Focused ion beam ultrathin section sample preparation pretreatment method for wafer sample

Abstract

The invention relates to a focused ion beam ultrathin section sample preparation pretreatment method for a wafer sample, and belongs to the technical field of wafer material microscopic experiments. The wafer sample preparation pretreatment method provided by the invention comprises the following steps: (1) depositing a metal oxide on the surface of a wafer sample by adopting an atomic layer deposition technology to obtain an ALD layer; (2) coating a curing glue solution on the surface of the ALD layer, and curing to obtain a curing glue layer; and (3) plating a conductive protection layer on the surface of the cured adhesive layer to finish sample preparation pretreatment. The sample preparation pretreatment method disclosed by the invention can well solve the problems of irradiation damage and deformation of a fine structure which is not resistant to electron beam irradiation, curtain effect in a cutting process, unobvious structural boundary in a shooting process and the like in focused ion beam ultrathin section sample preparation, and has good application prospects in the technical field of wafer material microscopic experiments. And the practical value is very high.

Description

Technical Field

[0001] The invention relates to the technical field of wafer material microscopic experiments, and in particular to a focused ion beam ultrathin sectioning sample pretreatment method for wafer samples. Background Art

[0002] When focusing ion beam ultra-thin slices on certain delicate wafer structures that are not resistant to radiation, problems such as sample surface deformation caused by electron beam / ion beam radiation damage and thermal damage, surface fine structure damage, and inaccurate structure size measurement often occur. In addition, since the graphic structures contained in some semiconductor wafers are very small in size and the material contrast is relatively poor, especially some graphics composed of non-metallic materials, such as silicon oxide grooves or silicon grooves, the edge boundary contours of the groove sidewalls will be unclear during shooting, which greatly affects the accuracy of size measurement. When cutting these deep groove structures, the surface morphology of the sample is uneven or the material composition is different, which will cause differences in etching rates during ion beam cutting, resulting in vertical stripes (curtain effect) on the sample cut section, affecting the observation of the fine morphology of the sample section.

[0003] At present, in the process of focused ion beam ultra-thin sectioning of such wafer samples containing fine structures that are not resistant to radiation, in order to avoid electron beam / ion beam radiation damage and structural deformation, a conductive protective layer is often plated under electron beam or ion beam induction through a dual-beam focused ion beam device. However, electron beam / ion beam radiation damage will also occur during the electron beam / ion beam induced plating of the protective layer, and a very high temperature will also be generated on the surface of the wafer, causing thermal damage to the material. In addition, it is difficult for the conductive protective layer to fully fill the deep groove structure, which makes it easy to produce large scratches during cutting, and the effect is not ideal.

[0004] Therefore, developing a sample preparation pretreatment scheme that can overcome the existing problems of surface deformation, surface fine structure damage, inaccurate structure size measurement, etc. of focused ion beam ultrathin section samples and improve the measurement accuracy of fine structure size has high practical value in microscopic experiments of wafer materials that are not resistant to radiation. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a focused ion beam ultrathin sectioning sample pretreatment method for wafer samples. The pretreatment method provided by the present invention is applied to the dual-beam focused ion beam ultrathin sectioning sample preparation, making the sample flatter and the wafer fine structure not deformed. When photographing, the fine structure morphology is clear and the boundaries are obvious, which significantly improves the measurement accuracy of the fine structure size.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] In a first aspect, the present invention provides a method for preprocessing a wafer sample by focused ion beam ultrathin sectioning, comprising the following steps:

[0008] (1) using atomic layer deposition technology to deposit metal oxide in a target sample preparation area of ​​a wafer sample to obtain an ALD layer;

[0009] (2) coating a curing adhesive solution on the surface of the ALD layer and curing the solution to obtain a curing adhesive layer;

[0010] (3) A conductive protective layer is plated on the surface of the cured adhesive layer to complete the sample preparation pretreatment of the wafer sample.

[0011] In advanced process wafer manufacturing, wafers with fine structures that are not resistant to electron beam irradiation are prone to surface structure deformation, curtain effect, unclear microstructure boundaries, etc. during focused ion beam slicing and sample preparation due to electron beam / ion beam irradiation damage and thermal damage of the focused ion beam, resulting in inaccurate subsequent observation and measurement results. The focused ion beam ultra-thin slicing sample preparation pretreatment method for wafer samples provided by the present invention aims to solve the problems of irradiation damage to fine structures that are not resistant to electron beam irradiation, deformation of fine structures, curtain effect during cutting, and unclear structure boundaries during shooting.

