JPH03148055A - X-ray topography apparatus - Google Patents

Abstract

PURPOSE:To make it possible to perform the photographing of X-ray topograph by providing a rotary base on a scanning stage, and arranging a first crystal supporting post and a second crystal supporting post on the rotary base. CONSTITUTION:A scanning stage 8 is arranged on an omega rotary plate 3 which can be rotated with one axial line omega1 as the center. A first crystal supporting post 11 is fixed on the stage 8 and moved in parallel with the rotary plate 3 together with the stage 8. At this time, the supporting post 11 is moved so as to cross the rotary axial line of the rotary plate 3. A rotary base 10 is provided on the stage 8 in addition to the supporting post 11. The base 10 is not fixed to the stage 8 but can be turned with the supporting post 11 as the center. Since a second crystal supporting post 12 is provided on the base 10, the post 12 is turned around the supporting post 11 as a result. A sample 17 which is an object to be measured is mounted on either of the supporting post 11 or the supporting post 12. Thus, photographing of X-ray topography is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an X-ray topography apparatus for observing lattice defects and lattice strains in a single crystal.

Silicon, Ga, used as a material for semiconductor devices
Lattice defects contained in single-crystal wafers such as A s or lattice defects generated during the manufacturing process of semiconductor devices are one of the causes of lower device yields, and therefore it is necessary to control lattice defects. has become an important issue.

Methods for observing the lattice defects include etching, electron microscopy, and X-ray topography.

Among these, X-ray topography has the advantage of being able to observe samples non-destructively, and is therefore widely used, particularly in the semiconductor industry, for inspecting materials and improving processes.

[Prior Art] The above-mentioned X-ray topography is for directly observing lattice defects and the like inside the crystal of a single crystal material. Broadly speaking, this X-ray topography can be divided into methods such as the Lang method and the Bergpalette method, in which primary X-rays generated from an
In other words, the one-crystal method is such that the -order X-ray is incident on a first crystal, the X-ray beam diffracted by the first crystal is used as the incident X-ray to the sample crystal, and an image is formed using the X-rays diffracted by the sample crystal again. There is a two-crystal method for forming.

In the single-crystal method, black and white contrast corresponding to lattice defects occurs due to changes in the degree to which diffraction conditions are satisfied due to partial deviations in crystal orientation, and due to diffraction effects such as extinction effects and Bormann effects. In contrast, in the two-crystal method, the first
By diffracting X-rays twice with the crystal and the second crystal (sample), the angular range that satisfies the diffraction conditions is reduced from several tens of minutes to several hundredths, compared to the single crystal method described above. Therefore, according to the two-crystal method, it is possible to detect minute lattice defects and minute strains that cannot be detected using the single-crystal method.

However, the two-crystal method is applied to the observation of sample crystals that are closer to perfection, and is extremely sensitive to distortions within the crystal. Therefore, if it is used for crystals with low perfection, The area of the obtained image is extremely limited, making it difficult to observe.

In X-ray topography, the above-mentioned one-crystal method and two-crystal method are used depending on the type of defect, the size of the silkworm, etc., and the perfection of the crystal. Furthermore, each of the above methods uses a transmission arrangement in which X-rays are incident on the front surface of the sample and diffracted X-rays are extracted from the back surface, and a surface arrangement in which X-rays are incident on the front surface of the sample and diffracted X-rays are extracted from the same surface. Divided into reflective arrangements.

The transmission configuration is used to observe lattice defect images inside the crystal, whereas the surface reflection configuration is used to observe lattice defects only in the surface layer of the crystal.

Conventional X-ray topography devices include those based on a single-crystal method with a transmission arrangement such as the Lang method, those based on a single-crystal method with a surface reflection method such as the Berg-Basitt method, and the two-crystal method with a surface-reflection arrangement. There were four types, each based on a two-crystal method with a transmission arrangement, each existing independently as a dedicated machine.

[Problems to be Solved by the Invention] As described above, conventional X-ray topography apparatuses have been implemented using one crystal method with a transmission arrangement, one crystal method with a surface reflection arrangement, a two crystal method with a surface reflection arrangement, and a two crystal method with a transmission arrangement. There were four types of X-ray topography equipment prepared separately, so if an operator wanted to perform measurements based on all types of methods, he would have to prepare all the X-ray topography equipment based on each method. However, it was extremely uneconomical.

