Online optical interference flatness measuring method for high-resistance silicon wafer

Abstract

The invention relates to an on-line optical interference flatness measuring method for a high-resistance silicon wafer, which belongs to the technical field of semiconductor silicon wafer processing and comprises the following operation steps: step 1, feeding and positioning are carried out, and the silicon wafer is placed at a specified position of a measuring table; and 2, starting the rapid automatic focusing system to complete the focal length adjustment of the objective lens. 3, the piezoelectric ceramic driver pushes the reference mirror to move according to the set step length, and meanwhile the high-speed camera synchronously collects a plurality of phase-shift interferograms; and 4, a built-in high-performance processor operates a phase shift algorithm in real time, reconstructs a three-dimensional morphology graph of the whole silicon wafer, and immediately calculates key flatness parameters. And fifthly, sorting and discharging are conducted. By avoiding electrical measurement, the problem that the high-resistance silicon wafer is difficult to detect by a traditional method due to poor conductivity is solved. The whole process is highly automatic, rapid focusing, synchronous phase shift acquisition, real-time calculation and automatic sorting are integrated, and efficient and accurate flatness detection on a production line is realized.

Description

Technical Field

[0001] This invention relates to the field of semiconductor silicon wafer processing technology, and more specifically to an online optical interference flatness measurement method for high-resistivity silicon wafers. Background Technology

[0002] The existing mainstream eddy current method for measuring high resistivity (>100Ω·cm) silicon wafers is severely affected by the non-uniformity of electrical parameters such as "resistivity striations" inside the silicon wafer, because its principle is based on indirectly estimating the thickness by measuring the dielectric constant. This leads to distortion of the thickness and flatness measurement values.

[0003] While traditional offline optical interferometers offer high precision, they are bulky, sensitive to environmental vibrations, and relatively slow in measurement speed, making them difficult to integrate into semiconductor manufacturing lines to achieve 100% online rapid inspection.

[0004] Traditional capacitive or eddy current flatness measurement methods rely on the conductivity of silicon wafers. However, high-resistivity silicon wafers have extremely poor conductivity, resulting in low accuracy or even failure of these electrical methods.

[0005] Therefore, there is an urgent need on the production line for a flatness measurement solution that can take into account high precision, high speed, non-contact operation, and is completely unaffected by the resistivity of silicon wafers, so as to achieve efficient and accurate control of the quality of high-resistivity silicon wafers. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing an online optical interferometry flatness measurement method for high-resistivity silicon wafers. By circumventing electrical measurements, it solves the problem of high-resistivity silicon wafers being difficult to inspect using traditional methods due to their poor conductivity. The entire process is highly automated, integrating rapid focusing, synchronous phase-shift acquisition, real-time calculation, and automatic sorting, achieving efficient and accurate flatness inspection on the production line.

[0007] The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions: An online optical interference flatness measurement method for high-resistivity silicon wafers includes a silicon wafer. The online optical interference flatness measurement device includes an objective lens for detecting the silicon wafer, a CCD camera is provided on the side of the objective lens, a light source is provided above the objective lens, a beam splitter is provided between the light source and the objective lens, and a reference mirror is provided between the side of the beam splitter and the CCD camera.

[0008] The online optical interferometric flatness measurement method includes the following steps: Step 1: Loading and positioning. The robotic arm takes the silicon wafer to be tested out of the wafer transfer box and places it in the designated position on the measuring table.

[0009] Step 2: Perform rapid focusing. The rapid autofocus system is activated to complete the focal length adjustment of the objective lens.

[0010] Step 3: Perform synchronous phase shifting and acquisition. The piezoelectric ceramic actuator drives the reference mirror to move at a predetermined step size, while the high-speed camera simultaneously acquires multiple phase shifting interferograms.

[0011] Step 4: Real-time calculation and output. The built-in high-performance processor runs the phase-shifting algorithm in real time to reconstruct the three-dimensional topography of the entire silicon wafer and immediately calculates and outputs the key flatness parameters of TTV, GBIR and SFQR.

[0012] Step 5: Sorting and unloading. The system automatically determines good or bad products based on the measurement results and instructs the robotic arm to send the silicon wafers to different wafer transfer boxes.

[0013] Preferably, the light source is a low-coherence light source, and the reference mirror is precisely moved and phase shifted by a piezoelectric ceramic phase shifter; the beam splitter, the reference mirror and the piezoelectric ceramic phase shifter are combined to form the core interference optical path, and the light is reflected after shining on the silicon wafer surface and interferes with the reference optical path.

