CN102969394B - Limit mold for back lapping of infrared focal plane detector and preparation method - Google Patents

Abstract

The invention discloses a limiting mold for thinning the back of an infrared focal plane detector and a preparation method thereof. The special limit design of the limit mold can precisely control the consistency and uniformity of the thickness of the detector chip; the main material of the mold is two pieces of white gemstones with very high hardness, and the thinning, grinding and polishing conditions of the back of the detector chip have almost no effect on it. It works; according to the characteristic size of the detector, use a laser to open a rectangular hole in the center of two white sapphire sheets and use Disco cutting to divide it into two along the diagonal of the rectangular hole; then use special DW3 low-temperature glue to bond the two layers solidified. The raw material of the limiting mold designed by the invention is simple and easy to obtain; it has precise thickness controllability; the process is controllable and the operation process is small; the mold can be reused and has wide applicability.

Description

A limiting mold for thinning the back of an infrared focal plane detector and its preparation method

technical field

The invention relates to the field of infrared focal plane detector manufacturing, in particular to a device preparation process for an infrared focal plane detector, specifically a limiting mold and a preparation method used in the device back thinning process.

Background technique

The infrared focal plane detector is composed of a chip (infrared photosensitive element), a readout circuit and a gemstone substrate flip-welded interconnection. The back thinning of the focal plane detector is to obtain the chip thickness and optical surface that match the optical system within the deviation range, reduce the internal stress on the photosensitive element of the chip, improve the low-temperature reliability of the device, and also improve the back-illuminated type. Backside transmission of HgCdTe infrared focal plane detectors. Therefore, the back thinning process of the focal plane detector is a key basic process technology that affects device performance, responsivity and reliability. With the requirement of integrated and polychromatic focal plane devices, current large-scale devices are generally formed by seamless splicing of several or even dozens of focal plane detectors as modules. When splicing, the system requires the photosensitive element chips of each focal plane module to be in the same focal plane, and the thickness consistency and uniformity of the chips are precisely controlled, which requires good control when the back of the focal plane module is thinned and polished. and repeatability.

In the existing focal plane module back thinning process, in order to prevent the exposed parts of the detector from being damaged, the edge of the chip to collapse, and to obtain the required thickness of the system, it adopts the method of sequentially accumulating the same device type in the places with ups and downs around the device. Materials and multi-layer accompanying sheets of similar thickness are processed. The specific processing process is as follows: firstly, choose the companion piece of different materials, the readout circuit and the gemstone substrate use Si slice as the companion piece, and the chip uses the material of the same chip type as the companion piece; The thickness and specifications of each part of the detector are matched with the specifications of the accompanying sheet. Then use paraffin to melt and dewax the 12 pieces of the lower Si-based companion, the middle Si-based companion, and the upper chip in batches, and protect them by three-layer superimposition.

There are many shortcomings in the above method: first, the consistency and uniformity of the chip thickness of each focal plane module cannot be guaranteed; Accumulate multiple layers of accompanying sheets. After each layer of accompanying sheets is pasted and fixed, it is easy to cause the interlayer movement of the accompanying sheets when the wax is melted again, making the operation complicated and uncontrollable; finally, the preparation work of the early stage and the cleaning of the middle and lower layers of accompanying sheets The amount is large and the work efficiency is low.

Contents of the invention

Based on the many problems in the back thinning of the focal plane module based on the above method, the purpose of the present invention is to provide a thickness control method for the back thinning of the infrared focal plane detector, and discloses a method for back thinning of the infrared focal plane detector. Limiting mold and preparation method.

