A method for improving the morphology quality of focused ion beam (FIB) etching

Abstract

The embodiment of the present application relates to a kind of methods for improving the appearance quality of focused ion beam FIB etching, comprising: making mask layer on the sample to be etched;The sample to be etched is fixed on FIB etching pedestal;During FIB etching, the FIB etching pedestal is heated, and rotation is carried out in horizontal plane or non-horizontal plane, so that the sample to be etched is rotated at multiple angles, and the same or different FIB etching time is kept at each rotation angle;During FIB etching or after FIB etching, the sample to be etched is etched auxiliary;Remove the mask layer.

Description

Technical Field

[0001] This invention relates to the field of semiconductor processing technology, and in particular to a method for improving the morphology quality of focused ion beam (FIB) etching. Background Technology

[0002] Focused ion beam (FIB) etching is an important nanofabrication technique widely used in semiconductors, optics, materials science, and other fields. It uses a focused ion beam to process the sample surface, achieving nanoscale etching and morphology control. FIB etching technology features high resolution, high precision, and high controllability, enabling precise device analysis, sample repair, device modification, and in-situ observation.

[0003] The key component of FIB etching technology is the ion beam column. The ion beam column consists of an ion source, a focusing system, and a scanning system. The ion source generates the ion beam, the focusing system focuses and concentrates the ion beam, and the scanning system controls the movement of the ion beam across the sample surface. By adjusting the ion beam's energy, flux density, scanning mode, and etching parameters, morphological etching, material removal, and pattern definition of the sample can be achieved.

[0004] FIB etching technology utilizes the interaction between ions and atoms on the sample surface to achieve etching. The bombardment energy of the ion beam removes atoms from the solid surface of the sample, thus achieving etching. Compared with traditional photolithography, FIB etching offers higher resolution and more flexible processing capabilities.

[0005] FIB etching technology has wide applications in device analysis and nanofabrication. It can be used to create nanoscale patterns, channels, and pathways for morphological control and structural repair of samples. Furthermore, FIB can be combined with other characterization techniques, such as scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), to achieve in-situ observation, elemental analysis, and measurement of device properties.

[0006] However, FIB etching technology also has some challenges and limitations. In particular, it suffers from shortcomings in processing large-area samples, including efficiency, uniformity, and the perpendicularity and flatness of the etched sidewall structures that can cause sample damage. These shortcomings include increased surface roughness, sidewall chamfering, bevels, and sidewall ripple structures (such as...). Figure 1 As shown in the figure, there is still room for improvement in the quality control of etching morphology. Summary of the Invention

[0007] The purpose of this invention is to provide a method for improving the morphology quality of focused ion beam (FIB) etching. This method can improve the control of the etched surface quality, has good area expansion, and good lateral accuracy, resulting in a smoother sidewall structure of the etched sample.

[0008] Therefore, embodiments of the present invention provide a method for improving the morphology quality of focused ion beam (FIB) etching, characterized in that the method includes:

[0009] A mask layer is fabricated on the sample to be etched;

[0010] The sample to be etched is fixed on the FIB etching base;

[0011] During the FIB etching process, the FIB etching base is heated and rotated in a horizontal or non-horizontal plane, so that the sample to be etched rotates at multiple angles, and the same or different FIB etching time is maintained at each rotation angle.

[0012] During or after FIB etching, the sample to be etched is subjected to auxiliary etching.

[0013] Remove the mask layer.

[0014] Preferably, the method for fabricating a mask layer on the sample to be etched includes:

[0015] Perform surface treatment on the sample to be etched;

[0016] A mask material is prepared for the surface-treated sample to be etched; the mask material is an oxide and / or a nitride, and the preparation method includes physical vapor deposition (PVD) and / or chemical vapor deposition (CVD);

[0017] A mask pattern is prepared on the mask material using photolithography.

[0018] Preferably, the heating temperature of the FIB etching substrate is 20℃-250℃.

[0019] More preferably, the heating temperature of the FIB etching substrate is 50℃-100℃.

[0020] Preferably, the multi-angle rotation in the horizontal or non-horizontal plane specifically means: rotating continuously in the horizontal or non-horizontal plane, or rotating intermittently in the horizontal or non-horizontal plane, and staying at each rotation position for the same or different time.

[0021] Preferably, the FIB etching base rotates in a horizontal or non-horizontal plane, causing the sample to be etched to rotate. During the rotation, the angle between the upper surface of the sample to be etched and the horizontal plane is maintained within ±15°; the angle between the ion beam and the upper surface of the sample to be etched is between 75° and 105°.

[0022] Preferably, the auxiliary etching includes: electron beam assisted etching (EBIE), low-energy ion beam assisted etching (LEIBAE), gas assisted etching (GAE), or dark electron implantation (DFEI).

