JPH11256368A - Etching liquid for thin copper foil and etching method of thin copper foil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable uniform etching on a substrate even when the etching rate is decreased to a rate suitable for etching of a thin copper foil, by using an aq. soln. of iron (III) sulfate as the main component. SOLUTION: Since iron (III) sulfate has a significantly slow etching rate compared to iron (III) chloride or the same concn., an aq. soln. of iron (III) sulfate of high concn, can be used. The concn. is preferably controlled to 10 to 35 wt.%. In order to prevent production of hydroxides and to improve the etching rate, a small amt. of sulfuric acid by about 0.2 to 5 wt.% is preferably added to the etching liquid. When this etching liquid is used to etch a thin copper foil, the compsn. of the liquid is controlled in such a manner that the specific gravity of the liquid is maintained const. by supplying water based on the measurement result of the specific gravity of the liquid, and that the oxidation-reduction potential of the etching liquid is maintained const. by supplying an aq. soln. containing iron (III) sulfate and/or an aq. soln. contg. iron (II) sulfate and sulfuric acid to the liquid based on the measurement result of the oxidation-reduction potential of the liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an etching solution for a thin copper foil and a method for etching a thin copper foil.
In particular, the present invention relates to an etching solution for a thin copper foil and a thin copper foil etching method suitable for etching a fine circuit with high precision.

[0002]

2. Description of the Related Art Circuits on printed circuit boards have been miniaturized year by year, and the thickness of thin copper foil used for printed circuit boards has been reduced in order to cope with this trend. May be used. In a plasma display, a power supply circuit is formed on a glass substrate by etching a copper vapor deposition film.

As an etching agent for copper, aqueous solutions of ferric chloride, cupric chloride and the like have been used so far, but these are for etching a thick copper foil, and these etching agents have conventionally been used. When the thin copper foil is etched at a low concentration, the etching is completed in a very short time, so that it is difficult to control the circuit width dimension.

Therefore, as a method for delaying the etching, there are methods such as lowering the temperature and lowering the spray pressure, but none of these methods is sufficient, for example, the circuit sectional shape is deteriorated.

There is also a method in which the concentration of ferric chloride, cupric chloride, or the like is reduced, but in this method, the relative speed of etching between the circuits is reduced, and in the case of several parallel circuits, the outer circuit is not used. Thinning appears and the side etching width also increases. In addition, there arises a problem that copper in the anchor portion between the circuits (the portion in which the copper surface is made uneven in the resin layer in order to increase the adhesion strength) tends to remain.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to achieve uniform etching at any point on a substrate even if the etching rate is reduced to a value suitable for etching thin copper foil, and to obtain a circuit sectional shape. It is an object of the present invention to provide an etching solution for a thin copper foil and a method of etching the thin copper foil, which has a good finish and has no copper residue at an anchor portion between circuits.

[0007]

That is, the present invention provides an etching solution for thin copper foil, wherein the main component is an aqueous solution of ferric sulfate. The present invention also provides an etching solution for thin copper foil as described above, wherein the etching solution further contains a small amount of sulfuric acid. Further, the present invention provides a method for etching a thin copper foil, which comprises using an aqueous solution of ferric sulfate as an etching solution when etching the thin copper foil. Still further, the present invention provides the above method for etching a thin copper foil, wherein an aqueous solution containing a small amount of sulfuric acid is used as an etching solution. Also, the present invention provides a specific gravity control step of maintaining the specific gravity of the etchant constant by supplying water to the etchant based on the specific gravity measurement result of the etchant, and an aqueous ferric sulfate solution based on the measurement result of the oxidation-reduction potential of the etchant. And / or an oxidation-reduction potential control step of supplying an aqueous solution containing ferrous sulfate and sulfuric acid to the etching solution to keep the oxidation-reduction potential of the etching solution constant. An etching method is provided. Further, the present invention provides a specific gravity control step of supplying water to the etching solution based on the measurement result of the specific gravity of the etching solution to keep the specific gravity of the etching solution constant, and mainly using ferric sulfate based on the measurement result of the oxidation-reduction potential of the etching solution. An oxidation-reduction potential control step of supplying an aqueous solution containing a small amount of sulfuric acid as a component and / or an aqueous solution containing ferrous sulfate and sulfuric acid to the etching solution to keep the oxidation-reduction potential of the etching solution constant; The present invention provides a method for etching a thin copper foil as described above.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Ferric sulfate has a significantly lower etching rate than ferric chloride of the same concentration, and a high-concentration aqueous solution can be used.

The concentration of ferric sulfate may be appropriately adjusted depending on the thickness of the thin copper foil to be etched, the circuit width when a circuit is to be formed by etching, and the like. It is preferably from 10 to 35% by weight.

