Infrared sensor bridge arm structure, chip with bridge arm structure and preparation method of chip
Patent Information
- Application Number
- CN202511716588.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-20
- Publication Date
- 2026-03-17
AI Technical Summary
The infrared sensor bridge arm structure is prone to deformation or breakage after the release of the bottom polyimide sacrificial layer, which affects chip yield and performance. Existing technical solutions have the risk of increased thermal conductivity or deterioration of the thermistor material performance.
By adjusting the power, frequency, temperature, and reaction chamber pressure of the chemical vapor deposition process, a bridge structure with positive stress in the upper film layer, negative stress in the lower film layer, and an absolute stress value of 100 MPa in both the upper and lower film layers was prepared. The film thickness was also adjusted so that the upper film layer thickness was less than the lower film layer thickness.
This improved the stability and mechanical strength of the bridge arm structure after the release of the polyimide sacrificial layer, reduced the deformation rate, and enhanced the reliability and performance of the chip.
Smart Images
Figure CN121677947A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of semiconductor technology, and particularly relates to an infrared sensor bridge arm structure, a chip with a bridge arm structure, and a method for fabricating the same. Background Technology
[0002] In the field of infrared sensors, the manufacturing of bridge arm structures is extremely complex. A bridge arm (BRG) is the structure in an infrared sensor that connects the thermistor to the underlying processing circuitry. It is typically composed of a dielectric-metal-dielectric combination. Its main functions are to absorb external infrared signals and conduct the infrared thermal signals to the thermistor for thermoelectric signal conversion; and to conduct the current changes generated by the thermistor to the underlying ASIC processing circuitry for circuit connections. The stability of the bridge arm structure directly determines the electrical and thermal performance of the infrared sensor. The manufacturing process of the bridge arm involves the deposition of multiple layers of film, and the entire infrared sensor manufacturing process also involves processes at different temperatures, which leads to a complex stress distribution inside the bridge arm.
[0003] After the bottom polyimide sacrificial layer (PI) is released, the bridge arm is prone to deformation or even breakage, causing the entire chip to fail. Even if the bridge arm does not deform after the polyimide sacrificial layer (PI) is released, the chip may still experience bridge arm deformation during subsequent reliability tests (such as mechanical shock resistance tests). Moreover, the deformation of the bridge arm, which is composed of dielectric-metal-dielectric, is usually related to the thickness of the film and the internal stress. Therefore, improving the deformation resistance of the bridge arm is particularly important for improving the yield, performance and reliability of the chip.
[0004] Traditional infrared sensor designs only consider the overall thickness of the film layer and the CD of the bridge arm, while ignoring the distribution of the film layer thickness and stress adaptation. This leads to the bridge arm being prone to deformation or even breakage after the release of the bottom polyimide sacrificial layer (PI) or after mechanical impact testing, affecting the chip yield, performance, and even causing the chip to be scrapped.
[0005] To address the issue of easily deformable bridge arms in infrared sensors, existing fabrication processes mainly employ two solutions: Solution one involves increasing the dielectric thickness of the upper and lower film layers of the bridge arm to make the structure more robust and less prone to deformation. However, this solution has drawbacks. Increasing the dielectric thickness increases the thermal conductivity of the bridge arm structure. The thermistor cannot convert the thermal signal into an electrical signal quickly enough, and the heat is conducted away by the bridge arm structure. This significantly reduces the responsivity of the infrared chip and lowers product performance. Option two involves adding a high-temperature annealing process (such as rapid annealing at 1100℃) after the bridge arm structure is formed. This annealing process can eliminate stress between different film layers in the bridge arm, making the structure less prone to deformation after PI release. However, this option also has drawbacks. Since the bridge arm structure is formed after the thermistor, many thermistor materials (such as vanadium oxide) are highly sensitive to thermal processes. For example, after the formation of the vanadium oxide thermistor, processes exceeding 250℃ should be avoided; otherwise, the valence state of vanadium will change, potentially leading to chip performance degradation. Therefore, how to prepare an infrared sensor bridge arm structure that remains stable and not easily deformed after the release of the bottom polyimide sacrificial layer (PI) or after mechanical impact testing has become an urgent problem to be solved. Summary of the Invention
[0006] This application provides an infrared sensor bridge arm structure, a chip with the bridge arm structure, and a method for fabricating the same. By adjusting the power, frequency, temperature, and reaction chamber pressure of the chemical vapor deposition process, a bridge arm structure is fabricated with positive stress in the upper film layer, negative stress in the lower film layer, and an absolute stress value of 100 MPa for both the upper and lower film layers. Furthermore, by adjusting the deposition time of the chemical vapor deposition process, the thickness of the upper and lower film layers is changed, with the upper film layer thickness being less than the lower film layer thickness, resulting in the lowest deformation rate of the bridge arm.
