A monitoring method for germanium epitaxial process and germanium epitaxial wafer

Abstract

The present application provides a monitoring method for a germanium epitaxial process and a germanium epitaxial wafer. The 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 using a machine equipped with an optical microscope, and judging the flatness of the bottom of the groove during the germanium epitaxial process using the monitoring image. By designing a structural pattern and etching the wafer according to the structural pattern, the structural pattern can effectively represent the bottom of the etched groove, so that the flatness of the bottom of the groove can be effectively observed under an optical microscope; thus, the flatness of the bottom of the groove can be monitored in a timely manner through an optical microscope without the need for slicing, saving time and cost.

Description

Technical Field

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

[0002] At room temperature, silicon has a cutoff wavelength of 1.1 μm, limiting its application to the near-infrared range of 1.3-1.55 μm. Germanium, with a narrower bandgap than silicon, can efficiently absorb near-infrared light. Its high light absorption efficiency makes it an ideal material for Si-based long-wavelength photodetectors.

[0003] During the chip manufacturing process, the bottom of the trench is flat after etching, but 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 crystal quality such as the electrical properties and reliability of the device, so it needs to be monitored.

[0004] In the prior art, wafer slicing is often used to effectively understand the germanium growth process. This involves observing the trenches and germanium growth through SEM slices. However, this method wastes wafers and time, and cannot detect anomalies in a timely manner, making it difficult to apply to mass wafer production. Summary of the Invention

[0005] In view of this, the purpose of this application is to provide a monitoring method for germanium epitaxial process and germanium epitaxial wafer, so as to solve the problem in the prior art of observing the bottom of the groove by slicing the wafer, resulting in waste of wafers and time and inability to monitor in time.

[0006] An embodiment of the present application provides a monitoring method for a germanium epitaxial process, the monitoring method comprising:

[0007] providing a silicon substrate;

[0008] forming a required barrier film layer on the silicon substrate;

[0009] Etching a groove penetrating the required barrier film layer and invading the silicon substrate according to a preset pattern; the preset pattern is a square;

[0010] growing a germanium epitaxial layer in the groove;

[0011] A monitoring image of the bottom of the groove is collected by a machine equipped with an optical microscope, and the flatness of the bottom of the groove during the germanium epitaxial process is determined by the monitoring image.

[0012] Furthermore, the side length of the preset pattern ranges from 80 to 100 μm.

[0013] Furthermore, etching a groove penetrating the required barrier film layer and invading the silicon substrate according to a preset pattern includes:

[0014] Coating photoresist on the upper surface of the required barrier film layer;

[0015] Developing and cleaning the photoresist on the upper surface within the preset pattern range;

[0016] Etching the required blocking film layer and the silicon substrate within the preset pattern range to penetrate the required blocking film layer and form the groove on the silicon substrate;

[0017] The photoresist on the remaining portion of the upper surface is developed and cleaned.

[0018] Furthermore, the barrier film layer is used to prevent the germanium from being broken due to stress release caused by lattice mismatch during epitaxial growth.

[0019] 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.

[0020] Furthermore, the thickness of the first barrier film layer is in the range of 100-200 Å, and the thickness of the second barrier film layer is in the range of 4000-6000 Å.

[0021] Furthermore, the monitoring method further includes:

[0022] Etching the germanium epitaxial layer using a chemical etching agent;

[0023] Collecting experimental images of the germanium epitaxial layer through a scanning electron microscope;

[0024] The crystal quality of the germanium epitaxial layer is determined based on the density of the etching pits in the experimental picture.

[0025] Furthermore, judging the flatness of the bottom of the groove during the germanium epitaxial growth process using the monitoring image includes:

[0026] The flatness of the bottom of the groove is determined manually or by an image processing algorithm through the monitoring image; wherein the uneven position appears as an abnormal point with color difference in the monitoring image.

[0027] The embodiment of the present application further provides a germanium epitaxial wafer, the germanium epitaxial wafer comprising:

[0028] A silicon substrate and a desired barrier film layer formed on the silicon substrate; the desired 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 ensure that the flatness of the bottom of the groove can be effectively observed through an optical microscope.

[0029] Furthermore, the side length of the preset pattern ranges from 80 to 100 μm.

[0030] The embodiments of the present application provide a monitoring method for a germanium epitaxial process and a germanium epitaxial wafer. By designing a square structural pattern and etching the wafer according to the structural pattern, 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, the flatness of the bottom of the groove can be monitored in a timely manner through an optical microscope without the need for slicing, saving time and cost.

