JPH0125221B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a soft X-ray exposure apparatus in the field of X-ray phosphorography capable of copying fine patterns of about 1 micron.

Publication Electronics Published in 1972
Letters (ELECTRONICS LETTERS) No. 8
Since the report on reproduction of high resolution patterns using soft X-rays in Vol. 4, pp. 102-104, research and development on X-ray lithography has been carried out. An outline of the prior art is shown in FIG. For example, the publication IEEE TRANSACTIONS ON ELECTRON published in 1975
DEVICES), Volume ED-22, No. 7, pp. 429-433
A similar figure is included in the patent application publication No. 51-41551 Soft X-ray lithography method and apparatus. Fixed or rotating metal target 11
An electron movie 12 is applied to the specimen, and soft X-rays 13 excited downward, for example, strike a sample consisting of a mask 14 and a resist-coated substrate 15 and copy the pattern on the mask onto the substrate. A tube section 16 with a high vacuum of about 10 ^-6 Torr and a sample chamber 17 with a low vacuum of about 10 ^-2 Torr or about 1 Torr of He gas where soft X-rays are less attenuated are separated by a window section 18 . 19
20 indicates high vacuum evacuation of the tube section, and 20 indicates low vacuum evacuation or He gas replacement of the sample chamber.

X-ray lithography has the following advantages: 1) Since the wavelength used is in the so-called soft X-ray range of several to several tens of angstroms, there are essentially no problems with diffraction or reflection;
Suitable for creating fine patterns of about 1 micron, 2) Removes dirt and dust from the mask or substrate.
Because the line passes through, there are no effects from these, 3)
As a line exposure system, it has features such as being structurally simple and relatively inexpensive compared to electron beam exposure systems. Despite having such various advantages, the state of research and development of soft X-ray exposure apparatuses is still somewhat congested. One important factor in this regard is the lack of a practical soft x-ray source that is relatively inexpensive and readily available. In the early days, a method was used for basic research in which a fixed metal target was irradiated with an electron beam to generate soft X-rays, but this method had poor cooling efficiency for the fixed metal target, making it impossible to increase the excitation electron beam output. The intensity of the obtained soft X-rays is extremely low and is not practical. In recent years, high-power soft X-ray sources of 10 to 20 KW using water-cooled rotating targets have been developed and used. However, since a rotating target rotates at a high speed of more than 6,000 revolutions per minute, the vibration caused by the rotor such as a motor is large, which can cause misalignment of the installed mask and substrate, and strongly affect the accuracy of the copied pattern. There is a concern that the gap between the mask and the substrate may change. Also
From the experience of using a 10KW water-cooled rotating target,
1) The rotating part of the rotating target is sealed in a high vacuum by an oil seal, but due to high speed rotation, the oil seal part is prone to wear and damage, 2)
Abnormal discharge is likely to occur due to a decrease in the cleanliness of the vacuum inside the tube caused by oil gas entering the tube. Because of the irradiation, surface contamination, gas boiling, etc. are likely to occur, and as a result, problems such as abnormal discharge are likely to occur. In a normal device, if an abnormal discharge occurs inside the bulb, a safety mechanism is activated and the power is shut off. In that case, it takes several tens of minutes to reset the voltage to 20 KV and current to 500 mA, for example. Furthermore, once abnormal discharge occurs, a habit of discharge tends to occur, in which case maintenance such as disassembly and cleaning of the bulb, or replacement of parts is required. Although it is possible to obtain high-intensity soft X-rays by using a water-cooled rotating target, this rotating target is unstable for long-term stable operation, and requires a lot of effort for maintenance, making it impractical. is not suitable. Although it is conceivable to use X-ray radiation from synchrotron radiation as a device that can obtain extremely high-intensity and highly parallel soft X-rays, this device is extremely expensive and is therefore completely impractical.

Therefore, the purpose of the present invention is to consider a practical soft X-ray exposure apparatus that features a stationary surface soft X-ray source, and to propose a method for eliminating the geometric distortion of copied patterns caused by the structure of the radiation source. It is to be.

