Preparation method of cross-section samples

Abstract

The present invention discloses a method for preparing a cross-sectional sample, comprising: step one, forming a first mark for coarse positioning. Step two, measuring the relative distance between the first mark and the target structure on the chip sample. Step three, forming a plurality of FIB marks for fine positioning according to the relative distance, the FIB marks comprising second to fifth marks. The second mark and the third mark extend along the Y direction and are distributed on both sides of the target structure along the X direction. The fourth mark extends along the X direction and is located at a first prompt distance on the upstream side of the target structure in the Y direction. The fifth mark comprises a flush structure flush with the X-direction extension section of the target structure and a first and second straight line connected to the flush structure and located on the upstream side of the flush structure. Step four, performing sample preparation grinding, comprising: grinding until the fourth mark is observed. Grinding is continued until the flush structure of the fifth mark is observed. The present invention can achieve efficient point-to-point preparation of cross-sectional samples and can achieve efficient point-to-point analysis.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a semiconductor integrated circuit, in particular to a method for preparing a cross-section sample. Background Art

[0002] In order to find the root cause of chip failure, it is necessary to prepare cross-sectional samples that locate specific structures in failure analysis. Unlike conventional planar sample preparation, there is no cross-sectional layout reference when preparing cross-sectional samples. Engineers need to manually grind the samples, which makes it difficult to locate the target position of the cross section from the millimeter-level sample to the nanometer-level cross-sectional target position. Figure 1 The figure shows a schematic diagram of a plane layout of an existing chip sample; the chip sample 101 is relatively large in size. Figure 1 FIG. 1 shows a chip sample 101 having a length of 30.0 mm and a width of 1.2 mm; a target structure for failure analysis is located in region 102 a; Figure 1 , an enlarged view of region 102a is further shown, and the target structure is further located in region 102b within region 102a; Figure 1 102b, the target structure is further located in region 102c within region 102b. The size of region 102c is nanometer-scale, which is a million times smaller than that of chip sample 101. Figure 1 Only the plan view is shown, which has a layout; however, there is no layout reference on the cross section. If a cross-sectional sample corresponding to area 102c is to be obtained, it is difficult to achieve if only the engineer manually grinds and controls, and the success rate of sample preparation is low.

[0003] Furthermore, existing, inaccurate positioning marks have large errors and are of limited help in sample positioning. The target structure can easily be missed during the grinding process, leading to sample preparation failure. Preparing cross-section samples for fixed-point analysis requires repeated use of a scanning electron microscope (SEM) to confirm position during the grinding process, resulting in low sample preparation efficiency. Therefore, a method is needed to improve the success rate and efficiency of preparing fixed-point cross-section samples. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing cross-sectional samples, which can realize efficient fixed-point preparation and efficient fixed-point analysis of cross-sectional samples, greatly improve the success rate of sample preparation and shorten the sample preparation time.

[0005] To solve the above technical problems, the present invention provides a method for preparing a cross-section sample, comprising:

[0006] Step 1: forming a first mark for coarse positioning on the chip sample.

[0007] Step 2: Measure the relative distance between the first mark and the target structure on the chip sample, including a first X-direction distance and a first Y-direction distance; the Y-direction is the sample preparation and grinding direction, and the X-direction and the Y-direction are perpendicular.

[0008] Step three: forming a plurality of FIB marks for fine positioning according to the relative distance between the first mark and the target structure, wherein the FIB marks include a second mark, a third mark, a fourth mark and a fifth mark.

[0009] The second mark and the third mark are linear structures extending along the Y direction and are distributed on both sides of the target structure along the X direction. The second mark and the third mark are used to locate the position of the target structure in the X direction.

[0010] The fourth mark is a straight line structure extending along the X direction; the fourth mark is located on the upstream side of the target structure along the Y direction and there is a first prompt distance between the fourth mark and the target structure in the Y direction, and the first prompt distance is used to indicate that the target position corresponding to the target structure is about to be reached during sample preparation and grinding; the upstream side is the side that is ground first during the sample preparation and grinding process.

