CN115323332A - Preparation method of Mo/Si multilayer film reflecting mirror suitable for EUV lithography - Google Patents
Preparation method of Mo/Si multilayer film reflecting mirror suitable for EUV lithography Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title claims abstract description 11
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- 238000000034 method Methods 0.000 claims abstract description 24
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- 239000013078 crystal Substances 0.000 claims abstract description 8
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 4
- 238000011065 in-situ storage Methods 0.000 claims abstract description 3
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- 239000000463 material Substances 0.000 claims description 12
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 8
- 239000007789 gas Substances 0.000 claims description 5
- 229910052786 argon Inorganic materials 0.000 claims description 4
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- 230000001427 coherent effect Effects 0.000 description 2
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- 229910021641 deionized water Inorganic materials 0.000 description 2
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- C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
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- C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
- C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
- C23C14/14—Metallic material, boron or silicon
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- G02B5/085—Multilayer mirrors, i.e. having two or more reflecting layers at least one of the reflecting layers comprising metal
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Abstract
A Mo/Si multilayer film reflector preparation method suitable for EUV lithography is characterized in that a direct-current magnetron sputtering method is adopted to grow a Mo/Si periodic multilayer film on a convex mirror, the convex mirror is subjected to sputtering treatment in a direct-current magnetron sputtering growth cavity to clean surface adsorbed gas and enable the surface of a sample to be flat, so that a high-quality sample is obtained, the sputtering cleaning power is 5-10W, and the sputtering cleaning time is 5-10 minutes; mo and Si are both high-energy Ar + Sputtering by bombardment with separately controlled direct currentSputtering power to control the deposition rate of the two elements; the periodic alternate growth of Mo/Si is realized by continuously switching and controlling baffle plates at the top ends of Mo and Si sources in a magnetron sputtering cavity, and the last Si layer with the growth of 1.5nm is covered to prevent oxidation. A quartz crystal oscillator is required in the magnetron sputtering cavity as an in-situ deposition rate calibration means. The method has the advantages of accurate film thickness control, simplicity, feasibility and high repeatability.
Description
Technical Field
The invention belongs to the field of Extreme Ultraviolet (EUV) lithography, and particularly provides a preparation technology of a Mo/Si multilayer film reflecting mirror suitable for EUV lithography. Specifically, the Mo/Si multilayer film is prepared by a direct-current magnetron sputtering technology, the thickness of a single-layer film is modulated by accurately controlling the sputtering power by the direct-current magnetron sputtering technology, and the periodic alternate growth of Mo and Si is realized by continuously switching and controlling baffle plates at the top ends of Mo and Si sources in a magnetron sputtering cavity. The growth thickness of the Mo and Si layers is accurately regulated and controlled through time in the growth process, so that the Mo/Si multilayer film reflecting mirror with accurate thickness, low average roughness, high reflectivity and clear interface is obtained.
Background
Photolithography is one of the most critical technologies in integrated circuit fabrication processes, and has determined the upper limit of the development of electronic devices toward miniaturization, and high integration. At present, the most widely used 193nm wavelength lithography system in integrated circuit technology is approaching the limit of lithography design, and further increasing the lithography process of the system will greatly increase the complexity of the lithography system design, so that the lithography cost is increased sharply. The ultra-deep ultraviolet lithography system with the working wavelength of 13.5nm can greatly reduce the requirements of process factors and numerical aperture of the objective lens, so that the ultra-deep ultraviolet lithography is expected to become an optimal solution, the development of the ultra-deep ultraviolet lithography technology is greatly promoted, the resolution of the lithography process is further improved, and the element integration with higher density is realized.