The limit mold structure of the present invention is as shown in Figure 1, and it is made up of the left half part a of the limit mold and the right half part b of the limit mold, wherein the left half part a of the limit mold is composed of the lower gemstone sheet The left half 1 and the left half 3 of the upper gemstone are bonded and cured by DW3 low-temperature glue, and the right half b of the limiting mold is formed by the left half 2 of the lower gemstone and the right half 4 of the upper gemstone through DW3 It is formed by bonding with low-temperature glue and curing; the thickness of the left half part 1 of the lower layer gem sheet and the right half part 2 of the lower layer gem sheet are the same as the thickness of the processed detector gem substrate base, and the two together form a Rectangular, its external dimension is 1-2cm larger than the size of the processed detector gem substrate base, and there is a rectangular hole in the center, the size of the hole is the same as the processed detector gem substrate base size; the left half of the upper gemstone sheet The thickness of 3 and the right half of the upper gem piece 4 is the thickness of the readout circuit on the substrate base of the processed detector gemstone plus the thickness of the chip that needs to be reserved for tens of microns, and the two together form a rectangle of the same size , there is a rectangular hole in the middle, its position and size are the same as the readout circuit on the substrate base of the processed detector gem, when the left half part a of the limit mold and the right half part b of the limit mold are combined together, The processed detector just fits into the rectangular hole in the middle of the limit mold.

The method of using the limiting mold is as follows: fix the required back-thinned focal plane detector in the center of the back-thinning glass substrate with paraffin, and snap the corresponding two halves of the triangular-shaped limiting mold from the two opposite corners of the detector , place the whole on the heating furnace, melt the wax around the mold, and carefully press it evenly with special tweezers. Take off the glass substrate and put it on the operating platform, cool it down, wait for the wax to solidify, and then wipe off the excess solid wax around it, and then you can get the focal plane module that is protected by a limiting mold and can be polished for back thinning. Fig. 2 is a schematic cross-sectional view of a focal plane module with a limited mold pasted with paraffin.

The step of spacer mold preparation of the present invention is specifically as follows:

1. Select two white sapphire rectangles whose size is larger than the size of the gemstone substrate of the detector (1-2cm is appropriate) and whose hardness is much larger than that of the chip substrate material. Among them, the white sapphire sheet whose thickness is equal to the thickness of the gemstone substrate of the focal plane detector is used as the lower layer, and the white sapphire sheet whose thickness is the thickness of the readout circuit plus the actual chip thickness (tens of microns) that needs to be reserved is used as the upper layer.

2. Using laser cutting, a rectangular hole is opened in the center of the lower rectangular white sapphire sheet, the size of which is the same as the area of the focal plane detector gem substrate base; according to the relative position of the detector readout circuit and the gem substrate, the lower rectangular hole is As a benchmark, open a rectangular hole on the upper layer of white sapphire, the size of which is consistent with the size of the detector readout circuit.

3. Use Disco cutting to cut the upper and lower layers of white gemstones with rectangular holes into two along the diagonals of the respective rectangular holes.

4. Soak the designed 4 pieces of triangular-shaped white gemstones in chromic acid, ultrasonically clean them with trichlorethylene, ether, acetone, and absolute ethanol for 15 minutes, then rinse them with deionized water, and dry them with nitrogen.

5. Combine the cleaned 4 pieces of triangular-shaped white sapphire pieces according to the positions of the upper and lower rectangular holes, and use the DW3 low-temperature liquid glue produced by Shanghai Synthetic Resin Research Institute to bond them under an optical microscope, and go through a special temperature-changing process. Curing, that is, at 35°C and 60°C, it requires constant temperature for 24 hours, 48~72 hours. That is, the limit mold for the back thinning and polishing of the focal plane module is obtained.

The advantages of the present invention are:

1. The limit die described in the present invention solves the uncontrollability of the thinning thickness of the back of the detector in the existing method, and considers the reserved thickness of the chip and the grinding and polishing effects of different materials under the same grinding and polishing conditions, and achieves the limit. effect. Ensure the consistency and uniformity of chip thickness in different batches of back-thinning and polishing focal plane modules, and can be in the same focal plane according to the designed optical path system during infrared imaging to achieve the purpose of confocal;

2. The thickness control method of the present invention simplifies the operation process, and avoids the uncontrollable operation of multiple layers of accumulative attachment of the attachment sheet by melting and condensing wax in the back thinning process of the existing attachment sheet;

3. The limiting mold material of the present invention is simple and easy to obtain, easy to manufacture, reusable, high in stability, and has wide applicability.

