JP2003332194A - Exposure method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exposure method which is capable of realizing a resolution equivalent to that of a phase shift mask by the use of a binary mask used for forming a contact hole pattern and reducing an error in the size of the contact hole patterns. <P>SOLUTION: The exposure method irradiates a binary mask, where light transmitting parts are arranged between light shading members so as to form a periodic contact hole pattern on a wafer, with light rays to project the image of the mask pattern on the wafer for exposure through a projection optical system. The mask is moved in the direction perpendicular to an optical axis corresponding to the peculiar movement of the mask pattern, and an exposure operation is carried out several times, whereby the periodic contact hole pattern having a period corresponding to half the period of the mask pattern is transferred onto the wafer. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure method for printing a pattern of a mask as an original plate on a photosensitive substrate when manufacturing a semiconductor device, a liquid crystal display device or the like by using a photolithography technique.

[0002]

2. Description of the Related Art When manufacturing a semiconductor device or a liquid crystal display device using a photolithography technique, a mask pattern is exposed through a projection optical system onto a substrate (wafer or glass plate) coated with a photosensitive material. Projection exposure apparatus is used. FIG. 1 is a diagram schematically showing the outline of a projection exposure apparatus. In FIG. 1, reference numeral 11 is a mask as an original plate, which is composed of a light-shielding portion and a light-transmitting portion.
Irradiate at 4. The light that has passed through the light transmitting portion is diffracted by the mask, but the diffracted light can be condensed by the projection optical system 12 and a predetermined pattern on the mask can be exposed as an optical image on the substrate.

Improvements have been made to the projection optical system, the illumination optical system, and the mask in order to miniaturize the photolithography technique using the projection exposure apparatus.
Generally, a method of shortening the exposure wavelength of the projection exposure apparatus and increasing the numerical aperture (NA) of the projection optical system has been adopted. However, the adoption of this means means the development of the projection exposure apparatus itself, and there remains a problem in terms of development cost.

On the other hand, there is a so-called phase shift mask method as one of means for dramatically improving the resolution of the projection exposure apparatus. The phase shift mask is a mask designed to have a certain phase difference between the light incident on the mask and the light transmitting portions adjacent to each other. Normally, the phase difference is 180 degrees. To design. FIG. 2A is a diagram schematically showing the cross-sectional structure of the phase shift mask.

Various types of phase shift masks have been proposed, and depending on the type of phase shift mask, FIG.
It is said that it is possible to realize a line width which is about half that of a so-called binary mask having only a light-shielding portion and a light-transmitting portion as shown in the schematic sectional structure in (b). This is because the lights that are adjacent to each other have a phase difference of 180 degrees,
This is because the amplitudes of the central portions of lights adjacent to each other are canceled out.

A phase shift mask capable of improving the resolving power by changing the mask shape has attracted a great deal of attention because it does not involve the improvement of the projection exposure apparatus. However, there is a phenomenon that a desired pattern is not formed unless the phase difference of the light transmitted through the adjacent mask light-transmitting portions is accurately kept at 180 degrees, or the pattern on the mask is not faithfully transferred onto the wafer. As a result, the phase shift mask is difficult to manufacture.

Therefore, there is a need for a method of improving the resolution with a binary mask that is easy to make and has a straight imaging characteristic.

[0008]

Although the improvement of the resolution by the phase shift mask using the existing projection exposure apparatus is a useful means, it is difficult to apply it to actual use in many cases. The present invention provides an exposure method capable of realizing a resolution equivalent to that of a phase shift mask by using a binary mask for forming a contact hole pattern and reducing an error in the size of each contact hole pattern.

[0009]

In the exposure method according to the present invention, for example, as shown in FIG. 3 schematically showing a part of a periodic pattern, a transparent portion 4 arranged between light shielding members 5 is formed on a wafer. In a method of illuminating a binary mask arranged so as to form a periodic contact hole pattern and exposing the image of the mask pattern onto a wafer through a projection optical system, the mask or the wafer is perpendicular to the optical axis. It is characterized in that a periodic contact hole pattern having a cycle corresponding to half of the cycle of the mask pattern is transferred onto the wafer by performing a plurality of exposures by moving the mask according to a movement amount specific to the mask pattern. It is a thing.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the outline of the present invention will be described. The numerical aperture NA of the projection exposure apparatus is 0.
6, the exposure wavelength λ is 248 nm, and the reduction ratio is 1/4. FIG. 4A is a schematic diagram of a binary mask composed of a light-transmitting portion and a light-shielding portion, which is designed to transfer a contact hole pattern onto a wafer. As shown in the figure, xy is perpendicular to the optical axis. It is assumed that the coordinate system is used and that the patterns continue periodically. The shape of the transparent portion is a square, and the length of one side is a. Further, the distance between adjacent light transmitting portions in the x-axis direction and the y-axis direction is also a.

However, when the length a of one side of the mask light-transmitting portion is in the range of 0.5λ / NA to 1.0λ / NA, the state of contact hole formation can be expressed by the following equation. However, the wafer surface is represented by xy coordinates corresponding to the mask, the defocus amount is z, the amplitudes of the 0th and ± 1st order diffracted lights are A ₀ and A ₁ , and the wave number of the illumination light is k.
₀ , the x component, the y component, and the z component of the wave number of the diffracted light are set as k _x , k _y , and k _z , respectively.

[0012]

[Equation 1]

Here, the second term and the third term of the mathematical expression 1 represent the projection optical image having a period different by the magnification of the mask pattern and the projection system. The fourth term is the second and third terms of the mask pattern.
Represents a projected optical image with half the period of the term.

In order to investigate the meaning of Expression 1, consider dividing the area on the wafer into the following three types. Region 1 is a portion corresponding to the light transmitting portion on the mask. The region 2 is a part sandwiched in the region 1 only in the x-axis direction or the y-axis direction. The area 3 is a portion that does not belong to the areas 1 and 2, that is, a portion that is vertically and horizontally embedded in the area 2.
A method of dividing the area corresponding to FIG. 4A is shown in FIG.

As is clear from Equation 1, the light intensity distributions in the respective regions are different. The maximum values of the light intensity distribution in area 1, area 2, and area 3 are p, q, and
And let r. Normally, q is r when defocus is 0
Since it is larger and p is larger than q, if the slice level is incorrectly taken, an irregular contact hole row as shown in FIG. 4C appears (for easy understanding,
Exaggerated drawing). Therefore, in actual use, by setting the slice level to be larger than q, the diameter of about a
A series of contact holes with a spacing of / 4 are manufactured.

When exposure is performed using a mask in which contact hole patterns are periodically continued as described above, the maximum value of the light intensity in each region on the wafer corresponds to FIG. 4 (c). , As schematically shown in FIG. Next, the wafer is moved by a / 4 in the x direction for exposure. Further, exposure is performed by moving the wafer by a / 4 in the y direction. Finally, exposure is performed by moving the wafer by a / 4 in both the x and y directions.

When the results of the above four exposures are added together, the maximum value of the light intensity in each area is finally p + 2q + r.
As a result, if the slice level is appropriately set, the result shown in FIG.
As shown schematically, contact holes are formed with a diameter of about a / 8 and arranged at intervals of a / 8 in the x direction and the y direction, which is comparable to a phase shift mask using a binary mask. The periodic contact hole pattern is formed by the resolution.

When such exposure is performed, the coherence degree is preferably as small as possible, and the coherence degree is preferably 0.3 or less. As the resist, as represented by a chemically amplified resist for KrF, a resist having a small change in transmittance due to irradiation of exposure light is suitable. This is because the use of such a resist improves the reproducibility of the light intensity distribution in each region for each of four exposures.

The same effect can be obtained by moving the mask and performing four exposures instead of moving the wafer and performing four exposures.

This method is a result derived from the fact that the presence of the fourth term in Expression 1 contributes, and although this exposure method lowers the contrast on the wafer,
By exposing four times, the effect of defocusing can be made uniform, and a contact hole width error due to defocusing can be eliminated.

In the equation (1), since the second term depends on the defocus, if the defocus amount is set so as to cancel the third term, only the fourth term corresponds to a pattern corresponding to a half cycle of the remaining mask pattern on the wafer. Formed on. JP-A-8
In No. 288211, the L / S pattern corresponding to a half cycle of the mask pattern is formed by applying defocusing and exposing a plurality of times. A method of forming a contact hole by applying defocusing and performing a plurality of exposures can be considered, but the third term of Formula 1 makes this effect impossible.

[0022]

【Example】

EXAMPLE 1 Consider a projection exposure apparatus in which the wavelength of exposure light is 248 nm, the coherence degree is 0.3, the numerical aperture NA of the projection optical system is 0.6, and the reduction ratio is 1/4. In this embodiment, a mask as shown in FIG. 6 is considered. The coordinate system is as shown in FIG. 6, and the xy plane is taken perpendicular to the optical axis. The mask light-transmitting part is square and the length of one side is 0.6 NA / λ.
The spacing between adjacent light transmitting portions in the x and y directions is 0.6 NA /
is λ. Also, instead of the infinitely periodic contact hole pattern, the contact hole pattern is 7 in the x direction.
Now consider seven mask patterns in the y direction.

The area on the wafer is divided into three types. Region 1 is a portion corresponding to the light transmitting portion on the mask. The region 2 is a part sandwiched in the region 1 only in the x-axis direction or the y-axis direction. The area 3 is a portion that does not belong to the areas 1 and 2, that is, a portion that is vertically and horizontally embedded in the area 2.

By performing the first exposure, the area 1
If the maximum value of the light intensity in 1 is 1, the maximum value of the light intensity of region 2 is about 0.1, and the maximum value of the light intensity of region 3 is about 0.08. Here, the position of the wafer when the first exposure is performed will be called the original position.

The second exposure is performed by moving the wafer from the original position in the x direction by a / 4. The third exposure is performed by moving the wafer from the original position in the y direction by a / 4. Finally, in the fourth exposure, the exposure is performed by moving the wafer from the original position by a / 4 in the x direction and a / 4 in the y direction.

FIG. 7 shows the result of performing the exposure four times. Since the contact hole pattern is not an infinite period, a clean contact hole pattern cannot be reproduced at the edge of the wafer, but 12 x 12 contact holes are formed at a half period of the result of exposure with a normal binary mask. I understand. The above method can be reproduced by moving the mask instead of moving the wafer and repeating the exposure.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various exposure methods can be adopted without departing from the scope of the present invention.

[0028]

According to the present invention, contact holes can be formed with a conventional binary mask in half the period of the conventional method. Further, as a secondary effect, there is an advantage that it is less likely to be affected by defocus. The principle is that the maximum value of the light intensity at the desired position on the wafer is equalized by performing exposure while moving the wafer or mask. As described above, according to the present invention, fine processing can be performed by the conventional projection exposure apparatus using the binary mask.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a projection exposure apparatus.

FIG. 2A is a diagram schematically showing a sectional structure of a phase shift mask, and FIG. 2B is a diagram schematically showing a sectional structure of a binary mask.

FIG. 3 shows a binary-type mask used for forming a periodic contact hole pattern for four periods in the x direction and y
It is the figure which showed typically four periods for the direction.

FIG. 4A is a diagram schematically showing a binary-type mask used for forming a periodic contact hole pattern for two cycles in the x direction and two cycles in the y direction.
FIG. 4B is a diagram showing a method of dividing a region on a wafer surface used in the present invention, and FIG. 4C is a schematic diagram showing an exposure result with a binary mask used for forming a periodic contact hole pattern. FIG.

FIG. 5A shows a light intensity distribution formed on a wafer by a binary-type mask used for forming a periodic contact hole pattern for 1.5 cycles in the x direction and y.
5 is a diagram showing 1.5 cycles in the direction, showing the formation of contact hole patterns by the conventional exposure method, FIG.
(B) is the figure which showed typically the exposure result after performing the exposure by this invention.

FIG. 6 is a view schematically showing a mask for forming a contact hole pattern used in one embodiment of the present invention.

FIG. 7 is a contact hole pattern having a double period of a mask pattern formed on a wafer according to an embodiment of the present invention.

[Explanation of symbols]

1 mask substrate 2 light-shielding film 3 phase shifter 4 Mask translucent part 5 Mask light-shielding part 11 masks 12 Projection optical system 13 Wafer substrate 14 Lighting system

Claims (2)

[Claims] 1. A binary mask arranged such that a light-transmitting portion arranged between light-shielding members forms a periodic contact hole pattern on a wafer, and an image of the mask pattern is projected by a projection optical system. In the method of exposing on the wafer via the mask, the mask is moved in the direction perpendicular to the optical axis according to the amount of movement peculiar to the mask pattern, and a plurality of times of exposure is performed, so that the period corresponding to half the period of the mask pattern is changed. An exposure method characterized in that the periodic contact hole pattern is transferred onto a wafer. 2. A binary mask arranged such that a light-transmitting portion arranged between light-shielding members forms a periodic contact hole pattern on a wafer, and an image of the mask pattern is projected by a projection optical system. In the method of exposing on the wafer through the wafer, the wafer is moved in the direction perpendicular to the optical axis according to the amount of movement peculiar to the mask pattern, and a plurality of times of exposure is performed, so that the period corresponding to half the period of the mask pattern is changed. An exposure method characterized in that the periodic contact hole pattern is transferred onto a wafer.