CN110373719B - High-selectivity polysilicon etching solution and preparation method thereof - Google Patents

High-selectivity polysilicon etching solution and preparation method thereof Download PDF

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CN110373719B
CN110373719B CN201910744727.3A CN201910744727A CN110373719B CN 110373719 B CN110373719 B CN 110373719B CN 201910744727 A CN201910744727 A CN 201910744727A CN 110373719 B CN110373719 B CN 110373719B
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nitroxyl
etching
acid
polysilicon
acetic acid
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CN110373719A (en
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李少平
万杨阳
贺兆波
张庭
尹印
张演哲
冯凯
王书萍
蔡步林
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Hubei Xingfu Electronic Materials Co ltd
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Hubei Sinophorus Electronic Materials Co ltd
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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/02—Elements
    • C30B29/06—Silicon
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B33/00—After-treatment of single crystals or homogeneous polycrystalline material with defined structure
    • C30B33/08—Etching
    • C30B33/10—Etching in solutions or melts

Abstract

The invention relates to a polysilicon etching liquid with high selectivity ratio and a preparation method thereof. The polysilicon etching liquid consists of nitric acid, nitroxyl ionic salt, organic alkali hydrofluoride, acetic acid and deionized water. By controlling the addition amount and the sequence of the components, deionized water, nitric acid and acetic acid are added according to the mass ratio, the organic base hydrofluoride is added after the mixture is uniformly stirred, and finally the nitroxyl ionic salt is added. In the etching solution, nitric acid is used as a main oxidant, nitroxyl ion salt is used as an auxiliary oxidant, nitroxyl ions are generated by decomposition in an acidic environment, the nitroxyl ions have strong oxidizing property, the oxidation rate of the nitroxyl ions to polysilicon is improved, hydrofluoric acid is slowly released by organic base hydrofluoride, silicon oxide is dissolved, the mass transfer resistance of the hydrofluoric acid is increased due to the steric hindrance of organic base groups, and the corrosion rate of the hydrofluoric acid to silicon dioxide is reduced. The polysilicon etching liquid can greatly meet the requirement of high selection ratio in the process, and can also ensure the stability of the etching rate of the etching liquid.

Description

High-selectivity polysilicon etching solution and preparation method thereof
Technical Field
The invention belongs to the technical field of wet electronic chemicals and TFT display manufacturing intersection, and particularly relates to a polycrystalline silicon selective etching solution and a using process thereof.
Background
In the manufacture of TFT display, its main structure is composed of metal gate layer, gate insulating layer (silicon dioxide or silicon nitride), active layer (amorphous silicon layer and polysilicon layer), n+Amorphous silicon layer, source electrode, drain electrode, imageElement electrode, silicon nitride protective layer. As the core layer active layer of the TFT, the mobility of the carrier of polycrystalline silicon is higher than that of amorphous silicon, and the mobility is generally 200cm2.v.s-1The mobility of 600cm can be obtained by adopting a special technology2.v.s-1P-Si-TFT of (1). Compared with amorphous silicon (a-Si) -TFT, the resolution is high, the response speed is fast, the function is stronger, and the cost is lower. Therefore, research on the polysilicon TFT production technology becomes an industrial hotspot. The pattern of the polysilicon active layer is determined by utilizing a photoetching technology, the Poly layer is etched cleanly by utilizing a wet etching technology without residue, and the silicon oxide gate insulating substrate layer is not etched as far as possible. The existing wet etching technology has low selectivity, which causes over-etching of the silicon dioxide layer of the substrate and influences the electrical characteristics of the TFT.
Therefore, the development of the polysilicon etching solution with high selectivity ratio accelerates the etching rate of the polysilicon layer, shortens the time of the process procedure, effectively saves the production cost, ensures no residue in the etching of the polysilicon layer, and reduces the damage to the silicon dioxide layer of the substrate.
Disclosure of Invention
In view of the above, an object of the present invention is to provide a polysilicon etching solution with a high selectivity ratio. The etching rate of the polysilicon layer is accelerated, the process time is shortened, and the cost is saved; the etching rate of the silicon dioxide layer of the substrate is reduced, thereby reducing damage to the substrate.
The second purpose of the invention is to provide a preparation method of the polysilicon etching solution with high selectivity ratio.
