Electronic grade silicon carbide block matrix metal impurity detection method

Abstract

The invention provides an electronic grade silicon carbide block matrix metal impurity detection method, and relates to the technical field of silicon carbide. The method comprises the following steps: crushing a silicon carbide block into small blocks, and weighing a silicon carbide block sample; soaking the silicon carbide block sample in a first mixed acid; cleaning the silicon carbide block sample with ultrapure water; putting the silicon carbide block sample into a digestion tube, and adding a second mixed acid; sealing the digestion tube and putting the digestion tube into a digestion instrument for digestion; after digestion is completed, acid removal and volume metering are carried out, and then detection is carried out through an inductively coupled plasma mass spectrometer; wherein a blank sample is prepared in advance, and the blank sample is sequentially subjected to digestion, acid removal and volume metering and is finally detected through a mass spectrometer. The detection result is prevented from being influenced by matrix interference, the detection cost is reduced, and pretreatment complexity is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon carbide, and particularly relates to a method for detecting metal impurities in an electronic-grade silicon carbide block matrix. Background Art

[0002] Silicon carbide materials have the advantages of large bandgap, high breakdown field strength, fast mobility, high thermal conductivity, etc. Semi-insulating and conductive products can meet the manufacturing requirements of radio frequency devices and power electronic devices, and are widely used in fields such as 5G communication, radar electronics, new energy vehicles, energy storage, etc., which are related to national defense security and national economic construction. As a strategic material, the self-control of silicon carbide substrates is the key to ensuring the implementation of national key industrial chains and major tasks, and is also the core of ensuring national economic construction. At present, 6-inch silicon carbide single crystal substrates have been mass-produced, and 8-inch ones have been produced in small batches. The large size is an important development direction for silicon carbide substrate preparation technology. Because the larger the substrate size, the more chips can be manufactured per unit substrate, the lower the chip cost, and the larger the substrate size, the less waste at the edge, which is conducive to further reducing the chip cost. With the explosive growth of fields such as new energy vehicles and energy storage, the demand for silicon carbide devices will continue to rise. It is estimated that the global silicon carbide power semiconductor market size will reach hundreds of billions in 2027 and reach the scale of 300 billion in 2030. Silicon carbide will become an important pillar industry for the energy revolution.

[0003] Electronic-grade silicon carbide (SiC) blocks are epitaxially grown on the substrate surface by chemical vapor deposition (CVD) method, using methane (CH4) and silane (SiH4) as carbon / silicon precursors. Its purity and production process stability directly affect the electrical properties of SiC crystals. During the complete process of the precursor from synthesis, transportation to the reaction chamber, production devices (such as synthesis reactors), process pipelines (stainless steel / polymer pipelines), and high-temperature reaction furnaces (graphite / quartz materials) may introduce metal impurities through the following paths:

[0004] (1) Thermal dissipation of metal atoms caused by high-temperature corrosion (such as surface migration of Fe and Cr impurities in the graphite components of the reaction furnace);

[0005] (2) Desorption of adsorbed impurities on the inner wall of the pipeline under the scouring of the gas flow (such as oxygen-containing complexes of siliconophilic metals such as Ni and Al);

[0006] (3) Residual organometals in the precursor (such as methylaluminum, iron silicate complex).

[0007] During the CVD reaction process, such metal impurities are transported to the substrate surface along with the main gas flow and participate in the SiC deposition through the adsorption-nucleation mechanism, eventually forming lattice substitution defects or metal carbide inclusions. Due to the strong chemical inertness of SiC, the attached contaminants on the surface can be removed through the cleaning process, while there is no effective way to remove the impurities deposited in SiC.

[0008] Currently, the mainstream growth of SiC single crystals is mainly by physical vapor transport method, with a reaction temperature as high as 2200 °C. The matrix metal impurities in the raw material SiC will migrate to the single crystal ingot together with SiC during the reaction process. These impurities will form deep-level defects, significantly reducing the carrier lifetime (from the μs level to the ns level), leading to the degradation of chip performance and directly affecting the reliability and yield of the device. For example, 10 ppb of Fe impurities can increase the reverse leakage current of MOSFET by 50% and the breakdown voltage fluctuation by more than 15%. Therefore, monitoring the matrix metal impurities in silicon carbide blocks is of great significance for the production of silicon carbide substrates and wafers.

