Wafer inspection device

Abstract

The application relates to the technical field of wafer detection, in particular to a wafer detection device which comprises a scanning electron microscope and an atomic force microscope. The scanning electron microscope comprises a lens barrel, an objective lens and a sample chamber. The objective lens is arranged in the sample chamber. A sample stage for carrying a wafer to be detected is arranged in the sample chamber. The objective lens is used for acquiring a two-dimensional topographic image of the surface of the wafer to be detected. The atomic force microscope is arranged in the sample chamber. The atomic force microscope is not in contact with the sample stage. The atomic force microscope comprises a cantilever and a probe arranged at the end of the cantilever. The probe is used for acquiring a three-dimensional structure of the wafer to be detected. In the application, the atomic force microscope is not in contact with the sample stage, so that the transmission of the vibration and heat of the sample stage to the atomic force microscope is effectively isolated, and the measurement error caused by the vibration noise and thermal expansion mismatch is reduced. The cantilever adopts three different mounting modes, which can adapt to different detection scenes such as the surface, edge area and deep cavity structure of a conventional wafer, eliminate the detection blind area and improve the application range of the device.

Description

Technical Field

[0001] This application relates to the field of wafer inspection technology, and more particularly to a wafer inspection device. Background Technology

[0002] In semiconductor wafer manufacturing, high-precision inspection of wafer surface defects (such as high aspect ratio holes, etching steps, and metal interconnect defects) and critical dimensions is required. Scanning electron microscopy (SEM), with its electron beam imaging advantage, can quickly acquire two-dimensional images of the wafer surface, offering high inspection efficiency. However, it cannot clearly identify the height information of three-dimensional structures such as bevels and curved surfaces. Atomic force microscopy (AFM), through the interaction of a nanoscale probe with the sample surface, can accurately characterize three-dimensional structures (such as height, bevels, and curved surfaces), but its scanning speed is slow, resulting in low inspection efficiency when used alone. Combining SEM and AFM improves inspection accuracy while maintaining high-speed inspection.

[0003] However, existing SEM-AFM coupling devices have significant drawbacks: atomic force microscopes are typically directly fixed to the sampling stage of the scanning electron microscope via rigid structural components. This connection method leads to two major problems: first, mechanical vibration transmission, where the mechanical vibration generated during sample stage translation is directly transmitted to the AFM cantilever, increasing AFM scanning noise by 3-5 times and severely affecting measurement accuracy; second, thermal expansion mismatch, where heat generated by electron beam irradiation and mechanical friction on the sample stage is transferred to the AFM base and cantilever. Due to the difference in thermal expansion coefficients between the metal sample stage and the silicon / silicon nitride cantilever, probe spatial positioning shifts and cantilever thermal bending occur, further reducing detection accuracy. Utility Model Content

[0004] This application provides a wafer inspection device to solve the problems in the prior art where mechanical vibrations generated during sample stage translation and heat generated by electron beam irradiation and mechanical friction affect the measurement accuracy of atomic force microscopes.

[0005] This application provides a wafer inspection device, comprising: A scanning electron microscope (SEM) consists of a tube, an objective lens, and a sample chamber. The objective lens is located in the sample chamber, which contains a sample stage for holding the wafer to be inspected. The SEM is used to acquire two-dimensional morphological images of the surface of the wafer to be inspected. An atomic force microscope (AFM) is set up in a sample chamber and does not contact the sample stage. The AFM includes a cantilever and a probe mounted on the end of the cantilever. The probe is used to acquire the three-dimensional structure of the wafer to be inspected.

[0006] In one possible design, the cantilever is mounted on the outer wall of the lens barrel.

[0007] In one possible design, the cantilever is mounted on the pole shoe of the objective lens.

[0008] In one possible design, the cantilever is mounted on the inner wall of the sample chamber.

[0009] In one possible design, an initial position adjustment mechanism is also included, which is used to adjust the initial relative position of the probe and the wafer to be inspected.

[0010] In one possible design, the initial position adjustment mechanism may also include an optical lens or a second laser interference module.

[0011] In one possible design, a piezoelectric ceramic is provided at the end of the cantilever away from the probe, and the piezoelectric ceramic achieves fine adjustment of the probe's horizontal and vertical directions through directional deformation.

