JPH04304614A - X-ray mask structure and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide by an easy process an X-ray mask structure which has an X-ray absorber pattern of an optional shape having an irregular cross section. CONSTITUTION:In a X-ray mask structure, which contains an X-ray absorber 3 having a desired pattern and an X-ray transmitting film 2 holding the absorber 3, the X-ray mask structure is characterized by the above X-ray absorber 3 pattern whose sidewall has an irregular shape.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to large-scale integrated circuits (LSI).
The present invention relates to an X-ray mask structure used when printing fine patterns such as those of ) or micromachines onto a wafer or the like by X-ray exposure, and a method of manufacturing the same.

0002

[Prior Art] Large-scale integrated circuits represented by DRAM are currently in the mass production period of 4M DRAM, and even 16M DRAM.
Technology is rapidly progressing from M to 64M DRAM. Along with this, the minimum line width required for devices has also been reduced from half a micron to a quarter micron. These semiconductor devices are transferred from a mask to a semiconductor substrate using near-ultraviolet light or far-ultraviolet light, but the line width of devices that can be processed using these wavelengths of light is approaching its limit. Further, the depth of focus inevitably decreases with miniaturization. Therefore, lithography technology using X-rays has high expectations as a solution to the above problems at the same time.

In a mask structure used for X-ray exposure, generally, as shown in FIG. 1, a fine pattern 3 of an X-ray absorber is further formed on an X-ray transmitting film 2 formed on a suitable support frame 1. It has a structure in which Materials used as X-ray absorbers include heavy metals, particularly Au, W, and Ta. Furthermore, the X-ray absorber pattern is supported and fixed.
Silicon compounds such as SiN and SiC have been announced for the light-transmitting film. Methods for forming this X-ray absorber pattern include a plating method for a "shaped pattern" using a resist,
There are methods of patterning a thin film of heavy metal absorber using a dry process such as reactive ion etching, or a method of patterning a thin film of a heavy metal absorber using a wet process using an appropriate etching solution.

On the other hand, regarding the shape of the absorber, when considering Fresnel diffraction of X-rays incident on the mask, the uneven cross-sectional shape of the side wall of the absorber pattern is
It has been proposed that it is desirable for pattern transfer to resist (see Japanese Patent Laid-Open No. 2-52416). Furthermore, by providing unevenness on the side walls of the absorber, the problem of X-rays incident on the mask being reflected on the sides of the absorber, reducing the contrast of the X-ray intensity on the resist and causing a decrease in resolution, is resolved. You can. This will be discussed in detail.

When transferring a pattern onto a resist using an X-ray exposure mask, in order to prevent damage to the mask,
As shown in the figure, the masks (2, 3) are several tens of μm away from the resist 4.
placed apart. Then, X-rays 5 are irradiated through the mask to transfer the absorber pattern 3 onto the resist. In this case, some of the irradiated X-rays 5 are incident on the side surface of the absorber 3 at a grazing angle because the irradiated X-rays are not necessarily parallel and the side surface of the absorber is not necessarily perpendicular due to the manufacturing process. A part of these X-rays 5 is reflected by the side surface of the absorber 3 and travels in a direction different from that of the irradiated X-rays 5, so that the portions of the resist 4 that would otherwise be blocked by the absorber 3 and where the X-rays 5 would not reach are As a result, a problem arises in that the resolution of the transferred pattern is reduced. This problem can be solved by making the side wall of the absorbent body 3 uneven.

[0006] When X-rays are incident on a substance, the reflectance depends on the angle of incidence. When X-rays are incident on the surface of a material at a grazing angle, that is, when the angle of incidence is close to 90°, total internal reflection occurs and the reflectance is close to 100%;
The reflectance decreases rapidly as the value decreases from . FIG. 3 shows the dependence of the reflectance on the incident angle when X-rays with a wavelength of 1 nm are incident on the gold surface. At an incident angle of 90 to 88 degrees, the reflectance is 50% or more, but as the incident angle becomes smaller, the reflectance decreases rapidly, and at an incident angle of 85 degrees or less, the reflectance is 1% or less. If the side surface of the X-ray mask absorber is smooth with no irregularities, the X-rays will be incident on the absorber's surface at a grazing angle, resulting in a high reflectance.

However, as shown in FIG. 4, if the side wall of the absorber 3 is uneven, the X-rays near the absorber will be absorbed by the absorber 3.
Since the light is incident on the surface at a small angle, the reflectance is very low. In other words, if unevenness with an inclination of 5° or more is formed on the side wall of the absorber 3, the reflectance of the X-rays 5 will be 1% or less, so unnecessary reflected X-rays will expose the resist 4 and transfer it. The problem of reduced pattern resolution can be solved. However, X with such an arbitrary cross-sectional shape
Creating a radiation absorber pattern requires a complicated process, making it difficult to provide a highly accurate X-ray mask. Therefore, an object of the present invention is to provide an X-ray mask structure having an X-ray absorber pattern having an arbitrary uneven cross-sectional shape through a simple process.

[0008]

[Means for Solving the Problems] The above object is achieved by the following present invention. That is, the present invention provides an X-ray mask structure including an X-ray absorber having a desired pattern and an X-ray transparent film holding the absorber, wherein the X-ray absorber pattern has an uneven side wall. An X-ray mask structure characterized by being a laminated structure, and an X-ray transparent film that is to hold an X-ray absorber pattern are provided with at least two types of X-rays having different etching rates under arbitrary etching conditions.
The method for manufacturing the above-mentioned X-ray mask structure is characterized in that radiation absorber pattern materials are alternately laminated and then the absorber patterns are etched under arbitrary etching conditions.

[0009]

[Operation] In view of the above-mentioned problems of the prior art, the inventors of the present invention have conducted extensive research and have developed an X-ray absorber pattern material with a laminated structure of two or more materials having different etching rates under arbitrary etching conditions. The inventors have come to the conclusion that by etching the absorber pattern under arbitrary etching conditions, it is possible to obtain an absorber pattern having irregularities in the cross-sectional shape of the sidewall, leading to the present invention.

0010

[Preferred Embodiment] The X-ray mask structure of the present invention, as schematically shown in FIG. As shown in the enlarged view drawn in a circle, the X-ray absorber pattern 3 is characterized by being a laminated structure whose side walls have an uneven shape. In addition to these materials, a protective film or a conductive film for an X-ray absorber may also be used. X
As a line-transmitting film, Si or SiO with a thickness of 1 to 10 μm is used.
2. Known materials such as inorganic materials such as SiC, SiN, BN, and BNC, and radiation-resistant organic films such as polyimide can be used. In addition, any other material that can be used as an X-ray transparent membrane may be used. Various sputtering methods, chemical vapor deposition methods, and other methods can be used to form these films. Further, the X-ray absorber pattern is preferably formed by a plating method, and known materials such as Au, Ni, and Cu can be used as the X-ray absorber pattern material. The basic process of the present invention, which is a method for controlling the uneven shape of the sidewall cross section of the X-ray absorber, is to alternately plate materials with different etching rates for arbitrary etching, and then perform arbitrary etching after forming the absorber pattern. The desired structure can be obtained by processing.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in more detail with reference to embodiments shown in the drawings. It goes without saying that the present invention is not limited to these examples. Example 1 A substrate having a 2 μm thick SiN film formed on a silicon wafer by chemical vapor deposition was used as an experimental substrate. 50% each of Cr and Au were placed on this substrate as plating electrodes.
It was formed by EB deposition to a thickness of 500 angstroms. On top of this, PMMA, which is an electron beam resist, was spin-coated to a thickness of 1.3 μm, and EB drawing was performed at an accelerating voltage of 20 kV, and after development, the thickness was 0.25 μm.
A stencil pattern for plating was formed. Thereafter, Au, which is an X-ray absorber, was plated to a thickness of 0.1 μm using a sulfite-based Au plating solution. Next, using a Ni plating solution, Ni was plated on the Au layer to a thickness of 0.1 μm. By repeating these two types of plating operations five times each, an X-ray absorber pattern having a thickness of 1.0 μm was formed. This substrate was immersed in an aqueous solution of potassium iodide, and Au
Only the portions were selectively etched for a short period of time. Furthermore, the electrodes on the substrate used for plating were removed by sputtering. Also, back-etch the Si substrate according to the usual method,
Finally, this mask substrate was mounted on a Pyrex frame to form an X-ray mask of the present invention.

Example 2 An X-ray mask structure of the present invention was obtained by performing the same operations as in Example 1 except that Cu plating was used instead of Ni plating in Example 1. Example 3 The cross-sectional shapes of the X-ray absorber patterns obtained in Examples 1 and 2 were evaluated using a SEM. Both examples are made of Au
layer was selectively etched, and a periodic uneven shape was confirmed on the side wall of the absorber. This period was equivalent to the period of the thickness of each plating layer, 0.2 μm, and the depth of the unevenness was about 200 angstroms.

[0013]

[Brief explanation of the drawing]

FIG. 1 is a sectional view schematically showing an X-ray mask of the present invention.

FIG. 2 is a schematic diagram of pattern transfer using an X-ray mask.

FIG. 3 is a diagram showing the dependence of reflectance on the angle of incidence when X-rays with a wavelength of 1 nm are incident on a gold surface.

FIG. 4 is a schematic diagram of X-ray irradiation using an X-ray mask with an uneven side wall of an absorber.

[Explanation of symbols] 1: Support frame 2: Permeable membrane 3: X-ray absorber 4: Resist 5: X-ray

Claims (3)

[Claims] 1. An X-ray mask structure comprising an X-ray absorber having a desired pattern and an X-ray transparent film holding the absorber, wherein the X-ray absorber pattern is a laminated layer whose sidewalls have an uneven shape. An X-ray mask structure characterized by being a structure. 2. The X-ray mask structure according to claim 1, wherein the absorber pattern is a laminated structure made of at least two types of materials. 3. At least two or more types of X-ray absorber pattern materials having different etching rates under arbitrary etching conditions are alternately laminated on the X-ray transparent film, and then the absorber pattern is etched under arbitrary etching conditions. The method for manufacturing an X-ray mask structure according to claim 1, characterized in that: