Method for preparing TEM pore sample by using focused ion beam

Abstract

The invention relates to the technical field of semiconductor manufacturing, in particular to a pore sample with large depth, and provides a method for observing a bottom structure by preparing the pore sample through a focused ion beam (FIB). According to the method, by means of filling special resin for ion thinning into pores, introducing an improved back-cutting technology and the like, the problems of pore structure deformation and large damage of focused ion beams to the interiors of the pores during sample preparation in the prior art are solved; the method has the technical effects that the stability of the bottom structure of the pore sample can be improved, and damage to the pore structure in the thinning process is avoided.

Description

Technical Field

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

[0002] In the fields of materials science and nanotechnology, observing the bottom structure of porous samples is an important means to understand the internal characteristics of materials and optimize material properties. Existing preparation methods mostly rely on traditional methods such as mechanical grinding and chemical etching, but these methods have many limitations. For example, mechanical grinding can easily cause scratches and damage on the surface of the sample, making it difficult to accurately control the thickness and shape of the sample; chemical etching may introduce unnecessary chemical components, affecting the purity of the sample and the accuracy of subsequent analysis results.

[0003] In recent years, focused ion beam technology, as a high-precision micro-nano processing tool, has been gradually applied to the preparation of porous samples. FIB technology accelerates the focused ion beam to bombard the sample surface, sputtering and peeling off atoms, thereby achieving fine processing of the sample. However, the existing method of preparing porous samples using FIB still has some technical difficulties when observing the bottom structure, such as the difficulty in accurately controlling the pore shape and the difficulty in directly observing the bottom structure.

[0004] Inaccurate control of pore shape: It is difficult to accurately control the shape and size of pores when preparing pore samples using existing FIB technology, especially when preparing pore structures with greater depths, 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 preparation method for preparing a porous sample and observing the bottom structure by using a focused ion beam to solve the above problems existing in the prior art. The method achieves accurate preparation and direct observation of the bottom structure of the porous sample by filling a special resin for ion thinning and introducing an improved back-cutting technology.

[0008] Sample pretreatment: Fix the porous sample on the nail table with conductive Cu glue, and use conductive Cu glue to adhere the sample to the nail table. The conductive Cu glue wraps the sample and leaves the position to be processed. Since the hollow structure of the porous sample is easily destroyed, the ion thinning special resin needs to be applied to the surface of the porous sample. Under the action of gravity, the resin glue will flow into the pores until they are filled. Let it stand for the resin glue to solidify. The ion thinning resin is M-bond610 resin glue.

[0009] FIB etching: Fix the prepared sample on the 0° sample stage, inject the sample, and use FIB to etch the porous sample. Use the U-shaped cutting method to form the initial wedge-shaped sample. Combined with the in-situ nanomanipulator, the wedge-shaped sample is extracted to form the required observation area. During the etching process, the etching effect is optimized and the damage to the sample is reduced by adjusting the FIB parameters (such as acceleration voltage, ion beam current, etc.).

[0010] In the FIB etching process, a tungsten protective layer is plated on the target position of the TEM pore sample, 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. Specifically, the following steps are included: S201, tilt the sample stage to 52°, perform tungsten layer deposition, set the electron beam voltage to 20-30 kV, the current to 80 pA-0.79 nA, and plate 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 process deep pits on the upper and lower sides and the left side of the tungsten coating; S203, performing Cross-Sectional Shaping on the upper edge and the lower edge of the tungsten layer when the tilt angle of the sample stage 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.

[0011] Improved inverted cutting technique: Rotate the sample stage so that the copper column faces right. Rotate the nanomanipulator with the wedge-shaped sample bonded to it 180° at the initial position, use FIB to polish the surface of the wedge-shaped sample to be bonded flat, adjust the relative position of the nanomanipulator and the copper column, and use the tungsten layer to weld the sample and the lower end of the copper column together. At this time, the bottom of the porous sample becomes the top of the sample to be thinned, and then cut off the tungsten needle.

[0012] Change the sample stage: transfer the copper mesh loaded with the sample from the 0° sample stage to the 38° sample stage, and achieve accurate processing of the sample thickness by precisely controlling the cutting and thinning process of the sample. Inject the sample again, turn the sample stage so that the copper column faces upward, and plate a tungsten protective layer on the top of the sample slice.

[0013] The method of coating a tungsten protective layer is as follows: a 2-3 μm thick tungsten protective layer is coated under the conditions of ion beam of 30 kV and 0.23-0.25 nA.

[0014] Fine grinding: First, the sample is finely ground by gradually reducing the ion beam voltage to thin the TEM pore sample to less than 80-100 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. At the same time, the sample is further characterized and analyzed to ensure that its quality and performance meet the requirements.

[0015] The sample was finely polished and thinned by gradually reducing the ion beam voltage. Under the condition 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.

[0016] 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 rear 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 rear surfaces of the sample are purged for 30-60 seconds each.

[0017] Compared with the prior art, the advantages of this patent are: 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.

[0018] 2. Direct observation of bottom structure: The introduction of an improved inverted cutting method enables direct observation of the bottom structure of porous samples and improves the accuracy of analysis results.

[0019] 3. Simplified sample preparation process: This method simplifies the sample preparation process, reduces the operation steps and time consumption, and improves work efficiency.