[0012] In one possible design, a first laser interference module is also included. The first laser interference module includes a first light source, a first beam splitter, a reference mirror, a measuring mirror, and a first interference signal detector. The first light source and the first beam splitter are located outside the sample chamber, and the reference mirror is located inside the sample chamber. The laser emitted by the first light source is split into a measuring beam and a reference beam by the first beam splitter. The reference beam is reflected back to the first interference signal detector by the reference mirror, and the measuring beam is reflected back to the first interference signal detector by the cantilever.

[0013] In one possible design, a focusing and tracking module is also included. The focusing and tracking module includes a laser emitter, a first reflector, a second reflector, and a laser detector. The laser emitter and the laser detector are located outside the sample chamber. The first reflector and the second reflector are located on both sides of the lens tube, respectively. The laser beam emitted by the laser emitter is reflected by the first reflector to the surface of the wafer to be tested, then reflected by the surface of the wafer to be tested to the second reflector, and then reflected by the second reflector to the laser detector.

[0014] In one possible design, a second laser interference module is also included. The second laser interference module includes a second light source, a second beam splitter, and a second interference signal detector. The second light source and the second beam splitter are located above the wafer to be tested. The laser emitted by the second light source is split into a measurement beam and a reference beam by the second beam splitter. The reference beam is reflected back to the second interference signal detector by the upper surface of the wafer, and the measurement beam is reflected back to the second interference signal detector by the probe.

[0015] The beneficial effects of this application are as follows: The wafer inspection device provided in this application does not involve contact between the atomic force microscope and the sample stage. Instead, it is installed through the outer wall of the microscope tube, the objective lens pole shoe, or the inner wall of the sample chamber, effectively isolating the transfer of sample stage vibration and heat to the atomic force microscope and reducing measurement errors caused by vibration noise and thermal expansion mismatch.

[0016] The cantilever adopts three different installation methods, and with components such as universal joint structure and turntable, it can be adapted to different detection scenarios such as conventional wafer surface, edge area, and deep cavity structure, eliminating detection blind spots and expanding the applicability of the device.

[0017] Precise probe position control is achieved through a combination of an initial position adjustment mechanism, piezoelectric ceramic fine-tuning, and multi-laser module monitoring. The initial position adjustment mechanism ensures the probe is safely close to the wafer; the piezoelectric ceramic enables nanometer-level fine-tuning; and the laser interference module and focusing tracking module monitor displacement and height changes in real time, promptly compensating for external interference and ensuring detection accuracy. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the wafer inspection device provided in Embodiment 1 of this application; Figure 2 This is a schematic diagram of the wafer inspection device provided in Embodiment 2 of this application; Figure 3 This is a schematic diagram of the wafer inspection device provided in Embodiment 3 of this application; Figure 4 This is a schematic diagram of the wafer inspection device provided in Embodiment 4 of this application; Figure 5 This is a schematic diagram of the wafer inspection device provided in Embodiment 5 of this application; Figure 6 This is a schematic diagram of the wafer inspection device provided in Embodiment 6 of this application; Figure 7 This is a schematic diagram of the wafer inspection device provided in Embodiment 7 of this application; Figure label: 1. Lens tube; 2. Objective lens; 201. Polar shoe; 3. Sample chamber; 4. Sample stage; 5. Cantilever; 6. Probe; 7. Mounting base; 8. Turntable; 9. Support; 10. Initial position adjustment mechanism; 11. Optical lens; 12. Piezoelectric ceramic; 131. First light source; 132. First beam splitter; 133. Reference mirror; 134. Measuring mirror; 141. Laser emitter; 142. First reflecting mirror; 143. Second reflecting mirror; 144. Laser detector; 151. Second light source; 152. Second beam splitter; 16. Coarse adjustment mechanism; 17. Fine adjustment mechanism. Detailed Implementation

[0020] The technical solutions of this application will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] The following is combined Figures 1-7 This describes the wafer inspection apparatus provided in the embodiments of this application.

[0022] This application provides a wafer inspection device, including a scanning electron microscope and an atomic force microscope.

[0023] The scanning electron microscope includes a tube 1, an objective lens 2, and a sample chamber 3. The objective lens 2 is set inside the sample chamber 3. The scanning electron microscope is used to acquire two-dimensional morphological images of the surface of the wafer to be inspected. The sample chamber 3 is equipped with a sample stage 4 for supporting the wafer to be inspected. The sample stage 4 can move in the horizontal, vertical, and height directions to adjust the inspection position of the wafer.

[0024] The atomic force microscope is set inside the sample chamber 3 and does not contact the sample stage 4 to avoid the vibration and heat of the sample stage 4 being transferred to the atomic force microscope. The atomic force microscope includes a cantilever 5 and a probe 6 installed at the end of the cantilever 5. The probe 6 is used to contact or approach the wafer surface to obtain the three-dimensional structure of the wafer to be tested (such as height, roughness, hole depth and other parameters).

