JPH01105256A - Photomask - Google Patents

Abstract

PURPOSE:To maintain large focal depth, to facilitate the focusing of an optical system and to improve the integration of conductor devices by providing a photomask structure with light shielding layers on both surface sides of a transparent layer. CONSTITUTION:The same circuit patterns 3a and 3b are formed correspondingly on both main sides of a fused quartz 2. Thus the reticule has two focal depths 6a and 6b on a wafer 4 and when two focal depths 6a and 6b are composed in succession on the wafer by means of adjusting a thickness (d) of the fused quartz 2, the focal depth can be nearly doubled practically. Thus the focusing of the optical system is greatly facilitated and the integration of semiconductor devices is further improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a technique that is effective for use in photomasks for light exposure used in the manufacture of semiconductor devices.

[Conventional technology]

Regarding light exposure technology, for example, Kogyo Kenkyukai Co., Ltd.
Published on November 20, 1985, “Electronic Materials Special Volume, Super L
"SI Manufacturing/Testing Equipment Guidebook" P95 to P102, which lists and explains various light exposure techniques.

The present inventor studied a photomask used in the exposure process. Note that, unless otherwise noted, the term photomask used below includes a reticle used for 1:1 equal-magnification exposure to a reticle used for reduction exposure.

In the projection exposure process for forming a predetermined circuit on a semiconductor wafer (hereinafter simply referred to as wafer), a photomask with a light-shielding film such as chromium (Cr) formed in a predetermined circuit pattern shape is used on one surface of a transparent quartz substrate. A process is performed in which this circuit pattern is transferred onto a resist layer coated on the surface of a wafer, and a predetermined resist pattern is formed by utilizing chemical changes in the resist layer due to irradiation with light.

Incidentally, as semiconductor devices become more highly integrated and circuit patterns formed on wafers become finer, high resolution is also required for circuit patterns on resist layers.

Here, the resolution of a circuit pattern in the reduction projection exposure technique is generally expressed by the following equation.

R=Cλ/ (NA) In the above formula, R indicates resolution, and the smaller this value is, the higher the resolution can be obtained. Also, C is a constant and λ
is the wavelength, NA (Numerical Aperture)
e) shows the aperture of the reduction lens.

As is clear from this equation, in order to follow the pattern miniaturization and obtain high resolution, the wavelength λ must be made shorter, or the aperture NA of the reduction lens must be increased. .

[Problems to be solved by the invention] However, by achieving such high resolution,
The inventor has discovered that the depth of focus of the reduction lens is sacrificed.

That is, in an optical system using a reduction lens, the depth of focus Δδ is expressed by the following equation.

Δδ=Cλ/ (NA)” As is clear from the above equation, when the wavelength λ is decreased or the aperture NA is increased, the depth of focus Δδ is also inevitably decreased, making it difficult to adjust the focus position of the optical system. Not only is adjustment difficult, but if there are steps or the like in the base under the resist layer, it is not possible to ensure a specified resolution, and there is a risk that poor resolution of the resist pattern may occur.

The present invention has been made focusing on the above problems,
The purpose is to provide a light exposure technology that can maintain high resolution while ensuring a wide depth of focus.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means for solving problems]

A brief overview of typical inventions disclosed in this application is as follows.

That is, the photomask structure has at least one transparent layer and light shielding layers disposed on both sides of the transparent layer with the transparent layer interposed therebetween.

[Effect]

According to the above-mentioned means, by forming the light-shielding layer through the transparent layer, it is possible to synergistically ensure a wider depth of focus than when the light-shielding layer is formed on only one side of the transparent layer. , focus positioning of the optical system becomes extremely easy, and it is possible to further increase the degree of integration of semiconductor devices.

〔Example〕

FIG. 1 is a conceptual diagram of an optical system in a reduction projection exposure apparatus using a reticle according to an embodiment of the present invention, and FIG. 2 is an enlarged partial sectional view showing the reticle of this embodiment.

The reticle 1 (photomask) of this embodiment is used to transfer a large number of circuit patterns 3a, 3b formed on a quartz glass 2 onto a wafer 4 at a reduction ratio of, for example, 5:1.

In this embodiment, a pair of identical circuit patterns 3a and 3b are formed at corresponding locations on both main surfaces of the quartz glass 20. These circuit patterns 3a and 3b are obtained by, for example, uniformly forming a vapor deposited film of chromium (Car) on the entire surface of the quartz glass 2, and then processing it into a predetermined circuit pattern by means such as electron beam exposure. It is.

In this way, the circuit patterns 3a and 3b formed on both sides of the quartz glass 2 function as follows in the reduction exposure process.

That is, in FIG. 1, 5 is a reduction lens, and 6 is a reduction lens.
a and 6b indicate the depth of focus corresponding to the respective circuit patterns 3a and 3b.