[0007] Other objects and advantages of the present invention can be further understood from the technical features disclosed herein.
[0008] To achieve one or more of the above objectives or other objectives, the present invention provides an infrared sensor bridge arm structure, a chip having the bridge arm structure, and a method for fabricating the same.
[0009] An infrared sensor bridge arm structure, comprising: Upper film layer, metal layer, and lower film layer; The stress in the upper film layer is positive, and the stress in the lower film layer is negative; The upper film layer and the lower film layer have the same absolute stress value, which is 100 MPa. The bridge arm structure is an S-shaped bend structure.
[0010] The total thickness of the upper and lower film layers is fixed, and the thickness of the upper film layer is 1 / 3 to 1 / 2 of the thickness of the lower film layer.
[0011] The upper film material is silicon nitride or silicon oxide; The metal layer material is titanium, titanium nitride, or aluminum; The lower film layer is made of the same material as the upper film layer.
[0012] An infrared sensor chip with a bridge arm structure includes: A semiconductor substrate including a readout circuit, wherein a bridge arm structure and a thermistor are disposed on the semiconductor substrate; The bridge arm structure is an S-shaped bending structure, consisting of a lower membrane layer, an intermediate metal layer, and an upper membrane layer.
[0013] A method for fabricating an infrared sensor chip with a bridge arm structure includes the following steps: Step S1: Provide a semiconductor substrate containing a readout circuit, deposit a sacrificial layer on the semiconductor substrate, and photolithographically etch and etch the sacrificial layer to form a contact hole; Step S2: The lower film layer of the bridge arm structure is formed by chemical vapor deposition, wherein the stress of the lower film layer is negative; Step S3: A thermistor layer is formed by physical vapor deposition, and the thermistor layer is photolithographically etched and etched to form a thermistor; Step S4: Photolithography and etching of the contact holes until the electrodes of the readout circuit are exposed; Step S5: Form the intermediate metal layer of the bridge arm structure using physical vapor deposition (PVD) process; Step S6: The upper film layer of the bridge arm structure is formed by chemical vapor deposition process. The stress of the upper film layer is positive, and the absolute value of the stress of the upper film layer and the lower film layer is the same, which is 100 MPa. Step S7: Photolithography and etching of the upper film layer, metal layer and lower film layer to form a bridge arm structure; Step S8: Release the sacrificial layer.
[0014] The step of depositing the sacrificial layer includes: Polyimide is spin-coated onto the semiconductor substrate and then cured to form the sacrificial layer.
[0015] The thickness of the upper film layer is the same as that of the lower film layer, both being 1000 Å.
[0016] The upper film material is silicon nitride or silicon oxide; The thermistor layer material is vanadium oxide; The metal layer material is titanium, titanium nitride, or aluminum; The lower film layer is made of the same material as the upper film layer.
[0017] The temperature of the chemical vapor deposition process is 200±50℃.
[0018] By adjusting the deposition time of the chemical vapor deposition process, the thicknesses of the upper and lower films are changed, with the thickness of the upper film being 1 / 3 to 1 / 2 of the thickness of the lower film.
