JP2765016B2 - Photomask blank and photomask - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a photomask blank for semiconductor production and a photomask manufactured therefrom.

[Prior art and its problems] It is an object of the present invention to provide a photomask blank having a lower reflectance over a wider wavelength range than in the past, and to suppress side etching during etching to make a pattern cross section vertical. The present invention provides an improved photomask blank (hereinafter simply referred to as a blank) and a photomask so that the following can be achieved.

[Means for Solving the Problems] The object of the present invention is to provide a blank and a photomask according to the present invention,
That is, in a photomask blank in which a thin film made of chromium metal containing at least one element selected from the group consisting of oxygen and nitrogen is formed on a transparent substrate and a photomask manufactured therefrom, at least one of oxygen and nitrogen is provided. This is achieved by providing a photomask blank and a photomask, wherein the concentration of the element is continuously reduced from the thin film surface toward the transparent substrate.

[Action] The following paper (Applied Physics Selection 3, “Thin Films”, published by Shokabo, pp. 218-2)
20, and "Thin Film Engineering Handbook" II-299, published by Ohm Co., Ltd.). It is concluded that it is necessary to continuously change the refractive index of the laminated film up to this point. In particular, it is understood that the point is to bring the refractive index of the surface closer to 1 which is the value of air.

The present inventors have made intensive studies based on such knowledge, and as a result, (1) To obtain an anti-reflection function, change the refractive index continuously in the depth direction to obtain an inhomogeneous film (2) In order to lower the reflectivity, a specific method for approaching the refractive index of the film surface to 1.0, which is the refractive index of air, is at least one of oxygen, nitrogen, fluorine, and carbon, particularly oxygen. It has been found that the first object of the present invention is to achieve a low reflectance by increasing the concentration of nitrogen and nitrogen at the surface as much as possible.

On the other hand, the degree of “eave” of the antireflection film generated on the pattern cross section by isotropic etching is considered to be determined by the relative potential between the layers. From this model, it is necessary to achieve the vertical pattern cross section. "The potential distribution in the film is made negatively larger from the upper layer to the lower layer. This should also contribute to the effect of suppressing the side etching."

However, according to the studies by the inventors, it has been found that the formation of a so-called "eave" cannot be avoided simply by setting such conditions.

As a countermeasure to solve this, it was found that the element distribution in the film should be continuously distributed, and it was found that the perpendicularity of the pattern cross section, which is the second object of the present invention, could be achieved. .

That is, the verticalization of the pattern cross section in the present invention is as follows.
This is achieved only by the combined use of two means of continuously increasing the distribution of elements in the film and increasing the potential distribution in the film from the upper layer to the lower layer in the negative direction.

When the concentration of additive components such as nitrogen and oxygen becomes higher in the upper layer, the electrochemical potential of each layer in the etching solution gradually becomes lower. As a result, the layer whose cross section is exposed by the etching is always negatively charged, and thus elution of positive ions from the etched cross section is suppressed. This means suppression of side etching. The layer structure for exhibiting the mechanism is the element distribution proposed by the present invention as described above, and the electrochemical potential is lower as the lower layer, and the refractive index changes continuously. As described above, according to the photomask of the present invention, a low reflectance can be realized over a wider wavelength, and at the same time, the side etching can be suppressed and the pattern cross section can be made vertical (overetch rate can be suppressed). Naturally, achieving a low reflectance means a high resolution by preventing the halation.

[Examples] Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to only the examples.

Example An example of one of the specific methods for continuously changing the element distribution described above will be described.

A DC magnetron sputtering method was used for blank film formation. In this case, the in-line sputtering apparatus ILC-803 manufactured by Nidec Anelva was used, and instead of two rectangular targets having a target size of 20 ″ × 6 ″, six fine targets of 20 ″ × 2 ″ were used. Were used in close proximity to each other. In the magnetron sputtering method, a magnet is inserted under the target, so that a high-density plasma is formed in the shape of a donut along the target shape. .

As shown in FIGS. 1 and 2, in this embodiment, the discharge current of each target can be controlled by dividing the target into multiple parts. Thus, the following has been realized.

That is, when performing reactive sputtering, for example, when performing DC magnetron sputtering in a gas in which nitrogen and oxygen are mixed in argon, the nitrogen / oxygen concentration ratio in the film changes depending on the current value. Since this also appears in a change in discharge color, control can be performed by spectrally analyzing and monitoring the emission of plasma.

For example, in the case of a constant gas composition, when the current value is increased, chromium turns blue. It turns pink at small current values. The middle changes continuously, but the center becomes white. In the case of blue color, the nitrogen concentration in the film increases, and oxygen decreases significantly. In the case of pink, it becomes almost oxygen and little nitrogen enters the film. It is in the middle for white. The layer constitution of the present invention is realized by using the method.

In FIG. 2, the current was reduced from one target toward 6. The difference from the ordinary sputtering method is this point, and a blank is formed by a single pass, and the productivity is improved.

Specifically, 1.5A for 1 target, 1A for 2 and 0 for 3
A current of 0.8 A was applied to 9 A, 4 and 0.7 A to 5, and a current of 0.6 A to 6 was discharged. The discharge colors of the targets 1 and 2 were blue, 3 and 4 were white, and 5 and 6 were pink. Their colors changed continuously from blue to pink.

 The traveling speed of the tray on which the substrate was placed was 150 mm / min.

The thickness of the formed film was 1100 °, and the element distribution was as shown in FIG. 3 according to Auger electron spectroscopy.

FIG. 4 shows the relationship between the distribution of the element concentration in the laminated film of the blank obtained in this example and the refractive index. The surface refractive index is reduced by the continuous reduction of nitrogen and oxygen concentration.
It can be seen that the refractive index of chromium converges downward, approaching 1.0.

Further, the blank obtained by this example had a vertical etched cross section, and had a surface reflectance of 5 at 436 nm.
%.

[Effects of the Invention] The present invention provides an improved photomask blank and an improved photomask having a lower surface reflectance over a wide wavelength range than before and having a vertically etched cross section.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing the arrangement of a conventional DC magnetron sputtering apparatus, FIG. 2 is an explanatory view showing the arrangement of a DC magnetron sputtering apparatus used in an embodiment of the present invention, and FIG. FIG. 4 is an explanatory view showing the element distribution in the film of the blank obtained in Example 1; FIG. 4 is a diagram showing the element distribution and refraction in the metal mask film constituting the photomask blank and the photomask obtained by the Example of the present invention; It is explanatory drawing which shows the relationship with a rate distribution.

Claims (2)

(57) [Claims] 1. A photomask blank in which a thin film made of chromium metal containing at least one element selected from the group consisting of oxygen and nitrogen is formed on a transparent substrate, the photomask blank comprising at least one of oxygen and nitrogen. A photomask blank whose concentration is continuously reduced from the surface of the thin film toward the transparent substrate. 2. A photomask in which a thin film made of chromium metal containing at least one element selected from the group consisting of oxygen and nitrogen is patterned on a transparent substrate, the photomask comprising at least one of oxygen and nitrogen. A photomask in which the concentration is continuously reduced from the surface of the thin film toward the transparent substrate.