JPH05335217A - Manufacture of mask for x-ray exposure - Google Patents

Abstract

PURPOSE:To offset the strain of a mask substantially and to form the mask in a desired shape by a method wherein, when an X-ray absorber film is patterned to a desired mask shape, the strain of the mask which is caused due to a change in the distribution of a stress is simulated and a patterning operation is performed by using a pattern which is deformed in the opposite direction so as to compensate the strain of the mask. CONSTITUTION:The surface of an X-ray absorber 3 is coated with an electron- beam resist film. A mask pattern incorporating a strain pattern whose phase is opposite to that of a mask-strain estimation value obtained by a simulation is exposed on the electron-beam resist film by means of an electron-beam lithography apparatus. Then, a reactive ion etching operation is performed by making use of the resist film as a mask; the X-ray absorber 3 is patterned. A chip region 8 which has been etched selectively is deformed by a change in the distribution of the internal stress. When the mask of the electron-beam resist film is removed, it is possible to form a mask, for X-ray exposure, in which a selective X-ray transmission region has been formed. At this time, the pattern is deformed in an exposure operation, and the mask can be formed in a desired shape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an X-ray exposure mask, and more particularly to a method for manufacturing an X-ray exposure mask including processing of an X-ray absorber film formed on an X-ray transparent film (mask substrate). Regarding

[0002] In recent years, along with the promotion of high performance, multi-functionality, miniaturization and weight reduction of electronic equipment, the super L which should be called the heart of the electronic equipment.
It is improving without knowing where the degree of SI integration remains. Taking a DRAM, which is a typical device of VLSI, as an example, the degree of integration is increasing four times in three years according to the reduction rule, and a 16 Mbit DRAM has already been commercialized.

A 256 Mbit DRAM, which is planned to be commercialized in the latter half of the 1990s, has a memory cell area of 10
The line width is expected to be 0.3 μm ² or less and the line width is 0.3 μm or less.

Due to the reduction of the wiring line width due to the increase in the degree of integration as described above, the wavelength of the lithography light source required for the patterning is shifted to the short wavelength side, and the X-ray exposure method is mainly used in the highly integrated region of 256 Mbits or more. It is considered.

Since X-rays have a short wavelength of, for example, several A, high resolution can be easily achieved because the diffraction at the mask edge can be ignored and there is no proximity effect that occurs in electron beam exposure. The minimum patterning dimension is 0.1-
0.5 μm is obtained.

However, since it is difficult to manufacture a reduction projection optical system for X-rays, only patterning with a 1 × mask can be used. For example, a 1 × mask having a line width of about 0.1 μm to 0.3 μm is formed in a mask area of about 20 to 50 mm square, and the resist film on the Si substrate is exposed by the step and repeat method.

Since the production of the equal-magnification mask is carried out by etching the thin X-ray absorber film on the thin X-ray transmission film into an arbitrary pattern, it is technically difficult in combination with the small processing size, and therefore the mask is produced. It becomes a key technology of X-ray exposure technology.

[0008]

2. Description of the Related Art An X-ray absorber, which is an X-ray mask material, is
Elemental metals having a large atomic number such as Ta, W, and Au are used. Since the X-ray exposure mask is formed in a thin film shape, a mask substrate (X-ray transmissive film) made of an X-ray transmissive material slightly thicker than the mask film is used as a supporting plate thereof. That is,
The X-ray absorber film is processed while being deposited on the mask substrate.

As the mask substrate material, a material having a small atomic number, a high X-ray transmissivity and a relatively large Young's modulus, such as SiC, Si or diamond-like carbon, is used. The mask substrate transmits X through the opening of the X-ray absorber film.
In order to irradiate an object to be exposed such as a resist film on a Si wafer with rays, it is formed in a thin film in order to reduce X-ray absorption. This mask substrate is formed by depositing it on a thick base substrate, usually a Si wafer.

Thereafter, the peripheral portion of the back surface of the Si wafer is fixed to a support, and the Si wafer other than the fixed portion is removed by etching from the back surface to form a membrane region. The membrane region consists of the mask substrate and the X-ray absorber film deposited on it. After forming the membrane region, the X-ray absorber film is patterned into a desired shape such as a predetermined line and space pattern to obtain an X-ray exposure mask.