Although the main component of the etching solution used in the present invention is ferric sulfate, it is preferable to add a small amount of sulfuric acid to the etching solution in order to prevent the formation of hydroxide and improve the etching rate. The content is approximately 0.1 to 10% by weight, preferably 0.2 to 5% by weight.

If the thin copper foil to be etched is relatively thick and it is necessary to increase the etching rate,
Chloride ions, such as hydrochloric acid and salt, may be appropriately added as desired within a range that does not adversely affect the effects of the present invention. Further, amines, polyhydric alcohols, surfactants, and the like may be appropriately added to improve the etching performance, if desired, as long as the effects of the present invention are not adversely affected.

In the present invention, the thin copper foil is etched by using the above-mentioned etching solution. The etching may be performed by any of the dipping method and the spraying method, and the temperature of the etching solution is not particularly limited and may be appropriately selected as desired. But about 20
C. to 70.degree. C., and preferably 30.degree. C. to 60.degree. C. for practical purposes from the viewpoint of the material of the apparatus, the etching rate and the difficulty of control. The spray pressure in the spray method is, for example, preferably about 0.2 to 10 kg / cm ² , and more preferably 0.5 to 5 kg / cm ² for maintenance of the apparatus.

Further, the present invention is to control the composition of the etching solution when etching a thin copper foil using the above-mentioned etching solution. That is, a specific gravity control step of supplying water to the etchant based on the measurement result of the specific gravity of the etchant to keep the specific gravity of the etchant constant, and an aqueous ferric sulfate solution (or a smaller amount thereof based on the measurement result of the oxidation-reduction potential of the etchant) And / or an aqueous solution containing ferrous sulfate and sulfuric acid is supplied to the etching solution to control the oxidation-reduction potential of the etching solution to be constant. Is the way.

The supply of water to the etching solution based on the result of the measurement of the specific gravity of the etching solution is performed to replenish water lost by evaporation. In the present invention, since the volatile component is only water, there is no odor, and there is little irritation to the skin, so that the environment is not polluted and handling is easy.

There are two factors that change the oxidation-reduction potential in the etching solution. One is a reduction in the oxidation-reduction potential caused by the fact that ferric sulfate reacts with copper and is consumed as the etching proceeds, and ferric ions change to ferrous ions. In response to the decrease in the oxidation-reduction potential, by supplying a ferric sulfate aqueous solution to the etching solution, the oxidation-reduction potential of the etching solution can be controlled. As described above, when a small amount of sulfuric acid is added to the etchant to prevent hydroxide generation and improve the etching rate, add sulfuric acid to the aqueous ferric sulfate solution to be supplied and adjust the sulfuric acid concentration in the etchant to the same value. It is good to keep the sulfuric acid concentration of

Another factor is an increase in the oxidation-reduction potential due to the etching solution undergoing air oxidation. When etching is performed by a spray method, etc., for example, when ferrous ions are oxidized by oxygen in the air and changed to ferric ions due to spray blowing or the like, the ratio of ferric ions becomes too large and redox The potential rises. In response to this increase in the oxidation-reduction potential, the oxidation-reduction potential of the etching solution can be controlled by supplying an aqueous solution of ferrous sulfate to the etching solution.

Further, such air oxidation proceeds by the following reaction. H ₂ SO ₄ + 2FeSO ₄ + 1 / 2O ₂ → Fe
₂ (SO ₄ ) ₃ + H ₂ O (where the sulfuric acid on the left side is sulfuric acid when a small amount of sulfuric acid is added to the etching solution in order to prevent the above-mentioned hydroxide from being formed and to improve the etching rate. Since sulfuric acid is consumed as described above, sulfuric acid is also supplied together with ferrous sulfate in order to maintain a constant etchant composition.
The amount of sulfuric acid to be supplied can be appropriately determined by previously examining the relationship between the amount of ferrous sulfate corresponding to a certain air oxidation and the amount of sulfuric acid consumed in this air oxidation.

As described above, the change in the oxidation-reduction potential of the etching solution essentially uniformly changes in the direction of "decreasing", but the air oxidation results in an increase in ferric sulfate. So, depending on the conditions, this "drop" can be offset,
In some cases, it may change in the direction of “rising” uniformly. Therefore, at the time of actual etching, an upper limit value and a lower limit value of a desired oxidation-reduction potential are set by using an etching apparatus having both of the above control steps, and when the oxidation-reduction potential of the etching solution falls below the lower limit value, sulfuric acid is used. An aqueous ferric solution (or further containing a small amount of sulfuric acid) may be supplied, and when the oxidation-reduction potential exceeds the upper limit, an aqueous solution containing ferrous sulfate and sulfuric acid may be supplied.