[0019] Compared with the prior art, the beneficial effects of the present invention mainly include: This application prepares a bridge arm structure with positive stress in the upper film layer, negative stress in the lower film layer, and an absolute stress value of 100 MPa in both the upper and lower film layers by adjusting the power, frequency, temperature, and reaction chamber pressure of the chemical vapor deposition process. Furthermore, by adjusting the deposition time of the chemical vapor deposition process, the thickness of the upper and lower film layers is changed, with the upper film layer being thinner than the lower film layer, resulting in the lowest deformation rate of the bridge arm.
[0020] To make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description
[0021] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0022] Figure 1 This is a schematic diagram of the infrared sensor structure provided in Embodiment 1 of this application.
[0023] Figure 2 This is a top view of the infrared sensor chip provided in Embodiment 2 of this application.
[0024] Figure 3 This is a schematic diagram of the infrared sensor structure provided in Embodiment 2 of this application.
[0025] Figure 4 This is a schematic diagram of tensile stress and compressive stress provided in Embodiment 3 of this application.
[0026] Figure 5 This is a schematic diagram of the infrared sensor bridge arm structure provided in Embodiment 3 of this application.
[0027] Figure 6 This is a SEM diagram of a normal bridge arm structure provided in Embodiment 3 of this application.
[0028] Figure 7 This is a SEM schematic diagram of the deformable bridge arm structure provided in Embodiment 3 of this application. Detailed Implementation
[0029] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of a preferred embodiment with reference to the accompanying drawings. The directional terms mentioned in the following embodiments, such as up, down, left, right, front, or back, are merely for reference to the accompanying drawings. Therefore, the directional terms used are for illustrative purposes and not for limiting the present invention.
[0030] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.
[0031] Example 1 like Figure 1 As shown, an infrared sensor bridge arm structure includes: The upper film layer 5, the metal layer 6, and the lower film layer 7.
[0032] This application prepares a bridge structure 4 with positive stress in the upper film layer 5 and negative stress in the lower film layer 7 by adjusting the power, frequency, temperature and reaction chamber pressure of the chemical vapor deposition process. The absolute stress values of the upper film layer 5 and the lower film layer 7 are the same (both are 100 MPa). In addition, by adjusting the deposition time of the chemical vapor deposition process, the thickness of the upper and lower film layers can be changed. With the total thickness of the upper and lower film layers fixed, the deformation rate of the bridge arm structure 4 is the lowest when the thickness of the upper film layer 5 is less than the thickness of the lower film layer 7. The thickness of the upper film layer 5 is 1 / 3 to 1 / 2 of the thickness of the lower film layer 7.
[0033] The lower film layer 7 and the upper film layer 5 are made of the same material, with the upper film layer 5 being made of silicon nitride or silicon oxide; the metal layer 6 is made of titanium, titanium nitride, or aluminum.
[0034] Example 2 like Figure 3 As shown, an infrared sensor chip with a bridge arm structure includes: The semiconductor substrate 1 (ASIC substrate) includes a readout circuit, electrodes 2 of the readout circuit (ASIC), a sacrificial layer (PI) 3, a bridge arm structure 4, a thermistor layer 8, and a contact hole 9. Among them, the bridge arm structure 4 is an S-shaped bending structure, which consists of a lower membrane layer 7, an intermediate metal layer 6 and an upper membrane layer 5.
[0035] In a preferred embodiment of the present invention, the lower film layer 7 and the upper film layer 5 are made of the same material, the upper film layer 5 is made of silicon nitride or silicon oxide; the metal layer 6 is made of titanium, titanium nitride or aluminum; and the thermistor layer 8 is made of vanadium oxide or amorphous silicon.
[0036] Specifically, the sacrificial layer (PI) 3 serves as the structure supporting the thermistor and the electrode 2 of the readout circuit (ASIC), keeping the thermistor away from the semiconductor substrate 1. The thermistor receives infrared thermal signals from the outside, and different signal intensities will cause different temperature changes in the thermistor, thereby causing changes in its resistance. The electrical signal is transmitted to the electrode 2 of the readout circuit (ASIC) through the contact hole 9 via the bridge arm structure 4, and infrared thermal imaging can be formed after signal conversion.
