Seed crystal cleaning method

Abstract

The seed crystal cleaning method comprises the following steps: S1, washing germanium seed crystals with purity and dislocation meeting requirements by using pure water; s2, the seed crystals are sequentially placed in trichloroethane, acetone, methanol and pure water for ultrasonic treatment; s3, alkali corrosion: S31, placing the seed crystal in an alkali corrosion liquid, submerging the seed crystal, boiling for 5-10 min, and taking pure water, hydrogen peroxide and sodium hydroxide in a volume ratio of 100: (10-20): (1-2) as the alkali corrosion liquid; s32, then adding normal-temperature pure water, so that the alkaline corrosion liquid is cooled in a gradient manner and kept at a constant temperature; s33, after constant-temperature keeping is finished, normal-temperature pure water is used for flushing; s4, acid corrosion: S41, carrying out water bath on an acid corrosion liquid to 5-10 DEG C, and taking hydrofluoric acid and nitric acid as the acid corrosion liquid according to a volume ratio of 1: (8-10); s42, the seed crystals are put into an acid corrosion solution to be corroded for 1-2 min; s43, then adding normal-temperature pure water into the corrosive liquid until the corrosive liquid does not react any more; s44, the seed crystals are taken out and washed with normal-temperature pure water; s5, dehydrating the seed crystals in a dehydration organic solvent; and S6, storing in a nitrogen cabinet.

Description

Technical Field

[0001] The present disclosure relates to the field of crystal growth, and more particularly to a seed crystal cleaning method. Background Art

[0002] In the growth of germanium crystals by the Czochralski method, seed crystals are usually used for seeding. Before the seed crystals are installed on the seed crystal fixture, they need to be corroded and cleaned. The seed crystal cleaning method affects the amount of seed crystal removed. If the amount of seed crystal removed during the cleaning process is large, it will affect the stability of the contact between the seed crystal and the seed crystal chuck, and further affect the uniformity of the resistivity and dislocation density of the crystal. If the cleaning process reacts violently, due to the small size of the seed crystal (i.e., the diameter) itself, the violent reaction will cause damage to the seed crystal, resulting in an increased risk of seed crystal breakage and significant losses during the pulling of large-sized single crystals. The seed crystal needs to be re-cleaned before each use, and the violent reaction causes a large amount of removal, which in turn leads to a low reuse rate of the seed crystal. Summary of the invention

[0003] In view of the problems existing in the background technology, an object of the present disclosure is to provide a seed crystal cleaning method, which can ensure clean cleaning, guarantee the quality of the seed crystal, and improve the reuse rate of the seed crystal while minimizing the amount of seed crystal removed.

[0004] Thus, a seed crystal cleaning method comprises the steps of: S1, washing a germanium seed crystal with purity and dislocation meeting the requirements with pure water; S2, placing the seed crystal in trichloroethane, acetone, methanol, and pure water ultrasonically in sequence; S3, alkaline corrosion, comprising the sub-steps of: S31, placing the seed crystal in a beaker filled with alkaline corrosion liquid, the alkaline corrosion liquid covering the seed crystal, heating to boiling for 5-10 minutes, and using pure water: hydrogen peroxide: sodium hydroxide = 100: (10-20): (1-2) as the alkaline corrosion liquid in a volume ratio; S32, then, adding room temperature pure water to make the alkaline corrosion liquid gradient in the beaker Cooling and maintaining the constant temperature; S33, after the constant temperature maintenance is completed, rinsing with pure water at room temperature; S4, acid corrosion, including sub-steps: S41, bathing the acid corrosion liquid to 5-10°C, using hydrofluoric acid: nitric acid in a volume ratio of 1: (8-10) as the acid corrosion liquid; S42, placing the seed crystal in the acid corrosion liquid for corrosion for 1-2 minutes; S43, then, adding pure water at room temperature to the acid corrosion liquid until the acid corrosion liquid no longer reacts; S44, taking out the seed crystal and rinsing with pure water at room temperature; S5, placing the seed crystal in a dehydrating organic solvent for dehydration; S6, storing in a nitrogen cabinet after dehydration.

