A purification process and device for CVD-SiC coating precursor methyltrichlorosilane

Abstract

The application relates to a purification process and device for CVD-SiC coating precursor methyltrichlorosilane, and the purification process comprises the following steps: filtering methyltrichlorosilane raw material by using a pre-filter to obtain filtered methyltrichlorosilane; sequentially adsorbing the filtered methyltrichlorosilane by using two adsorption columns connected in series to obtain adsorbed methyltrichlorosilane, wherein porous SiO2 microspheres are used as adsorbents; filtering the adsorbed methyltrichlorosilane by using a terminal filter to obtain high-purity methyltrichlorosilane. The process adopts a normal-temperature liquid-phase route of pre-filtering, double-column series adsorption and terminal filtering, uses porous SiO2 microspheres as adsorbents, removes B and P impurities by using the Lewis acid-base coordination of Si-OH on the surface of SiO2 and BCl3 and PCl3 under the protection of anhydrous and slightly pressurized nitrogen, controls metal impurities such as Na, Mg, Al, K, Ca, Fe, Ni and Cu through a 316L EP metal-dissolution-free system, and prevents secondary pollution.

Description

Technical Field

[0001] This invention relates to the field of semiconductor material purification technology, and in particular to a purification process and apparatus for methyltrichlorosilane, a precursor for CVD-SiC coating. Background Technology

[0002] Methyltrichlorosilane (MTS) is a core precursor for the preparation of high-purity silicon carbide (SiC) coatings by chemical vapor deposition (CVD). The purity and electrical properties of the SiC coating are highly dependent on the impurity control level of the MTS precursor. Currently, high-purity semi-insulating SiC coatings achieve impurity control at the 6N level or higher. Boron (B), as a key shallow-energy impurity, needs to be controlled below 5 ppb; metallic impurities such as nickel (Ni) and iron (Fe) need to be controlled below 10 ppb. During the high-temperature CVD deposition process, impurities such as B, Ni, and Fe are difficult to remove with the gaseous byproducts and will dop into the solid-phase SiC lattice. Experiments show that if the B content in the MTS is >10 ppb, the final SiC product can be enriched to over 50 ppb, directly leading to semi-insulating performance failure. Only when the B content in the MTS is stably controlled below 1 ppb can the B content in SiC meet the industry standard of ≤5 ppb. Therefore, pre-purification of key impurities such as B and P in MTS without introducing impurities such as Ni and Fe is a necessary prerequisite for preparing high-purity SiC coatings.

[0003] Currently, there is a lack of dedicated purification processes and equipment for MTS suitable for high-purity SiC coatings. Traditional purification methods all have insurmountable defects and cannot meet the requirements for small-scale MTS purification. (1) Distillation purification: The equipment investment is high, the energy consumption is large, the operation is complicated, and the maintenance cost is high. It is only suitable for large-scale centralized production of MTS and is difficult to match the purification needs of small and medium-sized MTS for self-use.

[0004] (2) Alumina / molecular sieve adsorption: The material skeleton itself contains metal impurities such as Al, Na, K, and Ca. Long-term contact in the liquid chlorosilane system will cause metal ions to dissolve, resulting in secondary pollution of MTS and failing to meet the impurity control requirements.

[0005] (3) Resin / activated carbon adsorption: Organic resins are easily hydrolyzed, swollen and broken in chlorosilanes, and activated carbon easily introduces organic carbon, ash and metal impurities, all of which will destroy the purity of MTS and are not suitable for semiconductor-grade high-purity systems.

[0006] (4) Conventional filtration: It can only remove particulate pollutants, but has no effect on removing B, P and metal ions, and cannot achieve deep purification.

[0007] Existing industrial-grade and electronic-grade MTS raw materials have high purity, with boron content typically below 10 ppbw. However, due to the influence of production, transportation, storage, and conveying processes, the impurity content fluctuates significantly from batch to batch, making it difficult to consistently meet the zero-tolerance control requirements of SiC coatings for precursors. Therefore, there is an urgent need for a stable, efficient, and non-contaminating deep purification technology for MTS. Summary of the Invention

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A purification process for methyltrichlorosilane, a precursor for CVD-SiC coatings, includes the following steps: The methyltrichlorosilane feedstock was filtered using a pre-filter to obtain filtered methyltrichlorosilane. Filtered methyltrichlorosilane was sequentially adsorbed using two adsorption columns connected in series to obtain adsorbed methyltrichlorosilane. The adsorption columns used porous SiO2 microspheres as adsorbents. The adsorbed methyltrichlorosilane was filtered using a terminal filter to obtain high-purity methyltrichlorosilane.