When internal stress acts on the X-ray absorber film,
When the X-ray absorber film is processed into a desired pattern, the stress distribution changes, and the X-ray transmissive film and the X-ray absorber film are deformed (strained). Therefore, the obtained pattern is deformed.

Therefore, conventionally, a laminated structure of X-ray absorber film / X-ray transparent film (mask substrate) is selected by selecting the film-forming conditions and film-forming materials so that the internal stress of the X-ray absorber film is as low as possible. Had formed.

[0013]

However, it is extremely difficult to completely cancel the internal stress of the X-ray absorber film. In particular, when the area of the membrane region is large, when the X-ray absorber film is patterned after the etching of the Si wafer, the generated strain becomes a size that cannot be ignored.

Since the pattern of the VLSI is effective by repeating the mask process on the same Si substrate on which the device is to be formed, the patterns are displaced from each other if each mask is distorted.

Therefore, high precision patterning cannot be performed, and the yield is greatly reduced. An object of the present invention is to provide a method for manufacturing an X-ray exposure mask that can obtain an X-ray transmission pattern that is less deformed from a desired shape.

[0016]

A method of manufacturing an X-ray exposure mask according to the present invention comprises a step of forming an X-ray absorber film on an X-ray transparent film and an internal stress acting on the X-ray absorber film. The step of measuring, the step of simulating the mask strain caused by the change of the stress distribution when the X-ray absorber film is patterned into a predetermined mask shape, and the deformation in the opposite direction so as to compensate the mask strain. Patterning the X-ray absorber film with a pattern.

[0017]

When the strain is folded in the opposite phase in the process of drawing the mask pattern, the strain of the mask deformed by the internal stress after etching is substantially canceled and the desired pattern can be obtained.

The present invention will be described in more detail below based on examples.

[0019]

1 shows the structure of an X-ray exposure mask according to an embodiment of the present invention. In the figure, a plan view is shown in the upper part and a sectional view is shown in the lower part.

First, an X-ray transmission film (mask substrate) 2 made of a material that transmits X-rays is deposited on a Si wafer 1. In this state, the surface flatness of the Si wafer 1 is measured. When a tensile stress or a compressive stress is generated in the mask substrate 2, the Si wafer is bent downward or upward, so that the internal stress can be known from the deformation amount.

After that, the X-ray absorber film 3 is formed on the mask substrate 2.
Is deposited, and the surface flatness of the Si wafer 1 is measured again. From this result, the internal stress in the stack of the X-ray absorber film and the mask substrate can be known. The internal stress generated inside the X-ray absorber film 3 can be known by comparing the measurement data before and after the X-ray absorber film formation.

Therefore, a change in the internal stress distribution that occurs when the X-ray absorber film 3 is selectively etched off in the next step is expected, and the change occurs in the X-ray absorber film 3 and the mask substrate 2 thereunder. Strain distribution (deformation) can be simulated. Therefore, in order to arrange the deformed pattern at a desired position, it is possible to know how to initially displace it.

After that, the peripheral portion of the back surface of the Si wafer 1 is fixed to the support frame 4, and Si other than the portion in contact with the support frame is fixed.
A region (central region) of the wafer 1 is removed by wet etching to form a membrane region 7.

Next, an electron beam resist film is applied to the surface of the X-ray absorber film 3, and a mask pattern in which a strain pattern having a phase opposite to the predicted mask strain value obtained by the above-described simulation is folded is formed by an electron beam drawing apparatus. The electron beam resist film is exposed. When the electron beam resist film is exposed to light, a mask deformed in advance is obtained.

Next, the X-ray absorber film 3 is patterned by reactive ion etching (RIE) using the resist film as a mask. The chip region 8 subjected to the selective etching is deformed due to the change of the internal stress distribution. When the mask of the electron beam resist film 5 is removed, an X-ray exposure mask having a selective X-ray transmitting region is completed.

Here, by intentionally deforming (displacement) the pattern at the time of exposure, the mask shape obtained after the selective etching of the X-ray absorber film can be made a desired shape.

If the internal stress has a certain degree of distribution or it is difficult to predict the change in the stress distribution due to the selective etching of the X-ray absorber film with sufficiently high accuracy, the X-ray absorber film is temporarily analyzed based on a simulation. It is more preferable to perform selective etching, measure the mask pattern actually obtained as a result, and feed back the result to perform selective etching of a new X-ray absorber film again.