[0019]

EXAMPLES Examples of the present invention and comparative examples will be described below. Example 1 Etching was performed using an etcher having an effective etching length of 0.9 m and a liquid holding amount of 300 liters. The size of the substrate to be etched is 500 mm × 350 mm,
The copper foil thickness is 5 μm, the line width is 40 μm, and the space between the lines is 40 μm. As the resist, a dry film having a thickness of 20 μm was used. The ferric sulfate concentration of the used etching solution was 28.
0% by weight and the sulfuric acid concentration is 0.5% by weight. The etching conditions are as follows: temperature 40 ° C., spray pressure 1.5 kg / cm
^{2. The} conveyor speed was 0.98 m / min. When the substrate after the etching treatment was observed under a microscope, there was no copper residue between the circuits, and the circuit width was 36 μm.

Comparative Example 1 Etching was performed in the same manner as in Example 1 except that an etching solution having a ferric chloride concentration of 10.5% by weight and a hydrochloric acid concentration of 0.5% by weight was used instead of the etching solution used in Example 1. did. When the substrate after the etching treatment was observed under a microscope, there was copper residue between the circuits, and the circuit width was 17 μm. It can be seen that although the copper between the circuits is hardly etched, the copper in the circuit is excessively etched and the circuit is easily thinned.

Example 2 Etching was performed using the etching apparatus shown in FIG. 1 in which an etcher was provided with additional equipment for controlling an etchant. The effective etching length of the etcher is 1.5m,
The liquid holding capacity is 800 liters.

The operation mechanism of the apparatus will be described with reference to FIG. The etchant in the etcher 1 is sent to the specific gravity / oxidation-reduction potential detecting unit 2 through an etchant feed pipe 9 by an etchant feed pump 5, and returned to the etcher 1 through an etchant return pipe 10. The measurement of the specific gravity is always performed in the detection unit 2, and the detection result is sent to the replenishing liquid / water supply control unit 14 connected to the detection unit 2, and when the specific gravity exceeds the set value, the electromagnetic valve opening and closing related to the specific gravity is performed. Signal wiring A
To open the water supply electromagnetic valve 8 to supply water through the water supply pipe 11, and close the water supply electromagnetic valve 8 when the value becomes equal to or less than the set value. Further, the measurement of the oxidation-reduction potential is performed by the detecting unit 2.
The detection result is sent to the replenishing liquid / water supply control unit 14 connected to the detection unit 2, and when the oxidation-reduction potential falls below the set value, the operation of the pump related to the supply of the replenishment liquid A is stopped. The supply pump 6 for the replenishment liquid A is operated using the signal wiring B, and the replenishment liquid A is supplied from the replenishment liquid A storage tank 3 to the etcher 1 through the supply pipe 12 for the replenishment liquid A, and the desired oxidation-reduction potential set value is set. Is stopped, the pump 6 is stopped. Similarly, when the oxidation-reduction potential becomes equal to or higher than the set value, the pump 7 for supplying the replenishing liquid B is operated using the pump operation stop signal line C related to the supply of the replenishing liquid B, and the supply pipe 13 for the replenishing liquid B is supplied. The replenishing liquid B is supplied from the replenishing liquid B storage tank 4 to the etcher 1, and when the desired oxidation-reduction potential set value is reached, the liquid sending pump 7 is stopped.

The substrate to be etched is 1050 mm × 55
0 mm, laminated in the order of chromium / copper / chromium / transparent conductive film / glass, in which etching of the uppermost layer of chromium has been completed. The thickness of the copper film is 2 μm. As a replenishing solution A for keeping the performance of the etching solution constant, a solution having a ferric sulfate concentration of 14.8% by weight and a sulfuric acid concentration of 0.5% by weight was used. The replenisher B has a ferrous sulfate concentration of 11.1% by weight and a sulfuric acid concentration of 4.2% by weight. First, 14 g / liter of copper was dissolved in a solution having the same composition as that of the replenishing solution A, and charged into the etcher 1 as an etching solution composition in a steady state. Raise the temperature of the etching solution to 40 ° C and spray pressure 0.8 kg /
cm ² and a conveyor speed of 1.5 m / min. The specific gravity control set value was 1.172, and water was supplied when the specific gravity exceeded the set value. Set the control value of the oxidation-reduction potential to the lower limit of 4
30 mV, the upper limit value is 435 mV. When the number of processed sheets per hour is large and the oxidation-reduction potential is 430 mV or less, the replenishing solution A is supplied, and the number of processed sheets is small and air oxidation precedes and the oxidation-reduction potential becomes 435 mV or more. Replenisher B
Was sent. After processing 5,000 sheets, the analysis and measurement results of the etching solution are as shown in Table 1 below, and it is understood that the specific gravity and the oxidation-reduction potential are well controlled. When the substrate after the etching treatment was observed under a microscope, there was no copper residue and no excessive etching portion.
425 liters of replenisher A sent during this time, replenisher B
Was 52 liters.

[0024]

[Table 1] Table 1 処理 Treatment amount Redox potential Specific gravity Copper concentration (sheets) (mV) (40 ° C.) (g / liter) ０ 0 435 1.171 15.2 1000 431 1 .170 15.3 2000 433 1.170 15.3 3000 433 1.169 15.2 5000 431 1.170 15.2} ━━━━━━━━━

Example 3 The same etcher and substrate as in Example 1 were used for etching and the substrate to be etched were used. The ferric sulfate concentration of the used etching solution was 28.0% by weight, and sulfuric acid was not added. The etching conditions were a temperature of 40 ° C., a spray pressure of 1.5 kg / cm ² , and a conveyor speed of 0.92 m.
/ Min. When the substrate after the etching treatment was observed with a microscope, there was no copper residue between the circuits and the circuit width was 3
It was 5 μm.

Example 4 Etching was performed using the same etcher, etchant control device and substrate to be etched as in Example 2. A solution having a ferric sulfate concentration of 12.0% by weight was used as a replenishing solution A for keeping the performance of the etching solution constant. First, 5 g / liter of copper was dissolved in a solution having the same composition as the replenishing solution A, and charged into the etcher 1 as an etching solution composition in a steady state. The temperature of the etching solution was raised to 40 ° C., the spray pressure was set at 0.8 kg / cm ² , and the conveyor speed was set at 2.1 m / min. The specific gravity control set value was 1.160, and water was supplied when the specific gravity exceeded the set value. The control set value of the oxidation-reduction potential was set to 490 mV, and when the oxidation-reduction potential became lower than the set value due to the etching of the substrate, the replenisher was fed into the etcher 1. When 1000 substrates were processed, the analysis result of the etching solution showed that the oxidation-reduction potential was 489 to 492 m.
V, specific gravity 1.160 to 1.156, copper concentration 4.8 to
When the substrate after the etching treatment was observed under a microscope, there was no copper residue and there was no excessive etching portion. In this example, there was no increase in the oxidation-reduction potential due to air oxidation.
No solution of ferrous sulfate was pumped.

[0027]

The effect of the present invention is that even if the etching rate is reduced to a value suitable for etching thin copper foil, uniform etching can be performed at any point on the substrate, and the circuit cross-sectional shape becomes a good finish. It is an object of the present invention to provide an etching solution for a thin copper foil and a method of etching the thin copper foil, which have no copper residue at an anchor portion between circuits.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an apparatus for implementing the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Etcher 2 Specific gravity / oxidation-reduction potential detection part 3 Reservoir of replenishment liquid A to be sent when the oxidation-reduction potential of an etching solution becomes lower than a set value 4 When the oxidation-reduction potential of an etching solution becomes higher than a set value Storage tank for replenishment liquid B to be sent in 5 Etch liquid supply pump 6 Replenishment liquid A supply pump 7 Replenishment liquid B supply pump 8 Water supply pipe solenoid valve 9 Etch liquid supply pipe 10 Etch liquid return pipe 11 Water supply pipe 12 Replenishment liquid A supply pipe 13 Replenishment liquid B supply pipe 14 Replenishment liquid / water supply control unit A Control signal wiring related to specific gravity B Control signal wiring related to supply of replenishment liquid C Control signal wiring related to supply of replenishment liquid B

Claims (6)

[Claims] 1. An etching solution for thin copper foil, wherein the main component is an aqueous solution of ferric sulfate. 2. The etching solution for a thin copper foil according to claim 1, wherein the etching solution further contains a small amount of sulfuric acid. 3. A method of etching a thin copper foil, wherein an aqueous solution of ferric sulfate is used as an etching solution when etching the thin copper foil. 4. The method for etching a thin copper foil according to claim 3, wherein an aqueous solution further containing a small amount of sulfuric acid is used as the etching solution. 5. A specific gravity control step of supplying water to the etching solution based on the measurement result of the specific gravity of the etching solution to keep the specific gravity of the etching solution constant, and a ferric sulfate aqueous solution based on the measurement result of the oxidation-reduction potential of the etching solution. 4. An oxidation-reduction potential control step of supplying an aqueous solution containing ferrous sulfate and sulfuric acid to an etching solution to keep the oxidation-reduction potential of the etching solution constant. Etching method of thin copper foil. 6. A specific gravity control step of supplying water to the etching solution based on the measurement result of the specific gravity of the etching solution to keep the specific gravity of the etching solution constant, and mainly using ferric sulfate based on the measurement result of the oxidation-reduction potential of the etching solution. An oxidation-reduction potential control step of supplying an aqueous solution containing a small amount of sulfuric acid as a component and / or an aqueous solution containing ferrous sulfate and sulfuric acid to the etching solution to keep the oxidation-reduction potential of the etching solution constant; The method for etching a thin copper foil according to claim 5, characterized in that: