Preparation method of thin film transmission sample

Abstract

The invention relates to the technical field of thin film transmission samples, and discloses a thin film transmission sample preparation method which comprises the following steps: selecting a dense metal thin film of a silicon substrate prepared by physical vapor deposition as a thin film sample, cutting the thin film sample, and cleaning with absolute ethyl alcohol; adhering the film surface of the film sample to a glass sheet, adhering the glass sheet to a sample grinding device, exposing one side of the silicon substrate of the film sample, and grinding and thinning the silicon substrate on abrasive paper according to an 8-shaped path; the thin film sample polished in the second step is taken down from the glass sheet, and secondary polishing and thinning are carried out after cleaning, the plane transmission sample of the thin film sample can be prepared, the defect that only the cross section transmission area is observed in a focused ion beam and opposite bonding mode is overcome, meanwhile, the demand quantity of the sample is small, and the utilization rate of the sample is greatly increased; a two-step grinding mode is adopted for a brittle film sample, and the risk that the brittle sample is broken in the grinding process can be effectively avoided.

Description

Technical Field

[0001] The invention relates to the technical field of thin film transmission samples, and in particular to a method for preparing a thin film transmission sample. Background Art

[0002] With the continuous upgrading of my country's manufacturing industry, aerospace, precision manufacturing, and navigation technology have achieved great development, and higher and higher requirements have been put forward for the mechanical properties, wear resistance, corrosion resistance and other aspects of the material surface. High-performance film is one of the effective technical means to improve the service performance of the material surface. The film can be used as a gold-plated layer, optical reflection layer, etc. for daily necessities such as tool coatings and watch cases, and has a wide range of application value. Non-toxic ceramic films also have important application value in medical fields such as orthopedics and dentistry. Such films are generally prepared by physical vapor deposition-magnetron sputtering, and the thickness of the film is generally several hundred nanometers. This puts forward higher requirements for the preparation of transmission samples. The films prepared by magnetron sputtering, especially nitride films, have high hardness and poor toughness. When the thickness drops to a certain extent, it is very easy to break and cannot meet the requirements of transmission electron microscopy sample preparation. Generally, one of the methods for preparing transmission samples of thin films is to glue the film surfaces together, and use diamond cutting to cut the sample into a thin slice with a thickness of about 0.5 mm, and glue the copper support ring to the sample, and manually grind and ion thin to the final thickness. The second method is to use a focused ion beam to prepare a transmission cross-sectional sample, but the cost is relatively high. Although both of the above methods can prepare transmission samples, the samples prepared are all cross-sectional samples. And although the cost of ion thinning and bonding samples is reduced, the requirements for the bonding position and the area during thinning are relatively high. If the thin area during thinning offsets the film bonding position, it is impossible to accurately prepare the transmission sample of the cross-sectional area. Both methods cannot prepare planar transmission samples, and the traditional double-spray thinning for preparing planar samples is not suitable for the preparation of thin film transmission samples. On the one hand, it is difficult to control the corrosion area and depth, and the film is easily damaged. On the other hand, for thin films prepared on silicon wafer substrates, electrolytic double-spraying cannot be used for sample preparation.

[0003] In view of the above technical problems, the present invention proposes a method for preparing a brittle film plane transmission sample. The method mainly adopts the ion thinning method, which can be calibrated and thinned in a targeted manner for a special area of ​​the film, solving the problems of difficulty in preparing a brittle film plane transmission sample, low efficiency, and fragile samples. Summary of the invention

[0004] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a method for preparing a thin film transmission sample.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A method for preparing a thin film transmission sample comprises the following steps: Step 1: Select a dense metal film on a silicon substrate prepared by physical vapor deposition as a film sample, cut the film sample and clean it with anhydrous ethanol; Step 2: Glue the thin film surface of the thin film sample to a glass sheet, and then glue the glass sheet to a sample grinder to expose one side of the silicon substrate of the thin film sample, and grind and thin the silicon substrate with sandpaper in an "8" path; Step 3: Remove the film sample polished in step 2 from the glass sheet, clean it, and repeat the operation in step 2 for secondary polishing and thinning; Step 4: After washing and drying the film sample obtained in step 3, use a special resin for ion thinning to stick the film surface to a molybdenum support ring with an inner hole diameter of 1.5 mm; Step 5: After the resin is solidified, stick the molybdenum support ring on the glass sheet, and then stick the glass sheet on the sample grinder, and repeat the operation of step 2 to grind and thin again; Step 6: After cleaning the thin film sample obtained in step 5, the silicon substrate is thinned by ion thinning to obtain a thin film transmission sample.