Therefore, the EUV lithography system with higher resolution and greatly improved integration density of components attracts the attention of many researchers. Because almost all materials have extremely strong absorption characteristics to extreme ultraviolet light, only a reflective lithography system can realize establishment of an EUV lithography system, and how to reduce the loss of the materials to the extreme ultraviolet light in the reflective lithography system still is a problem to be solved urgently. The property that extreme ultraviolet light can be strongly absorbed by almost all known optical materials determines that conventional refractive optical systems cannot be directly adopted by EUV lithography systems, so that the illumination system, the mask and the projection objective of EUV lithography systems are designed in a reflective manner. The reflector made of the traditional optical material has great loss to the extreme ultraviolet light, a multilayer film structure is established by selecting two materials (usually Mo and Si) with high and low refractive indexes to the extreme ultraviolet light, and the coherent superposition of the extreme ultraviolet light intensity can be realized under the condition of satisfying Bragg diffraction, so that the function of high reflection of the multilayer film to the extreme ultraviolet light is realized. However, this solution still has the following drawbacks: diffusion phenomenon is easy to occur between the film layers of the prepared multilayer film, so that the structure of the multilayer film is lost. Two electromagnetic waves with the same or opposite propagating directions of incident waves exist in the multilayer film, the two waves have strong coherence, and standing waves can be formed so as to generate loss of extreme ultraviolet light. The traditional film coating means is difficult to realize the precise control of the film thickness during the periodic alternate film coating. Currently, the most commonly used evaporation coating means can form an island-shaped structure in the deposition process, which continuously prevents deposition atoms from depositing into surrounding vacancies, thereby increasing the internal pore structure of the film and reducing the reflectivity of the film to extreme ultraviolet light.
Therefore, designing a Mo/Si extreme ultraviolet multilayer film structure with high reflectivity and developing a Mo/Si multilayer film preparation method which is simple and easy to implement, has high repeatability and can realize accurate control of film thickness during periodic alternate film plating is urgent for researchers.
Disclosure of Invention
The invention aims to provide a method for periodically and alternately growing Mo/Si multilayer film samples under the combination of high vacuum and optimal sputtering parameters by using direct-current magnetron sputtering, so that the requirements of the multilayer film of an EUV photoetching reflector can be better met.
In order to achieve the purpose, the technical scheme of the invention is thatA method for preparing a Mo/Si multilayer film reflecting mirror for EUV lithography comprises the steps of growing a Mo/Si periodic multilayer film on a convex mirror by adopting a direct-current magnetron sputtering method, carrying out sputtering treatment on the convex mirror in a direct-current magnetron sputtering growth cavity to clean surface adsorbed gas and enable the surface of a sample to be flat, and thus obtaining a high-quality sample, wherein the sputtering cleaning power is 5-10W, and the sputtering cleaning time is 5-10 minutes; mo and Si are both high-energy Ar + Bombarding to sputter, and controlling the deposition rates of the two elements by respectively controlling the direct current sputtering power; the periodic alternate growth of Mo/Si is realized by continuously switching and controlling baffle plates at the top ends of Mo and Si sources in a magnetron sputtering cavity, and the last Si layer with the growth of 1.5nm is covered to prevent oxidation. A quartz crystal oscillator is required in the magnetron sputtering cavity as an in-situ deposition rate calibration means.
Furthermore, the background vacuum degree of the direct current magnetron sputtering chamber needs to reach 10 -7 On the Torr scale. When Mo and Si are sputtered and grown, the convex mirror needs to keep the rotation speed of 5rpm without revolution.
Furthermore, when Mo and Si are sputtered and grown, the distance between the convex mirror and the target needs to be kept at 100mm.
Furthermore, the particles sputtered from the two targets can be uniformly deposited on the surface of the convex mirror at the same growth position.
Further, the DC sputtering power of the Mo target was 10W, and that of the Si target was 20W.
Furthermore, a ventilation pipeline which can be filled with pure argon is needed in the magnetron sputtering cavity.
Furthermore, the purity of the argon introduced into the magnetron sputtering chamber should reach 99.99%, and the sputtering pressure of the two elements of Mo and Si needs to be controlled to be about 7 mTorr.
