A bonding method for an infrared detector chip

Abstract

This application discloses a bonding method for an infrared detector chip, relating to infrared detector technology. The method includes: applying a third organic grease C to the exposed circuit area of ​​a hybrid chip and curing it to form a primary protective layer; heating a glass substrate to the melting point of a second organic grease B, applying the second organic grease B onto the glass substrate, and mounting the hybrid chip onto the bonding area; heating the glass substrate to the melting point of a first organic grease A; coating the hybrid chip with the first organic grease A around its perimeter, and placing a strip around the hybrid chip such that the strip encloses the hybrid chip, with the lower surface of the strip contacting the first organic grease A; and then cooling the glass substrate to cure the first organic grease A and the second organic grease B. This application proposes a highly efficient and non-destructive bonding process for infrared detector chips, ensuring smooth thinning of the photosensitive chip and improving the yield of infrared detector chips.

Description

Technical Field

[0001] This application relates to the field of infrared detector technology, and in particular to a bonding method for infrared detector chips. Background Technology

[0002] Infrared focal plane detectors are developing towards the third generation of infrared detectors, characterized by large array size, high performance, and low cost. They have been widely used in various fields such as security, industry, and medicine, and the market's requirements for their performance indicators are constantly increasing.

[0003] Infrared detectors are constructed by interconnecting a photosensitive chip and a silicon readout circuit using flip-chip bonding technology. Infrared light is back-illuminated onto the photosensitive chip, passing through the semiconductor material and being absorbed by the photosensitive element, converting the optical signal into an electrical signal. However, excessive thickness of the semiconductor material can significantly impact the photoelectric performance of the detector chip, necessitating substrate thinning. Detector chip substrate thinning involves bonding the chip to a glass plate and then performing upside-down grinding and polishing on a polishing fixture. During polishing, it is crucial to protect the solder pads and leads on the circuitry to prepare for subsequent Dewar testing. However, effectively protecting the circuitry while ensuring uniform bonding remains a major challenge in detector thinning.

[0004] To enhance the infrared light transmittance of infrared detector chips and improve chip performance, the back substrate of the interconnected detector chips needs to be thinned. The circuitry within the interconnected detector chips needs to have exposed pads for lead packaging, allowing for performance testing of the detector chips. However, these areas are highly susceptible to defects during the thinning process, being corroded by etching solutions and polishing solutions, ultimately damaging the pads to the point of being unusable and affecting the yield of the thinned chips.

[0005] To improve the yield of infrared detector chips after thinning, a circuit pad protection process is required during the thinning and bonding process. Improper protection during chip bonding can not only damage the pads but also easily cause the protective adhesive to flow into the bottom of the chip, resulting in an uneven chip surface, uneven chip thinning profile, and even damage such as missing corners.

[0006] Chip thinning primarily involves bonding the chip to a glass plate (the glass plate must have a TTV of less than 1μm), followed by inverted grinding after bonding. The hybrid chip bonding process for infrared detectors generally involves placing a glass plate with acceptable flatness on a heated plate. Once the heated plate reaches a certain temperature, organic grease is applied to the center area of ​​the glass plate. After the grease melts, the chip and protective strip are placed on the glass plate. The chip is then manually leveled, and a flatness test is performed. If the flatness test is passed, circuit pad protection is applied, and polishing is performed after bonding. During the infrared detector bonding process, the flatness test before the protective pads is passed may be compromised after the organic grease melts and breaks open the protective strip, leading to an imbalance in the detector chip's flatness and causing damage to the detector chip during thinning. Summary of the Invention

[0007] This application provides a bonding method for an infrared detector chip, which proposes an efficient and non-destructive bonding process for infrared detector chips, ensuring that the thinning process of the photosensitive chip is normal and improving the yield of infrared detector chips.

