CN117646215A

CN117646215A - Mixed acid type pure molybdenum etching solution and etching method of pure molybdenum film layer

Info

Publication number: CN117646215A
Application number: CN202311601966.6A
Authority: CN
Inventors: 顾梦佳; 沈夏军; 徐杨; 章佳寅; 吴晓芳; 朱龙; 李涛
Original assignee: JIANGYIN JIANGHUA MICROELECTRONICS MATERIALS CO LTD
Current assignee: JIANGYIN JIANGHUA MICROELECTRONICS MATERIALS CO LTD
Priority date: 2023-11-28
Filing date: 2023-11-28
Publication date: 2024-03-05

Abstract

The invention discloses a mixed acid type pure molybdenum etching solution, which mainly comprises the following components in percentage by mass: 2 to 7 percent of nitric acid, 50 to 60 percent of phosphoric acid, 21 to 30 percent of acetic acid, 2.5 to 7 percent of additive and 6 to 17 percent of deionized water; the additive is a combination of two or more selected from phosphate, nitrate, acetate, molybdate and hydrogen phosphate. The mixed acid type pure molybdenum etching solution is added with salt on the basis of a mixed acid system of nitric acid, phosphoric acid and acetic acid, and the etching rate of pure molybdenum is regulated by utilizing the optimized content of each acid component and salt additive, so that the mixed acid type pure molybdenum etching solution is compatible with the etching of molybdenum single layers with various thicknesses, the etching dip angle is stabilized at 40-55 degrees, the critical dimension deviation of the molybdenum layers is effectively reduced, and the etching technical requirements of the pure molybdenum layers with various thicknesses are met; the molybdenum ion load of the etching solution can reach 5000ppm at most, and the service life is long. The invention also discloses an etching method of the pure molybdenum film layer.

Description

Mixed acid type pure molybdenum etching solution and etching method of pure molybdenum film layer

Technical Field

The invention relates to the technical field of wet etching of metal film layers, in particular to a mixed acid type pure molybdenum etching solution and an etching method.

Background

In the production of TFT (thin film field effect transistor) substrates, mixed acid type etching solutions are often found in copper molybdenum, aluminum molybdenum or metal stacks of molybdenum aluminum molybdenum to form circuits of a predetermined pattern. The main components of the mixed acid type etching solution are nitric acid, phosphoric acid and acetic acid, wherein the nitric acid is used for oxidizing copper, aluminum and molybdenum to generate corresponding metal oxides, the phosphoric acid reacts with the metal oxides to generate corresponding salts, and the acetic acid is used as the main component of the buffer solution to control the etching reaction speed.

In some special processes, such as LTPS low temperature polysilicon device production, it is known to use pure molybdenum metal layers as circuit materials, and thus it is necessary to adaptively prepare pure molybdenum etching solutions. The thickness of the common pure molybdenum layer is in the range ofFor example

Based on the precision and quality requirements of the high-density fine wire image of the current liquid crystal display, in order to ensure the continuity of the metal wire in the subsequent evaporation process, the technical specification of the super (etching dip angle) is smaller than 55 degrees, preferably 40-55 degrees; CD-Bias (critical dimension Bias) is specifically determined according to line width and film thickness, e.g. glass substrateThe CD-Bias bilateral of the molybdenum layer is preferably not more than 0.5m, silicon substrate +.>The CD-Bias double edge of the molybdenum layer is preferably not more than 1.5 μm. The whole etching of Mo by treating pure Mo with a combined mixed acid of 2% nitric acid, 65% phosphoric acid and 18% acetic acid as etching solution within the range described in CN103255417AThe morphology is obviously different from the morphology obtained by etching molybdenum aluminum molybdenum or aluminum molybdenum metal lamination, and the pure molybdenum morphology is expressed as follows: when the thickness of the molybdenum layer is smaller thanThe deviation of the critical dimension of the half reaches 0.26 mu m, and the etching dip angle is 65-80 degrees, as shown in figure 1; when the thickness of the Mo layer is larger thanThe half critical dimension deviation reaches 0.42 μm, and the etching dip angle is 60-70 degrees, as shown in fig. 2. Nitrate was added to the improved etchant but the effect of improving the etch tilt angle was limited for thinner and thicker molybdenum layers. Because of poor etching compatibility to molybdenum layers with different film thicknesses, the existing copper-molybdenum and molybdenum-aluminum-molybdenum etching solution is not suitable for being used for etching pure molybdenum.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a mixed acid type pure molybdenum etching solution, which is suitable for etching pure molybdenum film layers with various thicknesses by adding a combined salt into a mixed acid system as an additive, wherein the etching dip angle and the critical dimension deviation can be controlled within a preset technical specification range.

