JPS6362231A - X-ray reduction stepper - Google Patents

Abstract

PURPOSE:To easily obtain a fine pattern, by installing a reduction optical system, which is positioned in the X-ray traveling direction between the first and second substrates, and a means for position alignment of the second substrate against the first substrate. CONSTITUTION:This system comprises the following components: a wafer 3 which is coated with a resist and serves as the second substrate, a mask 6 on which a contrast with X rays is formed and which serves as the first substrate, and a concave mirror 7 which serves as a reduction optical system. X rays 5 incident to the mask 6 become a reflective flux in conformity with absorptive patterns formed on the mask 6 and reduced in a two-dimensional shape by the concave mirror 7 and focused on the wafer 3 coated with the resist. Namely, an image on a point A0 of the mask 6 is focused into that on a point A1 of the wafer 3, and that on a point B0 is focused into that on a B1. In order that exact image focusing for a figure on the mask 6 is performed on the wafer 3, a means for position alignment of the wafer 3 against the wafer 6 is provided. Therefore, a fine pattern can easily be obtained by such composition of the reduction stepper ranging from a X-ray region to a vacuum ultraviolet-ray region.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an X-ray reduction projection exposure apparatus that forms fine patterns on a wafer using a light source in the X-ray to vacuum ultraviolet region.

[Conventional technology]

The conventional fine pattern forming method uses a wavelength of 400 nm.
Exposure methods using front and back ultraviolet rays have been used,
When the pattern size is around 1 μm, there is a physical resolution limit due to diffraction and interference, and this method is not useful as a method for forming patterns of 1 μm or less. Shortening the wavelength may be considered as a measure to improve resolution, but in this case, there will be no lens material with an appropriate refractive index. Although fine patterns can be easily formed using electron beams, there are still problems with productivity.

Therefore, a method is desired in which a mask is manufactured by electron beam exposure and the mask is transferred onto a wafer.

As this method, a method using soft X-rays (0.4 to 4 nm) was proposed in 1972 by Smith (So+1th) et al. of MIT. As shown in Fig. 7, this method uses a mask 2 on which an X-ray absorbing pattern is formed on a film transparent to X-rays, and a wafer 3 coated with a resist in a thickness of several tens of μm. By placing the masks parallel to each other at intervals and irradiating the X-rays 1 from the direction perpendicular to the two mask surfaces,
The pattern on the mask 2 is transferred onto the wafer 3. This method has been confirmed to be an excellent transfer technology with features such as high resolution and stain resistance, but due to the same magnification projection, the transfer performance of (Performance such as resolution 2 alignment accuracy) cannot be improved. Furthermore, since proximity exposure is used, the minimum pattern size d that can be transferred is d=K(Sλ) I/ ! The gap S is defined by the mask 2. Since there is a limit to the flatness of each wafer 3, it cannot be made smaller beyond a certain level, and the minimum pattern dimension d cannot be made smaller than a certain value.

Further, when a diverging light source is used as a light source, a lateral positional deviation amount Δb called a run-out error as shown in FIG. 8 occurs. FIG. 8 shows a case where the gap of the mask 2a is 68 minutes larger than the gap S of the mask 2 due to large warpage. Here, if the distance between the light source 1a and the mask 2 is D, the target exposure area radius is R, and the gap variation from mask 2 to mask 2a is ΔS, then Δb=(R/D)ΔS is expressed. , Δb increases in proportion to the gap variation amount ΔS. Therefore, in order to obtain a highly accurate pattern using proximity exposure, in addition to a position detection mechanism that detects the relative position between the mask 2 and the wafer 3, a mechanism that precisely controls the gap between the mask 2 and the wafer 3 is required. As a result, equipment configurations are required to become more complex and sophisticated.

On the other hand, as shown in Figure 9, a method using total internal reflection is used as a reduction projection method in the X-ray region (% Formula % Pattern Transfer Using Reflection Exposure, written by Matsumura, Hiroshima University)
is proposed. That is, when a parallel light beam is incident on the mask 2 obtained by forming a pattern of Au (gold) absorber on a Si wafer at an incident angle that causes total reflection, a reflected light beam corresponding to the pattern is obtained. If the wafer 3 is placed perpendicular to the reflected beam, a pattern with a reduction ratio equal to the sine of the angle of incidence is obtained. Note that 4 in FIG. 9 is a mirror.