Originally, when the circuit pattern 3b is formed only on one surface of the quartz glass 2, the depth of focus on the wafer 4 is limited to the range represented by 6b, and only a narrow depth of focus can be ensured. The disadvantages caused by such a narrow range of depth of focus are as described above.

On the other hand, according to the first embodiment, since the same circuit patterns 3a and 3b are formed correspondingly on both main surfaces of the quartz glass 20, the reticle is 6 on the wafer 4.
It will have two depths of focus, a and 6b.

Therefore, if the thickness d of the quartz glass 2 is adjusted so that the two depths of focus 5a and 5b are continuous on the wafer, the depth of focus can be substantially doubled. Become.

Here, the thickness of the quartz glass 2 that needs to be adjusted will be explained using specific numerical values as follows. That is, if the amount of displacement of the reticle 1 on the optical axis is generally ΔX, then the amount of displacement of the focal point on the wafer 4 side Δy
is expressed by the following relational expression.

Δy=-M2 ΔX In the above formula, M indicates the magnification of the reduction lens.

Therefore, assuming that the reduction exposure apparatus has a reduction ratio of 115, ΔX and Δy are as follows.

IΔxl=251Δy1 That is, from the above equation, in a reduction lens with a depth of focus of 4 μm, the thickness d of the quartz glass 2 is 100 μm.

By forming the same circuit patterns 3a and 3b on both sides, the depth of focus can be doubled, that is, 8μ.
It becomes possible to expand up to m.

As described above, according to this embodiment, the following effects can be obtained.

[1) Same circuit pattern 3a on both sides of 9 quartz glass 2
, 3b, the depth of focus on the wafer 4 can be expanded up to twice that of a circuit pattern formed only on the negative side.

(2) Since the depth of focus is expanded by the above (1), it becomes easy to adjust the focal position of the optical system in the reduction projection exposure apparatus, and it becomes possible to perform exposure work efficiently.

(3) According to the above (1), the resolution margin of the ultra-fine pattern is improved, and it becomes possible to prevent poor resolution of the resist pattern.

(4) According to (1) to (3) above, the yield of wafers 4 can be improved and a highly reliable semiconductor device can be provided.

[Embodiment 2] FIG. 3 is a sectional view showing a reticle according to another embodiment of the present invention.

In this Example 2, chromium (Cr
) is formed, a transparent layer 7 made of, for example, 5i02 or the like is formed with a predetermined thickness d on top of the first circuit pattern 13a; A second circuit pattern 13b having the same shape as 13a is formed.

In this way, the second embodiment also makes it possible to expand the depth of focus as in the first embodiment. Furthermore, according to the second embodiment, since the transparent layer 7 is formed of a SiO2 film or the like, the depth of focus can be arbitrarily adjusted by controlling the thickness of this film during the manufacturing stage.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the Examples and can be modified in various ways without departing from the gist thereof. Nor. For example, although a case has been described in which quartz glass 2 is used as the transparent substrate, the present invention is not limited to this. Further, as the transparent layer 7, a material other than the 5iOz film may be employed.

In the above explanation, the invention made by the present inventor is mainly applied to a so-called reticle, which is the field of use thereof, but the invention is not limited to this, and for example, it is used for 1:1 equal magnification exposure. It may also be applied to photomasks.

Moreover, although the circuit pattern has been described only with a two-layer structure, it may be a circuit pattern with three or more layers.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

That is, by forming a middle mask structure having at least one transparent layer and light-shielding layers disposed on both sides of the transparent layer with the transparent layer in between, a plurality of light-shielding layers are formed through the transparent layer. As a result, compared to the case where a single light-shielding layer is formed on one side of the transparent layer, the depth of focus can be synergistically widened, making it extremely easy to align the focus position of the optical system, and increasing the height of semiconductor devices. Integration can be further increased.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of an optical system in a reduction projection exposure apparatus using a reticle according to the first embodiment of the present invention, FIG. 2 is an enlarged partial cross-sectional view showing the reticle according to the first embodiment, and FIG. FIG. 3 is an enlarged partial cross-sectional view showing a reticle according to a second embodiment. 1... Reticle (photomask), 2... Quartz glass, 3a, 3b... Circuit pattern, 4... Wafer, 5
...reducing lens, 5a, 5b...depth of focus, 7...
・Transparent layer, 13a...first circuit pattern, 13b・
...Second circuit pattern. Figure 1 Figure 2 n

Claims (1)

Claims: 1. A photomask comprising at least one transparent layer and light shielding layers disposed on both sides of the transparent layer with the transparent layer interposed therebetween. 2. Claim 1, wherein the transparent layer is formed of a transparent substrate, and the light shielding layer is a metal film formed in a predetermined pattern shape on both main surfaces of the transparent substrate.
Photomask as described in section. 3. The photomask according to claim 1, wherein the transparent layer and the light shielding layer are alternately deposited on a transparent substrate.