In order to achieve the technical effects, the technical scheme of the invention is as follows: the mixed acid type pure molybdenum etching solution mainly comprises the following components in percentage by mass: 2 to 7 percent of nitric acid, 50 to 60 percent of phosphoric acid, 21 to 30 percent of acetic acid, 2.5 to 7 percent of additive and 6 to 17 percent of deionized water;

the additive is a combination of two or more selected from phosphate, nitrate, acetate, molybdate and hydrogen phosphate.

Further, the sum of the mass percentages of nitric acid, phosphoric acid, acetic acid, additives and deionized water is not less than 95%, and further not less than 98%. The hydrogen phosphate includes monohydrogen phosphate and dihydrogen phosphate. The sum of the mass percentages of 2% -7% of nitric acid, 50% -60% of phosphoric acid, 21% -30% of acetic acid, 2.5% -7% of additive and 6% -17% of deionized water can be selected as 95%, 96%, 97%, 98%, 99%, 100% point values and a range taking the two point values as a maximum value and a minimum value.

The preferable technical scheme is that the additive is one or more than two selected from lithium salt, potassium salt, sodium salt and ammonium salt;

further, the additive is one or a combination of more than two of lithium salt, potassium salt and sodium salt.

The preferable technical scheme is that the additive is a combination of more than one of nitrate and phosphate, acetate, molybdate and hydrogen phosphate; further, the additive is a combination of phosphate and nitrate.

The preferable technical proposal is that the main composition by mass percent is as follows: 3 to 6 percent of nitric acid, 50 to 60 percent of phosphoric acid, 23 to 29 percent of acetic acid, 3 to 6 percent of additive and 7 to 13 percent of deionized water.

The preferable technical scheme is that the mass ratio of the phosphate to the nitrate is (0.7-1.2): 1, a step of;

further, the mass ratio of the phosphate to the nitrate is (0.9-1.2): 1.

specifically, the mass ratio of phosphate to nitrate is 0.7:1, 0.8:1, 0.9:1, 0.10:1, 1.1:1, 1.2:1 point value and a section having the two point values as a maximum value and a minimum value.

Preferably, the phosphate and/or nitrate is potassium salt.

The preferable technical proposal is that the mixed acid type pure molybdenum etching solution also comprises 0.03 to 0.75 percent of sulfonic acid compound; the sulfonic acid compound is at least one selected from methane sulfonic acid, 2-hydroxy ethane sulfonic acid, 3-hydroxy propane sulfonic acid and 1, 4-butane sulfonic acid. Specifically, the mass percentage of the sulfonic acid compound in the mixed acid type pure molybdenum etching solution is 0.03%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.75% point values and the interval using the two point values as the maximum value and the minimum value.

The preferable technical proposal is that the mass percentage of the sulfonic acid compound in the mixed acid type pure molybdenum etching solution is 0.1 percent to 0.55 percent;

further, the sulfonic acid compound is 3-hydroxy propane sulfonic acid and/or 1, 4-butanedisulfonic acid.

The second object of the present invention is to provide a method for etching a pure molybdenum film layer, wherein the mixed acid type pure molybdenum etching solution is used, and the molybdenum layer is covered on a substrate.

The preferable technical proposal is that the etching temperature is not more than 45 ℃;

further, the etching temperature is 37-44 ℃;

further, the thickness of the pure molybdenum film layer is

Further, the substrate is an ITO (indium tin oxide) substrate, a glass substrate, or a silicon substrate.

The invention has the advantages and beneficial effects that:

the mixed acid type pure molybdenum etching solution is added with salt on the basis of a mixed acid system of nitric acid, phosphoric acid and acetic acid, and the etching rate of pure molybdenum is regulated by utilizing the optimized content of each acid component and salt additive, so that the mixed acid type pure molybdenum etching solution is compatible with the etching of single molybdenum layers with various thicknesses, the etching dip angle is stabilized at 40-55 degrees, the critical dimension deviation of the molybdenum layer is effectively reduced, and the etching technical requirements of pure molybdenum with various thicknesses are met;

the molybdenum ion load of the etching solution can reach 5000ppm at most, and the service life is long.