[0025] In some embodiments, the cantilever 5 of the atomic force microscope is mounted on the outer wall of the microscope tube 1.

[0026] Specifically, the cantilever 5 is mounted on the outer wall of the lens barrel 1 via the mounting base 7. For example, the mounting base 7 is made of a low thermal expansion material (such as Invar, with a thermal expansion coefficient of 0.5ppm / ℃; or carbon fiber reinforced polymer, with a thermal expansion coefficient of 1.2ppm / ℃) to avoid deformation of the mounting base 7 due to temperature changes, which would affect the positional accuracy of the cantilever 5 and the probe 6.

[0027] A shock-absorbing component is provided between the mounting base 7 and the outer wall of the lens barrel 1. For example, the mounting base 7 and the outer wall of the lens barrel 1 are connected by a metal bellows or a flexible hinge. In this way, the vibration of the lens barrel 1 can be effectively isolated from the transmission to the cantilever 5, and the vibration noise can be reduced.

[0028] In some embodiments, the cantilever 5 of the atomic force microscope is mounted on the pole shoe 201 of the objective lens 2.

[0029] Specifically, the cantilever 5 is mounted on the outside of the pole shoe 201 of the objective lens 2 via a turntable 8. The turntable 8 can rotate around the axis of the pole shoe 201 to adjust the relative position of the cantilever 5 and the pole shoe 201.

[0030] When using a scanning electron microscope alone, the cantilever 5 can be rotated away from the electron beam via the turntable 8 to avoid damage to the cantilever 5 and probe 6 by electron beam irradiation; when combined with detection, the cantilever 5 is rotated to the working position to ensure that the probe 6 can be aligned with the wafer detection area.

[0031] In other embodiments, the cantilever 5 can also be mounted on the inside of the pole shoe 201 of the objective lens 2 via a turntable 8.

[0032] In some embodiments, the cantilever 5 of the atomic force microscope is mounted on the inner wall of the sample chamber 3.

[0033] Specifically, the cantilever 5 is mounted on the inner wall of the sample chamber 3 via a bracket 9. The bracket 9 is made of a low thermal expansion material (such as Invar or carbon fiber reinforced polymer) to reduce the impact of heat transfer from the inner wall of the sample chamber 3 on the cantilever 5. A universal joint structure is provided between the bracket 9 and the inner wall of the sample chamber 3, which can achieve ±10° angle adjustment. This is used to adjust the tilt angle of the cantilever 5 so that the probe 6 can fit against the surface of special areas such as wafer edges and deep cavities, eliminating detection blind spots.

[0034] In some embodiments of this application, the wafer inspection device further includes an initial position adjustment mechanism 10, which is used to adjust the initial relative position of the probe 6 and the wafer to be inspected, so as to ensure that the probe 6 can move accurately from the initial state (100-200μm away from the wafer surface) to the working state (5-20nm away from the wafer surface) and avoid the probe 6 from colliding with the wafer.

[0035] Specifically, the initial position adjustment mechanism can adopt a structure combining coarse and fine adjustment. The coarse adjustment mechanism 16 can use an electric lead screw or rack and pinion drive system or a magnetic levitation drive platform to achieve rapid and wide-range movement of the probe 6 with a displacement accuracy of ±1μm. The fine adjustment mechanism 17 can use a flexible hinge precision positioning stage and a voice coil motor drive system to achieve minute-range adjustment of the probe 6 with a displacement accuracy of ±10nm.

[0036] To assist in initial position adjustment, the device also includes an optical lens 11, preferably an integrated optical lens 11 for white light interferometers. The optical lens 11 is set in the sample chamber 3 (and can be installed on the mounting base 7 or the bracket 9). The position of the lens is adjusted by a three-dimensional adjustment mechanism to obtain the macroscopic relative position of the probe 6 and the wafer to be tested, providing a visual reference for initial position adjustment and reducing the risk of collision between the probe 6 and the wafer.

[0037] During the testing process, the position of probe 6 will shift slightly due to the effects of vibration, thermal deformation and airflow.

[0038] Therefore, in some embodiments, a piezoelectric ceramic 12 is provided at the end of the cantilever 5 away from the probe 6. The piezoelectric ceramic 12 can make fine adjustments to the probe 6 in the horizontal (X, Y axis) and height (Z axis) directions by extension and retraction, so as to compensate for the positional displacement of the probe 6 caused by external interference (such as vibration and temperature change) during the detection process.

