JPH06120113A - Projection aligner - Google Patents

Abstract

PURPOSE:To facilitate the control of the size of a transferred pattern, by constituting a tightly closed system wherein the part from at least a photomask to a wafer support is tightly closed with s single medium or a plurality of mediums, in a projection aligner. CONSTITUTION:A projection aligner includes a condenser lens 2, a photomask 3, a projection lens 4, a wafer 5, and a wafer support 10, in a closed system 9. The light outputted from a light source 1 is directed to the condenser lens 3 through a first reflecting mirror 13, an integrator 14 and a second reflecting mirror 15. The effect of diffraction is controlled by a medium 6 whose real refractive index is (n), and the wavelength is shortened. This light is directed to the photomask 3, and the wafer 5 is irradiated with the light through the projection lens 4. The light whose wavelength is shortened scarcely enters a light shielding part, and a fine pattern is formed. Thereby the size of a fine pattern can be controlled and corrected.

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.
More specifically, it relates to a projection exposure apparatus that can easily control the size of a transfer pattern.

[0002]

2. Description of the Related Art The photolithography technology by the reduced projection exposure method is approaching the limit of resolution with the reduction of design dimensions and the miniaturization of processing patterns. The phase shift method is well known as a method for improving the resolution limit. According to this method, theoretically, the resolution limit is improved about twice as compared with the conventional mask. Therefore, even considering the decrease in the depth of focus due to the shortening of the wavelength,
It is expected that fine processing of 0.1 to 0.2 μm size can be realized. For recent phase shift methods, for example,
International Electron Device Meeting Technical Di
gest, 3.1.1 to 3.1.4, pp51 to 54, (1991), Proc. of 19
91 Intern. MicroProcess Conference, pp10-15.

In the above literature, when a fine pattern having an exposure wavelength or less is formed by using the phase shift method, it is considered that the method using a shifter light shielding type, edge light shielding type or edge enhancing type phase shift mask is the easiest. . An explanatory view of each type of phase shift mask is shown in FIG. (A) in the figure
Shows a shifter light shielding type phase shift mask, (b) shows an edge light shielding type phase shift mask, and (c) shows an edge enhancement type phase shift mask.

As the processing pattern becomes finer and its size reaches the exposure wavelength, the amount of light transmitted through the mask opening decreases, and the transmitted light component is affected by the oblique propagation (diffraction) component with respect to the vertical propagation component. Grows larger. Therefore, the maximum value of the light intensity on the projection surface decreases, the distribution width widens, the contrast decreases, and it becomes difficult to control the resist line width. As described above, the size of the fine resist line width is strongly dependent on the diffraction of light and the proximity effect, and thus is difficult to control.

To control the conventional resist line width,
For example Proc. Of 1991 Intern. MicroProcess Conference
, pp10-15, International Electron Device Meetin
g Technical Digest, 33.3.1 ~ 33.3.4, pp825 ~ 828,
As described in (1990), the mask pattern size, the exposure amount, the resist process condition, and the like have been changed, but these methods cannot be used as the processing pattern becomes finer. In particular, in the case of a fine pattern that requires a phase shift method, various methods have been proposed as a control method of the resist line width for the shifter light shielding type or the edge enhancement type phase shift mask as described above, All of them require precise processing of the phase shift mask and strict control of the exposure amount, and are difficult to put to practical use in terms of cost.

FIG. 6 shows a conventional projection exposure apparatus.
According to this apparatus, the exposure light emitted from the light source 1 passes through the first reflecting mirror 13, the integrator 14 and the second reflecting mirror 15 and is applied to the condenser lens 2. The exposure light passes through the photomask 3 and the projection lens 4 and is applied to the wafer 5 as the exposure light. Such conventional projection exposure is generally performed in the atmosphere.

[0007]

Thus, according to the present invention, a condensing system for condensing light for exposure from a light source,
A photomask for forming transmitted light capable of forming incident light from the condensing system on a projection surface on the wafer through a plurality of light transmission parts, and for projecting the transmitted light from the photomask on the wafer A projection optical system having a projection optical system and a supporting section for supporting a wafer, and comprising a closed system for sealing at least the photomask to the wafer supporting section with a single medium or a plurality of media. A featured projection exposure apparatus is provided.

The present invention controls the effect of diffracting light to the outside of the opening by changing the actual refractive index n of the light propagation medium, and this effect corresponds to shortening the exposure wavelength. Here, the real refractive index n represents the real part of the complex refractive index (N) of the medium, and when the absorption coefficient is k, it is expressed as N = n-ik (i represents an imaginary unit). For example, the actual refractive indices of Ar gas, water (liquid), Br gas, and diiodomethane (DM, liquid) are nAr = 1.000284 and nH ₂ O = 1.333, respectively.
0, nBr = 1.001125 and nDM = 1.737 (where 0 ° C., 1 atom, λ = real refractive index for light of 589 nm).