Drawings

FIG. 1 is an SEM photograph of one of samples A after etching of comparative example 1;

FIG. 2 is an SEM photograph of one of the samples B after etching of comparative example 1;

FIG. 3 is an SEM photograph of one of samples A after etching of example 1;

FIG. 4 is an SEM photograph of one of samples B after etching according to example 1;

FIG. 5 is an SEM photograph of one of samples A after etching of comparative example 3;

FIG. 6 is an SEM photograph of sample B after etching of comparative example 3;

FIG. 7 is an SEM photograph of one of samples A after etching of example 6;

FIG. 8 is an SEM photograph of sample B after etching according to example 6;

FIG. 9 is an SEM photograph of sample A after etching according to example 8;

FIG. 10 is an SEM photograph of sample B after etching according to example 8;

FIG. 11 is an SEM photograph of sample C after etching according to example 8;

Detailed Description

The following describes the embodiments of the present invention further with reference to the drawings and examples. The following examples are only for more clearly illustrating the technical aspects of the present invention, and are not intended to limit the scope of the present invention.

Composition of mixed acid type pure molybdenum etching solution

Specifically, in addition to nitric acid, phosphoric acid, acetic acid, salt additives, deionized water and sulfonic acid compounds, common auxiliaries of etching solutions such as surfactants, defoamers and the like can be included.

It is understood that the reagent purity of nitric acid, phosphoric acid, acetic acid, salt additives, and sulfonic acid compounds, which are raw materials of the electronic chemical reagent, is controlled to be higher, so as to avoid or control the adverse effect of impurities on the etching rate and the morphology of the molybdenum layer.

Additive agent

Specifically, based on the mass percent of the additive, the salt as the additive is soluble in a mixed acid system of a predetermined composition and forms a uniformly clear etching solution.

Compared with the conventional copper-molybdenum etching solution, the acetic acid content in the pure molybdenum etching solution is slightly increased by 21-30%, the pure molybdenum etching solution containing high-concentration acetic acid has stronger permeability to the molybdenum layer and higher etching speed, and the salt additive can inhibit the etching speed of molybdenum. The two opposite effects are balanced in the etching process of molybdenum layers with different thicknesses by regulating and controlling the contents of acetic acid and salt additives.

The lithium ions, potassium ions and sodium ions in the lithium salt, potassium salt and sodium salt have less influence on the etching of the molybdenum layer and less influence on the fluctuation of the pH value of the etching liquid system than the ammonium salt. The lithium salt, sodium salt and potassium salt have an inhibiting effect on the etching speed of molybdenum, and the slower etching speed is beneficial to modifying the etching dip angle and reducing the critical dimension deviation. Wherein, the potassium salt has better effect on improving the etching speed and morphology of molybdenum than sodium salt, and the potassium salt is less used in pure molybdenum etching solution.

Sulfonic acid compound

The sulfonic acid compound is used for further adjusting the etching rate of the etching solution, so as to improve the etching dip angle and the critical dimension deviation of the thicker molybdenum layer. Preferred 3-hydroxy propane sulfonic acid and/or 1, 4-butanesulfonic acid are preferred over thicker molybdenum layers (thickness less than) The suppression of critical dimension bias is more excellent.

Pure molybdenum substrate

The existing pure molybdenum substrates are mainly three types, namely ITO, glass substrates or silicon substrates, and the mixed acid type pure molybdenum etching solution is generally used for the molybdenum layers of the three types of substrates. The silicon substrate is specifically made of a known silicon compound such as silicon oxide or silicon nitride.

1. Pure molybdenum etching solution components and configuration methods:

nitric acid-70% nitric acid (electronic grade);

phosphoric acid-85.4% phosphoric acid (electronic grade);

acetic acid-100% acetic acid (electronic grade);

additives-potassium phosphate, sodium phosphate, potassium nitrate, sodium nitrate, monopotassium phosphate (chemically pure);

sulfonic acid compounds-methanesulfonic acid, 1, 4-butanesulfonic acid (chemically pure);

preparing pure molybdenum etching solution: mixing additive salt with water to prepare a salt solution, adding nitric acid, phosphoric acid, acetic acid and the salt solution (and a sulfonic acid compound) into a mixing tank according to a proportion, adding water to adjust the content of the components to a preset content, and uniformly mixing to obtain the novel mixed acid pure molybdenum etching solution.

2. Etching sample substrates, specifications, and etching methods were arranged:

a substrate-molybdenum layer thickness of glass substrateTechnical specification: CD-Bias (bilateral) is less than or equal to 0.5 mu m, and the per is 40-55 degrees;

molybdenum layer thickness of B substrate-silicon (SiOx/SiNx) substrateTechnical specification: CD-Bias (bilateral) is less than or equal to 1.5 mu m, and the per is 40-55 degrees;

c substrate-molybdenum layer thickness of ITOTechnical specification: CD-Bias (bilateral) is less than or equal to 0.4 mu m, and the per is 40-55 degrees;

heating and preserving the temperature of the copper etching liquid sample by adopting etching equipment to 40+/-2 ℃ to etch the sample substrate; after etching, pure water is used for cleaning and drying, and the etching time is set according to 50% of the conventional OE in actual production.

