Deep trench capacitor tem sample preparation method

Abstract

The application discloses a deep trench capacitor TEM sample preparation method, comprising the following steps: 1) using a micro-light microscope or a photoresistance change detection to position a hot spot of a deep trench capacitor product, and determining a failure area; 2) depositing a positioning protection layer at the hot spot position by using a focused ion beam, and polishing the product to a first distance in front of the positioning protection layer; 3) vertically placing the polished sample on a sample table, and preparing an initial TEM sample by using a focused ion beam (FIB); 4) using an Easy-Lift technology to transfer the initial TEM sample to a Grid; and 5) observing the sample on the Grid by TEM after thinning according to three positions of top, middle and bottom (TMB). The application can eliminate the risk of distortion, warping and even fragmentation of a high aspect ratio sample in an ultrathin thinning process, finally obtain a deep trench capacitor TEM sample which is uniform in thickness, complete in structure and free of distortion, and complete high-resolution observation and failure analysis of internal micro defects.

Description

Technical Field

[0001] This invention relates to the field of semiconductors, and in particular to a method for preparing deep trench capacitor TEM samples. Background Technology

[0002] Deep trench capacitors are key passive components widely used in semiconductor memories and advanced logic devices. Their core characteristics are large vertical depth, extremely small lateral dimensions, and an extremely high trench aspect ratio (AR), typically reaching approximately 40:1, making them typical high aspect ratio three-dimensional micro / nano structures. For transmission electron microscopy (TEM) failure analysis of such high aspect ratio structures, traditional focused ion beam (FIB) sample preparation methods face significant technical bottlenecks, failing to meet the stringent requirements of locating minute defects and performing high-resolution characterization.

[0003] Traditional TEM sample preparation relies entirely on FIB ion beam etching layer by layer, which presents several unavoidable drawbacks when preparing deep trench capacitor samples: Firstly, due to the load effect during the ion beam cutting process, the ion beam distribution inside the deep trench is uneven, sputtered material is redeposited, and the etching rate varies significantly, resulting in poor thickness consistency and uneven thickness of the prepared TEM sheet, which directly affects the subsequent imaging quality and defect interpretation. Secondly, when the sample preparation depth is large, U-cut can easily lead to problems such as sample structure breakage and truncation of the target failure area. Third, when a large focused ion beam cutting depth is set to cover the entire trench depth, the ion beam needs to remove a large amount of material layer by layer, making the preparation process cumbersome, significantly increasing the time consumption, and resulting in extremely low sample preparation efficiency. Fourth, during the process of thinning high aspect ratio samples to the ultrathin thickness required for TEM, the residual stress inside the material and the stress introduced by the ion beam are superimposed, which can easily cause the overall distortion, warping or even breakage of the sample, making it impossible to properly load it into the TEM for effective observation, which seriously restricts the development of failure analysis.

[0004] The combined effects of these multiple defects make it impossible for traditional focused ion beam (FIB) sample preparation methods to reliably prepare complete, flat, and distortion-free deep trench capacitor transmission electron microscopy (TEM) samples. This hinders the precise localization and high-resolution failure analysis of minute defects within the trenches (such as lattice dislocations, interface defects, and dielectric layer damage), severely impacting the improvement of deep trench capacitor yield and reliability optimization. Therefore, there is an urgent need to develop a novel TEM sample preparation scheme that is adapted to high aspect ratio deep trench structures, enables precise location of failure regions, avoids loading effects, suppresses stress distortion, and provides stable and reliable preparation. Summary of the Invention

[0005] The summary of this invention introduces a series of simplified concepts, all of which are simplifications of existing technologies in the field, and will be further explained in detail in the detailed description section. This summary is not intended to limit the key features and essential technical features of the claimed technical solution, nor is it intended to determine the scope of protection of the claimed technical solution.

[0006] The technical problem to be solved by the present invention is that the existing deep trench capacitor TEM sample preparation methods have problems such as uneven sample thickness, easy truncation, long preparation cycle, and inability to observe stress distortion, which makes it impossible to achieve precise location and failure analysis of small defects.

[0007] To solve the above-mentioned technical problems, the present invention provides a method for preparing deep trench capacitor TEM samples, comprising the following steps: 1) Use a micro-microscope or photoresistivity change detection to locate hot spots in deep trench capacitor products and determine the failure area; 2) A positioning protective layer is deposited at the hot spot location using a focused ion beam, and the product is polished to a first distance in front of the positioning protective layer; 3) Place the polished sample vertically on the sample stage and prepare the initial TEM sample using focused ion beam (FIB); 4) The initial TEM sample was transferred to the grid using Easy-Lift technology; 5) Thin the sample on the grid at three locations: top, middle, and bottom (TMB) and then perform TEM observation.

[0008] Optionally, the deep trench capacitor TEM sample preparation method can be further improved by using a platinum layer as the protective layer.

