Monitoring method of germanium epitaxial process and germanium epitaxial wafer

Abstract

The invention provides a germanium epitaxial process monitoring method and a germanium epitaxial wafer. The method comprises the following steps: providing a silicon substrate; forming a required barrier film layer on the silicon substrate; according to a preset pattern, etching a groove which penetrates through the required barrier film layer and intrudes into the silicon substrate; the preset pattern is square; growing a germanium epitaxial layer in the groove; a monitoring image of the bottom of the groove is collected through a machine table provided with an optical microscope, and the flatness of the bottom of the groove in the germanium epitaxy process is judged through the monitoring image. A structural pattern is designed and a wafer is etched according to the structural pattern, and the structural pattern can effectively represent the condition of the bottom of an etched groove, so that the flatness of the bottom of the groove can be effectively observed under an optical microscope; thus, slicing treatment is not needed, the flatness of the bottom of the groove can be monitored in time through the optical microscope, and time and cost are saved.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and more particularly to a monitoring method for germanium epitaxial process and a germanium epitaxial wafer. Background Art

[0002] At room temperature, the cut-off wavelength of silicon is 1.1 um, which limits the application of silicon in the near-infrared band of 1.3 - 1.55 um. Germanium has a narrower bandgap than silicon and can efficiently absorb near-infrared light. At the same time, its high light absorption efficiency makes it the most ideal material for Si-based long-wavelength photodetectors.

[0003] During the chip manufacturing process, after etching the trench, the bottom is flat. However, after the germanium epitaxial process, the bottom of the trench may become uneven. Such an uneven bottom structure will directly affect the crystal quality such as the electrical properties and reliability of the device. Therefore, it is necessary to monitor it.

[0004] In related technologies, during the germanium process growth, in order to effectively understand the process growth, the wafer slicing method is usually used, that is, the trench and the germanium growth are observed through SEM slicing. However, such a method will cause waste of wafers and time, and it is impossible to monitor abnormalities in a timely manner, making it difficult to apply to the mass production process of wafers. Summary of the Invention

[0005] In view of this, the purpose of the present application is to provide a monitoring method for germanium epitaxial process and a germanium epitaxial wafer to solve the problem in the prior art that observing the bottom of the trench through wafer slicing causes waste of wafers and time and cannot monitor in a timely manner.

[0006] The embodiment of the present application provides a monitoring method for germanium epitaxial process, and the monitoring method includes: Providing a silicon substrate; Forming a required barrier film layer on the silicon substrate; Etching a groove that penetrates the required barrier film layer and invades the silicon substrate according to a preset pattern; the preset pattern is a square; Growing a germanium epitaxial layer in the groove; Collecting a monitoring image of the bottom of the groove through a machine equipped with an optical microscope, and judging the flatness of the bottom of the groove during the germanium epitaxial process through the monitoring image.

[0007] Further, the side length range of the preset pattern is 80 - 100 um.

[0008] Further, etching a groove that penetrates the required barrier film layer and invades the silicon substrate according to a preset pattern includes: Coating a photoresist on the upper surface of the required barrier film layer; Develop and clean the photoresist on the upper surface within the preset pattern range. Etch the required barrier film layer and the silicon substrate within the preset pattern range, penetrating through the required barrier film layer and forming the groove on the silicon substrate. Develop and clean the remaining photoresist on the upper surface.

[0009] Furthermore, the required barrier film layer is used to prevent fragmentation caused by stress release due to lattice mismatch during the germanium epitaxial growth process.

[0010] Furthermore, the required barrier film layer includes a first barrier film layer and a second barrier film layer; the second barrier film layer is located above the first barrier film layer; the material of the first barrier film layer is thermal oxidation process silicon oxide; the material of the second barrier film layer is HDP silicon oxide.

[0011] Furthermore, the thickness range of the first barrier film layer is 100 - 200 Å, and the thickness range of the second barrier film layer is 4000 - 6000 Å.

[0012] Furthermore, the monitoring method further includes: Etch the germanium epitaxial layer using a chemical etching reagent. Collect experimental pictures of the germanium epitaxial layer through a scanning electron microscope. Determine the crystal quality of the germanium epitaxial layer according to the density of corrosion pits in the experimental pictures.

[0013] Furthermore, judging the flatness of the bottom of the groove during the germanium epitaxial process through the monitoring image includes: Judge the flatness of the bottom of the groove through the monitoring image by manual or image processing algorithm; among them, the uneven position appears as abnormal points with color difference in the monitoring image.

