JPH0480756A - Photomask - Google Patents

Abstract

PURPOSE:To expand the depth of focus by providing a high reflecting film, which multiply reflects one part of light passed between light shielding patterns and expands the depth of the focus in a resist film, on one main surface side of a transparent substrate. CONSTITUTION:The transparent substrate 1, the light shielding patterns 5 which are formed on one main surface side of the transparent substrate 4 and the high reflecting film 10 which multiply reflects one part of the light passed between the patterns 5 and which expands the depth of the focus in the resist film 8 are provided. In the case, since the high reflecting film 10 is formed on one main surface side of the substrate 4, a focusing position in the resist film 8 with respect to the light transmitted through the high reflecting film 10 as it is and a focusing position in the film 8 with respect to the light which is multiply reflected by the film 10 exist apart along the thickness direction of the film 8. Thus, the depth of the focus is expanded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a photomask used when processing a workpiece such as a semiconductor wafer using lithography technology.

[Conventional technology]

FIG. 9 shows a schematic configuration diagram of an exposure apparatus including a photomask conventionally used in a photolithography process, and FIG. 10 shows an enlarged view of the main parts thereof.

As shown in both figures, light Ll emitted from a light source 1 is focused by a lens system 2 and irradiated onto a photomask 3.

The photomask 3 has a light-shielding pattern 5 formed on one main surface of the transparent substrate 4, and among the light L2 incident on the photomask 3, the light incident on the area corresponding to the light-shielding pattern 5 is blocked. , the light incident on the remaining area is transmitted. The light L3 selectively transmitted through the photomask 3 passes through a projection lens system 6 with a magnification of m, for example, and is focused and imaged within the Lenost film 8 formed on the substrate 7 of the workpiece.

In this way, the resist film 8 is partially exposed to light, and the mask pattern is transferred onto the resist film 8.

[Invention or problem to be solved]

The conventional photomask 3 is configured as described above.
Each light L3 that has selectively passed through the photomask 3 passes through the lens system 6 onto a focal plane 9 that includes the focal point P (a plane that passes through the focal plane P and is perpendicular to the optical axis of the lens system 6). is imaged. In this case, the lens system 6 has a predetermined depth of focus DOF expressed by the following equation for light of wavelength λ, where NA is the numerical aperture.

λ The resist film 8 substantially has the above focal depth along the thickness direction of the resist film 8 with the focal plane 9 as the center.

Since the resist film is exposed within the range of F, the value of the depth of focus DOF is preferably 2 or more sufficiently large relative to the thickness of the resist film 8.

However, in recent years, with the miniaturization of LSIs, the numerical aperture NA of the lens system 6 tends to increase in consideration of its light-gathering ability, and as a result, the depth of focus DOF tends to decrease.

In the current LSI manufacturing process, for example, the wavelength λ or 436n
In some cases, a lens system 6 with a numerical aperture NA of about 038 is used for ultraviolet rays of m, and the depth of focus DOF in this case is about 1.5 μm according to equation 1) above. On the other hand, the thickness of the resist film 8 is also approximately 15 μm, which is approximately equal to the depth of focus DOF. Therefore, in order to accurately position the resis perium 8 within the depth of focus DOF, not only is the precision of the exposure device required, but also the workpiece setting work is required, and a slight decrease in these precisions is required. However, there was a problem in that the resist film 8 had areas with poor exposure.

Therefore, this invention was made to solve the above-mentioned problem, and it is an object of the present invention to provide a photomask that can increase the depth of focus.

[Means to solve the problem]

The invention according to claim 1 is a photomask used when transferring a predetermined pattern to a resist film on a workpiece using lithography technology, and in order to achieve the above object, a transparent substrate and a A light shielding pattern formed on one main surface of a transparent substrate and a light shielding pattern formed on one main surface of the transparent substrate, which multiple-reflects a portion of the light that has passed between the light shielding patterns and focuses the light within the resist film. Equipped with a highly reflective film that expands depth.

According to a second aspect of the invention, in the photomask according to the first aspect, the high reflection film is formed on one main surface of the transparent substrate, and the light shielding pattern is formed on the high reflection film.

In the photomask according to claim 3, in the photomask according to claim 1, the light-shielding pattern is formed on one main surface of the transparent substrate, and the high-reflection film covers the light-shielding pattern. It is formed on one main surface of the substrate.

[Effect]

According to the inventions according to claims 1 to 3, since the high reflection film is formed on one main surface side of the transparent substrate, the focal position within the resist film for light that has passed through the high reflection film as it is, and the high reflection The focal positions within the resist film for the light multiple reflected by the film are separated along the thickness direction of the resist film, and as a result, the depth of focus is expanded.

〔Example〕

FIG. 1 shows a block diagram of essential parts of an exposure apparatus including a photomask, which is a first embodiment of the present invention. The overall configuration of this exposure apparatus is the same as the exposure apparatus shown in FIG. 9, and therefore will be described below using the same reference numerals for the same or corresponding parts.

As shown in FIG. 1, the photomask 3 includes a transparent substrate 4 and a high reflection film 1 formed on one main surface side of the transparent substrate 4.
0, and a light shielding pattern 5 formed on the high reflection film]0.

