JPS6088946A - Chromium mask washing method - Google Patents

Abstract

PURPOSE:To prevent a defect of a Cr film by retaining the oxidative effect of a washing soln. in washing the Cr mask of a semiconductor element. CONSTITUTION:A Cr film pattern is formed on a glass base to form a Cr mask, and its surface is oxidized in the air and it is covered with a Cr oxide film. When the Cr mask is washed with a washing soln. contg. sulfuric acid and a small piece of aluminum is present as a dust in the solution, the Cr oxide layer is reduced to metallic Cr, and the Cr oxide film is dissolved off. On the other hand, when nitric acid as an oxidizing agent is mixed with the sulfuric acid and the mask is washed with the soln., even if the Cr oxide is reduced into metallic Cr, since it is immediately oxidized to Cr oxide with the oxidizing agent and covers the metallic Cr, and Cr oxide is not dissolved into the soln. The nitric acid is, preferably, added >=5mol% of the sulfuric acid. Oxidizig agents such as H2O2, KMnO4 etc. can be used. As a result, a defect of the Cr film can be prevented by retaining the oxidation action of the washing soln., disconnection of the pattern, and occurrence of insular Cr films can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cleaning a chrome mask used in the manufacture of semiconductors such as semiconductor elements, ICs, and LSIs.

Here, the chrome mask refers to a blank in which a chromium film is coated on a glass substrate, a blank in which a chromium oxide film is laminated on the chrome crotch, or a blank in which indium oxide, tin oxide, etc. is deposited between the glass substrate and the chromium film. The chromium film or the chromium oxide film is patterned into a predetermined shape using a blank or the like with a transparent conductive film interposed therebetween.A typical example is a chrome mask in which a chromium film is patterned. can be mentioned.

Dust often adheres to this chrome mask during the manufacturing process of semiconductor devices and the like.

Conventionally, as a method for cleaning such kimonos, a method has been proposed in which a chrome mask is immersed in sulfuric acid.

According to this proposal, Chrome 13! The surface of the mask is oxidized by oxygen in the air and is always covered with a layer of chromium oxide of several rims, so even if the chrome mask is immersed in sulfuric acid, the chromium group will not be eluted. 11 It is possible to wash the kimono, but if small pieces of metal such as aluminum are mixed in as dust and adhere to the chromium oxide layer on the surface of the chromium film, the following effects will occur and the chromium will be washed away. The membrane is eluted in sulfuric acid. 1. In other words, a part of a small piece of metal such as aluminum dissolves into cations in sulfuric acid, and the electrons remaining in the metal piece move into the chromium oxide layer beneath the metal piece. go. this is,
Electrons were given to the chromium oxide layer on the surface of the chromium film, in other words, the chromium oxide layer was reduced. Then, the chromium oxide layer on the surface is reduced to metallic chromium, and since this metallic chromium is soluble in sulfuric acid, eventually
The chromium oxide layer, which has become metallic chromium, is eluted into the sulfuric acid, and the chromium film underneath it is also eluted, resulting in the chromium film being missing. A chromium mask with a missing chromium film in this manner cannot be used for manufacturing semiconductor devices or the like because it causes disconnection in the pattern or the island-like chromium film is missing.

An object of the present invention is to provide a photomask cleaning method that eliminates the above-mentioned drawbacks and does not cause chipping of the chromium film.

In order to achieve such an objective, the present inventor focused on the fact that the cause of chromium film loss is the reduction of the chromium oxide layer on the surface of the chromium film to become metallic chromium, as described above, and developed a cleaning solution that has an oxidizing effect. We discovered that as long as the chromium oxide layer is reduced to metallic chromium, it is immediately oxidized and the surface of the chromium film is covered with a chromium oxide layer again, so that the chromium film will not be eluted into the cleaning solution. , we have completed the present invention. The gist of the present invention is that by adding an oxidizing agent to sulfuric acid, the oxidizing effect is sustained in the cleaning liquid.

The present invention will be explained below with reference to the drawings.

