CN115197705B - An etching solution and a thinning method for a mercury cadmium telluride infrared focal plane hybrid chip - Google Patents

Abstract

The invention proposes an etching solution, the components of which include nitric acid, hydrofluoric acid, lactic acid and water; and a method for thinning a mercury cadmium telluride infrared focal plane hybrid chip, which can quickly remove tellurium by wet etching Zinc-cadmium substrate, the corrosion rate of cadmium zinc telluride substrate can reach more than 500 microns/minute, and this etching solution can completely corrode the cadmium zinc telluride substrate within 2 minutes, and will form a stop layer on the transition layer of mercury cadmium telluride , the stop layer is only tens of nanometers, and then the stop layer is removed by etching with an aqueous solution of bromine and hydrobromic acid. The etching time is about 10 seconds, and finally a bright and fresh mercury cadmium telluride surface is obtained. This method can quickly remove the substrate with an original thickness of 900-1000 microns, effectively eliminate the damage caused by the physical thinning process of the substrate, and keep the photoelectric performance of the mercury cadmium telluride infrared detector from being affected by the substrate thinning process.

Description

An etching solution and a thinning method for a mercury cadmium telluride infrared focal plane hybrid chip

technical field

The invention relates to the technical field of etching, in particular to an etching solution and a method for thinning a mercury cadmium telluride infrared focal plane hybrid chip.

Background technique

The mercury cadmium telluride infrared focal plane hybrid chip is the core component of the mercury cadmium telluride infrared focal plane detector assembly. The hybrid chip set is prepared by interconnecting the mercury cadmium telluride infrared focal plane array chip and the silicon readout circuit through indium column flip-chip. Mercury cadmium telluride infrared focal plane array chip is based on the infrared photosensitive material of cadmium zinc telluride substrate epitaxy technology, which is prepared by a series of semiconductor processes such as surface treatment, passivation, photolithography, implantation, etching, and electrode forming. The bottom thickness is about 900 to 1000 microns, as shown in Fig. 1 . Thinning and removing the CdZnTe substrate of the HgCdTe infrared focal plane detector hybrid chip can effectively reduce the internal stress of the photosensitive element of the chip due to temperature shock, improve the transmittance of infrared radiation, and improve the stability of the detector components. ,reliability.

At present, the main technical route of the substrate thinning and removal process is to thin the substrate through physical methods (including grinding and polishing, single-point diamond turning, etc.), so that the CdZnTe substrate remains about 10 microns; the remaining about 10 microns The CdZnTe substrate is then completely removed by chemical etching. Grinding and polishing is to buckle the hybrid chipset upside down on the grinding and polishing disc or polishing pad of the grinding and polishing equipment, and drip the grinding and polishing liquid by applying pressure, and through the rotation and revolution of the grinding and polishing disc, grinding and polishing pad and chipset, the substrate and the grinding and polishing are realized. The grinding and polishing effect of the throwing liquid achieves the purpose of thinning the substrate. The single-point diamond turning adopts the method of flying cutter milling, fixes the hybrid chipset on the workpiece table, and turns the substrate through the combined action of the lateral feed of the flying cutter and the longitudinal feed of the workpiece table to achieve the thinning of the CdZnTe substrate Purpose. Relevant equipment and auxiliary materials are required for substrate thinning and removal by physical methods. These equipment and auxiliary materials are expensive, which makes the cost of substrate thinning and removal higher. Moreover, in the process of thinning the substrate by grinding and polishing, there is a certain probability that scratches will appear on the surface, and the appearance of scratches will affect the performance of the corresponding pixel on the detector, thereby affecting the image quality; Under the action of stress, micro-cracks and chipping are easy to form around the planar array chip, which affects the photoelectric performance of the detector.

In the process of thinning the substrate by single-point diamond turning, since the cutting fluid is sprayed to cool down the detector chip, the turning residue will cover the surface, and scratches are likely to occur in the subsequent turning. There is a high probability of edge chipping and the stress of turning, which will affect the photoelectric performance of the detector. In addition, this technical solution has complicated process, long period and low efficiency.

Therefore, the substrate thinning and removal process is a key process technology that affects the performance and reliability of HgCdTe infrared focal plane detector components.

Contents of the invention

In order to solve the above-mentioned problems in the prior art, the present invention proposes an etching solution and a method for thinning a mercury cadmium telluride infrared focal plane hybrid chip.

In the first aspect, the present invention provides an etching solution whose components include nitric acid, hydrofluoric acid, lactic acid and water.

