A dynamic voltage control method for anodic bonding process

Abstract

The present invention relates to the technical field of MEMS manufacturing, and it relates to a dynamic voltage control method for anodic bonding process. The initial voltage value is set to 50% - 70% of the fixed voltage value, and the resistance value of the bonding interface, the distribution of the interface temperature field and the change of local stress are monitored in real time. Voltage level response is carried out according to the interface resistance decline rate and the temperature gradient: the fuzzy PID and the sliding mode variable structure control are fused, and the control parameters are dynamically adjusted according to the current density deviation and the temperature overshoot, so that the voltage output ripple is less than ±0.5%. If the local temperature of the electrode exceeds 90% of the material tolerance threshold, the reverse voltage pulse sequence is activated to offset the inertia of ion migration and re-initialize the current regulation period. Through multi-modal feedback monitoring and hierarchical dynamic regulation, the present invention can adjust the voltage in real time, avoid uneven current distribution and local overheating, thereby significantly reducing the risk of electrode burnout and improving the bonding reliability.

Description

Technical Field

[0001] The present invention relates to the technical field of MEMS manufacturing. More specifically, it relates to a dynamic voltage control method for anodic bonding process. Background Art

[0002] Anodic bonding, a key microfabrication joining technology in the semiconductor and MEMS fields, can firmly bond two or more different materials, such as silicon wafers and glass, metals and glass, etc. In the standard anodic bonding process, metal electrodes are required to apply voltage to generate an electrostatic field and heat the bonding interface simultaneously. As the voltage rises, it can drive the movement of charged ions, ultimately achieving atomic-level bonding between materials.

[0003] However, when using equipment like EVG bonding machines for anodic bonding with metal electrodes, the metal electrodes often burn out. Once the electrodes burn out, the bonding reliability is greatly reduced, and the device performance is also affected. Uneven current distribution is the primary factor for electrode burnout. Ideally, the current should evenly cover the entire bonding area, but in reality, it is very difficult to achieve perfection. Poor performance in any link, such as electrode design, contact condition, and wafer surface state, may cause uneven current distribution. Especially when the local current density is high, the Joule heat will increase, and if the heat dissipation cannot keep up, the local temperature is likely to exceed the standard, exceeding the tolerance limit of the electrode material, and burnout is inevitable.

[0004] Anodic bonding itself is a heating process. The electric field force drives the movement of ions, and the current generates heat through resistance (Joule heat). Also, if the voltage is too high, the time is too long, or the cooling efficiency is poor, heat is likely to accumulate. Especially when the current distribution is uneven, heat is more likely to concentrate in areas with high current density, resulting in more serious local overheating.

[0005] In the traditional anodic bonding process, the voltage control generally uses a constant voltage mode, and the voltage remains unchanged throughout the bonding process. Using this method will cause the current to rise too fast at the initial stage of the process, especially when the resistance of the bonding interface is still relatively large, resulting in local overheating of the electrode and burnout conditions. Summary of the Invention

[0006] Therefore, the purpose of the present invention is to provide a dynamic voltage control method for anodic bonding process to solve the problem that metal electrodes are prone to burnout during anodic bonding. By optimizing the process parameter control method and the overall operation process, the risk of electrode burnout is fundamentally reduced, ensuring the stability and reliability of the anodic bonding process.

[0007] To achieve the above purpose, the present invention provides the following technical solutions:

[0008] A dynamic voltage control method for anodic bonding process, comprising the following steps:

[0009] S1. Set the initial voltage: Set the initial voltage value to 50%-70% of the fixed voltage value, and the range of the initial voltage is 200V-300V;

[0010] S2. Multimodal feedback monitoring: Monitor the resistance value of the bonding interface, the distribution of the interface temperature field and the change of local stress in real time;

[0011] S3. Hierarchical dynamic regulation: Perform voltage level response according to the interface resistance decline rate and temperature gradient:

