A hafnium oxide composite film and preparation method thereof

Abstract

The present invention relates to the field of thin film optical technology, and in particular to a hafnium oxide composite film and a preparation method thereof. The present invention aims to solve the problem that the hafnium oxide film prepared by the ion beam assisted deposition process has a large roughness due to easy crystallization and dense surface void defects, as well as the problem that the film has a large absorption caused by ion beam bombardment. The present invention inserts a thin layer of silicon oxide film into the preparation of the traditional pure hafnium oxide film, and separates the thick layer of hafnium oxide into several nano-thin layers. On the one hand, it can effectively inhibit the crystallization of the hafnium oxide film, reduce the hole defects on the surface of the film, and thus reduce the roughness of the film; on the other hand, the introduction of a partial content of silicon oxide will also reduce the absorption of the hafnium oxide film. Compared with the prior art, the present invention can effectively reduce the surface roughness and absorption of the hafnium oxide film prepared by the ion beam assisted deposition process, and at the same time, the production cost is low, it is easy to promote, and has broad application prospects in the field of ultra-high precision laser measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of optical thin films, and in particular to a hafnium oxide composite thin film and a preparation method thereof. Background Art

[0002] Ultra-high precision laser measurement systems such as laser gyroscopes, gravitational wave detection systems, and the recently popular cavity ring-down spectroscopy measurement systems and femtosecond "optical clocks" are important cutting-edge measurement technologies in basic science, applied technology, and national defense. The sensitivity, signal-to-noise ratio, and other excellent performance of these high-precision laser measurement systems strongly depend on the total loss of the core thin film components in the system. Solving the absorption loss and scattering loss problems of optical thin films is of great significance.

[0003] The thin film prepared by ion beam assisted deposition has the advantages of dense film layer and low loss, and is a common technical means for preparing low-loss laser thin films. Compared with high-refractive index materials such as tantalum oxide and titanium oxide, hafnium oxide thin film has a wider band gap and lower film absorption, and is a commonly used high-refractive index material for high damage threshold laser thin films. Therefore, hafnium oxide thin films prepared by ion beam assisted deposition are expected to reduce both the absorption loss and scattering loss of the film. However, when hafnium oxide thin films are prepared by conventional processes using ion beam assisted deposition, several problems are prone to occur: first, under high-temperature coating processes, the film is easy to crystallize; second, oxygen inclusions are prone to appear on the surface of the film due to the adsorption of excess oxygen atoms, resulting in open and dense hole defects on the surface and inside of the film; third, the film is prone to stoichiometric mismatch under ion beam bombardment. The first two problems will cause the film roughness to increase, and open and dense hole defects will contribute more to the roughness, while stoichiometric mismatch will cause the film absorption to increase. Currently, there is no method that can simultaneously solve the crystallization, hole defects and high absorption problems of hafnium oxide thin films prepared by ion beam assisted deposition and reduce the absorption loss and roughness of the thin film.

[0004] In view of the above problems, it can be seen that the hafnium oxide film prepared by ion beam assisted deposition urgently needs a method that can inhibit film crystallization, inhibit the appearance of hole defects, and reduce film absorption, thereby reducing the surface roughness and absorption of the film. Summary of the invention

[0005] In order to solve the above problems, the purpose of the present invention is to provide a hafnium oxide composite film and a preparation method thereof. In the present invention, when preparing the hafnium oxide film by ion beam assisted deposition technology, nanometer-thick hafnium oxide nanofilms and silicon oxide nanofilms are alternately deposited, that is, in the preparation of the traditional pure hafnium oxide film, a thin layer of silicon oxide nanofilm is inserted to separate the thick layer of hafnium oxide into several nanometer thin layers; on the one hand, the crystal nucleus of the nanometer-thin layer of hafnium oxide is unstable, not easy to crystallize, and not easy to adsorb oxygen atoms, which can effectively inhibit the crystallization of the hafnium oxide film and reduce the hole defects on the surface of the film, and the amorphous and dense film structure is also helpful to reduce the probability of the occurrence of open and dense holes, thereby playing a role in smoothing the surface of the hafnium oxide film and reducing the roughness of the film; on the other hand, the inserted thin layer of silicon oxide nanofilm is equivalent to "doping" a part of the content of silicon oxide in the hafnium oxide. Since silicon oxide has lower absorption and wider band gap, the prepared hafnium oxide composite film has lower absorption. Compared with the prior art, the present invention can effectively reduce the surface roughness and absorption of hafnium oxide thin films prepared by ion beam assisted deposition process, and at the same time has low production cost and is easy to promote, and has broad application prospects in the field of ultra-high precision laser measurement.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] The first object of the present invention is to provide a hafnium oxide composite film, wherein the hafnium oxide composite film is composed of a plurality of HfO2 nanofilm layers and a plurality of SiO2 nanofilm layers, wherein a SiO2 nanofilm is disposed between adjacent HfO2 nanofilms, and the thickness of the hafnium oxide composite film is d;

[0008] Wherein, the value B is defined as d / 25, and the value N is defined as [d / 25];

[0009] If N<B≤N+0.8, the coating system is: S|(80n H / λH 20n L / λL)^N 4n H (d-25N) / λH|A,

[0010] If N+0.8<B≤N+1, the coating system is: S|(80n H / λH 20n L / λL)^N 80n H / λH4n L (d-25N-20) / λL|A;

[0011] Wherein, S represents substrate, A represents air, H represents HfO2 nanofilm with optical thickness of λ / 4, L represents SiO2 nanofilm with optical thickness of λ / 4; λ is the central wavelength of the film system in which each film layer is located; the numbers before H and L are the proportional coefficients of the λ / 4 optical thickness.

[0012] In one embodiment of the present invention, the thickness of the HfO2 nanofilm is less than 20 nm.

[0013] In one embodiment of the present invention, the thickness of the SiO2 nanofilm is less than 5 nm.

[0014] A second object of the present invention is to provide a method for preparing a hafnium oxide composite film, comprising the following steps:

[0015] The HfO2 nanofilm and the SiO2 nanofilm are sequentially deposited on the substrate using an ion beam assisted deposition process.

[0016] In one embodiment of the present invention, the substrate is an ultra-polished quartz substrate with a surface roughness of less than 0.3 nm.

[0017] In one embodiment of the present invention, during the ion beam assisted deposition process, when depositing the HfO2 nanofilm, the oxygen partial pressure is 1.8×10 -2 Pa; when depositing SiO2 nanofilm, the oxygen partial pressure is 1.5×10 -2 Pa.

[0018] In one embodiment of the present invention, during the ion beam assisted deposition process, the substrate temperature is 100-150°C.

[0019] In one embodiment of the present invention, during the ion beam assisted deposition process, the evaporation rate is 1 nm / s.

[0020] In one embodiment of the present invention, during the ion beam assisted deposition process, the ion source voltage is 900V.

[0021] In one embodiment of the present invention, during the ion beam assisted deposition process, the ion source current is 1000 mA.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The roughness of the hafnium oxide composite film prepared by the present invention is low: when the hafnium oxide composite film is prepared by ion beam assisted deposition technology, nanometer-thick hafnium oxide nanofilms and silicon oxide nanofilms are deposited alternately, that is, in the preparation of the traditional pure hafnium oxide film, a thin layer of silicon oxide film is inserted to separate the thick layer of hafnium oxide into several nanometer-thin layers. By taking advantage of the unstable and difficult-to-crystallize crystal nuclei of nanometer-thin layers of hafnium oxide, the crystallization of the hafnium oxide film can be effectively inhibited, and the probability of the occurrence of open dense pores can also be reduced. Therefore, the film has a more dense and amorphous structure, which will be beneficial to reducing the roughness of the film. At the same time, the hafnium oxide film prepared by traditional ion beam assisted deposition is very prone to open hole defects, which is the main reason for the deterioration of the roughness of the hafnium oxide film prepared by ion beam. The intercalation process is used to divide hafnium oxide into nano-thin layers, which can effectively inhibit the adsorption of oxygen atoms during the preparation process, thereby avoiding the formation of open and dense pores, smoothing the surface of the hafnium oxide film, and reducing the roughness of the film; the roughness of the hafnium oxide film prepared by the present invention is basically consistent with that of the blank substrate.

