiment of the present invention further optimizes the process flow of preparing the highly reflective metal layer, which can not only accurately measure the thickness of silicon oxide above the metal layer, but also solve the problem of residual metal on the side wall of the waveguide while ensuring the accuracy of the silicon oxide thickness measurement result, thereby reducing the transmission loss of the silicon optical modulator device and improving the optical performance of the optical modulator device. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0028] Figure 1 is a schematic flow chart of a method for monitoring silicon oxide thickness according to an embodiment of the present invention;
[0029] Figure 2 is a first schematic diagram of a method for monitoring silicon oxide thickness in a first embodiment of the present invention;
[0030] Figure 3 is a second schematic diagram of the silicon oxide thickness monitoring method in the first embodiment of the present invention;
[0031] Figure 4 is a third schematic diagram of the silicon oxide thickness monitoring method in the first embodiment of the present invention;
[0032] Figure 5 is a fourth schematic diagram of the silicon oxide thickness monitoring method in the first embodiment of the present invention;
[0033] Figure 6 is a fifth schematic diagram of the silicon oxide thickness monitoring method in the first embodiment of the present invention;
[0034] in, Figure 2-Figure 6 In the figure, 10-silicon substrate, 11-thermal oxide silicon layer, 12-silicon-rich silicon nitride layer, 13-silicon nitride layer, 14-chemical vapor deposited silicon oxide layer, 15-high reflective metal layer;
[0035] Figure 7 is a first schematic diagram of a method for monitoring silicon oxide thickness in a second embodiment of the present invention;
[0036] Figure 8 is a second schematic diagram of a method for monitoring silicon oxide thickness in a second embodiment of the present invention;
[0037] Fig. 9 is a third schematic diagram of the silicon oxide thickness monitoring method in the second embodiment of the present invention;
[0038] Fig.10 is a fourth schematic diagram of the silicon oxide thickness monitoring method in the second embodiment of the present invention;
[0039] Fig.11 is a fifth schematic diagram of the silicon oxide thickness monitoring method in the second embodiment of the present invention;
[0040] in, Figure 7-Figure 11In the figure, 20 is a silicon substrate, 21 is a thermally oxidized silicon layer, 22 is a silicon-rich silicon nitride layer, 23 is a silicon nitride layer, 24 is a chemical vapor deposited silicon oxide layer, and 25 is a highly reflective metal layer;
[0041] Fig.12 is a first schematic diagram of a method for monitoring silicon oxide thickness in a third embodiment of the present invention;
[0042] Fig.13 is a second schematic diagram of the silicon oxide thickness monitoring method in the third embodiment of the present invention;
[0043] Fig.14 is a third schematic diagram of a method for monitoring silicon oxide thickness in a third embodiment of the present invention;
[0044] Fig.15 is a fourth schematic diagram of the silicon oxide thickness monitoring method in the third embodiment of the present invention;
[0045] Fig.16 is a fifth schematic diagram of the silicon oxide thickness monitoring method in the third embodiment of the present invention;
[0046] in, Figure 12-16 In the figure, 30 is a silicon substrate, 31 is a thermally oxidized silicon layer, 32 is a silicon-rich silicon nitride layer, 33 is a silicon nitride layer, 34 is a chemical vapor deposited silicon oxide layer, 35 is an etched groove, and 36 is a highly reflective metal layer. DETAILED DESCRIPTION
[0047] The embodiments of the present application are described in detail below with reference to the accompanying drawings.
[0048] The following describes the implementation methods of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present application.