As a specific embodiment of the present invention, the preparation method of the etching solution comprises mixing nitric acid, hydrofluoric acid, lactic acid and water.

As a specific embodiment of the present invention, the molar ratio of nitric acid, hydrofluoric acid, lactic acid and water is 12:1:6: (6-50).

Specifically, by adjusting the ratio of water and changing the pH value of the etching solution, the corrosion rate can be adjusted; when the water is 6 moles, the corrosion rate is the fastest, and when the water exceeds 50 moles, the corrosion rate drops significantly, and cannot reach a fast rate. The effect of corrosion, and the uniformity of corrosion becomes poor.

In the second aspect, the present invention provides the application of the etching solution in the field of cadmium zinc telluride materials.

In the third aspect, the present invention provides a method for thinning the HgCdTe infrared focal plane hybrid chip, which uses the etching solution to etch and remove the CdZnTe substrate of the HgCdTe infrared focal plane hybrid chip.

As a specific embodiment of the present invention, the thinning method includes the following steps:

S1: Coat the periphery of the HgCdTe infrared focal plane hybrid chip with photoresist, bake, expose, develop, photolithography, and form a film;

S2: placing the glue-coated and film-formed chip obtained in step 1 in the etching solution described in claim 1 or 2, and cleaning after removing the cadmium zinc telluride substrate;

S3: placing the chip obtained in step S2 from which the CdZnTe substrate has been removed is etched in a stop layer etching solution to remove the stop layer;

S4: Clean and dry the chip obtained in step S3 from which the termination layer has been removed, to obtain a HgCdTe infrared focal plane hybrid chip with a thinner substrate.

As a specific embodiment of the present invention, in the step S1, the photoresist is a positive photoresist; the positive photoresist preferably includes AZ6130, Kehua BP218; specifically, taking AZ6130 as an example, the glue The method can be spin-coating, and the spin-coating speed is 2000-3000 rpm.

The thickness of the photoresist coating is 4-10 μm; when actually applying the coating, the thickness of the photoresist is 4-10 μm, and the thickness of the flat area is 4 μm, but the phenomenon of photoresist accumulation will occur at the corners of the hybrid chip. The glue thickness is about 6-10μm;

The baking temperature is 80-100°C; the baking time is 1-10 minutes;

The exposure method is contact exposure; the exposure time is 10-20s;

The developing time is 30-90s; specifically, the chip is immersed in the developing solution for 30-90s to complete the developing;

The film-forming temperature is 50-80° C.; the film-forming time is 1-3 hours; specifically, the film-forming method is preferably oven baking.

As a specific embodiment of the present invention, the process of gluing is to coat the entire surface, and then select the required pattern through the photolithography process; the process of the lithography process includes gluing, pre-baking, exposure, development, film hardening, etc. Process; positive photoresist is fine, but a certain thickness of the photoresist must be ensured, and unnecessary photoresist can be removed by development after exposure. The size of the photolithography plate is 5 microns larger than the size of the CdZnTe substrate of the hybrid chip in each direction; it is to ensure that the CdZnTe substrate can be fully exposed and can be removed by etching in the subsequent etching process; the size is 5 microns larger, and a It is for photolithography registration, and the second is to fully expose the CdZnTe substrate and prepare for subsequent corrosion.

As a specific embodiment of the present invention, in the step S2, the components of the etching solution include nitric acid, hydrofluoric acid, lactic acid and water, wherein the molar ratio of nitric acid, hydrofluoric acid, lactic acid and water is 12:1:6 : (6-50); the corrosion time is 1-3 min.

As a specific embodiment of the present invention, in the step S3, the stop layer etching solution components include bromine, hydrobromic acid and water; the volume ratio of bromine, hydrobromic acid and water in the stop layer etching solution components 0.1:10:90; the concentration of hydrobromic acid is 50%; the corrosion time is 5-15s.

As a specific embodiment of the present invention, in the step S4, the cleaning includes three steps of rinsing with deionized water, soaking in acetone, and rinsing with absolute ethanol.

As a specific embodiment of the present invention, the deionized water rinsing time is 3-8 minutes; the acetone soaking time is 3-5 minutes; the ethanol rinsing is 3-5 times;

The above-mentioned raw materials in the present invention can be self-made or commercially available, which is not particularly limited in the present invention.

