JPS63250122A - X-ray aligner - Google Patents

Abstract

PURPOSE:To enhance the parallelism of X-rays by a method wherein, while a recessed part formed at a counter-cathode is irradiated with electron rays, the X-rays are generated so that the X-rays whose beam is spread narrowly and whose directivity is good can be obtained. CONSTITUTION:A rotary counter-cathode 2 is turned by a shaft 11; electron rays are generated from an electron gun 1. The electron rays which have been bent by a deflection magnet 7 hit a recessed face 13 at an X-ray generation part 8. The electron rays lose its kinetic energy here and generate X-rays. In addition, slits 5, 6 to make the X-rays in parallel are installed in such a way that they are overlapped one upon another. A mask 3 is installed in front of the composite slits 5, 6. In the mask 3 an absorber 16 of a desired pattern is distributed on one face of an X-ray transmitting material 15. By this setup, it is possible to generate the X-rays whose directivity is strong to be suitable as a light source for X-ray lithography.

Description

DETAILED DESCRIPTION OF THE INVENTION (7) Technical field This invention relates to
It relates to a line exposure device.

Photolithography is a method of forming n-areas, n-areas on a semiconductor wafer.
Commonly used to selectively form regions, insulator films, electrodes, etc.

Conventionally, light from a mercury lamp or the like has been used as a light source.

A mask is placed on a resist or the like, and light is irradiated from above the mask to create exposed areas and non-exposed areas on the resist.

After this, develop and leave the desired resist film and proceed with the necessary wafer processing. ``As mask patterns become finer, dust surrounding light becomes a problem. The longer the wavelength of the light, the more the diffracted light from the mask edge goes directly under the mask. If there is diffraction, it is not possible to perform exposure in the same shape as the mask pattern.

In order to faithfully expose a mask pattern, it is better to have a shorter wavelength of light. Therefore, light such as a mercury lamp with a short wavelength is used.

The degree of rotation of light due to diffraction is approximately on the order of the wavelength.

As the patterning of ICs progresses, submicron wiring pattern widths are required. In this case, since the wavelength of visible light and the width of the pattern are approximately the same, blurring of the pattern due to diffraction cannot be ignored.

Therefore, attempts have been made to perform photolithography using X-rays with shorter wavelengths as light sources.

The wavelength of X-rays is from a few to several tens of wavelengths, and compared to visible light,
The wavelength is about /100 to 1/1000.

Since X-rays are used as the light source for exposure, this is called X-ray phosphorography. Since the wavelength is short, diffraction from pattern edges is not a problem.

However, there is a problem that the X-rays are not parallel.

(a) Prior art In X-ray phosphorography, an electron beam is emitted from an electron gun in a vacuum chamber and hits a flat anticathode.

Since X-rays are generated from the anticathode, the semiconductor wafer is irradiated with the X-rays.

In the present invention, the shape of the anticathode of the X-ray generator is improved. The anticathode is sometimes called the target.

Conventionally, the anticathode has been flat. For this reason, the generated
The problem was that the direction of the lines was not uniform.

A conventional example of X-ray phosphorography is briefly illustrated in FIG.

The part where the X-rays are emitted is in a high vacuum, but the vacuum chamber is not shown here.

In the electron gun 1, a high-speed electron beam is generated. The configuration of the electron gun 1 is well known. There is a cathode with a filament.

When electricity is applied to the filament, the filament becomes hot and thermoelectrons are emitted. This is applied to several tens of kV using an accelerating electrode.
Accelerate to N number 100kV. The acceleration voltage is determined by the wavelength of the X-rays you want to obtain. A high-speed electron beam hits the anticathode 12.

The surface LM of the anticathode 12 is oblique to the direction of the electron beam. LM is a plane.

However, although the anticathode 12 can be a fixed pole, it can also be a rotating pole. When electrons hit the metal at the anticathode, these electrons enter the metal's internal electrons.

Enter one of the electronic levels within the atom. Then, X-rays are generated according to the difference between the initial energy and the energy at the electron level.

However, the momentum of the electrons is transferred to the metal atoms, inducing lattice vibrations in the metal atoms. As lattice vibrations increase, the temperature of the metal increases. Mo,CulAg,.