[0024] (2) Low film absorption: The inserted thin layer of silicon oxide nanofilm is equivalent to "doping" a portion of silicon oxide into hafnium oxide. Since silicon oxide has lower absorption and a wider band gap, the prepared hafnium oxide composite film has lower absorption.

[0025] (3) The present invention is simple and easy to implement, has strong operability and high efficiency; it will have a wider range of applications in the preparation of low-loss laser films. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is an atomic force surface morphology image of the hafnium oxide composite film prepared in Example 1;

[0027] Figure 2 This is an atomic force surface morphology image of the hafnium oxide single-layer film prepared in Comparative Example 1;

[0028] Figure 3 It is a comparison diagram of XRD patterns of the hafnium oxide composite thin film of Example 1 and the hafnium oxide single-layer film of Comparative Example 1;

[0029] Figure 4 This is a comparison diagram of the refractive index dispersion of the hafnium oxide composite thin film of Example 1 and the hafnium oxide single-layer film of Comparative Example 1. DETAILED DESCRIPTION

[0030] The present invention provides a hafnium oxide composite film, which is composed of a plurality of HfO2 nanofilm layers and a plurality of SiO2 nanofilm layers, wherein a SiO2 nanofilm is arranged between adjacent HfO2 nanofilms, and the thickness of the hafnium oxide composite film is d;

[0031] Wherein, the value B is defined as d / 25, and the value N is defined as [d / 25];

[0032] If N<B≤N+0.8, the coating system is: S|(80n H / λH 20n L / λL)^N 4n H (d-25N) / λH|A,

[0033] If N+0.8<B≤N+1, the coating system is: S|(80n H / λH 20n L / λL)^N 80n H / λH4n L (d-25N-20) / λL|A;

[0034] Wherein, S represents substrate, A represents air, H represents HfO2 nanofilm with optical thickness of λ / 4, L represents SiO2 nanofilm with optical thickness of λ / 4; λ is the central wavelength of the film system in which each film layer is located; the numbers before H and L are the proportional coefficients of the λ / 4 optical thickness.

[0035] In one embodiment of the present invention, the thickness of the HfO2 nanofilm is less than 20 nm.

[0036] In one embodiment of the present invention, the thickness of the SiO2 nanofilm is less than 5 nm.

[0037] The present invention provides a method for preparing a hafnium oxide composite film, comprising the following steps:

[0038] The HfO2 nanofilm and the SiO2 nanofilm are sequentially deposited on the substrate using an ion beam assisted deposition process.

[0039] In one embodiment of the present invention, the substrate is an ultra-polished quartz substrate with a surface roughness of less than 0.3 nm.

[0040] In one embodiment of the present invention, during the ion beam assisted deposition process, when depositing the HfO2 nanofilm, the oxygen partial pressure is 1.8×10 -2 Pa; when depositing SiO2 nanofilm, the oxygen partial pressure is 1.5×10 -2 Pa.

[0041] In one embodiment of the present invention, during the ion beam assisted deposition process, the substrate temperature is 100-150°C.

[0042] In one embodiment of the present invention, during the ion beam assisted deposition process, the evaporation rate is 1 nm / s.

[0043] In one embodiment of the present invention, during the ion beam assisted deposition process, the ion source voltage is 900V.

[0044] In one embodiment of the present invention, during the ion beam assisted deposition process, the ion source current is 1000 mA.

[0045] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] In the following examples, unless otherwise specified, all reagents used are commercially available reagents, and all detection means and methods used are conventional detection means and methods in the art.