In order to achieve the aim, the technical scheme of the invention provides the polycrystalline silicon etching liquid with the high selection ratio, and the polycrystalline silicon etching liquid with the high selection ratio consists of nitric acid, nitroxyl ionic salt, organic base hydrofluoride, acetic acid and deionized water.
The nitric acid is electronic grade nitric acid, and the concentration of the nitric acid is 70-75%;
the acetic acid is electronic grade acetic acid, and the concentration is more than 99.95%;
the nitroxyl ionic salt is of high-grade purity, and the content is more than or equal to 99 percent;
the organic alkali hydrofluoride is super-pure, and the content is more than or equal to 97 percent;
the water is ultrapure water with the resistivity of 18M omega cm (25 ℃).
Wherein, the weight content of nitric acid in the polysilicon etching is 60-70%; the weight content of the acetic acid is 0.5 to 5 percent; the weight content of the nitroxyl ionic salt is 0.05-1%; the weight content of the organic alkali hydrofluoride is 3-10 percent; the weight content of the deionized water is the balance.
Wherein the weight content of the nitric acid in the polysilicon etching solution is 65 percent; the weight content of the acetic acid is 0.8 to 1.2 percent; the weight content of the nitroxyl ionic salt is 0.2 to 0.5 percent; the weight content of the organic alkali hydrofluoride is 4-8 percent; the weight content of the deionized water is the balance.
Wherein the nitroxyl ionic salt in the polysilicon etching liquid comprises at least one of tetrafluoroborate nitroxyl cation, hexafluorophosphate nitroxyl cation, acetic acid nitroxyl, ammonium dinitramide, nitroxyl chloride and fluorinated nitroxyl. And preferably a tetrafluoroborate nitroxyl cation, a hexafluorophosphate nitroxyl cation.
Wherein the organic alkali hydrofluoride in the polysilicon etching liquid comprises at least one of triethylamine trihydrofluoride, tetraethylammonium fluoride tetrahydrofluoride, tetraethylammonium fluoride trihydrofluoride, pyridine hydrofluoride and N, N-diisopropylethylamine trihydrofluoride.
The technical scheme of the invention also provides a preparation method of the polycrystalline silicon etching liquid with high selectivity ratio, which comprises the following steps:
adding ultrapure water into a container, adding nitric acid into the ultrapure water by using a circulating pump, adding acetic acid into the solution, fully mixing uniformly, adding organic base hydrofluoride, stirring while adding, finally adding nitroxyl ionic salt, dissolving and stirring uniformly, and then circularly mixing uniformly between the two containers by using the circulating pump to obtain the polycrystalline silicon etching solution.
In the preferred scheme, a certain amount of ultrapure water is added into a container, nitric acid with a certain mass is slowly pumped into the ultrapure water by using a circulating pump, acetic acid with a certain mass is slowly pumped into the solution, the solution is circulated between the two containers for 8 times by using the circulating pump after the addition is finished, organic base hydrofluoride with a certain mass is added after the solution is fully and uniformly mixed, stirring is carried out while adding, finally, nitroxyl ionic salt with a certain mass is added, and the polycrystalline silicon etching solution is obtained after the solution is dissolved and uniformly stirred.
Wherein, the IBC ton bucket that the container is HDPE, pipeline, agitator material are in PFA or PTFE, and the circulating pump is fluoroplastics acidproof alkali pump.
The invention has the advantages of
The invention has the advantages and beneficial effects that: in the invention, nitroxyl ion salt is taken as pro-oxidant, nitroxyl ion generated by decomposition in strong acid environment with pH less than 1, nitrogen in linear nitroxyl ion is positively charged, the bond length is shorter than that of general N-O bond, and the nitrogen tends to attack rich electrons, and NO is added2 +Stronger electron-capturing capability can be obtained through bending deformation, so that the oxidation rate of the polycrystalline silicon is improved. The organic base hydrofluoride slowly releases hydrofluoric acid to dissolve silicon oxide, the mass transfer resistance of the hydrofluoric acid is increased due to the steric hindrance of organic base groups, intermolecular hydrogen bonds are easily formed between the organic base hydrofluoride and anion groups in the nitroxyl ion salt, and the ionization of the hydrofluoric acid is synergistically reduced, so that the corrosion rate of the hydrofluoric acid on silicon dioxide is reduced. And the content of acetic acid is optimized, the etching rate of the acetic acid to the silicon dioxide layer of the substrate is reduced, and the polysilicon etching solution with high selectivity ratio is formed. Meanwhile, the manufacturing cost is considered, the using process is optimized, and the cost is saved for process replacement while the stable etching rate and the optimal etching surface are obtained.