[0009] Optionally, the deep trench capacitor TEM sample preparation method can be further improved by setting the focused ion beam parameters for platinum deposition in step 2) to 30 kV and 0.23 nA.

[0010] Optionally, the deep trench capacitor TEM sample preparation method can be further improved. In step 3), the focused ion beam parameters for preparing the initial TEM sample include: 30 kV, 9.3 nA for coarse cutting; 30 kV, 2.5 nA for U-cut; and 30 kV, 0.23 nA for fine polishing.

[0011] Optionally, the deep trench capacitor TEM sample preparation method can be further improved, with the first distance range being 1μm~3μm.

[0012] Optionally, the deep trench capacitor TEM sample preparation method can be further improved, and the FIB parameters of the thinned sample in step 5) are: 30 kV, 80 pA.

[0013] Optionally, the deep trench capacitor TEM sample preparation method can be further improved by including, before step 1), the removal of the passivation layer and metal layer on the surface of the deep trench capacitor product.

[0014] The working principle of the present invention is explained below based on the above technical solution; This invention addresses the unique challenges in sample preparation for deep trench capacitors with high aspect ratios by developing an integrated preparation process that includes positioning, protection, repositioning and cutting, and segmented thinning. First, by combining optical microscopy (EMMI) and photoresistivity change (OBIRCH) with hotspot localization technology, the failure hotspots such as micro-leakage and abnormal luminescence on the device surface are precisely located, achieving high-precision localization of the target failure area. Second, a platinum (PT) protective layer is deposited at the hotspot location and controlled polishing is performed to remove surface interference materials in advance and protect the target area. Third, the polished sample is placed upright and rotated, and focused ion beam (FIB) cutting is performed from the vertical direction of the trench, fundamentally and effectively avoiding the loading effect of the ion beam in the deep trench and avoiding the sample truncation problem that is prone to occur during U-cut in the depth direction of the deep trench. Finally, a segmented thinning strategy of top, middle and bottom (TMB) is adopted for the transferred sample to gradually release residual stress in different regions, eliminating the risk of distortion, warping or even breakage during the ultra-thinning process of high aspect ratio samples, and finally obtaining a deep trench capacitor TEM sample with uniform thickness, complete structure and no distortion, to complete high-resolution observation and failure analysis of internal micro-defects.

[0015] Based on the above technical solution and working principle, the present invention can achieve at least the following technical effects compared with the prior art; Traditional TEM sample preparation methods rely entirely on single-shot, unidirectional etching using focused ion beam (FIB), lacking crucial process steps such as precise fault hotspot localization, target area protection, directional cutting, and segmented thinning. On one hand, traditional methods cannot avoid the ion beam loading effect within deep trenches, resulting in poor etching uniformity and easily causing sample thickness inhomogeneity. On the other hand, traditional methods often truncate samples during U-cut, failing to obtain a complete deep trench structure, and deep material removal is time-consuming. Furthermore, traditional one-shot thinning methods cannot release the internal stress of high aspect ratio samples, inevitably leading to sample distortion and deformation. Due to the lack of core technologies such as precise localization, loading effect suppression, and stress control, traditional methods cannot solve key technical challenges such as sample inhomogeneity, structural truncation, and stress distortion, making them unsuitable for the high-precision failure analysis requirements of minute defects in deep trench capacitors.

[0016] 1) This invention can effectively avoid the ion beam loading effect, significantly improve the etching uniformity inside the deep trench, and ensure the consistency of TEM sample thickness. From a process perspective, it avoids the sample truncation problem that is prone to occur when the U-cut position is too deep, greatly reduces the sample preparation failure rate, and at the same time reduces the amount of deep material removal, significantly shortens the overall preparation cycle, and improves sample preparation efficiency.

[0017] 2) This invention effectively eliminates stress distortion and warping deformation problems in the ultrathinning process of high aspect ratio samples by segmented thinning and step-by-step stress release through TMB, ensuring the flatness and stability of the sample, guaranteeing the clarity of TEM imaging and the accuracy of defect identification, and achieving effective observation.

[0018] 3) This invention can flexibly adapt to deep trench structures in different positions and orientations within a chip (die), breaking through the limitation of traditional methods that can only prepare samples locally, and realizing TEM sampling and analysis of any target area; it can accurately locate minute failure features such as lattice dislocations, interface damage, and dielectric defects inside the trench, meeting the high-precision and high-reliability failure analysis requirements of deep trench capacitors, and providing key technical support for improving device yield and optimizing processes. Attached Figure Description

[0019] The accompanying drawings are intended to illustrate the general characteristics of the methods, structures, and / or materials used in specific exemplary embodiments of the invention, supplementing the description in the specification. However, the drawings are schematic diagrams not drawn to scale and may not accurately reflect the precise structural or performance characteristics of any of the given embodiments. The drawings should not be construed as limiting or restricting the range of numerical values ​​or properties covered by exemplary embodiments of the invention. The invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0020] Figure 1 This is a schematic diagram of the invention process. Figure 1 .