[0037] like Figure 2 As shown, the bridge arm structure 4 of this application is an S-shaped bending structure, which can effectively reduce heat exchange with the outside world and increase the heat signal conducted to the thermistor. However, the S-shaped bending structure is prone to deformation.
[0038] like Figure 3 As shown, since the thermistor needs to receive infrared signals from the outside, the presence of the sacrificial layer (PI) 3 will conduct away the thermal signal, causing the thermistor to not receive an effective signal. Therefore, after the thermistor and bridge arm structure 4 are fabricated, the sacrificial layer (PI) 3 is released by gas to form a vacuum region. However, the bridge arm structure 4 is prone to deformation after the sacrificial layer (PI) 3 is released.
[0039] Example 3 A method for fabricating an infrared sensor chip with a bridge arm structure includes the following steps: Step S1: Provide a semiconductor substrate 1 containing a readout circuit, spin-coat polyimide (PI) on the semiconductor substrate 1 and cure it to form a sacrificial layer 3; The sacrificial layer 3 is photolithographically etched and etched to form the contact hole 9; Step S2: The lower film layer 7 of the bridge arm structure 4 is formed by chemical vapor deposition process, and the stress of the lower film layer 7 is negative; Step S3: The thermistor layer 8 is formed by physical vapor deposition process, and the thermistor layer 8 is photolithographically etched and etched to form a thermistor; Step S4: Photolithography and etching of contact holes 9 until the electrodes 2 of the readout circuit are exposed; Step S5: Form the intermediate metal layer 6 of the bridge arm structure 4 using a physical vapor deposition process; Step S6: The upper film layer 5 of the bridge arm structure 4 is formed by chemical vapor deposition. The stress of the upper film layer 5 is positive, and the absolute stress values of the upper film layer 5 and the lower film layer 7 are the same, both being 100 MPa. Step S7: Photolithography and etching of the upper film layer 5, the metal layer 6 and the lower film layer 7 to form the bridge arm structure 4; Step S8: Release the sacrificial layer 3, so that the bridge arm structure 4 is suspended.
[0040] This application modifies the stress in the upper and lower film layers by adjusting the power, frequency, temperature, and reaction chamber pressure of the chemical vapor deposition process. The stress range is -200MPa to 200MPa.
[0041] Specifically, adjusting the power of the chemical vapor deposition process, increasing the radio frequency power will increase plasma energy, enhance the ion bombardment effect, make the film denser, and increase compressive stress; if the power is too low, the film will be loose and prone to tensile stress. The range of radio frequency power includes, but is not limited to, 0~500W. Adjusting the frequency of the chemical vapor deposition process: low frequency tends to generate high-energy ion bombardment, forming compressive stress; high frequency reduces ion energy, generating tensile stress. The frequency range includes, but is not limited to, 30KHz~100MHz. Adjusting the temperature of the chemical vapor deposition process can promote the escape of byproducts and reduce the disordered structure inside the film, thereby reducing compressive stress. The temperature range includes, but is not limited to, 200~400℃. Adjusting the pressure in the reaction chamber of the chemical vapor deposition process increases the collision of internal gas molecules and increases compressive stress. The pressure range includes, but is not limited to, 0.1~10 Torr.
[0042] This application adjusts the above parameters to change the stress in the upper and lower membrane layers of the bridge arm structure 4, and conducts four sets of experiments, namely: (1) Compressive stress of the upper film layer, compressive stress of the lower film layer; (2) Compressive stress in the upper film layer, tensile stress in the lower film layer; (3) Tensile stress in the upper film layer, tensile stress in the lower film layer; (4) Tensile stress in the upper film layer and compressive stress in the lower film layer.
[0043] When the upper membrane layer 5 is under tensile stress and the lower membrane layer 7 is under compressive stress, the bridge arm structure 4 is the most stable and not easily deformed.
[0044] This application also conducted an experiment on the stress magnitude of the optimal combination, and finally found that when the absolute value of the stress in both the upper and lower membrane layers was 100 MPa, the deformation ratio of the bridge arm structure 4 was the lowest.