[0009] Preferably, the porous SiO2 microspheres have a particle size of 0.3–0.8 mm, a specific surface area of ​​300–500 m² / g, a pore size of 2–50 nm, and a pore volume of 0.8–1.2 cm³ / g.

[0010] Preferably, the height-to-diameter ratio of the adsorption column is 3:1–8:1, and the adsorbent penetration capacity is ≥0.5 mg B / g SiO2.

[0011] Preferably, the pre-filter is a 1μm semiconductor-grade pre-filter and the terminal filter is a 0.1μm semiconductor-grade terminal filter.

[0012] Preferably, nitrogen is used for propulsion, with a nitrogen pressure of 10 kPa (G) and a space velocity of 0.3 h⁻¹.

[0013] A purification device for methyltrichlorosilane, a precursor for CVD-SiC coating, includes a storage tank, a pre-filter, a primary adsorption column, a secondary adsorption column, a terminal filter, and a finished product tank connected in series from upstream to downstream. The storage tank stores the incoming methyltrichlorosilane. The pre-filter is used to filter the incoming methyltrichlorosilane to obtain filtered methyltrichlorosilane. Both the primary and secondary adsorption columns use porous SiO2 microspheres as adsorbents. The primary and secondary adsorption columns are used to sequentially adsorb the filtered methyltrichlorosilane to obtain adsorbed methyltrichlorosilane. The terminal filter filters the adsorbed methyltrichlorosilane to obtain high-purity methyltrichlorosilane; the finished product tank is used to hold the high-purity methyltrichlorosilane.

[0014] Preferably, the storage tank is provided with an air inlet for introducing methyltrichlorosilane and nitrogen gas, with a nitrogen pressure of 10 kPa (G) and a space velocity of 0.3 h⁻¹.

[0015] Preferably, the nitrogen purity is ≥99.999%, H2O ≤5 ppm, and oxygen content ≤1 ppm.

[0016] Preferably, the purification device further includes a liquid seal tank connected downstream of the finished product tank, and a pilot-operated nitrogen release valve and a check valve are installed on the pipeline between the finished product tank and the liquid seal tank.

[0017] Preferably, the storage tank, primary adsorption column, secondary adsorption column and finished product tank are all electropolished using 316L EP.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This process employs a pre-filtration → dual-column series adsorption → terminal filtration at room temperature liquid phase. Using porous SiO2 microspheres as the adsorbent, under anhydrous and slightly positive pressure nitrogen protection, it utilizes the Lewis acid-base coordination between Si-OH on the SiO2 surface and BCl3 and PCl3 to specifically remove B and P impurities. Simultaneously, it controls metal impurities such as Na, Mg, Al, K, Ca, Fe, Ni, and Cu through a full 316L EP metal-free leaching system, eliminating secondary pollution.

[0019] The device employs a triple venting and backflow prevention structure: bottom inlet, top outlet flow channel, nitrogen micro-positive pressure drive, pilot-operated nitrogen release valve, check valve, and inert liquid seal. This structure can stably reduce B in MTS from 2–10 ppbw to <1 ppbw, and P to <1 ppbw. This invention requires no distillation, no custom-made components, has low investment, and offers stable operation, making it particularly suitable for small- to medium-scale MTS purification. Attached Figure Description

[0020] Figure 1 A schematic flow chart of the purification process for methyltrichlorosilane, a precursor for CVD-SiC coatings, provided by this invention.

[0021] Figure 2 A schematic diagram of the structure of the purification device for methyltrichlorosilane, a precursor for CVD-SiC coating, provided by the present invention. Detailed Implementation

[0022] The present invention will now be described in more detail with reference to the accompanying drawings. It should be noted that the following description of the present invention with reference to the accompanying drawings is merely illustrative and not restrictive. Various different embodiments can be combined with each other to form other embodiments not shown in the following description.

[0023] like Figure 1As shown, the present invention provides a purification process for methyltrichlorosilane, a precursor for CVD-SiC coatings, comprising the following steps: The methyltrichlorosilane feedstock was filtered using a pre-filter to obtain filtered methyltrichlorosilane. Filtered methyltrichlorosilane was sequentially adsorbed using two adsorption columns connected in series to obtain adsorbed methyltrichlorosilane. The adsorption columns used porous SiO2 microspheres as adsorbents. The adsorbed methyltrichlorosilane was filtered using a terminal filter to obtain high-purity methyltrichlorosilane.

