JP2002129361A - Etching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for etching metals in order to form a fine electrode and a metallic wiring in a manufacturing process of a substrate for a semiconductor device or for a liquid crystal element, which easily keeps the etching rate in a desired range over a long period of time. SOLUTION: This etching method for metal, which employs an aqueous agent solution containing an acid component and an oxidizing component, is characterized by keeping the mol number of the oxidizing agent in the etching solution, larger than the product of the mol number of an etched metal ion generated by the etching and a valence number of the ionized metal. This method is particularly effective for the metal to be etched of Al, silver, copper, or an alloy including at least one or more of either of these.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal etching method, and more particularly, to a method of forming fine electrodes and metal wiring on a metal (layer) in a manufacturing process of a semiconductor device substrate or a liquid crystal element substrate, for example, a photosensitive resin or the like. The present invention relates to an etching method suitable for a fine etching step using a method.

[0002]

2. Description of the Related Art In recent years, in semiconductor device substrates and liquid crystal element substrates, the miniaturization and high integration of such devices and elements have been remarkable. The demands are becoming more demanding. For example, in the case of liquid crystal devices, in addition to increasing the size of the display device screen and increasing the density of images, there is a demand for increased image information to be displayed, resulting in suppression of heat generation in display on portable devices, power saving, and the like. Is even higher.

[0003] In response to such a demand, instead of the conventionally used chromium (Cr) alloy wiring material such as CrMo, a material having a low electric resistance suitable for fine etching and capable of withstanding an increase in the electric demand of equipment. Is being considered. For example, at present, a new material made of aluminum (Al), silver, copper, an alloy thereof, or the like is cited, and etching of fine wiring with such a new material is also being studied.

In conventional etching of a wiring material such as Cr (alloy), since the oxidation potential of Cr is high, an etching solution containing a high oxidation potential oxidizing agent such as cerium (Ce) (in the present invention, (Sometimes referred to as an etchant).
On the other hand, Al, silver, copper, and the like described above have a low oxidation potential, and can be oxidized using a relatively inexpensive oxidizing agent such as nitric acid, which has a lower oxidation potential than Ce, and can be etched. Usually, in metal etching, an etching solution (etchant) to which an acid component is added for the purpose of dissolving a metal to be etched together with an oxidizing agent is used, and phosphoric acid is generally used as the acid component.

In order to adjust the etching rate, it is common to add a diluent component such as acetic acid in addition to an acid component and an oxidizing component, and to use it in the form of, for example, a mixed acid of three kinds of phosphoric acid, nitric acid and acetic acid. Has been done.

[0006]

Even in the absence of an oxidizing agent such as nitric acid, etching is possible because the metal to be etched such as Al is dissolved by emitting hydrogen gas. However, since the surface of the metal to be etched is covered with hydrogen gas due to the generation of hydrogen gas, there is a problem that contact with the etchant is hindered and the etching rate is reduced. In order to suppress this, a method has been conceived in which the etching is quickly completed by using an etchant having a higher oxidizing agent concentration (molar number) from the beginning of the etching.

However, if an etchant having a high mole number of the oxidizing agent is used from the beginning of the etching for the purpose of increasing the efficiency of the etching process, the etching rate becomes unnecessarily high and control becomes difficult in some cases. .

[0008] Such an etchant having a high mole number of the oxidizing agent also strongly oxidizes a photosensitive resin or the like that protects a metal wiring portion and deteriorates adhesion between the photosensitive resin and a metal to be etched. In addition, there is a problem that an unnecessary taper angle is formed (for example, JP-A-6-122982).

For this reason, a method has been considered in which a diluent component such as acetic acid is added to the etchant to suppress the etching rate. However, when the diluent component is added in this manner, the period during which the etchant can maintain a constant etching rate is shortened, and the etchant having a desired etching rate or less must be discarded, and contains acetic acid which is an organic substance. However, there is still a problem that the burden on the environment is large, for example, the disposal method is difficult.

[0010]

SUMMARY OF THE INVENTION In view of such circumstances, the present inventors have intensively studied an etching method for making the etching rate of an etchant easy and a desired range for a long period of time.

For example, a chemical mechanism in a reaction (in an etching system) in an etchant when Al is etched using an acid component and an oxidizing agent is represented by the following chemical formula (the oxidizing agent is nitric acid).

[0012]

Embedded image Al (metal) + HNO ₃ + 3H ⁺ = Al ³⁺ + NO +
2H ₂ O In order for the reaction of the above chemical formula to proceed to the right, an excess component greater than the equilibrium constant of this chemical formula is required on the raw material side (left side).
The equilibrium constant K is expressed by the following equation.

[0013]

## STR2 ## K = [Al] [HNO ₃ ] [H ⁺ ] ³ / [A
l ³⁺ ] [NO] [H ₂ O] ^{2 In} these chemical formulas, the metal to be etched A
Assuming that a large amount of l, acid component and H ₂ O are present, and NO comes out of the etching system as a gas, the above chemical formula (Formula 1)
In order to make the reaction proceed to the right, that is, to dissolve Al and promote etching, the relationship between the K value proportional to [HNO ₃ ] / [Al ³⁺ ] and the etching rate may be known.

Here, the present inventors consider that when the metal to be etched is Al, the equilibrium constant K is a value larger than 3, that is, the number of moles exceeding three times the number of moles of Al ions dissolved and increased in the etching system. If the number of moles of the oxidizing agent (nitric acid) is maintained in the etching system, the etching rate remains almost constant,
The inventors have found that when the value falls below this value, the etching rate starts to decrease sharply, thereby completing the present invention.

That is, the gist of the present invention is a metal etching method using an etching solution containing an acid component and an oxidizing agent component, wherein the number of moles of the oxidizing agent in the etching system is determined by the number of moles of metal ions to be etched generated by etching. The present invention provides an etching method characterized by maintaining the value larger than the product of the number and the ionization valence of the metal.

Further, according to the present invention, the oxidizing agent concentration in the etching system is continuously measured, and the oxidizing agent for the shortage is automatically calculated from the oxidizing agent concentration. It is possible to maintain the etching rate in the system for a long time.

Further, the number of moles of the oxidizing agent in the etchant is
Before use in etching (before starting), the equilibrium constant K in the etching reaction is set to be equal to or more than the number of moles necessary for the etching reaction to become larger than the ionization valency of the metal to be etched in the etchant during etching. Then, after the etching is started, if the oxidizing agent is supplied such that the equilibrium constant K in the etching reaction becomes larger than the ionization valency of the metal to be etched with a decrease in the number of moles of the oxidizing agent, the etching rate is adjusted from the beginning. It was also found that the addition of a diluent component or the like became unnecessary, and that a rapid increase in the etching rate could be prevented. These are particularly effective when the metal to be etched is Al, silver, copper, or an alloy containing at least one of them.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

The metal to be etched in the present invention may be any metal. Among them, Al, silver, copper or an alloy containing at least one of these metals, particularly Al, has a remarkable effect. In the following, a description will be given by taking the etching of Al, silver and copper as an example. If necessary, see FIG.
This will be described with reference to the schematic diagram of the etching apparatus described in the above section.

Generally, in metal etching, an oxidizing agent for oxidizing the metal surface and an acid for dissolving the oxidized metal surface are used. Further, an object to be etched is an indium-tin compound (IT) used for a transparent electrode or the like.
In the case of an oxide such as O), since the object to be etched is already an oxide, etching can be performed only with an appropriately selected acid without using an oxidizing agent.

It has been known that when a metal surface is oxidized, the surface is easily dissolved in an acid. As the acid component in the present invention, any conventionally known acid component can be used, and any one of an inorganic compound-based strong acid to an organic compound-based weak acid can be used. In particular, when the metal to be etched is Al, silver and copper or an alloy containing one or more of these,
It is preferable to use phosphoric acid, which is a weak acid.

As the oxidizing agent component in the present invention, any one can be used as long as it basically has an oxidation potential higher than the inherent oxidation potential of the metal to be etched. For example, when the metal to be etched is Cr, Ce having an oxidation potential higher than the oxidation potential of Cr is used, and this oxidizing agent action is used. Since it is possible to oxidize a metal having a low oxidation potential such as Al, silver and copper without using a metal having a high oxidation potential such as Ce, it is preferable to use cheaper nitric acid as the oxidizing agent.

In the present invention, the number of moles of the acid component and the oxidizing agent component in the etchant is determined so as to obtain a desired etching rate by the combination of the metal species to be etched and the acid component and the oxidizing agent component, and furthermore, the fineness of the patterning. What is necessary is just to select suitably.

The concentration of the acid component in the etchant when the metal to be etched is Al is generally 50 to 80% by weight, preferably 70 to 80% by weight. If the concentration of the acid component is low, the etching rate is reduced and the etching efficiency is reduced.

When the metal to be etched is Al, the concentration of the oxidizing agent component in the etchant is 0.1 to 20% by weight, preferably 0.5 to 12% by weight. The etching rate increases with an increase in the oxidizing agent component concentration, but if it is too high, the etching rate may decrease.

When nitric acid is used as an oxidizing agent at the time of Al etching, if the nitric acid concentration is too high, the photosensitive resin used for patterning or the like on an object to be etched may be peeled off. If the etching rate is too low, the etching rate is remarkably reduced. Therefore, the concentration of nitric acid in the etchant is preferably 0.5 to 12% by weight, particularly preferably 3 to 8% by weight.

The etchant used for etching in the present invention is water-soluble, and is mainly water except for the acid component and the oxidizing agent component. If necessary, other components and other components may be used as long as the effects of the present invention are not impaired. It may contain additives. Specifically, for example, when the object to be etched has fine patterning such as a semiconductor device manufacturing substrate or a liquid crystal element substrate, the surface tension of the water-soluble etchant increases as the pattern line width becomes smaller. Since it is preferable to improve the wettability, a conventionally known surfactant or the like may be added to the etchant at this time. The amount added is usually 0.001 to the total weight of the etchant.
It is 1.0% by weight, preferably 0.1-1% by weight, especially 0.2-0.5% by weight.

As such another component, a diluent component such as acetic acid described above for adjusting the etching rate may be contained. However, in the etching method of the present invention, such a diluent is used. The feature is that the etching rate in the etching system can be easily maintained for a long period even in the absence. When an etchant diluent component is used in the present invention, the type, concentration, and the like may be appropriately selected depending on the metal to be etched. For example, in Al etching, it is preferable to use acetic acid, which has a remarkable effect, as a diluent component, and its concentration is generally 2 to 50% by weight, especially 2 to 10% by weight based on the total weight of the etchant. preferable.

In the etching method of the present invention, using the etchant as described above, the number of moles of the oxidizing agent in the etching system is determined by the number of moles of the metal ions to be etched generated by etching and the ionization valence of the metal. It is characterized in that it is kept larger than the product of The method of reproducing this is arbitrary, but specifically, for example, the number of moles of the oxidizing agent in the etching system is measured, and the number of moles of the oxidizing agent in the etching system is equal to the number of moles of the metal ion to be etched generated by etching and the ionization of the metal. It is preferable to add an oxidizing agent to the etching system so as to be larger than the product of the valence.

Above all, before using the mole number of the oxidizing agent in the etchant for the etching process, the mole number necessary for the equilibrium constant K in the etching reaction to become larger than the ionization valence of the metal to be etched in the etchant at the time of etching. After the etching is started, the equilibrium constant K in the etching reaction becomes larger than the ionization valence of the metal to be etched with the decrease in the number of moles of the oxidizing agent generated with time (that is, the oxidizing agent in the etching system). If an oxidizing agent is supplied into the etching system so that the number of moles is maintained larger than the product of the number of moles of the metal ion to be etched and the ionization valency of the metal, a diluent component or the like for adjusting the etching rate from the beginning can be obtained. No addition is required, and a rapid increase in the etching rate can be prevented beforehand, and stable. Since the etching rate can sustain the etching while maintaining a long period of time, and more preferable.

In the etching method of the present invention, as described above, the number of moles of the oxidizing agent in the etching system may be kept larger than the product of the number of moles of the metal ion to be etched and the ionization valence of the metal. The amount may be appropriately selected. Generally, 10 to 200 millimoles (mmol), especially 5
It is preferably from 0 to 150 mmol, particularly preferably from 70 to 130 mmol.

In the present invention, especially when the metal to be etched is Al, silver or copper, by adding an oxidizing agent such as nitric acid to the etchant as described above, it is possible to increase the etchant compared to the conventional etchant. Although it is possible to maintain the etching rate constant over a long period of time, with the increase in the number of moles of the oxidizing agent in the etchant, to avoid a situation where the rate control becomes difficult due to a rapid increase in the etching rate, Due to the problem of oxidative deterioration of the photosensitive resin, it is preferable not to increase the number of moles of the oxidizing agent to a certain value or more. For example, when the metal to be etched is Al and nitric acid is used as an oxidizing agent, the concentration of nitric acid in the etchant is generally preferably 12% by weight or less, and particularly preferably 10% by weight or less.

The etching apparatus and the method of applying the etchant to the metal to be etched are optional, and any method and apparatus may be used as long as the metal to be etched contacts the etchant. Specific examples include a spray method, a batch or continuous immersion method, and conventionally known methods used for these methods.

In the present invention, nitric acid is added to the etchant by a programming feedback setting method 8 as shown in FIG. Can be used. In particular, in order to keep the number of moles of nitric acid constant, a feedback system of analysis results is preferable.

For example, in the etching step by the immersion method, after the etching, the etchant adheres to a work or the like (not shown) for supporting the object 4 to be etched, and the etchant is taken out, or as shown in FIG. It is possible to suppress the accumulation of dissolved Al in the etching system by (partially) fractionating the etchant from the etching tank 1. In such a case, a new nitric acid solution 5 corresponding to the amount obtained by subtracting the reduced amount of dissolved Al corresponding to the reduced amount of the etchant, and a new etchant are introduced to compensate for the acid component such as phosphoric acid reduced by the fractionation. What is necessary is just to add to the etching tank 1 from the line 10. By performing such a periodic extraction of a part of the etchant or the like, the increase in the number of moles of nitric acid in the etchant can be adjusted, so that continuous etching can be performed without replacing the entire amount of the etchant.

The concentration of dissolved Al in the etchant may be analyzed outside the etching bath 1 or the etching target 4 may be analyzed.
For example, a value estimated from a mass balance such as the number of processes may be used.

The etching temperature is arbitrary, but is generally 20 to 50 ° C., preferably 2
It is in the range of 5 to 40C.

[0038]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited to the following Examples unless it exceeds the gist of the invention. Further, unless otherwise specified,% means% by weight. Each experiment was performed using an etching apparatus capable of adding nitric acid as shown in the schematic diagram of FIG. The analysis of the number of moles of nitric acid was performed by an ultraviolet (300 nm wavelength) absorption method using a process titrator ECOSAVER-100 (manufactured by Mitsubishi Chemical Corporation).

Example 1 2.85% nitric acid, 70 phosphoric acid
% Of acetic acid and 10% of acetic acid (the remainder being water) were charged into the etching tank 1 shown in FIG. 1 in an amount of 200 g, and the heating device 7 and the stirring device 11 were used. Was planned. The object to be etched 4 having a thickness of 1.2 μm of aluminum metal provided on a glass substrate and patterned with a photosensitive resin is immersed in an etchant in an etching tank 11 and time measurement is started simultaneously with immersion. Then, the completion of etching was visually confirmed, and the etching rate was calculated.

The amount of Al dissolved in the etchant by this etching was determined by measuring the area of the portion removed by etching from the workpiece 4. The etching rate is shown in FIG.

When the cumulative amount of Al treatment reached about 540 mg, a new nitric acid solution 5 (70% nitric acid aqueous solution) was added to the etching tank 1 by the pump 6. At this time, the number of moles of nitric acid in the etchant is determined by the amount of dissolved A in the etchant.
15m more than 3 times the molar amount calculated from 1 concentration
A new nitric acid solution 5 was added to increase the amount by about mol, and the number of moles of nitric acid was maintained. In this manner, the number of moles of nitric acid in the etchant was increased, and the total number of moles of nitric acid was 136 mmol.
(5.2% with respect to the total amount of the etchant), and etching was continued.

Comparative Example 1 Etching was performed in the same manner as in Example 1 except that nitric acid was not supplied. The etching rate is shown in FIG.

As is clear from FIG. 1, the etching rate in Example 1 was almost constant up to about 1200 mg of Al dissolved by etching (2200 [２ /
Min]). Further, there was no problem in the shape of the patterning on the etching target 4.

On the other hand, the change in the etching rate in Comparative Example 1 was such that the amount of Al dissolved by etching was 600 m.
Up to about g, the value was kept almost constant (2200 [Å / min]), but after that, the etching rate dropped sharply and did not recover.

As described above, in Example 1 of the present invention, the period during which a constant etching rate could be maintained was extended to about twice that of the comparative example. This means that the etchant replacement period (liquid life) is about twice as long, while maintaining the etching function, the labor for liquid replacement is reduced by half, and the amount of waste can be reduced. It is.

Example 2 Nitric acid concentration was set to 0.6% without using acetic acid in the starting composition of the etchant. After the start of etching, nitric acid was supplied into the etching system, and the nitric acid concentration in the etching system was dissolved. Etching was performed in the same manner as in Example 1 except that the supply was performed so as to have a value obtained by adding the initial nitric acid concentration (0.6%) to 3 times the Al concentration.

The change in the etching rate is the same as that in the first embodiment.
An almost constant value (2200 [Å / min]) was maintained up to 00 mg. Further, there was no problem in the shape of the patterning on the etching target 4. From this, it is apparent that stable etching can be performed only with the acid component and the oxidizing component without adjusting the etching rate by adding a diluent component such as acetic acid.

Further, since the etchant does not contain acetic acid, which is an organic substance, the waste liquid after the prolongation of the liquid life contains only inorganic components such as nitric acid, phosphoric acid, and aluminum phosphate. CO2 in waste environment
D rise can be suppressed, and the environmental load can be reduced.

When the pH of the waste liquid is neutralized with caustic soda until it becomes 6 or more, Al in the waste liquid precipitates as aluminum hydroxide, so that solids can be separated. Furthermore, since the residual liquid after the separation becomes an aqueous solution containing sodium nitrate and sodium phosphate, these can be reused as fertilizer components and the like.

[0050]

According to the etching method of the present invention, it is possible to extend the liquid life of the conventional etchant about twice. At the same time, long-term stable etching can be performed with only an acid component and an oxidizer component without adding a diluent component such as acetic acid in the etchant composition before use and adjusting the etching rate. Furthermore, the amount of waste has been halved by doubling the liquid life,
In addition, since the waste can be free of organic matter, the possibility of reuse as an inorganic industrial chemical such as a fertilizer component is opened.

[Brief description of the drawings]

FIG. 1 is a diagram showing the results of Example 1 and Comparative Example 1 of the present invention.

FIG. 2 is a schematic diagram of an etching apparatus used in the present invention.

[Explanation of symbols]

1: Etching tank and initial etchant 2: Circulating pump for analyzer 3: Nitric acid concentration analyzer 4: Object to be etched 5: New nitric acid solution 6: New nitric acid solution adding pump 7: Heating device 8: Analytical device Receives nitric acid concentration output signal Nitric acid feed amount control line 9: Etch solution purge line 10: New etchant introduction line 11: Stirrer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kenichi Haga 1-1 Kurosaki Castle Stone, Yawatanishi-ku, Kitakyushu City F-term (reference) 4K057 WA10 WB01 WB04 WB05 WE02 WE04 WE12 WG03 WM03 WM04 WM13 WM17 WN01 WN02 4M104 BB02 BB04 BB08 DD09 HH20 5F033 HH08 HH11 HH14 QQ20 XX00 5F043 AA22 AA24 BB16 DD13 EE07 EE23 GG02 GG10

Claims (5)

[Claims] 1. A method of etching a metal using an etching solution containing an acid component and an oxidizing agent component, wherein the number of moles of the oxidizing agent in the etching system is determined by the number of moles of metal ions to be etched generated by etching and the number of moles of the metal. An etching method characterized by maintaining the product larger than the product of the ionization valence. And measuring the number of moles of the oxidizing agent in the etching system so that the number of moles of the oxidizing agent in the etching system is larger than the product of the number of moles of the metal ion to be etched generated by etching and the ionization valence of the metal. The etching method according to claim 1, wherein an oxidizing agent is added to the etching system. 3. An oxidizing agent concentration in an etching solution is set to be equal to or more than a mole number necessary for an etching reaction equilibrium constant to be equal to or more than an ionization valency of a metal to be etched in an etching system at the time of etching before starting etching. And supplying an oxidizing agent into the etching system so as to be larger than the product of the number of moles of the metal ion to be etched and the ionization valence of the metal.
3. The etching method according to 1. 4. The metal to be etched is aluminum, silver,
4. The etching method according to claim 1, wherein the etching method is copper or an alloy containing at least one of them. 5. The etching method according to claim 1, wherein phosphoric acid is used as an acid component, and nitric acid is used as an oxidizing agent component.