[0023] The method for improving the morphology quality of focused ion beam (FIB) etching provided in this invention can effectively reduce surface damage through a mask layer; heating the FIB etching substrate can reduce surface damage, increase the etching rate, and improve the surface morphology; furthermore, heating can change the interaction between the ion beam and the sample, optimizing the etching effect; multi-angle rotation etching can improve the accuracy of lateral etching, making the sidewall structure of the etched sample smoother and reducing the generation of sidewall ripples. Attached Figure Description

[0024] Figure 1 An electron microscope image of the sidewall ripple structure that appears in FIB etching in the prior art;

[0025] Figure 2 This is a flowchart of a method for improving the morphology quality of focused ion beam (FIB) etching according to an embodiment of the present invention.

[0026] Figure 3 This is an electron microscope image of the FIB etching process in an embodiment of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0028] This invention provides a method for improving the morphology quality of focused ion beam (FIB) etching, the main steps of which are as follows: Figure 2 As shown, it includes:

[0029] Step 110: Create a mask layer on the sample to be etched.

[0030] First, the sample to be etched undergoes surface treatment. This treatment ensures a clean and smooth sample surface, removing contaminants and particles. Conventional wafer cleaning methods can be used, including ultrasonic cleaning and solvent cleaning. After cleaning, the sample is dried.

[0031] Then, a mask material is prepared on the surface-treated sample to be etched; the mask material can be selected according to the sample to be etched, and it should have good etching resistance. Preferably, oxides and / or nitrides are used as masks, and the preparation methods include physical vapor deposition (PVD) and / or chemical vapor deposition (CVD);

[0032] Finally, a mask pattern is fabricated on the mask material using photolithography.

[0033] Since FIB etching utilizes an ion source to accelerate and focus an ion beam into an incident beam, a mask layer can effectively reduce damage to the etched surface. In practice, the mask material can be selected based on the material to be etched in the sample.

[0034] Step 120: Fix the sample to be etched onto the FIB etching base.

[0035] The base can be set horizontally or at a certain angle to the horizontal direction, so that the sample to be etched is horizontal or at a certain angle to the horizontal direction.

[0036] Step 130: During the FIB etching process, the FIB etching substrate is heated and rotated in a horizontal or non-horizontal plane, so that the sample to be etched rotates at multiple angles, and the same or different FIB etching time is maintained at each rotation angle.

[0037] The heating temperature of the FIB etching substrate is 20℃-250℃, more preferably 50℃-100℃. In practice, the characteristics of the sample to be etched and the etching requirements determine the choice of heating temperature. For example, if high-precision etching is required, a relatively low heating temperature is needed to reduce positional drift caused by thermal expansion of the sample.

[0038] Heating the FIB etching substrate can reduce surface damage, increase etching rate, and improve the morphology of the etched surface. In addition, for some specific materials, heating can also change the interaction between the ion beam and the sample, thereby optimizing the etching effect.

[0039] The aforementioned rotation in a horizontal or non-horizontal plane specifically refers to: rotating continuously in a horizontal or non-horizontal plane, or rotating intermittently in a horizontal or non-horizontal plane, and staying at each rotation position for the same or different amounts of time.

[0040] Since FIB etching utilizes an ion source to accelerate and focus an ion beam as the incident beam, high-energy ions collide with atoms on the solid surface, sputtering and stripping away solid atoms to achieve etching. Therefore, by rotating at multiple angles, the incident beam can be more evenly distributed across the entire surface of the sample to be etched. This avoids the problems of uneven etching and sidewall ripple structures caused by the Gaussian distribution of ions within the focused beam spot concentrating towards the center.

[0041] The purpose of rotating the sample in the horizontal or non-horizontal plane is to allow for multi-angle rotation of the sample to be etched. If the surface of the FIB etching base supporting the sample is set at an angle to the horizontal plane, the FIB etching base can rotate in the horizontal plane; if the surface of the FIB etching base supporting the sample is set along the horizontal plane, the base needs to rotate in a non-horizontal plane. This is because, as the etching depth increases, the taper of the etched cross-section gradually increases, resulting in tilted sidewalls. By rotating the sample at multiple angles, the angle of ion beam incident on the sample can be tilted, reducing the deviation between the cross-sectional taper and the incident angle, thereby obtaining vertical sidewalls and further eliminating sidewall ripple structures.

[0042] In one specific embodiment of the present invention, the FIB etching substrate is configured not to rotate within a horizontal plane. The upper surface of the FIB etching substrate has a horizontal structure and is initially positioned horizontally. The angle between the tilt angle during rotation and the horizontal plane is within ±15°. The sample to be etched is tilted and fixed on the upper surface of the FIB etching substrate. During rotation, the angle between the upper surface of the sample to be etched and the horizontal plane remains within ±15°; the angle between the ion beam and the upper surface of the sample to be etched is between 75° and 105°.

