Method and system for rapidly preparing chip sample

Abstract

The invention provides a method for rapidly preparing a chip sample. The method comprises the following steps: S1, obtaining a target area of failure analysis; s2, directly bombarding the target area with laser to obtain a rough cut hole; s3, cutting the exposed surface of the rough cutting hole by using a focused ion beam to obtain an observation section; and S4, imaging the observation section by using an electron microscope, and judging whether the sample can obtain the cause of chip failure or not. The laser and the focused ion beam are cooperatively used for preparation, the overall time is greatly shortened, the sample preparation process can be further optimized due to the fact that time compression is achieved, the process evaluation and the sample preparation quality are enhanced, and higher reliability of failure analysis is facilitated; the system for rapidly preparing the chip sample provided by the invention has corresponding advantages.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor technology, and in particular relates to a method for rapidly preparing chip samples by comprehensively utilizing laser and focused ion beam and a corresponding system. Background Art

[0002] Cross-sectional analysis is one of the important areas of physical failure analysis. With the continuous reduction in the size of CMOS devices, sample preparation for physical failure analysis (PFA) has become more challenging and time-consuming. In the prior art, focused ion beam (FIB) and mechanical polishing are two ways to prepare samples. However, mechanical polishing can easily produce artificial defects due to mechanical force, especially in some advanced processes where the failure site of the sample is very small, and artificial defects can easily destroy the failure point, making it impossible to determine the cause of chip failure. Focused ion beam is a more accurate and non-invasive chip sample preparation method. It uses very high-energy ions such as gallium ions, then accelerates them using an electric field, and then uses an electrostatic lens to focus the high-energy gallium ions to a specified point, and then slices or otherwise processes the sample. Focused ion beams are widely used in chip sample preparation in the semiconductor industry, and are often used in conjunction with scanning electron microscopes to form dual-beam electron microscopes to achieve the purpose of processing and observing at the same time. The range of slicing by focused ion beam is generally tens of microns. When processing large-area sample cross-section slices or chips with thick covering layers such as thick metal layers, the sample preparation time is often very long due to the large cross-sectional slice area or the location of chip failure under the thick covering layer. At the same time, the sample preparation cost is also very high. If samples are to be prepared in batches, the use of FIB is limited by its excessively long working time, and its current practical application is limited.

[0003] Therefore, there is an urgent need to study a method for quickly preparing chip samples. Under the premise of meeting the requirements of failure analysis samples, when there is a need for sample preparation with a thicker covering layer and a larger cross-section, the sample preparation can be achieved at a reasonable cost and in a shorter time, so as to promote the optimization of failure analysis processes and the in-depth development of semiconductor technology. Summary of the invention

[0004] The present invention aims to solve all or part of the problems of the above-mentioned prior art. The present invention proposes a method for quickly preparing chip samples, which comprehensively utilizes laser technology and focused ion beam technology to prepare samples that meet the application requirements of failure analysis in a shorter time, and is suitable for practical applications of batch preparation of samples.

[0005] The present invention provides a method for rapidly preparing chip samples, comprising: step S1. obtaining a target area for failure analysis; step S2. directly bombarding the target area with a laser to obtain a rough cut hole; step S3. cutting the surface exposed by the rough cut hole with a focused ion beam to obtain an observation section; step S4. imaging the observation section with an electron microscope to determine whether the sample can obtain the cause of chip failure. The sample is prepared by using laser and focused ion beam, and the uneven problem of flat physical failure analysis can be effectively dealt with by first using laser to process the surface after determining the target area, and thicker covering layers that are not needed in sample preparation can be removed. For example, in the sample preparation requirement of a large piece of metal, there is no need to use expensive focused ion beam or other processes to spend a lot of time to process the metal layer; the rough cut hole can be quickly obtained by laser, which can meet the sample requirements and greatly shorten the preparation process time compared to the sample preparation relying solely on the focused ion beam process, and the sample obtained by further cutting the focused ion beam based on the obtained rough cut hole can obtain a higher cross-sectional imaging quality.

[0006] The step S1 includes: marking the position where there may be a problem; selecting a position as the target area based on the mark; imaging the target area after the step S2, and judging whether the target area needs to be reselected according to the imaging result; if the position of the target area needs to be changed, after changing the position of the target area, returning to the step S2 and re-executing.

[0007] By marking the suspected problem area and selecting a position as the target area, the laser can be used for bombardment. After the rough cut, the target area can be imaged at any stage to confirm the current state of the target area. If the rough cut is too deep or penetrates the target area, making it impossible to perform subsequent processing, the target area can be replaced in time and bombarded with laser again. The entire time can be further compressed, which is not only more efficient, but also more flexible in sample preparation. Selecting the appropriate stage for imaging evaluation can further ensure the sample quality and the reliability of failure analysis.

[0008] The method for obtaining the target area includes but is not limited to performing detection to obtain marks of suspicious positions; the detection method includes electrical testing, scanning acoustic microscope CSAM (C-mode Scanning Acoustic Microscope), micro-light microscope EMMI (Emission Microscope), and infrared microscope for marking. For chips, generally, after the chip parameters are abnormally measured electrically, the chip sample preparation analysis is performed to confirm the cause of failure, that is, failure analysis. The methods of electrical testing and analysis include but are not limited to: OBIRCH (voltage is added to detect current changes), TIVA (current is added to detect voltage changes), and VBA (voltage is added to detect voltage changes). In the method of preparing samples by a single focused ion beam FIB, it is necessary to accurately position first, and then FIB is used for cutting. Because the working time of FIB cutting is very long, if the positioning is not accurate, the time for rework and sample preparation is long. When the problem area is difficult to locate, the area is relatively large or there are many, a large area sample preparation is required to confirm the position, so the speed of sample preparation is limited.

[0009] The method for obtaining a rough cut hole comprises: presetting a depth threshold of the rough cut hole; adjusting the power and spot size of the laser; bombarding the target area with a laser while observing the target area with an optical microscope; and controlling the hole depth to be within the depth threshold.

[0010] Between step S2 and step S3, the following steps are performed: imaging the rough cut hole, obtaining the depth and opening width of the rough cut hole according to the imaging result, and evaluating whether to re-execute step S2. It is determined whether the rough cut hole is sufficient, and if the depth or opening width is insufficient, step S2 is promptly re-executed.

[0011] In step S4, if the cause of chip failure cannot be obtained by imaging the observation cross section, the process returns to step S2 and steps S2 to S4 are executed again.

[0012] In the step S3, current parameters and voltage parameters are preset; the observation section is cut according to the current parameters and voltage parameters; wherein the current parameters and voltage parameters are set based on material characteristic parameters of the target area, and the characteristic parameters include strength.

[0013] On the other hand, the present invention also provides a rapid chip sample preparation system for executing the rapid chip sample preparation method of the present invention, comprising a dual-beam electron microscope module and a laser rough cutting module; the dual-beam electron microscope module is used to perform focused ion beam cutting on the rough cut opening to obtain the observation section and image; the laser rough cutting module comprises a display device for displaying imaging results and measurement results; a workbench for carrying and moving the chip for alignment; a laser marking device and a microscope group arranged above the workbench for performing laser rough cutting and synchronously observing the target area.

[0014] Compared with the prior art, the main beneficial effects of the present invention are:

[0015] The present invention provides a method for rapidly preparing chip samples. The method first uses a laser to bombard the target area, and then performs focused ion beam refinement to obtain an observation cross section. The overall time is greatly shortened by using laser and focused ion beam preparation. Since the time compression is achieved, the sample preparation process can be further optimized, and the process evaluation can be strengthened to improve the quality of sample preparation, which is conducive to higher reliability of failure analysis. The rapid chip sample preparation system provided by the present invention has the corresponding advantages of the method of the present invention through an independently arranged dual-beam electron microscope module and a laser rough cutting module, and can separate the process steps, which is particularly conducive to mass preparation of samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of a method for rapidly preparing chip samples by combining laser and focused ion beam according to an embodiment of the present invention.

[0017] Figure 2 Schematic diagram of the structure of the laser rough cutting module in an embodiment of the present invention.

[0018] Figure 3 Schematic diagram of the process of preparing chip samples in an embodiment of the present invention.

[0019] FIG. 4( a ) and FIG. 4( b ) are images of rough cut openings provided in an embodiment of the present invention.

[0020] Figure 5 This is an image of the target area to be FIBed provided in an embodiment of the present invention.

[0021] FIG. 6( a ) and FIG. 6( b ) are observation cross-sectional images obtained after FIB according to an embodiment of the present invention.

[0022] FIG. 7( a ) and FIG. 7( b ) are observation cross-sectional images obtained after FIB according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The technical solutions in the specific embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0024] In the embodiment of the present invention, Figure 1 The method for rapidly preparing chip samples exemplified includes: step S1. obtaining the target area for failure analysis; step S2. directly bombarding the target area with a laser to obtain a rough cut hole; step S3. cutting the surface exposed by the rough cut hole with a focused ion beam to obtain an observation section; step S4. imaging the observation section with an electron microscope to determine whether the sample can obtain the cause of chip failure. Rough cut holes can be quickly obtained by laser, which can meet the sample requirements and greatly shorten the preparation process time compared to preparing samples only by relying on the focused ion beam process. In addition, the sample obtained by further cutting the rough cut hole obtained by the focused ion beam can obtain a higher imaging quality.

