Method of preparing a transmission electron microscopy sample

Abstract

The application provides a preparation method of a transmission electron microscope sample, which comprises the following steps: forming at least two layers of stacked ion beam protective layers on a target layer, each layer of the ion beam protective layers comprising a first protective layer and a second protective layer made of different materials; etching at least one layer of the ion beam protective layers by using a focused ion beam; and judging whether the etching angle of the focused ion beam is a preset etching angle according to the etching image of the surface of the etched ion beam protective layer. Since the contrast of the images of the first protective layer and the second protective layer is also different, the etching angle of the focused ion beam can be judged according to the contrast of the etching image, and when the etching angle does not conform to the preset etching angle, the etching angle of the focused ion beam can be adjusted according to the judgment result in time, so that the observation target unit is prevented from being damaged or deformed, the information integrity of the transmission electron microscope sample is ensured, and the success rate of the sample preparation of the transmission electron microscope sample is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor manufacturing, and particularly relates to a preparation method of a transmission electron microscope sample. BACKGROUND

[0002] In the semiconductor manufacturing technology, the transmission electron microscope (TEM) analysis is to use a focused ion beam (FIB) to micro-cut a sample to take out a defect buried on the surface of the sample and analyze the same. The use of the transmission electron microscope to analyze the sample improves the timeliness of the defect analysis and is an indispensable analysis method in the present semiconductor factory. Specifically, the preparation method of the transmission electron microscope sample includes: firstly, extracting an entire failure region of a sample to obtain a chip sample, as shown in FIG. 1, the chip sample includes a non-target layer 10 and a target layer 20, and the target layer 20 has an observation target unit 20a; and then, thinning the chip sample to a predetermined thickness by using an etching process to form a transmission electron microscope sample. However, in the present preparation method of the transmission electron microscope sample, when the sample that has been thinned to the target layer is thinned, the etching angle of the focused ion beam cannot be adjusted in time according to the structure of the sample, and the etching angle of the focused ion beam deviates from the preset etching angle, which causes the observation target unit 20a in the target layer to be etched too much. As shown in FIG. 2, the observation target unit 20a in the target layer 20 is etched too much, and thus information is lost, which increases the difficulty of subsequent failure analysis. Figure 1 Figure 2 SUMMARY

[0003] The present application aims to provide a preparation method of a transmission electron microscope sample to adjust the etching angle of the focused ion beam in real time, so that the etching angle of the focused ion beam is equal to the preset etching angle.

[0004] To solve the above technical problems, the present application provides a preparation method of a transmission electron microscope sample, which includes the following steps:

[0005] providing a chip sample, the chip sample including an exposed target layer, the target layer having an observation target unit;

[0006] forming at least two layers of ion beam protective layers on the target layer, each of the ion beam protective layers including a first protective layer and a second protective layer stacked from bottom to top, and the second protective layer being different in material from the first protective layer;

[0007] etching at least one of the ion beam protective layers by using a focused ion beam;

[0008] ​​acquire an etching image of the surface of the ion beam protection layer after etching, and determine whether the etching angle of the focused ion beam is equal to the preset etching angle according to the contrast of the etching image; if not, adjust the etching angle of the focused ion beam until the etching angle of the focused ion beam is equal to the preset etching angle, wherein the etching image comprises an image of the first protection layer and / or an image of the second protection layer; and

[0009] thin the surface of the chip sample away from the surface of the ion beam protection layer by using the focused ion beam to form a transmission electron microscope sample, wherein the transmission electron microscope sample comprises the observation target unit.

[0010] Optionally, in the method for preparing the transmission electron microscope sample, after adjusting the etching angle of the focused ion beam, the method further comprises:

[0011] Step 1: etch at least one layer of the ion beam protection layer by using the focused ion beam again, and perform Step 2; and

[0012] Step 2: acquire an etching image of the surface of the ion beam protection layer after etching, and determine whether the etching angle of the focused ion beam is equal to the preset etching angle according to the contrast of the etching image; if not, adjust the etching angle of the focused ion beam, and perform Step 1 until the etching angle of the focused ion beam is equal to the preset etching angle.