[0047] Example 1

[0048] This embodiment provides a hafnium oxide composite film and a preparation method thereof.

[0049] The optical thickness of the hafnium oxide film of the 0 degree 1064 nm high reflector often used in laser films is 1 quarter wavelength and the physical thickness is 135 nm. This embodiment takes this typical thickness as an example to provide a hafnium oxide film that can effectively reduce the surface roughness and absorption of the film layer.

[0050] (1) Film layer design: The hafnium oxide composite film is composed of several layers of HfO2 nanofilms and several layers of SiO2 nanofilms. SiO2 nanofilms are arranged between adjacent HfO2 nanofilms. The thickness of the hafnium oxide composite film is 135 nm; the thickness of each HfO2 nanofilm is 20 nm, and the thickness of the SiO2 nanofilm is 5 nm;

[0051] (2) Film preparation: HfO2 nanofilm and SiO2 nanofilm were sequentially deposited on an ultra-polished fused quartz substrate with a size of φ30 mm×5 mm and a roughness of 0.117 nm using an ion beam assisted deposition process to obtain a hafnium oxide composite film with a thickness of 135 nm;

[0052] In this embodiment, the physical thickness of the hafnium oxide composite film is d=135 nm, then B=d / 25=5.4, N=[d / 25]=5;

[0053] Since 5<5.4≤5.8, the coating film system is: S|(80n H / λH 20n L / λL)^N 4n H (d-25N) / λH|A, which is S|(20nmH 5nmL)^5 10nm H|A;

[0054] During the ion beam assisted deposition process, the oxygen partial pressure was 1.8×10 -2 Pa; when depositing SiO2 nanofilm, the oxygen partial pressure is 1.5×10-2 Pa; substrate temperature is 100-150°C; the evaporation rates of HfO2 and SiO2 are both 1 nm / s; the ion source voltage is 900 V, and the ion source current is 1000 mA.

[0055] Comparative Example 1

[0056] This comparative example provides a hafnium oxide composite film and a preparation method thereof (existing conventional technology).

[0057] (1) Film design: hafnium oxide single layer film, optical thickness is 1 quarter wavelength, physical thickness is 135nm;

[0058] (2) Film preparation: Using an ion beam assisted deposition process, a 135 nm thick hafnium oxide composite film was sequentially deposited on an ultra-polished fused quartz substrate with a size of φ30 mm×5 mm and a roughness of 0.117 nm;

[0059] During the ion beam assisted deposition of hafnium oxide, the oxygen partial pressure was set to 1.8×10 -2 Pa; substrate temperature is 100-150°C; evaporation rate is 1 nm / s; ion source voltage is 900 V, and ion source current is 1000 mA.

[0060] The hafnium oxide composite film prepared in Example 1 and the hafnium oxide single-layer film prepared in Comparative Example 1 were tested:

[0061] (1) Surface morphology test:

[0062] Test instrument: Bruker atomic force microscope, scanning range: 5 microns. Figure 1-2 As shown, the hafnium oxide monolayer film prepared in Comparative Example 1 ( Figure 2 ), the surface has many holes; because the microstructure of the hafnium oxide film is sensitive to the oxygen partial pressure during the ion beam assisted deposition process, the excess oxygen atoms are absorbed on the surface of the growing film, which will form oxygen inclusions in the film layer, and these oxygen voids gradually merge or merge into holes. This dense distribution of holes leads to a larger roughness of the hafnium oxide. The roughness of the hafnium oxide film prepared by this traditional process is as high as 4.31nm.

[0063] Hafnium oxide composite film prepared in Example 1 ( Figure 1 ), the surface is smooth, and the surface roughness is only 0.127nm, which is almost the same as the surface roughness of the empty substrate; it fully illustrates that the preparation method of Example 1 plays an important role in inhibiting the appearance of holes on the surface of the hafnium oxide film and reducing the surface roughness of the film.