[0031] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 A schematic diagram showing an uneven bottom of a trench after a germanium epitaxial process according to an embodiment of the present application is shown;

[0034] Figure 2 A flow chart of a method for monitoring a germanium epitaxial process provided in an embodiment of the present application is shown;

[0035] Figure 3 A cross-sectional view of a germanium epitaxial wafer provided in an embodiment of the present application is shown;

[0036] FIG4 (a) shows a comparison pattern and a schematic diagram of slice observation provided in an embodiment of the present application;

[0037] FIG4( b ) shows a schematic diagram of a monitoring image of a contrast pattern provided in an embodiment of the present application;

[0038] FIG4 (c) shows a schematic diagram of a preset pattern and slice observation provided in an embodiment of the present application;

[0039] FIG4( d ) shows a schematic diagram of a monitoring image of a comparison pattern and a preset pattern provided in an embodiment of the present application;

[0040] Figure 5 One of the schematic diagrams showing the experimental results of a preset pattern provided in an embodiment of the present application is shown;

[0041] Figure 6 The second schematic diagram shows the experimental results of a preset pattern provided in an embodiment of the present application. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application for which protection is claimed, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, each other embodiment obtained by those skilled in the art without making creative work falls within the scope of protection of the present application.

[0043] At room temperature, silicon has a cutoff wavelength of 1.1 μm, limiting its application to the near-infrared range of 1.3-1.55 μm. Germanium, with a narrower bandgap than silicon, can efficiently absorb near-infrared light. Its high light absorption efficiency makes it an ideal material for Si-based long-wavelength photodetectors.

[0044] like Figure 1 As shown in Figure 1, during chip manufacturing, the bottom of the trench is flat after etching. However, after the germanium epitaxial growth process, the bottom of the trench may become uneven. This uneven bottom structure directly affects the crystal quality, such as the electrical properties and reliability of the device, and therefore needs to be monitored. In reality, this unevenness is affected by many factors, such as the oxygen content on the silicon surface, plasma residue during the etching process, and the airtightness control of the machine itself.

[0045] In the prior art, wafer slicing is often used to effectively understand the germanium growth process. This involves observing the trenches and germanium growth through SEM slices. However, this method wastes wafers and time, and cannot detect anomalies in a timely manner, making it difficult to apply to mass wafer production.

[0046] Based on this, an embodiment of the present application provides a monitoring method for a germanium epitaxial process to solve the problem in the prior art of observing the bottom of the trench by slicing the wafer, resulting in waste of wafers and time and inability to monitor in a timely manner.

[0047] See also Figure 2 , Figure 2 This is a flow chart of a method for monitoring a germanium epitaxial process provided in an embodiment of the present application. Figure 2 As shown in , the monitoring method provided in the embodiment of the present application includes:

[0048] S201. Provide a silicon substrate.

[0049] S202, forming a required barrier film layer on the silicon substrate.

[0050] The barrier film layer is used to prevent the germanium from being broken due to stress release caused by lattice mismatch during epitaxial growth.

[0051] 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.

[0052] S203 , etching a groove that penetrates the required barrier film layer and invades the silicon substrate according to a preset pattern.

[0053] The preset pattern is a square. This is because, through research, the present application embodiment found that the square design can effectively balance the stress caused by the differences in the lattice constant and thermal expansion coefficient of silicon and germanium during the heteroepitaxial growth process in the trench. If these stresses cannot be effectively eliminated, dislocation defects will be introduced into the epitaxial film layer, thereby affecting the results of the pattern judgment under optical microscope observation, and whether the pattern difference is caused by the dislocation stress of the growing germanium or the difference caused by the uneven bottom. Moreover, this pattern is simple, practical, easy to implement, and suitable for actual industrial production.

[0054] In specific implementation, step S203 may include:

[0055] S2031 , coating photoresist on the upper surface of the required blocking film layer.

[0056] S2032: Develop and clean the photoresist on the upper surface within the predetermined pattern. The photoresist forms a pattern through exposure and development during the photolithography process, serving as a protective layer during the etching process, covering the areas to be retained. In this step, the photoresist on the upper surface of the wafer within the predetermined square pattern is developed and cleaned.

[0057] S2033 , etching the required blocking film layer and the silicon substrate within the preset pattern range to penetrate the required blocking film layer and form the groove on the silicon substrate.

[0058] S2034, developing and cleaning the remaining portion of the photoresist on the upper surface.

[0059] S204 , growing a germanium epitaxial layer in the groove.

[0060] See also Figure 3 , Figure 3 This is a cross-sectional view of a germanium epitaxial wafer provided in an embodiment of the present application. Figure 3 As shown, the germanium epitaxial wafer consists of a silicon substrate, a thermally oxidized silicon oxide (POX) layer, and a high-density photodiode (HDP) silicon oxide layer. The silicon substrate has a recess on which the germanium epitaxial layer is grown. The recess is 800 Å thick, the thermally oxidized silicon oxide layer is 110 Å thick, the HDP silicon oxide layer is 5000 Å thick, and the germanium epitaxial layer is 1 μm thick.

