KR20050106825A - Recovery of phosphoric acid from semiconductor waste etchant - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating and recovering ultra-high purity phosphoric acid from a semiconductor waste etching solution, and more particularly, to a method of recycling waste etching liquid discharged from a semiconductor etching process, wherein a silicon nitride film (Si ₃ N ₄ ) etching process for a silicon wafer is performed. The present invention relates to a method for separating and recovering ultrahigh-purity phosphoric acid, respectively, by performing a film-melt crystallization process without adding an additive or a solvent from the waste etching solution discharged from the wastewater.

Description

Separation and recovery method of ultra high purity phosphoric acid from semiconductor waste etching solution

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating and recovering ultrapure phosphoric acid from a semiconductor waste etching solution, and more particularly, to a method of recycling waste etching liquid discharged from a semiconductor etching process, wherein a silicon nitride film (Si ₃ N ₄ ) etching process of a silicon wafer is performed. The present invention relates to a method for separating and recovering ultra-high purity phosphoric acid by performing a film-melt crystallization process without addition of an additive or a solvent from the waste etching solution discharged from the reactor.

High purity inorganic acids such as hydrofluoric acid (HF), nitric acid (HNO ₃ ), acetic acid (CH ₃ COOH), phosphoric acid (H ₃ PO ₄ ) and sulfuric acid (H ₂ SO ₄ ) are widely used as wet etchant in semiconductor manufacturing processes. Is being used. The inorganic acid discarded after the etching process is a strong acid having a very low pH, and the metal impurities contained in the etching solution are substances that constitute various films and electrodes on the wafer (substrate) and are very harmful to the environment. As a conventional treatment method for the hazardous waste acid, neutralization, incineration, reverse osmosis, evaporation, and the like are known.

Neutralization is generally used as a method for treating waste acid. In order to neutralize the waste acid, various bases are continuously added until the point of neutralization is reached. The disadvantage of this method is that excessive base is required to treat the waste acid, compared to the treated waste goat, and at the same time, excessive heat of neutralization accompanied with the neutralization reaction and a large amount of salt are generated as a by-product [US Patent No. 5,603,812, US Patent] 4,540,512, US Pat. No. 4,222,997].

Reverse osmosis is a method by which waste acid is passed through a filtration system by reverse osmosis to reduce the acid concentration in the effluent to a level capable of normal treatment. The method requires an expensive filtration system that is difficult to install and maintain and is effective in treating a small amount of low concentration waste (Korean Patent Publication No. 2003-53247 and Korean Patent Publication No. 2002-51206).

Evaporation requires excessive energy consumption to remove water from aqueous waste acid solutions (US Pat. No. 4,980,032, US Pat. No. 4,197,139, US Pat. No. 5,082,645).

Incineration requires excessive energy consumption, similar to the evaporation method, and is an environmentally inadequate method due to the concern of acid rain caused by SO _x and NO _x generated from decomposition of waste acid [US Pat. No. 4,490,347]. , US Pat. No. 4,376,107, US Pat. No. 3,635,664.

Due to the limitations of current waste acid treatment methods, there is a need for a technology that is inexpensive, environmentally friendly, and reduces the amount of acid waste generated and recycled.

The semiconductor etching solution, which is the object of processing and recycling of the present invention, is generated during the silicon wafer etching process. The photolithography process of the semiconductor device manufacturing process is completed by the process of applying a photoresist to a wafer (substrate) and forming a pattern, followed by an etching process. Semiconductor waste etchant is discharged from wet acid etching. In the case of N-metal-oxide-semiconductor (NMOS), a process of removing other than selected portions from various films formed on the wafer surface, that is, forming circuits, is performed by using a photoresist pattern as a mask. Removed. In general, the etching solution used is shown in Table 1 according to the wafer surface film material.

Membrane material Etching solution Oxide (SiO ₂ ) HF, HF + NH ₄ F Silicon Nitride (Si ₃ N ₄ ), Nitride Oxide (SiON) H ₃ PO ₄ , HF Silicon (Poly-Si) HF / HNO ₃ , KOH Aluminum (Al (Si) Cu) Mixed acid

From Table 1, it can be seen that phosphoric acid (H ₃ PO ₄ ), which occupies most of the semiconductor waste etching solution component of the present invention, is used in the etching process of the silicon nitride film (Si ₃ N ₄ ).

Silicon nitride film (Si ₃ N ₄ ) is the most resistant to thermal and impact among the ceramic materials currently used because of its low thermal expansion rate and high strength, and its excellent mechanical resistance due to its high dielectric constant resulting from the strong covalent bonds between its atoms. It exhibits chemical corrosion resistance and is used as a mask layer of local oxidation of silicon (LOCOS) and a protective layer of integrated circuit. As a result, a gate pattern circuit is formed by acting as a mask at the same time as the protective film of SiO ₂ .