[0012] The sample preparation pretreatment method of the present invention specifically combines the method of metal oxide ALD+thermal curing glue coating+conductive protective layer plating, firstly, the metal oxide ALD coating is carried out, then the curing glue is coated on the coating for curing, and finally the conductive protective layer is plated on the formed curing glue layer. Among them, the function of the ALD layer is to prevent the electron beam / ion beam from damaging the wafer surface; in addition, the difference in contrast between metal oxide and non-metallic materials, organic materials, etc. in the transmission electron microscope can make the boundary of the wafer fine structure in the transmission electron microscope more obvious; the function of the glue coating is to ensure sufficient filling, flatten the sample surface, reduce the curtain effect, and prevent the electron beam / ion beam from damaging the wafer surface; the function of the conductive protective layer plating is to prevent the curing glue layer from being severely damaged by the electron beam / ion beam during cutting, thereby bending the wafer surface structure and deforming it.

[0013] According to the pretreatment scheme provided by the present invention, three protective layers of atomic layer deposition (ALD) layer + curing glue layer + conductive protective layer can be obtained in the target sample preparation area of ​​the wafer sample in sequence, and the synergistic effect ensures that the subsequent sample preparation process will not damage any protective layer of the previous step. Without the curing glue layer, the fine structure of the wafer will be damaged; without the ALD layer, the boundary of the fine structure of the wafer in the transmission electron microscope is not clear, making it difficult to measure accurately.

[0014] The pretreatment scheme of the present invention is used to process fine wafer structure samples that are not resistant to electron beam irradiation. During the focused ion beam slicing sample preparation process, the structure of the target sample preparation area will not be damaged, and it is conducive to subsequent shooting. However, the commonly used treatment method in the prior art of using a focused ion beam device to plate a conductive protective layer under the induction of an electron beam or an ion beam will cause radiation damage and structural deformation of fine wafer structure samples that are not resistant to radiation, and the cutting effect is not ideal.

[0015] The present invention improves the sample preparation method of focused ion beam slicing of fine wafer structures that are not resistant to radiation in the prior art by introducing the method of ALD layer + glue coating + conductive layer plating in the sample preparation pretreatment, so that the fine structure morphology is clear and the boundaries are obvious during shooting, and the measurement accuracy of the fine structure size is significantly improved. It has high application value in applications such as wafer material microscopic measurement experiments.

[0016] As a preferred solution, before pretreatment, a diamond pen is used to split the target area of ​​the wafer to obtain a wafer sample of appropriate size, and the target area is observed to confirm that there is no damage. A picture is kept for subsequent confirmation of the sample preparation position before starting pretreatment.

[0017] Preferably, in step (1), the metal oxide includes at least one of hafnium oxide and aluminum oxide.

[0018] Preferably, in step (1), the thickness of the ALD layer is ≤15 nm.

[0019] Preferably, in the atomic layer deposition technology, the temperature is controlled below 100°C and the deposition cycle is 20-50 times. The deposition thickness on the surface of the wafer sample needs to determine the number of deposition cycles according to different test requirements. After the deposition is completed, the wafer sample is placed in a dust-free environment with tweezers to cool and standby to avoid contamination of the wafer sample surface due to manual operation errors.

[0020] Preferably, in step (2), the curing glue solution comprises thermal curing carbon glue and acetone, and the volume ratio of the thermal curing carbon glue to acetone is (0.8-1): (0.8-1).

[0021] Further preferably, the volume ratio of the thermal curing carbon adhesive to acetone is 0.8:1.

[0022] When the volume ratio of the curing adhesive solution is moderate, the fluidity is good, the filling is sufficient, and the damage to the fine structure of the wafer is smaller.

[0023] Preferably, in step (2), the coating thickness of the curing glue solution is 200-500 nm.

[0024] Preferably, in step (2), the method for coating the curing adhesive solution is spin coating, the rotation speed used in the spin coating method is 8000-9000 r / min, and the spin coating time is more than 60 s.

[0025] Preferably, in step (2), the curing condition is baking at 100° C. for 20-30 min.

[0026] Preferably, in step (3), before the conductive protective layer is plated on the surface of the cured adhesive layer, silver glue and gold are first applied to the edge of the wafer sample. The purpose of this step is to enhance the conductivity of the sample after glue coating and ensure that the surface of the wafer sample has sufficient conductivity.

[0027] Preferably, in step (3), the components of the conductive protective layer include at least one of Pt, C and W.

[0028] As a preferred solution, the conductive protective layer is composed of at least one of Pt and W. The damage of the C-plated protective layer is more obvious, while the W-plated and Pt-plated layers can provide better protection, and the efficiency of the plating is higher and the required time is shorter.