[0043] In another specific embodiment of the invention, the FIB etching substrate is set to rotate in a horizontal plane. The upper surface of the FIB etching substrate has an inclined structure, and the angle between the inclined angle and the horizontal plane is within 15°. The sample to be etched is fixed on the inclined upper surface of the FIB etching substrate. During rotation, the angle between the upper surface of the sample to be etched and the horizontal plane remains within 15°; the angle between the ion beam and the upper surface of the sample to be etched is between 75° and 105°.

[0044] Furthermore, by adjusting the process to maintain a continuous uniform rotation speed, or to pause at different positions for different durations, it is possible to more flexibly match the actual needs of sample etching.

[0045] Step 140: During or after FIB etching, perform auxiliary etching on the sample to be etched.

[0046] Assisted etching methods may include, as needed:

[0047] Electron Beam Assisted Etching (EBIE): During FIB etching, an electron beam is used simultaneously for auxiliary etching. The electron beam can provide additional energy and momentum to promote the interaction between the ion beam and the sample, accelerate the etching rate, and improve the surface and edge quality of the etched material.

[0048] Low-energy ion beam assisted etching (LEIBAE): In the FIB etching process, a low-energy ion beam is introduced to assist etching. The low-energy ion beam can improve the etching rate and etching quality and reduce surface damage through effects such as surface activation, enhanced material diffusion, and localized heating.

[0049] Gas-assisted etching (GAE): In FIB etching, an appropriate gas is introduced as an aid to interact with the ion beam and alter the surface reaction kinetics. This can adjust the etching rate, control the etching morphology, and reduce or prevent sidewall or bottom deposition caused by ion beam etching.

[0050] Dark Field Electron Injection (DFEI): During FIB etching, a dark electron beam is injected into the sample surface to adjust the surface potential and charge state. This alters the interaction between the ion beam and the sample, regulating the etching rate and quality, and optimizing the etching results.

[0051] The specific applications of these auxiliary etching methods vary depending on the actual needs and the materials to be processed. They can improve the control performance, processing quality, and processing efficiency of the etching process, and expand the application scope of FIB technology. In practical applications, engineers can decide which auxiliary etching method to use and set the corresponding process parameters as needed.

[0052] Step 150: Remove the mask layer.

[0053] Depending on the choice of mask layer fabrication method, the appropriate method for removing the mask layer can be selected. Those skilled in the art are familiar with how to fabricate and remove mask layers, and will not be elaborated upon here.

[0054] Figure 3 This is an electron microscope image of the FIB etching process according to an embodiment of the present invention. It can be seen that the morphology of the etched surface has been improved.

[0055] The method for improving the morphology quality of focused ion beam (FIB) etching provided in this invention can effectively reduce surface damage through a mask layer; heating the FIB etching substrate can reduce surface damage, increase the etching rate, and improve the surface morphology; furthermore, heating can change the interaction between the ion beam and the sample, optimizing the etching effect; multi-angle rotation etching can improve the accuracy of lateral etching, making the sidewall structure of the etched sample smoother and reducing the generation of sidewall ripples.

[0056] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for improving the morphology quality of focused ion beam (FIB) etching, characterized in that, The method comprises: making a mask layer on the sample to be etched; fixing the sample to be etched on a FIB etching base; during the FIB etching process, heating the FIB etching base and rotating it in a horizontal plane or a non-horizontal plane, so that the sample to be etched is rotated at multiple angles and the FIB etching time is kept the same or different at each rotation angle; during the FIB etching process or after the FIB etching, performing auxiliary etching on the sample to be etched; removing the mask layer; wherein the heating temperature of the FIB etching base is 20-250℃, and the heating of the FIB etching base is used to improve the etching surface morphology; the multiple-angle rotation in the horizontal plane or the non-horizontal plane is used to reduce the generation of side wall ripple structure, specifically including: continuously rotating in the horizontal plane or the non-horizontal plane, or intermittently rotating in the horizontal plane or the non-horizontal plane and staying at each rotation position for the same or different time.

2. The method of claim 1, wherein, The method for making a mask layer on the sample to be etched comprises: surface treatment of the sample to be etched; mask material preparation after surface treatment of the sample to be etched; the mask material includes oxide and / or nitride, and the preparation method includes physical vapor deposition (PVD) and / or chemical vapor deposition (CVD); mask pattern preparation on the mask material using photolithography technology.

3. The method of claim 1, wherein, The heating temperature of the FIB etching base is 50-100℃.

4. The method of claim 1, wherein, The FIB etching base is rotated in a horizontal plane or a non-horizontal plane, so that the sample to be etched is rotated, and during the rotation, the included angle between the upper surface of the sample to be etched and the horizontal plane is kept within ±15°; the included angle between the ion beam and the upper surface of the sample to be etched is between 75° and 105°.

5. The method of claim 1, wherein, The auxiliary etching includes electron beam assisted etching (EBIE), low energy ion beam assisted etching (LEIBAE), gas assisted etching (GAE) or dark field electron injection (DFEI).

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