Drawings
FIG. 1 is a graph showing the effect of acetic acid content on etch rate of example 3.
FIG. 2 is a graph showing the effect of acetic acid content on the Poly/Oxide selectivity of example 3.
FIG. 3 is a graph showing the effect of example 5 on a silicon wafer having a two-layer structure after etching.
FIG. 4 is a graph showing the effect of comparative example 1 on a silicon wafer having a two-layer structure after etching.
Detailed Description
For a better understanding of the present invention, the present invention is further described in detail below with reference to the following figures and examples, but the scope of the present invention is not limited to the following examples.
Example 1
Embodiment 1 provides a polysilicon etching solution, a preparation process thereof and an etching result, and specifically comprises the following steps:
the mass fraction of nitric acid used is 70%, the mass fraction of acetic acid is 99.95%, triethylamine trihydrofluoride is super pure, the content is not less than 97%, the content of tetrafluoroborate nitroxyl cation is super pure, the content is not less than 99%, and water is ultrapure water with the resistivity of 18M omega cm (25 ℃).
500kg of polysilicon etching solution is prepared by using the raw materials, 65 percent of nitric acid, 3 percent of acetic acid, 4 percent of triethylamine trihydrofluoride salt and 0.3 percent of tetrafluoroboric acid nitroxyl cation by weight content are prepared according to the weight content, and the balance is deionized water.
The preparation process comprises the following steps:
1) adding a certain amount of ultrapure water into an IBC ton barrel of HDPE;
2) slowly pumping nitric acid with certain mass into the ultrapure water by using an acid-alkali-resistant circulating pump;
3) slowly pumping acetic acid with a certain mass into the solution by using an acid-alkali resistant circulating pump;
4) after fully and uniformly mixing, adding triethylamine trihydrofluoride with certain mass, and stirring by using a stirring rod while adding;
5) after fully and uniformly mixing, slowly adding a certain mass of tetrafluoroborate nitroxyl cation, and dissolving and uniformly stirring;
6) and after the addition is finished, circulating for 8 times between the two containers by using an acid-base resistant circulating pump to fully and uniformly mix the two containers to obtain the polysilicon etching solution.
The prepared polysilicon etching solution is used for etching a silicon wafer with a double-layer structure at 23 ℃, wherein the first layer is a 250nm silicon dioxide layer, and the second layer is a 400nm polysilicon layer. The etching mode is rotary spray etching, the first etching is carried out for 3s, the thickness of different layers before and after etching is recorded by an ellipsometer, the etching is continued for 7s, the thickness of different layers before and after etching is recorded by the ellipsometer, and the etching rate are calculatedEtch selectivity ratio, SiO2Layer etching rate ═ H3-H4)/t2Poly layer etch rate H1/[(t1-(H2-H3)*t2/(H3-H4)],
H1Thickness of the polysilicon layer before reaction, H2Thickness of the pre-reaction silicon dioxide layer, H3Thickness of silicon dioxide after the first etching, H4Is the thickness of the silicon dioxide layer after the second etching, t1Time of the first etching reaction, t2The time for the second etching reaction. And the calculation results are recorded in table 1.
Example 2
Embodiment 2 provides a polysilicon etching solution, a preparation process thereof and an etching result, and specifically comprises the following steps:
the mass fraction of nitric acid used is 70%, the mass fraction of acetic acid is 99.95%, tetraethylammonium fluoride tetrahydrofluoride is super-pure, the content is not less than 97%, the content of hexafluorophosphate nitroxyl cation is super-pure, the content is not less than 99%, and water is ultrapure water with the resistivity of 18M omega cm (25 ℃).
500kg of polysilicon etching solution is prepared by using the raw materials, 65 percent of nitric acid, 3 percent of acetic acid, 4.36 percent of tetraethyl ammonium fluoride tetrahydrofluoride and 0.46 percent of hexafluorophosphate nitroxyl cation are prepared according to the weight content, and the balance is deionized water.
