JP2000089450A - Reticle and projection aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reticle usable even if an exposure wavelength is as short as 157 nm of an F2 laser and an aligner using the reticle. SOLUTION: A fluoride crystal material is used as the reticle material and the directions of one crystal axis of the crystal and at least one of the X-, Y- and Z-axes of the projection aligner are aligned or are perpendicular. The fluoride crystal material is preferably CaF2 or MgF2 or LiF.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reticle and a projection exposure apparatus for manufacturing a semiconductor, and more particularly to a reticle and a projection exposure apparatus suitable for use in a short wavelength region such as an F2 laser.

[0002]

2. Description of the Related Art With the recent increase in the density of integrated circuits, a semiconductor exposure apparatus is required to project and expose a circuit pattern on a reticle surface onto a wafer surface with high resolution. Currently, the minimum line width required for each DRAM is 0.35 to 0.50 μm for 16M DRAM and 0.30 to 0.35 μ for 64M DRAM
m, 0.25μm for 256M DRAM, 0.18μm for 1G DRAM.

In order to realize the above high resolution performance,
In projection exposure equipment, with the increase in the NA of the projection optical system,
Shortening of the exposure wavelength has been promoted. The wavelength of a projection exposure apparatus ranges from 365 nm (i-line) using a mercury lamp as a light source to 248 nm using an excimer laser as a light source.
It has been developed up to the development of 193nm using a laser as a light source.

FIG. 4 shows a basic configuration of a projection exposure apparatus. The reticle 22 is mounted on a reticle stage 23. The pattern on the reticle 22 is illuminated by the illumination system 21 and is imaged on the wafer 25 by the projection optical system 24. The wafer 25 is placed on a wafer stage 26, and the reticle 22 is moved by an alignment system and a focus system (not shown).
Is determined.

At present, the reticle 22 has a thickness of 6 inches square.
6.35 mm or 5 inch square and 2.25 mm thick outer diameter is used. Quartz glass is most widely used as a reticle material, and a circuit pattern is drawn with Cr or the like. Quartz has a transmittance of 90% for the above exposure wavelength.
The material is suitable for a reticle because it is high as described above and has a small change in physical properties with respect to environmental fluctuations such as temperature and atmospheric pressure.

[0006]

Today, miniaturization for higher densities of integrated circuits is progressing further, and as a means for realizing miniaturization, the exposure wavelength is made shorter than that of ArF.
Attempts have been made to develop a projection exposure apparatus using a 157 nm F2 laser or the like as a light source.

However, quartz glass, which is a conventional reticle material, has a problem that when the wavelength is shortened to 157 nm, the transmittance is almost 0% and cannot be used as a reticle material.

Conventional crown-based or flint-based optical glass other than quartz glass cannot be used as a reticle material from the viewpoint of transmittance.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a reticle which can be used even when the exposure wavelength is reduced to 157 nm, and an exposure apparatus using the reticle. The purpose is.

That is, in the present invention, a fluoride crystal material is adopted as the reticle material, and one of the crystal axes of the crystal is made to coincide with at least one of the X, Y, and Z axes of the projection exposure apparatus, or is set to be vertical. It is characterized by doing. By using a fluoride crystal material, a high transmittance can be obtained even for an exposure wavelength of 157 nm,
It can be used as a reticle in a projection exposure apparatus. In addition, by aligning one of the crystal axes with at least one of the X, Y, and Z axes of the projection exposure apparatus, or by making it perpendicular, it is possible to match the direction of the crystal with the direction of the projection exposure apparatus. Features. Note that, here, the X and Y axes of the projection exposure apparatus correspond to the directions of the sides of the reticle viewed from above, that is, the main movement directions of the stage on which the wafer is mounted and move, and the Z axis is the optical axis of the projection optical system. Match the direction.

Table 1 summarizes the transmittance near 157 nm and general properties of a fluoride crystal material usable as a reticle material. The transmittance in the table is the transmittance at a thickness of 6.35 mm according to the shape of the current 6-inch reticle.

[0012]

[Table 1] Since CaF2 and LiF have high transmittance at 157 nm of 72% and 74%, respectively, they have basically suitable properties as a reticle material, and are easy to handle because their crystal structures are equiaxial. Crystals have directionality with respect to the crystal axis and differ in thermal or mechanical properties. However, the X and Y axes of the projection exposure apparatus (that is, the directions of the sides of the reticle viewed from above) or the projection exposure apparatus
By aligning at least one of the Z-axis with at least one of the crystal axes of the crystal as a reticle material, or by making it perpendicular, the orientation of the crystal and the direction of the projection exposure apparatus are matched. And Here, the consistency means the consistency with respect to the thermal expansion of the crystal and the consistency with the easiness of polishing derived from mechanical properties.

