Thinning method for preparing pore sample by using focused ion beam

Abstract

The invention relates to the technical field of semiconductor manufacturing, in particular to a sample with a pore structure, and provides a thinning method for preparing a pore sample by using a focused ion beam. According to the method, the front face of a target sample is thinned through FIB, then the back face of the target sample is thinned, the problem that in the prior art, a TEM target sheet generated when the front face and the back face of the target sample are thinned alternately is not of a pore internal structure is solved, and the technical effects of the method are that the efficiency of preparing the pore sample can be improved; and the picture shooting quality of the pore structure sample is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor manufacturing, and particularly relates to a thinning method for observing internal structure of a pore sample by using a focused ion beam (FIB). BACKGROUND

[0002] In the field of material science and nanotechnology, observing the internal structure of a pore sample is an important means to understand the internal characteristics of materials and optimize material performance. 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 is prone to scratches and damage on the sample surface, and it is 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 has been gradually applied to the preparation of pore samples as a high-precision micro-nano processing tool. FIB technology realizes fine processing of samples by accelerating and focusing ion beams to bombard the sample surface and sputter atoms to separate them. However, existing methods for preparing pore samples using FIB still have some technical defects when observing the internal structure of the pores, such as not cutting the largest diameter position on the pore during thinning.

[0004] Objective defects of the prior art: Difficult to observe pore structure: Since the pore structure is hollow, ion beam bombardment of the sample surface can easily damage the pore structure, causing the pore structure to collapse and deform, and existing methods often cannot directly observe the internal structure of the pore, which limits the comprehensive understanding of the internal characteristics of the material.

[0005] Inaccurate control of pore shape: Existing FIB technology has difficulty in accurately controlling the shape and size of the pore when preparing the pore sample, especially when preparing pore structures with small pore sizes, the target sheet is prone to fall between the pores without characteristic structures, resulting in large errors. SUMMARY

[0006] The present application aims to provide a thinning method for observing the internal structure of a pore sample by using a focused ion beam, to solve the above-mentioned problems in the prior art. This method realizes accurate preparation and direct observation of the internal structure of the pore sample by first thinning the front surface of the target sample and then thinning the back surface of the target sample.

[0007] Sample pretreatment: Fix the porous sample to the nail stage using conductive C adhesive, and then use conductive Cu adhesive to bond the sample to the nail stage, encapsulating the sample with the conductive Cu adhesive, leaving the areas to be processed exposed. Since the hollow structure of the porous sample is easily damaged, apply a special ion-thinning resin to the surface of the porous sample. Under gravity, the resin will flow into the pores until they are filled. Let it stand for 15 minutes to allow the resin to cure.

[0008] FIB etching: The prepared sample is fixed on a 38° sample stage, and the sample is injected. First, a protective layer is deposited at the location to be processed using an ion beam. Then, FIB etching is used to etch the porous sample, forming an initial wedge-shaped sample using a U-shaped cutting method. Combined with an in-situ nanomanipulator, the wedge-shaped sample is extracted to form the desired observation area. During the etching process, the etching effect is optimized and sample damage is reduced by adjusting the FIB parameters (such as accelerating voltage and ion beam current).

[0009] Wedge Correction: For wedge-shaped samples formed during initial cutting, a U-shaped cutting tilt angle method is used. By adjusting the cutting angle of the ion beam, the wedge shape of the sample is gradually reduced. Simultaneously, combined with an in-situ nanomanipulator and a gas injection system (GIS), the cutting and thinning process of the sample is precisely controlled. During the thinning process, the front side of the sample is thinned first, followed by the back side, achieving precise processing of the target sample.

[0010] Sample post-processing: The prepared TEM samples undergo post-processing such as purging and cleaning to remove the amorphous and damaged layers on the surface. Simultaneously, the samples are further characterized and analyzed to ensure their quality and performance meet requirements.

[0011] Experiments were conducted on a Thermos Helios 5 UC-type FIB equipped with an in-situ nanomanipulator and a gas injection system (GIS). The invention is described in detail below with reference to specific embodiments: S1. Sample pretreatment: Fix the TEM pore sample on the sample stage and cure the TEM pore sample with resin adhesive. In step S1, the porous sample is fixed to the sample stage using conductive C adhesive to ensure its stability. Next, conductive Cu adhesive is used to bond the sample to the sample stage, forming a stable support structure. A uniformly thick layer of ion-thinning special resin is then coated onto the surface of the porous sample.

