JP2003055780A - Etching solution and etching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress side etching as far as possible. SOLUTION: In carrying out etching of laminated films consisting of silver or a silver alloy by using an etching solution consisting of mixed acids composed of a phosphoric acid, nitric acid and acetic acid, the etching solution is made to flow and the flow intensity thereof is specified to a range from the fluid intensity at which the etching reaction starts up to the fluid intensity of 67% thereof.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an etching solution and a method for etching a laminated film made of silver or a silver alloy.

[0002]

2. Description of the Related Art At present, aluminum or aluminum alloy is mainly used as a wiring material for electronic devices and a reflective pixel electrode material for reflective liquid crystal display elements. However, aluminum and aluminum alloys have the following problems.

(1) Since the specific resistance is large, the wiring capacitance becomes large. (2) Dissolve in an alkaline solution. (3) The reflectance is not so high.

Various measures have been taken against these problems. The wiring capacitance can be solved by increasing the cross-sectional area of the wiring, but it is necessary to reduce the width of the wiring as the device becomes finer. Therefore, the wiring must be thickened accordingly. However, there is a limit to thickening the wiring due to a problem such as disconnection of another wiring arranged in the upper layer.

Therefore, attempts have been made to use copper as a wiring material having a low specific resistance, but it has not been put to practical use because it is difficult to process. The resistance to alkali is taken by forming a passivation layer on the wiring, but the number of steps is increased and the cost is increased. Regarding the reflectance, measures have been taken to make the shape of the reflective pixel electrode uneven so that the diffused component of the reflected light becomes large, but the current reflective liquid crystal display element is not as good in visibility as the transmissive liquid crystal display element. , A material with higher reflectance is required.

On the other hand, recently, attention has been focused on silver and its alloys as wiring materials and reflective electrode materials capable of solving all of the above problems. Silver is the material having the lowest specific resistance among metals, and even a silver alloy containing a few% of an additive element has a low specific resistance. It also has excellent alkali resistance,
The reflectance is about 5% higher than that of aluminum.

Despite being such an excellent material, the fact that silver or a silver alloy has not been adopted so far is that aluminum is sufficient in physical properties, and that silver is expensive in terms of cost. Was strong.

However, recently, since physical properties of aluminum have come to the limit of miniaturization of wiring due to high density of devices, it has been attempted to make devices using silver or silver alloys, but it is not possible to However, there is a problem that the adhesion to the insulating film such as SiOx or SiNx is poor. Therefore, SiOx and Si
A metal such as Nx having good adhesion to an insulating film, for example, molybdenum is provided between the insulating film and the silver or silver alloy layer.

[0009]

Generally, the same phosphoric acid / nitric acid / acetic acid mixed acid as aluminum is used for etching silver or silver alloys, but the etching rate of silver and silver alloys is different from that of aluminum. It is more than three times as large as that in comparison and difficult to control. Further, there is a problem that etching of a laminated film made of molybdenum and silver and a silver alloy causes large side etching, which makes it difficult to process fine wiring.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an etching solution and an etching method capable of suppressing side etching as much as possible.

[0011]

[Means for Solving the Problems] The etching method according to the present invention is characterized in that when an etching solution containing a mixed acid of phosphoric acid, nitric acid and acetic acid is used to etch a laminated film made of silver or a silver alloy, the etching solution is The flow strength is characterized by being in the range from the flow strength at the boundary where the etching reaction starts to the flow strength of 67% thereof.

The etching solution according to the present invention has a nitric acid concentration of 0.6 to 1.4 wt%.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. First, a plurality of samples as shown in FIG. 7 are prepared. That is, a thin film 2 made of silicon oxide and having a film thickness of 600 nm is formed on the glass substrate 1 by the PE-CVD method. After forming a thin film 3 of molybdenum having a film thickness of 25 nm on the thin film 2 by a sputtering method,
A silver alloy thin film 4 having a film thickness of 660 nm and made of 98 at% silver and 2 at% additive element is formed. A wiring pattern resist pattern 5 having a width of 10 μm is formed on the silver alloy thin film 4 by PEP. The size of this sample is 15mm x 20
mm.

Next, etching solutions mixed with phosphoric acid, nitric acid and acetic acid having the composition shown in FIG. 3 are prepared in beakers. The etching solution contains phosphoric acid 35 to 55 wt%, nitric acid 0.6 to 2.2 wt%, and acetic acid 30.
It is a solution in the range of ˜40 wt%. Subsequently, the sample having the laminated film made of silver and silver alloy and molybdenum is placed in the beaker and subjected to etching treatment. In this etching process, the sample was etched without flowing the etching solution, and the results are shown in FIG. The temperature of the etching solution at this time is room temperature (room temperature).

