A measuring device and a measuring method for measuring the thickness of a silicon wafer

Abstract

This invention provides a measuring device and method for measuring the thickness of silicon wafers. The measuring device for measuring the thickness of silicon wafers includes: a light-emitting element for emitting incident light; a multifaceted cone including multiple facets, with its central axis coinciding with a vertical axis and its tip vertically downward; a driving mechanism connected to the multifaceted cone for driving the multifaceted cone to rotate uniformly around the vertical axis; and a capacitance probe disposed above the silicon wafer. The light-emitting element emits light in the direction of its light emission towards the facets of the multifaceted cone. The multifaceted cone rotates around its central axis, and the incident light emitted by the light-emitting element irradiates different facets of the multifaceted cone. The light is reflected by the facets and passes through the through-hole of the capacitance probe to form reflected light spots on the silicon wafer. The position of the reflected light spots changes over time, so that multiple light spots are formed within the scanning area of ​​the silicon wafer surface within a certain time period of the capacitance probe scanning, eliminating the shadow effect.

Description

Technical Field

[0001] This invention relates to the field of semiconductor testing technology, and more specifically, to a measuring device and method for measuring the thickness of silicon wafers. Background Technology

[0002] The capacitance method is commonly used to measure the thickness of silicon wafers. This method offers advantages such as being non-contact, having a fast response time, and offering high accuracy, making it widely applicable in online thickness inspection during semiconductor manufacturing. The basic principle involves using a capacitance probe and the silicon wafer to form a parallel-plate capacitor; the wafer thickness is then calculated by measuring the capacitance value.

[0003] However, for high-resistivity silicon wafers, the concentration of free carriers within the wafer is extremely low, and its conductivity is close to that of an insulator. In this case, the capacitance probe cannot obtain a stable measurement signal, limiting the application of capacitance methods in online detection of high-resistivity silicon wafers. To solve this problem, existing technologies often employ illumination methods, using near-infrared light to irradiate the silicon wafer surface. Through the photogenerated carrier effect, electron-hole pairs are generated in the surface layer, temporarily reducing the surface resistivity and making capacitance measurement possible. Common illumination schemes include fixed-direction oblique illumination: using a single LED to obliquely illuminate the silicon wafer surface from a fixed direction. This scheme is simple in structure and generates little heat, but because the light intensity on the side closer to the light source is higher than on the side farther away, it leads to an asymmetrical distribution of photogenerated carrier concentration, producing a "shadowing effect." When the orientation of the silicon wafer changes, the measurement value of the capacitance probe fluctuates accordingly, resulting in poor stability and repeatability. To eliminate the shadowing effect, some schemes use multiple LEDs arranged in a ring to simultaneously illuminate the silicon wafer from different directions. This scheme can achieve multi-directional illumination, but the simultaneous operation of multiple LEDs generates a large amount of heat, which is conducted to the capacitance probe, causing thermal expansion and resulting in capacitance measurement drift. Meanwhile, this scheme is complex in structure and expensive. It also includes coaxial vertical illumination, where the light source is positioned on the central axis of the probe, allowing the light to shine vertically downwards onto the silicon wafer. While this scheme produces a circular light spot without elliptical distortion, due to the anisotropic characteristics of the silicon wafer surface, such as crystal orientation, defects, and electrode patterns, even with perpendicular incident light, illumination from a fixed horizontal direction will still cause differences in the photogenerated carrier generation efficiency at different locations, and the measured values ​​will still fluctuate with the orientation of the silicon wafer.

[0004] In summary, existing technical solutions for measuring the thickness of high resistivity silicon wafers using the capacitance method cannot simultaneously meet the requirements of low heat generation, simple structure, and uniform illumination. In particular, there is a lack of a uniform illumination device that can fundamentally eliminate the shadowing effect caused by fixed-direction illumination and generate little heat. Summary of the Invention

[0005] In view of the problems existing in the prior art of measuring silicon wafer thickness by capacitance method, this application provides a measuring device and method for measuring silicon wafer thickness, which solves the problem that it is difficult to avoid shadowing effect when measuring silicon wafer thickness by capacitance method in the prior art.

