JPH052143B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for etching a photomask blank when producing a photomask, and more specifically to a photomask having a multilayer light-shielding layer of chromium and chromium oxide on a transparent substrate. The present invention relates to a method of etching a photomask blank, which comprises providing a covering of a desired pattern, such as a photoresist, on the light-shielding layer of the blank according to a conventional method, and etching the portions not covered with the covering to form windows.

(Prior Art) Conventionally, as a method for etching this type of photomask blank, there has been a method for etching a photomask blank e, which has a multilayer light shielding layer d of a chromium layer b and a chromium oxide layer c on a transparent substrate a, as shown in FIG. A coating f such as photoresist is provided on the light-shielding layer d according to a conventional method to form a desired pattern, and then, as shown in the second figure, the portions of the light-shielding layer d not covered with the coating f are coated with cerium (). A method of forming the window h by etching with a salt-based etching solution is known.

(Problems to be Solved by the Invention) However, according to the conventional method, there is a difference in etching rate of 4:1 between chromium and chromium oxide by the cerium () salt-based etching solution, and as shown in the second figure, The chromium layer b is etched too much and there is an overhang part g on the chromium oxide layer c.
is formed, causing variations in critical dimensions, and the overhang portion g.
If the photomask is missing, the edges of the pattern may become jagged, resulting in a disadvantage that the pattern accuracy of the resulting photomask is not very good.

(Means for Solving the Problems) The present inventors have obtained the knowledge that permanganate-based etching solution has the property of selectively etching only the chromium oxide layer, and based on this knowledge, A photomask that allows the end faces of the chromium oxide layer and the chromium layer to be precisely aligned on the same plane after etching by combining etching treatment with an acid salt-based etching liquid and etching treatment with a cerium salt-based etching liquid. A method of etching a blank is provided, and the first invention is a photomask blank having a multilayer light shielding layer of chromium and chromium oxide on a transparent substrate. In the etching method for photomask blanks in which a window portion is formed by providing a covering body and etching the portion not covered by the covering body, first, both the chromium oxide layer and the chromium layer are etched with a cerium () salt-based etching solution. Then, the end surfaces of the chromium oxide layer and the chromium oxide layer are brought together while etching the overhanging portion of the chromium oxide layer with a permanganate-based etching solution.

In addition, the second invention of the present application provides a photomask blank having a multilayer light-shielding layer of chromium and chromium oxide on a transparent substrate. In the etching method for photomask blanks in which windows are formed by etching the areas not covered by the coating, only the chromium oxide layer is first etched with a permanganate-based etching solution, and then cerium () salt is etched. The method is characterized in that the end surfaces of the chromium oxide layer and the chromium layer are brought together while etching the chromium oxide layer and the chromium layer with an etching solution.

Photomask blanks to be etched generally have a chromium layer and a chromium oxide layer formed on a transparent substrate such as glass to form a multilayer light-shielding layer by vapor deposition or sputtering.

In order to coat the multilayer light-shielding layer of photomask blanks in a desired pattern, generally the photoresist is coated over the entire surface of the light-shielding layer, only the predetermined area is exposed to light through the original pattern, and then this is developed. It is formed by a photoresist method or the like in which only the exposed area or the unexposed area is left on the light shielding layer.

Note that a photomask blank provided with a photoresist coating layer that is not patterned in advance may also be used.

Permanganate-based etching solutions generally include zinc, ammonium, cadmium, potassium,
Calcium, silver, strontium, cesium, sodium, barium, magnesium, lithium,
A 1/10N to 3N solution of permanganate such as rubidium is used.

Further, as the cerium salt-based etching solution, a mixed aqueous solution of ceric ammonium nitrate and perchloric acid is generally used.

In order to align the end faces of the chromium layer and the chromium oxide layer using both of these etching solutions, the temperature of each etching solution and the immersion time of the photomask blank in each etching solution are adjusted.

(Example) Examples of the first invention and the second invention of the present application will be described below as Example 1 and Example 2, respectively, with reference to the accompanying drawings.

Example 1 First, as shown in the third diagram, a photomask blank 5 was prepared, which was provided with a multilayer light shielding layer 4 consisting of a chromium layer 2 with a thickness of 61 nm and a chlorine oxide layer 3 with a thickness of 25 nm on a transparent substrate 1 made of glass. Then, a coating layer of photoresist (for example, AZ1350 (manufactured by Hoechst)) is provided on the light-shielding layer 4, and the coating layer is subjected to a conventional development process to form a coating 6 in a desired pattern.