[0008] This application provides a bonding method for an infrared detector chip, comprising a hybrid chip, a glass substrate, a strip, a first organic grease A, a second organic grease B, and a third organic grease C. The first organic grease A and the second organic grease B are solid at room temperature, and the melting point of the first organic grease A is higher than that of the second organic grease B. The third organic grease C is liquid at room temperature, and its sealing performance after curing is superior to that of the first organic grease A and the second organic grease B. The bonding method includes the following steps: The third organic grease C is coated onto the exposed circuit area of ​​the hybrid chip and cured to form a primary protective layer. The glass substrate is heated to the melting point of the second organic grease B, the second organic grease B is coated on the glass substrate to form an adhesive area with an area larger than that of the hybrid chip, and the hybrid chip is mounted on the adhesive area. The glass substrate is heated to the melting point of the first organic grease A, and the second organic grease B is in a molten state. The first organic grease A is coated around the hybrid chip, and a strip is placed around the hybrid chip so that the strip wraps around the hybrid chip and the lower surface of the strip is in contact with the first organic grease A; then, the glass substrate is cooled to cure the first organic grease A and the second organic grease B.

[0009] This application employs three organic greases, A, B, and C, for a hybrid chip bonding process. Organic greases A and B are solids, with A having a higher melting point than B. Organic grease C is liquid, offering better sealing performance with the chip than A and B. This provides a highly efficient and non-destructive bonding process for infrared detector chips, ensuring smooth thinning of the photosensitive chip and improving the yield of infrared detector chips.

[0010] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0011] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a flowchart illustrating the bonding method of the infrared detector chip according to an embodiment of this application; Figure 2 This is a schematic diagram of a primary protection method for the bonding method in this application embodiment; Figure 3 This is a schematic diagram of hybrid chip bonding using the bonding method described in this application embodiment; Figure 4 This is a schematic cross-section of the completed bonding of the strip in the bonding method of this application embodiment; Figure 5 This is a schematic cross-section of the bonding method according to an embodiment of this application after bonding is completed. Detailed Implementation

[0012] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0013] This application provides a bonding method for an infrared detector chip, comprising a hybrid chip (infrared detector chip), a glass substrate, a strip, a first organic grease A, a second organic grease B, and a third organic grease C. The first organic grease A and the second organic grease B are solid at room temperature, and the melting point of the first organic grease A is higher than that of the second organic grease B. The third organic grease C is liquid at room temperature, and its sealing performance after curing is superior to that of the first organic grease A and the second organic grease B. like Figure 1 As shown, the bonding method described in this application embodiment includes the following steps: In step S101, the third organic grease C is applied to the exposed circuit area of ​​the hybrid chip and cured to form a primary protective layer. For example, the organic grease C is applied to the exposed circuit area of ​​the hybrid chip in a thin layer, and then dried on a hot plate at 50℃-70℃ to complete the primary protection of the hybrid chip circuit area.

[0014] In step S102, the glass substrate is heated to the melting point of the second organic grease B, the second organic grease B is coated onto the glass substrate to form an adhesive area larger than the area of ​​the hybrid chip, and the hybrid chip is mounted onto the adhesive area. In some embodiments, after mounting the hybrid chip onto the adhesive area, the method further includes: pressing the hybrid chip until the four corners are at the same height, and removing the second organic grease B that has overflowed from around the chip. In some examples, the area of ​​the hybrid chip with adhesive grease B can be manually flattened, the height of the four corners measured, and the residual grease B around the edges cleaned.

[0015] In step S103, the glass substrate is heated to the melting point of the first organic grease A, and the second organic grease B is in a molten state.

[0016] In step S104, the first organic grease A is coated around the hybrid chip, and a strip is placed around the hybrid chip so that the strip wraps around the hybrid chip and the lower surface of the strip is in contact with the first organic grease A; then, the glass substrate is cooled to cure the first organic grease A and the second organic grease B.