[0020] 4. Improved sample thickness uniformity: The improved inverted cutting technology can achieve precise control of the sample bottom thickness, avoiding the problem of uneven sample thickness caused by greater depth in traditional methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a TEM sample image of the bottom structure of the pore sample prepared in Example 1. DETAILED DESCRIPTION

[0022] Example 1 The experiment was carried out 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 in conjunction with specific embodiments: 1. Sample preparation: Fix the porous sample on the sample table with conductive Cu glue to ensure the stability of the sample. Then, use conductive Cu glue to adhere the sample to the sample table to form a stable support structure. Coat a uniform layer of ion thinning special resin on the surface of the porous sample.

[0023] 2. Initial cutting: In the FIB equipment, the porous sample is initially cut by precisely controlling the focused ion beam. First, the sample stage is tilted to 52°, and a 2-micron tungsten protective layer is plated on the target position of the sample. The ion beam voltage is adjusted to 30 kV. During this process, the beam current of the ion beam is set to a lower value (such as 80 pA-0.79 nA) to reduce damage to the sample surface. A large beam current of 30 kV and 9.3-27 nA is selected to process deep pits on the upper and lower sides and left side of the tungsten coating. The rectangular frame should not be too close to the tungsten coating to avoid large beam reverse deposition and ensure cutting accuracy. After rough processing, the upper and lower edges of the coating are CCS refined at the tilt angles of the sample stage of 50° and 54°, respectively, to form a preliminary sample slice. After the sample stage returns to the 0° state, the sample slice is processed into a cantilever beam state.

[0024] 3. Sample transfer: Adjust the relative position of the nanomanipulator and the sample slice, use W for welding, then cut off the cantilever arm, quickly cut off and separate the sample, and extract the sample. Adjust the direction of the sample stage so that the copper column faces right. Enter the nanomanipulator, rotate the nanomanipulator with the sample slice bonded 180° in the Park Position, use FIB to polish the surface of the sample slice to be bonded, adjust the relative position of the nanomanipulator and the copper column again, use the tungsten layer to weld the sample and the lower end of the copper column together, at this time the bottom of the porous sample becomes the top of the sample to be thinned, and then cut off the tungsten needle.

[0025] 4. Change the sample stage: Take out the sample stage, transfer the copper mesh loaded with the sample from the 0° sample stage to the 38° sample stage, and re-inject the sample. Adjust the direction of the sample stage again so that the copper column faces upward, and plate a 2-micron tungsten protective layer on the top of the sample slice.

[0026] 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. In order to further improve the quality and observation effect of the sample, 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 rear 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 rear surfaces of the sample are purged for 60 s each. Stop at any time according to the actual situation of the sample to ensure that the tungsten layer is still residual. This step can remove the amorphous layer and damaged layer on the surface of the sample and retain the original structure and characteristics of the sample.

[0027] 6. Final inspection: Conduct final inspection on the prepared pore bottom TEM sample and measure the pore size. Ensure that the sample meets the test requirements through TEM observation.

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 treatment 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 grind the surface of the sample slice to be bonded flat, adjust the relative position of the nanomanipulator and the copper column, and use the tungsten layer to weld the sample and the lower end of the copper column 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, changing 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, turn the sample stage so that the copper column faces upward, and plate a tungsten protective layer on the top of the sample sheet; S5. Fine polishing: firstly, fine polish the sample by gradually reducing the ion beam voltage to thin the TEM pore sample to less than 100 nm, and then purge and clean the thinned TEM slice to remove the amorphous layer and damaged layer on the surface to obtain the TEM pore sample.

2. The method for preparing TEM pore samples using a focused ion beam according to claim 1, characterized in that: In step S1, the process 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 conductive Cu glue.

3. The method for preparing TEM pore samples using a focused ion beam according to claim 1, characterized in that: In step S1, the resin glue curing treatment step includes: coating an 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, characterized in that: 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 tungsten plated 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°, perform tungsten layer deposition, set the voltage of the electron beam to 20-30 kV, the current to 80pA-0.79 nA, and plate 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 process deep pits on the upper and lower sides and the left side of the tungsten coating; S203, performing Cross-Sectional Shaping on the upper edge and the lower edge of the tungsten layer when the tilt angle of the sample stage 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 TEM pore samples using a focused ion beam according to claim 1, characterized in that: In step S3, the direction of the sample stage is adjusted so that the copper column faces right, and the nanomanipulator is moved in. 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 then the tungsten needle is cut off.

7. The method for preparing TEM pore samples using a focused ion beam according to claim 1, characterized in that: In step S4, a 2-3 μm thick tungsten protective layer is deposited under the conditions of 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, characterized in that: In step S5, the sample is finely polished to achieve thinning by gradually reducing the ion beam voltage. Under the condition 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 TEM pore samples using a focused ion beam according to claim 1, characterized in that: In step S5, the purging process and the cleaning process include the following steps: First, the sample stage was tilted to ±3°, and the ion beam voltage and current were reduced to 5-10 kV and 30-15 pA, respectively. The front and back surfaces of the sample were purged for 30-60 s each, and this process was repeated 2-3 times. Then, the sample stage was further tilted to ±5°, and the ion beam voltage and current were reduced to 2-1 kV and 9-5 pA, respectively. The front and back surfaces of the sample were purged for 30-60 s each.

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