Method for removing sacrificial layer in wafer level packaging process
By releasing the sacrificial layer through a three-step process—using oxygen plasma to oxidize and extract volatile gases, combined with Ar plasma bombardment and N2 to prevent oxygen plasma recombination—the problem of sacrificial layer removal in wafer-level packaging has been solved, achieving a damage-free, residue-free, and highly efficient release effect.
Patent Information
- Application Number
- CN202511313145.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-15
- Publication Date
- 2026-02-06
AI Technical Summary
In wafer-level packaging processes, existing technologies struggle to effectively remove the three-layer PI sacrificial layer without damaging or deforming the focal plane pixel unit structure, and the release speed is slow, affecting production efficiency.
A three-step process is used to release the sacrificial layer. First, the third sacrificial layer is removed with O2+Ar gas. Then, the second and first sacrificial layers are removed with weaker O2+N2 gas. Oxygen plasma is used to oxidize PI to generate volatile gas, which is then extracted by vacuum. Ar plasma provides physical bombardment, and N2 prevents oxygen plasma from recombinizing, thus avoiding structural damage.
It achieves complete release of the three sacrificial layers without residue and integrity of the focal plane pixel unit structure, shortening operation time and improving production efficiency.
Smart Images
Figure CN121487364A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to the field of uncooled infrared detectors, and more specifically to a method for removing a sacrificial layer in a wafer-level packaging process. Background Technology
[0002] Wafer-level packaging, also known as wafer-scale packaging, has become an important component of advanced packaging technology in the semiconductor industry. Its packaging method is also called flip-chip bonding. It involves performing most or all of the packaging and testing procedures directly on the infrared detector wafer, followed by dicing. It is an improved and refined chip-scale packaging solution that meets the demands for small size, light weight, portability, handheld operation, low cost, and high production efficiency. The challenge lies in the high level of process requirements.
[0003] Currently, there are two forms of wafer-level packaging for uncooled infrared detectors: the first is Wafer-to-Wafer (W2W), and the second is Chip-to-Wafer (C2W). W2W packaging refers to bonding the wafer-level silicon window (also known as the cap wafer) to the infrared detector wafer, after which it is diced into independent devices. C2W packaging refers to bonding the diced independent infrared window to the infrared detector wafer, after which it is diced into independent devices.
[0004] In the wafer-level packaging process of a dual-layer microbridge infrared detector, three layers of polyimide (PI) are used on the infrared detector wafer. The first two PI layers (i.e., the first sacrificial layer and the second sacrificial layer) support the bridge surfaces, legs, and umbrella surfaces of all focal plane pixel units in the pixel structure array, respectively. The thickness of the first two PI layers determines the height of the infrared detector resonant cavity. The third PI layer (i.e., the third sacrificial layer) is an umbrella surface passivation layer, the purpose of which is to create solder rings. That is, after the focal plane pixel unit array of each pixel structure is formed, the third PI layer is uniformly coated on the surface of the pixel structure array to protect the focal plane pixel unit array from damage. Then, the solder ring array pattern is formed by photolithography, and finally, the solder ring array is deposited on the third PI layer. After the solder ring array is completed, the three layers of PI for each pixel structure need to be removed (i.e., released).
[0005] The release of the three-layer PI (sacrificial layer) not only requires a clean release without any fibrous residue, but also ensures that the structure of the focal plane pixel units (bridge, leg, umbrella) remains undamaged and undeformed. Furthermore, for mass production, the faster the release speed of the three-layer PI (sacrificial layer), the more beneficial it is to improving production efficiency. Summary of the Invention
[0006] In view of the problems existing in the background art, one object of this disclosure is to provide a method for removing the sacrificial layer in a wafer-level packaging process, which can completely release the sacrificial layer without any fibrous residue and without damage or deformation to the structure of the focal plane pixel unit.
