A boron-aluminum diffusion source and a method of making the same

Abstract

This application relates to the field of semiconductor silicon wafer manufacturing technology, and particularly to a boron-aluminum diffusion source and its preparation method. A boron-aluminum diffusion source has a metal impurity content of <20 ppm and a sodium ion content of <15 ppm. The components of the boron-aluminum diffusion source include 15-35% silicate ester, 2-5% water, 25-35% lower alcohols, 25-35% ethers, 2-12% boron source, 5-20% aluminum source, 0.01-1% acid, and 0.01-0.5% dispersant. The preparation method includes: 1) mixing and dissolving the boron source, aluminum source, and ether; 2) mixing the silicate ester with water for hydrolysis and condensation; and 3) blending. This application controls the metal impurity content in the boron-aluminum diffusion source to <20 ppm, and the sodium content to <15 ppm, which can effectively improve the TRR value of the chip's electrical parameters. Controlling the metal impurity content and sodium content in the boron-aluminum diffusion source can also improve the problem of uneven and rough film formation during the baking process, resulting in a product with lower sheet resistance and PN junction depth dispersion.

Description

Technical Field

[0001] This application relates to the field of semiconductor silicon wafer manufacturing technology, and in particular to a boron-aluminum diffusion source and its preparation method. Background Technology

[0002] Diffusion sources are essential microelectronic chemicals used in the diffusion process of semiconductor device manufacturing. Based on different diffusion types, diffusion sources can be divided into two main categories: P-type diffusion sources, which form P-type semiconductor materials, primarily composed of group III elements boron and aluminum; and N-type diffusion sources, which form N-type semiconductor materials, primarily composed of group V elements phosphorus. This application mainly studies the boron-aluminum diffusion source used in P-type diffusion.

[0003] Boron-aluminum diffusion sources are one of the main raw materials for preparing P-type semiconductors. During semiconductor device manufacturing, boron and aluminum are doped into the crystal lattice of single-crystal silicon using boron-aluminum diffusion sources. Since boron and aluminum atoms have three valence electrons, while silicon atoms have only four electrons in their outermost shell, when boron and aluminum atoms are doped into the single-crystal silicon lattice, one electron is missing, forming a hole. Under the influence of an external electric field, these holes flow, forming an electric current. The addition of a small amount of boron and aluminum results in a large number of holes, hence this type of semiconductor is called a hole-type semiconductor or P-type semiconductor.

[0004] In chip manufacturing, boron-aluminum diffusion sources are applied to the chip using spin coating. The pre-process of high-temperature burning diffusion is the film baking process, with a baking temperature of around 120°C. This process results in significant dispersion in sheet resistance and PN junction depth, and the dried film is uneven and rough. Meanwhile, in chip manufacturing, special requirements such as lightning protection place high demands on the electrical parameter TRR value, but currently, the TRR value is generally low. Therefore, these problems urgently need to be solved in actual production. Summary of the Invention

[0005] To address the technical challenges of large dispersion in sheet resistance and PN junction depth distribution, as well as improving the electrical parameter TRR value, this application provides a boron-aluminum diffusion source and its preparation method.

[0006] In a first aspect, this application provides a boron-aluminum diffusion source, which adopts the following technical solution:

[0007] A boron-aluminum diffusion source, wherein the content of metallic impurities in the boron-aluminum diffusion source is <20ppm; wherein the content of sodium ions is <15ppm;

[0008] The boron-aluminum diffusion source components include 15-35% silicate ester, 2-5% water, 25-35% lower alcohols, 25-35% ethers, 2-12% boron source, 5-20% aluminum source, 0.01-1% acid, and 0.01-0.5% dispersant.

[0009] Through the above technical solution, in this application, the silicate ester in the boron-aluminum diffusion source serves as the main substance of the latex, primarily undergoing hydrolysis and condensation reactions to gradually form a uniform colloidal solution; low-carbon alcohols serve as dispersants in the latex, increasing the uniform dispersion of boron and aluminum elements into ethers to form a low-viscosity solution; acids serve as auxiliary agents, catalyzing the hydrolysis and condensation process of silicate esters while preventing cross-linking reactions that could form spheres, thus avoiding agglomeration; the dispersant can prevent agglomeration between particles, inhibit gelation of the latex, and prevent the precipitation of effective substances.