[0014] The embodiment of the present application also provides a germanium epitaxial wafer, which includes: A silicon substrate and a required barrier film layer formed on the silicon substrate; the required barrier film layer is etched through according to a preset pattern, and a groove is etched on the silicon substrate; a germanium epitaxial layer grows in the groove; the preset pattern is a square; the preset pattern is used to enable the flatness of the bottom of the groove to be effectively observed through an optical microscope.

[0015] Furthermore, the side length range of the preset pattern is 80 - 100 μm.

[0016] A monitoring method for a germanium epitaxial process and a germanium epitaxial wafer provided by an embodiment of the present application etch a wafer according to a designed square structural pattern, and the structural pattern can effectively show the bottom condition of the etched groove, so that the flatness of the bottom of the groove can be effectively observed under an optical microscope; in this way, without slicing treatment, the flatness of the bottom of the groove can be monitored in a timely manner through an optical microscope, saving time and cost.

[0017] To make the above objects, features, and advantages of the present application more obvious and understandable, the following specifically enumerates preferred embodiments and, in conjunction with the accompanying drawings, details are described as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present application and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 FIG. 12 shows a schematic diagram of unevenness at the bottom of a trench after a germanium epitaxial process provided by an embodiment of the present application; Figure 2 FIG. 15 shows a flowchart of a monitoring method for a germanium epitaxial process provided by an embodiment of the present application; Figure 3 FIG. 18 shows a cross-sectional view of a sliced germanium epitaxial wafer provided by an embodiment of the present application; FIG. 4(a) shows a schematic diagram of a comparison pattern and sliced observation provided by an embodiment of the present application; FIG. 4(b) shows a schematic diagram of a monitoring image of a comparison pattern provided by an embodiment of the present application; FIG. 4(c) shows a schematic diagram of a preset pattern and sliced observation provided by an embodiment of the present application; FIG. 4(d) shows a schematic diagram of a monitoring image of a comparison pattern and a preset pattern provided by an embodiment of the present application; Figure 5 FIG. 29 shows one of the schematic diagrams of the experimental results of a preset pattern provided by an embodiment of the present application; Figure 6 FIG. 32 shows another schematic diagram of the experimental results of a preset pattern provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only some of the embodiments of this application, rather than all the embodiments. The components of the embodiments of this application described and illustrated herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. Based on the embodiments of this application, every other embodiment obtained by those skilled in the art without creative efforts belongs to the scope of protection of this application.

[0021] At room temperature, the cut-off wavelength of silicon is 1.1 um, which limits the application of silicon in the near-infrared band of 1.3 - 1.55 um. Germanium has a narrower bandgap than silicon and can efficiently absorb near-infrared light. At the same time, its high light absorption efficiency makes it the most ideal material for Si-based long-wavelength photodetectors.

[0022] As Figure 1 shown, during the chip manufacturing process, after etching the trench, its bottom is flat. However, after the germanium epitaxial process, the bottom of the trench may become uneven. Such an uneven bottom structure will have a direct impact on the electrical properties and reliability of the device, such as crystal quality. Therefore, it is necessary to monitor it. In fact, such unevenness is affected by many factors, such as the oxygen content on the silicon surface, plasma residues during the etching process, and the control of the airtightness environment of the machine itself, etc.

[0023] In the related art, during the germanium process growth, in order to effectively understand the process growth, the wafer slicing method is usually used, that is, the trench and the germanium growth are observed through SEM slicing. However, such a method will cause waste of wafers and time, and it is impossible to monitor abnormalities in a timely manner, making it difficult to apply to the mass production process of wafers.

[0024] Based on this, the embodiments of this application provide a monitoring method for germanium epitaxial process to solve the problem in the prior art that observing the bottom of the trench through wafer slicing causes waste of wafers and time and cannot monitor in a timely manner.

[0025] Please refer to Figure 2 , Figure 2 which is a flowchart of a monitoring method for germanium epitaxial process provided by the embodiments of this application. As Figure 2 shown, the monitoring method provided by the embodiments of this application includes: S201. Provide a silicon substrate.

[0026] S202. Form a required barrier film layer on the silicon substrate.

[0027] Wherein, the required barrier film layer is used to prevent fragmentation caused by stress release due to lattice mismatch during the germanium epitaxial growth process.