[0039] Specifically, the piezoelectric ceramic 12 includes a first driving layer, a second driving layer, and a buffer insulating layer. The first driving layer is connected to the cantilever 5. By applying voltage to the first driving layer, the probe 6 can be driven to achieve fine adjustment in the Z-axis direction. Specifically, when a positive voltage is applied between the upper and lower electrodes, the piezoelectric ceramic 12 undergoes elongation deformation along the Z-axis direction; when a reverse voltage is applied, it undergoes contraction deformation along the Z-axis direction, thereby causing the cantilever 5 to move up and down along the Z-axis, thus achieving height adjustment of the probe 6. By applying voltage to the second driving layer, the probe 6 can be driven to achieve fine adjustment in the Y-axis and X-axis directions. Specifically, when a positive voltage is applied between the left and right electrodes, the piezoelectric ceramic 12 undergoes elongation deformation along the X-axis direction; when a reverse voltage is applied, it undergoes contraction deformation along the X-axis direction, thereby causing the cantilever 5 to move left and right along the X-axis. When a positive voltage is applied between the front and rear electrodes, the piezoelectric ceramic 12 undergoes elongation deformation along the Y-axis direction; when a reverse voltage is applied, it undergoes contraction deformation along the Y-axis direction, thereby causing the cantilever 5 to move back and forth along the Y-axis, thus achieving horizontal adjustment of the probe 6. The buffer insulation layer is located between the first driving layer and the second driving layer. It is made of polyimide-glass fiber composite film with a thickness of 50μm, which achieves electrical insulation between the two driving layers (volume resistivity ≥1×10). 16 Ω cm (breakdown voltage ≥30kV / mm), and can also absorb the stress generated when the two driving layers are deformed, avoiding mutual interference.

[0040] To monitor the horizontal displacement of probe 6 in real time, the device also includes a first laser interference module.

[0041] Specifically, the first laser interference module includes a first light source 131, a first beam splitter 132, a reference mirror 133, and a first interference signal detector. The first light source 131 and the first beam splitter 132 are located outside the sample chamber 3 to avoid the influence of the vacuum environment of the sample chamber 3. The reference mirror 133 is located inside the sample chamber 3 and can be fixed to the sample stage 4, the inner wall of the sample chamber 3, or the pole piece 201.

[0042] The laser emitted by the first light source 131 is split into a measurement beam and a reference beam by the first beam splitter 132. The reference beam is reflected back to the first interferometric signal detector by the reference mirror 133, and the measurement beam is reflected back to the first interferometric signal detector by the cantilever 5. If the surface reflectivity of the cantilever 5 is insufficient, a measurement mirror 134 can be set at the end of the cantilever 5 away from the probe 6. The measurement mirror 134 is made of a high-reflectivity material to ensure effective reflection of the measurement beam.

[0043] The first interference signal detector receives the interference fringes resulting from the superposition of two reflected beams, converts the optical signal into an electrical signal, and transmits it to the controller. The controller calculates the horizontal displacement of probe 6 based on the changes in the interference fringes. If the displacement exceeds the allowable range (±0.1nm), the controller controls the piezoelectric ceramic 12 to perform horizontal compensation to ensure the horizontal position of probe 6 is stable.

[0044] To ensure that probe 6 is always within the focusing range (5-10nm) of the wafer surface, the device also includes a focusing tracking module.

[0045] Specifically, the focusing and tracking module includes a laser emitter 141, a first reflector 142, a second reflector 143, and a laser detector 144. The laser emitter 141 and the laser detector 144 are located outside the sample chamber 3, and the first reflector 142 and the second reflector 143 are located on both sides of the lens tube 1, close to the objective lens 2.

[0046] The laser beam emitted by the laser emitter 141 is directed through the transparent window of the sample chamber 3 to the first reflector 142, and then reflected by the first reflector 142 to the surface of the wafer to be tested. After being reflected on the wafer surface, the laser beam is directed to the second reflector 143, and then reflected by the second reflector 143 to the laser detector 144.

[0047] When the wafer surface has unevenness (such as high aspect ratio holes or etching steps) that causes the distance between the probe 6 and the wafer surface to exceed the focusing range, the laser reflection position received by the laser detector 144 will be offset. The controller calculates the height adjustment amount based on the offset and controls the piezoelectric ceramic 12 to drive the probe 6 to move along the Z-axis, maintaining the focusing state between the probe 6 and the wafer surface, avoiding repeated measurements caused by interlayer focusing instability, and improving detection efficiency and accuracy.

