A method for preparing TEM pore samples using focused ion beam

Abstract

The present invention relates to the field of semiconductor manufacturing technology, particularly to samples with relatively deep pores. It provides a method for preparing pore samples using a focused ion beam (FIB) and observing their bottom structure. This method addresses the problems of pore structure deformation and significant damage to the pores caused by the focused ion beam during sample preparation in existing techniques by filling the pores with a specialized resin for ion thinning and introducing an improved back-cutting technique. The technical advantage of the present invention lies in its ability to improve the stability of the bottom structure of the pore sample and prevent damage to the pore structure during the thinning process.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing technology, and in particular to a method for preparing a TEM pore sample by utilizing a focused ion beam. Background Art

[0002] In materials science and nanotechnology, observing the structure beneath porous samples is crucial for understanding the internal characteristics of materials and optimizing their properties. Existing preparation methods often rely on traditional methods such as mechanical grinding and chemical etching, but these methods have numerous limitations. For example, mechanical grinding can easily scratch and damage the sample surface, making it difficult to precisely control the sample's thickness and shape. Chemical etching can also introduce unwanted chemical components, affecting sample purity and the accuracy of subsequent analytical results.

[0003] In recent years, focused ion beam technology, as a high-precision micro- and nanofabrication tool, has been increasingly used in the preparation of porous samples. FIB technology bombards the sample surface with an accelerated, focused ion beam, sputtering and exfoliating atoms, thereby achieving fine-grained processing. However, existing FIB methods for preparing porous samples still present technical difficulties in observing the underlying structure, such as the difficulty in precisely controlling the pore shape and directly observing the underlying structure.

[0004] Inaccurate control of pore shape: When preparing porous samples with existing FIB technology, it is difficult to accurately control the shape and size of pores, especially when preparing pore structures with greater depth, the error is large.

[0005] Difficulty in observing the bottom structure: Due to the complexity of the pore structure, existing methods often find it difficult to directly observe the bottom structure, which limits the comprehensive understanding of the internal characteristics of the material.

[0006] The sample preparation process is cumbersome: Existing sample preparation methods usually include multiple steps, and each step requires precise control, which is cumbersome and time-consuming. Summary of the Invention

[0007] The present invention aims to provide a method for preparing porous samples using a focused ion beam for observing their bottom structure, addressing the aforementioned problems in the prior art. By filling the sample with a specialized resin for ion thinning and introducing an improved back-cutting technique, this method enables precise preparation and direct observation of the bottom structure of the porous sample.

[0008] Sample pretreatment: Secure the porous sample to the nail base with conductive Cu glue, and then adhere the sample to the nail base using conductive Cu glue. Wrap the sample with the conductive Cu glue, leaving space for processing. Because the hollow structure of the porous sample is easily damaged, apply a special ion thinning resin to the surface of the porous sample. Under the action of gravity, the resin glue will flow into the pores until it fills the pores. Allow the resin to solidify. The ion thinning resin used is M-bond610 resin glue.

[0009] FIB Etching: The prepared sample is fixed on a 0° sample stage, sample is loaded, and the porous sample is etched using the FIB. A U-shaped cutting method is used to form an initial wedge-shaped sample. Combined with an in-situ nanomanipulator, the wedge-shaped sample is extracted to form the desired observation area. During the etching process, FIB parameters (such as accelerating voltage and ion beam current) are adjusted to optimize the etching effect and minimize sample damage.