[0006] Preferably, the thickness of the film sample selected in step 1 is 1 μm to 5 μm, and the size of the film sample after cutting is a 3 mm×3 mm square.

[0007] Preferably, when anhydrous ethanol is used to clean the surface of the film sample, ultrasonic cleaning can be used to remove oil stains such as coolant on the surface of the film sample.

[0008] Preferably, in step 2, the adhesive used to adhere the film surface of the film sample to the glass sheet includes hot melt adhesive and glue soluble in an organic solvent.

[0009] Preferably, in step 2, the adhesive used to adhere the film surface of the film sample to the glass sheet includes hot melt adhesive and glue soluble in acetone.

[0010] Preferably, the film surface of the film sample is adhered to a glass sheet using glue soluble in an organic solvent, and the glass sheet is adhered to a manual transmission sample grinder using an organic hot melt adhesive to maintain the parallelism of the sample. If the sample is not sensitive to temperature, the sample can be adhered to the glass sheet using hot melt adhesive.

[0011] Preferably, the sandpaper used in step 2 is of type 800#-3000#, and in step 2 the silicon substrate is ground to a thickness of 150-250 μm.

[0012] Preferably, in step 2, a grinder is used to grind the silicon substrate surface of the thin film sample. To prevent the thin film sample from breaking during the grinding process, a small grinder and SiC sandpaper are selected for step-by-step grinding. The SiC sandpaper models used are 800#, 1000#, 1500#, 2000#, and 3000#, respectively. The above-mentioned sandpaper models are used for step-by-step grinding, and the next-level sandpaper removes the wear marks of the previous-level sandpaper until the thickness of the silicon substrate is reduced to 150~200 μm.

[0013] Preferably, in step 3, the size of the sample grinder is smaller than that of the sample grinder used in step 2, and the sandpaper model is 1000#~5000#, until the substrate thickness is ground down to 30-50 μm.

[0014] Preferably, in step 4, when the selected ion thinning special resin is cured, a heating table can be used to heat and promote the curing, and the ion thinning special resin will not melt when heated again after curing.

[0015] Preferably, in step 5, after the resin glue of the thin film sample and the molybdenum support ring is cured, glue or hot melt adhesive is used to stick the thin film surface of the support ring to the glass sheet, and the glass sheet is stuck to a manual grinder with a model size smaller than the model size of the grinder used in steps 3 and 2.

[0016] Preferably, in step 5, a manual grinder is used to grind the silicon substrate surface on sandpaper. It should be noted that the silicon substrate is relatively thin at this time. If it is directly glued to a glass sheet for grinding, it is very easy to break during the grinding process or when sampling. Therefore, a molybdenum support ring is used for support to increase the success rate. In this step, a higher mesh sandpaper is used for grinding. The sandpaper models are 2000#, 3000#, and 5000#. The surface is ground to about 30μm, or until the edge of the sample is reduced by naked eye observation.

[0017] Preferably, in step 5, in order to prevent the support ring from being damaged due to a long thinning time of the silicon substrate, a molybdenum support ring with an inner hole diameter of 1.5 mm is selected instead of a copper support ring.

[0018] Preferably, in step 6, when cleaning the film sample obtained in step 5, since the film sample is relatively thin, in order to avoid breakage when taking it out, the glass sheet and the film sample are soaked in acetone at the same time until the film sample and the glass sheet fall off. During this process, ultrasonic cleaning is not used, and the use of sharp objects such as tweezers to damage the film sample is avoided.