[0011] The fifth mark is formed by connecting multiple line segments, including a flush structure flush with the X-direction extension of the target structure and a first straight line and a second straight line connected to the flush structure, wherein the flush structure is a vertex or a straight line; the first straight line and the second straight line are both connected to the flush structure, and the first straight line and the second straight line are both located on the upstream side of the flush structure.

[0012] Step 4: preparing and grinding the chip sample to form a cross-sectional sample, including:

[0013] The sample preparation and grinding is started on the upstream side of the fourth mark until the fourth mark is observed.

[0014] The sample preparation and grinding is continued until the flush structure of the fifth mark is observed, and the first straight line and the second straight line of the fifth mark disappear simultaneously.

[0015] Further improvements include:

[0016] Step 5: Use SEM to confirm the position of the target structure on the cross-section sample.

[0017] Further improvements include:

[0018] Step 6: Perform positioning analysis on the target structure.

[0019] A further improvement is that, in step 1, the planar position of the target structure on the chip sample is roughly located with the help of a planar layout.

[0020] The first mark is formed at a selected position according to the planar position of the target structure.

[0021] The first mark is formed by using a laser cutter.

[0022] A further improvement is that, in step 1, the first mark is formed at a distance of 100 μm to 300 μm from the target structure.

[0023] The first mark is a rectangle with a side length of 10 μm to 20 μm.

[0024] A further improvement is that, in step 2, infrared rays are used to perform back-transmission imaging from the back side of the chip sample to measure the first X-direction distance and the first Y-direction distance.

[0025] A further improvement is that, in step three, the distance between the second mark and the target structure in the X direction is 10 μm to 20 μm; and the second mark and the third mark are symmetrical about the center of the target structure.

[0026] A further improvement is that, in step three, the first prompt distance is 2 μm to 3 μm.

[0027] A further improvement is that in step three, the fifth mark is in an inverted V shape, and the flush structure is a point.

[0028] A further improvement is that, in step 4, the sample preparation and grinding includes:

[0029] Grind coarsely.

[0030] When the grinding surface is 20 μm to 50 μm away from the fourth mark, the grinding surface is polished successively with diamond sandpaper from coarse to fine until the sample preparation grinding is completed.

[0031] A further improvement is that the particle size of the diamond sandpaper used for the rough grinding is greater than 30 μm.

[0032] The particle size of each diamond sandpaper used in the successive grinding of the grinding surface changes from coarse to fine and gradually changes from 30 μm to 0.1 μm.

[0033] A further improvement is that the chip sample includes a semiconductor device formed in an active area (AA) of a semiconductor substrate and a metal interconnection structure formed on top of the semiconductor device.

[0034] The first mark has a depth reaching the active region.

[0035] The depths of the second mark, the third mark, the fourth mark, and the fifth mark reaching the active region and penetrating into the active region are 5 μm to 10 μm.

[0036] A further improvement is that in step 2, the infrared ray used in the back transmission imaging is a laser with a wavelength of 1064 nm.

[0037] A further improvement is that, in step six, a nanoprobe tester (Nanoprober) is used to perform the positioning analysis.

[0038] A further improvement is that the positioning analysis includes SCM analysis.

[0039] The present invention utilizes coarse positioning on the plane of the chip sample and combines it with precise measurement of the distance between the first mark and the target structure, such as through back-transmitted imaging measurement, to form multiple precisely positioned marks on the chip sample. Subsequently, the finely positioned marks are utilized to achieve precise control of grinding during sample preparation and grinding, thereby enabling efficient, point-specific preparation of cross-sectional samples and greatly improving the success rate of sample preparation.

[0040] At the same time, the marks used to control sample preparation and grinding in the present invention can be directly observed using an optical microscope (OM) without the need for SEM observation. SEM observation is only required for confirmation after the sample preparation and grinding is completed. Since SEM observation is less efficient and more expensive, the present invention can also greatly improve sample preparation efficiency and save machine costs, and can shorten the sample preparation time by nearly half. Skilled engineers can shorten the sample preparation time to 2 days.