[0028] More specifically, the required barrier film layer includes a first barrier film layer and a second barrier film layer; the second barrier film layer is located above the first barrier film layer; the material of the first barrier film layer is thermal oxidation process silicon oxide; the material of the second barrier film layer is HDP silicon oxide.

[0029] S203. Etch a groove that penetrates the required barrier film layer and invades the silicon substrate according to a preset pattern.

[0030] Wherein, the preset pattern is a square. This is because, through research, it is found in the embodiments of the present application that designing it as a square can effectively balance the stress caused by the differences in the lattice constants and thermal expansion coefficients of silicon and germanium itself during the heteroepitaxial process in the trench. And if these stresses cannot be effectively eliminated, they will bring dislocation defects to the epitaxial film layer, which will affect the result of pattern determination by optical microscope observation, whether it is the pattern difference caused by the dislocation stress of growing germanium or the difference caused by the uneven bottom. Moreover, this pattern is simple and practical, easy to implement, and suitable for actual industrial production.

[0031] In specific implementation, step S203 may include: S2031. Coat photoresist on the upper surface of the required barrier film layer.

[0032] S2032. Develop and clean the photoresist on the upper surface within the range of the preset pattern; wherein, the photoresist forms a pattern through exposure and development in the photolithography process and serves as a protection layer for the etching process, covering the area to be retained. In this step, the photoresist on the upper surface of the wafer within the range of the square pattern is developed and cleaned.

[0033] S2033. Etch the required barrier film layer and the silicon substrate within the range of the preset pattern, penetrate the required barrier film layer and form the groove on the silicon substrate.

[0034] S2034. Develop and clean the remaining photoresist on the upper surface.

[0035] S204. Grow a germanium epitaxial layer in the groove.

[0036] Please refer to Figure 3 , Figure 3 which is a sectional view of a slice of a germanium epitaxial wafer provided by the embodiments of the present application. As Figure 3As shown, the germanium epitaxial wafer sequentially includes a silicon substrate, a thermal oxidation process silicon oxide (POX) layer, and an HDP silicon oxide layer; there is a groove on the silicon substrate, and a germanium epitaxial layer is grown. The groove has a thickness of 800 Å, the thermal oxidation process silicon oxide layer has a thickness of 110 Å, the HDP silicon oxide layer has a thickness of 5000 Å, and the germanium epitaxial layer has a thickness of 1 μm.

[0037] Among them, the side length range of the preset pattern (i.e., the side length range of the square) is 80 - 100 μm.

[0038] S205. Collect a monitoring image of the bottom of the groove through a machine equipped with an optical microscope, and judge the flatness of the bottom of the groove during the germanium epitaxial process through the monitoring image.

[0039] In specific implementation, the flatness of the bottom of the groove is judged manually or by an image processing algorithm; among them, the uneven position appears as abnormal points with color differences in the monitoring image.

[0040] Next, the preset pattern in the embodiments of the present application will be specifically introduced. In the embodiments of the present application, the preset pattern is a square, and the side length range is 80 - 100 μm.

[0041] On the one hand, FIG. 4(a) is a schematic diagram of a comparison pattern and slice observation provided by an embodiment of the present application; FIG. 4(b) is a schematic diagram of a monitoring image of a comparison pattern provided by an embodiment of the present application.

[0042] As shown in FIG. 4(a), using a 300 nm * 50 μm bar-shaped monitoring pattern MP1 and a 600 nm * 50 μm bar-shaped monitoring pattern MP3 as comparison patterns, it can be found that at the center (C, Center) / middle part (M, Middle) / edge (E, Edge) positions of the pattern, unevenness exists at the bottom of the pure germanium where the grooves grow in the SEM pictures of the slices. However, in FIG. 4(b), combined with the monitoring image taken by the optical microscope (OM) corresponding to the pattern, whether MP1 and MP3 are under the conditions of magnification by 50 times and 150 times, the bottom of the groove shows normal growth conditions. It can be seen that under the optical microscope, the situation of the bottom of the groove cannot be reflected by such bar-shaped patterns.

[0043] On the other hand, FIG. 4(c) is a schematic diagram of a preset pattern and slice observation provided by an embodiment of the present application; FIG. 4(d) is a schematic diagram of a monitoring image of a comparison pattern and a preset pattern provided by an embodiment of the present application.