The transparent substrate 4 is made of quartz, for example, and has a refractive index n1 of 1.47 and a thickness dl of about 511111.

The high reflection film 10 is made of, for example, lead glass or silicon nitride. It is desirable that the high reflection film 10 is made of a material whose refractive index n2 is larger than the refractive index n1 of the transparent substrate 4 and whose light absorption ability is small. When the refractive index n2 of the high-reflection film 10 increases, the reflectance at the interface with the transparent substrate 4 and the interface with the air layer increases, and multiple reflections by the high-reflection film 10 are promoted.

Further, when the light absorption ability of the high reflection film 10 becomes small, absorption of multiple reflected light within the high reflection film 10 is suppressed. An example of a material that satisfies the above conditions is La, which is a type of lead glass.
It is desirable to use F2 glass (manufactured by Hoya Corporation) or TaFD6 glass.

When LaF2 glass is used, the refractive index n2 is 1
．． 78H1 Transmittance for light with a wavelength of 360 nm is 0.8
becomes. Note that the thickness d2 of the high reflection film 10 is determined in consideration of the depth of focus, the details of which will be described later.

The light shielding pattern 5 is made of Cr, MoSi, etc., and its thickness d3 is usually about 0.1 μm.

The projection lens system 6 is composed of a plurality of combined lenses, and is finished to be telecentric with respect to both the input and output directions. The magnification m of this lens system 6 is, for example, 1
15 is set. However, the magnification m is not limited to the above value, and may be, for example, m −1/]0, or m
-1 may be sufficient.

The resist film 8 formed on the sea urchin substrate 7, which is the workpiece, is made of a conventionally well-known resist material. For example, when using MCPR2000H (manufactured by Mitsubishi Kasei Corporation), the refractive index n4 is 168 and the thickness d4 is approximately 1.
It is 5 μm.

In an exposure apparatus including this photomask 3, a light source 1
For example, when ultraviolet light L1 with a wavelength of 436 nm is irradiated from (see FIG. 9), it is focused by the lens system 2 and irradiated onto the photomask 3 as light L2, which then enters the high reflection film 10 via the transparent substrate 4. be done.

In the area where the light shielding pattern 5 is not provided,
A part of the light L is directly emitted toward the lens system 6 as transmitted light L3, while the remaining light is sequentially reflected by the lower and upper surfaces of the high reflection film 10 and then emitted from the lens system as one burst of incident light L4. It is emitted towards 6. Note that multiple reflections occur within the high reflection film 10, so in addition to the primary reflected light L4, high-order reflected light of secondary or higher order is emitted toward the lens system 6; The light intensity of high-order reflected light becomes extremely small and can be ignored in practical terms.

On the other hand, in the region where the light shielding pattern 5 is provided, transmission of light to the lens system 6 is blocked.

In this way, the transmitted light L selectively transmitted through the photomask 3
The 3rd and 1st blown emitted light beams L4 pass through the projection lens system 6 to the Si
The light is focused and imaged within the resist film 8 formed on the substrate 7.

In this case, the transmitted light L3 is imaged on the focal plane 9 including the condensing point P, as in the conventional example shown in FIG. On the other hand, one burst of emitted light L4 travels to a point Q, which is far away from the condensing point P along the optical axis direction of the lens system 6, due to the optical path difference that occurs within the high reflection film. The image is formed on a focal plane 11 containing the image.

Now, the optical distance n4D between points P and Q is the high reflection film 10
Using the optical path difference 2n2d2 generated within the lens system 6 and the magnification m of the lens system 6, it is expressed as nD-mx(2n2d2), so the thickness d2 of the high reflection film 10 is as follows. Here, since the refractive indices n, n4 and magnification m are known, the thickness d2 can be determined if the distance is known.

By the way, as shown in FIG. 2, the depth of focus by the lens system 6 is DOF and DOF4 centered on points P and Q for each of the transmitted light L3 and the one-shot incident light L4, respectively.
Permitted within a certain range expressed as Therefore, in order to expose the entire area of the resist film 8 along the thickness direction, the depth of focus range DOF, D
It is necessary to form OF4 continuously, that is, it is necessary to satisfy the following conditions.

Since the depths of focus DOF and DOF4 are each expressed by equation (1), the above equation (3>) can be rewritten as follows.

λ 2°NA, 2°(“) D < DOF − Since the numerical aperture NA of the lens system 6 and the wavelength λ of the incident light are known, the distance is determined from equation (4), and further, (2
) The thickness d2 of the highly reflective film 10 can be found from the equation.

For example, NA = 0.38. λ=436nm
, n2=1.78fi6. n 4-1.68.
For m-1,5, D<1.5μmd 2217.6
It becomes μm.

As described above, since the resist film 8 is exposed using the transmitted light L3 and the single burst light L4 from the high reflection film 10, the depth of focus can be expanded up to twice as much as in the conventional method.

3 to 6 show modifications of the photomask 3 of the above embodiment, respectively.