[0009] Currently, for the matrix metal impurities in silicon carbide, the main method is glow discharge mass spectrometry, and there are several problems with this method:

[0010] 1. Since the aerosol introduced into the mass spectrometer also contains the matrix of silicon carbide, there is a large matrix interference in mass spectrometry analysis. Therefore, the detection accuracy of the current most advanced glow discharge mass spectrometer is still at the ppb level;

[0011] 2. Glow discharge only excites plasma on the sample surface to generate high-temperature gasification of the sample. Due to the limitation of the detection power, this method can only gasify the superficial sample, and the gasification spot is generally micron-sized, with a narrow detection range. The single-point detection cannot reflect the whole, and the detection data has a large deviation;

[0012] 3. The glow discharge method requires a powerful power supply system, so the glow discharge mass spectrometer is expensive. The prices of the current mainstream brand glow discharge mass spectrometers all exceed ten million, and the single-sample analysis cost exceeds 3000 yuan;

[0013] 4. The glow discharge method detects superficial impurities and has high requirements for the pretreatment of the sample. For example, cutting, grinding, cleaning, etc. are required, with cumbersome operations and high risks. Summary of the Invention

[0014] The purpose of the present invention is to develop a detection method for matrix metal impurities in electronic-grade silicon carbide blocks that avoids matrix interference affecting the detection results, reduces the detection cost, and avoids complex pretreatment.

[0015] The present invention is realized through the following technical solutions:

[0016] A detection method for matrix metal impurities in electronic-grade silicon carbide blocks includes the following steps:

[0017] S1. Crush the silicon carbide blocks into small pieces and weigh the silicon carbide block sample;

[0018] S2. Immerse the silicon carbide block sample in the first mixed acid;

[0019] S3. Wash the silicon carbide block sample with ultrapure water;

[0020] S4. Put the silicon carbide block sample into a digestion tube and add the second mixed acid;

[0021] S5. Seal the digestion tube and put it into a digestion instrument for digestion;

[0022] S6. After digestion is completed, carry out acid expulsion and volume fixation, and then detect by a mass spectrometer;

[0023] Among them, a blank sample is prepared in advance, and the blank sample also sequentially undergoes steps S5 and S6, for digestion, acid expulsion, volume fixation, and finally detection by a mass spectrometer.

[0024] Optionally, the first mixed acid uses UPS-grade acid, which is a combination of any one or more of hydrofluoric acid, nitric acid, hydrogen peroxide, perchloric acid, sulfuric acid, and hydrochloric acid.

[0025] Optionally, the second mixed acid uses imported reagents with a purity above AA grade, which is a combination of any one or more of hydrofluoric acid, nitric acid, hydrogen peroxide, perchloric acid, sulfuric acid, and hydrochloric acid.

[0026] Optionally, in step S5, the microwave digestion parameters are: pressure 0.1 - 40 MPa, temperature 150 - 300 °C, time 30 min - 6 h, and digestion times 1 - 5 times.

[0027] ]>Optionally, in step S6, the acid expulsion parameters are: pressure -0.1 MPa - 0 MPa, temperature 150 - 300 °C, time 30 min - 3 h, and acid expulsion times 1 - 5 times.

[0028] Optionally, the standard curve of the mass spectrometer is determined according to the actual impurity concentration of the sample, and it is required that the test value is in the middle position of the standard curve points.

[0029] Optionally, the mass spectrometer is an inductively coupled plasma mass spectrometer.

[0030] Optionally, the blank sample is the same second mixed acid used in step S4.

[0031] The beneficial effects of the present invention are:

[0032] After digestion and acid expulsion, the matrix (SiC) of silicon carbide is removed by the acid and will not cause matrix interference to the mass spectrometer, and the detection limit can reach 1 ppt;

[0033] This solution directly digests and analyzes bulk samples, and the detected results represent all impurities in the sample. The detection range is several orders of magnitude wider than that of glow discharge inductively coupled plasma mass spectrometry;

[0034] This solution uses a general inductively coupled plasma mass spectrometer, and the instrument price (of the same level / manufacturer) is about 5 times lower than that of glow discharge inductively coupled plasma mass spectrometry. The detection cost can be as low as a few hundred yuan, and the detection cost is reduced;

[0035] After digestion and acid expulsion for volume fixation, the operation is simple, avoiding complex pretreatment. People with clean room operation experience can easily start the operation, and the operation difficulty is low. Specific implementation mode

[0036] In the following text, only some exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present invention. Therefore, the following description is considered to be exemplary in nature rather than restrictive.

[0037] The embodiments of the present invention will be described in detail below.

[0038] The present invention discloses a method for detecting metal impurities in an electronic-grade silicon carbide block matrix, including the following steps:

[0039] S1. Break the silicon carbide block into small pieces, and weigh about 0.5 - 2 g of the silicon carbide block sample;

[0040] S2. Immerse the silicon carbide block sample in the first mixed acid;

[0041] S3. Wash the silicon carbide block sample with ultrapure water;

[0042] S4. Put the silicon carbide block sample into a digestion tube and add the second mixed acid;

[0043] S5. Seal the digestion tube and put it into a digester for digestion;

[0044] S6. After digestion, perform acid expulsion and volume fixation, and then detect by inductively coupled plasma mass spectrometry;

[0045] Among them, the first mixed acid uses UPS-grade acid, which is any one or a combination of hydrofluoric acid, nitric acid, hydrogen peroxide, perchloric acid, sulfuric acid, and hydrochloric acid;