A metal that can withstand high heat, such as W, is used as the anticathode, but even these metals deteriorate rapidly when heated by the electron beam.

To prevent deterioration, the anticathode must be strongly cooled. Cooling water is passed through the anticathode to cool it.

However, when the energy of the electron beam is high or the density of the electron beam is high, cooling may not be able to keep up.

In this case, the anticathode 12 is made to have a rotationally symmetrical shape and is rotated around a vertical axis while cooling water is passed inside. When it rotates, the surface hit by the electron beam immediately shifts to the side, which cools it down. This means that the new LPQM is always exposed to the electron beam for only a short period of time. Thus, when the electron beam energy is high, a rotating anticathode is used.

Then, it is possible to obtain high-power X-rays.

Not all of the energy of the electron beam is converted into X-rays, but phonons are generated, so the wavelength of the X-rays becomes a continuous spectrum. In other words, white X-rays are produced.

Since it is a light source for photolithography, it goes without saying that white X-rays may be used.

However, no matter which point of the anticathode 12 the X-rays are generated,
There is a spread in the radiation direction of X-rays. This spread is quite wide.

A mask 3 is placed below the anticathode 12. Assume that the mask 3 has an opening with a width d. Let the lower side of the opening be RlS.

Assume that the wafer 4 is located under the mask 3. Actually, there is a resist formed on the wafer, but its illustration is omitted here.

Let G be the distance between the lower surface of the mask and the upper surface of the wafer. The edges of the opening d of the mask are R and S. Let R' and S' be the legs of perpendicular lines extending down from points R and S to the wafer surface.

If the X-rays passing through the aperture d of the mask 3 are irradiated only onto the line segment R/S/, the mask pattern will be faithfully reflected on the resist.

However, in reality, this is not the case because the points P and Q where the X-rays are generated are different. X generated at point P of anticathode 12
All lines contained within /SPR are incident on the resist. The X-rays generated at point P project the shadow of mask edge S onto point U. Here, the U point is the intersection of the extension of the straight line PS and the wafer surface. Point U, not 81, is P.
This is the shadow of S caused by X-rays from a point.

The X-rays generated from point Q project the shadow of point R onto point T. R
' It is not a point.

The problem is that the shadow of S can be cast on U instead of S', and that the shadow of H can be cast on T instead of R'.

The shadow of point S becomes thinner continuously from S' to U in S'U. In this way, the shadows of the mask edge dots do not appear sharply, and their shading continuously changes. this"
The inventor calls this "reflection blur".

Reflection blur includes TR', SIU, and the like. This is a blur caused by the presence of the gap G between the mask and the wafer. This is a blur caused by differences in the positions where X-rays are generated. The blur is not due to diffraction.

Let K be the distance between the anticathode and the mask. The maximum value of reflection blur is given by Gα δ=(1). LM is the length of the horizontal surface of the anticathode, and is approximately 1.4 to 5c+++. G from 0.1 to 0.
About 2 birds. Even if K is about 10c+++, δ
= several tens/im.

Bring the mask into close contact with the wafer, G = 0.01fff
f,! : Then, δ becomes several μm. Even with this, the reflection blur is too large. Sharp exposure is not possible.

This is a drawback due to the fact that the X-rays are not generated from a single point. It is not possible to generate X-rays at one point. It is difficult to concentrate the electron beam, and even if it were concentrated, the metal surface would deteriorate rapidly, making it useless.

In other words, it is not possible to emit light from a single point. It is not necessary to emit light from a single point, as long as parallel X-rays can be obtained.

However, the X-rays generated at points P and Q often have a rotationally symmetrical distribution around the normal line and have a large divergence angle. Since the emission angle is large, the radiation does not become parallel X-rays.

If it is visible light, it can be focused with a lens, so it is also possible to create parallel light.

However, since there is no good lens for X-rays, it is not possible to condense the light, and it is also not possible to make X-rays into parallel X-rays. In other words, there is no way to make X-rays in random directions parallel once they are generated.

(1) Problems to be Solved by the Invention The device that applies an electron beam to the plane LM and generates X-rays obliquely from this plane has another problem.

This means that the X-ray intensity per unit solid angle is weak. At points P and Q, X-rays are generated in approximately equal directions. Almost all of the generated X-rays do not fly toward the mask and wafer. Therefore, the X-ray intensity per unit solid angle is weak. This does not mean that all of the generated X-rays are used effectively.