[0012] S31. When the interface resistance decline rate is higher than the first threshold, start the linear voltage slow rise mode and increase the voltage according to the rate ratio;

[0013] S32. When the resistance drops to the preset quantile, trigger stepwise voltage boost, and the increase amplitude of each step decreases by 20%-30%;

[0014] S33. When the uniformity index of the interface temperature field is lower than 0.9, switch to pulse voltage control to relieve local heat accumulation;

[0015] S4. Adaptive fuzzy sliding mode control: Integrate fuzzy PID and sliding mode variable structure control, and dynamically adjust the control parameters according to the current density deviation and temperature overshoot, so that the voltage output ripple is less than ±0.5%.

[0016] S5. Self-repair logic trigger: If the local temperature of the electrode exceeds 90% of the material tolerance threshold, activate the reverse voltage pulse sequence to offset the ion migration inertia and re-initialize the current regulation cycle.

[0017] The present invention is further configured as: The preset quantiles are 80%, 50% and 20% of the initial value.

[0018] The present invention is further configured as: The stepwise voltage boost stage further includes a degradation mechanism: If it is monitored that the resistance fluctuation amplitude exceeds 10% of the corresponding value of the current voltage, then return to the previous step voltage and extend the dwell time by 20%-50%.

[0019] The present invention is further configured as: The frequency of the pulse voltage control is 10Hz-50Hz, and the rising edge and falling edge time of a single pulse do not exceed 1ms.

[0020] The present invention is further configured as: The single pulse amplitude of the reverse voltage pulse sequence is 30%-60% of the forward voltage, the pulse width is 0.2-0.5 times of the forward period, and the sequence duration is 10ms-50ms.

[0021] The present invention is further configured such that: in step S4, the sliding mode surface function of the fuzzy sliding mode control is defined as: ;

[0022] where is the voltage deviation, and are dynamically adjusted by the fuzzy rule base according to the temperature field uniformity and the voltage reduction rate.

[0023] The present invention is further configured such that: the first threshold is 70%-80% of the initial bonding interface resistance value.

[0024] The present invention is further configured such that: the multimodal feedback monitoring includes:

[0025] Using an infrared thermal imager to obtain the temperature field distribution of the bonding interface at a sampling rate of 100Hz - 200Hz;

[0026] Measuring the interface resistance value by the four-probe method, with the distance between the measuring electrodes less than 1mm and concentrically distributed with the bonding area;

[0027] Using a piezoelectric sensor array to monitor the interface stress change.

[0028] The present invention is further configured such that: when stepping back to the previous step voltage, the electrode contact pressure adjustment is synchronously started:

[0029] Dynamically adjusting the contact pressure between the electrode and the wafer through a pneumatic servo mechanism, with the pressure adjustment range being 5N - 20N;

[0030] The pressure adjustment rate is positively correlated with the resistance fluctuation amplitude, satisfying where represents the pressure adjustment rate; is the resistance fluctuation amplitude; is the initial resistance value, is the adjustment coefficient, and ;

[0031] After the pressure is stabilized, it needs to be maintained for at least 3 step cycles before the voltage increase can be triggered again.

[0032] Comparing with the deficiencies of the prior art, the beneficial effects of the present invention are:

[0033] Through multimodal feedback monitoring and hierarchical dynamic regulation, the voltage can be adjusted in real time, avoiding uneven current distribution and local overheating, thereby significantly reducing the risk of electrode burnout and improving the bonding reliability.