[0005] The beneficial effects of the present disclosure are as follows: in the seed crystal cleaning method according to the present disclosure, step S2 is used to remove organic impurities attached to the surface of the seed crystal during the seed crystal addition process; the alkaline corrosion of step S3 is performed first and then the acid corrosion of step S4 is performed. The alkaline corrosion is relatively mild, and the surface of the seed crystal is first corroded and smooth to form a layer of "protective film", which plays a passivation role during acid corrosion. While ensuring that the impurities on the surface of the seed crystal are removed cleanly, the severity of acid corrosion is reduced, the removal amount is reduced, the internal damage of the seed crystal is reduced, the quality of the seed crystal is guaranteed, and the reuse rate of the seed crystal is improved; in the alkaline corrosion sub-step S32 of step S3, room temperature pure water is added to make the alkaline corrosion liquid in the beaker gradually cool down and maintain a constant temperature, which can avoid the large temperature difference between the inside and outside of the seed crystal and the generation of internal impurities in the seed crystal caused by directly rinsing with room temperature pure water after step S31 is executed. The problem of damage; for the sub-step S41 of the acid corrosion in step S4, the acid corrosion liquid is bathed in water to 5-10°C. Due to the violent acid corrosion reaction, the acid corrosion liquid heats up quickly, resulting in a large temperature difference between the inner and outer surfaces of the seed crystal, causing damage to the inside of the seed crystal. The violent reaction also causes a large amount of removal of the seed crystal during acid corrosion. Before executing step S42, step S4 is executed to bathe the acid corrosion liquid in water to 5-10°C, and then the seed crystal is placed and corroded in step S42. In this way, the temperature difference between the inner and outer surfaces of the seed crystal can be reduced, the severity of the corrosion reaction can be reduced, the internal damage of the seed crystal can be reduced, and the amount of removal of the seed crystal during acid corrosion can be reduced; for the execution of step S43, it is avoided that step S44 is directly executed after the acid corrosion of step S42 is completed, resulting in the acid on the surface of the seed crystal contacting with the air, causing oxidation of the surface of the seed crystal. As further verified by the test, the seed crystal cleaning method disclosed in the present invention can ensure clean cleaning when the amount of seed crystal removed is small, ensure the quality of the seed crystal, and improve the reuse rate of the seed crystal. DETAILED DESCRIPTION

[0006] It will be understood that the disclosed embodiments are merely examples of the present disclosure, which may be implemented in various forms, and therefore, the specific details disclosed herein should not be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one of ordinary skill in the art to implement the present disclosure in various ways.

[0007] [Seed crystal cleaning method]

[0008] The seed crystal cleaning method according to the present disclosure comprises the steps of:

[0009] S1, washing the germanium seed crystal with purity and dislocation meeting the requirements with pure water;

[0010] S2, placing the seed crystal in trichloroethane, acetone, methanol, and pure water in turn for ultrasonication;

[0011] S3, alkaline corrosion, includes the following sub-steps:

[0012] S31, place the seed crystal in a beaker filled with alkaline etching solution, the alkaline etching solution covers the seed crystal, heat to boiling for 5-10 minutes, and use a volume ratio of pure water: hydrogen peroxide: sodium hydroxide

[0013] =100:(10-20):(1-2) as alkaline corrosion solution;

[0014] S32, then, adding pure water at room temperature to gradually cool the alkaline corrosion solution in the beaker and maintain the temperature at a constant level;

[0015] S33, after the constant temperature maintenance is completed, rinse with room temperature pure water;

[0016] S4, acid etching, comprises the sub-steps of:

[0017] S41, put the acid etching solution in a water bath at 5-10℃, and add hydrofluoric acid: nitric acid in a volume ratio

[0018] =1:(8-10) as acid corrosion liquid;

[0019] S42, placing the seed crystal in an acid etching solution for 1-2 minutes;

[0020] S43, then, adding room temperature pure water to the acid etching solution until the acid etching solution no longer reacts;

[0021] S44, taking out the seed crystal and washing it with pure water at room temperature;

[0022] S5, placing the seed crystal into a dehydrating organic solvent for dehydration;

[0023] S6, after dehydration, store in a nitrogen cabinet.