Has the advantages that: the method utilizes a direct current magnetron sputtering method to grow a Mo/Si multilayer film with 40 periodic layers on the convex mirror, wherein in each period, the thickness of the Mo layer is 2.76nm, the thickness of the Si layer is 4.13nm, and finally a Si covering layer with 1.5nm is grown to prevent the sample from being oxidized. In the growth process, mo and Si periodically alternate growth is realized by continuous switching control of the baffle plates at the top ends of the Mo and Si sources of the magnetron sputtering cavity. The crystal oscillator device is utilized to calibrate the growth rates of the Mo source and the Si source under certain power, rotation speed and vacuum degree, and the growth thicknesses of the Mo layer and the Si layer are respectively adjusted by controlling the sputtering time. After the growth is finished, the surface roughness of the Mo/Si multilayer film is observed by an Atomic Force Microscope (AFM) so as to measure the reflection efficiency of the Mo/Si multilayer film applied to a reflecting mirror of an EUV photoetching system. The method has the advantages of accurate film thickness control, simplicity, practicability and high repeatability, and the film prepared according to the method has the advantages of stable property, clear interface, extremely low roughness and higher reflectivity. The sample structure involved in the invention sequentially comprises a convex mirror, a Mo/Si periodic multilayer film and a Si protective layer.
Drawings
FIG. 1 is a schematic diagram of a sample convex mirror structure according to the present invention;
FIG. 2 is a schematic representation of the microstructure of a sample in accordance with the present invention;
FIG. 3 is a schematic view of a magnetron sputtering system used in the present invention;
FIGS. 4 (a), (b), and (c) are Atomic Force Microscope (AFM) images of different regions of a sample according to the present invention. The average surface roughness was about 0.4nm.
Detailed Description
Generally speaking, the invention uses a direct current magnetron sputtering growth system to prepare a Mo/Si multilayer film, and obtains the EUV multilayer film reflecting mirror with low roughness and high reflectivity by designing the periodic structure of the extreme ultraviolet multilayer film and accurately controlling the growth conditions of the multilayer film.
For a Mo/Si multilayer film structure applied to a reflector of an EUV lithography system, reflectivity is one of the most important performance indexes. The structure determines the performance, and the selection of the design of the periodic multilayer film, including the thickness of the monolayer film, the periodic thickness, and the number of layers grown, will directly affect its performance. Therefore, to obtain a mirror for EUV lithography systems with a high reflectivity, a scientifically rational design of the periodic multilayer film is a primary task.
The thickness of each Mo, si single-layer film is determined according to two conditions of (1) making reflected light interference strongest; and (2) minimal absorption of extreme ultraviolet light. Materials with high and low reflectivity for extreme ultraviolet are stacked together, and when the periodic structure of the formed film meets the Bragg diffraction condition, reflected waves of incident light on the film interface of two different materials can form a coherent stacking effect, so that the reflectivity of the multilayer film is improved.
In the Mo/Si multilayer film, the Mo layer is an absorption layer, and the Si layer is a spacing layer. When the film thickness is d, the incident wavelength is lambda, and the grazing incidence angle is theta, the film thickness can be obtained by a Bragg formula:
m is the Bragg diffraction order, theta is the grazing incidence angle,
is a weighted average of the real parts of the refractive indices of the two materials:
d is the sum of the thicknesses of the Mo layer and the Si layer in one period, also called the period thickness:
d＝t A +t S
Γ is the ratio of the thickness of the absorbing layer to the thickness of the period, also called the ratio:
the larger the value of Γ, the greater the stress effect in the film layer, which may lead to an increase in surface roughness, thereby affecting light collection and transmission.
The structure of the multilayer film is described by four parameters: material pair, period number (N), period thickness (d), ratio Γ.
For a Mo/Si multilayer film with a central wavelength of 13.0nm, we take:
1. material pair: mo is used as an absorption layer, and Si is used as a spacing layer;
the periodic thickness d of the Mo/Si multilayer film sample film is 0.51 times of the working wavelength, and is 3.5 multiplied by 0.51=6.89nm;
3.Γ =0.4, where Mo layer 2.76nm, si layer 4.13nm;
4. the number of cycles N may be 30-50, preferably N =40 in the present invention;
when the design parameters of the Mo/Si multilayer film structure are taken, the purposes of strongest reflected light interference and minimum ultraviolet light absorption can be achieved.
In addition, for the Mo/Si multilayer film structure applied to the reflecting mirror of the EUV photoetching system, even if the thickness of the multilayer film has deviation of a few tenths of nanometers, the working wavelength is positioned outside the reflectivity passband of the multilayer film, so that the reflection of the multilayer film to extreme ultraviolet light is greatly reduced. Therefore, the control of the film thickness of the multilayer film is a central priority in the preparation of the multilayer film of the reflecting mirror of the EUV lithography system. The key to accurately controlling the thickness of the single-layer film in the multilayer film is to obtain the deposition rate of each single element under the optimal sputtering parameters.