[0048] To precisely adjust the initial distance between probe 6 and the wafer surface and to monitor the height change of probe 6 during the detection process, the device also includes a second laser interference module.

[0049] Specifically, the second laser interference module includes a second light source 151, a second beam splitter 152, and a second interference signal detector. The second light source 151 and the second beam splitter 152 are located above the wafer to be tested, for example, they can be mounted on the initial position adjustment mechanism or the bracket 9.

[0050] The laser emitted by the second light source 151 is split into a measurement beam and a reference beam by the second beam splitter 152. The reference beam is reflected back to the second interference signal detector by the upper surface of the wafer, and the measurement beam is reflected back to the second interference signal detector by the probe 6.

[0051] The second interference signal detector calculates the distance between probe 6 and the wafer surface based on the interference fringes of the two reflected beams, providing precise data for initial position adjustment. During the detection process, if the distance changes, it can be fed back to the controller in real time to assist the focusing and tracking module in achieving precise adjustment of the probe 6 height.

[0052] To more clearly illustrate the wafer inspection apparatus of this application, a description will be provided in conjunction with specific embodiments.

[0053] Example 1: Reference Figure 1 As shown, the atomic force microscope is fixed to the top of the scanning electron microscope tube 1 via a mounting base 7, a coarse adjustment mechanism 16, a fine adjustment mechanism 17, and a piezoelectric ceramic 12. The mounting base 7 is made of Invar steel and is connected to the top of the tube 1 via four sets of flexible hinges. The flexible hinges can absorb minor vibrations of the tube 1 and block heat transfer. The coarse adjustment mechanism 16 uses an electric lead screw drive system, which can quickly move the probe 6 from its initial position to its working range. The fine adjustment mechanism 17 uses a flexible hinge precision positioning stage, connecting the coarse adjustment mechanism 16 and the piezoelectric ceramic 12, and is used for final calibration of the distance between the probe 6 and the wafer to ensure initial focusing. One end of the piezoelectric ceramic 12 is connected to the fine adjustment mechanism 17, and the other end is rigidly bonded to the end of the cantilever 5 away from the probe 6. The system is equipped with a first laser interferometer module. The reference mirror 133 is fixed to the edge of the sample stage 4 (moving synchronously with the sample stage 4), and the measuring mirror 134 is integrated into the end of the cantilever 5 (moving synchronously with the cantilever 5). When the translation of the sample stage 4 causes airflow disturbance, resulting in a horizontal shift of the AFM cantilever 5, the laser interferometer can capture the displacement signal within 50μs and compensate through the piezoelectric ceramic 12X / Y axis drive, with a compensation accuracy of ±0.05nm. The mounting base 7 integrates a dedicated optical lens 11 for white light interferometers. The lens position can be adjusted through a three-dimensional adjustment mechanism, allowing for rapid observation of the macroscopic distance between the probe 6 and the wafer surface before AFM operation, thus avoiding collisions between the probe 6 and the wafer during the coarse adjustment stage.

[0054] Example 1 is applicable to the surface defect detection of conventional 8-12 inch wafers (such as scratches on metal interconnects and shallow etch steps), and is especially suitable for the initial screening of mass production lines with high requirements for detection efficiency, with a detection speed of up to 15 minutes / wafer.

[0055] Example 2: Reference Figure 2As shown, the atomic force microscope (AFM) is mounted on the outer periphery of the SEM tube 1 via a mounting base 7 and a coarse adjustment mechanism 16. The mounting base 7 has a ring-shaped structure, is made of Invar steel, and has an inner ring covered with a PTFE wear-resistant layer, allowing it to slide up and down along the outer periphery of the tube 1. Three sets of manually locking bolts (including rubber anti-slip pads) are evenly distributed on the outer side of the mounting base 7. Loosening the bolts allows for free adjustment of the height of the mounting base 7, while tightening them secures the bolts against the outer wall of the tube 1. The coarse adjustment mechanism 16 uses a magnetic levitation drive platform integrated below the mounting base 7, enabling rapid movement of the AFM. The fine adjustment mechanism 17 and the piezoelectric ceramic 12 have the same structure as in Example 1, but the Z-axis drive stroke of the piezoelectric ceramic 12 is increased to ±100nm (to accommodate height differences in wafers of different thicknesses). The reference mirror 133 of the first laser interferometer module is now fixed to the bottom inner wall of the sample chamber 3 (not the sample stage 4), using the sample chamber 3 as a fixed reference standard to avoid interference from the vibration of the sample stage 4 on horizontal displacement monitoring, further reducing the compensation error to ±0.03nm.