[0010] Controlling the metal impurity content in the boron-aluminum diffusion source to <20ppm, with sodium content <15ppm, can effectively improve the TRR value of the chip's electrical parameters. This is because the TRR value is highly sensitive to the metal impurity content in the boron-aluminum diffusion source; reducing the metal impurity content, especially the sodium ion content, can significantly improve the TRR value. Furthermore, the control of metal impurity and sodium content in the boron-aluminum diffusion source in this application can also improve the problem of uneven and rough film formation during the baking process, resulting in a product with lower sheet resistance and PN junction depth dispersion.

[0011] Preferably, the silicate ester is one or more of methyl orthosilicate, tetraethyl orthosilicate, and diethyl orthosilicate; the silicate ester is preferably tetraethyl orthosilicate.

[0012] Through the above technical solution, tetraethyl orthosilicate is preferred as the silicate ester, and the macromolecular framework formed after hydrolysis, which is mainly composed of silicic acid, is more likely to adhere to the silicon crystal surface.

[0013] Preferably, the lower alcohol is one or more of methanol, ethanol, isopropanol, and butanol; the lower alcohol is preferably ethanol.

[0014] Through the above technical solution, ethanol is preferred as a low-carbon alcohol and used as a dispersant in the latex solution to increase the uniform dispersion of boron and aluminum elements into the ether to form a low-viscosity solution. At the same time, the physicochemical properties of ethanol are clear.

[0015] Preferably, the ether is one or more of ethylene glycol methyl ether, ethylene glycol monomethyl ether, and ethylene glycol ethyl ether; the ether is preferably ethylene glycol monomethyl ether.

[0016] The above technical solution uses ethylene glycol monomethyl ether to dissolve the boron and aluminum sources, while preventing the hydrolysis of aluminum during the preparation of the boron-aluminum diffusion source.

[0017] Preferably, the boron source is one or more of boron oxide, boric acid, methyl borate, and ethyl borate; the preferred boron source is boron oxide.

[0018] Based on the above technical solutions, boron oxide is the preferred boron source, as it has more stable properties and can be used as a better choice for boron-aluminum diffusion source.

[0019] Preferably, the aluminum source is one or more of aluminum nitrate nonahydrate and aluminum carbonate; the aluminum source is preferably aluminum nitrate nonahydrate.

[0020] Preferably, the acid is one or more of hydrochloric acid, acetic acid, and sulfuric acid; hydrochloric acid is preferred.

[0021] Through the above technical solution, hydrochloric acid is preferred as the acid. During the preparation of the boron-aluminum diffusion source, hydrochloric acid volatilizes during long-term constant-temperature stirring.

[0022] Preferably, the dispersant is one or more of polyethylene glycol and polyvinyl alcohol; polyethylene glycol is the preferred dispersant.

[0023] Through the above scheme, when polyethylene glycol dissolves in water, its serrated long chains become tortuous, easily forming strong hydrogen bonds with the surface of the particles in the raw material system. This creates a macromolecular hydrophilic film on the particle surface, acting as a steric hindrance. The steric hindrance effect of the polymer chains prevents particles from approaching each other, thus preventing aggregation, gelation of the boron-aluminum diffusion source latex, and precipitation of effective substances. Simultaneously, polyethylene glycol also acts as a surfactant, reducing the surface tension of ethylene glycol monomethyl ether and promoting the dissolution of boron and aluminum sources.

[0024] Preferably, the ethylene glycol monomethyl ether is obtained by distillation purification, specifically including the following steps:

[0025] Step 1): Add ethylene glycol monomethyl ether to the bottom of the column and heat the ethylene glycol monomethyl ether to raise the temperature.

[0026] Step 2) Collect the fraction at 123-127℃ at the top of the column, and obtain ethylene glycol monomethyl ether purified by distillation after condensation.

[0027] Through the above technical solution, the quality of ethylene glycol monomethyl ether can be effectively improved by distillation and purification. Low-boiling-point and high-boiling-point impurities in ethylene glycol monomethyl ether can be removed, which can effectively reduce the dispersion of sheet resistance and PN junction depth distribution and make them more concentrated, so that the film formed by drying is flat and uniform. At the same time, metal impurities are also removed, which improves the electrical parameter TRR value to a certain extent.