[0024] In this process, methyltrichlorosilane is supplied under nitrogen-sealed conditions via a 316L EP pipeline. Particulate impurities are removed through a 1μm 316L EP pre-filter. After filtration, the methyltrichlorosilane flows from bottom to top through a first adsorption column, which is filled with 5N / 6N grade high-purity metal-free functionalized porous SiO2 microspheres. Through complexation, boron (B) is reduced from 2–10 ppbw to <1 ppbw. MTS continues to flow from bottom to top through a second adsorption column, where trace amounts of phosphorus (P) and polar impurities are further removed using the same adsorbent, achieving stable control of all impurity levels. Finally, a 0.1μm 316L EP terminal filter intercepts adsorbent powder and particles detached from the pipeline, yielding high-purity MTS.

[0025] The mechanism is as follows: BCl3 (Lewis acid) + Si–OH (Lewis base) → Si–O–BCl2 + HCl, specifically removes B; Polar impurities such as PCl3 are adsorbed on the surface and captured in the pores; Metals such as Fe, Ni, Na, Mg, Al, and Ca are not removed by SiO2 adsorption, but by incoming material control + ensuring no metal leaching throughout the system; The entire process is water-free and oxygen-free to prevent the hydrolysis of MTS from generating SiO2 and HCl, which can cause blockage and corrosion.

[0026] Preferably, the porous SiO2 microspheres have a particle size of 0.3–0.8 mm, a specific surface area of ​​300–500 m² / g, a pore size of 2–50 nm, a pore volume of 0.8–1.2 cm³ / g, and are free of impurities such as Al, Na, Mg, K, Ca, Fe, and Ni. More preferably, they are electronic-grade, high-purity, metal-free functionalized porous SiO2 microspheres. Preferably, the adsorption column has a height-to-diameter ratio of 3:1–8:1, and an adsorbent penetration capacity ≥0.5 mg B / g SiO2.

[0027] like Figure 2As shown, a purification device for methyltrichlorosilane, a precursor for CVD-SiC coating, includes a storage tank 1, a pre-filter 2, a primary adsorption column 3, a secondary adsorption column 4, a terminal filter 5, and a finished product tank 6 connected in series from upstream to downstream. The storage tank 1 stores the incoming methyltrichlorosilane. The pre-filter 2 filters the incoming methyltrichlorosilane to obtain filtered methyltrichlorosilane. Both the primary adsorption column 3 and the secondary adsorption column 4 use porous SiO2 microspheres as adsorbents. The primary and secondary adsorption columns 3 and 4 sequentially adsorb the filtered methyltrichlorosilane to obtain adsorbed methyltrichlorosilane. The terminal filter 5 filters the adsorbed methyltrichlorosilane to obtain high-purity methyltrichlorosilane. The finished product tank 6 is used to hold the high-purity methyltrichlorosilane. The purification device also includes a liquid-sealed tank 9 connected downstream of the finished product tank 6. A pilot-operated nitrogen release valve 7 and a check valve 8 are installed on the pipeline between the finished product tank 6 and the liquid-sealed tank 9.

[0028] Preferably, the storage tank 1 is equipped with an air inlet for introducing methyltrichlorosilane and nitrogen gas. The nitrogen pressure is 10 kPa (G), the space velocity is 0.3 h⁻¹, the nitrogen purity is ≥99.999%, H₂O ≤5 ppm, and the oxygen content is ≤1 ppm. The storage tank 1, the primary adsorption column 3, the secondary adsorption column 4, and the finished product tank 6 are all electropolished using 316L EP.

[0029] The present invention will be further described below with reference to embodiments.

[0030] Example 1

[0031] Incoming material: MTS purity 99.96%, B=6.8 ppbw, P=2.1 ppbw, Fe=0.6 ppbw, Ni=0.4 ppbw, and the remaining 22 metals are all <1 ppbw; Adsorbent: High-purity SiO2 microspheres, particle size 0.5 mm, specific surface area 420 m² / g; Adsorption column: Φ50×300 mm, height-to-diameter ratio 6:1, packing weight 500 g; Process: 25℃, nitrogen pressure 10 kPa (G), space velocity 0.3 h⁻¹, bottom inlet, top outlet; Filtration: 1 μm + 0.1 μm 316L EP; Test method: GB / T 29056-2012, ICP-MS, collision cell He mode to eliminate Cl interference; The purification results showed that all 26 impurities, including B (0.62 ppbw), P (0.78 ppbw), Fe (0.58 ppbw), and Ni (0.39 ppbw), were ≤1 ppbw, meeting the requirements for CVD-SiC semi-insulating coatings.