From equation (1), the problem of reflection blur can be alleviated by widening the distance K between the anticathode and the mask. If K is large, the X-rays will be close to parallel light. The blur TR/, 31 U becomes smaller.

Increasing K means that less energy of the X-rays is used effectively. Then, X-ray exposure-
In order to obtain a sufficient amount, it is necessary to increase the electron beam energy density and expand the anticathode.

In this case, the X-ray generator becomes large.

Furthermore, since the anticathode rapidly generates heat, the metal deteriorates quickly.

It is sufficient to have an X-ray generator that does not significantly reduce the amount of X-rays even if K is increased. In other words, an X-ray generator with strong directivity is desired.

However, the X-rays generated from the flat anticathode surface have an isodirectional spread, and it is difficult to give them directivity.

However, although LM in FIG. 4 is referred to as a plane, it is actually a conical surface. It is called a plane because its cross section is flat. Since it is a wide conical surface, it is almost equivalent to a flat surface.

00 Purpose The first object of the present invention is to provide an X-ray generator with strong directivity suitable as a light source for X-ray phosphorography.

A second object of the present invention is to provide an X-ray generator capable of generating X-rays with good parallelism when performing XAI lithography.

(6) Configuration The electron gun 1 generates a high-speed electron beam. As already mentioned, this is a cathode with a filament that generates hot electrons, which are accelerated by an accelerating electrode. The accelerating voltage is several 10 kV to several 100 kV.

The electron beam is bent by a deflecting magnet 7.

The magnetic field of the deflection magnet is formed perpendicular to the plane of the paper. Then, the trajectory of the electron beam, which was traveling straight, is bent, and it travels along a part of a circular orbit, such as m%n, l. A rotating anticathode 2 is provided to block the trajectory of the electron beam.

The rotating anode cathode 2 is sometimes called an X-ray target. Here, to avoid confusion, it is referred to as a rotating anticathode.

The rotating anticathode 2 has a rotating shaft 11 and a truncated cone-shaped X-ray generating section 8 supported by the rotating shaft 11. truncated cone,
There is a cooling water cavity 9 inside.

The rotating shaft 11 has a space and communicates with the cooling water cavity 9. This space is called a cooling water inlet/outlet 10.

The cooling water enters the cavity 9 from the cooling water inlet/outlet 10 and cools the metal of the X-ray generating section 8.

The metal of the X-ray generating section 8 is a metal that can withstand high heat well, such as Mo%Cu, Ag, or W.

The feature of the present invention is that the surface of the X-ray generating section 8 that is hit by electrons is not a flat surface but a concave surface 13.

The concave surface ABODE can be a circular arc surface or a quadratic curved surface determined by a quadratic function.

With C as the origin, the X and Y axes are taken on the tangential plane at the 0 point, and the direction of the normal line drawn downward from the 0 point is the Z axis. Assume that this cross section is parallel to the xZ plane.

If it is a parabolic shape, generally Z=ax2 (2).

Alternatively, it may be a part of a hyperboloid. In this case, in general, z=V/b+cx (3), and it may also be a part of a circular arc surface. In this case, Z=J1=12 (4).

However, since it is a rotating anticathode, the concave surface has a shape rotated around the rotation axis 11.

In other words, the curved surface is concave in the X direction, but convex in the X direction, that is, in the circumferential direction.

The electron beam bent by the deflection magnet 7 hits the concave surface 13 of the X-ray generating section 8 . Here, the electron beam loses kinetic energy and generates X-rays.

In conventional X-ray lithography, in the direction of X-ray travel,
Masks and wafers are left in place.

In the present invention, slits 5 and 6 for collimating X-rays are further provided in an overlapping manner.

The slit 5.6 is a thin plate with a number of parallel grooves cut into it.

FIG. 2 shows a schematic plan view of the slit 5.6. Groove 20.
The slits 5.6 in which are arranged at equal intervals are made of 18% Ti,
It can be made by processing metals such as Mo.

One slit has grooves parallel to the X direction, and the other slit has grooves parallel to the X direction.

By combining X slit 5 and X slit 6,
A lattice appears when viewed from the direction in which the X-rays come.