[0019] Preferably, in step 6, the specific steps of thinning the silicon substrate by ion thinning are: S1: Place the molybdenum ring face down in the ion thinning fixture, and make the silicon substrate face up. Set the ion thinning voltage to 5-6 kV, and the angle of the ion gun to 10-12°. Thin the silicon substrate on one side until a hole is formed. S2: Adjust the ion thinning voltage to 4-5 kV, the ion gun angle to 8-10°, and thin for 30 min to expand the thin area; S3: Then the ion thinning voltage is adjusted to 3-4 kV, the ion gun angle is 6-8°, and the thinning area is further expanded; S4: Keep the thinning voltage at 3 kV, adjust the angles of at least two ion guns, one of which is at 0~8° and the other at -8~0°, and perform double-sided thinning on the thin area to obtain the thickness and area requirements of the thin area that meet the requirements of the transmission electron microscope.

[0020] The beneficial effects of the present invention are: 1. The present invention can prepare planar transmission samples of thin film samples, which makes up for the deficiency of focusing ion beam and adhering method that only observe the cross-sectional transmission area. At the same time, the demand for samples is small, which greatly improves the utilization rate of samples.

[0021] 2. The present invention adopts a two-step grinding method for brittle film samples, which can effectively avoid the risk of brittle samples breaking during the grinding process.

[0022] 3. The sample sticking method adopted by the present invention is simple and will not cause damage to the sample. The method for removing the hot melt adhesive is simple and will not cause residual contamination to the ion thinning equipment.

[0023] 4. The thin area and thickness of the brittle film sample prepared by the present invention meet the requirements of transmission electron microscopy observation. The thin area is larger and more regional morphologies can be collected. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the positions of the sample, support ring, and glass sheet when the sample is polished; Figure 2 This is a low-magnification planar TEM image of the magnetron sputtered Ni film; Figure 3 This is a high-magnification planar TEM image of the magnetron sputtered Ni film; Figure 4 This is the TEM image of the indentation plane of the magnetron sputtered CrCoNi film after nanoindentation deformation; Figure 5 This is a high-magnification planar TEM image of the indentation area of ​​the magnetron sputtered CrCoNi film; Figure 6 This is a low-magnification planar TEM image of magnetron sputtered HfNbTaTiZr film; Figure 7HRTEM image of magnetron sputtered HfNbTaTiZr film. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0026] Embodiment 1: This embodiment includes the following steps: Step 1: Cut small square pieces with a length and width of 3 mm from the Ni film sample on the magnetron sputtered silicon substrate using a diamond wire saw, and clean them in an ultrasonic cleaner with acetone and anhydrous ethanol for 15 min to remove surface oil and cutting coolant. The thickness of the Ni film here is 3 μm.

[0027] Step 2: Heat the glass slide and the sample grinder with an electric heating table, and use hot melt adhesive to stick the sample to the glass slide and the glass slide to the sample grinder. Here, stick one side of the sample film to the glass slide, exposing the silicon substrate side.

[0028] Step 3: Use a handheld grinder to grind on SiC sandpaper to reduce the thickness of the silicon substrate. The sandpaper models used are 800#, 1000#, 1500# and 2000#. Use an "8"-shaped path to grind step by step. The next sandpaper will remove the grinding marks of the previous one until the sample thickness is reduced to about 250 μm.

[0029] Step 4: Place the sample after the first polishing on the electric heating table, turn on the heating until the hot melt adhesive softens, remove the glass sheet and sample with tweezers, and place them in acetone for ultrasonic cleaning for 15 minutes until the residual hot melt adhesive around the sample is completely removed, then use anhydrous ethanol for ultrasonic cleaning again, and use a hair dryer to blow the sample dry.

[0030] Step 5: Use a special resin glue for ion thinning to stick the film surface to the support ring, select a molybdenum support ring with an inner hole diameter of 1.5 mm, and place the sample on a heating table for curing. The curing temperature is 60 °C and the curing time is 8 h.