3. Examples and comparative examples etch duration and result detection:

1. SEM observing the etching dip angle and CD-Bias of the etched sample (6 parallel samples are averaged);

the SEM photo measured single-sided CD-Bias, and the double-sided CD-Bias of the above specifications was regarded as 2-fold single-sided CD-Bias in the etching test.

2. And (3) detecting the service life of the mixed acid type pure molybdenum etching solution: molybdenum powder is added into the etching solution until the content of molybdenum ions in the pure molybdenum etching solution is 1000ppm, 3000ppm and 5000ppm, the etching solution with the preset molybdenum ion content is adopted to etch the sample substrate, and the copper ion loading capacity of the etching solution is explored by utilizing SEM.

4. Examples and comparative examples

1. The compositions of examples 1-3 and comparative examples 1-4, with respect to the composition of the mixed acid, are shown in the following table, and each component in the etching table is expressed in mass% for the two sample substrates of A, B:

SEM photo measurements of examples 1-3 and comparative examples 1-4 are shown in the following table:

as is clear from the table, the pure molybdenum etching solution of comparative example 1 contains no additive, the contents of nitric acid and acetic acid are low, but the content of phosphoric acid is high, the etching inclination angle of the sample A and the sample B is too large, and the CD-Bias value of the sample A is high.

On the basis of comparative example 1, nitrate is added alone to the pure molybdenum etching solution of comparative example 2 as an additive, and the etching dip angle does not reach the predetermined technical specification, but is obviously reduced compared with comparative example 1, and the edge of the photoresist coated on the surface of the molybdenum layer is flat and has no warpage.

On the basis of comparative example 2, comparative example 3 adjusts the concentration of three mineral acids, wherein the mass percent of nitric acid and acetic acid is increased, the mass percent of phosphoric acid is reduced, the etching dip angle is further reduced, wherein the etching dip angle of sample A reaches a preferred value, and the etching dip angle of sample B is too small, which indicates that the pure molybdenum etching solution of comparative example 3 has poor compatibility for molybdenum layers with different thicknesses. SEM pictures show that warping occurs at the edge of the photoresist coated on the surface of the molybdenum layer of the substrate, which indicates that the overall nitric acid concentration in the etching solution is too high and the oxidizing property is too high when nitrate is independently added as an additive, so that the positive photoresist plated on the substrate can be damaged.

Comparative example 4 based on the same three inorganic acid concentrations as comparative example 3, using potassium phosphate as an additive, CD-Bias was reduced as compared to comparative example 3, but the etching tilt angle was significantly increased.

In examples 1-3, potassium phosphate and potassium nitrate were added simultaneously as additives, and the example AOE50% etching duration of example 1 was 75s; the appearance of the etched molybdenum layers of the sample A and the sample B is obviously improved, and the etching dip angle and the unilateral CD-Bias reach respective technical specifications. Considering the compatibility of pure molybdenum etchant with sample A, B, the molybdenum layer morphology of example 1 is better than examples 2 and 3.

2. The compositions of examples 4-6 regarding cations in the salt additives are shown in the following table, wherein the components are expressed in mass percent:

SEM photo measurements of examples 1,4, 5, 6 are given in the following table:

compared with example 1, the etching dip angle of the samples A, B treated in examples 4 and 5, which adopt part of sodium salt and part of potassium salt as additives, meets the technical specification, but the single-side CD-Bias of the sample A increases more, which shows that the regulation effect of the sodium salt on the CD-Bias is weaker than that of the potassium salt.

In the embodiment 6, the mass percentage of sodium salt and potassium salt in the etching solution is increased simultaneously, the appearance of the etched molybdenum layer of the sample A is similar to that of the embodiment 1, and the etching dip angle of the sample B is slightly smaller but within the technical specification range; indicating that more sodium salt addition is needed to achieve the effect of improving the appearance of the molybdenum layer, which is close to less potassium salt. From the viewpoint of the etching inclination and cost of sample B, potassium salt is preferably used as an additive.