[0041] The marking of the cross-section sample prepared by the present invention can also facilitate positioning analysis, thereby enabling efficient fixed-point analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0043] Figure 1 This is a schematic diagram of the layout of an existing chip sample;

[0044] Figure 2 is a flow chart of a method for preparing a cross-section sample according to an embodiment of the present invention;

[0045] Figure 3A 1 is a schematic plan view of a chip sample after forming a first mark according to a method for preparing a cross-sectional sample according to an embodiment of the present invention;

[0046] Figure 3B 1 is a schematic plan view of a chip sample after forming the second to fifth marks according to the method for preparing a cross-sectional sample according to an embodiment of the present invention;

[0047] Figure 3C yes Figure 3B An enlarged view of the region where the second to fifth marks are formed;

[0048] Figure 4A It is a schematic plan view of the sample preparation and grinding to the fourth mark in the method for preparing a cross-section sample according to an embodiment of the present invention;

[0049] Figure 4B yes Figure 4A Corresponding cross-sectional schematic diagram;

[0050] Figure 5A It is a schematic plan view of the sample being ground to the flush structure of the fifth mark in the method for preparing a cross-section sample according to an embodiment of the present invention;

[0051] Figure 5B yes Figure 5A Corresponding cross-sectional schematic diagram;

[0052] Figure 6 1 is a schematic diagram of the cross-sectional structure of a chip product corresponding to the cross-sectional sample preparation method of an embodiment of the present invention when applied to the preparation of a cross-sectional sample of a chip product;

[0053] Figure 7A This is an optical microscope (OM) photograph of a chip sample after a first mark is formed when the cross-sectional sample preparation method of an embodiment of the present invention is applied to the preparation of a cross-sectional sample of a chip product;

[0054] Figure 7B The image of the chip sample observed on the meridian machine after the first mark is formed when the cross-sectional sample preparation method of the embodiment of the present invention is applied to the cross-sectional sample preparation of a chip product;

[0055] Figure 7C This is a SEM photograph of a chip sample after the second to fifth marks are formed when the cross-sectional sample preparation method of an embodiment of the present invention is applied to the preparation of a cross-sectional sample of a chip product;

[0056] Figure 8A This is an OM photograph of the cross-sectional sample preparation method of an embodiment of the present invention applied to the cross-sectional sample preparation of a chip product, when the sample is ground to the flush structure of the fifth mark;

[0057] Figure 8B This is an SEM photograph of the cross-sectional sample preparation method of an embodiment of the present invention applied to the preparation of a cross-sectional sample of a chip product, where the sample is ground to the level structure of the fifth mark;

[0058] Figure 9AThis is a surface topography photograph obtained by a nanoprobe tester when positioning and analyzing a target structure when the cross-sectional sample preparation method of an embodiment of the present invention is applied to the cross-sectional sample preparation of a chip product;

[0059] Figure 9B This is an SCM image obtained by a nanoprobe tester when positioning and analyzing a target structure when the cross-sectional sample preparation method of an embodiment of the present invention is applied to the cross-sectional sample preparation of a chip product. DETAILED DESCRIPTION

[0060] like Figure 2 FIG. 1 is a flow chart of a method for preparing a cross-sectional sample according to an embodiment of the present invention. The method for preparing a cross-sectional sample according to an embodiment of the present invention includes:

[0061] Step 1: Figure 3A As shown, a first mark 203 a for coarse positioning is formed on the chip sample 201 .

[0062] In the embodiment of the present invention, the planar position of the target structure 202 on the chip sample 201 is roughly located with the help of a planar layout.

[0063] A first mark 203a is formed at a selected position according to the planar position of the target structure 202. The selected position corresponding to the first mark 203a only needs to satisfy the coarse positioning and define the second mark 203b to the fifth mark 203e for subsequent fine positioning according to the result of the coarse positioning.