A feature of the present invention is that an electron beam is irradiated from the back side of a metal foil target, and a sample consisting of a mask and a substrate is exposed to soft X-rays that pass through the front side, and the distance between the sample and the metal foil target is adjusted. In a soft X-ray exposure apparatus in which the metal foil target is a stationary surface source consisting of a plurality of soft X-ray sources, the sample is sized to be included in the metal foil target, and A mechanism is provided in which the sample moves in two directions perpendicular to each other with respect to the metal foil target. Next, the configuration of the present invention will be explained in detail with reference to the drawings.

One embodiment according to the invention is shown in FIG. A substantially parallel electron beam 22 generated from an electron beam generator 21 is irradiated onto one side (for convenience, the back side is referred to as the back side) of a metal foil target 23. A sample consisting of a mask 25 and a substrate 26 is exposed using soft X-rays 24 that are transmitted to the opposite side (for convenience, the front side) of the target, and an absorber pattern 27 of, for example, Au on the mask is exposed to the substrate. upper resist film 28
Copy to. In order to increase the intensity of soft X-rays incident on the resist film, a configuration is adopted in which the sample is brought as close as possible to the target by several tens to several millimeters. 29 indicates a high vacuum evacuation for generating an electron beam. If the soft X-rays generated from the entire surface of the metal foil target were to be incident on the entire surface of the sample, an extremely large amount of oblique component gas would be incident, causing large penumbra blur and geometric distortion in the copied pattern. A shielding structure 30 is provided. Blur and distortion will be explained using FIG. 3, which is a diagram of the principle. For example, if the size of the aperture in the shield structure is G cm square, the length is 1 cm, and the gap between the mask and the substrate is 5 microns, the geometric distortion will be reduced to △microns△=sG/2l. can. In addition, a focal point smaller than the size of the aperture of the shield structure is provided. For example, if the size of one focal point is d centimeters (d<G), the penumbra blur δ microns can be reduced to about δ=sd/D, where the distance between the source and the sample is D centimeters. In this structure, the metal foil target consists of a plurality of soft X-ray sources 41 as shown in FIG.

The blur δ and the distortion Δ will be further considered.
As can be seen from FIG. 3, if the focus size of each soft X-ray source is the same and the sample is placed close to the source, the blur δ will be the same at any position on the sample. However, the strain Δ takes a value that periodically fluctuates with each G centimeter square soft X-ray source as a unit. For example, G=2cm, l=2.5cm, s=
If it is 0.5 μm, the maximum value of Δ in one G centimeter angle is Δ=sG/2l=0.2 μm, and the range of values of Δ is 0Δ0.2 μm. This occurs repeatedly in the copy pattern of the sample immediately below each of the soft X-ray sources. In copying fine patterns of about 1 μm or less, the periodic occurrence of this geometric distortion △ within a small section of about 2 cm square is an important problem, especially in device fabrication that involves multiple alignment steps. be.

Therefore, in the present invention, a mechanism is provided for moving a sample consisting of a mask and a substrate in two directions perpendicular to each other with respect to a transmission metal foil target. Third again
This will be explained using figures. In the figure, if the sample is moved in the x direction, x of Δ=sx/2l changes in the range of 0xG, and Δ can be made zero on average. Since the x-direction component of △ can be canceled by moving the sample in the x-direction, the y-direction that is perpendicular to the x-direction
If the sample is moved in this direction, the y-direction component of Δ can also be eliminated, and in the end, Δ can be completely eliminated. What is important at this time is that the sample passes directly below the focal point of each soft can be easily passed through. In addition, it can be said that the intensity distribution of soft X-rays in the surface source is almost uniform over a wide area, and it is easier and more advantageous to provide the above-mentioned sample moving mechanism.