Silicon nitride films (Si ₃ N ₄ ) can be etched with HF, buffered HF (phosphorused HF), phosphoric acid (H ₃ PO ₄ ) and high temperature phosphoric acid is generally used because of the selective etching characteristics for SiO ₂ . The reaction formula of silicon nitride and phosphoric acid is as follows.

3Si ₃ N ₄ + 27H ₂ O + 4H ₃ PO ₄ ---> 4 (NH ₄ ) ₃ PO ₄ + 9H ₂ SiO ₃

From the reaction scheme, nitrogen of silicon nitride was present as ammonium phosphate and silicon as silicic acid, and according to Le Chatelier's principle, silicic acid (H ₂ SiO ₃ ) component was judged to inhibit SiO ₂ etching on the wafer.

The semiconductor waste etching solution discharged from the wet etching process of Si 3 N 4 is attracting attention as a large by-product of the electronic industry that can be recycled as a high value-added product when the acid contained therein is separated and recovered from metal impurities and salts.

Korean Laid-Open Patent No. 2004-10825 discloses a semiconductor etching waste liquid consisting of phosphoric acid, nitric acid and acetic acid, which is first concentrated at a high temperature to prepare a purified waste liquid having a phosphoric acid content of 70 to 80 wt%, and then reacted with ammonia to react 98% ammonium phosphate. Known production techniques.

As a method for recovering a useful component from a waste etching solution containing a metal component and a large amount of salts and acids, the following techniques are known.

U.S. Patent No. 5,149,515 discloses nitric acid (HNO ₃ ) or nitric acid and hydrofluoric acid through spraying and condensation at surface treatment wastewater (cleaning, etching) containing metal ions such as Fe, Cr, Ni, Al, Zr (300 ° C). Techniques for recovering mixtures of HF) are known.

Japanese Patent Publication No. Hei 4-101912 discloses by reacting the waste etching solution and the O ₃ gas ejected from the Ni-Fe alloy etching with FeCl ₃ solution was recovered MnO _2, FeCl ₂ and 4H ₂ O, FeCl ₃ solution was etched Recycled as a solution.

Japanese Patent Application Laid-Open No. 4-346680 recovered high-purity AlCl ₃ .6H ₂ O and HCl from the waste liquid generated during the Al foil etching process, and the remaining liquid was recycled into the etching liquid.

However, there is no known method for removing metal impurities contained in the semiconductor waste etching solution and separating and recovering the high purity of phosphoric acid.

Therefore, the present inventors have studied to separate and recover phosphoric acid from the semiconductor waste etching solution with high purity. As a result, by developing a method for separating and recovering high purity phosphoric acid through a film-melt crystallization operation requiring no special solvent or device, The present invention has been completed.

Accordingly, an object of the present invention is to provide a method for recycling a semiconductor waste etching solution, wherein the ultrapure phosphoric acid is separated and recovered from the waste etching solution.

The present invention

1) After maintaining the waste etching solution containing phosphoric acid discharged from the silicon nitride film (Si ₃ N ₄ ) etching process of the silicon wafer at -20 ~ 30 ℃, inoculated seed crystals and inoculated the waste etching solution 0.1 Cooling to −40 to 20 ° C. at a cooling rate of ˜10 K / min to form a phosphate crystal layer; And

2) partially melting the phosphate crystal layer to 0-40 ° C. at a rate of 0.01-10 K / min to remove impurities from the crystal layer to purify

It is characterized by a method of separating and recovering ultra-high purity phosphoric acid from a semiconductor waste etching solution comprising a.

Referring to the present invention in more detail as follows.

The present invention relates to a film-melt crystallization process for forming a crystal layer without addition of an additive or a solvent from a waste etching solution containing phosphoric acid discharged from a silicon nitride film (Si ₃ N ₄ ) etching process of a silicon wafer, and partially melting and refining the crystal layer. The present invention relates to a method for separating and recovering ultrapure phosphoric acid, respectively.

Metal impurities of the semiconductor waste etching solution used in the present invention are Al 1 to 1,000 ppb, As 1 to 3,000 ppb, Ca 1 to 4,000 ppb, Cd 1 to 100 ppb, Cu 1 to 100 ppb, Fe 1 to 1,000 ppb, K 1 to 1,000 ppb, Li 1 to 50 ppb, Na 1 to 100,000 ppb, Ni 1 to 10 ppb, Pb 1 to 50 ppb, Si 1 to 20,000 ppb Sn 1 to 50 ppb, Mo 1 to 1,000 ppb, waste etching solution The main acid component constituting is phosphoric acid.

