An annealing method for cadmium zinc telluride wafers

Abstract

The application discloses an annealing method of a cadmium zinc telluride wafer, which comprises the following steps: S1, placing the cadmium zinc telluride wafer and tellurium powder into different positions of an annealing furnace, and sealing the annealing furnace and then vacuumizing; S2, slowly heating the annealing furnace to 790-805 DEG C, and then performing heat preservation; and S3, slowly cooling, and thus obtaining the cadmium zinc telluride wafer. The annealing method has the advantages of easy operation, short technological process, strong controllability, short time required, low number of bright spots of the cadmium zinc telluride wafer with a diameter of 0.3 microns after annealing (less than 30), low internal stress, uniform composition, high resistivity, few particle inclusions, and the like, and the method can process hundreds of wafers at one time, so that the processing efficiency is high, and the method has considerable application prospect.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor substrate manufacturing technology, and specifically relates to an annealing method for cadmium zinc telluride wafers. Background Technology

[0002] Currently, two important development directions for CdZnTe detectors are multi-piece large-volume parallel detectors and surface array detectors. The former consists of multiple CdZnTe crystal arrays with volumes greater than 1 cm². This type of detector solves the problems of small individual detector size and low overall detection efficiency, significantly shortening measurement time. It is particularly suitable for portable spectrometer systems and can be applied to radioactive monitoring in environments, ports, and railway cargo. The latter consists of CdZnTe crystal surface arrays and is mainly used for energy-spectral imaging in fields such as nuclear medicine and astrophysics.

[0003] The development and use of CdZnTe detectors have made it possible to obtain high-performance photons through efficient detectors. With the continuous improvement of high-quality CdZnTe semiconductor crystal preparation technology, a deeper understanding of the carrier collection process, and the rapid development of low-noise microelectronics, CdZnTe detectors will surely be applied in a wider range of fields.

[0004] However, CdZnTe wafers used in detectors not only require uniform crystal composition, high resistivity, and low internal stress, but also face increasingly stringent quality requirements, particularly regarding controlling the number of bright spots on the wafer surface. While existing technologies disclose methods for heat-treating CdZnTe wafers to improve performance, these methods still cannot fully meet customer requirements. Existing modification methods suffer from long processing times and produce wafers with insufficient internal resistance, numerous bright spots, and high internal stress.

[0005] CN102220644A discloses a method for improving the performance of zinc cadmium telluride crystals. This method utilizes the adsorption of impurities by the precipitate / impurity phase of Te to open up a new process for driving impurity movement through gradient temperature field annealing, which can effectively remove impurities and significantly improve the performance and yield of crystals. However, this method is for annealing crystal rods, and impurities in the product are difficult to precipitate, so the problem of many bright spots on the surface cannot be solved.

[0006] CN1422995A discloses an annealing modification method for cadmium zinc telluride crystals. Although this method can produce wafers with high resistivity and relatively uniform composition, the wafers produced by this method are prone to defects, such as wafer deformation, and there are also technical problems such as safety hazards and cost waste.

[0007] CN102168313B discloses a vapor phase annealing modification method for cadmium zinc telluride crystals. Although this method can eliminate the inclusion phase in the wafer and improve the carrier transport performance and crystal quality, it requires a long processing time, has low production efficiency, is complex, and has a high cost. Moreover, the number of bright spots on the surface of the modified wafer cannot be significantly improved.

[0008] CN106192014B discloses a moving cyclic annealing modification method for cadmium zinc telluride (CZT) crystals. This method employs moving cyclic annealing, using an external device to move the annealing tube alternately between high and low temperature zones in the annealing furnace, rapidly bringing the CZT wafer to the required temperature. The large temperature gradient during annealing promotes diffusion and accelerates the elimination of small inclusions in the crystal. This method typically completes the annealing process within 16 hours, achieving 100% removal efficiency for small inclusions. However, due to the difficulty in moving the wafer during annealing, movement at high temperatures can easily cause defects such as wafer deformation. Furthermore, it is unsuitable for large-scale production, and the pre-annealing preparation is cumbersome. Summary of the Invention

[0009] To address the above problems, this invention provides an annealing method for cadmium zinc telluride wafers.

[0010] To address the aforementioned technical issues, the following solutions are proposed:

[0011] An annealing method for cadmium zinc telluride wafers, comprising:

[0012] S1. Place the zinc cadmium telluride wafers and tellurium powder into different positions in the annealing furnace, seal the annealing furnace and then evacuate it.

[0013] S2. Slowly heat the annealing furnace to 790-805℃ and hold it at that temperature.