[0025] The example step S1 includes: conducting electrical testing and analysis on the chip to determine whether it is abnormal. If it is abnormal, combining other testing methods to mark the problem area; selecting a position as the target area based on the mark. The methods of electrical testing and analysis include but are not limited to: OBIRCH (applying voltage to detect current changes), TIVA (applying current to detect voltage changes), and VBA (applying voltage to detect voltage changes). Problem area marking test methods include but are not limited to scanning acoustic electron microscope CSAM (C-mode Scanning Acoustic Microscope), micro-light electron microscope EMMI (Emission Microscope), and infrared electron microscope testing. In the example case, the target area is obtained according to the mark. The specific situation is not limited here.

[0026] In this embodiment, the method for obtaining a rough cut hole includes: presetting a depth threshold of the rough cut hole; adjusting the power and spot size of the laser; bombarding the target area with the laser while observing the target area with an electron microscope; and controlling the hole depth to be within the depth threshold. By controlling the pulse frequency, energy, and spot size of the laser, and observing through an electron microscope while punching, the power and spot size of the laser are adjusted to prevent the hole from being punched too deep.

[0027] like Figure 2As shown, a rapid chip sample preparation system is also provided in this embodiment, which is used to perform the rapid chip sample preparation method of this embodiment, including a dual-beam electron microscope module and a laser rough cutting module; the dual-beam electron microscope module (not shown) is used to perform focused ion beam cutting on the rough cut opening to obtain the observation section and image; the laser rough cutting module includes a display device 1 for displaying the imaging results and measurement results; a workbench 2 for carrying and moving the chip C for alignment; a laser marking device 3 and a microscope group 4 arranged above the workbench 2 for laser rough cutting and synchronous observation of the target area. The microscope group 4 is connected to the display device 1 in communication. In this embodiment, a PD-2000Pro laser marker is used, and the exemplary laser process parameters are: a green laser with a laser wavelength of 532nm, a mode of HighEnergy, an energy level of 70%, a high light energy of 2.5mJ, and a Single Shot (times) of 10.

[0028] Figure 3 In the case of the example, the process of rapid sample preparation is as follows: electrical testing and analysis of the chip is performed to confirm chip abnormality, and the problem area is marked by corresponding detection equipment such as a scanning acoustic electron microscope to obtain the target area, i.e., step S1; after obtaining the rough cut hole, the target area is imaged (to determine whether the laser rough cut meets the requirements, whether there is a situation where the hole is too deep or penetrated). Between step S2 and step S3, the following is also performed: imaging the rough cut hole, obtaining the depth and opening width of the rough cut hole according to the imaging results, and evaluating whether to re-execute step S2. Direct imaging after rough cutting is mainly used to confirm whether the depth or width is sufficient, or whether it is over-done, so as to determine whether step S3 can be performed. In some embodiments, the target area is marked incorrectly at the beginning, or the laser is off-position and does not hit the target area. In other cases, the rough cut hole is too deep or even penetrated. When these situations require the re-selection of a new target area for laser bombardment, it is not appropriate to continue the FIB fine-tuning process, and then return to step S1 to re-operate. In step S4, if the cause of chip failure cannot be obtained by observing the cross section for imaging, the process returns to step S2 and steps S2 to S4 are executed again.

[0029] Partial examples of the rough cut opening imaging photos obtained in this embodiment are shown in Figures 4(a) and 4(b). In this embodiment, the BF (Bright field) bright field observation method is adopted, the image type is a color snapshot, and the image size (pixel) is 1200×1200. Referring to Figure 4(a), the image size (μm) is 194×194, the objective lens adopts the Olympus plan semi-apochromatic polarizing objective lens MPLFLN10XBDP, the zoom is 10X, and the total magnification is 1400X. Referring to Figure 4(b), the image size (μm) is 271×271, the objective lens adopts the Olympus plan semi-apochromatic polarizing objective lens MPLFLN10XBDP, the zoom is 7.1X, and the total magnification is 1000X.

[0030] The width of the rough cut opening obtained in this embodiment can be 34.5 microns, 41.41 microns, 42 microns, 43.9 microns, 44.4 microns, etc. The length of the rough cut opening can be 142.2 microns, 144.3 microns, 145.5 microns, etc.