[0056] Example 2 is suitable for scenarios involving the production of multi-specification wafers, such as simultaneously inspecting conventional silicon wafers (0.72 mm thick) and thin power device wafers (0.1 mm thick). There is no need to change the AFM mounting structure, and the time to switch between inspected products is reduced from 30 minutes to 5 minutes.

[0057] Example 3: Reference Figure 3 As shown, the AFM is directly connected to the outer periphery of the lens barrel 1 via the coarse adjustment mechanism 16. The coarse adjustment mechanism 16 adopts a combination of worm gear and harmonic reducer, with a manual crank wheel on the outside that can slide up and down quickly, driving the AFM probe 6 to move along the axial direction of the lens barrel 1. The electromagnetic locking device is integrated at the contact point between the coarse adjustment mechanism 16 and the lens barrel 1, and the positioning accuracy after locking is ±0.1mm, preventing the AFM from shifting during the detection process. The mounting material, fine adjustment mechanism 17, piezoelectric ceramic 12, and first laser interference module are all the same as in Example 2.

[0058] Example 3 is applicable to the mass production of single-product wafers, such as 3D NAND wafer production lines, where frequent switching of wafers for testing is required, but the specifications are uniform. Through rapid height adjustment and positioning, the testing efficiency can be improved to 12 minutes / wafer.

[0059] Example 4: Reference Figure 4As shown, the AFM is directly fixed to the inner wall of the sample chamber 3 via a bracket 9. The bracket 9 is an L-shaped Invar bracket 9, with one end fixed to the inner wall of the sample chamber 3 by bolts and the other end extending above the sample stage 4. The surface of the bracket 9 is covered with a polyimide heat insulation layer to block heat transfer from the inner wall. The coarse adjustment mechanism 16 uses a voice coil motor drive system, integrated at the end of the bracket 9, which can realize rapid small-range movement of the AFM to adapt to the detection area of ​​the wafer edge. The fine adjustment mechanism 17 and the first laser interference module are the same as in Example 1, but the X-axis travel of the fine adjustment mechanism 17 is increased to ±200nm to compensate for the slight tilt of the wafer edge. The end of the bracket 9 adopts a universal joint structure (which can realize ±10° angle adjustment), which, together with the fine adjustment mechanism 17, can adjust the tilt angle of the AFM cantilever 5, so that the probe 6 can fit the arc surface of the wafer edge (such as the wafer chamfer area), solving the "blind zone" problem of edge detection in conventional devices (edge ​​detection coverage is increased from 80% to 100%).

[0060] Example 4 is applicable to wafer edge defect detection, such as edge chipping, coating peeling, and short circuits at the edges of metal interconnects, and is especially suitable for power semiconductor wafers (such as IGBT wafers) with high edge quality requirements.

[0061] Example 5: Reference Figure 5 As shown, this embodiment adds a focusing and tracking module to the existing embodiment 1. The laser emitter 141 is mounted on the side wall of the sample chamber 3. The first reflecting mirror 142 (45° reflection, coated with an anti-reflection film) is fixed to the bottom left side of the microscope tube 1. The second reflecting mirror 143 (symmetrical to the first reflecting mirror 142) is fixed to the bottom right side of the microscope tube 1. The laser detector 144 is mounted on the other side of the sample chamber 3. The focusing and tracking module calculates the height difference on the wafer surface (e.g., the height difference between the opening and bottom of a high aspect ratio hole in a 3D NAND flash memory can reach 5 μm) by changing the laser reflection position. When the height difference exceeds the AFM focusing range (10 nm), the Z-axis of the piezoelectric ceramic 12 adjusts the height of the probe 6 within 10 μs to maintain the focused state.

[0062] A second laser interferometer (with the same structure as the first laser interferometer) is added and installed at the bottom of the coarse adjustment mechanism 16. It is specifically used to monitor the initial distance between the AFM probe 6 and the wafer surface. Combined with the focusing and tracking module, it avoids collisions between the probe 6 and the wafer.

[0063] Example 5 is suitable for high-precision three-dimensional structure inspection, such as high aspect ratio holes (aperture ≤ 50 nm, aspect ratio ≥ 20:1) on 3D NAND wafers and step heights (step difference ≤ 10 nm) in FinFET structures. The inspection accuracy can reach ± ​​0.05 nm, meeting the critical dimension measurement requirements of advanced process wafers.