Next, as shown in Figure 4, the photomask blank 5 is immersed for 60 seconds in an etching solution containing 100 g of ceric ammonium nitrate, 26 c.c. of perchloric acid, and 440 c.c. of pure water at a temperature of 20°C. The window portion 7 is formed by etching both the chromium oxide layer 3 and the chromium layer 2, and the etching solution is washed away with water.

Finally, as shown in Figure 5, the photomask blank 5 is immersed in an etching solution of 0.5N potassium permanganate aqueous solution at a temperature of 60°C for 180 seconds to etch the overhanging portion of the chromium oxide layer 3. The etching solution was washed with water to complete the etching process.

The end faces of the chromium oxide layer 3 and the chromium layer 2 of the obtained photomask were extremely accurately aligned to the same plane.

Example 2 As shown in the sixth figure, a photoresist coating 6 of a desired pattern is formed on a photomask blank 5 in the same manner as in Example 1.

Next, as shown in Figure 7, the photomask blank 5 is immersed in an etching solution of 0.5N potassium permanganate at a temperature of 60°C for 180 seconds to remove the chromium layer from the cerium salt-based etching solution. Only the chromium oxide layer 3, which is more difficult to be etched than the chromium oxide layer 2, is etched in advance, and the etching solution is washed with water.

Finally, as shown in Figure 8, the photomask blank 5 was mixed with 100 g of ceric ammonium nitrate.
The window portion 7 is formed by immersing it in an etching solution containing 26 c.c. of perchloric acid and 440 c.c. of pure water at a temperature of 20° C. for 40 seconds to etch both the chromium oxide layer 3 and the chromium layer 2. Then, the etching solution was washed with water to complete the etching process.

The end faces of the chromium oxide layer 3 and the chromium layer 2 of the obtained photomask were extremely accurately aligned to the same plane.

(Effects of the Invention) As described above, according to the photomask blank etching methods of the first and second inventions of the present application, the difference in the etching rate between chromium oxide and chromium in the cerium () salt-based etching solution and the difference in the etching rate of permanganate By utilizing the selective etching of chromium oxide by a salt-based etching solution, the end faces of the chromium oxide layer and the chromium layer of the multilayer light-shielding layer after etching can be easily and extremely accurately aligned on the same surface.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views of photomask blanks before and after treatment with an etching solution by a conventional photomask blank etching method, respectively, and FIGS. 3 to 5 are cross-sectional views of photomask blanks of the first invention of the present application, respectively. Method 1 of etching blanks
6 to 8 are cross-sectional views of the photomask blanks before treatment with an etching solution, after treatment with a cerium () salt-based etching solution, and after treatment with a permanganate-based etching solution according to the embodiment, respectively, according to the second invention of the present application. FIG. 3 is a cross-sectional view of a photomask blank before being treated with an etching solution, after being treated with a permanganate-based etching solution, and after being treated with a cerium salt-based etching solution according to an embodiment of the method for etching photomask blanks. DESCRIPTION OF SYMBOLS 1...Transparent substrate, 2...Chromium layer, 3...Chromium oxide layer, 4...Multilayer light shielding layer, 5...Photomask blank, 6...Coating, 7...Window part.

Claims (1)

[Scope of Claims] 1. A photomask blank having a multi-layered light-shielding layer of chromium and chromium oxide on a transparent substrate. A coating of a desired pattern such as photoresist is provided on the light-shielding layer according to a conventional method, and the coating is coated with a desired pattern. In the etching method for photomask blanks in which windows are formed by etching the portions not covered with chromium oxide, both the chromium oxide layer and the chromium layer are etched using a cerium salt-based etching solution, and then the chromium oxide layer is etched. A photomask blank etching method characterized by aligning the end surfaces of the chromium layer and the chromium oxide layer while etching the overhanging portion with a permanganate-based etching solution. 2. A photomask blank having a multilayer light-shielding layer of chromium and chromium oxide on a transparent substrate. A coating of a desired pattern such as photoresist is provided on the light-shielding layer according to a conventional method, and the portions not covered with the coating are In the etching method for photomask blanks that forms windows by etching the chromium oxide layer, first, only the chromium oxide layer is etched with a permanganate-based etching solution, and then the chromium oxide layer is etched with a cerium salt-based etching solution. A method for etching photomask blanks, which comprises aligning the end faces of the chromium oxide layer and the chromium layer while etching the chromium layer.