[0034] The dynamic voltage control strategy can be adaptively adjusted according to the interface resistance change and the temperature gradient, shortening the bonding time and improving the production efficiency. Description of the Drawings

[0035] Figure 1 is the process flow chart of the present invention;

[0036] Figure 2 is the implementation flow chart of the present invention. Detailed implementation manners

[0037] Refer to Figures 1 to 2 to further illustrate a dynamic voltage control method for anodic bonding process of the present invention, including the following steps:

[0038] The first step is to set the initial voltage: set the initial voltage value to 50%-70% of the fixed voltage value,

[0039] wherein, the initial voltage value is dynamically calculated according to the characteristics of the bonding material, and the formula is ;

[0040] wherein =50%-70%, is the fixed voltage value (the standard bonding voltage of the material), generally 400-600V, so the range of this initial voltage is 200V-300V. A material database is loaded in the system, including the recommended values and thermal expansion coefficient matching parameters of 30 common MEMS materials.

[0041] The second step is multi-modal feedback monitoring: use a FLIR A65 infrared camera (thermal sensitivity <0.05°C) to capture a bonding area with a diameter of 50mm at a sampling rate of 100-200Hz, and generate a temperature matrix of 128×128 pixels. Eliminate noise through Gaussian filtering, and calculate the temperature field uniformity index U T , when U T <0.9 triggers pulse control.

[0042] Adopt a tungsten probe group with a concentric circle layout (inner circle diameter 2mm, outer circle diameter 4mm), apply a 10mA constant current source, extract the interface resistance value through a lock-in amplifier, and the measurement accuracy reaches ±0.1Ω.

[0043] Embed 16 piezoelectric sensors (PZT-5H) in the bonding stage, distribute them in a 4×4 matrix, and detect local stress changes in real time and generate a stress gradient vector diagram.

[0044] The third step is hierarchical dynamic regulation: perform voltage level response according to the interface resistance drop rate and temperature gradient: when the interface resistance drop rate is higher than the first threshold, and the first threshold is 70%-80% of the initial bonding interface resistance value, start the linear voltage slow rise mode, and increase the voltage according to the rate ratio; the maximum boost rate is limited to 50V / s to prevent thermal shock.

[0045] Linear voltage slow rise mode: Among them, is the rate of change of resistance with time, is the initial resistance, is the threshold resistance, is the target bonding time, preset to 120 s,

[0046] The voltage increment formula is: (k = 0.15 V / Ω / s). If the resistance decreases at a rate of 10 Ω / s, the voltage is linearly increased at 1.5 V / s until the threshold or U T < 0.9.

[0047] When the resistance drops to the preset quantiles, which are 80%, 50%, and 20% of the initial value, stepped voltage boosting is triggered, and the increase in each step decreases by 20% - 30%.

[0048] The stepped voltage boosting stage also includes a degradation mechanism: if the monitored resistance fluctuation amplitude exceeds 10% of the value corresponding to the current voltage, it returns to the previous stepped voltage and extends the dwell time by 20% - 50%, such as from stepped voltage V3 to V2.

[0049] When returning to the previous stepped voltage, the electrode contact pressure adjustment is synchronously started: specifically, the contact pressure between the electrode and the wafer is dynamically adjusted through a pneumatic servo mechanism, and the pressure adjustment range is 5 N - 20 N;

[0050] The pressure adjustment rate is positively correlated with the resistance fluctuation amplitude and satisfies ;

[0051] Among them represents the pressure adjustment rate; is the resistance fluctuation amplitude; is the initial resistance value, is the adjustment coefficient, and ;

[0052] After the pressure is stabilized, it needs to be maintained for at least 3 stepped cycles before the voltage increase can be triggered again.

[0053] When the interface temperature field uniformity index U T is lower than 0.9, it switches to pulse - type voltage control to alleviate local heat accumulation; the frequency of the pulse - type voltage control is 10 Hz - 50 Hz, and the rise and fall times of a single pulse do not exceed 1 ms.

[0054] The fourth step is adaptive fuzzy sliding - mode control: integrating fuzzy PID and sliding - mode variable - structure control, dynamically adjusting the control parameters according to the current density deviation and temperature overshoot, so that the voltage output ripple is less than ±0.5%.

[0055] The sliding - mode surface function of the fuzzy sliding - mode control is defined as: ;

[0056] where is the voltage deviation, and are dynamically adjusted by the fuzzy rule base according to the temperature field uniformity and the step-down rate.