[0045] Specifically, as shown in Table 1, Table 1 lists the stress of the upper and lower film layers of several groups of bridge arm structures 4 and the deformation rate of the chip bridge arm structure 4 after the release of the sacrificial layer (PI) 3. The thickness of the upper film layer 5 and the lower film layer 7 are the same, both being 1000A.
[0046] When the chemical vapor deposition process is low power (e.g., <300W), high frequency (>30MHz), and high pressure (>1Torr), the film exhibits tensile stress; when the chemical vapor deposition process is high power (e.g., >300W), low frequency (<500KHz), and low pressure (<1Torr), the film exhibits compressive stress.
[0047] like Figure 4 As shown in (a), tensile stress stretches the film, causing the film layer in contact with it to tend to contract inward. The unit of tensile stress is generally positive.
[0048] like Figure 4 As shown in (b), compressive stress causes the film to shrink, causing the film layer in contact with it to tend to bulge upwards. The unit of compressive stress is generally negative.
[0049] In a preferred embodiment of the present invention, the thermistor layer 8 is made of vanadium oxide. Since the valence state of vanadium is unstable at high temperatures, the film formation temperature of the chemical vapor deposition process in this application is 200±50℃.
[0050] Table 1 As shown in Table 1, when the stress of the upper membrane layer 5 is positive (i.e., tensile stress) and the stress of the lower membrane layer 7 is negative (i.e., compressive stress), the deformation rate of the bridge arm structure 4 is the lowest. In the second set of data, the deformation rate of the bridge arm is only 5%. However, in the fourth set of data, when the upper membrane layer 5 is under compressive stress and the lower membrane layer 7 is under tensile stress, the bonding between the upper and lower membrane layers and the metal layer 6 is poor, and the deformation rate of the bridge arm structure 4 is as high as 40%.
[0051] like Figure 5 As shown ( Figure 5 (The deformation state of the membrane layer has been exaggerated to illustrate the deformation state of the membrane layer.) When the upper membrane layer 5 is under tensile stress, it tends to shrink inwards towards the metal layer 6, resulting in a tight bond between the upper membrane layer 5 and the metal layer 6. When the lower membrane layer 7 is under compressive stress, it tends to bulge upwards towards the metal layer 6, which also results in a tight bond between the upper membrane layer 7 and the metal layer 6. Therefore, the bonding force inside the bridge arm structure 4 is very stable at this time, and it can maintain a stable shape after the sacrificial layer (PI) 3 is released, with a small probability of deformation.
[0052] like Figure 6 As shown, after the sacrificial layer (PI) 3 is released, the bridge arm structure 4 remains normal and maintains a stable shape.
[0053] like Figure 7 As shown in the white dashed box, it can be clearly seen that after the sacrificial layer (PI) 3 is released, the bridge arm structure 4 has been deformed and deviated from the original design direction. This deformation can affect chip performance at best, and break directly in severe cases, causing chip failure.
[0054] In addition, this application changes the thickness of the upper film layer 5 and the lower film layer 7 by adjusting the deposition time of the chemical vapor deposition process, while keeping the total thickness of the upper and lower film layers constant, ranging from 300 Å to 3000 Å.
[0055] Specifically, as shown in Table 2, Table 2 lists the deformation rate of the chip when the sacrificial layer (PI) 3 is released with different upper and lower film thicknesses. At this time, the stress of the upper film 5 is 100 MPa and the stress of the lower film 7 is -100 MPa.
[0056] Table 2 As shown in Table 2, when the thickness of the upper membrane layer 5 is less than that of the lower membrane layer 7, the deformation rate of the bridge arm structure 4 is the lowest. This is because the lower membrane layer 7 mainly supports the bridge arm structure 4. The thicker the lower membrane layer 7, the higher the mechanical strength of the bridge arm structure 4, and the lower the probability of deformation after the sacrificial layer (PI) 3 is released.