4. The preparatory work in the early stage and the cleaning workload in the later stage are greatly reduced, which improves work efficiency and saves labor.

Description of drawings

Fig. 1 is a schematic diagram of a limit mold structure;

In the figure, (a) is the left half of the limit mold;

(b) is the right half of the limit mold;

Among them, (1) is the left half of the lower gem piece;

(2) is the right half of the lower gem piece;

(3) is the left half of the upper gem piece;

(4) is the right half of the lower gem slice.

Fig. 2 is a schematic cross-sectional view of a focal plane module with a limited mold pasted with paraffin.

Fig. 3 is the components of the 32x4 focal plane module limiting mold of the embodiment, where (a) is the structural diagram of the left half of the lower gemstone sheet, and (b) is the structural diagram of the right half of the lower gemstone sheet, and Fig. (c ) is the structure diagram of the left half of the upper gem slice, and figure (d) is the structure diagram of the left half of the upper gem slice.

Detailed ways

The implementation of this patent will be described in detail below by taking a mercury cadmium telluride infrared focal plane device with a photosensitive element array of 32x4 as an example:

The upper chip of the 32x4 HgCdTe infrared focal plane device in this example is made of GaAs substrate material, the readout circuit of the middle layer is made of Si-based material, and the substrate material is gemstone. The thickness of the GaAs substrate is 350 μm, the thickness of the intermediate circuit is 450 μm, and the thickness of the lower gemstone substrate is 330 μm. According to the project requirements, the thickness of the final chip reserved is 20 μm.

The method for controlling the thinning thickness of the back of the infrared focal plane detector according to the present invention is used to prepare corresponding limiting molds according to the specific specifications of the 32x4 focal plane module.

First, choose two rectangular white gemstones with moderate thickness and suitable size. Select a rectangular white sapphire sheet with a thickness of 330 μm as the lower layer of the mold, and a rectangular white sapphire sheet with a thickness of 470 μm as the upper layer of the mold. The area of the base of the gemstone substrate of the focal plane device is 9.0x7.3mm ² , the area of the base of the Si-based readout circuit is 6.6x5.2mm ² , and the size of two rectangular white gemstones is 20.2x16.3mm ² .

Second, determine the dimensions of the laser cut center rectangular hole. According to the base area of the Si-based readout circuit of the focal plane device and the gem substrate in the example, laser cutting is used to open a rectangular hole in the center of the upper and lower layers of the white gemstone of the limit mold. The size of the upper hole is the area of the Si-based readout circuit. 6.6x5.2mm ² , the size of the hole in the lower layer is 9.0x7.3mm ² in the base area of the gemstone substrate.

Using the Disco cutting method, the two pieces of white gemstones are cut into two along the diagonal of the rectangular hole in the center. Among them, the slit width of the Disco cutting hard knife blade is 200 μm. Figure 3 is the components of the 32x4 focal plane module stop mold. Among them, (a) and (b) are the two parts of the disco-cut white sapphire sheet on the lower layer of the mold, and (c) and (d) are the two disco-cut parts of the white sapphire sheet on the upper layer of the mold.

Finally, make a limiting mold for thinning the back of the infrared focal plane module. Soak the designed white gem pieces (a), (b), (c), and (d) in chromic acid for 4 hours, then ultrasonically clean them with trichloroethylene, ether, acetone, and absolute ethanol for 15 minutes, and then wash them with deionized water Rinse and blow dry with nitrogen. Combine the gem pieces (a), (c) and (b), (d), and use the pre-prepared DW3 low-temperature liquid glue to bond and cure under the optical microscope. Wipe off the liquid low-temperature glue extruded from the edge, put the whole in a 35°C and 60°C incubator and bake for 24 hours, 48-72 hours. That is, the back thinning limit mold of the focal plane module is obtained, and its structural schematic diagram is shown in FIG. 1 .

Place the 32x4 focal plane module that needs back thinning and polishing on the center of the thinning and polishing glass substrate, put a small amount of solid wax around it and heat until the wax melts; Snap in on the side and carefully press evenly with special tweezers. Remove the whole body and put it on the operating platform, cool it down, wait for the wax to solidify, and then wipe off the excess solid wax around it to obtain a focal plane module that is protected by a limiting mold and can be back-thinned and polished, as shown in Figure 2.