[0029] Preferably, the step (3) specifically comprises: plating a first conductive protective layer on the surface of the cured adhesive layer, and then plating a second conductive protective layer on the surface of the first conductive protective layer.

[0030] Further preferably, in the step (3), the first conductive protective layer is plated by an electron beam induction method, and the second conductive protective layer is plated by an ion beam induction method.

[0031] Further preferably, the thickness of the first conductive protective layer is 190-500 nm, and the thickness of the second conductive protective layer is 290-1000 nm.

[0032] As a preferred solution, the voltage of the electron beam induction method is 30 kV and the current is 11 nA; the voltage of the ion beam induction method is 30 kV and the current is 80 pA-0.23 nA.

[0033] The purpose of plating the first conductive protective layer under electron beam induction is to prevent the deformation of the cured glue caused by ion beam irradiation damage: compared with the traditional ion beam induced conductive protective layer plating method, first plating a protective layer under electron beam induction can ensure that the cured glue in the target area of ​​the sample will not deform or bulge under the initial contact of the ion beam, thereby improving the accuracy of the sample preparation area and ensuring that the cured glue under the plating layer will not be damaged.

[0034] In a second aspect, the present invention provides the use of the above-mentioned wafer sample focused ion beam ultrathin section sample preparation pretreatment method in focused ion beam section sample preparation. The wafer sample focused ion beam ultrathin section sample preparation pretreatment method is mainly aimed at the pretreatment improvement of focused ion beam ultrathin section sample preparation.

[0035] As a preferred solution, after completing the sample preparation pretreatment of the wafer of the present invention, the treated target sample preparation area is dug out and transferred to a copper mesh for thinning to 100-150nm; then the sample stage is rotated to 57-60° to perform low-voltage cleaning on the target sample preparation area to avoid scratches caused by too long a time; after obtaining a wafer sample slice with a thickness of 20-50nm, subsequent slicing and transmission electron microscopy (TEM) photography are performed. The thinning parameters are voltage 30kV, current 0.23-0.79nA; the low-voltage cleaning parameters are voltage 5-8kV, current 63pA-0.12nA.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The present invention optimizes the sample preparation pretreatment means of wafer samples in the prior art, and by combining the pretreatment method of metal oxide ALD deposition layer + thermal curing glue coating + conductive protective layer plating and the target sample preparation area of ​​the processed wafer sample, the sample of focused ion beam ultra-thin section can be made flatter; and under the protection of the protective layer, the fine structure of the wafer will not be deformed, thereby ensuring the accuracy of the analysis result; the metal oxide deposited by the ALD technology has a different contrast with the non-metallic material of the semiconductor wafer, so that the fine structure morphology in the wafer sample is clearer and the boundary is more obvious during subsequent shooting, which greatly improves the measurement accuracy of the fine structure size; the present invention solves the problems of sample surface deformation, surface fine structure damage, inaccurate structure size measurement, etc. caused by electron beam / ion beam radiation damage and thermal damage when focusing ion beam ultra-thin sectioning is performed on certain radiation-intolerant fine wafer structures in the prior art, and has high practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a photographic effect diagram of a sample after being processed by the focused ion beam ultrathin sectioning sample pretreatment method for wafer samples in Example 1 of the present invention;

[0039] Figure 2 This is a photographic effect diagram of a sample after being processed by the focused ion beam ultrathin sectioning sample pretreatment method for wafer samples in Example 2 of the present invention;

[0040] Figure 3 This is a photographic effect diagram of a sample after being processed by the focused ion beam ultrathin sectioning sample pretreatment method for wafer samples in Example 3 of the present invention;

[0041] Figure 4 This is a photograph of the sample after being processed by the focused ion beam ultrathin sectioning sample pretreatment method of the wafer sample in Comparative Example 2. DETAILED DESCRIPTION

[0042] In order to better illustrate the purpose, technical scheme and advantages of the present invention, the present invention will be further described below in conjunction with specific examples. The test methods used in the following examples are conventional methods unless otherwise specified; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0043] Example 1

[0044] An embodiment of the method for pretreating wafer samples by focused ion beam ultrathin sectioning of the present invention is as follows:

[0045] S1. Use a diamond pen to split the target area of ​​the wafer sample to obtain a 4×4 cm wafer sample. Observe under an electron microscope (OM) to confirm that the target sample preparation area is not damaged, and keep a picture for subsequent confirmation of the sample preparation position.

[0046] S2. A layer of metal oxide film is deposited on the surface of the obtained wafer sample split using atomic layer deposition technology: the metal oxide component is hafnium oxide, the process temperature is controlled below 65°C, and the deposition cycle is repeated 25 times to obtain a 5nm thick hafnium oxide film layer, which is the ALD layer, deposited on the wafer surface. After the deposition is completed, use tweezers to place the wafer sample in a dust-free environment for cooling and standby use.