FIG. 5 shows an embodiment of the present invention. Samples 52 lined up in the x direction with respect to the transmission type surface source 51 are △x→△
Move by step movement alternately y → △x → △y.
When state c is reached, the direction of Δy is reversed and the same process is repeated. In this way, it is possible to continuously process the sample while continuously eliminating the strain Δ. What is important during movement is that the sample must not be continuously moved in the x and y directions at the same time. If this is done, the sample will eventually move in one diagonal direction, making it impossible to eliminate the Δ in all directions. In FIG. 5, the size of the sample is smaller than the size of the planar source, which is one of the key points of the present invention. In other words, by making the sample large enough to be included in the surface source, it is possible to move the sample in two directions perpendicular to each other while intermittent exposure of the entire surface of the sample. The characteristics of a surface source can be used to advantage. The same effect can be obtained by moving the surface source, that is, the entire radiation source system, instead of moving the sample in FIG. Movement of the sample and movement of the radiation source relative to each other are within the scope of the present invention, and the same applies to the examples described below.

The effects of the present invention will be described. First, one feature of the present invention is that the intensity of soft X-rays is increased by bringing the sample close to a stationary surface soft X-ray source.
In this sense, various maintenance related to the use of a rotating target is unnecessary and it can be said to be a practical device. Second, by providing a mechanism for moving the sample in two directions perpendicular to each other with respect to the surface source of the present invention, it is possible to eliminate geometric distortion of the copied pattern caused by the structure of the radiation source, and It is advantageous for the fabrication of devices that involve less micropattern reproduction and, most importantly, multiple alignment steps. Thirdly, by making the size of the sample of the present invention so large that it can be included in the plane source, it is possible to process a large number of samples continuously, which is the most important issue for fine pattern copying systems. Leads to improved productivity. Fourth, it is more efficient in terms of exposure time than when using a rotating target as a conventional point source. The fourth point will be specifically explained. First, the incident energy of soft X-rays per square centimeter of substrate area in the present invention is determined. Consider a two-layer target consisting of a 3 micron thick _A1 film and a 25 micron thick Be foil in a 20 cm square planar source. In Figure 3, G=2.0
cm, l=2.5cm, d=1.12cm, D=2.8cm, s=
0.5μm, total electron beam output to the entire surface area of the surface source is 5kW
(acceleration voltage 20kV, beam current 250mA).
The publication IEEE TRANSACTIONS ON 1975
ELECTRON DEVICES), Volume ED-22, No. 7
According to No., pp. 421-428, when the accelerating voltage is 20 kV, characteristic X-rays (wavelength 8.34 angstroms) per unit input 1W from _one target, per unit solid angle.
The radiation power of is 58×10 ^-6 W. Adding to this value, the transmittance of a 1 micron thick A ₁ film, assuming that the electron beam output per opening (2 cm square) of the surface source is 50 W and the electron beam penetrates about 1 micron through a 3 micron thick A ₁ film. Transmittance at 0.9, 25 micron thick is 0.4, transmittance at 3 micron thick polyimide mask is 0.708, ratio of electron beam irradiated to the focal point of one aperture is 0.314 = (= (d/G) ² ), substrate Solid angle occupied by 1 square centimeter: 0.128 (=1/(2.8) ² )
, and multiplied by the transmittance of 0.985 when soft X-rays pass through He gas of approximately 1 atm and length of 2.8 cm, the irradiation input per unit area of the substrate is approximately 30 μW/cm ²
is obtained. Next, we will consider the case where a normal rotating target is used. As an effective soft X-ray irradiation area
The condition is to obtain a large diameter area equivalent to 20 cm square. 7 from a point source with a diameter of 4 mm
Thickness 50 microns, diameter in centimeters
If a 3.5 cm Be window is installed (a large-diameter window with a diameter of 3.5 cm with a pressure resistance of about 1 atm will practically require a thickness of about 50 microns), it will be possible to An effective diameter of 20 cm can be obtained at a distance of about 45 cm. When the substrate is placed at this position, the incident energy of soft X-rays per unit area of the substrate is determined. In addition to the above-mentioned value of 58×10 ^-6 W, the electron beam output is 5 kW, the transmittance of the Be window is 0.164, the transmittance of the 3 micron thick polyimide mask is 0.708, and the solid angle occupied by 1 square centimeter of the substrate is 4.94×10 ^-4 (=
1/(45) ² ) and the transmittance through 38 cm of He gas, 0.815, yields an irradiation input per unit area of the substrate of approximately 14 μW/cm ² . Therefore, the value in the case of a planar source is slightly more than twice that.
Since the exposure time is inversely proportional to the illumination input, the use of a planar source can be more efficient in terms of exposure time than the use of a rotating target as a point source.