Compared with prior art, the beneficial effect of the present invention is:

1. The present invention is an etching solution, which can quickly remove the cadmium zinc telluride substrate by wet etching. The corrosion rate of the cadmium zinc telluride substrate can reach more than 500 microns/minute, and the etching solution can completely remove the cadmium zinc telluride substrate within 2 minutes. The CdZnTe substrate is etched away, and a stop layer will be formed on the HgCdTe transition layer. The stop layer is only tens of nanometers, and then the stop layer is removed by etching with an aqueous solution of bromine and hydrobromic acid. The etching time is about 10 seconds, and finally Shiny fresh HgCdTe surface. The method can quickly remove the substrate with an original thickness of 900-1000 microns, effectively eliminate the damage caused by the physical thinning process of the substrate, and keep the photoelectric performance of the mercury cadmium telluride infrared detector from being affected by the thinning process of the substrate.

2. The examples of the present invention show that the etching solution of the present invention significantly improves the efficiency of the CdZnTe substrate thinning and removal process, saves equipment, manpower, and material costs, and eliminates the cost of substrate thinning by physical means. Stress damage ensures that the performance of the infrared detector is not affected by the substrate thinning and removal process, and improves the yield of the substrate thinning process.

3. The etchant has low cost and high substrate removal efficiency, and is especially suitable for thinning and removing the substrate of a small-pitch CdZnTe-based HgCdTe infrared detector hybrid chip.

Description of drawings

FIG. 1 is a schematic structural diagram of a HgCdTe infrared focal plane hybrid chip in an embodiment of the present invention;

FIG. 2 is a schematic diagram of a HgCdTe infrared focal plane hybrid chip after coating obtained in step S1 in an embodiment of the present invention;

3 is a schematic diagram of the exposure process of the HgCdTe infrared focal plane hybrid chip obtained in step S1 of the embodiment of the present invention after coating;

4 is a schematic diagram of a cadmium-mercury infrared focal plane hybrid chip with a CdZnTe substrate completely exposed after development obtained in step S1 in an embodiment of the present invention;

5 is a schematic diagram of a HgCdTe infrared focal plane hybrid chip obtained in step S2 in an embodiment of the present invention without the CdZnTe substrate;

FIG. 6 is a schematic diagram of the thinned HgCdTe infrared focal plane hybrid chip obtained in step S3 in the embodiment of the present invention after removing the stop layer.

Among them, 1-CdZnTe substrate, 2-HgCdTe epitaxial film, 3-interconnected indium pillars; 4-readout circuit chip.

Detailed ways

The present invention will be further described below in conjunction with specific examples, but this does not constitute any limitation to the present invention.

The reagent information used in each embodiment of the present invention is as follows:

Nitric acid, Tianjin Fengchuan TSVL grade, concentration 98%, density about 1.52g/ml, molecular weight 63;

Hydrofluoric acid, Tianjin Fengchuan TSVL grade, concentration 40%, density about 1.12g/ml, molecular weight 20;

Lactic acid, Tianjin Fengchuan TSVL grade, density about 1.2g/ml, molecular weight 90;

Water, deionized water, resistivity 18M ohm, molecular weight 18;

Bromine, Tianjin sailboat, purity 5N;

Hydrobromic acid, Tianjin sailboat TSVL grade, the concentration is 50%.

Example 1

This embodiment provides an etching solution, and the specific component information is as follows:

Nitric acid 50ml, hydrofluoric acid 5ml, lactic acid 45ml, deionized water 10ml;

Mix the nitric acid, hydrofluoric acid, lactic acid and water in the above ratio, and rotate and stir on a magnetic stirrer for 3 minutes to obtain a uniformly mixed etching solution.

The pH value of the etching solution obtained in Example 1 was 0.

Embodiment 2-5

The preparation method of the etching solution provided in Examples 2-5 is the same as that of Example 1, except that the proportion of water is different, and the specific details are as shown in Table 1:

Etching solution components and ratio information provided in Table 1 Examples 1 to 5

nitric acid hydrofluoric acid lactic acid Deionized water pH value Corrosion rate (micron/min) Example 1 50ml 5ml 45ml 10ml 0 ≥620 Example 2 50ml 5ml 45ml 50ml 0 ≥550 Example 3 50ml 5ml 45ml 90ml 0 ≥520 Example 4 50ml 5ml 45ml 100ml 0 ≤150 Example 5 50ml 5ml 45ml 150ml 0 ≤50

Comparative example 1

This comparative example provides an etching solution, and the specific component distribution ratio information is as follows:

Nitric acid 50ml, hydrochloric acid (37%) 5ml, lactic acid 45ml, deionized water 10ml;

Mix the nitric acid, hydrochloric acid (concentration: 37%), lactic acid and water in the above ratio, and rotate and stir on a magnetic stirrer for 3 minutes to obtain a uniformly mixed etching solution.