[0010] The FIB etching process involves plating a tungsten protective layer on the target location of the TEM pore sample, machining deep pits on the upper and lower sides and left side of the tungsten-plated layer, and then fine-trimming to obtain a sample slice. Specifically, the following steps are included:

[0011] S201, tilt the sample stage to 52°, perform tungsten layer deposition, set the electron beam voltage to 20-30 kV, and the current to 80 pA-0.79 nA, and deposit a tungsten layer with a thickness of 1-2 μm on the target processing area of ​​the porous sample as a protective layer;

[0012] S202, selecting an ion beam voltage and current of 20-30 kV and a large beam current of 9.3-27 nA, respectively, to machine deep pits on the upper and lower sides and the left side of the tungsten coating;

[0013] S203, performing cross-section shaping on the upper and lower edges of the tungsten layer when the sample stage tilt angle is 50° and 54°, respectively, to obtain a wedge-shaped sample slice having an initial observation area;

[0014] S204. After the sample stage returns to the 0° state, the sample slice is processed into a cantilever beam state.

[0015] Improved undercutting technique: Rotate the sample stage so that the copper pillar faces right. Rotate the nanomanipulator, with the wedge-shaped specimen bonded to it, 180° from its initial position. Use FIB to smooth the surface of the wedge-shaped specimen to be bonded. Adjust the relative position of the nanomanipulator and the copper pillar. Use a tungsten layer to weld the specimen and the lower end of the copper pillar together. This way, the bottom of the porous sample becomes the top of the sample to be thinned. The tungsten needle is then cut off.

[0016] Changing the sample stage: The copper mesh loaded with the sample is transferred from the 0° sample stage to the 38° sample stage. By precisely controlling the cutting and thinning process of the sample, the sample thickness can be precisely machined. The sample is loaded again, and the sample stage is rotated so that the copper pillar faces upward. A protective tungsten layer is plated on the top of the sample slice.

[0017] The method for coating a tungsten protective layer is as follows: a tungsten protective layer with a thickness of 2-3 μm is coated under the conditions of an ion beam of 30 kV and 0.23-0.25 nA.

[0018] Fine Polishing: First, the sample is finely polished using a stepwise reduction of the ion beam voltage to thin the TEM porous sample to less than 80-100 nm. The thinned TEM slice is then purged and cleaned to remove the amorphous and damaged layers on the surface, producing the TEM porous sample. Simultaneously, the sample is further characterized and analyzed to ensure its quality and performance meet the requirements.

[0019] The sample was finely polished to achieve thinning by gradually reducing the ion beam voltage. Under the conditions of a tilt angle of ±1°~±0.8°, the thinning voltage was maintained at 25-30 kV, and the ion beam current was gradually reduced from 0.23 nA to 40pA until the sample thickness was between 80-100 nm.

[0020] The purging and cleaning treatments include the following steps: first, the sample stage is tilted to ±3°, the ion beam voltage and current are reduced to 5-10 kV and 30-15 pA, respectively, and the front and back surfaces of the sample are purged for 30-60 seconds each, back and forth 2-3 times; then the sample stage is further tilted to ±5°, the ion beam voltage and current are reduced to 2-1 kV and 9-5 pA, respectively, and the front and back surfaces of the sample are purged for 30-60 seconds each.

[0021] Compared with the existing technology, the advantages of this patent are:

[0022] 1. Precise control of pore shape: By optimizing FIB processing parameters, the shape and size of the pores can be precisely controlled to meet different research needs.

[0023] 2. Direct observation of bottom structure: The introduction of an improved inverted cutting method enables direct observation of the bottom structure of porous samples, improving the accuracy of analysis results.

[0024] 3. Simplified sample preparation process: This method simplifies the sample preparation process, reduces the number of operating steps and time consumption, and improves work efficiency.

[0025] 4. Improved sample thickness uniformity: The improved inverted cutting technology can achieve precise control of the thickness of the sample bottom, avoiding the problem of uneven sample thickness caused by the large depth in traditional methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a TEM sample image of the bottom structure of the pore sample prepared in Example 1. DETAILED DESCRIPTION

[0027] Example 1

[0028] The experiments were conducted in a Thermos Helios 5 UC FIB equipped with an in-situ nanomanipulator and a gas injection system (GIS). The present invention is described in detail below with reference to specific examples:

[0029] 1. Sample Preparation: Secure the porous sample to the sample stage with conductive Cu adhesive to ensure sample stability. Next, adhere the sample to the sample stage with conductive Cu adhesive to form a stable support structure. Apply a uniform layer of ion-thinning resin to the surface of the porous sample.

