JPS6038022B2 - etching liquid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a silicon oxide etching solution, and more particularly to a silicon oxide etching solution that coexists with two or more metals having different ionization tendencies.

When forming semiconductor elements and beam leads, T is deposited on silicon oxide (hereinafter abbreviated as Si02) as an insulating film
A widely used method is to interpose a metal with good adhesion to Si02, such as i-Au or Mo-Au, and then laminate Au. Therefore, it becomes necessary to selectively etch only Sj02 coexisting with Ti-Au and Mo-Au. Also, in this technical field, it is known to form a film of Si02 on the element by sputtering and then etch the Si02 in order to provide contact openings in the film. Ammonium saturated aqueous solution to hydrofluoric acid 7:1
An etching solution is known in which these materials are mixed at a ratio of ~4:1 and a polyhydric alcohol is further added thereto at a ratio of approximately 10% to 30% (Japanese Patent Publication No. 47-29349).

The present inventors first used hydrofluoric acid and ammonium fluoride, which are widely known as etching solutions for Sj02, in order to etch SJ02, which coexists with two or more dissimilar metals with different ionization tendencies as described above. When etching was performed on the metal component alone and in combination with the metal component and Si02 using a mixed solution of (hydrofluoric acid: saturated aqueous ammonium fluoride solution = 1:6 volume ratio), when these metals were used alone, Confirmed that it was not etched.

Next, the material on which the Si02 layer, Mo layer, Au layer, and photoresist layer were provided on the substrate was etched. Figure 1 shows a photoresist layer 1, an Au layer 2, a Mo layer 3,
A model element consisting of a Si02 layer 4 and a substrate 5,
B shows the state in which the photoresist pattern has been prepared, B shows the state in which the conductor has been etched, and C shows the state in which Si02 has been etched. When etching the conductor and SiO2 according to the processes A, B, and C in Figure 1, the etching can be performed without any abnormality up to the etching of Mo as shown in B in Figure 1, but when the etching progresses to C, the Mo undercuts. It was recognized that the circuit of the desired shape could not be formed. When the cause of this was investigated, it was found that a battery was constructed in which Au was used as a cathode and Mo was used as an anode in the above-mentioned etching solution, and as a result of anodic dissolution of Mo, Mo was undercut. The present invention was made in order to eliminate the above-mentioned defects, and an object of the present invention is to provide an etching solution for Si02 that can increase polarization of metal and reduce the occurrence of undercuts due to local cell reactions.

According to the invention, the above object is achieved by
It has been found that this can be achieved by adding chlorine to the etching solution.

That is, the present invention provides an etching solution for silicon oxide coexisting with two or more dissimilar metals having different ionization tendencies, which is composed of hydrofluoric acid, a buffer solution, and a polyhydric alcohol, and in which the amount of the polyhydric alcohol is greater than that of the hydrofluoric acid and the buffer solution. 4 for the total amount of
The present invention relates to an etching solution characterized in that the concentration is 0 to 60% (volume %).

According to experiments conducted by the present inventors, polyhydric alcohols such as glycerin were added to an etching solution consisting of hydrofluoric acid and a buffer solution, especially an ammonium fluoride buffer solution, by 40 to 60% (by volume) of the total amount of hydrofluoric acid and buffer solution. %) was found to reduce the undercut, ie, d in FIG. 1. Considering this from the polarization behavior, the anode reaction is Mo→Mo310$, and the force sword reaction is 100$→2000.The vertical axis is the current (anode and cathode current), and the horizontal axis is the potential. Figure 2 shows the polarization behavior as a model.

In Figure 2, the anode curve where Mo melts is a, and M
The cathode curve on o is b. The natural electrode potential in this case is E. It is. When Au is in contact with Mo, the cathodic reaction increases by the amount of cathodic reaction that occurs on the surface of Au, and the cathodic curve becomes as shown by c. In this case, the natural electrode potential shifts in that direction and becomes E2, and the anodic reaction in which Mo dissolves increases from 1,a to 12a, promoting the etching of A mosquitoes and causing undercutting. a becomes large. On the other hand, the polarization behavior in an etching solution containing a polyhydric alcohol is shown as a model in FIG.

In other words, in the cathodic reaction on Mo, which is shown by the anodic reaction of dissolving Mo, shown by a', the increase in current is small (large polarization) even when the potential is increased, and the cathodic reaction on the surface of Au is added, resulting in a natural reaction. Even if the electrode potential moves from E,' to E2', 1,
Since the values of a' and 12a' are approximately equal, it can be seen that undercutting of Mo in contact with Au can be prevented from occurring. As the buffer solution in the present invention, an aqueous solution of ammonium fluoride, acidic ammonium fluoride, or acidic alkali metal fluoride salt is used, but it is commercially desirable to use a saturated (40%) aqueous solution of ammonium fluoride; The mixing ratio of acid and ammonium fluoride saturated aqueous solution is 1
:2 to 1:6 is desirable.

Glycerin, ethylene glycol, pinacol, etc. are used as polyhydric alcohols, but when added in an amount of about 30%, the reduction effect during undercutting is small, and when the amount is 70%
In the above case, the etching rate of Si02 becomes slow, resulting in problems that it takes a long time to etch Si02 and that the linearity of the pattern deteriorates.

Next, the present invention will be described with reference to Examples, but the present invention is not limited thereto in any way.

Example 1 A mixed aqueous solution of hydrofluoric acid and a saturated ammonium fluoride aqueous solution at a mixing ratio of 1:4 (volume ratio) and an aqueous solution in which the same amount of glycerin was mixed with this aqueous solution (hydrofluoric acid: saturated ammonium fluoride aqueous solution: glycerin = A mixed aqueous solution with a volume ratio of 1:4:5 was prepared.