The pH of the etching solution obtained in Comparative Example 1 was 0, and the etching rate was about 10 μm/min.

Comparative example 2-5

The preparation method of the etching solution provided in Comparative Examples 2-5 is the same as that of Example 1, and the components and ratio information are shown in Table 2:

Etching solution components and ratio information provided in Table 2 Comparative Examples 1 to 5

nitric acid hydrochloric acid lactic acid Deionized water pH value Corrosion rate (micron/min) Comparative example 1 50ml 5ml 45ml 10ml 0 about 10 Comparative example 2 50ml 15ml 45ml 10ml 0 about 15 Comparative example 3 20ml 20ml 45ml 10ml 0 about 8 Comparative example 4 20ml 20ml 10ml 10ml 0 about 10 Comparative example 5 15ml 45ml 45ml 10ml 0 about 5

Table 3 Other etching solution components and ratio information

nitric acid hydrochloric acid Potassium dichromate Deionized water pH value Corrosion rate (micron/min) Comparative example 6 30ml 20ml 20g 50ml 0 about 8

The chemical reaction of wet etching belongs to the reaction between liquid phase and solid phase, which is a process controlled by diffusion effect. The corrosion rate of Comparative Examples 1-6 is too slow, and with the passage of time, the corrosion rate will further decrease, and the uniformity of corrosion is also poor. In addition, due to long-term immersion in the etching solution, the photoresist is not enough to provide effective protection. After 10-15 minutes, the phenomenon of floating glue will appear, so that the etching solution erodes the pad of the readout circuit, causing the circuit to fail. Even if the adhesion promoter is applied before the glue coating, the phenomenon of floating glue will occur after 20-25 minutes of corrosion. It can be seen that the slow rate cannot be applied to the non-destructive thinning and removal of the substrate.

Example 6

This embodiment provides a method for thinning a HgCdTe infrared focal plane hybrid chip, and the specific details are as follows:

S1: HgCdTe infrared focal plane hybrid chip (hereinafter referred to as the chip) is spin-coated with positive photoresist, the photoresist model is AZ6130, the spin-coating speed is 2500 rpm, and the photoresist thickness is 4-10 μm;

Pre-bake the glue-coated chip on a hot plate at 95°C for 3 minutes; then expose it by contact exposure for 15 seconds; the size of the photolithography plate is 5 microns larger in each direction than the size of the CdZnTe substrate of the hybrid chip;

Then immerse the exposed chip in AZ300MIF (2.38%) developer solution, keep the temperature at 23°C, and develop for 60 seconds; after the development, rinse with deionized water for 30 seconds, then place it in an oven at 60°C to dry and harden the film for 2 hours;

S2: Place the chip obtained in step 1 after coating and forming a film in the etching solution prepared in Example 1, corrode for 2 minutes, remove the cadmium zinc telluride substrate, and clean it with deionized water for 5 minutes;

S3: Mix bromine, hydrobromic acid with a concentration of 50%, and deionized water according to a volume ratio of 0.1:10:90, and rotate and stir on a magnetic stirrer for 3 minutes to obtain a stop layer etching solution; The chip from which the CdZnTe substrate was removed was placed in a stop layer etching solution for etching, and the stop layer was removed by etching for 10 seconds;

S4: Rinse the chip obtained in step S3 with the stop layer removed for 5 minutes, then soak it in acetone for 3 minutes, and finally wash it with absolute ethanol for 3 times, and dry it with nitrogen to obtain the final thinned substrate. HgCdTe Infrared Focal Plane Hybrid Chip.

The HgCdTe infrared focal plane hybrid chip obtained in Example 6 was observed by an optical microscope, and the substrate removal rate reached 100%.

Embodiment 7-15

Examples 7-15 use the etching solutions provided in Examples 2-5 and Comparative Examples 1-5, and the thickness of the CdZnTe substrate is 920-930 μm. Using the thinning method provided in Example 6 to carry out the chip thinning treatment, the specific effects obtained are shown in Table 3:

The etchant of Table 3 Examples 1-5 and Comparative Examples 1-5 are used for chip thinning treatment effect

Comparison of comparative examples and examples shows that after hydrofluoric acid is replaced by hydrochloric acid, the fastest reaction rate is only 15 μm/min, and it is also highly corrosive to mercury cadmium telluride films; if sulfuric acid is too oxidizing, it will react with lactic acid .