[0057] Fuzzy rule base table:

[0058]

[0059] The fifth step is the self-repair logic trigger: If the local temperature of the electrode exceeds 90% of the material tolerance threshold (assuming 90% of the material tolerance threshold of 330 °C), activate the reverse voltage pulse sequence to cancel the ion migration inertia and re-initialize the current regulation cycle. The single pulse amplitude of the reverse voltage pulse sequence is 30% - 60% of the forward voltage, the pulse width is 0.2 - 0.5 times of the forward period, and the sequence duration is 10 ms - 50 ms. After the reverse pulse ends, the voltage is reset to 80% of the value before triggering, and the step-by-step voltage boost is restarted according to step three.

[0060] For example: The reverse pulse amplitude V rev is 50% of the forward pulse amplitude V forward . When V forward = 300 V, V rev = -150 V. The reverse pulse width is 30% of the reciprocal of the forward pulse frequency f forward , that is, 1 / f forward × 0.3 = 30 ms (assuming the original frequency f forward = 10 Hz). The total duration of the reverse pulse sequence is 30 ms, including 3 reverse pulses.

[0061] The silicon-glass anodic bonding (bonding area of 20 × 20 mm²) is detected respectively by using this method, the traditional constant voltage mode, the traditional step-up voltage mode and the conventional PID control, with the ambient temperature of 25 ± 1 °C and the humidity < 30%RH.

[0062] Equipment configuration:

[0063] External thermal imager: FLIR A65, temperature resolution 0.05 °C;

[0064] Voltage source: Keysight B2900A, accuracy ±0.1%;

[0065] Pressure sensor: Kistler 9317B, measuring range 0 - 50 N, error ±0.5%.

[0066] Key parameter: Initial voltage: 300 V.

[0067] Traditional step-up voltage mode detection method:

[0068] Step 1: Set a fixed voltage of 300V without any voltage adjustment; start the bonding process and monitor the interface resistance value, interface temperature field distribution, and local stress changes in real time; record data such as bonding time, temperature uniformity index (UT), residual stress, and whether the electrode is burned out.

[0069] Traditional step-up voltage mode detection method: Set the initial voltage to 300V; start the bonding process and monitor the interface resistance value, interface temperature field distribution, and local stress changes in real time; when the resistance drops to the preset quantiles (80%, 50%, 20% of the initial value), increase the voltage in a step-up voltage mode, with each step increase decreasing by 20%-30%; record data such as bonding time, temperature uniformity index (UT), residual stress, and whether the electrode is burned out.

[0070] Conventional PID control detection method: Set the initial voltage to 300V; start the bonding process and monitor the interface resistance value, interface temperature field distribution, and local stress changes in real time; dynamically adjust the voltage according to the PID control algorithm to make the voltage output ripple less than ±0.5%; record data such as bonding time, temperature uniformity index (UT), residual stress, and whether the electrode is burned out.

[0071] The comparison table of the experiments of this method with the traditional constant voltage mode, traditional step-up voltage mode, and conventional PID control is as follows:

[0072]

[0073] Based on the above experimental data:

[0074] Bonding duration: This method shortens the bonding duration by 41.7% compared with the traditional constant voltage mode (180s → 105s);

[0075] Improvement in temperature uniformity: The uniformity index of this method is 0.9, which is 15.79% higher than that of conventional PID (0.85); Residual stress control: The <18MPa threshold is much lower than that of the traditional constant voltage mode (>50MPa);

[0076] Breakthrough in scrap rate: The 0.9% scrap rate sets a new industry record (8.7% for the traditional mode);

[0077] Improvement in voltage stability: The 6% ripple coefficient is optimized by 50% compared with conventional PID (1.2%);

[0078] Energy consumption economy: The energy consumption is 3kW·h / batch, which is 21% lower than that of the step-up voltage mode (3.8).

