Semiconductor Device TEM Sample Preparation and Measurement Method

Abstract

The present application relates to the preparation of TEM samples and a method for measuring the critical dimensions of air gaps in semiconductor devices, including the steps of: providing a wafer, the wafer including a region to be detected having at least an air gap; cutting the wafer to obtain a sample including the region to be detected; grinding and thinning the sample; implementing high-energy FIB processing to roughly thin the sample until the air gap is cut open; filling the air gap with a filling material; implementing low-energy FIB processing to finely thin the sample, so as to finally obtain a TEM sample and observe the critical dimensions of its air gap. Filling the air gap with epoxy resin can effectively reduce the morphological deformation of the air gap during the FIB processing, improve the quality of measurement and analysis, and improve the measurement accuracy of the critical dimensions; at the same time, a process combining FIB rough thinning first and FIB fine thinning after epoxy resin filling is adopted to further reduce the damage and morphological deformation caused by FIB, thereby improving the measurement accuracy.

Description

Technical Field

[0001] This application relates to the field of semiconductor manufacturing and size observation, and particularly to the preparation and measurement methods of samples for detection by a transmission electron microscope (TEM). Background Art

[0002] In semiconductor manufacturing, there are various detection devices. Among them, the transmission electron microscope (TEM) is an important tool for detecting the morphology, size, and characteristics of thin films that make up semiconductor devices. Its working principle is to thin the sample to be detected to about 0.2 μm by means of cutting, polishing, ion milling with a focused ion beam (FIB), etc. Then, the sample is placed in the TEM observation chamber, and a high-energy electron beam accelerated by high voltage irradiates the sample. The electron beam penetrates the sample and is divided into several electron beams, which coincide on the image plane after being refracted by the objective lens, and then transmit to the fluorescent screen. By adjusting the focal length of the intermediate lens to coincide with the image plane of the objective lens, a morphology image is obtained, and then the sample morphology is magnified and projected onto the screen, photographed, and then analyzed. A prominent advantage of the TEM is its high resolution, which can observe the morphology and size of extremely thin films. Since the gate oxide layer of semiconductor devices below the 0.35 μm process is extremely thin, we can almost say that the TEM is currently the device that can relatively accurately measure this thickness.

[0003] Sample preparation is a very important part of TEM analysis technology. To thin the sample to about 0.2 μm, in many cases, cutting, polishing, and ion milling with a focused ion beam (FIB) are required for the TEM sample to be observed. However, during the FIB treatment process, the ion beam accelerated by high voltage bombards the sample, which will cause damage to the sample (ion beam damage). Among them, the damage to the surface of the sample parallel to the ion beam will cause the morphology change of the air gap in the sample, thus seriously affecting the quality of the TEM sample prepared by this method, and further affecting the accuracy of the final analysis result.

[0004] Therefore, it is necessary to develop a new preparation and measurement method for TEM samples, so as to meet the measurement and evaluation requirements of the critical dimensions of the air gap. Summary of the Invention

[0005] The object of this application is achieved through the following technical solutions:

[0006] According to one or more embodiments, this application discloses a method for preparing a TEM sample, which is characterized by including the steps:

[0007] Provide a wafer, on which there is at least a region to be detected having an air gap;

[0008] Cut the wafer to obtain a sample piece including the region to be detected;

[0009] Grind and thin the sample piece;

[0010] Perform high-energy FIB processing to roughly thin the sample piece until the air gap is cut open;

[0011] Fill the air gap with a filling material;

[0012] Perform low-energy FIB processing to finely thin the sample piece to finally obtain a TEM sample.

[0013] According to one or more embodiments, the present application also discloses a method for measuring the critical dimension of an air gap in a semiconductor device, which prepares a TEM sample by using the above preparation method, and then observes and measures the critical dimension of the air gap in the TEM sample by using TEM.