[0049] like Figure 1 As shown, an embodiment of the present invention provides a method for monitoring silicon oxide thickness, comprising:
[0050] 101. Forming a silicon oxide lower cladding layer, a waveguide layer and a first silicon oxide upper cladding layer in sequence on a substrate, so that the first silicon oxide upper cladding layer completely fills the gap of the waveguide layer;
[0051] 102. Depositing a silicon oxide protective layer on the waveguide layer, and depositing a high-reflection metal layer on the silicon oxide protective layer;
[0052] 103. Patterning the highly reflective metal layer to form a thickness monitoring structure above the waveguide layer;
[0053] 104. Form a second silicon oxide upper cladding layer, so that the thickness monitoring structure, the waveguide layer and the first silicon oxide upper cladding layer are completely covered by the second silicon oxide upper cladding layer to obtain a silicon optical device to be tested;
[0054] 105. Emit a measuring light beam to a position on the silicon optical device to be tested that corresponds to the thickness monitoring structure and receive reflected light, and analyze and obtain the thickness of the second silicon oxide upper cladding layer of the silicon optical device to be tested based on the obtained reflected light spectrum.
[0055] The embodiment of the present invention can accurately measure the thickness of silicon oxide above the metal layer by preparing a highly reflective metal layer. In specific implementation, judgment is mainly made by online spectral measurement. First, an optical measuring instrument emits a light beam to illuminate the thickness monitoring structure of the silicon optical device to be tested and receives reflected light, and a series of spectra will be obtained. Then, the spectrum obtained by the test and the optical model of the thin film are fitted and analyzed, and different film layers can be distinguished, and the thickness of different film layers can be calculated at the same time. In the embodiment of the present invention, a highly reflective metal layer is prepared under the silicon oxide layer. After receiving the reflected light, the fitted spectral curve obtained will be smoother, the fitting coefficient will be large, and the test result will be more accurate. In addition, SEM / FIB slice test can also be used to more accurately observe the thickness of different film layers and verify the accuracy of the results of online spectral measurement. This method is suitable for the current verification stage; in the subsequent device tape-out stage, after fixing the recipe (precisely defined process parameters and operating procedures), online spectral measurement is usually used.
[0056] Among them, the optical model of the above-mentioned film is a theoretical model constructed based on Maxwell's equations and Fresnel's formula. When a beam of polarized light is incident on the surface of the film, its polarization state will change due to the reflection and refraction of the light at different interfaces between the film and the substrate. This change can be described by two parameters, namely the amplitude ratio and the phase difference. By measuring these two parameters and combining them with the optical model of the film, the optical properties of the film, such as the thickness and refractive index, can be inferred. The model and test principle are as described above. Usually, professional spectral data analysis software is used to select the silicon oxide film model, and the thickness of the film layer is obtained by automatic numerical fitting calculation through the software.
[0057] In specific implementation, after the high-reflection metal layer is prepared, residual metal will be formed at the edge and gap of the waveguide structure when the high-reflection metal layer is subsequently etched, which will increase the transmission loss of the silicon optical device and affect its optical performance. Therefore, the embodiment of the present invention optimizes the process flow of preparing the high-reflection metal layer and adopts different processes such as flattening the surface before growth, synchronous etching after growth, or groove growth, so as to avoid residual metal at the edge of the waveguide, thereby reducing the transmission loss of the silicon optical device and improving the optical performance of the device.
[0058] In order to optimize the preparation process of the high-reflective metal layer and avoid residual metal in the edge gap and other positions of the waveguide structure, in some embodiments of the present invention, before depositing the silicon oxide protective layer on the waveguide layer, it also includes: chemically mechanical polishing the first silicon oxide upper cladding layer, and stopping when polishing the first silicon oxide upper cladding layer to the waveguide layer, and then depositing the silicon oxide protective layer on the waveguide layer.
[0059] In this embodiment, first, a silicon oxide lower cladding layer, a waveguide layer, and a first silicon oxide upper cladding layer are sequentially formed on the substrate from bottom to top, wherein the waveguide layer is a patterned waveguide core, and the gap of the waveguide core is completely filled by the first silicon oxide upper cladding layer; then, the first silicon oxide layer is subjected to chemical mechanical polishing until the first silicon oxide layer is polished to the waveguide layer, at which time the waveguide layer serves as a polishing stop layer, and then a thin layer of the silicon oxide protective layer is deposited on the waveguide layer, and a high-reflection metal layer is deposited on the silicon oxide protective layer. A thin silicon oxide protective layer is prepared between the high-reflective metal layers, so that the structure of the waveguide layer will not be affected during the subsequent etching process of the high-reflective metal layer, and no residual metal will be formed on the waveguide layer. The high-reflective metal layer is then etched and patterned to form the thickness monitoring structure on the waveguide structure. Finally, a second silicon oxide upper cladding layer is grown on the thickness monitoring structure to protect the substrate surface, and a CMP process is performed to flatten the surface. At this time, the thickness monitoring structure is used for measurement monitoring, and the silicon oxide thickness is obtained by means of data fitting analysis and the like.