A Mo/Si multilayer film with 40 period layers grows on a convex mirror by utilizing magnetron sputtering equipment customized by Shanghai real-route vacuum technology engineering Limited, the thickness of the layer in each period is 6.89nm, the thickness of the Mo layer is 2.76nm, the thickness of the Si layer is 4.13nm, and finally the Si layer with the thickness of 1.5nm is deposited on the film to serve as an anti-oxidation covering layer.
In the present invention, the deposition rate of each target under a selected combination of sputtering parameters is scaled by a quartz crystal oscillator. We adjust the deposition rate by adjusting the sputtering power, and fix the deposition rate of Mo
Fixing the deposition rate of Si in
And the periodic alternate film plating is realized by continuously switching and controlling baffle plates at the top ends of the Mo and Si sources in the magnetron sputtering cavity. The deposition rate of the sputtering coating device is very stable under the same process parameters, so that the thicknesses of the Mo layer and the Si layer can be accurately controlled by controlling the deposition time.
In the present invention, the convex mirror specification is Φ 1016 x 7.23mm, overall thickness 16.45mm, depression height about 9mm, material JGS1. Before the convex mirror is installed in a magnetron sputtering device, firstly, the surface of the convex mirror is cleaned, and the specific method is that the convex mirror is sequentially placed in acetone, isopropanol and deionized water for 10 minutes respectively through ultrasonic treatment; and then deionized water is put into the sample preparation chamber to clean off the solvent adsorbed on the surface, and then the sample preparation chamber is dried on a heating table at the temperature of 180 ℃ and finally put into a sample preparation chamber of magnetron sputtering equipment. When the vacuum of the sample preparation chamber reaches 10 -7 After the Torr magnitude, the convex mirror is transferred into the magnetron sputtering growth cavity, and the position of the convex mirror is adjusted to the growth position. Before growing a sample, a sample heating filament behind the convex mirror is used for heating the convex mirror to 300 ℃ for 5 minutes to remove gas and water adsorbed on the surface of the convex mirror.
Then, the surface is flattened by using a magnetron sputtering surface cleaning function, so that a high-quality multilayer film is obtained. After cleaning, the baffle at the top end of the Mo source is opened and the baffle at the top end of the Si source is confirmed to be in a closed state, the growth height is adjusted to be 100mm, and the sputtering pressure is adjusted to be 7mTorr (Ar) 2 99.99%), the autorotation speed of the convex mirror is 5rpm and no revolution, the sputtering power of the Mo target is set to be DC10W, the growth is carried out for 1min for 25s, and a Mo layer with the thickness of 2.76nm is obtained as a first layer; then the shutter at the top of the Mo source was closed and the shutter at the top of the Si source was opened, the whole growth height was 100mm, and the sputtering pressure was 7mTorr (Ar) 2 99.99%), the rotation speed of the convex mirror is 5rpm and no revolution, the sputtering power of the Si target is set to DC20W, and the Si layer with the thickness of 4.13nm is obtained after 1min and 42s of growth. At this point, the deposition of the first periodic layer is completed, whereby the above operation is repeated 39 more times. And when the Si thin film is deposited at the last time, the sputtering time is adjusted to be 2min 30s so as to cover a Si anti-oxidation layer with the thickness of 1.5nm on the top end of the multilayer film.
In the invention, the growth rates of Mo and Si sources under the optimal sputtering parameters are calibrated by the crystal oscillator device, the thickness of the obtained sample is tested by using the step profiler, the thickness is compared with the data given by the crystal oscillator device, the parameters of the crystal oscillator device are further corrected, and then the growth thicknesses of the Mo layer and the Si layer are controlled by controlling the time, so that the thickness of the single-layer film is accurately controlled. We fix MoAt a deposition rate of
Deposition rate of Si of
The sputtering power of the corresponding Mo target was 10W, that of the corresponding Si target was 20W, and the sputtering pressure was 7mTorr (Ar) 2 99.99%), growth height of 100mm, rotation speed controlled at 5rpm and no revolution. And the periodic alternate film plating is realized by continuously switching and controlling baffle plates at the top ends of the Mo and Si sources in the magnetron sputtering cavity.