In this method, since the angle of total reflection in the X-ray region is as small as 1 to 2 degrees or less, a very large reduction ratio can be achieved, but on the other hand, the transfer mask 2 requires a large area. Further, in this system, since there is no imaging effect between the mask 2° and the wafer 3, there are drawbacks such as blurring of the pattern due to the influence of diffraction when the distance between the mask 2° and the wafer 3 is increased. Also,
This method results in -dimensional, ie, linear, reduction, and cannot perform two-dimensional, ie, planar, reduction.

(Problems to be Solved by the Invention) As mentioned above, in the conventional apparatus, the resolution in proximity exposure is low, and it is difficult to create a mask to increase the resolution because it is the same size. Gap control to increase alignment accuracy requires highly accurate six-axis alignment (three axes and three rotation angles with respect to these axes), and furthermore, it is difficult to judge whether the mask pattern, which has a fine structure, is good or bad. There were problems such as.

[Means for solving problems]

In order to solve these problems, the present invention provides a first substrate having a graphic, an incident means for injecting X-rays onto the first substrate, and a second substrate having photosensitivity to X-rays. A substrate and
The apparatus includes a reduction optical system located between the first substrate and the second substrate along the traveling direction of X-rays, and an alignment means for aligning the second substrate with respect to the first substrate. It was designed to be provided.

Further, as another invention, there is provided a first substrate having a figure, an entrance means for injecting X-rays onto the first substrate, a second substrate having sensitivity to X-rays, and a second substrate having a direction in which the X-rays travel. a reduction optical system located between the first substrate and the second substrate along The device is provided with a light-shielding plate having an arc-shaped notch and a moving means for moving the first substrate and the second substrate in synchronization with respect to the light-shielding plate.

[Effect]

In the present invention, the pattern on the mask is reduced and projected onto the wafer, and the mechanism that holds the mask and the mechanism that holds the wafer move synchronously.

〔Example〕

The resolution of the image point in Franjossofer diffraction of the reduction optical system is
If the wavelength of the light source is λ and the numerical aperture of the optical system is NA, then ε=
This can be considered from the relationship between O, SXλ/NA. Now, assuming that the resolution on the image plane is 0.1 μm and the wavelength λ=100 people, the NA is 0.05. When designing a reduction optical system in the X-ray region, since the wavelength λ is small, the NA can be reduced by one order of magnitude or more compared to the NA in ultraviolet light having the same resolution.

Next, the depth of focus fd is given by fd=±λ/(2NA).As the NA becomes smaller, fd becomes larger, and the margin for the depth of focus also increases.For example, in the above example, N
A=0.05, and when λ=100 people, fd=±2μ
m. This value is larger than the depth of focus when obtaining the same resolution with a normal optical system, and is advantageous in terms of device configuration.

The wavelength λ can be determined from the viewpoint of the reflectance of the multilayer mirror used. That is, the reflectance R of the multilayer mirror is the wavelength λ
In order to obtain a certain reflectance that is proportional to the fourth power of A film of In addition, when configuring a reflective optical system with multiple multilayer mirrors, the wavelength peaks of the spectral reflectances of the multiple multilayer mirrors must overlap, and the mea/Δλ must be small. The wider the bandwidth, the more advantageous it is.
λ/Δλ is proportional to the square of the number of layers. Therefore, in a reduction optical system, the longer the set wavelength is, the more advantageous it becomes. Further, the relationship between the surface roughness and reflectance of the multilayer mirror is given by R=exp (-2C2ttaCO8ot/λ)2). Here, α is the incident angle, σ is the surface roughness,
It can be seen that the larger λ is, the smaller the influence of surface roughness is.

Furthermore, when using continuous wavelengths such as synchrotron radiation, it is necessary to cut off wavelength components other than the design wavelength λ of the multilayer film because they have an adverse effect on image formation. becomes large, making it difficult to extract only the design wavelength. Filter materials with good transmittance in the wavelength band of 40 Å or more include kl, Mg, Si,
SC, and the longer wavelength side than these absorption edges, that is, 40
Advantageously, the wavelength range is from 1 to 400 people.