[0024] In the seed crystal cleaning method according to the present disclosure, step S2 is used to remove organic impurities attached to the surface of the seed crystal during the seed crystal processing; the alkaline corrosion of step S3 is performed first and then the acid corrosion of step S4. The alkaline corrosion is relatively mild, and the surface of the seed crystal is first corroded and smooth to form a layer of "protective film", which plays a passivation role during acid corrosion. While ensuring that the impurities on the surface of the seed crystal are removed cleanly, the severity of acid corrosion is reduced, the removal amount is reduced, the internal damage of the seed crystal is reduced, the quality of the seed crystal is guaranteed, and the reuse rate of the seed crystal is improved; in the alkaline corrosion sub-step S32 of step S3, room temperature pure water is added to make the alkaline corrosion liquid in the beaker gradually cool down and maintain a constant temperature, which can avoid the problem of large temperature difference between the inside and outside of the seed crystal and damage to the inside of the seed crystal caused by directly rinsing with room temperature pure water after step S31 is executed. Question: Regarding the sub-step S41 of the acid corrosion of step S4, the acid corrosion liquid is placed in a water bath at 5-10°C. Due to the violent acid corrosion reaction, the acid corrosion liquid heats up quickly, resulting in a large temperature difference between the inner and outer surfaces of the seed crystal, causing damage to the inside of the seed crystal. The violent reaction also causes a large amount of seed crystal removed during acid corrosion. Before executing step S42, step S4 is performed to place the acid corrosion liquid in a water bath at 5-10°C, and then the seed crystal is placed in and corroded in step S42. This can reduce the temperature difference between the inner and outer surfaces of the seed crystal, reduce the severity of the corrosion reaction, reduce damage to the inside of the seed crystal, and reduce the amount of seed crystal removed during acid corrosion. Regarding the execution of step S43, it is avoided that step S44 is directly executed after the acid corrosion of step S42 is completed, which causes the acid on the surface of the seed crystal to contact with the air, causing oxidation of the seed crystal surface. As further verified by subsequent tests, the seed crystal cleaning method disclosed in the present invention can ensure clean cleaning with a small amount of seed crystal removed, ensure the quality of the seed crystal, and improve the reuse rate of the seed crystal.

[0025] In step S1, for example, the purity of the germanium seed crystal is that the carrier concentration of the seed crystal is less than 2E11cm -3 For example, the dislocation of the germanium seed crystal is 0-3000cm -2 .

[0026] In step S2, for example, the ultrasonication is performed for 5-10 minutes.

[0027] In sub-step S32, in one example, the gradient cooling and constant temperature maintenance are cooling to 70°C and maintaining for 2-5 min, cooling to 40°C and maintaining for 2-5 min, and cooling to 20°C and maintaining for 2-5 min.

[0028] In sub-step S33, for example, rinse with pure water at room temperature for 20-30 minutes.

[0029] In one example, in sub-step S44, flushing is performed for 20-30 minutes.

[0030] In step S5, for example, the dehydration organic solvent is methanol or ethanol.

[0031] In step S6, for example, the purity of nitrogen gas is 7N.

[0032] [test]

[0033] Example 1

[0034] The seed crystal cleaning method of Example 1 adopts the following steps:

[0035] S1, rinse the germanium seed crystal with purity and dislocation that meet the requirements with pure water. The purity of the germanium seed crystal is 5E10cm -3 , the dislocation of the germanium seed crystal is 2000cm -2 ;

[0036] S2, the seed crystals were ultrasonically placed in trichloroethane, acetone, methanol, and pure water in turn, each ultrasonication lasting 8 min;

[0037] S3, alkaline corrosion, uses the following sub-steps:

[0038] S31, placing the seed crystal in a beaker filled with alkaline etching solution, the alkaline etching solution covers the seed crystal, heating to boiling for 8 minutes, and using a volume ratio of pure water: hydrogen peroxide: sodium hydroxide = 100:15:1.5 as the alkaline etching solution;

