Method for testing minority carrier lifetime

Abstract

The invention discloses a minority carrier lifetime testing method, which comprises the following steps: S110, carrying out chemical polishing on a tested surface to remove an oxide layer; s120, cleaning and blow-drying the test surface; s130, forming a CdTe and ZnS composite passivation layer on the test surface; s140, carrying out a minority carrier lifetime test on the test surface through a minority carrier lifetime tester; wherein the microwave frequency of the minority carrier lifetime tester is 9.5 GHz-10.5 GHz, the power of the minority carrier lifetime tester is 30-50mW, and the temperature of the minority carrier lifetime tester is less than or equal to 300K. By adopting the minority carrier lifetime test method, the nonuniformity of the test surface can be effectively reduced, and the accuracy of minority carrier lifetime test is improved.

Description

Technical Field

[0001] The present application belongs to the technical field of mercury cadmium telluride material performance testing, and specifically relates to a minority carrier lifetime testing method. Background Art

[0002] For HgCdTe chips, the performance of HgCdTe materials determines the yield and accuracy of the chip process. Among the performance tests of HgCdTe materials, the electrical performance test is a more critical test. The electrical performance test includes relevant parameters such as carrier concentration, mobility, Hall coefficient, and minority carrier lifetime. Among them, minority carrier lifetime, as an important parameter of HgCdTe materials, directly reflects the quality of the material. Being able to accurately test this parameter is of great significance for chip preparation. Summary of the invention

[0003] The technical problem to be solved by the present application is that the data accuracy of the existing minority carrier lifetime test is low. In order to solve this technical problem, a minority carrier lifetime test method that can accurately test the minority carrier lifetime is provided.

[0004] The technical solution proposed in this application is: A method for testing minority carrier lifetime comprises the following steps: S110, chemically polishing the test surface to remove the oxide layer; S120, cleaning and drying the test surface; S130, forming a CdTe and ZnS composite passivation layer on the test surface; S140, performing a minority carrier lifetime test on the test surface by using a minority carrier lifetime tester; The microwave frequency of the minority carrier lifetime tester is 9.5 GHz to 10.5 GHz, the power is 30 to 50 mW, and the temperature is ≤300 K.

[0005] The above-mentioned minority carrier lifetime test method can effectively reduce the non-uniformity of the test surface and improve the accuracy of the minority carrier lifetime test.

[0006] Furthermore, in step S110, the polishing liquid for chemical polishing includes methanol, ethylene glycol and bromine, and the volume ratio of methanol to ethylene glycol is (3-5): (0.5-1.5), and the volume percentage of bromine is 0.2-0.5%.

[0007] Furthermore, step S110 includes: S111, chemical polishing pad wetted by methanol; S112, soaking the chemical polishing pad with a polishing liquid; S113, chemically polishing the test surface using a chemical polishing pad.

[0008] Further, in step S113, the dripping speed of the polishing liquid is 10-40 ml / min, the rotation speed of the chemical polishing pad is 20-50 r / min, and the duration of chemical polishing is 5-20 s.

[0009] Further, step S120 includes: S121, cleaning the test surface with methanol; S122, spray-washing the test surface with ethanol; S123, blow dry the test surface by nitrogen.

[0010] Furthermore, in step S130, the thickness of the CdTe layer and the ZnS layer are both 2500-3500Å.

[0011] Further, step S150 includes: S141, evacuate the test space; S142, introducing liquid nitrogen into the test space; S143, performing a lifetime test on the test surface by using the minority carrier lifetime tester. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings are used to provide further understanding of the present application and constitute a part of the specification. They are used to explain the present application together with the embodiments of the present application and do not constitute a limitation of the present application.

[0013] Figure 1 Schematic diagram of the process of minority carrier lifetime testing method provided in this application; Figures 2~4 The test surface diagram of the test piece on the minority carrier lifetime tester in Examples 1 to 3; Figure 5 10 is a test surface diagram of the test piece on the minority carrier lifetime tester in comparative examples 1 to 7. DETAILED DESCRIPTION

[0014] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0015] The results of minority carrier lifetime testing in the prior art are of low accuracy. The present application provides a minority carrier lifetime testing method, which has high test accuracy. The minority carrier lifetime testing method comprises the following steps: S110, chemically polish the test surface to remove the oxide layer.

[0016] The polishing liquid for chemical polishing includes methanol, ethylene glycol and bromine, and the volume ratio of methanol to ethylene glycol is (3-5): (0.5-1.5), and the volume percentage of bromine is 0.2-0.5%. For example, methanol is 300 ml, ethylene glycol is 100 ml, and bromine is 0.8 ml.