[0014] S3. Slowly cool down to obtain the desired product.

[0015] Preferably, in step S2, the heat preservation time is 12-15 hours.

[0016] Preferably, in step S2, the slow heating rate is 0.4-1.3℃ / min.

[0017] Preferably, in step S1, the vacuum is evacuated to 1×10⁻⁶. -4 Below Pa.

[0018] Preferably, in step S3, the slow cooling includes cooling to below 300°C at a cooling rate of 1-1.2°C / min.

[0019] Preferably, before placing the zinc-cadmium telluride wafers into the annealing furnace, a cleaning step is also included; the cleaning includes: passing the zinc-cadmium telluride wafers with a mixture of concentrated hydrochloric acid and concentrated nitric acid, then washing with water, and repeating the mixture cleaning-water washing multiple times.

[0020] Preferably, the drug application time is 30 seconds and the rinsing time is 60 seconds.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The annealing method of this invention is easy to operate, has a short process flow, strong process controllability, and requires little time. The modified 0.3μm cadmium zinc telluride wafers produced by this invention have fewer than 30 bright spots, low internal stress, uniform composition, high resistivity, and few particle inclusions. Furthermore, this method can process hundreds of wafers at a time, thus exhibiting high processing efficiency and promising application prospects. Attached Figure Description

[0023] Figure 1 Tencor image of unannealed cadmium zinc telluride wafers.

[0024] Figure 2 This is a Tencor image of the cadmium zinc telluride wafer after annealing in Example 1.

[0025] Figure 3 This is a Tencor image of the cadmium zinc telluride wafer after annealing in Example 2.

[0026] Figure 4 The image shows the Tencor pattern of the cadmium zinc telluride wafer after annealing in Comparative Example 1.

[0027] Figure 5 The image shows the Tencor pattern of the cadmium zinc telluride wafer after annealing in Comparative Example 2. Detailed Implementation

[0028] This invention provides an annealing method for cadmium zinc telluride wafers, comprising:

[0029] S1. Place the zinc cadmium telluride wafers and tellurium powder into different positions in the annealing furnace, seal the annealing furnace and then evacuate it.

[0030] S2. Slowly heat the annealing furnace to 790-805℃ and hold it at that temperature.

[0031] S3. Slowly cool down to obtain the desired product.

[0032] In some preferred embodiments, the heat preservation time in step S2 is 12-15 hours. Too short a time will affect the amount of bright spots removed, while too long a time will easily lead to wafer defects.

[0033] In some preferred embodiments, in step S2, the slow heating rate is 0.4-1.3℃ / min. A heating rate that is too low will affect production efficiency, while a rate that is too high will affect the electrical performance of the wafer.

[0034] In a partially preferred embodiment, in step S1, the vacuum is evacuated to 1×10⁻⁶. -4 Below Pa. Low vacuum levels easily generate oxides, while high vacuum levels place high demands on production auxiliary materials, which can easily lead to pipe bursts and production waste.

[0035] In some preferred embodiments, step S3, the slow cooling includes cooling to below 300°C at a cooling rate of 0.5-1.2°C / min. Excessive cooling or excessively high cutoff temperatures during slow cooling can easily cause abnormal electrical performance of the wafer, as well as problems such as uneven stress and excessive stress. Excessively high temperatures when removing the wafer from the furnace can affect the furnace lifespan and easily lead to safety hazards such as burns.

[0036] In some preferred embodiments, step S1 includes a step of cleaning the zinc-cadmium telluride wafers before placing them into the annealing furnace; the cleaning includes: passing the zinc-cadmium telluride wafers through a mixture of concentrated hydrochloric acid and concentrated nitric acid, then washing them with water, and repeating the mixture-water washing process multiple times.

[0037] In some preferred embodiments, in step S1, the time for applying the medicine is 30-40 seconds, and the time for rinsing with water is 60-90 seconds.

[0038] In some embodiments, in step S1, a batch of cadmium zinc telluride wafers are first inserted into a quartz boat, and then placed in an annealing furnace.

[0039] The present invention will be further described below with reference to specific embodiments and accompanying drawings, but the present invention is not limited to the following embodiments. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention.

[0040] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0041] In the following embodiments and comparative examples, cadmium zinc telluride wafers from the same production batch were used for annealing, so the surface quality before annealing was almost identical. One wafer was taken without annealing, polished, and then inspected using a Tencor optical surface analyzer. The results are as follows. Figure 1 As shown, the number of bright spots in a circular wafer with a diameter of 0.3 μm before annealing is 4306.

[0042] Example 1

[0043] An annealing method for cadmium zinc telluride wafers, comprising:

[0044] (1) Pre-cleaning before annealing: Use a mixture of concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 1:3 as a cleaning agent to clean the zinc cadmium telluride wafers. The cleaning time is 30s, the rinsing time is 60s, and the acid washing and water washing are repeated twice. The wafers are then spun dry for 600s.

[0045] (2) The wafers to be annealed are inserted into a quartz boat and placed in an annealing furnace (each furnace can process 130 wafers). 50 grams of pure tellurium are added to the quartz cap, the furnace lid is closed, and the vacuum system is turned on to achieve a vacuum of 1×10⁻⁶. -4 Pa, close the vacuum valve and start the annealing process, including:

[0046] The first stage is heating: the temperature is increased from room temperature to 800℃ in 13 hours. The purpose is to gradually increase the temperature of the wafer so that the annealing zone is heated evenly, so as to avoid defects such as abnormal electrical performance, excessive internal stress and uneven internal stress of the wafer.

[0047] The second stage is constant temperature: 800±5℃ for 12-15 hours, the purpose of which is to gradually precipitate tellurium deposits inside the wafer;

[0048] The third stage is cooling: the product is cooled from 800℃ to 300±5℃ within 11 hours. The product is cooled slowly to avoid defects such as uneven internal stress, excessive internal stress, and abnormal electrical performance caused by rapid cooling.

[0049] Fourth stage of cooling: From 300℃ to room temperature, remove from the annealing furnace and allow to cool naturally. After cooling is complete, close the vacuum system, open the vacuum valve to purge the vacuum, open the furnace lid and remove the wafer.

[0050] After annealing, the wafers were polished and then inspected using a Tencor optical surface analyzer. The results are as follows: Figure 2 As shown, the number of bright spots in the circular wafer with a diameter of 0.3 μm after processing in Example 1 is 4. Figure 2 As shown.

[0051] Example 2

[0052] An annealing method for cadmium zinc telluride wafers, comprising:

[0053] (1) Pre-cleaning before annealing: A mixture of concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 1:3 was used as a cleaning agent to clean the zinc cadmium telluride wafers. The cleaning time was 30s, the rinsing time was 60s, and the acid washing and water washing were repeated 3 times. The wafers were then spun dry for 600s.

[0054] (2) The wafers to be annealed are inserted into a quartz boat and placed in an annealing furnace (each furnace can process 130 wafers). 50 grams of pure tellurium are added to the quartz cap, the furnace lid is closed, and the vacuum system is turned on to achieve a vacuum of 1×10⁻⁶. -4 Pa, close the vacuum valve and start the annealing process, including:

[0055] The first stage is the temperature increase: the temperature rises from room temperature to 800℃ within 13 hours;

[0056] The second stage is constant temperature: 800±5℃ for 12-15 hours;

[0057] The third stage is cooling: the temperature drops from 800℃ to 300±5℃ within 11 hours.

[0058] The fourth stage of cooling: from 300℃ to room temperature, remove from the annealing furnace, and allow to cool naturally.

[0059] After cooling is complete, shut off the vacuum system, open the vacuum valve to purge the vacuum, open the furnace lid, and remove the wafer.

[0060] The obtained wafers were inspected; the number of bright spots on a 0.3μm wafer was 15. Figure 3 As shown.

[0061] Comparative Example 1

[0062] An annealing method for cadmium zinc telluride wafers, comprising:

[0063] (1) Pre-cleaning before annealing: A mixture of hydrochloric acid and nitric acid in a ratio of 1:3 was used as a cleaning agent to clean the zinc cadmium telluride wafers. The cleaning time was 30s, the rinsing time was 60s, and the acid washing and water washing were repeated twice. The wafers were then spun dry for 600s.

[0064] (2) The wafers to be annealed are inserted into a quartz boat and placed in an annealing furnace (each furnace can process 130 wafers). 50 grams of pure tellurium are added to the quartz cap, the furnace lid is closed, and the vacuum system is turned on to achieve a vacuum of 1×10⁻⁶. -4 Pa, close the vacuum valve and start the annealing process, including:

[0065] The first stage is the temperature increase: the temperature rises from room temperature to 650±5℃ in 18 hours;

[0066] The second stage is constant temperature: heat preservation at 650±5°C for 26-30 hours;

[0067] The third stage is cooling: the temperature will drop from 650℃ to 300±5℃ within 11 hours;

[0068] The fourth stage of cooling: from 300℃ to room temperature, remove from the annealing furnace, and allow to cool naturally.

[0069] Turn off the vacuum system, open the vacuum valve to purge the vacuum, open the furnace lid and remove the wafer.