Further, MgF2 has birefringence due to its crystal structure, and has a transmittance of 32% in a direction parallel to the crystal axis (c-axis).
However, if the thickness is 2.25 mm, the transmittance is about 67%, and it can be used as a reticle material.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 (A) shows a first embodiment of the present invention.
1 shows a basic configuration of a projection exposure apparatus using a reticle using a fluoride crystal. The 157 nm light emitted from the F2 laser of the light source 1 is illuminated by the illumination system 2 to the reticle stage 4
Illuminates the reticle 3 on the. Wafer stage 8
A wafer 7 is arranged on the top, and an alignment system (not shown)
The exposure position for the reticle 3 is determined by the focus system. FIG. 1 shows a projection exposure apparatus using a reflection type optical system, and a circuit pattern drawn on a reticle 3 is transferred onto a wafer 7 via a trapezoidal mirror 5 and an exposure optical system 6.

This embodiment is characterized in that CaF2 is used for the reticle 3 as a fluoride crystal material. On the lower surface of the reticle 3, a circuit pattern is drawn by Cr or the like.

Although CaF2 is equiaxial as a crystal, when it is expanded by heat absorption by irradiating an F2 laser for a long time, it does not expand uniformly like quartz but in the crystal axis direction (FIG. 1).
(A) and b directions in (b) Characteristic expansion occurs.

In the projection exposure apparatus according to the present invention, one of the crystal axes of the crystal material forming the reticle is set to X by the projection exposure apparatus.
The directionality of the crystal is matched with the directionality of the projection exposure apparatus by matching or perpendicular to at least one of the Y, Z, and Z axes. Matching matches the direction of the above thermal properties, and
This also corresponds to matching the mechanical properties during polishing. In terms of thermal properties, the expansion due to exposure in the X and Y directions is calculated in advance, or the expansion is measured by the projection exposure apparatus, and the magnification of the projection optical system is corrected. Accurate exposure becomes possible.

Further, making one of the crystal axes of the crystal material constituting the reticle coincide with or at least perpendicular to at least one of the X, Y, and Z axes of the projection exposure apparatus means that the side of the reticle including the thickness direction is also included. Is coincident with at least one direction of the crystal axis.

FIG. 2 shows a second embodiment of the present invention.
It is characterized by using MgF2 as a reticle.

As described above, MgF2 has a uniaxial crystal structure (see FIG.
2) (a) When the refractive indices in the a, b, and c axis directions are na, nb, and nc, na = nb ≠ nc), it has birefringence, and the transmittance at 157 nm is It depends on the direction. The present embodiment is characterized in that the direction of the crystal axis (c-axis) is configured to be parallel to the optical axes of the illumination system and the projection optical system. The a and b axes having the same refractive index and thermal properties are aligned with the sides of the reticle. The reason for matching the crystal axis with the X, Y, and Z axes of the projection exposure apparatus is as described in the first embodiment.

FIG. 3 shows a third embodiment of the present invention.
FIG. 3 is a cross-sectional view of a reticle in the case of using LiF. Table 1 shows that LiF has a high deliquescence of 0.27 / 100g at 18 ℃, so it is inappropriate to use it as a reticle material. The present embodiment is characterized in that an antireflection coating is applied to the surface of a LiF reticle as a protective film, and the environmental resistance is improved by the protective film to block the influence from the outside air.

Since the LiF reticle is also equiaxial as the CaF2 reticle, one of the crystal axes of the crystal material constituting the reticle must be coincident with at least one of the X, Y, and Z axes of the projection exposure apparatus, or be perpendicular. And the direction of the crystal
The directionality of the projection exposure apparatus can be matched.
Matching corresponds to matching the directionality of the thermal properties with matching the mechanical properties during polishing of LiF. Speaking of thermal properties, X, Y
By correcting the magnification of the projection optical system by calculating the expansion due to exposure in the direction in advance or measuring the expansion on the side of the projection exposure apparatus, high-precision exposure can be performed.

In this embodiment, an F2 excimer laser of 157 nm is taken as an example, but the present invention can be similarly applied to a projection exposure apparatus of 250 nm or less.

Next, an embodiment of a method of manufacturing a semiconductor device using the above-described exposure apparatus will be described. FIG. 5 shows a manufacturing flow of a semiconductor device (a semiconductor chip such as an IC or an LSI, or a liquid crystal panel CCD or the like). In step 1 (circuit design), the circuit of the semiconductor device is designed. Step 2 (mask fabrication) forms a mask on which the designed circuit pattern is formed.

On the other hand, in step 3 (wafer manufacturing), a wafer is manufactured using a material such as silicon. Step 4
The (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the prepared mask and wafer.

The next step 5 (assembly) is called a post-process, and is a process of forming a semiconductor chip using the wafer prepared in step 4, such as an assembly process (dicing and bonding), a packaging process (chip encapsulation), and the like. Step. Step 6 (inspection)
Perform inspections such as an operation check test and a durability test of the semiconductor device created in 5. Through these steps, a semiconductor device is completed and shipped (step 7).