[0030] 2. Initial Cutting: In the FIB instrument, the porous sample is initially cut using precisely controlled focused ion beams. First, the specimen stage is tilted 52°, and a 2-micron tungsten protective layer is deposited on the target location of the specimen. The ion beam voltage is adjusted to 30 kV. During this process, the ion beam current is set to a low value (e.g., 80 pA-0.79 nA) to minimize damage to the specimen surface. A high ion beam voltage and current of 30 kV and 9.3-27 nA are selected, respectively, to machine deep pits on the upper, lower, and left sides of the tungsten coating. The rectangular frame should be positioned close to the tungsten coating to avoid high-beam back-deposition and ensure cutting accuracy. After rough machining, CCS finishing is performed on the upper and lower edges of the coating at 50° and 54° tilt angles, respectively, to form a preliminary thin specimen slice. After the specimen stage is returned to 0°, the thin specimen slice is machined into a cantilever configuration.

[0031] 3. Sample Transfer: Adjust the relative position of the nanomanipulator and the sample slice, weld them using a W welder, then cut the cantilever arm, quickly cut and separate the sample, and extract it. Adjust the orientation of the sample stage so that the copper pillar faces right. Insert the nanomanipulator and rotate it 180° in the Park position with the sample slice attached. Use FIB to smooth the surface of the sample slice to be bonded. Adjust the relative position of the nanomanipulator and the copper pillar again, and weld the sample and the lower end of the copper pillar together using a tungsten layer. At this point, the bottom of the porous sample becomes the top of the sample to be thinned. Then cut the tungsten needle.

[0032] 4. Change the sample stage: Remove the sample stage and transfer the copper mesh loaded with the sample from the 0° sample stage to the 38° sample stage. Re-inject the sample. Adjust the sample stage again so that the copper pillar faces upward. Plate a 2-micron tungsten protective layer on top of the sample sheet.

[0033] 5. Fine grinding: During the thinning process, the tilt angle is set to ±1°, the thinning voltage is 30 kV, and the ion beam current is gradually reduced from 0.23 nA to 80 pA and 40 pA until the sample thickness is between 80-100 nm. To further improve the quality of the sample and the observation effect, the sample is finely polished by gradually reducing the ion beam voltage. First, the sample stage is tilted to ±3°, the ion beam voltage and current are reduced to 5 kV and 15 pA, respectively, and the front and back surfaces of the sample are purged for 30 s each, back and forth 2-3 times. Then, the sample stage is further tilted to ±5°, the ion beam voltage and current are reduced to 2 kV and 9 pA, respectively, and the front and back surfaces of the sample are purged for 60 s each. The process can be stopped at any time according to the actual situation of the sample to ensure that the tungsten layer still remains. This step can remove the amorphous layer and damaged layer on the surface of the sample, preserving the original structure and characteristics of the sample.

[0034] 6. Final Inspection: Perform final inspection on the prepared pore bottom TEM sample and measure the pore size. TEM observation ensures that the sample meets the test requirements.

Claims

1. A method for preparing a TEM pore sample using a focused ion beam, characterized in that: The following steps are involved: S1. Sample pretreatment: Fix the TEM pore sample on the sample stage and perform resin glue curing on the TEM pore sample; S2, FIB etching: In the FIB equipment, the porous sample is initially cut by precisely controlling the focused ion beam; S3, undercutting: Use FIB to smooth the surface of the sample sheet to be bonded, adjust the relative position of the nanomanipulator and the copper pillar, and use a tungsten layer to weld the sample and the lower end of the copper pillar together. At this time, the bottom of the porous sample becomes the top of the sample to be thinned, and the tungsten needle is cut off; S4. Change the sample stage: transfer the copper mesh loaded with the sample from the 0° sample stage to the 38° sample stage, inject the sample again, rotate the sample stage so that the copper column faces upward, and plate a tungsten protective layer on the top of the sample slice; S5. Fine polishing: First, the sample is finely polished by gradually reducing the ion beam voltage to thin the TEM pore sample to less than 100 nm, and then the thinned TEM slice is purged and cleaned to remove the amorphous layer and damaged layer on the surface to obtain the TEM pore sample.