[0064] Example 6: Reference Figure 6As shown, the AFM is mounted on the outside of the lower pole piece 201 of the objective lens 2 (in the non-electron beam channel area), shortening the distance between the probe 6 and the electron beam to achieve synchronous imaging. The turntable 8 is a rotary stage driven by a stepper motor. When using the SEM alone, the AFM can be rotated to a position away from the electron beam to avoid damage to the AFM cantilever 5 by electron beam irradiation; when switching to the combined mode, it rotates back to the working position.

[0065] Example 6 is suitable for simultaneous SEM and AFM imaging inspection, such as dynamically observing the morphological changes of wafer surface defects under electron beam irradiation (e.g., photoresist thermal deformation), or simultaneously acquiring the two-dimensional morphology (SEM) and three-dimensional dimensions (AFM) of defects, improving the inspection efficiency to 10 minutes / wafer.

[0066] Example 7: Reference Figure 7 As shown, the AFM is installed in the annular groove inside the lower pole shoe 201 of the objective lens 2, using a miniaturized mounting assembly.

[0067] Example 7 is specifically designed for wafer deep cavity structure inspection, such as deep trench isolation structures of power devices (trench depth 50μm, width 2μm) and deep cavity bodies of MEMS devices (depth 100μm, diameter 10μm). It can accurately measure the roughness (Ra≤0.1nm) of the bottom of the deep cavity and the tilt angle of the sidewalls (accuracy ±0.1°).

[0068] The working process of the wafer inspection device in this application is as follows: First, based on the type of wafer to be inspected (e.g., conventional silicon wafer, 3D NAND wafer, FinFET wafer), select the mounting method and calibrate the position of the atomic force microscope cantilever 5: For routine surface inspection, the cantilever 5 is installed on the outer wall of the lens barrel 1, or the cantilever 5 is installed on the outside of the pole piece 201 of the objective lens 2. The cantilever 5 is adjusted to the initial standby position (the probe 6 is 500-1000μm away from the surface of the sample stage 4) by adjusting the mounting base 7 / turntable 8. For edge / deep cavity detection, select cantilever 5 to be installed on the inner wall of sample chamber 3, and adjust the tilt angle of cantilever 5 (0-10°) through universal joint structure to ensure that probe 6 can cover the target detection area.

[0069] Then, the wafer to be tested is placed on the wafer carrier area of ​​the sample stage 4 and fixed by a vacuum chuck or mechanical clamp to ensure that the wafer is flat (flatness error ≤ 5μm) and to avoid wafer displacement during the testing process.

[0070] The drive system of the sample stage 4 moves the center region of the wafer to directly below the scanning electron microscope objective 2; the coarse adjustment module (such as an electric lead screw) of the initial position adjustment mechanism drives the cantilever 5 of the atomic force microscope to move, so that the probe 6 is close to the wafer surface (100-200μm).

[0071] Start the vacuum system (such as a molecular pump) to evacuate the sample chamber 3 to a vacuum level of ≤1×10⁻⁶. -5 Pa meets the environmental requirements for scanning electron microscopy electron beam imaging and atomic force microscopy nanoscale detection.

[0072] The electron gun and imaging system of the scanning electron microscope (SEM) are activated. After the electron beam is focused by the condenser lens and objective lens 2, it performs a two-dimensional scan on the wafer surface in the X / Y axis directions. The detector of the SEM receives the signal generated by the interaction between the electron beam and the wafer surface, converts it into a two-dimensional morphological image, and displays it in real time. Through image analysis algorithms (such as automatic defect identification algorithms), defects on the wafer surface (such as scratches, particles, holes, and etching step deviations) are screened, and the coordinate position of the defect area is recorded (accuracy ±1μm), providing a positioning basis for subsequent precise detection by atomic force microscopy.

[0073] Based on the defect coordinates marked by the scanning electron microscope, the drive system of the sample stage 4 is activated to move the target defect area directly below the atomic force microscope probe 6; the distance between the probe 6 and the defect area is monitored in real time through the second laser interference module (measurement accuracy ±0.05nm) to ensure that the defect area is completely within the scanning range of the probe 6.

[0074] The probe 6 drive system of the atomic force microscope is activated. According to the preset scanning mode (such as tapping mode for fragile surfaces and contact mode for high-precision measurement), the probe 6 performs point-by-point scanning along the X / Y axis of the wafer surface. At the same time, the height change of the probe 6 is recorded through the Z-axis feedback system to construct the three-dimensional structure of the defect area.