The present invention has been made in view of the above-mentioned problems with conventional devices, and can be applied to a single-crystal method with a transmission arrangement, a single-crystal method with a surface reflection arrangement, and a two-crystal method with a surface-reflection arrangement with just a simple operation. and X based on all methods of two-crystal method in transmission configuration
An object of the present invention is to provide an X-ray topography device capable of photographing a line topography.

[Means for Solving the Problems] In order to achieve the above object, the X-ray topography apparatus of claim 1 includes a zero-rotation plate that is rotatable about one axis, and a device disposed on the zero-rotation plate. a scanning stage,
A first crystal support that is fixedly arranged on the scanning stage, a rotation base that is arranged on the scanning stage and can be rotated about the first crystal support, and a rotation base that is arranged on the scanning stage. and a second crystal support stand arranged thereon.

The Kouki scanning stage moves parallel to the zero rotation plate.

The first crystal support is fixed on the scanning stage and moves together with the scanning stage in parallel to the zero rotation plate. In this case, this first crystal support base moves so as to cross the rotation axis of the 0-rotation plate.

A rotation base is provided on the scanning stage in addition to the first crystal support stand. However, this rotating base is not fixed to the scanning stage, but is rotatable about the first crystal support.

Since the second crystal support is provided on the above-mentioned rotating base, it will eventually rotate around the first crystal support.

The sample to be measured is placed on the first crystal support stand or the second crystal support stand.
It is attached to one of the crystal support stands. That is, when performing measurements based on the two-crystal method with one reflection arrangement and one transmission arrangement, the sample is mounted on the second crystal support, while the first crystal is mounted on the j11 crystal support. On the other hand, when performing measurements based on the single crystal method, the sample is mounted on the first crystal support, and nothing in particular is mounted on the second crystal support.

According to the second aspect of the invention, a slit (first slit) is provided between the first crystal and the second crystal. This slit is held by a rotary plate (slit rotary plate) that rotates coaxially with the rotation axis of the 0-rotation plate.

The invention of claim 3 provides a 20-rotation plate that can rotate coaxially with the 0-rotation plate, and further provides a 20-rotation plate that can be moved in a tangential direction with respect to the rotational direction of the 0-rotation plate on top of the 0-rotation plate. The X-ray detector is held by a movable stage that can be moved.

As the X-ray detector, a means for detecting and observing an X-ray image using an X-ray television camera, an X-ray image intensifier, etc., or other X-ray intensity detecting means such as a scintillation eye counter may be used. Can be done.

[Operation] In the invention of claim 1, the moving direction (A-A direction) of the scanning stage (8) can be freely changed by rotating the zero rotation plate (3). The second crystal support stand (12) is placed on the rotation base (10), and by rotating the rotation base (10) about the first crystal support stand (11), the second crystal support stand (12) is placed on the rotation base (10).
The position of 12) can also be changed freely.

a scanning movement direction (A-A direction) of the scanning stage (8);
By appropriately changing the combination of the position of the second crystal support stand (12) with respect to the first crystal support stand (11), the conditions of the optical system of the X-ray topography apparatus can be changed.

It is possible to freely change between at least four types of measurement methods: a single crystal method with a transmission arrangement, a single crystal method with a surface reflection arrangement, a two crystal method with a surface reflection arrangement, and a two crystal method with a transmission arrangement.

In the invention of claim 2, the first slit (22) allows only the X-rays diffracted by the first crystal (16) to pass through, and blocks other X-rays.

As a result, extra X-rays other than the diffracted X-rays, such as -order X
The line is prevented from going towards the second crystal (17). This first slit is held by a slit rotating plate (25) that can rotate Q-10- coaxially with the zero rotating plate, so that the first crystal (16) supported on the first crystal support stand (11) The alignment with respect to the first crystal is therefore very simple.

In the invention of claim 3, the 20-turn plate (20) can rotate coaxially with the 0-turn plate (3), and further, the movable table (27) is tangential to the rotational direction of the 20-turn plate. It is possible to move in the direction (D-D direction). The X-ray detector (28) is used to adjust the angular position of each crystal, the position of each slit, etc.
This X-ray detector is installed on the above-mentioned movable table.