[0006] To achieve the above and other related objectives, the present invention provides a measuring device and method for measuring the thickness of silicon wafers, comprising:

[0007] Light-emitting elements are used to emit incident light;

[0008] A multifaceted cone includes multiple facets, each facet forming a predetermined angle with a horizontal plane. The central axis of the multifaceted cone coincides with a vertical axis, and the tip of the multifaceted cone is vertically downward.

[0009] A drive mechanism is connected to the multifaceted cone and is used to drive the multifaceted cone to rotate uniformly around the vertical axis.

[0010] A capacitive probe is positioned above the silicon wafer, and a through hole is formed in the center of the capacitive probe, with the center of the through hole coinciding with the central axis of the multifaceted pyramid.

[0011] The light-emitting element emits light in the direction of the facet of the multifaceted cone. The multifaceted cone rotates around the central axis. The incident light emitted by the light-emitting element illuminates different facets of the multifaceted cone. The light is reflected by the facets and passes through the through-hole of the capacitive probe to form a reflected light spot on the silicon wafer. The position of the reflected light spot changes over time.

[0012] Optionally, the polyhedron is a regular polyhedron with at least three facets; when the number of facets is even, the included angle between two opposite facets of the polyhedron is 90°.

[0013] Optionally, the light-emitting element emits incident light in a horizontal direction, and any of the facets makes a predetermined angle of 45° with the horizontal direction.

[0014] Optionally, it further includes: a control module, which is electrically connected to the drive mechanism and the capacitance probe. The control module is used to control the rotational speed of the drive mechanism, receive the capacitance signal output by the capacitance probe, and calculate the thickness of the silicon wafer based on the capacitance signal.

[0015] Optionally, the height of the polyhedron is defined as H1, and the vertical distance between the horizontal plane where the light-emitting element's light exit end is located and the bottom surface of the polyhedron is defined as H2, where H1 and H2 satisfy: H1≤H2≤ H1.

[0016] Optionally, the rotational speed of the polyhedron is defined as n, in rpm, and the integration time of the capacitor probe is defined as T, in seconds. Within each integration time T, the polyhedron rotates k times, k≥1, and satisfies n*T≥60k.

[0017] Optionally, the rotational speed of the drive mechanism is 6000 rpm, and the integration time of the capacitor probe is 10 ms.

[0018] Optionally, the surface of the multifaceted cone is coated with a high-reflectivity metal film.

[0019] This application also provides a method for measuring the thickness of a silicon wafer, comprising:

[0020] Provide incident light;

[0021] A polyhedron rotates at a constant speed around a vertical axis, and each facet of the polyhedron forms a predetermined angle with the horizontal plane;

[0022] The rotating multifaceted cone reflects the incident light sequentially, forming multiple reflected light spots on the silicon wafer surface;

[0023] Adjust the rotational speed of the multifaceted cone and / or the integration time T of the capacitive probe so that the multifaceted cone rotates at least one full revolution in each integration time.

[0024] During the integration time of the ring capacitance probe, the capacitance value corresponding to the silicon wafer is measured, wherein during the integration time, the reflected light spot completes at least one complete cycle of scanning, so that each point in the scanning area receives light from multiple different horizontal directions in sequence.

[0025] The thickness of the silicon wafer is calculated based on the capacitance value.

[0026] Optionally, adjusting the rotational speed and / or integration time of the multifaceted cone includes: selecting the integration time T based on the response speed of the capacitive probe; and adjusting according to n≥ Determine the minimum rotational speed; increase the rotational speed within the mechanical limits to increase the number of revolutions per integral time.

[0027] As described above, the measuring device and method for measuring silicon wafer thickness provided by the present invention have at least the following beneficial technical effects:

[0028] In the measuring device and method for measuring silicon wafer thickness of the present invention, a single fixed light-emitting element is used in conjunction with a rotating multifaceted cone. The LED emits incident light in a horizontal direction, which is reflected by the facets of the multifaceted cone and becomes vertically downward light, forming a reflected light spot on the surface of the silicon wafer. When the multifaceted cone rotates at a uniform speed, the position of the light spot changes periodically, so that each point in the scanning area on the silicon wafer surface receives illumination from multiple different horizontal directions at different times. By adjusting the rotation speed of the multifaceted cone and the integration time of the capacitance probe, it can be ensured that the light spot completes at least one full scan in each integration cycle. This eliminates the problem of asymmetric photogenerated carrier concentration (shadowing effect) caused by fixed-direction illumination, improving measurement stability and repeatability. Furthermore, the present invention uses only a single light-emitting element, which significantly reduces heat generation compared to the ring-shaped multi-LED scheme, eliminating the need for a complex heat dissipation structure. At the same time, the light-emitting element can be installed separately from the multifaceted cone, further isolating the heat source and avoiding thermal expansion of the capacitance probe caused by heat conduction, thereby ensuring the long-term stability and repeatability accuracy of capacitance measurement. Attached Figure Description

[0029] Figure 1 The diagram shown is a structural schematic of a measuring device for measuring the thickness of a silicon wafer provided in Embodiment 1 of the present invention.

[0030] Figure 2 The diagram shows the distribution of light spots on the silicon wafer surface when the multifaceted cone rotates continuously as provided in Example 1.

[0031] Figure 3 The diagram shown is a structural schematic of the method for measuring the thickness of a silicon wafer provided in Example 2.

[0032] Reference numerals: 1. Light-emitting element; 2. Polyhedron; 21. Facet; 3. Drive mechanism; 4. Capacitive probe; 41. Through hole; 5. Silicon wafer; 6. Housing; 7. Control module. Detailed Implementation

[0033] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0034] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Although the illustrations only show components related to the present invention and are not drawn according to the actual number, shape and size of the components, the shape, quantity, positional relationship and proportion of each component can be arbitrarily changed under the premise of realizing the technical solution of this invention, and the layout of the components may also be more complex.

[0035] Example 1

[0036] This embodiment provides a measuring device for measuring the thickness of silicon wafers, such as... Figure 1 As shown, the measuring device for measuring the thickness of a silicon wafer includes: a light-emitting element 1 for providing incident light; a multifaceted cone 2 including multiple facets 21, the facets 21 forming a predetermined angle with the horizontal plane, the central axis of the multifaceted cone coinciding with the vertical axis, and the tip of the multifaceted cone 2 vertically downward; a driving mechanism 3, connected to the multifaceted cone 2 for driving the multifaceted cone 2 to rotate uniformly around the vertical axis; and a capacitance probe 4 disposed above the silicon wafer 5, the center of which has a through hole 41, the center of which coincides with the central axis of the multifaceted cone; wherein, the light emission direction of the light-emitting element points to the facets of the multifaceted cone, the multifaceted cone rotates around the central axis, the incident light emitted by the light-emitting element irradiates different facets of the multifaceted cone, and is reflected by the facets to form reflected light spots on the silicon wafer, and the position of the reflected light spots changes with time.

[0037] like Figure 1 As shown, the horizontal direction is defined as the X direction, and the vertical downward direction is defined as the Z direction. The light-emitting element 1 is fixedly mounted on the side of the multifaceted pyramid 2, and the light-emitting element 1 and the side of the multifaceted pyramid 2 are located on the same horizontal plane. The light-emitting element 1 is used to emit incident light in the horizontal direction. Generally, the light emitted by the light-emitting element 1 needs to be able to be effectively absorbed by the silicon material, thereby exciting a sufficient concentration of photogenerated carriers. Generally, the light-emitting element 1 includes an LED light source, a laser diode, a pulsed light-emitting device, etc. In this embodiment, the light-emitting element 1 uses an LED light source. Specifically, the wavelength emitted by the light-emitting element 1 is between 850 nm and 1050 nm. This wavelength band is used for near-infrared operation in the field of silicon wafer photoelectric detection, which highly matches the intrinsic absorption spectrum of silicon and can efficiently excite photogenerated carriers inside the silicon wafer. Preferably, the light-emitting element 1 emits a near-infrared LED with a wavelength of 940 nm, balancing absorption efficiency and penetration depth. Generally, the output power of the light-emitting element 1 is between 50 mW and 500 mW. In this embodiment, the output power of the light-emitting element 1 is 200 mW.