FIG. 6 shows a detailed flow of the wafer process. Step 11 (oxidation) oxidizes the wafer's surface. Step 12 (CVD) forms an insulating film on the wafer surface.

In step 13 (electrode formation), electrodes are formed on the wafer by vapor deposition. Step 14 (ion implantation) implants ions into the wafer. Step 15
In (resist processing), a photosensitive material is applied to the wafer. Step 16 (exposure) uses the above-described exposure apparatus to expose a circuit pattern on the mask onto the wafer by exposure.

In step 17 (development), the exposed wafer is developed. Step 18 (etching) removes portions other than the developed resist image. Step 19 (resist stripping) removes unnecessary resist after etching. By repeating these steps, multiple circuit patterns are formed on the wafer.

[0030]

As described above, in the reticle and the projection exposure apparatus of the present invention, by using a fluoride crystal material as a reticle material, a high transmittance can be obtained even at 157 nm of an F2 laser. .

Further, in the present invention, one of the crystal axes of the fluoride crystal material constituting the reticle is defined by X, Y, Z of the projection exposure apparatus.
By making the axis coincide with at least one of the axes or making it perpendicular, it is possible to match the direction of the crystal with the direction of the projection exposure apparatus. The matching is to match the direction of the thermal properties of the crystal with the characteristics of the device, and to match the mechanical properties at the time of polishing the crystal material with the characteristics such as flatness of the reticle required by the device. Made it possible.

[Brief description of the drawings]

1A is a schematic view of a main part of a projection exposure apparatus using a reticle of the present invention, and FIG. 1B is a view showing a relationship between an optical axis and a crystal axis of a projection optical system of the present invention.

FIG. 2 is a schematic view of a main part of a second embodiment of the present invention,

FIG. 3 is a schematic diagram of a main part of a third embodiment of the present invention,

FIG. 4 is a schematic view of a main part of a conventional projection exposure apparatus,

FIG. 5 is a flow chart for manufacturing a semiconductor device according to the present invention;

FIG. 6 is a detailed flow chart of a wafer process according to the present invention;

[Explanation of symbols]

 1 light source, 2, 21 illumination system, 3, 10, 12, 22 reticle, 4, 23 reticle stage, 5 trapezoidal mirror, 6 reflection optical system, 7, 25 wafer, 8, 26 wafer stage, 11 light of projection optical system Axis, 13 anti-reflective coating, 24 projection optics

Claims (13)

[Claims] 1. A reticle using a fluoride crystal, wherein at least one axis of the crystal coincides with a direction of a side of the reticle. 2. The reticle according to claim 1, wherein said fluoride crystal is CaF2. 3. The reticle according to claim 1, wherein said fluoride crystal is MgF2. 4. The apparatus according to claim 3, wherein a crystal axis (c axis) of the fluoride crystal is oriented in a direction parallel to an optical axis of a projection optical system of the projection exposure apparatus to which the reticle is mounted. Reticle. 5. The reticle according to claim 1, wherein said fluoride crystal is LiF 2. 6. The reticle according to claim 1, wherein said reticle surface is coated with an antireflection film. 7. A projection exposure apparatus for manufacturing a semiconductor device using a reticle of a crystalline material with a short wavelength of 250 nm or less as an exposure wavelength, wherein the axis of a projection optical system of the projection exposure apparatus is Z
When the directions orthogonal to the Z axis are X and Y axes, respectively, one of the crystal axes constituting the reticle is X, Y
Semiconductor exposure apparatus, wherein the apparatus is aligned with at least one of the Z-axis and vertical. 8. The projection exposure apparatus according to claim 7, wherein the exposure is performed while measuring the thermal expansion of the reticle and correcting the magnification of the projection optical system. 9. Preliminarily calculating the thermal expansion of the reticle,
8. The projection exposure apparatus according to claim 7, wherein the exposure is performed while correcting the magnification of the projection optical system. 10. The projection exposure apparatus according to claim 7, wherein said projection optical system is a reflection optical system. 11. The projection exposure apparatus according to claim 7, wherein the exposure light source is an F2 laser. 12. A projection exposure apparatus having an exposure wavelength of 250 nm or less, a projection optical system, an axis of the projection optical system as a Z axis,
When the directions orthogonal to the Z axis are X and Y axes, respectively, it is made of a fluoride crystal material, and one of the crystal axes of the crystal material coincides with at least one of the X, Y, and Z axes.
Or a semiconductor device manufactured using a vertical reticle. 13. A projection exposure apparatus having an exposure wavelength of 250 nm or less, a projection optical system, an axis of the projection optical system as a Z axis,
When the directions orthogonal to the Z axis are X and Y axes, respectively, it is made of a fluoride crystal material, and one of the crystal axes of the crystal material coincides with at least one of the X, Y, and Z axes.
Alternatively, a method for manufacturing a semiconductor device manufactured using a vertical reticle.