[0047] S3. Glue coating: Use M-Bond thermosetting carbon glue and prepare a thermosetting carbon glue solution with a volume ratio of thermosetting carbon glue to acetone of 0.8:1; use a spin coater to coat the glue, set the parameters to a speed of 8000r / min, and spin coat the thermosetting carbon glue solution on the ALD layer for more than 60s until the cured glue is fully filled to obtain an organic layer with a thickness of 300nm; transfer the spin-coated wafer sample to a thermal processing platform and bake it at 90℃ for 25min to fully cure the carbon glue to obtain a cured glue layer.

[0048] S4. Fix the wafer sample completed in S3 onto the sample stage with carbon tape, apply silver glue on the edge of the sample, and then evaporate gold 2-3 times in a gold plating machine.

[0049] S5. Plating a W conductive protective layer: The target sample preparation area of ​​the wafer sample that has undergone the above steps is plated with a W conductive protective layer with a thickness of 200±10nm under the induction of an electron beam with a voltage of 30kV and a current of 11nA, which is the first conductive protective layer; and then, using an ion beam as a carrier, a W conductive protective layer with a thickness of 300±10nm is plated on the first conductive protective layer under the induction of an ion beam with a voltage of 30kV and a current of 0.23nA, which is the second conductive protective layer, thereby completing the sample preparation pretreatment of the wafer described in this embodiment.

[0050] Example 2

[0051] The focused ion beam ultrathin sectioning sample pretreatment method of the wafer sample in Example 2 is different from that in Example 1 only in that, in step S3, a heat-curing carbon glue solution having a volume ratio of heat-curing carbon glue to acetone of 1:1 is prepared.

[0052] Example 3

[0053] The focused ion beam ultrathin sectioning sample pretreatment method for wafer samples in Example 3 is different from that in Example 1 only in that, in step S3, a heat-curing carbon glue solution is prepared with a volume ratio of heat-curing carbon glue to acetone of 1:0.8.

[0054] Example 4

[0055] The focused ion beam ultrathin sectioning sample pretreatment method for wafer samples in Example 4 is different from that in Example 1 only in that, in step S5, the materials of the first and second conductive protective layers are both C material.

[0056] Example 5

[0057] The focused ion beam ultrathin sectioning sample pretreatment method for wafer samples in Example 5 is different from that in Example 1 only in that, in step S5, the materials of the first and second conductive protective layers are both Pt materials.

[0058] Comparative Example 1

[0059] The difference between Comparative Example 1 and Example 1 is that steps S2 to S4 are not performed, and only the conductive protective layer plating process of step S5 is performed.

[0060] Comparative Example 2

[0061] The difference between Comparative Example 2 and Example 1 is that the glue coating process in step S3 is not performed.

[0062] Comparative Example 3

[0063] The difference between Comparative Example 3 and Example 1 is that the atomic deposition layer technology treatment in step S2 is not performed.

[0064] Effect Example 1

[0065] In order to explore the application effect of the focused ion beam ultrathin sectioning sample preparation pretreatment method of the wafer sample provided by the present invention in the focused ion beam ultrathin sectioning sample preparation, the following experiment was carried out:

[0066] The round crystal samples treated by the pretreatment method in the embodiment and the comparative example are thinned and then photographed: the target sample preparation area of ​​the treated wafer sample is dug out and transferred to a copper mesh, and thinned with a voltage of 30 kV and a current of 0.23-0.79 nA. After thinning to 100-150 nm, a smaller voltage (5-8 kV) and a smaller current (63 pA-0.12 nA) are used, the sample stage is rotated to 57-60°, and the target sample preparation area is cleared at low voltage for 15-20 s to obtain a wafer sample slice with a thickness of 20-50 nm, and double-beam focused ion beam slicing and subsequent transmission electron microscopy (TEM) photography are performed, and the shooting effect is observed.

[0067] The photographic effect of the sample after being processed by the focused ion beam ultrathin sectioning sample pretreatment method of the wafer sample in Example 1 of the present invention is as follows: Figure 1 ; It can be seen that the sliced ​​sample is flat and the fine structure on the wafer sample is not deformed. The fine structure morphology in the photographed wafer sample is clear and the boundaries are obvious, which can improve the measurement accuracy of the fine structure size;

[0068] The photographing effects of the samples after being processed by the focused ion beam ultrathin sectioning sample pretreatment method of the wafer sample in Examples 2 and 3 of the present invention are as follows: Figure 2 , 3 It can be seen that by changing the volume ratio of the heat-cured carbon glue on the basis of Example 1, the fluidity and filling effect change, and the fine structure of the wafer is damaged to varying degrees. By comparing Examples 1-3, it can be seen that the volume ratio of the heat-cured carbon glue is appropriately small, which can improve the fluidity, facilitate full filling, and reduce the damage to the fine structure of the wafer.