[0064] In some embodiments, the first mark 203a is formed by laser cutting.

[0065] The first mark 203 a is formed at a distance of 100 μm to 300 μm from the target structure 202 .

[0066] The first mark 203 a is a rectangle with a side length of 10 μm to 20 μm.

[0067] In the embodiment of the present invention, please refer to the following Figure 4B As shown, the chip sample 201 includes a semiconductor device formed in an active region of a semiconductor substrate 401 and a metal interconnection structure 402 formed on top of the semiconductor device.

[0068] The first mark 203a has a depth reaching the active region.

[0069] Figure 3A In FIG, the first mark 203a is also represented by Mark1.

[0070] Step 2: Figure 3AAs shown, the relative distance between the first mark 203a and the target structure 202 on the chip sample 201 is measured, including a first X-direction distance and a first Y-direction distance; the Y-direction is the sample preparation and grinding direction, and the X-direction and the Y-direction are perpendicular.

[0071] Figure 3A In the figure, the first X-direction distance is directly represented by X, and the first Y-direction distance is directly represented by Y.

[0072] In the embodiment of the present invention, infrared rays are used to perform back-transmission imaging from the back side of the chip sample 201 to measure the first X-direction distance and the first Y-direction distance.

[0073] In some embodiments, the infrared light used for back-transmission imaging is a laser with a wavelength of 1064 nm. Preferably, back-transmission imaging is performed directly on a meridian machine. Before performing back-transmission imaging, the backside of the chip sample 201 needs to be processed to a state that can be observed by the meridian machine. The meridian machine is equipped with a laser with a wavelength of 1064 nm. The 1064 nm laser is used to penetrate the base structure on the backside of the chip sample 201, such as a silicon substrate, to achieve imaging. The first X-direction distance and the first Y-direction distance are measured based on the imaging structure.

[0074] Step 3: Figure 3B As shown, a plurality of FIB marks for fine positioning are formed according to the relative distance between the first mark 203a and the target structure 202, and the FIB marks include a second mark 203b, a third mark 203c, a fourth mark 203d and a fifth mark 203e. The FIB marks are marks formed by FIB cutting.

[0075] The second mark 203b and the third mark 203c are linear structures extending along the Y direction and are distributed on both sides of the target structure 202 along the X direction. The second mark 203b and the third mark 203c are used to locate the position of the target structure 202 in the X direction.

[0076] Depend on Figure 3B It can be seen that the positions of the second mark 203b and the third mark 203c are both obtained through the first mark 203a. Figure 3B In FIG, the distance between the second mark 203 b and the first mark 203 a in the X direction is represented by X1, and the distance between the third mark 203 c and the first mark 203 a in the X direction is represented by X2; thus, the distance between the second mark 203 b and the target structure 202 in the X direction is X-X1; and the distance between the third mark 203 c and the target structure 202 in the X direction is X2-X.

[0077] In some embodiments, in step three, the distance between the second mark 203 b and the target structure 202 in the X direction is 10 μm to 20 μm; the second mark 203 b and the third mark 203 c are symmetrical about the center of the target structure 202 .

[0078] The fourth mark 203d is a straight structure extending along the X direction; the fourth mark 203d is located on the upstream side of the target structure 202 along the Y direction and there is a first prompt distance between the fourth mark 203d and the target structure 202 in the Y direction. The first prompt distance is used to prompt that the target position corresponding to the target structure 202 is about to be reached during sample preparation and grinding; the upstream side is the side that is ground first during the sample preparation and grinding process.

[0079] Figure 3B In the figure, the Y-direction position of the fourth mark 203d can be obtained through the first mark 203a. Figure 3B As shown in FIG. 2 , the distance between the fourth mark 203 d and the first mark 203 a in the Y direction is represented by Y1 , and the first prompt distance is Y1 −Y.

[0080] In some embodiments, the first prompt distance is 2 μm to 3 μm.