Since the roughness of the euv multilayer film directly affects the reflectivity of the multilayer film, and the roughness of the multilayer film surface can be accurately and directly measured by an Atomic Force Microscope (AFM), the roughness of the euv multilayer film surface becomes one of the evaluation criteria for measuring the reflectivity. Generally, the surface roughness of the multilayer film of the reflector of the EUV lithography system is lower than 0.7nm to realize high reflection of extreme ultraviolet light.
In the invention, fig. 4 shows atomic force microscope images intercepted from different areas on the sample convex mirror, and the average roughness of the Mo/Si multilayer film on the sample convex mirror obtained from the images is about 0.4nm, and the surface is relatively smooth, so that the Mo/Si multilayer film has high reflectivity and meets the standard of a reflector applied to an EUV lithography system. The Mo/Si reflector multilayer film obtained by the direct-current magnetron sputtering is beneficial to improving the reflectivity of an EUV photoetching system.
Claims (10)
1. A preparation method of a Mo/Si multilayer film reflecting mirror suitable for EUV lithography adopts a direct current magnetron sputtering method to grow a Mo/Si periodic multilayer film on a convex mirror, and is characterized in that the convex mirror is subjected to sputtering treatment in a direct current magnetron sputtering growth cavity to clean the surface to adsorb gas and flatten the surface of a sample, so that a high-quality sample is obtained, the sputtering cleaning power is 5-10W, and the sputtering cleaning time is 5-10 minutes; mo and Si are both high-energy Ar + Bombarding for sputtering, and controlling the deposition rate of two elements by respectively controlling the DC sputtering power(ii) a The periodic alternate growth of Mo/Si is realized by continuously switching and controlling baffle plates at the top ends of Mo and Si sources in a magnetron sputtering cavity, and the last Si layer with the growth of 1.5nm is covered to prevent oxidation.
2. The method of claim 1 wherein a quartz crystal oscillator is required in the magnetron sputtering chamber as an in-situ deposition rate scaling means.
3. The method for preparing a Mo/Si multilayer film mirror for EUV lithography according to claim 1, wherein the background vacuum of the DC magnetron sputtering chamber needs to reach 10 -7 On the Torr scale. When Mo and Si are sputtered and grown, the convex mirror needs to keep the rotation speed of 5rpm without revolution.
4. The method of claim 1, wherein the distance between the convex mirror and the target is maintained at 100mm during sputter growth of Mo and Si.
5. The method of claim 1, wherein particles sputtered from two targets are deposited uniformly on the convex mirror surface at the same growth location.
6. The method for producing a Mo/Si multilayer film mirror for EUV lithography according to claim 1, wherein the DC sputtering power of the Mo target is 10W and the DC sputtering power of the Si target is 20W.
7. The method for producing a Mo/Si multilayer film mirror for EUV lithography according to claim 1, characterized in that a vent pipe through which pure argon gas can be vented is required in the magnetron sputtering chamber.
8. The method for preparing a Mo/Si multilayer film reflecting mirror for EUV lithography according to claim 1, wherein the purity of argon gas introduced into the magnetron sputtering chamber should reach 99.99%, and the sputtering pressure of Mo and Si elements needs to be controlled to be about 7 mTorr.
9. A method for making a Mo/Si multilayer film mirror for EUV lithography according to claim 1, wherein the convex mirror specification is Φ 101.6 × 7.23mm, overall thickness is 16.45mm, recess height is about 9mm, and material is JGS1.
10. The method for producing a Mo/Si multilayer film mirror for EUV lithography according to claim 1, wherein for a Mo/Si multilayer film with a center wavelength of 13.0nm, mo is used as an absorbing layer and Si is used as a spacer layer; the periodic thickness d of the Mo/Si multilayer film sample film is 0.51 times of the working wavelength, and is 3.5 multiplied by 0.51=6.89nm; Γ =0.4, with Mo layer 2.76nm, si layer 4.13nm; the number of cycles N may be 30 to 50, and N =40 is preferred in the present invention.
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