Further, if the aspect ratio obtained by removing the deposited thickness of the X-ray absorber film 3 by the patterning width (line and space width) of the X-ray mask becomes large, the two-dimensional strain distribution prediction alone becomes insufficient.

That is, in the line-shaped X-ray shielding pattern, the stress in the direction perpendicular to the line is easily released, but the stress in the direction parallel to the line is difficult to be released. Since the degree of stress release depends on the height from the X-ray transparent film surface, three-dimensional analysis is desired.

In this case, for example, by simulating the stress distribution in the X-ray mask longitudinal section with the aspect ratio as a variable, predicting the mask strain due to the three-dimensional stress distribution in addition to the stress distribution based on the two-dimensional analysis, It is preferable to obtain an internal strain distribution and perform mask patterning in which an antiphase strain pattern is folded to perform an X-ray exposure mask.

Hereinafter, more specific examples will be described. Used as a supporting substrate, for example, Si having a diameter of 4 inches
2.5 μm thick Si is formed on the wafer 1 by the CVD method.
A mask substrate 2 made of C is formed, and an X-ray absorber film 3 made of Ta and having a thickness of 0.8 μm is formed thereon by a sputtering method.
Deposit. The flatness of the Si wafer 1 is measured before and after the sputtering to calculate the built-in stress of the Ta film.

Next, the strain (deformation) that would occur when the X-ray absorber film 3 is selectively etched is simulated based on the stress distribution. FIG. 2A shows the strain distribution in the chip region 8 including the selection pattern predicted by this method. The size of the arrow in the figure represents the magnitude of strain, and the direction of the arrow represents the direction of strain. In the strain simulation, the chip region 8 was divided into small regions of 2 mm square, and the strain at the center point of each region was obtained.

Next, the periphery of the back surface of the Si wafer 1 is adhesively fixed to the support frame 4 made of ceramic SiC, and the Si wafer 1 is etched from the back surface using a mixed solution of fluorinated nitric acid. Through this process, as shown in FIG.
Is etched off except for the bonding portion with the support frame 4 to form a thin membrane region 7.

Next, an electron beam resist film (not shown) is applied to the surface of the X-ray absorber film 3 made of Ta, and a desired mask pattern in which a strain pattern having a phase opposite to the above-described strain prediction value is folded is formed. The electron beam resist film is drawn by an electron beam drawing apparatus and developed.

At this time, it is more accurate if the position and shape of each pattern are corrected, but it is easy to divide the target surface into small sections, leave the mask shape in the small sections unchanged, and move only the center position. You can do it. This can be performed only by adjusting the position of the stage on which the mask is placed in the EB exposure.

While the EB exposure is performed by the step-and-repeat method, for example, the distortion can be easily corrected by adjusting the stage position. After exposure, the resist film is developed to obtain a resist mask.

Using the resist film 5 thus patterned as a mask, reactive ion etching (RI
According to E), the X-ray absorber film 3 is patterned. RIE is performed, for example, using a chlorine-based gas without heating.

Since the etching rate of this anisotropic dry etching is large for metal and small for SiC, the mask substrate 2
Acts as a stopper. As a result, for example, the chip area 8 including a line and space pattern with a width of 0.8 μm
Is formed.

By removing the electron beam resist film 5, an X-ray exposure mask having the structure shown in FIG. 1 is obtained. FIG. 2B shows an example of the resist having an antiphase distortion pattern formed in the chip region 8 before the selective etching of the X-ray absorber film. In the case of a chip area of about 25 mm square, the maximum value of strain can be, for example, about 0.2 μm or less. If one field of the electron beam exposure apparatus is suppressed to 1 mm ² or less, deterioration of the connection accuracy of each area is 0.02 μm even if feedback is applied only to the stage by the step-and-repeat method.
It is suppressed to the following and there is no practical problem.

When the lower X-ray absorber film is selectively etched using the resist mask shown in FIG. 2B, the stress distribution changes and the mask deforms as a whole. As a result of the deformation, as shown in FIG. 2C, an X-ray exposure mask having a pattern with a very small deviation from the desired pattern is obtained. The center points of the respective small areas are arranged at almost desired positions.