The preparation process comprises the following steps:
1) adding a certain amount of ultrapure water into an IBC ton barrel of HDPE;
2) slowly pumping nitric acid with certain mass into the ultrapure water by using an acid-alkali-resistant circulating pump;
3) slowly pumping acetic acid with a certain mass into the solution by using an acid-alkali resistant circulating pump;
4) fully and uniformly mixing, adding a certain mass of tetraethylammonium fluoride tetrahydrofluoride, and stirring by using a stirring rod while adding;
5) after fully and uniformly mixing, slowly adding a certain mass of hexafluorophosphoric acid nitroxyl cation, and dissolving and uniformly stirring;
6) and after the addition is finished, circulating for 8 times between the two containers by using an acid-base resistant circulating pump to fully and uniformly mix the two containers to obtain the polysilicon etching solution.
The prepared polysilicon etching solution is used for etching a silicon wafer with a double-layer structure at 23 ℃, wherein the first layer is a 250nm silicon dioxide layer, and the second layer is a 400nm polysilicon layer. The etching mode is rotating spray etching, the first etching is carried out for 3s, the ellipsometer is used for recording the thicknesses of different layers before and after etching, the etching is continued for 7s, the ellipsometer is used for recording the thicknesses of different layers before and after etching, and the etching rate, the etching selection ratio and the SiO2Layer etching rate ═ H3-H4)/t2Poly layer etch rate H1/[(t1-(H2-H3)*t2/(H3-H4)],
H1Thickness of the polysilicon layer before reaction, H2Thickness of the pre-reaction silicon dioxide layer, H3Thickness of silicon dioxide after the first etching, H4Is the thickness of the silicon dioxide layer after the second etching, t1Time of the first etching reaction, t2The time for the second etching reaction. And the calculation results are recorded in table 1.
Example 3
Embodiment 3 provides a polysilicon etching solution, a preparation process thereof and an etching result, and specifically comprises the following steps:
the mass fraction of nitric acid used is 70%, the mass fraction of acetic acid is 99.95%, triethylamine trihydrofluoride is super pure, the content is not less than 97%, the content of tetrafluoroborate nitroxyl cation is super pure, the content is not less than 99%, and water is ultrapure water with the resistivity of 18M omega cm (25 ℃).
The raw materials are used for preparing a series of 500kg of polysilicon etching liquid with different acetic acid contents, 65% of nitric acid, 4% of triethylamine trihydrofluoride and 0.28% of tetrafluoroboric acid nitroxyl cation by weight are prepared, the acetic acid with different contents of 0%, 0.5%, 1%, 2%, 2.5% and 2.7% are respectively added under the premise of keeping the contents of other components unchanged, and the weight content of deionized water is the balance.
The preparation process comprises the following steps:
1) adding a certain amount of ultrapure water into an IBC ton barrel of HDPE;
2) slowly pumping nitric acid with certain mass into the ultrapure water by using an acid-alkali-resistant circulating pump;
3) slowly pumping acetic acid with a certain mass into the solution by using an acid-alkali resistant circulating pump;
4) after fully and uniformly mixing, adding triethylamine trihydrofluoride with certain mass, and stirring by using a stirring rod while adding;
5) after fully and uniformly mixing, slowly adding a certain mass of tetrafluoroborate nitroxyl cation, and dissolving and uniformly stirring;
6) and after the addition is finished, circulating for 8 times between the two containers by using an acid-base resistant circulating pump to fully and uniformly mix the two containers to obtain the polysilicon etching solution.
The prepared polysilicon etching solution is used for etching a silicon wafer with a double-layer structure at 23 ℃, wherein the first layer is a 250nm silicon dioxide layer, and the second layer is a 400nm polysilicon layer. The etching mode is rotating spray etching, the first etching is carried out for 3s, the ellipsometer is used for recording the thicknesses of different layers before and after etching, the etching is continued for 7s, the ellipsometer is used for recording the thicknesses of different layers before and after etching, and the etching rate, the etching selection ratio and the SiO2Layer etching rate ═ H3-H4)/t2Poly layer etch rate H1/[(t1-(H2-H3)*t2/(H3-H4),
H1Thickness of the polysilicon layer before reaction, H2Thickness of the pre-reaction silicon dioxide layer, H3Thickness of silicon dioxide after the first etching, H4Is the thickness of the silicon dioxide layer after the second etching, t1Time of the first etching reaction, t2The time for the second etching reaction. The influence of the change in the acetic acid content on the etching rate and selectivity is shown in fig. 1 and 2.
Example 4
Embodiment 4 provides a polysilicon etching solution, a preparation process thereof and an etching result, and specifically includes:
the mass fraction of nitric acid used is 70%, the mass fraction of acetic acid is 99.95%, the pyridine hydrofluoride is super pure, the content is more than or equal to 97%, the content of the tetrafluoroborate nitroxyl cation is super pure, the content is more than or equal to 99%, and the water is ultrapure water with the resistivity of 18M omega cm (25 ℃).
500kg of polysilicon etching solution is prepared by using the raw materials, 65 percent of nitric acid, 1 percent of acetic acid mixed solution, 7.53 percent of pyridine hydrofluoride, 0.28 percent of tetrafluoroborate nitroxyl cation and the balance of deionized water by weight content.
The preparation process comprises the following steps:
1) adding a certain amount of ultrapure water into an IBC ton barrel of HDPE;
2) slowly pumping nitric acid with certain mass into the ultrapure water by using an acid-alkali-resistant circulating pump;
3) slowly pumping acetic acid with a certain mass into the solution by using an acid-alkali resistant circulating pump;
4) after fully and uniformly mixing, adding a certain mass of pyridine hydrofluoride, and stirring by using a stirring rod while adding;
5) after fully and uniformly mixing, slowly adding a certain mass of tetrafluoroborate nitroxyl cation, and dissolving and uniformly stirring;
6) and after the addition is finished, circulating for 8 times between the two containers by using an acid-base resistant circulating pump to fully and uniformly mix the two containers to obtain the polysilicon etching solution.
The prepared polysilicon etching solution is used for etching a silicon wafer with a double-layer structure at 23 ℃, wherein the first layer is a 250nm silicon dioxide layer, and the second layer is a 400nm polysilicon layer. The etching mode is rotating spray etching, the first etching is carried out for 3s, the ellipsometer is used for recording the thicknesses of different layers before and after etching, the etching is continued for 7s, the ellipsometer is used for recording the thicknesses of different layers before and after etching, and the etching rate, the etching selection ratio and the SiO2Layer etching rate ═ H3-H4)/t2Poly layer etch rate H1/[(t1-(H2-H3)*t2/(H3-H4)],
H1Thickness of the polysilicon layer before reaction, H2Thickness of the pre-reaction silicon dioxide layer, H3For the first etchingThickness of the post-silicon dioxide, H4Is the thickness of the silicon dioxide layer after the second etching, t1Time of the first etching reaction, t2The time for the second etching reaction. And the calculation results are recorded in table 1.
Example 5
Embodiment 5 provides a polysilicon etching solution, a preparation process thereof and an etching result, specifically comprising:
the mass fraction of nitric acid used is 70%, the mass fraction of acetic acid is 99.95%, triethylamine trihydrofluoride is super pure, the content is not less than 97%, the content of tetrafluoroborate nitroxyl cation is super pure, the content is not less than 99%, and water is ultrapure water with the resistivity of 18M omega cm (25 ℃).
500kg of polysilicon etching solution is prepared by using the raw materials, 65 percent of nitric acid, 1 percent of acetic acid mixed solution, 4 percent of triethylamine trihydrofluoride, 0.28 percent of tetrafluoroborate nitroxyl cation and the balance of deionized water by weight content.
The preparation process comprises the following steps:
1) adding a certain amount of ultrapure water into an IBC ton barrel of HDPE;
2) slowly pumping nitric acid with certain mass into the ultrapure water by using an acid-alkali-resistant circulating pump;
3) slowly pumping acetic acid with a certain mass into the solution by using an acid-alkali resistant circulating pump;
4) after fully and uniformly mixing, adding a certain mass of pyridine hydrofluoride, and stirring by using a stirring rod while adding;
5) after fully and uniformly mixing, slowly adding a certain mass of tetrafluoroborate nitroxyl cation, and dissolving and uniformly stirring;
6) and after the addition is finished, circulating for 8 times between the two containers by using an acid-base resistant circulating pump to fully and uniformly mix the two containers to obtain the polysilicon etching solution.
The prepared polysilicon etching solution is used for etching a silicon wafer with a double-layer structure at 23 ℃, wherein the first layer is a 250nm silicon dioxide layer, and the second layer is a 400nm polysilicon layer. The etching method is rotary spray etching, the first etching is carried out for 3s, and an ellipsometer is used for recording the thicknesses of different layers before and after etchingEtching is continued for 7s, the thickness of different layers before and after etching is recorded by an ellipsometer, and the etching rate, the etching selectivity and SiO are calculated2Layer etching rate ═ H3-H4)/t2Poly layer etch rate H1/[(t1-(H2-H3)*t2/(H3-H4)],
H1Thickness of the polysilicon layer before reaction, H2Thickness of the pre-reaction silicon dioxide layer, H3Thickness of silicon dioxide after the first etching, H4Is the thickness of the silicon dioxide layer after the second etching, t1Time of the first etching reaction, t2The time for the second etching reaction. And the calculation results are recorded in table 1. The surface after the first etching is clean, mirror-like and residue-free, as shown in fig. 3.
Comparative example 1:
comparative example 1 provides a polysilicon etching solution, a preparation process thereof and an etching result, and specifically comprises the following steps:
the nitric acid used was 70% by mass, the hydrofluoric acid 50% by mass, the acetic acid 99.95% by mass, and the water was ultrapure water having a resistivity of 18M Ω cm (25 ℃).
500kg of polycrystalline silicon etching solution is prepared by using the raw materials, a mixed solution of 65% nitric acid, 1.6% hydrofluoric acid and 5% acetic acid is prepared according to the weight content, and the weight content of deionized water is the balance.
The preparation process comprises the following steps:
1) adding a certain amount of ultrapure water into an IBC ton barrel of HDPE;
2) slowly pumping nitric acid with certain mass into the ultrapure water by using an acid-alkali-resistant circulating pump;
3) slowly pumping acetic acid with a certain mass into the solution by using an acid-alkali resistant circulating pump;
4) slowly pumping hydrofluoric acid with a certain mass into the solution by using an acid-alkali resistant circulating pump;
5) after the addition is finished, the acid and alkali resistant circulating pump is utilized to circulate between the two containers for 8 times to ensure that the materials are fully and uniformly mixed;
mixing the aboveThe prepared polysilicon etching solution is used for etching a silicon wafer with a double-layer structure at 23 ℃, wherein the first layer is a 250nm silicon dioxide layer, and the second layer is a 400nm polysilicon layer. The etching mode is rotating spray etching, the first etching is carried out for 3s, the ellipsometer is used for recording the thicknesses of different layers before and after etching, the etching is continued for 7s, the ellipsometer is used for recording the thicknesses of different layers before and after etching, and the etching rate, the etching selection ratio and the SiO2Layer etching rate ═ H3-H4)/t2Poly layer etch rate H1/[(t1-(H2-H3)*t2/(H3-H4)],
H1Thickness of the polysilicon layer before reaction, H2Thickness of the pre-reaction silicon dioxide layer, H3Thickness of silicon dioxide after the first etching, H4Is the thickness of the silicon dioxide layer after the second etching, t1Time of the first etching reaction, t2The time for the second etching reaction. And the calculation results are recorded in table 1. The surface after the first etching is engraved with patterns, and brown polysilicon residues appear on the edge, as shown in fig. 4;
comparative example 2
The comparative example 2 provides a polysilicon etching solution, a preparation process and an etching result thereof, and specifically comprises the following steps:
the mass fraction of nitric acid used is 70%, the mass fraction of hydrofluoric acid is 50%, the mass fraction of acetic acid is 99.95%, the mass fraction of nitroboric acid salt is superior pure, the content is not less than 99%, and water is ultrapure water with the resistivity of 18M omega cm (25 ℃).
500kg of polycrystalline silicon etching solution is prepared by using the raw materials, and a mixed solution of 65% of nitric acid, 1.6% of hydrofluoric acid, 3% of acetic acid, 0.28% of nitroxyl cation salt of tetrafluoroborate and the balance of deionized water are prepared according to the weight content.
The preparation process comprises the following steps:
1) adding a certain amount of ultrapure water into an IBC ton barrel of HDPE;
2) slowly pumping nitric acid with certain mass into the ultrapure water by using an acid-alkali-resistant circulating pump;
3) slowly pumping acetic acid with a certain mass into the solution by using an acid-alkali resistant circulating pump;
4) slowly pumping hydrofluoric acid with a certain mass into the solution by using an acid-alkali resistant circulating pump;
5) after fully and uniformly mixing, slowly adding a certain mass of tetrafluoroborate nitroxyl cation salt, and dissolving and uniformly stirring;
6) and after the addition is finished, circulating for 8 times between the two containers by using an acid-base resistant circulating pump to fully and uniformly mix the two containers to obtain the polysilicon etching solution.
