Wafer resistivity and surface metal film thickness detection method based on double coils

Abstract

The invention discloses a wafer resistivity and surface metal film thickness detection method based on double coils, and the method comprises the steps: integrating a low-frequency inductance coil and a high-frequency inductance coil on a probe, detecting the wafer resistivity and the wafer surface metal film thickness in real time through the low-frequency inductance coil, and detecting an LOD value in real time through the high-frequency inductance coil. Correcting the measured resistivity of the wafer and the thickness of the metal film on the surface of the wafer according to the LOD value, namely, correcting the thickness of the metal film on the surface of the wafer according to the relationship between the resistivity of the wafer and the thickness of the metal film on the surface under different LOD values and the output voltage value of the low-frequency coil, and the resistivity value of the wafer to be detected and the thickness value of the metal film on the surface of the wafer corresponding to the LOD value detected by the current high-frequency coil in real time are obtained.

Description

Technical Field

[0001] This invention belongs to the field of detection technology, specifically relating to a method for detecting wafer resistivity and surface metal film thickness based on a dual-coil system. Background Technology

[0002] Wafers are the fundamental material for integrated circuit manufacturing and the cornerstone of integrated circuit development. Currently, most integrated circuit chips are manufactured on wafers using bulk silicon processes. During integrated circuit manufacturing, the resistivity of the wafer and the thickness of the metal thin film on its surface are crucial process parameters. Therefore, high-precision and high-efficiency measurement of wafer resistivity and the thickness of the metal thin film on the wafer surface is necessary.

[0003] Currently, traditional testing methods such as the four-probe method are widely used for wafer resistivity testing due to their high accuracy and stability. However, the four-probe method is a contact testing method, and during the testing process, the contact between the probe and the wafer may cause damage and contamination to the wafer surface. Furthermore, the four-probe method has low testing efficiency and a small testing range, making it difficult to adapt to working scenarios with high requirements for wafer surface integrity. Therefore, it is necessary to develop high-precision and high-efficiency non-destructive testing technologies to solve the problems existing in traditional testing methods.

[0004] Non-contact wafer resistivity measurement methods include inductive methods, microwave methods, and laser methods. These methods provide rapid and non-destructive approaches to measuring wafer resistivity and the thickness of the metal thin film on the wafer surface. Among these methods, the inductive method is widely favored due to its advantages of speed, high accuracy, and low cost. In the inductive method, an AC signal drives an inductor coil, generating an alternating induced current in the wafer. This alternating induced current changes the impedance of the inductor coil through mutual inductance. Different wafer resistivities correspond to different alternating induced current intensities, causing different changes in the coil impedance through mutual inductance. Therefore, by measuring the impedance value of the inductor coil, the resistivity of the wafer can be measured.

[0005] The accuracy of the inductive method is primarily affected by changes in the lift-off height (LOD), the distance between the inductor coil and the wafer surface. Changes in LOD during testing increase the detection error. Due to environmental vibrations and positional errors during testing, LOD variation is unavoidable. To improve the accuracy of the inductive method, traditional inductive wafer resistivity testing typically employs a high-precision mechanical positioning system to maintain a constant LOD. While this significantly improves accuracy, the high-precision mechanical positioning system also drastically increases the manufacturing cost of the testing equipment. Summary of the Invention

[0006] To address the problems of existing wafer inspection technologies, such as wafer surface damage, low inspection efficiency, low inspection accuracy, and high manufacturing costs, this invention provides a method for detecting wafer resistivity and surface metal film thickness based on dual coils. This method integrates a low-frequency inductor coil and a high-frequency inductor coil on a probe. The low-frequency coil detects wafer resistivity and surface metal film thickness in real time, while the high-frequency coil detects the LOD value in real time. The measured wafer resistivity and surface metal film thickness are then corrected based on the LOD value.

[0007] This invention is achieved through the following technical solution:

[0008] A method for detecting wafer resistivity and surface metal film thickness based on dual coils includes an XY-axis stage and a detection probe mounted on the XY-axis stage. The XY-axis stage controls the detection probe to any detection position in the XY plane.

[0009] The detection probe includes a low-frequency coil, a high-frequency coil, an electronic potting compound, and a housing. Both the low-frequency and high-frequency coils are embedded inside the housing, with the high-frequency coil located at the center of the low-frequency coil. They are coaxially arranged, and the bottom surfaces of the low-frequency and high-frequency coils are on the same horizontal plane. The housing is filled with electronic potting compound to fix the positions of the low-frequency and high-frequency coils. The low-frequency coil is used to detect the resistivity of the wafer and the thickness of the metal film on the wafer surface. The high-frequency coil is used to measure the LOD (Level of Displacement) value between the detection probe and the wafer.