[0017] In some embodiments, step S105 further includes processing the solid second organic grease B into a shape that matches the exposed circuit area after the first protection and placing it on the exposed circuit area. The glass substrate is heated to the melting point of the second organic grease B, causing the second organic grease B to melt and cover the exposed area of ​​the circuit, forming a secondary protective layer.

[0018] In some embodiments, the thickness of the accompaniment strip is configured such that when the hybrid chip is suspended on the molten second organic grease B, the upper surface of the hybrid chip tends to be flush with the upper surface of the accompaniment strip under the action of surface tension. Specifically, the first organic grease A is coated around the hybrid chip, and the accompaniment strip is placed around the chip, completely enclosing it. After bonding, the glass plate is cooled, and the height of the four corners of the chip is measured to ensure that the four corners are consistent.

[0019] In some embodiments, the melting point of the second organic grease B is 60°C-80°C, the melting point of the first organic grease A is 85°C-110°C, and the difference in melting points between the first organic grease A and the second organic grease B is not less than 15°C. In some embodiments, the third organic grease C is a silicone gel or a polyisobutylene sealant, and the first organic grease A and the second organic grease B are wax-based or rosin-based hot melt adhesives.

[0020] In some embodiments, the heating curing temperature of the third organic grease C is 50°C-70°C, and the cured primary protective layer remains solid and stable at the melting point temperature of the first organic grease A.

[0021] In some embodiments, after placing the solid second organic grease B on the exposed circuit area, a polytetrafluoroethylene film is covered thereon. After the second organic grease B melts and cools, the polytetrafluoroethylene film is removed to obtain a smooth secondary protective layer surface.

[0022] like Figure 1 As shown, it also includes mechanical polishing of the back side of the hybrid chip on which the secondary protective layer is formed, in order to achieve chip thinning.

[0023] This application also provides an implementation example of a method for attaching an infrared detector chip, including the following steps: Apply the third organic (liquid) adhesive C evenly to the exposed circuit area and cure it at 50℃-80℃ for 1-2 hours. Figure 2 As shown.

[0024] After the glass weighing plate is heated to the melting point of the second organic grease B on the heating plate, it is melted onto the glass plate (the area is slightly larger than the hybrid chip). The hybrid chip is then placed on the grease surface and manually leveled to ensure no air bubbles are generated between the hybrid chip and the glass substrate. A non-contact thickness measuring microscope is then used to measure the levelness around the perimeter. Figure 3 As shown.

[0025] After the chip is leveled, the second organic adhesive B at the edge of the hybrid chip is cleaned to ensure that there is no adhesive around the edges.

[0026] The hot plate temperature is raised to the melting point of the first organic adhesive A, and then coated around the perimeter of the chip. After the adhesive melts, the liner material is bonded to the glass substrate, ensuring the liner length covers the entire perimeter of the chip. After bonding, the height of the four corners of the chip is repeatedly measured to ensure that the height of the four corners and the center area are consistent. Figure 4 As shown.

[0027] Cut the second organic grease B to the same size as the exposed circuit area, place it around the exposed area, and then place it on a heating plate. Adjust the heating plate temperature to the melting point of the second organic grease B. After the second organic grease B around the circuit is completely melted, carefully remove it. After cooling and solidification, observe it under a microscope to see if the circuit is completely protected. If it is completely protected, then polishing can be performed. Figure 5 As shown, if the protection is not complete, this step can be repeated.

[0028] This application's method includes a process flow of primary circuit protection, hybrid chip bonding, strip bonding, and secondary circuit protection. Primary circuit protection addresses the unevenness of the circuit surface wiring by using liquid grease to protect the circuit area, ensuring a tight bond between the circuit and the grease, thus preventing circuit damage. Hybrid chip / strip bonding enhances the stability of the hybrid chip during polishing. The strip bonding uses organic grease A with a melting point higher than the hybrid chip. During the secondary circuit protection process with grease B, it prevents excessive grease melting from breaking the strip, which could lead to poor chip uniformity and corner defects during subsequent polishing, effectively improving the chip yield. Secondary circuit protection uses low-temperature organic grease B for secondary circuit protection. Manual operation completely fills the gaps between the circuit and the chip, preventing dust and residue from adhering to the circuit surface and being difficult to remove during thinning. The cured integrated structure helps reduce edge and corner chipping during thinning. The curing temperature of the grease used for bonding and coating throughout the entire process does not exceed 80℃ to avoid causing significant thermal stress to the chip.