[0064] (2) XRD test:

[0065] Test instrument: X-ray diffractometer, scanning angle: 20-80 degrees. Figure 3 As shown, according to PDF-06-0318 of the ICDD database, a series of diffraction peaks including (1,1,0), (-1,1,1), (1,1,1) and (2,2,0) were observed in the XRD crystal phase of the hafnium oxide single-layer film prepared in Comparative Example 1, corresponding to the monoclinic phase of HfO2, and preferentially grew mainly along the (1,1,1) crystal direction; while the hafnium oxide thin film prepared in Example 1 had no diffraction peaks and the film was amorphous, which fully demonstrated that the preparation method of Example 1 played an important role in inhibiting the crystallization of the hafnium oxide thin film and reducing the surface roughness of the film.

[0066] (3) Refractive index comparison:

[0067] Fitting software: optichar, fitting wavelength: 250-1500nm. Figure 4 As shown in the figure, after inserting the SiO2 nanofilm, the refractive index of hafnium oxide at 1064nm decreases from 2.03 to 1.93; this is because the refractive index of the inserted SiO2 nanofilm is low, so the equivalent refractive index of the entire hafnium oxide composite film becomes lower. Properly adjusting the optical thickness ratio of high and low refractive index materials in the multilayer film can compensate for the spectral drift caused by the reduction of the refractive index of the hafnium oxide composite film.

[0068] (4) Absorption test:

[0069] Test instrument: SPTS PCI-3 weak absorption instrument, test wavelength: 1064nm. The absorption of the hafnium oxide monolayer prepared in Comparative Example 1 is 23ppm, and the weak absorption of the nano-thin layer hafnium oxide film prepared in Example 1 is 9ppm. The inserted SiO2 nanofilm is equivalent to "doping" a part of silicon oxide in hafnium oxide. Since silicon oxide has lower absorption and wider band gap, the prepared hafnium oxide film has lower absorption. The intercalation process proposed in Example 1 plays an important role in reducing the absorption of the film.

[0070] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the explanation of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A hafnium oxide composite film, characterized in that: The hafnium oxide composite film is composed of several layers of HfO2 nanofilms and several layers of SiO2 nanofilms, SiO2 nanofilms are arranged between adjacent HfO2 nanofilms, and the thickness of the hafnium oxide composite film is d; Wherein, the value B is defined as d / 25, and the value N is defined as [d / 25]; If N<B≤N+0.8, the coating system is: S|(80n H / λH 20n L / λL)^N 4n H (d-25N) / λH|A, If N+0.8<B≤N+1, the coating system is: S|(80n H / λH 20n L / λL)^N 80n H / λH4n L (d-25N-20) / λL|A; Wherein, S represents substrate, A represents air, H represents HfO2 nanofilm with an optical thickness of λ / 4, and L represents SiO2 nanofilm with an optical thickness of λ / 4; λ is the central wavelength of the film system in which each film layer is located; The preparation of the hafnium oxide composite film comprises the following steps: The HfO2 nanofilm and the SiO2 nanofilm are sequentially deposited on the substrate by using an ion beam assisted deposition process; The thickness of HfO2 nanofilm is less than 20nm, and the thickness of SiO2 nanofilm is less than 5nm; The surface roughness of the hafnium oxide composite film is 0.127 nm, there is no diffraction peak, the film is amorphous, and the weak absorption is 9 ppm; Wherein, the substrate is an ultra-polished quartz substrate with a surface roughness of less than 0.3 nm; During the ion beam assisted deposition process, the oxygen partial pressure was 1.8×10 -2 Pa; when depositing SiO2 nanofilm, the oxygen partial pressure is 1.5×10 -2 Pa; During the ion beam assisted deposition process, the substrate temperature is 100-150°C; During the ion beam assisted deposition process, the evaporation rate is 1 nm / s; During the ion beam assisted deposition process, the ion source voltage was 900 V; During the ion beam assisted deposition process, the ion source current is 1000 mA.

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