[0013] Optionally, in the method for preparing the transmission electron microscope sample, the method for determining whether the etching angle of the focused ion beam is equal to the preset etching angle comprises: determining whether the etching image has a contrast; if yes, it is determined that the etching angle of the focused ion beam is equal to the preset etching angle; if not, it is determined that the etching angle of the focused ion beam is not equal to the preset etching angle.

[0014] Optionally, in the method for preparing the transmission electron microscope sample, the etching image is obtained by scanning the surface of the ion beam protection layer by using an electron beam.

[0015] Optionally, in the method for preparing the transmission electron microscope sample, the etching angle is an angle between the emission direction of the focused ion beam and an etching surface, and the emission direction of the focused ion beam is parallel to the etching surface when the etching angle is equal to the preset etching angle.

[0016] Optionally, in the method for preparing a transmission electron microscope sample, before thinning the surface of the chip sample away from the ion beam protection layer by using the focused ion beam, the method further comprises rotating the chip sample horizontally by a preset rotation angle, so that the surface of the chip sample away from the ion beam protection layer faces the focused ion beam.

[0017] Optionally, in the method for preparing a transmission electron microscope sample, the first protection layer is made of carbon, and the second protection layer is made of platinum.

[0018] Optionally, in the method for preparing a transmission electron microscope sample, the first protection layer and the second protection layer are formed by ion beam electroplating.

[0019] Optionally, in the method for preparing a transmission electron microscope sample, before forming the at least two layers of ion beam protection layers on the target layer, the method further comprises forming an electron beam protection layer on the target layer, and the ion beam protection layers cover the electron beam protection layer.

[0020] Optionally, in the method for preparing a transmission electron microscope sample, the electron beam protection layer is made of carbon.

[0021] In the method for preparing a transmission electron microscope sample, two layers of ion beam protection layers are first formed on the target layer, each layer of ion beam protection layer comprises a first protection layer and a second protection layer made of different materials, then at least one layer of ion beam protection layer is etched by using a focused ion beam, and whether the etching angle of the focused ion beam is a preset etching angle is determined according to the etching image of the surface of the etched ion beam protection layer. Since the first protection layer and the second protection layer are made of different materials, the contrast of the images of the two layers is different, so that whether the etching angle of the focused ion beam is the preset etching angle can be determined according to the contrast of the etching image. When the etching angle does not conform to the preset etching angle, the etching angle of the focused ion beam can be adjusted according to the determination result in time, so that the surface of the chip sample away from the ion beam protection layer can be thinned at the preset etching angle, the observation target unit in the target layer is prevented from being damaged or deformed, the information integrity of the transmission electron microscope sample is ensured, and the success rate of sample preparation of the transmission electron microscope sample is improved. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a cross-sectional TEM image of a chip sample of the prior art;

[0023] Figure 2 is a TEM image of a target layer of the prior art;

[0024] Figure 3is a flowchart of a preparation method of a transmission electron microscope sample provided by an embodiment of the present application;

[0025] Figures 4-5 is a structural diagram formed in the preparation method of the transmission electron microscope sample provided by an embodiment of the present application;

[0026] Figure 6 is an electron beam scanning diagram of a chip sample section in the preparation method of the transmission electron microscope sample provided by an embodiment of the present application;

[0027] Figure 7 is an electron beam scanning diagram of an ion beam protection layer in the preparation method of the transmission electron microscope sample provided by an embodiment of the present application;

[0028] Figure 8 is a TEM diagram of the transmission electron microscope sample in the preparation method of the transmission electron microscope sample provided by an embodiment of the present application;

[0029] In the drawings, the reference signs are explained as follows:

[0030] 10-target layer; 10a-observation target unit; 20-non-target layer;