[0028] Preferably, after distillation and purification, the ethylene glycol monomethyl ether has a purity >99.9% and a metal impurity content <200 ppb.

[0029] Through the above technical solution, ethylene glycol monomethyl ether is purified by distillation, resulting in superior purity and metal impurity content. In the film drying process, impurities with boiling points above 120℃ can be avoided from causing uneven film, while impurities with boiling points between 115-120℃ can be avoided from affecting the smoothness of the film. Controlling the metal impurity content of ethylene glycol monomethyl ether can improve the electrical parameter TRR value to a certain extent.

[0030] Preferably, aluminum nitrate nonahydrate is obtained through electrochemical purification, specifically including the following steps:

[0031] Step 1) Add aluminum nitrate nonahydrate to ethylene glycol monomethyl ether and stir at a constant temperature of 15-50℃ for 0.5-4h to fully dissolve and obtain aluminum nitrate-ethylene glycol monomethyl ether solution. Transfer the solution to an electrolytic cell and add ion exchange resin to the electrolytic cell at the same time.

[0032] Step 2): The electrolytic cell uses aluminum foil as the anode and platinum electrode as the cathode; anion exchange resin is placed at the anode and cation exchange resin is placed at the cathode; electrolysis is carried out with an operating voltage of 0-2V and a scan rate of 5-10mV / s.

[0033] Step 3): When the working voltage reaches 2V and there is no reaction current, stop electrolysis. After stopping electrolysis, the metal impurity content of the aluminum nitrate-ethylene glycol monomethyl ether solution is <3ppm.

[0034] Step 4): After filtering the aluminum nitrate-ethylene glycol monomethyl ether solution obtained in step 3), the solution is evaporated and crystallized at a constant temperature of 60-80℃ under an inert atmosphere to obtain purified aluminum nitrate nonahydrate.

[0035] The above technical solution utilizes electrochemical purification of aluminum nitrate. After electrolysis, the content of metal impurities in the aluminum nitrate-ethylene glycol monomethyl ether solution is <3ppm. The purification of aluminum nitrate nonahydrate significantly improves the TRR value of the chip's electrical parameters.

[0036] In the electrolytic cell, aluminum foil is used as the anode and a platinum electrode as the cathode. Aluminum loses electrons to form Al. 3+ Ions replenish the cations in the electrolytic cell that are reduced to elemental metals by gaining electrons at the cathode; at the cathode, the aluminum nitrate-ethylene glycol monomethyl ether solution contains more H... + Inert metal ions are reduced to elemental form and adhere to the platinum electrode; the aluminum nitrate-ethylene glycol monomethyl ether solution contains H+. + Active metal ions such as potassium, sodium, calcium, and magnesium are removed by ion exchange resin in an electrolytic cell through electrophoresis.

[0037] Preferably, the aluminum nitrate content in the aluminum nitrate-ethylene glycol monomethyl ether solution is 20-50 wt%; the anion exchange resin is a nitrate anion exchange resin; and the cation exchange resin is an aluminum ion exchange resin.

[0038] Through the above technical solution, ion exchange resin is used to remove potassium, sodium, calcium, and magnesium ions from aluminum nitrate-ethylene glycol monomethyl ether solution, thereby reducing the content of metallic impurities in aluminum nitrate.

[0039] Secondly, this application provides a method for preparing a boron-aluminum diffusion source, which adopts the following technical solution:

[0040] A method for preparing a boron-aluminum diffusion source specifically includes the following steps:

[0041] Step 1): Dissolve the ether, boron source, and aluminum source at a constant temperature of 15-50℃ in proportion. After all the solids have dissolved, add the dispersant in proportion and stir for 0.5-4 hours to obtain mixture A.

[0042] Step 2): Stir silicate ester, water, and low carbon alcohol at a constant temperature of 15-50℃ for 0.5-4 hours, gradually adding acid in proportion during the process to obtain mixture B;

[0043] Step 3): Mixture A and mixture B are respectively pressure filtered and then mixed. After stirring for 0.5-4 hours, they are pressure filtered again to obtain the boron-aluminum diffusion source.