In summary, the etching solution formulation for rapid corrosion removal of CdZnTe substrates of the present invention is effectively applied to the thinning and removal process of CdZnTe-based HgCdTe infrared focal plane detector hybrid chip substrates. The application of this etching solution significantly improves the efficiency of the CdZnTe substrate thinning and removal process, saves equipment, manpower, and material costs, eliminates stress damage caused by physical substrate thinning, and ensures the performance of infrared detectors It is not affected by the substrate thinning and removal process, and the yield of the substrate thinning process is improved.

Any reference to any numerical value in this invention includes all values in increments of one unit from the lowest value to the highest value if there is a separation of only two units between any lowest value and any highest value. For example, if it is stated that the amount of a component, or the value of a process variable such as temperature, pressure, time, etc., is 50-90, in this specification it means that 51-89, 52-88...and 69 Values such as -71 and 70-71. For non-integer values, 0.1, 0.01, 0.001 or 0.0001 may be considered as a unit as appropriate. These are just some specifically indicated examples. In the present application, in a similar manner, all possible combinations of values between the lowest value and the highest value enumerated are considered to have been disclosed.

It should be noted that the above-mentioned embodiments are only used to explain the present invention, and do not constitute any limitation to the present invention. The invention has been described with reference to typical embodiments, but the words which have been used therein are words of description and explanation rather than words of limitation. The present invention can be modified as prescribed within the scope of the claims of the present invention, and the present invention can be revised without departing from the scope and spirit of the present invention. Although the invention described therein refers to specific methods, materials and examples, it is not intended that the invention be limited to the specific examples disclosed therein, but rather, the invention extends to all other methods and applications having the same function.

Claims (8)

1. The application of the etching solution in the field of tellurium-zinc-cadmium materials is characterized in that the etching solution comprises nitric acid, hydrofluoric acid, lactic acid and water;

the volume ratio of nitric acid to hydrofluoric acid to lactic acid to water is 10:1:9:2; or (b)

Nitric acid, hydrofluoric acid, lactic acid and water in a water volume ratio of 10:1:9:10; or (b)

Nitric acid, hydrofluoric acid, lactic acid and water in a ratio of 10:1:9:18;

wherein the nitric acid concentration is 98%; the hydrofluoric acid concentration was 40%.

2. A thinning method of a tellurium-cadmium-mercury infrared focal plane hybrid chip is characterized in that the etching solution of claim 1 is adopted to etch and remove a tellurium-zinc-cadmium substrate of the tellurium-cadmium-mercury infrared focal plane hybrid chip.

3. The thinning method according to claim 2, characterized by comprising the steps of:

s1: coating photoresist around the tellurium-cadmium-mercury infrared focal plane hybrid chip, baking, exposing, developing, photoetching and forming a film;

s2: placing the chip obtained in the step 1 after the glue coating and film forming in the etching solution of claim 1, and cleaning after removing the tellurium-zinc-cadmium substrate;

s3: placing the chip with the tellurium-zinc-cadmium substrate removed obtained in the step S2 in a stop layer etching solution for etching, and removing the stop layer;

s4: and (3) cleaning and drying the chip with the termination layer removed, which is obtained in the step (S3), to obtain the tellurium-cadmium-mercury infrared focal plane hybrid chip with the thinned substrate.

4. A thinning method according to claim 3 wherein in step S1, the photoresist is a positive photoresist; and/or the photoresist coating thickness is 4-10 mu m;

and/or the baking temperature is 80-100 ℃; the baking time is 1-10 min;

and/or, the exposure mode is contact exposure; the exposure time is 10-20 s;

and/or the development time is 40-90 s;

and/or the film forming temperature is 50-80 ℃; the film forming time is 1-3 h.

5. The thinning method according to claim 3, wherein in the step S2, the etching time is 1 to 3 minutes.

6. The method according to claim 3, wherein in the step S3, the stop layer etching liquid component includes bromine, hydrobromic acid and water; the volume ratio of bromine, hydrobromic acid and water in the components of the etching solution of the stop layer is 0.1:10:90; the hydrobromic acid concentration is 50-60%; and/or the etching time is 5-15 s.

7. A thinning method according to claim 3, wherein in step S4, the cleaning comprises three steps of deionized water rinsing and acetone soaking, and absolute ethanol rinsing.

8. The thinning method according to claim 7, wherein the deionized water rinse time is 3-8 min; and/or the acetone soaking time is 3-5 min; and/or washing the substrate with ethanol for 3-5 times; and/or, the drying is performed by adopting nitrogen.