[0014] In the method for preparing a TEM sample in the present application, epoxy resin is used to fill the air gap, so as to effectively reduce the morphological deformation of the air gap during the FIB processing, improve the quality of measurement and analysis, and improve the measurement accuracy of the critical dimension; at the same time, a process combining FIB rough thinning first and then FIB fine thinning after filling epoxy resin is adopted to further reduce the damage and morphological deformation caused by FIB, thereby improving the measurement accuracy.

[0015] Other features and advantages of the present application will be described in the subsequent specification, and part of them will become obvious from the specification, or part of the features and advantages can be inferred from the specification or determined without doubt, or understood by implementing the embodiments of the present application. The objectives and other advantages of the present application can be achieved and obtained through the structures specifically pointed out in the written specification, claims, and drawings. Description of the Drawings

[0016] By reading the detailed description of the preferred embodiments below, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present application. Moreover, throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0017] Figure 1 is a topographical photograph of the pattern to be detected of the TEM sample in the embodiment of the present application.

[0018] Figure 2It is a schematic diagram of performing FIB processing on a TEM sample according to an embodiment of the present application.

[0019] Figure 3 It is a topographic photograph of the pattern to be detected of the TEM sample after being filled with epoxy resin according to an embodiment of the present application. Specific Embodiments

[0020] The present application will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the present application are shown. However, the present application is not limited to the embodiments set forth herein. On the contrary, these embodiments are provided so as to thoroughly and completely illustrate the present application and fully convey the scope of the present application to those skilled in the art. In the drawings, the thicknesses of layers and regions may be exaggerated for clarity. The same numerals designate the same elements throughout the text. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0021] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the present application. As used herein, unless clearly stated otherwise in the text, the singular forms "a", "the", and "said" etc. also include the plural forms. It should also be understood that the term "comprising" used in the specification indicates the presence of the described features, wholes, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or combinations thereof.

[0022] It should be understood that when an element such as a layer, region, or substrate is referred to as "on another element" or "extending onto another element", it can be directly on another element or directly extend onto another element or there is an intermediate element. In contrast, when an element is referred to as "directly on another element" or "directly extending onto another element", there is no intermediate element. It should also be understood that when an element is referred to as "connected" or "coupled" to another element, it can be directly connected or coupled to another element or there is an intermediate element. In contrast, when an element is referred to as "directly connected" or "directly coupled" to another element, there is no intermediate element.

[0023] It should be understood that although terms such as first, second, etc. may be used herein to describe different elements, components, regions, layers, and / or parts, these elements, components, regions, layers, and / or parts are not limited by these terms. These terms are only used to distinguish one element, component, region, layer, or part from another element, component, region, layer, or part. Thus, without departing from the spirit of the present application, the first element, component, region, layer, or part discussed hereinafter may be referred to as the second element, component, region, layer, or part.

[0024] Moreover, relative terms, such as "below" or "bottom" and "above" or "top" are used herein to describe the relationship of one element to another as shown in the figures. It should be understood that relative terms include different orientations of the device in addition to the orientations described in the figures. For example, if the device in the figure is flipped, an element described as below another element becomes above the other element. Thus, the exemplary term "below" includes both the direction of "below" and "above" depending on the specific orientation of the figure. Similarly, if the device in a figure is flipped, an element described as "below other elements" or "beneath other elements" is oriented above the other elements. Thus, the exemplary terms "below" or "beneath" include both the above and below directions.

[0025] Embodiments of the present application are described herein with reference to cross-sectional views (and / or plan views) of idealized embodiments of the present application. Similarly, deviations from the shapes of the schematic diagrams can be expected due to, for example, manufacturing processes and / or tolerances. Thus, the embodiments of the present application are not to be considered as limiting the specific shapes of the regions illustrated herein, but include deviations in shape caused by, for example, manufacturing. For example, an etched region described as or depicted as rectangular typically has rounded or curved features. Thus, the regions illustrated in the figures are schematic in nature, and their shapes do not represent the precise shape of the device regions nor limit the scope of the present application.