[0007] Therefore, a method for removing a sacrificial layer in a wafer-level packaging process includes the following steps: S1, providing a dual-layer infrared detector wafer with a solder ring array of completed pixel structure arrays to be released, wherein in each pixel structure of the pixel structure array, a focal plane pixel unit array is disposed within each solder ring, a first sacrificial layer is disposed between the readout circuit substrate corresponding to the focal plane pixel unit array on the dual-layer infrared detector wafer and the bridge surface and bridge leg pattern of all focal plane pixel units of the focal plane pixel unit array, and a second sacrificial layer is disposed between the umbrella surface pattern of all focal plane pixel units of the focal plane pixel unit array and the bridge surface and bridge leg pattern of all focal plane pixel units of the focal plane pixel unit array. Between the leg patterns, a third sacrificial layer covers the umbrella pattern of all focal plane pixel units in the focal plane pixel unit array. The first, second, and third sacrificial layers are all attached to the inner circumferential surface of the solder ring. The first, second, and third sacrificial layers are all polyimide resin. S2, the double-layer infrared detector wafer is placed in the vacuum chamber of the device for releasing the sacrificial layer. S3, the sacrificial layer is released using a three-step process: first, O2+Ar gas is ionized to release the third sacrificial layer; second, O2+N2 gas is ionized weakly than in the first step to release the second sacrificial layer; third, O2+N2 gas is ionized weakly than in the second step to release the first sacrificial layer.
[0008] The beneficial effects of this disclosure are as follows.
[0009] In the method for removing the sacrificial layer in the wafer-level packaging process according to the present disclosure, O2 is ionized into oxygen plasma in a vacuum chamber, the oxygen plasma oxidizes PI and generates volatile gas, and the volatile gas is extracted by the device for releasing the sacrificial layer, thereby realizing the release of the three sacrificial layers.
[0010] Ar is an inert gas, and Ar plasma provides physical bombardment, which can increase the etching (release) rate and shorten the operation time. Therefore, the first step of ionizing O2 + Ar gas to release the third sacrificial layer will quickly remove the third sacrificial layer on the umbrella surface pattern of all focal plane pixel units in the focal plane pixel unit array.
[0011] The role of N2 is to prevent oxygen plasma after ionization from recombinizing into O2 and to enhance ion bombardment. In the second step, which is weaker than the first step, and the third step, which is weaker than the second step, ionized O2+N2 gas is used to release the second and third sacrificial layers, respectively. This avoids damage to the structure of the focal plane pixel units (bridge, bridge legs, umbrella). In the third step, the ionization of O2+N2 gas is weaker than in the second step. This is because after the second step is completed, the third step releases the polyimide of the first sacrificial layer. As the release proceeds, the amount of polyimide in the first sacrificial layer will decrease, especially the residual polyimide flocculents formed. Only a weaker ionization than in the second step is needed for oxygen plasma and nitrogen plasma to remove these polyimide flocculents. Attached Figure Description
[0012] Figure 1 This is a schematic diagram of the cap wafer used in wafer-level packaging technology.
[0013] Figure 2 This is a schematic diagram of the solder ring array after the pixel structure array of the dual-layer infrared detector wafer used in wafer-level packaging process is set up, where the third sacrificial layer is not shown.
[0014] Figure 3 yes Figure 2 A partial schematic diagram of an example corresponding to a single cell structure, where the third sacrificial layer is shown.
[0015] Figure 4 yes Figure 3 The exploded diagram.
[0016] Figure 5 yes Figure 3 A partial cross-sectional view, in which a single focal plane pixel unit is shown, but the solder ring is not shown.
[0017] Figure 6 yes Figure 5 The diagram after all the sacrificial layers have been released.
[0018] Figure 7 This is a schematic diagram showing the selection of focal plane pixel units in the top, bottom, left, and right regions of a dual-layer infrared detector wafer after all the sacrificial layers have been released.
[0019] Figure 8 It is in Example 1 Figure 7 SEM images of slices of the bridge deck and umbrella structure, taken from the focal plane pixel units in the four regions (top, bottom, left, and right).
[0020] Figure 9 It is in Example 1 Figure 7 SEM images of the bottom slice of the focal plane pixel units in the four regions of top, bottom, left, and right. Detailed Implementation
[0021] It will be understood that the disclosed embodiments are merely examples of this disclosure, which can be implemented in various forms. Therefore, the specific details disclosed herein should not be construed as limiting, but are intended only as the basis for the claims and as an illustrative basis to teach those skilled in the art how to implement this disclosure in various ways.
[0022] Methods for removing sacrificial layers in wafer-level packaging processes Reference Figures 1 to 6 The method for removing the sacrificial layer in the wafer-level packaging process according to this disclosure includes the following steps: S1, a dual-layer infrared detector wafer with a solder ring array configuration of a completed pixel structure array to be released sacrificial layer (e.g., a wafer with a solder ring array configuration of a sacrificial layer to be released). Figure 1 The dual-layer infrared detector wafer shown is used with Figure 2 The capped wafer with a solder ring array shown is used for wafer-level packaging to achieve W2W or C2W packaging. In each pixel structure of the pixel structure array (refer to...), Figures 3 to 5 In the dual-layer infrared detector wafer, the focal plane pixel unit array is disposed within each solder ring. The first sacrificial layer is disposed between the readout circuit substrate corresponding to the focal plane pixel unit array and the bridge surface and leg pattern of all focal plane pixel units of the focal plane pixel unit array. The second sacrificial layer is disposed between the umbrella surface pattern of all focal plane pixel units of the focal plane pixel unit array and the bridge surface and leg pattern of all focal plane pixel units of the focal plane pixel unit array. The third sacrificial layer covers the umbrella surface pattern of all focal plane pixel units of the focal plane pixel unit array. The first, second, and third sacrificial layers are all attached to the inner circumferential surface of the solder ring. The first, second, and third sacrificial layers are all polyimide (PI) resin. S2, Place the double-layer infrared detector wafer in the vacuum chamber of the device for releasing the sacrificial layer; S3 employs a three-step process to release the sacrificial layer. The first step is to ionize O2 + Ar gas to release the third sacrificial layer; The second step involves weaker ionization of O2 + N2 gas than the first step to release the second sacrificial layer; The third step involves weakly ionizing the O2+N2 gas compared to the second step to release the first sacrificial layer.
[0023] In the method for removing the sacrificial layer in the wafer-level packaging process according to the present disclosure, O2 is ionized into oxygen plasma in a vacuum chamber, the oxygen plasma oxidizes PI and generates volatile gas, and the volatile gas is extracted by the device for releasing the sacrificial layer, thereby realizing the release of the three sacrificial layers.
[0024] Ar is an inert gas, and Ar plasma provides physical bombardment, which can increase the etching (release) rate and shorten the operation time. Therefore, the first step of ionizing O2 + Ar gas to release the third sacrificial layer will quickly remove the third sacrificial layer on the umbrella surface pattern of all focal plane pixel units in the focal plane pixel unit array.
[0025] The role of N2 is to prevent oxygen plasma after ionization from recombinizing into O2 and to enhance ion bombardment. In the second step, which is weaker than the first step, and the third step, which is weaker than the second step, ionized O2+N2 gas is used to release the second and third sacrificial layers, respectively. This avoids damage to the structure of the focal plane pixel units (bridge, bridge legs, umbrella). In the third step, the ionization of O2+N2 gas is weaker than in the second step. This is because after the second step is completed, the third step releases the polyimide of the first sacrificial layer. As the release proceeds, the amount of polyimide in the first sacrificial layer will decrease, especially the residual polyimide flocculents formed. Only a weaker ionization than in the second step is needed for oxygen plasma and nitrogen plasma to remove these polyimide flocculents.
[0026] In one example, in step S1, the thickness of the first sacrificial layer is greater than the thickness of the second sacrificial layer, and the thickness of the second sacrificial layer is not less than the thickness of the third sacrificial layer. Further, in step S1, the thickness of the first sacrificial layer is 2.5 μm, the thickness of the second sacrificial layer is 2 μm, and the thickness of the third sacrificial layer is 2 μm. That is, the total thickness of the first, second, and third sacrificial layers is 6.5 μm.
[0027] In step S1, for example, the first sacrificial layer, the second sacrificial layer and the third sacrificial layer are all formed by spin coating, drying and curing of a polyimide resin solution, the polyimide solution is PI2610 and the viscosity of the polyimide solution is 3000CP.
[0028] In step S2, for example, the device for releasing the sacrificial layer is a Tepla Plasma device (i.e., a device that uses a microwave source to ionize O2, Ar, and N2 to form their respective plasmas).
[0029] In one example, in step S3, the power, O2 flow rate, Ar flow rate, and pressure of the process parameters used in the first step of ionizing O2+Ar gas are higher than those of the process parameters used in the second step of ionizing O2+N2 gas. The time of the process parameters used in the first step of ionizing O2+Ar gas is shorter than that of the process parameters used in the second step of ionizing O2+N2 gas. The power, O2 flow rate, N2 flow rate, pressure, and time of the process parameters used in the third step of ionizing O2+N2 gas are lower than those of the process parameters used in the second step of ionizing O2+N2 gas. Further, in step S3, the temperature of the process parameters used in the first step of ionizing O2+Ar gas, the second step of ionizing O2+N2 gas, and the third step of ionizing O2+N2 gas are the same.
[0030] Specifically, in step S3, the process parameters for the first step of ionizing O2 + Ar gas are: power 1600-1800W, O2 flow rate 1400-1600sccm, Ar flow rate 25-45sccm, pressure 1600-1900mT, temperature 160-220°C, and time 15-20min; the process parameters for the second step of ionizing O2 + N2 gas are: power 1200-1300W, O2 flow rate 1100-1... The first step, ionization of O2 and N2 gas, uses the following parameters: power 900-1000W, O2 flow rate 850-950 sccm, N2 flow rate 10-15 sccm, pressure 1000-1200 mT, temperature 160-220°C, and time 5-10 minutes. In other words, the total release time for the first, second, and third sacrificial layers is 45-60 minutes.
[0031] More specifically, in step S3, the process parameters for the first step of ionizing O2 + Ar gas are: power 1800W, O2 flow rate 1600 sccm, Ar flow rate 40 sccm, pressure 1600 mT, temperature 180°C, and time 15 min; the process parameters for the second step of ionizing O2 + N2 gas are: power 1300W, O2 flow rate 1200 sccm, N2 flow rate 30 sccm, pressure 1300 mT, temperature 180°C, and time 30 min; the process parameters for the third step of ionizing O2 + N2 gas are: power 900W, O2 flow rate 850 sccm, N2 flow rate 12 sccm, pressure 1000 mT, temperature 180°C, and time 10 min. That is, the total release time for the first, second, and third sacrificial layers is 55 min.