[0029] It should be noted that, in the embodiments of this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0030] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0031] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims. All of these forms are within the protection scope of this application.

Claims

1. A method for bonding an infrared detector chip, characterized in that, The invention provides a hybrid chip, a glass substrate, a strip, a first organic grease A, a second organic grease B, and a third organic grease C. The first organic grease A and the second organic grease B are solid at room temperature, and the melting point of the first organic grease A is higher than that of the second organic grease B. The third organic grease C is liquid at room temperature, and its sealing performance after curing is superior to that of the first organic grease A and the second organic grease B. The bonding method includes the following steps: The third organic grease C is coated onto the exposed circuit area of ​​the hybrid chip and cured to form a primary protective layer. The glass substrate is heated to the melting point of the second organic grease B, the second organic grease B is coated on the glass substrate to form an adhesive area with an area larger than that of the hybrid chip, and the hybrid chip is mounted on the adhesive area. The glass substrate is heated to the melting point of the first organic grease A, and the second organic grease B is in a molten state. The first organic grease A is coated around the hybrid chip, and a strip is placed around the hybrid chip so that the strip wraps around the hybrid chip and the lower surface of the strip is in contact with the first organic grease A; then, the glass substrate is cooled to cure the first organic grease A and the second organic grease B.

2. The bonding method for the infrared detector chip as described in claim 1, characterized in that, Also includes: The solid second organic grease B is processed into a shape that matches the exposed circuit area after the first protection and placed on the exposed circuit area; The glass substrate is heated to the melting point of the second organic grease B, causing the second organic grease B to melt and cover the exposed area of ​​the circuit, forming a secondary protective layer.

3. The bonding method for the infrared detector chip as described in claim 1, characterized in that, After attaching the hybrid chip to the bonding area, the process further includes: The hybrid chip is pressed until the four corners are at the same height, and the second organic grease B that has overflowed from around the chip is removed.

4. The bonding method for the infrared detector chip as described in claim 1, characterized in that, The thickness of the accompaniment strip is configured such that when the hybrid chip is suspended on the second organic grease B in a molten state, the upper surface of the hybrid chip tends to be flush with the upper surface of the accompaniment strip under the action of surface tension.

5. The bonding method for the infrared detector chip as described in claim 1, characterized in that, The melting point of the second organic grease B is 60℃-80℃, the melting point of the first organic grease A is 85℃-110℃, and the difference in melting points between the first organic grease A and the second organic grease B is not less than 15℃.

6. The bonding method for the infrared detector chip as described in claim 5, characterized in that, The curing temperature of the third organic resin C is 50℃-70℃, and the cured primary protective layer remains solid and stable at the melting point temperature of the first organic resin A.

7. The bonding method for the infrared detector chip as described in claim 1, characterized in that, The third organic grease C is an organosilicon gel or a polyisobutylene sealant, and the first organic grease A and the second organic grease B are wax-based or rosin-based hot melt adhesives.

8. The bonding method for the infrared detector chip as described in claim 2, characterized in that, After placing the solid second organic grease B on the exposed circuit area, a polytetrafluoroethylene film is then placed on it. After the second organic grease B melts and cools, the polytetrafluoroethylene film is removed to obtain a smooth secondary protective layer surface.

9. The bonding method for the infrared detector chip as described in claim 2, characterized in that, It also includes mechanical polishing of the back side of the hybrid chip on which the secondary protective layer is formed, in order to achieve chip thinning.

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