FIG. 1 is a block diagram showing a first embodiment of the present invention. 1st
In the figure, 3 is a wafer coated with a resist as a second substrate, 5 is an X-ray, 6 is a mask as a first substrate that generates contrast for the X-ray, and 7 is a concave mirror as a reduction optical system. It is. The X-rays incident on the mask 6 from the incident means (not shown) become a reflected light beam according to the absorption pattern formed on the mask 6, are reduced two-dimensionally by the concave mirror 7, and are directed onto the wafer 3 coated with resist. image is formed. That is, the point AO on the mask 2 in the figure is imaged on the point A1 on the wafer 3, and the point BO is imaged on the point B1. The optical system as shown in FIG. 1 includes positioning means (not shown) for positioning the wafer 3 with respect to the mask 6 in order to accurately image the shape of the mask 6 on the wafer 3.

In FIG. 1, when the concave mirror 7 is a multilayer mirror in which thin films made of heavy elements and light elements are alternately formed,
Since it is possible to construct an imaging system with substantially perpendicular incidence, and to arrange the mask 2 and wafer 3 on the axis of the concave mirror 7 or in the vicinity thereof, it is possible to construct an imaging optical system with small aberrations. Here, it is possible to use a transmission type as the mask 2 when the wavelength λ is 50 people, but as the wavelength becomes longer, the absorption of X-rays increases, and there is no suitable transparent material, so it is not possible to use a transmission type mask. A stencil mask consisting only of an absorber must be used, and it is difficult to create a somewhat complicated LSI pattern. On the other hand, a reflective mask in which a light element is used as an absorbing layer and a heavy element with high X-ray amplitude reflectance is used as a reflecting surface, that is, a desired pattern, is easy to manufacture, makes it easy to obtain pattern contrast against XvA, and has a wide Can be used in a wavelength range.

FIG. 2 is a block diagram showing a second embodiment of the present invention. In FIG. 2, 7 is a concave mirror formed with a multilayer film, 8 is a light-shielding plate having an arcuate notch 8a, 9 is a total reflection mirror with curvature, 10 is a mask holding and aligning mechanism, 1
1 is a wafer holding and aligning mechanism, and a concave mirror 7 and a light shielding plate 8 constitute a reduction optical system.

In Figure 2, light that is incident parallel to the optical axis of the specular mirror and is close to the axis intersects on the axis with the value of 1/2 the radius of curvature of the spherical surface, but as it deviates from the axis, the spherical surface Due to the aberration, the intersection point on the axis moves, and the pattern at the imaging point becomes increasingly blurred. However, for light that has passed through a position at a certain height from the axis and light that has passed near it, the narrower the width at that position, the smaller the variation in the intersection with the axis after reflection, which means that the pattern blur at the imaging point can be made smaller. Therefore, by placing a light-shielding plate 8 having a narrow arc-shaped notch at this position and cutting off other components, an imaged pattern with small blur can be obtained. As explained at the beginning of this [Example] section, the NA required to obtain fine resolution in the X-ray region is small because the wavelength is short, and only a portion of one concave mirror is required. For example, in an example where the reduction magnification is 1/l O and the wavelength is 100 and the resolution ε = 0.1 μm on the human image plane,
The numerical aperture NA of incidence on the mask surface may be 0.005, and if the distance between the notch and the object is 100 mm, the notch may be provided with a length of 0.5 mm.

The imaged pattern at this time is a reduced version of the notch 8a on the arc of the light shielding plate 8, so in order to obtain a large area exposure pattern, a moving means (not shown) is used to reduce the size of the notch 8a. By synchronizing the holding and aligning mechanisms 10 and 11 with respect to the light shielding plate 8 which is fixed and concentric with the axis of the optical system, and by moving the wafer holding and aligning mechanism 11 at a low speed by the reduction magnification relative to the mask holding and aligning mechanism 10, the mask is removed. 6 can be formed on the wafer 3 over a wide area.

The incident light is incident on the reflection mirror 9 at an angle that causes total reflection. The reflecting mirror 9 is provided to improve the mirror incidence efficiency when the incident light 5 is synchrotron radiation, and it focuses the rectangular synchrotron radiation into an arc shape, and adjusts the wavelength selectivity depending on the incident angle. As the zero-reflection mirror 9, a diffraction grating or a multilayer mirror can be used instead of a total reflection mirror.

Although the mask 6 is of a reflective type, the same effect can be obtained even if a transmissive type is used.

FIG. 3 is a configuration diagram showing a third embodiment of the present invention,
In order to reduce aberrations of the formed pattern, a second
A convex mirror 12 is added to the concave mirror 7 shown in the figure. In FIG. 3, a concave mirror 7, a light shielding plate 8, and a convex mirror 12 constitute a reduction optical system.

FIG. 4 shows a fourth embodiment of the present invention, in which the mask 13 is of a transmission type.