[0044] Through the above technical solution, in this application, ethers, boron sources and aluminum sources are first dissolved and mixed, and then a mixture A with uniform boron and aluminum elements is obtained under the action of a dispersant. Then, a mixture B obtained by mixing silicate ester, water and low carbon alcohol and acid is a sol macromolecular framework structure. Then, mixture A and mixture B are mixed, so that the boron and aluminum elements in mixture A enter the sol macromolecular framework, which has a significant effect on improving the smoothness and uniformity of the final film, and the product has a better TRR value.

[0045] In summary, this application has at least one or more of the following beneficial effects:

[0046] 1. Since this application controls the content of metal impurities in the boron-aluminum diffusion source to <20ppm, of which the sodium content is <15ppm, it can effectively improve the electrical parameter TRR value of the chip.

[0047] 2. The preferred ethylene glycol monomethyl ether of this application is purified by distillation, which can effectively improve the quality of ethylene glycol monomethyl ether, effectively reduce the dispersion of sheet resistance and PN junction depth distribution, making them more concentrated, and making the film formed by drying smooth and uniform; at the same time, metal impurities are also removed, which improves the electrical parameter TRR value to a certain extent.

[0048] 3. This application preferably uses electrochemical purification of aluminum nitrate nonahydrate. After electrolysis, the content of metal impurities in the aluminum nitrate-ethylene glycol monomethyl ether solution is <3ppm. Purification of aluminum nitrate nonahydrate significantly improves the electrical parameter TRR value of the chip.

[0049] 4. In this application, silicate ester is used as the main substance of the latex solution, which mainly undergoes hydrolysis and condensation reaction to gradually form a uniform colloidal solution; low-carbon alcohol is used as a dispersant in the latex solution to increase the uniform dispersion of boron and aluminum elements into the ether to form a low-viscosity solution; acids are used as auxiliary agents to catalyze the hydrolysis and condensation process of silicate ester, while preventing cross-linking reaction during the reaction to form spheres and avoid agglomeration; the dispersant can prevent the agglomeration between particles, prevent the gelation of the latex solution, and prevent the precipitation of effective substances. Attached Figure Description

[0050] Figure 1 This is the electrochemical voltammetric scan from Preparation Example 2 of this application. Detailed Implementation

[0051] The boron-aluminum diffusion source is spin-coated onto the chip. In the pre-process baking stage of high-temperature diffusion (around 120°C), significant dispersion in sheet resistance and PN junction depth occurs, resulting in an uneven and rough film. The applicant discovered that at approximately 120°C, low-boiling-point impurities volatilize, while impurities above 120°C cause film inhomogeneity during high-temperature diffusion. Impurities with boiling points between 115-120°C affect film smoothness. Therefore, the applicant purified the ethers used in the boron-aluminum diffusion source, increasing purity while reducing metal impurity content. In chip manufacturing, special requirements such as lightning protection place high demands on the electrical parameter TRR, but current TRR values ​​are generally low. The applicant found that the TRR value is highly sensitive to the metal ion content in the boron-aluminum diffusion source, and effectively reducing the metal impurity content is an effective means to improve the TRR value. Based on this, the applicant developed a boron-aluminum diffusion source.

[0052] The following embodiments further illustrate this application in detail. It should be noted that: unless otherwise specified, the conditions in the following embodiments are carried out under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments can be obtained from commercially available sources.

[0053] Preparation Example

[0054] Preparation Example 1

[0055] The distillation and purification of ethylene glycol monomethyl ether specifically includes the following steps:

[0056] Step 1): Add ethylene glycol monomethyl ether to the bottom of the column and heat the ethylene glycol monomethyl ether to raise the temperature.

[0057] Step 2) Collect the fraction at 124-125℃ at the top of the column, and obtain ethylene glycol monomethyl ether purified by distillation after condensation.

[0058] The impurity test results for the purified ethylene glycol monomethyl ether in Preparation Example 1 are shown in Table 1:

[0059] Table 1

[0060]

[0061]

[0062] Preparation Example 2

[0063] The electrochemical purification process for aluminum nitrate nonahydrate includes the following steps:

[0064] Step 1) Add aluminum nitrate nonahydrate to ethylene glycol monomethyl ether and stir at 50°C for 4 hours to fully dissolve and obtain aluminum nitrate-ethylene glycol monomethyl ether solution with an aluminum nitrate mass fraction of 35 wt%. Transfer the solution to an electrolytic cell and add ion exchange resin to the electrolytic cell at the same time.

[0065] Step 2): The electrolytic cell uses aluminum foil as the anode and platinum electrode as the cathode; nitrate anion exchange resin is placed at the anode and aluminum ion cation exchange resin is placed at the cathode; electrolysis is carried out with an operating voltage of 0-2V and a scan rate of 10mV / s.

[0066] Step 3): When the working voltage reaches 2V and there is no reaction current, stop electrolysis.

[0067] Step 4): After filtering the aluminum nitrate-ethylene glycol monomethyl ether solution obtained in step 3), the solution is evaporated and crystallized at 80°C under an inert atmosphere to obtain purified aluminum nitrate nonahydrate.

[0068] Electrochemical voltammetry scans were performed during the above-mentioned operating voltage range of 0-2V, as shown in the figure. Figure 1 As shown, by Figure 1 The electrochemical voltammetry results show several current peaks in the 0-2V range, indicating that an electrochemical reaction has occurred. Near 2V, there is virtually no reaction current, suggesting that the metallic impurities in the solution system have been reduced.

[0069] The impurity test results for aluminum nitrate nonahydrate after electrochemical purification in Preparation Example 2 are shown in Table 2:

[0070] Table 2

[0071]

[0072]

[0073] Example

[0074] The ethylene glycol monomethyl ether and aluminum nitrate nonahydrate used in the following examples were obtained by purification in Preparation 1 and Preparation Example 2.

[0075] Example 1

[0076] A boron-aluminum diffusion source, the preparation method of which includes the following steps: raw materials are calculated in 100 kg;

[0077] Step 1): Add 30.00 kg of ethylene glycol monomethyl ether, 2.00 kg of boron oxide and 5.00 kg of aluminum nitrate nonahydrate to the reaction vessel (1) and stir to dissolve at a constant temperature of 50°C. After all the solids in the reaction vessel have dissolved, add 0.01 kg of polyethylene glycol and stir for 4 hours.

[0078] Step 2), add 35.00 kg of tetraethyl orthosilicate, 2.00 kg of water and 25.98 kg of low carbon alcohol to the reaction vessel (2) and stir at a constant temperature of 50°C for 4 hours, gradually adding 0.01 kg of acid during the process;

[0079] Step 3): The solutions in reactor (1) and reactor (2) are pressure filtered through a 0.2 μm filter element and then transferred to reactor (3) in a mass ratio of 1:1 for mixing. After stirring for 4 hours, the solutions are pressure filtered again through a 0.2 μm filter element to obtain the boron-aluminum diffusion source.

[0080] The difference between the boron-aluminum diffusion source provided in Examples 2-5 and that in Example 1 is that the amount of raw material components added is shown in Table 3.

[0081] Table 3

[0082]

[0083] The boron-aluminum diffusion source provided in Examples 6-9 differs from that in Example 5 in that the preparation temperature and stirring time are shown in Table 4.

[0084] Table 4

[0085]

[0086] Comparative Example

[0087] Comparative Examples 1-3

[0088] The difference between the boron-aluminum diffusion source provided in Comparative Examples 1-3 and the boron-aluminum diffusion source prepared in Example 5 is that the ethylene glycol monomethyl ether and aluminum nitrate nonahydrate in Comparative Examples 1-3 were purchased from different manufacturers. The boron-aluminum diffusion source was prepared according to the method in Example 5, and the total metal impurity content and sodium content were tested. The test results are shown in Table 5 below.

[0089] Comparative Example 4

[0090] The difference between the boron-aluminum diffusion source provided in Comparative Example 4 and that in Example 5 is that the raw materials used in Comparative Example 4, ethylene glycol monomethyl ether and aluminum nitrate nonahydrate, were not purified before use, and were specifically prepared by the following steps:

[0091] Step 1): Mix 20 kg of tetraethyl orthosilicate and 30 kg of ethanol evenly and heat to 65°C;

[0092] Step 2), add 28 kg of ethylene glycol monomethyl ether and stir until homogeneous;

[0093] Step 3) Add 8 kg of aluminum nitrate nonahydrate and 12 kg of boron oxide, stir for 3 hours, and then cool to room temperature to obtain the final product.