20 rotations and tangential movements can be freely combined, which makes it easy to align the X-ray detector with the direction of the diffracted X-rays when making the above adjustments in the four types of X-ray topography methods. be able to.

[Embodiment] FIG. 1 shows an 11-1 embodiment of the X-ray topography apparatus according to the present invention. In the figure, a main body base 2 is placed on a base frame 1.

As shown in FIG. 2, this main body base 2 includes:
A zero rotation plate 3 is provided above it.

This zero rotation plate 3 has one axis (perpendicular line in the case of the embodiment)
It is provided on the main body base 2 so as to be able to rotate around ω1, and is clamped at a predetermined position during normal measurement. In addition, by loosening the clamp, you can manually set the appropriate angle, e.g.
It can be rotated by 0°.

As shown in FIG. 3, a signer 4 is attached to the rotating shaft 3a of the 0-rotation plate 3, and a clamp knob 31 is provided at the left end of the signer 4. On the other hand, on the right end of the signer 4, there is a pulse motor 5, a gear 3
2a, 32b, a micrometer head 33, and a pressure spring 34 are arranged. Clamp knob 31
When pulse motor 5 is rotated with
3-12 ~ The micrometer head rotates, and at that time, the end face of the micrometer spindle is aligned with the sign par 4.
Press to rotate the 0 rotation plate 3. Thereby, the 0-rotation plate 3 can also be slightly rotated. The pressing spring 34 functions to press the sign par 4 against the micrometer head 33.

Returning to FIG. 1, the stage block 6 is placed on the 0-rotation plate 3.
is provided. This stage block 6 has a base 7 fixed on the zero-rotation plate 3 and a scanning stage 8 placed on the base 7. The scanning stage 8 is driven by a motor 9 fixed to the base 7 and moves while sliding on the base 7. This results in
As shown by the arrow A-A in Fig. 82, the scanning stage 8 is
It can move parallel to the rotating plate 3.

A rotation base 10 and a first crystal support stand 11 are provided on the scanning stage 8 . In this case, the first crystal support stand 11 is fixed to the scanning stage 8, while the rotation base 10 can rotate around the first crystal support stand 11. The center of the first crystal support stand 11 coincides with the axis ωl which is the rotation center of the ω rotary plate 3, and when the scanning stage 8 moves in the direction of arrow A-A, the first crystal support stand 11 moves across the axis ω1.

The rotating base 10 can be rotated manually around the first crystal support stand 11 within an appropriate range, for example, within a range of ±30°. Further, it can be clamped, that is, fixedly held at an appropriate position, which will be described later.

As shown in FIG. 4, the rotating base 10 has a generally triangular shape, and the above-mentioned first crystal support stand 11 is disposed at the left end thereof. Further, a second crystal support stand 12 is provided at the right end of the rotating base 10, and a motor 13 is provided at the upper end thereof.

The second crystal support stand 12 has an axis ω relative to the rotation base 10.
2 (see Figure 2). In this case, the second crystal support stand 12 has a so-called two-stage coaxial structure.

13-14- A signer 14 is connected to the first stage part, and a pulse motor 15 is connected to the other first stage part via a worm and a worm wheel.

The sign par 14 is moved by the motor 13 mentioned above via a worm and a worm wheel. With the above configuration, the second crystal support stand 12 can be roughly rotated about the axis ω2 by the pulse motor 15. Further, the second crystal support stand 12 can be slightly rotated by the signer 14 driven by the motor 13.

In the apparatus according to this embodiment, as will be described later, one apparatus can perform at least four types of one-crystal method with transmission arrangement, one-crystal method with surface reflection, two-crystal method with one surface-reflection arrangement, and two-crystal method with transmission arrangement. It is now possible to take pictures. When performing imaging using the two-crystal method, the first crystal 1 is placed on the first crystal support stand 11.
6 is set, while the sample 17 is set on the second crystal support stand 12.
is set. On the other hand, when performing determination using the one-crystal method, the sample 17 is set 15- on the first crystal support 11, and nothing is set on the second crystal support 12.

In FIG. 4, a film holder 18 is attached to the right side of both the first crystal support stand 11 and the second crystal support stand 12, and image recording is selectively performed on either one of these film holders. A photographic plate, that is, a film 19, is set. The angular position of each of these film holders 18 with respect to the first crystal support stand 11 and the second crystal support stand 12 can be changed freely.