The prepared polysilicon etching solution is used for etching a silicon wafer with a double-layer structure at 23 ℃, wherein the first layer is a 250nm silicon dioxide layer, and the second layer is a 400nm polysilicon layer. The etching mode is rotating spray etching, the first etching is carried out for 3s, the ellipsometer is used for recording the thicknesses of different layers before and after etching, the etching is continued for 7s, the ellipsometer is used for recording the thicknesses of different layers before and after etching, and the etching rate, the etching selection ratio and the SiO2Layer etching rate ═ H3-H4)/t2Poly layer etch rate H1/[(t1-(H2-H3)*t2/(H3-H4)],
H1Thickness of the polysilicon layer before reaction, H2Thickness of the pre-reaction silicon dioxide layer, H3Thickness of silicon dioxide after the first etching, H4Is the thickness of the silicon dioxide layer after the second etching, t1Time of the first etching reaction, t2The time for the second etching reaction. And the calculation results are recorded in table 1.
Comparative example 3
The comparative example 3 provides a polysilicon etching solution, a preparation process and an etching result thereof, and specifically comprises the following steps:
the mass fraction of nitric acid used is 70%, the mass fraction of acetic acid is 99.95%, triethylamine trihydrofluoride is super pure, the content is more than or equal to 97%, and water is ultrapure water with the resistivity of 18M omega cm (25 ℃).
500kg of polysilicon etching solution is prepared by using the raw materials, 65 percent of nitric acid, 3 percent of acetic acid mixed solution, 4 percent of triethylamine trihydrofluoride and the balance of deionized water by weight content are prepared according to the weight content.
The preparation process comprises the following steps:
1) adding a certain amount of ultrapure water into an IBC ton barrel of HDPE;
2) slowly pumping nitric acid with certain mass into the ultrapure water by using an acid-alkali-resistant circulating pump;
3) slowly pumping acetic acid with a certain mass into the solution by using an acid-alkali resistant circulating pump;
4) after fully and uniformly mixing, adding triethylamine trihydrofluoride with certain mass, and stirring by using a stirring rod while adding;
5) and after the addition is finished, circulating for 8 times between the two containers by using an acid-base resistant circulating pump to fully and uniformly mix the two containers to obtain the polysilicon etching solution.
The prepared polysilicon etching solution is used for etching a silicon wafer with a double-layer structure at 23 ℃, wherein the first layer is a 250nm silicon dioxide layer, and the second layer is a 400nm polysilicon layer. The etching mode is rotating spray etching, the first etching is carried out for 3s, the ellipsometer is used for recording the thicknesses of different layers before and after etching, the etching is continued for 7s, the ellipsometer is used for recording the thicknesses of different layers before and after etching, and the etching rate, the etching selection ratio and the SiO2Layer etching rate ═ H3-H4)/t2Poly layer etch rate H1/[(t1-(H2-H3)*t2/(H3-H4)],
H1Thickness of the polysilicon layer before reaction, H2Thickness of the pre-reaction silicon dioxide layer, H3Thickness of silicon dioxide after the first etching, H4Is the thickness of the silicon dioxide layer after the second etching, t1Time of the first etching reaction, t2The time for the second etching reaction. And the calculation results are recorded in table 1.