[0017] Furthermore, step S110 includes: S111, chemical polishing pad wetted by methanol.

[0018] S112, soaking the chemical polishing pad with the polishing liquid.

[0019] S113, chemically polishing the test surface using a chemical polishing pad.

[0020] In step S123, the duration of chemical polishing is 5 to 20 seconds, the rotation speed of the chemical polishing pad is 20 to 50 r / min, and the dripping speed of the polishing liquid is 10 to 40 ml / min. In a preferred embodiment, the duration of chemical polishing is 10 seconds, the rotation speed of the chemical polishing pad is 40 r / min, and the dripping speed of the polishing liquid is 20 ml / min.

[0021] After the test surface is chemically polished, it needs to be further processed, that is, step S120 is executed.

[0022] S120, clean and dry the test surface.

[0023] Wherein, step S120 includes: S121, cleaning the test surface with methanol to rinse off the polishing liquid on the surface.

[0024] Specifically, the test surface is first rinsed with methanol, and then the test surface is immersed in methanol and scrubbed 6 to 8 times.

[0025] S122, spray the test surface with ethanol for 1 to 2 minutes to ensure that the residue on the test surface is removed.

[0026] S123, blow dry the test surface by nitrogen.

[0027] After the test surface is processed, the test surface may be passivated, that is, step S130 is performed.

[0028] S130, a CdTe and ZnS composite passivation layer is formed on the test surface, and the thickness of the CdTe layer and the ZnS layer are both 2500~3500 Å, in order to reduce the surface recombination rate, reduce its impact on the test lifetime value, and increase the minority carrier lifetime. Among them, the CdTe layer and the ZnS layer are both formed by magnetron sputtering growth.

[0029] After the passivation treatment of the test surface is completed, a minority carrier lifetime test may be performed on the test surface, that is, step S140 is executed.

[0030] S140, performing a minority carrier lifetime test on the test surface by using a minority carrier lifetime tester.

[0031] Among them, the model of the minority carrier lifetime tester is WT-2000MCT. The scanning resolution of the minority carrier lifetime tester is 0.5mm, the microwave frequency is 9.5GHz~10.5GHz, the wavelength is 904mm, the power is 30~50mW, and the temperature is ≤300k.

[0032] The minority carrier lifetime test method provided in the present application can effectively improve the accuracy of the minority carrier lifetime test.

[0033] In order to facilitate understanding of the advantages of the minority carrier lifetime test method provided by the present application, the following is explained through examples and comparative examples: Example 1 Prepare a polishing solution, which includes methanol, ethylene glycol and bromine, with a volume ratio of methanol to ethylene glycol of 3:1 and a volume percentage of bromine of 0.2%. Before chemical polishing, rinse the polishing pad with methanol for 10 minutes, and then rinse the polishing pad with the polishing solution for 5 minutes.

[0034] Use bamboo tweezers to transfer the test piece to the fixture groove after methanol soaking, then soak the test surface with methanol, and then perform chemical polishing. The polishing time is 10s, the dripping speed of the polishing liquid is 20ml / min, and the speed of the polishing pad is 40r / min.

[0035] After polishing, the test surface was rinsed with methanol, and then the test piece was immersed in methanol and brushed 8 times. Then, the test surface was sprayed with ethanol, and the test surface was blown dry with nitrogen after the spraying was completed. After the test surface was blown dry, a CdTe and ZnS composite passivation layer was grown on the test surface by magnetron sputtering, and the thickness of the CdTe layer and the ZnS layer were both 3000Å.

[0036] After the test surface passivation is completed, the test piece is placed on the minority carrier lifetime tester, and then the space where the test piece is located is evacuated and liquid nitrogen is added; the scanning resolution of the minority carrier lifetime tester is set to 0.5mm, the microwave frequency is set to 10GHz, the wavelength is set to 904nm, the power is set to 35mW, and the temperature is set to 80K. The test surface in the minority carrier lifetime tester is shown in the figure below: Figure 2 As shown, its surface unevenness is 9% and the accuracy of minority carrier lifetime test is 94%.

[0037] It should be explained that the accuracy of the minority carrier lifetime test can be determined based on the subsequent Hall data matching and comparison of the relevant chip process. This is a conventional method and will not be elaborated here.

[0038] Example 2 In this embodiment, the volume ratio of methanol to ethylene glycol in the polishing liquid is 5:1, and the volume ratio of bromine is 0.5%. Other aspects are the same as those in Example 1. Figure 3 As shown, its surface unevenness is 10% and the accuracy of minority carrier lifetime test is 93%.