[0010] First, calibration is performed: a standard wafer sample is selected for calibration, whose resistivity ρ and surface metal film thickness are known; the voltage output of the low-frequency coil is detected and recorded at different LOD values, thereby obtaining the relationship between the wafer resistivity and wafer surface metal film thickness and the voltage output of the low-frequency coil at different LOD values.

[0011] Testing: For the wafer to be tested, the position of the detection probe is adjusted by controlling the XY axis stage to perform single-point or multi-point global testing at any position. During the testing process, the low-frequency coil of the detection probe detects the wafer in real time and outputs a voltage value, while the high-frequency coil detects the LOD value in real time. The resistivity value and surface metal film thickness value measured by the low-frequency coil are corrected based on the LOD value. That is, based on the relationship between the wafer resistivity and surface metal film thickness and the output voltage value of the low-frequency coil under different LOD values ​​obtained by calibration, the resistivity value and surface metal film thickness value of the wafer to be tested corresponding to the LOD value detected by the high-frequency coil in real time are obtained.

[0012] In the above technical solution, the XY dual-axis worktable includes a base, an X-axis moving mechanism and a Y-axis moving mechanism. The X-axis moving mechanism is mounted on the base, and the Y-axis moving mechanism is mounted on the X-axis moving mechanism. The X-axis moving mechanism drives the Y-axis moving mechanism to move along the X-axis direction. The detection probe is mounted on the Y-axis moving mechanism, and the Y-axis moving mechanism drives the detection probe to move along the Y-axis direction.

[0013] In the above technical solution, a first drive motor is provided at one end of the X-axis moving mechanism as the drive source of the X-axis moving mechanism; a second drive motor is provided at one end of the Y-axis moving mechanism as the drive source of the Y-axis moving mechanism.

[0014] In the above technical solution, a wafer stage is also provided on the XY-axis worktable. The wafer stage is fixedly installed on the base of the XY-axis worktable by bolts. A U-shaped groove is provided on the wafer stage for placing the wafer to be tested into the U-shaped groove.

[0015] In the above technical solution, the operating frequency of the low-frequency coil is 0.5MHz-0.6MHz; the operating frequency of the high-frequency coil is 2.5MHz-3MHz.

[0016] In the above technical solution, a control system is also provided on the XY two-axis worktable.

[0017] Advantages and beneficial effects of the present invention:

[0018] High sensitivity: capable of detecting resistivity changes in the range of 1×10⁻⁵ to 1×10² Ω·cm.

[0019] Automatic calibration: When the LOD changes, the test results can be automatically detected and calibrated.

[0020] No contact required: The testing process does not require direct contact with the wafer, avoiding potential damage to the material surface.

[0021] Fast and efficient: Enables rapid overall detection, improving detection efficiency.

[0022] Instant results: Results are available immediately after testing, without waiting.

[0023] Wide applicability: Suitable for various conductive materials, including ferromagnetic and non-ferromagnetic materials. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the detection device of the present invention.

[0025] Figure 2 This is a schematic diagram of the cross-section of the detection probe.

[0026] Figure 3This is a flowchart of the detection method of the present invention.

[0027] Figure 4 This is a flowchart of the detection process in Embodiment 2 of the present invention.

[0028] Figure 5 This is a schematic diagram of the host computer testing operation software interface. In the diagram, the left side shows the communication settings area, parameter detection area, and function area, while the right side is used for the overall characterization of the wafer during global testing.

[0029] For those skilled in the art, other related figures can be obtained from the above figures without any creative effort. Detailed Implementation

[0030] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0031] Example 1

[0032] This patent proposes a method for detecting wafer resistivity and surface metal thin film thickness based on a dual-coil system. (See appendix.) Figure 1 The detection equipment used in this method includes an XY two-axis stage 1 and a detection probe 2 mounted on the XY two-axis stage. The XY two-axis stage 1 can control the detection probe 2 to any detection position in the XY plane, thereby scanning and detecting the wafer on the XY two-axis stage and detecting the resistivity of the wafer.