First, as shown in FIG. 1, the method of separating and recovering ultra-high-purity phosphoric acid from a semiconductor waste etching liquid through a film | membrane melt crystallization operation is as follows.

Step 1) is a step of forming a phosphate crystal layer by injecting phosphate seed crystals to separate and recover ultra-high purity phosphoric acid. First, the semiconductor waste etching solution is supplied to a film molten crystallizer and maintained at -20 to 30 ° C. At this time, it is preferable to use a mixture of ethylene glycol and water as the refrigerant to maintain the temperature.

In the film melt crystallization operation for producing high purity phosphoric acid, the temperature and subcooling of the cooling surface for forming the crystal layer are the most important variables that determine the purity of the crystal. Therefore, in consideration of the concentration range of phosphoric acid normally used as the etching solution of the semiconductor wafer silicon nitride film, the holding temperature of the phosphoric acid solution is preferably -20 to 30 ° C, which is approximately 0 to 10 ° C lower than the saturation temperature.

Phosphoric acid seed crystals are then introduced into the dura melt crystallizer. The reason why phosphate seed crystals are introduced in the separation and recovery of ultra-high purity phosphoric acid from semiconductor waste etching solution is that it is difficult to induce spontaneous nucleation due to various metal impurities, salts and high viscosity at low temperature which constitute silicon wafer. Because. Therefore, the amount of phosphate seed crystals is preferably 1 to 10% by weight with respect to the waste etching solution due to the suppression of secondary nucleation which induces spontaneous nucleation and rapid formation of microcrystals, causing separation problems with the residual liquid. .

In addition, the shape and particle size range of the phosphate seed crystal are preferably needle-shaped crystals having an average particle diameter of 0.1 to 3 mm. The phosphate seed crystals thus injected induce nucleation and crystal growth in the duramelt crystallizer to form acicular phosphate crystal layers. After the seed phosphate seed crystal is charged, the phosphoric acid crystal layer is formed by cooling to -40 to -20 ° C at a rate of 0.1 to 10 K / min. In general, when the cooling rate is high in species crystallization, the formation of crystal layers containing a large amount of impurities occurs by mass formation and aggregation of very small small crystals, and when the cooling rate is slow, the crystal growth rate and nucleation rate are slowed down. Can be produced, but in terms of economy, relatively low yields are a problem. Therefore, it is desirable to determine the cooling rate in a range where the two points can be compromised.

In step 2), the grown phosphate crystal layer is separated from the residual liquid by the density difference, and the phosphate crystal layer is partially melted and purified to 0 to 40 ° C. at a heating rate of 0.01 to 10 K / min. Dissolve and recover ultra-high purity phosphoric acid.

Partial sweating is the removal of impurities in the crystals and the residual liquid by partially melting the crystal surface to which the residual liquid adheres. The partial melting temperature of the crystal is set to 0 to 40 ° C., which is a range as high as 0 to 10 ° C. from the concentration of the phosphate crystal recovered and the phase equilibrium phosphoric acid melting point data. In the case where impurities are mainly present on the crystal surface, as the difference between the partial melting temperature and the melting temperature of the produced crystal becomes larger under similar crystal layer formation conditions, the removal efficiency of the impurity becomes higher.

The heating rate during partial melting is closely related to the structure of the resulting phosphoric acid crystal layer and the rate of impurity movement in the crystal layer. In other words, under fast cooling conditions, the crystal layer shows very poor shape of porosity and high impurity content. In this case, when the partial melting operation is performed at a high heating rate, a high purity improvement effect of the resulting crystal layer can be expected. In the present invention, it is preferable to set the heating rate in the range of 0.01 to 10 K / min in consideration of the partial melting amount, the impurity content and the yield. The remaining mother liquor, which has undergone partial melting and dura-crystallization, is recovered and recycled as a feed.

Therefore, the method of separating and recovering high-purity phosphoric acid from the semiconductor waste etching solution according to the present invention is a simple process without a special device or operation, and is a waste etching solution recycling method without the use of additives and solvents. It can be recycled to ceramic alumina etching solution, semiconductor etching solution, inorganic salt phosphate production, medicines, analytical reagents, etc.

Hereinafter, the present invention will be described in more detail based on the following examples and comparative examples, but the present invention is not limited thereto.