[0060] In some embodiments of the present invention, the waveguide layer may be a double-layer waveguide, that is, the waveguide layer includes a patterned first waveguide layer and a second waveguide layer in sequence from bottom to top; before depositing the silicon oxide protective layer on the waveguide layer, the process further includes: performing chemical mechanical polishing on the first silicon oxide upper cladding layer, and stopping when polishing the first silicon oxide upper cladding layer to the second waveguide layer, and then depositing a thin layer of the silicon oxide protective layer on the second waveguide layer.
[0061] In a specific implementation, the first waveguide layer may be a silicon-rich silicon nitride layer, and the second waveguide layer may be a silicon nitride layer. The first silicon oxide upper cladding layer above the silicon nitride layer is subjected to chemical mechanical polishing until the silicon nitride layer is exposed, and then a thin layer of the silicon oxide protective layer is deposited on the silicon nitride layer.
[0062] In order to optimize the preparation process of the high-reflection metal layer and avoid residual metal in the edge gap and other positions of the waveguide structure, in some embodiments of the present invention, the waveguide layer is a waveguide layer that has not been patterned. In order to deposit a thin silicon oxide protective layer on the waveguide layer, the waveguide layer in this embodiment has not been patterned, and a thin silicon oxide protective layer can be directly deposited on the waveguide layer, and a high-reflection metal layer is deposited on the silicon oxide protective layer. Since a thin silicon oxide protective layer is prepared between the waveguide layer and the high-reflection metal layer, the structure of the waveguide layer will not be affected in the subsequent etching process of the high-reflection metal layer, and residual metal will not be formed on the waveguide layer. Then, the high-reflection metal layer is etched and patterned to form the thickness monitoring structure on the waveguide layer.
[0063] In specific implementation, since the waveguide layer has not been patterned, after the high-reflection metal layer is patterned, the waveguide layer needs to be patterned to form a desired optical structure, and then the second silicon oxide upper cladding layer is formed on the patterned waveguide layer and the high-reflection metal layer to protect the substrate surface, and the CMP process is performed to flatten the surface. At this time, the thickness monitoring structure is used for measurement monitoring, and the silicon oxide thickness is obtained by means of data fitting analysis and the like.
[0064] In some embodiments of the present invention, the waveguide layer may be a double-layer waveguide, that is, the waveguide layer includes a first waveguide layer and a second waveguide layer from bottom to top; wherein the first waveguide layer may be a waveguide layer that has been patterned, and the second waveguide layer is a waveguide layer that has not been patterned. Since the second waveguide layer has not been patterned, a thin layer of the silicon oxide protective layer is directly deposited on the second waveguide layer.
[0065] In a specific implementation, the first waveguide layer may be a silicon-rich silicon nitride layer that has been patterned, and the second waveguide layer may be a silicon nitride layer that has not been patterned. A thin layer of the silicon oxide protective layer is deposited on the silicon nitride layer to protect the waveguide layer.