Returning to FIG. 1, below the 0-rotation plate 3, a slit rotary plate 25 is provided which is a rotary plate that can rotate coaxially with the 0-rotation plate. As shown in FIG. 5, a bracket 29 is formed on the slit rotating plate 25, and a support 23 and a beam 21 are arranged on the bracket.

A first slit 22 is rotatably supported at the tip of the beam 21 and suspended downward. The column 23 can be moved in the direction of the arrow C-c along a guide projection 30 installed on the bracket 29, while the beam 21 can be moved in the direction of the arrow B-c with respect to the column 23.
It is now possible to move in the H direction.

With the above configuration, the first slit 22 can be set to any desired position. This first slit 22
Usually, as shown in FIG.
It is placed on the right side of the first crystal 16 (or sample 17 as the case may be) supported by the film holder 18, that is, on the side where the film holder 18 is located.

In FIG. 1, below the slit rotary plate 25, there is another rotary plate 2 that can rotate coaxially with the zero rotation plate 3.
A zero rotation plate 20 is provided. As shown in FIG. 6, the 20-turn plate 20 is provided with a moving table 27 that moves linearly in a tangential direction (D-D direction) with respect to the rotational direction of the 20-turn plate 20. An X-ray detector 28 is fixed to this movable table, and a beam 26 is further attached to the upper end thereof. This beam 26 is connected to the moving table 27 by arrow E.
It is possible to move in the -E direction, that is, in the direction toward or away from the center of the 0-rotation plate 3. A second slit 24 is rotatably suspended from the tip of the beam 26.

This second slit 24 is usually as shown in FIG.
It is placed to the right of the position where the second crystal (sample) 17 is set. Furthermore, as will be described later, this second slit 24 is necessary only for the two-crystal method with a transmission arrangement, and is unnecessary for the other three types of imaging, so it is designed so that it can be attached to and detached from the beam 26. It has become.

In FIG. 1, X-rays generated from an X-ray generation source (not shown) are guided to a generation section slit 36 through an X-ray introduction tube 35. The X-rays are transmitted through the slit 36 through the 11
And the height is limited to fIg, and the first crystal 16 or sample 17 on the ω1 axis is irradiated, where it is diffracted.

The X-rays diffracted by the first crystal 16 and the like then pass through the first slit 22 . At this time, primary X-rays other than diffracted X-rays are blocked. As mentioned above, the first slit 22 is 0
It is supported by a slit rotary plate 25 which can rotate coaxially with the rotary plate 3, and a fifth
As shown in the figure, since it can be moved in two directions (B-B direction and C-C direction) that are orthogonal to each other, it can be easily placed at a desired position.

As will be described in detail later, the X-rays diffracted by the first crystal 16 etc. are then incident on the film 19 attached to the first crystal support stand 11 in the case of the single crystal method, and in the case of the two crystal method. It is guided to the second crystal (sample) 17. In this case, the X-rays
The light is diffracted again by the crystal (sample) 17, and then enters the film 19 attached to the second crystal support 12. At this time, the second slit 24 arranged between the second crystal (sample) 17 and the film 19 allows only the X-rays diffracted by the second crystal (sample) 17 to pass toward the film 19.

As already explained in connection with FIG.
direction and E-E direction), it can be easily placed at the above-mentioned desired position.

The X-ray detector 28 placed on the movable table 27 is adjusted to match the direction of the diffracted X-rays at the stage of adjusting the angular position of each crystal. Its position can be easily adjusted by rotating and moving in the tangential direction (D-D direction).

As the X-ray detector 28, one that can detect diffracted X-rays as an X-ray image, such as an X-ray television camera or an X-ray image intensifier, or an X-ray intensity detection means such as a scintillation counter, is used. be able to.

The X-ray topography apparatus according to this embodiment has one or more configurations, so you can use the two-crystal method with a reflection arrangement or the two-crystal method with a transmission arrangement as desired by simply performing the operations described below. At least four types of measurements can be performed: the two-crystal method and the one-crystal method of transmission and surface reflection.

+Order 20- This method is called the Lang method, and the optical system is arranged as shown in FIG.

First, the sample 17 is mounted on the first crystal support stand 11 in parallel to the scanning direction (A-A direction) of the scanning stage 8. The zero rotation plate 3 is roughly set at a predetermined angle and fixed (clamped). The X-ray detector 28 is set at a diffraction angle (2θ) corresponding to the lattice plane of interest. This is 2
The zero rotation plate 20 is set at that diffraction angle, and the tangential direction (D-D
This is achieved by not performing any movement in the direction).

Next, the X-ray detector 28 is activated to generate X-rays. Then, the sample 17 is slightly rotated around the ω1 axis by the sign par 4 (Fig. 3), and the X-ray detector 28
Set the ω angle at the position where the maximum intensity is shown. Actually, ω
In addition to angle adjustment, orientation adjustment is also required by in-plane rotation and off-plane rotation of the crystal.

Next, the position of the first slit 22 is adjusted.

That is, while monitoring the X-ray intensity with the X-ray detector 28, only diffracted X-rays are allowed to pass, and unnecessary X-rays such as direct X-rays are blocked.

Then, the film 19 for X-ray detection is placed on the first crystal support stand 1.
1 and expose the X-ray there.

During this exposure, by reciprocating the scanning stage 8 in the AA direction at a constant speed, an X-ray topography over a wide area can be obtained.

In this method, the optical system is placed in the position shown in FIG.

The major difference from the transparent arrangement shown in Fig. 7 is this.

The angle of incidence of the X-rays on the sample 17 is small. This is because in the case of single-surface reflection, X-rays are often diffracted by a lattice plane that is appropriately inclined with respect to the sample surface. To achieve such a small X-ray incidence angle, 0
The rotation angle of the rotating plate 3 has been changed significantly compared to the case shown in FIG. In addition, the position of the X-ray detector 28 and therefore the rotation angle of the 20-turn plate 20 are also changed accordingly.

In this method, the sample 17 is mounted on the first crystal support 11 parallel to the scanning direction (A-A direction) -21 22- of the scanning stage 8, and the The adjustment, position adjustment of the first slit 22, etc., and the ability to obtain a wide area X-ray topography by scanning the scanning stage 8 in the A-A direction are the same as in the case of the transmission arrangement shown in FIG. It is.

In the case of the two one-crystal methods described above, no special crystal is placed on the second crystal support 12, so that part is not shown in FIGS. 7 and 8.

- The arrangement of the optical system in this method is shown in FIG.

First, the first crystal 16 is a one-crystal method in which the first crystal 16 is in a transmission arrangement (Fig. 7).
It is mounted on the first crystal support stand 11 using the same procedure as in the case of . Next, the rotating base 10 is rotated in the direction of the diffracted X-rays by the first crystal 16, and the second crystal (sample) 17 is mounted on the second crystal support 12. Next, the 20-turn plate 20 is returned to the angular position 0' (reference position), and the X-ray detector 2823 is moved in the tangential direction (DD direction) to match the direction of the diffracted X-rays.

Next, the second crystal (sample) 17 is coarsely and finely rotated around the ω2 axis to adjust the ω angle of the second crystal (sample) 17. In addition, orientation adjustment is also performed, and the second crystal (
Sample) 17 is set at the optimal position relative to the diffraction X-rays.

Thereafter, the second slit 24 is placed at a predetermined position, the film 19 is attached to the second crystal support 12, and the film 19 is exposed to X-rays. Also in this case, by scanning the scanning stage 8, an X-ray topography over a wide area can be obtained.

The arrangement of the optical system in this method is shown in FIG.

In this method, the first crystal 16 is mounted on the first crystal support 11 in the same procedure as in the one-crystal method of surface reflection (FIG. 8). Further, the rotation of the rotating base 10, the movement of the X-ray detector 28 in the tangential direction (D-D direction), and the second
The 24-ω angle adjustment etc. of the crystal (sample) 17 are performed and they are placed in the position shown in the figure.6 Although the placement position is different, the operation procedure itself for the rotating base 10 etc. is the same as that of the transmission arrangement shown in FIG. This is the same as in the case of the two-crystal method.

In addition, in the case of the two-crystal method of surface reflection, as shown in the figure, the second
Slit 24 is not used.

As described above, according to this embodiment, one device can perform measurements based on at least four different methods, and there is no need to prepare dedicated devices for each method.

Although the present invention has been described above with reference to one embodiment, the present invention is not limited to that embodiment and can be modified in various ways.