[0044] As can be seen from FIGS. 4(c) and 4(d), for the preset pattern MP5 which is square and has a side length range of 80 - 100 um in the embodiments of the present application, it can be seen from the TEM section that the bottom of the pattern is also an uneven structure. At the same time, through the observation of OM, it can be clearly found that due to the unevenness of the bottom, abnormal color difference points appear in the observation image of OM. This is the dislocation color difference generated during the single crystal epitaxial process due to the uneven bottom, and such color differences are similar to small black dots one by one. It can be seen that through the preset pattern MP5, the flatness of the bottom of the groove can be effectively observed under an optical microscope. However, in the comparative case MP4 length: 1 - 2 um, MP4 width: 80 - 100 um, this phenomenon cannot be observed under an optical microscope.

[0045] Continue to refer to Figure 5 , Figure 5 which is one of the schematic diagrams of the experimental results of a preset pattern provided by the embodiments of the present application. As Figure 5 shown, germanium epitaxial wafers #1 and #2 are prepared using the preset pattern. Among them, the monitoring image of germanium epitaxial wafer #1 under an optical microscope contains abnormal color difference points, indicating that the bottom of the groove is uneven; while the monitoring image of germanium epitaxial wafer #2 under an optical microscope does not contain abnormal color difference points, indicating that the bottom of the groove is flat. And the results after optimizing the pure germanium epitaxial growth process show that the monitoring results of the bottom flatness confirmed by TEM and EDS are consistent with the monitoring results of the optical microscope. That is, TEM and EDS confirm the flatness of the bottom of the groove, and its corresponding monitoring pattern also shows normal conditions. Therefore, the experiment proves that the flatness of the groove structure can be effectively shown under an optical microscope through the pattern designed in the embodiments of the present application.

[0046] Furthermore, the monitoring method further includes: etching the germanium epitaxial layer with a chemical etching reagent; collecting experimental pictures of the germanium epitaxial layer through a scanning electron microscope; and determining the crystal quality of the germanium epitaxial layer according to the density of corrosion pits in the experimental pictures.

[0047] In this experiment, the through - density can be tested using the chemical etching reagent through this preset pattern, and the through - density can effectively reflect the crystal quality of the specific pure germanium epitaxy. The experimental data is shown in Table 1 below: Table 1 Experimental data of crystal quality

[0048] At the same time, refer to Figure 6 , Figure 6 which is the second schematic diagram of the experimental results of a preset pattern provided by the embodiments of the present application. As Figure 6As shown, in the through-density test experiment, wafers 1 and 2 were fabricated. Wafer 1 showed a large number of abnormal points under an optical microscope through the preset pattern MP5; in the EPD inspection, the inspection result (number of abnormal particles / area) was also abnormal, and the density of the abnormal points far exceeded the allowable range. Wafer 2 did not show abnormal points under the optical microscope through the preset pattern MP5; in the EPD inspection, the inspection result (number of abnormal particles / area) was normal, and the density of the abnormal points was within the allowable range. Therefore, the experiment proves that the preset pattern designed in the embodiment of the present application can also accurately reflect the crystal quality and is consistent with the inspection result of EPD.

[0049] A monitoring method for a germanium epitaxial process provided by an embodiment of the present application etches a wafer according to a designed square structural pattern, and the structural pattern can effectively show the bottom situation of the etched groove, effectively balancing the stress caused by the differences in the lattice constants and thermal expansion coefficients of silicon and germanium itself during the heteroepitaxial process in the trench, so that the flatness of the bottom of the groove can be effectively observed under an optical microscope; in this way, without slicing treatment, the flatness of the bottom of the groove can be monitored in a timely manner through an optical microscope, saving time and cost; furthermore, when it is found that the flatness of the bottom does not meet the requirements, corresponding measures can be taken in a timely manner to ensure the smooth progress of wafer production.

[0050] Based on the same inventive concept, an embodiment of the present application also provides a germanium epitaxial wafer, which includes: A silicon substrate and a demand blocking film layer formed on the silicon substrate; the demand blocking film layer is etched through according to a preset pattern, and a groove is etched on the silicon substrate; a germanium epitaxial layer is grown in the groove; the preset pattern is square; the preset pattern is used to enable the flatness of the bottom of the groove to be effectively observed through an optical microscope.

[0051] Further, the side length range of the preset pattern is 80 - 100 um.

[0052] Further, the demand blocking film layer is used to prevent fragments from being generated due to stress release caused by lattice mismatch during the germanium epitaxial growth process.

[0053] Further, the demand blocking film layer includes a first blocking film layer and a second blocking film layer; the second blocking film layer is located above the first blocking film layer; the material of the first blocking film layer is thermal oxidation process silicon oxide; the material of the second blocking film layer is HDP silicon oxide.

[0054] Further, the thickness range of the first blocking film layer is 100 - 200 A, and the thickness range of the second blocking film layer is 4000 - 6000 A.

[0055] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the systems, devices, and units described above can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0056] In several embodiments provided in the present application, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of the units is only a logical function division, and there may be other division methods in actual implementation. For another example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections to each other can be through some communication interfaces. The indirect couplings or communication connections of the devices or units can be in electrical, mechanical, or other forms.

[0057] The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they can be located in one place or distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0058] In addition, in each embodiment of the present application, the functional units can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit.

[0059] If the functions are implemented in the form of software function units and sold or used as independent products, they can be stored in a non-volatile computer-readable storage medium executable by a processor. Based on such an understanding, the technical solution of the present application, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in each embodiment of the present application. The foregoing storage medium includes: various media that can store program codes such as USB flash drives, mobile hard disks, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical discs.

[0060] Finally, it should be noted that the above-described embodiments are only specific implementation manners of the present application, used to illustrate the technical solutions of the present application, rather than limiting it. The protection scope of the present application is not limited thereto. Although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that any person skilled in the technical field of the present application can still modify the technical solutions recorded in the foregoing embodiments or can easily think of changes, or perform equivalent replacements on some of the technical features; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A monitoring method for a germanium epitaxial process, characterized in that, The monitoring method includes: Providing a silicon substrate; Forming a demand barrier film layer on the silicon substrate; Etching a groove that penetrates the demand barrier film layer and invades the silicon substrate according to a preset pattern; the preset pattern is a square; Growing a germanium epitaxial layer in the groove; Collecting a monitoring image of the bottom of the groove by a machine equipped with an optical microscope, and judging the flatness of the bottom of the groove during the germanium epitaxial process through the monitoring image.

2. The method according to claim 1, wherein The side length range of the preset pattern is 80 - 100um.

3. The method according to claim 2, wherein Etching a groove that penetrates the demand barrier film layer and invades the silicon substrate according to a preset pattern, including: Coating a photoresist on the upper surface of the demand barrier film layer; Developing and cleaning the photoresist on the upper surface within the range of the preset pattern; Etching the demand barrier film layer and the silicon substrate within the range of the preset pattern, penetrating the demand barrier film layer and forming the groove on the silicon substrate; Developing and cleaning the remaining photoresist on the upper surface.

4. The method according to claim 1, wherein The demand barrier film layer is used to avoid fragmentation caused by stress release due to lattice mismatch during germanium epitaxial growth.

5. The method according to claim 1, wherein The demand barrier film layer includes a first barrier film layer and a second barrier film layer; the second barrier film layer is located above the first barrier film layer; the material of the first barrier film layer is thermal oxidation process silicon oxide; the material of the second barrier film layer is HDP silicon oxide.

6. The method according to claim 5, wherein The thickness range of the first barrier film layer is 100 - 200A, and the thickness range of the second barrier film layer is 4000 - 6000A.

7. The method according to claim 1, characterized in that The monitoring method further includes: Etching the germanium epitaxial layer with a chemical etching reagent; Collecting an experimental picture of the germanium epitaxial layer by a scanning electron microscope; Determining the crystal quality of the germanium epitaxial layer according to the density of corrosion pits in the experimental picture.

8. The method according to claim 1, wherein Judging the flatness of the bottom of the groove during the germanium epitaxial process through the monitoring image, including: Judging the flatness of the bottom of the groove by artificial or image processing algorithm through the monitoring image; wherein, the uneven position appears as an abnormal point with color difference in the monitoring image.

9. A germanium epitaxial wafer, characterized in that, The germanium epitaxial wafer includes: A silicon substrate and a demand barrier film layer formed on the silicon substrate; the demand barrier film layer is etched through according to a preset pattern, and a groove is etched on the silicon substrate; a germanium epitaxial layer is grown in the groove; the preset pattern is a square; the preset pattern is used to enable the flatness of the bottom of the groove to be effectively observed through an optical microscope.

10. The germanium epitaxial wafer according to claim 9, wherein, The side length range of the preset pattern is 80 - 100um.

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