[0021] Figure 2 This is a schematic diagram of the invention process. Figure 2 .

[0022] Figure 3 This is a schematic diagram of the invention process. Figure 3 .

[0023] Figure 4 This is a schematic diagram of the invention process. Figure 4 .

[0024] Figure 5 This is a schematic diagram of the invention process. Figure 5 .

[0025] Figure 6 This is a schematic diagram of the invention process. Figure 6 .

[0026] Figure 7 This is a schematic diagram of the invention process. Figure 7 .

[0027] Figure 8 This is a schematic diagram of the invention process. Figure 8 . Detailed Implementation

[0028] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can fully understand other advantages and technical effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through different specific embodiments, and various details in this specification can also be applied based on different viewpoints, with various modifications or changes made without departing from the overall design concept of the invention. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. The following exemplary embodiments of the present invention can be implemented in many different forms and should not be construed as being limited to the specific embodiments set forth herein. It should be understood that these embodiments are provided to make the disclosure of the present invention thorough and complete, and to fully convey the technical solutions of these exemplary embodiments to those skilled in the art. It should be understood that when an element is referred to as "connected" or "combined" to another element, the element can be directly connected or combined to the other element, or there may be intermediate elements. The difference is that when an element is referred to as "directly connected" or "directly combined" to another element, there are no intermediate elements. Throughout the drawings, the same reference numerals always denote the same elements. Example

[0029] This invention provides a method for preparing deep trench capacitor TEM samples, comprising the following steps: Surface treatment to remove the passivation layer and metal layer from the surface of deep trench capacitor products. Hotspot localization involves scanning the processed product using EMMI / OBIRCH technology to locate failure hotspot areas, referencing... Figure 1 As shown; For location protection, based on the deep trench orientation, a protective layer is formed by depositing a potential material (PT) at the hotspot location using FIB at 30 kV and 0.23 nA parameters. (Refer to...) Figure 2 As shown; Polishing treatment: Mechanically polish the product until it reaches 1~3μm in front of the PT positioning protective layer; The sample was prepared upright using FIB. The polished sample was vertically fixed on the sample stage, and the TEM sample was prepared using FIB with the following parameters: 30 kV, 9.3 nA for coarse cutting; 30 kV, 2.5 nA for U-cut; and 30 kV, 0.23 nA for fine polishing, to obtain the initial TEM sample. Sample transfer: The initial TEM sample was transferred to the grid support using the Easy Lift technique, reference... Figure 3 , Figure 4 As shown; Segmented thinning and observation: The sample on the grid was thinned at three locations along the TMB (Figures 3-5) under parameters of 30 kV and 80 pA. After thinning, TEM was used for observation, which clearly showed the internal defects of the deep trench. (Reference) Figures 5-8 As shown; Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It will also be understood that, unless explicitly defined herein, terms such as those defined in a general dictionary shall be interpreted as having the meaning consistent with their meaning in the relevant field context, and not as having an idealized or overly formal meaning.

[0030] The present invention has been described in detail above through specific embodiments and examples, but these are not intended to limit the invention. Many modifications and improvements can be made by those skilled in the art without departing from the principles of the invention, and these should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a deep trench capacitor TEM sample, characterized in that, Includes the following steps: 1) Use a micro-microscope or photoresistivity change detection to locate hot spots in deep trench capacitor products and determine the failure area; 2) A positioning protective layer is deposited at the hot spot location using a focused ion beam, and the product is polished to a first distance in front of the positioning protective layer; 3) Place the polished sample vertically on the sample stage and prepare the initial TEM sample using focused ion beam (FIB); 4) The initial TEM sample was transferred to the grid using Easy-Lift technology; 5) Thin the sample on the grid at three locations: top, middle, and bottom (TMB) and then perform TEM observation.

2. The method for preparing deep trench capacitor TEM samples according to claim 1, characterized in that: The protective layer is made of platinum.

3. The method for preparing deep trench capacitor TEM samples according to claim 2, characterized in that: The focused ion beam parameters for platinum deposition in step 2) are: 30 kV, 0.23 nA.

4. The method for preparing deep trench capacitor TEM samples according to claim 3, characterized in that: The focused ion beam parameters for preparing the initial TEM sample in step 3) include: 30 kV, 9.3 nA for coarse cutting; 30 kV, 2.5 nA for U-cut; and 30 kV, 0.23 nA for fine polishing.

5. The method for preparing deep trench capacitor TEM samples according to claim 4, characterized in that: The first distance range is 1μm to 3μm.

6. The method for preparing deep trench capacitor TEM samples according to claim 5, characterized in that: In step 5), the FIB parameters for the thinned sample are: 30 kV, 80 pA.

7. The method for preparing deep trench capacitor TEM samples according to claim 1, characterized in that: Step 1) also includes: removing the passivation layer and metal layer from the surface of the deep trench capacitor product.

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