JP2002030469A - Etching solution and etching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an etching solution and an etching method, in etching using an etching solution containing cerium (TV) nitrate ammonium capable of surely preventing the precipitation of insoluble compounds, further good in the etching rate and excellent in mass-productivity. SOLUTION: In this etching solution, the concentration of nitric acid is 8 to 15 wt.%, and the concentration of cerium (TV) nitrate ammonium is >20 to 30 wt.%. The etching method uses the same etching solution. In the etching method, cerium (TV) nitrate ammonium is replenished into the etching solution in the process of etching in such a manner that the weight ratio of quadrivalent cerium to hexavalent chromium is controlled to >=17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an etching solution and an etching method, and more particularly to an etching solution and an etching method suitably used for etching a Cr (chromium) thin film on a transparent substrate in manufacturing a liquid crystal display panel.

[0002]

2. Description of the Related Art A liquid crystal display panel has transparent substrates which are arranged to face each other with a liquid crystal interposed therebetween, and the light transmittance of each pixel is independently controlled by electrodes formed in a matrix on the surface of the transparent substrate. It is configured to be able to. Therefore, signal lines, electrodes, and the like are finely and complicatedly processed and arranged on at least one of the transparent substrates on the liquid crystal side.

It is known to use Cr as a material for forming such signal lines or electrodes, and an etching method using a photolithography technique for processing the Cr is known. Specifically, after forming a Cr thin film on the entire surface of the transparent substrate by vapor deposition or the like, a photoresist is formed on the upper surface in a desired shape, and the Cr thin film not covered with the photoresist is appropriately etched. By dissolving and removing using a liquid, signal lines and electrodes made of Cr are formed on the transparent substrate.

In etching the Cr thin film, Cr
Conventionally, as an etchant for dissolving and removing
Ceric ammonium nitrate (Ce (NH ₄ ) ₂ (NO
₃ ) ₆ ) and an aqueous solution of nitric acid or perchloric acid, for example, having a concentration of ceric ammonium nitrate of 10 to 15% by weight,
A nitric acid or perchloric acid concentration of 3 to 5% by weight was used.

However, when etching is performed using an etching solution having such a composition, an insoluble compound containing cerium as a main component derived from the etching solution is deposited on the substrate surface in a washing step after the etching, and this insoluble compound causes There is a problem that the fine processing etching of the thin film is hindered.

Japanese Patent Application Laid-Open No. H11-131263 discloses an etchant having a ceric ammonium nitrate concentration of 10 to 20% by weight and a nitric acid concentration of 5 to 10% by weight as a Cr etching solution for suppressing the precipitation of the insoluble compound. Proposed. In Japanese Unexamined Patent Application Publication No. 11-131263, ceric ammonium nitrate under the following conditions is premised on the premise that a material on which a photoresist is formed is immersed in warm water at 50 to 100 ° C. prior to etching. -Defines the concentration of nitric acid based etchant. Nitric acid concentration is 5% by weight or more to prevent white precipitate generation. Nitric acid concentration is 10% by weight or less to secure taper angle. Ceric ammonium nitrate concentration is 10% by weight or more to prevent fine residue. The concentration of ceric ammonium nitrate is less than 20% by weight

[0007]

SUMMARY OF THE INVENTION Japanese Patent Application Laid-Open No. H11-1312
No. 63 proposes that the concentration of nitric acid be 5% by weight or more in order to prevent the precipitation of insoluble compounds (white precipitates). That is, it was not possible to prevent the precipitation of insoluble compounds while maintaining the etching rate at a mass production level.

In Japanese Patent Application Laid-Open No. H11-131263, the composition of the etchant is defined based on the above four conditions. Of these four conditions, the precipitation of an insoluble compound is the most significant factor that hinders productivity. In practice, it becomes impossible to continue the production when the insoluble compound is precipitated.

That is, in the etching process, it is the most important requirements to surely prevent the precipitation of the insoluble compound and to secure the etching rate, rather than to secure the taper angle and prevent the generation of fine residues. In order to secure the taper angle and prevent the generation of fine residue, it is possible to cope with the mechanical adjustment by improving the etching apparatus.

Accordingly, an object of the present invention is to provide an etching solution and an etching method which can surely prevent precipitation of an insoluble compound, have a good etching rate, and are excellent in mass productivity.

[0011]

The etching solution of the present invention has an ceric ammonium nitrate concentration of more than 20% by weight and not more than 30% by weight in an etching solution containing ceric ammonium nitrate, nitric acid and water. And a nitric acid concentration of 8 to 15% by weight.

The etching method of the present invention (claim 2)
In an etching method using an etching solution containing ceric ammonium nitrate, nitric acid and water, the concentration of ceric ammonium nitrate in the etching solution is more than 20% by weight and 30% by weight or less, and the concentration of nitric acid is 8 to 1%.
5% by weight.

[0013] The etching method of the present invention (claim 3) comprises:
In a method of etching Cr using an etching solution containing ceric ammonium nitrate, nitric acid, and water, the etching solution during etching is adjusted so that the weight ratio of tetravalent cerium to hexavalent chromium in the etching solution is 17 or more. Is supplemented with ceric ammonium nitrate.

In a conventional etching solution, an insoluble compound is precipitated by the following mechanism.

That is, while the etching solution is prepared and stored, a very small amount of insoluble Ce (OH) ₄ precipitates in the etching solution, and furthermore, during the pure water washing (rinsing) following the etching process. As a result, the pH is increased by diluting the etching solution, and as a result, Ce (OH) ₄ is deposited with existing Ce (OH) ₄ as a nucleus.

Therefore, in this series of precipitation reactions, Ce (OH) ₄ precipitated during storage has a large effect. That is, since Ce (OH) ₄ precipitated during storage acts as a nucleus, precipitation during dilution is promoted, and a large amount of precipitate finally adheres to the substrate surface. Ce (O
If the precipitation reaction of H) ₄ is prevented, a large amount of Ce (OH) ₄ will not be precipitated within a realistic time until the end of the cleaning even in the pure water cleaning step in which the etching solution is diluted thereafter.

The chemical formula that produces an insoluble compound (Ce (OH) ₄ ) in the etching solution during storage is as shown in the following formula (1). Ce (OH) ³⁺ + 3H ₂ O → Ce (OH) ₄ + 3H ⁺ ...... (1)

From the above equation (1), it can be seen that in an etching solution having a low pH and an increased hydrogen ion concentration, H ^{+ on the} right side increases, and the reaction from the left side to the right side is suppressed.
That is, it is effective to increase the acid concentration in order to lower the pH of the etching solution in order to suppress the precipitation during storage. In addition, as a result of experiments, it has been found that adding nitric acid is more effective in preventing precipitation than adding perchloric acid as an acid, so that nitric acid may be used as the pH adjusting acid. desirable.

Since ceric ammonium nitrate itself is acidic in an aqueous solution, the concentration of hydrogen ions in an etching solution containing ceric ammonium nitrate and nitric acid must be adjusted by adjusting the concentration of ceric ammonium nitrate. And the adjustment of nitric acid concentration are both required. However, since the molecular weight of ceric ammonium nitrate is larger than that of nitric acid, the decrease in the pH per weight of addition by adding nitric acid is larger than that by adding ceric ammonium nitrate. .

FIGS. 2 and 3 show how insoluble compounds are precipitated with respect to the concentrations of nitric acid and ceric ammonium nitrate. FIG. 2 shows the time required for the deposition in the etching solution when the etching solution was kept at 80 ° C. FIG. 3 shows the residue on the substrate surface when the substrate was etched with each etching solution. It shows the degree of. In both FIGS. 2 and 3, the higher the concentration of nitric acid and ceric ammonium nitrate, the less the precipitation.

Since the reaction of the above formula (1) is accelerated under a high temperature condition according to the Arrhenius equation, the temperature of the etching solution must be 40 ° C. or less, particularly preferably 35 ° C. or less. Since the etching rate also depends on the temperature, the temperature of the etching solution must be 20 ° C. or higher, and more preferably 25 ° C. or higher, in order to secure an etching rate higher than a certain level. Therefore, in the present invention, the temperature of the etching solution is 20 to 40 ° C.,
Particularly, the temperature is preferably 25 to 35 ° C.

When perchloric acid is added to the etching solution, there is no correlation between the amount of perchloric acid and the etching rate. However, when nitric acid is added, there is a large difference in the etching rate depending on the amount of nitric acid added. Was found to appear. Therefore, when adjusting the pH of the etching solution by adding nitric acid, it is necessary to consider not only simply lowering the pH but also that the etching rate is sufficiently high.

[0023] Just edge to etchant composition
FIG. 4 shows the ching time. In mass production,
A composition having a switching time of 100 seconds or less can be used.
Slow etching rate with etchant with high nitric acid concentration
This is because the oxidizing action of nitric acid makes the Cr surface passivated.
That's because. That is, ceric ammonium nitrate
Cr₂O₃Passivation can be dissolved, but "Cr → Cr₂O₃
(Passive) → Cr₂O ₇ ^2-"Than the reaction of" Cr →
Cr³⁺→ Cr₂O₇ ^2-Response is faster,
Etchant with a high concentration of nitric acid
Is an etchant with low nitric acid concentration where the latter reaction is dominant
The etching rate is lower than that of the etching solution. Also,
Liquid containing too much ceric ammonium nitrate
Same phenomenon due to nitric acid group derived from ceric ammonium
Occurs, the etching rate is reduced.

As described above, in order to prevent the deposition of insoluble compounds, a low pH etching solution containing a large amount of nitric acid or ceric ammonium nitrate is preferable. Passivation slows down the etching rate. For this reason, it is necessary to employ a well-balanced etchant composition in order to secure the etching rate at a mass production level and to prevent the precipitation of insoluble compounds.

According to the study of the present inventors, as a condition satisfying both the prevention of the precipitation of the insoluble compound and the securing of the etching rate, as shown in FIG. 1, the concentration of ceric ammonium nitrate is more than 20% by weight and 30% by weight. %, And a nitric acid concentration of 8% by weight to 15% by weight.

In particular, when a chromium etchant having a ceric ammonium nitrate concentration of 25% by weight and a nitric acid concentration of 9% by weight is used, almost no insoluble compound is deposited on the substrate surface even after the etching and washing steps, and the etching rate Was also confirmed to be sufficiently high.

In the Cr etching solution of the present invention having such a composition, an insoluble compound of Ce (OH) ₄ is not generated in the etching solution even after a relatively long period of time. In the selective etching of the fine and complicated pattern of the Cr thin film in the material to be etched, the adverse effect of the insoluble compound can be prevented.

Further, the precipitation of the insoluble compound is promoted even when the concentration of hexavalent chromium in the etching solution increases. That is, the amount of chromium that can be dissolved in a certain amount of the etching solution is limited, and when the amount exceeds the limit, cerium is easily precipitated.
An experiment confirmed that when the weight ratio of cerium (IV) to hexavalent chromium in the aqueous solution (Ce ⁴⁺ / Cr ⁶⁺ ) was less than 17, an insoluble compound was precipitated. Also, maintaining the chromium concentration contained in the solution at a low level is
This means that the frequency of replacement of the etching solution is increased more than necessary, which is wasteful. Therefore, practically, it is desirable that the weight ratio of tetravalent cerium to hexavalent chromium in the etching solution is 40 or less.

From the above, 6% in the etching solution is used.
Weight ratio of tetravalent cerium to trivalent chromium (Ce ⁴⁺ / C
r ⁶⁺ ) is preferably 17 or more, particularly preferably 17 to 40.

In order to keep the concentration of the etching solution within this range, it is conceivable to always add ceric ammonium nitrate in an amount corresponding to the amount of chromium dissolved in the etching solution. In this case, however, the etching solution is infinitely high. Concentration, and eventually exceed the limit of the amount dissolved in water, so discard all or part of the liquid that has reached a certain concentration or more,
Mix water, ceric ammonium nitrate, nitric acid,
Alternatively, they are preferably added individually. The upper limit of the chromium concentration, which is a measure for changing the etching solution, is generally 0.15% by weight.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings.

First, the composition of the etching solution of the present invention will be described.

The etching solution of the present invention contains ceric ammonium nitrate as a main component and contains nitric acid as an acid for adjusting pH.

In the present invention, the concentration of ceric ammonium nitrate in the etching solution is more than 20% by weight and 30% by weight.
In the range of not more than% by weight, it is determined by comprehensively considering the consumption amount of ceric ammonium nitrate required for etching a unit amount of Cr, the etching rate, the etching result, and the like.

That is, when the etched material to be etched is taken out of the etching step, a part of the etching solution adheres to the material to be etched and is taken out, so that the consumption of ceric ammonium nitrate is reduced. It is preferable that the concentration of ceric ammonium nitrate in the etching solution is low. On the other hand, if the concentration of ceric ammonium nitrate is too high, the viscosity of the etchant increases in addition to the waste of cerium ammonium nitrate, making it difficult for the etchant to enter between fine resist patterns, resulting in poor etching. May cause Therefore, the upper limit of the concentration of ceric ammonium nitrate is 30
% By weight, preferably 28% by weight.

On the other hand, if the concentration of ceric ammonium nitrate is too low, the etching rate is reduced. From this point, it is desirable that the concentration of ceric ammonium nitrate be high. Concentration, preferably at least 22% by weight.

If the concentration of nitric acid in the etching solution is too high, there is no danger that crystals such as cerium oxide will precipitate, but the etching rate will be low. Conversely, if it is too low, there is a problem of insoluble compound precipitation, and the etching performance tends to decrease.
Therefore, in the present invention, the concentration of nitric acid in the etching solution is set to 8 to 15% by weight, preferably 9 to 12% by weight.

The etching solution of the present invention basically comprises the above three components of cerium ammonium nitrate, nitric acid and water, but may contain other auxiliaries as required. For example, in order to reduce the surface tension of the etching solution, a cationic or nonionic surfactant may be contained up to about 1% by weight.

The etching process in the present invention may be performed by immersing the material to be etched in an etching tank containing the etching solution, holding the material in the solution for a predetermined time, and then rinsing with water, or applying the etching solution to the moving material to be etched. After spraying, any of a continuous method in which water is further sprayed and washed with water can be used, and the continuous etching process can be performed using, for example, an etching apparatus shown in FIG.

FIG. 5 is a schematic diagram showing an example of a Cr etching apparatus used for manufacturing a liquid crystal display panel.

In this apparatus, the material 6 to be etched passes through the transport path 3 and is sequentially processed in the Cr etching tank 1 and the washing tank 2. The etching tank 1 is provided with a plurality of etching liquid nozzles 4 on the upper part thereof, and the etching liquid is sprayed from the nozzles 4 onto the material 6 to be etched on the transport path 3. The etching solution sprayed from the nozzle 4 onto the material 6 to be etched is supplied to the etching tank 1 through a pipe (not shown).
It is withdrawn from the bottom and recycled through a circulation tank. The washing tank 2 is provided with a plurality of pure water nozzles 5 at an upper part thereof, and pure water for washing away the etching solution onto the material 6 to be etched on the transport path 3 is sprayed from the nozzles 5.

In general, as shown in FIG. 6, a material 6 to be etched in the manufacture of a liquid crystal display panel has a Cr layer 8 formed on the entire surface of a main plate of a glass substrate 7 and a C layer formed on the surface thereof.
A photoresist 9 for selectively etching the r layer 8 is formed.

In general, the etching operation is performed while replenishing ceric ammonium nitrate and, if necessary, nitric acid or water, to the etching solution in either the batch system or the continuous system. The replenishing amount is adjusted so that the weight ratio of tetravalent cerium to hexavalent chromium in the etching solution is usually 17 or more, preferably 17 to 40, more preferably 20 to 40, and even more preferably nitric acid in the etching solution. When the concentration of ceric ammonium is more than 20% by weight and not more than 30% by weight, the concentration of nitric acid is 8%.
It is adjusted to be about 15% by weight.

If the weight ratio of tetravalent cerium to hexavalent chromium in the etching solution falls below 17, white insoluble compounds will precipitate on the etched surface, so the lower limit of this weight ratio is set to 17. . On the other hand, a large ratio is safe against the formation of precipitates, and the etching rate is also high. However, as this ratio is large, ceric ammonium nitrate contained in the etching solution discharged out of the system is increased. Is increased, wasting ceric ammonium nitrate. Therefore, the upper limit of the weight ratio of tetravalent cerium to hexavalent chromium in the etching solution is preferably set at 40 from the viewpoint of securing a sufficient etching rate and suppressing the consumption of cerium ammonium nitrate.

Such concentration control of the etching solution can be performed in a batch system or a continuous system. In the case of the batch system, the ratio of tetravalent cerium to hexavalent chromium in the etching solution in the etching tank or the circulation tank is controlled. Supplemented with ceric ammonium nitrate, regularly or irregularly, by analysis or calculation, so that this ratio is within the above range. Further, water is supplied in an amount corresponding to the reduced amount of the etching solution, and nitric acid is further supplied as needed.

In this batch system, the concentration of hexavalent chromium in the etching solution gradually increases, and impurities accumulate and the etching solution deteriorates. Is removed and discarded, and replaced with a new etching solution. Etch 6
The degree to which the chromium (VI) concentration is increased before the replacement of the etching solution depends on the operating conditions and the material to be etched, but generally before the hexavalent chromium concentration of the etching solution reaches 0.15% by weight. It is preferable to perform this replacement.

On the other hand, in the continuous operation, a part of the etching solution is continuously or intermittently withdrawn from the etching bath or the circulation bath containing the etching solution, and a new etching solution is supplied at the same time. The ratio of tetravalent cerium to hexavalent chromium in the etching solution can be in the range specified in the present invention.

In the present invention, the temperature of the etching solution is 20 to 40 ° C., particularly 25 to 35 ° C. for the above-mentioned reason.
It is preferably set to ° C.