[0031] Step 6. After the resin glue is cured, repeat step 2 and use hot melt glue to stick the molybdenum support ring to the glass sheet and stick the glass sheet to the handheld sample grinder. Use a smaller sample grinder and expose one side of the silicon substrate. The structure of the sample stuck to the glass sheet is as follows: Figure 1 shown.

[0032] Step 7. Repeat step 3 and use the "8" path to grind one side of the silicon substrate to continuously reduce the thickness of the silicon substrate. The sandpaper used here has a higher grit, such as 2000#, 3000# and 5000#, until the sample is ground to a thickness of 30~50 μm.

[0033] Step 8: Place the manually polished sample together with the sample stage on a heating table for heating until the hot melt adhesive melts, then remove the glass sheet and the sample, and soak the glass sheet together with the sample in acetone to avoid damaging the sample when removing it with tweezers.

[0034] Step 9. After the sample is detached from the glass sheet, remove it from the acetone, clean it with alcohol and blow it dry to ensure that there is no hot melt adhesive or contamination residue on the surface.

[0035] Step 10: Place the sample on the ion thinning fixture with the molybdenum support ring facing downward and the silicon substrate facing upward, and place the fixture in the ion thinning equipment.

[0036] Step 11: Set the ion thinning voltage parameter to 5 kV and the ion gun angle to 12°, and perform single-sided thinning on the center position of one side of the silicon substrate.

[0037] Step 12: After the hole is thinned, thin for 20 minutes to expand the hole, change the parameters, set the voltage parameter to 4 kV, the ion gun angle to 10°, and the thinning time to 30 minutes to expand the thin area of ​​the sample.

[0038] Step 13. Subsequently, the electron gun voltage parameters are adjusted to 3 kV, and the ion gun angle is 8°, and further thinning of the thin area is carried out for 15 minutes. After that, while keeping the voltage unchanged, the angles of the two ion guns are adjusted, one of which has an angle of 8° and the other has an angle of -8°, and double-sided thinning is carried out for 15 minutes. At this time, the silicon substrate in the thin area has been completely removed, and the thin area is further polished and thinned to improve the quality.

[0039] Embodiment 2: This embodiment includes the following steps: Step 1: Select a CrCoNi film sample of a magnetron sputtered silicon substrate with a film thickness of 3 μm, cut a square block with a length and width of 3 mm using a diamond wire cutting machine, and clean it in an ultrasonic cleaning machine with acetone and anhydrous ethanol for 15 minutes to remove surface oil and cutting coolant. Use nanoindentation to perform a multi-point nanoindentation experiment at any edge position, keep the indentation parameters consistent, and the indentation depth is 300 nm. This embodiment is to observe the structural characteristics after deformation.

[0040] Step 2 to step 4 are the same as in Example 1.

[0041] Step 5: glue the sample onto the molybdenum support ring using a special resin for ion thinning. Different from Example 1, in this example, one edge of the nano-pressed sample is placed in the middle of the molybdenum support ring, and a gap is reserved in the support ring to facilitate positioning during ion thinning.

[0042] Steps 6 to 12 are the same as in Example 1.

[0043] Step 13. The difference between this embodiment and embodiment 1 is that in order to observe the structural features of the indentation deformation area, it is necessary to avoid removing the indentation area during the thinning process. Therefore, in this embodiment, the final double-sided thinning time is reduced to 5 minutes to obtain complete morphological features of the indentation area.

[0044] Embodiment 3: This embodiment includes the following steps: Step 1: Select a HfNbTaTiZr thin film sample on a magnetron sputtered silicon substrate with a thickness of 2 μm, cut a square piece with a length and width of 3 mm using a diamond wire saw, and clean it in an ultrasonic cleaner with acetone and anhydrous ethanol for 15 minutes to remove surface oil and cutting coolant.