[0033] For details, please see the appendix. Figure 1 The XY-axis two-axis worktable 1 includes a base 101, an X-axis moving mechanism 102, and a Y-axis moving mechanism 103. The X-axis moving mechanism 102 is mounted on the base 101, and the Y-axis moving mechanism 103 is mounted on the X-axis moving mechanism 102. The X-axis moving mechanism 102 drives the Y-axis moving mechanism 103 to move along the X-axis. The detection probe 2 is mounted on the Y-axis moving mechanism 103 via a mounting bracket 201. The Y-axis moving mechanism 103 drives the detection probe 2 to move along the Y-axis. Thus, through the combined action of the X-axis moving mechanism 102 and the Y-axis moving mechanism 103, the detection probe 2 can be moved to any position in the XY plane. Furthermore, one end of the X-axis moving mechanism 102 is equipped with a first drive motor 1021, serving as the drive source for the X-axis moving mechanism; one end of the Y-axis moving mechanism 103 is equipped with a second drive motor 1031, serving as the drive source for the Y-axis moving mechanism.

[0034] See appendix Figure 2The detection probe 2 includes a low-frequency coil 01, a high-frequency coil 02, an electronic potting compound 03, and a housing 04. Both the low-frequency coil 01 and the high-frequency coil 02 are embedded inside the housing 04, with the high-frequency coil 02 located at the center of the low-frequency coil 01. They are coaxially arranged, and the bottom surfaces of the low-frequency coil 01 and the high-frequency coil 02 are on the same horizontal plane. The housing 04 is filled with the electronic potting compound 03 to fix the positions of the low-frequency coil 01 and the high-frequency coil 02. The electronic potting compound has good insulation properties, preventing electrical short circuits between the coils. It also has certain heat resistance and impact resistance, adapting to the temperature and vibration conditions of the working environment, protecting the internal coils and electronic components, and providing a fixing function. After encapsulation, it can effectively isolate interference from the external environment (such as humidity and dust). The low-frequency coil 01 is used to detect the resistivity of the wafer and the thickness of the metal thin film on the wafer surface. The low-frequency coil 01 generates a large eddy current response through excitation, which can penetrate deep into the metal layer of the wafer thin film, thereby analyzing the thickness and resistivity of the metal thin film. The high-frequency coil 02 is used to measure the lift-off height (LOD) between the detection probe 2 and the wafer. The high frequency of the high-frequency coil makes the coil sensing depth shallow, which is suitable for detecting the lift-off height close to the wafer surface. The high-frequency signal is more susceptible to changes in distance and can provide accurate real-time feedback.

[0035] A wafer stage 3 is also provided on the XY-axis worktable 1. The wafer stage 3 is fixedly installed on the base 101 of the XY-axis worktable 1 by bolts. A U-shaped groove is provided on the wafer stage 3 for placing the wafer to be tested into the U-shaped groove.

[0036] A control system 4 is also provided on the XY two-axis worktable 1 to control the operation of the testing equipment.

[0037] The method for detecting wafer resistivity and surface metal thin film thickness based on dual coils of the present invention is described in the appendix. Figure 3 The details are as follows:

[0038] 1. For first-time use, calibration is performed: Select a standard wafer sample for calibration, whose resistivity ρ and surface metal film thickness are known; then use the detection equipment of this invention to test the sample, fix the sample on the wafer stage 3, detect and record the voltage value output by the low-frequency coil 01 under different LOD values, thereby obtaining the relationship between resistivity and surface metal film thickness and the voltage value output by the low-frequency coil 01 under different LOD values.

[0039] 2. Testing: For the wafer to be tested, the sample is fixed on the wafer stage 3. By controlling the XY axis stage 1, the position of the testing probe 2 is adjusted to perform single-point or multi-point global testing at any position. During the testing process, the low-frequency coil 01 of the testing probe 2 detects the wafer in real time and outputs a voltage value (the working frequency of the low-frequency coil is 0.5MHz-0.6MHz), while the high-frequency coil 02 detects the LOD value in real time (the working frequency of the high-frequency coil is 2.5MHz-3MHz). Based on this LOD value, the resistivity value and surface metal film thickness value measured by the low-frequency coil 01 are corrected: that is, based on the relationship between the wafer resistivity and surface metal film thickness and the output voltage value of the low-frequency coil 01 under different LOD values ​​obtained by calibration, the resistivity value and surface metal film thickness value of the wafer to be tested corresponding to the LOD value detected in real time by the high-frequency coil 02 are obtained.

[0040] Example 2

[0041] Based on Example 1, this example further provides a detection process method, see Appendix Figure 4 The specific process is as follows:

[0042] S1: Turn on the power switch to connect the power source.

[0043] S2: Open the host computer detection operation software interface (see appendix) Figure 5 ).

[0044] S3: Configure software communication settings, set the serial port number to COM5, baud rate to 9600, and parity bit to NONE.

[0045] S4: Place the wafer to be tested on the wafer stage and select single-point testing or global testing as needed.