When small pieces of metal such as aluminum adhere to the chromium oxide layer on the surface of the chromium film and the chrome mask is immersed in a sulfuric acid solution, some of the metal pieces become cations and dissolve, and the remaining electrons are transferred to the chromium oxide layer. The phenomenon of movement is the same as placing two electrodes in a sulfuric acid solution, using a chromium film covered with a chromium oxide layer as one electrode, and applying a negative voltage to this electrode. Based on this knowledge, the present invention will be explained using an experimental apparatus shown in FIG. In the figure, a constant temperature bath 1 contains water 2 that maintains the temperature of the liquid in an electrolytic cell 3 at approximately 50°C, and a sulfuric acid/nitric acid mixture 4 containing nitric acid as an oxidizing agent is contained in the electrolytic cell 3. Then, add chrome mask 5 to this mixture 4.
Soak the vine. As is well known, this chrome mask 5 is made of chrome l! on a glass substrate 6. 7 is patterned into a predetermined shape, and the surface of the chromium film 7 is coated with a chromium oxide layer 8 by oxygen in the air. A DC power source 10 is connected to the chromium oxide layer 8 described above as a cathode plate and the opposing copper plate 9 as an anode plate.

Therefore, the elution start voltage of the chromium film 7 was measured while gradually increasing the voltage applied between the two electrodes from 1 O volt using each mole % of sulfuric acid and nitric acid in the mixed liquid 4 as parameters. The results are shown in Table 1.

Table 1 The results show that as the proportion of nitric acid in the mixed liquid 4 increases, the oxidizing effect of this mixed liquid 4 becomes stronger, and the chromium oxide layer 8 on the surface of the chromium film 7 becomes less likely to be reduced. .

Next, prepare a chrome mask 5 on which 100 patterns of 2 μm 0 chromium film 7 are formed, and this chrome mask 5
A mixture of sulfuric acid and nitric acid with the mol% of nitric acid as a parameter (liquid temperature: 5
0℃) and chromium! We observed how many l*7 patterns were missing.

The results are shown in Table 2.

From this result, even if a very small amount of nitric acid is contained, the chromium film 7 can be prevented from being chipped, and if the chromium mask 5 is cleaned by immersing it in a sulfuric acid/nitric acid mixture 4 containing 5 mol% or more of nitric acid. , Chrome If! It was found that the omission of 7 did not occur.

Furthermore, as a result of investigating the conditions for sustaining the oxidizing effect of a sulfuric acid/nitric acid mixture containing 5 mol% or more of nitric acid, it was found that nitric acid should be added to the cleaning solution at a rate of 1.5 mol% per hour. did.

Regarding the changes in the properties of the chrome mask due to the addition of nitric acid, none of the optical density, surface reflectance, film thickness, and pattern line width changed during normal cleaning time (approximately 10 minutes).

As described above, according to the present invention, the
If a sulfuric acid/nitric acid mixture containing preferably 5 mol % or more is used, cleaning can be performed without causing any loss of the chromium film without changing the properties of the chromium mask.

In addition, in the above example, nitric acid was used as the oxidizing agent, but
The present invention is not limited thereto, and even if hydrogen peroxide, permancanic acid, potassium nitrate, ozone, or the like is used as the oxidizing agent, the same effects as in the above embodiments can be obtained. Further, in addition to the chromium mask in the narrow sense of only a chromium film mentioned in the embodiment, a chromium mask in which chromium oxide is laminated on a chromium film is used to prevent chipping of the thick end face of the chromium film.

〉The same effect as in the above embodiment can be obtained even when a transparent conductive film is interposed between the glass substrate and the chromium film. Therefore, the chromium mask of the present invention uses a chromium film as a light-shielding mask. It may take any form as long as it is formed.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an experimental apparatus for explaining the present invention. 1... Constant temperature bath, 2... Water, 3... Electrolytic mountain, 4...
・Sulfuric acid/nitric acid mixture, 5...Chromium mask, 6...Glass substrate, 7...Chromium film, 8...Chromium oxide layer, 9
...Copper plate, 10...DC power supply Figure 1. 0)

Claims (2)

[Claims] (1) A method for cleaning a chrome mask, which comprises using a solution prepared by adding an oxidizing agent to sulfuric acid as a cleaning liquid, and immersing a chrome mask in the cleaning liquid. (2) The method for cleaning a chrome mask according to claim 1, characterized in that nitric acid as the oxidizing agent is 5 mol % or more.