[0012] In step S1, fixing the pore sample on the sample stage includes the following steps: fixing the pore sample on the sample stage with conductive Cu adhesive, and wrapping the sample with conductive Cu adhesive.

[0013] In step S1, the resin curing process includes: coating the surface of the porous sample with an ion-thinning resin, wherein the ion-thinning resin is M-bond610 resin adhesive.

[0014] S2, FIB Etching: In the FIB equipment, the porous sample is initially cut by precisely controlling the focused ion beam; In the FIB (Film Injection Block) equipment, the porous sample is initially cut by precisely controlling the focused ion beam. First, the sample stage is tilted to 52°, and a 3-micron tungsten protective layer is deposited on the target location of the sample. 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 reduce damage to the sample surface. Then, a high ion beam voltage and current of 30 kV and 9.3-27 nA are selected to create deep pits on the upper, lower, and left sides of the tungsten coating. The rectangular frame should not be too close to the tungsten coating to avoid back deposition due to the high beam current and ensure cutting accuracy. After rough machining, the upper and lower edges of the coating are refined using CCS (Continuous Ceramic Staining) at sample stage tilt angles of 50° and 54°, respectively, forming a preliminary sample sheet. After the sample stage returns to 0°, the sample sheet is machined into a cantilever beam configuration.

[0015] S3. Sample transfer and cutting: Adjust the relative position of the nanorobot and the sample sheet, use W to weld to obtain the sample, adjust the tilt angle of the sample stage so that the copper column is facing down, enter the nanorobot, adjust the relative position of the nanorobot and the copper column again, use tungsten layer to weld the right side of the sample and the left end of the copper column together, and then cut off the tungsten needle. In some preferred cases, the relative positions of the nanomanipulator and the sample sheet are adjusted, and welding is performed using a W-type welding method. The cantilever arm is then cut off to quickly sever and separate the sample, allowing for sample extraction. The sample stage tilt angle is adjusted to 52° so that the copper pillar faces downwards. The nanomanipulator is then inserted, and the relative positions of the nanomanipulator and the copper pillar are readjusted. A tungsten layer is used to weld the right side of the sample to the left end of the copper pillar, followed by cutting off the tungsten needle. The sample stage orientation is then adjusted back to 0° so that the copper pillar faces upwards.

[0016] S4. Fine polishing: First, the front side of the sample is thinned to a certain extent to form a preliminary observation area. Then, the back side of the sample is thinned to a degree that can be observed by transmission electron microscopy. Finally, the observation area is cleaned and purged to obtain the TEM porous sample.

[0017] S401. First, set the tilt angle to 1° and thin the front side of the sample; during the thinning process, the thinning voltage and ion beam current are 20-30 kV and 0.08nA-0.23nA, respectively. S401. Adjust the tilt angle to -1° and thin the back side of the sample. During the thinning process, the thinning voltage and ion beam current are 20-30 kV and the current is 0.08nA-0.23nA, respectively.

[0018] S4 also includes further reducing the ion beam current to 24-80 pA to thin the sample to a thickness observable by transmission electron microscopy.

[0019] Furthermore, S4 also includes a method of gradually reducing the ion beam voltage to perform fine polishing on the sample. First, the sample stage is tilted to ±3°, and the ion beam voltage and current are reduced to 5-10 kV and 15-30 pA, respectively. The front and rear surfaces of the sample are purged for 10-30 seconds each, and this is repeated 2-3 times.

[0020] The sample stage was then tilted to ±5°, and the ion beam voltage and current were reduced to 1-3 kV and 5-10 pA, respectively. The front and rear surfaces of the sample were then purged for 10-60 seconds each.

[0021] In some preferred cases, during the thinning process, the thinning voltage and ion beam current are 30 kV and 0.23 nA, respectively. The tilt angle is initially set to 1°, and thinning is performed on the front side of the sample (e.g., Figure 1 When the sample is thinned to the point where the internal porous structure is visible (e.g.) Figure 2 The tilt angle was adjusted to -1°, and the back side of the sample was thinned. The ion beam current was further reduced to 80 pA, and the sample was thinned to a thickness observable by transmission electron microscopy. To further improve the quality of the sample and the observation effect, the sample was finely polished using a method of gradually reducing the ion beam voltage. First, the sample stage was tilted to ±3°, and the ion beam voltage and current were reduced to 5 kV and 15 pA, respectively. The front and back surfaces of the sample were purged for 30 seconds each, 2-3 times. Then, the sample stage was tilted to ±5°, and the ion beam voltage and current were reduced to 2 kV and 9 pA, respectively. The front and back surfaces of the sample were purged for 1 minute each, stopping as needed based on the actual condition of the sample to ensure that the tungsten layer was still present. This step can remove the amorphous layer and damaged layer on the sample surface, preserving the original structure and properties of the sample.