[0032] [test] Example 1 The method for removing the sacrificial layer in the wafer-level packaging process of Example 1 adopts the following steps: S1, a dual-layer infrared detector wafer with a solder ring array of completed pixel structure arrays to be released is provided. In each pixel structure of the pixel structure array, the focal plane pixel unit array is disposed within each solder ring. A first sacrificial layer is disposed between the readout circuit substrate corresponding to the focal plane pixel unit array on the dual-layer infrared detector wafer and the patterns of the bridge surfaces and legs of all focal plane pixel units of the focal plane pixel unit array. A second sacrificial layer is disposed between the patterns of the umbrella surfaces of all focal plane pixel units of the focal plane pixel unit array and the patterns of the bridge surfaces and legs of all focal plane pixel units of the focal plane pixel unit array. Between them, the third sacrificial layer covers the umbrella pattern of all the focal plane pixel units of the focal plane pixel unit array. The first, second and third sacrificial layers are all attached to the inner circumferential surface of the solder ring. The first, second and third sacrificial layers are all polyimide resins. The thickness of the first sacrificial layer is 2.5 μm, the thickness of the second sacrificial layer is 2 μm, and the thickness of the third sacrificial layer is 2 μm. The first, second and third sacrificial layers are all formed by spin coating, drying and curing of polyimide resin solution. The polyimide solution is PI2610 and the viscosity of the polyimide solution is 3000 CP. S2, the double-layer infrared detector wafer is placed in the vacuum cavity of the device for releasing the sacrificial layer, wherein the device for releasing the sacrificial layer is a Tepla Plasma device; S3 employs a three-step process to release the sacrificial layer. The first step is to ionize O2+Ar gas to release the third sacrificial layer. The process parameters for ionizing O2+Ar gas in the first step are: power of 1800W, O2 flow rate of 1600sccm, Ar flow rate of 40sccm, pressure of 1600mT, temperature of 180°C, and time of 15min. The second step involves weakly ionizing the O2+N2 gas compared to the first step to release the second sacrificial layer. The process parameters for ionizing the O2+N2 gas in the second step are as follows: power of 1300W, O2 flow rate of 1200sccm, N2 flow rate of 30sccm, pressure of 1300mT, temperature of 180°C, and time of 30min. The third step involves weakly ionizing the O2+N2 gas compared to the second step to release the first sacrificial layer. The process parameters for ionizing the O2+N2 gas in the third step are as follows: power of 900W, O2 flow rate of 850sccm, N2 flow rate of 12sccm, pressure of 1000mT, temperature of 180°C, and time of 10min.
[0033] After step S3 is completed, SEM sample cutting is performed to check the release effect. Figure 7 This is a schematic diagram showing the selection of focal plane pixel units in the top, bottom, left, and right regions of a dual-layer infrared detector wafer after the sacrificial layer has been fully released. (See diagram for reference.) Figure 7 The release effect was checked by SEM sampling of the focal plane pixel units in the top, bottom, left, and right regions of the dual-layer infrared detector wafer.
[0034] Figure 8 It is in Example 1 Figure 7 SEM images of slices of the bridge deck and umbrella structure, taken from the focal plane pixel units in the four regions (top, bottom, left, and right). Figure 9 It is in Example 1 Figure 7 SEM images of the bottom slice of the focal plane pixel units in the four regions of top, bottom, left, and right.
[0035] from Figure 8 It can be seen that the structure of the focal plane pixel unit (bridge surface, bridge leg, umbrella surface) is flat, without tilting, and without collapse (i.e., without damage and without deformation).
[0036] from Figure 9 It can be seen that there is no polyimide flocculent residue above or below the bridge deck, indicating that the first, second, and third sacrificial layers have been completely released without any residue.
[0037] Several exemplary embodiments have been described in detail above, but this document is not intended to limit itself to the explicitly disclosed combinations. Therefore, unless otherwise stated, the various features disclosed herein can be combined to form several other combinations, which are not shown for simplicity.
Claims
1. A method for removing a sacrificial layer in a wafer-level packaging process, characterized in that, Including the following steps: S1, a dual-layer infrared detector wafer with a solder ring array of completed pixel structure arrays to be released is provided. In each pixel structure of the pixel structure array, the focal plane pixel unit array is disposed in each solder ring. The first sacrificial layer is disposed between the readout circuit substrate corresponding to the focal plane pixel unit array on the dual-layer infrared detector wafer and the bridge surface and bridge leg pattern of all focal plane pixel units of the focal plane pixel unit array. The second sacrificial layer is disposed between the umbrella surface pattern of all focal plane pixel units of the focal plane pixel unit array and the bridge surface and bridge leg pattern of all focal plane pixel units of the focal plane pixel unit array. The third sacrificial layer covers the umbrella surface pattern of all focal plane pixel units of the focal plane pixel unit array. The first sacrificial layer, the second sacrificial layer and the third sacrificial layer are all attached to the inner circumferential surface of the solder ring. The first sacrificial layer, the second sacrificial layer and the third sacrificial layer are all polyimide resin. S2, Place the double-layer infrared detector wafer in the vacuum chamber of the device for releasing the sacrificial layer; S3 employs a three-step process to release the sacrificial layer. The first step is to ionize O2 + Ar gas to release the third sacrificial layer; The second step involves weaker ionization of O2 + N2 gas than the first step to release the second sacrificial layer; The third step involves weakly ionizing the O2+N2 gas compared to the second step to release the first sacrificial layer.