[0081] The fifth mark 203e is formed by connecting multiple line segments, including a flush structure flush with the X-direction extension segment of the target structure 202 and a first straight line and a second straight line connected to the flush structure, where the flush structure is a vertex or a straight line; the first straight line and the second straight line are both connected to the flush structure, and the first straight line and the second straight line are both located on the upstream side of the flush structure. Figure 3B In FIG. 2 , dashed line 302 indicates alignment between the alignment structure and the target structure 202 .

[0082] Figure 3B In the figure, the fifth mark 203e is in an inverted V shape, and the flush structure is a point. Figure 3A The arrow line shown by the middle mark 301 indicates the grinding direction, that is, when viewed along the grinding direction, the fifth mark 203e is in an inverted V shape.

[0083] In other embodiments, the fifth mark 203e may be a trapezoid with an open bottom edge, and the flush structure may be a straight line, that is, when viewed along the grinding direction, the fifth mark 203e may be a trapezoid with an open bottom edge. Figure 3C In the figure, the second mark 203b is represented by Mark2, the third mark 203c is represented by Mark3, the fourth mark 203d is represented by Mark4, and the fifth mark 203e is represented by Mark5.

[0084] In some embodiments, the depth of the second mark 203b, the third mark 203c, the fourth mark 203d, and the fifth mark 203e reaches the active region and penetrates into the active region to a depth of 5 μm to 10 μm. The second mark 203b, the third mark 203c, the fourth mark 203d, and the fifth mark 203e penetrate into the active region, which facilitates precise positioning in subsequent sample preparation, grinding, and positioning analysis.

[0085] Step 4: preparing and grinding the chip sample 201 to form a cross-sectional sample, including:

[0086] like Figure 4A As shown, sample preparation and grinding are started on the upstream side of the fourth mark 203d until the fourth mark 203d is observed. Figure 4A In FIG. 2 , area 201 a represents a ground area. It can be seen that the ground surface reaches the interface corresponding to the fourth mark 203 d. Figure 4B for Figure 4A The corresponding cross-sectional diagram shows that fourth mark 203d is visible on the polished surface, indicating that the polishing process has approached the target structure 202. It can be seen that the first and second lines of fifth mark 203e appear on the polished surface. Since the first and second lines do not intersect, two vertical lines appear on the polished surface, representing the cross-sections of the first and second lines, respectively. Since fourth mark 203d and fifth mark 203e are both large, SEM is not required to confirm their corresponding positions.

[0087] In the embodiment of the present invention, before sample preparation and grinding, a transparent gasket needs to be attached to the surface of the chip sample 201 to protect the surface of the chip sample 201 from being damaged during the cross-section grinding, i.e., sample preparation and grinding process. Figure 4B As shown, the top of the metal interconnect structure 402 is adhered to the glass slide 404 by AB glue 403.

[0088] Continue to grind the sample until the flush structure of the fifth mark 203e is observed, and the first straight line and the second straight line of the fifth mark 203e disappear at the same time. Figure 5A As shown, the region 201a extends to the cross section flush with the dotted line 302, that is, the grinding surface reaches the cross section corresponding to the dotted line 302, and the sample preparation grinding is completed. Figure 5B for Figure 5A The corresponding cross-sectional view is given by Figure 5B As shown, only a vertical line remains of the fifth mark 203e, which corresponds to the cross-sectional view of the flush structure, i.e., the vertex. That is, when the inverted V-shaped line Mark5, i.e., the fifth mark 203e, becomes a line, it indicates that it is basically at the target position.

[0089] In other embodiments, when Mark 5 is a trapezoid with an open bottom edge, when the first and second straight lines of the fifth mark 203e disappear simultaneously during sample preparation and grinding, Mark 5 will appear as a planar structure on the ground surface. This planar structure is a flat, straight, and flat structure when viewed from above. In other words, when the cross-sectional appearance of Mark 5 changes from two separate straight lines to a single plane, grinding has reached the target position and the sample preparation and grinding are complete.