For example, the scanning stage 8 shown in FIGS. 7 to 10,
The arrangement position of the rotation base 10 etc. is just an example,
Other suitable placement positions may be used as required.

The shape and structure of the scanning stage 81, rotating base 10, etc. may also be arbitrary other than those in the embodiment.

As an image recording medium for recording the X-rays diffracted by the sample 17 as an image, a so-called stimulable phosphor can also be used in addition to the film 19 in the embodiment. In this case, an energy latent image corresponding to one diffracted X-ray is formed inside the stimulable phosphor.

In the above embodiment, the coarse rotation of the 0-rotation plate 3 has been described as being performed manually, but instead of this, it is also possible to perform the rough rotation automatically using a driving means such as a motor.

[Effects of the Invention] According to the invention of claim 1, the first crystal support stand (11) and the second crystal support stand (11) are placed directly on the scanning stage (8).
Rather than installing 2).

A rotating base (10) is interposed on the scanning stage (8), and a first crystal support stand (1) is placed on the rotating base (10).
1) and the second crystal support stand (12), the first crystal (16) and the second crystal (sample: 17)
As a result, one crystal method with a transmission arrangement and one crystal with a surface reflection method, which previously had to be carried out using separate dedicated machines, are now possible. It is now possible to take topographic images using at least four different methods: the two-crystal method with a surface reflection arrangement, and the two-crystal method with a transmission arrangement.

According to the invention of claim 2, even when the positions of the scanning stage (8), single rotation base (10), etc. are changed between the above-mentioned methods, the first slit (22) relative to the first crystal (16)
) can be set extremely easily.

According to the third aspect of the invention, even when the positions of the scanning stage (8), one-rotation base (10), etc. are changed between the above-mentioned methods, the X-ray detector (28) can be very easily converted to the diffraction The direction of the line can be matched, and the second slit (
24) relative to the X-ray detector (28) can also be easily set.

[Brief explanation of the drawing]

FIG. 1 is a side view of an embodiment of the X-ray topography apparatus according to the present invention, FIG. 2 is a 27- perspective view showing the main parts of FIG. 1, and FIG. FIG. 4 is a plan view showing one embodiment of the rotating base, FIG. 5 is a perspective view showing other main parts of FIG. 1, and FIG. 6 is a further main part of FIG. 1. FIGS. 7 to 10 are plan views showing examples of the arrangement of optical systems in different X-ray imaging methods. 17... Sample, ω1... Axis line, 8... Scanning stage, 11... First crystal support stand, 17... Second crystal (sample). 25...Slit rotating plate. 20...20 rotating plate, 28...X-ray detector, 19...film, 3...0 rotating plate, 16...first crystal, 10... rotating base. 12...Second crystal support stand 22...First slit. 27...Moving table. 24...Second slit 28- Figure 1

Claims (3)

[Claims] (1) An X-ray topography device that creates an X-ray topography by irradiating a single crystal sample with X-rays and recording the X-ray image diffracted by the sample on an image recording medium, which rotates around one axis. a scanning stage disposed on the ω rotating plate and movable parallel to the ω rotating plate; and a scanning stage fixedly disposed on the scanning stage; a first crystal support on which the first crystal is placed so as to cross the axis when the crystal is moved; and a first crystal support, which is arranged on the scanning stage and rotates about the first crystal support. and a second crystal support stand disposed on the rotation base at a distance from the first crystal support stand and on which the second crystal is placed; An X-ray topography apparatus characterized in that a sample is placed on a first crystal support stand or a second crystal support stand, and X-ray topography is taken of the sample. (2) a slit rotary plate that can rotate coaxially with the rotational axis of the ω rotary plate; The diffracted X-ray beam is passed through, and the other
The X-ray topography apparatus according to claim 1, further comprising a first slit that blocks the radiation. (3) A 2θ rotary plate that can rotate coaxially with the ω rotary plate; a movable table disposed on the 2θ rotary plate and movable in the tangential direction to the rotation of the 2θ rotary pole; and a movable table disposed on the movable table. an X-ray detector disposed on its movable stage and between the second crystal and the image recording body, which transmits the X-ray beam diffracted by the second crystal and transmits other X-rays. The X-ray topography apparatus according to claim 1 or 2, further comprising a second slit that blocks the radiation.