[0026] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It should also be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Those skilled in the art should understand that a reference to a structural or functional component disposed adjacent to another component may have an overlapping or underlying portion with respect to the other component.

[0027] The present application discloses a method for preparing a TEM sample and a method for observation and measurement. The TEM sample in the present application is cut and separated from, for example, a wafer to be detected, and the region to be detected of the sample has a pattern fabricated through processes such as deposition, photolithography, etching, etc., which can be, for example, polysilicon, active regions, etc., and is particularly applicable to the preparation of a TEM sample for a pattern to be detected having an air gap and the precise observation of the critical dimension of the air gap.

[0028] The method for preparing the TEM sample of the application embodiment will be described in detail below.

[0029] First, a wafer sample including a region to be detected can be provided. In this embodiment, the region to be detected can be, for example, as Figure 1The shown air gap 1 is an air gap located on both sides of the bit line in the semiconductor device.

[0030] Next, a first mark can be formed at the corresponding position where the air gap in the area to be detected is cut open. In this embodiment, the method of forming the first mark can be, for example, a laser etching method. The wavelength of the laser is 200 nm to 800 nm, the frequency is 10 Hz to 30 Hz, and the energy is 50%-80% (effective work). For example, the wavelength is 530 nm and the frequency is 20 Hz. Of course, for different test samples, different methods can also be used to form the mark. For example, for test samples with a dielectric layer or metal surface, the etching method can also be used. The first mark is strip-shaped on the surface of the wafer sample, and the depth from the surface is 10 μm to 30 μm. The length of the first mark is greater than or equal to 100 nm, and the width is less than 100 nm. This can ensure that the mark can be exposed and clear after the sample is thinned. Of course, in addition, the sample can also be of other shapes, so its length, width, etc. can also be of other sizes.

[0031] Next, a second mark can be formed at the corresponding position outside the area to be observed and measured in the area to be detected, that is, outside the critical dimension pattern area of the air gap to be observed. Except for the formation area, the formation method, size, shape, etc. of the second mark are similar to those of the first mark.

[0032] Next, a test sample can be cut from the wafer sample including the area to be detected. The test sample includes the area to be detected and the first and second marks. Specifically, a diamond saw can be used to cut the test sample at a relatively precise position. For the convenience of sample grinding, generally, the intercepted sample is a rectangular sample strip with a length less than 8 cm and a width less than 4 cm.

[0033] Next, the test sample can be thinned along one cut side of the test sample. The thinning method well-known to those skilled in the art can be used, and the test sample can be thinned from one cut side, such as the long side surface, by chemical mechanical polishing or physical polishing. Specifically, for example, the cut test sample can be placed on a polishing table with heated molten paraffin, and the test sample can be pressed tightly until the paraffin solidifies, so that the test sample adheres tightly to the polishing table. For example, an automatic polishing device (Auto Polishing) can be selected for polishing until it is thinned to less than 100 μm, and then the thinned side is bonded to a clamping copper ring (Cu Grid).

[0034] Then, as Figure 2The detection sample 2 can be cut again according to the outer boundary of the copper ring 1, and the two thinned side regions 3 of the detection sample are bombarded by the ion beam of FIB, so as to form pits 4 on both sides of the pattern to be detected and thin the detection sample between the pits 4 to a thickness of about 20-30 μm, so as to obtain a detection sample with a size of about 50 μm in the transverse direction, 20 μm in the longitudinal direction, and 20-30 μm in thickness. The Ga ion beam can be used for bombardment, with an energy of about 20-30 keV. A high-energy ion beam is used for rough thinning to quickly form pits and thin to a certain thickness. Subsequently, the current is also reduced from high to continue rough thinning until the first mark is exposed, indicating that the air gap in the pattern to be detected has been cut open.