[0045] Steps 2 to 10 are the same as those in Example 1. The difference from Example 1 is that the film in this example is more brittle and is prone to cracking during the thinning process. Therefore, in order to reduce damage to the sample, in Steps 11 to 13, the electron gun angle is adjusted to 10°, and the parameters are adjusted immediately after the hole is exited, the voltage is changed to 4 kV, the ion gun angle is 8°, the thinning is performed for 30 minutes, the thinning area is expanded, and then the thinning is performed for 20 minutes at a voltage of 3 kV and an ion gun angle of 6°, and the thinning is performed at an angle of ±6° for 20 minutes, which can effectively avoid the breakage of the brittle film sample.

[0046] The microstructure and performance of the TEM films prepared in Examples 1 to 3 of the present invention were characterized. Figure 2~Figure 7 shown.

[0047] The present invention discloses a method for preparing a brittle film transmission sample. The substrate is thinned by mechanical grinding, a support ring and single-sided ion thinning, so that a plane transmission sample of a magnetron sputtered film can be obtained. By adjusting the process parameters of mechanical grinding and ion thinning, the breakage of the brittle film sample during the grinding process can be avoided, and the integrity of the sample is retained. In addition, the indentation after deformation in a nano-indentation experiment can be observed, thereby reducing the cost of using a focused ion beam and ion thinning.

[0048] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a thin film transmission sample, characterized in that: The following steps are involved: Step 1: Select a dense metal film on a silicon substrate prepared by physical vapor deposition as a film sample, cut the film sample and clean it with anhydrous ethanol; Step 2: Glue the thin film surface of the thin film sample onto a glass sheet, and then glue the glass sheet onto a sample grinder to expose one side of the silicon substrate of the thin film sample. Grind and thin the silicon substrate using sandpaper in an "8" path. Step 3: Remove the film sample polished in step 2 from the glass sheet, clean it, and repeat the operation in step 2 for secondary polishing and thinning; Step 4: After washing and drying the film sample obtained in step 3, use a special resin for ion thinning to stick the film surface to a molybdenum support ring with an inner hole diameter of 1.5 mm; Step 5: After the resin is solidified, stick the molybdenum support ring on the glass sheet, and then stick the glass sheet on the sample grinder, and repeat the operation of step 2 to grind and thin again; Step 6: After cleaning the thin film sample obtained in step 5, the silicon substrate is thinned by ion thinning to obtain a thin film transmission sample.

2. A method for preparing a thin film transmission sample according to claim 1, characterized in that: The thickness of the film sample selected in step 1 is 1 μm~5 μm, and the size of the film sample after cutting is a 3 mm×3 mm square.

3. A method for preparing a thin film transmission sample according to claim 1, characterized in that: In step 2, the adhesive used to adhere the film surface of the film sample to the glass sheet includes hot melt adhesive and glue dissolved in an organic solvent.

4. The method for preparing a thin film transmission sample according to claim 1, characterized in that: The sandpaper used in step 2 is of type 800#~3000#, and in step 2 the thickness of the silicon substrate is ground down to 150-250 μm.

5. The method for preparing a thin film transmission sample according to claim 1, characterized in that: In step 3, the size of the sample grinder is smaller than that used in step 2, and the sandpaper model is 1000#~5000#, until the substrate thickness is ground down to 30-50μm.

6. A method for preparing a thin film transmission sample according to claim 1, characterized in that: In step 6, the specific steps of thinning the silicon substrate by ion thinning are: S1: Place the molybdenum ring face down in the ion thinning fixture, and make the silicon substrate face up. Set the ion thinning voltage to 5-6 kV, and the angle of the ion gun to 10-12°. Thin the silicon substrate on one side until a hole is formed. S2: Adjust the ion thinning voltage to 4-5 kV, the ion gun angle to 8-10°, and thin for 30 min to expand the thin area; S3: Then adjust the ion thinning voltage to 3-4 kV and the ion gun angle to 6-8° to further expand the thinning area; S4: Keep the thinning voltage at 3 kV, adjust the angles of at least two ion guns, one of which is at 0~8° and the other at -8~0°, perform double-sided thinning on the thin area to obtain the thickness and area requirements of the thin area that meet the requirements of the transmission electron microscope.

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