As can be seen from the results shown in FIG. 3, when the etching solution is not flowed, the side etching amount 6 of the silver alloy thin film 4 shown in FIG. 4 is 3 μm or more in all the etching solutions having the above compositions. It was

FIG. 3 shows the etching rate of the etching solution of each composition, and FIGS. 5 and 6 show the relationship between the nitric acid concentration and the etching rate in a system in which the concentration of phosphoric acid or acetic acid is constant. As can be seen from FIGS. 5 and 6, the composition range of the etching solution at which the etching rate is 500 nm / min or less is phosphoric acid 35 to 45 wt.
%, Nitric acid 0.6 to 1.4 wt%, and acetic acid 30 to 35 wt%.

Next, phosphoric acid: nitric acid: acetic acid = 45: 1.
An etching solution having a composition of 0:35 (wt%) is prepared in a beaker. Then, in a state where the solution temperature was controlled at 30 ° C., the etching solution was caused to flow at each flow intensity (adjusted by the scale of the stirrer) shown in Table 2 and the above sample was put into the etching solution to perform etching. The flow of the etching solution is performed by stirring the etching solution, and a magnetic stirrer is used to stir the etching solution, and the sample is fixed at a predetermined position with tweezers so that the film formation surface of the sample is perpendicular to the flow of the solution. Further, similar etching was performed even when the solution temperature was controlled at 45 ° C. The result is shown in FIG.

As can be seen from the results shown in FIG. 1, when the solution flow is strong, the etching reaction does not start, and when the flow is weakened, the flow strength at the boundary where the etching reaction starts is 67%. In the etching up to the strength, the side etching amount became 1 μm or less. For example, when the solution temperature is 30 ° C., the flow intensity at which the etching reaction starts is 6 on the scale of the stirrer,
Since the minimum value of the flow intensity when the side etching amount is 1 μm or less is 4, the side etching amount is 1 μm or less in the etching from the flow intensity at the boundary where the etching reaction starts to the flow intensity of 67%. . When the silver alloy thin film substrate after the etching treatment of the sample with the flow intensity in this range was observed using an optical microscope and a scanning electron microscope, the cross-sectional shape of the wiring was forward tapered or vertical as shown in FIG. However, the side etching amount was 1 μm or less, and there was no residue, the workability was good, and no adverse effect on the photoresist was confirmed.

As described above, in order to keep the etching rate of the laminated film of silver alloy and molybdenum at 500 nm / min or less, the concentration of nitric acid in the etching solution is 0.6-1.
It may be in the range of 4 wt%. Further, in order to keep the side etching amount to 1 μm or less, it is necessary to flow the etching solution, and the flow strength is 67% from the flow strength at the boundary where the etching reaction starts.
It is preferable that the range is up to the flow strength of.

In the above embodiment, the etching of the laminated film of silver alloy and molybdenum has been described, but the same applies to the etching of the laminated film of silver and molybdenum. In addition, in the above-described embodiment, the laminated wiring using molybdenum as the base was processed and evaluated.
Similar results were obtained by using a three-layer structure wiring with silver in the middle layer and molybdenum in the upper layer.

The concentration of nitric acid is 0.6 to 1.4% by weight.
Even if the etching treatment was carried out 500 times with the etching solution in the range, no significant change was observed in the etching rate.

[0022]

As described above, according to the present invention, side etching can be suppressed as much as possible.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the effect of the etching method of the present invention.

FIG. 2 is a sectional view of a silver alloy thin film obtained by the etching method of the present invention after etching.

FIG. 3 is a diagram showing measurement results of etching rate and side etching in etching without solution flow, each composition of phosphoric acid / nitric acid / acetic acid system.

FIG. 4 is a cross-sectional view after etching a silver alloy thin film when etching is performed without flow.

FIG. 5 is a graph showing the relationship between the nitric acid concentration and the etching rate when the phosphoric acid concentration is constant (45%).

FIG. 6 is a graph showing the relationship between the nitric acid concentration and the etching rate when the acetic acid concentration is constant (35%).

FIG. 7 is a cross-sectional view of a sample having a silver alloy thin film used for etching.

[Explanation of symbols]

1 glass substrate 2 Silicon oxide thin film 3 Molybdenum thin film 4 Silver alloy thin film 5 resist 6 Side etching amount

Claims (2)

[Claims] 1. When etching a laminated film made of silver or a silver alloy by using an etching solution composed of a mixed acid of phosphoric acid, nitric acid and acetic acid, the etching solution is caused to flow, and the flow strength is such that the etching reaction An etching method characterized in that the flow strength is from the flow strength at the starting boundary to a flow strength of 67% thereof. 2. When etching a laminated film made of silver or a silver alloy using an etching solution made of a mixed acid of phosphoric acid, nitric acid and acetic acid, the nitric acid concentration of the etching solution is 0.6 to 1.4 wt. Etching solution characterized by being in the range of%.