The element shown in FIG. 1 was etched at room temperature (25 qo) using these two mixed aqueous solutions, and the undercut was measured, and the relationship between this and the etching time is shown in FIG. Note that the etching time is expressed as a time index, which is the ratio of the etching time divided by the optimum etching time required for desired etching. In Fig. 4, a shows the results of the etching solution without adding glycerin, and b shows the results of the etching solution with glycerin added, indicating that by adding glycerin, the undercut is reduced to 1/10 to 1/15. was recognized.

Example 2 As in Example 1, the mixing ratio of hydrofluoric acid and a saturated aqueous ammonium fluoride solution was set to 1:4, and various amounts of glycerin were added thereto to etch the device at room temperature (25 CO).

Figure 5 shows the measurement results during undercut. When the amount of glycerin added is 20% (volume ratio), it may take 2 to 6 μm during undercutting, and when it is 30%, it may be about 3 μm, whereas when it is 40% to 60%, it takes about 3 times the time required for etching. Even when soaked, the amount was about 1 to 2 degrees, giving practical results. Example 3 An experiment similar to Example 2 was conducted except that the mixing ratio of hydrofluoric acid and saturated aqueous ammonium fluoride solution was 1:2.

The relationship between the amount of glycerin added and undercut is similar to the results of Example 2, and the amount of glycerin added is 10 to 60%.
The range was good. Example 4 An experiment similar to Example 2 was conducted using a mixture ratio of hydrofluoric acid and a saturated ammonium fluoride aqueous solution of 1:6 (volume ratio) and a solution containing various amounts of glycerin as an etching solution. .

Similar to Example 2, the relationship between the amount of glycerin added and the undercut was good when the amount of glycerin added was 40 to 60%. When the mixing ratio of hydrofluoric acid and ammonium fluoride saturated aqueous solution was set to 1:11 according to the above experiment, and
: When the amount of glycerin added was changed to 8, and the relationship between it and undercut was examined, the linearity (pattern accuracy) of the pattern was poor regardless of the presence or absence of glycerin, indicating that the effect of adding glycerin was poor. was not clear.

From the above points, the mixing ratio of hydrofluoric acid and ammonium fluoride saturated aqueous solution is 1:2 to 1:6, and the amount of glycerin added is 40
It can be seen that good results are obtained at ~60% (volume ratio).

Example 5 Hydrofluoric acid: Mixing ratio of ammonium fluoride saturated aqueous solution 1:2
Experiments similar to those in Example 2 were conducted by adding various amounts of ethylene glycol instead of glycerin to the ~1:6 composition solution.

The effective range of the amount of ethylene glycol added was 40 to 60% (volume ratio) as in the case of glycerin, and the undercut had the highest density of 4.0%, and the pattern accuracy was also good.

Example 6 An experiment similar to Example 5 was conducted using pinacol instead of ethylene glycol.

As in Example 5, the effective range of the amount of pinacol added is 40
~60% (volume ratio).

From the above experiments, it was recognized that polyhydric alcohols other than glycerin are similarly effective.

Instead of Mo-Au shown in the above example, Cr-Ag,
Si02 coexisting with two or more metals with different ionization directions such as Cr-Au, Ti-Mo-Au, NjCr-Au, etc.
When etching was performed using the etching solution according to the present invention, the amount of polyhydric alcohol added was 40 to 60%.
% (volume ratio), the number of undercuts was the lowest in all cases, and it was recognized that the pattern accuracy was also good.

In view of the above results, at least two
The effect of adding polyhydric alcohol to the etching solution for Si02, which coexists with more than one metal, is extremely specific in terms of the range of its effective addition amount, and also because the allowable time for etching treatment is long. As can be seen, there are many advantages in manufacturing this type of semiconductor device.

[Brief explanation of the drawing]

Figure 1 shows two types (Au and Mo) with different ionization characteristics.
FIGS. 2 and 3 are diagrams illustrating the process of etching a model element provided with a Si02 layer that coexists with two metals, and the states in each process. FIGS. Figure 2 is a diagram showing the polarization behavior of metals as a model. Figure 2 shows the case where polyhydric alcohol is not added to the etching solution, and Figure 3 shows the case where polyhydric alcohol is added to the etching solution according to the present invention. FIG. 4 is a graph comparing a case (a) in which glycerin is not added to the etching solution and a case (b) in which glycerin is added to the etching solution according to the present invention in relation to undercutting and etching time. is a graph showing that changing the amount of glycerin added to the etching solution affects the relationship between undercutting and etching time. In FIG. 1, 1...photoresist layer, 2...
...Au layer, 3...Mo layer, 4...S
j02 layer, 5...substrate, a...undercutting. Spear 1 Spear 2 Spear 3 Spear 4 Ice 5

Claims (1)

[Scope of Claims] 1. An etching solution for silicon oxide coexisting with two or more dissimilar metals having different ionization tendencies, which comprises fluorine, a buffer solution, and a polyhydric alcohol, and the amount of the polyhydric alcohol is equal to that of fluoric acid and the buffer solution. 40-60% of the total amount of liquid (
% by volume). 2. The etching solution according to claim 1, wherein the buffer solution is a saturated ammonium fluoride aqueous solution. 3. Claim 2, wherein the mixing ratio of hydrofluoric acid and ammonium fluoride saturated aqueous solution is 1:2 to 1:6 (volume ratio).
Etching liquid described in section. 4. The etching solution according to claims 1 to 3, wherein the polyhydric alcohol is glycerin or ethylene glycol.