When the line-and-space width is shortened and the aspect ratio, which is the ratio of the thickness of the X-ray absorber film 3 to the width, is increased, the two-dimensional strain prediction becomes insufficient. For example, when the line width is 0.4 μm and the aspect ratio is 2, the accuracy is sufficiently high even if correction is performed using the two-dimensional strain distribution simulated by the two-dimensional analysis from the stress measurement values before and after Ta sputtering in the above-described embodiment. Will not be obtained.

FIG. 3A shows an example of strain distribution obtained when an X-ray transmission mask is actually formed. A chip area of 24 mm on a side is divided into small sections of 2 mm on a side, and movement of the reference point in each small section is shown by a pin-shaped line segment. From the comparison between FIG. 2A and FIG. 3A, it can be seen that an error occurs in the two-dimensional strain distribution due to the stress distribution that changes due to the formation of the mask pattern. This can be explained as follows.

In a mask longitudinal section obtained by cutting a mask having a large aspect ratio perpendicularly to the surface, the degree of stress relief varies depending on the size of the aspect ratio. In the case of a line-shaped X-ray shielding mask, stress is not easily released in the direction parallel to the line, but stress is easily released in the direction perpendicular to the line.

When the strain distribution in the longitudinal section is simulated assuming that the internal stress of the Ta film before etching is uniform at 5.0 × 10 ⁸ dyne / cm ² , a distribution as shown in FIG. 3B is obtained, for example. Be done.

As is clear from FIG. 3B, most of the stress in the direction perpendicular to the line is released when the line width becomes narrow. On the other hand, the stress in the direction parallel to the line remains. By obtaining such a strain distribution in the vertical cross section according to the pattern to be formed and obtaining the three-dimensional strain distribution folded into the strain distribution in the plane of the chip region 8, the strain actually generated can be simulated with high accuracy.

By correcting the position of the mask pattern by using the distortion thus obtained as an antiphase and returning to the stage of the electron beam drawing apparatus, a highly accurate X-ray exposure mask can be manufactured.

Although Ta is used as the material of the X-ray absorber film 3 in the above embodiment, it is obvious that other heavy metal materials such as W and Au can be used. Further, as the material of the mask substrate 2, another material having a high Young's modulus, for example, S
i, diamond-like carbon or the like can be used. Of course, the material of the support frame 4 can be variously selected.

The present invention has been described above with reference to the embodiments.
The present invention is not limited to these. For example,
It will be apparent to those skilled in the art that various modifications, improvements, combinations and the like can be made.

[0049]

As described above, according to the present invention,
As a result, an X-ray exposure mask with high positional accuracy can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of an X-ray exposure mask according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram for explaining a method of manufacturing an X-ray exposure mask according to an embodiment of the present invention.

FIG. 3 shows a simulation example of mask distortion depending on a pattern shape.

[Explanation of symbols]

 1 Si wafer 2 Mask substrate 3 X-ray absorber film 4 Support frame 7 Membrane area 8 Chip area

Claims (5)

[Claims] 1. A step of forming an X-ray absorber film (3) on an X-ray transparent film (2); a step of measuring an internal stress acting on the X-ray absorber film (3); When the absorber film (3) is patterned into a predetermined mask shape, a step of simulating the distortion of the mask caused by a change in stress distribution, and the X-ray with a pattern deformed in the opposite direction so as to compensate the mask distortion A method of manufacturing a mask for X-ray exposure, which comprises a step of patterning the absorber film (3). 2. The step of measuring the internal stress comprises:
The method for producing an X-ray exposure mask according to claim 1, which comprises measuring the flatness of the surface before and after the formation of the line absorber film (3). 3. The method for manufacturing an X-ray exposure mask according to claim 1, wherein the step of simulating the distortion of the mask is performed in consideration of the plane arrangement and the thickness of a desired mask shape. 4. In the step of patterning the X-ray absorber film (3), a resist film is formed on the X-ray absorber film (3) and a support substrate (1) supporting the X-ray transmission film is staged. 4. The method for manufacturing an X-ray exposure mask according to claim 1, further comprising: placing on top of the mask and performing exposure by controlling a stage position so as to compensate for a positional variation obtained by simulation. 5. The patterning position of the X-ray absorber film which is further patterned to compensate for strain is measured,
5. The method of manufacturing an X-ray exposure mask according to claim 4, including a step of detecting a difference from a desired pattern position and patterning a new X-ray absorber film so as to compensate for the difference.