[0094] Comparative Example 5

[0095] The difference between the boron-aluminum diffusion source provided in Comparative Example 5 and that in Example 5 is that Comparative Example 5 is prepared by the following steps:

[0096] Step 1): Add 28.00 kg of ethylene glycol monomethyl ether, 12.00 kg of boron oxide, and 8.00 kg of aluminum nitrate nonahydrate to a reaction vessel and stir to dissolve at a constant temperature of 50°C. After all the solids in the reaction vessel have dissolved, add 0.01 kg of polyethylene glycol and stir for 4 hours.

[0097] Step 2): Add 20.00 kg of tetraethyl orthosilicate, 1.50 kg of water, and 30.00 kg of low-carbon alcohol to a reaction vessel and stir at a constant temperature of 50°C for 4 hours. Gradually add 0.01 kg of acid during the process to obtain a boron-aluminum diffusion source.

[0098] Comparative Example 6

[0099] The difference between the boron-aluminum diffusion source provided in Comparative Example 6 and Example 5 is that polyethylene glycol is not added in Comparative Example 6, but is replaced by ethylene glycol monomethyl ether in equal amounts.

[0100] Comparative Example 7

[0101] The difference between the boron-aluminum diffusion source provided in Comparative Example 7 and Example 5 is that hydrochloric acid is not added in Comparative Example 7, but is replaced by an equal amount of ethylene glycol monomethyl ether.

[0102] Comparative Example 8

[0103] The difference between the boron-aluminum diffusion source provided in Comparative Example 8 and Example 5 is that ethanol is not added in Comparative Example 8, but is replaced by an equal amount of ethylene glycol monomethyl ether.

[0104] Performance testing

[0105] The viscosity, metal impurity content, and sodium content of the boron-aluminum diffusion source obtained in Examples 1-9 and Comparative Examples 1-8 of this application were tested, and the sheet resistance, PN junction depth, and electrical parameter TRR value of the source after it was coated onto silicon crystal and diffused at high temperature were also tested.

[0106] In this application, the content of metal ions and sodium ions was tested according to GB / T 23942—2009 "General Rules for Inductively Coupled Plasma Atomic Emission Spectrometry of Chemical Reagents"; the viscosity was tested according to Q / HG033 2303-2015 "Boron-Aluminum Source"; the sheet resistance was tested according to GB / T1551-2021 "Determination of Resistivity of Silicon Single Crystal by Straight-Line Four-Probe Method and DC Two-Probe Method"; the PN junction depth was tested according to YS / T15-2015 "Determination of Thickness of Silicon Epitaxial Layer and Diffusion Layer by Grinding Angle and Staining Method"; and the electrical parameter TRR value was tested using a dynamic and static parameter testing device, model LEMSYS TRds4045-4070 (Switzerland).

[0107] The performance tests of the examples and comparative examples are shown in Table 5.

[0108] Table 5

[0109]

[0110]

[0111] In Examples 1-9, the purification of ethylene glycol monomethyl ether and aluminum nitrate nonahydrate reduces the dispersion of sheet resistance and PN junction depth, making the distribution more concentrated. During the film drying process, the resulting film is smooth and uniform. Furthermore, due to the purification of raw materials, especially the control of metal impurities, the electrical parameter TRR value is significantly improved, meeting the requirement of a lightning protection electrical parameter TRR value >2200.

[0112] Compared to Example 5, Comparative Examples 1-3 used ethylene glycol monomethyl ether and aluminum nitrate nonahydrate purchased from different manufacturers. The boron-aluminum diffusion source was prepared according to the method in Example 5. As can be seen from the data, due to the use of unpurified ethylene glycol monomethyl ether and aluminum nitrate nonahydrate, the content of metal impurities was relatively high. The resulting integrated circuit products were prone to surface scratches, short lines in the pattern, short circuits, and peeling, resulting in a lower electrical parameter TRR value. At the same time, the electrical parameter TRR value was significantly different from the data in Example 5.

[0113] Comparative Example 4 uses the existing method for preparing a boron-aluminum diffusion source. As can be seen from the data, the boron-aluminum diffusion source prepared using the existing method has a large degree of dispersion in sheet resistance and PN junction depth. At the same time, the electrical parameter TRR value is significantly lower than that of Example 5.