[0069] By comparing the photographing effects of the samples after being treated by the focused ion beam ultrathin sectioning sample pretreatment method of the wafer samples in Examples 1, 4, and 5 of the present invention, it can be seen that in Example 4, the C protective layer is plated, and the damage to the fine structure of the wafer is more obvious; in comparison, the use of W and Pt conductive protective layers can have a better protection effect, and the efficiency during plating is higher and the time required is shorter.

[0070] From the photographic results of the sample after being treated by the sample preparation pretreatment method in Comparative Example 1, it can be seen that direct coating under the induction of electron beam causes electron irradiation to cause severe deformation of the fine structure, resulting in the collapse of the groove structure.

[0071] The photographic effect of the sample after the sample preparation pretreatment method of comparative example 2 is as follows Figure 4 , it can be seen that the fine structure of the wafer sample is obviously damaged.

[0072] From the photographic results of the samples after the sample preparation pretreatment method in Comparative Example 3, it can be seen that the boundary of the wafer fine structure in the transmission electron microscope is not obvious and is difficult to measure accurately; this is because the contrast of the fine structure and the cured adhesive layer in the transmission electron microscope is similar and difficult to distinguish.

[0073] In summary, by adopting the focused ion beam ultrathin sectioning sample pretreatment method of wafer sample provided by the present invention, three layers of protection of ALD layer, curing glue layer and conductive protective layer are obtained in sequence. Under the synergistic protection, the sample preparation method of focused ion beam ultrathin sectioning of fine wafer structure that is not resistant to radiation in the prior art is improved, so that the fine structure morphology is clear and the boundaries are obvious during shooting, which significantly improves the measurement accuracy of fine structure size, and has high application value in applications such as wafer material microscopic measurement experiments.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A focused ion beam ultrathin sectioning sample pretreatment method for wafer samples, characterized in that: The following steps are involved: (1) using atomic layer deposition technology to deposit metal oxide in a target sample preparation area of ​​a wafer sample to obtain an ALD layer; (2) coating a curing adhesive solution on the surface of the ALD layer and curing the solution to obtain a curing adhesive layer; (3) A conductive protective layer is plated on the surface of the cured adhesive layer to complete the sample preparation pretreatment of the wafer sample.

2. The method for preparing a wafer sample by focused ion beam ultrathin sectioning according to claim 1, characterized in that: In the step (1), the metal oxide includes at least one of hafnium oxide and aluminum oxide.

3. The method for preparing a wafer sample by focused ion beam ultrathin sectioning according to claim 1, characterized in that: In the step (1), the thickness of the ALD layer is ≤15 nm.

4. The method for preparing a wafer sample by focused ion beam ultrathin sectioning according to claim 1, characterized in that: In the step (2), the curing glue solution includes thermal curing carbon glue and acetone, and the volume ratio of the thermal curing carbon glue to acetone is (0.8-1): (0.8-1).

5. The method for preparing a wafer sample by focused ion beam ultrathin sectioning according to claim 1, characterized in that: In the step (2), the coating thickness of the curing glue solution is 200-500nm.

6. The method for preparing a wafer sample by focused ion beam ultrathin sectioning according to claim 1, characterized in that: In the step (3), the component of the conductive protective layer includes at least one of Pt, C, and W.

7. The method for preparing a wafer sample by focused ion beam ultrathin sectioning according to claim 1, characterized in that: The step (3) specifically comprises: plating a first conductive protective layer on the surface of the cured adhesive layer, and then plating a second conductive protective layer on the surface of the first conductive protective layer.

8. The method for preparing a wafer sample by focused ion beam ultrathin sectioning according to claim 7, characterized in that: In the step (3), the first conductive protective layer is plated by an electron beam induction method, and the second conductive protective layer is plated by an ion beam induction method.

9. The method for preparing a wafer sample by focused ion beam ultrathin sectioning according to claim 7, characterized in that: The thickness of the first conductive protective layer is 190-500 nm, and the thickness of the second conductive protective layer is 290-1000 nm.

10. Use of the focused ion beam ultrathin sectioning sample preparation pretreatment method of wafer samples as claimed in claims 1 to 9 in focused ion beam sectioning sample preparation.

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