JP2000077309A - Reduced exposure method and reduction stepper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ease dependence of the linear width or space width of a reduction projection pattern on an original pattern (reticule pattern). SOLUTION: This reduction stepper in a deformation illumination system is constituted of a intensity distribution varying optical system 21 for minimizing the central intensity distribution of light beams, a fly-eye lens 22 for inputting and outputting the light beams outputted from the intensity distributing varying optical system 21, a deformation illuminating filter 23 for changing the intensity distribution of the light beams from the fly-eye lens 22, a variable transmissivity filter 24 for transmitting the light beams from the deformation illuminating filter 23, a control part 34 for controlling the transmissivity of the transmissivity variable filter 24, so that a reticule pattern 29 illuminated by the light beams can be reduced and projected. Then, the transmissivity of the transmissivity variable filter 24 can be changed, based on the data of the reticule pattern by a control part 34.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reduced projection method and apparatus, and more particularly to a reduced projection method and apparatus for shielding a predetermined portion of a reticle in accordance with a pattern in a modified illumination method using super-resolution.

[0002]

2. Description of the Related Art Hitherto, it has been known that the image contrast at the resolution limit can be improved more than the super-resolution phenomenon by darkening the central portion of a light source surface or a pupil plane of a projection lens conjugate with the light source surface. One of the reduction projection apparatuses (steppers) utilizing this phenomenon is a modified illumination method in which a filter is attached to a fly-eye lens to illuminate a mask (reticle).

FIG. 4 shows an example of such a modified illumination method, which is disclosed in JP-A-7-122478 ("Pattern projection method"). As shown in FIG. 4, the mask 15 is illuminated with laser light from the KrF excimer laser unit 1 and is incident on the pupil of the reduction projection lens 16 so that the wafer
7 is to project a pattern.

[0004] In order to prevent speckles and generate a minimum intensity distribution at the center of the beam, the laser beam is split into four beams by the beam splitter unit 6 and immediately superimposed by the prism unit 7. . Then, the laser light is further supplied to a relay lens 8, a fly-eye lens 9, a relay lens 10, a masking blade 12, a relay lens 13, and a condenser lens 14.
Are sequentially illuminated on the mask 15.

In this optical system, a fly-eye lens 9
Is an effective light source surface and is conjugate with the reduction projection lens 16. The fly-eye lens 9 is provided with a four-hole filter or an annular zone to control the shape of the effective light source.

As described above, according to the conventional modified illumination method, the illumination light causing three-beam interference, which causes a decrease in the depth of focus on the wafer surface, is shielded in advance before mask (reticle) illumination,
By obtaining an image on the wafer surface by two-beam interference, the depth of focus is expanded, and the resolution is also improved.

[0007]

However, the conventional modified illumination method described above has a problem that the line width of the pattern on the wafer depends on the reticle pattern.

FIG. 5 illustrates a reticle pattern. The pattern (A) and the pattern (C) have a line width a and a different line direction by 45 °, and the pattern (B) has a line width b,
The line direction is different from the line direction of the pattern (A) by 90 °. Each of the three types of patterns in FIG. 5 is a line pattern, and is a repetitive pattern in which the widths of the chrome portion and the transmissive portion of the reticle are the same. If such patterns with different dimensions and directions coexist on the same reticle, the image contrast and depth of focus for each pattern will be different.
It is impossible to give a pattern as the original pattern on the wafer.

FIG. 6 (D) shows the result of reducing and projecting the pattern (A), the pattern (B) and the pattern (C) at a magnification M by attaching an annular zone to the fly-eye lens. FIG. 6 (D)
As shown in the figure, the exposure amount giving the line width (b / M) on the wafer is E1, the exposure amount giving the line width (a / M) on the wafer is E2, and E1 and E2 are different. . The patterns (A) and (C) having the same width a have the same exposure amount E2.
In the pattern of (C) having a large width, since the diffraction angle is small, a difference in the positional relationship between the optimal obliquely incident light beam and the annular light-shielding portion occurs.
Is relatively overexposed compared to (A) and (C).
The design dimension value is obtained at E1 smaller than 2.

FIG. 6E shows a result obtained by mounting a four-hole filter ring on a fly-eye lens and reducing and projecting the pattern (A), the pattern (B) and the pattern (C) at a magnification M. Is shown. As shown in FIG. 6E, the line width (b
/ M) is E3. The exposure amount giving the line width (a / M) on the wafer is E4 for the pattern (A) and E5 for the pattern (C).
Here, E3, E4 and E5 are different from each other.

Accordingly, the present invention is to alleviate the dependence of the line width or space width of the reduced projection pattern on the original pattern (reticle pattern), specifically, the line width (or space width) of the original pattern and the line width. The task is to mitigate the dependence on the direction.

[0012]

According to a first aspect of the present invention, there is provided a reduction projection apparatus according to the present invention, comprising: a variable intensity distribution optical system for minimizing the intensity distribution at the center of a light beam; A fly-eye lens for inputting and outputting the light beam output from the lens, a modified illumination filter for changing the intensity distribution of the light beam from the fly-eye lens, and transmitting the light beam from the modified illumination filter A variable transmittance filter, a control unit that controls the transmittance of the variable transmittance filter, and a reduced projection device of a modified illumination system that reduces and projects a reticle pattern to be illuminated by the light beam, wherein the control unit includes: The transmittance of the transmittance variable filter is changed based on the data of the reticle pattern.

The reduction projection method according to the present invention may further comprise a step of illuminating the reticle pattern with the transmittance of the variable transmittance filter uniform over the entire surface, and setting the transmittance of the variable transmittance filter to the reticle pattern. Illuminating the reticle pattern.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a reduction projection apparatus according to the present invention. As shown in FIG. 1, the reduction projection device of the present invention comprises:
A light source 20, an intensity distribution variable optical system 21 for changing the intensity distribution of the light from the light source 20, a fly-eye lens 22 for passing light having the changed intensity, and a light-emitting lens 22 for the light emitted from the fly-eye lens Deformation illumination filter 23 for controlling shape
And a transmittance variable filter 24 for emitting the light emitted from the modified illumination filter 23. The light emitted from the transmittance variable filter 24 passes through a relay lens 25, a reticle blind 26, a relay lens 27, and a condenser lens 28. Then, the reticle 29 is illuminated, and a reduced image of the reticle pattern is formed on the wafer 32 by the reduction projection lens 30.

Here, the variable intensity distribution optical system may be any optical system that minimizes the intensity of the light beam from the light source at the center. The modified illumination filter 23 is a fly-eye lens 2
The filter is set on the exit side of No. 2 and an annular zone or a four-hole filter is preferably used. The transmittance variable filter 24 is set on the emission side of the modified illumination filter 22.

The variable transmittance filter 24 is formed of a variable transmittance material such as a liquid crystal panel, so that an arbitrary position on the filter surface can be shielded or transmitted by an electric signal. The control unit 34 uses the shutter opening / closing signal of the illumination light to
The data 33 created in advance is input, and the light shielding (or transmission) position and timing of the transmittance variable filter 24 are controlled by an electric signal.

That is, the light shielding position and the timing when the shutter is open are programmed in advance according to the pattern type on the reticle, and the control unit 34 controls the variable transmittance filter 24 after inputting the shutter open / close signal. I do.

Next, a reduced exposure method according to the present invention will be described with reference to FIG. It is assumed that the three types of patterns (A), (B), and (C) shown in FIG. 5 are mixed on the reticle.

Further, as shown in FIG. 2A, it is assumed that the modified illumination filter 23 is an annular zone having a light shielding portion 40 at the center.

First, at time t0, an exposure shutter (not shown) is opened. The exposure shutter release signal is sent to the control unit 34.

Until the initial time t1 after the shutter is opened, the transmittance variable filter 24 is made to be entirely transparent. Therefore, until time t1, only the central portion of the reticle is shielded and illuminated by the shield 40 of the annular filter. In this illumination, the first exposure is performed until the cumulative exposure amount specified in advance by the program is reached. That is, the time required to reach the predetermined cumulative exposure amount is calculated in advance using the reticle pattern, the luminance of the light source, and the reduction projection optical system as given parameters.

Next, a time t when a predetermined cumulative exposure amount is reached
In step 3, an electric signal for designating the light shielding position is transmitted to the transmittance variable filter 24. The transmittance variable filter 24 shields the light shielding unit 41 specified in advance by a program. That is, the pattern (A) and the pattern (B) are generated on the transmittance variable filter in order to compensate for the lack of the exposure amount for the pattern (A) and the pattern (B). FIG. 2 (B)
For simplicity, only two vertical lines and two 45 ° lines are illustrated. Thus, the transmittance variable filter 2
Second, a reticle pattern is generated in step 4 and exposed for a predetermined time.
Upon completion of the exposure, the entire reduction projection process ends. The reticle pattern, the brightness of the light source, and the reduction projection optical system are calculated as given parameters in advance as the given time, similarly to the required time required to reach the above-described predetermined cumulative exposure amount.

FIG. 3 shows the line width on the wafer obtained by the above-described exposure process. As shown in FIG. 3, the shortage of exposure for the patterns (A) and (C) is resolved,
A reticle pattern is faithfully reduced and projected at the same exposure amount EO. Here, the exposure amount shown in FIG. 3 is an amount obtained by multiplying the luminance of the light source 20 by the total exposure time when the luminance of the light source 20 is constant.

Although the embodiment of the present invention for generating a reticle pattern on a variable transmittance filter has been described above, the present invention is not limited to this, and a virtual reticle pattern may be generated on a variable transmittance filter. Good. Here, the virtual reticle pattern may be, for example, one pattern having an average line width and an average angle when the reticle pattern includes a plurality of types of line widths and a plurality of types of direction angles.

Further, the above-described second exposure may be performed first, and then the first exposure may be performed.

[0027]

According to the present invention described above, it is possible to reduce a dimensional difference between patterns due to a pattern dependency when the modified illumination method is used.

[Brief description of the drawings]

FIG. 1 is a reduction projection apparatus according to the present invention.

FIG. 2 is an example of a transmittance pattern of a filter in the reduction projection method of the present invention.

FIG. 3 is a graph showing a relationship between a line width on a wafer and an exposure amount according to the reduction projection method of the present invention.

FIG. 4 shows a conventional reduction projection device.

FIG. 5 is an example of a reticle pattern.

FIG. 6 is a graph showing a relationship between a line width on a wafer and an exposure amount by a conventional reduction projection method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 22 fly's eye lens 23 deformed illumination filter 24 transmittance variable filter 29 reticle 30 reduction projection lens 32 wafer 40 annular light shield 41 light shield of variable transmittance filter

Claims (6)

[Claims] A variable intensity distribution optical system for minimizing the intensity distribution at the center of the light beam; a fly-eye lens for inputting and outputting the light beam output from the variable intensity distribution optical system; A modified illumination filter that changes the intensity distribution of the light beam from the lens, a transmittance variable filter that transmits the light beam from the modified illumination filter, and a control unit that controls the transmittance of the transmittance variable filter. A reduced projection exposure apparatus of a modified illumination method for reducing and projecting a reticle pattern illuminated by the light beam, wherein the control unit changes a transmittance of the transmittance variable filter based on data of the reticle pattern. A reduction projection exposure apparatus. 2. The reduction projection exposure apparatus according to claim 1, wherein the control section causes the transmittance variable filter to generate the transmittance pattern like the reticle pattern. 3. The reticle pattern has a plurality of types of line widths and a plurality of types of line direction angles, and the control unit executes a pattern having an average value of the line widths and an average value of the line direction angles. 2. The reduction projection exposure apparatus according to claim 1, wherein the variable transmittance filter generates the light. 4. The reduction projection exposure apparatus according to claim 1, wherein the transmittance variable filter is a two-dimensional liquid crystal shutter. 5. A variable intensity distribution optical system for minimizing the intensity distribution at the center of the light beam, a fly-eye lens for inputting and outputting the light beam output from the variable intensity distribution optical system, and a fly-eye lens. A modified illumination filter that changes the intensity distribution of the light beam from the lens, a transmittance variable filter that transmits the light beam from the modified illumination filter, and a control unit that controls the transmittance of the transmittance variable filter. A reduced projection exposure method using a reduced projection exposure apparatus of a modified illumination system for reducing and projecting a reticle pattern illuminated by the light beam, wherein the transmittance of the transmittance variable filter is uniform over the entire surface, and the reticle pattern is illuminated. And illuminating a reticle pattern with the transmittance of the transmittance variable filter being the same as the reticle pattern. Reduction projection exposure method. 6. A variable intensity distribution optical system for minimizing the intensity distribution at the center of the light beam, a fly-eye lens for inputting and outputting the light beam output from the variable intensity distribution optical system, and a fly-eye lens. A modified illumination filter that changes the intensity distribution of the light beam from the lens, a transmittance variable filter that transmits the light beam from the modified illumination filter, and a control unit that controls the transmittance of the transmittance variable filter. A reduced projection exposure method using a reduced projection exposure apparatus of a modified illumination system for reducing and projecting a reticle pattern illuminated by the light beam, wherein the transmittance of the transmittance variable filter is uniform over the entire surface, and the reticle pattern is illuminated. And if the reticle pattern has a plurality of types of line widths and a plurality of types of line direction angles, the average value of the line widths and the line direction angles The average pattern having an average value, and generates the variable transmittance filter, reduction projection exposure method which comprises the step of illuminating the reticle pattern.