FIG. 6 shows another embodiment of the invention. First, samples lined up in two rows in the x direction relative to the transmission type surface source 61 are continuously moved in the y direction. Next, the sample 62 is rotated 90 degrees and continuously moved in the reverse y direction. By doing this, the same effect as equivalently moving the sample in two directions perpendicular to each other with respect to the plane source can be obtained. Moreover, in this case, the entire area of the planar source can be used effectively, and further improvement in productivity can be expected. In FIG. 6, the effect is the same even if the surface source, that is, the entire radiation source system is moved up and down in the y direction instead of moving the sample.

FIG. 7 shows another embodiment of the invention. Samples 72 lined up in a row in the y-direction with respect to the transmission type surface source 71 are continuously moved in the y-direction on the outward path, and when returning to the return path, the samples are rotated by 90 degrees and continuously moved in the reverse y-direction. By doing so, the same effect as described in FIG. 6 can be obtained.

As explained above, according to the present invention, by using a practical stationary transmission-type soft surface X-ray source, it is possible to eliminate geometric distortion of copied patterns, improve productivity, and achieve high efficiency. A soft X-ray exposure device can be obtained. In the above explanation, the case where the target material is _A1 has been explained, but the present invention has the same effect on other materials such as Cu, Si, Mo, Rh, Pd, etc., as well as target materials for X-ray lithography. do. Furthermore, the effect is the same whether the sample is moved in any two directions that are perpendicular to each other with respect to the plane source.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a conventional soft X-ray exposure apparatus, in which 11... fixed or rotating target, 12... electron beam, 13... soft X-ray, 14... mask, 15 ... Board, 16...
Tube section, 17...Sample chamber, 18...Window section, 19...
...High vacuum exhaust section, 20...Low vacuum exhaust section or
It is a He substitution part. FIG. 2 is a schematic diagram showing an embodiment of a soft X-ray exposure apparatus according to the present invention, in which 21...
Electron beam generator, 22... Parallel electron beam, 2
3...Metal foil target, 24...Soft X-ray, 25
...mask, 26 ... substrate, 27 ... absorber pattern, 28 ... resist film, 29 ... high vacuum exhaust section, 30 ... soft X-ray resistant structure. FIG. 3 is a diagram showing the principle of penumbra blur δ and geometric distortion Δ. FIG. 4 is a schematic diagram (top view) of a transmission type surface source, and in the figure, 41... is a soft X-ray generation source. FIG. 5 shows an embodiment of the present invention, in which 51...a transmission type surface source, and 52...a sample. FIG. 6 shows another embodiment of the present invention, in which 61...a transmission type surface source, and 62...a sample. FIG. 7 shows another embodiment of the present invention, in which 71 is a transmission type surface source and 72 is a sample.

Claims (1)

[Claims] 1 includes an electron beam generating section, a metal foil target, and a vacuum evacuation system, the electron beam generated from the electron beam generating section is irradiated from the back side of the metal foil target, and the soft X-rays transmitted to the front side are used to mask and A sample made of a substrate is exposed to light, the distance between the sample and the metal foil target is several tens to several millimeters, and the metal foil target has a plurality of soft X-ray generation sources having a structure that is resistant to soft X-rays. The soft X-ray exposure apparatus has a surface source that uses soft X-rays emitted from almost the entire front side of the metal foil target by irradiating an electron beam onto almost the entire back side of the metal foil target, wherein the sample is the metal foil target. The metal foil target has a size that is included in the metal foil target, and is characterized by having a mechanism for moving the sample relative to the metal foil target in two directions perpendicular to each other so as not to overlap in time. Soft X-ray exposure equipment.