[0031] In some embodiments, in step S3, current parameters and voltage parameters are preset; the observation section is obtained by cutting according to the current parameters and voltage parameters; wherein the current parameters and voltage parameters are set based on the characteristic parameters of the material of the target area. In the example, the characteristic parameter selects the strength of the material. In general, the material of the target area is divided into dielectric material and metal material. The current parameters and voltage parameters set for metal materials with high strength are also higher. However, the positive correlation between strength and parameter setting is not limited. In some actual situations, the parameter setting is adjusted according to the progress of cutting. It is not necessarily that the current parameters and voltage parameters are higher when the intensity is greater. If the setting is too high, the required section may not be obtained. The specific situation is not limited here. From another perspective, this is also the advantage of combining laser rough cutting and FIB in this embodiment. When the target area has a thicker covering layer, such as metal material, the laser can be used to remove the layer first. In this way, the current parameters and voltage parameters are set more flexibly in step S3, and they do not have to be set particularly high. It not only reduces energy consumption but also saves the working time of FIB.

[0032] Figure 5 The target area image to be refined by FIB is illustrated, where FIB1 marks a position for refinement, and FIB2 marks another position for refinement. The example parameters for FIB are voltage 2.0kV and current 0.1nA. Combined with the observation cross-sectional imaging results of FIB1 shown in reference Figures 6(a) and 6(b). The position of FIB1 illustrated in Figures 6(a) and 6(b) is a cross-sectional image obtained by FIB after laser rough cutting of the layer (thick metal). The thickness of different layers is marked in Figure 6(b): 4.382μm, 150.6nm, 438.2nm, 684.8nm. It can be seen that the method for rapid preparation of chip samples in this embodiment can achieve rapid removal of metal layers and rapid sample preparation, and the general sample preparation speed can be increased by more than 30%. The position of FIB2 illustrated in Figures 7(a) and 7(b) is a large-area cross-sectional image. It can be seen that the method for rapid preparation of chip samples in this embodiment can effectively meet the sample preparation requirements of large-area cross sections.

[0033] In order to facilitate the description, some common English nouns or letters used in the present invention are only used for exemplary reference rather than restrictive interpretation or specific usage, and the protection scope of the present invention should not be limited by their possible Chinese translations or specific letters.

Claims

1. A method for rapidly preparing chip samples, characterized in that: include: Step S1. Obtaining the target area for failure analysis; Step S2. directly bombarding the target area with a laser to obtain a rough cut hole; Step S3. Cutting the surface exposed by the rough cut hole with a focused ion beam to obtain an observation cross section; Step S4: Use an electron microscope to image the observation section to determine whether the sample can obtain the cause of chip failure.

2. The method for rapidly preparing chip samples according to claim 1, characterized in that: The step S1 includes: Marking locations where problems may occur; selecting a location as the target area based on the marking; After step S2, the target area is imaged, and it is determined whether the target area needs to be reselected according to the imaging result. If the position of the target area needs to be changed, after the position of the target area is changed, the process returns to step S2 and is executed again.

3. The method for rapidly preparing chip samples according to claim 1, characterized in that: The method of acquiring the target area includes but is not limited to performing detection to obtain marks of suspicious locations; the detection method includes electrical testing, scanning acoustic microscope testing, low-light microscope testing, and infrared imaging microscope testing.

4. The method for rapidly preparing chip samples according to claim 1, characterized in that: The method for obtaining a rough cut hole comprises: presetting a depth threshold of the rough cut hole; adjusting the power and spot size of the laser; bombarding the target area with a laser while observing the target area with an optical microscope; and controlling the hole depth to be within the depth threshold.

5. The method for rapidly preparing chip samples according to claim 4, characterized in that: Between step S2 and step S3, the following is further performed: imaging the rough cut hole, obtaining the depth and opening width of the rough cut hole according to the imaging result, and evaluating whether to execute step S2 again.

6. The method for rapidly preparing chip samples according to claim 1, characterized in that: In step S4, if the cause of chip failure cannot be obtained by imaging the observation cross section, the process returns to step S2 and steps S2 to S4 are executed again.

7. The method for rapidly preparing chip samples according to any one of claims 1 to 6, characterized in that: In the step S3, current parameters and voltage parameters are preset; the observation section is cut according to the current parameters and voltage parameters; wherein the current parameters and voltage parameters are set based on material characteristic parameters of the target area, and the characteristic parameters include strength.

8. A system for rapidly preparing chip samples, characterized in that: Used to perform the rapid chip sample preparation method according to any one of claims 1 to 7, comprising a dual-beam electron microscope module and a laser rough cutting module; The dual-beam electron microscope module is used to perform focused ion beam cutting on the rough cut hole to obtain the observation section and image it; The laser rough cutting module comprises: A display device, used to display imaging results and measurement results; A workbench, used to carry and move the chip for alignment; The laser marking equipment and microscope group arranged above the workbench are used for performing laser rough cutting and synchronously observing the target area.

Images