[0061] The side length range of the preset pattern (ie, the side length range of the square) is 80-100 μm.

[0062] S205 , collecting a monitoring image of the bottom of the groove by using a machine equipped with an optical microscope, and judging the flatness of the bottom of the groove during the germanium epitaxial growth process by using the monitoring image.

[0063] In a specific implementation, the flatness of the bottom of the groove is determined manually or by an image processing algorithm; wherein, the uneven position appears as an abnormal point with color difference in the monitoring image.

[0064] The following will specifically introduce the preset pattern in the embodiment of the present application. In the embodiment of the present application, the preset pattern is a square with a side length ranging from 80 to 100 μm.

[0065] On the one hand, FIG4(a) is a schematic diagram of a contrast pattern and slice observation provided in an embodiment of the present application; FIG4(b) is a schematic diagram of a monitoring image of a contrast pattern provided in an embodiment of the present application.

[0066] As shown in Figure 4(a), using the 300nm x 50µm stripe monitoring pattern MP1 and the 600nm x 50µm stripe monitoring pattern MP3 as comparison patterns, SEM images of the sections reveal unevenness at the bottom of the pure germanium grown in the trenches at the center (C), middle (M), and edge (E) of the patterns. However, in Figure 4(b), combined with the corresponding optical microscope (OM) monitoring images of the patterns, both MP1 and MP3 exhibit normal growth at both 50x and 150x magnifications. This demonstrates that the stripe pattern cannot reveal the condition of the trench bottom under an optical microscope.

[0067] On the other hand, FIG4( c ) is a schematic diagram of a preset pattern and slice observation provided in an embodiment of the present application; FIG4( d ) is a schematic diagram of a monitoring image of a comparison pattern and a preset pattern provided in an embodiment of the present application.

[0068] As can be seen from Figures 4(c) and 4(d), the square MP5 pattern with a side length of 80-100 μm in this embodiment also exhibits an uneven bottom structure, as seen in TEM slices. OM observation also reveals that this uneven bottom structure manifests as chromatic aberrations in the OM image. This is due to dislocation chromatic aberration caused by the uneven bottom during the single crystal epitaxy process, which resembles small black dots. This indicates that the MP5 pattern effectively demonstrates the flatness of the groove bottom under an optical microscope. However, in the comparative example with MP4 length: 1-2 μm and MP4 width: 80-100 μm, this phenomenon is not observable under an optical microscope.

[0069] Continue reading Figure 5 , Figure 5 This is one of the experimental results diagrams of a preset pattern provided in the embodiment of the present application. Figure 5 As shown, germanium epitaxial wafer #1 and germanium epitaxial wafer #2 were produced using a preset pattern. The monitoring image of germanium epitaxial wafer #1 under an optical microscope contained abnormal points of chromatic aberration, indicating that the bottom of the groove was uneven; while the monitoring image of germanium epitaxial wafer #2 under an optical microscope did not contain abnormal points of chromatic aberration, indicating that the bottom of the groove was flat. The results after optimizing the pure germanium epitaxial growth process showed that the monitoring results of the bottom flatness confirmed by TEM and EDS were consistent with the monitoring results of the optical microscope. That is, TEM and EDS confirmed the flatness of the bottom of the groove, and the corresponding monitoring pattern also showed normal conditions. Therefore, the experiment proved that the flatness of the groove structure can be effectively demonstrated under an optical microscope through the pattern designed in the embodiment of the present application.

[0070] Furthermore, the monitoring method further includes:

[0071] The germanium epitaxial layer is etched using a chemical etching agent; an experimental image of the germanium epitaxial layer is collected using a scanning electron microscope; and the crystal quality of the germanium epitaxial layer is determined based on the density of etching pits in the experimental image.

[0072] In this experiment, the penetration density can be tested by using chemical etching reagents through the preset pattern, and the penetration density can effectively reflect the crystal quality of the specific pure germanium epitaxial growth. The experimental data is shown in Table 1 below:

[0073] Table 1 Crystal quality experimental data

[0074]

[0075] See also Figure 6 , Figure 6 This is a second schematic diagram of experimental results of a preset pattern provided in an embodiment of the present application. Figure 6 As shown, wafers 1 and 2 were produced in a through-density test experiment. Wafer 1 displayed a large number of abnormal points under an optical microscope using the preset pattern MP5. During EPD inspection, the inspection results (abnormal particle count / area) also showed abnormalities, with the density of abnormal points far exceeding the allowable range. Wafer 2 displayed no abnormal points under an optical microscope using the preset pattern MP5. During EPD inspection, the inspection results (abnormal particle count / area) were normal, with the density of abnormal points within the allowable range. Therefore, the experiment demonstrated that the preset pattern designed in the embodiments of this application can accurately reflect crystal quality, consistent with the EPD inspection results.