[0039] S32, then, adding room temperature pure water to make the alkaline corrosion solution in the beaker gradually cool down and keep it at a constant temperature, wherein the gradient cooling and constant temperature keeping are cooling down to 70°C and keeping it for 4 minutes, cooling down to 40°C and keeping it for 4 minutes, and cooling down to 20°C and keeping it for 4 minutes;

[0040] S33, after the constant temperature maintenance, rinse with room temperature pure water for 25 minutes;

[0041] S4, acid etching, uses the following sub-steps:

[0042] S41, bathing the acid etching solution at 5°C, using a volume ratio of hydrofluoric acid to nitric acid of 1:9 as the acid etching solution;

[0043] S42, placing the seed crystal in an acid etching solution for 2 minutes;

[0044] S43, then, slowly adding room temperature pure water to the acid etching solution until the acid etching solution no longer reacts (i.e., visually observing the reaction without yellow smoke and the liquid surface is calm and without fluctuation);

[0045] S44, taking out the seed crystal and washing it with pure water at room temperature for 25 minutes;

[0046] S5, placing the seed crystal into a dehydrating organic solvent, methanol, for dehydration;

[0047] S6, after dehydration, is stored in a nitrogen cabinet with a purity of 7N.

[0048] Example 2

[0049] Except for the following differences, the rest is the same as Example 1:

[0050] In sub-step S31, pure water: hydrogen peroxide: sodium hydroxide = 100:10:1.

[0051] Example 3

[0052] Except for the following differences, the rest is the same as Example 1:

[0053] In sub-step S31, pure water: hydrogen peroxide: sodium hydroxide = 100:20:2.

[0054] Comparative Example 1

[0055] Step S4 is not performed, and the rest is the same as in Example 1. That is, Comparative Example 1 only uses alkaline etching.

[0056] Comparative Example 2

[0057] Step S3 is not performed, and the rest is the same as in Example 1. That is, Comparative Example 2 only uses acid etching.

[0058] Comparative Example 3

[0059] Only the alkaline etching solution in step S31 is replaced by pure water: sodium hydroxide=100:1.5 in volume ratio, and the rest is the same as in Example 1.

[0060] Comparative Example 4

[0061] Except that step S32 is not executed in step S3 and step S33 is modified to directly use room temperature pure water for cleaning after step S31 is executed, the rest is the same as embodiment 1.

[0062] Comparative Example 5

[0063] Except that the step S41 is modified from "bathing the acid etching solution at 5° C." to "bathing the acid etching solution at room temperature," the rest is the same as in Example 1. That is, in step S41 of Comparative Example 5, the acid etching solution is at room temperature.

[0064] Comparative Example 6

[0065] Except that step S43 is not executed, the rest is the same as embodiment 1.

[0066] An infrared defect detector was used to detect whether there were cracks inside the seed crystals after cleaning of Examples 1-3 and Comparative Examples 1-6.

[0067] The cleaned seed crystals of Examples 1-3 and Comparative Examples 1-6 were used to prepare a crystal rod by the following pulling method:

[0068] Sa, loading the etched 12N high purity germanium polycrystal into the crucible of the pulling furnace;

[0069] Sb, first evacuate the vacuum, then pass nitrogen with a purity of 7N, and purge the pulling furnace by evacuating the vacuum and filling the nitrogen 4 times. After the purging is completed, stop evacuating the vacuum and stop passing nitrogen, and then maintain the pressure at 1×10 -4 Pa;

[0070] Sc, switch to introduce 9N purity hydrogen and maintain exhaust to maintain flowing vacuum in the pulling furnace, and the flowing vacuum pressure is 0.1MPa;

[0071] Sd, under the flow vacuum, the pulling furnace is heated to 980°C to melt the 12N high purity germanium polycrystallized material in the crucible;

[0072] Se, after the material is oxidized, lower the seed crystal to 15mm from the liquid surface of the melt in the crucible and preheat the seed crystal for 30min;

[0073] Sf, turn on the crucible rotation and the seed crystal rotation in opposite directions, insert the seed crystal 5mm below the liquid surface, and an aperture appears, and then seeding, necking, neck thinning, shoulder release, equal diameter, and tailing are performed, and the product crystal rod is grown by pulling, wherein the rotation speed of the crucible rotation and the crystal rotation is 4rpm, and the pulling speed is 22mm / h;

[0074] Sg. After step Sf is completed, the temperature is naturally lowered to room temperature, the crystal turner and the crucible turner are turned off, the hydrogen is stopped, and the nitrogen with a purity of 7N is switched to be filled and the exhaust is maintained to make the pulling furnace reach normal pressure, then the nitrogen filling and exhaust are stopped, the pulling furnace is opened, and the crystal rod is cut off.