[0038] Optionally, the measuring device for measuring the thickness of the silicon wafer also includes a collimating lens to collimate the light emitted by the light-emitting element 1 into a horizontal parallel beam, thereby ensuring the stability and uniformity of the light spot. The mounting position of the light-emitting element 1 is such that its emitted light beam points horizontally towards the central axis of the multifaceted pyramid 2.

[0039] like Figure 1As shown, the polyhedron 2 is a regular polyhedron with its central axis coinciding with the vertical Z-direction, and its tip pointing vertically downwards. The polyhedron 2 includes multiple facets 21. Generally, the number of facets 21 in the polyhedron 2 is selected based on the requirements for illumination uniformity, the precision of light spot scanning, the overall structural dimensions, and the speed matching conditions. A larger number of facets results in a smaller step size for the horizontal azimuth angle jump of the reflected light from adjacent facets, a more circular light spot scanning trajectory, better average cancellation of anisotropy on the silicon wafer surface, and higher illumination uniformity. However, this also increases the processing difficulty and rotational inertia, and places higher demands on the torque of the drive mechanism. Conversely, too few facets result in an excessively large step size and insufficient azimuth sampling points. Optionally, in this embodiment, a regular polyhedron structure with ≥3 facets is selected, and the number of facets 21 includes 3, 4, 6, 8, 12, etc. Specifically, when the number of facets is even, the included angle between two opposite facets 21 is 90°.

[0040] Generally, the predetermined angle between the facet 21 and the horizontal plane can be selected according to the desired emission direction of the reflected light. In this embodiment, the polyhedron 2 is a regular hexagonal pyramid with six identical isosceles triangular facets 21. The angle between any two facets 21 is 90°. The light-emitting element 1 emits incident light in a horizontal direction, and the angle between the facet 21 and the horizontal plane is 45°. At this time, the incident light becomes vertically downward light after reflection. Optionally, the angle between each facet 21 and the horizontal plane is between 30° and 60°. The cone angle can be adjusted according to actual needs to change the emission direction. In other embodiments, the predetermined angle can be adjusted within the range of 30° to 60° to adapt to different measurement requirements (e.g., when oblique illumination is required). In this embodiment, the angle between each facet 21 and the horizontal plane is 45°. The angle design ensures that the horizontally incident light becomes vertically downward after reflection by the facet 21, and the main direction of the reflected light always remains vertical. Generally, the multifaceted cone 2 is made of aluminum alloy. The bottom diameter D1 of the multifaceted cone 2 is between 5mm and 20mm, and the height H1 is between 5mm and 15mm. In this embodiment, the bottom diameter D1 of the multifaceted cone 2 is 15mm, and the height H1 is 10mm.

[0041] Specifically, the light-emitting element 1 is mounted on the same horizontal plane as the central region of the facet 21 of the multifaceted pyramid 2, meaning the light emitted by the light-emitting element 1 is positioned between the tip and the base of the facet 21, close to the geometric center of the facet. For example... Figure 1As shown, preferably, the light-emitting element 1 is installed at the end away from the tip of the multifaceted cone 2 and close to the bottom surface of the multifaceted cone 2, that is, close to the end of the driving mechanism 3, so as to avoid the light shining too close to the tip of the cone. The reflective area of ​​the facet 21 near the tip is too small, the light energy capture rate is low, and the processing error of the tip can easily cause the reflection direction to deviate. If the light from the light-emitting element 1 is close to the bottom surface of the multifaceted cone 2, the reflected light is easily blocked by the through hole 41 of the capacitor probe 4.

[0042] Specifically, the height of the polyhedron 2 (the vertical distance from the tip to the base) is H1, and the vertical distance between the horizontal plane where the light-emitting element 1's light exit end is located and the base of the polyhedron 2 is H2. Then: H1≤H2≤ H1, further, H1≤H2≤ H1; In this embodiment, taking the incident light from the light-emitting element 1 and the central region of the multifaceted cone 2 as an example where they are on the same horizontal line, i.e., H2= H1. At this time, the light shines near the geometric center of the facet 21, balancing the light energy capture rate and the stability of the reflection direction, and the reflected beam can pass through the through hole 41 of the capacitive probe 4 without obstruction.