[0014] As a preferred method, a series of phase-shifting interference patterns are captured by a high-speed CCD camera; using the phase-shifting interference algorithm, the precise height difference of each point on the silicon wafer surface relative to the reference wavefront is directly calculated, thereby directly obtaining its three-dimensional morphology and completely avoiding the influence of electrical parameters.

[0015] As a preferred method, the precise phase corresponding to each pixel is calculated using the Hariharan algorithm and the least squares method, and then the height difference of the point relative to the reference plane is calculated. Finally, the three-dimensional topography of the entire silicon wafer is stitched together.

[0016] Ideally, 5 to 13 phase-shift interferograms should be acquired. Fewer than 5 images typically cannot effectively suppress noise and errors, resulting in insufficient computational accuracy. More than 13 images increase acquisition and processing time, affecting the speed of online measurement, while offering limited accuracy improvement and thus not being cost-effective.

[0017] The present invention can achieve the following effects: This invention provides an online optical interferometric flatness measurement method for high-resistivity silicon wafers. Compared with existing technologies, it utilizes an optical system based on a low-coherence light source and phase-shift interferometry to directly measure the three-dimensional morphology of the silicon wafer surface, thereby calculating key flatness parameters such as TTV, GBIR, and SFQR. By avoiding electrical measurements, it solves the problem that high-resistivity silicon wafers are difficult to inspect using traditional methods due to their poor conductivity. The entire process is highly automated, integrating rapid focusing, synchronous phase-shift acquisition, real-time calculation, and automatic sorting, achieving efficient and accurate flatness inspection on the production line.

[0018] Highly targeted: It accurately identifies the measurement pain points in the niche market of high-resistivity silicon wafers, and the technical solution is highly matched with the problem.

[0019] Advanced technology: It adopts mainstream technologies in modern optical measurement (low coherence interference, phase shift technology), which in principle can realize high-precision, non-contact measurement.

[0020] High practicality: It fully considers the industrial production environment and emphasizes "online", "high speed", "real-time" and "automation", which meets the actual needs of the semiconductor manufacturing industry. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the present invention.

[0022] In the diagram: 1. Light source; 2. Beam splitter; 3. Reference mirror; 4. CCD camera; 5. Silicon wafer; 6. Objective lens. Detailed Implementation

[0023] The technical solution of the invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings.

[0024] Example: Figure 1 As shown, an online optical interference flatness measurement method for high-resistivity silicon wafers includes a silicon wafer 5. The online optical interference flatness measurement device includes an objective lens 6 for detecting the silicon wafer 5. A CCD camera 4 is provided on the side of the objective lens 6. A light source 1 is provided above the objective lens 6. A beam splitter 2 is provided between the light source 1 and the objective lens 6. A reference mirror 3 is provided between the side of the beam splitter 2 and the CCD camera 4.

[0025] An online optical interferometric flatness measurement method includes the following steps: Step 1: Loading and positioning. The robotic arm takes the silicon wafer 5 to be tested from the wafer transfer box and places it in the designated position on the measuring stage.

[0026] Step 2: Perform rapid focusing. The rapid autofocus system is activated to complete the focal length adjustment of objective lens 6.

[0027] Step 3: Perform synchronous phase shifting and acquisition. The piezoelectric ceramic actuator drives the reference mirror to move at predetermined step sizes, while the high-speed camera simultaneously acquires multiple phase-shifted interferograms. The number of phase-shifted interferograms acquired is 5 to 13.

[0028] Light source 1 uses a low-coherence light source, and reference mirror 3 achieves precise movement and introduces phase shift through piezoelectric ceramic phase shifter; combined with beam splitter 2, reference mirror 3 and piezoelectric ceramic phase shifter, it forms the core interference optical path. After the light shines on the surface of silicon wafer 5, it is reflected and interferes with the reference optical path.

[0029] A series of phase-shifting interference patterns are captured by a high-speed CCD camera 4; using the phase-shifting interference algorithm, the precise height difference of each point on the silicon wafer surface relative to the reference wavefront is directly calculated, thereby directly obtaining its three-dimensional morphology and completely avoiding the influence of electrical parameters.

[0030] Step 4: Real-time calculation and output. The built-in high-performance processor runs the phase-shifting algorithm in real time to reconstruct the three-dimensional topography of the entire silicon wafer and immediately calculates and outputs the key flatness parameters of TTV, GBIR and SFQR.

[0031] The precise phase of each pixel is calculated using the Hariharan algorithm and the least squares method, and then the height difference of that point relative to the reference plane is calculated. Finally, the three-dimensional topography of the entire silicon wafer is stitched together.

[0032] Step 5: Sorting and unloading. The system automatically determines good or bad products based on the measurement results and instructs the robotic arm to send the silicon wafers to different wafer transfer boxes.

[0033] In summary, this online optical interferometric flatness measurement method for high-resistivity silicon wafers utilizes an optical system based on a low-coherence light source and phase-shift interferometry technology to directly measure the three-dimensional morphology of the silicon wafer surface, thereby calculating key flatness parameters such as TTV, GBIR, and SFQR. By avoiding electrical measurements, it solves the problem of high-resistivity silicon wafers being difficult to inspect using traditional methods due to their poor conductivity. The entire process is highly automated, integrating rapid focusing, synchronous phase-shift acquisition, real-time calculation, and automatic sorting, achieving efficient and accurate flatness inspection on the production line.

[0034] Absolute accuracy and authenticity: Direct measurement of geometric shape, the measurement results are completely unaffected by the electrical properties of silicon wafer such as resistivity and resistance lines, and the obtained flatness data is the true geometric shape of the silicon wafer, with an accuracy of up to the nanometer level.

[0035] True Online Capability: Through integrated vibration-resistant design and high-speed phase acquisition technology, high-precision interferometry technology has been successfully transferred from the laboratory environment to the noisy production line, achieving online, high-speed, and 100% inspection. Full-Parameter Non-Destructive Measurement: Non-contact measurement causes zero damage to the silicon wafer. A single measurement can obtain three-dimensional data of the entire surface, enabling analysis of all flatness parameters (TTV, Bow, Warp, SFQR, etc.), providing more comprehensive quality information. Enhanced Production Line Intelligence: Real-time, accurate data provides the most direct feedback for process control, helping to achieve closed-loop control of the manufacturing process, improving overall yield and product consistency.

[0036] The above description is only a specific embodiment of the present invention, but the structural features of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. An in-line optical interferometric flatness measurement method for high resistivity silicon wafers, comprising a silicon wafer (5), characterized in that: The online optical interference flatness measuring device comprises an objective lens (6) for detecting a silicon wafer (5), a CCD camera (4) arranged at the side end of the objective lens (6), a light source (1) arranged above the objective lens (6), a beam splitter (2) arranged between the light source (1) and the objective lens (6), and a reference mirror (3) arranged between the side edge of the beam splitter (2) and the CCD camera (4). The online optical interference flatness measuring method comprises the following steps: Step 1: loading and positioning, a robot takes the silicon wafer (5) to be measured from a wafer conveying box and places it at a specified position on a measuring table; Step 2: rapid focusing, a rapid automatic focusing system is started to adjust the focal length of the objective lens (6); Step 3: synchronous phase shifting and collecting, a piezoelectric ceramic driver drives the reference mirror to move at a predetermined step length, and a high-speed camera synchronously collects multiple phase shift interference patterns; Step 4: real-time calculation and output, a built-in high-performance processor runs a phase shift algorithm in real time to reconstruct a three-dimensional topography of the entire silicon wafer and immediately calculates and outputs the key flatness parameters of TTV, GBIR and SFQR; Step 5: sorting and unloading, the system automatically judges the good or bad products according to the measurement results, and instructs the robot to send the silicon wafer to different wafer conveying boxes.

2. The method for in-line optical interferometric flatness measurement of high resistivity silicon wafers as claimed in claim 1, wherein: The light source (1) is a low coherence light source, the reference mirror (3) is precisely moved and introduced with a phase shift by a piezoelectric ceramic phase shifter; the beam splitter (2), the reference mirror (3) and the piezoelectric ceramic phase shifter constitute a core interference light path, and the light reflected after irradiating the surface of the silicon wafer (5) interferes with the reference light path.

3. The method for in-line optical interferometric flatness measurement of high resistivity silicon wafers as claimed in claim 2, wherein: A series of phase shift interference patterns are captured by a high-speed CCD camera (4); the phase shift interference algorithm is used to directly calculate the accurate height difference of each point on the surface of the silicon wafer relative to the reference wave front, so as to directly obtain the three-dimensional topography, and the influence of the electrical parameters is completely avoided.

4. The method for in-line optical interferometric flatness measurement of high resistivity silicon wafers as claimed in claim 1, wherein: The accurate phase corresponding to each pixel point is calculated by the Hariharan algorithm and the least square method, and then the height difference of the point relative to the reference plane is converted, and finally the three-dimensional topography of the entire silicon wafer is spliced.

5. The method for in-line optical interferometric flatness measurement of high resistivity silicon wafers as claimed in claim 1, wherein: The number of collected phase shift interference patterns is 5-13.

Images