A mask 3 is provided further in front of the composite slit 5.6.

The mask 3 has absorbers 16 distributed in a desired pattern on one surface of an X-ray transparent material 15.

X-rays can pass through the transparent material 15. However, the X-rays are absorbed by the absorber 16. Because the absorber is distributed in this way, it functions as a mask.

A wafer 4 is placed further in front of the mask 3.

The mask 3 and the wafer 4 are almost in contact with each other. However, a transparent material 15 is interposed between the upper end of the absorber 16 and the slit 5 to support the absorber.

The thickness of the transparent material can be considered to be approximately G, and there is room for reflection blur as shown in equation (1) to occur.

The distance between the bottom surface of slit 5.6 and the top surface of mask 3 is 10
It is about 0 μm.

a) Operation The rotating anode cathode 2 has an internal cooling water cavity 9 through which cooling water is passed. A mask 3 is placed on a wafer 4, and an X slit 5 and an X slit 6 are further placed on top of the mask 3. The rotating anode cathode 2 is rotated by a rotating shaft 11.

An electron beam is generated from an electron gun 1. The electron beam is bent by the magnet 7 and hits the concave surface 13 of the rotating anticathode 2. The electron beam traces a circular orbit of l, n1m and reaches the concave surface.

The reason why the magnetic field is used to bend the electron beam in this way is that in order to make the electron beam hit a deep concave surface, it is not enough to just make the electron beam go straight from the side as shown in Figure 4. If the electron beam were to be applied from the side, the arc ABC would not be sufficiently exposed to the electron beam. On the other hand, there is a problem in that the ODE part is exposed to too much electron beam. Therefore, the deflection magnet 7 is used to cause the electrons to move circularly by the Lorentz force.

In orbits l, n, m, the cyclotron angular frequency e
Concave surface A with constant H/mc but different acceleration energy
The electron beam hits each part of the BCDE evenly, so
X-rays are generated at each concave surface from which X-rays are generated. The X-rays generated near AB are distributed in the same direction, but since the plane is tilted, the distribution of X-rays is directed inward. The same applies to X-rays generated near the CD.

As a result, the direction of the X-rays does not spread out as widely as shown in Figure 4, but is narrowed down more narrowly. A narrower directional angle means that directional X-rays can be obtained. This means that the energy density of X-rays around the unit solid is high.

In other words, stronger X-rays can be obtained.

As already mentioned, the problem of reflection blur can be solved to the extent that the distance between the X-ray generating surface and the wafer mask is increased. For this purpose, an X-ray source with good directivity and high energy density per unit solid angle is required. For this purpose, generation of X-rays from a concave surface is extremely effective.

Further, according to the present invention, a wafer is placed behind the mask, and an X slit and a y slit are placed in front of the mask. X-rays reach the mask through the slit grooves 20.

If viewed minutely, the slit 20 is a groove that is longer in the vertical direction. In other words, regarding the X slit, the depth in the Z direction is greater than the width in the y direction of the groove. For this reason, the Z axis (
X-rays parallel to the axis (perpendicular to the slit plane) can pass through the groove, but X-rays having an oblique angle larger than a certain angle with respect to the Z-axis cannot pass through the groove 20.

In other words, the slit 5.6 allows only the X-rays whose traveling direction is parallel to or close to the Z-axis to pass through. By doing this, only substantially parallel X-rays are applied to the mask 3.

Slit 5.6 is an X direction slit,
As shown in FIG. 3, two slits are stacked so that the grooves are perpendicular to each other.

The reason why the two slits are overlapped is that it is easier to finely machine grooves on a flat plate than holes. ,x
The slits in the y-force direction are overlapped to form effective holes in the portions that correspond to the lattice points.

If a large number of thin holes can be made on a flat plate, one perforated plate is sufficient.

Therefore, including two xy slits and one perforated plate,
We will call it a porous rectifier plate. The number of multi-grooved or perforated plates is not limited to two, and three or more multi-grooved or perforated plates may be combined.

In this way, by interposing a porous rectifying plate between the X-ray source and the mask, parallel X-rays can be obtained, but this is different from oblique X-rays.
This does not mean that the line has been changed to a parallel X-ray (parallel to the Z axis). This simply means that oblique X-rays have been removed. Since the slits are combined in a grid, many X-ray components hit the grid sides and are lost.