[0079] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any ordinary changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included within the protection scope of the present invention.

Claims

1. A dynamic voltage control method for anodic bonding process, characterized in that, It includes the following steps: S1. Set the initial voltage: Set the initial voltage value to 50%-70% of the fixed voltage value, and the range of the initial voltage is 200V-300V; S2. Multi-modal feedback monitoring: Monitor the resistance value of the bonding interface, the distribution of the interface temperature field and the change of local stress in real time; S3. Hierarchical dynamic regulation: Perform voltage level response according to the interface resistance decline rate and temperature gradient: S31. When the interface resistance decline rate is higher than the first threshold, start the linear voltage slow-rise mode and increase the voltage according to the rate ratio; S32. When the resistance drops to the preset quantile points, trigger stepwise voltage boost, and the increase amplitude of each step decreases by 20%-30%; S33. When the uniformity index of the interface temperature field is lower than 0.9, switch to pulse voltage control to relieve local heat accumulation; S4. Adaptive fuzzy sliding mode control: Integrate fuzzy PID and sliding mode variable structure control, and dynamically adjust the control parameters according to the current density deviation and temperature overshoot, so that the voltage output ripple is less than ±0.5%; S5. Self-repair logic trigger: If the local temperature of the electrode exceeds 90% of the material tolerance threshold, activate the reverse voltage pulse sequence to offset the ion migration inertia and re-initialize the current regulation cycle.

2. The dynamic voltage control method for anodic bonding process according to claim 1, characterized in that, The preset quantile points are 80%, 50% and 20% of the initial value.

3. A dynamic voltage control method for anodic bonding process according to claim 1, characterized in that, The stepwise voltage boost stage also includes a degradation mechanism: If it is monitored that the resistance fluctuation amplitude exceeds 10% of the corresponding value of the current voltage, then return to the previous step voltage and extend the dwell time by 20%-50%.

4. A dynamic voltage control method for anodic bonding process according to claim 3, characterized in that, The frequency of the pulse voltage control is 10Hz-50Hz, and the rise time and fall time of a single pulse do not exceed 1ms.

5. A dynamic voltage control method for anodic bonding process according to claim 4, characterized in that, The single pulse amplitude of the reverse voltage pulse sequence is 30%-60% of the forward voltage, the pulse width is 0.2-0.5 times of the forward period, and the sequence duration is 10ms-50ms.

6. A dynamic voltage control method for anodic bonding process according to claim 5, characterized in that, The sliding surface function of the fuzzy sliding mode control described in step S4 is defined as: ; wherein is the voltage deviation; and is dynamically adjusted by the fuzzy rule base according to the temperature field uniformity and the voltage reduction rate.

7. A dynamic voltage control method for anodic bonding process according to claim 2, characterized in that, The first threshold is 70%-80% of the initial bonding interface resistance value.

8. A dynamic voltage control method for anodic bonding process according to claim 1, characterized in that, The multi-modal feedback monitoring includes: Use an infrared thermal imager to obtain the distribution of the bonding interface temperature field at a sampling rate of 100Hz-200Hz; Measure the interface resistance value by the four-probe method, and the distance between the measurement electrodes is less than 1mm and is concentrically distributed with the bonding area; Use a piezoelectric sensor array to monitor the interface stress change.

9. A dynamic voltage control method for anodic bonding process according to claim 3, characterized in that, When returning to the previous step voltage, synchronously start the electrode contact pressure adjustment: Dynamically adjust the contact pressure between the electrode and the wafer through a pneumatic servo mechanism, and the pressure adjustment range is 5N-20N; The pressure adjustment rate is positively correlated with the resistance fluctuation amplitude and satisfies , where represents the pressure adjustment rate; is the resistance fluctuation amplitude; is the initial resistance value, is the adjustment coefficient, and ; After the pressure is stabilized, it needs to be maintained for at least 3 step cycles before triggering the voltage increase again.

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