Thickness test and edge morphology characterization of the back-thinned and polished 32x4 focal plane module. There is no obvious edge collapse on the edge of the chip; the thickness uniformity is good through the optical microscope test, which is consistent with the actual thickness reserved; and the whole process is simple to operate and highly controllable; since the hardness of the gemstone is much higher than that of GaAs, the chip Grinding and polishing conditions have almost no effect on the mold, and the limiting mold can be reused after taking the piece. This shows that adopting the thickness control method of the present invention to thin the back of the focal plane module is effective and easy, and the limiting mold used in the method is reasonable, which can solve many problems existing in the thinning and polishing of the back of the module by the existing method of attaching the companion sheet.

Claims (2)

1. a limit mold for infrared focal plane detector back thinning, it is made up of the left half part (a) of limit mold and the right half part (b) of limit mold, it is characterized in that: described The left half of the limiting mold (a) is made of the left half of the lower gemstone (1) and the left half of the upper gemstone (3) through DW3 low-temperature adhesive and then cured, and the right half of the limiting mold (b) It is formed by bonding the left half (2) of the lower gem sheet and the right half (4) of the upper gem sheet by DW3 low-temperature glue and curing; the left half (1) of the lower gem sheet and the lower gem sheet The thickness of the right half (2) of the gem piece is the same as the thickness of the processed detector gem substrate base, and the two together form a rectangle, and its external dimension is 1-2cm larger than the processed detector gem substrate base size. There is a rectangular hole in the center, and the size of the hole is the same as that of the processed detector gem substrate base; the thickness of the left half (3) and the right half (4) of the upper gem slice is the processed detection The thickness of the readout circuit on the base of the gemstone substrate of the sensor plus the actual thickness of the chip to be reserved, the two together form a rectangle of the same size, with a rectangular hole in the middle, its position and size are the same as the processed gemstone substrate of the detector The readout circuit on the base is the same, when the left half (a) of the limit mold and the right half (b) of the limit mold are combined, the processed detector can just fit into the rectangular hole in the middle of the limit mold middle. 2. a kind of method for preparing the limiting mold that is used for infrared focal plane detector back thinning as claimed in claim 1, is characterized in that comprising the following steps: 1) Select two rectangular white sapphire sheets as the upper and lower layers. The hardness of the rectangular white sapphire sheet is much greater than the hardness of the chip substrate material, and the thinning and polishing conditions of the chip substrate have little effect on it; the thickness is selected as the detector gemstone substrate. The thickness of the white sapphire sheet is used as the lower layer, and the thickness of the white sapphire sheet is the thickness of the readout circuit plus the thickness of the chip that needs to be reserved in tens of microns as the upper layer; The perimeter length should be greater than the side length of the detector gemstone substrate to protect the chip edge, readout circuit and gemstone substrate; 2) Make a rectangular hole in the center of the upper and lower rectangular white sapphire sheets selected in step 1) by laser cutting according to the size of the detector readout circuit and the gemstone substrate. The size of the gemstone substrate of the detector is the same, and the size of the rectangular hole of the upper gemstone sheet is consistent with the size of the readout circuit; 3) Two pieces of white sapphire sheets with rectangular holes and different thicknesses obtained in step 2) are divided into two along the diagonal of the rectangular holes by Disco cutting; 4) Soak the 4 pieces of white gemstones designed in step 3) with chromic acid, ultrasonically clean them with trichlorethylene, ether, acetone, and absolute ethanol respectively, then rinse them with deionized water, and dry them with nitrogen; 5) Use the DW3 low-temperature liquid glue produced by Shanghai Synthetic Resin Research Institute to bond the upper and lower white sapphire sheets cleaned in step 4) under an optical microscope based on the central rectangular hole, and then heat them at 35°C and 60°C. The environment requires constant temperature for 24 hours and 48 to 72 hours respectively to obtain a thinning mold for the back of the detector with a limit function and clean it.