For this reason as well, it is desirable that the X-ray source be powerful. The X-rays generated by applying an electron beam to a concave surface have strong directionality and high energy density, so even if they are lost by the slit, they still have the energy necessary for exposure.

(→The surface of the X-ray generating part of the rotating anticathode in the example was made into a concave surface.The shape of the concave surface was assumed to be parabolic, and in equation (2), a=1.311ff
-1.

The diameter AE of the concave surface is 10 mm. The depth FC is 32.5 mm, and the radius F A =FE = 5 mrtt. This is because the spread of the electron beam is set to 10 mm in diameter, so the size of the concave surface is made to match this. It is a fairly deep concave surface. The one in FIG. 1 is a schematic representation and does not correspond to the concave curvature of this embodiment. The rotating anode is Mo
And so.

The parallel X-ray slit is made of a Ta plate with a thickness of 0.2 and a width of 1
Microwave grooves were repeatedly formed. I made a grid-like hole by putting two of these together. The vertical width of the groove is 200 μm and the horizontal width is 1 μm.
m, it is possible to select only X-rays with a fairly high degree of parallelism.

The distance between the mask and the slit was set to 100 μm.

The distance between the anticathode and the mask was 20 cm.

An electron gun generates an electron beam accelerated at 10kV,
This is bent with a magnet and irradiated onto the concave surface of the anticathode. X-rays are generated on the concave surface. Because of the deep concave surface, extremely highly directional X-rays can be obtained.

The spread angle of X-rays was measured near the mask. The X-ray divergence angle was 20 mrad or less. The reflection blur is given by the product Gθ of the spread angle θ and the mask-to-wafer distance G. A small divergence angle θ is effective in suppressing reflection blur.

According to the conventional X-ray generator, the divergence angle is 50 to 40 mrad in the best case, so it can be seen that the effect of the present invention is great.

Effect: A concave surface is formed on the anticathode, and an electron beam is applied to the concave surface to generate X-rays. Therefore, X-rays with a narrow beam spread and good directivity can be obtained. Since the energy density is high and the directivity is good, the distance between the anticathode and the wafer can be increased. Therefore, the parallelism of X-rays is improved.

Mata, create a slit on the wafer mask and parallel
I try to extract only the lines. Therefore, according to the present invention, it is possible to greatly improve the blurring of the edge of a mask, that is, the blurring of shadows, which has conventionally been a problem in X-ray exposure.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical sectional view of an X-ray exposure apparatus according to the present invention. FIG. 2 is a schematic plan view of the slit. FIG. 3 is a schematic plan view of two slits stacked one on top of the other. FIG. 4 is a schematic longitudinal sectional view of a conventional X-ray exposure apparatus. 1......Electron gun 2...
・・・・・・Rotating anode cathode 3・・・・・・・・・Mass 4 curved wafer 5.6・・・・・・・・・Slit door・
...... Deflection magnet 8...
・・・・・・X-ray generation part 9・・・・・・・・・・・・
Cooling water cavity 10 - Cooling water inlet/outlet 11 Rotating shaft 12 Rotating anode cathode 13 Concave surface 15... Transparent material 16... Absorbing material Inventors Takashi Nakagashi Yoshitaka Kiyosetoguchi

Claims (3)

[Claims] (1) Electron gun 1 that generates an electron beam and X
A rotating or non-rotating anticathode 2 that generates a beam, a deflection magnet 7 that curves the electron beam generated by the electron gun 1 and guides it to the anticathode 2, and a magnet that transmits or transmits the X-rays generated by the anticathode 2. A mask 3 having an absorbing pattern formed thereon and to be superimposed on the wafer; and a porous rectifying plate provided between the mask 3 and the anticathode 2 and having a large number of holes or grooves with a depth greater than width. An X-ray exposure apparatus characterized in that the anticathode 2 is formed with a concave surface 13, and an electron beam hits the concave surface 13 to generate X-rays. (2) The X-ray exposure apparatus according to claim (1), wherein the cross-sectional shape of the concave surface 13 is a parabola. (3) The depth of the cross-sectional shape of the concave surface 13 is 32.5 mm;
The X-ray exposure apparatus according to claim (2), characterized in that the diameter is 10 mm.