[0031] 110-non-target layer; 111-semiconductor substrate; 112-silicon oxide layer; 120-target layer; 121-metal layer; 122-dielectric layer; 120a-observation target unit; 130-electron beam protection layer; 140-ion beam protection layer; 141-first protection layer; 142-second protection layer; 150-transmission electron microscope sample. DETAILED DESCRIPTION

[0032] The preparation method of the transmission electron microscope sample proposed by the present application is further described in detail below in combination with the drawings and specific embodiments. The advantages and features of the present application will be clearer according to the following description. It should be noted that the drawings are all very simplified and use non-precise proportions, only for the purpose of facilitating and clearly assisting the description of the embodiments of the present application.

[0033] Figure 3 is a flowchart of a preparation method of a transmission electron microscope sample provided by an embodiment of the present application. As shown in Figure 3 , the present embodiment provides a preparation method of a transmission electron microscope sample, comprising:

[0034] Step S1: providing a chip sample, the chip sample comprising an exposed target layer, the target layer having an observation target unit therein;

[0035] Step S2: forming at least two layers of stacked ion beam protection layers on the target layer, each of the ion beam protection layers comprising a first protection layer and a second protection layer stacked from bottom to top, the second protection layer being different in material from the first protection layer;

[0036] Step S3: etching at least one of the ion beam protection layers by using a focused ion beam;

[0037] Step S4: obtaining an etching image of the surface of the ion beam protection layer after etching, and determining whether the etching angle of the focused ion beam is equal to a preset etching angle according to the contrast of the etching image, if not, adjusting the etching angle of the focused ion beam until the etching angle of the focused ion beam is equal to the preset etching angle, wherein the etching image comprises an image of the first protection layer and / or an image of the second protection layer; and,

[0038] Step S5: thinning the surface of the chip sample away from the surface of the ion beam protection layer by using the focused ion beam until a transmission electron microscope sample is formed, the transmission electron microscope sample comprising the observation target unit.

[0039] Figures 4-5 is a structural schematic diagram formed in the preparation method of the transmission electron microscope sample provided by the embodiment of the present application; Figure 6 is an electron beam scanning diagram of a chip sample section in the preparation method of the transmission electron microscope sample provided by the embodiment of the present application; Figure 7 is an electron beam scanning diagram of an ion beam protection layer in the preparation method of the transmission electron microscope sample provided by the embodiment of the present application; Figure 8 is a TEM diagram of a transmission electron microscope sample in the preparation method of the transmission electron microscope sample provided by the embodiment of the present application.

[0040] The following will be described in combination with the accompanying drawings Figures 4-8 The preparation method of the transmission electron microscope sample of the embodiment will be described in more detail.

[0041] Firstly, step S1 is performed, as shown in FIG. 1, a chip sample 1 is provided, and a target layer 2 is formed on the chip sample 1, wherein the target layer 2 comprises an observation target unit 3. Figure 4As shown, a chip sample is provided, which includes an exposed target layer 120 having an observation target unit 120a therein. Specifically, the chip sample can be a finished chip or a semiconductor structure formed during chip fabrication. In this embodiment, the chip sample includes a semiconductor substrate 111 having a shallow trench therein, the shallow trench being filled with a silicon oxide layer 112, and further includes a target layer 120 covering the shallow trench and the silicon oxide layer 112; the target layer 120 can be a composite structure film layer composed of film layers such as a dielectric layer 122, a polysilicon layer, a metal layer 121 and a metal plug, and the target layer 120 is a film layer in which the observation target unit 120a to be analyzed by a transmission electron microscope is located. The observation target unit 120a can be a region in the target layer 120, or can be a single or composite structure in the target layer 120, for example, the observation target unit 120a can be the metal layer 121 in the target layer 120. The semiconductor substrate 111 and the silicon oxide layer 112 are non-target layers 110. It should be understood that the structure of the chip sample provided in this embodiment is only an example, and the chip sample can also be other possible structures. The target layer 120 and the non-target layer 110 are also only examples, and the target layer 120 and the non-target layer 110 can also be other film layers or combinations of film layers.