[0090] In an embodiment of the present invention, sample preparation and grinding include:

[0091] Perform coarse grinding. Coarse grinding is the opposite of fine grinding. Coarse grinding uses larger abrasive particles, enabling faster grinding. Fine grinding uses smaller abrasive particles, enabling fine grinding and reducing sample scratches. In some embodiments, the diamond sandpaper used for coarse grinding has a particle size of 30 μm or greater.

[0092] When the distance between the grinding surface and the fourth mark 203d is 20 μm to 50 μm, the grinding surface is polished successively using diamond sandpaper from coarse to fine until the sample grinding is completed. In some embodiments, the particle size of each diamond sandpaper used in the successive polishing of the grinding surface gradually changes from 30 μm to 0.1 μm.

[0093] In an embodiment of the present invention, the following further comprises:

[0094] Step 5: Use SEM to confirm the position of the target structure 202 on the cross-section sample.

[0095] Step 6: Perform positioning analysis on the target structure 202.

[0096] In the embodiment of the present invention, a nanoprobe tester is used to perform positioning analysis.

[0097] Positioning analysis includes SCM analysis.

[0098] The embodiment of the present invention utilizes coarse positioning on the plane of the chip sample 201 and combines it with precise measurement of the distance between the first mark 203a and the target structure 202, such as through back-transmitted imaging measurement, to form multiple precisely positioned marks on the chip sample 201. Subsequently, the finely positioned marks are utilized to achieve precise control of grinding during sample preparation and grinding, thereby enabling efficient, point-specific preparation of cross-sectional samples and greatly improving the success rate of sample preparation.

[0099] At the same time, the marks used to control sample preparation and grinding in the embodiment of the present invention can be directly observed using an optical microscope (OM) without the need for SEM observation. SEM observation is only required for confirmation after the sample preparation and grinding is completed. Since SEM observation is less efficient and more expensive, the present invention can also greatly improve sample preparation efficiency and save machine costs, and can shorten the sample preparation time by nearly half. Skilled engineers can shorten the sample preparation time to 2 days.

[0100] The marking of the cross-sectional sample prepared in the embodiment of the present invention can also facilitate positioning analysis, thereby enabling efficient fixed-point analysis.

[0101] The following further describes the method for preparing a cross-sectional sample according to an embodiment of the present invention in conjunction with a process for preparing a cross-sectional sample applied to a specific chip product.

[0102] In a 55HV chip product, after testing, it was found that the simulated positive voltage (AVDD) high current failed (fail), and abnormal leakage was found from the deep N-well (DNW) to the P-type substrate (Psub) and from the DNW to the P-well (PW). It was suspected that the ion implantation at the DNW position was abnormal. It was necessary to perform cross-sectional scanning capacitance microscopy (SCM) analysis on the DNW to determine whether the cross-sectional ion implantation type was normal. Figure 6 , which is a schematic diagram of the cross-sectional structure of a chip product corresponding to the method for preparing a cross-sectional sample according to an embodiment of the present invention; Figure 6 Only the structure of the chip product on the semiconductor substrate 401 is shown, and the metal interconnection structure 402 is not shown. Figure 6 The structure includes: a deep N-well 501 , a P-well 502 , an N-well (NW) 503 , an N-type shallow drain doped implantation region (NLDD) 504 , an N+ region 505 , a P+ region 506 , and a shallow trench isolation 507 .

[0103] A deep N-well 501 is formed in a P-type substrate 401 . Figure 6 The semiconductor device in FIG. 5 is an input / output (IO) device, the P-well 502 is IOPW, the N-well 503 is IONW, and the N-type shallow drain doped implantation region 504 is IONLDD.

[0104] In order to perform cross-sectional SCM analysis on DNW503 at a specific point, it is necessary to use the method of the embodiment of the present invention to prepare a cross-sectional sample, including the following steps:

[0105] Mark rough positioning is step one:

[0106] like Figure 7AAs shown, with the help of Layout, the target structure 202' is located on the aluminum layer. At a lateral distance of about 140 μm from the target structure 202', a Mark 1, i.e., a first mark 203a', is made by a laser cutter. The Mark 1 has a depth of AA and a size of 10 μm*10 μm.