Although the above embodiment has been described for the case of etching a Cr thin film, it is needless to say that the material to be etched is not limited to Cr in the present invention. Further, in the above-described embodiment, as the material to be etched 6, one of the transparent substrates disposed to face each other via the liquid crystal, and the Cr layer formed on the main plate surface of the transparent substrate is used. Although an example in which a mask for selective etching is formed on the surface is illustrated, the material to be etched of the present invention is not necessarily limited to such a member, and may be a member in a process of manufacturing an electronic component. Thus, the present invention can be applied to a member or the like that requires fine processing of a metal layer.

[0050]

The present invention will be described more specifically below with reference to examples and comparative examples.

Examples 1 to 4 and Comparative Examples 1 to 3 A resist film having a predetermined shape was formed on a chromium film of a glass substrate having a chromium film formed by sputtering chromium metal. This glass substrate was cut into a size of 50 × 50 mm to obtain a sample.

A 200 cc beaker was charged with 100 cc of an etchant having the composition shown in Table 1 and maintained at 25 ° C. The sample was immersed in the solution, and the time was measured until the chromium film disappeared while moving the sample by hand. did. Next, the sample was taken out, washed with pure water and air-dried, and the state of the etched surface was visually observed. The results are shown in Table 1.

The state of the etched surface was evaluated on the following three levels. ；: Transparent, no precipitate was observed. Δ: White thing is slightly recognized. X: White precipitate is clearly observed.

[0054]

[Table 1]

[0055]

As described above in detail, according to the present invention, it is possible to effectively prevent the deposition of insoluble compounds that inhibit stable production while securing the etching rate at a mass production level, thereby enabling the production Stability can be improved.

[Brief description of the drawings]

FIG. 1 is a graph showing a concept of deriving an optimum composition of an etching solution according to the present invention.

FIG. 2 is a graph of experimental data showing the relationship between the composition of an etching solution and the deposition of an insoluble compound according to the present invention.

FIG. 3 is a graph of experimental data showing a relationship between an etchant composition and defective residues according to the present invention.

FIG. 4 is a graph of experimental data showing a relationship between an etching solution composition and a just etching time according to the present invention.

FIG. 5 is a schematic configuration diagram showing an embodiment of an etching apparatus used in the present invention.

FIG. 6 is a sectional view showing an embodiment of an etching material according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cr etching tank 2 Rinse tank 3 Transport path 4 Etching liquid nozzle 5 Pure water nozzle 6 Material to be etched 7 Glass substrate 8 Cr layer 9 Photoresist

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomoaki Takahashi 3300 Hayano, Mobara City, Chiba Prefecture Within Hitachi Display Group, Ltd. (72) Inventor Masaru Miyoshi 1-1, Joishi, Yawatanishi-ku, Kitakyushu-shi, Fukuoka Prefecture F-term (reference) 4K057 WA10 WB08 WE02 WG02 WG03 WK01 WM06 WN02 5F043 AA26 BB18 EE07 EE23 EE29 FF10 GG10

Claims (7)

[Claims] Cerium ammonium nitrate, nitric acid,
And an etching solution containing water, wherein the concentration of ceric ammonium nitrate is more than 20% by weight and not more than 30% by weight, and the concentration of nitric acid is 8 to 15% by weight. 2. Cerium ammonium nitrate, nitric acid,
And an etching solution using an etching solution containing water, wherein the concentration of ceric ammonium nitrate in the etching solution is more than 20% by weight and 30% by weight or less, and the concentration of nitric acid is 8 to 15% by weight. Etching method. 3. Cerium ammonium nitrate, nitric acid,
In a Cr etching method using an etching solution containing water and water,
An etching method, characterized in that ceric ammonium nitrate is supplied to the etching solution during etching so that the weight ratio of cerium (V) is 17 or more. 4. The method according to claim 3, wherein a part of the etching solution is continuously or intermittently extracted from the etching bath or the circulation bath for the etching solution, and ceric ammonium nitrate, nitric acid is added to the etching bath or the circulation bath. And one or more kinds of water. 5. The method according to claim 3, wherein ceric ammonium nitrate is replenished to the etching solution such that the concentration of ceric ammonium nitrate in the etching solution is more than 20% by weight and 30% by weight or less. An etching method characterized by the above-mentioned. 6. The etching method according to claim 3, wherein nitric acid is supplied to the etching solution so that the concentration of the nitric acid in the etching solution is 8 to 15% by weight. 7. The etching method according to claim 3, wherein the etching is performed at 20 to 40 ° C.