The usable exposure light may be i-line, g-line, KrF excimer light or the like which is generally used in the projection exposure technique. The preferred range of the actual refractive index n is 1.0 to
It is 3.0, more preferably 1.0 to 2.3, and it is desirable that it can be freely changed by changing the medium.

The medium in the projection exposure apparatus can be any medium other than a medium having a strong absorption in the wavelength region of the light source used, and an inert gas such as Xe, Ar, Ne, He having an actual refractive index n, or N.
Various gases such as ₂ , O ₂ and H ₂ or liquids such as pure water, methyl alcohol and chloroform can be used. Of these, considering the maintenance and easy handling of the device, A
It is preferable to use r, He, pure water or the like. Furthermore, by combining a plurality of these media, the actual refractive index can be changed and used. For example, when using pure water and chloroform, the mixing ratio is pure water: chloroform = 1: 3.
If it is (weight ratio), the light source is Hg i-line (λ = 365n
m), the real refractive index n becomes about 1.43, and it can be applied to the projection exposure apparatus of the present invention. Further, the refractive index can be changed by applying pressure to the medium, and depending on the medium used, it can be used for controlling and correcting the actual refractive index by pressurizing the medium to several atoms (10 atm or less). .

Known lenses can be used for the condensing system and the projection optical system used in the projection exposure apparatus of the present invention. For example, a lens composed of a plurality of lenses made of several kinds of optical glass is used. Can be used.

In the hermetically closed system, the hermetically sealed range needs to be hermetically sealed with a medium from at least the photomask to the wafer support in order to control the diffraction effect of light after passing through the photomask, and includes this range. In that case, it is possible to make the entire apparatus a closed system. The closed system may include an intake system for inhaling the medium and an exhaust system for exhausting the medium. It is desirable that the suction system is provided at the base of the projection exposure apparatus and the exhaust system is provided above the projection exposure apparatus. With such a configuration, it is possible to prevent the upper surface of the wafer and the upper surface of the photomask from being damaged, which is more preferable.

As the photomask, a mask having only a light-shielding pattern which is usually used or a phase shift mask using a phase shifter can be mentioned. The closed system is not particularly limited. The resist material used may be the same as the conventional resist.

Furthermore, the present invention is particularly effective when a fine pattern is transferred using a phase shift mask as a photomask. Examples of such a phase shift mask include a shifter light shielding type, an edge light shielding type, or an edge enhancement type phase shift mask. This is because the phase shift method utilizes the mutual interference effect of light from adjacent openings, and in particular, in the case of the above three types of phase shift masks, the light shielding effect determines the width of the light shielding portion, which is effective. large. That is, the line width of a finer pattern can be accurately controlled and adjusted by controlling the refractive index of the propagation medium.

The material that can be used for the phase shift mask is not particularly limited. For example, glass as a phase shifter, S
OG, SiO ₂ etc. can be used, Cr as a light shielding mask,
Examples thereof include CrO and MoSi ₂ .

The apparatus shown in FIG. 1 will be described as an example of the projection exposure apparatus of the present invention. In this apparatus, a condenser lens 2, a photomask 3, a projection lens 4, a wafer 5 and a wafer support 10 are included in an airtight system 9. There is also an inhalation system 12 at the base of the device for inhalation of the medium.
However, an exhaust system 11 is installed in the upper part of the device for exhaust, and the medium entered from the intake system 12 flows from the bottom to the top toward the exhaust system 11 (the arrow in the figure indicates the flow of the medium). ). In the process of exposure, the light emitted from the light source 1
The condenser lens 2 is irradiated with light through the reflecting mirror 13, the integrator 14, and the second reflecting mirror 15. The light with which the condenser lens 2 is irradiated has its diffraction effect controlled by the medium having the actual refractive index n, and the wavelength thereof is shortened. This light having a short wavelength is applied to the photomask 3, passes through the projection lens 4, and
The wafer 5 is exposed by being irradiated. The light of which the wavelength is shortened in this way has less light sneaking into the light-shielding portion, so that it is possible to form a finer pattern.

[0017]

EXAMPLES The present invention will be described below with reference to examples. Example 1 First, as a photomask, a conventional mask using only a light shielding pattern is used. Simulation results when exposure is performed by the conventional method using such a simple pattern are shown in FIGS. 2 (a) and 2 (b). Here, the upper part of the figure shows a cross-sectional view of the mask, the middle part shows the amplitude of light transmitted through the mask, and the lower part shows an image of the light intensity on the resist surface. Further, a glass substrate is used as the substrate in the mask used, and the light-shielding pattern in FIG.
0 μm (actual size on the mask is 15.0 μm), thickness 0.1
2 (b), a width of 0.3 μm (the actual size on the mask is 1.5 μm) and a thickness of 0.
1 μm chromium was used.