[0043] Specifically, the multifaceted cone 2 is made of aluminum alloy, and each facet 21 is coated with a high-reflectivity metal film to improve the reflection efficiency of near-infrared light. Generally, the thickness of the metal film is between 100nm and 500nm. In this embodiment, the thickness of the metal film is 200nm. Generally, the metal film includes an aluminum film or a silver film. In this embodiment, the metal film is a silver film. The reflectivity of the silver film in the near-infrared band (such as 940nm) can reach more than 95%, thus improving the reflectivity.

[0044] The drive mechanism 3 is connected to the multifaceted cone 2 and is used to drive the multifaceted cone 2 to rotate uniformly around its central axis Z. Optionally, the drive mechanism 3 includes a stepper motor or a micro brushless DC motor. The drive mechanism 3 is installed directly above the multifaceted cone 2, and its output shaft is fixedly connected to the center of the top surface of the multifaceted cone 2.

[0045] Generally, the rotational speed of the drive mechanism 3 is adjustable, and the rotational speed is matched with the integration time of the capacitor probe 4, so that the multifaceted cone 2 rotates at least one full revolution in each integration cycle, ensuring that all facets 21 can reflect light sequentially to achieve omnidirectional average illumination. Generally, the rotational speed of the drive mechanism 3 is between 3000 rpm and 8000 rpm, and in this embodiment, the preferred rotational speed is 6000 rpm.

[0046] The capacitive probe 4 is horizontally positioned directly above the silicon wafer 5. Generally, the distance between the capacitive probe 4 and the silicon wafer 5 is between 1 and 4 mm. In this embodiment, the distance between the capacitive probe 4 and the silicon wafer 5 is 2 mm, and the central axis of the capacitive probe 4 coincides with the central axis of the multifaceted pyramid 2. For example... Figure 1 As shown, the center of the capacitive probe 4 has a through hole 41, the center of which coincides with the central axis of the multifaceted cone 2, allowing the reflected light 22 to pass through and irradiate the silicon wafer 5 below.

[0047] Generally, the diameter D of the through hole 41 is greater than or equal to the horizontal cross-sectional diameter D2 of the multifaceted cone 2 at the height of the reflected light 22. The height corresponds to the position where the horizontal light emitted by the light-emitting element 1 illuminates the facet 21. This ensures that the reflected light passes through the through hole 41 without obstruction, while not excessively reducing the effective electrode area of ​​the capacitance probe 4. In this embodiment, the bottom diameter D1 of the multifaceted cone 2 is between 5 mm and 20 mm, the diameter of the middle cross-section D2 is between 3 mm and 10 mm, and the diameter of the through hole 41 is between 3 mm and 8 mm, slightly larger than the diameter of the middle cross-section but smaller than the bottom diameter, balancing optical transmittance and capacitance measurement sensitivity. Specifically, in this embodiment, the diameter of the through hole 41 is 7.5 mm.

[0048] Optionally, the measuring device for measuring the thickness of a silicon wafer also includes a housing 6, which is used to fix the light-emitting element 1, the multifaceted cone 2, the driving mechanism 3, and the capacitance probe 4. Generally, the housing 6 is made of a material with electromagnetic shielding properties and good heat dissipation properties.

[0049] Optionally, the measuring device for measuring the thickness of the silicon wafer also includes a vibration damping structure disposed between the drive mechanism 3 and the annular capacitor probe 4, for isolating the vibration generated by the rotation of the multifaceted cone.

[0050] like Figure 2 The image shown is a top view of the light spot scanning path on the silicon wafer surface during continuous rotation of the multifaceted cone provided in this embodiment, with the projection point of the vertical axis of the cone's center onto the silicon wafer as the central reference. During the uniform rotation of the multifaceted cone 2 with the drive mechanism, the position change of the reflected light spot on the surface of the silicon wafer 5 and the corresponding horizontal azimuth angle of the light rays are shown as the multifaceted cone 2 rotates one revolution. Specifically, with the projection point O of the probe axis onto the silicon wafer surface as the center, multiple light spots are evenly distributed on a circle of radius r, with a central angle of 60° between adjacent light spots. Because the multifaceted cone 2 rotates at a high speed, the light spots rapidly cycle and appear sequentially within the integration time of the capacitive probe. Figure 2 The location is shown. Although only one spot of light exists at any given moment, after averaging over time, the entire circumferential area is illuminated from six different horizontal directions, which is equivalent to uniform illumination from all directions at 360°.

