JPH0471332B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to an X-ray generator and an X-ray lithography apparatus using the same, and particularly to an X-ray generator with long life and excellent reproducibility. and an X-ray lithography apparatus equipped with the same.

(Background of the Invention) In recent years, there has been remarkable progress in electronics technology, especially in terms of fineness in high-density integrated circuits, and there has been a need to reduce the thickness (line width) of patterns written on semiconductor wafers to 1 μm or less. Ta.

In order to transfer such a fine pattern onto a wafer, conventional methods using visible light, ultraviolet light, etc. could not achieve their purpose due to blurring caused by diffraction phenomena.

Therefore, X-rays with wavelengths shorter than these sources,
In particular, lithography technology using X-rays with wavelengths of 1 to several tens of angstroms, called soft X-rays, was announced (Electronics Letters Vol. 8, No. 4, p. 102-104,
(1972), research on X-ray lithography technology has progressed since then.

However, there were many difficulties in putting this technology into practical use. The biggest one is to generate a predetermined soft X-ray with high intensity and good reproducibility - in other words, to
It has been extremely difficult to generate X-rays while minimizing fluctuations in their wavelength and intensity.

Furthermore, when the generated X-rays include hard X-rays with short wavelengths, there is a problem that they pass through an X-ray mask for pattern transfer.

Furthermore, if the intensity of the generated soft X-rays is low, multiple exposures are required to transfer one pattern. In this case, if the X-ray generation position fluctuates, the pattern transfer position shifts, resulting in multiple images or short circuits between adjacent patterns, resulting in a disadvantage of lowering the transfer accuracy and product yield.

Furthermore, from the perspective of mass production, multiple exposures mean a long transfer time, which has been a factor in reducing productivity.

For example, as a method to obtain high-intensity soft X-rays,
Review of Scientific Instruments Vol.48, No.
8.1055-1062, 1977, a method is known in which plasma generated by discharge is irradiated with an electron beam.

FIG. 3 is a schematic diagram of an X-ray lithography apparatus equipped with an X-ray generator based on the plasma principle as shown in the above-mentioned document.

In the X-ray generator 1, a plasma generator 30 and an electron beam injection device 4 are arranged in a container 2 filled with gas (for example, Ne) that generates required soft X-rays as characteristic X-rays.

The plasma generator 30 includes electrodes 3 and 5 and a hollow cylindrical insulator 6. In addition,
In this conventional example, a coil 7 disclosed in Japanese Patent Laid-Open No. 57-147855 is also shown.

The electrodes 3 and 5 are connected to the container 2 via a switch 10.
It is connected to a capacitor 8 provided externally.
Plasma 11 is generated in the hollow portion of the hollow cylindrical insulator 6 by discharging the accumulated charge in the capacitor 8 charged by the charging device 9 in response to the closing of the switch 10.

The electron beam generator 4 is connected to a capacitor 12 provided outside the container 2 via a switch 14. The electron beam is generated as described above by applying the voltage across the terminals of the capacitor 12 charged by the charging device 13 between the electron beam generator 4 and the electrode 5 in response to the closing of the switch 14. The electron beam 15 is irradiated onto the plasma 11 .

As a result, soft X-rays are generated from the plasma 11. This soft X-ray is absorbed by materials with low absorption.
For example, it is taken out through a window 16 made of beryllium.

Note that the coil 7 is connected to a secondary winding of a step-up transformer 17 provided outside the container 2. A capacitor 18 charged by a power supply device (not shown) is connected to the primary winding of the transformer 17 and is connected to a switch 19.
connected via.

Therefore, when high frequency and high voltage is applied to the coil 7 by closing the switch 19, a discharge is induced on the inner surface of the insulating cylinder 6. This means that electrodes 3 and 5
This facilitates plasma generation due to the discharge between the two.

The lithography apparatus 20 includes the X-ray generator 1
In order to prevent the attenuation of the soft X-rays 21 generated by
It includes a chamber 22 maintained at a pressure of less than 10 ^-2 Torr.

Inside the chamber 22 are an X-ray mask 23 having a predetermined pattern, an X-ray resist 25 on its surface, and a substrate 24 (for example, a silicon wafer) to which the pattern of the X-ray mask 23 is to be transferred. is stored. Then, the pattern of the X-ray mask 23 is transferred onto the X-ray resist 25 as a latent image.

In the conventional example described above, the plasma 11 is generated by inducing a creeping discharge on the inner surface of the hollow insulator 6 using the coil 7 provided in the plasma generator, and then generating a large current discharge between the electrodes 3 and 5. It is something that generates.