As can be seen from this figure, when the target width is sufficiently wide as 3.0 μm on the wafer (see FIG. 2).
In (a), the obtained projected image light intensity has a high contrast. However, the target width is 0.3 μm on the wafer.
2 (b), the obtained contrast of the projected image light intensity is small and it is difficult to obtain a fine pattern.

The simulation result when the projection exposure apparatus of the present invention is used is shown in FIG. The substrate used in the mask used is a glass substrate, and the light-shielding pattern has a width of 0.5 μm on the wafer (actual size on the mask is 2.5 μm).
The line and space of is using chromium with a thickness of 0.1 μm. As shown in FIG. 2C, when the actual refractive index n of the medium in the apparatus is changed, as the value of n increases, the diffraction effect of light is suppressed, and the light intensity distribution corresponding to the resist line width is reduced. It is shown that the width of I becomes smaller.

Example 2 FIG. 3 shows the result when the photomask in the apparatus of FIG. 1 was applied to an edge light shielding type shift mask. The cross-sectional structure of the mask is shown in the upper part, and the light intensity distribution image on the resist surface is shown in the lower part. Here, FIG. 3A shows a conventional mask having only a light-shielding pattern and having a width of 0.2 μm on the wafer.
A chromium line having a thickness of 0.1 μm (actual size on the mask is 1.0 μm) is provided. FIG. 3B shows a case where a conventional phase shift mask is used, and an SOG having a thickness of about 0.4 μm is used for the phase shifter. The actual refractive index n of the medium in the exposure apparatus is 1.0. FIG. 3C shows the above-mentioned FIG.
The same mask as in (b) is used, and the actual refractive index n of the medium in the exposure apparatus is set to 1.7. Further, FIG.
As conditions common to FIGS. 3B and 3C, the exposure wavelength λ = 365 nm, the numerical aperture N.V. A. = 0.45, coherency σ = 0.5, incident light energy dose amount = 10
It was set to 0 mJ / cm ² .

Further, in FIG. 3C, when the actual refractive index n is variable, the light intensity distribution width I.D. W. Fig. 4 shows the relationship with
Shown in. Here, the light intensity distribution width I. W. Is calculated from the value when the relative light intensity is 0.40. When the actual refractive index n of the medium in the apparatus is changed as described above, the diffraction effect of light is suppressed and the width of the light intensity distribution corresponding to the resist line width becomes smaller as the value of n becomes larger. Is shown.

[0022]

According to the projection exposure apparatus of the present invention, the size of a fine transfer pattern can be controlled and corrected without changing other exposure conditions or resist process conditions, and a finer resist pattern can be used in combination with a phase shift mask. Can be formed.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a projection exposure apparatus of the present invention.

FIG. 2 is a diagram showing a calculation result when a projection exposure apparatus of the present invention is used, a cross-sectional view of a conventional mask having only a light shielding pattern, a transmitted light amplitude, and a transmitted image light intensity.

FIG. 3 is a schematic cross-sectional view of a mask of the present invention and a conventional example and a diagram showing calculation results when this mask is used.

FIG. 4 is a diagram showing calculation results when the refractive index of the projection exposure apparatus of the present invention is changed.

FIG. 5 is a cross-sectional view of a conventional phase shift mask, showing the amplitude and light intensity of transmitted light.

FIG. 6 is a schematic sectional view of a conventional projection exposure apparatus.

[Explanation of symbols]

 1 Light Source 2 Condenser Lens 3 Mask 4 Projection Lens 5 Wafer 6 Medium with Real Refractive Index n 7 Light-shielding Pattern 8 Phase Shift Mask 9 Sealing System 10 Wafer Support 11 Exhaust System 12 Intake System 13 First Reflector 14 Integrator 15 Second Reflector

Claims (4)

[Claims] 1. A light condensing system for condensing exposure light from a light source, and transmitted light capable of forming incident light from the light condensing system on a projection surface on a wafer through a plurality of light transmitting portions. And a projection optical system for projecting transmitted light from the photomask onto a wafer, and a supporting portion for supporting the wafer, which is at least the photomask. A projection exposure apparatus comprising a closed system for closing from the wafer to the wafer support with a single medium or a plurality of mediums. 2. The projection exposure apparatus according to claim 1, wherein the medium has a real refractive index of 1.0 to 3.0. 3. The projection exposure apparatus according to claim 1, wherein the photomask is a phase shift mask. 4. The projection exposure apparatus according to claim 3, wherein the phase shift mask is a shifter light shielding type phase shift mask, an edge enhancement type phase shift mask or an edge light shielding type phase shift mask.