[0066] In some embodiments of the present invention, the thickness of the silicon oxide protective layer is 30-50nm, and this thickness setting needs to take into account both the design requirements and the process window: the silicon oxide protective layer is used to protect the silicon nitride waveguide from being damaged during the etching process of the high-reflection metal layer. A second silicon oxide cladding layer still needs to be grown and CMP-treated. At this time, the thickness of the cladding layer needs to be controlled to be 100nm higher than the silicon nitride film for subsequent bonding of the lithium niobate film and optimization of the optical modulation performance; since the second silicon oxide cladding layer covers the waveguide structure, the silicon oxide protective layer and the high-reflection metal layer, the silicon oxide protective layer, the high-reflection metal layer, and the high-reflection metal layer after CMP treatment are not damaged. The reflective metal layer and the second silicon oxide cladding are superimposed on a total of 100nm. According to the process processing requirements and test requirements, the thickness of the silicon oxide protective layer is set to 30-50nm, the high-reflective metal layer is 30nm, and the second silicon oxide cladding is 20-40nm (this thickness is to meet the spectral test requirements. The test result deviation is larger when the film layer is thinner); in addition, in terms of the process etching process, the thickness is set at this time so that the over-etching phenomenon generated when etching the high-reflective metal layer will not completely corrode the silicon oxide protective layer, which is sufficient to protect the underlying waveguide material. Silicon oxide and highly reflective metal need to have a larger etching selectivity ratio.
[0067] In order to optimize the preparation process of the high-reflective metal layer and avoid residual metal in the edge gap and other positions of the waveguide structure, in some embodiments of the present invention, the method also includes: preparing an etching groove on the first silicon oxide upper cladding layer, the position of the etching groove corresponds to the position of the waveguide layer, and the bottom of the etching groove extends to the waveguide layer; using the first silicon oxide upper cladding layer except the etching groove as the silicon oxide protective layer, and depositing the high-reflective metal layer on the surface of the first silicon oxide upper cladding layer and the surface of the etching groove.
[0068] In specific implementation, this embodiment deposits a highly reflective metal layer by grooving. In order not to affect the waveguide layer, an etching groove is prepared only above the waveguide layer, and the first silicon oxide upper cladding layer originally on the waveguide layer is used as the silicon oxide protective layer, and there is no need to prepare the silicon oxide protective layer separately. After the etching groove is prepared on the waveguide layer, a highly reflective metal layer is formed on the surface of the etching groove and the surface of the first silicon oxide upper cladding layer. Next, the highly reflective metal layer is etched and patterned to remove the highly reflective metal layer on the surface of the first silicon oxide upper cladding layer. The highly reflective metal layer in the etching groove is used as the thickness monitoring structure. Finally, the second silicon oxide upper cladding layer is formed on the thickness monitoring structure in the etching groove, and the second silicon oxide upper cladding layer completely fills the remaining part in the etching groove to protect the substrate surface, and the CMP process is performed to flatten the surface. At this time, the thickness monitoring structure is used for measurement monitoring, and the silicon oxide thickness is obtained by means of data fitting analysis and the like.
[0069] Next, if Figure 2-Figure 16 As shown, three different embodiments are used to further illustrate the present invention. A method of preparing a highly reflective metal layer by optimizing the preparation process is proposed to solve the problem of residual metal on the side wall and avoid the problem of low measurement accuracy and poor repeatability. 3 N 4 The process steps are described in detail by taking the waveguide substrate as an example (all schematic diagrams are cross-sectional views unless otherwise specified).
[0070] Embodiment 1: A waveguide material is used as a chemical mechanical polishing (CMP) stop layer, and a monitoring metal is grown on a flat waveguide layer.
[0071] First, prepare a silicon nitride waveguide substrate such as Figure 2 As shown, the silicon nitride waveguide substrate includes, from bottom to top, a silicon substrate 10, a thermally oxidized silicon layer 11 (the silicon oxide lower cladding), a silicon-rich silicon nitride layer 12, a silicon nitride layer 13, and a chemical vapor deposition silicon oxide layer 14 (the first silicon oxide upper cladding). The thermally oxidized silicon layer 11 and the chemically vapor deposition silicon oxide layer 14 are two layers of silicon oxide thin film structures that are not in the same layer, and there is a silicon nitride waveguide structure in the middle: the first silicon oxide layer is prepared by thermal oxidation, which has the best density and film quality, and can be used as a lower silicon oxide layer to grow a silicon nitride thin film layer with good crystal quality to optimize the optical performance; after the silicon nitride thin film layer is grown, it is impossible to continue to prepare silicon oxide by thermal oxidation, so the upper cladding silicon oxide is prepared by chemical vapor deposition, and its film quality is slightly worse than that of the thermally oxidized silicon layer, but it can be used as a cladding to protect the silicon nitride waveguide structure.
[0072] Next, chemical mechanical polishing is performed on the chemical vapor deposited silicon oxide layer 14 on the surface of the substrate, and the upper silicon oxide layer is polished to the silicon nitride layer 13 and stopped. Figure 3 shown.
[0073] Next, a thin silicon oxide protective layer and a highly reflective metal layer 15 are deposited on the silicon nitride layer 13. The silicon oxide protective layer is used to protect the waveguide from being damaged in the subsequent etching process, and the highly reflective metal layer 15 is used for monitoring and measurement, such as Figure 4 shown.
[0074] Next, the high-reflective metal layer 15 is etched and patterned to form a monitoring structure on the dummy pattern region of the waveguide layer, such as Figure 5 shown.
[0075] Finally, a silicon oxide cladding layer (the second silicon oxide upper cladding layer) is grown to protect the substrate surface, and a CMP process is performed to flatten the surface. At this time, the high-reflective metal layer 15 can be used for measurement monitoring, such as Figure 6 shown.
[0076] Embodiment 2: A waveguide layer and a high-reflection metal layer are prepared by a method of growing all film layers and then performing simultaneous etching.
[0077] First, prepare an unpatterned waveguide substrate, such as Figure 7 As shown, the waveguide substrate includes a silicon substrate 20, a thermally oxidized silicon layer 21 (the silicon oxide lower cladding layer), a silicon-rich silicon nitride layer 22, a silicon nitride layer 23 and a chemical vapor deposited silicon oxide layer 24 (the first silicon oxide upper cladding layer).
[0078] Secondly, a silicon oxide protective layer is grown to protect the silicon nitride, and a highly reflective metal layer 25 is grown for measurement and monitoring, such as Figure 8 Again, the highly reflective metal layer 25 is etched to form a monitoring structure, as shown in FIG. Fig. 9 As shown. Again, the silicon nitride waveguide layer is etched to form the desired optical structure, as shown Fig.10 shown.
[0079] Finally, a silicon oxide cladding layer (the second silicon oxide upper cladding layer) is grown, and the wafer is subjected to chemical mechanical polishing to flatten the surface. At this time, the high reflective metal layer 25 can be used as a measurement monitoring layer, such as Fig.11 shown.
[0080] Example 3: Deposition of a highly reflective metal layer by grooving.
[0081] First, prepare a silicon nitride waveguide substrate such as Fig.12 As shown, the silicon nitride waveguide substrate includes a silicon substrate 30, a thermally oxidized silicon layer 31 (the silicon oxide lower cladding layer), a silicon-rich silicon nitride layer 32, a silicon nitride layer 33 and a chemical vapor deposited silicon oxide layer 34 (the first silicon oxide upper cladding layer).
[0082] Next, the chemical vapor deposition silicon oxide layer 34 is etched onto the waveguide layer dummy pattern structure, such as Fig.13 As shown, an etching groove 35 is formed. Again, the chemical vapor deposition silicon oxide layer 34 is used as a silicon oxide protective layer, and a high reflective metal layer 36 is prepared on the etching groove 35 and the chemical vapor deposition silicon oxide layer 34, as shown in FIG. Fig.14 shown.
[0083] Next, the high reflective metal layer 36 is etched by dry / wet etching process to form the desired monitoring structure, such as Fig.15 Finally, a silicon oxide cladding layer (the second silicon oxide upper cladding layer) is prepared and the surface is planarized. At this time, the high reflective metal layer 36 can be used as a monitoring structure, such as Fig.16 shown.
[0084] The embodiment of the present invention can accurately measure the thickness of silicon oxide above the metal layer by preparing a highly reflective metal layer; by optimizing the process flow of preparing the highly reflective metal layer and adopting different processes such as flattening the surface before growth, simultaneous etching after growth, or groove growth, it is possible to avoid residual metal at the edge of the waveguide, reduce the transmission loss of the silicon optical device, and improve the optical performance of the device.