2. The method for removing the sacrificial layer in the wafer-level packaging process according to claim 1, characterized in that, In step S1, the thickness of the first sacrificial layer is greater than the thickness of the second sacrificial layer, and the thickness of the second sacrificial layer is not less than the thickness of the third sacrificial layer.
3. The method for removing the sacrificial layer in the wafer-level packaging process according to claim 2, characterized in that, In step S1, the thickness of the first sacrificial layer is 2.5 μm, the thickness of the second sacrificial layer is 2 μm, and the thickness of the third sacrificial layer is 2 μm.
4. The method for removing the sacrificial layer in the wafer-level packaging process according to claim 1, characterized in that, In step S1, the first sacrificial layer, the second sacrificial layer, and the third sacrificial layer are formed by spin coating, drying, and curing of a polyimide resin solution. The polyimide solution is PI2610, and the viscosity of the polyimide solution is 3000 CP.
5. The method for removing the sacrificial layer in the wafer-level packaging process according to claim 1, characterized in that, In step S2, the device for releasing the sacrificial layer is the Tepla Plasma device.
6. The method for removing the sacrificial layer in the wafer-level packaging process according to any one of claims 2-5, characterized in that, In step S3, The power, O2 flow rate, Ar flow rate, and pressure in the first step of ionizing O2+Ar gas are higher than those in the second step of ionizing O2+N2 gas. The time in the first step of ionizing O2+Ar gas is shorter than that in the second step of ionizing O2+N2 gas. The power, O2 flow rate, N2 flow rate, pressure, and time used in the third step of ionizing O2+N2 gas are lower than those used in the second step of ionizing O2+N2 gas.
7. The method for removing the sacrificial layer in the wafer-level packaging process according to claim 6, characterized in that, In step S3, The temperature in the process parameters used for the first step of ionizing O2+Ar gas, the second step of ionizing O2+N2 gas, and the third step of ionizing O2+N2 gas are the same.
8. The method for removing the sacrificial layer in the wafer-level packaging process according to claim 6, characterized in that, In step S3, The process parameters used for the first step of ionizing O2 + Ar gas are as follows: power 1600-1800W, O2 flow rate 1400-1600sccm, Ar flow rate 25-45sccm, pressure 1600-1900mT, temperature 160-220°C, and time 15-20min. The process parameters used for the second step of ionizing O2 and N2 gas are as follows: power 1200-1300W, O2 flow rate 1100-1400sccm, N2 flow rate 20-40sccm, pressure 1200-1600mT, temperature 160-220°C, and time 25-30min. The process parameters used in the third step of ionizing O2 and N2 gas are as follows: power 900-1000W, O2 flow rate 850-950sccm, N2 flow rate 10-15sccm, pressure 1000-1200mT, temperature 160-220°C, and time 5-10min.
9. The method for removing the sacrificial layer in the wafer-level packaging process according to claim 8, characterized in that, In step S3, The process parameters used for the first step of ionizing O2 + Ar gas are: power of 1800W, O2 flow rate of 1600sccm, Ar flow rate of 40sccm, pressure of 1600mT, temperature of 180°C, and time of 15min. The process parameters used for the second step of ionizing O2 + N2 gas are: power of 1300W, O2 flow rate of 1200sccm, N2 flow rate of 30sccm, pressure of 1300mT, temperature of 180°C, and time of 30min. The process parameters used in the third step of ionizing O2 and N2 gas are as follows: power of 900W, O2 flow rate of 850sccm, N2 flow rate of 12sccm, pressure of 1000mT, temperature of 180°C, and time of 10min.