[0107] Measuring distance through the Meridian back imaging is step 2:

[0108] 1. Process the back side of the chip sample 201' to a Meridian observable state;

[0109] 2. Measure the relative distance between Mark 1 and the target structure 202', where the 1064nm wavelength laser light in the Meridian machine can penetrate the silicon substrate to form an image and thus measure the distance. Figure 7B FIG. 2 shows an imaging diagram of a chip sample 201 ′ in a Meridian machine.

[0110] FIB Mark fine positioning is step three:

[0111] Based on the distance between Mark 1 and the target area, i.e., the target structure 202', FIB is used to bond Marks 2 and 3 at 15μm to the left and right of the target structure in the X direction. Mark 4 is bonded at 2.5μm in the Y direction. In the Y direction, an inverted V-shaped line Mark 5 is bonded outside Mark 3 and flush with the target structure, with the top of the inverted V flush with the target structure. FIB Marks 2-5 are bonded to a depth of AA, approximately 10μm. Figure 7C As shown, the SEM photos corresponding to FIB Marks 1 to 5 are shown, and Marks 2 to 5 are also marked with marks 203b' to 203e' respectively.

[0112] Cross-section sample preparation is step four:

[0113] A transparent gasket is attached to the surface of the chip sample 201' to protect the surface from damage during the grinding process. The sample cross section is coarsely ground to about 40μm from Mark4, and then the sample cross section is polished successively with diamond sandpaper from coarse to fine (30μm to 0.1μm) until Mark5 gradually approaches and forms a line. Figure 8A Shown is the OM photo after grinding until Mark 5 becomes a line.

[0114] After that, use SEM to accurately locate the position, that is, proceed to step five, such as Figure 8B As shown, it is a photograph formed by performing SEM scanning on the cross-section sample after completing step 4. Under the positioning function of Mark2 and Mark3, the SEM scanning can quickly obtain the SEM image of the target structure 202'.

[0115] Sample analysis is step six:

[0116] The SCM analysis of the samples was performed using an atomic force microscope (AFM) based on a nanoprobe tester. Figure 9A As shown in the figure, it is the corresponding surface morphology photo; Figure 9B As shown in the figure, it is the corresponding SCM image. Figure 9B It can be observed that there is a leakage path between the P-subs at the dotted circle 501, suggesting that the P-subs are too close together. After adjusting the feedback line and increasing the P-sub spacing, this problem was resolved.

[0117] As can be seen from the above, the method of the embodiment of the present invention realizes cross-section fixed-point sample preparation, which greatly improves the success rate of sample preparation. At the same time, it assists positioning through optical microscope observation, reduces the number of SEM observations, greatly improves sample preparation efficiency and saves machine costs. Skilled engineers can shorten the sample preparation time to 2 days.

[0118] The present invention has been described in detail above by means of specific embodiments, but these do not constitute limitations of the present invention. Without departing from the principles of the present invention, those skilled in the art may make many variations and improvements, which should also be considered as the scope of protection of the present invention.