The photomask 3 in FIG.
It also has 2. The antireflection film 12 is made of, for example, chromium oxide, and has a refractive index n5 of about 1.4. Highly reflective film 10 anti-reflective film 12. Refractive index n2n of light shielding pattern 5 5. Between n, n < n
Since the relationship 5<ne holds true, a good antireflection effect can be obtained by setting the thickness d5 of the antireflection film 12 to, for example, λ.

If this anti-reflection film 12 is not provided, part of the light reflected at the interface between the high-reflection film 10 and the light-shielding pattern 5 may become stray light after multiple reflections within the high-reflection film 10. The light is emitted to the lens system 6 side. The antireflection film 12 prevents the occurrence of such stray light and improves exposure accuracy.

The photomask 3 shown in FIG. 4 further includes an antireflection film 13 on the other main surface of the transparent substrate 4. The photomask 3 shown in FIG. The antireflection film 13 is made of, for example, MgF2, and has a refractive index n7 of 1.378. Air layer 1 Anti-reflection film 13. The refractive index n of the transparent substrate 4.

n7. Between n, no < n 7 < n I
Since the relationship holds true, the thickness d7 of the antireflection film 13
For example, by setting λ to λ, a good antireflection effect can be obtained.

If this anti-reflection film] 3 is not provided, part of the light incident on the photomask 3 from the light source is reflected on the upper surface of the transparent substrate 4 and becomes stray light, or
A part of the incident light reflected on the lower surface of the transparent substrate 4 is reflected again on the upper surface of the transparent substrate 4 and becomes stray light, which is emitted to the lens system 6 side. The antireflection film 13 prevents the occurrence of such stray light and improves exposure accuracy.

The photomask 3 shown in FIG. 5 further has an antireflection film 4 formed on the surface of the light shielding pattern 5 on the projection lens 6 side. The antireflection film 14 prevents reflection of light incident on the lower surface side of the light shielding pattern 5, thereby improving exposure accuracy.

Of course, the antireflection coating 1 shown in FIGS. 3 to 5
2, 13, and 14 may be formed in the photomask 3 in an appropriate combination. FIG. 6 shows the antireflection coatings 12 and 13.
．． An example of a photomask 3 equipped with all 14 is shown below.

FIG. 7 shows a configuration diagram of main parts of an exposure apparatus including a photomask according to a second embodiment of the present invention.

As shown in FIG. 7, this photomask 3 is formed on one main surface of a light shielding pattern 5 or a transparent substrate 4, and a high reflection film 10 is formed on the transparent substrate 4 so as to cover the light shielding pattern 5. On the other hand, it is formed on the main surface. Other configurations are
Since it is the same as the first embodiment shown in FIG. 1, the same or equivalent parts are given the same reference numerals and the explanation thereof will be omitted.

Even when this photomask 3 is used, the high reflection film 10
The focal position P in the resist film 8 for the light L3 that has passed through the resist film 8 as it is, and the focal position atQ in the resist film 8 for the one-shot incident light L4 by the high reflection film 10 are in the thickness direction of the resist film 8. The depth of focus will be expanded.

FIG. 8 shows an example in which an antireflection film 15 is formed on the other main surface of the transparent substrate 4 in the second embodiment. This anti-reflection film 15 performs the same function as the anti-reflection film 13 shown in FIG.

〔Effect of the invention〕

According to the photomask of the invention according to claims 1 to 3, since the high reflection film is formed on one main surface side of the transparent substrate, the focal position within the resist film for light that has passed through the high reflection film as it is and , the focal position within the resist film for the light that has been multiple-reflected by the high reflection film is located apart along the thickness direction of the resist film, thereby providing the effect that the depth of focus can be expanded.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the main parts of an exposure apparatus including a photomask, which is the first embodiment of the present invention, Fig. 2 is a diagram for explaining the expansion of depth to Hayabusa, and Figs. 3 to 6 are the above-mentioned Figures illustrating modified examples of the photomask according to the first embodiment, FIG. 7 is a configuration diagram of main parts of an exposure apparatus including a photomask according to the second embodiment of the present invention, and FIG. 8 is a diagram showing the second embodiment of the invention. FIG. 9 is a schematic configuration diagram of an exposure apparatus including a photomask conventionally used in the photolithography process. Figure C1 is an enlarged view of the main part. In the figure, 3 is a photomask, 4 is a transparent substrate, 5 is a light shielding pattern, 7 is a substrate, and 8 is a resist film. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (3)

[Claims] (1) A photomask used when transferring a predetermined pattern to a resist film on a workpiece using lithography technology, the photomask comprising a transparent substrate and a light-shielding pattern formed on one main surface side of the transparent substrate. and a high-reflection film formed on one main surface side of the transparent substrate, which multiple-reflects a portion of the light that has passed between the light-shielding patterns and expands the depth of focus within the resist film. mask. (2) The photomask according to claim 1, wherein the high reflection film is formed on one main surface of the transparent substrate, and the light shielding pattern is formed on the high reflection film. (3) The photomask according to claim 1, wherein the light-shielding pattern is formed on one main surface of the transparent substrate, and the high reflection film is formed on the one main surface of the transparent substrate so as to cover the light-shielding pattern. .