For this reason, impurities are generated in the form of evaporation from the insulator surface and electrode during the plasma generation process. If such impurity vapor exists in the gas space inside the container 2, it will absorb the generated soft X-rays, so that the X-rays incident on the lithography apparatus 20 will be
This causes the line strength to decrease.

Further, if impurity vapor adheres to the beryllium window 16 and forms an impurity film, this will cause a reduction in X-ray intensity.

In this way, if creeping discharge or interelectrode discharge is used as a plasma generation method, the reproducibility of X-ray intensity will be low, so gas exchange and beryllium copper windows 1
6 had to be replaced or cleaned, which caused a problem in terms of productivity as equipment for producing high-quality products in large quantities such as high-density integrated circuits.

As detailed above, the X-ray generators of conventional X-ray lithography systems have the following problems: (1) The reproducibility of discharge plasma generation is not good, and (2) Electrodes, insulators, etc. are evaporated and consumed by discharge. (3) The X-ray intensity is weakened due to the absorption of soft X-rays by the evaporated gas mentioned in the previous section.

The predetermined soft X-ray generation intensity and the reproducibility of the X-ray generation position are extremely important as an X-ray generator for industrial production, especially from the point of view of reducing quality variations during mass production of high-density integrated circuits. This is an important issue, and there has been a demand for the development of an X-ray generator with high intensity and excellent reproducibility.

(Objective of the Invention) An object of the present invention is to provide a soft X-ray generator that has high intensity, has little variation in intensity and X-ray generation position within plasma, and has a long life.

Another object of the present invention is to provide an X-ray lithography apparatus that is equipped with a soft X-ray generation position as described above and is capable of accurately and efficiently transferring a fine pattern onto a semiconductor wafer. be.

(Summary of the Invention) In order to achieve the above object, the present invention generates high-temperature plasma by theta pinch, increases the electron temperature of the plasma by the pinch effect, and generates characteristic X-rays from the high-energy electrons. This is a characteristic feature.

Furthermore, the present invention raises the temperature of the plasma by irradiating the plasma generated by the theta pinch with an electron beam or applying an electric field in the axial direction of the plasma, It is characterized by generating characteristic X-rays. The plasma generated by the theta pinch is: (1) Since it is located at the center of the coil with good reproducibility,
(2) Since the line generation position does not move, (2) electrode material is not mixed in as impurities due to electrodeless discharge, and (3) in a pinch state, the area around the plasma is almost in a vacuum. Soft X-rays generated from plasma are not absorbed by surrounding gas, and high-intensity soft X-rays can be extracted.

These characteristics make it extremely preferable as a plasma for soft X-ray sources.

FIGS. 4 and 5 show the principle of plasma generation by theta pinch and explanatory diagrams of the pinch process.

In FIG. 4, a capacitor 31 charged by a power supply device (not shown) is discharged through a coil 33 by turning on a switch 32, and a current i is applied to the coil 33 as indicated by an arrow 34 in the figure. flow in the direction.

As a result, a magnetic field B is generated within the coil 33 in a direction perpendicular to the plane of the paper, from the front toward the plane of the paper.
Now, when the current i is changed over time, the magnetic field B also changes accordingly, and an electric field E is thereby generated within the coil 33.

The electric field E is at its maximum on the inner surface of the coil 33. When the gas in the coil inner space is ionized by this electric field E, a current i' flows in the direction of the electric field.

As clearly shown in FIG. 4, this current i' is a current in the opposite direction to the coil current i due to discharge of the capacitor 31. Due to the interaction between this current i' and the magnetic field B, the ionized charges receive a force F directed toward the center of the coil 33, and are concentrated at the center of the coil 33. This phenomenon is called the theta pinch effect.

FIG. 5 shows the plasma particle density within the coil 33 of FIG. 4 over time, with the horizontal axis indicating the radial position within the coil 33 and the vertical axis indicating the plasma particle density.

At time t=0, ionization occurs near the inner wall of the coil 33. Due to the aforementioned pinch effect, the ionized plasma layer increases its density toward the inside of the coil 33 as time progresses from t ₁ to t ₂ while ionizing the inner gas.

In other words, just as if the snow in the circle is being shoveled to the center, the gas in the coil 33 is also turned into plasma, and the generated plasma layer is pinched to the center.

The state at time _t3 is the maximum pinch state, at which time the plasma density is the maximum and the plasma temperature is also the highest. In this state, the gas within the coil 33 is almost completely ionized and collected at its center, that is, on the axis of the coil 33. The area around it is almost a vacuum.

Such characteristics during plasma generation make it suitable as a soft X-ray generator for X-ray lithography.

