JPH0541346A - Projection aligner of fine pattern - Google Patents

Abstract

(57) [Summary] [Object] To realize an inverted conical tilted illumination by using an optical element without imposing an excessive force on the configuration of an illumination optical system of a projection exposure apparatus. [Structure] A prism 11 as an optical element arranged above a mask 21 tilts an illumination light I perpendicular to the mask surface by an angle α. Here, α is an angle corresponding to the numerical aperture of the projection optical system. The illumination light inclined by the prism 11 illuminates the mask 21. Here, the prism 11 is rotated in the direction of arrow 10 about an axis l-l 'perpendicular to the mask surface.
The light I _M that illuminates an arbitrary point Q on the mask 21 is shown in FIG.
As shown in (b), the tilted illumination has an inverted conical shape. ..

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus for forming a fine pattern such as an LSI on a wafer (substrate) using a projection lens.

[0002]

2. Description of the Related Art A projection exposure apparatus for forming a fine pattern such as an LSI is required to have high resolution, and a projection lens of the projection exposure apparatus has a resolution close to a theoretical limit determined by the wavelength of light. However, in order to form even finer patterns, the phase shift method has been studied recently.

In the phase shift method, as shown in FIG. 7A, when a pattern exists on the mask 21 at a cycle d, 1
A shifter 22 is provided every other space. As a result, a negative amplitude can be obtained in the portion where the shifter 22 is present, so that the period viewed from the light becomes 2d and the DC component becomes zero. For this reason,
The diffraction opening angle α is about half that of the conventional method, and it is possible to form an image of a pattern with a period up to 1/2 of that of the conventional method. In addition,
In FIG. 7, I indicates the illumination light that illuminates the mask 21, and 23 indicates an aperture (aperture stop) arranged under the mask 21.
Is.

Based on this principle, in Japanese Patent Application No. 3-135317 filed by the same applicant, as shown in FIG. 7B, the light ray I illuminating the mask 21 corresponds to the numerical aperture of the projection lens. The method of giving the inclination of the angle is described. With this method, the same effect as that of the phase shift method can be obtained while using the ordinary mask 21, not only the step of forming the shifter is eliminated, but also the resolution is improved even for the pattern in which the shifter is difficult to arrange. Has the advantage that it can.

To provide such a tilted illumination on the mask surface, an annular aperture is used, or a mask is directly used as described in Japanese Patent Application No. 3-142782 filed by the same applicant. There is a method of placing an optical element for tilting the optical axis on the upper part. Optical element is a simple method,
Especially with prisms, manufacturing errors of optical elements are difficult to enter,
It has the advantage that near-ideal tilt illumination can be obtained.

[0006]

In the method of using a prism as an optical element to provide tilted illumination, the method of FIG.
As shown in (a), the inclined illumination from one direction is applied to the mask 21.
Of the prism 25 having almost the same size as the transfer pattern existing area of
However, introduction into an existing projection exposure apparatus does not pose any particular problem. However, in the case of the prism 26 that is tilted from two directions, the size of the prism in the tilted direction as shown in FIG. 6B needs to be about twice the size of the mask 21 to be irradiated. is there. Further, it is necessary to secure the distance between the prism 26 and the mask 21 according to the tilt angle. The same restriction is also applied when using the prism 27 having an oblique illumination in four directions shown in FIG. 6C. These restrictions become a serious obstacle in assembling the illumination optical system of the projection exposure apparatus.

When transferring a circuit pattern of a semiconductor integrated circuit, tilted illumination from one direction has a drawback that the image position shifts when the wafer surface deviates from the image plane, that is, when defocused. .. In order not to cause this image shift, light that symmetrically contributes to image formation at the image formation point is necessary, and in this sense, tilted illumination from two directions is required. Further, since there are patterns of various directions in the circuit pattern, it is desirable to use not only two directions but also four directions or an inverted conical inclined illumination.

The present invention has been made in view of the above points, and it is an object of the present invention to realize an inverted cone-shaped inclined illumination by using an optical element without giving any undue force to the configuration of an illumination optical system of a projection exposure apparatus. Another object is to provide a fine pattern projection exposure apparatus that does.

[0009]

In order to achieve the above object, a fine pattern projection exposure apparatus of the present invention uses an irradiation light perpendicular to a mask surface at a predetermined angle up to an angle corresponding to the numerical aperture of a projection lens. An optical element having a function of tilting is held on the light source side of the mask of the projection exposure apparatus, and a mechanism for rotating the optical element about an axis perpendicular to the mask surface as a central axis is provided.

[0010]

The operation of the present invention will be described with reference to FIG. 1 by taking the case of using a single prism as an example. In FIG. 1A, the one-sided prism 11 arranged above the mask 21 tilts the illumination light I perpendicular to the mask surface by an angle α. Here, α is an angle corresponding to the numerical aperture of the projection optical system. The illumination light inclined by the prism 11 illuminates the mask 21. Here prism 11
Is rotated in the direction of arrow 10 about an axis l-1 'perpendicular to the mask surface. The light I _M that illuminates an arbitrary point Q on the mask 21 is an inverted cone-shaped inclined illumination as shown in FIG.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a principle explanatory view showing one embodiment of the present invention. In this embodiment, a single prism 11 is used as an optical element for inclining the illumination light I perpendicular to the mask surface at an angle corresponding to the numerical aperture of the projection lens. The prism 11 is held on the light source side of the mask 21 and the prism 11 Is rotated about an axis l-1 'perpendicular to the mask surface as a central axis. The same reference numerals in the drawings indicate the same or corresponding parts.