[0042] Then, step S2 is performed, as shown in Figure 5 and Figure 6 At least two layers of ion beam protection layers 140 are formed on the target layer 120, each of the ion beam protection layers 140 including a first protection layer 141 and a second protection layer 142 stacked from bottom to top, the second protection layer 142 being different in material from the first protection layer 141.

[0043] For example, two layers of ion beam protection layers 140 are formed on the target layer 120, and in other embodiments, three, four or more layers of ion beam protection layers 140 can be formed on the target layer 120. The ion beam protection layers 140 can protect the target layer 120, and can also adjust the etching angle through the etching image of the ion beam protection layers 140.

[0044] Preferably, the first protection layer 141 is made of carbon (C) and the second protection layer 142 is made of platinum (Pt), so that the image on the surface of the first protection layer 141 and the image on the surface of the second protection layer 142 have different contrasts. As shown in Figure 7As shown, the electron beam scanning images of the first protective layer 141 and the second protective layer 142 have obvious contrast differences, which can be clearly distinguished under electron beam scanning, and is beneficial to adjusting the etching angle of the focused ion beam. Further, the first protective layer 141 and the second protective layer 142 are formed by ion beam electroplating, so as to have better compactness.

[0045] In this embodiment, as shown in the figure, before forming the ion beam protective layer 140, an electron beam protective layer 130 is formed on the target layer 120, i.e., the electron beam protective layer 130 is formed between the target layer 120 and the ion beam protective layer 140. The material of the electron beam protective layer 130 is carbon, and the electron beam protective layer 130 is looser than the ion beam protective layer 140. The electron beam protective layer 130 can be used as a stop layer for subsequent etching of the ion beam protective layer 140, thereby protecting the target layer 120 in the subsequent etching process of the ion beam protective layer 140. Figure 4

[0046] After forming the ion beam protective layer 140, the chip sample with the ion beam protective layer 140 is extracted onto a sample carrier by welding, and the sample carrier is used to support the chip sample.

[0047] Then, step S3 is performed, and at least one layer of the ion beam protective layer 140 is etched by a focused ion beam (FIB). Specifically, the surface of the ion beam protective layer 140 is directed towards the focused ion beam, and the ion beam protective layer 140 is etched in a direction parallel to the surface of the ion beam protective layer 140, i.e., by focusing the ion beam on the surface of the ion beam protective layer 140, and using the ion beam to bombard to achieve the purpose of etching the ion beam protective layer 140. Part of the thickness of the second protective layer 142 can be etched, or the second protective layer 142 and part of the thickness of the first protective layer 141 can be etched.

[0048] Then, step S4 is performed, and an etching image of the surface of the ion beam protective layer 140 after etching is obtained, and whether the etching angle of the focused ion beam is equal to a preset etching angle is determined according to the contrast of the etching image. If not, the etching angle of the focused ion beam is adjusted until the etching angle of the focused ion beam is equal to the preset etching angle, wherein the etching image includes an image of the first protective layer 141 and / or an image of the second protective layer 142.

[0049] ​In the embodiment, the etching angle is an angle between a direction of emission of the focused ion beam and the etching surface. The etching surface refers to a surface of a film layer etched by the focused ion beam. In the step, the etching surface is an etching surface of the ion beam protection layer 140. The etching angle is equal to the preset etching angle, and the direction of emission of the focused ion beam is parallel to the etching surface.

[0050] After the ion beam protection layer 140 is etched by the focused ion beam, the etching surface of the ion beam protection layer 140 can be scanned by an electron beam of a focused ion beam (FIB) machine to obtain a surface image of the ion beam protection layer 140.