[0076] An embodiment of the present application provides a monitoring method for a germanium epitaxial process. By designing a square structural pattern and etching a wafer according to the structural pattern, the structural pattern can effectively represent the bottom condition of the etched groove, effectively balancing the stress caused by the difference in lattice constant and thermal expansion coefficient of silicon and germanium themselves during the heteroepitaxial growth process in the groove, thereby enabling the flatness of the bottom of the groove to be effectively observed under an optical microscope; in this way, the bottom flatness of the groove can be monitored in a timely manner through an optical microscope without the need for slicing, saving time and cost; and when it is found that the bottom flatness does not meet the requirements, corresponding measures can be taken in a timely manner to ensure the smooth progress of wafer production.

[0077] Based on the same inventive concept, an embodiment of the present application further provides a germanium epitaxial wafer, the germanium epitaxial wafer comprising:

[0078] A silicon substrate and a desired barrier film layer formed on the silicon substrate; the desired 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 ensure that the flatness of the bottom of the groove can be effectively observed through an optical microscope.

[0079] Furthermore, the side length of the preset pattern ranges from 80 to 100 μm.

[0080] Furthermore, the barrier film layer is used to prevent the germanium from being broken due to stress release caused by lattice mismatch during epitaxial growth.

[0081] 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.

[0082] Furthermore, the thickness of the first barrier film layer is in the range of 100-200 Å, and the thickness of the second barrier film layer is in the range of 4000-6000 Å.

[0083] Those skilled in the art will 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 aforementioned method embodiments and will not be repeated here.

[0084] In the several embodiments provided in this 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 schematic. For example, the division of the units is merely a logical function division. There may be other division methods in actual implementation. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed may be through some communication interface, indirect coupling or communication connection of devices or units, which may be electrical, mechanical or other forms.

[0085] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0086] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0087] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a non-volatile computer-readable storage medium that is executable by a processor. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes various media that can store program code, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0088] Finally, it should be noted that the above-described embodiments are only specific implementation methods of the present application, which are used to illustrate the technical solutions of the present application, rather than to limit them. The scope of protection of the present application is not limited thereto. Although the present application has been described in detail with reference to the above-mentioned embodiments, those skilled in the art should understand that any person skilled in the art can modify or easily conceive of changes to the technical solutions described in the above-mentioned embodiments within the technical scope disclosed in the present application, or perform equivalent replacements for some of the technical features thereof. These modifications, changes, or replacements do not deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for monitoring a germanium epitaxial process, characterized in that: The monitoring method comprises: providing a silicon substrate; forming a required barrier film layer on the silicon substrate; Etching a groove penetrating the required barrier film layer and invading 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 using a machine equipped with an optical microscope, and judging the flatness of the bottom of the groove during the germanium epitaxial growth process using the monitoring image; The side length of the preset pattern ranges from 80 to 100 μm; The required barrier film layer includes a first barrier film layer and a second barrier film layer; the second barrier film layer is located on 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; Determining the flatness of the bottom of the groove during the germanium epitaxial process using the monitoring image includes: The flatness of the bottom of the groove is determined manually or by an image processing algorithm through the monitoring image; wherein the uneven position appears as an abnormal point with color difference in the monitoring image.

2. The method according to claim 1, characterized in that Etching a groove penetrating the required barrier film layer and invading the silicon substrate according to a preset pattern, comprising: Coating photoresist on the upper surface of the required barrier film layer; Developing and cleaning the photoresist on the upper surface within the preset pattern range; Etching the required blocking film layer and the silicon substrate within the preset pattern range to penetrate the required blocking film layer and form the groove on the silicon substrate; The photoresist on the remaining portion of the upper surface is developed and cleaned.

3. The method according to claim 1, characterized in that The required barrier film layer is used to prevent the germanium from being broken due to stress release caused by lattice mismatch during epitaxial growth.

4. The method according to claim 1, wherein The thickness of the first barrier film layer is in the range of 100-200 Å, and the thickness of the second barrier film layer is in the range of 4000-6000 Å.

5. The method according to claim 1, wherein The monitoring method further comprises: Etching the germanium epitaxial layer using a chemical etching agent; Collecting experimental images of the germanium epitaxial layer through a scanning electron microscope; The crystal quality of the germanium epitaxial layer is determined based on the density of the etching pits in the experimental picture.

6. A germanium epitaxial wafer, characterized in that: Prepared by the method according to any one of claims 1 to 5; the germanium epitaxial wafer comprises: A silicon substrate and a desired barrier film layer formed on the silicon substrate; the desired 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 ensure that the flatness of the bottom of the groove can be effectively observed through an optical microscope.

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