Next, examples of the present invention will be shown below by exemplifying specific numerical values. As a projection exposure apparatus, the numerical aperture NA of the projection lens is 0.5 and the reduction magnification is 1/5. If it can be considered that the mask illumination light is perfectly parallel and the size of the light source is not, the tilted illumination angle α corresponding to the projection optical system is

Sin α = (1/5) * 0.5 = 0.1 (1)

Therefore, α = 5.7 degrees. However, in general, the light source has a size, and the illumination light I has an opening angle η as shown in FIG. When the optical axis is tilted by the prism 11, the opening angle of the illumination light I changes from η to η ′.
The difference is very small, and η ′ = η may be set. In this case, (α + η) must correspond to the projection optical system.

Sin (α + η) = (1/5) * 0.5 = 0.1 (2)

It is set as Such an inclined illumination angle α is
It can be selected by optimizing the apex angle φ of the one-sided prism 11. For example, if the prism material is quartz glass with a refractive index of 1.465, and η = 0.0 and sin α = 0.1, then φ = 1
Get 2.2 degrees. Since the size of the prism needs to cover the pattern area of the mask, the pattern area of the mask must be 75
If it is a square mm, the diameter of the prism needs to be 80 mm, for example. A circular shape centered on the rotation axis is desirable because it can avoid unnecessary disturbance of air.

Since the exposure time for one exposure is usually about 0.5 seconds, in order to obtain a substantially uniform irradiation regardless of the timing of starting and ending the exposure, the number of rotations is 2000 to 3 per minute.
It is necessary to make 000 rotations. It is desirable to avoid such high rotation if possible from the viewpoint of vibration, reliability due to wear of parts, and the like. Therefore, during exactly one exposure time, n
There is a method of controlling to rotate. Here, n is about 1 to 10 and may be in a range that does not impair the rotation mechanism.

In the rotating mechanism, the rotating shaft needs to pass through the center of gravity of the rotating body. In FIG. 3 (a), the one-sided prism 11 has a circular shape, and a columnar collar 12 is attached to the periphery thereof.
Process with quartz integrated. FIG. 3B is the same as FIG.
In the cross-sectional view, a frame 13 made of metal is further fitted to the flange 12, and a balancer is attached to the metal frame 13 so that the rotating shaft can be adjusted so as to pass through the center of gravity of the rotating body. The outer side surface of the metal frame 13 can be used, for example, as a surface against which a rotating shaft for applying a rotating force is pressed.

If the one-sided prism 11 is used as it is, such a device is required to balance the rotation, but there is a wavy prism 15 as shown in FIG. 4 as a simpler optical element. This prism 15 does not need to be rotationally balanced because it can be regarded as a substantially flat surface, or it can be rotated with a slight balance adjustment, and since it is thinner than a single prism as a whole,
Easy to rotate at high speed.

FIG. 5 shows a case where a phase type one-dimensional grating 16 is used as an optical element. Tilt angle α is si
nα = 0.1 and the wavelength used is the i-line (36
5 nm), the period of the grating 16 is 3.6.
It becomes 5 μm. The one-dimensional grating 16 can realize tilted illumination from two directions without being rotated, but by rotating the tilted illumination, an inverted cone-shaped tilted illumination is possible.

Although FIGS. 4 and 5 show only optical elements for tilting the illumination light in a certain direction, in reality, since these elements are rotated, as shown in FIG. A mechanical component that transmits power is required.

[0022]

As described above, according to the present invention, by rotating the optical element placed on the light source side of the mask, the inclined illumination light from only a limited direction is rotated and any point on the mask is rotated. Are illuminated in the shape of an inverted cone, and as a result, integrated circuit patterns having various directions can be transferred at the highest resolution of the projection optical system.

[Brief description of drawings]

FIG. 1 is a principle explanatory view showing an embodiment of the present invention,
(A) is the schematic block diagram, (b) is a figure which shows the inclination illumination of the reverse cone shape.

FIG. 2 is a diagram showing how illumination light is opened in this embodiment.

3A is a perspective view showing a specific example of the prism of FIG. 1, and FIG. 3B is a sectional view thereof.

4A is a plan view of a wavy prism used as an optical element in the present embodiment, and FIG. 4B is an enlarged view of a portion A of FIG.

5A is a plan view of a phase type one-dimensional grating used as an optical element in the present embodiment, and FIG. 5B is an enlarged view of a portion A of FIG.

FIG. 6 is an explanatory diagram showing an example of an exposure method by inclined illumination proposed by the same applicant.

FIG. 7A is an explanatory diagram of a conventional phase shift method,
(B) is explanatory drawing of the inclined illumination method proposed by the same applicant.

[Explanation of symbols]

 11 Prism 12 Prism collar 13 Prism frame 15 Wavy prism 16 Phase-type one-dimensional grating 21 Mask

Front page continuation (72) Inventor Ryo Watanabe 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Inventor Katsuyuki Harada 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp. (72) Inventor Yoshiaki Mimura 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp.

Claims (1)

[Claims] 1. A projection exposure apparatus for projecting and exposing a pattern on a mask onto a wafer through a projection optical system, wherein irradiation light perpendicular to a mask surface is at a predetermined angle up to an angle corresponding to a numerical aperture of a projection lens. A fine pattern projection exposure apparatus having a mechanism for holding an optical element having a function of tilting on a light source side of a mask of a projection exposure apparatus and rotating the optical element about an axis perpendicular to the mask surface as a central axis.