Claims

1. A method for preparing a cross-section sample, characterized in that: include: Step 1: forming a first mark for coarse positioning on the chip sample; Step 2: measuring the relative distance between the first mark and the target structure on the chip sample, including a first X-direction distance and a first Y-direction distance; the Y-direction is the sample preparation and grinding direction, and the X-direction and the Y-direction are perpendicular; Step 3: forming a plurality of FIB marks for fine positioning according to the relative distance between the first mark and the target structure, wherein the FIB marks include a second mark, a third mark, a fourth mark, and a fifth mark; The second mark and the third mark are straight line structures extending along the Y direction and are distributed on both sides of the target structure along the X direction, and the second mark and the third mark are used to locate the position of the target structure in the X direction; The fourth mark is a straight line extending in the X direction; the fourth mark is located on the upstream side of the target structure in the Y direction, and a first prompt distance is defined between the fourth mark and the target structure in the Y direction, the first prompt distance being used to indicate that a target position corresponding to the target structure is about to be reached during sample preparation and grinding; the upstream side is the side that is ground first during the sample preparation and grinding process; The fifth mark is formed by connecting a plurality of line segments, including a flush structure flush with the X-direction extension of the target structure, and a first straight line and a second straight line connected to the flush structure, wherein the flush structure is a vertex or a straight line; the first straight line and the second straight line are both connected to the flush structure, and are both located upstream of the flush structure; Step 4: preparing and grinding the chip sample to form a cross-sectional sample, including: Starting the sample preparation and grinding on the upstream side of the fourth mark until the fourth mark is observed; The sample preparation and grinding is continued until the flush structure of the fifth mark is observed, and the first straight line and the second straight line of the fifth mark disappear simultaneously.

2. The method for preparing a cross-section sample according to claim 1, wherein: Also includes: Step 5: Use SEM to confirm the position of the target structure on the cross-section sample.

3. The method for preparing a cross-section sample according to claim 2, wherein: Also includes: Step 6: Perform positioning analysis on the target structure.

4. The method for preparing a cross-sectional sample according to claim 1, wherein: In step 1, the planar position of the target structure on the chip sample is roughly located using a planar layout; forming the first mark at a selected position according to the planar position of the target structure; The first mark is formed by laser cutting.

5. The method for preparing a cross-sectional sample according to claim 1, wherein: In step 1, the first mark is formed at a distance of 100 μm to 300 μm from the target structure; The first mark is a rectangle with a side length of 10 μm to 20 μm.

6. The method for preparing a cross-sectional sample according to claim 1, wherein: In step 2, infrared rays are used to perform back-transmission imaging from the back of the chip sample to measure the first X-direction distance and the first Y-direction distance.

7. The method for preparing a cross-sectional sample according to claim 1, wherein: In step three, the distance between the second mark and the target structure in the X direction is 10 μm to 20 μm; the second mark and the third mark are symmetrical about the center of the target structure.

8. The method for preparing a cross-section sample according to claim 1, wherein: In step three, the first prompt distance is 2 μm to 3 μm.

9. The method for preparing a cross-section sample according to claim 1, wherein: In step 3, the fifth mark is in an inverted V shape, and the flush structure is a point; Alternatively, the fifth mark is in the shape of a trapezoid with an open bottom edge, and the flush structure is a straight line.

10. The method for preparing a cross-section sample according to claim 1, wherein: In step 4, the sample preparation and grinding includes: Perform a coarse grind; When the grinding surface is 20 μm to 50 μm away from the fourth mark, the grinding surface is polished successively with diamond sandpaper from coarse to fine until the sample preparation grinding is completed.

11. The method for preparing a cross-section sample according to claim 10, wherein: The particle size of the diamond sandpaper used in the rough grinding is greater than 30 μm; The particle size of each diamond sandpaper used in the successive grinding of the grinding surface changes from coarse to fine and gradually changes from 30 μm to 0.1 μm.

12. The method for preparing a cross-section sample according to claim 1, wherein: The chip sample includes a semiconductor device formed in an active area of ​​a semiconductor substrate and a metal interconnection structure formed on top of the semiconductor device; The depth of the first mark reaches the active area; The depths of the second mark, the third mark, the fourth mark, and the fifth mark reaching the active region and penetrating into the active region are 5 μm to 10 μm.

13. The method for preparing a cross-section sample according to claim 6, wherein: In step 2, the infrared ray used in the back transmission imaging is a laser with a wavelength of 1064 nm.

14. The method for preparing a cross-section sample according to claim 3, wherein: In step six, a nanoprobe tester is used to perform the positioning analysis.

15. The method for preparing a cross-section sample according to claim 14, wherein: The positioning analysis includes SCM analysis.

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