[0070] The obtained wafer was inspected, and the number of bright spots in a circular wafer with a diameter of 0.3 μm was 409. Figure 4 As shown.

[0071] Comparative Example 2

[0072] An annealing method for cadmium zinc telluride wafers, comprising:

[0073] (1) Pre-cleaning before annealing: Use a mixture of concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 1:3 as a cleaning agent to clean the zinc cadmium telluride wafers. The cleaning time is 30s, the rinsing time is 60s, and the acid washing and water washing are repeated twice. The wafers are then spun dry for 600s.

[0074] (2) The wafers to be annealed are inserted into a quartz boat and placed in an annealing furnace (each furnace can process 130 wafers). 50 grams of pure tellurium are added to the quartz cap, the furnace lid is closed, and the vacuum system is turned on to achieve a vacuum of 1×10⁻⁶. -4 Pa, close the vacuum valve and start the annealing process, including:

[0075] The first stage is the temperature increase: the temperature rises from room temperature to 800℃ in 13 hours;

[0076] The second stage is constant temperature: 800±5℃ for 30 hours;

[0077] The third stage is cooling: the temperature drops from 800℃ to 300±5℃ within 11 hours;

[0078] The fourth stage of cooling: from 300℃ to room temperature, remove from the annealing furnace, and allow to cool naturally.

[0079] The obtained wafers have mounting marks on their surface and uneven electrical properties, making them unqualified.

[0080] Comparative Example 3

[0081] An annealing method for cadmium zinc telluride wafers, comprising:

[0082] (1) Pre-cleaning before annealing: A mixture of concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 1:3 was used as a cleaning agent to clean the zinc cadmium telluride wafers. The cleaning time was 30s, the rinsing time was 60s, and the acid washing and water washing were repeated 3 times. The wafers were then spun dry for 600s.

[0083] (2) The wafers to be annealed are inserted into a quartz boat and placed in an annealing furnace (each furnace can process 130 wafers). 50 grams of pure tellurium are added to the quartz cap, the furnace lid is closed, and the vacuum system is turned on to achieve a vacuum of 1×10⁻⁶. -4 Pa, close the vacuum valve and start the annealing process, including:

[0084] The first stage is the temperature increase: the temperature rises from room temperature to 800℃ within 13 hours;

[0085] The second stage is constant temperature: 800±5℃ for 6 hours;

[0086] The third stage is cooling: the temperature drops from 800℃ to 300±5℃ within 11 hours.

[0087] The fourth stage of cooling: from 300℃ to room temperature, remove from the annealing furnace, and allow to cool naturally.

[0088] After cooling is complete, shut off the vacuum system, open the vacuum valve to purge the vacuum, open the furnace lid, and remove the wafer.

[0089] The obtained wafers were inspected, and the number of bright spots in a circular wafer with a diameter of 0.3 μm was 1730. Figure 5 As shown.

[0090] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An annealing method for cadmium zinc telluride wafers, characterized in that, include: S1. Place the zinc cadmium telluride wafers and tellurium powder into different positions in the annealing furnace, seal the annealing furnace and then evacuate it. S2. Slowly heat the annealing furnace to 790-805℃ and hold it at that temperature for 12-15 hours; the slow heating rate is 0.4-1.3℃ / min. S3. Slowly cool down to obtain the product; in step S3, the slow cooling includes cooling down to below 300℃ at a cooling rate of 0.5-1.2℃ / min.

2. The annealing method for cadmium zinc telluride wafers as described in claim 1, characterized in that, In step S1, the vacuum is evacuated to 1×10⁻⁶. -4 Below Pa.

3. The annealing method for cadmium zinc telluride wafers as described in claim 1, characterized in that, Before placing the zinc-cadmium telluride wafers into the annealing furnace, a cleaning step is also included; the cleaning includes: passing the zinc-cadmium telluride wafers with a mixture of concentrated hydrochloric acid and concentrated nitric acid, then washing with water, and repeating the mixture cleaning-water washing multiple times.

4. The annealing method for cadmium zinc telluride wafers as described in claim 3, characterized in that, The time for applying the medicine is 30-40 seconds, and the rinsing time is 60-90 seconds.

5. The annealing method for cadmium zinc telluride wafers as described in any one of claims 1-4, characterized in that, In step S1, a batch of cadmium zinc telluride wafers are first inserted into a quartz boat, and then placed in an annealing furnace.

6. The annealing method for cadmium zinc telluride wafers as described in any one of claims 1-4, characterized in that, In step S1, the purity of the tellurium powder is 7N or higher.

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