[0085] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.
Claims
1. A method for monitoring silicon oxide thickness, characterized in that: include: forming a silicon oxide lower cladding layer, a waveguide layer and a first silicon oxide upper cladding layer in sequence on the substrate, so that the first silicon oxide upper cladding layer completely fills the gap of the waveguide layer; Depositing a silicon oxide protective layer on the waveguide layer, and depositing a high-reflection metal layer on the silicon oxide protective layer; Patterning the highly reflective metal layer to form a thickness monitoring structure above the waveguide layer; forming a second silicon oxide upper cladding layer, so that the thickness monitoring structure, the waveguide layer and the first silicon oxide upper cladding layer are completely covered by the second silicon oxide upper cladding layer to obtain a silicon optical device to be tested; A measuring light beam is emitted to a position on the silicon optical device to be tested corresponding to the thickness monitoring structure and reflected light is received. The thickness of the second silicon oxide upper cladding layer of the silicon optical device to be tested is analyzed and obtained based on the obtained reflected light spectrum.
2. The method for monitoring silicon oxide thickness according to claim 1, characterized in that: Before depositing the silicon oxide protective layer on the waveguide layer, the method further comprises: The first silicon oxide upper cladding layer is subjected to chemical mechanical polishing, and the polishing of the first silicon oxide upper cladding layer is stopped when the polishing reaches the waveguide layer, and then the silicon oxide protective layer is deposited on the waveguide layer.
3. The method for monitoring silicon oxide thickness according to claim 1, characterized in that: The waveguide layer is a waveguide layer that has not been patterned.
4. The method for monitoring silicon oxide thickness according to claim 3, characterized in that: After the highly reflective metal layer is patterned, the method further comprises: The waveguide layer is patterned, and then the second silicon oxide upper cladding layer is formed on the patterned waveguide layer.
5. The method for monitoring silicon oxide thickness according to claim 2, characterized in that: The waveguide layer includes a patterned first waveguide layer and a second waveguide layer in order from bottom to top; before depositing the silicon oxide protective layer on the waveguide layer, it also includes: The first silicon oxide upper cladding layer is subjected to chemical mechanical polishing, and the polishing of the first silicon oxide upper cladding layer is stopped when the polishing reaches the second waveguide layer, and then the silicon oxide protective layer is deposited on the second waveguide layer.
6. The method for monitoring silicon oxide thickness according to claim 3, characterized in that: The waveguide layer includes a first waveguide layer and a second waveguide layer from bottom to top; wherein the second waveguide layer is a waveguide layer that has not been patterned.
7. The method for monitoring silicon oxide thickness according to claim 1, characterized in that: The thickness of the silicon oxide protective layer is 30-50 nm.
8. The method for monitoring silicon oxide thickness according to claim 1, characterized in that: The method further comprises: Forming an etched groove on the first silicon oxide upper cladding layer, wherein the position of the etched groove corresponds to the position of the waveguide layer, and the bottom of the etched groove extends to the waveguide layer; The first silicon oxide upper cladding layer except the etching groove is used as the silicon oxide protective layer, and the high-reflection metal layer is deposited on the surface of the first silicon oxide upper cladding layer and the surface of the etching groove.
9. The method for monitoring silicon oxide thickness according to claim 8, characterized in that: The method further comprises: The high-reflective metal layer is patterned to remove the high-reflective metal layer on the surface of the first silicon oxide upper cladding layer, so that the high-reflective metal layer in the etched groove serves as the thickness monitoring structure.
10. The method for monitoring silicon oxide thickness according to claim 8, characterized in that: The method further includes: forming a second silicon oxide upper cladding layer, allowing the second silicon oxide upper cladding layer to completely fill the remaining portion of the etched groove, and performing a planarization process on the second silicon oxide upper cladding layer to obtain the silicon optical device to be tested.