[0022] Final testing: The prepared TEM samples with porous structures undergo final testing, and the pore size is measured. TEM observation ensures the samples meet the testing requirements. If necessary, further post-processing or optimization can be performed on the samples to improve observation results.

[0023] Compared with existing technologies, the advantages of this patent are: 1. Precise control of pore shape: By optimizing the FIB processing parameters, the shape and size of the pores can be precisely controlled to meet different research needs.

[0024] 2. Direct observation of internal structure: The introduction of an improved thinning method enables direct observation of the internal structure of porous samples, improving the accuracy of analytical results.

[0025] 3. Simplified sample preparation process: This method simplifies the sample preparation process, reduces operation steps and time consumption, and improves work efficiency.

[0026] 4. Improved sample preparation success rate: The improved thinning method enables real-time observation and precise control of the internal structure of the sample, avoiding the problem of incorrect TEM sample position caused by large pore spacing in traditional methods. Attached Figure Description

[0027] Figure 1 This is a top view of the thinning process of the porous sample prepared in Example 1.

[0028] Figure 2 This is a front view of the thinning process of the porous sample prepared in Example 1.

[0029] Figure 3 This is a TEM image of the internal structure of the porous sample prepared in Example 1. Detailed Implementation

[0030] Experiments were conducted on a Thermos Helios 5 UC-type FIB equipped with an in-situ nanomanipulator and a gas injection system (GIS). The invention is described in detail below with reference to specific embodiments: 1. Sample Preparation: Fix the porous sample to the sample stage using conductive C adhesive to ensure sample stability. Next, use conductive Cu adhesive to bond the sample to the sample stage, forming a stable support structure. Then, coat the surface of the porous sample with a uniformly thick layer of ion-thinning resin.

[0031] 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 3-micron tungsten protective layer is deposited on the target location of the sample. 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 reduce damage to the sample surface. A high ion beam voltage and current of 30 kV and 9.3-27 nA are selected to machine deep pits on the upper, lower, and left sides of the tungsten coating. The rectangular frame should not be too close to the tungsten coating to avoid back deposition due to the high beam current and ensure cutting accuracy. After rough machining, the upper and lower edges of the coating are refined using CCS at sample stage tilt angles of 50° and 54°, respectively, forming a preliminary sample sheet. After the sample stage returns to 0°, the sample sheet is machined into a cantilever beam configuration.

[0032] 3. Sample Transfer: Adjust the relative positions of the nanorobotics and the sample sheet, weld them together using a W-shaped welding method, then cut the cantilever arm to quickly sever and separate the sample, extracting it. Adjust the tilt angle of the sample stage to 52°, with the copper pillar facing downwards. Insert the nanorobotics, readjust the relative positions of the nanorobotics and the copper pillar again, and weld the right side of the sample to the left end of the copper pillar using a tungsten layer, then cut off the tungsten needle. Adjust the sample stage orientation back to 0°, with the copper pillar facing upwards.

[0033] 4. Fine Refinement: During the thinning process, the thinning voltage and ion beam current are 30 kV and 0.23 nA, respectively. First, the tilt angle is set to 1°, and the front side of the sample is thinned (e.g., ...). Figure 1 When the sample is thinned to the point where the internal porous structure is visible (e.g.) Figure 2 Adjust the tilt angle to -1° and then thin the back side of the sample. Continue to reduce the ion beam current to 80 pA, thinning the sample to a thickness observable by transmission electron microscopy. To further improve the sample quality and observation effect, a method of gradually reducing the ion beam voltage is used to finely polish the sample. First, tilt the sample stage to ±3°, reduce the ion beam voltage and current to 5 kV and 15 pA respectively, and purge the front and back surfaces of the sample for 30 s each, repeating 2-3 times. Then, continue to tilt the sample stage to ±5°, reduce the ion beam voltage and current to 2 kV and 9 pA respectively, and purge the front and back surfaces of the sample for 1 min each, stopping as needed based on the actual condition of the sample to ensure that there is still a residual tungsten layer (e.g., Figure 3 This step removes the amorphous and damaged layers from the sample surface, preserving the sample's original structure and properties.