[0051] Since the ion beam protection layer 140 includes the first protection layer 141 and the second protection layer 142, when the etching angle of the focused ion beam is equal to the preset etching angle, that is, the direction of emission of the focused ion beam is parallel to the surface of the focused ion beam, only the first protection layer 141 or the second protection layer 142 is etched. When the etching angle of the focused ion beam is not equal to the preset etching angle, that is, the direction of emission of the focused ion beam is inclined to the surface of the focused ion beam, the first protection layer 141 and the second protection layer 142 are etched simultaneously. Since the first protection layer 141 and the second protection layer 142 are made of different materials, the contrast of the images of the two layers is different, and there is a large difference. Therefore, whether the etching angle of the focused ion beam is equal to the preset etching angle can be determined according to the contrast of the etching image.

[0052] Further, the method for determining whether the etching angle of the focused ion beam is equal to the preset etching angle includes: determining whether the etching image has a certain contrast. If yes, it is determined that the etching angle of the focused ion beam is equal to the preset etching angle. If no, it is determined that the etching angle of the focused ion beam is not equal to the preset etching angle.

[0053] When it is determined that the etching angle of the focused ion beam is not equal to the preset etching angle, the etching angle of the focused ion beam can be adjusted by rotating the focused ion beam or rotating the chip sample. The rotation angle of the focused ion beam or the rotation angle of the chip sample can be 10°-360°.

[0054] In the embodiment, after the etching angle of the focused ion beam is adjusted, the method further includes:

[0055] Step one: etching at least one of the ion beam protection layers 140 by the focused ion beam again, and performing step two; and,

[0056] Step two: obtain an etching image of the surface of the ion beam protection layer 140 after etching, and determine whether the etching angle of the focused ion beam is equal to the preset etching angle according to the contrast of the etching image. If not, adjust the etching angle of the focused ion beam, and perform step one until the etching angle of the focused ion beam is equal to the preset etching angle.

[0057] After the etching angle of the focused ion beam is equal to the preset etching angle, the ion beam protection layer 140 and the electron beam protection layer 130 on the target layer 120 can be removed by the focused ion beam, so that the target layer 120 is exposed.

[0058] Then, step S5 is performed, and the surface of the chip sample away from the ion beam protection layer 140 is thinned by the focused ion beam until a transmission electron microscope sample including the observation target unit 120a is formed. By thinning the chip sample to a certain thickness, a sample for transmission electron microscope observation is formed, for example, the thickness of the transmission electron microscope sample after thinning is 100-150 nm, for example, 100 nm, 110 nm or 150 nm. The sample in this thickness range can be better observed by electron transmission microscopy.

[0059] In this embodiment, the chip sample can be first rotated horizontally by a preset rotation angle to make the surface of the chip sample away from the ion beam protection layer 140 face the focused ion beam. The preset rotation angle can be, for example, 180°.

[0060] After the chip sample is rotated horizontally by the preset rotation angle, the etching angle of the focused ion beam and the surface of the chip sample away from the ion beam protection layer 140 can be the preset etching angle, i.e., the emission direction of the focused ion beam is parallel to the surface of the chip sample away from the ion beam protection layer 140, so that the surface of the chip sample away from the ion beam protection layer 140 is thinned at the preset etching angle, preventing the observation target unit 120a in the target layer 120 from being damaged or deformed, ensuring the information integrity of the transmission electron microscope sample 150, and improving the success rate of sample preparation of the transmission electron microscope sample 150. As shown in FIG. 6, the structure of the observation target unit 120a is relatively complete. Figure 8

[0061] ​As can be seen from the above, in the preparation method of the transmission electron microscope sample provided by the application, two layers of ion beam protective layers are first formed on the target layer, each layer of the ion beam protective layer comprises a first protective layer and a second protective layer made of different materials, then at least one layer of the ion beam protective layer is etched by using a focused ion beam, and whether the etching angle of the focused ion beam is a preset etching angle is judged according to the etching image of the surface of the etched ion beam protective layer. Since the first protective layer and the second protective layer are made of different materials, the contrast of the images of the two layers is also different, so whether the etching angle of the focused ion beam is the preset etching angle can be judged according to the contrast of the etching image. When the etching angle does not conform to the preset etching angle, the etching angle of the focused ion beam can be adjusted in time according to the judgment result, so that the surface of the chip sample far from the ion beam protective layer can be thinned at the preset etching angle, the observation target unit in the target layer is prevented from being damaged or deformed, the information integrity of the transmission electron microscope sample is ensured, and the success rate of the sample preparation of the transmission electron microscope sample is improved.