In FIGS. 3 and 4, the X-rays reflected or transmitted by the mask 6 or 13 are magnified and reflected by the convex mirror 12 formed with a multilayer film, condensed by the concave mirror 7 formed with a multilayer film, and are focused on the wafer 3. Mask 6 or 1 on the face
3. Image the pattern above. As in FIG. 2, the pattern on the wafer 3 is an arcuate pattern due to the light shielding plate 8, so by moving the holding and aligning mechanisms 10 and 11 in synchronization with the light shielding plate 8, it is possible to widen the pattern. The pattern on the area mask can be exposed onto the wafer. In this case, the curvature radius ratio of the two mirrors is optimized to minimize aberrations using methods such as ray tracing, and the value of the curvature radius ratio is set to 2.
．． By setting it in the range of 4 to 2.6, optimum structural conditions can be obtained and pattern formation with small aberrations can be achieved.

Figure 5 shows an example of calculation results of spherical aberration for two mirrors, with the horizontal axis showing the amount of aberration and the vertical axis showing the distance from the optical axis (perpendicular to the axis), and the radius of curvature of the concave surface relative to the radius of curvature of the convex surface. is shown as a parameter.

When the radius ratio is 2.4, the condition where the aberration amount changes is small is found near 11 mm on the axis, and when the radius ratio is 2.5, it is near 8 mm on the axis, and by configuring an optical system that passes only in this vicinity. , a good imaging pattern can be obtained.

In the example shown in FIG. 5, the radius of the convex spherical surface is 20 mm, but the same applies to other cases as shown in FIG. FIG. 6 shows the results when the radius of the convex spherical surface was varied from 10 mm to 100 mm.

〔Effect of the invention〕

As explained above, the present invention provides reduction projection exposure in the vacuum ultraviolet region from X-rays by installing a reduction optical system between the first substrate and the second substrate along the traveling direction of the X-rays. As it can be configured, it is possible to easily obtain fine patterns of 1 μm or less, and the pattern size on the mask is 5 to 10 μm.
A retifle pattern twice as large is required, which simplifies production, and allows the use of conventional equipment for mask inspection and repair techniques, making it possible to utilize the current manufacturing process of about 1 μm.

Furthermore, the reduced projection exposure configuration increases the margin for alignment of the mask and wafer, and has the effect of eliminating the need for strict mechanical precision in proximity exposure.

Furthermore, by placing a light shielding plate with a notch concentrically with the optical axis of the reduction optical system and synchronizing the mask and wafer,
It is possible to reduce and transfer a large number of aberration-free patterns onto a wide area of a wafer, and it has the effect of solving the narrow field of view size that is a problem with refractive optical systems of 2500 Å or less.

[Brief explanation of the drawing]

1 to 4 are configuration diagrams showing first to fourth embodiments of an X-ray reduction projection exposure apparatus according to the present invention, and FIGS.
The figure is a graph showing the calculation results of spherical aberration, Figure 7 is a configuration diagram to explain the conventional fine pattern forming method, Figure 8 is an explanatory diagram showing runout error, and Figure 9 is a graph showing the conventional total reflection type. 1 is a configuration diagram showing an X-ray reduction projection exposure apparatus.

Claims (3)

[Claims] (1) A first substrate having a figure, an incidence means for injecting X-rays onto the first substrate, a second substrate having photosensitivity to X-rays, and a second substrate having a shape along the traveling direction of the X-rays. An X-ray reduction device comprising: a reduction optical system located between a first substrate and a second substrate; and alignment means for aligning the second substrate with respect to the first substrate. Projection exposure equipment. (2) A first substrate having a figure, an incidence means for injecting X-rays onto the first substrate, a second substrate having photosensitivity to X-rays, and a second substrate having a shape along the traveling direction of the X-rays. a reduction optical system located between the first substrate and the second substrate; and an arc-shaped reduction optical system located between the reduction optical system and the light source and concentric with the axis of the reduction optical system. a light shielding plate having a notch;
X characterized by comprising a moving means for moving the first substrate and the second substrate in synchronization with respect to the light shielding plate.
Line reduction projection exposure equipment. (3) The reduction optical system consists of a concave and convex spherical mirror,
3. The X-ray reduction projection exposure apparatus according to claim 2, wherein the ratio of the radius of curvature of the concave spherical mirror to the radius of curvature of the convex spherical mirror is 2.4 to 2.6.