[0034] 5. Final Testing: The prepared TEM samples with porous structures undergo final testing, and the pore size is measured. TEM observation ensures the samples meet the testing requirements. If necessary, further post-processing or optimization can be performed on the samples to improve observation results.

Claims

1. A method for thinning porous samples using focused ion beam, characterized in that, Includes the following steps: S1. Sample pretreatment: Fix the TEM pore sample on the sample stage and cure the TEM pore sample with resin adhesive. S2, FIB Etching: In the FIB equipment, the porous sample is initially cut by precisely controlling the focused ion beam; S3. Sample transfer and cutting: Adjust the relative position of the nanorobot and the sample sheet, use W to weld to obtain the sample, adjust the tilt angle of the sample stage so that the copper column is facing down, enter the nanorobot, adjust the relative position of the nanorobot and the copper column again, use tungsten layer to weld the right side of the sample and the left end of the copper column together, and then cut off the tungsten needle. S4. Fine polishing: First, the front side of the sample is thinned to a certain extent to form a preliminary observation area. Then, the back side of the sample is thinned to a degree that can be observed by transmission electron microscopy. Finally, the observation area is cleaned and purged to obtain the TEM porous sample.

2. The method for thinning porous samples using focused ion beam according to claim 1, characterized in that, In step S1, fixing the pore sample on the sample stage includes the following steps: fixing the pore sample on the sample stage with conductive Cu adhesive, and wrapping the sample with conductive Cu adhesive.

3. The method for thinning porous samples using focused ion beams according to claim 1, characterized in that, In step S1, the resin curing process includes: coating the surface of the porous sample with an ion-thinning resin, wherein the ion-thinning resin is M-bond610 resin adhesive.

4. The method for thinning porous samples using focused ion beams according to claim 1, characterized in that, S2 includes the following steps: S201. Tilt the sample stage to 52° and deposit a tungsten layer. Set the electron beam voltage to 20-30 kV and the current to 80pA-0.79 nA. Deposit a tungsten layer with a thickness of 3-4 μm on the target processing area of ​​the porous sample as a protective layer. S202. Select a large ion beam with voltage and current of 20~30kV and 9.3-27 nA respectively, and process deep pits on the upper and lower sides and the left side of the tungsten coating. S203. At sample stage tilt angles of 50° and 54° respectively, cross-sectional shaping is performed on the upper and lower edges of the tungsten layer to obtain a wedge-shaped sample sheet with an initial observation area. S204. After the sample stage returns to 0°, the sample sheet is processed into a cantilever beam state.

5. The method for thinning porous samples using focused ion beam according to claim 1, characterized in that, S3 includes the following steps: S301. Adjust the relative positions of the nano-manipulator and the sample sheet, use W to weld, then cut the cantilever arm to quickly cut and separate the sample and extract the sample. S302. Adjust the tilt angle of the sample stage to 52° so that the copper pillar is facing downwards; S303, use the nano-manipulator, readjust the relative positions of the nano-manipulator and the copper column, use a tungsten layer to weld the right side of the sample and the left end of the copper column together, and then cut off the tungsten needle; S304. Adjust the sample stage orientation back to 0° so that the copper pillar is facing upwards.

6. The method for thinning porous samples using focused ion beam according to claim 1, characterized in that, S4 includes the following steps: S401. First, set the tilt angle to 1° and thin the front side of the sample. S401. Adjust the tilt angle to -1° and thin the back of the sample.

7. The method for thinning porous samples using focused ion beam according to claim 6, characterized in that, During the thinning process, the thinning voltage and ion beam current are 20-30 kV and 0.08nA-0.23nA, respectively.

8. The method for thinning porous samples using focused ion beam according to claim 7, characterized in that, S4 also includes further reducing the ion beam current to 24-80 pA to thin the sample to a thickness observable by transmission electron microscopy.

9. The method for thinning porous samples using focused ion beam according to claim 8, characterized in that, S4 also includes a method of gradually reducing the ion beam voltage to perform fine polishing of the sample.

10. The method for thinning porous samples using focused ion beam according to claim 9, characterized in that, First, tilt the sample stage to ±3°, reduce the ion beam voltage and current to 5-10 kV and 15-30 pA respectively, and purge the front and rear surfaces of the sample for 10-30 s each, repeating 2-3 times. The sample stage was then tilted to ±5°, and the ion beam voltage and current were reduced to 1-3 kV and 5-10 pA, respectively. The front and rear surfaces of the sample were then purged for 10-60 seconds each.

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