[0062] The above description is only a description of the preferred embodiments of the application and does not limit the scope of the application in any way. Any modification or change made by a person skilled in the art according to the above disclosure is within the protection scope of the claims.

Claims

1. A method of preparing a transmission electron microscopy sample, characterized by, The method comprises the following steps: providing a chip sample, the chip sample comprising an exposed target layer having an observation target unit in the target layer; forming at least two layers of ion beam protection layers on the target layer, each of the ion beam protection layers comprising a first protection layer and a second protection layer stacked from bottom to top, the second protection layer being different in material from the first protection layer, the material of the first protection layer being carbon, the material of the second protection layer being platinum, and the electron beam scanning image of the surface of the first protection layer being different in contrast from the electron beam scanning image of the surface of the second protection layer; etching at least one of the ion beam protection layers by using a focused ion beam; acquiring an etching image of the surface of the ion beam protection layer after etching by electron beam scanning, and determining whether the etching angle of the focused ion beam is equal to a preset etching angle according to the contrast of the etching image, if not, adjusting the etching angle of the focused ion beam until the etching angle of the focused ion beam is equal to the preset etching angle, wherein the etching image comprises an image of the first protection layer and / or an image of the second protection layer; and thinning the surface of the chip sample away from the ion beam protection layer by using the focused ion beam to form a transmission electron microscope sample, the transmission electron microscope sample comprising the observation target unit.

2. The method of preparing a transmission electron microscope sample of claim 1, wherein, After adjusting the etching angle of the focused ion beam, the method further comprises: step one: etching at least one of the ion beam protection layers by using the focused ion beam again, and performing step two; and step two: acquiring an etching image of the surface of the ion beam protection layer after etching, and determining whether the etching angle of the focused ion beam is equal to a preset etching angle according to the contrast of the etching image, if not, adjusting the etching angle of the focused ion beam and performing step one until the etching angle of the focused ion beam is equal to the preset etching angle.

3. The method of preparing a transmission electron microscope sample according to claim 1 or 2, wherein The method of determining whether the etching angle of the focused ion beam is equal to a preset etching angle comprises: determining whether the etching image has a certain contrast, if yes, determining that the etching angle of the focused ion beam is equal to the preset etching angle, if not, determining that the etching angle of the focused ion beam is not equal to the preset etching angle.

4. The method of preparing a transmission electron microscope sample of claim 3, wherein, The etching angle is the angle between the emission direction of the focused ion beam and the etching surface, and the emission direction of the focused ion beam is parallel to the etching surface when the etching angle is equal to the preset etching angle.

5. The method of preparing a transmission electron microscopy sample of claim 1, wherein, Before thinning the surface of the chip sample away from the ion beam protection layer by using the focused ion beam, the method further comprises rotating the chip sample horizontally by a preset rotation angle so that the surface of the chip sample away from the ion beam protection layer faces the focused ion beam.

6. The method of preparing a transmission electron microscopy sample of claim 1, wherein, The first protection layer and the second protection layer are formed by ion beam electroplating.

7. The method of preparing a transmission electron microscopy sample of claim 1, wherein, Before forming at least two layers of ion beam protection layers on the target layer, the method further comprises forming an electron beam protection layer on the target layer, and the ion beam protection layers cover the electron beam protection layer.

8. The method of preparing a transmission electron microscope sample of claim 7, wherein, The material of the electron beam protection layer is carbon.

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