Example 1

500 g of semiconductor waste etching solution containing phosphoric acid (68% by weight) was maintained at -5 ° C in a duramelt crystallizer, and then 4% by weight of phosphoric acid seed crystal having an average particle diameter of 0.5 mm was added to the waste etching solution. It was. After adding the phosphate seed crystals, the mixture was cooled to −15 ° C. at a cooling rate of 1 K / min. Phosphoric acid species crystallization led to nucleation and crystal growth, forming a phosphate crystal layer. The residual liquid and the phosphate crystal layer were separated by a density difference after 2 hours. The amount of the obtained phosphoric acid crystal layer was 350 g. The phosphoric acid crystal layer was melted to 30 ° C. at a heating rate of 0.5 K / min to separate and recover ultra high purity phosphoric acid. The residue was also recycled and used as feed. The amount of the phosphate crystal layer obtained after the partial melting operation is 306 g. The concentration of recovered ultra high purity phosphoric acid and the content of metal impurities are shown in Tables 2 and 3 below.

Example 2

Under the same conditions as in Example 1, the cooling temperature was changed to -30 ° C. The amount of the phosphate crystal layer prepared was 382.02 g. The amount of the phosphate crystal layer recovered through the partial melting operation is 321.5 g. The concentration of recovered ultra high purity phosphoric acid and the content of metal impurities are shown in Tables 2 and 3 below.

Example 3

Under the same conditions as in Example 1, the heating rate for partial melting of the phosphoric acid crystal layer was changed to 10 K / min. The amount of the phosphate crystal layer prepared was 376.9 g. The amount of the phosphate crystal layer recovered through the partial melting operation is 263.82 g. The concentration of recovered ultra high purity phosphoric acid and the content of metal impurities are shown in Tables 2 and 3 below.

Comparative Example 1

Phosphoric acid seed crystals were not inoculated under the same conditions as in Example 1. The amount of phosphate crystal layer recovered was 390.8 g. The amount of the phosphate crystal layer recovered through the partial melting operation is 312.6 g. The concentration of recovered ultra high purity phosphoric acid and the content of metal impurities are shown in Tables 2 and 3 below.

Metal Content of Ultra-Pure Phosphoric Acid Recovered (Unit: ppb) Metallic impurities Example 1 Example 2 Example 3 Comparative Example 1 Al 5.51 11.6 1.65 232.4 As 4.29 10.2 1.3 431 Ca 5.07 11.1 1.52 321.7 CD 44.61 59 13.4 35.7 Cu 16.94 25.33 5.1 20.6 Fe 0.57 5.7 0 506.6 K 15.40 23.5 4.6 113.7 Li 11.11 18.3 3.3 29.6 Na 32.73 44.28 9.82 3650.7 Ni 6.05 12.3 1.82 8.5 Pb 7.65 14.2 2.3 24 Si 21.83 73.4 15.9 1170.6 Sn 5.46 11.6 1.64 23.5 Mo 1.53 6.84 0 136.7

Recovered ultra high purity phosphoric acid concentration (unit: wt%) ingredient Example 1 Example 2 Example 3 Comparative Example 1 Phosphoric Acid 88.81 89 90.21 87 moisture 12.19 11 9.79 13

As described above, the ultrapure phosphoric acid separation and recovery method of the ultra-high purity phosphoric acid from the semiconductor waste etching solution according to the present invention is performed by a film-melt crystallization operation for forming a crystal layer on the cooling surface, and the resulting crystal layer is partially melted and purified to obtain ultrapure phosphoric acid. Can be separated and recovered. In addition, the ultra-high purity phosphoric acid obtained in the present invention can be recycled as a metal aluminum etching solution, alumina etching solution for ceramics, inorganic phosphate production, food, medicine, analytical reagents. In addition, by presenting an efficient recycling method of the etching liquid discharged in a large amount of semiconductor process, various positive effects such as reducing the consignment processing cost, utilization of waste resources, prevention of environmental pollution are expected.

1 is a schematic diagram showing a process of separating and recovering ultrahigh purity phosphoric acid from a semiconductor waste etching solution.

Claims (2)

1) After the waste etching solution discharged from the silicon nitride film (Si ₃ N ₄ ) etching process of the silicon wafer is maintained at -20 to 30 ° C, phosphoric acid seed crystals are inoculated, and the waste etching solution is 0.1 to 10 K /. cooling to −40 to 20 ° C. at a cooling rate of min to form a phosphate crystal layer; And 2) A purification step of partially melting the phosphate crystal layer to 0 to 40 ℃ at a rate of 0.01 to 10 K / min to remove impurities contained in the crystal layer Separation and recovery method of ultra-high purity phosphoric acid from semiconductor waste etching liquid comprising a. The ultra-pure phosphoric acid separation and recovery of claim 1, wherein the seed crystal is a needle-shaped crystal having a thickness of 0.1 to 3 mm, and is added in a range of 1 to 10% by weight based on the waste etching solution. Way