[0046] The second mixed acid uses imported reagents with a purity above AA grade, which is any one or a combination of hydrofluoric acid, nitric acid, hydrogen peroxide, perchloric acid, sulfuric acid, and hydrochloric acid;

[0047] In step S5, the microwave digestion parameters are as follows: pressure 0.1 - 40 MPa, temperature 150 - 300 °C, time 30 min - 6 h, digestion times 1 - 5 times;

[0048] In step S6, the acid expulsion parameters are as follows: pressure -0.1 MPa - 0 MPa, temperature 150 - 300 °C, time 30 min - 3 h, acid expulsion times 1 - 5 times;

[0049] Prepare a blank sample in advance. The blank sample is the same second mixed acid used in step S4. The blank sample also undergoes steps S5 and S6 in sequence for digestion, acid expulsion, volume fixation, and finally detection by an inductively coupled plasma mass spectrometer;

[0050] The inductively coupled plasma mass spectrometer is optimized according to appropriate tuning parameters. The standard curve of the inductively coupled plasma mass spectrometer is determined according to the actual impurity concentration of the sample, and it is required that the test value be in the middle position of the standard curve points.

[0051] The beneficial effects of the present invention are as follows:

[0052] After digestion and acid expulsion, the matrix of silicon carbide (SiC) is removed by the acid and will not cause matrix interference to the mass spectrometer. The detection limit can reach 1 ppt;

[0053] This solution directly digests and analyzes bulk samples, and the detected results represent all impurities in the sample. The detection range is several orders of magnitude wider than that of a glow discharge plasma mass spectrometer;

[0054] This solution uses a common inductively coupled plasma mass spectrometer. The price of the instrument (same grade / manufacturer) is about 5 times lower than that of a glow discharge plasma mass spectrometer, and the detection cost can be as low as a few hundred yuan, reducing the detection cost;

[0055] After digestion, acid expulsion, and volume fixation, the operation is simple, avoiding complex pretreatment. People with clean room operation experience can easily operate it, and the operation difficulty is low.

[0056] The above embodiments are only the preferred embodiments of the present invention and do not limit the technical solutions of the present invention. Any technical solutions that can be achieved on the basis of the above embodiments without creative labor shall be regarded as falling within the scope of the patent rights of the present invention.

Claims

1. An electronic-grade silicon carbide block matrix metal impurity detection method, characterized in that, The package includes the following steps: S1. Crush the silicon carbide blocks into small pieces and weigh the silicon carbide block samples; S2. Immerse the silicon carbide block samples in the first mixed acid; S3. Wash the silicon carbide block samples with ultrapure water; S4. Put the silicon carbide block samples into a digestion tube and add the second mixed acid; S5. Seal the digestion tube and put it into a digester for digestion; S6. After digestion, perform acid removal and volume fixation, and then detect by a mass spectrometer; Among them, a blank sample is prepared in advance, and the blank sample also sequentially undergoes steps S5 and S6, for digestion, acid removal, volume fixation, and finally detection by a mass spectrometer.

2. The method for detecting matrix metal impurities of the electronic-grade silicon carbide block according to claim 1, wherein The first mixed acid uses UPS-grade acid, which is a combination of any one or more of hydrofluoric acid, nitric acid, hydrogen peroxide, perchloric acid, sulfuric acid, and hydrochloric acid.

3. The method for detecting matrix metal impurities of the electronic-grade silicon carbide block according to claim 1, characterized in that The second mixed acid uses imported reagents with a purity above AA grade, which is a combination of any one or more of hydrofluoric acid, nitric acid, hydrogen peroxide, perchloric acid, sulfuric acid, and hydrochloric acid.

4. The method for detecting matrix metal impurities of electronic-grade silicon carbide blocks according to claim 1, wherein, In the step S5, the microwave digestion parameters are: pressure 0.1 - 40 MPa, temperature 150 - 300 °C, time 30 min - 6 h, and the number of digestion times is 1 - 5 times.

5. The method for detecting matrix metal impurities of electronic-grade silicon carbide blocks according to claim 1, characterized in that, In the step S6, the acid removal parameters are: pressure -0.1 MPa - 0 MPa, temperature 150 - 300 °C, time 30 min - 3 h, and the number of acid removal times is 1 - 5 times.

6. The method for detecting matrix metal impurities of electronic-grade silicon carbide blocks according to claim 1, characterized in that, The standard curve of the mass spectrometer is determined according to the actual impurity concentration of the sample, and it is required that the test value is in the middle position of the standard curve points.

7. The method for detecting matrix metal impurities of the electronic-grade silicon carbide block according to claim 1, characterized in that, The mass spectrometer is an inductively coupled plasma mass spectrometer.

8. The method for detecting matrix metal impurities of the electronic-grade silicon carbide block according to claim 1, wherein The blank sample is the same second mixed acid used in step S4.