[0039] Example 3 In this embodiment, the power of the minority carrier lifetime tester is set to 50 mW, the microwave frequency is 10.5 GHz, and the rest is the same as in Example 1. Figure 4 As shown, its surface unevenness is 11% and the accuracy of minority carrier lifetime test is 90%.

[0040] Comparative Example 1 In this comparative example, the power of the minority carrier lifetime tester is set to 70mW, and the other steps and parameters are the same as those in the embodiment. Figure 5 As shown, its surface unevenness is 68% and the accuracy of minority carrier lifetime test is 61%.

[0041] Comparative Example 2 In this comparative example, the temperature of the minority carrier lifetime tester is set to 350K, and the other steps and parameters are the same as those in the embodiment. Figure 6 As shown, its surface unevenness is 51% and the accuracy of minority carrier lifetime test is 75%.

[0042] Comparative Example 3 In this comparative example, the microwave frequency of the minority carrier lifetime tester is set to 13 GHz, and the other steps and parameters are the same as those in the embodiment. Figure 7 As shown, its surface unevenness is 27% and the accuracy of minority carrier lifetime test is 84%.

[0043] Comparative Example 4 In this comparative example, the polishing liquid includes methanol, ethylene glycol and bromine, the volume ratio of methanol to ethylene glycol is 3:1, and the volume percentage of bromine is 1% (for example, 300 ml of methanol, 100 ml of ethylene glycol, and 4 ml of bromine). The other steps and parameters are the same as those in the embodiment. The test surface diagram of the minority carrier lifetime tester in this comparative example is as follows Figure 8 As shown, the surface unevenness is 61% and the accuracy of the minority carrier lifetime test is 69%.

[0044] Comparative Example 5 In this comparative example, during surface passivation, a CdTe layer (3000 Å) was grown by magnetron sputtering, and the other steps and parameters were the same as those in the embodiment. Fig. 9 As shown, the surface unevenness is 32% and the accuracy of the minority carrier lifetime test is 83%.

[0045] Comparative Example 6 In this comparative example, when the surface is passivated, a ZnS layer (3000 Å) is grown by magnetron sputtering, and the other steps and parameters are the same as those in the embodiment. Fig.10 As shown, the surface unevenness is 47% and the accuracy of the minority carrier lifetime test is 79%.

[0046] In order to more intuitively compare the embodiments and comparative examples, the accuracy of the surface non-uniformity and minority carrier lifetime tests in the embodiments and comparative examples are summarized in Table 1.

[0047] Table 1 It should be noted that the test pieces in the above embodiments and comparative examples are made of mercury cadmium telluride material. Combining Table 1, it can be seen that the minority carrier lifetime test method provided by the present application can effectively reduce the non-uniformity of the test surface and improve the accuracy of the minority carrier lifetime test.

[0048] Although the embodiments of the present application have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present application, and that the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A minority carrier lifetime testing method, characterized in that: Includes steps: S110, chemically polishing the test surface to remove the oxide layer; S120, cleaning and drying the test surface; S130, forming a CdTe and ZnS composite passivation layer on the test surface; S140, performing a minority carrier lifetime test on the test surface by using a minority carrier lifetime tester; The microwave frequency of the minority carrier lifetime tester is 9.5 GHz to 10.5 GHz, the power is 30 to 50 mW, and the temperature is ≤300 K.

2. The minority carrier lifetime testing method according to claim 1, characterized in that: In step S110 , the polishing liquid for chemical polishing includes methanol, ethylene glycol and bromine, and the volume ratio of methanol to ethylene glycol is (3-5): (0.5-1.5), and the volume percentage of bromine is 0.2-0.5%.

3. The minority carrier lifetime testing method according to claim 1, characterized in that: Step S110 includes: S111, chemical polishing pad wetted by methanol; S112, soaking the chemical polishing pad with a polishing liquid; S113, chemically polishing the test surface using a chemical polishing pad.

4. The minority carrier lifetime testing method according to claim 4, characterized in that: In step S113, the dripping speed of the polishing liquid is 10-40 ml / min, the rotation speed of the chemical polishing pad is 20-50 r / min, and the duration of chemical polishing is 5-20 s.

5. The minority carrier lifetime testing method according to claim 1, characterized in that: Step S120 includes: S121, cleaning the test surface with methanol; S122, spray-washing the test surface with ethanol; S123, blow dry the test surface by nitrogen.

6. The minority carrier lifetime testing method according to claim 1, characterized in that: In step S130, the thickness of the CdTe layer and the ZnS layer are both 2500-3500Å.

7. The minority carrier lifetime testing method according to claim 1, characterized in that: Step S150 includes: S141, evacuate the test space; S142, introducing liquid nitrogen into the test space; S143, performing a lifetime test on the test surface by using the minority carrier lifetime tester.

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