[0051] Optionally, the measuring device for measuring the thickness of the silicon wafer also includes a control module 7, which is electrically connected to the light-emitting element 1, the driving mechanism 3, and the capacitance probe 4. The control module 7 controls the rotation speed signal of the driving mechanism 3 to adjust the rotation speed of the multifaceted cone 2 in real time; the control module 7 is used to receive the capacitance signal output by the capacitance probe 4 and calculate the thickness of the silicon wafer 5 based on the relationship between capacitance and thickness.

[0052] Specifically, to ensure that the device of this invention achieves omnidirectional uniform illumination within the integration time of the capacitive probe, the following must be satisfied: during one rotation of the polyhedron (i.e., all facets reflect once in sequence), the capacitive probe must complete at least one complete signal acquisition. Defined as: the rotational speed n of the polyhedron (in rpm); the number of facets N of the polyhedron; and the integration time T of the capacitive probe (in seconds). Then, in each integration time, the number of rotations m of the polyhedron is: m = T. During the integration time T, the relationship between the number of revolutions k of the polyhedron and its rotational speed is: m = T≥k, i.e., n*T≥60k, where k≥2. When there is at least one chance of the light ray being reflected (i.e., the light spot sweeps across at least all N directions): T≥1, that is, n*T≥60.

[0053] The silicon wafer thickness measuring device provided in this embodiment uses a fixed light-emitting element and a rotating multifaceted cone to reflect horizontally incident light into vertically downward light, forming a moving light spot on the silicon wafer surface. During the integration time of the capacitance probe, uniform illumination is achieved in all directions, eliminating the asymmetry in photogenerated carrier concentration caused by fixed-direction illumination. This makes the capacitance measurement independent of the silicon wafer's orientation, significantly improving measurement stability and repeatability. Furthermore, the use of only a single light-emitting element greatly reduces heat generation, eliminating the need for complex heat dissipation structures.

[0054] Example 2

[0055] This embodiment also provides a method for measuring the thickness of a silicon wafer, such as... Figure 3 The diagram illustrates a method for measuring silicon wafer thickness provided in this embodiment. S1: Provide incident light; S2: Adjust the rotational speed n of the multifaceted cone and / or the integration time T of the capacitance probe, ensuring the multifaceted cone rotates at least one full revolution within each integration time; S3: The multifaceted cone rotates uniformly around a vertical axis, with each facet of the cone forming a predetermined angle with the horizontal plane; S4: The rotating multifaceted cone sequentially reflects the incident light, forming multiple light spots on the silicon wafer surface; S5: Within the integration time of the annular capacitance probe, measure the capacitance value corresponding to the silicon wafer, wherein within the integration time, the light spots complete at least one full cycle of scanning, ensuring that each point within the scanning area sequentially receives illumination from multiple different horizontal directions; S6: Calculate the silicon wafer thickness based on the capacitance value.

[0056] Specifically, S1: Turn on the fixed light-emitting element 1 to emit incident light. Optionally, the direction of the incident light can be adjusted according to measurement requirements, such as setting it to a horizontal direction, an oblique direction, or other predetermined direction. In this embodiment, the incident light is adjusted to a horizontal direction, so that it emits a horizontally aligned parallel beam, pointing towards the central axis of the multifaceted cone 2. Generally, the wavelength of the incident light is in the near-infrared band of 850 nm to 1050 nm, which can be effectively absorbed by the silicon material and excited to generate photogenerated carriers. In this embodiment, the light-emitting element 1 uses a 940 nm near-infrared LED light source with an output power of 200 mW.

[0057] S2: Adjust the rotational speed n of the multifaceted cone and / or the integration time T of the capacitive probe. Adjust the rotational speed n of the multifaceted cone 2 and / or the integration time T of the capacitive probe 4 so that the multifaceted cone 2 rotates at least one full revolution in each integration time, ensuring that all facets 21 reflect light sequentially. Specific parameter matching relationship: Number of revolutions m of the multifaceted cone in each integration time: m = T; To ensure that each of the N facets has at least one chance to reflect light (i.e., the light spot sweeps across all N directions at least once), the following must be satisfied: T≥1, i.e., n*T≥60. Furthermore, if we want each facet to be illuminated multiple times within the integration time to improve uniformity, we can require the number of rotations m≥k. Generally, k≥2, i.e., m= T≥k, that is, n*T≥60k.

[0058] In practical applications, the rotational speed n of the polyhedron, the number of facets N of the polyhedron, and the integration time T of the capacitance probe can be adjusted according to the specific requirements of the equipment, including:

[0059] Fixed integration time T, adjustable rotational speed n: When the integration time of the capacitance probe is preset by the measurement system, then the rotational speed n ≥ Assuming T = 10 ms = 0.01 s, then n ≥ 6000 rpm. If the number of irradiations k needs to be increased, the rotation speed n can be increased proportionally.

[0060] Fixed speed n, adjusted integral time T: When the speed of the drive mechanism is fixed, for example, n = 3000 rpm, the integral time can be appropriately extended to satisfy n ≥ For example, when n=3000rpm, T≥ =0.02s. However, it should be noted that an excessively long integration time may affect the measurement speed or introduce low-frequency noise; therefore, the maximum integration time should not exceed 20 ms.

[0061] Changing the number of facets N: The number of facets N directly affects the azimuth jump step size Δθ of the light spot. The rotational speed and integration time satisfy n*T≥60. Regardless of the value of N, all facets will be traversed within one revolution. The larger N is, the smaller the angular interval between adjacent directions, and the more thoroughly the shading effect is eliminated. Therefore, when rotational speed and integration time are limited, increasing N is an effective means to improve uniformity.

[0062] Optionally, to achieve the best measurement results, firstly, select a reasonable integration time T based on the response speed of the capacitance probe. Generally, the integration time T is between 1ms and 20ms. Secondly, according to n≥ First, determine the minimum rotational speed. Second, within the mechanical limits, increase the rotational speed as much as possible to increase the number of revolutions m per integration cycle (i.e., increase the number of irradiations in each direction). Optionally, select the number of facets N based on processing costs and uniformity requirements (generally, N≥3). After coordination, the light spot on the silicon wafer surface can be equivalent to 360° omnidirectional uniform irradiation within the integration time, thereby completely eliminating the shading effect.

[0063] S3: The multifaceted cone rotates at a constant speed around its vertical axis. The drive mechanism 3 is activated, causing the multifaceted cone 2 to rotate at a constant speed around its central axis (vertical direction). Each facet 21 of the multifaceted cone 2 forms a predetermined angle with the horizontal plane. In this embodiment, the predetermined angle is 45°.

[0064] S4: The rotating polyhedron reflects the incident light sequentially, forming a moving reflected light spot on the silicon wafer surface. Different facets 21 of the rotating polyhedron 2 reflect the incident light sequentially, forming a reflected light spot on the silicon wafer 5 surface, and the position of the reflected light spot changes periodically with the rotation of the polyhedron 2.

[0065] S5: Measure the capacitance value within the integration time. Within the integration time T of the capacitance probe 4, the light spot completes at least one full cycle of scanning, such that each point within the scanning area sequentially receives illumination from multiple different horizontal directions. The capacitance probe 4 acquires and outputs the average capacitance signal within this integration time.

[0066] S6: Calculate the silicon wafer thickness based on the capacitance value. The control module 7 receives the capacitance signal output by the capacitance probe 4 and calculates the thickness value of the silicon wafer 5 according to the pre-stored capacitance-thickness relationship formula or calibration curve.

[0067] The measurement method provided by this invention uses a rotating multifaceted cone to sequentially reflect horizontally incident light into vertically downward light rays, forming a moving light spot on the silicon wafer surface. Controlling the rotation speed *n* and integration time *T* ensures that the light spot completes at least one full revolution in each integration cycle. This fundamentally eliminates the problem of asymmetric photogenerated carrier concentration caused by fixed-direction illumination, preventing capacitance measurements from fluctuating with changes in the silicon wafer azimuth angle. Furthermore, it allows for fixing one parameter and flexibly adjusting others according to actual needs: fixing *T* and adjusting *n* to adapt to different measurement speed requirements; fixing *n* and adjusting *T* to match the integration time of existing equipment; changing *N* to adjust the azimuth angle jump step size, further improving uniformity. It is adaptable to different types of capacitance probes and drive mechanisms, exhibiting wide applicability.

[0068] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A measuring device for measuring the thickness of a silicon wafer, characterized by include: Light-emitting elements are used to emit incident light; A multifaceted cone includes multiple facets, each facet forming a predetermined angle with a horizontal plane. The central axis of the multifaceted cone coincides with a vertical axis, and the tip of the multifaceted cone is vertically downward. A drive mechanism is connected to the multifaceted cone and is used to drive the multifaceted cone to rotate uniformly around the vertical axis. A capacitive probe is positioned above the silicon wafer, and a through hole is formed in the center of the capacitive probe, with the center of the through hole coinciding with the central axis of the multifaceted pyramid. The light-emitting element emits light in the direction of the facet of the multifaceted cone. The multifaceted cone rotates around the central axis. The incident light emitted by the light-emitting element illuminates different facets of the multifaceted cone. The light is reflected by the facets and passes through the through-hole of the capacitive probe to form a reflected light spot on the silicon wafer. The position of the reflected light spot changes over time.

2. The measuring device for measuring the thickness of a silicon wafer according to claim 1, characterized in that, The polyhedron is a regular polyhedron with at least three faces; when the number of faces is even, the included angle between two opposite faces of the polyhedron is 90°.

3. The measuring apparatus for measuring the thickness of a silicon wafer according to claim 1, wherein The light-emitting element emits incident light in a horizontal direction, and the predetermined angle between any of the facets and the horizontal direction is 45°.

4. The measuring apparatus for measuring the thickness of a silicon wafer according to claim 1, wherein Also includes: The control module is electrically connected to the drive mechanism and the capacitance probe. The control module is used to control the rotation speed of the drive mechanism, receive the capacitance signal output by the capacitance probe, and calculate the thickness of the silicon wafer based on the capacitance signal.

5. The apparatus for measuring the thickness of a silicon wafer as recited in claim 1, wherein The height of the polyhedron is defined as H1, and the vertical distance between the horizontal plane where the light-emitting element's light exit end is located and the bottom surface of the polyhedron is defined as H2. H1 and H2 satisfy: H1≤H2≤ H1.

6. The measuring device for measuring silicon wafer thickness according to claim 1, characterized in that, The rotational speed of the polyhedron is defined as n, in rpm, and the integration time of the capacitor probe is defined as T, in seconds. Within each integration time T, the polyhedron rotates k times, k≥1, and satisfies n*T≥60k.

7. The measuring apparatus for measuring the thickness of a silicon wafer according to claim 6, wherein The drive mechanism rotates at 6000 rpm, and the integration time of the capacitor probe is 10 ms.

8. The apparatus for measuring the thickness of a silicon wafer as defined in claim 1, wherein The surface of the multifaceted cone is coated with a high-reflectivity metal film.

9. A measurement method of measuring a thickness of a silicon wafer, characterized by, include: Provide incident light; Adjust the rotational speed n of the multifaceted cone and / or the integration time T of the capacitive probe so that the multifaceted cone rotates at least one full revolution in each integration time. A polyhedron rotates at a constant speed around a vertical axis, and each facet of the polyhedron forms a predetermined angle with the horizontal plane; The rotating multifaceted cone reflects the incident light sequentially, forming multiple reflected light spots on the silicon wafer surface; During the integration time of the ring capacitance probe, the capacitance value corresponding to the silicon wafer is measured, wherein during the integration time, the reflected light spot completes at least one complete cycle of scanning, so that each point in the scanning area receives light from multiple different horizontal directions in sequence. The thickness of the silicon wafer is calculated based on the capacitance value.

10. The method for measuring silicon wafer thickness according to claim 9, characterized in that, Adjusting the multi-faceted cone rotation speed and / or integration time includes: selecting an integration time T according to the response speed of the capacitive probe; increasing the rotation speed to increase the number of rotations per integration time within the mechanical allowable range according to n≥ Determining the lowest rotation speed; increasing the rotation speed to increase the number of rotations per integration time within the mechanical allowable range.

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