[0035] Next, the air gap in the pattern to be detected can be filled. Specifically, diluted epoxy resin or spin-on glass (SOG) can be selected to coat the milled surface of the detection sample to fill the air gap. In this embodiment, epoxy resin is specifically used for filling. In order to obtain a better filling effect, an epoxy resin mixture with a ratio of epoxy resin curing agent: epoxy resin of 1:9 is used for filling. The filling effect is as Figure 3 shown.

[0036] Then, the copper ring can be continuously clamped, and the Ar ion beam is used to continue ion bombardment thinning on the surface of the pattern to be detected until the second mark is exposed, indicating that the pattern area to be detected is in an exposed state convenient for observation and measurement. In this embodiment, the energy of the Ar ion beam can be selected to be about 0-5 keV. By fine thinning with a lower-energy ion beam, the ion beam damage can be reduced while maintaining the morphology of the air gap, so as to more accurately measure the key dimensions of the air gap.

[0037] The manufactured TEM sample can be fixed by using a copper ring, and then the pattern area to be detected can be observed by using TEM.

[0038] In the method for preparing the TEM sample in this application, materials such as epoxy resin are used to fill the air gap, so that the morphological deformation of the air gap can be effectively reduced during the FIB treatment process, the quality of measurement and analysis can be improved, and the measurement accuracy of key dimensions can be improved; at the same time, a process combining FIB rough thinning first, filling epoxy resin, and then FIB fine thinning is adopted to further reduce the damage and morphological deformation caused by FIB, thereby improving the measurement accuracy.

[0039] In the above description, no detailed explanations are given for the technical details such as the composition and etching of each layer. However, those skilled in the art should understand that various technical means can be used to form layers, regions, etc. of the required shapes. Additionally, in order to form the same structure, those skilled in the art can also design methods that are not exactly the same as the methods described above. Moreover, although the embodiments are described separately above, this does not mean that the measures in each embodiment cannot be used advantageously in combination.

[0040] The embodiments of the present disclosure have been described above. However, these embodiments are merely for illustrative purposes and not for limiting the scope of the present disclosure. The scope of the present disclosure is defined by the appended claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art can make various substitutions and modifications, and these substitutions and modifications should all fall within the scope of the present disclosure.

Claims

1. A method for preparing a TEM sample, characterized in that, Including the steps of: Providing a wafer, on which there is a region to be detected having at least an air gap; the air gap is an air gap located on both sides of the bit line; Cutting the wafer to obtain a sample piece including the region to be detected; Grinding and thinning the sample piece; Performing high-energy FIB processing to roughly thin the sample piece until the air gap is cut open; a first mark is formed at the corresponding position where the air gap in the region to be detected is cut open; Filling the air gap with a filling material; Performing low-energy FIB processing to finely thin the sample piece, and a second mark is formed at the corresponding position of the pattern to be detected in the region to be detected; Finally obtaining a TEM sample.

2. The preparation method according to claim 1, characterized in that: The filling material includes epoxy resin or spin-on glass.

3. The preparation method according to claim 1, characterized in that: The filling material includes epoxy resin and its curing agent, and the ratio of the curing agent to the epoxy resin is 1:

9.

4. The preparation method according to claim 1, characterized in that: The rough thinning is carried out until the first mark is exposed.

5. The preparation method according to claim 1, characterized in that: The fine thinning is carried out until the second mark is exposed.

6. The preparation method according to claim 1, characterized in that: The grinding and thinning thins the sample piece to less than 100 μm.

7. The preparation method according to claim 1, characterized in that: After the rough thinning, the size of the obtained sample piece is 50 μm in the transverse direction, 20 μm in the longitudinal direction, and 20 - 30 μm in thickness.

8. A method for measuring the critical dimension of an air gap in a semiconductor device, characterized in that: For the TEM sample prepared by the preparation method according to any one of claims 1 - 7, observing and measuring the key dimensions of its air gap by TEM.

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