[0075] During the testing process, the various compensation modules work together to ensure measurement accuracy. Horizontal displacement compensation: The first laser interference module emits a laser, which is split into a measurement beam (illuminating the cantilever 5 / measuring mirror 134) and a reference beam (illuminating the reference mirror 133) by a beam splitter. The interference fringes of the two beams are received by the interference signal detector, and the horizontal displacement of the probe 6 is calculated. If the displacement exceeds the threshold, the controller immediately drives the X / Y axis drive layer of the piezoelectric ceramic 12 to extend and retract to compensate for the displacement deviation.

[0076] High-focus compensation: The laser emitter 141 of the focus tracking module emits a laser, which is reflected by the first reflector 142 to the wafer surface, and then reflected by the second reflector 143 to the laser detector 144. If there are undulations on the wafer surface, causing the distance between the probe 6 and the wafer surface to exceed the focusing range, the laser reflection position received by the laser detector 144 will be offset. The controller calculates the height adjustment amount based on the offset, drives the Z-axis drive layer of the piezoelectric ceramic 12 to extend and retract, adjusts the height of the probe 6, maintains the focusing state, and avoids repeated measurements caused by interlayer focusing instability.

[0077] It should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0078] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0079] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between components; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0080] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0081] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A wafer inspection device, characterized in that, include: A scanning electron microscope (SEM) includes a tube, an objective lens, and a sample chamber. The objective lens is disposed in the sample chamber, and a sample stage for holding a wafer to be inspected is disposed in the sample chamber. The SEM is used to acquire two-dimensional morphological images of the surface of the wafer to be inspected. An atomic force microscope (AFM) is provided, which is located in the sample chamber and does not contact the sample stage. The AFM includes a cantilever and a probe mounted at the end of the cantilever. The probe is used to acquire the three-dimensional structure of the wafer to be inspected.

2. The wafer inspection apparatus according to claim 1, characterized in that, The cantilever is installed on the outer wall of the mirror tube.

3. The wafer inspection apparatus according to claim 1, characterized in that, The cantilever is mounted on the pole shoe of the objective lens.

4. The wafer inspection apparatus according to claim 1, characterized in that, The cantilever is installed on the inner wall of the sample chamber.

5. The wafer inspection apparatus according to any one of claims 1-4, characterized in that, It also includes an initial position adjustment mechanism, which is used to adjust the initial relative position between the probe and the wafer to be tested.

6. The wafer inspection apparatus according to claim 5, characterized in that, The initial position adjustment mechanism also includes an optical lens or a second laser interference module.

7. The wafer inspection apparatus according to any one of claims 1-4, characterized in that, The end of the cantilever away from the probe is equipped with a piezoelectric ceramic, which enables fine-tuning of the probe in the horizontal and vertical directions through directional deformation.

8. The wafer inspection apparatus according to claim 7, characterized in that, It also includes a first laser interference module, which includes a first light source, a first beam splitter, a reference mirror, a measuring mirror, and a first interference signal detector. The first light source and the first beam splitter are located outside the sample chamber, the reference mirror is located inside the sample chamber, and the measuring mirror is disposed at the end of the cantilever away from the probe. The laser emitted by the first light source is split into a measuring beam and a reference beam by the first beam splitter. The reference beam is reflected back to the first interference signal detector by the reference mirror, and the measuring beam is reflected back to the first interference signal detector by the cantilever.

9. The wafer inspection apparatus according to claim 7, characterized in that, It also includes a focusing and tracking module, which includes a laser emitter, a first reflector, a second reflector, and a laser detector. The laser emitter and the laser detector are located outside the sample chamber. The first reflector and the second reflector are located on both sides of the lens barrel. The laser beam emitted by the laser emitter is reflected by the first reflector to the surface of the wafer to be tested, then reflected by the surface of the wafer to be tested to the second reflector, and then reflected by the second reflector to the laser detector.

10. The wafer inspection apparatus according to claim 6, characterized in that, It also includes a second laser interference module, which includes a second light source, a second beam splitter, and a second interference signal detector. The second light source and the second beam splitter are located above the wafer to be tested. The laser emitted by the second light source is split into a measurement beam and a reference beam by the second beam splitter. The reference beam is reflected back to the second interference signal detector by the upper surface of the wafer, and the measurement beam is reflected back to the second interference signal detector by the probe.

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