[0057] In summary, this application prepared a bridge arm structure with positive stress in the upper film layer, negative stress in the lower film layer, and an absolute stress value of 100 MPa in both the upper and lower film layers by adjusting the power, frequency, temperature, and reaction chamber pressure of the chemical vapor deposition process. Furthermore, by adjusting the deposition time of the chemical vapor deposition process, the thickness of the upper and lower film layers was changed, with the upper film layer being thinner than the lower film layer, resulting in the lowest deformation rate of the bridge arm.
[0058] The common English terms or letters used in this invention for clarity of description are for illustrative purposes only and are not limiting interpretations or specific uses. They should not be used to limit the scope of protection of this invention based on their possible Chinese translations or specific letters.
[0059] It should also be noted that in this article, relational terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations.
Claims
1. An infrared sensor bridge arm structure, characterized by, The bridge arm structure comprises: an upper film layer, a metal layer and a lower film layer; the upper film layer has a positive stress, and the lower film layer has a negative stress; the upper film layer and the lower film layer have the same absolute stress value, both being 100 MPa; the bridge arm structure is an S-shaped bending structure.
2. The infrared sensor bridge arm structure of claim 1, wherein, The total thickness of the upper and lower film layers is fixed, and the thickness of the upper film layer is 1 / 3-1 / 2 of the thickness of the lower film layer.
3. The infrared sensor bridge arm structure of claim 1, wherein, The material of the upper film layer is silicon nitride or silicon oxide; the material of the metal layer is titanium, titanium nitride or aluminum; the material of the lower film layer is the same as that of the upper film layer.
4. An infrared sensor chip having a bridge arm structure, characterized by The bridge arm structure comprises: a semiconductor substrate comprising a readout circuit, and the semiconductor substrate is provided with a bridge arm structure and a thermistor; the bridge arm structure is an S-shaped bending structure, which comprises a lower film layer, an intermediate metal layer and an upper film layer.
5. A method for manufacturing an infrared sensor chip having a bridge arm structure, characterized by, The method comprises the following steps: Step S1: providing a semiconductor substrate comprising a readout circuit, depositing a sacrificial layer on the semiconductor substrate, and photoetching and etching the sacrificial layer to form a contact hole; Step S2: forming a lower film layer of the bridge arm structure by a chemical vapor deposition process, and the lower film layer has a negative stress; Step S3: forming a thermistor layer by a physical vapor deposition process, photoetching and etching the thermistor layer to form a thermistor; Step S4: photoetching and etching the contact hole until the electrode of the readout circuit is exposed; Step S5: forming an intermediate metal layer of the bridge arm structure by a physical vapor deposition process; Step S6: forming an upper film layer of the bridge arm structure by a chemical vapor deposition process, and the upper film layer has a positive stress, and the upper film layer and the lower film layer have the same absolute stress value, both being 100 MPa; Step S7: photoetching and etching the upper film layer, the metal layer and the lower film layer to form a bridge arm structure; Step S8: releasing the sacrificial layer.
6. The method for fabricating an infrared sensor chip with a bridge arm structure according to claim 5, characterized in that, The step of depositing the sacrificial layer comprises: spinning and curing polyimide on the semiconductor substrate to form the sacrificial layer.
7. The method for fabricating an infrared sensor chip with a bridge arm structure according to claim 5, characterized in that, The thickness of the upper film layer is the same as that of the lower film layer, both being 1000 A.
8. The method for fabricating an infrared sensor chip with a bridge arm structure according to claim 5, characterized in that, The material of the upper film layer is silicon nitride or silicon oxide; the material of the thermistor layer is vanadium oxide; the material of the metal layer is titanium, titanium nitride or aluminum; the material of the lower film layer is the same as that of the upper film layer.
9. The method for fabricating an infrared sensor chip with a bridge arm structure according to claim 5, characterized in that, The temperature of the chemical vapor deposition process is 200±50℃.
10. The method for fabricating an infrared sensor chip with a bridge arm structure according to claim 9, characterized in that, The thickness of the upper film layer is 1 / 3-1 / 2 of the thickness of the lower film layer by adjusting the deposition time of the chemical vapor deposition process. The thickness of the upper film layer is 1 / 3-1 / 2 of the thickness of the lower film layer by adjusting the deposition time of the chemical vapor deposition process.