As at time _t3 in FIG. 5, if the plasma temperature reaches the temperature required for X-ray generation in the pinched state, it can be used as an X-ray source with only theta pinch.

In addition, if the theta pinch described above is insufficient to generate X-rays, it is recommended to irradiate the theta pinched plasma with an electron beam or to apply an electric field in the plasma axis direction to increase the electron temperature. preferable.

The mechanism of soft X-ray generation from high-temperature plasma is that when high-energy electrons collide with atoms, they eject electrons in orbits close to the atomic nucleus, causing electrons in orbits immediately outside to transition to that orbit. As a result, X-rays of a certain wavelength are emitted.

Therefore, if the ion temperature becomes higher than necessary and ionization progresses too much, electrons in orbits close to the atomic nucleus will also be ionized, and X-rays will no longer be generated.

From the above, it is preferable to maintain the ion temperature at a relatively low state and raise only the electron temperature to a temperature necessary to expel electrons in orbits close to the atomic nucleus.

Therefore, as mentioned above, by irradiating the plasma obtained by the theta pinch with an electron beam,
A preferred method is to use a method such as applying an electric field in the axial direction.

(Embodiment of the Invention) An embodiment of the invention based on the above principle will be described below with reference to FIGS. 1 and 2. FIG. 1 is a side sectional view of one embodiment of the present invention, and FIG. 2 is a -
This is a cross-sectional view along the line. In these figures, the same reference numerals as in FIG. 3 represent the same or equivalent parts.

The X-ray generator 1 has the required wavelength (for example, 5
Gases (e.g. Ne, Xe, Ga, etc.) that generate soft X-rays (~20 angstroms) as characteristic X-rays
It has a container 2 filled with.

Inside the container 2 are a coil 41 that generates plasma by theta pinch, and an electrode 4 that applies a voltage in the axial direction of the coil 41 to flow current.
2, 43, and supports and supports the electrodes 42, 43.
It has end plates 44 and 45 for fixing. The coil 41 is a plate-shaped one-turn coil, and the entire coil 41 is shaped into a substantially cylindrical shape.

The end plates 44 and 45 are supported by insulating support members 46 and 4.
7, it is electrically insulated from and supported by the theta pinch coil 41. Further, a part of the coil 41 has an opening 4 for extracting soft X-rays.
8 is drilled. This opening 48 is sealed with a material that easily transmits soft X-rays, such as beryllium.

The theta pinch coil 41 includes a charging device 49.
A capacitor 50 charged to a predetermined voltage is connected via a switch 51. and,
By turning on the switch 51 in accordance with a command from the starter 52, a high frequency large current is passed through the coil 41, and a pinch of plasma 53 is generated in the center of the coil 41 (along its axis).

At this time, if the temperature of the plasma 53 is sufficiently high, characteristic X-rays are emitted from the plasma 53, as is clear from the above description.

In this embodiment, in order to ensure the generation of X-rays, electrodes 42 and 43 are provided for flowing current in the axial direction of the coil 41 or the plasma 53, and the electrodes are charged by a charging device 54. The capacitor 55 charged to a predetermined voltage is connected to the switch 5
6.

Then, by turning on the switch 56 in accordance with the command from the starter 57, the electrodes 42, 43
A voltage is applied to the plasma 53 and a current is caused to flow through the plasma 53. As a result, the pinched plasma 53 as described above emits soft X-rays of a specific wavelength determined by the gas filled in the container 2.

It goes without saying that the time to turn on the switch 56 is preferably close to the time when the plasma 53 is pinched at the center of the coil 41 due to the theta pinch. To do this, the switch 5 must be activated near the time when the current flowing through the coil 41 reaches its maximum value.
It is better to put in 6.

Furthermore, it is preferable to apply a high voltage that rises quickly to the electrodes 42, 43 in order to increase the electron temperature for generating soft X-rays.

Soft X-rays generated from pinched plasma 53 are guided to lithography apparatus 20 through beryllium window 48 . And X-ray mask 23
pattern on an X-ray resist 25 formed on the surface of a semiconductor substrate 24 such as a silicon wafer.
Transfer as a latent image.

The configuration of the lithography apparatus 20 is the same as that in the prior art shown in FIG.

According to this embodiment, electrodeless discharge by theta pinch is used to generate pinch plasma for generating soft X-rays, so a large current is passed in the axial direction to generate pinch plasma (Z pinch plasma). , traditional methods (Applied Physics
Letters Vol. 44 No. 7 p. 667-669, 1984), there is less electrode wear and less impurity generation.