3. The compositions of examples 7 to 10 concerning the sulfonic acid compounds are shown in the following table, wherein each component is represented by mass percent:

SEM photo measurements for examples 1, 7-10 are given in the following table:

sample a of examples 7, 8, 9, 10 had 50% OE etch times of 74s, 72s, 74s, respectively, which were shorter than example 1, indicating that the sulfonic acid compound helps to accelerate the molybdenum layer etch while maintaining good molybdenum layer etch morphology. The AB samples processed in example 7 have a greater etch tilt difference than those of examples 8 and 9, indicating that examples 8 and 9 have better etch compatibility with molybdenum layers of different thicknesses.

The mass percentages of 1, 4-butanedisulfonic acid in examples 8 to 10 are increased, which shows that the higher the 1, 4-butanedisulfonic acid content is, the higher the single-side CD-Bias average value is, and the influence on the etching dip angle is not obvious in the mass percentage range of 0.4% -0.6% of 1, 4-butanedisulfonic acid. Based on CD-Bias and cost, the pure molybdenum etching solution of example 8 has better compatibility with molybdenum layers with different thicknesses than that of example 9.

4. Samples C of examples 1, 6, 8 used to etch ITO substrates were measured by SEM photographs as follows:

as can be seen from the above table, the pure molybdenum etching solution is also suitable for etching a molybdenum layer using ITO as a substrate.

5. The service lives (in terms of the maximum load of molybdenum ions in the pure molybdenum etching solutions) of the pure molybdenum etching solutions of examples 1, 6, 8 are shown in the following table:

sample preparation	Pure molybdenum etchant life (ppm)
		Example 1	5000ppm
Example 6	3000ppm
		Example 8	5000ppm

As can be seen from the above table, the pure molybdenum etching solutions of examples 1 and 8 have a longer lifetime than example 6, indicating that too high a concentration of sodium ions in the etching solution is detrimental to maintaining a longer lifetime of the pure molybdenum etching solution.

The foregoing is merely a preferred embodiment of the present invention, and it should be noted that it will be apparent to those skilled in the art that several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the scope of the invention.

Claims

1. The mixed acid type pure molybdenum etching solution is characterized by comprising the following main components in percentage by mass: 2 to 7 percent of nitric acid, 50 to 60 percent of phosphoric acid, 21 to 30 percent of acetic acid, 2.5 to 7 percent of additive and 6 to 17 percent of deionized water;

the additive is a combination of more than two selected from phosphate, nitrate, acetate, molybdate and hydrogen phosphate.

2. The mixed acid type pure molybdenum etching solution according to claim 1, wherein the additive is one or a combination of two or more selected from lithium salt, potassium salt, sodium salt and ammonium salt;

3. The mixed acid type pure molybdenum etching solution according to claim 1, wherein the additive is a combination of nitrate and one or more selected from phosphate, acetate, molybdate and hydrogen phosphate; further, the additive is a combination of phosphate and nitrate.

4. The mixed acid type pure molybdenum etching solution according to claim 1, which is characterized by comprising the following main components in percentage by mass: 3 to 6 percent of nitric acid, 50 to 60 percent of phosphoric acid, 23 to 29 percent of acetic acid, 3 to 6 percent of additive and 7 to 13 percent of deionized water.

5. The mixed acid type pure molybdenum etching solution according to claim 1, wherein the mass ratio of the phosphate to the nitrate is (0.7-1.2): 1, a step of;

further, the mass ratio of the phosphate to the nitrate is (0.9-1.2): 1.

6. the mixed acid type pure molybdenum etching solution according to claim 2, wherein the phosphate and/or nitrate is potassium salt.

7. The mixed acid type pure molybdenum etching solution according to claim 1, wherein the mixed acid type pure molybdenum etching solution further comprises 0.03% -0.75% of sulfonic acid compound; the sulfonic acid compound is at least one selected from methane sulfonic acid, 2-hydroxy ethane sulfonic acid, 3-hydroxy propane sulfonic acid and 1, 4-butane sulfonic acid.

8. The mixed acid type pure molybdenum etching solution according to claim 7, wherein the mass percentage of the sulfonic acid compound in the mixed acid type pure molybdenum etching solution is 0.1% -0.55%;

9. A method for etching a pure molybdenum film, characterized in that the mixed acid type pure molybdenum etching solution according to any one of claims 1 to 8 is used, and the molybdenum film is coated on a substrate.

10. The etching method according to claim 9, wherein the etching temperature is not more than 45 ℃;

further, the etching temperature is 37-44 ℃;

further, the thickness of the pure molybdenum film layer is

Further, the substrate is an ITO substrate, a glass substrate or a silicon substrate.