[0114] Compared to Example 5, Comparative Example 5 first dissolved the boron and aluminum sources, and then added silicate esters for dissolution. The data shows that the sheet resistance and PN junction depth have a larger degree of dispersion. At the same time, the electrical parameter TRR value has decreased significantly compared to Example 5. This indicates that the preparation method of this application can make the boron and aluminum elements more uniformly dispersed, and controlling metal impurities can significantly improve the electrical parameter TRR value.

[0115] Comparative Examples 6-8 investigated the effects of not adding polyethylene glycol, hydrochloric acid, and ethanol compared to Example 5. The data showed that the sheet resistance and PN junction depth were more dispersed. At the same time, the electrical parameter TRR value decreased significantly compared to Example 5. The possible reason for this is that the uneven distribution of boron and aluminum elements in the solution due to the absence of these three substances led to uneven doping in the later stages.

[0116] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A boron-aluminum diffusion source, characterized in that, The boron-aluminum diffusion source contains <20 ppm of metallic impurities, of which <15 ppm is sodium ion. The components of the boron-aluminum diffusion source include 15-35% tetraethyl orthosilicate, 2-5% water, 25-35% ethanol, 25-35% ethylene glycol monomethyl ether, 2-12% boron oxide, 5-20% aluminum nitrate nonahydrate, 0.01-1% hydrochloric acid, and 0.01-0.5% polyethylene glycol. The ethylene glycol monomethyl ether is obtained by distillation and purification, specifically including the following steps: Step 1), add ethylene glycol monomethyl ether to the column bottom and heat the ethylene glycol monomethyl ether to raise the temperature; Step 2), collect the fraction at 123-127℃ at the top of the column, and obtain purified ethylene glycol monomethyl ether by condensation; After distillation and purification, the purity of ethylene glycol monomethyl ether is >99.9%, and the content of metal impurities is <200 ppb. The aluminum nitrate nonahydrate was prepared by electrochemical purification, specifically including the following steps: Step 1) Add aluminum nitrate nonahydrate to ethylene glycol monomethyl ether and stir at a constant temperature of 15-50℃ for 0.5-4h to fully dissolve and obtain aluminum nitrate-ethylene glycol monomethyl ether solution. Transfer the solution to an electrolytic cell and add ion exchange resin to the electrolytic cell at the same time. Step 2), the electrolytic cell uses aluminum foil as the anode and platinum electrode as the cathode; anion exchange resin is placed at the anode and cation exchange resin is placed at the cathode; electrolysis is carried out with an operating voltage of 0-2V and a scan rate of 5-10mV / s. Step 3) When the working voltage reaches 2V and there is no reaction current, stop electrolysis. The metal impurity content of the aluminum nitrate-ethylene glycol monomethyl ether solution is <3ppm. Step 4): After filtering the aluminum nitrate-ethylene glycol monomethyl ether solution obtained in Step 3), the solution is evaporated and crystallized at a constant temperature of 60-80℃ under an inert atmosphere to obtain purified aluminum nitrate nonahydrate.

2. The boron-aluminum diffusion source according to claim 1, characterized in that, The aluminum nitrate-ethylene glycol monomethyl ether solution contains 20-50 wt% aluminum nitrate; the anion exchange resin is a nitrate anion exchange resin; and the cation exchange resin is an aluminum ion exchange resin.

3. The method for preparing a boron-aluminum diffusion source according to any one of claims 1-2, characterized in that, Specifically, the following steps are included: Step 1): Dissolve ethylene glycol monomethyl ether, boron oxide, and aluminum nitrate nonahydrate in a constant temperature of 15-50°C. After all the solids have dissolved, add polyethylene glycol in a certain proportion and stir for 0.5-4 hours to obtain mixture A. Step 2), tetraethyl orthosilicate, water and ethanol are stirred at a constant temperature of 15-50℃ for 0.5-4h in proportion, and hydrochloric acid is gradually added in proportion during the process to obtain mixture B; Step 3): Mixture A and mixture B are respectively pressure filtered and then mixed. After stirring for 0.5-4 hours, they are pressure filtered again to obtain the boron-aluminum diffusion source.

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