In addition, in this example, the purpose of flowing current in the axial direction is not to pinch the plasma, but to increase the electron temperature of the already pinched plasma, so there is no need to flow a large current. Compared to the case of plasma generation by Z-pinch, electrode wear is much less, and the life of the X-ray source can be maintained for a long time. Furthermore, in this embodiment, since the theta pinch coil 41 is constructed of a one-turn plate-shaped coil, the inductance and resistance of the coil can be kept lower than when a so-called solenoid coil having a spiral structure is used. Therefore, even low voltage sources can supply large currents,
Moreover, it becomes possible to generate a uniform magnetic field (magnetic field) within the coil. As a result, it becomes possible to flow a high frequency large current without using a large power supply device, and it becomes possible to generate uniform and stable plasma.

(Another Embodiment of the Invention) FIG. 6 shows another embodiment of the invention. In this figure, the same parts as in FIGS. 1 and 2 are indicated by the same reference numerals, and the plasma generation method is the same as that in FIG. 1, so the explanation will be omitted.

In this embodiment, the pinch plasma 53 generated by the theta pinch is irradiated with an electron beam 61 from the radial direction of the theta pinch coil 41, and soft X-rays are generated from the irradiation.

For this purpose, an electron beam injection device 62 is provided outside the theta pinch coil 41.

When the plasma 53 pinches, the starting device 6
When the switch 63 is turned on in accordance with the command from the coil 4, the capacitor 65 charged by the charging device 64 is discharged, and the electron beam 61 is transferred to the coil 4.
The plasma 53 is irradiated through an opening 67 formed in a part of the plasma 1 . As a result, soft X-rays are generated from the irradiation point of the electron beam 61.

According to this embodiment, the soft X-ray source is placed at one point on the theta coil axis - in other words, the pinched plasma 5
It becomes possible to restrict the number of points to one point above 3. Therefore, the soft X-ray generation source can be positioned accurately, a latent image with good resolution can be obtained on the X-ray resist 25, and a finer pattern can therefore be drawn.

FIG. 7 is a sectional view showing still another embodiment of the present invention, and in the figure, the same symbols as in FIG.
Represents the same or equivalent parts.

In this embodiment, the pinch plasma 53 generated by the theta pinch is irradiated with an electron beam 61 from the theta pinch coil 41 or the axial direction of the pinch plasma 53, and soft X-rays are applied to the pinch plasma 53.
It is designed to be taken out from the axial direction.

According to this embodiment, since the chance of interaction between the electron beam 61 and the plasma 53 increases, the soft X-ray intensity can be increased.

Furthermore, in this embodiment, the gas necessary for X-ray generation can be sealed only in the discharge tube 71, so the theta pinch coil 41 and the electron beam injection device 62 can be placed in the atmosphere. ,
It also has the effect of making maintenance and inspection easier.

In the embodiment of the present invention shown in FIGS. 1 and 2, the soft X-rays are extracted in the radial direction of the pinch plasma, but the soft X-rays are extracted in the radial direction of the pinch plasma. Also in the radiation source, it is possible to extract soft X-rays in the axial direction of the pinch plasma, as in the embodiment shown in FIG.

(Effects of the Invention) As is clear from the above description, according to the present invention, the following effects are achieved.

(1) Plasma is generated by theta pinch, so the reproducibility of the plasma generation position is good.

(2) As a result of (1) above, the X-ray source, that is, the X-ray generation position, can be accurately controlled, so especially when used as an X-ray source in an X-ray lithography apparatus,
A pattern image can be formed at a correct position on a semiconductor substrate.

Furthermore, since the positional deviation of each image when multiple exposure is performed is reduced, it becomes possible to print fine patterns, and high-density integration is realized.

(3) High-intensity soft X-rays can be generated within the plasma.

(4) The area around the pinched plasma becomes a thin space with few residual gas particles, so the generated soft X
There is less radiation absorption, making it easier to obtain high-intensity soft X-rays, improving operating efficiency.

(5) Evaporative consumption of electrodes and insulators is reduced, so
The life of the X-ray generator can be extended, and the operating rate of the X-ray lithography apparatus can be improved.

(6) As mentioned in the previous section, since there is less evaporated gas, the absorption of soft X-rays is even lower. In addition, since contamination of the X-ray extraction is reduced, the absorption of soft X-rays on this surface is also reduced, and the frequency of replacing the extraction window is also reduced.

[Brief explanation of drawings]

FIG. 1 is a side cross-sectional view of an X-ray lithography apparatus that employs the X-ray generator according to the present invention, FIG. 2 is a cross-sectional view taken along the - line in FIG. A cross-sectional view of an X-ray lithography apparatus employing the generator, FIG. 4 is a schematic configuration diagram showing the principle of theta pinch, FIG. 5 is a conceptual diagram explaining the pinching process by theta pinch, and FIGS. FIG. 2 is a sectional view showing another embodiment of the present invention. 1... X-ray generator, 2... Container, 20... Lithography device, 23... X-ray mask, 24...
Substrate, 25... Substrate resist, 41... Theta pinch coil, 42, 43... Electrode, 48... Beryllium window, 53... Pinched plasma, 6
1...Electron beam, 62...Electron beam injection device.

Claims (1)

[Scope of Claims] 1. A one-turn theta pinch coil configured by forming a plate-like body into a cylindrical shape, a plasma gas sealed in an internal space of the theta pinch coil, and a plasma gas in the theta pinch coil. X characterized by comprising means for supplying a generating current.
Line generator. 2. The X-ray generator according to claim 1, wherein a part of the theta pinch coil is provided with an X-ray extraction window. 3. The X-ray generator according to claim 1, wherein the gas is one of Ne, Xe, and Ga, and the generated X-rays are soft X-rays. 4. A one-turn theta pinch coil configured by forming a plate-like body into a cylindrical shape, a plasma gas sealed in the internal space of the theta pinch coil, and supplying plasma generation current to the theta pinch coil. An X-ray generator comprising: means for irradiating an electron beam to a pinch plasma generation position within the theta pinch coil. 5. The electron beam is irradiated from a direction perpendicular to the axis of the pinch plasma, and a part of the theta pinch coil is provided with an X-ray extraction window. The X-ray generating device described. 6. The X-ray generator according to claim 4, wherein the gas is one of Ne, Xe, and Ga, and the generated X-rays are soft X-rays. 7. The X-ray generator according to claim 4, wherein the electron beam is irradiated from the axial direction of the pinch plasma. 8. A one-turn theta pinch coil configured by forming a plate-like body into a cylindrical shape, a plasma gas sealed in the internal space of the theta pinch coil, and supplying a plasma generation current to the theta pinch coil. An X-ray generator comprising: means for applying a voltage in the axial direction of the theta pinch coil to pinch plasma generated inside the theta pinch coil. 9. The X-ray generator according to claim 8, wherein a part of the theta pinch coil is provided with an X-ray extraction window. 10 The X according to claim 4, wherein the gas is one of Ne, Xe, and Ga, and the generated X-rays are soft X-rays.
Line generator. 11. A one-turn theta pinch coil configured by forming a plate-like body into a cylindrical shape, a plasma gas sealed in the internal space of the theta pinch coil, and supplying a plasma generation current to the theta pinch coil. an X-ray generating device comprising an X-ray generating device, and an X-ray extraction window disposed in a part of the X-ray generating device; An X-ray lithography apparatus comprising an X-ray mask and a workpiece holding means. 12. The X-ray lithography apparatus according to claim 11, wherein the X-ray mask and workpiece holding means are arranged in a vacuum chamber. 13. A one-turn theta pinch coil configured by forming a plate-like body into a cylindrical shape; a plasma gas sealed in the internal space of the theta pinch coil; and supplying plasma generation current to the theta pinch coil. and means for irradiating an electron beam to a pinch plasma generation position in the theta pinch coil, further comprising an X-ray extraction device disposed in a part of the X-ray generation device. An X-ray lithography apparatus comprising: a window for taking out X-rays; and an X-ray mask and workpiece holding means arranged in an X-ray radiation area outside the X-ray extraction window. 14. Claim 13, characterized in that the electron beam is irradiated from a direction perpendicular to the axis of the pinch plasma, and a window for extracting X-rays is formed in a part of the theta pinch coil. The X-ray lithography apparatus described. 15. The X-ray lithography apparatus according to claim 13, wherein the electron beam is irradiated from the axial direction of the pinch plasma. 16. A one-turn theta pinch coil configured by forming a plate-like body into a cylindrical shape; a plasma gas sealed in the internal space of the theta pinch coil; and supplying plasma generation current to the theta pinch coil. and means for applying a voltage in the axial direction of the theta pinch coil to the pinch plasma generated inside the theta pinch coil, further comprising a part of the X-ray generator. An X-ray lithography comprising: an X-ray extraction window disposed in the X-ray extraction window; and an X-ray mask and workpiece holding means disposed in an X-ray radiation area outside the X-ray extraction window. i device. 17. The X-ray lithography apparatus according to claim 16, wherein a part of the theta pinch coil is provided with an X-ray extraction window.