JP2590774B2 - Etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to patterning of an aluminum electrode of a semiconductor integrated circuit, a thermal head or the like, and more particularly to an etching method for forming an etching surface of a step portion at 90.degree. About.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor integrated circuit, a thermal head, or the like, an aluminum film is used as a metal wiring, and a silicon compound such as silicon oxide or silicon nitride is used as an insulating film. At this time, if the step portion of the aluminum electrode obtained by patterning the aluminum film is almost perpendicular to the surface, it becomes difficult to completely cover the aluminum electrode with the insulating film, and cracks are formed in the insulating film. When the metal film is formed on the insulating film, the aluminum electrode and the metal film are short-circuited.

For this reason, there is a method of tapering a step portion of an aluminum film. FIG. 6 shows a conventional taper etching method for an aluminum film, and FIG.
6 to 6D are cross-sectional views of the wafer.

[0006] As shown in FIG. 6A, an alumina layer 23 is formed on the surface of an aluminum film 22 formed on a substrate 21 by anodic oxidation, and as shown in FIG. A photoresist 24 is applied to the surface of the substrate to form a predetermined pattern. Subsequently, as shown in FIG. 6C, the aluminum film 22 and the alumina layer 23 are etched using the pattern as a mask, and then the photoresist 24 is peeled off as shown in FIG. It is removed by etching.

At this time, in the step of etching the aluminum film 22 and the alumina layer 23 shown in FIG. 6C, etching is performed with an aqueous solution containing phosphoric acid, acetic acid, nitric acid, and ammonium fluoride solution. Since the etching rate of the alumina layer 23 is 15 times or more as compared with the etching rate of the aluminum film 22, the step portion can be tapered as shown in FIG. However, since an aqueous solution containing an ammonium fluoride solution is used as the etching solution, the surface of the substrate 21 that is the base of the aluminum film 22 is also etched.
Since the surface of the alumina layer 23 has the irregularities 23a, the irregularities 21a also occur on the surface of the substrate 21 during the taper etching step. Therefore, the aluminum film 22
In the case where metal wiring is formed on the substrate 21 which is the base of the above, or when the metal wiring is formed on this insulating film in a process after taper etching even if the substrate 21 is an insulating film such as silicon oxide, The current density was likely to be non-uniform in a local portion of the metal wiring, causing a reduction in reliability.

As a technique for flattening the irregularities 21a, a method disclosed in Japanese Patent Application Laid-Open No. 58-93328 is known. This is because, after forming a first insulating film other than silicon nitride on a base surface having irregularities, the surface of the first insulating film is etched using a reactive ion etching method to smooth the steps of the insulating film, Next, after forming a second insulating film containing silicon nitride as a main component on the first insulating film, a reactive ion etching method in which the etching rate of the concave region of the second insulating film is lower than that of the convex region. This is a method in which the surfaces of the second insulating film and the first insulating film are etched using the method.

[0007]

However, according to the above-mentioned planarization method, it is possible to planarize the irregularities on the surface of the insulating film formed on the substrate and the aluminum film, but the irregularities on the surface of the substrate as the base do not exist. It remains. For this reason,
When metal wiring is formed on the substrate that is the base of the aluminum film that is the problem described above, or when metal wiring is formed on the insulating film in a process after taper etching even if the substrate is an insulating film, Since unevenness is present on the metal wiring, the current density is likely to be uneven at a local portion of the metal wiring, and the use of the above-described planarization method does not solve the problem of reduced reliability.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems. In an aluminum or aluminum alloy etching process using a photolithography method, an etching surface of a step portion is formed at 90 ° or less. Another object of the present invention is to provide an etching method for preventing irregularities on the surface of a substrate as a base.

[0009]

According to the etching method of the present invention, an aluminum or aluminum alloy thin film for metal wiring is formed on the surface of a substrate, and an alumina layer is formed on the surface of the thin film by anodic oxidation. A predetermined pattern is formed by applying a photoresist on the alumina layer, and using the pattern as a mask, the alumina layer and the aluminum or aluminum alloy are etched using a predetermined etching solution to form an inclined surface of 90 ° or less. This is an improved etching method. The improvement means that in the etching step, first, a first etching solution composed of an aqueous solution containing a phosphoric acid, acetic acid, nitric acid and ammonium fluoride solution is used, and thereafter, at a predetermined timing, the first etching solution is used. The second etching solution is obtained by excluding the ammonium fluoride solution from the components of the etching solution.

According to a second aspect of the present invention, in the etching method according to the first aspect, the timing of switching from the first etchant to the second etchant is adjusted by the first etchant. The layer and the aluminum or aluminum alloy are set at a point of 80% to 90% of the time to be completely etched.

According to a third aspect of the present invention, in the etching method of the first aspect, the initial electrical conductivity of the first etchant is I ₀ , and the alumina layer and the aluminum or aluminum alloy are completely etched. If the electric conductivity of the first etchant and I ₁ when the the timing of replacement from the first etchant to the second etchant, the electrical conductivity of the first etchant It is characterized in that it is set when "I ₀ + 0.8 * (I ₁ -I ₀ )" or more and "I ₀ + 0.9 * (I ₁ -I ₀ )" or less.

[0012]

[Function] Substrate, thin film of aluminum or aluminum alloy,
The alumina layer and the thin film of aluminum or aluminum alloy are etched by using the laminated pattern of the alumina layer and the photoresist in this order as a mask. At this time, first, a first etching solution composed of an aqueous solution containing phosphoric acid, acetic acid, nitric acid and an ammonium fluoride solution is used. Since the etching rate of the alumina layer by the first etchant is 15 times or more as compared with the etching rate of the aluminum film, the etching surface is tapered. Next, a second etchant containing no ammonium fluoride solution is used. The second etchant does not have the effect of taper etching, but has little or no effect of etching the substrate. Therefore, the surface of the substrate is protected.

[0013]

1 and 2 show an embodiment of an etching method according to the present invention. FIG. 1 is a flowchart, and FIG.
Is a cross-sectional view showing each step.

First, an aluminum film 2 is formed to a thickness of 0.6 μm on a substrate 1 by a sputtering method or an electron beam evaporation method, and the surface is oxidized in a 5% oxalic acid aqueous solution at an applied voltage of 0.5 V using the aluminum film 2 as an anode. Is performed to form an alumina layer 3 of 0.15 μm (FIG. 1 [S1]). At this time, the thickness of the portion that has not been anodized is 0.5 μm, and this is shown in FIG. Then, FIG.
As shown in FIG. 1, a photoresist 4 is applied to the surface of the alumina layer 3 to a thickness of 0.7 μm to form a predetermined pattern (FIG. 1 [S
2)).

Next, the alumina layer 3 and the aluminum film 2 are etched using the pattern as a mask. In this etching step, an aqueous solution containing phosphoric acid, acetic acid, nitric acid, and ammonium fluoride solution is used.
A first etching solution having a component ratio of phosphoric acid 16, acetic acid 2, nitric acid 1, and ammonium fluoride solution 1.74, and a second etching in which the ammonium fluoride solution is excluded from the first etching solution And two types of etching solutions. As shown in FIG. 2C, the aluminum film 2 is exposed to a position just before the surface of the substrate 1 is exposed with the first etching solution.
After etching (FIG. 1 [S3]), as shown in FIG. 2 (d), the remaining aluminum film 2 is etched by replacing the etching solution with a second etching solution (FIG. 1 [S4]). 5)) Two-step etching is performed. In the first etching step of the two-step etching, the etching rate of the alumina layer 3 with respect to the first etching solution is 15 times smaller than the etching rate of the aluminum film 2.
Since it is twice or more, the angle of the etching surface is formed to be 90 ° or less due to the stirring property of the etching solution. Since the alumina layer 3 is microscopically extremely porous, the etching selectivity is larger than that of the aluminum film 2 and this greatly contributes to the tapering of the etched surface. Since there are many irregularities 3a, if etching is performed with the first etchant until the substrate 1, which is the base, is exposed, the substrate 1 is etched in a manner that the irregularities 3a are dragged. Therefore, by providing a second etching step using an etching solution containing no ammonium fluoride solution, the surface of the substrate 1 is protected.

In the two-step etching process, the first
There are two methods for detecting the timing of replacement of the etching solution with the second etching solution.

As a first method, an aluminum film 2 and an alumina layer 3 are prepared by using only a first etching solution in advance.
Is etched, the etching time t for complete removal is checked, and the replacement timing is set to 0.8t to 0.9t.
Set to t. In this embodiment, the first temperature at 25 ° C.
2B, the aluminum film 2 and the alumina layer 3 were completely etched for 10 minutes. FIG. 3 shows the angle of the etched surface when the replacement timing is changed from 1 minute to 10 minutes in steps of 30 seconds. The angle of the etched surface in 8 minutes or more is a plateau region and 3
It was formed at an angle of 0 ° or less, and in the case of 9 minutes or less, the presence of irregularities on the surface of the substrate 1 was not recognized. here,
The substrate 1 is a silicon oxide. For this reason, it is desirable to set the replacement timing between 8 minutes and 9 minutes.

A second method is to monitor the electric conductivity of the etching solution. In the first etching step of the two-step etching, as the etching proceeds, the aluminum concentration of the first etchant increases, and the electrical conductivity increases. Therefore, the timing of the change of the etchant can be detected by monitoring this. Becomes possible. FIG. 4 shows a change in the electric conductivity with respect to the etching time when the wafer is immersed in the state of FIG. 2B in 100 ml of the first etching solution at a temperature of 25 ° C. in the present embodiment. Since the electrical conductivity increases with the etching amount of the aluminum film, it has a linear relationship with the etching time. From this, when the amount of increase in the electrical conductivity I ₁ when the alumina layer 2 and the aluminum film 3 are completely removed by etching with respect to the initial electrical conductivity I ₀ of the first etching solution is defined as ΔI, electrical conductivity of the first etching solution I ₀ + 0.8 △ I from I ₀ + 0.9 △
It is desirable that the timing reaches I, as the timing for exchanging the etching solution. Further, since the etching rate depends on the temperature of the etching solution, when the temperature control is difficult, the timing of changing the etching solution is more reliable in this method than in the first method.

After the completion of the two-step etching process, FIG.
As shown in (e), the photoresist 4 and the alumina layer 3 are removed (FIG. 1 [S6]).

As another embodiment of the etching method according to the present invention, the present invention is applied to the formation of an electrode portion of an ink jet thermal head as shown in FIG. Here, the silicon substrate 11
A thermal oxide film having a thickness of 1.35 μm is provided thereon as a heat insulating layer, and aluminum is formed as an electrode 13 on the oxide film. Then, a portion serving as the heat generating portion 12 and an adjacent portion are formed by the above-described two-step etching method. The portions between the electrodes 13 and 13 'are removed to form electrodes 13 and 13' having a thickness of 0.5 μm.

Next, on the electrodes 13 and 13 ', a film of tantalum having a thickness of 0.25 .mu.m was
A portion between the resistor 3 ′ and the adjacent resistor is continuously removed so as to continuously cover the heat generating portion 12 to form a resistor pattern.
When the surface of the resistor 14 is anodized in a 0.1% phosphoric acid aqueous solution, a 0.3 μm tantalum pentoxide anodic oxide film is formed as the protective layer 15. At this time, the film thickness of the resistor 14 that has not been anodized is 0.1 μm. In the thermal head having such a structure, when a voltage is applied to the electrodes 13 and 13 ′, a current flows through the electrodes 13 and 13 ′ and the resistor 14. Since the value is high, heat is generated in the heat generating portion 12, and the ink (not shown) on the thermal head is heated and boiled, thereby generating bubbles and discharging the ink.
Printing is performed on printing paper (not shown). In this thermal head, the input power to the heat generating portion 12 required to generate bubbles is 700 W / mm ² .

As a result of comparison between the case where the present invention is applied and the case where the present invention is not applied, the breakdown power value of the heat generating portion is 1400 W / mm ² when the present invention is not applied.
On the other hand, when the present invention was applied, the destructive power value of the heat generating portion was 1540 W / mm ² , and a 10% improvement in power durability was recognized. Therefore, by applying the present invention, since the presence of the unevenness of the heating resistor 12 was eliminated, the current density in the thickness direction was made uniform, the breakdown power value was increased, and the reliability was further improved.

[0023]

According to the present invention, when taper-etching an aluminum film or an aluminum alloy film, first, a first etching solution comprising an aqueous solution containing phosphoric acid, acetic acid, nitric acid and ammonium fluoride solution is used. And then the first
Since the second etchant obtained by excluding the ammonium fluoride solution from the components of the etchant is used, it is possible to prevent the occurrence of unevenness on the surface of the substrate as the base. Therefore, it is possible to prevent the occurrence of cracks and the resulting short circuit of the insulating film further formed on the aluminum electrode formed by the etching, and to prevent the occurrence of unevenness of the wiring formed on the substrate surface after the etching, The reliability of the semiconductor integrated circuit and the thermal head can be improved.

[Brief description of the drawings]

FIG. 1 is a flowchart showing one embodiment of an etching method according to the present invention.

FIG. 2 is a cross-sectional view showing one embodiment of the etching method according to the present invention, and FIGS. 2 (a) to (e) show respective steps.

FIG. 3 is a graph showing an angle of an etching surface when changing a timing of changing from a first etching solution to a second etching solution.

FIG. 4 is a graph showing the electrical conductivity of the etchant with respect to the etching time when etching is performed using only the first etchant.

FIG. 5 is a sectional view showing another embodiment of the etching method according to the present invention.

FIG. 6 is a cross-sectional view showing a conventional etching method, and FIGS. 6A to 6D show respective steps.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Aluminum film or aluminum alloy film 3 Alumina layer 4 Photoresist 11 Substrate 12 Heating part 13, 13 'Electrode 14 Resistor 15 Protective layer 21 Substrate 22 Aluminum film or aluminum alloy film 23 Alumina layer 24 Photoresist

Claims (3)

(57) [Claims] An aluminum or aluminum alloy thin film for metal wiring is formed on a surface of a substrate, an alumina layer is formed on the surface of the thin film by anodic oxidation, and a photoresist is applied on the alumina layer to form a predetermined layer. In a method of etching the alumina layer and the aluminum or aluminum alloy using a predetermined etchant to form an inclined surface of 90 ° or less using the pattern as a mask, First consisting of an aqueous solution containing phosphoric acid, acetic acid, nitric acid and ammonium fluoride solution
An etching method characterized by using a second etching solution obtained by removing the ammonium fluoride solution from the components of the first etching solution at a predetermined timing. 2. The timing of switching from the first etching solution to the second etching solution is set to 80 times of the time required for completely etching the alumina layer and the aluminum or aluminum alloy by the first etching solution. 2. The etching method according to claim 1, wherein the etching rate is set in a range of% to 90%. 3. The initial electric conductivity of the first etching solution is I ₀ , and the electric conductivity of the first etching solution when the alumina and the aluminum or aluminum alloy are completely etched is I ₁ . In this case, the timing of replacing the first etchant with the second etchant is determined by determining whether the electrical conductivity of the first etchant is “I ₀
+ 0.8 × (I ₁ −I ₀ ) ”or more and“ I ₀ + 0.9 ×
2. The etching method according to claim 1, wherein the time is set at (I ₁ −I ₀ ) ”or less.