[0046] S5: Single-point detection:

[0047] S5.1: Input the X and Y coordinates for detection in the software parameter detection area;

[0048] S5.2: Click to move a single point, and the detection probe will automatically move to the point to be measured according to the set detection coordinates;

[0049] S5.3: Click "Detect," and the detection probe will perform a single-point detection. The detection result will be displayed on the software.

[0050] S5.4: Complete a single-point detection.

[0051] S6: Global Detection

[0052] S6.1: Click Auto Detect;

[0053] S6.2: The detection probe automatically returns to its initial position;

[0054] S6.3: The detection probe performs global detection on the entire wafer according to the preset path. After the detection probe reaches a point, it automatically detects 10 times and takes the average value. Then, according to the voltage of each point, different colored blocks are displayed. These colored blocks are used to characterize the wafer as a whole.

[0055] S6.4: Complete a global check.

[0056] The above description is merely an illustration of the present invention and is not intended to limit the present invention to the structures and uses shown and described. Therefore, all corresponding modifications and equivalents made within the spirit and principles of the present invention shall fall within the scope of the patent application of the present invention.

Claims

1. A method for detecting wafer resistivity and surface metal film thickness based on dual coils, characterized in that: It includes an XY two-axis workbench and a detection probe installed on the XY two-axis workbench, and the detection probe is controlled by the XY two-axis workbench to move to any detection position in the XY plane; The detection probe comprises a low-frequency coil, a high-frequency coil, an electronic potting compound and a shell. The low-frequency coil and the high-frequency coil are both embedded in the shell. The high-frequency coil is located at the center of the low-frequency coil. The two are coaxially arranged, and the bottom surface of the low-frequency coil and the bottom surface of the high-frequency coil are in the same horizontal plane. The inside of the shell is filled with electronic potting compound to fix the positions of the low-frequency coil and the high-frequency coil. The low-frequency coil is used to detect the resistivity of the wafer and the thickness of the metal film on the surface of the wafer. The high-frequency coil is used to measure the LOD value between the detection probe and the wafer. First, calibration is performed: a standard wafer sample for calibration is selected, the resistivity ρ and the thickness of the surface metal film of the sample are known; The voltage value output by the low-frequency coil at different LOD values ​​is detected and recorded, so as to obtain the relationship between the wafer resistivity and the thickness of the metal film on the wafer surface and the voltage value output by the low-frequency coil at different LOD values; Conduct detection: For the wafer to be tested, by controlling the XY two-axis worktable and adjusting the position of the detection probe, single-point or multi-point global detection is performed at any position. During the detection process, the low-frequency coil of the detection probe detects the wafer in real time and outputs the voltage value, while the high-frequency coil detects the LOD value in real time. According to the LOD value, the resistivity value and the surface metal film thickness value measured by the low-frequency coil are corrected: that is, according to the relationship between the wafer resistivity and the surface metal film thickness and the output voltage value of the low-frequency coil at different LOD values ​​obtained by calibration, the resistivity value of the wafer to be tested and the metal film thickness value on the wafer surface corresponding to the LOD value detected by the current high-frequency coil in real time are obtained.

2. The method for detecting wafer resistivity and surface metal film thickness based on double coils according to claim 1 is characterized in that: The XY two-axis workbench includes a base, an X-axis moving mechanism and a Y-axis moving mechanism. The X-axis moving mechanism is installed on the base, and the Y-axis moving mechanism is installed on the X-axis moving mechanism. The Y-axis moving mechanism is driven by the X-axis moving mechanism to move along the X-axis direction. The detection probe is installed on the Y-axis moving mechanism, and the detection probe is driven by the Y-axis moving mechanism to move along the Y-axis direction.

3. The method for detecting wafer resistivity and surface metal film thickness based on double coils according to claim 2 is characterized in that: A first driving motor is arranged at one end of the X-axis moving mechanism as a driving source of the X-axis moving mechanism; a second driving motor is arranged at one end of the Y-axis moving mechanism as a driving source of the Y-axis moving mechanism.

4. The method for detecting wafer resistivity and surface metal film thickness based on double coils according to claim 2, characterized in that: A wafer table is also provided on the XY two-axis workbench. The wafer table is fixedly mounted on the base of the XY two-axis workbench by bolts. A U-shaped groove is provided on the wafer table for placing the wafer to be inspected into the U-shaped groove.

5. The method for detecting wafer resistivity and surface metal film thickness based on double coils according to claim 2, characterized in that: A control system is also provided on the XY two-axis workbench.

6. The method for detecting wafer resistivity and surface metal film thickness based on dual coils according to claim 1, characterized in that: The operating frequency of the low-frequency coil is 0.5MHz-0.6MHz; the operating frequency of the high-frequency coil is 2.5MHz-3MHz.

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