[0075] The crystal rods prepared by the Czochralski method using the cleaned seed crystals of Examples 1-3 and Comparative Examples 1-6 were used to make a disc with a diameter of 10 mm and a thickness of 1 mm at the center of the shoulder for carrier concentration detection. The carrier concentration was detected by HL9900 of Toho Technology, USA.

[0076] The results of cleaning the seed crystals of Examples 1-3 and Comparative Examples 1-6, the results of internal crack detection, and the results of detection of the wafers of the crystal rods are shown in Table 1.

[0077] Table 1 Results of seed crystal cleaning in Examples 1-3 and Comparative Examples 1-6 and test results of wafers of crystal rods

[0078]

[0079] The above detailed description is used to describe multiple exemplary embodiments, but this document is not intended to be limited to the explicitly disclosed combinations. Therefore, unless otherwise stated, the various features disclosed herein can be combined together to form multiple additional combinations that are not shown for the sake of simplicity.

Claims

1. A seed crystal cleaning method, characterized in that: Includes steps: S1, washing the germanium seed crystal with purity and dislocation meeting the requirements with pure water; S2, placing the seed crystal in trichloroethane, acetone, methanol, and pure water in turn for ultrasonication; S3, alkaline corrosion, includes the following sub-steps: S31, placing the seed crystal in a beaker filled with alkaline etching solution, the alkaline etching solution covering the seed crystal, heating to boiling for 5-10 minutes, and using a volume ratio of pure water: hydrogen peroxide: sodium hydroxide = 100: (10-20): (1-2) as the alkaline etching solution; S32, then, adding pure water at room temperature to gradually cool the alkaline corrosion solution in the beaker and maintain the temperature at a constant level; S33, after the constant temperature maintenance is completed, rinse with room temperature pure water; S4, acid etching, comprises the sub-steps of: S41, bathing the acid etching solution to 5-10° C., using a volume ratio of hydrofluoric acid: nitric acid = 1: (8-10) as the acid etching solution; S42, placing the seed crystal in an acid etching solution for 1-2 minutes; S43, then, adding room temperature pure water to the acid etching solution until the acid etching solution no longer reacts; S44, taking out the seed crystal and washing it with pure water at room temperature; S5, placing the seed crystal into a dehydrating organic solvent for dehydration; S6, after dehydration, store in a nitrogen cabinet.

2. The seed crystal cleaning method according to claim 1, characterized in that: In step S1, the purity of the germanium seed crystal is that the carrier concentration of the seed crystal is less than 2E11cm -3 .

3. The seed crystal cleaning method according to claim 2, characterized in that: In step S1, the dislocation of the germanium seed crystal is 0-3000cm -2 .

4. The seed crystal cleaning method according to claim 1, characterized in that: In step S2, the ultrasonic treatment is performed for 5-10 min.

5. The seed crystal cleaning method according to claim 1, characterized in that: In sub-step S32, the temperature is gradually lowered and kept at a constant temperature, namely, lowered to 70°C and kept for 2-5 min, lowered to 40°C and kept for 2-5 min, and lowered to 20°C and kept for 2-5 min.

6. The seed crystal cleaning method according to claim 5, characterized in that: In sub-step S33, rinse with room temperature pure water for 20-30 minutes.

7. The seed crystal cleaning method according to claim 1, characterized in that: In sub-step S44, rinse for 20-30 minutes.

8. The seed crystal cleaning method according to claim 1, characterized in that: In step S5, the dehydration organic solvent is methanol or ethanol.

9. The seed crystal cleaning method according to claim 1, characterized in that: In step S6, the purity of nitrogen is 7N.

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