2. The method for preparing a TEM pore sample using a focused ion beam according to claim 1, wherein: In step S1, the step of fixing the pore sample on the sample stage includes the following steps: fixing the pore sample on the sample stage with conductive Cu glue, and wrapping the sample with the conductive Cu glue.

3. The method for preparing TEM pore samples using a focused ion beam according to claim 1, wherein: In step S1, the resin glue curing treatment step includes: coating ion thinning resin on the surface of the pore sample, and the ion thinning resin is M-bond610 resin glue.

4. The method for preparing TEM pore samples using a focused ion beam according to claim 1, wherein: In step S2, a tungsten protective layer is plated on the target position of the TEM pore sample during the FIB etching process, deep pits are processed on the upper and lower sides and the left side of the plated tungsten layer, and a sample slice is obtained after fine trimming.

5. The method for preparing TEM pore samples using a focused ion beam according to claim 4, characterized in that: S2 includes the following steps: S201, tilt the sample stage to 52 degrees, perform tungsten layer deposition, set the electron beam voltage to 20-30 kV, and the current to 80 pA-0.79 nA, and deposit a tungsten layer with a thickness of 1-2 μm on the target processing area of ​​the porous sample as a protective layer; S202, selecting an ion beam voltage and current of 20-30 kV and a large beam current of 9.3-27 nA, respectively, to machine deep pits on the upper and lower sides and the left side of the tungsten coating; S203, performing cross-section shaping on the upper and lower edges of the tungsten layer when the sample stage tilt angle is 50° and 54°, respectively, to obtain a wedge-shaped sample slice having an initial observation area; S204. After the sample stage returns to the 0° state, the sample slice is processed into a cantilever beam state.

6. The method for preparing a TEM pore sample using a focused ion beam according to claim 1, wherein: In step S3, the direction of the sample stage is adjusted so that the copper column faces right, and the nanomanipulator is inserted. The nanomanipulator with the sample slice bonded thereto is rotated 180° in the Park Position. The surface of the sample slice to be bonded is polished and smoothed using an ion beam. The relative position of the nanomanipulator and the copper column is adjusted again, and the sample and the lower end of the copper column are welded together using a tungsten layer. At this time, the bottom of the porous sample becomes the top of the sample to be thinned, and the tungsten needle is then cut off.

7. The method for preparing a TEM pore sample using a focused ion beam according to claim 1, wherein: In step S4, a 2-3 μm thick tungsten protective layer is deposited under the conditions of an ion beam of 30 kV and 0.23-0.25 nA.

8. The method for preparing TEM pore samples using a focused ion beam according to claim 1, wherein: In step S5, the sample is finely polished to achieve thinning by gradually reducing the ion beam voltage. Under the conditions of a tilt angle of ±1°~±0.8°, the thinning voltage is maintained at 25-30 kV, and the ion beam current is gradually reduced from 0.23 nA to 40 pA until the sample thickness is between 80-100 nm.

9. The method for preparing a TEM pore sample using a focused ion beam according to claim 1, wherein: In step S5, the purging and cleaning process includes the following steps: First, tilt the sample stage to ±3°, reduce the ion beam voltage and current to 5-10 kV and 30-15 pA, respectively, and purge the front and back surfaces of the sample for 30-60 s each, back and forth 2-3 times; then continue to tilt the sample stage to ±5°, reduce the ion beam voltage and current to 2-1 kV and 9-5 pA, respectively, and purge the front and back surfaces of the sample for 30-60 s each.

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