[0032] Example 2

[0033] The incoming material B = 10.0 ppbw, and the rest is the same as in Example 1; after purification, B = 0.91 ppbw, which is still < 1 ppbw, and all 26 impurities are ≤ 1 ppbw.

[0034] Example 3

[0035] Continuous feeding for 72 hours, with sampling every 12 hours, showed that B was stable at 0.55–0.93 ppbw and P was stable at 0.70–0.95 ppbw, with no metal rise, dissolution, or blockage.

[0036] As can be seen from the above embodiments, the present invention achieves the following effects: (1) B steadily decreases from 2–10 ppbw to <1 ppbw; (2) P decreases to <1 ppbw; (3) All 26 impurities are ≤1 ppbw; (4) The entire system is 316L EP, with no metal leaching and no secondary pollution; (5) Normal temperature and pressure, no distillation, no pump, standard parts, low investment; (6) It is suitable for small and medium-scale MTS purification and can operate continuously and stably.

[0037] (7) Explosion-proof: Hydrogen / combustible gas detection, interlock shutdown; (8) Corrosion protection: 316L EP, resistant to HCl / MTS corrosion; (9) Tail gas: Alkali solution absorbs HCl, and activated carbon adsorbs MTS waste gas; (10) Waterproofing: Triple venting to prevent backflow, nitrogen with slight positive pressure, oxygen ≤1 ppm, H2O ≤5 ppm.

[0038] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A purification process for methyltrichlorosilane, a precursor for CVD-SiC coatings, characterized in that, Includes the following steps: The methyltrichlorosilane feedstock was filtered using a pre-filter to obtain filtered methyltrichlorosilane. Filtered methyltrichlorosilane was sequentially adsorbed using two adsorption columns connected in series to obtain adsorbed methyltrichlorosilane. The adsorption columns used porous SiO2 microspheres as adsorbents. The adsorbed methyltrichlorosilane was filtered using a terminal filter to obtain high-purity methyltrichlorosilane.

2. The purification process as described in claim 1, characterized in that, The porous SiO2 microspheres have a particle size of 0.3–0.8 mm, a specific surface area of ​​300–500 m² / g, a pore size of 2–50 nm, and a pore volume of 0.8–1.2 cm³ / g.

3. The purification process as described in claim 1, characterized in that... The height-to-diameter ratio of the adsorption column is 3:1–8:1, and the adsorbent breakthrough capacity is ≥0.5 mg B / g SiO2.

4. The purification process as described in claim 1, characterized in that, The pre-filter is a 1μm semiconductor-grade pre-filter, and the terminal filter is a 0.1μm semiconductor-grade terminal filter.

5. The purification process as described in claim 1, characterized in that, Nitrogen gas was used for propulsion at a pressure of 10 kPa (G) and a space velocity of 0.3 h⁻¹.

6. A purification apparatus for methyltrichlorosilane, a precursor for CVD-SiC coatings, characterized in that, The system comprises a storage tank (1), a pre-filter (2), a primary adsorption column (3), a secondary adsorption column (4), a terminal filter (5), and a finished product tank (6) connected in series from upstream to downstream. The storage tank (1) stores methyltrichlorosilane. The pre-filter (2) is used to filter the methyltrichlorosilane to obtain filtered methyltrichlorosilane. Both the primary adsorption column (3) and the secondary adsorption column (4) use porous SiO2 microspheres as adsorbents. The primary adsorption column (3) and the secondary adsorption column (4) are used to sequentially adsorb the filtered methyltrichlorosilane to obtain adsorbed methyltrichlorosilane. The terminal filter (5) filters the adsorbed methyltrichlorosilane to obtain high-purity methyltrichlorosilane; the finished product tank (6) is used to hold the high-purity methyltrichlorosilane.

7. The purification apparatus as described in claim 6, characterized in that, The storage tank (1) is provided with an air inlet for introducing methyltrichlorosilane and nitrogen gas. The nitrogen gas pressure is 10 kPa (G) and the space velocity is 0.3 h⁻¹.

8. The purification apparatus as described in claim 7, characterized in that, Nitrogen purity ≥ 99.999%, H2O ≤ 5 ppm, oxygen content ≤ 1 ppm.

9. The purification apparatus as described in claim 6, characterized in that, The purification device also includes a liquid seal tank (9) connected downstream of the finished product tank (6), and a pilot-operated nitrogen release valve (7) and a check valve (8) are provided on the pipeline between the finished product tank (6) and the liquid seal tank (9).

10. The purification apparatus as described in claim 6, characterized in that, The storage tank (1), primary adsorption column (3), secondary adsorption column (4) and finished product tank (6) are all 316L EP electropolished.

Images