As can be seen from the experimental data in Table 1, by comparing comparative example 2 with comparative example 1, in which a nitroxyl ion salt is added and generated by decomposition in a strongly acidic environment having a pH of < 1, the nitrogen band in a linear nitroxyl cation is positiveThe bond length of the carbon is shorter than that of the general N-O bond, and the carbon tends to attack rich electrons, and NO is added2 +Stronger electron-capturing capability can be obtained through bending deformation, so that the oxidation rate of the polycrystalline silicon is improved. Comparing the comparative example 3 with the comparative example 1, the hydrofluoric acid is replaced by the organic base hydrofluoride, the hydrofluoric acid is slowly released, the mass transfer resistance of the hydrofluoric acid is increased due to the steric hindrance of the organic base group, the dissolving speed of the hydrofluoric acid is reduced, and the corrosion rate of the hydrofluoric acid on silicon dioxide is reduced. In examples 1 and 2, the fluorine hydrogen bond in the organic base hydrofluoride and the fluorine in the anion group tetrafluoroborate or hexafluorophosphate in the nitroxyl ion salt form an intermolecular hydrogen bond, and the ionization of hydrofluoric acid is reduced by the synergistic effect, so that the corrosion rate of the hydrofluoric acid on silicon dioxide is reduced. In embodiment 3, the content of acetic acid is optimized, the acetic acid can dilute the concentration of the reaction substance, and the higher insulating constant of the acetic acid replaces water with a lower insulating constant, so that the ionization degree of nitric acid is reduced, the dissolution of nitric acid is reduced, and the oxidation reaction speed is reduced, but the acetic acid can reduce the mass transfer resistance of the etching solution at the same time, so that hydrofluoric acid is easier to diffuse to the surface of the silicon wafer, and the etching rate is obviously increased, therefore, a dynamic balance exists in the etching system, as shown in fig. 1 and 2, as the content of acetic acid is increased, the etching rate of polysilicon is increased first and then decreased, the etching rate of silicon dioxide is decreased first and then increased, when the content of acetic acid is 1%, the etching rate of polysilicon is the largest, the etching rate of silicon dioxide is the lowest, and the. Therefore, the optimized content of the acetic acid not only reduces the etching rate of the acetic acid to the silicon dioxide layer of the substrate, but also improves the oxidation rate of the acetic acid to the polysilicon to form the polysilicon etching solution with high selection ratio.
Table 1 experimental results obtained by conducting an etching experiment for examples 1 to 5 and comparative examples 1 to 3.
Figure GDA0002169905480000101

Claims (4)

1. A polysilicon etching solution with high selectivity ratio is characterized in that: the high-selectivity ratio polysilicon etching solution
Consists of nitric acid, nitroxyl substances, organic alkali hydrofluoride, acetic acid and water;
the nitric acid is electronic grade nitric acid, and the concentration of the nitric acid is 70-75%;
the acetic acid is electronic grade acetic acid, and the concentration is more than 99.95%;
the nitroxyl substance is super-pure, and the content is more than or equal to 99 percent;
the organic alkali hydrofluoride is super-pure, and the content is more than or equal to 97 percent;
the water is ultrapure water with the resistivity of 18M omega cm at the temperature of 25 ℃;
the nitroxyl substance in the polysilicon etching liquid is at least one of tetrafluoroboric acid nitroxyl cation, hexafluorophosphoric acid nitroxyl cation, acetic acid nitroxyl, ammonium dinitramide, nitroxyl chloride and fluorinated nitroxyl; the organic alkali hydrofluoride in the polysilicon etching liquid is at least one of triethylamine trihydrofluoride, tetraethylammonium fluoride tetrahydrofluoride, tetraethylammonium fluoride trihydrofluoride, pyridine hydrofluoride or N, N-diisopropylethylamine trihydrofluoride;
the weight content of nitric acid in the polycrystalline silicon etching solution is 60-70%; the weight content of the acetic acid is 0.5-5%; the weight content of the nitroxyl substances is 0.05% -1%; the weight content of the organic base hydrofluoride is 3-10%; the balance being water.
2. The polysilicon etching liquid according to claim 1, wherein: the nitroxyl substance in the polysilicon etching liquid is tetrafluoroborate nitroxyl cation or hexafluorophosphate nitroxyl cation.
3. The polysilicon etching liquid according to claim 1, wherein: the weight content of nitric acid in the polysilicon etching solution is 65 percent; the weight content of the acetic acid is 0.8-1.2%; the weight content of the nitroxyl substances is 0.2-0.5%; the weight content of the organic base hydrofluoride is 4-8%; the weight content of the deionized water is the balance.
4. The method for producing a polycrystalline silicon etching solution according to any one of claims 1 to 3, wherein: adding ultrapure water into a container, adding nitric acid into the ultrapure water by using a circulating pump, adding acetic acid into the solution, fully mixing uniformly, adding organic base hydrofluoride, stirring while adding, finally adding nitroxyl substances, dissolving and stirring uniformly, and then circularly mixing uniformly between the two containers by using the circulating pump to obtain the polycrystalline silicon etching solution.
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